Spent rather than pristine LiFePO₄ cathode materials can catalytically activate sulfite for organic pollutants decontamination

Lab-prepared Fe-bearing materials have demonstrated their ability to activate sulfite (S(IV)) to generate reactive radicals, which is however limited by their costs and inefficiencies for practical application. Here we report that spent LiFePO₄ (SLFP) cathode materials can function as a robust catalyst for S(IV) activation and consequent decontamination of organic pollutants like 4,4′-sulfonyldiphenol (BPS). Unexpectedly, SLFP materials with lithium defects and oxygen vacancies (O_v) are significantly effective than pristine LiFePO₄. BPS degradation undergoes an induction period when rapid adsorption of O₂ and HSO₃⁻ in water occurs, followed by a slow release of HSO₅⁻, as evidenced by the same depletion trends of BPS and sulfite, and confirmed by theoretical calculations. The HSO₅⁻ is activated by Fe(II) on the SLFP surface, with ^•OH being the main reactive species via a multi-step reaction. The potential environmental application of this SLFP/S(IV) process are evaluated ultimately.