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Preparation, Characterization, and Applications of Electrospun Carbon Nanofibers and Its... DOI: http://dx.doi.org/10.5772/intechopen.88317 Figure 4. (a–c) Cross-sectional TEM images of CNFs thermally treated at 2800°C [PAN:PMMA (a) 5:5, (b) 7:3, and (c) 9:1] and (d) TEM image of CNFs showing structurally developed core walls after thermal treatment [39]. Figure 5. FE-SEM images of electrospun PAN/PMMA nanofibers with different mixing ratios. (a) CNFs; (b) PAN/ PMMA, 7:3; (c) PAN/PMMA, 5:5; and (d) PAN/PMMA, 3:7 [41]. The FE-SEM images of CNFs, 7:3, and CNFs, 5:5, showed that the CNFs have several hollow cores along the fiber axis. Notably, the morphology of the u-CNFs (3:7) was completely changed. The morphology of CNFs (3:7) fibers was homogenous, continuous, and a cylindrical shape with an average diameter of ~50 nm. In fact, the complete decomposition of PMMA during the thermal treatment is the main reason. The BET specific surface area of the u-CNFs-3,7 was determined to be 467.57 m2/g and pore volume of 1.15 cm3 g−1 and an average pore size of 9.48 nm. Chang et al. [42] introduced a novel technique of centrifuged-electrospinning for the preparation of ultrathin carbon fibers. Figure 6 shows the preparation dia- gram of the ultrathin porous CNFs by centrifuged-electrospinning. In a typical pro- cedure, PAN/PMMA polymer blend was prepared in DMF at different weight ratios of 80/20 (PAN80/PMMA20) and 10/90 (PAN10/PMMA90). The polymer blends were used for the preparation of PAN/PMMA nanofibers by centrifuged electro- spinning. The centrifuged-electrospinning conditions were as follows: an applied positive voltage of 45 kV, a three-phase induction motor spinning at 4000 rpm, a syringe feed rate of 1.5 mL/min, and a stainless steel ring with a diameter of 50 cm as the collector. Finally, the resultant PAN/PMMA nanofibers were stabilized at 280°C for 2 h at a heating rate 0.5°C/min in air atmosphere and then carbonized at 800°C for 4 h under argon atmosphere at a heating rate of 5°C/min. Figure 6 (b, c, and d) shows the TEM images of ultrathin micro-/mesoporous CNFs. 5PDF Image | Preparation, Characterization, and Applications of Electrospun Carbon Nanofibers
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