Introduction of phosphate groups into metal-organic frameworks to synthesize MIL-101(Cr)-PMIDA for selective adsorption of U(VI)

Metal-organic frameworks (MOFs) MIL-101(Cr)-PMIDA with phosphate groups were prepared for the adsorption of U(VI). The morphology and structure of the samples were characterized by SEM, TEM, FT-IR, BET, XPS and XRD. This study investigated the effects of the initial U(VI) concentration, contact time, pH, adsorption temperature and coexisting ions on the adsorption of U(VI) by MIL-101(Cr)-PMIDA. The experimental results showed that the adsorption capacity of MIL-101(Cr)-PMIDA was 267.92 mg g−1 at C0 (U) = 40 mg L−1, pH = 6.0 and T = 298 K, which was much higher than that of MIL-101(Cr)-NH2 (71.10 mg g−1). More importantly, the material exhibited excellent selective removal performance for U(VI) in an aqueous solution. Furthermore, adsorption thermodynamics and kinetic studies showed that the adsorption was spontaneous (∆G < 0) and exothermic (∆H ˃ 0), following the pseudo-second-order kinetic model (R2 > 0.99).Graphical abstract