Properties Of Nitrogen-doped Carbon Nanotubes Research Articles

Effect of the Activation Time on the Piezoelectric Properties of Nitrogen-Doped Carbon Nanotubes

Recently, there is an increasing need to create energy-efficient power supplies for wearable devices. In recent studies, we found that carbon nanotubes doped with nitrogen, which exhibit anomalous piezoelectric properties, can be used as the basis for such devices. This paper presents the results of studying the effect of the activation time of catalytic centers during the growth of carbon nanotubes on the value of their piezoelectric strain coefficient and the value of the generated current. It was found that with an increase in the activation time of the catalytic centers from 1 to 90 min, the value of the piezoelectric strain coefficient decreased from 19.78pm/V to 4.49pm/V, which is associated with a change in the geometric dimensions of the catalytic centers and, consequently, the N-CNT and structures of the N-CNTs. Also, the data obtained are confirmed by the measured value of the current generated by N-CNTs during deformation. Its value decreased from 15 to 2 nA in proportion to the decrease in the piezoelectric strain coefficient. The results obtained can be used to create energy-efficient piezoelectric nanogenerators

Effect of the Dopant Configuration on the Electronic Transport Properties of Nitrogen-Doped Carbon Nanotubes.

Nitrogen-doped carbon nanotubes (N-CNTs) show promise in several applications related to catalysis and electrochemistry. In particular, N-CNTs with a single nitrogen dopant in the unit cell have been extensively studied computationally, but the structure-property correlations between the relative positions of several nitrogen dopants and the electronic transport properties of N-CNTs have not been systematically investigated with accurate hybrid density functional methods. We use hybrid density functional theory and semiclassical Boltzmann transport theory to systematically investigate the effect of different substitutional nitrogen doping configurations on the electrical conductivity of N-CNTs. Our results indicate significant variation in the electrical conductivity and the relative energies of the different dopant configurations. The findings can be utilized in the optimization of electrical transport properties of N-CNTs.

Synthesis, Structural Analysis and Oxygen Reduction Catalyst Properties of Nitrogen-Doped Carbon Nanotubes Having Bamboo-Like Structure

Synthesis, Structural Analysis and Oxygen Reduction Catalyst Properties of Nitrogen-Doped Carbon Nanotubes Having Bamboo-Like Structure

Physicochemical properties of nitrogen-doped carbon nanotubes from metallocenes and ferrocenyl imidazolium compounds

Shaped carbon nanomaterials (SCNMs) were synthesized via the chemical vapour deposition (CVD) technique by using typical metallocenes (ferrocene, nickelocene, cobaltocene, and ruthenocene), and more interestingly, by use of novel ferrocenyl imidazolium derivatives, containing -Cl (FcImCl), -NO2 (FcImNO2) and -CH3 (FcImCH3) substituents as catalysts. Acetonitrile was applied both as a carbon and nitrogen source at temperatures 800–900 °C. The SCNMs, namely, carbon nanotubes (CNTs), carbon spheres (CS), carbon fibres (CF) and amorphous carbons (ACs) were obtained in varying ratios depending on the catalyst and carbon sources. The ferrocenyl imidazolium catalysts produced nitrogen-doped CNTs (N-CNTs) with bamboo-like structures. The yields of various reactions were temperature-dependent, with the highest amount of N-CNTs obtained at 850 °C. In all samples, the composition was mainly of CS and N-CNTs except for nickelocene at 800 °C that gave CFs as a “minor” product. Ferrocene and nickelocene in acetonitrile produced well-aligned N-CNTs while cobaltocene and ruthenocene gave ‘spaghetti-like’ structures. In the case of ferrocenyl imidazolium catalyst, a coiled N-CNTs morphology was produced from FcImCl catalyst. Also, higher percentage of N-CNTs with traces of CS were obtained from the FcImCl and FcImCH3 catalysts in acetonitrile at 850 °C, while higher percentage of CS and AC were obtained for FcImNO2 catalyst. In all the catalysts, the use of acetonitrile promoted nitrogen-doping (samples with more disordered and with smaller outer-diameters). Thus, this study demonstrates that the synthesis of N-CNTs from nitrogen-containing ferrocenyl imidazolium compounds as catalyst sources, provided higher percentage of N-CNTs which can be suitable for various application.

Parametric study on the influence of synthesis variables in the properties of nitrogen-doped carbon nanotubes

Nitrogen doped carbon nanotubes (N-CNT) were synthesized by a Modified Chemical Vapor Deposition method, using pyridine as carbon and nitrogen source, and ferrocene as catalytic agent for the nanotubes growth. The influence of synthesis parameters as the temperature, carrier gas flow rate, concentration of the reactants and preheating temperature over the morphology and physical properties of the N-CNT, were investigated by high-resolution scanning electron microscopy, transmission electron microscopy and X ray diffraction. The statistical analysis for the length of the N-CNT forest revealed that the synthesis temperature and carrier gas flow rate have significantly influenced on the physical properties of the material. The synthesis temperature not only affected the length of N-CNT forest, but also influenced the mass production, as well as, in diameter and the nitrogen content in the nanotubes. This is an important step towards the high yield production of N-CNT for applications in hydrogen storage, electrocatalysts for fuel cells and other electrochemical devices.

A reevaluation of the correlation between the synthesis parameters and structure and properties of nitrogen-doped carbon nanotubes

Nitrogen-doped carbon nanotubes (NCNTs) were synthesized by chemical vapor deposition using cobalt-based oxides as catalyst and ethylenediamine (EDA) as carbon/nitrogen precursor. The influence of growth time, EDA concentration and growth temperature on the morphology, yield, composition, graphitization and oxidation resistance of the NCNTs was systematically investigated by using Raman spectroscopy, temperature-programmed oxidation and other techniques. The NCNT growth from ethylenediamine with a high N/C ratio involves several processes including mainly (1) catalytic growth of NCNTs, (2) homogeneous gas-phase decomposition of EDA, (3) non-catalytic deposition of pyrolytic carbon/nitrogen species and (4) surface etching of amorphous carbon or carbon at defect sites through gasification. At a later growth stage the etching process appears to be dominating, leading to the thinning of nanotubes and the decrease of yield. Moreover, the surface etching through carbon gasification strongly influences the structure and degree of graphitization of NCNTs.

Transport regimes in nitrogen-doped carbon nanotubes: Perfect order, semi-random, and random disorder cases

The electronic structure and the transport properties of nitrogen-doped carbon nanotubes are investigated using a tight-binding model and a real-space Kubo-Greenwood approach, respectively. The transport regimes of various axial and helical doping configurations, from perfectly periodic to fully random disordered cases, are examined through the time dependence of the diffusivity. By varying the degree of disorder, a rich set of transient regimes is predicted going from persisting quasiballistic to momentarily localized regimes. A spectacular long-time ballistic regime is also observed for a specific semi-random disorder doping configuration owing to symmetry effects.

Tuning the nitrogen content and surface properties of nitrogen-doped carbon nanotubes synthesized using a nitrogen-containing ferrocenyl derivative and ethylbenzoate

Aligned nitrogen-doped carbon nanotubes (N-CNTs) containing 6.4–15.7 wt% of nitrogen were synthesized by pyrolysis of 3-ferrocenyl-2-(4-cyanophenyl)acrylonitrile as the catalyst in either acetonitrile or a solution of acetonitrile and ethylbenzoate. For comparison, N-CNTs were synthesized by pyrolysis of 3-ferrocenyl-2-(4-cyanophenyl)acrylonitrile in toluene. The effect of oxygen and the carbon source used during synthesis was investigated. The use of 3-ferrocenyl-2-(4-cyanophenyl)acrylonitrile in acetonitrile as a nitrogen and carbon source selectively yielded mainly N-CNTs, while use of toluene as a carbon source yielded both N-CNTs and carbon spheres. Elemental analysis of the N-CNTs synthesized using both acetonitrile and ethylbenzoate (source of oxygen) indicated that addition of oxygen enhanced the nitrogen content of N-CNTs. This was further supported by results from Raman spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy and inverse gas chromatography surface energy analysis. The higher nitrogen-containing N-CNTs were less graphitic and showed a higher base constant (Kb) compared to N-CNTs synthesized without oxygen. Analysis of transmission electron microscopy images showed that the outer diameters of the N-CNTs decreased upon increasing the oxygen composition by mass in the synthesis precursors from 1 to 4 wt% oxygen, the oxygen was derived from ethylbenzoate. In addition, the scanning electron microscopy and XRD revealed that the alignment of N-CNTs increased upon addition of oxygen. Electrical conductivity measurements of N-CNTs showed a negative relationship between the amount of oxygen in the starting materials and the conductivity of N-CNTs.

Nitrogen Doping Effects on Microstructure of Multi-Walled Carbon Nanotubes

Taking Fe/NaY zeolite as catalysts, a range of nitrogen doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor deposition method (CVD) at 1073K using ethanediamine, dimithylethanediamine and tetramethyl ethanediamine as nitrogen source and carbon source, respectively. The structural and compositional properties of N-CNTs were characterized by XRD, SEM and TEM. The results illustrate the microstructure of N-CNTs is strongly dependent on the N/C ratio of precursors. With the increase of N content in precursors, N-CNTs became shorter, more disorder, coarser surface and the average bamboo segment distance increased from 40 nm to 60 nm. A mechanism for the formation of the N-CNTs grown from three precursors with different N/C ratio has been proposed based on experimental observations.

En route to controlled catalytic CVD synthesis of densely packed and vertically aligned nitrogen-doped carbon nanotube arrays.

The catalytic chemical vapour deposition (c-CVD) technique was applied in the synthesis of vertically aligned arrays of nitrogen-doped carbon nanotubes (N-CNTs). A mixture of toluene (main carbon source), pyrazine (1,4-diazine, nitrogen source) and ferrocene (catalyst precursor) was used as the injection feedstock. To optimize conditions for growing the most dense and aligned N-CNT arrays, we investigated the influence of key parameters, i.e., growth temperature (660, 760 and 860 °C), composition of the feedstock and time of growth, on morphology and properties of N-CNTs. The presence of nitrogen species in the hot zone of the quartz reactor decreased the growth rate of N-CNTs down to about one twentieth compared to the growth rate of multi-wall CNTs (MWCNTs). As revealed by electron microscopy studies (SEM, TEM), the individual N-CNTs (half as thick as MWCNTs) grown under the optimal conditions were characterized by a superior straightness of the outer walls, which translated into a high alignment of dense nanotube arrays, i.e., 5 × 108 nanotubes per mm2 (100 times more than for MWCNTs grown in the absence of nitrogen precursor). In turn, the internal crystallographic order of the N-CNTs was found to be of a ‘bamboo’-like or ‘membrane’-like (multi-compartmental structure) morphology. The nitrogen content in the nanotube products, which ranged from 0.0 to 3.0 wt %, was controlled through the concentration of pyrazine in the feedstock. Moreover, as revealed by Raman/FT-IR spectroscopy, the incorporation of nitrogen atoms into the nanotube walls was found to be proportional to the number of deviations from the sp2-hybridisation of graphene C-atoms. As studied by XRD, the temperature and the [pyrazine]/[ferrocene] ratio in the feedstock affected the composition of the catalyst particles, and hence changed the growth mechanism of individual N-CNTs into a ‘mixed base-and-tip’ (primarily of the base-type) type as compared to the purely ‘base’-type for undoped MWCNTs.

The effect of temperature on the morphology and chemical surface properties of nitrogen-doped carbon nanotubes

One of the most effective ways to tune the physical and chemical properties of CNTs is to dope them with a foreign element, such as nitrogen. Nitrogen atoms that are incorporated into the CNT structure can drastically change the properties of CNTs. The properties of nitrogen-doped carbon nanotubes (N-CNTs) originate from their structure; thus, it is practical to create a desired structure during synthesis. We have investigated the effects of synthesis parameters, mainly temperature, on various characterizations of N-CNTs, such as their morphologies, dimensions (diameter and length), defects, nitrogen inclusions and thermal stability. The results revealed strong correlations between the synthesis parameters and the properties of the synthesized N-CNTs. XPS characterization indicated that the percentage of nitrogen inclusion decreased with increasing synthesis temperature up to 850°C and then increased at 950°C. Raman spectroscopy showed a decrease in the number of defects in the N-CNT structure with increasing synthesis temperature. Finally TGA demonstrated a trend of increasing thermal stability of N-CNTs with increasing synthesis temperature, up to 850°C then a reduced thermal stability at 950°C. Based on these results, one can control the properties of N-CNTs and obtain materials with the desired characteristics by choosing the appropriate synthesis conditions.

The effects of catalyst on the morphology and physicochemical properties of nitrogen-doped carbon nanotubes

Doping of carbon nanotubes with foreign elements, such as boron or nitrogen, is one of the most effective ways to change their properties to make them suitable for various applications. As the properties of nitrogen-doped carbon nanotubes (N-CNTs) originate from their structure, it is practical to manipulate their structure during synthesis. We have investigated the influence of catalyst on the chemical surface properties and morphology of N-CNTs. Different catalysts, such as iron, nickel, cobalt and copper, have been tested for the synthesis of N-CNTs. The results revealed strong correlations between the properties of N-CNTs and the growth catalyst. The highest percentage of nitrogen incorporated in the N-CNTs structure was found for the N-CNTs synthesized on the nickel catalyst. The use of nickel, cobalt or copper catalysts led to the formation of N-CNTs with higher numbers of pyrrolic nitrogen doped in the structure, while N-CNTs with higher numbers of quaternary nitrogen were synthesized with the iron catalyst. The N-CNTs synthesized on iron, nickel and copper had a bamboo-shaped structure; and, the majority of the N-CNTs had a hollow-channel structure if synthesized on the cobalt catalyst. A higher yield and lower N-CNT diameter were obtained using cobalt as the growth catalyst.

First-principles calculations for nitrogen-containing single-walled carbon nanotubes

We present calculations for possible configurations of nitrogen-containing single-walled carbon nanotubes and their electronic properties obtained with the ab initio tight-binding FIREBALL method. It is found that nitrogen atoms can be energetically incorporated into the carbon network in three forms: Substitution, substitution with formation of a vacancy structure, and chemical adsorption. The different forms exhibit different local densities of states near the Fermi levels, which might suggest a potential method to control the electronic properties of nitrogen-doped carbon nanotubes.