Cationic Metal–Organic Framework with Amino-Functionalized Isonicotinic Acid for Chromium(VI) Removal

The removal of hexavalent chromium, Cr(VI), from wastewater remains a significant environmental challenge. In this study, we explored the effectiveness of a novel cationic metal–organic framework (MOF), designated as NU-56, for Cr(VI) removal from wastewater. NU-56, composed of a Zr6O8 cluster, monomeric Ni2+, and 3-aminoisonicotinic acid, exhibits a remarkable Cr(VI) removal capacity. Several factors contribute to its efficacy, including the presence of free exchangeable Cl– ions within the network, protonated amino groups on the ligand, and μ3-O/OH on the Zr6O8 cluster, all of which synergistically enhance NU-56's ability to capture Cr(VI) efficiently under acidic aqueous conditions ranging from pH 4 to 6. In comparison to its isostructural counterpart lacking amino-functionalized isonicotinic acid, amino-functionalized NU-56 demonstrates superior structural integrity during the Cr(VI) elimination process. Additionally, we conducted comprehensive studies on the adsorption kinetics, isotherms, and selectivity of NU-56 for Cr(VI) removal, revealing its potential as a promising candidate with a maximum adsorption capacity of 68 mg/g. This research underscores the significance of developing functionalized MOFs as a viable approach for the removal of oxy-anions from wastewater, offering a straightforward and effective solution to address this pressing environmental concern.