Design and synthesis of a novel bifunctional polymer with malonamide and carboxyl group for highly selective separation of uranium (VI)

A novel malonamide-carboxyl bifunctional crosslinked polymer (MCFCP) and the related monofunctional polymers including malonamide or carboxyl as comparative adsorbent (MFCP and CFCP) were firstly prepared by polymerization reaction, and which was applied to adsorption of uranium (VI) in uranium-containing wastewater. The structures and compositions of the functional crosslinked polymers (FCPs) were characterized by FT-IR, SEM and XPS analysis. The effect of some factors on adsorption property, such as pH, initial concentration of uranium (VI) and adsorption kinetics, was investigated by batch experiment. Introduction of the bifunctional groups endowed MCFCP with the higher adsorption capacity and excellent selectivity due to the combined effect of amide and carboxyl groups. MCFCP afforded the largest saturated capacity of 239.6 mg/g for uranium (VI) at pH 4.0. In addition, MCFCP also showed the excellent selectivity for uranium (VI) in the presence of abundant environmental ions or lanthanide metal ions. The regeneration research demonstrated that MCFCP could be reused for four cycles, and still maintained the good adsorption property. Based on the density functional theory (DFT) calculation, it was further confirmed that uranium (VI) interacted with amide group of MCFCP to form [UO2MCFCP(H2O)3]2+ and [UO2(MCFCP)2]2+ complex in aqueous solution.