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Vertical graphene (VG) films can be fabricated on the surface of nickel foil from fullerene soot (FS) under microwave plasma irradiation (MPI) in a mixture gas of H2 and Ar at 1200 W for 15 min. The resulting FS-derived VG films mostly consist of few-layer graphene sheets with large domain graphene sizes, high graphitization order, and high purity, as characterized by scanning and transmission electron microscopies, Raman spectroscopy, and X-ray photoelectron spectroscopy. Combined the present and previous results, MPI technique is an effective and versatile approach to synthesize vertically oriented graphene sheets from any carbon-containing sources.

The composites consisting of graphene oxides (GOs) and carbon spheres (CSs), which were hydrothermally derived from the aqueous solution of glucose with average diameter of 200 nm, were mechanically mixed, and the GOs/CSs (GCSs) were thermally treated at high temperatures in the range of 700–900 °C. In the GCS composites, the CSs as spacers located between the GO sheets prevent the aggregation and restacking of graphene sheets. The GCS composites (GO/CS = 1) treated at 800 °C (GCS@800) have the high specific capacitances of 272.8 and 197.5 F g−1 in a three-electrode cell at the current density of 0.2 and 10 A g−1, respectively, in 6 M KOH aqueous solution, and demonstrated high rate capability and good cycling stability. The excellent electrochemical performance of the GCS@800 electrode is attributed to its structure with hierarchical porous structures including overwhelming micropores and a few of macropores. This work provides an effective and simple technique by integrating CSs and graphene sheets into composite structures for high-performance energy storage devices.

Nitrogen-doped porous carbon monoliths (NDP-CMs) have long been pursued as the desirable supercapacitor electrode materials. However, the currently effective template methods and Lewis acid/base activation strategy suffer from the drawbacks of either high costs or tedious steps. We report on a simple and practicable novel method to the production of CNTs constructed NDP-CMs. Polyacrylonitrile (PAN) contained carbon nanotubes (CNTs), being dispersed into tubular level of dispersions (mono-dispersions), were used as the starting material and NDP-CMs were obtained through a direct carbonization process. First, PAN/CNT based mesostructured polymeric monoliths with interconnected networks were formed using a template-free temperature-induced phase separation (TTPS) method and the mono-dispersed CNTs networks act as the backbones of PAN molecules. Then, NDP-CMs with a surface area of 840 m2/g and a pore diameter 2.48 nm were obtained through heat treatment. Thus, the NDP-CMs based supercapacitor demonstrated a reversible specific capacitance of 246 F/g. Furthermore, pyridinic nitrogen and quaternary nitrogen species contribute significantly to the advantageous electrochemical activities of NDP-CMs.

Graphitization of carbon materials plays an important role their microstructures and conductivity, and then influences their applications. However, the graphitization of hydrothermal carbon spheres (CSs) has not systemically investigated heretofore. The CSs with 60–250 nm in diameter were prepared from aqueous glucose solution by hydrothermal carbonization, and were treated at the high temperatures of 900–2900 °C in Ar atmosphere. The heat-treated CSs have demonstrated that their surface structure, microstructure, porosity, and polygonization strongly depend on the treatment temperatures. These results are supported by scanning and transmission electron microscopes, energy dispersive x-ray spectrometry, Raman, X-ray diffraction, and BET surface area analyses. We also investigated the electrical properties of the heat-treated CSs under compression, and found that the resistivity of the carbon particles is very dependent on their surface, microstructure, density, and polygonization. Therefore, high temperature treatment is an effective method to tailor the structure, morphology, and property of the hydrothermal CSs.

Here, we present a facile technique for synthesis of graphene nanosheet (GNS)-grafted double-walled carbon nanotube (DWCNT) hybrid carbon nanostructures (here after referred to as G-DWCNTs) by directly growing GNSs along the sidewalls of DWCNTs using a two-step chemical vapor deposition (CVD). DWCNTs were synthesized by floating catalyst CVD at 1300 °C using ferrocene and thiophene dissolved in ethanol. Then, GNSs were grafted onto the synthesized DWCNT bundles by thermal CVD at 1300 °C using ethanol. The sharp-edged petal-like structure of GNSs were grown along the sidewalls of DWCNT bundles while maintaining the one-dimensional structure of DWCNT. Next, DWCNTs and G-DWCNTs were dispersed in ethanol, then deposited on the paper using vacuum filtration method and used for ethanol detection. G-DWCNTs sensor exhibited a 3-fold improvement in the response to ethanol vapor compared to the DWCNTs sensor. The sensing mechanism of DWCNTs and G-DWCNTs can be described in terms of charge transfer between the gas molecules and sensing material. These results demonstrate that the facile technique by two-step CVD method provides a promising approach for simple and low-cost technique to synthesize the hybrid nanostructure of GNSs and DWCNTs. The new hybrid carbon nanostructures are attractive for gas sensing application.

Due to its unique structure and amazing physiochemical properties including high chemical inertness, large specific surface area, and high electric conductivity, graphene, a two-dimensional single sheet of carbon atoms consisting of honeycomb lattices, has attracted great scientific interest in the enormous applications, for example, optical electronics, photovoltaic cells, energy storage, composite materials, filter membranes, and biological engineering, and is regarded as a basic building block for graphitic materials of all other dimensionalities. Recently, another two-dimensional graphitic sheet, vertical graphene (VG), which is typically aligned vertically on a substrate, is attractive for the abovementioned graphene-based applications. The novel vertical orientation and open structures of VGs make it more suitable for sensing biomarkers with high sensitivity and selectivity in complex biological conditions. Until now, VG biosensors have been investigated for detecting diverse biomolecules with or without the modification of metal nanoparticles. More importantly, the plasma technique for the growth and modification of VG is useful but simple tool to optimize the biosensor performance and capabilities. In this chapter, we will simply introduce the synthesis, characteristics, and fundamental properties of VG and carefully discuss the recent studies of VG-based biosensors including electronic and electrochemical biosensors.

Recently, graphene and carbon nanotube (CNT) composites have attracted great interest of scientists and exhibited fascinating properties even better than they could on their own. Here, we have synthesized the graphenated CNTs (g-CNTs), one of graphene–CNT composites, from waste rice husk (RH) by one-step microwave plasma irradiation (MPI) process. The RH-derived g-CNTs were composed of graphene standing on the sidewalls of CNTs, in which the graphene sheets possessed a large amount of sharp edges, which mainly consisted of 2–6 layers, and the CNTs had several tens of micrometers in length and 50–200 in diameter. They offer great promise in the application of electrochemical electrodes due to their special features including high surface area and specific capacitance. The successful MPI technique can be spread to other waste biomass, in which their components are made of cellulose, hemicellulose, and lignin similar to RHs, to fabricate high-added-value nanocarbons including graphene, CNTs, and g-CNTs, which were dependent of experimental pressure.

Graphite whiskers (GWs) are obtained from coffee grounds (CGs) treated at 2500 °C for 1 h in the presence of Ar gas at 1 atm. The majority of the GWs formed inside the CGs shell are rod‐like with a conical tip with diameter and length in the range between 1 to 3 µm and 4 to 10 µm, respectively. At first, the carbon layer might be grown in a turbostratic manner, and then progressively graphitized at higher temperature. The strong G′ peak intensity might be induced by the disclination of graphitized carbon layers.

We report the synthesis of high purity double-wall carbon nanotubes encapsulating GdCl 3 nanowires (GdCl 3 @DWCNTs). The obtained GdCl 3 @DWCNTs were characterized by transmission electron microscopy (TEM), Raman spectroscopy, UV–Vis-NIR spectroscopy, and fluorescence spectroscopy. TEM measurements show that GdCl 3 impurities were absent on the exterior of the tubes and bundles. Furthermore, significant changes of the optical properties of the inner tubes were not triggered by being filled with GdCl 3 nanowires, which suggests that significant charge transfer does not occur between the encapsulated GdCl 3 and the inner tubes. Our results indicate that GdCl 3 @DWCNTs could be useful for various applications using the expected magnetic properties of GdCl 3 and almost unchanged optical properties of DWCNTs. [TANSO 2013 (No. 260) 279–83.]

The quantitatively limited use of hydrogen peroxide in supercritical water allows for the in situ formation of iron oxides and graphitic carbon from ferrocene in one step. The structure of the particles prepared at 400–500 °C is comprised of nano- to micro-meter size of magnetite and maghemite cores covered with graphitic carbon shells. The morphology and size of the core–shell particles and the phase composition of iron-oxide cores are different dependent on the preparation conditions. The particles prepared at 400 °C contain, as dominant iron-oxide phase, the magnetite core particles ranging from nano- to micro-meter scales with no morphological regularity, while those prepared at 500 °C are comprised of hexagram shape and micro-meter size of maghemite cores. The observed morphology, the dimension of the core particles, and the dominant phase composition suggested that the iron-oxide cores would be formed through the oxidation of iron(II) to iron(III) and two different hydrolysis paths. Furthermore, the higher preparation temperature of 500 °C has shown a tendency to form smaller crystallite sizes of polycrystalline iron-oxide cores. The decrease of subcrystal sizes in the vicinity of superparamagnetic thresholds effects the reduction of coercivity in the ferromagnetic hysteresis.

A limited use of hydrogen peroxide in supercritical water has produced graphitic carbons from hydrocarbons at the low temperature of 400 °C. The choice of precursor hydrocarbons leads to morphological and microstructural variations. The use of n-hexane has provided chain-like interlinked nanoparticles comprised of graphitic layers, while benzene has been converted to a fine spherical shape of colloidal carbons with sub-micron size. The microstructure of the colloidal carbons is comprised of smaller aromatic clusters than the hexane-derived graphitic layers. Furthermore, the graphitization of the colloidal carbons at 2300 °C has induced not closed shell-like graphitic layers with concentric arrangement but ribbon-like graphitic layers growing in no particular direction. The arbitrary direction of the graphitization demonstrates the smallness of the aromatic clusters allowing for their flexible rearrangement.

A simple construction of sol–gel sheaths onto the surface of multi-walled carbon nanotubes (MWCNTs) has been carried out in water by a hydrophobicity-induced covering with the assistance of ultrasound. The ultrasound assistance prevents in water an unregulated agglomeration induced by the hydrophobicity of MWCNTs and phenyl-containing sols, leading to a selective construction of sol–gel sheaths on the nanotube surface. The phenyl groups of the resulting sol–gel sheaths were successfully removed by air-oxidation to provide the MWCNTs covered with amorphous SiO 2 sheaths. The effect of the SiO 2 sheaths on the electrical and thermal properties of the SiO 2 -MWCNT nanocomposites was evaluated from the electrical resistivities of the nanocomposites with two different SiO 2 concentrations and the thermal conductivities of their phenol-resin composites. The results indicate that the small increase of the SiO 2 concentration remarkably increases the electrical resistivity of the SiO 2 -MWCNT nanocomposites. Furthermore, the SiO 2 sheaths have more directly influenced the thermal property of the polymer composites than the inside nanotubes.

Article, SCRIPTA MATERIALIA. 58(4): 267-270 (2008)

A high dispersion of carbon-supported Pt–Ru alloy nanoparticles have been prepared in an alkaline aqueous solution by using glyoxylate as a reducing agent. The glyoxylate monoanion is converted to oxalate dianion with the reduction of metal precursor ions. The surface-potential analysis of unsupported Pt–Ru black in the presence of all the anion species coexistent in the preparation system suggests a possibility of oxalate dianion as the most effective particle stabilizer. In the glyoxylate-reduction system, a precursor–support interaction is significantly promoted to affect the formation and stabilization of nanoparticles. The glyoxylate reduction at 20-wt% metal loading has provided a higher Pt(0)/Ru concentration ratio in the near-surface region than that of 60-wt% catalyst. The structural and morphological features and advantageous surface composition of the 20-wt% catalyst contribute to the high mass activity for methanol oxidation in the anode overpotential range of typical direct methanol fuel cells.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in APPLIED PHYSICS LETTERS. 92(6):63105 (2008) and may be found at https://doi.org/10.1063/1.2842411 ., Article, APPLIED PHYSICS LETTERS. 92(6):63105 (2008)