PAN-based Carbon Nanofibers Research Articles

Preparation of Platinum Catalyst Supported on Porous Carbon Nanofibers

Low-temperature fuel cells have been attracting more and more attentions for the direct conversion of chemical energy into electricity. Efficiencies of fuel cells to a great extent depend on the activity of the catalytic platinum and its alloys. Increasing the reaction surface area and decreasing the diameter of platinum particles can enhance the activity of the platinum. In this paper, we report a platinum catalyst supported on porous carbon nanofibers. Two kinds of PAN terpolymers with various molecular weights of 15 kDa (PAN-1) and 30 kDa (PAN-2) were first prepared by aqueous precipitation polymerization. The mixtures of PAN with various molecular weights and PMMA were then electrospun, stabilized and carbonized to provide the porous carbon nanofibers. It was found that the PAN with lower molecular weight results in the even fibrous surface and thick diameter, indicating a stable spinning process. Moreover, the PAN-based carbon nanofibers were immersed into a platinum complex solution to support the platinum positive ions. After calcination, the platinum ions deposited on the carbon nanofibers were converted into nanoplatinum particles to provide the platinum catalyst supported on the porous carbon nanofibers.

Improved bioactivity of PAN-based carbon nanofibers decorated with bioglass nanoparticles

Composite nanofibers composed of polyacrylonitrile (PAN)-based carbon nanofibers and bioactive glass (BG) nanoparticles have been prepared by electrospinning and in situ sintering. Morphology observation showed that the BG nanoparticles of size 20–50 nm were uniformly distributed on the surface of composite nanofibers with 350 nm average diameter after carbonization. Biological mineralization indicated the formation of apatite-like layer on the surface of composite nanofibers, in which the composition of carbonate hydroxyapatite was proved by FTIR and XRD analysis. Cell growth dynamics according to cellular morphology, CCK-8 assay, and alkaline phosphatase activity assay exhibited better cell adhesion, proliferation, and osteogenic induction of bone marrow-derived mesenchymal stem cells cultured on the composite nanofibers, which suggested the higher bioactivity of composite nanofibers compared to pure PAN-based carbon nanofibers.

Solution blowing of continuous carbon nanofiber yarn and its electrochemical performance for supercapacitors

A facile spinning-based process was presented as a new method to fabricate continuous nanofiber yarn. In this process, a funnel-like nanofiber net with aligned structure was formed to collect nanofibers and the net was twisted and attenuated to the nanofiber yarn. The morphologies and structures of the prepared polyacrylonitrile (PAN) nanofiber yarn and PAN-based carbon nanofiber yarn (CNFY) were examined. The PAN and carbon nanofibers were well aligned, with average diameters of 231 and 136nm, respectively. The electrochemical properties of CNFY were studied. The results showed that CNFY possessed high conductivity, mass specific capacitance (15.8Fg−1 at the current density of 2Ag−1) and extremely excellent cycling performance at high current density (only 8.8% capacitance loss after 1200 cycles at a high rate of 2Ag−1), which imply the potential application of CNFY as a novel electrode for supercapacitors.

A review: carbon nanofibers from electrospun polyacrylonitrile and their applications

Carbon nanofibers with diameters that fall into submicron and nanometer range have attracted growing attention in recent years due to their superior chemical, electrical, and mechanical properties in combination with their unique 1D nanostructures. Unlike catalytic synthesis, electrospinning polyacrylonitrile (PAN) followed by stabilization and carbonization has become a straightforward and convenient route to make continuous carbon nanofibers. This paper is a comprehensive and state-of-the-art review of the latest advances made in development and application of electrospun PAN-based carbon nanofibers. Our goal is to demonstrate an objective and overall picture of current research work on both functional carbon nanofibers and high-strength carbon nanofibers from the viewpoint of a materials scientist. Strategies to make a variety of carbon nanofibrous materials for energy conversion and storage, catalysis, sensor, adsorption/separation, and biomedical applications as well as attempts to achieve high-strength carbon nanofibers are addressed.

PAN-based carbon nanofiber absorbents prepared using electrospinning

This study takes polyacrylonitrile (PAN) as a raw material for PAN-based nanofiber nonwoven prepared using electrospinning. First we construct a thermal-stable process for the fabrication of oxidized nanofiber nonwovens as the precursor. A semi-open high-temperature erect furnace is then used with steam as the activator, through carbonization and activation processes to prepare carbon nanofiber absorbents continuously. The experiment varies the production rate and activator flow rate to prepare carbon nanofiber absorbents. Experimental results show that carbon nanofiber adsorbents are primarily made up of micropores and mesopores, averaging under 20 A. Given a production rate of 10–20 cm/min with a matching activator feed rate of 120 ml/min, the specific surface area can reach about 1000 m2/g, producing an adsorption ratio of carbon tetrachloride over 200 %.

PAN Based Carbon Nanofibers as an Active ORR Catalyst for DMFC

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Structure and Morphological Evolvement of Electrospun Polyacrylonitrile/Organic–Modified Fe-Montmorillonite Composite Carbon Nanofibers

In the present work, a facile compounding and electrospinning method was used to prepare PAN/Fe-OMT composite nanofibers. Electrospinning solution properties including viscosity, surface tension, and conductivity were measured and combined with the results of Fourier transform-infrared (FT-IR) spectra, high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM) to investigate the effects of Fe-OMT on the structure and morphology of electrospun PAN nanofibers, respectively. It was found from FT-IR and HRTEM that the silicate clay layers were well dispersed within the composite nanofibers and were oriented along the fiber axis. The SEM images indicated that the loading of Fe-OMT decreased the average diameters of composite nanofibers due to the increased conductivity of composite solutions. Then, the prepared PAN nanofibers and PAN/Fe-OMT composite nanofibers were further pre-oxidized and carbonized. The effects of Fe-OMT on the structure and morphology of PAN-based carbon nanofibers were also investigated by FT-IR and SEM. The FT-IR spectra indicated that there were different characteristic absorption peaks for pure PAN nanofibers and PAN/Fe-OMT composite nanofibers during the pre-oxidation and carbonization processes. The SEM images revealed that the morphology of nanofibers underwent marked changes before and after carbonization. The Fe-OMT loadings might promote the dehydrogenation, cyclization, and cross-linking reactions of the PAN composite nanofibers during carbonization.

Reticular Sn nanoparticle-dispersed PAN-based carbon nanofibers for anode material in rechargeable lithium-ion batteries

Reticular tin nanoparticle-dispersed carbon (Sn/C) nanofibers were fabricated by stabilization of electrospun SnCl 4/PAN composite fibers and subsequent carbonization at different temperatures. These Sn/C composite nanofibers used as anode materials for rechargeable lithium-ion batteries (LIBs) show that the Sn/C nanofibers at 700 and 850 °C present much higher charge (785.8 and 811 mA h g − 1) and discharge (1211.7 and 993 mA h g − 1) capacities than those at 550 and 1000 °C and the as-received CNFs at 850 °C, corresponding to coulombic efficiencies of 64.9% and 81.7%, respectively. The superior electrochemical properties of the intriguing Sn/C nanofibers indicate a promising application in high performance Li-ion batteries.

Hydrogen Adsorption of PAN-based Porous Carbon Nanofibers using MgO as the Substrate

In this study, porous electrospun carbon fibers were prepared by electrospinning with PAN and <TEX>$MgCl_2$</TEX>, as a MgO precursor. MgO was selected as a substrate because of its chemical and thermal stability, no reaction with carbon, and ease of removal after carbonization by dissolving out in acidic solutions. <TEX>$MgCl_2$</TEX> was mixed with polyacrylonitrile (PAN) solution as a precursor of MgO with various weight ratios of <TEX>$MgCl_2$</TEX>/PAN. The average diameter of porous electrospun carbon fibers increased from 1.3 to 3 <TEX>${\mu}m$</TEX>, as the <TEX>$MgCl_2$</TEX> to PAN weight ratio increased. During the stabilization step, <TEX>$MgCl_2$</TEX> was hydrolyzed to MgOHCl by heat treatment. At elevated temperature of 823 K for carbonization step, MgOHCl was decomposed to MgO. Specific surface area and pore structure of prepared electrospun carbon fibers were decided by weight ratio of <TEX>$MgCl_2$</TEX>/PAN. The amount of hydrogen storage increased with increase of specific surface area and micropore volume of prepared electrospun carbon fibers.

Growth of carbon nanostructures on carbonized electrospun nanofibers with palladiumnanoparticles

This paper studies the mechanism of the formation of carbon nanostructureson carbon nanofibers with Pd nanoparticles by using different carbonsources. The carbon nanofibers with Pd nanoparticles were produced bycarbonizing electrospun polyacrylonitrile (PAN) nanofibers includingPd(Ac)2. Such PAN-based carbon nanofibers were then used as substrates to grow hierarchicalcarbon nanostructures. Toluene, pyridine and chlorobenzine were employed as carbonsources for the carbon nanostructures. With the Pd nanoparticles embedded in thecarbonized PAN nanofibers acting as catalysts, molecules of toluene, pyridine orchlorobenzine were decomposed into carbon species which were dissolved into the Pdnanoparticles and consequently grew into straight carbon nanotubes, Y-shaped carbonnanotubes or carbon nano-ribbons on the carbon nanofiber substrates. X-ray diffractionanalysis and transmission electron microscopy (TEM) were utilized to capture themechanism of formation of Pd nanoparticles, regular carbon nanotubes, Y-shapedcarbon nanotubes and carbon nano-ribbons. It was observed that the Y-shapedcarbon nanotubes and carbon nano-ribbons were formed on carbonized PANnanofibers containing Pd-nanoparticle catalyst, and the carbon sources playeda crucial role in the formation of different hierarchical carbon nanostructures.

Preparation of PAN-based carbon nanofibers by hot-stretching

Partially aligned and oriented polyacrylonitrile (PAN) nanofibers were electrospun from PAN solution in dimethylformamide (DMF) for the preparation of carbon nanofibers. The as-spun polyacrylonitrile nanofibers were hot-stretched by weighing metal in a temperature controlled oven to improve its crystallinity and molecular orientation. Then they were stabilized at 250°C under stress, and carbonized at 1000°C in N2 atmosphere by fixing the length of the stabilized nanofibers to convert them into carbon nanofibers. The result showed that the average diameter of the carbon nanofibers was 140 nm. The degree of crystallinity of the stretched fibers confirmed by X-ray diffraction analysis was enhanced 4-fold in comparison with that of as-spun fibers. The improved fiber alignment and crystallinity resulted in the increased modulus and tensile strength of the nanofibers as much as 5.7-fold and 4.7-fold, respectively. The modulus and tensile strength the of carbon nanofiber increased up to 2243 ± 120 MPa and 170 ± 15.8 GPa, respectively. Thus, the hot-stretched nanofiber can be used as a potential precursor to produce high-performance carbon composites.

A Study on Electrical Resistivity Behaviors of PAN-based Carbon Nanofiber Webs

The influences of various carbonization temperatures on electrical resistivity and morphologies of polyacrylonitrile (PAN)-based nanofiber webs were studied. The diameter size distribution and morphologies of the nanofiber webs were observed by a scanning electron microscope. The electrical resistivity behaviors of the webs were evaluated by a volume resistivity tester. From the results, the volume resistivity of the carbon webs was ranged from <TEX>$5.1{\times}10^{-1}\;{\Omega}{\cdot}cm$</TEX> to <TEX>$3.0{\times}10^{-2}\;{\Omega}{\cdot}cm$</TEX>, and the average diameter of the fiber webs was varied in the range of 310 to 160 nm with increasing the carbonization temperature. These results could be explained that the graphitic region of carbon webs was formed after carbonization at high temperatures. And the amorphous structure of polymeric fiber webs was significantly changed to the graphitic crystalline, resulting in shrinking the size of fiber diameters.

Raman spectroscopic evaluation of polyacrylonitrile‐based carbon nanofibers prepared by electrospinning

AbstractPoly(acrylonitrile) (PAN) solutions in N,N‐dimethylformamide were electrospun into webs consisting of 350 nm ultra‐fine fibers. The webs were oxidatively stabilized and followed by heat treatment in the range of 700–1000°C. Characterization of the microstructure of PAN‐based carbon nanofibers was performed by x‐ray diffraction, field‐emission scanning electron microscopy, electrical conductivity and Raman spectroscopy. The Lc(002) and La(10) values were calculated to be 1.85–2.15 and 2.23–3.36 nm, respectively. The Lc(002) and La(10) values increased by about 86% and 66%, respectively, when the heat treatment temperature (HTT) was increased from 700 to 1000°C. The electrical conductivity of carbonized PAN nanofiber webs increased with increasing carbonization temperature, being 6.8 × 10−3 and 1.96 S cm−1 at 700 and 1000°C, respectively. The D and G bands from Raman scattering were fitted into a Gaussian–Lorentzian hybridized function, and the crystallite sizes in the nanofibers were evaluated from the R‐values determined from the ratios of the intensity of the G band to that of the D band. The domain size of the graphitic layers was in the range 1.6–3.2 nm with higher values at higher HTT. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Cabon Nanofibrous Materials Prepared from Electrospun Polyacrylonitrile Nanofibers for Hydrogen Storage

ABSTRACTElectrospun PAN nanofibers were carbonized with or without iron(III) acetylacetonate to induce catalytic graphitization within the range of 900–1500°C, resulting in ultrafine carbon fibers with the diameter of about 90–300 nm. The structural properties and morphologies of the resulting carbon nanofibers were investigated using XRD, Raman IR, SEM, TEM, and surface area/pore analysis. The PAN-based carbon nanofibers carbonized without a catalyst had amorphous structures, with d002 = 0.37 nm, and smooth surfaces with very low surface areas of 22–31 m2/g. The carbonization of PAN-based nanofibers in the presence of the catalyst produced the graphite nanofibers (GNF) with d002 = 0.341 nm, indicating turbostrate structures. The graphite structures were grown by increasing the catalyst contents and the carbonization temperature. The hydrogen storage capacities of the aforementioned carbon nanofiber materials were evaluated through the gravimetric method using Magnetic Suspension Balance (MSB) at room temperature and at 100 bars. The storage data were obtained after the buoyancy correction. The CNFs showed hydrogen storage capacities of 0.16–0.50 wt.%, increasing with the increase of carbonization temperature, but that of the CNF at 1500°C was lowest. The hydrogen storage capacities of the GNFs with low surface areas of 100–250m2/g were 0.14–1.01 wt%.

Conductivity measurement of electrospun PAN-based carbon nanofiber

Although electrostatic generation, or electrospinning, of ultrafine fibers was invented as early as in 1930s [1], the technique has been used to produce conductive polymer fibers only recently [2]. Reneker and Chun et al. [3] electrospun polyaniline fibers from sulfuric acid into a coagulation bath. Chun et al. [4] electrospun polyacrylonitrile (PAN) nanofibers, and pyrolyzed them into carbon nanofibers. Because of their obvious high specific surface area, electrospun ultrafine fibers are expected to be used as high performance filters, or scaffolds in tissue engineering [5]. For the same reason, one may expect that chemisorbed gases may modulate the electrical conductivity, leading to the fabrication of sensor devices. Unfortunately, the electrical transport properties of these electrodeposited materials have caught the interest of few researchers except for Norris et al. [5], who used the indirect four-point probe method to measure the conductivity of the electrospun non-woven ultra-fiber mat of polyaniline doped with camphorsulfonic acid blended with polyethylene oxide (PEO). As the non-woven mat is highly porous and the “fill factor” of the fibers is less than that of a cast film, the measured conductivity tends to be lower than that of bulk [5]. In this paper, a direct method is used to measure the I -V curve and conductivity of the electrospun PAN-based carbon nanofibers. Commercial PAN powder and N,N-Dimethyl Formamide (DMF), in a ratio of 600 mg PAN to 10−5 m3 DMF, were used to prepare a solution. This mixture was vigorously stirred by an electromagnetically driven magnet at room temperature before it became a homogeneous polymer solution. The electrospinning was conducted in a homemade setup shown in Fig. 1. The DC power supply was an ES30-0.1P Model HV