Experiments-Guided Modeling of MCM-41: Impact of Pore Symmetry on Gas Adsorption

Among mesoporous ordered silica-based materials, MCM-41 is widely employed in both experimental and computational investigations of gas adsorption. Specific surface area and pore size distribution are typically obtained by analyzing the N-2 adsorption isotherm. To this aim, different models and theories are available, and which one is more accurate is under debate. On the computational side, the in silico model ought to match the characteristics of real samples and reproduce the macroscopic performance. While the typical hexagonal symmetry is usually considered, the tetragonal one is sometimes applied without any explained rationale. Interestingly, during the last decade, the preparation of mesoporous silica-based materials with rare tetragonal symmetry is reported, indeed, but these are never tested as gas sorbents. In the present work, computer models with different symmetry are compared for their ability to reproduce the available experimental data from real samples. The combination of grand-canonical Monte Carlo and molecular dynamics simulations is used to probe the differences at the microscopic level. The surface-adsorbed gas molecules are differently ordered and a different type of N-2 adsorption isotherm is correspondingly found.