Hydrogen-Modified Waste Iron Catalysts Drive PMS Activation to ¹ O ₂ for Tetracycline Degradation in High-Salt Wastewater

To overcome the limitations of conventional degradation methods in high-salt wastewater, attributed to the formation of stable complexes between tetracycline (TC) and salt, as well as the inhibitory effects of anions on free radical processes, this study proposes a novel nonradical oxidation approach utilizing recycled waste warm paste resources. Through the hydrogenation modification of the iron-based materials in waste warm paste, a highly effective nonradical-driven H 2 -warm paste (H 2 –WP) catalyst was developed for activating PMS to achieve targeted degradation of TC in high-salt conditions. Analysis using XRD and XPS techniques demonstrated that hydrogenation modification notably improved the Fe 3 O 4 crystallinity (enhanced from 42.96% to 86.53%) and surface Fe 2 + /Fe 3 + ratio (raised from 0.89 to 1.32) in the catalyst, thereby enhancing PMS activation for singlet oxygen ( 1 O 2 ) generation. The H 2 –WP/PMS system exhibited an 86% TC removal efficiency in high-salt conditions, displaying a 2-fold increase in the degradation rate constant compared to the WP/PMS system. Notably, the catalyst retained 95.37% of its initial activity after four consecutive cycles, showcasing remarkable stability against salt-induced degradation. Radical quenching experiments and EPR spectroscopy revealed that 1 O 2 was selective in TC oxidation, contributing to 63.24% of the degradation process. Complementary XPS and UPLC-MS analyses provided insights into the degradation mechanisms and pathways. This study establishes a novel waste-to-catalyst approach for treating hypersaline wastewater and enhances the understanding of nonradical oxidation mechanisms in complex aquatic environments with a multicomponent system.