Transport Properties of Plasticized Membranes Based on Organic Ion Exchangers

Transport properties of ion-exchange membranes selective to surface-active substances are studied. The membranes are based on assorted electrode-active compounds, such as Methyl Green–dodecyl sulfate and cetylpyridinium–tetraphenylborate, which exhibit anion or cation selectivity, and cetylpyridinium–dodecyl sulfate, which displays cation–anion selectivity. On the basis of the data obtained with the electroconductivity, EMF, and applied-voltage methods, a conclusions is drawn about the majority charge carriers in the membranes and it is shown that the processes at the membrane/solution interface are reversible.     

Performance improvement of polysulfone ultrafiltration membrane by blending with polyaniline nanofibers

Polyaniline (PANI) nanofibers were used to improve hydrophilic property and permeability of polysulfone (PS) membrane. PS membrane and PS/PANI nanofibers blended membranes with different PANI–PS mass ratios (1, 5, 10, and 15 wt.%) were prepared by phase inversion process. The blended membranes showed similar bovine serum albumin (BSA) and albumin egg (AE) rejections to PS membrane. The blended membranes had larger porosity and better hydrophilic property than PS membrane, which caused the improvement of their permeability. Pure water fluxes of the blended membranes with PANI–PS mass ratios of 1 and 15 wt.% were 1.6 and 2.4 times that of PS membrane, respectively. During the filtration of BSA solution, the blended membranes had slower flux decline rate than PS membrane. Moreover, stable permeate fluxes of the blended membranes with PANI–PS mass ratios of 1 and 15 wt.% were 2.0 and 2.5 times that of PS membrane, respectively. Compared with PS membrane, mechanical property and thermal stability of the blended membranes with less PANI–PS mass ratio, e.g. 1 wt.%, had no obvious change. For the blended membrane with PANI–PS mass ratio of 15 wt.%, breaking strength increased 28% and elongation at break decreased 30.6%.     

Effect of using mixed ion-pairs on PVC-membrane electrodes for ephedrine

Mixed ion-pairs based on the use of ephedrinium (EPH)-TPB plus EPH-reineckate (II) and phenylephrine-TPB plus EPH-reineckate (III) were tried for use in plastic membranes. The results were compared to those of an EPH-reineckate (I) single ion-pair electrode. The Nernstian slopes were 50, 49 and 55 mV decade^–1 for membranes I, II and III, respectively. The linear concentration ranges were 10^–5–10^–1, 4.0 × 10^–5–10^–1 and 6.3 ×^–5–10^–1 M ephedrine. The detection limits were 4 ×^–6,10^–5 and 1.2 × 10^–5 M ephedrine for membranes I, II and III, respectively. The pH ranges were 4–9, 3–9 and 2–8 for I, II and III-membranes, respectively. Selectivity coefficient values for membrane II were better than those for membranes I and III. The effects of increasing KC1 concentration and temperature changes were explained for the three electrodes. The isothermal temperature coefficients were 0.00145, 0.0007 and 0.00055 V/ °C for electrodes I, II and III. Electrode III was applied for the determination of ephedrine in its pharmeaceutical preparations with an overall relative standard deviation range of 1.3–2.4% and an overall mean recovery value of 98.1%.     

Surface redox polymerized SPEEK–MO2–PANI (M = Si, Zr and Ti) composite polyelectrolyte membranes impervious to methanol

We reported sulfonated poly(ether ether ketone) (SPEEK, 61% degree of sulfonation)–metal oxides (MO₂:SiO₂, TiO₂ and ZrO₂)–polyaniline composite membranes. Metal oxides were incorporated into the swelled SPEEK membrane by sol–gel method and cured by thermal treatment. SPEEK–metal oxide membranes surfaces were modified with polyaniline (PANI) by a redox polymerization process. It was observed that water retention capacity of membrane was increased and methanol permeability was reduced due to synergetic effect of metal oxides and surface modification with polyaniline. These composite membranes showed extremely low methanol permeability (1.9–1.3 × 10⁻⁷ cm² s⁻¹), which was lower than till reported values either for SPEEK–metal oxide or SPEEK/PANI membranes. Relatively high selectivity parameter (SP) values at 343 K of these membranes, especially S–SiO₂–PANI and S–TiO₂–PANI, indicated their great advantages over Nafion117 (N117) membrane for targeting on moderate temperature applications due to the synergetic effect of MO₂ and PANI in SPEEK matrix. S–TiO₂–PANI and N117 showed comparable cell performance in direct methanol fuel cell (DMFC).     

A Comparative Study of the Electric Transport of Ions and Water in Sulfonated Cation-Exchange Polymeric Membranes of the New Generation

This work presents the results of the studies concerning the electric transport of ions and water through sulfonated cation-exchange membranes synthesized on the basis of polysulfone (PS) and poly(ether–ether–ketone) (PEEK). The concentration dependences of the water absorption capacity, specific conductance, and diffusion and electroosmotic permeabilities measured in sodium chloride solutions are compared to the analogous characteristics of some commercial membranes (MK-40, MF-4SK, CL-25T) under the same experimental conditions. The model concepts concerning the permeability of ion-conducting membranes as disperse systems are found to be applicable for interpreting the set of the electric transport properties of the membrane samples studied. A cluster–channel type of the membrane structure is identified. The polymeric films based on PS and PEEK are shown to possess characteristics comparable to those of commercial ion-exchange membrane samples and can be recommended for producing polymer compositions with an optimum set of electric transport properties.     

Pervaporation dehydration of ethylene glycol with chitosan–poly(vinyl alcohol) blend membranes: Effect of CS–PVA blending ratios

Chitosan–poly(vinyl alcohol), CS–PVA, blended membranes were prepared by solution casting of varying proportions of CS and PVA. The blend membranes were then crosslinked interfacially with trimesoyl chloride (TMC)/hexane. The physiochemical properties of the blend membranes were determined using Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), tensile test and contact angle measurements. Results from ATR-FTIR show that TMC has crosslinked the blend membranes successfully, and results of XRD and DSC show a corresponding decrease in crystallinity and increase in melting point, respectively. The crosslinked CS–PVA blend membranes also show improved mechanical strength but lower flexibility in tensile testing as compared to uncrosslinked membranes. Contact angle results show that crosslinking has decreased the surface hydrophilicity of the blend membranes. The blend membrane properties, including contact angle, melting point and tensile strength, change with a variation in the blending ratio. They appear to reach a maximum when the CS content is at 75 wt%. In general, the crosslinked blend membranes show excellent stability during the pervaporation (PV) dehydration of ethylene glycol–water mixtures (10–90 wt% EG) at different temperatures (25–70 °C). At 70 °C, for 90 wt% EG in the feed mixture, the crosslinked blend membrane with 75 wt% CS shows the highest total flux of 0.46 kg/(m² h) and best selectivity of 986. The blending ratio of 75 wt% CS is recommended as the optimized ratio in the preparation of CS–PVA blend membranes for pervaporation dehydration of ethylene glycol.     

Immobilization of Urease and Cholinesterase on the Surface of Semiconductor Transducer for the Development of Light-Addressable Potentiometric Sensors

Various methods for the immobilization of urease and butyrylcholinesterase on the insulator surface of a laser-scanned semiconductor transducer (LSST) have been tested and compared for the development of an enzyme-based light-addressable potentiometric sensor (LAPS). The method of preparing photocurable membranes on LAPS is presented, and a new type of enzyme LAPS with photocurable polymeric enzyme membranes has been elaborated. It was found that sensors prepared by means of covalent bonding and cross-linking with inactive protein (type SIII) and with photocurable membrane matrices (type SIV) are more prospective. The enzyme LAPSensors with photocurable membranes demonstrate a degree of sensitivity close to the theoretical value and working ranges of 6.3·10^–5–1.1·10^–2 and 1·10^–4–1·10^–1molL^–1 urea for acrylamide and acrylate-based membrane matrices, respectively, and 2.5·10^–4–2·10^–1molL^–1 butyrylcholine for an acrylamide membrane matrix. It is shown that such sensors can be also used for the analysis of enzyme inhibitors.     

Sulfonated poly(ether ether ketone)-based silica nanocomposite membranes for direct ethanol fuel cells

This paper reports on the preparation and characterization of sulfonated poly(ether ether ketone) (sPEEK)-based mixed matrix membranes. The inorganic matrix consisted of silica: Aerosil^®380, tetraethoxysilane (TEOS) or a combination of both to obtain an interconnected silica network. The behavior of these membranes in ethanol–water systems was studied for application in a direct ethanol fuel cell (DEFC). Uptake measurements showed that the converted TEOS content had a strong influence on the hydrophilicity of the membranes. Proton conductivity was strongly related to the water content in the membrane, but the proton diffusion coefficients of membranes with various Aerosil^®380–TEOS combinations were similar. Dynamic measurements in liquid–liquid (L–L) and liquid–gas (L–G) systems were performed to study the ethanol transport through the membrane. No reduction in ethanol permeability was obtained in the L–L system, but a remarkable reduction was obtained in the L–G system when 2 M ethanol was applied. The reinforcing characteristic of the combined Aerosil^®380–TEOS-system were best observed at 40 °C with 4 M ethanol. The fuel cell performance prediction based on the selectivity of proton diffusion coefficient to ethanol permeability coefficient showed for nearly all composite membranes an improvement with respect to the polymeric reference. The presence of an inorganic phase led to relatively constant proton diffusion coefficients and lower ethanol permeability coefficients in comparison with the polymeric reference.     

Effect of preparative conditions of a porous surface layer on the hydrogen permeability of palladium/ruthenium alloy membranes

The possibility of producing a porous surface layer on membranes formed from palladium alloys with mercury and lanthanum has been investigated. Membranes with the highest permeability to hdyrogen produced at temperatues in the range 500–550 K with zinc and 560–570 K with copper had maximum surface porosity.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1308–1312, June, 1991.     

Ultrafiltration of triglyceride from biodiesel using the phase diagram of oil–FAME–MeOH

To continuously obtain biodiesel of high purity, a membrane separator integrated with liquid–liquid extraction for the oil–FAME–MeOH system is studied. The liquid–liquid phase equilibrium data for the oil–FAME–MeOH are determined experimentally and compared with the general prediction of the modified UNIFAC. The tie line test demonstrates that composition of the methanol-rich phase is free of TG at 20 °C. Using the continuous cross-flow ultrafiltration, the oil-rich phase can be rejected by the ceramic membranes while the methanol-rich phase permeates through the membranes. When the feed bulk composition is controlled within the two-phase zone, such as the oil:FAME:MeOH of 20:30:50 wt.%, the permeate is found to be free of oil while the obtained permeate flux is higher than 300 kg/m² h under the transmembrane pressure of 600 mmHg and the inlet flow rate of 300 ml/min at 20 °C. By contrast, it shows almost no separation when the inlet concentration of oil–FAME–MeOH locates on its boundary line or within the single-phase zone. The quantitative filtration tests show that the compositions in the two liquid phases and the operating parameters are also considered simultaneously to screen the origin oil and get the FAME product of high purity.     

Selectivity of the membrane action of a cytotoxin from the venom of the Central Asian cobra

It has been shown that the selectivity of the direct hemolytic effect of the cytotoxin on different erythrocytes correlates with its influence on the ionic permeability of the membranes of these erythrocytes. It has been established on bilayer phospholipid membranes that the influence of the cytotoxin on their ionic permeability depends on the amount of cholesterol in them. It is assumed that the resistance of the cells to the cytotoxin is determined by the stability of the phospholipid backbone of their membranes.Institute of Biochemistry of the Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 813–817, November–December, 1980.     

Influence of Heterogeneity of Ion-Exchange Membranes on the Limiting Current and Current–Voltage Curves

A heterogeneous-membrane model is employed to demonstrate that, following a decrease in the ionite fraction in membranes, true values of limiting currents in electrolytes of different nature are not lower than in a pure ionite, while relative (measured) values drop by 2–5 times, which is explained by a decrease in the conducting surface areas of membranes. The formation of a limiting state on a heterogeneous surface is described qualitatively with allowance made for the morphology of membranes. The region of inflection in experimental and calculated current–voltage curves, which corresponds to a limiting state, is shown to degenerate with a decrease in the ionite fraction in membranes, which is due to the effect the membrane structure has on the polarization. The activation energy of the limiting state is determined.     

Ion-Selective Electrodes Based on Adamantylcalix[4,8]arenes for the Determination of Alkali Cations

Calix[4,8]arenes bearing adamantyl substituents in the upper rim and ethoxycarbonylmethoxy groups in the lower rim of the macrocycle were proposed as ionophores in membranes of ion-selective electrodes (ISEs) for determining alkali cations. Depending on the number of phenolic fragments (n) in the calixarene molecule, ISEs respond to either sodium (n = 4) or cesium (n = 8) ions. Sensors based on membranes that, along with ionophores, contain tetraphenyl borate ions as a lipophilic additive are selective for Na and Cs ions in the presence of other alkali metals. They exhibit almost theoretical responses over the concentration range from 1 × 10^–4 to 1 × 10^–1 M at pH 5.5–12 for Na-SE and pH 3–11 for Cs-SE, respectively.     

Hydrogen–oxygen fuel cells

Ion exchange non-fluorinated membranes were tested in half-cells used as models for hydrogen–oxygen fuel cells. The lower acidity of the membranes allowed us to reduce the chemical stability requirements for the construction and catalytic materials. The maximum energy yield at room temperature was close to 65% at a current density of 40–60 mA cm^–2.Presented at the 3rd International Meeting on Advanced Batteries and Accumulators, 16–20 June 2002, Brno, Czech Republic     

Ionic liquids to the rescue? Overcoming the ionic conductivity limitations of polymer electrolytes

Polymer electrolytes – solid polymeric membranes with dissolved salts – are being intensively studied for use in all-solid-state lithium-metal-polymer (LMP) batteries to power consumer electronic devices. The low ionic conductivity at room temperature of existing polymer electrolytes, however, has seriously hindered the development of such batteries for many applications. The incorporation of salts molten at room temperature (room temperature ionic liquids or RTILs) into polymer electrolytes may be the necessary solution to overcoming the inherent ionic conductivity limitations of ‘dry’ polymer electrolytes.     

Electrosurface and Ion-Selective Properties of Track-Etched Nanofilters: The Effect of Polyvalent Metal Adsorption

The effect of polyvalent metal adsorption on the performance and ion selectivity of poly(ethylene terephthalate) track-etched membranes with pores of 10 nm in diameter was studied. Membrane samples were prepared from the track-etched membranes with pores of 20 nm in diameter by thermal shrinkage. It was shown that an effective pore diameter decreases and selectivity of track-etched membranes increases upon filtration of Al(NO₃)₃ and Cr(NO₃)₃ solutions. The results obtained are explained by ion adsorption leading to the formation of complexes between polyvalent metals and carboxyl groups on the pore surface that is confirmed by IR spectroscopy data. The study of electrosurface properties of modified membranes and the dependence of ion selectivity of track-etched membranes on the concentration of Al³⁺ ions in 10^–2 M KCl solution indicates the decrease of membrane negative surface charge resulted from Al³⁺ adsorption and membrane charge reversal at Al³⁺ concentration in a solution higher than 10^–6 M. The dependences of the ion selectivity on pH and Al³⁺ concentration C _Al in a solution are similar. At pH < 3 and C _Al > 10^–6 M, the _1–2 > _1–1 > _2–1 ion selectivity series characteristic of the initial negatively charged membranes for the 1–1, 1–2, and 2–1 electrolyte solutions is reversed into the _2–1 > _1–1 > _1–2 series characteristic of positively charged membranes.     

Influence of the heterogeneous structure on the electrochemical properties of anion exchange membranes

In this study, the influence of the degree of the heterogeneity on the electrochemical behaviors was investigated for commercial anion exchange membranes using three monovalent organic electrolytes with sodium form (acetate, d-gluconate and monovalent citrate), which can be produced from fermentation processes, and an inorganic electrolyte (NaCl). As indicators of the heterogeneity for anion exchange membranes, the fraction of the inter-gel phase and the conducting phase in the membrane structure were considered in this study. Using the isoconductance value of an anion exchange membrane, the diffusion coefficient through the joint-gel phase in the membrane structure showed the sequence of chloride > acetate > gluconate > monovalent citrate. The fraction of the inter-gel phase of the heterogeneous membranes was much higher than that of the homogeneous membranes due to the heterogeneous structure. In addition, the fractions of conducting phase of heterogeneous membranes were estimated as much lower than those of homogeneous membranes. It was shown in the study that the heterogeneous structures affected the electrochemical properties of anion exchange membranes, which were characterized by the chronopotentiometry and the current–voltage relationship.     

Development of polyelectrolyte complexes of chitosan and phosphotungstic acid as pervaporation membranes for dehydration of isopropanol

Using a solution technique, chitosan-based polyelectrolyte complexes (PECs) were developed as pervaporation membranes by incorporating phosphotungstic acid (PTA). The resulting membranes were characterized by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Membranes were tested for their ability to separate water–isopropanol mixtures by pervaporation in the temperature range of 30–50 °C. The experimental results demonstrated that both flux and selectivity were increased simultaneously with increasing PTA content in the membrane. The permeation flux of pure chitosan membrane was increased dramatically from 4.13 to 11.70 × 10⁻² kg/m² h and correspondingly its separation factor was increased from 4490 to 11,241 and then decreased to 7490 at 30 °C for 10 mass% of water in the feed. The total flux and flux of water were found to be almost overlapping particularly for PECs membranes, suggesting that these could be used effectively to break the azeotropic point of water–isopropanol mixtures. From the temperature dependency of diffusion and permeation values, the Arrhenius activation parameters were estimated and discussed in the context of membranes efficiency. The pure chitosan and a small amount of PTA-incorporated PECs membranes exhibited positive heat of sorption while other PECs membranes exhibited negative heat of sorption, giving exothermic contribution.     

Ion-Selective Electrodes for the Determination of Nitrogen-Containing Medicinal Substances

Stoichiometric ratios and solubility products were determined for medicinal substance–tetraphenyl borate ion pairs. The influence of the nature of the medicinal substance cation incorporated into ionophores and the effect of the solvent–plasticizer on analytical characteristics were studied. The optimal composition of membranes was determined. Ion selective electrodes were used for the potentiometric determination of dimedrol, papaverine, novocaine, and lidocaine in medicinal forms.     

Isolation of a ca-channel blocker from the venom of the spiderAgelena labirintica

From the venom of the spider Ageiena labirintica we have isolated the neurotoxin Agll (IV-6-1) with a molecular mass of 1000 Da, which effectively blocks the Ca channels of presynaptic membranes of frog nerve-muscle synapses.Institute of Physiology and Biophysics, Academy of Sciences of the Republic of Uzbekistan, 700095, Tashkent, ul. Niyazova, 1. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 467–470, May–June, 1995. Original article submitted October 24, 1994.