Picolinic Acid-Mediated Catalysis of Mn(II) for Peracetic Acid Oxidation Processes: Formation of High-Valent Mn Species

Abstract

Metal-based advanced oxidation processes (AOPs) with peracetic acid (PAA) have been extensively studied to degrade micropollutants (MPs) in wastewater. Mn(II) is a commonly used homogeneous metal catalyst for oxidant activation, but it performs poorly with PAA. This study identifies that the biodegradable chelating ligand picolinic acid (PICA) can significantly mediate Mn(II) activation of PAA for accelerated MP degradation. Results show that, while Mn(II) alone has minimal reactivity toward PAA, the presence of PICA accelerates PAA loss by Mn(II). The PAA-Mn(II)-PICA system removes various MPs (methylene blue, bisphenol A, naproxen, sulfamethoxazole, carbamazepine, and trimethoprim) rapidly at neutral pH, achieving >60% removal within 10 min in clean and wastewater matrices. Coexistent H 2 O 2 and acetic acid in PAA play a negligible role in rapid MP degradation. In-depth evaluation with scavengers and probe compounds (tert-butyl alcohol, methanol, methyl phenyl sulfoxide, and methyl phenyl sulfone) suggested that high-valent Mn species (Mn(V)) is a likely main reactive species leading to rapid MP degradation, whereas soluble Mn(III)-PICA and radicals (CH 3 C(O)O • and CH 3 C(O)OO • ) are minor reactive species. This study broadens the mechanistic understanding of metal-based AOPs using PAA in combination with chelating agents and indicates the PAA-Mn(II)-PICA system as a novel AOP for wastewater treatment.

Hierarchical Porous Bimetallic FeMn Metal–Organic Framework Gel for Efficient Activation of Peracetic Acid in Antibiotic Degradation

“… Moreover, PAA oxidizes Mn­(II) into Mn­(IV) through continuous electron transfer, producing CH 3 C­(O)­O • (eq ). Mn­(IV) is reduced back to Mn­(II) by H 2 O 2 , forming a redox cycle (eq ). What is more is that the standard redox potential of Mn­(IV)/Mn­(II) is higher than that of Fe­(III)/Fe­(II) (1.23 vs 0.77 V), resulting in electron transfer from Fe­(II) to Mn­(IV) (eq ).…”

“… What is more is that the standard redox potential of Mn­(IV)/Mn­(II) is higher than that of Fe­(III)/Fe­(II) (1.23 vs 0.77 V), resulting in electron transfer from Fe­(II) to Mn­(IV) (eq ). This electron transfer process generates Mn­(II) and Fe­(III), which in turn accelerates the redox cycle and formation of primary radicals. , However, both Fe­(II) and Mn­(II) may react with PAA to generate • OH, which could be negligible in the process (eqs and ). , The generated CH 3 C­(O)­O • rapidly reacts with PAA and forms more CH 3 C­(O)­OO • , which plays a vital role in OFX degradation (eq ). Other secondary radicals, most likely contributing minor effects to OFX degradation, are produced by reactions between primary radicals with PAA and H 2 O 2 (eqs and) According to the literature, • CH 3 could be produced by self-decay of CH 3 C­(O)­O • (eq ); however, this trait is not obvious in the process, plausibly because of its low concentration …”

Overlooked Role of Coexistent Hydrogen Peroxide in Activated Peracetic Acid by Cu(II) for Enhanced Oxidation of Organic Contaminants

“…Nevertheless, PAA alone could only directly degrade certain organic contaminants with electron-rich structures (e.g., sulfur moiety, aromatic ring, and CC bond) . Up to now, a number of activation strategies have been proposed to enhance the oxidative performance of PAA, such as energy input (e.g., ultraviolet, , heat, electrochemistry, microwave, and ultrasound), metal catalysts (e.g., homogeneous − and heterogeneous − transition metals), carbon materials, , and anionic catalysts (e.g., phosphate, bromide, , iodine, , chloride, and nitrite), etc.…”

How Do Metal Oxides Mislead Spin-Trapping Electron Paramagnetic Resonance Analysis?

“…However, a false DMPO–OH signal has been demonstrated to be originated from direct oxidation in electrocatalytic process . In addition, the DMPO–OH formation caused by the nucleophilic dosing of water to DMPO has been observed in the presence of transition metal ions such as Cu 2+ and Fe 3+ . , These ions are well-known for catalyzing the oxidation of organic compounds by peroxides, leading to Fenton and Fenton-like reactions. − Consequently, as transition metal-based heterogeneous catalysts are developed for radical-dominant catalytic oxidation processes, − the possibility of nonradical transformations of DMPO warrants investigations. Given the tendency of metal ions to dissolve into aqueous environments from solid phases, , we propose that nanomaterials containing transition metals could be significant sources of unrecognized false-positive EPR signals in radical identification.…”