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 CO capture and the thickness of supported IL films plays a critical role in the CO mass transfer rate. However, the dependence of CO 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 CO mass transfer. A monotonic and almost linear relationship for supported IL films is obtained between the resistance of CO mass transfer (1/k) and the nanofriction coefficient (μ), avoiding the controversy over the effect of supported IL film thickness on CO adsorption. The enhanced mass transfer of CO 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 CO with the 'blank-clean' ions of the ILs, and thus accelerating the CO mass transfer. The proposed correlation links the nanoscale friction with the mass transfer of CO adsorption, providing a fresh view on the design of ultra-low frictional supported ILs for enhanced CO capture and separation processes.