Study On Controlled Synthesis And Oxidation Perfomance Of Bi-based Photocatalysts

In recent years,because of the special layer-to-layer alternate structure,strong oxidizing property shown in the reaction and more appropriate fixed band gap breadth,Bi-based semiconductor materials have come to the fore in multiplex catalysts.It is expected to replace precious metals in more and more practical applications.However,due to its wide band gap,the charges are not easily separated,and poor adoption proportion of visible light,etc.,the application of this series of photocatalysts in the optical field is limited.For this reason,by modifying it,it is hopeful to enhance the parting efficiency of its electron-hole pairs,and at the same time raise its comprehensive forthputting efficiency in daylightt,so as to further improve its oxidability.The following research has been done for the above aspects:（1）Bi₂O₂CO₃ with different morphologies was prepared by hydrothermal synthesis method,and the indoor volatile organic compounds,mainly paraformaldehyde,were oxidized and removed under simulated sunlight.Within 10minutes,the best removal efficiency of flower-shaped bismuth subcarbonate on paraformaldehyde is 99.173%,and the performance is stable in twenty cycles.At the same time,it also showed outstanding removal effect to toluene and benzene,after three hours of light,the oxidation rate reached 91.89%and 80.71%,respectively.This is attributed to the tightly self-assembled flower-like structure of bismuth subcarbonate,making the specific surface area and pore structure are significantly subjoined,and increases the number of exposed active sites,and thus facilitate the transfer,adsorption and reaction of gaseous pollutants on the surface layer of the material.Owing to the compact assembly,the flower-like structure is not easy to disperse,thereby greatly improving the stability of the catalyst.On the other hand,the band gap narrows and the light absorption wavelength shifts to the visible light region,which enhances the photocatalytic effect of the catalyst in the visible light region.（2）In order to further enhance the oxidizability of bismuth subcarbonate materials,the F-Bi₂O₂CO₃/MnO₂composite phase was synthesized through a simple composite method with bismuth subcarbonate as the substrate.In addition,benzene,which is the most difficult to be broken in VOCs,is used as the elimination substrate to improve the oxidation of bismuth subcarbonate.After three hours of visible light irradiation,the highest efficiency of F-Bi₂O₂CO₃/MnO₂is 95.72%,and the degradation rate and efficiency are higher than those of F-Bi₂O₂CO₃and MnO₂pure phases.This is due to the formation of a"Z"type heterojunction after the recombination of F-Bi₂O₂CO₃and MnO₂,which accelerates the detachment of electron-cavity couples,thereby strengthening the catalytic activity.（3）The Bi₂O₂CO₃/Bi₂O₃ composite phase was prepared by a two-step thermal synthesis method.The mixing ratio of the composite phase was changed by adjusting the calcination temperature.And beneath the cover of visible light,the elimination of the kind of fluoroquinolone antibiotics,mainly ciprofloxacin,was carried out with different ratios of composite phases.Among them,the composite phase synthesized at 400℃calcination temperature has the best degradation effect.After 3 hours exposured to visible light,the degradation degree of CIP can reach 94.87%,which is about 1.3 times than that of pure Bi₂O₃and 7.9 times than the degradation of pure Bi₂O₂CO₃.At the same time,the composite also showed remarkable removal effects to ofloxacin,levofloxacin,norfloxacin,and pefloxacin.After three hours of light,the degradation efficiency was 83.6%,78.1%,86.6%and 76.9%,respectively.This is due to the type Z heterojunction formed between Bi₂O₂CO₃and Bi₂O₃,which improves the efficiency of charge separation.