XRD-DSC: a screening tool for identifying effective MOFs for selective gas sorption from humid gas streams

Abstract

A commercially available combined X-ray diffraction – differential scanning calorimetry (XRD-DSC) stage was adapted for studies of gas loading in microporous materials, including metal organic frameworks (MOFs). Insertion of a custom-built humid atmosphere swing chamber (HASC) between a humidity generator and the XRD-DSC stage facilitates both humid atmosphere and vacuum swing gas loading. The HASC is necessary to buffer between the humidity generator and the XRD-DSC stage, allowing the gas mixture to homogenize prior to sample exposure, so that both humid atmosphere and vacuum swings could be performed. The changes in XRD can be used to follow structural changes, including collapse, which is indicative of a lack of microporosity upon activation, and the flexibity of frameworks upon gas sorption–desorption cycles. Measurements of the area under the DSC curve allows for calculation of the isosteric heat of adsorption (Qst; kJ molGAS−1). Vacuum-atmosphere swing experiments performed at different pressure steps allow for the reconstruction of the enthalpy of gas adsorption before and after a phase transition. These modes of operation are illustrated in three case studies from a program of exploratory MOF synthesis used to discover novel materials for selective gas sorption from humid gas streams: (1) gas binding in Stony Brook metal organic framework-1, (2) zeolitic imidazolate framework-7 response to variable pressure vacuum-atmosphere swing, and (3) high throughput evaluation of the selectivity of novel MOFs synthesized from customized linkers.

Thermochemical Investigation of Oxyanion Coordination in a Zirconium-Based Metal–Organic Framework

“…When researchers can isolate diffraction-quality single crystals, they can precisely determine the atomic connectivity of the parent lattice and, in many instances, subsequent host–guest interactions (e.g., adsorbate–sorbent, active center–support, etc. ). − Moreover, methods such as Rietveld refinement , and difference envelope density rely on powder X-ray diffraction data and allow for the structural examination of a broader set of powder crystalline materials, whereas in-sequence PXRD may permit structural characterization of guest-loaded samples . Beyond their facile characterization, MOFs, comprising inorganic nodes and organic linkers, offer unprecedented pre- and postsynthetic tunability due to the wide variety of building blocks available. ,,− Moreover, exchangeable structural motifs afford a platform material useful for systematically exploring structure–property relationships. − …”