Morphology Of Carbon Nanofibers Research Articles

Flexible centrifugally spun PVP based SnO2@carbon nanofiber electrodes

Sodium-ion batteries (SIBs) have attracted significant attention because of the abundant resource and low-cost of sodium. Furthermore, flexible and wearable functional electronics have been presented as one of the most important emerging technology. Carbon nanofibers are promising candidates for flexible electrodes due to their high electronic conductivity and high surface area, while it is vital to use non-petroleum-based polymers considering environmental concerns. Developing flexible nanostructured electrodes by using environment friendly polymers with a fast and low-cost technique is critical to develop high performance flexible electronics. Electrochemical properties are influenced by the morphology and average fiber diameters of nanofibers. In this study, poly(vinylpyrrolidone) (PVP) solutions with various concentrations and two different solvent systems (ethanol/water and ethanol/dimethylformamide) were successfully spun into nanofibers by the fast, safe, low-cost, and environment friendly technique of centrifugal spinning. The effect of solvent system and solution concentration was investigated by using scanning electron microscopy images, and the average fiber diameters varied from 436 nm to 3 µm. Moreover, nine different heat treatments were studied, and the effect of time and temperature during stabilization and carbonization on the morphology of carbon nanofibers (CNFs) was investigated. Furthermore, flexible carbon nanofibers were fabricated and used as binder-free anodes in sodium-ion batteries. In order to enhance the electrochemical properties of flexible CNFs, flexible SnO2@CNFs were fabricated by combining centrifugal spinning and heat treatment. The electrochemical performance of the flexible SnO2@carbon nanofiber anodes was evaluated by conducting galvanostatic charge/discharge tests and cycling voltammetry. A high rate of performance was also presented. The high reversible capacity of 400 mA h/g was delivered when flexible centrifugally spun PVP based SnO2@carbon nanofiber electrodes were used in SIBs.

An experimental and theoretical approach to organic functionalization of carbon nanofibers using fresh neem leaves

Carbon nanofibers (CNF) are state-of-the-art materials that have been actively explored for several applications. In this study, we have given organic functionalization treatment to CNF using fresh neem leaves (FNL) following a simple ultrasonication methodology. The effects of dispersion treatment (using Triton X-100) on the functionalization of CNF are also investigated. The samples are characterized via FESEM, EDX, XPS, XRD, CHNS, XRF, and FTIR studies. The FESEM and XRD analyses confirm that the CNF morphology remains intact upon organic treatment. The EDX, XRF, CHNS, and FTIR studies reveal the functionalization of CNF with several heteroatoms (N: 7.41 at.%, O: 4.38 at.%, S: 0.027 at.%, P: 0.42 at.%, etc.), and nutrients present in the FNL. The electrocatalytic activity of the modified CNF is tested via cyclic voltammetry and linear sweep voltammetry studies in 0.1 M KOH electrolyte. The onset potential is −0.018 V, the half-wave potential is −0.35 V, and the limiting current density is 3.26 mA/cm2 for this sample. The oxygen reduction at FNL modified-CNF occurs via a four-electron pathway (n = 3.76) in the alkaline medium. The direct functionalization treatment of CNF is more effective for the observed intermolecular charge interactions between CNF and the FNL extract, however, the Triton X-100 coating on CNF acts as a mask to suppress these interactions. The simulation studies reveal that the upper and edge sites in the cup-stacked CNF are most active for ORR catalysis. It includes a detailed interaction study of the CNF-alanine molecule, which could be beneficial for designing novel biosensors.

Electrochemical Sensing of 1-hydroxypyrene on a Colloidal Gold Modified Zeolitic Imidazolate Frameworks-67/Carbon Nanofiber Paste Electrode

Urinary 1-hydroxypyrene (1-OHP) is generally used as an exposure biomarker of polycyclic aromatic hydrocarbons (PAHs). In this work, a colloidal gold modified zeolitic imidazolate frameworks-67/carbon nanofiber paste electrode (Au@ZIF-67/CNFPE) was fabricated for the rapid and sensitive detection of 1-OHP. The morphologies of carbon nanofibers (CNF), ZIF-67, colloidal gold and colloidal gold@ZIF-67 (Au@ZIF-67) were studied by transmission electron microscopy (TEM). The electrochemical behavior of 1-OHP was investigated by square wave voltammetry (SWV). The effect factors like pH value, amount of colloidal gold, accumulation potential and accumulation time have been optimized. Under the optimal conditions, the constructed sensor responded to 1-OHP linearly in the concentration range of 0.0005–10 μM, and the detection limit was 0.1 nM. The reproducibility, stability and selectivity of this sensor were also examined. Finally, the electrode was successfully applied for the analysis of 1-OHP in human urine samples.

Carbon nanofibers grown on carbon fibers by chemical vapor deposition using the iron catalyst

Carbon nanofibers (CNFs) were synthesized by the catalytic chemical vapour deposition (CCVD) process using iron catalyst below the iron-carbon eutetic temperature (1147 oC). CNFs were formed on carbon fibers as substrates at the growth temperatures of 750, 800, and 850 oC. The effect of processing temperature on the formation and the morphology of CNFs was studied. Moreover, the effect of composition of gase mixture (C2H4, H2, and Ar) on the morphology of CNFs was also performed. The morphology and microstructure of as-obtained CNFs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED). Results revealed that temperature and gas composition play an important role in forming of CNFs.

One-step synthesis of carbon nanotubes with secondary growth of carbon nanofibers: effect of chlorine, synthesis time and temperature

Applications of carbon nanotubes (CNTs) in nanoscale electronic, filtration and adsorption platforms, requires the production of a high density network structure of the CNTs, which are intermeshed and/or chemically connected to each other. Strong network structures can be created if a stable connection is established through cross-linked CNTs. In a previous preliminary study, we reported the secondary growth of carbon nanofibers (CNFs) that grew on top of the CNTs during the CNT synthesis through decomposition of 1,2-dichlorobenzene (DCB). In the current study, we studied in detail the effect of synthesis time and temperature on the secondary growth of CNFs on CNTs as well as the morphology of CNFs that were grown. The amount of CNFs that grew onto the main CNTs increased with an increase in the synthesis time for reactions performed at 60 and 90 min but decreased with a 120 min growth time. It is proposed that decomposition of the DCB let to Cl/carbon radicals that either (i) eroded the CNT surface or (ii) deposited on the CNT surface, depending on the synthesis parameters. The CNFs grew at defective sites of the CNT walls. A synthesis temperature of 700 °C and synthesis time of 90 min were the growth conditions that resulted in the highest formation of the CNFs, presumably due to formation of defects that were uncovered by carbon deposition and allowed for the secondary growth of CNFs. The types of defects created were identified as on-site defects in the graphene sheet by Raman spectroscopy. All other studied synthesis temperatures (i.e. 600, 650, and 750) were unfavorable for growth of secondary CNFs.

Electrospun carbon nanofiber-based electrochemical biosensor for the detection of hepatitis B virus

The purpose of this work was to design the electrochemical DNA biosensor based on carbon nanofibers (CNFs) for detecting hepatitis B virus (HBV). The CNFs, due to high conductivity and surface-to-volume ratio, was known as an effective material in the electrochemical biosensor. In this work, we directly used electrospun CNF as the electrode. CNF electrode was modified with electropolymerized glutamic acid (Glu). Then, the probe DNA (pDNA) was conjugated to Glu modified CNFs electrode. The surface morphology of CNFs and Glu modified CNFs were characterized via scanning electron microscopy (SEM). Electropolymerized Glu on the surface of CNF electrode was characterized by Fourier transform infrared spectroscopy (FTIR) as well. The cyclic voltammetry (CV) was used to monitor the target DNA (tDNA). The tDNA was quantified at a linear range from 1 × 10-12 to 1 × 10-6 M with a detection limit of 1.58 × 10-12 M. This electrochemical HBV biosensor had good stability, repeatability, and selectivity for distinguishing complementary DNA from non-complementary and mis-matched DNA sequences.

Electrospun carbon nanofiber-based composites for lithium-ion batteries: Structure optimization towards high performance

Carbon nanofibers (CNFs) have witnessed extensive application in lithium-ion batteries (LIBs) over the last decade. CNFs are characterized by its one-dimensional nanosized structure and excellent mechanical and electrical properties. They are desirably assembled into porous, flexible and robust platforms, on which a variety of anode and cathode active materials are loaded resulting in a promising family of LIB electrodes. Structures of the as-fabricated CNF-based composites have been verified to be of great importance to electrochemical performance. Therefore, this review aims at elaborating the relation between the structures and the electrochemical performance of CNF-based composites. Specifically, the review is sectioned by the morphology of CNFs, i.e., solid, porous and hollow, the type of active materials and the morphology of active materials. In addition, some thoughts for future progress are provided. • A comprehensive collection of carbon nanofiber-based composites for lithium-ion batteries. • A deep insight into the relation between structures and electrochemical performance of carbon nanofiber-based composites. • Constructive suggestions on a route toward high electrochemical performance for carbon nanofiber-based composites.

The Influences of Chemical and Mechanical Treatment on the Morphology of Carbon Nanofibers

Oxidation by acid treatment is one of the chemical methods used to introduce surface oxygen functional group (SOFG) and defects on the surface of carbon nanofibers (CNFs). Therefore, many researchers used this method to improve the dispersion ability of CNFs in aqueous media. However, only few researchers used combination of chemical and mechanical method for oxidation of CNFs. In this work, as-received CNFs were treated using chemical method with an addition of mechanical method. On the first experiment (Method A) concentrated sulphuric acid and nitric acid were used and followed by combinations of mechanical method using ultrasonication water bath under reflux. The addition mechanical method through reflux was eliminated and different times of ultrasonication were used in method B and method C. Outer diameter of each CNFs samples were determined from FESEM images and were found to be in range of 50 nm–190 nm. Whereas, Raman spectroscopy was used to analyse any structural defects of CNFs samples during each treatment methods. From the findings, acid treatment of CNFs with addition of mechanical method using ultrasonication showed remarkably effect on the CNFs morphology.

The Differentiation of Human Endometrial Stem Cells into Neuron-Like Cells on Electrospun PAN-Derived Carbon Nanofibers with Random and Aligned Topographies.

Electrospun carbon nanofibers (CNFs) have great potential for applications in neural tissue regeneration due to their electrical conductivity, biocompatibility, and morphological similarity to natural extracellular matrix. In this study, we cultured human endometrial stem cells (hEnSCs) on electrospun CNFs with random and aligned topographies and demonstrated that hEnSCs could attach, proliferate, and differentiate into neural cells on both random and aligned CNFs. However, the proliferation, differentiation, and morphology of cells were affected by CNF morphology. Under the proliferative condition, hEnSCs showed lower proliferation on aligned CNFs than on random CNFs and on tissue culture plate (TCP) control. When cultured on aligned CNFs in neural induction media, hEnSCs showed significant upregulation of neuronal markers, NF-H and Tuj-1, and downregulation of neural progenitor marker (nestin) compared to that on random CNFs and on TCP. In contrast, hEnSCs showed higher expression of nestin and slight upregulation of oligodendrocyte marker (OLIG-2) on random CNFs compared to that on aligned CNFs and on TCP. SEM imaging revealed that differentiated cells extended along the CNF main axis on aligned CNFs but stretched multidirectionally on random CNFs. These findings suggest electrospun CNFs as proper substrate for stem cell differentiation into specific neural cells.

Direct growth of carbon nanofibers on carbon-based substrates as integrated gas diffusion and catalyst layer for polymer electrolyte fuel cells

One-dimensional carbon nanostructures are considered promising for application as catalyst support in polymer electrolyte fuel cells, replacing the most widely used carbon black, due to their physico-chemical properties and high surface area. Different morphologies of carbon nanofibers, by varying the graphene layers orientation with respect to the fibre axis, exhibit different amount of available open edges that can act as anchorage site for catalyst nanoparticles. CNF are grown on graphite paper by a controlled plasma enhanced chemical vapour deposition and then used as substrates for Pt electrodeposition. The CNF direct growth on carbon paper allows having single layer electrodes with both diffusive and catalytic layer function. Moreover, the replacement of conventional ink deposition methods with electrodeposition for platinum dispersion, allows greatly reducing the catalyst load, increasing at the same time its utilization and performance. The innovative electrodes are characterized by field emission gun scanning electron microscopy and X-ray photoelectron spectroscopy to assess the morphological properties, and by cyclic voltammetry in H2SO4 and H2SO4 + CH3OH to determine the electrocatalytic activity and long term stability. The comparison with an electrode made of conventionally deposited Pt catalyst by ink method on commercial carbon black shows better performance for the developed Pt/CNF electrodes.

Template-Assisted Synthesis and Catalytic Property of Copper Nanowires

Porous anodic aluminum (PAA) templates with uniform diameter pores were prepared by two step anodic oxidation method. The resultant PAA was characterized using field emission scanning electron microscopy (FESEM), and the preparation parameters of PAA templates were investigated. The barrier of PAA was dissolved by electrolyzing neutral solutions with PAA as a cathode and carbon electrode as an anode. Copper nanowires were synthesized with PAA templates by direct current electrodeposition. The resultant copper nanowires were characterized using FESEM. Carbon nanofibers were synthesized by using acetylene as carbon source and copper nanowires as catalysts through chemical vapor deposition. The morphology of carbon nanofibers was characterized using FESEM. It is observed that the product was a film-like and the diameter of fibers was tens of nanometers.

Optimized Distribution and Morphology of Carbon Nanofibers for a Field Emitter Grown by Nickel and Chromium Cosputtering

To obtain a high field emission (FE) current with a low driving voltage, it is important to control and optimize carbon nanofiber (CNF) array patterns for FE. While there have been various means for controlling CNF array patterns reported over the past few decades, array patterning using lithography is the method typically used to control CNF morphology. Because lithography uses many masks and is costly, it is necessary to establish a simpler process. In this study, the grain size and distribution of catalysts with phase separation were controlled. A system which controls the morphology of small bundles of CNFs was constructed with the distance between the bundles kept constant in order to obtain a higher FE current. The Ni catalyst layer for forming the CNF morphology was separated by noncatalytic Cr grains formed by cosputtering. As a result, it was possible to control the Ni content, the grain size and synthesis density of CNFs in the alloy with a varying number of nickel pellets placed on the chromium target. This method is an epochmaking CNF patterning technique very different from lithography.

Gas-Induced Formation of Cu Nanoparticle as Catalyst for High-Purity Straight and Helical Carbon Nanofibers

The facile preparation of high-purity carbon nanofibers (CNFs) remains challenging due to the high complexity and low controllability in reaction. A novel approach using gas-induced formation of Cu crystals to control the growth of CNFs is developed in this study. By adjusting the atmospheric composition, controllable preparation of Cu nanoparticles (NPs) with specific size and shape is achieved, and they are further used as a catalyst for the growth of straight or helical CNFs with good selectivity and high yield. The preparation of Cu NPs and the formation of CNFs are completed by a one-step process. The inducing effect of N(2), Ar, H(2), and C(2)H(2) on the formation of Cu NPs is systematically investigated through a combined experimental and computational approach. The morphology of CNFs obtained under different conditions is rationalized in terms of Cu NP and CNF growth models. The results suggest that the shapes of CNFs, namely, straight or helical, depend closely on the size, shape, and facet activity of Cu NPs, while such a gas-inducing method offers a simple way to control the formation of Cu NPs.

Effect of Reaction Temperature on the Morphology of Carbon Nanofibers

Carbon nanofibers with various morphologies were synthesized by the catalytic pyrolysis of acetylene using nickel catalyst nanoparticles at different reaction temperatures. Experimental results demonstrate that temperature is a critical parameter for controlling the size and morphology of carbon fibers. Twin coiled fibers and linearly bifurcating fibers emanating from nickel particles were formed at 400 °C; whereas, only linear carbon nanofibers were obtained at reaction temperatures of 450 °C, 500 °C, and 550 °C. At low temperatures, nickel nanoparticles remain in the middle of two fibers, while nickel particles are positioned at one end of the linear fibers at high temperatures.

Influence of Catalyst for Synthesis of Carbon Nanofibers from the Flame

Carbon nanofibers synthesis from the flame is a new method. The method needs simple laboratory equipments and normal atmosphere pressure. The experimental system is introduced. Carbon source is the carbon monoxide and the nitric acid nickel is served as catalyst. The carbon nanofibers were characterized by scanning electron microscope and transmission electron microscope. Carbon nanofibers with less impurity were captured successfully in the flame. The diameter of carbon nanofibers was approximate from one to two hundred nanometers, and its length was dozens of microns. The growth process and mechanism of carbon nanofiber from the flame is very complicated. The influence of catalyst can reveal the growth mechanism of carbon nanofiber. This study aims to examine the catalyst formation condition for carbon nanofibers in pyrolysis flame and to characterize the morphology. Carbon nanofibers with less impurity can be prepared when the diameter of catalyst in is between twenty and thirty nanometers. The catalyst particle size can determine the morphology of carbon nanofibers.

Tuning the size and shape of Fe nanoparticles on carbon nanofibers for catalytic ammonia decomposition

Fe nanoparticles on the top of carbon nanofibers (CNFs) were synthesized by catalytic CVD on a purpose as catalysts for ammonia decomposition. The size and shape of Fe particles on the top of CNFs depended on the Fe particle reconstruction and CNF morphology. On a mica support Fe catalyst, platelet structure of CNFs was obtained with small, uniform, and unwrapped Fe particles on the top. HRTEM illustrated that the Fe particle surface is covered by a few graphene layers, which redissolves into the Fe particle and does not prevent the access of NH3 to active surface sites at reaction conditions. The catalyst is highly active and stable because the Fe particles are highly dispersed and physically isolated by CNFs, and the surfaces are largely exposed to the reactants.

Synthetic hierarchical nanostructures: growth of carbon nanofibers on microfibers by chemical vapor deposition

In this paper the synthesis of three-dimensional hierarchical nanostructures by pyrolysis of acetylene to grow carbon nanofibers (CNFs) on carbon microfibers (CMFs) and glass microfibers (GMFs) is reported. The morphology and structure of the as-prepared CNFs were studied by scanning electron microscopy and high-resolution transmission electron microscopy. CNFs grown on both substrates typically exhibited two types of morphology: the coil-like CNFs with frequent change in orientation and the relatively straight and long CNFs with parallel graphene sheets. The ethanol pretreatment was effective at improving the yield and distribution of the as-grown CNFs on CMFs, but showed an adverse effect to the CNF growth on GMFs. The influence of different substrates and growth temperatures on CNF morphology and the possible growth mechanism for the observed microstructures was discussed.

The effect of graphitization temperature on the structure of helical-ribbon carbon nanofibers

Structural rearrangement of helical-ribbon carbon nanofibers (CNFs) was studied as a function of graphitization temperature. The as-produced nanofibers are composed of a helical ribbon of graphene spiralled about and angled to the fiber axis. The discrete layers of graphene ribbon overlap each other forming the helical-ribbon in contrast to the discontinuous cones of the more common stacked-cup CNF morphology. After heat treatment to 2400 °C and above, the CNFs were completely free of residual metal catalyst inclusions, principally nickel used in their synthesis, and other functionalities. The formation of loops at the graphene edges was also observed. Heat treatment through the temperature range 1500–2800 °C resulted in a relatively minor contraction in interlayer spacing d 002 from 0.3381 to 0.3363 nm. This was attributed to the highly graphitic character of the as-produced CNFs. However, there were significant increases in the crystallite thickness L c through this temperature range. In addition, heat treatment above 2400 °C induced a marked change of the nanofiber morphology from circular to faceted polygonal cross-section resulting from the re-ordering of the turbostratic, curved graphene layers to regions of planar graphene layers with 3-dimensional graphitic structure (AB stacking).

Synthesis of Carbon Nanofibers: A Catalyst Derived from Cupric Carbonate Basic during Acetylene Decomposition

Two types of helical and straight carbon nanofibers, have been synthesized by the decomposition of acetylene using cupric carbonate basic as catalyst precursor at low temperature. The obtained carbon nanomaterials were characterized by transmission electron microscope, scanning electron microscope, and X-ray power diffraction. The size of the catalyst nanoparticles remaining inside the resultant nanofibers was determined. The carbon nanofiber diameters, ranging from 30 to 400 nm, closely correlated with the size of the catalytic nanoparticle. The growth mechanism of carbon nanomaterials was also studied. The nanocopper particle size had a considerable effect on the morphology of carbon nanofibers. The helical carbon nanofibers with a symmetric growth mode were synthesized with the nanocopper catalyst particles having a grain size less than 50 nm. When the average catalyst particle size determined was around 50–300 nm, the straight carbon nanofibers were obtained dominantly.

Morphological Control of Ion-Induced Carbon Nanofibers and Their Field Emission Properties

Carbon nanofibers (CNFs) were fabricated on graphite plates using “Ar+ ion sputtering method” in large amount at room temperature. The morphology of CNFs was controlled by a simultaneous carbon supply during ion sputtering. CNF-tipped cones were formed on graphite plate surfaces without carbon supply whereas those with a simultaneous carbon supply featured mainly needle-like protrusions of large size. The field electron emission (FE) properties, measured using parallel plate configurations in 10-4 Pa range, showed the threshold fields of 4.4 and 5.2V/µm with a current density of 1 µA/cm2 for CNF-tipped cones and needle-like protrusion, respectively. Reliability test results indicated that CNF-tipped cones were more stable than needle-like protrusion. The morphological change after reliability test showed a so-called “self-regenerative” process and structure damage for CNF-tipped cones and needle-like protrusions, respectively.