Porous Bismuth Vanadate And Titania Materials: Microstructure-Tuning Of Their Functions

Semiconductor has been widely applied in our daily living and industrial producingdue to its peculiar physicochemical properties. More importantly, its regulated functionprovides more possibilities and hopes for investigation and application. So far, enormousefforts have been devoted to researching the design synthesis and function optimization ofsemiconductor materials. It has been demonstrated that macro-function of semiconductorcan be developed or enhanced by microstructure-regulating. Therefore, to clarify themicrostructure-regulating mechanism of macro-function for semiconductor is needed forthe development of functional semiconductor materials. Bismuth vanadate （BiVO₄） andtitania （TiO₂） are two kinds of typical semiconductors. BiVO₄with narrow band gap isregarded as a novel and potential visible-light photocatalyst for photodegradation oforganics and water splitting. In addition, TiO₂has been intenstively studied because of itslow cost, nontoxicity, acid-base resistance and outstanding chemical and physical properties,which are of interest for such applications as pigments, catalysts, gas sensors,photocatalysts, optics and photovoltaic cells.This thesis focuses on the controllable preparation of porous BiVO₄and TiO₂materialsand the microstructure-regulating of photoelectric and photocatalytic functions. This studynot only makes the mechanism of microstructure-regulating function be more clear, but alsoprovides more valuable basis and reference for the development of new function semiconductor materials.First, Macroporous V₂O₅-BiVO₄composites with a heterojunction structure have beensuccessfully synthesized under the assistance of colloidal carbon spheres. The as-preparedcomposite exihibits enhanced photocatalytic performance for MB degradation. Thebehavior of photogenerated charges in samples have been investigated through surfacephotovoltage spectroscopy （SPS） and transient photovoltage （TPV） techniques. It isdemonstrated that the formation of heterojunction structure in the V₂O₅-BiVO₄compositeplays an important role in the kinetic behaviors （including separation, transport, andrecombination） of photogenerated charges. The heterojunction greatly increases theseparation extent and the lifetime of the photogenerated charges in the composites.Second, a vanadium-doped porous titania rich in active hydrogen （V-TiO₂（H^*）） hasbeen sucessfully prepared through photo-induced method and demonstrated to be anefficient and green reductant with renewable capacity. This V-TiO₂（H^*） material caninstantly （<10s） and selectively reduce nitroarenes to aminoarenes under ambientcondition without catalysts. It has been demonstrated that V-doping effectively increases theH^*content in TiO₂and then improves the reduction capacity of V-TiO₂（H^*） reductant.Third, a porous titania with heavily self-doped Ti3+species （Ti3+-TiO₂） has beenprepared though a novel “self-doping” strategy. The resulting material can be used as anefficient room-temperature gas-sensing material for CO detection with high selectivity andfast response/recovery. The self-dopant （Ti3+） in the titania material has proved to decreasethe resistance of TiO₂on the one hand, and to increase the chemisorbed oxygen species,thus enhancing the surface reaction activity on the other. This “self-doping” strategyovercomes simultaneously both difficulties of “high resistance” and “low reaction rate”,which have always been encountered for room-temperature operation ofsemiconductor-based sensors.Finally, a room-temperature spontaneous crystallization of porous amorphous titania tohigh-surface-area anatase TiO₂material was observed in the absence of any solvents,additives and catalysts. The as-obtained anatase TiO₂material was shown to serve as anefficient photocatalyst for H2evolution reaction, and its activity was more than twice that ofthe benchmark P25TiO₂. This outstanding performance can be attribute to the room-temperature crystallization method which not only obtain advantageous crystallinephase for photocatalysis, but also maintain the most pore structures and large BET surface...