In Situ EPR Spectroscopy to Track Gas Exchange Kinetics in Porous Liquids under Variable Gas Pressure

Porous liquids (PLs) are novel promising materials, which demand development of informative spectroscopic tools to track their functioning in situ and operando. In this work we demonstrate in situ electron paramagnetic resonance (EPR) spectroscopy as a versatile method to investigate variable-pressure gas exchange in PLs of the third type based on metal–organic frameworks (MOFs) and sterically excluded solvents. The use of permanently encapsulated in-MOF spin probes (stable nitroxide radicals) allows tracking evolution of EPR spectral shapes under applied gas pressure, and following theoretical analysis reveals contributions of gas exchange kinetics in MOF particles, gas diffusion through the bulk sample and gas dissolution in PL. We exemplify this approach with two PLs based on MOF ZIF-8 dispersed in dibutyl phthalate or ionic liquid [Bmim]BF4. In both PL examples EPR provides unique information on gas exchange kinetics (air-to-CO2 and CO2-to-air) vs pressure in situ, which is indispensable for adjusting target functioning of PLs and their applications in future.