Fabrication of a thin palladium membrane supported in a porous ceramic substrate by chemical vapor deposition

A thin, gas-tight palladium (Pd) membrane was prepared by the counter-diffusion chemical vapor deposition (CVD) process employing palladium chloride (PdCl₂) vapor and H₂ as Pd precursors. A disk-shaped, two-layer porous ceramic membrane consisting of a fine-pore γ-Al₂O₃ top layer and a coarse-pore -Al₂O₃ substrate was used as Pd membrane support. A 0.5–1 μm thick metallic membrane was deposited in the γ-Al₂O₃ top layer very close to its surface, as verified by XRD and SEM with a backscattered electron detector. The most important parameters that affected the CVD process were reaction temperature, reactants concentrations and top layer quality. Deposition of Pd in the γ-Al₂O₃ top layer resulted in a 100- to 1000-fold reduction in He permeance of the porous substrate. The H₂ permeation flux of these membranes was in the range 0.5–1.0 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 350–450°C. The H₂ permeation data suggest that surface reaction steps are rate-limiting for H₂ transport through such thin membranes in the temperature range studied.     

A new route for the fabrication of TiO2 ultrafiltration membranes with suspension derived from a wet chemical synthesis

Titania ultrafiltration membranes were successfully fabricated by a new route, which was directly derived from the nanoparticles suspension that was the intermediate product prior to dry and calcine in the synthesis of nanoparticle by a wet chemical method. The morphology and the crystal structure of the prepared membrane were analyzed by SEM and XRD. The effect of various dipping time on the membrane thickness was investigated. The rejection of the bovine serum albumin (BSA, 67,000 Da) was used to evaluate the separation characteristics of these membranes, and the relationship between the dipping time and the optimization thickness of the membrane was built on the base of the data of the pure water flux. SEM images showed that the surface of the membrane was defect-free and XRD revealed that the titania crystalline phase was pure anatase. The membrane thickness increased linearly with the square root of the dipping time and the dipping time of 30 s was necessary to form a defect-free titania layer on the top of supports. The titania layer derived from the dipping time of 30 s could be of thickness of 5.9 μm and an average pore size of 60 nm. The pure water permeability of the membrane was 860 × 10⁻⁵ L/(m² h Pa) (860 L/(m² h bar)), and the BSA rejections of the membranes prepared reached to 90% after 20 min running.     

Phosphoric acid‐doped imidazolium ionomers with enhanced stability for anhydrous proton‐exchange membrane applications

Phosphoric acid‐doped crosslinked proton‐conducting membranes with high anhydrous proton conductivity, and good chemical stability in phosphoric acid were synthesized and characterized. The synthetic procedure of the acid‐doped composite membranes mainly involves the in situ crosslinking of polymerizable monomer oils (styrene and acrylonitrile) and vinylimidazole, and followed by the sulfonation of pendant imidazole groups with butanesultone, and further doped with phosphoric acid. The resultant phosphoric acid‐doped composite electrolyte membranes are flexible and show high thermal stability and high‐proton conductivity up to the order of 10^?2 S cm^?1 at 160 °C under anhydrous conditions. The phosphoric acid uptake, swelling degree, and proton conductivity of the composite membranes increase with the vinylimidazole content. The resultant composite membranes also show good oxidative stability in Fenton's reagent (at 70 °C), and quite good chemical stability in phosphoric acid (at 160 °C). The properties of the prepared electrolyte membranes indicate their promising prospects in anhydrous proton‐exchange membrane applications. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 , 51, 1311–1317     

Preparation,chemical features,structure and applications of membrane materials based on graphene oxide

1. Download : Download high-res image (225KB)
2. Download : Download full-size image

     

Aromatic polysulfone copolymers for gas separation membrane applications

New polysulfone (PSF) copolymers from bis(4-fluorophenyl)sulfone and based on equimolar mixtures of the rigid/compact naphthalene moiety with bulky connectors from bisphenols: tetramethyl, hexafluoro, and tetramethyl hexafluoro, respectively, were synthesized to measure significant physical properties related to the gas separation field. The flexible and transparent polymer dense films TM-NPSF, HF-NPSF and TMHF-NPSF show high glass transition temperatures T_g  230 °C and high decomposition temperatures T_D  400 °C (10 wt.% loss, in air). Free volume cavity sizes, as determined by PALS, are in the range of 94–139 Å³. Their gas permeability and selectivity combinations of properties, measured at 35 °C and 2 atm, are very attractive since their selectivity for the pair of gases H₂/CH₄, O₂/N₂, and CO₂/CH₄ are higher than those for commercial PSF membranes, having similar or superior permeability coefficients for the most permeable gases H₂, O₂, and CO₂. Especially important is the tetramethyl naphthalene polysulfone TM-NPSF membrane which reports selectivities for H₂/CH₄, O₂/N₂ and CO₂/CH₄ of 122, 7.6 and 38 with corresponding permeability coefficients (in Barrers) of 17 for H₂, 1.2 for O₂, and 5.2 for CO₂. These results are interpreted in terms of free volume size and glass transition temperature together with the respective contribution of gas solubility and diffusivity to the overall selectivity coefficients.     

Fabrication and chemical surface modification of nanoporous silicon for biosensing applications

In this work, porous silicon (PS) films with varied porosity (68–82%) were formed on the p-type, boron-doped silicon wafer (100) by the electrochemical anodisation in an aqueous hydrofluoric acid and isopropyl alcohol solution at different current densities (I _d) ranging from 20–70 mA cm^?2, respectively. Biofunctionalisation of the PS surface was carried out by chemically modifying the surface of PS by the deposition of 3-aminopropyltriethoxysilane thermally leading to high density of amine groups covering the PS surface. This further promotes the immobilisation of immunoglobulin (human IgG and goat anti-human IgG binding) on to the PS surface. Formation of nanostructured PS and the attachment of antibody–antigen to its surface were characterised using photoluminescence (PL), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques, respectively. The possibility of using these structures as biosensors has been explored based on the significant changes in the PL spectra before and after exposing the PS optical structures to biomolecules. These experimental results open the possibility of developing optical biosensors based on the variation of the PL position of the PL spectra of PS-based devices.     

Characterization of microporous membranes for use in membrane contactors

Methods of selecting applicable membranes for use in membrane contactors for flue gas desulfurization are proposed in this paper. The mass transfer mechanism for SO₂ diffusion through gas filled pores is explored by simple measurements in order to identify suitable membrane structures for use in contactors for flue gas cleaning. It is attempted to correlate the experimentally determined membrane mass transfer coefficient to intrinsic physical properties of the membrane by applying theoretical and empirical correlations for the porosity-tortuosity relationship of the porous structure. Thereby limiting fluxes can be predicted with good accuracy from data quoted in the manufactures catalogue.     

Mathematical simulation of capillary filtration process for the preparation of tubular ceramic ultrafiltration membrane

A model based on capillary theory and filtration theory has been established to simulate the process for preparation of asymmetrical tubular ceramic ultrafiltration membranes. Methods for measuring parameters in the model were proposed and adopted. The calculated membrane thickness by the model has a good consistency with the measured one. Further calculated results show that in the process of first layer imbibing slip, the gel thickness developed at a rate proportional to the square root of the casting time; however, in the process of the second layer imbibing slip, the gel thickness did not maintain the square root relationship with the casting time; in the process of the third layer imbibing slip, the relationship between the gel thickness and the casting time was more and more close to a square root when the casting time was prolonged longer and longer. The influences of Methyl Cellulose (MC) concentration in sol on the gel membrane development had also been discussed. The higher the MC concentration was the more slowly the gel membrane developed.     

Advances in coatings on Mg alloys and their anti-microbial activity for implant applications

Magnesium matrix composites reinforced by calcium phosphate could not show the desired effect on the magnesium breakdown rate. Rapid disintegration rate limited the magnesium alloys used as biodegradable implant material. The rate of degradation can be minimized and biological activity can be improved in the magnesium alloy by Hydroxyapatite (HA) coating with the improvement of bone induction and conduction abilities. Various alkali post-treatment and conversion coating methods are applied to deposit HA coatings and biocompatible dicalcium phosphate dihydrate (DCPD) on magnesium alloy so that corrosion resistance and surface biocompatibility can be improved to be used in bone tissue engineering applications. Magnesium's corrosion resistance will weaken its antibacterial properties, which are linked to and proportional to the alkaline pH at the time of breakdown. The goal of this study is to bring together and compare contemporary research on different coatings on magnesium and related alloys in relation to antibacterial functionalized activities. A though review has been performed on in vivo and in vitro cytocompatibility, material property, corrosion resistance, and antibacterial properties of the coatings. Increased degradation behavior, biocompatibility, and bioactivity have been achieved following multiple procedures such as alkali treatment with HA electrochemical deposition on magnesium alloy. Multifunctional coatings can make safe and bioactive magnesium alloy surfaces for biodegradable implant applications.     

Mechanical stability and transport properties of the Sn-promoted SrCo0.8Fe0.2O3−δ ceramic membrane

In this article, the phase compositions, thermal, mechanical and transport properties of both the SrCo_0.8Fe_0.2O_3−δ (SCF) and the SrCo_0.8Fe_0.1Sn_0.1O_3−δ (SSCF) ceramic membranes were investigated systematically. As compared with the SCF membrane, the SSCF one had a more promoted thermal shock resistance, which related to its small thermal expansion coefficient between them and an enhanced composite structure for it. For the SCF membrane, a permeation rate of 1.9 × 10⁻⁶ mol cm⁻² s⁻¹ was obtained at 1000 °C and under the oxygen partial pressure gradient of P_O2 (h)/P_O2 (l) = 0.209 atm/0.012 atm; however, the permeation rate was 2.5 × 10⁻⁶ mol cm⁻² s⁻¹ for the SSCF one in the same measuring condition. In addition, both peak values of total electrical conductivity (σ_e) for SSCF sample appeared with increasing temperature. The second peak value of σ_e for SSCF one was regarded as the contribution from its minor phase, which appeared with the mixed conducting behavior resulting from partly Co-dissolving into its lattice.     

The preparation and characterization of silver‐loading cellulose acetate hollow fiber membrane for water treatment

Silver‐loading asymmetric cellulose acetate (CA) hollow fiber membrane was spun via the dry jet‐wet spinning technique. The spinning solution was prepared by dissolving AgNO₃ and CA in N,N‐dimethylformamide (DMF). The silver ions were reduced in the spinning dope into silver nano‐particles. The morphology of the resulting hollow fibers was examined using a scanning electron microscope and the silver content in the fiber was measured using an inductively coupled plasma atomic emission spectrometer. The antibacterial activities were evaluated. These hollow fibers had a sponge‐like structure and dense inner and outer surfaces. At a 50 k magnification, the pore on the skin layer was not observable, while the nodule size was smaller than 10 nm. The residual silver content of as‐spun hollow fiber was about 60% of the original silver added in the polymer solution. After immersing in water bath for 180 days, the silver content in the bulk of the hollow fibers decreased to 60% and the silver content on the surface reduced to 10%, yet still showed antibacterial activity against Escherichia coli and Staphylococcus aureus. After permeating with water for 5 days, the silver content in the hollow fibers decreased, and did not show antibacterial activity against E. coli and S. aureus. Thus, silver content must be periodically replenished after permeation. The proper range of AgNO₃ in the spinning solution for CA hollow fiber should be about 100–1000 ppm. Copyright © 2005 John Wiley & Sons, Ltd.     

Side chain crosslinking of aromatic polyethers for high temperature polymer electrolyte membrane fuel cell applications

Novel aromatic polymers bearing polar pyridine units in the main chain and side chain crosslinkable hydroxyl and propargyl groups have been successfully synthesized. The polymers have been investigated in terms of their critical properties related to their application in high temperature polymer electrolyte membrane fuel cells, such as doping ability, mechanical properties, and thermal stability. Crosslinked membranes were prepared by direct crosslinking of hydroxyl side chain groups with decafluorobiphenyl used for the first time as a crosslinking agent. However, further functionalization of hydroxyl groups to the propargyl derivative has also led to crosslinked polymers after thermal curing. Both types of crosslinked membranes exhibited higher glass transition temperatures as well as lower doping levels when doped in phosphoric acid compared with the non crosslinked analogs, confirming the formation of a successfully crosslinked network. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A simple method for preparation of macroporous polydimethylsiloxane membrane for microfluidic chip-based isoelectric focusing applications

A new, simple method was reported to prepare PDMS membranes with micrometer size pores for microfluidic chip applications. The pores were formed by adding polystyrene and toluene into PDMS prepolymer solution prior to spin-coating and curing. The resulting PDMS membrane has a thickness of around 10 μm and macropores with a diameter ranging from 1 to 2 μm measured using scanning electron microscope (SEM) imaging. This PDMS membrane was validated by integrating it with PDMS microfluidic chips for protein separation using isoelectric focusing mechanism coupled with whole channel imaging detection (IEF-WCID). It has been shown that five standard pI markers and a mixture of two proteins, myoglobin and β-lactoglobulin, can be separated using these chips. The results indicated that this macroporous PDMS membrane can replace the dialysis membrane in PDMS chips for the IEF-WCID technique. The preparation method of macroporous PDMS membrane may be potentially applied in other fields of microfluidic chips.     

Sulfonated multiblock copoly(ether sulfone)s as membrane materials for fuel cell applications

Arylene ether multiblock copolymers of the (AB)_n-type with various degrees of sulfonation have been prepared by a two-step polycondensation procedure. Multiblock copolymers in high yields and of high molecular weights were obtained. For comparison random copolymers with the same overall composition were synthesized. The theoretical ion-exchange capacities (IEC) of the materials were ranging from 0.50 mmol/g to 1.25 mmol/g. The water-uptake of the multiblock copolymers showed a linear dependency from the IEC and was increasing with increasing IEC. No differences were observed between random and block copolymers. Furthermore, the hydrolytic stability of aromatic sulfonic acid groups was investigated in this study. Aromatic sulfonic acids, having additional electron donating groups, especially in ortho- or para-position to the sulfonic acid group are sensitive to hydrolytic desulfonation. On the other hand electron-withdrawing groups in meta-position showed a stabilizing effect.     

Recent advances on electroactive CNT-based membranes for environmental applications: The perfect match of electrochemistry and membrane separation

Global climate change, growing population, and environmental pollution underscore the need for a greater focus on providing advanced water treatment technologies. Although electrochemical based-processes are becoming promising solutions, they still face challenges owing to mass transport and upscaling which hinder the exploitation of this technology. Electrode design and reactor configuration are key factors for achieving operational improvements. The electroactive membrane has proven to be a breakthrough technology integrating electrochemistry and membrane separation with an enhanced mass transport by convection. In this review article, we discuss recent progress in environmental applications of electroactive membranes with particular focus on those composed of carbon nanotubes (CNT) due to their intriguing physicochemical properties. Their applications in degradation of refractory contaminants, detoxification and sequestration of toxic heavy metal ions, and membrane fouling alleviations are systematically reviewed. We then discuss the existing limitations and opportunities for future research. The development of advanced electroactive systems depends on interdisciplinary collaborations in the areas of materials, electrochemistry, membrane development, and environmental sciences.     

Thermal,chemical, biological and mechanical properties of chitosan films with powder of eggshell membrane for biomedical applications

Journal of Thermal Analysis and Calorimetry - The objective of this work was to develop chitosan films incorporated with the eggshell membrane powder (MCO) by the solvent evaporation method with...     

Acrylonitrile-acrylic acid copolymer membrane imprinted with uric acid for clinical uses

The preparation of new polymeric membranes using molecular imprinting technology for application in blood filtration devices is described. Membranes, based on an acrylic acid-acrylonitrile copolymer, produced through phase inversion, were modified by introducing specific binding sites for uric acid into their structure. The materials prepared are intended for use to selectively remove uric acid from the blood in the case of increased serum uric acid values associated with different pathologies. The interactions at a molecular level between the membrane forming copolymer and the template were investigated by means of calorimetry, infrared spectroscopy and morphological analysis. The presence of interactions between the template and the copolymer, and a good thermal stability of the imprinted membranes were observed. In addition, the results of rebinding tests on the imprinted membranes indicated a good capacity of molecular recognition for the template and satisfactory selectivity properties towards compounds of similar structure such as theophylline. Membrane permeability values suggest their application as (ultra) haemofiltration devices. Poly(acrylonitrile-co-acrylic acid) membrane.     

Novel hydrogel membrane based on copoly(hydroxyethyl methacrylate/p-vinylbenzyl-poly(ethylene oxide)) for biomedical applications: properties and drug release characteristics

The aim of this study was to synthesize and characterize a novel biocompatible polymeric membrane system and demonstrate its potential use in various biomedical applications. Synthetic hydrogels based on poly(hydroxyethyl methacrylate), poly(HEMA), have been widely studied and used in biomedical fields. A novel copolymer hydrogel was prepared in the membrane form using 2-hydroxyethyl methacrylate monomer (HEMA) and a macromonomer p-vinylbenzyl-poly(ethylene oxide) (V-PEO) via photoinitiated polymerization. A series of poly(HEMA/V-PEO) copolymer membranes with different compositions was prepared. The membranes were characterized using infrared, thermal and SEM analysis. The thermal stabilities of the copolymer membranes were found to be lowered by an increase in the ratio of macromonomer (V-PEO) in the membrane structure. Because of the incorporation of PEO segments, the copolymers exhibited significantly higher hydrophilic surface properties than pure poly(HEMA), as demonstrated by contact angle measurements. Equilibrium swelling studies were conducted to investigate the swelling behavior of the membranes. The equilibrium water uptake was reached in about 4 h. Moreover, the blood protein adsorption and platelet adhesion were significantly reduced on the surface of the PEO containing copolymer membranes compared to control pure poly(HEMA). Drug release experiments were performed in a continuous release system using model drug (vancomycin) loaded copoly(HEMA/V-PEO) membranes. A specific poly(HEMA/V-PEO) membrane formulation possessing the highest PEO content (with a HEMA:V-PEO (mmol:mmol) feed ratio of 112:1 and loaded with 40 mg antibiotic/g polymer) released about 81% of the total loaded drug in 24 h at pH 7.4. This membrane composition provided the best results and can be considered as a potential candidate for a transdermal antibiotic carrier and various biomedical and biotechnological applications.     

Surface characteristics of high corrosion resistant Ni–Nb–Zr–Ti–Ta glassy alloys for nuclear fuel reprocessing applications

This work firstly discovered that the Ni₆₀Nb₁₅Zr₅Ti₁₅Ta₅ metallic glass exhibits high corrosion resistance in boiling 6 N HNO₃ solutions with and without Cr⁶⁺ ions, which may be of great potential for nuclear fuel reprocessing applications. The high corrosion resistance of the alloy is due to the formation of the passive film composed exclusively of Nb⁵⁺ and Ta⁵⁺ cations after immersion in the solution without Cr⁶⁺ ions, and Nb⁵⁺, Ta⁵⁺ and Cr³⁺ cations after immersion in the solution with Cr⁶⁺ ions.