Adsorptive performance of ship-type nano-cage polyoxometalates for U(VI) in aqueous solution

In this work, a novel ship-type nanomaterial of nano-cage polyoxometalates (CO-POM) was synthesized, and the adsorption performance of CO-POM for U(VI) has been comprehensively studied. The scanning electron microscope (SEM), thermogravimetry (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) have been utilized to characterize the adsorbent of CO-POM. The adsorption kinetics, isotherms and thermodynamics have been comprehensively investigated. The results of batch experiments show that the solution pH strongly affects the adsorption of U(VI) on CO-POM. The main interaction mechanism is complexation and electrostatic interaction on the surface of the structure. At pH = 4.0 and T = 298 K, the adsorptive capacity of CO-POM for U(VI) is 232.04 mg/g, the equilibrium time was within 180 min. The adsorption selectivity of CO-POM toward U(VI) was above 50% when pH ranged from 3.0 to 5.0, and reached to top (54.98%) at pH 5.0. In addition, FT-IR and XPS analysis indicated that the high adsorption capacity of CO-POM for U(VI) is mainly attributed to coordination interaction between U(VI) and phosphonate groups on CO-POM. The simple preparation and high efficiency of CO-POM may be a promising candidate for adsorption of U(VI) in the radionuclide contamination.