Fabrication of MOF-carbonized materials as ozone catalysts for water purification: Exploration of catalytic mechanisms

Due to their stability, the advent of MOF-derived catalysts ensures the applications of MOF-based materials, and they have been used in many catalytic systems. However, their application in ozone catalysis is limited, and the relevant mechanisms remain unclear. In this study, three MOF-carbonized materials (Me-MOF-C, Me: Fe, Cu, and Zn) were synthesized as ozone catalysts for water purification. When combined with ozone, all the Me-MOF-C promoted target removal compared to the Me-MOF/O-3 systems, and Fe-MOF-C was optimal due to its superior ozone utilization efficiency. ROS quantification indicated that the center dot OH in the Fe-MOF-C/O-3 system was approximately 48.0 times that of the single ozone system. Kinetic analysis demonstrated that over 90% of the target was removed by center dot OH in the Fe-MOF-C/O-3 system. Then, the catalytic mechanism of Fe-MOF-C was investigated. The surface hydroxyl and protonation effect of Fe-MOF-C presented limited activity. In comparison, H2O2 in the solution and Fe2+ on the Fe-MOF-C surface were more crucial. AcOH control experiments revealed a positive correlation between center dot OH and H2O2. H2O2 decomposition experiments further indicated that although the Fe-MOF-C/O-3 system utilized H2O2 faster, only the coexistence of ozone and Fe-MOF-C could facilitate it more. Results of Fe2+ regulation suggested that it was related to the way of surface Fe2+ acted. The main contribution of Fe2+ to producing center dot OH was not through Fe2+ ozonation or reaction with H2O2, but it likely involved the efficient conversion of H2O2 into HO2-, which subsequently decomposed ozone to produce center dot OH more efficiently. Finally, a possible catalytic pathway was proposed.