Synthesis of La9.33Si6O26 Pore–Solid Nanoarchitectures via Epoxide-Driven Sol–Gel Chemistry

Abstract

Silicate-based oxides are of interest as electrolytes and electrode materials in intermediate-temperature solid-oxide fuel cells (SOFCs).[1–7] We have developed a sol–gel-based strategy for the production of mesoporous, nanostructured, singlephase La9.33Si6O26 apatite in an aerogel-type framework. Silicon alkoxides react with lanthanum(III) aqueous ions in alcohol solutions driven by a proton-scavenging agent, propylene oxide. Varying the means by which pore fluid is removed from the resultant lanthanum silicate gels yields three distinct pore–solid monolithic nanoarchitectures: aerogels, ambigels, and xerogels. The ambigel and aerogel nanoarchitectures exhibit high specific surface areas (from 285 to 408 m2 g–1), aperiodic through-connected networks of mesopores, and covalently bonded networks of non-agglomerated nanoparticles. Calcination at relatively mild temperatures for this oxide (800 °C) converts the amorphous gels to nanocrystalline apatite La9.33Si6O26. Although densified during calcination, the aerogel and ambigel nanoarchitectures retain porosity, high surface area, and limited particle agglomeration.