Activation of peroxymonosulfate by single atom Co-N-C catalysts for high-efficient removal of chloroquine phosphate via non-radical pathways: Electron-transfer mechanism

Cheap and abundant Fe based catalysts in advanced oxidation progresses (AOPs) usually exhibit radicals or high-valent Fe species (HV-Fe) dominated activation mechanism. In this contribution, the atomically dispersed Fe on g-C3N4 (SAFe-CN) was fabricated for peroxymonosulfate (PMS) activation to degrade o-phenylphenol (OPP). OPP removal was not impeded by common radical scavengers, indicating the absence of SO4•− and •OH. The involvement of 1O2 and HV–Fe was excluded and the mediated electron transfer was finally identified as the dominated mechanism. Atomically dispersed Fe sites in SAFe-CN were verified as active sites for reacting with O O bond of PMS and ulteriorly electron shuttling in pollutants degradation. A water treatment filter was fabricated using SAFe-CN and it remained 100% of OPP removal after 100 h of operation. These results provide new insights into the mechanism of mediated electron transfer as well as potential application of non-radical dominated process at device level.

Activation of peroxymonosulfate via mediated electron transfer mechanism on single-atom Fe catalyst for effective organic pollutants removal

High-valent iron(IV)-oxo complexes are of great significance as reactive intermediates implicated in diverse chemical and biological systems. The aqueous iron(IV)-oxo complex (FeaqIVO2+) is the simplest but one of the most powerful ferryl ion species, which possesses a high-spin state, high reduction potential, and long lifetime. It has been well documented that FeaqIVO2+ reacts with organic compounds through various pathways (hydrogen-atom, hydride, oxygen-atom, and electron transfer as well as electrophilic addition) at moderate reaction rates and show selective reactivity toward inorganic ions prevailing in natural water, which single out FeaqIVO2+ as a superior candidate for oxidative water treatment. This review provides state-of-the-art knowledge on the chemical properties and oxidation mechanism and kinetics of FeaqIVO2+, with special attention to the similarities and differences to two representative free radicals (hydroxyl radical and sulfate radical). Moreover, the prospective role of FeaqIVO2+ in Feaq2+ activation-initiated advanced oxidation processes (AOPs) has been intensively investigated over the past 20 years, which has significantly challenged the conventional recognition that free radicals dominated in these AOPs. The latest progress in identifying the contribution of FeaqIVO2+ in Feaq2+-based AOPs is thereby reviewed, highlighting controversies on the nature of the reactive oxidants formed in several Feaq2+ activated peroxide and oxyacid processes. Finally, future perspectives for advancing the evaluation of FeaqIVO2+ reactivity from an engineering viewpoint are proposed. 

Aqueous Iron(IV)–Oxo Complex: An Emerging Powerful Reactive Oxidant Formed by Iron(II)-Based Advanced Oxidation Processes for Oxidative Water Treatment

In this study, the performance of periodate (PI) on sulfadiazine (SDZ) degradation was evaluated using coagulation solid waste fabricated catalyst (CWBC), obtained by simple pyrolysis. SDZ effectively underwent 98.94% remove within 90 min in the CWBC/PI system. Electron transfer was the predominant mechanism due to the development of an electronic cycle among SDZ, CWBC and PI, where the O 2 •− , PFRs, and the reactive iodine species had minor roles. Density functional theory calculations identified that Fe and N could change the electron configuration and break the chemical inertness of carbonaceous material. As a result, electrons on the carbon matrix of CWBC are inclined to travel through the formed Fe–O covalent bond to PI. Further analysis demonstrated that SO 4 2− , humic acid (HA), as well as anoxic conditions greatly facilitated SDZ degradation. This study provides a facile protocol for converting coagulation waste to an efficient catalyst and provides fundamental insights into the degradation mechanisms of micropollutants by activating PI. • A carbonaceous catalyst was prepared from coagulation waste to activate periodate. • Electron transfer has a dominant effect on sulfadiazine degradation. • Fe and N could change the electron configuration of carbonaceous catalyst. • Chemisorption between Fe and PI was the key step for the catalytic process. • Sulfadiazine removal can be significantly enhanced under anoxic conditions. 

Fe, N-doped carbonaceous catalyst activating periodate for micropollutant removal: Significant role of electron transfer

Potassium periodate (PI, KIO4) was readily activated by Fe(II) under acidic conditions, resulting in the enhanced abatement of organic contaminants in 2 min, with the decay ratios of the selected pollutants even outnumbered those in the Fe(II)/peroxymonosulfate and Fe(II)/peroxydisulfate processes under identical conditions. Both 18O isotope labeling techniques using methyl phenyl sulfoxide (PMSO) as the substrate and X-ray absorption near-edge structure spectroscopy provided conclusive evidences for the generation of high-valent iron-oxo species (Fe(IV)) in the Fe(II)/PI process. Density functional theory calculations determined that the reaction of Fe(II) with PI followed the formation of a hydrogen bonding complex between Fe(H2O)62+ and IO4(H2O)-, ligand exchange, and oxygen atom transfer, consequently generating Fe(IV) species. More interestingly, the unexpected detection of 18O-labeled hydroxylated PMSO not only favored the simultaneous generation of ·OH but also demonstrated that ·OH was indirectly produced through the self-decay of Fe(IV) to form H2O2 and the subsequent Fenton reaction. In addition, IO4- was not transformed into the undesired iodine species (i.e., HOI, I2, and I3-) but was converted to nontoxic iodate (IO3-). This study proposed an efficient and environmental friendly process for the rapid removal of emerging contaminants and enriched the understandings on the evolution mechanism of ·OH in Fe(IV)-mediated processes.

Zhenyu Zhao

Papers

Enhanced Oxidation of Organic Contaminants by Iron(II)-Activated Periodate: The Significance of High-Valent Iron-Oxo Species.