Herbert Gleiter Institute of Nanoscience, Department of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China.
Chemistry of Interfaces, Luleå University of Technology, 97187 Luleå, Sweden.
Phys Chem Chem Phys. 2020 Jan 21;22(3):1097-1106. doi: 10.1039/c9cp05900h. Epub 2020 Jan 2.
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.
担载离子液体（ILs）是 CO 捕集的有吸引力的替代品，担载 IL 膜的厚度在 CO 传质速率中起着关键作用。然而，由于系统的变化，CO 吸收量对 IL 膜厚度的依赖关系也不同。在这项工作中，原子力显微镜（AFM）被用来探测“纳米摩擦系数”，以表征 IL 在固-液界面上的迁移率，其中纳米摩擦系数越小，离子迁移率和 CO 传质速率越快。在担载 IL 膜之间，CO 传质（1/k）的阻力和纳米摩擦系数（μ）之间得到了一个单调且几乎线性的关系，避免了担载 IL 膜厚度对 CO 吸附影响的争议。在较小的阻力 1/k 和摩擦系数μ处观察到 IL-固界面上 CO 吸附的增强传质。增强了 IL 在固-液界面处的低摩擦驱动的局部迁移率（扩散），促进了吸附 CO 的 IL 与 IL 的“空白清洁”离子之间的交换混合，从而加速了 CO 的传质。所提出的相关性将纳米尺度的摩擦与 CO 吸附的传质联系起来，为设计超低摩擦担载 IL 以增强 CO 捕集和分离过程提供了新的思路。
