Upcycling polystyrene microplastics to Fe/Mo-doped sponge-carbon: Mo⁵⁺ enhanced electron transfer for boosting Fenton-like performance

The rate-limiting steps of promoting the conversion of Fe³⁺ to Fe²⁺ in Fenton-like systems are crucial for achieving efficient degradation of organic contaminants in aquatic environments. Herein, a novel magnetic Fe/Mo bimetallic doped sponge carbon (Fe/Mo-N-C) derived from polystyrene microplastics was successfully synthesized and the presence of metastable Mo⁵⁺ remarkably synergized the electron transfer of Fe²⁺ in internal microenvironment. In the Fe/Mo-N-C activating peroxymonosulfate (PMS) system, Mo⁵⁺ boosted the oxidation of Fe²⁺, and the conversion of Mo⁴⁺/Mo⁶⁺ accelerated the restoration of Fe²⁺ from Fe³⁺, resulting in nearly 100 % of 17α-ethinylestradiol (EE2) degradation with the kinetic rate constant of 0.343 min⁻¹, which was 8.1 times faster than that of Fe-N-C. Moreover, Fe/Mo-N-C possessed excellent resistance to interference from various coexisting anions (especially chloride, sulfate, and nitrate ions up to 500 mM), natural organic matter, nano-plastics, and different water matrices. Density functional theory analysis demonstrated that Mo centers regulated the electron rearrangement of the Fe 3d orbital, enhancing the activation performance of Fe/Mo-N-C towards PMS. This study lays the groundwork for understanding the mechanism of metastable Mo, which holds significant importance for the up-recycling of polyethylene plastics and environmental remediation.