Adsorption of 2-nitrophenol in aqueous phase on multi-wall carbon nanotubes (MWNTs) and functionalized multi-wall carbon nanotubes having covalent attachments of carboxylic groups (MWNTs-COOH) has been considered. Adsorption behavior of 2-nitrophenol onto carbon nanotubes was studied by varying the parameters such as agitation time, 2-nitrophenol concentration and pH. The presence of surface functional groups affected the adsorption capacity of MWNTs for this removal of 2-nitrophenol. Kinetic studies were performed and pseudo-second-order kinetic model successfully represented the kinetic data. The Freundlich, Langmuir and Tempkin adsorption models were used for the mathematical description of adsorption equilibrium and it was found that the experimental data fitted very well to the Langmuir model. However, for MWNTs-COOH, Tempkin model may be recommended because of the strong adsorbent-adsorbate interactions arising from the functional groups present on the surface of MWNTs. The results of the study show that the carbon nanotubes can be used as potential adsorbent for phenolic derivate in water/wastewater. (C) 2010 Elsevier B.V. All rights reserved.