Transport properties of Nafion membranes modified with tetrapropylammonium ions for direct methanol fuel cell application

This work presents a study of transport properties (proton conductivity, methanol permeability, and water uptake) and acid-base properties of commercial Nafion-112, -115, and -117 membranes modified with tetrapropylammonium (TPA) cations. In the interaction between TPA hydroxide and protons of sulfonate groups in the Nafion matrix, some of the protons are shown to be bound to sulfonate groups and do not participate in transport processes. These findings are confirmed by IR spectroscopy, acid-base titration, and data on proton conductivity of the modified membranes. Proton conductivity of the modified membranes is shown to be effectively described by a percolation model with parameters that agree with published data for commercial Nafion membranes. Based on these results, a model is proposed for the interaction of TPA cations with the sulfonate groups in Nafion membranes. According to this model, TPA cations form hydrophobic clusters in hydrophilic regions of the polymer matrix, thus preventing some of the protonated sulfonate groups from participating in transport processes.     

Mobility of water molecules in Li+, Na+ and Cs+ ionic forms of Nafion membrane studied by NMR

Correlation times and diffusion coefficients of water molecules were measured for the first time by ¹H spin relaxation and pulsed field gradient NMR in Li⁺, Na⁺ and Cs⁺ ionic forms of Nafion 117 membrane. Hydration numbers of Li⁺, Na⁺ and Cs⁺ cations were calculated. It was shown that at high humidity macroscopic transfer is controlled by the local translational motion of water molecules.     

间歇式水热合成制备丝光沸石膜及其异丙醇脱水应用

采用市售廉价大孔α-Al₂O₃管作为基质材料,通过热浸渍法在管外表面涂敷晶种,随后在无模板剂体系下,利用新型的间歇式水热合成法制备丝光沸石膜。对比了传统加热和间歇式加热对丝光沸石膜形貌、结构及渗透蒸发异丙醇脱水分离性能的差异。考察了合成液中Na₂O/SiO₂、SiO₂/Al₂O₃和NaF/SiO₂物质的量之比在间歇式水热合成下对丝光沸石膜的影响。研究结果表明,当合成液中Na₂O/SiO₂、SiO₂/Al₂O₃和NaF/SiO₂物质的量之比分别为0.24、16.7和0.25时,制备的丝光沸石膜渗透蒸发异丙醇脱水分离性能最佳,在75℃下,对异丙醇/水(9∶1,w/w)的渗透通量达5.60 kg·m^-2·h^-1,水对异丙醇的分离因数大于10 000。     

间歇式水热合成制备丝光沸石膜及其异丙醇脱水应用

采用市售廉价大孔α-Al₂O₃管作为基质材料,通过热浸渍法在管外表面涂敷晶种,随后在无模板剂体系下,利用新型的间歇式水热合成法制备丝光沸石膜。对比了传统加热和间歇式加热对丝光沸石膜形貌、结构及渗透蒸发异丙醇脱水分离性能的差异。考察了合成液中Na₂O/SiO₂、SiO₂/Al₂O₃和NaF/SiO₂物质的量之比在间歇式水热合成下对丝光沸石膜的影响。研究结果表明,当合成液中Na₂O/SiO₂、SiO₂/Al₂O₃和NaF/SiO₂物质的量之比分别为0.24、16.7和0.25时,制备的丝光沸石膜渗透蒸发异丙醇脱水分离性能最佳,在75℃下,对异丙醇/水(9:1,w/w)的渗透通量达5.60 kg·m^-2·h^-1,水对异丙醇的分离因数大于10 00...     

Infrared study of hydration and association of functional groups in a perfluorinated Nafion membrane. — Part 2

The state of sulfonic acid groups in a thoroughly dried and slightly hydrated Nafion membrane has been analysed applying infrared spectroscopy. IR spectra in thevOH stretching vibration region were analysed in detail. A computer-curve resolution technique was used to determine band parameters of each OH band. The results of this analysis indicate a rather complex process of association of sulfonic groups in the Nafion membrane. The association of these groups in the Nafion membrane differs in several respects from that in the polystyrenesulfonic acid membrane which results from the differencies in membrane structures, both on molecular and supermolecular level.     

Mobility of Li+, Na+, and Cs+ cations in Nafion membrane,as studied by NMR techniques

The local mobility and diffusion of Li⁺, Na⁺, and Cs⁺ cations in Nafion 117 membrane were explored by ⁷Li, ²³Na, and ¹³³Cs spin relaxation and pulsed field gradient NMR techniques. It was shown that the macroscopic mass transfer of cations is controlled by ion motion near sulfonate groups. Lithium and sodium cations, whose hydrated energy is higher than the water hydrogen bond energy, are moving together with water molecules, but cesium cations possessing a low hydrated energy are jumping directly between the neighboring sulfonate groups.     

The effect of spatial confinement of Nafion in porous membranes on macroscopic properties of the membrane

Polyelectrolytes were incorporated into porous reinforcing materials to study the properties of ionomers in confined spaces and to determine the effect of the porous material on the behaviour of the membranes. Nafion^® was imbibed into porous polypropylene (Celgard^®), ultra-high-molecular weight polyethylene (Daramic^®), and polytetrafluoroethylene (PTFE) films. Through the use of reinforcing materials, it is possible to prepare membranes that are thinner, but stronger than pure ionomer membranes. Thin reinforced membranes have advantages such as lower areal resistance (as low as 0.14 Ω cm² for 57 μm CG3501 + Nafion^® compared to 0.34 Ω cm² for 89 μm cast Nafion^®) and lower dimensional changes due to swelling (as low as a 4% change in length and width for WDM + Nafion^® compared to 13% for cast Nafion^®). Using reinforcing materials results in a reduction in important membrane properties compared to bulk Nafion^®, such as proton conductivity (as low as 0.016 S cm⁻¹ for CG3401 + Nafion^® compared to 0.076 S cm⁻¹ for cast Nafion^®), effective proton mobility (as low as 3.2 × 10⁻⁴ cm² V⁻¹ s⁻¹ CG3401 + Nafion^® compared to 7.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ for cast Nafion^®), and water vapour permeance (as low as 0.036 g h⁻¹ Pa⁻¹ m⁻² for WDM + Nafion^® compared to 0.056 g h⁻¹ Pa⁻¹ m⁻² for cast Nafion^®). By normalizing the membrane properties with respect to ionomer content, it was possible to examine the properties of the Nafion^® inside the pores of the membranes. The proton conductivity (as low as 0.032 S cm⁻¹ for CG3401 + Nafion^®), effective proton mobility (as low as 3.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ for CG3401 + Nafion^®), and water vapour permeability (as low as 2.7 × 10⁻⁶ g h⁻¹ Pa⁻¹ m⁻¹ for PTFE MP 0.1 + Nafion^®) of the ionomer in the membrane are also diminished compared to bulk Nafion^® due to decreased connectivity of the ionomer and a restriction in macromolecular motions caused by the pore walls. A series of porous materials with increasing pore were also examined. As the pore size of the PTFE MP materials increased from 0.1 μm to 10 μm, the proton conductivity (0.022 S cm⁻¹ to 0.041 S cm⁻¹), effective proton mobility ((4.1 to 5.6) × 10⁻⁴ cm² V⁻¹ s⁻¹), and water vapour permeability ((2.4 to 4.3) × 10⁻⁶ g h⁻¹ Pa⁻¹ m⁻¹) of the reinforced membranes improved with increasing pore size and the properties of the ionomer inside the membranes approached the value of bulk Nafion^®.     

Preparation and properties of Nafion/SiO2 composite membrane derived via in situ sol–gel reaction: size controlling and size effects of SiO2 nano‐particles

A novel technique in controlling the size of SiO₂ nano‐particles in the preparation of Nafion/SiO₂ composite membranes via in situ sol–gel method, as well as the effects of nano‐particle size on membrane properties and cell performance, is reported in this paper. Nafion/SiO₂ composite membranes containing SiO₂ nano‐particles with four different diameters (5 ± 0.5, 7 ± 0.5, 10 ± 1, and 15 ± 2 nm) are fabricated by altering the reactant concentrations during in situ sol–gel reaction. Sequentially, size effects of SiO₂ nano‐particles on membrane properties and cell performance are investigated by SEM/EDAX, TEM, TGA, mechanical tensile, and single cell tests, etc. The results suggest that 10 nm is a critical diameter for SiO₂ incorporated into Nafion matrix, exhibiting desirable physico‐chemical properties for operation at elevated temperature and low humidity. At 110°C and 59% RH, the output voltage of the cell equipped with Nafion/SiO₂ (10 nm) obtains an output voltage of 0.625 V at 600 mA/cm², which is 50 mV higher than that of unmodified Nafion. Copyright © 2010 John Wiley & Sons, Ltd.     

Glass-transition temperature,electrical conductance,viscosity, molar volume,refractive index,and proton magnetic resonance study of chlorozinc complexation in the system ZnCl2+LiCl+H2O

Several physicochemical techniques have been utilized to study mixed aqueous solutions of ZnCl₂ and LiCl along selected pseudobinary composition lines in the concentration range from 2.8 to 22.2m. Measurements of glasstransition temperature, electrical conductance, viscosity, molar volume, refractive index, and proton chemical shift indicate with varying sensitivity that the behavior of these electrolytes is dominated by chlorozinc complexation. The effects of complexation are most sensitively shown by the PMR spectra. In solutions containing more than 6 moles of water per mole of salt, it is probable that several complexation equilibria occur. When the water content is reduced to less than 6 moles per mole of salt, formation of tetrachlorozincate anions appears almost exclusively to be responsible for the composition variation of the physical properties of the solutions. ZnCl ₄ ⁼ appears to be an even weaker base than ClO ₄ ^– .     

Optimizing the degradation of dichlorvos in aqueous solution using nZVI DTPA+H2O2 and its detection using ac conductivity measurement with the help of response surface methodology

Degradation of organic pollutants in wastewater is a common subject of discussion under advanced oxidation process. To detect the degradation of colourless organic pollutants conventional analytical techniques are available but their sophistication makes it difficult to pursue in all form of chemical laboratories. In the present study it was found that during degradation of Dichlorvos using diethylene triamine pent acetic acid (DTPA) stabilized nano zero valent iron (nZVI), COD removal and ac conductivity change has been done simultaneously. In this degradation study the heterogeneous Fenton type oxidation method was employed and an LCR circuit (which contains inductor, capacitor and resistor) was used to measure the ac conductivity. This study aims to find out a correlation between ac conductivity and COD removal using simple response surface methodology (RSM) so that the degradation of colourless pollutants can be estimated easily and also to identify the best processing parameters to optimise Dichlorvos degradation. It was found that COD removal in most of all cases, was more than 60% when the change in final ac conductivity more than 600% with respect to initial value. All of the experimental results were in good accord with the projected outcome.     

Kinetics and mechanism of ion exchange of Fe3+, Cd2+ and Na+/H+ on Lewatite S-100 cation exchanger in aqueous and aqueous-detergent media

Sorption mechanism of Fe (III), Cd (II) and Na (I) on cation exchange resins in H-form was investigated from aqueous and aqueous-detergent media by a modified limited batch technique. The cation exchange studies involved the sorption of metallic ions onto a Lewatite S-100 exchanger. Effects of mesh size of the exchanger, temperature and detergent on the exchange rate have been investigated. The mechanisms of cation exchanges have been determined in the temperature range of 25–65°C. In all cases of the reactions ions, diffusion is found to be the rate determining step in the exchange process. The exchange rate in the exchange process was found to increase with a decrease of particle size and an increase of temperature. However, in case of the influence of detergent, the exchange reactions are dependent on the reaction technique. The effective-diffusion coefficients have been evaluated at three different temperatures. The energy barriers (ΔE_a), entropies of activation (ΔS*), (ΔH*) and (ΔG*) for various sorption systems have also been calculated. The results are discussed in terms of size and valences of the counter ions. No change in the internal structure of Lewatite S-100 is inferred due to the sorption of counter ions.     

Thermodynamic quantities for the interaction of H+ and Na+ with C2H3O 2 − and Cl− in aqueous solution from 275 to 320°C

The aqueous reactions, {ie865-1}were studied as a function of ionic strength at 275, 300, and 320°C using a flow calorimetric technique. Log K, H and S values were determined from the fits of the calculated and experimental heats while Cp values were calculated from the variation of H values with temperature. The log K and H values for the first two reactions agree well with literature values at these temperatures. No previous results have been reported for the third reaction. The use of equations containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was applied to the log K values determined in this study. The resulting plots of log K for the isocoulombic reactions vs. I/T were approximately linear, which demonstrates that the Cp values for these reactions are approximately zero.Deceased 5 September 1987     

Thermodynamic quantities for the interaction of SO 4 2− with H+ and Na+ in aqueous solution from 150 to 320°C

The aqueous reactions,

Oxygenation of methane with atmospheric oxygen in aqueous solution promoted by H2O2 and catalyzed by a vanadate ion—pyrazine-2-carboxylic acid system

Methane is oxidized in aqueous solution with atmospheric oxygen and hydrogen peroxide in a reaction catalyzed by a NaVO₃-pyrazine-2-carboxylic acid system. Methyl hydroperoxide is selectively formed at 50°C. The turnover number of the catalyst after 24 h amounts to 480, and the yield of methyl hydroperoxide is 24% with respect to H₂O₂. Formaldehyde and formic acid are mainly formed at 120°C. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1897–1899, October, 1997.     

Screening anaphylactic components of MaiLuoNing injection by using rat basophilic leukemia‐2H3 cell membrane chromatography coupled with HPLC–ESI‐TOF‐MS

MaiLuoNing injection is a traditional Chinese medicine that used clinically since the 1950s in China. However, anaphylactic reactions, through the potentiation of mast cell degranulation, have been reported. In the present study, a rat basophilic leukemia‐2H3 cell membrane chromatography coupled with high‐performance liquid chromatography and electrospray ionization‐ion trap‐time of flight‐mass spectrometry method was established for screening, analyzing, and identifying the potential anaphylactic components of MaiLuoNing injection. Harpagoside, a potential degranulator of rat basophilic leukemia‐2H3 cells, was retained in rat basophilic leukemia‐2H3 cell membrane chromatography. We aimed to evaluate the retained components to determine which of those were capable of inducing degranulation of basophilic leukemia cells. A β‐hexosaminidase assay revealed that harpagoside can induce rat basophilic leukemia‐2H3 cell degranulation in a dose‐dependent manner. BLBA/c mice also exhibit passive cutaneous anaphylaxis in response to harpagoside. These results indicate that rat basophilic leukemia‐2H3 cell membrane chromatography coupled with high‐performance liquid chromatography and electrospray ionization ion trap time‐of‐flight mass spectrometry is effective in screening for the anaphylactic components of MaiLuoNing injection.     

Hypervalent radical formation probed by electron transfer dissociation of zwitterionic tryptophan and tryptophan‐containing dipeptides complexed with Ca2+ and 18‐crown‐6 in the gas phase

The relationship between peptide structure and electron transfer dissociation (ETD) is important for structural analysis by mass spectrometry. In the present study, the formation, structure and reactivity of the reaction intermediate in the ETD process were examined using a quadrupole ion trap mass spectrometer equipped with an electrospray ionization source. ETD product ions of zwitterionic tryptophan (Trp) and Trp‐containing dipeptides (Trp‐Gly and Gly‐Trp) were detected without reionization using non‐covalent analyte complexes with Ca²⁺ and 18‐crown‐6 (18C6). In the collision‐induced dissociation, NH₃ loss was the main dissociation pathway, and loss related to the dissociation of the carboxyl group was not observed. This indicated that Trp and its dipeptides on Ca²⁺(18C6) adopted a zwitterionic structure with an NH₃⁺ group and bonded to Ca²⁺(18C6) through the COO^? group. Hydrogen atom loss observed in the ETD spectra indicated that intermolecular electron transfer from a molecular anion to the NH₃⁺ group formed a hypervalent ammonium radical, R‐NH₃, as a reaction intermediate, which was unstable and dissociated rapidly through N–H bond cleavage. In addition, N–C_α bond cleavage forming the z₁ ion was observed in the ETD spectra of Trp‐GlyCa²⁺(18C6) and Gly‐TrpCa²⁺(18C6). This dissociation was induced by transfer of a hydrogen atom in the cluster formed via an N–H bond cleavage of the hypervalent ammonium radical and was in competition with the hydrogen atom loss. The results showed that a hypervalent radical intermediate, forming a delocalized hydrogen atom, contributes to the backbone cleavages of peptides in ETD. Copyright © 2015 John Wiley & Sons, Ltd.     

Determination of a selective Na+/H+ exchanger inhibitor, 4-cyano(benzo[b]thiophene-2-carbonyl)guanidine (KR-33028) in rat plasma by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometric (LC/MS/MS) method was developed for the determination of a selective Na(+)/H(+) exchanger inhibitor 4-cyano(benzo[b]thiophene-2-carbonyl)guanidine (KR-33028) in rat plasma. KR-33028 and the internal standard, linezolid, were extracted from rat plasma with ethyl acetate at neutral pH. The analytes were separated on an XBridge C(18) column with a mixture of methanol-0.1% formic acid (35:65, v/v) as mobile phase and detected using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The standard curve was linear (r = 0.9998) over the concentration range of 2.0-1000 ng/mL. The coefficients of variation of intra- and inter-assay were 1.3-6.8% and the relative error was 0.8-5.0%. The recoveries of KR-33028 and linezolid were 70.5 and 84.6%, respectively. The lower limit of quantification for KR-33028 was 2.0 ng/mL using 50 microL plasma sample. This method was successfully applied to the pharmacokinetic study of KR-33028 in rats.     

Potentiometric properties of membrane electrodes with an immobilized aqueous phase in the solutions of complexes coordinatively solvated by tri-n-butyl phosphate. (Complexes: UO(2) (NO(3))(2).2TBP, Co(NO(3))(2).3TBP, Ca(NO(3))(2).6H(2)O.2TBP)

The paper presents the results of studies on potential dependent properties of typical extraction systems: UO(2)(NO(3))(2)-H(2)O-TBP, Ca(NO(3))(2)-H(2)O-TBP, Co(NO(3))(2)-H(2)O-TBP (TBP-tri-n-butyl phosphate) treated as membrane systems with an immobilized aqueous phase. It was shown that the processes influencing on the membrane potential in the studied system depended mainly on extraction constants. The electrode functions of the systems depended on concentration of salts in the immobilized aqueous phase and concentration of solvate in the organic phase. It was found that the activity coefficients could be determined from the dependence describing the electrode potential in the concentrated solvate solutions.