CNx Nanotubes Research Articles

Orientation ordering of N2 molecules in vertically aligned CN x nanotubes

Arrays of vertically aligned nitrogen-doped carbon (CNx) nanotubes have been synthesized by decomposition of aerosol mixture of acetonitrile and ferrocene at 850°C. Nitrogen concentration in the outer shells of the CNx nanotubes was found from X-ray photoelectron spectroscopy (XPS) data to reach ∼6%. The XPS N 1s spectra and N 1s near-edge X-ray absorption fine structure (NEXAFS) spectra identified three chemical forms of nitrogen in the CNx nanotube arrays: pyridine-like, graphitic, and molecular nitrogen. The π* resonance of molecular nitrogen showed clear polarization dependence that indicates predominant orientation of N2 molecules along the nanotubes axis. The estimated range of the polar angle distribution of the N2 molecules orientation in the CNx nanotube array amounts to 15°.

Effect of nitrogen doping on Raman spectra of multi‐walled carbon nanotubes

AbstractMulti‐walled carbon nanotubes (CNTs) and nitrogen‐doped carbon (CNx) nanotubes have been synthesized by the aerosol‐assisted chemical vapour deposition (CVD) method. The samples were prepared from toluene and acetonitrile taken in different proportion. The structure of CNTs and CNx nanotubes was compared using first‐ and second‐order Raman spectra. The disorder‐induced D band was found to up‐shift with increase of the acetonitrile fraction. The ID/IG and IG′/IG ratios showed the opposite dependence on the doping level of CNTs. Both kinds of the substitute nitrogen: graphitic‐like and pyridinic‐like contribute to the disorder in CNx nanotube layers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrochemistry of Nitrogen‐Doped Carbon Nanotubes (CNx) with Different Nitrogen Content and Its Application in Simultaneous Determination of Dihydroxybenzene Isomers

AbstractThe bamboo‐shaped nitrogen‐doped carbon nanotubes (CNx) with different nitrogen content were synthesized using Fe‐containing SBA‐15 molecular sieve as catalyst with thermal decomposition. The CNx nanotubes prepared were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (XRD) and Raman spectroscopy. The results suggest that there are a larger amount of defective sites on CNx nanotubes surfaces due to the nitrogen doping and CNx nanotube with higher nitrogen content possesses lower graphitic ordering in the framework. Furthermore the effects of nitrogen content on the electrochemistry of CNx modified electrodes were investigated by cyclic voltammetry (CV). CNx modified electrodes exhibit better electrocatalytic activities to the oxidation of hydroquinone. Moreover CNx with lower nitrogen content is in favor of the electron transfer between dihydroxybenzene and electrode surface, while CNx with higher nitrogen content possesses high surface adsorptive ability. CNx modified electrodes can be applied to determine dihydroxybenzene isomers directly and simultaneously by linear sweep voltammetry technique without previous separation.

Bamboo-shaped aligned CNx nanotubes synthesized using single feedstock at different temperatures and study of their field electron emission

The present investigation deals with the synthesis of N-doped aligned bamboo-shaped carbon nanotubes (CNx) by chemical vapour deposition of monoethanolamine/ferrocene mixture on quartz substrate over the temperature range 700–900 °C. All nanotubes exhibited bamboo-like morphology with transverse carbon bridges forming compartments in this temperature range. The concentration of nitrogen content has been controlled in the range 4.8–5.8 at% by controlling the deposition temperature. Scanning electron microscopy, transmission electron microscopy (TEM)/high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and thermogravimetric analysis were used to characterize the composition and structural analysis of the as-grown nanotubes. HRTEM revealed that nanotubes prepared at high temperature with low nitrogen content have high graphitization degree. XPS analysis indicated that N 1s signal was split into three peaks. The decomposition of monoethanolamine at reaction temperature produces ammonia which may provide an efficient route of higher nitrogen content on carbon nanotubes. Field emission measurements indicated that N-doped carbon nanotubes prepared at 800 °C showed nice field emission performance with turn-on and threshold field of 1.6 and 2.3 V µm−1, respectively.

Fast and reversible surface redox reduction in V2O5 dispersed on CNx nanotubes

V(2)O(5) nanofilms (NFs) uniformly distributed on N-doped carbon nanotubes (CNTs) exhibit significantly stable capacitive performance; the synthesized composites are promising as an instantaneous power supply in consumer electronics or electrical vehicles.

CNx nanotubes as catalyst support to immobilize platinum nanoparticles for methanol oxidation

Pt nanoparticles with sizes of 3–9 nm were well dispersed on carbon nitride (CNx) nanotubes without needing pre-surface modification on the CNx nanotubes due to the inherent chemical activity. The products were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. All the experimental results revealed that Pt nanoparticles were immobilized on the CNx nanotubes due to the N-participation in the connection of Pt species with the support. The electrocatalytic property of the as-prepared Pt/CNx catalyst in methanol oxidation was examined by cyclic voltammetry. The results reveal that the so-constructed Pt/CNx catalyst has obvious catalytic activity, suggesting potential applications in fuel cells.

Electrical properties of CNx nanotubes probed in a transmission electron microscope

Knowledge of the mechanical and electrical characteristics of one-dimensional nanostructures is critical for their future integration in nanoelectronic circuits. The present study analyses the behaviour of N-doped carbon nanotubes (CNx,x<0.1) under applied stresses inside a transmission electron microscope. The electrical resistance changes observed were substantial, with figures ranging from 42 to 182 k Ω, and are largely correlated with the extension of the contact area (electrode–nanotube or nanotube–nanotube). Despite the repeated deformation cycles and high bending angles achieved, the nanotubes kept their metallic nature throughout. In addition to this, it was noticed that the CNx nanotubes presented sections with several structural defects which acted as joints during their controlled bending. These areas represent high-resistive points which may lead to fatal structural failure, as demonstrated in the current induced failure experiments here reported.

Encapsulation of molecular nitrogen in multiwall CNx nanotubes

AbstractMultiwall CNx nanotubes have been grown in the result of acetonitrile decomposition over Fe catalyst (CVD method). The random nanotubes samples have been produced by classical technique using catalyst nanoparticles formed by iron bimaleate thermolysis. The aligned nanotubes have been synthesized by aerosol assisted CVD method where ferrocene was used as a catalyst source. X‐ray photoelectron spectroscopy (XPS) showed the random sample contains two kinds of nitrogen, while additional high‐energy peak was detected in the N 1s‐spectrum of the aligned CNx nanotubes. X‐ray absorption spectra measured near the N K‐edge (NEXAFS) of the samples exhibited three peaks for both type of CNx nanotubes. The relative intensity of the high‐energy peak was found to be much higher in the spectrum of aligned nanotubes. Assignment of the NEXAFS peaks was made using results of quantum‐chemical calculations on carbon tube model incorporating pyridinic, three‐fold coordinated and molecule nitrogen. The high‐energy peak was shown to correspond to N2 molecules and its absence in the XPS spectrum of random CNx nanotubes indicates the gaseous nitrogen is mainly concentrated in the interior region of nanotubes. The larger encapsulation of molecules in the aligned CNx nanotubes could be due to the higher diffusion of nitrogen atoms trough the catalytic particles formed directly in the CVD process. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Grafting of Polystyrene on Nitrogen-Doped Multi-Walled Carbon Nanotubes

Polymer grafting of polystyrene (PS) on nitrogen-doped multiwall carbon nanotubes (CNx) was successfully obtained by a "grafting from" technique. The production method involves the immobilization of initiators, using wet chemistry, onto the nanotube surface, followed by an in situ surface-initiated polymerization. The polymer-grafting carbon nanotubes synthesis includes the free radical functionalization of CNx and the "controlled/living" Nitroxide Mediated Radical Polymerization (NMRP). The obtained products were studied using several microscopic techniques as scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS). The characterization also includes thermogravimetric analysis (TGA), Raman spectroscopy, infrared spectroscopy, and electron spin resonance (ESR), among others. The analyzed samples were also compared with solutions fabricated by physical blending of the polymer and CNx nanotubes. These results indicate that the nanotube radical functionalization, the chemical grafting, and the polymerization reaction were obtained over CNx when NMRP method was successfully used, giving rise to a uniform PS layer of several nanometers grafted on the outer surface of the CNx nanotubes. Several properties of the PS-grafted CNx nanotubes were also studied. It is shown that the production method leads to a narrower distribution of the external diameters. Moreover, their solubilization in organic solvents is greatly improved. Finally, the dispersion of PS-grafted CNx into a PS matrix is studied to determine the differences in filler dispersion and interfacial adhesion strength, in comparison with nanocomposites elaborated with as-produced CNx.

Synthesis of CNx nanotubes using catalysts prepared from zinc and nickel bimaleates

Nitrogen-containing carbon nanotubes have been prepared via acetonitrile (CH3CN) pyrolysis at 850°C catalyzed by nanoparticles produced by the thermal decomposition of zinc and nickel bimaleates and their solid solutions. The synthesized samples have been characterized by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. The results demonstrate that increasing the zinc content of catalyst nanoparticles reduces the yield of carbon nanotubes and increases the nitrogen content of the material. The high synthesis temperature gives rise to zinc vaporization, which influences the growth process, increasing the nanotube diameter, reducing the wall thickness, and lowering the structural perfection of the graphite layers.

Y-junction bamboo-like CN x nanotubes

The method for the production of multiwall Y-junction bamboo-like CNx nanotubes by the resistive heating of graphite is described. Different branched bamboo-like CNx nanotubes have been observed. The possible mechanism of the formation of branched nanotubes is proposed.

Ion–electron emission from CNx nanotube cathode

AbstractThe first experiments on registration of ion current accompanying the field electron emission from carbon nanotubes have been carried out. Emitted cathode has been made from multiwall CNx nanotubes synthesized by thermolysis of a ferrocene and acetonitrile mixture. Since the ion current peaked at the electron emission threshold, its origin was attributed to autoionization of the residual gas molecules adsorbed on the nanotube caps. Complex voltage dependence of the ion current could be related to the change in the autoionization potential of the adsorbed molecules with variation of nanotube diameter. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Biocompatibility and Toxicological Studies of Carbon Nanotubes Doped with Nitrogen

In this report, we compare the toxicological effects between pure carbon multiwalled nanotubes (MWNTs) and N-doped multiwalled carbon (CNx) nanotubes. Different doses of tubes were administered in various ways to mice: nasal, oral, intratracheal, and intraperitoneal. We have found that when MWNTs were injected into the mice's trachea, the mice could die by dyspnea depending on the MWNTs doses. However, CNx nanotubes never caused the death of any mouse. We always found that CNx nanotubes were far more tolerated by the mice when compared to MWNTs. Extremely high concentrations of CNx nanotubes administrated directly into the mice's trachea only induced granulomatous inflammatory responses. Importantly, all other routes of administration did not induce signs of distress or tissue changes on any treated mouse. We therefore believe that CNx nanotubes are less harmful than MWNTs or SWNTs and might be more advantageous for bioapplications.

Fluorination of multiwall nitrogen-doped carbon nanotubes

A film of oriented nitrogen-doped multiwall carbon nanotubes was grown on a silicon substrate as a result of the thermolysis of an acetonitrile + ferrocene mixture. The fluorination of the film by BrF3 vapor at room temperature removed the substrate; however, the vertical orientation of the nanotubes was not destroyed. Analysis of micrographs of a fluorinated sample obtained with a high-resolution transmission electron micro-scope showed that only the surface walls of the nanotubes were fluorinated. The fluorine concentration of the product as determined from X-ray photoelectron spectroscopy was about 16%. A comparison of the N1s spectra of the starting and fluorinated samples showed that the nitrogen atoms of CNx nanotubes changed their electronic state as a result of fluorination. Matching of the X-ray photoelectron spectroscopic data with the results of quantum-chemical calculations for fragments of fluorinated nitrogen-doped nanotubes showed that fluorine atoms preferred to attach to pyridine-like nitrogen atoms or to carbon atoms in the ortho or meta positions relative to a nitrogen atom.

Platinum Nanoparticles Uniformly Dispersed on Arrayed CNx Nanotubes with High Electrochemical Activity

not Available.

Electronic transport characteristic of an individual CNx/C nanotube Schottky junction

Electrical transport properties of a Schottky junction consisting of carbon nanotube and nitrogen-doped carbon nanotube were studied. The current-voltage characteristics of the junction exhibited reproducible rectifying behavior which could be explained by the Schottky barrier junction. The barrier height and the ideal factor were determined by fitting the current-voltage characteristics to the generalized diode equation. A near power-law dependence of I∼Vm was observed, where the exponent m increases with decreasing temperature. This effect can be accounted for by filling of deep traps at lower temperatures. The charge transport in the nanotubes is found to be strongly controlled and limited by the highly defective trap state originated from structural and chemical defects due to the doping of nitrogen in the CNx nanotube part.

Synthesis of Multi‐Walled and Bamboo‐Like Well‐Crystalline CNx Nanotubes with Controllable Nitrogen Concentration (x = 0.05‐1.02).

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Multi-Walled and Bamboo-like Well-Crystalline CNx Nanotubes with Controllable Nitrogen Concentration (x = 0.05−1.02)

The multi-walled and bamboo-like well-crystalline CNx nanotubes with controllable nitrogen concentration (x = 0.05-1.02) were synthesized. The stoichiometry of as-prepared CNx (x congruent with 1.02) is close to that of the theoretically predicted graphite-like CN.

Electronic state of nitrogen incorporated into CNx nanotubes

CNx nanotubes have been prepared by acetonitrile decomposition over Ni, Co and Ni/Co catalysts. X-ray photoelectron spectroscopy study on the samples revealed a change of nitrogen concentration and shape of N 1s line with variation of the catalyst used. Quantum-chemical calculations on tube fragments showed the energy of N 1s level depends on the atomic structure of carbon tube and kind of incorporated nitrogen. The largest binding energies were found to be characteristic of three-coordinated nitrogen atoms doping the zigzag and chiral carbon nanotubes.

Ultrafine Platinum Nanoparticles Uniformly Dispersed on Arrayed CNx Nanotubes with High Electrochemical Activity

The structure and electrochemical properties of arrayed nitrogen-containing carbon nanotube (CNx NT)−platinum nanoparticle (Pt NP) composites directly grown on Si substrates have been investigated. The CNx nanotube arrays were grown by microwave-plasma-enhanced chemical vapor deposition first and then acted as the template and support for Pt dispersion in the following sputtering process. Under the same sputtering conditions, it was found that well-separated Pt NPs would form with an average diameter of 2 nm on the arrayed NTs while a continuous Pt thin film was observed on the bare Si substrate. X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and electron microscopy were employed to study bonding and structure changes with increasing deposition time. Implications of the C1s and N1s bonding changes in XPS and their possible relation to the NT−Pt composite structures with self-limited size distribution are discussed. Cyclic voltammograms show well-behaved curves in methanol oxidation, suggesting an efficient electronic conduction mechanism from the substrate via CNx NTs to reach individual Pt NPs is in operation. Such an integrated nanocomposite approach possesses a high potential for micro direct methanol fuel cell applications.