Preferential separation of lanthanides using graphene oxide membranes

Spectroscopic and morphological properties of different graphene oxide (GO)-lanthanide (Ln) composites were analysed with the aim of preparing GO membranes for preferential separation of Ln(3+) ions from composite solutions. These studies indicated that the extent of Ln(3+) ion uptake on GO sheets and consequent carboxylate/ hydroxide complex formation are strongly determined by interaction ability of Ln(3+) ion, relative proportions of GO functional groups and ionization of composite ambience. Membrane filters prepared using fresh and aged GO dispersions of varying GO concentrations and pH have been evaluated for their individual and overall Ln(3+) ion removal efficiencies. Among the studied lanthanide ions, Nd3+ and Ce3+ ions are found to be preferentially separated by fresh GO (similar to 8%) and aged GO (similar to 16 %) membranes, respectively, while Eu3+ ions are removed moderately under all the membrane preparation conditions. Preferential separation of these Ln(3+) ions may be attributed to relatively stronger polarization effects and formation of strong chelation bonds during their interaction with functional groups. The overall Ln removal efficiency of GO membranes was found to increase with aging of GO (25 %-54 %), mass of GO on membrane (54 %-154 %) and optimum in pH range of 3-5 (32-36 %), which is attributed to availability of large surface area, abundant functional groups, sufficiently ionized ambience and ample porous GO mass for the Ln(3+) ion adsorption.