Efficient removal of tetracycline from MOF-on-MOF heterojunctions driven by visible light: Evaluation of photocatalytic mechanisms and degradation pathway

The low photocatalytic efficiency of a single MOF limits its application, and the assembly of different MOF into MOF-on-MOF heterojunctions can construct fine charge transfer interfaces, thereby improving the photocatalytic ability. In addition, the heterojunction constructed by the two MOFs can maintain the porous structure of the MOF material to a large extent, which is conducive to the adsorption behavior. In this paper, Z-scheme heterojunction is prepared by solvothermal growth of MIL-88B on NH2-MIL-125 matrix. The Z-scheme heterojunction of NH2-MIL-125@MIL-88B greatly improves the photo-response range and charge separation efficiency. It showed good photocatalytic activity for tetracycline (TC) degradation. Under visible light irradiation, the removal efficiency of NM-3 catalyst with the best performance reached 96.26 % within 120 min, and the rate constant was 0.02428 min−1, which was about 9.75 times and 4.16 times of NH2-MIL-125 and MIL-88B alone. The results of free radical trapping and ESR indicated that O2− and OH take important parts in the photodegradation of TC. The active sites and degradation pathways of TC vulnerable to attack were predicted by DFT calculation and intermediate analysis. The design and preparation of Z-scheme heterojunction provide a new strategy for visible light degradation of TC.