Photocatalytic performance and mechanism of Z-Scheme CuBi_2O_4/Ag_3PO_4 in the degradation of diclofenac sodium under visible light irradiation: Effects of pH, H_2O_2, and S_2O_8~(2-)

摘要

Highly efficient visible-light-responsive Z-Scheme CuBi_2O_4/Ag_3PO_4 photocatalysts were prepared by a hydrothermal synthesis and in-situ deposition method and characterized comprehensively. Under visible-light irradiation, the photocatalytic performance of CuBi_2O_4/Ag_3PO_4 in the degradation of diclofenac sodium (DS) in aqueous solutions was studied under different conditions such as different catalyst composition, solution pH, and concentration of S_2O_8~(2-) or H_2O_2, and the response surface methodology (RSM) was used to analyze the interaction effect of the parameters. The optimal activity of CuBi_2O_4/ Ag_3PO_4 was achieved at the mass ratio of 3:7 and pH of 4.42. Moreover, the introduced S_2O_8~(2-) could significantly enhance the catalytic activity of CuBi_2O_4/Ag_3PO_4; when 1 mM S_2O_8~(2-) was added to the catalytic system, 10 mg/L of DS could be completely degraded within 60 min, but the structure of CuBi_2O_4/Ag_3PO_4 was severely destroyed. While when H_2O_2 was introduced into the system, both the activity and stability of CuBi_2O_4/Ag_3PO_4 were improved significantly. Finally, the photodegradation pathway of DS is proposed and the photocatalytic mechanism of CuBi_2O_4/Ag_3PO_4 under different conditions is explained. CuBi_2O_4/Ag_3PO_4 and CuBi_2O_4/Ag_3PO_4 (S_2O_8~(2-)) photocatalytic systems follow the Z-Scheme theory, and Ag° formed on the surface of catalyst serves as the recombination center for the photogenerated e~ from the conduction band (CB) of Ag_3PO_4 and h~+ from the valence band (VB) of CuBi_2O_4; meanwhile, the catalytic degradation of DS by CuBi_2O_4/Ag_3PO_4 in the presence of H_2O_2 follows the heterojunction energy band theory.