Nitrogen-containing Carbon Nanotubes Research Articles

Facile synthesis of nitrogen-containing multiwalled carbon nanotubes as a worth metal-free electrocatalyst for hydrogen evolution reaction and semicarbazide oxidation

Studies of metal-free carbon nanostructures prove effective in energy and environmental applications due to their molecular tunability and vast chemical space. Herein, we synthesize nitrogen-containing multi-walled carbon nanotubes (N-MWCNTs) via. acid-catalysed incorporation of 3, 4-diaminopyridine into multi-walled carbon nanotubes (MWCNTs), and demonstrating their efficacy in electrocatalytic hydrogen evolution reaction (HER) and semicarbazide (SCB) oxidation for energy and environmental waste management, respectively. Successful synthesis is further confirmed by analysis techniques, i.e. Fourier transform infrared (FTIR) spectral analysis shows the diminishing OH frequency around 3250 cm−1 in MWCNTs after functionalization and the formation of an OC–NH bond in N-MWCNTs at 1710 cm−1. X-ray diffraction (XRD) confirms the incorporation of N-species, while Raman spectroscopic analysis indicates an increase in the ID/IG ratio MWCNTs (∼1) to N-MWCNTs (∼1.25), suggesting more defective sites in the N-MWCNTs nanocomposite. X-ray photoelectron spectroscopy (XPS) reveals peaks at 399.38, 400.49, and 402.05 eV, attributed to pyridinic-N, aromatic amide-N, and protonated amine groups, respectively. N₂ adsorption-desorption studies shows a high Brunauer-Emmett-Teller (BET) surface area for N-MWCNTs (119.22 m2/g) compared to MWCNTs (74.94 m2/g). Linear sweep voltammetry (LSV) profiles demonstrate enhanced activity of N-MWCNTs for both HER and SCB oxidation at an ultralow potential of E = −0.55 V vs RHE at 10 mA/cm2, with a lower Tafel slope of 108 mV.dec−1. Moreover, the electrochemical sensing studies indicates on N-MWCNTs were demonstrating an efficient electron transfer to SCB with the lower detection limit of 0.004 μmol. This work provides carbon-based metal-free electrocatalysts for energy harvesting and environmental management.

Tailored synthesis of a palladium catalyst supported on nitrogen-doped carbon nanotubes for gas-phase formic acid decomposition: A strong influence of a way of nitrogen doping

Palladium catalysts supported on different nitrogen-containing carbon nanotubes (N-CNTs) were successfully used in the continuous gas-phase formic acid decomposition for hydrogen production. A strong influence of a way of carbon tubes doping by nitrogen on the activity of catalysts comprising metallic nanoparticles of ca. 1 nm in size and single-atom Pd2+ species was found. A key role of the single-atom species, demonstrating excellent stability in various chemically aggressive media, in the catalyst activity was discovered when bamboo-like N-CNTs synthesized by catalytic chemical vapor deposition were used as a support. A substantial increase in the activity of Pd nanoparticles was achieved by the use of N-СNTs prepared by the post-treatment of oxidized multiwalled carbon nanotubes by ammonia resulting in the formation of the dominating surface amine groups. The combination of the electron-rich palladium nanoparticles and surface amine groups leads to an increase in the TOF value by a factor of 7 at 70 °C. The catalyst operates stable at >99 % selectivity to hydrogen with the mass specific performance 200 l H2/gPd ⋅ h.

Comparative Study of the Structural Features and Electrochemical Properties of Nitrogen-Containing Multi-Walled Carbon Nanotubes after Ion-Beam Irradiation and Hydrochloric Acid Treatment.

Using a set of microscopic, spectroscopic, and electrochemical methods, a detailed study of the interrelation between the structural and electrochemical properties of the as-prepared nitrogen-containing multi-walled carbon nanotubes (N-MWCNTs) and their modified derivatives is carried out. It was found that after treatment of nanotubes with hydrochloric acid, their structure is improved by removing amorphous carbon from the outer layers of N-MWCNTs. On the contrary, ion bombardment leads to the formation of vacancy-type structural defects both on the surface and in the bulk of N-MWCNTs. It is shown that the treated nanotubes have an increased specific capacitance (up to 27 F·g−1) compared to the as-prepared nanotubes (13 F·g−1). This is due to an increase in the redox capacitance. It is associated with the reversible Faraday reactions with the participation of electrochemically active pyridinic and pyrrolic nitrogen inclusions and oxygen-containing functional groups (OCFG). Based on the comparison between cyclic voltammograms of N-MWCNTs treated in HCl and with an ion beam, the peaks on these curves were separated and assigned to specific nitrogen inclusions and OCFGs. It is shown that the rate of redox reactions with the participation of OCFGs is significantly higher than that of reactions with nitrogen inclusions in the pyridinic and pyrrolic forms. Moreover, it was established that treatment of N-MWCNTs in HCl is accompanied by a significant increase in the activity of nitrogen centers, which, in turn, leads to an increase in the rate of redox reactions involving OCFGs. Due to the significant contribution of redox capacitance, the obtained results can be used to develop supercapacitors with increased total specific capacitance.

Oxygen functionalization and electronic band gap control in the disordered multi-walled carbon nanotubes

Functionalization by oxygen-containing groups, electronic band gap, and conductivity produced by the functionalization in the disordered metallic nitrogen-containing multi-wall carbon nanotubes (N-MWCNTs), are investigated experimentally and theoretically. Oxygen in the carboxyl groups is located in top sites at the nanotube surface and produces the bang gap. The energy gap is found to have a width of approximately 1.3 eV which does not depend on diameter, oxygen concentration, and structure of the groups. Oxygen localized in the bridge position in the hydroxyl group promotes the appearance of charge carriers in a gap. The charge carrier’s concentration and conductivity produced by oxygen groups are shown to be determined by the features of electron scattering. Theory connecting the functionalization, bang gap, and electronic properties of the nanotubes, is developed.

In English

Nitrogen-containing carbon nanotubes (CNTs) were synthesized by the CVD method on oxide catalysts of Al-Fe-Mo-O by adding acetonitrile or ethylenediamine to the carbon source (propylene), or completely replacing it, as well as impregnating the original CNTs with urea, followed by heat treatment. The structure of nitrogen-containing CNTs (N-CNT) was characterized by the method of Raman scattering, transmission electron microscopy (TEM), differential thermal and gravimetric analysis (DTA, DTG) and X-ray photoelectron spectroscopy (XPS). The influence of the synthesis method on the number and chemical state of nitrogen heteroatoms in the structure of the carbon matrix is found. According to the TEM, nitrogen-containing CNTs have a characteristic bamboo-like structure, which is less perfect compared to the structure of the original CNTs: the characteristic Raman bands (G and D) are shifted to higher frequencies, their half-width and band D intensity increase relative to G. This is also manifested in the lower thermal stability of nitrogen-containing CNTs. According to the XPS, the direct synthesis of nitrogen-containing CNTs increases the total content of nitrogen atoms and the proportion of pyrrolic and quaternary nitrogen against the background of a significant decrease in the amount of pyridinic form. This can be explained by the fact that nitrogen is evenly distributed throughout the carbon matrix of CNTs, and during nitriding of CNTs with urea, nitrogen is included mainly in the surface layers and defects, because the pyridine form is characteristic of the edge location of the nitrogen atom in the graphene plane.The catalytic effect of multilayer nitrogen-containing carbon nanotubes (N-CNT) on the kinetics of decomposition of hydrogen peroxide in aqueous solutions at different pH values is considered. It is concluded that the method of direct synthesis of nitrogen-containing CNTs allows to obtain more catalytically active carbon nanotubes containing more nitrogen, mainly pyrrolic and quaternary type. It has been found that regardless of the method of synthesis, the maximum catalytic activity in the decomposition of hydrogen peroxide is observed at pH 7.

Formation of Polymer-Dispersed Nematic Liquid Crystals Doped by Nitrogen-Containing Carbon Nanotubes in Magnetic Field

Formation of Polymer-Dispersed Nematic Liquid Crystals Doped by Nitrogen-Containing Carbon Nanotubes in Magnetic Field

Conducting polypyrrole nanotubes: a review

Polypyrrole nanotubes rank among the most conducting polymer materials. The role of the templates in the formation of nanotubes is analysed and various models are discussed. Special attention has been paid to the role of methyl-orange dye in guiding one-dimensional morphology. The tuning of reaction conditions by varying temperature, acidity, or the introduction of additives, such as dyes, affects both the morphology and conductivity of polypyrrole. The increase in conductivity need not always be associated with nanotubular morphology. In addition to conductivity, also other physical properties are reviewed with the special attention paid to the characterization by UV–visible, infrared, and Raman spectroscopies. The chemical properties are demonstrated by the ability of polypyrrole to reduce noble-metal compounds, and by salt–base transition associated with the conductivity decrease. Polypyrrole nanotubes maintain the most of conductivity under physiological conditions, and they are still conducting under alkaline conditions in the contrast to globular polypyrrole. Polypyrrole nanotubes convert to nitrogen-containing carbon nanotubes at elevated temperature, thus producing useful carbonaceous materials. To improve the processing, the nanotubes have been used in composites, colloids, or hydrogels. The applications of polypyrrole nanotubes extend to adsorbents, actuators, antioxidants, biomedicine, catalysts and electrocatalysts, electrorheological suspensions, electromagnetic interference shielding, and sensors, especially to those exploiting electrical conductivity and electrochemical activity, such as electrodes in batteries and supercapacitors.

Synthesis of Polypyrrole-based Nitrogen-containing Porous Carbon Nanotubes for CO 2 Adsorption

Synthesis of Polypyrrole-based Nitrogen-containing Porous Carbon Nanotubes for CO 2 Adsorption

Catalytic dehydrochlorination of lindane by nitrogen-containing multiwalled carbon nanotubes (N-MWCNTs)

This paper reports a nonreductive dechlorination pathway (dehydrochlorination) of lindane in the presence of N-MWCNTs (CNT-N1 and CNTN2) under environmentally relevant conditions. The enhanced catalytic dehydrochlorination at mild pH values (7.0–9.0) was mainly attributed to the Lewis base nature of nitrogen functional groups on the surface of N-MWCNTs, based on FT-IR spectra, X-ray photoelectron spectroscopy and CO2-TPD profile. Amine and pyridinic nitrogen species were inferred as the main basic sites that were responsible for the dehydrochlorination of lindane. The concentration of lindane was unchanged in homogenous alkaline aqueous solutions at pH7.0 and 8.0 within 6 d, and up to 89.5% of lindane remained at pH9.0. In sharp contrast, the reaction rate constant (kobs) increased from 0.024 to 0.876 d−1 with the increasing pH from 7.0 to 9.0 when CNT-N2 catalyst was used. All lindane was transformed in the presence of CNT-N2 at pH9.0, leading to a much greater kobs as compared to that obtained in homogenous solution (0.876 vs 0.019 d−1). Even at neutral pH condition, the kobs obtained in the presence of CNT-N2 was higher than that observed in weakly alkaline solution (0.024 d−1 at pH7.0 vs 0.019 d−1 at pH9.0). γ-1,3,4,5,6-pentachlorocyclohexene and trichlorobenzene isomers were detected as the intermediate and final products, respectively. It might be inferred that amine and pyridinic nitrogen species could attack the hydrogen atom attached to the β‑carbon, and the dehydrochlorination of lindane followed a β-elimination mechanism. This study provides an alternative dechlorination way for making lindane less toxic and better biodegradable under mild conditions, which is beneficial for complete mineralization of lindane when coupled with microbial degradation.

Electronic structure of nitrogen-containing carbon nanotubes irradiated with argon ions: XPS and XANES studies

Using the methods of X-ray photoelectron (XPS) and X-ray absorption near edge structure (XANES) spectroscopies with synchrotron radiation, data on changes in the electronic structure and chemical composition of nitrogen-containing multiwalled carbon nanotubes (N-MWCNTs) upon their exposure to the radiation of argon ions with an energy of 5 keV are obtained. It is found that the exposure leads to an increase in the degree of defectiveness of the N-MWCNTs structure and to the carbon oxidation with formation of various oxygen-containing groups (C–OH, C=O/COOH, C–O–C/O–C–O, and CO3). The presence of carbon–oxygen bonds on the surface of carbon nanotubes is associated with the formation of radiation defects. It is shown that an increase in the fraction of nitrogen atoms present in the substituting configuration in the N-MWCNTs wall structure due to the irradiation does not give rise to an increase in the density of the occupied states near the Fermi level against the background of an increase in the degree of structure defectiveness, carbon oxidation, and a decrease in the total nitrogen concentration. The obtained results show that the irradiation of N-MWCNTs with argon ions allows one to successfully functionalize their surface.

Changes in the chemical state and concentration of iron in carbon nanotubes obtained by the CVD method and exposed to pulsed ion irradiation

Data on the distribution of iron in nitrogen-containing multiwall carbon nanotubes (N-MWCNTs) and changes in its chemical state and concentration under different parameters of irradiation by a pulsed ion beam are obtained by methods of transmission electron microscopy, X-ray photoelectron spectroscopy, and energy dispersion analysis. It is shown that the irradiation of N-MWCNTs with an energy density of 0.5 J/cm2 lead to the formation, on their lateral surfaces, of structures with a size of 2–10 nm, consisting of metallic iron encapsulated in a carbon shell. An increase in the energy density to 1–1.5 J/cm2 leads to a substantial removal of iron clusters from the tips of carbon nanotubes and a reduction in the amount of iron in the bulk of the N-MWCNT layer.

Graphitic and pyridinic nitrogen in carbon nanotubes: energetic and polarization aspects

The incorporation of nitrogen atoms into carbon nanotube (CNT) walls occurs mainly via bonding with three or two carbon atoms, and the obtained configurations are referred to as graphitic and pyridinic nitrogen forms. Here, we evaluate the energy of formation of these nitrogen defects in an armchair (6,6) CNT and the static polarizability of the obtained nitrogen-containing carbon (CNx) nanotubes using a dispersion-corrected hybrid functional. The calculations showed that the graphitic nitrogen atoms prefer to be in the pentagonal rings located at a nanotube cap. The CNx nanotubes with such nitrogen impurities have enhanced polarizability as compared to their nondoped counterparts. The formation of the pyridinic nitrogen defect requires ∼7.1 eV; however, if the CNT already contains a vacancy, this energy reduces to ∼0.2 eV. The presence of pyridinic nitrogen atoms in CNx nanotubes should not increase the polarization response. Our results suggest that the electromagnetic properties of CNx nanotubes can be tuned by interconverting between graphitic and pyridinic nitrogen forms.

Field emission properties of aligned CNx nanotube arrays synthesized by pyrolysis of a ferrocene/acetonitrile aerosol at different temperatures

Nitrogen-containing carbon (CNx) nanotubes have been grown vertically on silicon substrates by decomposition of a ferrocene/acetonitrile aerosol at temperatures 750, 800, 850, and 900 °С. A CNx nanotube array, produced at 850 °С, had the greatest height ∼220 μm and the smallest nitrogen content ∼3.8 at%. The content of graphitic nitrogen form, referred to a nitrogen atom with three carbon neighbors in a hexagonal lattice, increased gradually with the synthesis temperature. Field electron emission measurements showed that the CNx nanotube arrays have better characteristics than aligned non-doped carbon nanotubes. To reveal effect of nitrogen on the filed threshold, we calculated current–voltage dependencies for CNx nanotube models containing different amount of graphitic and pyridinic nitrogen species. Influence of the synthesis temperature on the height and total nitrogen content in CNx nanotube array and relation of these parameters with the threshold of field emission appearance.

Ammonia borane confined by nitrogen-containing carbon nanotubes: enhanced dehydrogenation properties originating from synergetic catalysis and nanoconfinement

AB@PPy composites synthesized by a solution method show favorable dehydrogenation properties.

How structural parameters affect the reactivity of saturated and non-saturated nitrogen-doped single-walled carbon nanotubes of different chiralities: a density functional theory approach

Nitrogen-containing carbon nanotubes, or N-CNTs, are a class of materials with interesting catalytic properties and with less toxic properties than bare carbon nanotubes. Herein, the relative stability, the oxidation potential, conductivity, and structural characteristics of finite, open H-terminated single-walled N-CNTs and their saturated structures are investigated by density functional theory methods at the B3LYP/6-31G(d) level of theory. The principal aim is to understand the way different structural features can determine or modify N-CNTs properties and reactivity. Frequency calculations indicate that all of the final optimized nanostructures correspond to a minimum on the potential energy surface. The formation energies, band gaps, atomic charges, and reactivity descriptors such as chemical potential, hardness, electrophilicity index, and softness are compared. The results indicate that changes in hybridization, chirality, and diameter strongly modify the properties of N-CNTs. The nitrogen content and the length of the nanotubes also contribute to changes in their properties, albeit to a lesser degree. For instance, a (8,0) zigzag N-CNT with 4 nitrogen atoms exhibits a band gap of 0 eV. Moreover, the configuration or relative positions of the nitrogen atoms in the central part of the nanotube do not significantly affect the nanotube properties. Compared with zigzag and chiral nanotubes, armchair N-CNTs exhibit a favorable electrical charge distribution and are revealed as potentially good catalysts for oxygen reduction reactions.

High oxygen reduction activity of few-walled carbon nanotubes with low nitrogen content

Nitrogen-containing few-walled carbon nanotubes (N-FWCNTs) with very low nitrogen content (0.56at.%) were obtained by a process involving the coating of acid functionalized FWCNTs with polyaniline (PANI) followed by pyrolysis at high temperatures. The resulting N-FWCNTs exhibited a remarkable electrocatalytic activity for the oxygen reduction reaction (ORR), despite significantly lower nitrogen content than previously reported in literature. The N-FWCNTs performed on par or better than Pt-C in the cathode of an alkaline direct methanol fuel cell, corroborating the ORR activity observed in the electrochemical cell and exhibiting a higher methanol tolerance. Interestingly, N-FWCNTs showed a high activity for the hydrogen evolution reaction and for the hydrogen peroxide decomposition, suggesting that the active sites involved in ORR can simultaneously catalyze other reactions. This unprecedentedly high activity for such a low N-content can be explained by the exceptional accessibility for the catalytic sites located in open and porous N-doped layer surrounding the FWCNT core, along with the minimization of inactive inner volume and mass compared to larger nitrogen doped multiwalled tubes.

On the origin of the high capacitance of nitrogen-containing carbon nanotubes in acidic and alkaline electrolytes.

The synthesis of nitrogenated carbon nanotubes (N-CNTs) with up to 6.1 wt% N, via the use of pyridine as the nitrogen containing carbon precursor, can provide a facile route to significantly enhance the low intrinsic specific capacitance of carbon nanotubes. The nitrogen functionalities determine this, at least, five-fold increase of the specific capacitance.

Evaluating the hydrogen chemisorption and physisorption energies for nitrogen-containing single-walled carbon nanotubes with different chiralities: a density functional theory study

The hydrogen adsorption energies for nitrogen-containing carbon nanotubes (N-CNTs) and for bare carbon nanotubes were calculated using the density functional theory methods at the B3LYP/6–31-G(d) level, including dispersion force corrections. The N-CNTs were finite saturated and non-saturated single-walled carbon nanotubes that contained one or more pyrimidine units, the relative positions of which defined the different configurations of the nanotube. The chemisorption of atomic hydrogen to a full exocyclic monolayer of zigzag, armchair, and chiral N-CNTs was studied as a function of the structural parameters. Zigzag N-CNTs of any configuration, with a larger number of nitrogen atoms, a small diameter and a small length, are more reactive compared to chiral and armchair N-CNTs. The presence of nitrogen in the carbon nanotubes enhances their reactivity to chemisorb atomic hydrogen, showing exothermic energy values. In contrast, the physisorption of molecular hydrogen was endothermic for most of the studied saturated N-CNTs, even when including corrections for van der Waals interactions. The endothermicity was greatest for zigzag nanotubes, then decreased for chiral nanotubes and decreased again for armchair nanotubes. In general, the endothermicity decreased for longer nanotubes, which have larger diameters, and a small number of nitrogen atoms. The results of this study suggest that, with saturated bare carbon nanotubes, saturated, and unsaturated N-CNTs could potentially have a higher capacity as hydrogen-storage media than the corresponding unsaturated carbon nanotubes.

Effect of the manufacturing parameters on the structure of nitrogen-doped carbon nanotubes produced by catalytic laser-induced chemical vapor deposition

Nitrogen-containing carbon nanotubes (CNx-NTs), with a relatively high level of nitrogen doping were prepared by the catalytic laser-induced CVD method. The nanotubes were catalytically grown directly on a silicon substrate from C2H2/NH3 gaseous precursors. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) give firm evidence for the nitrogen doping. As determined by XPS, the N concentration for the prepared CNx-NTs increases from 3.6 to 30.6 at.% with increasing ammonia concentration and pressure. TEM images indicate that the nanotubes are bamboo like. As the nitrogen content increases, there is a transition from the bamboo shape with few defects and little distortion to a corrugated structure with a much larger number of defects. Raman spectroscopy revealed that with increasing nitrogen concentration, there is more disorder and defects, together with an increase in ID/IG ratio. By energy-filtering TEM, a higher N concentration was found on the outer amorphous nanolayer than in the compartment core of the nanotubes.

Preparation of nitrogen-containing carbon nanotubes and study of their performance as basic catalysts

Nitrogen-containing carbon nanotubes were prepared, characterized and used as catalysts for two reactions of interest in the biomass upgrading processes: acetone aldol and acetic acid decarboxylative condensations. N-CNT were synthesized in a fluidized bed reactor by catalytic chemical vapor decomposition of acetonitrile on iron-, cobalt- and nickel-supported catalysts. Ni-N-CNT catalyst exhibits the highest activity, attributed to the surface concentration of basic sites, particularly the pyridinic species detected by X-ray photoelectron spectra (XPS). Likewise, the selectivity toward the final products of the reaction pathway is related both to the strength of basic sites (Ni-N-CNT) and to the morphology and chemical environment of the active sites (Fe-N-CNT). Synthesized catalysts show high stability for acetone condensation, whereas for ketonic condensation the catalyst stability decreases, mainly due to acic–base interactions with the active sites.