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.