Combining Soft-Templating and Post-Synthetic Methods for the Rational Design of an Amidoximated Metal–Organic Framework with Mesopores for Efficient Uranium Extraction

Recently, metal-organic frameworks (MOFs) have been widely studied for uranium extraction from seawater to resolve the shortage of uranium resources. However, traditional MOF-based adsorbents are microporous structures, which are unfavorable to the mass transfer of guest molecules and the modification of functional groups. Herein, a novel mesoporous MOF (meso-UiO-66-NH-CN) is designed by the synergy of perchlorate and Pluronic F127, which gives meso-UiO-66-NH-CN with more accessible active sites and high mass transfer rates. Subsequently, mesoporous amidoximated MOFs (meso-UiO-66-NH-AO) were constructed via a one-step postsynthetic amidoximation, improving the stability and uranium selectivity of the material. The effect of acetic acid on the synthetic process is further investigated to regulate the inherent characteristics of meso-UiO-66-NH-AO. The mesopore structure endows meso-UiO-66-NH-AO with a rapid adsorption rate (k2 = 1.32 × 10-4 g mg-1 min-1), and the modification of the amidoxime group gives the material high adsorption capacity (Qmax = 312.5 mg g-1) and brilliant selectivity (Kd = 213 × 105 mL g-1). Meanwhile, meso-UiO-66-NH-AO exhibits a clear uranium adsorption performance in natural seawater. This work aims to provide a theoretical guideline for designing hierarchically porous MOFs and reveals their promising prospects for effective uranium extraction in seawater.