Superior selective adsorption of trace CO2 induced by chemical interaction and created ultra-micropores of ionic liquid composites

Abstract

Effective capture of trace CO2 in atmosphere or confined spaces to ensure human beings safety draw a lot of attention, however, how to simultaneously improve CO2 capacity and selectivity still faces great challenge. Herein, combining porous molecular sieves (SBA-15 and MCM-41) and the anion-functionalized ionic liquid (IL) tetraethylammonium glycinate ([N2222][Gly]), a series of hierarchically porous IL composites with different IL loadings were designed and prepared. Compared with pristine supports, the incorporation of [N2222][Gly] simultaneously improves CO2 capacity and CO2/N2 selectivity by orders of magnitude, especially for confined spaces (<5000 ppm) and air (415 ppm). When the IL loading was 60 wt%, novel micropores were created, especially ultra-micropores (<0.65 nm), which are not present in bare supports and other [N2222][Gly]@SBA-15 (15, 30 and 45 wt%). Among them, 60 wt%[N2222][Gly]@SBA-15 showed the highest CO2 uptake of 1.45 and 1.88 mmolCO2/g-adsorbent at 0.0005 and 0.005 bar under 313 K along with recyclability, which are much superior to the state-of-the-art reported values. Moreover, superb ideal CO2/N2 selectivity of 11,545 at 0.005 bar and 288 K was achieved, which was 288 times that of SBA-15. Meanwhile, mixed gas breakthrough experiments demonstrated that 60 wt% [N2222][Gly]@SBA-15 shows outstanding CO2 separation performance under simulative confined spaces and ambient air. The ultra-high CO2 separation performance was attributed to the synergy of chemical interaction between the IL anion and CO2 as well as newly created micro- and ultra-micropores effect. This work provides guidelines for the design of IL composites with ultra-micropores for efficient trace CO2 removal.