Nitrogen Doping Of Carbon Nanotubes Research Articles

Single walled carbon nanotubes band gap width measurement and the influence of nitrogen doping research.

The adjustment and measurement of the band gap width of single-walled carbon nanotubes are crucial for optimizing the design and enhancing the performance of carbon-based devices. This study utilizes the relationship between the band gap and temperature of semiconductor-based carbon nanotubes. The electrical conductivity of carbon nanotubes was obtained at various temperatures, and the corresponding band gap width (0.57 eV) was determined. The introduction of nitrogen results in a reduction of the band gap width and an increase in current flow between the device source and drain electrodes. Theoretical calculation demonstrated that nitrogen doping not only increases the conductivity of carbon nanotubes but also effectively inhibits the Schottky barrier between carbon nanotubes and metal electrodes. The Schottky barrier and the internal electric field can be effectively modulated via nitrogen doping in carbon nanotubes, which enhances the performance of carbon-based devices.

Theoretical and experimental investigations of enhanced carbon nanotube-gold interface conductivity through nitrogen doping.

It is necessary to establish high-quality contact between carbon nanotubes and metals in carbon-based devices. However, how to control and reduce contact resistance still remains unsolved. In this study, the effect of N doping in single-walled carbon nanotubes on the contact resistance with gold was studied by combining theoretical calculation with experimental methods. The theoretical results indicate that nitrogen doping in carbon nanotubes can control the bottom of the carbon nanotube conduction band downward, the Fermi level enters the conduction band, the height of the Schottky barrier between the bottom of the carbon nanotube conduction band and the gold Fermi level decreases, and the increase in doping concentration leads to the decrease of Schottky barrier width. As a result, the conductivity between the gold and carbon nanotube interface is enhanced. During experiments, the carrier density and the current of the gold and carbon nanotube device increase gradually with the increase in N doping concentration and a good electron transport channel is established between the gold and carbon nanotubes. The high-quality contact is crucial to reducing the size, improving the performance, and reducing the power consumption of carbon-based devices.

Influence of the aspect ratio of nitrogen-doped carbon nanotubes on their piezoelectric properties

Recent studies have shown that nitrogen doping of carbon nanotubes (CNTs) can lead to the formation of piezoelectric properties in them, not characteristic of pure CNTs. In this work, nitrogen-doped CNTs were grown by plasma-enhanced chemical vapor deposition and the effect of the aspect ratio of the nanotube length to its diameter on its piezoelectric coefficient [Formula: see text] was shown. It was observed that as the aspect ratio of the nanotube increased from 7 to 21, the value of [Formula: see text] increased linearly from 7.3 to 10.7 pm/V. This dependence is presumably due to an increase in curvature-induced polarization because of an increase in the curvature and the number of bamboo-like “bridges” in the nanotube cavity formed as a result of the incorporation of pyrrole-like nitrogen into the nanotube structure. The obtained results can be used in the development of promising elements of nanopiezotronics (nanogenerators, memory elements, and strain sensors).

Nitrogen Doping of Carbon Nanotubes Synthesized in Flowing Acetylene and Ammonia

A method has been demonstrated for doping carbon nanotubes (CNTs) with nitrogen during synthesis in an acetylene + ammonia atmosphere at different temperatures in the range 550–750°C, and conditions have been found for effective nitrogen doping of CNTs depending on synthesis temperature. The concentrations of various elements in the synthesized CNTs have been determined by X-ray photoelectron spectroscopy. Raman measurements with the use of a Raman microscope have made it possible to follow variations in the relative intensities of the G and D bands as functions of nitrogen dopant concentration in the CNTs. We have detected strong Raman overtone combination satellites whose parameters depend on the structural perfection of the synthesized CNTs.

Tailoring electronic properties and kinetics behaviors of Pd/N‐CNTs catalysts for selective hydrogenation of acetylene

AbstractPd catalyzed selective hydrogenation of acetylene shows remarkable electronic effects. In this work, a strategy is proposed to tailor the electronic properties of Pd nanoparticles by nitrogen doping of carbon nanotubes (CNT) support toward the improved reaction kinetics. While excluding the Pd size effects, the intrinsic promotional effects of the nitrogen doping are demonstrated, which are mainly due to the increased Pd electron density resultant from the presence of more graphitic nitrogen species based on X‐ray photoelectron spectroscopy measurements and density functional theory (DFT) calculations. Kinetics analysis and C2H2/C2H4‐temperature‐programmed desorption (TPD) measurements reveal that the electron‐rich Pd catalyst with the moderately weakened adsorption strength can give rise to the decreased activation energy and thus the simultaneously enhanced activity, selectivity, and stability. The aspects demonstrated here could guide the rational design and optimization of Pd catalysts for the selective hydrogenation of acetylene.

Conflicting Roles of Nitrogen Doping in Carbon Nanotubes As Anode and Cathode Catalyst Support for Direct Methanol Fuel Cells

Nitrogen doping in carbon nanotubes (CNTs) is of great interest because it endows the inherently inert surface of CNTs with a variety of chemical functionalities. For instance, nitrogen-doped carbon nanotubes (NxCNTs) have been shown a promising electrode catalyst support for polymer electrolyte membrane fuel cells because the doped nitrogen atoms can promote a high dispersion of the metal catalyst nanoparticles on the NxCNT surface, which is essential for achieving a high utilization and thus high catalytic performance. However, beyond the role in nanoparticle dispersion, how nitrogen doping affects the catalytic performance in the anode and in the cathode of a realistic membrane-electrode-assembly (MEA), still remains elusive. In this report, we performed a comparative study of NxCNTs at three different N doping levels as the anode and cathode catalyst support in both rotating disk electrode (RDE) and realistic direct methanol fuel cell (DMFC) test. Our results show that nitrogen doping can play significantly conflicting roles in the anode and cathode performance: (i) A very low doping level (1at.%) is sufficient to induce a homogenous distribution of both anode (PtRu) and cathode (Pt) catalyst nanoparticles. (ii) In RDE test, while nitrogen doping can substantially increase the specific activity of the anodic methanol oxidation, it brings no specific activity enhancement in the cathodic oxygen reduction reaction (ORR), suggesting that nitrogen doping can hardly affect the ORR electrocatalysis on the Pt surface. (iii) In MEA test, a low nitrogen doping level at 1 at.% in NxCNTs as anode catalyst support resulted in a higher power density compared to non-doped CNT support at both 30 and 60°; increasing nitrogen-doping content decreased the power density, likely due to a decreased electron conduction. In contrast, at the cathode, NxCNTs support mainly showed a lower power density, particularly at 60°, which is rationalized by the increased hydrophicility and thus unflavored removal of the water. Taken together, our results provide important guidelines for application of NxCNT support at the appropriate electrode of DMFCs.

In-situ nitrogen doping in carbon nanotubes using a fluidized bed reactor and hydrogen storage behavior of the doped nanotubes

Nitrogen atoms were successfully doped into the lattice of carbon nanotubes (hereafter called N-CNT) by chemical vapor deposition in a fluidized bed reactor using a solid precursor Imidazole. X-ray Photoelectron Spectroscopy estimated that ∼5.4 atom% of nitrogen was doped in the synthesized CNTs. The successful formation of N-CNTs was also confirmed by Fourier Transforms Infrared Spectroscopy. Transmission electron microscopy revealed the morphological features of N-CNTs and their changes with temperature. The use of fluidized bed resulted in the formation of uniform nature of N-CNTs. In-depth studies of influence of nitrogen doping in CNTs for hydrogen storage was studied by comparing with bare CNTs, also synthesized by a the same fluidized bed reactor. The hydrogen storage capacity for N-CNTs (0.8 wt.%) was enhanced significantly at very low temperature (163 K), compared to bare CNTs (0.28 wt.%).

Corking Nitrogen-Doped Carbon Nanotube Cups with Gold Nanoparticles for Biodegradable Drug Delivery Applications.

Carbon nanomaterials have been proposed as effective drug delivery devices; however their perceived biopersistence and toxicological profile may hinder their applications in medical therapeutics. Nitrogen doping of carbon nanotubes results in a unique "stacked-cup" structure, with cups held together through van der Waals forces. Disrupting these weak interactions yields individual and short-stacked nanocups that can subsequently be corked with gold nanoparticles, resulting in sealed containers for delivery of cargo. Peroxidase-catalyzed reactions can effectively uncork these containers, followed by complete degradation of the graphitic capsule, resulting in effective release of therapeutic cargo while minimizing harmful side effects. The protocols reported herein describe the synthesis of stacked nitrogen-doped carbon nanotube cups followed by effective separation into individual cups and gold nanoparticle cork formation resulting in loaded and sealed containers.

Sulfur/Nitrogen Doped Carbon Nanotube Binder-Free Electrode for High Performance Li/S Batteries

Introduction Due to low cost, environmental friendliness and high theoretical capacity of sulfur, rechargeable Li/S batteries are very promising power sources for various applications. However, the insulating nature of sulfur and solubility of polysulfides as discharge products restrict its practical application [1]. Among the approaches to overcome these problems, carbon nanotubes are widely used to obtain a flexible conductive matrix for S cathode [2]. Nitrogen doping of carbon nanotubes (N-CNTs) significantly improves its electronic conductivity because the nitrogen atoms provide additional free electrons for the conduction band [3].In this work, we report for the first time on a high performance S/N-CNT cathode for Li/S battery. Exclusion of heat-treatment in the composite preparation avoided the sulfur loss; the composite contained 61 wt% of sulfur. Thanks to the self-weaving behavior of N-CNT, binders and current collectors are rendered unnecessary, thereby simplifying the electrode manufacturing process and increasing the sulfur content in the total electrode weight. The N-CNT core provides a highly conductive and mechanically flexible framework, enhancing the electronic conductivity and consequently the rate capability of the material. This resulting composite cathode sustains 833 mAh g-1 reversible specific discharge capacity after 100 cycles at 0.1 C, and 676 mAh g-1at 1 C with a coulombic efficiensy about 100%. Experimental The S/N-CNT composite preparation is schematically shown in Fig. 1. Nitrogen doped carbon nanotubes were dispersed in deionized water by sonication at room temperature. The obtained N-CNT suspension was mixed ultrasonically with the aqueous suspension of nano-sulfur. The resulting system was vacuum-filtered and thoroughly washed with deionized water and ethanol. The binder-free S/N-CNT composite was obtained by further drying in a vacuum oven at 60 °C overnight to remove the solvent. Acknowledgments This research was supported by a Research Grant from the Ministry of Education and Science of Kazakhstan and by a Subproject supported under the Technology Commercialization Project by the World Bank and the Government of Kazakhstan.

Nitrogen-doped multi-walled carbon nanotubes for paracetamol sensing

A novel sensor consisting of nitrogen-doped multi-walled carbon nanotubes was fabricated by means of chemical vapor deposition technique with decomposition of acetonitrile onto oxidized silicon wafer using ferrocene as catalyst. The electrochemical response of carbon nanotubes-based sensor towards oxidation of paracetamol to N-acetyl-p-quinone imine was investigated in phosphate buffer solution (pH 7.0) by means of standard electrochemical techniques. A quasi-reversible response for oxidation of paracetamol was identified on carbon nanotubes-based sensor with detection limit and sensitivity of 0.485 μM and 0.8406 A M−1 cm−2, respectively. It was found that the nitrogen doping in carbon nanotubes enhances the sensor's detection ability. Namely, electrochemical studies performed on film consisting of pristine carbon nanotubes reveal as well quasi-reversible response towards oxidation of paracetamol but nevertheless poorer detection ability and sensitivity (0.950 μM; 0.601 A M−1 cm−2). The findings strongly suggest the application of nitrogen-doped carbon nanotubes in biosensing.

Corking Carbon Nanotube Cups with Gold Nanoparticles

Nitrogen doping of carbon nanotubes during chemical vapor deposition synthesis can create unique stacked cup-shaped structures termed as nitrogen-doped carbon nanotube cups (NCNCs). These cups have semielliptical hollow cavities and elevated reactivity which could lead to various applications. In this work, by applying intense ultrasonication to the as-synthesized NCNCs, we demonstrated an effective mechanical method to isolate the individual cups with opened cavities from their stacks. The graphitic structures of the isolated cups and their inherent nitrogen functionalities were characterized by comprehensive microscopic and spectroscopic methods. In particular, we quantitatively determined the existence of amine functionalities on NCNCs and found that they were preferentially distributed at the open edges of the cups, providing localized reactive sites. Further, by thiolating the amine groups with 3-mercapto-propionic acid, we were able to effectively cork the isolated cups by gold nanoparticles with commensurate diameters. These cup-shaped carbon nanomaterials with controlled inner volumes and gold nanoparticle corks could find potential applications as nanoscale reaction containers or drug delivery vehicles.

Differences in cytocompatibility and hemocompatibility between carbon nanotubes and nitrogen-doped carbon nanotubes

The cytocompatibility and hemocompatibility of multiwalled carbon nanotubes and N-doped multiwalled carbon nanotubes grown on carbon papers by chemical vapor deposition were investigated. These materials were characterized using contact-angle measurements, cell- and platelet-adhesion assays, and hemolytic-rate testing, revealing significant effects of nitrogen doping in carbon nanotubes. The results showed that mouse fibroblast cells and mouse adipose-derived stem cells cultured on N-doped multiwalled carbon nanotubes displayed the higher cell-adhesion strength, viability, proliferation, and stretching than those on multiwalled carbon nanotubes without N doping and carbon paper, indicating that N-doped multiwalled carbon nanotubes possessed good cytocompatibility. No toxicity reactions were observed during the culturing period. It also displayed the lowest hemolytic rate.

Effect of Nitrogen Concentration on Capacitance, Density of States, Electronic Conductivity, and Morphology of N-Doped Carbon Nanotube Electrodes

Heteroatom doping (e.g., boron and nitrogen) of graphitic carbon lattices affects various physicochemical properties of sp2 carbon materials. The influence of nitrogen doping in carbon nanotubes (N-CNTs) on their electrochemical and electrical properties such as the differential capacitance, density of states at the Fermi level (D(EF)), bulk conductivity, and work function is presented. Studies were performed on free-standing N-CNTs electrode mats to understand the intrinsic physicochemical properties of the material without relying on the secondary influence of another conductive support. N-Doping levels ranging from 0 to 7.4 atom % N were examined, and electrochemical impedance spectroscopy (EIS) was used to evaluate the differential capacitance and to estimate the effective density of states, D(EF). X-ray photoelectron spectroscopy (XPS) and Raman microscopy were used to assess the compositional and structural properties as a function of nitrogen doping. XPS N1s spectra show three principle types of ni...

Enhanced stability of Pt electrocatalysts by nitrogen doping in CNTs for PEM fuel cells

Electrochemical stabilities of Pt deposited on carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (CN x ) of different nitrogen contents are compared with accelerated durability tests (ADT) for the first time. Transmission electron microscopy (TEM) images reveal the different structures of CNTs and CN x , and the decrease of Pt particle size with the nitrogen incorporation into CNTs. Based on the loss of electrochemical surface area (ESA) and TEM images, Pt/CN x exhibited much higher stability than Pt/CNTs, and the Pt stability increases with the increase of nitrogen contents in the CN x supports.

Synthesis of high nitrogen doping of carbon nanotubes and modeling the stabilization of filled DAATO@CNTs (10,10) for nanoenergetic materials

In this work, we have performed synthesis of nitrogen-doped carbon nanotubes using chemical vapor deposition method. Morphology, structure and composition of the carbon nanotubes (CNTs), as well as concentration and distribution of nitrogen inside CNTs are characterized by scanning electron microscopy, transmission electron microscopy, X-ray dispersive spectroscopy and X-ray photoelectron spectroscopy techniques. A bamboo-like structure of the nitrogen-doped CNTs has been observed. Temperature dependency on the synthesis of nitrogen-doped carbon nanotubes has been investigated and discussed. Diameter and growth rate of these hybrid materials are obviously temperature dependent. Nitrogen concentration inside the CNTs increases with declining synthesis temperature. Nitrogen-doped CNTs with nitrogen content up to 10.4 at% can be achieved at a low temperature of 800 oC. Synthesis of the high nitrogen CNTs proposes a feasible way to develop novel nanoenergetic materials. Besides the experimental study, we have carried out Density Functional Theory calculations on five energetic molecules named n-oxides of 3,3′-azo-bis(6-amino-1,2,4,5-tetrazine) (DAATO), where n=1–5 refer to oxygen atoms, encapsulated in CNTs (10,10), in order to investigate the chemical stabilization of filled DAATO_n inside CNTs (10,10). In fact, the predicted adsorption energy values confirmed the chemical stability of the hybrid systems DAATO_n@CNTs (10,10) under normal conditions.

Tailored Field-Emission Property of Patterned Carbon Nitride Nanotubes by a Selective Doping of Substitutional N(sN) and Pyridine-like N(pN) Atoms

It is determined by first-principle calculations and experiments that the threshold field to achieve 1 mA/cm2 emission current density is reduced from 4.8 to 2.3 V/μm by changing pyridine-like nitrogen doping into substitutional nitrogen doping in carbon nanotubes.

Nitrogen Doping in Carbon Nanotubes

Nitrogen doping of single and multi-walled carbon nanotubes is of great interest both fundamentally, to explore the effect of dopants on quasi-1D electrical conductors, and for applications such as field emission tips, lithium storage, composites and nanoelectronic devices. We present an extensive review of the current state of the art in nitrogen doping of carbon nanotubes, including synthesis techniques, and comparison with nitrogen doped carbon thin films and azofullerenes. Nitrogen doping significantly alters nanotube morphology, leading to compartmentalised 'bamboo' nanotube structures. We review spectroscopic studies of nitrogen dopants using techniques such as X-ray photoemission spectroscopy, electron energy loss spectroscopy and Raman studies, and associated theoretical models. We discuss the role of nanotube curvature and chirality (notably whether the nanotubes are metallic or semiconducting), and the effect of doping on nanotube surface chemistry. Finally we review the effect of nitrogen on the transport properties of carbon nanotubes, notably its ability to induce negative differential resistance in semiconducting tubes.

Nitrogen doping and chirality of carbon nanotubes

We have theoretically studied nitrogen doping of carbon nanotubes in a periodic supercell using density functional theory. We find that the most stable isomer is different for different chiralities of the tube. In the (10,0) tube, N atoms tend to be uniformly distributed, while they prefer to be adjacent to each other in (5,5) tube. As more nitrogen atoms are introduced in (5,5) tube, they are aligned parallel to the tube axis in two rows, breaking the $\mathrm{N}\mathrm{N}$ single bonds and forming aromatic $(4n+2)\ensuremath{\pi}$ systems. This leads us to conjecture that the armchair tubes are more easily subject to the opening of the tubular sheets than the zigzag tubes under the existence of a nitrogen source. The hole formation recently proposed by Czerw et al. [Nano Lett. 1, 457 (2001)] is also shown to be energetically favorable. Calculation of the electronic density of states shows that the doping-induced electronic states near the Fermi energy are sensitive to the chirality.