Doped Nitrogen Atoms Research Articles

3D nitrogen-doped hierarchical porous carbon framework for protecting sulfur cathode in lithium–sulfur batteries

A three-dimensional carbon substrate integrating a hierarchical porous network structure with rich nitrogen atom doping is designed for lithium–sulfur batteries.

Tiny nano-scale junction built on B/N doped single carbon nanotube

The characteristic sizes of carbon nanotube (CNT)-based devices are constantly being reduced. However, this continuing miniaturization is still facing many problems and requires innovative ideas and structures. By regular doping of boron and nitrogen atoms in a semiconducting single-wall carbon nanotube (SWCNT), we have constructed a nano-scale junction with rectifying characteristics. The I–V curve of our junction resembles the I–V curve of an ideal diode with a p-n junction. This junction channel is about 0.6 nm wide and 3.4 nm long, and the footprint is 5.1 nm long. Under a 0.5 V bias, the junction has a leakage current of −8.8 × 10−3 μA, a rectifying ratio Ion/Ioff of 0.716 × 103, and a current density of 10.52 mA μm−1. Our study also shows how different dopant distributions influence the I–V curve. Such a regular nano-scale doping method is effective and important, compared with the traditional random doping method.

Doping-induced giant rectification and negative differential conductance (NDC) behaviors in zigzag graphene nano-ribbon junction

By p-type and n-type doping on the electrode edges of V-notched zigzag graphene nano-ribbons (ZGNRs), four V-notched ZGNR-based PN-junctions are designed theoretically. The electronic transport properties of the doped and un-doped V-notched ZGNRs are studied applying non-equilibrium Green's function method combined with the density functional theory. The numerical results show that, the doped systems are less conductive than the un-doped system, because after doping the transition states become localized. To our surprise, the ZGNR-based PN-junctions do not show obvious rectification by purely doping the boron atoms and nitrogen atoms on the edges of two ZGNR electrodes respectively. However, after hydrogenated the doped boron atoms and nitrogen atoms, the ZGNR systems present giant rectifications with the maximum rectification ratios up to 106∼107, which attributed to the vanishing of overlap between left-electrode sub-band and right-electrode sub-band in the negative bias regime after the doped boron and nitrogen atoms being hydrogenated. Due to the same reason, the hydrogenated doping systems also show large negative differential conductance behaviors.

Chemical bonds in nitrogen-doped amorphous InGaZnO thin film transistors

Abstract We investigated the chemical bonds in nitrogen-doped amorphous InGaZnO (a-IGZO:N) thin films with an X-ray photoelectron spectrometer (XPS). The doped nitrogen atoms preferentially combined with Ga cations and formed stable Ga N bonds for low nitrogen-doping (N-doping), but additionally formed less stable In N and Zn N bonds for high N-doping. The stable Ga N bonds and few defects made the variation in oxygen vacancy (VO) more difficult and hence achieved better stability of thin film transistors (TFTs) with low doped a-IGZO:N channel layers. Contrarily, the less stable In N and Zn N bonds as well as excess defects led to an easier change in VO and thus more unstable a-IGZO:N TFTs for high N-doping.

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.

Fiber network composed of interconnected yolk-shell carbon nanospheres for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are a promising candidate for next-generation energy storage devices. However, rapid performance decay at high-sulfur-loading condition is emerged as one of the main obstacles restricting the practical application of Li-S batteries. Here we develop a facile electrospinning method for synthesizing the interconnected yolk-shell carbon nanospheres assembled fiber network to construct self-supporting sulfur cathodes. Benefiting from high surface area, nitrogen atom doping, and synergetic effect between yolk and shell, the yolk-shell carbon fiber network is a promising sulfur hosting material for high-sulfur-loading Li-S batteries. With 70 wt% and 4 mg cm−2 of sulfur, the yolk-shell carbon fiber network derived self-supporting cathode exhibits a high capacity retention of 82.8% after 500 cycles at 1 C. In addition, the self-supporting cathode with 16 mg cm−2 of sulfur delivers a stable areal capacity of 15.5 mAh cm−2. This work provides a new strategy for the development of high-performance Li-S batteries.

Janus N-Doped Carbon@Silica Hollow Spheres as Multifunctional Amphiphilic Nanoreactors for Base-Free Aerobic Oxidation of Alcohols in Water

The hydrophobicity/hydrophilicity of nanocatalysts has a significant impact on their performances via modulating the adsorption, transfer, and desorption of reactants/products. In this work, we reported a novel multifunctional amphiphilic nanoreactor composed of Janus nitrogen-doped carbon@silica hollow nanostructure and ultrasmall Pt nanoparticles. The core/shell polybenzoxazine@mesosilica spheres were used as the precursor for pyrolysis. It was found that the internal polybenzoxazine was decomposed from interior to exterior and transformed into a nitrogen-doped carbon hollow shell that partly embedded into the mesosilica layer, forming the Janus hollow spheres. The obtained nanoreactor showed remarkable activity and selectivity for base-free aerobic oxidation of alcohols in water using air as the oxidant. A one-pot oxidation-condensation cascade reaction was also successfully demonstrated to synthesize imines from alcohols and amines with good yields. The sorption analyses revealed that the superior hydrophilicity/hydrophobicity strengthened both adsorption of hydrophobic alcohols from water and desorption of byproduct water molecules from the active sites. The doped nitrogen atoms in the carbon matrix were used not only as anchoring sites for stabilizing ultrasmall Pt nanoparticles but also as basic active sites for accelerating the deprotonation process. Moreover, due to the anchoring effect of nitrogen and the extremely stable amphiphilicity, this nanoreactor exhibited excellent catalytic stability.

Work function variation of monolayer MoS2 by nitrogen-doping

Monolayer MoS2 films with substantial sulfur vacancies are obtained using the laser molecular beam epitaxy (L-MBE) technique benefitted by high substrate temperature and ultrahigh vacuum growth conditions. The intrinsic sulfur vacancies present an excellent opportunity for varying the work function of monolayer MoS2 films by nitrogen doping. The in-plane doping of nitrogen atoms on L-MBE-synthesized monolayer MoS2 films is realized on the basis of rapid thermal annealing in a nitrogen environment. The as-grown and nitrogen-doped monolayer MoS2 films are evaluated by using Raman and photoluminescence spectroscopies. In accordance with the X-ray photoelectron spectroscopy results, the ultraviolet photoelectron spectroscopy investigation shows that the work function of the monolayer MoS2 films increases by 0.29 eV after covalent nitrogen doping. Nitrogen doping on monolayer MoS2 is further treated theoretically using first-principles calculations. Based on theoretical calculations and experimental validations, it is illustrated that nitrogen is a promising in-plane heteroatom dopant for work function variation of monolayer MoS2.

Triazine-graphdiyne: A new nitrogen-carbonous material and its application as an advanced rechargeable battery anode

Existing methodological strategies for the doping of nitrogen (N) atoms in carbon materials usually contain more than one species with indefinite N content, which made it difficult to study the role of each type of N atoms played duing the doping and severely restrict the wide application. Herein, we reported a developed synthetic strategy for preparing carbonous materials contained with specific N atoms. The well-defined carbonous network triazine-graphdiyne (TA-GDY), which comprising merely one type of N atoms with fixed amount, has been prepared through bottom-up way with triethynyltriazine as the starting molecule. TA-GDY is an unique two-dimensional (2D) carbonous material, including sp- and sp2-hybridized carbon atoms, as well as quantitative pyridine-like sp2-hybridized N atoms. All the N atoms are placed on the plane of the carbon skeleton, and the high N content provides plenty of active heteroatom sites decorated uniformly in the hexagonal honeycomb-like pores. Based on theoretical prediction, the wide interlayer spacing and large amount of pyridinic-N as well as uniform honeycomb-like pores are favorable for Li-ion storage and diffusion. As expected, the TA-GDY-based electrodes exhibit outstanding Li-ion storage performance, such as superior rate capability, larger capacity, and excellent stability.

In Situ High-Level Nitrogen Doping into Carbon Nanospheres and Boosting of Capacitive Charge Storage in Both Anode and Cathode for a High-Energy 4.5 V Full-Carbon Lithium-Ion Capacitor.

To circumvent the imbalances of electrochemical kinetics and capacity between Li+ storage anodes and capacitive cathodes for lithium-ion capacitors (LICs), we herein demonstrate an efficient solution by boosting the capacitive charge-storage contributions of carbon electrodes to construct a high-performance LIC. Such a strategy is achieved by the in situ and high-level doping of nitrogen atoms into carbon nanospheres (ANCS), which increases the carbon defects and active sites, inducing more rapidly capacitive charge-storage contributions for both Li+ storage anodes and PF6- storage cathodes. High-level nitrogen-doping-induced capacitive enhancement is successfully evidenced by the construction of a symmetric supercapacitor using commercial organic electrolytes. Coupling a pre-lithiated ANCS anode with a fresh ANCS cathode enables a full-carbon LIC with a high operating voltage of 4.5 V and high energy and power densities thereof. The assembled LIC device delivers high energy densities of 206.7 and 115.4 Wh kg-1 at power densities of 0.225 and 22.5 kW kg-1, respectively, as well as an unprecedented high-power cycling stability with only 0.0013% capacitance decay per cycle within 10 000 cycles at a high power output of 9 kW kg-1.

Nitrogen-doped carbon aerogels with high surface area for supercapacitors and gas adsorption

Doping of nitrogen atoms has been considered to be a common strategy for improving the performance of carbon aerogels. In this work, two kinds of nitrogen-doped carbon aerogels with high porosity (NCA-800 and NCA-900) are prepared through polymerization of pyrrole and formaldehyde monomers under a hypersaline condition and subsequent carbonization at different temperatures (800 and 900 °C). In the whole preparation process, zinc chloride is not only used to provide a hypersaline environment for the polymerization of pyrrole and formaldehyde, but also applied as a catalyst and an activating agent. The as-prepared aerogels possess high specific surface area values (1450 m2 g–1 for NCA-800 and 1670 m2 g–1 for NCA-900) and moderate nitrogen contents (10.86 atom% for NCA-800 and 4.09 atom% for NCA-900). As gas adsorbents, they show high uptake capacities for carbon dioxide (∼16 wt%) at 273 K under 1.0 bar on the basis of high porosity and nitrogen contents. When applied as electrodes for supercapacitors, the as-prepared aerogels exhibit good electrochemical performances.

N-doped carbon nanotubes-reinforced hollow fiber solid-phase microextraction coupled with high performance liquid chromatography for the determination of phytohormones in tomatoes

A N-doped carbon nanotubes-reinforced hollow fiber solid-phase microextraction (N-doped CNTs-HF-SPME) method was developed for determination of two naphthalene-derived phytohormones, 1-naphthalene acetic acid (NAA) and 2-naphthoxyacetic acid (2-NOA), at trace levels in tomatoes. N-doped CNTs were dispersed in ultrapure water with the assistance of surfactant, and then immobilized into the pores of hollow fiber by capillary forces and sonification. The resultant N-doped CNTs-HF was wetted with 1-octanol, subsequently immersed into the tomato samples to extract the target analytes under a magnetic stirring, and then desorbed with methanol by sonication prior to chromatographic analysis. Compared with CNTs, the surface hydrophilicity of N-doped CNTs was improved owing to the doping of nitrogen atoms, and a uniform dispersion was formed, thus greatly simplifying the preparation process and reducing waste of materials. In addition, N-doped CNTs-HF exhibits a more effective extraction performance for NAA and 2-NOA on account of the introduction of Lewis-basic nitrogen. It is worth to mention that owing to the clean-up function of HF, there are not any complicated sample pretreatment procedures prior to the microextraction. To achieve the highest extraction efficiency, important microextraction parameters including the length and the concentration level of N-doped CNTs in surfactant solution, extraction time, desorption conditions such as the type and volume of solvents, pH value, stirring rate and volume of the donor phase were thoroughly investigated and optimized. Under the optimal conditions, the method showed 165- and 123-fold enrichment factors of NAA and 2-NOA, good inter-fiber repeatability and batch-to-batch reproducibility, good linearity with correlation coefficients higher than 0.9990, low limits of detection and quantification (at ng g−1 levels), and satisfactory recoveries in the range of 83.10–108.32% at three spiked levels. The proposed method taking advantages of both excellent adsorption performance of N-doped CNTs and the clean-up function of HF, was a simple, green, efficient and cost-effective enrichment procedure for the determination of trace NAA and 2-NOA in tomatoes.

Highly Efficient Catalytic Oxidation of Inert C(sp3)–H Bonds by the Synergistic Effect of Copper Nanoparticles/N‐Doped Graphene

The applicability of Cu is still limited in the heterogeneous catalytic oxidation of C(sp3)–H bonds. This problem was resolved by exploiting the synergistic effect existing between Cu nanoparticles (Cu NPs) and N‐doped graphene. We demonstrate a highly efficient, green protocol for the catalytic oxidation of inert C(sp3)–H bonds with only oxygen as the oxidant catalyzed by Cu NPs/N‐doped graphene (Cu‐N‐rGO). The new composite materials were obtained through a very simple one‐pot solvothermal process. Remarkably, newly prepared Cu‐N‐rGO showed 34.5 % conversion and 89.2 % selectivity for the catalytic oxidation of cyclohexane to KA oil [mixture of cyclohexanone (K) and cyclohexanol (A)] in a single cycle and thus exhibited significantly higher efficiency than the N‐free Cu catalysts. Cu‐N‐rGO has good stability because the doped nitrogen atoms allow strong interactions between the Cu species and graphene, so that the conversion and selectivity can be maintained over five runs. The delicate relationship between the Cu NPs and nitrogen was investigated by accurate control of the ratio of nitrogen and Cu in doped graphene. A hypothesized free‐radical chain mechanism and a peroxidative oxidation process were proven and explained, and the synergistic effect of the Cu NPs and N‐doped graphene in facilitating the oxidation process was also elucidated.

Nitrogen doped yolk-shell carbon spheres as cathode host for lithium-sulfur battery

Suppressing the shuttle effect while maintaining high sulfur content is the primary challenge for the development of lithium-sulfur (Li-S) batteries. An effective encapsulator for Li-S battery is supposed to have enough void space for sulfur accommodation and alleviation of volume expansion. Moreover, an excellent electronic conductivity is also crucial for high sulfur utilization. Thus, we designed mesoporous nitrogen doped yolk-shell carbon (NYSC) spheres as novel sulfur encapsulators. This unique structure design greatly fulfills the synergistic effect of chemisorption and physisorption for polysulfides, specially at high sulfur loading. The inner mesoporous “yolk” acts as a sulfur reservoir to entrap polysulfide species. Meanwhile, the outer “shell” serves as a physical barrier to alleviate the dissolution of polysulfides. Additionally, the doped nitrogen atom in carbon lattice can modify the electron distribution, introduce more defects and active sites for the chemisorption of polysulfides, improve the reversibility of Li2S/polysulfide/S conversion and the electronic conductivity, contributing to the enhanced electrochemical performance for Li-S batteries (a high specific capacity of 1329 mA h g−1 at 0.2 C and an extended cycle life).

Nitrogen-doped graphene prepared by a millisecond photo-thermal process and its applications

Doping graphene with heteroatoms such as nitrogen is a significant strategy to improve its electrochemical performance. Here, a unique millisecond photo-thermal process which is simple, safe for preparing N-doped Graphene (NG) under ammonia atmosphere was adopted. The obtained NGs were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectra, Scanning Electron Microscope (SEM), and electrochemical techniques. The nitrogen content of the NG can as 14 times as that of original rGO according to the XPS results. The intensity ratio of D band to G band in Raman spectra is increased from 1.12 to 1.18, which also demonstrates the doping of nitrogen atoms and creation of some structure defects. The SEM picture clearly demonstrates that the space between graphene planes was significant enlarged. Furthermore, nitrogen adsorption/desorption test indicated that the specific surface area of NG (267.3 m2 g−1) is much higher than that of original rGO (198.9 m2 g−1), which indicates more surfaces are available after photo-thermal process. The electro-catalysis activity of the NG was characterized by electrochemical reduction of hydrogen peroxide (2 electron process) and oxygen (4 electron process). The hydrogen peroxide reduction potential at the NG electrode was 200 mV positive shift and the peak current increase 15 times compare to bare glassy carbon electrode. The oxygen reduction reaction (ORR) testes shows an obvious reductive peak in −0.39 V vs Ag/AgCl on the NG electrode, which demonstrated that the NG also has the catalysis effect on four-electron process. As well as that, the obtained NG was also used to assemble supercapacitances, it was found that the specific capacitance of NG achieved as high as 350 F g-1 with well cyclic stability and rate capability.

Direct Nitradated Graphite Felt as an Electrode Material for the Vanadium Redox Flow Battery

The vanadium redox flow battery (VRFB) is one of the most promising electrochemical energy storage systems for grid support. However, the electrochemical performance of the VRFB should be further improved for successful penetration into the large‐scale energy storage system market. Among all the components of the VRFB, the electrode, which provides an active site for the vanadium ion redox reaction, plays an important role in determining the electrochemical properties of the VRFB. In this work, nitrogen‐doped graphite felts prepared via a direct nitridation route using NH3 were investigated as electrode materials for the VRFB. The resulting N‐doped graphite felt electrode showed much improved voltage efficiency and energy efficiency of 87.1 and 85.0%, respectively, compared to those of pristine graphite felt (82.13 and 79.6%, respectively). These improvements can be attributed to doped nitrogen atoms in the graphite felt electrode acting as an efficient electrocatalyst for the vanadium redox reaction in a VRFB system.

Effects of chemical bonds between nitrogen and its neighbor carbon atoms on fluorescence properties of carbon quantum dots

The nitrogen atoms have been attracting enormous attention in improving the fluorescent properties of carbon quantum dots (CQDs), but the contribution varies widely. In this work, the effects of chemical bonds between nitrogen and its neighbor carbon atoms as well as the nitrogen/carbon molar ratio (N/C) on fluorescence properties of CQDs were investigated. Importantly, the former was disclosed based on two kinds of well-designed nitrogen doped CQDs (N-CQDs-1 and N-CQDs-2) that show differences in chemical bonds of doped nitrogen atoms but contain the same N/C ratio and are common in the content of sp2 hybridized carbon atoms and particle size. We concluded that pyridine N rather than pyrrole N is beneficial to increasing the emission intensity of CQDs, probably caused by the enhancement of electron exchange of complex luminescent centers, and the formation and introduction of electron traps. And the emission intensity does increase with the amount of doped nitrogen atoms. Therefore, the N-CQDs-1 containing the most amount of N atoms as forms of pyridine and pyrrole shows amazing fluorescent properties and highly quantum yield (QY) up to 34.23%.

Triazasumanene: An Isoelectronic Heteroanalogue of Sumanene

AbstractBuckybowls, which are represented by sumanene and corannulene, have attracted considerable attention for their unique bowl structures and interesting physicochemical properties. However, still few heteroatom-doped buckybowls have been reported to date. Here we show the successful synthesis of triazasumanene, an isoelectronic heteroanalogue of sumanene, which possesses a deeper bowl with stable bowl chirality and unique helical columnar packing in the crystal as an enantiopure form. In contrast, the crystal packing of the racemate shows a unidirectional columnar structure, which resembles that of the pristine sumanene. Doping of nitrogen atoms into the periphery of the sumanene framework also leads to perturbations of the electronic structure as shown by a significant decrease of the lowest unoccupied molecular orbital (LUMO) level and the optical band gap in comparison to all-carbon sumanene. The pyridine ring of triazasumanene shows unusual susceptibility towards acidic hydrolysis due to the highly strained curved structure.

Graphene-organic small molecule hybrid electrocatalyst for oxygen reduction reaction

ABSTRACTA graphene-organic small molecule hybrid electrocatalyst (NG-TD) was prepared by a simple wet-chemical reaction between graphene oxide and the ortho-diamine-containing organic small molecule TPA-DAB. Due to the efficient doping of nitrogen atoms into the carbon-based network and the good structural restoration of the graphitic structures, NG-TD exhibits promising electrocatalytic activity for the oxygen reduction reaction (ORR) in alkaline electrolyte. Furthermore, the NG-TD hybrid electrocatalyst demonstrated additional advantages during the ORR process, such as high selectivity, excellent long-term stability, and very high resistance to methanol crossover.

ADSORPTION OF THIOPHENE ON N-DOPED TiO2/MoS2 NANOCOMPOSITES INVESTIGATED BY VAN DER WAALS CORRECTED DENSITY FUNCTIONAL THEORY

Comparison of structural and electronic properties between pristine and N-doped titanium dioxide-(TiO2)/molybdenum disulfide (MoS2) nanocomposites and their effects on the adsorption of thiophene molecule were performed using density functional theory calculations. To correctly estimate the adsorption energies, the van der Waals interactions were taken into account in the calculations. On the TiO2/MoS2 nanocomposite, thiophene molecule tends to be strongly adsorbed by its sulfur atom. The five-fold coordinated titanium atom of TiO2 was found to be an active binding site for thiophene adsorption. The results suggest that the thiophene molecule has not any mutual interaction with MoS2 nanosheet. The electronic structures of the complex systems are discussed in terms of the density of states and molecular orbitals of the thiophene molecules adsorbed to the TiO2/MoS2 nanocomposites. It was also found that the doping of nitrogen atom is conductive to the interaction of thiophene with nanocomposite. Thus, it can be concluded that the interaction of thiophene with N-doped TiO2/MoS2 nanocomposite is more energetically favorable than the interaction with undoped nanocomposite. The sensing capability of TiO2/MoS2 toward thiophene detection was greatly increased upon nitrogen doping. These processes ultimately lead to the strong adsorption of thiophene on the N-doped TiO2/MoS2 nanocomposites, indicating potential applicability of these nanocomposites as novel gas sensors.