[Show abstract][Hide abstract] ABSTRACT: 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 promising 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.
[Show abstract][Hide abstract] ABSTRACT: Microwave plasma-induced graphene-sheet fibers from waste coffee grounds Zhipeng Wang *a,b, Hironori Ogatac,d, Shingo Morimotoa, Masatsugu Fujishigea, Kenji Takeuchia, Hiroyuki Muramatsub, Takuya Hayashib, Josue Ortiz-Medinaa, Mohd Zamri Mohd Yusope,f, Masaki Tanemurae, Mauricio Terronesg, Yoshio Hashimotoa,b and Morinobu Endoa Graphene-sheet fiber, a novel structure of graphitic carbon, grows from coffee grounds under the condition of microwave plasma irradiation. The resulting fiber consisting of only few-layer graphene without hollow structure inside possesses a large amount of graphene edges and high conductivity. Duet to these advantages, graphene-sheet fibers may be find applications in the electrochemical energy conversion and storage.
Journal of Materials Chemistry A 06/2015; 3(28). DOI:10.1039/C5TA03833B · 7.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Double- and triple-walled carbon nanotubes are studied in detail by laser energy-dependent Raman spectroscopy in order to get a deeper understanding about the second-order G' band Raman process, general nanotube properties, such as electronic and vibrational properties, and the growth method itself. In this work, the inner nanotubes from the double- and triple-walled carbon nanotubes are produced through the encapsulation of fullerene peapods with high-temperature thermal treatments. We find that the spectral features of the G' band, such as the intensity, frequency, linewidth, and line shape are highly sensitive to the annealing temperature variations. We also discuss the triple-peak structure of the G' band observed in an individual triple-walled carbon nanotube taken at several laser energies connecting its Raman spectra with that for the G' band spectra obtained for bundled triple-walled carbon nanotubes.
Physical Review B 01/2015; 91(7). DOI:10.1103/PhysRevB.91.075402 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have experimentally and theoretically clarified the effect of oxygen functional groups on capacitive performance of the photochemically treated activated carbon electrode. A high density of C=O group at the mouth of the micropores, where the chemically active edge sites are predominantly available, increase the energy barrier for ions to enter the pores, thereby resulting in a large decrease in the specific capacitance.
[Show abstract][Hide abstract] ABSTRACT: Changes in the optical properties of single walled carbon nanotubes (SWNTs) caused by the encapsulation of molybdenum (Mo) clusters were investigated in the current research. Detailed transmission electron microscope observations showed that the encased Mo clusters within the hollow core of SWNTs exhibited in the form of short rod-like structure, indicating the growth of the clusters within the confined nano space. The upshifted G-band frequency as well as the quenched photoluminescence and absorption signals signified the modulation in the electronic properties of SWNTs caused by a strong coupling interaction between the nanotube and the Mo clusters.
[Show abstract][Hide abstract] ABSTRACT: A new synthetic method is demonstrated for transforming rice husks into bulk amounts of graphene through its calcination and chemical activation. The bulk sample consists of crystalline nano-sized graphene and corrugated individual graphene sheets; the material generally contains one, two, or a few layers, and corrugated graphene domains are typically observed in monolayers containing topological defects within the hexagonal lattice and edges. Both types of graphenes exhibit atomically smooth surfaces and edges.
Small 07/2014; 10(14). DOI:10.1002/smll.201400017 · 8.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nanoscale defects in the outer tube to preserve the electrical and optical features of the inner tube can be engineered to exploit the intrinsic properties of double walled carbon nanotubes (DWCNTs) for various promising applications. We demonstrated a selective way to make defects in the outer tube by the fluorination of DWCNTs followed by the thermal detachment of the F atoms at 1000 degrees C in argon. Fluorinated DWCNTs with different amounts of F atoms were prepared by reacting with fluorine gas at 25, 200, and 400 degrees C that gave the stoichiometry of CF0.20. CF0.30, and CF0 43, respectively. At the three different temperatures used, we observed preservation of the coaxial morphology in the fluorinated DWCNTs. For the DWCNTs fluorinated at 25 and 200 degrees C, the strong radial breathing modes (ABMs) of the inner tube and weakened RBMs of the outer tube indicated selective fluorine attachment onto the outer tube. However, the disappearance of the RBMs in the Raman spectrum of the DWCNTs fluorinated at 400 C showed the introduction of F atoms onto both inner and outer tubes. There was no significant change in the morphology and optical properties when the DWCNTs fluorinated at 25 and 200 degrees C were thermally treated at 1000 degrees C in argon. However, in the case of the DWCNTs fluorinated at 400 degrees C, the recovery of strong RBMs from the inner tube and weakened RBMs from the outer tube indicated the selective introduction of substantial defects on the outer tube while preserving the original tubular shape. The thermal detachment of F atoms from fluorinated DWCNTs is an efficient way to make highly defective outer tubes for preserving the electrical conduction and optical activity of the inner tubes.
Chinese Journal of Catalysis 06/2014; 35(6):864–868. DOI:10.1016/S1872-2067(14)60107-8 · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: R2O3 (R = Y, Eu, Er) metal oxides were synthesized from metal–ethylenediaminetetraacetic acid (EDTA) complexes using a flame spray technique. As this technique enables high deposition rates, films with thickness of several tens of micrometers were obtained. Films of yttria, europia, and erbia phase were synthesized on stainless-steel substrates with reaction assistance by H2–O2 combustion gas. The oxide films consisted of the desired crystalline phase with micropores. The porosity of the films was in the range of 6–15%, varying with the metal used. These results suggest that the true density of the metal oxide obtained from metal–EDTA powder through the thermal reaction process plays an important role in achieving film with the desired porosity.
[Show abstract][Hide abstract] ABSTRACT: The dependence of the radial breathing modes (RBMs) and the tangential mode (G-band) of triple-wall carbon nanotubes (TWCNTs) under hydrostatic pressure is reported. Pressure screening effects are observed for the innermost tubes of TWCNTs similar to what has been already found for DWCNTs. However, using the RBM pressure coefficients in conjunction with the histogram of the diameter distribution, we were able to separate the RBM Raman contribution related to the intermediate tubes of TWCNTs from that related to the inner tubes of DWCNTs. By combining Raman spectroscopy and high-pressure measurements, it was possible to identify these two categories of inner tubes even if the two tubes exhibit the same diameters because their pressure response is different. Furthermore, it was possible to observe similar RBM profiles for the innermost tubes of TWCNTs using different resonance laser energies but also under different pressure conditions. This is attributed to changes in the electronic transition energies caused by small pressure-induced deformations. By using Raman spectroscopy, it was possible to estimate the displacement of the optical energy levels with pressure.
The Journal of Physical Chemistry C 04/2014; 118(15):8153–8158. DOI:10.1021/jp4126045 · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Resonant Raman spectroscopy studies are performed to access information about the intertube interactions and wall-to-wall distances in double- and triple-walled carbon nanotubes. Here, we explain how the surroundings of the nanotubes in a multi-walled system influence their radial breathing modes. Of particular interest, the innermost tubes in double- and triple-walled carbon nanotube systems are shown to be significantly shielded from environmental interactions, except for those coming from the intertube interaction with their own respective host tubes. From a comparison of the Raman results for bundled as well as individual fullerene-peapod-derived double- and triple-walled carbon nanotubes, we observe that metallic innermost tubes, when compared to their semiconducting counterparts, clearly show weaker intertube interactions. Additionally, we discuss a correlation between the wall-to-wall distances and the frequency upshifts of the radial breathing modes observed for the innermost tubes in individual double- and triple-walled carbon nanotubes. All results allow us to contemplate fundamental properties related to DWNTs and TWNTs, as for example diameter- and chirality-dependent intertube interactions. We also discuss differences in fullerene-peapod-derived and chemical vapor deposition grown double- and triple-walled systems with the focus on mechanical coupling and interference effects.
[Show abstract][Hide abstract] ABSTRACT: We report the preparation of hybrid paper-like films consisting of alternating layers of graphene (or graphene oxide) and different types of multi-walled carbon nanotubes (N-doped MWNTs, B-doped MWNTs and pristine MWNTs). We used an efficient self-assembly method in which nanotubes were functionalized with cationic polyelectrolytes in order to make them dispersible in water, and subsequently these suspensions were mixed with graphene oxide (GO) suspensions, and the films were formed by casting/evaporation processes. The electronic properties of these films (as produced and thermally reduced) were characterized and we found electrical resistivities as low as 3x10(-4) Ω cm. Furthermore, we observed that these films could be used as electron field emission sources with extraordinary efficiencies; threshold electric field ca. 0.55 V/μm, β factor as high as of 15.19x10(3) and operating currents up to 220 µA. These values are significantly enhanced when compared to previous reports in the literature for other carbon nanostructured film-like materials. We believe these hybrid foils could find other applications as scaffolds for tissue regeneration, thermal and conducting papers and laminate composites with epoxy resins.
[Show abstract][Hide abstract] ABSTRACT: Chemical stability of 6-coodinated SrO is a fundamental problem when
this is used for various applications. In this study, optical and
chemical stabilities of 8-coordinated SrO:Eu2+ phosphor were
investigated. SrO:Eu2+ phosphor was synthesized from thermal
treatment of SrO:Eu powder located on a single crystalline MgO at
1500° C under reduction atmosphere. Obtained 8-coordinated
SrO:Eu2+ phosphor exhibit strong blue luminescence and
chemical stability in distilled water for 3 days. Our findings prove
that obtained 8-coordinated SrO:Eu2+ possesses relative
optical and chemical stabilities in water.
Journal of Solid State Chemistry 08/2013; 204:186-189. DOI:10.1016/j.jssc.2013.05.015 · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Eu2+-doped SrO (SrO:Eu2+) phosphors were synthesized and their luminescence properties were investigated. Phosphors doped with different Eu2+ concentrations were synthesized by the thermal treatment of SrO and Eu powders on a single crystalline MgO substrate at 1500 °C in a reducing atmosphere of Ar and H2. X-ray diffraction measurements showed that the synthesized phosphors contained 8-coordinated SrO with an orthorhombic crystal system. The phosphors showed a strong blue emission at 456 nm, which was attributed to the Eu2+ concentration. In addition, a phosphor doped with 2 at% Eu2+ showed an internal quantum efficiency of 30%.
Ceramics International 08/2013; 39(6):7115-7118. DOI:10.1016/j.ceramint.2013.02.053 · 2.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have used in situ current-voltage measurements of cup-stacked carbon nanotubes (CSCNTs) to establish reversible strain induced (compressive bending) semiconducting to metallic behavior. The corresponding electrical resistance decreases by two orders of magnitude during the process, and reaches values comparable to those of highly crystalline multi-walled carbon nanotubes (MWCNTs) and graphite. Joule heating experiments on the same CSCNTs showed that the edges of individual cups merge to form "loops" induced by the heating process. The resistance of these looped CSCNTs was close to that of highly deformed CSCNTs (and crystalline MWCNTs), thus suggesting that a similar conduction mechanism took place in both cases. Using a combination of molecular dynamics and first-principles calculations based on density functional theory, we conclude that an edge-to-edge interlayer transport mechanism results in conduction channels at the compressed side of the CSCNTs due to electronic density overlap between individual cups, thus making CSCNTs more conducting. This strain-induced CSCNT semiconductor to metal transition could potentially be applied to enable functional composite materials (e.g. mechanical sensors) with enhanced and tunable conducting properties upon compression.
[Show abstract][Hide abstract] ABSTRACT: Despite extensive research for more than 200 years, the experimental isolation of monatomic sulphur chains, which are believed to exhibit a conducting character, has eluded scientists. Here we report the synthesis of a previously unobserved composite material of elemental sulphur, consisting of monatomic chains stabilized in the constraining volume of a carbon nanotube. This one-dimensional phase is confirmed by high-resolution transmission electron microscopy and synchrotron X-ray diffraction. Interestingly, these one-dimensional sulphur chains exhibit long domain sizes of up to 160 nm and high thermal stability (~800 K). Synchrotron X-ray diffraction shows a sharp structural transition of the one-dimensional sulphur occurring at ~450-650 K. Our observations, and corresponding electronic structure and quantum transport calculations, indicate the conducting character of the one-dimensional sulphur chains under ambient pressure. This is in stark contrast to bulk sulphur that needs ultrahigh pressures exceeding ~90 GPa to become metallic.
[Show abstract][Hide abstract] ABSTRACT: We have demonstrated the ability to control the interlayer spacing of scrolled reduced graphene nanotubes through a high-temperature thermal treatment. The thermal annealing-induced variation of the interlayer spacing from 0.385 to 0.339 nm allowed us to study the change in the electronic and transport properties of the scrolled tubes.
[Show abstract][Hide abstract] ABSTRACT: In this work, we carried out chemical oxidation studies of nitrogen-doped multiwalled carbon nanotubes (CNx-MWCNTs) using potassium permanganate in order to obtain nitrogen-doped graphene nanoribbons. Reaction parameters such as oxidation reaction, reaction time, the oxidizer to nanotube mass ratio, and the temperature were varied, and their effect was carefully analyzed. The presence of nitrogen atoms makes CNx-MWCNTs more reactive toward oxidation when compared to undoped multiwalled carbon nanotubes (MWCNTs). High-resolution transmission electron microscopy studies indicate that the oxidation of the graphitic layers within CNx-MWCNTs results in the unzipping of large diameter nanotubes and the formation of a disordered oxidized carbon coating on small diameter nanotubes. The nitrogen content within unzipped CNx-MWCNTs decreased as a function of the oxidation time, temperature, and oxidizer concentration. By controlling the degree of oxidation, the N atomic % could be reduced from 1.56% in pristine CNx-MWCNTs down to 0.31 atom % in nitrogen-doped oxidized graphene nanoribbons. A comparative thermogravimetric analysis reveals a lower thermal stability of the (unzipped) oxidized CNx-MWCNTs when compared to MWCNT samples. The oxidized graphene nanoribbons were chemically and thermally reduced and yielded nitrogen-doped graphene nanoribbons (N-GNRs). The thermal reduction at relatively low temperature (300 °C) results in graphene nanoribbons with 0.37 atom % of nitrogen. This method represents a novel route to preparation of bulk quantities of nitrogen-doped unzipped carbon nanotubes, which is able to control the doping level in the resulting reduced GNR samples. Finally, the electrochemical properties of these materials were evaluated.