Fabrication of amidoxime-appended UiO-66 for the efficient and rapid removal of U(VI) from aqueous solution

In this study, an amidoxime-appended zirconium metal-organic framework [Zr6O4(OH)4(BDC-NHCH2CH2C(=N–OH)NH2)6](UiO-66-AO, BDC = 1,4-benzenedicarboxylate) for efficiently and rapidly removing uranium from aqueous solution was fabricated through post-modifications. The chemical structure and composition of original and modified UiO-66 MOFs were investigated in detail. The principal factors affecting the adsorption of U(VI) ions have been investigated, including pH of the aqueous solution, contact time, temperature, and coexisting cations through batch adsorption experiments. The adsorption kinetics conformed to the pseudo-second-order model. It was found that the maximum adsorption capacity reached 232.8 mg/g at pH 5.0 and 328 K based on the Langmuir isotherm. The thermodynamics parameters revealed that this adsorption process was spontaneous and endothermic. The sorption experiment in a simulated nuclear industry effluent demonstrated a high adsorption efficiency (about 95.3%) and selectivity toward uranium. The extended X-ray absorption fine structure (EXAFS) analysis revealed the coordination mechanism of amidoxime-appended UiO-66 and uranyl.