Enhanced hydrothermal conversion of surfactant-modified diatom microshells into barium titanate replicas

The three-dimensional nanostructured SiO₂-based microshells of diatoms have been converted into nanocrystalline BaTiO₃ via a series of shape-preserving reactions. The microshells, obtained as diatomaceous earth, were first exposed to a surfactant-induced dissolution/reprecipitation process [C.E. Fowler, et al., Chem. Phys. Lett.398, 414 (2004)] to enhance the microshell surface area, without altering the microshell shape. The SiO₂ microshells were then converted into anatase TiO₂ replicas via reaction with TiF₄ gas and then humid oxygen. Hydrothermal reaction with a barium hydroxide-bearing solution then yielded three-dimensional nanocrystalline microshell replicas composed of BaTiO₃. The enhanced surface area of the surfactant-treated microshells resulted in faster conversion into phase-pure BaTiO₃ at 100 °C.