Ferrate(VI)-Driven Transformation of Organophosphorus Compounds: Structure-Dependent Reactivity and Implications for Phosphorus Control

Abstract

Anthropogenic organophosphorus compounds (OPCs) are water contaminants of concern because of their ecotoxicity and contribution to phosphorus loading. We investigated the quantitative reaction chemistry and phosphorus fate of 17 OPCs during ferrate(VI) treatment. Second-order rate constants ranged from 12.2 to 353.1 M–1 s–1 at pH 7.0, with phosphonates generally reacting faster than organophosphate esters. A speciation-based kinetic model identified HFeVIO4– and partially deprotonated OPCs as kinetically relevant reactants. Direct Fe(VI) accounted for 83.7–98.9% of their transformation, whereas Fe(V)/Fe(IV) and •OH made minor contributions. Product identification and theoretical analyses revealed oxidative dephosphorylation as an important transformation pathway. C–P bond cleavage predominated for glyphosate (GLY), converting 92.9% of its phosphorus to orthophosphate at an Fe(VI)-to-GLY ratio of 20:1 and pH 7.0. Even for less reactive chlorpyrifos and trichlorfon, phosphate yields could approach 18.6% and 20.4%, respectively. Ferrate-derived Fe(III) nanoparticles captured the released phosphate, achieving 71.5% total phosphorus and 67.2% total organic carbon removal. A quantitative structure–activity relationship model, independently evaluated with five additional OPCs (R2 = 0.807), identified oxidation potential, molecular complexity, phosphorus functional-group identity, and phosphorus-centered steric hindrance as reactivity determinants. These findings deepen mechanistic understanding of ferrate reactions with OPCs and inform rational ferrate application for organophosphorus pollution control.