Catalytic thermal degradation of tetracycline based on iron-based MOFs and annealed derivative in dark condition

Abstract

Excessive use of tetracycline (TC) in livestock farming has led to serious pollution. The catalytic thermal degradation of TC by iron-based metal-organic frameworks (MOFs) was proposed for the first time, and the mechanism was studied. Three Fe-based MOFs with the same composition (MIL-53, MIL-88B, and MIL-101) and their annealing derivatives (collectively designated as Fe-MILs) have the ability to thermo-catalytic TC degradation. Meanwhile, the annealing derivatives showed more excellent degradation performance than raw materials. The improvement of properties after annealing at 350 °C was attributed to the exposure of Fe–O clusters and the formation of oxygen vacancies, which caused by the removal of dicarboxylate ligands. The optimum sample in Fe-MILs exhibited a degradation efficiency of 94.22% for TC within 60min at 70 °C. In addition, the TC removal rate at room temperature (25 °C) could also reach 90.6% by extending the reaction time to 10h. The Mars-van Krevelen mechanism and the surface electron transfer between the catalyst and contaminant were the thermal catalysis mechanisms of the Fe-MILs. The hydroxyl radical was the main active species in the degradation of TC. TC was also found to promote the generation of singlet oxygen and superoxide radical to participate in the subsequent decolorization and degradation of dyes on the catalyst system. In this study, iron-based MOFs and annealed derivative with thermal catalytic performance were discovered, and it was proposed that the influence of thermal catalysis should be considered in the photocatalytic degradation of TC by iron-based MOFs.