Molten-Salt-Asisted self-Assembly (MASA)-synthesis of mesoporous metal titanate-titania, metal sulfi de-titania, and metal selenide-titania thin films

Abstract

New synthetic strategies are needed for the assembly of porous metal titanates and metal chalcogenite-titania thin films for various energy applications. Here, a new synthetic approach is introduced in which two solvents and two surfactants are used. Both surfactants are necessary to accommodate the desired amount of salt species in the hydrophilic domains of the mesophase. The process is called a molten-salt-assisted self-assembly (MASA) because the salt species are in the molten phase and act as a solvent to assemble the ingredients into a mesostructure and they react with titania to form mesoporous metal titanates during the annealing step. The mesoporous metal titanate (meso-Zn2TiO4 and meso-CdTiO3) thin films are reacted under H2S or H2Se gas at room temperature to yield high quality transparent mesoporous metal chalcogenides. The H2Se reaction produces rutile and brookite titania phases together with nanocrystalline metal selenides and H2S reaction of meso-CdTiO3 yields nanocrystalline anatase and CdS in the spatially confined pore walls. Two different metal salts (zinc nitrate hexahydrate and cadmium nitrate tetrahydrate) are tested to demonstrate the generality of the new assembly process. The meso-TiO2-CdSe film shows photoactivity under sunlight.