Composite Reverse Osmosis Membranes Research Articles

Polyamide reverse osmosis membranes containing 1D nanochannels for enhanced water purification

Thin-film composite (TFC) reverse osmosis (RO) membrane is the gold-standard for desalination and water reuse. Recent literature highlights the importance of polyamide (PA) rejection layer containing nanovoids to manipulate the water permeability and salt rejection. In this study, a facile template-assisted approach was applied to generate one-dimensional (1D) nanochannels in the polyamide rejection layer of RO membranes by preloading copper nanorods inside the PA layer followed by acid etching. In addition, a TFC RO membrane containing 0D nanovoids was also fabricated to compare the dimensional effect of nanochannels on membrane morphologies and performances. Specifically, the TFC-0D membrane only exhibited 61% higher water permeability compared to that of the control TFC, while the TFC-1D membrane showed 126% higher water flux with similar NaCl rejection, probably due to the dimensional improvement of the nanochannels inside the rejection layer. This templates-assisted approach paves a feasible way for fabricating high-performance next-generation RO membranes.

Zwitterionic coating on thin-film composite membranes to delay gypsum scaling in reverse osmosis

Precipitation of calcium sulfate dihydrate (i.e., gypsum) on the membrane active layer negatively impacts the efficiency of reverse osmosis (RO) systems by increasing overall operation and maintenance costs. The interfacial free energy between RO membranes and scalants is expected to play a paramount role in crystal nucleation and adsorption. In this work, we modified the surface of a thin-film composite RO membrane with a zwitterionic polymer brush via atom transfer radical polymerization (ATRP) to impart superhydrophilicity for enhanced resistance to gypsum scaling. The zwitterionic polymer coating was optimized and a highly hydrophilic membrane surface displaying a water contact angle of <20° was achieved. Characteristics of both the control and the zwitterion-modified RO membranes such as surface roughness, chemical composition, and surface energy components, were investigated to elucidate the factors controlling gypsum scaling behavior. Results from bench-scale RO scaling experiments indicate that membranes modified with the zwitterionic brush effectively delay gypsum surface nucleation and crystal adsorption relative to the control membrane. At the end of the RO scaling experiments with only-heterogeneous gypsum nucleation, the zwitterion-modified membrane exhibited a flux decline of 23.7% (relative to the initial water flux), much smaller than a 49.5% flux decline of the control RO membrane. We further verified that a precipitous flux decline by deposition of gypsum crystals in the combined homogeneous and heterogeneous nucleation pathway was about 1.6 times delayed for the zwitterion-modified membrane compared to the control RO membrane. Our results highlight that developing a more hydrophilic membrane surface is crucial to resisting gypsum scaling in RO systems.

Bioinspired chlorine-resistant tailoring for polyamide reverse osmosis membrane based on tandem oxidation of natural α-lipoic acid on the surface

Active chlorine-vulnerability is the Achilles' heel for polyamide thin film composite (PA-TFC) reverse osmosis (RO) membranes during water desalination and/or purification. Chlorination disrupts the delicate PA skin layer on porous support, resulting in significantly deteriorative membrane permselectivity and rising maintenance cost. Inspired by the superior antioxidative capacity of biologically endogenous α-lipoic acid (LA), this work was dedicated to tailoring a chlorine-resistant RO membrane with LA sacrificial unit on the surface. It was evidenced that the characteristic dithiolane within LA preferentially reacted with active chlorine in feedwater, and the intimal PA selective layer was thus safeguarded from chlorine-triggered oxidation. The modifier was pre-assembled with LA and polyethylenimine (PEI) as the mediator, subsequently tethered onto membrane surface via one-step chemical coupling without any catalysts. A pretty balance between membrane permselectivity and grafted modifier amount was achieved via regulating the modifier concentration. The modified membrane exhibited significantly ameliorative chlorine-resistance relative to the pristine one, with normalized salt rejection still remained (99.3 ± 0.6)% and only (17 ± 5)% final flux loss after a rigorous static chlorine exposure of 8000 ppm·h under acidic condition (confidence level, P = 95%). The electronic energy differences of chlorination-involved chemical procedures were determined by density functional theory (DFT) calculation, and an energy-favored three-stage tandem oxidation mechanism of LA moiety was proposed. Accordingly, up to 5 equiv. of active chlorine can be captured by a single sacrificial unit. Such intrinsically high chlorine-consumption efficacy of LA-based sacrificial layer would retard the chlorination saturation that commonly invalidates sacrificial layers. This bioinspired work shed light on a novel, facile, and effective anti-chlorine strategy for PA-TFC RO membrane to maintain the stability of service performance.

Cryosectioning diagnosis and enzymatic cleaning of reverse osmosis membrane biofouling: Part I

Biofouling of reverse osmosis membranes is one of the main reasons for the flux decline in water reuse applications in the filtration industry. A simple screening approach to evaluate such membranes for their propensity to biofouling and a means of removing biofoulants, without changing surface physicochemical properties, would be of benefit to this sector. The objectives of this research are to investigate the mode of action of Subtilisin protease- and lipase-based enzymatic cleaning of thin-film composite reverse osmosis membrane biofoulants, and characterise the effects of the biofilm-resistant membrane surfaces by using cryosectioning of the membrane with biofilm on its surface. The first instalment of this article, which appears here, provides an introduction to the research, the materials and methods used and the first part of the results, which discusses biofilm formation, and quantitative measurements and visualisation of biofoulants on reverse osmosis membranes. Part II will be published in the September 2020 issue of Membrane Technology.

Surface functionalization of reverse osmosis membranes with sulfonic groups for simultaneous mitigation of silica scaling and organic fouling

Organic fouling and inorganic scaling are the main hurdles for efficient operation of reverse osmosis (RO) technology in a wide range of applications. This study demonstrates dual-functionality surface modification of thin-film composite (TFC) RO membranes to simultaneously impart anti-scaling and anti-fouling properties. Two different grafting approaches were adapted to functionalize the membrane surface with sulfonic groups: (i) non-specific grafting of vinyl sulfonic acid (VSA) via redox radical initiation polymerization and (ii) covalent bonding of hydroxylamide-O-sulfonic acid (HOSA) to the native carboxylic groups of the polyamide layer via carbodiimide mediated reaction. Both approaches to graft sulfonic groups were effective in increasing surface wettability and negative charge density of the TFC-RO membranes without significant alteration of water and salt permeabilities. Importantly, we verified through surface elemental analysis that covalently bound HOSA effectively covers the native carboxylic groups of the PA layer. Both the VSA and HOSA membranes exhibited lower flux decline during silica scaling and organic (alginate) fouling relative to the control unmodified membrane, demonstrating the unique versatility of sulfonic groups to endow the TFC-RO membranes with dual functionality to resist scaling and fouling. In particular, the HOSA membrane showed excellent physical cleaning efficiencies with water flux recoveries of 92.5 ± 1.0% and 88.4 ± 6.4% for silica scaling and alginate fouling, respectively. Additional results from silica nucleation experiments and atomic force measurements provided insights into the mechanisms of improved resistance to silica scaling and organic fouling imparted by the surface-functionalized sulfonic groups. Our study highlights the promise of controlled functionalization of sulfonic groups on the polyamide layer of TFC membranes to enhance the applications of RO technology in treatment and reuse of waters with high scaling and fouling potential.

Comprehensive studies of membrane rinsing on the physicochemical properties and separation performance of TFC RO membranes

Transport behaviour of thin film composite (TFC) reverse osmosis (RO) membrane is highly dependent on the physicochemical property of the uppermost polyamide (PA) layer. In this work, we provide a comprehensive understanding of the impacts of post interfacial polymerization (IP) rinsing using either organic solvents (i.e., hexane, cyclohexane and isoparaffin-G) or aqueous solution on the structure and chemistry of PA layer and correlate the properties change to membrane performance. Evidently, the desalination performance of the aqueous-rinsed membrane is better than the organic solvents-rinsed membrane. Compared to the un-rinsed membrane, the aqueous-rinsed membrane also showed 28% higher pure water flux and 13% lower water contact angle (i.e., greater hydrophilicity) with least compromised NaCl rejection (97.70%). This is possibly caused by its reduced PA cross-linking degree and/or hydrolysis of acyl chloride monomers that alter the membrane surface chemistry. It is also found that the introduction of air-drying prior to the rinsing process could improve the membrane reproducibility as a result of extensive polymerization. The findings from this experimental work confirmed that aqueous solution is the best rinsing solution for TFC RO membrane fabrication, improving both physicochemical properties and water permeability of membrane.

Precise assembly of a zeolite imidazolate framework on polypropylene support for the fabrication of thin film nanocomposite reverse osmosis membrane

Polypropylene (PP) has been widely used in the fields of lithium battery separators, proton exchange membranes, membrane bioreactors and polyamide (PA) thin film composite (TFC) reverse osmosis (RO) membranes owing to its excellent mechanical strength, chemical durability and low cost. Nevertheless, its inherent strong hydrophobicity and low surface porosity severely limit its in-depth development in the field of polyamide TFC membranes. Herein, we propose a general strategy for the precise assembly of ZIF-8 nanoparticles on PP support for the fabrication of RO membrane. By this method, position induced nanoporous surface (PINS) was introduced via in-situ synthesis of ZIF-8 assisted by diazonium-induced anchoring process (DIAP) on PP support, and it would achieve precise repair of non-porous regions of PP support, thereby increasing its surface porosity and hydrophilicity of PP support. Subsequently, a high-performance ZIF-8 hybrid reverse osmosis (HPP-ZIF-8-RO) membrane was fabricated by conventional interfacial polymerization (IP) on modified commercialized PP support for the first time. The optimal rejection of HPP-ZIF-8-RO for NaCl is ~99%, and the water flux is up to 50 kg m−2 h−1 under the operating pressure of 1.55 MPa. In addition, the HPP-ZIF-8-RO membrane has a superior chemical stability after the solvent resistance test. To prove the university of DIAP and PINS, we have successfully fabricated other types of HPP-MOF-RO (HPP-ZIF-67-RO, HPP-HKUST-1-RO) which also show enhanced desalination performance. Hence, DIAP and PINS could provide a convenient and versatile method for precise repairing the defect area of the hydrophobic porous substrates.

Enhancing the permeability of reverse osmosis membrane by embedding the star‐like rigid supports in the substrate

AbstractThin film composite (TFC) reverse osmosis (RO) membranes with high permeability have been prepared by interfacial polymerization based on tailoring the polysulfone (PSf) substrate structure by in situ embedded poly(p‐phenylene terephthamide) (PPTA) star‐like rigid supports. The star‐like rigid supports were observed by the polarizing optical microscopy (POM) and transmission electron microscope (TEM). The surface properties of the substrates were investigated by FTIR, the water contact angle (WCA), FESEM and AFM. The WCA was decreased from 88.5° to 72.3° with the PPTA increasing from 0% to 8%, and the surface roughness increased from 24.2, 25.1, 33.5 and 58.6 nm, respectively. Furthermore, numerous interconnect micro‐structures were constructed in the substrate when the PPTA content was up to 8%. The pure water flux of 8% PPTA/92%PSf substrate was up to 377.0 L m−2 h−1 and the flux decline rate was lowest (64%) after compacted at 5.5 MPa for 30 min. Otherwise, increasing the PPTA contents in the substrate enhanced the roughness, encouraged nanosheet formation and improved the permeability of TFC RO membranes. The pure water flux of the TFC RO membranes increased from 36.32 to 58.42 L m−2 h−1, where the NaCl rejection was about 99.5% at 5.5 MPa.

Tuning thin-film composite reverse osmosis membranes using deep eutectic solvents and ionic liquids toward enhanced water permeation

Deep eutectic solvents (DES) have invoked an enormous interest as inexpensive, greener and biorenewable solvents and additives with promising applications. In the present study, we investigated a choline chloride-urea based DES and a series of commercial ionic liquids (ILs) as additives including 1-hexyl-3-methyl-imidazolium chloride, 3-methyl-1-octyl-imidazolium tetra fluoroborate, N-butyl pyridinium and betaine monohydrate to modify the polyamide (PA) layer of reverse osmosis (RO) membranes. The ILs were selected from various categories to find better of them in RO modification. Accordingly, the DES and ILs with different concentrations were added to the MPD aqueous solution. The results of SEM and AFM analyses showed a smoother surface for the DES and ILs-modified membranes. The membrane modified with 1 wt% of DES achieved the pure water flux of 56.7 L/m2h and the observed salt rejection of 96.4%, exhibiting a 27% and 3% increase in water flux and salt rejection, respectively, as compared with the unmodified membrane. Among the used ILs, the membranes modified with N-butyl pyridinium and betaine monohydrate showed the best desalination performance, with the pure water flux of 78.9 L/m2h and 51.7 L/m2h and the NaCl rejection of 97.3% and 94.4%, respectively. Also, choline hydroxide IL was used for the surface modification of the SO3H-g-C3N4 nanosheets to examine efficiency of ILs on membranes, when located on nanosheet surface. The results of the desalination experiments showed that the incorporation of the modified nanosheets at low concentrations was effective in enhancing the membrane performance. Although increasing the concentrations of nanosheets in the PA layer of the membranes resulted in the enhanced water flux, the salt rejection was decreased.

Enhancing the Chlorine Stability and Antifouling Properties of Thin-Film Composite Reverse Osmosis Membranes via Surface Grafting L-Arginine-Functionalized Polyvinyl Alcohol

Polyamide (PA) thin film composite reverse osmosis (RO) membranes have been extensively used in desalination industry today. However, the poor chlorine resistance and anti-fouling properties greatl...

Plugging nanoscale imperfections in the polyamide active layer of thin-film composite reverse osmosis membrane to inhibit advective solute transport

The objective of this study is to inhibit advective solute passage through reverse osmosis (RO) membranes by filtering a small volume of polyvinyl alcohol (PVA) aqueous solution for 1 min at 0.1 MPa to selectively plug nanoscale imperfections. The PVA plugging the nanoscale imperfections was stabilized by cross-linking with glutaraldehyde. Experimental data showed that PVA treatment with PVA concentrations of up to 20 ppm did not decrease the water permeability, but it improved the solute removal efficiencies significantly. Specifically, at an applied pressure of 2.0 MPa, the NaCl and Rhodamine-WT rejection improved from 97.4% to 98.8% (a 67% decrease in NaCl flux) and 99.74% to 99.96% (a 85% decrease in Rhodamine-WT flux), respectively. Modeling analysis using a solution-diffusion model coupled with unhindered advection through nanoscale imperfections demonstrated that these improvements in solute rejection were due to selective plugging of nanoscale imperfections by PVA without building up an additional resistive layer on the polyamide active layer. Experimental data also showed that the cross-linked PVA plugging the nanoscale imperfections was stable under repeated exposure to citric acid, sodium hydroxide, and ethylenediaminetetraacetic acid.

Oily Wastewater Treatment Using Polyamide Thin Film Composite Membrane Technology.

In this study, polyamide (PA) thin film composite (TFC) reverse osmosis (RO) membrane filtration was used in edible oil wastewater emulsion treatment. The PA-TFC membrane was characterized using mechanical, thermal, chemical, and physical tests. Surface morphology and cross-sections of TFCs were characterized using SEM. The effects of edible oil concentrations, average droplets size, and contact angle on separation efficiency and flux were studied in detail. Purification performance was enhanced using activated carbon as a pre-treatment unit. The performance of the RO unit was assessed by chemical oxygen demand (COD) removal and permeate flux. Oil concentration in wastewater varied between 3000 mg/L and 6000 mg/L. Oily wastewater showed a higher contact angle (62.9°) than de-ionized water (33°). Experimental results showed that the presence of activated carbon increases the permeation COD removal from 94% to 99%. The RO membrane filtration coupled with an activated carbon unit of oily wastewater is a convenient hybrid technique for removal of high-concentration edible oil wastewater emulsion up to 99%. Using activated carbon as an adsorption pre-treatment unit improved the permeate flux from 34 L/m2hr to 75 L/m2hr.

Structure regulation for synergistically improving the permeation properties of the reverse osmosis membrane based on an amphiphilic hyperbranched polymer

The aromatic polyamide (PA) thin film composite (TFC) reverse osmosis (RO) membrane has been widely used in the desalination processes to settle the global water crisis. To further decrease the desalination cost, in this work, an amphiphilic hyperbranched polymer of HBPO-star-PEO-COCl with abundant end groups of acyl chloride and core-shell hydrophilic/hydrophobic phase separation structure was synthesized and used as the functional nanomaterial to modify the conventional polyamide TFC RO membrane through interfacial crosslinking reaction. The modified RO membrane with 0.005% HBPO-star-PEO-COCl presents the optimal structure and permeation properties. Its PA layer becomes thinner and denser, and its water flux reaches 69.8LMH nearly double that of the original membrane (33.27LMH), at the same time, its NaCl rejection rate reaches 99.22% higher than that of the original membrane. It can attribute to the unique amphiphilic core-shell structure of HBPO-star-PEO-COCl. On the one hand, the PEO shell of HBPO-star-PEO-COCl is highly hydrophilic while the internal HBPO is highly hydrophobic and collapses easily in water to form a three-dimensional quasi-spherical structure, which leads to the formation of the core-shell two-phase interface, thereby facilitating the water molecules to rapidly pass through the PA layer along the hydrophobic wall surface. On the other hand, the end acly chloride groups of HBPO-star-PEO-COCl take part in the crosslinking reaction, which makes the PA layer have higher crosslinking degree and become denser, thereby enhancing the salt retention. Therefore, this study provides an effective way to fabricate a new reverse osmosis composite membrane with favorable comprehensive separation performance based on amphiphilic hyperbranched polymer.

Emerging sandwich-like reverse osmosis membrane with interfacial assembled covalent organic frameworks interlayer for highly-efficient desalination

Covalent organic frameworks (COFs) have emerged as promising candidate for the construction of advanced separation membranes due to their well-defined pore structure and highly ordered porous channels. Nevertheless, the implementation of high-efficient COFs-incorporated membranes still suffers from harsh synthetic conditions and possible agglomeration of COFs. Herein, a kind of sandwich-like thin film composite reverse osmosis (RO) membranes was fabricated to overcome such challenges via interfacial assembly of a COFs interlayer on polysulfone substrate, then followed by the formation of a polyamide skin layer via traditional interfacial polymerization (IP) process. The COFs interlayer not only tailored the pore structure and interfacial properties of the substrate, but also manipulated the uptake and release of the amine monomer during the IP process, which would contribute to forming a more ordered polyamide separation layer. The resultant COFs-interlayered RO membrane exhibited a nearly 33.8% higher water permeance (16.78 L m−2 h−1 MPa−1) along with a slightly increased NaCl rejection (99.2%) compared with the pristine RO membrane. More importantly, the emerging RO membrane presented a superior chemical (critic acid and NaOH) resistance and desirable long-term filtration stability, which paved a new pathway to construct high-performance RO membranes for desalination.

Low-fouling biomimetic membranes fabricated by direct replication of self-cleaning natural leaf

ABSTRACT The membrane fouling has always been a big issue for developing membrane applications. Surface morphology and roughness affect remarkably on the membrane tendency to fouling. In this study, a biomimetic technique, as a simple, cost-effective and time-saving method was employed to replicate Tropaeolum majus (nasturtium) leaf surface on the surface of a commercial thin-film composite (TFC) reverse osmosis (RO) membrane using polyethersulfone (PES) moulds. Morphology of surface and hydrophilicity of membranes were investigated by scanning electron microscope (SEM), atomic force microscope (AFM) and water contact angle measurements. AFM and SEM photos of membrane surface declared that replication of nasturtium leaf improved the surface characteristics of membranes. The average roughness of membranes heated at 130°C and 150°C was 81.1 and 152.4 nm, respectively. The similar measurement was lower for the virgin membrane. Also, the roughened membranes showed higher hydrophilicity than the virgin membrane. In addition, the performance of the membrane was assessed by evaluating pure water flux (PWF) and flux recovery (FR) after the filtration of whey solution as a severe foulant for membranes. The findings exhibited that the replicated membranes had higher PWF and FR values, indicating the lower fouling tendency of modified membranes.

Facile dual-functionalization of polyamide reverse osmosis membrane by a natural polypeptide to improve the antifouling and chlorine-resistant properties

Long-term durability is of significant importance for the polyamide thin film composite (PA-TFC) reverse osmosis (RO) membranes under the complicated operation conditions of the water treatment. Herein, dual-functional RO membranes with improved antifouling and chlorine-resistant properties were facilely fabricated. A natural polypeptide, ε-poly-l-lysine (PL), was employed as the surface modifier for RO membrane, and covalently immobilized on the PA-TFC membrane surface through one-step chemical coupling under ambient conditions, without sacrificing the permselectivity. Surface properties of the PL-modified membranes were systematically characterized, and the modification method was also optimized. The greatly enhanced surface hydrophilicity derived from PL layer resulted in less propensity to the deposition of organic foulants. Moreover, the topmost PL sacrificial layer effectively improved the membrane chlorine-resistance, with the normalized salt rejection higher than 99.5% after accelerating chlorination. The readily available modifier and straightforward modification process make PL modification on PA layer a potential strategy for the fabrication of antifouling and chlorine-resistant RO membrane.

Imaging of membrane concentration polarization by NaCl using 23Na nuclear magnetic resonance

Forward osmosis (FO) and reverse osmosis (RO) membrane processes differ in their driving forces: osmotic pressure versus hydraulic pressure. Concentration polarization (CP) can adversely affect both performance and lifetime in such membrane systems. In order to mitigate against CP, the extent and severity of it need to be predicted more accurately through advanced online monitoring methodologies. Whilst a variety of monitoring techniques have been used to study the CP mechanism, there is still a pressing need to develop and apply non-invasive, in situ techniques able to produce quantitative, spatially resolved measurements of heterogeneous solute concentration in, and adjacent to, the membrane assembly as caused by the CP mechanism. To this end, 23Na magnetic resonance imaging (MRI) is used to image the sodium ion concentration within, and near to, both FO and RO composite membranes for the first time; this is also coupled with 1H MRI mapping of the corresponding water distribution. As such, it is possible to directly image salt accumulation due to CP processes during desalination. This was consistent with literature expectations and serves to confirm the suitability of 23Na MRI as a novel non-invasive technique for CP studies.

Water transport properties of boron nitride nanosheets incorporated thin film nanocomposite membrane for salt removal

This work has focused on the fabrication of thin film composite (TFC) and thin film nanocomposite (TFN) membranes for reverse osmosis (RO) application. Raw boron nitride (BN) and chemically activated boron nitride (A-BN) were used as nanofillers in polysulfone support layer and trimesoyl chloride (TMC) to improve the membrane performance. Different concentrations of BN and A-BN (ranging from 0 to 1 wt %) were added to the polysulfone (PSf) microporous support and polyamide layer was formed on top of PSf support through interfacial polymerization of 1,3-Phenylendiamine and trimesoyl chloride. The fabricated TFN membranes were characterized in terms of membranes structure, contact angle, separation properties, as well as RO performance. According to AFM and SEM images, TFN membranes showed larger average pore size and higher surface roughness as compared with TFC membrane. Thus, TFN membrane showed higher pure water flux but lower NaCl rejection. The addition of BN led to increase in pore size of membrane without increase the selectivity of membrane. The addition of both BN and A-BN into polyamide layer does not aid to improve the properties of membrane. In conclusion, BN nanoparticles showed the potential to be used as nanofillers that aid in formation of larger pore size.

Mitigating biofouling with a vanillin coating on thin film composite reverse osmosis membranes.

Several methods, such as pretreatment, membrane surface modification, feed water chlorination, and chemical cleaning, have recently been applied to control biofouling on reverse osmosis (RO) membranes-with limited success. As an alternative, compounds that inhibit bacterial quorum sensing can be used to disrupt formation of bacterial colonies. In this study, anti-biofouling using vanillin, which is a natural substance among quorum sensing inhibitor compounds, was trialed, by modifying RO membrane surfaces with vanillin, at various concentrations. We then reviewed consequential changes to membrane surface characteristics and vanillin anti-biofouling properties. A long-term RO membrane simulator was used to analyze permeability, contact angle was measured for hydrophilicity evaluation, and membrane surface morphology was analyzed, through atomic force microscopy and scanning electron microscopy. A quorum quenching effect was confirmed by utilizing Petrifilm to count bacteria on the surface of a modified membrane. As a result, the permeability of the surface modified membranes was slightly decreased compared to the pristine membrane, but the hydrophilicity was increased, and the number of colonies decreased remarkably, the membrane modified with 0.5M vanillin outperforming that modified with 0.25M vanillin.

Novel thin-film composite reverse osmosis membrane with superior water flux using parallel magnetic field induced magnetic multi-walled carbon nanotubes

Abstract In this work, magnetic multi-walled carbon nanotubes (MWCNTs) were aligned vertically in thin film nanocomposite (TFN) reverse osmosis (RO) membranes. Magnetic MWCNTs were synthesized by in situ co-precipitation of MWCNTs, Fe2+ and Fe3+. Meanwhile, a parallel magnetic field created by two ferrite magnets was used to align magnetic MWCNTs. To simulate the magnetic field, the computer software COMSOL-Multiphysics® was applied. In order to demonstrate the impact of parallel magnetic field, two groups of TFN RO membranes (Group A and Group B) were prepared. Before the phase inversion process, polymer solutions of Group A were treated in the parallel magnetic field for 2 min, while polymer solutions of Group B were exposed to air for 2 min. As a result, under magnetic field, magnetic MWCNTs were aligned vertically on the polysulfone surface, and provided efficient water transport channels. The optimized membrane with 0.7 wt% magnetic MWCNTs of Group A obtained remarkable water flux of 11.389 L m−2 h−1 while maintaining high NaCl rejection. The results indicated that a simple and efficient method to improve water flux of TFN RO membranes was successfully developed.