Construction Of Bismuth Tungstate-based Photocatalytic Heterojunction For Degradation Of Rhodamine B And Cr(Ⅵ)

Photocatalytic technology has shown excellent performance in addressing the problem of environmental pollution in recent decades.Photocatalyst,as the heart of photocatalytic technology,has also undergone much study and growth.As a consequence of the bismuth tungstate study（Bi₂WO₆）,two distinct semiconductor heterojunction structures were constructed to improve the photocatalytic activity and stability of Bi₂WO₆.The first is combined with tungsten trioxide（WO₃）to form a Type-Ⅱ conventional heterojunction structure,and the second with cadmium sulphide（CdS）to form a novel Z-scheme semiconductor photocatalytic heterojunction.The photocatalytic enhancement mechanism of two different heterojunctions was explored and applied to the degradation of organic pollutants（Rhodamine B）and the removal of heavy metal ions（Cr（Ⅵ））research by comparing their structural composition,microscopic morphology,surface composition,and light absorption performance.The following are the primary research findings:1.WO₃-loaded Type-Ⅱ WO₃/Bi₂WO₆ heterojunction photocatalyst was prepared by a facile hydrothermal synthesis method.By varying the mass ratios,hydrothermal temperatures,and precursor p H,the impacts of preparation conditions on the photocatalytic performance of WO₃/Bi₂WO₆ were examined.The findings of the study demonstrate that the specific surface area（70.692 m²/g）and pore volume（0.182 cm³/g）of the 5%WO₃/Bi₂WO₆ photocatalyst prepared at a hydrothermal temperature of 140°C and a p H of 1.50 in the precursor solution increased significantly and the separation efficiency of the photogenerated carriers become higher,demonstrating greater catalytic activity in the experiments for Rh B degradation and and the removal of Cr（Ⅵ）.2.Based on the study of Type-Ⅱ heterojunction,the Z-scheme heterojunction CdS/Bi₂WO₆catalyst was produced utilizing a one-step hydrothermal approach using CdS and Bi₂WO₆.For CdS/Bi₂WO₆,the optimal composite mass ratio is 15%,the hydrothermal temperature is 120℃,and the p H value of the precursor solution is 5.93.It is found that CdS/Bi₂WO₆ is a small sized hierarchical microsphere（2μm）,the visible light response range is broadened to 450 nm,and the light absorption performance is significantly enhanced（2.36 e V）.It exhibits high redox ability in the simultaneous degradation of Rh B and Cr（Ⅵ）,and both the degradation rate and the reaction rate constant are several times of the single degradation.At the same time,the reusability of the catalyst also proved that CdS/Bi₂WO₆ had excellent stability.It is superior to5%WO₃/Bi₂WO₆ in preparation conditions,physical and chemical properties and photocatalytic properties.3.The effect of the degradation conditions of Rh B on the degradation of 5%WO₃/Bi₂WO₆ and15%CdS/Bi₂WO₆ was investigated.the optimal initial concentration of Rh B solution is 50 mg/L,the original p H,and the dosage of degrading catalyst is 0.1 g/100 m L,the degradation effect is the best.4.Radical trapping experiments show that holes（h⁺）and hydroxyl radicals（·OH）play the main active roles in the 5%WO₃/Bi₂WO₆ composite system.Combined with the energy band theory,it is inferred that the reaction mechanism of WO₃/Bi₂WO₆ is the traditional Type-Ⅱ heterojunction structure theory.For CdS/Bi₂WO₆,superoxide radicals（·O₂^-）and electrons（e^-）are the main active species in the reaction process,which proves that the photocatalytic mechanism is a novel Z-scheme carrier transport mechanism.Secondly The Z-scheme heterojunction structure can inhibit the photocorrosion phenomenon of CdS.