Advanced polystyrene nanoplastic remediation through electro-Fenton process: degradation mechanisms and pathways

Nanoplastics are increasingly recognized as emerging pollutants posing significant ecological risks and necessitating the development of effective remediation strategies. Heterogeneous electro-Fenton (EF) processes have demonstrated excellent capabilities in degrading various persistent organic contaminants. Here, we propose a novel approach for the degradation of polystyrene nanoplastics (PS-NPs) by incorporating a copper-cobalt carbon aerogel (CuCo-CA) as a bifunctional cathode. The Cu/Co bimetallic pair was selected due to the complementary redox potentials of copper and cobalt, which can synergistically enhance the activation of H₂O₂, thus significantly improving catalytic efficiency. The bifunctional capability of CuCo-CA for H2O2 electro-synthesis and in situ activation induced the efficient generation of hydroxyl radicals for the oxidative decomposition of PS-NPs. Under optimized conditions (current: 20 mA, initial pH: 7.0, electrolyte 0.05 M, initial PS-NPs dosage: 20 mg/L), a PS-NPs removal efficiency of 94.8 % using UV-Vis spectroscopy, and total organic carbon removal of 73.7 % were achieved within 6 h. The CuCo-CA cathode maintained an excellent degradation rate and preserved active functional groups after five consecutive cycles. Characterization identified critical changes in morphology, particle size, composition, and functional groups of PS-NPs after electro-Fenton treatment. Density functional theory calculations were used to identify reactive sites on polystyrene, and the degradation pathways of PS-NPs were proposed for the first time. Analysis identified various chain-break and oxidation products, attributed to aggressive oxidative attack, while toxicity assessments confirmed that final products were substantially less harmful. Overall, this study addresses the critical environmental challenge of nanoplastics through an electro-Fenton system for sustainable remediation under mild conditions.