Gas adsorption and separation: tuning the channel electrostatics for CO2

Metal-Organic frameworks (MOFs) and porous molecular materials represent a new platform for achieving and exploring high-performance sorptive properties and gas transport. The key lies in the modular nature of these materials, which allows for tuning and functionalization towards improved gas capture. Self-assembly of polyfunctional molecules containing multiple charges, namely, tetrahedral tetra-sulfonate anions and bi-functional linear cations, resulted in a permanently porous crystalline material in which the channels are decorated by double helices of electrostatic charges that governed the association and transport of CO2 molecules (Fig. 1). These channels electrostatically compliment the CO2 molecules and forms strong interactions of 35 kJ mol−1, ideal for CO2 capture/release cycles.[1] The CO2 adsorption properties were modulated for an isoreticular series of Fe-MOFs by varying the decoration of fluorine atoms within their channel (Fig. 2). A host of complementary experimental and computational techniques gives a holistic view of the host-CO2 properties towards the potential selective removal of CO2 from other gases. GCMC and DFT were employed for a detailed description of the CO2 diffusion and interactions in the porous materials. CO2–matrix adsorption enthalpies of 33 kJ mol−1 was accurately measured in-situ by simultaneous acquisition of micro-calorimetric and volumetric-isotherm data. Direct measurements of adsorption heats are not common and such data helps to validate mathematical models and protocols for sorption-derived adsorption enthalpies. [2]