Ternary transition metal organic frameworks (MOFs) CuZn-MIL101 (Fe) for peroxymonosulfate activation to degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA): A non-radical pathway dominated by singlet oxygen

In this study, ternary CuZn-MIL101(Fe) MOFs were prepared by introducing Cu and Zn ions into MIL-101(Fe) to obtain catalysts with excellent peroxymonosulfate (PMS) activation properties. The comprehensive characterization analysis revealed that although the adsorption performance of CuZn-MIL101(Fe) decreased, the PMS activation performance was significantly improved and complete degradation of MCPA was reached in 20 min. Calculation of the specific rate constants (kSA) yielded that the intrinsic activity of CuZn-MIL101(Fe) for PMS was 34 and 37 times higher than that of CuZn0.25-MIL101(Fe) and Cu0.25Zn-MIL101(Fe), respectively. The quenching experiments combined with electron paramagnetic resonance (EPR) spectroscopy verified the composition of the active substances in the system, whose contributions were in the order of O21 > ·OH > SO4⋅− > O2⋅. Using PMSO as a probe, an important role of high-valent iron was found in the system. The HOMO-LUMO gap of MCPA was calculated to be 0.205 eV by density functional theory (DFT), and the difference in adsorption energy of MCPA when adsorbing different radicals was investigated. The intermediate products were obtained by GC-MS and analyzed for toxicity, and the mechanism of singlet oxygen-dominated degradation of MCPA was proposed, which laid the foundation for the subsequent in-depth study of phenoxyacetic acid-based herbicides.