Enhanced sulfamethoxazole degradation using an efficient Co-doped MnO2 activator for peroxymonosulfate activation

Manganese oxide-based catalysts have been frequently adopted to activate peroxymonosulfate (PMS) for the degradation of refractory contaminants such as sulfamethoxazole (SMX). In this study, the Co-doped ɑ-MnO 2 catalyst was prepared to validate the concept that the introduction of additional oxidation states and structural defects due to the doping process would significantly enhance the efficiency of PMS activation. Among all Co@ ɑ-MnO 2 catalysts prepared, the activator with the mole ratio of Co/Mn 0.05:1 exhibited the highest SMX degradation. A near 100% removal of SMX (1000 μ g / L $\mathrm{\mu }\mathrm{g}/\mathrm{L}$ ) was achieved within 1 min in a condition with 10.0 mmol/L PMS and 0.5 g/L Co 0.05 @ ɑ - MnO 2 at 25 ℃ $\mathrm{℃}$ . The effects of catalyst dose, PMS concentration, initial SMX concentration, solution pH, temperature, and coexisting cations, anions, and humic acid (HA) on SMX degradation were studied. The impressive sustainability of the Co 0.05 @ ɑ-MnO 2 /PMS system was confirmed by its capability of operating over a wide pH range, its stability after multiple cycles, and its insensitivity to the coexisting of cations. The presence of high electrophilic anions, such as NO 2 ¯ and HCO 3 ¯ , on the other hand, would compromise the SMX degradation. Furthermore, reactive oxygen species (ROS) generated in the Co@ ɑ-MnO 2 /PMS system were identified by scavenger tests and electron paramagnetic resonance (EPR). Singlet oxygen ( 1 O 2 ) was verified to be the major route contributing to the degradation of SMX. In addition, sulfate radicals ( SO4 •¯ ), superoxide radicals (O 2 •¯ ), and hydroxyl radicals (ּ • OH) were also generated in the Co@ ɑ-MnO 2 /PMS system and participated in SMX degradation. Therefore, the Co@ ɑ-MnO 2 is a promising catalyst for PMS activation in the degradation of SMX.