Synthesis Of CNT-TiO₂ Composite By Chemical Vapor Deposition

Carbon nanotube（CNT）-TiO₂ composites can significantly improve the performance of photocatalytic activity and photoelectric conversion efficiency of TiO₂. The traditional composite procedures are synthesizing CNT or TiO₂ firstly. However, the common problem of the fabrication process is poor dispersibility, agglomeration and the complex process. In this paper, the CNT-TiO₂ composite was prepared via chemical vapor deposition （CVD） method by using floating CNT as carrier in gas phase. Mainly for mixing-type, coating-type and coaxial-type structure of CNT-TiO₂ composite materials were synthesized.In H2 atmosphere, the product was a mixing-type CNT-TiO₂ composite. The CNT bundles act as skeleton which support bamboolike CNT, amorphous carbon, TiO₂ particles. The morphology and content of CNT could be controlled by adding the solvent such as ethanol and methanol into TBOT. The content of TiO₂ in the product was up from 30 wt% to 65 wt% when the mole ratio of TBOT and ethanol was in the range from 1:100 to 10:100 in the precursor. The mixing-type CNT-TiO₂ composite materials had large specific surface area which reached 1581 m2/g when the mole ratio of TBOT and ethanol was 3:100.When the reaction atmosphere was the mixture of H2 and Ar, the product was a coating-type CNT-TiO₂ composite material. The TiO₂ particles were coated in the outer wall of CNT. The crystal structure of TiO₂ in the composite was the mixed phase of anatase and rutile（the mass ratio of anatase to rutile was 2:1） and the CNT was multiwall and had defects.The specific surface area of the composite was 50.24 m2/g and it exhibited excellent visible light photocatalytic activity. The degradation rate of methyl orange was above 80% after 6 h visible light irradiation.The coaxial-type structure CNT-TiO₂ composite was prepared when the carbon source was injected in the ahead of the reactor and titanium source was injected in the reactor tail. The single or few wall CNT was served as axis and the TiO₂ particles were coating along the CNT axis. There was a little amorphous carbon in the interspace of TiO₂ particles. The TiO₂ had a mixed phase structure, the mass percentage of anatase and rutile was about 81% and 19%, respectively.