Efficient removal of organic pollutants by a Co/N/S-doped yolk-shell carbon catalyst via peroxymonosulfate activation

Carbon-based catalysts with heteroatom doping and hollow structures are desired for advanced oxidation processes (AOPs). Herein, dual-shelled Co, N, and S codoped hollow carbon nanocages were developed by wrapping zeolitic imidazolate framework-67 (ZIF-67) with trithiocyanuric acid (TCA) and performing subsequent carbonization. The optimal composite catalyst (Co-NC-CoS) exhibited excellent catalytic performance toward different organic pollutants. Almost complete removal of 4-NP (60 mg/L-1) was achieved within 20 min by 10 mg of catalyst and 0.2 g/L-1 peroxymonosulfate (PMS). Moreover, the catalyst showed good stability and reusability. The effects of catalyst and PMS dose, pollutant concentration, pH and common anions were investigated, and reactive oxygen species (ROS) were studied by scavenger experiments and electron paramagnetic resonance (EPR) tests. The results show that multidoped atoms S, Co and N all contributed to the degradation system. Several lines of evidence suggested that S could change the catalytic process from Co3+/Co2+ to Co3+ / Co2+ /Co-0 reduction due to its low redox potential. Degradation was achieved through both radical and nonradical pathways, where sulfate radicals (SO4-), hydroxyl radicals (OH) and singlet oxygen (O-1(2)) were primary reactive species. Overall, this work may suggest that the novel multi heteroatom-doped catalysts with complex structures can be developed for environmental remediation.

Automated summary

A dual-shelled Co, N, and S codoped hollow carbon nanocages catalyst was successfully developed and showed excellent catalytic performance for various organic pollutants, achieving almost complete removal of 4-NP within 20 minutes. The catalyst exhibited good stability, reusability, and degradation efficacy through both radical and nonradical pathways involving sulfate radicals, hydroxyl radicals, and singlet oxygen as primary reactive species. The study suggests that novel multi heteroatom-doped catalysts with complex structures can be effective for environmental remediation.