DOI: 10.1002/cphc.201402554 Graphene Oxide Nanosheets at the Water–Organic Solvent Interface: Utilization in One-Pot Adsorption and Reactive Extraction of Dye Molecules Ponchami Sharma,* Dipankar J. Borah, and Manash R. Das* [a] 1. Introduction Pollution of water resources by different types of industrial ef- fluents is one of the major environmental issues of the modern world. Synthetic dyes used in different industries con- tribute towards water pollution. The presence of dye mole- cules in water reduces light penetration, which inhibits the photosynthetic activities of aquatic flora and thereby severely affects the food source of aquatic organisms. [1] The thin layer of discharged dyes that forms over water surfaces also de- creases the amount of dissolved oxygen, which affects aquatic fauna. Furthermore, dye-containing effluents increase the bio- chemical oxygen demand in water. [1] Many of these dyes have carcinogenic and mutagenic effects. [2] Therefore, the dye mole- cules must be removed from industrial effluents before being released into the main water stream. A number of technolo- gies have been studied for dye removal from aqueous systems over the years, among which adsorption technology has at- tracted researchers, due to its simplicity, cost effectiveness, and high efficiency. However, separation of dye-adsorbed materials from a water system is still a challenge for its practical applica- tion. Recovery of the dye molecules from the aqueous to or- ganic phase by using the reactive extraction technique will provide a simple solution to this challenge. Reactive extraction is a type of liquid–liquid extraction process in which material is extracted from the aqueous to the organic phase by using a suitable carrier. The carrier reacts with the material in the aqueous phase and the reaction complexes formed are then extracted to the organic phase. For this technique, selection of a suitable carrier and organic solvent is extremely important. Reactive extraction has been shown to be highly effective for the separation of hydrophilic compounds from aqueous solu- tions by using a chemical reaction that improves their solubili- ty in an organic solvent. This method is widely used for extrac- tion of carboxylic acids from aqueous solution, enantioselec- tive separation, biodiesel production, and so forth. [3–7] However, to our knowledge, one-pot adsorption and reactive extraction of dye molecules by using an adsorbent as a carrier from the aqueous to the organic phase has not been reported. Graphene oxide (GO) has attracted considerable attention of researchers of different disciplines in recent years due to its unique characteristics, such as large surface area, excellent me- chanical properties, and hydrophilic nature. GO consists of a number of oxygen-containing functionalities, such as carbox- yl, phenolic, and epoxide groups, which make GO a somewhat hydrophilic material. [8, 9] However, recent research has shown that GO also has a hydrophobic nature depending on certain factors, such as pH of the medium and the presence of inor- ganic ions. [10–12] The hydrophobicity of GO might be attributed to the presence of polyaromatic islands of unoxidized benzene rings at the basal plane. [10] Another unique character of GO is Graphene oxide (GO) is amphiphilic in nature, due to its struc- ture, which consists of hydrophilic oxygen-containing function- al groups and a hydrophobic basal plane of polyaromatic ben- zene 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 ali- phatic solvents, due to p–p 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 reac- tive extraction of cationic and anionic dye molecules is ex- plored in toluene, kerosene, and carbon tetrachloride at pH 2 and 25 8C. The kinetics of the adsorption of the dyes onto GO nanosheets that takes place in the aqueous phase is also eval- uated with different models, and a pseudo-second-order (linear) model is found to be the best fit. The adsorption iso- therm data are also analyzed with different isotherm models. The electrostatic interaction and p–p interaction between the dye molecules and GO nanosheets leads to dye extraction of up to 98.2 % using this technique. The dye extraction is maxi- mum in toluene and at low dye concentration. [a] P. Sharma, D. J. Borah, Dr. M. R. Das Materials Science Division CSIR-North East Institute of Science and Technology Jorhat-785006, Assam (India) Fax: + 91-376-2370011 E-mail : ponchi.du@gmail.com mnshrdas@yahoo.com Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201402554.  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemPhysChem 2014, 15, 4019 – 4025 4019 CHEMPHYSCHEM ARTICLES