Sodium Chloride Rejection Research Articles

High rejection seawater reverse osmosis TFC membranes with a polyamide-polysulfonamide interpenetrated functional layer

Current polyamide thin-film composite (TFC) membranes for seawater reverse osmosis (SWRO) require enhanced rejection capabilities for high salinity application and the removal of neutral micropollutants. In this study, we developed high rejection SWRO membranes utilizing m-phenylenediamine (MPD) as the water phase monomer, trimethyl chloride (TMC) as the organic phase monomer, and naphthalene-1,3,6-trisulfonyl chloride (NTSC) as a molecular plug. Xylene was added to the heated organic phase to compensate for the flux loss due to the tightened functional layer. The membranes were characterized in detail with ATR-FTIR, XPS, SEM, AFM, WCA, surface zeta potential, Positron annihilation spectroscopy (PALS), and quartz crystal microbalance (QCM). Our results indicate that adding xylene into the organic phase enhances flux, while heating the organic phase to 90oC benefits both flux and rejection. Furthermore, the addition of NTSC further improves the rejection. The variation in membrane flux correlates with the functional layer morphology under SEM and the membrane rejection properties correspond well with the functional layer free volume results by PALS. Due to the low reactivity of sulfonyl chloride, NTSC can only form oligomers embedding into the polyamide network, resulting in significantly higher rejection of sodium chloride (99.90 %) and boron (92.39 %) with a flux of 37.85 L m−2 h−1 under the conditions of 35000 ppm NaCl and 5 ppm boric acid at 800 psi. This work demonstrates that high rejection SWRO membranes can be successfully achieved by an in situ “swelling and filling” method.

An Innovative Surface Modification Technique for Antifouling Polyamide Nanofiltration Membranes.

In this study, we developed a novel surface coating technique to modify the surface chemistry of thin film composite (TFC) nanofiltration (NF) membranes, aiming to mitigate organic fouling while maintaining the membrane's permselectivity. We formed a spot-like polyester (PE) coating on top of a polyamide (PA) TFC membrane using mist-based interfacial polymerization. This process involved exposing the membrane surface to tiny droplets carrying different concentrations of sulfonated kraft lignin (SKL, 3, 5, and 7 wt %) and trimesoyl chloride (TMC, 0.2 wt %). The main advantages of this surface coating technique are minimal solvent consumption (less than 0.05 mL/cm2) and precise control over interfacial polymerization. Zeta potential measurements of the coated membranes exhibited enhancements in negative charge compared to the control membrane. This enhancement is attributed to the unreacted carboxyl functional groups of the SKL and TMC monomers, as well as the presence of sulfonate groups (SO3) in the structure of SKL. AFM results showed a notable decrease in membrane surface roughness after polyester coating due to the slower diffusion of SKL to the interface and a milder reaction with TMC. In terms of fouling resistance, the membrane coated with a polyester composed of 7 wt % SKL showed a 90% flux recovery ratio (FRR) during Bovine Serum Albumin (BSA) filtration, showing a 15% improvement compared to the control membrane (PA). PE-coated membranes provided stable separation performance over 40 h of filtration. The sodium chloride rejection and water flux displayed minimal variations, indicating the robustness of the coating layer. The final section of the presented study focuses on assessing the feasibility of scaling up and the cost-effectiveness of the proposed technique. The demonstrated ease of scalability and a notable reduction in chemical consumption establish this method as a viable, environmentally friendly, and sustainable solution for surface modification.

Evaluating Post-Treatment Effects on Electrospun Nanofiber as a Support for Polyamide Thin-Film Formation.

Poly(acrylonitrile-co-methyl acrylate) (PAN-co-MA) electrospun nanofiber (ENF) was used as the support for the formation of polyamide (PA) thin films. The ENF support layer was post-treated with heat-pressed treatment followed by NaOH hydrolysis to modify its support characteristics. The influence of heat-pressed conditions and NaOH hydrolysis on the support morphology and porosity, thin-film formation, surface chemistry, and membrane performances were investigated. This study revealed that applying heat-pressing followed by hydrolysis significantly enhances the physicochemical properties of the support material and aids in forming a uniform polyamide (PA) thin selective layer. Heat-pressing effectively densifies the support surface and reduces pore size, which is crucial for the even formation of the PA-selective layer. Additionally, the hydrolysis of the support increases its hydrophilicity and decreases pore size, leading to higher sodium chloride (NaCl) rejection rates and improved water permeance. When compared with membranes that underwent only heat-pressing, those treated with both heat-pressing and hydrolysis exhibited superior separation performance, with NaCl rejection rates rising from 83% to 98% while maintaining water permeance. Moreover, water permeance was further increased by 29% through n-hexane-rinsing post-interfacial polymerization. Thus, this simple yet effective combination of heat-pressing and hydrolysis presents a promising approach for developing high-performance thin-film nanocomposite (TFNC) membranes.

Piezoelectric reverse osmosis (RO) membrane: Fabrication and anti-fouling effect

In this study, a novel piezoelectric RO membrane with vibrating mechanism when exposed to an electric field was developed. The vibration due to the piezoelectric effect can disturb the concentration polarization layer on the membrane surface and minimize membrane fouling. Polyvinylidene fluoride (PVDF) which has piezoelectric properties was selected as the porous substrate for a thin film composite (TFC) polyamide RO membrane in this study. Electrical poling was performed to enhance the piezoelectric properties of the PVDF substrate. RO membranes fabricated via interfacial polymerization using different PVDF substrates (i.e., with and without pre-wetting the PVDF substrate, with and without polyethylene terephthalate (PET) non-woven fabric support (denoted as NWF and no-NWF, respectively), with and without electrical poling) were systematically investigated. The results indicated that RO membrane fabricated on poled PVDF-NWF substrate shows reasonable pure water permeability of ∼2 LMH/bar and sodium chloride (NaCl, 2000 ppm) rejection of ∼98.9 % when tested at 15 bar. In the accelerated fouling study using colloidal silica particles (∼20 nm in diameter, 200 ppm with background of 2000 mg/L NaCl), when the RO membrane fabricated using both unpoled and poled PVDF-NWF substrates were excited with AC signal, membrane fouling was significantly reduced. These findings suggested that electrical poling may not be necessary for such piezoelectric RO membrane.

Rod-coated PVA interlayer induced nanofiltration membrane: Method development and application for separation of dye/NaCl with greater performance

The textile industry consumes large quantities of freshwater and discharges large quantities of dye/salt wastewater, causing serious environmental problems. Nanofiltration (NF) has proven to be able to achieve efficient dye/salt separation. However, conventional polyamide (PA) NF membranes are often constrained by the trade-off between selectivity and permeability. Herein, we developed a highly dye/NaCl selective nanofiltration membrane with a rod-coated PVA interlayer. The rod-coating approach allows better control of PVA dosage to create a perfect PVA interlayer. The formation and effect of rod-coated PVA interlayer significantly improved the permeability. With an optimal PVA dosage of approximately 0.32 g/m2, the permeance of the iTFC membrane (>30.0 L/(m2 h bar)) was almost 3 times that of the control membrane. Moreover, the iTFC-PVA membrane had an outstanding Rhodamine B rejection (99.8 %), low sodium chloride (NaCl) rejection, and maximum NaCl/dye selectivity ratio as high as 428. It is anticipated that the iTFC membrane has great potential in the field of dyehouse wastewater treatment. Furthermore, our study proves that the Mayer rod-coating approach is suited to fabricating high-performance PA-NF membranes with PVA interlayers. It is anticipated that organic-containing wastewater can better be treated by the developed membrane to achieve a better water environment and resource recovery.

Polysulfone/sepiolite nanocomposites and disulfonated polysulfone as desalination membranes

This research targeted the preparation of new sepiolite-based nanocomposites and sulfonated polysulfone and compare them as desalination dense membranes. At the first step, a polysulfone with appropriate molecular weight was synthesized by condensation polymerization. The hydrophilic nature of the synthesized polymer was improved using two different methods: addition of various percentage (0.5–5% by weight) of sepiolite nanorods into the polymeric matrix, and introduction of sulfonated groups with 35–45 wt% sulfonation content to the polysulfone main chain. Precipitation by solvent evaporation was used to produce dense membranes after casting polymer solutions. FTIR, 1HNMR, and EDAX were used to identify the chemical structures of polysulfone, related nanocomposites, and sulfonated polysulfone. Also, the prepared samples were evaluated by equilibrium volume fraction of water, contact angle, water absorption, density, SEM, TGA, DSC, AFM and tensile test. Finally, the operation tests of the membrane including water flux, sodium chloride rejection, hydraulic water permeability, and salt permeability were investigated.

Enhancing boron rejection in low-pressure reverse osmosis systems using a cellulose fiber–carbon nanotube nanocomposite polyamide membrane: A study on chemical structure and surface morphology

Nanocomposite membranes based on carbon nanotubes (CNTs) or cellulose nanofibers (CNFs) are promising solutions for water filtration technologies such as seawater desalination, brackish water purification, and wastewater treatment. In this study, we investigated the effect of integrating CNTs and CNFs into a polyamide membrane (CNT–CNF–PA) on boron rejection in low−pressure reverse osmosis (RO) systems (0.75 MPa). A NaCl (500 ppm) and boron (5 ppm) based solution at pH = 7 was tested in an RO filtration system. The CNT–CNF–PA membrane exhibited a high boron rejection rate (up to 74%) and high permeation (greater than 1.0 m3/m2∙day). The chemical structure played a significant role in boron rejection performance. We conducted principal component analysis (PCA) to statistically study the changes in bond vibrations obtained by Fourier transform infrared (FTIR) spectroscopy, comparing the oxygenated and hydrogenated changes to sodium chloride rejection, boron rejection, and water permeation of the membranes. Additionally, the surface morphology, i.e., roughness, exhibits a direct positive effect on boron rejection, whereas the pore structure is linked to both sodium chloride and boron rejections. Molecular dynamic simulations revealed that the CNF and CNT structures suppress the hydrogen bonds between the PA matrix and boric acid, negatively affecting its diffusion and rejection. These findings help clarify the boron rejection mechanism, enabling further development of PA membranes.

Trimethylamine N-oxide-derived zwitterionic polyamide thin-film composite nanofiltration membranes with enhanced anti-dye deposition ability for efficient dye separation and recovery

Organic dyes from textile industries are becoming the second largest pollutants in the world. In this study, inspired by the seawater fish, a new diamine monomer, N,N-bis(3-aminopropyl)methylamine N-oxide (DNMAO) with a trimethylamine N-oxide (TMAO)-derived “N+─O−” zwitterionic functionality, has been designed for the fabrication of polyamide thin-film composite (TFC) membranes to purify dye-contaminated water and recover organic dyes. The fabricated membranes show enhanced permeability and improved anti-dye-deposition performance. The optimum membrane fabricated at 0.5 wt% of DNMAO feed solution exhibits an ultrahigh pure water permeability (PWP) of 37.5 LMH bar−1, a superior Congo red (CR) rejection of 99.93%, and a low sodium chloride (NaCl) rejection of 9.3%, indicating its outstanding performance for dye/salt separation. It can also achieve the complete CR removal from a feed with a low CR concentration of 1 ppm, demonstrating its superior separation performance for the production of clean potable water. In addition, the low dye loss rate (6.22%) and high salt removal rate (85.6%) are achieved during the purification and recovery test with CR/NaCl mixtures. Furthermore, the optimum membrane possesses an excellent anti-dye-deposition performance with a flux recovery ratio (FRR) of 92.1%. All these results demonstrate its potential for applications in not only textile wastewater treatment but also organic dye purification and recovery.

Eco-friendly surface modification approach to develop thin film nanocomposite membrane with improved desalination and antifouling properties

IntroductionNanomaterials aggregation within polyamide (PA) layer of thin film nanocomposite (TFN) membrane is found to be a common issue and can negatively affect membrane filtration performance. Thus, post-treatment on the surface of TFN membrane is one of the strategies to address the problem. ObjectiveIn this study, an eco-friendly surface modification technique based on plasma enhanced chemical vapour deposition (PECVD) was used to deposit hydrophilic acrylic acid (AA) onto the PA surface of TFN membrane with the aims of simultaneously minimizing the PA surface defects caused by nanomaterials incorporation and improving the membrane surface hydrophilicity for reverse osmosis (RO) application. MethodsThe TFN membrane was first synthesized by incorporating 0.05 wt% of functionalized titania nanotubes (TNTs) into its PA layer. It was then subjected to 15-s plasma deposition of AA monomer to establish extremely thin hydrophilic layer atop PA nanocomposite layer. PECVD is a promising surface modification method as it offers rapid and solvent-free functionalization for the membranes. ResultsThe findings clearly showed that the sodium chloride rejection of the plasma-modified TFN membrane was improved with salt passage reduced from 2.43% to 1.50% without significantly altering pure water flux. The AA-modified TFN membrane also exhibited a remarkable antifouling property with higher flux recovery rate (>95%, 5-h filtration using 1000 mg/L sodium alginate solution) compared to the unmodified TFN membrane (85.8%), which is mainly attributed to its enhanced hydrophilicity and smoother surface. Furthermore, the AA-modified TFN membrane also showed higher performance stability throughout 12-h filtration period. ConclusionThe deposition of hydrophilic material on the TFN membrane surface via eco-friendly method is potential to develop a defect-free TFN membrane with enhanced fouling resistance for improved desalination process.

Performance prediction of flat sheet commercial nanofiltration membrane using Donnan-Steric Pore Model

The rejection of sodium chloride (NaCl) and calcium chloride (CaCl2) single salt solutions were carried out for commercial nanofiltration NFDK membrane. Results showed that the NFDK membrane had a negative surface charge and had a higher observed rejection of 93.65% for calcium (Ca2+) ion and 78.27% for sodium (Na+) ions. Prediction of rejection for aqueous solutions of both salts was made using Donnan Steric Pore Model based on Extended Nernst-Planck Equation in addition to concentration polarization film theory. A MATLAB program was developed to execute the model calculations. Absolute Average Relative Error (% AARE) was found below 5% for real rejection of the NFDK membrane. This research could be used successfully to assess the membrane characterization parameter using a proposed procedure which can reduce the number of experiments.

High-Performance Polyacrylic Acid-Grafted PVDF Nanofiltration Membrane with Good Antifouling Property for the Textile Industry.

In the textile industry, a high-efficiency dye removal and low-retention of salt is demanded for recycling wastewater. In this study, polyvinylidene fluoride (PVDF) ultrafiltration membrane was transformed to a negatively charged loose nanofiltration (NF) membrane through UV-grafting of acrylic acid. At the optimal exposure of PVDF membrane in UV light for 5 min, the membrane had a high dye recovery above 99% (Congo red and Eriochrome® Black T) and a low sodium chloride (NaCl) rejection of less than 15% along with pure water flux of 26 L∙m−2∙h−1∙bar−1. Its antifouling and oleophobicity surface properties were verified using fluorescent- bovine serum albumin (BSA) and underwater mineral oil contact angle, respectively. According to the fluorescent microscopic images, the modified membrane had ten times lower adhesion of protein on the surface than the unmodified membrane. The underwater oil contact angle was raised from 110° to 155°. Moreover, the salt rejection followed this sequence: Na2SO4 > MgSO4 > NaCl > MgCl2, which agreed with the typical negatively charged NF membrane. In addition, the physicochemical characterization of membranes was further investigated to understand and link to the membrane performance, such as surface functional group, surface elements analysis, surface roughness/morphology, and surface hydrophilicity.

Charge Property Modeling of Nanofiltration Hollow Fiber Membranes

The development of models that predict membrane performance has contributed a better understanding of the basic principles and mechanisms of solute rejection and deposition. It also serves as fundamental properties that allow specific characterization determination. This work fabricates hollow fiber membranes using Polyethersulfone (PES). The membranes were fabricated in-house using phase inversion technique by modification with synthesized charged-surface modifying macromolecules (cSMM). The cSMM comprise with end-group component of Hydroxybenzene sulfonate or Hydroxybenzene carboxylate. The electrical properties of the membranes were modeled by utilizing the combination of irreversible thermodynamic model, Steric- Hindrance Pore (SHP) model and Teorell-Meyer-Sievers (TMS) model. The negatively-charged of the modified hollow fiber membranes was calculated based on sodium chloride rejection experimental performance. The analysis of the modeling results revealed that the modification of nanofiltration membrane using sulfonate induce negative 1.61 electrical properties compared to carboxylate that is negative 1.49 for both type modified PES membranes.

Prediction of long term filtration by coupled gel layer and pore transport model for salt removal using mixed matrix hollow fiber ultrafiltration membrane

Characterization and performance of lanthanum cobalt oxide nanoparticle doped hollow fiber ultrafiltration membrane are reported in this paper. Nanoparticles (1 wt%) having zeta potential −30 mV at pH 7 imparted high surface charge (surface potential ~19 mV) to the hollow fibers. At this composition, the membrane became more hydrophilic with contact angle reduced to 520 from 570 corresponding to without nanoparticles. Permeability of hollow fiber with 1 wt% nanoparticles increased by 40% compared to that without nanoparticle. At this composition, the membrane molecular weight cut off was 4000 Da (with average pore diameter 34 nm) belonging to ultrafiltration range. Rejection of sodium chloride was 47% in 1000 mg/l synthetic solution at transmembrane pressure drop 69 kPa and cross flow rate 20 l/h. Performance of developed hollow fiber membrane was also tested using actual seawater with a rejection of 40% total dissolved solids at 138 kPa at 20 l/h with 15 l/m2h permeate flux. A combined gel polarization and pore flow model was used to quantify the long term flux decline and salt concentration in the permeate as function of time.

Novel pyridine-based polysulfone, sulfonated polysulfones, and sonicated sepiolite-based nanocomposites for water desalination

Abstract In this study new types of polysulfone, related sulfonated polysulfones, and also nanocomposites were prepared and characterized. The potential of reverse osmosis polysulfone membrane for desalination of saline water was investigated. For this aim, a novel monomeric pyridine-based diol and the related polysulfones were prepared and characterized. In the second step with the aim of improving the hydrophilic nature of the polymer, the sulfonated groups were introduced into the structure of polysulfone and copolymers with 20–50 wt% sulfonation content were prepared. Another strategy for improving the hydrophilicity of the polysulfones was applied via the inclusion of hydrophilic sepiolite as a nanoparticle into the polymeric chains. In this part, by addition of 1, 3, 5, 7, and 10 wt% of sepiolite to the polymer solution, the related nanocomposites were prepared. At the final part, their related flat membranes were cast and the operation tests including contact angle, water flux, and sodium chloride rejection were investigated.

Enhancing desalination performance of thin film composite membrane through layer by layer assembly of oppositely charged titania nanosheet

Reverse osmosis (RO) is a mature desalination technology that provides an effective solution to solve global water scarcity issues. In this study, thin film nanocomposite (TFN) membrane for RO desalination was fabricated by depositing positively charged titania nanosheet (pTNS) and negatively charged titania nanosheet (nTNS) on the surface of polyamide (PA) layer through layer by layer (LbL) assembly. The pTNS was synthesized through solid-state calcination and acid ion-exchange. Though the additional step of exfoliation, single sheet nTNS with improved hydrophilicity property was obtained. The hydration layer created on the surface of TNS-PA could hinder the direct contact of salt ions with the surface of TFN membrane, hence significantly enhance the water permeability and salt rejection. The membrane surface hydrophilicity was improved and surface roughness was decreased with the increasing number of bilayers. However, the excessive pTNS/nTNS bilayer coating has imposed additional hydraulic resistance hence resulted in the reduction of water permeability. The highest water permeability of 0.8L·m−2·h−1·bar−1 (60% improvement) was achieved with the 2 bilayers of TNS-PA TFN as compared to the pristine PA membrane. The sodium chloride (NaCl) rejection was 98.45% which was also higher than pristine membrane with rejection of 96.65%.

Controlled pore collapse to increase solute rejection of modified PES membranes

Pore collapse upon drying is a well-known phenomenon in ultrafiltration PES membranes. Here we demonstrate how alteration of membrane surface chemistry can be used to control the extent of pore collapse and ultimately to tailor membrane properties. Commercial hollow-fiber PES membranes were modified via surface-initiated ATRP to obtain different polymer-grafted membranes and were subsequently dried to facilitate pore collapse. The different polymer grafts could be used for controlling the water flux and solute rejection characteristics of the membranes. Controlled membrane pore collapse could be exploited to obtain higher rejection of sodium chloride, magnesium sulfate and calcein. Calcein as the largest solute showed almost full rejection (98.9 ± 0.3%) on the membrane. The chemical nature of the grafted polymer was directly reflected in the water flux-to-rejection ratio and the extent of pore collapse.

Effect of Short-Term Contact with C1-C4 Monohydric Alcohols on the Water Permeance of MPD-TMC Thin-Film Composite Reverse Osmosis Membranes.

In this paper, we discuss the effect of alcohol contact on the transport properties of thin-film composite reverse osmosis membranes. Five commercial membranes were studied to quantify the changes in water permeance and sodium chloride rejection from contact with five C1–C4 monohydric, alcohols. Water permeance generally increased without decreasing rejection after short-term contact. The extent of these changes depends on the membrane and alcohol used. Young′s modulus measurements showed decreased stiffness of the active layer after contacting the membranes with alcohol, suggesting plasticization. Data analysis using a dual-mode sorption model identified positive correlations of the initial water permeance, as well as the change in free energy of mixing between water and the alcohols, with the increase in water permeance after alcohol contact. We suggest that the mixing of water with the alcohols facilitates alcohol penetration into the active layer, likely by disrupting inter-chain hydrogen bonds, thus increasing the free volume for water permeation. Our studies provide a modeling framework to estimate the changes in transport properties after short-term contact with C1–C4 alcohols.

Manipulating the separation performance of nanofiltration membranes by coating thickness of organic phase during interfacial polymerization

ABSTRACTNanofiltration (NF) membranes have excellent separation capabilities and selective performance, and are widely applied in the field of concentration and separation of salt and inorganic salt mixtures. In this article, NF membranes with a higher comprehensive performance were fabricated using a thinner coated organic phase during interfacial polymerization, which greatly reduced the rejection of sodium chloride and significantly improved the water flux without reducing the rejection of magnesium sulfate. Structure comparison found that thinner polyamide separation layer resulted in the higher crosslinking degree, smaller particle, and relatively rough surface. Based on these analyses, we hypothesized that thermodynamically efficiency in the system varies with the coating thickness. Finally, the mechanism of the influence of the coating thickness of organic phase during heat treatment on the interfacial polymerization process and membrane structure was discussed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48284.

Boron Can Be Used to Predict Trace Organic Rejection through Reverse Osmosis Membranes for Potable Reuse.

Potable water reuse is a viable option for communities with extreme water scarcity. Improvements in measurement capabilities and greater occurrence of contaminants of emerging concern (CECs) have made the investigation of the removal of CECs through advanced treatment facilities essential for further reuse considerations. Reverse osmosis (RO) has been demonstrated to remove many CECs, but poor removal has been observed for many low molecular weight (MW), neutral organic compounds. With the availability of many RO membrane products on the market, it is increasingly important to be able to predict organics rejection through different products without detailed information about the RO membrane's properties or structure. This laboratory-scale study investigated the rejection of low-MW, neutral organics, boron, and sodium chloride by six RO membrane products. The experimental results were used to develop a correlation between the removal of organics and boron. If the rejection of boron and a neutral organic through one reference membrane is available, then the rejection of that organic through any other membrane product can be estimated using the rejection of boron through that membrane.

Modification of the Selectivity Properties of Tubular Ceramic Membranes after Alkaline Treatment.

This work focuses on the selectivity modification of ceramic membranes after a mild alkaline treatment. Filtration of pure salt-water solutions was carried out with commercial titania membranes before and after the treatment. After treatment, the rejection of NaF significantly decreased, while the rejection of NaCl and NaBr increased. Additionally, NaI and Na2SO4 remained close to zero. Pore size and electrical charge being almost unchanged, only significant modifications in the dielectric effects can explain this modification of selectivity. Therefore, the surface chemistry and the interaction (nature and magnitude) with the solvent and with the species present in the solution appear to be modified by the alkaline treatment. This trend is also illustrated by discussing the electric and the dielectric properties that were numerically identified before and after treatment. The alkaline treatment significantly decreased the apparent dielectric constant of NaCl-water solution in the pore, highlighting the rejection of sodium chloride. Contrariwise, the modification of the surface chemistry increased the apparent dielectric constant of NaF-water solution by promoting fluoride transmission.