Target adsorption of indomethacin sodium from aqueous solutions using mixed-ligand MIL-101(Cr)

In this study, we report the adsorption removal of indomethacin sodium (IDM) by the mixed-linker Materials of Institute Lavoisier (MIL)-101(Cr)s. The MIL-101(Cr)s were synthesized by controlling the ratios of 1,4-benzene dicarboxylic acid (H₂BDC) and 2-amino-1,4-benzene dicarboxylic acid (NH₂–H₂BDC). Then their adsorption performances toward IDM were investigated. Due to the increase in specific surface area and the contribution of enhanced multiple action mechanisms, MIL-101(20) was proved to have the optimal IDM absorption among all the mixed-ligand MIL-101(Cr)s. The adsorption kinetic data was found to accord with the pseudo-second-order kinetic model, and the rate constant (k₂) was calculated as 0.0059 ​g ​mg⁻¹ ​min⁻¹. The selected MIL-101(20) exhibited the maximum IDM adsorption capacity of approximately 641 ​mg ​g⁻¹ (318 ​K), calculated from the Langmuir linear plots. The simulation results of the thermodynamic model suggest that the adsorption could be a spontaneous, endothermic process with increasing randomness. The adsorption mechanism analysis indicates that the synergistic effects of electrostatic interaction, hydrogen bond interaction, and π-π stacking could be responsible for efficient IDM adsorption. In addition, the adsorbent also presented good reproducibility over six successive adsorption/desorption cycles. Therefore, the mixed-ligand MIL-101(Cr) could be recommended as a promising adsorbent for the preferential removal of IDM from polluted wastewater.