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Sreetama Ghosh1 Ramaprabhu Sundara1 R. Sarathi1

1, Indian Institute of Technology Madras, Chennai, , India

Carbon dioxide is a major anthropogenic greenhouse gas produced primarily from the combustion of fossil fuels, automobile emission and from industrial exhausts that have posed a huge danger to the environment in recent times. One such way to capture CO2 in porous materials is by adsorption process. In recent times, a wide range of materials such as zeolites, porous carbon, organic polymers, metal−organic frameworks (MOFs) etc. have been extensively studied for CO2 capture. Porous carbonaceous materials are especially attractive because of their large specific surface area, regular porosity, and ease of synthesis, abundant availability and thermal stability. An effective CO2 adsorbent must possess high adsorption capacity, high selectivity, moderate heat of adsorption, fast adsorption and desorption kinetics and excellent chemical and mechanical stability. The nitrogen content of the samples also plays very important role in CO2 adsorption. One of the most important reasons is that the N content improves the electron density of the carbon framework and thereby increases the basicity of the framework. As a result, it becomes easier for the electron deficient C atom of CO2 to get anchored in the framework by Lewis acid (CO2)-Lewis base (N) interactions. Ionic liquids (ILs) are molten salts mainly composed of organic cations and organic or inorganic anions having melting point lower than 100 °C. Room temperature ionic liquids exhibit some significant properties such as low vapor pressure, high chemical and thermal stability, tunable properties, good ionic conductivity and high CO2 solubility. The interaction of IL with CO2 is quite fast that effectively increases the sorption kinetics. The present work basically focuses on a solvent-free facile synthesis of ionic liquid functionalized nitrogen doped porous carbon by a simple thermal decomposition technique. This ionic functionalized micro-mesoporous nanocomposites sample showed large CO2 adsorption capacity along with fast adsorption kinetics when compared to only porous carbon. The ionic liquid used in this particular work is 1-Butyl-3-Methylimidazolium bis(trifluoromethyl sulfonyl)imide ([BMIM][TFSI]). It has already been reported that surface functionalization with ionic liquids basically increases the anchoring sites which leads to a higher CO2 adsorption capacity. The CO2 adsorption-desorption studies were carried on at different temperatures and in both high as well as sub-ambient pressure conditions. These studies show that the nanocomposite exhibit excellent cyclic stability in storage performance. In addition, thermodynamic studies suggest that the adsorption takes place mainly by physicochemical adsorption mechanism and therefore easy regeneration process is also possible which is considered as another critical property of an adsorbent. Thus it can be concluded that this particular material has the potential to serve as a good CO2 adsorbent both in pre as well as post-combustion CO2 capture.

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