Direct formation of anatase TiO2 nanoparticles on carbon nanotubes by atomic layer deposition and their photocatalytic properties

TiO2 with different morphology was deposited on acid-treated multi-walled carbon nanotubes ( CNTs) by atomic layer deposition at 100 degrees C-300 degrees C to form a TiO2@CNT structure. The TiO2 fabricated at 100 degrees C was an amorphous film, but became crystalline anatase nanoparticles when fabricated at 200 degrees C and 300 degrees C. The saturation growth rates of TiO2 nanoparticles at 300 degrees C were about 1.5 and 0.4 angstrom/cycle for substrate-enhanced growth and linear growth processes, respectively. It was found that the rate constants for methylene blue degradation by the TiO2@CNT structure formed at 300 degrees C were more suitable to fit with second-order reaction. The size of 9 nm exhibited the best degradation efficiency, because of the high specific area and appropriate diffusion length for the electrons and holes.