Synthesis And Photocatalytic Activity Of Novel Bismuth Oxide-based Composite Photocatalysts

Bi₂O₃,a kind of visible-light-driven photocatalyst,has been widely explored due to its stable photocatalytic activity,nontoxicity and low cost.However,single Bi₂O₃has the problems of wide band gap and high recombination rate of photogenerated electron-hole pairs.In order to broaden the photoresponse range and improve the separation efficiency of photo-induced carriers,three new composite photocatalysts were prepared in this thesis,which are Ca Fe₂O₄/Bi₂O₃,C₆H₅SBr/Bi₂O₃（4-Br/Bi₂O₃）and Ag/4-Br/Bi₂O₃ photocatalyst samples,respectively.Besides,the photocatalytic properties and catalytic mechanisms of the three new photocatalysts were studied by XRD,TEM,UV-VIS and PL and other characterization methods.The results show that Ca Fe₂O₄/Bi₂O₃ photocatalyst has heterojunction structure,which can make the absorption edge of single Bi₂O₃ red shift,reduce the band gap,expand the light response range,and promote carrier transport.The degradation effect of malachite green by Ca Fe₂O₄/Bi₂O₃ sample is higher than that of Ca Fe₂O₄ or Bi₂O₃catalyst.After 240 minutes of irradiation by visible light,the degradation rate of malachite green with the content of 10 mg/L by 10%Ca Fe₂O₄/Bi₂O₃ heterojunction photocatalys can reach 86.9%,while the degradation rates of malachite green by Bi₂O₃ and Ca Fe₂O₄ under the same conditions are only 70.6%and 58.6%respectively.4-Br/Bi₂O₃ photocatalyst sample has a fiber-like structure,which can provide more active sites for photocatalysis and improve visible light adsorption capacity and photocatalytic performance of the photocatalyst.12h-4-Br/Bi₂O₃ composite has the best photocatalytic activity.After 80 minutes of illumination,99.4%of malachite green solution with initial concentration of 35 mg/L can be degraded by 0.5 g/L12h-4-Br/Bi₂O₃,which is much higher than that of pure Bi₂O₃（4.4%degradation rate）.This is due to the enlargement of the light response range and the improvement of carrier separation efficiency in composite materials.The loading of Ag further enhanced the photocatalytic activity of 4-Br/Bi₂O₃.After 80 minutes under visible light,the degradation rate of 15 mg/L methyl orange by 0.5 g/L Ag/4-Br/Bi₂O₃ composite photocatalyst is 89.8%,while the degradation rates of Bi₂O₃ and 4-Br/Bi₂O₃ are only 5.1%and 63.1%,respectively.The reasons for the enhancement of photocatalytic activity of Ag/4-Br/Bi₂O₃ composites are as follows:first,Ag can be used as an electron trap to capture photogenerated electrons,which is helpful for the separation of electron-hole pairs;second,the plasma resonance effect of Ag improves the light utilization efficiency of the composites.In short,the three composite photocatalysts designed and synthesized for the first time can make full use of visible light,prolong the lifetime of photogenerated electron-hole pairs,and thus improve the photocatalytic activity.