Mulberry branch-derived Ru-biochar activation of periodate via a surface-confined Ru(V)=O pathway: Selective oxidation of sulfonamide antibiotics at near-neutral pH.

A ruthenium-loaded biochar catalyst (Ru-BC) derived from mulberry branch waste was developed to activate periodate (IO4-, PI) for efficient degradation of sulfamethoxazole (SMX). The Ru-BC/PI system exhibited rapid SMX removal, wide pH applicability, and strong tolerance to inorganic and organic constituents in both ultrapure phosphate-buffered solutions and more challenging fresh and hydrolyzed urine matrices. Mechanistic investigations revealed that SMX degradation was dominated by a surface-confined, non-radical oxidation pathway mediated by high-valent Ru(V)=O species. Although reactive oxygen species (e.g., •OH, O2•-, 1O2) and iodate radicals (e.g., IO3•) were detected, their contributions to SMX degradation were minor. Quantitative contribution analysis confirmed that the Ru(V)=O pathway accounted for 85.7% of SMX degradation. Kinetics modeling successfully fit the temporal concentration profiles of SMX and probe compounds for high-valent metal-oxo species under various reaction conditions. The kinetics model rationalized the rapid transformation of one probe by IO3•, while confirming the negligible role of IO3• in SMX oxidation. Comparative degradation of structurally related sulfonamide antibiotics further revealed a pronounced substrate-dependent reactivity, providing independent evidence for site-specific, Ru(V)=O-dominated oxidation rather than indiscriminate radical-driven reactions. Overall, this study demonstrates a robust, non-radical Ru-BC/PI system capable of efficiently degrading SMX under near-neutral pH conditions and in challenging matrices, highlighting a promising, new strategy for treatment of recalcitrant contaminants in complex aqueous environments.