Half-salen Fe(III) covalently post-modified MIL-125(Ti)-NH2 MOF for effective photocatalytic peroxymonosulfate activation

In this work, an amino functionalized metal organic framework (MOF), MIL-125(Ti)-NH2, is modified by salicylaldehyde via Schiff-base reaction, and the grafted organic substituent is further coordinated with ferric ions to form a half-salen Fe(III) covalently functionalized MOF, MIL-125(Ti)-Sal-Fe. The as-prepared composite is evaluated by light-driven catalytic activation of peroxymonosulfate (PMS) for the degradation of tetracycline hydrochloride (TC). The results imply that the TC removal given by MIL-125(Ti)-Sal-Fe/PMS/light is > 88.9% after 40 mins in a wide pH range from 3 to 9; still, the kinetic constant for the degradation reaction under the optimized condition is 0.03553 min(-1), which is much higher than that of either decomposition conducted by MIL-125(Ti)-NH2 (0.01801 min 1) or salicylaldehyde modified MOF, MIL-125(Ti)-Sal (0.01987 min(-1)). The significant enhancement of the photocatalytic performance can be attributed to the ligand-to-metal charge transfer (LMCT) within the integrated half salen Fe(III) complex, highly accelerating the redox cycle from Fe(III) to Fe(II). Our study opens up a novel insight into the amelioration of MOF-based PMS activation.