Study On The Synthesis And Photocatalytic Properties Of Flower-like BiVO₄

With the advancement of social life and the growing problem of water pollution,the green and environmentally friendly photocatalytic technology is applied to degrade organic pollutants in water,which has become a research hotspot in water environmental protection.Bismuth vanadate?BiVO₄?with a band gap semiconductor?².4eV?,being one of semiconductor materials,can absorb visible light,which is simple to prepare and has received great attention.In view of the fact that the electron-hole pairs of the BiVO₄monomer are easily recombined,the photocatalytic efficiency is affected.Silver sulfide?Ag₂S?with excellent chemical stability and large specific surface area is a p-type narrow bandgap semiconductor,which has a wide range of applications in catalysis.The two materials are combined into Ag₂S/BiVO₄,which is further reduced to Ag/Ag₂S/BiVO₄.The photocatalytic activity of the Ag/Ag₂S/BiVO₄ is improved due to the local surface plasmon resonance effect of Ag nanoparticles and the effective separation of electron-hole pairs in the heterojunction structure.In this paper,BiVO₄ was prepared by hydrothermal method.The photocatalytic activity was used as an evaluation index to explore the process parameters for the preparation of flower-like BiVO₄.The growth mechanism of flower-like BiVO₄ was analyzed.Based on the optimized process parameters of flower-like BiVO₄,Ag/Ag₂S/BiVO₄ was further prepared by in-situ deposition method to characterize the photocatalytic activity of the composites and analyze its photocatalytic mechanism.The main research contents are as follows:1.Based on the single factor experimental theory,the preparation conditions of flower-like BiVO₄ were explored.Four factors,such as hydrothermal temperature,hydrothermal time,Bi³⁺concentration[Bi³⁺]and[Bi³⁺]/[VO₄^3-],were used as experimental objects.The results showed that the first three factors can produce flower-like BiVO₄ at different levels.However,[Bi³⁺]/[VO₄^3-]can only produce flower-like BiVO₄ at a certain level.2.Based on the conclusion of the flower-like BiVO₄ prepared by hydrothermal method single factor experiment,the three-factor four-level orthogonal table was designed to explore the process parameters for the preparation of flower-like BiVO₄.The photocatalytic degradation of oxytetracycline hydrochloride?OTH?was used as the evaluation index.The experimental results show that the influence relationship of three factors on the photocatalytic efficiency of the prepared product is:[Bi³⁺]>T>t,and the optimized process parameters are[Bi³⁺]=5mmol/L,T=150°C,t=10h.In view of the fact that[Bi³⁺]has the greatest influence on the photocatalytic efficiency of the prepared product,the[Bi³⁺]is further refined to 4mmol/L,5mmol/L and 6mmol/L under the condition of constant temperature T and hydrothermal time t.Three experiments were performed to prepare BiVO₄.The results show that when[Bi³⁺]is 4mmol/L,the photocatalytic effect is the best.The final optimized BiVO₄ preparation process parameters were:[Bi³⁺]=4mmol/L,T=150°C,t=10h.Finally,the growth dependence of flower-like BiVO₄ on time was studied.The results show that the size of the flower-like BiVO₄ and the fullness of the flower-like structure increases as the reaction time increases.However,with the reaction time continues to increase,Bi₂O₃ is formed.3.Based on the final optimized process parameters,Ag₂S/BiVO₄ composites were prepared by in-situ deposition of Ag₂S for 10 h.The degradation efficiency of Ag₂S/BiVO₄composites to OTH was 65.85%under visible light irradiation for 120 min.The Ag₂S/BiVO₄ composite was reduced to Ag/Ag₂S/BiVO₄ composite material under UV light for 5h,and its photocatalytic efficiency was 73.20%.The gradual decrease of the photoluminescence intensity of BiVO₄,Ag₂S/BiVO₄ and Ag/Ag₂S/BiVO₄ shows that the separation efficiency of electrons and holes is gradually improved.It is shown that the heterojunction and the plasma effect of Ag nanoparticles is beneficial to improve the photocatalytic efficiency.