Nanospace Molecular Science and Adsorption

Abstract

The relationships between the enhanced interaction potential and intensive confinement effect of slit-shaped and cylindrical nanospaces are shown. The structures of water molecules and aqueous ions confined in nanospaces of activated carbon fiber (ACF) and single wall carbon nanohorn (SWNH)s were studied by adsorption, in situ small angle X-ray scattering(SAXS), GCMC simulation, and EXAFS spectroscopy. Water molecules are associated with each other to form the clusters, being stabilized in the carbon nanospaces. This stabilization mechanism of water in carbon nanospaces were evidenced by the interaction potential calculation, GCMC simulation, and the density fluctuation analysis of in situ SAXS. The Ornstein-Zernike analysis of in situ SAXS profiles lead to the conclusion that the critical size of water clusters for predominant water adsorption in hydrophobic carbon nanospaces is about 0.5 nm corresponding to the octomer to decamer. The adsorption hysteresis of water adsorption isotherm of nanoporous carbon was interpreted by the cluster growth, which is confirmed by the density fluctuation analysis. The Rb and Br ions confined in the carbon nanospaces were examined by EXAFS spectroscopy. The remarkable decreases in the hydration number and the water-Rb ion distance of the solution confined in the nanospaces were observed. In particular, the hydration number of the Rb ion in the nanospaces of SWNH is less than 3, being much smaller than the hydration number (6) of the bulk solution. The electrical double layer structure in the nanospaces should be quite different from that in the bulk solution.

Individual Liquids and Liquid Solutions Under Confinement

“…Figure 9.3c shows the relative changes in the normalized scattering intensities for both the negative and positive potentials applied to the ACF working electrode as a function of the pore size. The data obtained support the previously reported results that indicated the enhancement of organic electrolyte ion adsorption in the small sub-nanometer pores in porous carbon materials [5,8,9]. …”

Hofmeister Effect in Confined Spaces: Halogen Ions and Single Molecule Detection

“…Hence, the confined space presents more favorable conditions for PEG to compete with ions for water, indicating that the confined water is more accessible to PEG (and, probably, for other analytes (cosolute)). The existence of water that is accessible to nonionic analytes (confined water) accords with the presence of a hydration water layer at nanopore surfaces, where the presence of ions is severely restricted (30,31) and with remarkable decreases in the hydration number for ions confined in nanospaces (32).…”

Displacement of Methane by Coadsorbed Carbon Dioxide Is Facilitated In Narrow Carbon Nanopores

“…Note that the carbon content in anthracite is between 92 and 98% . Although we acknowledge the importance of H 2 O sorption in coals and activated carbons, − this effect is not considered in this article.…”