Adsorption CO2, CH4 and N2 on two different spacing flexible layer MOFs

Adsorption of CO2, CH4 and N2 was measured in two differently spaced flexible layer metal–organic frameworks (MOFs), [Cu(dhbc)2(bpy)] (Kitagawa S, 2003) and [Cu(BF4)2(bpy)2] (ELM-11, Kaneko K, 2002), using a gravimetric method at temperatures of 77–298 K with a high pressure 20 bar. It was found that the gate-opening pressure was much lower at reduced temperatures in the flexible layer MOFs. Gas molecules were easily adsorbed into the widely spaced layers, but the organic ligands which play a supportive role in the layers prevent the spread of more molecules, because more of the space between the layers was occupied. The experimental results also showed the gate phenomenon and implied that these materials would be applicable for gases separated, especially the adsorption ratio of CH4/N2 in [Cu(dhbc)2(bpy)] was up to 42 at normal pressure when the temperature decreased to 195 K.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Pointed out the gas molecules were easier adsorbed into the widely layers at lower pressure. ► More organic ligands which prop up the layers prevented more molecules diffusing in the material. ► It reveals that the gate-opening pressure was much lower at reduced temperatures. ► The adsorption ratio of CH4/N2 was up to 42 at 1 bar and decreased to 195 K in (Cu(dhbc)2(bpy)).