Degradation of tetracycline by percarbonate activated by both UV and wasted Acorus calamus-sourced biochar

Aquatic plants used in lake remediation accumulate heavy metals, turning biomass into waste. Herein, biochar (M-AcBC) derived from metal-laden Acorus calamus was combined with sodium percarbonate (SPC) and UV light to degrade tetracycline (TC). M-AcBC contained dispersed CuO, ZnO, and Fe3O4, exhibited defect structures, higher graphitization, and larger surface area than pristine biochar. Under optimal conditions (1.0 g/L M-AcBC, 0.3 mM SPC, pH 3, 900 µW/cm² UV), 90% TC removal was achieved. During the dark phase (0–40 min), functional groups, persistent radicals, and Fe₃O₄ activated SPC to generate •OH, •O2-, and 1O2. Upon UV irradiation (40–120 min), ZnO produced electron-hole pairs that further formed •OH and •O2-. The system exhibited synergistic effects, good reusability, broad applicability to various antibiotics, and reduced ecotoxicity of intermediates. This work provides a waste-to-resource strategy and new insights into the M-AcBC/SPC/UV system for water treatment.