Molecular Modeling and Adsorption Properties of Ordered Silica-Templated CMK Mesoporous Carbons

Realistic molecular models of silica-templated CMK-1, CMK-3, and CMK-5 carbon materials have been developed by using carbon rods and carbon pipes that were obtained by adsorbing carbon in a model MCM-41 pore. The interactions between the carbon atoms with the silica matrix were described using the PN-Traz potential, and the interaction between the carbon atoms was calculated by the reactive empirical bond order (REBO) potential. Carbon rods and pipes with different thicknesses were obtained by changing the silica-carbon interaction strength, the temperature, and the chemical potential of carbon vapor adsorption. These equilibrium structures were further used to obtain the atomic models of CMK-1, CMK-3, and CMK-5 materials using the same symmetry as found in TEM pictures. These models are further refined and made more realistic by adding interconnections between the carbon rods and carbon pipes. We calculated the geometric pore size distribution of the different models of CMK-5 and found that the presence of interconnections results in some new features in the pore size distribution. Argon adsorption properties were investigated using GCMC simulations to characterize these materials at 77 K. We found that the presence of interconnection results greatly improves the agreement with available experimental data by shifting the capillary condensation to lower pressures. Adding interconnections also induces smoother adsorption/condensation isotherms, and desorption/evaporation curves show a sharp jump. These features reflex the complexity of the nanovoids in CMKs in terms of their pore morphology and topology.