Preparation, Photocatalytic And Photoelectrochemical Properties Of Nanostructured Titanium Dioxide

Titanium dioxide (TiC2) nano-materials has attracted considerable attention due to its low-cost, nontoxicity and widespread applications. Meanwhile, dimensionality and size of the materials have been regarded as critical factors in the areas of material preparation and application. TiO2 ordered nanostructures has caused great interest and is expected to have potential applications in photocatalysts and solar cells due to its unique topological structure and dimensionality. Traditional nanometer-scale powders are likely to aggregate. The conversion efficiency of polycrystalline films is limited. In this work, three-dimensional (3D) TiO2 nanostructures with various microstructures and TiO2 nanorod array films have been successfully synthesized via a surfactant-free and single-step solvothermal route. CdS nanoparticles were deposited on the TiO2 nanorod array films. Growth mechanisms of the TiO2 nanostructures and films were discussed. The photocatalytic and photoelectrochemical properties of the samples were investigated. The main results are as follows.Three-dimensional TiO2 nanostructures with various microstructures have been successfully synthesized by altering the solvent via a surfactant-free and single-step solvothermal route.3D dandelion-like TiO2 structures self-assembled of nanorods were synthesized in non-polar solvent based on water-nonpolar solvent interface. Microspheres composed of nanoparticles are obtained using low polar or polar solvent, which are also amphiphilic solvents. Only bulky aggregated TiO2 nanoparticles were obtained when pure water is used as the solvent due to the fast hydrolysis of titanium precursor. Mechanisms of the self-assembly of 3D TiO2 structures indifferent solvents were proposed.Acid media, reaction temperatures and reactant concentrations have highly impact on the microstructure, optical properties and photocatalytic activity of the 3D TiO2 nanostructures.3D dandelion-like microspheres assembled of radial rutile nanorods are obtained in the sample prepared with HC1. For the products derived from either HNO3 or HAc,3D spheres composed of anatase nanoparticles are present.3D dandelion-like structures with tapered tips showed lower reflectance, more efficient light harvesting, higher surface area and consequently higher photocatalytic activity compared with those with flat tops and fragment of nanorod sectors. The growth mechanism of the 3D dandelion-like nanostructures under various preparation conditions was discussed.The results indicated that the rod geometries, especially the tip morphologies, of the TiO2 nanorod array films were found to be crucial to photoelectrochemical performance of the film electrodes. TiO2 nanorod array film electrodes with different rod geometries were fabricated via solvothermal route. By controlling the solution growth conditions, the rod geometries, especially tip structures, of TiO2 were tuned. The vertical aligned hierarchical nanorod array s possessed conically shaped tip geometry, which was favorable for film electrode due to the reduced reflectance, enhanced light harvesting, fast charge carrier separation and transfer, suppression of carrier recombination, sufficient electrolyte penetration and subsequent efficient quantum dot assembly. CdS quantum dots were deposited on the TiO2 nanorod array films. CdS quantum dots sensitized TiO2 film electrode with tapered tips exhibited an enhanced photoelectrochemical performance, a photocurrent intensity of 5.13 mA/cm2 at a potential of 0 V versus saturated calomel electrode and IPCE of 22%in the visible light region from 400 to 500 nm.