Study On Preparation Of Bismuth Tungstate And Its Composites And Photocatalytic Reduction Of Cr(?)

Hexavalent chromium Cr(?)is one of the most toxic inorganic contaminants in water,which was considered to be a carcinogenic and mutant substance.Photocatalyst technology was applied to restore Cr(?)due to its advantages of economical and environmental protection,but the high complement of electron-hole in photocatalyst reaction will lead to a decrease in efficiency.To solve this problem,the study used Bi₂WO₆with the Aurivillius structure as a basic material,and the composite material was prepared by solvent thermal method to restore Cr(?).Although Bi₂WO₆had a unique electronic structure and excellent optical performance,its band gap was not advantageous which compared with most materials.As a narrow bandgap semiconductor,CuS was improved by the composite of Bi₂WO₆.At the same time,CNFs was added to enhance material stability,and recycling is easier.The main work of the study is as follows:First,the CuS/Bi₂WO₆composite material was prepared by solvothermal method.Through analysis and characterization,the absorption of bismuth tungstate and copper sulfide in the visible light region was enhanced,and more photo-generated electron-hole pairs participate in the photocatalytic reaction.At the same time,the introduction of CuS accelerated the separation of photogenerated electron-hole pairs and improved the photocatalytic activity.When the CuS compound content was 5%,the photocatalytic reduction of Cr(?)was the best among them,which is 87%.Secondly,5%CuS/Bi₂WO₆composite material was also loaded on CNFs by solvothermal method to prepare CNFs/CuS/Bi₂WO₆ternary material.Through analysis and characterization,it was found that the adsorption performance of the composites was significantly enhanced after the introduction of CNFs and the photoluminescence intensity was weakened.The effective photoelectron transfer between CNFs and CuS,Bi₂WO₆promoted the interfacial charge transfer and improved the photocatalytic activity of CNFs/CuS/Bi₂WO₆ternary materials.When the composite amount of CNFs was 1%,the composite material could completely100%reduction of Cr(?)within 3 hours,and the photocatalytic activity could still be maintained at 90%after four cycles of reuse,which proved that CNFs/CuS/Bi₂WO₆composite material had good stability.Secondly,5%CuS/Bi₂WO₆composites were also loaded on CNFs by solvothermal method to prepare CNFs/CuS/Bi₂WO₆three-phase composites.Through analysis and characterization,it was found that after the introduction of CNFs,the adsorption capacity of the composite material is significantly enhanced,and the photoluminescence intensity was weakened.The effective transfer of photo-induced electrons between CNFs and CuS,Bi₂WO₆promotes the separation of electrons and holes,thereby increasing CNFs/Photocatalytic activity of CuS/Bi₂WO₆composite material.When the composite amount of CNFs was 1%,the composite material could completely 100%reduction of Cr(?)within 3 hours,and the photocatalytic activity can still be maintained at 90%after four cycles of reuse,which proves that CNFs/CuS/Bi₂WO₆composite material had good stability.Finally,Cr(?)was used as the target pollutant.The effects of three influencing factors,namely the initial p H value of the solution,the initial concentration of the solution and the dosage of photocatalyst,on the reduction of Cr(?)were investigated,and the pseudo-first-order reaction kinetics analysis was carried out.Under certain photocatalytic conditions,the reduction rate of Cr(?)decreased with the increase of the initial p H value of the solution.When the optimal p H=3,the photocatalytic reduction rate gradually decreased with the increase of the initial concentration,and the effect was best when the initial concentration is 10 mg/L.With the increase of the photocatalyst dosage,the reduction rate of Cr(?)also showed an upward trend,and the 80mg photocatalyst could be almost completely reduced within 60min.Through the active group capture experiment,it could be seen that the main active groups for photocatalytic reduction of Cr(?)was superoxide radicals(·O₂^-).When illuminated by visible light,photogenerated electrons transited from the valence band to the conduction band of Bi₂WO₆and CuS,forming a large number of holes.The electrons were transported at high speed by CNFs,while the excess holes remain in Bi₂WO₆in the valence band and react with H₂O or OH-.·OH,inhibited the combination of electrons and holes,and improved the photocatalytic activity.