High-pressure investigation of ionic functionalized graphitic carbon nitride nanostructures for CO2 capture

- High-pressure CO2 adsorption studies on bulk g-C3N4 as well as g-C3N4 nanosheets.
- Increase in adsorption capacity with the incorporation of ionic liquid [BMIM][TFSI].
- High surface area, high nitrogen content and porous nature of g-C3N4 nanosheets have synergistically resulted in higher CO2 adsorption capacity.
- Further increment in sorption capacity due to high solubility of CO2 in ionic liquid.

Carbon dioxide is a major greenhouse gas responsible for the increase in global temperature which poses serious threat to the earth's environment and is a burning topic of research now-a-days. So, one of the promising and energy-efficient techniques adopted these days in order to capture this toxic gas is high pressure adsorption. In this particular work, we report the synthesis of graphitic carbon nitride nanosheets (NS-g-C3N4) using a very facile synthesis technique and its utility in adsorption of CO2 along with the ionic functionalization of NS-g-C3N4 with ionic liquid 1-Butyl-3-Methylimidazolium bis(trifluoromethyl sulfonyl)imide ([BMIM][TFSI]) and its CO2 adsorption properties. The CO2 adsorption analyses were carried on using high pressure Sievert's apparatus. NS-g-C3N4 shows a CO2 sorption capacity of 19.78 mmol/g at 15 bar pressure and 25 °C which is almost two times more than that of bulk g-C3N4 (8.54 mmol/g) under identical conditions. Besides, when NS-g-C3N4 is functionalized with ionic liquid, the interface between ionic liquid and NS-g-C3N4 significantly increases the sorption capacity to 42.93 mmol/g under nearly ideal conditions. The temperature is varied from 25 to 100 °C and pressure is varied from 2 to 25 bar. The high nitrogen content in graphitic carbon nitride nanostructures (56.6 at.%) acts as the active sites for binding the CO2 molecules while the non-covalent ionic liquid functionalization allows CO2 to interact with NS-g-C3N4/[BMIM][TFSI] by physicochemical adsorption mechanism and thereby enhances the CO2 capture.

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