Modification And Photocatalytic Performance Of TiO₂ And Bi₂WO₆ Photocatalytic Materials

With the steady exploitation and overuse of fossil fuels,energy crisis and environmental pollution are becoming increasingly serious.Photocatalysis to convert clean low-density solar energy into high-density chemical energy is considered to be one of the most promising technology to alleviate energy and environmental problems in the 21st century.TiO₂ and Bi₂WO₆ are considered to be the typical UV-and visible-light responsive semiconductor materials,they have the disadvantages of quick recombination of electron-hole pairs and poor solar light harvesting ability,which hamper the widespread practical applications.In this thesis,we tried to improve the photocatalytic activity of TiO₂ and Bi₂WO₆ by modification,and the strategies are as follows:Doping high energy TiO₂ nanocrystals with silicon:Si-doped high energy TiO₂ nanocrystals with exposed?001?facets was prepared by hydrothermal reaction and calcination,using titanium tetrachloride?TiCl₄?,tetraethyl orthosilicate?TEOS?,and sodium fluoride?NaF?as titanium source,dopant and shape-direction reagent,respectively.The photoreactivity of the photocatalyst was evaluated by degradation of X3B dye and hydrogen production.Results showed that the photoreactivity of high eneryg TiO₂ nanocrystals were greatly improved after Si-doping.At the weight ratio of F:Ti=3:1,the reactivity of Si-doped TiO₂ nanocrystals improved 4.6 times and hydrogen production rate increased 21 times,respectively.The enhanced photoreactivity of Si-doped high energy TiO₂ nanocrystals was attributed to the improved light-harvesting ability,increased BET surface areas and retarded recombination of photo-generated electron-hole pairs.Formation of core-shell structured Bi₂WO₆@Bi₂S₃ heterojunction:2D core?shell structured Bi2WO6@Bi2S3 nanoplates were prepared by calcination of a mixture of Bi₂WO₆ and a certain amount of Na₂S·9H₂O at 350°C for 2 h.The reactivity of the resulting photocatalyst materials was evaluated by photocatalytic degradation of X3B,an anionic dye,under visible light irradiation??>420 nm?.As the amount of Na2S·9H2O was increased to 1.5 g,the degradation rate constant of X3B sharply increased by 16.5 times.The enhanced photocatalytic activity of Bi₂WO₆@Bi₂S₃ was attributed to the photosensitization of Bi₂S₃,which greatly extended the light?responsive range from the visible to the NIR,and the formation of a heterojunction,which retarded the recombination rate of photogenerated electron?hole pairs.However,further increases in the amount of Na2S·9H2O resulted in a decrease of the photocatalytic activity of the Bi₂WO₆@Bi₂S₃ nanoplates owing to the formation of a photo?inactive NaBiS₂ layer covering the Bi₂WO₆ surface,Which occupys the photocatalytic activity sites.