Small Carbon Nanotubes Research Articles

Effect of varied Ag nanoparticles functionalized CNTs on its anti-bacterial activity against E. coli

In this paper, we present the effect of the functionalization time of silver nanoparticles with carbon nanotubes (CNTs) for its antibacterial activity. CNTs were synthesized via conventional CVD process. Iron nanoparticles used as catalysts were deposited by buffer layer assisted growth (BLAG). The structure and morphology of the synthesized CNTs were examined by the scanning electron microscopy (SEM) and X-ray diffraction (XRD). Raman spectroscopy confirmed the formation of small diameter CNTs of semiconducting nature. The synthesized CNTs were purified and then functionalized for varied time with Ag nanoparticles, as confirmed by the FTIR spectroscopy. Functionalization of CNTs at different times resulted in the formation of different sized Ag nanoparticles attached to the CNTs. Finally the antibacterial assays were performed against Escherichia coli to quantify the effect of varied sized Ag-NPs on the sensitivity of CNTs. It was revealed that the antibacterial activity was dependent on the size of Ag nanoparticles as it showed an inverse relation between the dilution factor and the susceptibility. The minimal inhibitory concentration of CNTs-Ag conjugate was also determined for its antibacterial activity.

Nonlinear buckling analyses of a small-radius carbon nanotube

Carbon nanotube (CNT) was first discovered by Sumio Iijima. It has aroused extensive attentions of scholars from all over the world. Over the past two decades, we have acquired a lot of methods to synthesize carbon nanotubes and learn their many incredible mechanical properties such as experimental methods, theoretical analyses, and computer simulations. However, the studies of experiments need lots of financial, material, and labor resources. The calculations will become difficult and time-consuming, and the calculations may be even beyond the realm of possibility when the scale of simulations is large, as for computer simulations. Therefore, it is necessary for us to explore a reasonable continuum model, which can be applied into nano-scale. This paper attempts to develop a mathematical model of a small-radius carbon nanotube based on continuum theory. An Isotropic circular cross-section, Timoshenko beam model is used as a simplified mechanical model for the small-radius carbon nanotube. Theoretical part is mainly based on modified couple stress theory to obtain the numerical solutions of buckling deformation. Meanwhile, the buckling behavior of the small radius carbon nanotube is simulated by Molecular Dynamics method. By comparing with the numerical results based on modified couple stress theory, the dependence of the small-radius carbon nanotube mechanical behaviors on its elasticity constants, small-size effect, geometric nonlinearity, and shear effect is further studied, and an estimation of the small-scale parameter of a CNT (5, 5) is obtained.

Growth of small diameter multi-walled carbon nanotubes by arc discharge process

Multi-walled carbon nanotubes (MWCNTs) are grown by arc discharge method in a controlled methane environment. The arc discharge is produced between two graphite electrodes at the ambient pressures of 100 torr, 300 torr, and 500 torr. Arc plasma parameters such as temperature and density are estimated to investigate the influences of the ambient pressure and the contributions of the ambient pressure to the growth and the structure of the nanotubes. The plasma temperature and density are observed to increase with the increase in the methane ambient pressure. The samples of MWCNT synthesized at different ambient pressures are analyzed using transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. An increase in the growth of MWCNT and a decrease in the inner tube diameter are observed with the increase in the methane ambient pressure.

Small Band-gap-based CNT for Modeling of Nano Sensor

Modeling phenomena of small band-gap Carbon Nanotube (CNT) is analyzed in this paper. Device physics of CNT is studied and do the calculation of sub-band for zigzag CNT to model small band-gap tubes. Each carbon nanotube is illustrated as a single graphite sheet turned round into a cylindrical shape so that the arrangement is one dimensional with axial proportion. A comparison is made with the current literature to show that the proposed chirality CNT with small band-gap which performs the modeling of nano sensor. Furthermore, a sensing device is modeled and discussed in this paper. This carbon nanotube based sensing device makes it possible produce huge amount of nano chips as a disposable cartridge for diagnostic purposes. The optimum CNT is proposed in this paper to model a nano-electrode device. This research outcome shows that the importance of identification with verified uniqueness of high reliability and economical micro-fabrication for cost effectiveness.

Simultaneous voltammetric determination of ascorbic acid and uric acid using a seven-hole carbon nanotube paste multielectrode array

Simultaneous determination of ascorbic acid and uric acid using a multielectrode array system, including six small carbon nanotube paste working electrodes, a large carbon nanotube paste counter electrode, an Ag/AgCl micro-reference electrode and a novel ‘micro-drop’ cell.

Structure of Lennard—Jones nanowires encapsulated by carbon nanotubes

Molecular dynamics simulations have been performed to investigate the structures of Lennard—Jones (LJ) nanowires (NWs) encapsulated in carbon nanotubes (CNTs). We find that the structures of NWs in a small CNT only adopt multi-shell motifs, while the structures of NWs in a larger CNT tend to adopt various motifs. Among these structures, three of them have not been reported previously. The phase boundaries among these structures are obtained regarding filling fractions, as well as the interaction between NWs and CNTs.

Promoting Formation of Noncrystalline Li2O2 in the Li–O2 Battery with RuO2 Nanoparticles

Low electrical efficiency for the lithium-oxygen (Li-O2) electrochemical reaction is one of the most significant challenges in current nonaqueous Li-O2 batteries. Here we present ruthenium oxide nanoparticles (RuO2 NPs) dispersed on multiwalled carbon nanotubes (CNTs) as a cathode, which dramatically increase the electrical efficiency up to 73%. We demonstrate that the RuO2 NPs contribute to the formation of poorly crystalline lithium peroxide (Li2O2) that is coated over the CNT with large contact area during oxygen reduction reaction (ORR). This unique Li2O2 structure can be smoothly decomposed at low potential upon oxygen evolution reaction (OER) by avoiding the energy loss associated with the decomposition of the more typical Li2O2 structure with a large size, small CNT contact area, and insulating crystals.

First-principles investigation on B/N co-doping of ultra small diameter metallic single-walled carbon nanotubes

The electronic structure of two ultra small diameter metallic single-walled carbon nanotubes (SWCNTs) with B/N co-doping are investigated by using the first-principles theory. The results show that the B/N co-doping configuration is the energetically stable structure. The electronic structures of ultra small diameter metallic SWCNTs evolve from metallic to semiconducting as a result of B/N co-doping, in most case the energy gaps increase with increasing the symmetry destruction factor δ. In addition, we also discuss the electronic structures of B/N co-doped SWCNTs with B- or N-rich impurities, which are converted into metal from semiconductor due to B- or N-impurities.

Ab‐initio modeling of carbon nanotubes functionalized with pyrrolidine

AbstractRecently it was found non‐oxidative unzipping of functionalized multiwall carbon nanotubes (CNT) in solvent‐free reaction. In order to relate the effect of functionalization to the unzipping process we have modelled, using ab‐initio methods, various small diameter single wall CNT functionalized with pyrrolidine. Using a density functional theory code we have studied the electronic and vibrational properties of these structures where the pyrrolidine on the external wall is either at longitudinal or transversal position. The hydrogenation of the nanotube along an axial unzipping direction is also simulated in order to evaluate its effect on the opening of hexagonal carbon structure as suggested in other works. We have found that only the longitudinal position of pyrrolidine along with hydrogenation induces the spontaneous opening of the CNT. This unzipping effect increases with the decreasing of CNT diameter. We also found important differences for the calculated local vibrational modes between longitudinal and transversal positions of pyrrolidine. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modeling and simulation of carbon nanotube-semiconductor heterojunction vertical field effect transistors

The scaling behavior of carbon nanotube (CNT)-organic semiconductor heterojunction enabled vertical field effect transistors are comprehensively examined by two-dimensional consistent device simulations. Tunneling current is modeled by introducing tunneling induced carrier generation into the current continuity equation. Modulation of both the CNT-semiconductor Shottky barrier height and thickness are examined. The tunneling current and thermionic current dominate at on-state and off-state, respectively. Barrier height modulation plays an important role and improves the on-off current ratio and sub-threshold swing considerably. Small diameter CNT is preferred for enhancing the gate control on the CNT-channel barrier height. Reducing the effective gate oxide thickness by either a thin oxide or a high-κ gate insulator gives improvement of device performance, but the former one works more efficiently. The channel length and CNT spacing should be carefully engineered due to the trade-off between device characteristics in the sub-threshold and above-threshold region.

Growth of vertically aligned multiwall carbon nanotubes columns

Capability of patterning carbon nanotubes (CNTs) growth is of tantamount importance for a number of applications ranging from thermal to electronic. This article reports on the columnar growth of vertically aligned multiwall carbon nanotubes (VA-MWCNTs) on patterned Silicon (Si) surface. We have developed procedures based on negative as well as positive masking approaches which allows the growth of predetermined MWCNTs patterns. We describe in detail the process steps leading to Si surface patterning. As quoted above, patterns are exploited to grow VA-MWCNTs. We have focused in particular on the growth of CNT pillars by chemical vapor despoition (CVD) technique at 850°C with camphor and ferrocene as carbon precursors and catalyst respectively. Field emission scanning electron microscopy (FESEM) is employed at low magnification to verify the correct patterning, and at high magnification to examine the surface morphology of CNTs pillars. The pillars are up to 2 mm high, their height being tailored through the deposition time. The diameter of each MWCNT is in the range 30–70 nm and the length is up to few hundred micrometers. The small CNT pillars produced, have several electrical and thermal applications. For instance they can be very useful for heat transfer systems as the lower thermal conductivity of fluids can be improved by the inclusion of nanotubes thanks to their peculiar 1-dimensional heat transfer characteristics.

H2 adsorption in Ni and passivated Ni doped 4 Å single walled carbon nanotube

Adsorption binding energies have been calculated for Nickel-doped single-walled carbon nanotubes (CNTs). Density Functional Theory (DFT) with double numerical polarization (DNP) has been used for finding the total energies of the structures. It is found that the Nickel doped CNTs show fluctuation in the binding energies of hydrogen adsorption which is overcome by passivating the Nickel atom with two hydrogen atoms. The density of states (DOS) and Mullikan atomic charge analysis have been carried to confirm the charge transfer from Ni to the carbon atoms of the CNT. The smallest CNT (diameter ≈ 4 Å) with the chirality of (5,0) has been taken for hydrogen adsorption studies. Geometry optimization shows that Ni atom prefers bridge site rather than the centre of the hexagon. The H2 binding energies obtained in the present study reveal that desorption would take place above room temperature in Ni doped (5,0) CNTs.

Elastic Properties of Carbon Nanotubes

The geometric structure of carbon nanotubes (CNTs) can be considered to be the curling of graphene (graphite sheet) (Gao & Li, 2003; Shen, 2004). The physical parameters of carbon in graphite are widely adopted in the molecule dynamics (MD) simulations or other theoretical studies of CNTs, such as the bond energy and length of C-C, the bond angle of C-C-C, etc (Belytschko et al., 2002; Mayo et al., 1990; Xin et al., 2007, 2008). Previous researches have shown that the elastic modulus of small CNTs changes a lot when the radius varies. However, the elastic modulus of CNTs fairly approaches that of graphene, while the radius of CNTs is large enough. Therefore, it is necessary to have a clear understanding of the mechanical properties of graphene for the further realization of the properties of CNTs. Numerous researchers carried out experiments to measure the effective elastic modulus of CNTs (Krishnan et al.,1998; Poncharal et al., 1999). They reported the effective Young’s modulus of CNTs ranging from 0.1 to 1.7 TPa, decreasing as the diameter increased, and the average was about 1.0~1.2 TPa. MD simulations have provided abundant results for the understanding of the buckling behavior of CNTs. The Young’s modulus of the CNTs was predicted about 1.0~1.2 TPa through various MD methods (Jin & Yuan, 2003; Li & Chou, 2003; Lu, 1997). Hu et al. (Hu et al., 2007) proposed an improved molecular structural mechanics method for the buckling analysis of CNTs, based on Li and Chou’s model (Hwang et al., 2010) and Tersoff-Brenner potential (Brenner, 1990). Due to the different methods employed on various CNTs in these researches, the reported data scattered around an average of 1.0 TPa. The elastic properties were also discussed in the theoretical analysis by Govinjee and Sackman (Govinjee and Sackman, 1999) based on Euler beam theory, which showed the size dependency of the elastic properties at the nanoscale, which does not occur at continuum scale. Harik (Harik, 2001) further proposed three non-dimensional parameters to validate the beam assumption, and the results showed that the beam model is only proper for CNTs with small radius. Liu et al (Liu et al., 2001) reported the decrease of the elastic modulus of CNTs with increase in the tube diameter. Shell model was also used in some researches (Wang et al., 2003), to study axially compressed buckling of multi-walled CNTs. And studies by Sudak (Sudak, 2003) reported that the scale effect of CNTs should not be ignored. Wang et al (Wang et al., 2006) investigated the buckling of CNTs and the results showed that the critical buckling load drawn with the classical continuum theory is higher than that

Facile filling of metal particles in small carbon nanotubes for catalysis

A versatile wet chemistry method is developed for filling of subnanometer sized metal particles in carbon nanotubes with a diameter smaller than 1.5 nm. As an example, we showed that a confined bi-component Pd-V catalyst exhibit a higher benzene hydroxylation activity compared with that within multi-walled carbon nanotubes.

The effect of dimensionality of nanostructured carbon on the architecture of organic–inorganic hybrid materials

The natural tendency of carbon nanotubes (CNTs) to agglomerate is an underlying reason that prevents the realization of their full potential. On the other hand, covalent functionalization of CNTs to control dispersion leads to disruption of π-conjugation in CNTs and the non-covalent functionalization leads to a weak CNT-polymer interface. To overcome these challenges, we describe the characteristics of fostering of direct nucleation of polymers on nanostructured carbon (CNTs of diameters (~2-200 nm), carbon nanofibers (~200-300 nm), and graphene), which culminates in interfacial adhesion, resulting from electrostatic and van der Waals interaction in the hybrid nanostructured carbon-polymer architecture. Furthermore, the structure is tunable through a change in undercooling. High density polyethylene and polypropylene were selected as two model polymers and two sets of experiments were carried out. The first set of experiments was carried out using CNTs of diameter ~2-5 nm to explore the effect of undercooling and polymer concentration. The second set of experiments was focused on studying the effect of dimensionality on geometrical confinements. The periodic crystallization of polyethylene on small diameter CNTs is demonstrated to be a consequence of the geometrical confinement effect, rather than epitaxy, such that petal-like disks nucleate on large diameter CNTs, carbon nanofibers, and graphene. The application of the process is illustrated in terms of fabricating a system for cellular uptake and bioimaging.

Elution behavior of shortened multiwalled carbon nanotubes in size exclusion chromatography

We present a rigorous investigation on elution behaviors of ultrasonically shortened multiwalled carbon nanotubes in size-exclusion chromatography. The size separation of five carbon nanotube samples that underwent ultrasonic shortening for varying lengths of time revealed the existence of three kinds of carbon species: large nanotubes, small nanotubes, and amorphous carbon species. Separation of the three different carbon species was confirmed by SEM analyses on the fractionated eluates and also by light scattering/UV absorbance double detection. The chromatographic peak intensity ratio between the large and small nanotubes suggested an increased amount of small carbon nanotubes upon longer mechanical treatment time. The effect of the concentration of carbon nanotube dispersion on elution behavior was examined, and the elution volume of the shortened nanotubes was found to decrease upon dilution while that of the large nanotubes showed the opposite tendency. Unusual elution behaviors of the multiwalled carbon nanotubes were also observed by altering the flow rate, and these behaviors could be explained by the longer equilibration time taken for large nanotubes to access the pores of the packing materials and a possible morphology change of small carbon nanotubes.

Combination of small size and carboxyl functionalisation causes cytotoxicity of short carbon nanotubes

The use of carbon nanotubes (CNTs) could improve medical diagnosis and treatment provided they show no adverse effects in the organism. In this study, short CNTs with different diameters with and without carboxyl surface functionalisation were assessed. After physicochemical characterisation, cytotoxicity in phagocytic and non-phagocytic cells was determined. The role of oxidative stress was evaluated according to the intracellular glutathione levels and protection by N-acetyl cysteine (NAC). In addition to this, the mode of cell death was also investigated. CNTs <8 nm acted more cytotoxic than CNTs ≥20 nm and carboxylated CNTs more than pristine CNTs. Protection by NAC was maximal for large diameter pristine CNTs and minimal for small diameter carboxylated CNTs. Thin (<8 nm) CNTs acted mainly by disruption of membrane integrity and CNTs with larger diameter induced mainly apoptotic changes. It is concluded that cytotoxicity of small carboxylated CNTs occurs by necrosis and cannot be prevented by antioxidants.

Role of height and contact interface of CNT microstructures on Si for high current field emission cathodes

Regular arrays of vertically aligned microstructures consisting of entangled carbon nanotubes (CNTs) of different height and contact interface were grown on Si substrates with a bimetallic catalyst by water-assisted chemical vapor deposition. The arrays of high and wide CNT blocks (150–300 μ m, 50–140 μ m square) showed the ability to reach high stable field emission (FE) currents per block up to 300 μ A due to the presence of multiple CNT emitters. However, significant outgrowth of the CNTs and limited mechanical stiffness of such blocks led to a limited FE homogeneity and alignment of the emitters. For the arrays of small rounded CNT bundles ( ∼ 5 μ m, 20 μ m diameter), well-aligned and highly efficient FE with maximum currents up to 40 μ A per CNT bundle have been achieved. Unusual I - V curves with current saturation, strong activation effects and glowing spots just before destruction have been observed and are discussed by means of band structure considerations.

Organic fiber reinforced plastics based on complex hybrid matrices including polysulfone and carbon nanotubes as modifiers of epoxy resins

Organic Fiber Reinforced Plastics (OFRP) based on aramid fibers are as a rule used in constructions working under extremal conditions. In view of this, the possibility of increasing the resistance of OFRP to destruction by modifying matrices with thermoplastic polymers and carbon nanotubes (CNTs) offers much promise. In this work, we present the results obtained in a study of the properties of OFRP based on Rusar fibers and epoxy matrices containing either CNTs or a thermoplastic (PSK-1 polysulfone) or both these components simultaneously. The data obtained substantiate the possibility of using epoxypolysulfone matrices for the preparation of wound composites. This modification noticeably increases crack and impact resistance of OFRP based on aramid fibers without decreasing the glass transition temperature, as when matrices are plasticized by rubber and active diluents. The strongest effect of polysulfone introduced into an epoxy matrix is observed at a large (20 wt %) content of PSK-1. The modification of epoxypolysulfone matrices by CNTs also increases the shear strength of OFRP and almost does not change the fracture toughness and compression strength. The introduction of CNTs into epoxy matrices is less effective and can increase crack growth resistance of OFRP by approximately 30% only at a large (1%) content of CNTs. Small CNT admixtures (0.3–0.6%) do not influence the fracture toughness. Possible mechanisms of the changes observed are considered.

Exploring Aligned‐Carbon‐Nanotubes@Polyaniline Arrays on Household Al as Supercapacitors

Herein, we demonstrate a new approach towards the construction of supercapacitors consisting of carbon nanotubes (CNTs) and conducting polymers (ECPs) with high specific power, high specific energy, and stable cycling performance through a 3D design of a thin film of polyaniline (PANI) on an aligned small carbon nanotube (ACNT) array on household Al foils. The thin-film strategy is used to fully exploit the specific capacitance of PANI, and obtain regular pores, strong interaction between PANI and CNTs, and reduced electrical resistance for the electrodes. A facile process is developed to fabricate a highly flexible supercapacitor using this binder-free composite on household Al foil as the current collector. It exhibits high specific energy of 18.9 Wh kg(-1) , high maximum specific power of 11.3 kW kg(-1) of the active material in an aqueous electrolyte at 1.0 A g(-1) , and excellent rate performance and cycling stability. A high specific energy of 72.4 Wh kg(-1) , a high maximum specific power of 24.9 kW kg(-1) , and a good cycling performance of the active material are obtained in an organic electrolyte.