# Ionic Liquids Hybridization for Carbon Dioxide Capture: A Review
## 4 Application of ILs Hybrid Material in Carbon Dioxide
### ILs/Activated Carbon  
The usage of activated carbon (AC) for CO2 capture had been widely applied due to its porous structure, highly resistant towards toxic environment and complete adsorption reversibility during regeneration process [88; 89]. An abundant source of biomass available as AC feedstock such as coconut coir, palm shell, nut shell and bamboo simultaneously provide a major solution to our agricultural waste management. Numerous studies related to the application of these carbonaceous materials have been conducted, in which excellent adsorption capacity was observed. For example, [PERSON] and co-workers utilized AC from date seed for CO2 adsorption and the CO2 loading capacity exhibited by the date seed AC is comparable to commercial AC. However, though AC provides larger surface area for CO2 capture, its inert surface chemistry led to low capacity at low partial pressure [90]. Additionally, the presence of water vapor in flue gas has caused AC to exhibit low CO2 adsorption selectivity [91]. Therefore, the modification of AC through immobilization of ILs via grafting or impregnation methods is introduced with the aim to improve the affinity of the carbonized adsorbent toward CO2. [PERSON] et al. functionalized two commercial ACs with different textural properties, F600-900 and RGC30, with [HMIM][BF4] and [EMIM][Gly], respectively [92]. The impregnation process of AC with [HMIM][BF4] and [EMIM][Gly] was conducted by using bath stirred system in ethyl acetate and methanol, respectively. After a week, the impregnated solid was collected by filtration. All functionalized AC was dried overnight at 70 \({}^{\circ}\)C. Then, AC/[HMIM][BF4] was further dried by purging N2 into column packed with impregnated AC, while for AC/[EMIM][Gly], the adsorbent was placed under vacuum at 100 \({}^{\circ}\)C for 5 h. It has been observed that the CO2 adsorption capacity of F600-900/[HMIM][BF4] and RGC30/[HMIM][BF4] was lower than raw AC at low temperature. However, the difference in CO2 adsorption capacity between impregnated adsorbent and raw AC was relatively low at 80 \({}^{\circ}\)C due to the insignificant effect of pores clogging caused by high reaction temperature. On the other hand, while the presence of [EMIM][Gly] did not induce the adsorption capacity of CO2 for F600-900 and RGC30 at 30 \({}^{\circ}\)C, an improvement was begun to be seen at 50 \({}^{\circ}\)C. According to authors, the presence of an amino group in [EMIM][Gly] may form carbamate with CO2, a mechanism that is similar to amine-based solvent reaction thus resulting in a comparable performance of functionalized samples with raw AC. Consequently, this contributed to the large CO2 adsorption capacity of F600-900/[EMIM][Gly] and RGC30/[EMIM][Gly] at 80 \({}^{\circ}\)C. Thus, impregnating AC with amino acid base IL shows a promising result for CO2 capture. The modification of IL structure by amine functionalization through amino-based IL with intention to mimic the commercial amine usage but with better thermal stability and heat capacity values is expected to benefit this application. On the other hand, incorporating AC with [HMIM][BF4] is found to be unsuitable for CO2 removal from flue gas as the presence of IL was unable to counteract the reduction of AC micropore. Meanwhile, [PERSON] and co-workers studied the effect of different methods, namely, impregnation and grafting, for AC surface functionalization [91]. In this work, the immobilized AC was prepared with different loading of [P8883][Tf2N]. In the impregnation method, AC was added into mixture containing IL and anhydrous ethanol and the mixture was stirred at room temperature for 24 h. The solid was filtered and dried under vacuum at 80 \({}^{\circ}\)C for 24 h. For the grafting technique, the mixture containing anhydrous ethanol, AC and ILs was stirred at reflux temperature for 36 h followed by extraction using acetone via Soxhlet extraction.