Proficiency of Graphene Oxide in Adsorption of Zn(II) Ions from Aqueous Solution

The efficient adsorption of metals on graphene oxide is often affected by the preparation method. Graphene oxide was prepared using a typical modified Hummers method for adsorptive removal of Zn2+ from aqueous solution. The experimental data were fitted into the Langmuir isotherm. The reaction was irreversible, but had a small energy of adsorption which was indicated by Freundlich isotherm model. Tempkin model and Dubinin Radushkevich revealed a physical adsorption process driven by a slow adsorptive process. The Pseudo 2nd order had the best correlation coefficient at 0.9958 while Langmuir was 0.9545. Elovich function indicated a non-spontaneous reaction, while the intra-particle diffusion was not the rate-determining step. The slow adsorption rate in pseudo 1st order correlated with the small adsorption energy shown by the Freundlich isotherm, and also correlated with the small boundary layer thickness shown by intra-particle diffusion. All adsorptive functions showed that some other competing mechanisms should exist. XRD showed an increased number of graphene layers, d-spacing and improved crystallite size. FTIR data showed the oxygen-containing groups on the graphene oxide surface. The study showed that the prepared graphene oxide could efficiently adsorb Zn2+, and that the adsorption is affected by the method of synthesis.