Density functional theory of in situ synchrotron powder x-ray diffraction on mesoporous crystals: Arson adsorption on MCM-41

The process of gas adsorption on mesoporous crystals can be explored by in situ synchrotron powder X-ray diffraction (XRD) that provides direct information about the distribution of adsorbate with the pore channels. We presented a rigorous theoretical framework for interpretation of the in situ XRD data based on the novel quenched solid density functional theory (QSDFT) model of adsorption on mesoporous materials. QSDFT accounts for the molecular level roughness of the pore walls that is shown to be one of the major factors affecting both the adsorption isotherms and the XRD patterns. Drawing on the example of Ar adsorption in pores of MCM-41, we demonstrate that, using the intermolecular potentials established from the adsorption data and the structural parameters (pore size and roughness) determined from the XRD data, the QSDFT model describes the in situ synchrotron powder XRD intensities on a quantitative level. The QSDFT model provides an opportunity for a unified interpretation of adsorption and XRD measurements on mesoporous materials reconciling these two independent experimental methods widely employed for pore structure characterization. Combined with QSDFT, in situ synchrotron XRD measurements offer a powerful tool for studies of the specifics of adsorption mechanisms and phase transformations in nanoconfined fluids.