Preparation And Photocatalytic Properties Of WO <3> And Its Composite Semiconductor Catalysts

In the high speed of today’s society, it is the New Era with high demand of energy conservation and environmental protection. Semiconductor photocatalytic technology, because of its unique properties, using the inexhaustible solar energy resources to promote chemical catalytic reactions, has been widely applied in many areas. However, individual semiconductor photocatalysts have low solar energy utilization efficiency, high photogenerated electronic-hole recombination rates and low quantum efficiency which restrict its application in industries. Therefore, it makes us more resonable to have a in-depth study of traditional semiconductors, designing high quality of heterojunction interface and hierarchical structures in fabrication of multicomponent semiconductors, especially by one-pot reaction. Tungsten oxide（WO₃） is known as a familiar semiconductor photocatalyst has been received much attention due to its small band gap（ 2.5 to 2.8 e V）, capture capability of nearly 12% solar spectrum and high oxidation power of photogenerated holes. WO₃ is widely used in adsorption, catalysis, energy storage and sensitive devices, etc. Hence, in view of how to export effective electronics, around the semiconductor photocatalyst WO₃, our research work is mainly consists of the following several aspects.（1） WO₃ semiconductor photocatalyst synthesised with controlled inner/surface oxygen vacancy with high photocatalytic water oxidation performanceBecause WO₃ is easy to have valence change and reversible. Through conventional hydrothermal synthesis method, design a direct synthesis of WO₃ with W⁵⁺, calcine the catalysts in the air with different time, different temperature, study the content of inner and surface W⁵⁺, test the photocatalytic properties of water oxidation. The results show excellent performance, which can be ascribed to the proper atomic ratio of W⁵⁺/W⁶⁺ out of the catalyst surface. Photogenerated electrons transfer to the oxygen vacancy which act as capture trap of charge transfer. With Enhanced seperation efficiency of electron-hole pairs, it makes the catalysts show good oxidation properties with visible light irradition. Further, instead of the traditional co-catalysts, noble-metals such as Pt Ox, Ru O₂, and form W⁵⁺ to the catalyst’ surface through H₂ reduction processing, our method is simple, convenient and lower costs with stability.（2） One-pot synthesis of heterojuncted Ti O₂/WO₃ composites with tailored hierarchical yolk-shell structure for photocatalysisYol k-shell semiconductors with special structure is widely used among different areas. However, most of the researches are focused on single component. High quality of heterojunction interface and hierarchical structures are highly desired in fabrication of multi-component semiconductors, especially by one-pot reaction. In this work, we explore a general idea of using ethylene glycol as a connection agent to form bridge-linked metal-organic complexes（BMCs） and induce self-assembly of different metal-oxide nanocrystals into hierarchical yolk-shell structure. The TiO₂ nanocrystals highly dispersed on the surface of WO₃ nanorods forming enhanced heterojunction interface. This concept successfully conducts the one-pot synthesis of hierarchical crystalline Ti O₂/WO₃ composites with tailored interior space from solid, core-shell, yolk-shell to full hollow structure. This idea can expands to synthesis TiO₂/V₂O₅,TiO₂/ZrO₂ yolk-shell composites. With urchin-like prickly shell, yolk-shell interior space and heterojunction interface, these unique crystalline TiO₂/WO₃ composites demonstrate effective synergistic effect and high catalytic performance toward photocatalytic degradation of acetaldehyde（g）.（3） Two-dimensional WO₃ nanosheets with Solid-State Z-Scheme system applied to photocatalystic water splittingFollowing the first part of the research, WO₃ with nanoparticle structure has higher electronic-hole recombination rate and lower noble metal deposition rate then those two-dimensional（2D） catalysts. Therefore, We designed and synthesized 2D WO₃ nanosheets with hydrothermal method. The results show that structure is stable with have good carrier mobility, it can reduce electronic-hole recombination rate. Through spin-coating process, on one hand, to solve the shortcoming of powder catalyst difficult to recycle. On the other hand, using photoelectric catalysis technology, build a Solid-State Z-Scheme system, build p-n heterojunction system, effectively improve the efficiency of the separation of electrons and holes. Combine 2D WO₃ nanosheets films with proper hydrogen production materials to realize pure water splitting research.