查看更多>>摘要：A green electrochemical method was developed for the synthesis of new types of spiro and dispiro pyrimidine derivatives. The electrochemical generation of reactive intermediates from para-nitrophenol (PNP) and their reactions with barbituric acids (BA1-BA3) is a key step in the formation of target products (P1-P3). Our data show that the reactivity of the nucleophile (barbituric acids) plays an important role in the type of product. Accordingly, when barbituric acid (BA1) or thiobarbituric acid (BA2) is used as a nucleophile, dispiro product (P1 or P2) is formed in a convergent paired electrochemical reaction. However, when 1,3-dimethylbarbituric acid (BA3) is used as a nucleophile, due to its higher reactivity than BA1, the final product is an spiro compound that results from the reaction of BA3 with cathodically generated para-nitrosophenol. The highly symmetric dispiro and spiro compounds (P1-P3) have been successfully synthesized in a water/ethanol mixture at the carbon electrode in an undivided cell using the constant current electrolysis method. Also, the antibacterial tests indicated that the products P1-P3 showed good antibacterial performance against gram-positive bacteria (Bacillus cereus and Staphylococcus aureus). In this work, we synthesized a number of new spiro and dispiro pyrimidine compounds (P1-P3) using a convergent paired electrochemical method, by electrolysis of PNP in the presence of barbituric acids (BA1-BA3), under mild and green conditions for the first time.
查看更多>>摘要：Efficient, low-cost and stable eletrocatalysts for oxygen evolution reaction (OER) is critical in commercial largescale water electrolysis. Herein, a 3D self-supporting porous NiFe2O4-Ni3P-Fe2P film with sea urchin-like structure was fabricated by one-step electrodeposition, phase separation during the annealing, and selective oxidation thermal treatment. The multi-phase NiFe2O4-Ni3P-Fe2P film exhibited superior OER elerocatalytic activity and the long-term stability in alkaline solution. The overpotentials were 102 and 641 mV at current densities of 10 and 200 mA cm-2, respectively. The Tafel slope was 42 mV dec-1. The excellent performance could be attributed to the plentiful active sites provided porous sea urchin-like structure, the good conductivity of NiFe2O4, the synergetic effect of multiphase structure and the superior wettability. The features of NiFe2O4Ni3P-Fe2P film display promising application potential in the field of electrochemistry.
查看更多>>摘要：The simultaneous determination of growth regulator daminozide (DMZ) and its degradation product N,N-dimethylhydrazine (DMH) via their direct electrochemical oxidation was investigated for the first time and the mechanism of DMZ oxidation has been proposed. With regard to the very positive values of the oxidation potentials of both substances, a boron doped diamond electrode (BDDE) was used as the working electrode and Britton-Robinson buffer of pH 9 was applied as the suitable supporting electrolyte. First, a differential pulse voltammetric method for DMZ determination was developed, which provided a very low detection limit (LOD = 4.56 x 10(-7) mol L-1). DMH could also be determined under the same experimental conditions (LOD = 2.16 x 10(-7) mol L-1). The proposed extraction technique then allowed the determination of concentrations up to 50 times lower. In case of the mixture analysis, while the determination of DMH was not affected by the presence of DMZ, the results of the DMZ analysis were significantly influenced by the presence of its degradation product. Therefore, a method for removing DMH from a sample was also developed in this work. Finally, real samples of a commercially available pesticide preparation and spiked natural and rinsing waters were successfully analyzed.
查看更多>>摘要：Supercapacitors are one of the most frequently explored devices for energy storage applications. In comparison with conventional dielectric capacitors, supercapacitors have energy storage capacities several orders of magnitude higher, however much lower than those of secondary batteries. Their long-life cycles, high power densities, and relatively less carbon footprint over their counterparts have encouraged industries to explore and build reliable energy systems for the future. One family of materials that have garnered attention for supercapacitor applications since their discovery in 2011 are 2D transition metal carbides and nitrides (MXenes). Unlike 3D carbon, which possesses complex ion diffusion pathways, 2D nanosheets directly offer large active sites to the electrolyte. With a high surface area, shorter ion diffusion pathways, and high conductivity, MXenes enhance the energy storage characteristics of a supercapacitor. The key to high rate pseudocapacitive energy storage in MXene electrodes is the hydrophilicity of MXenes combined with their metallic conductivity and surface redox reactions. In this review, we have explored different types of supercapacitors, charge storage mechanisms, and modified synthesis methods of MXene and its properties. Finally, we discuss the advancement in this field while evaluating future challenges and prospects of MXene composites, which will provide a guide for developing high-performance MXene-based energy storage devices with high throughput and sustainable derivatives.
Santos, Aymara da SilvaPires Mecca, Carolina ZeniFerreira, Tiago LuizSimoes, Fabio Ruiz...
7页
查看更多>>摘要：The use of pesticides has been increased to obtain higher agricultural yields, prevent the proliferation of harmful organisms and ensure durability in food storage. The inappropriate use of these substances present risks to the environment and human health, and in the presence of metal ions can interact, forming complexes with different properties. Thus, in this work, the interaction between the metal ion Pb2+ and carbendazim was evaluated by electrochemical techniques using a glassy carbon electrode. The metal ion Pb2+ showed a reduction peak at - 0.570 V, and, in systematic studies in the presence of CBZ, this peak shifted to a more negative potential, indicating the complex formation. The K-f value founded for the complex formed was 4.5 x 10(16) , and the estimated proportion metal:pesticide was 1:3.7, using the data collected from these experiments. On the other hand, CBZ showed an oxidation peak at 0.989 V and a reduction peak at 0.919 V, with the characteristic of a quasi-reversible process. A shift of the oxidation peak to less positive potentials was observed when in the presence of the metallic ion. Furthermore, experiments on the analysis of carbendazim in the presence of Pb2+ were performed in aqueous solutions and natural water, indicating that the metal ion affects the electrochemical signal of the pesticide. The electrochemical impedance spectroscopy results showed that Pb2+ ions do not interfere in the electrochemical double layer during oxidation of carbendazim, indicating that the interaction between the metallic ion and the pesticide occurs in solution. The analyses performed using samples of natural water showed an increase in charge transfer resistance without alteration of the electrical double layer or significant changes in the oxidation potential of the pesticide. The results showed that the electroanalytical method is feasible for the analysis of CBZ in the presence of Pb2+ and analysis of the influence of the metal on the electrochemical response of the pesticide, with low sample preparation.
查看更多>>摘要：In this study, we have fabricated a flexible supercapacitor with outstanding pseudocapacitive performance using hierarchical CoMoO4/CoMoO4 core/shell dandelion-like nanoarrays. The dandelion-like CoMoO4/CoMoO4 nanostructure electrode yields a high specific capacitance (1548 F g(-1) at a current density of 1 A g(-1)) and superior cycling stability performance (94% capability retention after 5000 cycles at 8 A g(-1)) in the 3 mol L-1 KOH solution. Furthermore, a flexible asymmetric supercapacitor device was assembled based on nickel foam/CoMoO4/CoMoO4 dandelion-like as positive electrode and activated carbon (AC) as negative electrode. The CoMoO4/CoMoO4 nanostructure//AC asymmetric supercapacitor device represents remarkable electrochemical performance such as good specific capacitance of 152 F g(-1) and maximum energy and power densities of 54.04 Wh kg(-1) and 8.83 kW kg(-1), respectively. These encouraging results depict great potential in developing energy storage devices by making heterostructure nanomaterials.
Kuzikov, Alexey, VFilippova, Tatiana A.Masamrekh, Rami A.Shumyantseva, Victoria V....
8页
查看更多>>摘要：An electrochemical method for the quantitative determination of (S)-7-hydroxywarfarin as a metabolite of the vitamin K antagonist warfarin has been developed to analyze the catalytic activity of cytochrome P450 2C9 (CYP2C9). The electrochemical properties of (S)-7-hydroxywarfarin were investigated using screen-printed carbon electrodes. We have shown by cyclic voltammetry that irreversible (S)-7-hydroxywarfarin electrochemical oxidation, in contrast to (S)-warfarin, can be registered by an oxidation peak at approximately 0.6 V (vs. Ag pseudo-reference electrode). A linear dependence of the oxidation peak amplitude in the range of 0.57-0.61 V on (S)-7-hydroxywarfarin concentration (in the range of 0.1-1 mu M) was shown by the square-wave voltammetry method. The limit of (S)-7-hydroxywarfarin detection and the sensitivity were calculated as 0.091 mu M and 0.0075 A/M, respectively. Using an electrochemical system based on recombinant human CYP2C9 immobilized on screen-printed carbon electrodes modified by didodecyldimethylammonium bromide, we have shown the possibility of (S)-7-hydroxywarfarin electrochemical quantification without separation of the enzymatic system component. The (S)-7-hydroxywarfarin quantitative electrochemical determination was used to calculate the kinetic parameters of CYP2C9 immobilized on electrode toward (S)-warfarin: the values of the maximal reaction rate (Vmax) and the Michaelis constant (KM) were calculated as 0.1 +/- 0.002 min-1 and 3.03 +/- 0.38 mu M, respectively. The usage of an enzymatic CYP2C9-containing electrode as a catalyst and an indicator electrode as a sensor for the formation of metabolite allows to effectively register the kinetic parameters of the process. Such a two-electrode system can be applied to assess drug-drug interactions.
查看更多>>摘要：In this research, the micro-morphologies, electrochemical behaviors and battery discharge performances of the Mg-2Zn-xCa alloys as potential anode materials were investigated. The micro-morphology results showed that for the alloy with low Ca content (x = 0.1 and 0.2), only the Ca2Mg6Zn3 phase was observed to precipitate in a punctate form within the crystal. As the Ca content rose, the amount of the punctate Ca2Mg6Zn3 increased while the strip-shaped Ca2Mg6Zn3 phase precipitated at the grain boundary was also observed. When the Ca content reached 0.5 wt% and higher, the second phases were observed to be both Mg2Ca and Ca2Mg6Zn3 phase which precipitated at the grain boundary and the morphology of second phases gradually changes into a con-tinuous network. Among the four tested alloys, the Mg-2Zn-0.2Ca sample delivered the best electrochemical activity with more negative corrosion potential and larger corrosion resistance in electrochemical experiments. Battery performance tests showed that the Mg-2Zn-0.2Ca anode exhibited an improved specific capacity of 1344.1 mAh g(-1) and high anodic efficiency of 61.0% at 10 mA cm(-2). The discharge order of the precipitated phase has been derived as follows: Mg2Ca > Mg > Ca2Mg(6)Zn(3).
查看更多>>摘要：To enhance the solar photoelectrocatalytic water splitting, an effective photoanode was designed by electrophoretic depositing of graphene oxide (GO) on FTO/c-TiO2/Bi@g-C3N4. The photoelectrocatalytic performance of g-C3N4 was improved by Bi doping and GO loading as a cocatalyst on the surface of photoanode through the efficient charge cascade to increase an effective charge separation and reduce activation barriers for oxygen evolution reaction. The current-potential curve of Bi@g-C3N4/GO displayed about five and two times more photocurrent density (0.3 mA cm(-2) at 1.23 V vs RHE) with respect to those of g-C3N4 and Bi@g-C3N4, following with a 110 and 80 mV cathodically shifted onset potential, respectively. The conduction band edge was calculated using the flat band potential of the photocatalysts which was estimated by Butler-Gartner model. GO loading leads to yield the photo-voltage of 176 mV compared with 81 and 113 mV for g-C3N4 and Bi@g-C3N4, respectively. The optimum of thickness of GO cocatalyst was 0.9 mu m. If the thickness exceeds this optimum value, the recombination centers increase and active sites of photocatalytic layer are blocked. The charge separation and injection efficiency for Bi@g-C3N4/GO photoanode were determined by using H2O2 as an effective hole scavenger. Among fabricated electrodes, Bi@g-C3N4/GO electrode represented the lowest charge transfer resistance. The results showed that much improvement in photoelectrocatalytic per-formance was achieved by GO loading on the surface of photoanode with respect to Bi doping in the structure of photocatalyst.
Komkova, Maria A.Zarochintsev, Alexander A.Karyakin, Arkady A.
5页
查看更多>>摘要：Prussian Blue based nanozymes are able to catalyze reduction of organic peroxides similarly to the enzyme peroxidase. For the whole range of peroxides under study the catalytic rate constant for 3,3',5,5'-tetramethylben-zidine in case of nanozymes is significantly higher as compared to horseradish peroxidase. Moreover, the selectivity of nanozymes towards hydrogen peroxide relatively organic peroxides reduction is higher than that for the enzyme, which can be explained in terms of different ability of peroxides to penetrate to the bulk of catalytically synthesized Prussian Blue nanoparticles. On the contrary, selectivity of Prussian Blue film modified electrodes is much lower and even negligible among hydrogen, urea and methyl ethyl ketone peroxides. An ability to tune the selectivity would allow individual detection of peroxides in their complex mixtures with Prussian Blue nanostructures.
NSTL
Elsevier