The effect of nanoscale friction of mesoporous carbon supported ionic liquids on the mass transfer of CO adsorption.

Supported ionic liquids (ILs) are attractive alternatives for CO2 capture and the thickness of supported IL films plays a critical role in the CO2 mass transfer rate. However, the dependence of CO2 uptake on the IL film thickness differs as the system varies. In this work, atomic force microscopy (AFM) is employed to probe the 'nanofriction coefficient' to characterize the mobility of ILs at the solid interface, in which, the smaller the nanofriction coefficient, the faster are the ionic mobility and CO2 mass transfer. A monotonic and almost linear relationship for supported IL films is obtained between the resistance of CO2 mass transfer (1/k) and the nanofriction coefficient (μ), avoiding the controversy over the effect of supported IL film thickness on CO2 adsorption. The enhanced mass transfer of CO2 adsorption at IL-solid interfaces is observed at smaller resistance 1/k and friction coefficient μ. The low-friction driven local mobility (diffusion) of ILs at solid interfaces is enhanced, promoting the exchange mixing of the ILs adsorbing CO2 with the 'blank-clean' ions of the ILs, and thus accelerating the CO2 mass transfer. The proposed correlation links the nanoscale friction with the mass transfer of CO2 adsorption, providing a fresh view on the design of ultra-low frictional supported ILs for enhanced CO2 capture and separation processes.