Few-layered graphene oxide nanosheets as superior sorbents for heavy metal ion pollution management

Graphene has attracted multidisciplinary study because of its unique physicochemical properties. Herein, few-layered graphene oxide nanosheets were synthesized from graphite using the modified Hummers method, and were used as sorbents for the removal of Cd(II) and Co(II) ions from large volumes of aqueous solutions. The effects of pH, ionic strength, and humic acid on Cd(II) and Co(II) sorption were investigated. The results indicated that Cd(II) and Co(II) sorption on graphene oxide nanosheets was strongly dependent on pH and weakly dependent on ionic strength. The abundant oxygen-containing functional groups on the surfaces of graphene oxide nanosheets played an important role on Cd(II) and Co(II) sorption. The presence of humic acid reduced Cd(II) and Co(II) sorption on graphene oxide nanosheets at pH < 8. The maximum sorption capacities (C(smax)) of Cd(II) and Co(II) on graphene oxide nanosheets at pH 6.0 ± 0.1 and T = 303 K were about 106.3 and 68.2 mg/g, respectively, higher than any currently reported. The thermodynamic parameters calculated from temperature-dependent sorption isotherms suggested that Cd(II) and Co(II) sorptions on graphene oxide nanosheets were endothermic and spontaneous processes. The graphene oxide nanosheets may be suitable materials in heavy metal ion pollution cleanup if they are synthesized in large scale and at low price in near future.