Unraveling the High-Activity Origin of Single-Atom Iron Catalysts for Organic Pollutant Oxidation via Peroxymonosulfate Activation

Abstract

Single-atom catalysts (SACs) have emerged as efficient materials in the elimination of aqueous organic contaminants; however, the origin of high activity of SACs still remains elusive. Herein, we identify an 8.1-fold catalytic specific activity (reaction rate constant normalized to catalyst’s specific surface area and dosage) enhancement that can be fulfilled with a single-atom iron catalyst (SA-Fe-NC) prepared via a cascade anchoring method compared to the iron nanoparticle-loaded catalyst, resulting in one of the most active currently known catalysts in peroxymonosulfate (PMS) conversion for organic pollutant oxidation. Experimental data and theoretical results unraveled that the high-activity origin of the SA-Fe-NC stems from the Fe–pyridinic N4 moiety, which dramatically increases active sites by not only creating the electron-rich Fe single atom as the catalytic site but also producing electron-poor carbon atoms neighboring pyridinic N as binding sites for PMS activation including synchronous PMS reduction and oxidation together with dissolved oxygen reduction. Moreover, the SA-Fe-NC exhibits excellent stability and applicability to realistic industrial wastewater remediation. This work offers a novel yet reasonable interpretation for why a small amount of iron in the SA-Fe-NC can deliver extremely superior specific activity in PMS activation and develops a promising catalytic oxidation system toward actual environmental cleanup.

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

“…The specific activity of CoN x catalysts is found to be linearly related to the Bader charges of Co single atom and the most electron‐poor C atom adjacent to pyridinic N in CoN x models (Figure 4b), but the regression coefficient of the former is slightly higher than that of the latter, which suggests that the electron density of single Co atom mainly governs the Fenton‐like performance of CoN x . Our previous works [ 6–8 ] demonstrated that the electron‐rich and electron‐deficient areas were responsible for PMS reduction and oxidation, respectively. In the case of CoN x for PMS activation, the electron‐rich single Co atoms and electron‐poor pyridinic N‐coordinated C atoms can act as catalytic sites toward PMS adhesion and successive conversion.…”

“…In other words, the pyridinic N‐coordinated electron‐poor C atoms are responsible for PMS oxidation resulting in the production of PMS anion radical (SO 5 •‒ ), which subsequently transforms into singlet oxygen ( 1 O 2 ) through reaction with water molecules, consistent with previous works. [ 6–8,37 ] In this context, the CoN 4 catalyst with single‐atomic Co–pyridinic N 4 moiety possesses more electron‐deficient C atoms adjacent to pyridinic N should produce the larger amount of 1 O 2 resulting from PMS oxidation, which is evidenced by the stronger 1 O 2 signal intensity for the EPR spectrum of CoN 4 /PMS as compared to that for CoN 3 /PMS (see Figure 3b above). However, the further decrease of coordination number to two for CoN x in turn enhances the generation of 1 O 2 in CoN 2 /PMS (Figure 3b).…”

“…Moreover, an evident enhancement of the absorption peak intensity for the used CoN 2 is observed, which reflects the strong interaction between CoN 2 and PMS. [8,38] The C 1s XPS spectra of CoN 2 before and after PMS activation (Figure 5c) show an insignificant shift for CC/CC peak but an obvious negative shift for the CN peak in the used CoN 2 . Moreover, a new peak emerges at 286.4 eV referring to the CO species [17,39] in the spent catalyst, which can be ascribed to the adsorption of organic pollutant degradation intermediates, consistent with the above XPS O 1s analysis result.…”

Carbon Nitride Supported High‐Loading Fe Single‐Atom Catalyst for Activation of Peroxymonosulfate to Generate 1O2 with 100 % Selectivity

“…Consequently, the generation of COH, SO 4 C À , and other radicals have not been eliminated to date. [12] Furthermore, the sparse doping of N, which fixes the metal atoms by coordination, causes the low metal loading, which retards the generation of 1 O 2 . [13] Therefore, the SACs having uniformly structured supports and abundant active sites are required for the selective generation of 1 O 2 .…”

Towards single‐atom photocatalysts for future carbon‐neutral application

“…Conceptually, the pyrolysis method means that the metal precursor is dispersed through a space confinement strategy, and then the precursor material is reduced by high‐temperature heating to generate a single‐atom catalyst in situ 108,132 . The pyrolysis method is widely applicable to various carriers, such as zeolite, 133 MOFs, 134 covalent organic frameworks (COFs), 135,136 g‐C 3 N 4 83,137 ‐modified carbon‐based materials, 138,139 and so on.…”