Key Takeaways & Executive Findings
- •• M-Nx-C active sites, particularly unconventional UM-Nx-C (x≠4), are crucial for non-radical persulfate activation in single-atom catalysts. • Direct and indirect synthesis methods for M-Nx-C sites are systematically reviewed, with emphasis on UM-Nx-C formation. • Catalyst supports such as g-C3N4, MOFs, COFs, and other carbon materials significantly influence the formation and performance of M-Nx-C sites. • The review highlights the role of M-Nx-C in non-radical pathways (e.g., high-valence metals, singlet oxygen, electron transfer) for organic contaminant degradation.
Abstract
In recent years, numerous single-atom catalysts (SACs) have been synthesized to activate persulfate (PS) by a non-radical pathway because of its high selectivity, and activity for the catalyst. Metal-nitrogen-carbon (M-Nx-C) has been identified as the key active site in SACs. Although methods for preparing SACs have been extensively reported, a systematic summary of the direct construction of M-Nx-C, especially unconventional metal-nitrogen-carbon (UM-Nx-C, x≠4), on SACs for PS non-radical activation has still not been reported. The role of the M-Nx-C active sites on PS non-radical activation is discussed and methods for the formation of M-Nx-C and UM-Nx-C active sites in SACs and the effect of catalyst carriers such as carbon nitride (g-C3N4), MOFs, COFs, and other carbon materials are reviewed. Direct and indirect methods, especially for UM-Nx-C active site formation, are also elaborated. Factors affecting the formation of a M-Nx-C active site on SACs are also discussed. Prospects for the use of M-Nx-C active sites for the non-radical activation of PS by SACs to remove organic contaminants from wastewater are evaluated.
1. Introduction
In recent years, a large amount of wastewater has been discharged with the development of the chemical industry. The wastewater produced from the chemical manufacturing processes contains a lot of organic contaminants, which are difficult to remove through traditional wastewater treatment technology. The chemical wastewater usually contains phenolic compounds, halogenated hydrocarbons, organic pesticides, hydrocarbons, and endocrine disruptors. These contaminants are carcinogenic, teratogenic, mutagenic, and toxic, and would cause irreversible harm to humans[1–3]. Those refractory organics usually have a stable chemical structure, and the traditional wastewater treatment technologies such as coagulation, adsorption, precipitation, membrane separation are difficult to remove them.
In recent years, advanced oxidation processes (AOPs) have been widely used to treat refractory organic contaminants in wastewater[4]. Activated persulfate (PS), as one of the AOPs, is widely used to oxidize refractory organic contaminants in wastewater. The sulfate radical (SO4·−) produced by PS activation has a wider pH range, better reaction activity, and a longer half-time than that of hydroxyl radicals (·OH)[5–6]. PS mainly consists of peroxymonosulfate (PMS) and perdisulfate (PDS), which have different characteristics due to the asymmetric structure of PMS. Compared with PDS, PMS has an asymmetric molecular structure, shorter O―O bond length (1.453 π), positive peroxy bond, higher activity, and is easier to activate[7]. PS can be activated using different methods, such as heating, alkali, ultraviolet (UV) light, ultrasound, and other physical methods[8–9]. Meanwhile, incorporating transition metals (including Fe/...
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SI Wen-hao, SI Jin-xuan, WANG Kang-jun, QI Fei, CHEN Jia-bin, ZENG Ze-quan, HUANG Zhang-gen (2025). Methods for the formation of M-Nx-C active sites on single-atom catalysts and their role in persulfate activation by non-radical paths. SinoTechIntel Verified Research. https://doi.org/10.1016/S1872-5805(NCM2025-5-3)
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
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Frequently Asked Questions
What are M-Nx-C active sites in single-atom catalysts?
M-Nx-C active sites refer to metal atoms coordinated with nitrogen atoms within a carbon matrix, which are key catalytic sites in single-atom catalysts (SACs). They play a crucial role in activating persulfate via non-radical pathways for organic pollutant degradation.
Why are unconventional M-Nx-C (UM-Nx-C) sites important?
UM-Nx-C sites, where the coordination number x is not equal to 4, can exhibit unique electronic properties and enhanced catalytic activity compared to conventional M-N4-C sites, offering new opportunities for efficient persulfate activation.
What methods are used to construct M-Nx-C active sites?
Methods include direct construction techniques such as impregnation, atomic layer deposition, and coprecipitation, as well as indirect methods involving post-treatment of supports. The choice of support (e.g., g-C3N4, MOFs, COFs) also influences the formation of M-Nx-C sites.
How do M-Nx-C sites activate persulfate via non-radical pathways?
M-Nx-C sites can activate persulfate through non-radical mechanisms such as the formation of high-valence metal-oxo species, singlet oxygen generation, and electron transfer processes, leading to selective oxidation of organic contaminants.
What is the significance of this review for wastewater treatment?
This review provides a systematic understanding of M-Nx-C active site formation and their role in non-radical persulfate activation, which is essential for designing efficient SACs for the removal of refractory organic contaminants from wastewater.
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