Oxygen Vacancy-Induced Nonradical Degradation of Organics: Critical Trigger of Oxygen (O₂) in the Fe–Co LDH/Peroxymonosulfate System

Abstract

Ubiquitous oxygen vacancies (Vo) existing in metallic compounds can activate peroxymonosulfate (PMS) for water treatment. However, under environmental conditions, especially oxygenated surroundings, the interactions between Vo and PMS as well as the organics degradation mechanism are still ambiguous. In this study, we provide a novel insight into the PMS activation mechanism over Vo-containing Fe−Co layered double hydroxide (LDH). Experimental results show that Vo/PMS is capable of selective degradation of organics via a single-electron-transfer nonradical pathway. Moreover, O 2 is firstly demonstrated as the most critical trigger in this system. Mechanistic studies reveal that, with abundant electrons confined in the vacant electron orbitals of Vo, O 2 is thermodynamically enabled to capture electrons from Vo to form O 2•− under the imprinting effect and start the activation process. Simultaneously, Vo becomes electron-deficient and withdraws the electrons from organics to sustain the electrostatic balance and achieve organics degradation (32% for Bisphenol A without PMS). Different from conventional PMS activation, under the collaboration of kinetics and thermodynamics, PMS is endowed with the ability to donate electrons to Vo as a reductant other than an oxidant to form 1 O 2 . In this case, 1 O 2 and O 2•− act as the indispensable intermediate species to accelerate the circulation of O 2 (as high as 14.3 mg/L) in the micro area around Vo, and promote this nanoconfinement electron-recycling process with 67% improvement of Bisphenol A degradation. This study provides a brand-new perspective for the nonradical mechanism of PMS activation over Vo-containing metallic compounds in natural environments.

Mineral Modulated Single Atom Catalyst for Effective Water Treatment

“…The process of electron transfer could be confirmed by the obviously increased cathodic current densities for the p‐CoSi 1 N 3 @D electrode with the addition of PMS in the LSV analysis (Figure S41, Supporting Information). [ 18,58 ] In this case, PMS is decomposed to be SO 5 •− and to subsequently form 1 O 2 (Equations (1) and (2)), which agreed well with the EPR and scavenging experiment results [ 61,62 ] …”

“…•− and to subsequently form 1 O 2 (Equations ( 1) and ( 2)), which agreed well with the EPR and scavenging experiment results [61,62] HSO e SO H 5 5…”

Coordination Number Dependent Catalytic Activity of Single‐Atom Cobalt Catalysts for Fenton‐Like Reaction

“…The blue shift of SO 3 − peak means the electron transfer from PMS to the CoN 2 catalyst, suggesting the occurrence of PMS oxidation. [ 41 ] On the other hand, the red shift of SO 3 − peak is attributable to the electron accumulation of PMS from CoN 2 resulting in PMS reduction. [ 41 ] The similar blue and red shifts of SO 3 − peak are also noted for in situ Raman spectra of CoN 4 /PMS and CoN 3 /PMS suspensions (Figure S19, Supporting Information), further testifying to simultaneous PMS reduction and oxidation over all CoN x catalysts.…”

“…[ 41 ] On the other hand, the red shift of SO 3 − peak is attributable to the electron accumulation of PMS from CoN 2 resulting in PMS reduction. [ 41 ] The similar blue and red shifts of SO 3 − peak are also noted for in situ Raman spectra of CoN 4 /PMS and CoN 3 /PMS suspensions (Figure S19, Supporting Information), further testifying to simultaneous PMS reduction and oxidation over all CoN x catalysts. Therefore, the PMS conversion mechanisms by CoN x are illustrated in Figure 5e, where modulation of coordination number can tune PMS conversion pathway over CoN x .…”

“…The blue shift of SO 3 − peak means the electron transfer from PMS to the CoN 2 catalyst, suggesting the occurrence of PMS oxidation. [41] On the other hand, the red shift of SO 3 − peak is attributable to the electron accumulation of PMS from CoN 2 resulting in PMS reduction. [41] The similar blue and red shifts of…”