Co/Al2O3-EPM as peroxymonosulfate activator for sulfamethoxazole removal: Performance, biotoxicity, degradation pathways and mechanism

Co/Al2O3-EPM (i.e., prepared by electroless plating method) is a new potential catalyst with high catalytic capacity and stability, which has not been used for peroxymonosulfate (PMS) activation. In this study, the sulfamethoxazole (SMX) in aqueous solution was degraded by the Co/Al2O3-EPM/PMS system. First, characteristics of Co/Al2O3-EPM were analyzed by using X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Then, the key parameters of Co/Al2O3-EPM dosage, PMS dosage and initial pH were optimized, respectively. The maximum SMX removal (98.5%) and total organic carbon (TOC) removal (25.6%) were obtained under the optimal conditions of Co/Al2O3-EPM = 0.8 g/L, PMS = 0.2 mM, initial pH = 6.3 and treatment time = 10 min. Also, the ions effects in Co/Al2O3-EPM/PMS system for SMX removal were investigated integrally. Besides, three control experiments (i.e., Co/Al2O3-EPM alone, PMS alone and homogeneous Co(II)/PMS systems) were conducted under the optimal conditions to verify the superiority of Co/Al2O3-EPM/PMS system. Furthermore, the degradation pathways of SMX were proposed according its intermediates detected by high performance liquid chromatography-mass spectrometry (HPLC-MS), and their biological toxicity were evaluated by activated sludge. In addition, the free radical identification experiment confirms that sulfate radical (SO4−) was the dominant active matter for SMX removal. The generation of SO4− during the reaction process in Co/Al2O3-EPM/PMS system was quantified indirectly via high performance liquid chromatography (HPLC). Finally, the possible reaction mechanism of Co/Al2O3-EPM/PMS system for SMX removal was proposed thoroughly. In brief, this study provided a new catalyst for PMS activation and all the results confirm that Co/Al2O3-EPM is a robust and high efficient catalyst for PMS activation.