Performance and mechanism of tetracycline removal by peroxymonosulfate-assisted double Z-scheme LaFeO3/g-C3N4/ZnO heterojunction under visible light drive

Abstract

The photocatalytic persulfate activation technology has attracted attention due to the synergistic effect that can be generated by the coupling of photocatalysis and persulfate. In this study, a ternary heterostructure LaFeO₃/g-C₃N₄/ZnO was successfully formed, and a coupled photocatalytic/PMS system was constructed. The coupled system exhibited synergistic effect and achieved high tetracycline removal efficiency and quick kinetic, as 85.89 % tetracycline was degraded within 40 min. Additionally, the coupled system has a wider pH adaptation range and can better resist the influence of coexisting ions (Cl⁻, ${\mathrm{CO}}_3^{2-}$) and humic acid. Mechanism investigation indicated that the double-Z scheme heterojunction between LaFeO₃, g-C₃N₄ and ZnO provides driving force for charge transfer and improves the separation of photogenerated electron-hole pairs, and PMS can act as an electron acceptor to prevent photogenerated electron hole recombination. ${•\mathrm{SO}}_4^{-}$, $•$OH, ${•O}_2^{-}$, h⁺, and ¹O₂ work together in photocatalysis/PMS coupled system, with $•$OH and ${•\mathrm{SO}}_4^{-}$ play a major role. Compared to solo photocatalytic system, the toxicity of tetracycline degradation intermediate products is lower and the mineralization degree of tetracycline is higher in the coupled system. Besides, LaFeO₃/g-C₃N₄/ZnO also exhibiting superior photocatalytic performance after four cycles. This work provides reference for photocatalytic persulfate activation technology to degrade tetracycline in water.