Microstructural Regulation,Properties And Photo-produced Electron Transfer Mechanism Of The Titanium Dioxide With Special Morphologies

Energy shortage and environmental pollution have been two major problems affecting the development of human society.Therefore,the development of renewable clean energy is an important means to solve the problems of energy and environmental.The photocatalytic technology based on photocatalytic materials can realize the efficient conversion of solar energy to chemical energy,which is a promising way to solve the problems of energy shortage and environmental pollution.As one of the classical photocatalytic materials,TiO₂ has potential applications in fuel cells,solar cells,and photocatalysis for its advantages of low toxicity,high chemical stability and diverse preparation methods,and has aroused widespread attentions from researchers at home and abroad.Because titanium dioxide can only absor ultraviolet light（a small part of the sunlight）,it is of great practical significance to modify TiO₂ in order to obtain a TiO₂-based photocatalyst with excellent properties.It is found that the photocatalytic performance of TiO₂ semiconductor can be improved in a large extent by microstruactual-regulation of TiO₂with special morphologies.In this thesis,three new photocatalysts based on titanium dioxide were successfully prepared by hydrothermal method and solvent thermal method.The main contents are as follows:A new type of nanohybrid(TNTs-Cr³⁺-DPyE)was prepared by the coordination of 1,2-di（pyridine-4-ly）ethyne（DPyE）with chromium ions(Cr³⁺)implanted in TiO₂ nanotube（TNTs）.The role of Cr³⁺in the nanohybrid was studied by UV-vis spectrum and photocurrent response in detail.It was found that the Cr³⁺implanted in the TNTs can enhance the interaction between TNTs and DPyE,which effectively improved the electron transfer of TNTs,and broadened the light absorption range of the system.Subsequently,the photoelectric properties of TNTs was greatly improved.It provids a new idea for the design and preparation of highly active TNTs-based photoelectric materials.With Cu nanoparticles（Cu NPs）as a linker between TiO₂ microsphere（TiO₂ MS）and 5,10,15,20-meso-tetra（4-carboxyphenyl）porphyrin（TCPP）,a novel nano-micro hybrid（TiO₂MS-Cu-TCPP）was prepared via electrostatic interaction and coordination interaction.It was found that the visible light absorption and electron transfer of TiO₂ MS can be greatly improved by bridging TiO₂ MS and TCPP with Cu NPs.When the TiO₂ MS-Cu-TCPP was employed as the photocatalyst for hydrogen evolution,it exhibited higher activity and stability than that of the TiO₂ MS,the TiO₂ MS-Cu and the TiO₂ MS-TCPP,TiO₂MS-Cu-CuTCPP and TiO₂ MS-TCPP-Cu.The photocatalytic activity was enhanced for about6 times with respect to that of the pristine TiO₂ MS.A wide light absorption range,more active sites and efficient electron transfer with Cu NPs as the linker and cocatalyst can profitable for the improved activity of the target product.Therefore,the TiO₂ MS-Cu-TCPP nano-micro hybrid showed high and stable photocatalytic activity,which further indicated that the interfacial modification played an important role in regulating the photocatalytic activity of semiconductors.This result provides a theoretical and experimental basis for the construction of semiconductor photocatalyst with special structure.TiO₂ mesoporous microspheres（TiO₂ MS）implanted with well dispersal and small-sized Cu nanoparticles（TiO₂ MS-Cu）were obtained by in-situ reduction of the loaded copper species on the mesoporous TiO₂ microspheres and subsequent etching with moderate alkali.The morphology and structure of the composites were studied in detail by electron microscopy,UV-vis absorption spectroscopy and XPS.It was found that the small-sized Cu nanoparticles implanteded into the hybrid mainly existed in the form of Cu⁰ with high dispersibility and stability.Furthermore,the influence of the special Cu nanoparticles on the photocatalytic hydrogen production of TiO₂ microspheres was studied in detail.And the mechanism of electron transfer was explored by transient photocurrents and electrochemical impedance spectrum.It was found that the TiO₂ MS-Cu hybrid possessed higher photocatalytic hydrogen production and good stability compared with those of the P25-Cu.It indicated the advantages of controlling the growth of Cu nanoparticles by mesoporous TiO₂microspheres:it is the small-sized,monodispersal Cu nanoparticles as the active site for photocatalytic hydrogen production.Therefore,the electron transfer rate not only can be significantly accelerated,but also the absorption of TiO₂ can be improved and the overpotential of hydrogen evolution can be reduced to some extent.Thereby,the photocatalytic activity for hydrogen production over the TiO₂ MS-Cu microsphere hybrids was improved.