The Photocatalytic Performance Of Bismuth Oxyiodide Composites

Photocatalysis is a novel wastewater treatment technology driven by solar energy with photocatalyst as a carrier.Bi5O7I is a new kind of bismuth oxyhalide photocatalytic material.Its unique layered structure can accelerate the carrier transport and improve the photocatalytic activity of the material.However,Bi5O7I has a wide band gap and the photocatalytic activity almost only occurrs in the ultraviolet light region,which restricts the effective utilization of the visible light.Moreover,the electron-hole pairs easily recombine and the catalytic activity of Bi₅O₇I is still not satisfactory.Therefore,in order to solve the above two weaknesses,three methods?metal doping,conducting polymer modification and composite with semiconductor material?were used to modify Bi5O7I.The dyes as simulated pollutants,the photocatalytic performance of modified composites under visible light are studied.The main conclusions are as follows:1.Ag-doped Bi₅O₇I composites?Ag/Bi₅O₇I?were prepared via a simple one-pot hydrothermal method.Ultraviolet-visible diffuse reflectance spectra?DRS?showed that the composites exhibited better light utilization than pure Bi₅O₇I.The absorption edge of visible light shifted from 425 nm to about 500 nm,and there was stronger absorption in the whole range of visible light to near-infrared light.Ag/Bi5O7I composites possessed a higher photocatalytic activity than Bi₅O₇I on the degradation of rhodamine B?RhB?and methyl orange?MO?under visible-light irradiation???420 nm?.When the content of Ag was 1.0%,the degradation efficiency of the Ag/Bi5O7I composites toward RhB and MO reached the maximum value.The degradation efficiency toward RhB was 99.7%within 20 min and the reaction rate constant?k?was 0.1816 min^-1 which was about 20.2 times than Bi₅O₇I.For degradation of MO,the degradation efficiency was 80.6%within 100 min and the k value was 0.0159 min^-1 which was about 7.6 times than Bi₅O₇I.After three cycles of experiments,the degradation efficiency toward RhB could still reach up to 89.5%.2.Polyaniline?PANI?decorated Bi₅O₇I composites?Bi₅O₇I/PANI?was prepared by chemical oxidation and solvothermal method.The DRS results showed that the introduction of PANI could significantly extend the light absorption edge of Bi₅O₇I from 425 to about 450-480 nm,and the absorption intensity was larger in the whole visible light range?400-800 nm?.The experiment results showed that all the composites exhibited the higher degradation efficiency than Bi5O7I.When the loading of PANI was 5%,the catalytic efficiency was the best.For degradation of RhB,the degradation efficiency was 84%within 60 min and the k value was 0.0305 min^-1which was about 3.9 times than Bi5O7I.After three cycles of experiments,the degradation efficiency could still reach up to 75%.3.The novel composites of Bi₅O₇I modified with metal organic framework photocatalysts?BOI/MIL?was prepared by a solvothermal method.DRS results showed that the light absorption edge of the composites extended to 450-530 nm and the absorption intensity was larger in the visible light range 400-600 nm.The experiment results showed that all the composites exhibited the higher degradation efficiency than Bi₅O₇I.When the weight ratio of MIL-53?Fe?was 3%,the catalytic efficiency was the best.For degradation of RhB,the degradation efficiency was 99.8%within 60 min and the k value was 0.0992 min^-1 which was about 12.7 times than Bi₅O₇I.After three cycles of experiments,the degradation efficiency could still reach up to 93.5%.