Synthesis of High-Surface-Area Alumina Aerogels without the Use of Alkoxide Precursors

Abstract

Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl3·6H2O or Al(NO3)3·9H2O, followed by drying with supercritical CO2. This technique affords low-density (60−130 kg/m3), high-surface-area (600−700 m2/g) alumina aerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterized using elemental analysis, high-resolution transmission electron microscopy, powder X-ray diffraction, solid-state NMR, acoustic measurements, and nitrogen adsorption/desorption analysis. Powder X-ray diffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl3 in water or ethanol possessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2−5 nm in diameter and of varying lengths, whereas the aerogels prepared from hydrated Al(NO3)3 in ethanol were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5−15 nm ra...