Transition metal catalysts are known to activate persulfate, but the properties that govern the intrinsic activity of these catalysts are still unknown. Here, we developed a series of catalysts with transition metals anchored on carbon nanotubes (denoted M–N–CNTs, where M = Co, Fe, Mn, or Ni) containing single-atom M–N moieties, to activate peroxymonosulfate for the efficient nonradical oxidation of sulfamethoxazole. The spin state of M–N–CNTs strongly determined their catalytic activity. A large effective magnetic moment with a high spin state (e.g., Co–N) favored the overlap of d orbitals with oxygen-containing adsorbates (such as peroxo species) on metal active sites and promoted electron transfer, which facilitated peroxymonosulfate adsorption and enhanced the oxidation capacity of the reactive species. These findings advance the mechanistic understanding of transition metal-mediated persulfate activation and inform the development of efficient spintronic catalysts for environmental applications.

A mixed ionic−electronic conducting (MIEC) double perovskite, PrBaCo 2 O 5+δ (PBC), was synthesized and evaluated as the heterogeneous catalyst to generate radicals from peroxymonosulfate (PMS) for the oxidative degradation of organic wastes in aqueous solution. A superior catalytic activity was obtained for PBC, which was much higher than that of the most popular Co 3 O 4 nanocatalyst. More importantly, a detailed mechanism of PMS activation on the MIEC perovskite was proposed. Electron paramagnetic resonance (EPR) and radical competitive reactions suggested that both sulfate radicals (SO 4 •−) and hydroxyl radicals ( • OH) participated in and played important roles in the catalytic oxidation processes. Oxygen temperature-programmed desorption (O 2 -TPD) demonstrated that the PBC perovskite oxide is capable of facilitating an easier valence-state change of the B-site cation (cobalt ions) to mediate a redox process. Additionally, the oxygen vacancies could facilitate the bonding with PMS molecules and promote the reactivity of cobalt ions for PMS activation. Electrochemical impedance spectroscopy (EIS) was also performed to evidence charge transfer and surface reaction rates of the PBC catalyst that are much faster than those of Co 3 O 4 . Additionally, suppressed cobalt leaching was also achieved through tailoring the pH value of the reaction solution. This study provides insight into MIEC perovskites in catalytic reactions and applications.

Nitrogen-doped carbon materials attract broad interest as catalysts for peroxymonosulfate (PMS) activation toward an efficient, nonradical advanced oxidation process. However, synthesis of N-rich carbocatalysts is challenging because of the thermal instability of desirable nitrogenous species (pyrrolic, pyridinic, and graphitic N). Furthermore, the relative importance of different nitrogenous configurations (and associated activation mechanisms) are unclear. Herein, we report a “coating-pyrolysis” method to synthesize porous 2D N-rich nanocarbon materials (PCN-x) derived from dopamine and g-C3N4 in different weight proportions. PCN-0.5 calcined at 800 °C had the highest surface area (759 m2/g) and unprecedentedly high N content (18.5 at%), and displayed the highest efficiency for 4-chlorophenol (4-CP) degradation via PMS activation. A positive correlation was observed between 4-CP oxidation rates and the total pyridinic and pyrrolic N content. These N dopants serve as Lewis basic sites to facilitate 4-CP adsorption on the PCN surface and subsequent electron-transfer from 4-CP to PMS, mediated by surface-bound complexes (PMS–PCN-0.5). The main degradation products were chlorinated oligomers (mostly dimeric biphenolic compounds), which adsorbed to and deteriorated the carbocatalyst. Overall, this study offers new insights for rational design of nitrogen-enriched carbocatalysts, and advances mechanistic understanding of the critical role of N species during nonradical PMS activation.

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