Wedge Pore Model as an Alternative to the Uniform Slit Pore Model for the Determination of Pore Size Distribution in Activated Carbon

We present a grand canonical Monte Carlo simulation of argon adsorption in wedge-shaped carbon mesopores and show that the conventional model, based on open-ended slit pores of uniform width, frequently underestimates the pore size in the determination of mesopore size distribution. We propose that characterization can be significantly improved by taking account of the variation in pore width along the pore axial direction. A study of the effects of pore length and wedge angle on the form of the hysteresis loop shows that the shape and position of the loop are strongly affected by the angle (which is the principal reason for the underestimation of pore size) but not by the pore length, except when the pore is very short. To quantify the interplay between the capillary force and the solid–fluid interaction, we carried out a mesoscopic analysis of the interface separating the gas-like phase and the condensed phase and show that desorption from a filled wedge pore can be described by the Derjaguin–Broekhoff–de Boer (DBdB) equation.1−4 We find that the interfacial energy parameter is greater than the bulk value, suggesting that the cohesiveness of the interface is enhanced by the presence of an adsorbent potential energy field. At 77 K, the hysteresis loop is stepped at the desorption boundary due to a transition between commensurate and incommensurate packing,5 but this feature is not manifested at higher temperatures.