Adsorption mechanism of water on carbon micropore with in situ small angle x-ray scattering

摘要

The in situ small-angle X-ray scattering (SAXS) profiles of water adsorbed on pitch-based activated carbon fibers (ACF) of the pore width omega = 0.8 and 1.1 nm were measured at 303K and different relative pressures. The SAXS spectrum of ACF of omega = 1.1 nm in the direction of desorption did not overlap that in the adsorption direction, showing the hysteresis behavior. The Ornstein-Zernike (OZ) theory was applied to analyze the SAXS data in order to investigate hte structure of water molecular assembly in the carbon micropore using the density fluctuation of the system. These data lead that water molecules produce the large clusters in the micropore, and these clusters have different structures on the courses of adsorption and desorption. On the other hand, the SAXS profiles of ACF of omega = 0.8 nm at different relative pressures has no hysteresis coinciding that the water adsorption isotherm has no hysteresis. These results explicitly suggest that the structures of the water molecular assemblies on absorption and desorption are different from each other in case of the presence of adsorption hysteresis.