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. © 2015 American Chemical Society