Formation and Anisotropic Dissolution Behavior of NH4TiOF3 Mesocrystals

We have conducted an investigation into the growth and anisotropic dissolution of NH4TiOF3 mesocrystals, which are converted into anatase TiO2 in an aqueous environment. Growth and dissolution are two competing processes when NH4TiOF3 mesocrystals are formed in an aqueous solution of (NH4)(2)TiF6, in the presence of fluoride scavenger H3BO3 and surfactant Brij 58 at 35 degrees C. At the initial stage of fast mesocrystal growth, surfactant molecules are occluded in the central region of the final mesocrystal, which destabilize the mesocrystal. There is a driving force for dissolution of the mesocrystal, whereby the metastable NH4TiOF3 is converted to stable TiO2 by losing N and F elements. An anisotropic propagation of dissolution is observed, as there is a variation in activation energy for dissolution in association with the planar densities of N and F elements on the corresponding planes of NH4TiOF3 mesocrystals. By controlling the competing growth and dissolution processes, NH4TiOF3 mesocrystals of varying morphology and dimension can be obtained.