Rozprawy doktorskie na temat „Graphitic Carbon Nitrides”

Solid state carbon nitride materials are useful in a number of areas in industry, ranging from heat retardation, photocatalysis, electrochemistry, as well as the potential to form a new super hard material to rival diamond. The flexible nature of the chemical bonding and environment of C and N atoms in a carbon nitride system gives rise to wide structural diversity, which present challenges in characterisation of the material. Theoretical modeling for such a versatile system is an essential part of scientific research. Quantum mechanical computational methods are employed to study carbon nitride materials in dense sp3 bonded and planar polymeric graphitic phases. The computer codes used for this study are CRYSTAL and CASTEP, both based on DFT. Synthesis of dense and graphitic carbon nitride materials, using ionothermal and thermal methods were also conducted towards part of this research. The results from each theoretically calculated investigation in this thesis are compared with experimental data, to guide the understanding of the experimental results for the system under study. Experimentally synthesised and recovered carbon nitride material, with defective wurtzite structure and C2N3H stoichiometry, was investigated for its stability over a range of pressures. Three possible C2N3H phases arising from different proton arrangements were modeled to determine the most stable arrangement. A metastable C2N3H phase was detected experimentally; an ab initio structure prediction method was employed, which identified a structure that complied with experimental observations. CASTEP was tested and used to calculate NMR chemical shifts for 13C and 15N atoms for a number of carbon nitride materials. Predictions were focused on determining the atom connectivity and structural topology for thermal synthetic methods that yielded dense and graphitic carbon nitride solid‐state materials. Calculated NMR chemical shifts were also employed in a collaborative study to guide the understanding of planetary tholins, formed in Titan’s atmosphere.

It was first performed a special method of pyrolysis of melamine in order to study the possibility of coproduction of carbon nitride and its oxidized derivatives. New compound as a graphite-like carbon nitride oxide (g-C3N4)O, which is isostructural analogue of graphite oxide, and doped with oxygen ( ~ 8.1 % ), carbon nitride (O-g-C3N4) were obtained. In contrast to known methods for the preparation of samples doped with oxygen carbon nitride a new route does not provide a preliminary synthesis of g-C3N4.The synthesized carbon nitride oxide is easily stratified and dissolved in water to form a flocculent solution which may contain not only ultra-thin nanosheets from several heptazine oxidized layers, but also the individual twodimensional monolayers. These monolayers can be a precursor for making reduced heptazine monolayer (or azagraphene). The synthesized substunces were investigated by methods chemical and X-ray analyses, IR spectroscopy, temperature-programmed desorption mass spectrometry (TPDMS) obtained products.

As a potential solution to the global energy and environmental pollution, design and synthesis of artificial photocatalysts with high activities have attracted increasing scientific interests worldwide. In recent years, the graphitic carbon nitride (g-C3N4) has shown new possible applications in the photocatalytic field due to its unique properties. However, the photocatalytic efficiency of the pristine g-C3N4 is greatly limited by the high recombination rate of the photo-induced electron-hole pairs. In this thesis, the aim is to design and fabricate efficient g-C3N4 based photocatalysts with enhanced photocatalytic activities under a visible light irradiation. In order to achieve this goal, two strategies have been employed in the present thesis. First, the as-obtained g-C3N4 was used as the host material to construct staggered-aligned composite photocatalysts by selecting semiconductors with suitable band positions. By this method, three kinds of g-C3N4-based composite photocatalysts such as g-C3N4/ZnS nanocage, g-C3N4/m-Ag2Mo2O7 and g-C3N4/MIL-88A were successfully fabricated. Second, the microstructure of the g-C3N4 was modified by the H2O2-treatment at an elevated temperature and ambient pressure. In this study, the g-C3N4 was prepared by a simple pyrolysis of urea. As for all the as-synthesized phtocatalysts, the structures, morphologies and the optical properties were carefully characterized by the following techniques: XRD, SEM, TEM, FT-IR and DRS. Also, the band edge positions of m-Ag2Mo2O7 and MIL-88A were studied by the Mott-Schottky methods. Thereafter, the photocatalytic activities were evaluated by using a solution of rhodamine B (RhB) as a target pollutant for the photodegradation experiments performed under a visible light irradiation. The results showed that all the aforementioned g-C3N4-based photocatalysts exhibited enhanced photocatalytic activities in comparison with the pristine g-C3N4. For the case of the g-C3N4-based composite photocatalysts, the enhancement factor over the pristine g-C3N4 can achieve values ranging from 2.6 to 3.4. As for the H2O2-treated g-C3N4, the degradation rate constant can be 4.6 times higher than that of the pristine g-C3N4. To understand the key factors in new materials design, we also devote a lot of efforts to elucidate the basic mechanisms during the photocatalytic degradation of organic pollutant. Based on the results of the active species trapping (AST) experiments, the main active species in each photocatalytic system were determined. In the g-C3N4/m-Ag2Mo2O7 and the g-C3N4/MIL-88A system, three kinds of active species of ·O2-, h+ and ·OH were found to be involved in the photocatalytic reaction. Among them, the ·O2- and h+ were the main active species. In the g-C3N4/ZnS and H2O2-treated g-C3N4 photocatalytic systems, the main active species was determined as the ·O2-. The reaction pathways of these active species were also demonstrated by comparing the band edge positions with the potentials of the redox couple. In addition, the relationship between the active species and the photocatalytic behaviors of N-de-ethylation and conjugated structure cleavage were studied. Finally, possible mechanisms to explain the enhanced photocatalytic activities were proposed for each photocatalytic system. The results in this thesis clearly confirm that the photocatalytic activity of the g-C3N4 based photocatalyst can efficiently be enhanced by constructions of staggered-aligned composites and by modification of the microstructure of the g-C3N4. The enhanced photocatalytic performance can mainly be ascribed to the efficient separation of the photo-induced electron-hole pairs and the increase of the active sites for the photocatalytic reaction.

QC 20150909

Photocatalytic solar fuel generation is the most green, sustainable and viable approach to deal with both the ever-growing energy crisis and environmental issues, simultaneously. The work presented in this thesis is focused on the development of new organic carbonaceous semiconductors, typically, carbon quantum dots (CQDs) and graphitic carbon nitride (g-C3N4), and porphyrin small molecules and their hybrids with graphitic carbon nitride, meanwhile, their application in the field of photocatalytic solar fuel generation. In the chapter 1, a general review about background and mechanism of photocatalytic solar fuel generation are introduced first. Next, the features and developments of porphyrin and graphitic carbon nitride for the photocatalytic redox reaction are discussed. In chapter 2, the synthesis, characterization methods and photocatalytic experiment in details are described. In chapter 3, gram-scale CQDs are facilely synthesized by simple thermal treatment of citric acid monohydrate, and microporous 1D nanorods of g-C3N4 are prepared through template-free chemical approach. The photocatalytic properties of 1D protonated g-C3N4 (HCN) modified with different amount of CQDs were evaluated by the rate of H2- evolution under visible light irritation. The results demonstrate that g-C3N4/CQDs with the optimal CQDs amount of 0.25 wt.% afford the highest H2-production rate of 382 μmol h-1 g-1 with apparent quantum yield (AQY) of 1.9% which was about 3-fold of pure g- C3N4. The composite g-C3N4/CQDs show a remarkable stability against the photocorrosion within a continuous experiment period over 12h. The enhanced photocatalytic H2-production activity could be attribute to the intimate interface between CQDs and g-C3N4, which not only significantly improves the visible-light absorption, but also prolongs the lifetime of charge carriers and suppresses the recombination of photogenerated electron-hole pairs. This work showed that low-cost and metal-free CQDs could be an efficient photosensitizer to promote photocatalytic hydrogen generation. In chapter 4, we reported a new array of push-pull isomeric naphthalimide- porphyrins (ZnT(p-NI)PP) to investigate the effect of naphthalimide and molecular constitution on light driven hydrogen evolution from water splitting. These compounds were synthesized by integration of four naphthalimide moieties on meso-substituion of porphyrin macrocycle through para phenyl linker. Porphyrins were characterized by UV- Vis, Fluorescence and DFT calculations and compared with those of zinc tertapheylporphyrin (ZnTPP). When these porphyrins were employed as photocatalyst for the photocatalytic hydrogen production (PHP) with platinum co-catalyst, they delivered high hydrogen efficiency compared to that of ZnTPP. Particularly, ZnT(p-NI)PP exhibited 203 times higher hydrogen efficiency than the ZnTPP. This could be ascribed to the efficient exciton dissociation into holes and electrons at the photoexcited state of ZnT(p-NI)PP and then electrons were transferred to the proton through platinum. These results indicate that introduction of naphthalimide at meso-position of porphyrin through para phenyl linker is a versatile strategy to improve the photocatalytic hydrogen evolution of porphyrin based materials. In addition, the other two isomeric naphthalimide conjugated porphyrins through meta-and ortho-phenyl linker, ZnT(m-NI)PP and ZnT(o-NI)PP are also developed for photocatalytic H2 production. The para-linked isomer, ZnT(p-NI)PP delivered a much higher H2 production rate of 973 μmol h−1g -1 compared to that of ZnT(m-NI)PP (597 μmol h−1g −1) and ZnT(o-NI)PP (54 μmol h−1g −1), respectively. This could be attributed to the efficient intramolecular energy transfer from the naphthalimide to the porphyrin ring. In chapter 5, a series of NP/g-C3N4 hybrids of graphitic carbon nitride (g-C3N4) with naphthalimide-porphyrin (ZnT(p-NI)PP, labelled as NP) have been developed for photocatalytic hydrogen production. Planar naphthalimide-porphyrins are adsorbed onto flexible two-dimensional g-C3N4 through π-π stacking, which are characterized by scanning electronic microscopy and X-ray photoelectron spectroscopy. Except for its function as photosensitizer, NP in the hybrids could efficient inhibit the charge recombination by electron transfer for the lower lowest unoccupied molecular orbital of NP than g-C3N4, whereas facilitate energy transfer from g-C3N4 donor to NP acceptor for efficient overlap of emission spectrum of NP and absorption of g-C3N4. As a result, the hybrid containing weigh ratio of 2% NP (2%NP/g-C3N4) exhibits an enhanced photocatalytic hydrogen production rate (HPR) of 2297 μmol g−1 h −1, while pristine g- C3N4 shows a HPR of 698 μmol g−1 h −1. The 2%NP/g-C3N4 shows the best performance when compared with the reported hybrids of g-C3N4 with Zn(II) -tetrakis(4- carboxylphenyl) porphyrin (ZnTCPP/g-C3N4) and Zn(II)-tetrakis(4- hydroxyphenyl)porphyrin (ZnTHPP/g-C3N4) in photocatalytic hydrogen production under the same conditions. In the chapter 6, the future work on photocatalytic CO2 reduction, perspectives and conclusions are included

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.

Thesis advisor: Dunwei Wang
Water splitting has been recognized as a promising solution to challenges associated with the intermittent nature of solar energy for over four decades. A great deal of research has been done to develop high efficient and cost-effective catalysts for this process. Among which tantalum nitride (Ta₃N₅) has been considered as a promising candidate to serve as a good catalyst for solar water splitting based on its suitable band structure, chemical stability and high theoretical efficiency. However, this semiconductor is suffered from its special self-oxidation problem under photoelectrochemical water splitting conditions. Several key unique properties of graphitic carbon nitride (g-C₃N₄) render it an ideal choice for the protection of Ta₃N₅. In this work, Ta₃N₅/g-C₃N₄ hybrid photoanode was successfully synthesized. After addition of co-catalyst, the solar water splitting performance of this hybrid photoanode was enhanced. And this protection method could also act as a potential general protection strategy for other unstable semiconductors
Thesis (MS) — Boston College, 2018
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

Carbon nitrides are a unique family of nitrogen-rich carbon materials with multiple beneficial properties for effective alkali metal ion transport/storage. Graphitic carbon nitride (g-C3N4) is considered the most viable member of the carbon nitride family because of its high nitrogen content, wide structure with several nitrogen-defect pore sites, ease of synthesis, affordability, and scalability. Also, g-C3N4 delivers a lithium ion battery (LIBs) theoretical capacity of 524 mAh/g unlike graphite which records only 327 mAh/g. However, due to the ineffective intercalation/deintercalation reaction of Li+ with C3N4 it suffers low capacity, poor conductivity and structural deformation when applied as an anode material for battery application. Due to this problem, the application of g-C3N4 for LIBs has slowed down, and the prospects of g-C3N4 for emerging battery systems such as potassium ion batteries (KIBs) have not been explored. In this thesis, we present unique strategies to resolve the problems of irreversible Li+ intercalation, poor conductivity, and structural destruction, and explore g-C3N4-based composites for KIB system. In the first study, one-dimensional carbon nitride nanofibers were designed and proved to be a more effective and better performing anode material for LIBs than bulk g-C3N4. This work was accomplished by combining theoretical computing and experimental techniques, Density functional theory calculation showed that the edges of the 1D-g- C3N4 nanofibers exhibited a suitable Li adsorption energy for stress-free adsorption and desorption of adsorbed Li-atoms. Moreover, our synthesized 1D-g-C3N4 nanofiber possessed edges and pores, as well as higher pyridinic nitrogen content unlike the bulk g-C3N4. The 1D-g-C3N4 nanofiber delivered a superior specific capacity of 181.7 mAh/g, a specific capacity of 138.6 mAh/g after 5000 cycles when cycled at 10C along with excellent stability and power density. This performance remains the highest amongst reported C3N4 anode materials in literature. Carbon nitride/graphene (C3N4/graphene) heterostructure is commonly reported for lithium ion batteries and this heterostructure design occurs in different configurations of 1D/2D or 2D/2D. However, a clear theoretical understanding of how the configuration of such heterostructure affects battery performance is not established. By using a first principle theory approach we studied the 1D/2D and 2D/2D C3N4/graphene heterostructures with a focus on their conductivity, charge transfer, bond structure and rearrangement/breakage and theoretical reversible capacity. In all our study, the DFT results showed that 1D/2D C3N4/graphene delivers superior charge transfer, electronic conductivity, theoretical capacity, and structural integrity compared to 2D/2D configuration. This work expanded upon the relationship between the heterostructure configuration and the electrochemical performance, this work will encourage the design of effective heterostructures for rechargeable batteries. Motivated by the result of the 1D/2D C3N4/graphene heterostructure for LIBs, we employed it for potassium ion battery application. When the fabricated 1D-g-C3N4 nanofiber was employed in potassium ion batteries, the high nitrogen content facilitated K+ adsorption; however, the K-atom diffusion barrier was too high for effective adsorption/desorption. Therefore, we combined the 1D-g-C3N4 nanofiber with 2D reduced graphene oxide (rGO) to design a 1D/2D C3N4/rGO composite for stable and effective potassium storage. In this work, we also combined the use of Density Functional Theory calculations and experimental battery testing along with high powered characterization techniques to study the storage mechanism of the composite electrode material for potassium ion battery. The 1D/2D composite benefitted from the larger surface area and conductivity of 2D reduced graphene oxide and the nitrogen rich active sites of the 1D-g-C3N4 nanofiber. Additionally, DFT calculations showed that the graphene structure from 2D rGO possessed lower K-atom diffusion barrier and superior conductivity which provided shorter ionic transport distances and boosted electronic conductivity in the composite. Thanks to the synergistic interaction between the 1D-g-C3N4 nanofiber and 2D rGO, the electrode delivered a remarkable specific capacity of 464.9 mAh/g after 200 cycles at 1 A/g and 228.6 mAh/g after 1000 cycles at 10 A/g, which is one of the best potassium ion battery anode material performance reported so far. Another approach to exploring the benefits of the 1D-g-C3N4 nanofiber is to use it as a source of N-doped carbon. Metal oxides such as cobalt oxide (Co3O4) have been widely applied as anode materials in rechargeable LIBs but the small d-spacing limits their application for large-sized metal ion batteries such as potassium ion batteries. Moreover, through DFT calculations we proved that the poor performance of Co3O4 for KIBs is due to poor conductivity, high diffusion barrier, and weak potassium interaction. Thanks to the concept of interfacial engineering, we fabricated a hierarchical composite of Co3O4@N-doped carbon in which the N-doped carbon is derived from 1D-g-C3N4. The material design approach for the composite involved coating the surface of Co3O4 with N-doped carbon such K+ can be effectively transported through the that at the interface both materials via multiple ionic pathways. Furthermore, the structural design of the composite enabled increased Co3O4 spacing for effective K+ diffusion, improved conductivity, and protection of the core structure from damage. Based on the entire composite, a capacity of 448.7 mAh/g was delivered after 40 cycles, and 213 mAh/g was retained after 740 cycles when cycled at 500 mA/g. This work combined the principle of material boundary engineering with theoretical computation to design a composite anode material whose performance exceeded that of most metal-oxide-based KIB anodes reported in literature. In summary, the strategies presented in this thesis show that the morphology and electronic properties of g-C3N4 can be manipulated to resolve the problems of irreversible intercalation/deintercalation, poor conductivity, and structural deformation. Moreover, the application of g-C3N4 has been extended to potassium ion batteries and we are the first research group to demonstrate this in literature. Also, the electrochemical performances recorded from experimental battery testing and theoretical computation (DFT simulation) shows that g-C3N4 and g-C3N4-based materials are promising advanced anode materials for LIBs and KIBs. These strategies can be extended to other members of the carbon nitride family such as CN, C2N, C3N etc. for different metal-ion batteries.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text

Afin de résoudre les problèmes environnementaux et énergétiques modernes, ces dernières années ont vu le développement de catalyseurs photocataytiques capables d’utiliser la lumière solaire. En effet, les possibles applications des semiconducteurs présentant des propriétés photocatalytiques dans les domaines de la production d’hydrogène ou la dégradation de polluants organiques ont généré un grand intérêt de la part de la communauté scientifique. Actuellement, les photocatalyseurs à base de dioxyde de titane (TiO₂) et de nitrure de carbone graphitique (g-C₃N₄) sont considérés comme les matériaux les plus étudiés pour leurs faibles coûts et leurs propriétés physico-chimiques exceptionnelles. Cependant, la performance photocatalytique de ces matériaux reste encore limitée, à cause de la recombinaison rapide des porteurs de charge et et d'une absorption limitée de la lumière. En générale, malgré des caractéristiques exceptionnelles, ces matériaux ne contribuent pas significativement à la séparation de charge et l’absorption de la lumière lorsqu’ils sont produits par des méthodes conventionnelles. L'objectif de cette thèse est de développer de nouvelles voies pour la production de matériaux efficaces basés sur TiO₂ et g-C₃N₄). Nous avons d'abord préparé de la triazine (CxNy) qui fonctionne comme un co-catalyseur d'oxydation ce qui facilite la séparation des paires «électron-trou» dans le système du photocatalyseur creux de type Pt-TiO₂-CxNy. La présence simultanée de Pt et de CxNy, qui servent comme co-catalyseurs de réduction et d'oxydation, respectivement, a permis une amélioration remarquable des performances photocatalytiques du TiO₂. De plus, nous avons développé une nouvelle approche, en utilisant un procédé de combustion de sphère de carbone assisté par l’air, pour préparer du C/Pt/TiO₂ . Ce matériau possède de nombreuses propriétés uniques qui contribuent de manière significative à augmenter la séparation « électron-trou », et en conséquence, à améliorer la performance photocatalytique. Dans le but de développer un matériau qui soit capable de fonctionner sous les rayons du soleil et dans l'obscurité, nous avons développé un photocatalyseur creux à double enveloppes : le Pt-WO₃/TiO₂-Au. Ce matériau a montré non seulement une forte absorption de la lumière solaire, mais aussi une séparation des charges élevée et une haute capacité de stockage d'électrons. Par conséquent, ce type de photocatalyseurs a montré une dégradation efficace des polluants organiques, à la fois sous la lumière visible (λ ≥ 420 nm) et dans l'obscurité. En ce qui concerne le g-C₃N₄, nous avons exploité la relation entre les lacunes d’azote et les propriétés plasmoniques des nanoparticules d’or (Au). Ce type de photocatalyseur du Au/g-C₃N₄ a été préparé en présence d’alcali suivi par une post calcination. En effet, les lacunes d’azote ainsi produites permettent le renforcement des interactions entre l’or et le g-C₃N₄ et des propriétés plasmoniques de l’or. Ces caractéristiques exceptionnelles renforcent l'utilisation efficace de l’énergie solaire ainsi que la séparation des paires « électron-trou », ce qui contribuent à la performance photocatalytique pour la production d'hydrogène du photocatalyseur. Afin d’améliorer la capacité d’absorption de la lumière visible de g-C₃N₄, une nouvelle voie de synthèse dénommée « poly-alcaline » a été développée. La possibilité d’ajouter du polyéthylèneimine (PEI) et de l’hydroxyde de potassium (KOH) pour générer de nombreux centres lacunaires en azote ainsi que des groupes hydroxyles dans la structure du matériau, a été explorée afin d’optimiser l’efficacité du matériau. De telles modifications ont démontré leurs capacités à réduire la bande interdite et à provoquer plus facilement la séparation de charges améliorant ainsi les propriétés photocatalytiques du photocatalyseur vis-à-vis de la production d’hydrogène. Cette méthode ouvre donc une nouvelle voie d’avenir pour préparer des photocatalyseurs nanocomposites efficaces possédant à la fois, une forte d’absorption de la lumière et une bonne séparation de charges.
Afin de résoudre les problèmes environnementaux et énergétiques modernes, ces dernières années ont vu le développement de catalyseurs photocataytiques capables d’utiliser la lumière solaire. En effet, les possibles applications des semiconducteurs présentant des propriétés photocatalytiques dans les domaines de la production d’hydrogène ou la dégradation de polluants organiques ont généré un grand intérêt de la part de la communauté scientifique. Actuellement, les photocatalyseurs à base de dioxyde de titane (TiO₂) et de nitrure de carbone graphitique (g-C₃N₄) sont considérés comme les matériaux les plus étudiés pour leurs faibles coûts et leurs propriétés physico-chimiques exceptionnelles. Cependant, la performance photocatalytique de ces matériaux reste encore limitée, à cause de la recombinaison rapide des porteurs de charge et et d'une absorption limitée de la lumière. En générale, malgré des caractéristiques exceptionnelles, ces matériaux ne contribuent pas significativement à la séparation de charge et l’absorption de la lumière lorsqu’ils sont produits par des méthodes conventionnelles. L'objectif de cette thèse est de développer de nouvelles voies pour la production de matériaux efficaces basés sur TiO₂ et g-C₃N₄). Nous avons d'abord préparé de la triazine (CxNy) qui fonctionne comme un co-catalyseur d'oxydation ce qui facilite la séparation des paires «électron-trou» dans le système du photocatalyseur creux de type Pt-TiO₂-CxNy. La présence simultanée de Pt et de CxNy, qui servent comme co-catalyseurs de réduction et d'oxydation, respectivement, a permis une amélioration remarquable des performances photocatalytiques du TiO₂. De plus, nous avons développé une nouvelle approche, en utilisant un procédé de combustion de sphère de carbone assisté par l’air, pour préparer du C/Pt/TiO₂ . Ce matériau possède de nombreuses propriétés uniques qui contribuent de manière significative à augmenter la séparation « électron-trou », et en conséquence, à améliorer la performance photocatalytique. Dans le but de développer un matériau qui soit capable de fonctionner sous les rayons du soleil et dans l'obscurité, nous avons développé un photocatalyseur creux à double enveloppes : le Pt-WO₃/TiO₂-Au. Ce matériau a montré non seulement une forte absorption de la lumière solaire, mais aussi une séparation des charges élevée et une haute capacité de stockage d'électrons. Par conséquent, ce type de photocatalyseurs a montré une dégradation efficace des polluants organiques, à la fois sous la lumière visible (λ ≥ 420 nm) et dans l'obscurité. En ce qui concerne le g-C₃N₄, nous avons exploité la relation entre les lacunes d’azote et les propriétés plasmoniques des nanoparticules d’or (Au). Ce type de photocatalyseur du Au/g-C₃N₄ a été préparé en présence d’alcali suivi par une post calcination. En effet, les lacunes d’azote ainsi produites permettent le renforcement des interactions entre l’or et le g-C₃N₄ et des propriétés plasmoniques de l’or. Ces caractéristiques exceptionnelles renforcent l'utilisation efficace de l’énergie solaire ainsi que la séparation des paires « électron-trou », ce qui contribuent à la performance photocatalytique pour la production d'hydrogène du photocatalyseur. Afin d’améliorer la capacité d’absorption de la lumière visible de g-C₃N₄, une nouvelle voie de synthèse dénommée « poly-alcaline » a été développée. La possibilité d’ajouter du polyéthylèneimine (PEI) et de l’hydroxyde de potassium (KOH) pour générer de nombreux centres lacunaires en azote ainsi que des groupes hydroxyles dans la structure du matériau, a été explorée afin d’optimiser l’efficacité du matériau. De telles modifications ont démontré leurs capacités à réduire la bande interdite et à provoquer plus facilement la séparation de charges améliorant ainsi les propriétés photocatalytiques du photocatalyseur vis-à-vis de la production d’hydrogène. Cette méthode ouvre donc une nouvelle voie d’avenir pour préparer des photocatalyseurs nanocomposites efficaces possédant à la fois, une forte d’absorption de la lumière et une bonne séparation de charges.
The utilization of solar light-driven photocatalysts has emerged as a potential approach to deal with the serious current energy and environmental issues. Over the past decades, semiconductor-based photocatalysis has attracted an increasing attention for diverse applications including hydrogen production and the decomposition of organic pollutants. Currently, titanium dioxide (TiO₂) and graphitic carbon nitride (g-C₃N₄)-based photocatalysts have been considered as the most investigated materials because of their low cost, outstanding physical and chemical properties. However, their photocatalytic performances are still moderate owing to the fast charge carrier recombination and limited light absorption. The main target of the research presented in this thesis is to develop novel routes to prepare efficient materials based on TiO₂ and g-C₃N₄. These materials possess prominent features, which contribute to address the fast charge separation and light absorption problems. We firstly have prepared triazine (CxNy) acting as an oxidation co-catalyst, which efficiently facilitates electron-hole separation in a Pt-TiO₂-CxNy hollow photocatalyst system. The co-existence of Pt and CxNy functioning as the reduction and oxidation co-catalysts, respectively, has remarkably enhanced the photocatalytic performance of TiO₂. Next, we have also developed a new approach employing the air- assisted carbon sphere combustion process in preparing C/Pt/TiO₂. This material possesses many salient properties that significantly boost the electron-hole separation leading to enhanced photocatalytic performance. In an attempt to design a material that can operate under sunlight and in darkness, we have introduced Pt-WO₃/TiO₂-Au double shell hollow photocatalyst. The material has shown not only strong solar light absorption but also efficient charge separation and electron storage capacity. As a result, this type of photocatalyst exhibits a high activity performance for the degradation of organic pollutants both under visible light (λ ≥ 420 nm) and in the dark. Regarding to g-C₃N₄, we have explored the relationship between nitrogen vacancies and the plasmonic properties of Au nanoparticles employing alkali associated with the post-calcination method to prepare Au/g-C₃N₄. In fact, the produced nitrogen vacancies in the structure of g-C₃N₄ essentially enhance the interaction at Au/g-C₃N₄ interface and the plasmonic properties of Au nanoparticles. These outstanding features contribute to enhance the utilization of solar light and electron-hole separation that prompt the photocatalytic performance towards hydrogen production. Finally, we have employed a novel poly-alkali route to prepare a strong visible light absorption photocatalyst-based g-C₃N₄. The co-existence of PEI and KOH, which induces numerous nitrogen vacancies and incorporated hydroxyl groups in the structure of the resulted material, has been explored for the first time. These modifications have been proved to narrow the bandgap and facilitate the charge separation leading to enhance the solar light-driven hydrogen production. This method also opens up a new approach to prepare efficient nanocomposite photocatalysts possessing both strong light absorption and good charge separation.
The utilization of solar light-driven photocatalysts has emerged as a potential approach to deal with the serious current energy and environmental issues. Over the past decades, semiconductor-based photocatalysis has attracted an increasing attention for diverse applications including hydrogen production and the decomposition of organic pollutants. Currently, titanium dioxide (TiO₂) and graphitic carbon nitride (g-C₃N₄)-based photocatalysts have been considered as the most investigated materials because of their low cost, outstanding physical and chemical properties. However, their photocatalytic performances are still moderate owing to the fast charge carrier recombination and limited light absorption. The main target of the research presented in this thesis is to develop novel routes to prepare efficient materials based on TiO₂ and g-C₃N₄. These materials possess prominent features, which contribute to address the fast charge separation and light absorption problems. We firstly have prepared triazine (CxNy) acting as an oxidation co-catalyst, which efficiently facilitates electron-hole separation in a Pt-TiO₂-CxNy hollow photocatalyst system. The co-existence of Pt and CxNy functioning as the reduction and oxidation co-catalysts, respectively, has remarkably enhanced the photocatalytic performance of TiO₂. Next, we have also developed a new approach employing the air- assisted carbon sphere combustion process in preparing C/Pt/TiO₂. This material possesses many salient properties that significantly boost the electron-hole separation leading to enhanced photocatalytic performance. In an attempt to design a material that can operate under sunlight and in darkness, we have introduced Pt-WO₃/TiO₂-Au double shell hollow photocatalyst. The material has shown not only strong solar light absorption but also efficient charge separation and electron storage capacity. As a result, this type of photocatalyst exhibits a high activity performance for the degradation of organic pollutants both under visible light (λ ≥ 420 nm) and in the dark. Regarding to g-C₃N₄, we have explored the relationship between nitrogen vacancies and the plasmonic properties of Au nanoparticles employing alkali associated with the post-calcination method to prepare Au/g-C₃N₄. In fact, the produced nitrogen vacancies in the structure of g-C₃N₄ essentially enhance the interaction at Au/g-C₃N₄ interface and the plasmonic properties of Au nanoparticles. These outstanding features contribute to enhance the utilization of solar light and electron-hole separation that prompt the photocatalytic performance towards hydrogen production. Finally, we have employed a novel poly-alkali route to prepare a strong visible light absorption photocatalyst-based g-C₃N₄. The co-existence of PEI and KOH, which induces numerous nitrogen vacancies and incorporated hydroxyl groups in the structure of the resulted material, has been explored for the first time. These modifications have been proved to narrow the bandgap and facilitate the charge separation leading to enhance the solar light-driven hydrogen production. This method also opens up a new approach to prepare efficient nanocomposite photocatalysts possessing both strong light absorption and good charge separation.

Carbon-based nanomaterials have attracted significant attention due to their unique optical, electrical, thermal and mechanical properties. In recent years, a large number of carbon-based nanomaterials have been investigated including carbon nanotubes, graphitic carbon nitride (g-C3N4), graphene, carbon nanofibers, carbon nanodots (CNDs), heteroatom-doped carbon, and carbon-based materials obtained from biomass etc. The unique and superior properties of such carbon-based materials make them useful for a wide range of applications in the fields such as environmental remediation and energy conversions. Although significant progress has been made over the past decade or so, few drawbacks of carbon-based materials still remain unresolved. For example, as a photocatalyst, the weak van der Waals interactions between adjacent conjugated planes of g-C3N4 and poor electronic properties affect negatively on the photocatalytic activity. Despite a variety of synthetic methods have been investigated, to fabricate undoped and doped carbon-based materials, the efficiency and level of control on the resultant products are far from satisfactory. Majority of these approaches either involve tedious and complex experimental procedures or require using harsh reaction conditions, or possessing low yield production. Furthermore, to achieve heteroatom-doped carbon-based materials, the reported approaches almost exclusively require the use of synthetic chemicals as carbon and heteroatom sources, respectively. The large-scale application of fuel cells and dye-sensitized solar cells (DSSCs) using Pt-based catalysts is hindered by the inherent disadvantages of Pt such as high cost, scarcity and low resistance to crossover effect of methanol molecule. It is therefore highly desirable to realize heteroatom doping by simple, low-cost, high yield and environmentally benign synthesis methods for fabrication of commercially viable carbon-based materials for applications in solar cells and fuel cells.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

In this work, we have investigated temperature dependent electrical transport properties of carbon based two-dimensional (2D) nanomaterials. Various techniques were employed to synthesize the samples. For instance, high quality large area graphene and boron, nitrogen doped graphene (BNC) were grown using thermal catalytic chemical vapor deposition (CVD) method. Liquid phase exfoliation technique was utilized to exfoliate graphene and graphitic carbon nitride samples in isopropyl alcohol. Chemical reduction technique was used to reduce graphene oxide (rGO) by utilizing ascorbic acid (a green chemical) as a reducing agent. Detailed structural and morphology characterization of these samples was performed using state of the art microscopy as well as spectroscopic techniques (for example; Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), UV-Visible spectroscopy as well as Raman Spectroscopy). The low temperature (5 K< T <400 K) electrical transport properties of these materials show substantial difference from sample to sample studied. For instance, CVD grown graphene film has displayed metallic behavior over a wide range of temperature (5 K < T <300 K). At higher temperatures, resistivity followed linearly with the temperature (ρ(T) ~T). A power law dependence (ρ(T) ~ T4) observed at lower temperatures. Where as liquid phase exfoliated graphene and graphitic carbon nitride samples displayed nonmetallic nature: increasing resistance with decrease in temperature over a wide range (8 K < T < 270 K) of temperature. Electrical transport behavior in these samples was governed by two different Arrhenius behaviors in the studied temperature range. In the case of rGO and BNC layers, electrical conduction show two different transport mechanisms in two different temperature regimes. At higher temperatures, Arrhenius-like temperature dependence of resistance was observed indicating a band gap dominating transport behavior. At lower temperatures, Mott's two dimensional-Variable Range Hopping (2D-VRH) behavior was observed.

Graphitic carbon nitride (g-C3N4) heterojunction composites with the semiconducting metal oxides, CeO2, ZnO and TiO2 are prepared in situ by co-calcination of the precursor materials or by a solvothermal method. The structural, morphological and the optical properties of the prepared materials are studied using various microscopy and spectroscopy techniques. The synthesized composite materials, CeO2/g-C3N4, ZnO/g-C3N4 and TiO2/g-C3N4 are more efficient in the photocatalytic degradation of the water pollutants indigo carmine (IC) and atrazine than the pure metal oxide, g-C3N4, or their physical mixtures. The CeO2/g-C3N4 and ZnO/g-C3N4 composites also exhibit improved degradation efficiencies of atrazine as compared to the individual metal oxide or g-C3N4 materials. The improved photocatalytic activity of the composites are attributed to the effective electron-hole charge separation within composite heterojunction, resulting from the well matched energy levels of the metal oxide and g-C3N4. This strategy could be helpful for the synthesis of other metal oxide and g-C3N4 composites for photocatalytic applications.

The path towards mitigation of anthropogenic greenhouse gas emissions lies in the transition from conventional to sustainable energy resources. The Hydrogen Economy, a cyclic economy based on hydrogen as a fuel, is suggested as a tool in the necessary energy transition. Photocatalysis makes use of sunlight to promote thermodynamically non-favoured reactions such as water splitting, allowing for sustainable hydrogen production. Harvesting thermal energy along with photonic energy is an interesting concept to decrease the activation energy of water splitting (i.e. ΔG = + 237.2 kJ∙mol−1). This work aims to confront this hypothesis in a gas phase photo-thermal reactor designed specifically for this study. The photocatalyst chosen is graphitic carbon nitride (g-C3N4), an organic semiconductor possessing a narrow band gap (i.e. 2.7 eV) as well as a band structure which theoretically permits water splitting. The photocatalytic performance of Pt/g-C3N4 for hydrogen evolution was tuned by altering its synthetic temperature. Electron paramagnetic resonance was used to gain insight on the evolution of the photocatalyst activity with synthesis temperature. Then, gold nanoparticles were deposited on g-C3N4 surface. Localized surface plasmon resonance properties of gold nanoparticles are reported in the literature to be influenced by temperature. Therefore Au/g-C3N4 appeared as a promising candidate for photo-thermal water splitting. X-ray spectroscopy unveiled interesting observations on the gold oxidation state. Moreover, under specific reduction conditions, gold nanoparticles with a wide variety of shapes characterized by sharp edges were formed. Finally, the development of the photo-thermal reactor is presented. The design process and the implementation of this innovative reactor are discussed. The reactor was successfully utilized to probe photoreactions. Then, the highly energy-demanding photocatalytic water splitting was proven not to be activated by temperature in the photo-thermal apparatus.

The need for green and renewable fuels has led to the investigation of ways to exploit renewable resources. Solar among all the renewables is the most powerful and its conversion into usable energy would help in solving the energy problem our society is facing. Photocatalytic water splitting for hydrogen production is an example of solar energy storage into chemical bonds. The hydrogen produced in this way can then be employed as carbon free fuel creating the “Hydrogen Cycle”. This work investigates the structure and the activity of graphitic carbon nitride (g-C₃N₄), an organic semiconductor that proved a suitable photocatalyst for hydrogen production from water. Synthesised by thermal polycondensation of melamine it is a graphitic like material with a band gap of 2.7 eV which makes it a visible light active catalyst. In a first instance the effect of the synthesis conditions on its structure and morphology are investigated to find the optimum parameters. The temperature of condensation is varied from 450°C up to 650°C and the length from 2.5 h to 15 h. The structural changes are monitored via X-ray diffraction (XRD) and elemental analysis while the effect on the morphology and the band gap of g-C₃N₄ are investigated by mean of scanning electron microscopy and UV-Vis absorption. Subsequently, a study of the crystal structure of the catalyst is carried out. Using structures proposed in the literature, X-ray diffraction and neutron scattering simulations are used to narrow down the number of possible 3D structures. After structural characterisation, the activity of g-C₃N₄ for photocatalytic hydrogen evolution is evaluated. It is confirmed that loading 1 wt.% Pt on its surface significantly increases the hydrogen evolution rate. The attention then focuses on the loading procedures, the reduction pre treatments of the co-catalyst and the reasons of the different performances when different procedures are employed. The catalytic system is characterised by mean of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and XRD. By investigating the composition and the morphology of the platinum nanoparticles under different conditions, the main factors responsible for the changes in activity of g-C₃N₄ for hydrogen evolution are identified. Additionally, the role of the co catalyst and its interaction with g-C₃N₄ is also elucidated. Finally, taking forward the knowledge acquired on the Pt-g-C₃N₄ system, the effect on the hydrogen evolution rate of alloying platinum with a second metal (Cu, Ag, Ni and Co) is studied. The nanoparticles are characterised by XRD and TEM. A screening of the loading procedures and bimetallic systems is performed to identify the most promising for photocatalytic hydrogen evolution with the aim of bringing them towards further investigation.

This thesis is a study of gas separation by low-dimensional nanomaterials through selective adsorption and membrane separation. The study uses first-principles quantum mechanical simulations and classical molecular dynamic simulations to study the gas separation behaviour of doped fullerenes, porous boron nitride membranes and graphitic carbon nitride membranes. The thesis further demonstrates how chemical affinity and size exclusion behaviour of the adsorbent and membrane materials are tweaked to achieve the targeted separation and how the separation behaviour can be tuned to match the application by charge tuning, strain tuning and structure tuning.

This thesis is an exploratory study of nanomaterials stabilized Pickering emulsions and their applications. The study illustrates some novel emulsion behaviour through dynamic observation and develops a mechanically switchable emulsion based on the microstructure design of nanomaterials. The droplets of emulsion are demonstrated as an effective microreactor for chemical reactions that happen at the oil-water interface, showing the potential application of Pickering emulsion in catalysis.

Pure g-C3N4 and MoS2 modified g-C3N4 materials were synthesized using a facile heating method and a low-temperature hydrothermal method, respectively. The obtained samples were characterized by XRD pattern and N2 adsorption-desorption technique at 77K. The adsorption and photocatalytic performance of all obtained samples were investigated by discoloration of direct black 38 dye in the dark and under visible light irradiation. The results showed that all obtained samples exhibited good discoloration efficiency of direct black 38 dye. The two factors including pH values and Mo loading effected mainly on elimination efficiency of direct black 38 dye. MoS2 modified g-C3N4 materials possessed the more enhanced adsorption and photocatalytic performance in comparison to pure g-C3N4 at pH value of 3.5, with adsorbent dosage of 0.1 g/L. Furthermore, it was found that the adsorption process and photo-catalysis simultaneously occurred under visible light irradiation and followed up a pseudo-second-order kinetic reaction of Langmuir - Hinshelwood model.
g-C3N4 và g-C3N4 biến tính bởi MoS2 đã được tổng hợp theo phương pháp nung đơn giản và phương pháp thủy nhiệt ở nhiệt độ thấp tương ứng. Các mẫu tổng hợp đã được đánh giá đặc trưng bởi các phương pháp hiện đại như giản đồ nhiễu xạ tia X, phương pháp hấp phụ-khử hấp phụ N2 ở 77K. Khả năng hấp phụ và quang hóa xúc tác của các vật liệu tổng hợp đã được nghiên cứu bởi quá trình phân hủy màu thuốc nhuộm direct black 38 trong điều kiện bóng tối và chiếu sáng bởi ảnh sáng nhìn thấy của đèn chiếu sáng sợi đốt wolfram (220V-100W). Các kết quả nghiên cứu chỉ ra rằng các mẫu tổng hợp đều có hiệu suất xử lý màu cao đối với thuốc nhuộm direct black 38. Hai yếu tố gồm pH dung dịch và hàm lượng MoS2 ảnh hưởng chính đến hiệu suất xử lý màu direct black 38. g-C3N4 biến tính bởi MoS2 luôn thể hiện hiệu suất hấp phụ và quang hóa cao hơn so với g-C3N4 tinh khiết. Hơn nữa, khi được chiếu sáng bởi ánh sáng nhìn thấy thì quá trình hấp phụ và quá trình quang hóa thuốc nhuộm direct black 38 trên các vật liệu tổng hợp đã xảy ra đồng thời và mô hình Langmuir - Hinshelwood động học bậc 2 đã được đề xuất cho quá trình này.

In this thesis, we have attempted to understand the working principle of Li(Na)-S(Se) battery and following such understandings we have attempted towards the design of various S(Se)- cathode materials for the alkali based chalcogen batteries. In the final chapter, we have focussed on the development of anode materials for full Li-ion cell. The summary of the various chapters is as follows. Chapter 2 discusses about NaY-xS-PAni exhibiting remarkable electrochemical performance as a cost-effective sulfur cathode for rechargeable Li-S batteries. The superior electrochemical stability and performance of the NaY-xS-PAni is directly correlated to the novel NaY electrode structure in combination with the host polarity and ionic conductivity. The zeolite provides an optimum geometrical and chemical environment for precise confinement of the sulfur while the polyaniline coating provides electron conduction pathway along with extra polysulfide confinements. This cathode material exhibits very stable cycling for more than 200 cycles with relatively low specific capacity and modest rate capability. To develop a material for obtaining high specific capacity value we moved to carbon based host and the details are covered in chapter 3 and 4. To summarize Chapter 3, we have successfully extended the pressure induced capillary filling method for confinement of sulfur and selenium in the interior core of the MWCNTs. This method results in ultra-high loading yields of the chalcogens inside the MWCNTs. The ensuing composites S-CNT have been convincingly demonstrated as prospective cathodes in Li-S rechargeable batteries exhibiting very high specific capacities ~ 1000 mAh g-1 at C/10 current rates. The novelity of this host has been established by extending the work in encapsulating Se with the similar protocol and studying its electrochemical activity. The high efficiency of the Li-S/Se electrochemical reaction observed here is directly attributed to the efficacy of the encapsulation protocol of S/Se inside the CNTs. The polyselenides/polysulfides are completely confined within the precincts of the CNT cavity leading to an exceptionally stable battery performance at widely varying current densities. With the success of this encapsulation technique for the carbon based host, we developed another interconnected mesoporous microporous carbon host for sulfur encapsulation the details of which constitute the next chapter. In chapter 4, we have discussed here a novel S-cathode where the sulfur confining hierarchical carbon host synthesized using a sacrificial template can be very effectively employed for in Li-S rechargeable battery. The hierarchical mesoporous-microporous architecture comprising of both mesopores and micropores provide an optimal potential landscape which in turn traps high amounts of sulfur as well as polysulfides formed during successive charge-discharge cycles. The uniqueness of the carbon matrix translates to exceptionally stable reversible cycling and rate capability for Li. Such promising result with Li-S battery compelled us to check the performance with Na anode. This led to the development of intermediate temperature Na-S battery with JNC-S as the prospective cathode. It is envisaged that such materials design will be very promising in general for battery chemists especially for higher valent metal-sulfur systems (e.g. magnesium, aluminum). The host discussed here will be ideally suitable for introduction of dopants such as nitrogen, boron, thus enhancing it’s versatility as a heterodoped mesoporous-microporous host for varied applications. In all the preceding chapters, the focus was to encapsulate sulfur in some host structures. Chapter 5 deals with an alternative configuration for the Li-S battery that uses an oxide based interlayer to restrict the polysulfides. From the study discussed here, it can be concluded that NiOH-np/NiO-np can act as an efficient interlayer material for superior anode protection. The interlayer provides an anchor to hold back the polysulfides primarily on the cathode side by forming intermediates such as NiS3(OH) and NiS4(OH). Although, the specific capacity is less compared to the theoretically estimated value for S-cathode, the high cyclability coupled with extremely good rate capability performance makes this a very promising configuration of Li-S cell assembly for practical applications and deployment. The success of this strategy is expected to decrease the need for design of sophisticated S-scaffolds and lead to simpler Li-S rechargeable batteries. After an extensive discussion on development of cathodes for alkali based chalcogen batteries, we shifted gears and tried our hands in developing some eco-friendly anode materials. The details of graphitic carbonitride as an anode material for Li-ion cell has been discussed in chapter 6. To conclude, we have discussed here in detail the unique layered structure of the as-synthesized gCN and its impact on the intrinsic charge transport properties. Both factors eventually determine their electrochemical performance. The gCN discussed here is obtained using a very simple synthesis protocol in large yields from a very cheap organic precursor. The work highlights again the important role of chemical composition and structure on the functionality of the intercalation host. These have a strong bearing on the electronic charge distribution in the host and its eventual interaction with the intercalating ions. Compared to several non-trivial layered carbonaceous structures, the gCN interestingly displays 3-D ion transport. Additionally, it also sustains facile electron transport (2-D) despite the low concentration of carbon. In spite of the modest specific capacities as observed in case of the half cells, the gCN when assembled with (high) voltage cathodes in full Li-ion cells, the performance is quite encouraging. To the best of our knowledge this is for the first time that graphitic carbon nitrides have been demonstrated as an anode in full Li-ion cells. The potential of majority of the reported high surface area and high capacity complex carbonaceous structures in Li-ion cells are inconclusive. This is mainly due to the fact that the percentage of reports on full Li-ion cell performance is very rare. The full cell analysis of the gCN discussed here conclusively rules out the necessity of the requirement of high specific capacity materials in practical/commercial full cells. We envisage that the work discussed here will pave the way for synthesis of many such electrode materials from renewable resources resulting in the development of green and sustainable batteries. Overall we have been able to address some of the potential problems of Li-S and Li-ion battery systems. There is further scope of betterment with extensive study and this work opens the scope for it in future.

碩士
國立中興大學
環境工程學系所
106
A visible-light-driven graphitic carbon nitride/reduced graphene oxide/α-Sulfur composite (CNRGOS8) was synthesized as efficient photocatalysts for environmental applications. The photocatalytic reactivity of the fabricated CNRGOS8 was determined by the degradation of Rhodamine B (RhB) and tetracycline (TC). The effects of pH, mixed ratio of catalysts, dosage of photocatalyst were optimized, and the reaction kinetics and reaction pathway were studied. The results indicated the optimized pH values for RhB and TC degradation was 3 and 7, respectively. In addition, no deterioration of the efficiency was found for CNRGOS8 (70:5:25) after 5 cycles of operation. Such a result was indicative of a prolonged lifetime of the CNRGOS8 (70:5:25). With probing by the scavengers, 2-Propanol (·OH capture reagent), benzoquinone (O2•－ capture reagent) and sodium oxalate (h+ capture reagent), the major reactive species were identified as superoxide radicals and hydroxyl radicals. The abundant natural organic matter such as humic acid (HA) oftentimes coexists with the pollutants in the aquatic environment, which may affect the efficiency and alter reaction pathways of photodegradation of the pollutants. An enhanced electron transfer and reactive oxide species production were found for CNRGOS8 (70:5:25) in the presence of humic acid. However, the overall removal efficiency of the pollutants was suppressed due to the competition between CNRGOS8 (70:5:25) and the coexisting HA for the active sites.

碩士
國立中興大學
環境工程學系所
107
Photocatalytic degradation has emerged as a promising technique owing to its promising ability toward resolving the limitations of the conventional wastewater treatment progress. Graphitic carbon nitride (CN), a polymeric metal-free semiconductor, the narrower bandgap (approximately 2.7 eV) enables its utilization of natural light, and therefore, great progress has been made in the use of this material in a wide range of applications. In the present work, photocatalytic performance and photostability of CN was systematically investigated. CN synthesized from various precursors and with varying exfoliated degree was studied. For the durability test, chemical instability of CN caused by photogenerated radicals was found. The deterioration products of CN depend on different working conditions. Efficient degradation of emerging contaminant such as diclofenac (DCF) by CN and great reusability was observed, with O2•⁻ being the major reactive oxygen species and •OH playing the minor role. Finally, photostability under practical use was evaluated in the presence of target pollutants. It was found that the stability of CN has been much more improved while coexisting with target pollutants, otherwise, CN will suffer from photocorrosion due to the attack of reactive oxygen species.

碩士
逢甲大學
化學工程學系
106
In this study, molybdenum oxides with various oxidation states were decorated on two-dimensional graphitic carbon nitride (gCN) to enhance the photocatlytic activity of CO2 reduction under visible light irradiation and to correlate the characteristics of photocatalysts to the efficiency of CO2 conversion. Part 1: Preparation and Properties of Molybdenum Trioxide / Graphitic Carbon Nitride Composite for Photocatalysis Molybdemum trioxide/graphitic carbon nitride was prepared by calcination and hydrothermal method. Ammonium molybdate tetrahydrate was the precursor of molybdenum and melamine was for gCN. Molybdenum trioxide (MoO3) was obtained by hydrothermal method (210 °C) and graphitic carbon nitride was by calcination method (450 °C) at Air or Ar. XRD result confirmed the crystal phase of MoO3 and characteristic peaks of gCN. SEM images confirmed the morphology of MoO3 and gCN. TEM images presented the distribution of MoO3. A significant red shift, compared to pure MoO3, revealed from UV-VIS spectra of samples with the presence of gCN. After calcination under Ar, some MoO3 reduced to MoO2 as evidenced from ESCA results of MoO3-gCN-Ar and thus increased photocatalytic activity. Photocatalytic reduction of CO2 showed MoO3-gCN-Ar (8 W, 254 nm) could successfully convert CO2 into CO, and the yield of CO was 0.067 mol/gcat. Part 2: Preparation and Properties of Molybdenum Oxide Quantum Dots / Graphitic Carbon Nitride Composite for Photocatalysis In order to further improve the photocatalytic activity of CO2, molybdenum oxide quantum dots/graphitic carbon nitride composites (MoOx-QDs-gCN) were prepared in the second part of this study. Molybdenum oxide quantum dots were prepared by hydrothermal method (80 °C) using molybdenum powder as the precursor. The melamine was used as a precursor to prepare graphitic carbon nitride (gCN) by calcining at 500 °C and 550 °C under air atmosphere. The obtained molybdenum oxide quantum dots were mixed with gCN and then calcined at 300 °C. XRD, ESCA and EDX results confirmed that the catalyst contained molybdenum oxide with various oxidation states on gCN. TEM images showed after calcination graphitic carbon nitride still mentain their characteristic structure. A significant red shift of the absorption edge of MoOx-QDs-gCN, compared to gCN, was observed from UV-VIS spectra. Carbon dioxide photocatalytic reduction results showed MoOx-0.3gCN (8 W, 254 nm) had the best conversion yield of CO and the yield of CO was 0.418 mol/gcat. Part 3：In-Situ Preparation and Properties of Molybdenum Oxide / Graphitic Carbon Nitride Composite for Photocatalysis In the third part of this study, in-situ preparation of molybdenum oxide (MoOx) on gCN was attemped to improve the interaction of gCN and MoOx. Thermal condensation method was applied to fabricate graphitic carbon nitride(gCN). Different amounts of molybdenum disulfide (MoS2) were dissolved with hydrogen peroxide solution, followed by the addition of gCN. Strong oxidation of hydrogen peroxide with molybdenum disulfide was ulilized to replace the sulfur atoms of molybdenum disulfide to oxygen atoms. The presence of nitrogen active sites on gCN surface has electronic affinity with molybdenum ions. After the deposition of molybdenum oxide particals on gCN, the remained sulfur ions were removed by neutralization by alkali. After centrifugated and washed, we could obtain the composite photocatalysts and named XMS-0.1CN, where X indicates the volume of MoS2. The results of XPS-Mo3d confirmed that the photocatalyst 30MS-0.1CN had the highest ratio of Mo4+ (compared with the other photocatalyst). The appearance of Mo4+ could improve the charge transport capacity and promote photocatalytic activity. The UV-Vis and Tauc Plot analysis results were shown that the in-situ synthesized photocatalyst had a red shift of the absorption edge compared with pure gCN and the band-gap was narrowed by 0.1 to 0.2 eV. The results of PL spactrum analysis showed that the photoluminescence intensity of in-situ prepared photocatalyst was lower than that from that emitted from pure gCN. This result indicated that molybdenum oxide after in-situ growth could effectively reduce the recombination efficiency of photogenerated electron-holes. In the photocatalytic reduction of carbon dioxide, carbon monoxide was the only successful conversion product. 30MS-0.1CN had the highest conversion yield, 3.937 mol/gcat, as the highest Mo4+ ratio was estimated by ESCA. This study showed that the in-situ growth of the photocatalyst was indeed effective at improving photocatalytic activity compared to pure gCN.

博士
國立清華大學
生醫工程與環境科學系
106
Graphitic carbon nitride (g-C3N4) is a promising material for photocatalytic applications such as solar fuels production through CO2 reduction and water splitting, and environmental treatment through the degradation of organic pollutants. This promise reflects the advantageous photophysical properties of g-C3N4 nanostructures, notably high surface area, quantum efficiency, interfacial charge separation and transport, and ease of modification through either composite formation or the incorporation of desirable surface functionalities. For heterogeneous catalytic processes, organic compounds and metal derivatives could bind or intercalate into the matrix of g-C3N4 through the surface anchoring sites to improve the catalytic reaction rate, and thus broaden the catalytic application of g-C3N4 toward organic decomposition. The unique architecture of g-C3N4 and the outstanding catalytic performance of Au nanoparticles provide a great impetus to use g-C3N4 as a promising support to judiciously decorate Au NPs for the formation of highly active and green heterogeneous catalyst. Therefore, this thesis focuses on developing novel g-C3N4-based-nanomaterirals modifying with TiO2/ZnFe2O4, which can offer further performance enhancements in photo-electrocatalytic activity for organic pollutant removal. The 1 wt% ZnFe2O4-TiO2 nanocomposites exhibit the excellent recycling and reusable ability and can retain the stable photocatalytic activity toward Bisphenol A (BPA) photodegradation for at least 10 cycles of reaction with rate constants of 0.191 – 0.218 min-1 under visible light irradiation. The photodegradation rate of BPA by ZnFe2O4-TiO2 (which was highly dependent on the water chemistry including pH, anions, and humic acid) was 20.8−21.4 times higher than that of commercial TiO2 photocatalysts. The visible-light-driven degradation of tetracycline (TE) is enhanced remarkably by the ZnFe2O4/TiO2/g-C3N4 photocathode due to the more efficient light absorption and photogenerated charge separation. By applying photoelectrocatalytic (PEC) process, the degradation rate constant of TE is increased by 48 and 24 times as much as that of photocatalytic (PC) and electrocatalytic (EC), respectively. Results clearly demonstrate the superior visible-light-driven photoactivity of g-C3N4-based-photocatalysts toward organic pollutants degradation and can open an avenue to industrial application in the future with a wide variety of potential application in the fields of photocatalysis, water splitting and energy conversion. Moreover, a photochemical green synthesis using thermal exfoliation process is developed to fabricate Au@graphitic carbon nitride (g-C3N4) nanocomposite, highly recyclable and reusable, for the catalytic reduction of nitrophenols by NaBH4. The rate constant of 4-nitrophenol reduction over Au@g-C3N4 (2 wt%) is 26.4 times that of pure Au NP in the presence of 7 mM of NaBH4 at pH 5. Besides, I have demonstrated a simple and facile synthesis method for the fabrication of Au@meso-carbon nitride (meso-CN) nanocomposite with various Au loadings for highly recyclable reduction of nitrophenols. The integration of high surface area, regular mesopores, graphitic nature of the meso-CN support as well as highly dispersed and spatially imbedded Au NPs on the Au@meso-CN composites make them excellent as catalytic reduction of 4-nitrophenol. The kobs for 4-nitrophenol reduction over 2 wt% Au@ meso-CN nanocatalysts can be up to 3.558 min-1 in the presence of NaBH4. In both cases of using graphitic carbon nitride supported Au nanocomposites for nitrophenol reduction, The detection of H radical adducts by EPR indicates that Au NPs adsorbs BH4- ions and forms Au-H species and subsequent electron transferfrom the Au-H species to nitrophenols. Results clearly demonstrate that Au@carbon-nitride nanocomposites are promising green catalysts of great application potential for nitroaromatic reduction, which can provide a new venue for tailoring Au-based nanomaterials in elucidation of a wide variety of heterogeneous catalytic reactions in water and wastewater treatment

碩士
國立臺北科技大學
機電整合研究所
104
In the recent years, with the continuous development of economic globalization, the quality of our living have gone from good to well, when people enjoy the convenience technology, I also need to face the problem of energy shortage and environmental pollution. So far oil as a major energy source in the world, resulting in crude oil prices continue to rise in recent years. Fossil fuels easy to produce emissions of carbon dioxide and other harmful gases, so the development of high energy density secondary battery that reduce environmental pressure is the development of technology the main direction. The study synthesized rod-like structure of different cobalt selenide compound material (CoSe2@g-C3N4) by simple hydrothermal method for cathode of lithium-air battery. The study explored what is the influence as catalytic process if CoSe2 grafted in g-C3N4. I identified the phase and crystallinity by X-ray diffraction (XRD), observed the morphology by scanning electron microscope(SEM), observed material structure by transmission electron microscopes (TEM). X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) were used to observe the oxidation states and the coordination conditions.I found the surface of CoSe2 existed highest ratio of Co2+. Identified by the electrochemical method, CoSe2 grafted in 50mg g-C3N4 can get low over potential and high capacity(2158 mAh•g-1). The conductivity of cathode material was calculated by performing the electrochemical impedance spectroscopy (EIS). I found that CoSe2 grafted in g-C3N4 can get lower impedance. Electrode surface will be easy for oxidation and reduction.

No
Recently, nanoscale metal-organic frameworks (NMOFs) have started to be developed as a promising platform for bioimaging and drug delivery. On the other hand, combination therapies using multiple approaches are demonstrated to achieve much enhanced efficacy. Herein, we report, for the first time, core-shell nanoparticles consisting of a photodynamic therapeutic (PDT) agent and a MOF shell while simultaneously carrying a chemotherapeutic drug for effective combination therapy. In this work, core-shell nanoparticles of zeolitic-imadazolate framework-8 (ZIF-8) as shell embedded with graphitic carbon nitride (g-C3N4) nanosheets as core are fabricated by growing ZIF-8 in the presence of g-C3N4 nanosheets. Doxorubicin hydrochloride (DOX) is then loaded into the ZIF-8 shell of the core-shell nanoparticles. The combination of the chemotherapeutic effects of DOX and the PDT effect of g-C3N4 nanosheets can lead to considerably enhanced efficacy. Furthermore, the red fluorescence of DOX and the blue fluorescence of g-C3N4 nanosheets provide the additional function of dual-color imaging for monitoring the drug release process.

碩士
中原大學
化學工程研究所
106
Photocatalytic-Membrane Reactor (PMR) has been widely used in wastewater removal in recent years. Compared to batch photodegradation system, not only photocatalyst can be separated from liquid phase in PMR, but also the removal efficiency can be increased significantly. In this study, we design a PMR system to remove wastewater containing methyl blue, methyl orange, phenol, and mixed organic dyes. In this study, phosphorus-doped graphite-type carbon nitride (PCN) was prepared in an attempt to coat on the substrate. XRD patterns show the diffraction peaks of PCN are located at 13.1° and 27.1°, which can be confirm as the (100) and (002) crystal plane of graphite-type carbon nitride(C3N4). In PL analysis, the emission peak of PCN is lower than C3N4, which can be contributed to the phosphorus doping. In photodegradation reactions, 10 wt% of phosphorus-doped C3N4 (10PCN) showed the highest degradation activity under visible light irradiation among the samples. In the hollow fiber membrane system, an inorganic hollow fiber membrane was prepared by spinning using an alumina solution. SEM images revealed the pore diameter of the membrane was approximately 1.2 mm and the membrane thickness was around 200 μm. To fabricate a PMR system, PCN was integrated with PMR system for wastewater treatment under irradiation of metal halide lamp. The removal efficiency of the PMR system is 1.63 and 1.22 times higher than the batch photodegradation system and the membrane system, respectively. The PMR system show high stability and can effectively removal different kinds of organic wastewater. KEYWORDS: Photocatalytic-Membrane Reactor, phosphorus doping, graphite carbon nitride, methyl blue, visible light

碩士
國立臺北科技大學
化學工程與生物科技系化學工程碩士班
107
Part I：In this study, a simple and environmentally friendly hydrothermal method was used to prepare a porous graphite carbonitride/manganese dioxide nanocomposite (GCN/MnO2), which was modified on a screen printed carbon electrode(SPCE), and for the first time applied to the electrochemical detection of nitrite, the rapid and sensitive detection efficiency of the nanocomposite electrode is helpful for the development of nitrite electrochemical detection. In this experiment, various physical and chemical techniques were used to detect properties: X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption isotherm Field emission scanning electron microscopy (FE-SEM) and high-resolution field emission transmission electron microscopy (HR-TEM) were used to verify its morphology and structural properties, using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV), graphite nitride/manganese dioxide modified screen-printed carbon electrodes were studied for nitrite redox performance. In the study, GCN / MnO2 modified electrodes have high sensitivity (24.1777 μA μM-1 cm-2), low detection limit (1.23 nM), and a wide linear range (0.01–1520 μm), and in actual samples (rotation) In the detection of beef, tap water and water filter, it shows good electrocatalytic properties and good anti-interference properties, which means it has high practical value and can be applied to food safety related testing. Part II：In this study, a simple hydrothermal method was used to synthesize a nickel-nickel oxide/graphene oxide (NiS2 / GO) nanocomposite, and a glass probe was modified to further detect the toxic substance 4-hydroxynitrobenzene (4-HNB) in electrochemical sensing. In the experiment, the groups of the nanomaterials were first determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and then the high-resolution field emission transmission electron microscope (HR-TEM) was used to laminate the nano composites. The appearance of the study; Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were also used to verify the electrochemical performance of nickel disulfide/graphene oxide modified glass probe (NiS2 / GO-GCE) with unmodified glassy carbon. Compared to the electrode (GCE), the sensor's sensing performance for 4-HNB is very significant, while the measured sensor has a wide linear range (0.1000-1053 μM) and a very low detection limit (59.5 nM). On the other hand, the detection of real river water samples also has a detection rate of more than 96%, which means that NiS2 / GO-GCE is very suitable for the detection of poisons in real water quality.

碩士
國立臺灣大學
化學研究所
104
Based on the latest statistics from the Ministry of Health and Welfare, malignant tumor continues to be on top of disease, and then followed by the heart disease and cerebrovascular disease, so the diagnosis and medical treatment has become one of the major issues. Nowadays, cancer treatments still focus on surgical resection, chemotherapy and radiation therapy, but it still can be improved for the more effective treatment. As a result, human beings have continued to investigate novel adjuvant cancer therapy in recent years, photodynamic therapy (PDT) is now becoming a widely used medical tool. Compared with the traditional therapy, photodynamic therapy is recognized as a minimally invasive procedure, also has little side effect and can selectively lead to tumor necrosis. The purposes of this research is to fabricate a lanthanide-doped upconversion nanoparticles (UCNPs) nanocomposite by combining with graphitic carbon nitride (g-C 3 N 4 ) photosensitizer for near-infrared (NIR) light mediated PDT application. First, we synthesized upconversion nanoparticles by high temperature co-precipitation method, and then the ligand on the surface were removed via the treatment with hydrochloric acid to obtain water-dispersible nanoparticles. Furthermore, ligand-free upconversion nanoparticles modified with poly-L-lysine (PLL) in order to render the positive-charged group which can allow the attachment of the g-C 3N4 by electrostatic assembling. Through the excitation of continuous wave NIR laser, upconversion nanoparticles can convert the low-energy NIR light to high energy ultraviolet (UV) or visible light. Owing to this unique optical property of upconversion nanoparticles, the UV light will further photoexcites g-C3N4 at 365 nm, emit the green light and release reaction oxygen species (ROS). Meanwhile, we also modified different concentration of PLL to achieve a moderate condition for high g-C3N4 loading and ensuring maximum energy transfer from UCNPs to g-C3N4 photosensitizer, so as to generate a significant amount of ROS, which can result in tumor cell necrosis and apoptosis for efficient PDT effect.

碩士
國立臺中教育大學
科學教育與應用學系科學教育碩士班
103
In this study, a series of the bismuth oxyiodide composite graphene oxide (GO) or graphitic carbon nitride (g-C3N4) are prepared using autoclave hydrothermal methods. In the preparation procedure, g-C3N4 is synthesized by calcinations at 540℃ in muffle furnace , and graphene oxide is synthesized by Hummer method modified. Graphene and g-C3N4 are the two-dimensional atomic crystal available for enhancing electron-hole transfer surface and reduce the recombination rate of photocatalyst. Bismuth oxyiodide, with different crystalline in different pH vm alue, can synthesize different bismuth oxyiodide composite graphene or g-C3N4 photocatalysts. The structures and morphologies of BiOxIy/g-C3N4 or graphene oxide photocatalysts are characterized by XRD, FE-TEM, SEM-EDS, HR-XPS, DR-UV, BET, EPR and PL. Discuss different crystalline bismuth oxyiodide composite graphene or g-C3N4 affect the photocatalytic efficiency. Crystal Violet and Salicylic acid is a common organic pollutants in the environment. The study is useful for photocatalytic degradation of organic samples and use HPLC-PDA-MS for separation and identification of degradation intermediates. The study is useful for degrading the organic compounds in the future applications of environmental pollution and control.

碩士
中原大學
化學工程研究所
107
Graphitic carbon nitride (g-C3N4) is a promising visible light-driven photocatalyst with a band gap energy of 2.70 eV. However, abundant surface defects and unwanted carbon or nitrogen vacancies may lead to high charge recombination that results in a decrease of photocatalytic activity. In this study, P and S were co-doped on oxygenated g-C3N4(PSOCN) using a thermal condensation method with different weight ratio of P and S (PxSyOCN, x, y =5,10,15). Photoelectrochemical properties including impedance spectroscopy, Mott-Schottky analysis, and photocurrent density, and the degradation of organic pollutants under visible light irradiation were investigated. XRD diffraction peaks of PSOCN located at 13.1° and 27.1° were assigned to (100) and (002) crystal plane of graphite-type carbon nitride (CN). The SEM images showed that both CN and PSOCN had irregular stacked shape and plate-like morphologies, indicated that doping were not affect the surface morphologies. In the UV-vis spectra, the absorption wavelength of PSOCN exhibited a shoulder at approximately 440-500 nm, and its band gap is a little smaller than that of CN. In Mott-Schottky test, PSOCN and CN samples are n-type semiconductors, and Fermi level of PSOCN all move to negative potential, indicating electronic of PSOCN are more easily moved to conduction band. Especially, P10S5OCN had the most large photocurrent density. In addition, PSOCN hydrogel was fabricated using photoinduced polymerization method. PSOCN hydrogel enables not only to decompose a commonly seen dye, methyl blue, but also to be recycled easily. In summary, P10S5OCN is the best weight ratio in PSOCN. Its photocurrent density is larger than others, and P10S5OCN hydrogel also has better degradation efficiency of methyl blue.

碩士
國立交通大學
電子物理系所
105
Graphitic-like carbon nitride (g-C3N4) modified with plasmonic Ag@SiO2 core-shell nanoparticles has attracted considerable interest as a means to enhance photocatalytic solar hydrogen evolution under visible light. High-rate charge carrier recombination is a key factor limiting the photocatalytic activity of g-C3N4. In this study, the SiO2 shell generated a nanogap separating the plasmonic silver nanoparticles and g-C3N4. The plasmon resonance energy transfer (PRET) and energy-loss Förster resonance energy transfer (FRET) induced by the localized surface plasmon resonance (LSPR) in the silver nanoparticles could be perfectly balanced by engineering the size of the nanogap. The LSPR of the Ag nanoparticles could enhance the visible-light photoactivity of graphitic carbon nitride. Nanosized gaps between the plasmonic Ag nanoparticles and g-C3N4 were created and precisely modulated to be 8, 12, 17, and 21 nm by coating SiO2 shells on the surface of Ag nanoparticles. For this study, the PRET effect and the FRET effect were well balanced with the photocatalytic solar hydrogen evolution performance achieved at a nanogap of 12 nm. In situ X-ray absorption spectroscopy (XAS) was employed to investigate the electronic structure of these photocatalysts. The C and N K-edges were conducted to reveal both the density of unoccupied states in the conduction band and how these states changing at different illumination conditions. In situ XAS directly probe the dynamic charge redistribution indicated that the shift of the conduction band edge as well as the modification of the density of the unoccupied states engendered the improved photocatalytic activity. The SiO2 shell between the Ag nanoparticles and g-C3N4 limit the energy loss of the FRET process by limiting the photocatalytic activity of g-C3N4/Ag@ SiO2 to g-C3N4/Ag. These results reveal a strong correlation between the dynamics of the semiconductor structure and its electronic properties, which explains the LSPR effect in the photocatalytic mechanism.

碩士
國立臺中教育大學
科學教育與應用學系碩士班
104
In this study, a series of the bismuth silicate and bismuth silicate composite graphitic carbon nitride (g-C3N4) are prepared using autoclave hydrothermal methods. The novel heterojunctions of BixSiOy/g-C3N4 is fabricated by the hydrothermal method for the first time, in which g-C3N4 is synthesized by calcinations at 540℃ in muffle furnace. Bismuth silicate is prepared by Bi(NO3)3 and Na2SiO3, dissolved in an 1M HNO3 aqueous solution and adjusted the pH value, and then the aqueous solution is transferred into a 15 mL Teflon-lined autoclave and is heated to 150 oC for 8 hours. Finally, the BixSiOy and g-C3N4 are mixed in different ratio in a autoclave and is heated to 150oC for 4 hours. The products are characterized by XRD, SEM-EDS, FE-TEM, HR-XPS, PL, DR-UV, BET, FT-IR, and EPR. inorder to discuss the photocatalytic efficiency of bismuth silicate and bismuth silicate composite g-C3N4. Photocatalytic efficiency of the catalyst is use of photocatalytic degrading of organic pollutants - crystal violet (CV) by measuring crystal violet (CV) concentration.

碩士
國立臺中教育大學
科學教育與應用學系碩士在職專班
105
In this study, bismuth silicate and bismuth silicate composite graphene oxide (GO) and composite graphitic carbon nitride (g-C3N4) are prepared using autoclave hydrothermal methods. The novel heterojunctions of Bi12SiO20/GO and Bi12SiO20/g-C3N4 are fabricated by the hydrothermal method for the first time. Bismuth silicate is prepared by Bi(NO3)3 and Na2SiO3, dissolved in an 3M NaOH aqueous solution and adjusted the pH value . The aqueous solution is then transferred into a 15 mL Teflon-lined autoclave and heated to 100oC for 4 hours. Bi12SiO20/GO or Bi12SiO20/g-C3N4 is mixed in different weight ratio independently in a autoclave and heated to 100 oC for 4hours. The products are characterized by XRD, SEM-EDS, FE-TEM, HR-XPS, PL, DR-UV, BET, FT-IR, and EPR. To discuss bismuth silicate and bismuth silicate composite with graphene oxide and graphitic carbon nitride for photocatalytic efficiency, photocatalytic efficiency of the catalyst is used for the photocatalytic degradation of organic pollutants - crystal violet (CV) and 2-hydroxybenzoic acid . The measurement of crystal violet (CV) concentration, that the reaction rate constant k of Bi12SiO20 / 20wt%-GO and 5wt%-Bi12SiO20/g-C3N4 is 0.050h-1 and 0.078 h-1, respectively. This study shows that the ratio of Bi12SiO20：GO and Bi12SiO20： g-C3N4 strongly affect composite morphology, light response and photocatalytic activity.

abstract: Photocatalytic water splitting over suspended nanoparticles represents a potential solution for achieving CO2-neutral energy generation and storage. To design efficient photocatalysts, a fundamental understanding of the material’s structure, electronic properties, defects, and how these are controlled via synthesis is essential. Both bulk and nanoscale materials characterization, in addition to various performance metrics, can be combined to elucidate functionality at multiple length scales. In this work, two promising visible light harvesting systems are studied in detail: Pt-functionalized graphitic carbon nitrides (g-CNxHys) and TiO2-supported CeO2-x composites. Electron energy-loss spectroscopy (EELS) is used to sense variations in the local concentration of amine moieties (defects believed to facilitate interfacial charge transfer) at the surface of a g-CNxHy flake. Using an aloof-beam configuration, spatial resolution is maximized while minimizing damage thus providing nanoscale vibrational fingerprints similar to infrared absorption spectra. Structural disorder in g-CNxHys is further studied using transmission electron microscopy at low electron fluence rates. In-plane structural fluctuations revealed variations in the local azimuthal orientation of the heptazine building blocks, allowing planar domain sizes to be related to the average polymer chain length. Furthermore, competing factors regulating photocatalytic performance in a series of Pt/g-CNxHys is elucidated. Increased polymer condensation in the g-CNxHy support enhances the rate of charge transfer to reactants owing to higher electronic mobility. However, active site densities are over 3x lower on the most condensed g-CNxHy which ultimately limits its H2 evolution rate (HER). Based on these findings, strategies to improve the cocatalyst configuration on intrinsically active supports are given. In TiO2/CeO2-x photocatalysts, the effect of the support particle size on the bulk/nanoscale properties and photocatalytic performance is investigated. Small anatase supports facilitate highly dispersed CeO2-x species, leading to increased visible light absorption and HERs resulting from a higher density of mixed metal oxide (MMO) interfaces with Ce3+ species. Using monochromated EELS, bandgap states associated with MMO interfaces are detected, revealing electronic transitions from 0.5 eV up to the bulk bandgap onset of anatase. Overall, the electron microscopy/spectroscopy techniques developed and applied herein sheds light onto the relevant defects and limiting processes operating within these photocatalyst systems thus suggesting rational design strategies.
Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2019

Niniejsza rozprawa opisuje syntezę, badania fizykochemiczne oraz systematyczne badania właściwości adsorpcyjnych dwóch typów adsorbentów: (i) materiałów opartych na grafitopodobnym azotku węgla oraz (ii) materiałów węglowych. Materiały te dedykowane są do usuwania związków organicznych i/lub jonów metali z roztworów wodnych. Materiały oparte na grafitopodobnym azotku węgla modyfikowano poprzez domieszkowanie litowcami (lit, sód, potas) lub berylowcami (magnez, wapń, stront, bar). Uzyskane produkty szczegółowo przeanalizowano w celu określenia morfologii, składu chemicznego i fazowego, fizykochemii powierzchni oraz właściwości adsorpcyjnych względem modelowego barwnika (błękitu metylowego) oraz modelowych jonów metali ciężkich (kationów miedzi (II)). Ponadto, celem badań nad grafitopodobnym azotkiem węgla było zbadanie możliwości fotodegradacji oranżu metylowego z roztworu wodnego.Drugim rodzajem badanych adsorbentów były materiały węglowe, w tym utleniony węgiel aktywny utlenione włókna węglowe. Uzyskane materiały poddano analizie, w celu określenia morfologii, właściwości fizykochemicznych oraz adsorpcyjnych względem jonów metali (miedzi (II) i/lub kobaltu (II)). Ostatnie opisane badania obejmowały serię syntez materiałów grafenopodobnych. Proces syntezy polegał na plazmowym rozkładzie n-alkoholi alifatycznych (n-dekanol-etanol) w strumieniu plazmy termicznej. Wykonano także testy badające wpływ dodatku gazowego tlenu na przebieg procesu rozkładu n-dekanolu. Uzyskane materiały szczegółowo zanalizowano w celu określenia morfologii, właściwości fizykochemicznych oraz adsorpcyjnych względem 4-chlorofenolu.W toku badań uzyskano wysokowydajne adsorbenty związków organicznych lub jonów metali. Uzyskane wartości pojemności adsorpcyjnych są porównywalne lub wyższe w porównaniu do innych adsorbentów opisywanych w literaturze.
This dissertation describes the synthesis, physicochemical properties and systematic studies of adsorption performance of two types of adsorbents: (i) materials based on graphitic carbon nitride and (ii) carbon materials. These materials are dedicated to the adsorptive removal of organic compounds and/or metal ions from aqueous solutions.The materials based on graphitic carbon nitride were modified via doping with alkali metals (lithium, sodium, potassium) or alkaline earth metals (magnesium, calcium, strontium, barium). The obtained products were thoroughly studied to determine the morphology, chemical and phase composition, surface chemistry features and adsorption performance in relation to the model dye (methyl blue) and model heavy metal ions (copper (II) cations). Additionally, the studies on graphitic carbon nitride included the photodegradation of methyl orange from aqueous solution. The second type of adsorbents involved various carbon materials, including oxidized activated carbon and oxidized carbon fibers. The obtained materials were examined in order to determine the morphology, physicochemical properties and adsorption performance in relation to the metal ions (copper (II) and/or cobalt (II)). The research included also a series of syntheses of graphene-based materials. The synthesis process included the decomposition of aliphatic n-alcohols (n-decanol-ethanol) in the thermal plasma jet. The tests were also carried out to investigate the effect of oxygen gas addition on the course of decomposition of n-decanol. The obtained materials were thoroughly analyzed to determine the morphology, physicochemical properties and adsorption performance inrelation to 4-chlorophenol.To conclude, efficient adsorbents of organic compounds and metal ions were synthesized. The obtained values of adsorption capacities were comparable or even higher in comparison to other adsorbents described in the literature.