Change in the Affinity of Ethylene Glycol Methacrylate Phosphate Monomer and Its Polymer Anchored on a Graphene Oxide Platform toward Uranium(VI) and Plutonium(IV) Ions

The complexation behavior of the carbonyl and phosphoryl ligating groups bearing ethylene glycol methacrylate phosphate (EGMP) monomer and its polymer fixed on a graphene oxide (GO) platform was studied to understand the coordination ability of segregated EGMP units and polymer chains toward UO22+ and Pu4+ ions. The cross-linked poly(EGMP) gel and EGMP dissolved in solution have a similar affinity toward these ions. UV-initiator induced polymerization was used to graft poly(EGMP) on the GO platform utilizing a double bond of EGMP covalently fixed on it. X-ray photoelectron spectroscopy (XPS) of the GO and GO-EGMP was done to confirm covalent attachment of the EGMP via a -C-O-P- link between GO and EGMP. The extent of poly(EGMP) grafting on GO by thermal analyses was found to be 5.88 wt %. The EGMP units fixed on the graphene oxide platform exhibited a remarkable selectivity toward Pu4+ ions at high HNO3 conc. where coordination is a dominant mode involved in the sorption of ions. The ratio of distribution coefficients of Pu(IV) to U(VI) (D-Pu(IV)/D-U(VI)) followed a trend as cross linked poly(EGMP) (0.95) < EGMP in solvent methyl isobutyl ketone (1.3) < GO-poly(EGMP) (25) < GO-EGMP (181); the D-Pu(IV)/D-U(VI) values are given in parentheses. The density functional theory computations have been performed for the complexation of UO22+ and Pu4+ ions with the EGMP molecule anchored on GO in the presence of nitrate ions. This computational modeling suggested that Pu4+ ion formed a strong coordination complex with phosphoryl and carbonyl ligating groups of the GO-EGMP as compared to UO22+ ions. Thus, the nonselective EGMP becomes highly selective to Pu(IV) ions when it interacts as a single unit fixed on a GO platform.