Mechanochemical biochar enables electron-transfer-mediated ferrate(VI) activation for enhanced micropollutant degradation

Carbocatalysts have recently emerged as promising enhancers for improving the decontamination efficiency of ferrate (Fe(VI)) in water treatment applications. In this study, a simple, solvent-free, and environmentally benign ball milling approach was employed to substantially enhance the activation capability of biochar (BC) toward Fe(VI), enabling sustainable and effective degradation of micropollutants. Sulfamethoxazole (SMX) was efficiently degraded and detoxified through Fe(VI) activation by ball milling biochar (BBC), with the SMX degradation kinetic rate increased by a factor of 6.7 relative to unmodified BC. Mechanistic investigations revealed that the electron transfer-mediated non-radical pathway played a predominant role in SMX degradation, whereas iron intermediates (Fe(IV)/Fe(V)) contributed only marginally. A quantitative correlation analysis showed that the observed rate constant for SMX degradation was strongly correlated with the oxygen-containing functional groups generated by ball milling. Density functional theory (DFT) calculations further revealed that the introduction of hydroxyl groups on BBC strengthened adsorption energies, induced bond elongation and reduced energy gap, thereby facilitating greater electron transfer. Additionally, high SMX removal efficiency was maintained across a broad pH range, in real water matrices, and after consecutive reuse cycles of BBC. This work demonstrates a mechanochemical strategy to enhance the catalytic performance of BC for Fe(VI) activation, offering a promising approach for the development of more sustainable oxidation processes.