Gas Adsorption Mechanism and Kinetics of an Elastic Layer-Structured Metal–Organic Framework

Abstract

The gate adsorption mechanism and kinetics of an elastic layer-structured metal–organic framework (ELM), [Cu­(bpy)₂(BF₄)₂]_<i>n</i> (ELM-11), that shows typical single-step CO₂ gate adsorption/desorption isotherms accompanied with dynamic structural transformation in a wide temperature range were investigated. Adsorption of quite a small amount of CO₂ on the external surface of ELM-11 crystals was observed at the pressure just below a gate adsorption pressure and induced a slight structural change in ELM-11. The structural change should start occurring at the outer parts of ELM-11 and transmit to more inner parts with rising pressure. The adsorption provides the stabilization of the framework through the interaction between fluid–solid and fluid–fluid and enables the framework to expand largely along the stacking direction. The CO₂ adsorption rate of ELM-11 is almost comparable to that of Zeolite 5A at around ambient temperatures and shows temperature dependence with an anti-Arrhenius trend: higher adsorption rate with lower temperature