Efficient activation of peroxymonosulfate by C3N5 doped with cobalt for organic contaminant degradation

Abstract

The activation of peroxymonosulfate (PMS) by metal-doped C–N-based materials has been used extensively for pollutant degradation but usually suffers from low efficiency and stability due to the relatively few N coordination sites, particularly for the degradation of persistent organic pollutants (POPs). To overcome these issues, we have developed a novel N site-abundant C₃N₅ doped with cobalt for PMS activation to degrade a typical POP (2,4,4′-trichlorobiphenyl, PCB28). It was found that cobalt-doped C₃N₅ (Co-C₃N₅) exhibited high activity towards activating PMS for the complete degradation of PCB28 within 30 min (k_obs = 0.1998 min⁻¹), which was 11.8–27.8 times higher than that with conventional metal-based persulfate activation processes. X-ray absorption fine structure (XAFS) spectroscopy, electron paramagnetic resonance (EPR), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), density functional theory (DFT) calculations, and radical quenching experiments were combined to clarify the activation mechanism of PMS by Co-C₃N₅. It was unveiled that isolated single Co atoms coordinated by pyridinic N (Co–N₄) were the main active sites for the catalytic decomposition of PMS to produce sulfate radicals for contaminant degradation. In addition, Co-C₃N₅ has stable catalytic performance with limited Co dissolution within five cycles over a wide range of pH values. This study provides a novel strategy to design highly effective metal-doped C–N-based catalysts for PMS-based advanced oxidation technologies for environmental remediation.