Zujin Shi

Growth of Manganese Oxide Nanoflowers on Vertically-Aligned Carbon Nanotube Arrays for High-Rate Electrochemical Capacitive Energy Storage

Manganese oxide nanoflower/carbon nanotube array (CNTA) composite electrodes with hierarchical porous structure, large surface area, and superior conductivity was controllable prepared by combining electrodeposition technique and a vertically aligned CNTA framework. This binder-free manganese oxide/CNTA electrode presents excellent rate capability (50.8% capacity retention at 77 A/g), high capacitance (199 F/g and 305 F/cm (3)), and long cycle life (3% capacity loss after 20,000 charge/discharge cycles), with strong promise for high-rate electrochemical capacitive energy storage applications.

Fabrication, Mechanical Properties, and Biocompatibility of Graphene-Reinforced Chitosan Composites

Few-layered graphene sheets, synthesized by direct current arc-discharge method using NH(3) as one of the buffer gases, were dispersed in chitosan/acetic acid solutions. FTIR and X-ray photoelectron spectroscopy showed the presence of oxygen-containing functional groups on the surface of graphene sheets that may assist the good dispersion of graphene in chitosan solution. Graphene/chitosan films were produced by solution casting method. The mechanical properties of composite films were tested by nanoindentation method. With the addition of a small amount of graphene in chitosan (0.1-0.3 wt %), the elastic modulus of chitosan increased over ∼ 200%. The biocompatibility of graphene/chitosan composite films was checked by tetrazolium-based colorimetric assays in vitro. The cell adhesion result showed that the L929 cell can adhere to and develop on the graphene/chitosan composite films as well as on pure chitosan film, indicating that graphene/chitosan composites have good biocompatibility. Because there is no metallic impurity in graphene raw materials, the time-consuming purification process for removing metal nanoparticles entrapped in carbon nanotubes is thus avoided when graphene is used to prepare biomedical materials. Graphene/chitosan composites are potential candidates as scaffold materials in tissue engineering.

Electrocatalytic Oxidation of Norepinephrine at a Glassy Carbon Electrode Modified with Single Wall Carbon Nanotubes

The voltammetric behavior of norepinephrine (NE) was studied at a glassy carbon (GC) electrode modified with single wall carbon nanotubes (SWNTs). In pH 5.72 B-R buffer solution, the SWNT-modified electrode shows high electrocatalytic activity toward NE oxidation. One well-defined reversible redox couple is obtained at scan rates lower than 0.15 V s−1. The peak current increases linearly with the concentration of NE in the range of 1.0×10−5 - 1.1×10−3 mol dm−3. The detection limit is 6.0×10−6 mol dm−3 and the diffusion coefficient (D) of NE is 8.53×10−6 cm2 s−1. The SWNT was characterized with scanning electron microscope (SEM). Furthermore, the SWNT-modified electrode has favorable electrocatalytic activity with dopamine, epinephrine, and ascorbic acid.

Mass-production of single-wall carbon nanotubes by arc discharge method

Abstract With a Y–Ni alloy composite graphite rod as anode for d.c. arc discharge, a cloth-like soot was produced, containing about 40% single wall carbon nanotubes (SWCNTs). By characterization with high resolution transmission electron microscope (HREM) and Raman spectroscopy, it is found that the SWCNTs have nearly the same diameter of 1.3 nm and belong to armchair (n, n) type carbon nanotubes (n=8, 9, 10 and 11). It is also proposed that a large temperature gradient and the addition of Y–Ni alloy in the anode are the two most important factors influencing the formation of SWCNTs.

Mixed low-dimensional nanomaterial: 2D ultranarrow MoS2 inorganic nanoribbons encapsulated in quasi-1D carbon nanotubes.

Quasi-one-dimensional nanotubes and two-dimensional nanoribbons are two fundamental forms of nanostructures, and integrating them into a novel mixed low-dimensional nanomaterial is fascinating and challenging. We have synthesized a stable mixed low-dimensional nanomaterial consisting of MoS(2) inorganic nanoribbons encapsulated in carbon nanotubes (which we call nanoburritos). This route can be extended to the synthesis of nanoburritos composed of other ultranarrow transition-metal chalcogenide nanoribbons and carbon nanotubes. The widths of previously synthesized MoS(2) ribbons are greater than 50 nm, while the encapsulated MoS(2) nanoribbons have uniform widths down to 1-4 nm and layer numbers down to 1-3, depending on the nanotube diameter. The edges of the MoS(2) nanoribbons have been identified as zigzag-shaped using both high-resolution transmission electron microscopy and density functional theory calculations.

Electrocatalytic oxidation of 3,4-dihydroxyphenylacetic acid at a glassy carbon electrode modified with single-wall carbon nanotubes

Abstract The voltammetric behavior of 3,4-dihydroxyphenylacetic acid (DOPAC) was studied at a glassy carbon (GC) electrode modified with single-wall carbon nanotubes (SWNTs). In 0.1 M HAc–NaAc buffer solution (pH 4.4), the SWNT-modified electrode shows high electrocatalytic activity toward oxidation of DOPAC. One well-defined redox couple is obtained. The peak current increases linearly with the concentration of DOPAC in the range of 1.0×10 −6 –1.2×10 −4 M. The detection limit is 4.0×10 −7 M. The results indicate that DOPAC undergoes a two-electron oxidation to o -quinone followed by a dimerization reaction. Rate constant for this dimerization reaction was calculated to be 2.10×10 3 dm 3 mol −1 s −1 . The SWNT was characterized with scanning electron microscope (SEM). This SWNT-modified electrode can also separate the electrochemical responses of DOPAC and 5-hydroxytryptamine (5HT).

Temperature dependence of the Raman spectra of single-wall carbon nanotubes

Raman spectra of single-wall carbon nanotubes (SWCNTs) were measured at different temperatures by varying the incident laser power. The elevated temperature of the SWCNTs and multiwall carbon nanotubes (MWCNTs) is confirmed to be due to the presence of impurities, defects, and disorder. The temperature coefficient of the frequency of the C–C stretching mode E2g (GM) and that of the radial breathing mode in the SWCNT were determined to be ∼−0.038 and ∼−0.013 cm−1/K, respectively. It is found that the temperature coefficient of the GM in the SWCNT is larger than that of the MWCNT, highly oriented pyrolytic graphite, and the graphite. This is attributed to the structural characteristic of the SWCNT—a single tubular carbon sheet with smaller diameter.

Multilayered graphene used as anode of organic light emitting devices

In this report, we find multilayered graphene, which has good transparency, conductivity and suitable work function, can be used as the anode for the organic light emitting device. Our device structure is Al/glass/multilayered graphene/V2O5/NPB/CBP:(ppy)2Ir(acac)/Bphen/Bphen:Cs2CO3/Sm/Au. The maximum luminance efficiency and maximum power efficiency reach 0.75 cd/A and 0.38 lm/W, respectively. We believe that by optimizing the hole density and uniforming the thickness of the multilayered graphene anode, the device efficiency can be remarkably increased in the future.

Structure modification of single-wall carbon nanotubes

Various purification processes were applied to single-wall carbon nanotubes synthesized by metal catalyzed laser ablation. Structure modifications introduced by these processes were investigated by high-resolution transmission electron microscopy and Raman spectroscopy. An apparent structure modification after purification was the increase of bundle size although breaking of nanotubes and a change of nanotube diameter distribution were also observed. More vigorous attacking of single-wall carbon nanotube structure was identified by a strong mixed-acid treatment.

TEMPERATURE DEPENDENCE OF THE RAMAN SPECTRA OF CARBON NANOTUBES

We report on a temperature dependence of the frequency of all the major peaks in the Raman spectra of carbon nanotubes, using different excitation laser powers at the sample. The frequency decreases with increasing temperature for all peaks, and the shifts in Raman frequencies are linear in the temperature of the sample. In comparison, a similar dependence is found in active carbon, but no shift is observed for the highly ordered pyrolytic graphite within the same range of variation in laser power. A lowering of frequency at higher temperature implies an increase in the carbon–carbon distance at higher temperature. The relatively strong temperature dependence in carbon nanotubes and active carbon may be due to the enhanced increase in carbon–carbon distance. This enhancement may originate from the heavy defects and disorder in these materials.