Metal-organic frameworks with oxygen-rich adsorption sites for efficient capture of uranium and thorium in acidic environments

The capture and separation of uranium and thorium from acidic nuclear waste streams are imperative for safeguarding the environment and human well-being. Metal-organic frameworks (MOFs), an emerging class of porous materials, offer considerable potential for U(VI)/Th(IV) adsorption owing to their customizable pore size and processability. Nonetheless, the development of MOFs with robust adsorption capabilities for U(VI)/Th(IV) in acidic conditions poses a significant challenge. In this study, we introduce a feasible MOF design approach: the integration of high-valent metal centers with oxygen-rich organic ligands. Employing this strategy, we have successfully engineered a novel MOF adsorbent, SU-102(Hf), comprising hafnium-based metal clusters and ellagic acid as the organic linker. In a 0.3 M nitric acid environment, SU-102(Hf) demonstrates outstanding chemical stability and exhibits a high adsorption capacity for both uranium (27.38 mg g −1 ) and thorium ions (32.03 mg g −1 ), which represent a record of simultaneous adsorption capacity of uranium and thorium binary components by MOFs in a highly acidic environment (0.3 M HNO 3 ). Simultaneously, SU-102(Hf) also displays rapid adsorption kinetics, excellent selectivity, and recyclability for U(VI)/Th(IV) separation at pH = 3. Experimental investigations and theoretical calculations further unravel the adsorption mechanisms and key differences for Th(IV) and U(VI) ions.