Synthesis and field emission properties of carbon nanotube films modified with amorphous carbon nanoparticles by a simple electrodeposition method

Amorphous carbon nanoparticles （a-CNPs） on a multi-walled carbon nanotube （MWCNT） film, deposited on a silicon substrate, were synthesized using an electrodeposition combination from a methanol suspension of polydiallyldimethylammonium chloride-modified MWCNTs. A low-voltage electropho- retic deposition of the MWCNTs and a high-voltage electrochemical deposition of the a-CNPs were carried out to yield homogenously attached a-CNPs on the surfaces of the MWCNTs, and form a composite film with good adhesion to the substrate. This scalable technology can produce a large area of a-CNP/MWCNT film. And the field emission investigations show that the a-CNP/MWCNT film has turn- on electric field of 3.17 V μm- 1 （at 10 μA cm-2） and threshold field of 4.62 V μm-1 （at 1 mA cm-2）, which are lower than those of the MWCNT film. The a-CNP/MWCNT film can be deposited simply with large areas and may be a promising cathode material applied in field emission displays.     

Predominating stable adsorption and direct electrochemistry of glucose oxidase on carbon nanotubes by oxygen-containing groups

Stable adsorption and direct electrochemistry of glucose oxidase (GOx) occurred on nitric acid (HNO3)-treated multi-walled carbon nanotubes (MWNTs) instead of as-received MWNTs, demonstrating the critical roles of oxygen-containing groups in stableadsorption and direct electrochemistry of GOx on carbon nanotubes (CNTs).     

The effect of gas adsorption on the field emission mechanism of carbon nanotubes

We have investigated systematically the effects of various gas adsorbates (H2, N2, O2, and H2O) on the electronic structures and the field emission properties of open edges of single-walled carbon nanotubes by density functional calculations. All of the molecules, except N2, dissociate and chemisorb on open nanotube edges with large adsorption energies. The Fermi levels are moved toward the valence (conduction) bands for O2 (H2, H2O) adsorption induced by the Mulliken charge transfer on the tube edge. The Fermi level shift for N2 adsorption is negligible. Adsorption of H2O enhances the field emission current, whereas H2 adsorption does not affect the field emission current much because of the absence of the density of states near the Fermi level. The correlation of the electronic structures and the field emission current is further discussed.     

Surface structure and adsorption properties of multiwalled carbon nanotubes

The pore structure, sorption parameters, and chemical composition of the surface of multiwalled carbon nanotubes synthesized by catalytic pyrolysis were determined. The dependences of the amount of cholic acid adsorbed by the nanotube surface on time, pH, and concentration of an equilibrium solution were studied. Physical adsorption of cholic acid is mainly the outcome of nonspecific interactions between the acid and the surface of the nanotubes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1712–1715, October, 2006.     

Effect of oxidation treatment of multi-walled carbon nanotubes on the adsorption of pentachlorophenol from aqueous solution: Kinetics study

Multi-walled carbon nanotubes (MWCNTs) were oxidized using different oxidizing agents and the produced oxidized MWCNTs were characterized using different techniques. IR measurements showed the presence of carboxylic acid function groups especially for the MWCNTs oxidized with nitric acid and hydrogen peroxide. The adsorption of pentachlorophenol (PCP) to pristine and oxidized multi-walled carbon nanotubes (MWCNTs) has been studied. The results showed that the oxidation of the MWCNTs decreased their abilities to adsorb PCP compared with the pristine MWCNTs. The adsorption was studied kinetically and the results showed that the adsorption process occurs in two different steps. The first step involves the transfer of PCP to the surface of the oxidized MWCNTs, which was very fast due to the diffusion of PCP from the liquid phase to the solid phase. This step followed by a second slower step of adsorption could be due to intra-particle diffusion.     

Electrically conducting electrospun silk membranes fabricated by adsorption of carbon nanotubes

We present a simple method of obtaining electrically conducting electrospun silk non-woven membranes consisting of nanofibers with multi-walled carbon nanotubes (MWCNTs) adsorbed on their surface. Nanofibrous membranes with fibroin diameters of 460 ± 40 nm were formed from aqueous Bombyx mori fibroin solution by electrospinning. The MWCNTs adhered well to the surface of the highly porous silk nanofibrous membranes when Triton X-100 was used as the surfactant for the dispersion of the MWCNTs in aqueous media. The electrical conductivity of the membranes was 2.4 × 10⁻⁴ S/cm due to the presence of the MWCNTs on their surface. In addition, the strong interaction between the MWCNTs and nanofibers keeps them from separating each other, even after ultrasonication. The combination of the high conductivity of the membranes and the simple process used to fabricate them could lead to significant advances in the development of new materials, such as electromagnetic interference shielding or electrostatic dissipation membranes.     

Removal of anionic and cationic dyes from wastewater by adsorption using multiwall carbon nanotubes

This paper evaluated the efficiency and reusability of multiwall carbon nanotubes (MWNTs) on removal of cationic and anionic dyes under effect of pH, dose of MWNTs and concentration of dyes. The characterization of MWNTs is characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectra and BET (Brunauer, Emmett and Teller) surface area. SEM and TEM analyses showed that MWNTs had size within nano scale range of 10–50 nm. The experimental results indicated that the efficiency of removal of MWNTs increase under condition of normal pH, at contact time 60 min with agitation speed 240 rpm and initial concentration of dyes 10 mg/l. Under these optimal conditions, the removal reached 98.7% and 97.2% for anionic dyes and cationic dyes, respectively. For economic use, MWNTs can be used more than one time where the same experiments with the already used MWNTs was repeated and it was found that the percent removal is almost the same.     

Behavior of ethylene and ethane within single-walled carbon nanotubes. 1-Adsorption and equilibrium properties

Endohedral adsorption properties of ethylene and ethane onto single-walled carbon nanotubes were investigated using a united atom (2CLJQ) and a fully atomistic (AA-OPLS) force fields, by Grand Canonical Monte Carlo and Molecular Dynamics techniques. Pure fluids were studied at room temperature, T=300 K, and in the pressure ranges 4×10⁻⁴<p<47.1 bar (C₂H₄) and 4×10⁻⁴<p<37.9 bar (C₂H₆). In the low pressure region, isotherms differ quantitatively depending on the intermolecular potential used, but show the same qualitative features. Both potentials predict that ethane is preferentially adsorbed at low pressures, and the opposite behavior was observed at high loadings. Isosteric heats of adsorption and estimates of low pressure Henry’s constants, confirmed that ethane adsorption is the thermodynamically favored process at low pressures. Binary mixtures of C₂H₄/C₂H₆ were studied under several (p,T) conditions and the corresponding selectivities towards ethane, S, were evaluated. Small values of S<4 were found in all cases studied. Nanotube geometry plays a minor role on the adsorption properties, which seem to be driven at lower pressures primarily by the larger affinity of the alkane towards the carbon surface and at higher pressures by molecular volume and packing effects. The fact that the selectivity towards ethane is similar to that found earlier on carbon slit pores and larger diameter nanotubes points to the fact that the peculiar 1-D geometry of the nanotubes provides no particular incentive for the adsorption of either species.     

Fluoride and lead adsorption on carbon nanotubes

The properties and applications of CNT have been studied extensively since Iijima discovered them in 1991[1,2]. They have exceptional mechanical properties and unique electrical property, highly chemical stability and large specific surface area. Thus far, they have widely potential applications in many fields. They can be used as reinforcing materials in composites[3], field emissions[4], hydrogen storage[5], nanoelectronic components[6], catalyst supports[7], adsorption material and so on.…     

The conversion of polyaniline nanotubes to nitrogen-containing carbon nanotubes and their comparison with multi-walled carbon nanotubes

Polyaniline (PANI) nanotubes were prepared by the oxidation of aniline in solutions of acetic or succinic acid, and subsequently carbonized in a nitrogen atmosphere during thermogravimetric analysis running up to 830 °C. The nanotubular morphology of PANI was preserved after carbonization. The molecular structure of the original PANI and of the carbonized products has been analyzed by FTIR and Raman spectroscopies. Carbonized PANI nanotubes contained about 8 wt.% of nitrogen. The molecular structure, thermal stability, and morphology of carbonized PANI nanotubes were compared with the properties of commercial multi-walled carbon nanotubes.     

Influence of amine-grafted multi-walled carbon nanotubes on physical and rheological properties of PMMA-based nanocomposites

In this work, poly(methyl methacrylate) (PMMA) was grafted onto amine treated multi-walled carbon nanotubes (NH-MWNTs) and the physical and rheological properties of the NH-MWNTs–g-PMMA nanocomposites were investigated. The graft reaction of NH-MWNTs and the PMMA matrix was confirmed from the change of the N_1S peaks, including those of amine oxygen and amide oxygen, by X-ray photoelectron spectroscopy (XPS). The thermal and mechanical properties of the NH-MWNT–g-PMMA nanocomposites were enhanced by the graft reaction between NH-MWNTs and PMMA matrix. In addition, the viscosity of the nanocomposites was increased with the addition of NH-MWNTs. Storage (G′) and loss modulus (G″) were significantly increased by increase in the NH-MWNT content compared to acid-treated MWNTs/PMMA nanocomposites. This increase was attributed to the strong interaction by the grafting reaction between NH-MWNTs and the PMMA matrix.     

碳纳米管内N2吸附行为及等量吸附热的GCMC分子模拟研究

碳纳米管及石墨烯具有高比表面积、高化学稳定性以及高耐蚀性等优点,被认为是一种理想的吸附材料。分子模拟技术的发展和应用丰富了人们对吸附机理研究的方式,而简单气体吸附体系的吸附机理研究对吸附理论的发展有着重要的推动作用。本文以单壁碳纳米管（SWCNT）-N₂吸附体系为研究对象,首先通过透射扫描电镜和氮气吸/脱附测试对所选用碳纳米管的微观孔形貌及吸/脱附等温线进行了表征,然后根据对应孔径参数采用巨正则蒙特卡罗方法对该体系的吸附过程进行了分子模拟,并详细研究了碳纳米管孔径和温度对该体系吸附行为的影响。结果显示,SWCNT孔径越小,吸附能力则越强;孔半径为0.746nm的SWCNT的吸附体系发生凝聚相变的临界温度为66K。通过对等量吸附热进行计算发现,孔半径0.746、1.15、1.56和1.83 nm的SWCNT-N₂吸附体系对应的初始固-液等量吸附热分别为10.9、9.2、8.6和8.4 kJ/mol。67.5K时,孔半径1.56和1.83 nm的吸附体系的等量吸附热有热峰出现。     

Flexible supercapacitors based on carbon nanotubes

This review provides an overview of recent progress towards the development of flexible supercapacitors based on macroscopic carbon nanotubes-based electrodes, including one-dimensional (1D) fibers, 2D films, and 3D foams, with a focus on electrode preparation and configuration design as well as their integration with other multifunctional devices.     

Influence of high vacuum annealing treatment on some properties of carbon nanotubes

Carbon nanotubes (CNTs) were synthesized using a chemical vapour deposition (CVD) method. The properties of CNTs before and after vacuum annealing treatment were studied using scanning electron microscopy (SEM), scanning tunneling microscopy/spectroscopy (STM/STS) and thermogravimetric analysis (TG). Field emission characteristics of the raw and vacuum heated (up to 650°C) carbon nanotube films (CNTFs) were measured in a diode system. Emissive properties of the CNTFs depend on an annealing process during which structural changes in the nanotube walls take place. The structural changes, related to saturation of dangling bonds, influence a rate of oxidation process and also improve the emissive field properties.     

Structural characterization and electrochemical lithium insertion properties of carbon nanotubes prepared by the catalytic decomposition of methane

Carbon nanotubes (CNTs) were synthesized by the catalytic decomposition of methane at 773, 873 and 973 K. Structures of these carbon nanotubes were characterized by TEM, HRTEM, XRD and Raman spectra, respectively. The results showed that with the increase of preparation temperature, the d ₀₀₂ value of the CNTs decreased, while the L _a values and the degree of crystallinity of the samples increased. Electrochemical lithium insertion properties of the CNTs used as positive electrodes in CNTs/Li cells were also investigated. The first charge capacities of CNTs/Li cells were 290, 254 and 202 mAh/g for samples produced at 773, 873 and 973 K, respectively. The sample from 773 K showed a larger charge capacity, which is attributed to the accommodation of lithium at microcavities, at edges of graphitic layers and at the surface of single graphitic layers. Its potential hysteresis during Li insertion and deinsertion processes may be related to the interstitial carbon atoms. Electronic Publication     

Polymer/carbon nanotube nanocomposites: Influence of carbon nanotubes on EVA photodegradation

The influence of carbon nanotubes on the photodegradation of EVA/carbon nanotube nanocomposites was studied by irradiation under photooxidative conditions (at λ > 300 nm, at 60 °C and in the presence of oxygen). The influence of the nanotubes on both the photooxidation mechanism of EVA and the rates of oxidation of the matrix was characterized on the basis of infrared analysis. On one hand, it was shown that the carbon nanotubes act as inner filters and antioxidants, which contribute to reduction in the rate of photooxidation of the polymeric matrix. On the other hand, it was shown that light absorption could provoke an increase in the local temperature and then induce the photooxidation of the polymer. The competition between these three effects determines the global rate of photooxidation of the polymeric matrix. Several factors are involved, the concentration of the carbon nanotubes, the morphology of the nanotubes and the functionalization of the nanotube surface.     

Physical properties of silicone foams filled with carbon nanotubes and functionalized graphene sheets

Free-rising silicone foams were made with loading fractions of up to 0.25 wt.-% functionalized graphene sheets (FGS) and up to 1.0 wt.-% carbon nanotubes (CNTs) using hydrogen as blowing agent. Scanning electron microscopy of the samples revealed an open cellular structure and a homogeneous dispersion of both types of nanofillers. The incorporation of nanofiller affected the foaming process and thus the final foam density and cellular structure. Transmission electron microscopy revealed the formation of a CNT network throughout the sample, while FGS presented an exfoliated and intercalated dispersion. The thermal stability of the samples was drastically affected by the presence of both nanofillers. Both nanofillers showed a positive effect on the compressive response of the foams. However, the nanocomposite foams were found to decrease the acoustic absorption with nanofiller content probably due to the variable foam structure and improved stiffness.     

Tip-enhanced near-field optical microscopy of carbon nanotubes

We review recent experimental studies on single-walled carbon nanotubes on substrates using tip-enhanced near-field optical microscopy (TENOM). High-resolution optical and topographic imaging with sub 15 nm spatial resolution is shown to provide novel insights into the spectroscopic properties of these nanoscale materials. In the case of semiconducting nanotubes, the simultaneous observation of Raman scattering and photoluminescence (PL) is possible, enabling a direct correlation between vibrational and electronic properties on the nanoscale. So far, applications of TENOM have focused on the spectroscopy of localized phonon modes, local band energy renormalizations induced by charge carrier doping, the environmental sensitivity of nanotube PL, and inter-nanotube energy transfer. At the end of this review we discuss the remaining limitations and challenges in this field. Figure Tip-enhanced Raman scattering and photoluminescence spectroscopy with sub 15 nm spatial resolution provides novel insights into the electronic and vibronic properties of single-walled carbon nanotubes.     

Single-walled carbon nanotubes as stationary phase in gas chromatographic separation and determination of argon, carbon dioxide and hydrogen

A chromatographic technique is introduced based on single-walled carbon nanotubes (SWCNTs) as stationary phase for separation of Ar, CO₂ and H₂ at parts per million (ppm) levels. The efficiency of SWCNTs was compared with solid materials such as molecular sieve, charcoal, multi-walled carbon nanotubes and carbon nanofibers. The morphology of SWCNTs was optimized for maximum adsorption of H₂, CO₂ and Ar and minimum adsorption of gases such as N₂, O₂, CO and H₂O vapour. To control temperature of the gas chromatography column, peltier cooler was used. Mixtures of Ar, CO₂ and H₂ were separated according to column temperature program. Relative standard deviation for nine replicate analyses of 0.2 mL H₂ containing 10 μL of each Ar or CO₂ was 2.5% for Ar, 2.8% for CO₂ and 3.6% for H₂. The interfering effects of CO, and O₂ were investigated. Working ranges were evaluated as 40-600 ppm for Ar, 30-850 ppm for CO₂ and 10-1200 ppm for H₂. Significant sensitivity, small relative standard deviation (RSD) and acceptable limit of detection (LOD) were obtained for each analyte, showing capability of SWCNTs for gas separation and determination processes. Finally, the method was used to evaluate the contents of CO₂ in air sample.     

Electrosynthesis of the poly(N-vinyl carbazole)/carbon nanotubes composite for applications in the supercapacitors field

Electrochemical polymerization of N-vinyl carbazole (VK) on carbon nanotube (CN) films was studied by cyclic voltammetry in LiClO₄/acetonitrile solutions. Cyclic voltammograms recorded on a blank Pt electrode were compared with those obtained when single or multi-walled CN films were deposited on the Pt electrode; in the latter case, a down-shift of the VK reduction peak potential was observed. Functionalization of CNs with poly(N-vinyl carbazole) (PVK) was invoked by Raman scattering and UV-VIS-NIR spectroscopic studies. The influence of sweep rate on the electrochemical properties of the PVK/CN nanocomposite and the performance of supercapacitors constructed using PVK-functionalized single-walled carbon nanotube electrodes were also evaluated.