Nitrogen-doped Single-walled Carbon Nanotubes Research Articles

Adsorption behavior of HFCO and COF2 gasses on pristine, Al-doped, and N-doped (8, 0) single-wall carbon nanotubes and pristine aluminum nitride nanotube: A first-principles study

The detection of organic pollutants in the environment is crucial due to their significant impact on human health. Formyl fluoride (HFCO) and carbonyl fluoride (COF2) are toxic gasses that contribute to stratospheric ozone depletion. To explore a potential sensor material for these compounds, the adsorption properties of HFCO and COF2 on pristine (8, 0) single-walled carbon nanotubes (SWCNTs), aluminum-doped SWCNTs (Al-SWCNTs), nitrogen-doped SWCNTs (N-SWCNTs), and aluminum nitride nanotube (AlNNTs) were investigated using density functional theory (DFT) calculations. Obtained structural and electronic results reveal no significant after HFCO and COF2 adsorption on pristine SWCNT. However, the conductivity and polarizability of Al- SWCNT increases throw HFCO and COF2 adsorption. It was shown that this adsorption strongly depends on molecular orientation toward SWCNT. Structural and electronic findings show that studied molecules undergoes a physical adsorption to N- SWCNT. However, AlNNT was also found to show significant changes in structural and electronic properties after HFCO and COF2 adsorption. This adsorption leads to a significant (nearly 45%) reduction in the HOMO-LUMO gap of AlNNTs. Therefore, it is proposed from this study that Al-SWCNTs and AlNNTs are promising candidates for HFCO and COF2 gas sensors. Moreover, AlNNTs exhibit intrinsic detection capabilities without structural manipulation via doping which makes AlNNTs particularly attractive for sensor applications. Moreover, the capability of AlNNT without manipulating makes this nanotube a good and easy made candidate for these compounds adsorption.

Nitrogen-Doped Single-Walled Carbon Nanotubes by Floating-Catalyst CVD Process

Due to the properties of single-walled carbon nanotube (SWCNT), thin film SWCNTs have been used for many versatile applications. Direct synthesis of the nanotube films with desired electronic structures without prerequisite of post treatment process then becomes one important step. Here, we present the synthesis of nitrogen-doped SWCNTs by floating-catalyst chemical vapor deposition process. With low nitrogen level incorporated into the sp2 carbon network, substitutional and pyridinic nitrogens become predominance. The electronic structure of N-doped SWCNT film could be changed into n-type doping. The localized structures of carbon and nitrogen bonding environments were also revealed by x-ray absorption spectroscopy. The formation of p-n junction was also obtained from the I-V characteristic of N-doped SWCNT heterojunction diode revealing n-type behavior of the sample.

Floating Catalyst Chemical Vapor Deposition Patterning Nitrogen‐Doped Single‐Walled Carbon Nanotubes for Shape Tailorable and Flexible Micro‐Supercapacitors

AbstractMicro‐supercapacitors (MSCs) as high‐power density energy storage units are designed to meet the booming development of flexible electronics, requiring simple and fast fabrication technology. Herein, a fast and direct solvent‐free patterning method is reported to fabricate shape‐tailorable and flexible MSCs by floating catalyst chemical vapor deposition (FCCVD). The nitrogen‐doped single‐walled carbon nanotubes (N‐SWCNTs) are directly deposited on a patterned filter by FCCVD with designable patterns and facilely dry‐transferred on versatile substrates. The obtained MSCs deliver an excellent areal capacitance of 3.6 mF cm−2 and volumetric capacitance of 98.6 F cm−3 at a scan rate of 5 mV s−1 along with excellent long‐term cycle stability over 125 000 circles. Furthermore, the MSCs show good performance uniformity, which can be readily integrated via connection in parallel or series to deliver a stable high voltage (4 V with five serially connected devices) and large capacitance (5.1 mF with five parallel devices) at a scan rate of 100 mV s−1, enabling powering the light emitting displays. Therefore, this method blazes the trail of directly preparing flexible, shape‐customizable, and high‐performance MSCs.

Silicon-, Nitrogen-Doped Single-Walled Carbon Nanotubes as Oxygen Reduction Reaction Catalysts

Silicon-, Nitrogen-Doped Single-Walled Carbon Nanotubes as Oxygen Reduction Reaction Catalysts

Heterostructure NiS2/NiCo2S4 nanosheets array on carbon nanotubes sponge electrode with high specific capacitance for supercapacitors

Nickel cobalt sulfur is attracting more attention due to its great electrical conductivity and high specific capacitance for faraday pseudo-capacitors. Here, by evaporation-induced drying, heterostructure NiS 2 /NiCo 2 S 4 nanosheets on self-supporting substrate of nitrogen-doped single-walled carbon nanotubes sponge (NSCS) are obtained with the sponge volume significantly being reduced. With the electrode film thickness being 80 μm, the as-prepared heterostructure NiS 2 /NiCo 2 S 4 /NSCS electrode shows outstanding areal/gravimetric/volumetric capacitance of 10.5 F cm −2 /2905 F g −1 /1307.2 F cm −3 at 1 A g −1 . With the increase of current density from 1 to 60 A g −1 , the current retention rate maintains at 61%. When the active material loading is increased to 14 mg cm −2 , the gravimetric capacitance can still maintain at 1725 F g −1 , indicating the high ratio performance. After 10,000 cycles, the capacity retention still remains 83% at current density of 10 A g −1 . In addition, an asymmetric supercapacitor (ASC) delivers have high gravimetric/volumetric energy density of 58.1 W h kg −1 /52.3 W h L −1 with excellent cycle stability after 20,000 cycles. Therefore, the electrode material with high loading and high rate performance can be realized by this method. • By evaporation-induced drying, the volume of NiS 2 /NiCo 2 S 4 /NSCS shrinks obviously. • The electrode has high areal and volumetric capacitance with high loading. • Heterostructure material of NiS 2 /NiCo 2 S 4 greatly improves the electrochemical performance. • The asymmetric supercapacitor delivers high gravimetric/volumetric energy density.

Nonresonant Polarized Raman Spectra Calculations of Nitrogen-Doped Single-Walled Carbon Nanotubes: Diameter, Chirality, and Doping Concentration Effects.

Raman spectra of nitrogen-doped single-walled carbon nanotubes are calculated using the spectral moment's method combined with the bond polarizability model. The influence of the nanotube diameter and chirality is investigated. We also address the important question of the effect of the N-doping concentration, and we propose an equation to estimate the doping concentration from the knowledge of the tube diameter and the frequency of the radial breathing mode.

Suppression of conductance fluctuation of disordered carbon nanotubes caused by thermal atomic vibration

We have numerically succeeded in evaluating the conductance fluctuations of nitrogen-doped single-walled carbon nanotubes (N-SWCNTs), as a typical example of disordered quasi-one-dimensional materials, including the effect of thermal atomic vibration from the viewpoint of conductance histograms. We show that conductance histograms even of N-SWCNTs with over 100 nm length are described by a log-normal distribution function at tens of kelvins, which suggests that the N-SWCNTs shows localization at low temperature. On the other hand, conductance of the N-SWCNT are no longer described by a log-normal distribution function at hundreds of kelvins. Instead, the histograms are described by a Gaussian distribution function, which indicates that the N-SWCNTs definitely deviate from localization regime. In addition, we confirm that the conductance fluctuations of the N-SWCNTs are also suppressed as the temperature increases because of delocalization due to quantum decoherence caused by thermal atomic vibration.

The influence of γ-irradiation on nitrogen configuration in nitrogen-doped single-walled carbon nanotubes

Electronic properties of nitrogen-doped single-walled carbon nanotubes (N-doped SWCNTs) depend on carbon and nitrogen configuration. Depending on the intrinsic nitrogen structure, it can be either intrinsic p- or n- doping. Here, we have investigated the influence of soft gamma (γ)-irradiation on the nitrogen configuration in vertically aligned N-doped SWCNT arrays. As the irradiation dose increased, pyridinic and graphitic nitrogens become more predominant. In general, the presence of holes refer to p-doping. However, XPS spectra show n-doping features, whereas the slight downshift in the G line position in Raman spectra is from compensating the ambient p-doping. The local transition of π* nitrogen was also revealed by X-ray absorption spectroscopy.

Diameter dependent doping in horizontally aligned high-density N-doped SWNT arrays

We reported the growth of horizontally aligned nitrogen-doped single-walled carbon nanotubes (SWNTs) on quartz substrates. The synthesized SWNTs were comprehensively characterized at the single nanotube level. Owing to the highly aligned nature of the nanotubes, we were able to investigate the diameter dependent doping mechanism through systematic resonant Raman spectroscopy studies. Other than the formerly found narrowing effect by N-doping, we proposed that the nanotube diameter affects the introduction of N atoms into the carbon lattice in an elaborate way. The obtained doping level increased along with the nanotube diameter but lost the increasing trend when the diameter became larger and experienced a slight decrease after reaching the local peak value. These insights about the heteroatom doping into the carbon nanotubes could benefit the development of the carbon nanotube based functional materials and extend their application in a broad range of areas.

Organophosphorus pesticides detection using acetylcholinesterase biosensor based on gold nanoparticles constructed by electroless plating on vertical nitrogen-doped single-walled carbon nanotubes

ABSTRACTAn acetylcholinesterase (AChE) biosensor was constructed based on gold nanoparticles (AuNPs) using electroless plating on vertical nitrogen-doped single-walled carbon nanotubes (VNSWCNTs) for detecting organophosphorus pesticides (OPs). AChE was immobilised on AuNPs via Au–S bonding, and VNSWCNTs were produced by spontaneous chemical adsorption of NSWCNTs on gold electrode, also via Au–S bonding. This modified electrode exhibited excellent electron transfer capacity due to the synergy between AuNPs and VNSWCNTs. The developed biosensor showed good linear relations at concentrations of 10−5 – 1 ppb, and the detection limits were 3.04 × 10−6 ppb for methyl parathion, 1.96 × 10−6 ppb for malathion and 2.06 × 10−6 ppb for chlorpyrifos, respectively. The AChE biosensor revealed satisfactory stability, excellent sensitivity and good repeatability. These results suggest that this biosensor has good application prospects and can function as a sensitive device in OPs analysis.

Synergy of carbocatalytic and heat activation of persulfate for evolution of reactive radicals toward metal-free oxidation

Abstract Persulfate (or peroxydisulfate, PDS) is one of green and low-cost sources of sulfate radicals (SO4 −) in advanced oxidation processes (AOPs) for in situ remediation of contaminated soil and water. The key in AOPs is to develop an effective technique for PDS activation. In this paper, nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) were employed as a metal-free catalyst to activate PDS for oxidation of a diversity of organic contaminants such as nitrobenzene (NB), phenol, benzoquinone and sulfachlorpyridazine. For the first time, the coupling effects of carbocatalysis and heat were investigated in a range of 5–75 °C on PDS activation, which indicated that organic oxidation efficiency was enhanced at elevated temperatures. The presence of the carbocatalyst impressively decreased the PDS activation energy from 53.4 (by heat) to 10.3–22.5 kJ/mol (heat/carbocatalysis). Intriguingly, the mechanisms of heat-assisted carbocatalysis were temperature-dependant and the synergy of the heat/carbon integrated system appeared to be phenomenal at a high temperature region (55–75 °C). The thermal stimulation promoted PDS to generate hydroxyl radicals via heterogeneous water oxidation and mutual transformation from sulfate radicals, evidenced by the selective radical quenching and spin trapping techniques. The carbocatalyst boosted the radical production by simultaneously activating the reactants (PDS and organics) with the N-doped carbon atoms and facilitating the electron transport as a conductive substrate. Therefore, this study advances the understanding in the effect of reaction temperature on persulfate activation and unveils the synergy of carbocatalysis with heat for enhanced PDS activation.

Work function, carrier type, and conductivity of nitrogen-doped single-walled carbon nanotube catalysts prepared by annealing via defluorination and efficient oxygen reduction reaction

Pyridinic and graphitic nitrogen atoms can be doped into carbon nanomaterials to create intrinsic structural defects and improve catalytic activity for the oxygen reduction reaction (ORR). An understanding of the relationship between the electronic properties and ORR activity of nitrogen-doped carbon nanomaterials could help design catalysts with better ORR performance. Here we report on the synthesis of nitrogen-doped single-walled carbon nanotubes (SWCNTs) by a combination of defluorination-assisted nanotube-substitution reaction and high-temperature annealing treatment using edge-free highly crystalline SWCNTs. The electronic properties of the prepared samples, such as the work function, carrier type, and conductivity were measured and correlated with their ORR activity in an acid electrolyte. Graphitic nitrogen-rich SWCNTs with n-type carrier, low work function, and high conductivity exhibited efficient ORR activity. The work function, carrier type, conductivity, and O2 dissociative adsorption sites are dependent on both the species/number of doping nitrogen atoms and the structural defects. The tuning of these two structural factors is necessary for achieving high ORR activity.

Oxygen Evolution Reaction Kinetic Barriers on Nitrogen-Doped Carbon Nanotubes.

We investigate kinetic barriers for the oxygen evolution reaction (OER) on singly and doubly nitrogen-doped single-walled carbon nanotubes (NCNTs) using the climbing image nudged elastic band method with solvent effects represented by a 45-water-molecule droplet. The studied sites were chosen based on a previous study of the same systems utilizing a thermodynamic model which ignored both solvent effects and kinetic barriers. According to that model, the two studied sites, one on a singly nitrogen-doped CNT and the other on a doubly doped CNT, were approximately equally suitable for OER. For the four-step OER process, however, our reaction barrier calculations showed a clear difference in the rate-determining *OOH formation step between the two systems, with barrier heights differing by more than 0.4 eV. Thus, the simple thermodynamic model may alone be insufficient for identifying optimal OER sites. Of the remaining three reaction steps, the two H2O forming ones were found to be barrierless in all cases. We also performed solvent-free barrier calculations on NCNTs and undoped CNTs. Substantial differences were observed in the energies of the intermediates when the solvent was present. In general, the observed low activation energy barriers for these reactions corroborate both experimental and theoretical findings of the utility of NCNTs for OER catalysis.

Non-Enzymatic Electrochemical Detection of Urea on Silver Nanoparticles Anchored Nitrogen-Doped Single-Walled Carbon Nanotube Modified Electrode

Herein, we demonstrated synthesis and application of silver nanoparticles (Ag-NPs) decorated nitrogen doped single-walled carbon nanotube through a one-step thermal-reduction method using melamine as the nitrogen source. Field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction data confirmed the successful synthesis of Ag-NPs functionalized nitrogen doped single-walled carbon nanotubes(Ag-N-SWCNTs). The nitrogen-doping notably modified the properties of the SWCNT and it showed stronger affinity for the attachment of Ag-NPs. By integrating the high surface area and electrical properties of N-SWCNTs with Ag-NPs, the obtained Ag-N-SWCNTs nanocomposite showed high catalytic activity than N-SWCNTs and pristine-SWCNTs. The enzyme-based methods have some disadvantages. For example, high fabrication cost and poor stability, due to these intrinsic disadvantages, non-enzymatic sensors have received more interest in fabrication of sensors. A non-enzymatic electrochemical urea sensor was developed by modifying glassy carbon electrode (GCE) with Ag-N-SWCNTs and a layer of Nafion (Nf). Thus, the fabricated sensor exhibited lower limit of detection (4.7 nM), with an enhanced sensitivity of 141 μAmM−1cm−2 for urea detection in the range of 66 nM to 20.6 mM(R2 = 0.966). The reliability of the as-fabricated sensor was successfully investigated by using it to detect urea in tap water and milk samples. The NF/Ag-N-SWCNTs based urea sensor offers several advantages such as simple fabrication procedure, non-enzymatic and low-cost, so this sensor can be applied to detect urea in various samples from food, fertilizer industries and environmental fields. Moreover, the modified electrode showed phenomenal stability with no loss in activity of storage under ambient conditions. In addition, the novel hybrid NF/Ag-N-SWCNTs/GCE showed high selectivity toward urea with good repeatability and reproducibility further confirmed that this method can be utilized for detection of urea.

Feedstock-dependent nitrogen configurations of nitrogen-doped single-walled carbon nanotubes in a CVD process.

The modification of nitrogen configurations is a viable way to control the electronic properties of nitrogen-doped single-walled carbon nanotubes (N-doped SWCNTs). N-doped SWCNTs were synthesized by a conventional chemical vapor deposition process with a mixed carbon/nitrogen (C/N) feedstock. While higher feedstock flow rates promote the formation of encapsulated N2 molecules, lower flow rates show a predominance of pyridinic and graphitic nitrogen structures as revealed by X-ray photoemission spectroscopy. Therefore, the nitrogen doping in the sp2 carbon network can be controlled by the flow rate of the C/N feedstock.

$$\hbox {N}_{2}$$ N 2 adsorption on the inside and outside the single-walled carbon nanotubes by density functional theory study

The adsorption energies, bond order, atomic charge, optical properties, and electrostatic potential of nitrogen molecules of armchair single-walled carbon nanotubes (SWCNTs) and nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) were investigated using density functional theory (DFT). Our results show that adsorption of the $$\hbox {N}_{2}$$ molecules on the external wall of a nanotube is more effective than on the internal wall in SWCNTs. The results show that $$\hbox {N}_{2}$$ molecule(s) are weakly bonded to SWCNTs and N-SWCNTs through van der Waals-type interactions. The interaction of $$\hbox {N}_{2}$$ molecules with SWCNTs and N-SWCNTs is physisorption as the adsorption energy and charge transfer are small, and adsorption distance is large. The electronic transitions from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) ( $$\hbox {H}\rightarrow \hbox {L}$$ ) have the maximum wavelength and the lowest oscillator strength. The potential sensor on the surface of pristine SWCNTs and N-SWCNTs for the adsorption of $$\hbox {N}_{2}$$ molecule(s) is investigated. The N-loaded single-walled carbon nanotube is introduced as a better $$\hbox {N}_{2}$$ molecule(s) detector when compared with SWCNTs.

Enhanced Lithium–Oxygen Battery Performances with Pt Subnanocluster Decorated N-Doped Single-Walled Carbon Nanotube Cathodes

Achieving dramatic improvement in long-term cycling performance in Li–O2 batteries continues to remain a challenge, which is imperative for turning their alluring promise into reality. Developing a bifunctional cathode material capable of reducing overpotentials and enhancing the long-term cycling performances holds the key. Herein, bifunctional cathodes for Li–O2 batteries were prepared by electrodeposited Pt subnanoclusters on pristine as well as nitrogen-doped single-walled carbon nanotubes (SWCNTs) using rotating disk electrode voltammetry techniques. Diffraction, microscopic, and spectroscopic techniques were used to characterize the prepared materials, and the phase purity of the materials was confirmed. Microscopic analysis depicted a fine dispersion of ≤2 nm Pt nanoclusters on single-walled carbon nanotubes. Rotating disk electrode voltammetry measurements indicated low overpotentials as well as high catalytic ORR/OER activities with Pt nanocluster decorated SWCNTs in comparison to Pt-free SWCNTs....

Hydrogen physisorption energies for bumpy, saturated, nitrogen-doped single-walled carbon nanotubes

Finite saturated regular carbon nanotubes (CNTs) are predicted to exhibit higher capacity as hydrogen storage media compared to unsaturated regular CNTs. In the present study, molecular hydrogen physisorption energies (MHPEs) for finite saturated and unsaturated bumpy defected CNTs were calculated by density functional theory (DFT-D3) methods at the B3LYP/6-31G(d) theory level, with rigorous inclusion of van der Waals interactions. The calculated MHPEs for both regular and bumpy defected armchair, chiral and zigzag CNTs with similar diameters and lengths, with and without nitrogen doping, were compared in terms of Eph/H2, defined as the MHPE per hydrogen molecule adsorbed inside the nanotube. For all studied systems, Eph/H2 increased with the number of physisorbed hydrogen molecules. Nitrogen doping of regular and bumpy CNTs resulted in an increase in the Eph/H2 values, with the exception of bumpy chiral nanotubes. The results of this study demonstrate that bumpy defects are important nanotube structural features whose effects depend on nanotube chirality. For instance, bumpy defects were beneficial for undoped and doped zigzag nanotubes, resulting in a decrease in Eph/H2 values for regular structures from 0.5 and 0.74 to 0.26 and 0.42 eV, respectively. By contrast, for doped armchair regular structures with an Eph/H2 value of 0.38 eV, bumpy defects increased Eph/H2 to 0.45 eV. These Eph/H2 values for bumpy doped armchair and the zigzag nanotubes are all within the range of 0.1–0.5 eV/H2 reported as ideal for reversible hydrogen storage under environmental conditions.

Specific pH Sensor Based on Nitrogen/Carbon Nanotube-Modified Commercial Field-Effect Transistor for Detection of Rumen pH in Ruminants In Situ

A small and stroke resistant pH sensor was fabricated using a commercial metal-oxide field-effect transistor and was modified with single-walled carbon nanotubes (SWCNTs) for direct evaluation of the rumen pH in cows via a stomach tube. Integrated circuit (IC: BS250) was selected as the selective probe for pH detection. For this purpose, the plastic cover on the surface of the drain was drilled to bare the drain surface, followed by modification with nitrogen-doped SWCNTs by the hot-wall chemical vapor deposition process. According to the figures of merit, fabricated sensor was linear from 4.2 to 8.1 pH unit. Detection limit was 1.23 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> M. Relative standard deviation for five replicate analyses was 3.47%. Based on 90% of maximum response, the response times were estimated to be ~60 s for in vivo and ~12.4 s for in vitro measurements. Calibration sensitivity was measured to -62.1 pH/decade. No interference was observed after setting at least 200-fold of interfering agents, such as PO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-</sup> , SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-</sup> , Ca <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> , globulin, and acetic acid in a rumen fluid with 6.61 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> M of H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> . The ease of conducting of the sensor to the rumen through a stomach tube and in situ measurement of the rumen pH was evaluated in four dairy cows. The results were reliable compared with those obtained by a glass membrane electrode on samples drained by rumenocentesis. Slaughterhouse testing of the sensor on rumen contents of sheep (n=8) and cows (n=2) revealed that its relative error percentage could approach to maximum 10% compared with glass membrane sensors.

First-principles study of structural and work function properties for nitrogen-doped single-walled carbon nanotubes

The structural and electronic properties of the capped (5, 5) single-walled carbon nanotube (SWNT), including the structural stability, the work function, and the charge transfer performance, are investigated for the substitutional nitrogen atom doping under different concentrations by first-principles density functional theory. The geometrical structure keeps almost intact with single or two N atom doping, while CN bonds may break up with serious defects for N concentrations of 23.3at.% and above. The SWNT remains metallic and the work function drops after doping due to the upward shift of Fermi level, leading to the increase of the electrical conductivity. N doping enhances the oxygen reduction activity stronger than N adsorption because of higher charge transfers.