Preparation and catalytic degradation performance of cobalt ferrite based on the recycling of retired lithium-ion battery cathode materials.

In response to dual demands of advanced oxidation of organic pollutants and recycling of retired lithium-ion batteries, this research proposed a high-value recycling method to convert cobalt resources from retired lithium-ion batteries into high-performance cobalt ferrite (CoFe2O4) catalysts. Cobalt leaching and cobalt ferrite synthesis were coupled into an integrated process to achieve efficient cobalt leaching (> 98%). By optimising the sol-gel process, optimal conditions were identified: tartaric acid-to-total metal ion molar ratio 2:1, pH = 7.0, and calcination at 500°C for 2 h. The spinel-type cobalt ferrite particles obtained under these conditions are well-structured, with high catalytic activity, and stable magnetic properties. The cobalt ferrite material catalyzed the degradation of rhodamine B (RhB) by activated peroxymonosulfate (PMS) with excellent performance. Under the optimised reaction conditions (PMS concentration of 0.50 mmol/L, cobalt ferrite concentration of 75 mg/L, initial pH = 7, RhB concentration of 20 mg/L, and reaction time of 90 min), the degradation rate of RhB could reach 99.46%, with an apparent rate constant of 0.0387 min-1. The quenching experiments showed that sulfate radical (SO4-·) was the main reactive oxygen species for the degradation of RhB, while hydroxyl radical (·OH) and superoxide radical (·O2-) also promoted the activation of PMS. Moreover, the cobalt ferrite catalyst could maintain high catalytic activity after multiple cycles, with the degradation rate of RhB remaining above 81%, demonstrating favourable cycling stability. This research offers a novel approach for retired lithium-ion battery valorisation and theoretical support for advanced heterogeneous catalyst development.