Applications of Small Angle X-Ray Scattering Techniques for Characterizing High Surface Area Carbons

Abstract

Small angle X-ray or neutron scattering (SAXS or SANS) techniques offer a powerful means of investigating the adsorption of vapour by high surface area carbons. While traditional vapour phase adsorption methods yield overall adsorbed amounts, scattering observations give complementary direct information on the location of the adsorption sites as well as an independent measure of the internal surface area of the substrate. Data collected from the traditional small angle region (range of transfer momentum q < 1 Å⁻¹) may be used to calculate the density of the condensed phase in the micropores, while that collected from the higher resolution range (q > 1 Å⁻¹) contains information both on the adsorbed amount and on spatial correlations within the adsorbed phase, as well as between it and the substrate. The effects of adsorption of a single species of molecule can be monitored by SAXS alone. The presence of more than one species, however, requires the use of SANS combined with contrast variation, i.e., employing selective isotopic substitution, for instance by replacing hydrogen by deuterium. In this article we discuss the ­adsorption of water vapour on two nanoporous carbons.