Long range structural and textural changes in [Zn(bdc)(ted)0.5] upon spontaneous dispersion of LiCl and hysteretic adsorption and desorption of carbon dioxide and hydrogen

Abstract

A LiCl containing Zn(bdc)(ted)0.5 metal–organic framework (MOF) was prepared via an innocuous impregnation and thermal spontaneous dispersion process. The dispersion of the LiCl and crystallinity of the modified microporous framework were verified via standard and in situ high temperature X-ray diffraction (XRD). Pure component CO2 and H2 equilibrium adsorption–desorption analyses were performed on Zn(bdc)(ted)0.5 and (LiCl)[Zn(bdc)(ted)0.5] at 25 °C. The latter exhibited unexpected adsorption–desorption hystereses for both adsorbates and, according to XRD data, these were due to what appears to be a framework or pore contraction. Pore volumes estimated via a fit of desorption data with a Modified Dubinin–Astakhov model indicated that the LiCl containing material framework voids were at least 74% smaller as compared to the apohost. XRD patterns also indicated that the (LiCl)[Zn(bdc)(ted)0.5] structure expanded back to the apohost original state upon a nearly complete desorption of the CO2 adsorbate, suggesting that the apparent phase transition was reversible for this case. The overall adsorptive behavior of the (LiCl)[Zn(bdc)(ted)0.5] materials suggests that these could be suitable for gas capture applications under ambient conditions. For instance, the resulting average H2 heat of adsorption value is among the highest reported so far for a MOF.