PNNL

Abstract

Metal organic frameworks are an important class of solid-state materials with high potential for applications such as energy storage, separation, catalysis and bio-medical technology. Here, we report a detailed structural refinement and analysis of the synchrotron X-ray powder diffraction data with in situ gas loading along with complementary Density Functional Theory (DFT) calculations revealed that xenon and krypton adsorb in a hexagonal arrangement inside the Ni-DOBDC channel and are bound by van der Waals dispersion interactions dominated by the host metal sites, Ni in this case. The measured temperature-dependent adsorption capacity of Xe, as derived from X-ray diffraction analyses, is substantially larger than that for Kr at room temperature and above, indicating the selectivity of Xe over Kr in Ni-DODBC and is consistent with the larger adsorption energy predicted from DFT. X-ray measurements under sequential and mixed gas species also unambiguously confirm the preferential adsorption of Xe over Kr in Ni-DOBDC. Our results reveal critical structural and energetic information about host-guest interactions that dictate the selective adsorption mechanism of these two inert gases, providing guidance for the design and synthesis of new MOF materials for separation environmentally hazardous gases from nuclear re-processing applications.