Cyclotriphosphazene (P3N3) derived FeOx@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 FexO atoms could significantly improve catalytic performance, however, developing a robust catalyst with quaternary heteroatom-doped carbons and FexO is rarely addressed. We fabricated FeOx@SPNO-C core-shell nanospheres by using cyclotriphosphazene (P3N3)-derived covalent organic-inorganic hybrid frameworks (COIFs) and Fe3O4. The assynthesized FeOx@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-Nx 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 FexO 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 pi electrons. Lastly, the presence of N/Fe-Nx 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 FeOx@SPNO-C under harsh experimental conditions makes it a potential candidate for the commercial-scale Fenton-like catalyst.

Automated summary

In this study, FeOx@SPNO-C core-shell nanospheres as a catalyst for degradation of sulfamethoxazole (SMX) were successfully synthesized. The synergistic interaction between FeOx and SPNO-C, high carbon charge density, and the presence of C = O groups and N/Fe-Nx sites were found to be key factors for the enhanced degradation of SMX.