Nitrogen-doped Graphene Nanosheets Research Articles

Study on urea precursor effect on the electroactivities of nitrogen-doped graphene nanosheets electrodes for lithium cells

Nitrogen-atom doped graphene oxide was considered to prevent the dissolution of polysulfide and to guarantee the enhanced redox reaction of sulfur for good cycle performance of lithium sulfur cells. In this study, we used urea as a nitrogen source due to its low cost and easy preparation. To find the optimum urea content, we tested three different ratios of urea to graphene oxide. The morphology of the composites was examined by field emission scanning electron microscope. Functional groups and bonding characterization were measured by X-ray photoelectron spectroscopy. Electrochemical properties were characterized by cyclic voltammetry in an organic electrolyte solution. Compared with thermally reduced graphene/sulfur (S) composite, nitrogen-doped graphene/S composites showed higher electroactivity and more stable capacity retention.

Platinum Nanoparticles Supported on Nitrogen-Doped Graphene Nanosheets as Electrocatalysts for Oxygen Reduction Reaction

This paper deals with nitrogen-doped graphene nanosheets prepared using dicyandiamide precursor as a catalyst support for oxygen reduction reaction (ORR). Platinum nanoparticles supported on N-doped graphene nanosheets (Pt/NG) were studied as electrocatalysts for ORR in acid and alkaline solutions employing the rotating disk electrode (RDE) technique. Pt/NG nanomaterials were synthesised by chemical reduction of hexachloroplatinic acid using sodium borohydride or ethylene glycol as reducing agents. Surface morphology and composition of the prepared catalysts were examined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM images showed a high dispersion of Pt nanoparticles on N-doped graphene nanosheets due to strong interaction of Pt with nitrogen functionalities. The average nitrogen content was between 6 and 7 at.% according to the XPS analysis. In acidic solution, 20 wt% Pt/NG catalyst prepared by borohydride reduction showed the highest specific activity for O2 reduction from all the Pt/NG materials studied. Pt/NG nanomaterials exhibited excellent electrocatalytic activity in alkaline media, and their half-wave potentials were similar to that of commercial Pt/C catalyst. The RDE data analysis showed that the ORR on the Pt/NG catalysts proceeded via four-electron pathway.

Nitrogen-doped graphene-decorated LiVPO4F nanocomposite as high-voltage cathode material for rechargeable lithium-ion batteries

Abstract In this study, nitrogen-doped graphene decorated LiVPO4F cathode material is firstly synthesized via a facile method. Well-dispersed LiVPO4F nanoparticles are embedded in nitrogen-doped graphene nanosheets, forming an effective conducting network. The added nitrogen-doped graphene nanosheets greatly enhance the electronic conductivity and Li-ion diffusion of LiVPO4F sample. When tested as cathode material for rechargeable lithium-ion batteries, the hybrid electrode exhibits superior high-rate performance and long-term cycling stability between 3.0 and 4.5 V. It delivers a large discharge capacity of 152.7 mAhg−1 at 0.1 C and shows a capacity retention of 97.8% after 60 cycles. Moreover, a reversible capacity of 90.1 mAhg−1 is maintained even after 500 cycles at a high rate of 20 C. The charge-transfer resistance of LiVPO4F electrode is also reduced in the nitrogen-doped graphene, revealing that its electrode-electrolyte complex reactions take place easily and thus improve the electrochemical performance. The above results provide a facile and effective strategy for the synthesis of LiVPO4F cathode material for high-performance lithium-ion batteries.

Nitrogen-doped graphene nanosheets decorated Li3V2(PO4)3/C nanocrystals as high-rate and ultralong cycle-life cathode for lithium-ion batteries

We report here the integration of high voltage Li3V2(PO4)3/C cathode material and nitrogen-doped graphene nanosheets, which has led to high-speed electron and Li-ion transfer channels. The hybrid materials are synthesized through a microwave-assisted hydrothermal method. The Li3V2(PO4)3/C with typical size of 50–100nm are uniformly anchored on the nitrogen-doped graphene nanosheets. The hybrid nanocomposites as cathode material for lithium-ion batteries exhibit a specific discharge capacity of 191.5mAhg−1 at 0.1C within the voltage range of 3.0–4.8V; 172.6mAhg−1 and 160.5mAhg−1 at higher rates of 5C and 10C, respectively. More importantly, it shows a stable cycling performance with 87.3% capacity retention after 1000 cycles at 20C. Thus, we can speculate that the nitrogen-doped graphene decorated Li3V2(PO4)3/C is a promising cathode material for use in high-rate and ultralong cycle-life lithium-ion batteries. Meanwhile, this synthesis strategy and design conception for Li3V2(PO4)3 could be employed to develop other cathode or anode materials for advanced energy storage.

An electrochemical DNA biosensor based on nitrogen-doped graphene/Au nanoparticles for human multidrug resistance gene detection

Multidrug resistance (MDR) has become a major obstacle to the adequate treatment of cancer patients; thus, there is an urgent need for exploring new strategies for early diagnosis of MDR in clinic. Here, we report a novel electrochemical biosensor based on nitrogen-doped graphene nanosheets functionalized with Au nanoparticles (N-G/Au) for sensitive and selective DNA detection. The highly conductive nanocomposite layer was characterized by using scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. DNA with thiol groups at the 5′ end was immobilized on the N-G/Au surface via the strong Au–S bond. Differential pulse voltammetry was applied to monitor the target DNA hybridization event using methylene blue as an electrochemical indicator. Under optimal conditions, the biosensor could detect target DNA down to 3.12×10−15M with a linear range from 1.0×10−14 to 1.0×10−7M, showing high sensitivity. Further, the sensing strategy was successfully used for detecting MDR1 DNA in real clinical samples. These results will aid in developing a new portable detection system for MDR that will allow effective diagnosis in the early stages of related cancer.

Nitrogen-doped graphene nanosheets as reactive water purification membranes

Oxidation of organic pollutants by sulfate radicals produced via activation of persulfate has emerged as a promising advanced oxidation technology to address various challenging environmental issues. The development of an effective, environmentally-friendly, metal-free catalyst is the key to this technology. Additionally, a supported catalyst design is more advantageous than conventional suspended powder catalysts from the point of view of mass transfer and practical engineering applications (e.g. post-use separation). In this study, a metal-free N-doped reduced graphene oxide (N-rGO) catalyst was prepared via a facile hydrothermal method. N-rGO filters were then synthesized by facile vacuum filtration, such that water can flow through nanochannels within the filters. Various advanced characterization techniques were employed to obtain structural and compositional information of the as-synthesized N-rGO filters. An optimized phenol oxidative flux of 0.036 ± 0.002 mmol·h–1 was obtained by metal-free catalytic activation of persulfate at an influent persulfate concentration of 1.0 mmol·L–1 and filter weight of 15 mg, while a N-free rGO filter demonstrated negligible phenol oxidation capability under similar conditions. Compared to a conventional batch system, the flow-through design demonstrates obviously enhanced oxidation kinetics (0.036 vs. 0.010 mmol·h–1), mainly due to the liquid flow through the filter leading to convection-enhanced transfer of the target molecule to the filter active sites. Overall, the results exemplified the advantages of organic compound removal by catalytic activation of persulfate using a metal-free catalyst in flowthrough mode, and demonstrated the potential of N-rGO filters for practical environmental applications.

Effect of nitrogen-doped graphene nanofluid on the thermal performance of the grooved copper heat pipe

Thermal performance of a grooved heat pipe using aqueous nitrogen-doped graphene (NDG) nanofluids was analysed. This study in particular focused on the effect of varying NDG nanosheets concentrations, heat pipe inclination angles and input heating powers. The results indicated that the inclination angle had a major influence on the heat transfer performance of heat pipes and the inclination angle (θ) of 90° was corresponded to the best thermal performance. The maximum thermal resistance reduction of 58.6% and 99% enhancement in the evaporator heat transfer coefficient of the heat pipe were observed for NDG nanofluid with concentration of 0.06wt%, inclination angle of θ=90° and a heating power of 120W in comparison to DI-water under the exact same condition. Additionally, the surface temperature distribution was decreased by employing NDG nanosheets, which can in return increase the thermal performance of a grooved heat pipe. The present investigation indicated that the thermal performance of the grooved heat pipe can be improved significantly by using NDG nanofluids.

Interfacial interactions and synergistic effect of CoNi nanocrystals and nitrogen-doped graphene in a composite microwave absorber

We reported a facile one-pot polyol route for the fabrication of CoNi/nitrogen-doped graphene hybrids as synergistic microwave absorber. Microstructure investigations suggest that all the CoNi nanocrystals are uniformly anchored on the nitrogen-doped graphene nanosheets without aggregation and the hybrids are stable under ultrasound treatment, which suggest that these nonvalent CoNi alloys are in-situ grown on nitrogen-doped graphene with a strong interaction. Taking both the synergistic benefits of magnetic CoNi nanocrystals and electric nitrogen-doped graphene, the CoNi/nitrogen-doped graphene hybrids show a maximum reflection loss of −22 dB at 10 GHz with a matching thickness of only 2.0 mm, and the effective absorption bandwidth with reflection loss exceeding −10 dB is 3.6–18 GHz with the absorber thickness of 1.35–5.0 mm. Compared with the single CoNi nanocrystals and graphene oxide, the CoNi/nitrogen-doped graphene hybrids show improved microwave absorption properties. These results indicate that the interface interactions and synergistic effect between the CoNi nanocrystals and nitrogen-doped graphene play a significant role on the enhancement of microwave absorption properties. This work suggests that the CoNi/nitrogen-doped graphene hybrids can be used as candidate materials for the design and manufacture of electronic nanodevices with high efficient microwave absorption properties.

Nitrogen-Doped Graphene/Sulfur Composite As Cathode Material for Room-Temperature Sodium-Sulfur Battery Application

Sodium is a promising alternative anode material with advantages of high abundance, low cost, and suitable redox potential (~2.71 V). Sulfur, as one of the most abundant elements on earth, is considered as an attractive cathode material owing to its high theoretical capacity of 1675 mA h g-1 and high energy density of 2600 W h kg-1. It is well known that sodium-sulfur (Na-S) battery has been widely used for stationary energy storage, operating at a high temperature condition. In recent years, much effort has been devoted to develop Na-S batteries at ambient temperature to overcome the safety drawback [1-3]. However, more challenges exist in room temperature (RT) NaS batteries such as dissolution of intermediate polysulfides into the electrolyte, low utilization of active material, and poor cycle life. In this work, nitrogen-doped graphene nanosheets (NGNS) interlinked with sulfur has been used as an electrode material for RT Na-S batteries. This nanocomposite was synthesized via an chemical reaction-deposition and thermal treatment strategy. Two series samples with both high and low sulfur content levels in the nanocomposites have been developed. Characterizations testing such as SEM, XPS and XRD have been conducted and the results from electrochemical testing show that the first cycle discharge/charge capacities of the low loading sulfur-NGNS composite at 0.05C have been reached 212 mA h g-1 and 181 mA h g-1. The low loading sulfur-NGNS composite also presented notable cycling life with 300 cycles at 0.1C and the capacity remained at 55 mA h g-1, indicating good cyclic retention. Detailed discussion on the characterization and electrochemical performance of the synthesized NGNS/S nanocomposite will be presented in the meeting.

Superior cycle stability of nitrogen-doped graphene nanosheets for Na-ion batteries

Sodium ion battery (SIB) is a promising power storage system for sustainable energy storage and conversion (ESC) due to the abundant worldwide Na resources and its much lower cost. In this paper, the electrochemical performance of Na+ intercalation/extraction in nitrogen-doped graphene nanosheets (N-GNS) were studied. The experimental results showed that the N-GNS exhibited high Na+ storage capacity (260mAhg−1 at 50mAg−1), good rate capability and excellent cycle performance even at a very high current density (90mAhg−1 at 500mAg−1 for 600 cycles). The superior electrochemical performance of N-GNS is due to the N-doping-induced defects structure, which makes the N-GNS suitable for the fast diffusion of the relatively large-sized Na+ with low ion-transport resistance and effective storage of Na+ during discharge–charge processes.

Nitrogen-doped graphene-chitosan matrix based efficient chemiluminescent immunosensor for detection of chicken interleukin-4

Chicken interleukin-4 (ChIL-4), which is released by activated type 2 helper (Th2) cells following their stimulation in vitro, is an important indicator for the study of cell-mediated immunity in chickens after infection or vaccination. In this work, the first ChIL-4 chemiluminescent (CL) immunosensor was developed via the immobilization of monoclonal ChIL-4 antibodies on a nitrogen-doped graphene (NG)-chitosan nanocomposite matrix. NG nanosheets were used for the first time in the CL immunoassay to provide a biocompatible microenvironment for the immobilized capture antibody. The ChIL-4 immunosensor was characterized systematically. The proposed immunosensor displayed a wide linear range from 0.05 to 70ngmL−1 and a low detection limit of 0.02ngmL−1 at a signal-to-noise ratio of 3. Compared to traditional assay methods, this system was more flexible, simple, rapid, and sensitive. Moreover, this CL immunoassay system had an excellent detection and fabrication reproducibility, a high specificity, an acceptable accuracy, and a high stability. This work enables the specific detection of ChIL-4 and the further study of its role in the immune responses of poultry.

Modified solar power: electrochemical synthesis of Nitrogen doped few layer graphene for supercapacitor applications

Hetero atom doped few layers of reduced graphene have been synthesized by single step approach called solar power modified electrochemical technique and investigated for supercapacitor applications. The structure and morphology of nitrogen doped graphene nanosheets (S-NGNS) was characterized with powder X-ray diffraction (XRD), SEM, HR-TEM, FTIR, Raman and XPS. The electrochemical activity of the S-NGNS was evaluated using CV, charge–discharge and impedance spectroscopy (EIS) in 0.5 M H2SO4 electrolyte solution. From X-ray photoelectron spectroscopy (XPS) analysis, it was confirmed that the trace amount (0.48 %) of N doping in the reduced graphene oxide (rGO) nanosheets. As an electrode for supercapacitor the proposed S-NGNS showed the specific capacitance (Scp) values of 85 F/g at constant current density of 0.125 A/g.

Toward improved engine performance with crumpled nitrogen-doped graphene based water–ethylene glycol coolant

Crumpled nitrogen-doped graphene nanosheet (CNDG) is considered a promising carbon-based nanosheet due to its high surface area, superior electrical, thermal and mechanical properties. Herein, CNDG is first prepared and tested as an additive for preparing a new engine coolant. The prepared two-dimensional CNDG feature high electrical conductivity, excellent thermal conductivity and heat transfer properties, permitting the CNDG-based water-ethylene glycol coolants to exhibit excellent Mouromtseff number, electrical properties and heat transfer performance for all temperatures and weight concentrations in a car radiator. Further, steady-state forced convective heat transfer experiments have been performed to evaluate the cooling capabilities of the prepared coolants.

Chemiresistive gas sensor for the sensitive detection of nitrogen dioxide based on nitrogen doped graphene nanosheets

Nitrogen doped graphene nanosheet coated interdigitated electrodes for sensitive detection of NO2gas at room temperature.

Nitrogen-doped graphene nanosheets as metal-free catalysts for dehydrogenation reaction of ethanol

N-Doped graphene is used to catalyze the dehydrogenation of ethanol, wherein acetaldehyde is obtained with a hundred percent selectivity.

Hydrothermally functionalized biocompatible nitrogen doped graphene nanosheet based biomimetic platforms for nitric oxide detection.

Hydrothermal synthesis of nanocomposites is of significant importance, as it affords facile, biocompatible, nontoxic, and economic fabrication. Herein, we report a hitherto unexplored cytocompatible and reusable biomimetic electrochemical sensor based on pyridyl porphyrin functionalized nitrogen doped graphene nanosheets. The porphyrin functionalized nitrogen doped graphene nanosheets (PFNGS) were prepared by a low temperature hydrothermal method via non-covalent strategies with a minimal impact on their physicochemical properties. Owing to their exceptional attributes like operational ease, low cost, portability, and sensitivity, the as-synthesized PFNGS, formed by π-π interactions, were employed for sensing nitric oxide (NO), which is a key regulator of diverse biological processes. Compared to porphyrin and nitrogen doped graphene nanosheets alone, PFNGS exhibited exceptional sensitivity (3.6191 μA μM-1) and remarkable electrocatalytic properties (0.61 V). This clearly outperforms the previously reported modified electrode materials for the electrochemical detection of NO. Cyclic voltammetry (CV) data also suggested that the PFNGS modified electrode possessed an increased reactive surface area, which results in an increase in the number of reactive sites and low charge transfer resistance. These results also demonstrated that the PFNGS modified electrode showed high stability and reproducibility, the limit of detection (LOD) (S/N = 3) of which was estimated to be 1 nM. Our PFNGS were found to be highly biocompatible and could also detect NO released from macrophage cells. This blend of biocompatibility, electrode stability, electrocatalytic activity along with enhanced sensitivity and selectivity makes PFNGS a powerful and reliable nanomaterial for various biomedical applications in complex biological systems.

Graphene Nanosheets Based Cathodes for Lithium-Oxygen Batteries

Lithium-oxygen batteries have attracted considerable attention as a promising energy storage system. Although these batteries have many advantages, they face several critical challenges. In this work, we report the use of graphene nanosheets (GNSs), nitrogen-doped graphene nanosheets (N-GNSs), exfoliated nitrogen-doped graphene nanosheets (Ex-N-GNSs), and a blend of Ex-N-GNSs with nitrogen-doped carbon (Hybrid 1) as oxygen cathodes. These cathode materials were characterized by the Brunauer-Emmett-Teller (BET) surface area analysis, cyclic voltammetry (CV) and scanning electron microscopy (SEM). In order to mitigate safety issues, all solid-state cells were designed and fabricated using lithium aluminum germanium phosphate (LAGP) as ceramic electrolyte. The cathodes prepared from GNSs, N-GNSs, Ex-N-GNSs, and Hybrid 1 exhibit remarkable enhancement in cell capacity in comparison to conventional carbon cathodes. This superior cell performance is ascribed to beneficial properties arising from GNSs and nitrogen doped carbon. GNSs have unique morphology, higher oxygen reduction activity, whereas nitrogen-doped carbon has higher surface area.

Full Protection for Graphene-Incorporated Micro-/Nanocomposites Containing Ultra-small Active Nanoparticles: the Best Li-Storage Properties

In recent years, graphene-incorporated micro-/nanocomposites represent one of the hottest developing directions for the composite materials. However, a large number of active nanoparticles (NPs) are still in the unprotected state in most constructed graphene-containing designs, which will seriously impair the effects of the graphene additives. Here, a fully protected Fe3O4-based micro-/nanocomposite (G/Fe3O4@C) is rationally developed by carbon-boxing the common graphene/Fe3O4 microparticulates (G/Fe3O4). The processes and results of full protection are tracked in detail and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and nitrogen absorption–desorption isotherms, as well as scanning and transition electron microscopy. When used as the anode for lithium-ion batteries, the fully protected G/Fe3O4@C exhibits the best lithium-storage properties in terms of the highest rate capabilities and the longest cycle life compared to the common G/Fe3O4 composites and commercial Fe3O4 products. These much improved properties are mainly attributed to its novel structural features including complete protection of active Fe3O4 nanoparticles by the surface carbon box, a robust conductive network composed of nitrogen-doped graphene nanosheets, ultra-small Fe3O4 NPs of 4–5 nm, abundant mesopores to accommodate the volume variation during cycling, and micrometer-sized secondary particles.

Experimental and numerical investigation of the effective electrical conductivity of nitrogen-doped graphene nanofluids

Electrical conductivity is an important property for technological applications of nanofluids that have not been widely investigated, and few studies have been concerned about the electrical conductivity. In this study, nitrogen-doped graphene (NDG) nanofluids were prepared using the two-step method in an aqueous solution of 0.025 wt% Triton X-100 as a surfactant at several concentrations (0.01, 0.02, 0.04, 0.06 wt%). The electrical conductivity of the aqueous NDG nanofluids showed a linear dependence on the concentration and increased up to 1814.96 % for a loading of 0.06 wt% NDG nanosheet. From the experimental data, empirical models were developed to express the electrical conductivity as functions of temperature and concentration. It was observed that increasing the temperature has much greater effect on electrical conductivity enhancement than increasing the NDG nanosheet loading. Additionally, by considering the electrophoresis of the NDG nanosheets, a straightforward electrical conductivity model is established to modulate and understand the experimental results.

Design of N-graphene-NbOx hybrid nanosheets with sandwich-like structure and electrocatalytic performance towards oxygen reduction reaction

Advanced materials for electrocatalytic oxygen reduction reaction (ORR) is crucial to a number of renewable energy applications. Herein, a hybrid of nitrogen-doped graphene (N-graphene) and NbOx (x=2∼2.5) semiconductor nanosheets with sandwich-like structure has been designed and synthesized via a strategy of intercalation-in situ carbonization. The obtained multilayer hybrid material exhibits quite positive onset potential of ORR, good stability and excellent selectivity for ORR with high methanol tolerance. The enhanced performance could be attributed to the active oxygen vacancy from the partial reduction of Nb (V) during the carbonization process and the synergetic coupling effect resulting from the molecular level contact of N-graphene and NbOx (x=2∼2.5) nanosheets, which makes it a promising substitute of platinum-based materials for renewable energy applications.