Membrane Casting Research Articles

Porous polyether sulfone for direct methanol fuel cell applications: Structural analysis

Porous poly ether sulfone (PES) membranes were prepared using two different solvents which were N-methyl-2-pyrrolidone and dimethylacetamide (DMAc) via dry/wet non-solvent phase inversion (NIPS) techniques. PES with the compositions of 18 wt% is prepared for each dope solution. During the membrane casting process, 0 to 5 minutes delay prior to immersion in coagulant bath is set in order to allow solvent evaporation to take place. Water is used as the non-solvent for solvent exchange process. The prepared membranes are characterised based on their morphological aspect using scanning electron microscopy towards the effect of solvent evaporation time and solution viscosity. The changes in proton conductivity, methanol permeability, water uptake and hydrophilicity/hydrophobicity behaviours are also studied. Conclusively, the 18 wt% PES membranes prepared with DMAc as solvent at 3 minutes solvent evaporation time exhibited desirable pore size for proton conduction (0.04 × 10−3 Scm−1) and methanol resistant effect that consequently contribute to considerably low methanol permeability rate at 0.06 × 10−7 cm2 s−1 which could elevate the direct methanol fuel cell performance.

Utilization of used polyethylene terephthalate (PET) bottles for the development of ultrafiltration membrane

Polyethylene terephthalate (PET) bottle is commonly used as a single-use packaging for beverages. The recycling of used PET bottles is very important since the huge amount of used PET bottles creates serious environmental concerns. In this work, used PET bottles were utilized as a raw material to develop ultrafiltration membranes by phase inversion technique. The results of this study revealed that lowering the polarity of the non-solvent by using various types of non-solvents, namely water-ethanol, water-n-propanol, and water-n-butanol, resulted in an increase in the water permeate flux of the membrane. The membranes also exhibited higher water permeate fluxes by increasing the molecular weight and the concentration of the additive for the membrane casting solution. Ultrafiltration experiment using aqueous solution containing Bovine Serum Albumin as a model feed solution showed rejection values of up to 91 %.

Altering membrane structure to enhance water permeability and performance of anion exchange membrane fuel cell

Water management has been proven significant for enhancing both performance and durability of anion exchange membrane fuel cell. Besides searching new material, decreasing membrane thickness and modifying operation parameters, a simple and universal method of altering membrane structure is proposed in this work. Composite membranes made by unique processing method that includes both casting and electrospinning processes were compared with traditional casting membrane, all with the same thickness of 40 µm. Comparing to traditional casting membrane, the composite membrane put at proper position shows a higher water permeability, thus even more than 50% enhancement of the peak performance.

Study on thermo-kinetic modeling of green route synthesized inorganic loading on PVDF membrane for Cr(VI) removal and its optimization

Mathematical modeling of a phase inversion membrane was studied to predict the morphology. The effect of different concentrations of TiO2 nanoparticles on the thermodynamic and kinetic properties of polyvinylidene fluoride (PVDF) membrane casting solutions was investigated. The addition of green synthesized TiO2 increases the viscosity, and a sufficient amount results in the formation of two phases. Thermodynamics enhances the demixing rate, whereas kinetics delays the demixing rate; this trade-off between thermodynamic and kinetic parameter will affect the membrane morphology. A quadratic phase diagram for PVDF/ TiO2/solvent/Water system was drawn experimentally at different concentrations of TiO2 using a new method. Synthesized membranes were characterized by the contact angle, porosity, and permeability. Surface morphologies at different compositions were also examined using High Resolution scanning electron microscope (HRSEM). At TiO2 concentration of 2 wt% in the polymer casting solution, thermodynamics parameter dominates kinetics parameter; thus, maximum porosity with enhanced permeability was achieved experimentally. The importance of thermo-kinetic parameters was further assessed using response surface optimization. The study suggested an optimum value of 2.165% of weight% TiO2 at 5.125 pH giving excellent agreement to the experimental data.

Solid‐state ion sensor for on‐chip determination of potassium ion in body fluid

AbstractThis article describes a synthetic route for the fabrication of all‐solid‐state potentiometric ion‐sensing device for on‐chip determination of potassium ion in body fluid. The sensing electrodes comprised of (a) a solid‐state reference electrode made from a Ag/AgCl‐printed electrode covered with a solid‐electrolyte‐embedded membrane made from siloxane polymer and (b) solid‐state ion‐selective electrode as working electrode made by assembling ionophore‐impregnated PVC membrane casting solution over a ion exchanger‐impregnated membrane. The ion exchanger‐impregnated membrane is cast by assembling siloxane–polyindole nanodispersion over working electrode of screen‐printed electrode to yield constant dipolar potential. The screen‐printed electrodes comprising of all‐solid‐state reference and working electrode can be operated under zero current flow to monitor potassium ion in given sample. The configuration of the printed electrodes is designed to fix a microneedle assembly over the working portion of both reference and working electrodes for transdermal ion sensing. The functional alkoxysilanes derived from nanodispersion allow to make solid‐state reference electrode avoiding the use of internal filling solution providing innovation in designing potentiometric sensor. In one aspect, a potentiometric device for detecting analyte in biological fluid that can include a array of hollowed microneedle in which each needle acts as protruded needle structure including an exterior wall forming a hollow interior covering both solid‐state working and reference electrode with an opening at terminal end in such that one microneedle is converted into a potassium ion‐selective electrode.

Suitability of different tests for characterization of the dimpled concrete‐to‐concrete interface

AbstractThe main aim of this study was to assess the suitability of different existing test setups for the mechanical characterization of a dimpled interface obtained by casting concrete against dimpled high‐density polyethylene (HDPE) membrane. Even though this type of interface roughening is widely used, especially for monolithic connections between precast elements, to the best of the authors' knowledge there is no research providing any data regarding its roughness parameters, tension, and shear strength, nor its failure modes. To this end, a two‐fold objective was established for this research: (a) to identify and analyze, from a technical standpoint, the available test configurations for characterizing the mechanical performance of interfaces, and (b) to perform an extensive experimental program devoted to characterizing the mechanical performance of a dimpled HDPE membrane—cast concrete interface. The suitability of each test for reproducing the expected stress state and the actual resistance mechanism was analyzed. Moreover, a comparison between tension and shear tests, including its main advantages and disadvantaged are also presented.

Preparation and properties of glutaraldehyde crosslinked poly(vinyl alcohol) membrane with gradient structure

Poly(vinyl alcohol) (PVA) is an attractive polymer for various applications based on membranes. To increase water resistance, PVA material has to be adequately crosslinked. However, crosslinking behavior on the whole PVA membrane generally leads to obviously increased brittleness and deteriorated transparency. In the present research, a kind of glutaraldehyde crosslinked PVA membrane with gradient structure has been successfully designed and prepared by the casting membrane of pure PVA aqueous solution and the following surface post-crosslinking processes. The method can endow the PVA membrane with the gradiently decreased crosslinking degree from the surface to inside. Such gradient cross-linked PVA membrane not only keeps good flexibility and transparency, but also possesses satisfactory water-proof property. The structure and properties of the prepared the gradient acetalized PVA (GAPVA) membranes were analyzed and characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscope (SEM), tensile measurement, water resistance test and transparency observation, etc. Compared with pure PVA membrane and uniform acetalized PVA (UAPVA) one, such GAPVA membrane displays excellent performance including good water resistance, transparency and mechanical properties, much higher than those of UAPVA membrane.

Synthesis of 2,2′-hindered pyridine containing semifluorinated polytriazoles and investigation for low-temperature proton exchange membrane application with enhanced oxidative stability

A series of new sulfonated copolytriazoles were prepared from a novel fluorinated diazide monomer with pyridine moiety to enhance both the oxidative stability and proton conductivity of proton exchange membranes. These proton donor–acceptor based copolymers and homopolymers were synthesized by click cycloaddition polymerization of the dialkyne monomer 1,2,4,5-tetrafluoro-3,6-bis(prop-2-yn-1-yloxy)benzene (TFAK) with or without the pyridine containing diazide monomer 2,2′-bis(4-(4-azidophenoxy)-3-(trifluoromethyl)phenyl)pyridine (PYFAZ) and the sulfonated diazide monomer 4,4′-diazido-2,2′-stilbenedisulfonic acid disodium salt (DSSAZ). 1H, 13C, and 19F NMR, in addition to FTIR analyses, confirm the formation of polytriazoles with a graded degree of sulfonation between 70% and 100%. The solution cast membranes were flexible and showed high chemical, thermal and mechanical properties. Inclusion of pyridine moiety proved to play a significant role in increasing peroxide stability by quenching hydroxyl and hydroperoxide radicals and forming pyridine-N-oxide, which was analyzed by EPR and FTIR spectroscopy. The presence of pyridine moiety also enhanced proton conductivity owing to the presence of the weakly basic nitrogen in pyridine that acts as a proton hopping site. AFM and HR-TEM images of the membranes indicated the formation of phase-separated morphology and that became more pronounced with the increase in the degree of sulfonation. The membranes obtained from PYFTSH-90 copolymer exhibited proton conductivity of 125 mS cm−1 at 80 °C, which is comparable to Nafion-117. The proton conductivity of PYFTSH-90 was further increased to 139 mS cm−1 at 90 °C. Thus, three significant objectives have been fulfilled in this work, namely (i) high proton conductivity, (ii) high hydrolytic stability, and (iii) high peroxide stability. These properties demonstrate that these copolymer membranes are potentially highly suitable for application in low-temperature proton exchange membrane fuel cell (PEMFC).

A comprehensive study on phase inversion behavior of a novel polysulfate membrane for high-performance ultrafiltration applications

The microorganisms and natural organic matters (NOM) in the water significantly threaten the health of human being, thus, it is an emerging demand for removal of those pollutes via the cost-efficient ultrafiltration technique. Non-solvent induced phase separation (NIPS) is the most frequently employed method for preparing ultrafiltration membrane in industry, however, the intrinsic weaknesses of porous polymeric membranes, e.g. weak mechanical property, foulants adsorption, and low-resistance to acidic/basic conditions, greatly hamper their applications. Thus, novel polymer materials are required to tackle the issues. In this study, we used a novel polymer, polysulfate (PSE) and adopted it for preparing ultrafiltration membrane via NIPS approach. The phase inversion process of the PSE casting membrane was comprehensively studied by choosing different solvents and water as coagulation bath. The top surface (TS) pore size of the resultant membranes was tailored by changing the solvent or tuning the polymer concentration, reaching as small as 10 nm with a porosity of 82.6 ± 0.9%. The ultrafiltration performance of the optimized membrane outperforms most of the polymeric membranes, which shows both high flux of 135.8 ± 10.7 LMH and rejection efficiency of 99.1 ± 0.83% for 100 ppm HA aqueous solution. Furthermore, the prepared membrane also owns antifouling and acid/alkaline-resistance characters, which endow the PSE membrane with great promise in the future industrially ultrafiltration applications.

Stimuli responsive mixed matrix polysulfone ultrafiltration membrane for humic acid and photocatalytic dye removal applications

Current work discusses the synthesis and characterization of a pH and thermo-responsive poly (N-vinylcaprolactam-TiO2-acrylic acid) (VCL-TiO2-AA) polymer nanocomposite in various compositions of TiO2 and application of these nanocomposites for the modification of polysulfone (PSF) membranes. The stimuli responsive nanocomposite was directly blended to the membrane casting solution and this casting solution was used to synthesize membranes by phase inversion method. The modified membranes were analyzed for their hydrophilic, photocatalytic, pH, and thermo-responsive behavior. The membranes were characterized for their morphology by using FESEM. FTIR and FESEM-EDX analysis were carried out to analyze their elemental analysis. Furthermore, the effect of the synthesized stimuli responsive VCL-TiO2-AA polymer nanocomposite was analyzed on the membrane performance in terms of fouling, temperature and pH responsiveness, and photocatalytic removal of MB dye under dark and UV light conditions at different pH values. Furthermore, the ultrafiltration performance and antifouling nature of the modified membranes were investigated and analyzed.

PEG/PPG-PDMS-Based Cross-Linked Copolymer Membranes Prepared by ROMP and In Situ Membrane Casting for CO2 Separation: An Approach to Endow Rubbery Materials with Properties of Rigid Polymers.

Rubbery polymer membranes prepared from CO2-philic PEO and/or highly permeable PDMS are desired for efficient CO2 separation from light gases (CH4 and N2). Poor mechanical properties and size-sieving ability, however, limit their application in gas separation applications. Cross-linked rubbery polymer-based gas separation membranes with a low Tg based on both PEG/PPG and PDMS units with various compositions between these two units are prepared for the first time in this work by ring-opening metathesis polymerization type cross-linking and in situ membrane casting. The developed membranes display excellent CO2 separation performance with CO2 permeability ranging from 301 to 561 Barrer with excellent CO2/N2 selectivity ranging from 50 to 59, overcoming the Robeson upper bound (2008). The key finding underlying the excellent performance of the newly developed cross-linked x(PEG/PPG:PDMS) membranes is the formation of a well-connected interlocked network structure, which endows the rubbery materials with the properties of rigid polymers, e.g., size-sieving ability and high thermomechanical stability. Moreover, the membrane shows long-term antiaging performance of up to eight months and antiplasticization behavior up to 25 atm pressure.

The transformation and degradation of Nafion® solutions under ultrasonic treatment. The effect on transport and mechanical properties of the resultant membranes

This work addresses the study of the effect of ultrasonic (US) treatment on the properties of alcohol solutions of perfluorinated sulfonic acid polymer Nafion® and cast membranes. The effect of the duration of US treatment on the physico-chemical properties (water uptake, transport and mechanical properties) of the resulted membranes is described for the first time. Upon the US treatment, viscosity of the polymer solutions irreversibly decreases due to deagglomeration and rupture of macromolecular chains. As a result of the US treatment, mechanical properties of the Nafion® membranes are deteriorated. The dependences of water uptake and conductivity of the Nafion® membranes in the proton form on sonication time pass the maximum (at 30–45 min). Due to the sonication of polymer solutions, proton conductivity of the membranes increases by 40–45%. Upon extended sonication, the content of sulfonic acid groups decreases, and carboxyl groups are formed at the ends of macromolecules. Thus, water uptake of the membranes prepared from the polymer solutions after the US treatment for 60 min decreases, and conductivity of the obtained membranes in the H+-form is reduced. However, for the Nafion® membranes in the Na+-form, as the duration of the US treatment is extended, their conductivity and diffusion permeability tend to increase due to the enhanced connectivity of pores and channels as well as due to the participation of carboxyl groups in the ionic transport. Upon extended sonication, selectivity of the cation transfer through the membranes is reduced. The results of this work highlight the importance of the proper selection of favorable conditions of the US treatment of the solutions of perfluorinated sulfonic acid polymers for the preparation of hybrid membranes and for the development of catalytic layers of membrane-electrode assemblies for fuel cells.

Efficient removal of dyes from aqueous solution: the potential of cellulose nanocrystals to enhance PES nanocomposite membranes

A novel nanocomposite membrane produced with polyether sulfone (PES) and cellulose nanocrystal (CNC) was developed for efficient removal of dye. The nanocomposite membranes were prepared using PES and different contents of CNCs (0.1, 0.3, 0.5, 0.8 and 1.0 wt%). The morphologies, surface properties, permeability, rejection and fouling analysis were carefully examined. The dye solution flux of PES/CNC membrane significantly increased with an increase of CNC content of the membrane casting solution, maximized to 4.13 times higher compared with dye solution flux of pristine PES membrane. Dye rejections were achieved as 95.8 and 93.6% respectively for an addition of 0.5 and 1% of CNCs into membrane casting solution. Moreover, the antifouling properties of PES membranes improved with adding CNCs due to the hydrophilic character of CNCs. Consequently, the obtained results showed that synthesized PES/CNC membranes can be effectively used for the removal of dyes due to their performance. However, the production cost of CNC is main challenge to be addressed for full-scale application.

Phosphoric Acid-Doped Ion-Pair Coordinated PEMs with Broad Relative Humidity Tolerance

Proton exchange membrane (PEM) capable of working over a broad operating condition window is critical for successful adoption of PEM-based electrochemical devices. In this work, phosphoric acid (PA)-doped biphenyl-backbone ion-pair coordinated PEMs were prepared by quaternization of BPBr-100, a precursor polymer, with three different tertiary amines including trimethylamine, 1-methylpiperidine, and 1,2-dimethylimidazole followed by membrane casting, ion exchange reaction to hydroxide ion, and doping with PA. The resulting PA-doped ion-pair PEMs were characterized in terms of PA doping level, proton conductivity, relative humidity (RH) tolerance, thermal stability, and mechanical properties. PA doping levels were between six and eight according to acid-base titration. The size and structure of the cation group of ion-pair polymers were found to affect the PA doping level and water uptake. Proton conductivity was studied as a function of RH over a wide range of 5% to 95% RH. Stable conductivity at 80 °C was observed up to 70% RH for 10 h. Mechanical property characterization indicates that the PA doping process resulted in more ductile membranes with significantly increased elongation at break due to the plasticization effect of PA. A combination of high proton conductivity at low RH conditions, and good humidity tolerance makes this new class of PEMs great potential candidates for use in electrochemical devices such as proton exchange membrane fuel cells and electrochemical hydrogen compressors.

Optimization of patterned polysulfone membranes for microalgae harvesting

Membranes with a wave pattern on the membrane surface are now proposed for the first time to alleviate microalgal fouling and increase the membrane flux. The membrane morphology was observed via scanning electron microscope, and the clean water permeance, microalgae harvesting efficiency and membrane flux in a real broth were determined to investigate the effects of polysulfone (PSF) and polyethylene glycol (PEG) concentrations in the membrane casting solution. Furthermore, the influence of the height of the patterned waves and the inter-pattern distance on the fouling prevention were investigated. Higher PSF and PEG concentrations resulted in better pronounced patterns. Patterned membrane showed higher fluxes and critical pressures than the corresponding flat membranes. Larger patterns gave higher membrane fluxes and less fouling. Computational fluid dynamics simulation showed a higher velocity and shear on the pattern apexes.

Synthesis of Calcium Fluoride Ultrafine Particles for the Preparation of Integral Asymmetric Cellulose Acetate/Calcium Fluoride Membranes

The present work reports on the synthesis of cellulose acetate (CA) asymmetric membranes with the incorporation of inorganic fluorides, CaF2 particles. These fillers of polymeric composites can, according to the literature, promote the ordering of the polymer matrix, which can lead to interesting permeation properties. In order to achieve that, fluorite (CaF2 ) fine particles were prepared by a double jet injection method using CaCl2 and NaF solutions as precursors and polyvinylpyrrolidone as a stabilizing agent. The fluorite particles were incorporated in the casting solutions of cellulose acetate/acetone/formamide. Dynamic light scattering measurements showed that formamide acting as the poor solvent in the membrane casting solutions can lead to some agglomeration of the fluorite particles and evident changes in structure and permeation properties. The CA/CaF2 composite membranes were casted by the phase inversion method at different solvent evaporation times. The permeation experiments indicated that the active layer of the membranes prepared with shorter solvent evaporation times is composed of an organic-inorganic network with bigger pores, which allows the permeation of molecules approximately two times the size of those retained by the CA membranes. Further increase in the solvent evaporation time has the opposite effect, as particle agglomerates may be formed.

Benchtop-fabricated lipid-based electrochemical sensing platform for the detection of membrane disrupting agents

There are increasing concerns about the danger that water-borne pathogens and pollutants pose to the public. Of particular importance are those that disrupt the plasma membrane, since loss of membrane integrity can lead to cell death. Currently, quantitative assays to detect membrane-disrupting (lytic) agents are done offsite, leading to long turnaround times and high costs, while existing colorimetric point-of-need solutions often sacrifice sensitivity. Thus, portable and highly sensitive solutions are needed to detect lytic agents for health and environmental monitoring. Here, a lipid-based electrochemical sensing platform is introduced to rapidly detect membrane-disrupting agents. The platform combines benchtop fabricated microstructured electrodes (MSEs) with lipid membranes. The sensing mechanism of the lipid-based platform relies on stacked lipid membranes serving as passivating layers that when disrupted generate electrochemical signals proportional to the membrane damage. The MSE topography, membrane casting and annealing conditions were optimized to yield the most reproducible and sensitive devices. We used the sensors to detect membrane-disrupting agents sodium dodecyl sulfate and Polymyxin-B within minutes and with limits of detection in the ppm regime. This study introduces a platform with potential for the integration of complex membranes on MSEs towards the goal of developing Membrane-on-Chip sensing devices.

Photocatalytic and antimicrobial multifunctional nanocomposite membranes for emerging pollutants water treatment applications

Emerging pollutants represent a new global problem for water quality. As these compounds get into the environment, they cause severe threats to aquatic environments and human health and are typically resistant to conventional wastewater treatments. In this work, TiO2 nanoparticles surface was functionalized with silver (Ag) nanoparticles, and solvent cast and electrospun membranes of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) were prepared with different concentrations of TiO2 and Ag–TiO2 to produce a multifunctional material. The photocatalytic activity of the nanocomposites was evaluated through the degradation of norfloxacin under ultraviolet (UV) and visible radiation. It is shown that nanocomposites with Ag–TiO2 show the highest degradation efficiencies: 64.2% under UV and 80.7% under visible radiation, for 90 and 300 min, respectively.Furthermore, the recyclability of the membranes has also been demonstrated. Finally, it is shown the antimicrobial activity of the nanocomposite membranes, demonstrating the suitability of the Ag–TiO2/PVDF-HFP nanocomposites as multifunctional photocatalytic and antimicrobial membranes for water remediation applications.

Low‐fouling polysulfone ultrafiltration membranes with amphiphilic sulfobetaine polyamide as additive

AbstractIn this study, amphiphilic sulfobetaine polyamide (sPA) oligomers with sulfobetaine as end groups and arylamide as backbone were synthesized as the pore‐forming additive for the preparation of polysulfone membranes. This additive showed good solubility and compatibility with the membrane casting solution due to the self‐assembly behaviors of sPA in organic solvent. Moreover, the effects of hydrophobic chain length and additive dosage on membrane morphology, hydrophilicity, permeability, antifouling, and mechanical properties were systematically studied. In view of these results, it can be concluded that the higher content and smaller size of sPA in the casting solution correlated with better filtration and separation performances of the membranes. Results showed that the pure water flux increased from 68.2 L m−2 hr−1 for the pristine membrane to a maximum of 205 L m−2 hr−1 for the blend membrane, meanwhile, the protein rejection ratio was above 95.2% and the flux recovery ratio was promoted from 68.3% to above 85.0%. The fouling resistance of the blend membranes was further demonstrated by significantly reduced protein/bacteria adhesion. And consistent high‐performances in filtration and separation were demonstrated after the blend membranes were treated at 90°C.

Highly permselective tadpole-type ionic anion exchange membranes for electrodialysis desalination

A series of tadpole-type ionic ionomers PPO-DMODAs with long alkyl side chains designed for electrodialysis (ED) desalination were synthesized successfully from dimethyloctadecylamine (DMODA) and brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO). The series of AEMs display stably low water uptakes ranging from 6.2% to 15.1% and high dimensional stabilities with swelling rations of 1.9%–4.8% at temperatures of 25 °C–60 °C. The nano-phase separated tadpole-type ionic structures ensure that the PPO-DMODAs membranes show excellent permselectivities with values above 94.6% and outstanding ED performances in the mostly reported desalination system of NaCl aqueous solutions. Especially, PPO-DMODA-3 surpasses commercial membrane TWEDA1 in ED competitions and ED-stability matches with current efficiency (η) of 88.7%, salt flux (J) of 80.61 mg m−2 s−1, energy consumption (EC) of per kg of NaCl of 2.56 kWh kg−1 and η retentions of the repeated runs higher than 97% of that of the origin run. Moreover, PPO-DMODA-3 membrane obtained from the ethanol solution exhibits stable aggregate structure and ED performances comparable to those of the PPO-DMODA-3 membranes cast with NMP and TCE solutions. Good solubility of PPO-DMODAs in ethanol offers an environmentally friendly green method to fabricate ED AEMs. In consideration of the advantages of low cost, simple synthesis process and green membrane casting technology, PPO-DMODA-3 membrane has a strong potential for ED-desalination application.