BACKGROUND: Inadequate surface oxidization can potentially destroy the structure and chemical characteristics of the carbon nanotubes (CNTs) and result in loss of sorption capacity and weight. It is necessary to carefully oxidize CNTs using an adequate NaOCl concentration before using it as a sorbent. RESULTS: FE-SEM images showed that the structure of CNTs oxidized with 7% NaOCl concentration was significantly destroyed and agglomerated as larger carbon particles instead of nanotubes. The surface acidities of CNTs oxidized with 3% and 5% NaOCl concentration were almost the same, with maximum values 6.20 and 6.25 mmol g(-1), respectively, in all studied cases. Conversely, increasing NaOCl concentration to 7% decreased the acidity from 6.25 to 5.0 mmol g(-1), indicating that 7% NaOCl concentration is not suitable for oxidization of CNTs. Assessing the factors (CNTs mass, contact time, pH, and ionic strength), that influence adsorption performance showed that CNTs oxidized with 5% NaOCl concentration performed better than those with 1%, 3% and 7% concentrations. CONCLUSION: Considering simultaneously the percentage recovery, adsorption performance and isotherms of CNTs oxidized by NaOCl solutions at four different concentrations, an optimum NaOCl concentration of 5% is suggested by this study. (C) 2010 Society of Chemical Industry