Separation of europium using graphene oxide supported membranes

Spectroscopic and morphological properties of graphene oxide (GO)-europium (Eu(III)) composite sheets prepared at different Eu(III) concentrations and pH are examined to ascertain interaction mechanism of Eu(III) ions with diverse oxygen functionalities of GO. Incorporation of Eu(III) ions deteriorates absorption characteristics of GO, quenches GO luminescence, originates irregular wrinkles on GO sheets, which infer reorganization in structure of GO in composites. Preparation of composites at large Eu(III) concentrations and sufficiently ionized ambience results in formation of Eu(III) hydroxide and/or carboxylate complexes and consequent aggregation of composite sheets. Based on these inferences, conditions for optimum Eu(III) uptake together with perseverance of GO characteristics are derived. Further, membrane filters are prepared using different size/multiple layers of GO and their Eu(III) adsorption abilities are examined by percolation of aqueous Eu(III) solutions. These membranes displayed enhancement in Eu(III) filtration efficiency with increase in number of GO layers, attributed to formation of uninterrupted and multiple filtration layers for improved Eu(III) ion adsorption. These studies also emphasize significance of larger surface area and availability of un-aggregated GO sheets for superior adsorption of Eu(III) ions. In the present work, GO membranes showed an optimum Eu(III) removal efficiency of similar to 35% and average Eu(III) adsorption capacity of similar to 115 mg/g.