Thèses sur le sujet « Photocatalyst material »

This dissertation presents a method for enhancement of the efficiency and scalability of photocatalytic water purification systems, along with an experimental validation of the concept. A 3-dimensional photocatalyst structure, made from a TiO2-SiO2 composite, has been designed and fabricated for use in a custom designed LED-source illumination chamber of rotational symmetry that corresponds with the symmetry of the photocatalyst material. The design of the photocatalyst material has two defining characteristics: geometrical form and material composition. The design of the material was developed through the creation of a theoretical model for consideration of the system's photonic efficiency. Fabrication of the material was accomplished using a Ti alkoxide solution to coat a novel 3D support structure. The coatings were then heat treated to form a semiconducting thin-film. The resulting films were evaluated by SEM, TEM, UV-vis spectroscopy and Raman spectroscopy. The surface of the material was then modified by implantation of TiO2 and SiO2 nanoparticles in order to increase catalytic surface area and improve the photoactivity of the material, resulting in increased degradation performance by more than 500%. Finally, the efficiency of the photocatalytic reactor was considered with respect to energy usage as defined by the Electrical Energy per Order (EEO) characterization model. The effects of catalyst surface modification and UV-illumination intensity on the EEO value were measured and analyzed. The result of the modifications was an 81.9% reduction in energy usage. The lowest EEO achieved was 54 kWh per cubic meter of water for each order of magnitude reduction in pollutant concentration -- an improvement in EEO over previously reported thin-film based photoreactors.

This research focuses on plasmonic materials as photocatalyst in fine organic synthesis under visible light irradiation. It was illustrated that noble metal (silver) nanoparticles performed well as photocatalyst in toluene oxidation reaction, which was not only achieved in mind reaction condition, but also controlled with high selectivity of product. In addition, titanium nitride (TiN) material and transition metal (Pd) nanoparticles both can be applied in the cleavage of lignin models with two different reaction pathway and product selectivity. Finally, the analysis of all the reaction mechanism is significant for the further study of related organic synthesis.

This thesis presents the achievements pursued during the doctoral course. The work was carried out in the context of the project ERiCSol (Energia RInnovabile e Combustili SOLari), as part of the University of Trento strategic plan for the years 2017-2021. The project was conceived to establish an interdepartmental area to promote the challenge of developing scientific research and technological innovation to increase the competitiveness of Trento at national and international level in the areas of energy and environment. Among all the goals of the project, this work dedicates special attention to 1) development of novel materials for solar photocatalytic reactions and 2) use of renewable energy to push forward applications in water remediation. To accomplish these goals, the research brings a full collection of experimental activities regarding the employment of solar concentration for the environment industry and therefore this document is organized in 9 chapters. In chapter 1, it is presented the introduction outlining the overview of the environment industry, the employment of solar light as energy source and the general and specific objectives. Chapter 2 presents a literature review regarding the last 30 years of applications correlating the use of solar light towards wastewater purification. The chapter reviews the engineering features of solar collectors, photocatalyst materials employed and the panorama of the pollutants investigated up to the present date in solar photocatalysis, presenting comparisons between models and real wastewater approaches. Chapter 3 details the experimental techniques and characterizations employed to sustain the investigation proposed in the thesis. The first part of the chapter explains the features of parabolic dish solar concentrator designed and manufactured by the IdEA group at the physics department of the university of Trento. After, it is presented the pulsed laser deposition, a thin films fabrication technique employed to produce the photocatalysts used on water purification experiments. The second part of the chapter presents the description of the characterization techniques used to reveal the fabricated photocatalyst materials properties. Based on the review on the fundamentals of solar photocatalysis and the experimental techniques, chapters 4 and 5 present a discussion in the field of novel photocatalytic materials capable to operate under concentrated sunlight irradiation. Chapter 4 in special presents the investigation regarding the fabrication of tungsten trioxide (WO3) thin film coatings, bringing the novelty of using pulsed laser deposition as the fabrication method and the evaluation of this material in photocatalysis for the degradation of methylene blue dye model pollutant. Chapter 5 instead, presents the development on Zinc Oxide (ZnO) nanoparticles, bringing an innovative point of view on a “green-synthesis” approach and the material immobilization in film for heterogeneous photocatalysis routes. Chapters 6 and 7 discuss solar photocatalysis aiming to shift applications from model pollutants to real wastewater remediation conditions. Important comparisons are performed and discussed regarding the advantages and existing drawbacks. To fulfill this purpose, chapter 6 presents an application case of solar photocatalysis to the degradation of a surfactant-rich industrial wastewater whereas chapter 7 presents the approach focused on the remediation of organic lead contaminants present on a local water well site in the city of Trento. The last experimental approach of concentrated solar light is presented on chapter 8, dedicated to the application of concentrated sunlight towards waste biomass valorization. Conversely to the application on water previously described, this chapter presents the activity on designing, fabricating and coupling a hydrothermal reactor with concentrated sunlight using it as the driving force to promote degradation of grape seeds evolving into hydrochars with possible valorization of the carbonized material. Lastly, chapter 9 presents the conclusions and suggestions, this item expresses the final considerations on the results of the experimental investigations, advantages and limitations observed, and suggests possible actions for future works.

Au cours des dernières décennies, le développement d'une chimie durable est devenu une priorité pour notre société Dans ce contexte, la biocatalyse, par l’utilisation d’enzymes naturelles, modifiées ou artificielles constituées d’un catalyseur de synthèse greffé au sein d’une protéine apparait comme une solution intéressante.Dans ce projet, nous cherchons à développer des photocatalyseurs bio-hybrides combinant un photosensibilisateurs (RuPhot) et un catalyseurs (RuCat) au sein d'un cristal protéique pour la photocatalyse hétérogène d’oxydation asymétrique de substrats organiques en utilisant l’eau comme seule source d’atome d’oxygène. La protéine sélectionnée est le domaine d'oligomérisation de la protéine Leafy du Ginkgo biloba. Cette protéine est capable de générer des structures poreuses par auto-assemblage. A l'intérieur des tubes, une chaîne peptidique d'environ 30 acides aminés par monomère est présente et servira de plateforme de greffage. Trois systèmes hybrides cristallins avec RuPhot et RuCat seuls ainsi qu’avec une combinaison des deux ont été obtenus. La mise au point des techniques de caractérisation a été faite sur l’hybride RuCat apportant des informations intéressantes sur la cinétique et la sélectivité du greffage ainsi que sur une modification du catalyseur intervenant au cours du greffage. Les études réalisées sur l’hybrides RuPhot ont quant à elles montrées qu’il était possible, comme cela était planifié de greffer plusieurs chromophores par protéine et de pouvoir bénéficier ainsi d’un effet d’antenne pour une efficacité maximisée. Les études catalytiques pour l'oxydation des sulfures et des alcènes sont en cours.Dans un tout autre domaine, 16% de cette thèse a été consacré à un contrat de doctorat conseil auprès de l'entreprise NMRBio. L'objectif était de développer de nouvelles voies de synthèses de composés marqués par des isotopes stables en vue d'études structurales et dynamiques de protéines par RMN
For the last decades the development of sustainable chemistry became a priority for our society. In this context, biocatalysis appears to be an interesting solution, through the use of natural, modified or artificial enzymes consisting of a synthetic catalyst grafted into a protein.In this project, we aim to develop bio-hybrid photocatalysts combining a photosensitizer (RuPhot) and a catalyst (RuCat) within a protein crystal for heterogeneous asymmetric oxidation photocatalysis of organic substrates using water as the only source of oxygen atoms. The selected protein is the oligomerization domain of the Leafy protein of Ginkgo biloba. This protein is able to generate porous structures by self-assembly. Inside the tubes, a peptide chain of about 30 amino acids per monomer is present and it will serve as grafting platform. Three crystalline hybrid systems were obtained with RuPhot and RuCat alone as well as a combination of the two. The characterization was carried out on the RuCat hybrid providing interesting information on the kinetics and selectivity of grafting as well as on a modification of the catalyst during grafting. The studies carried out on the RuPhot hybrids have shown that it was possible, as planned, to graft several chromophores per protein and thus benefit from an antenna effect for maximum efficiency. Catalytic studies for the oxidation of sulphides and alkenes are underway.In a completely different field, 16% of this thesis was devoted to a doctoral consulting contract with the company NMRBio. The objective was to develop new pathways for the synthesis of stable isotope-labelled compounds in order to perform structural and dynamic NMR studies in proteins

Material science is an interdisciplinary area of research, which in part, designs and characterizes new materials. Research is concerned with synthesis, structure, properties, and performance of materials. Discoveries in materials science have significant impact on future technologies, especially in nano-scale applications where the physical properties of nanomaterials are significantly different than their bulk counterparts. The work presented here discusses the use of ferritin, a hollow sphere-like biomolecule, which forms metal oxo-hydride nanoparticles inside its protein shell for uses as a bio-inorganic material.Ferritin is capable of forming and sequestering 8 nm metal-oxide nanoparticles within its 2 nm thick protein shell. A variety of metal-oxide nanoparticles have been synthesized inside ferritin. The work herein focuses on three distinct areas:1) Ferritin's light harvesting properties: namely band gaps. Discrepancies in the band gap energies for ferritin's native ferrihydrite mineral and non-native minerals have been previously reported. Through the use of optical absorption spectroscopy, I resolved the types of band gaps as well as the energy of these band gaps. I show that metal oxides in ferritin are indirect band gap semiconductors which also contain a direct transition. Modifications to the ferrihydrite mineral's band gaps are measured as a result of co-depositing anions into ferritin during iron loading. I demonstrate that these band gaps can be used to photocatalytically reduce gold ions in solution with titanium oxide nanoparticles in ferritin. 2) A new method for manganese mineral synthesis inside ferritin: Comproportionation between permanganate and Mn(II) forms new manganese oxide minerals inside ferritin that are different than traditional manganese oxide mineral synthesis. This reaction creates a MnO2, Mn2O3, or Mn3O4 mineral inside ferritin, depending on the synthesis conditions. 3) Ferritin as an energetic material: Ferritin is capable of sequestering various metals and anions into its interior. Perchlorate, an energetic anion, is sequestered through a co-deposition process during iron loading and is tested with energetic binding materials. Peroxide, which can be used as an oxidant, is also shown to be sequestered within apoferritin and combined with an aluminum based fuel for solid rocket propellants.

Materials with one-dimensional (1D) nanostructure are important for catalysis. They are the preferred building blocks for catalytic nanoarchitecture, and can be used to fabricate designer catalysts. In this thesis, one such material, alumina nanofibre, was used as a precursor to prepare a range of nanocomposite catalysts. Utilising the specific properties of alumina nanofibres, a novel approach was developed to prepare macro-mesoporous nanocomposites, which consist of a stacked, fibrous nanocomposite with a core-shell structure. Two kinds of fibrous ZrO2/Al2O3 and TiO2/Al2O3 nanocomposites were successfully synthesised using boehmite nanofibers as a hard temperate and followed by a simple calcination. The alumina nanofibres provide the resultant nanocomposites with good thermal stability and mechanical stability. A series of one-dimensional (1D) zirconia/alumina nanocomposites were prepared by the deposition of zirconium species onto the 3D framework of boehmite nanofibres formed by dispersing boehmite nanofibres into a butanol solution, followed by calcination at 773 K. The materials were characterised by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), N2 adsorption/desorption, Infrared Emission Spectroscopy (IES), and Fourier Transform Infrared spectroscopy (FT-IR). The results demonstrated that when the molar percentage, X, X=100*Zr/(Al+Zr), was > 30%, extremely long ZrO2/Al2O3 composite nanorods with evenly distributed ZrO2 nanocrystals formed on their surface. The stacking of such nanorods gave rise to a new kind of macroporous material without the use of any organic space filler\template or other specific drying techniques. The mechanism for the formation of these long ZrO2/Al2O3 composite nanorods is proposed in this work. A series of solid-superacid catalysts were synthesised from fibrous ZrO2/Al2O3 core and shell nanocomposites. In this series, the zirconium molar percentage was varied from 2 % to 50 %. The ZrO2/Al2O3 nanocomposites and their solid superacid counterparts were characterised by a variety of techniques including 27Al MAS-NMR, SEM, TEM, XPS, Nitrogen adsorption and Infrared Emission Spectroscopy. NMR results show that the interaction between zirconia species and alumina strongly correlates with pentacoordinated aluminium sites. This can also be detected by the change in binding energy of the 3d electrons of the zirconium. The acidity of the obtained superacids was tested by using them as catalysts for the benzolyation of toluene. It was found that a sample with a 50 % zirconium molar percentage possessed the highest surface acidity equalling that of pristine sulfated zirconia despite the reduced mass of zirconia. Preparation of hierarchically macro-mesoporous catalyst by loading nanocrystallites on the framework of alumina bundles can provide an alternative system to design advanced nanocomposite catalyst with enhanced performance. A series of macro-mesoporous TiO2/Al2O3 nanocomposites with different morphologies were synthesised. The materials were calcined at 723 K and were characterised by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), N2 adsorption/desorption, Infrared Emission Spectroscopy (IES), and UV-visible spectroscopy (UV-visible). A modified approach was proposed for the synthesis of 1D (fibrous) nanocomposite with higher Ti/Al molar ratio (2:1) at lower temperature (<100oC), which makes it possible to synthesize such materials on industrial scale. The performances of a series of resultant TiO2/Al2O3 nanocomposites with different morphologies were evaluated as a photocatalyst for the phenol degradation under UV irradiation. The photocatalyst (Ti/Al =2) with fibrous morphology exhibits higher activity than that of the photocatalyst with microspherical morphology which indeed has the highest Ti to Al molar ratio (Ti/Al =3) in the series of as-synthesised hierarchical TiO2/Al2O3 nanocomposites. Furthermore, the photocatalytic performances, for the fibrous nanocomposites with Ti/Al=2, were optimized by calcination at elevated temperatures. The nanocomposite prepared by calcination at 750oC exhibits the highest catalytic activity, and its performance per TiO2 unit is very close to that of the gold standard, Degussa P 25. This work also emphasizes two advantages of the nanocomposites with fibrous morphology: (1) the resistance to sintering, and (2) good catalyst recovery.

This thesis describes the synthesis, characterization and photocatalytic applications of carbon nitride (C3N4) and titanium dioxide (TiO2) materials. C3N4 was prepared from the thermal decomposition of a trichloromelamine (TCM) precursor. Several different reactor designs and decomposition temperatures were used to produce chemically and thermally stable orange powders. These methods included a low temperature glass Schlenk reactor, a high mass scale stainless steel reactor, and decomposition at higher temperatures by the immersion of a Schlenk tube into a furnace. These products share many of the same structural and chemical properties when produced by these different methods compared to products from more common alternate precursors in the literature, determined by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and elemental analysis. C3N4 is capable of utilizing light for photocatalysis due to its moderate band gap (Eg), measured to be between 2.2 and 2.5 eV. This enables C3N4 to be used in the photocatalytic degradation of organic dyes and the production of hydrogen via the water-splitting reaction. C3N4 degraded methylene blue dye to less than 10% of its initial concentration in less than an hour of UV light illumination and 60% under filtered visible light in 150 minutes. It also degraded methyl orange dye to below 20% in 70 minutes under UV light and below 60% in 150 minutes under visible light. Using precious metal co-catalysts (Pt, Pd, and Ag) photo-reduced onto the surface of C3N4, hydrogen was produced from a 10% aqueous solution of triethanolamine at rates as high as 260 μmol h-1 g-1. C3N4 was also modified by mixing the precursor with different salts (NaCl, KBr, KI, KSCN, and NH4SCN) as hard templates. Many of these salts reacted with TCM by exchanging the anion with the chlorine in TCM. The products were mostly prepared using the high temperature Schlenk tube reactor, and resulted in yellow, orange, or tan-brown products with Eg values between 2.2 and 2.7 eV. Each of these products had subtle differences in the IR spectra and elemental composition. The morphology of these C3N4 products appeared to be more porous than unmodified C3N4, and the surface area for some increased by a factor of 4. These products demonstrated increased activity for photocatalytic hydrogen evolution, with the product from TCM-KI reaching a peak rate as high as 1,300 µmol h-1 g-1. C3N4 was coated onto metal oxide supports (SiO2, Al2O3, TiO2, and WO3) with the goal of utilizing enhanced surface area of the support or synergy between two different semiconductors. These products typically required higher temperature synthesis conditions in order to fully form. The compositions of the SiO2 and Al2O3 products were richer in nitrogen and hydrogen compared to unmodified C3N4. The higher temperature reactions with C3N4 and WO3 resulted in the formation of the HxWO3 phase, and an alternate approach of coating WO3 on C3N4 was used. The degradation of methyl orange showed a significant increase in adsorption of dye for the composites with SiO2 and Al2O3, which was not seen with any of the individual components. The composite between C3N4 and TiO2 showed improved activity for hydrogen evolution compared to unmodified C3N4. The surface of TiO2 was modified by the reductive photodeposition of several first row transition metals (Mn, Fe, Co, Ni, and Cu). This process resulted in the slight color change of the white powder to shades of light yellow, blue or grey. Bulk elemental analysis showed that these products contained between 0.04-0.6 at% of the added metal, which was lower than the targeted deposit amount. The Cu modified TiO2 had the largest enhancement of photocatalytic hydrogen evolution activity with a rate of 8,500 µmol h-1 g-1, a factor of 17 higher than unmodified TiO2.

Photocatalytic processes are of widespread interest. Among different types of photocatalytic material TiO2 is the generally considered amongst the best due to its favourable physical and chemical properties. In recent decades, photovoltaic devices have been widely studied to provide alternative routes to energy and reduce dependency upon fossil fuel. Solar photovoltaic are cells capable of harvesting of sunlight into electrical power. This technology is one of the most promising routes in the search for sustainable and renewable sources of energy. The study presented in this thesis relates to the preparation and characterization of a range of different materials which can be applied in photocatalytic processes and for photovoltaic devices. The photocatalysis work has been focused mainly upon modification of the various phases of titanium dioxide. This has been undertaken via doping with nitrogen by treatment with ammonia at different temperatures. In addition, samples containing Al, Co and Cu dopants, as well as their N doped counterparts, have been prepared, characterized and tested. The photocatalytic activity was screened by following photocatalytic decomposition of an aqueous solution of methylene blue using a light source containing various components in the UV and visible regions. For selected samples, the photocatalytic activity for polymerization of methyl methacrylate and styrene has been determined with the aim of producing composites. In terms of potential photovoltaic materials, the synthesis of novel viologen compounds and polymerization via electrochemical and chemical means has been undertaken. Different viologen monomers have been synthesized with various moieties in conjugation to a phenanthroline core to afford novel push-pull systems. These compounds have incorporated both TCNE and TCNQ moieties as strong electron acceptors and hence yield chromophore with large dipole moments. In addition, novel ruthenium complexes were prepared featuring bipyridine and phenanthroline ligands. The optical and redox properties of these materials have been investigated. DSSCs have been fabricated form some of these systems and their properties have been compared to dye 719.

The primary aim of the work presented in this thesis was to design and synthesise well-characterised material that would exploit visible light to promote photocatalysis, involving the degradation of organic compounds in water, or generation of hydrogen from the water splitting reaction. In doing so, both environmental concerns, such as the removal of pollutants in wastewater, and energy concerns, such as the generation of a clean and safe form of hydrogen for use as a renewable fuel could be addressed. The approach used was to employ existing methods to synthesise high surface area quasi-amorphous material that is active in UV light for photocatalysis, and then design and employ post synthetic modification to promote the material for visible light photocatalysis. Niobium (V) oxide was synthesised in a high surface area form, successfully scaling up the synthesis from 2 g to over 200 g quantities of as made material. This UV active photocatalyst was fully characterized by methods including X-ray diffraction and thermal gravimetric analysis. The material was used to degrade the model dye Methyl Orange and generate hydrogen from a methanol / water solution without further modification. By adding platinum group metals (PGMs) to the niobium (V) oxide, a greatly enhanced efficiency for hydrogen generation was realized. A survey of metals (platinum rhodium and palladium) and weight percentages of metal added (0.01 – 1%) was carried out, with the PGM added materials characterised for hydrogen generation using a methanol / water sacrificial reagent system, as well as PGM dispersion, TEM imaging, EDX and X-ray photoelectron spectroscopy for characterising the higher weight percentage material. Finally, chromium (III) oxide was added to the surface of the niobium (V) oxide in various weight percentages (1% - 5%). The optical properties of this composite material, in comparison with the starting materials were investigated, in particular the difference in diffuse reflectance of the starting materials and composite were highlighted to demonstrate charge transfer between the chromium (III) on the surface, and niobium (V), in the bulk of the material, with the oxidation states being confirmed by XPS. Furthermore, this material was found to degrade methyl orange under visible light. An action spectrum was carried out measuring the quantum efficiency of the reaction at different wavelengths, which proved it was the chromium – niobium charge transfer absorbance in isolation that was responsible for the methyl orange degradation.

Des films du type polyoxométallates-porphyrines ont été synthetisés et sont basés sur des interactions du types covalentes ou électrostatiques. Les films polyoxométallates–porphyrines sont obtenus par électro-oxydation de l’octaéthylporphyrine de zinc (ZnOEP) ou la 5,15-ditolylporphyrine (H2T2P) en présence de différents types of polyoxométallates (POMs) portant deux groupes pyridyles pendants (py-POM-py) Trois type de systèmes py-POM-py ont été utilises : i) un Lindqvist polyoxovanadate fonctionalisé via deux groupes tris-alkoxo , ii) un derive organosilyl fonctionalisé du type Keggin ou Dawson, et iii) des briques du type Dawson [P2W15V3O62]9− fonctionalisée avec des groupements organiques bis-pyridine de géométrie variée via un greffage diolamide). Tous ces films ont été testé pour la génération de photocourant et la photocatalyse de la réduction de métaux (Ag et Pt). Des films électrostatiques POM-porphyrin ont été également préparés par incorporation de polyanion du type Preyssler [NaP5W30O110]14- sur les films de porphyrine polycationic (poly-ZnOEP) électropolymérisés avec des espaceurs viologènes ou bis-viologènes. [NaP5W30O110]14- agit comme relais d’électron entre une porphyrine excitée ZnOEP* et le viologène (ou le bis-viologène) retardant la recombinaison de charge ce qui permet une augmentation du photocourant. Enfin, des nanoparticules POM@NPs (Pt, Au, Ag) ont été introduites en surface de copolymère polycationique à base de bis-porphyrine par métathèse afin d’augmenter l’efficacité de la génération de photocourant. La résonance de plasmon de surface localisée qui se produit à la surface des nanoparticules d'argent a sensiblement améliorée l'excitation électronique de porphyrine
Polyoxometalates-porphyrin hybrid films were synthesized based on covalent or electrostatic interactions. Copolymeric polyoxometalate–porphyrin films were obtained by the electro-oxidation of zinc octaethylporphyrin (ZnOEP) or 5,15-ditolyl porphyrin (H2T2P) in the presence of a different type of polyoxometalates (POMs) bearing two pyridyl groups (py-POM-py). Three type of py-POM-py have been used: i) a tris-alkoxo functionalized Lindqvist polyoxovanadate, ii) an organosilyl functionalized Keggin-type [PW11Si2O40C26H16N2]3- and Dawson-type [P2W17Si2O62C26H16N2]6-, and iii) a bis-pyridine-substituted organo-polyoxometallic bricks using [P2W15V3O62]9− diolamide-grafting method with various geometries of the pendant group. All are applied for photocurrent generation and photocatalytical recovery of metals (Ag and Pt). Electrostatic POM-porphyrin films were also prepared by incorporated Preyssler type polyanion [NaP5W30O110]14- onto the electropolymerized polycationic porphyrin (poly-ZnOEP) with viologen or bis-viologen as spacers. [NaP5W30O110]14- as an efficient electron shuttle between the excited ZnOEP and viologen (or bis-viologen) which effectively retarded the fast charge pair recombination and enhanced the photocurrent magnitude. Later, we introduced nanoparticles POM@MNPs to a bis-porphyrin copolymer through metathesis reaction to further improve the efficiency of the photocurrent generation in which the localized surface plasmon resonance that occurs at the surface of silver nanoparticles has substantially enhanced the electronic excitation of surface-anchored porphyrin

Photocatalysis on semiconductor surfaces has grown tremendously in the last four decades. One reason for this is its analogy with photosynthesis, the most important natural photochemical process. Semiconductors to some extent can mimic the key steps of this fascinating heterogeneous photocatalytic process, i.e., photochemical charge generation, charge trapping, interfacial electron exchange and subsequent reaction. Building on this premise this thesis constitutes an investigation into the photocatalytic properties and applications of semiconducting layered framework carbon nitride based materials. Similar to traditional photocatalysts, the photocatalytic activity and efficiency of carbon nitride systems developed thus far is limited mainly by the fast recombination and low mobility of photogenerated excitons. Here, by exploiting the band alignment strategy, carbon nitride isotype (type II) and carbon nitride-niobium oxide of type II semiconductor heterojunctions were successfully constructed with the aim of suppressing the exciton recombination and improving charge extraction for the successful initiation of desirable redox chemistry. These features were demonstrated by employing the materials in heterogeneous photocatalysis for water splitting, organic pollutant decomposition and photochemical organic synthesis. Carbon nitride isotype heterojunctions constructed by controlled thermal condensation are shown to exhibit lower recombination of excitons relative to the pristine carbon nitride. As a consequence photocurrent generation and visible light driven H2 production activity was enhanced. This increase is attributed to the surface passivation and improved electron mobility of built-in electric field which arises from the topology-induced band offset of favoured type II heterojunction configuration. Building on the insights into the heterojunction-activity dependence, new type II graphitic carbon nitride (C3N4), Nb2O5 (C3N4-Nb2O5), heterojunctions synthesised via a hydrothermal method were exploited for their photodegradation ability of the organic pollutants. The synergic effect of carbon nitride and Nb2O5 coupling leads to the substantial photocatalytic activity improvement which can be attributed to the formation of an intimate interface and gradual attenuation of energy-wasteful charge recombination processes in C3N4-Nb2O5 heterojunctions materials. While water splitting and pollutant decomposition using semiconductors has received the bulk of attention, the possibilities concerning chemical synthesis are only beginning to be meaningfully exploited. We, therefore, employed carbon nitride to catalyse photo organic synthesis. It was demonstrated for the first time that carbon nitride can efficiently catalyse the photoacetalization reactions of aldehydes/ketones with alcohols, forming acetals at high yields using visible light under ambient conditions. Mechanistic studies suggest that the transient charge separation at the surface of this material is sufficient to catalyse the reaction in the absence of Lewis or Brønsted acids or solvent systems. Since the photoacetalization of aldehydes occurs under conditions similar to those of alcohols oxidation, both using visible light and carbon nitride as a catalyst, the two reactions actually proceed via different mechanisms. This study also demonstrates, visible light induced heterogeneous auto-tandem catalysis, coupling the oxidation and subsequent acetalization of alcohols in a single chemical process. This green strategy can be applicable to a wide variety of organic photo-induced synthesis.

Photocatalysis is a process to convert light energy into chemical energies. This advanced process has been extensively applied in different areas, such as water splitting to evolve hydrogen, organic/ inorganic pollutants decomposition, artificial photosynthesis (CO2 reduction), disinfection, heavy metal recovery, organic synthesis and nitrogen fixation (reduction). The difficulty for photocatalysis applied in practical is primarily due to the low quantum yield as for the high recombination of photogenerated charge carriers. Various strategies have been implemented to overcome these challenges. As recently developed advanced materials, two dimensional materials have attracted lots of attentions as for their superiorities such as large specific surface area and high conductivity. These advantages for two dimensional materials make them be promising cocatalysts in enhance catalytic activity. In this thesis, various two dimensional materials (such as MoS2, SnS, BN as well as C3N4) other than graphene were prepared and investigated in the promotion of photocatalytic activity. Specifically, the focus of present work is on two dimensional materials enhanced photocatalysis in environmental remediation, including organic pollutants detoxification as well as bacteria inactivation. It was found that two dimensional materials, including MoS2, SnS, BN, may be excellent candidates as cocatalysts to enhanced visible-light-driven photocatalytic activity. And g-C3N4 as an effective photocatalyst exhibited excellent photocatalytic oxidation activity, and its activity can be further enhanced with surface modification by hydroxyl functional groups (a modification method reported in the thesis). Suggestions for future work were also proposed in this thesis.

Photoactive semiconductors are a hot topic of research due to their applications in environmental remediation, photovoltaics, smart devices, light-activated synthesis and self-cleaning surfaces. Among them, oxide semiconductors play a main role thanks to their wide availability, stability, ease of preparation and tunable surface properties. In this context, my Ph.D. focused on the application of oxide semiconductors for three main purposes: pollutant remediation, photocatalytic synthesis of hybrid materials, and smart systems for the controlled release of active substances. Alongside this main research project, I developed two original hands-on activities based on oxide systems for public engagement. Oxide semiconductors for environmental remediation. Photocatalysis is an advanced oxidation process that can achieve the complete degradation of contaminants without the addition of reagents. However, its real-life application has been hindered by several limitations, such as the use of nanosized powder, costs of light irradiation, possible accumulation of toxic reaction intermediates and the sensitivity to complex water matrices. During my Ph.D., I investigated the deposition of photocatalyst powder on macroscopic devices based on aluminum plates for air purification. Aluminum is a cheap and technologically-relevant substrate, but its application as substrate for photocatalyst immobilization has been hampered by adhesion issues and metal ion diffusion within the photocatalytic layer that increases recombination of photogenerated carriers. Thus, I investigated the use of silica interlayers to promote adhesion, efficiency and reusability of TiO2 films on aluminum plates. Films were prepared from stable titania sols and deposited on aluminum substrates with different surface morphology and with silica interlayers of different thickness. The study of the coating structure, morphology, optical properties, adhesion and hardness showed that the nature of the substrate and its surface roughness determined the optimal number of silica interlayers. When the silica interlayer was too thin, moderate cracking was still observed, whereas a too thick silica interlayer led to peeling off of the film. The use of rougher surfaces, as in the case of sand-papered aluminum, required a higher number of silica layers to promote a more homogeneous surface where the titania coating could effectively adhere. However, the addition of a thicker silica layer did not erase the effect of the sand-paper pre-treatment on surface roughness. Films on sand-papered substrates showed promoted photocatalytic activity with respect to the smoother counterparts, possibly due to their larger exposed contact area. The prepared films exhibited excellent light-induced superhydrophilicity and self-cleaning properties towards fouling agents (alkylsilanes). Photocatalytic degradation tests were carried out using both a model volatile organic compound (ethanol) and NOx. The silica interlayer proved crucial to promote the film robustness, effectively increasing the mechanical stability and reusability when a thicker interlayer was adopted on sand-papered aluminum plates. In order to cut the costs associated with lamp irradiation, the visible-light promotion of large band gap photocatalysts is a widely investigated approach. In this regard, I studied the modification of TiO2 with Sn and N species aiming to improve the photocatalyst visible-light absorption for the solar-light photocatalityc degradation of emerging pollutants. Three different synthetic routes were investigated: a bulk synthesis, where Ti and Sn precursors were both added in the sol-gel synthesis, a seeded procedure, where pre-formed SnO2 crystals were added to TiO2 synthesis, and a mechanical mixture, where the oxides were mixed together then calcined. Marked differences were observed in the final composites’ structural, morphological and optical properties, leading to notable changes in the photocatalytic performance. Interestingly, bulk and seeded samples showed notable photochromic properties under UV light, which varied based on the doping level: this is the first time photochromic effects have been observed in Sn-promoted TiO2. These findings can be related to the different nature of the defects introduced in the oxide lattices depending on the synthetic route, which reflect in the photocatalytic performances of the modified semiconductors. The photocatalytic degradation of wastewater pollutants in complex matrices requires a close scrutiny of the generated byproducts to avoid possible accumulation of intermediates even more toxic than the parent compound. In this respect, I determined that the degradation of tetracycline, a widely used antibiotic, by a benchmark TiO2 sample, despite the fast pollutant disappearance, leads to poor mineralization and byproduct accumulation, especially in the presence of common electrolytes, such as HCO3-. Conversely, the use of commercial ZnO samples with the same surface area resulted in a faster tetracycline degradation kinetics and a much higher mineralization degree compared to TiO2 in all the investigated water matrices. These results can be attributed to different photo-degradation pathways followed by the two oxides, as shown by tests with radical scavengers and by-product analyses. While TiO2 degradation pathways are strongly dependent on both hydroxyl radicals and holes, ZnO mineralization activity is mostly related to holes, which limits the interference of •OH-scavenger species such as bicarbonates. Photo-induced synthesis of oxide-polyaniline composites for environmental remediation. To date, photocatalysis remains a comparatively slower and costlier wastewater treatment compared to adsorption. For this reason, during my Ph.D I also investigated new generation adsorbents characterized by easier regeneration and ability to perform a controlled release of the adsorbed species to be further treated or reused. To this aim, I investigated polyaniline (PANI) composites prepared via an innovative photocatalytically-induced synthesis. PANI materials have been recently adopted as sorbents for environmental remediation due to their stability, redox properties and acid-base characteristics. However, PANI traditional oxidative synthesis (here labeled as PANI-aniline) adopts noxious and toxic reagents (aniline and (NH4)2S2O8) and leads to carcinogenic by-products and large amounts of waste. The alternative photocatalytic approach I developed is a two-step synthesis starting from aniline dimer (N-(4-aminophenyl)aniline) and exploiting TiO2 photocatalyst to initiate the oligomerization, and a greener oxidant (H2O2) in the polymerization step. The resulting PANI-TiO2 nanocomposites showed very different structural, morphological and surface properties with respect to PANI-aniline, resulting in fast and efficient removal of water pollutants. To better understand the reaction pathway and tailor the material properties, the relative roles played by TiO2 and H2O2 in the synthetic procedure were investigated in depth. UV-irradiated TiO2 was found to promote PANI crystallinity and polymer-oxide interactions. The amount of added H2O2 has a crucial role on the composite properties by promoting either surface growth of PANI chains or polymerization in the liquid bulk. High H2O2 amounts seem to promote a homogenous polymer formation mechanism, leading to nanocomposites with high PANI content and thermal stability, but low crystallinity degree and surface area. Low H2O2 quantities give rise to highly porous, large surface area nanocomposites with good crystallinity but low PANI content. The latter samples exhibited the best performance in pollutant sorption tests, achieving a fast and complete removal of dyes and heavy metals also in the presence of electrolytes. These samples also showed reusability in consecutive stress tests and could be regenerated simply by treatment with alkaline aqueous solution at room temperature. The next step was to investigate the role of the nature and morphological features of the semiconductor: commercial TiO2 photocatalysts with either 50 m2g-1 (labeled TiO2-P25) and 12 m2g-1 (TiO2-Kronos) were compared with WO3 either lab-synthesized (3.5 m2g-1, named WO3-Synt) or commercial (6.1 m2g-1, WO3-Comm). The composites showed a nanorod / nano-wire morphology: the length of the polymeric rods and the embedding of the oxide particles within the polymer network strongly depended on the nature and morphology of the photocatalyst. Furthermore, while > 80% total dye removal capacity was observed for all samples (with the exception of PANI-WO3-Comm), notable differences were observed in terms of released tests. In particular, PANI-oxide composites consistently showed dye-release capacities far higher than PANI-aniline. The ease of desorption opened the door to the facile regeneration of the adsorbent and to the adsorbate recovery for its recycle in a circular economy perspective. Therefore, I investigated an adsorption-photocatalysis coupled system which exploited the reversibility of the pollutant removal process. In particular, after consecutive dye adsorption cycles, the contaminant was released by the PANI-oxide adsorbent and subsequently mineralized by a ZnO driven photocatalytic process. The nature of the adsorption process was deeply investigated and selectivity tests with cationic and anionic dye mixtures proved the preferential adsorption of PANI-oxide adsorbents towards anionic dyes. In the end, the promising and reversible adsorption capability of PANI composites prompted me to investigate their possible application in CO2 capture systems. Thus I have worked on reviewing the literature works on the topic, comparing the performances of different PANI materials towards CO2 removal. Smart systems based on light-responsive oxides. The intrinsic characteristics of semiconductor oxides, such as their photocatalytic and surface properties, can be exploited in the design of smart systems for the controlled release of unstable active substances, such as essential oils. Among them, cinnamaldehyde (CIN) is a low-cost natural compound endowed with antibacterial, anti-cancer, antifungal, and anti-inflammatory properties. However, CIN has poor water solubility, high volatility and very poor stability in environmental conditions, undergoing degradation when exposed to heat, light or even oxygen. These issues hinder CIN applicability, thus smart systems able to store this active substance and to safely release it at will, are of extreme interest for the scientific community. In this context, during my Ph.D. I developed oxide-based hybrid systems for the release of CIN catalyzed by acidic pH. The smart system was obtained by a grafting method based on amino-silane linkers and imine chemistry: (3-aminopropyl)triethoxysilane (APTES) was adopted for the functionalization of the oxide surface. The terminal amine group of the silane (-NH2) was used for a condensation reaction with the aldehydic group of CIN (-HC=O), yielding an imine bond (-HC=N-) between APTES and CIN and a loading of ca. 5 molecules/nm2, determined with CHN and TG analyses. The covalent grafting of cinnamaldehyde, showed by FTIR spectra, preserved the molecule stability, simplifying storage. Release tests were performed at pH values between 5.0 and 7.4: thanks to the pH-sensitivity of imine bonds, a fast CIN release was observed at pH 5.0. The grafting procedure was also performed on a porous semiconductor film, demonstrating the versatility of this method. Exploiting the oxide photoactivity, the fouled film was regenerated upon 1h UV irradiation, opening the door to reusable devices for CIN controlled release. Besides the conventional approach of loading bioactive compounds on solid drug carriers, smart systems based on particle-stabilized emulsions (i.e., Pickering emulsions) are receiving increasing attention from the scientific community. In this regard, during my last year of Ph.D. I investigated oil-in-water Pickering emulsions prepared with food-grade vegetable oils and stabilized with bare ZnO particles. FTIR studies highlighted that, during emulsification, ZnO particles undergo an in situ functionalization by fatty acids present in the vegetable oil. This procedure gives rise to very stable and homogeneous emulsions (mean droplet size ca. 1 μm). Confocal microscopy images demonstrated the high stability of the system towards long time storage (more than 9 months), temperature variations, mechanical stress and increased ionic strength. ZnO-Pickering emulsions were loaded with CIN in the oil phase, in order to store the active molecule and release it at will by the application of five different stimuli. In particular, thanks to the semiconductor and amphoteric properties of ZnO, the developed smart system was able to release CIN by switching to a water-in-oil Pickering emulsion when subjected to acidification, UV and solar light irradiation, CO2 bubbling and the addition of bi/trivalent cations. This is the first report of an emulsion system responsive to five different stimuli. Depending on the type of stimulus, either a burst release or a controlled release over the course of several hours could be achieved. The emulsion switching can be attributed to the oxide surface charge: when ZnO is negatively or slightly positively charged, the oil-in-water emulsion is stable, while, when the oxide surface has high positive charge, the oil droplets’ intrinsic negative charge is neutralized and coalescence phenomena occur. A more positive ZnO surface charge can be achieved through the addition of acidic species (such as H+ and H2CO3 via CO2 bubbling), multivalent cations, which give specific adsorption on ZnO surface, and through light irradiation, which activates the photocatalyst and generates acidic species. The starting oil-in-water emulsion could be reobtained by basification, N2 bubbling and storage in the dark. The ZnO Pickering emulsions were able to safely store and release CIN molecules, which did not undergo any degradation neither during storage, nor after release in water solution. In the end, I have contributed to a work on near infrared (NIR)-emitting GdVO4:Nd systems. This composite material proved promising for bioimaging applications, thus, I exploited my experience oxide synthesis to investigate the role of the synthetic procedure on the material properties and NIR-emitting activity. Moreover, test on GdVO4:Nd functionalization with silane molecules (octylsilane and APTES) were carried out. The modification of the material surface with organic compounds can led to a possible increase in the material biocompatibility, as well as to the possible grafting of active molecules, such as cinnamaldehyde, for application in theragnostic. Chemistry dissemination activities. During my PhD, I was involved in chemistry dissemination activities in the framework of the “Piano Lauree Scientifiche, PLS”. In this context, I helped to develop two laboratory activities for high school teachers and students. The first one, aimed at teaching the basic concepts of surface science, focused on the preparation of superhydrophobic coatings based on films of surface functionalized oxide particles. The film’s superhydrophobicity was tested for different applications (anti-stain, self-cleaning, liquid transportation) and compared with model hydrophobic, hydrophilic, and superhydrophilic surfaces. The second activity mimicked the chemistry of stained glass, introducing basic concepts of redox reactions, chemistry of color, and plasmonic nanoparticles. Stained glass colors were copied through the deposition, on glass slides, of silica coatings colored by metal ions and nanoparticles. A silica sol was used as matrix to embed metal ions, which were reduced in situ by thermal treatment on a hot plate. The formation of metal nanoparticles by this procedure induces plasmonic colors in the glass coating, thus “mimicking” the ancient procedure of stained-glass fabrication. These works led to two publications on the Journal of Chemical Education.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 2014.
Cataloged from PDF version of thesis. "October 2013."
Includes bibliographical references (pages 90-109).
This thesis focuses on the design of novel inorganic water-splitting photocatalysts for solar applications using first principles computations. Water-splitting photocatalysts are materials that can photo-catalyze the water-splitting reaction under certain conditions. They provide an alternative way to capture and store the energy from the sun. Currently, the energy conversion efficiency of photocatalytic devices under solar illumination and in pure water (pH=7) is still far from the commercialization target. The design of new photocatalysts with better potentials is the key to solve this problem. We have first developed a so-called three-step method to compute the relative position of a semiconductor's conduction band (valence band) vs. the H₂/H₂O (O₂/H₂O) level in solution from first principles. The merits of the method have been highlighted, and the performance of the method has been tested and compared with the performance of other methods. We conclude that the three-step method provides the desired accuracy for high throughput screening at an acceptable computational cost. We have designed a three-tier first principles high throughput screening system to identify new water-splitting photocatalysts by examining the phase stability, band gap and band edge positions of the candidate compounds. We construct the screening system by integrating the three-step method together with other previously developed methods in our group. We use the system to screen about 3000 different materials. Through the screening, most of the known water-splitting photocatalysts have been reproduced and, more importantly, sixteen new promising candidates have been proposed. Properties of these new candidates have been analyzed and compared to those of the known photocatalysts. Some particularly promising ones are highlighted. Ti₃O₃N₂ is one of the identified candidates from the high throughput screening, and is particularly interesting as it has good phase stability, a low band gap and suitable band edge positions. In addition, it has the same crystal structure as Ta₃N₅ , which is also a photocatalyst with a low band gap. This leads to our study on the Ta₃N₅:Ti₃O₃N₂ solid solution as a water-splitting photocatalyst. Using first principles computations, we study the phase stability, band gap and band edge positions of the solid solution. The results suggest that the Ta₃N₅:Ti₃O₃N₂ solid solution may have a better potential than both its end members as a water-splitting photocatalyst.
by Yabi Wu.
Ph. D.

La recherche scientifique contemporaine en matière de matériaux est largement orientée autour de l’optimisation et l’élaboration de nouveaux matériaux poly-fontionnels, multi-structurés et aux dimensions réduites. De tels matériaux conduisent à s’intéresser à la problématique des comportements spécifiques résultant des différentes interfaces mises en jeu ; il peut s’agir d’interfaces physiques entre différents milieux (états différents, compositions chimiques différentes …) ou des interfaces entre différentes propriétés. Dans ce contexte, nous nous sommes intéressés aux corrélations pouvant exister entre les propriétés de luminescence et la réactivité de surface de films mésoporeux d’oxyde métalliques dopés avec des ions EuIII. Ces deux propriétés étant fortement dépendantes de la structure des matériaux, une grande partie de notre travail a été dédiée à la caractérisation de cette dernière. Un intérêt particulier a été porté à l’étude des conséquences de la présence des ions EuIII et à la localisation de ces derniers au sein des matrices étudiées. Finalement, il est apparu que la luminescence des ions EuIII au sein des films mésoporeux à base de TiO2 peut permettre de suivre les réactions redox se produisant au sein des pores, comme par exemple la photo-dégradation de composés organiques ou la photo-réduction de sels métalliques. La photo-réduction in situ permet la formation de réseaux périodiques de nanoparticules métalliques. Ces matériaux offrent donc de nombreuses perspectives d’applications dans des domaines aussi variés que les télécommunications optiques, la photonique, la photocatalyse…
Materials contemporary scientific research is largely devoted to the optimization and the elaboration of new poly-functional, multi-structured and size-reduced materials. Then, specific behaviors due to the different interfacial aspects of those materials – physical interfaces between different matter states, different chemical phases… or properties interfaces – have become a major issue requiring further investigations. In this context, our work deals with correlations that could be established between luminescence properties and surface reactivity of EuIII-doped metal oxide mesoporous thin films. As properties can be linked to materials structure, an important part of our work has been dedicated to structural characterization. EuIII ions incorporation specific effects and ions location within film walls have been particularly studied. Finally, it appeared that EuIII ions luminescence could provide a mean to follow redox reactions occurring within pores, such as organic compounds photo-degradation or metallic salts photo-reduction. In situ photo-reduction can lead to periodic arrays of metallic nanoparticles. La photo-réduction in situ permet la formation de réseaux périodiques de nanoparticules métalliques. Those materials can open up the way in many applications such as optical telecommunication, photonics, photocatalysis…

本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである
Kyoto University (京都大学)
0048
新制・論文博士
博士(工学)
乙第9830号
論工博第3320号
新制||工||1114(附属図書館)
UT51-98-G429
(主査)教授 吉田 鄕弘, 教授 川﨑 昌博, 教授 横尾 俊信
学位規則第4条第2項該当

Maintaining a constant supply of clean drinking water is among the most pressing global challenges in our time. About one-third of the population is affected by the water scarcity and it can only get worse with climate change, rapid industrialization, and the population growth. Even though nearly 70 percent of the planet is covered by water, the consumable freshwater content is only 2.5 percent of it. Unfortunately, the accessible portion of it is only 1 percent. Even so, most of the freshwater bodies are choked with pollution. Considering the vast availability of saline water on the planet and the increasing wastewater generation, seawater desalination, and wastewater treatment and recycling seem to have the potential to address current water-related issues. Therefore, it is necessary to find efficient techniques for seawater desalination and wastewater treatment. The use of nanostructured materials for these applications is becoming a popular approach due to the unique chemical and physical properties they possess compared to bulk materials Solar energy is the cleanest and most abundant renewable natural resource available. Materials for solar photothermal energy conversion are highly sought after for their cost savings, clean environment, and broad utility in providing water heating and/or steam for many applications including domestic water heating and solar-driven desalination. Extensive research efforts have been made to develop efficient solar absorbers with characteristics such as low weight, low thermal conductivity, broad solar absorption and porosity to be able to float on water to provide more efficient and cost-effective solar steam generation systems. Metal NPs have been proposed to take advantage of the high efficiency of the photothermal energy conversion associated with surface plasmon resonance absorption. Nanostructured carbon-based materials such as graphene oxide, carbon nanotubes, carbonized biomass are also in use due to their excellent photothermal energy conversion ability over the range of the visible and near infra-red region of the electromagnetic spectrum. In this dissertation, five projects based on the utility of nanostructured materials for desalination, photocatalysis and water treatment will be discussed. The first three projects involve the fabrication and design of plasmonic and carbon-based photothermal materials for applications in solar steam generation, water desalination, and wastewater treatment. In the fourth project, a unique shape of ZnO nanostructure was synthesized for photodegradation of organic dyes in industrial wastewater. The final project demonstrates the shape-controlled synthesis of iron carbide nanostructures and composite materials of aminated graphene oxide for the removal of Cr(VI) from wastewater.

La recherche de nouveaux matériaux en tant que photocatalyseurs en lumière visible pour la dépollution de l’environnement (eaux, atmosphères) est un domaine de recherche très actif et suscite l’intérêt d’une large communauté scientifique en Physique, Chimie et Sciences des matériaux. Des recherches exhaustives sont actuellement menées pour améliorer l’efficacité photocatalytique de certaines classes de matériaux photoactifs connus, et pour développer la synthèse de nouveaux matériaux fonctionnels. Dans ce contexte, les semiconducteurs oxydes photoactifs à base de vanadates de bismuth (BiVO4) possédant une bande électronique au milieu du spectre visible, offrent une sérieuse alternative aux photocatalyseurs classiques efficaces (TiO2, ZnO) dont la photo-excitation requiert uniquement la fraction UV du spectre solaire. Le travail effectué dans le cadre de cette thèse est donc dédié aux matériaux à base BiVO4 sous forme d’architectures mésoporeuses ou d’assemblages hybrides associant des groupes organiques à transfert de charges.Deux contributions majeures ont été développées dont la première portant sur la réalisation expérimentale d’architectures mésoporeuses inédites, fonctionnalisées par des groupes organiques sensibilisateurs et l’étude de leurs propriétés électroniques et optiques en vue d’optimiser leurs efficacités photocatalytiques. La deuxième partie porte sur des simulations numériques de nanostructures hybrides par des approches exploitant la méthode DFT, ab-initio ou des modèles de chimie quantique. Des systèmes modèles ont été construits associant des nanoclusters (NC) et des groupes organiques (GO). Les propriétés électroniques et optiques ainsi que les caractéristiques structurelles et vibrationnelles des systèmes (NC-GO) ont été déterminées et confrontées aux données expérimentales. Les phénomènes de transfert de charges impliqués entre les groupes organiques et la structure inorganique ont été caractérisés ainsi que leur rôle dans l’efficacité des réponses photo-catalytiques des systèmes hybrides
The search for new materials as photocatalysts invisible light for the depollution of the environment (waters, atmospheres) is a very active field of research and attracts the interest of a large scientific community in Physics, Chemistry and Materials Science. Recent research developpements are conducted to improve the photocatalytic efficiency of certain classes of known photoactive materials, and to develop the synthesis of new functional materials. In this context, photoactive oxide semiconductors based on bismuth vanadate (BiVO4) having an electronic band in the middle of the visible spectrum, offer a serious alternative to efficient conventional photocatalysts (TiO2, ZnO) whose photo-excitation requires only the UV fraction of the solar spectrum.The work done in this thesis is therefore dedicated toBiVO4-based materials in the form of mesoporous architectures or hybrid assemblies associating organic groups with charge transfer processes. Two major contributions have been developed, one of which is the experimental realization of novel mesoporous architectures, functionalized by sensitizing organic groups and the study of their electronic and optical properties in order to optimize their photocatalytic efficiencies. The second part deals with numerical simulations of hybrid nanostructures using approaches as the DFT method, ab-initio or quantum chemistry codes. Model systems have been constructed associating BiVO4nanoclusters (NC) and organic groups (GO). The electronic and optical properties as well as the structural and vibrational characteristics of the systems (NC-GO) were determined and compared with the experimental data. The charge transfer phenomena involved between the organic groups and the inorganic structure were characterized as well as their role in the efficiency of photo-catalytic responses of hybrid systems

The results presented in this Ph.D. thesis are focused on the use of nanostructured titanium dioxide for environmental remediation and for biomedical applications. In the first part, the importance of the choice of a suitable and reliable synthetic route for obtaining nanomaterials with tailored properties for a specific application is highlighted. Several research projects on the design and sol-gel synthesis of TiO2 nanoparticles have been carried out. The experimental evidences suggest that sol-gel synthesis allow tailoring the morphological and superficial properties of the samples. The latter are strictly correlated to the photocatalytic activity of TiO2 home-made samples for the degradation of pollutants in air (e.g., toluene and nitrogen oxides). Moreover, exploiting the capability of sol-gel synthesis, the light absorption of the photocatalyst is extended from UV to the visible spectrum via a nitrogen doping. The morphology, bulk superficial properties, and photocatalytic activity of TiO2 nanoparticle are also influenced by the direct physical/chemical effects of ultrasounds. Interestingly, using ultrasonic spray pyrolysis (USP), we can exploit indirect effects of ultrasounds to synthesized nanostructured materials. Here, it is presented the design, synthesis, characterization, and application in photocatalysis of porous TiO2 microsphere with tunable physico-chemical properties obtained through USP. The second part of this Ph.D. thesis is focused on the study of the interaction among inorganic surfaces and biomolecules or, in general, biological systems. In a first work, we have synthesized sol-gel TiO2 nanoparticles with different morphology and use them for preliminary study of acetyl salicylic acid delivery. Moreover, the possibility to use TiO2 as a material for scaffold for bone regeneration is reported. This study has led to unravel a new bio-inspired crystallization pathway toward the bioactivity of synthetic bone substitutes. Other examples in the biomedical field are reported in Appendix A.

The basis of prosperity of 20th centrury is oil. As oil is going to be used up, people need to find alternatives to meet the earth’s energy demand in 21st centrury. For each second, there are about 1.2×1017 J energy hitting the earth. The energy in 1 hour of sunlight is about 4.32×1020 J, which almost meets the energy consumed on earth in 2016. It determines solar energy may be a potential candidate to solve the energy crisis. As for techniques to utilize solar energy, the most popular one is using photovoltaic (PV) cells. PV cell is a device to convert solar energy into electricity. There are also some other techniques trying to utilize solar energy. Photocatalysis is one of them, which is to convert solar energy into chemical energy. Applications of photocatalysis have extended from hydrogen evolution via water splitting to environemtnal remediation, CO2/ N2 reduction and so on. Photocatalysis, as an advanced oxidation process, has been extensively studied and applied to the purification and remediation of contaminated water and wastewater, and exhibits advantages over conventional treatment technologies. When considering solar energy as an energy source for photocatalysis, it is key to prepare visible light-responsive materials. Bismuth-based semiconductors are promising materials as visible light-responsive photocatalysts primarily due to their suitable band gaps, well-dispersed valence bands, and commercial availabilities at reasonable costs, as well as the possibility of preparing them under mild conditions. Recent work focusing on the preparation, characterization and activity testing of bismuth-based photo-active materials as well as their associated photoreactor designs are introduced herein. In order to enhance the photocatalytic activities of the new materials, different precursors, additives, preparation procedures and process parameters, as well as surface treatments were explored to obtain binary and ternary heterostructures, with different doping, surface modification, nanoparticle sizes and morphologies. It was found that formation of heterojunction and loading metal nanoparticle on the surface are very effective to imrove the photocatalytic activity of the support. In this work, we found that palladium nanoparticles modified BiVO4 exhibited excellent activity in the decomposition of phenol, which was even higher than TiO2. To facilitate the separation process of catalysis particels from a slurry system, magnetically separable composites were also prepared, and it was found that it is very effective to remove the particles from the slurry system using external magnets. To further scale up this process, two different types of immbolized photoreactors (flat-plate and packed beads photoreactor) were also developed. Suggestions were made for further work in this research area.

As a promising and green method, wastewater purification techniques based on photocatalyst have received much attention in recent years. However, problems such as low quantum efficiency, limited light responding range and recovery problems limit the further applications of photocatalyst-based materials. In this study, a Ag3PO4 photocatalyst with tube-like structure has been synthesized by self-assembly at room temperature. The properties of the catalyst are investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM) and N2 adsorption-desorption. The photocatalytic activities of the tube-like Ag3PO4 are mainly studied by degradations of methyl orange (MO) and rhodamine B (RhB) organic dyes. The effects of pH values and stabilities on photocatalytic performance are studied as well. The results reveal that the tube-like Ag3PO4 exhibits greatly high activities for the degradation of RhB solution under acidic condition. The excellent activities of the photocatalyst are due to the small dimension, unique nanostructure and specific surface property. Importantly, Ag3PO4 photocatalysts are found with unexpected photocatalytic activity (completion degradation of RhB-MO mixed dyes in 28 h) under natural indoor weak light, of which the light intensity (72 cd) is one in a thousand that of a 300 W Xe lamp (68.2*103 cd). The degradation of simulated wastewater containing organic dyes and inorganic ions by Ag3PO4 under indoor weak light also reveals the potential of Ag3PO4 in practical applications of wastewater cleaning and environmental remediation by solar energy-driven photocatalysis.

Les matériaux pour la photocatalyse en lumière visible ont attiré un grand intérêt car ils peuvent exploiter tout le spectre d'irradiation solaire notamment afin de détruire des polluants organiques pour l'environnement comme dans la purification de l’eau. Dans ce contexte, le bismuth de vanadates (BiVO4) est digne d'intérêt en raison de sa largeur de bande interdite électronique (~ 2,3 eV) et sa potentielle activité photocatalytique. Des études systématiques ont été menées pour les caractéristiques physico- chimiques de poudres BiVO4 synthétisées par voie hydrothermale et par broyage mécanique à haute énergie. La pertinence de la méthode de mécano-synthèse a été démontrée grâce notamment à son faible coût de fonctionnement, de mise en œuvre facile ainsi que le nombre limité de paramètres et la possibilité d’obtenir des particules à taille réduite (20-100 nm) avec une phase cristalline monoclinique. En couches minces, les matériaux BiVO4 ont été synthétisés par pulvérisation ultrasonique (USP) et par pulvérisation cathodique radiofréquence (rf). Les paramètres pour des dépôts optimaux ont été identifiés permettant d’obtenir des films minces sans fissures, suffisamment denses avec des surfaces texturées à morphologies contrôlées. Les études structurales, vibrationnelles, et les propriétés électroniques et optiques ainsi que leur interprétation grâce à des modèles ont été menées pour une parfaite connaissance des caractéristiques des matériaux BiVO4. Pour les applications visées, BiVO4 sous forme de poudres et de films minces ont été utilisés comme photocatalyseurs pour la dégradation de rhodamine 6G (Rh6) et le bleu de méthylène (MB) sous irradiation en lumière visible. La structure scheelite monoclinique de nanoparticules sphérique de BiVO4 obtenues par mécano-synthèse, ont montré une efficacité améliorée (+50%) de l’activité photocatalytique par rapport à des particules de forme aciculaire obtenues par voie hydrothermale. Dans le cas de films minces, le taux de dégradation du BM est de l’ordre est de 66% pour les films synthétisés par USP alors qu’un taux de 99% a été atteint avec des films obtenus par pulvérisation cathodique rf. Ces travaux valident les propriétés photocatalytiques remarquables de BiVO4 par rapport aux matériaux existants avec des applications prometteuses, notamment dans la résolution de problèmes environnementaux
Visible light photocatalysts have attracted a great interest since it may exploit the wide solar irradiation spectrum to destroy organic dyes as required for environmental need such as water purification. In this context, bismuth vanadate (BiVO4) is worth of interest due to its narrow band gap (~ 2.3 eV) and the ability to exhibit efficient photocatalytic activity. Systematic studies have been carried out on the physico-chemistry of BiVO4 synthesized as powders by hydrothermal and mechano-chemical techniques. The relevance of ball milling method was demonstrated through its low processing cost and easy scaling up as well as limited variable parameters to obtain reduced particle sizes down to (20-100 nm). As thin films, BiVO4 were grown by ultrasonic spray pyrolysis (USP) and rf-sputtering techniques. Optimum deposition parameters were identified, leading to the formation of crack free, dense media with textured surfaces composed by controlled morphologies. Analysis of the structural, vibrational, electronic and optical experiments, interpretation and development of models were carried out for deep insight on the properties of BiVO4 materials. For concrete applications, BiVO4 as powders and thin films were used as photocatalysts for the degradation of rhodamine 6G (Rh6) and methylene blue (MB) under visible light irradiation. Monoclinic scheelite structure of spherical-like BiVO4 nanoparticles obtained by mechano-chemical process, have shown 50% more efficient photocatalytic activity compared to acicular-like BiVO4 grains obtained by hydrothermal method. The average degradation rate of MB using USP grown films was found to be 66% during 120 minutes. A significant rate increase in the photocatalytic activity up to 99% was achieved by using rf-sputtered films. Thus, BiVO4 was demonstrated as efficient photocatalysts compared to existing materials with promising applications notably in solving environmental problems

Carbon-semiconductor hybrid materials (CSHMs) are promising candidates for solar energy conversion because of their enhanced light harvesting ability and the prolonged charge carrier separation. In this thesis, a series of CSHMs has been successfully fabricated and applied in photocatalysis and dye-sensitized solar cells. The aim of this thesis is to develop cost-effective methods to prepare CSHMs with appropriate morphologies, compositions, and interfacial contact to promote the efficiency of photocatalysis and solar energy conversion.

The development of mesoporous titania (meso-TiO2) films is a considerable research goal in the field of mesoporous material development due to their proven applicability in solar cells and phtocatalysts. In this work, the meso-TiO2 films were fabricated through different methods and these home-made titania structures were applied in DSSCs and photocatalysts. Meso-TiO2 powders were first prepared from ethanol/water or ethanol solvent. The meso-TiO2 made from the ethanol/water solvent did not have an ordered mesostructure, but that made from ethanol solvent had 2D-hexagonal mesostructure. Films were prepared by adding ordered meso-TiO2 particles into paste formulations of P25 nanoparticles with weight proportion ranging from 0 to 100%. These were used to form films by doctor blading, and the influence of paste composition on film structure, morphology, porosity, optical properties and cell performance were investigated. Secondly, ordered meso-TiO2 films were fabricated by dip coating from aqueous or ethanol solvent. Both films had cubic mesostructures, but the film coated from aqueous solvent was not uniform. The film formed from ethanol solvent was doped with sulphur. The effects of doping on the mesostructure, morphology, structure, optical properties and photocatalytic activity were studied. The thickness of films was increased by repeated coating. The number of layers had an influence on the mesostructure, morphology, optical properties and cell performance when these films were applied in DSSCs Finally, a novel method was adopted to prepared meso-TiO2 films. Molecular titania precursors or titania colloidal seeds were used as the titania source. Both of them can be used to prepare free-standing hybrid films at air-water interface by a self-assembly method, however the one synthesised from the molecular titania precursor did not contain very much titania and became a powder after calcination. In contrast, after calcination, the films formed from the colloidal titania solution remained intact, and were composed of mixtures of TiO2 nanoparticles and nanowires with mesopores arising from interparticle porosity. These films were applied in DSSCs. This interfacial method was also successfully extended to prepare free-standing ZnO films from a molecular precursor. After calcination, the free-standing ZnO films were found to be composed of rough spheres formed by flocculation of smaller nanoparticles.

Water pollution is a major concern in vast countries such as India and other developing nations. Several methods of water purification have been practiced since many decades, Semiconductor photocatalysis is a promising technique, for photodegradation of various hazardous chemicals that are encountered in waste waters. The great significance of this technique is that, it can degrade (detoxify) various complex organic chemicals, which has not been addressed by several other methods of purification. This unique advantage made this field of research to attract many investigators particularly in latter eighties and after. This thesis incorporates the studies on the various semiconductor photocatalysts that have been employed for the detoxification purposes. The fundamental principles involved in the photoelectrochemistry, reactions at the interface (solid - liquid or solid - gas) and photocatalytic reactions on fine particles are briefed. General nature and size quantization in semiconductor particles, photocatalytically active semiconductors, TiCh and ABO3 systems, chemical systems and modifications for solar energy conversions are brought out in the introduction chapter besides giving brief description about photocatalytic mineralization of water pollutants with mechanism involved, formation of reactive species and the factors influencing photomineralization reactions. Scope of the present work is given at the end of the first chapter. Second chapter deals with the materials used for the preparation of photocatalyst, preparative techniques, methods of analysis, instruments employed for the photodegradation experiments and a brief description of material characterization methods such as X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, differential thermal analysis, optical absorption spectro photometry, Electron paramagnetic resonance (EPR), and gas chromatograph - mass spectroscopy (GC - MS). Various preparative routes such as wet chemical and hydrothermal methods for obtaining TiO2 (both rutile and anatase forms), BaTiOs and SrTiO3 fine particles and the chemical analysis of their constituents have been described in brief. Third chapter presents the results of materials characterization. T1O2 (rutile and anatase), BaTiO3 and SrTiO3 have been characterized separately using various techniques. Different routes of obtaining the photocatalyst fine particles, heat treatment at various temperature ranges, experimental procedures and the results of characterization are brought out in this chapter. Fourth and fifth chapters present the details of degradation studies carried out on the photomineralization of chlorophenol, trichloroethylene and formaldehyde. Studies include photodegradation of the pollutants with different catalysts varying experimental conditions to check the effects of change in concentration of pollutants, oxidizer, pH, surface hydroxylation, etc. The most favorable conditions for the complete mineralization of the pollutants have been studied. In case of TiO2, anatase form has shown greater photoactivity when compared to rutile and complete mineralization of chlorophenols has been achieved at low pollutant concentrations, neutral pH, with H2O2 and UV illumination. Retarding effects of surface hydroxylation and the formation of peroxotitanium species during photodegradation have been presented. TCE and HCHO degradation with BaTiO3/SrTiO3 has been studied. Photocatalyst heat-treated at 1100°G-1300°C is found to be highly active in combination with H2O2 as electron scavenger. HCHO is not getting degraded to its completeness in aqueous conditions owing to the strong competition in surface adsorption posed by H2O molecules. Vapour-solid phase reaction however gave good results in the detoxification of HCHO via disproportionation. Summary and conclusions are given at the end of the thesis.

Ø
The dissertation is presented on 252 content pages which has been framed in five chapters and two annexures while the title page opens into a list of abbreviations followed by a foreword on the work. The core theme of the research work is to validate the extended photocatalytic properties of porphyrin-POM materials in evolving from UV to visible light range of solar spectrum. Which describing additional modes for synthesis of hybrid materials (i) electrostatic multilayer’s comprising of Dawson , sandwich Dawson type and preyssler,s POM in combination with free base tetracationic porphyrin [H₂TPhN(Me)₃P⁴⁺] (ii) an easy method of synthesis of two dimers with a pyridinium spacer (abbreviated 4-H₂–Zn and 3-H₂–Zn) (iii) Langmuir Schafer approach for hybrid monolayer. The prepared photoactive thin layers have been characterized by UV-visible spectroscopy and fluorescence spectroscopy for optical properties. Cyclic voltammetry for electrochemistry and ionic permeability studies. Atomic force microscopy (AFM) for surface morphology and its role in physical mechanism of reduction process and shape of nanostructures obtained. Transmission electron microscopy (TEM) has been used to interpret size and shape of dendritic silver nanoparticles obtained as photoreduction product. Although ,the ultimate goal is the photoreduction of heavy metals (Cr(VI), Hg(II), Cd(II), Pb(II) ), reduction of a simpler system like Ag⁺ ion has been chosen as a model system due to single electron simpler oxidation reduction process. A novel application of photocurrent generation from these hybrid films has been demonstrated in the fifth chapter of the manuscript as an initial studies which has enhanced the significance of all previously fabricated systems upto by many folds .The foresaid development of photovoltaic application has paved the way for future studies to enhance the photocurrent yield further by tuning the electron donor-acceptor system. Both components porphyrin and POM can be tuned with different axial substituent’s and stereo chemical properties to achieve maximum yield of solar energy as well as diversified metal nanostructure for nanoelectronics, e.g. silver dendrites for sensor applications. At the end of the manuscript, three appendices describe successively the experimental techniques used to carry out this work, the Job method used to determine the stoichiometry and formation constants of complex electrostatic and coordination, and then finally the origin or Protocols for the synthesis of various compounds used

This study are based on the premise that the incorporation of metal ions into nano titania-PHEMA [poly (2-hydroxyethyl methacrylate)] hydrogels would enhance the desirable properties in the photodecomposition of pollutants. The investigation are centered in the use of Cu(II) as metal ion of interest. The development of TiO2-PHEMA-Cu hydrogels was conducted, and the characterization of the materials by FT-IR, XRD and fluorescence was performed. The absorption of copper(II) from the solution was monitored by UV-Vis. The FT-IR are found too, be the most effective tool too, analyze the interaction of Cu(II) with PHEMA in the nanocomposite hydrogels. The free carbonyl group has the IR band at 1715 cm-1 in the TiO2-PHEMA. Upon uptaking Cu(II), the hydrogels showed a new band at 1595 cm-1. Further examination establishes the relationship between the two bands. The time-dependent study revealed that the intensity of band at 1595 cm-1 would increase while that at 1715 cm-1 would decrease as the time for uptaking Cu(II) increased. A concentration-dependent study also demonstrated the same trend that showed the intensities of the two bands moved in the opposite directions.

Ces travaux s'appuient sur un contexte de santé lié à la dégradation de la qualité de l'air intérieur induite par la présence de micro-organismes. Dans les environnements intérieurs humides, les matériaux de construction sont des cibles de contamination et de prolifération microbienne importantes. La photocatalyse est un procédé de dépollution qui présente une action contre une large gamme de polluants organiques (aqueux, gazeux ou biologiques). Son principe repose sur l'excitation d'un photocatalyseur par une irradiation lumineuse, généralement située dans les UV, qui va permettre de dégrader les polluants environnants par une succession de réactions d'oxydo-réduction. Le photocatalyseur le plus courant est le dioxyde de titane (TiO2). Outre la production d'espèces oxydo-réductrices agressives, le TiO2 illuminé présente également un caractère super-hydrophile qui lui confère un caractère autonettoyant intéressant. Une autre solution est envisagée pour lutter contre la prolifération microbienne sur matériaux de construction : l'utilisation de molécule bio-sourcées d'ester de glycérol aux propriétés naturellement antimicrobienne. L'objectif de cette étude est de développer des revêtements pour matériaux de construction intérieurs et d'étudier leur propriété de résistance à la prolifération microbienne et les modes d'action de ces dispositifs passifs formulés soit à base de particules de TiO2, soit à base d'ester de gycérol. Dans un premier temps, un travail de développement et de mise en œuvre de dispositifs expérimentaux a été nécessaire afin d'adapter des méthodes d'évaluation microbiologiques sur ces matériaux particuliers (particules, lasures, matériaux cimentaires). Ainsi, plusieurs essais ont été adaptés afin d'évaluer les performances antimicrobiennes en terme (i) d'activité antibactérienne, (ii) d'effet bactéricide, (iii) de résistance à la formation de biofilm et (iv) de résistance à la prolifération par contamination " naturelle ". Les premiers essais visent à mettre en évidence l'impact des facteurs méthodologiques sur l'activité antibactérienne des particules de TiO2 utilisées seules comme agent désinfectant. Dans un deuxième temps, des lasures photocatalytiques sont formulées sur la base de travaux antérieurs ayant montrés de bonnes efficacités de dépollution de l'air contre les NOx, NO et différents COV. Une fois les paramètres d'influence de l'activité du TiO2 mis en exergue, les lasures ont été testées dans des conditions optimales. Le développement d'un essai de résistance à la prolifération de biofilm montre l'importance de coupler différentes méthodes d'évaluation microbiologique (dénombrement des UFC et observation au microscope à épifluorescence). La dernière partie de cette étude explore le potentiel antimicrobien de la molécule d'ester de glycérol, sous-produit de la synthèse de biocarburant. La molécule montre des propriétés antibactériennes et bactéricides puissantes en quelques minutes de contact seulement. Elle présente également une protection très efficace contre la prolifération microbienne une fois recouverte sur matériaux de construction (placo-plâtre). Ces performances remarquables encouragent la poursuite des études sur cette molécule
This work is included in a health-related context: the degradation of the indoor air quality induced by the presence of microorganisms. In damp environments, indoor building materials are among the main proliferation substrates for microorganisms. Photocatalysis is a decontamination process which is active against a wide range of organic pollutants (aqueous, gaseous or biological). The principle is based on the excitation of a photocatalyst by light irradiation, usually located in the UV-range, which leads to the degradation or mineralization of surrounding pollutants through a series of oxidative reactions. The most common photocatalyst is titanium dioxide (TiO2). In addition to produce aggressive redox species, the illuminated TiO2 also shows super-hydrophilicity, which has an impact on the first step of microbial biofilm formation: the adhesion of microorganisms. Another technology to protect indoor building materials is explored: the use of glycerol esters, which are bio-based molecules with inherent antimicrobial properties. The main objective of this study is to develop semi-transparent coatings for indoor building materials and to study the resistance to microbial growth conferred by these passive devices, which are formulated using TiO2 nanoparticles or glycerol esters. Initially, the development and implementation of experimental devices has been necessary to adapt microbiological evaluation methods to these particular materials (nanoparticles, surface coatings, cementitious materials). Thus, several tests have been carried out in order to assess the antimicrobial performances in terms of (i) antibacterial activity, (ii) bactericidal effect, (iii) resistance to biofilm formation and (iv) resistance to proliferation by "natural" contamination. First tests aimed to underline the influence of methodological parameters on the efficiency of TiO2 particles used alone as antimicrobial agent. Then, semi-transparent coatings were formulated on the basis of previous works which have shown good efficiencies on the depollution of ambient air from NOx, NO and VOC. Once the parameters that influence TiO2 activity were identified, coatings were tested in optimum conditions. The evaluation of the resistance to biofilm formation shows the importance of overlapping different microbiological evaluation methods (e.g. CFU counting and epifluorescence observations). The last part was an exploratory work on the antimicrobial properties of a glycerol ester molecule, by-product from the synthesis of biofuels. The molecule shows potent antibacterial and bactericidal properties, several log of inactivation within only few minutes of contact. It also provides very effective protection against microbial growth once covered on building materials (plasterboard). These remarkable performances encourage further studies on this molecule

Tesis por compendio
[ES] La conversión de energía solar a productos químicos se considera una de las estrategias más viables para abordar los problemas derivados del uso masivo de combustibles fósiles y la excesiva emisión antropogénica de CO2. En catálisis asistida con luz, incluida la fotocatálisis y la catálisis fototérmica, el punto clave es el desarrollo de fotocatalizadores eficientes y robustos que puedan utilizar al máximo la energía solar y que sean lo suficientemente estables como para su comercialización. Los materiales basados en perovskitas híbridas orgánicas-inorgánicas han revolucionado el campo de la fotovoltaica en la última década, alcanzando una eficiencia de conversión de luz solar del 23%. Dado que los campos de la fotocatálisis y la fotovoltaica comparten procesos comunes, se abre la posibilidad de aplicación de estos materiales en fotocatálisis. Con el objetivo de confirmar esta posible aplicación de las perovskitas híbridas en fotocatálisis, en esta Tesis Doctoral, se han sintetizado nuevos materiales híbridos de perovskita con el objetivo de mejorar su estabilidad frente a la humedad aprovechando la gran variedad de ligandos orgánicos disponibles, que además pueden ser usados para promover modificaciones superficiales capaces de ajustar las propiedades hidrofílicas / hidrofóbicas. La actividad fotocatalítica de estos nuevos materiales de perovskita se ha estudiado en reacciones modelo para confirmar su estabilidad en las condiciones de reacción. Por otro lado, la reacción de fijación de nitrógeno fotoasistida también ha sido estudiada en detalle en esta Tesis Doctoral. Por un lado, se han sintetizado, caracterizado y testado nuevos complejos organometálicos como foto- y electrocatalizadores homogéneos para esta reacción. Estos han demostrado ser capaces de activar la molécula de dinitrógeno bajo un potencial electroquímico de reducción para formar amoníaco. Por otro lado, se han preparado nanopartículas de rutenio depositadas sobre un material de perovskita a base de titanato como fotocatalizador heterogéneo para la producción de amoniaco en flujo continuo. Además, se ha demostrado que la incorporación de metales alcalinos a este fotocatalizador puede potenciar su actividad fotocatalítica en esta reacción. Así, este material compuesto ha demostrado estar entre los fotocatalizadores más eficientes del estado del arte en la actualidad para esta reacción demostrando además una su elevada estabilidad en las condiciones de reacción.
[CA] La conversió d'energia solar en productes químics es considera una de les estratègies més viables per abordar els problemes derivats de l'ús massiu de combustibles fòssils i l'excessiva emissió antropogènica de CO2. En catàlisi assistida amb llum, inclosa la fotocatàlisi i la catàlisi fototèrmica, el punt clau és el desenvolupament de fotocatalitzadors eficients i robustos que puguen utilitzar al màxim l'energia solar i que siguen prou estables com per a la seva comercialització. Els materials basats en perovskites híbrides orgàniques-inorgàniques han revolucionat el camp de la fotovoltaica en l'última dècada, aconseguint una eficiència de conversió de llum solar del 23%. Atès que els camps de la fotocatàlisi i la fotovoltaica comparteixen processos comuns, s'obre la possibilitat d'aplicació d'aquests materials en fotocatàlisi. Amb l'objectiu de confirmar aquesta possible aplicació de les perovskites híbrides en fotocatàlisi, en aquesta tesi doctoral, s'han sintetitzat nous materials híbrids de perovskita amb l'objectiu de millorar la seva estabilitat enfront de la humitat aprofitant la gran varietat de lligands orgànics disponibles, que amés poden ser usats per a promoure modificacions superficials capaços d'ajustar les propietats hidrofíliques / hidrofòbiques. L'activitat fotocatalítica d'aquests nous materials de perovskita s'ha estudiat en reaccions model per confirmar la seva estabilitat en les condicions de reacció. D'altra banda, la reacció de fixació de nitrogen fotoassistida també ha sigut estudiada en detall en aquesta tesi doctoral. D'una banda, s'han sintetitzat, caracteritzat i testat nous complexos organometàl·lics com foto- i electrocatalitzadors homogenis per a aquesta reacció. Aquests han demostrat ser capaços d'activar la molècula de dinitrogen sota un potencial electroquímic de reducció per formar amoníac. D'altra banda, s'han preparat nanopartícules de ruteni depositades sobre un material de perovskita a força de titanat com fotocatalitzador heterogeni per a la producció d'amoníac en flux continu. A més, s'ha demostrat que la incorporació de metalls alcalins a aquest fotocatalitzador pot potenciar la seva activitat fotocatalítica en aquesta reacció. Així, aquest material compost ha demostrat estar entre els fotocatalitzadors més eficients de l'estat de l'art actualment per a aquesta reacció seva demostrant amés una elevada estabilitat en les condicions de reacció.
[EN] Solar energy to chemicals conversion is regarded to be one of the most plausible strategies addressing the issues of fossil fuel crisis and excessive anthropogenic CO2 emission. For photo-assisted catalysis, including photocatalysis and photothermal catalysis, the key point is the development of efficient and robust photocatalysts that can efficiently utilize the solar energy as well as they are stable enough that meets the requirements for commercialization. Hybrid organic-inorganic perovskites have revolutionized the photovoltaic field in the last decade, reaching a certified sunlight conversion efficiency of 20 %. Since photocatalysis and photovoltaics share common processes, the application of these materials in photocatalysis would be possible. In this Doctoral Thesis, novel hybrid perovskite materials have been synthesized with the aim to improve their stability against moisture by taking advantage large variety of the available organic ligand, which can promote surface modifications capable to adjust the hydrophilic/hydrophobic properties. Additionally, the photocatalytic activity of these novel perovskite materials has been studied in model reactions in order to confirm their stability under reaction conditions. On the other hand, the photo-assisted nitrogen fixation reaction has been also studied in detail in this Doctoral Thesis. on one hand, new organometallic complexes have been synthetized, characterized and tested as homogeneous photo and electrocatalysts for this reaction. They have been demonstrated to be able to activate dinitrogen molecule under electrochemical cathodic potentials to form ammonia. On the other hand, ruthenium nanoparticles deposited on a titanate-based perovskite material have been prepared and tested as heterogeneous photocatalyst for ammonia production in continuous flow. Moreover, it has been demonstrated that the addition of alkali metals to this photocatalyst can boost the photocatalytic activity of this reaction. Thus, this composite material has demonstrated to be among the most efficient photocatalysts in the current state-of-the art for this reaction, as well as very stable under reaction conditions. Considering the large industrial importance of N2 fixation and the mild conditions of pressure and temperature used in the present study, the results of the photo-assisted N2 hydrogenation to ammonia can have a large impact in the area.
Peng, Y. (2021). Hybrid Lead Perovskites as Photocatalysts and Materials for Photo- and Electrocatalytic N2 Reduction [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/171731
TESIS
Compendio

The development of sustainable and green technologies powered by renewable energy sources is highly desired to address the growing global energy need and water scarcity problems. Heterogeneous photocatalysis emerged in the past decades as promising solar-powered technology for environmental remediation applications such as wastewater treatment. The photoactivity of the materials is believed to be governed by complex mechanisms, still it was shown that it may be critically dependent on the following material properties (i) ability and effectiveness to absorb incident photons, (ii) charge separation efficiency, (iii) charge utilization efficiency, (iv) morphology including the size and shape of the nanostructure and its distribution and (v) the crystal structure, phase composition and crystallinity ... etc. Hence, most strategies aiming to improve the performance of photocatalytic materials may focus on one or more of the aforementioned aspects. Beside developing new materials or modifying existing systems, the development of sustainable, easy-to-operate systems are highly desired for developing countries such as Africa where almost half of the population are affected by water scarcity of some sort. For this motivation the immobilization of powder catalyst could be one attractive solution. In this thesis three experimental systems are presented. In the first two the effect of material properties on the photoactivity whereas in the third chapter the immobilization of powder catalyst was investigated. The first experimental project aimed to study the effect of synthesis parameters of WO3 nanostructures on its morphology, phase composition, optical properties and ultimately on the photoactivity. Understanding the role of process parameters to gain control over the material properties is still a challenge but is of great interest in photocatalysis. Here, a hydrothermal synthesis method was employed to synthesize WO3 nanostructures with various morphologies, crystal phases and optical properties. The effect of the solution pH, the polymeric surface modulator and the added EtOH was investigated on the material properties and on the photocatalytic activities. It was found that the crystal structure and the morphology of WO3 was influenced by the solution pH in the first place. It was proposed that stabilization effects between the crystal phase and the morphology could also influence the crystallization process beside supersaturation. It was revealed that despite the highest surface area of W-2.01-P20E, reduced oxidation state did not promote high photo-response. Instead the photoactivity of WO3 was seen as the compromise of the material properties including the optical, structural properties and the oxidation state. In the second experimental project the effect of Ag co-catalysis was studied on TiO2- Cu2O heterostructure formation. Coupling a wide band gap (TiO2) and a narrow band gap (Cu2O) semiconductor could benefit from extended light absorption properties and additionally from enhanced charged separation. In this study a facile wet chemical synthesis method was coupled with a UV treatment step to fabricate TiO2-Ag-CuxO ternary hybrid nano-materials. The effect of the Ag loading (1-5%) and the synthesis sequence of the Ag deposition step was evaluated on the material properties as well as on the visible photocatalytic activity. It was revealed that both the amount and the order of the Ag-deposition altered the material properties considerably. Typically TiO2/CuxO/Ag (TCA) catalysts had better visible light absorption properties but reduced affinity to adsorb methyl orange (MO) to their surface. Whereas, TiO2/Ag/CuxO (TAC) catalysts in general had better dye adsorption properties relative to TCA and had more efficient decoloration properties under visible light. TOC and HPLC-MS analysis revealed that MO and possibly its degradation products were mainly mineralized and/or adsorbed to the surface of TAC catalyst with 5% nominal Ag content in the visible process generating limited amount of byproducts in the final solution. The third experimental project focused on the immobilization of the previously prepared powder TiO2-Cu2O nanostructure. In this work a fluorine-doped tin oxide (FTO) glass sheet was used as a substrate and the doctor-blade coating technique has been employed to make TiO2-Cu2O thin films. Although this technique has a widespread use in the fabrication of solar cells to the best of our knowledge this is the first report on supported TiO2-Cu2O photocatalytic systems prepared by this method. To optimize the performance of the TiO2- Cu2O thin film under visible light irradiation, the chemical composition of the doctor-blading paste and the temperature of the final thermal treatment step was studied. It was found that both the paste composition and the heat treatment step played an important role in the material properties. When the film contained ethyl cellulose the minimum temperature to remove organic additives was 350 °C. Whereas for the films containing only alpha terpineol 300 °C was sufficient. It was revealed that the higher temperature treatment resulted in more oxidized films which were also shown in their deeper colour. The most effective film under visible light irradiation was TC-0-300 which contained no cellulose and was treated at the lowest temperature.

Carbon nanomaterials are gaining more attention due to some special features, such as the excellent photoluminescent (PL) properties, low toxicity and biocompability of carbon dots (CDs) and good conductivity, high mechanical strength and stability of graphene based nanomaterials or membranes, inspiring emerging area for applications. Considering the drawbacks including limitations in large-scale synthesis, cost, low yields and pollutions, efforts should be devoted to improve the synthetic technique to achieve green, economic and mass synthesis, and explore novel applications. In this thesis, different types of CDs were prepared through hydrothermal/solvothermal method, modifying the surface of CDs to improve the chemical and optical properties. In addition, the performance of graphene based nanomaterials and membranes in water purification are investigated as well. Two types of CDs are synthesized in this thesis, including organosilane functionalized CDs (OS-CDs) and nitrogen-doped CDs (NCDs). The products show high quantum yields (QY) and good stability after hydrothermal treatment, with QY as high as 51 % for OS-CDs and around 20% for the NCDs. These CDs show sensitivity to some parameters such as temperature, pH value and metal ions (Hg2+ or Fe3+), which renders them great potential as sensors. More interestingly, the NCDs exhibit certain photocatalytic activity on MO degradation and can enhance the activity of TiO2, which means the NCDs may be a good sensitizer for photocatalyst.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
Full Text

This thesis focuses on the application of nanocrystalline transition metal oxide TiO2, WO3 and NiO thin films in new “green” building technologies. Specifically, their physicochemical properties in photocatalytic, self-cleaning and gas sensing applications are studied. There is an intimate connection between comfort issues, health, with connections to energy efficiency, leading to a need for intelligent building materials and green architecture. The importance of good indoor environment is augmented by the fact that modern man in developed countries spends some 90 % of his time inside buildings and vehicles. Poor air quality may lead to discomfort of the person inhabiting a building and in ultimately cause adverse health effects. Thin films of nanocrystalline TiO2 were prepared using reactive DC magnetron sputtering. Crystalline mesoporous films of WO3 and NiO were prepared using advanced gas deposition technique (AGD). The crystal structure, morphology, optical and chemical properties of the films were characterized by using grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), UV/Vis spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. The photocatalytic properties and adsorption of both organic and inorganic molecules on pure and functionalized films were probed by in situ Fourier transform infrared spectroscopy (FTIR). The gas sensing properties of sensors based on TiO2, WO3 and NiO were investigated by conductivity measurements and noise spectroscopy. It was found for the first time that NiO based thin film sensors can be used to detect H2S and NO2 at low temperatures – down to room temperature. Hybrid WO3 sensors functionalized with multiwalled carbon nanotubes (MWCNTs) were used to detect NO2, CO and NH3 gases. These hybrid gas sensors show improved recovery properties compared to unmodified WO3 sensors. TiO2 based gas sensors were able to detect low concentrations of H2S by noise spectroscopy provided that the sensors were irradiated by UV light. Furthermore we show that sulphur is photo-fixated in crystalline TiO2 films upon simultaneous SO2 gas exposure and UV irradiation. Studies of the kinetics and identity of the photo-fixated sulphur complexes show that these are formed by photo-induced reactions between oxygen and SO2 at oxygen surface vacancy sites in TiO2. The sulphur modified TiO2 films show interesting self-cleaning properties compared to the pure films.
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 739

Environmental pollution has grown to become a problem affecting air, water, soil and ecosystems, mainly due to the growth of the world population in combination with rapid economic development, which has led to a massive increase of global production. Indeed, it is linked to the increased use and complexity of chemicals in many human activities. In particular, the global aquatic environment has been affected by widely spread anthropogenic chemicals and, among these, contaminants of emerging interest (CEC), including pharmaceuticals and personal care products, are of particular relevance as they can have a impact on aquatic life and human health. CEC is a term used to describe synthetic or naturally occurring chemicals or any microorganisms that are not commonly monitored in the environment but have the potential to enter the environment and cause known or suspected adverse effects. The main groups of CEC are pharmaceuticals, personal care products, endocrine disruptors, surfactants, persistent organic contaminants, industrial additives and artificial sweeteners. These contaminants are difficult to trace due to the need for specific detection methods, raising the question of how long these contaminants are prevalent in the ecosystem and how the contamination process can be reversed or reduced. Furthermore, several CECs are unlikely to be removed from conventional wastewater treatment (WWT) processes. Advanced wastewater treatment technologies have been identified to be effective in treating contaminated water, such as nanofiltration, reverse osmosis, ozonation and chemical oxidation. Among the different solutions, adsorption, an established technology, is still considered a reliable and robust method to purify aqueous solutions at low cost and with high efficiency. One of the main advantages of adsorption-based technologies is that they are capable of removing contaminants in very low concentration ranges, an operating condition in which most other separation techniques are poorly efficient due to the small concentration gradients involved. . Furthermore, adsorption is a versatile method that can remove many different organic and inorganic compounds at the same time, provided a suitable blend of adsorbent materials is employed.This thesis focused on evaluating different strategies for removing pollutants from the aqueous matrix. In particular, we have studied methods based on adsorption, and in this case we have selected adsorbent materials different from each other in terms of structure, chemical composition and operating conditions, which can be divided into two classes: (i) microporous silica aluminate adsorbent (zeolites) and (ii) carbon-based mixed matrix (MMM) membranes. In this thesis the adsorbing properties of zeolites towards different classes of CEC (drugs, PFAS and organic contaminants) in aqueous solutions were studied in order to study the efficiency of these siliceous materials in two applications, namely: (1) the removal of contaminants from aqueous matrix, (2) the pre-concentration phase for the analysis of micropollutants. Furthermore, the properties of MMM adsorption towards perfluorinated compounds were also investigated. MMMs are composed of a continuous polymeric phase and a dispersed inorganic filler. This thesis includes a study on advanced oxidation processes for the degradation of pharmaceutical products in an aqueous environment. In particular, two different photocatalysts have been studied: (i) sodium decatungstate and (ii) tungsten trioxide, these semiconductors have the common ability to photoproduce .OH radicals in aqueous solutions.
L'inquinamento ambientale è cresciuto fino a diventare un problema che colpisce l'aria, l'acqua, il suolo e gli ecosistemi, principalmente a causa della crescita della popolazione mondiale in combinazione con un rapido sviluppo economico, che ha portato a un massiccio aumento della produzione globale. In effetti, è legato all'aumento dell'utilizzo e della complessità delle sostanze chimiche in molte attività umane. In particolare, l'ambiente acquatico globale è stato influenzato da sostanze chimiche antropogeniche ampiamente diffuse e, tra queste, i contaminanti di interesse emergente (CEC), compresi i prodotti farmaceutici e i prodotti per la cura personale, sono di particolare rilevanza poiché possono avere un impatto sulla vita acquatica e salute umana. CEC è un termine usato per descrivere sostanze chimiche sintetiche o presenti in natura o qualsiasi microorganismo che non è comunemente monitorato nell'ambiente ma ha il potenziale di entrare nell'ambiente e causare effetti negativi noti o sospetti. I principali gruppi di CEC sono prodotti farmaceutici, prodotti per la cura personale, interferenti endocrini, tensioattivi, contaminanti organici persistenti, additivi industriali e dolcificanti artificiali. Questi contaminanti sono difficili da rintracciare a causa della necessità di metodi di rilevamento specifici, sollevando la domanda su quanto tempo questi contaminanti siano prevalenti ell'ecosistema e come il processo di contaminazione possa essere invertito o ridotto. Inoltre, è improbabile che diversi CEC vengano rimossi dai processi convenzionali di trattamento delle acque reflue (WWT). Le tecnologie avanzate di trattamento delle acque reflue sono state identificate per essere efficaci nel trattamento delle acque contaminate, come la nanofiltrazione, l'osmosi inversa,l'ozonizzazione e l'ossidazione chimica. Tra le diverse soluzioni, l'adsorbimento, una tecnologia consolidata, è ancora considerata un metodo affidabile e robusto per purificare soluzioni acquose a basso costo e con alta efficienza. Uno dei principali vantaggi delle tecnologie basate sull'adsorbimento è che sono in grado di rimuovere i contaminanti in intervalli di concentrazione molto bassi, una condizione operativa in cui la maggior parte delle altre tecniche di separazione sono scarsamente efficienti a causa dei piccoli gradienti di concentrazione coinvolti. Inoltre, l'adsorbimento è un metodo versatile che può rimuovere contemporaneamente molti diversi composti organici e inorganici, a condizione che venga impiegata una miscela adatta di materiali adsorbenti.Questa tesi si è concentrata sulla valutazione di diverse strategie per rimuovere gli inquinanti dalla matrice acquosa. In particolare, abbiamo studiato metodi basati sull'adsorbimento, e in questo caso sono stati selezionati materiali adsorbenti diversi tra loro per struttura, composizione chimica e condizioni operative, che possono essere suddivisi in due classi: (i) adsorbente microporoso silico alluminato (zeoliti) e (ii) membrane a matrice mista a base di carbonio (MMM). In questa tesi sono state studiate le proprietà adsorbenti delle zeoliti verso diverse classi di CEC (farmaci, PFAS e contaminanti organici) in soluzioni acquose al fine di studiare l'efficienza di questi materiali silicei in due applicazioni, ovvero: (1) la rimozione di contaminanti da matrice acquosa, (2) la fase di pre-concentrazione per l'analisi dei microinquinanti. Inoltre, sono state studiate anche le proprietà di adsorbimento MMM verso i composti perfluorurati. Le MMM sono composti da una fase polimerica continua e da una carica inorganica dispersa. Questa tesi include uno studio sui processi di ossidazione avanzati per la degradazione di prodotti farmaceutici in ambiente acquoso. In particolare sono stati studiati due diversi fotocatalizzatori: (i) decatungstato di sodio e (ii) triossido di tungsteno, questi semiconduttori hanno la capacità comune di fotoprodurre radicali .OH in soluzioni acquose.

Abstract Water contamination is a global problem and the growing utilization of limited water resources creates a need for efficient purification methods. Industrial effluents are polluting the natural waters, e.g. uncontrolled mining activities in developing countries have created numerous environmental hazards and different types of pollutants. This study focuses on novel adsorbents and photocatalytic materials in order to reach the aim of more efficient and affordable water treatment. This thesis aimed at making active, efficient, and viable adsorbents out of waste materials, as well as using photocatalysis in water treatment for organic pollutants originating from different types of industries. Local Peruvian agro-waste was used as a precursor for activated carbon that was used in adsorption studies for single (As(V) and methylene blue, MB), and multicomponent mixtures (As(V)/Pb/Cd), and real polluted river water. An industrial intermediate product, hydrous TiO2, was used for As(III)/As(V) removal. Photocatalytic materials included a commercial photoactive TiO2 (P25), and tailor-made TiO2 based nanofibers (NF) decorated with Pt/Pd. The results show that the agro-waste based activated carbons show high potential as adsorbents (e.g. ~100% As(V) removal in 2 h). With the multicomponent solution there is evidently competition for the adsorption sites; Pb was removed most efficiently. The specific surface area and pore size distribution play an important role in MB adsorption, as with As(V) the ash content is the most influential parameter. The industrial intermediate product has a high adsorption capacity towards both As(III) and As(V) (over 96% removals in 4 h), and is promising for use in natural and wastewater treatment due to its adsorption properties, availability, low cost, and non-toxicity. Photocatalysis was found to be an efficient removal method for the pollutants tested, also in the diluted industrial wastewater matrix, e.g. diuron was removed 99% in 1 h. The NFs are promising for the efficient photocatalytic degradation of organic effluents in aqueous streams such as wastewaters originating from e.g. biofuel production or fine chemicals and pharmaceutical industry. This study provides new and valuable knowledge for the purification of waters, especially when aiming at developing inexpensive water treatment materials and methods for different applications
Tiivistelmä Puhtaan veden puute on maailman laajuinen ongelma, ja raskasmetallien ja orgaanisten haitta-aineiden päätymistä ympäristöön ja luonnonvesiin voidaan vähentää hyvällä ja tehokkaalla teollisuuden jätevesien käsittelyllä. Uusia ja tehokkaita, ympäristön kannalta suotuisia ja kestäviä vedenpuhdistustekniikoita tarvitaan erityisesti kehitysmaissa, joissa esim. kontrolloimaton kaivostoiminta aiheuttaa ympäristö- ja terveyshaittoja. Työn kokeellisessa osassa valmistettiin perulaisesta maatalousjätteistä aktiivihiiltä kemiallisella aktivoinnilla, ja seurattiin niiden kykyä adsorboida haitta-aineita (As(V), Pb, Cd, metyleenisini) yksi- ja monikomponenttiliuoksista ja saastuneesta luonnonvedestä (Puyango-Tumbesjoki, Peru). Lisäksi tutkittiin teollisuuden välituotteen (TiO2) aktiivisuutta arseenin, As(III) ja As(V), adsorptiossa. Viimeisessä osiossa tutkittiin valokatalyysiä orgaanisten haitta-aineiden poistossa vesiliuoksista sekä kaupallisella TiO2 P25 -katalyytillä että kokeellisilla Pd/Pt-dopatuilla TiO2 -nanokuiduilla. Tulokset osoittavat, että paikallisesta raaka-aineesta valmistetut aktiivihiilet ovat hyvin potentiaalisia vedenpuhdistusmateriaaleja saavuttaen jopa 100% As(V) poistuman (2h). Adsorboitavien ionien välillä on nähtävissä kilpailua monikomponettiadsorptiossa; lyijyn havaittiin poistuvan tehokkaimmin tutkituissa olosuhteissa. Adsorbentin ominaispinta-ala ja huokoskokojakauma ovat tärkeitä tekijöitä metyleenisinin adsorptiossa, kun taas tuhkapitoisuudella on arseenin adsorptioon suurempi vaikutus. Teollisuuden TiO2-välituotteella havaittiin olevan korkea adsorptiokapasiteetti sekä As(III)- että As(V)-spesieksiä kohtaan saavuttaen yli 96% poistumat (4h). Se on lupaava materiaali edelleen kehitettäväksi ja käytettäväksi esimerkiksi luonnonvesien ja jätevesien puhdistuksessa johtuen sen hyvistä adsorptio-ominaisuuksista, saatavuudesta, edullisuudesta ja myrkyttömyydestä. Valokatalyysin havaittiin olevan toimiva menetelmä orgaanisten molekyylien hajottamiseen, myös laimeasta teollisuuden jätevesimatriisista, esim. diuroni poistui 99% tunnissa. Nanokuitujen tapauksessa aktiivinen metalli vaikutti merkittävämmin reaktion tehokkuuteen kuin ominaispinta-ala. Tämä työ tarjoaa uutta ja tärkeää tietoa vesien puhdistukseen kun tavoitteena on löytää tehokas ja edullinen menetelmä erityyppisiin sovelluksiin

Dans ce travail, nous nous sommes tout d’abord intéressés à l’influence du traitement de la mésophase hybride sous ammoniac et des conditions de cristallisation sur les propriétés d’oxydes de titane mésoporeux. Le protocole de synthèse de ces matériaux a été mis au point auparavant au laboratoire à l’aide d’une méthode combinant le mécanisme transcriptif à partir des cristaux liquides du copolymère bloc P123 et la méthode EISA. Une cristallisation sous atmosphère oxydante, augmente le degré de cristallinité et favorise une croissance des particules d’anatase. En conséquence, la photodégradation du méthylorange, utilisé comme molécule modèle est augmentée. Lorsque la cristallisation est réalisée sous azote pur, l’anatase n’est pas favorisée et la photoactivité est alors gouvernée par la surface spécifique des matériaux. Nous avons également montré qu’au cours de la synthèse, l’interaction de NH3 avec le titane amorphe promeut la formation de la structure rutile de TiO2 et défavorise par conséquent la cristallisation sous forme anatase. Par conséquent lorsque le traitement sous ammoniac de la mésophase hybride est prolongé ou lorsqu’ il est réalisé à pression élevée, l’activité photocatalytique des oxydes de titane, obtenus après cristallisation du TiO2 amorphe sous air synthétique, diminue. L’introduction d’un second niveau de mésoporisité permet d’accroitre l’efficacité des photocatalyseurs, car la diffusion et l’accès aux sites actifs des molécules de colorant sont améliorés. Les matériaux à double mésoporisité présentent une activité photocatalytique deux fois et demie supérieure à celle des oxydes de titane mésoporeux monomodaux. Des catalyseurs pour l’hydrodésulfuration des gazoles ont également étés conçus en dispersant la phase active MoS2 à la surface des oxydes de titane mésoporeux mono- et bimodaux. Le dibenzothiophène (DBT) et le 4,6-diméthylbenzodiophène (46DMDBT) ont été utilisées comme molécules modèles. Contrairement au catalyseur conventionnel MoS2/Al2O3, pour lequel l’hydrodésulfuration se produite selon la voie hydrogénante, grâce à la présence de sites acides de Brönsted, les catalyseurs supportés sur TiO2 mésoporeux favorisent la désulfurisation directe du 46DMDBT. Pour terminer, la méthode de synthèse mise au point pour TiO2 a été transposée à l’oxyde de zirconium. Toutefois, dans ce cas seul un arrangement vermiforme des canaux est obtenu. Ce phénomène est probablement lié à la présence du propanol contenu dans la source du précurseur inorganique. L’incorporation d’étain au sein des zircones mésoporeuses a également été réalisée et nous avons mis en évidence que cet élément est favorable à la cristallisation de ZrO2
In this work, we have first investigated the effect of both the crystallization conditions and of the hybrid mesophase treatment under ammonia atmosphere on the properties of mesoporous TiO2, for which the preparation was developed previously via a method combining Liquid Crystal Templating (LCT) and EISA mechanisms, using P123 as template. The photocatalysis efficiency of the materials crystallized under oxidizing conditions increases with the calcination temperature thanks to the enhancement of crystallinity and the growth of anatase particles. By contrast, when the crystallization is performed under pure nitrogen the anatase is not favored and the photocatalytic activity is governed by the materials’ specific surface area. We have also shown that during the mesoporous TiO2 synthesis, interactions between ammonia and amorphous titania promote the formation of rutile, which is a drawback for the transformation of amorphous titania into anatase. Consequently, when the treatment under ammonia is prolonged or when it is performed at high NH3 pressure, the activity of the photocatalysts recovered after crystallization under synthetic air decreases. The introduction of a second mesoporosity level enhances the degradation rate. In that case the diffusion and the accessibility of the dye molecules to the active sites are favored. Catalysts for gazole hydrodesulfurization have also been designed by dispersing the active MoS2 phase onto the surface of the mono and dual mesoporous titania. The obtained catalysts have been tested for the hydrodesulfurization of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (46DMDBT), used as model molecules. We highlight that thanks to the intrinsic Brönsted acidity, the CoMoS/mesoporous TiO2 catalysts favor the direct desulfurization route of 46DMDBT, in contrary to the conventional CoMoS/alumina catalyst. The synthesis procedure developed for mesoporous TiO2 has also been adapted for the preparation of mesoporous ZrO2. However, only mesoporous materials with a wormhole-like structure have been obtained. This phenomenon is likely due to the presence of propanol contained in the source of the inorganic precursor. We have also incorporated tin into the zirconia framework. The presence of thin favors the crystallization of ZrO2

The development of future electronics depends on the availability of suitable functional materials. Printed electronics, for example, relies on access to highly conductive, inexpensive and printable materials, while strong light absorption and low carrier recombination rates are demanded in photocatalysis industry. Despite all efforts to develop new materials, it still remains a challenge to have all the desirable aspects in a single material. One possible route towards novel functional materials, with improved and unprecedented physical properties, is to form composites of different selected materials. In this work, we report on hydrothermal growth and characterization of graphene/zinc oxide (GR/ZnO) nanocomposites, suited for electronics and photocatalysis application. For conductive purposes, highly Al-doped ZnO nanorods grown on graphene nanoplates (GNPs) prevent the GNPs from agglomerating and promote conductive paths between the GNPs. The effect of the ZnO nanorod morphology and GR dispersity on the nanocomposite conductivity and GR/ZnO nanorod bonding strength were investigated by conductivity measurements and optical spectroscopy. The inspected samples show that growth in high pH solutions promotes a better graphene dispersity, higher doping and enhanced bonding between the GNPs and the ZnO nanorods. Growth in low pH solutions yield samples characterized by a higher conductivity and a reduced number of surface defects. In addition, different GR/ZnO nanocomposites, decorated with plasmonic silver iodide (AgI) nanoparticles, were synthesized and analyzed for solar-driven photocatalysis. The addition of Ag/AgI generates a strong surface plasmon resonance effect involving metallic Ag0, which redshifts the optical absorption maximum into the visible light region enhancing the photocatalytic performance under solar irradiation. A wide range of characterization techniques including, electron microscopy, photoelectron spectroscopy and x-ray diffraction confirm a successful formation of photocatalysts. Our findings show that the novel proposed GR-based nanocomposites can lead to further development of efficient photocatalyst materials with applications in removal of organic pollutants, or for fabrication of large volumes of inexpensive porous conjugated GR-semiconductor composites.

Le stockage de l'énergie solaire en énergie chimique est une approche hautement souhaitable pour résoudre le défi énergétique. Les cellules photo-électrochimiques combinent la collecte de l'énergie solaire et la décomposition de l'eau. Les nanofeuillets semiconducteur 2D de di-chalcogenures de métaux de transition (TMDC) sont considérés comme des matériaux attrayants pour l'élaboration de photocatalyseur efficace pour la conversion de l'énergie solaire en hydrogène. Malgré les propriétés optoélectroniques uniques des TMDC, la passivation de défauts de surface présents en concentration élevée est un défi important pour le développement de cette classe de matériaux. Dans ce contexte, le présent travail a concerné l'élaboration d'un photocatalyseur 2D TMDC pour la photo-décomposition de l'eau. Le développement de photocatalyseurs de haute performance a été examiné suivant deux axes principaux. Un premier axe de recherche consiste à passiver les défauts de surface des nanofeuillets 2D p-WSe2 à l'aide de complexes Mo-S pour diminuer la recombinaison des porteurs de charge photo-générés et améliorer l'activité photocatalytique. Nous avons démontré que des couches ultra minces de complexes thio et oxo-thio-Mo moléculaires représentent une classe idéale de catalyseurs, bien adaptée pour fonctionnaliser les matériaux 2D car ils sont stables dans des environnements aqueux, bon marché, respectueux de l'environnement. Des densités de courant de -2 mA cm-2 à -0.2 V par rapport à l'électrode d'hydrogène (NHE) ont été obtenues pour la nouvelle photocathode p-WSe2/ MoxSy. En plus d'offrir une activité électro-catalytique élevée, les films complexes Mo se sont révélés capables de guérir les défauts de surface. Les contributions respectives aux effets catalytiques et cicatrisants observées expérimentalement pour les divers complexes moléculaires de Mo impliquaient la forte adsorption sur les défauts ponctuels du substrat 2D WSe2 de complexes de Mo tels que (MoS4)2-, (MoOS3)2- et (Mo2S6O2)2-. Il a été démontré que ces couches de co-catalyseur Mo-S formés à un pH bien défini présentent un comportement n-semi-conducteur et l'ingénierie des bandes formées avec p-WSe2 s'est révélée appropriée pour assurer la séparation des charges et la migration efficace des électrons photo-induits pour la RDH, représentant un exemple de couche de passivation multi-composant avec de multiples propriétés. Un deuxième axe de travail concerne l'optimisation de la nanostructure du film de WSe2 comme objectif l'obtention d'une surface spécifique élevée et des parois de pores composées de quelques monofeuillets. Des films de WSe2 nanostructurés de haute surface et à bonne collecte de porteurs de charge ont été obtenus par co-assemblage des nanofeuillets de WSe2 et des nanofeuillets d'oxyde de graphène réduit (rGO) avec un rapport de nanofeuillets rGO/WSe2 optimal.[...]
Collecting and storing solar energy in chemical energy is a highly desirable approach to solve energy challenge. The great potential of a photoelectrochemical cell technology combines the harvesting of solar energy with the water splitting into a single device. 2D semiconducting nanosheets of Transition Metal Di-Chalcogenides (TMDC) are seen as an attractive material to design an efficient photocatalyst for the conversion of solar energy into hydrogen. Despite the unique optoelectronic properties of the TMDCs, the passivation of surface defects in high concentration is a remaining challenge for the development of this class of materials. In this context, the present work has aimed the elaboration of thin 2D TMDC photocatalyst for solar water splitting. The development of high performance photocatalysts was evaluated following two main axis. A first strategy consists in the surface defects passivation of 2D p-WSe2 nanosheets using Mo-S complexes to decrease the photogenerated charge carrier recombination and improve photocatalytic activity. We demonstrated these Mo thio and oxo-thio- molecular complexes films as an ideal class of catalysts, well-suited to functionalize 2D materials since they are stable in aqueous environments, cheap and environmentally benign. Current densities of -2 mA cm-2 at -0.2 V vs NHE electrode were obtained for the new p-WSe2/MoxSy photocathode. Besides developing high electro-catalytic activity, the Mo complexes films were shown to display ability to heal surface defects. The respective contributions in catalytic and healing effects observed experimentally for the various molecular Mo complexes involved strong adsorption on point defects of the 2D WSe2 substrate of Mo complexes such as (MoS4)2-, (MoOS3)2-and (Mo2S6O2)2-. The Mo complexes films spontaneously formed at well-defined pH were demonstrated to present n-semi-conducting behaviour and band engineering formed with p-WSe2 showed to be suitable for ensuring charge separation and efficient migration of the photo-induced electrons for the Hydrogen Evolution Reaction, thus representing an example of multicomponent passivation layer exhibiting multiple properties. A second strategy focus in the nanostructure optimization of WSe2 with high specific surface area and pore walls composed of few layers. Nanostructured WSe2 films of high surface area and good charge carrier collection were obtained by co-assembling WSe2 nanosheets and reduced graphene oxide (rGO) nanosheets with an optimal rGO/WSe2 nanosheet ratio. After deposition of co-catalyst thin layer, the new layered nanojunctions of rGO-WSe2/MoxSy exhibited photocurrents up to -5 mA cm-2 at -0.2V vs NHE. Incident-photon-to-current efficiency conversion of 10% were achieved for WSe2 nanoflakes of 70 nm thickness in presence of rGO and MoxSy co-catalyst.[...]

The presences of heavy metals, organic contaminants and natural toxins in natural water bodies pose a serious threat to the environment and the health of living organisms. Therefore, there is a critical need to identify sustainable and environmentally friendly water treatment processes. In this dissertation, I focus on the fundamental studies of advanced oxidation processes and magnetic nano-materials as promising new technologies for water treatments. Advanced oxidation processes employ reactive oxygen species (ROS) which can lead to the mineralization of a number of pollutants and toxins. The rates of formation, steady-state concentrations, and kinetic parameters of hydroxyl radical and singlet oxygen produced by various TiO2 photocatalysts under UV or visible irradiations were measured using selective chemical probes. Hydroxyl radical is the dominant ROS, and its generation is dependent on experimental conditions. The optimal condition for generation of hydroxyl radical by of TiO2 coated glass microspheres is studied by response surface methodology, and the optimal conditions are applied for the degradation of dimethyl phthalate. Singlet oxygen (1O2) also plays an important role for advanced processes, so the degradation of microcystin-LR by rose bengal, an 1O2 sensitizer was studied. The measured bimolecular reaction rate constant between MC-LR and 1O2 is ~ 106 M-1 s-1 based on competition kinetics with furfuryl alcohol. The typical adsorbent needs separation after the treatment, while magnetic iron oxides can be easily removed by a magnetic field. Maghemite and humic acid coated magnetite (HA-Fe3O4) were synthesized, characterized and applied for chromium(VI) removal. The adsorption of chromium(VI) by maghemite and HA-Fe3O4 follow a pseudo-second-order kinetic process. The adsorption of chromium(VI) by maghemite is accurately modeled using adsorption isotherms, and solution pH and presence of humic acid influence adsorption. Humic acid coated magnetite can adsorb and reduce chromium(VI) to non-toxic chromium (III), and the reaction is not highly dependent on solution pH. The functional groups associated with humic acid act as ligands lead to the Cr(III) complex via a coupled reduction-complexation mechanism. Extended X-ray absorption fine structure spectroscopy demonstrates the Cr(III) in the Cr-loaded HA-Fe3O4 materials has six neighboring oxygen atoms in an octahedral geometry with average bond lengths of 1.98 Å.

General abstract 1. Introduction During these last years, the innovation and development processes lead pollution to its highest level; the air pollution is one the most prominent and dangerous form of it. Causes are several, from fuel combustion to factories activity, which increase the level of organic molecules and nitrogen or sulfur oxides in atmosphere (WHO Global Urban Ambient Air Pollution Database, update 2016). Unfortunately, effects are more than evident: from the global warming, to the acid rains, from the sudden climate changes, to the increase of diseases such as asthma and lung cancer (Ambient (outdoor) air quality and health, WHO). Outdoor air pollution is the major environmental health problem affecting everyone in developed and developing countries alike, however, unlike one might usually think, indoor levels of organic pollutants are often higher than outdoor (Viegi et al., 2004). The problem is even more important because people live mainly indoors, constantly exposed to all the pollutants present in these close environments (Chen et al., 2016; Allen et al., 2016). For this reason, demands to improve the air quality situation have been largely extended, finding new strategies for waste reduction or for the oxidation and degradation of pollutants (Ambient (outdoor) air quality and health, WHO). Among several processes, considering that very important factors are saving energy and reducing emissions, photocatalysis has been exploited as very suitable technique to reduce pollution. In a photocatalytic reaction (eq. 1), a semiconductor material, the photocatalyst, is activated by light and, thanks to the formation of some electron-hole couples between his valence and conduction bands, it is able to reduce or oxidize molecules that adsorb on his surface (J.M. Herrmann, 2005). In heterogeneous photocatalysis, the reaction implies the previous formation of an interface between the semiconductor and the reactants of the reaction (K. Demeestere et al., 2007; M. Schiavello, 1997). (Ox1)ads + (Red2)ads Red1 + Ox2 (1) Among a large variety of semiconductor materials, which are mainly metal oxides, only few of them are considered to be applicable photocatalysts, in relation with their specific photocatalytic properties. Titanium dioxide (TiO2) induced photocatalysis is an example of AOP processes and it has been demonstrated its efficiency in the decomposition of various organic contaminants. TiO2 is a very well known and well-researched material due to the stability of its chemical structure, biocompatibility, physical, optical, and electrical properties (M. Serpone et al., 1989). The crystalline forms of TiO2 are anatase, rutile and brookite (A. Linsebigler et al., 1995). In general, TiO2 is preferred in anatase form because of its high photocatalytic activity, however the major drawbacks of TiO2-based photocatalysts is related to the rapid charge recombination of the electron−hole pairs, and the wide band gap, which restricts light absorption to only ultraviolet region (wavelength <390 nm), restraining the practical applications of TiO2-based photocatalysts under solar light or visible light. TiO2-based photocatalysts are used for a variety of applications such as degradation of volatile organic compounds (VOCs) and decomposition of nitrogen pollutants (NOx) or also organic dyes, like Methylene Blue (K. Demeestere et al., 2007; P.K.J. Robertson et al., 2005). When TiO2 is irradiated with energies equal to or higher than its band gap (>3.0 eV), electrons are excited from the valence band into the conduction band, leading to excited electrons in the conduction band and positive holes in the valence band. This fundamental process can be expressed by the following reaction equations (eq. 2): TiO2 + hv → e- + h+ (2) As electrons have a reducing potential, holes can oxidize water and lead to the formation of more oxidant species such as hydroxyl radicals, able to oxidize organics. As mentioned above, the field of practical applications of TiO2-based photocatalysts becomes less expanded under solar light or visible light. In this sense, different strategies have been developed (X. Li et al., 2011; S. Afzal et al., 2013; S. Wu et al., 2013; Y. Cho et al., 2001), starting from the chemical modification of TiO2 lattice using non-metals, particularly carbon, nitrogen and sulfur (S. Khan et al., 2002; J. Gole et al., 2003; T. Umebayashi et al., 2003). The presence of metal nanoparticles on TiO2 surface can promote charge transfer process in the composite systems (N. Chandrasekharan et al., 2000; A. Dawson et al., 2001), because of the electron injection that occurs from the nanosurface to the conduction band of TiO2 and the metal particle. In recent years, formation of photocatalytic heterostructures based on TiO2 with other semiconductor/noble metal has emerged as an important strategy to increase the separation of charge carriers and suppress the recombination rate of photoinduced electron−hole pairs, resulting in improved photocatalytic efficiency (F.X. Xiao et al., 2012; B. Liu et al., 2011; V. Etacheri et al., 2013; V. Etacheri et al., 2010; V. Etacheri et al., 2012; Y. Wang et al., 2013). Aims of the work The aims of the work regard different points of the TiO2 study and improvement. Starting from the choice of the best commercial powder of TiO2 to replace the titanium oxide nano-powders, through its modification to make it useful in visible light, until the application on ceramic supports to prepare building materials appropriate for outdoor and indoor pollution abatement, to improve the air quality and the quality of our life as well. The purposes of this research project can be therefore summarized as follows: • Study in depth the real potential of a micrometer TiO2, finding the best candidate among several commercial samples to obtain benefits such as economic saving, safety, ease in product handling in industry; • Improve the use and application of micro-TiO2 on building materials to optimize their performances in pollution abatement, with particular attention to realistic settings; in this sense, find innovative methods to test materials and assesses the photocatalytic potentials; • Make micro-TiO2 active under visible light, modifying it with noble metals and in particular combining the process with the use of high-energy ultrasound (US). 2. Experimental details 2.1 Commercial samples of TiO2 In this work, the starting point was the study of different commercial powders of TiO2. Five commercial TiO2 materials by Kronos, Hundsman, Sachtleben (two different powders) and Cristal (respectively quoted with the B–E letters) have been selected. They are all available in the market as pigmentary powders, and they have the following key features: pure anatase phase, uncoated surface, undoped material, not sold as photocatalytic material. P25 by Evonik is the nanometric commercial TiO2 reference for photocatalytic applications, and it is the most used and studied. All commercial powders were used as received without any further treatment or activation process (C.L. Bianchi et al., 2015). The crystallographic phase composition have been valued by XRD patterns and all the samples are pure anatase, except for P25. Crystallite size of 1077 by Kronos endorses its micro-sized nature, always connects to a low surface area. As expected, P25 is a nano-sized powder. Studying more thoroughly the morphological characteristics particularly by TEM analysis, it can be notice that the reference P25 powder is made up of well-crystallized particles of rather roundish shape, closely packed and with an average size of 20–30 nm. XPS results give information about the surface states of TiO2 and there are not differences among all the present samples concerning binding energy (BE). Even the band gap values, evaluated by means of diffuse reflectance UV–Vis analysis, do not exhibit large differences among the various samples. 2.2 Selected pollutants Photocatalysts, whether commercial as such or modified as explained in the next sections, have been tested on VOCs molecules referring to indoor pollution, and on nitrogen oxides (NOx) in reference to outdoor pollution. Some reagents are liquid, other are gaseous and stored in cylinders under pressure. All substances were used as purchased without any particular pre-treatments or purification. 2.3 Photocatalytic reactors VOCs degradation Photocatalytic degradations were conducted in a Pyrex glass cylindrical reactor with diameter of 200 mm and effective volume of 5 L. The catalyst in powder form has been deposited on a flat glass sheet (100cm2) as thin film, from a suspension in 2-propanol. The catalyst amount used in each tests was 0.05 g. The atmosphere in the reactor was obtained by mixing hot chromatographic air humidified at 40%, and a fixed amount of volatilized pollutant, in order to avoid condensation. Photon sources were provided by a 500 W iron halogenide lamp (Jelosil, model HG 500) emitting in the 315–400nm wavelength range (UV-A) at 30Wm-2, or by a LED (MW mean well, 350 mA rated current, 9–48 V DC voltage range, 16.8 W rated power) with an emission between 400 and 700 nm. The actual concentrations of pollutant in the reactor were determined directly by micro-GC sampling or by Proton transfer reaction mass spectrometry (PTR-MS) (detailed description is reported in the next sections). Nitrogen oxides degradation ➢ NOx photocatalytic degradations were conducted in a Pyrex glass cylindrical reactor with an effective volume of 20 L in batch mode. The catalyst in the form of powder has been deposited from 2-propanol suspension on a flat glass sheet (40cm2), and the amount used in each tests was 0.05 g. The gaseous mixture in the reactor was obtained by mixing NOx (mixture of NO and NO2 in air) with air humidified at 40%. The initial concentrations of NOx in the reactor were 1000 ppb in order to follow the same pollutant concentration requested by the ISO 22197-1 rules (www.iso.org) and 200 ppb that is very close to the alert threshold set by the EU Directive 2008/50/CE for NO2 (http://eur-lex.europa.eu). Photon source was provided by a 500 W iron halogenide lamp (Jelosil, model HG 500) emitting in the 320–400 nm wavelength range (UV-A). The specific UV power on the surface of the samples was 10 Wm-2. The concentration of pollutants in the reactor was determined directly by chemiluminescence (Teledyne, Mod. 200E). ➢ The continuous flow reactor has been used only for testing photocatalytic building materials; it has got walls of 10 mm in thickness, and an internal size of 625 × 625 × 115 mm3, with four inlets and one opposite outlet and can house a sample of 600 × 600 × 10 mm3. It is equipped with a thermo-hygrometer model HT- 3006A to measure the temperature and humidity during the tests. The relative humidity inside the reactor is maintained constant around a value between 40 and 50%. The experiments were carried out either using UV lamps (UV-A region, 20 Wm−2) or using sunlight from July to September. The degradation was performed at different initial NOx concentrations ranging from 100 ± 10 ppb to 200 ± 10 ppb, at room temperature and working with total gas flow rates of 140 and 180 NL h−1. Even for these tests, the concentration values were chosen in order to work closely to the limit values reported on Directive 2008/50/EC, in particular, 106 ppb (equal to 200 μg m−3) and 213 ppb (400 μg m−3, alert threshold). The duration of each continuous run was set at 6, 12 or 24 h. The final design of the reactor was selected among several possibilities by considering the good homogeneity of the reactant in the gas phase and a contact between the reactant and the photocatalytic material that effectively reproduce the real working conditions. 2.4 Samples characterization The morphology of TiO2 in form of powder, both commercial and synthesized or modified, was inspected by means of high-resolution transmission microscopy (HR-TEM) (Jeol JEM 3010 instrument, equipped with LaB6 filament and operating at 300 kV), and the surface area of all the catalysts was determined by conventional N2 adsorption (BET) at 77 K using a Sorptometer (Costech Mod. 1042). XRD spectra were collected using a PW 3830/3020 X’ Pert Diffractometer from PANalytical working Bragg-Brentano, using the Cu Kα1 radiation (k = 1.5406 Å). X-ray photoelectron spectra (XPS) were taken in an M-probe apparatus (Surface Science Instruments). Diffuse reflectance spectroscopy (DRS) of the ground powders was performed with a Thermo Scientific Evolution 600 spectrophotometer, equipped with a diffuse reflectance accessory Praying-Mantis sampling kit (Harrick Scientific Products, USA). A Spectralon1 disk was used as reference material, and the experimental absorption versus lambda plot was elaborated using the Kubelka–Munk function. Absorption/transmission IR spectra were obtained on a Perkin-Elmer FT-IR System 2000 spectrophotometer equipped with a Hg–Cd–Te cryo-detector. Particularly for metals-modified TiO2, ICP/OES analysis has been performed using a Perkin Elmer Optima 8300 instrument. HR-SEM-EDX analysis was performed particularly on photocatalytic building materials (tiles) (Field Emission Gun Electron Scanning Microscopy LEO 1525, metallization with Cr. Elemental composition was determined using Bruker Quantax EDS). The surface wettability was evaluated by static contact angle (CA) measurements performed with an OCA20 instrument (DataPhysics Co., Germany) equipped with a CCD camera and a 500μL-Hamilton syringe to dispense liquid droplets. 2.5 Metal NPs modified TiO2: synthesis procedure To obtain the surface modification of the commercial powder of TiO2, in this work we performed a synthesis by means of high-energy US. Procedure steps are slightly different from a metal to another, but in general they follow the same scheme, described in the next lines. The precursor materials are organic or inorganic salts of different metals, selected in accordance with characteristics that will be detailed in the following chapters. For the US generation, we used A Bandelin SONOPLUS HD 3200 utilizing a 200W U/S generator and a sonication extension horn of 13mm diameter. Generally, the metal precursor and the commercial powder of TiO2 have been put together in a 100 ml glass flask, and they have been solved with the preferred solvent (aqueous or organic). The solution is then sonicated at constant temperature with a specific amplitude and intensity (Wcm-2). At the end the solution is centrifuged many times to remove all the solvent and the final powder is washed before evaporation and/or calcination steps. 2.6 Building materials production: ACTIVE® photocatalytic tiles (by GranitiFiandre S.p.A) Airless spray classic preparation Industrial porcelain grés tiles are manufactured under high pressure by dry-pressing fine processed ceramic raw materials with large proportions of quartz, feldspar, and other fluxes and finally fired at high temperatures (1200–1300°C) in a kiln. To obtain photoactive porcelain grés tiles, they were subsequently covered by airless spray with a mixture of micro-TiO2 (specifically, 1077 by Kronos has been selected as best commercial powder) mixed with an aqueous suspension of a commercial SiO2-based compound (process developed by GranitiFiandre S.p.A, patent n. EP2443076). At the end of the preparation procedure, tiles were fired at high temperature (min 680°C) for 80 min. Finally, the powder present at the sample surface and not completely stuck was brushed and removed. Digital Printing technology: DigitaLife Project The digital printing technology is based on suitably designed print heads using a tailored solvent-based ink, micro-sized TiO2 and additives (process developed by GranitiFiandre S.p.A, DigitaLife project). Specific and more detailed information will be given in the various chapters dedicated. 3. Results and discussion 3.1 Characterization of the TiO2 powders and materials Among the starting selected commercial samples, 1077 by Kronos has been chosen as best micrometer candidate to replace the nanometric reference P25. For this reason, all the results that will be presented in this thesis refers to P25 or 1077 as commercial references, nano and micro-sized respectively, and, all the structural modification studies, synthesis, tests, have been performed using 1077 as TiO2 support on which make changes. HR-TEM images confirm the nanometric nature of P25 and the micrometric dimension of the TiO2 particles of 1077 commercial sample. Results are absolutely completely in line with the results about the surface area (gm-2), which is very low in case of bigger TiO2 particles. From the same characterization analysis performed on the various modified samples, it is shown that this structure composition has not been changed by thermic treatments (calcination steps) or modification steps of the original sample with metals, or by classical impregnation methods either by using ultrasound as will be described in the dedicated chapters. XRD spectra give particularly information about the crystallographic phase composition. As presented in the table above, 1077 consists completely of anatase, which is a very good feature in term of photocatalytic activity. Any modification steps have not altered even this composition. All the samples presented in this work, except P25, consist of anatase. Useful in term of photocatalytic activity is also the distribution on the TiO2 surface of the OH groups, which are measurable in relation to the total oxygen (OTOT), particularly by means of XPS analysis; 1077 by Kronos presents a higher OH/OTOT ratio (0.14 and 0.32 for P25 and 1077 respectively) than P25, and this value, ascertainable even more accurately using the IR spectra, increases modifying 1077 TiO2 by metals. When TiO2 is decorated on surface with noble metal or metal-oxides nanoparticles (for every modified-metals-TiO2 sample presented in this work, we have usually a mixture of metal and metal-oxides NPs) the UV-VIS spectra show that the absorption shifts to the visible wavelengths, more or less depending on the metal species and its amount deposited on TiO2. UV-VIS spectra collected on the references, P25 and 1077 respectively, confirm the slight absorption in the visible of P25, because of the presence of rutile, and the absence of absorption in visible of 1077 by Kronos, which can be activated only by UV irradiation, even because its band gap, typical of anatase TiO2 (3.2 eV). Referring to the surface area, presented above for the references commercial powders, deposition of NPs on TiO2 surface can have slights effects on the final surface area, which increases, even if the value is very small and almost negligible. Finally, SEM characterization is very useful to study the ceramic surfaces when TiO2 is deposited in them. In particular, the main points in case of the two photoactive grés ceramic tiles samples are a) the fact that 1077 TiO2 does not change its nature so remains anatase and micrometer; b) changing the deposition method the distribution of the TiO2 particles completely changes. 3.2 Pollutants photodegradation: Nitrogen Oxides The use of a pigmentary powder of TiO2 as 1077 by Kronos, consisting in micrometer particles with a lower surface area, is absolutely effective in case of NOx abatement. The comparison between 1077 and P25 (as reported in Table 4) shows that the degradation percentage obtained after 120 minutes of photocatalytic reaction is very slight and almost negligible, if we consider the advantages in term of economic saving (2$/kg for P25 vs. 0.45$/Kg for 1077) and safety. The main reasons why 1077 shows to be a very good candidate between various pigmentary and commercial TiO2 in photocatalysis, are firstly its phase composition, i.e. anatase, without rutile. Moreover we have to consider that 1077 surface present a wide population of OH groups, which both for the adsorption of pollutant molecules and for them degradation are crucial. Therefore, especially for NOx abatement, micro-TiO2 as it is proves to be efficient. Thus, a modification of the material with metals, which increase the final cost, is unnecessary. 1077 however presents a very low activity if irradiated only by visible wavelengths, as confirmed by the UV-VIS spectra, which do not show absorption peaks after 400nm (visible spectrum from 400nm to 700nm). In this case, the surface modification of TiO2 with metal NPs is a key factor to have effective samples in nitrogen oxides abatement. Preparation methods are different and they will be deeply described in the dedicated chapters. To summarize the most important results, as can be seen from the presented graphs (Fig. 4-6), the presence of silver nanoparticles clearly improve the photocatalytic activity of the sample, and the key factor related to a better NOx degradation are particularly the metal-NPs amount and dimension. Finally, after showing that 1077 by Kronos is effective, it has been deposited on ceramic grés tiles as already mentioned. The borderline between samples Z23 and S24 is the method with which the deposition is obtained. Digital printing technology leads to a better and more uniform distribution of the TiO2 powder, as well as to a lower loss of it during the process, with the final results clear presented in the kinetics graphs (see Fig. 4). 3.3 Pollutants degradation: VOCs Commercial powders of TiO2 have been already exploited in VOCs photodegradation (C.L. Bianchi et al., 2014; S.B. Kim et al., 2002; G.M. Zuo et al., 2006), showing very good results against various molecules (see tab.5). However, and it is more evidently than in nitrogen oxides photodegradation, 1077 by Kronos is slightly less effective mainly due to its lower surface area. Moreover, the oxidation of more complex molecules, as in case of toluene that is an aromatic compound, both P25 or 1077 are not able to reach the complete degradation of it after 6 hours of UV irradiation. For this reason, even for this kind of application, the modification and improvement of the TiO2 photocatalyst is necessary. The presence of metals and metal oxides on the TiO2 influences the electrons-holes separation, the number of available electrons, the band gap value and the organic molecule adsorption respectively (V.E. Henrich, 1994; H. Al-Abadleh and Grassian, 2003). Among different metals, with properties that will be deeply explained in the dedicated chapters, silver seems to be the best in term of organics oxidation, showing a consistent improvement in the degradation reaction of toluene as reported in fig. 7. Metals-surface decoration is essential under visible light. Anatase-TiO2 with a band gap of 3.2 eV (C. Dette et al., 2014) is not photocatalytically active. Thus, the presence of metals on its surface is needful. The most important factors that influence the final result are i) metal species and the nature of the species deposited on the TiO2 surface; ii) metal amount; iii) metal NPs average dimension; iv) metal NPs distribution. In this sense, the synthesis method is very important because can change these latter parameters, and the use of US during the TiO2 decoration step as reported in (M. Stucchi et al., 2016; M. Stucchi et al., 2014) are very important. US do not change the morphology of TiO2, but they are crucial for the formation of metal and metal oxides nanoparticles as well as for their good distribution on the semiconductor surface, as well as, particularly in case of silver, to obtain bigger spherical particles. The number of silver nanoparticles distributed onto TiO2 surface affects the final photoactivity, and finally a higher number of NPs leads to a better caption of the visible light electrons. 4. Conclusion As a conclusion to this work, some final remarks can be claimed: ➢ Comparing the photocatalytic performances of various commercial TiO2 powders with those of the reference P25 system, in the degradation of different VOCs, such as acetone, toluene, or ethanol, or NOx, different performances have been achieved. The different performances achieved by the various materials are representative of the different physico-chemical features of them. With the main aim to replace the nanosized P25 with a micrometer powder of TiO2, 1077 by Kronos shows the best performances. Thus, the present research indicates first that also micro-sized TiO2 powders, of commercial origin and normally employed as pigments, are very promising materials to be used in the photocatalytic degradation of VOCs and NOx, which would help limiting the risks for human health deriving from the use of nanoparticles. ➢ Then, comparing specifically the photocatalytic performance of P25 and 1077 by Kronos, it is shown that: the adsorption of the pollutant molecule at the semiconductor surface is important to promote the photocatalytic reaction, and in this sense, FTIR analysis of the OH stretching region demonstrated the presence of a good amount of Ti-OH-Ti bridged species on the surface of the micro-sized TiO2, which plays a key role in driving the photocatalytic activity. ➢ Through the innovations introduced by sonochemistry, it was possible to obtain a new type of surface decoration of the pigmentary micro-TiO2, proving that this modification method can improve the photocatalytic activity of the material, in particular under the visible light, where pure TiO2 is not an effective photocatalyst. Indeed, when TiO2 is irradiated by visible wavelengths only, the photocatalytic activity is completely lost and particularly, the deposition of both metal or metal oxides nanoparticles, can positively affect its activation under visible light. ➢ In this research project, the features of Ag, Cu and Mn, have been respectively studied, in particular focusing the attention of the preparation method and the metal amount deposited on the TiO2 surface. It is possible to summarize that: i) high energy US is a facile and fast method to obtain the surface decoration, even when the support is commercial and micrometric; US do not change the morphology of TiO2, but they are crucial for the formation of metal and metal oxides nanoparticles as well as for their good distribution on the semiconductor surface; ii) copper proves to be a good candidate, and its amount is crucial, because as a higher amount of copper both increases the absorption of the visible light and improves the electron-hole separation, over a certain amount of metal the performance decreases, because of the excessive coverage of the active sites of TiO2; iii) Ag shows even better properties in term of TiO2 activation under visible light. Even in this case US do not change the morphology of the micrometric support, and they are important to obtain bigger spherical particles of silver as well. Moreover, the number of silver nanoparticles distributed onto TiO2 surface affects the final photoactivity, and the correlation is linear, because an higher number of NPs leads to a better caption of the visible light electrons first, as well as they reduce the electron-hole recombination, acting as electron traps. Suggestions for the continuation of the work concern the development of production processes to apply the new metal-modified TiO2 powders on ceramic materials, to obtains building products active and effective particularly in indoor environment. Secondly, concerning the use of ultrasound in metal NPs synthesis and their application on TiO2, study further its effects in the pollutants degradation kinetics, as well as in the photocatalytic reactors rheology. Finally, investigate further the degradation of organic molecules with different effects from air pollution: ethylene is harmless for human health, but it is the fruit-ripening hormone. Thus TiO2-materials can be studied for applications regarding food storage and preservation.

The exploration in the use of nanomaterials for a multitude of different applications has grown within the last few years. This is largely due to the vast number of features exhibited by nanoscale materials when compared to their bulk counterparts. The use of nanomaterials in environmental applications can come in different facets, such as, the production of clean energy in solar cells and the application of nanotechnologies in coatings for building exterior surfaces. The first section of the thesis focuses on the use of nanomaterials for water remediation, since purified groundwater is still not globally accessible. Chapter 2 focuses on the use of Pd nanoparticles supported on TiO₂ (Pd@TiO₂) to photo-generate H₂ while using bacterial cells as sacrificial electron donors (SEDs) rather than chemical reagents. Different conditions were examined to investigate the photo-destruction of gram negative bacteria, E. coli, which is a microbial pollutant often found in a number of different water sources. Samples containing photocatalyst in solution were irradiated using a solar simulator, which is a light source that is similar to the solar spectrum, for applications in a flow system. Chapter 3 is a project in collaboration with Dr. Edith Amuhaya and her research group in Nairobi, Kenya exploring the use of porphyrins, an organic compound, supported on glass wool for water treatment in a flow system. Porphyrins are photosensitizers that generate reactive oxygen species (ROS) when exposed to light and oxygen. However, their high solubility in aqueous media makes it difficult to use them for water remediation and can add an extra step in the process of water purification. Therefore, we suggest attaching the porphyrins to glass wool, which is an inexpensive and inert support that can easily be removed from a flow system. Here, we explore the use of glass wool as a support for a series of different conjugated porphyrins and metalloporphyrins. We have synthesized different porphyrins bearing carboxylic group substituents to enable ease of deposition onto the amino-functionalized glass surface (glass surface modified with (3-Aminopropyl) triethoxysilane, APTES). The characterization of the materials suggests some of the porphyrins retain the ability to absorb solar light and generate reactive oxygen species upon irradiation. Antimicrobial activity and degradation of selected pollutants were also explored. The last section of the thesis discusses a different approach regarding nanoparticles. Typically, nanoparticles are used for their reactivity when they absorb light, often producing a high number of free radicals in the process. However, this high reactivity can become an issue when these free radicals cause unintended damage to biological environments. This is the case for TiO₂ used for photo-protection sunscreens, where there has been some concern regarding the free radical damage to skin. Previously, the group has synthesized TiO₂ particles in a thin shell of lignin, a natural biopolymer. Lignin is an antioxidant that can scavenge the radicals produced by the photo-excited TiO₂ and prevent them from being released into the surrounding media. Here, we further characterize and investigate the properties of the lignin on TiO₂ nanoparticles and attempt to scale up the production of the particles.

Two novel materials have been developed: TiO2/poly(dimethylsiloxane) (PDMS) beads as buoyant photocatalyst materials for water remediation, and copper rhodamine‑B silane (Cu‑RBS) as an n ‑type organic/inorganic hybrid for thermoelectric applications. The approach to incorporate TiO2 into low‑density PDMS beads addresses many of the challenges traditionally encountered when creating buoyant photocatalysts, an area which is crucial for wide‑spread remediation of water resources, including natural bodies of water. The performance and reusability of the buoyant photocatalyst materials, demonstrated by using methylene blue as a model degradation target, is strong enough for environmental application. The use of a kinetic model and the introduction of a parameter to allow comparison of buoyant photocatalysts is also included as part of the analysis. The performance of Cu‑RBS was investigated as a low‑temperature thermoelectric material. Clear improvements in the electrical conductivity and Seebeck coefficient are observed for RBS upon coordination to Cu2+. Evidence explaining this improvement is provided by computational analysis and by concentration‑dependent optical absorption and fluorescent emission measurements, all of which indicate that a metal‑to‑ligand charge transfer occurs from Cu2+ to RBS. Although the power factor of Cu‑RBS is low compared to other materials reported in the literature, these results provide a promising approach to increasing both the Seebeck coefficient and electrical conductivity of n‑type small molecule organic systems.

La photocatalyse hétérogène est une technique d'oxydation avancée prometteuse dans le domaine de la dépollution d’effluents aqueux ou gazeux industriels contenant des composés organiques tels que les colorants, engrais, pesticides ou composés organiques volatils (COV). La photocatalyse met en oeuvre l'excitation d’un matériau semi-conducteur par une radiation lumineuse et dans ce contexte le dioxyde de titane (TiO2) est le photocatalyseur le plus couramment employé. Cependant, son activité est liée à de nombreux paramètres (longueur d'onde d'irradiation, paramètres texturaux, composition cristalline…) qu'il convient de maitriser si on veut concevoir un système de dépollution efficace. Afin d’améliorer les performances du TiO2, différentes approches ont émergé durant les dernières décennies, telles que ledopage par des métaux de transition ou le dopage par des composés organiques.Le sujet de la thèse s’est inscrit dans ce contexte et a porté sur le développement de systèmes photocatalytiques élaborés en présence de cyclodextrines (molécules cages formées par l’enchainement d’unités glucosidiques) pour la dégradation de polluants organiques en phase aqueuse. Il s'articule en trois parties principales. La première partie a été consacrée à la possibilité de combiner directement l’action d’un dioxyde de titane commercial (P25) en suspension aqueuse en présence de cyclodextrines pour améliorer le rendement de réactions photocatalysées. Appliquée à la dégradation photocatalytique d’un COV hydrophobe (toluène) dans l’UV, l’étude n’a pas montré d’impact positif des cyclodextrines. Les résultats ont été rationnalisés par l’évaluation des capacités d’adsorption des cyclodextrines sur la surface duphotocatalyseur et des constantes d’association 1:1 CD:toluène. Le deuxième partie a porté sur la synthèse d’une série de matériaux mésoporeux TiO2 par voie sol-gel colloïdale en utilisant comme agents structurants des assemblages supramoléculaires de type Pluronic 123-cyclodextrine partiellement méthylée (micelles). L’introduction de cyclodextrine méthylée en quantité contrôlée permet de jouer sur le glonflement des micelles. Après élimination de l’agent template par calcination, il est mis en évidence qu’il est possible de moduler les paramètres texturaux et structuraux du dioxyde de titane. Ces matériaux ont été évalués dans la réaction de dégradation de l’acide phénoxyacétique en phase aqueuse sous une irradiation proche du rayonnement visible (365 nm). Dans la troisième partie, le développement de matériaux mésoporeux TiO2 par voie sol-gel colloïdale a été poursuivi en substituant les assemblages supramoléculaires comme agents structurants par des cyclodextrines seules. Les paramètres de synthèse ont été optimisés avec différentes types de cyclodextrines (natives ou modifiées) et différentes concentrations.Les meilleurs résultats en termes de dégradation photocatalytique de l’acide phénoxyacétique à 365 nm ont été obtenus avec le matériau R25-T500 préparé à partir de cyclodextrine alétoirement méthylée à 25 g/L. Enfin, l’incorporation d’or sous forme HAuCl4 durant le protocole de synthèse a même permis d’observer une augmentation de l’activité photocatalytique sous irradiation à 420 nm comparativement au catalyseur référence TiO2 P25
Photocatalysis is a promising advanced oxidation process (AOPs) to efficiently removing non biodegradable pollutants from atmosphere. Among photocatalysts, titanium dioxide (TiO2) remains certainly one of the most attractive materials because it is relatively inexpensive, nontoxic and photochemically stable. However, several factors such as wavelength of irradiation, the crystal phase composition, the surface area and the adsorption properties of the catalyst are likely to affect the hotocatalytic efficiency. The design of semiconductor metal oxide nanoparticles with tunable pore size and morphology andcontrollable composition is so important to create an efficient remediation process. To improve the photoactivity of the semi-conductor, several approaches have already been reported such as the combination of metallic or organic material to titanium dioxide. Cyclodextrins (CDs) are natural cyclic oligosaccharides derived from starch that can include in their hydrophobic cavity many organic compounds by host-guest interaction and thus increase the solubility of the guest. Taking advantage of their inclusion capacity, CDs can play a major role in catalytic processes. Numerous works involving the combined use of cyclodextrins and titanium dioxide have been reported but depending on the structure of the reactants and the reaction conditions, the CD may or may not improve the photocatalytic degradation of pollutants and it seems difficult to predict the effect of CDs on a photocatalytic process. To further understand the interactions between CD and TiO2 and to improve the performance of a photocatalytic remediation process, we studied the effect of different CDs on the properties of commercial or synthesized titanium dioxide nanoparticules. The performances of our catalysts were evaluated on thephotodegradation of two pollutants in aqueous phase: the toluene (VOC) and the phenoxyacetic acid (herbicide). This work has been divided into 3 parts: first we evaluated the impact of different CDs on the photocatalytic degradation of toluene in aqueous phase by a commercial titanium dioxide (P25). Then in a second part we investigated a template-directed colloidal self-assembly strategy for the production, in aqueous phase, of nanostructured TiO2 materials with tunable porosity and crystalline framework. The approach employs the supramolecular assemblies formed between a methylated β-cyclodextrin and the block copolymer P123 as soft templates and TiO2 nanocrystals as building blocks. Finally, we have investigated the possibility of using the cyclodextrin alone as soft templates for the preparation of a series of mesoporous titania materials with tunable properties The results show that a modified cyclodextrin can modulate the textural and structural parameters of TiO2 in order to maximize the degradation of phenoxyacetic acid in aqueous phase under near visible radiation. The incorporation of gold in our synthesis method has even increased the photocatalytic activity of our semi-conductor compared to the commercial P25 for an irradiation of 420 nm