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Photochemical and Photoelectrochemical Water Splitting and CO2 Conversion by Bi and Ti based Oxides

Zeeshan Haider (Graduate School, Sogang University)

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Chapter 2 Abstract: This work describes synthesis of hierarchical nanostructures via hydrothermally transformed titania nanotubes membrane (TiO2-memb). It was firstly etched in hydrogen per oxide to make peroxotitanium solution. This solution was further treated hydrothermally in presence of alkalin...
Chapter 2 Abstract: This work describes synthesis of hierarchical nanostructures via hydrothermally transformed titania nanotubes membrane (TiO2-memb). It was firstly etched in hydrogen per oxide to make peroxotitanium solution. This solution was further treated hydrothermally in presence of alkaline environment (NaOH). Titanate nanostructures were washed with acid solution and annealed to produce hierarchical TiO2 nanostructures. Heating condition of TiO2-memb critically influenced on morphologies of hierarchical TiO2 nanostructures. TiO2-memb as it is or heated under low temperature (< 300 oC) produced three dimensional hierarchical (3DH) TiO2. High temperature (> 300 oC) heated TiO2-memb produced mixed 1D/3D (HHC) hierarchical structures. Variable amount of peroxide and alkali controlled size and morphologies of hydrothermal products. Crystal structure was also tuned to anatase or brookite. Photo catalytic activities were monitored by analyzing rate of H2 production under UV irradiation using pt co-catalyst and methanol as sacrificial donor. Chapter 3 Abstract: In this study we describe surfactant less synthesis of {001} faceted Bismuth Oxychloride (BiOCl) nanocrystals. Octagonal shaped particles were synthesized by simple approach. Mechanism for growth was studied by investigating the role of solvents and trying several precursors of bismuth and iodine. Exposed degree of {001} facet was analyzed with the help of geometrical models and SEM images. Thinner nanosheets had long lifetime of carriers. “I” doping was responsible to narrow bandgap of {001} BiOCl. “I” doping also decreased PL emission signal. Role of charge carriers lifetime on photocatalytic performance as well as photocatalytic mechanism have been discussed. Photonic efficiencies were measured to monitor dye (RhB) degradation process. Photodegradation mechanism was discussed by taking into account both photosensitization of dye and bandgap excitation of photocatalyst. Dye degradation mechanism also studied with the help of probing molecules. Active radicals participated in photocatalysis were identified. Photostability of catalyst and recycling studies were also performed. Chapter 4 Abstract: This work is aimed on design and preparation of modified Bi2WO6 photocatalyst for its application in one pot reaction for photochemical CO2 reduction in gas phase reaction. Synthesis strategy was designed to integrate synergetic effects of oxygen vacancies and making hybrid structure. Ultimate aim is to attract CO2 molecules near catalyst surface and facilitate the multi-electron transfer and proton transfer during artificial photosynthesis reaction. For this purpose Bi2WO6 nanoparticles were prepared by hydrothermal method. Ultra-small TiO2 nano particles were decorated on surface of Bi2WO6 nanoplates to produce Bi2WO6/TiO2 composite with controlled morphology. GO was prepared by modified hummers method for making Bi2WO6/TiO2/rGO ternary heterostructure. Thin overlayer of poly-4-vinyl pyridine (P4VP) and nafion will be coated further on hydrogenated Bi2WO6/TiO2/rGO composite. Preliminary result has shown that the hydrogenated Bi2WO6 has enhanced CO2 reduction, in line with previous findings in literature. Photochemical CO2 reduction by functionalized Bi2WO6/TiO2/rGO will be evaluated further to find out the role of surface functionalization in performance efficiency. Chapter 5 Abstract: This work is aimed on photoelectrochemical (PEC) CO2 reduction using BiVO4 photoanode and Cu/rGO/PEI/nafion as dark cathode. BiVO4 film was chosen due to higher stability. Functional cathodes were fabricated by spin and dip coating. Polymer layers were coated on Cu substrate to enhance the performance of the functional cathode. Both photoanode and functional cathode were characterized by various techniques. PEC performance was checked in two compartment artificial photosynthesis (AP) cell. CO2 saturated KHCO3 was adopted as electrolyte. Photoanode was separated from functional cathodes by nafion membrane. EIS analysis was performed to determine influence of functional layers on charge transfer impedance of the interface during AP process. This study shows PEC and EIS investigations of BiVO4 photoanode and Cu/rGO/PEI/nafion functional cathode in CO2 saturated electrolyte.