N-doped Nanotubes Research Articles

NiCoSe2/Ni3Se2 lamella arrays grown on N-doped graphene nanotubes with ultrahigh-rate capability and long-term cycling for asymmetric supercapacitor

In this paper, we report a one-step electrodeposited synthesis strategy for directly growing NiCoSe2/Ni3Se2 lamella arrays (LAs) on N-doped graphene nanotubes (N-GNTs) as advanced free-standing positive electrode for asymmetric supercapacitors. Benefiting from the synergetic contribution between the distinctive electroactive materials and the skeletons, the as-constructed N-GNTs@NiCoSe2/Ni3-Se2 LAs present a specific capacitance of ~1308 F g−1 at a current density of 1 A g−1. More importantly, the hybrid electrode also reveals excellent rate capability (~1000 F g−1 even at 100 A g−1) and appealing cycling performance (~103.2% of capacitance retention over 10,000 cycles). Furthermore, an asymmetric supercapacitor is fabricated by using the obtained N-GNTs@NiCoSe2/Ni3Se2 LAs and active carbon (AC) as the positive and negative electrodes respectively, which holds a high energy density of 42.8 W h kg−1 at 2.6 kW kg−1, and superior cycling stability of ~94.4% retention over 10,000 cycles. Accordingly, our fabrication technique and new insight herein can both widen design strategy of multicomponent composite electrode materials and promote the practical applications of the latest emerging transition metal selenides in next-generation high-performance supercapacitors.

Temperature-directed synthesis of N-doped carbon-based nanotubes and nanosheets decorated with Fe (Fe3O4, Fe3C) nanomaterials.

The coupling of N-doped carbon materials with transition-metal-based materials shows great promise for electrochemical energy conversion and storage. However, it is still a big challenge to achieve high-performance carbon-based composites with a simplified preparation process and a general synthesis strategy. Herein, a facile and efficient one-pot synthetic strategy was developed for the simultaneous preparation of N-doped one-dimensional carbon nanotube-based hybrids and two-dimensional carbon nanosheet-based hybrids through temperature-directed fabrication. A mixture containing dicyandiamide (DCDA), glucose, and FeCl3·6H2O as precursors was used. C3N4, derived from the pyrolysis of DCDA, acted not only as the self-sacrificing template to guide the formation of the distinct shape and structure of the hybrids, but also as the N and C sources for N-doped carbon materials. Meanwhile, FeCl3·6H2O served both as the catalyst to induce the transformation of the structure and as the reactive template affording an Fe reservoir to generate various Fe species. Effects of temperature on the structure and morphology as well as on the corresponding electrochemical performance of the hybrids were further studied in detail. Moreover, the as-prepared products demonstrated good capacitive performance. This work provides good guidance for the facile and efficient preparation of N-doped carbon-based materials with a distinct shape and structure.

Large scale N-doped GNTs@a-SiOx(x=1–2)NPs: template-free one-step synthesis, and field emission and photoluminescence properties

N-doped graphene nanotubes coated by amorphous SiOx(x=1–2) nanoparticles (N-doped GNTs@a-SiOx(x=1–2)NPs) were synthesized by a simple template-free one-step calcination method.

Oxygen-vacancy Bi2O3 nanosheet arrays with excellent rate capability and CoNi2S4 nanoparticles immobilized on N-doped graphene nanotubes as robust electrode materials for high-energy asymmetric supercapacitors

An asymmetric supercapacitor with high energy was assembled by using the N-GNTs@OV-Bi2O3 NSAs and N-GNTs@CoNi2S4 NPs as negative and positive electrodes, respectively.

Tuning the electronic and chemisorption properties of hexagonal MgO nanotubes by doping – Theoretical study

Oxide materials offer a wide range of interesting physical and chemical properties. Even more versatile behavior of oxides is seen at the nanoscale, qualifying these materials for a number of applications. In this study we used DFT calculations to investigate the physical and chemical properties of small hexagonal MgO nanotubes of different length. We analyzed the effect of Li, B, C, N, and F doping on the properties of the nanotubes. We find that all dopants favor the edge positions when incorporated into the nanotubes. Doping results in the net magnetization whose value depends on the type of the impurity. Using the CO molecule as a probe, we studied the adsorption properties of pristine and doped MgO nanotubes. Our results show that the dopant sites are also the centers of significantly altered chemical reactivity. While pristine MgO nanotubes adsorb CO weakly, very strong adsorption at the dopant sites (B-, C-, and N-doped nanotubes) or neighboring edge atoms (F- and Li-doped nanotubes) is observed. Our results suggest that impurity engineering in oxide materials can be a promising strategy for the development of novel materials with possible use as selective adsorbents or catalysts.

Bifunctional Electrocatalysts for Overall Water Splitting from an Iron/Nickel-Based Bimetallic Metal-Organic Framework/Dicyandiamide Composite.

Pyrolysis of a bimetallic metal-organic framework (MIL-88-Fe/Ni)-dicyandiamide composite yield a Fe and Ni containing carbonaceous material, which is an efficient bifunctional electrocatalyst for overall water splitting. FeNi3 and NiFe2 O4 are found as metallic and metal oxide compounds closely embedded in an N-doped carbon-carbon nanotube matrix. This hybrid catalyst (Fe-Ni@NC-CNTs) significantly promotes the charge transfer efficiency and restrains the corrosion of the metallic catalysts, which is shown in a high OER and HER activity with an overpotential of 274 and 202 mV, respectively at 10 mA cm-2 in alkaline solution. When this bifunctional catalyst was further used for H2 and O2 production in an electrochemical water-splitting unit, it can operate in ambient conditions with a competitive gas production rate of 1.15 and 0.57 μL s-1 for hydrogen and oxygen, respectively, showing its potential for practical applications.

Morphology Conserving High Efficiency Nitrogen Doping of Titanate Nanotubes by NH3 Plasma

Titanate nanotubes offer certain benefits like high specific surface area, anisotropic mesoporous structure and ease of synthesis over other nanostructured titania forms. However, their application in visible light driven photocatalysis is hindered by their wide band-gap, which can be remedied by, e.g., anionic doping. Here we report on a systematic study to insert nitrogen into lattice positions in titanate nanotubes. The efficiency of N2+ bombardment, N2 plasma and NH3 plasma treatment is compared to that of NH3 gas synthesized in situ by the thermal decomposition of urea or NH4F. N2+ bombarded single crystalline rutile TiO2 was used as a doping benchmark (16 at.% N incorporated). Surface species were identified by diffuse reflectance infrared spectroscopy, structural features were characterized by scanning electron microscopy and powder X-ray diffraction measurements. The local chemical environment of nitrogen built into the nanotube samples was probed by X-ray photoelectron spectroscopy. Positively charged NH3 plasma treatment offered the best doping performance. This process succeeded in inserting 20 at.% N into nanotube lattice positions by replacing oxygen and forming Ti–N bonds. Remarkably, the nanotubular morphology and titanate crystal structure were both fully conserved during the process. Since plasma treatment is a readily scalable technology, the suggested method could be utilized in developing efficient visible light driven photocatalysts based on N-doped titanate nanotubes.

N-doped graphene-carbon nanotube hybrid networks attaching with gold nanoparticles for glucose non-enzymatic sensor

Herein, we successfully developed a novel three dimensional (3D) opened networks based on nitrogen doped graphene‑carbon nanotubes attaching with gold nanoparticles (N-GR-CNTs/AuNPs) to apply for non-enzymatic glucose determination. It was demonstrated that the N-GR-CNTs/AuNPs modified electrode exhibited good behavior for glucose detection with a long linear range of 2 μM to 19.6 mM, high sensitivity of 0.9824 μA·mM−1·cm−2, low detection limit of 500 nM, and negligible interference effect. The high performance of the N-GR-CNTs/AuNPs based sensor was assumed due to the outstanding catalytic activity of AuNPs well dispersing on N-GR-CNTs networks, which exhibited as a perfect supporting scaffold due to the enhanced electrical conductivity and large surface area. The obtained results indicated that the N-GR-CNTs/AuNPs hybrid is highly promising for sensitive and selective detection of glucose in sensor application.

Electrochemical Enhancement of Photocatalytic Disinfection on Aligned TiO₂ and Nitrogen Doped TiO₂ Nanotubes.

TiO2 photocatalysis is considered as an alternative to conventional disinfection processes for the inactivation of waterborne microorganisms. The efficiency of photocatalysis is limited by charge carrier recombination rates. When the photocatalyst is immobilized on an electrically conducting support, one may assist charge separation by the application of an external electrical bias. The aim of this work was to study electrochemically assisted photocatalysis with nitrogen doped titania photoanodes under visible and UV-visible irradiation for the inactivation of Escherichia coli. Aligned TiO2 nanotubes were synthesized (TiO2-NT) by anodizing Ti foil. Nanoparticulate titania films were made on Ti foil by electrophoretic coating (P25 TiO2). N-doped titania nanotubes and N,F co-doped titania films were also prepared with the aim of extending the active spectrum into the visible. Electrochemically assisted photocatalysis gave higher disinfection efficiency in comparison to photocatalysis (electrode at open circuit) for all materials tested. It is proposed that electrostatic attraction of negatively charged bacteria to the positively biased photoanodes leads to the enhancement observed. The N-doped TiO2 nanotube electrode gave the most efficient electrochemically assisted photocatalytic inactivation of bacteria under UV-Vis irradiation but no inactivation of bacteria was observed under visible only irradiation. The visible light photocurrent was only a fraction (2%) of the UV response.

Utilizing Electrical Characteristics of Individual Nanotube Devices to Study the Charge Transfer between CdSe Quantum Dots and Double-Walled Nanotubes

To study the charge transfer between cadmium selenide (CdSe) quantum dots (QDs) and double-walled nanotubes (DWNTs), various sizes of CdSe–ligand–DWNT structures are synthesized, and field-effect transistors from individual functionalized DWNTs rather than networks of the same are fabricated. From the electrical measurements, two distinct electron transfer mechanisms from the QD system to the nanotube are identified. By the formation of the CdSe–ligand–DWNT heterostructure, an effectively n-doped nanotube is created due to the smaller work function of CdSe as compared with that of the nanotube. In addition, once the QD–DWNT system is exposed to laser light, further electron transfer from the QD through the ligand, specifically, 4-mercaptophenol (MTH), to the nanotube occurs and a clear QD size-dependent tunneling process is observed. The detailed analysis of a large set of devices and the particular methodology employed here for the first time allowed for extracting a wavelength and quantum dot size-dependent charge transfer efficiency—a quantity that is evaluated for the first time through electrical measurement.

Large-scale template-free synthesis of N-doped graphene nanotubes and N-doped SiO 2 -coated graphene nanotubes: Growth mechanism and field-emission property

Abstract The use of dopants and other functional materials has been proven to be an effective approach in tailoring the electronic properties of the composition of graphene nanosheets. However, investigations into doping and compositing of tubular graphene are still at an early stage. Herein, the first large-scale synthesis of N-doped graphene nanotubes (GNTs) and the N-doped graphene coaxial nanotubes with amorphous SiO 2 coating layer (GNTs@SiO 2 ) have been performed in a facile free-template, one-step chemical vapor deposition method, and the growth mechanism was investigated in detail. This approach both simplifies the synthetic process and protects the nanotubes from destruction caused by template removal. Moreover, a high ratio of graphitic-N to pyridinic-N doping (∼6.5:1) was achieved, which is an important factor required to improve the various properties of graphene. The N-doped GNTs and GNTs@SiO 2 displayed excellent field emission properties, with E to of 1.2 and 0.5 V/μm and E thr of 3.4 and 4 V/μm, respectively, and a synergistic effect mechanism has been proposed to interpret the enhanced FE properties. This present research not only offers a new route for large-scale synthesis of N-doped tubular graphene and its nanocomposite, along with excellent field emission properties and electroconductivity, but also establishes a foundation for their application in various fields.

Ni-Mo Nanocatalysts on N-Doped Graphite Nanotubes for Highly Efficient Electrochemical Hydrogen Evolution in Acid.

Developing noble-metal-free catalysts for electrochemical hydrogen evolution reactions (HER) with superior stability in acid is of critical importance for large-scale, low-cost hydrogen production from water electrolysis. Herein, we report a highly efficient and stable noble-metal-free HER catalyst, which is composed of Ni and Mo2C nanocrystals supported on N-doped graphite nanotubes. This catalyst shows very low overpotential (65 mV in 0.5 M H2SO4 at a current density of 10 mA cm-2 with a Tafel plot of 67 mV/dec) and good stability for HER in acidic electrolyte, which is a promising noble-metal-free HER catalyst.

Nitrogen doped anatase-rutile heterostructured nanotubes for enhanced photocatalytic hydrogen production: Promising structure for sustainable fuel production

Nitrogen doped anatase-rutile heterostructure nanotubes were prepared by controlled ammonia annealing of TiO2 nanotubes synthesized by rapid break down anodization technique. The presence of anatase and rutile phases in a single nano-tube is confirmed by HRTEM. X-ray photoelectron spectroscopy confirmed the presence of oxygen vacancy and N-doping. The band gap studies revealed visible light absorption of the N-doped samples and Mott–Schottky analysis showed cathodic shift in flat band potential for the N doped samples indicating an increase in n-type conductivity. The photoelectrochemical studies revealed higher photocurrent and photon to current conversion efficiency for N-doped samples supporting the Mott Schottky results. The photo-catalysts were prepared by loading Pt on to the pristine and N-doped nanotubes by NaBH4 reduction. The synergistic role of non-stoichiometry and Pt loading towards photocatalytic activity is demonstrated from the H2 generation studies by water splitting. The enhanced photocatalytic performance of the Pt loaded N–TiO2 nanotubes is ascertained from the H2 generation rate of ∼30 mmol h−1 g−1, which is one of the highest observed rate under simulated solar radiation of 1.5 AM as well as visible light. The significance of surface area, mesoporous structure and visible light absorption in enhancing H2 generation is ascertained by BET and band gap studies. The present strategy of preparing high surface area Pt loaded N doped anatase-rutile TiO2 heterostructure nanotubes is a promising method for the synthesis of highly efficient composite photocatalysts for solar light harvesting.

Ab initio simulations on N and S co-doped titania nanotubes for photocatalytic applications

In this paper we present the results of quantum chemical modeling for energetically stable anatase (001) TiO2 nanotubes, undoped, doped, and codoped with N and S atoms. We calculate the electronic structure of one-dimensional (1D) nanotubes and zero-dimensional (0D) atomic fragments cut out from these nanotubes, employing hybrid density functional theory with a partial incorporation of an exact, nonlocal Hartree–Fock exchange within the formalism of the linear combination of atomic orbitals, as implemented in both CRYSTAL and NWChem total energy codes. Structural optimization of 1D nanotubes has been performed using CRYSTAL09 code, while the cut-out 0D fragments have been modelled using the NWChem code. The electronic properties of the studied systems prove that the band structure of the pristine TiO2 nanotube can be substantially modified by introducing substitutional impurity defects. The N-doped nanotube creates a midgap state that largely has a nitrogen character. The S-doped nanotube has a defect state that almost coincides with the top of the valence bond for the pristine material. For nanotubes codoped with both S and N, we observe a downward shift of the gap state of nitrogen relative to the purely N-doped state by about 0.3 eV. This results in a system with a filled gap state about 0.3 eV below the O2/H2O oxidation level, making it a very promising candidate for photocatalytic hydrogen generation under visible light, because due to the presence of sulfur, the bottom of the conduction band is only about 2.2 eV above the occupied midgap state, and also, clearly above the standard hydrogen electrode level.

Investigation on field emission properties of N-doped graphene-carbon nanotube composites

The aim of this paper is to improve the field emission properties of graphene-carbon nanotube composites by doping nitrogen atom. The electronic structure and field emission mechanism of the composite have been investigated by first principle methods. Compared to pristine graphene-carbon nanotube composite, work functions and ionization potentials with ten different doping positions decrease drastically as well as energy gap, which illustrates the enhancement of field emission properties. In this study, the most preferable doping position (doping position 2) can be inferred. Due to the doping of nitrogen atom, coupled electron states is generated, more electrons aggregate at the doping position. All results suggest that the field emission properties of graphene-carbon nanotube composite can be improved by doping nitrogen atom. The work we have done is significant for obtaining better electron sources with less energies, our investigation will provide a theoretical reference for the design and manufacture of new field emission devices.

Effect of graphene and Au@SiO2 core–shell nano-composite on photoelectrochemical performance of dye-sensitized solar cells based on N-doped titania nanotubes

We have investigated the role of graphene and Au@SiO2 core–shell nano-composite (NC), on the performance of dye-sensitized solar cells (DSSC) based on nitrogen doped TiO2 nanotubes (N-TNTs) as photoanodes.

Electronic properties of B- and N-doped graphyne nanotubes

Density functional theory calculations were utilized to study the electronic properties of B- and N-doped graphyne nanotubes. The armchair and zigzag nanotubes formed based on α-graphyne were considered. The electronic band structures and density of states were calculated. The results reveal that analogous to ordinary carbon nanotubes, graphyne nanotubes show a rich variety of metallic and semiconducting behavior depending on their chirality. Doping has a significant effect on the electronic properties of graphyne nanotubes. The graphyne nanotubes doped with B and N impurity become p- and n-type semiconductors, respectively.

Plasmonic silver nanoparticles matched with vertically aligned nitrogen-doped titanium dioxide nanotube arrays for enhanced photoelectrochemical activity

The plasmonic Ag nanoparticles match with vertically aligned N-doped TiO2 nanotube arrays, which display improving photoelectrochemical performance. N-doped anatase nanotube arrays are fabricated firstly, and then cubic Ag nanoparticles of diameter 5 nm are deposited on TiO2 nanotubes without organic additives at room temperature. X-ray photoelectron spectroscopy shows that the oxygen vacancies and N impurity are revealed in N-doped TiO2. The electrical properties of samples are investigated by systematic photoelectrochemical measurement. The charge transfer ability of TiO2, N-doped TiO2 and Ag/N-doped TiO2 is presented directly by Electrochemical impedance spectroscopy and Mott–Schottky measurement, respectively. The carrier density of Ag/N-doped TiO2 is higher 2 orders of magnitude enhancement of TiO2. Furthermore, its photocurrent responds rapidly with illumination owing to fast photoelectron transport. And photocurrent density is 0.14 mA cm−2 at 1.23 VRHE, which is the highest among samples. Finally, the mechanism of improving photoelectrochemical activity is schematically displayed. The plasmonic Ag/N-doped TiO2 composties are favorable for the separation for photoelectron-hole pairs and increasing electron transfer, leading to a considerably photoelectrochemical performance under sunlight. The modified nanotube arrays provide potential application in photoelectrochemical cell.

Effects of N doping on photoelectric properties of along different directions of ZnO bulk and nanotube

The electronic structures and optical properties of N-doped ZnO bulks and nanotubes are investigated using the first-principles density functional method. The calculated results show that the main optical parameters of ZnO bulks are isotropic (especially in the high frequency region), while ZnO nanotubes exhibit anisotropic optical properties. N doping results show that ZnO bulks and nanotubes present more obvious anisotropies in the low-frequency region. Thereinto, the optical parameters of N-doped ZnO bulks along the [100] direction are greater than those along the [001] direction, while for N-doped nanotubes, the variable quantities of optical parameters along the [100] direction are less than those along the [001] direction. In addition, refractive indexes, electrical conductivities, dielectric constants, and absorption coefficients of ZnO bulks and nanotubes each contain an obvious spectral band in the deep ultraviolet (UV) (100 nm ∼ 300 nm). For each of N-doped ZnO bulks and nanotubes, a spectral peak appears in the UV and visible light region, showing that N doping can broaden the application scope of the optical properties of ZnO.

“Brick-like” N-doped graphene/carbon nanotube structure forming three-dimensional films as high performance metal-free counter electrodes in dye-sensitized solar cells

The “brick-like” N-doped graphene-carbon nanotube (NGC) composites are designed by mechanically grinding the filtration films, which are fabricated to form a three-dimensional structure film as a counter electrode (CE). The N-doped graphene/carbon nanotube films with a three-dimensional “brick-like” structure can provide numerous vertical active edge sites. The excellent electrochemical catalytic activities of CE can be obtained by adjusting the different ratio of graphene to CNTs to control the size and N-doping content of breaking particles. NGC17 CE based dye-sensitized solar cells (DSSC) have reached a high efficiency (6.74%) close to platinum-based cells (6.89%). The excellent efficiency may be attributed to the following factors: a) the ΔEP of NGC17 (304 mV) is lower than that of the Pt electrode (389 mV); b) the charge transfer resistance (Rct) at the NGC17-CE/electrolyte interface was 1.78 Ω cm−2, which is lower than that of a Pt-CE/electrolyte interface (8.97 Ω cm−2).