Reversible Structural Change of Cu-MOF on Exposure to Water and Its CO₂ Adsorptivity

It is important to study the interaction between water molecules and a host structure for understanding the adsorption mechanism of metal-organic framework (MOF) materials. The evolution of the structure of a flexible Cu-MOF, {[Cu(bpy)(H2O)2(BF4)2](bpy)} (bpy=4,4'-bipyridine), upon dehydration and rehydration was studied by thermogravimetric analysis (TGA), infrared (IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and water adsorption. A nearly reversible structural change was observed upon rehydration. More importantly, a unique CO2 "gate adsorption" phenomenon was observed despite the exposure of the Cu-MOF to water. This shows that the Cu-MOF has relatively good stability after exposure to water.