In situ formed metal (hydr)oxide colloids enable rapid permanganate oxidation of sulfonamides via interfacial...

Permanganate (PM, Mn(VII)) oxidation is attractive for water treatment because of its stability and operational simplicity, yet its moderate oxidizing power often limits the removal of recalcitrant trace organic contaminants, such as sulfonamide antibiotics. Here, we show that metal hydrolysis in situ generates dispersed metal (hydr)oxide colloids that markedly enhance PM oxidation of sulfonamides. Among the tested metals, Fe(III) showed the strongest promotion of sulfamethoxazole (SMX) degradation in a strongly pH-dependent manner. Transmission electron microscopy, zeta potential measurements, graded membrane filtration and preformed-colloid control experiments identified that Fe(OH)₃ nanocolloids (80-120 nm) as the dominant active phase. Multiple probe experiments, electron paramagnetic resonance, sulfoxide probing, and Mn(III)-pyrophosphate assays revealed no measurable contribution from reactive oxygen species or reactive Mn intermediates under our experimental conditions. Instead, electrochemical measurements, selective probe reactions, and DFT calculations support a proximity-enabled interfacial electron-transfer pathway, in which Fe(OH)₃ colloids associate with MnO₄^-, weaken Mn-O bonding, and co-enrich MnO₄^- and SMX at the interface. At a realistic PM dose (10 µM) and an optimized Fe(III) dosage of 0.1 mM, this colloid-assisted system rapidly removed five sulfonamides, with apparent rate constants enhanced by 6-151 times. ECOSAR predictions suggested reduced ecotoxicity of the degradation products, and the system remained effective in multiple real water matrices. These results establish hydrolysis-derived metal colloids as interfacial nanoreactors and offer a tunable strategy to improve PM-based removal of sulfonamide antibiotics.