Synthesizing and characterizing Fe3O4 embedded in N-doped carbon nanotubes-bridged biochar as a persulfate activator for sulfamethoxazole degradation

Abstract

Nitrogen-doped magnetic carbon nanotubes-bridged biochar (Fe3O4@NCNTs-BC) was prepared by facile impregnation and pyrolysis strategies and showed an excellent capacity in activating persulfate for sulfamethoxazole (SMX) degradation. The airtight structure of iron oxide (Fe3O4) nanoparticles embedded in N-doped CNTs (NCNTs) was supported by biochar (BC) that could both promote the electron transfer and avoid large amounts of metal leaching. Quenching experiments, electron spin resonance (ESR) and in situ Raman spectroscopy analysis were performed to explore the dominant active species. In contrast to the superoxide radical (O2•-) dominated radical mechanism in the peroxymonosulfate (PMS) activation process, a direct electron transfer regime involving surface-bound metastable complexes was found to play a decisive role in the Fe3O4@NCNTs-BC800/peroxydisulfate (PDS) system. HSO5− was decomposed to active radicals for SMX oxidation in the Fe3O4@NCNTs-BC800/PMS/SMX system, yet carbon-PDS* complexes could be consumed by extracting electrons from the SMX. The surface hydroxyl groups of carbon-based catalysts and the structure discrepancies between PMS and PDS could lead to the differences in degradation performances and activation regimes. The degradation intermediates of SMX were also evaluated, and the toxicity analysis was undertaken. This work provides insight into the underlying mechanisms of persulfate activation and mediated electron transfer by carbon-metal nanohybrids.