Adsorption of organic contaminants by graphene nanosheets: Comparison with carbon nanotubes and activated carbon

In this study, pristine graphene nanosheets (GNS) and graphene oxide (GO) was characterized and compared with those of a coal-base activated carbon, a single-walled carbon nanotube (CNT), and a multi-walled CNT. Adsorption of synthetic organic contaminants (SOCs) by these adsorbents was examined in distilled and deionized water and in the presence of natural organic matter (NOM). In the presence of NOM, aromatic compound uptake of all adsorbents was reduced; however, graphenes exhibited comparable or better adsorption capacities than CNTs and GAC. The impact of NOM on the organic contaminant adsorption was smaller on graphenes than CNTs and activated carbons. Furthermore, biphenyl with its flexible molecular structure was less impacted from NOM preloading than phenanthrene. Phenanthrene has a planar and rigid molecular structure inhibiting the molecule form adjusting the structure to inner pores. In order to further investigate the intermolecular interactions between the graphene nanomaterials and organic contaminants, a suite of halogenated aliphatic contaminants were selected (TeCE, 1,2-DCP, 1,2-DBA, 1,2-DB-3-CP, TCE, TeCA, 1,1,1-TCA, 1,1,2-TCA, 1,1-DCE, CCl4) and their adsorption affinities were tested in distilled and deionized water and under NOM preloading conditions. Aliphatics were adsorbed less than aromatics as expected due to their higher solubilities; however, aliphatic adsorption results confirmed that the graphene and graphene oxide nanoparticles showed very little capacity reduction under NOM preloading. This finding was attributed to the sheet-like structure of graphene layers minimizing the NOM � SOC competition. These results indicated that graphenes might serve as alternative adsorbents for removing organic contaminants from waste streams. The lack of competition under NOM preloading may also favor the use of graphene nanoparticles. In addition, it can be concluded that once released to environment, graphenes will adsorb organic contaminants influencing their fate and impact in the environment.