Nitrogen-doped Multi-walled Carbon Nanotubes Research Articles

Features of the image contrast of doped carbon nanotubes in electrostatic force microscopy

The features of the image contrast of nitrogen-doped multiwall carbon nanotubes (CNTs) in electrostatic force microscopy (EFM) are studied. It is established that the magnitude and shape profile of the EFM signal depend on the CNT conductivity and diameter. It is shown that an increase in the conductivity of CNT leads to increasing magnitude and variation of the shape profile of the EFM signal.

Nitrogen-doped multi-walled carbon nanotubes modified with platinum, palladium, rhodium and silver nanoparticles in electrochemical sensing

Nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapour deposition technique and decorated with platinum (PtNPs), palladium (PdNPs), rhodium (RhNPs) and silver (AgNPs) nanoparticles possessing diameter 2.7, 2.6, 2.7 and 3.4 nm, respectively. The electrochemical responses of composite films, further denoted as N-MWCNTs/MNPs (M: Pt, Pd, Rh and Ag) towards ferrocyanide/ferricyanide, [Fe(CN)6]3−/4− were investigated in large concentration range (0.099–0.990 mM) in potassium chloride solution (1.0 M). The findings demonstrate that the electrochemical response and sensitivity of N-MWCNTs are improved significantly upon modification with metal nanoparticles. A strong dependence of film’s electrochemical fineness on type of metal nanoparticles used for modification can be observed. Namely, the current response, the charge-transfer kinetics, and the detection capability of novel composite films enhance with the following order: N-MWCNTs < N-MWCNTs/RhNPs < N-MWCNTs/PdNPs < N-MWCNTs/PtNPs < N-MWCNTs/AgNPs. The findings demonstrate that the novel N-MWCNTs/MNPs composite films can be considered as powerful and useful materials for electrochemical sensing.

Nitrogen-doped carbon nanotubes with hydrazine treatment as cathode materials for lithium-oxygen batteries

Nitrogen-doped multi-wall carbon nanotubes (N-MWCNTs) were obtained by hydrazine reflux treatment. The introduction of hydrazine leads to successful nitrogen insertion in the form of mostly pyrrolic N. Meanwhile, the intrinsic characteristics of carbon nanotubes were retained. In addition, the N-MWCNTs exhibited superior electrochemical performance to that of pristine multi-wall carbon nanotubes (MWCNTs). The prepared N-MWCNTs delivered an initial discharge capacity of 2,927 mAh g−1 at a current density of 0.05 mA cm−2 and presented better reversibility especially at high rate and better electrocatalytic activity than MWCNTs. The results revealed that nitrogen doping into MWCNTs facilitated the reduction of oxygen and it was beneficial for Li2O2 decomposition as well.

Synthesis and characterization of HDPE/N-MWNT nanocomposite films.

In this work, a series of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) with several weight percentages (0.1, 0.4, 0.8, and 1.0 wt.%) were synthesized by catalytic chemical vapor deposition (CCVD) technique. The N-MWCNTs were first characterized and then dispersed in high-density polyethylene (HDPE) polymer matrix to form a nanocomposite. The HDPE/N-MWCNT nanocomposite films were prepared by melt mixing and hot pressing; a good dispersion in the matrix and a good N-MWCNT-polymer interfacial adhesion have been verified by scanning electron microscopy (SEM). Raman spectroscopy measurements have been performed on prepared samples to confirm the presence and nature of N-MWNTs in HDPE matrix. The X-ray diffraction (XRD) analysis demonstrated that the crystalline structure of HDPE matrix was not affected by the incorporation of the N-MWNTs.

Synthesis, Characterization and Magnetic Properties of Defective Nitrogen-Doped Multiwall Carbon Nanotubes Encapsulating Ferromagnetic Nanoparticles

Nitrogen-doped multi-walled carbon nanotubes (CNxMWNTs) with multiple morphological defects were produced using a modified chemical vapor deposition (CVD) method. In a typical CNxMWNTs synthesis by CVD, an acetone trap is used to catch organic by-products from pyrolysis. In the present work, an aqueous solution of NaCl (26.82 wt%) was used in the trap, instead of acetone. Carbon nanotubes with sharp tips and lumps were found in the products. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy showed the formation of nanoparticles of different shapes inside the nanotubes. The electronic and magnetic properties were studied using a physical properties measurement Evercool system (PPMS). With this simple change in the CVD-trap, it is possible to control the morphology of carbon nanotubes and metallic nanoparticles. Differences in gas flow are proposed as a possible mechanism to produce these changes in both nanoparticles and CNxMWNTs.

Synthesis, characterization and magnetic properties of Co@Au core-shell nanoparticles encapsulated by nitrogen-doped multiwall carbon nanotubes

Co/Au bilayer thin films were deposited on Si/SiOx substrates using the magnetron sputtering method and used as a catalytic support to grow forests of aligned nitrogen-doped multiwalled carbon nanotubes (N-MWCNT) via chemical vapor deposition (CVD) at 850°C, using benzylamine (C6H5CH2NH2) as a carbon and nitrogen source. Interestingly, the resulting N-MWCNT contains Co@Au core-shell nanoparticles located at their tips. We found that the metal particle cores consist of cobalt coated by an Au shell of few nanometers. Magnetic measurements revealed a ferromagnetic behavior of the system composed of Co@Au nanoparticles encapsulated inside N-MWCNT. The results are compared with pristine N-MWNT containing only Co nanoparticles encapsulated in their cores.

An investigation of the fracturing process in nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs). Evidence for directional unzipping

The reduction of nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) with Li/NH3 results in deep longitudinal cuts in the nanotubes structure. As the N-MWCNTs are anisotropic, we were able to investigate whether the unzipping process proceeds with equal efficiency from the tip end or from the root (catalyst) end of the N-MWCNT structure. To accomplish this we prepared polymer-filled aligned arrays of N-MWCNTs, then exposed one or the other end. Through this approach we were able to shield the sidewalls and either end of the nanotubes from the Li/NH3 solution We have found that when the top end of the N-MWCNTs array was exposed to the reaction mixture, very few nanotubes suffered significant ‘unzipping’. However, when the root (substrate) side of the array is exposed to the reaction mixture, we observe the features characteristic of nanotubes with longitudinal cuts. Our finding provides some insight into the mechanism of the unzipping process, and provides evidence that the unzipping process has a directional preference-unzipping from the root end towards the tip end. And may provide a method for selective functionalization of the interior of tubes and create a new form of nanotube-based porous membrane.

Surface modification of nitrogen-doped carbon nanotubes by ozone via atomic layer deposition

The use of ozone as an oxidizing agent for atomic layer deposition (ALD) processes is rapidly growing due to its strong oxidizing capabilities. However, the effect of ozone on nanostructured substrates such as nitrogen-doped multiwalled carbon nanotubes (NCNTs) and pristine multiwalled carbon nanotubes (PCNTs) are not very well understood and may provide an avenue toward functionalizing the carbon nanotube surface prior to deposition. The effects of ALD ozone treatment on NCNTs and PCNTs using 10 wt. % ozone at temperatures of 150, 250, and 300 °C are studied. The effect of ozone pulse time and ALD cycle number on NCNTs and PCNTs was also investigated. Morphological changes to the substrate were observed by scanning electron microscopy and high resolution transmission electron microscopy. Brunauer-Emmett-Teller measurements were also conducted to determine surface area, pore size, and pore size distribution following ozone treatment. The graphitic nature of both NCNTs and PCNTs was determined using Raman analysis while x-ray photoelectron spectroscopy (XPS) was employed to probe the chemical nature of NCNTs. It was found that O3 attack occurs preferentially to the outermost geometric surface of NCNTs. Our research also revealed that the deleterious effects of ozone are found only on NCNTs while little or no damage occurs on PCNTs. Furthermore, XPS analysis indicated that ALD ozone treatment on NCNTs, at elevated temperatures, results in loss of nitrogen content. Our studies demonstrate that ALD ozone treatment is an effective avenue toward creating low nitrogen content, defect rich substrates for use in electrochemical applications and ALD of various metal/metal oxides.

Nitrogen-doped-CNTs/Si3N4 nanocomposites with high electrical conductivity

Abstract Novel highly electrically conducting nanocomposites consisting of a silicon nitride (Si 3 N 4 ) ceramic matrix containing up to 13.6 vol.% of nitrogen-doped multi-walled carbon nanotubes (CNx) were fabricated. As-synthesized CNx were treated with hydrogen peroxide in order to efficiently detach/isolate the nanotubes from bundles, then they were mixed with the ceramic powders and fully densified using the spark plasma sintering (SPS) technique. Composites containing 13.6 vol.% CNx reached an electrical conductivity of 2174 S m −1 that is the highest value reported hitherto for carbon nanotubes/Si 3 N 4 nanocomposites. The nitrogen doping also favored a strong mechanical interlocking between the nanotubes and the Si 3 N 4 matrix; when compared to the undoped carbon nanotubes. These novel nanocomposites could be used in devices associated to power generation or telecommunications.

Thermodynamic investigation of ferrocyanide/ferricyanide redox system on nitrogen-doped multi-walled carbon nanotubes decorated with gold nanoparticles

Films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique with decomposition of acetonitrile. The N-MWCNTs-based films were modified with gold nanoparticles (AuNPs) with diameter either 5 or 35nm and applied for the electrochemical investigation of ferrocyanide/ferricyanide, [Fe(CN)6]3−/4− redox system in the temperature range of 283.15–303.15K. The findings demonstrate that on N-MWCNT films modified with AuNPs (further denoted as N-MWCNTs/AuNPs) the [Fe(CN)6]3−/4− redox system is quasi-reversible and its reversibility is improved with increasing temperature. Namely, it was established that with the rise in temperature the barrier for interfacial electron transfer decreases leading to an enhancement of kinetics of charge transfer reaction. The Gibbs free energies display that the exergonic redox process occurring on N-MWCNTs/AuNPs is shifted toward formation of [Fe(CN)6]3− with increasing temperature. With the increase of diameter of AuNPs a slight improvement of kinetics of redox process occurs.

Electrocatalytic Activity of Nitrogen-Doped Carbon Nanotubes Decorated with Gold Nanoparticles

Films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique and decorated with gold nanoparticles (AuNPs) of different diameters (5, 14, and 35 nm). The electrochemical responses of AuNPs-modified N-MWCNTs films, further denoted as N-MWCNTs/AuNPs, were investigated towards ferrocyanide/ferricyanide, [Fe(CN)6]3−/4− redox system in aqueous potassium chloride solutions. The findings reveal strong dependence of film’s electrochemical response on diameter of AuNPs. Namely, the electrochemical response expressed in terms of peak current density enhances and the kinetic of electron transfer tends to be faster with the increase of diameter of AuNPs. Furthermore, an obvious improvement of film’s detecting capability towards [Fe(CN)6]3−/4− occurs with the increase of diameter of AuNPs. The findings demonstrate that by varying the size of AuNPs attached onto N-MWCNTs/AuNPs, the film’s electrochemical response and detection capability can be tuned.

Voltammetric study on pristine and nitrogen-doped multi-walled carbon nanotubes decorated with gold nanoparticles

Films consisting of pristine multi-walled carbon nanotubes (MWCNTs) and nitrogen-doped MWCNTs (N-MWCNTs) were fabricated by means of chemical vapor deposition and chemically decorated with gold nanoparticles (AuNPs). Optical microscopy and image analysis reveal that the deposited AuNPs have diameters of 50–200 nm and 100–400 nm, respectively. The AuNP-modified films of MWCNTs and of N-MWCNTs were initially investigated with respect to their response to the ferro/ferricyanide redox system. The N-MWCNTs/AuNPs exhibit lower detection limit (0.345 μM) for this redox system compared to that of MWCNTs/AuNPs (0.902 μM). This is probably due to the presence of nitrogen that appears to enhance the electrocatalytic activity of MWCNTs. The findings demonstrate that the electrochemical responses of both films are distinctly enhanced upon deposition of AuNPs on their surfaces. The detection limits of MWCNTs/AuNPs and N-MWCNTs/AuNPs systems are lower by about 43 % and 27 %, respectively, compared to films not modified with AuNPs. The electrocatalytic activity of the films towards the oxidation of ascorbic acid (AA), uric acid (UA), and dopamine (DA) was studied. The findings reveal that N-MWCNTs/AuNPs represent a powerful analytical tool that enables simultaneous analysis of AA, UA, and DA in a single experiment.

A co-pyrolysis route to synthesize nitrogen doped multiwall carbon nanotubes for oxygen reduction reaction

Nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) have been synthesized by a co-pyrolysis route of iron(II) phthalocyanine (FePc) loaded and PEO20–PPO70–PEO20 retained in mesoporous silica. In this process, FePc was used as both Fe-catalyst, carbon and nitrogen sources, and P123-containing mesoporous silica was employed as both the substrate and carbon seeds/source for the growth of N-MWCNTs. The obtained samples have well-defined morphology and graphitic structure, and show high electrochemical catalytic activity and stability for oxygen reduction reaction, attributing to the highly graphitic structure and the pyridinic-type nitrogen in the N-MWCNTs. The power density of a single fuel cell using N-MWCNT as cathodic catalyst was measured to be 67.7% of that of a standard single cell using 40% Pt/C as cathodic catalyst.

Nitrogen-doped carbon nanotubes modified with gold nanoparticles for simultaneous analysis of N-acetylcysteine and acetaminophen

A novel film consisting of nitrogen-doped multi-walled carbon nanotubes modified with gold nanoparticles (further denoted as N-MWCNTs/AuNPs) was fabricated and applied for the simultaneous electrochemical analysis of N-acetylcysteine (NAC) and acetaminophen (AC) in phosphate buffer solution (PBS, pH 7.0). The fabricated film exhibits powerful response towards simultaneous analysis of NAC and AC followed by well-separated cyclic voltammetric waves (∼440 mV). The oxidation peak currents of NAC and AC increase linearly with their concentrations in the ranges of 0.100–1.510 mM and 0.063–0.190 mM, respectively. The detection limits of N-MWCNTs/AuNPs towards NAC and AC were estimated to be 3.0 and 0.35 μM, respectively. The good catalytic activity, the high detection ability, and the great stability of N-MWCNTs/AuNPs verify that such composite materials are extremely promising for the construction of biosensors.

Boron- and nitrogen-doped multi-wall carbon nanotubes for gas detection

The response of pristine, nitrogen and boron doped carbon nanotube (CNT) sensors to NO2, CO, C2H4 and H2O at ppm concentrations was investigated at both room temperature and 150°C. N-doped CNTs show the best sensitivity to nitrogen dioxide and carbon monoxide, while B-doped CNTs show the best sensitivity to ethylene. All tubes (including undoped) show strong humidity response. Sensing mechanisms are determined via comparison with density functional calculations of gas molecule absorption onto representative defect structures in N and B-doped graphene. N-CNTs show decreased sensitivity with temperature, and detection appears to occur via gas physisorption. B-CNTs appear to react chemically with many of the absorbed species as shown by their poor baseline recovery and increasing sensitivity with temperature. This limits their cyclability. Overall gas sensitivity is as good or better than post-growth functionalised nanotubes, and used in combination, CNTs, N-CNTs and B-CNTs appear highly promising candidates for cheap, low power, room temperature gas sensing applications.

Spectroscopic Studies on Nitrogen-doped Multi-Walled Carbon Nanotubes Using Monochromated STEM-EELS at Low-Voltage

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Electrochemical Sensor Consisting of Nitrogen-Doped Multi-Walled Carbon Nanotubes Decorated with Platinum Nanoparticles

Electrochemical Sensor Consisting of Nitrogen-Doped Multi-Walled Carbon Nanotubes Decorated with Platinum Nanoparticles

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.

Effect of a variety of carbon nanotubes on the iodine–iodide redox pair

The iodide (I−)-triiodide (I3-) redox pair was used as a model system to evaluate the potential catalytic activity of various carbon nanotubes. Aqueous solutions of hydroiodic acid were irradiated with ultraviolet light in the presence of single wall, multi-wall, boron-doped and nitrogen-doped multi-wall carbon nanotubes. The nitrogen-doped multi-wall carbon nanotubes showed significant catalytic activity in the generation of hydrogen triiodide, while the other carbon nanotubes studied inhibited the generation of hydrogen triiodide. The photoconversion of hydroiodic acid to hydrogen triiodide, catalyzed by the nitrogen-doped multi-wall carbon nanotubes, was further accelerated by the presence of dissolved oxygen, offering an additional decomposition pathway for hydroiodic acid.

Electrocatalytic Activity of Pt Grown by ALD on Carbon Nanotubes for Si-Based DMFC Applications

We present an anode design for silicon-based direct methanol fuel cell (DMFC) applications. Platinum was deposited conformally by atomic layer deposition (ALD) onto vertically aligned, nitrogen-doped multi-walled carbon nanotubes (MWCNTs) grown on porous silicon. The deposition was carried out in a top-flow ALD reactor at 250{degree sign}C, using MeCpPtMe3 and O2 as precursors. The anode was tested for the methanol oxidation reaction (MOR) in a three-electrode electrochemical set-up and it showed improved catalytic activity compared to a reference sample of Pt deposited on flat Si. It is demonstrated that ALD could be a MEMS compatible deposition technique for Si-based fuel cell applications.