Imaging of Gas Molecules Adsorbed in the Mesoporous Material by the High Brilliance Synchrotron Powder Diffraction.

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Mesoporous materials are amorphous materials without ordered structure on an atomic scale. The amorphous forms the pore structure of a meso scale. The arrangement and the rough shape of mesopores were investigated by the electron crystallography or X-ray diffraction to date. But no information on molecules adsorbed in the mesopore was revealed. The purpose of this research is to obtain the structural information of molecules adsorbed in the mesopores by the high brilliance synchrotron powder diffraction experiment and the maximum entropy method (MEM).The shape of mesopore of MCM-41 with a one-dimensional mesopore was analytically expressed using parameters of size, density, etc.. Comparing the simulated and observed diffraction intensities revealed the change of the size and shape of mesopores before and after calcination.The in-situ synchrotron powder diffraction experiment of gas adsorption was performed for MCM-48 with a three-dimensional mesopore.For the data without guest molecules, the combination of rough pore shape obtained by the conventional method and the pore volume estimated from the isotherm enabled us to scale the structure factors. The mesopore structure was successfully imaged by MEM. The MEM electron density distribution showed clear image and the size of the mesopore was found to be underestimated to date. This technique would be effective for the analysis of more complicated network and fine structure of pore surfaces.The gas adsorption process was observed as the change of electron density. The structural information on the gas adsorption process was able to be obtained, that is, the mono-layer adsorption state in the low pressure region, the capillary condensation in threshold value of pressure and the saturation adsorption state. Although the examination should be required for the treatment of phases, this technique is expected to be effective as the observation technique of a gas adsorption state.