Green and efficient synthesis of Co-MOF-based/g-C3N4 composite catalysts to activate peroxymonosulfate for degradation of the antidepressant venlafaxine.

Based on single metal-organic framework (MOF) composite catalyst ZIF-67/g-C3N4 (ZG), the composite catalysts ZIF-67/MOF-74(Ni)/g-C3N4 (ZNG) and ZIF-67/MIL-100(Fe)/g-C3N4 (ZMG) with double MOFs were synthesized, used to effectively activate peroxymonosulfate (PMS) for degrade venlafaxine (VEN). Various characterization methods (XRD, FT-IR, Raman, SEM, EDS, TEM and TG) showed that ZIF-67 and g-C3N4; ZIF-67, MOF-74(Ni) and g-C3N4; as well as ZIF-67, MIL-100(Fe) and g-C3N4 successfully formed heterostructures. The series of catalytic degradation results showed that within 120 min, the degradation rate of VEN by ZMG achieved 100% and the mineralization rate reached 51.32%. The removal rate of VEN by ZNG was 91.38%, while that by ZG was only 27.75%. Free radical quenching tests and EPR further confirmed the production of OH and SO4-, which could be conducive to the degradation of VEN. The mechanism analysis of PMS activation confirmed that the interaction of Fe2+/Co3+ was stronger than that of Ni2+/Co3+, and it was an important driving force to significantly enhance the synergistic effect. Finally, Gauss theory calculation and HPLC-MS/MS were used to analyze the intermediate products of VEN. It was verified that the main chemical reactions in the degradation process of VEN were hydroxylation, dehydration, demethylation and tertiary amine substitution.