Chemical vapor-deposited carbon nanofibers on carbon fabric for supercapacitor electrode applications

Entangled carbon nanofibers (CNFs) were synthesized on a flexible carbon fabric (CF) via water-assisted chemical vapor deposition at 800°C at atmospheric pressure utilizing iron (Fe) nanoparticles as catalysts, ethylene (C₂H₄) as the precursor gas, and argon (Ar) and hydrogen (H₂) as the carrier gases. Scanning electron microscopy, transmission electron microscopy, and electron dispersive spectroscopy were employed to characterize the morphology and structure of the CNFs. It has been found that the catalyst (Fe) thickness affected the morphology of the CNFs on the CF, resulting in different capacitive behaviors of the CNF/CF electrodes. Two different Fe thicknesses (5 and 10 nm) were studied. The capacitance behaviors of the CNF/CF electrodes were evaluated by cyclic voltammetry measurements. The highest specific capacitance, approximately 140 F g⁻¹, has been obtained in the electrode grown with the 5-nm thickness of Fe. Samples with both Fe thicknesses showed good cycling performance over 2,000 cycles.     

Surface functionalization and characterization of graphitic carbon nanofibers (GCNFs)

The preparation and characterization of herringbone graphitic carbon nanofibers (GCNFs) surface-derivatized with reactive linker molecules derived from four diamines and three triamines is reported. Surface carbon sites of as-prepared GCNFs are oxidized to carboxylic acid groups by nitric acid and covalently bound to seven different linker molecules containing pendant amino groups using carboxylate amidation chemistry. GCNF materials are characterized by TEM, IR, TGA, laser-desorption/ionization (LDI) mass spectrometry, and by elemental analysis. Approximate GCNF/(linker molecule)_x compositions are proposed consistent with acid-uptake and elemental analysis data. Direct evidence for the presence and composition of surface-bound linker molecules is provided by LDI mass spectrometry and by quantitative XPS analysis of trifluoroacetylated derivatives. The reactivity of pendant amino groups present within attached linker molecules is determined quantitatively via Fmoc analysis and synthetically by effecting nucleophilic ring-opening oligomerization of epoxy monomer.     

Electrospun salicylic acid/polyurethane composite nanofibers for biomedical applications

Salicylic acid (SA)/polyurethane (PU) composite nanofiber mats were fabricated by introducing SA in PU solution during the electrospinning process. Cell viability assays showed that the as-prepared composite nanofibers had a good biocompatibility. Further, the composite mats showed good antibacterial performance against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria. Easy fabrication, good mechanical properties, good biocompatibility as well as the antibacterial activity of PU nanofibers containing SA indicated their significant promise for a variety of potential medical applications such as tissue engineering, wound healing, and drug delivery system.     

The effect of the functionalization of carbon nanofibers on their electronic conductivity

The effects of the functionalization of carbon nanofibers (CNFs) on their electronic conductivity, in addition to their physico-chemical properties have been studied. Oxygen surface groups have been created on the surface of three CNFs with different properties, following three oxidation treatments with diverse severity. The oxygen content increased from two to six times the original content, depending on the CNF texture, from 1.5–2.6 wt.% up to 15.1 wt.%. Whereas some important properties are not significantly modified after functionalization (texture, crystalline structure, etc.), other properties like the electronic conductivity are affected depending on the extent of the process. The electronic conductivity of CNFs decreases from 200–350 S m⁻¹ up to 20–100 S m⁻¹ (the precise value depends on carbon crystallinity and compaction degree) when surface oxygen content increases from 1.5 wt.% to 5 wt.%. A further oxidation degree leads to a 90% decrease in conductivity, and in the end can even destroy the original fibrous structure. As a first approach, oxidizing at room temperature with rather strong acid solutions is a better strategy to create functional groups and maintain the electronic conductivity than increasing the process temperature with less severe oxidizing agents.     

Electrocatalytic properties of Pt/carbon composite nanofibers

Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of Pt nanoparticles were controlled by the electrodeposition time. The resulting Pt/carbon composite nanofibers were characterized by running cyclic voltammograms in 0.20 M H₂SO₄ and 5.0 mM K₄[Fe(CN)₆] + 0.10 M KCl solutions. The electrocatalytic activities of Pt/carbon composite nanofibers were measured by the oxidation of methanol. Results show that Pt/carbon composite nanofibers possess the properties of high active surface area and fast electron transfer rate, which lead to a good performance towards the electrocatalytic oxidation of methanol. It is also found that the Pt/carbon nanofiber electrode with a Pt loading of 0.170 mg cm⁻² has the highest activity.     

Micro-Raman investigation of vanadium-oxide coated tubular carbon nanofibers for gas-sensing applications

Commercial tubular carbon nanofibers were uniformly coated with a 5 nm thick vanadium oxide layer via a modified approach to atomic layer deposition. The composition and microstructure of the resulting hybrid material was analyzed by micro-Raman spectroscopy. The effect of the post-synthesis thermal treatment in air at temperatures in the range of 25–375 °C was investigated in order to more deeply understand the behavior of the hybrid material in gas sensing devices. The obtained results demonstrate that the thermal treatment primarily affects the oxide coating-layer that is responsible for the sensing properties. The best sensor performance was obtained at the temperature at which the oxide layered-structure exhibits the highest structural order.     

Degree of functionalization of carbon nanofibers with benzenesulfonic groups in an acid medium

Benzene sulfonic groups have been successfully attached to a carbon nanofiber surface by reaction of diazonium benzenesulfonic salt in sulfuric acid. The extent of the functionalization reaction was determined by X-ray photoelectron spectroscopy, energy dispersive X-ray analysis, elemental analysis, and thermogravimetric analysis complemented with temperature-programmed desorption experiments. Good agreement between the degrees of functionalization provided by these techniques was observed. The results pointed to a higher extent of anchorage of -SO₃H groups when the nanofibers were treated in fuming sulfuric acid, for which a surface S/C (%) atomic ratio of 2.4 was obtained. Raman spectroscopy revealed that the D-band does not fully disappear after CNF treatment, indicating that a certain degree of structural disorder is maintained. However, a decrease in the D-band was observed after the diazotization reaction and this was attributed to the chemical change occurring at the edges. No significant changes to the morphological and textural characteristics of the CNFs by surface treatment were observed. This study may offer an important guideline in the application of CNFs modified with benzenesulfonic groups in polymeric membranes for fuel cells.     

Lignin-based carbon fibers for composite fiber applications

Carbon fibers have been produced for the first time from a commercially available kraft lignin, without any chemical modification, by thermal spinning followed by carbonization. A fusible lignin with excellent spinnability to form a fine filament was produced with a thermal pretreatment under vacuum. Blending the lignin with poly(ethylene oxide) (PEO) further facilitated fiber spinning, but at PEO levels greater than 5%, the blends could not be stabilized without the individual fibers fusing together. Carbon fibers produced had an over-all yield of 45%. The tensile strength and modulus increased with decreasing fiber diameter, and are comparable to those of much smaller diameter carbon fibers produced from phenolated exploded lignins. In view of the mechanical properties, tensile 400–550 MPa and modulus 30–60 GPa, kraft lignin should be further investigated as a precursor for general grade carbon fibers.     

Organic/inorganic composite materials for coating applications

A new organic/inorganic coating material based on the modification of a conventional melamine/polyol system has been developed. Polyhydroxyethylmethacrylate functionalized with alkoxysilane group was mixed with hexamethoxymethylmelamine. Upon heating under an acid catalyzed condition, both sol–gel reaction and melamine/polyol reactions occurred simultaneously, leading to highly crosslinked hybrid composites. The synthesis and characterization of the hybrid materials are reported. The organic/inorganic material was also coated and cured on polycarbonate substrates. The coated/cured samples exhibited excellent optical property. Surface scratch and abrasion resistance of the samples was found better than those of pristine polycarbonate substrate. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1341–1346, 1999     

Antibacterial ciprofloxacin HCl incorporated polyurethane composite nanofibers via electrospinning for biomedical applications

We report on the preparation and characterization of polyurethane (PU) composite nanofibers by electrospinning. Two different approaches were adopted to obtain the PU composite nanofibers. In the first approach, a homogeneous solution of 10 wt% PU containing ciprofloxacin HCl (CipHCl) drug was electrospun to obtain PU/Drug composite nanofibers. And in the second approach, the PU with ciprofloxacin HCl drug and ceramic hydroxyapatite (HA) particles were electrospun to obtain the PU/Drug and PU/Drug/HA composite nanofibers. The surface morphology, structure, bonding configuration, optical and thermal properties of the resultant products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and UV–vis spectroscopy. The antibacterial activity was tested against common food borne pathogenic bacteria, namely, Staphylococcus aureus, Escherichia coli by the minimum inhibitory concentration (MIC) method. Our result results demonstrate that these composite nanofibers possess superior characteristics which can utilized for variety of applications.     

Electrospun gelatin/nylon‐6 composite nanofibers for biomedical applications

We describe the preparation and characterization of gelatin‐containing nylon‐6 electrospun fibers and their potential use as a bioactive scaffold for tissue engineering. The physicochemical properties of gelatin/nylon‐6 composite nanofibers were analyzed using field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, TGA and contact angle and tensile measurements. FE‐SEM and TEM images revealed that the nanofibers were well oriented and showed a good incorporation of gelatin. FTIR spectroscopy and TGA also revealed that there was good interaction between the two polymers at the molecular level. The adhesion, viability and proliferation properties of osteoblast cells on the gelatin/nylon‐6 composite nanofibers were analyzed by an in vitro cell compatibility test. Our results suggest that the incorporation of gelatin can increase the cell compatibility of nylon‐6 and therefore the composite mat obtained has great potential in hard tissue engineering. © 2012 Society of Chemical Industry     

Formation and electrochemical performance of copper/carbon composite nanofibers

Copper-loaded carbon nanofibers are fabricated by thermally treating electrospun Cu(CH₃COO)₂/polyacrylonitrile nanofibers and utilized as an energy-storage material for rechargeable lithium-ion batteries. These composite nanofibers deliver more than 400 mA g⁻¹ reversible capacities at 50 and 100 mA g⁻¹ current densities and also maintain clear fibrous morphology and good structural integrity after 50 charge/discharge cycles. The relatively high capacity and good cycling performance of these composite nanofibers, stemmed from the integrated combination of metallic copper and disordered carbon as well as their unique textures and surface properties, make them a promising electrode candidate for next-generation lithium-ion batteries.     

Preparation of carbon nanofibers/carbon foam monolithic composite from coal liquefaction residue

Carbon nanofibers/carbon foam composites that are made by growing carbon nanofibers (CNFs) on the surface of a carbon foam (CF) have been prepared from coal liquefaction residues (CLR) by a procedure involving supercritical foaming, oxidization, carbonization, and catalytic chemical vapour deposition (CCVD) treatment. These new carbon/carbon composites were examined using SEM, TEM and XRD. The results show that the as-made CF has a structure with cell sizes of 300-600 μm. X-ray diffraction studies show that iron-containing contaminates are present in the CLR. However, these species may act as a catalyst in the CCVD process as established in the literature. After the CCVD treatment, the cell walls of CF are covered by highly compacted CNFs that have external diameters of about 100 nm and lengths of several tens of micrometers. This work may open a new way for direct and effective utilization of the CLR.     

Synthesis, functionalization and bioimaging applications of highly fluorescent carbon nanoparticles

Highly fluorescent crystalline carbon nanoparticles (CNPs) have been synthesized by one step microwave irradiation of sucrose with phosphoric acid at 100 W for 3 min 40 s. This method is very simple, rapid and economical and hence can be used for large scale applications. The average particle sizes are 3 to 10 nm and they emit bright green fluorescence under the irradiation of UV-light. Therefore, the particles can be used as a unique material for bioimaging as well as drug delivery. To further increase the fluorescence property of the synthetic carbon nanoparticles we simply functionalized them by using different organic dyes, such as fluorescein, rhodamine B and α-naphthylamine; the maximum fluorescence intensity was observed for the particles functionalized with fluorescein. It is very interesting to note that all of those compounds show maximum fluorescence intensity at 225 nm excitation wavelength and for any excitation wavelength the peak positions are exactly same the position as that of CNPs itself, which is completely different from the individual precursors (dyes). All of the above compounds, including CNPs, have also been successfully introduced into the erythrocyte enriched fraction of healthy human blood cells with minimum cytotoxicity.     

纳米碳纤维的微观结构调控与催化作用

纳米碳纤维（CNF）是一种新型一维结构纳米炭材料,因其具有许多独特的性质而备受研究者关注。按照CNF基本结构单元石墨片层与生长轴的夹角不同,可以将CNF分为板式、鱼骨式和管式3种不同微观结构。采用催化化学气相沉积法合成CNF时,微观结构可以通过改变生长动力学进行调控。CNF微观结构的不同导致表面棱边与基面原子比例不同,进而影响着表面含氧基团分布等性质。当CNF用作催化剂载体时,利用这些性质的不同可以调控负载金属颗粒的形貌以及载体与金属作用力等性质,从而改变催化剂的性能。CNF自身具有催化活性,其活性主要来自表面杂原子基团,因此也与CNF的微观结构密切相关。     

Evidence of sidewall covalent functionalization of single-walled carbon nanotubes and its advantages for composite processing

Single-walled carbon nanotubes (SWCNTs) were functionalized in a three-step procedure. The first step is a radical reaction creating a covalent bond between the carbon nanotube surface and grafted p-methoxyphenyl functional groups. In a second step, a deprotection of the methoxy functions generates free alcohol groups and in the final step an esterification is done in order to install a double bond for further polymerization. Evidence that functionalization has actually occurred on the SWCNT sidewalls is furnished through investigations involving several complementary techniques (visual dispersion tests, transmission electron microscopy, thermal gravimetric analysis and adsorption volumetry). We show that surface properties of SWCNTs are changed throughout the chemical treatments and that the obtained level of functionalization is low. Incorporation of functionalized SWCNTs in a polymer (poly(methyl methacrylate)) matrix was done through an in situ polymerization process. Observations of the obtained composites using scanning and transmission electron microscopy illustrate that interactions between the SWCNT surface and the polymer matrix are improved.     

Electrospun polymeric nanofibers for dental applications

Electrospinning is an economical, efficient, and versatile process for the preparation of continuous nanofibers with desired patterns, tailored fiber diameters, and orientations. Since its invention, electrospinning has been utilized to prepare nanofibers from several natural polymers and synthetic polymers for use as scaffolds in tissue engineering, regeneration, and biomedical applications. Furthermore, complex scaffolds were prepared by electrospinning complex polymer solutions formulated by blending natural and synthetic organic polymers with bioceramics and other inorganic molecules. Lately, coaxial electrospinning has emerged as a promising technology in the preparation of drug-loaded biodegradable core-shell structured micro/nanofibers for sustained drug delivery applications. This paper will discuss the basic mechanism of electrospinning, parameters governing the electrospinning process, various materials investigated for use in the electrospinning process, and its recent advances.     

Surface functionalization of polymer nanofibers by ITO sputter coating

In this study, transparent conductive films of tin-doped indium oxide (ITO) were deposited onto the polyamide 6 (PA6) nanofiber substrates at room temperature. Atomic force microscopy (AFM) was employed to study the morphology of the nanofibers, respectively. The AFM results indicated a significant change in the morphology of the nanofibers before and after the ITO sputter coatings. The light transmittance and surface conductivity of the ITO-deposited nanofibers were also investigated. It was found that the surface resistivity of the PA6 nanofiber with the ITO deposition had a significant drop and the ITO deposition obviously affected the light transmittance of the PA6 nanofibers.     

Electrospun porous carbon nanofibers/TiO2 composite coated over carbon cloth- A flexible electrode for capacitive deionization

The combination of porous carbon matrix and metal oxide is trending for capacitive deionization (CDI) due to their synergistic electrochemical behaviour and properties. In this research, a flexible electrode based on electrospun porous carbon nanofibers and TiO₂ nanoparticles (particle size ～7 nm) i.e., PCNFs/TiO₂ composite coated over carbon cloth is developed. A facile in-situ activation procedure using sacrificial polymer is adopted over typical chemical activation treatment to synthesize PCNFs/TiO₂ composite. PCNFs/TiO₂ composite is prepared in two steps, possessing a high specific surface area of ～343 m² g^?1 and pore volume of 0.038 cm³ g^?1. Interestingly, CDI unit assembled with PCNFs/TiO₂ composite based flexible electrodes delivers the large salt electrosorption capacity of 204.8 mg g^?1 at voltage 1.2 V in a salt solution of concentration 500 ppm and conductivity 880 μS cm^?1. The excellent adsorption capacity retention of 96.4% up to ten adsorption-regeneration cycles can be a tempting option for future flexible CDI applications.