Use Of Membranes Research Articles

Sulfonated aromatic copoly(ether–amide) membranes: preparation and characterization for possible application in polymer electrolyte membrane fuel cells

Sulfonated membranes from highly aromatic copoly(ether–amide)s with sulfonation degrees (SDs) between 20 mol% and 55 mol% were prepared from the combination of diamines, 4,4′-(hexafluoroisopropylidene)-bis-( p-phenyleneoxy)dianiline (HFD), and different molar concentrations of 2,4-diaminobenzenesulfonic acid (DABS) that were reacted with equimolar amounts of isophthalic acid (ISO). The ionic membranes show–SO3H groups in the expected concentrations as assessed by Fourier transform infrared and proton nuclear magnetic resonance. Sulfonated copoly(ether–amide) membranes show the first thermal decomposition at 281°C for the sulfonic moieties and a second thermal loss at 439°C for the rigid nonsulfonated backbone which imparts them their high thermal stability. The ion-exchange capacity and water absorption in the sulfonated copoly(ether–amide)s increase steadily with SD. The copoly(ether–amide) with the larger SD, 55 mol% of DABS, HFD- co-ISO/DABS-55, shows the highest proton conductivity (91 mS cm−1) at 75°C. These results situate HFD- co-ISO/DABS-55 as a possible electrolyte membrane for use in polymer electrolyte membrane fuel cell with high thermal and mechanical stability.

Nanofiber Supported Thin-Film Composite Membrane for Pressure-Retarded Osmosis

Sustainable energy can be harnessed from fluids of differing salinity using a process known as pressure-retarded osmosis (PRO). We address one of the critical challenges of advance PRO by introducing a novel electrospun nanofiber-supported thin-film composite PRO membrane platform. The support was tiered with layers of nanofibers of different diameters to better withstand hydraulic pressure. The membranes successfully withstood an applied hydraulic pressure of 11.5 bar and exhibited performance that would produce an equivalent peak power density near 8.0 W/m(2) under real conditions (using 0.5 M NaCl and deionized water as the draw and feed solutions, respectively). This result shows the immense promise of nanofiber supported thin-film composite membranes for use in PRO.

Testing of various membranes for use in a novel sediment porewater isolation chamber for infaunal invertebrate exposure to PCBs

In benthic sediment bioassays, determining the relative contribution to exposure by contaminants in overlying water, porewater, and sediment particles is technically challenging. The purpose of the present study was to assess the potential for membranes to be utilized as a mechanism to allow freely dissolved hydrophobic organic contaminants into a pathway isolation exposure chamber (PIC) while excluding all sediment particles and dissolved organic carbon (DOC). This investigation was conducted in support of a larger effort to assess contaminant exposure pathways to benthos. While multiple passive samplers exist for estimating concentrations of contaminants in porewater such as those using solid-phase micro extraction (SPME) and polyoxymethylene (POM), techniques to effectively isolate whole organism exposure to porewater within a sediment system are not available. We tested the use of four membranes of different pore sizes (0.1–1.2μm) including nylon, polycarbonate, polyethylsulfone, and polytetrafluoroethylene with a hydrophilic coating. Exposures included both diffusion of radiolabeled and non-labeled contaminants across membranes from aqueous, sediment slurry, and whole sediment sources to assess and evaluate the best candidate membrane. Data generated from the present study was utilized to select the most suitable membrane for use in the larger bioavailability project which sought to assess the relevance of functional ecology in bioavailability of contaminated sediments at remediation sites. The polytetrafluoroethylene membrane was selected for use in the PIC, although exclusion of dissolved organic carbon was not achieved.

Characterization and performance study of sulfonated poly ether ether ketone/Fe3O4 nano composite membrane as electrolyte for microbial fuel cell

The influence of Fe3O4 in proton conductivity, oxygen crossover, water absorption and performance of Sulfonated Poly Ether Ether Ketone (SPEEK) matrix was studied in single chamber microbial fuel cell at various weight percentages (2.5%, 5%, 7.5%, 10%) of SPEEK/Fe3O4. The fabricated composite membranes were characterized by FT-IR, SEM, and XRD which were also tested for their surface roughness, water absorption, proton conductivity and transportation of cations were also studied for its suitability in microbial fuel cell operation. Escherichia coli (E. coli), an electrogenic bacteria, was used as the biocatalyst in anodic chamber and platinized carbon (Pt/C) was used as the catalyst in the air cathode. The low oxygen crossover, selective transfer of protons and water mediated proton hopping mechanism in Fe3O4 composite membrane (7.5% Fe3O4) resulted in a maximum power density of 104mWm−2 which was higher than that of the power density of Nafion® 117 (47mWm−2) under the same operating conditions. The results of the study suggested that SPEEK/Fe3O4 (7.5wt%) composite membrane would be more commercially viable and efficient than the existing Nafion membranes for use in microbial fuel cells.

Insight into the pore tuning of triazine-based nitrogen-rich organoalkoxysilane membranes for use in water desalination

Variation of water ratio played an important role in the separation properties of TTESPT membranes in reverse osmosis applications.

Chemical Synthesis, Characterisation, and Biocompatibility of Nanometre Scale Porous Anodic Aluminium Oxide Membranes for Use as a Cell Culture Substrate for the Vero Cell Line: A Preliminary Study

In this preliminary study we investigate for the first time the biomedical potential of using porous anodic aluminium oxide (AAO) membranes as a cell substrate for culturing the Cercopithecus aethiops (African green monkey) Kidney (Vero) epithelial cell line. One advantage of using the inorganic AAO membrane is the presence of nanometre scale pore channels that allow the exchange of molecules and nutrients across the membrane. The size of the pore channels can be preselected by adjusting the controlling parameters of a temperature controlled two-step anodization process. The cellular interaction and response of the Vero cell line with an in-house synthesised AAO membrane, a commercially available membrane, and a glass control were assessed by investigating cell adhesion, morphology, and proliferation over a 72 h period. The number of viable cells proliferating over the respective membrane surfaces revealed that the locally produced in-house AAO membrane had cells numbers similar to the glass control. The study revealed evidence of focal adhesion sites over the surface of the nanoporous membranes and the penetration of cellular extensions into the pore structure as well. The outcome of the study has revealed that nanometre scale porous AAO membranes have the potential to become practical cell culture scaffold substrates with the capability to enhance adhesion and proliferation of Vero cells.

Surface self-assembled zwitterionization of poly(vinylidene fluoride) microfiltration membranes via hydrophobic-driven coating for improved blood compatibility

A facile surface self-assembled zwitterionization process is presented, aiming at improving the blood compatibility of poly(vinylidene fluoride) (PVDF) membranes. Zwitterionic diblock copolymers containing hydrophobic propylene oxide and hydrophilic sulfobetaine methacrylate blocks were prepared with well controlled molecular weights via atom-transfer radical polymerization (ATRP). Poly(propylene oxide)-block-poly(sulfobetaine methacrylate) (PPO-b-PSBMA) copolymers with varying zwitterionic PSBMA lengths were coated by self-assembling process onto the surface of PVDF microfiltration membranes in order to enhance their surface hydrophilicity and protein resistance. A systematic study regarding the effect of block lengths of PPO-b-PSBMA copolymers on the hemocompatibility of zwitterionic PVDF membranes in human blood solution was then performed. Protein adsorption from single-protein solutions and 100% blood plasma solutions was measured on the PVDF surfaces covered with PPO-b-PSBMA brushes. If the increase in PPO content in copolymer increased the efficiency of coating on the membrane, resistance to human fibrinogen adsorption was enhanced when increasing the PSBMA content. The control of the anchoring structures of zwitterionic copolymer layers highly regulates the adsorption of plasma proteins, the adhesion of platelets, and the coagulation of human plasma. PVDF membranes coated with PPO-b-PSBMA containing a high amount of zwitterionic SBMA units presented a high hydration capability, believed to allow improving significantly the hemocompatible character of PVDF membranes. This work suggests that the hemocompatible nature of self-assembled zwitterionic brushes gives them a great potential in the molecular design of antithrombogenic membranes for use in human blood applications.

A novel poly(2,6-dimethyl-1,4-phenylene oxide) with pendant imidazolium groups for high-temperature proton exchange membrane

We designed and synthesized a novel poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with imidazolium-functionalized aromatic side chains by the reaction of imidazole-functionalized PPO and methyl iodide, and then prepared the acid doped PPO membrane by immersing the polymer membrane in phosphoric acid (PA). To achieve a high acid doping level and a high dimensional stability, the cross-linked membranes were prepared by the reaction of the imidazole groups of the polymer and 1,4-bis(bromomethyl) benzene. The PA content, area swelling, and tensile strength of the non-crosslinked and the crosslinked membranes doped with a H3PO4 solution were measured. The results showed that the crosslinked membrane with a PA content of 438% possessed the highest conductivity of 54 mS cm−1 at 140 °C with high dimensional stability and high tensile strength. Moreover, no shape change of the membranes was observed in 15 days in a Fenton solution containing 3% H2O2 and 4 ppm Fe2+ at 80 °C, indicating a high oxidative stability. Therefore, this new polymer can be considered as a promising candidate for preparing a high temperature proton exchange membrane for use in fuel cells.

Anhydrous Phosphoric Acid Functionalized Sintered Mesoporous Silica Nanocomposite Proton Exchange Membranes for Fuel Cells

A novel inorganic proton exchange membrane based on phosphoric acid (PA)-functionalized sintered mesoporous silica, PA-meso-silica, has been developed and investigated. After sintering at 650 °C, the meso-silica powder forms a dense membrane with a robust and ordered mesoporous structure, which is critical for retention of PA and water within the porous material. The PA-meso-silica membrane achieved a high proton conductivity of 5 × 10(-3) to 5 × 10(-2) S cm(-1) in a temperature range of 80-220 °C, which is between 1 and 2 orders of magnitudes higher than a typical membrane Nafion 117 or polybenzimidazole (PBI)/PA in the absence of external humidification. Furthermore, the PA-meso-silica membranes exhibited good chemical stability along with high performance at elevated temperatures, producing a peak power density of 632 mW cm(-2) using a H2 fuel at 190 °C in the absence of external humidification. The high membrane proton conductivity and excellent fuel cell performance demonstrate the utility of PA-meso-silica as a new class of inorganic proton exchange membranes for use in the high-temperature proton exchange membrane fuel cells (PEMFCs).

A ratiometric fluorescence sensor for the detection of ammonia in water

The shift in the fluorescence emission spectrum of oxazine 170 perchlorate (O17) when being deprotonated and bound with ammonium ions in water was exploited to fabricate a ratiometric ammonia sensor. The ratiometric fluorescence sensing was performed by using the ratio of the fluorescence intensities of two emission wavelengths at λem=565nm and λem=630nm. Ethyl cellulose (EC) was combined with the O17 to allow for the configuration of a thin membrane for the convenient detection of ammonia in water. Good compatibility of the O17 and EC has produced a successful ammonia-sensing membrane for use in the NH3 range of 1–60ppm with a short response time (t95=10s), high reversibility, less interference, and long-term stability. The ammonia-sensing membrane (O17-EC membrane) was applied for the determination of ammonia in artificial waste water containing different ions. The results obtained were in good agreement with the concentrations of ammonia added to the artificial waste water samples.

Hydrogen Permeation Properties and Hydrothermal Stability of Sol–Gel‐Derived Amorphous Silica Membranes Fabricated at High Temperatures

The sol–gel method was applied to the fabrication of amorphous silica membranes for use in hydrogen separation at high temperatures. The effects of fabrication temperature on the hydrogen permeation properties and the hydrothermal stability of amorphous silica membranes were evaluated. A thin continuous silica separation layer (thickness = <300 nm) was successfully formed on the top of a deposited colloidal silica layer in a porous glass support. After heat treatment at 800°C for an amorphous silica membrane fabricated at 550°C, however, it was quite difficult to distinguish the active separation layer from the deposited colloidal silica layer in a porous glass support, due to the adhesion of colloidal silica caused by sintering at high temperatures. The amorphous silica membranes fabricated at 700°C were relatively stable under steam atmosphere (500°C, steam = 70 kPa), and showed steady He and H2 permeance values of 4.0 × 10−7 and 1.0 × 10−7 mol·m−2·s−1·Pa−1 with H2/CH4 and H2/H2O permeance ratios of ~110 and 22, respectively. The permeance ratios of H2/H2O for membranes fired at 700°C increased drastically over the range of He/H2 permeance ratios by factors of ~3–4, and showed a value of ~30, which was higher than those fired at 500°C. Less permeation of water vapor through amorphous silica membranes fabricated at high temperatures can be ascribed to the dense amorphous silica structure caused by the condensation reaction of silanol groups.

Severe Acute Respiratory Syndrome Coronavirus Nonstructural Proteins 3, 4, and 6 Induce Double-Membrane Vesicles

ABSTRACTCoronaviruses (CoV), like other positive-stranded RNA viruses, redirect and rearrange host cell membranes for use as part of the viral genome replication and transcription machinery. Specifically, coronaviruses induce the formation of double-membrane vesicles in infected cells. Although these double-membrane vesicles have been well characterized, the mechanism behind their formation remains unclear, including which viral proteins are responsible. Here, we use transfection of plasmid constructs encoding full-length versions of the three transmembrane-containing nonstructural proteins (nsps) of the severe acute respiratory syndrome (SARS) coronavirus to examine the ability of each to induce double-membrane vesicles in tissue culture. nsp3 has membrane disordering and proliferation ability, both in its full-length form and in a C-terminal-truncated form. nsp3 and nsp4 working together have the ability to pair membranes. nsp6 has membrane proliferation ability as well, inducing perinuclear vesicles localized around the microtubule organizing center. Together, nsp3, nsp4, and nsp6 have the ability to induce double-membrane vesicles that are similar to those observed in SARS coronavirus-infected cells. This activity appears to require the full-length form of nsp3 for action, as double-membrane vesicles were not seen in cells coexpressing the C-terminal truncation nsp3 with nsp4 and nsp6.

Conformational analysis investigation into the influence of nano-porosity of ultra-permeable ultra-selective polyimides on its diffusivity as potential membranes for use in the "green" separation of natural gases

Nano-porous polymers of intrinsic microporosity, PIM, have exhibited excellent permeability and selectivity characteristics that could be utilized in an environmentally friendly gas separation process. A full understanding of the mechanism through which these membranes effectively and selectively allow for the permeation of specific gases will lead to further development of these membranes. Three factors obviously influenced the conformational behavior of these polymers, which are the presence of electronegative atoms, the presence of non-linearity in the polymeric backbones (backbone kinks) and the presence of bulky side groups on the polymeric chains. The dipole moment increased sharply with the presence of backbone kinks more than any other factor. Replacing the fluorine atoms with bulky alkyl groups didn't influence the dipole moment greatly indicating that the size of the side chains had much less dramatic influence on the dipole moment than having a bent backbone. Similarly, the presence of the backbone kinks in the polymeric chains influenced the polymeric chains to assume less extended configuration causing the torsional angles around the interconnecting bonds unable to cross the high potential energy barriers. The presence of the bulky side groups also caused the energy barriers of the cis-configurations to increase dramatically, which prevented the polymeric segments from experiencing full rotation about the connecting bonds. For these polymers, it was clear that the fully extended configurations are the preferred configurations in the absence of strong electronegative atoms, backbones kinks or bulky side groups. The addition of any of these factors to the polymeric structures resulted in the polymeric chains being forced to assume less extended configurations. Rather interestingly, the length or bulkiness of the side groups didn't affect the end-to-end distance distribution to a great deal since the presence of quite large bulky side chain such as the pentyl group has caused the polymeric chains to revert back to the fully extended configurations possibly due to the quite high potential energy barriers that the chains have to cross to reach the less extended configurational states.

Nanofluidic crystal: a facile, high-efficiency and high-power-density scaling up scheme for energy harvesting based on nanofluidic reverse electrodialysis

The great advances in nanotechnology call for advances in miniaturized power sources for micro/nano-scale systems. Nanofluidic channels have received great attention as promising high-power-density substitutes for ion exchange membranes for use in energy harvesting from ambient ionic concentration gradient, namely reverse electrodialysis. This paper proposes the nanofluidic crystal (NFC), of packed nanoparticles in micro-meter-sized confined space, as a facile, high-efficiency and high-power-density scaling-up scheme for energy harvesting by nanofluidic reverse electrodialysis (NRED). Obtained from the self-assembly of nanoparticles in a micropore, the NFC forms an ion-selective network with enormous nanochannels due to electrical double-layer overlap in the nanoparticle interstices. As a proof-of-concept demonstration, a maximum efficiency of 42.3 ± 1.84%, a maximum power density of 2.82 ± 0.22 W m−2, and a maximum output power of 1.17 ± 0.09 nW/unit (nearly three orders of magnitude of amplification compared to other NREDs) were achieved in our prototype cell, which was prepared within 30 min. The current NFC-based prototype cell can be parallelized and cascaded to achieve the desired output power and open circuit voltage. This NFC-based scaling-up scheme for energy harvesting based on NRED is promising for the building of self-powered micro/nano-scale systems.

Synthesis and characterization of polysulfone/layered double hydroxides nanocomposite membranes for fuel cell application

In the present study, sulfonated polysulfone (SPSU)/layered double hydroxide (LDH) composite membranes for use in proton exchange membrane fuel cells (PEMFCs) were investigated. Polysulfone (PSU) was sulfonated with trimethylsilyl chlorosulfonate in 1,2 dichloroethane at room temperature.Composite membranes were prepared by blending different amount (0, 1, 2, and 5%) of LDH nanoparticles with SPSU in dimethylacetamide (DMAc). The membranes were prepared by the casting method and the samples obtained were characterized by XRD, FTIR spectroscopy. The thermal behavior for all samples was evaluated by thermogravimetrical analysis (TGA). Finally electrochemical impedance spectroscopy (EIS) was used to study the membranes electrical properties. The EIS measurements were carried out with the membranes in contact with HCl solutions at different concentrations (10−3 ≤ c ≤ 10−1). Results show a clear dependence of the membrane electrical resistance with the sulfonation degree and the amount of the LDH added.

Surface Zwitterionization of Expanded Poly(tetrafluoroethylene) Membranes via Atmospheric Plasma-Induced Polymerization for Enhanced Skin Wound Healing

Development of bioinert membranes to prevent blood clotting, tissue adhesion, and bacterial attachment is important for the wound healing process. In this work, two wound-contacting membranes of expanded poly(tetrafluoroethylene) (ePTFE) grafted with zwitterionic poly(sulfobetaine methacrylate) (PSBMA) and hydrophilic poly(ethylene glycol) methacrylate (PEGMA) via atmospheric plasma-induced surface copolymerization were studied. The surface grafting chemical structure, hydrophilicity, and hydration capability of the membranes were determined to illustrate the correlations between bioadhesive properties and wound recovery of PEGylated and zwitterionic ePTFE membranes. Bioadhesive properties of the membranes were evaluated by the plasma protein adsorption, platelet activation, blood cell hemolysis, tissue cell adhesion, and bacterial attachment. It was found that the zwitterionic PSBMA-grafted ePTFE membrane presented high hydration capability and exhibited the best nonbioadhesive character in contact with protein solution, human blood, tissue cells, and bacterial medium. This work shows that zwitterionic membrane dressing provides a moist environment, essential for "deep" skin wound healing observed from the animal rat model in vivo and permits a complete recovery after 14 days, with histology of repaired skin similar to that of normal skin tissue. This work suggests that the bioinert nature of grafted PSBMA polymers obtained by controlling grafting structures gives them great potential in the molecular design of antibioadhesive membranes for use in skin tissue regeneration.

Glycosylation of Polyphosphazene Nanofibrous Membrane by Click Chemistry for Protein Recognition

AbstractA novel core/sheath glycosylated polyphosphazene nanofibrous membrane for use in protein recognition is fabricated via coaxial electrospinning process with alkyl polyphosphazene as the sheath and polyacrylonitrile (PAN) as the core, followed by introduction of saccharide residues to the surface of the polyphosphazene nanofibrous membrane using alkyne–azide “click” chemistry. A glucose/protein binding assay effectively demonstrates that this nanofibrous membrane can selectively recognize Con A while showing almost no binding with bovine serum albumin (BSA). Furthermore, the affinity capability of proteins (BSA and Con A) for the glycosylated polyphosphazene surface is investigated quantitatively using a surface plasmon resonance (SPR) technique.magnified image

Surface-Modification of Poly(dimethylsiloxane) Membrane with Self-Assembled Monolayers for Alcohol Permselective Pervaporation

The use of self-assembled monolayers (SAMs) has recently been recognized as an effective way to tailor the surface properties of films used in various applications. However, application of SAMs in the preparation of separation membranes remains unexplored. In the present study, surface-modified poly(dimethylsiloxane) (PDMS) membranes were prepared using SAMs to fabricate a membrane for use in pervaporation separation of ethanol/water mixtures. A cross-linked PDMS/polysulfone (PSf) composite membrane was transformed by introducing hydroxyl functionalities on the PDMS surface through a UV/ozone conversion process. (Tridecafluoroctyl)triethoxysilane was allowed to be adsorbed on the resulting Si-OH substrate to increase the hydrophobicity of the membrane. Results from Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry, atomic force microscopy, and contact angle analyses suggest that the fluoroalkylsilane monolayer was successfully formed on the modified PDMS/PSf membrane treated by 60 min UV/ozone exposure. The newly SAM-modified membrane exhibited a separation factor of 13.1 and a permeate flux of 412.9 g/(m(2) h), which are higher than those obtained from PDMS membranes.

Polymer-controlled release of tobramycin from bone graft void filler.

Despite clinical, material, and pharmaceutical advances, infection remains a major obstacle in total joint revision surgery. Successful solutions must extend beyond bulk biomaterial and device modifications, integrating locally delivered pharmaceuticals and physiological cues at the implant site, or within large bone defects with prominent avascular spaces. One approach involves coating clinically familiar allograft bone with an antibiotic-releasing rate-controlling polymer membrane for use as a matrix for local drug release in bone. The kinetics of drug release from this system can be tailored via alterations in the substrate or the polymeric coating. Drug-loaded polycaprolactone coating releases bioactive tobramycin from both cadaveric-sourced cancellous allograft fragments and synthetic hybrid coralline ceramic bone graft fragments with similar kinetics over a clinically relevant 6-week timeframe. However, micron-sized allograft particulate provides extended bioactive tobramycin release. Addition of porogen polyethylene glycol to the polymer coating formulation changes tobramycin release kinetics without significant impact on released antibiotic bioactivity. Incorporation of oil-microencapsulated tobramycin into the polymer coating did not significantly modify tobramycin release kinetics. In addition to releasing inhibitory concentrations of tobramycin, antibiotic-loaded allograft bone provides recognized beneficial osteoconductive potential, attractive for decreasing orthopedic surgical infections with improved filling of dead space and new bone formation.

Preparation of electrospun fiber mats using siloxane‐containing vaterite and biodegradable polymer hybrids for bone regeneration

An electrospun fiber mat using a new composite consisting of siloxane-containing vaterite (SiV) and poly(lactic-co-glycolic acid) (PLGA) (denoted by SiPLGVH) was prepared with the aim of applying it as a membrane for use in a guided bone regeneration (GBR) system. Another electrospun fiber mat using a previously described composite consisting of SiV and poly(L-lactic acid) (denoted by SiPVH) was also prepared as a comparative sample. SiPLG VH fiber mats showed superior results in terms of mechanical tensile properties and cellular behavior. Their elongation before failure was about eight times higher than that of SiPVH. The numbers of osteoblast-like cells that proliferated on the SiPLGVH fiber mats, regardless of the hydroxyapatite coating, were comparable to that of SiPVH. The cells spread more, two dimensionally, on the SiPLGVH fiber mats, since the pores between fibers were narrowed down because of swelling of the PLGA matrix during cell culture. This two-dimensional cellular proliferation quality on the SiPLGVH fiber mats is expected to be suitable for materials used in GBR, leading to control of infiltration of the soft tissue and great tissue integration with the surrounding tissue.