Molten Salt Assisted Self Assembly (MASA): Synthesis of Mesoporous Metal Titanate (CoTiO₃, MnTiO₃, and Li₄Ti₅O₁₂) Thin Films and Monoliths

Mesoporous metal titanates are very important class of materials for clean energy applications, specifically transition metal titanates and lithium titanates. The molten salt assisted self-assembly (MASA) process offers a new synthetic route to produce mesoporous metal titanate thin films. The process is conducted as follows: first a clear solution that contains two solvents (namely the hydrated salt (Co­(NO₃)₂·6H₂O or Mn­(NO₃)₂·6H₂O, or LiNO₃·<i>x</i>H₂O, and ethanol), two surfactants (cethyltrimethylammonium bromide, CTAB, and 10-lauryl ether, C₁₂EO₁₀), an acid and titanium source (titanium tetrabutoxide, TTB) is prepared and then spin or spray coated over a substrate to form a thin or thick lyotropic liquid crystalline (LLC) film, respectively. Finally, the films are converted into transparent spongy mesoporous metal titanates by a fast calcination step. Three mesoporous metal titanates (namely, CoTiO₃, MnTiO₃, and Li₄Ti₅O₁₂) have been successfully synthesized and structurally/thermally characterized using microscopy, spectroscopy, diffraction, and thermal techniques. The mesoporous cobalt and manganese titanates are stable up to 500 °C and collapse at around 550 °C into nanocrystalline Co₃O₄–TiO₂ and Mn₂O₃–TiO₂; however, lithium titanate is stable up to 550 °C and crystalline even at 350 °C. The crystallinity and pore size of these titanates can be adjusted by simply controlling the annealing and/or calcination temperatures