Breathing Effects of CO2 Adsorption On Flexible 3D Lanthanide Metal-Organic Frameworks

The discovery of flexible and dynamic MOFs has changed many of our ideas of crystalline porous solids. These so-called “third generation MOFs” exhibit extraordinary structure flexibility on adsorption/desorption of specific gases or liquids. Such structural transformation is often directly related to the functionality of these frameworks, such as pore size/shape change, gate-opening effects, and controlled molecular diffusion. Related potential applications may involve selective separation, molecular sensing, controlled drug storage and delivery, and as nanoreactors for polymerization. However, breathing effects of 3D flexible MOFs are still far from clear, and exploring the mechanism and potential application of flexibility in MOFs are of high fundamental interest. In this work, a new three-dimensional flexible lanthanide metal-organic framework is reported in our lab. This MOF possesses an uncommon chiral space group, very high thermal stability up to 560 ^oC, high surface area (experimental 1014 m²/g and calculated 1385 m²/g), and demonstrates a large adsorption hysteresis loop on the N₂ isotherm at 77K after activation at 300 ^oC. Powder X-ray thermodiffraction experiments reveal structural transformation on this flexible MOF, and high pressure gravimetric adsorption of CO₂, CH₄, and N₂ demonstrates the interesting "gate" opening and closing phenomena. Particularly, equilibrium and kinetic investigation of CO₂ adsorption provided deeper information about the mechanism and potential application of adsorption breathing effects.