Argon and krypton adsorption on templated mesoporous silicas: molecular simulation and experiment
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Argon and krypton adsorption on templated mesoporous silicas: molecular simulation and experiment Francisco R. Hung · Supriyo Bhattacharya · Benoit Coasne · Matthias Thommes · Keith E. Gubbins
Received: 29 April 2007 / Revised: 17 July 2007 / Accepted: 23 July 2007 / Published online: 21 September 2007 © Springer Science+Business Media, LLC 2007
Abstract In this work we report molecular simulation results for argon and krypton adsorption on atomistic models of templated mesoporous silica materials. These models add atomistic levels of detail to mesoscale representations of these porous materials, which were originally generated from lattice Monte Carlo simulations mimicking the synthesis process of templated mesoporous silicas. We generate our atomistic pore models by carving out of a silica block a ‘mathematically-smooth’ representation of the pores from lattice MC simulations. Following that procedure, we obtain a model material with mean mesopore and micropore diameters of 5.4 nm and 1.1 nm, respectively (model A).
F.R. Hung Department of Chemical and Biological Engineering, University of Wisconsin, Madison, WI 53706-1691, USA S. Bhattacharya · K.E. Gubbins () Center for High Performance Simulation and Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695-7905, USA e-mail: [email protected] S. Bhattacharya City of Hope National Medical Center, Beckman Research Institute, Duarte, CA 91010, USA B. Coasne Institut Charles Gerhardt Montpellier, CNRS (UMR 56253), University Montpellier 2, and ENSCM, 34095 Montpellier cedex 5, France
Two additional model materials were considered: one with no microporosity, and with mesopores similar to those of model A (model B), and a regular cylindrical pore (model C). Simulation results for Ar and Kr adsorption on these model materials at 77 K and 87 K shows that model A provides the best agreement with experimental data; however, our results suggest that fine-tuning the microporosity and/or the surface chemistry (i.e., by decreasing the density of OH groups at the pore surface) of model A can lead to better agreement with experiments. The filling of the mesopores in model materials A and B proceeded via a classical capillary condensation mechanism, where the pores fill at slightly different pressures. This observation contrasts with what was observed in our previous study (Coasne, et al. in Langmuir 22:194–202, 2006), where we considered atomistic silica mesopores with an important degree of surface roughness at length scales below 10 Å, for which we observed a quasicontinuous mesopore filling involving intermediate phases with liquid-like “bridges” and gas-like regions. These results suggest that pore surface roughness, and other morphological features such as constrictions, play an important role in the mechanism of adsorption and filling of the mesopores. Keywords Templated mesoporous silica materials · MCM-41 · SBA-15 · Gas adsorption · Molecular simulation · Monte Carlo
1 Introduction M. Thommes Quantachrome Instruments, Boynt
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