Study On The Preparation Of Multilayer TiO₂/BFO Thin Films And Photocatalytic Performance

The photocatalysis-based wastewater treatment system has become the most promising technology in the field of environmental protection with its advantages of high efficiency,simplicity and low cost.As a well-known semiconductor photocatalyst,titanium dioxide（TiO₂）has unique properties,such as non-toxic,low cost,and high stability,and plays an excellent role in degrading photocatalytic pollutants and photo-electrochemical solar cells.However,due to the large band gap of TiO₂ and the high ineffective recombination rate of electron-hole pairs,the utilization of visible light is low,which limits its use in the photocatalytic degradation of organics.In order to improve the photocatalytic activity of TiO₂ thin film materials in the visible light range and increase the number of repeated uses of the catalyst to meet the requirements of wastewater treatment applications based on visible light photocatalysis,this paper proposes the electron beam evaporated titanium dioxide/bismuth ferrite（BFO）multilayer composite photocatalytic structure.Firstly,in order to determine the best film preparation parameters,TiO₂ and BFO monolayer films were prepared under different vacuum pressure and deposition powers,and then annealed at the temperature of 450℃-850℃.The structure,surface morphology and other properties were characterized,the characterization results show that TiO₂ thin film has improved crystallinity when the annealing temperature of TiO₂is 550℃-650℃,the deposition pressure is 5.5×10^-4 Pa,and the power is 4.7 kW.In the case of co-evaporated BFO,the purest BFO phase with rhombohedral R3c structure were obtained when the annealing temperature is 550℃-650℃,the deposition pressure is 2.4×10^-4 Pa,and the power of the Bi₂O₃ and Fe target are 4.7 kW and 3.5 kW,respectively.Secondly,multilayer TiO₂/BFO and BFO/TiO₂ films were prepared under the optimal parameters determined after the monolayer film was prepared.In order to compare the experiment effectively,the total deposition time remains unchanged.Finally,the monolayer TiO₂,monolayer BFO,multilayer TiO₂/BFO and multilayer BFO/TiO₂ films have been tested for visible light photocatalysis experiments.After irradiating with 350W xenon lamp for 4 hours,their degradation rates of methylene blue were 67%,84%,87%and 91%,respectively.The results show that the multilayer structure improves the photocatalytic performance of TiO₂ in visible light.The film prepared by electron beam evaporation is smooth and has strong adhesion,which has certain applications in photocatalysis-based wastewater treatment.