Correlation between two- and three-dimensional condensations in cylindrical mesopores of active carbons Original Research Article

Adsorption interactions in narrow cylindrical capillaries decay with radii approximately as r−1.1 and this slowly decreasing adsorption potential is responsible for adsorption behavior in the capillary condensation region. Filling of mesopores with concave curvatures is considered to be an evolution of the two-dimensional (2D) condensation, which occurs on the mesopore walls at the critical condensation pressure. An adsorption isotherm in the individual mesopore exhibits the feature characteristic of condensation: a vertical jump at a pressure approximately corresponding to the critical pressure of a 2D-condensation. Mesopore filling pressures are found proceeding from statistical mechanical theories of adsorption on the planar surface taking into account lateral adsorbate–adsorbate interactions. The model describes the adsorption branch of the hysteresis loop. The underlying reason of the hysteresis loop is discussed. Analysis of adsorption isotherms for benzene and nitrogen shows that the developed model and the classical Kelvin equation lead to close values of mesopore radii.