Composite Reverse Osmosis Membranes Research Articles

Monitoring the process of interfacial polymerization for fabrication of polyamide reverse osmosis membrane via molecular simulation based on π-π interaction between surfactant and monomer

Accurate regulation of the interfacial polymerization (IP) process is prerequisite for preparation of thin film composite reverse osmosis (RO) membranes with ideal polyamide (PA) layers, and surfactant assembly-regulated IP (SARIP) is proved to be an effective approach. However, mechanism in molecular level for modulation of IP based on surfactants is still inadequate. Here, sodium dodecylbenzene sulphonate (SDBS) and sodium dodecyl sulfate (SDS) have been chosen as surfactants to make comparison of the IP process based on π-π interaction between surfactant and monomer via molecular simulation. As illustrated by Molecular Dynamics (MD) simulations, surfactants enlarge the width of the miscible zone, increase the diffusion rate together with the relative concentration of MPD in the miscible zone, as well as regulate the position of IP reaction towards the aqueous phase. Compared to SDS, SDBS makes the diffusion of MPD in good order, thus avoiding the severe variation in structure and morphology on PA layer. As calculated by DFT, higher interaction energy between the phenyl group of MPD and SDBS based on the π-π interaction is achieved, leading to uniform distribution of MPD close to the phenyl group of SDBS instead of escaping violently into miscible zone. Thus, strong consistency between the position of IP reaction and the height of the phenyl group in SDBS is emerged, which further explains the intrinsic reason for the variation of the IP position and the modulation of the PA microstructure. The mechanism for IP regulation based on SARIP at molecular level is finally proposed via molecular simulation, providing new idea for the preparation of high-performance RO membranes.

Adsorption of steroid hormone micropollutant by polyethersulfone ultrafiltration membranes with varying morphology

The effective removal of micropollutants necessitates the use of dense membranes, such as thin-film composite (TFC) reverse osmosis (RO) and nanofiltration (NF) membranes. TFCs have a polyamide active layer interfacially polymerized on a support layer that is typically made of polysulfone (PSu) or polyethersulfone (PES). Retention by NF and RO is often incomplete because micropollutants are adsorbed to the polymer material and subsequently permeate via a combination of convection and diffusion, which evidences a breakthrough curve. When describing breakthrough phenomena, the role of the support membrane is commonly neglected, even though the adsorption in this layer can be significant. This work investigated the adsorption of steroid hormone micropollutants (17β-estradiol, E2) by fabricated and commercial PES ultrafiltration membranes with varying morphology.By increasing the coagulation bath temperature between 10 and 70 °C, the pure water permeability increased from 13 to 3800 L/m2·h−1·bar−1, and consequently, the average pore size rose from 12 to 191 nm. The fabricated membranes with smaller pore sizes showed higher E2 removal via adsorption which can be attributed to the higher internal surface area. The adsorbed mass of fabricated PES membranes (using dimethylformamide (coded as PDG) and N-methyl-2-pyrrolidone (coded as PNG) and PES (Istanbul Technical University (ITU), with non-woven supports) varies from 0.30 to 0.60, 0.27–0.60 and 1–1.2 ng·cm−2, respectively. These values are lower than the adsorbed masses with commercial Biomax (Millipore Inc.) membranes (0.5–2.0 ng·cm−2). Ultrafiltration membranes used as support for composite membranes, nanofiltration or as filters in sample preparation benefit from lower micropollutant adsorption.

Exploring mass transfer mechanisms in reverse osmosis membranes: A comparative study of SDM and DSPM-DE models

Thin-film composite reverse osmosis (RO) membranes have dominated desalination technology for decades, with the solution diffusion model (SDM) serving as the gold standard for interpreting mass transfer phenomena since its inception. However, debates still persist regarding the effect of charge on separation performance, owing to the SDM's inability to explore membrane charge. In this study, polyethyleneimine (PEI) was utilized to modify the surface of a commercial seawater desalination membrane (SW30, Dupont Company), imparting regulatable charge properties based on the solution pH. The separation performance of the modified RO membrane was experimentally validated under varying NaCl feed salinities. Specifically, the Donnan-steric pore model with dielectric exclusion (DSPM-DE), known as a charge-responsive model, was employed and juxtaposed with SDM to authenticate the experimental findings. The results indicated that the dielectric effect primarily governed ion distribution (Na+ and Cl−) within the membrane, followed by the steric effect, and ultimately, the Donnan effect. Consequently, DSPM-DE aligned well with the observed salt rejection only when the membrane was strongly charged (that is, under acidic or alkaline conditions), but performed poorly in the neutral state. This observation, rarely revealed in previous research, stems from conventional desalination membranes being negatively charged in most natural water environments. Conversely, the SDM aligned well with the experimental data because it solely considered the solutes' solubility parameters and diffusion coefficient, independently of the surface charge of the desalination membranes. Given the extensive research on surface modification, our study demonstrates the limited influence of charge effects on the selective enhancement of RO membranes.

Polyamide reverse osmosis membrane compaction and relaxation: Mechanisms and implications for desalination performance

This work investigates the compaction and relaxation behavior of composite reverse osmosis (RO) polyamide (PA) selective layers, utilizing non-equilibrium molecular dynamic (NEMD) simulations and well-controlled permeation experiments. Composite PA-RO membranes are prepared by interfacial polymerization of para and meta diamine monomer blends to achieve different PA film crosslinking degrees (CD). Wet-testing results suggest that “tighter” (higher CD) composite RO membranes undergo 65 % less compaction and recover 17 % more of their initial permeability (termed “relaxation”) when the pressure is relieved compared to lower CD PA layers. NEMD simulations provide a visual and quantitative characterization of PA layer's free volume changes in operando. NEMD simulations also corroborate experimental findings and elucidate the viscoelastic properties of the PA layer that govern compaction and relaxation behavior. The mechanisms of compaction under water permeation derived from NEMD simulations further support the notion of viscous flow of water through interconnected free volume elements (i.e., “pores”) within crosslinked PA films.

Prompted by surface-engineered honeycomb Turing nanostructures: Reflections on polyamide structure, growth and performance

The robust correlation between the performance of thin-film composite (TFC) reverse osmosis membranes and the polyamide (PA) active layer determines the necessity of precise design of the PA layer, and this regulation primarily involves the surface morphology and internal characteristics of the PA layer. In this study, we fabricated honeycomb Turing structure or nanovoid-rich TFC series membranes using polar/nonpolar organic phase additives. Characterization and simulation results confirmed that the enhancement of membrane performance relied more on the abundant nanovoids within the PA layer rather than the ordered honeycomb lattice surface. Notably, the TFC-nDCE membrane with multilayer nanovoids exhibited an approximately 89 % improvement in water permeability while maintaining satisfactory salt rejection (98.29 %). We emphasized the significant role of nanovoids in the diffusion process of amine monomers and investigated the potential relationship between nanovoids and the degree of surface cross-linking. Building upon this, a new insight into the formation of nanovoids induced by PA anisotropic growth was presented through a careful analysis of the amine monomer diffusion rate and the morphological evolution of nanovoids. The structure-property relationship between internal structures, surface morphologies, and performances was systematically and thoroughly investigated, pointing out the direction for the rational design of TFC membranes.

More resilient polyester membranes for high-performance reverse osmosis desalination.

Thin-film composite reverse osmosis membranes have remained the gold standard technology for desalination and water purification for nearly half a century. Polyamide films offer excellent water permeability and salt rejection but also suffer from poor chlorine resistance, high fouling propensity, and low boron rejection. We addressed these issues by molecularly designing a polyester thin-film composite reverse osmosis membrane using co-solvent-assisted interfacial polymerization to react 3,5-dihydroxy-4-methylbenzoic acid with trimesoyl chloride. This polyester membrane exhibits substantial water permeability, high rejection for sodium chloride and boron, and complete resistance toward chlorine. The ultrasmooth, low-energy surface of the membrane also prevents fouling and mineral scaling compared with polyamide membranes. These membranes could increasingly challenge polyamide membranes by further optimizing water-salt selectivity, offering a path to considerably reducing pretreatment steps in desalination.

Engraving Polyamide Layers by In Situ Self-Etchable CaCO3 Nanoparticles Enhances Separation Properties and Antifouling Performance of Reverse Osmosis Membranes.

Nanovoids within a polyamide layer play an important role in the separation performance of thin-film composite (TFC) reverse osmosis (RO) membranes. To form more extensive nanovoids for enhanced performance, one commonly used method is to incorporate sacrificial nanofillers in the polyamide layer during the exothermic interfacial polymerization (IP) reaction, followed by some post-etching processes. However, these post-treatments could harm the membrane integrity, thereby leading to reduced selectivity. In this study, we applied in situ self-etchable sacrificial nanofillers by taking advantage of the strong acid and heat generated in IP. CaCO3 nanoparticles (nCaCO3) were used as the model nanofillers, which can be in situ etched by reacting with H+ to leave void nanostructures behind. This reaction can further degas CO2 nanobubbles assisted by heat in IP to form more nanovoids in the polyamide layer. These nanovoids can facilitate water transport by enlarging the effective surface filtration area of the polyamide and reducing hydraulic resistance to significantly enhance water permeance. The correlations between the nanovoid properties and membrane performance were systematically analyzed. We further demonstrate that the nCaCO3-tailored membrane can improve membrane antifouling propensity and rejections to boron and As(III) compared with the control. This study investigated a novel strategy of applying self-etchable gas precursors to engrave the polyamide layer for enhanced membrane performance, which provides new insights into the design and synthesis of TFC membranes.

The role of sheet-like TiO2 in polyamide reverse osmosis membrane for enhanced removal of endocrine disrupting chemicals

Thin film composite (TFC) reverse osmosis (RO) membrane shows good promise for treating wastewater containing endocrine disrupting chemical (EDC) pollutants. The incorporation of functional materials with exceptional structural and physico-chemical properties offers opportunities for the membranes preparation with enhanced permselectivity and better antifouling properties. The present study aims to improve the EDC removal efficiency of TFC RO membrane using two-dimensional titania nanosheets (TNS). RO membrane was prepared by incorporating TNS in the dense layer of polyamide (PA) layer to form thin film nanocomposite (TFN) membrane. The TNS loading was varied and the influences on membrane morphology, surface hydrophilicity, surface charge, as well as water permeability and rejection of EDC were investigated. The results revealed that the inclusion of TNS in the membrane resulted in the increase of water permeability and EDC rejection. When treating the mixture of bisphenol A (BPA) and caffeine at 100 ppm feed concentration, the TFN membrane incorporated with 0.05% TNS achieved water permeability of 1.45 L/m2·h·bar, which was 38.6% higher than that of unmodified TFC membrane, while maintaining satisfactory rejection of >97%. The enhancement of water permeability for TFN membrane can be attributed to their hydrophilic surface and unique nanochannel structure created by the nanoscale interlayer spacing via staking of TiO2 nanosheets. Furthermore, the 0.05TFN membrane exhibited excellent fouling resistance towards BPA and caffeine pollutants with almost 100% flux recovery for three cycles of operations.

Advanced reverse osmosis membranes prepared by counter-diffusion of organic phase monomers induced by polypyrrole additives

Highly permeable thin film composite (TFC) reverse osmosis (RO) membranes with abundant free volume are desirable for water treatment. However, the strategy of controlling the microstructure of the separation layer with high free volume rate is still a challenge. In this work, a modified strategy for the preparation of high-performance TFC RO membrane with inverse diffusible polypyrrole nanoparticles (PPYN) as organic phase additive was developed. The combination of PPYN and trimesoyl chloride (TMC) would diffuse backwards from the organic phase into the aqueous phase during the reaction process to disrupt the normal interfacial polymerization (IP) and thus introduce more free volume in the RO membrane due to the nanobubbles from violent reactions. Moreover, the thickness of the modified membrane decreased and the hydrophilicity increased based on the modulation of IP by PPYN, which facilitated the water molecules to transport. The prepared RO-PPYN membranes showed nearly three times the flux compared with the pristine RO membrane without sacrificing separation selectivity. Furthermore, the anti-biofouling property of the modified membrane was also improved. This work successfully demonstrated the potential use of PPYN as an organic filler to enhance the performance of seawater desalination in RO membranes. Our modification strategy provides an efficient and convenient way to prepare novel RO membranes with high permeability.

Novel polyamide-hydrazide based reverse osmosis membrane with enhanced antifouling properties

The typical “ridge-valley” structure of traditional reverse osmosis (RO) membranes ensures good permeability with high risk of inducing membrane fouling. It is a challenge to develop a smooth RO membrane without loss of permeability. In this study, cyclobutane-1,2,3,4-tetracarbohydrazide (CBTH) was designed and synthesized, and a composite RO membrane based on CBTH and cyclobutane-1,2,3,4-tetracarboxylic acid chloride (BTC) was constructed. The CBTH-BTC membrane exhibits a smooth selective layer with thickness of 45 nm. The desalination performance test results show that the CBTH-BTC membrane has permeability and desalination performance comparable to the traditional RO membrane (the water permeability coefficient reaches 3.0 L·m−2·h−1·bar−1, and the rejection of NaCl reaches 99.2 %). Importantly, the hydrophilic and smooth surface imparts the membrane with good antifouling properties to hydrophilic, hydrophobic and surfactant pollutants. In this study, RO membranes with good permeability and excellent antifouling performance were successfully prepared from the perspective of reaction monomer design, which provides a new idea to regulate the morphology and antifouling properties of RO membranes.

Transformation of brackish water Reverse Osmosis membranes to nanofiltration & ultrafiltration membranes by NaOCl treatment: Kinetic and characterization studies

Thin Film Composite (TFC) Reverse Osmosis (RO) membranes used in desalination, reach their End-of-Life (EoL) due to fouling and chemical degradation and pose disposal problem. Their lifetime can be increased by converting them into Ultrafiltration (UF) or Nanofiltration (NF) membranes. The present work demonstrates a systematic methodology in terms of ‘ppm-h/ppm∙h exposure’ to chemically convert brackish water RO membranes into NF and subsequently into UF membranes using sodium hypochlorite (NaOCl). Post-performance studies of pure water flux, monovalent and bivalent salt rejection are carried at each treatment level. RO membrane has transformed into NF at 3000–3 ppm-h, 2000–6 ppm-h, 3000–6 ppm-h and in to UF membrane beyond 10000–3 ppm-h. Gradual changes in physicochemical properties of membrane during conversion are ascertained from Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), Attenuated Total Reflection – Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-Ray Photoelectron Spectroscopy (XPS), contact angle, zeta potential etc. The rate of chlorination of polyamide is derived using XPS elemental data from initial stages of NaOCl exposure, and rate of hydrolysis from the membrane resistance, and pH. The overall rate equation is combination of both. The membrane thickness calculated from the kinetics match with experimental data. This study gives account of depolymerization of polyamide upon NaOCl exposure (ppm-h) which can be useful in chemical recycling/treatment of EoL membranes on a plant scale.

In-situ complexation of silver nanoparticle on thin film composite reverse osmosis membrane for improving desalination and anti-biofouling performance

The study on the state-of-art desalination membranes related to their fundamental structure, property and performance has been sparked by the demand for commercially attractive high-performance membranes. In this study, the surface of polyamide (PA) reverse osmosis (RO) membrane was modified by integrating tannic acid (TA) and silver nanoparticles (Ag NPs) to increase the water flux, anti-biofouling and antifouling properties of the membrane. The anti-biofouling properties was optimized by varying the duration required for the in-situ formation of Ag NPs on the surface grafted TA. The findings revealed that the PES/PA-TA-Ag(20 min) membrane prepared from the in-situ reduction of Ag precursor for 20 min exhibited the maximum flux of 20.56 L/m2·h. The PES/PA-TA-Ag(40 min) membrane also demonstrated increased antibacterial ability as proven by an increase in the number of dead bacteria (48 ± 1.71 μm3/μm2) and a reduction in biofilm thickness (1.6 ± 0.12 μm) for E. coli. The antifouling performance of the SA-fouled PES/PA-TA-Ag(40 min) membrane is appealing, with higher FRR of 98.05 % observed. The PES/PA-TA-Ag(40 min) membrane showed minimal silver leaching of ≤2.5 % and reduced flux loss of 25 % upon filtration. The facile surface modification through complexation of TA and Ag NPs offers an opportunity to heighten the desalination productivity and antifouling characteristics of PA TFC membranes.

Ti2NTx quasi-MXene modified polyamide thin film composite reverse osmosis membrane with effective desalination and antifouling performance

In this study, considering the serious problem of lack of fresh water worldwide and the effectiveness of reverse osmosis (RO) membranes in water purification, we prepared improved RO membranes with two-dimensional quasi-MXene nanosheets. In this study, the MAX phase with the chemical formula of Ti2AlN was prepared through the reactive sintering route. Prosperous preparation of the MAX phase with the hexagonal crystalline structure was approved by an X-ray diffraction pattern. Compacted sheets morphology was recognized for the prepared MAX phase from transmittance electron microscopy and scanning electron microscopy micrographs. Then, Ti2NTx quasi-MXene nanosheets were prepared by selective ultrasonic-assisted exfoliation of the MAX phase. Polyamide (PA) thin-layer composite RO membranes with different weight percentages of Ti2NTx quasi-MXene were fabricated by the interfacial polymerization (IP) method. The addition of ultrasonic-assisted prepared quasi-MXene creates numerous and coherent nanochannels on the surface of the membrane. The optimum membrane with 0.01 wt% of quasi-MXene showed the highest pure water flux of 31.9 L m−2. h−1 with an improved salt rejection of 98.2%. Therefore, these nanosheets showed that they can partially solve the trade-off between water permeability and salt rejection, which is a serious challenge in RO membranes. Also, the membranes containing quasi-MXene showed good resistance against fouling by humic acid. This research can be a scalable development in making high-performance membranes.

Cross-flow separation characteristics and piloting of graphene oxide nanofiltration membrane sheets and tubes for kraft black liquor concentration

Dewatering of weak black liquor (WBL) in the kraft cycle by evaporation is highly energy intensive. Membranes are an attractive alternative for energy-efficient dewatering, but existing commercial polymeric or ceramic membranes are either degraded in BL or have high capital costs. Our recent works have demonstrated the engineering of graphene oxide (GO) nanofiltration membranes, their stability and promising performance in BL conditions, and preliminary scale-up into sheets and tubes. Here, we describe in detail the separation characteristics of GO membrane sheets and tubes under real BL conditions and crossflow operation. Recycle-mode piloting of a GO tubular membrane showed average “production flux” of 16 L/m2/h (LMH) and high rejections of lignin (98.3%), total solids (66%), and total organic carbon (83%), with no signs of irreversible fouling identified. A corresponding GO sheet membrane produced an average flux of ~25 LMH and maintained high lignin rejection of ~97% during a slipstream pilot at a kraft mill site using WBL with ~16 wt% total solids (TS). Finally, we piloted a Dow/DuPont XUS1808 polyamide composite reverse osmosis (RO) membrane for last-mile processing of the GO nanofiltration membrane permeate. The RO membrane showed a steady state flux of 19 LMH at 65 bar and produced ~0.02 wt% TS water product, which is highly suitable for reuse in pulp washing operations in the kraft process. The results have strong positive implications for the industrial application of GO membranes in BL concentration and other related applications.

Reuse of end—of—life membranes through accelerated polyamide degradation

End—of—life (EoL) thin—film composite (TFC) reverse osmosis membranes were converted into ultrafiltration—like (UF) membranes in an accelerated degradation process of the polyamide (PA) using an oxidant (NaOCl) in the presence of either MgCl2 or CaCl2. The PA degradation was evaluated by measuring pure water permeability (PWP), MgSO4 passage and molecular weight cut—off; the more PWP increased, and the less MgSO4 was retained after treatment, the more the PA was degraded. By adding 10 mM of metal ions, PWP increased 2.1 (MgCl2) and 3.1 (CaCl2) times compared to the increase achieved with hypochlorite alone (2560 ppm∙h of free chlorine). Changes in the membranes after treatment were analyzed by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE—SEM), and by measuring their surface charge and contact angle. FTIR and FE—SEM confirmed the PA layer degradation. FE—SEM micrographs showed that full removal of the PA layer can be achieved by using an oxidation dose of 12,700 ppm∙h when Ca2+ is used but doses as high as 300,000 ppm*h are needed without catalyst. The results proved that by controlling the oxidation process it was possible to control the cut—off (MWCO) value of the membrane from 16,100 g∙mol—1 to 27,100 g∙mol—1. Before treatment, EoL membranes showed a MWCO of approximately 1200 g∙mol—1, meaning that molecules with that size could be retained in a 90%. In summary, the presented method enables reducing waste by the conversion EoL membranes into tailored UF—like membranes and by decreasing the amount of oxidant used in the conversion process.

Enhancing the antifouling and chlorine resistance capabilities of thin-film composite reverse osmosis via surface grafting of dipeptide

There has been constant progress in the development of innovative polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membranes to address limitations in fouling potential, chlorine resistance, salt rejection and water flux trade-offs. In this work, dipeptide of zwitterionic amino acid L-arginine, i.e., arginyl-arginine (Arg-Arg), was grafted on the surface of PA TFC RO membrane in order to simultaneously improve the antifouling properties, chlorine resistance, and separation performance. The interactions between the Arg-Arg dipeptide and PA layer were evidenced by Fourier transforms infrared spectroscopy and nuclear magnetic resonance spectroscopy, which have indicated the distinguished chemical grafting of Arg-Arg dipeptide on the RO membrane surface. The grafting of Arg-Arg dipeptide led to a thinner, smoother, more hydrophilic, and less negatively charged PA surface. The surface-modified membranes simultaneously exhibited enhanced desalination performances, antifouling and chlorine resistance properties. Compared to the neat TFC membrane, the water flux of Arg-Arg dipeptide-modified membrane was improved by 26.19%. The salt rejection also slightly increased from 96.25% to 98%. The roles of Arg-Arg dipeptide in altering the surface chemistry and the structure of the membranes are discussed to highlight the potential of surface-modified membranes in heightening the desalination performances of RO TFC membranes.

Thin film composite reverse osmosis membranes with metal-organic coordination complexes stabilized CNTs interlayer for enhanced removal of trace organic contaminants

Reverse osmosis (RO) has been recognized as a reliable technique for wastewater reclamation. To enhance its rejection of trace organic contaminants (TrOCs), a novel strategy was proposed to improve reverse osmosis (RO) membranes by fabricating thin-film nanocomposite membrane (TFNi) with a TA-Fe3+/CNTs interlayer. The TFNi-30 membrane was obtained by optimizing the loading capacity. This optimized membrane gave rise to an enhanced water permeance of 3.2 ± 0.2 L m-2 h-1 bar-1, which was two times higher than that of the control membrane (1.1 ± 0.2 L m-2 h-1 bar-1), while achieving a considerably higher rejection of inorganic salts and trace organic contaminants (TrOCs) thanks to the formation of a denser polyamide rejection layer. In addition, the specific roles of the interlayer structure in determining the separation performance of RO membranes were investigated by tailoring the support-free RO membranes and comparing them with the conventional membranes. This study would provide a peer reference for designing high performance RO membranes for wastewater reclamation via the TFNi strategy.

Incorporation of an Intermediate Polyelectrolyte Layer for Improved Interfacial Polymerization on PAI Hollow Fiber Membranes.

In a single-step spinning process, we create a thin-walled, robust hollow fiber support made of Torlon® polyamide-imide featuring an intermediate polyethyleneimine (PEI) lumen layer to facilitate the integration and covalent attachment of a dense selective layer. Subsequently, interfacial polymerization of m-phenylenediamine and trimesoyl chloride forms a dense selective polyamide (PA) layer on the inside of the hollow fiber. The resulting thin-film composite hollow fiber membranes show high NaCl rejections of around 96% with a pure water permeability of 1.2 LMH/bar. The high success rate of fabricating the thin-film composite hollow fiber membrane proves our hypothesis of a supporting effect of the intermediate PEI layer on separation layer formation. This work marks a step towards the development of a robust method for the large-scale manufacturing of thin-film composite hollow fiber membranes for reverse osmosis and nanofiltration.

Treatment of radionuclide-containing wastewater using thin film composite reverse osmosis membrane with spray coating-assembled titania nanosheets

Reverse osmosis (RO) process is a promising technology for treating radionuclide-containing wastewater owing to its reliability and effectiveness in ion separation. The long-term stability of RO membranes in terms of water flux and radionuclide rejection is a crucial factor for their practical application. In this study, thin film composite (TFC) RO membrane with high long-term stability and antifouling properties for radionuclide-containing wastewater treatment was developed by spray coating the surface of polyamide (PA) layer with oppositely charged titania nanosheets (TNS). Caesium ion (Cs+) as model radionuclide was used to assess the RO performance of the manufactured membranes, including permeability and radionuclide rejection The highest permeability of 1.53 L·m−2·h−1·bar−1, which was 45.8 % higher than that of neat TFC membrane, was achieved by thin film nanocomposite (TFN) membrane sprayed-coated with 15 ppm TNS bilayer. Compared to TFC membrane which exhibited CsCl rejection of 99.32 %, the rejection of all TNS spray-coated TFN membranes was improved to almost complete rejection. During the long-term testing, the optimum TFN/TNS(15) membrane demonstrated well-retained water flux and ion rejection. The roles of the TNS bilayer in improving the long-term stability and antifouling properties are discussed. The findings of this study highlight the potential of a tailored TFC RO membrane in treating radioanuclide-containing wastewater.

Enhanced water permeability of hollow fiber composite reverse osmosis membrane using porous α-cellulose/polysulfone hollow fiber membrane as the substrate

The hollow fiber composite (HFC) reverse osmosis (RO) membrane with a special self-supporting structure has attracted a great deal of attention in the fields of separation and purification. However, low permeability is an urgent problem restricting its wide application. A porous polysulfone (PSF) hollow fiber support membrane was fabricated through the dry–wet spinning technique and hydrophilic α-cellulose © powder was incorporated in the PSF membrane matrix to improve the membrane’s water permeability. The HFC RO membrane was prepared via the interfacial polymerization process on the inner surface of the C/PSF support membrane. The membrane morphology and surface hydrophilicity were evaluated through scanning electron microscopy observation and dynamic water contact angle (WCA) measurement. The effects of α-cellulose incorporation on the separation performance of PSF hollow fiber membranes and HFC RO membranes were investigated. The results showed that the surface hydrophilicity and water permeability of the PSF membrane were significantly improved after the introduction of α-cellulose. The WCA of the modified PSF support membrane decreased from 84.6° for the neat PSF membrane to 70.25°, and the pure water flux can reach a maximum value of 102.1 L/(m2 · h) (0.1 Mpa), which was 1.3 times that of the pristine membrane. The HFC RO membrane using the hydrophilic modified PSF membrane as the substrate exhibited an enhanced water flux of 15.6 L/(m2 · h) and, meanwhile, the membrane salt rejection remained above 97.6% (1.0 wt% NaCl aqueous solution, 0.7 Mpa). The HFC RO membrane showed extremely high rejection rates (99%) for different dyes (congo red and methylene blue). No obvious performance deterioration was observed for the HFC RO membrane during continuous vacuum membrane distillation (VMD) experiments for 60 h.