Enhanced activation of peroxymonosulfate using ternary MOFs-derived MnCoFeO for sulfamethoxazole degradation: Role of oxygen vacancies

Herein, ternary metal-organic frameworks (MOFs)-derived MnCoFeO with different levels of oxygen vacancies (Ov) were designed by adjusting the doping amount of Mn and employed to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. The MnCoFeO-2 with the largest Ov content exhibited the highest SMX degradation efficacy. Almost 100% of SMX was removed within 5 min using the MnCoFeO-2/PMS system. The reaction rate constant (kobs) was 1.7321 min-1, which was 4.1 times that of CoFeO (0.4195 min-1). Both the SO4•- and 1O2 were the dominant reactive oxygen species. Significantly, the relationship among Ov, radical pathways, and non-radical pathways was explored for the first time. The results showed that Ov could regulate the radical pathways by promoting the adsorption of PMS onto MnCoFeO-2. Ov was positively correlated with 1O2 (P < 0.05) and facilitated the direct electron transfer. The superior catalytic activity of MnCoFeO was attributed to the Fe, Co, Mn active sites, Lewis basic sites and Ov in MnCoFeO. Mn(II) not only contributed to the formation of Ov, but also facilitated the reduction of Fe(III). Additionally, Ov was mainly concentrated near the low-valent metal ions, thus the synergistic effect between the metal active sites and Ov promoted the activation of PMS.