Preparation Of Bismuth Molybdate Based Photocatalyst And Its Performance In Reducing Cr（Ⅵ）

Bismuth molybdate has been widely studied because of its narrow band gap（2.6-2.7 e V）,stable chemical properties,simple synthesis conditions and adjustable morphology and properties.It has been widely used in the fields of industrial wastewater degradation,photocatalytic hydrogen production,carbon dioxide reduction and antibiotic degradation.However,single bismuth molybdate has the disadvantages of easy electron hole recombination and low quantum efficiency,which limits its photocatalytic activity.In order to overcome these defects,researchers have proposed many strategies,such as element doping,heterostructure construction and morphology control.In this paper,a patterned bismuth molybdate microsphere was prepared by solvothermal method.Rare earth cerium（Ce）doped bismuth molybdate microsphere and Bi/Bi₂MoO₆ composite photocatalyst were designed by one-step solvothermal method,and their photocatalytic activity was evaluated by their photocatalytic reduction of Cr（VI）.The relevant test results show that the two modification methods can effectively improve the kinetic behavior of photogenerated carriers and broaden the light absorption range of photocatalyst,So as to improve its photocatalytic activity.Firstly,a series of bismuth molybdate microspheres were prepared by solvothermal method with ethylene glycol and isopropanol as solvents.Under the irradiation of xenon lamp,bismuth molybdate prepared with different solvent ratios showed different photocatalytic activities for hexavalent chromium solution.Among them,when the volume ratio of ethylene glycol to isopropanol was 1∶3,it showed the highest photocatalytic activity（the reduction rate was about 84.6%）.The phase structure,microstructure and optical properties were analyzed by relevant characterization.Secondly,in order to improve the photocatalytic activity of Bi₂MoO₆,Bi₂MoO₆microspheres with different Ce doping were successfully prepared by one-step solvothermal method,and their photocatalytic reduction of Cr（VI）was used.The relevant test results show that Ce doping can effectively improve the charge separation and transfer efficiency of photocatalyst.When the theoretical molar ratio of Ce to Bi is1∶4,it has the best photocatalytic activity.The reduction efficiency is 96.3%after50 min illumination,and the reduction rate constant is 1.8 times that of pure Bi₂MoO₆.In addition,under the conditions of five repeated experiments and coexisting ions,the photocatalyst still maintains high reduction activity,indicating that Ce doped Bi₂MoO₆has strong stability.The study shows that Ce doped Bi₂MoO₆ has the characteristics of simple synthesis process and high photocatalytic efficiency,and has potential application value in the treatment of Cr（VI）in wastewater.Finally,based on the preparation of bismuth molybdate microspheres by solvothermal method,by adding sodium borohydride in the solvothermal process,part of bismuth nitrate is reduced to elemental bismuth by its strong reducibility,so as to synthesize Bi/Bi₂MoO₆ composite photocatalyst.Through the photocatalytic activity test,it was found that the reduction rate of pure bismuth molybdate to hexavalent chromium solution was only 74%after 50 minutes of xenon lamp illumination,but after the combination of metal Bi and bismuth molybdate,the photocatalytic activity of Bi/Bi₂MoO₆ composite photocatalyst to hexavalent chromium was significantly improved（the reduction rate was about 94.4%）,and the reduction rate constant of Bi/Bi₂MoO₆ composite photocatalyst was about twice that of pure bismuth molybdate.UV-vis（absorption spectrum）results show that the surface plasmon resonance effect of metal Bi particles can effectively broaden the light absorption range of bismuth molybdate.In addition,the electrochemical test results show that the SPR effect of metal Bi is conducive to promoting the storage and shuttle of electrons,and can effectively improve the transmission efficiency of charge carriers in Bi/Bi₂MoO₆.Combined with the optical and electrochemical test results,the possible photocatalytic mechanism of charge separation and transmission of Bi/Bi₂MoO₆ photocatalyst was proposed.