Unveiling the structure–activity relationships of ofloxacin degradation by Co3O4-activated peroxymonosulfate: From microstructures to exposed facets

As a fluoroquinolone antimicrobial agent, ofloxacin (OFX) has been widely used, consequently causing serious damage to the ecological environment. Advanced oxidation processes based on persulfate activation (SR-AOPs) are widely applied to degrade stubborn organic contaminants in wastewater treatment. Co3O4 is being extensively investigated as a promising persulfate catalyst in SR-AOPs. In this work, four Co3O4 polycrystals with specific morphologies were synthesized and used to activate peroxymonosulfate (PMS) for OFX degradation. The obtained samples and corresponding precursors were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and N2 adsorption/desorption isotherms. Experimental results showed that 30 mg·L-1 OFX could be completely removed in the lamella-like Co3O4/PMS system within 30 min under ordinary conditions. The underlying degradation mechanism was elaborated by high-resolution TEM (HRTEM) combined with density functional theory (DFT) calculations. Based on quenching experiments and the electron paramagnetic resonance (EPR) technique, sulfate radicals were identified as the dominant reactive oxygen species (ROS) in the lamella-like Co3O4/PMS system, and superoxide radicals, hydroxyl radicals, and singlet oxygen made minor contributions to the degradation of OFX. Possible degradation pathways were proposed based on DFT calculations and Fukui theory and confirmed by ultrahigh-performance liquid chromatography-quadrupole-time of flight mass spectrometry (UHPLC-QTOF/MS). Furthermore, quantitative structure–activity relationship (QSAR) prediction was used to evaluate the developmental toxicity of the corresponding intermediates.