以原子層沉積法成長TiO2薄膜/奈米碳管之殼-核結構及其光催化性質研究

Abstract

A series of TiO2 films coated on carbon nanotubes with different thicknesses and phase ratios were doped with nitrogen and used as catalyst for photodecomposition of organic pollutants. The TiO2 thin film was directly deposited on multiwall carbon nanotubes (MWCNTs) by atomic layer deposition (ALD) method using TiCl4 and H2O as precursors. The different phase ratios were controlled by thermal treatment in vacuum to enhance the catalytic efficiency. The purpose to get mixed phases of TiO2 is to lower the electron/hole recombination rate to enhance the photo-induced decomposition ability. In addition, nitrogen was doped to TiO2 by ammonia gas to increase visible light absorption for better efficiency of photocatalyst. The support for TiO2 deposition was commercial MWCNTs that were inert and not easy to deposite with TiO2 by ALD method without treatment. By reaction with HNO3, defects and functional groups could be produced on the surface of MWCNTs so that TiO2 could be deposited on the surface as photocatalyst. The physical and chemical properties of modified carbon nanotubes were analyzed by BET and XPS. The pollutants chosen for photo-induced decomposition test was phenol. The compositions and properties of the photocatalysts were analyzed by XRD, TEM-EDS, DSC, SEM-EDS, XPS, and UV-vis spectrometry. The result showed that the saturation growth rate of TiO2 was about 0.55 A/cycle for pristine and acid treated MWCNTs with sufficient TiCl4 and H2O pulse time. The penetration depth of TiO2 deposition was about 4 μm for CNTs dispersed on silicon wafer. The anatase phase of TiO2 was obtained by heating at above 300 oC, and the rutile phase was found when annealed at above 800 oC. The doping of TiO2/CNT composite with nitrogen could be achieved in NH3 atmosphere at 500 to 600 oC. The content of nitrogen increased from 0.9 at % to 12 at % as temperature increased.