Photocatalytic performance and mechanism of Z-Scheme CuBi2O4/Ag3PO4 in the degradation of diclofenac sodium under visible light irradiation: Effects of pH, H2O2, and S2O82.

Highly efficient visible-light-responsive Z-Scheme CuBi2O4/Ag3PO4 photocatalysts were prepared by a hydrothermal synthesis and in-situ deposition method and characterized comprehensively. Under visible-light irradiation, the photocatalytic performance of CuBi2O4/Ag3PO4 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 S2O82- or H2O2, and the response surface methodology (RSM) was used to analyze the interaction effect of the parameters. The optimal activity of CuBi2O4/Ag3PO4 was achieved at the mass ratio of 3:7 and pH of 4.42. Moreover, the introduced S2O82- could significantly enhance the catalytic activity of CuBi2O4/Ag3PO4; when 1 mM S2O82- was added to the catalytic system, 10 mg/L of DS could be completely degraded within 60 min, but the structure of CuBi2O4/Ag3PO4 was severely destroyed. While when H2O2 was introduced into the system, both the activity and stability of CuBi2O4/Ag3PO4 were improved significantly. Finally, the photodegradation pathway of DS is proposed and the photocatalytic mechanism of CuBi2O4/Ag3PO4 under different conditions is explained. CuBi2O4/Ag3PO4 and CuBi2O4/Ag3PO4 (S2O82-) photocatalytic systems follow the Z-Scheme theory, and Ag0 formed on the surface of catalyst serves as the recombination center for the photogenerated e- from the conduction band (CB) of Ag3PO4 and h+ from the valence band (VB) of CuBi2O4; meanwhile, the catalytic degradation of DS by CuBi2O4/Ag3PO4 in the presence of H2O2 follows the heterojunction energy band theory.