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[en] A polycrystalline boron-doped diamond (BDD) electrolyte solution-gate field effect transistor (SGFET) for use as a pH sensor was developed. The polycrystalline diamond films with a boron-doped layer possessed semiconducting properties that were comparable to hydrogen-terminated non-doped diamond. The hydrogen-terminated BDD surface was successfully transferred to a partially oxygen-terminated surface by ozone exposure, and its SGFET current–voltage (I–V) characteristics were evaluated with bias voltages within the potential window of diamond. The drain-source current(Ids)–drain-source voltage(Vds) characteristics showed pinch-off and saturation. In addition, they stably operated in electrolyte solutions with pH values from 2 to 12. The transfer characteristics exhibited a pH sensitivity of approximately 30 mV/pH, which is comparable with the pH sensitivity of the conventional oxygen-terminated non-doped SGFET and the single-crystal BDD SGFET investigated in our previous work. Furthermore, the BDD SGFET exhibited improved long-term stability, and the coefficient of variation (CV) of Ids for 10 months was up to 10%.
[en] Highlights: • Dissolved O_2 molecules in H_2O-EG system react with carbon atoms on GO sheets. • EG in mixed solvents reduces holey GO into holey graphene sheets. • Holey graphene sheets assemble into aerogel at higher GO concentration. • The aerogel built with holey graphene show improved ion transport property. - Abstract: A green yet effective solution-based route for scalable preparation of holey graphene was developed by solvothermal reaction of graphene oxides (GO) in water-ethylene glycol system (H_2O-EG). The O_2 molecules dissolved in H_2O-EG system was found to serve as a moderate oxidant which can oxidize partial carbon atoms on GO sheets, leaving behind nanopores on graphene sheets. Importantly, by increasing the GO concentration to 2.0 mg mL"−"1, these holey graphene sheets can assemble into macroscopic aerogel (HGA). Benefiting from the in-plane nanopores, HGA showed much improved surface area as compared with the graphene aerogel built with non-holey graphene sheets (GA). The electrochemical characterization results showed that holey graphene sheets in HGA contributed to a higher specific capacitance, an improved rate capability and faster ion kinetic when serving as binder-free supercapacitor electrode.
[en] Porous hierarchical LiMn_0_._5Fe_0_._5PO_4 spheres were synthesized via a novel template-engaged method using pre-synthesized hollow spherical Li_3PO_4 as template and FeCl_2·4H_2O/MnCl_2·4H_2O as Fe"2"+/Mn"2"+ source. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the porous hierarchical spheres exhibit hollow structure and have a size distribution of 0.4–1 um consisting of aggregated ∼50 nm nanoparticles. A mechanism of the reaction from Li_3PO_4 to LiMn_0_._5Fe_0_._5PO_4 was proposed on the basis of the phase and morphology transformation of the intermediates. With the short Li"+ diffusion path and porous structure, the carbon coated LiMn_0_._5Fe_0_._5PO_4 spheres show high specific capacity and superior rate capability with the discharge capacities of 159.3 mA h g"−"1 at 0.1C and 80.6 mA h g"−"1 at 20C. The porous hierarchical spheres also exhibit an excellent cycling stability with about 90.7% of the initial value at 1C after 100 cycles.
[en] Highlights: • ECL properties of NGQDs were investigated. • QDs induced ECL enhancement was discovered in homogenous solution. • The enhancement is free of electrode modification. • CdTe/CdS QDs enlarge 21-fold of the ECL intensity toward NGQDs. • Applied for ascorbic acid detection in fruits. - Abstract: Herein, a CdTe/CdS QDs (with a CdTe core and a CdS shell) amplified electrogenerated chemiluminescence (ECL) of nitrogen functional graphene quantum dots (NGQDs) platform is reported. The utilization of CdTe/CdS QDs could facilitate the production of NGQDs radical, and then, a high yield of NGQDs* was formed due to the interaction of NGQDs radical with O_2·"−, leading to an ∼21-fold ECL enhancement. This ECL enhancing system does not require the addition of coreactant and modification of electrode which is carried out in homogeneous solution. Benefiting from the remarkable ECL enhancement effect, a feasible and sensitive ECL sensor was constructed for ascorbic acid (AA) quantification. The proposed method features a detection limit of 70 nM with a linear calibration range from 100 nM to 100 μM, and exhibits good stability, practicability, and acceptable fabrication reproducibility, showing promising application in real-sample.
[en] The mechanisms of the electrochemical oxidation of orientin and its interaction with deoxyribonucleic acid have been investigated using glassy carbon electrode. The electrochemical response of orientin is due to oxidation of phenolic hydroxyl groups on orientin. The whole process is controlled by the adsorption step and concerned 4 electrons and 4 protons. Negative shift of potential and decrease of peak current for electrochemical oxidation of orientin can be observed at bare glassy carbon electrode and deoxyribonucleic acid modified electrode in 0.05 M Na_2HPO_4-KH_2PO_4 (pH 7.48), confirming the dominant electrostatic interaction between orientin and deoxyribonucleic acid. Moreover, a reliable and sensitive method of reversed-phase high-performance liquid chromatography-electrochemical detection has been developed for simultaneous determination of the isomer pair orientin/isoorientin. Chromatographic separation was carried out on a reversed-phase C_1_8 column and a mobile phase comprised of acetonitrile and acetate (0.5%, pH 2.97) by amperometric detection with a glassy carbon electrode at the working potential of +1.00 V. The method was validated for linearity, accuracy, precision, and limit of detection. Under the optimized conditions, linear regression analysis for the calibration curve showed a good linear relationship between peak area and their concentrations in the linear range of 89.2 nM to 59.5 μM for orientin with detection limit of 14.9 nM and 78.0 nM to 52.0 μM for isoorientin with a detection limit of 13.0 nM, respectively. Compared to the method using ultraviolet detection, the detection limits are greatly lowered. Finally, the proposed method has been successfully applied to the determination of orientin and isoorientin in Lophatherum gracile Brongn.
[en] Mechanochemical synthesis of non-platinum group metal catalysts for fuel cells is shifting the synthesis paradigm away from liquid chemistry to materials processing that is more benign and scalable for manufacturing. Mechanochemical synthesis is practiced in conjunction with the sacrificial support method for the preparation of Fe- Methylenediantipyrine (Fe-DAAPyr) cathode catalysts. This is a new catalyst from the transition Metal-Nitrogen-Carbon family, which is viewed as the most promising for practical applications and technology introduction. Detailed characterization using scanning electron microscopy, X-ray photoelectron spectroscopy and rotating ring disk electrode reveals correlations between activity and structural properties defining the differences in the mechanism of the oxygen reduction reaction (ORR) in acid and alkaline media. In an alkaline environment, an outer-sphere electron transfer is facilitated by the presence of hydroxyls rather than the contribution of active centers established from structure-to-property correlations found in acid. In acid, an increase in the numbers of defect sites, manifested by the presence of carbon oxides, leads to the increase in ORR activity.
[en] We demonstrate a method for incorporating plasmon metallic nanoparticles in hierarchical rutile TiO_2 clusters (RTC) assembled from single-crystal nanospindles. The RTC could efficiently improve the diffusion of the photoelectrons, which can be ascribed to the improvement of the connectivity by bridging the neighbouring microflowers through the single-crystal nanospindles. But not all the nanospindles are tightly interconnected, hence organic colloid has been prepared for post-treatment of the device based on RTC by the generation of TiO_2 nanoparticles. When added into Au nanoparticles, localized electric fields can be produced, because Au can excite dye molecules more intensively than incident far-field light. The surface plasmon synergistic effect had been investigated by Uv-vis absorption spectrum of Au@ organic colloid and the relative change of the IPCE. As a result, the cell based on RTC exhibits an overall conversion efficiency of 7.68%, indicating a 17% promotion compared with that derived from commercial P25 (6.58%) which could be ascribed to faster electron transfer of single-crystal nanospindles. With the Au nanoparticles incorporation in RTC, the device achieves a conversion efficiency of 9.15%, resulting in a 11% increase compared to the RTC device post-treated by organic colloid without Au nanoparticles (8.24%), which is attributed to the surface plasmon synergistic of Au nanoparticles.
[en] N-doped mesoporous carbon was prepared by a one-step method of pyrolyzing the mixture of milk powder and potassium hydroxide without templates. The N-doped mesoporous carbon (NMPC) with microporous and mesoporous had a specific surface area of 2145.5 m"2 g"−"1 and a pore volume of 1.25 cm"3 g"−"1. X-ray photoelectron spectroscopy analysis showed that the nitrogen content of NMPC was 2.5 at%. The NMPC exhibited a high specific capacitance (396.5 F g"−"1 at 0.2 A g"−"1) and excellent stability (capacitance retention of 95.9% after 2000 cycles at 50 mV s"−"1) as a supercapacitor electrode material. Moreover, the NMPC as a fuel cell cathode catalyst also showed effective activity for oxygen reduction reaction in alkaline solution. The results demonstrate that the NMPC is a promising electrode material for supercapacitors and fuel cells.
[en] Highlights: • A novel hollow mesoporous ternary @M-TiN/N-G/Pt electrocatalysts were synthesized. • The @M-TiN/N-G/Pt electrocatalysts displayed outstanding activity and stability toward MOR and ORR. • The activity and stability of @M-TiN/N-G/Pt electrocatalysts were higher than Pt/TiN, @M-TiN/Pt, and Pt/C catalysts. • The excellent electrocatalytic performance rooted in its unique configuration. • Several reasons were proposed to explain the enhanced electrocatalytic performance of @M-TiN/N-G/Pt. - Abstract: A novel hollow mesoporous TiN/N-graphene (N-G) hybrid architecture (@M-TiN/N-G) composed of N-doped graphene wrapped mesoporous TiN nanoparticle shells was constructed for the first time. It can be used as an efficient support for creating a highly efficient ternary @M-TiN/N-G/Pt electrocatalyst with superior catalytic activity and stability for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) through decorating well-dispersed Pt nanoparticles on @M-TiN/N-G surface. By optimizing the content of N-G in catalysts, the @M-TiN/N-G/Pt catalysts display superior catalytic activity and stability toward MOR and ORR to traditional Pt/C and graphene-free Pt/TiN and @M-TiN/Pt catalysts. The various characterization results reveal that the outstanding electrocatalytic performance of @M-TiN/N-G/Pt catalyst roots in its large surface area, high porosity, strong interaction among Pt, TiN, and N-G, excellent electron transfer property facilitated by N-doped graphene, and small size of Pt and TiN nanocrystals. The synthetic approach may be available for constructing other graphene based hollow metal nitrides, carbides, and phosphides for various electrocatalytic applications.
[en] Ultrasmall molybdenum carbide (MoC) nanocrystals coupled with reduced graphene oxide (RGO) hybrid was successfully synthesized and applied as support for Pt nanoparticles (Pt/MoC-RGO). Compare to the commercial Pt/C, the Pt/MoC-RGO catalyst show remarkable enhanced electrocatalytic activity for methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). The peak current density of Pt/MoC-RGO is 2.4 times of Pt/C. The Pt/MoC-RGO also shows a significant improved CO resistance ability, which likely originates from the abundant Pt-MoC-RGO three-phase interfaces in Pt/MoC-RGO. The long-term stability results show that the electrochemical durability of the Pt/MoC-RGO for MOR is much better than Pt/C, making it a promising next generation electrocatalysts in DMFCs. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analyses reveal the strong synergetic chemical coupling interaction between the Pt nanoparticles and MoC-RGO, which result in significantly enhanced electrocatalytic activity for MOR.