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

Abstract

Single‐atom catalysts (SACs) are widely investigated in Fenton‐like reactions for environmental remediation, wherein their catalytic performance can be further improved by coordination structure modulation, but the relevant report is rare. Herein, a series of atomically dispersed cobalt catalysts with diverse coordination numbers (denoted as CoNx, x represents nitrogen coordination number) are synthesized and their peroxymonosulfate (PMS) conversion performance is explored. The catalytic specific activity of CoNx is found to be dependent on coordination number of single atomic Co sites, where the lowest‐coordinated CoN2 catalyst exhibits the highest specific activity in PMS activation, followed by under‐coordinated CoN3 and normal CoN4. Experimental and theoretical results reveal that reducing coordination number can increase the electron density of single Co atom in CoNx, which governs the Fenton‐like performance of CoNx catalysts. Specifically, the entire Co–pyridinic NC motif serves as active centers for PMS conversion, where the single Co atom, and pyridinic N‐bonded C atoms along with nitrogen vacancy neighboring the unsaturated Co–pyridinic N2 moiety account for PMS reduction and oxidation toward radical and singlet oxygen (1O2) generation, respectively. These findings provide a useful avenue to coordination number regulation of SACs for environmental applications.

Low Concentration of Peroxymonosulfate Triggers Dissolved Oxygen Conversion over Single Atomic Fe–N3O1 Sites for Water Decontamination

“…The more significant suppression effect for FFA on BPA degradation suggests that 1 O 2 is the primary ROS, which can be also evidenced by the enhancement of BPA oxidation (Figure 4e) and improvement of 1 O 2 formation (Figure 4f) in Fe-CN 0.05 /PMS with the solvent exchange from H 2 O to deuterium oxide (D 2 O), owing to the tenfold extension for the lifetime of 1 O 2 in D 2 O relative to that in H 2 O. [15,47] Small 2023, 19, 2205583 As for Fe-based catalysts applied in organic pollutant degradation, high-valence Fe species have been reported to form and involve in the catalytic oxidation reaction. [48,49] In this regard, methyl phenyl sulfoxide (PMSO) was poured into the air-equilibrated Fe-CN 0.05 /PMS system to evaluate the contribution of high-valent Fe species to BPA degradation.…”

“…The more significant suppression effect for FFA on BPA degradation suggests that 1 O 2 is the primary ROS, which can be also evidenced by the enhancement of BPA oxidation (Figure 4e) and improvement of 1 O 2 formation (Figure 4f) in Fe‐CN 0.05 /PMS with the solvent exchange from H 2 O to deuterium oxide (D 2 O), owing to the tenfold extension for the lifetime of 1 O 2 in D 2 O relative to that in H 2 O. [ 15,47 ]…”

“…Li et al [10] reported the first application of singleatom cobalt (Co) catalyst by anchoring single Co atoms onto nitrogen-doped graphene in peroxymonosulfate (PMS) activation, and revealed that the CoN 4 center accounted for PMS conversion into singlet oxygen ( 1 O 2 ) to efficiently oxidize organic pollutant adsorbed on the adjacent pyrrolic N site. Afterward, multifarious carbon-based SACs, such as single-atom Co, [11][12][13][14][15] Fe, [16][17][18][19][20] Mn, [21] and Cu [22,23] catalysts with M-N 4 coordination configuration, have been exploited and applied for the activation of PMS, where the radical process and non-radical pathways, including electron transfer, high-valent metal species formation, and singlet oxygenation, have been proposed. Unlike the aforementioned PMS activation mechanisms, our previous work [16] demonstrated the simultaneous PMS reduction and oxidation over single atomic Fe-N 4 sites in terms of PMS reduction at the electron-rich single-atomic Fe site for • OH and SO 4…”

Generating dual-active species by triple-atom sites through peroxymonosulfate activation for treating micropollutants in complex water

“…It is noteworthy that in the Co-BOC/PMS system, the SO 3 − (HSO 5 − ) peak splits into two small peaks located at 1,051 cm −1 and 1,062 cm −1 . And the characteristic vibrational peaks of the SO 3 − (HSO 5 − ) appear both red shifted (1,051 cm −1 ) and blue shifted (1,062 cm −1 ), suggesting that electron transfer occurs between the asymmetric sites and the PMS as well as the orientation may be different ( 47 – 49 ). Combined with XPS analysis, it can be concluded that the red shift and blue shift come from PMS gaining electrons from the Bi site and losing electrons at the Co site, respectively.…”

Single-Atom MnN5 Catalytic Sites Enable Efficient Peroxymonosulfate Activation by Forming Highly Reactive Mn(IV)–Oxo Species

“…The coordination number of M–N moieties in SACs strongly affects the geometric and electronic properties, as well as the catalytic activity of SACs. While SACs with a coordination number higher than four have been used for selective conversion of hydrocarbons and oxygen reduction reactions − and play prominent roles in biomimetic and enzymatic oxidation reactions, − the five-nitrogen coordinated SACs are seldom explored for persulfate activation except for Fe–N 5 SACs. , This represents a fundamental knowledge gap and a missed opportunity for coordination chemistry using other transition metal SACs (such as Co, Mn, Cu, and Ni) to boost PMS activation and enhance the degradation of recalcitrant organic pollutants. For instance, while Mn SACs have been tested for HVMO-dominated persulfate activation, five-nitrogen coordinated Mn SACs have not.…”