Quantitative Characterization of Pore Corrugation in Ordered Mesoporous Materials Using Image Analysis of Electron Tomograms

Abstract

Electron tomography and image analysis are combined to characterize ordered mesoporous silica SBA-15. The morphology of the mesopores with average diameter 6 nm is analyzed in terms of cylinders having variable radii and centers that are statistically centered on the points of a distorted hexagonal lattice. The variations in the mesopore centers and radii add up and result in pore wall corrugation with amplitude of 1.6 nm. The correlation length of the corrugation along the pore axis was found to be 4-5 nm. The amplitude of the corrugation compared well with the 1.9 nm thick microporous corona obtained from X-ray diffraction (XRD). In general, the present approach provides a detailed microscopic 3D model of nanostructured materials that complements macroscopic measurements such as physisorption and XRD.

Systematic Simulation of Disordered Cylindrical Nanoporous Materials

“…Outstanding examples of such materials are cylindrical porous substrata such as MCM-41 and SBA-15 materials. Due to their uniform pore structure and high surface areas, they have been studied extensively in the fields of catalysis, separation and adsorption (Corma 1997;Lee et al 2004;Yun and Ihm 2008). In addition, they have been used as model adsorbents for the verification, improvement and/or development of characterization methods (Kruk et al 2001), as well as standard media for testing the accuracy of theoretical models such as Density Functional Theory (DFT) (Thommes et al 2002;Ustinov and Do 2005) or computational methods such as Molecular Monte Carlo (Frenkel and Smit 2002).…”

“…However, the assumption of their presumed perfect shape is not entirely true as has been shown by recent experimental results obtained via accurate imagery techniques (Gommes et al 2009). The latter authors have illustrated that these materials may possess small irregularities, mainly represented by variations in their cross-sectional areas.…”

“…For example, Naumov et al (2008) have shown that the first part of the adsorption curve, within the hysteresis loop, turns out to be displaced to lower relative pressure values. In addition, it was found very recently that disordered pore tubes may yield sorption hysteresis very similar to that found with three-dimensional disordered pore networks such as porous glasses ).…”

Kinetic Analysis of the Adsorption of Polar and Nonpolar Molecules onto Ordered Mesoporous Silica Using the Pressure-feedback Method

“…For gas-storage applications, it is important that not only large amounts of gases can be stored, but quick and low-energy adsorption/desorption switching is also desirable. Mesoporous silica attracts attention in the areas of catalysis, 24 photosensitive materials, 37 and other new functionalized mesoporous materials, 8,9 and understanding of adsorption kinetics is of great importance to such applications. Furthermore, knowledge about the rate of adsorption of water is important because the adsorption of the target gas is frequently obstructed by the adsorption of water.…”

“…The mesopore surface roughness has a strong effect on pore condensation. 23,24 The interaction between the molecule surface also affects. The rate-determining step would be associated with the formation of the bridge structure, and the rate of adsorption strongly depends on the frequency of bridge formation.…”