# Carbon Dioxide Adsorption on Carbon Nanofibers with Different Porous Structures
###### Abstract  
Electrospinning techniques have become an efficient way to produce continuous and porous carbon nanofibers. In view of CO\({}_{2}\) capture as one of the important works for alleviating global warming, this study intended to synthesize polyacrylamide(PAN)-based activated carbon nanofibers (ACNFs) using electrospinning processes for CO\({}_{2}\) capture. Different structures of PAN-based ACNFs were prepared, including solid, hollow, and porous nanofibers, where poly(methyl methacrylate) (PMMA) was selected as the sacrificing core or pore generator. The results showed that the PMMA could be removed successfully at a carbonization temperature of 900 \({}^{\circ}\)C, forming the hollow or porous ACNFs. The diameters of the ACNFs ranged from 500 to 900 nm, and the shell thickness of the hollow ACNFs was approximately 70-110 nm. The solid ACNFs and hollow ACNFs were microporous materials, while the porous ACNFs were characterized by hierarchical pore structures. The hollow ACNFs and porous ACNFs possessed higher specific surface areas than that of the solid ACNFs, while the solid ACNFs exhibited the highest microporosity (94%). The CO\({}_{2}\) adsorption capacity on the ACNFs was highly dependent on the ratio of V\({}_{\text{v-0.7 nm}}\) to V\({}_{t}\), the ratio of V\({}_{\text{m}t}\) to V\({}_{t}\), and the N-containing functional groups. The CO\({}_{2}\) adsorption breakthrough curves could be curve-fitted well with the Yoon and Nelson model. Furthermore, the 10 cyclic tests demonstrated that the ACNFs are promising adsorbents. activated carbon nanofibers; electrospinning; carbon dioxide; adsorption breakthrough 2021  
Y.-C.-C.-C.-C.-C.-C.-C.-C.-C.-C.-C.C.-C.C.-C.C.-C.C.-C.C. the concentration is increased, beaded fibers and further uniform fibers can be observed sequentially [16]. A fibrous structure is stabilized above a minimum concentration, but the fiber diameter increases with molecular weight and concentration [15]. For the polymers with higher molecular weights, uniform fibers can be formed at a lower polymer concentration compared with those having lower molecular weights [17]. Thus, the intermolecular entanglements play an important role in stabilizing the fibrous structure [18]. The co-electrospinning of polymer solutions from a spinneret set containing two coaxial capillaries has been developed to serve as an alternative technique for the fabrication of hollow fibers [19]. Using this method, co-electrospinning immiscible and miscible pairs of polymer solutions forms nanofibers with core/shell structures [19]. Subsequently, the core material can be removed by thermal decomposition [19; 20] or extraction with mineral oil or solvent [21]. In general, it is suggested that the core-polymer capillary protrude \(\sim\)1 mm below the end of the shell capillary to produce a good Taylor cone at the end of the nozzle [19; 22]. [PERSON] et al. [22] found that good morphologies of polyacrylonitrile (PAN)/poly(methyl methacrylate) (PMMA) nanofibers were obtained from the coaxial nozzle electrospinning at 15 kV. For an applied voltage of 10 kV, the injection was retarded for a period until the electrostatic force was strong enough to inject the solution jet, and some of the nanofibers were fused together as a bundle of fibers. If the applied electrical voltage was greater than 20 kV, the extraction rate of the polymer solution was too fast to evaporate the solvent. Thus, wet nanofibers were fused together to form a bundle morphology. Another type of PAN carbon nanofiber with a nanometer porous structure in individual electrospun nanofibers can be produced by blending a sacrificial polymer (e.g., PMMA) into a PAN solution [23]. After thermal treatment, the decomposition of the PMMA results in the formation of a porous structure. The use of PAN-based blends is recognized as an efficient way to create a hierarchical porous structure in carbon nanofibers. [PERSON] et al.