Selective degradation of sulfamethoxazole by N-doped iron-based carbon activated peroxymonosulfate: Collaboration of singlet oxygen and high-valent iron-oxo species

Fe-based catalysts activating peroxymonosulfate (PMS) for the generation of hydroxyl radicals ((OH)-O-center dot) and sulfate radicals (SO4 center dot-) have attracted widespread interest to efficient degrade contaminants. However, their limitations, including the leaching of metals and the instability of free radicals, are still thorny issues that plague researchers. In this study, an N-doped graphite catalyst (Fe-NC-4) was developed to activate PMS for the degradation of sulfamethoxazole (SMX). Transmission electron microscopy, X-ray diffraction and Raman spectroscopy found that Fe-N active site was evenly distributed in the catalyst, and the iron leached under any experimental conditions was far below the instrument detection limit. Fe-NC-4 performed superior capacity in PMS activation, as evidenced by approximately 100% degradation of SMX after 10 min of treatment. Multiple experiments confirmed that (OH)-O-center dot, SO4 center dot-, and superoxide radical (O-2(center dot-)) exerted negligible contribution. The Fe-NC-4/PMS system degraded SMX mainly through non-radical pathway of singlet radical (O-1(2)) and high-valent iron-oxo species (equivalent to Fe(IV)=O). Moreover, the Fe-NC-4/PMS system had satisfactory stability in natural water and showed excellent selective oxidation of different contaminants. This work will shed new light on effective PMS activation by Fe-based catalysts to efficiently degrade aqueous contaminants via the non-radical pathway.