Dimensional Carbon Nanostructures Research Articles

Size effect on transverse free vibrations of ultrafine nanothreads

Due to their unique properties and appealing applications, low dimensional sp3 carbon nanostructures have attracted increasing attention recently. Based on the beam theory and atomistic studies, this work carries out a comprehensive investigation on the vibrational properties of the ultrathin carbon nanothreads (NTH). Size effect is observed in transverse free vibrations of NTHs. To quantify such effects, the modified couple stress theory (MCST) is utilized to modify the Timoshenko beam theory. According to the first four order frequencies of NTHs from atomistic simulations, the critical length scale parameter of MCST is calibrated as 0.1 nm. It is shown that MCST has minor effect on the first four order modal shapes, except for the clamped boundary. MCST makes the modal shapes at the clamped boundary closer to those observed in atomistic simulations. This study suggests that to some extent the MCST-based Timoshenko beam theory can well describe the transverse vibration characteristics of the ultrafine NTHs, which are helpful for designing and fabricating the NTH-based nanoscale mechanical resonators.

Tensile properties of functionalized carbon nanothreads

Low dimensional sp3 carbon nanostructures have attracted increasing attention recently, due to their unique properties and appealing applications. Based on in silico studies, this work exploits the impacts from functional groups on the tensile properties of carbon nanothreads (NTH) – a new sp3 carbon nanostructure. It is found that functional groups will alter the local bond configuration and induce initial stress concentration, which significantly reduces the fracture strain/strength of NTH. Different functional types lead to different local bond re-configurations, and introduce different impacts on NTH. Further studies reveal that the tensile properties decreases generally when the content of functional groups increases. However, some NTHs with higher content of functional groups exhibit higher fracture strain/strength than their counterparts with lower percentage. Such observations are attributed to the synergetic effects from the sample length, self-oscillation, and distribution of functional groups. Simulations show that the tensile behaviour of NTH with the same functional percentage differs when the distribution pattern varies. Overall, ethyl groups are found to induce larger degradation on the tensile properties of NTH than methyl and phenyl groups. This study provides a comprehensive understanding of the influence from functional groups, which should be beneficial to the engineering applications of NTH.

Interface engineering integrates fractal-tree structured nitrogen-doped graphene/carbon nanotubes for supercapacitors

To construct atomic-scale and seamless interface between various dimensional carbon nanostructures is essential for maximizing the componental attributes and benefiting the transport of masses, electrons, ions and energies involved in reactions and energies storages. Inspired by the structure of ‘Catalpa bungei’ tree which arranges its thorns regularly as nodes to bridge leaves and branches for nutrient transport, herein, NiMgAl layered double hydroxides (LDHs) are used to grow the graphene/carbon nanotubes (CNTs) host matrix, and then CO2 etching is employed to create defective sites within the matrix for anchoring the metal nanoparticles and grafting the tiny graphene oxide (GO) sheets. Based on such strategy, CNTs as the ‘branches’ can be grown over the metal nanoparticles and GO as the ‘leaves’ can be covalently bonding with the matrix with chemical vapor deposition (CVD), so that an all-in-one and omnidirectional fractal-tree structure of N-G/CNTs composite can be prepared deliberately. The results demonstrate that the N-G/CNTs composite has a high specific surface area of 190.66 m2 g−1, a narrow pore size distribution of 4–6 nm, uniform microstructural and compositional distribution, and excellent electron and ion conductivity. As a net consequence, the N-G@CNTs electrode exhibits excellent capacitor performance. In addition, three quasi-solid-state symmetrical supercapacitors assembled from the optimized N-G@CNTs composite can illuminate LED lamps. Our strategy can build solid ladder for manupulating structural units and integrating interfaces in a deliberate way to synergize the materials performance.

Covalently bonded polyaniline-reduced graphene oxide/single-walled carbon nanotubes nanocomposites: influence of various dimensional carbon nanostructures on the electrochromic behavior of PANI

In this paper, water-dispersible and covalently bonded polyaniline-carbon nanostructures, including polyaniline-reduced graphene oxide (PANI-rGO), polyaniline-single-walled carbon nanotubes (PANI-SWCNTs), and polyaniline-reduced graphene oxide/single-walled carbon nanotube (PANI-rGO/SWCNTs) nanocomposites, were synthesized by grafting PANI onto p-phenylenediamine (PPD)-functionalized graphene oxide (GO) or single-walled carbon nanotubes (SWCNTs) using polystyrene sulfonate (PSS) as a macromolecular dopant agent. The structures and morphologies of the PANI, PANI-rGO, PANI-SWCNTs, and PANI-rGO/SWCNTs nanocomposites were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The cyclic voltammetry and UV–vis spectra were performed on an electrochemical workstation and a UV–vis spectrometer, respectively. The results show that the electrochromic and electrochemical properties of nanocomposites can benefit from the high conductivity of SWCNTs and the abundant active sites of rGO. When SWCNTs and rGO work together, their respective shortcomings are overcome, allowing the nanocomposite to exhibit the best electrochemical and electrochromic properties. The optical contrast increased from 0.38 for PANI to 0.52 for PANI-rGO/SWCNTs. The coloring and bleaching times decreased from 2.59 s and 2.39 s, respectively, for PANI to 1.33 and 0.78 s, respectively, for PANI-rGO/SWCNTs. The charge transfer resistance (Rct) decreased from 135 Ω for PANI to 30 Ω for PANI-rGO/SWCNTs. The synergistic effect of PANI, rGO, and SWCNTs can significantly improve the electrochromic ability of PANI. Electrochromic properties of covalently bonded polyaniline-reduced graphene oxide/single walled carbon nanotubes nanocomposites. A high performance electrochromic material was prepared using polyaniline (PANI) and two different dimensional carbon nanostructures, single-walled carbon nanotubes (SWCNTs) and reduced graphene oxide (rGO) as the components. The covalent bond was introduced to interface between PANI and two carbon nanostructures to form a three-dimensional conductive network. Owing to the high electron conduction through directly connected covalent bond and loose molecular chain aggregation brought by two various dimensional carbon nanostructure, PANI-rGO/SWCNTs nanocomposites exhibit superior electrochemical and electrochromic properties (high optical contrast and short switching time) compared with PANI.

Zeolitic imidazolate frameworks as novel precursors for microwave synthesis of carbon nanotubes

Till date metallocenes, especially ferrocene is the only reliable precursor for microwave synthesis of carbon nanotubes (CNT). In this manuscript we report the utility of cobalt or palladium based ZIF (Zeolitic imidazolate frameworks) as a single precursor for microwave synthesis of CNT. Nitrogen doped, bamboo structured, micrometer long carbon nanotubes are grown on microwave susceptible surfaces such as graphene and carbon fibers using Co-ZIF or Pd-ZIF as the CNT source to give unique mesoporous three dimensional carbon nanostructures (G-Co@NCNT and G-Pd@NCNT). The utility of synthesized G-Co@NCNT as anode in lithium ion batteries and G-Pd@NCNT in electro-oxidation of formic acid is also reported.

Achievement of nearly super hydrophobicity in plasma enhanced chemical vapour deposited one and two dimensional carbon nanostructures

Plasma enhanced chemical vapour deposition (PECVD) has been employed in order to synthesis different one, two and mixed dimensional carbon nanostructures on catalyst modified silicon substrate. The microstructures of all the as prepared samples were characterized by field emission scanning electron microscopes. The bonding and hybridization states of all the samples were analysed with the help of Fourier transformed infrared spectroscopy and Raman spectroscopy in depth. It has been shown that the roughness of the silicon substrates as well as the thickness of the catalyst layer casts a marked effect on the sample morphology of the as synthesized samples.The response of all the samples towards water droplets has been studied in detail and it has been shown that it is possible to achieve nearly super hydrophobicity in the samples simply by varying the deposition condition, surface roughness as well as catalyst layer.The surface energies of all the samples were calculated following modified Young's equation by measuring the contact angles of two different liquids. Also efforts has been given in order to relate the hydrophobic response of the samples with the constituent components of the surface energy.This systematic effort can play an important role in determining the structure energy relationship in PECVD synthesized carbon nanomaterials.

Novel Multi-Dimensional Nanocarbons and Their Applications in Electrochemical Energy Storage

In order to realize next generation energy storage devices with high efficiency, large energy/power density, and long life cycle, novel carbon-based nanomaterials are needed as electrodes. In here, we present interesting multidimensional carbon nanostructures which could find potential applications in electrodes for energy storage devices. We synthesized carbon nanoplatelets (CNPs) by simple thermal treatment of expandable graphites. By using carbon nanoplatelets (CNPs), multi- dimensional (1D+2D) carbon nanostructures (CNP-CNTs) were synthesized by use of metal catalysts and CVD process. Basic cyclic voltammetry study on the CNPs and CNP-CNTs reveals that CNP-CNTs possessed enhanced mass specific capacitances compared to those of CNPs. We will also present recent progress on our multi-dimensional carbons including WGO-CNTs and silica coated CNP-CNTs. Our multi-dimensional carbon nanostructures showed excellent electrochemical properties probably due to large surface area and unique geometry. These results suggest that the multi-dimensional carbon nanostructures could be promising in the applications for electrodes of next generation energy storage devices.

Geometric dependence of transport and universal behavior in three dimensional carbon nanostructures

Carbon nanostructures with the spherical voids exhibit interesting temperature and magnetic field dependent transport properties. By increasing the void size, the structures are tuned from metallic to insulating; in addition, the magnetoresistance (MR) is enhanced. Our investigation in the magnetic fields (B) up to 18 T at temperatures (T) from 250 mK to 20 K shows that at high temperatures (T > 2 K), the MR crosses over from quadratic to a non-saturating linear dependence with increasing magnetic field. Furthermore, all MR data in this temperature regime collapse onto a single curve as a universal function of B/T, following Kohler's rule. Remarkably, the MR also exhibits orientation insensitivity, i.e., it displays a response independent of the direction on the magnetic field.

CdS nanoparticle coated carbon nanotube through magnetron sputtering and its improved field emission performance

Carbon nanotubes (CNTs) are the most famous cold cathodes for display technology. However, graphene and other two dimensional carbon nanostructures and advanced II-VI semiconductor nanostructures are strongly emerging as strong competitors challenging the well established performance of CNTs in this field. Hence several technologies to improve field emission (FE) properties of CNTs are being developed. Here we report a facile technique to improve the cold emission performance of multiwalled CNTs (MWCNTs) by coating the same with chalcogenide semiconductor. MWCNT thin films were synthesized via chemical vapor deposition (CVD) technique and the same was coated by cadmium sulfide (CdS) nanoparticles via radio frequency magnetron sputtering technique. The pure and coated thin films were characterized by Fourier transform infrared spectroscopy and Raman spectroscopy to confirm presence of CdS on CNT surfaces. X-ray photoelectron spectroscopy revealed the compositional and valance state information of the as prepared samples. Field emission scanning electron microscopy and high resolution transmission electron microscopic studies were carried out to obtain information regarding morphology and nanocrystallinity of the CNTs and the coated CdS nanoparticles. Field assisted electron emission of pristine CNTs developed significantly with improved turn-on field and very high current density by CdS nanoparticle coating.

π-Plasmon model for carbon nano structures: Application to porphyrin

In traditional concept, the optical properties of semiconductors and semimetals near their fundamental optical band gaps are attributed to single excitations (such electron-hole pairs, excitons...). In our earlier article, we proposed the collective mechanism of π-plasmons for optical properties of low dimensional carbon nano structures. A simple way to calculate the peak positions of UV-vis absorption spectra was pointed out and gave a good agreement with experimental data. In this work we analyze different schemas to calculate the UV-vis absorption peaks. A new parameter k which characterizes the dependence of schema on geometry and number of carbon sites is defined. As an example, the case of porphyrin was investigated.

Photovoltaic properties of graphene oxide sheets beaded with ZnO nanoparticles

A hybrid material of graphene oxide (GO) sheets beaded with ZnO nanoparticles was prepared. The material extends over a few hundred square nanometers, in which the ZnO nanoparticles (average diameter (∼5 nm)) are dispersed evenly on the GO sheet. Both the surface photovoltage or surface photocurrent intensity for the material are much stronger than for pure ZnO nanoparticles, meaning that the free charge carriers can effectively be transferred from ZnO nanoparticles to GO sheets, which can serve as a probe to monitor the electron transfer from excited ZnO to GO. Anchoring ZnO nanoparticles on two dimensional carbon nanostructures such as GO can pave a way towards the design of ordered nanostructure assemblies that can harvest light energy efficiently.

A comparative study of field-emission from different one dimensional carbon nanostructures synthesized via thermal CVD system

Different one dimensional (1D) carbon nanostructures, such as carbon nanonoodles (CNNs), carbon nanospikes (CNSs) and carbon nanotubes (CNTs) have been synthesized via thermal chemical vapour deposition (TCVD) technique. The different 1D morphologies were synthesized by varying the substrate material and the deposition conditions. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). FESEM and TEM images showed that the diameters of the CNNs and CNTs were ∼40 nm while the diameters of the CNSs were around 100 nm. Field emission studies of the as-prepared samples showed that CNSs to be a better field emitter than CNNs, whereas CNTs are the best among the three producing large emission current. The variation of field emission properties with inter-electrode distance has been studied in detail. Also the time dependent field emission studies of all the nanostructures have been carried out.