CNT/TiO2 core-shell structures prepared by atomic layer deposition and characterization of their photocatalytic properties

• The acid treatment of CNTs generated more oxygen-containing functional groups that facilitated the growth of TiO2 by ALLD.
• The different rate constants k, kspm and kspa were discussed to investigate the factors affecting MB degradation.
• The thickness of 22-nm exhibited the best efficiency of MB degradation due to the highest concentration of –OH groups generated on the TiO2 surface.

TiO2 film was coated on acid-treated and pristine multiwall carbon nanotubes (CNTs) with different thicknesses by atomic layer deposition at 100 °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 Å/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 °C and 800 °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.