This study compares aqueous copper (II) adsorbed onto as-grown and modified carbon nanotubes (CNTs), using H2SO4 and H2SO4/KMnO4 processes. H2SO4 and H2SO4/KMnO4 modifications reduced pH(iep) and Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed that some functional groups were formed on modified CNTs. The adsorption capacity of copper (II) onto modified CNTs was greater than that of as-grown CNTs, especially at pH 6. The results demonstrate that the modified processes increased the adsorption capacity because the functional groups were generated on the modified surfaces of the CNTs. Additionally, the adsorption capacity of copper (II) onto as-grown and modified CNTs both increased with temperature, and the results indicated that the Langmuir isotherm fitted the experimental data well. Simulation results indicated that the Delta H-0 values of as-grown, H2SO4-modified CNTs and H2SO4/KMnO4-modified CNTs were 4.83, 14.37 and 29.92 kJ/mol, respectively. Based on Delta H-0, the adsorption of Cu2+ onto H2SO4/KMnO4-modified CNTs is suggested to proceed simultaneously by physisorption and chemisorption but that onto as-grown and H2SO4-modified CNTs may proceed only by physisorption. (C) 2009 Elsevier B.V. All rights reserved.