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The organic solvent forward osmosis (OSFO) process provides unprecedented opportunities for simultaneous concentration of active pharmaceutical ingredients (APIs) and recovery of organic solvents. However, the fabrication of membranes with precise sieving effects that can realize high solvent permeance and minimize reverse salt flux remains an enormous challenge. Through engineering the functionality of artificial subnanochannels, here, we report a metal–organic framework (MOF)-based membrane with ion-selective subnanochannels to achieve excellent OSFO performance, which overcomes the trade-off between solvent permeance and reverse salt flux. The sulfonated NH2-UiO-66 (SA-NH-UiO-66) composite membranes effectively inhibit the conduction of LiCl in aqueous and organic solutions driven by a potential difference, with conductivities of up to 2 orders of magnitude lower than that of the porous polymer substrate, which is mainly attributed to the high-density sulfonic acid groups that offer negative charges and narrow down the channel size of the MOF membrane. Moreover, the SA-NH-UiO-66 membranes have well-defined pore sizes and high porosity, showing a methanol permeance of 40.2 LMH, a low reverse salt flux of 2.1 gMH, and a 99% rejection of APIs under the osmotic pressure in the OSFO process, which surpass those of state-of-the-art polymer membranes. This work sheds light on developing artificial ion-selective subnanochannel-based membranes for sustainable separation in the pharmaceutical industry. [ABSTRACT FROM AUTHOR]

Separating xylene isomers is a challenging task due to their similar physical and chemical properties. In this study, we developed a molecular sieve incorporating a reduced graphene oxide (rGO) membrane for the precise differentiation of xylene isomers. We fabricated GO membranes using a vacuum filtration technique followed by thermal-induced reduction to produce rGO membranes with precisely controllable interlayer spacing. Notably, we could finely tune the interlayer spacing of the rGO membrane from 8.0 to 5.0 Å by simply varying the thermal reduction temperature. We investigated the reverse osmosis separation ability of the rGO membranes for xylene isomers and found that the rGO membrane with an interlayer spacing of 6.1 Å showed a high single component permeance of 0.17 and 0.04 L m -2 h -1 bar -1 for para- and ortho -xylene, respectively, exhibiting clear permselectivity. The separation factor reached 3.4 and 2.8 when 90:10 and 50:50 feed mixtures were used, respectively, with permeance 1 order of magnitude higher than that of current state-of-the-art reverse osmosis membranes. Additionally, the membrane showed negligible permeance and selectivity decay even after continuous operation for more than 5 days, suggesting commendable membrane resistance to solvent swelling and operating pressure.

An efficient separation technology involving ammonia (NH 3 ) and carbon dioxide (CO 2 ) is of great importance for achieving low-carbon economy, environmental protection, and resource utilization. However, directly separating NH 3 and CO 2 for ammonia-based CO 2 capture processes is still a great challenge. Herein, we propose a new strategy for selective separation of NH 3 and CO 2 by functional hybrid membranes that integrate polyimide (PI) and ionic liquids (ILs). The incorporated protic IL [Bim][NTf 2 ] is confined in the interchain segment of PI, which decreases the fractional free volume and narrows the gas transport channel, benefiting the high separation selectivity of hybrid membranes. At the same time, the confined IL also provides high NH 3 affinity for transport channels, promoting NH 3 selective and fast transport owing to strong hydrogen bonding interaction between [Bim][NTf 2 ] and NH 3 molecules. Thus, the optimal hybrid membrane exhibits an ultrahigh NH 3 /CO 2 ideal selectivity of up to 159 at 30 °C without sacrificing permeability, which is 60 times higher than that of the neat PI membrane and superior to the state-of-the art reported values. Moreover, the introduction of [Bim][NTf 2 ] also reduces the permeation active energy of NH 3 and reverses the hybrid membrane toward "NH 3 affinity", as understood by studying the effect of temperature. Also, NH 3 molecules are much easier to transport at high temperature, showing great application potential in direct NH 3 /CO 2 separation. Overall, this work provides a promising ultraselective membrane material for ammonia-based CO 2 capture processes.

Nanoporous carbon nanomembranes (CNMs) created by self-assembled monolayers ideally combine a high water flux and precise ion selectivity for molecular separation and water desalination. However, their practical implementation is often challenged by the availability of large epitaxial substrates, limiting the membrane up-scaling. Here, we report a scalable synthesis of CNMs from poly(4-vinylbiphenyl) (PVBP) spin-coated on SiO 2 /Si wafers. Electron irradiation of the amorphous PVBP molecular layers induces the formation of a continuous membrane with a thickness of 15 nm and a high density of subnanometer pores, providing a water permeance as high as 530 L m -2 h -1 bar -1 , while repelling ions and molecules larger than 1 nm in size. A further introduction of a reinforced porous block copolymer layer enables the fabrication of centimeter-scale CNM composites that efficiently separate organic dyes from water. These results suggest a feasible route for large-scale nanomembrane fabrication.

Subnanometer interlayer space in graphene oxide (GO) laminates is desirable for use as permselective membrane nanochannels. Although the facile modification of the local structure of GO enables various nanochannel functionalizations, precisely controlling nanochannel space is still a challenge, and the roles of confined nanochannel chemistry in selective water/ion separation have not been clearly defined. In this study, macrocyclic molecules with consistent basal plane but varying side groups were used to conjunct with GO for modified nanochannels in laminates. We demonstrated the side-group dependence of both the angstrom-precision tunability for channel free space and the energy barrier setting for ion transport, which challenges the permeability-selectivity trade-off with a slightly decreased permeance from 1.1 to 0.9 L m -2 h -1 bar -1 but an increased salt rejection from 85% to 95%. This study provides insights into the functional-group-dependent intercalation modifications of GO laminates for understanding laminate structural control and nanochannel design.

This study systematically investigated phenol removal from water and phenol fouling of membranes in forward osmosis (FO) using thin-film composite (TFC) polyamide and silver chloride (AgCl) mineralized thin-film composite (MTFC) membranes. The influence of operating parameters (membrane orientation, phenol concentration, draw solution concentration, pH, and ionic strength) on phenol rejection and phenol adsorption to the membrane was investigated to elucidate the phenol transport behaviors in the FO process. Overall, phenol rejection improved with increased draw solution concentration or feed solution pH. At a feed solution pH of 11, TFC membranes exhibited their highest phenol rejection of 97.0% and MTFC membranes exhibited their highest phenol rejection of 98.8%. Phenol adsorption on the membrane surface may be related to the solute hydrophobic character, electrostatic interaction, and reverse salt diffusion. Six-hour fouling experiments show that the phenol fouling of FO membranes is reversible and easily cleaned by physical flushing. Additionally, compared with the TFC membranes, the MTFC membranes have an increased flux and rejection for phenol in FO. [ABSTRACT FROM AUTHOR]

Membrane separation technologies have shown a brilliant potential in the field of water treatment and biotechnology and pharmaceutical industries. Surface biofouling featuring inherent complexity and hard treatability severely impedes the development of polymeric membranes, posing a significant decline in their performance and lifespan. Silver nanoparticles (Ag NPs) offer the best solutions to inhibit bacteria growth and proliferation, whereas it remains challenging to confer a long-term bactericidal ability to membranes. In this study, we developed a novel approach to in situ anchor Ag NPs on membrane surface by implementing natural clay (halloysite nanotubes, HNTs) as an interlayer. The combination of well-aligned HNTs and nanosilver endows the membranes with high dye retention, salt permeation, and water permeability. Most importantly, this novel membrane exhibited a strong, long-lasting antibacterial behavior toward Escherichia coli. This strategy furnishes a new pathway in the rational assembly of Ag/HNTs antibacterial layer for potent dye/salts fractionation. [ABSTRACT FROM AUTHOR]

To reduce unwanted variation in the passage speed of DNA through solid-state nanopores, we demonstrate nanoscale preconfinement of translocating molecules using an ultrathin nanoporous silicon nitride membrane separated from a single sensing nanopore by a nanoscale cavity. We present comprehensive experimental and simulation results demonstrating that the presence of an integrated nanofilter within nanoscale distances of the sensing pore eliminates the dependence of molecular passage time distributions on pore size, revealing a global minimum in the coefficient of variation of the passage time. These results provide experimental verification that the inter- and intramolecular passage time variation depends on the conformational entropy of each molecule prior to translocation. Furthermore, we show that the observed consistently narrower passage time distributions enables a more reliable DNA length separation independent of pore size and stability. We also demonstrate that the composite nanofilter/nanopore devices can be configured to suppress the frequency of folded translocations, ensuring single-file passage of captured DNA molecules. By greatly increasing the rate at which usable data can be collected, these unique attributes will offer significant practical advantages to many solid-state nanopore-based sensing schemes, including sequencing, genomic mapping, and barcoded target detection. [ABSTRACT FROM AUTHOR]

Wastewaters with high concentrations of organic pollutants pose a great challenge for membrane filtration due to their severe fouling propensity. In this study, a hydrogel forward osmosis (FO) membrane is explored for treating wastewaters of high concentration organic pollutants. This FO membrane has an ultrathin hydrogel selective layer, which is highly hydrophilic (water contact angle as low as 18°) and smooth (surface roughness <5 nm). Investigated with typical organic foulants (protein, alginate, humic acid, and oil) of high concentration (2000-20 000 mg/L), this hydrogel FO membrane exhibits remarkably superior antifouling capability, with its water flux decline ratio lower than a quarter that of commercial FO membrane under identical experimental conditions. The foulants on hydrogel membrane surface can be easily removed by simple physical cleaning without any chemical usage. At the same time, this hydrogel FO membrane achieves ~2 times higher separation efficiency than commercial FO membrane in terms of specific water flux (JW/JS). The antifouling capability and separation efficiency of this FO membrane can be flexibly tailored during selective layer fabrication process. This study opens a new avenue for the treatment of high-strength organic wastewaters by developing a highly antifouling hydrogel-based FO membrane. [ABSTRACT FROM AUTHOR]

Layered polymeric systems are widely used in membrane separation applications; chain mobility in these layered systems is a key consideration in the design of the membranes. The transport properties of membrane polymers can be significantly altered by the perturbations in chain dynamics induced by the presence of an interface and also by the topological properties of the polymers constituting the layered systems. In this work, we use molecular dynamics (MD) simulations to determine the effects of polymer backbone flexibility and interlayer interactions on the glass transition and chain dynamics of polymer layers in the layered systems. We observed that the onset of glass transition of the entire layered system is governed by the stiffer polymer layer and is independent of the type of interactions between the layers. However, the interlayer interactions govern the strength of the glass transition of the entire layered system. Polymer mobility, on the other hand, exhibits a strong dependence on both the chain flexibility and the interlayer interactions. In systems with attractive interactions between the layers, the fully flexible polymer chains at the interface have a lower mobility than those in the bulk region of the layer; the behavior differs from that of rigid polymers, which have a higher mobility at the interface compared to that in the bulk. On the other hand, when the interactions between the layers are repulsive, each layer acts as a free-standing film with chains in both the layers exhibiting higher mobility at the interface. [ABSTRACT FROM AUTHOR]

Two-dimensional covalent organic frameworks (COFs) were used to create the first asymmetric, thin-film composite (TFC) nanofiltration (NF) membrane with a COF active layer. NF membrane active layers of polyimine COF were synthesized via the interfacial polymerization (IP) of terephthalaldehyde and tris(4-aminophenyl)benzene monomers on top of a poly(ether sulfone) (PES) ultrafiltration membrane support. Rutherford backscattering spectrometry and Fourier transform infrared spectroscopy analyses confirmed the presence of an imine-linked film with a thickness of ~10 nm that was formed reproducibly. The rejection efficiencies of the COF NF membrane for a model organic compound, Rhodamine-WT, and a background electrolyte, NaCl, were higher than those of the PES support without the COF film. This enhanced solute rejection is the first successful demonstration of a TFC membrane with a thin COF active layer. However, this work also demonstrates the need for COF NF membranes with smaller active layer pores and alternative support materials. The former should result in greater solute rejection, and the latter is key because the PES used for support in the COF membranes is incompatible with the organic solvents used for the COF IP process. [ABSTRACT FROM AUTHOR]

Membranes made of layer-stacked two-dimensional molybdenum disulfide (MoS2) nanosheets have recently shown great promise for water filtration. At present, the reported water fluxes vary significantly, while the accountable structure and properties of MoS2 nanochannels are largely unknown. This paper aims to mechanistically relate the performance of MoS2 membranes to the size of their nanochannels in different hydration states. We discovered that fully hydrated MoS2 membranes retained a 1.2 nm interlayer spacing (or 0.9 nm free spacing), leading to high water permeability and moderate-to-high ionic and molecular rejection. In comparison, completely dry MoS2 membranes had a 0.62 nm interlayer spacing (or 0.3 nm free spacing) due to irreversible nanosheet restacking and were almost impermeable to water. Furthermore, we revealed that the interlayer spacing of MoS2 membranes in aqueous solution is maintained by comparable van der Waals and hydration forces, thereby ensuring the aqueous stability of MoS2 membranes without the need of cross-linking. In addition, we attributed the high water flux (30-250 L m-2 h-1 bar-1) of MoS2 membranes to the low hydraulic resistance of smooth, rigid MoS2 nanochannels. We also concluded that compaction of MoS2 membranes with a high pressure helps create a more neatly stacked nanostructure with minimum voids or looseness, leading to stable water flux and separation performance. Besides, this paper systematically compares MoS2 membranes with the widely studied graphene oxide membranes to highlight the uniqueness and advantages of MoS2 membranes for water-filtration applications. [ABSTRACT FROM AUTHOR]

Organic solvent separations could revolutionize the field of separations by enabling new low energy, low carbon emission technologies. Microporous materials are potential game changers for these challenging separations due to their ability to provide superb size and shape discrimination; however, large-scale application of these materials has yet to be adopted. This critical perspective will discuss the current state of the art in the separation of similarly sized organic molecules via microporous membranes and provide key focus areas for future research. [ABSTRACT FROM AUTHOR]

Miaoscale damages to membranes used in large-scale filtration processes for water treatment can result in severe degradation of product water quality. One promising technology to address this issue is in situ healing of compromised membranes via healing agents that are added to the feed side of a membrane system and seal the defect site because of increased hydraulic drag through damage site during filtration. We herein introduce an improved in situ membrane healing method using amine-functionalized silica micropartides that is effective under varying operating conditions, overcoming limitations faced by previous healing agents such as chitosan agglomerates. The silica micropartides are functionalized with branched polyethylenimine (PEI) molecules for efficient interparticle cross-linking with glutaraldehyde. The PEI-decorated silica micropartides (SiO2 a PEI MPs) were characterized using scanning electron microscopy, dynamic light scattering, and zeta potential analysis. This study investigates the selective deposition of the SiOz@PEI MPs on the damage area using confocal laser scanning microscopy under variable cross-flow rate (0S-2.0 L/min) and flushing time (10 to 30 min) conditions. The in situ healing technique recovered the particle rejection of compromised membranes to 99.1% of the original membrane's performance without any flux decline. The results of this study show that the use of SiOz@PEI MPs is a promising and practical approach to ensure membrane process integrity. [ABSTRACT FROM AUTHOR]

A catalysis/membrane filtration system combining a catalytic reaction and a separation process can realize the in situ separation of ultrafine catalysts from the reaction mixture and make the production continuous. In this study, a side-stream catalysis/membrane filtration system was developed for the first time for the continuous liquid-phase hydrogenation of phenol over Pd@CN to produce cyclohexanone. The operating parameters including the reaction and filtration conditions were optimized by balancing their influences on the catalytic and separation properties. It was found that the properties of the side-stream catalysis/membrane filtration system depended strongly on the operating conditions. Continuous phenol hydrogenation over Pd@CN was performed under the optimized operating conditions. A stable operation of 30 h was achieved with both a phenol conversion and a cyclohexanone selectivity of greater than 85%, and the ceramic membrane showed excellent stability. This study is a contribution to the development of green cyclohexanone production processes. [ABSTRACT FROM AUTHOR]

Fouling has been a persistent issue within applications ranging from membrane separation to biomedical implantation. Research to date focuses on fouling-resistant coatings, where electrical conductivity is unnecessary. In this study, we report the synthesis of multifunctional thin films with both fouling resistance and electrical conductivity for their potential applications in the electrolysis-based self-cleaning of separation membranes and in the field of bioelectronics. This unique combination of properties results in multifunctional coatings that are a zwitterionic derivative of intrinsically conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) synthesized via oxidative chemical vapor deposition (oCVD). Their fouling resistance is shown to be comparable to that of known dielectric fouling-resistant surfaces, such as a poly(4-vinylpyridine)-co-divinylbenzene (p4VP-DVB)-derived zwitterionic coating, an amphiphilic poly(1H,1H,2H,2H-perfluorodecyl acrylate-co-2-hydroxyethyl methacrylate) (pPFDA-HEMA) coating, and a glass surface, and are far superior to the fouling resistance of gold or polydimethylsiloxane (PDMS) surfaces. The fouling resistances of seven surfaces are quantitatively characterized by molecular force probe (MFP) analysis. In addition, four-point probe electrical measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), variable-angle spectroscopic ellipsometry (VASE), profilometry, water contact angle (WCA) measurements, surface ζ-potential measurements, and atomic force microscopy (AFM) were employed to characterize the physiochemical properties and morphology of the different surfaces. [ABSTRACT FROM AUTHOR]

Zero Discharge Desalination (ZDD) is a very-high-recovery hybrid desalination system, typically comprised of a primary desalter (such as reverse osmosis (RO) or nanofiltration (NF)) and electrodialysis metathesis (EDM). The EDM acts as a "kidney" by removing troublesome salts from the concentrate of the primary desalter, which allows for additional recovery of potable water. A mathematical model was developed to simulate ZDD system performance using mass balance, desalination design equations, and experimental data. Model results confirm that ZDD can achieve >97% system recovery for brackish water with (a) a feed total dissolved solids (TDS) concentration of <3 g/L; (b) relatively high fractions of multivalent ions (e.g., calcium and sulfate mass concentrations of >60% of the TDS); and (c) a silica content of <40 mg/L. Furthermore, model results indicate that the required ZDD specific energy consumption (a) increases by 0.77 kWh per 1 g/L of feed TDS; (b) increases with lower permeate TDS, especially below 500 mg/L; and (c) generally decreases with higher recovery on the primary desalter (e.g., RO or NF). ZDD system recovery generally decreases by -1% per 1 g/L of feed TDS. Higher TDS feedwater (e.g., 3.5 to 5 g/L) limits ZDD system recoveries to 94% to 90%, respectively. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs), as porous fillers possessing molecular sieving properties, have been combined with polymers to give mixed-matrix membranes (MMMs) with enhanced separation performance. This field of research has produced a large number of different membranes, and many MOF/polymer combinations have been tested and reported to show potential application to industrial gas separation. Although MOFs have been proposed as novel additives with high porosity and tunable pore size, which were supposed to outperform other porous fillers, due to restrictions in separation performance of the filler and challenges concerning the compatibility of polymer and MOF, only a small fraction of these works report both improved permeability and selectivity. In this review these challenges are set into the context of MOF synthesis and membrane fabrication by the choice of appropriate polymer/MOF combinations, utilization of the MOF functional sites, modification of the MOF surface chemistry or pore texture and size, and also targeted influence of the size and shape of the filler particles. The effect of the highlighted MOF additives on the gas separation performance is analyzed and discussed by comparison of the gas permeability and selectivity. This emphasizes strategies by which high performing MMMs can be achieved through accessing the full potential of the porous MOF fillers. [ABSTRACT FROM AUTHOR]

Achieving a high rate of ionic transport through porous membranes and ionic channels is important in numerous applications ranging from energy storage to water desalination, but it still remains a challenge. Herein we show that ions can quickly pass through interlayer spaces in hydrated boron nitride (BN) membranes. Measurements of surfacecharge governed ionic currents between BN nanosheets in a variety of salt solutions (KC1, NaCl and CaCl2) at low salt concentrations (<10-4 M) showed several orders of magnitude higher ionic conductivity compared to that of the bulk solution. Moreover, due to the outstanding chemical and thermal stability of BN, the ionic conduits remain fully functional at temperatures up to 90 °C. The BN conduits can operate in acidic and basic environments and do not degrade after immersing in solutions with extreme pH (pH ~ 0 or 14) for 1 week. Those excellent properties make the BN ionic conduits attractive for applications in nanofluidic devices and membrane separation. [ABSTRACT FROM AUTHOR]

High mechanical strength is essential for pressure-driven membrane separations with nanoporous single-layer graphene, but its ability to withstand high pressures remains to be demonstrated. We monitored failure of centimeter-scale single-layer graphene membranes on porous supports subjected to high pressures. Consistent with theory, the membranes were found to withstand higher pressures when placed on porous supports with smaller pore diameters, but failure occurred over a surprisingly broad range of pressures, attributed to heterogeneous susceptibility to failure at wrinkles, defects, and slack in the suspended graphene. Remarkably, nonwrinkled areas withstood pressure exceeding 100 bar at which many kinds of membrane suffer from compaction. Our study shows that single-layer graphene membranes can sustain ultrahigh pressure especially if the effect of wrinkles is isolated using supports with small pores and suggests the potential for the use of single-layer graphene in high-pressure membrane separations. [ABSTRACT FROM AUTHOR]

Iptycene molecules, featuring three-dimensional [2,2,2]-ring configurations with 120° contortion sites and unique internal free volume (IFV) elements, have recently been identified for their great potential in the design of polymers for gas separation membranes. Some of these novel iptycene-containing polymers have already displayed unprecedented separation performance. This review summarizes the progression of the gas separation membranes, utilizing iptycene structures over the past five years by dividing the polymers into three categories: nonladder polymers, semiladder polymers, and ladder polymers. The focus lies on examining macromolecular design strategies of these novel polymers and consequential effects on chain packing, free volume architecture, and gas transport properties to provide useful guidance on the design of new membrane materials. Finally, we provide some perspectives and future research directions for designing and utilizing iptycene-containing polymers for gas separation membranes. [ABSTRACT FROM AUTHOR]

Removal of recalcitrant anthropogenic contaminants from water calls for the development of cost-effective treatment technologies. In this work, a novel electrochemical membrane filtration (EMF) process using a conducting microfiltration membrane as the cathode has been developed and the degradation of sulphanilic acid (SA) examined. The electrochemical degradation of SA in flow-by mode followed pseudo-first-order kinetics with the degradation rate enhanced with increase in charging voltage. Hydrogen peroxide as well as oxidants such as HO• and Fe(IV)O2+ were generated electrochemically with HO• found to be the dominant oxidant responsible for SA degradation. In addition to the anodic splitting of water, HO• was formed via a heterogeneous Fenton process with surface-bound Fe(II) resulting from aerobic corrosion of the steel mesh. In flow-through mode, the removal rate of SA was 13.0% greater than obtained in flow-by mode, presumably due to the better contact of the contaminant with the oxidants generated in the vicinity of the membrane surface. A variety of oxidized products including hydroquinone, p-benzoquinone, oxamic acid, maleic acid, fumaric acid, acetic acid, formic acid, and oxalic acid were identified and an electrochemical degradation pathway proposed. These findings highlight the potential of the cathodic EMF process as an effective technology for water purification. [ABSTRACT FROM AUTHOR]

In spite of the huge research interest, ionic polymers could not have been synthesized in the vapor phase because the monomers of ionic polymers contain nonvolatile ionic salts, preventing the monomers from vaporization. Here, we suggest a new, one-step synthetic pathway to form a series of cross-linked ionic polymers (CIPs) in the vapor phase via initiated chemical vapor deposition (iCVD). 2-(Dimethylamino)ethyl methacrylate (DMAEMA) and 4-vinylbenzyl chloride (VBC) monomers are introduced into the iCVD reactor in the vapor phase to form a copolymer film. Simultaneously in the course of the deposition process, the tertiary amine in DMAEMA and benzylic chloride in VBC undergo a Menshutkin nucleophilic substitution reaction to form an ionic ammonium-chloride complex, forming a highly cross-linked ionic copolymer film of p(DMAEMA-co-VBC). To the best of our knowledge, this is the first report on the synthesis of CIP films in the vapor phase. The newly developed CIP thin film is further applied to the surface modification of the membrane for oil/water separation. With the hydrophilic and underwater oleophobic membrane whose surface is modified with the CIP film, excellent separation efficiency (>99%) and unprecedentedly high permeation flux (average 2.32 x 105 L m-2 h-1) are achieved. [ABSTRACT FROM AUTHOR]

The further advancement of membrane separation processes will require the development of more selective membranes. In this study, membranes that take inspiration from the mosaic structure of cell walls and use multiple functionalities of unique chemical design to control solute transport through chemical factors as well as steric factors are detailed. Specifically, a poly{acrylonitrile-co[oligo(ethylene glycol) methyl ether methacrylate]-co-(3-azido-2-hydroxypropyl methacrylate)} copolymer tailor-made for the generation of nanofilters, which possess a high density of well-defined pores that are lined by azido moieties, allowed for the generation of chemically patterned mosaic membranes in a rapid manner through the use of printing devices. By engineering the composition of the reactive ink solutions printed on the membrane to allow for the rapid, one-to-one covalent attachment of alkynyl-functionalized groups to the azido moieties, we generated large areas of patterned membranes in seconds rather than hours as detailed in previous reports. Charge mosaic membranes, in particular, were used as an example of this novel platform. These membranes possess distinct cationic and anionic domains that traverse the membrane thickness, which results in the emergence of negative osmosis. As demonstrated through transport testing, this novel transport mechanism results in the preferential permeation of electrolytes over neutral molecules and solvents. For example, a negative rejection of -15% was observed for an aqueous feed solution containing 0.1 mM potassium chloride. The versatile and precise control over membrane chemistry at the nanoscale provided by the technique suggests that it could be engineered to prepare a variety of highly selective mosaic membranes. [ABSTRACT FROM AUTHOR]

An ideal molecular filtration membranes should be highly permeable and selective, thus desiring the membranes to be ultrathin, be highly porous, and consists of small and uniform pores or channels. In this work, we report the molecular filtration by freestanding ultrathin silica nanochannel membranes (SNMs) using a U-shaped cell and spectrophotometric detection, focusing on the quantitative evaluation of permeability and selectivity of SNMs. Thanks to the ultrasmall channel size, namely, ~ 2--3 nm, and the negatively charged channel surface arising from the deprotonation of silanol groups, the SNM displayed excellent size and charge selectivity for molecular filtration. The selectivity coefficient for separation of small m ethyl viologen from large cytochrome c is as high as 273, because of the uniform pore/channel size. The charge-based filtration can be modulated by the salt concentration and solution pH, which control the overlap of radial electrical double layer and surface charge sign/density, respectively. Owing to the high relative pore density, namely, 16.7%, and the straight and vertical channel orientation, the SNM is highly permeable, displaying a molecule flux much higher than commercially available dialysis membrane and others reported previously. In addition, we demonstrated that, by biasing a small voltage across the SNM, both the flux and separation selectivity could be significandy enhanced. [ABSTRACT FROM AUTHOR]

In today�s perspective, natural gas has gained considerable attention, due to its low emission, indigenous availability, and improvement in the extraction technology. Upon extraction, it undergoes several purification protocols including dehydration, sweetening, and inert rejection. Although purification is a commercially established technology, several drawbacks of the current process provide an essential impetus for developing newer separation protocols, most importantly, adsorption and membrane separation. This Review summarizes the needs of natural gas separation, gives an overview of the current technology, and provides a detailed discussion of the progress in research on separation and purification of natural gas including the benefits and drawbacks of each of the processes. The transportation sector is another growing sector of natural gas utilization, and it requires an efficient and safe on-board storage system. Compressed natural gas (CNG) and liquefied natural gas (LNG) are the most common forms in which natural gas can be stored. Adsorbed natural gas (ANG) is an alternate storage system of natural gas, which is advantageous as compared to CNG and LNG in terms of safety and also in terms of temperature and pressure requirements. This Review provides a detailed discussion on ANG along with computation predictions. The catalytic conversion of methane to different useful chemicals including syngas, methanol, formaldehyde, dimethyl ether, heavier hydrocarbons, aromatics, and hydrogen is also reviewed. Finally, direct utilization of methane onto fuel cells is also discussed. [ABSTRACT FROM AUTHOR]

More than 80 years ago, artificial materials with molecular recognition sites emerged. The application of molecular imprinting to membrane separation has been studied since 1962. Especially after 1990, such research has been intensively conducted by membranologists and molecular imprinters to understand the advantages of each technique with the aim of constructing an ideal membrane, which is still an active area of research. The present review aims to be a substantial, comprehensive, authoritative, critical, and general-interest review, placed at the cross section of two broad, interconnected, practical, and extremely dynamic fields, namely, the fields of membrane separation and molecularly imprinted polymers. This review describes the recent discoveries that appeared after repeated and fertile collisions between these two fields in the past three years, to which are added the worthy acknowledgments of pioneering discoveries and a look into the future of molecularly imprinted membranes. The review begins with a general introduction in membrane separation, followed by a short theoretical section regarding the basic principles of mass transport through a membrane. Following these general aspects on membrane separation, two principles of obtaining polymeric materials with molecular recognition properties are reviewed, namely, molecular imprinting and alternative molecular imprinting, followed the methods of obtaining and practical applications for the particular case of molecularly imprinted membranes. The review continues with insights into molecularly imprinted nanofiber membranes as a promising, highly optimized type of membrane that could provide a relatively high throughput without a simultaneous unwanted reduction in permselectivity. Finally, potential applications of molecularly imprinted membranes in a variety of fields are highlighted, and a look into the future of membrane separations is offered. [ABSTRACT FROM AUTHOR]

Membrane science and technology is growing rapidly worldwide and continues to play an increasingly important role in diverse fields by offering high separation efficiency with low energy consumption. Membranes have also shown great promise for "green" separation. A majority of the investigations in the field are devoted to the membrane fabrication and modification with the ultimate goals of enhancing the properties and separation performance of membranes. However, less attention has been paid to membrane life cycle management, particularly at the end of service. This is becoming very important, especially taking into account the trends toward sustainable development and carbon neutrality. On the contrary, this can be a great opportunity considering the large variety of membrane processes, especially in terms of the size and capacity of plants in operation. This work aims to highlight the prominent aspects that govern membrane life cycle management with special attention to life cycle assessment (LCA). While fabrication, application, and recycling are the three key aspects of LCA, we focus here on membrane (module) recycling at the end of life by elucidating the relevant aspects, potential criteria, and strategies that effectively contribute to the achievement of green development and sustainability goals.

Herein we demonstrate that chabazite zeolite SAPO-34 membranes effectively separated Kr/Xe gas mixtures at industrially relevant compositions. Control over membrane thickness and average crystal size led to industrial range permeances and high separation selectivities. Specifically, SAPO-34 membranes can separate Kr/Xe mixtures with Kr permeances as high as 1.2 X 10-7 mol/m² s Pa and separation selectivities of 35 for molar compositions close to typical concentrations of these two gases in air. In addition, SAPO-34 membranes separated Kr/Xe mixtures with Kr permeances as high as 1.2 X 10-7 mol/m² s Pa and separation selectivities up to 45 for molar compositions as might be encountered in nuclear reprocessing technologies. Molecular sieving and differences in diffusivities were identified as the dominant separation mechanisms. [ABSTRACT FROM AUTHOR]

We report a new ultrathin filtration membrane prepared from silk nanofibrils (SNFs), directly exfoliated from natural Bombyx mori silk fibers to retain structure and physical properties. These membranes can be prepared with a thickness down to 40 nm with a narrow distribution of pore sizes ranging from 8 to 12 nm. Typically, 40 nm thick membranes prepared from SNFs have pure water fluxes of 13?000 L h-1 m-2 bar-1, more than 1000 times higher than most commercial ultrathin filtration membranes and comparable with the highest water flux reported previously. The commercial membranes are commonly prepared from polysulfone, poly(ether sulfone), and polyamide. The SNF-based ultrathin membranes exhibit efficient separation for dyes, proteins, and colloids of nanoparticles with at least a 64% rejection of Rhodamine B. This broad-spectrum filtration membrane would have potential utility in applications such as wastewater treatment, nanotechnology, food industry, and life sciences in part due to the protein-based membrane polymer (silk), combined with the robust mechanical and separation performance features. [ABSTRACT FROM AUTHOR]

The feasibility of continuous phosphate recovery, by adsorption on powdered Ca-activated zeolite (PAZ), was assessed in a hybrid sorption-membrane ultrafiltration (UF) system. The objective was to explore the influence of process parameters such as initial P(V) concentration, pH, and PAZ dose on P(V) recovery from a tertiary treatment effluent. The hydrodynamic parameters of the UF operation were also evaluated as a function of the PAZ dose. The P(V) recovery profiles as a function of the initial P(V) concentrations, at pH 8 and 2.5 gPAZ/L, indicated that the sorbent was not saturated, and recoveries reported were 1.8 ± 0.2, 5.7 ± 0.3, and 47.2 ± 2 mg P(V)/gPAZ for 10 ± 1, 25 ± 2, and 100 ± 6 mg P(V)/L, respectively. The increase of the pH of the feed solution from 8 to 9 increased the P(V) recovery up to 70 ± 4%. A P(V) fractionation protocol of the loaded samples confirmed that the phosphate-sorption process involves the formation of calcium phosphate mineral forms. [ABSTRACT FROM AUTHOR]

A straightforward chemical functionalization strategy using aminosilanes for high-flux yttria-stabilized zirconia capillary membranes is presented (macroporous, d50 = 144 nm, open porosity =49%, membrane flux ~150 L/(m²hbar)). Three different aminosilanes with one, two or three amino groups per silane molecule, namely 3-aminopropyltriethoxysilane (APTES), N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AE-APTES) and N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA), are used to generate the amino-functionalized membranes. With a higher number of amino groups per silane molecule increased loading capacities between 0.44 and 1.01 accessible amino groups/nm2 membrane are achieved. Streaming potential measurements confirm that the zeta-potential of the membrane surface is converted from negative (non-functionalized) to positive (amino-functionalized). By operation in dead-end filtration mode using the model virus MS2 (diameter = 25 nm, IEP = 3.9) the virus retention capacity of the amino-functionalized membranes is significantly increased and log reduction values (LRVs) of up to 9.6 ± 0.3 (TPDA) are obtained whereas a LRV < 0.3 is provided by the non-functionalized membranes. Long-term dead-end filtration experiments for 1 week reveal a high stability of immobilized aminosilanes (TPDA), being robust against leaching. By iterative backflushing with desorption buffer MS2-loaded membranes are successfully regenerated being reusable for a new filtration cycle. The presented functionalization platform is highly promising for controlled virus retention. [ABSTRACT FROM AUTHOR]

A dual-membrane module is able to provide higher separation performance for H2/CO2 gas mixtures compared to conventional single-membrane modules. In this work, the flow patterns of dual-membrane modules are studied, and the results indicate that the co(H2):counter(CO2) flow pattern is the optimal flow pattern for H2 recovery. The co(H2):counter(CO2) flow pattern employs cocurrent (permeate flow parallel to bulk flow) to the H2-selective membrane and counter-current (permeate flow reverse to bulk flow) to the CO2-selective membrane; the flow pattern reduces the permeation flux of CO2 in the H2-selective membrane, resulting in a higher H2 separation factor. The evaluations show that the H2 product purity could be raised by 35% (from 62 mol % to 84 mol %) compared to conventional membrane modules. The results indicate that enhancing the membrane separation performance through flow pattern is a practical and effective method for process engineering. [ABSTRACT FROM AUTHOR]

Nanoporous titania nanoparticles(NTNs) were synthesized and usedas an additive at a low concentration of 0.1–1 wt % in thefabrication of poly(ethersulfone) (PES) ultrafiltration membranesvia non-solvent-induced phase separation. The structure and propertiesof nanoparticles were characterized using nitrogen sorption, X-raydiffraction, scanning electron microscopy, and transmission electronmicroscopy. The NTNs have a size distribution with a particle sizeof mainly <100 nm and have a Brunauer, Emmett, and Teller surfacearea of ∼100 m2g–1. The modifiedmembranes were fabricated and investigated in terms of their purewater flux, solute rejection, and fouling resistance. The water permeabilityand molecular weight cutoffs (MWCOs) of membranes were determinedunder constant-pressure filtration in dead-end mode at 100 kPa. Themembrane fouling resistance was characterized under constant fluxoperation using bovine serum albumin as a model foulant. The membraneswere characterized in terms of morphology, porosity, pore size distribution,energy-dispersive X-ray spectroscopy, contact angle goniometry, surfacefree energy, and viscosity of the dope solution. Overall, the modifiedmembrane showed increased wettability and reduced surface free energyand pore size. The modified UF membrane with 0.5 wt % NTN loadingexhibited improved fouling resistance (fouling rate of 0.58 kPa/mincompared to a rate of 0.70 kPa/min for the control membrane) with∼80% water flux recovery. The same membrane showed an ∼20%increase in water flux, an improvement in MWCO, and a narrower poresize distribution. [ABSTRACT FROM AUTHOR]

Combinatorial methodology is described for rapid screening of selectivity in polymeric pervaporation membrane materials for alcohol-water separations. The screening technique is demonstrated for ethanol-water separation using a model polyacrylate system. The materials studied are cross-linked random copolymers of a hydrophobic comonomer (n-butyl acrylate, B) and a hydrophilic comonomer (2-hydroxyethyl acrylate, H). A matrix of materials is prepared that has orthogonal variations in two key variables, H:B ratio and cross-linker concentration. For mixtures of ethanol and water, equilibrium selectivities and distribution coefficients are obtained by combining swelling measurements with high-throughput HPLC analysis. Based on the screening results, two copolymers are selected for further study as pervaporation membranes to quantify permeability selectivity and the flux of ethanol. The screening methodology described has good potential to accelerate the search for new membrane materials, as it is adaptable to a broad range of polymer chemistries. [ABSTRACT FROM AUTHOR]

Accumulation of greenhouse gases especially CO2 in the atmosphere leading to global warming with undesirable climate changes has been a serious global concern. Major power generation in the world is from coal based power plants. Carbon capture through pre- and post- combustion technologies with various technical options like adsorption, absorption, membrane separations, and chemical looping combustion with and without oxygen uncoupling have received considerable attention of researchers, environmentalists and the stake holders. Carbon capture from flue gases can be achieved with micro and meso porous adsorbents. This review covers carbonaceous (organic and metal organic frameworks) and noncarbonaceous (inorganic) porous adsorbents for CO2 adsorption at different process conditions and pore sizes. Focus is also given to noncarbonaceous micro and meso porous adsorbents in chemical looping combustion involving insitu CO2 capture at high temperature(>400 °C). Adsorption mechanisms, material characteristics, and synthesis methods are discussed. Attention is given to isosteric heats and characterization techniques. The options to enhance the techno-economic viability of carbon capture techniques by integrating with CO2 utilization to produce industrially important chemicals like ammonia and urea are analyzed. From the reader's perspective, for different classes of materials, each section has been summarized in the form of tables or figures to get a quick glance of the developments. [ABSTRACT FROM AUTHOR]

Propylene/propane separation is one of the most challenging separations, currently achieved by energy-intensive cryogenic distillation. Despite the great potential for energy-efficient membrane-based separations, no commercial membranes are currently available due to the limitations of current polymeric materials. Zeolitic imidazolate framework, ZIF-8, with the effective aperture size of ~4.0 Å, has been shown to be very promising for propylene/propane separation. Despite the extensive research on ZIF-8 membranes, only a few reported ZIF-8 membranes have displayed good propylene/propane separation performances presumably due to the challenges of controlling the microstructures of polycrystalline membranes. Here we report the first well-intergrown membranes of ZIF-67 (Co-substituted ZIF-8) by heteroepitaxially growing ZIF-67 on ZIF-8 seed layers. The ZIF-67 membranes exhibited impressively high propylene/propane separation capabilities. Furthermore, when a tertiary growth of ZIF-8 layers was applied to heteroepitaxially grown ZIF-67 membranes, the membranes exhibited unprecedentedly high propylene/propane separation factors of ~200 possibly due to enhanced grain boundary structure. [ABSTRACT FROM AUTHOR]

The efficacy of coagulation and membranefiltration was studiedfor the treatment of boiler-blowdown (BBD) wastewater to enable reuseand minimize the overall water consumption in steam-assisted-gravity-drainage(SAGD), thermally enhanced, oil recovery operations. Direct nanofiltrationof chemically unadjusted BBD at its original pH was the optimal treatmentoption with respect to the flux stability and the removal of dissolvedorganic material and salinity, which if not removed would result inthe fouling and failure of downstream process equipment. The naturallyhigh solute hydrophilicity allowed for prolonged operation with anelevated flux of 60 L m−2h−1(LMH)and recovery up to 85% while maintaining solute removal as high as80% and 45% for dissolved organic carbon and total dissolved solids,respectively. Comparatively, neither precoagulation nor preacidificationimproved the rejection of dissolved organic material or salinity andconsistently resulted in increased membrane surface fouling and fluxdecline. The proposed filtration treatment solution would result inasmuchas a 4-fold reduction in the volume of makeup water required and BBDwastewater disposed compared to a conventional SAGD facility. [ABSTRACT FROM AUTHOR]

Long-term physical aging and plasticization,two mobility-based phenomena that are counterintuitivein the context of “rigid”polymers of intrinsic microporosity (PIMs), were evaluated using pure-and mixed-gas permeation data for representative ladder and semiladderPIMs. PIMs between 1 and 4 years old retained from 10- to 1000-foldhigher H2and O2permeabilities than commercialmembrane materials with similar or higher selectivities. A triptycene-basedladder polymer (TPIM-1) exhibited very large selectivity gains outweighingpermeability losses after 780 days, resulting in unprecedented performancefor O2/N2(P(O2) = 61 Barrer, α(O2/N2) = 8.6) and H2/N2(P(H2) = 1105 Barrer, α(H2/N2) = 156)separations. Interestingly, TPIM-1 aged more and faster than its more flexiblecounterpart, PIM-1, which exhibited P(O2) = 317 Barrer and α(O2/N2) =5.0 at 1380 days. Additionally, the more “rigid” TPIM-1plasticized more significantly than PIM-1 (i.e., TPIM-1 endured ∼93%increases in mixed-gas CH4permeability over pure-gas valuescompared to ∼60% for PIM-1). A flexible 9,10-bridgehead (i.e.,TPIM-2) mitigated the enhancements induced by physical aging but reducedplasticization. Importantly, intra-chain rigidityalone, without consideration of chain architecture and ultra-microporosity, is insufficient for designing aging- and plasticization-resistantgas separation membranes with high permeability and high selectivity [ABSTRACT FROM AUTHOR]

Thisstudy aims to evaluate the feasibility of using novel nanofiltration(NF) membranes for decaffeination of coffee wherein caffeine presentin the feed solution is recovered at the permeate of the membrane.The NF hollow fiber membranes were fabricated and tested with modelsolutions to evaluate the recovery of caffeine as functions of molecularweight/size of organic molecules, caffeine concentration, and feedtemperature. The results show that the recovery of caffeine and thepermeate flux decrease with an increase in molecular weight/size ofthe organic molecules and the caffeine concentration in the feed.On the other hand, both recovery and flux increase with increasingfeed temperature. Decaffeination of coffee is subsequently demonstratedat 55 °C using a roasted coffee solution wherein a 25% reductionof caffeine is achieved with a volume reduction factor of ∼1.2. [ABSTRACT FROM AUTHOR]

Forwardosmosis (FO) has the potential to improve the energy efficiencyof membrane-based water treatment by leveraging waste heat from steamelectric power generation as the primary driving force for separation.In this study, we develop a comprehensive FO process model, consistingof membrane separation, heat recovery, and draw-solute regeneration(DSR) models. We quantitatively characterize three alternative processesfor DSR: distillation, steam stripping, and air stripping. We thenconstruct a mathematical model of the distillation process for DSRthat incorporates hydrodynamics, mass- and heat-transport resistances,and reaction kinetics, and we integrate this into a model for thefull FO process. Finally, we utilize this FO process model to derivea first-order approximation of the water production capacity giventhe rejected-heat quantity and quality available at U.S. electricpower facilities. We find that the upper bound of FO water treatmentcapacity using low-grade heat sources at electric power facilitiesexceeds process water treatment demand for boiler water makeup andflue-gas-desulfurization wastewater systems. [ABSTRACT FROM AUTHOR]

In forward osmosis (FO), reversesalt diffusion not only reduceswater flux but also increases the requirement of draw solute replenishment.FO would be very desirable if there was no draw solute leakage andthe recovery of draw solutes was easy. In this study, a novel drawsolute, ethylenediaminetetraacetic acid (EDTA)-2Na coupled with TritonX-100 was explored with the aim of minimizing reverse salt diffusion.The results indicated that reverse salt diffusion achieved zero thefirst time when using 0.1 M EDTA-2Na coupled with 0.5 mM Triton X-100as draw solution and DI water as feed solution. A water flux of 4.6L/m2h was reached when 35 g/L NaCl of model seawater wasused as the feed solution and 1 M EDTA-2Na coupled with 0.5 mM TritonX-100 was used as the draw solute. Moreover, a nanofiltration (NF)membrane was employed to recover the draw solute, achieving a highrejection of 95% due to the high charge and large size of the drawsolute. [ABSTRACT FROM AUTHOR]

A fast, low cost, and sensitive sample pretreatment method was specially developed for laser-induced breakdown spectroscopy (LIBS) based on metal precipitation and membrane separation for simultaneous elemental analysis in liquid samples. The metal elements were reacted with the chelating reagent 2,4,6-trimercapto-1,3,5-triazine (TMT) in the first step and separated by mixed cellulose ester microfiltration membrane subsequently. A specific membrane supporter with smaller aperture than the commercially available needle filter was designed and assembled in the presented research to increase the sensitivity. As a result, the detection limits of Cu, Ag, Mn, and Cr obtained in this research were 2.59 ng·mL–1, 0.957 ng·mL–1, 0.958 ng·mL–1, and 1.29 ng·mL–1 respectively, which were greatly improved from direct liquid analysis by LIBS. Satisfactory linearity, reproducibility, and accuracy were also obtained in the concentration range of 10–120 ng·mL–1 for all four elements tested at the optimized experimental conditions. The analytical figures of merits of the proposed method are at an advanced level and are comparable to those reported among other non-LIBS research. In addition, the separation mechanism in this research was initially explored and further varied to be based on metal precipitates adsorption by membrane fibers, rather than a regular size-dependent obstruction. [ABSTRACT FROM AUTHOR]

In this work, imidazolate frameworkZIF-8 nanoparticles were synthesizedand incorporated into a poly(vinylamine) (PVAm) coating solution.The chemical structure of a PVAm/ZIF-8 film was characterized by X-raydiffraction and attenuated total reflectance Fourier transform infraredspectroscopy techniques. Mixed-matrix membranes (MMMs) were developedby coating the PVAm/ZIF-8 mixed dispersion on a polysulfone (PSf)support membrane. Surface and cross-sectional scanning electron microscopyimages of the MMMs were employed to observe the dispersion of nanoparticlesin the polymer matrix. The CO2permeance and CO2/N2selectivity of the MMMs were evaluated by using aCO2/N2mixture gas. Optimal preparation parametersfor the MMMs were achieved by varying the incorporated ZIF-8 contentsin the coating solution and the wet coating thickness. The effectof incorporated ZIF-8 on improving the gas permselectivity was revealed,and the mechanism of CO2-facilitated transport in the PVAm/ZIF-8/PSfmembrane was analyzed. The CO2/N2separationperformance of PVAm/ZIF-8/PSf membranes with different wet coatingthicknesses was also evaluated at 22–60 °C to analyzethe changes of the gas permselectivity with increasing temperature. [ABSTRACT FROM AUTHOR]

In this study, polyetherimide (PEI) ultrafiltration (UF) membranes were fabricated by incorporating different amounts of hydrophilic polyvinylpyrrolidone (PVP) via the phase inversion technique. The PEI/PVP blended membrane showed the highest pure water flux (147.1 L m-2 h-1), water content (70.2%), and surface energy (112.1 mN/m) when the 8 wt % of PVP was blended into the base polymer PEI. This particular membrane, designated as PVP 8, also showed the lowest contact angle (56.1°), hydraulic resistance (2.2 kPa/(L m-2 h-1)), and shrinkage ratio (4.3%). The addition of PVP has reduced the tensile strength of the PEI membrane because of the decrease in rigidity. The UF experiments with the following proteins, bovine serum albumin (BSA), egg albumin (EA), pepsin, and trypsin, had experienced a decrease in protein rejection whereas permeate flux increased by increasing PVP loading. The BSA adsorption experiment revealed that the adsorbed amount of BSA on the surface of the membrane was notably decreased from 0.17 mg cm-2 of neat PEI membrane to 0.08 mg cm-2 of PVP 8. The flux recovery ratio (FRR) experiment also showed that the fouling resistance property of the membrane was enhanced with the increment of PVP. [ABSTRACT FROM AUTHOR]

Toobtain high-performance membranes for the separation of aromatic/aliphatichydrocarbons, AgCl nanoparticles were synthesized in a water-in-oilmicroemulsion using the ionic liquid 1-dodecyl-3-methyl imidazoiumchloride (C12mimCl) as surfactant and methyl methacrylate-styrene(MMA-St) mixture as oil phase. Then, AgCl/poly(MMA-co-St) hybrid membranes were prepared by microemulsion by in situ polymerization.UV–visible spectrophotometry and transmission electron microscopy(TEM) were used to explore the influence of the St-to-MMA ratio inthe oil phase on the morphology of AgCl nanoparticles in the microemulsion.The change in morphology of AgCl in membranes after polymerizationwas characterized by scanning electron microscopy and TEM. The separationperformance of different hybrid membranes was evaluated by swelling–sorptionexperiments and pervaporation experiments. Results showed that addinga low amount of St slightly influenced the size and distribution ofAgCl particles. Given the improvement in benzene separation, the performanceof hybrid membranes after adding St was higher than that of AgCl/PMMAmembranes. The maximum separation factor of hybrid membranes usingMMA and St as the oil phase reached about 27 and exceeded twice thatof AgCl/PMMA membranes. When the ratio of MMA and St was less than2, the strong π combination between St and AgCl caused a largeaggregation of AgCl particles both in the microemulsion and in themembranes, which evidently reduced the separation performance of themembranes. Increased AgNO3concentration led to the formationof more AgCl particles in the microemulsion, which enhanced the separationperformance of hybrid membranes. At high AgNO3concentration,more particles with short distances more easily aggregated, therebyobviously reducing the separation performance of the membranes. [ABSTRACT FROM AUTHOR]

Effluent from the secondary treatmentof municipal wastewater wastreated with membrane filtration to reduce its toxicity. Five differentinorganic membranes were tested, namely, an α-alumina microfiltrationmembrane, an anatase titania ultrafiltration membrane, a γ-aluminananofiltration membrane, an amorphous titania nanofiltration membrane,and an amorphous hybrid organo-silica membrane. The permeabilitiesand selectivities (color, UV254-absorbing components, conductivityand inorganic nitrogen compounds) of the membranes were determined,and the γ-alumina nanofiltration membrane was found to be themost promising membrane for the treatment of the effluent. The effluentflux was measured to be approximately 40 L m–2h–1for the γ-alumina nanofiltration membrane,and it removed nearly 75% of the UV254-absorbing componentsand 15% of the ions. It also removed 40% of the CuCl and 25% of theCuSO4from the spiked effluent. The fouling resistancewas less pronounced for the γ-alumina membrane compared withthe other membranes. The removal of fecal indicator bacteria was determinedby measuring the amounts of Escherichia coliand Enterococci, and the removalof toxic compounds was investigated in bioassays with Daphnia magnaand Aliivibrio fischeri. The γ-alumina nanofiltration membrane reduced the wastewaterconcentration of E. coli(97.3%) and Enterococci(98.4%), and the bioassays demonstratedthat filtration with the γ-alumina nanofiltration membrane reducedthe overall toxicity of the effluent. [ABSTRACT FROM AUTHOR]

Concentration polarization (CP) and membrane fouling are two major drawbacks for pressure-driven membrane filtration processes (PDMPs) because they cause severe flux decline, which requires effective control strategies. Many articles have proposed the diverse potential applications of various control strategies in reducing CP and membrane fouling. This paper reviews various mechanisms and influencing factors on flux decline, as well as their control strategies in PDMPs. Nine effective control strategies are summarized, generalized, and compared in this paper. On the basis of their functions and influences, they can be also classified as the following: (1) modification: pretreatment of feed, modification of feed characteristics, selection and modification of membrane; (2) design: shear-enhanced filtration modules, applied field enhancement and CP drawer; (3) operation: optimization of operating parameters, hydraulic flushing and two-phase flow. Then, the general and practical guidelines are given. On the basis of this review, future research perspectives related to flux decline control strategies are proposed. [ABSTRACT FROM AUTHOR]

Membrane filtration provides effective solutions for removing contaminants, but achieving high permeability, good selectivity, and antifouling ability remains a great challenge for existing membrane filtration technologies. In this work, membrane filtration coupled with electrochemistry has been developed to enhance the filtration performance of a CNTs/Al2O3 membrane. The as-prepared CNTs/Al2O3 membrane, obtained by coating interconnected CNTs on an Al2O3 substrate, presented good pore-size tunability, mechanical stability, and electroconductivity. For the removal of a target (silica spheres as a probe) with a size comparable to the membrane pore size, the removal efficiency and flux at +1.5 V were 1.1 and 1.5 times higher, respectively, than those without electrochemical assistance. Moreover, the membrane also exhibited a greatly enhanced removal efficiency for contaminants smaller than the membrane pores, providing enhancements of 4 orders of magnitude and a factor of 5.7 for latex particles and phenol, respectively. These results indicated that both the permeability and the selectivity of CNTs/Al2O3 membranes can be significantly improved by electrochemical assistance, which was further confirmed by the removal of natural organic matter (NOM). The permeate flux and NOM removal efficiency at +1.5 V were about 1.6 and 3.0 times higher, respectively, than those without electrochemical assistance. In addition, the lost flux of the fouled membrane was almost completely recovered by an electrochemically assisted backwashing process. [ABSTRACT FROM AUTHOR]