Preparation And Characterization Of Modified TiO₂ Photocatalyst With Visible-light Photocatalytic Performance

Environmental pollution and energy crisis are the two problems that we urgently need to solve.Photocatalytic technology can effectively degrades environmental pollutants and prepares hydrogen energy,so it has attracts attention in a wide range of academic disciplines.In numerous photocatalysis,TiO₂ has been widely studies for its advantages of stable chemical properties,safety and non-toxicity,excellent photocatalytic performance.However,TiO₂ has a large band gap?3.2 eV?,which can only absorbs ultraviolents light with a wavelength of less than 380nm.In addition,it has a high photogenerated electron-hole recombination rate and low quantum efficiency,which seriously limits the application of TiO₂in practical applications.Therefore,we try to modify the TiO₂ to expand the light response range to improve the utilization of solar energy and reduce the photo-electron-hole recombination rate.To solve these problems,the following work has been done in this thesis:?1?Commercial TiO₂ is modified with a simple and economical vacuum activation method.After vacuum activation,TiO₂ crystalline structure,morphology and size did not change significantly.By controlling the temperature and time of vacuum deoxidation,the ratio of oxygen vacancies in the bulk phase to oxygen vacancies in the surface is controlled so as to improve the photocatalytic activity.The results showed that TiO₂ with 300?vacuum treatment had the best photocatalytic activity,and the degradation rate of Rhodamine B reached 94%after 240 min of visible light irradiation.The XPS,UV-Vis diffuse reflectance,Raman spectroscopy and other analysis proved that oxygen vacancy can be generated on the surface of TiO₂ by vacuum activation.During the test of photocatalyst activity of cycling powder and vacuum P25 storage for 3 months,it suggested no significant reduction in photocatalyst activity.These results indicated that vacuum P25 has good reusability and storage stability.We also proposed to establish a mechanism model of oxygen vacancies to enhance photocatalytic activity:oxygen vacancies can form an intermediate energy level between the conduction band and the valence band,narrowing the band gap of TiO₂,helping to expand the photo-responsive range of TiO₂,the transfer rate of the carrier and can effectively improved the photocatalytic activity.?2?The results of XRD and EPMA show that Fe/N-doped anatase phase TiO₂ is synthesized by hydrothermal,and oxygen deficiency is introduced into the Fe-N-TiO₂ sample by vacuum activation treatment.It was found that the photocatalytic activity was Fe-N-TiO₂?300?,3h?>Fe-N-TiO₂>N-TiO₂>Fe-TiO₂.The results of UV-Vis diffuse reflectance spectroscopy showed that the band gap of TiO₂ has been obviously reduced after doping and Vacuum activated,and the absorption range of visible light wided.EIS and photocurrent measurements show that after co-doping,carriers are more easily separated and transferred to the surface of the catalyst.The composite rate is lower,and the photocatalytic activity is better.This is mainly because of the synergetic effect between iron-nitrogen co-doping,which narrows the bandgap of Fe-N-TiO₂ to 3.04 eV due to the formation of the intermediate bandgap and the electron capture of Fe³⁺/Fe²⁺traps to improve photocatalytic efficiency.In addition,the vacuum vacancy level will be introduced to reduce the bandgap of TiO₂ by vacuum treatment and increase the photocatalytic activity.?3?Preparation of N-TiO₂ by one-step solvothermal method.The N-TiO₂ was prepared under solvothermal conditions at 180°C and the product was a single uniform anatase phase.At 60min visible light,the degradation rate of methyl orange reached 98%.UV-Vis test showed that N doping effectively reduced the band gap of Ti O₂.The mixed state of O 2p and N 2p makes the bandgap of TiO₂ narrow,which promotes the absorption of the catalyst in the visible region.EIS and photocurrent tests show that N-TiO₂ has high electron-hole separation efficiency and low recombination rate.The method is simple and easy to operate,does not require subsequent heat treatment,reduces production costs,and produces a product with high visible activity.