Cyclotriphosphazene (P₃N₃) derived FeO_x@SPNO-C core–shell nanospheres as peroxymonosulfate activator for degradation via non-radical pathway

Though synergistic interactions between quaternary heteroatom (S, N, P, O) and Fe_xO atoms could significantly improve catalytic performance, however, developing a robust catalyst with quaternary heteroatom-doped carbons and Fe_xO is rarely addressed. We fabricated FeO_x@SPNO-C core–shell nanospheres by using cyclotriphosphazene (P₃N₃)-derived covalent organic–inorganic hybrid frameworks (COIFs) and Fe₃O₄. The as-synthesized FeO_x@SPNO-C nanospheres catalyst attained superior PMS activation for degradation of sulfamethoxazole (SMX), achieving 99.5 % removal efficiency in 18 min, 65.1 % mineralization rate, lower iron leaching (0.014 mg/L), and reaction rate constant was 73.6 % higher than sole SPNO-C, counterpart. Non-radical ¹O₂ generation was the dominant pathway for SMX degradation, which was confirmed by electron paramagnetic resonance (EPR), radical quenching inorganic ions addition experiments, and density functional theory (DFT) calculations. Structural defects, C = O, C = C–C groups, and N/Fe-N_x sites atoms have been revealed to be active sites. The improved degradation of SMX may be attributed to many essential characteristics. Firstly, there is a synergistic impact between Fe_xO and SPNO-C. Additionally, the carbon charge density is high, and there are numerous structural defects present. Furthermore, there is a significant presence of C = O groups, with a higher proportion of sp² carbon containing sufficient free-flowing π electrons. Lastly, the presence of N/Fe-N_x sites also contributes to the enhanced degradation of SMX. Several intermediate products were found, and a potential degradation mechanism was postulated. The high performance of FeO_x@SPNO-C under harsh experimental conditions makes it a potential candidate for the commercial-scale Fenton-like catalyst.