Graphene oxide nanosheets at the water-organic solvent interface: utilization in one-pot adsorption and reactive extraction of dye molecules.

Graphene oxide (GO) is amphiphilic in nature, due to its structure, which consists of hydrophilic oxygen-containing functional groups and a hydrophobic basal plane of polyaromatic benzene rings. Due to this amphiphilicity, GO can create stable bubbles at water-organic solvent interfaces. In this study, the formation of bubbles at aqueous-organic interfaces in the presence of GO is investigated with different organic solvents. Bubble formation and transfer of GO from water to the organic phase is more prominent in aromatic solvents compared to aliphatic solvents, due to π-π interactions. Maximum transfer of GO from the aqueous to the organic phase is achieved at pH 2, and decreases with rising pH of the aqueous phase. Based on this property, and the ability of GO to adsorb cationic and anionic dye molecules, its application as a carrier for reactive extraction of cationic and anionic dye molecules is explored in toluene, kerosene, and carbon tetrachloride at pH 2 and 25 °C. The kinetics of the adsorption of the dyes onto GO nanosheets that takes place in the aqueous phase is also evaluated with different models, and a pseudo-second-order (linear) model is found to be the best fit. The adsorption isotherm data are also analyzed with different isotherm models. The electrostatic interaction and π-π interaction between the dye molecules and GO nanosheets leads to dye extraction of up to 98.2% using this technique. The dye extraction is maximum in toluene and at low dye concentration.