Crystal-size Effect on the Kinetics of CO Adsorption in Metal Organic Frameworks Studied by NMR

We study the dynamics and the exchange of carbon dioxide (CO) adsorbed in a metal organic framework (MOF) by C NMR for various sizes of the host crystal ranging from micrometers to millimeters. We found that the guest CO molecules adsorbed in [Zn(1,4-NDC)(dabco)] MOF undergo exchange at a rate that depends on the size of the host crystal, revealing that the smaller the host crystals are, the faster the exchange becomes. Such a trend can be explained by the size-dependent surface-to-volume ratio.