Enhanced alcohol and H2O adsorption and separation performances by introducing pyridyl ligand in a MOF

Abstract

MOFs (Metal-Organic Framework), as promising crystalline materials of adsorption and separation, has been the subject of many recent investigations. However, the H2O stability of MOFs and the variation of adsorption selectivity in humid environments largely hinder attempts as excellent adsorbents in numerous scenarios. This study employs hydro-thermal synthesis [Cd0.5(DPETA)0.5]n using 2,3′,5,5′-Diphenyl tetracarboxylic acid (DPETA) and Cd(NO3)2·4H2O as ligands and metal ions, respectively. And it is modified by adding auxiliary ligands 4-4′-bipyridyl (bpy) and 1,2-bis (4-pyridyl) ethylene(bpe) to obtain [Cd1.5bpy2(DPETA)]n and [Cd2bpe2(DPETA)]n.The phase purity of the MOFs is examined using PXRD and FT-IR spectrum. The adsorption capacities of three MOFs are tested separately for water, ethanol and methanol using vapor adsorption. Their adsorption conformations and hydrogen bond lengths are also calculated by the GCMC method. The adsorption selection ratios of methanol and ethanol are deduced in combination with the IAST method under three components of water, methanol and ethanol. The results shows a methanol/ethanol adsorption separation ratio of 45 for [Cd1.5bpy2(DPETA)]n at 297 K, which is consistent with the of GCMC demonstrated. These results suggest that the methanol/ethanol adsorption selectivity ratio can be improved by increasing the adsorption force on methanol through by adding of auxiliary pyridyl ethylene. It can be used for efficient methanol/ethanol separation in humid environments.