BMIM][OAc] coating layer makes activated carbon almost completely selective for CO2

Abstract

Tuning the molecular affinity of porous materials towards desired gases is important to achieve superior selectivity for a target separation. Herein, we report a novel composite, prepared by coating an ordinary activated carbon (AC) with an ionic liquid (IL) (1-butyl-3-methylimidazolium acetate, [BMIM][OAc]) offering an almost complete CO2 selectivity over N2 and CH4. Data indicated that pore blockage by the IL accompanied with the enhancement in polarity and reduction in the hydrophobic character of the surface hindered the sorption of N2 and CH4. For CO2, on the other hand, new chemisorption and physisorption sites became available associated with the IL layer on the surface, making the composite material significantly selective. Newly formed chemisorption sites attributed to the cation's acidic C2H sites, which become available with bi-layer formation. Presence of multiple competitive sorption sites with different energies was further proven with thermal analysis and detailed spectroscopic analysis. Data showed that CO2/CH4 and CO2/N2 ideal selectivities boosted from 3.3 to 688.3 (2.3 to 54.7) and from 15.6 to 903.7 (7.1 to 74.3) at 0.1 (1) bar and 25 °C, respectively, upon the deposition of IL layer. Especially at lower pressures, the IL/AC material became almost fully selective for CO2 offering ideal selectivities in the order of several tens of thousands. To the best of our knowledge, the remarkable enhancement in the ideal CO2 selectivity by a straightforward post-synthesis modification of an ordinary AC, as reported here, sets a new benchmark in high-performance and efficient gas separation for similar porous materials.