Graphene oxide/cellulose membranes in adsorption of divalent metal ions

Abstract

In this paper, graphene oxide/cellulose membranes were prepared in order to perform effective adsorption of heavy metal ions: cobalt, nickel, copper, zinc, cadmium and lead. Two types of membranes were fabricated, i.e. pressed and non-pressed membranes. The experiment showed that the pressed membranes are highly durable at different pH values, even in basic solutions, and they can be applied in separation/removal of heavy metal ions during vigorous shaking in the aqueous solution. The non-pressed membranes were proved to be less stable, however, they can be successfully applied in the filtration process at the high flow-rates. The results of the batch experiments and the measurements by the inductively coupled plasma atomic emission spectroscopy (ICP-OES) indicated that the maximum adsorption can be achieved at pH 4–8. Adsorption isotherms and kinetic studies indicated that the sorption of the metal ions on the membranes occurs in a monolayer coverage, hence it is controlled by the chemical adsorption involving the strong surface complexation of metal ions with the oxygen-containing groups on the surface of graphene oxide. The maximum adsorption capacity values of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) on the graphene oxide/cellulose membranes at the pH of 4.5 are 15.5, 14.3, 26.6, 16.7, 26.8, 107.9 mg g⁻¹, respectively. The competitive adsorption experiments showed the affinities of prepared membranes for the metal ions in the order of Pb > Cu > Cd > Zn ≥ Ni ≥ Co. The affinity order agrees with the first stability constant of the associated metal hydroxide and acetate. The adsorption properties of the graphene oxide/cellulose membranes, their reusability (more than 10 cycles) and durability in the aqueous solutions open the path to removal of heavy metals from water solution. The membranes can be also used in the field of analytical chemistry for the preconcentration and/or separation of trace and ultratrace metal ions.