| TiO2 semiconductor has been considered one of the best photocatalytic materials because of its low cost, long-term thermodynamic stability, strong oxidizability and relative nontoxicity. Besides the use of purifying wastewater and dye-sensitized solar cells, it can also been used to produce hydrogen by water splitting under the irradiation of light with the wavelength lower than that corresponding to the band-gap energy of TiO2, which has attracted extensive attention since the pioneer work of Fujishima and Honda for the discovery of splitting water on TiO2 electrodes. However, the photoinduced electrons and holes in TiO2 may experience a rapid recombination, which diminishes the efficiency of the photocatalytic reaction significantly. In this thesis, TiO2 nanotube(TiO2NTs) were prepared by a hydrothermal method, and the advanced carbon materials such as MWCNT and graphene were introduced into TiO2NTs. Besides, a novel process to fabricate MWCNT/CdS/TiO2 composites was proposed. The main results and conclusions can be summarized as following:1. MWCNTs/TiO2NTs composite has been synthesized by a hydrothermal method and firstly used in photocatalytic hydrogen production. The obtained TiO2NTs/MWCNTs composites were characterized by X-ray diffraction, transmission electron microscopy (TEM), Raman spectrum and ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy. The experimental results revealed that the MWCNTs were decorated with well dispersed anatase TiO2 nanotubes with a diameter of 8-15 nm and 80-120nm in length. A slight blue shift and weak symmetry was observed for the strongest Raman peak which resulted from strain gradients originating from interface integration between TiO2 nanotubes and MWCNTs. The composite showed a better absorbance than P25 in UV-Vis region. The photocatalytic activity of the as-prepared samples was evaluated by hydrogen evolution from water splitting using Na2S and Na2SO3 as sacrificial reagents under UV-Vis light irradiation. Enhanced photocatalytic activity compared with P25 has been observed for the resulted samples. The nanocomposite with optimized MWCNTs content of 1%displayed a hydrogen production rate of 161μmol·h-1·g-1, which is 1.8 times higher than P25.Well photocatalytic stability of the as-synthesized samples was observed as well.2. GS/TiO2NTs composite photocatalysts were prepared by a reductive method in hydrothermal process. XRD,TEM,FT-IR,Raman spectrum,and UV-Vis diffuse reflectance spectroscopy were used to characterize the as-prepared photocatalyst. TiO2NTs were proved to exist on the layer structure of graphene, which was used for improving electron-collecting efficiency and reducing carries recombination. The obtained graphene has a tremendous surface area attributed to the larger distance between each carbon atom layer. The GS/TiO2NTs composite has showed a well thermodynamic stability demonstrated by TG results. Better performance in water splitting under UV-vis light irradiation was observed for both the GS/TiO2NTs and GO/TiO2NTs photocatalysts, the former one displayed a hydrogen production rate of 179.4μmol·h-1·g-1, which is higher than the later one. It implied that GO and GS can transfer photoelectron effectively. The photocatalysts should be promising in the potential applications in water splitting and light sensitive photocatalysis.3. MWCNTs modified TiO2 particles with different contents of CdS were prepared by sol-gel method. SEM patterns confirmed the composite had a smaller size distribution and a better disperse addition the MWCNTs. This structure exhibited well catalysis due to the absorption of light. CdS could also contribute to the absorption of the light in visible region. It is found that hydrogen production (14.0μmol) from water photo-splitting can be enhanced by introducing MWCNTs into CdS/TiO2 composites, in comparison to CdS/TiO2 photocatalysts (11.6μmol). The average hydrogen production rate can be improved by 18% and the highest improvement can be up to 21%. However, hydrogen production in water photo-splitting displayed decline by introducing 1%SWCNTs when the CdS existed a rather more content (30%,100% rate of TiO2). This implied the amount of CdS in the composites is an important parameter. The appropriate percentage is necessary for each componds in the composite for the best photocatalytic performance. |
PDF Full Text Request