Doped Nitrogen Atoms Research Articles

Electrochemical oxidation of sulfamethoxazole by nitrogen-doped carbon nanosheets composite PbO2 electrode: Kinetics and mechanism

In this study, nitrogen-doped carbon nanosheets (NCNSs) were prepared and successfully combined into the PbO2 electrode by the composite electrodeposition technology, thereby NCNS–PbO2 electrode was obtained. The electrochemical degradation of sulfamethoxazole (SMX) in aqueous solution by NCNS–PbO2 electrode was studied. The main influence factors on the degradation of SMX, such as the initial concentration of SMX, current density, electrolyte concentration and initial pH value, were analyzed in detail. Under the optimal process conditions, after 120 min of treatment, the removal ratio of SMX and chemical oxygen demand (COD) reached 99.8 % and 60.7 %, respectively. The results showed that the electrochemical degradation of SMX fitted pseudo-first-order reaction kinetics. The electrochemical performance of NCNS–PbO2 electrode was better than that of PbO2 electrode by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, as well as the use of cyclic voltammetry and electrochemical impedance spectroscopy for electrochemical performance testing. This was because the doping of nitrogen atoms improved the properties of carbon nanosheets. After the composite, the active sites on the surface of PbO2 were improved, the particle size of PbO2 was reduced, and the electrical conductivity and electrocatalytic activity of the electrode were improved. In addition, the intermediate products were determined by GC-MS method, and the possible degradation pathways of SMX were proposed.

Density functional theory study on concentration of intrinsic point defects in growing N-doped Czochralski Si crystal

In silicon (Si) crystal growth done using the Czochralski method, doping of nitrogen (N) atoms at a concentration of about 1014 atoms/cm3 reduces the size of void defects. Therefore, N-doping technology is commonly used to improve the quality of Si wafers. However, the mechanism behind the effect of N-doping on intrinsic point defects (vacancy V and self-interstitial Si I) during Si crystal growth remains unclear. Specifically, it is confusing that N-doping increases the total concentration of V to about 10% and yet also reduces the size of void defects. In this study, a density functional theory (DFT) study was performed to investigate the effect of N-doping on the concentration of V and I in Si crystal. We performed DFT calculations of the formation energy and formation (vibration) entropy of interstitial N (Nint) atoms, substitutional N (Nsub) atoms, Nint-Nint pairs, and V and I in the area influenced by the N atom in supercells composed of 64 and 216Si atoms, and we then obtained the concentration of point defects incorporated at the melt/solid interface on the basis of the results. Our main findings are as follows. (1) Nint atoms at the [161] dumbbell (D)-site were the most dominant at the melt/solid interface when the N concentration was less than about 3 × 1014/cm3. (2) The N impact on the V concentration was larger than that on the I concentration and became apparent when the N concentration was higher than about 5 × 1013/cm3. (3) The experimental finding of the N impact on the concentration of intrinsic point defects is explained quantitatively.

Effects of nitrogen-doping structural changes of spherical hollow graphene on the growth of MoS2+x nanosheets and the enhanced hydrogen evolution reaction

MoS2, a two-dimensional (2D) layered structural transition metal dichalcogenide (TMDs), has been widely investigated towards hydrogen evolution reaction (HER) in previous few years. Except for the inert basal plane sites of the MoS2 itself, its inherent low conductivity also hinders the electron transfer process, which adversely affects its efficiency towards HER. Therefore, how to expose more edge active sites and at the same time improve the conductivity of MoS2, either intrinsically or with the help of high conductive substrates, is a key means to improve the HER performance of MoS2. Herein, the polystyrene (PS) nanospheres are used not only as an intercalation agent of graphene carbon sheets, but also as a spherical template for the preparation of 3D spherical hollow graphene. Different nitrogen precursors and nitrogen doping methods are used to prepare the 3D spherical hollow graphene substrate materials with different nitrogen-doping structures, such as amine N, pyrrolic N, pyridinic N or quaternary N. The investigation results show that the structure of doped nitrogen atom has a great influence on the loading of molybdenum disulfide. Among them, amine N was the most favorable for the loading of molybdenum disulfide, followed by pyrrole N, quaternary N and pyridine N. Moreover, the structure of doped N active sites synthesized by different preparation methods can also affect the uniform distribution of molybdenum disulfide on 3D spherical hollow graphene and the corresponding HER performance. The results show that, using ammonia as nitrogen source and PS microspheres as template, the prepared molybdenum disulfide loaded 3D spherical hollow graphene electrode material has the best HER performance, which should be attributed to the uniform distribution of the molybdenum disulfide and its close combination with the substrate, as well as the 3D spherical hollow structure. Moreover, the amorphous structure of molybdenum disulfide formed in the hydrothermal process can also improve the activity of HER.

Effect of target power on microstructure, tribological properties of the graphite-like carbon based nanocomposite coating

The graphite-like carbon (GLC) based nanocomposite coating have attracted great attention in tribology, however, its high-temperature tribological behavior is not well investigated. In this study, the GLC-based nanocomposite coatings with different target power by direct current magnetron sputtering were fabricated, and the influence of target power on microstructure, tribological property of these coatings was investigated. The results indicates that these coatings show the graphite-like carbon (with doped nitrogen atom)/amorphous-(Si3N4, TiO2, Ti2O3)/nanocrystalline-TiC structure. With the target power increasing, the content of TiC nanocrstallines fluctuates, yet the carbon content basically is unchanged. The hardness and wear resistance are related to the ratio of nanocrystallines to amorphous phase. The maximum hardness of as-deposited coatings is about 18 GPa. The minimum COF (coefficient of friction) of coatings sliding against Al2O3 was 0.22, and the lowest wear rate is 3.2 × 10−5 mm3/(N·m). At elevated temperature, due to the cracks and the transformation in graphite-like carbon from the sp2 bond carbon clusters (sp2-C) to sp3 bond carbon clusters (sp3-C), the load-bearing capacity becomes worse, and the carbon clusters deteriorate with increasing temperature, resulting in higher COF and wear rate.

Capacitive deionization of carbon spheres with a carbon shell derived from the quantum dots of urea-citric acid grown in situ

Limited by the cost of electrode materials with a pore structure designed, there is an urgent need to prepare a low-cost carbon material with a strong salt absorption capacity (SAC) for capacitive deionization (CDI) to produce fresh water at an affordable price. The preparation of core-shell porous carbon spheres (CSs) derived from the melamine-formaldehyde (MF) spheres with a urea-citric acid quantum dot (UCQD) layer grown in situ has been reported here. Benefiting from their large specific surface area (2667.44 m2·g−1) and the uniformly doped nitrogen atoms (1.03 at.%), the prepared CSs have abundant active sites for ion absorption. Their SAC reaches up to 19.80 mg·g−1 in the NaCl solution of 1000 mg·L−1 with a working voltage of 1.2 V. Moreover, no SAC attenuation occurs after 17 cycles. This work provides a possible way to prepare low-cost core-shell CSs for CDI.

Electronic structure of nitrogen-doped carbon nanotubes under stress

Due to the demand for miniaturization and low energy consumption of electronic device, field-effect transistors based on carbon nanotubes have received extensive attention. However, the electronic properties of carbon nanotubes, especially when subjected to stress and doping, are not very clear. In this study, first-principles calculations are used to investigate the deformation of carbon nanotubes under the action of nitrogen doping and tensile stress, as well as the changes in electronic energy bands. The results show that nitrogen atom doping will reduce the tensile strength of carbon nanotubes and increase the conductivity of carbon nanotubes, while stress helps to open the band gap. Our research has guiding significance for the prediction of electronic properties of carbon nanotubes under doping and stress.

Fabricating high-loading Fe-N4 single-atom catalysts for oxygen reduction reaction by carbon-assisted pyrolysis of metal complexes

Iron-based single-atom catalysts with nitrogen-doped carbon as support (Fe-SA/NPC) are considered effective alternatives to replace Pt-group metals for scalable application in fuel cells. However, synthesizing high-loading Fe-SA catalysts by a simple procedure remains challenging. Herein, we report a high-loading (7.5 wt%) Fe-SA/NPC catalyst prepared by carbon-assisted pyrolysis of metal complexes. Both the nitrogen-doped porous carbon (NPC) support with high specific surface area and ο-phenylenediamine (o-PD) play key roles role in the preparation of high-loading Fe-SA/NPC catalysts. The results of X-ray photoelectron spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, and X-ray absorption fine structure spectroscopy experiments show that the Fe atoms are anchored on the carbon carriers in a single-atom site configuration and coordinated with four of the doped nitrogen atoms of the carbon substrates (Fe-N4). The activities of the Fe-SA/NPC catalysts in the oxygen reduction reaction increased with increasing iron loading. The optimized 250Fe-SA/NPC-800 catalyst exhibited an onset potential 0.97 V of and a half-wave potential of 0.85 V. Our study provides a simple approach for the large-scale synthesis of high-loading single-atom catalysts.

A DFT study of graphene-FeNx (x = 4, 3, 2, 1) catalysts for acetylene hydrochlorination

In this paper, we used density functional theory (DFT) to systematically study the mechanism and activity of a graphene-FeNx (x = 4, 3, 2, 1) series of non-noble metal catalysts for acetylene hydrochlorination at the B3LYP/6–31 G** level, and the LANL2DZ effective core pseudo-potentials basis set was applied to Fe atom. Dispersion-corrected DFT-D3 was considered in the calculation. In the process of the graphene-FeNx catalytic reaction, all the catalysts adsorbed acetylene first and adsorbed hydrogen chloride later to form a co-adsorption structure. The calculation results displayed that with a decrease in doped nitrogen atoms in the catalyst, the activity of the reaction decreased successively. Graphene-FeN4 showed excellent catalytic performance, and its energy barrier was only 16.80 kcal/mol. Accordingly, it is a latent non-noble metal catalyst for hydrochlorination of acetylene.

Effect of plasma nitriding temperature on microstructure and wear properties of electroless nickel-boron coatings

This study investigates the effects of plasma nitriding (PN) temperature on the microstructural properties and wear behavior of electroless nickel‑boron (ENB) coatings. To this end, the ENB coatings are deposited on the mild steel substrates and submitted to PN treatment at 350, 400, and 450 °C. The Morphology, roughness, microstructure, microhardness and wear resistance of the coatings are evaluated and compared to the conventional heat-treated ENB coatings. The results indicate that a crystalline structure has appeared in the as-deposited amorphous ENB coatings through PN treatment, leading to enhancement of their hardness. The highest hardness value (1406 HV0.1) and consequently the highest wear resistance are obtained for the PN-treated ENB coating at 350 °C. These results could be assigned to the grain growth suppression achieved by doping nitrogen atoms into the coating through PN treatment. Moreover, the precipitation of the lubricant h-BN phase during PN treatment of the ENB coatings has decreases the coefficient of friction in the sliding wear test.

Temperature-dependent synthesis of MOF-derived Co@N-doped carbon nanotube nanocomposites toward accelerated reduction of 4-nitrophenol

Designing advanced catalysts with atomic level control over the heterointerfaces and active sites is of great importance for the boosted catalytic reduction reactions. Here, we show that Co nanoparticle-wrapped by N-doped carbon nanotube heterostructures synthesized by the temperature-dependent pyrolysis of zeolitic imidazolate framework-67 (ZIF-67) precursors have relatively higher catalytic activity toward the reduction of 4-nitrophenol. The well-constructed Co@N-doped carbon nanotube hybrid catalyst calcined at 435 °C exhibited catalytic reduction activity superior to those of nanocomposites calcined at other temperatures. The enhanced reduction of 4-nitrophenol performance may be attributed to strong synergistic interactions between well-defined Co nanoparticles and in-situ formed N-doped carbon nanotubes. It is proposed that N-doped carbon nanotubes not only act as the support for Co nanoparticles, but also provide protection for Co nanoparticles from aggregation and oxidation. Furthermore, N-doped carbon nanotubes can enhance the surface adsorption between the components to facilitate electron transfer due to the presence of doped nitrogen atoms. The catalyst also showed high stability with small losses in catalytic activity in recycled experiments, indicating great potential to be cost-effective non-precious metal-based catalysts for scalable and high-performance catalytic reduction reactions.

γ-Graphyne rectifier and NDR tunable by doping, line edge roughness and twist

The armchair γ-graphyne nanoribbon (A-γ-GyNR) based on doping boron and nitrogen atoms in left and right leads, respectively, was proposed as the initial sample of a rectifier device. Afterwards, the next five devices were presented by applying line edge roughness (LER) defect, increasing its roughness, doping concentration, and its position and twisting under six different angles to the center of the initial model. Also, the effect of width was investigated. The computational method for investigating the electronic transfer properties was a combination of the non-equilibrium Green’s function (NEGF) and the tight binding method. The current curve and transmission spectrum revealed the negative differential resistance (NDR) behavior, which underwent the most changes under the influence of LER. Density of state (DOS) peaks indicated that p-orbital had a more significant effect on transmission in all devices; on the other hand, the localization of molecular projected self-consistent Hamiltonian (MPSH) structure in positive biases resulted from the suppression of electron tunneling. Based on the findings, the maximum rectification ratio in the M″3 device, twisted by an angle of 75°, was equal to 5.86 × 108, which was 41.2 times higher than that of the initial sample; the highest NDR value of the M′1 device was 56.

Regulating the Bonding Nature and Location of C–F Bonds in Fluorinated Graphene by Doping Nitrogen Atoms

Chemical regulation of fluorinated graphene (FG) is of great importance for promoting its practical application but is still challenging due to the complexity of its chemical structure. Here, we demonstrate that the introduction of nitrogen (N) into graphene sheets is a feasible method to regulate the bonding nature and location of C–F bonds in the corresponding FG product. The fluorination reactivity of graphene materials is improved by doping N atoms into graphene sheets, which can even be increased by 2.7 times. Under the same F/C ratio, more covalent C–F bonds existed in fluorinated N-doped graphene than in fluorinated reduced graphene without doped N atoms. Results of DFT calculations, polarized ATR-FTIR, and WAXD confirmed that doped N atoms could significantly enhance the fluorination reactivity of their surrounding C atoms and thus localized C–F bonds around them. The local enrichment of C–F bonds certainly improved the covalent bonding nature; even the F/C ratio is not high enough. Meanwhile, this work provides a method for preparing N, F bifunctional graphene in large quantities, and an ultrahigh-bifunctional graphene with N/C ratio of 0.24 and F/C ratio of 0.56 has been obtained here, which has potential contributions to the industrialization of the preparation of ultrahigh-functional graphene.

In situ electrochemical Raman investigation of charge storage in rGO and N-doped rGO.

In this study, in situ electrochemical Raman spectroscopy was applied to clarify the charge storage mechanism in three types of anodes, synthetic graphite, reduced graphene oxide (rGO), and nitrogen-doped reduced graphene oxide (N-rGO). The Li+ intercalation phenomenon was measured in LiPF6 electrolyte solution using a modified coin cell setup. The synthetic graphite anode showed the splitting of the G peak at the potential E < 0.2 V vs. Li/Li+, corresponding to the formation of a graphite intercalation compound (GIC) and its second-order 2D peak was found to be red-shifted due to charge transfer and induced strain in the potential region of 0.5 to 0.15 V vs. Li/Li+. In the case of rGO, the lattice defects assisted in large and early intercalation of electrolyte ions, which is confirmed by the red-shift in the G peak (∼36 cm-1) and its early disappearance below 0.3 V vs. Li/Li+, respectively. Unlike rGO, nitrogen vacancies in N-rGO provide active sites for Li+ intercalation, resulting in enhanced charge transfer, displayed by the large red-shift in the G peak (∼55 cm-1) and blue-shift in the D peak. In addition, a new Raman peak at 1850 cm-1 was observed in N-rGO for the first time, corresponding to the formation of a reversible intermediate species from the interaction between Li+ and nitrogen vacancies. This work demonstrates the use of a simple in situ technique to get insight into the nano-carbon electrodes during device operation and to reveal the role of doped nitrogen atoms for Li+ intercalation.

Bamboo-like nitrogen-doped carbon nanotubes on iron mesh for electrochemically-assisted catalytic oxidation

In this study, bamboo-like nitrogen-doped carbon nanotubes (BN-CNTs) are successfully deposited on etched iron mesh (d-Fe) using chemical vapor deposition (CVD) method with acetonitrile as precursor. The acidic etching process is necessary for the special BN-CNTs structure formation by exposing more Fe0 sites. The BN-CNTs/d-Fe is then evaluated for the electrochemically-assisted PMS activation to degrade phenol. Under cyclic voltammetry (CV, 0–1 V vs. RHE) assistant, 20 ppm phenol can be degraded in 30 min with a rate constant of 0.2837 min−1, ~78 times more than that without CV. Some Fe3+ species in the catalyst will be reduced at the initial stage, a two-step pseudo-first-order kinetic is thus used for the degradation curves fitting. Both the structure defects and doped nitrogen atoms are responsible for the high catalytic activity of BN-CNTs. According to the quenching tests, both radical and non-radical processes are present for PMS activation, thus obtaining enhanced organics removal efficiency. The electrochemically assistant could enhance the PMS adsorption on the electrode as well as electrons transfer between Fen+ and PMS, thus increasing the PMS activation efficiency. The utilization of earth-abundant Fe mesh for the fabricating free-standing electrodes provide a potential low-cost and effective strategy of waste water remediation.

Sulfur encapsulated in nitrogen-doped graphene aerogel as a cathode material for high performance lithium-sulfur batteries

Lithium-sulfur batteries are considered to be an ideal high-performance rechargeable lithium battery. However, some problems have seriously hindered the practical application of lithium-sulfur batteries. A simple one-step hydrothermal method has been applied to design nitrogen-doped graphene aerogel (N-GA) with three different nitrogen sources. Subsequently, sulfur was encapsulated in N-GA by chemical deposition method to synthesize sulfur encapsulated in N-GA (N-GA/S) composites. Among them, the N-GA1/S composite with sulfur content reaching 75.5 wt% has a discharge specific capacity of 723.9 mAh g−1 after 100 cycles at 0.7 C, and the capacity retention rate is up to 87.4% while the coulombic efficiency still remains 98%. The outstanding electrochemical performance is owing to the good coating of sulfur by nitrogen-doped graphene aerogel, the improvement of the conductivity of the graphene skeleton by nitrogen doping, and the strong adsorption capacity of the doped nitrogen atom to lithium polysulfide. The graphene skeleton also helps to reduce the volume effect while charging and discharging. Furthermore, the proportion of pyridinic-N in N-GA1/S composites is higher than that in the two other composites, and it has a better adsorption capacity for lithium polysulfide.

MOFs Reinforce CNTs Sponge Derived Functional Carbon Network As Sulfur Host for Lithium Sulfur Battery

Lithium sulfur battery is one of the most prospective alternatives for lithium ion battery. It possesses high theoretical capacity of 1672 mAh/g and high theoretical gravimetric energy density of a Li-S cell is approximately 2,510 Wh/kg, which is about eight folds compare to transition metal oxide [1]. The mechanism of lithium sulfur battery is based on the conversion reaction of sulfur to lithium sulfide (Li2S) which create high capacity. The transfer of two electrons per sulfur atom is more preferred than one or less than one electron per transition-metal ion [2]. However, tremendous challenges such as natural insulator characteristic of sulfur and lithium sulfide, dissolution of mediators into electrolyte, significant volume change during cycling and lithium metal anode corrosion have hindered the commercialization in industry [3].To overcome these drawbacks, the design of the sulfur cathode material plays an important role in boosting sulfur electrochemistry and accelerating the battery performance. In the past few years, metal–organic frameworks (MOFs) which consist of metal ions and organic moiety as linker have been used as novel sulfur host materials in lithium sulfur batteries [4]. Particularly, MOFs are prospective as both a precursor and derived materials. The porous carbon materials created from MOFs shows a uniform porosity due to its highly ordered crystalline structures [5]. Besides the confining sulfur within the porous carbon materials, the functional materials have been recently employed to supply both a strong interaction surface with lithium polysulfides and to provide electron transport for enhancing the redox reaction [6]. Moreover, the polysulfide shuttle effect could be manipulated by electrocatalysis [7]. Recent researches found that the atomic cobalt dopants can serve as active sites to improve the kinetics of the sulfur redox reactions. It is therefore pivotal to design an effective electrode that not only improve the electrochemical processes of sulfur but also could efficiently suppress the intermediate polysulfide shuttle effect [8].In this study, we designed a novel sulfur film coated on the three-dimensional nitrogen and cobalt co-doped carbon polyhedral wrapped on multi-walled carbon nanotubes sponge composite as a high-performance cathode material for rechargeable lithium-sulfur batteries. CNTs is employed to supply an interconnected conductive carbon network. Along with the abundant uniform micropores that provided by carbon derived from ZIF 67, sponge-like structure provides abundant mesopores that create favorable pathway for the electrolyte permeability and lithium ion diffusion. The doping of nitrogen and cobalt atom leads to improve electrical conductivity and enhance the surface polarity of the composite. Moreover, the strong interaction between cobalt and lithium polysulfides leads to efficiently suppress the shuttle effect. Figure 1 presents the photo of sponge-like composite and SEM image of composite after sulfur infiltration. We will report in detail about the latest results achieved on as cathode material for lithium-sulfur batteries.

Iron catalysts supported on nitrogen functionalized carbon for improved CO2 hydrogenation performance

Preparation of highly efficient Fe-based catalysts is a reliable and achievable goal for catalyzing CO2 hydrogenation. Herein, ethylene diamine as a benign modifier well regulates the surface properties of carbon support, achieving a good dispersion of active small-size iron carbide sites. With the further incorporation of alkaline K promoter, heavy hydrocarbon selectivity (C5+) is increased from 14.8% to 39.8%. Combining several catalyst characterization (XRD, CO2-TPD, H2-TPR, TEM, and XPS) and reaction data, discloses that good dispersion, enhanced reduction/carburization behavior, and small-size carbides formation are essential for improving CO2 performance. Simultaneous doping of nitrogen atoms and alkali metal provides a promising means for CO2 fixation and rational design of functionalized metal-supported carbon catalysts.

Li adsorption on nitrogen-substituted graphyne for hydrogen storage

The adsorptions of hydrogen on Li-decorated nitrogen-substituted graphyne are investigated by density functional theory. The substitutional doping of nitrogen atoms can change the electronic structure of graphyne, which is beneficial to the adsorption of Li atoms. The results show that isolate Li atom is preferred to locate hollow site above the center of the acetylenic ring with binding energies more than 3.10 eV. A maximum of three hydrogen molecules can bind to Li atom decorated graphyne on one side. The average binding energy per H2 molecule for Li-decorated nitrogen-substituted graphyne is higher than that of pure graphyne.

Electronic transport induced by doping on the electrodes in molecular devices

The electronic transport properties of molecular device based on photochromic diarylethene with carbon nanotube electrode are investigated by density functional theory and non-equilibrium Green’s function. The devices with open and closed configurations show a switching effect. It is found that doping of different amounts of nitrogen atoms on left electrodes results in different electronic transport properties. In addition, we discuss the observed oscillation of current in the devices induced by doping using transmission eigenstates and transmission spectra of the device. The local density of states of the device is calculated to analyze the observed rectifying behavior. The results suggest that doping of nitrogen atoms on the left electrode can be considered as a factor to modulate the electronic transport properties of molecular device.

Atomic-Level Electronic Properties of Carbon Nitride Monolayers.

Heteroatom-doped carbon-based materials are of significance for clean energy conversion and storage because of their fascinating electronic properties, low cost, high durability, and environmental friendliness. Atomically precise fabrication of carbon-based materials with well-defined heteroatom-dopant positions and atomic-scale understanding of their atomic-level electronic properties is a challenge. Herein, we demonstrate the bottom-up on-surface synthesis of 1D and 2D monolayer carbon nitride nanostructures with precise control of the nitrogen-atom doping sites and pore sizes. We also observe an electronic band offset at the C-N heterojunction. Using high-resolution scanning tunneling microscopy, the atomic structure of the as-prepared carbon nitride nanoporous monolayers are revealed, indicating successful and precise control of the structures and N atom doping sites. Furthermore, corroborated by theoretical calculations, scanning tunneling spectroscopy measurements reveal a valence band shift of 140 meV that results in an electric field of 2.9 × 108 V m-1 at the C-N heterojunction, indicating efficient separation of the electron-hole pair at the N doping site. Our finding offers direct atomic-level insights into the local electronic structure of the heteroatom-doped carbon-based materials.