Defect-rich hierarchical Zn-HHTP MOFs via ammonia-modulated assembly for superior uranium sequestration

Owing to their high density of active coordination sites, metal-organic frameworks (MOFs) have been extensively explored for uranium(VI) removal. However, the adsorption performance of pristine ZnHHTP is often limited by strong interlayer π-π stacking interactions, which reduce the effective porosity, hinder mass transport, and restrict the accessibility of uranium-binding sites. Herein, we demonstrate a facile ammonia-triggered assembly and etching strategy to construct defect-rich hierarchical pores within ZnHHTP nanostructures. Morphological and structural characterizations demonstrate that ammonia modulation introduces abundant mesopores into the originally low-porosity framework, creating a hierarchical architecture. This structural evolution leads to a significantly increased specific surface area, enriched defect sites, and enhanced surface hydrophilicity. Consequently, the optimized m-ZnHHTP-25 exhibits outstanding uranium(VI) elimination performance, reaching near-equilibrium within only 100 min and a remarkable maximum adsorption capacity of 521.41 mg·g −1 . Mechanism studies revealed a synergistic effect contributing to the enhanced performance. The hierarchical mesopores function as ion-transport channels, significantly accelerating the mass transfer kinetics. Moreover, the abundant and highly accessible defect sites function as high-density binding locations, where catechol oxygen atoms form strong chemical coordination bonds with UO 2 2+ . This study not only presents a promising candidate material for radioactive wastewater treatment but also offers a powerful protocol for rationally designing hierarchical porosity in porosity-deficient coordination networks for environmental remediation.