Stepped enhancement of CO2 adsorption and separation in IL-ZIF-IL composites with shell-interlayer-core structure

Development of materials with excellent separation performance remains an ongoing challenge in separation science and technology. Herein, a novel strategy was proposed to gradually enhance gas separation performance in micro/nano-materials, by constructing a shell-interlayer-core structure using ionic liquid (triethylenetetramine lactate, [TETA]L) and zeolitic imidazolate framework (ZIF-8). Such structure includes outer [TETA]L shell, interlayer of ZIF-8, and inner [TETA]L core, endowing the composite with more evident molecular sieving separation for CO2 mixtures than the reported materials. A high CO2 adsorption amount (1.53 mmol/g at 298 K and 1.0 bar) is maintained, while the uptakes for CH4 and N-2 are very low. Corresponding ideal adsorbed solution theory selectivities are 260-1,990 and 1,688-5,572 for CO2/CH4 and CO2/N-2 mixtures at the range of tested pressures. In addition, the separation performance can be controlled by varying the shell-interlayer-core structure with IL inside, outside or on both sides of ZIF-8 and the thickness of outer shell.