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Tailored-Made and Surface Modification of Anatase TiO2 Towards High Photocatalytic Performance
Keywords: TiO2, Nanostructures, Photocatalytic activity
Nanostructured TiO2 with a high percentage of reactive {001} facets has currently attracted significant interest among materials researchers (Yang 2008). The {001} facet of anatase TiO2 is more reactive than the {101} facet, which promises a wide range of applications from high-performance photocatalysts, Li-ion battery cells. Since the biocompatibility of TiO2 is superior to many other inorganic nanomaterials, nanostructured TiO2 is also expected to the use in bio-medical applications, such as drug delivery system, bio-coating and bio-imaging. Towards to these multidisciplinary applications, it is requested to improve the performance of nanostructured TiO2. It is reported that the {001} surface of anatase TiO2 is the oxidation site, whereas the {101} surface is the reduction site (Ohno 2002). The shape-tailored TiO2 has strict boundary for {001} and {101} surfaces, which is greatly helpful for promotion of the space-induced electron-hole separation. Therefore, the shape control of TiO2 is an effective approach to improve photocatalytic activity. On the other hand, it is well known that the photocatalytic activity of TiO2 also depends on particle size (Almquist 2002). Small size offers a large surface area for light absorption and numerous photocatalytic reaction active sites, so that small nanosheets exhibit high photocatalytic activity, mostly by influencing charge-carrier dynamics, adsorption rate, and the adsorbed amount of reaction species. A particle size of 25 to 40 nm was suggested for the optimum photocatalytic activity of TiO2. Therefore, controlling both the size and morphology of nanostructured TiO2 is necessary to effectively improve the photocatalytic activity and comprehensively evaluate the performance. Furthermore, the doping and/or surface modification also suggest an effective approach to improve the photocatalytic performance by the comprehensive enhancements of surface reactivity and reaction site, charge carrier dynamics, and the energy band gap. Here we report a tailored synthesis of size-controllable TiO2 nanosheets with highly exposed {001} facets and particle sizes ranging from 25 nm to several micrometres by adjusting the F/Ti ratio in a conventional hydrothermal synthesis process (Tan 2013). A tuneable percentage of {001} surface area ranged from 50% to 90% according to the particle size. The photocatalytic activity of TiO2 nanosheets in the degradation of organic dyes was evaluated systematically. Our results show that TiO2 nanosheets smaller than 100 nm have higher photocatalytic activity normalised by unit mass and are more stable, whereas larger TiO2 nanosheets have higher photocatalytic activity normalised by unit surface area. Furthermore, we successfully synthesized Pt nanoparticles coated TiO2 nanosheets in high-density coating, which attributed to a 6-times enhancement in the photocatalytic performance in comparison with the bare TiO2 nanosheets. The controlled particle size, tunable percentage of {001} surface area, surface modification, and high photocatalytic activity of TiO2 nanosheets with highly exposed {001} facets are expected to render this advance important for the use in a variety of applications.
Zhenquan Tan,
Joining and Welding Research Institute, Osaka University
Ibaraki, Osaka

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