Facile synthesis of > 99% phase-pure brookite TiO2 by hydrothermal conversion from Mg2TiO4

The synthesis of pure brookite is generally much more difficult than that of pure anatase. The hydrothermal conversion, recently developed by Kozawa et al., is a facile method to synthesize brookite TiO2 from inverse spinel-type Mg2TiO4 under a mild hydrothermal condition e.g. in 1 M HCl solution at 100 degrees C. However, slight rutile TiO2 is usually co-existed under the reported conditions. The aim of this study is to prepare a high-purity brookite TiO2 powder by the hydrothermal conversion from Mg2TiO4. We investigated the conditions of Mg2TiO4 preparation and hydrothermal conversion, and it was found that the most important factor for the high-purity brookite synthesis, i.e. decreasing the co-existing rutile TiO2, was to prepare the Mg2TiO4 precursor without MgTiO3. Using an MgO-rich composition and adding a second calcination step for the Mg2TiO4 preparation yielded a high-purity (99.3 wt%) brookite powder with a surface area of 27.7 m(2)/g. Under the current experimental conditions, addition of a surfactant or an alcohol for the hydrothermal treatment was not apparently effective for the high-purity brookite synthesis.