(506d) Pore Characterization of Chromatographic Particles—Adsorption Isotherms for Complex Pore Shapes

Gas adsorption has been widely used to characterize porous materials, providing information on pore volume, surface area, and pore size distribution. In this work, we compare argon adsorption and desorption isotherms obtained from Monte Carlo simulations for various pore models with amorphous silica walls and those from experiments for superficially porous chromatographic particles. The model pore shapes investigated here include three canonical pore shapes used in pore characterization models (i.e., slit, cylindrical, and spherical pores) and three more complex models: a missing cylinder in an array of hexagonally packed cylinders, the void space between spheres packed in a simple cubic lattice, and a missing sphere in an array of spheres packed in a face-centered cubic lattice. Two pore sizes (largest cavity diameter of 30 and 90 Å) are considered. The results of geometric pore size distributions and those obtained from non-local density functional theory (NL-DFT) analysis of isotherms are discussed. The comparison between the predicted isotherms and the experimental measurements on the chromatographic particles demonstrates that the non-convex morphology and a wide pore size distribution are essential to capture the adsorption behavior. Analyses of simulation trajectories provide insights into the structure of the adsorbates, sorbate-sorbent interactions, and the sorption mechanism.