Peroxymonosulfate Activation by Fe(III)–Picolinate Complexes for Efficient Water Treatment at Circumneutral pH: Fe(III)/Fe(IV) Cycle and Generation of Oxyl Radicals

Abstract

Improving the reactivity of Fe(III) for activating peroxymonosulfate (PMS) at circumneutral pH is critical to propel the iron-activated PMS processes toward practical wastewater treatment but is yet challenging. Here we employed the complexes of Fe(III) with the biodegradable picolinic acid (PICA) to activate PMS for degradation of selected chlorinated phenols, antibiotics, pharmaceuticals, herbicides, and industrial compounds at pH 4.0− 6.0. The Fe III −PICA complexes greatly outperformed the ligand-free Fe(III) and other Fe(III) complexes of common aminopolycarboxylate ligands. In the main activation pathway, the key intermediate is a peroxymonosulfate complex, tentatively identified as PICA−Fe III − OOSO 3 − , which undergoes O−O homolysis or reacts with Fe III − PICA and PMS to yield Fe IV =O and SO 4•− without the involvement of commonly invoked Fe(II). PICA−Fe III −OOSO 3 − can also react directly with certain compounds (chlorophenols and sulfamethoxazole). The relative contributions of PICA−Fe III −OOSO 3 − , Fe IV =O, and SO 4•− depend on the structure of target compounds. This work sets an eligible example to enhance the reactivity of Fe(III) toward PMS activation by ligands and sheds light on the previously unrecognized role of the metal−PMS complexes in directing the catalytic cycle and decontamination as well.

Critical Role of Mineral Fe(IV) Formation in Low Hydroxyl Radical Yields during Fe(II)-Bearing Clay Mineral Oxygenation

“…This result suggests that structural Fe­(II), rather than aqueous Fe 2+ dominated the formation of PMSO 2 [i.e., Fe­(IV)]. Many previous studies have demonstrated the formation of aqueous Fe­(IV) during the oxidation of Fe 2+ in advanced oxidation processes. − Our results extended the generation of Fe­(IV) from homogeneous Fe 2+ systems to structural Fe­(II) associated with clay minerals.…”

A manganese-based catalyst system for general oxidation of unactivated olefins, alkanes, and alcohols

“…Furthermore, picolinic acid derivatives have been used for (noble)metal-catalysed reactions in the fields of water oxidation, 25 photochemistry, 26,27 and others. 28–32…”

Enhanced Degradation of Micropollutants in a Peracetic Acid/Mn(II) System with EDDS: An Investigation of the Role of Mn Species

“…In contrast, diethylenetriaminepentaacetic acid (DTPA) and ethylenediaminetetraacetic acid (EDTA) are nonbiodegradable, and NTA is carcinogenic. The widely used 2-pyridinecarboxylic acid (PICA) will also increase the organic load and nitrogen content, which is unfavorable for wastewater treatment . Moreover, EDDS has been shown to improve the efficiency of Fenton and Fenton-like oxidation and is gradually being extensively studied. , Therefore, EDDS was considered as a candidate to enhance the catalytic efficiency of the Mn­(II)/PAA system.…”