Advanced porous polyphenylsulfone membrane with ultrahigh chemical stability and selectivity for vanadium flow batteries

Porous polyphenylsulfone (PPSU) membranes are facilely prepared via the nonsolvent-induced phase separation method. The typical asymmetric structure of such prepared porous membranes can be controlled by optimizing the sulfonation degree of the sulfonated poly(ether ether ketone) to 84.7% in the casting solution. Scanning electron microscopy images show that the porous membrane comprises a thin dense top skin layer, a sublayer structure with distinct long finger-like pores and the large pores in the substructure. The porous PPSU membrane was then used in vanadium flow battery (VFB). The optimized porous membrane yields an admirable performance, including excellent selectivity, chemical stability, and high columbic efficiency. Furthermore, the low cost of porous PPSU membranes indicates the promise of this technology for use in VFB applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47752.     

Modification of Porous Silica with Activated Carbon and its Application for Fixation of Yeasts

Mixtures of small silica particles and activated carbon were heated at 1250–1450°C in an inert atmosphere to make nano- and macro-sized porous silica for incorporating yeast in the porous strucrure. Without activated carbon, porous silica of 45–60% porosity and 15–30 m pore diameter was produced with a specific surface area below 1 m²/g. By the addition of 8 wt% of activated carbon granules, the surface area of porous silica increased to 100 m²/g at 1250°C. It was confirmed that there were micropores(1.2 nm) and mesopores(4.0 nm) due to activated carbon granules in porous silica when granule type activated carbon was used. However, in the case of activated carbon fiber, its micro- and mesoporous structure was destroyed in the firing process. The fixation of Z. rouxii yeasts was promoted on the porous silica with activated carbon.     

A kinetic and electrochemical study of the zincate immersion process for aluminium

To plate aluminium, its surface is often first coated with a thin layer of zinc which is formed by immersion in an alkaline zincate solution. This paper describes a kinetic and electrochemical study of the zincate immersion reaction. Using an aluminium sample in the form of a rotating disc, the effects of varying the zinc concentration (0.01–0.5 m), disc rotation speed (66–1380 rpm), temperature (5–72°C), and sodium hydroxide concentration (1.5–9.0 m) on the kinetics were investigated. It was found that the reaction was usually first order. When the zincate concentration was 0.1 m, the reaction was chemically controlled with an activation energy of 35 ± 7 kJ mol^–1. At high zincate concentrations, high disc rotation speeds and low sodium hydroxide concentrations, a thin film of zinc metal was formed on the aluminium surface, blocking the subsequent reaction. It was found that the most compact and adherent zinc films were formed at high zincate concentrations. This finding is consistent with industrial practice. These results are explained using mixed potential measurements and Evans' diagrams.     

Zeolite-based composite membranes for high temperature direct methanol fuel cells

Composite Nafion membranes containing three natural zeolites (Mordenite, Chabazite and Clinoptilolite) were prepared by using a recast procedure for application in high temperature Direct Methanol Fuel Cells (DMFCs). The Nafion-zeolite membranes have shown good properties for high temperature DMFC application, due to their improved water retention characteristics. A maximum power density of 390 mW cm^–2 was achieved at 140 °C with the mordenite-based composite membranes in the presence of oxygen feed. The electrochemical behaviour of the composite membranes was interpreted in the light of surface properties and acidic characteristics of the fillers.     

A study of copper electrowinning parameters using a statistically designed methodology

This study employs a factorial experimental design to relate current efficiency with current density (180 and 300 A m^–2), copper concentration (25 and 65 g l^–1), and temperature (40 and 60 °C). Pure, synthetic electrolyte with a constant acid concentration of 180 g l^–1 was used. The designed study produced a linear relationship where the independent variables of current density, copper concentration, temperature and their interactions were found to be statistically significant. It was shown that current efficiency could not solely be used as a predictor of copper cathode quality. The quality of the deposit is difficult to incorporate into a model or relation. It was determined that other measures, such as cathode morphology and crystal structure should be considered. This was done through XRD and SEM analysis.     

Swelling behavior and pervaporation properties of new composite membrane systems: Porous polyethylene film‐poly(acrylic acid) hydrogel

A new type of composite membrane for pervaporation has been developed. These membranes were prepared by free‐radical copolymerization of acrylic acid with a macromolecular polyfunctional crosslinker (allylhydroxyethylcellulose) inside the porous polyethylene (PE) film. It was shown that the porous structure of the PE matrix is filled with poly(acrylic acid) (PAA), and a layer of acid is formed on the film surface. To investigate the effect of the porous matrix on the composite membrane properties, a hydrogel membrane of crosslinked PAA was also prepared without the matrix using the same procedure. PAA in both membranes was in the neutralized form (K⁺). Swelling behavior of the membranes and their separation characteristics for pervaporation were investigated in water–ethanol solutions depending on the ethanol concentration. All membranes exhibited a high degree of equilibrium swelling (Q = 20–50 g/g) in dilute ethanol solutions (0–30 vol %), and Q sharply dropped to 1.5–2 g/g at a EtOH concentration of 30–40 vol % due to collapse of the gel. All membranes under study were highly permeable and selective to water over a wide range of ethanol concentrations in the feed (50–96 vol %), but composite membranes had a higher separation factor due to the restriction effect of the matrix porous structure on swelling of PAA(K⁺) inside the pores. However, composite membranes were characterized by a lower permeation rate, compared to the crosslinked PAA membranes without a matrix, because of their lower effective surface for diffusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1461–1465, 2004     

Preparation of a cellulose acetate/organic montmorillonite composite porous ultrafine fiber membrane for enzyme immobilization

Four types of fibrous membranes based on cellulose acetate (CA)—CA membranes with nonporous fibers, CA/organic montmorillonite (O‐MMT) membranes with nonporous fibers, CA membranes with porous fibers, and CA/O‐MMT membranes with porous fibers—were prepared by electrospinning, and then, they were used for enzyme immobilization. The surface morphologies of the composite fibrous membranes were investigated with scanning electron microscopy and transmission electron microscopy. The optimum pH was 3.5 for all of the immobilized enzymes, and the optimum temperature was 50 °C. Compared with the free enzyme, the immobilized enzyme showed better stability for pH and temperature changes. Moreover, the addition of O‐MMT and the pores on the fibers improved the storage stability and the operational stability. Among the four kinds of fibrous membranes, the CA/O‐MMT membranes with porous fibers showed the best stability for the immobilized enzymes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43818.     

Removal of lipopolysaccharide from protein solution using nanostructured porous supports bearing lipid membranes

Polymeric lipid membranes of N-octadecylchitosan, which consists of 70 mol% of 2-(octadecylamino)-2-deoxy-d-glucopyranose, 17 mol% of 2-amino-2-deoxy-d-glucopyranose, and 13 mol% of 2-acetamido-2-deoxy-d-glucopyranose, were covalently immobilized to carboxylated porous supports composed of chitosan and used for the adsorption of pyrogenic lipopolysaccharide. When human serum albumin solution, including 5 mg mL^-1 of albumin and 5.6 ng mL^-1 of lipopolysaccharide, was passed through a column packed with the resulting porous supports bearing lipid membranes assembled in nanoscale, lipopolysaccharide was removed to as low as a detection limit of 0.020 ng mL^-1 with a quantitative recovery of protein. On the other hand, in the case of directly N-octadecylated porous supports having cationic and hydrophobic ligands which are not assembled as lipid membranes, lipopolysaccharide could not be removed to the detection limit and protein recovery was lower than the porous supports bearing lipid membranes. The difference above as well as difference from conventional adsorbents suggested that the selectivity was attributable to an interaction between the cationic lipid membranes of N-octadecylchitosan and lipopolysaccharide as well as protein. The porous supports bearing lipid membranes were stable in 0.5 M NaOH and 0.1 M HCl at ambient temperature. Considering the confirmed excellent selectivity and chemical stability, their practical use as separation media in the pharmaceutical manufacturing can be expected.     

Galvanostatic anodization of pure Al in some aqueous acid solutions Part I: Growth kinetics, composition and morphological structure of porous and barrier-type anodic alumina films

The growth kinetics of anodic films formed on the surface of high purity Al by anodization under galvanostatic conditions at current densities in the range 5–75 mA cm^–2 in thermostatically controlled and vigorously stirred solutions of chromic, sulfuric, phosphoric, citric, tartaric and oxalic acids at different temperatures, were studied. It has been shown that chromic acid solution produces a typical barrier type oxide growth at any given temperature, while the specific kinetic curve representing the combined barrier/porous type film growth is observed when the anodization process is carried out in a nonstirred chromic acid solution. The oxide growth in the rest of the anodizing solutions occurs in different ways depending on the bath temperature. Barrier oxide growth is observed at temperatures lower than 30 °C. Above this temperature, combined barrier/porous oxide growth is observed. In all cases, the slope of the linear part of the potential against time curves, and therefore the rate of barrier oxide growth, increases with increasing anodizing current density and acid concentration, while it decreases with increase in temperature. The composition and surface morphology of the anodic films have been studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM).     

Development of a method of production of porous fillers from refractory clays and kaolins

Conclusions The basic production parameters were developed for production of chamotte porous fillers with an apparent density of 0.35–1.3 g/cm³ by expansion of refractory clays and kaolins in the 1500–1700°C range.It was established that DN2 clay expands sufficiently effectively with a heating rate of not less than 20°C/min and KV-2 kaolin with a rate of 60°C/min.The specified apparent density of the filler is obtained by varying the temperature, the hold, and the expanding addition content. At 1500–1700°C the maximum expansion effect is observed in the first 1–5 min. The optimum time for obtaining a constant volume filler is determined by the form of the clay raw material, the sulfate addition content, and the expansion temperature.A necessary condition for high-quality production of a porous filler is conformance of the hold and the size of granulated material to the selected expansion temperature.Testing of the method developed in small rotating kilns showed the possibility of production of a porous refractory filler with an apparent density of 1.2–1.3 g/cm³.Translated from Ogneupory, No. 7, pp. 32–36, July, 1985.     

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.     

Production and characterization of durable self-cleaning and engineering porous Al2O3/CaAl12O19 ceramic membranes

The rapid development of engineering filtering process suggests that it is imperative to produce membrane substrates with a fine pore size, high gas permeation, and antifouling properties for efficient and long-term application. This study reports on a novel fabrication method of a porous Al₂O₃/CaAl₁₂O₁₉ ceramic membrane substrate by a direct foaming method combined with cement solidification and tape-casting technology. The microstructure of the produced ceramic membrane consisted of pores with a size of 50-150 μm, which were interconnected with each other with a large number of small filtering functional pores of <10 μm. By increasing the amount of the foaming agent, the porosity of the porous Al₂O₃/CaAl₁₂O₁₉ ceramic membranes was tailored from 64.8% to 80.5%, and the bending strength decreased from 32.1 ± 1.0 to 9.6 ± 0.9 MPa, respectively. The sintered hydrophilic ceramic substrate was successfully modified to a hydrophobic one (with water contact angles of 143°) by pyrolysis of dimethyldichlorosilane and dichloromethylsilane. The resultant membrane displayed high chemical stability and self-cleaning features. The membrane with a porosity of 64.8% had a N₂ permeation of 3.0 (±0.5) × 10⁷ L m⁻² h⁻¹ at 0.5 bar and a water flux which could be totally suppressed at a liquid entry pressure of 0.45 bar.     

A bipolar electrode cell for aluminium electrorefining

Electrorefining of aluminium was carried out at 750 °C using bipolar electrode cells with centre holes 2, 10 or 20 mm in diameter. Through the centre holes liquid electrorefined aluminium rises to the electrolyte surface. The bipolar electrode cell consists of graphite cathodes, Al–Cu–Fe–Mn or Al–Cu–Fe–Zn alloy anodes and a BaCl₂–NaCl–AlF₃–NaF electrolytic melt. The centre hole size of more 20 mm in diameter is required to continuously float up the aluminium electrodeposited onto the electrolyte surface, while the current efficiency of the cell decreases with increase of the centre hole size, from 97% at 2 mm diameter to 92% at 20 mm diameter. Aluminium of 99.97% purity precipitates at the cathode. Iron, manganese and zinc included in the alloy as impurities are hardly deposited and the concentrations of these elements in the deposit are 100, 80 and 170 ppm, respectively. In this process aluminium can be produced with an energy consumption of about 4.9 × 10³ kWh(t-Al)^–1, which is one-third smaller than that of the Gadeau process.     

Gas-Transport Characteristics of PdCu–Nb–PdCu Membranes Modified with Nanostructured Palladium Coating

A method for obtaining composite gas-diffusion PdCu–Nb–PdCu membranes modified with a nanostructured crystalline coating was developed to increase the performance of Nb-based membranes. A modifying functional layer with a controlled size and composition was synthesized by electrochemical deposition, which made it possible to determine a certain geometric shape for palladium nanocrystallites. Developed PdCu–Nb–PdCu membranes have demonstrated flux values up to 0.232 mmol s⁻¹ m⁻² in the processes of diffusion purification of hydrogen at 400 °C. A very significant difference in the hydrogen fluxes through the modified and non-modified composite PdCu–Nb–PdCu membranes reached 1.73 times at the lower threshold temperature of 300 °C. Cu doping of protective layer did not affect the selective properties of the membranes, which was confirmed by the obtained high selectivity values up to 1323, and made it possible to reduce the noble metal content. The research data indicate that the modification of the membrane surface significantly accelerates the hydrogen transfer process at sufficiently low temperatures due to the acceleration of dissociative–associative processes on the surface. The reported approach demonstrates new possibilities for creating productive and cost-efficient membranes based on niobium.     

Salt‐leaching technique for the synthesis of porous poly(2,5‐benzimidazole) (ABPBI) membranes for fuel cell application

The first instance of synthesizing porous poly(2,5‐benzimidazole) (ABPBI) membranes for high‐temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs), using solvent evaporation/salt‐leaching technique, is reported herein. Various ratios of sodium chloride/ABPBI were dissolved in methanesulfonic acid and cast into membranes by solvent evaporation, followed by porogen (salt) leaching by water washing. The membranes were characterized using SEM, FTIR, TGA, and DSC. The proton conductivity, water and acid uptake of the membranes were measured and the chemical stability was determined by Fenton's test. SEM images revealed strong dependence of sizes and shapes of pores on the salt/polymer ratios. Surface porosities of membranes were estimated with Nis Elements‐D software; bulk porosities were measured by the fluid resaturation method. Thermogravimetric analysis showed enhanced dopant uptake with introduction of porosity, without the thermal stability of the membrane compromised. Incorporating pores enhanced solvent uptake and retention because of capillarity effects, enhancing proton conductivities of PEMs. Upon acid doping, a maximum conductivity of 0.0181 S/cm was achieved at 130 °C for a porous membrane compared with 0.0022 S/cm for the dense ABPBI membrane at the same temperature. Results indicated that with judicious optimization of porogen/polymer ratios, porous ABPBI membranes formed by salt‐leaching could be suitably used in HT‐PEMFCs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45773.     

Electroplating and electroless plating of Ni through/onto a porous polymer in a flow cell

Porous Ni coatings on electrodes were produced by electroplating through the cells and pores of a generic high internal phase emulsion polymer (PHIPE), a styrene-ethylhexylacrylate-divinylbenzene copolymer, and subsequent thermal decomposition of the polymer template. Electroplating was carried out from flowing solutions through a polymer block fitted in the interelectrode gap of a flow-by cell. The mass transfer conditions and the flow regime in the cell were also characterized. The structure of the porous electrodeposits thus produced was determined by the distortion of the electric field through the cells and pores of the insulating polymer and depends on the current density and the thickness of the polymer layer. Porous deposits plated at 5 mA cm^–2 showed high utilization of electroactive surface area when used as hydrogen evolving cathodes from alkaline solutions. Finally, Ni/PHIPE composite foams were prepared by Ni electroless plating through the polymer pores and their electrochemical surface area was evaluated.     

Complex anticorrosion coating for ZK30 magnesium alloy

This work aims at developing a new complex anticorrosion protection system for ZK30 magnesium alloy. This protective coating is based on an anodic oxide layer loaded with corrosion inhibitors in its pores, which is then sealed with a sol–gel hybrid polymer. The porous oxide layer is produced by spark anodizing. The sol–gel film shows good adhesion to the oxide layer as it penetrates through the pores of the anodized layer forming an additional transient oxide–sol–gel interlayer.The thickness of this complex protective coating is about 3.7–7.0 μm. A blank oxide–sol–gel coating system or one doped with Ce³⁺ ions proved to be effective corrosion protection for the magnesium alloy preventing corrosion attack after exposure for a relatively long duration in an aggressive NaCl solution.The structure and the thickness of the anodized layer and the sol–gel film were characterized by scanning electron microscopy (SEM). The corrosion behaviour of the ZK30 substrates pre-treated with the complex coating was tested by electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET), and scanning ion-selective electrode techniques (SIET).     

Advanced Sn/C composite anodes for lithium ion batteries

Metallic tin was deposited in fine particulate form on the surface of carbonaceous mesophase spherules (CMS) and in the pores of porous carbon by the decomposition and reduction of tin(II) 2-ethylhexanoate at 450 °C. The Sn/C composite powders obtained were used as anode materials for lithium ion cells. Electrochemical cycling tests of coin cells show that the dispersion of tin into the carbonaceous materials enhances the reversible capacity of the electrodes. The capacity retention at the 50th cycle is 91 % for Sn/CMS composite containing 22% tin, against 428 mAh g^–1 at the first cycle. With further increase in tin content, the capacity fade upon cycling is more rapid.     

Pore Structure and Thermal Stability of Mesoporous Mullite Fibers Prepared by Crystallization and Selective Leaching of Al2O3-SiO2 Glass Fibers

Porous mullite fibers were prepared by crystallization and selective leaching of Al2O3-SiO2 glass fibers using buffered HF-NH4F(BHF) aqueous solutions. The optimum concentration of BHF solution for selective leaching of the fibers was 0.9 mass% HF and 17.0 mass% NH4F. By firing at 1000–1300°C, the glass fibers changed into composite texture of mullite and glassy phase. Since the pores in the fibers were formed by selective leaching of glassy phase among mullite grains, they were tunable by changing the firing conditions of fibers. Pore size of the samples changed from around 4 nm in the 1100°C fired sample to 16 and 40 nm in the 1200 and 1300°C fired samples, respectively. The highest specific surface area obtained was around 30 m2/g, when the fibers were heat treated at 1200°C for 24 h and leached for 20 h in 0.9 mass% HF-17.0 mass% NH4F solution. From the thermal stability tests of the porous mullite fibers, its specific surface area was found to be maintained up to 1200–1300°C.     

Permselective membrane separators for organic electrolyte batteries

The electrical resistances, transference numbers and Li⁺Cu⁺⁺ and Br^–ClO ₄ ^– interdiffusion rates through a variety of cation-exchange and neutral membranes were measured in propylene carbonate (PC) solutions at 25°C. Of the 19 commercial and specially prepared membranes which were studied, the only membranes with electrical resistances in 0.50m LiClO₄/PC low enough to be of further interest as separators for organic electrolyte batteries were the AMF C-322, Amicon UM-05, Ionac MC-3470 and Corning No. 7930 porous glass (0.25 mm thick). The resistances of these membranes were 117, 2.3×10², 3.4×10² and 75.0 , cm², respectively.In order to benefit from the reduced resistance of thin membranes without sacrificing mechanical strength, laminated phenolsulfonic acid-formaldehyde (PF) membranes consisting of a thin layer of cation exchange resin on an inert porous support were prepared. Interdiffusion measurements showed that the laminated PF membranes are a more effective diffusion barrier towards anions in PC solutions than a commercial ultrafiltration membrane, the Amicon UM-05. The anion inter-diffusion fluxes for Br^– between 0.10m LiBr/PC and 0.10m LiClO₄/PC through the PF and UM-05 membranes were 6.17×10^–11 and 1.5×10^–10 mole s^–1 cm², respectively.