Synergistic Adsorption by Easily Retrievable Magnetic MOF Composites for Enhanced Removal of Benzoic Acid from Water

In this study, we prepared a magnetic University of Oslo-66 (UiO-66) composite material, Fe3O4@SiO2@UiO-66, and applied it as an adsorbent for the effective removal of benzoic acid from wastewater. The resulting magnetic MOF composite retained the structural and property characteristics of MOFs, along with magnetic separation capabilities, allowing for swift recovery from water through external magnetic fields. A potential synergistic effect between magnetic particles and UiO-66 was observed, leading to enhanced benzoic acid adsorption. The adsorption capacity per Zr6 cluster unit in Fe3O4@SiO2@UiO-66 measured 569.5 g/mol, surpassing that of UiO-66 by more than 26%. We conducted investigations into adsorption properties as a function of initial concentration, contact time, and pH values. The adsorption of magnetic UiO-66 composites was well described by pseudo-second-order and Langmuir models, indicating predominant chemisorption on the homogeneous surface. Thermodynamic studies of adsorption revealed a spontaneous exothermic process. Furthermore, we analyzed possible mechanisms of benzoic acid adsorption, highlighting the contributions of electrostatic interactions, coordination interactions, and π–π stacking interactions. Magnetic UiO-66 exhibited remarkable adsorption capacity, along with reliable regeneration performance and convenient magnetic separation capabilities, making it an exceptional adsorbent for industrial applications in the removal of benzoic acid.