Recycling different crystal forms of MnO2 from spent Li-ion batteries cathodes for SDZ degradation

Environmental pollution due to antibiotics usage and spent Li-ion batteries is escalating. To solve this issue, MnO2 with different crystalline phases were prepared as catalysts (recovered from spent lithium-ion battery cathode materials) for the degradation of sulfadiazine (SDZ) in this study by acid leaching and hydrothermal methods, respectively. The morphological and structural characteristics of catalysts were examined by XRD, SEM, XPS, and BET. The catalyst MnO2-6h (β-MnO2) synthesized in six hours by hydrothermal method showed higher performance in destroying SDZ compared to MnO2-3h (λ-MnO2) obtained by acid leaching method. Over 95% of SDZ was degraded by 0.2 g/L MnO2-6h, 1 mM peroxymonosulfate (PMS) at pH 6 by pseudo-first-order kinetics. Density Functional Theory (DFT) calculations and related experimental analyses revealed that the main ROS within the MnO2-6h/PMS system is SO4－·, which contributes about 67.49% to the degradation of SDZ. The high crystallinity and high Mn(III) ratio of MnO2-6h are the key to the high catalytic activity of MnO2-6h, which is highly stable and has potential for practical wastewater treatment. The study provides a new approach to managing the solid waste of spent Li-ion batteries and controlling emerging pollutants resulting from heavy antibiotic use.