Structural Characteristics and Characterization Techniques for Mesoporous Silica

1 Structural Characteristics and Characterization Techniques for Mesoporous Silica 

In general, there are two main methods to control the mesostructures (1) change various reactant concentrations, reaction temperature, and reaction-mixture composition  

According to the structure and composition of materials and analysis requirements of the researcher, the following analysis techniques can be selected for the characterization of mesoporous materials XRD, TEM, adsorption-desorption (N2 or other gas), solid MAS NMR (29Si, 27Al, 13C, etc.), scanning electron microscopy (SEM), catalysis test, Fourier Transform infra-red (FT-IR), thermal analysis, UV-visible, and chemical analysis. IR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure XANES, extended X-ray absorption fine structure EXAFS and other spectral methods are commonly used to analyse metal elements such as Ti in the mesoporous material frameworks. 

Because of the large unit cell, the XRD diffraction peaks appear at very low angles of 28. Some problems for structural analysis of mesoporous materials by powder XRD are the lack of enough diffraction peaks, overlapping of the peaks, and loss of structure-factor phase information. Since most samples have the low crystalline quality, the calibration of equipment is very important. The normal standards for calibrating a diffractometer (e.g., Si, quartz) are not very efficient, so standards for low-angle calibration should be used (e.g., lead stearate). 

The defects (faults) and intergrowth can be often found in zeolite or microporous molecular sieve crystals. Mesoporous material synthesis is controlled kinetically and there is no defect-free mesoporous material. Various defects can be found easily in mesoporous materials, even for so-called high-quality materials.[106] 

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