Application of polysulfone (PSf)– and polyether ether ketone (PEEK)–tungstophosphoric acid (TPA) composite membranes for water electrolysis

The ion exchange membrane using polysulfone (PSf) and polyether ether ketone (PEEK) as a basic material was prepared to apply in the polymer electrolyte membrane electrolysis (PEME). The sulfonated block copolymer of PSf and poly(phenylene sulfide sulfone) (SPSf-co-PPSS) and the sulfonated PEEK (SPEEK) were blended with tungstophosphoric acid (TPA) to avoid water swelling at elevated temperatures led to decrease in mechanical strength. These prepared ion exchange membranes showed some interesting characteristics including physicochemical stabilities, mechanical and membrane properties.The prepared ion exchange membrane was utilized to prepare the membrane electrode assembly (MEA). MEA consisted of Pt/PEM/Pt was prepared by equilibrium and non-equilibrium impregnation–reduction (I–R) methods. The prepared MEA by non-equilibrium I–R method was used in the PEME unit cell. The cell voltages of the MEA using SPSf-co-PPSS/TPA and SPEEK/TPA membranes were 1.83 V and 1.90 V at 1 A/cm² and 80 °C, with platinum loadings of 1.12 and 1.01 mg/cm², respectively.     

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%.     

Sulfonated poly(ether ether ketone)/polyaniline composite proton-exchange membrane

Sulfonated poly(ether ether ketone) (PEEK) was prepared by sulfonation of commercial Victrex^@ PEEK and degree of sulfonation was found to be about 44.5% by ¹H NMR. Sulfonated PEEK/polyaniline composite membranes, in order to prevent methanol crossover, were prepared by chemical polymerization of a thin layer of polyaniline (PANI) in the presence of a high oxidant concentration on a single face modification. FTIR and PANI coating density studies confirmed the loading of PANI in sulfonated PEEK membrane matrix. PANI composite membranes with different polymerization time were prepared and subjected to thermogravimetric analysis as well as electrochemical and methanol permeability study to compare with sulfonated PEEK and Nafion 117 membrane. Ion-exchange capacity, water uptake, proton transport numbers and proton conductivities for different PANI composite sulfonated PEEK (SPEEK) membranes were found to be dependent on the coating density of the PANI in the membrane matrix and were slightly lower than that of Nafion 117 membrane. Methanol permeability of these membranes (especially SPEEK/PANI-1.5) was about four times lower than Nafion 117 membrane. Among the all SPEEK membranes synthesized in this study, SPEEK-1.5 appears to be more suitable for direct methanol fuel cell (DMFC) application considering optimum physicochemical and electrochemical properties, thermal stability as well as very low methanol permeability. Above all, the cost-effective and simple fabrication technique involved in the synthesis of such composite membranes makes their applicability quite attractive.     

Experimental analysis, modeling, and theoretical design of McMaster pore-filled nanofiltration membranes

A side-by-side comparison of the performance of McMaster pore-filled (MacPF) and commercial nanofiltration (NF) membranes is presented here. The single-salt and multi-component performance of these membranes is studied using experimental data and using a mathematical model. The pseudo two-dimensional model is based on the extended Nernst–Planck equation, a modified Poisson–Boltzmann equation, and hydrodynamic calculations. The model includes four structural properties of the membrane: pore radius, pure water permeability, surface charge density and the ratio of effective membrane thickness to water content. The analysis demonstrates that the rejection and transport mechanisms are the same in the commercial and MacPF membranes with different contributions from each type of mechanism (convection, diffusion and electromigration). Solute rejection in NF membranes is determined primarily by a combination of steric and electrostatic effects. The selectivity of MacPF membranes is primarily determined by electrostatic effects with a significantly smaller contribution of steric effects compared to commercial membranes. Hence, these membranes have the ability to reject ions while remaining highly permeable to low molecular weight organics. Additionally, a new theoretical membrane design approach is presented. This design procedure potentially offers the optimization of NF membrane performance by tailoring the membrane structure and operating variables to the specific process, simultaneously. The procedure is validated at the laboratory scale.     

Transport Properties of Selective Membranes Reversible to Nitrogen-Containing Organic Base Cations: Permeability and Ion Flow

Main transport properties were studied for selective membranes with low dielectric constants based on liquid ion exchangers involving nitrogen-containing organic base cations. Permeabilities and ion flows through a membrane were calculated for major and interfering ions. Dependences of the transport properties of membranes on the concentrations of the ion exchanger and near-membrane solution and their potentiometric characteristics are presented. It was demonstrated that the transport properties of liquid membranes are determined by two main factors: the transfer of counterions through the phase boundary by the extraction–exchange mechanism and the leaching of the ion exchanger from the membrane.     

Electrochemical Parameters of Heterogeneous Bipolar Membranes: Dependence on the Structure and Nature of Monopolar Layers

The current–voltage curves, transport numbers of ions, and electrochemical impedance spectra are obtained for pilot samples of heterogeneous bipolar membranes synthesized from cation- and anion-exchange membranes. In the synthesis, the composition of the monopolar layers of membranes was varied or a catalyst was introduced into them. The voltage drop and the frequency spectra at the pilot membranes are close to those for industrial membrane MB-3. The transport numbers of co-ions in the pilot membranes are smaller and those of the hydrogen and hydroxyl ions are larger than in MB-3. The effective water dissociation constants in the pilot membranes, calculated from the impedance spectra, are close to those of MB-3.     

Electrokinetic Phenomena in Sulfonated Cation-Exchange Membranes with Tetraalkylammonium Ions

The electric transport of solvent ions and molecules through membrane systems containing cations of tetraalkylammonium bases is studied. The interrelation between electrokinetic characteristics of sulfonated cation-exchange membranes at different degrees of their saturation with tetrabutylammonium ions and the content of water in membranes at equilibrium is established. A new type of conductor-insulator percolation transitions is revealed for homogeneous MF-4SK perfluorinated membranes saturated with organic counterions. This transition is interpreted with allowance for the concept of the governing role of narrow channels in the membrane microstructure. The electroosmotic permeability of MF-4SK membranes in solutions of sodium and tetraethylammonium chloride, as well as in their mixtures, is studied. An experimentally observed abnormally high amount of water transferred by tetraethylammonium ions is discussed with allowance for the dynamic hydration characteristics of ions.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 4, 2005, pp. 485–493.Original Russian Text Copyright © 2005 by Kononenko, Berezina, Shkirskaya.     

On-Line Multielement Preconcentration and Inductively Coupled Plasma Atomic Emission Spectrometric Determination of Transition Metals Using a Flow Injection Hydraulic High-Pressure Nebulization–Desolvation Sample Introduction System

A method was developed for simultaneous preconcentration and on-line determination of 15 transition metals (Ag, Au, Cd, Cr, Cu, Fe, In, Ni, Pb, Pd, Pt, Ti, Tl, V, Zn). A polyether–ether–ketone (PEEK) loop as preconcentration unit introduced by us earlier was used for the multielement flow injection (FI) preconcentration of transition metal–pyrrolidinedithiocarbamate complexes. The preconcentrated complexes were eluted with isobutylmethyl ketone and introduced into the inductively coupled plasma with a hydraulic high-pressure nebulizer (HHPN) and desolvation unit. The desolvation system, the use of which was necessary for aerosol of isobutylmethyl ketone eluant, was optimized. The enrichment factors of the 15 transition metals were 14–67 due to 2 min of preconcentration time.     

Transfer of electrolyte ions and water dissociation in anion-exchange membranes under intense current conditions

Polarization characteristics of electromembrane systems (EMS) based on the Russian commercial heterogeneous membranes MA-40 and MA-41, the anion-exchange heterogeneous membrane AMH (Mega, Czech Republic), and the modified membrane MA-40M are studied by the method of rotating membrane disk in dilute sodium chloride solutions. The effective transport numbers of ions are found; the partial voltammetric characteristics (VAC) with respect to chloride and hydroxyl ions are measured; the limiting current densities are calculated as a function of the membrane disk rotation rate. In terms of the theory of the overlimiting state of EMS, based on experimental VAC and the dependences of the effective transport numbers on the current density, the following internal parameters of systems under study are calculated: the space charge and electric field strength distribution over the diffusion layer and the membrane. It is shown that water dissociation can be virtually completely eliminated by substituting chemically stable quaternary ammonium groups inert with respect to water dissociation in the surface layer of a heterogeneous anion-exchange membrane MA-40 for the active ternary and secondary functional amino groups. The maximum electric field strength values at the membrane/solution interface, which were found in the framework of the theory of over-limiting state, turned out to be close for all anion-exchange membranes studied, namely, (7?C9) × 10⁶ V/cm. This suggests that it is the nature of ionogenic groups in the surface layer rather than the field effect that plays the decisive role in the membrane ability to accelerate the water dissociation reaction. It is proved experimentally that in highly intense current modes of the electrodialysis process, the thermal hydrolysis of quaternary ammonium bases occurs in strongly basic MA-41 and AMH membranes by the Hofmann reaction to form ternary amino groups catalytically active in water dissociation reaction. Based on the concept on the catalytic mechanism of water dissociation, the fraction of ternary amino groups formed by thermal hydrolysis in the surface layer (the space charge region) of monopolar anion-exchange membranes MA-41 and AMH is assessed quantitatively as 0.7 and 6.5%, respectively.     

Transport–Structural Parameters of Domestic and Foreign Anion-Exchange Membranes

The concentration dependences of the electroconductivity, diffusion penetrability, and transport numbers for water in anion-exchange membranes of domestic and foreign production are studied in identical conditions in NaCl solutions with the aid of a complex of standardized methods of conditioning the samples and measuring their properties. The dependences of the electroconductivity and the diffusion flux of the salt are used to calculate transport–structural parameters, which characterize conducting properties of membranes in the framework of a heterogeneous model. Electrotransport properties of anion-exchange membranes are compared and factors that affect them are discussed.     

Water-swollen cation-exchange membranes prepared using poly(vinyl alcohol) (PVA)/poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA)

A water-swollen type of poly(vinyl alcohol) (PVA)/poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA) cation-exchange membrane was prepared and characterized in terms of its electrochemical properties including ion-exchange capacity (IEC), electrical resistance, and transport number, etc. PVA/PSSA-MA membranes exhibited low electrical resistance and highly swelling property. In spite of 2–4 times higher water swelling ratio (WSR) than that of CMX (Tokuyama Corp., Japan), the transport number of the prepared membrane was comparable to that of the commercial membrane (t_n>0.93). Moreover, the electric resistance of PVA/PSSA-MA membrane was measured as low as 1.0–1.5 Ω cm². Further, in this study, interrelation between the membrane characteristics and crosslinking was investigated, and the result exhibited that the crosslinking degree is one of major factors affecting the ion transport through a water-swollen ion-exchange membrane (IEM).     

Preparation and characterization of Type II anion exchange membranes from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)

To separate hydrophilic anions from hydrophobic ones, Type II PPO-based anion exchange membranes were developed. Different from Type I (with both trimethylbenzylammonium and triethylbenzylammonium groups), Type II has an excellent hydrophobicity modifier as fixed groups: dimethyethanolammonium groups, which were introduced into PPO (poly(2,6-dimethyl-1,4-phenylene oxide)) by following benzyl bromination of PPO and subsequent quaternary amination with a dimethylethanolamine (DMEA) aqueous solution. The membrane's intrinsic properties are dependent on DMEA concentration and amination temperature. The optimum conditions for membrane preparation are as follows: amination temperature 70 °C, time 30–48 h, and DMEA concentration 1:3–1:5 (v/v, DMEA to water). The obtained Type II anion exchange membranes had an IEC of 1.5 mmol/g dry membrane, water content of 30%, and membrane area resistance of 30 Ω cm². The introduced dimethyethanolammonium groups can block hydrated anions from the access to membranes but let hydrophobic anions transport; hence, an effective separation between hydrophilic and hydrophobic anions can be achieved during electro-membrane operation.     

High throughput screening and measurements of proton conductivity of newly developed PEM materials based on proton transport visualization

An electrochemical method for proton transport visualization was developed and applied to the investigation of proton-conducting membrane materials. The method employs the change in the visual appearance of chemo-chromic tungsten oxide WO₃ in the presence of atomic hydrogen. An all-solid electrochemical cell arranged by substituting a fuel cell cathode with a thin film of WO₃-electrode was built and shown to generate both optical and electrical response to hydrogen gas exposure. The design of the cell was extended to a high throughput screening system that was utilized to characterize proton transport properties of samples, including a number of new compounds synthesized in-house by sol–gel wet chemistry. Non-destructive introduction of superacidic groups promoting proton hopping in the membrane materials was achieved by photodecomposition of a photoacid generator just after membrane casting. A model quantitatively describing current–voltage relation in the cell was developed and successfully applied to derive area-specific resistance of proton-conductive membranes from the experimental results. Area-specific resistances of membranes are derived from the slopes of optically reconstructed voltage–current curves. Sensitivity and dynamic range of the screening method are discussed.     

Biofouling potentials of microporous polysulfone membranes containing a sulfonated polyether-ethersulfone/polyethersulfone block copolymer: correlation of membrane surface properties with bacterial attachment

Multivariate methods were used to identify relationships between bacterial attachment (biofouling potential), water transport, and the surface properties of nine modified polysulfone (MPS) membranes comprising blends of polysulfone (PS) with a sulfonated polyether-ethersulfone/polyethersulfone block copolymer. The topology of the microporous MPS membranes, including surface roughness, surface height, pore size and pore geometry were determined by atomic force microscopy (AFM) and digital image analysis. Other measurements included relative surface hydrophobicity by captive bubble contact angle, surface charge (i.e., degree of sulfonation) by uranyl cation binding, wt% solids, porosity, membrane thickness, water flux, and the affinity of membranes for a hydrophilic Flavobacterium and hydrophobic Mycobacterium species. The mycobacteria attached best to the MPS membranes, but the attachment of both organisms was inversely correlated with the mean aspect ratio of pores, suggesting that irregular or elliptic pores discouraged attachment. Multivariate regression analyses identified the pore mean aspect ratio, mean surface height, PS content, and the n-methylpyrrolidone+propionic acid (NMP–PA) solvent concentration as influential factors in Mycobacterium attachment, whereas membrane thickness, surface roughness, pore mean aspect ratio, porosity, and the mean pore area/image area ratio influenced Flavobacterium attachment. Cluster analyses revealed that Mycobacterium attachment was associated with hydrophobic determinants of the MPS membranes, including PS content, wt% solids, and air bubble contact angle. In contrast, Flavobacterium attachment was primarily associated with membrane thickness and charge (i.e., uranyl cation binding or degree of sulfonation). Membrane flux was inversely correlated with surface hydrophobicity and PS content, but (in contrast to cell attachment) positively correlated with most pore geometry parameters including the mean aspect ratio, suggesting that pore geometry can be optimized to minimize cell attachment and maximize water transport. Other variables influencing water flux included the NMP–PA solvent concentration and membrane roughness. The results should facilitate the design of novel microporous PS membranes having reduced biofouling potentials and greater water fluxes.     

Peculiarities of Steady-State and Unsteady-State Mass Transfers through Pervaporation Membranes Based on Sulfonated Aromatic Polyamides

Permeability and selectivity of pervaporation membranes based on homopolymers of sulfonated aromatic amides and their random copolymer are studied. It is shown that slight differences in macromolecular configuration of homopolymers caused by the introduction of benzene rings into polymer chain in meta or para positions substantially change the membrane transport properties with respect to water–organic solutions. During an unsteady-state process, in the course of film swelling, the polymers undergo structural transformations that intensify nonlinear relaxation processes. In particular, periodic selectivity inversions are observed in these highly hydrophilic systems. The nonlinear character of the set of the processes accompanying mass transfer can cause different membranes taken from the same batch of films to demonstrate selective permeability with respect to both water and an organic component in the steady-state regime of the pervaporation unit operation.     

牛血清白蛋白在修饰氯离子金纳米通道中的迁移研究

采用化学镀的方法在聚碳酸酯模板上沉积金,制成金纳米通道膜,并对它进行Cl-修饰得到带负电荷的通道。再采用电化学方法(i-t法)对牛血清白蛋白(BSA)在修饰通道中的迁移进行研究。在pH7.4PBS中,对通道两端施加1.0V电压,溶液中离子迁移通过纳米通道时产生电流响应。当溶液中加入BSA后,电流响应减小,且响应变化量与浓度在1.50×10-10~1.35×10-9mol/L范围内呈线性关系,其线性回归方程为|Δi|(μA)=0.0069 0.125c(×10-9mol/L),相关系数为0.9980,检出限为9.46×10-11mol/L(S/N=3)。     

Electrodialysis of uranium(VI) through cation exchange membranes and modeling of electrodialysis processes

The transport of ionic species through ion exchange membranes found several applications for water effluents purification and metal ion separation. To enhance the transport performance, the effect of electric fields was suggested in this work. The transport of U(VI) species in nitric acid solutions across cation exchange membranes was investigated. Different parameters affecting the transport of U(VI) were studied. These parameters include: nitric acid concentration in the feed solution, stripping solution concentration and applied electric field. From the results obtained, the cationic flux of U(VI) was 6.5^.10^–8 geq^.cm^–2.s^–1 at the optimal conditions of 10^–3M HNO₃ in the feed solution, 0.5M Na₂CO₃ in the stripping solution and 30 V. The modeling of the electrodialysis process was also made. The model correlates the mass transfer as a function of current density and voltage as variables and takes into account the electro-osmotic effect. The model is applied to the experimental data.     

Water diffusion through hydrogel membranes: A novel evaporation cell free of external mass-transfer resistance

A novel evaporative cell is used to measure steady-state gradient-driven diffusion rates of water through hydrogel membranes in the absence of external mass-transfer resistance. In this cell, the bottom surface of a hydrogel membrane is exposed to pure water vapor at known activity (a_w) less than unity, while a sealed liquid-water reservoir bathes the upper membrane surface. Induced by the chemical-potential gradient between the two surfaces, the water evaporation rate is monitored by the rate of weight loss of the water reservoir.Results at ambient temperature are compared with those from measured water flux through soft-contact-lens (SCL) materials and with other published experimental results. Concentration-dependent water diffusivities are obtained by interpreting measured water fluxes for 0.11 ≤ a_w ≤ 0.93 with extended Maxwell–Stefan (EMS) diffusion theory. Thermodynamic non-ideality is taken into account through Flory–Rehner polymer–solution theory. Shrinking/swelling is modeled by conservation of the total polymer mass assuming volume additivity. In spite of correction for thermodynamic non-ideality, EMS–water-diffusion coefficients increase with the water volume fraction, especially strongly for those hydrogel materials with low liquid-saturated water contents. The evaporation cell described here provides a simple robust method to establish water transport rates through soft-contact-lenses and other hydrogel membranes without the need to correct for external mass-transfer resistance.     

The dependence of electro-osmotic flow on current density and time

The dependence of the water transport number on current density is examined for three membranes whose characteristics cover a wide spectrum: poly(vinylbenzenesulfonate), porous Vycor glass and cellulose. Experiments and theory show that non-linear volume—time plots in electro-osmotic experiments arise from displacements of the membrane in the electric field, and that reliable water transport numbers can be obtained at a given current density. When the current density is varied, experiments show that the observed water transport number can: (a) increase at low current densities because of osmotic flow superimposed on water transport by the electric field; (b) decrease at higher current densities because of accumulation of salt in the membrane; (c) decrease more at current densities near and above the limiting value because of an increased contribution of hydrogen and hydroxide ions to transport. These phenomena arise from a combination of diffusion films at both membrane—solution interfaces and from the dependence of counteflon and water transport numbers on external salt concentration.     

Transport properties and electroanalytical response characteristics of drotaverine ion-selective sensors

The construction and electroanalytical response characteristics of poly(vinyl chloride) matrix ion-selective sensors (ISSs) for drotaverine hydrochloride are described. The membranes incorporate ion-association complexes of drotaverine with tetraphenylborate, picrate, tetraiodomercurate, tetraiodobismuthate, Reinecke salt, and heteropolycompounds of Keggin structure—molybdophosphoric acid, tungstophosphoric acid, molybdosiliconic acid and tungstosiliconic acid as electroactive materials for ionometric sensor controls. These ISSs have a linear response to drotaverine hydrochloride over the range 8×10^–6 to 5×10^–2 mol L^–1 with cationic slopes from 51 to 58 mV per concentration decade. These ISSs have a fast response time (up to 1 min), a low determination limit (down to 4.3×10^–6 mol L^–1), good stability (3–5 weeks), and reasonable selectivity. Permeabilities and ion fluxes through a membrane were calculated for major and interfering ions. Dependences of the transport properties of the membranes on the concentrations of the ion exchanger and near-membrane solution and their electrochemical characteristics are presented. The ISSs were used for direct potentiometry and potentiometric titration (sodium tetraphenylborate) of drotaverine hydrochloride. Results with mean accuracy of 99.1±1.0% of nominal were obtained which corresponded well to data obtained by use of high-performance liquid chromatography.