Preparation And Characterization Of Porous Spherical TiO₂ Photocatalytic Materials

With the excess exploitation of resources and serious pollution of nature, environment has been destroyed seriously. It is urgent to develop functional materials which can use energy sources effectively. Nano-scale titanium dioxide is the green functional material which can purify environment. Titanium dioxide has been widely and intensively investigated because of its various merits, such as optical and electronic properties, strong oxidazing power, no-selectivity, low cost, high photocatalytic activity, chemical stability, non-toxicity and long-term photostability. Especially, porous TiO₂ microspheres particles (including porous solid spheres and hollow spheres) have received more and more attention due to their large specific surface area and high pore volume. In this dissertation, valuable explorations have been carried out on the synthesis of porous TiO₂ microspheres photocatalysts, and study of their properties. The main points could be summarized as follows:Bimodal size-distributed microporous titania microspheres with a smaller diameter of 600-900 nm and a larger diameter of 2.0-2.5μm could be easily prepared by a controlled hydrolysis of tetrabutyl titanate in a ethanol-water mixed solution in the presence of polyethylene glycol 400(PEG-400). The results displayed that the as-prepared TiO₂ microspheres appeared amorphous status and had a high specific surface area (> 240.0 m²/g). The concentration of PEG obviously influenced the size and size distribution of TiO₂ microspheres. With increasing concentration of PEG, the size of TiO₂ microspheres decreased. At an appropriate PEG concentration, the prepared TiO₂ microspheres appeared bimodal size distribution. In addition to PEG-400, PEG-1000 and cetyltrimethyl ammonium bromide (CTAB) could also be used to synthesize the bimodal size-distributed TiO₂ microspheres. A possible growth mechanism was proposed to account for the formation of the bimodal size-distributed TiO₂ microspheres. This work may provide a method for the synthesis of TiO₂ photocatalysts with controlled size and morphology.A simple one-step template method for the fabrication of crystalline titania hollow microspheres, based on the template-directed deposition and then in-situ template-sacrificial dissolution, is developed in pure water using SiO₂ microspheres as templates and TiF₄ as the precursor at 60℃. The wall thickness and size of TiO₂ hollow spheres can be controlled by adjusting the concentration of precursor TiF₄ and the size of SiO₂ spheres, respectively. The prepared TiO₂ hollow spheres show an interesting hierarchically nanoporous spherical structure and high photocatalytic activity. This hierarchically micro-meso-macrostructured titania hollow microspheres should find various potential applications in photocatalysis, catalysis, solar cell, separation and purification processes. This work may provide new insights into preparing other hollow oxide structured materials.