UiO-66 for the Removal of Tetracycline Antibiotic: Do We Need Modulators?

Abstract

Metal organic frameworks (MOFs) have been widely applied in water treatment studies to remove organic pollutants by either adsorption or photocatalysis. The chemical and structural properties of the MOF are controlled by various parameters including the initial precursors used and their concentrations, the method of preparation, and the addition of modulators during synthesis. In this work, the effect of modulation of UiO-66 on its final properties as well as its adsorption and degradation efficiencies for the removal of tetracycline antibiotic from water was studied. UiO-66 was synthesized with seven different acidic modulators: formic, acetic, trifluoroacetic, benzoic, bromoacetic, decanoic, and dodecanoic acids, each tested at the highest reported in the literature and at half that value. In total, 14 modulated UiO-66 samples and a non-modulated sample were prepared and extensively characterized by PXRD, BET, XPS, FTIR, TGA, UV–Vis, and SEM. The influence of modulator acidity, chain length, and steric bulk on crystallinity, porosity, and defect formation was systematically investigated. Adsorption and degradation tests under visible light revealed that modulators can either enhance or deteriorate the performance of UiO-66. In particular, trifluoroacetic-acid-modulated UiO-66 (TFA18) exhibited the highest adsorption efficiency (93\% after 300 min), which was 60\% higher than that of non-modulated UiO-66. Photocatalytic degradation under a 100 W white LED or real solar irradiation showed negligible dependence on modulation, as the band-gap energy of UiO-66 remained largely unaffected. These observations were confirmed using statistical analysis conducted in JMP. Modulation of UiO-66 is therefore recommended for adsorption applications, whereas non-modulated UiO-66 is preferable for photocatalytic degradation when using mesoporous MOFs. These findings highlight modulation as a versatile strategy for optimizing MOF preparation to enhance performance in environmental remediation applications.