Gaoling Zhao

Sol—gel preparation and photoelectrochemical properties of TiO2 films containing Au and Ag metal particles

Abstract TiO 2 film electrodes with a TiO 2 overlayer containing dispersed Au or Ag metal particles were prepared by the sol-gel method, and the effect of the metal particles on the photoelectrochemical properties of the TiO 2 electrodes were investigated. An increase in the anodic photocurrent in the visible region was observed for both the Au and Ag particle dispersed electrodes, which was thought to result from the surface plasma resonance of the metal particles. The introduction of Au metal particles, however, reduced the anodic photocurrent in the ultraviolet region, resulting in a decrease of the anodic photocurrent under the illumination of xenon lamp light. On the other hand, for the Ag particle dispersed electrodes, the anodic photocurrent in the ultraviolet region increased and then decreased with an increasing amount of Ag particles. These effects of the dispersed metal particles on the photoelectrochemical properties of the TiO 2 electrodes were explained on the basis of the band models.

Sol-gel preparation of Ti1−xVxO2 solid solution film electrodes with conspicuous photoresponse in the visible region

Titanium–vanadium oxide films have been prepared by the sol-gel method using a starting solution containing titanium isopropoxide and vanadium(IV) oxyacetyl acetonate. Solid solubility of VO2 in TiO2 matrix and the effects of vanadium incorporation on the crystallization behavior of TiO2 were investigated by an X-ray diffraction analysis. It was found that the absorption edge of Ti1−xVxO2 films shifted to longer wavelengths when x increased. The sol-gel derived Ti0.95V0.05O2 film electrode was found to exhibit a conspicuous photoresponse in the visible region. Moreover, this film electrode was proved to be photoelectrochemically quite stable.

Effects of the incorporation of silver and gold nanoparticles on the photoanodic properties of rose bengal sensitized TiO2 film electrodes prepared by sol-gel method

Abstract Rose bengal-deposited TiO 2 film electrodes bearing dispersed Ag or Au nanoparticles were prepared by the sol-gel method. The dye-induced visible region photoresponse of the electrodes decreased with increasing Ag content up to a mole ratio of Ag/TiO 2 = 0.0207, while the UV photoresponse increased. On the other hand, the dye-induced visible region photoresponse decreased to a less extent by incorporation of a larger amount of Au particles of Au/TiO 2 = 0.06, along with decreased UV photoresponse. The effects of the metal particles on the dye sensitization of the electrodes were discussed in terms of band edge fluctuation induced by the surface metal particles, Schottky barriers at TiO 2 /metal interfaces, and surface plasma resonance.

Photoelectrochemical properties of sol–gel-derived anatase and rutile TiO2 films

Anatase and rutile film electrodes with comparable porosities were prepared by the sol–gel dip-coating method, and the photoelectrochemical properties were studied based on photocurrent measurement and impedance analysis in a three-electrode wet cell. The photocurrent was found to increase with the donor density, both in anatase and rutile electrodes. For the same donor density, however, rutile electrodes exhibited higher photocurrents than anatase electrodes, which was ascribed to the more beneficial bandgap structure of the former.

Preparation and photoelectrochemical properties of Ti1−xVxO2 solid solution thin film photoelectrodes with gradient bandgap

A design of a gradient bandgap Ti1−xVxO2 thin film electrode for wet-type solar cells is provided. The gradient bandgap film electrodes were prepared by heating stacked layers of varying V/Ti ratios using the sol-gel method. A composition gradient was observed for some of the samples by X-ray photoelectron spectroscopy although it was not very large. For the Ti1−xVxO2 film electrodes, conspicuous visible light photoresponse and photoelectrochemical stability were observed. The photocurrent increased with increasing bias potential. However, the photocurrent onset potentials of the Ti1−xVxO2 film electrodes were more positive than those of TiO2 film electrodes, probably owing to the high surface state density introduced by the diffusion of vanadium ions.

Preparation and photoelectrochemical properties of porous thin films composed of submicron TiO2 particles

Abstract Porous thin films composed of spherical TiO 2 particles of 0.6–0.7 and 0.3–0.4 μm in diameter were prepared from Ti(OC 2 H 5 ) 4 solutions containing HPC (hydroxypropylcellulose) and HNO 3 , respectively, and the photoelectrochemical properties as a photoanode were investigated in a wet cell. The electrode samples showed higher anodic photocurrent and higher UV photoresponse than relatively dense TiO 2 thin film electrodes prepared by dip-coating, and exhibited weak but distinct visible light photoresponse. These experimental results show that the submicron colloidal electrodes have high specific surface area effective for the photo-induced redox reactions. It also suggests the formation of the band bending that contributes to the photocurrent generation. The colloidal electrodes prepared from the HPC-containing solution were found to exhibit higher anodic photocurrent than those from the HNO 3 -containing solution, probably because of the larger amount of Ti 3+ species and mesopores formed in the former electrodes. The effects of post-heat-treatment on the photoanodic properties were also investigated.

Control of optical properties of gel-derived oxide coating films containing fine metal particles

Control of the optical properties of gel-derived oxide films containing fine metal particles is described. The duration of the aging of Si(OC2H5)4-derived sols and the amount of water for hydrolyzing Si(OC2H5)4 were found to greatly affect the size and the shape of Au particles formed in the silica matrix, and accordingly the optical absorption of the Au/SiO2 composite films. Employing dielectric media with high refractive indices like TiO2 was shown to shift the absorption peak of Au particles to longer wavelengths. Pd/TiO2 and Pt/TiO2 composite films showed absorption in the visible region.

Low temperature synthesis of visible light-driven vanadium doped titania photocatalyst.

A simple method based on sol-gel method was developed to prepare vanadium ions doped TiO(2) nanocrystalline at low temperature. Thus-obtained vanadium doped TiO(2) was proved to be V(x)Ti(1-x)O(2) solid solution. Doping vanadium could enhance the formation of stable phase. Its optical absorption spectrum shows a red shift to 445 nm. Photodegradation experiments suggest that thus-prepared vanadium doped TiO(2) nanocrystalline can be excited by visible light and is a good photocatalyst under daylight. These properties are the same as the vanadium doped TiO(2) prepared under high temperature conditions (> or = 350 degrees C). However, in the present work, the vanadium doped TiO(2) crystal particle is very uniform and fine, about 5 nm. It is much smaller than the production prepared under high temperature.

Effect of dispersed Ag on the dielectric properties of sol–gel derived PbTiO3 thin films on ITO/glass substrate

Abstract Ag-dispersed PbTiO 3 films were prepared on ITO/glass substrate by the sol–gel process. XRD was carried out to characterize the crystalline phases. A spectrophotometer and LCZ meter were used to measure the UV–VIS absorption spectra and dielectric properties of the films. Ag particles had formed in the PbTiO 3 matrix. Their size and quantity increase with the increase in silver concentration. Ag particles are found to have an effect on the dielectric properties of PbTiO 3 films. With the addition of Ag nanoparticles into PbTiO 3 films initially, the dielectric constant of the films increases and the dissipation factor of the films decreases. Then with increasing of silver concentration, the dissipation factor of the film increases. However, the effect of the dispersed silver nanoparticles on dielectric constant gives different results at different frequency ranges. At low frequency it increases with the increase in silver concentration, which coincides well with percolation law. At high frequency, when silver concentration reaches 5 mol%, the dissipation factor markedly increases and the dielectric constant decreases, which departs from percolation law due to the interaction of ferroelectrics domains and silver particles.

Effects of acid on the microstructures and properties of three-dimensional TiO2 hierarchical structures by solvothermal method

Three-dimensional (3D) TiO2 hierarchical structures with various microstructures have been successfully synthesized via a surfactant-free and single-step solvothermal route, in which hydrochloric acid (HCl), nitric acid (HNO3), and acetic acid (HAc) are employed as the acid medium, respectively. The effects of acid medium on the microstructures and properties of 3D TiO2 hierarchical structure have been studied. The results indicate that 3D dandelion-like microspheres assembled of radial rutile nanorods are obtained in the sample prepared with HCl. Both the fraction of rutile and the diameter of nanorod enhance with the increasing HCl concentration. For the products derived from either HNO3 or HAc, 3D spheres composed of anatase nanoparticles are present. The 3D dandelion-like TiO2 hierarchical structures show low reflectance and efficient light harvesting since this ordered rod geometry offers a light-transfer path for incident light as well as multiple reflective and scattering effects. Moreover, 3D TiO2 with this unique topology shows superior photocatalytic activity despite low surface area, which can be ascribed to the enhanced light harvesting, fast electron transport, and low electron/hole recombination loss.