ELECTROSPUN NANOFIBERS FOR CARBON DIOXIDE CAPTURE

The enormous release of greenhouse gases has resulted in global warming, which is an alarming threat to the environment and public health; thus, it has been the urgent concern of scientists to solve this issue (Arenillas et al., 2005; Hartono et al., 2009; Qi et al., 2011; Yu, 2012). Numerous greenhouse gases, such as SOx, NOx, CH4, CO2, etc., are being released into the environment, however, CO2 makes up the highest proportion among them all, owing to its huge emissions from various sources which include power plants, automobiles and industries (Powell and Qiao, 2006; Lee et al., 2014). At this writing, up to 400 ppm of CO2 exist in the atmosphere, which is much higher than the recommended value (300 ppm) of the US International Energy Agency (Qi et al., 2011; Chestnut, 2009). To mitigate global warming, the Kyoto Protocol (Yu, 2012) urges industrialized nations and the European Union to reduce their greenhouse gas emissions to an average level of 5.2% lower than those of the 1990s during the period of 2009e16 (Yang et al., 2008). It is therefore essential to develop and employ CO2 capture and storage (CCS) technologies to cope with the global demand of CO2 reduction (Yoon et al., 2008). To limit CO2 emissions from power stations into the atmosphere, CCS strategies need to be capable of  capturing CO2 from the power stations, compress it into some transportable form, transport it from the power plants to proper storage places, and properly store it in a secure environment (Yave et al., 2010). It is a very critical, as well as challenging, job for CCS to be highly sensitive to CO2, so that it can capture the maximum CO2 quantity from a mixed stream of various gases, as CO2 is nowhere released singly. CCS techniques have been focused on three strategies, i.e., precombustion, postcombustion, and oxyfuel processes (Thavasi et al., 2008; Ramakrishna et al., 2006; Frenot and Chronakis, 2003).

Intensive research in recent decades has illustrated various technologies, such as chemical and physical absorption, cryogenics, separation via membranes, and adsorption, that could be employed for CCS; however, these technologies are still not very mature for use at a large scale (Arenillas et al., 2005). Therefore, there is still an extreme need for thorough research to commercialize these technologies, to make them capable of processing huge amounts of flflue gas and signifificantly transferring the captured mass to secure storage compartments, which is not possible unless appropriate materials are synthesized. Among these techniques, adsorption is gaining vital attention owing to its low capital requirement, easier application, and low energy consumption (Bechelany et al., 2015; Arenillas et al., 2005). A variety of materials have been synthesized for CO2 adsorption, such as zeolites and activated carbons; they are still being investigated to enhance their CO2-capturing capacity and to overcome their current limitations, such as their fragile nature (Li et al., 2011; Przepio rski et al., 2004). Nanomaterials, offering higher specifific surface area, tailorable porous structure, and large numbers of N-containing groups, have high potential for CCS (Dassanayake et al., 2016). The higher surface area of  such materials provides more reaction sites, leading to enhanced adsorption capacity, and offers lower weight and material cost for resultant substrates; hence, they are preferred over traditional materials. For instance, Adeniran and Mokaya (2016) reported porous nitrogen-doped carbon with high surface area (860 m2 /g) showed higher CO2 capture capacity of 4 mmol CO2/(g sorbent) with a micropore volume of 0.39e0.40 cm3 /g, compared with pristine carbon nanofifibers (CNFs).

The tailorable nature of nanomaterials, which allows one to alter their characteristics, and their feasibility for producing materials in all dimensions are key to their wider acceptability. Of these nanomaterials, the one-dimensional (1D) materials offer the lowest possible resistance to gas transport and tremendously fast kinetics (Rabbani et al., 2012); therefore, they are believed to be prospective materials for CCS (Wang et al., 2013b). There are various nanofabrication techniques capable of producing fifibers in nanoscale. However, among them all, electrospinning is believed to be the most robust, versatile, and scalable nanofabrication technique (Wang et al., 2011; Babar et al., 2017). It is capable of producing a variety of fifibrous structures (porous, solid, hollow, coreeshell, etc.) from a very wide range of polymeric materials for numerous applications (Tang et al., 2005; Babar et al., 2018). The process is capable enough to directly produce fifibrous mats comprising nanofifibers ready for use. In addition, the process also offers the feasibility of producing nanofifibers from all kinds of materials (organic as well as inorganic polymers), solutions, mixtures, and even melts (Kim et al., 2015; Huang et al., 2003; Baji et al., 2010). Moreover, the surface of resultant substrates produced via electrospinning can also be easily functionalized to obtain desired properties depending on the application demands (Baji et al., 2010). This chapter provides an overview of the emerging materials for CCS produced via the electrospinning process and compares their performance with commercially available materials and the substrates produced at microscale via various techniques. At the end, current research efforts and future research opportunities in designing effificient CCS materials via electrospinning technique are summarized.

Paper link：https://www.sciencedirect.com/book/9780323512701/electrospinning-nanofabrication-and-applications