Molten salt assisted self assembly (MASA): synthesis of mesoporous metal titanate (CoTiO3, MnTiO3, and Li4Ti5O12) thin films and monoliths

Abstract

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·xH2O, 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.