Two-dimensional ionic liquids with an anomalous stepwise melting process and ultrahigh CO2 adsorption capacity

Abstract

Ultrathin ionic liquid (IL) films have shown wide applications in the chemistry and materials fields. However, the structure feature and quantitative controlling mechanism of thin IL films have rarely been reported to date. Here, computational simulations combined with scanning tunnel microscope experiments are used to quantify the structure and function of the thinnest possible IL films, two-dimensional (2D) ILs, which consist of 2D ordered mono-ionic IL structures. Interestingly, the 2D ILs exhibit anomalous stepwise melting processes, involving localized rotated, out-of-plane flipped, and fully disordered states, which are different from 3D ILs. Meanwhile, a theoretical model and temperature-surface phase diagram are constructed to evaluate the critical stepwise melting behaviors. Furthermore, the 2D ILs also possess ultrahigh CO 2 adsorption capabilities and structural robustness during the CO 2 adsorption-desorption process. These findings are promising for the rational design of an IL-solid interface for CO 2 -capture-fixation chemistry and related applications. • 2D ionic liquid with ordered mono-ionic structure • The anomalous stepwise melting processes of 2D ionic liquids is revealed • A theoretical model is developed to evaluate the critical melting points • The 2D ionic liquids possess extremely high CO 2 adsorption capabilities Combining STM experiments and molecular dynamics simulations, Wang et al. investigate 2D ionic liquids that exhibit anomalous stepwise melting processes and superhigh CO 2 adsorption capacity. The 2D modification technique may provide a strategy for the precise control and function design of liquids.