Solvothermal growth of three-dimensional TiO2 nanostructures and their optical and photocatalytic properties

Three-dimensional (3D) titania nanostructures assembled with ordered rutile nanorods have been fabricated via a surfactant-free and single-step solvothermal route. The effects of preparation parameters, including the reaction temperatures and the reactant concentrations, on the microstructure, optical properties and photocatalytic activity of the 3D TiO2 nanostructures were investigated. The results revealed that 3D TiO2 microspheres possessed a dandelion-like morphology composed of radially packed rutile nanorods. Increasing the reaction temperature leads to the formation of larger rutile crystals, but reduced the aspect ratios of nanorods. The morphology of products was dominated by irregular shapes with low titanium precursor concentration. The optical reflectance, absorption and photocatalytic properties of the samples were found to be significantly dependent on their morphology. 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. Moreover, TiO2 products prepared with 0.4 M titanium precursor solution at 150 and 120 °C showed better or equivalent photocatalytic activity compared with Degussa P25 owing to high light harvesting ability as well as less aggregation for the unique 3D dandelion-like hierarchical structure. The growth mechanism of the 3D dandelion-like nanostructures under various preparation conditions was also discussed.