Room temperature synthesis of titanium dioxide nanoparticles of different phases in water in oil microemulsion

We report the synthesis of crystalline titanium dioxide nanoparticles of two different phases (rutile and anomalous pseudobrookite) at room temperature by a novel microemulsion technique. In this method, one of the reactants (titanium tetrachloride) is dissolved in the continuous organic phase, whereas the second reactant (ammonium hydroxide) is added as an aqueous solution. The site of the reaction has been controlled by using two different addition methods for the second reactant. The size and the crystalline phase of the titanium dioxide nanoparticles varied according to the site of the reaction between the two reactants. Reaction in the aqueous core gives rutile titanium dioxide nanoparticles having an average size of 4.2 nm verified by X-ray diffraction and FTIR. The reaction in the organic phase gives rise to crystalline anomalous pseudobrookite titanium dioxide nanoparticles of much larger size (10-40 nm). This anomalous pseudobrookite structure is thermally unstable and converts to rutile on high temperature treatment. (C) 2010 Elsevier B.V. All rights reserved.