# Ionic Liquids Hybridization for Carbon Dioxide Capture: A Review
###### Abstract  
CO\({}_{2}\) absorption has been driven by the need for efficient and environmentally sustainable CO\({}_{2}\) capture technologies. The development in the synthesis of ionic liquids (ILs) has attracted immense attention due to the possibility of obtaining compounds with designated properties. This allows ILs to be used in various applications including, but not limited to, biomass pretreatment, catalysis, additive in lubricants and dye-sensitive solar cell (DSSC). The utilization of ILs to capture carbon dioxide (CO\({}_{2}\)) is one of the most well-known processes in an effort to improve the quality of natural gas and to reduce the green gases emission. One of the key advantages of ILs relies on their low vapor pressure and high thermal stability properties. Unlike any other traditional solvents, ILs exhibit high solubility and selectivity towards CO\({}_{2}\). Frequently studied ILs for CO\({}_{2}\) absorption include imidazolium-based ILs such as [HMIM][Tf\({}_{2}\)N] and [BMIM][OAc], as well as ILs containing amine groups such as [Cho][Gly] and [C\({}_{1}\)ImPA][Gly]. Though ILs are being considered as alternative solvents for CO\({}_{2}\) capture, their full potential is limited by their main drawback, namely, high viscosity. Therefore, the hybridization of ILs has been introduced as a means of optimizing the performance of ILs, given their promising potential in capturing CO\({}_{2}\). The resulting hybrid materials are expected to exhibit various ranges of chemical and physical characteristics. This review presents the works on the hybridization of ILs with numerous materials including activated carbon (AC), cellulose, metal-organic framework (MOF) and commercial amines. The primary focus of this review is to present the latest innovative solutions aimed at tackling the challenges associated with IL viscosity and to explore the influences of ILs hybridization toward CO\({}_{2}\) capture. In addition, the development and performance of ILs for CO\({}_{2}\) capture were explored and discussed. Lastly, the challenges in ILs hybridization were also being addressed. ionic liquids; ILs hybridization; hybrid material; carbon dioxide capture 202328709113390/202328709113390/20232870911390/  
capturing CO\({}_{2}\) in natural gas including pre-combustion, post-combustion and oxyfuel. In the meantime, several CO\({}_{2}\) capture techniques have been developed based on chemical absorption, physical separation, membrane separation and cryogenic distillation [3; 4]. The usage of alkanoamines such as MDEA, DEA and MEA are by far the most developed process in gas sweetening. Amines offer a reliable and effective solution for CO\({}_{2}\) capture, particularly in post-combustion capture applications due to their affordability, high CO\({}_{2}\) absorption efficiency and selectivity [5]. Nevertheless, amines have low thermal stability and high volatility which renders them unsuitable for operation under high-temperature conditions. Consequently, the loss of amines during the absorption process becomes inevitable. Furthermore, the degradation of amines through oxidation or thermal processes resulted in the formation of chemical compounds that exhibits low absorption capacity such as organic acids, amides, dimers and trimers [6]. Besides that, aqueous amines consume high energy during the regeneration process due to the strong interaction between CO\({}_{2}\) and the sorbent [7; 8]. For instance, in the case of MEA regeneration, the physical treatment was conducted at 160 \({}^{\circ}\)C to desorb CO\({}_{2}\). The process resulted in a substantial 95% loss of amines [9]. Meanwhile, ionic liquids (ILs) are a class of molten salt that is formed by the combination of organic cation with organic or inorganic anion. They were initially introduced in 1914. However, the interest towards ILs started around 1997 after being identified as promising solvents for green technology.