Fine tuning of pore size in metal-organic frameworks for superior removal of U(vi) from aqueous solution

The pore structure of metal-organic frameworks (MOFs) is crucial to their adsorption performance, and it is still a challenge to precisely control the pore size to realize superior removal of uranium. The pore size of MOF-A, MOF-B and MOF-C was fine-tuned by using three organic chains with different lengths (fumaric acid, terephthalic acid and naphthalene dicarboxylic acid, respectively). The synthesized MOF-A, MOF-B and MOF-C had ordered increase in pore sizes with 3.8 & Aring;, 5.7 & Aring; and 7.6 & Aring;, respectively. Pore size of 7.6 & Aring; in MOF-C was a little larger than the geometric dimension of the UO22+ ion (maximum length 6.04-6.84 & Aring;), which facilitated diffusion of UO22+ ions and achieved highly efficient adsorption. The maximum adsorption capacity (584 mg g(-1)) and removal rate (99.75%) of uranium for MOF-C were higher than those for MOF-A and MOF-B. The excellent adsorption performance of MOF-C was attributed to the specific pore structure of MOF-C and effective complexation of oxygen-containing groups with U(VI). Our work proposes a new strategy for the outstanding removal of uranium by using different organic chains to precisely regulate the pore size of MOF.