Synthesis Of Carbon Nanotubes/ Titanium Dioxide Composite Photocatalyst By Fluidized Bed Chemical Vapor Deposition (FBCVD) And Its Photocatalytic Properties

Titanium dioxide(TiO2) photocatalysis, has been widely studied for decomposing the various environmental pollutants. A lot of attention is paid on the extension of the light absorption of TiO2 from ultraviolet to visible region and restraining the combination of the holes-electrons. In this paper, TiO2 was modified by carbon nanotubes(CNTs) grown in situ and by CdS coated on the surface of TiO2. The application in the photocatalytic degeneration of aqueous organic compound was investigated.As the catalyst for the growth of CNTs, NiO-TiO2 catalyst was prepared by modified citric acid sol-gel method. CNTs-Ni-TiO2 composite was prepared by growing CNTs on TiO2 surface by fluidized bed chemical vapor deposition (FBCVD) with N2 and C2H2 as protection gas and carbon source gas respectively. The effect of the catalyst, FBCVD temperature, acethylene concentration and dosage of Ni in NiO-TiO2 catalyst on the morphology and structure of CNTs was investigated. The photocatalytic performance of CNTs-Ni-TiO2 was evaluated by degradation of methylene blue under the UV light. When Ni was used as the catalyst, the CNTs can grow on the surface of TiO2 well. To control the crystal structure of TiO2 and the growth of CNTs, the suitable temperature was 550℃. It was also found that the high-quality CNTs could be prepared when the volume ratio of C2H2 and N2 was 1:15. The content of CNTs was 7.3% when the dosage of Ni was 5%, and the photocatalytic activity was good.To improve the response to the visible light, CdS with narrow band-gap was was deposited on the surface of TiO2 doped with Ni oxide by liquid-phase deposition (LDP). CNTs were in-situ grown on CdS/NiO-TiO2 in fluidized bed reactor. Crystal structure of CdS was investigated by XRD, and the results showed that the high temperature and the reducing atmosphere induced the phase transformation of CdS from cubic zinc blend to cubic wurtzite during the process of FBCVD. TEM and Raman confirmed that synthesized CNTs were multi wall and had a good crystalline quality. Using the CNTs-CdS/TiO2(Ni) composite, the degradation rate of methylene blue(MB) reached 80% in 4 hours under visible light.