Adsorption of Supercritical Carbon Dioxide in Aerogels as Studied by SANS and Neutron Transmission Techniques

Small-angle neutron scattering (SANS) has been used to study the adsorption behavior of supercritical carbon dioxide (CO2) in porous Vycor glass and silica aerogels. Measurements were performed at T = 35C and 80C as a function of pressure up to P = 25 MPa. The neutron transmission data were used to monitor the ``excess'' adsorption of CO2 at different pressures. The adsorption of CO2 is significantly higher in aerogels than in activated carbons and silica gels. SANS data have revealed the existence of highly compressed adsorbed phase with the density close to the density corresponding to van der Waals volume of carbon dioxide. The results demonstrate the utility of SANS combined with transmission measurements to study the adsorption of supercritical fluids in porous materials.