Preparation And Photocatalytic Properties Of Bi₂O₃/（Bi₂WO₆）/g-C₃N₄ Compounds

While urbanization is growing and people’s living standards are improving,environmental pollution and energy crisis also pose serious threats to human health and sustainable development.Semiconductor photocatalytic degradation technology is considered as a promising method for organic pollutant degradation because of its green,mild and high degradation efficiency.Graphite-like carbon nitride（g-C₃N₄）,as an excellent photocatalytic material with high chemical stability,abundant sources and no precious metals,has become a hot research topic in recent years.However,g-C₃N₄suffers from the shortcomings of high photogenerated electron-hole complex rate and low utilization of visible light,and pure g-C₃N₄usually exhibits poor photocatalytic performance.In this paper,bismuth oxide（Bi₂O₃）and bismuth tungstate（Bi₂WO₆）were used as co-catalysts to compound with g-C₃N₄to construct heterojunctions to address the above deficiencies of g-C₃N₄.The morphological structure,electron-hole pair compounding efficiency and photogenerated carrier migration rate of the heterojunctions were investigated by XRD,SEM,TEM,PL,EIS,UV-Vis DRS and other characterization methods.And the degradation rate of methylene blue（MB）by each composite was analyzed and compared,and finally the photocatalytic mechanism of the composites was explored and studied.In this paper,Bi₂O₃/g-C₃N₄ and Bi₂WO₆/g-C₃N₄composite photocatalysts were prepared by thermal polycondensation and hydrothermal methods,respectively.When the doping amounts of Bi₂O₃and Bi₂WO₆were 7%and 10%,respectively,the best photocatalytic ability was exhibited,reaching 55.6%and80.61%at 240 min,which were both higher than that of g-C₃N₄single semiconductor（34.26%）.The reaction rate constant of 10%-Bi₂WO₆/g-C₃N₄is0.00549 min^-1by the first-level reaction kinetic simulation,which is 1.94 and 4times higher than that of Bi₂WO₆and g-C₃N₄,respectively.In addition to this,the formation of heterojunctions,which led to enhanced visible light absorption and improved separation efficiency of photogenerated electrons from holes,these factors helped the prepared composites to exhibit better photocatalytic degradation of pollutants.Based on the experimental results of trapping agents and the valence and conduction band positions,a possible photocatalytic reaction mechanism is not proposed for traditional type II heterojunction structures,but all Z-scheme heterojunction structures.In addition,Bi₂O₃/Bi₂WO₆ and Bi₂WO₆/Bi₂O₃/g-C₃N₄（BBCN）composite photocatalysts were prepared by hydrothermal method.7%-Bi₂O₃/Bi₂WO₆and7%-BBCN,showed the best photocatalytic capacity at 240 min with 68.16%and51.07%,respectively,relative to Bi₂O₃（43.86%）and Bi₂WO₆（48.33%）with great improvement.The reaction rate constant of 7%-Bi₂O₃/Bi₂WO₆is 0.00468min^-1,which is 1.66 times higher than that of Bi₂O₃and Bi₂WO₆,and still has high catalytic activity after four cycles of experiments by first-stage reaction kinetic simulations.In addition,the formation of the composite heterojunction results in a narrower band gap,improved separation efficiency of photogenerated electrons and holes,and enhanced absorption in the visible region.According to the corresponding valence band and conduction band positions,Bi₂O₃/Bi₂WO₆is proposed as the conventional type II heterojunction structure,and the photocatalytic mechanism of the ternary composites is explored.