(263d) The Evaluation of the Temperature Dependence of Gate-Opening Phenomena in ZIF-8

ZIF materials have attracted significant attention due to their exceptional chemical and thermal stability, as well as the documented flexibility of their pore apertures. While it’s been made clear that some degree of linker flexibility plays a major role in understanding the diffusion of certain species into these frameworks, the gate-opening phenomena exhibited in many isotherms has not been well studied. Specifically, the understanding of how framework deformation occurs as a function of temperature and adsorbate is not yet well understood in ZIFs. Many adsorbate/adsorbent pairs exhibit a sharp increase in uptake capacity at certain pressures, generally attributed to the structural deformation of pore opening. It is clear that this material property could have significant effects on its adsorptive behavior, especially during operation of a packed bed column. Investigations of various adsorbate isotherms will help elucidate the nature of gate-opening phenomena and its potential effect on future adsorptive processes.

In this work, the onset of gate-opening behavior in ZIF-8 is evaluated through a detailed gas adsorption study. Increases in temperature show a shift in the gate-opening pressure of the adsorbent, in some instances disappearing at higher temperatures. The adsorbate pressures and loadings at gate-opening are evaluated as a function of adsorbate, and the disappearance of the phenomena is related to material properties.  Various gas isotherms are presented in a wide temperature range to investigate the thermodynamics of adsorption and structural deformation of ZIF-8. The fundamental understanding of the conditions under which this material deformation occurs is important to the successful application of ZIFs in industrial processes.