SAXS Characterization of Solid/Vapor Interfaces in Polymer-Based Microporous Carbons With Different Surface Chemistry

The equilibrium adsorption of non-polar and polar molecules, n-hexane and water, in activated carbons, functionalized by oxidation with concentrated nitric acid, is investigated by small angle x-ray scattering (SAXS). As condensed fluid modifies the electronic contrast of the carbon, the resulting changes in the SAXS intensity reveal the way in which the pores are filled. Filling of the pores from the vapour or the liquid phase is found to depend both on the surface treatment and on the nature of the liquid. For n-hexane vapour at p/p₀ ≈ 0.4 the dispersion interaction ensures complete filling of the narrow pores, while larger pores are unpopulated. For water vapour cluster formation and the degree of filling depend on the relative humidity and the extent of surface oxidation. At a given applied relative pressure, the pores are completely filled by n-hexane, while, at the same relative pressure, water only partially fills the pores, even in the most oxidized carbon.

Keywords: activated carbon; water vapour; adsorption; contrast variation