Introduction of amidoxime groups into metal-organic frameworks to synthesize MIL-53(Al)-AO for enhanced U(VI) sorption

Good application of metal-organic frameworks (MOFs) on uranium adsorption has attracted increasing attention recently. MIL-53(Al)-AO, synthesized by introducing amidoxime groups to MIL-53(Al)-NH2 aimed to adsorb U(VI), was characterized by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis and fourier transformed infrared spectroscopy. The sorption capacity of MIL-53(Al)-AO for U(VI) in aqueous solutions has been enhanced to 2.36 times compared with MIL-53(Al)-NH2 at pH 6.0 under the same conditions according to the experimental results, possibly due to the strong chelation of amidoxime. Effects of contact time, pH, interfering ions, and U(VI) concentration on the sorption of U(VI) for MIL-53(Al)-AO were also investigated. The sorption was strongly dependent on pH and independent of coexist ions. Result of this study shows that the MIL-53(Al)-AO was a kind of potential material to enrich U(VI) from aqueous solutions, and amidoxime could be introduced to MOFs sorbent by transforming the grafted amino groups on MIL-53(Al)-NH2.