Sol−Gel Strategies for Pore Size Control of High-Surface-Area Transition-Metal Oxide Aerogels

Abstract

Titania, zirconia, and niobia aerogels were prepared by the sol−gel synthesis from alcoholic metal alkoxide solutions under acidic conditions and the subsequent supercritical drying with carbon dioxide. At a stoichiometric amount of water and a constant alkoxide concentration the nitric acid contents were varied to examine the characteristics of gel formation behavior and the produced aerogel properties. The range of acid content in which transparent polymeric gels were obtained was determined. Under these conditions there was little effect of acid content on the surface area of their calcined aerogel samples. On the other hand, the pore size distributions were significantly affected by the acid contents. The resulting titania, zirconia, and niobia aerogels, after calcination at 773 K for 2 h, had BET surface areas of about 200, 100, and 200 m2/g, respectively, and relatively narrow pore size distributions in the mesopore region. The results suggest a simple way to control the pore sizes of the high-surface-area aerogel only by adjusting the amount of nitric acid used in the sol−gel synthesis.