Recent Advances in Mesoporous and Nanocrystalline TiO2 for Photocatalytic Degradation of Pollutants in Water and Air

G.Q. Max Lu
Australian Research Council Centre for Functional Materials, University of Queensland, Brisbane QLD 4072, Australia. Fax: 6173365 6074; Tel: 617 3365 3885

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     Last modified: February 28, 2006

Abstract
Photocatalytic processes involving nano-TiO2 for degradation of organic pollutants in water and air have been extensively investigated and are promising technologies for environmental quality improvement. However, there are some limitations of TiO2 nanoparticles due to their relatively low surface area, and UV-range photoactivity. To address these limitations, in recent years, there have been many studies aiming at developing highly ordered mesorporous titania with good nanocrystallinity and high surface area. More and more studies are devoted to narrowing the bandgap and achieving good visble light photoactivity as well.

We have developed a novel synthesis route to obtain large surface area, mesoporous and crystalline titania, using an anatase seeded hydrothermal process. Block-copolymer surfactants were used as template. This synthesis route is inspired by the concept of auto-assembly zeolite seeds into mesoporous aluminosilicate. Anatase seeds (crystal size < 4 nm) obtained under neutral and acidic condition were subsequently interacted with neutral and acidic aqueous block-copolymer solution to obtain the desired highly mesostructured titania powders. Nitrogen doped mesoporous titania is found to be 5 and 10 times more active for the photodegradation of methylene blue than P25 and undoped mesoporous titania under UV-vis (contain 4.9% UV light only at 366 nm) irradiation. What is more remarkable is that the photocatalytic performance of the nitrogen doped mesoporous titania is high even when the longpass cutoff glass filters with > 420 nm and > 540 nm are employed . The powerful combined effects of nitrogen doping and a mesoporous structure on photocatalytic performance are demonstrated for the first time in this work. In this paper, other methods of making nanocrystalline TiO2 for air and water purification will be also presented.