[Show abstract][Hide abstract] ABSTRACT: Highly oriented strontium oxide (SrO) whiskers were obtained using a chemical vapor deposition technique at atmospheric pressure. The SrO whiskers were synthesized on a single-crystalline Si(100) substrate from strontium bis-dipivaloylmethanate, Sr(C11H19O2)2. The presence of face-centered cubic (fcc) SrO structures was confirmed. The hexagonal SrO whiskers were preferentially oriented in the <111> direction upon increasing deposition time. This phenomenon is based on equilibrium figure in the <111> direction of fcc crystals.
[Show abstract][Hide abstract] ABSTRACT: MgO films were epitaxially grown on single crystal MgO substrates by atmospheric-pressure chemical vapor deposition (CVD). Reciprocal lattice mappings and X-ray reflection pole figures were used to evaluate the crystal quality of the synthesized films and their epitaxial relation to their respective substrates. The X-ray diffraction profiles indicated that the substrates were oriented out-of-plane during MgO crystal growth. Subsequent pole figure measurements showed how all the MgO films retained the substrate in-plane orientations by expressing the same pole arrangements. The reciprocal lattice mappings indicated that the whisker film showed a relatively strong streak while the continuous film showed a weak one. Hence, highly crystalline epitaxial MgO thin films were synthesized on single crystal MgO substrates by atmospheric-pressure CVD.
[Show abstract][Hide abstract] ABSTRACT: In this investigation, rare earth metal oxide films were synthesized from metal complexes of ethylenediaminetetraacetic acid (metal-EDTA) by utilizing a flame spray technique. Two raw metal-EDTA powders were prepared as starting materials in order to synthesize (Y,Er)2O3 films on stainless steel (SUS) substrates by a reaction that is promoted by the combustion of gaseous H2-O2. Molecularly mixed EDTA·(Y,Er)·H and mechanically mixed EDTA·Y·H + EDTA·Er·H complexes were subsequently prepared. The existence of Y2O3 and Er2O3 crystalline phases was confirmed for the EDTA·Y·H + EDTA·Er·H mixtures. Lamellar structures were formed on the film with a porosity of 9.5%. Alternatively, a homogenous, (Y,Er)2O3 film was obtained from the EDTA·(Y,Er)·H complex, with a film porosity of 31.8%. These results indicate that uniform (Y,Er)2O3 films were synthesized on SUS substrates from molecularly mixed EDTA·(Y,Er)·H powders.
No preview · Article · Jan 2016 · MATERIALS TRANSACTIONS
[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: Herein, we demonstrate improvements to the compressive strength of cementitious mortar by incorporating rice husk-derived graphenes (GRHs). Several manufacturing trials were undertaken to synthesize optimized GRHs using different dosages of rice husk ash and potassium hydroxide as well as a range of activation temperatures. The incorporation of GRHs into mortar exhibits a generally enhanced reinforcing effect compared to graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWNTs) because of its high specific surface area. SEM/TEM image analyses confirm that GRH has a corrugated graphene structure and clean edges at the atomic scale. GRH showed extremely high BET surface area (2274 m2/g) compared to those of multi-walled carbon nanotubes and GNPs (50-200 m2/g).
No preview · Article · Oct 2015 · Construction and Building Materials
[Show abstract][Hide abstract] ABSTRACT: Carbon nanotubes (CNTs)/lead sulfide (PbS) quantum dots (QDs) nanohybrids have been synthesized through the controlled decoration of CNTs by PbS-QDs by means of the pulsed laser deposition technique. The size of the PbS-QDs and their surface coverage of the CNTs' surface are monitored through the number of laser ablation pulses. Here, while comparing both single-walled (SW) and double-walled (DW) CNTs based nanohybrids, focus is put on the investigation of their interfacial structure and the effect of inner tube. Anchoring PbS through direct sulfur-carbon chemical bonding between CNTs' outer wall and PbS-QDs, which are thought to be profitable for efficient charge transfer but not for charge transport along CNT's tube axis, are confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. In the case of double-walled CNTs (DWCNTs), inner tube remains unaffected by ablated PbS species, then it serves efficient conduction way for transferred photo-generated charges. This unique feature of the DWCNTs based nanohybrid, where the photocharges are generated by the chemically bonded PbS-QDs to the outer tube and then efficiently conveyed by the inner tube of the nanotubes, is highly likely at the origin of their significantly higher photo-activity (several hundred times than in SWCNTs-based nanohybrids).
[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.
Full-text · Article · Jun 2015 · Journal of Materials Chemistry A
[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.
[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.
[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.
No preview · Article · Jun 2014 · Journal of Thermal Spray Technology
[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.
No preview · Article · Jun 2014 · Chinese Journal of Catalysis
[Show abstract][Hide abstract] ABSTRACT: Double walled carbon nanotubes (DWCNTs) are considered an ideal model for studying the coupling interactions between different concentric shells in multi-walled CNTs. Due to their intrinsic coaxial structures they are mechanically, thermally, and structurally more stable than single walled CNTs. Geometrically, owing to the buffer-like function of the outer tubes in DWCNTs, the inner tubes exhibit exciting transport and optical properties that lend them promise in the fabrication of field-effect transistors, stable field emitters, and lithium ion batteries. In addition, by utilizing the outer tube chemistry, DWCNTs can be useful for anchoring semiconducting quantum dots and also as effective multifunctional fillers in producing tough, conductive transparent polymer films. The inner tubes meanwhile preserve their excitonic transitions. This article reviews the synthesis of DWCNTs, their electronic structure, transport, and mechanical properties, and their potential uses.
[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.
No preview · Article · Apr 2014 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: CO2 adsorption has been measured in different types of graphitic nanostructures (MWCNTs, acid treated MWCNTs, graphene nanoribbons and pure graphene) in order to evaluate the effect of the different defective regions/conformations in the adsorption process, i.e., sp3 hybridized carbon, curved regions, edge defects, etc. This analysis has been performed both in pure carbon and nitrogen-doped nanostructures in order to monitor the effect of surface functional groups on surface created after using different treatments (i.e., acid treatment and thermal expansion of the MWCNTs), and study their adsorption properties. Interestingly, the presence of exposed defective regions in the acid treated nanostructures (e.g., uncapped nanotubes) gives rise to an improvement in the amount of CO2 adsorbed; the adsorption process being completely reversible. For N-doped nanostructures, the adsorption capacity is further enhanced when compared to the pure carbon nanotubes after the tubes were unzipped. The larger proportion of defect sites and curved regions together with the presence of stronger adsorbent-adsorbate interactions, through the nitrogen surface groups, explains their larger adsorption capacity.
Full-text · Article · Mar 2014 · International Journal of CO2 Utilization
[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: Coalescing carbon nanotubes is a major challenge for designing structures with novel physical and chemical properties and for creating three-dimensional carbon networks with improved mechanical and transport properties. We have coalesced adjacent triple walled carbon nanotubes (TWNTs) covalently, using catalytic boron atoms at high temperatures. The two outermost and then the two inner nanotubes of adjacent TWNTs merged in order to create an enlarged flattened double-walled carbon nanotube which encapsulated the two innermost single-walled carbon nanotubes.