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1.
Methanol diffusion in two polymer electrolyte membranes, Nafion 117 and BPSH 40 (a 40% disulfonated wholly aromatic polyarylene ether sulfone), was measured using a modified pulsed field gradient NMR method. This method allowed for the diffusion coefficient of methanol within the membrane to be determined while immersed in a methanol solution of known concentration. A second set of gradient pulses suppressed the signal from the solvent in solution, thus allowing the methanol within the membrane to be monitored unambiguously. Over a methanol concentration range of 0.5–8 M, methanol diffusion coefficients in Nafion 117 were found to increase from 2.9 × 10 −6 to 4.0 × 10 −6 cm 2 s −1. For BPSH 40, the diffusion coefficient dropped significantly over the same concentration range, from 7.7 × 10 −6 to 2.5 × 10 −6cm 2 s −1. The difference in diffusion behavior is largely related to the amount of solvent sorbed by the membranes. Increasing the methanol concentration results in an increase in solvent uptake for Nafion 117, while BPSH 40 actually excludes the solvent at higher concentrations. In contrast, diffusion of methanol measured via permeability measurements (assuming a partition coefficient of 1) was lower (1.3 × 10 −6 and 6.4 × 10 −7 cm 2 s −1 for Nafion 117 and BPSH 40 respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of methanol in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 μm for Nafion 117 and BPSH 40 respectively) whereas the NMR method observes diffusion over a length of approximately 4–8 μm. Regardless of the measurement technique, BPSH 40 is a greater barrier to methanol permeability at high methanol concentrations. 相似文献
2.
Trace amounts of nickel(II) can function as a trigger (=reaction initiator) in an autocatalytic reaction with the sodium sulfite/hydrogen peroxide system. Based on this finding, sub-μg L −1 levels of nickel(II) were determined by a time measurement using the autocatalytic reaction. The detection range using the above method was 10 −9–10 −5 M, the detection limit (3 σ) was 8.1 × 10 −10 M (0.047 μg L −1), and the relative standard deviation was 2.66% at nickel(II) concentration of 10 −7 M ( n = 7). This method was applied to length detection-flow injection analysis. The detection range for the flow injection analysis was 2 × 10 −9–2 × 10 −3 M. The detection limit (3 σ) was 1.4 × 10 −9 M (0.082 μg L −1), and the relative standard deviation was 1.86 at initial nickel(II) concentration of 10 −6 M ( n = 7). 相似文献
3.
Rate coefficients for the reactions of cyclohexadienyl ( c-C 6H 7) radicals with O 2 and NO were measured at 296 ± 2 K. The c-C 6H 7 radicals were detected selectively by laser-induced fluorescence. The rate coefficient for the reaction of c-C 6H 7 with O 2, (4.4 ± 0.5) × 10 −14 cm 3 molecule −1 s −1, was independent of the bath-gas (He) pressure (13–80 Torr). In the reaction of c-C 6H 7 with NO, thermal equilibrium among c-C 6H 7, NO, and C 6H 7NO was observed. The forward and reverse reactions were in the falloff region, and the equilibrium constant was (1.5 ± 0.6) × 10 −15 cm 3 molecule −1. 相似文献
4.
A novel voltammetric method for the determination of β-d-glucose (GO) is proposed based on the reduction of Cu(II) ion in Cu(II)(NH 3) 42+–GO complex at lanthanum(III) hydroxide nanowires (LNWs) modified carbon paste electrode (LNWs/CPE). In 0.1 mol L −1 NH 3·H 2O–NH 4Cl (pH 9.8) buffer containing 5.0 × 10 −5 mol L −1 Cu(II) ion, the sensitive reduction peak of Cu(II)(NH 3) 42+–GO complex was observed at −0.17 V (versus, SCE), which was mainly ascribed to both the increase of efficient electrode surface and the selective coordination of La(III) in LNW to GO. The increment of peak current obtained by deducting the reduction peak current of the Cu(II) ion from that of the Cu(II)(NH 3) 42+–GO complex was rectilinear with GO concentration in the range of 8.0 × 10 −7 to 2.0 × 10 −5 mol L −1, with a detection limit of 3.5 × 10 −7 mol L −1. A 500-fold of sucrose and amylam, 100-fold of ascorbic acid, 120-fold of uric acid as well as gluconic acid did not interfere with 1.0 × 10 −5 mol L −1 GO determination. 相似文献
5.
Antigen I/II can be found on streptococcal cell surfaces and is involved in their interaction with salivary proteins. In this paper, we determine the adsorption enthalpies of salivary proteins to Streptococcus mutans LT11 and S. mutans IB03987 with and without antigen I/II, respectively, using isothermal titration calorimetry. In addition, protein adsorption to the cell surfaces was determined spectrophotometrically. S. mutans LT11 with antigen I/II, yielded a much higher, exothermic adsorption enthalpy at pH 6.8 (ranging from −2073 × 10 −9 to −31707 × 10 −9 μJ per bacterium) when mixed with saliva than did S. mutans IB03987 (−165 × 10 −9 to −1107 × 10 −9 μJ per bacterium) at all bacterial concentrations studied (5 × 10 9, 5 × 10 8, and 5 × 10 7 ml −1), largest effects per bacterium being observed for the lowest concentration. However, the enthalpy of salivary protein adsorption to S. mutans LT11 became smaller at pH 5.8. Adsorption isotherms for the S. mutans LT11 showed considerable protein adsorption at pH 6.8 (1.2–2.1 mg/m 2), that decreased only slightly at pH 5.8 (1.1–1.6 mg/m 2), with the largest amount adsorbed at the lowest bacterial concentration. This suggests that the protein(s) in the saliva with the strongest affinity for antigen I/II is (are) readily depleted from saliva. In conclusion, antigen I/II surface proteins on S. mutans play a determinant role in adsorption of salivary proteins through the creation of enthalpically favorable adsorption sites. 相似文献
6.
A series of hydroxyl-conducting anion-exchange membranes were prepared by blending chloroacetylated poly(2,6-dimethyl-1,4-phenylene oxide) (CPPO) with bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO), and their fuel cell-related performances were evaluated. The resulting membranes exhibited high hydroxyl conductivities (0.022–0.032 S cm −1 at 25 °C) and low methanol permeability (1.35 × 10 −7 to 1.46 × 10 −7 cm 2 s −1). All the blend membranes proved to be miscible or partially miscible under the investigations of scanning electron microscopy (SEM) and differential scanning calorimeters (DSC). By condition optimization, the blend membranes with 30–40 wt% CPPO are recommended for application in direct methanol alkaline fuel cells because they showed low methanol permeability, excellent mechanical properties and comparatively high hydroxyl conductivity. 相似文献
7.
The electrochemiluminescent (ECL) response of allopurinol was studied in aqueous media over a wide pH range (pH 2–13) using flow injection (FI) analysis. It was revealed that allopurinol itself had no ECL activity, but could greatly enhance the ECL of Ru(bpy) 32+ in alkaline media giving rise to a sensitive FI-ECL response. The effects of experimental conditions including the mode of applied voltage signal, the potential of working electrode, pH value, the flow rate of carrier solution, and the concentration of Ru(bpy) 32+ and allopurinol on the ECL intensity were investigated in detail. The most sensitive FI-ECL response of allopurinol was found at pH 12.0, where the FIA-ECL intensity showed a linear relationship with concentration of allopurinol in the range 1 × 10 −8 mol L −1 to 5 × 10 −7 mol L −1, and the detection limit was 5 × 10 −9 mol L −1. 相似文献
8.
The rate constants, k1 and k2 for the reactions of C 2F 5OC(O)H and n-C 3F 7OC(O)H with OH radicals were measured using an FT-IR technique at 253–328 K. k1 and k2 were determined as (9.24 ± 1.33) × 10 −13 exp[−(1230 ± 40)/ T] and (1.41 ± 0.26) × 10 −12 exp[−(1260 ± 50)/ T] cm 3 molecule −1 s −1. The random errors reported are ±2 σ, and potential systematic errors of 10% could add to the k1 and k2. The atmospheric lifetimes of C 2F 5OC(O)H and n-C 3F 7OC(O)H with respect to reaction with OH radicals were estimated at 3.6 and 2.6 years, respectively. 相似文献
9.
Polyallylamine (PAAm) was synthesized by free radical polymerization and characterized by Fourier transform infrared resonance (FT-IR) spectroscopy, hydrogen nuclear magnetic resonance ( 1H NMR) spectroscopy and differential scanning calorimetry (DSC). The composite membranes were prepared by using PAAm–poly(vinyl alcohol) (PVA) blend polymer as the separation layer and polysulfone (PSF) ultrafiltration membranes as the support layer. The surface and cross-section morphology of the membrane was inspected by environmental scanning electron microscopy (ESEM). The gas transport property of the membranes, including gas permeance, flux and selectivity, were investigated by using pure CO 2, N 2, CH 4 gases and CO 2/N 2 gas mixture (20 vol% CO 2 and 80 vol% N 2) and CO 2/CH 4 gas mixture (10 vol% CO 2 and 90 vol% CH 4). The plots of gas permeance or flux versus feed gas pressure imply that CO 2 permeation through the membranes follows facilitated transport mechanism whereas N 2 and CH 4 permeation follows solution–diffusion mechanism. Effect of PAAm content in the separation layer on gas transport property was investigated by measuring the membranes with 0–50 wt% PAAm content. With increasing PAAm content, gas permeance increases initially, reaches a maximum, and then decreases gradually. For CO 2/N 2 gas mixture, the membranes with 10 wt% PAAm content show the highest CO 2 permeance of about 1.80 × 10 −5 cm 3 (STP) cm −2 s −1 KPa −1 and CO 2/N 2 selectivity of 80 at 0.1 MPa feed gas pressure. For CO 2/CH 4 gas mixture, the membranes with 20 wt% PAAm content display the highest CO 2 permeance of about 1.95 × 10 −5 cm 3 (STP) cm −2 s −1 KPa −1 and CO 2/CH 4 selectivity of 58 at 0.1 MPa feed gas pressure. In order to explore the possible reason of gas permeance varying with PAAm content, the crystallinity of PVA and PAAm–PVA blend polymers was measured by X-ray diffraction (XRD) spectra. The experimental results show an inverse relationship between crystallinity and gas permeance, e.g., a minimum crystallinity and a maximum CO 2 permeance are obtained at 20 wt% PAAm content, indicating that the possibility of increasing CO 2 permeance with PAAm content due to the increase of carrier concentration could be weakened by the increase of crystallinity. 相似文献
10.
NaY zeolite tubular membranes in an industrial scale of 80 cm long were synthesized on monolayer and asymmetric porous supports. The quality of synthesized membranes were evaluated by pervaporation (PV) experiments in 80 cm long at 75 °C in a mixture of water (10 wt.%)/ethanol (90 wt.%), resulting in higher permeation fluxes of 5.1 kg m −2 h −1 in the monolayer type membrane and of 9.1–10.1 kg m −2 h −1 in the asymmetric-type membranes, respectively. The uniformity with small performance fluctuation in longitudinal direction of the membranes were observed by PV for 10–12 cm long samples at 50 °C in a mixture of methanol (10 wt.%)/MTBE (90 wt.%). The ethanol single component permeation experiments in PV and vapor permeation (VP) up to 130 °C and 570 kPa were performed to determine the relations between the ethanol flux and the ethanol pressure difference across the membrane which is represented by permeance (Π, mol m −2 s −1 Pa −1) for estimate of potential of ethanol extraction through the present NaY zeolite membranes applying feasible studies. Results indicate that (1) the permeation fluxes are linearly proportional to the driving force of vapor pressure for each sample in VP and PV. The permeances through an asymmetric support type membrane were rather constant of 0.6–1.2 × 10 −7 mol m −2 s −1 Pa −1 in the wide temperature range of 90–130 °C in PV and VP, indicating that the ethanol permeances have weak temperature dependency with the feed at the saturated vapor pressure. The results of superheating VP experiments showed that ethanol permeation fluxes are increased with increasing of the degree of superheating at a given constant feed vapor pressure. The ethanol permeances are increased with increasing of temperature at a given feed vapor pressure. The superheating VP could be a feasible process in industry. 相似文献
11.
The hydrogen abstraction reactions of C 2F 5CHO with OH radicals and Cl atoms have been investigated theoretically by a dual-level direct dynamics method. In this study, the optimized geometries and frequencies of the stationary points are calculated at the MP2/cc-pVDZ level of theory. The energies of the stationery points and the selected points along the minimum energy paths are further refined at the MC-QCISD level using the MP2 geometries. Complexes with energies less than those of the reactants or products are located at the entrance or the exit channels of the two reactions. This result indicates that both of reactions proceed via indirect reaction mechanisms. The enthalpies of formation for the reactant C 2F 5CHO and the product radical C 2F 5CO are estimated by isodesmic reactions at the MC-QCISD//MP2/cc-pVDZ level. At the same level, the rate constants are calculated by canonical variational transition state theory (CVT) incorporating with the small-curvature tunneling correction (SCT) in the temperature range 200–1000 K. Good agreement between the calculated and experimental rate constants is obtained at the room temperature. Due to the lack of the kinetic data of these reactions, the fitted three-parameter expressions based on the CVT/SCT rate constants within 200–1000 K are k1 = 1.64 × 10 −24 T4.33 exp (−566.1/ T) and k2 = 6.33 × 10 −15 T1.35 exp (550.3/ T) cm 3 molecule −1 s −1, respectively. 相似文献
12.
A novel copper(II) thiocyanate complex [Cu(im) 2(NCS) 2] 1 (im=imidazole) has been prepared and characterized by spectroscopic analysis and crystallographic method. This supramolecular compound exhibits a three-dimensional solid state structure constituted by N–HS hydrogen bonds and π–π stacking interactions. The compound in DMF solutions has a very strong third-order non-linear optical (NLO) behavior with absorption coefficient and refractive index 2=1.18×10 −11 mw −1, n2=−9.00×10 −16 m 2w −1, respectively, and third-order NLO susceptibility χ (3) of 7.00×10 −10 esu. 相似文献
13.
Derivative photometric methods for trace analysis of Th(IV) and UO 2(II), and their simultaneous determination in mixtures using 5,8-dihydroxy-1,4-naphthoquinone in a micellar medium are reported. Molar absorptivity and Sandell's sensitivity of 1:2 Th(IV) and 1:1 UO 2(II) complexes at their λ max, 614.5 nm and 637.0 nm are, 1.19 × 10 4 1/mol/cm and 1.12 × 10 4 1/mol/cm and 1.95 × 10 −2 μg/cm 2 and 2.13 × 10 −2 μg/cm 2 μg/cm 2, respectively. Calibration graph is linear over the range 9.28 × 10 −2−18.56 μg/ml of Th(IV) and 9.52 × 10 −2−19.04 μg/ml of UO 2(II). Though presence of Th(IV) and UO 2(II) causes interference in each others determination, 9.28 × 10 −1−9.28 μg/ml Th(IV) and 9.52 × 10 −1−9.52 μg/ml UO 2(II) when present together, can be simultaneously determined using derivative spectra. 相似文献
14.
A thin layer (30–40 nm) of a dual-element silica–alumina composition was deposited on a porous alumina support by chemical vapor deposition (CVD) in an inert atmosphere at high temperature. Prior to CVD, an intermediate layer of γ-alumina was coated on the macroporous alumina support. The intermediate layer was prepared by the dip-coating and calcination of boehmite sols of different sizes to give a graded structure that was substantially free of defects. The resulting supported composite membrane had high permeance for hydrogen in the order of 2–3 × 10 −7 mol m −2 s −1 Pa −1 at 873 K with selectivities of H 2 over CH 4, CO and CO 2 of 940, 700 and 590, respectively. The membrane operated by a hopping mechanism involving jumps of permeating molecules between solubility sites. The presence of aluminum improved the hydrothermal stability of the membranes for periods in excess of 500 h at 873 K in 16% steam, allowing the permeance to remain above 10 −7 mol m −2 s −1 Pa −1, although with decreased selectivities. 相似文献
15.
We have applied cavity ring-down spectroscopy to a kinetic study of the reaction of NO 3 with CH 2I 2 in 25–100 Torr of N 2 diluent at 298 K. The rate constant of reaction of NO 3 + CH 2I 2 is determined to be (4.0 ± 1.2) × 10 −13 cm 3 molecule −1 s −1 in 100 Torr of N 2 diluent at 298 K. The rate constant increases with increasing pressure of buffer gas below 100 Torr. The reaction of CH 2I 2 with NO 3 has the potential importance at nighttime in the atmosphere. 相似文献
16.
Electrochemical studies of famotidine were carried out using voltammetric techniques: cyclic voltammetry, linear sweep and square wave adsorptive stripping voltammetry. The dependence of the current on pH, buffer concentration, nature of the buffer, and scan rate was investigated. The best results for the determination of famotidine were obtained in MOPS buffer solution at pH 6.7. This electroanalytical procedure enabled to determine famotidine in the concentration range 1 × 10 −9–4 × 10 −8 mol L −1 by linear sweep adsorptive stripping voltammetry (LS AdSV) and 5 × 10 −10–6 × 10 −8 mol L −1 by square wave adsorptive stripping voltammetry (SW AdSV). Repeatability, precision and accuracy of the developed methods were checked. The detection and quantification limits were found to be 1.8 × 10 −10 and 6.2 × 10 −10 mol L −1 for LS AdSV and 4.9 × 10 −11 and 1.6 × 10 −10 mol L −1 for SW AdSV, respectively. The method was applied for the determination of famotidine in urine. 相似文献
17.
UV spectra and kinetics for the reactions of alkyl and alkylperoxy radicals from methyl tert-butyl ether (MTBE) were studied in 1 atm of SF 6 by the pulse radiolysis-UV absorption technique. UV spectra for the radical mixtures were quantified from 215 to 340 nm. At 240 nm. σ R = (2.6 ± 0.4) × 10 −18 cm 2 molecule −1 and σ RO2 = (4.1 ± 0.6) × 10 −18 cm 2 molecule −1 (base e). The rate constant for the self-reaction of the alkyl radicals is (2.5 ± 1.1) × 10 −11 cm 3 molecule −1 s −1. The rate constants for reaction of the alkyl radicals with molecular oxygen and the alkylperoxy radicals with NO and NO 2 are (9.1 ± 1.5) × 10 −13, (4.3 ± 1.6) × 10 −12 and (1.2 ± 0.3) × 10 −11 cm 3 molecule −1 s −1, respectively. The rate constants given above refer to reaction at the tert-butyl side of the molecule. 相似文献
18.
The construction and performance under flow-injection conditions of an integrated amperometric biosensor for hydrogen peroxide is reported. The design of the bioelectrode is based on a mercaptopropionic acid (MPA) self-assembled monolayer (SAM) modified gold disk electrode on which horseradish peroxidase (HRP, 24.3 U) was immobilized by cross-linking with glutaraldehyde together with the mediator tetrathiafulvalene (TTF, 1 μmol), which was entrapped in the three-dimensional aggregate formed. The amperometric biosensor allows the obtention of reproducible flow injection amperometric responses at an applied potential of 0.00 V in 0.05 mol L−1 phosphate buffer, pH 7.0 (flow rate: 1.40 mL min−1, injection volume: 150 μL), with a range of linearity for hydrogen peroxide within the 2.0 × 10−7–1.0 × 10−4 mol L−1 concentration range (slope: (2.33 ± 0.02) × 10−2 A mol−1 L, r = 0.999). A detection limit of 6.9 × 10−8 mol L−1 was obtained together with a R.S.D. (n = 50) of 2.7% for a hydrogen peroxide concentration level of 5.0 × 10−5 mol L−1. The immobilization method showed a good reproducibility with a R.S.D. of 5.3% for five different electrodes. Moreover, the useful lifetime of one single biosensor was estimated in 13 days. The SAM-based biosensor was applied for the determination of hydrogen peroxide in rainwater and in a hair dye. The results obtained were validated by comparison with those obtained with a spectrophotometric reference method. In addition, the recovery of hydrogen peroxide in sterilised milk was tested. 相似文献
19.
Pentaerythrityl tetraethylenediamine (PETEDA) dendrimer was synthesized from pentaerythrityl tetrabromide and ethylenediamine. Its molecular structure was characterized by elemental analysis, Fourier transform infrared resonance (FT-IR) and hydrogen nuclear magnetic resonance ( 1H NMR) spectroscopy. The composite membranes for selectively permeating CO 2 were prepared by using PETEDA-PVA blend polymer as the active layer and polyethersulfone (PES) ultrafiltration membrane as the support layer and their permselectivity was tested by pure CO 2 and CH 4 gases and the gas mixture containing 10 vol.% CO 2 and 90 vol.% CH 4, respectively. For pure gases, the membrane containing 78.6 wt% PETEDA and 21.4 wt% PVA in the blend has a CO 2 permeance of 8.14 × 10 −5 cm 3 (STP) cm −2 s −1 cmHg −1 and CO 2/CH 4 selectivity of 52 at 143.5 cmHg feed gas pressure. While feed gas pressure is 991.2 cmHg, CO 2 permeance reaches 3.56 × 10 −5 cm 3 (STP) cm −2 s −1 cmHg −1 and CO 2/CH 4 selectivity is 19. For the gas mixture, the membrane has a CO 2 permeance of 6.94 × 10 −5 cm 3 (STP) cm −2 s −1 cmHg −1 with a CO 2/CH 4 selectivity of 33 at 188.5 cmHg feed gas pressure, and a CO 2 permeance of 3.29 × 10 −5 cm 3 (STP) cm −2 s −1 cmHg −1 with a CO 2/CH 4 selectivity of 7.5 at a higher feed gas pressure of 1164 cmHg. A possible gas transport mechanism in the composite membranes is proposed by investigating the permeating behavior of pure gases and the gas mixture and analyzing possible reactions between CO 2/CH 4 gases and the PETEDA-PVA blend polymer. The effect of PETEDA content in the blend polymer on permselectivity of the composite membranes was investigated, presenting that CO 2 permeance and CO 2/CH 4 selectivity increase and CH 4 permeance decreases, respectively with PETEDA content. This is explained by that with increasing PETEDA content, the carrier content increases, and the crystallinity and free volume of the PETEDA-PVA blend decrease that were confirmed by the experimental results of X-ray diffraction spectra (XRD) and positron annihilation lifetime spectroscopy (PALS). 相似文献
20.
Phosphate selective electrodes have been produced based upon rubbery membranes containing heterocylic macrocycles as sensors covalently bound to a cross-linked polystyrene-block–polybutadiene-block –polystyrene (SBS) polymer. The membranes were robust and the best HPO 42−-selective membrane fabricated was composed of 7.1% (m/m) dicumyl peroxide, 28.3% (m/m) 2-nitrophenyloctylether, 9.8% (m/m) 3-(10-undecenyl)-1,5,8-triazacyclodecane-2,4-dione, 31.0% (m/m) SBS and 23.8% (m/m) PoleStar™ 200R (clay-based filler). The characteristics of this electrode were a linear Nernstian range of 3.9×10 −3 to 1×10 −6 mol dm −3 HPO 42− with a limit of detection of 1.0×10 −6 mol dm −3 HPO 42−, a slope of −29.7±0.9 mV per activity decade and a pH range from 6 to 8. Selectivity coefficients for phosphate against various interfering anions (chloride, sulfate and nitrate) were determined. Response times were 2 min or under, stability of response and electrode lifetime in continuous use were also very satisfactory. The response behavior of HPO 42−-ISEs based upon mobile and bound ionophores was comparable and suggests that mobility of the ionophore is not necessary to obtain a working ISE and that covalent binding of ionophores can be used to produce ISEs of increased stability and robustness. 相似文献
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