Green Glyphosate Treatment with Ferrihydrite and CaO2 via Forming Surface Ternary Complex

Abstract

Glyphosate (PMG) is a globally used broad-spectrum herbicide and receives environmental concerns because of its moderate persistence and potential carcinogenicity. Traditional PMG treatment methods often suffer from the generation of a more toxic and persistent aminomethylphosphonic acid (AMPA) intermediate. Herein, we develop a green method with ferrihydrite (FH) and CaO₂ (FH/CaO₂) via regulating the coordination of PMG with FH and Ca²⁺, where the phosphonate group of PMG preferentially binds to FH and its carboxylate side complexes with Ca²⁺ released by CaO₂, forming a FH-PMG-Ca ternary surface complex. This unique ternary complex can redistribute electrons within the PMG molecule for its C–P activation and C–N bond stabilization, favoring the selective C–P bond attack of superoxide radical produced by the Fenton reaction between CaO₂-derived H₂O₂ and FH, thus generating environment-friendly glycine instead of AMPA. The FH/CaO₂ process realizes over 99% PMG degradation in industrial wastewater within 1 h, with residual PMG < 0.1 ppm and AMPA < 40 ppb. More importantly, the CaO₂ consumption was as low as 3.1 mg of CaO₂/mg of PMG, one-fifth those of previously reported CaO₂-based counterparts. This study provides an effective and environment-friendly PMG treatment strategy and highlights the importance of surface coordination modes on the degradation pathway of PMG.