Defect-coordination coupled engineering of Fe-based electro-Fenton catalysts for efficient nanoplastic degradation

Electro-Fenton technology has emerged as a promising strategy for plastic oxidation due to its high oxygen reduction reactions (ORR) activity. However, conventional Fe-based catalysts often suffer from sluggish Fe²⁺/Fe³⁺ redox kinetics and excessive O₂ reduction via the 4e⁻ ORR pathway to H₂O, which limits H₂O₂ generation and degrades overall efficiency. Here, we report a multiscale catalyst design that integrates atomic defect engineering with molecular coordination. Fe/Zn species were co-deposited on a natural polymer matrix, followed by alkaline etching to induce spinel-like structures with partial Zn vacancies and subsequent in-situ growth of Co-MOF to construct hierarchical electron transport channels. Theoretical calculation reveals that residual Zn sites optimize O₂ binding energy, preventing over-reduction of O₂. Co sites actively participate in both H 2 O₂ activation and Fe valence cycling. The catalyst enabled efficient H 2 O 2 generation (9708 μM/h) for deep degradation of 10 mg·L⁻¹ polystyrene nanoplastics within 1 h at 40 mA (93.96% total organic carbon removal rate), while maintaining high activity across wide ranges of experiment conditions, as well as for expanded type of nanoplastics (polyethylene terephthalate and polypropylene) and repeated cycles. The degradation pathway and mechanism were detailly discussed. Overall, the coupled defect-coordination strategy substantially enhances the activity, selectivity, and stability of Fe-based electro-Fenton catalysts, offering new insights for advanced oxidation processes in nanoplastic remediation. • A multiscale design coupling atomic Zn-vacancies with molecular coordination creates hierarchical electron channels for superior electro-Fenton activity. • The partial Zn-vacancies structure serves as traps for anchoring Co and tunes O₂ binding to favor the 2e⁻ ORR pathway. • Synergy between Co²⁺ and the Fe/Zn matrix accelerates both H₂O₂ activation and the Fe²⁺/Fe³⁺ cycle, while Zn also stabilizes the structure. • The catalyst achieves deep nanoplastic degradation in 1 h with high efficiency across wide pH, salinity, and concentration ranges, demonstrating robust stability. • Mechanistic studies unveil •OH/ClO• as key radicals, and DFT calculations confirm modulated electron density and optimized O₂ adsorption for high H₂O₂ selectivity.