ZIF-8-induced fluorescence-enhanced multifunctional MOF-on-MOF hydrogels for efficient adsorption and sensitive detection of uranyl ions in water.

Accidental leakage of uranium causes a huge threat to human health and environmental security. Herein, a novel fluorescent MOF-on-MOF hydrogel complex, namely Tb-MOF@ZIF-8@PAM, is constructed using a "three-in-one" synthetic strategy for the simultaneous adsorption enrichment and sensitive detection of uranyl ions (UO22+) in water. Combining ZIF-8 with Tb-MOF enables the composite to exhibit remarkable fluorescence enhancement, large fluorescence quantum yield, and exceptional stability. When used to detect of UO22+ in water, the method demonstrates excellent sensitivity (LOD = 0.551 nmol/L). Experimental characterizations suggest that the static quenching effect (SQE) and photoinduced electron transfer (PET) may be possible sensing mechanisms. Furthermore, Tb-MOF@ZIF-8@PAM is rich in amino and carboxyl groups and exhibits superior hydrophilicity, an abundant pore structure, and numerous active adsorption sites, which leads to a remarkable absorption capability of 603 mg/g specifically for UO22+. Tb-MOF@ZIF-8@PAM has a straightforward recycling strategy, and its adsorption efficiency remains above 80 % after 4 cycles of use. Thus, this research introduces an innovative approach for synthesis of a low-cost and multifunctional adsorbent MOF-on-MOF hydrogel composite, which can be employed for the simultaneous adsorption and detection of UO22+.