Harnessing Synergistic Free Carboxyl Sites in Zr-MOFs for High-Performance Heavy Metal Separation: Bridging Theory, Experiment, and Economic Assessment

This work highlights a scientific breakthrough in the postfunctionalization of Zr-based metal–organic frameworks, focusing on UiO-66-NH2. The new compound, UiO-66-@DDB@SA, was synthesized using dihydroxybenzaldehyde (DDB) and succinic anhydride (SA) as ligands. This enables the selective removal and separation of Fe3+, Co2+, Cu2+, and Ni2+ ions. The effectiveness of the grafting process was confirmed through FTIR, XRD, SEM/EDX mapping, TGA/DTG, 1H NMR, and N2 sorption analysis. The separation of metal ions demonstrates that functionalization significantly enhances the efficiency with which ions are removed in both single- and multicomponent systems. Kinetic modeling suggests that physical and chemical interactions occur during adsorption due to the formation of dative and electrostatic bonds between the ions and the material. This hypothesis has been confirmed by theoretical DFT studies and Monte Carlo simulations, thereby highlighting the key role of −COOH oxygen atoms in the studied process. A study of selectivity conducted in the presence of Al3+, Pb2+, Cr3+, Cd2+, Bi3+, Zn2+, Mg2+, Ni2+, Cu2+, Ca2+, Co2+, and Fe3+ revealed a strong affinity between UiO-66-@DDB@SA and Fe3+ and Cu2+ ions, with distribution coefficients of approximately 11221 and 4791 mL/g, respectively. The maximum adsorption capacities were found to be 1340.7, 74.6, 1132.4, and 157.1 mg/g for the Cu2+, Ni2+, Fe3+, and Co2+ ions, respectively. UiO-66-@DDB@SA proved stable in a strongly acidic environment during prolonged exposure and retained significant adsorption capacity after six consecutive adsorption cycles. The adsorption capacity was influenced by surface and river water, compared to distilled and tap water. The cost analysis shows that the UiO-66-@DDB@SA material is a cost-effective alternative for purifying water containing heavy metal ions.