TiO2 film was coated on acid-treated and pristine multiwall carbon nanotubes (CNTs) with different thicknesses by atomic layer deposition at 100 degrees C to form a CNT/TiO2 core-shell structure. The relationship between oxygen containing functional groups on the surface of CNTs and growth rate of TiO2 film was studied. The saturation growth rate of TiO2 was 0.55 angstrom/cycle for acid-treated CNTs with sufficient durations of pulse time for the precursors of TiCl4 and H2O. The as-prepared TiO2 film was amorphous, and the anatase and rutile phases of TiO2 were obtained by heating to 300 degrees C and 800 degrees C, respectively. The shell thickness of anatase TiO2 on CNTs was a key factor to determine the efficiency of methylene blue (MB) degradation. The thickness of 22 nm exhibited the best efficiency of MB degradation due to lower electron-hole recombination rate and higher amount of hydroxyl group generated on the surface of TiO2 after UV irradiation. (C) 2016 Elsevier B.V. All rights reserved.