Electrokinetic property of ZrO2/cordierite composite MF membrane and its influence on the permeate flux

ZrO₂/cordierite composite microfiltration (MF) membrane was prepared by the combination of extrusion and slip casting techniques. The electrokinetic properties of as-prepared membrane were characterized by streaming potential measurements operated in tangential microfiltration mode. The influences of pH, electrolyte species and concentrations of filtered solutions on the electrokinetic properties and permeate flux were investigated. Results show that the streaming potentials are dependent on the pH, types of the electrolyte and concentrations of filtered solutions. The isoelectric point (IEP) of membranes moved from 4.2 to 5.4 with different types of 10^− 3 M electrolyte solutions. The change of ionic concentration of NaCl solution does not alter the IEP of the membranes, but does make the streaming potential tend to be zero at high salt concentration. The specific adsorption of Ca²⁺ and SO₄²⁻ ions in CaCl₂ and Na₂SO₄ solutions onto the pore wall can alter the IEP and the net charge sign of the membrane. The as-prepared ZrO₂/cordierite membrane shows a maximal permeate volume flux near the IEP.     

Role of Surface Area, Primary Particle Size, and Crystal Phase on Titanium Dioxide Nanoparticle Dispersion Properties

Characterizing nanoparticle dispersions and understanding the effect of parameters that alter dispersion properties are important for both environmental applications and toxicity investigations. The role of particle surface area, primary particle size, and crystal phase on TiO₂ nanoparticle dispersion properties is reported. Hydrodynamic size, zeta potential, and isoelectric point (IEP) of ten laboratory synthesized TiO₂ samples, and one commercial Degussa TiO₂ sample (P25) dispersed in different solutions were characterized. Solution ionic strength and pH affect titania dispersion properties. The effect of monovalent (NaCl) and divalent (MgCl₂) inert electrolytes on dispersion properties was quantified through their contribution to ionic strength. Increasing titania particle surface area resulted in a decrease in solution pH. At fixed pH, increasing the particle surface area enhanced the collision frequency between particles and led to a higher degree of agglomeration. In addition to the synthesis method, TiO₂ isoelectric point was found to be dependent on particle size. As anatase TiO₂ primary particle size increased from 6 nm to 104 nm, its IEP decreased from 6.0 to 3.8 that also results in changes in dispersion zeta potential and hydrodynamic size. In contrast to particle size, TiO₂ nanoparticle IEP was found to be insensitive to particle crystal structure.     

Relation between salt rejection and electrokinetic properties on Shirasu porous glass (SPG) membranes with nano-order uniform pores

The salt rejection by Shirasu porous glass (SPG) membranes having nano-order uniform pores was investigated for understanding the electrokinetic mechanism resulting from the surface charge developed on the membrane when in contact with salt solutions. Due to the dissociation of the hydroxyl groups such as silanol groups on the membrane surface, the membrane was negatively charged over a pH range of 3–10 from electrophoretic measurements. Cross-flow filtration experiments showed that up to 63% of NaCl was rejected by an SPG membrane having a mean pore diameters of 33 nm in a 1 mol m⁻³ NaCl solution at pH 7 under a transmembrane pressure of 74 kPa, even though the pore diameter is much larger than the ion diameter. This is a consequence of the electrostatic repulsive interaction between the co-ions (Cl⁻ ions) and the membrane surface. At the same pH, the rejection factor of NaCl decreased with increasing salt concentration due to an increase in the ionic strength. More negative charge on the membrane surface at higher pH resulted in higher rejection factors of NaCl for a fixed salt concentration. Higher rejection factors of NaCl by SPG membranes with smaller pore sizes for a fixed concentration are due to the higher ratio of the thickness of the electric double layer (Debye length) to the pore radius. The SPG membrane showed a salt rejection sequence: Na₂SO₄, NaCl and CaCl₂ at the same pH. This is because divalent anions (SO₄²⁻) are more strongly repelled by the negatively charged membrane, while divalent cations (Ca²⁺) adsorb specifically onto the membrane surface than monovalent cations (Na⁺). The salt rejection factor increased with increasing permeate volume flux. Due to the stronger acidity of the membrane materials, SPG membranes had a higher rejection factor and a lower isoelectric point (IEP < 3) than ceramic membranes.     

不同电解质溶液及其离子浓度和pH值对改性微滤膜流动电势的影响(英文)

采用商品级α-Al2O3微滤膜.由均质共沉淀法制备了TiO2改性α-Al2O3微滤膜.研究了不同的电解质溶液、溶液的离子浓度和pH值对TiO2 改性的α-Al2O3微滤膜流动电势的影响规律.结果表明:对于NaCl溶液,膜流动电势随溶液离子浓度的增大向降低,其等电点在4.3左右:随着溶液的pH值由3增加到10.膜流动电势由值逐渐变为负值.而对于FeSO4,CaSO4,Na2SO4,NaCl和CaCl2溶液,当溶液的离子浓度固定时,膜流动 电势则随溶液的电导率的增加而降低.     

The effect of acids and bases on the dispersion and stabilization of ceramic particles in ethanol

The dispersion and stability of alumina, titania, and silicon carbide powders in ethanolic medium have been investigated. An operational pH-scale, pH*, based on an ethanol-based reference electrode, was used to systematize the suspension properties. The electrokinetic behavior was determined as a function of pH*. The isoelectric points in ethanol — pH¹_iep(SiC)=7.5; pH¹_iep(Al₂O₃)=4.4 and pH¹_iep(TiO₂)=4.2 — were discussed in relation to the dissociation constants of the charge determining reactions at the powder surfaces. We have evaluated the long-term stability of the ethanolic dispersions through settling studies which showed that the primary particle size could be retained for extended times providing that the surface potential and ionic strength were optimized.     

流动电位和通量法表征中空纤维超滤膜的污染程度及清洗效果

用流动电位和通量法表征PS中空纤维膜，研究离子强度、离子种类及pH值对膜的流动电位和通量的影响，同时测量了膜的等电点，结果表明流动电位系数（v）随浓度的增大而减小，等电点随电解质中阳离子价态增大而升高.对0.001mol/L的CuCl2，FeCl3和AlCl3溶液，在pH=6.8时的污染实验，发现污染后流动电位和通量值都有所下降，等电点则有所上升，且通量下降到一定值以后几乎不再下降，经过有效清洗后，流动电位和膜通量恢复到了原来的99%以上，这表明污染只发生在膜表面.     

Controlled synthesis of TiO2 nanorod arrays immobilized on ceramic membranes with enhanced photocatalytic performance

In this work, TiO₂ nanorod arrays (NRAs) were synthesized directly on flat sheet Al₂O₃ ceramic membrane (CM) substrates by a two-step hydrothermal method. The effects of the addition of anions and cations and the preparation parameters in the second step on the morphology and size of TiO₂ were investigated in detail, and the photocatalytic activities of the as-synthesized TiO₂-loaded ceramic membranes were investigated by the degradation of methylene blue (MB) under UV light. The results highlighted that the growth of TiO₂ on the CM strongly depended on the synthesis conditions. The anions of Cl^- and Br^- were favorable for the further growth of TiO₂ nanorods, while the anions of SO₄^2- and PO₄^3- with larger ionic radius and higher charge number could retard the growth of TiO₂ nanorods. The SO₄^2- and PO₄^3- could accelerate the formation of nanospheres or nanosheets, respectively. The cation like Na⁺, K⁺, Mg²⁺ and Ca²⁺ had no obvious impact on the formation of TiO₂ NRAs. TiO₂ nanorods exhibited the highest photocatalytic activity, as about 2.2 and 1.9 times larger than those of TiO₂ nanosheets and TiO₂ nanospheres, respectively. More importantly, the as-synthesized TiO₂ NRAs-loaded ceramic membrane could be easily reused and exhibited better photocatalytic stability. These findings would aid the development of TiO₂ photocatalytic materials with high performance.     

An amphoteric Ion-permselective membrane

A membrane made by reacting sulphochlorinated polyethylene with 1-amino-3-dimethylamino-propane containing water, was found to be amphoteric: about $\text{5}\text{6}$ of its capacity was due to dimethylamino groups while sulphonic acid groups accounted for the remaining $\text{1}\text{6}$ of its capacity. In acid the dimethylamino groups are ionised and the membrane behaves as a week anion-selective membrane. In alkali the aminogroups are deionised and the sulphonic acid groups are set free to make the membrane cation-active.These changes in ionisation with pH have the following consequences: (1)The membrane de-swells in length and in weight in its isoelectric region between pH 8–11. (2)The electric resistance increases by 3–4 orders of magnitude in this pH region as against both acid and strongly basic pH solutions. (3)In acid solutions the membrane is anion-selective, crosses the neutrality line at about pH 10 and becomes cation-selective in strongly basic solutions. (4)In the open states, that is in acid and strongly basic solutions, the membrane hardly distinguishes between the ion pairs Cl^- and SO⁼₄ or Na⁺ and K⁺. However, in the closed, high resistance, region Cl^- is transferred 7–8 times more easily than SO⁼₄. The difference between transference of the two alkali ions remains slight. (5)A bipolar (sandwich) membrane made with adjoining layers of the above-mentioned membrane and a layer of polyethylene sulphonic acid was prepared. This sandwich rectifies the current in acid solutions but has a low, voltage-independent, resistance in strong alkali where it ceases to be bipolar and changes into a cation-selective membrane. It has a high, voltage-independent, resistance in its isoelectric region where the amphoteric side is uncharged and represents a high series-resistance beside the low resistance cation-selective layer.     

Polyelectrolyte multilayer modified nanofiltration membranes for the recovery of ionic liquid from dilute aqueous solutions

The feasibility of nanofiltration membranes fabricated by static polyelectrolyte layer‐by‐layer deposition of poly(styrene sulfonate) and poly(allylamine hydrochloride) on poly(ether sulfone) ultrafiltration and alumina microfiltration membranes for the recovery of ionic liquid from low molecular weight sugar was investigated. The surface properties of these modified membranes were correlated with their performances. The selectivity for 1‐butyl‐3‐methylimidazolium chloride over cellobiose and glucose was found to be as high as 50.5/2.3 for modified alumina and 32.3/3.5 for modified poly(ether sulfone) membranes with optimized number of bilayers. The values for membrane permeance were 4.8 and 2.5 L m^?1 h² bar^?1, respectively. For low depositions, the separation mechanism was predominantly governed by size‐exclusion. For higher depositions, the enhanced negative zeta potential of the modified membranes suggested preferred dominating electrostatic interactions, resulting in high selectivity of ionic liquids over low molecular weight sugars. At very high depositions, the molecular weight cut‐off of the membrane becomes constricting for size‐exclusion effect. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45349.     

Nano SiO2 and TiO2 embedded polyacrylonitrile/polyvinylidene fluoride ultrafiltration membranes: Improvement in flux and antifouling properties

Polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) ultrafiltration (UF) membranes are widely used in drinking water and wastewater applications. These membranes are prone to fouling and membrane efficiency decreases with time under constant operation. Significant improvements/modifications are necessary to apply these polymers as sustainable membrane materials. In this study, PVDF and PAN UF membranes were modified through incorporation of nanoparticles (NPs) namely SiO₂ and TiO₂. PVDF and PAN UF membranes were prepared by phase inversion method from polymer solutions having dispersed SiO₂ and TiO₂ NPs in it. Membrane surface hydrophilicity, charge, roughness, and morphology were studied. Equilibrium water content and molecular weight cut-off of the membranes were also measured. Addition of NPs increased membrane surface hydrophilicity, equilibrium water content, and surface potential. NPs modified membranes exhibited better membrane flux (35–79% higher) and antifouling properties (flux recovery ratio values 28–41% higher) than the virgin membranes.     

Streaming effect of single electrolyte mass transfer in nanofiltration: potential application for the selective defluorination of brackish drinking waters

This work deals with electrical properties of nanosurfaces in contact with electrolyte solutions. Single halide ion solutions were studied by streaming potential (SP) measurements and observed retention (R_obs) of the F⁻, Cl⁻, and Br⁻ ions across nanofiltration (NF) membranes. The detailed understanding of an electrolyte solution mass transfer requires an intimate knowledge of the physicochemical interactions occurring between nanoporous materials and electrolyte solutions across the first-generation composite membranes called NF55, NF70 and NF90. These membranes are composed of a polysulfone mesoporous sublayer and a microporous skin layer in polyamide. In order to get a better understanding of these effects, it seems attractive to compare the mass transfer permeation of the monovalent ions F⁻, Cl⁻, and Br⁻ with the electrokinetic characterizations deduced from a properly developed SP apparatus. SP measurements is a very simple method to show the intrinsinc charges on membrane pore walls. The membrane's electrical properties are studied with SP design modeling pH, ionic strength and kind of electrolyte solutions. We have observed that the isoelectric point (IEP) of the membrane materials is both dependent on the ionic strength and on the kind of electrolyte solution. The IEP in the presence of KCl is 4.4 at 0.0001 mol/L and 5.8 at 0.001 mol/L, showing an increasing adsorption of the cation K⁺ by increasing its solution concentration. For a fixed concentration, the effect of the electrolyte solution has shown that a higher adsorption of Ca⁺⁺ occurs in comparison to K⁺ and Na⁺. But the adsorption of these electrolyte solutions is essentially reversible as observed under dilution conditions. Furthermore SP measurements were used for the first time to characterize the transmembrane pressure ranges where a convective and/or a diffusional mass transfer occurs. Such an approach was developed to correlate the R_obs of the halide ions F⁻, Cl⁻ and Br⁻ with the kind of mass transfer (diffusional and/or convective) occurring predominantly under transmembrane pressure variations. Thus the NF70 membrane shows at low pressure (under 3 bar) the order of R_obs following the hydrated ionic radius: R_obs.(F⁻)>R_obs.(Cl⁻)>R_obs.(Br⁻). For a higher pressure (> 3 bar) an inversion occurs between Cl⁻ and Br⁻, but F⁻ was not affected. These results open a new prospective area for selective defluorination of brackish drinking waters using NF membranes under low transmembrane pressure.     

Electrical Properties of Modified Aromatic Polyamide Membranes

Abstract

The effects of chemical structure on the values of different electrical parameters measured with novel aromatic polyamide (aramid) membranes were studied. Poly-(isophthalamides) containing pendant groups were considered since they can be transformed into dense membranes, suitable for the determination of characteristic transport parameters such as ion transport numbers, electrical resistances and capacitances. Measurements were carried out with the membranes in contact with different NaCl and MgCl₂ solutions. Results show that resistance values are strongly dependent on concentration, but membrane capacitance is almost constant for the whole range of concentrations studied (10^?3 < C(N) < 5 × 10²). The ionic permeabilities in the membrane were determined from membrane potential and resistance results. The presence of polar side substituents causes lower resistivity in modified polyamides compared with the unsubstituted parent, and the higher the polarity of the substitutent, the lower the resistivity. This trend is valid for both NaCl and MgCl₂ solutions.     

Preparation,characterization and alkali metal ion permeation through nylon 666-g-maleic acid membranes

Nylon 666-g-maleic acid membranes were prepared by ⁶⁰Co γ-ray irradiation. The membranes were characterized by measuring their thickness, tensile strength, electrical resistance, membrane potential and permselectivity. Permeability coefficients of KCI, NaCl, Na₂SO₄, NaOH, urea and creatinine were evaluated from dialysis experiments. The charged membranes facilitated the active transport of alkali metal ions under a pH gradient.     

Electrophoretic mobility of alumina,titania and their mixtures in aqueous dispersions

The electrophoretic mobility of commercial alumina and titania powders and their mixtures (ratio of alumina:titania mixtures (by weight) 1:2 and 4:1) dispersed in 10⁻³ mol dm⁻³ KNO₃ was determined as a function of pH in the range pH 3–11, using both microelectrophoresis and mass transport methods. The results are in good agreement with the previous experimental results. The value of the isoelectric point (IEP) for alumina and titania was found to be at pH9 and 5.5, respectively. It appears that the dispersion concentration has no significant effect on the electrophoretic mobility versus pH. The results also suggest that the addition of titania to alumina has lowered the IEP value from pH ∼9 to ∼8.4 and the addition of alumina to titania has increased the IEP value from pH ∼5.5 to 6. The electrophoretic mobility versus pH profiles for the mixtures of alumina and titania powders appear to represent the electrokinetic behavior of both alumina and titania powders; however, the shape of the electrophoretic mobility versus pH profiles and the position of the isoelectric point appear to be governed by the powder with a large total surface area in the mixture, but not necessarily the weight.     

TiO2-incorporated polyelectrolyte composite membrane with transformable hydrophilicity/hydrophobicity for nanofiltration separation

The wettability of the membrane surface has shown obvious influent on the separation performance of the membrane. In this work, a hydrophilic PDA-[PDDA/TiO₂]⁺ Cl⁻ membrane was prepared by a one-step codeposition of poly(diallyldimethylammonium chloride) (PDDA) polyelectrolyte solution containing positively charged TiO₂@PDDA nanoparticles with the assistance of dopamine (DA). Such positively charged membrane can be transformed into a hydrophobic membrane PDA-[PDDA/TiO₂]⁺ PFO⁻ via the counterion exchange between Cl⁻ and PFO⁻ (perfluorooctanoate). The transformation between hydrophilicity and hydrophobicity is reversible. For both hydrophilic and hydrophobic membranes, the nanofiltration performances were respectively investigated by the aqueous solution and ethanol solution of dyes including methyl blue (MB), Congo red (CR) and Evans blue (EB), and as well metal salt aqueous solution. The consecutive running stability and anti-fouling performance of both hydrophilic and hydrophobic membranes were explored. The results revealed that both membranes showed high nanofiltration performances for retention of dyes in (non)aqueous solution. For the hydrophilic membrane, the rejection of salts in a sequence is MgSO₄ > Na₂SO₄ > MgCl₂ > NaCl. Moreover, both of the hydrophilic and hydrophobic membranes showed high stability and antifouling property.     

Interfacial properties of polyelectrolyte-cellulose systems. IV. Electrokinetic properties of carboxymethylcellulose fibers with adsorbed multilayers of cationic polyelectrolyte

Zeta potential measurements by the streaming current method were performed on carboxymethylcellulose (CMC) with and without irreversibly adsorbed multilayers of cationic polyelectrolyte. Factors affecting the electrokinetic properties such as the amount of adsorbed polymer, polymer molecular weights (M_n 50,000 and 200,000), ionic strength (10^?5 ～ 10^?2M KCl), and pH of the streaming medium (KCl solutions) were examined. The negative zeta potential of CMC decreased to the point of monolayer formation and increased from that point to the saturated multilayer formation. The polarity of the zeta potential was negative throughout every adsorption stage. The negative zeta potential increase was attributed to: (a) binding of anions (Cl^? and OH^?) to the outermost layer of the multilayer from KCl solutions and (b) change in chemical potentials of counterions in a diffuse double layer due to expansion of the double layer in the presence of the adsorbed multilayer on CMC. The results suggest that the carboxyl groups under the monolayer are undetectable electrokinetically; however, the negative charge, due to unneutralized carboxyl groups under the monolayer, appears to cause further adsorption forming a saturated multilayer. When the effect of unneutralized carboxyls of CMC are shielded at higher levels of adsorption, the outermost layer of the multilayer becomes a potential-determining layer.     

Adsorption of Co2+ and Cs1+ by polyethylene membrane with iminodiacetic acid and sulfonic acid modified by radiation‐induced graft copolymerization

Two modified hollow fiber membranes, the chelating hollow fiber membrane with iminodiacetic acid and the cation‐exchange hollow fiber membrane with sulfonic acid group ( SO₃H), were prepared by radiation‐induced grafting of glycidyl methacrylate onto polyethylene hollow fiber membrane and its subsequent iminodiacetation and sulfonation. The adsorption characteristics of Co²⁺ and Cs¹⁺ for the 2 hollow fiber membranes were examined when the solutions of Co²⁺ and Cs¹⁺ permeate across the 2 membranes, respectively. Without regard to the chelating membrane with iminodiacetic acid group and the cation‐exchange membrane with sulfonic acid group ( SO₃H), 2 membranes were observed to adsorb Co²⁺ higher than Cs¹⁺. The adsorption curves of Co²⁺ by IDA group‐chelating fiber membrane in the presence of Na¹⁺ and Ca²⁺ showed that the chelating hollow was found to have a very high selectivity for Co²⁺, even though there is a high concentration of Na¹⁺ and Ca²⁺ in the inlet solution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 999–1006, 1999     

Retention of mineral salts by a polyamide nanofiltration membrane

Retention measurements with single salt solutions (KCl, K₂SO₄, MgSO₄ and MgCl₂) were carried out with an AFC 30 organic membrane. The membrane showed high retentions for K₂SO₄ and MgSO₄ solutions and moderate ones for MgCl₂ and KCl solutions. The effective pore radius and the effective thickness to the porosity ratio of the membrane were determined from the limiting retention of glucose and permeability measurements, respectively. The Donnan Steric Pore Model (DSPM), based on the extended Nernst-Planck equation and a modified Donnan equilibrium accounting for steric effects, was used to characterize the membrane in terms of effective membrane volume charge. It appears that the membrane is positively charged in presence of MgCl₂ and MgSO₄ solutions and negatively charged for KCl and K₂SO₄ solutions. This was attributed to ionic adsorption at the interface membrane/solution.     

Asymmetric TiO2 hybrid photocatalytic ceramic membrane with porosity gradient: Effect of structure directing agent on the resulting membranes architecture and performances

Asymmetric TiO₂ hybrid photocatalytic ceramic membranes with porosity gradient have been fabricated via acid-catalyzed sol–gel method. Different structure directing agents (SDAs) i.e. Pluronic P-123, Triton X-100, Tween 20 and Tween 80 were incorporated in the preparation of TiO₂ sol to obtain a porous multilayered TiO₂ coated on the alumina ceramic support. Six different SDA-modified membrane specimens were fabricated. Four of which were coated with the TiO₂ sols prepared using only one type of SDA. The remaining two specimens were fabricated via multilayer coating of different TiO₂ sols prepared using different types of SDAs. Physico-chemical and morphological properties of different TiO₂ layers were thoroughly investigated. The membrane M1 which had the most porous TiO₂ sub-layers showed a high pure water permeability of 155 L m⁻² h⁻¹ bar⁻¹. The membrane showed a relatively high Rhodamine B (RhB) removal of 2997 mg m⁻² over 8 h treatment duration in the batch photoreactor, second only to the Pluronic-based TiO₂ membrane (specific RhB removal of 3050 mg m⁻²). All membrane specimens exhibited good performances while operated in the flow-through photocatalytic membrane reactor. Over 91% of RhB removal capability was retained after 4 treatment cycles. All membranes also showed self-cleaning property by retaining >90% of initial flux after 4 treatment cycles. The flexibility of optimizing membrane performances by fine-tuning the porosity gradient configuration of the photocatalytic layer has also been demonstrated.     

Ionic transport in conducting polymers/nickel tetrasulfonated phthalocyanine modified electrodes

This work describes the study of the ionic transport in polyaniline (PANI) and polypyrrole (PPY) modified electrodes polymerized in presence of nickel tetrasulfonated phthalocyanine (NiTsPc). Elemental analysis and infrared spectroscopy were used to characterize the resulting composite films. The impact of the phthalocyanine incorporation was evaluated by electrochemical quartz crystal microbalance under potentiodynamic conditions. Results have shown that the presence of the negative charge (SO₃⁻ groups) modifies the nature of the ‘ionic exchange’ membranes, during the cycling. In the case of PANI/NiTsPc modified electrodes, the electroneutralization is mainly achieved by the participation of protons both in HCl and in camphorsulfonic acid (HCSA) electrolyte solutions. For PPY/NiTsPc composites, the cation contribution is dominant in the case of LiCl and NaCl solutions and the anion transport becomes important when CsCl and BaCl₂ solutions are used.