Removal of aqueous pharmaceuticals by magnetically functionalized Zr-MOFs: Adsorption Kinetics, Isotherms, and regeneration

The functionalization of metal–organic frameworks (MOFs) is imperative and challenging for the development of practical MOF-based materials. Herein, a magnetically functionalized Zr-MOF (Fe 3 O 4 @MOF-525) was synthesized via secondary-growth approach to obtain an easily-separated and recyclable adsorbent for the removal of pharmaceuticals (tetracycline (TC) and diclofenac sodium (DF)). After loading Fe 3 O 4 nanoparticles (NPs), due to the increase of micropore volume and specific surface area caused by defects, the adsorption performance of Fe 3 O 4 @MOF-525 was improved. The kinetics could be described by the pseudo-second-order kinetic model. The different adsorption capacity and initial rate were attributed to the properties of the pharmaceuticals, including the molecular size and hydrophobicity/hydrophilicity. In isotherm experiments, the maximum adsorption capacities of DF and TC on Fe 3 O 4 @MOF-525 calculated by Sips model reached 745 and 277 mg·g −1 , respectively. The thermodynamic studies indicated the adsorption was endothermic and spontaneous. The effect of pH suggested that electrostatic interaction, π-π interaction, anion-π interaction, and H-bonding were possibly involved in the adsorption process. The adsorbent was separated by magnetic and regenerated. Washed with ethanol, Fe 3 O 4 @MOF-525 remained about 80% adsorption capacity after four cycles. In-situ photo-regeneration under visible-light irradiation was another attractive method, where > 95% TC was degraded in 4 h. The reaction with scavengers revealed that 1 O 2 was the dominant reactive species in our system, indicating the occurrence of Type II photosensitization. The separability, excellent adsorption performance, and recyclability of Fe 3 O 4 @MOF-525 may lead to its beneficial applications in water treatment.