Nitrogen-doped Graphene Sheets Research Articles

Synergistic effects of nitrogen-doped graphene and Fe2O3 nanocomposites in catalytic oxidization of aldehyde with O2

Promotion of nitrogen-doped graphene (NG) by incorporation of ferric oxide (NG-Fe2O3) is found to strongly enhance the activity in the catalytic oxidization of aldehyde to synthesize carboxylic acid with O2. The composite NG-Fe2O3 catalysts can be fabricated by a facile one-pot hydrothermal method. The characterization results of the composite catalysts have revealed that the Fe2O3 nanoparticles (NPs) with sizes of 40–90nm are not only on both sides of NG sheets but also tightly enwrapped by the graphene layers. In comparison to NG and Fe2O3 NPs, synergistic adsorption that confirmed by DFT studies has been created on the NG-Fe2O3 composites, where both NG and Fe2O3 are proposed to be involved in the adsorptive interaction. The synergistic adsorption can lead to strengthen O2 molecule adsorption of NG and weaken O2 molecule adsorption of Fe2O3 NPs. More importantly, the NG-Fe2O3 composite is found to considerably facilitate the longest elongation of O-O bonds and contribute to the striking enhancement of the catalytic performance. The highly active NG-Fe2O3 composite shows wide scope for catalysis of oxidation of aldehydes to carboxylic acids and good stability for recycle six times.

Nitrogen-doped Graphene Sheets Prepared from Different Graphene-Based Precursors as High Capacity Anode Materials for Lithium-Ion Batteries

Nitrogen-doped Graphene Sheets Prepared from Different Graphene-Based Precursors as High Capacity Anode Materials for Lithium-Ion Batteries

Efficient gaseous thermal insulation aerogels from 2-dimension nitrogen-doped graphene sheets

Gaseous thermal conductivity takes up a great proportion of the thermal conductivity of aerogels. In this work, we present a new strategy to restrain the gaseous thermal conductivity, using 3-dimension nanoporous aerogels from 2-dimension sheets. Experimental results show that the N-doped graphene aerogels, typical nanoporous aerogels from 2-dimension sheets, exhibit very low gaseous thermal conductivity (12.58mWm−1K−1 at room temperature) at extremely low bulk density (0.0320gcm−3), suggesting that the nanoporous aerogels from 2-dimension sheets can restrain the gaseous thermal conductivity more efficiently than that from 0-dimension pearls. This finding may significantly contribute to the next generation of thermal insulation materials with lower thermal conductivity and much lower density.

Facile hydrothermal synthesis of nanocomposites of nitrogen doped graphene with metal molybdates (NG-MMoO4) (M=Mn, Co, and Ni) for enhanced photodegradation of methylene blue

A facile one-pot hydrothermal synthesis of nanocomposites of nitrogen doped graphene with MnMoO4/CoMoO4/NiMoO4 is reported. The morphological and structural characteristics of prepared NG-MMoO4 nanocomposites have been characterized by Powder X-ray diffraction, Fourier transform vibrational spectroscopy, Scanning electron microscopy, Transmission electron microscopy and Thermal analysis. The molybdates are well-anchored and uniformly distributed on the surface of nitrogen doped graphene sheets. The nanocomposites exhibit excellent photocatalytic activity as demonstrated by photodegradation of methylene blue under Ultraviolet–Visible irradiation by using NG-MnMoO4 as catalyst.

Nitrogen Doped Graphene Nickel Ferrite Magnetic Photocatalyst for the Visible Light Degradation of Methylene Blue.

A facile approach has been devised for the preparation of magnetic NiFe2O4 photocatalyst (NiFe2O4-NG) supported on nitrogen doped graphene (NG). The NiFe2O4-NG composite was synthesized by one step hydrothermal method. The nanocomposite catalyst was characterized by Powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Ultraviolet-visible spectroscopy (UV-Vis) and Vibrating sample magnetometry (VSM). It is found that the combination of NiFe2O4 nanoparticles with nitrogen-doped graphene sheets converts NiFe2O4 into a good catalyst for methylene blue (MB) dye degradation by irradiation of visible light. The catalytic activity under visible light irradiation is assigned to extensive movement of photogenerated electron from NiFe2O4 to the conduction band of the reduced NG, effectively blocking direct recombination of electrons and holes. The NiFe2O4 nanoparticles alone have efficient magnetic property, so can be used for magnetic separation in the solution without additional magnetic support.

Custom designed ZnMn2O4/nitrogen doped graphene composite anode validated for sodium ion battery application

pH control synthesised ZnMn2O4 nanoparticles embedded in nitrogen doped graphene sheets demonstrate themselves to be a potential anode for sodium-ion batteries.

First-principles study on hydrogen adsorption on nitrogen doped graphene

In this paper we have investigated the adsorption of Hydrogen on Nitrogen doped graphene in detail by means of first-principles calculations. A comprehensive study is performed of the structural, electronic and optical properties of hydrogen atoms adsorbed on dopant atoms sites and on carbon atoms neighboring dopant atoms. The effect of doping has been investigated by varying the concentration of doping atoms from 3.125%( one atom of nitrogen in 32 host atoms) to 6.25% ( two nitrogen atoms in 32 host atoms). Similarly the effect of adsorption has been investigated by varying the concentration of hydrogen atoms and also varying the adsorption sites. Band structure, partial density of states (PDOS) and optical properties of pure, nitrogen doped and hydrogen adsorbed graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with nitrogen doped graphene and Hydrogen adsorbed graphene sheet. It is found that upon nitrogen doping the Dirac point in the graphene band structure shifts below the Fermi Energy level and energy gap appears at the high symmetric K-point. On the other hand, by adsorption of Hydrogen atom, there is further change in the band structure near the Fermi level and also the energy gap at the high symmetric K-point is increased. There is change in the dielectric function and refractive index of the graphene after H atoms adsorption on N-doped graphene. The overall absorption spectra is decreased in case of nitrogen doping and after adsorption process of Hydrogen atoms. However a significant red shift in absorption towards visible range of radiation is found to occur for hydrogen atoms adsorbed on nitrogen doped graphene sheet. The reflectivity peak of graphene increases in low energy region after H adsorption on N-doped graphene. The results can be used to tune the Fermi Energy level and to tailor the optical properties of graphene sheet in visible region.

Worm-Shape Pt Nanocrystals Grown on Nitrogen-Doped Low-Defect Graphene Sheets: Highly Efficient Electrocatalysts for Methanol Oxidation Reaction.

Although direct methanol fuel cell offers high energy use efficiency and low pollution emission, the lack of suitable electrode materials poses a great challenge to its commercial application. Herein, a facile and scalable approach is developed to fabricate a hybrid electrocatalyst consisting of strongly coupled worm-shape Pt nanocrystals and nitrogen-doped low-defect graphene (N-LDG) sheets. Interestingly, it is found that the formation of Pt nanoworms (NWs) is induced by the N atoms in the high-quality carbon matrix, which also allows the integration of their respective structural advantages and leads to a strong synergetic coupling effect. As a result, the obtained Pt NW/N-LDG catalyst exhibits an extremely high mass activity of 1283.1 mA mg-1 toward methanol oxidation reaction, accompanied by reliable long-term stability and good antipoisoning ability, which are dramatically enhanced as compared with conventional Pt nanoparticle catalysts dispersed on undoped LDG, reduced graphene oxide, and commercial carbon black supports.

Electrochemical sensing of nicotine using screen-printed carbon electrodes modified with nitrogen-doped graphene sheets

Rapid and accurate detection of nicotine is important due to its detrimental effects on human beings and recent surge in the usage of electronic cigarettes. In this paper, we report an electrochemical sensor for nicotine detection by using screen-printed carbon electrodes (SPCE) modified with nitrogen-doped graphene sheets (NGS). NGS was synthesized and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectrometry. Due to the superior electron transfer capability and the doped nitrogen atoms, NGS shows high catalytic activity for the electro-oxidation of nicotine, with a significant decrease in the overpotential. Using the NGS-based nicotine sensor, we obtained detection sensitivity at 0.627mA·cm−2mM−1 with the limit of detection at 47nM nicotine. Moreover, the sensor shows favorable selectivity and long-term stability for detecting nicotine in urine and tobacco samples.

Improvement of methane uptake inside graphene sheets using nitrogen, boron and lithium-doped structures: A hybrid molecular simulation

We investigated the storage capacity of methane on the pristine and doped graphene sheets using hybrid molecular dynamics - grand canonical Monte Carlo simulation method. Methane adsorption on two parallel graphene sheets with various distances was estimated at various pressures. According to the isotherm curves, the maximum amount of adsorbed methane was observed for graphene sheets with a distance layer of 1.2 nm. This optimum structure was further doped separately with lithium, nitrogen and boron atoms in various atomic percentages to examine methane storage contents. Results showed that lithium and nitrogen-doped graphene sheets could enhance the methane storage capacity of graphene sheets whereas boron did not have any significant effect on the methane uptake. The minimum content of dopant atoms for lithium and nitrogen was estimated as 1/12 (lithium atoms/carbon atoms) and 18.5 atomic percentage, respectively, to meet new DOE’s target for methane uptake.

Few-Layer Graphene Island Seeding for Dendrite-Free Li Metal Electrodes

Li metal batteries such as Li-air and Li-S systems have increasingly attracted the attention of researchers because of their high energy densities, which are enhanced by the use of Li metal negative electrodes. However, poor cycle efficiency and safety concerns, which are mainly related to dendritic Li growth during cycling, need to be addressed. Here we propose a solution to the Li dendrite problems. We distributed chemically prepared nitrogen-doped few-layer graphene (N-FLG) sheets on Cu substrates to create island structures. The island-type FLG on the Cu electrode was prepared via spin-coating using slurries that included a polymer binder. When the electrode was used for Li deposition, Li ions were first inserted into the graphene layers. Then, Li metal nucleation occurred at the N-FLG sheets owing to their high electrical conductivity; meanwhile, an insulating polymer layer on the Cu prevented the growth of metallic Li there. Lastly, Li metal grew from the edges of N-FLG sheets in both the lateral and vertical direction, and Li metal deposits filled the gaps between the N-FLG islands as well as covering the remainder of the electrode surface. Thus, stable cycling with flat voltage profiles was demonstrated over 100 cycles at a current density of 2 mA cm-2. The materials and electrochemical characterization results highlight the effectiveness of this method, which paves the way for the development of robust, dendrite-free Li metal electrodes.

Hydrothermal Synthesis of Few-Layer and Edge-Rich Cobalt-Doped Molybdenum Selenide/Nitrogenated Graphene Composite and Investigation of Its Electrocatalytic Activity for Hydrogen Evolution Reaction

Cobalt-doped MoSe2/nitrogenated graphene composite has been successfully synthesized via a facile hydrothermal route and is investigated as an electrocatalyst for hydrogen evolution reaction (HER). The as-prepared samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and Raman spectrum. The results reveal that Co-doped MoSe2 nanosheets which are characteristic of few layers (2–4 layers) and abundant exposed active edge sites are well anchored on the nitrogen-doped graphene sheets to constitute robust composites. When evaluated as catalysts for HER, the obtained composites demonstrate superior electrocatalytic activities toward HER.

Cascading Boost Effect on the Capacity of Nitrogen-Doped Graphene Sheets for Li- and Na-Ion Batteries.

Specific capacity and cyclic performance are critically important for the electrode materials of rechargeable batteries. Herein, a capacity boost effect of Li- and Na-ion batteries was presented and clarified by nitrogen-doped graphene sheets. The reversible capacities progressively increased from 637.4 to 1050.4 mAh g-1 (164.8% increase) in Li-ion cell tests from 20 to 185 cycles, and from 187.3 to 247.5 mAh g-1 (132.1% increase) in Na-ion cell tests from 50 to 500 cycles. The mechanism of the capacity boost is proposed as an electrochemical induced cascading evolution of graphitic N to pyridinic and/or pyrrolic N, during which only these graphitic N adjacent pyridinic or pyrrolic structures can be taken precedence. The original and new generated pyridinic and pyrrolic N have strengthened binding energies to Li/Na atoms, thus increased the Li/Na coverage and delivered a progressive capacity boost with cycles until the entire favorable graphitic N transform into pyridinic and pyrrolic N.

Au-Pt bimetallic nanoparticles supported on functionalized nitrogen-doped graphene for sensitive detection of nitrite

In this work, we report a novel Au-Pt bimetallic nanoparticles (Au-PtNPs) decorated on the surface of nitrogen-doped graphene (NG) functionalized with 1, 3, 6, 8-pyrene tetra sulfonic acid sodium salt (PyTS) by direct electrodeposition method. The results of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and electrochemical impendence spectrum (EIS) reveal that the Au-PtNPs were successfully anchored on the surface of NG sheets with a diameter of 20–40nm. Further, the prepared Au-PtNPs/PyTS-NG nanocomposite exhibits superior catalytic activity for the oxidation of nitrite. Under optimal experimental conditions, an amperometric sensor with a linear range of 0.5–1621μM and a detection limit of 0.19μM (S/N=3) for the detection of nitrite was set up and applied to real samples.

Modeling the effect of doping on the catalyst-assisted growth and field emission properties of plasma-grown graphene sheet

A theoretical model describing the effect of doping on the plasma-assisted catalytic growth of graphene sheet has been developed. The model accounts the charging rate of the graphene sheet, kinetics of all the plasma species, including the doping species, and the growth rate of graphene nuclei and graphene sheet due to surface diffusion, and accretion of ions on the catalyst nanoparticle. Using the model, it is observed that nitrogen and boron doping can strongly influence the growth and field emission properties of the graphene sheet. The results of the present investigation indicate that nitrogen doping results in reduced thickness and shortened height of the graphene sheet; however, boron doping increases the thickness and height of the graphene sheet. The time evolutions of the charge on the graphene sheet and hydrocarbon number density for nitrogen and boron doped graphene sheet have also been examined. The field emission properties of the graphene sheet have been proposed on the basis of the results obtained. It is concluded that nitrogen doped graphene sheet exhibits better field emission characteristics as compared to undoped and boron doped graphene sheet. The results of the present investigation are consistent with the existing experimental observations.

Nitrogen-doped graphene assists Fe2O3 in enhancing electrochemical performance

Abstract Fe 2 O 3 anode suffers from drastic volume change during cycling and poor electronic conductivity, resulting in inferior electrochemical performance. To address these problems, the Fe 2 O 3 /nitrogen-doped graphene sheets hybridization strategy is proposed by a hydrothermal/annealing process. In this composite, Fe 2 O 3 nanoparticles are tightly confined in graphene sheets matrix and the porous structure is obtained due to the crumpled and cross-like graphene framework, which can alleviate the volume expansion, maintain integrity of the electrode, and improve electrical conductivity and Li + diffusion. As a result, benefiting from the synergistic effect of N-doped graphene sheets matrix and Fe 2 O 3 nanoparticles, the composite exhibits a reversible capacity up to 952 mAh g −1 at a current density of 100 mA g −1 and excellent rate capability (348 mAh g −1 at a current density 5000 mA g −1 ).

Electrochemical Exfoliation of Graphite into Nitrogen-doped Graphene in Glycine Solution and its Energy Storage Properties

Electrochemically anodic exfoliation of graphite has been developed for nitrogen-doped few-layer graphene sheets (N-FLGS), demonstrating high N-doping levels of 6.05 atom%. The process for the preparation of N-FLGS is involved with the intercalation of glycine anions H2NCH2COO− into the graphite layers, electro-polymerization of large electro-oxidation products H2NCH2CONHCH2−, and in situ N-doping in the graphite layer. Transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy were employed to characterize the structure and properties of the N-FLGS. The as-fabricated N-FLGS utilized as electrode materials for supercapacitor exhibit enhanced electrochemical performance, including excellent cycling stability (the capacitance ratios after 10 000 cycles is 96.1%) and a remarkable rate capability (184.5Fg−1 at 1Ag−1, 132.7Fg−1 at 50Ag−1).

Production of N-Graphene By Microwave N2-Ar Plasmas (invited)

Nitrogen doped graphene sheets, have attracted much attention due to their exceptional performance as parts of fuel cells, lithium-ion batteries and supercapacitors. Free-standing Nitrogen-doped graphene sheets where produced in a low pressure microwave N2-Ar plasma. Graphene sheets were treated by plasma at different exposure times and doped with nitrogen atoms, which incorporated the hexagonal carbon lattice, mainly, in pyridinic, pyrrolic and quaternary functional groups. Optical emission spectroscopy were applied to monitor the nitrogen atoms, gas temperature and electron density at the substrate position. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques were applied to characterize the produced N-graphene, along with transmission electron microscopy (TEM) to study the morphology and structure of the samples. Doping levels as high as 5.6 % were achieved and an increase in the sp2/sp3ratio was observed for a relatively short exposure times. This study shows that by incorporating nitrogen atoms into graphene, its physico-chemical properties are considerably altered. Acknowledgements: This work was supported by Fundação para a Ciência e a Tecnologia, under Project Pest-OE/UID/FIS/50010/2013 and grant SFRH/BD/52413 (PD-F APPLAuSE) .

Facile Synthesis of Fe2O3 Nano-Dots@Nitrogen-Doped Graphene for Supercapacitor Electrode with Ultralong Cycle Life in KOH Electrolyte.

Fe2O3 nanodots supported on nitrogen-doped graphene sheets (denoted as Fe2O3 NDs@NG) with different loading masses are prepared through a facile one-pot solvothermal method. The resulting Fe2O3 NDs@NG composites exhibit outstanding electrochemical properties in aqueous KOH electrolyte. Among them, with the optimal loading mass of Fe2O3 NDs, the corresponding Fe2O3 NDs@NG-0.75 sample is able to deliver a high specific capacitance of 274 F g(-1) at 1 A g(-1) and the capacitance is still as high as 140 F g(-1) even at a ultrahigh current density of 50 A g(-1), indicating excellent rate capability. More remarkably, it displays superior capacitance retention after 100,000 cycles (about 75.3% at 5 A g(-1)), providing the best reported long-term cycling stability for iron oxides in alkaline electrolytes to date. Such excellent electrochemical performance is attributed to the right combination of highly dispersed Fe2O3 NDs and appropriately nitrogen-doped graphene sheets, which enable the Fe2O3 NDs@NG-0.75 to offer plenty of accessible redox active sites, facilitate the electron transfer and electrolyte diffusion, as well as effectively alleviate the volume change of Fe2O3 NDs during the charge-discharge process.

Advanced Sulfur Cathode Enabled by Highly Crumpled Nitrogen-Doped Graphene Sheets for High-Energy-Density Lithium-Sulfur Batteries.

Herein, we report a synthesis of highly crumpled nitrogen-doped graphene sheets with ultrahigh pore volume (5.4 cm(3)/g) via a simple thermally induced expansion strategy in absence of any templates. The wrinkled graphene sheets are interwoven rather than stacked, enabling rich nitrogen-containing active sites. Benefiting from the unique pore structure and nitrogen-doping induced strong polysulfide adsorption ability, lithium-sulfur battery cells using these wrinkled graphene sheets as both sulfur host and interlayer achieved a high capacity of ∼1000 mAh/g and exceptional cycling stability even at high sulfur content (≥80 wt %) and sulfur loading (5 mg sulfur/cm(2)). The high specific capacity together with the high sulfur loading push the areal capacity of sulfur cathodes to ∼5 mAh/cm(2), which is outstanding compared to other recently developed sulfur cathodes and ideal for practical applications.