Steric and barrier effects for a Langmuirian adsorption process at an irregular surface

Two-dimensional (2-D) Monte Carlo simulations for a simple Langmuirian adso rption process on columnar-structured solid substrates (csss) were made to establish the influence of pore width and depth on the adsorption parameter s. The geometry of the substrate was adjusted using the cross section of th e adsorbable particle (a) as the yardstick. The difference in the adsorptio n isotherm parameters from columnar-structured substrates as compared to a smooth substrate (ss) was expressed by a correction factor (f) defined as t he apparent adsorption free energy ratio resulting from csss and ss. The va lue off diminishes with the roughness factor (R) of the substrate according to f proportional to R-n For this model the value of n changes from 1/5 to 1 as the pore mouth diameter approaches the yardstick size. The value off reflects the influence of various effects such as the excluded volume, the barrier at pore entrances, the plugged bottleneck effect and tortuosity at pores, as concluded from the analysis of the Monte Carlo snapshots. (C) 199 8 Elsevier Science Ltd. All rights reserved.