Synthesis of PPy-BiVO4-Cu2+ heterojunction and its visible-light-driven photocatalytic degradation of 2,4-dichlorophenol.

2,4-Dichlorophenol (2,4-DCP) as a persistent organic pollutant, poses significant health risks to humans through chronic exposure. Photocatalysis is an efficient and green treatment technology, which has great advantages in the degradation of organic pollutants in wastewater. In this study, the PPy-BiVO4-Cu2+ photocatalyst - modified with both transition metal copper ions (Cu2+) doping and conductive polypyrrole (PPy) composite - was synthesized via a two-step process combining sol-gel method and chemical oxidative polymerization method. The results show that the pristine BiVO4 is monoclinic scheelite phase. After Cu2+ modification, new crystalline phases of BiCu2VO6 and CuO were formed. And it is found that the modification of Cu2+ and the combination of PPy can effectively improve the charge separation and migration efficiency of the photocatalyst, and achieving full-spectrum light absorption across 230-800 nm. The degradation experimental results showed that the 3 %PPy-BiCu-4 composite material achieved 91.51 % degradation efficiency of 2,4-DCP in 1.5 h under visible light irradiation. Mechanistic studies demonstrated that the dual p-n heterojunctions formed among BiVO4, CuO, and BiCu2VO6, combined with the Z-scheme heterojunction between PPy and BiVO4. Driven by the built-in electric field, these heterostructures facilitated efficient separation and directional migration of electron-hole pairs. Ultimately, electrons (e-) in the conduction band of PPy and holes (h+) in the valence band of CuO generated reactive species (•O2- and •OH), achieving highly efficient degradation of 2,4-DCP. This study elucidates the interfacial charge transfer pathways within the PPy-BiVO4-Cu2+ composite photocatalyst, which provides a new idea for the photocatalytic degradation of 2,4-DCP wastewater.