Cup-stacked Carbon Nanofibers Research Articles

Cooperative Control of Bioelectrocatalytic Activity for Thermo- and Photo-Switchable Cup-Stacked Carbon Nanofiber Electrodes Modified with Phase Transition Polymer and Heme Peptide.

Empowering biocatalyst-modified electrodes with the ability to both enforce and perceive will enable the development of intrinsically switchable bioelectrode systems, which exhibit autonomous and heteronomous actions specific to living organisms. However, the electrocatalytic activity of switchable bioelectrodes reported so far has been controlled by changes in the rate of substrate transport to biocatalysts. Here, we prepared a cup-stacked carbon nanofiber (CSCNF) electrode modified with a thermoresponsive N-isopropylacrylamide-based polymer containing peroxidase model compounds (HP). As CSCNFs worked as a converter from near-infrared (NIR) light to heat, bioelectrocatalytic activity of the electrode to H2O2 reduction was reversibly controlled by changes in the amount of electroactive HP, based on expanded and contracted states of the polymers induced by not only environmental temperature changes but also external NIR light irradiation. This intrinsically switchable bioelectrode technique would hold promise for adding new performances in electrochemical biosensors and biofuel cells, for example, autonomous and heteronomous tunable sensitivity and capacity.

Autonomous and heteronomous control of selectivity to pyrocatechol derivatives for near-infrared light-responsive cup-stacked carbon nanofiber/FTO electrodes modified with thermo-responsive polymers

Autonomous and heteronomous switchable selectivity for electrochemical reactions was examined in an electrolyte solution containing pyrocatechol (PC) and dopamine (DA) using a fabricated thermo- and photo-responsive poly(N-isopropylacrylamide) (PNIPA)-modified cup-stacked carbon nanofiber (CSCNF) electrode. PNIPA can be autonomously and reversibly switched by environmental temperature changes between hydrophilic expanded coil structure and hydrophobic collapsed globule structure. CSCNFs as the electrode materials can effectively convert absorbed external near-infrared (NIR) light into heat. Although the molecular size of DA is larger and the octanol-water partition coefficient of DA is smaller than those of PC, both PC and DA could permeate to the CSCNF electrode surface through the expanded coil structure of the PNIPA layer at 25 ˚C, which temperature is below the lower critical solution temperature (LCST), causing their electrochemical signal readout. In contrast, transport of DA to the electrode surface was selectively suppressed by exposing the polymer to temperature at 45 ˚C, which value is above the LCST, or NIR light irradiation (> 940 nm, ca. 77 mW cm–2) to the CSCNF electrode surface even at 25 ˚C due to the steric hindrance and hydrophobicity of collapsed globule structure of the polymer layer. This resulted in the preferential electrochemical signal of PC. The switchable sensitivity of the electrode also allowed it to be successfully demonstrated for the simultaneous determination of PC and DA even at a single transducer, though electrode arrays with different sensitivity and selectivity are widely used for the determination of multiple chemicals simultaneously.

Amino-functionalized Cup-stacked Carbon Nanofibers as Electrode Materials for Suppressing Protein Fouling

Amino-functionalized Cup-stacked Carbon Nanofibers as Electrode Materials for Suppressing Protein Fouling

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.

Solution Combustion Synthesis of Ni/Al2O3 Catalyst for Methane Decomposition: Effect of Fuel

The synthesis of a 90% Ni/Al2O3 catalyst via solution combustion synthesis with various fuels was studied in this work. Catalysts with a high content of the active component (i.e., nickel) were obtained as a result of the combustion of Ni(NO3)2·6H2O and Al(NO3)3·9H2O mixtures with fuel. The fuels, such as hexamethylenetetramine, glycine, urea, starch, citric acid, and oxalic acid, were investigated. The synthesis was carried out in a furnace, with the temperature being raised from room temperature to 450 °C at a rate of 1 °C per min. The paper evaluates the efficiency of fuels and their effect on the structure and properties of catalysts, as well as their catalytic activity. The catalyst was used for the synthesis of hydrogen and carbon nanofibers by methane decomposition at 1 bar and 550 °C. The catalysts were tested in a vertical flow reactor without preliminary reduction. The obtained samples of catalysts and carbon nanomaterials were studied by transmission electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction. The highest activity of the catalyst was obtained when citric acid was used as a fuel. The specific yields of hydrogen and carbon nanofibers were 17.1 mol/gcat and 171.3 g/gcat, respectively. Catalytic decomposition of methane led to the formation of cup-stacked carbon nanofibers.

Short side chain perfluorosulfonic acid composite membrane with covalently grafted cup stacked carbon nanofibers for polymer electrolyte fuel cells

Efficient proton conduction through polymer electrolyte membrane is critical in the performance of low temperature polymer electrolyte fuel cells (LT-PEFC). Herein, polystyrene sulfonic acid grafted cup stacked carbon nanofiber (PSSA-g-CSNF) incorporated short side chain (SSC)-perfluorosulfonic acid (PFSA) ionomer composite polymer electrolyte is discussed. An optimum level of PSSA-g-CSNF introduced as an additive to SSC-PFSA matrix exhibit higher proton conductivity, improved mechanical, chemical stability, and limited hydrogen crossover towards PEFC application in comparison to recast pristine SSC-PFSA membranes (Aquivion®-720). Maximum current density of 2.5 A cm−2 at 0.5 V and peak power density of 1.4 W cm−2 under H2 and O2 condition is seen for the optimized nanocomposite membrane. Besides, the peak power density of the nanocomposite membrane shows an enhancement higher than 22% and 42% in relation to recast pristine Aquivion and Nafion212 respectively. In addition to this, nanocomposite membrane shows higher chemical stability and retention of 80% initial OCV even after 100 h of accelerated stress test (AST) as compared to 73% for pristine Aquivion. Uniform dispersion of PSSA-g-CSNF in Aquivion facilitates facile proton transport by limiting fuel cross-over via hydrogen bonding interaction with closely spaced hydrophilic groups in the membrane matrix in LT-PEFC.

Compositional and Structural Modifications by Ion Beam in Graphene Oxide for Radiation Detection Studies

In the present study, graphene oxide foils 10 μm thick have been irradiated in vacuum using same charge state (one charge state) ions, such as protons, helium and oxygen ions, at the same energies (3 MeV) and fluences (from 5 × 1011 ion/cm2 to 5 × 1014 ion/cm2). The structural changes generated by the ion energy deposition and investigated by X-ray diffraction have suggested the generation of new phases, as reduced GO, GO quantum dots and graphitic nanofibers, carbon nanotubes, amorphous carbon and stacked-cup carbon nanofibers. Further analyses, based on Rutherford Backscattering Spectrometry and Elastic Recoil Detection Analysis, have indicated a reduction of GO connected to the atomic number of implanted ions. The morphological changes in the ion irradiated GO foils have been monitored by Transmission Electron, Atomic Force and Scanning Electron microscopies. The present study aims to better structurally, compositionally and morphologically characterize the GO foils irradiated by different ions at the same conditions and at very low ion fluencies to validate the use of GO for radiation detection and propose it as a promising dosimeter. It has been observed that GO quantum dots are produced on the GO foil when it is irradiated by proton, helium and oxygen ions and their number increases with the atomic number of beam gaseous ion.

Compression-torsion coupling behaviours in double-helix nanofibers assembled from negatively curved nanographenes

The recently synthesised one-dimensional (1D) double-helix nanofibers that are self-assembled from negatively curved nanographenes, i.e., 1-H nanofibers are expected to have new applications in materials science and biology. In this paper, the mechanical behaviours of 1-H nanofibers are investigated by using molecular dynamics simulations. 1-H nanofibers are found to possess a Young’s modulus comparable to that of conventional cup-stacked carbon nanofibers. Meanwhile, a large plastic deformation is observed in the axially stretched 1-H nanofibers before their final breaking. In addition, 1-H nanofibers possess a bending stiffness significantly larger than that of many other 1D nanomaterials, making 1-H nanofibers behave more like an elastic rod or beam. More importantly, a unique compression-torsion coupling behaviour is observed in 1-H nanofibers, which is strongly dependent on the rotation direction. Specifically, when 1-H nanofibers are rotated along the helix direction, a residual tensile stress or, equivalently, an axial contraction is generated. However, no significant compression-torsion coupling behaviour is observed in 1-H nanofibers rotated along the direction reverse to helix. Furthermore, due to the compression-torsion coupling effect, a unique helical buckling behaviour can occur in 1-H nanofibers under pure axial compression, which is totally different from the conventional Euler buckling behaviour observed in many other 1D nanomaterials.

Bioelectrochemical detection of histamine release from basophilic leukemia cell line based on histamine dehydrogenase-modified cup-stacked carbon nanofibers

Histamine released from mast cells plays an important role as not only a physiological active substance for the trigger of allergic reactions but also a neurotransmitter in a nervous system. To detect histamine directly, we immobilized oxygen-independent histamine dehydrogenase (HmDH) onto the surface of cup-stacked carbon nanofibers (CSCNFs), which work both as an electrical nanowire and an enzyme support, and investigated the direct electron transfer reaction from HmDH reduced by histamine to CSCNF. Current responses of histamine oxidation at the HmDH-modified CSCNF electrode showed a linear relationship between 0.3 µM and 300 µM with detection limit of 0.1 µM in a Briton Robinson buffer (pH 9.4) and was about 25 times larger than those at a flat glassy carbon electrode modified with HmDH because of its three-dimensional network. Using the HmDH-modified CSCNF electrode, we successfully observed histamine release from rat basophilic leukemia cell line RBL-2H3 after stimulation with degranulation agents, such as antigen 2,4-dinitrophenylated bovine serum albumin and calcium ionophore A23187. The present sensing system might be applied to at least advanced in vitro allergic diagnostic methods.

Defect-mediated synthesis of Pt nanoparticles uniformly anchored on partially-unzipped carbon nanofibers for electrochemical biosensing

Abstract Defect-mediated engineering has been proven as a novel and effective strategy to integrate two individual materials into a nanocomposite to boost the performance. In the present work, nanocomposite of partially-unzipped stacked-cup carbon nanofibers (PUSCNFs) decorated with platinum nanoparticles (Pt NPs) have been successfully synthesized through the defect-mediated formation method. Owing to the introduction of abundant structural defects during the chemical oxidation process, Pt NPs with an average diameter of 2–3 nm were uniformly anchored on the PUSCNFs without any surfactant involved. As comparison, the Pt NPs grown on the stacked-cup carbon nanofibers (SCNFs) possessed markedly larger nanoparticle size and trended to aggregate. The electrochemical properties of the nanocomposite-modified electrodes for biosensing were examined. Our results showed the Pt-PUSCNFs nanocomposite possessed optimal electrocatalytic activities and biosensing performance for detection of biomolecules, which could be attributed to a synergistic effect between the PUSCNFs and Pt NPs on electron transport and catalytic properties. We anticipate that the PUSCNFs may be a potential support material for construction of nanocomposites with good performance.

A biomimetic approach to improve the dispersibility, interfacial interactions and toughening effects of carbon nanofibers in epoxy composites

Abstract In this work, the surface of stacked-cup carbon nanofibers (CNFs) was coated with polydopamine (PDA) via a facile biomimetic method based on catecholic chemistry. The modified CNFs (D-CNFs) were incorporated into an epoxy resin in a solvent-free manner. In addition to hydrogen bonding, covalent bonding is also present between amino groups in PDA and epoxy, as verified by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Owing to the strong interfacial interactions brought by PDA, D-CNFs show significantly improved dispersibility in epoxy matrix. Consequently, the reinforcing effects of D-CNFs clearly outperform those of pristine CNFs (P-CNFs), especially in terms of fracture toughness. Dynamic thermo-mechanical studies show that the addition of D-CNFs can increase storage modulus more effectively without deteriorating the thermal stability of epoxy matrix. This study confirms that enhancing interfacial interactions in polymer composites by coating nanofillers with PDA is a useful strategy to obtain simultaneous stiffening and toughening in rigid thermoset polymers.

Dendritic unzipped carbon nanofibers enable uniform loading of surfactant-free Pd nanoparticles for the electroanalysis of small biomolecules.

In this study, graphene nanofibers (GNF), which are a superior support material, are successfully synthesized via the dendritic unzipping of stacked-cup carbon nanofibers (SCNF). Ultrasmall Pd nanoparticles are uniformly dispersed on the GNF (Pd/GNF) via chemical reduction under mild conditions without any surfactant involved. The components and structure of Pd/GNF are evaluated via scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectroscopy (XPS). The characterization results indicate that the Pd nanoparticles have a uniform size of 3-6 nm without significant aggregation and the overall Pd content is about 11.2 wt% in the Pd/GNF composite. Moreover, a modified electrochemical sensor based on the Pd/GNF composite is successfully fabricated. In the two investigated redox probes (IrCl6 2- and [Fe(CN)6]3-), Pd/GNF shows a superior electrochemical response compared to the Pd nanoparticles loaded on SCNF and bare glass carbon electrode. For the detection of small biomolecules, Pd/GNF could individually or simultaneously detect ascorbic acid (AA), dopamine (DA) and uric acid (UA) through differential pulse voltammetry. The linear concentration ranges of UA, DA and AA are 0.1-1200 μM, 1-180 μM and 0.1-6000 μM, respectively.

Controlled direct electron transfer kinetics of fructose dehydrogenase at cup-stacked carbon nanofibers.

Graphene edge sites not only facilitate heterogeneous electron transfer reactions of redox species because of localization of electrons, but also allow sensitivities and selectivities to be tuned by controlling the atomic oxygen/carbon (O/C) ratio. Here, we immobilized fructose dehydrogenase (FDH) onto the surface of cup-stacked carbon nanofibers (CSCNFs), which provide highly ordered graphene edges with a controlled O/C ratio, and investigated the direct electron communication with FDH. As the O/C ratio decreased at the CSCNF surface, the negative zeta potential was mitigated and the electrochemical communication with FDH was facilitated. This is likely due to improved orientation of FDH molecules on the CSCNF surface. CSCNFs with a controlled O/C ratio could be applied to FDH-based d-fructose biosensors with tunable dynamic range and fructose biofuel cells with a controlled maximum current.

Direct Electron Transfer Kinetics of Peroxidase at Edge Plane Sites of Cup-Stacked Carbon Nanofibers and Their Comparison with Single-Walled Carbon Nanotubes.

Electron transfer kinetics at the graphene edge site is of great interest from the viewpoints of application to sensing and energy conversion and storage. Here we analyzed kinetics of direct electron transfer of horseradish peroxidase (HRP) adsorbed through surfactant sodium dodecyl sulfate at cup-stacked carbon nanofibers (CSCNFs), which provide highly ordered graphene edges, and compared it with that at single-walled carbon nanotubes (SWCNTs), which consist of a rolled-up basal plane graphene. The heterogeneous electron transfer rate constant of the Fe(2+/3+) couple of the HRP reaction center at CSCNFs (ca. 34.8 s(-1)) was an order of magnitude larger than that at SWCNTs (ca. 4.7 s(-1)). In addition, the overall rate constant of the electron transfer reaction from CSCNFs to HRP oxidized by H2O2 was higher than that from SWCNTs by a factor of 3. CSCNFs also allowed enhancement of the complex-formation reaction rate of HRP with H2O2, in comparison with that at SWCNTs. CSCNFs would therefore be applied to not only biosensors but also biofuel cells with enhanced performance.

Manufacture and evaluation of cup-stacked carbon nanofiber-modified screen printed electrodes as electrochemical tools

Cup-stacked carbon nanofibers (CSCNFs) are carbon nanofilaments comprising continuous helix-rolled graphene layers. This interesting and cheap carbon nanomaterial presents a lot of possibilities for electrochemical and electroanalytical applications, although it still remains almost unknown in both fields. In this work, studies about CSCNFs for the modification of screen-printed carbon electrodes (SPEs) are presented and compared against multi-walled carbon nanotubes (MWCNTs). Acid oxidized CSCNFs were dispersed in water and used to modify SPEs. The effect of the CSCNFs on important electrochemical parameters, such as capacitances, faradic currents and heterogeneous electron transfer rate constants, was studied and compared with data obtained by the modification of SPEs with acid oxidized MWCNTs. Several common benchmark redox systems were tested (ferricyanide, hydroquinone, dopamine and 4-aminophenol) and electroanalytical properties were optimized for the determination of 4-aminophenol by cyclic voltammetry.

Oxygenated Cup-Stacked Carbon Nanofibers/TiO2 Composite Films with Enhanced Photocatalytic Currents

Abstract Oxygenated cup-stacked carbon nanofibers (ox-CSCNFs), the surface of which provides highly ordered graphene edges and oxygen-containing functional groups, were introduced to a nanoporous TiO2 photoelectrode for enhanced photocatalytic currents. The ox-CSCNFs are characterized by good electric conductivity and high dispersibility in solvents. Under UV irradiation, short-circuit photocurrents based on water oxidation at the photoelectrode and oxygen reduction at a counter electrode were enhanced by about 15 times by introduction of the ox-CSCNFs. The oxygen-containing functional groups, which may facilitate good contact between the ox-CSCNFs and TiO2, are essential for the dramatic enhancement in the photocurrent. Recombination efficiency between excited electrons and generated holes may be reduced by facilitated electron transport from excited TiO2 to a substrate electrode via ox-CSCNFs. Photocurrents for photocatalytic oxidation of glucose were also enhanced by about 20-fold. The present composite materials would be applied to photocatalytic and photovoltaic cells with enhanced performances.

Enhanced fracture toughness of carbon fabric/epoxy laminates with pristine and functionalized stacked-cup carbon nanofibers

The fracture toughness of carbon fiber reinforced plastic laminates was investigated in term of modifying the epoxy matrix with the pristine and functionalized stacked-cup carbon nanofibers. The results showed that the highest enhancements in Mode I (13.6%) and Mode II (45.3%) fracture toughness were achieved by adding 0.5wt% and 1.0wt% functionalized nanofibers, respectively. The toughening mechanism was analyzed based on the morphology evaluations of the fracture surfaces. The evidence of bridging, pull-out, peeling-off and unravelling of nanofibers were clearly observed, which contributed to dissipating more energy for crack propagation, resulting in the improvement of fracture toughness.

Graphitized stacked-cup carbon nanofibers as anode materials for lithium-ion batteries

The electrochemical performance as anodes in lithium-ion batteries (LIBs) of graphitized stacked-cup carbon nanofibers (CNFs) with different degree of structural order is investigated by galvanostatic cycling. To this end, two types of commercial CNFs (PR19 and PR24) bearing this microstructure were heat treated in the range of 1800-2800°C. The discharge capacity provided at the end of cycling, the capacity retention along cycling (cyclability) and the cycling efficiency (charge capacity/discharge capacity) of these nanomaterials improve significantly after heat treatment. Specifically, a progressive increase of the discharge capacity with the growth of the crystallites sizes (Lc, La) and the decrease of the structural defects (ID/It) is observed. All heat-treated CNFs exhibit cyclabilities > 80% after 50 cycles and efficiencies > 90%. Particularly outstanding is the performance of PR19-2800 which provides a discharge capacity of 295 mAh g−1 with capacity retention up to 88%. The CNFs heat treated at 2800°C also show good rate capabilities, keeping reversible capacities > 200 mAh g−1 at a 2C (744mA g−1) rate, and > 100 mAh g−1 after prolonged cycling (500 cycles) at a 1C rate, clearly outperforming synthetic graphite having micrometric particle size and much larger development of the crystalline structure.

Functions of amorphous carbon in catalyst fabrication for carbon nanofiber growth in the poly(ethylene glycol) thermal decomposition method

To investigate the growth mechanism of carbon nanofibers (CNF) through a process using the thermal decomposition of poly(ethylene glycol) (PEG), we researched the phenomena that occurred from PEG decomposition to CNF growth during a temperature elevation process of CNF synthesis. In the PEG thermal decomposition method, the selective synthesis of platelet CNF (PCNF) and cup-stacked CNF was accomplished by changing only the ramp rate (without any other difference in experimental conditions). As a result, it was confirmed that carbon-containing gases generated by PEG thermal decomposition were converted to amorphous carbon and deposited on the substrate. There was a clear correlation between the amount of deposited amorphous carbon and the size of the nickel catalyst particle for CNF growth. Therefore, in the PEG thermal decomposition method, amorphous carbon deposition was found to be important to control the dispersity and morphology of the catalyst particle, and it was probably crucial to the determination of the type of CNF. In addition, the PCNF prepared in this study showed multidirectional growth from polyhedral catalyst particles, and this could be why the PEG thermal decomposition was able to create PCNF with small diameters compared to PCNF synthesized by conventional methods.

Electrochemical properties of oxygenated cup-stacked carbon nanofiber-modified electrodes.

Oxygenated cup-stacked carbon nanofibers (CSCNFs), the surface of which provides highly ordered graphene edges and oxygen-containing functional groups, were investigated as electrode materials by using typical redox species in electrochemistry, Fe(2+/3+), [Fe(CN)6](3-/4-), and dopamine. The electron transfer rates for these redox species at oxygenated CSCNF electrodes were higher than those at edge-oriented pyrolytic graphite and glassy carbon electrodes. In addition, the oxygen-containing functional groups also contributed to the electron transfer kinetics at the oxygenated CSCNF surface. The electron transfer rate of Fe(2+/3+) was accelerated and that of [Fe(CN)6](3-/4-) was decelerated by the oxygen-containing groups, mainly due to the electrostatic attraction and repulsion, respectively. The electrochemical reaction selectivities at the oxygenated CSCNF surface were tunable by controlling the amount of nanofibers and the oxygen/carbon atomic ratio at the nanofiber surface. Thus, the oxygenated CSCNFs would be useful electrode materials for energy-conversion, biosensing, and other electrochemical devices.