A nonradical oxidation process via metal-free peroxymonosulfate (PMS) activation has recently attracted considerable attention for organic pollutant degradation; however, the origin of singlet oxygen ( 1 O 2 ) generation still remains controversial. In this study, nitrogen-doped carbon nanosheets (NCN-900) derived from graphitic carbon nitride were developed for activation of PMS and elucidation of 1 O 2 production. With a large specific surface area (1218.7 m 2 g −1 ) and high nitrogen content (14.5 at %), NCN-900 exhibits superior catalytic activity in PMS activation, as evidenced by complete degradation of bisphenol A within 2 min using 0.1 g L −1 NCN-900 and 2 mM PMS. Moreover, the reaction rate constant fitted by pseudofirst-order kinetics for NCN-900 reaches an impressive value of 3.1 min −1 . Electron paramagnetic resonance measurements and quenching tests verified 1 O 2 as the primary reactive oxygen species in the NCN-900/PMS system. Based on X-ray photoelectron spectroscopy analysis and theoretical calculations, an unexpected generation pathway of 1 O 2 involving PMS oxidation over the electron-deficient carbon atoms neighboring graphitic N in NCN-900 was unraveled. Besides, the NCN-900/PMS system is also applicable for remediation of actual industrial wastewater. This work highlights the important role of electron-deficient carbon atoms in 1 O 2 generation from PMS oxidation and furnishes theoretical support for further relevant studies.

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.

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