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Interfacial polymerization (IP) is considered as an emerging technique for fabricating pervaporation (PV) membranes. Typically, PV membranes fabricated through IP achieve high separation efficiency and overall performance as they possess characteristics that play vital roles in defying the limiting trade-off between permeation flux and separation factor. There is a great deal of flexibility in the IP technique. Therefore, this article reviews evolving trends in developing PV membranes fabricated through IP in terms of methods of fabrication and modification strategies, active layer and membrane support selections, and potential industrial applications. Moreover, we also emphasized the free volume analysis of the membranes prepared through IP. Future plans for furthering IP as a fabrication technique for PV membranes are also explored.

• Promoting the separation efficiency of pervaporation membranes is a must to meet the growing demands of society. In this study, acetone-assisted interfacial polymerization was employed to produce thin-film composite (TFC) pervaporation membranes with improved performance. Two monomers were considered—diethylenetriamine (DETA) and trimesoyl chloride (TMC); they reacted with each other to form a thin polyamide layer, which was deposited on a hydrolyzed polyacrylonitrile (HPAN) substrate. Aqueous solutions containing different concentrations of acetone were used to dissolve DETA. Introducing acetone as a cosolvent of water enhanced the sorption of DETA in the HPAN support. It also altered and improved the physicochemical properties of the TFC membranes. An optimum concentration of 50 wt% aqueous acetone solution was established. Through acetone-assisted interfacial polymerization, a TFC membrane was then fabricated, and it exhibited a high separation efficiency: permeation flux = 1641 ± 134 g∙m−2 h−1 and water concentration in the permeate = 98%–99% (feed =70 wt% aqueous isopropanol solution). Moreover, the modified TFC membrane displayed a high separation performance at a wide range of operating conditions.

Separation technology by using membranes is an effective choice for water treatment, but fouling is a significant problem for membrane applications. Recently, transition-metal dichalcogenide nanosh...

In this study, we fabricated ultrafiltration mixed-matrix membranes through wet phase-inversion method of cellulose acetate (CA) blended with polydopamine (PDA) particles solution. PDA, as an organic and hydrophilic particle, altered the physicochemical and antifouling property of CA membranes. X-ray photoelectron spectroscopy confirmed the presence of PDA particles on the membrane surface. Adding PDA particles led to the formation of macrovoids onto the cross-sectional morphology of CA membranes. This also improved the membrane porosity, pore size, and hydrophilicity. At an optimum concentration of 0.2 wt% PDA, the membrane presented the highest pure water flux of 771.98 L m−2 h−1 at 1 bar and significant oil rejection (93–99%). Furthermore, the modified membrane exhibited better antifouling property (flux recovery = 87%; irreversible fouling = 12%; Reversible fouling = 80%) contrasted to a pristine CA membrane (flux recovery ratio = 70%; irreversible fouling = 25%; reversible fouling = 45%).

Choosing the property of the supporting membrane is crucial in preparing high performing nanofiltration membranes through interfacial polymerization. In this study, an oxygen rich membrane – cellulose triacetate (CTA) – was used to fabricate the support membrane. Polyamide was deposited onto the CTA support using interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC). The concentration of the monomers was optimized. Furthermore, the polyamide layer prepared on CTA support exhibited higher separation efficiency for sodium sulfates and dyes compared to using traditional polysulfone (PSf) support. The oxygen groups of CTA facilitate better adsorption of amines on the surface; thus, using low concentration of PIP could still provide a defect-free polyamide layer. Utilizing the optimum condition, the polyamide/CTA membrane delivered a high pure water flux (operating at 6 bar) of 179.5 L/m2h with the following rejections: Na2SO4 = 98.4%; MgSO4 = 60.3%; MgCl2 = 15.0%; NaCl = 3.7%; Rose Bengal = 95.5%; Brilliant Blue R = 99.9%; Amido Black 10B = 90.6%; Orange G = 67.3%. Moreover, the polyamide/CTA membrane had excellent stability at a wide range operating conditions.

Graphene quantum dots(GQDs) were used to possibly cover the structural defects on the graphitic regions of reduced graphene oxide(rGO). The resulting homostructure nanocomposite fillers(rGO + GQD) were incorporated in an alginate solution creating a dense composite membrane for pervaporation. The membranes were applied to separate alcohol/water mixtures in which the successful covering of structural defects was observed with good separation performance of lower molecular weight alcohols. The Raman spectra and elemental analyses confirmed the successful changes on the physical and chemical structures of the homostructured fillers. The X-ray diffraction pattern showed that the crystallinity of the membrane was greatly affected when incorporated with rGO + GQD. The alginate incorporated with 3 wt% of rGO + GQD(Alg-rGO + GQD) has the best pervaporation performance in separating methanol/water mixture with a permeation flux of 2323 g m−2 h−1 and water concentration in permeate of 92.7% at 70 °C. While the positron annihilation lifetime spectroscopy results supported that the minimization of the structural defects enhanced the water selectivity of the membrane by easy transport of water molecules through the free volume spaces and blocks methanol molecules. The results in this study may provide the possible sealing or curing the defects on rGO with GQDs and improve the interfacial interaction with the polymer matrix.

We modified thin-film nanofiltration membranes by embedding in them silica nanoparticles (SiNPs) coated with polydopamine (PDA), which is well-known to mimic the adhesive characteristics of mussels. The coating process was triggered by the oxidative self-polymerization of dopamine on the surface of SiNPs, and the membranes were fabricated through interfacial polymerization (reaction between piperazine and trimesoyl chloride, TMC). Thin-film nanofiltration membranes embedded with PDA-SiNPs (TFNPDA-SiNPs) were compared with pristine polyamide membrane, as well as with polyamide membrane embedded with uncoated SiNPs. Energy-dispersive X-ray spectroscopy confirmed that TFNPDA-SiNPs contained more nanoparticles than the polyamide membrane with uncoated SiNPs. Accordingly, the hydrophilicity of TFNPDA-SiNPs was higher. TFNPDA-SiNPs fabricated from using a concentration of 0.35 g PDA-SiNPs/g TMC delivered the highest pure water flux of 80.0 ± 4.6 L⋅m−2⋅h−1 at 6 bar; salt rejections were as follows: RNa2SO4 = 97%; RMgSO4 = 94%; RMgCl2 = 68%; RNaCl = 35%. The TFNPDA-SiNPs also demonstrated the greatest antifouling ability, as its flux was the highest at the end of three cycles of antifouling tests, where bovine serum albumin was used as model protein foulant.

A thin-film composite (TFC) polyurea membrane was fabricated for the dehydration of an aqueous tetrahydrofuran (THF) solution through interfacial polymerization, wherein polyethyleneimine (a water-soluble amine monomer) and m-xylene diisocyanate (an oil-soluble diisocyanate monomer) were reacted on the surface of a modified polyacrylonitrile (mPAN) substrate. Cosolvents were used to tailor the membrane properties and increase the membrane permeation flux. Four types of alcohols that differed in the number of carbon (methanol, ethanol, isopropanol, and tert-butanol) were added as cosolvents, serving as swelling agents, to the aqueous-phase monomer solution, and their effect on the membrane properties and pervaporation separation was discussed. Attenuated total reflection Fourier transform infrared spectroscopy confirmed the formation of a polyurea layer on mPAN. Field emission scanning electron microscopy and surface water contact angle analysis indicated no change in the membrane morphology and hydrophilicity, respectively, despite the addition of cosolvents for interfacial polymerization. The TFC membrane produced when ethanol was the cosolvent exhibited the highest separation performance (permeation flux = 1006 ± 103 g·m−2·h−1, water concentration in permeate = 98.8 ± 0.3 wt.%) for an aqueous feed solution containing 90 wt.% THF at 25 °C. During the membrane formation, ethanol caused the polyurea layer to loosen and to acquire a certain degree of cross-linking. The optimal fabrication conditions were as follows: 10 wt.% ethanol as cosolvent, membrane curing temperature = 50 °C, membrane curing time = 30 min.

Thin-film nanocomposite (TFN) membranes enjoy advantages over the traditional membranes for water purification purposes. TFN membranes are fabricated primarily through interfacial polymerization: d...

A series of thin-film composite (TFC) polyamide membranes was fabricated through interfacial polymerization on a modified polyacrylonitrile (mPAN) substrate, where an aqueous solution of diamine was reacted with an organic solution of diacyl chloride. Various monomers were used: two different diamines [1,3-diamino-2-propanol (DAPL) and hydrazine] and two different diacyl chlorides [succinyl chloride (SCC) and trans-5-norbornene-2,3-dicarbonyl chloride]. Combining these monomers resulted in a new polyamide layer. We investigated the effect of the monomer chemical structure and interfacial polymerization conditions on the membrane pervaporation performance in dehydrating an aqueous solution of ethanol. According to field emission scanning electron microscopy, DAPL-SCC provided the thinnest polyamide layer, which was also confirmed through positron annihilation lifetime spectroscopy. The results were used to correlate the variation in the membrane microstructure with the pervaporation performance of the fabricated TFC polyamide membranes. Both microstructural characteristics and surface properties affected the pervaporation performance. DAPL-SCC/mPAN membranes with lower free-volume sizes and suitable hydrophilicity were evaluated to deliver the highest water concentration in permeate and the lowest permeation flux (on the basis of the pervaporative dehydration of an aqueous solution of 90 wt% ethanol at 25 °C).

We propose in this study a facile and versatile strategy for fabricating thin-film nanocomposite (TFN) membranes, wherein polydopamine-piperazine (PDP) nanoparticles were formed in situ from the oxidative polymerization reaction of dopamine and its subsequent reaction with piperazine. Accordingly, PDP nanoparticles were then directly used as nanofillers for TFN membranes fabricated through interfacial polymerization. The characteristics of PDP nanoparticles and the performance of TFN membranes were easily tailored by varying the water-ethanol ratio in the PIP solution, solution pH, dopamine concentration, and reaction time. The TFN-PDP membranes exhibited an optimum separation performance (high water permeability and high salt selectivity): JH2O = 59.1 ± 3.3 L m−2 h−1; RNa2SO4 = 98.0%; RNaCl = 44.1% (6 bar, 25 °C). Moreover, the TFN-PDP membranes demonstrated high water flux recovery and enhanced antifouling property during cycles of filtration tests, with bovine serum albumin protein used as model foulant.

Zwitterion augmented forward osmosis (FO) membranes were fabricated having polyamide active layer on the polysulfone support to improve the overall performance and antifouling characteristics. FTIR and XPS were employed in evidencing the incorporation of zwitterion in terms of functional groups and relative compositions of hetero atoms. AFM, SEM, water contact angle and zeta potential measurement are used to characterize the zwitterion augmented surface in terms of surface morphology, surface charge and hydrophilicity/hydrophobicity. Augmentation of zwitterion was found to enhance the hydrophilicity and surface roughness resulting the enhancement in the water permeability. The anionic moiety of the zwitterion was exposed outside, while the cationic moieties of the zwitterion mostly retained towards the core as suggested by negative zeta potential and protein absorption. Incorporation of zwitterion was found to enhance the antifouling property of the membrane as evident from static and dynamic test. The relative composition of zwitterion on active membrane surface was optimized by investigating the tradeoff between water permeability and reverse salt flux.

Our present study used 3,3′-diaminobenzidine (DAB) to prepare nanofiltration polyamide membranes. A polyamide layer was formed on a polysulfone (PSf) support through interfacial polymerization; DAB was reacted with different polyacyl chlorides: isophthaloyl chloride, succinyl chloride, and trimesoyl chloride (TMC). Attenuated total reflectance-Fourier transform infrared confirmed the polyamide layer formation. Scanning electron microscopy illustrated that only the reaction between DAB and TMC yielded a defect-free polyamide layer. The membrane preparation conditions comprised the following parameters: DAB and TMC concentrations, immersion time (PSf support in DAB solution), and polymerization reaction time. The optimized membrane delivered an average permeability of 12.5 L m−2 h−1 MPa−1. Its salt rejection followed this order: Na2SO4 (84.2%) > MgSO4 (48.8%) > MgCl2 (14.5%) or NaCl (15.3%). Moreover, the membrane was stable at feed pH of 5–10, at operating temperatures of 25–70 °C, and within a long-term nanofiltration period of 148 h.

Nanocomposite membranes have gained growing attention in various application fields, especially in the separation and purification of resource substances. However, the nanomaterials and their membranes fabrication strategies usually suffer from complex procedures, high-energy consumption and lack of universality. Inspired by the unique self-polymerization and adhesion characteristic of marine mussels, we proposed a facile and versatile approach to synthesize zwitterionic dopamine nanoparticles via dopamine induced oxidative polymerization method, followed by the interfacial cross-linking on porous supporting layer to fabricate thin-film nanocomposite (TFN) membranes. The influences of nanoparticle composition, particle size and loading content on the membrane structure and performance were studied to optimize the fabrication conditions. The resultant TFN membrane exhibited high water permeance (98.0 L m−2 h−1 MPa−1) and good selectivity for di-/mono-valent salts (SNa2SO4/NaCl = ~4.50, SMgSO4/NaCl = ~4.49). Furthermore, by utilizing the protein, polysaccharide, and humic acid as model foulants, the zwitterionic dopamine nanoparticles based TFN membranes have been demonstrated with excellent fouling resistance and cleaning recovery property in separation applications.

We synthesized silica particles with varying sizes of 50, 200, and 500 nm. These particles were added to a trimesoyl chloride (TMC) solution and used as fillers to produce thin-film nanocomposite (TFN) polyamide membranes through interfacial polymerization. The effect of the particle size and concentration on the nanofiltration membrane performance was systematically investigated. Scanning electron microscopic images showed that small particles were dispersed in the membrane with spaces between them, but large particles clustered together and gathered into a crowd or mass, forming a layer of particles. When the particle concentration was low (0.35 g silica/g TMC), TFN50 (membrane with 50-nm particles, the smallest of the additives used in this study) delivered the highest pure water flux (58.3 ± 3.8 L m−2 h−1); the salt rejection [RNa2SO4 (99.0 ± 0.6%) > RMgSO4 (96.5 ± 2.6%) > RMgCl2 (67.2 ± 1.3%) > RNaCl (42.6 ± 2.3%)] was comparable with that for the other membranes. At a high concentration of particles (0.75 g silica/g TMC), the water flux delivered by membranes that differed in the size of embedded particles was the same; however, the salt rejection decreased with increasing particle size. In antifouling tests with bovine serum albumin used as model foulant, membranes with silica particles indicated high water flux recovery and remarkable antifouling property.

Thin-film composite polyamide membranes were fabricated through cosolvent-assisted interfacial polymerization on a polyvinylidene fluoride (PVDF) hollow fiber support. An m-phenylenediamine (MPD) monomer was dissolved in an aqueous solution containing acetone of varying concentrations. Upon contact of this MPD solution with PVDF, the acetone enhanced the PVDF swelling, resulting in a higher MPD sorption. When an organic phase of toluene comprising a trimesoyl chloride (TMC) monomer was contacted with the wet PVDF, the acetone also enhanced the miscibility between water and toluene, facilitating the diffusion of MPD through the organic phase toward TMC. Hence, MPD cross-linked with TMC at a higher degree. Field emission scanning electron microscopy revealed that the formed polyamide layer grew thicker with increasing acetone concentration. The composite membrane fabricated from using 75 wt% aqueous acetone solution delivered optimal pervaporative dehydration of a 90 wt% aqueous tert-butanol solution: permeation flux = 437.2 g/m2 h; water concentration = 99.88 wt%. At varying feed temperatures and concentrations, flux increased with temperature but decreased with increasing tert-butanol content. The membrane performance on aqueous n-butanol and isobutanol feed systems was high - 93.47 and 93.37 wt% water in permeate, respectively. Overall, the composite membrane performed well on different aqueous butanol feed solutions.

In recent years, layer-by-layer self-assembly technology is one of the methods of preparing thin film composite membrane with ultra-thin selection layer. In this study, a single bilayer polyelectrolyte/hydrolyzed polyacrylonitrile (HPAN) hollow fiber membranes were fabricated by self-assembly technique for pervaporation. Branched polyethyleneimine (BPEI) and polyacrylic acid (PAA) were used as the cation polyelectrolyte and anion polyelectrolyte, respectively. Polycation/HPAN composite hollow fiber membranes were prepared by self-assembling BPEI onto the outer surface of HPAN hollow fiber membranes through electrostatic interaction. Subsequently, polycation/HPAN composite hollow fiber membranes were self-assembled with PAA to form polyanion/polycation/HPAN composite hollow fiber membranes. The effect of hydrolyzed and self-assembly on the property and pervaporation performances of aqueous ethanol solution through resulted hollow fiber membranes were investigated. By using the BPEI/PAA self-assembly, a single bilayer polyanion/polycation/HPAN composite hollow fiber membrane with excellent pervaporation performances was obtained. Furthermore, the effects of pervaporation conditions such as feed concentration, feed temperature, and downstream pressure on the pervaporation performances through BPEI/PAA/HPAN composite hollow fiber membranes were also investigated in this study.

The advancement in membrane science and technology, particularly in nanofiltration applications, involves the blending of functional nanocomposites into the membranes to improve the membrane property. In this study, Ag-polydopamine (Ag-PDA) particles were synthesized through in situ PDA-mediated reduction of AgNO3 to silver. Infusing Ag-PDA particles into polyethersulfone (PES) matrix affects the membrane property and performance. X-ray photoelectron spectroscopy (XPS) analyses confirmed the presence of Ag-PDA particles on the membrane surface. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) describe the morphology of the membranes. At an optimum concentration of Ag-PDA particles (0.3 wt % based on the concentration of PES), the modified membrane exhibited high water flux 13.33 L∙m−2∙h−1 at 4 bar with high rejection for various dyes of &gt, 99%. The PESAg-PDA0.3 membrane had a pure water flux more than 5.4 times higher than that of a pristine membrane. Furthermore, in bacterial attachment using Escherichia coli, the modified membrane displayed less bacterial attachment compared with the pristine membrane. Therefore, immobilizing Ag-PDA particles into the PES matrix enhanced the membrane performance and antibacterial property.

In this study, cellulose acetate (CA) mixed-matrix membranes were fabricated through the wet-phase inversion method. Two types of montmorillonite (MMT) nanoclay were embedded separately: sodium montmorillonite (Na-MMT) and organo-montmorillonite (O-MMT). Na-MMT was converted to O-MMT through ion exchange reaction using cationic surfactant (dialkyldimethyl ammonium chloride, DDAC). Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) compared the chemical structure and composition of the membranes. Embedding either Na-MMT and O-MMT did not change the crystallinity of the CA membrane, indicating that the nanoclays were dispersed in the CA matrix. Furthermore, nanoclays improved the membrane hydrophilicity. Compared with CANa-MMT membrane, CAO-MMT membrane had a higher separation efficiency and antifouling property. At the optimum concentration of O-MMT in the CA matrix, the pure water flux reaches up to 524.63 &plusmn, 48.96 L∙m&minus, 2∙h&minus, 1∙bar&minus, 1 with over 95% rejection for different oil-in-water emulsion (diesel, hexane, dodecane, and food-oil). Furthermore, the modified membrane delivered an excellent antifouling property.

In this study, polydopamine (PDA) particles were embedded into polyethersulfone (PES) membrane through wet-phase separation. We considered two concentration of PES solution—17 and 19 wt%. Adding different concentration of PDA (0–0.7 wt%) into the two solutions revealed an opposite effect on the characteristic and performance of the membrane. Incorporating PDA particles in 17 wt% PES solution was resulted in a decreased in pure water flux, and increased in dye rejection; Whereas, incorporating PDA particles in 19 wt% PES solution boosted the pure water flux with keep dye rejection of ~99.0%. At the optimum concentration of 0.5 wt% PDA added to 19 wt% PES solution, the following dye rejections were obtained: RMethylene Blue = 99.90 ± 1.45%; RProcion Blue H-5R = 98.33 ± 0.57%; RDirect Red 23 = 99.90 ± 1.82%; RBrilliant Blue = 99.90 ± 0.94%; RRose Bengal = 99.90 ± 0.0%; RDirect Red 80 = 99.12 ± 0.41%; for the salt rejections: (RNaCl = 10.59 ± 5.23%; RNa2SO4 = 8.87 ± 4.99%; RMgCl2 = 10.45 ± 6.85%; RMgSO4 = 10.02 ± 3.87%). This shows that the selectivity of the fabricated membrane towards different dyes and common inorganic salts is high. PDA is a favorable option for fabricating membranes for dye desalination under appropriate PES concentration.

In this study, the basal spacing of montmorillonite (MMT) was modified through ion exchange. Two kinds of MMT were used: sodium-modified MMT (Na-MMT) and organo-modified MMT (O-MMT). These two particles were incorporated separately into the thin-film nanocomposite polyamide membrane through the interfacial polymerization of piperazine and trimesoyl chloride in n-hexane. The membrane with O-MMT (TFNO-MMT) has a more hydrophilic surface compared to that of membrane with Na-MMT (TFNNa-MMT). When various types of MMT were dispersed in the n-hexane solution with trimesoyl chloride (TMC), O-MMT was well-dispersed than Na-MMT. The poor dispersion of Na-MMT in n-hexane led to the aggregation of Na-MMT on the surface of TFNNa-MMT. TFNO-MMT displayed a uniform distribution of O-MMT on the surface, because O-MMT was well-dispersed in n-hexane. In comparison with the pristine and TFNNa-MMT membranes, TFNO-MMT delivered the highest pure water flux of 53.15 &plusmn, 3.30 L∙m&minus, 2∙h&minus, 1 at 6 bar, while its salt rejection for divalent ions remained at 95%&ndash, 99%. Furthermore, it had stable performance in wide operating condition, and it exhibited a magnificent antifouling property. Therefore, a suitable type of MMT could lead to high separation efficiency.

Composite polyelectrolyte pervaporation membranes were fabricated through layer-by-layer self-assembly method. Cationic polyethyleneimine (PEI) and anionic poly(4-styrene sulfonic acid-co-maleic acid) (PSSMA) polyelectrolytes were deposited one after the other on a porous asymmetric modified polyacrylonitrile (mPAN) substrate. Attenuated total reflection–Fourier transform infrared spectral analysis and X-ray photoelectron spectrometry confirmed the deposition of polyelectrolytes on the mPAN support. Field emission scanning electron microscopy depicted that pores in the mPAN support were covered with layers of polyelectrolytes. Atomic force microscopy illustrated that the deposition of polyelectrolytes led to a smooth surface of the membrane. Moreover, the membrane exhibited improved hydrophilicity. We investigated the effect of polyelectrolyte concentrations on the efficiency of dehydrating 90 wt% aqueous alcohol solutions through pervaporation. The results established that bilayer polyelectrolyte membranes fabricated from 0.9 wt% PEI and 0.1 w% PSSMA delivered maximal dehydration efficiency.

Polydopamine (PDA) simulates the adhesive properties of mussels and modifies the surface of hydrophobic materials. In this study, the mussel-inspired deposition of PDA on a polyvinylidene fluoride support was adopted. Afterward, the catecholamine in PDA was cross-linked with trimesoyl chloride (TMC). Attenuated total reflectance-Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy validated the success of the cross-linking process. Scanning electron microscopy illustrated that the cross-linking induced the reduction of nodules. Water contact angle measurements indicated that the cross-linked membrane exhibited a higher contact angle compared with the pristine membrane. Atomic force microscopy showed that the cross-linked membrane surface was smoother than that of the membrane without cross-linking. Pervaporation tests demonstrated that the cross-linked membrane could separate water from isopropanol. Several parameters were varied: dopamine concentration, buffer solution pH, self-polymerization time, TMC concentration, cross-linking time, and annealing time. At optimum conditions, the permeate flux was 2411 ± 33 g·m−2·h−1 and the water concentration in permeate was 95.72 ± 0.44 wt% (feed = 70 wt% isopropanol at 25 °C). At a feed temperature of 70 °C, the permeate flux was 11001 ± 989 g·m−2·h−1 and the water concentration in permeate was 93.61 ± 0.45 wt%. This indicates that a composite membrane containing cross-linked PDA is stable at a high feed temperature.

In this investigation, a new concept for fabrication polyamide (PA)/polyacrylonitrile (PAN) composite hollow fiber membrane by using a triple orifice spinneret was explored. Tetraethylenepentamine (TEPA) and trimesoyl chloride (TMC) were used as the monomers of aqueous solution and acid chloride solution, respectively. The PAN dope, TEPA solution and TMC solution were pumped into the outermost, middle and inner channel of the triple orifice spinneret, respectively, and then co-extruded into water from the outlet of the spinneret simultaneously. The PA layer then was formed on the lumen surface of the synchronous wet-spun PAN hollow fiber membrane. SiO2 was added into the dope to increase the hydrophilicity of the dope. The resultant PA/PAN composite hollow fibers were characterized by using FTIR-ATR, SEM, light transmission, contact angle and positron annihilation spectroscopy (PAS). The effects of SiO2 content, TEPA concentration, as well as the TEPA solution flow rate on the properties and pervaporation performances of resultant PA/PAN composite hollow fibers were investigated. The PA layer was completely attached to the lumen surface of the resulted hollow fibers through the spinning and interfacial polymerization synchronous procedure. The pervaporation performances with 419 g/m2h of permeation flux and 96.6 wt% of water content in permeate of the 90 wt% aqueous isopropanol solution at 25 °C can be obtained through the synchronous fabricated PA/PAN composite hollow fiber membrane which was fabricated by the 18 wt% PAN dope containing 5 wt% SiO2, 1 ml/min of 14 wt% TEPA solution and 2 ml/min of 1 wt% TMC solution.

Novel poly(dopamine-sulfobetaine methacrylate) [P(DA-SBMA)] nanoparticles were synthesized through oxidative polymerization and aza-Michael addition. By means of interfacial polymerization (IP), they were embedded in the selective polyamide (PA) layers of thin-film nanocomposite (NF) membranes with the intention of improving membrane separation efficiency and hydrophilicity. The organic solution, trimesoyl chloride (TMC) in n-hexane, was chosen as the dispersing medium for the nanoparticles in preference to the aqueous solution, piperazine (PIP) in water, to ensure their effective entrapment within the two layers. This was supported by data from Attenuated Total Reflection – Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, and X-Ray Photoelectron Spectroscopy. The optimal performance was demonstrated by TFN membranes with a weight ratio [g P(DA-SBMA)/g TMC] of 0.55 [TFNP(DA-SBMA)-0.55], delivering a pure water flux of 73.11 ± 6.78 L·m−2 ·h−1 and salt rejections of 98%, 95%, 54%, and 42% for Na2SO4, MgSO4, MgCl2, and NaCl, respectively, at 30 °C, 6.0 bar. Furthermore, TFNP(DA-SBMA)-0.55 membranes exhibited excellent antifouling properties against bovine serum albumin (BSA), indicating that exposure to proteins does not heavily affect the performance of P(DA-SBMA)-embedded nanofiltration membranes.

The pervaporation process is an energy-conservative and environmentally friendly method to separate organic solvent from water. It efficiently separates close boiling point and azeotrope mixtures unlike the distillation process. Herein, primary amine-terminated polyamidoamine (PAMAM) dendrimers are proposed to interact with the highly hydrophilic and negatively charged sodium alginate (SA) polymer chains for the preparation of pervaporation composite membranes. Different generations of PAMAM dendrimer (G0, G1, and G2) have different number of terminal primary groups (P4, P8, and P16). That is, a higher generation number means there are more terminal amine groups available for interaction. The addition of PAMAM contributed to the stronger hydrogen bonding of SA and inhibited the swelling of pristine SA/PVDF composite membranes. Interestingly, the free volume characteristics of the SA/PVDF membranes with PAMAM altered the number and size of the free volume spaces as confirmed by positron annihilation spectroscopy (PAS). The more terminal primary amine groups of PAMAM resulted to a higher ionic interaction with the sodium alginate polymer chains producing a denser structure. The denser structure of SA-P8/PVDF and SA-P16/PVDF resulted to a lower flux than with SA-P4/PVDF. The SA-P4/PVSDF at 40 ppm loading achieved the highest separation performance for the dehydration of 90/10 wt% ethanol/water mixture at 25 °C with a permeation flux of 1,039 g m-2h−1 and a water concentration in permeate of 99.41 wt%. Furthermore, the SA-P4/PVDF membrane can withstand high water content in feed up to 50 wt% and high operating temperature of 70 °C showing enhanced stability of the selective layer due to the interactions between SA and PAMAM dendrimer.

Nanofiltration membrane performance is enhanced to attain an economical water purification system. Herein, we developed a series of high-performance thin-film composite nanofiltration polyamide (PA) membranes by incorporating different monoamines containing carboxylic terminal groups such as 4-aminobenzoic acid (ABA), 6-aminocaproic acid (ACA), and 3-aminopropanoic acid (APA). Each monoamine was added to an aqueous piperazine (PIP) solution, which was reacted with trimesoyl chloride through interfacial polymerization on a porous polysulfone support. The chemical structures and compositions of the obtained membranes were characterized using attenuated total reflectance-Fourier transform infrared and x-ray photoelectron spectrometry. The PA membranes were measured for their contact angle and streaming potential. Both the membrane hydrophilic property and surface charge density were enhanced as a result of introducing carboxylic monoamines. The membrane separation performance was tailored by adjusting the monoamine structure and content. The pure water flux of the membranes increased in the following order: PAM H2O = 71.2 L m −2 h −1 ; salt rejections: R Na2SO4 = 93.2% and R NaCl = 15.6% (for 1000 ppm aqueous salt solution, operating at 0.6 MPa and 25 °C). Moreover, PAM-ABA delivered stable performance at various operating conditions and exhibited excellent antifouling properties.

A graphene oxide (GO) nano-additive was incorporated into a polyelectrolyte complex (PEC) to prepare water selective membranes for a water desalination process. The synthesized thin film composites consisted of a PEC-GO separation layer, a microporous poly(vinylidene fluoride) layer, and a non-woven substrate. The crosslinking agent glutaraldehyde (GA) was used to enhance the stability of the PEC composite membranes. The resulting membranes were investigated in nanofiltration systems to examine their permeance and salt rejection efficiency. The results demonstrated that 100 ppm GO in the PEC exhibited a high desalination efficiency on a 1000 ppm NaCl solution. This composite exhibited permeance values in the range of 69–89 kg m−2 h−1 MPa−1 for various salt solutions. The Na2SO4 solution resulted in the highest rejection ratio of 62.1%, followed by the NaCl rejection (38.6%). The MgCl2 and MgSO4 solutions had lower rejections of 12.2% and 22.0%. It seems that the GA_PEC-GO composite was more efficient in removing divalent ions than monovalent ions, while maintaining high filtration flux.

In this study, Polyamide (PA)/polyacrylonitrile (PAN) thin-film composite (TFC) hollow fiber membranes were fabricated to investigate the dehydration performances of ethanol mixtures by pervaporation. Amine monomers (ethylenediamine (EDA), 1, 6-hexanediamine (HDA), diethylenetriamine (DETA), and tetraethylenepentamine (TEPA)) with difference number of functional groups or chain length were selected to react with trimesoyl chloride (TMC) to prepare a PA dense thin-film onto the surface of asymmetric PAN hollow fiber membranes by way of interfacial polymerization. Attenuated total reflection infrared spectroscopy (FTIR-ATR), scanning electron microscope (SEM), atomic force microscope (AFM), light transmission, contact angle and positron annihilation spectroscopy (PAS) were used to characterize the physicochemical properties, morphologies and microstructure of the PA thin layer. The pervaporation performances of aqueous ethanol solution showed the permeation flux decreased while water content in permeate increased with increasing number of amine groups. The effects of monomer concentration and reaction time on the pervaporation performances of aqueous ethanol solution through TEPA-TMC/PAN TFC hollow fiber membranes were also investigated. A 342.0 ± 22.3 g/m 2 h permeation flux and 97.6 ± 0.3 wt.% water content in permeate were obtained for the pervaporation of 90 wt.% aqueous ethanol solution at 25 °C through the PA/PAN TFC hollow fiber membrane which was fabricated by immersing PAN hollow fiber membrane into 2 wt.% TEPA aqueous solution for 1 min and then contacting 1 wt.% TMC solution for 0.5 min.

A thin-film composite membrane was prepared through the interfacial polymerization of tannic acid (TA), a natural oligomer, and acyl chloride monomers – terephthaloyl chloride (TPC) or trimesoyl chloride (TMC). Thin-film nanocomposite (TFN) membranes were also prepared by loading a new class of carbon nanoparticles – nitrogen-doped graphene quantum dots (NGQDs). The composite membranes were characterized with ATR-FTIR, XPS, SEM and water contact angle. The TA-TMC membrane provided lower flux and better water permselectivity than those prepared with TA-TPC due to availability of more reactive acyl chloride. The concentrations of each reactant used, appropriate loading amount of NGQD and contact time between TA and acyl chloride monomers were all determined and investigated to separate 90/10 wt% n-butanol/water mixture at 25 °C. The TA-TMC was found to have higher surface hydrophilicity due to more hydroxyl groups present. The incorporation of 50 ppm NGQD during the interfacial polymerization enhanced the pervaporation performance by providing additional hydrophilicity and mass transfer resistance to larger permeating molecule. The TA0.075-TMC0.4-NGQD(50) membrane at 3-min contact time had a total flux of 1100 g m−2 h−1 and a water concentration in permeate of 97.1 wt% compared to TA0.075-TPC0.4-NGQD(50) membrane with 2196 g m−2 h−1 and 93.2 wt% in separating 90/10 wt% n-butanol/water mixture at 25 °C. The water permselectivity was also found to be more efficient for isobutanol/water mixtures due to the sterically hindered structure of the alcohol. Furthermore, the TA0.075-TMC0.4-NGQD(50) membrane was also tested to separate all butanol isomer/water mixtures at 25 °C showing better separation performance for sterically hindered or branched butanol isomer. The membrane fabricated herein shows the potential use of cheap and natural oligomer (TA) to produce thin-film composite membranes that provided enough barrier to separate butanol from water through pervaporation.

Carbon molecular sieve (CMS) membranes were prepared by controlled pyrolysis of polyetherimide (PEI) blended with polyimide (PI). The microstructure and gas separation properties of the precursor membranes and supported CMS membranes were characterized in terms of the different weight ratios of PI to PEI. The thermogravimetric analysis indicated that the co-pyrolysis in the PEI/PI appeared above 450 °C. Both permeability and selectivity of supported CMS membranes increased with increasing PI content in the precursors. The positron annihilation lifetime (PAL) results showed that the free volume size and the pore size were enhanced as the PI content is increased and that there is a close relationship between the microstructures of polymer blend precursors and CMS membranes. These results confirmed that the microstructure and gas separation performance of CMS membranes can be adjusted by blending two thermally stable polymers. For CMS membrane derived from a precursor containing 75 wt% PI and pyrolyzed at 700 °C, the gas permeance for CO2 was 40 GPU and CO2/N2 selectivity was 39.

The type of organic solvents used in interfacial polymerization affects the surface property, free volume, and separation performance of the thin-film composite (TFC) polyamide membrane. In this study, TFC polyamide membrane was fabricated through interfacial polymerization between diethylenetriamine (DETA) and trimesoyl chloride (TMC). Four types of organic solvent were explored in the preparation of pervaporation membrane. These are tetralin, toluene, hexane, and isopentane. The solubility parameter distance between organic solvents and DETA follows in increasing order: tetralin (17.07 MPa1/2) &lt, toluene (17.31 MPa1/2) &lt, hexane (19.86 MPa1/2) &lt, isopentane (20.43 MPa1/2). Same trend was also observed between the organic solvents and DETA. The larger the solubility parameter distance, the denser and thicker the polyamide. Consequently, field emission scanning electron microscope (FESEM) and positron annihilation spectroscopy (PAS) analysis revealed that TFCisopentane had the thickest polyamide layer. It also delivered the highest pervaporation efficiency (permeation flux = 860 &plusmn, 71 g m&minus, 2 h&minus, 1, water concentration in permeate = 99.2 &plusmn, 0.8 wt%, pervaporation separation index = 959,760) at dehydration of 90 wt% aqueous ethanol solution. Furthermore, TFCisopentane also exhibited a high separation efficiency in isopropanol and tert-butanol. Therefore, a suitable organic solvent in preparation of TFC membrane through interfacial polymerization enables high pervaporation efficiency.

In this study, a series of pervaporation membranes is fabricated through interfacial polymerization involving a diamine and trimesoyl chloride (TMC). Three diamines are used: 2-bis(2-aminoethoxy)ethane (BAE); 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro[5,5]undecane (BATO); and 1,8-octanediamine (ODA). They differ in chemical structures and functional groups. The functional groups between the two terminal amines in BAE and BATO comprise ether groups, whereas ODA has only alkane groups. BAE or BATO reacts with TMC producing polyetheramide; the product of ODA and TMC is polyamide. Among the diamines, BAE results in a composite membrane with the most compact active layer (hence, the least free volume). This result is attributed to the two ether groups that have strong hydrogen bonding and electrostatic interaction with the amide groups. In addition, the linear orientation of the ether group contributes no steric hindrance between BAE and TMC. The polyetheramide membrane from BAE and TMC exhibits a high permeation flux of 1399 ± 132 g m−2 h−1 and a high concentration of water in the permeate of 99% (feed = 90% aqueous tetrahydrofuran solution at 30 °C). Therefore, composite polyetheramide membranes with a suitable chemical structure, fabricated under optimum conditions, deliver high efficiency for separating water from tetrahydrofuran through pervaporation.

Spherical, cubic, or rodlike hollow silica nanoparticles were embedded in nanofiltration polyamide membranes. Each nanoparticle was separately added to an n-hexane solution of trimesoyl chloride, which was reacted with piperazine through interfacial polymerization. The modified membranes exhibited higher hydrophilicity. Field emission scanning electron microscopy depicted less aggregation in the case of the embedded spherical silica nanoparticles, on account of the smallest dimensions. Moreover, the corresponding modified membrane delivered the greatest water flux. The weight ratio of the spherical nanoparticles to trimesoyl chloride was established to be optimum at 0.5, at which the membrane yielded a pure water flux of 90 ± 3 L/m2 h (6 bar), and the rejection of different salts followed this trend: Na2SO4 (92%) > MgSO4 (70%) > MgCl2 (14%) > NaCl (11%). Therefore, the shape of hollow silica nanoparticles exerts an influence on the separation efficiency of the modified nanofiltration membranes.

We fabricated thin-film composite nanofiltration polyamide membranes through the interfacial polymerization of two monomers: polyethyleneimine (PEI) and trimesoyl chloride (TMC). Three different types of surfactants with varied chemical structures were added to aqueous PEI solutions: sodium dodecyl sulfate (SDS), sodium octyl sulfate, and sodium dodecylbenzenesulfonate; the aim was to improve the rejection of divalent ions. Adding the surfactants led to increased isoelectric point, and, in turn, enhanced the membrane hydrophilic properties, heightened the membrane surface charge, and augmented the rejection of MgCl2. Among the three surfactants, SDS effected the most favorable conditions: the resultant composite membrane delivered the highest pure water flux (44.87 ± 3.22 L∙m−2∙h−1), and exhibited high rejections of divalent salts (RNa2SO4 = 92.26 ± 3.30%; RMgSO4 = 93.83 ± 3.22%; RMgCl2 = 94.15 ± 2.52%). SDS had long alkane chains and highly polar heads, which were conducive to bringing about an effective interaction between PEI and the polysulfone (PSf) support, thereby increasing the sorption of PEI in PSf. Accordingly, the reaction of PEI with TMC produced more amide and amine functional groups that were instrumental in raising the rejections of divalent salts and enhancing the membrane surface properties.

In this study, polyacrylic acid (PAA) was grafted onto a polyamide (PA) surface through ultraviolet-initiated graft polymerization to improve the pervaporative dehydration of aqueous alcohol solutions. The PA layer was formed on the surface of a polyacrylonitrile support by the interfacial polymerization of 1,4-bis(3-aminopropyl)piperazine and trimesoyl chloride. Afterward, the PAA was deposited under varying grafting conditions—different acrylic acid concentrations, periods of irradiation time, and irradiation distances. Attenuated total reflectance-Fourier transform infrared and X-ray photoelectron spectra indicated the presence of more carboxyl groups on the membrane surface after grafting PAA. Images from field emission scanning electron microscopy and atomic force microscopy illustrated that the membrane became rougher. PAA also improved the membrane hydrophilicity. The dehydration of 90 wt% aqueous ethanol solutions by pervaporation demonstrated that the flux and water concentration in permeate were enhanced from 803 ± 55 to 830 ± 59 g m−2 h−1 and 84.9 ± 2.5 to 99.5 ± 0.3 wt%, respectively. Furthermore, the PAA-PA membranes showed stable performance at wide operating conditions.

In this work, amorphous amino-modified silica nanoparticles (AAMSN) were successfully synthesized via the sol-gel method and combined with the polyimide (PI) 4,4′-oxydiphthalic anhydride-2,2′-bis(trifluoromethyl) benzidine (ODPA-TFMB) to prepare mixed matrix membranes (MMMs) for gas separation. The physicochemical properties of the AAMSNs were characterized by thermogravimetric analysis, X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy, and the CO2 capture and O2 enrichment behaviors of MMMs with different AAMSN contents were compared with those of a control PI membrane. The sorption isotherm and permeation data revealed that addition of AAMSNs not only increases the diffusion coefficient of the resulting membranes but also increases their adsorption coefficient due to the amorphous characteristics of the nanoparticles and good adhesion between these particles and the PI. The CO2 permeation properties and CO2/N2 selectivity of the MMM with 20 wt% AAMSN were 210.1 barrer and 30.8, respectively, while those of the control membrane were 66.7 barrer and 27.8, respectively. Mixed gas permeation results also showed that the gas permeability of the MMMs improves and their gas selectivity is maintained compared with those of the control PI membrane. The unique structure of the AAMSN/PI membrane makes it an attractive candidate for CO2 capture and O2 enrichment applications.

Nanofiltration membranes have evolved as a promising solution to tackle the clean water scarcity and wastewater treatment processes with their low energy requirement and environment friendly operating conditions. Thin film composite nanofiltration membranes with high permeability, and excellent antifouling and antibacterial properties are important component for wastewater treatment and clean drinking water production units. In the scope of this study, thin film composite nanofiltration membranes were fabricated using polyacrylonitrile (PAN) support and fast second interfacial polymerization modification methods by grafting polyethylene amine and zwitterionic sulfobutane methacrylate moieties. Chemical and physical alteration in structure of the membranes were characterized using methods like ATR-FTIR spectroscopy, XPS analysis, FESEM and AFM imaging. The effects of second interfacial polymerization to incorporate polyamide layer and &lsquo, ion pair&rsquo, characteristics, in terms of water contact angle and surface charge analysis was investigated in correlation with nanofiltration performance. Furthermore, the membrane characteristics in terms of antifouling properties were evaluated using model protein foulants like bovine serum albumin and lysozyme. Antibacterial properties of the modified membranes were investigated using E. Coli as model biofoulant. Overall, the effect of second interfacial polymerization without affecting the selectivity layer of nanofiltration membrane for their potential large-scale application was investigated in detail.

In this work, superfast surface modification of forward osmosis (FO) membranes was accomplished using zwitterionic species with improved antibacterial and antifouling properties. Asymmetric thin film composite (TFC) FO membranes were fabricated using superfast second interfacial polymerization (SIP). The active sides of the TFC membranes were modified with zwitterionic polyamide moieties. Subsequently, the effects of surface modification on the surface properties, morphologies, and surface charges of the TFC membranes were investigated. The TFC membranes exhibited drastically improved performance in FO processes with model and real produced water samples. The zwitterion-augmentation significantly enhanced surface hydrophilicity and shielded negative surface charge distribution on the membrane surface. Furthermore, static protein absorption and dynamic protein fouling tests with model foulant sodium alginate (SA) revealed that the antifouling characteristics of the asymmetric TFC membranes had improved remarkably. SIP with zwitterion incorporation reduced protein absorption and promoted consistent flux during permeation with the model foulant solution. The antimicrobial characteristic of these FO membranes is also demonstrated with bacterial attachment on membrane surface using Escherichiacoli. Overall, the zwitterion-augmented surface modification of these FO membranes resulted in enhanced permeability and reduction in surface structure parameter leading to improved antifouling properties with respect to organic proteins and gram-positive bacteria.

Zwitterionic copolymers, poly(glycidyl methacrylate-sulfobetaine methacrylate) [poly(GMA-SBMA)], was incorporated into graphene oxide (GO) to form a GO–poly(GMA-SBMA) framework. This compound was then deposited onto a polysulfone support through pressure-assisted filtration to fabricate hybrid membranes. Optimum fabrication conditions were determined by varying the poly(GMA-SBMA) loading. Attenuated total reflectance-Fourier transform infrared and X-ray photoelectron spectroscopy confirmed the covalent bonding between poly(GMA-SBMA) and GO. On account of loading incremental amounts of poly(GMA-SBMA), the membrane thickness was increased (illustrated by field emission scanning electron microscopic images), the interlayer spacing between GO sheets was expanded (shown by X-ray diffraction patterns), and the membrane hydrophilic properties were enhanced (indicated by water contact angle data). Relative to the pristine GO membrane, hybrid membranes fabricated at optimum conditions exhibited superior separation performance (99.60 wt% water concentration in permeate and 1102 g m−2⋅h−1 permeation flux) on dehydrating a 70 wt% aqueous isopropanol solution by pervaporation. This present study explored the potential of poly(GMA-SBMA) for developing hybrid membranes with excellent pervaporation performance.

Membrane support properties influence the performance of thin-film composite nanofiltration membranes. We fabricated several polysulfone (PSf) supports. The physicochemical properties of PSf were altered by adding polyethylene glycol (PEG) of varying molecular weights (200⁻35,000 g/mol). This alteration facilitated the formation of a thin polyamide layer on the PSf surface during the interfacial polymerization reaction involving an aqueous solution of piperazine containing 4-aminobenzoic acid and an organic solution of trimesoyl chloride. Attenuated total reflectance-Fourier transform infrared validated the presence of PEG in the membrane support. Scanning electron microscopy and atomic force microscopy illustrated that the thin-film polyamide layer morphology transformed from a rough to a smooth surface. A cross-flow filtration test indicated that a thin-film composite polyamide membrane comprising a PSf support (TFC-PEG20k) with a low surface porosity, small pore size, and suitable hydrophilicity delivered the highest water flux and separation efficiency (J = 81.1 ± 6.4 L·m-2·h-1, RNa2SO4 = 91.1% ± 1.8%, and RNaCl = 35.7% ± 3.1% at 0.60 MPa). This membrane had a molecular weight cutoff of 292 g/mol and also a high rejection for negatively charged dyes. Therefore, a PSf support exhibiting suitable physicochemical properties endowed a thin-film composite polyamide membrane with high performance.

Low permeation fluxes with high separation factors were obtained when hydrophilic dense membranes were used for the dehydration of tetrahydrofuran (THF) by pervaporation. To improve the pervaporation performance of a membrane, the polyamide thin-film composite (TFC) membranes were prepared through interfacial polymerization by reacting 1,3-diaminopropane (DAPE), 1,3-cyclohexanediamine (CHDA), or m -phenylenediamine (MPDA) with trimesoyl chloride (TMC) on the surface of a polyacrylonitrile (PAN) membrane (DAPE–TMC/PAN, CHDA–TMC/PAN, and MPDA–TMC/PAN). Pervaporation separation of an aqueous THF solution with polyamide TFC membranes was investigated as functions of diamine structure and operating conditions. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), positron annihilation spectroscopy (PAS), and water contact angle measurements were applied to analyze the chemical structure, surface chemical composition, morphology, surface roughness, free volume, and hydrophilicity of the active polyamide layer of TFC membrane. Varying the diamine structure did affect the physicochemical properties and pervaporation performance of the polyamide TFC membranes. Compared with the CHDA–TMC/PAN and MPDA–TMC/PAN membranes, the DAPE–TMC/PAN membrane showed a lower permeation flux and a higher water concentration in permeate. This was in good agreement with the result of characterization. With an increase in the operating temperature of pervaporation, an increase in the permeation flux and a high water concentration in permeate (>99 wt%) were obtained for the DAPE–TMC/PAN membrane. It was also found that the DAPE–TMC/PAN membrane exhibited a superior performance compared with the several hydrophilic polymers and commercial inorganic membranes discussed in the literature.

Hydrophobic composite membranes for dehydrating aqueous alcohol mixtures by pervaporation were investigated. It was suited for applications at high temperatures and for feed mixtures of water and alcohols with high number of carbon atoms. With increasing operating temperatures, pervaporation data indicated simultaneous increase in permeation flux and concentration of water in permeate. At 70 °C and for a feed mixture of 10 wt% water and 90 wt% ethanol, the composite poly(2,6-dimethyl-1,4-phenylene oxide) membrane delivered a high flux of 1333 g/(m2h) and a high permeate content of 96.4 wt% H 2 O. For a feed with higher water content, the membrane performance was further enhanced. The microstructure of the selective layer was probed with positron annihilation lifetime spectroscopy at varying temperatures. A bimodal free volume distribution was obtained, which described different shifts of free volume as temperature increased: a shift of smaller free volume to a region of much smaller free volume and a shift of bigger free volume to a region of much bigger free volume.

This work introduces the preparation of zeolite-filled porous mixed matrix membranes (MMMs) and discusses their potential use for air separation. Porous polysulfone (PSF) matrix membranes were prepared using the nonsolvent-induced phase separation process. Scanning electron microscope and gas permeation experiments suggested the presence of closed pores in the porous matrix membranes. Furthermore, porous MMMs containing zeolite 4A particles as filler were prepared and characterized. The permeation properties of porous MMMs were highly dependent on the zeolite content. The introduction of zeolite particles distorted the closed pores in the PSF matrix and formed nonselective voids which resulted in very high oxygen flux but low O2/N2 selectivity. The annealing technique for modifying the nonselective pores present in the polymer–zeolite interface is also described in this study. The resulting annealed porous MMMs had the ability to separate O2 from N2 more effectively than traditional dense MMMs.

The micro-structure of various novel polyelectrolyte complex membranes (PECMs) was investigated by means of molecular dynamics (MD) simulation and positron annihilation lifetime spectroscopy (PALS). These PECMs that differed in their chemical structure design were applied to dehydrate a 90 wt% ethanol aqueous solution by pervaporation, and their separation performance was correlated with their microstructure. Free-volume size and free-volume size distribution were determined both by the PALS and MD simulation techniques. To describe the free-volume shape and the polymer chain flexibility and stiffness, MD simulation analysis in terms of radial distribution function and mean square displacement was also conducted. Results obtained from PALS and those from MD simulation were in agreement with each other. These results were highly consistent with the chemical structure of the PECMs designed in this study and were demonstrated to correlate well with the membrane pervaporation separation performance.

To improve the pervaporation performance in separating an aqueous ethanol solution, polyamide thin-film composite (TFC) membranes (m-tolidine-H-TMC/mPAN) were prepared through the interfacial polymerization reaction between trimesoyl chloride (TMC) and 2,2'-dimethylbenzidine hydrochloride (m-tolidine-H) on the surface of a modified polyacrylonitrile (mPAN) membrane. The effects of the feed ethanol concentration on the pervaporation performance and the durability of m-tolidine-H-TMC/mPAN TFC membranes were investigated. To choose the optimal mPAN membrane as the TFC substrate, the effect of hydrolysis time on the chemical properties and separation performance of an mPAN substrate was also studied. An appropriate hydrolysis time of 15 min was chosen to obtain the mPAN substrate due to the corresponding high permeation flux. The m-tolidine-H-TMC/mPAN TFC membrane exhibited a high pervaporation performance for ethanol dehydration. A positron annihilation lifetime spectroscopy experiment was used to estimate the mean free-volume radius of the m-tolidine-H-TMC polyamide selective layer, which lay between the radii of the water and ethanol molecules. © 2013 Society of Chemical Industry

In this study, an atmospheric pressure high temperature plasma torch (APHTPT) was used to modify poly(dimethylsiloxane) (PDMS) membranes in order to form a thin SiO x layer on the membrane surface. The chemical properties of the PDMS and APHTPT-treated membranes, as well as the conversion of polysiloxane, were determined by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) microanalysis. The microstructure of the membranes as a function of depth was obtained with a variable monoenergy slow positron beam (VMSPB) spectroscopy. Results of XPS and EDX indicated that the conversion of polysiloxane to silica was favored with increasing plasma power. VMSPB data demonstrated that the treated membrane exhibited an asymmetric organic–inorganic hybrid structure. Based on the analysis of the treated membrane, the free-volume size increased with the depth and showed a bi-modal distribution. The gas permeation properties of O 2 , N 2 , and CO 2 were tested. The change in the applied plasma power was found to have a great effect on the membrane gas separation performance. The membrane selectivity for O 2 /N 2 and CO 2 /N 2 increased from 2.11 to 4.93 and from 9.54 to 17.19, respectively, after treatment at 10 kW. The APHTPT-treated PDMS membrane was found to have the advantages of both organic and inorganic membranes, leading to outstanding gas separation performance.

The development of the microstructure of carbon molecular sieve membranes (CMSMs) was examined using a variable monoenergy slow positron beam (VMSPB). To vary the structure of the CMSMs fabricated by pyrolyzing a Kapton precursor, different pyrolysis temperatures at a fixed heating rate under vacuum conditions and various periods of holding time at a given pyrolysis temperature were applied. The VMSPB was integrated with the platinum (Pt) capping technique, in which a layer of Pt was sputtered on the membrane surface to eliminate the back diffusion effect of positrons. On the basis of the depth profile obtained, the membranes carbonized at 800 and 900 °C were demonstrated to exhibit asymmetric microstructures at the top layer. The analysis of positron annihilation spectroscopic data of the membranes using a VEPFIT program revealed three structural layers at the most: a dense top layer, a transition layer, and an underlying layer. At prolonged holding time, it was found that the decrease in the gas permeat...