Insights on selective Ag+ adsorption in zirconium–based metal–organic frameworks: Morphology and structural regulation

Recovery of valuable silver (Ag) from wastewater is essential for environmental protection and resource recovery but still faces challenges. Herein, the morphology and structure of the Zr-MOF (DUT-67-PZDC) were regulated using trifluoroacetic acid (TFA), formic acid (FA) and acetic acid (AA) as modifiers by a green and simple preparation method. Through optimization of the type and amount of acid modifiers addition, DUT-67-PZDC-AA exhibits a smaller and more homogeneous morphology compared to DUT-67-PZDC-TFA/FA, and the weak coordination ability of AA leads to unsaturated coordination of Zr clusters, which results in chelation with Cl in the precursor. Benefitting from small crystal size, N active sites, and the presence of Cl element, DUT-67-PZDC-AA achieves a good adsorption capacity (211.4 mg g⁻¹), fast adsorption rate (5 min), as well as excellent interference resistance and adsorption selectivity for Ag⁺. Experimental characterization and theoretical calculation jointly prove that coordination interaction between Ag⁺ and N/O atoms and chemical precipitation facilitate Ag⁺ adsorption. Therefore, this work not only demonstrates the great potential of DUT-67-PZDC-AA in recovering Ag⁺ from wastewater but also provides insights into the effect of acid modifiers on the synthesis of high-efficiency MOF adsorbent.