Insight into the Specific Adsorption of Cu(II) by a Zinc-Based Metal-Organic Framework Mediated via a Proton-Exchange Mechanism.

In the context of scarce metal resources, the one-step separation and recovery of high-value copper metal ions from secondary resources is of significant importance and presents substantial challenges. This study identified a Zn-based triazole MOF (Zn(tr)(OAc)) with accessible and noncoordinated terminal hydroxyl groups within its framework. The Zn(tr)(OAc) surpasses most currently reported Cu-specific MOF adsorbents regarding adsorption capacity and Cu selectivity. Furthermore, in the one-step separation and recovery experiment of Cu, the Cu concentration was increased from 79.64% in the simulated secondary copper resource solution to 98.62% in the adsorbed phase. Both experimental and theoretical studies indicated that the high ion selectivity for Cu is primarily due to the specific recognition ability of the terminal hydroxyl (-OH) group, enabling only Cu to undergo proton exchange with the hydrogen. The strong adsorption capacity of the material was attributed not only to proton exchange between the hydroxyl groups in the framework and Cu but also to interactions between the nitrogen (N) and oxygen (O) atoms in the heterocyclic rings and Cu. In summary, Zn(tr)(OAc) demonstrates great potential in the separation and recovery of Cu from secondary copper resources and provides additional possibilities for enhancing Cu selectivity in MOF-based adsorbents.