Preparation And Properties Of TiO₂ Based Z-scheme Photocatalytic System

Currently,energy crisis and environmental pollution have still been two major problems for human society.As a typical catalyst,TiO₂ is well-known because of its advantageous properties including inexpensive,chemically stable,and environmental-friendly,etc.However,TiO₂ suffers from some intrinsic drawbacks including activation only by ultraviolet light and fast recombination of photon-generated electron-hole pairs,which hinder the practical applications of pristine TiO₂.To date,continuous attempts have been made to extend the light absorption range and improve the charge separation efficiency,such as chemical doping,construction of heterostructures and so on.Z-scheme is a kind of notable heterojunction and the mechanism is similar to the natural photosynthesis,which has been the focus of considerable attention.In this thesis,N/Ti³⁺-TiO₂/BiOBr（NT-TB_x）,N/Ti³⁺-TiO₂/Bi₂WO₆（NT-TBW_x）and Cu₂O/Cu/C-TiO₂（CCT-x）heterojunctions were constructured and invesgated.The main results are summarized as following:N/Ti³⁺co-doping multiphasic TiO₂/BiOBr heterojunctions（NT-TB_x）were prepared by one-step in situ hydrothermal process.The as-prepared samples are composed of anatase and rutile TiO₂ as well as BiOBr nanoplates which are intercalated in TiO₂ uniformly.The codoping of N/Ti³⁺and the coupling of BiOBr both decrease the band gap of TiO₂ and furtherly enhance its visible light response.The as-prepared samples exhibit better sonocatalytic activity for the degradation methylene blue,Rhodamine B,and p-Nitrophenol compared with pure TiO₂ and N/Ti³⁺co-doping multiphasic TiO₂.Especially,the highest degradation ratio of methylene blue is achieved for NT-TB_0.3 up to 98.2%after 50 min under ultrasonic irradiation.The high sonocatalytic activity can be kept after four cycles with the tiny decline,indicating the excellent stability of the as-prepared samples.Furthermore,superoxide radical（·O₂^-）is demonstrated to be the main reactive species for the degradation of MB under ultrasonic irradiation.The result confirms the heterojunction between TiO₂ and BiOBr can be explained by Z-scheme.N/Ti³⁺co-doping multiphasic TiO₂/Bi₂WO₆ heterojunctions（NT-TBW_x）were prepared through a simple hydrothermal process.The crystal phase,morphology,component,and optical properties of the heterojunctions were characterized respectively.TiO₂ nanoparticles distribute among Bi₂WO₆ nanoplates with good dispersity.A red shift of light absorption edge is observed for the composites compared with TiO₂ and NT-TiO₂.The NT-TBW_xsamples exhibit better catalytic activity for methyl blue degradation compared with pure TiO₂ and NT-TiO₂ under visible light irradiation,ultrasound irradiation and light/ultrasound irradiation.Additionally,the degradation experiments for Rhodamine B,p-nitrophenol and levofloxacin also further verify the effectiveness of the samples in the degradation of other pollutants.A ternary composite of Cu₂O/Cu/C-TiO₂ nanotube arrays were prepared by in-situ burning of TiO₂ nanotube arrays in Cu（CH₃COO）₂ ethanol solution.During the burning process,the crystallization of the TiO₂ nanotubes and the conversion of Cu（CH₃COO）₂ to Cu₂O/Cu occur jointly.The photoelectrochemical measurements of the resultants indicate that Cu₂O/Cu/C-TiO₂ nanotube arrays exhibit better visible light response and photoelectrochemical performance compared with C-TiO₂ nanotube arrays.The improved photoelectrochemical properties are related to the close interfacial contact between Cu₂O/Cu and C-TiO₂ as well as the localized surface plasmon resonance of Cu in the ternary composites,which can broaden the range of light response and enhance the effiency of charge separation,respectively.