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1.
A kind of aromatic diamine, 4′, 4″-(2, 2-diphenylethene-1, 1-diyl)dibiphenyl-4-amine (TPEDA), was successfully synthesized via Suzuki coupling reaction. The TPEDA containing nonplanar rigid moieties can be used as epoxy resins curing agent to improve the complex properties of cured composites. The curing kinetics during thermal processing of E51/TPEDA system was investigated by nonisothermal differential scanning calorimeter. The average activation energy (E α), pre-exponential factor (lnA), and reaction order (n) calculated from the Kissinger, the Ozawa, the Friedman and the Flynn–Wall–Ozawa methods were 55.8 kJ mol?1, 9.4 s?1 and 1.1, respectively. By the aid of estimated kinetic parameters, the predicted heat generation vs temperature curves fit well with the experimental data, which supported the validity of the estimated parameters and the applicability of the analysis method used in this work. By the introduction of nonplanar rigid moieties, the cured epoxy resins with TPEDA exhibited a higher glass transition temperature (T g = 258 °C), good thermal stability (≈395 °C at 10 % mass-loss), and high char yield (36.6 % at 700 °C under nitrogen) compared with conventional curing agents.  相似文献   

2.
The application of nonstoichiometric chromium oxide-based thin film cathodes in lithium rechargeable and primary batteries operating at high rates has been demonstrated. Films of varying composition have been obtained by anionic Cr (VI) species electrodeposition on a 1X18N10Т grade stainless steel cathode from fluoride-containing electrolytes. The effect of film doping by Li+ ions during its electrosynthesis has been сonsidered. As-prepared films were studied by scanning and transmission electron microscopies, 3D optical profiler, thermogravimetric analysis, chemical analysis, and X-ray diffraction (XRD). The main phase components of the electrodeposited films regardless of Li+ in an electrolyte are Cr2O3, α-CrOOH, β-CrOOH, and metallic chromium as shown by XRD pattern refinement. The electrochemical reduction rate in a non-aqueous electrolyte (1 M LiClO4 in PC/DME) correlates with the chromium oxide-hydroxide component content of film. Primary CrO x -Li CR2325 mock-up cathode coating can be discharged in a pulsed mode at 10 Ω external resistance with 80–84 mA cm?2 current densities for 10–100 ms. Thin film cathodes electrodeposited in the presence of lithium ions become rechargeable when the lithium content of the film reaches 0.02 wt.%. Mock-ups of CR2325 coin battery with a thin film cathode doped with lithium ions can be discharged more than 40 times with 136 mAh g?1 specific capacity, 461 Wh kg?1 specific energy and 154 W kg?1 power density at 30 kΩ external resistance. The simplicity of thin film preparation makes this technology promising for thin film lithium batteries.  相似文献   

3.
A novel boron–silicon hybrid polymer (PASB) was synthesized from polycondensation between phenylboron dichloride and dichloromethylsilane with Grignard reagent. The structure of PASB was characterized using fourier transform infrared spectra, 1H-NMR, 13C-NMR, and gel permeation chromatography. The curing behavior of PASB was investigated by means of non-isothermal differential scanning calorimetry and the kinetic parameters were determined by the Kissinger’s and Ozawa’s methods, respectively. The results showed that both the methods for calculating the activation energy value gave fairly close results of 104.4 and 107.7 kJ mol?1, respectively. A reasonable curing cycle for the resin system was also established, which suggested that it was reasonable to choose a curing temperature between T i0 (452.0 K) and T f0 (554.0 K). These results can provide theoretical guidance reference for determining the curing of the resin system. The thermal stability of cured PASB resin was studied by means of thermogravimetric analysis under nitrogen atmosphere and the temperature of 5 % mass loss (Td5) was 610.1 °C, the residue at 1,000 °C was 87.8 %, which showed that the cured PASB resin exhibited excellent thermal properties and made it potentially useful as high performance matrix resin and precursor for ceramics.  相似文献   

4.
The kinetics of dissociation of bis(2,4,6–tripyridyl-s-triazine) iron(II), ([Fe(TPTZ)2]2+) has been studied in CTAB/chloroform/hexane reverse micellar medium. In the absence of acid, the reaction is immeasurably slow and does not go to completion in conventional aqueous medium but is markedly accelerated and takes place with a rate constant equal to 55.3 × 10?3 s?1 and goes to completion in reverse micelles. The significant increase in rate is attributed to the special properties of the water pool in the reverse micelles like low dielectric constant, nucleophilic effect of Br- ion, and favorable partitioning of TPTZ in the organic phase. The rate of the reaction decreases with increase in W (=[H2O]/[CTAB]) at constant CTAB concentration and remains constant with increase in CTAB at fixed W. The results are compared with other closely related systems.  相似文献   

5.
We have reported the semi conducting and photoelectrochemical properties of SrWO4 prepared by chemical route. The phase purity is confirmed by X-ray diffraction and the oxide is characterized by scanning electron microscopy, diffuse reflectance, and electrochemical impedance spectroscopy. SrWO4 crystallizes in the scheelite structure with an average crystallite size of 378 ± 6 nm. The Raman spectrum gives an intense peak at 920 cm?1 assigned to A g mode while the infrared analysis confirms the hexagonal coordination of tungsten. The UV-visible spectroscopy shows an indirect optical transition at 2.60 eV. SrWO4 exhibits n-type conduction by oxygen deficiency, confirmed by the chrono-amperometry and the intensity potential J(E) curve shows a small hysteresis. The Mott-Schottky plot gives electrons density of 5.72 × 1018 cm?3 and a flat band potential of 0.27 VSCE, indicating that the conduction band derives mainly from W6+: 6s orbital. The electrochemical impedance spectroscopy (EIS), measured in the range (1–105 Hz), shows the predominance of the bulk contribution with a dark impedance of 38 kΩ cm2. As application, the ibuprofen is degraded by electrocatalysis on SrWO4 with a conversion rate of 42%. An improvement up to 77% has been obtained by electrophotocatalysis under UV light; the conversion follows a first order kinetic with a rate constant of 2.32 × 10?4 min?1.  相似文献   

6.
A sensitive electrochemical method was developed for the determination of doxorubicin at a glassy carbon electrode (GCE) modified with a nano-titania (nano-TiO2)/nafion composite film. Nano-TiO2 was dispersed into nafion to give a homogeneous suspension. After solvent evaporation, a uniform film of nano-TiO2/nafion composite was obtained on the GCE surface. The nano-TiO2/nafion composite film modified GCE exhibited excellent electrochemical behavior toward the reduction of doxorubicin. Compared to the reduction of doxorubicin at the bare GCE, the reduction current of doxorubicin at the nano-TiO2/nafion composite film modified GCE was greatly enhanced. Based on this, a novel voltammetric method was applied to the determination of doxorubicin. The experimental parameters that influence the reduction current of doxorubicin, were optimized. Under optimal conditions, a linear response of doxorubicin was obtained in the range from 5.0?×?10?9 to 2.0?×?10?6 mol L?1 (R?=?0.998) and with a limit of detection (LOD) of 1.0?×?10?9 mol L?1(S/N?=?3). The RSD of the measurement is 4.7%, and the RSD of the inter-electrode is of 5.1% which indicate the reproducibility of this method. The current response decreased only by around 3.8% of its initial response after 2 weeks exposing the electrode in air. The procedure was applied to assay doxorubicin in human plasma samples with the recoveries of 94.9–104.4%.  相似文献   

7.
A series of new modified epoxy resin (EP) cured products were prepared from epoxidized soybean oil and commercial epoxy resin, with methyl nadic anhydride as curing agent and 1-methylimidazole as promoting agent. The thermal properties of the resins were characterized by DMA and TG; DSC was used to determine the curing process. Fourier transform infrared spectroscopy was utilized to investigate their molecular structures and scanning electron microscopy was used to observe the micro morphology of their impact fracture surfaces. Tensile and impact testing was employed to characterize the mechanical properties of the cured products. The combination of commercial EP with 20 wt% ESO resulted in a bioresin with the optimum set of properties: 130.5 °C T g, 396.9 °C T 50 %, 74.89 MPa tensile strength, and 48.86 kJ m?2 impact resistance.  相似文献   

8.
Li4Ti5O12 thin films were prepared by solution deposition followed by rapid thermal annealing (RTA). The structural and electrochemical properties of the film were comparatively studied with the one prepared by conventional furnace annealing (CFA) through X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic lithium insertion–extraction experiments, and electrochemical impedance spectroscopy. The results show that the film prepared by RTA is homogeneous, crack-free, and pure spinel phase, and its grain size is smaller than that of the film prepared by CFA. The lithium extraction capacity of the film prepared by RTA is 59.5 μAh cm?2 μm?1, which is higher than 55.9 μAh cm?2 μm?1 of the film prepared by CFA. The capacity loss of the film prepared by RTA after being cycled 50 times is 3.1 %, which is 3.2 % lower than that of 6.3 % for the film prepared by CFA.  相似文献   

9.
Preparation and electrochemical behavior of new hybrid materials composed of multi-walled carbon nanotubes (CNTs) that were derivatized with poly(diallyldimethylammonium) chloride and modified with vanadium-mixed addenda Dawson-type heteropolytungstate, [P2W17VO62]8?, is described here. These nanostructured composite systems exhibited fast dynamics of charge propagation. They were characterized by the transport (effectively diffusional) kinetic parameter of approximately 8?×?10?8 cm?2 s?1/2 and the specific capacitance parameter of 82 F g?1 (at the charging/discharging current of 200 mA g?1). The latter parameter for bare CNTs was found to be only 50 F g?1 under analogous conditions. These observations were based on the results of galvanostatic charging–discharging, cyclic voltammetric, and AC impedance spectroscopic measurements. The improved capacitance properties were attributed to the systems’ pseudocapacitive features originating from the fast redox transitions of the [P2W17VO62]8? polyanions. In addition to the fast redox conduction, the proposed organic–inorganic hybrid materials exhibited interesting electrocatalytic activity toward reduction of bromate in the broad concentration range (sensitivity, 0.24 mA cm?2 mmol?1 dm3).  相似文献   

10.
《Analytical letters》2012,45(13):2148-2155
A new method for phytochelatins by high-performance liquid chromatography (HPLC) was developed based on a condensation reaction with monobromobimane to produce fluorescent derivatives. Glutathione, H-(γ-glutamic acid-cysteine)2-glycine-OH, H-(γ-glutamic acid-cysteine)3-glycine-OH, H-(γ-glutamic acid-cysteine)4-glycine-OH, H-(γ-glutamic acid-cysteine)5-glycine-OH, and H-(γ-glutamic acid-cysteine)6-glycine-OH were well separated, with retention times between 14.68 and 22.0 min. The HPLC method had good linearity (r < 0.9991) between 0.1 mg L?1 and 100 mg L?1. The limits of quantification for the analytes (S/N = 3) were 0.08, 0.3, 0.05, 0.3, 0.5, and 0.8 mg L?1, respectively. The recoveries were between 83.0% and 101.33% with relative standard deviations less than 2%. The reported method is simple, accurate, and suitable for the determination of phytochelatins.  相似文献   

11.
A simple extraction and determination method for folic acid (FA) in lentil samples was developed employing capillary electrophoresis. The analysis was performed in a 75 μm ID fused silica capillary using a running buffer of 10 mM sodium borate (10%, v/v, methanol, pH 9) at +18 kV and a detection wavelength at 200 nm. Methylparaben was used as the internal standard. FA signal response was linear in the range between 1.2 × 10?5 and 4.8 × 10?5 M. Limit of detection (inter-day) was determined at 6.12 × 10?7 M (3.3 σs?1). The amount of FA found in green, red and mignon lentils was found to range between 0.408 and 0.742 mg g?1.  相似文献   

12.
LiMn2O4 thin films were prepared by spin coating through intermediate amorphous layer route (IALR) and intermediate crystallized layer route (ICLR). The phase identification, surface morphology, and electrochemical properties of the films prepared by different crystallization routes were studied by X-ray diffraction, scanning electron microscopy, and galvanostatic charge–discharge experiments. The results show that both films prepared by different crystallization routes are homogeneous and crack free. Compared with the film prepared by IALR, the film prepared by ICLR shows smaller grain size and is smoother and denser. The LiMn2O4 film prepared by ICLR delivers the specific capacity of 39.8 μAh?cm?2?μm?1, which is higher than 35.6 μAh?cm?2?μm?1 for the one prepared by IALR. The capacity loss of the film prepared by ICLR after being cycled 100 times is 3.4 %, which is smaller than that of 5.5 % for the film prepared by IALR. The film prepared by ICLR shows higher specific capacity and better cycling behavior than the one prepared by IALR.  相似文献   

13.
In this paper, we fabricated electrically conductive adhesives using vinyl ester resin and micro silver flakes, and then cured the adhesives by heat without any catalysts or initiators. The curing temperature was above 200 °C, and the curing time about 30 min. Under these heat curing conditions, the double bonds in the adhesives reached a high conversion (α) around 98.88 % calculated from the Fourier transform infrared spectroscopy analysis. The curing kinetics of heat curing products was studied using Ozawa method and deduced by assuming a constant activation energy (E). The curing kinetic equation was obtained as dα/dt = e17.70(1 ? α)1.19 α 0.41e(?94.32)/RT) with E = 94.32 kJ mol?1. The heat curing followed the shrinking core model from the resin-particle system. The data calculated from the kinetic equation agreed well with the experimental data, showing that the Ozawa method could evaluate the curing kinetics effectively. Furthermore, a comprehensive and in-depth understanding of the curing kinetics of heat curing electrically conductive adhesives has been achieved with this Ozawa method.  相似文献   

14.
Fluorescence spectroscopy was used to characterize inclusion compounds between 4-amino-1,8-naphthalimides (ANI) derivatives and different cyclodextrins (CDs). The ANI derivatives employed were N-(12-aminododecyl)-4-amino-1,8-naphthalimide (mono-C12ANI) and N,N′-(1,12-dodecanediyl)bis-4-amino-1,8-naphthalimide (bis-C12ANI). The CDs used here were α-CD, β-CD, γ-CD, HP-α-CD, HP-β-CD and HP-γ-CD. The presence of CDs resulted in pronounced blue-shifts in the emission spectra of the ANI derivatives, with increases in emission intensity. This behavior was parallel to that observed for the dyes in apolar solvents, indicating that inclusion complexes were formed between the ANI and the CDs. Mono-C12ANI formed inclusion complexes of 1:1 stoichiometry with all the CDs studied. Complexes with the larger CDs (HP-β-CD, HP-γ-CD and γ-CD) were formed by inclusion of the chromophoric ANI ring system, whereas the smaller CDs (α-CD, HP-α-CD and β-CD) formed complexes with mono-C12ANI by inclusion of the dodecyl chain. Bis-C12ANI formed inclusion complexes of 1:2 stoichiometry with HP-β-CD, HP-γ-CD and γ-CD, but did not form inclusion complexes with α-CD, HP-α-CD and β-CD. The data were treated in the case of the large CDs using a Benesi-Hildebrand like equation, giving the following equilibrium constants: mono-C12ANI:HP-β-CD (K 11 = 50 M?1), mono-C12ANI:HP-γ-CD (K 11 = 180 M?1), bis-C12ANI:HP-β-CD (K 12 = 146 M?2), bis-C12ANI:HP-γ-CD (K 12 = 280 M?2).  相似文献   

15.
Depth profiling of titanium using the resonances at 1,007, 1,013 and 1,362 keV in 48Ti(p,γ)49V nuclear reaction (E γ  = 7.9 MeV) has been investigated. The resonance at 1,362 keV with a detection sensitivity of ~5.1 × 1020 at. cm?3 (~ 1 at.%), probing depth of ~800 nm and a depth resolution of ~24 nm in silicon is best suited for analytical applications. Lower probing depth and lesser detection sensitivity are the major limitations of the two other resonances. The applicability of the resonance at 1,362 keV is demonstrated by depth profiling Ti in Pd (32 nm)/Ti (57 nm)/Mg (300 nm)/Ti (57 nm)/Si multi-layered coating.  相似文献   

16.
A density functional theory calculation has been carried out to investigate the mechanism of W(CO)6 and W2(CO)10 catalyzed water-gas-shift reaction (WGSR). The calculations indicate that the bimetallic catalyst (W2(CO)10) would be likely to be more highly active than the mononuclear metal-based catalyst (W(CO)6) due to the possibility of metal–metal cooperativity in reducing the barriers for the WGSR. The energetic span model is a tool to compute catalytic turnover frequencies (TOFs) which is the traditional measure of the efficiency of a catalyst. The one with the highest efficiency usually gives the highest TOF. The bimetallic catalyst (W2(CO)10) exhibits high catalytic activity towards WGSR due to the highest value of the calculated TOF (3.62 × 10?12 s?1, gas phase; 8.74 × 10?15 s?1, solvent phase), which is higher than the value of TOF (8.96 × 10?20 s?1, gas phase; 3.96 × 10?19 s?1, solvent phase) proposed by Kuriakose et al. (Inorg Chem 51:377–385, 2012). Our results will be important for designing a better catalyst for the industrially important reaction.  相似文献   

17.
Hanwen Sun  Pan He 《Chromatographia》2008,68(11-12):969-975
The binding of fluoroquinolones to the transport protein, human serum albumin (HSA), under simulated physiological conditions has been studied by capillary electrophoresis–frontal analysis (CE–FA). The binding of these drugs to human plasma was evaluated by using ultrafiltration and capillary electrophoresis. The free drug concentration [D]f at each HSA concentration was determined by the plateau height in the electropherograms and the calibration lines. The binding constants of fluoroquinolones and HSA were estimated using nonlinear regression with origin 7.5 software. The fluoroquinolones were found to show low affinity toward HSA, with binding constants ranging from 1.73 × 102 to 5.40 × 102 M?1. The percentages of protein binding (PB) for fluoroquinolones to HSA were between 8.6 and 22.2%, while the PB percentages for fluoroquinolones to human plasma were between 10.2 and 33.1%. It can be found that the PB percentages for fluoroquinolones to HSA are mostly lower than those for fluoroquinolones to human plasma. It suggests that HSA is the primary protein responsible for the binding of fluoroquinolones in human plasma. The thermodynamic parameters were obtained by CE–FA. The positive ?H and ?S values obtained by CE–FA showed that the binding reaction was an endothermic process, and the entropy drive the binding and hydrophobic interaction played major roles in the binding of fluoroquinolones to HSA.  相似文献   

18.
Stir-bar-sorptive extraction with liquid desorption followed by large-volume injection and capillary gas chromatography coupled to mass spectrometry in selected ion monitoring acquisition mode (SBSE–LD/LVI-GC–MS(SIM)) has been developed to monitor ultra-traces of four musks (celestolide (ADBI), galaxolide (HHCB), tonalide (AHTN) and musk ketone (MK)) in environmental water matrices. Instrumental calibration (LVI-GC–MS(SIM)) and experimental conditions that could affect the SBSE-LD efficiency are discussed. Assays performed on 30-mL water samples spiked at 200 ng L?1 under optimized experimental conditions yielded recoveries ranging from 83.7?±?8.1% (MK) to 107.6?±?10.8% (HHCB). Furthermore, the experimental data were in very good agreement with predicted theoretical equilibria described by octanol–water partition coefficients (K PDMS/W?≈?K O/W). The methodology also showed excellent linear dynamic ranges for the four musks studied, with correlation coefficients higher than 0.9961, limits of detection and quantification between 12 and 19 ng L?1 and between 41 and 62 ng L?1, respectively, and suitable precision (< 20%). Application of this method for analysis of the musks in real water matrices such as tap, river, sea, and urban wastewater samples resulted in convenient selectivity, high sensitivity and accuracy using the standard addition methodology. The proposed method (SBSE–LD/LVI-GC–MS(SIM)) was shown to be feasible and sensitive, with a low-sample volume requirement, for determination of musk compounds in environmental water matrices at the ultra-trace level, overcoming several disadvantages presented by other sample-preparation techniques.  相似文献   

19.
《Analytical letters》2012,45(11):1721-1734
Abstract

A novel approach to assemble an H2O2 amperometric biosensor was introduced. The biosensor was constructed by entrapping horseradish peroxidase (HRP) labeled nano‐scaled particulate gold (nano‐Au) (HRP‐nano‐Au electrostatic composite) in a new silica sol‐gel/alginate hybrid film using glassy carbon electrode as based electrode. This suggested strategy fully merged the merits of sol‐gel derived inorganic‐organic composite film and the nano‐Au intermediator. The silica sol‐gel/alginate hybrid material can improve the properties of conventional sol‐gel material and effectively prevent cracking of film. The entrapment of HRP in the form of HRP‐nano‐Au can not only factually prevent the leaking of enzyme out of the film but also provide a favorable microenvironment for HRP. With hydroquinone as an electron mediator, the proposed HRP electrode exhibited good catalytic activity for the reduction of H2O2. The parameters affecting both the qualities of sol‐gel/alginate hybrid film and the biosensor response were optimized. The biosensor exhibited high sensitivity of 0.40 Al mol?1 cm?2 for H2O2 over a wide linear range of concentration from 1.22×10?5 to 1.46×10?3 mol L?1, rapid response of <5 s and a detection limit of 0.61×10?6 mol L?1. The enzyme electrode has remarkable stability and retained 86% of its initial activity after 45 days of storage in 0.1 mol L?1 Tris‐HCl buffer solutions at pH 7.  相似文献   

20.
Bi1?xCaxFeO3?y (0.40 ≤ x ≤ 0.55) perovskite oxides have been synthesized by solid-state reaction method to study their properties as a cathode material for intermediate temperature solid oxide fuel cells. The as prepared samples were characterized by X-ray diffraction, differential thermal analyzer/thermogravimetry, dilatometer, and impedance spectroscopy to study their structural, thermal, and electrical properties. The Rietveld refinement results confirmed that all the samples exhibit tetragonal structure with P4mm space group. In addition to this, sample x = 0.55 exhibits Ca2Fe2O5 as a secondary phase. It has been observed that lattice parameters decrease with increase in calcium content. The thermal expansion coefficient and ionic conductivity increases with increase in calcium content up to x = 0.50. The highest ionic conductivity is observed for Bi0.5Ca0.5FeO3?y i.e. 1.71 × 10?2 S cm?1.  相似文献   

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