Carbon nanotube–ZnO nanocomposite electrodes for supercapacitors

Carbon nanotube (CNT)–zinc oxide (ZnO) nanocomposite and gel poly(vinyl alcohol)–phosphomolybdic acid were employed as the electrode and electrolyte of the experimental supercapacitor cell, respectively. The ZnO nanodots were deposited onto CNT films by ultrasonic spray pyrolysis in different times. The results of electrochemical measurements showed that the electrode with ZnO deposited in 5 min had the optimal capacitive properties among the experimental series, with a lowest interfacial electron transfer resistance, a very high capacitance of 323.9 F/g and good reversibility in the repetitive charge/discharge cycling test.     

Finding tube–lead coupling strength in a single-walled carbon nanotube

For the first time, the electron–electron interaction energy relative to the coupling of a single-walled carbon nanotube to the involved leads is estimated analytically by considering a quantum box transversal to the longitudinal axis of the tube. In addition, the relation of our calculation to creation and annihilation operators associated with the above coupling is discussed.     

Magnetic properties of the Ashkin–Teller model on a hexagonal nanotube

A new theoretical model for nanomagnets represented by the Ashkin–Teller model on a core-shell hexagonal nanotube is proposed. The Mean Field Theory from the Bogoliubov inequality is applied to study the magnetizations, phase boundaries and tricritical points. For a positive couplings system (ferromagnetic), first order and continuous phase transitions between the stable, metastable and unstable states are observed. For a negative core-shell coupling system, only continuous phase transitions between the stable and unstable states are observed. The phase diagram is presented to illustrate the different phases and transitions exhibited by the model.     

Synthesis and characterization of CdS nanoparticle based multiwall carbon nanotube–maleic anhydride–1-octene nanocomposites

CdS nanoparticles were synthesized by sonication from cadmium chloride and thiourea using a multiwall carbon nanotube (MWCNT)–maleic anhydride (MA)–1-octene system as the matrix. The matrix was obtained by the “grafting from” approach from oxidized carbon nanotubes and maleic anhydride–1-octene. Multiwall carbon nanotubes used for reinforcing the matrix were synthesized by Catalytic Chemical Vapor Deposition using Fe–Co/Al₂O₃ as the catalyst. The obtained nanostructures were characterized by FTIR, XRD, Raman spectroscopy, TEM, SEM and UV–vis spectroscopy. The average CdS particle diameter was 7.9 nm as confirmed independently by TEM and XRD. UV–vis spectroscopy revealed that the obtained nanostructure is an appropriate base material for making optical devices. The novelty of this work is the use of the MWCNT–MA–1-octene matrix obtained via the “grafting from” approach for the synthesis of uniformly dispersed CdS nanocrystals by ultrasonic cavitation to obtain a polymer nanocomposite.     

High microwave absorption performances for single-walled carbon nanotube–epoxy composites with ultra-low loadings

Microwave-absorbing polymeric composites based on single-walled carbon nanotubes(SWNTs) are fabricated via a simple yet versatile method, and these SWNT–epoxy composites exhibit very impressive microwave absorption performances in a range of 2 GHz–18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT–epoxy composites(1.3-mm thickness) with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth,corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appropriate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix.     

Wave propagation in fluid-filled single-walled carbon nanotube on analytically nonlocal Euler–Bernoulli beam model

An analytically nonlocal Euler–Bernoulli beam model for the wave propagation in fluid-filled single-walled carbon nanotube (SWCNT) is established. The governing equations with the nonlocal effects are derived on the variational principle, and used in the wave propagation analysis of the SWCNT beam. Compared with the partially nonlocal Euler–Bernoulli beam models used previously, the analytically nonlocal model presented in the present study predicts well the effects of the stiffness enhancement and the wave damping at the high wavenumber or the strong nonlocal effects area for the fluid-filled SWCNT beam. Though the analytical model is less sensitive than the partially nonlocal model when the moving velocity of the internal fluid is high enough, it simulates more of the high-order nonlocal effecting information than the partially nonlocal model does in many cases.     

Photon-assisted mesoscopic transport through a quantum dot–carbon nanotube system perturbed by microwave fields

We have investigated the coherent mesoscopic transport through the system with a quantum dot coupled to single-wall carbon nanotubes (CN–QD–CN) interfered by microwave fields (MWFs). The investigation focuses on the tunneling behaviors induced by the double coherent MWFs and the nature of CN leads. The incoherent fields induce the tunneling current possessing symmetric resonant behaviors. The coherent fields induce the asymmetric tunneling current resulting from the interference of tunneling current branches to form asymmetric photon-assisted net current. The quantum leads possess specific density of state (DOS) structure, and the matching–mismatching behavior takes important role in the mesoscopic transport. The feature of coupled MWFs and the connected quantum wires together control the characteristics of the mesoscopic system.     

Carbon nanotube (CNT)–epoxy nanocomposites: a systematic investigation of CNT dispersion

A systematic investigation of the dispersion of carbon nanotubes (CNTs), 1–6 nm in diameter and a few microns in length, in a bisphenol F-based epoxy resin has been presented. Several dispersing techniques including high-speed dissolver, ultrasonic bath/horn, 3-roll mill, etc. have been employed. Optical microscopy has been extensively used to systematically characterise the state of CNT dispersion in the epoxy resin during the entire processing cycle from mixing CNT with resin to adding and curing with hardener. Complimentary viscosity measurements were also performed at various stages of nanocomposite processing. A method to produce a good CNT dispersion in resin was established, but the state of CNT dispersion was found to be extremely sensitive to its physical and chemical environments. The cured nanocomposites were further tested for their thermo-mechanical properties by dynamic mechanical thermal analysis (DMTA), and for flexural and compressive mechanical properties. The measured properties of various nanocomposite plates were then discussed in view of the corresponding CNT dispersion.     

Determination of band gaps of self-assembled carbon nanotube films using Tauc/Davis–Mott model

The band gaps of self-assembled single-walled carbon nanotube (SWNT) films have been determined through curve fitting using the semi-empirical Tauc and Davis–Mott model, based on the measurement of optical absorption at the visible and near infrared range. This study provides a practicable option for the determination of band gaps for ultra-thin SWNT films or multi-walled carbon nanotube films whose vHs peaks cannot be well resolved in absorption spectra.     

TiO2–carbon nanotube composites for visible photocatalysts – Influence of TiO2 crystal structure

We investigated the influence of the crystal structure of TiO₂ and the use of different TiO₂ precursors on the properties and photocatalytic activity of carbon nanotube (CNTs)–titania composites. We found that the crystal structure and properties of starting TiO₂ nanomaterial significantly affected the effect of CNTs incorporation on the photocatalytic activity under simulated solar and visible light illumination (simulated solar illumination with UV-blocking filter). In case of significant photocatalytic activity under visible light illumination (anatase TiO₂), likely due to the presence of native defects, composites exhibited lower activity under visible illumination only, but higher activity under simulated solar illumination. The opposite trends were observed for P25 (anatase + rutile) and rutile TiO₂, where incorporation of CNTs resulted in a significant increase of photocatalytic activity under visible illumination. Thus, control over crystal structure and native defects is essential for the development of efficient visible light activated photocatalysts.     

Multiwalled carbon nanotube supported Pt–Sn–M (M = Ru,Ni, and Ir) catalysts for ethanol electrooxidation

In the present study, Pt–Sn–M (M = Ru, Ni, and Ir) nanocatalysts were supported on multiwalled carbon nanotube and their electrocatalytic activity for ethanol oxidation in membraneless fuel cells was investigated. The combination of monometallic Pt/MWCNTs, bi-metallic Pt–Sn/MWCNTs, and tri-metallic Pt–Sn–Ru/MWCNT, Pt–Sn–Ni/MWCNT, and Pt–Sn–Ir/MWCNT nanocatalysts were prepared by the ultrasonic assisted chemical reduction method. Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) were used for the catalyst characterization. The electrocatalytic activities of the catalysts were investigated in half-cell experiments using cyclic voltammetry (CV), CO stripping voltammetry, and chronoamperometry (CA). During the experiments performed on a single membraneless ethanol fuel cell (MLEFC), the Pt–Sn–Ir/MWCNTs exhibited a better catalytic activity from among all the catalysts prepared, with a power density of 39.25 mW cm^?2.     

Li adsorption on a Fullerene–Single wall carbon nanotube hybrid system: Density functional theory approach

In this study, we investigate Li adsorption mechanisms on the C₆₀-SWCNT hybrid system using density functional theory. It is found that the Li adsorption energy of the C₆₀-SWCNT hybrid system is increased in comparison to that of the pure SWCNT. The Li adsorption energy ranges from −1.917 eV to −2.642 eV for the single-Li adsorbed system and from −2.351 eV to −2.636 eV for the double-Li adsorbed system. It is also found that the adsorption energy becomes similar at most positions throughout the structure. In addition, the Li adsorption energy of 31-Li system is calculated to be −1.863 eV, which is significantly lower than the Li–Li binding energy (−1.030 eV). These results infer that Li atoms will be adsorbed on the space 1) between C₆₀ and C₆₀; 2) between SWCNT and C₆₀; 3) the rest of the space (e.g. between SWCNTs), rather than form Li clusters. As more Li atoms are adsorbed onto the C₆₀-SWCNT hybrid system due to such improved Li adsorption capability, the metallic character of the system is enhanced, which is confirmed via the band structure and electronic density of states.     

Semiconductor to metal transition in strictly two dimension–a comparative study on GaAs and carbon nanotube

Choosing GaAs, donor binding energies in two dimension are obtained using Thomas–Fermi and Hartree screening functions within the effective mass approximation. Binding energies are computed both in the hydrogen atom model and D ^? ion model. The results show the non-feasibility of semiconductor-to-metal transition (SMT) in two-dimensional system of GaAs. For curiosity we have obtained the donor binding energies in carbon nanotube (CNT), a highly correlated system by considering it as two-dimensional structure. We could observe the feasibility of SMT in CNT. This indicates the strong confinement in nanostructures and the results will be useful for nanodevice fabrication.     

Carbon nanotube emitters and field emission triode

Based on our study on field emission from multi-walled carbon nanotubes (MWNTs), we experimentally manufactured field emission display (FED) triode with a MWNTs cold cathode, and demonstrated an excellent performance of MWNTs as field emitters. The measured luminance of the phosphor screens was 1.8 × 103 cd/m2 for green light. The emission is stable with a fluctuation of only 1.5% at an average current of 260 μA.     

A comparison of the magnetic and microwave absorption properties of Mn–Sn–Ti substituted strontium ferrite with and without multi-walled carbon nanotube

In this work, a comparison of magnetic and microwave properties between Mn–Sn–Ti substituted SrM ferrite and nanocomposite of Mn–Sn–Ti substituted SrM ferrite–20% volume multi-walled carbon nanotube (MWCNT) has been done. Phase characterization and crystal structure of the synthesized nanoparticles were tested by X-ray diffraction (XRD). Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectrometry (FTIR) analysis approved that the SrFe_12−x(MnSn_0.5Ti_0.5)_x/2O₁₉ nanoparticles were attached on the external surfaces of the MWCNTs. Mӧssbauer spectroscopy (M_S) showed the occupancy by non-magnetic Mn²⁺–Sn⁴⁺–Ti⁴⁺ cations into the hexagonal lattice structure. Magnetic properties were evaluated by a vibrating sample magnetometer (VSM). The results also indicated that saturation magnetization and coercivity were decreased with an increase in x content and also MWCNTs addition. Microwave absorption properties were investigated by a vector network analyzer (VNA). It was found that with an addition of 20 volume percentage of MWCNTs, the saturation magnetization coupled with coercivity decrease, but reflection loss (RL) increase broadly. Also it proved that with an increase in the thickness of absorption the frequency band shifts from K_u (12–18 GHz) to X (8–12 GHz) band.     

Preparation of multi-walled carbon nanotube–Fe composites and their application as light weight and broadband electromagnetic wave absorbers

Multi-walled carbon nanotube （MWCNT）-Fe composites were prepared via the metal organic chemical vapor deposi- tion by depositing iron pentacarbonyl on the surface of MWCNTs. The structural and morphological analyses demonstrated that Fe nanoparticles were deposited on the surface of the MWCNTs. The electromagnetic properties of the MWCNTs were significantly changed, and the absorbing capacity evidently improved after the Fe deposition on the MWCNT surface. A minimum reflection loss of -29.4 dB was observed at 8.39 GHz, and the less than -10 dB bandwidth was about 10.6 GHz, which covered the whole X band （8.2-12.4 GHz） and the whole Ku band （12.4-18 GHz）, indicating that the MWCNT-Fe composites could be used as an effective microwave absorption material.     

Facile synthesis of a sulfur/multiwalled carbon nanotube nanocomposite cathode with core–shell structure for lithium rechargeable batteries

A novel sulfur/multiwalled carbon nanotube nanocomposite (S/MWCNT) was prepared by a facile quasi-emulsion template method in an O/W system. Transmission and scanning electronic microscopy show the formation of a highly developed core–shell tubular structure consisting of S/MWCNT composite with uniform sulfur coating on its surface. The homogenous dispersion and integration of MWCNT in the S/MWCNT composite create a highly conductive and mechanically flexible framework, enhancing the electronic conductivity and consequently the rate capability of the material. The S/MWCNT composite cathode could deliver a stable discharge (the fifth cycle) capacity of about 903 mAh g^?1 at 0.1 C, 751 mAh g^?1 at 0.5 C, and 631 mAh g^?1 at 1 C.