Reverse Osmosis through Poly(4-Vinylpyridine-co-Methacrolein) Membranes Containing Functional Crosslinks of Complexing Ability

Abstract

Membranes containing complex-formable crosslinks were obtained from poly(4-vinylpyridine-co-methacrolein) (4VL) when 4VL was crosslinked by the reaction of formyl groups of 4VL with malonyl dihydrazide (MD) or triethylene tetramine. The effect of monomer composition of 4VL, MD charged, and metal salts on the membrane performance in reverse osmotic separation of NaCl and CoCl₂ was investigated. The membranes of a high methacrolein content tended to be permselective, showing a maximal difference of about 60% in rejection between the two salts. 4VL membranes were mostly more permselective than poly(4-vinylpyridine-co-methyl vinyl ketone) membranes containing analogous crosslinks.     

Solute separation by the amidoxime of poly(4-vinylpyridine-co-acrylonitrile)

The quantitatively amidoximated poly(4-vinylpyridine-co-acrylonitrile) (4VNX) could be cast with divinyl sulfone as a crosslinking agent to form membranes for reverse osmosis. They were stronger than a cellulose acetate membrane when dried for more then 45 min at 80°C, most balanced in their performance when 4VNX was composed of about 60 mol % acrylonitrile amidoxime, and highly rejected NaCl, CoCl₂, NiCl₂, and phenol as well at pH 12. They were superior in the performance to the membranes prepared from the amidoximes of poly(2,4-diamino-6-vinyl-s-triazine-co-acrylonitrile) and polyacrylonitrile. 4VNX membranes prepared by drying for about 30 min were capable of separating NaCl and transition metals under lower pressures because of great differences in rejections between NaCl and those metals. Potential use of 4VNX membranes in ultrafiltration was demonstrated, particularly to the effect that flux was enhanced while the rejection differences were hardly changed. It was also demonstrated that the isolation of transition metals of considerably different uptake from their mixture could be achieved by breakthrough of the column packed with divinylbenzene-crosslinked 4VNX resin.     

Preparation and modification of nano-porous polyimide (PI) membranes by UV photo-grafting process: Ultrafiltration and nanofiltration performance

Polyimide (PI) membranes were prepared via non-solvent induced phase separation. The prepared PI membranes were modified by ultraviolet light (UV) and graft polymerization of hydrophilic acrylic and amino monomers in the absence and presence of benzophenone (BP) onto the membrane surface to introduce more hydrophilic and lower fouling membranes. Acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) as acrylic monomers, 1,3-phenylenediamine (mPDA) as amino monomer and BP as photo-initiator were used. The unmodified and modified PI membranes were characterized by degree of grafting (DG) and contact angle measurements. They were also characterized by their ultrafiltration performance with pure water and non-skim milk and nanofiltration performance with 500 ppm NaCl and MgSO₄ single solutions. The DG was increased with increasing monomer concentration, especially at presence of BP. The contact angle measurements indicated that hydrophilicity of PI membrane was improved after UV photografting of hydrophilic monomers onto the membrane surface in all cases. The ultrafiltration results showed that the pure water fluxes and milk water permeation of PI membrane declined after monomer photo-grafting while the protein rejection was extremely increased. The decrease in permeability was remarkable in the presence of BP. The mean pore size of base and modified PI membranes ranged from 8.3 to 0.55 nm when calculated from the solute transport data. Moreover, the irreversible flux loss and flux recovery of PI membrane were modified by UV photo-grafting of hydrophilic monomers. All modified membranes showed considerable NaCl and MgSO₄ rejections. In addition, the membrane modified with mPDA at presence of BP showed highest NaCl and MgSO₄ rejections.     

Reverse Osmotic Separation of Sodium Chloride and Cobalt (II) Chloride through Membranes Prepared from Schiff Bases of Polyallylamine

Abstract

Crosslinked membranes from Schiff base derivatives of polyallylamine were prepared with 2-pyridinecarboxaldehyde (P) and with P followed by salicyl-aldehyde, and used for the reverse osmotic separation between sodium chloride (NaC1) and cobalt (II) chloride (CoCl₂). The membranes whose rejection (R) was high against CoCl₂ and low against NaCl at each single feed supply showed a reduced difference in R in the case of a mixed solute feed due to Donnan exclusion by fixed charges in the CoCl₂-complexed membrane. An approximate calculation of the complexed CoCl₂ revealed that a very small portion of Schiff base groups took part in the complexation. Composite membranes on a cellulosic sheet solved the problem of an extreme reduction of the membrane strength after complexation, enabling continuous and repeated use. Some transport parameters were determined. Since they indicated a semipermeable character for CoCl₂, multistage runs of a single membrane or low pressure runs of a more porous composite membrane were suggested for the effective separation of NaCl and CoCl₂.     

Flux,antifouling and separation characteristics enhancement of nanocomposite polyethersulfone mixed-matrix membrane by embedding synthesized hydrophilic adipate ferroxane nanoparticles

Polyethersulfone (PES) nanofiltration (NF) membranes were prepared by blending of synthesized hydrophilic adipate ferroxane nanoparticles (AFNPs) as a novel multifunctional nanofiller via the phase inversion method. The water contact angle measurement indicated the higher hydrophilicity of the NF membranes. The water flux of the membranes improved significantly after the addition of AFNPs, from 10.4 to 32.2 kg/m²h. Antifouling characteristics of AFNPs/PES membranes were improved by increased hydrophilicity and decreased membrane surface roughness. The 0.6 wt% AFNPs/PES membrane exhibited the highest FRR (96%) and the lowest irreversible fouling resistance (6%). The nanofiltration performance of the prepared membranes was evaluated by dye removal and salt retention. The results proved the high dye removal capability of modified membranes (98% rejection) compared with the unfilled PES membrane (89% rejection). The salt retention sequence for membrane with 0.2 wt% of nanoparticles was Na₂SO₄ (70%)>MgSO₄ (60%)>NaCl (18%).     

A thin film composite membrane supported by a hydrophilic poly(vinyl alcohol‐co‐ethylene) nanofiber membrane: Preparation,characterization, and application in nanofiltration

In this study, a fabricated hydrophilic poly(vinyl alcohol‐co‐ethylene) (PVA‐co‐PE) nanofiber membrane was used as the middle support layer to prepare thin film composite (TFC) membranes for nanofiltration. The effects of the supporting nonwoven layer, grams per square meter (GSM) of nanofiber, reaction time, heat treatment, monomer concentration, operating pressure, and pH value on the separation performance of the TFC membranes were analyzed. These results show that the TFC membranes prepared with the PVA‐co‐PE nanofiber membrane can be used to filtrate different metal ions. For NaCl, Na₂SO₄, CaCl₂, CuCl₂, CuSO₄, and methyl orange solutions, the rejection rates of the TFC membrane with nonwoven polyester as the supporting layer and a nanofiber GSM of 12.8 g/m² are 87.9%, 93.4%, 92.0%, 93.1%, 95.8%, and 100%, respectively. This indicates the potential application of the PVA‐co‐PE nanofiber membrane in the preparation of nanofiltration and reverse‐osmosis TFC membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46261.     

Innovative hydrophobic/hydrophilic perfluoropolyether (PFPE)/polyvinylidene fluoride (PVDF) composite membrane for vacuum membrane distillation

Though membrane distillation (MD) has gained more and more attention in the field of desalination, the wetting phenomenon was still a non-negligible problem. In this work, a method combined dip-coating and UV in situ polymerization for preparing hydrophobic/hydrophilic perfluoropolyether (PFPE)/polyvinylidene fluoride composite membranes. This composite membrane consisted of a top thin hydrophobic coating layer and hydrophilic substrate membrane. In terms of anti-wetting properties, contact angle and liquid entry pressure of all composite membranes (except for those based on 0.45 μm) exceeded 160° and 0.3 MPa, respectively. In particular, the desalination performance was tested in vacuum membrane distillation tests by feeding 3.5% (mass) saline solution (NaCl) at 60 ℃. The composite membranes with larger support pore size and lower PFPE content had higher membrane distillation flux. And for stability tests (testing the 0.22 μm membrane coated by 5% (mass) PFPE), the highest MD flux 29.08 kg·m^-2·h^-1 and stable salt rejection (over 99.99%) during the period. Except that, the effects of coating material concentration and pore sizes of substrate membrane were also investigated for surface morphology and topography, porosity, mechanical strength and pore size characteristics. This work provided a simple and effective alternative to prepare excellent hydrophobic composite membranes for MD applications.     

Improved separation performance of polyamide based reverse osmosis membrane incorporated with poly(dopamine) coated carbon nanotubes

A series of polyamide thin-film nanocomposite (PA TFN) membranes have been fabricated by incorporating hydrophilic poly(dopamine) (PDA) coated carbon nanotubes (CNTs@PDA) into the PA selective layer via interfacial polymerization. The effects of PDA coating thickness on surface characteristics and separation performances of membranes are studied in detail. The PDA coating makes the surface of PA TFN membrane more hydrophilic, smoother and less electronegative. The desalination performance is obviously influenced by the coating thickness of PDA and the loading concentration of PDA@CNTs. The water fluxes of PDA@CNTs incorporated PA TFN membranes have been improved without sacrificing NaCl rejections. When the loading concentration is 0.0010%, the maximum water flux is 48.1 L m⁻² h increasing by 45% compared with that of pristine PA membrane. Meanwhile, the NaCl rejection is up to 99.8%. The CNTs@PDA incorporated PA TFN membranes exhibit better anti-fouling property and separation performance durability. This work proves that CNTs@PDA has great potential application in PA TFN membranes.     

Desalination by membrane distillation adopting a hydrophilic membrane

Direct contact membrane distillation (MD) by means of composite membranes with a PVA/PEG hydrophilic layeron a hydrophobic PVDF substrate has been developed for desalination. The effects of brine temperature, salt concentration, running time and the addition of ethanol on the flux of composite membranes have been investigated. Results showed that the flux of the composite membrane did not deteriorate by adopting an additional hydrophilic membrane although durability was obviously improved. More than 99% of the separation coefficient in one run was achieved with the conductivity of the produced fresh water in the range of 6-10 μs/cm. The flux of the composite membrane retained 91% flux of substrate at 70°C, being 23.7 kg/h·m². When the brine temperature rose to 70°C, the composite membrane showed a declined concentration polarisation, with a smaller C_mb/C_b (3.89) than that of the substrate (5.79). Although the flux decreased with the increase of brine concentration, it retained 64% flux of pure water at brine solution containing 20% NaCl and was kept almost constant until 25% NaCl. In the continuous running experiments, there was no obvious drop of flux, even after adding 25% ethanol to the brine and running overnight. It is expected that adopting a hydrophilic layer can prohibit the wetting problem that faced traditional MD with hydrophobic membranes.     

Polyacrylic desalination membranes. I. Synthesis and characterization

A new class of desalination membranes has been developed. The membranes were prepared by polymerizing mixtures of two hydrophilic monomers (N-methyloacrylamide and acrylic acid), a hydrophobic monomer (ethyl acrylate) and a hydrophobic crosslinking monomer (trimethylol propane trimethacrylate) followed by heat treatment. The membranes were homogeneous, averaging about 6 mils in thickness. They were characterized by measuring water contents and salt distribution coefficients using an immersion technique. The fractional water contents in the membranes varied between 0.16 and 0.44 as the molal salt distribution coefficients increased from ca. 0.22 to 0.43. Increasing contents of the hydrophobic monomer and/or crosslinking monomer led to decreased water and salt contents, as expected. A model is postulated in which the water is assumed to be distributed within the polymer in two forms: (1) as primary water, hydrogen-bonded with hydrophilic polymer groups, and (2) secondary water, imbibed with salt from the external solution into hydrophilic regions or defects within the polymer matrix. It was found that primary water content was approximately constant for all compositions and varied between ca. 2–3 moles of primary water/mole of hydrophilic monomer in the membrane.     

Polypropylene membranes modified with interpenetrating polymer networks for the removal of chromium ions

Polypropylene (PP) membranes incorporating poly[(ar‐vinylbenzyl) trimethylammonium chloride] P(ClVBTA), and poly[sodium (styrene sulfonate)] P(SSNa) were modified via an “in situ” radical polymerization synthesis. Two methods were used for impregnation of the reactive solution: pressure injection and plasma superficial activation with argon gas. The following conditions were varied: the monomer concentrations, number of injections, and cross‐linked concentration. The modified polypropylene membranes were then characterized using scanning electron microscopy/energy dispersive X‐ray spectroscopy, Fourier transform‐infrared spectroscopy, electrokinetic potential, and Donnan dialysis for the chromium ions transport. The modified membranes exhibited a hydrophilic character with a water uptake capacity between 15% and 20% and a percent modification between 2.5% and 4.0%. This was compared with the results of an unmodified polypropylene membrane as the blank and the mentioned polypropylene membrane has not the capacity to uptake water because this kind of material is highly hydrophobic. Hexavalent chromium ions were efficiently transported by the modified membranes containing P(ClVBTA) via a plasma method and it achieved 59.2% extraction at pH 9.0 using a 1‐mol L^?1 NaCl extraction agent. Therefore, unmodified polypropylene membrane shows an extraction percentage close to 10% from the hexavalent chromium ions at pH 9.0. In the same way, the trivalent chromium transport using membranes modified with P(SSNa) achieved 49.0% extraction at pH 2.0 using 1 × 10^?1 mol L^?1 HNO₃ and 1 mol L^?1 NaCl as the extraction agents. Moreover, the unmodified polypropylene membrane reached a value close to 10% from the trivalent chromium ions using 1 × 10^?1 mol L^?1 HNO₃ and 1 mol L^?1 NaCl. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41953.     

三乙酸纤维素正渗透膜的制备与性能

以三乙酸纤维素（CTA）为膜材料,1,4-二氧六环、丙酮为溶剂,甲醇、乳酸为添加剂,采用相转换法制备了三乙酸纤维素正渗透膜。研究了不同1,4-二氧六环/丙酮配比、添加剂乳酸含量、挥发时间、膜厚度、热处理温度条件下正渗透膜性能的变化规律。研究表明,当采用纯水为原料液,0.56mol/L CaCl2为汲取液时,优化制备的CTA正渗透膜的水通量达到14.10L/(m2?h),溶质反扩散量为0.031mol/(m2?h);采用0.1mol/L NaCl为原料液,4mol/L葡萄糖为汲取液时,优化制备的CTA正渗透膜的水通量保持在5L/(m2?h)以上,对NaCl的截留率大于99%。CTA正渗透膜相比于HTI膜,具有较高的亲水性、水通量、截留率,稳定性更好。     

TiO2-incorporated polyelectrolyte composite membrane with transformable hydrophilicity/hydrophobicity for nanofiltration separation

The wettability of the membrane surface has shown obvious influent on the separation performance of the membrane. In this work, a hydrophilic PDA-[PDDA/TiO₂]⁺ Cl⁻ membrane was prepared by a one-step codeposition of poly(diallyldimethylammonium chloride) (PDDA) polyelectrolyte solution containing positively charged TiO₂@PDDA nanoparticles with the assistance of dopamine (DA). Such positively charged membrane can be transformed into a hydrophobic membrane PDA-[PDDA/TiO₂]⁺ PFO⁻ via the counterion exchange between Cl⁻ and PFO⁻ (perfluorooctanoate). The transformation between hydrophilicity and hydrophobicity is reversible. For both hydrophilic and hydrophobic membranes, the nanofiltration performances were respectively investigated by the aqueous solution and ethanol solution of dyes including methyl blue (MB), Congo red (CR) and Evans blue (EB), and as well metal salt aqueous solution. The consecutive running stability and anti-fouling performance of both hydrophilic and hydrophobic membranes were explored. The results revealed that both membranes showed high nanofiltration performances for retention of dyes in (non)aqueous solution. For the hydrophilic membrane, the rejection of salts in a sequence is MgSO₄ > Na₂SO₄ > MgCl₂ > NaCl. Moreover, both of the hydrophilic and hydrophobic membranes showed high stability and antifouling property.     

Polyacrylic desalination membranes. II. Reverse osmosis performance

A new class of polyacrylic membranes has been tested under reverse osmosis conditions on dilute (1%–4%) salt solutions. Fluxes up to 0.2 gal-mil/ft²-day at greater than 98% rejection have been achieved. The effect of membrane composition on product flux and salt rejection is discussed. Increased fluxes at even higher rejection should be possible by proper selection of the type and concentration of hydrophilic, hydrophobic, and crosslinking monomers. It is concluded that improved membranes should have as high as possible a concentration of hydrophilic groups, distributed randomly through a lightly crosslinked, rubbery polymer matrix.     

Green lignin-based polyester nanofiltration membranes with ethanol and chlorine resistance

As the main water treatment material, polymeric membranes inevitably suffer from membrane fouling. In this work, novel lignin-based polyester composite nanofiltration membranes (NFM) with ethanol and chlorine resistance were fabricated via interfacial polymerization. Lignin alkali (LA), a green lignin derivative, typically treated as chemical waste in the paper industry, was employed as the aqueous monomer, trimesoyl chloride (TMC) is served as the organic monomer. The structure and separation properties of the lignin-based NFM were studied, revealing that the dense polyester separation layer may show good performance for dye removal. The rejections of the optimized LA/TMC-3 membrane with an excellent permeation flux of 13.9 kg m^?2?h^?1 for rose Bengal sodium salt, brilliant blue, congo red, rhodamine B, MgSO₄, and NaCl are 97.6%, 97.3%, 97.8%, 71.34%, 51.4%, and 31.8%, respectively. Moreover, the LA/TMC-3 membrane also shows long-term tolerance in ethanol and sodium hypochlorite solution; the rejection of LA/TMC-3 to dye only decreases 8% after 8 days when immersed in alcohol, while the normalized rejection maintains 94% after 4000 ppm-hours of continuous exposure to chlorine. This lignin-based polyester membrane may broaden the sustainable utilization sphere of lignin derivatives, at that provide a referable direction for the development of membrane materials.     

Preparation of graphene oxide/polyamide composite nanofiltration membranes for enhancing stability and separation efficiency

Polyamide (PA) NF membranes are synthesized on a hollow fiber support by the interfacial polymerization (IP) of piperazine (PIP) and trimesoyl chloride (TMC). Then, GO is coated on the PA layer to decorate the NF membrane surface (denoted GO/PA-NF). This strategy aims to improve the hydrophilicity, chlorine resistance and separation stability of the membrane. The optimization, chemical composition, morphology, and hydrophilicity of the synthesized GO/PA-NF membrane are characterized. Results indicate that the optimized GO/PA-NF in terms of rejection rate and flux are with 0.05 wt% GO. The rejection of GO/PA-NF for Na2SO₄ and MgSO₄ is 99.4% and 96.9%, respectively. Even if the GO/PA-NF is immersed in 1000 ppm NaClO solution for 48 h, the NF membrane still maintains stable salt rejection. The developed NF membranes exhibit excellent treatment performance on dying wastewater. The permeate flux and rejection of GO/PA-NF toward Congo red solution are determined to be 44.2 L/m²h and 100%, respectively. Compared with the PA membrane, GO/PA-NF presents a higher rejection for Na₂SO₄ (99.4%) and a lower rejection for NaCl (less than 20%), which shows that the NF membranes have a better divalent/monovalent salt separation performance. This study highlights the superior performance of GO/PA-NF and shows its high potential for application in wastewater treatment.     

Interfacially polymerized thin film nanofiltration membranes on TiO2 coated polysulfone substrate

In this study, a new approach was developed to prepare the novel thin film composite nanofiltration membranes. In this new approach, nanoparticles were coated completely under the polymeric thin film layer. Thin film composite (TFC) membranes were fabricated by interfacial polymerization on polysulfone (PSf) sublayer using m-phenylenediamine (MPD) and trimesoyl chloride (TMC) respectively as amine monomer and acid chloride monomer. Scanning electron microscopy and atomic force microscopy were used to study surface morphology and roughness properties of NF membranes. Energy dispersive X-ray microanalysis (EDX) was used to analyze the elemental change before and after filtration experiment. Chemical structure and thickness of polyamide formed on TFC membranes were observed by Fourier transmission infrared attenuated total reflectance (FTIR-ATR) spectroscopy. Permeability, salt rejection and pepsin macromolecule rejection of prepared membranes were tested using dead end filtration cell. Antifouling behavior of the membranes was studied by filtering pure water before and after pepsin solution filtration. A smoother and thicker surface without any defect appeared as the concentration of nanoparticle was increased. NaCl rejection was increased from 70% for neat nanofiltration membrane to 84% for 0.5 wt% TiO₂ modified nanofiltration membrane. Antifouling and permeability behavior of the prepared membranes were improved in the new approach. Antibacterial property of prepared membranes was improved as a result of photocatalytic characteristic of TiO₂ nanoparticles.     

Sub-20 nm Bilayer Hydrophilic Poly(Vinyl Pyrrolidone) Coatings for Antifouling Nanofiltration Membranes

Fouling is a major concern in membrane technology. Neutral hydrophilic coatings alleviate fouling on membrane surfaces by passively resisting the adsorption of foulants without altering the properties of membranes. Coatings, however, often result in a trade-off of reduced water flux. Ultrathin hydrophilic coatings could minimize the influence on water flux, but its fabrication is challenging via traditional methods. Here, fabrication of sub-20 nm bilayer hydrophilic coating is reported that is grafted onto nanofiltration (NF) membranes via a one-step initiated chemical vapor deposition (iCVD) method. The iCVD coating is conducted by conformally depositing a crosslinked poly(vinyl pyrrolidone-co-ethylene glycol dimethacrylate) bottom layer on pretreated NF membrane, followed by in situ grafting of poly(vinyl pyrrolidone) homopolymer to further improve surface hydrophilicity. Both thickness and crosslinking degree of the bottom coating are systematically tailored to reduce its side effects on permeation rate and salt rejection. The modified NF membranes exhibit 99% lower microbial adhesion compared to the pristine membrane, with minor impact on permeation and salt rejection performance. The coating is also stable against continuous ultrasonication. The reported method is thus expected to shed light on facile novel ways of reducing membrane fouling in desalination and industrial wastewater treatment.     

Separation performance of thin-film composite nanofiltration membrane through interfacial polymerization using different amine monomers

Four kinds of thin-film composite (TFC) membranes were prepared via interfacial polymerization using diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA) and piperazidine (PIP) as water-soluble monomer, and trimesoyl chloride (TMC) as organic-soluble monomer. The surface chemical features of the resultant membranes were confirmed by contact angle measurement and Fourier transform infrared spectroscopy (FTIR). The membrane morphology and surface charges were investigated through Scanning electronic microscopy (SEM) and Zeta potential, respectively. Salt rejection was used to evaluate the separation performance of the four kinds of TFC membranes. The results showed that all the four kinds of TFC membranes exhibited typical negatively charged nanofiltration membrane characteristics. The salt rejections followed the sequence: Na₂SO₄ > MgSO₄ > MgCl₂ and the rejection of Na₂SO₄ was all over 80%. It was also found that the solubility of water-soluble monomer in organic solvent played an important role in manipulating the membrane structure, charge properties and thus the separation performance.     

The effect of short air exposure periods on the performance of cellulose acetate membranes from casting solutions with high cellulose acetate content

Highly productive cellulose acetate membranes were cast under conditions of very short air exposure periods from cellulose acetate–acetone–formamide casting solutions having a high cellulose acetate (CA) content and lying close to the phase boundary. Air exposure periods as short as 0.05 sec were used with CA content up to 32 wt-%. Membranes from a casting solution containing 30 wt-% cellulose acetate (E-398-3), 45 wt-% acetone, and 25 wt-% formamide perform as well as membranes from other compositions at all salt rejection levels for a 0.5 wt-% NaCl feed at 600 psig. Partial replacement of acetone by dioxane in the casting solution substantially increases the water flux from membranes cast with short air exposure periods at any given salt rejection level below 96% salt rejection. Addition of small amounts of ZnCl₂ to nondioxane casting solutions with 32 wt-% CA improves membrane performances remarkably for lower salt rejection levels, while the improvement in performance of membranes from 30 wt-% CA casting solutions with dioxane due to ZnCl₂ addition is marginal. Variation in air exposure from 0.05 to 2 sec results in minor performance variations in the membranes having any of these compositions. With air exposure periods beyond 2–3 sec, membrane fluxes drop drastically. The concept of a thinner skin satisfactorily explains the improvement in mixed solvent systems, whereas ZnCl₂ acts as a swelling salt. A Kimura-Sourirajan-type membrane performance plot indicates that for a 0.5 wt-% NaCl feed at 600 psig, membranes of the present work perform as well as the best performing membranes reported in the literature for conversion of brackish water.