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Through a simple method, a new kind of Mn 3 O 4 nanoparticles (Mn 3 O 4 NPs) decorated nitrogen-doped graphene (N-GR) was synthesized firstly, and then a Mn 3 O 4 NPs/N-GR modified carbon paste electrode (CPE) was fabricated. Several techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemistry, were performed to characterize Mn 3 O 4 NPs/N-GR. A large amount of N on the graphene surface (about 9.86% of atomic ratio) was detected by XPS. Mn 3 O 4 nanoparticles (50–80 nm) homogeneously coated on N-GR. Mn 3 O 4 NPs/N-GR/CPE was used for sensitive non-enzymatic glucose sensing, which exhibited the response current of glucose ca. 10-fold higher than that of pure CPE. Under the optimum determination conditions, Mn 3 O 4 NPs/N-GR/CPE provided glucose with a broader detection range of 2.5–529.5 μM with a low detection limit (1.0 μM, S/N = 3). This novel method was successfully used to determine glucose in human urine sample. [ABSTRACT FROM AUTHOR]

A facile one-pot solvothermal method based on exfoliating and disintegrating treatments for graphite oxide was developed to prepare water-soluble graphene quantum dots. Dimethylformamide served as a solvent and source of nitrogen, the as-prepared nitrogen-doped graphene quantum dots (N-GQDs) exhibited bright green emission under ultraviolet irradiation (∼365 nm). More importantly, an ultrasensitive paper-based electrochemiluminescence (ECL) immunoassay was developed with green-luminescent N-GQDs as ECL labels and α-fetoprotein antigen (AFP) as model protein. The N-GQDs were promising ECL labels because of their low anodic ECL potential of +0.84 V and high biocompatibity, which can facilitate highly sensitive ECL bioassays. A novel paper working electrode was fabricated through a seed-mediated growth approach and served as a promising platform for antibodies attachment. Upon the immunorecognition of the immobilized AFP to its antibody labeled with N-GQDs, the proposed immunoassay displayed increasing ECL intensity, leading to a wide calibration range of 0.005–100 ng mL −1 with a detection limit of 1.2 pg mL −1 [signal-to-noise ratio (S/N) = 3]. The ECL immunoassay for real samples displayed very similar results with the commercial ECL immunoassay, which provided a powerful avenue for the design of the ultrasensitive detection method for clinical application. [ABSTRACT FROM AUTHOR]

Functionalized nanoporous graphene has shown great promise as emerging membrane. Herein, we computationally demonstrate the separation performance using pyridinic-like nitrogen doped nanoporous graphene as reverse osmosis desalination membrane. The water permeation and salt rejection of the functionalized graphene membranes with various nitrogen-doping levels were simulated and characterized. We show that all functionalized graphenes investigated in this work exhibit higher water flux and acceptable salt rejection. In particular, the NOH graphene membrane with partial hydroxyl group inclusion shows excellent desalination efficiency. The interfacial properties of water and ions, as well as their free energy landscapes in passing through the graphene nanopores have been simulated in order to explore the desalination mechanism. The moderate free energy barriers for water passages confirm larger water fluxes in the functionalized graphene membranes. It was revealed that the salt rejection for the functionalized graphenes is the pore size exclusion of hydrated ions and the charged repulsion from pore surfaces is not the main factor. Overall, our results indicate that pyridinic-like nitrogen doped graphenes have a significant potential as nanostructured desalination membranes. [ABSTRACT FROM AUTHOR]

Nitrogen-enriched porous carbon nanofibers were successfully prepared by using water-soluble phenolic resin/polyvinyl alcohol blend solution as precursor via electrospinning followed by carbonization and NH 3 treatments. The NH 3 treatment time has a significant effect on the pore structure, thermal stability as well as the surface chemistry. The as-prepared carbon materials were studied as freestanding electrodes for supercapacitor without the addition of binders and conductive additives in 6 M KOH solution. The sample treated with NH 3 for 3 h exhibits a high specific surface area (763 m 2 g −1 ), rich surface functionalities (5.26 at.% nitrogen and 4.37 at.% oxygen), optimized pore structure, good thermal stability and electrical conductivity. It shows the maximum specific capacitance of up to 251.2 F g −1 at 0.1 A g −1 , about 25% higher than that of the sample treated with argon. Furthermore, the specific capacitance remains 193 F g −1 at 20 A g −1 with high rate capability of 77%, as well as excellent cycle stability (99% capacity retention after 2000 cycles). The outstanding performance of nitrogen-doped porous carbon nanofibers could be attributed to the synergistic effect of the proper pore size distribution, high effective surface area and certain amount of nitrogen- and oxygen-containing functional groups, resulting in both electrochemical double layer and faradaic capacitance contributions. [ABSTRACT FROM AUTHOR]

Polymer electrolyte membrane fuel cells (PEMFCs) convert chemical energy directly into electrical energy where catalysts composing of non-noble transition metals, nitrogen, and carbon compounds are the most promising materials to replace the expensive platinum catalysts for oxygen reduction reaction (ORR). In this research, cathodic vacuum arc plasma (CVAP) technique was used to fabricate porous nitrogen doped carbon (NC) and non-platinum catalyst on porous NC (Fe–NC) directly on ion exchange membrane for being used as an ORR catalyst at the cathode. The porous NC layer was fabricated on silicon wafer at 0.05 mTorr, 0.1 mTorr, 0.5 mTorr, 1 mTorr, and 5 mTorr of nitrogen gas inlet. The AFM, and SEM images are observed to be regularly big with quite high hillocks and thin NC layers; these results indicate that the optimum process pressure of nitrogen gas inlet is 5 mTorr for porous NC fabrication. The SEM–EDS detects Fe, N, and C elements in the prepared catalysts, and the XRD pattern reviews the iron nitride and the carbon nitride phases. The SEM images in the backscattered electron mode (BSE) reveal good dispersion of very small metal particles (bright spots) on the highly porous coral-like carbon film. The TEM images clearly show the spherical Fe nanoparticles (64 nm) dispersed on the porous carbon film. However, the XANES (X-ray absorption near edge structure) analysis specifies that the prepared Fe is in the form of iron(III). As a result of no FeN standard for confirmation, both the XRD and the XANES results are used to confirm the Fe(III) compound. In preparing the catalyst as FeN, all these results specify that the CVAP technique can be used to produce the catalyst on the membrane. [ABSTRACT FROM AUTHOR]

A highly sensitive and selective method was developed for simultaneous detection of uric acid (UA), xanthine (XA) and hypoxanthine (HX) based on a 1,3,6,8-pyrene tetra sulfonic acid sodium salt functionalized nitrogen-doped graphene (PyTS–NG) composite. The material was synthesized by utilizing a facile ultrasonic method via π–π conjugate action between 1,3,6,8-pyrene tetra sulfonic acid sodium salt (PyTS) and nitrogen-doped graphene (NG) molecule. Compared with pristine NG, the material had better dispersivity and conductivity, which might be attributed to a large number of edge-plane-like defective sites on the surface of PyTS–NG that would accelerate electron transfer between electrode and species in solution. The surface morphology was characterized by scanning electron microscopy and transmission electron microscopy. The electrochemical behaviors of UA, XA and HX on the surface of PyTS–NG were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimized condition, the linear ranges for the determination of UA, XA and HX were 9–1000, 8–800 and 8–200 μM, with the detection limits (S/N = 3) of 0.331, 0.0838 and 0.231 μM, respectively. Furthermore, the practical application of the present method was evidenced by determining UA, XA and HX in human blood serum and urine samples. [ABSTRACT FROM AUTHOR]

Hierarchical nitrogen-doped porous hollow carbon spheres (HNPHCS) with porous-thin mesoporous shell and hollow macroporous core structure have been prepared via in-situ oxidation polymerization method using polyaniline as the precursor. After carbonization at 900 °C, the average diameter of HNPHCS is ca. 140 nm with shell thickness of ∼1 nm. Pt nanoparticles with high dispersion and small size have been successfully deposited on the HNPHCS by a microwave-assisted polyol process to synthesize Pt/HNPHCS catalyst. The obtained samples are characterized by physical characterization and electrochemical measurements. Electrochemical studies reveal that the prepared Pt/HNPHCS catalyst possesses notably higher catalytic activity and CO-tolerance, and better stability toward methanol electrooxidation in comparison with Pt/nitrogen-doped porous carbon and the commercial Pt/C catalysts. It is likely that enhanced catalytic properties of the Pt/HNPHCS could be due to the high dispersion of small Pt nanoparticles, the presence of nitrogen species, developed porous-thin mesoporous shell and hollow macroporous core structure of support HNPHCS. As a result, the as-developed Pt/HNPHCS present attractive advantages for the application in fuel cell electrocatalyst. [ABSTRACT FROM AUTHOR]

Nitrogen, phosphorus and Fe doped carbon nanospheres have been synthesized by a facile method in which polyacrylonitrile nanospheres are pyrolyzed in the presence of diammonium phosphate and iron trichloride hexahydrate. The specific surface area of the catalyst is high up to 771.3 m 2 g −1 , and it has a hierarchical micro-meso-macroporous structure. In an alkaline medium, the catalyst exhibits high electrocatalytic activity towards the oxygen reduction reaction (ORR) as well as excellent stability and methanol tolerance—superior in each case to commercial Pt/C catalyst. The effects that adding Fe salt and phosphorus on the structure and performance of the catalyst are also investigated. We suggest that the catalyst's excellent electrocatalytic performance may be attributed to: (1) the synergistic effect, which provides more catalytic sites for the ORR, due to the nitrogen and phosphorus co-doping; (2) the strong promotion by trace Fe residues; and (3) the high surface area and excellent mass transport rate arising from the hierarchical porous structure. [ABSTRACT FROM AUTHOR]

Nitrogen-doped tin oxide (SnO 2 :N) thin films were deposited on flexible polyethylene terephthalate (PET) substrates at room temperature by RF-magnetron sputtering. Effects of oxygen partial pressure (0–4%) on electrical and optical properties of thin films were investigated. Experimental results showed that SnO 2 :N films were amorphous state, and O/Sn ratios of SnO 2 :N films were deviated from the standard stoichiometry 2:1. Optical band gap of SnO 2 :N films increased from approximately 3.10 eV to 3.42 eV as oxygen partial pressure increased from 0% to 4%. For SnO 2 :N thin films deposited on PET, transmittance was about 80% in the visible light region. The best transparent conductive oxide (TCO) deposited on flexible PET substrates was SnO 2 :N thin films preparing at 2% oxygen partial pressure, the transmittance was about 80% and electrical conductivity was about 9.1 × 10 −4 Ω cm. [ABSTRACT FROM AUTHOR]

Herein, a facile hydrothermal treatment of lime juice to prepare biocompatible nitrogen-doped carbon quantum dots (N-CQDs) in the presence of ammonium bicarbonate as a nitrogen source has been presented. The resulting N-CQDs exhibited excitation and pH independent emission behavior; with the quantum yield (QY) up to 40%, which was several times greater than the corresponding value for CQDs with no added nitrogen source. The N-CQDs were applied as a fluorescent probe for the sensitive and selective detection of Hg 2 + ions with a detection limit of 14 nM. Moreover, the cellular uptake and cytotoxicity of N-CQDs at different concentration ranges from 0.0 to 0.8 mg/ml were investigated by using PC12 cells as a model system. Response surface methodology was used for optimization and systematic investigation of the main variables that influence the QY, including reaction time, reaction temperature, and ammonium bicarbonate weight. [ABSTRACT FROM AUTHOR]

A facile, environmentally friendly and low-cost synthesis strategy is demonstrated to fabricate a MoO 2 /N-doped graphene (MoO 2 /N-GNS) hybrid, in which MoO 2 nanoparticles (NPs) are uniformly dispersed on N-GNS sheets by Mo–N chemical bond formed between MoO 2 and N-GNS. As an anode material in lithium ion batteries, the MoO 2 /N-GNS hybrid possesses superior rate capability, excellent cycling performance as well as high reversible capacity. A reversible capacity of 1138.5 mA h g −1 is maintained after 60 cycles at a current density of 100 mA g −1 , and even at a high current density of 1000 mA g −1 , the specific capacity of 873.7 mA h g −1 can be obtained after 60 cycles. The superior electrochemical performance of the MoO 2 /N-GNS hybrid can be attributed to the synergistic effects of nitrogen-doping, flexible and conductive GNS, and MoO 2 NPs. [ABSTRACT FROM AUTHOR]

In this paper, we report a template-free method to fabricate hollow nitrogen-doped carbon (HNC) by pyrolysis of hollow polyaniline microspheres, which were synthesized by suspension polymerization method. The entire synthesis is simple, environmentally benign, and economic. The oxygen reduction reaction (ORR) activity of the as-prepared HNC catalyst is close to that of the commercial Pt/C catalyst in alkaline media with four electron pathway. Moreover, the HNC shows much better fuel crossover resistance and long-term durability than the commercial Pt/C in alkaline medium. All these features make HNC a potentially promising and suitable substitute for the expensive noble metal catalysts in the next generation alkaline fuel cells. [ABSTRACT FROM AUTHOR]

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

Microbial fuel cells (MFCs) couple functions of waste removal and electricity generation. The future success of MFCs inevitably depends on the increase of performance at decrease of material cost. Therefore, the use of renewable and sustainable materials, e.g. cellulose, to prepare high performance materials for MFCs would be an inevitable trend. In this communication, nitrogen and phosphorus dual-doped carbons were prepared by pyrolysis of cellulose using ammonium phosphate as doping source and employed as oxygen reduction reaction (ORR) catalyst in air-cathode of MFCs. A maximum power density of 2293 ± 50 mW m −2 was generated by the air-cathode using the dual-doped carbon catalyst, which was higher than the air-cathode using Pt/C catalyst with Pt load of 0.5 mg cm −2 (1680 ± 32 mW m −2 ). This study provided a facile and sustainable way to prepare low-cost and high-efficient ORR catalyst for scaled-up MFC applications. [ABSTRACT FROM AUTHOR]