Molten Salt Hydrates in the Synthesis of TiO₂ Flakes

Abstract

Herein, we present a method for the preparation of titanium dioxide with a relatively large surface area, mesoporosity, and good thermal stability. We show that by utilizing molten salt hydrates (MSH) as non-trivial synthesis media, we prepare materials with thin, flake-like morphology with a large aspect ratio. The thickness of the synthesized flakes can be controlled by adjusting the salt/water (always in the MSH regime) and/or the salt/precursor molar ratio. The TiO2 flakes appear to be formed via the aggregation of small TiO2 nanoparticles (typically around 7–8 nm) in an apparent 2D morphology. We hypothesize that the ordered structure of water molecules within the ions of the salt in conjunction with the fast hydrolysis/condensation rates occurring in the presence of water of the precursor used are responsible for this agglomeration. We also report that the purity of materials (anatase vs brookite crystalline phase) appears to be a function of the LiBr/water ratio which is hypothesized to arise either from pH variation or due to lattice matching of the relevant orthorhombic structures (brookite and LiBrx·3H2O). Discussion on the potential for scalability of the presented method is also highlighted in this article.