Polyamide Reverse Osmosis Membranes Research Articles

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.

Secondary interfacial reaction of p-aminodiphenylamine enables polyamide reverse osmosis membrane with enhanced and regenerative chlorine resistance

Developing polyamide (PA) reverse osmosis (RO) membrane with chlorine resistance is of great significance for simplifying pretreatment processes and saving operating costs. Herein, we constructed an active layer capable of highly chlorine stability and regenerative chlorine resistance by introducing p-amino diphenylamine (p-ADA) with redox activity via a facile secondary interfacial reaction (s-IR) on PA membrane surface. The calculation of resistance-in-series model indicated that the introduction of p-ADA facilitated the increase of NaCl transmembrane resistance without sacrificing membrane permeance. Chlorination experiments under acid conditions proved the protection effect of p-ADA grafted layer due to its oxidation resistance, avoiding the direct attack by free chlorine to amide bonds of polyamide membrane. By virtue of the convertible modality of the p-ADA molecule between the quinone and benzene structures during redox process, modified membranes presented the capability of regenerative chlorine resistance. After the “chlorination-reduction” cycle experiments, the normalized flux of modified membranes remained 0.522 while contrasted PA membranes showed a flux of 0.278; and the corresponding normalized NaCl rejection of modified membranes maintained at 0.998 significantly higher than that of PA membranes (0.963). This study presents a straightforward and efficient approach to enhance the chlorine resistance of PA RO membranes.

Water/Salt Transport Properties of Polyamide Reverse Osmosis Membranes Using Quartz Crystal Microbalance

Water/Salt Transport Properties of Polyamide Reverse Osmosis Membranes Using Quartz Crystal Microbalance

Stoichiometric effect on the structural transformation and spatial variation of polyamide reverse osmosis membranes: A molecular dynamics study

Reverse osmosis based on polyamide membranes is currently the leading technology for desalination and water purification. However, the spatial variation of polyamide architecture, especially regarding stoichiometric criteria at the real reaction interface during membrane fabrication, is poorly understood. Here we conducted equilibrium molecular dynamic simulations, mimicking the practical construction of polyamide matrices using a variety of monomer component stoichiometries, to investigate resulting differences in both the morphological transformation and mass transport through the polymer network. Our simulations indicated that an equal stoichiometry of the reactive functional groups predominantly resulted in favorable polyamide matrix qualities such as a high crosslinking density, uniform pore size distribution, and adequate layer compactness. Despite the thickness-dependent water diffusion across the active layer, an analysis of polyamide membrane density revealed depth heterogeneity, particularly for membranes constructed under unequal concentrations. Consequently, uncontrollable defects are likely to be created, as evidenced by the partial penetration of Na+ across such membranes. In addition, the residual functional groups in the polyamide matrices (–COOH and –NH2) influenced the transport behavior of ions near the membrane surface. Overall, our simulations provide a visual platform for understanding the stoichiometry-induced relationship between membrane structure and performance, which may guide the future design of defect-free and scaling-resistant reverse osmosis membranes.

Demonstrating removal credits for contaminants of emerging concern in recycled water through a reverse osmosis barrier–A predictive framework

The performance of individual reverse osmosis (RO) systems varies significantly with different contaminants of emerging concern (CECs). As such, log reduction values (LRVs) of the concentration of these chemicals cannot be arbitrarily credited in water treatment and water recycling. This study looks to present an approach to the management of chemical risks by providing a systematic validation of RO barrier performance with respect to LRV credits for various classes of CECs. In this work, a one-off sampling campaign across five treatment barriers (strainer filtration, ultrafiltration, RO, ion exchange, chlorination) of a full-scale water recycling plant was conducted, followed by a systematic sampling campaign for a period of six weeks across just the RO barrier. The CECs screening methodology used GC–MS for quantification of 948 trace organic chemicals along with specific 44 per- and polyfluoroalkyl substances (PFAS) screening using LC-MS/MS to demonstrate the removal credits of the RO barrier to a wide spectrum of CECs. The work was used to validate an LRV barrier credit framework so as to predict the performance of a polyamide RO membrane for removal of a range of chemical classes, under typical operational conditions. Conductivity was validated as an efficient surrogate for membrane integrity and RO performance, along with specified operational conditions associated with permeate flux and recovery rate. A bioassay method (photobacterium test) showed good potential to be used as a quick measure to indicate the general toxicity of a sample caused by chemical contamination, because of its high detection sensitivity and time and cost efficiency.

In-situ rapid construction of aliphatic amine combined polyamide seawater reverse osmosis membrane for efficient boron removal

Polyamide (PA) reverse osmosis membranes are commonly employed in seawater desalination owing to their effective salt rejection and water permeability; however, the elimination of small and neutral boron molecules from seawater remains a significant hurdle in energy-efficient and cost-effective desalination processes. In this work, a seawater reverse osmosis (SWRO) membrane with powerful boron removal competence was designed by adopting an in-situ rapid integration protocol, which utilized aliphatic amines as hydrophobic barriers by bonding the residual chloride groups upon the membrane surface and as molecular plugs by embedding in the PA networks. Consequently, it resulted in a notable improvement in the rejection of neutral boron molecules due to enhanced steric hindrance caused by immobilized amine plugs and synergistically tunned hydrophobic interactions. The permeability coefficient of boron decreased from 4.8 to 0.9 L m−2 h−1, and the boron rejection increased from 80.7 to 90.5% under the modification conditions with the optimal type and concentration of amines, while displaying a NaCl rejection of 99.8% and an acceptable water permeability of 0.55 L m−2 h−1 bar−1. Meanwhile, the alteration of membrane chemical compositions and structure properties was kept to a minimum. This study offers intuitive insights into the critical roles played by the aliphatic amines in the selective layer of the membrane for the removal of neutral boron molecules and salts, thereby enabling the fabrication of highly selective SWRO membranes, which may have significant implications for more efficient membrane-based seawater desalination and boron removal.

High flux and highly fouling-resistant polyamide reverse osmosis membrane having inner and outer zwitterion-like layers

The development of high flux and highly fouling-resistant reverse osmosis (RO) membranes is crucial for addressing water crisis. However, it is still challenged to enhance the antifouling performance of the membrane against organic foulants, particularly charged small organic foulants. We herein reported the fabrication of antifouling thin-film composite (TFC) polyamide (PA) RO membranes having inner and outer zwitterion-like layers by a scalable layer-by-layer interfacial polymerization process. The inner zwitterion-like layer is constituted by the positive charges from the incorporated cationic surfactant of benzalkonium chloride (BAC) and the negative charges from carboxylic acid groups in the PA. Then, the outer zwitterion layer is the L-arginine molecules grafted on the PA. The modified RO membranes have a high water permeance of 3.92 L m−2 h−1 bar−1, while maintaining a NaCl rejection rate of 99.18 %. In addition, the obtained membranes exhibit excellent antifouling properties with the flux decline rate (FDR) of below 40 % and the flux recovery rate (FRR) of above 98 % against 200 ppm of positively and negatively charged surfactants as small organic foulant models, surpassing most of the reported membranes. Our work provides insights to engineer the polyamide RO membrane surface with superior separation performance and efficient anti-fouling properties.

Removal, Adsorption, and Cleaning of Pharmaceutical on Polyamide RO and NF Membranes.

Pharmaceuticals are present in various waters and can be almost completely rejected by membrane separation processes, i.e., nanofiltration (NF) and reverse osmosis (RO). Nevertheless, the adsorption of pharmaceuticals can decrease their rejection, so adsorption can be considered a very important removal mechanism. In order to increase the lifetime of the membranes, the adsorbed pharmaceuticals must be cleaned from the membrane. The used pharmaceutical (albendazole), the most common anthelmintic for threatening worms, has been shown to adsorb to the membrane (solute-membrane adsorption). In this paper, which is a novelty, commercially available cleaning reagents, NaOH/EDTA solution, and methanol (20%, 50%, and ≥99.6%) were used for pharmaceutical cleaning (desorption) of the NF/RO membranes used. The effectiveness of the cleaning was verified by Fourier-transform infrared spectra of the membranes. Of all the chemical cleaning reagents used, pure methanol was the only cleaning reagent that removed albendazole from the membranes.

Orientation matters: Measuring the correct surface of polyamide membranes with quartz crystal microbalance

The surface of polyamide reverse osmosis (RO) membranes which regulates interface-dominated phenomena, such as partitioning and fouling, is the one facing the feed during operation. However, the opposite surface of the polyamide selective layer, the one facing the permeate and in contact with the polysulfone porous support, is commonly analyzed in quartz crystal microbalance (QCM) measurements due to limitations of state-of-the-art transfer methodologies. Such measurements on the back surface cannot be generalized because the polyamide layer is chemically and morphologically asymmetric. Herein, we introduce a simple method to coat QCM sensors with polyamide active layers in the correct orientation (i.e., exposing their front surface) and show that interface-dominated phenomena differ significantly between orientations. We start by describing a transfer protocol to coat any surface with a polyamide layer on its front surface orientation. We then systematically analyze the chemical and morphological differences between the two surfaces of the polyamide layer of a commercial RO membrane. Finally, we demonstrate that interface-dominated phenomena depend on the orientation by showing that NaCl partitioning at pH 6 was 1.3 to 2.3-fold higher on the front surface and that organic fouling with humic acid occurred at a lower rate on this surface. The new method presented herein enables measurements on the front surface of polyamide RO membranes, which should be the standard in any future QCM studies.

Facile hydrophilization of polyethylene substrate by in situ polymerization of m-phenylenediamine for preparing high-performance polyamide reverse osmosis membrane

Polyethylene (PE) microporous membrane-supported thin-film composite (TFC) polyamide membranes have received growing attention owing to their low cost, superior separation performance, and excellent chemical robustness. Developing facile and cost-effective methods to hydrophilize PE membranes is essential for the scale-up of PE-supported TFC membranes. Here, a facile approach of in situ polymerization of m-phenylenediamine (MPD) was employed to hydrophilize the PE membranes for the first time. Characterizations showed that both the outer surface and the interior of the PE membrane were homogeneously coated with poly(m-phenylenediamine) (PMPD). The hydrophilicity of the modified PE membrane was dramatically enhanced with the water contact angle decreasing from ∼120° to ∼72° and water flux at 2 bar increasing from 0 to ∼640 L m−2 h−1. The high surface porosity and appropriate surface hydrophilicity of the MPD-modified PE membrane together with the excellent coating uniformity favor the formation of a highly permselective polyamide active layer. The outstanding coating stability was demonstrated through different tests. The cost of the MPD-modified PE membrane is estimated to be less than 1% of that of the conventional substrates. Furthermore, high-performance and low-cost reverse osmosis (RO) membranes were prepared via interfacial polymerization on the MPD-modified PE substrates. The PE-supported RO membrane exhibited an excellent separation performance with NaCl rejection of 99.3%, pure water permeance of 1.3 L m−2 h−1 bar−1, and long-term operating stability. The proposed hydrophilization strategy of PE membrane is facile, low-cost, environmentally friendly, and reliable, and thus has a brilliant prospect for industrialization.

Chlorine resistance property improvement of polyamide reverse osmosis membranes through cross-linking degree increment

Highly permeable polyamide reverse osmosis (RO) membranes are desirable for reducing the energy burden and ensuring future water resources in arid and semiarid regions. One notable drawback of thin film composite (TFC) polyamide RO/NF membranes is the polyamide's sensitivity to degradation by free chlorine, the most used biocide in water purification trains. This investigation demonstrated a significant increase in the crosslinking-degree parameter by the m-phenylenediamine (MPD) chemical structure extending in the thin film nanocomposite (TFN) membrane without adding extra MPD monomers to enhance the chlorine resistance and performance. Membrane modification was carried out according to monomer ratio changes and Nanoparticle embedding into the PA layer approaches. A new class of TFN-RO membranes incorporating novel aromatic amine functionalized (AAF)-MWCNTs embedded into the polyamide (PA) layer was introduced. A purposeful strategy was carried out to use cyanuric chloride (2,4,6-trichloro-1,3,5-triazine) as an intermediate functional group in the AAF-MWCNTs. Thus, amidic nitrogen, connected to benzene rings and carbonyl groups, assembles a structure similar to the standard PA, consisting of MPD and trimesoyl chloride. The resulting AAF-MWCNTs were mixed in the aqueous phase during the interfacial polymerization to increase the susceptible positions to chlorine attack and improve the crosslinking degree in the PA network. The characterization and performance results of the membrane demonstrated an increase in ion selectivity and water flux, impressive stability of salt rejection after chlorine exposure, and improved antifouling performance. This purposeful modification resulted in overthrowing two tradeoffs; i) high crosslink density-water flux and ii) salt rejection-permeability. The modified membrane demonstrated ameliorative chlorine resistance relative to the pristine one, with twice the increase in crosslinking degree, more than four times the enhancement of the oxidation resistance, negligible reduction in the salt rejection (0.83 %), and only 5 L/m2.h flux loss following a rigorous static chlorine exposure of 500 ppm.h under acidic conditions. The excellent performance of new chlorine resistant TNF RO membranes fabricated via AAF-MWCNTs together with the facile membrane manufacturing process offered the possibility of postulating them in the desalination field, which could eventually help the current freshwater supply challenge.

Improving permselectivity of the polyamide reverse osmosis membrane by a controlled-release sulfate radical modification

The sulfate radical (SO4.-) is an effective reactive oxidative species that can improve the permselectivity of polyamide membranes. However, the coexistence of hydroxyl radicals, which have been previously reported in a thermal-activated persulfate (PDS) system, have detrimental effects on membrane integrity and salt rejection. In this study, we adopted a facile citric acid chelated Fe(II)/PDS modification method to generate a controlled-release SO4.- oxidation condition at room temperature, which enhanced membrane performance. The rapid oxidation by Fe(II)/PDS significantly increased membrane water permeability. However, ferric oxyhydroxides were formed and deposited on the membrane surface, reducing surface hydrophilicity and negative charge. Citric acid was then introduced into the modification as a chelating agent to control the release of Fe(II) and improve the modification efficiency. The modified membrane showed further increased water permeability (from 26.0 to 53.0 L m−2h−1) and maintained a salt rejection of 98.4%. The optimized membrane enhanced surface hydrophilicity and negative charge, slightly improving anti-fouling ability. The membrane chemical composition characterization using ATR-FTIR and XPS indicated the formation of excess oxygenous groups. Furthermore, SO4.- oxidized the chlorine-sensitive sites, endowing the modified membrane with significantly improved chlorine resistance. The results from this study provide a facile SO4.--based modification method for comprehensively improving permselectivity, surface properties, and anti-fouling/anti-chlorine resistances of the polyamide membranes.

The Treatment of Endocrine-Disruptive Chemicals in Wastewater through Asymmetric Reverse Osmosis Membranes: A Review

Endocrine-disrupting chemicals (EDCs) present in aquatic environment have been regarded as detrimental organic pollutants that pose significant adverse impacts on human health and the aquatic ecosystem. The removal of EDCs is highly desired to mitigate their harmful effects. Physical treatment through membrane-based separation processes is an attractive approach, as it can effectively remove a wide range of recalcitrant organic and nonorganic EDCs. In particular, the reverse osmosis (RO) process has shown promise in removing EDCs of various concentrations and from different sources. Recently, the development of innovative asymmetric RO membranes has become the forefront in this field. Various membrane modification strategies have been commenced to address the limitations of commercial membranes. This review provides an overview of the recent advances in asymmetric RO membranes for EDC removal from water and wastewater system. The potential areas of improvement for RO processes and RO membranes are also highlighted. Based on the existing literature using RO for EDC removal from water, the most investigated EDCs are bisphenol A (BPA) and caffeine in the concentration range of 200 ppb to 100 ppm. Polyamide RO membranes have been shown to remove EDCs from water bodies with a removal efficiency of ~30 to 99%, largely depending on the type and concentration of the treated EDCs, as well as the properties of the RO membranes. It has been demonstrated that the performance can be further heightened by tailoring the properties of RO membranes and optimizing the operating conditions of the RO process.

When self-assembly meets interfacial polymerization.

Interfacial polymerization (IP) and self-assembly are two thermodynamically different processes involving an interface in their systems. When the two systems are incorporated, the interface will exhibit extraordinary characteristics and generate structural and morphological transformation. In this work, an ultrapermeable polyamide (PA) reverse osmosis (RO) membrane with crumpled surface morphology and enlarged free volume was fabricated via IP reaction with the introduction of self-assembled surfactant micellar system. The mechanisms of the formation of crumpled nanostructures were elucidated via multiscale simulations. The electrostatic interactions among m-phenylenediamine (MPD) molecules, surfactant monolayer and micelles, lead to disruption of the monolayer at the interface, which in turn shapes the initial pattern formation of the PA layer. The interfacial instability brought about by these molecular interactions promotes the formation of crumpled PA layer with larger effective surface area, facilitating the enhanced water transport. This work provides valuable insights into the mechanisms of the IP process and is fundamental for exploring high-performance desalination membranes.

Antibacterial and Antifouling Properties of Ag‐ and Cu‐Decorated Thin Film Composite Polyamide Reverse Osmosis Membranes

AbstractIn this work, silver and copper particles of different nanoparticle precursor concentrations were decorated on the surface of thin film composite polyamide (TFC‐PA) reverse osmosis (RO) membranes by in situ method. The modified membranes were characterized by different techniques including Field emission scanning electron microscopy (FE‐SEM), X‐ray Absorption Spectroscopy (XAS), and attenuated total reflection – Fourier transforms infrared spectroscopy (ATR‐FTIR), water contact angle (WCA), and antibacterial capacity. After that, the membrane performance was compared through normalized flux and the possibility of the removal of bovine serum albumin (BSA) protein; the anti‐fouling and anti‐biofouling properties were also compared through the maintained flux ratios (%) after 5‐hour filtration. The used organic foulants were BSA protein and humic acid (HA) solutions. The results showed that, compared to the flux of the base, the flux of AgNPs‐decorated membrane can improve the separation ability up to 24% while that of CuNPs‐decorated membrane was 14%. The anti‐fouling property of decorated membranes was significantly increased compared to that of the base (from 64% for the base to over 77% for decorated membranes). Especially, the anti‐biofouling property of nanoparticles decorated membranes was also increased because of the higher maintained flux ratios (from 50% for the base to over 75% for decorated membranes). It indicates that this method can be applied to produce reverse osmosis (RO) membranes for reclamation wastewater with a high content of organic matter.

Self-healing polyamide reverse osmosis membranes with temperature-responsive intelligent nanocontainers for chlorine resistance

Self-healing polyamide reverse osmosis membranes with temperature-responsive intelligent nanocontainers for chlorine resistance

Water transport in reverse osmosis membranes is governed by pore flow, not a solution-diffusion mechanism.

We performed nonequilibrium molecular dynamics (NEMD) simulations and solvent permeation experiments to unravel the mechanism of water transport in reverse osmosis (RO) membranes. The NEMD simulations reveal that water transport is driven by a pressure gradient within the membranes, not by a water concentration gradient, in marked contrast to the classic solution-diffusion model. We further show that water molecules travel as clusters through a network of pores that are transiently connected. Permeation experiments with water and organic solvents using polyamide and cellulose triacetate RO membranes showed that solvent permeance depends on the membrane pore size, kinetic diameter of solvent molecules, and solvent viscosity. This observation is not consistent with the solution-diffusion model, where permeance depends on the solvent solubility. Motivated by these observations, we demonstrate that the solution-friction model, in which transport is driven by a pressure gradient, can describe water and solvent transport in RO membranes.

Hydrophilic-hydrophobic heterogeneous interface enables the formation of a high-performance polyamide membrane for water purification

Polyamide reverse osmosis (RO) membranes possessing high water permeance and high salt rejection are highly beneficial for efficient desalination and wastewater treatment. However, achieving desired membrane properties toward both fast water transport and outstanding salt rejection remains a great challenge. Herein, we report the fabrication of high-performance polyamide RO membrane via interfacial polymerization (IP) on a heterogeneous substrate featuring a hydrophobic surface and polyaniline modified hydrophilic pores. The heterogeneous substrate, combining the advantages of conventional hydrophilic and hydrophobic substrates for IP process, leads to the formation of an ultra-thin polyamide film with rough morphology. The obtained RO membranes thereby not only have simultaneously enhanced water permeance (3.28 L m−2h−1 bar−1) and salt rejection (NaCl rejection 99.5 %), but also exhibit outstanding pH stability, anti-fouling performance, and long-term stability. In addition, the regulation mechanism of the heterogeneous substrate on IP was comprehensively investigated by combing molecular simulation and experiments. Our work provides a novel design direction of substrate used for fabricating RO membrane with outstanding performance.

Corrigendum to “Antifouling enhancement of thin-film composite polyamide reverse osmosis membrane by surface immersion deposition and in-situ crosslinking method with NaAlg-GA hydrogel” [Colloids Surf. A: Physicochem. Eng. Asp. 654 (2022) 130140

Corrigendum to “Antifouling enhancement of thin-film composite polyamide reverse osmosis membrane by surface immersion deposition and in-situ crosslinking method with NaAlg-GA hydrogel” [Colloids Surf. A: Physicochem. Eng. Asp. 654 (2022) 130140

Preparation and Desalination of Semi-Aromatic Polyamide Reverse Osmosis Membranes (ROMs)

Reverse osmosis membrane (ROM) technology has a series of advantages, such as a simple process, no secondary pollution, high efficiency, energy saving, environmental protection, and good separation and purification effects. High-performance semi-aromatic polyamide reverse osmosis membranes (ROMs) were prepared by interfacial polymerization (IP) of novel cyclopentanecarbonyl chloride (CPTC) and m-phenylenediamine (MPD) monomers. The surface morphology, hydrophilicity and charge of the ROMs were characterized by field-emission scanning electron microscopy (SEM), a contact angle tester and a solid-surface zeta potential analyzer. The effects of CPTC concentration, MPD concentration, oil-phase solvent type, IP reaction time and additive concentration on the performance of semi-aromatic polyamide ROMs were studied. SEM morphology characterization showed that the surface of the prepared polyamide ROMs presented a multinodal structure. The performance test showed that when the concentration of MPD in the aqueous phase was 2.5 wt.%, the concentration of sodium dodecylbenzene sulfonate (SDBS) was 0.2%, the residence time in the aqueous phase was 2 min, the concentration of CPTC/cyclohexane in the oil phase was 0.13 wt.%, the IP reaction was 20 s, the NaCl rejection rate of the semi-aromatic polyamide ROM was 98.28% and the flux was 65.38 L/m2·h, showing good desalination performance. Compared with an NF 90 commercial membrane, it has a good anti-BSA pollution ability.