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Polyphenylenesulfone (PPSU) and sulfonated polyphenylenesulfone (sPPSU) are widely used for liquid separations in the medical and food industries. However, their potential applications for gas separation have not been studied extensively owing to their low intrinsic gas permeability. We report here for the first time that blending with sPPSU can significantly improve the gas separation performance of highly permeable polymers of intrinsic microporosity (PIMs), specifically PIM-1, because of the strong molecular interactions of the sulfonic acid groups of sPPSU with CO2 and O2 . In addition, a novel co-solvent system has been discovered to overcome the immiscibility of these polymers. The presence of a higher degree of sulfonation in sPPSU results in better gas separation performance of the blend membranes close to or above the Robeson upper bound lines for O2 /N2 , CO2 /N2 and CO2 /CH4 separations. Interestingly, the blend membranes have comparable gas selectivity to sPPSU even though their sPPSU content is only 5-20 wt %. Moreover, they also display improved anti-plasticization properties up to 30 atm (3 MPa) using a binary CO2 /CH4 feed gas. The newly developed PIM-1/sPPSU membranes are potential candidates for air separation, natural gas separation, and CO2 capture., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Osmotic power holds great promise as a clean, sustainable and largely unexploited energy resource. Recent membrane development for pressure-retarded osmosis (PRO) is making the osmotic power generation more and more realistic. However, severe performance declines have been observed because the porous layer of PRO membranes is fouled by the feed stream. To overcome it, a negatively charged antifouling PRO hollow fiber membrane has been designed and studied in this work. An antifouling polymer, derived from hyperbranched polyglycerol and functionalized by α-lipoic acid and succinic anhydride, was synthesized and grafted onto the polydopamine (PDA) modified poly(ether sulfone) (PES) hollow fiber membranes. In comparison to unmodified membranes, the charged hyperbranched polyglycerol (CHPG) grafted membrane is much less affected by organic deposition, such as bovine serum albumin (BSA) adsorption, and highly resistant to microbial growths, demonstrated by Escherichia coli adhesion and Staphylococcus aureus attachment. CHPG-g-TFC was also examined in PRO tests using a concentrated wastewater as the feed. Comparing to the plain PES-TFC and non-charged HPG-g-TFC, the newly developed membrane exhibits not only the smallest decline in water flux but also the highest recovery rate. When using 0.81 M NaCl and wastewater as the feed pair in PRO tests at 15 bar, the average power density remains at 5.6 W/m(2) in comparison to an average value of 3.6 W/m(2) for unmodified membranes after four PRO runs. In summary, osmotic power generation may be sustained by properly designing and anchoring the functional polymers to PRO membranes., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Hydroxyl functionalized polytriazole-co-polyoxadiazole (PTA-POD) copolymers have been synthesized and cast as promising highly thermally stable, chemically resistant, and antiorganic/biological fouling porous substrates for the fabrication of thin-film composite (TFC) forward osmosis (FO) membranes. The roles of PTA/POD ratios in the membrane substrates, TFC layers, and FO membrane performance have been investigated. This study demonstrates that the substrate fabricated from the copolymer containing 40 mol % PTA is optimal for the TFC membranes. Compared to the POD-TFC membrane, the 40 mol % PTA-TFC membrane exhibits a remarkable decrease in structural parameter (S) of more than 3.3 times. In addition, the 40 mol % PTA-TFC membrane is characterized by high water fluxes of 24.9 LMH and 47.2 LMH using 1 M NaCl as the draw solution and DI water as the feed under FO and pressure retarded osmosis (PRO) modes, respectively. Compared to a polysulfone (PSU) supported TFC-FO membrane under similar fabrication conditions, the 40% mol PTA-TFC membrane shows better FO performance and enhanced antifouling properties on the support (lower protein binding propensity and improved bacterial inhibition). Moreover, the performance of the 40 mol % PTA supported TFC-FO membrane can be improved to 37.5 LMH (FO mode)/78.4 LMH (PRO mode) and potentially higher by optimizing the support morphology, the TFC formation, and the post-treatment process. Hence, the use of newly developed hydroxyl functionalized polytriazole-co-polyoxadiazole copolymers may open up a new class of material for FO processes.

High performance nanofiltration (NF) membranes for heavy metal removal have been molecularly designed by adsorption of chelating polymers containing negatively charged functional groups such as poly (acrylic acid-co-maleic acid) (PAM), poly (acrylic acid) (PAA) and poly (dimethylamine-co-epichlorohydrin-co-ethylenediamine) (PDMED) on the positively charged polyethyleneimine (PEI) cross-linked P84 hollow fiber substrates. Not only do these chelating polymers change the membrane surface charge and pore size, but also provide an extra mean to remove heavy metal ions through adsorption in addition to traditional steric effect and Donnan exclusion. The adsorbed membranes have comparable water permeability and superior rejections to heavy metals, for instance, Pb(NO3)2, CuSO4, NiCl2, CdCl2, ZnCl2, Na2Cr2O7 and Na2HAsO4, with rejections higher than 98%. The membranes also display excellent rejections to mixed ions with rejections more than 99%. The newly developed membranes show reasonably stability during 60-h tests as well as multiple washes., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

To sustain high performance of osmotic power generation by pressure-retarded osmosis (PRO) processes, fouling on PRO membranes must be mitigated. This is especially true for the porous support of PRO membranes because its porous structure is very prone to fouling by feeding river water. For the first time, we have successfully designed antifouling PRO thin-film composite (TFC) membranes by synthesizing a dendritic hydrophilic polymer with well-controlled grafting sites, hyperbranched polyglycerol (HPG), and then grafting it on poly(ether sulfone) (PES) hollow fiber membrane supports. Compared to the pristine PES membranes, polydopamine modified membranes, and conventional poly(ethylene glycol) (PEG)-grafted membranes, the HPG grafted membranes show much superior fouling resistance against bovine serum albumin (BSA) adsorption, E. coli adhesion, and S. aureus attachment. In high-pressure PRO tests, the PES TFC membranes are badly fouled by model protein foulants, causing a water flux decline of 31%. In comparison, the PES TFC membrane grafted by HPG not only has an inherently higher water flux and a higher power density but also exhibits better flux recovery up to 94% after cleaning and hydraulic pressure impulsion. Clearly, by grafting the properly designed dendritic polymers to the membrane support, one may substantially sustain PRO hollow fiber membranes for power generation.

We have investigated the instant and accumulative effects of salt permeability on the sustainability of high power density in the pressure-retarded osmosis (PRO) process experimentally and theoretically. Thin-film composite (TFC) hollow-fiber membranes were prepared. A critical wall thickness was observed to ensure sufficient mechanical stability and hence a low salt permeability, B. The experimental results revealed that a lower B was essential to enhance the maximum power density from 15.3 W/m(2) to as high as 24.3 W/m(2) when 1 M NaCl and deionized water were feeds. Modeling work showed that a large B not only causes an instant drop in the initial water flux but also accelerates the flux decline at high hydraulic pressures, leading to reduced optimal operating pressure and maximal power density. However, the optimal operating pressure to harvest energy can be greater than one-half of the osmotic pressure gradient across the membrane if one can carefully design a PRO membrane with a large water permeability, small B value, and reasonably small structural parameter. It was also found that a high B accumulates salts in the feed, leads to the oversalinization of the feed, and largely lowers both the water flux and power density along the membrane module. Therefore, a low salt permeability is highly desirable to sustain high power density not only locally but also throughout the whole module.

This study investigates a new approach to fabricate thin-film composite (TFC) hollow fiber membranes via interfacial polymerization for forward osmosis (FO) applications. Different degrees of sulfonation of polyphenylenesulfone (PPSU) were adopted as membrane substrates to investigate their impact on water flux. It has been established that the degree of sulfonation plays a role in both creating a macrovoid-free structure and inducing hydrophilicity to bring about higher water fluxes. The fabricated membranes exhibit extremely high water fluxes of 30.6 and 82.0 LMH against a pure water feed using 2.0 M NaCl as the draw solution tested under FO and pressure retarded osmosis (PRO) modes, respectively, while maintaining low salt reverse fluxes below 12.7 gMH. The structural parameter (S) displays remarkable decreases of up to 4.5 times as the membrane substrate is switched from a nonsulfonated to sulfonated one. In addition, the newly developed TFC-FO membranes containing 1.5 mol % sPPSU in the substrate achieves a water flux of 22 LMH in seawater desalination using a 3.5 wt % NaCl model solution and 2.0 M NaCl as the draw solution under the PRO mode. To the best of our knowledge, this value is the highest ever reported for seawater desalination using flat and hollow fiber FO membranes. The use of sulfonated materials in the FO process opens up a frontier for sustainable and efficient production of potable water.

A highly permeable yet highly selective pore-spanning biomimetic membrane embedded with aquaporin Z is molecularly designed and constructed via a combination of pressure-assisted vesicle adsorption and covalent-conjugation-driven vesicle fusion on a porous support. This approach represents a significant breakthrough in the architecture of biomimetic membranes embedded with aquaporin in a planar form., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The immobilization of biomolecules onto an insoluble carrier surface has always been a subject of great interest to enhance their resistance to pH and temperature, which aids in an increased activity lifespan as well as easy reuse of the said biomolecules. However, traditional methods are only able to provide single-layer biomolecular binding and require multiple chemical reactions to prepare the final substrate before the immobilization can be carried out properly. Here we report a facile one-step chemical synthesis of a new aldehyde-bearing graft copolymer via atom transfer radical polymerization (ATRP) for covalent protein capture in a multilayered approach to covalently capture bovine serum albumin (BSA) onto a polymeric membrane. The resultant protein-bound membrane illustrated the retention of BSA's stereoselective discrimination ability by binding to an excess of 2 mol of tryptophan/mol of BSA and demonstrated an enantioresolution of a 0.184 mM racemic tryptophan mixture with a time-averaged-separation factor of 2.9., (Copyright 2010 Elsevier B.V. All rights reserved.)

High-affinity membrane materials have been successfully synthesized through a combination of the polymer sulfonation reaction with transition metal counterion exchange treatment. This type of promising materials were embodied for the first time with the aid of dual-layer hollow fiber technology for protein separation. Three types of immobilized metal affinity membranes (Cu(2+), Ni(2+) and Zn(2+) forms) were developed in this work and they all exhibited enhanced protein separation performance compared to the as-spun hollow fiber in H(+) form due to the strong affinity between transition metal counterions and target protein molecules. Ultimately, the high-purity target protein (>99%, w/w) could be achieved via the membrane in Cu(2+) form.

6FDA-polyimide films modified by polyamidoamine (PAMAM) dendrimers with generations of 0, 1, and 2 are reported in this article. The actual molecular conformation and bulk size of these three generation dendrimers immobilized on polyimide surface were characterized by atomic force microscopy. After comparing with the results of dynamic simulation, we believe that the disk-shape cluster structure of dendrimers has been developed on the polymer surfaces. The amidation and cross-linking reaction between dendrimers and polyimide were examined and quantified by X-ray photoelectron spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, and gel content measurements. Modification time and the generations of PAMAM dendrimer have been verified as two important factors in determining the properties of modified polyimide films. These modified polyimide films exhibit excellent gas separation performance. The ideal selectivity of He/N(2) increases tremendously to about 200% as compared to that of the original polyimide film. Particularly, the separation performance of CO(2)/CH(4) gas pair can be improved beyond the upper bond limit possibly due to the strong interactions of dendrimer molecules with CO(2), which was verified by sorption tests.

Abstract: Ultrafiltration‐level polyacrylonitrile (PAN) flat sheet membranes were chemically modified through cross‐linking and hydrolysis to provide a suitable surface for the growth of a selective layer composed of a Zn benzene‐1,4‐dicarboxylic acid (Zn(BDC)) metal‐organic framework (MOF). Unlike typical membrane modification methods or conventional MOF synthesis procedures, deionized (DI) water was the only solvent used for each of the modification steps. To better understand the layer‐by‐layer MOF growth process, several MOF growth conditions were also studied, including the effects of solution concentration, growth temperature, membrane immersion time and the number of layers. Subsequently, organic solvent nanofiltration (OSN) was used to test the effectiveness of the modifications and compare the performances of the fabricated membranes. With the appropriate combination of the MOF growth conditions, the layer‐by‐layer method was used to produce an OSN membrane with an isopropanol permeance of 2.39 L m−2 h−1 bar−1 and an 86 % rejection of the dye Brilliant Blue R (Mw 825.97 g mol−1). [ABSTRACT FROM AUTHOR]

ABSTRACT A systematic strategy to molecularly design flexible tough hydrolyzed polymers of intrinsic microporosity (hPIM-1) films from the PIM-1 polymer is explored in this study. Flexible films can be fabricated from N-methyl-2-pyrrolidone (NMP) by appropriate hydrolysis conditions. The optimal weight ratio of NaOH/H2O/EtOH in the base-catalyzed reaction is 0.5/2/2. Because of the highly polar carboxylic acid groups, the resultant hPIM-1 has a lower water contact angle. The hPIM-1 has one-half fractional free volume compared to PIM-1 which is in good agreement with permeability. Moreover, hPIM-1 follows as the same dual-mode sorption model as PIM-1. To the best of our knowledge, this is the first ever reported flexible hPIM-1 film in the literature. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 344-354 [ABSTRACT FROM AUTHOR]

Novel fabrication perspectives have been demonstrated to molecularly construct robust hollow fiber membrane supports for high performance thin-film composite (TFC) pressure retarded osmosis (PRO) membranes. For the first time, we found that the desirable hollow fiber supports should possess high stretch resistance and acceptable ductility. The microstructure strength of the hollow fiber support may have more weights on overall robustness of the TFC PRO membranes than the apparent cross-section morphology. Effectively manipulating the kinetics of phase inversion during spinning by maneuvering bore fluid chemistry, and polymer solution composition is a promising method to tailor the strength of hollow fiber supports. Prestabilization of the TFC membranes at elevated lumen pressures can significantly improve their PRO performance. The newly developed TFC PRO hollow fiber membranes exhibit a power density as high as 16.5 W/m2 and a very low specific reverse salt flux (Js/Jw) of 0.015 mol/L at a hydraulic pressure of 15 bar using synthetic seawater brine (1.0 M NaCl) as the draw solution. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1107-1119, 2014 [ABSTRACT FROM AUTHOR]

A new cellulose acetate propionate (CAP) polymer has been synthesized and used to prepare high-performance forward osmosis (FO) membranes. With an almost equal degree of substitution of acetyl and propionyl groups, the CAP-based dense membranes show more balanced physicochemical properties than conventional cellulose acetate (CA)-based membranes for FO applications. The former have a lower equilibrium water content (6.6 wt. %), a lower salt diffusivity (1.6×1014 m2 s−1) and a much lower salt partition coefficient (0.013) compared with the latter. The as-prepared and annealed CAP-based hollow fibers have a rough surface with an average pore radius of 0.31 nm and a molecular weight cut off of 226 Da. At a transmembrane pressure of 1 bar, the dual-layer CAP-CA hollow fibers show a pure water permeability of 0.80 L m−2 h−1 bar−1 (LMH/bar) and a rejection of 75.5% to NaCl. The CAP-CA hollow fibers were first tested for their FO performance using 2.0 M NaCl draw solution and deionized water feed. An impressive water flux of 17.5 L m−2 h−1 (LMH) and a reverse salt flux of 2.5 g m−2 h−1 (gMH) were achieved with the draw solution running against the active CAP layer in the FO tests. The very low reverse salt flux is mainly resulting from the low salt diffusivity and salt partition coefficient of the CAP material. In a hybrid system combining FO and membrane distillation for wastewater reclamation, the newly developed hollow fibers show very encouraging results, that is, water production rate being 13-13.7 LMH, with a MgCl2 draw solution of only 0.5 M and an operating temperature of 343 K due to the incorporation of bulky propionyl groups with balanced physiochemical properties. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1245-1254, 2013 [ABSTRACT FROM AUTHOR]

Abstract: In this work, a novel sulphonated poly(ether ketone) (SPEK) polymer with super-hydrophilic nature was designed as the substrate material to fabricate high performance thin-film composite (TFC) membranes for desalination via forward osmosis (FO). m-Phenylenediamine (MPD) and 1,3,5-trimesoylchloride (TMC) were employed as the monomers for the interfacial polymerization reaction to form a thin aromatic polyamide selective layer. It has been demonstrated that blending a certain SPEK material into the polysulfone (PSU) substrate of TFC-FO membranes not only plays the key role to form a fully sponge-like structure, but also enhances membrane hydrophilicity and reduces structure parameter. The TFC-FO membrane comprising 50wt% SPEK in the substrate shows the highest water flux of 50 LMH against deionized water and 22 LMH against the 3.5wt% NaCl model solution, respectively, when using 2M NaCl as the draw solution tested under the pressure retarded osmosis (PRO) mode (draw solution flows against the selective layer). It is found that the hydrophilicity and thickness of the substrates for TFC-FO membranes play much stronger roles in facilitating high water flux in FO for desalination compared to those made from hydrophobic substrates full of finger-like structures. Moreover, the reduced membrane structural parameter indicates that the internal concentration polarization (ICP) can be remarkably reduced via blending a hydrophilic material into the membrane substrates. Thermal treatment of TFC-FO membranes with optimized conditions can also improve the membrane performance and mechanical strength. [Copyright &y& Elsevier]

Abstract: Industrial hydrogen production may prefer CO2-selective membranes because high-pressure H2 can therefore be produced without additional recompression. In this study, high performance CO2-selective membranes are fabricated by modifying a polymer–silica hybrid matrix (PSHM) with a low molecular weight poly(ethylene glycol) dimethyl ether (PEGDME). The liquid state of PEGDME and its unique end groups eliminate the crystallization tendency of poly(ethylene glycol) (PEG). The methyl end groups in PEGDME hinder hydrogen bonding between the polymer chains and significantly enhance the gas diffusivity. In pure gas tests, the membrane containing 50 wt% additive shows CO2 gas permeability and CO2/H2 selectivity of 1637Barrers and 13 at 35°C, respectively. In order to explore the effect of real industrial conditions, the gas separation performance of the newly developed membranes has been studied extensively using binary (CO2/H2) and ternary gas mixtures (CO2/H2/carbon monoxide (CO)). Compared to pure gas performance, the second component (H2) in the binary mixed gas test reduces the CO2 permeability. The presence of CO in the feed gas stream decreases both CO2 and H2 permeability as well as CO2/H2 selectivity as it reduces the concentration of CO2 molecules in the polymer matrix. The mixed gas results affirm the promising applications of the newly developed membranes for H2 purification. [Copyright &y& Elsevier]

Acetone dehydration via pervaporation is challenging, because acetone and water have close molecular sizes, and acetone has a much higher vapor pressure than water. Acetone is also a powerful solvent, which dissolves or swells most polymers. We have developed novel polybenzimidazole/BTDA-TDI/MDI (PBI/P84) dual-layer hollow fibers for pervaporation dehydration of acetone for industrial and biofuel separations. Both thermal and chemical crosslinking modifications were applied to the membranes to investigate their effectiveness to overcome acetone-induced swelling. Thermal treatment can effectively enhance separation performance, but performance stability can only be achieved through the crosslinking modification of PBI. Crosslinking by p-xylene dichloride followed by a thermal treatment above 250°C show significant effectiveness to improve and stabilize pervaporation performance. The fractional free volume of the PBI selective layer reduces from 3.27 to 1.98% and 1.33%, respectively, after thermal treatment and a combination of chemical/thermal crosslinking modifications characterized by positron annihilation spectroscopy. © 2011 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

Abstract: This study has successfully demonstrated that a proper combination of novel spinneret designs and spinning parameters can effectively counteract the die swell as well as flow instability phenomena, i.e. extrudate distortion, in the hyperbranched polyethersulfone (HPES) hollow fiber spinning. Attempts are also made to unravel the die swell and flow behavior differences between HPES and linear polyethersulfone (LPES) membranes spun using various spinneret designs and spinning conditions. In terms of flow stability, it is revealed that short conical spinnerets with a flow angle of 60° as well as short round flow channel spinneret with a flow angle of 30°, can reduce or eliminate extrudate distortions. Apart from spinneret designs, this study also accentuates the importance of a proper choice of spinning conditions for each specific spinneret to achieve flow stability and reduce die swell, namely: (1) bore fluid composition; (2) dope flow rate; (3) spinning temperature; and (4) take-up speed. Experimental results concluded that a proper combination of spinneret design and these four spinning parameters is the key to stabilize the spinning process. It is found that a high take-up speed spinning and a high non-solvent concentration in the bore fluid can fully eliminate die swell and enhance flow stability in the HPES hollow fiber spinning using short and conical or round spinnerets. [ABSTRACT FROM AUTHOR]

Abstract: The high demands on high performance membranes for energy, water and life science usages provide the impetus for membrane scientists to search for a comprehensive understanding of membrane formation from molecular level to design membranes with desirable configuration and separation performance. This pioneering work is to elaborate the importance of polymer rheology on hollow fiber formation and reveal the integrated science bridging polymer fundamentals such as polymer cluster size, shear and elongational viscosities, molecular orientation, stress relaxation to membrane microstructure and separation performance for gas separation. Torlon® poly(amide imide) was employed in this study with various solvent/nonsolvent additives. The effects of additives on polymeric cluster size, hydrogen bonding and dope rheology during the phase inversion have been examined. It is found that hydrogen bonding and strain-hardening characteristics play very important roles in dope rheology and membrane separation performance. Torlon® possesses strong hydrogen bonds with NMP/water mixtures, the addition of a small amount of water enlarges polymer cluster size, strengthen molecular network (i.e., strain hardening) and facilitate macrovoid-free morphology. However, strong hydrogen bonding may retard chain unfolding during spinning, induce faster relaxation for highly oriented dense-selective skin, and thus reduce gas-pair selectivity. By adjusting dope chemistry and spinning conditions with balanced solubility parameters and dope rheology, we have developed defect-free Torlon® hollow fiber membranes with an O2/N2 selectivity of 8.55 and an ultra-thin layer of 488Å simply using water as the additive. Fibers spun from dopes containing other additives have the optimal O2/N2 selectivity varying from 7.69 to 9.97 at 25±2°C, and the dense layer thickness varying from 500Å to 2000Å. Their corresponding mixed-gas O2/N2 selectivity for compressed air varies from 7.12 to 9.00. [Copyright &y& Elsevier]

Abstract: Highly porous and macrovoid-free PVDF hollow fiber membranes are of great interest for membrane contactor applications such as sea water desalination by membrane distillation in order to enhance the flux and long term stability of the process. For the first time in this paper, porous PVDF hollow fiber membranes with high outer surface porosity were fabricated by applying a two-phase flow consisting of a solvent and a dope solution in the air-gap region of spinning through a non-solvent induced phase separation process (NIPS). In this approach, the dope solution and the N-methylpyrrolidone (NMP) solvent were co-discharged from the middle and outer channels of a triple orifice spinneret, respectively. Then, the two-phase flow went through an air-gap region and finally entered the coagulation bath. It was observed that the introduction of the two-phase flow greatly increased the outer surface porosity of the PVDF fibers and eliminated the formation of macrovoids in the cross-section of the fibers as well. It was also found that the energy efficiency and the flux of the fibers spun through the solvent-dope solution co-exterusion were two to three times higher than the standard dry jet wet-spun fibers. A water vapor flux as high as 67kg/(m2 h) at 80°C was obtained through the newly spun fibers. [Copyright &y& Elsevier]

Abstract: The origins of macrovoid and the ways to eliminate it have received great attention and heavy debates during the last five decades, but no convincing and agreeable comprehension has been achieved. We have discovered, for the first time, that there should be critical values of polymer concentration, air gap distance and take-up speed, only above all of which the macrovoid-free hollow fibers can be successfully produced from a two-component (one-polymer and one-solvent) system. This observation has been confirmed for hollow fibers spun from different materials such as polysulfone, P84 and cellulose acetate, and may be universally applicable for other polymers. The major mechanisms why these critical parameters can effectively suppress macrovoids have been elaborated. The concept of acceleration of stretch was proposed and a quantitative relationship was observed to relate it with the number of macrovoids per unit area at the critical velocity and critical air gap distance. [Copyright &y& Elsevier]

Abstract: Two types of SPES polymers with different degrees of sulfonation (DS) were synthesized by adjusting the used amount of chlorosulfonic acid and confirmed via elemental analysis and XPS in this work. TGA degradation curves show a difference in the thermal stability between the PES and SPES polymers due to the graft of sulfonic groups. The SPES-H membranes with different DS values were fabricated using a solution-casting method and their gas separation results exhibit a decrease in the permeability and an increase in the selectivity with increasing the degree of sulfonation because of the effect of electrostatic crosslinking. Novel transition metal counterions (i.e. Ag+ and Zn2+) were applied to conduct the ion-exchange treatment of SPES-H polymer samples to change the affinity properties of some specific penetrants in the membrane. EDX data confirm the nearly complete replacement of the proton in the SPES-H sample by metal counterions. The SPES membrane containing Zn2+ exhibits the best gas separation performance in this study due to a combination of the strong electrostatic crosslinking and the affinity between Zn2+ and some specific gas molecules (e.g. O2 and CO2). Compared to flat dense PES membranes, the SPES membrane containing Zn2+ exhibits impressive permselectivity increments of approximately 140%, 86%, 18% and 57% for He/N2, H2/N2, O2/N2 and CO2/CH4 gas pairs, respectively. Both CO2-induced plasticization tests and CO2/CH4 mixed gas measurements have been carried out to examine the applicability of these newly developed SPES membranes with different ion forms in industry. Results prove that this type of membrane material is a promising candidate for hydrogen recovery and natural gas separation. [Copyright &y& Elsevier]

Abstract: A novel PBI/P84 co-polyimide dual-layer hollow fiber membrane has been specifically fabricated through the dry-jet wet phase inversion process, for the first time, for the dehydration pervaporation of tetrafluoropropanol (TFP). Polybenzimidazole (PBI) was chosen as the outer selective layer because of its superior hydrophilic nature and excellent solvent-resistance together with robust thermal stability, while P84 co-polyimide was employed as the inner supporting layer because of its good solvent-resistance and thermal stability. The PBI/P84 membrane exhibits superior water selectivity and relatively high permeation flux. At 60°C, the PBI/P84 dual-layer hollow fiber membrane shows a permeation flux of 332g/(m2 h) and a separation factor of 1990 for a feed solution containing of 85wt% TFP. The preferential water sorption and the significant diffusivity difference between TFP and water are the main causes of high separation factor. However, an increase in feed temperature will greatly increase the permeation flux but seriously decrease the water selectivity. The activation energy data verify that water can preferentially permeate the PBI membrane due to the strong water affinity of PBI and a much smaller molecular size of water. [Copyright &y& Elsevier]

Abstract: We have developed zeolite 5A and 13X embedded P84 co-polyimide membranes with enhanced permeability and selectivity for the pervaporation dehydration of isopropanol (IPA). It is found that a higher annealing temperature, i.e., is more favorable to improve adhesion between zeolite and polymer phase, and to enhance charge transfer complexes (CTCs) formation. FESEM, DSC and gas permeation results show that zeolite 13X has better compatibility with the matrix polymer than zeolite 5A because of stronger interactions between Na cations in zeolite 13X framework and electron acceptor groups of P84 polyimide. The addition of zeolite into the P84 dense membrane improves water sorption capacity and pervaporation separation performance significantly. Owing to the bigger pore size, larger pore volume, higher sorption capacity and better adhesion, the zeolite 13X incorporated P84 membranes has a much higher permeability than zeolite 5A filled membranes. Interestingly, both have comparably high selectivity possibly because of the effects of chain rigidification and partial pore blockage. The addition of zeolite 13X reduces activation energy for water permeation through the membrane but increases that for IPA permeation. However, the addition of zeolite 5A increases activation energy for both water and IPA permeation. Pervaporation permeability increases with zeolite 13X loading, while the selectivity achieves the maximum at 30wt% zeolite 13X loading. When the zeolite 13X loading approaches 40wt%, the adhesion between zeolite and polymer becomes poor and the membrane selectivity declines. A comparison between pervaporation and gas separation results reveals that pervaporation membranes can tolerate a higher degree of interstitial defects than gas separation membranes because of stronger molecular interactions between the feed and the polymer, and the larger molecular size difference between penetrants in the former. [Copyright &y& Elsevier]

Abstract: Dual-layer PES/P84 hollow fiber membranes with a PES–zeolite beta mixed matrix dense-selective layer of 0.55μm have been successfully fabricated in this study by adjusting the ratio of outer layer flow rate to inner layer flow rate during the spinning with the aid of heat-treatment at 235°C and two-step coating. To our best knowledge, this is the thinnest thickness that has ever been reported for dual-layer hollow fiber membranes with the mixed matrix outer layer. The newly developed dual-layer hollow fibers exhibit enhanced O2/N2 and CO2/CH4 selectivity of around 10–20% compared with that of neat PES dense films. Both the polymer chain rigidification and partial pore blockage of zeolite beta may be the main causes for the selectivity increment. The outer surface of wet-spun hollow fibers shows fewer defects than that of hollow fibers spun at 1.5cm air gap probably because of the overlarge elongation stress with an increase in air gap. Scanning electron microscope (SEM) images demonstrate that heat-treatment can effectively reduce or eliminate the voids induced by the unfavorable interaction between polymer and zeolite phases. Differential scanning calorimetry (DSC) results prove that heat-treated dual-layer hollow fiber membranes with a mixed matrix outer layer possess a higher glass transition temperature (T g) over neat PES dense film. The performance of these newly developed dual-layer hollow fiber membranes has also been confirmed in mixed gas tests. [Copyright &y& Elsevier]

Abstract: We have demonstrated that the incorporation of a small amount of polybenzimidazole (PBI) into Matrimid polyimide can significantly stabilize Matrimid''s polymeric chains for high-temperature pervaporation and remarkably enhance the separation factor/selectivity and flux/permeance for the dehydration of tert-butanol/water mixtures. The strong interactions between the carbonyl group of Matrimid and the Nf PBI are the cause for the enhanced chain stability, while the hydrophilic nature of PBI and the close chain packing may be the reasons for the high separation performance. Data from DSC, TMA, DMA and FTIR confirm that the PBI/Matrimid blends studied are miscible in molecular level, but the degree of miscibility apparently decreases with an increase in PBI. It is found that annealing plays an important role on membrane structure and separation performance. Not only can it induce chains rearrangement towards a dense packing and the formation of charge transfer complexes (CTC), but also significantly improve separation factor and selectivity. Pervaporation experiments conducted at room and elevated temperatures all indicate that the blend membrane with 3.55wt.% PBI has the best separation performance, which is consistent with the smallest d-space value measured by XRD. In addition, both DMA and pervaporation experiments verify that the blending of a small amount of PBI with Matrimid can efficiently overcome the plasticization of Matrimid at high temperature operation. [Copyright &y& Elsevier]

Abstract: We have identified that 1,3-cyclohexanebis(methylamine) (CHBA) can be effectively used as a new cross-linking agent for the chemical modification of polyimide membranes. We have also observed that the combined effects of diamino cross-linking and thermal annealing would significantly change the chemical compositions, micro-structure, gas sorption, gas transport properties and plasticization resistance of polyimide membranes. The membrane''s physicochemical changes after diamino cross-linking and thermal annealing were characterized by FTIR-ATR, XPS, gel content, UV, SEM-EDX and TGA and the possible reaction mechanisms during chemical modification and annealing have been proposed. Interestingly, it is found that the chemical reactions between diamino and polyimides are reversible during thermal annealing and the membrane micro-structures are modified and charge transfer complexes (CTCs) are formed during the post-treatments. The gas sorption and gas transport properties of membranes before and after modifications are reported and discussed. The gas sorption concentration continuously decreases with an increase in the degree of cross-linking and the subsequent thermal annealing. Experimental results illustrate that thermal annealing not only improves CO2/CH4 selectivity of the cross-linked membranes but also greatly enhances the plasticization resistance by the formation of CTCs. The critical plasticization pressure is significantly improved from about 300psia of the original samples to more than 720psia of the cross-linked and 200°C thermal treated samples. Based on the experimental results, a novel approach to enhance plasticization resistance of polyimide membranes by means of diamino cross-linking and followed by thermal annealing is elucidated. [Copyright &y& Elsevier]

Abstract: Asymmetric membranes with superior selectivity and relatively high flux for pervaporative dehydration of isopropanol (IPA) were successfully developed from a novel material P84 co-polyimide by a dry-wet phase inversion method. The best separation performance has a flux of 432g/m2 h and a separation factor of 3508 at 60°C for a feed stream containing 85wt.% IPA. The membrane shows imperceptible degree of swelling even at high feed water concentrations. Polymer dopes with or without non-solvent additives were studied and yielded different membrane skin layer structure. It is found that heat treatment at elevated temperatures can effectively enhance membrane performance because it not only smoothens membrane skin layer roughness but also reduces membrane defects and the d-space value of polymeric chains as indicated by XRD, FESEM, AFM and gas permeation tests. However, asymmetric P84 co-polyimide membranes’ performance was influenced by the history of thermal cycling. The testing cycle from 100°C to 60°C has a more stable performance compared with that from 60°C to 100°C, indicating that a conditioning at a higher temperature is recommended. Thickness-dependent pervaporation performance was observed when investigating dense P84 membranes, and the pervaporation data from asymmetric P84 membranes are consistent with this observation. [Copyright &y& Elsevier]

Abstract: A high T g material, which is 6FDA-durene (T g: 425 °C) polyimide, is applied to study the T g’s effect on the evolution of physicochemical and transport properties of membranes from polymeric, intermediate to carbon stages. T g greatly affects the configurational organization of membranes during pyrolysis especially at the intermediate stage (400–500 °C) and finally influences the pore size and pore size distribution of carbon membranes, which has been mostly ignored by the previous studies. The physicochemical and transport properties in various membrane stages are thoroughly characterized by TGA-FTIR, FTIR-ATR, XRD, thickness and gas transport tests. It is found that the membranes derived from the high T g polyimides show a significant increase in chain mobility and physicochemical development in the intermediate stage. Interestingly, the gas permeability with annealing temperature show double peaks for medium-size gases such as O2, N2 and CH4, and single peaks for light gases such as He, H2 and CO2. In addition, the ideal selectivity generally shows double minimum values with annealing temperature. These phenomena may arise from the fact that significant physicochemical changes take place around the T g, while the maximum degradation rate occurs at temperatures 70–100 °C above T g. As compared with the trade-off line [L.M. Robeson, J. Membr. Sci. 62 (1991) 165], the temperature for membranes derived from the high T g polyimide to surpass the trade-off line occurs around 450 °C. This temperature is just fall on the intermediate-stage temperature range. The resultant carbon membranes pyrolyzed with 1 °C/min heating rate show better transport performance at low pyrolysis temperatures than those pyrolyzed with 3 °C/min heating rate. However, when the pyrolysis temperature is elevated to 800 °C, the resultant carbon membranes pyrolyzed by different protocols all show similar and superior performance for gas separation. [Copyright &y& Elsevier]

Abstract: The polyethersulfone (PES)-zeolite 3A, 4A and 5A mixed matrix membranes (MMMs) were fabricated with a modified solution-casting procedure at high temperatures close to the glass transition temperatures (T g) of polymer materials. The effects of membrane preparation methodology, zeolite loading and pore size of zeolite on the gas separation performance of these mixed matrix membranes were studied. SEM results show the interface between polymer and zeolite in MMMs experiencing natural cooling is better (i.e., less defective) than that in MMMs experiencing immediate quenching. The increment of glass transition temperature (T g) of MMMs with zeolite loading confirms the polymer chain rigidification induced by zeolite. The experimental results indicate that a higher zeolite loading results in a decrease in gas permeability and an increase in gas pair selectivity. The unmodified Maxwell model fails to correctly predict the permeability decrease induced by polymer chain rigidification near the zeolite surface and the partial pore blockage of zeolites by the polymer chains. A new modified Maxwell model is therefore proposed. It takes the combined effects of chain rigidification and partial pore blockage of zeolites into calculation. The new model shows much consistent permeability and selectivity predication with experimental data. Surprisingly, an increase in zeolite pore size from 3 to 5Å generally not only increase gas permeability, but also gas pair selectivity. The O2/N2 selectivity of PES-zeolite 3A and PES-zeolite 4A membranes is very similar, while the O2/N2 selectivity of PES-zeolite 5A membranes is much higher. This implies the blockage may narrow a part of zeolite 5A pores to approximately 4Å, which can discriminate the gas pair of O2 and N2, and narrow a part of zeolites 3A and 4A pores to smaller sizes. It is concluded that the partial pore blockage of zeolites by the polymer chains has equivalent or more influence on the separation properties of mixed matrix membranes compared with that of the polymer chain rigidification. [Copyright &y& Elsevier]

Abstract: A linear aliphatic diamine, ethylenediamine (EDA), for the first time, was used to cross-link polyimides and the EDA modified polyimides were further thermally treated at different conditions to enhance anti-plasticization characteristics. The physicochemical properties of unmodified and modified polyimides were characterized by XPS, FTIR–ATR, DSC, UV and XRD. The results of XPS and FTIR–ATR show that EDA can effectively cross-link polyimides. DSC data indicate that EDA cross-linked polyimides experience significant changes during thermal treatment. Prolonging the cross-linking time decreases d-space between polymer chains. The coupling effects of EDA induced cross-linking and thermal annealing accelerates charge transfer complexes (CTCs) formation, which densifies polyimide membrane structure. As a result, the gas transport properties of modified polyimides generally show reduced permeability and enhanced selectivity during the cross-linking and thermal annealing. CO2 plasticization tests on the resultant membranes indicate that the coupling effects of EDA cross-linking and thermal annealing improve the plasticization resistance from around 300psia to more than 720psia, which may be attributed to the effective formation of CTCs. Mixed gas tests demonstrate that the CO2/CH4 selectivity of the EDA cross-linked polyimides was higher in mixed gas tests than that in pure gas tests because of the strong attractions between CO2 and secondary amines. This elucidates why the modified polyimides have better performance in actual separation situations. [Copyright &y& Elsevier]

Abstract: In this study, wholly aromatic main chain copoly(ester–amide)s containing tetrafluorophthalic acid (TFPA-ortho), tetrafluoroisophthalic acid (TFIA-meta) and tetrafluoroterephthalic acid (TFTA-para) were synthesized to study the effects of kinks on the formation of mesophase and crystal texture. The effects of kink moieties on these copoly(ester–amide)s were also investigated by the ‘RIS’ metropolis Monte Carlo simulation. Computational results indicate that all systems form thermotropic liquid crystalline polymers (LCPs) because the calculated persistence ratios for the ortho-, meta- and para-linkage systems are 6.51, 7.64 and 10.49, respectively. Both simulation and experimental results agree that ABA/AAA/TFTA (para) system has the greatest tendency to yield the liquid crystal (LC) phase due to its greater persistence ratio, linearity, and chain stiffness. The incorporation of TFPA (ortho) moiety can effectively reduce 30% of the molar stiffness function and 23% of the persistence length as compared to those of the TFTA (para) system. Yet, the ABA/AAA/TFPA system may form LC texture because of its large, rigid, disk-like TFPA moiety and the crankshaft structure induced by cis-configuration between AAA and TFPA moieties. The meta-linkage system has a slower LC growth rate, but it has a much higher tendency to form LC than the ortho-linkage. Both meta- and para-linkage systems have close critical ABA content to form LC texture. When comparing the requirements of critical ABA content between ABA/AAA/TFIA and ABA/AAA/IA (isophthalic acid) systems, we surprisingly observed that the former has a much lower critical ABA content than the latter. The four fluorine substituents of TFIA definitely help chain rigidity and stabilize the LC mesogens. Even though these fluorinated moieties exhibit different conformations and configurations, they yield similar end-stage crystalline structure. The spherulites are grown from the dark brushes around a single disclination, indicating that these are the lowest energy for crystallization. [Copyright &y& Elsevier]

Amic acid compound namely bisphthalamic acid of 2, 2'-dimethyl-4, 4'-diaminobiphenyl (amic acid) and its ionic salt with 3-(dimethylamino)propyl methacrylate (amic acid salt) were synthesized and characterized by FT-IR, mass spectroscopy, NMR and DSC. Effect of temperature and water content on these compounds was studied by1H-NMR and potentiometric titration. In the absence of added water, both amic acid and its ionic salt had undergone imidization followed by hydrolysis, which was attributed to the water formed as a result of an initial imidization reaction. Polyamic acid (PAA) was synthesized by reacting 4, 4'-oxydiphthalic anhydride and 2, 2'-dimethyl 4, 4'-diaminobiphenyl (m-tolidine) in N-methyl-2-pyrrolidone, which was then reacted with 3-(dimethylamino)propyl methacrylate to obtain PAS. Their storage stabilities were studied by monitoring their bulk viscosities and acid numbers as a function of time and temperature. PAS was found to be less stable than PAA. Similar observations were made for amic acid compounds. PAA and PAS showed two-step thermal degradation in air and nitrogen. [ABSTRACT FROM AUTHOR]

To expand industrial utilizations, membranes with fast transport of organic solvents and precision molecular separation, along with strong chemical stability, have great potential for minimizing energy consumption in separation processes. In this study, novel amino-cyclodextrin organic solvent nanofiltration (OSN) membranes containing P84 polymer were successfully fabricated using amino-cyclodextrin and amino-5-guanidinopentanoic acid (DL-A) as monomers through a two-step green modification process. The resulting membranes exhibit high stability in harsh organic solvents, such as dimethylsulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP), with a weight loss of less than 5 % after 30 days of immersion. These membranes also demonstrate rapid solvent transport for both polar solvents, such as methanol (86.56 L m−2 h−1 bar−1), and nonpolar solvents, such as n-hexane (48.97 L m−2 h−1 bar−1), along with high dye rejections. Additionally, the membranes possess rigid nanopores structures and consistent rejections across different pressures and solute concentrations. Most importantly, the newly synthesized amino-cyclodextrin OSN membranes are capable of separating molecules based on their 3D structures, particularly those with relatively similar molecular weights. Comparing to those reported cyclodextrin-based membranes, the newly developed amino-cyclodextrin OSN membranes show significant improvements in permeance for both polar and nonpolar organic solvents, while maintaining comparable dye rejection capabilities. The combination of fast solvent transport, excellent chemical stability, and shape selectivity makes these membranes highly promising for high-performance molecular separation in various industrial applications. [Display omitted] • A novel P84 co-polyimide organic solvent nanofiltration (OSN) membrane incorporated with amino-beta-cyclodextrin, was prepared. • The amino-β-cyclodextrin-based membrane has faster solvent transport for both polar and nonpolar solvents. • The amino-β-cyclodextrin-based membrane exhibits excellent stability in harsh organic solvents. • The newly synthesized amino-cyclodextrin OSN membrane demonstrates excellent shape selectivity to solutes with similar molecular weights. [ABSTRACT FROM AUTHOR]

Abstract: An assortment of Ultem/PIM-1 polymer blends was prepared and their transport properties to a series of gases were studied. Good dispersion between the PIM-1 and Ultem phases was found when the PIM-1 loading was low (<20wt%) or high (>90wt%). A slight shift of T g was observed when the PIM-1 loading increased from 0wt% to 50wt%, suggesting likely partially miscibility. The molecular-level interactions were further confirmed by the FTIR and XRD data, where shifts of peaks were detected at several compositions. Gas transport properties of pure gases including He, N2, O2, CH4, CO2 for all polymer blends and mixed gases including CO2/CH4 (50/50) and CO2/N2 (50/50) gas pairs for Ultem/PIM-1 (90:10) and Ultem/PIM-1 (80:20) blends were explored. Considerable increments in gas permeability were observed by adding only 5 or 10wt% PIM-1 without much compromising gas pair selectivity, i.e., the CO2 permeability increased impressively over 47% and 167%, respectively, compared with the pristine Ultem. When comparing the gas permeation properties with the predictions from semi-logarithm and Maxwell equations, they follow nicely with the semi-logarithm addition when the PIM-1 loadings are low (<20wt%), indicting relatively homogenous blends at these compositions, while the transport properties match closely with the Maxwell prediction at high PIM-1 loadings (>90wt%) due to the good dispersion of Ultem inside PIM-1. This study opens up the potential of employing PIM-1 as an organic filler to improve the permeability of low permeable materials for other industrial membrane applications. [Copyright &y& Elsevier]

The effects of nitrogen and air purge during thermal rearrangement of an ortho-functional polyamide (o-PA) and an ortho-functional polyimide (o-PI) towards a polybenzoxazole (PBO) structure have been investigated in terms of physicochemical changes and gas transport properties. The o-PA polymer was prepared from 2,2-bis(3-amino-4-hydroxyphenyl) hexafluropropane (BisAPAF) and 4,4′-biphenyl-dicarbonyl chloride (BPDC) while the o-PI polymer was derived from 4,4-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 3,3′-dihydroxybenzidine (HAB). Experimental results show that the purge environment for the conditions used does not affect the thermal rearrangement of the o-PA film but significantly affects the thermal conversion of the o-PI film. Nearly identical chemical structures and pure gas permeability values are observed for o-PA films thermally treated at 300 °C under air or N2. These properties become different in the o-PA films treated at 425 °C, which is presumed to be attributed to the influence of oxygen on the thermal stability of the derived PBO and probably the various degrees of thermal crosslinking reaction induced at a high temperature. The o-PI film was thermally rearranged at 425 °C because its thermal conversion takes place at a higher temperature range of 300 °C–450 °C. The o-PI film thermally rearranged in air exhibits improved gas permeation properties but significantly deteriorated mechanical properties. The air purge interrupts the thermal conversion of the ortho-functional imide to benzoxazole by oxidatively degrading the imide structure and forming the imine structure. As a result, both polymer structure and film properties change. [ABSTRACT FROM AUTHOR]

Abstract: The advantages of the implementation of dual-layer hydrophobic–hydrophilic hollow fiber membranes for membrane distillation (MD) have been highlighted in this work. The effects of incorporating methanol as a non-solvent additive and self-synthesized fluorinated silica (FSi) particles as a hydrophobic modifier on the resultant membrane morphology and MD performance were investigated. Employing a 3.5wt% sodium chloride solution at 80°C, the highest direct contact membrane distillation (DCMD) flux of 83.40±3.66kg/(m2 h) and separation factor higher than 99.99% were attained for the membrane spun with methanol additive. Moreover, the stability of the dual-layer hydrophobic–hydrophilic hollow fiber membrane has been demonstrated through continuous DCMD experiments for 5 days. The separation factor was maintained higher than 99.99% for the membrane spun with methanol additive, verifying the suitability of the dual-layer hydrophobic–hydrophilic hollow fiber membrane configuration for desalination processes. The morphological transformation of the outer membrane surface from a porous agglomerated globule structure into a denser interconnected globule structure may be accounted for by the stability improvement of the membrane spun with methanol additive. On the other hand, it was found that an enhanced hydrophobicity of the membrane spun with FSi particles did not result in an improvement of the membrane stability. The existence of the hydrophilic hydroxyl group on the FSi particle surface may favor the occurrence of membrane wetting. [Copyright &y& Elsevier]

Abstract: The thermally induced structure transformation and polymer chain rearrangement of a thermally rearranged (TR) material for gas separation has been explored in this work. A tremendous enhancement as high as 215 folds in CO2 permeability has been achieved by converting the pristine poly(hydroxyamide amic acid) (PHAA) to the final polybenzoxazole (PBO) via thermal cyclization at 400 °C for 2 h. The evolution of the pristine polymer PHAA derived from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluropropane (BisAPAF) and trimellitic anhydride chloride (TAC) by thermal treatment from 130 °C to 400 °C has been examined by various characterization techniques including elemental analysis, TGA, TGA-IR, DSC, ATR-FTIR, XPS, XRD and Positron Annihilation Lifetime Spectroscopy (PALS). The stepwise cyclization process commences with cyclodehydration followed by cyclodecarboxylation. At the first step, PHAA transforms to poly(imide benzoxazole) (PIBO) up to 300 °C, while at the second step, the final structure of PBO is formed at 400 °C. Following the changes in the cyclization process, gas transport properties also show the stepwise changes. The significant enlargements of polymer inter-chain distance and free volume cavity radius provide the fundamental understanding for the changes of gas transport properties at the molecular level. [Copyright &y& Elsevier]

Abstract: The design and engineering of membrane structure that produces low salt leakage and minimized internal concentration polarization (ICP) in forward osmosis (FO) processes have been explored in this work. The fundamentals of phase inversion of cellulose acetate (CA) regarding the formation of an ultra-thin selective layer at the bottom interface of polymer and casting substrate were investigated by using substrates with different hydrophilicity. An in-depth understanding of membrane structure and pore size distribution has been elucidated with field emission scanning electronic microscopy (FESEM) and positron annihilation spectroscopy (PAS). A double dense-layer structure is formed when glass plate is used as the casting substrate and water as the coagulant. The thickness of the ultra-thin bottom layer resulted from hydrophilic–hydrophilic interaction is identified to be around 95nm, while a fully porous, open-cell structure is formed in the middle support layer due to spinodal decomposition. Consequently, the membrane shows low salt leakage with mitigated ICP in the FO process for seawater desalination. The structural parameter (S t) of the membrane is analyzed by modeling water flux using the theory that considers both external concentration polarization (ECP) and ICP, and the S t value of the double dense-layer membrane is much smaller than those reported in literatures. Furthermore, the effects of an intermediate immersion into a solvent/water mixed bath prior to complete immersion in water on membrane formation have been studied. The resultant membranes may have a single dense layer with an even lower S t value. A comparison of fouling behavior in a simple FO-membrane bioreactor (MBR) system is evaluated for these two types of membranes. The double dense-layer membrane shows a less fouling propensity. This study may help pave the way to improve the membrane design for new-generation FO membranes. [Copyright &y& Elsevier]

Abstract: This article describes the research study on exploitation of polymer blending technology and dual-layer hollow fiber spinning process for the fabrication of a novel class of high performance gas separation membranes. The specific functional material employed for this purpose is a polymer blend constructed of the interpenetrated networks of PBI and Matrimid. It is within the scope of this study to unravel the effect of various key parameters on the microstructural evolution, transport properties and separation performance of the developed hollow fiber membranes. The resultant membranes possess desirable morphological and microstructural characteristics, particularly at the outer functional layer, and are free from any delamination at the interface. Analysis of the membranes suggests that both increase in the air-gap distance and application of elongational drawing have promoting effects on the membranes’ permeance. Results also indicate that membranes with H2/CO2 selectivities as high as 11.11 () can be obtained through spinning at sufficiently large air-gap distance. On the other hand, inducing the elongational drawing to the nascent fibers offers membranes with CO2/CH4 selectivities as high as 41.81 (). Therefore, either of these approaches can be employed for desirable tuning of the membrane''s properties to suit the specific application. The variation in outer dope flow rate is identified as another effective technique amenable for tailoring the properties of the hollow fiber membranes. Other findings also show the effectiveness of chemical modification for further enhancing the H2/CO2 separation performance of the membranes. Membranes developed in this research study exhibit a very good resistance toward CO2-induced plasticization and have viable potentials for various gas separation applications including hydrogen purification and natural gas separation. [Copyright &y& Elsevier]

Abstract: The objective of this study is to investigate a combination of ion exchange membranes and free-flow isoelectric focusing (FFIEF) technology for high-selectivity and high-flux protein separation, in which ion exchange membranes are used as the separation media. An FFIEF device has been designed and extensive experiments have been conducted to prove its effectiveness in enhancing the protein separation performance. Three types of membranes were employed in this work and they were commercial microfiltration (MF) ion exchange membranes, commercial neutral UF cellulose membranes, and home-made ultrafiltration sulfonated polysulfone (UF SPSf) ion exchange membranes. The protein separation results show that the home-made UF SPSf membranes have the superior selectivity and flux to other membranes. This is due to the fact that a stable pH gradient across the membranes as well as the interaction between the protein molecules and membrane surface plays an important role in the high-performance protein separation. By applying a semi-batch separation process and optimizing various experimental conditions, a high-purity () and concentrated target protein is obtained at the permeation side of the home-made UF SPSf membranes with a high flux. [Copyright &y& Elsevier]

Abstract: This study demonstrates the successful implications of blending technique cum chemical modification for the fabrication of high performance polymeric membranes for gas separation applications. The effect of variation in composition on miscibility and microstructure, gas permeability and selectivity of blend membranes is investigated. It is found that augmentation in PBI composition results in enhancement in gas separation performance of membranes which is attributed mainly to the effect of diffusivity selectivity. Analysis of the microstructure of membranes confirms the variations in chain packing density, d-spacing and segmental mobility of polymer chains as a result of blending. Separation performance of membranes is further ameliorated through chemical modification of blend constituents. Modification of PBI phase with p-xylene dichloride brings about slight improvements in selectivity performance, especially for H2/CO2 and H2/N2. In contrast, the selectivity of membranes is improved significantly after cross-linking of Matrimid phase with p-xylene diamine. The results indicate that higher tendency of Matrimid toward cross-linking reaction contributes more in controlling the transport properties of membranes through diffusion coefficient by increase in chain packing density and diminishing the excess free volumes. Results obtained in this study reveal the promising features of developed membranes for gas separation applications with great potential for hydrogen separation and purification on industrial scale. [Copyright &y& Elsevier]

Abstract: We have discovered two new miscible polymer blend systems, namely, Torlon® 4000T with Matrimid® 5218 and Torlon 4000T with polybenzimidazole (PBI). Both Matrimid 5218 and PBI are miscible at a molecular level with Torlon 4000T over the whole composition range as confirmed by microscopy, DSC, FTIR and DMA. DSC and DMA studies show the existence of a single glass transition in each blend. The T g-composition curve of Torlon/Matrimid blend system forms a sigmoid curve as a function of composition, while the T g-composition curve of the Torlon/PBI blend system is double parabola-like. FTIR spectra show the existence of hydrogen-bonding interactions in these two polymer blend systems. [Copyright &y& Elsevier]

Abstract: The purpose of this short note is to report, for the first time, the effect of elongational drawing on nano-particle distribution in hollow fiber membranes. The results shown in the short manuscript have multiple applications and impact for the fundamental understanding and development of hybrid solid composite fibers and mixed matrix hollow fiber membranes. nano-particles with sizes around 300–400nm are doped directly into the polyimide solution before spinning. The evolution of membrane morphology and nano-particle distribution has been investigated by SEM-EDX with an increase in elongational draw ratio. It is found that nano-particle distribution across the membrane wall varies from convex to concave profiles depending on elongational draw ratio. In other words, high elongational draw ratios result in particles moving radially inward to the bore fluid side and radially outward to the outer coagulant side. Therefore, one can control membrane morphology, particle distribution, and separation performance via the manipulation of elongational draw ratio with the aid of shear stress induced by dope flow within the spinneret and die swell out of the spinneret. [Copyright &y& Elsevier]

• Glycidol and δ-gluconolactone were grafted onto hyper-branched polyethyleneimine. • HPEI-Diol and HPEI-Gluconamide were used as the boron chelating polymers. • HPEI-Gluconamide polymer was found to have the highest boron retention efficiency. • Boron rejection of HPEI-Gluconamide was obtained to be around 94% at pH 4. Boron removal is an important separation process which requires an excessive operational cost owing to the complex nature of boron in aqueous solutions. Polymer-enhanced ultrafiltration (PEUF) has been widely adopted for boron separation due to the low operational cost and high separation productivity. In this study, novel hydroxyl-terminated poly(ethyleneimine) (HPEI) polymers; namely, HPEI-Diol and HPEI-Gluconamide, were designed and synthesized as the boron chelating polymers. A polyphenylenesulfone (PPSU) UF membrane was fabricated to have a pure water permeance of around 82.8 L.m−2.h−1.bar−1 with a molecular weight cut off (MWCO) of around 128 kDa. The boron rejection coefficient of the pristine PPSU UF membrane was as low as 6.38% which was attributed to the negatively charged surface of the PPSU membrane. Introducing either HPEI or HPEI-Diol polymer into the boron feed solution increased the boron rejection of the UF process to around 45%. Meanwhile, the HPEI-Gluconamide polymer was found to possess the highest boron retention efficiency with a boron rejection of around 94% at pH 4, which may be ascribed to the higher number of grafted hydroxyl groups. [ABSTRACT FROM AUTHOR]

This study explores the potential use of sulfolane, a green and sustainable solvent, as an alternative to toxic solvents in the fabrication of high-performance nanofiltration membranes. A comparison of Hansen solubility parameter (HSP) with N -methyl-2-pyrrolidone (NMP) indicates that sulfolane is a "poor" solvent for the sulfonated polyphenylenesulfone (sPPSU) polymer, which results in a lower critical polymer concentration (CPC) required to produce a macrovoid-free membrane structure. Moreover, the addition of a low molecular weight hyperbranched polyethyleneimine (HPEI) of MW = 800 g/mol as a crosslinker enhances the mechanical rigidity of the membranes without affecting the pore structure required for retaining salts from dye/salt mixtures, enabling practical applications in wastewater treatment. Notably, the membranes demonstrate exceptional dye/salt separation performance with a separation factor S D y e / S a l t of up to 69.32, even for low molecular weight dyes as low as 268 g/mol (i.e., a Disperse blue 1 and Na 2 SO 4 mixture). To the best of our knowledge, this is the lowest MW dye ever tested for dye/salt separation. The membranes also show good antifouling capability over an extended period of use. Literature comparison shows that the sPPSU/sulfolane membrane crosslinked with HPEI800 for 60 min, referred to as sPSlf-c60, exhibits superior dye/salt separation performance, indicating their potential for the treatment of textile wastewater effluents. [Display omitted] • A green solvent, sulfolane, was successfully employed to substitute a toxic one. • Hansen solubility parameter (HSP) is crucial in determining polymer–solvent matrix. • HSP and critical polymer concentration analyses result in macrovoid-free membranes. • A green and simple modification process was done by using a low MW HPEI polymer. • Excellent dye/salt separation towards multiple dye and salt mixtures was achieved. [ABSTRACT FROM AUTHOR]

The lack of effective membranes greatly hinders the use of pressure retarded osmosis (PRO) to harvest renewable osmotic energy. In comparison to the flat sheet and inner-selective hollow fiber configurations, the development of outer-selective hollow fiber membranes is much slower although it may be more attractive for real PRO applications. This study demonstrates that tuning the water content in polymer dopes can be an effective means to simultaneously enhance the mechanical robustness and water transport properties, boosting the PRO performance of outer-selective thin-film composite (TFC) hollow fiber membranes. Fundamental properties of polymer dopes with different water content and their influence on the hollow fiber supports as well as resultant TFC membranes were systematically investigated. With a low water content of 2 wt% in the polymer dope, the newly developed TFC membrane not only has the smallest structural parameter, highest toughness, and largest water permeability among all membranes studied but also displays an impressive peak power density of 10.05 W/m 2 at 22 bar using 1 M NaCl and DI water as feeds. To our best knowledge, this is the highest power density of outer-selective TFC PRO hollow fiber membranes reported in the literature. Mathematical models predict that approximately 25% performance increase can be further achieved if the external concentration polarization (ECP) effect is minimized. This study may provide useful insights to design high performance outer-selective TFC hollow fiber membranes for osmotic power generation. [ABSTRACT FROM AUTHOR]

Polymers of intrinsic microporosity, specifically PIM-1, have attracted significant attention for gas separation due to its relatively high permeability and reasonably good selectivity. Although few studies evaluated the potential of PIM-1 in pervaporation, their dehydration performance was not impressive because of low selectivity. In this work, we aim to develop a simple but effective approach to enhance the selectivity of PIM-1 while preserving its high permeability for pervaporation dehydration through blending it with different polyimides. The miscibility characteristics of the newly developed membranes in terms of free energy of mixing are examined by molecular simulation while the degrees of swelling in solvents and the changes in interstitial space are characterized by sorption analyses and X-ray diffraction (XRD), respectively. By optimizing the blend ratio, a simultaneously good flux and separation factor have been achieved. For example, the Matrimid membrane containing 20 wt% hydrolyzed PIM-1 (hPIM-1) possesses a high flux of exceeding 47.8 g/m 2 h and a separation factor of more than 5000 for the dehydration of 1-butanol. This work may provide an inspiration of exploring the potential of gas separation membranes for pervaporation applications. [ABSTRACT FROM AUTHOR]