Investigating the role of activation in CO2 and N2 adsorption in Flexible MOFs

Metal Organic Frameworks (MOFs) are a class of porous materials formed by the coordination of metal center and organic linkers. These materials are promising candidates for gas capture and separation due to distinctive properties of pore shape/size, selectivity, active sites and confinement effects. In the case of MOFs containing open metal sites (OMS), the coordination of small molecules in the framework, such as H2O and CO2, is essential for sorption applications. However, the high affinity of OMS requires that, before application in a capture process, these MOFs go through an activation step. This process consists in removing unwanted guest molecules and gases from the framework arising from post-synthesis or contact with the air. The activation of these materials is important not only for controlling sorption cycles, but also for preventing loss of the crystallinity or a phase change caused by hydrolysis of the framework. In this study, we employ Raman spectroscopy in different gas loading conditions to understand the effect of activation in N2 and CO2 adsorption in ZnBDC(TED)0.5, a flexible MOF. By conducting multiple sorption/activation cycles in sequence, we track changes to gas capture performance. By combining experimental results with DFT simulations, we investigate the effect of the OMS in guest-molecule adsorption and the effect of activation.