ZnO/TiO2-rGO heterojunctions: Synergistic charge transport and targeted photocatalytic conversion of protein-like dissolved organic matter in swine wastewater

Biorefractory protein-like dissolved organic matter (DOM) in swine wastewater presents a formidable challenge for photocatalytic degradation, whereas binary photocatalysts suffer from intrinsic limitations of inefficient charge separation and poor selective DOM adsorption. To mitigate these critical drawbacks, we designed ZnO/TiO 2 -rGO ternary photocatalysts with tunable oxygen vacancy (O V ) concentrations and a Type Ⅱ heterojunction by regulating rGO dosages via a two-step hydrothermal method, achieving dual optimization of charge transfer dynamics and selective DOM adsorption. The optimal ZTR-4 catalyst (O V concentration 45.32%) achieved 69.40% protein-like DOM removal, with a rate constant 3.4 and 2.3 times higher than binary composites (ZR and TR). Excitation-emission matrix (EEM) and UV–visible spectral analyses confirmed the conversion of labile protein-like DOM to refractory humic-like and fulvic-like substances via oxidative condensation and Maillard reactions, with superoxide anion radicals (·O 2 - ) and photogenerated holes ( h + ) serving as the dominant reactive species. The enhanced performance stemmed from the synergy of heterojunction-mediated charge separation, rGO-facilitated electron transport, π-π adsorption, and O V -induced photogenerated carrier recombination suppression. This work not only verifies the application potential of the as-prepared materials in real livestock wastewater, but also clarifies the intrinsic degradation and humification mechanisms of complex DOM.