N-doped Multi-walled Carbon Nanotubes Research Articles

Synthesis and Nitrogen-Plasma Treatment of Carbon Nanotube/Graphene Composites As Anode Materials for Lithium-Ion Batteries

Lithium ion batteries compared to other batteries (such as Ni-Cd, Lead-Acid, and Ni-MH) possess higher energy densities (100 – 150 Wh/kg), higher voltage, and lower maintenance [1]. Hybrid CNTs and graphene nanostructures applied in lithium ion batteries were directly grown by ambient pressure chemical vapor deposition (CVD); methane was introduced to form graphene on copper foils at 950 oC, then Fe catalysts were deposited on graphene/copper foils by e-beam evaporation, and ethylene was next introduced to grow pillar CNTs on graphene/copper foil at 750 oC [2]. To increase the accessibly specific surface area and the stability as well as conductivity between the carbon nanotube bundles as well as the nickel foam, three dimensional few layer graphene/multi-walled carbon nanotube architectures were fabricated on oxygen-plasma treated nickel foam coated with Fe catalysts by e-beam evaporation through a one-step ambient pressure CVD process using a mixture of acetylene and hydrogen [3]. N-doped multiwall carbon nanotubes prepared by a plasma enhanced chemical vapor deposition process contain wall defects through which lithium ions can diffuse so as to occupy a large portion of the interwall space as storage regions and then improve the Li storage capability [4]. N-doped graphene nanosheets prepared by heat treatment (800 oC and 2 h) of graphite oxide under an ammonia atmosphere exhibited a high reversible capacity due to N-doping inducing a large number of defects on the graphene layer as well as forming a disordered carbon structure (further enhancing Li intercalation properties) and enhanced cycling stability, which demonstrated the N-doped graphene nanosheets to be a promising candidate for anode materials of lithium ion batteries [5]. The effects of the electron-deficiency (making the defect graphenes have an electron-accepting tendency) of N-doped (pyridinic, pyrrolic, and graphitic) graphenes on their application in lithium ion batteries were investigated and the pyridinic graphene possessed the best as anode materials of lithium ion batteries, while graphitic graphene would be the weakest of the three defect structures [6]. To simultaneously synthesize carbon nanotubes and graphene on nickel foam without additional catalysts, it is tried to grow using one-step ambient pressure chemical vapor deposition (CVD) at different temperatures (700, 800, and 900 oC). Next, in order to add nitrogen-doped defects to the surface of carbon nanotube/graphene composites, it is modified by RF (radio frequency) nitrogen-plasma at different power levels (50, 100, and 150 W) and time periods (5, 15, and 30 min). Carbon nanotubes and graphene are simultaneously synthesized by CVD at 800 oC. Furthermore, the specific capacity (618.32 mAh/g) reached a maximum at the better nitrogen-plasma treatment conditions (power = 100 W and time = 15 min) due to the highest percentage of the pyridinic defect structure which is the most suitable for Li storage with a high storage capacity [6]. Moreover, it also shows higher electrochemical stability after carbon nanotube/graphene composites being treated by nitrogen-plasma.

Graphene loaded bimetallic Au@Pt nanodendrites enhancing ultrasensitive electrochemical immunoassay of AFP

A dual enhancing strategy has been employed to develop electrochemical immunosensor for the ultrasensitive detection of AFP, which is enhanced by poly-dopamine functionalized N-doped multi-walled carbon nanotube (PDA-N-MWCNT) and the nanocomposite of graphene loaded Au@Pt mesoporous nanodendrites. The fabricated immunosensor exhibited a wide linear range of 0.1pg/mL–10ng/mL, with an ultralow detection limit of 0.05pg/mL. The good performance of the developed immunosensor could be contributed to (1) PDA-N-MWCNT supplied good biocompatible surface for immobilizing primary antibody (Ab1); (2) PDA-N-MWCNT modified electrode endowed more electrochemical active area, which can effectively improve the sensitivity of the immunosensor; (3) graphene could load high amount of good conductive and high electrocatalytic active Au@Pt nanodendrites for signal amplification. The results imply that the as-fabricated immunosensors have great potential for clinic usage.

A Facile and Efficient Modification of CNTs for Improved Fischer–Tropsch Performance on Iron Catalyst: Alkali Modification

AbstractIn this paper, a facile and environmentally benign method is used to pretreat carbon nanotubes (CNTs) by alkali modification, which decreases the wall thickness, increases the inner diameter, and improves the graphitization degree of CNTs compared to conventional acid treatment. The iron catalyst supported on alkali modified CNTs shows extraordinary Fischer–Tropsch synthesis (FTS) activity and CO conversion (1.78 and 2.41 times, respectively) compared with those supported on either the acid treated or pristine CNTs. Additionally, the diesel (C10‐20) selectivity on Fe/CNTs‐Na is up to 60 %, which is much higher than that calculated from the Anderson–Schulz–Flory distribution (39 %). Similar results are also found by using activated carbon (AC) and N‐doped multiwall carbon nanotubes (NCNTs) as supports for FTS, proving the universal applicability of alkali modification on carbon material. The positive relationship between the C5+ selectivity and C2−C4 olefin/paraffin ratio of iron catalyst can also be achieved irrespective of the support type.

Critical insights into understanding the effects of synthesis temperature and nitrogen doping towards charge storage capability and microwave shielding in nitrogen-doped carbon nanotube/polymer nanocomposites

Herein, various N-doped multiwall carbon nanotubes were prepared by varying the synthesis temperature, and their charge storage capability and electromagnetic shielding effectiveness were assessed by incorporating them into a PVDF matrix.

Preparation of a graphitic N-doped multi-walled carbon nanotube composite for lithium–sulfur batteries with long-life and high specific capacity

One of the challenges for lithium–sulfur batteries is a rapid capacity fading owing to the insulating of sulfur and Li2S2/Li2S compounds, the dissolving and consequent shuttling of polysulfide.

Enhanced Adsorption of Hydroxyl- and Amino-Substituted Aromatic Chemicals to Nitrogen-Doped Multiwall Carbon Nanotubes: A Combined Batch and Theoretical Calculation Study.

A large effort is being made to develop nanosorbents with tunable surface chemistry for enhanced adsorption affinity and selectivity toward target organic contaminants. Heteroatom N-doped multiwall carbon nanotubes (N-MCNT) were synthesized by chemical vapor deposition of pyridine and were further investigated for the adsorptive removal of several aromatic chemicals varying in electronic donor and acceptor ability from aqueous solutions using a batch technique. Compared with commercial nondoped multiwall carbon nanotubes (MCNT), N-MCNT had similar specific surface area, morphology, and pore-size distribution but more hydrophilic surfaces and more surface defects due to the doping of graphitic and pyridinic N atoms. N-MCNT exhibited enhanced adsorption (2-10 folds) for the π-donor chemicals (2-naphthol and 1-naphthalmine) at pH ∼6 but similar adsorption for the weak π-donor chemical (naphthalene) and even lower adsorption (up to a 2-fold change) for the π-acceptor chemical (1,3-dinitrobenzene). The enhanced adsorption of 2-naphthol and 1-naphthalmine to N-MCNT was mainly attributed to the favored π-π electron-donor-acceptor (EDA) interaction between the π-donor adsorbate molecule and the polarized N-heterocyclic aromatic ring (π-acceptor) on N-MCNT. The proposed adsorption enhancement mechanisms were further tested through the pH effects on adsorption and the density function theory (DFT) calculation. The results show for the first time that the adsorptive interaction of π-donor aromatic compounds with carbon nanomaterials can be facilitated by N-doping.

Highly efficient electro-generation of hydrogen peroxide using NCNT/NF/CNT air diffusion electrode for electro-Fenton degradation of p-nitrophenol.

To promote the in situ generation of hydrogen peroxide (H2O2) in electro-Fenton system, a new air diffusion electrode (ADE) was put forward in the present work using N-doped multi-walled carbon nanotubes (NCNT) as the catalyst layer, multi-walled carbon nanotubes (CNT) as the diffusion layer, and nickel foam (NF) as the supporting material, respectively. The catalyst layer in ADE was characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. Then the performances of H2O2 accumulation and p-nitrophenol (p-NP) degradation with the electrode (NCNT/NF/CNT ADE) were investigated. The experimental results showed that H2O2 accumulation on the NCNT/NF/CNT ADE was greatly improved by the presence of N doping, and H2O2 accumulation concentration could reach 307 mg L(-1) after 120 min at the current intensity of 100 mA. Moreover, the NCNT/NF/CNT ADE presented more effective performance on p-NP degradation than the CNT/NF/CNT ADE or the NF ADE. p-NP of initial 50 mg L(-1) could be almost completely removed after 30 min, and the total organic carbon removal efficiency reached 62.61% after 120 min when 0.4 mM Fe(2+) was added into the system. The repeatability test suggested that the stability of the NCNT/NF/CNT ADE was very good.

Ultrafine CoP Nanoparticles Supported on Carbon Nanotubes as Highly Active Electrocatalyst for Both Oxygen and Hydrogen Evolution in Basic Media.

The development of low-cost and highly active electrocatalysts for two half reactions: H2 and O2 evolution reactions (HER and OER), is still a huge challenge to realize water splitting. Herein, we report that CoP nanoparticles (NPs) can act as a bifunctional catalyst for both HER and OER. Particularly, ultrafine CoP NPs decorated on N-doped multiwalled carbon nanotube (MWCNT) exhibit remarkable catalytic performance for OER in 0.1 M NaOH aqueous solution, with a low onset overpotential of 290 mV, a Tafel slope of 50 mV dec(-1), an overpotential (η) of 330 mV at 10 mA cm(-2), and approximately 100% Faradaic efficiency, paralleling the performance of state-of-the-art Co-based OER catalysts including Co3O4, CoSe2, and Co-Pi. The hybrid catalyst is capable of maintaining a high catalytic current density for at least 10 h without any loss of catalytic activity. Meanwhile, the noble-metal-free catalyst also shows good activity and duarability for HER under the same basic condition.

Enhanced Oxygen Reduction Activity of N-Doped Multiwalled Carbon Nanotubes in Alkaline Media

A great deal of work has been made to develop new electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. In order to replace expensive and scarce Pt-based catalysts that have been primarily employed as cathode catalysts in low-temperature fuel cells, different carbon-based materials that possess lower price, better availability and improved chemical stability have been studied. Nitrogen-doped nanocarbons can be used as alternatives to Pt-based cathode catalysts. Previously, we have investigated the reduction of O2 on CVD grown nitrogen-doped carbon nanotubes,1 on CNTs heat-treated in the presence of urea2 and on N-doped graphene3 and few-layer graphene/multiwalled carbon nanotube (FLG/MWCNT) composites.4 In this work the electrocatalysis of oxygen reduction on nitrogen-doped carbon nanotube (NCNT) catalysts has been investigated. These NCNT materials were prepared from two different nitrogen precursors and acid-treated MWCNTs. Cyanamide (CM) and dicyandiamide (DCDA) were used as nitrogen precursors and the doping was achieved by pyrolysing MWCNTs in the presence of these nitrogen-containing compounds at 800 °C. The MWCNT-to-nitrogen precursor mass ratio was 1:20. The N-doped carbon nanotube catalyst samples were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The electrocatalysis of the ORR was studied in 0.1 M KOH on glassy carbon (GC) electrodes modified with N-doped CNT electrocatalysts employing the rotating disk electrode (RDE) method. The NCNT-DCDA material showed a better ORR performance than the NCNT-CM catalyst. Fig. 1 presents the ORR polarization curves on NCNT-DCDA at various rotation rates and Fig. 2 shows the Koutecky-Levich plots for this catalyst. As can be seen, the number of electrons transferred (n) is close to 4, which is advantageous from the point of view of fuel cell application. A comparison of the RDE results indicated that these metal-free NCNT catalysts possess remarkable electrocatalytic activity toward the ORR in alkaline media similar to that of commercial Pt/C catalyst (Fig. 3). The results obtained in this work are important for the development of Pt-free cathode catalysts for alkaline membrane fuel cells (AMFC). In the next stage of work these materials will be tested in AMFC conditions.

High-efficiency PdCu alloy nanocube catalyst supported on N-doped multiwalled carbon nanotubes for alcohol electrooxidation

N-doped of the support is generally important to immobilize metal nanoparticles on the support, produce some active Me–N sites, and generate good electrocatalytic activity and stability. A facile and low-cost preparation of N-doped multiwalled carbon nanotube (N-MWCNTs)-supported hollow PdCu alloyed nanocube catalyst (H–PdCu/N-MWCNTs) was introduced in this paper. To increase the stability and utilization ratio of the noble metal, a two-step strategy was employed, which included the synthesis of N-MWCNTs using polypyrrole (ppy) as the source of nitrogen and the preparation of the hollow PdCu alloyed nanocubes. According to transmission electron microscopy (TEM) measurements, the as-prepared hollow PdCu alloyed nanocube catalyst has superior dispersibility, and the average diameter is about 50 nm. X-ray photoelectron spectroscopy (XPS) measurements reveal that N atoms have been doped in multiwalled carbon nanotubes (MWCNTs) and there is abundance of pyridinic N and graphitic N species on N-MWCNT surface. The electrochemical measurements indicate that the hollow PdCu alloyed nanocube catalyst has a better electrocatalytic activity and stability for the alcohol oxidation. It is concluded that the H–PdCu/N-MWCNTs would be a potential candidate as an anode electrocatalyst in direct alcohol fuel cell.

Surface and electrosurface characterization of surface-oxidized multi-walled N-doped carbon nanotubes

In our experiments, N-doped multi-wall carbon nanotubes (CNTs) were produced by chemical vapor deposition (CVD method). The bamboo-shaped carbon nanotubes were treated with various oxidizing agents, namely H2O2, HNO3, HClO4 and a binary mixture of H2SO4/HNO3 acid. The purity of the CNTs was tested with thermo-gravimetric methods.TEM and FTIR microscopy was used to investigate the relative content of oxygen-containing functional groups formed on the CNT surfaces. For the characterization of the electric double layer (EDL) of the surface-functionalized carbon nanotubes, the zeta-potential of the CNTs samples was measured as a function of pH and electrolyte concentration (for 1–1, 21–12 and 31–13 electrolytes). It has been shown that the electrokinetic behavior of CNTs essentially resembles the behavior of lyophobic colloids: (a) the ζ (CKCl) curves reveal a maximum or plateau region; (b) the addition of CaCl2 leads to a sharp decrease in the ζ-potential; (c) the increase of trivalent counterions leads to/causes a charge reversal of the surface. A correlation between the sedimentation stability of CNTs suspensions and the zeta-potential of nanotubes has been found.

Influence of acid treatment on N-doped multi-walled carbon nanotube supports for Fischer–Tropsch performance on cobalt catalyst

Nitrogen-doped carbon nanotubes (NCNTs) were acid treated and used as a support for Co catalysts. The effect of acid treatment time on the carbon structure, surface properties and the microstructure of Co catalysts was extensively characterized by BET, XRD, TPR, XPS, TEM and Raman spectroscopy. It was found that acid treatment affected the support structure, the Co reducibility, the Co dispersion and the Fischer–Tropsch (FT) synthesis performance significantly. The graphitization degree, cobalt particle size, cobalt particle location and the number of active sites determined the FT synthesis performance of the Co catalysts.

Electrocatalytic activity of atomic layer deposited Pt–Ru catalysts onto N-doped carbon nanotubes

Pt–Ru catalysts of various compositions, between 0 and 100at.% of Ru, were deposited onto N-doped multi-walled carbon nanotubes (N-CNTs) by atomic layer deposition (ALD) at 250°C. The Pt and Ru precursors were trimethyl(methylcyclopentadienyl)platinum (MeCpPtMe3) and bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2), respectively. O2 was used as the reactant in both processes. The composition of the catalysts was easily tuned by varying the Pt-to-Ru ALD cycle ratio. The catalysts were tested toward the CO oxidation and methanol oxidation reaction (MOR) in a three-electrode electrochemical set-up. For the compositions investigated, the catalysts with a Ru content of 29at.% exhibited highest catalytic activity.

Ru-decorated Pt nanoparticles on N-doped multi-walled carbon nanotubes by atomic layer deposition for direct methanol fuel cells

We present atomic layer deposition (ALD) as a new method for the preparation of highly dispersed Ru-decorated Pt nanoparticles for use as catalyst in direct methanol fuel cells (DMFCs). The nanoparticles were deposited onto N-doped multi-walled carbon nanotubes (MWCNTs) at 250 °C using trimethyl(methylcyclopentadienyl)platinum MeCpPtMe3, bis(ethylcyclopentadienyl)ruthenium Ru(EtCp)2 and O2 as the precursors. Catalysts with 5, 10 and 20 ALD Ru cycles grown onto the CNT-supported ALD Pt nanoparticles (150 cycles) were prepared and tested towards the electro-oxidation of CO and methanol, using cyclic voltammetry and chronoamperometry in a three-electrode electrochemical set-up. The catalyst decorated with 5 ALD Ru cycles was of highest activity in both reactions, followed by the ones with 10 and 20 ALD Ru cycles. It is demonstrated that ALD is a promising technique in the field of catalysis as highly dispersed nanoparticles of controlled size and composition can be deposited, with up-scaling prospects.

The Role of N-Doped Multiwall Carbon Nanotubes in Achieving Highly Efficient Polymer Bulk Heterojunction Solar Cells

This paper reports an improved solar cell performance of 8.6% by incorporation of N-doped multiwall carbon nanotubes (N-MCNTs) into BHJ solar cells composed of PTB7 and PC71BM. It was demonstrated for the first time that incorporation of N-MCNTs leads to not only increased nanocrystallite sizes but also smaller phase-separated domain sizes of both PTB7 copolymers and PC71BM from X-ray scattering study. The results show that N-MCNTs could serve as both exciton dissociation centers and charge transfer channels. The enhanced charge dissociation probabilities and effective charge carrier lifetime in the active layer material offer evidence to support the conclusion that N-MCNTs facilitated charge separation and transport.

Expansion of cardiac ischemia/reperfusion injury after instillation of three forms of multi-walled carbon nanotubes

BackgroundThe exceptional physical-chemical properties of carbon nanotubes have lead to their use in diverse commercial and biomedical applications. However, their utilization has raised concerns about human exposure that may predispose individuals to adverse health risks. The present study investigated the susceptibility to cardiac ischemic injury following a single exposure to various forms of multi-walled carbon nanotubes (MWCNTs). It was hypothesized that oropharyngeal aspiration of MWCNTs exacerbates myocardial ischemia and reperfusion injury (I/R injury).MethodsOropharyngeal aspiration was performed on male C57BL/6J mice with a single amount of MWCNT (0.01 - 100 μg) suspended in 100 μL of a surfactant saline (SS) solution. Three forms of MWCNTs were used in this study: unmodified, commercial grade (C-grade), and functionalized forms that were modified either by acid treatment (carboxylated, COOH) or nitrogenation (N-doped) and a SS vehicle. The pulmonary inflammation, serum cytokine profile and cardiac ischemic/reperfusion (I/R) injury were assessed at 1, 7 and 28 days post-aspiration.ResultsPulmonary response to MWCNT oropharyngeal aspiration assessed by bronchoalveolar lavage fluid (BALF) revealed modest increases in protein and inflammatory cell recruitment. Lung histology showed modest tissue inflammation as compared to the SS group. Serum levels of eotaxin were significantly elevated in the carboxylated MWCNT aspirated mice 1 day post exposure. Oropharyngeal aspiration of all three forms of MWCNTs resulted in a time and/or dose-dependent exacerbation of myocardial infarction. The severity of myocardial injury varied with the form of MWCNTs used. The N-doped MWCNT produced the greatest expansion of the infarct at any time point and required a log concentration lower to establish a no effect level. The expansion of the I/R injury remained significantly elevated at 28 days following aspiration of the COOH and N-doped forms, but not the C-grade as compared to SS.ConclusionOur results suggest that oropharyngeal aspiration of MWCNT promotes increased susceptibility of cardiac tissue to ischemia/reperfusion injury without a significant pulmonary inflammatory response. The cardiac injury effects were observed at low concentrations of MWCNTs and presence of MWCNTs may pose a significant risk to the cardiovascular system.

Heteroatom‐containing ferrocene derivatives as catalysts for MWCNTs and other shaped carbon nanomaterials

The effects of heteroatom‐containing ferrocene catalysts on the materials produced from chemical vapour deposition (CVD) floating catalyst synthesis were investigated. Specifically, the influence of nitrogen‐ and oxygen‐containing ferrocenoyl imidazolide and (N‐phenylcarbamoyl)ferrocene, and sulfur‐ and oxygen‐containing S,S‐bis(ferrocenylmethyl)dithiocarbonate on the structural morphology and distribution of the products as well as properties such as the thermal stability and crystallinity were studied. In addition, the influence of reaction parameters such as catalyst concentration and temperature were also investigated. The nitrogen‐containing catalysts produced N‐doped multi‐walled carbon nanotubes (N‐MWCNTs), whereas the sulfur‐containing catalyst produced primarily nano‐ and microspheres. A concentration of 2.5 wt% ferrocenoyl imidazolide was shown to be optimal for the synthesis of MWCNTs at 850 °C, with very low metal iron residue, highest thermal stability and highest yield (95%). In general, bamboo compartment length for N‐doped MWCNTs increased with temperature. Crystallinity trends were shown to be independent of catalyst and catalyst concentration in all cases and only dependent on temperature. The average diameter for MWCNTs was shown to be dependent on temperature, choice of catalyst and catalyst concentration in all cases. Copyright © 2012 John Wiley & Sons, Ltd.

Influence of ozone on N-doped multi-walled carbon nanotubes

Nitrogen-doped multi-walled carbon nanotubes (N-MWCNT) were selectively grown on oxidised silicon substrate by means of catalytic chemical vapour deposition with decomposition of acetonitrile in the presence of ferrocene (FeCp2) at 900°C. The synthesised N-MWCNT film was initially treated with continuous ozone flow for various time periods and characterised by means of scanning electron microscopy and Raman spectroscopy. The electrochemical response of ozone-treated N-MWCNT film towards ferrocyanide/ferricyanide, [Fe(CN)6]3−/4− redox couple was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy. The results were compared with those obtained for untreated N-MWCNT film. The findings reveal the occurrence of structural defects on surface of ozone-treated N-MWCNT film due to oxidation of nanotubes. Furthermore, the handling of N-MWCNT film with ozone increases the barrier for interfacial electron transfer and slows down the kinetics of redox reaction occurring on this particular electrode.

Nitrogen-doped carbon nanotubes synthesized by pyrolysis of nitrogen-rich metal phthalocyanine derivatives for oxygen reduction

Two kinds of N-doped multiwalled carbon nanotubes (N-MWCNTs) S1 and S2 are prepared by pyrolysis of nitrogen-rich metal phthalocyanine derivatives, i.e. a mixture of metal tetrapyridinoporphyrazines (MTAPs, M = Fe2+, Ni2+) and tetrapyrazinoporphyrazines (MPTpzs) in a chemical vapour deposition furnace. The N-MWCNTs S1 and S2 have a straight structure and a high N/C atomic ratio. The ratios of N/C in S1 and S2 are 20.01% and 18.50%, respectively. The N atoms in S1 exhibit a uniform distribution, and the majority of N atoms are present in a pyridine type environment, while the N atoms in S2 are concentrated in certain areas, and are mainly in a graphite type environment. The electrocatalytic activities of the N-MWCNTs obtained are measured by the rotating disk electrode technique and cyclic voltammetry in an oxygen-saturated 0.1 M KOH solution. The results show that S1 exhibits a one-step, four-electron pathway for the reduction of oxygen (ORR), whereas S2 exhibits a two-step, two-electron process for ORR, S1 has much higher catalytic activity than S2.

Structure–electrical resistivity relationship of N-doped multi-walled carbon nanotubes

Nitrogen-doped multi-walled carbon nanotubes (N-MWCNT) were synthesized by means of catalytic chemical vapor deposition technique using acetonitrile as carbon source material and ferrocene as catalyst. The structure of the synthesized N-MWCNT was characterized by means of microscopic (SEM, HRTEM) as well as spectroscopic (FTIR, Raman) techniques. Furthermore, the specific resistivity and the electrochemical properties of N-MWCNT were investigated and compared with those of pristine MWCNT. The results are discussed in terms of structural differences between pristine MWCNT and N-MWCNT.