Preparation And Photocatalytic Degradation Performance Of Ti-doped Bi₂O₃/Montmorillonite Composites

Dye wastewater has the characteristics of high chroma,high toxicity,high resistance to photolysis and antioxidant capacity,which poses a serious threat to the natural environment and human health.How to efficiently treat dye wastewater is an urgent problem to be solved.Photocatalytic technology has become an effective method for treating dye wastewater due to its high efficiency,low cost and no secondary pollution.The light absorption capacity of photocatalytic materials,the separation efficiency of photogenerated electron-hole pairs and the adsorption capacity of pollutants determine the degradation performance of photocatalytic materials.Therefore,it is necessary to prepare photocatalytic materials with excellent performance.In this paper,Ti-doped Bi₂O₃ photocatalytic materials（Ti/Bi₂O₃）and Ti-doped Bi₂O₃/montmorillonite composites（TBM）were prepared by chemical solution decomposition method based on visible light response narrow band gap photocatalytic material Bi₂O₃.The research contents are as follows:（1）When the amount of photocatalytic material was 1.0 g/L and the initial concentration of the solution was 20 mg/L,the degradation rate of Reactive blue 19 by pure Bi₂O₃ was 75.30%after 180 min illumination.When the doping ratio of Ti is 4%（4Ti/Bi₂O₃）,the degradation effect of Reactive blue 19 is the best,and the degradation rate can reach 93.27%.The degradation process conforms to the Langmuir-Hinshelwood first-order kinetic equation.When 4Ti/Bi₂O₃ was reused for 4 times,the degradation rate of Reactive blue 19 only decreased by 6.91%.Bi₂O₃ exists in the form of monoclinic phase,and Ti ions are doped into the Bi₂O₃ lattice in the form of Ti⁴⁺,which inhibits the growth of Bi₂O₃ grains.The pure Bi₂O₃ particles are large and the surface is smooth.With the increase of Ti doping ratio,the pore structure is formed inside the Bi₂O₃ particles until it is gradually cracked,and the nanofiber-like Bi₄Ti₃O₁₂is also formed on the surface of the particles.The doping of Ti enhances the light absorption ability,electron separation and transfer ability of Bi₂O₃,and the band gap is reduced from 2.81 e V to 2.75 e V,which makes Ti/Bi₂O₃ have higher photocatalytic activity.During the photocatalytic degradation process,·O₂^-and h⁺directly react with Reactive blue 19 to degrade it into water,carbon dioxide or other small molecules.（2）The optimum preparation process of TBM is as follows:the Ti doping ratio is4%,the montmorillonite mass is 0.5 g,the calcination temperature is 500℃,and the calcination time is 2 h.The composite material（4TBM）prepared under this condition has excellent adsorption performance and photocatalytic degradation performance.Bi₂O₃ exists in the form of tetragonal phase,and Ti ions are doped into the Bi₂O₃ lattice in the form of Ti⁴⁺,which inhibits the growth of Bi₂O₃ grains.The montmorillonite layers in the composites were exfoliated,and the specific surface area increased to 4.16m²/g.After Ti doping,the Ti 3d orbital is combined with the O 2p and Bi 6s orbitals to form the valence band of 4TBM,and the band gap is reduced from 2.59 e V to 2.52 e V,which enhances the light absorption ability and improves the photocatalytic degradation performance of 4TBM.（3）The adsorption process of 4TBM on Reactive blue 19 conforms to the pseudo-first-order kinetic equation,and the adsorption behavior belongs to uniform monolayer adsorption.When the dosage of 4TBM was 1.0 g/L and the initial concentration of the solution was 20 mg/L,the photocatalytic degradation of Reactive blue 19 was the best.After 120 min of illumination,the degradation rate reached 98.17%.The degradation process conformed to the Langmuir-Hinshelwood first-order kinetic equation.In the process of photocatalytic degradation,·O₂^-and h⁺react with Reactive blue 19 adsorbed on the surface of montmorillonite and degrade it into water,carbon dioxide or other small molecules.Moreover,4TBM has good stability and can be used repeatedly.In addition,4TBM has high photocatalytic degradation performance for Azo-dye（Carmine）,Triphenylmethane-dye（Rhodamine B）and Mixed-dyes.