Harnessing pollutant complexation for self-accelerated remediation: Glyphosate oxidation and toxicity mitigation in a...

High-concentration glyphosate (Gly) wastewater presents a formidable remediation challenge due to its recalcitrance and the inherent risk of generating toxic intermediates like aminomethylphosphonic acid (AMPA). Herein, we report a facile "waste-treats-waste" strategy utilizing a self-accelerated Fe(II)/O₂ system that operates efficiently under neutral pH, effectively circumventing the acidic constraints of traditional Fenton processes. This system achieved a 57% Gly removal efficiency (initial concentration 0.5 g/L) within 60 min, with a kinetic rate constant (k_obs = 0.029 min^-1) significantly outperforming conventional oxidation technologies. Mechanistic investigations reveal that Gly acts as a suicide ligand, forming an inner-sphere Fe(II)-Gly complex that lowers the Gibbs free energy barrier, thereby rendering O₂ activation thermodynamically favorable. The degradation proceeds via a dual-pathway mechanism, synergizing hydroxyl radical (•OH) attack (∼40%) with a dominant intramolecular ligand-to-metal charge transfer (LMCT) process (∼60%). Crucially, density functional theory (DFT) calculations elucidate that Fe(III) coordination induces a regioselective weakening of the C-N bond adjacent to the phosphonate group. This steric and electronic modulation steers the reaction pathway toward the preferential formation of benign glycine, successfully suppressing the generation of highly toxic AMPA. Bioassays using Tetrahymena thermophila confirmed that this glycine-selective pathway optimization significantly mitigates the acute toxicity of the effluent, validating the system as a sustainable and eco-safe solution for herbicide wastewater treatment.