Removal of sulfamethoxazole from water via activation of persulfate by Fe3C@NCNTs including mechanism of radical and nonradical process

In this work, the nitrogen-doped carbon nanotubes with encapsulated Fe 3 C nanoparticles (Fe 3 C@NCNTs) were prepared through a simple process by pyrolyzing the precursor of ferric trichloride hexahydrate and melamine composite. It was studied systematically that multiple Fe 3 C@NCNTs synthesized under 600–1000 °C activated persulfate (PS) for the degradation of sulfamethoxazole (SMX), a widely used antibiotic of sulfonamides. Raman spectrum , X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) were used to characterize the transformation of catalyst with the increase of annulling temperature. The Fe 3 C@NCNTs synthesized under 800, 900 and 1000 °C showed similar degradation ability to SMX with degradation rates of 0.650–0.893 min −1 . During catalytic process, the specific structure of Fe 3 C encapsulated NCNTs could both benefit the electron transfer and prevent the Fe 3 C dissolving in the solution. The results of quenching experiments coupling with electron paramagnetic resonance (EPR) spectra suggested the OH, SO 4 − and 1 O 2 contributed to the degradation of SMX and the singlet oxygen took effect for longer time. The degradation intermediates were mainly derived from the reactions of hydroxylation, oxidation , aniline ring opening, deamination, desulfonation, as well as bond cleavage. In terms of the density functional theory (DFT) calculations, the graphitic N exhibited the highest ΔE ads (−0.437 eV) for the PS molecule, and it was followed by the pyrrolic N (−0.304 eV), pristine graphene (−0.146 eV) and pyridine N (−0.072 eV), which means that the graphitic N is more favorable for the binding affinity with PS, forming the reactive complexes on the surface of the NCNTs catalysts to promote the nonradical oxidation.