Graphene nanocomposites modified with organic polymers as effective heavy metal sorbents in aqueous media

The sorption materials based on graphene oxide (GO) modified with a chitosan coating (GO/CS) and a lignin derivative, lignosulfonate (GO/LS), were developed by the authors to remove heavy metal ions from aqueous media. The technology for obtaining sorbents involved the formation of a hydrogel and its subsequent lyophilization in order to preserve the porous space. The synthesized nanostructured sorbents were characterized on the basis of transmission electron microscopy with the elemental analysis, the surface area measurement and the thermogravimetric analysis (BET). The thermogravimetric analysis showed that nanocomposites decompose in two stages: 3 – 5 % weight loss at temperatures up to 250 – 270 °С and 40 – 50 % weight loss at temperatures up to 750 – 770 °С. The measured BET surface area for GO/LS and GO/CS was 85.34 and 73.256 m2⋅g–1, respectively. Batch sorption experiments were carried out at pH = 6, followed by the quantitative adsorption of Cu2+ and Pb2+ using atomic absorption spectrometry. According to the results of the experimental studies, the best ratio of the initial components of the nanocomposites was established. For the GO/LS nanocomposite, the ratio of 2 : 1 was chosen for further studies, and 100 : 1 for the GO/CS nanocomposite. The value of the adsorption capacity for these compositions for lead was: 178.1 mg⋅g–1 for GO/LS; 197.38 mg⋅g–1 for GO/CS; and for copper: 162.39 mg⋅g–1 for GO/LS, 186.17 mg⋅g–1 for GO/CS.