Removal of Tetracycline from Water Using Ce-based UiO-66 Through Adsorption and Photocatalytic Degradation

Abstract

The removal of antibiotics from water remains a major environmental challenge due to their chemical stability and contribution to antimicrobial resistance. In this work, a series of cerium-zirconium mixed-metal UiO-66 metal-organic frameworks with different Ce/Zr ratios (U70/30, U60/40, U50/50, U40/60) were synthesized and systematically evaluated for the adsorption and visible-light-driven photocatalytic degradation of tetracycline (TC). The synthesis was completed in 30 min in an oil bath, and UiO-66(Zr), prepared using the traditional solvothermal method, was included for comparison. Structural and physiochemical characterizations confirmed the successful formation of mixed-metal cerium-based UiO-66 frameworks with preserved crystallinity and tunable defect density. FTIR, BET, and SEM analyses revealed that increasing Zr content enhanced framework rigidity while promoting surface hydroxylation and defect density. Among all samples, U4060 (40% Ce and 60% Zr) exhibited the highest adsorption capacity and photocatalytic degradation efficiency, achieving complete TC removal under white LED irradiation. The superior performance of U4060 (100% after 50 min, [1]=5 ppm, MOF loading 100 ppm, uncontrolled pH) was attributed to synergistic effects between enhanced adsorption, efficient ligand-to-metal charge transfer, Ce⁴⁺/Ce³⁺ redox cycling, and suppressed electron-hole recombination. A combined adsorption-photocatalytic degradation mechanism was proposed, highlighting the dominant role of superoxide radicals and photogenerated holes. This study demonstrates that rational tuning of the Ce/Zr ratio in UiO-66 provides an effective strategy for developing robust and efficient MOF-based materials for antibiotic removal from water.