Dissertations / Theses on the topic 'Photocatalysts'

The connection between ritual and the interior is interrogated through a theoretical framework integrating Van Gennep’s Rites of Passage Theory and Turner’s Theory of Liminality. A multi-faceted methodological framework is developed from the interrogation of the disciplinary edges of multiple methodologies, addressing the experiential, cultural and subjective dimensions of ritual. This new way of exploring the interior demonstrates how knowledge can be acquired from the body’s immersion in unfolding ritual situations, revealing elements of ritual and interior in relation to one another and the generation of new theories on the interior.

Advanced water purification methods are required to answer the growing demand for clean water throughout the world. Current methods of removing the pollutants rely on moving the pollutants from one place to another rather than breaking them down. The use of advanced oxidative processes (AOPs) presents a highly effective opportunity to achieve the full mineralisation of pollutants without the added cost of regeneration methods. Photocatalysts, such as titanium dioxide and zinc oxide, can be used as AOPs when activated by electromagnetic radiation in the form of ultraviolet and visible light. To facilitate the activation with visible light, titanium dioxide doped with rare earth elements was produced via a sol gel method. Both single doped and co-doped systems were investigated with efficiency determined by the percentage of degraded methylene blue over 48 hours under ultraviolet filtered visible light. The incorporation of rare earth ions restricted the growth of the more active anatase phase and the method produced highly agglomerated, sintered nano particles which exhibited as micron sized particles. The highest methylene blue removal rate achieved in 48 hours for a single doped system was 70% for the 1 mol% yttrium doped titanium dioxide. This was improved further on inclusion of 1 mol% praseodymium which showed an 86% removal of methylene blue over the same time period. The coating of known up-converting phosphors with the successfully developed doped titanium dioxide was investigated. Yttrium silicate doped with praseodymium and lithium, was found to be the most successful known phosphor when used with the commercially available P25 titanium dioxide. When coated with the doped titanium dioxide shell at a 2:1 ratio of phosphor to titanium dioxide, a methylene blue degradation of 94% was reached. Initial tests on the coating of titanium dioxide with the known up-converting phosphor showed that methylene blue was absorbed rather than broken down so was not developed further. An investigation into the incorporation of zinc oxide, both pure and doped with the same successful titanium dioxide system was carried out. Zinc oxide shells were coated onto doped titanium dioxide, the known up-converting phosphor and the doped titanium dioxide coated known phosphor. The crystalline form of zinc oxide was inhibited by the incorporation of rare earth ions, as with the titanium dioxide system, and from the thickness of the zinc oxide shell. The highest degradation achieved was a 91% removal rate for the ZnO-PrY:TiO2-PrY:Y2SiO5-Pr,Li core shell shell structure indicating there was no further improvement on incorporation of zinc oxide, either doped or un-doped.

Concern over the economics of accessing fossil fuel and widespread acceptance of the anthropogenic origin of rising CO2 emissions and associated climate change is driving academic and commercial research into new routes to sustainable fuels, to meet the demands of a rapidly rising global population and reduce an impact on the environment. The titania oxide semiconductor has attracted a great interest as a photocatalyst for wide-ranging applications including wastewater depollution, solar fuels via both H2 production and CO2 reduction. Tailoring the physicochemical properties of titania photocatalysts, and their resulting reactivity, in a predictable fashion remains challenging. The thesis explores the impact of thermal processing, macroporosity and metal deposition on the surfactant-templated mesoporous TiO2 and dual soft-hard templated macro-mesoporous TiO2 series and resulting activity in aqueous phase photocatalytic dye degradation, H2 production and CO2 reduction reactions. Control over the structural and photophysical properties of mesoporous titania enables systematic tuning of Methyl Orange photocatalytic depollution and H2 evolution. Hierarchical macro-mesoporous titanias exhibit uniform mesopores with macropore diameters that can be systematically tuned between 140-310 nm, resulting in a close-packed, ordered macropore framework. Hierarchically-structured TiO2 display two fold increase in photoactivity relative to mesoporous counterparts in the H2 production. Ultra-low concentrations (0.02-0.1 wt%) of copper introduced into the mesoporous and macro-mesoporous titania surfaces by wet-impregnation enhance activity for dye degradation by six fold, and for H2 production four fold, through the genesis of isolated Cu (I) species which suppress charge recombination. Furthermore, promotion with Pt increases photocatalytic activity in Methyl Orange degradation by eleven fold, H2 production 16-26 times and are the only series which display activity in the CO2 reduction reaction. Moreover, the impact of the macropore diameter on the activity of the Methyl Orange degradation is observed for Cu and Pt promoted macro-mesoporous TiO2 series. Nanostructured promoted titanias offer an insight into the relative importance of physicochemical and electronic properties upon their associated activity together with significantly enhanced photocatalytic performance.

This thesis describes the synthesis and characterisation of titania photocatalysts for incorporation into a polyethylene film. Monodisperse, anatase-phase titania nanoparticles are prepared and the synthesis conditions necessary for attraction to a laponite clay support are determined. Methods of preventing agglomeration of the laponite system such as the use of a polyethylene oxide surfactant or chemical modification of the laponite plate edges with a dimethyloctyl methoxysilane are also explored. Finally, photocatalytic studies on the laponite-supported titania nanoparticles are performed, and the compatibility and photoactivity of these materials in the polyethylene film are examined.

This thesis describes the synthesis and characterisation of titania photocatalysts for incorporation into a polyethylene film. Monodisperse, anatase-phase titania nanoparticles are prepared and the synthesis conditions necessary for attraction to a laponite clay support are determined. Methods of preventing agglomeration of the laponite system such as the use of a polyethylene oxide surfactant or chemical modification of the laponite plate edges with a dimethyloctyl methoxysilane are also explored. Finally, photocatalytic studies on the laponite-supported titania nanoparticles are performed, and the compatibility and photoactivity of these materials in the polyethylene film are examined.

Research concentrated on the absorption, transformation, and storage of light energy is useful for the energy challenges faced by humanity. In particular, photocatalysis using solar energy to generate useful fuels has become a primary research goal in the drive to replace fossil fuels for the future. In this dissertation it is shown that poly-tetra(4-aminophenyl)porphyrin (pTAPP) can be oxidatively polymerized using a variety of methods, including electropolymerization, chemical oxidation, and interfacial polymerization and that pTAPP has photocatalytic ability to reduce O2 to H2O2 for a storable fuel. Organic conductive polymers such as pTAPP are attractive catalysts because of their high surface area and ability to coat electrodes. pTAPP in a mixed oxidation state is shown to have both its minimum charge transfer resistance as well as its minimum impedance to electronic conductivity in the film. The UV-vis-NIR absorption spectra of pTAPP with increased oxidative doping are similar to hyperporphyrin spectra, characteristic of a two-plus charge localized on a single porphyrin unit. This suggests the presence of a bipolaron on the individual porphyrin units, and thus a bipolaron conductivity mechanism has been proposed. pTAPP changes color depending on its oxidation state, and therefore is a promising material for electrochromic devices. A novel Pourbaix diagram was created as a means of illustrating the redox and protonation states of pTAPP as a function of changes in pH, applied potential, electrochromic behavior, and electronic conductivity. Both pTAPP and pCoTAPP were shown to be effective catalysts for the reduction of oxygen to hydrogen peroxide, with pCoTAPP a better catalyst than pTAPP. When pCoTAPP is irradiated, oxygen reduction occurs close to the thermodynamic potential, indicating a promising system for storage of solar energy.

Photocatalysis is a series of advanced light-induced redox reaction processes resulting in the degradation and mineralization of organic pollutants in the presence of oxygen and water. Due to their capability to destroy contaminants under mild conditions, photocatalytic processes have attracted considerable attention in the field of waste-water treatment. However, photocatalytic reactions using the traditional TiO2 photocatalyst suffer from low energy efficiencies under solar irradiation. This low efficiency in the utilization of solar energy lies in its incapability in absorbing visible lights and also the high recombination rate of photo-excited species in photocatalysts. In addition, difficulties in the separation of fluids from micro- or nano-scale catalysts in large scale systems substantially impact cost efficiency in practice. In this thesis, strategies are explored which address these issues in order to improve the feasibility of solar photocatalysis. Two branches of photocatalytic transition metal-oxide semiconductor materials are investigated, namely bismuth-based and silver-based multi-phase heterogeneous photocatalysts. This research is focused on the design of visible-light-active metal-oxide photocatalysts to increase the absorption of visible light and to decrease the rates of electron-hole recombination, resulting in a high photocatalytic efficiency in regards to the degradation of organic pollutants. BiVO4 powder, synthesized from freshly made potassium metavanadate was prepared via hydrothermal treatment, characterized and experimentally investigated for the degradation of rhodamine B under visible light irradiation. The crystal structures and the specific surface areas of the composites, based on BiVO4 single phase crystal structures, are discussed. A multi-phase silver species (Ag2O/Ag3VO4/Ag4V2O7) photocatalyst was synthesized by adjusting the molar ratio of silver to vanadium (Ag to V) via hydrothermal method. The stabilities of as-prepared silver species composites regarding crystal structural changes due to photocatalytic reactions are investigated. Multi-phase silver species composites assisted with graphene oxide (GO-Ag2O/Ag3VO4/AgVO3) were synthesized at room temperature, and exhibited high visible-light photocatalytic activities regarding the degradation of model organic pollutants. The effect of graphene oxide addition on the photoactivity and on the photocorrosion of silver species composites under VLI is explored. The synergistic roles of each individual phase incorporated into the multi-phase composites are discussed regarding the photocatalytic performance.

Photocatalytic processes over semiconducting oxide surfaces have attracted worldwide attention aspotentially efficient, environmentally friendly and low cost methods for water/air purification as well as forrenewable hydrogen production. However, some limitations to achieve high photocatalytic efficiencies havebeen found due to the fast recombination of the charge carriers. Development of heterostucture photocatalystsby depositing metals on the surface of semiconductors or by coupling two semiconductors with suitable bandedge position can reduce recombination phenomena by vectorial transfer of charge carriers. To draw newprospects in this domain, three different kinds of heterostructures such as n-type/n-type semiconductor(SnO2/ZnO), metal/n-type semiconductor (RuO2/TiO2 and RuO2/ZnO) and p-type/n-type semiconductor(NiO/TiO2) heterojunction nanomaterials were successfully prepared by solution process. Their composition,texture, structure and morphology were thoroughly characterized by FTIR, X-ray diffraction (XRD), Ramanspectroscopy, transmission electron microscopy (TEM) and N2 sorption measurements. On the other hand, asuitable combination of UV-visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy(XPS) and ultraviolet photoemission spectroscopy (UPS) data provided the energy band diagram for eachsystem. The as-prepared heterojunction photocatalysts showed higher photocatalytic efficiency than P25 TiO2for the degradation of organic dyes (i.e. methylene blue and methyl orange) and the production of hydrogen.Particularly, heterostructure RuO2/TiO2 and NiO/TiO2 nanocomposites with optimum loading of RuO2 (5 wt %)and NiO (1 wt %), respectively, yielded the highest photocatalytic activities for the production of hydrogen.These enhanced performances were rationalized in terms of suitable band alignment as evidenced by XPS/UPSmeasurements along with their good textural and structural properties. This concept of semiconductingheterojunction nanocatalysts with high photocatlytic activity should find industrial application in the future toremove undesirable organics from the environment and to produce renewable hydrogen.

Due in no small part to an increasing need to augment existing water purification strategies, the synthesis of titania photocatalysts has been under considerable examination. However, in order to make the use of titania photocatalysts commercially viable there needs to be an increase in the efficiency of the catalysts while decreasing the potential toxicity. Due to its high porosity and novel optical properties, inverse opal titania derived from colloidal crystal templating offers one of the most efficient solutions. While a number of synthesis methods for inverse opal titania have been presented in the literature, the co�]deposition method offers the most effective method of generating the relative large areas of inverse opal material. The factors which affect the codeposition method and the mechanism by which titania inverse opals form in general remain relatively unstudied. This manuscript presents an examination of the morphology of inverse opals generated by the co�]deposition method while proposing a mechanism by which the inverse structures form.

This project was a step forward in developing new effective photocatalysts for fine organic synthesis under visible light irradiation. These kind of new photocatalysts are able to facilitate reaction rates by using visible light under moderate reaction conditions through a green, economical and environmentally friendly pathway. This thesis investigated the catalyst synthesis, characterization and the application in organic reactions with high activity and selectivity. The discovery of these new metal nanoparticle photocatalysts may inspire further studies on other efficient photocatalysts and enhance the potential to utilize sunlight via a controlled and environmentally friendly process.

Esta tesis doctoral se ha centrado en la preparación de fotocatalizadores nanoestructurados basados en TiO2 modificados con metales de transición o carbón activado para su aplicación en reacciones de interés medioambiental, concretamente, en la eliminación de tres contaminantes: ácido acético y diurón, en fase acuosa, y propeno en fase gas. Se ha estudiado la influencia de las propiedades fisicoquímicas (porosidad, cristalinidad, composición química, propiedades electrónicas) de cada material en su actividad fotocatalítica.

This research underlines the extensive application of nanostructured metal oxides in environmental systems such as hazardous waste remediation and water purification. This study tries to forge a new understanding of the complexity of adsorption and photocatalysis in the process of water treatment. Sodium niobate doped with a different amount of tantalum, was prepared via a hydrothermal reaction and was observed to be able to adsorb highly hazardous bivalent radioactive isotopes such as Sr2+ and Ra2+ions. This study facilitates the preparation of Nb-based adsorbents for efficiently removing toxic radioactive ions from contaminated water and also identifies the importance of understanding the influence of heterovalent substitution in microporous frameworks. Clay adsorbents were prepared via a two-step method to remove anionic and non-ionic herbicides from water. Firstly, layered beidellite clay was treated with acid in a hydrothermal process; secondly, common silane coupling agents, 3-chloro-propyl trimethoxysilane or triethoxy silane, were grafted onto the acid treated samples to prepare the adsorption materials. In order to isolate the effect of the clay surface, we compared the adsorption property of clay adsorbents with ƒ×-Al2O3 nanofibres grafted with the same functional groups. Thin alumina (£^-Al2O3) nanofibres were modified by the grafting of two organosilane agents 3-chloropropyltriethoxysilane and octyl triethoxysilane onto the surface, for the adsorptive removal of alachlor and imazaquin herbicides from water. The formation of organic groups during the functionalisation process established super hydrophobic sites along the surfaces and those non-polar regions of the surfaces were able to make close contact with the organic pollutants. A new structure of anatase crystals linked to clay fragments was synthesised by the reaction of TiOSO4 with laponite clay for the degradation of pesticides. Based on the Ti/clay ratio, these new catalysts showed a high degradation rate when compared with P25. Moreover, immobilized TiO2 on laponite clay fragments could be readily separated out from a slurry system after the photocatalytic reaction. Using a series of partial phase transition methods, an effective catalyst with fibril morphology was prepared for the degradation of different types of phenols and trace amount of herbicides from water. Both H-titanate and TiO2-(B) fibres coated with anatase nanocrystal were studied. When compared with a laponite clay photocatalyst, it was found that anatase dotted TiO2-(B) fibres prepared by a 45 h hydrothermal treatment followed by calcination were not only superior in performance in photocatalysis but could also be readily separated from a slurry system after photocatalytic reactions. This study has laid the foundation for the development of the ability to fabricate highly efficient nanostructured solids for the removal of radioactive ions and organic pollutants from contaminated water. These results now seem set to contribute to the development of advanced water purification devices in the future. These modified nanostructured materials with unusual properties have broadened their application range beyond their traditional use as adsorbents, to also encompass the storage of nuclear waste after concentrating from contaminated water.

Using visible light to accelerate fine organic synthesis reactions in the presence of photocatalyst is a step forward to the green chemical industry. This thesis developed gold, gold-palladium alloy and copper photocatalysts. Aqueous reactions system is introduced into photocatalysis for an eco-friendly process. The bi-metal nanoparticle is applied to expand the application of metallic photocatalysis in selective synthesis. The theory for copper nanostructure stabilisation on metal nitride is established and successfully applied in organic synthesis. This research is beneficial to the future of the organic chemical industry in terms of the new production model and energy saving.

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.

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.

The photocatalytic production of hydrogen from water and biomass derivatives such as ethanol, glycerol and sugars is a highly attractive strategy to generate environmentally benign hydrogen. Ethanol is more easily oxidized than water by holes in the valence band (VB) of photoexcited semiconductors, which also helps to suppress the recombination of electron-hole pairs, thus increasing the usage of electrons in the conduction band (CB) of photoexcited semiconductors to yield hydrogen. Titanium dioxide (TiO2) has been widely investigated in the field of photocatalysis due to its photosensitivity, low cost, natural abundance, non-toxicity, and good chemical and thermal stability. However, the solar energy conversion efficiency of TiO2 is hindered by its large bandgap (3.2 eV). Here, we demonstrate that the combination of TiO2 with Ni, Co and Cu can substantially promote local spatial charge separation and proton activation in TiO2, achieving high-efficiency for H2 photoproduction. In chapter 2, we present a strategy to produce porous NiTiO3/TiO2 nanostructures with excellent photocatalytic activity toward hydrogen generation. Nickel-doped TiO2 needle bundles were synthesized by a hydrothermal procedure. Through the sintering in air of these nanostructures, porous NiTiO3/TiO2 heterostructured rods were obtained. Alternatively, the annealing in argon of the nickel-doped TiO2 needle bundles resulted in NiOx/TiO2 elongated nanostructures. Porous NiTiO3/TiO2 structures were tested for hydrogen evolution in the presence of ethanol. Such porous heterostructures exhibited superior photocatalytic activity toward hydrogen generation, with hydrogen production rates up to 11.5 mmol h-1 g-1 at room temperature. In chapter 3, CoTiO3/TiO2 composite catalysts with controlled amounts of highly distributed CoTiO3 nanodomains for photocatalytic ethanol dehydrogenation are developed and studied. To take advantage of solar light, the CoTiO3 nanoparticles with a band gap around 2.3 eV were synthesized by a hydrothermal procedure. We demonstrate these materials to provide outstanding hydrogen evolution rates under UV and visible illumination. The origin of this enhanced activity is extensively analysed. In contrast to previous assumptions, UV-vis absorption spectra and ultraviolet photoelectron spectroscopy (UPS) prove CoTiO3/TiO2 heterostructures to have a type II band alignment, with the CB minimum of CoTiO3 below the H+/H2 energy level. Additional steady-state photoluminescence (PL) spectra, time-resolved PL spectra (TRPLS), and electrochemical characterization prove such heterostructures to result in enlarged lifetimes of the photogenerated charge carriers. These experimental evidences point toward a direct Z-scheme as the mechanism enabling the high photocatalytic activity of CoTiO3/TiO2 composites toward ethanol dehydrogenation. The optimization of photodehydrogenation of ethanol requires the use of highly active, stable and selective photocatalytic materials based on abundant elements, and the proper adjustment of the reaction conditions, including temperature. In chapter 3, Cu2O-TiO2 type-II heterojunctions with different Cu2O amounts are obtained by a one-pot hydrothermal method. The structural and chemical properties of the produced materials and their activity toward ethanol photodehydrogenation under UV and visible light illumination are evaluated. The structural and chemical properties of the produced materials and their activity toward ethanol photodehydrogenation under UV and visible light illumination are evaluated. The Cu2O-TiO2 photocatalysts exhibit high selectivity toward acetaldehyde production and up to tenfold higher hydrogen evolution rates compared to bare TiO2. We further discern here the influence of temperature and visible light absorption on photocatalytic performance.
La producció fotocatalítica d’hidrogen a partir de derivats de l’aigua i de la biomassa com l’etanol, el glicerol i els sucres és una reacció atractiva per proporcionar hidrogen benigne per al medi ambient. L’etanol s’oxida més fàcilment que l’aigua mitjançant forats de la banda de valència dels semiconductors fotoexcitats, suprimint la recombinació de parells electró-forat i, per tant, augmentant la reactivitat dels electrons en la banda de conducció dels semiconductors fotoexcitats per produir hidrogen. El diòxid de titani (TiO2) ha estat àmpliament investigat en el camp de la fotocatàlisi a causa de la seva fotosensibilitat, baix cost, abundància natural, no toxicitat i bona estabilitat química i tèrmica. No obstant això, l'eficiència de conversió d'energia solar de TiO2 es veu obstaculitzada per la seva gran amplada de banda (3,2 eV) i la alta taxa de recombinació dels portadors fotogenerats. Aquí demostrem que el Ni, Co i Cu poden promoure substancialment la separació de càrregues i l’activació de protons en el TiO2, aconseguint una alta eficiència per a la fotoproducció d¿H2. En el capitol 2, presentem una estratègia per produir nanoestructures poroses de NiTiO3/TiO2 amb una excel·lent activitat fotocatalítica cap a la generació d’hidrogen. Al capítol 2, es van sintetitzar agulles de TiO2 dopades amb níquel itjançant un procediment hidrotermal. Mitjançant la sinterització a l'aire d'aquestes nanoestructures es van obtenir agulles heterostructurades poroses de NiTiO3/TiO2. Com a alternativa, el tractament tèrmic en argó de les agulles de TiO2 dopades amb níquel va donar lloc a nanoestructures allargades de NiOx/TiO2. Es van provar les estructures poroses de NiTiO3/TiO2 per a la producció d’hidrogen en presència d’etanol. Aquestes heteroestructures poroses presentaven una activitat fotocatalítica superior cap a la generació d’hidrogen, amb taxes de producció de fins a 11.5 mmol h-1 g-1 d’hidrogen a temperatura ambient. Per aprofitar la il·luminació solar, es van sintetitzar nanopartícules de CoTiO3 amb una banda adequada al voltant de 2,3 eV mitjançant un procediment de sinterització hidrotermal. Al capítol 3, els catalitzadors compostos CoTiO3/TiO2 amb quantitats controlades de nanodominis distribuïts de CoTiO3 es van provarper a la deshidrogenació fotocatalítica d’etanol. Demostrem que aquests materials proporcionen velocitats devolució d’hidrogen excepcionals sota il·luminació UV i visible. S’analitza a fons l’origen d’aquesta activitat millorada. En contrast amb els supòsits anteriors, els espectres d’absorció UV-vis i l’espectroscòpia de fotoelectrons ultraviolats (UPS) demostren que les heteroestructures CoTiO3/TiO2 tenen una alineació de banda de tipus II, amb la banda de conducció mínima de CoTiO3 per sota del nivell d’energia H+/H2. Els espectres addicionals de fotoluminescència en estat estacionari (PL), espectres PL resolts en el temps (TRPLS) i caracterització electroquímica demostren que aquestes heteroestructures donen lloc a una vida més gran dels portadors de càrrega fotogenerats. Aquestes evidències experimentals apunten cap a un esquema Z directe com el mecanisme que permet l’alta activitat fotocatalítica dels compostos CoTiO3/TiO2 cap a la deshidrogenació de l’etanol. L’optimització de la fotodehidrogenació de l’etanol requereix l’ús de materials fotocatalítics altament actius, estables i selectius basats en elements abundants i l’adequat ajust de les condicions de reacció, inclosa la temperatura. Al capítol 3, s’obtenen heterojuncions de tipus Cu2O-TiO2 tipus II amb diferents quantitats de Cu2O mitjançant un mètode hidrotermal en una etapa. S’avaluen les propietats estructurals i químiques dels materials produïts i la seva activitat cap a la fotodehidrogenació d’etanol sota la il·luminació UV i llum visible. Els fotocatalitzadors Cu2O-TiO2 presenten una alta selectivitat cap a la producció d’acetaldehid i hidrogen fins a deu vegades més altes que el TiO2. Aquí també discernim la influència de la temperatura i l’absorció de llum visible en el rendiment fotocatalític. Els nostres resultats apunten a la combinació de fonts d’energia en reactors termofotocatalítics com una estratègia eficient per a la conversió d’energia solar. Els resultats es van publicar en Nanomaterials el 2021
La producción fotocatalítica de hidrógeno a partir de agua y derivados de biomasa como etanol, glicerol y azúcares es una reacción atractiva para proporcionar hidrógeno sin apenas impacto ambiental. El etanol se oxida más fácilmente que el agua por los huecos en la banda de valencia de los semiconductores fotoexcitados, suprimiendo la recombinación de pares electrón-hueco y, por lo tanto, aumentando la reactividad de los electrones en la banda de conducción de los semiconductores fotoexcitados para producir hidrógeno. Además, el etanol es un recurso renovable que se produce fácilmente mediante la fermentación convencional de azúcares y almidón. El dióxido de titanio (TiO2) ha sido ampliamente investigado en el campo de la fotocatálisis debido a su fotosensibilidad, bajo costo, abundancia natural, no toxicidad y buena estabilidad química y térmica. Sin embargo, la eficiencia de conversión de energía solar del TiO2 se ve obstaculizada por su gran banda prohibida (3,2 eV). Aquí, demostramos que la incorporación de Ni, Co y Cu puede promover sustancialmente la separación de cargas locales y la activación de protones por el TiO2, logrando una alta eficiencia en la fotoproducción de H2. En el capítulo 2, presentamos una estrategia para producir nanoestructuras porosas de NiTiO3/TiO2 con excelente actividad fotocatalítica hacia la generación de hidrógeno. En el capítulo 2, se sintetizaron agujas de TiO2 dopado con níquel mediante un procedimiento hidrotermal. Mediante la sinterización al aire de estas nanoestructuras se obtuvieron heteroestructuras en forma de varillas de NiTiO3/TiO2 porosas. Alternativamente, el tratamiento térmico bajo argón de las varillas de TiO2 dopado con níquel dió como resultado nanoestructuras alargadas de NiOx/TiO2. Las estructuras porosas de NiTiO3/TiO2 se ensayaron para determinar la producción de hidrógeno en presencia de etanol. Tales heteroestructuras porosas exhibieron una actividad fotocatalítica superior hacia la generación de hidrógeno, con tasas de producción de hasta 11,5 mmol h-1 g-1 de hidrógeno a temperatura ambiente. Este excelente rendimiento se relaciona con las propiedades optoelectrónicas y los parámetros geométricos del material. Los resultados se publicaron en Journal of Materials Chemistry A en 2019. Para aprovechar la luz solar, se sintetizaron nanopartículas de CoTiO3 con un intervalo de banda de alrededor de 2.3 eV mediante un procedimiento de sinterización hidrotermal. En el capítulo 3, se prepararon catalizadores compuestos CoTiO3/TiO2 con cantidades controladas de nanodominios CoTiO3 altamente distribuidos para la deshidrogenación fotocatalítica de etanol. Demostramos que estos materiales presentan una actividad fotocatalítica de generación de hidrógeno excepcionales bajo iluminación UV y visible. El origen de esta actividad se analiza ampliamente. En contraste con las suposiciones anteriores, los espectros de absorción UV-vis y la espectroscopia de fotoelectrones ultravioleta (UPS) demuestran que las heteroestructuras de CoTiO3/TiO2 tienen una alineación de banda de tipo II, con la banda de conducción del CoTiO3 por debajo del nivel de energía H+/H2. Los espectros de fotoluminiscencia (PL), los espectros de PL resueltos en el tiempo (TRPLS) y la caracterización electroquímica demuestran que tales heteroestructuras dan como resultado una mayor vida útil de los portadores de carga fotogenerados. Estas evidencias experimentales apuntan hacia un esquema Z directo como el mecanismo que permite la alta actividad fotocatalítica de los compuestos CoTiO3/TiO2 hacia la deshidrogenación del etanol. Además, se analizó el efecto de la temperatura en la actividad fotocatalítica de los materiales probados, lo que podría usarse para promover aún más el rendimiento en un reactor solar termo-fotocatalítico. Los resultados se publicaron en ACS Applied Materials & Interfaces en 2021. La optimización de la fotodeshidrogenación del etanol requiere el uso de materiales fotocatalíticos altamente activos, estables y selectivos basados en elementos abundantes y el adecuado ajuste de las condiciones de reacción, incluida la temperatura. En el capítulo 3, se obtuvieron heterouniones Cu2O-TiO2 tipo II con diferentes cantidades de Cu2O mediante un método hidrotermal en un solo paso. Se evalúan las propiedades estructurales y químicas de los materiales producidos y su actividad hacia la fotodeshidrogenación de etanol bajo iluminación UV y con luz visible. Los fotocatalizadores Cu2O-TiO2 muestran una alta selectividad hacia la producción de acetaldehído e hidrógeno hasta diez veces más altas en comparación con el TiO2. También discernimos aquí la influencia de la temperatura y la absorción de luz visible en el rendimiento fotocatalítico. Nuestros resultados apuntan a la combinación de fuentes de energía en reactores termo-fotocatalíticos como una estrategia eficiente para la conversión de energía solar. Los resultados se publicaron en nanomateriales en 2021
Enginyeria de processos químics

It is widely accepted that graphene as well as reduced graphene oxide (rGO) have shown many superior properties such as electron mobility, excellent thermal and electrical conductivity, and large theoretical specific surface area. Previous research has shown significant enhancement of the photocatalytic property of semiconductors by compositing with rGO, which was largely attributed to the function of rGO or graphene as the electron sink. Moreover, the incorporation of graphene in photocatalytic systems also renders new format and new properties to photocatalysts. This MPhil project focuses on the synthesis of photocatalytic membranes formed by the embedment of Cu2O and/ or TiO2 nanowires in reduced graphene oxide, and their photocatalytic applications in water purification, such as destruction of organic dyes and persistent organic pollutants, as well as hydrogen production from ammonia solution. The literature review summarizes various types of graphene-based photocatalysts through different synthesis methods, and points out major factors that can influence photocatalytic efficiency. In the second part of the research, the research was aimed at fabricating a graphene based photocatalyst which can show superior photocatalytic efficiency under UV-Vis range. For this purpose, a heterojunction photocatalytic membrane consisting of Cu2O and TiO2 nanowires was produced. The resulting membrane benefitted from in- between reduced graphene oxide (rGO) sheets which was fabricated by applying a facile process from colloidal suspension. The designed membrane exhibits significantly enhanced activity under UV-Vis range, surpassing nanowires dispersions, owing to heterojunction formation and concurrent electron and hole transfer on rGO sheets. Furthermore, the membrane also possesses increased permeability and photocorrosion resistance. The described design and fabrication method of a rGO facilitated heterojunction photocatalytic membrane can be used in significant areas of applications including energy and environment developments. The focus of the final part of the research was to design a photocatalyst to produce hydrogen from ammonia solution. My study showed that the rGO/TiO2 NWs membrane results in 30-fold enhancement in photocatalytic H2 production compared with TiO2 NWs alone.
Thesis (Masters)
Master of Philosophy (MPhil)
Griffith School of Engineering
Science, Environment, Engineering and Technology
Full Text

Photocatalysts, typically nanoparticulate semiconductors, can be used to split water into hydrogen and oxygen. If solar light is used for this, it opens the possibility of a renewable source of hydrogen. However, extension of photocatalytic response into the visible region of the solar spectrum is required. A new visible light activated photocatalyst is reported herein. Iron vanadate, FeVO4, was first synthesised using a low-temperature, aqueous precipitation reaction. The material prepared was found to be predominantly amorphous and required thermal treatment. The resultant material was characterised using XRD, SEM, IR spectroscopy, Raman spectroscopy and magnetic susceptibility measurements. Materials annealed above 600 °C were found to consist mainly of FeVO4, although traces of hematite were found. Diffuse-reflectance UV spectroscopy and subsequent Tauc plots revealed a band gap of ca. 2.00 eV corresponding to an indirect transition. Photocurrent-voltage characteristics recorded under simulated solar illumination indicate that photocurrents are sensitive to annealing temperature and the thickness of the deposit. However, although photocurrent-voltage plots show that electrodes prepared from a suspension of nanoparticulate FeVO4 powders were photo-responsive, these electrodes were found to be mechanically unstable. Films were prepared directly onto the electrode by using a sol-gel approach. Raman spectroscopy, XRD and diffuse-reflectance UV-visible spectroscopy has revealed the electrode films to be crystalline in nature, significantly more stable, with an indirect band gap in the visible region of 2.00 eV. Higher photocurrent densities were observed for the sol-gel prepared electrodes compared to those deposited from aqueous suspensions of pre-formed powders. It was determined that these photocurrents were dependant on film thickness, annealing time and temperature, and sol pH.

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.

Hydrogen energy is an ideal energy resource owing to its clean and efficient utilization. As an energy carrier without natural abundance, the limited reserve makes the high consumption a big challenge. In the meantime, fossil fuels, e.g., coal, oil and gas, have been important carbon carriers in the long-term carbon cycle, but their upgrading is restricted to conventional thermocatalysis. Solar energy with the advantages of large abundance, widespread distribution, and high flux appeals extensive attention, but unfortunately is underutilized at the moment. Photocatalysis initiated with semiconductors is a promising pathway towards the conversion and storage of solar energy into chemical stocks, and has been studied for several decades. However, due to the low photoresponse capacity and solar energy conversion efficiency of the existing photocatalysts, the prospect of their industrialization is still unclear. Photothermal catalysis integrating photocatalysis and thermocatalysis into one unit has been proposed in the past several years. Although its quantum efficiency and reaction turnover frequency were significantly improved, the reaction mechanisms have not yet been well illustrated. This PhD study is to develop photo assisted catalysis to obtain high performances for energy preparation and fossil fuels upgrading, and to have a deep insight into their reaction mechanisms. First, in-plane heterostructured graphene/carbon nitride photocatalyst was prepared via a hydrogeninitiated chemical epitaxial growth strategy. With the insert of nano-graphene into the porous carbon nitride, the quantum efficiency of the water splitting reaction for hydrogen generation was significantly enhanced (Chapter 3). Considering the unsatisfied incident light to electron efficiency, the study unveiled the potential difference as the internal electrical field affecting the separation, transfer and output of photoinduced charge carriers. Meanwhile, the quantum efficiency and utilization of solar light were both improved via the optimization of potential differences in photocatalytic systems (Chapter 4). In addition, the active sites (Chapter 5) and relationships between photocatalysis and thermocatalysis (Chapter 6) in photothermal catalytic systems were both in-depth studied. With the available reaction mechanism and optimization of reaction conditions, the photothermal catalytic performances in the upgrading of fossil fuels are increased to a industrialization level. This PhD project contributes to the improvements of quantum efficiency via catalyst modification, reaction optimization and mechanism investigation and then expects to provide both technological and scientific knowledge for the full storage and conversion of solar energy into fuels.

In this doctoral thesis, we have studied the oxidation of carboxylic acids to obtain the corresponding acyloxy radicals, using visible light and non-toxic and inexpensive organic dyes, as photocatalysts. On the one hand, we study the photooxidation of aromatic carboxylic acids to obtain acyloxy radicals, whose decarboxylation is relatively slow (Chapter I and Chapter II). On the other hand, we describe the photooxidation of aliphatic carboxylic acids, to take advantage of the rapid decarboxylation of the corresponding acyloxy radicals, to generate nucleophilic radicals that were trapped by different reagents (Chapter III to Chapter V). It should be noted that all the protocols are free of expensive and toxic noble metals, the reactions were promoted with visible light at room temperature and the scalability of some reactions was demonstrated in batch conditions or using flow chemistry. In addition, mechanistic studies were carried out to propose plausible photocatalytic routes to all the reactions studied.

Energy saving policies applied to modem buildings and air recirculation systems promote the build up of high levels of VOCs in indoor air. The growing concern related to the air quality in indoor environments requires the replacement of ineffective traditional purification methods, with an efficient and cost effective technology. Photocatalytic oxidation that utilise TiO2, represents a promising candidate for this purpose. However, the formulation of photocatalysts that can efficiently utilise a sustainable energy source (i.e. solar light), still represents an ambitious target in this field. In this study, different TiO2-based photocatalysts were synthesised by modified sol-gel and/or hydrothermal routes. The materials were characterised by XRD, SEM, N2 sorption (BET and BJH methods), UV-vis Spectroscopy and XPS. The photocatalytic activity of TiO2-based materials was systematically investigated at different light intensities, in a gas-phase flatplate photoreactor, using trichloroethylene (TCE) as model pollutant, and compared with that of the commercial product TiO2 Degussa P-25. This research provides insights into the influence of preparation parameters on different synthetical pathways for the preparation of highly active TiO2- based photocatalysts. The general approach to this investigation is based on the study of the influence of several processing parameters on morphological, textural and crystallographic properties of the photocatalysts, in order to correlate the material's features with their photocatalytic properties. The preparation of a wide range of pristine TiO2 allowed assessing a clear correlation between phase composition and crystal size and the photocatalytic performance. A series of highly active anatase photocatalysts was prepared. The best photocatalyst has an optimum crystal size of 28 nm and exhibits a photocatalytic activity that exceeds that of P-25 by a factor of over 2 times. A new TiO2/WO3 nanocomposites with peculiar crystallographic properties of the W component was developed by a novel one-step hydrothermal synthesis. The synthesis conditions were optimised with respect to the photocatalytic activity. Overall, the optimisation of the properties that enable an efficient interfacial charge transfer rate at the catalyst surface was found to be of fundamental importance for the design of improved TiO2-based photocatalysts.

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.

Photocatalytic water splitting has attracted significant interest in recent decades as it offers a clean and environmentally friendly route for the production of hydrogen. A key challenge remains the development of systems that employ abundant, non-toxic and inexpensive materials to dissociate water efficiently using sunlight. Titanium dioxide (TiO2), tungsten trioxide (WO3) and hematite (α-Fe2O3) are among the most studied photoanodes employed during water splitting because of the position of their valence band which is suitable for oxidising water to oxygen, and their low costs. However reported efficiencies for these materials are below the reported theoretical maximum values. A good understanding of the factors that are limiting the efficiency of these photoanodes is therefore desirable if improvements in the photocatalytic activity are to be achieved. This thesis is divided in four main sections. Chapters 3 and 4 describe transient absorption spectroscopy (TAS) studies in the microsecond-second timescales carried out on WO3 photoelectrodes and TiO2 nanowires respectively. TAS has been employed to follow the charge carriers dynamics in WO3 highlighting the presence of relatively long-lived holes (30 ms), which have been described as a requirement for the water oxidation reaction to take place. The electrons also appear to be long-lived (0.1 s), and this has been proposed to be due to slow electron transport through the film. TAS measurements have also been carried out on oxygen-deficient hydrogen-treated TiO2 nanowires, highlighting a more efficient suppression of the electron/hole recombination process in comparison with conventional anatase TiO2 photoanodes. Chapter 5 describes TAS and sum frequency generation (SFG) studies on TiO2 films which are designed to investigate the surface mechanisms of water oxidation. The dependence of the hole lifetime on the pH of the electrolytes employed has been examined by TAS and substantially faster decay rates have been found in highly alkaline solutions suggesting a change in the mechanism of water oxidation. Consequently, SFG has been employed in order to detect any possible intermediate at the interface TiO2/water. Initial measurements have provided the evidence of physisorbed and chemisorbed methanol (model probe) on the TiO2 surface and further studies at the TiO2/water interface have been carried out. Chapter 6 describes the development of a hybrid solar fuel reactor coupling a α-Fe2O3 based photoelecrochemical cell with luminescent solar concentrator plates. Initial tests have been carried out on a proof of principle prototype providing encouraging results.

This study focuses on the design of low-dimensional (LD) photocatalysts for water oxidation in oxygen evolution reaction (OER). Through skillful approaches, such as morphological control, interface construction, defect or vacancy engineering, we developed a series of LD hybrids and examined their photo- and photoelectrochemical performances in OER. Attribute to the stable LD structure and synergistic effect of the components, the heterojunction or hierarchical materials showed enhanced charge separation, transportation, water oxidation kinetics and quantum efficiency.

This thesis is a comprehensive study of plasmonic gold photocatalysts for organic conversions. It presents the advantages of plasmonic gold photocatalysts in the selective oxidation, reduction, and acetalisation. It is discovered that plasmonic gold photocatalysts exhibit better catalytic performance (higher selectivity or activity) in these organic conversions. The study in this thesis highlights the capacity of plasmonic gold photocatalysts in harvesting solar energy for converting organic raw materials to value-added chemicals, and the great potential of gold photocatalysts in chemical production.

Effective visible light photocatalysts for achieving organic reactions under mild conditions are long sought after and a rarely achieved aim in modern catalyst chemistry. Here, metal complexes and plasmonic metal NPs were assembled and used systematically for the first time as a novel photocatalyst to achieve this target. The new photocatalytic system was designed, established, and proved to be efficient in driving C-O bond cleavage of lignin model compounds and sugars dehydration to produce 5-HMF under visible light irradiation.

My doctoral activity deals with oxidative photocatalysis. This is based on the use of photosensitive materials, it employes molecular oxygen as oxidant and it operates under mild temperature and pressure conditions. In particular, I worked on the preparation and characterization of photocatalytic heterogeneous systems containing the decatungstate anion W10O324- or the complex Fe(III) meso-tetrakis (2,6-dichlorophenyl) porphyrin. The photocatalytic properties of these photocatalysts were evaluated in the selective oxidation of aliphatic alcohols. The chosen polyoxoanion and porphyrin have many similarities because both of them absorb in the near UV (λ > 300 nm) and their primary photochemical processes involve the reduction of the metal centre (tungsten or iron), the simultaneous oxidation of the alcohol and the closure of photocatalytic cycle by molecular oxygen. The (nBu4N)4W10O32 was incorporated into silica matrix by sol-gel procedure and two heterogeneous systems were obtained with loadings of 10% and 30%. Their photocatalytic properties were compared in the oxidation of primary and secondary aliphatic alcohols (1-pentanol, 2-pentanol, 3-pentanol, 1-heptanol, 4-heptanol, 2,6-dimethyl-4-heptanol). Photoexcitation (λ > 300 nm) led to the selective conversion of alcohols to the corresponding carbonylic products, with a mass balance higher than 90%. The system with 10% of loading, which is characterized by a pronounced micro- and mesoporous structure, favored the selective adsorption of primary aliphatic alcohols with respect to the homologous secondary compounds, so allowing the reaction between the photoexcited decatungstate and the less hindered OH group. The system with loading of 30% was less selective; that is attributed to its lower porosity and to the fact that part of the immobilized decatungstate was not caged inside silica but weakly adsorbed on its surface and, therefore, easily accessible to all substrates. Photoexcitation of Na4W10O32 dissolved in water led to the formation of OH• radicals which, in turn, were able to oxidize glycerol. This substrate was chosen as a model of polyfunctional alcohol and because its selective transformation is a process of great industrial interest. While the photocatalytic process in solution was scarcely selective, incorporation of Na4W10O32 in a silica matrix provided a heterogeneous system with good selectivity and stability: 90% of the products were carbonylic compounds and CO2 was formed only in negligible amounts. The surface played a fundamental role, favoring adsorption of glycerol, increasing its local concentration near the decatungstate and, thus, facilitating its reaction with the photogenerated OH• radicals. Iron (III) meso-tetrakis (2,6- dichlorophenyl)porphyrin, properly silanized, was linked covalently on the surface of a mesoporous MCM-41 material. The possible effects of the morphology of the solid support on the selectivity of the photooxidation of 1,4-pentandiol were considered. The mesoporous photocatalyst, due to its large surface area, is able to disperse the iron porhyrin. The diol coordinates to iron, but contrary to what occurs in solution, can not act as a bridge between two complexes. This prevents the formation of inactive oligomers. The photocatalytic system presented a good selectivity in the oxidation of the diol in the primary position, with accumulation of 4-hydroxypentanal. It is noteworthy that there is no evidence of formation of products of further oxidation.

Photocatalysis is an advanced oxidation process for the purification and remediation of contaminated waters and wastewaters, and is advantageous over conventional treatment technologies due to its ability to degrade emerging and recalcitrant pollutants. In addition, photocatalytic disinfection is less chemical-intensive than other methods such as chlorination, and can inactivate even highly resistant microorganisms with good efficacy. Process sustainability and cost-effectiveness may be improved by utilizing solar irradiation as the source of necessary photons for photocatalyst excitation. However, solar-induced activity of the traditionally-used titania is poor due to its inefficient visible light absorption, and recombination of photo-excited species is problematic. Additionally, mass transfer limitations and difficulties separating the catalyst from the post-treatment slurry hinder conversions and efficiencies obtainable in practice. In this research, various strategies were explored to address these issues using novel visible light active photocatalysts. Two classes of carbon-enhanced photocatalytic materials were studied: activated carbon adsorbent photocatalyst composites, and carbon-doped TiO2. Adsorbent photocatalyst composites based on activated carbon and plasmonic silver/silver chloride structures were synthesized, characterized, and experimentally investigated for their photocatalytic activity towards the degradation of model organic pollutants (methyl orange dye, phenol) and the inactivation of a model microorganism (Escherichia coli K-12) under visible light. The adsorptive behaviour of the composites towards methyl orange dye was also studied and described according to appropriate models. Photocatalytic bacterial inactivation induced by the prepared composites was investigated, and the inactivation mechanisms and roles of incorporated antimicrobial silver on disinfection were probed and discussed. These composites were extended towards magnetic removal strategies for post-use separation through the incorporation of magnetic nanoparticles to prepare Ag/AgCl-magnetic activated carbon composites, and the effect of nanoparticles addition on the properties and photoactivities of the resulting materials was explored. Another silver/silver halide adsorbent photocatalyst composite based on activated carbon and Ag/AgBr exhibiting visible light absorption due to both localized surface plasmon resonance and optical band gap absorption was synthesized and its photocatalytic activity towards organics degradation and microbial inactivation was studied. Carbon-doped mixed-phase titania was also prepared and experimentally investigated.

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.

博士
中華大學
科技管理學系(所)
96
The objective of this research is to obtain an optimal combination on improving the adsorption/photocatalysis capability of composite photocatalysts by means of design of experiments (DOE) and analysis of variance (ANOVA). Five control factors, including photocatalyst type, catalyst loading, support type, heat-treated temperature, and stirring speed, with four levels were considered to investigate the optimal parameter setting. The present work applied an L16 orthogonal array combined with ANOVA analysis to individually find out their improved parameters: adsorption and photocatalysis efficiencies. Two sets of parameter settings appeared a similar optimal combination, in which the type of support acts as the most crucial contribution to affect both of adsorption and photocatalysis capabilities. This can be attributed to the fact that vast pore structure of supports probably leads to uniform dispersion of catalysts, thus promoting the photocatalysis capability. The ANOVA result also confirmed that both the reliability of experiments and rationality of variances fall within a confidence level of 99%, indicating the robust design for these composite photocatalysts. The parameter settings via ANOVA and DOE methodologies provide an efficient approach not only in enhancing the adsorption/photocatalysis hybrid performance but also tuning the optimal controlling factors for preparation of the composite photocatalysts, based on economic and robust-design viewpoints.

碩士
國立高雄第一科技大學
環境與安全衛生工程系碩士班
105
This study investigated liquid-phase photocatalysis of sulfadiazine(SDZ) by both titanium dioxide (TiO2) and graphene doped TiO2 (GR/TiO2) thin-film. The thin-film photocatalysts were prepared with an electrophoretic deposition (EPD) technique by immobilizing P-25 TiO2, with various amount of GR, onto pure titanium (Ti) metal plates. This study explored the effects of preparation recipes on the photocatalytic activities of prepared samples, which were determined by the degradation rate of SDZ assisted by the prepared samples irradiated with a near-UV light. Several preparation parameters including applied DC biases (15~35 V), and terminal calcination temperatures (250~450℃) for the samples were evaluated. The study also used SEM and XRD to identify surface morphology, and crystal phase of prepared samples. Selected photocatalysts with better activities were further used for conducting SDZ photocatalytic degradation tests in variation pH levels and light sources. The results showed the photocatalysis of SDZ following pseudo first-order reaction kinetics. A better photocatalytic activities of prepared samples were achieved when the they were prepared with calcined in a 450℃ oven. Among them, TG0.5 photocatalyst has the highest activity (k = 0.348 hr-1), which is 13.7 % higher than that of TiO2 photocatalyst. In addition, the effect of EPD of DC biases on the degradation rate of SDZ, the photocatalytic activity of TiO2 increases with the increase of EPD of DC biases, with the highest activity at 35 V. The TG series of photocatalyst, it will be in a EPD of DC biases, with the fastest response rate, which are: TG0.5 (25 V), TG1.0 (20 V), TG1.5 (20 V). Based on the above results, it can be found that the calcination temperature is 450 ℃ with the highest activity, and different series of photocatalyst also has the best EPD of DC biases, can be assembled with a high activity of the photocatalyst, in order: 450TiO2-35V, 450TG0.5-25V, 450TG1.0-20V, 450TG1.5-20V. Finally, the effects of different light sources and pH values on degradation rate of SDZ were investigated. According to the experimental results, it was found that the degradation rate was the fastest and the proportion of pollutants adsorbed by the catalyst at pH= 3. In addition, the TiO2 photocatalyst itself is very poor for the visible light absorption capacity. The experimental results show that the photocatalyst doping of graphene can not only increase the activity of the original TiO2 photocatalyst, but also increase the absorption of the visible light source. Finally, the photocatalyst prepared in this study has the highest activity in UV light and LED light with photocatalyst doped with 0.5% graphene.

碩士
國立東華大學
材料科學與工程學系
94
Abstract Tantalum alkoxides (ex: NaTaO3, KTaO3) were prepared and decomposed of pure water into H2 and O2 without co-catalysts by illuminated UV light . In this study, we reported and prepared the similar niobium alkoxides (NaNbO3, KNbO3) as a new series of active photocatalytic materials. The tantalate and niobate pyrochlores were prepared by a solid state reaction with sodium or potassium hydroxide. The relative high sintering temperature (1100 oC) will caused sodium or potassium volatilization and generated the powder reaction incompletely. It will be strongly influence the crystallinity of photocatalysts oxides. Appropriate improvement the content ratio (1.05mole) of the sodium or potassium in the mixed compounds will be decreased the volatilization and enhanced the photocatalysis efficiency. The absorption wavelength range of tantalite and niobate pyrochlores by doped nitrogen will red shift to near visible light, but can not remarkable improvement the photocatalysis activity. When the oxides doped nitrogen by use ammonia gas under various reaction temperatures KTaO3 at 850 oC, NaNbO3 at 500 oC and KNbO3 at 550oC, respectively. The photocatalysis activity will be enhanced under ultraviolet light irradiation. In the recycle test, the photocatalysis activity of alkaline earth tantalates and niobates will be decrease with the cycle times.

Photocatalytic water splitting using solar irradiation has the potential to produce sustainable hydrogen fuel on a large scale. Practical solar energy conversion requires the development of new, stable photocatalysts that operate efficiently under a broad range of visible wavelengths. Organic semiconductors are increasingly being employed as photocatalysts due to their earth abundance, aqueous stability, and optical absorptions that can be tuned to the solar spectrum. However, much remains unknown about the mechanism of organic semiconductor photocatalysis, and significant efficiency improvements need to be made before organic photocatalysts can achieve practical solar energy conversion. In chapter 2 the effect of residual Pd on hydrogen evolution activity in conjugated polymer photocatalysts was systematically investigated using colloidal poly(9,9- dioctylfluorene-alt-benzothiadiazole) (F8BT) nanoparticles (NPs). Residual Pd, originating from the synthesis of F8BT via Pd catalysed polycondensation polymerisation, was observed in the form of homogenously distributed Pd NPs within the polymer. Residual Pd was essential for any hydrogen evolution to be observed from this polymer, and very low Pd concentrations (<40 ppm) were sufficient to have a significant effect on the hydrogen evolution reaction (HER) rate. The HER rate increased linearly with increasing Pd concentration from <1 ppm to approximately 100 ppm, at which point the rate began to saturate. Transient absorption spectroscopy experiments support these conclusions and suggest that residual Pd mediates electron transfer from the F8BT NPs to protons in the aqueous phase. Photocatalysts formed from a single organic semiconductor typically suffer from inefficient intrinsic charge generation, which leads to low photocatalytic activities. In chapter 3 we demonstrate that incorporating a heterojunction between a donor polymer and non-fullerene acceptor in organic NPs can result in hydrogen evolution photocatalysts with greatly enhanced photocatalytic activity. Control of the nanomorphology of these NPs was achieved by varying the stabilizing surfactant employed during NP fabrication, converting it from a core-shell structure to an intermixed donor/acceptor blend, and increasing H2 evolution by an order of magnitude. The resulting photocatalysts display an unprecedentedly high H2 evolution rate of over 60,000 µmolh-1g -1 under 350 to 800 nm illumination and external quantum efficiencies over 6% in the region of maximum solar photon flux.

碩士
淡江大學
化學工程與材料工程學系
92
TiO2 photocatalysts were prepared using a sol-gel method. Alcoholic solution of tetraethylorthotitanite was dropped into de-ionized water, followed by refluxing the liquid at 90 oC for 3 hr. The pH of liquid was adjusted using HNO3 and NH4OH. The obtained particles were dried at 90 oC and calcined at different temperatures. The resultant calcined particles were characterized using XRD, DSC, TG, IR, BET, SEM, and TEM. Photoactivity of the obtained particles was investigated by degrading methylene blue under illumination of 365nm UV and fluorescent light. The results indicated that HNO3 may react with tetraethylorthotitanite and result in the formation of structure defects in TiO2 after calcination. These structure defects retarded phase transformation of anatase to rutile. Effects of pH on crystallinity, phase transformation and sintering temperature were investigated. At pH = 7, anatase nanoparticles can be retained at temperatures as high as 900 oC without transforming to rutile phase. The specimen obtained at pH = 8 and at 800 oC showed the highest photoactivity on degrading methylene blue under either 365nm UV or fluorescent light illumination.

Photocatalytic processes over semiconducting oxide surfaces have attracted worldwide attention as potentially efficient, environmentally friendly and low cost methods for water/air purification as well as for renewable hydrogen production. However, some limitations to achieve high photocatalytic efficiencies have been found due to the fast recombination of the charge carriers. Development of heterostucture photocatalysts by depositing metals on the surface of semiconductors or by coupling two semiconductors with suitable band edge position can reduce recombination phenomena by vectorial transfer of charge carriers. To draw new prospects in this domain, three different kinds of heterostructures such as n-type/n-type semiconductor (SnO2/ZnO), metal/n-type semiconductor (RuO2/TiO2 and RuO2/ZnO) and p-type/n-type semiconductor (NiO/TiO2) heterojunction nanomaterials were successfully prepared by solution process. Their composition, texture, structure and morphology were thoroughly characterized by FTIR, X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and N2 sorption measurements. On the other hand, a suitable combination of UV–visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) data provided the energy band diagram for each system. The as-prepared heterojunction photocatalysts showed higher photocatalytic efficiency than P25 TiO2 for the degradation of organic dyes (i.e. methylene blue and methyl orange) and the production of hydrogen. Particularly, heterostructure RuO2/TiO2 and NiO/TiO2 nanocomposites with optimum loading of RuO2 (5 wt %) and NiO (1 wt %), respectively, yielded the highest photocatalytic activities for the production of hydrogen. These enhanced performances were rationalized in terms of suitable band alignment as evidenced by XPS/UPS measurements along with their good textural and structural properties. This concept of semiconducting heterojunction nanocatalysts with high photocatlytic activity should find industrial application in the future to remove undesirable organics from the environment and to produce renewable hydrogen.

博士
國立成功大學
化學工程學系碩博士班
99
Photocatalysts with semiconducting properties are attractive due to its potential on solar energy conversion. The physicochemical and optical properties of NaTaO3 and III-V group GaON were investigated in an attempt to improve the photocatalytic activities. Perovskite-like NaTaO3 powders have potential applications in photoluminescence and photocatalysis. In the first section, sol–gel, hydro-thermal and solid-state methods were used to synthesize NaTaO3 powders of different crystalline structures, which were identified by Rietveld refinement simulation of X-ray diffraction patterns and transmission electron microscopic diffraction. The refinement results show that the sol–gel specimen has a monoclinic phase with a Ta–O–Ta bond angle of 179° while the hydro-thermal and solid-state specimens have an orthorhombic phase with bond angles of 163° and 157°, respectively. By excitation with a 304 nm light source, these NaTaO3 specimens show photoluminescence emission at ca. 450 nm. The photoluminescence intensity of the specimens had an order solid-state ＞ hydro-thermal ＞ sol–gel, which is opposite to that of the Ta–O–Ta bond angle. On the other hand, the photocatalytic activity of the NaTaO3 specimens in water splitting showed the same order as that of the Ta–O–Ta bond angle. This paper directly evidenced that the Ta–O–Ta bond angle affects the separation rate of the photo-induced charges, as well as that structure tuning of tantalates is achievable and crucial for applications in photoluminescence and photocatalysis. In the second part of this study, the photocatalytic activity of NaTaO3 was improved by replacing some Na ions in the 12-coordinate sites with larger K ions. Na1-xKxTaO3 photocatalysts of x = 0?0.2 were synthesized with the sol–gel method. K-doping at x = 0.05 resulted in rectifying the distorted perovskite NaTaO3 to a pseudo-cubic phase as well as significantly promoting photocatalytic activity. The 180° bond angle of Ta?O?Ta in the pseudo-cubic phase may facilitate the separation of photogenerated charges for effective water splitting. Photoluminescence spectroscopic analysis confirmed that the flattened Ta?O?Ta linkage with K-doping suppresses the recombination of photogenerated charges. Further K-doping (with x ＞ 0.05) leads to impurity formation, which bends the Ta?O?Ta linkage and creates defect states, lowering the photocatalytic activity of the K-doped NaTaO3. This study demonstrates that an appropriate ion replacement to tune the crystal structure can significantly promote electron transport in photocatalysts and thus their activity. In the third part, sol–gel and solid-state synthesized NaTaO3 were loaded with NiO co-catalyst to enhance water splitting activity under UV illumination. Activity increased significantly with NiO loading and reached a maximum at 3 and 0.7 wt. %, respectively, for the sol–gel and solid-state synthesized NaTaO3. Beyond this point, photocatalytic activity decreased with further loading. Analysis using X-ray diffraction, high-resolution transmission electron microscopy, and diffuse reflectance spectroscopy shows that the interdiffusion of Na+ and Ni2+ cations created a solid-solution transition zone on the outer sphere of NaTaO3. For NiO contents less than 3 wt. %, no NiO clusters appeared on the NaTaO3 surface, and the reduction/oxidation pretreatment did not enhance photocatalytic activity. The high activity resulting from a low NiO loading suggests that the interdiffusion of cations heavily doped the p-type NiO and n-type NaTaO3, reducing the depletion widths and facilitating charge transfers through the interface barrier. In the synthesis of wurtzite-like gallium oxynitride (GaON) photocatalysts, the nitridation of Ga(OH)3 with NH3 at temperatures between 550 and 900 ?C were employed. Ga(OH)3 is a more suitable precursor for GaON synthesis than Ga2O3, because its crystal lattice contains unoccupied 12–coordinate sites that facilitate ionic transportation during nitridation. The prepared GaON catalysts had band gap energies from 2.2 to 2.8 eV, and showed significant activities in the visible-light promoted evolution of H2 and O2 gases from methanol and AgNO3 solutions respectively. The maximum H2 and O2 evolution rates occurred for catalysts synthesized at 625 and 700 ?C, respectively. These active catalysts had an N/O atomic ratio close to unity, suggesting that extensive hybridization of N2p and O2p orbitals promotes charge mobility, and thus enhances photocatalytic activity. This study highlights the interesting possibility of synthesizing a large diversity of visible-light active, III?oxynitride catalysts using this Ga(OH)3 route. Indium was introduced to activate gallium oxynitride in this section. Visible-light active Indium-doped GaON with a wurtzite-like structure were synthesized from nitridation of In(OH)3-containing Ga(OH)3 under NH3 flow at 625 ?C and used for photocatalytic water splitting. This synthesis method yielded a homogeneous In distribution in gallium oxynitride solid solutions for Ga replacement levels of up to 1 %. An appropriate amount of In substitution for Ga, approximately 0.5 %, significantly enhanced the activity of gallium oxynitride in the visible-light induced evolutions of H2 and O2 gases from methanol and AgNO3 solutions, respectively. X-ray photoelectron spectroscopy showed that In-doping increased the dispersion of hybridized orbitals in the valence band of gallium oxynitride. A higher degree of In-doping resulted in nucleation of InN-like oxynitride on the gallium oxynitride surface and degraded the photocatalytic activity. This study demonstrates that band structure engineering of gallium oxynitride powders with In-doping is a facile way to obtain visible-light sensitive photocatalysts.