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Preparation, Characterization, and Applications of Electrospun Carbon Nanofibers and Its... DOI: http://dx.doi.org/10.5772/intechopen.88317 (NPs) and g-C3N4 and excellent adsorption capacity of carbon nanofibers are the main reason for the excellent catalytic activity. 3.2 Carbon nanocomposites in catalytic reduction of 4-nitrophenol Catalytic transformation of 4-nitrophenol to 4-aminophenol is one of the very significant reactions in green chemistry [51]. It is well known that the nitro- phenols are harmful to the environment, and therefore the US Environmental Protection Agency has listed it as 114th organic pollutant [52]. In recent days, catalytic conversion of nitrophenols to aminophenols is widely studied. In fact, the catalytic product, aminophenols, can be used as an excellent intermedi- ate in synthesizing various drugs and reducing agent. The 4-nitrophenols are often employed as a photographic developer, corrosion inhibitor, anticorrosion lubricant, and hair-dyeing agent [53]. Although the reaction is very simple, greener, and most efficient, the reaction without metal catalysts is not achiev- able. To perform this reaction, various metal catalysts (based on graphene oxide, silica, alumina, activated carbon, CNTs, fullerenes, and so on) are developed and proven to be an excellent candidate for the reduction of 4-nitrophenols to 4-aminophenol. For example, RGO-ZnWO4-Fe3O4, AgNPs-rGO, PdNiP/RGO, and NiNPs/silica are reported for the reduction of nitrophenol [20]. Carbon nanofibers/silver nanoparticle (CNFs/AgNPs) composite nanofibers were used for the reduction of 4-nitrophenol (4-NP) with NaBH4 [46]. The reaction was tracked by time-dependent UV-visible spectroscopy (Figure 10). It was found that the CNF/AgNP composite demonstrated an excellent catalytic activity in the reduction of 4-nitrophenol. The catalytic efficiency was found to be enhanced with the increasing of the content of silver on the CNF/AgNP catalyst. Reaction kinetic was studied for the CNF/AgNP reduction of 4-nitrophenol. It was reported that the rate constant of 6.2 Ć 10ā3 sā1 was determined for the reduction of 4-nitrophenol over CNF/AgNP catalyst. The excellent active might be attributed to the high sur- face areas of Ag NPs and synergistic effect on delivery of electrons between CNFs and AgNPs. The CNF/AgNP composite nanofibers can be easily recycled and reused without any significant loss in its catalytic activity. 3.3 Carbon nanofiber composites in energy applications Due to the excellent properties such as high surface area, conductivity, and poros- ity, the CNF-based nanocomposites are widely used for the energy applications. Without a doubt, the development of electrochemical energy storage systems (EES) Figure 10. Catalytic evolution of CNFs/AgNPs. (a) UV-vis absorption spectra during the reduction of 4-nitrophenol over CNFs/AgNPs; (b) ln(C/C0) and C/C0 vs. reaction time for the reduction of 4-nitrophenol, S0 = fresh CNFs, S1 = CNFs/AgNPs, and S2 = CNFs/AgNPs; (c) proposed mechanism of the catalytic reduction of 4-nitrophenol with the CNF/AgNP composite nanofibers [46]. 9PDF Image | Preparation, Characterization, and Applications of Electrospun Carbon Nanofibers
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