Construction,Photocatalytic Hydrogen Production And The Mechanism Of Heterojunction Nanomaterials Based On TiO₂

Recently,with the rapid development of the society,traditional energy cannot meet the requirements of continuous industrial growth,energy and environment crisis have become the focus of world attention.Although much effort have been made in the development of new renewable and realistic sources such as hydroelectric power and wind power,their further applications in industry are impeded by geographical and ecological factors seriously.Therefore,the application of solar energy,which is a powerful,affordable,and renewable energy source,for energy conversion and pollutant elimination,is signaficant.Semiconductor photocatalysis,as a most promising candidate to solve these problems,has been paid great attention because its ability to directly take advantage of solar energy for producing solar fuels such as hydrogen?H₂?and organic fuel?CH₄,CH₃OH?by a“green”technology.However,there are many defects limiting the application of the photocatalysts with wide bandgap,such TiO₂.The wide band gap of semiconductor photocatalysts,leading to poor light absorption,and the low quantum yield caused by the rapid recombination of photogenerated electrons and holes are still challenges to enhancing the photocatalytic efficiency to meet practical application requirements.It is urgent to construct a photo-synthesis heterostructure system with efficient light utilization and electron-hole separation.Although the photocatalytic technology based on TiO₂ has been developed for many years,new materials and new mechanisms of photoelectric conversion have been continuously injecting new vitality and opportunity in this field.Inspired by the electron transport layer and hole transport layer of the perovskite solar cell,it is an effective way to construct effective hole and electron transport pathways to capture photo-generated electrons and holes,for the purpose of suppressing the recombination of photoinduced charge carriers.In this work,we used noble metal,heterostructure construction to modify TiO₂ nanofiber photocatalyst,and explained the path of photoinduced electrons transfer and the decomposition of water based on band structure.The composition and structure of the photocatalyst were confirmed by some basic characterizations.At the same time,photocurrent,impedance?EIS?and photocatalytic decomposition of water were used to study the photoelectric conversion efficiency of the samples.More importantly,we use ultraviolet photoelectron spectroscopy?UPS?to investigate the band structure of the heterostructure and photoinduced electrons transfer route.The main research contents as follow:?1?The TiO₂/WO₃ heterojunction nanofibers co-modified with Au nanoparticles and Pt nanoparticles were prepared by electrospinning technique and calcination method,and their photoelectric properties and photocatalytic efficiency were studied.The surface plasmon resonance effect?SPR?of Au nanoparticles enhanced the absorption and utilization of visible light and improved the quantum efficiency.In addition,the formation of Z-scheme TiO₂/WO₃ heterojunction promoted the trapping of photoinduced holes,and the schottky barrier at the interface of TiO₂/Pt facilitated the transfer of photoexcited electrons,which effectively suppressed the recombination of photogenerated charge-carriers and increased the photocatalytic hydrogen evolution.Otherwise,the photocatalysts could be effectively separated and recycled based on the nanofiber network structure.?2?In order to replace expensive noble metals and obtain photocatalysts with larger specific surface area,a heterogeneous heterojunction composite containing a few-layer MoS₂ nanosheets grown on the surface of TiO₂ nanofibers as a template was prepared by combining electrospinning and hydrothermal methods.The narrow bandgap of MoS₂ wass attributed promoting light-harvesting efficiency of visible light,and the photocatalytic performance was enhanced greatly because of more edge structures,active sites of Mo S₂ nanosheets,and the heterojunction between TiO₂ and MoS₂,where MoS₂ served as a“electrons collector”,which promoted the transfer of photo-generated electrons.In addition,we studied the band bending and electrons transfer paths at the interface of TiO₂/MoS₂ heterojunction,which provided a theoretical basis for the study of semiconductor heterostructures.?3?On the basis of previous work,we constructed a double heterostructure composite consisting of Z-scheme TiO₂/WO₃ heterojunction modified by vertical few-layered MoS₂ nanosheets.The results showed that in the double heterojunction structure,WO₃ served as a“holes collector”and MoS₂ served as an“electron collector”,which transfered photoinduced electrons and holes at the same time,suppressing the recombination of photogenerated electrons and holes.In addition,the large specific surface area and more active reaction sites of MoS₂ were beneficial to enhance the response of visible light,thus improving the hydrogen production by multiple channels.