Rational design of smart adsorbent equipped with a sensitive indicator via ligand exchange: A hierarchical porous mixed-ligand MOF for simultaneous removal and detection of Hg²⁺

The increasing accumulation of toxic mercury species in water environment has posed a serious health threat worldwide, making it inevitable to develop the versatile materials to achieve efficient prevention and remediation of mercury pollution. Guided by the solvent-assisted ligand exchange (SALE) approach, this work rationally constructed a mixed-ligand NH₂-UiO-66-SH (NSU66) with hierarchical-pore structure by incorporating the thiol-rich ligands (H₂DMBD) into the water-stable NH₂-UiO-66 (NU66) precursor to act as a smart adsorbent equipped with sensitive detector for simultaneous sensing and removal of Hg²⁺. Unlike the traditional adsorbents, the as-prepared NSU66 not only exhibits a remarkable removal ability with fast capture rate (within 60.0 min), large uptake capacity (265.29 mg/g), and qualified selectivity, but also possesses satisfactory sensing capability, accompanied by low detection limit (3.50 × 10^-2 µM), wide linear range (1.00-99.7 µM), high specificity, and strong anti-interference capability. The detection function plays a vital role in indicating the removal behavior and the pre-enrichment effect of adsorption process correspondingly improves the sensitivity of indicator. Notably, the sensing and trapping capabilities of NSU66 are significantly improved compared to the NU66, which stems from the delicate design of the mixed-ligand and hierarchical-pore structure. Furthermore, proven excellent stability and recyclability emphasize the feasibility of NSU66 in practical applications. These results suggest that the smart NSU66 adsorbent can serve as a favorable platform for early warning and guided removal of toxic Hg²⁺ in water.