Characterization of Polymer-Templated Micro- Mesoporous Silicas by Gas Adsorption, Small Angle X-Ray Scattering and Dft Modeling
Peter I. Ravikovitch1, Alexander V. Neimark2, Pasquale F. Fulvio3, Mietek Jaroniec3, and Leonid A. Solovyov4. (1) ExxonMobil Research and Engineering, 1545 Route 22 East, Annandale, NJ 08801, (2) TRI/Princeton, 601 Prospect Ave, Princeton, NJ 08542, (3) Kent State University, 201 Williams Hall, Chemistry Department, Kent, OH 44242, (4) Institute of Chemistry and Chemical Technology, Krasnoyarsk, 660049, Russia
We present a study of pore structure and pore wall properties of block-copolymer templated silicas of SBA-15 type. These materials possess dual porosity developed at two different length scales – ordered mesopores of ca. 10 nm in diameter and disordered micropores in the pore walls. The materials were characterized by nitrogen and argon adsorption and X-ray scattering. Traditional methods for determination of the microporosity, e.g. t-plot and comparison plot methods, cannot be used for reliable estimation due to a competition between micropore filling and multilayer adsorption on rough pore walls. Thus, to model adsorption/desorption isotherms in these materials we applied recently developed quenched solid density functional theory (QSDFT) of adsorption on amorphous silicas, which accounts explicitly for the pore wall roughness. The model parameters characterizing surface roughness were taken from small-angle x-ray scattering (SAXS) modeling. We find remarkable agreement between the results obtained by adsorption and SAXS methods.