Preparation of Hierarchically Porous Nanocrystalline CaTiO3, SrTiO3 and BaTiO3 Perovskite Monoliths

Abstract

Hierarchically porous nanocrystalline CaTiO3, SrTiO3, and BaTiO3 ceramics have been produced by impregnating corresponding alkaline‐earth metal ions into preformed macroporous TiO2 monoliths in a solution containing urea, followed by calcination. The macroporous TiO2 had been obtained via the sol–gel process accompanied by phase separation utilizing a chelating agent, ethyl acetylacetonate (EtAcAc), together with mineral salt and ammonium chloride, to decrease the reactivity of titanium alkoxide. Formations of CaCO3, SrCO3, and BaCO3 on the surface of TiO2 monoliths are promoted by CO2 generated by the concurrent two processes during impregnation; hydrolysis, and decarbonation of the chelating agent EtAcAc, and hydrolysis of urea at 60°C. The latter also raises pH of the impregnating solution which further promotes the mineralization of the carbonate salts. Calcination of the resultant monolithic composite of metal carbonate/TiO2 allows the crystallization of metal titanate. The addition of urea to the impregnating solution is found to be an effective strategy for the formation of perovskite monoliths by the impregnation process. This study provides a versatile approach to the preparation of hierarchically porous titania‐based perovskites.