The discovery of ordered mesoporous silicas (OMSs) opened a new and rapidly growing field of modern science and technology, expanding the range of periodic porous materials into the mesopore region. The structure of the majority of OMS shows a long range ordering of amorphous elements, which can be studied by powder X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) methods. On the other hand, the XRD/SAXS studies of these materials are not easy because the standard crystallographic procedures cannot be used for their characterization due to the lack of ordering at the atomic level. Various OMSs have been synthesized ranging from 2D hexagonal p6mm (MCM-41, SBA-15), 3D hexagonal P6₃/mmc (SBA-12), and cubic Ia3d (MCM-48 ), Im3m (SBA-16 ), Fm3m (FDU-1) structures to lamellar phases (MCM-50). The XRD/SAXS patterns for these OMSs contain small number of peaks (often about 3-5). They are located in the range of low angles (2q below 5^o) because of the presence of relatively large ordered pores. A major breakthrough in OMSs synthesis area was the synthesis of polymer templated OMSs (by using , for example, triblock copolymer – PEO₂₀PPO₇₀PEO₂₀) , namely SBA-15, which became very popular material because of larger mesopores, thicker pore walls and higher hydrothermal stability in comparison to his surfactant templated analogue, MCM-41. The XRD/SAXS patterns for the aforementioned ordered mesostructures often exhibit four or more reflections, the most intensive one, 100 peak, and three less intensive peaks, 110, 200, 210. So far, analysis of these patterns was usually limited for the evaluation of the unit cell parameter and the identification of the observed peaks. The value of unit cell parameter in combination with adsorption data provide information about the pore size and pore wall thickness.

In this work an attempt to analyze the XRD/SAXS patterns by including not only the position of observed peaks but also their intensity are presented.

On the basis of the XRD/SAXS structure modeling of the 110/200 intensity ratio in relation to the pore width/unit cell ratio the new method for estimating the pore width and pore wall thickness are presented [1]. The comparative analysis of results obtained by proposed new method and modified KJS method [2] was made.

Obtained results for many MCM-41 and SBA-15 samples ( even with organic group in skeleton) indicated that the pore widths estimated on the basis of the theoretical 110/200 intensity curve for cylindrically-shaped mesopores agree well with these obtained by improved KJS methods. This result indicates that the theoretical dependence of the 110/220 intensity ratio on the pore width/unit cell ratio obtained by assuming cylindrical shape of channels in SBA-15  or hexagonal prism in MCM-41 may be used for a quick  estimation of the pore widths of these materials.

 [1] Pikus S., Solovyov L.A, Kozak M., Jaroniec M., Appl. Surf. Sci, (2007), 253,5682

          [2]Jaroniec M., Solovyov L.A., Langmuir, (2006), 22, 6757.

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