The Competitive Role of Water in Sorption Processes on Porous Carbon Surfaces

Concurrent equilibrium adsorption on a highly porous activated carbon of both water vapour and toluene was studied to determine the extent and the location of toluene adsorption in the presence of water. We report small angle neutron scattering (SANS) measurements in which the H/D ratio of both the water and toluene components is varied. Measurements are made both in the lower transfer wave vector region (5 × 10−2 ≤ q ≤ 1 A−1) and in the high q region >1 A−1. Just below the Porod scattering region (0.3–1 A−1), the liquid/vapour interface contributes significantly. To solve the intrinsic ternary character of the signal in this region, contrast variation measurements with H2O/D2O mixtures alone and with toluene-D and toluene-H mixtures alone at constant relative pressure were performed. The carbon samples, of commercial origin (Norit R1), were previously treated with nitric acid to reduce the ash content, which simplifies the data treatment in the diffraction region at high q.