Activation of peroxymonosulfate by metal (Fe, Mn, Cu and Ni) doping ordered mesoporous Co3O4 for the degradation of enrofloxacin

Various transition metals (Fe, Mn, Cu and Ni) were doped into ordered mesoporous Co3O4 to synthesize Co3O4-composite spinels. Their formation was evidenced by transmission electronic microscopy (TEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis. It was found that Co3O4-composite spinels could efficiently activate peroxymonosulfate (PMS) to remove enrofloxacin (ENR) and the catalytic activity followed the order Co3O4-CuCo2O4 > Co3O4-CoMn2O4 > Co3O4-CoFe2O4 > Co3O4-NiCo2O4. Moreover, through the calculation of the specific apparent rate constant (k(sapp)), it can be proved that the Co and Cu ions had the best synergistic effect for PMS activation. The Co3O4-composite spinels presented a wide pH range for the activation of PMS, but strong acidic and alkaline conditions were detrimental to ENR removal. Higher reaction temperature could promote the PMS activation process. Sulfate radical was identified as the dominating reactive species in Co3O4-composite spinel/PMS systems through radical quenching experiments. Meanwhile, the probable mechanisms concerning Co3O4-composite spinel activated PMS were proposed.