Highly dispersed Co on N-doped carbon derived from metal-organic framework composite for enhanced peroxymonosulfate activation toward tetracycline degradation

Tetracycline (TC) plays an essential role in both medical treatment and animal husbandry, but its abuse and accumulation in aquatic environments undoubtedly threatens ecosystems and human health. The advanced oxidation processes (AOPs) based on the activation of peroxymonosulfate (PMS) for the degradation of TC and other organic contaminants has attracted increasing attentions. Although metal-organic framework (MOF) derived transition metal‑nitrogen‑carbon material (MNC) shows fascinating potential for PMS activation, the direct carbonization of MOF makes limited active sites available for reaction due to serious agglomeration of the metal species together with the low yield of MNC catalyst. Herein, MOF composite (ZIF-67/NG) is designed via the in-situ growth of ZIF-67 on the N-doped graphene-like carbon (NG). The obtained Co@NC/NG after pyrolysis of ZIF-67/NG enabled the exposure of more active sites without notable aggregation of the Co nanoparticles . Co@NC/NG could effectively degrade TC via the activation of PMS and showed relatively good stability. Meanwhile, it was also highly active in wide pH range and the coexistence of inorganic anions as well as humic acid. Compared to bare ZIF-67 derived Co@NC, Co@NC/NG exhibited higher TOF value. The quenching experiments combined with EPR analysis indicated that both radical and non-radical routes were involved during the TC removal. Superoxide radicals, singlet oxygen and the surface bounded reactive oxygen species were important to the reaction. In comparison, sulfate radicals only made slight contribution and the effect of hydroxyl radicals could be omitted.