Concentration-dependent binding of CO₂ and CD₄ in UiO 66(Zr)

Abstract

Porous metal−organic frameworks (MOFs) have emerged as promising materials for the capture of carbon dioxide (CO₂) and its separation from methane (CH₄) during the industrially important “sweetening” of sour natural-gas. The excellent thermal and chemical stability of the highly porous UiO-66(Zr) material, combined with good selectivity for CO₂ over CH₄, makes this material a prime candidate for such applications. Using a combination of neutron powder-diffraction and density-functional theory, we examine the details of the binding of CO₂ and CH₄ in UiO-66(Zr) over the industrially relevant 3.6-9.0 mmol/g concentration range, corresponding to the material that is half to fully saturated with CO₂. This work builds on the previously reported preferred site for CO₂ and CH₄ in UiO-66(Zr), establishing further sites and determining the strength and nature of the guest−host interaction at these. We find the UiO-66(Zr)···CO₂ interactions are significantly affected by the concentration of CO₂ as the binding of CO₂ is enhanced by interguest interactions.