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The preparation of silver nanoparticles (AgNPs) and their incorporation into the structure of a regenerated cellulose membrane by dip coating is presented. Morphological characterization of the AgNPs (average diameter of 20 ± 2 nm) was carried out by SEM/TEM, while elastic, electrical and antimicrobial properties of the hybrid membrane were also analyzed. The presence of silver nanoparticles in the membrane seems to increases its rigidity and its chemical stability against oxidation, but it only induces small changes in the transport parameters. As expected, AgNPs provide antimicrobial properties to the membrane and consequently the reduction of biofouling without affecting significantly other characteristic parameters, opening the application of the modified membrane to wastewaters treatment.

Changes associated to surface functionalization of nanoporous alumina membranes by atomic layer deposition (ALD) of metal oxides (Al2O3, SiO2, TiO2, Fe2O3, ZnO) are presented. ALD modification of the alumina membranes reveals a reduction up to 25–35% in porosity, and confirms the presence of the metal oxide layer coating the pores. Its effect on the membrane permselectivity and other characteristic transport parameters was determined from membrane potential measurements, being correlated with changes in morphology and physic–chemical characteristics of the alumina membranes. According to our results, ALD provides a straight-forward and efficient method to adjust membrane performance for specific applications.

Microcrystalline cellulose (MCC) and polyamide 66 (PA66) have been separately dissolved in solutions containing trifluoroacetic acid (TFA) as a common solvent, mixed after their dissolution and cast. After solvent evaporation, self-organized membranes have been formed with three dimensional (3D) porous, interconnected morphology, the porosity of which depends on the relative ratio of cellulose and PA66, and is lost when the initial MCC content exceeds 50% by weight. Thermal and chemical analysis and X-ray diffraction results indicate that the addition of cellulose induces the amorphisation of PA66, while possible chemical interaction exists between the amorphous parts of PA66 and the cellulose. The various membranes produced with different 3D porosities have been characterized in terms of dielectric constant and salt permeability and their relation to cellulose-PA66 ratio has been determined.

Polymer inclusion membranes (PIMs) have been prepared using cellulose triacetate (CTA) as polymer and derivatives of the commercial ionic liquid (IL) Aliquat 336, trioctyl methylammonium chloride (AlqCl), as extractants. The different ILs were prepared by exchanging chloride anion from AlqCl for other more lipophilic anions, obtaining IL derivatives AlqNO 3 and AlqSCN. PIMs containing these extractants at two different concentrations (30% and 60%) were prepared and characterized using X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), contact angle and impedance spectroscopy to obtain information on the material properties of both the surface and bulk membranes. The IL counter-anion affects the membrane's electrical parameters (dielectric constant and conductivity) as well as its hydrophobic character, which also depends on the IL concentration in the PIM formulation. Passive transport across the different PIMs using HCl and NaCl aqueous solutions was also considered, and the results obtained seem to be directly related to the hydrophilic/hydrophobic character of the studied membranes The financial support of the Spanish government through research project CTM2013-48967-C2-2-P is acknowledged. R. Vera acknowledges a grant from the Spanish Ministerio de Economía y Competitividad (ref. BES-2014-068314)

A new silicon carbide ceramic membrane consisting of a unique top layer on a SiC support for application in oily wastewaters filtration was produced and characterized in terms of morphology and chemical surface composition by scanning electron microscopy and X-ray photoelectron spectroscopy measurements. The manufacturing process of this new membrane allows time and economic savings when compared with a two layers membrane previously obtained. The new membrane has a smooth top layer with controlled porosity and a higher permeability compared to already developed commercial membranes. Moreover, it is extremely efficient to remove total suspended solids as well as oil and grease and, consequently, it can be applied to effective treatment of industrial oily wastewaters.

Surface modification of alumina nanomembrane (ANP) by theophylline derivative Theo 1 by dip-coating was successfully achieved. The hybrid material was characterized by SEM, XPS and confocal microscopy. The presence of Theo 1 on the ANP surface was established from salt diffusion and membrane potentials measurements. Changes in the electrical character and transport parameters of the modified sample, associated to Theo 1 deposition, were established. Stability of the material under diffusive flow was also ascertained. Moreover, as a result of Theo 1 bioactivation, streptavidin linkage to the ANP/Theo 1 -modified membrane was obtained, which is an indication of streptavidin capture.

Diaminobutane based poly(propyleneimine) dendrimer functionalized with sixteen thiol groups, DAB-3-(SH)16, was successfully embeded in a swollen cellulosic support in order to achieve an easily handle engineered membrane. The membrane was characterised by physicochemical, electrical and transport measurements, and the effect of the dendrimer was established by comparing these results with those obtained for the original cellulosic support. Results show that dendrimer inclusion improves the membrane elastic behaviour (Young modulus increase around 20%), while a significant reduction in the permeation of toxics heavy metals (Cd2+, Hg2+ and Pb2+) was also obtained, which avails the possible application of dendrimer-modified membrane in electrochemical devices for water remediation, The authors would like to thanks to Andalucía Tech Program (Universidad de Málaga, Spain) and the CICYT (MINECO, Spain, research project CTQ/2011-27770 FEDER funds) for partial financial support. Spanish Ministerio de Ciencia e Innovación (Project CTQ2009-12332-C02-01) is also acknowledged

The effect of the base-polymer and carrier concentration on the physical–chemical characteristics of polymer inclusion membranes (PIMs) is investigated. Two typical polymers used to manufacture PIMs have been tested, i.e. poly(vinyl chloride) (PVC) and cellulose triacetate (CTA), and different amounts of the ionic liquid (IL) Aliquat 336, used as extractant, were the PIMs constituents. The resulting PIMs have been characterized using different techniques to provide information on both the surface and bulk material properties. XPS results do not practically show differences in the surfaces of CTA and PVC based membranes with similar Aliquat 336 content, and the total surface coverage for Aliquat 336 concentration higher than 40% (w/w) was obtained, which was also corroborated with the results of contact angle measurements. However, membrane elastic response seems to be strongly dependent on both base-polymer and Aliquat 336 concentration, which affect Young modulus and elongation at break. The IL concentration also increases dielectric constant and the conductivity of the PIMs from both polymers according to impedance spectroscopy results, providing a rather conductive character to both kind of samples for Aliquat 336 content higher than 40% (w/w) (average conductivity around 10 −3 (Ω m) −1 ). CTA and PVC-based PIMs with Aliquat 336 content around 45% have been used in order to compare the influence of the polymer on the transport of As(V).

Changes in a protonated Nafion-112 membrane as a result of the incorporation of the cation n-dodecyltrimethylammonium (DTA+) by proton exchange mechanism are studied. Membrane surface modifications were analysed by AFM, XPS and contact angle measurements in order to obtain information about changes in the membrane surface roughness, chemical nature and hydrophobic character, while electrochemical impedance spectroscopy (EIS) and methanol permeation measurements were carried out to establish changes in the bulk membrane. The reduction obtained for the surface roughness and the hydrophobic character of Nafion-112/DTA+ equilibrated membrane as well as for the fluorine atomic concentration percentage and the increase in nitrogen percentage indicates modification of Nafion-112 membrane surface, while the increase of electrical resistance and the decrease of methanol permeability give information on bulk membrane changes. The higher thermal stability and lower water loss of the Nafion-112/DTA+ membrane are points of interest for applications such as PEMFC or DMFCs, respectively.

Poly(vinylidene fluoride) (PVDF) and regenerated cellulose (RC) membranes were surface-modified by the adsorption of one adenosine receptor antagonist: the theophylline-oligo(ethylene glycol)-alkene derivative, Theo1. Surface modification was carried out by immersion of the membrane in a dichloromethane solution of Theo1 (PVDF+Theo1 and RC+Theo1 samples). Membrane surfaces with partial coverage by theophylline and/or its inclusion in the membrane structures were studied by X-ray photoelectron spectroscopy (XPS), solid-state nuclear magnetic resonance (SNMR), impedance spectroscopy (IS) and contact angle (CA) measurements. The Theo1 orientation was inferred from the data. Streptavidin (SA) was immobilized onto the membrane/Theo1 hybrid material. The protein-theophylline Theo1 interaction was visualized with bright field microscopy (BFM).

The behavior of a fluorescent nanocomposite, obtained by means of a thiol polypropylenimine dendrimer of third generation coated with CdSe quantum dots, and embedded in a hydrophilic cellulosic membrane as support is electrochemically studied in order to evaluate its applicability as a sensor in liquid media. The characterization of the nanocomposite by TEM and EDAX shows uniform nano morphology (size comprised in the range 60–90 nm) and composition, respectively. The analysis of the engineered hybrid cellulose-dendrimer quantum dots material by confocal fluorescence microscopy indicates almost mono-dispersion distribution of the nanocomposite when irradiated under UV light, while its presence on the film surface was determined by X-ray photoelectron spectroscopy. Impedance spectroscopy measurements performed with dry membrane samples show a decrease in the conductivity and dielectric constant of the modified membrane in comparison with the raw support. Electrical changes in the modified film associated to the presence of Cd(II) uptakes from a Cl 2 Cd solution were also obtained. These results support the possible application of this nanocomposite material as heavy metal sensor in liquid media.

Highly ordered Nanoporous Alumina Membranes (NPAMs) with a precise control of the pore size and different porosity but thickness around 63 μm were fabricated by the two-step anodization process using different acidic aqueous solutions, oxalic (Al-Ox), sulfuric (Al-Sf), and phosphoric (Al-Ph) acids, respectively. The pore size was controlled by properly changing the anodization voltage and the electrochemical bath conditions, obtaining the following average pores diameter values, d(p), as determined by scanning electron micrographic analysis: Al-Ox (d(p)=46±2 nm), Al-Sf (d(p)=27±2 nm), and Al-Ph (d(p)=240±20 nm). A pore increasing of around 5% for samples Al-Ox and Al-Sf was obtained after membranes immersion in 5 wt.% phosphoric acid for a certain etching time. Electrochemical characterization of NPAMs was performed with the samples in contact with NaCl solutions at different electrolyte concentrations. Ionic transport numbers and effective membrane fixed charge were determined from membrane potential measurements, which clearly show the significant influence of the pore diameter on ions transport. Moreover, frictional and electrical effects on mass transfer parameters (salt and ions diffusion coefficients) into the pores of alumina membranes were also evaluated from these results.

Films from copolyimides containing side carboxylic acid groups were prepared in –COOH and COO − Na + forms to study the effect of the side groups content on some physical properties such as water absorption, thermal stability and electrical parameters. The thermal stability was evaluated by TGA and the results showed that degradation temperatures depended not only on the side groups content but also on the membrane ionic form. This dependence was also observed in the water sorption isotherms; the polyimides with the highest –COOH content showing the highest water sorption in the equilibrium. Dielectric impedance measurements revealed how the side groups and their ionic form affect the material electrical characteristics, in such a way that resistivity decreased and permittivity increased on introducing more –COOH groups in the polymer, which is also related to a higher water uptake of the films.

The effect of annealing temperature (25 °C < T < 97 °C) on transport and structural parameters for two different regenerated cellulose membranes (dense and nanoporous) is studied. Results show different temperature dependence for water permeability and NaCl diffusion coefficient depending on the membrane structure, with an increase from 25 °C to 60 °C and a more significant reduction between 70°°C and 97 °C for the dense sample, but practically constant for the nanoporous. These results seem to be directly related to the membrane’s elastic behaviour according to the temperature effect on degree of swelling. Moreover, diffusional permeability-concentration curves also allow the determination of other membrane parameters (fixed charge concentration and partition coefficient) which are independent of temperature.

Physicochemical and NaCl characteristic transport parameters determined for a lipid coated regenerated cellulose membrane are reported. The lipid studied consists of glyceryl triestearate, while l -α-phosphatidylcholine and sodium taurocholate were used as surfactants. The RC-support and the lipid-modified membrane were characterized by X-ray photoelectron spectroscopy (XPS) at three different take off angles and X-ray diffraction. Transport parameters (salt diffusion and electrical resistance) were determined from salt permeation and impedance spectroscopy measurements performed with the membranes in contact with a NaCl constant concentration ( C c = 0.01 M). These results show a reduction in the transport parameters across the lipid coated membrane due to the lipid presence as well as its stability under mass and ion fluxes, which supports its application in liquid systems.

Modifications caused in commercial dense regenerated cellulose (RC) flat membranes by low-dose γ-irradiation (average photons energy of 1.23 MeV) are studied. Slight structural, chemical and morphological surface changes due to irradiation in three films with different RC content were determined by ATR-FTIR, XRD, XPS and AFM. Also, the alteration of their mechanical elasticity has been studied. Modification of membrane performance was determined from solute diffusion coefficient and effective membrane fixed charge concentration obtained from NaCl diffusion measurements. Induced structural changes defining new and effective fracture propagation directions are considered to be responsible for the increase of fragility of irradiated RC membranes. The same structural changes are proposed to explain the reduction of the membrane ion permeability through a mechanism involving either ion pathways elongation and/or blocking.

Two highly hydrophilic regenerated cellulose planar sheets (RC-6 and RC-MD) with different morphological, structural and transport parameters were used as supports of lipid (lecithin-triestearine) nanoparticles (RC-6/LNPs and RC-MD/LNPs samples), which were embedded by immersion in a water dispersion of LNPs. Salt and ions transport (salt diffusion, ion transport numbers and effective fixed charge) were determined from measurements carried out with the samples in contact with NaCl solutions at different concentration and, consequently, osmotic pressures. Results do not show differences in the small fixed charge of the membranes as a result of nanoparticles inclusion (−0.012 M and −0.008 M for RC-6 and RC-MD, respectively) and stability of the LPNs-modified membranes for osmotic pressure up to 5 bars was established. TEM images shows the presence of LNPs in the RC-supports and Raman spectroscopy analysis was used for physic-chemical characterization of the RC-supports and RC/LNPs-modified membranes but also to determine the stability of modified samples under flow conditions. Different transport behaviour depending on the RC-support was obtained, and results seem to indicate the maintenance of nanoparticles into the dense RC-support structure till a concentration gradient of 0.1 M.

Ultrasound and high-pressure homogenized lipid (lecithin–tristearin)nanoparticles (NPs) were prepared and embedded into a regenerated cellulose (RC-MD) commercial membrane; the RC-support was also modified with the deposition of a lecithin–tristearine layer (RC-MD/LL sample). The lipid nanoparticles, RC-support and modified membranes were topographically and chemically characterized by Atomic Force Microscopy (AFM) and Raman spectroscopy. Electrical parameters (conductivity and capacitance) of both the original and modified membranes were determined by the impedance spectroscopy (IS) technique using a parallel resistance–capacitance equivalent circuit as a model. The results allow the lipid particle inclusion to be distinguished from the lipid layer deposition. Moreover, the paper shows the possibility of lipid nanoparticle inclusion into a solid support maintaining particle integrity.

Water effect in different physical–chemical and elastic parameters determined for a dense cellulose regenerated (RC) membrane is presented. Membrane samples characterization was carried out by obtaining XPS spectra, X-ray diffraction patterns and elasticity curves, and the significant differences determined when dry and wet samples are compared are basically associated to the water plasticization effect in this high hydrophilic material. Transport of different aqueous electrolyte solutions (NaCl, KCl, LiCl, MgCl 2 and CaCl 2 ) was study by measuring membrane potentials and diffusion, which allows the determination of effective membrane fixed charge concentration, ion transport numbers and permselectivity as well as diffusional permeability and diffusion coefficient of the different salts across the RC membrane. Differences associated to the kind of electrolyte (1:1 or 2:1 electrolytes) were obtained as a result of membrane–solute electrical interactions. Membrane dense structure significantly reduce both salt and water diffusional transport, being this latter determined by using tritiated water as permeate.

Diffusional NaCl transport across a microporous ceramic membrane was studied by measurements carried out at a constant feed concentration ( C f = 0.01 equiv./l) but different solutions stirring rates (0 ≤ ν (rpm) ≤ 1000), which allows the determination of both membrane system and true membrane diffusional permeability ( P sm and P s , respectively). Differences between both values are related with the stagnant solution layer on the membrane surface, and its thickness was also determined from these measurements. Moreover, modification in diffusional permeability and polarization layer thickness as a result of membrane static protein fouling due to membrane–protein contact for two different protein solution concentrations (0.5 and 2 g/l of bovine serumalbumin) was also studied and correlated with the system structure.

Nafion membranes were modified by incorporation of ionic liquid (IL) cations, at controllable degrees. These modified membranes were then characterised with the use of different techniques. X-ray photoelectron spectroscopy (XPS) demonstrated that the IL cations are incorporated in the membrane material and allowed to evaluate the distribution of the cation in the membrane surface layer. Electrochemical impedance spectroscopy (EIS) was used to monitor membrane modification by incorporation of IL cations, and to study the electrical properties of the modified membranes, with different degrees of cation incorporation. These results were adjusted to mathematical models of equivalent electrical circuits to extract data of membrane ionic conductivity. Finally, thermogravimetry studies allowed assessing the stability of the modified membranes with increasing temperature in terms of their water content, and these results were used to establish a possible relation between the membrane stability at high temperatures with their water content and degree of structuring. It was concluded that it is possible to obtain membranes with tailored properties depending on the type of IL cation and its degree of incorporation.

A comparison of the electrochemical and elastic parameters determined for three dense regenerated cellulose (RC) membranes with different cellulose content is presented in this work. Different values for structural (fractional void volume), electrical (fixed charge concentration and ion transport number) and diffusional (ionic and salt diffusion coefficients) parameters were obtained, and temperature effect on membrane diffusivity also seems to be related to RC content. Moreover, the elastic characterization of the three membranes carried out by obtaining the normal strain–stress curve also shows a certain correlation between diffusional and elastic properties.

Physical–chemical characterization of supported liquid membranes (SLMs), that is, a porous structure containing room temperature ionic liquids (RTILs) was carried out by analyzing XPS and FTIR spectra, while determination of cation transport number from concentration potentials measured with the membranes in contact with NaCl solutions gives transport/electrical information. SLMs filled with two different RTILs (C8MIMPF6 and C10MIMBF4) were studied, and the comparison of results obtained with fresh and aged membranes seems to indicate ion transport modification for aged samples at relatively high NaCl concentrations, which could be associated to changes in the polymer matrix–RTILs interactions.

A comparison of membrane fouling caused by filtration of a protein (BSA) through two macroporous membranes, one polymeric (polysulfone) and other ceramic (ZrO2/Al2O3), is carried out. Clean and fouled membranes were characterized by SEM micrographs, water permeability, streaming/zeta potential and impedance spectroscopy measurements. SEM micrographs show BSA on the polymeric and ceramic membranes surfaces but only the polymeric membrane is completely covered, while trans-membrane (or through membrane) zeta potential results indicate protein deposition on the pore walls of both membranes; moreover, differences in time evolution of permeate flow, protein rejection and water permeability for both membranes were also obtained. According to these results, two different main fouling mechanisms can be assumed: a cake layer on the surface of the polysulfone membrane and pore narrowing for the ceramic sample. Impedance spectroscopy measurements allow the estimation of membrane electrical resistance and a reduction in membrane porosity associated to protein deposition was estimated considering a simple system of non-conducting cylindrical capillaries filled by the (conducting) electrolyte solution.

A comparison of NaCl transport across two dense cellulosic membranes from different suppliers is presented. Hydraulic and diffusional permeabilities were determined from volume flow-applied pressure and concentration-time relationships, while cation transport number and membrane conductivity were determined from electromotrice force and impedance spectroscopy measurements, respectively. Chemical surface differences between both membranes are correlated to transport parameters and morphology, but differences in elastic properties of both membranes might also be considered in order to get a more complete picture of membrane behaviors and to obtain structural-transport parameters correlations.

This work studies the structural and chemical modifications of functionalised porous phosphate heterostructures (PPH) of zirconium phosphate. The modification consists in incorporation of propionitrile at two different percentages, but pressure was also applied in order to obtain pressurized discs. The application of pressure (4 T cm 2 ) provokes a migration of nitrile groups to the surface as observed by XPS analysis and it seems to be responsible for the drastic porosity decrease obtained by N 2 adsorption. Electrochemical characterization of the pressured-discs in contact with NaCl solutions at different concentrations was also carried out. These results show the cation exchange capacity of PPH, which is slightly reduced in the case of the functionalised materials with nitrile groups (10% lower cation transport number), while diffusional permeability and electrical resistance values also confirm structural changes for the modified materials.

Asymmetric sulfonated-polysulfone/polyamide membranes were modified by incorporating different amounts of lignosulfonate (LS) into the network (5, 10, 20 and 40 wt.%) in order to increase membrane conductivity due to the presence of sulfonic acid groups in the LS structure. LS-modified membranes were geometrically characterized by scanning electron microscopy (SEM) micrographs, which show two different substructures: a dense top layer (around 2.7 μm thickness) and a thick porous support (thickness between 95 and 102 μm, and porosity ranging between 37 and 42%). Chemical top layer characterization was carried out by XPS analysis, which shows the complete covering of the PS/PA membrane by LS and it is correlated with the increase of LS in the casting solution. Electrical characterization was carried out by impedance spectroscopy with the membranes in contact with HCl solution at different concentrations by using equivalent circuits as models. These results allow the separate determination of the electrical contribution associated to the top layer and the porous support; modified membranes and top layers conductivities were calculated from electrical resistance and geometrical values previously determined from SEM analysis. According to these results, 10 wt.% of LS seems to be the more appropriated figure to increase both membrane and top layer conductivity (σm ∼ 0.06 (Ω m)−1 for 1 M HCl solution).

The effect of ionizing radiation on the surface and electrokinetic characteristic parameters for a porous membrane of pore size 0.2 μm is determined and correlated with the irradiation dose (10 and 80 J/kg). Changes in NaCl permeability and membrane system electrical resistance determined from diffusion and impedance spectroscopy measurements are consistent with the increase of membrane pore radii/porosity, in agreement with SEM micrographs and reported results. Low irradiation dose seems to clean the membrane surface of impurities, according to XPS results, but the increase of irradiation doses could affect surface roughness. Due to the relatively high pore radius, ion transport numbers are practically independent of radiation and dose, but irradiation slightly modifies the membrane solution interface by increasing its weakly electronegative character, which could be of interest in the ultrafiltration of proteins or macromolecules.

Characteristic transport and interfacial parameters for a microfiltration ZrO2/Al2O3 membrane (sample Z100S) were obtained from filtration, membrane potential and streaming potential measurements, which were carried out with the membrane in contact with different NaCl solutions, while membrane chemical surface was analyzed by XPS spectra. Electrical parameters indicate a weak electropositive character for the studied membrane. Z100S sample was modified by gamma-irradiation (dose of 10 J/kg) delivered by a 60Co Unit (membrane Z100S-Ir10). A comparison of the results obtained with pristine and irradiated samples shows: (i) ion transport numbers and electrical interfacial parameter (zeta potential) modification (anionic permselectivity increases from 9% for the untreated membrane to 23% for the irradiated sample); (ii) a decrease in the hydrodynamic permeability (around 10%); (iii) a reduction (18% approximately) in the atomic concentration of carbon, a non-characteristic membrane material element attributed basically to membrane manufacture. The presence of this element in the membrane structure could be directly related to the observed modifications, affecting the membrane behaviour as a result of the irradiation itself or associated to local heating effect.

Two flat ceramic commercial membranes for filtration applications with similar composite structure (a fibrous stain steel network covered by a sublayer of Al 2 O 3 particles plus an external layer of ZrO 2 ) but different “nominal” pore size (25 and 100 nm) are studied. Chemical surface and morphological characterisation was carried out by X-ray photoelectron spectroscopy (XPS) and scanning electronic microscopy (SEM), while transport of NaCl solutions at different concentrations through both membranes was characterized by determining hydraulic and diffusional permeabilities, ion transport numbers and electrical resistance. Protein adsorption on membrane walls (membrane fouling) was considered by maintaining the membranes in contact with a protein solution for 48 h (2 g/l of bovine seroalbumin or BSA). The effect of protein adsorption on electrochemical parameters was determined by comparing the values obtained with clean and BSA-fouled samples. Results show reduction in diffusional permeability and increase in the electrical resistance (around 20%), but cation transport number hardly depends on membrane fouling.

Supported liquid membranes (SLMs), prepared by immobilising the room temperature ionic liquids (RTILs) [CnMIM]PF6 (n = 4 and 8) and [C10MIM]BF4 in a polyvinylidene (PVDF) supporting membrane, were prepared and characterised by electrochemical impedance spectroscopy (IS). This non-invasive technique allows the determination of the electrical properties of a given sample, such as the electrical resistance and capacitance under working conditions, i.e., in contact with saline solutions. Bearing in mind that the water content of the ionic liquids can drastically affect their physicochemical properties, impedance measurements of the SLMs, placed between two aqueous solutions, were carried out at regular time intervals, in order to assess the impact of the presence of water inside the RTILs on the electrical properties of supported ionic liquid membranes. The electrical resistance of the SLMs and its variation during long-term operation was also used as a physical parameter to identify the presence/loss of ionic liquid from the pores of the support. Additionally, the comparison of the IS results obtained for the SLMs with those obtained for the supporting membrane was carried out, in order to gather information about electrical changes associated with the presence of ionic liquid in the pores. © 2005 Elsevier B.V. All rights reserved.

This work is focused on the study of possible changes in the electrochemical transport parameters of cellulose membranes due to the effect of ionising radiation. A cellophane membrane (membrane C5) was irradiated with a dose of 80 Gy (membrane Ir80) and differences in the electrochemical parameters for pristine and irradiated samples are studied. Salt permeability, ion transport number, permselectivity and electrical resistance for C5 and Ir80 samples were determined from diffusion, membrane potential and impedance spectroscopy measurements, which were carried out with the membranes in contact with NaCl solutions at different concentrations. Modification of the electrochemical parameters as a result of membrane irradiation was obtained, which seems to reduce the matrix free volume and to increase the negative character of the cellophane membrane. The possible effect of membrane modification on protein adsorption was considered by comparing the electrochemical parameters of C5 and Ir80 samples with those obtained with the membranes after fouling with bovine seroalbumine (BSA). Results show a decrease in the fouling effect for the irradiated sample and the increase of ion permselectivity for both fouled membranes, which seems to indicate the control of ion transport by the protein.

Homogeneous PSf-LS membranes are formed by incorporating Lignosulfonate (LS) into the Polysulfone (PSf) network. LS obtained from sulfite pulping process contains sulfonic acid groups that will act as proton transport media. PSf-LS membranes were characterized by reflectance Infrared and scanning electron microscopy. LS showed significant influence on membrane morphology. Higher LS concentration caused a decrease in macrovoid formation and induced larger pores. Precipitation temperature was investigated as influencing parameter. Proton fluxes through PSf-LS membranes were measured by transport experiments. Impedance analysis confirmed that PSf-LS membranes possess ion conductivity. The selected PSf-LS membranes exhibited high selectivity for proton over methanol, which indicates their potential applicability in direct methanol fuel cell (DMFC).

Membrane parameters characteristic for the study of electrolyte solutions across microporous membranes such as salt permeability, ion transport numbers and membrane electrical resistance have been determined for a ceramic microfiltration membrane by measuring salt diffusion, membrane potential and impedance spectroscopy (IS), respectively. In order to see the effect of ion charge and concentration on these parameters, NaCl and MgCl2 solutions at different concentrations (0.001 M < c < 0.1 M) have been used, but only small differences depending on both electrolyte and concentration have been found. Changes in the different parameters due to the treatment of the ceramic membrane (2 h in a 1 M H2SO4 solution and calcined in air at 573 K for 1 h) have also been studied, and the results seem to indicate a modification (reduction) in the porosity and in the electrical nature of the original membrane. © 2004 Elsevier B.V. All rights reserved.

Modifications caused by different types of ionizing radiation and thermal treatment on transport, chemical and structural parameters of polymeric (regenerated cellulose) membranes have been studied. Particularly, the effect of different types of radiation (ultraviolet light (UV) and ionising radiation (Ir) with different doses) and heating at 60 °C on transport and electrical parameters for a cellophane membrane has been considered by determining salt permeability and electrical resistance for the different samples. These parameters were obtained from salt diffusion and impedance spectroscopy (IS) measurements with the membranes in contact with NaCl solutions at different concentrations. Chemical surface and structural modifications of the polymer matrix due to the treatments have also been determined by X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (ATR mode). Results obtained from infrared spectroscopy seem to indicate that ionising radiation modifies the proportion of OH links, which is related to the dose of irradiation. XPS analysis only shows small differences in the atomic concentration and shape of the C 1s spectra. On the other hand, an increase of salt permeability for heated and UV-treated membranes was obtained, while this parameter decreases in the case of irradiated membranes. This result could be related to a change in the packing of the polymer chains, which results in an increase of the fractional void volume in the case of heat- and UV-treated membranes and the opposite effect for the irradiated ones; for these latter, a correlation between the irradiation dose and the decrease in permeability values was also obtained. IS results show a decrease in the electrical resistance of all treated samples. This fact can be due to the most open structure of heated and UV-treated samples, previously indicated; however, due to the closer structure assumed for the irradiated sample, this point might be related to the presence of free radicals in agreement with ATR results.

Changes in the transport parameters and the chemical nature of the surface of composite polyamide/polysulfone membranes due to both aging and treatment with chemical products (HCl, H3NO, and NaOH) have been considered. Hydraulic and salt permeability were obtained from water flow and salt diffusion measurements, respectively, and their values seem to indicate a modification in the structural parameters (porosity/thickness) of aging samples, while HCl and HNO3 treatments will act in the opposite way. Chemical modifications in the membrane surfaces were studied by X-ray photoelectron spectroscopy (XPS), which mainly show the effect of H3NO and HCl on the polyamide active layer of the membranes (polyamide oxidation), but no chemical damage for that sublayer. Electrical characterization of both sublayers of the composite membranes were determined from impedance spectroscopy (IS) measurements using equivalent circuits as models, and these results indicate: (i) a strong increase of the membrane electrical resistance as a consequence of aging, mainly that associated with the active sublayer (30 times higher for an old sample than for a fresh one) and treatment with NaOH; (ii) the reduction of this effect when the samples were treated with HCl and HNO3 solutions. Changes in the values of the electrical resistance of the composite membranes are in agreement with those obtained for permeabilities, but the electrical parameter also allows the determination of the contribution of each sublayer.

Chemical, structural and electrochemical characterizations of two cellophane membranes depending on both cellulose content (20 and 25 kg/m 2 ) and thermal treatment (60 ◦ C during 4 h), have being carried out. Different transport parameters were determined by measuring water and salt fluxes, membrane potential and impedance spectroscopy using NaCl solutions at different concentrations. Chemical degradation of the membrane surfaces due to membrane heating was obtained from XPS spectra. Electrochemical results shown that treated and untreated samples behave as weak cation-exchangers, but small differences in their electrical parameters (membrane fixed charge concentration, cation transport number and electrical resistance) due to both the thermal treatment and the amount of cellulose were obtained. Results also indicate a more open structure for the membrane with higher content of cellulose. The influence of concentration/polarization layers on salt permeation was also studied by measuring salt diffusion at different stirring rates. Moreover, variation of water permeability with temperature for untreated samples seems indicate changes in the membrane structure around 40 ◦ C, which was confirmed by differential scanning calorimetry (DSC) thermograms. © 2003 Elsevier Science B.V. All rights reserved.

Electrokinetic and electrochemical characterisations of a composite polyamide/polysulfone membrane (PAC1) were carried out by measuring the streaming potential along the membrane surface (polyamide active layer) and the membrane potential at different pHs (3

The influence of concentration-polarisation on salt transport across three membranes with different structures, an ultrafiltration (PPS), an asymmetric nanofiltration (PES-10) and a symmetric for dialysis (C-5), was studied. Salt diffusion measurements were carried out in a dead-end cell, at different stirring rates of the solutions at both sides of the membrane (0 ti (rpm) I 1100) under the same NaCl concentration gradient (A,X’= 5x lo-’ M’). Salt permeability for the membrane system (P,) at each stirring rate, which includes both the membrane itself and the polarisation layers, was determined by the fitting of the corresponding concentration vs. time curves. The permeability of the solute in the membrane (P,v”*) and the thickness of the solution layers at a given stirring celerity, d, were estimated by the fit of P, as a function of the solution stirring rate. Differences found between PJand 9”’ for the studied samples clearly show the different influence of concentration-polarisation layers on salt diffusion depending on the membrane structure. In fact, salt permeability through the C-5 membrane was at least one order of magnitude higher than for the two other samples, while P,“’ is around 2.5 times higher for the ultrafiltration membrane than for the nanofiltration one. A comparison of the thickness of polarisation layers at a given stirring celerity shows the following values: d(C-5)=25 pm, d(PPS) = 1 mm and (PES-10) = 6 mm. On the other hand, a comparison of the membrane permeability obtained for the cellophane membrane in the dead-end cell (3~10~~ m/s) and that obtained in a tangential flow cell (5x 1 Omh m/s), shows rather good agreement, which can be considered as a proof of validity of the results.

The surface and the solid/liquid interface of two polyamide membranes, one experimental (B0) and one commercial (NF45), have been characterized by X-ray photoelectronic spectroscopy (XPS), atomic force microscopy (AFM), and zeta potential, respectively. The surface roughness, determined by AFM data analysis, is different for the two membranes, and results show that the commercial NF45 membrane presents a much lower roughness than the experimental B0 membrane. XPS data indicate that the surface of membrane NF45 is similar to that of pure polyamide, while membrane B0 contains a considerable amount of impurities. The homogeneity in depth of both membranes was also studied by determining the composition profile at different analysis angles. Streaming potential along the membrane surface or tangential streaming potential (TSP) measurements with NaCl solutions at different concentrations were carried out with both membranes to determine the zeta potential and the electrokinetic surface charge density, and a correlation between membrane surface and interface parameters is made. Some differences in atomic concentrations of membrane surface elements and X-ray photoelectronic spectra of the samples used in TSP measurements and after a drying process at 90 degrees C for 24 h can be observed when they are compared with those for fresh membranes. Electrokinetic parameters for membrane NF45 (TSP, zeta potential, and surface electrokinetic charge density) obtained from three different series of measurements strongly decrease as a result of membrane use, but for membrane B0 they are practically independent of the number of measurements. This difference in the electrokinetic behavior of the two membranes has been related to the hydration process of the surface for each sample studied by XPS and AFM.

Se ha modificado una membrana comercial de alumina para microfiltracion introduciendo en sus poros un precipitado inorganico (fenilfosfonato de uranilo o UPP). La membrana modificada se ha caracterizado: i) quimicamente, mediante el analisis por espectroscopia de fotoelectrones de rayos X de su superficie; ii) electroquimicamente, a partir de medidas del flujo salino y de la impedancia del sistema membrana/disolucion de NaCl. A partir de estos resultados se han obtenido las concentraciones atomicas de los elementos en la superficie de la membrana, la permeabilidad salina y la resistencia electrica de la membrana modificada, respectivamente. La comparacion de estos valores con los obtenidos para la membrana de alumina sin modificar, permite determinar la influencia del precipitado en los distintos parametros estudiados y el efecto de los rayos X sobre el precipitado de fenilfosfonato de uranilo..

Surface and bulk membrane have been electrically and chemically characterized by different kinds of measurements. Tangential streaming potential, impedance spectroscopy, membrane potential and salt diffusion were measured with a porous polysulfone membrane for ultrafiltration when it was in contact with NaCl solutions at different concentrations (5×10−5

Because of the diversity of streaming potential and zeta potential values reported in the literature, even for similar membranes and external conditions (hydrodynamics and solution chemistry), the influence of measuring cells and procedures in electrokinetic parameters has been studied. For this purpose, two different experimental systems (named EKA and NIS) with similar hydrodynamic parameters, but different electrodes and electrical devices, are used for the electrokinetic characterization of a commercial polysulfone membrane. Detailed descriptions of measurement procedures and the influence of external conditions (flow direction, electrode polarization, etc.) are made since they could contribute to the variability of experimental results. On the other hand, an electrokinetic characterization of the polysulfone membrane in contact with NaCl solutions at different concentrations and pH was carried out by using the EKA system. An heterogeneous specific adsorption of anions on the membrane surface (Freundlich isotherm) was assumed in order to determine parameters such as the membrane surface charge density, the Gibb’s free energy and the number of adsorption sites per unit of membrane area. However, at low salt concentration (∼10 −3 M) the membrane proper charge is mainly due to dissociation of some kind of acid groups on the membrane surface (isoelectric point: 3.1 ± 0.1), and the site dissociation model has been used to obtain the membrane acid equilibrium constant and the surface density of acid sites. © 2001 Elsevier Science B.V. All rights reserved.

Electrokinetic, structural and surface chemical characterizations of both active and porous sublayers of a composite (polyamide/polysulfone) reverse osmosis membrane were carried out by different techniques: (i) electrochemical impedance spectroscopy (EIS) allows both electrical and geometrical characterizations using equivalent circuits as models; (ii) surface chemical composition of the active layer was determined by X-ray photoelectron spectroscopy (XPS); (iii) salt diffusion, tangential streaming potential and membrane potential measurements allow the determination of different transport and electrokinetic parameters such as salt and ionic permeabilities, zeta potential and surface charge density. Electrical and electrokinetic parameters were determined with the membrane in contact with NaCl solutions at different concentrations, although the influence of pH and the use of the membrane on zeta potential values was also studied. Changes in the electrokinetic parameters as a result of the membrane use were obtained and, according to XPS results, they can be attributed to the hydratation of the polyamide active layer. For comparison, electrochemical measurements with a polysulfone ultrafiltration membrane similar to the porous sublayer of the composite RO membrane were also carried out. Good agreement was obtained for the electrical resistance and ionic permeabilities determined for both the ultrafiltration membrane and the porous sublayer of the RO membrane, which confirms the two-layer model assumed for composite membranes.

In this work, three samples of sulfonated polysulfones of different sulfonation degree have been characterized, and the electrical properties of dense membranes based on them have been evaluated. The polymers were characterized spectroscopically, and by their inherent viscosity, and water absorption. Electrical characterization of membranes was carried out on dense membranes in contact with NaCl solutions, by impedance spectroscopy (IS) measurements using equivalent circuits as models. The results showed how the sulfonation clearly affected the membrane electrical characteristics, strongly reducing the membrane resistance, and also changing the type of circuit associated to the membrane, which could be related to the increase of electrolyte taken by the membrane when the sulfonation degree increased. Concentration dependence of the electrical parameters was also studied.

Pressure induced electrical potential across a composite polyamide/polysulfone reverse osmosis membrane and a microporous polysulfone membrane similar to the porous layer of the composite one (Δ E and Δ φ st PS , respectively) were measured with NaCl and MgCl 2 solutions at different feed concentrations. Because of the high salt rejection and the two-layered structure assumed for reverse osmosis membranes, Δ E values do not represent the streaming potential in the active layer since other electrical potentials (diffusion potential in the active layer, streaming potential in the porous sub-layer and boundary potential) are also included. These different terms were evaluated and the streaming potential for the active and porous layers of the composite membrane, Δ φ st a and Δ φ st p , were estimated under the assumption of similar streaming potential coefficient g =Δ φ st /Δ P for the porous layer of the composite membrane and the microporous polysulfone membrane ( g PS = g p ). Differences between Δ E m i values obtained under filtration (Δ E m F , different feed and product concentrations) and dialysis conditions (Δ E m D , equal feed and product concentrations), for similar volumen fluxes show the influence of the porous sub-layer. A comparison between Δ E m F /Δ P and active layer streaming potential coefficient, g a , is also made. Results show that the diffusion potential in the active layer is 10–15% of the total electrical potential difference across the composite membrane, while the influence of the porous layer is practically lower than 3%. The electrical potential in filtration measurements was calculated from dialysis results, once diffusion and streaming potential in the porous layer are known, and good agreement between experimental and calculated values was obtained. Salt concentration dependences for streaming potential coefficient in porous and active layers of the reverse osmosis membrane were studied, while for the microporous polysulfone membrane the zeta potential ( ζ ) was determined by the Hemholtz–Smoluchowski expression.

The paper reports the results obtained on the physicochemical characterisation of activated composite membranes (ACMs). Membrane samples containing different concentrations of di-2-ethyl-hexyldithiophosphoric acid (DTPA) as a carrier were prepared and characterised by different analytical techniques. The amount of the carrier incorporated in ACM appears to be directly proportional to the concentration of carrier in the casting solution. Respective distribution dependencies can serve as calibration graphs applicable for pre-calculation of extractant concentration in the casting solution to manufacture an ACM with a given carrier content. The carrier distribution in the membrane was evaluated by X-ray microanalysis (EDS), which allowed us to determine that only a limited concentration of the carrier can be incorporated into the top polyamide membrane layer, resulting in redistribution of the excess of extractant along the polymeric structure of the membrane. These results also correlate with those obtained by impedance spectroscopy measurements. The equivalent circuits associated with the different membrane samples agree with a two-layer model for the ACM containing a high concentration of carrier (CDTPA > 0.5 M), which allows for the location of a larger amount of carrier into the polyamide layer. The results obtained by the indicated techniques are in good agreement with each other, and provide for the structural characterisation of the membrane. ©2000 Elsevier Science B.V. All rights reserved.

Membrane potential of native isolated pepper cuticles were measured with NaCl and CaCl2 solutions for a wide range of concentrations (10−3

Transport on single electrolyte solutions (NaCl and MgCl 2 ) due to pressure gradients across a commercial reverse osmosis membrane was studied by measuring volume flux ( J v ), salt rejection ( S ) and pressure induced electrical potential (Δ E ) in a crossflow cell. The influence on these parameters of different external conditions due to hydrodynamic or chemical changes in the feed solutions was also studied. Changes were carried out by variation of the feed solution velocity (Reynolds numbers between 1500 and 3300) or the concentration ratio of mixed electrolytes ( r =HCl/NaCl and HCl/MgCl 2 , r =1, 0.5 and 0. 1), respectively. Results show that J v , S and Δ E values slightly increase when the velocity of the feed solution increases, but the mixed electrolytes strongly affect both salt rejection and pressure-induced electrical potential. A change in the sign of both parameters with respect to the value determined with single electrolytes at the same concentration was obtained, which is attributed to a strong coupling among the fluxes of individual ions and their distribution in the membrane when transport of mixed salt is studied.