The effect of preparation parameters on performance of polyvinyl alcohol thin‐film composite membrane: Experimental study,modeling, and optimization

To systematically investigate the influence of preparation conditions on pure water permeability (PWP) and solute removal performance of polyvinyl alcohol (PVA) thin‐film composite (TFC) membrane, fractional factorial design was applied. The considered conditions were related to 3 steps of the TFC preparation, including support membrane preparation, PVA coating, and cross‐linking. The results showed that among the selected factors, polysulfone concentration (polymer of the support membrane), heat curing time (related to cross‐linking condition), and their interaction have the most significant effects on the both permeability and salt rejection. The effects of significant factors interaction on permeability and solute rejection of PVA TFC membrane were discussed. Finally, optimum preparation conditions were calculated by numerical optimization to achieve maximum permeability and solute removal, simultaneously. The prepared membrane at optimum conditions showed PWP of 1.74 L/m²hbar and 96.19% Na₂SO₄ rejection. It was realized that the prediction of mathematical models at optimum conditions was reliable with absolute average relative error 7.43% and 1.18% for PWP and rejection, respectively.     

Interlaboratory studies of highly permeable thin‐film composite polyamide nanofiltration membrane

The aim of this paper is to survey interlaboratory studies of performance data to produce highly permeable thin‐film composite (TFC) polyamide nanofiltration (NF) membrane in the form of flat sheet at bench scale. TFC polyamide NF membranes were fabricated via interfacial polymerization of 1,3‐phenylenediamine and trimesoyl chloride on porous polyethersulfone (PES) membrane. The NF membranes were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and cross‐flow filtration. The AFM and SEM analyses indicated that a rough and dense film was formed on the PES support membrane. The permeability and NaCl rejection of the NF membrane prepared at the presence of camphor sulfonic acid as pH regulator and triethylamine as accelerator in the aqueous solution were 21 l m^?2 h^?1 and 70%, respectively. In order to estimate the repeatability and reproducibility standard deviations, the development of an interlaboratory study was conducted by measurements of permeation flux and salt rejection of the synthesized membranes. Repeatability standard deviation of the permeation flux data for the membrane based on optimum formulation was 1.99, and reproducibility standard deviation was 3.55. Also based on this trend, repeatability standard deviation of the salt rejection data was 1.57, and reproducibility standard deviation was 4.11. The American Society for Testing and Materials standard E691‐05 was used for data validation of the repeatability and reproducibility standard deviations and consistency statistics. Copyright © 2011 John Wiley & Sons, Ltd.     

Impact of TiO2 nanoparticles on morphology and performance of crosslinked polyimide organic solvent nanofiltration (OSN) membranes

Chemically crosslinked polyimide organic–inorganic composite nanofiltration membranes suitable for application in harsh organic solvents were successfully prepared by phase inversion of dope solutions. TiO₂ nanoparticles were dispersed in these dope solutions, comprising polyimide (PI) in N,N-dimethylformamide/1,4-dioxane. The impact of TiO₂ on the resulting PI membranes was investigated using SEM, TGA, water contact angle, dope viscosity measurements and mechanical strength. The presence of TiO₂ nanoparticles within the membrane matrix was proved by the detection of a peak characteristic of TiO₂ in the WAXS pattern. SEM pictures of the cross-section of the PI/TiO₂ membranes showed dramatically changed morphology compared to reference membranes with no TiO₂ addition. Macrovoids present in reference membranes were suppressed by increasing loading of TiO₂ nanoparticles, and eventually disappeared completely at a TiO₂ loading above 3 wt.%. Decreasing water contact angle and an increase in ethanol flux indicated that hydrophilicity increased as nanoparticle loading increased. The effect of TiO₂ on the functional performance of the membranes was evaluated by measuring flux and rejection using cross-flow filtration. Perhaps surprisingly, the presence of TiO₂ improved the compaction resistance of the membranes, whereas rejection and steady flux were almost unaltered.     

Preparation and characterization of TiO2/Pebax/(PSf‐PES) thin film nanocomposite membrane for humic acid removal from water

New thin film composite (TFC) membrane was prepared via coating of Pebax on PSf‐PES blend membrane as support, and its application in wastewater treatment was investigated. To modify this membrane, hydrophilic TiO₂ nanoparticles were coated on its surface at different loadings via dip coating technique. The as‐prepared membrane was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), field emission SEM, and contact angle analysis. The Fourier transform infrared spectroscopy analysis and surface SEM images indicated that TiO₂ was successfully coated on the membrane surface. In addition, the results stated that the hydrophilicity and roughness of membrane surface increased by addition of TiO₂ nanoparticles. Performance of TFC and modified TFC membranes was evaluated through humic acid removal from aqueous solution. Maximum permeate flux and humic acid rejection were obtained at 0.03 and 0.01 wt% TiO₂ loadings, respectively. Rejection was enhanced from 96.38% to 98.92% by the increase of feed concentration from 10 to 30 ppm. Additionally, membrane antifouling parameters at different pressures and feed concentration were determined. The results indicated that surface modification of membranes could be an effective method for improvement of membrane antifouling property.     

Fabrication,characterization, and performance evaluation of polyethersulfone/TiO2 nanocomposite ultrafiltration membranes for produced water treatment

In the present work, development of neat and nanocomposite polyethersulfone membranes composed of TiO₂ nanoparticles is presented. Membranes are fabricated using nonsolvent phase inversion process with the objective of improving antifouling, hydrophilicity, and mechanical properties for real and synthetic produced water treatment. Membranes are characterized using scanning electron microscopy, Fourier‐transform infrared, contact angle, porosity measurement, compaction factor, nanoparticles stability, and mechanical strength. The performance of prepared membranes was also characterized using flux measurement and oil rejection. Fourier‐transform infrared spectra indicated that noncovalence bond formed between Ti and polyethersulfone chains. The contact angle results confirmed the improved hydrophilicity of nanocomposite membranes upon addition of TiO₂ nanoparticles owing to the strong interactions between fillers and water molecules. The increased water flux for nanocomposite membranes in comparison with neat ones can be due to coupling effects of improved surface hydrophilicity, higher porosity, and formation of macrovoids in the membrane structure. The membrane containing 7 wt% of TiO₂ nanoparticles was the best nanocomposite membrane because of its high oil rejection, water flux, antifouling properties, and mechanical stability. The pure water flux for this membrane was twice greater than that of neat membrane without any loss in oil rejection. The hydrophilicity and antifouling resistance against oil nominates developed nanocomposite membranes for real and synthetic produced water treatment applications with high performance and extended life span.     

Preparation and characterization of novel PES‐(SiO2‐g‐PMAA) membranes with antifouling and hydrophilic properties for separation of oil‐in‐water emulsions

In the present study, modification of nanoparticles (NPs) was investigated to mitigate aggregation of SiO₂ nanoparticles and improve the polymeric membrane's performance. For this purpose, the surface of SiO₂ nanoparticles was activated with amine groups, and polymethacrylic acid (PMAA) was grafted on the surface of NPs by atom transfer radical polymerization. Modified NPs were characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) tests. Polyethersulfone (PES) membranes were fabricated with both SiO₂ and SiO₂‐g‐PMAA NPs via nonsolvent‐induced phase separation method. The fabricated membranes were characterized regarding their permeability, hydrophilicity, and porosity properties, and their separation efficiency was tested using the synthetic oil‐in‐water emulsion. The surface and cross‐sectional morphologies of membranes were observed by field emission scanning electron microscopy (FESEM). The experimental trials showed that modified NPs dispersed more uniformly in the structure of membranes and hydroxyl groups on the surface of NPs acted more effectively. Modification of NPs enhance the membrane performance in terms of permeate flux, hydrophilicity, and porosity. NPs modification improved the permeate flux about 46%. Oil rejection for all tested membranes was more than 98%, and modification of NPs did not reduce the rejection of membranes. The optimum concentration was obtained as 1 wt.% and 1.5 wt.% for SiO₂ and SiO₂‐g‐PMAA, respectively. Aggregation effect dominated at concentrations beyond the optimum values that decreased the permeate flux, consequently.     

Silver nanoparticles immobilized on thin film composite polyamide membrane: characterization,nanofiltration, antifouling properties

Microbial biofouling is one of the major obstacles for reaching the ultimate goal of realizing a high permeability over a prolonged period of nanofiltration operation. In this study, the hybrid nanocomposite membranes consisting of silver (Ag) nanoparticles with antibiofouling capability on microorganism and polyamide (PA) were prepared by in situ interfacial polymerization and characterized by X‐ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The hybrid membranes were shown to possess the dramatic antibiofouling effect on Pseudomonas. In addition, Ag nanocomposite membranes had little influence on the performances of the membrane such as on water flux and salt rejection. SEM analysis results showed that all Pseudomonas were dead on the PA/Ag nanocomposite membrane, indicating the effectiveness of silver nanoparticles. This investigation offers a strong potential for possible use as a new type of antibiofouling membrane. Copyright © 2007 John Wiley & Sons, Ltd.     

Performance enhancement of thin‐film composite membranes in water desalination process by wood sawdust

In this study, polysulfone/wood sawdust (PSf/WSD) mixed matrix membrane (MMM) was prepared as a novel substrate layer of thin‐film composite (TFC) membrane in water desalination. The main aim was to evaluate how different amounts of WSD (0‐5 wt%) and PSf concentrations (12‐16 wt%) in the porous substrate affect the properties of the final TFC membranes in the separation of organic and inorganic compounds. Morphological and wettability studies demonstrated that the addition of small amount of WSD (less than or equal to 1 wt%) in the casting solution resulted in more porous but similar hydrophobic substrates, while high loading (greater than or equal to 2 wt%) of WSD not only changed the substrate wettability and morphology but also increased and decreased the swelling and mechanical properties of substrate layer. Therefore, PA layer formed thereon displayed extensively varying film morphology, interfacial properties, and separation performance. Based on approximately stable permeate flux (ASPF) and apparent salt rejection efficiency (ASRE), the best TFC membrane was prepared over the substrate with 12 to 14 wt% of PSf and around 0.5 to 1 wt% of WSD. Although notable improvements in permeate flux were obtained by adding a small amount of sawdust, the results clearly indicate that the salt rejection mechanism of TFC membrane was different from the glycerin rejection mechanism. Furthermore, durability results of TFC membranes showed that in continuous operation for 30 days, TFC‐14/0.5 and TFC‐14/01 have the maximum plateau levels of stable permeate flux and salt rejection among the all TFC membranes.     

PEG-coated reverse osmosis membranes: Desalination properties and fouling resistance

This study focuses on the use of surface-coated reverse osmosis (RO) membranes to reduce membrane fouling in produced water purification. A series of crosslinked PEG-based hydrogels were synthesized using poly(ethylene glycol) diacrylate as the crosslinker and poly(ethylene glycol) acrylate, 2-hydroxyethyl acrylate, or acrylic acid as comonomers. The hydrogels were highly water permeable, with water permeabilities ranging from 10.0 to 17.8 (L μm)/(m² h bar). The hydrogels were applied to a commercial RO membrane (AG brackish water RO membrane from GE Water and Process Technologies). The water flux of coated membranes and a series-resistance model were used to estimate coating thickness; the coatings were approximately 2 μm thick. NaCl rejection for both uncoated and coated membranes was 99.0% or greater, and coating the membranes appeared to increase salt rejection, in contrast to predictions from the series-resistance model. Zeta potential measurements showed a small reduction in the negative charge of coated membranes relative to uncoated RO membranes. Model oil/water emulsions were used to probe membrane fouling. Emulsions were prepared with either a cationic or an anionic surfactant. Surfactant charge played a significant role in membrane fouling even in the absence of oil. A cationic surfactant, dodecyltrimethyl ammonium bromide (DTAB), caused a strong decline in water flux while an anionic surfactant, sodium dodecyl sulfate (SDS), resulted in little or no flux decline. In the presence of DTAB, the AG RO membrane water flux immediately dropped to 30% of its initial value, but in the presence of SDS, its water flux gradually decreased to 74% of its initial value after 24 h. DTAB-fouled membranes had lower salt rejection than membranes not exposed to DTAB. In contrast, SDS-fouled membranes had higher salt rejection than membranes not exposed to SDS, with rejection values increasing, in some cases, from 99.0 to 99.8% or higher. In both surfactant tests, coated membranes exhibited less flux decline than uncoated AG RO membranes. Additionally, coated membranes experienced little fouling in the presence of an oil/water emulsion prepared from DTAB and n-decane. For example, after 24 h the water flux of the AG RO membrane fell to 26% of its initial value, while the water flux of a PEGDA-coated AG RO membrane was 73% of its initial value.     

High‐performance thin film composite membranes with well‐defined poly(dimethylsiloxane)‐b‐poly(ethylene glycol) copolymer additives for CO2 separation

A series of well‐defined diblock copolymers (BCPs) consisting of poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) were synthesized and blended with commercially available PEBAX® 2533 to form the active layer of thin‐film composite (TFC) membranes, via spin‐coating. BCPs with a PEG component ranging from 1 to 10 kDa and a PDMS component ranging from 1 to 10 kDa were synthesized by a facile condensation reaction of hydroxyl terminated PEG and carboxylic acid functionalized PDMS. The BCP/PEBAX® 2533 blends up to 50 wt % on cross‐linked PDMS gutter layers were tested at 35 °C and 350 kPa. TFC membranes containing BCPs of 1 kDa PEG and 1–5 kDa PDMS produced optimal results with CO₂ permeances of approximately 1000 GPU which is an increase up to 250% of the permeance of pure PEBAX® 2533 composite membranes, while maintaining a CO₂/N₂ selectivity of 21. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1500–1511     

Nanofiltration membrane cross‐linked by m‐phenylenediamine for dye removal from textile wastewater

In this work, m‐phenylenediamine (MPD) is used to prepare cross‐linked polyetherimide (PEI)‐based nanofiltration (NF) membrane for treatment of dye containing wastewater. The effects of dope solution composition, cross‐linking time, and dye concentration on membrane performance are investigated. Results indicate that the rejection of dye is increased with the increase of acetone concentration in the dope solution, cross‐linking time, and dye concentration. Meanwhile, membrane flux showed the opposite trend. With the aid of SEM and FTIR analysis, the cross‐linking between MPD and PEI is confirmed. The cross‐linked membrane has thicker and dense selective layer compared to the unmodified membrane. The cross‐linked NF membrane (PEI: 15 wt%; acetone: 20 wt%; cross‐linking time: 10 minutes) showed good performance in filtration of synthetic dye wastewater (Reactive Red 120, 1500 ppm) with 98% dye rejection and 0.013 L m^?2 hour^?1 of flux at relatively low operating pressure (60 psi).     

Thin‐film composite membranes incorporated with large‐area graphene oxide sheets and adjustable surface charges

In this research, composite membranes were prepared by cross‐linking of poly(vinyl alcohol) (PVA) and glutaraldehyde (GA) on amidoximated ultrafiltration membrane. During this procedure, it was taken advantage of large‐area graphene oxide sheets as graphitic nets in the active layer. These membranes were used to remove an industrial textile dye (Chrysophenine GX) from wastewater. Optimum condition for membrane preparation was 1.5% wt. of PVA, 1.5% wt. of GA, and 0.3% wt. of graphene oxide sheets. Permeation results showed that electrostatic charges on membrane surface have easily converted from positive into negative ones. Contact angle was significantly decreased (63.5° to 28.8°). Final nanofiltration membrane showed lowest fouling rate during removing the industrial direct dye (flux recovery ratio: 96.60%, reversible fouling ratio: 23.82%, and irreversible fouling ratio: 3.39%). Pore size of this membrane was <8 nm, and Chrysophenine GX was eliminated by 98.5% with water permeability of 12.23 L/m².h.bar.     

Preparation and properties of polysulfone/TiO2 composite ultrafiltration membranes

The influence of inorganic filler TiO₂ nanoparticles on the morphology and properties of polysulfone (PS) ultrafiltration membranes was investigated. PS/TiO₂ composite membranes were prepared by a phase‐inversion method. TiO₂ nanoparticles modified by sodium dodecyl sulfate were uniformly dispersed in an 18 wt % PS casting solution. The addition of TiO₂ resulted in an increase in the pore density and porosity of the membrane skin layer. The pore size distribution changed from the log‐normal distribution to the bimodal distribution because of the presence of TiO₂ nanoparticles, and some large pores were observed when the concentration of the filler was over 3 wt %. The skin layer was gradually thickened; meanwhile, the morphology sublayer changed from macrovoids to spongelike pores, in comparison with PS membranes without the filler. The addition of TiO₂ also induced increases in the hydrophilicity, mechanical strength, and thermal stability. The ultrafiltration experiments showed when the concentration of TiO₂ was less than 2 wt %, the permeability and rejection of the membrane was enhanced and then decreased drastically with a higher filler concentration (>3%). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 879–887, 2006     

Chitosan‐modified graphene oxide as a modifier for improving the structure and performance of forward osmosis membranes

Chitosan (CS) with good hydrophilicity and charged property was used to modify graphene oxide (GO), the obtained GO‐CS was used as a novel modifier to fabricate thin film composite forward osmosis (FO) membranes. The results revealed that the amino groups on CS reacted with carboxyl groups on GO, and the lamellar structure of the GO nanosheets was peeled off by CS, resulting in the reducing of their thicknesses. The GO‐CS improved the hydrophilicity of polyethersulfone (PES) substrate, and their contact angles decreased to 64° with the addition of GO‐CS in the substrate. GO‐CS also increased the porosity of the substrate and surface roughness of FO membrane, thereby optimizing the water flux and reverse salt flux of FO membrane. The average water flux of the FO membrane reached the optimal flux of 21.34 L/(m² h) when GO‐CS addition was 0.5 wt%, and further addition of GO‐CS to the substrate would decrease the water flux of FO membrane, and the reverse salt flux also decreased to the lowest value of 2.26 g/(m² h). However, the salt rejection of the membrane increased from 91.4% to 95.1% when GO‐CS addition increased from 0.5 to 1.0 wt% under FO mode using 1 mol/L sodium chloride (NaCl) solution as draw solution (DS). In addition, high osmotic pressure favored water permeation, and at the same concentration of DS, magnesium chloride (MgCl₂) exhibited better properties than NaCl. These results all suggested that GO‐CS was a good modifier to fabricate FO membrane, and MgCl₂ was a good DS candidate.     

Nanoporous membranes by cooperative self‐assembly of functionalized SEBS and titania

Sol–gel chemistry was adeptly exploited to fabricate nanoporous membranes by cooperative self‐assembly of modified triblock copolymer (SEBS‐NH₂) and titania network. Reinforcement of the matrix was achieved by hydrolytic condensation of tetraisopropoxytitanate without/with compatiblizing agent (3‐glycidyloxypropyl triethoxysilane), yielding two hybrid systems. Incorporation of different proportions of TiO₂ provoked well‐built variations in morphology of compatiblized SEBS‐NH₂/TiO₂ nanocomposites. At low titania loading, spherical nanoparticles were found well‐dispersed in regimented triblock domains while addition of higher amounts of TiO₂ generated nanoporous membranes by mutual self‐assembling of matrix and the reinforcement. Relative improvement of tensile and thermal properties over uncompatiblized nanocomposites was observed owing to enhanced interfacial interactions. Eventually, a combination of the two phases (17.5 wt. % titania in SEBS‐NH₂) demonstrated ample mechanical reinforcement, thermal and morphological profiles, ensuing robust self‐assembled nanostructures. Forthcoming prospects are envisioned as well. Copyright © 2013 John Wiley & Sons, Ltd.     

Polysulfone/Brij‐58 blend nanofiltration membranes: preparation,morphology and performance

In present research, novel asymmetric polysulfone (PSF) membranes with high hydrophilicity and noticeable rejection of arsenic, as one of the major environmental problems, were prepared from PSF/Brij‐58/NMP (1‐methyl‐2‐pyrrolidone) system via immersion precipitation. Pure water was used as gelation media. The variation effect of coagulation bath temperature (CBT) and addition of Brij‐58 on morphology, wettabiliy, pure water permeation flux and rejection of As (III) and As (V), as two dominant states of arsenic in the nature, were studied by scanning electron microscopy, contact angle measuring instrument and experimental setup. The results demonstrated that both hydrophilicity and rejection properties of the prepared membranes were significantly enhanced by small addition of Brij‐58 surfactant in the casting solution along with using the lowest level of CBT. Addition of 4 wt. % of Brij‐58 and using cold coagulation bath resulted in the highest rejection of As (V). Initial increase in Brij‐58 concentration, from 0 wt. % to 2 wt. %, resulted in higher rejection of As (III). However, higher Brij‐58 concentrations than 2 wt. % (increase from 2 wt. % to 6 wt. %) led to lower rejection of As (III). Also, it was found out that addition of Brij‐58 in the casting solution along with increasing the CBT resulted in formation of membranes with high permeability and sub‐layer porosity and thin top layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Antibacterial photocatalytic self‐cleaning poly(vinylidene fluoride) membrane for dye wastewater treatment

Membrane technology has been successfully applied for the removal of dyes from wastewater in the textile industry. A novel poly(vinylidene fluoride) (PVDF) membrane was prepared via blending with different dosages of Ag‐TiO₂‐APTES composite for dyeing waste water treatment in our study. And the effect of Ag‐TiO₂‐APTES blended into the PVDF membrane was discussed, including the rejection rate of methylene blue (MB) dye, membrane morphology, surface hydrophilicity, antibacterial activity, and a certain photocatalytic self‐cleaning performance. X‐ray diffraction and Fourier transform infrared characterization confirmed that Ag‐TiO₂ was functionalized by amount of hydroxyl group (−OH) and amino group (NH−), which provided by APTES. Contact angle measurement certified that the hydrophilicity of the membrane surface increased, with the contact angle decrease to 61.4° compared with 81.8° of original PVDF membrane. MB rejection rate was also increased to 90.1% after addition of Ag‐TiO₂‐APTES, and the rejection of original membrane was only 74.3%. The morphologies of membranes were observed by scanning electron microscope, which indicated that Ag‐TiO₂‐APTES had a good dispersion in membrane matrix and also improved the microstructure of membranes. Besides, UV irradiation experiments were performed on the composite films contaminated by MB, and the result showed that Ag‐TiO₂‐APTES nanoparticle provided PVDF membrane with a certain photodegradation capacity under UV irradiation. Moreover, antibacterial activity of the composite membrane was also demonstrated through antibacterial experiment, Escherichia coli as the representative bacteria. Perhaps, this research may provide a new way for PVDF blending modification.     

Effect of TiO2 nanoparticles on structure and properties of high density polyethylene membranes prepared by thermally induced phase separation method

Polyethylene/TiO₂ membranes were fabricated via thermally induced phase separation (TIPS) method. A set of characterization tests including FE‐SEM, EDX, XRD, DSC, TGA, DMA, mechanical test and relative pure water flux for characterization of membranes were carried out to investigate the effect of TiO₂ nanoparticles on membrane properties. The results of EDX, XRD and TGA analyses confirmed the presence of TiO₂ nanoparticles in the polymer matrix. The results of DSC analysis revealed that the melting point as well as the crystallinity of the membranes increased slightly with increasing TiO₂ content. However, the glass transition temperature of the membranes was not affected by the presence of particles. Addition of nanoparticles also increased storage modulus, loss modulus and tensile strength at break of the membranes due to the stiffness improvement effect of inorganic TiO₂. Finally, it was observed that incorporation of the nanoparticles improved pure water flux of the membranes. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of aqueous and organic solutions on the performance of polyamide thin‐film‐composite nanofiltration membranes

Polyamide/polyacrylonitrile thin‐film‐composite (TFC) nanofiltration (NF) membranes for the separation of oleic acid dissolved in organic solvents (methanol and acetone) were interfacially prepared by the reaction of trimesoyl chloride in an organic phase with an aqueous phase containing piperazine and m‐phenylene diamine. The interfacial reaction was confirmed by an investigation of the attenuated total reflection infrared spectrum. The surface morphology of the polyamide TFC membranes was examined with scanning electron microscopy. The hydrophilic properties of the membrane surfaces were conjectured on the basis of the ζ potential and contact angle. The effects of the monomer concentrations of the monomer blends (aliphatic and aromatic diamines) and drying times on various aspects of membrane performance, such as the solvents (water, alcohols, ketones, and hexane), permeation rates, and organic solute [poly(ethylene glycol) 200 and oleic acid] rejection rates, were investigated. All the membranes showed good solvent resistance. The polar solvent flux for water and methanol was higher than that for a nonpolar solvent (hexane). The membranes gave good rejection rates of oleic acid dissolved in methanol and acetone. The NF membranes were compared with various commercial membranes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2151–2163, 2002     

Amine‐Appended Hierarchical Ca‐A Zeolite for Enhancing CO2/CH4 Selectivity of Mixed‐Matrix Membranes

An amine‐appended hierarchical Ca‐A zeolite that can selectively capture CO₂ was synthesized and incorporated into inexpensive membrane polymers, in particular polyethylene oxide and Matrimid, to design mixed‐matrix membranes with high CO₂/CH₄ selectivities. Binary mixture permeation testing reveals that amine‐appended mesoporous Ca‐A is highly effective in improving CO₂/CH₄ selectivity of polymeric membranes. In particular, the CO₂/CH₄ selectivity of the polyethylene oxide membrane increases from 15 to 23 by incorporating 20 wt % amine‐appended Ca‐A zeolite. Furthermore, the formation of filler/polymer interfacial defects, which is typically found in glassy polymer‐zeolite pairs, is inhibited owing to the interaction between the amine groups on the external surface of zeolites and polymer chains. Our results suggest that the amine‐appended hierarchial Ca‐A, which was utilized in membrane fabrication for the first time, is a good filler material for fabricating a CO₂‐selective mixed‐matrix membrane with defect‐free morphology.