Nitrilotriacetic acid-assisted activation of periodate by Fe(III) for organic pollutant degradation: the critical roles of high-valent iron species formation and coordination inhibition by phenolic contaminants

Iron-activated periodate (PI)-based advanced oxidation technologies remain constrained by critical challenges including the facile oxidative deactivation of Fe(II) and the weak reactivity between Fe(III) and PI. This study developed an oxidation system based on readily biodegradable nitrilotriacetic acid (NTA)-chelated Fe(III) complexes for efficient PI activation. The Fe(III)-NTA complex significantly enhanced the reactivity of Fe(III) toward PI, enabling complete degradation of carbamazepine (CBZ, 20 μM) within 60 min. Mass spectrometry identified hydroxylation, ring cleavage, and decarboxylation as primary degradation pathways for CBZ. Results from quenching experiments, chemical probe tests, electron paramagnetic resonance (EPR), 18 O isotopic labeling, and mass spectrometry collectively demonstrated that high-valent iron-oxo species (Fe(V)-oxo) served as the dominant reactive species, assisted by synergistic hydroxyl radical ( • OH) participation. Experimental and density functional theory (DFT) results indicated that the Fe(III)–NTA complex activates PI via an oxygen atom transfer (OAT) pathway, generating reactive Fe(V)-oxo intermediates. This Fe(V)-oxo species may subsequently undergo single electron transfer (SET) to produce • OH. In the degradation of CBZ, Fe(V)-oxo species and • OH were found to contribute approximately 90.9 % and 9.1 %, respectively. Furthermore, pollutants containing strong coordinating groups or lone pair electron donors exhibited competitive coordination effects with the central Fe atom, hindering Fe(III)-NTA-PI interactions and thereby impeding degradation kinetics. Post-degradation, PI was exclusively converted to non-toxic iodate without reduced iodine species (e.g., hypoiodous acid (HOI), iodine (I 2 ), or triiodide (I 3 − )). Theoretical toxicity simulations indicated significantly reduced ecological risks of transformation products. Acute toxicity assays using luminescent bacteria confirmed moderate alleviation of CBZ product toxicity after Fe(III)-NTA-PI treatment. This work provides novel strategies for optimizing iron-activated PI systems, advancing mechanistic insights into chelation-regulated metal activation, pollutant competitive coordination effects, and structure-activity relationships.