Efficient degradation of sulfamethoxazole by NiCo2O4 modified expanded graphite activated peroxymonosulfate: Characterization, mechanism and degradation intermediates

Expanded graphite (EG) immobilized nickel ferrite (NiCo2O4) was successfully constructed by a simple hydro thermal approach and applied for the degradation of sulfamethoxazole (SMX) in model wastewater by peroxymonosulfate (PMS) activation. The features of prepared catalysts were characterized by SEM, TEM, EDS, XRD, BET, TPD and XPS techniques. The influences of several critical parameters including the prepared NiCo2O4-EG dosages, PMS concentrations, temperature, initial solution pH and inorganic ions on SMX removal were studied in details. In particular, the synthesized NiCo2O4-EG exhibits excellent catalytic performances for SMX depredation over a wide pH range (pH 3.0-11.0). Besides, the transformation of various reactive oxygen species (SO4 center dot-, HO center dot, O-2(center dot-) and O-1(2)) with the change of initial pH was investigated by the electron paramagnetic resonance (EPR) and quenching tests. In addition, twelve major degradation intermediates of SMX were detected by UPLC-QTOF-MS/MS. Finally, the PMS activation mechanism in NiCo2O4-EG/PMS system by the synergistic coupling of EG and NiCo2O4 were put forward. In brief, this work provided a promising and potential catalyst for PMS activation to remove SMX from wastewater.