Properties Of Carbon Nanofibers Research Articles

Effect of stabilization and carbonization treatment on the chemical and physical transformation of polyacrylonitrile (PAN) based electrospun carbon nanofibers

The present study delves into the production of carbon nanofibers (CNFs) utilising electrospun polyacrylonitrile (PAN) nanofiber mats, with a specific focus on the influence of oxidative stabilisation and carbonisation treatments. This research aims to thoroughly understand how variations in stabilisation time and temperature, as well as carbonisation temperature, impact the CNFs properties. These properties include fiber size, morphology, chemical and crystal structure transformation, thermal behaviour, and surface characteristics. Our methodology involved a detailed examination of the thermal treatment processes, where we observed a significant decrease in fiber size, though the surface morphology of the fibers remained largely unaffected. We employed Fourier-transform infrared (FTIR) spectroscopy to track the transformation of nitrile groups in PAN to imine groups, which indicated the progression of cyclisation reactions. Complementary analyses through differential scanning calorimetry (DSC) confirmed a high degree of these reactions, particularly at stabilisation temperatures extending to 250 °C and beyond. The cyclisation process was found to be complete during the carbonisation phase, at temperatures reaching 450 °C and above. Further, x-ray diffraction (XRD) patterns offered insight into the changes in the crystal structure, particularly in the packing of the d(002) spacing because of the stabilisation and carbonisation processes. This findings from this study not only elucidate the intricate process of CNFs production from electrospun PAN nanofiber mats but also highlight the critical factors that influence their final properties. These insights are invaluable for the development of advanced CNFs with tailored properties suitable for a range of applications, including but not limited to energy storage, electronics, and as supporting materials in various technological domains.

Advancing supercapacitor performance: a comprehensive review of electrochemical conversion of coconut shells into activated carbon nanofibers

This assessment provides a comprehensive evaluation of the limitations associated with the application of supercapacitors, along with the imperative to enhance their functionality. Following this, the advantages of Electrochemical Double Layer Capacitors (EDLC) are discussed in comparison to other types utilized in supercapacitor contexts. The transformation of coconut shells into carbon nanofibers is extensively investigated through various methodologies, highlighting both their benefits and limitations. It becomes evident that the current utilization of coconut shells has not yet achieved optimal sustainability or viability for energy storage purposes. Nevertheless, coconut shells offer a widely available and sustainable resource that can be converted into Activated Carbon nanofibers for energy storage applications. Diverse techniques have been employed to produce these ACB nanofibers, each targeting specific objectives including improved energy density, adaptable diameter, reduced energy consumption, and faster charging times. Despite these accomplishments, it is evident that numerous significant properties of carbon nanofibers derived from coconut shells remain unexplored, leading to substantial knowledge gaps that must be addressed for each technique. Therefore, further research is warranted to advance the comprehension of key parameters associated with various methods, ultimately facilitating the development of highly desirable carbon nanofibers sourced from coconut shells and catering to the requirements of sustainable energy storage applications.

Effect of etchant gases on the structure and properties of carbon nanofibers

The utilization of plasma-enhanced chemical vapor deposition (PECVD) for carbon nanofiber (CNF) growth using NH3 as the etchant gas has been extensively documented. Notably, NH3 serves a dual role by etching excess carbon and providing N heteroatoms. Most studies neglect to address this phenomenon, despite the well-known impact of N-doping on CNF properties. Furthermore, NH3 exhibits specific interactions with C2H2—it not only etches excess carbon, but also suppresses the dissociation of C2H2. The implications of this phenomenon on CNF micro- and macroscale morphology have not been comprehensively investigated. To elucidate the influence of etchant gases on CNF structure and properties, we fabricated two types of CNFs - N-doped CNFs (N-CNF) and undoped CNFs (U-CNF). Both were grown on identical substrates using the same carbon source (C2H2) but different etchants (NH3 and H2). Their microstructure and surface chemistry were analyzed using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Electrochemical properties were investigated using cyclic voltammetry (CV). U-CNFs were found to have a larger population density and a more disordered structure than N-CNFs. N-doping was confirmed in N-CNFs using XPS analysis, which also revealed differences in relative amounts of sp2 C and O functional groups. U-CNFs exhibited distinct electrochemical properties, including smaller pseudocapacitance, larger potential window, slower outer sphere redox (OSR) kinetics, and diminished dopamine sensitivity. Electrochemical differences were rationalized based on CNF structure and surface chemistry, which, in turn, were attributed to how different etchant gases influence the PECVD process.

Effect of metallic copper on the electrothermal properties of carbon nanofibers

Effect of metallic copper on the electrothermal properties of carbon nanofibers

Pore properties of carbon nanofibers fabricated using template method and alkali activation method

Pore properties of carbon nanofibers fabricated using template method and alkali activation method

High-frequency transmission properties of carbon nanofibers with carbonization temperature variations

Carbon nanofibers (CNFs) are promising materials in many fields because they can form multi-purpose matrices of carbon materials and have attractive electric conductivity, dielectric permittivity, thermal stability, and ultrahigh specific surface area. These properties of CNFs significantly depend on the carbonization temperature (CT). Thus, the effect of CT can be primarily crucial for zero- and high-frequency devices and circuits with CNFs. In this study, we report high-frequency transmission properties of the coplanar waveguide line (CPW line) with a CNF film synthesized at CTs of 700 °C, 800 °C, and 900 °C (denoted CNF-700, CNF-800, and CNF-900, respectively) in the frequency ranging from 0.5 to 10 GHz. For all samples, a bare CPW line, a CPW line with a tape, and a CPW line with three kinds of CNF films, the S11 magnitude (reflection coefficient) is less than −10 dB in the frequency range, and the S21 magnitude (transmission coefficient) significantly decreases linearly to −1.3 dB (CNF-700), −3.0 dB (CNF-800), and −5.5 dB (CNF-900) at 10 GHz. Furthermore, the effective permittivity (εeff) of CPW line with CNF films increases with CT, although εeff decreases with increasing frequency. Conversely, due to dielectric and conductive loss of CNF film, the attenuation constant (α) of CPW line with CNF film increases linearly with CTs and frequency. These results indicate that the CPW line with a CNF-900 (CPWCNF-900) shows lossier characteristic than the other CNF films because of finer three-dimensional network structure, higher conductivity, higher attenuation constant, higher shielding effectiveness, and larger effective permittivity. Furthermore, this study shows the possibility that thin CNF films with different CT variations can regulate signal transmission for high-frequency and high-speed circuit and device applications.

New discovery on the role of graphene nanoplates in enhancing the structural and electrical properties of carbon nanofibers

In this study, carbon nanofibers (CNFs) were successfully manufactured from special polyacrylonitrile (SPAN) copolymer/graphene nanoplates (GNPs) via an electrospinning process after that stabilization and carbonization approaches. The carbonization stage for stabilized SPAN/GNPs nanofibers was applied by heating the samples to 900 °C under an N2 inert atmosphere. The relationship of the GNPs concentration with morphological and structural properties of SPAN/GNPs composite nanofibers has been examined. The fineness and crystallinity of composite nanofiber increase with increasing concentration of GNPs from 0 to 4 wt%. With increasing the GNPs concentration in the SPAN/GNPs solutions from 0 to 4 wt%, the average diameter of nanofibers decreased from 480 ± 78 nm to 174 ± 18 nm. All CNFs samples synthesized at 900 °C have acceptable morphological, structural, and electrical properties. Moreover, the microstructure of the SCNFs can be controlled with GNPs concentration in composite nanofibers. The electrical conductivity of CNFs attained from neat nanofibers is 0.25 × 10+4 S/m, which is increased to 1.37 × 10+4 S/m with 4 wt% GNPs. Therefore, the unique 2D structure of GNPs is very suitable for the development of low-cost and conductive CNFs with low temperatures of carbonization.

Hexagonal crystalline nanofillers reinforced composite carbon nanofibers with optimized crystal structure and improved mechanical properties

The mechanical properties of carbon nanofibers (CNFs) are always restricted by their disorganized crystal structures. Herein, this paper utilizes two typical hexagonal crystalline flake materials, nanoscale flake graphite (NG) and hexagonal nitride boron (BN), as nanofillers to optimize the crystal domains of CNFs and achieves enhancement in fiber strength, modulus and toughness. For this purpose, in situ polymerization technique is developed for the rapid and uniform mixing of nanofillers with polyacrylonitrile (PAN) precursors of CNFs. The nanofillers are exfoliated in this process and wrapped with PAN to prevent potential agglomeration. The obtained core-shell nanocomposites can be produced into composite CNFs via electrospinning, stabilization and carbonization. Based on the attraction effect, the dispersed nanofillers can organize PAN molecular chains into oriented crystalline fibrils in as-spun nanofibers and accelerate their transformation to more ladder structures in stabilized nanofibers. On this basis, NG is shown to act as the templating and nucleating agent to promote the formation, growth and compact stacking of graphitic planes in CNFs. BN also improves fiber crystallinity, while its limited templating effect leads to looser and finer crystal domains. As a result, NG-doped CNFs have significantly improved strength and modulus, and BN-doped CNFs possess simultaneously enhanced strength and toughness.

Carbonization-Temperature-Dependent Electrical Properties of Carbon Nanofibers-From Nanoscale to Macroscale.

An exact understanding of the conductivity of individual fibers and their networks is crucial to tailor the overall macroscopic properties of polyacrylonitrile (PAN)-based carbon nanofibers (CNFs). Therefore, microelectrical properties of CNF networks and nanoelectrical properties of individual CNFs, carbonized at temperatures from 600 to 1000 °C, are studied by means of conductive atomic force microscopy (C-AFM). At the microscale, the CNF networks show good electrical interconnections enabling a homogeneously distributed current flow. The network's homogeneity is underlined by the strong correlation of macroscopic conductivities, determined by the four-point-method, and microscopic results. Both, microscopic and macroscopic electrical properties, solely depend on the carbonization temperature and the exact resulting fiber structure. Strikingly, nanoscale high-resolution current maps of individual CNFs reveal a large highly resistive surface fraction, representing a clear limitation. Highly resistive surface domains are either attributed to disordered highly resistive carbon structures at the surface or the absence of electron percolation paths in the bulk volume. With increased carbonization temperature, the conductive surface domains grow in size resulting in a higher conductivity. This work contributes to existing microstructural models of CNFs by extending them by electrical properties, especially electron percolation paths.

Fabrication of Carbon Nanofiber Incorporated with CuWO4 for Sensitive Electrochemical Detection of 4-Nitrotoluene in Water Samples

In the current work, copper tungsten oxide (CuWO4) nanoparticles are incorporated with carbon nanofiber (CNF) to form CNF/CuWO4 nanocomposite through a facile hydrothermal method. The prepared CNF/CuWO4 composite was applied to the electrochemical detection of hazardous organic pollutants of 4-nitrotoluene (4-NT). The well-defined CNF/CuWO4 nanocomposite is used as a modifier of glassy carbon electrode (GCE) to form CuWO4/CNF/GCE electrode for the detection of 4-NT. The physicochemical properties of CNF, CuWO4, and CNF/CuWO4 nanocomposite were examined by various characterization techniques, such as X-ray diffraction studies, field emission scanning electron microscopy, EDX-energy dispersive X-ray microanalysis, and high-resolution transmission electron microscopy. The electrochemical detection of 4-NT was evaluated using cyclic voltammetry (CV) the differential pulse voltammetry detection technique (DPV). The aforementioned CNF, CuWO4, and CNF/CuWO4 materials have better crystallinity with porous nature. The prepared CNF/CuWO4 nanocomposite has better electrocatalytic ability compared to other materials such as CNF, and CuWO4. The CuWO4/CNF/GCE electrode exhibited remarkable sensitivity of 7.258 μA μM−1 cm−2, a low limit of detection of 86.16 nM, and a long linear range of 0.2–100 μM. The CuWO4/CNF/GCE electrode exhibited distinguished selectivity, acceptable stability of about 90%, and well reproducibility. Meanwhile, the GCE/CNF/CuWO4 electrode has been applied to real sample analysis with better recovery results of 91.51 to 97.10%.

Electrospun Carbon Nanofibers and Their Applications in Several Areas.

Carbon nanofibers (CNFs) have a broad spectrum of applications, including sensor manufacturing, electrochemical catalysis, and energy storage. Among different manufacturing methods, electrospinning, due to its simplicity and efficiency, has emerged as one of the most powerful commercial large-scale production techniques. Numerous researchers have been attracted to improving the performance of CNFs and exploring new potential applications. This paper first discusses the working theory of manufacturing electrospun CNFs. Next, the current efforts in upgrading the properties of CNFs, such as pore architecture, anisotropy, electrochemistry, and hydrophilicity, are discussed. The corresponding applications due to the superior performances of CNFs are subsequently elaborated. Finally, the future development of CNFs is discussed.

Hydrothermally reinforcing hydroxyaptatite and bioactive glass on carbon nanofiber scafold for bone tissue engineering.

As a bone tissue engineering scaffold, the objective of this study was to design hierarchical bioceramics based on an electrospun composite of carbon nanofibers (CNF) reinforced with hydroxyapatite (HA) and bioactive glasses (BGs) nanoparticles. The performance of the nanofiber as a scaffold for bone tissue engineering was enhanced by reinforcing it with hydroxyapatite and bioactive glass nanoparticles through a hydrothermal process. The influence of HA and BGs on the morphology and biological properties of carbon nanofibers was examined. The prepared materials were evaluated for cytotoxicity in vitro using the water-soluble tetrazolium salt assay (WST-assay) on Osteoblast-like (MG-63) cells, and oste-ocalcin (OCN), alkaline phosphatase (ALP) activity, total calcium, total protein, and tar-trate-resistant acid phosphatase (TRAcP) were measured. The WST-1, OCN, TRAcP, total calcium, total protein, and ALP activity tests demonstrated that scaffolds reinforced with HA and BGs had excellent in vitro biocompatibility (cell viability and proliferation) and were suitable for repairing damaged bone by stimulating bioactivity and biomarkers of bone cell formation.

Loops at carbon edges: Boron-assisted passivation and tunable surface properties of carbon nanofibers

During thermal treatment of carbon materials, unstable edge sites can easily convert to structurally stable loop structures. Hence, in the present work, carbon edges are physically passivated via high-temperature treatment in the presence of boron atoms to accelerate loop formation. The highly accelerated loop formation, along with stacking multi-layers at the carbon edges, is systematically investigated via high resolution transmission electron micro microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and thermal gravimetric analysis (TGA). The boron-added carbon nanofibers (CNFs) at high temperature exhibit a greatly enhanced electrical conductivity due to the high mobility of boron atoms within the carbon structure. In particular, engineering of the loop structures on the carbon edges can alter the overall electrocatalytic activities of the carbon-based materials, as demonstrated in the reductive conversion of 4-nitrophenol (4-NP) and in the hydrogen evolution reaction (HER). This work not only suggests suitable methods for carbon edge passivation, but also opens up a route towards the advanced design of high-stability carbon materials in various fields.

Capacitive properties of carbon nanofibers derived from blends of cellulose acetate and polyacrylonitrile

In this study, porous carbon nanofibers were producedviathe one-step carbonization and activation of cellulose acetate/polyacrylonitrile (CA/PAN) hybrid nanofibers using electrospinning.

Fe-ZIF-derived hollow porous carbon nanofibers for electromagnetic wave absorption

The nanomaterials with multiple components and various heterogeneous interfaces have been considered as preferred efficient electromagnetic wave (EMW) absorbers. In this paper, Fe atoms were bonded to a zeolitic imidazole framework (Fe-ZIF) and Fe-ZIF-derived hollow porous carbon nanofibers (Fe-HPCNFs) were prepared by the microfluid electrospinning method. The EMW absorption properties of carbon nanofibers (CNFs), Fe-ZIF-derived carbon nanofibers (Fe-CNFs), and Fe-ZIF-derived hollow porous carbon nanofibers (Fe-HPCNFs) were systematically studied. The results showed that Fe-HPCNFs has the best performance, when the thickness was only 2.0 mm, the Fe-HPCNFs achieved a minimum RL loss of −46.9 dB at 17.38 GHz, with an effective absorption bandwidth of 3 GHz. The Fe-HPCNF is a flexible, ultralightweight, self-supported material as a potential high-efficiency EMW absorber.

Self-sensing of pulsed laser ablation in carbon nanofiber-based smart composites

Laser-to-composite interactions are becoming increasingly common in diverse applications such as diagnostics, fabrication and machining, and directed energy weapon systems. These interactions can induce seemingly imperceptible damage to the material. It is therefore desirable to have a means of sensing laser exposure. Smart or self-sensing materials may be a powerful method of addressing this need. Herein, we present a study on the potential of using changes in the electrical properties of carbon nanofiber (CNF)-modified composites as a way of detecting laser exposure and degradation. To test laser sensing capabilities, CNF composite specimens were exposed to an infra-red laser operating at 1064 nm, 35 kHz, and pulse duration of 8 ns for a total of 20 s. The resistances of the specimens were then measured post-ablation, and it was found that for 1.0 wt.% CNFs, the average resistance increased by approximately 18% thereby demonstrating laser sensing capabilities. In order to expand on this result, electrical impedance tomography (EIT) was employed for spatial localization of laser exposures of 1, 3, 5, 10, and 20 s on a larger, plate-like specimens. EIT was not only successful in detecting and localizing exposures, but it could also find laser damages that were virtually imperceptible to the naked eye. Based on these results, this research could lead to the development of novel carbon-based smart material systems for real-time detection and tracking of laser exposure in the measurement, fabrication, and defense industries.

Effects of carbon nanofibers on hydration and geopolymerization of low and high-calcium geopolymers

This paper discusses the different modifying mechanisms of carbon nanofiber (CNF) on the geopolymers with different calcium contents. First, the rheological and mechanical properties of CNF modified geopolymers with low and high-calcium content are measured. Results show that the modifying effect on rheological properties is more obvious on high-calcium geopolymers. The compressive and flexural strength of low-calcium geopolymers decrease, while the compressive and flexural strength of high-calcium geopolymers significantly improve. Based on XRD, MIP, and SEM analyses, it can be concluded that CNFs help to produce refined hydration products in high-calcium geopolymers, resulting in a denser structure. Promoting hydration can counteract the adverse effect caused by the agglomeration of CNFs. CNFs have a positive effect on high-calcium geopolymers in general. However, hydration reaction rarely happens in the low-calcium geopolymers because of the low calcium content, and XRD results show that CNFs do not significantly promote the geopolymerization reaction. Moreover, the agglomeration of CNFs leads to a decrease in compactness. CNFs negatively affect low-calcium geopolymers. Generally, CNFs can be applied in high-calcium geopolymers to form a denser structure and improve the mechanical properties.

Molecular structure effects of mesophase pitch and isotropic pitch on morphology and properties of carbon nanofibers by electrospinning

Carbon nanofibers (CNFs) with high specific surface area and flexible lap structure are highly desirable for numerous applications such as adsorption films, supercapacitors, heat dissipation elements, and composites. In this work, CNFs were prepared using two major categories of pitches, isotropic pitch (IP) and mesophase pitch (MP), as raw materials to compare their molecular structure effects on the morphology and properties of CNFs. The analysis of scanning electron microscopy results found that some fusions among nanofibers easily formed in IP-derived electrospun nanofibers (IP-SNFs) while an independent and smooth nanofiber morphology were observed in MP-derived electrospun nanofibers (MP-SNFs). Besides, composed of high aromatic molecules content and appropriate aliphatic components, MP-SNFs showed a mitigating exothermic reaction and MP-CNFs exhibited higher specific surface area, conductivity and thermal diffusion coefficient. While with too abundant aliphatic components in IP, there was a violent exothermic reaction of IP-SNFs during the stabilization process, endowing the corresponding IP-CNFs with poor performances. Therefore, thermal behavior of SNFs varied with the molecular structure differences of IP and MP, which had a significant influence on the microstructure and properties of their CNFs.

Tensile strain and damage self-sensing of flax FRP laminates using carbon nanofiber conductive network coupled with acoustic emission

The strain and damage self-sensing properties of carbon nanofibers (CNFs)/flax fiber-reinforced polymer (FFRP) laminates under tension were investigated via simultaneously measuring the changes of electrical resistance (ER) and acoustic emission (AE) signals. The piezoresistive mechanisms together with the damage evolution of CNFs/FFRP laminates were also explored. The results revealed that both ER and AE responses to tensile strains in CNFs/FFRP laminates could be segmented into three stages, which confirmed their good damage self-sensing ability. The isochronous and reversible electrical resistance responses to tensile strains proved the stability and repeatability of strain self-sensing capability for CNFs/FFRP laminates. Moreover, in-situ ER measurement is sensitive not only to new damages but also to existing damages, whereas AE signals are only sensitive to new damages. Therefore, adding a small amount of conductive CNFs into non-conductive FFRP laminates could provide an effective strategy to achieve the self-sensing ability in their strain and damage development.

Carbon Nanofibers Based on Potassium Citrate/Polyacrylonitrile for Supercapacitors.

Wearable supercapacitors based on carbon materials have been emerging as an advanced technology for next-generation portable electronic devices with high performance. However, the application of these devices cannot be realized unless suitable flexible power sources are developed. Here, an effective electrospinning method was used to prepare the one-dimensional (1D) and nano-scale carbon fiber membrane based on potassium citrate/polyacrylonitrile (PAN), which exhibited potential applications in supercapacitors. The chemical and physical properties of carbon nanofibers were characterized by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and the Brunnauer–Emmett–Teller method. The fabricated carbon nanofiber membrane illustrates a high specific capacitance of 404 F/g at a current density of 1 A/g. The good electrochemical properties could be attributed to the small diameter and large specific surface area, which promoted a high capacity.