Preparation And Application Of TiO₂ Composite Nanostructures

As a well-known semiconductor material with wide band gap, titanium dioxide has become a hotspot in the research fields of energy and environment due to its unique photocatalytic and optical properties. The three dimensional TiO2 nanomaterial with higher specific surface areas, such as nanoflowers, nanospheres, and nanotrees, ect, possesses more excellent photocatalytic and photoelectric properties compared to the low dimensional TiO2 nanomaterials, The photocatalytic and photoelectric properties of the TiO2 nanomaterials are determined by their structure and specific surface area. Therefore, how to optimize the structures of three dimensional TiO2 nanostructures has far reaching significance and applicable value. This thesis focuses on the design and preparation of several kinds of three dimensional TiO2 nanostructures, and applied to the fields of the photocatalytic degradation and the dye-sensitized solar cells (DSSCs). The main conclusions are as followings:A variety of new nanostructure materials of titanium dioxide, including TiO2 including TiO2 porous thin film, TiO2 nanorod array, TiO2 hollow spheres and pinecone-like TiO2, were prepared through hydrothermal method. In this thesis, the surface morphologies of these materials and the growth mechanism was analyzed; Meanwhile, their application prospects were also discussed. The success preparation.of these materials lay a foundation for design and preparation of Three-dimensional (3D) TiO2 in future.TiO2 nanoflowerclusters (TiO2 NFC) with TiO2 nanobelts as the growth frameworks were prepared through a simple hydrothermal synthesis. To analysis the formation mechanism of TiO2 NFC, the influences of the nanobelt content, the proportion of HCl and water, and the reaction time/temperature on the growth of TiO2 NFC were investigated in details. The novel TiO2 composite nanostructures exhibit higher photocatalytic activity for organic pollutants compare to commercially available nanoparticles (P25) in the photocatalysis field. Moreover, the novel nanocomposites were applied in the photoanodes of DSSCs fabricated from the mixture of TiO2 NFC and P25 nanoparticles in different weight ratios (wt)(TiO2 NFC:P25=0:10; 1:9; 3:7; 5:5; 7:3; 9:1; 10:0). The highest conversion efficiency of 6.38% is achieved for DSSCs with the photoanode containing a 5:5 (wt/wt) mixture of TiO2 NFC and P25. The high efficiency of the DSSCs using the mixed photoanode derives from high light harvesting, good transferring properties of TiO2 NFC, and reduced interface recombination. Moreover, the NFC enhances the light harvesting by light scattering and provides direct electrical transport pathways for photogenerated electrons.A novel strings of hierarchical TiO2 microspheres on nanobelts (TiO2 HSN) with larges specific surface area (191m2/g) was synthesized via a one-step hydrothermal method and applied in the photocatalytic degradation and DSSCs. TiO2 HSN exhibits higher photocatalytic activity for organic pollutants comparing to commercially available nanoparticles (P25) in the photocatalysis field, due to the high proportion of bare (001) face and larges specific surface area. Meanwhile, TiO2 HSN is also used as the scattering layer and the adsorption layer to prepare double and single layered DSSC, respectively. The experimental results show that the photoanode using TiO2 HSN as the scattering layer (with P25 as adsorption layer) adsorbs more dye and favors the light harvesting, leading to the increased conversion efficiency of the corresponding DSSCs. Moreover, the DSSCs employing single layered TiO2 HSN photoanode shows enhanced conversion efficiency as compared to the DSSCs using P25 photoanode. The enhancement of conversion efficiency in the former is probably due to the good crystallization, large specific surface area, good electronic transport and enhanced light scattering in the HSN based photoanode.In order to further enhance the electronic transport without decreasind the dye adsorption capacity, Ag/TiO2 core-shell heterostructure (AWT) was prepared via a simple hydrothermal synthesis. The effects of the additives content, the reaction time, and the temperature on the structure of AWT were investigated. The AWT nanostructures exhibit higher photocatalytic activity for organic pollutants as compared to P25 in the photocatalysis field due to the larger specific surface areas and the favored electron-hole dissociation by the Schottky junction. Meanwhile, AWT nanostructures were employed in the photoanodes of the DSSCs by incorporation of AWT in P25 nanoparticles with different mass ratio (0%,0.5%,1%,5%,10% and 20%). The conversion efficiency of the DSSCs with the AWT content< 5% increases with the AWTcontent, due to the high electrical transport for photogenerated electrons. With further increases of the AWT content, the conversion efficiency of the DSSC decreases. The highest conversion efficiency of 6.98% is achieved for DSSC with 5% AWT in the photoanode.