Degradation mechanisms of ofloxacin and cefazolin using peroxymonosulfate activated by reduced graphene oxide-CoFe2O4 composites

Abstract

In this work, reduced graphene oxide (rGO) sheets were integrated with CoFe2O4 to construct distinctive composites that were evaluated as heterogeneous catalysts activating peroxymonosulfate (PMS) for the oxidative degradation of ofloxacin (OFX) and cefazolin (CFZ), two widely used pharmaceuticals belonging to the fluoroquinolone and β-lactam antibiotic families, respectively. The results showed that of all of the catalysts tested, the composite with an CoFe2O4 to rGO weight ratio of 20:2 (CFGO202) had the best reactivity, and achieved superior stability with negligible leaching of cobalt and iron under mild acidic conditions. Radical quenching experiments showed that the degradation of OFX was a radical-based oxidation process, while the decomposition and transformation of CFZ were largely due to PMS-induced direct oxidation via direct two-electron transfer. The near-complete degradation of OFX and CFZ could be attained under optimal conditions: pH 6.0, 0.1 g L−1 CFGO202 and 1 mM (for OFX) or 100 μM PMS (for CFZ). In comparison with OFX, the degradation of CFZ suffered less interference from the water matrix. An underlying mechanism was proposed based on the detection of radicals and X-ray photoelectron spectroscopy spectral data. Degradation intermediates were identified and the possible degradation pathways were proposed with the aid of density functional theory (DFT) calculations.