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A novel electrochemical sensor based on nitrogen doped graphene (NGE) and palygorskite (Pal) for the simultaneous detection of hydroquinone (HQ) and catechol (CT) has been proposed. Pal is particularly pointed out for its appreciable specific surface area and reactive-OH groups on its surface. Acid treatment Pal demonstrated better physico-chemical properties, which are propitious to electrochemical sensor construction. The introduction of NGE not only improved the poor conductivity of Pal but also served as an excellent adherent matrix. The modified electrode demonstrated the enhanced redox peak currents of HQ and CT with good discrimination. Under optimized conditions, the linear ranges for HQ and CT were 2–50 μM and 1–50 μM, with detection limit (LOD) of 0.8 μM and 0.13 μM, respectively. The result designates that the Pal/NGE composite promises to be a new eco-friendly modified material for sensor fabrication. [ABSTRACT FROM AUTHOR]

Polypyrrole-grafted nitrogen-doped graphene (PPY-g-NGE) was successfully synthesized by simultaneous modification of graphene through nitrogen doping and polymeric grafting, and used for the detection of paraquat (PQ). The chemical structure, morphology and interaction of the obtained PPY-g-NGE were verified by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The PPY-g-NGE modified glassy carbon electrode (GCE) was fabricated to investigate its electrochemical behavior and sensitive detection of PQ by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the novel PPY-g-NGE modified GCE exhibited excellent electrochemical performance and electrocatalytic activity to the redox reaction of PQ, with comparison to NGE and non-grafted composite of PPY-NGE. The two reduction DPV peaks of PQ at −0.60 V and −1.00 V were significantly enhanced at the PPY-g-NGE modified electrode. Under the optimized condition, the reduction peak currents of PQ at the PPY-g-NGE modified electrode were linear over the concentration range from 5.00 × 10 −8 to 2.00 × 10 −6 M with detection limits of 41 nM and 58 nM for Peak 1 and Peak 2, respectively. Besides the good sensitivity, the sensor also exhibited fine stability and strong anti-interference ability due to the well-combination and synergistic effect of polypyrrole and nitrogen doped graphene. [ABSTRACT FROM AUTHOR]

A simple and sensitive label-free electrochemical biosensor for nimodipine was fabricated by using nitrogen-doped graphene (NGE) modified electrode. The surface morphology and electron transfer behavior of the modified electrodes were studied by scanning electron microscopy and electrochemical impedance spectroscopy, respectively. The electrochemical behaviors of nimodipine at the modified electrodes were investigated by using cyclic voltammetry. On the basis of the excellent electrocatalytic activity of NGE, an obvious cathodic peak of nimodipine could be caused at the NGE modified glassy carbon electrode (GCE), moreover, the electrochemical signal was greatly enhanced compared with the undoped graphene modified GCE. Under the optimized conditions, the present sensor showed excellent performances for nimodipine detection including wide linear range of 0.02–3 μM, low detection limit (9.1 nM), good selectivity to the general coexisted interferences, etc. The proposed biosensor was also successfully applied to validate its capability for the analysis of nimodipine in tablets. The work would promote the potential application of NGE as an excellent material in fabricating electrochemical sensors for chemical or biochemical analysis. [ABSTRACT FROM AUTHOR]

Poly(3-methylthiophene)/nitrogen doped graphene modified glassy carbon electrode (P3MT/NGE/GCE) was prepared through simple drop-casting of NGE, followed by the electrodeposition of P3MT film for sensitive electrochemical determination of trace amounts of pesticide phoxim. The morphology and structure of P3MT/NGE/GCE were characterized by scanning electron microscopy; the electrochemical behavior of P3MT/NGE/GCE was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and chronocoulometry. The preparation conditions of modified electrode, the dropping amount of NGE and polymerization laps of P3MT, were optimized. Under the optimized conditions, the reduction peak current of cyclic voltammetric curve varied linearly with the concentration of phoxim over the two linear ranges of 0.02–0.2 μM and 0.2–2.0 μM, and the low detection limit was 6.4 nM according to lower linear range (S/N = 3). The sensor also exhibited excellent selectivity to phoxim over a wide range of possible interferents including ions, biomolecules, common environment pollutants and widely-used organophosphate pesticides. Moreover, the satisfactory practical feasibility of the sensor was evaluated by the environmental phoxim measurements. [ABSTRACT FROM AUTHOR]

Highlights: [•] PEDOT/NGE modified electrode was fabricated via CV method using nitrogen-doped graphene (NGE) coated GCE. [•] Highly reversible and well-separated redox couples of hydroquinone (HQ) and catechol (CT) were obtained at PEDOT/NGE/GCE. [•] A facile electrochemical sensor based on PEDOT/NGE/GCE was developed for simultaneous detection of HQ and CT. [Copyright &y& Elsevier]

Rational design of transition metal catalysts with robust and durable electrocatalytic activity for hydrogen evolution reactions (HER) is extremely important for renewable energy conversion and storage, as well as water splitting. Heteroatom doping has emerged as a feasible strategy for enhancing electrocatalytic activity. Here, cobalt nanoparticles (Co-NPs) were coated with nitrogen-doped carbon nanotubes (NCNTs) prepared via an in situ growth on accordion-like Ti 3 C 2 T x -MXene (Co-NCNT/Ti 3 C 2 T x). Such an intriguing structure showed great features: abundant anchoring sites for NCNT in situ growth, intimate integration of Co-NPs and NCNTs, high-speed electron transfer between 1D NCNTs and 2D Ti 3 C 2 T x -MXenes, and a large number of effective catalytic active sites. This Co-NCNT/Ti 3 C 2 T x hybrid catalyst was demonstrated to possess excellent HER performance with low overpotential (η 10 , 190 mV), small Tafel slope (78.4 mV dec−1), large electrochemically active surface area, and good long-term stability, thus outperforming many reported electrocatalysts. The present strategy provided a facile route for the design of transition metal HER catalysts with NCNT and MXene. [Display omitted] • The 3D Co-NCNT/Ti 3 C 2 T x catalysts are prepared by a bottom-up approach. • The Ti 3 C 2 T x sheets was connected by NCNT, and high surface area was obtained. • The interconnected porous network is feasible to the high-speed charge transfer. • The as-prepared catalysts possesses superior electrocatalytic ability towards HER. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) plays a key role in the application of fuel cells. Here, we used shaddock peel to fabricate a set of N, P dual-doped hierarchical porous carbons, abbreviated as NPSPs, where the carbons were carbonized, activated and dual-doped via a simple one-step pyrolyzation. Contrast results indicate the contents of pyridinic-N, graphitic-N and P–C species increase with the rising of temperatures, and the temperature also affects the degree of graphitization, surface area, morphology, thus influences the ORR performance. More importantly, the NPSP-900 demonstrates an outstanding ORR activity with a comparable half-wave potential (0.83 V vs. RHE) and higher current density with respect to commercial Pt/C, following 4e transfer pathway. Our work illustrates that NPSP-900 is a promising cathode for fuel cells because of its simple preparation, waste utilization, excellent ORR performance, good methanol tolerance and superior stability. Image 1 • One-step pyrolysis can accomplish carbonization, activation and N,P-dual doping. • NPSPs own hierarchical porous structures with high BET surface areas. • Higher temperature can enhance ORR activities with improved doping N/P species. • NPSP-900 owns a close ORR activity compared with Pt/C, following 4e transfer way. • NPSP-900 shows a remarkable methanol tolerance and superior stability. [ABSTRACT FROM AUTHOR]

Abstract Oxygen reduction reaction (ORR) and Lithium storage both play the key roles in energy conversion and storage devices. Here, we report a honeycomb-like nitrogen-doped carbon derived from enteromorpha algae (N-EA), using a one-step pyrolysis process at only 600 °C to simultaneously achieve doping, carbonization and activation. After anchoring CoFe 2 O 4 on N-EA, CoFe 2 O 4 /N-EA, not only inherits the high surface area, porous structure, active nitrogen species from N-EA, but also benefits from the active sites and high theoretical specific capacity of Li storage from CoFe 2 O 4. The synergistic effect makes CoFe 2 O 4 /N-EA an alternative catalyst to commercial Pt/C for ORR with superior activity and stability. Moreover, CoFe 2 O 4 /N-EA exhibits a remarkable cycle performance with a 100% capacity retention (∼900 mAh g−1) after 500 cycles at 0.5 A g−1. Green preparation, waste utilization, good ORR performance and Li storage property of CoFe 2 O 4 /N-EA could make it a promising candidate for fuel cells and LIBs. [ABSTRACT FROM AUTHOR]

Abstract Sandwich-like ZIF-8 nanocrystal derived N-doped carbon decorated graphene sheets are developed through in-situ growth and followed by a thermal annealing treatment. The sandwich-like N-doped carbon decorated graphene sheets (NCGs) contain graphene substrate and the carbon nanoparticles with 30–50 nm in size. The sandwich-like NCGs generate a large specific surface area of 816.4 m2 g−1. With the high surface area and nitrogen doping, the as-fabricated NCGs as electrode materials for supercapacitor exhibit high specific capacitance of 225.0 F g−1 at 0.5 A g−1, an enhanced rate capability and excellent electrochemical stability with 96.8% retention after 10000 cycles even at 10 A g−1. The symmetry supercapacitor based on NCGs delivers an energy density of 12.7 Wh kg−1 at a specific power of 447 W kg−1. When the power density increases to 15126 W kg−1, the energy density can still keep 6.5 W h kg−1. Furthermore, the symmetry supercapacitor shows an excellent cycle stability with 96.6% capacitance retention at 2 A g−1 after 10000 cycles. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

We report a novel method adopting two RF fields to simultaneously excite 85Rb and 87Rb isotopes for an MZ type atomic magnetometer. The MZ magnetometer adopts a 6 mm3 microfabricated vapor cell with natural abundance rubidium and 0.74 amagat nitrogen as buffer gas inside. The excessively broadened magnetic resonance signals of the two rubidium isotopes overlap with each other and cause deterioration in accuracy and sensitivity performance. To solve this problem, a Double-RF Field Method (DRFM) is proposed, which adopts two RF fields with a central frequency ratio of 2:3. Compared with traditional Single-RF Field Method (SRFM), the DRFM reduces the detection error by over 50% and improves the sensitivity by more than 10%. The experiments are conducted at three temperatures and under various static magnetic fields. Theoretical models are also built to discuss the performance improvement of the magnetometer by the DRFM against the SRFM. This method provides a way to improve the performance of chip-scale MZ atomic magnetometers with low cost natural abundance rubidium. [ABSTRACT FROM AUTHOR]

Tin-based metal oxides usually suffer from severe capacity fading resulting from aggregation and considerable volume variation during the charge/discharge process in lithium ion batteries. In this work, a novel nanocomposite (MTO/N-RGO) of hollow amorphous MnSnO 3 (MTO) nanoparticles and nitrogen-doped reduced graphene oxide (N-RGO) has been designed and synthesized by a two-step method. Firstly, the nitrogen-doped graphene nanocomposite (MTO/N-RGO-P) with MnSn(OH) 6 crystal nanoparticles was synthesized by a facile solvothermal method. Subsequently, the MTO/N-RGO nanocomposite was obtained through the post heat treatment of MTO/N-RGO-P. The designed heterostructure and well-combination of the hollow amorphous MTO and N-RGO matrix can accelerate the ionic and electronic transport, and simultaneously accommodate the aggregation and volume variation of MTO nanoparticles during the lithiation–delithiation cycles. The as-prepared hybrid of MTO and N-RGO (MTO/N-RGO) exhibits a high reversible capacity of 707 mAh g −1 after 110 cycles at 200 mA g −1 , superior rate capability, and long-term cyclic life with high capacity of 610 mAh g −1 over 1000 cycles at 400 mA g −1 . Superior capacity retention of 97.3% over 1000 cycles was obtained. This work opens new opportunities to fabricate the high-performance electrode materials with heterostructure for lithium storage systems, especially for novel multi-metal oxide based nanocomposites with high cycling stability. [ABSTRACT FROM AUTHOR]