Salt Rejection Research Articles

Improving dye removal ability and fouling resistance of thin‐film nanocomposite nanofiltration membranes using a new citric acid functionalized FSM‐16 mesoporous

AbstractThe development of superior thin‐film nanocomposite (TFN) membranes with good separation performance and anti‐fouling capacity is required to address the larger‐scale freshwater need. In this study, a new citric acid‐functionalized FSM‐16 (CA‐FSM‐16) mesoporous was successfully synthesized and characterized. Subsequently, it was introduced on the surface of the sodium hydroxide/cyanuric chloride‐activated PES membrane to fabricate the CA‐FSM‐16 TFN membrane. It was investigated how various CA‐FSM‐16 loadings affected the overall physicochemical characteristics and performance of the membrane. The SEM analysis confirmed the TFN structure of the fabricated membranes. All manufactured membranes displayed improved hydrophilicity and flux. For the pristine membrane, the salt (Na2SO4) rejection was measured 73.20 ± 2.10%, whereas for the TFN‐0.08 membrane, it was measured 91.40 ± 1.80%. The dye rejection experiment in cross‐flow filtration showed that the TFN‐0.08 membrane had the maximum licorice retention among the membranes (99.10 ± 2.00%). In addition, the CA‐FSM‐16 TFN membranes demonstrated superior antifouling performance, especially the optimum membrane (TFN‐0.08), which showed a high flux recovery ratio (FRR) of 97.10 ± 1.90% and a low irreversible fouling ratio (DRir) of 2.90%. The introduction of CA‐FSM‐16 on the surface of the PES membrane via the surface modification method was a potentially useful technology to fabricate a high‐performing TFN membrane for water treatment applications.

Evaluating the efficiency of modified hydrophobic PVDF membrane for the removal of PFOA substances from water by direct contact membrane distillation

This study addresses the global issue of the contamination of water resources by per- and poly-fluoroalkyl substances (PFAS). PFAS are notoriously difficult to remove due to their resilient alkyl-fluorinated chains. We examined the potential of hydrophobic PVDF membranes in direct contact membrane distillation (DCMD) to eliminate perfluorooctanoic acid (PFOA) from Water. For desalination, both commercial and custom-made PVDF membranes exhibited a permeate flux of approximately 13 LMH, with salt rejections of 98.39 % and 99.95 %, respectively. In the case of PFOA removal, the fabricated PVDF membrane outperformed its commercial counterpart. It boasted an initial permeate flux of 16 LMH and a PFAS rejection of 95.8 %, compared to the commercial membrane's 13 LMH and 67.31 %. Furthermore, the custom membrane exhibited superior resistance to fouling, experiencing less flux decline. Employing response surface methodology (RSM), we identified the optimal combination of feed concentration (30 ppm), (60 °C), and flow rate (1.5 LPM) to yield a flux of 9 LMH and a PFOA rejection of 95.41 %. Feed temperature emerged as the most influential factor in DCMD performance. This study offers a novel approach to concentrating and removing emerging contaminants from wastewater and highlights the efficacy of tailored membrane technology in addressing pressing environmental challenges.

Affinity-based engineering of carbon nanotube embedded polyamide membranes for simultaneous desalination and boron removal

Reverse osmosis (RO) is the leading technology for obtaining drinking and irrigation water from seawater. Although currently developed RO membranes achieve high salt rejection; several challenges exist, such as permselectivity trade-off, biological/chemical contamination, and insufficient retention of small and neutral molecules like boric acid. Due to its toxicity to living organisms and strictly monitored levels in potable water, removal of boron has gained considerable attention in RO industry. Thin film nanocomposite (TFN) membranes have emerged by incorporating nanomaterials with superior water/salt selectivity into polyamide (PA) layer of composite membranes. For the first time, our group investigated the potential of carboxylated carbon nanotube (CNT) embedding in the selective layer of TFN membranes for boron removal. Within this frame, we hypothesize that embedding fillers with low boron affinity accompanied by high water permeability in the selective layer of TFN membranes improves boron removal without suffering from the permselectivity trade-off. In this study, we investigated the boron removal performance of functionalized CNT (f-CNT) embedded TFN membranes. Initially, CNTs were functionalized with three different functional groups (namely, biotin (BIO), 8-amino caprylic acid (ACA), and zwitterion (ZWT)) to narrow down the tube entrance, provide repulsive electrostatic interactions with boron, and interfere with the hydrogen bonding between water and boric acid molecules. Then, TFN membranes incorporating f-CNTs were fabricated, characterized, and tested. Showing high compatibility with PA, ZWT functionalization has increased water/boron selectivity of TFN membranes by 66% and water permeability by 44%, while maintaining the salt rejection at 98%. Furthermore, we employed molecular dynamics simulations and potential of mean force calculations to elucidate the boron exclusion mechanism in f-CNTs. With its flexible structure and “gate-keeper” ability, ZWT functional group was found to show the highest energy barrier against boron transport. Hence, engineering CNT/PA TFN membranes to promote steric hindrance and decrease solute affinity is promising for efficient removal of detrimental small molecules from seawater.

Plasmonic group 4 transition metal carbide interfaces for solar‐driven desalination

AbstractTo combat the dwindling supply of freshwater, solar‐driven desalination using plasmonic nanomaterials has emerged as a promising and renewable solution. Refractory plasmonic carbide nanomaterials are exciting candidates that are inexpensive and chemically robust but have not been widely explored. Herein, plasmonic carbide interfaces made of TiC, ZrC, and HfC nanoparticle aggregates loaded onto to a mixed cellulose ester (MCE) membrane were explored to gain insight into their solar‐vapor generation and desalination potential. Desalination using Atlantic Ocean water under 1 sun intensity yielded rates of 1.26 ± 0.01, 1.18 ± 0.02, and 1.40 ± 0.01 kg m−2 h−1, with efficiencies of 86%, 80%, and 96% for TiC, ZrC, and HfC, respectively. Carbide interfaces showed good stability and effectively removed heavy metal ions and salt from solutions with concentrations up to 35%. PVA hydrogel based TMC evaporators afforded rates of 3.31 ± 0.03 and 3.22 ± 0.03 kg m−2 h−1 for TiC and ZrC, respectively. The HfC‐PVA interface afforded a high solar desalination rate of 3.69 ± 0.04 kg m−2 h−1, corresponding to an efficiency of 97% under 1‐sun illumination. The hydrogel evaporators also retained their strong salt rejection action over time.

WITHDRAWN: Concentrate Management of Spent Geothermal Water Treated with Two- Step Membrane Processes for Agricultural Irrigation

This study examines a two-step membrane treatment to improve water quality by targeting electrical conductivity in reverse osmosis (RO) concentrate from spent geothermal water. The process involves RO treatment followed by electrodialysis reversal (EDR). Water samples were collected during different seasons to assess quality under varying conditions.Following the initial treatment by XLE-RO membrane test system, the large-pilot membrane (LPM-RO) concentrate achieved salt rejection of 98.6%, while the mini-pilot membrane (MPM-RO) concentrate achieved salt rejection of 95.6%. Conductivity values were 48.6µS/cm for LPM-RO and 226µS/cm for MPM-RO concentrate. Further passing the product water obtained from XLE-RO membrane through the EDR system improved overall product water quality. Treated LPM-RO product water had conductivities of 3.71µS/cm (5V) and 2.36µS/cm (10V). For MPM-RO product water, conductivities were 11.98µS/cm (5V) and 2.64µS/cm (10V). In this study, an additional experiment investigated the EDR treatment of RO concentrate without undergoing initial RO pretreatment. After the experiment, although the salt rejection reached 97.65%, it was observed that the product water quality at the end of the 90-minute treatment was 74.6µS/cm with lower quality as compared to when the RO concentrate underwent initial RO pre-treatment. Hence, the combination of RO-EDR can be successfully utilized to treat geothermal water concentrate for better quality which could be utilized in irrigation. This two-step membrane treatment shows potential for higher-quality water reclamation for various processes.

Construction of a high-performance hollow fiber composite NF membrane via the simultaneous modification of substrate and selective layer

Hollow fiber composite (HFC) nanofiltration (NF) membrane demonstrates significant commercial potential profiting from its self-supporting characteristic, high packing density and strong fouling resistance. In this work, a high-performance HFC NF membrane was successfully developed through simultaneous modification of the substrate via alkaline hydrolysis and incorporation of iopamidol (IPD) into the selective layer. Alkaline hydrolysis enhanced the hydrophilicity of the polyacrylonitrile (PAN) substrate by converting –CN groups into –COOH, thereby sharply improving the success rate of HFC NF membrane fabrication. The addition of IPD into piperazine (PIP) solution effectively increased the water permeability of the HFC NF membrane without compromising its salt rejection. Specifically, the optimized membrane sample denoted as NF-0.15P + 0.5I with 0.5 w/v% IPD added demonstrated a 44 % increase in PWP from 21.8 L·m−2·h−1·bar−1 to 31.5 L·m−2·h−1·bar−1, while maintaining a Na2SO4 rejection over 96.8 %. This improvement can be attributed to the decreased selective layer thickness and reduced MWCO. Furthermore, the membrane exhibited exceptional dye/salt separation performance. This work represents a novel approach leading to the development of a HFC NF membrane suitable for dye/salt separation.

Superhydrophobic composite membranes for membrane distillation based on CNTs networks: Overcoming the trade-off between water vapor permeability and wetting resistance

Enhancing the wetting resistance of the membrane is crucial for consolidating the stability of the membrane distillation (MD) process, but this generally leads to the decline of water vapor flux. Herein, we developed a superhydrophobic composite membrane composed of a highly hydrophobic polyvinylidene fluoride (PVDF) porous support layer and a functional superhydrophobic carbon nanotubes (CNTs) network. The CNTs network with high thermal conductivity not only reduces the temperature polarization effect, but also increases the effective evaporation area, thereby enhancing the mass transfer driving force of the MD process. Additionally, the CNTs network significantly reduces the maximum pore radius of the composite membrane, and the perfluorination treatment also reduces the surface energy of the CNTs network, thereby synergistically increasing the liquid entry pressure. The results showed that when treating high salinity water containing 3.5 wt% NaCl, the water vapor flux of the composite membrane increased from 20.0 LMH of the original PVDF membrane to 24.4 LMH, an increase of 22 %. Furthermore, the performance of the original PVDF membrane deteriorates rapidly when the concentration of surfactant in the feed exceeds 1.0 mM, while the composite membrane still maintains a stable water vapor permeability and salt rejection. More importantly, the composite membrane exhibits excellent resistance to wetting induced by gypsum scaling when using gypsum solution as the feed, which is attributed to its small surface pore size and high hydrophobicity. This research supplies new insights into the design of membrane structures used in MD processes to overcome the trade-off between water vapor permeability and wetting resistance.

Evaluating the advantage of turbulent flow to diminish concentration polarization in Roto-dynamic RO system

Concentration polarization (CP) is the major shortcoming of the reverse osmosis (RO) system for brackish/seawater desalination. The present study aims to understand the effect of induced shear stress, enhanced flow dynamics, and eddy diffusivity on CP, when the flow is turbulent. In roto-dynamic RO system turbulence can be easily generated by controlling the angular speed of the rotor without increasing the feed discharge. We have numerically simulated the salt rejection by the RO membrane and concentration polarization at the seawater salinity of 500 mol/m3 for two different configurations of roto-dynamic RO system when the flow is turbulent. We have used Reynolds stress model (RSM) and eddy viscosity-dependent eddy diffusivity models for salt transport. In turbulent flow regime, eddy diffusion enhances the mixing. In laminar flow regime, salt concentration over the membrane increases by 60%–110% for 70 bar feed pressure. In contrast, the increment of salt concentration is only about 3%–4% once the flow becomes turbulent, leading to 3–4 times higher permeate discharge for roto-dynamic RO system. Thus, it can increase the longevity of the membrane and improve overall performance of the RO module by delaying membrane scaling and fouling.

Are Hansen solubility parameters relevant in predicting the post-treatment effect on polyamide-based TFC membranes?

This study investigates the impact of solvent post-treatment on polyamide-based thin film composite (TFC) membranes, specifically examining the effect on commercial nanofiltration (NF) and reverse osmosis (RO) membranes. Na2SO4 rejection and increase in pure water permeance (PWP) were considered as the output parameters. The disparity in Hansen solubility parameters (HSP) between the post-treatment solution and the polyamide layer of the TFC membrane, denoted by Ra, is well adapted to understand the enhancement in water permeance through the membranes upon treatment. Aqueous solutions of dimethylformamide with a Ra value of 4, acetonitrile with a Ra value of 8.3, and ethanol with a Ra value of 12.7 were used as the post-treatment solutions. Our experimental design, based on the Box-Behnken design of Response Surface Methodology, incorporates variables such as the concentration of the solvent in the solution (% v/v), Ra value, and treatment time (s). Our findings demonstrate that the effect of post-treatment on the TFC membranes is not governed by the Ra value. Notably, while the post-treatment with the aqueous solution of acetonitrile, 80% v/v for 30 s, had considerable effects on NF membranes (124.5% enhancement in PWP; reduction of 3.5% in Na2SO4 rejection), its impact on RO membranes was negligible. Several factors explain this discrepancy, including the limitations of the HSP model for composite polymers, the inaccuracy of the PWP or salt rejection as a swelling indicator, variations in the HSP values of the polyamide layers for different membranes, and possible modifications in the interface between the support membrane and the polyamide layer. In summary, our study provides insights into the complex interactions between solvents and composite membranes, indicating that HSP alone is not a decisive factor in predicting post-treatment effects on polyamide-based TFC membranes.

Custom-tailoring zwitterion-based nanofiltration membranes for organic molecule desalination with sub-200 Da molecular weight

Organic molecule desalination with nanofiltration has important practical application significance. Zwitterion-based nanofiltration membranes (ZNFMs) with selective channels for monovalent salts have been prepared to improve the separation performance. However, most ZNFMs tend to be restricted by their loose structures, which results in unsatisfactory rejection for small molecules with sub-200 Da molecular weight. In this study, a synchronous modification strategy during the heat treatment of interfacial polymerization was proposed, in which various multi-amine solutions were employed as the novel medium of heat treatment to regulate the structures of ZNFMs. The pore size distribution of membranes could be narrowed to a certain degree through cross-linking by corresponding multi-amines. The optimized ZNFMs exhibited excellent retention to small molecules. For example, the retention of glucose was dramatically increased to 96.5%. Meanwhile, the ZNFMs also had low rejection for monovalent salts, such as KCl (26.7 %). Consequently, the separation factor between glucose and KCl reached 21.2, which demonstrated a great potential for organic molecule desalination with sub-200 Da molecular weight.

On the discrepancy between nominal and effective charge density of polyamide reverse osmosis membranes

Quantitative and reliable information on the ionization of functional groups in polyamide (PA) active layers of thin film composite membranes is of vital importance for understanding and modeling of ion transport. Independent measurements using Ag+ ion-probing with RBS, XPS, or ICP-MS, indicate a nominal charge density in the order of 0.5 M. Conversely, model fitting to salt rejection experiments suggests an effective membrane charge at least three orders of magnitude lower for brackish water (BWRO) and seawater (SWRO) membranes. In this study we show that the original interpretation of the ion-probe experiments is inconsistent with the principles of ion partitioning used in ion transport models. We provide an alternative interpretation of ion-probe experiments in the literature, explaining the results through binding of silver ions to the carboxylic groups. By using this interpretation, the discrepancy between nominal and effective charge can be resolved: the Ag measured in the ion-probe experiments is mostly bound to the membrane (-COOAg, not –COO−/Ag+), while the membrane is virtually uncharged. Consequently, the ion-probe experiments can quantify the concentration of functional groups, but not theirpKa. We propose that confinement affecting membrane ionization, should be explicitly included in ion-transport modeling.

Iron nanoparticle coating and plasma-activated water cleaning as a biofouling removal method for reverse osmosis membranes suitable for desalination

Desalination provides crucial freshwater, but biofouling on reverse osmosis (RO) membranes is a major challenge due to hard-to-remove biofilms. Conventional treatments are often ineffective, prompting a shift to coatings with nanoparticles like copper, silver, and iron to combat fouling. This study demonstrates a unique combination of coating RO membranes with iron nanoparticles (FeNPs) and treatment with plasma-activated water (PAW) for the removal of biofilm formation. Pure and unbound FeNPs showed no significant inhibition of Escherichia coli biofilms. However, the attachment of FeNPs to RO membranes led to a decrease in biofilm growth on the membrane, and an additional PAW treatment was shown to significantly inhibit mature biofilms. SEM imaging revealed a higher density and uniform distribution of FeNPs on the RO membranes after PAW treatment. Zeta potential measurements showed positively charged FeNPs in PAW, enhancing their attraction with the negative membrane surfaces. The coated membrane using PAW solution with FeNPs exhibited no degradation in terms of pure water flux, saline water flux, and salt rejection compared to the immersion process in DI with FeNPs.

Harmonic amide bond density as a game-changer for deciphering the crosslinking puzzle of polyamide

It is particularly essential to analyze the complex crosslinked networks within polyamide membranes and their correlation with separation efficiency for the insightful tailoring of desalination membranes. However, using the degree of network crosslinking as a descriptor yields abnormal analytical outcomes and limited correlation with desalination performance due to imperfections in segmentation and calculation methods. Herein, we introduce a more rational parameter, denoted as harmonic amide bond density (HABD), to unravel the relationship between the crosslinked networks of polyamide membranes and their desalination performance. HABD quantifies the number of distinct amide bonds per unit mass of polyamide, based on a comprehensive segmentation of polyamide structure and consistent computational protocols derived from X-ray photoelectron spectroscopy data. Compared to its counterpart, HABD overcomes the limitations and offers a more accurate depiction of the crosslinked networks. Empirical data validate that HABD exhibits the expected correlation with the salt rejection and water permeance of reverse osmosis and nanofiltration polyamide membranes. Notably, HABD is applicable for analyzing complex crosslinked polyamide networks formed by highly functional monomers. By offering a powerful toolbox for systematic analysis of crosslinked polyamide networks, HABD facilitates the development of permselective membranes with enhanced performance in desalination applications.

Preparation and performance of magnetic carbon nanotubes modified PVC substrate composite nanofiltration membranes

Polyamide (PA)/ferroferric oxide/oxidized multi-walled carbon nanotubes (Fe3O4/o-MWCNTs)/polyvinyl chloride (PVC) composite nanofiltration (NF) membranes were prepared by the interfacial polymerization (IP) process with the Fe3O4/o-MWCNTs/PVC porous membrane as the substrate membrane, which was prepared by the magnetic field assisted non-solvent induced phase separation method (NIPS) with the synthesized superparamagnetic Fe3O4/o-MWCNTs nanoparticles (NPs) as the additives of the functional intermediate layer integrated with the substrate. The effects of the magnetic carbon nanotubes modified PVC porous substrate membrane on the surface chargeability, PA layer thickness, mechanical properties, pressure resistance and permeability of the composite NF membranes were investigated, and the comprehensive performance of composite NF membranes was enhanced. The results indicated that the porosity and hydrophilicity of the Fe3O4/o-MWCNTs/PVC porous substrate membrane were improved by the migration of magnetic Fe3O4/o-MWCNTs NPs to the upper edge of the substrate membrane and uniform enrichment under magnetic field induction, which further affected the structure and properties of the PA/Fe3O4/o-MWCNTs/PVC composite NF membrane. The prepared NF membrane presented smaller roughness, thinner PA layer, larger pore size, with excellent mechanical properties and better pressure resistance. Meanwhile, the PA/Fe3O4/o-MWCNTs/PVC composite NF membrane presented excellent divalent salt rejection, with the rejection of MgSO4 and Na2SO4 maintaining more than 95.2% and 93.4%, respectively, while the permeation flux could reach 35.4 L·m−2·h−1. In summary, the modification of the substrate integrated with the functional intermediate layer had certain enlightening significance for the preparation of the NF membrane with excellent comprehensive performance.

Engineered eco-friendly composite membranes with superhydrophobic/hydrophilic dual-layer for DCMD system

Considerable advancements have been made in the development of hydrophobic membranes for membrane distillation (MD). Nonetheless, the environmentally responsible disposal of these membranes poses a critical concern due to their synthetic composition. Herein, an eco-friendly dual-layered biopolymer-based membrane was fabricated for water desalination. The membrane was electrospun from two bio-polymeric layers. The top hydrophobic layer comprises polycaprolactone (PCL) and the bottom hydrophilic layer from cellulose acetate (CA). Additionally, silica nanoparticles (SiO2 NPs) were electrosprayed onto the top layer of the dual-layered PCL/CA membrane to enhance the hydrophobicity. The desalination performance of the modified PCL-SiO2/CA membrane was compared with the unmodified PCL/CA membrane using a direct contact membrane distillation (DCMD) unit. Results revealed that silica remarkably improves membrane hydrophobicity. The modified PCL-SiO2/CA membrane demonstrated a significant increase in water contact angle of 152.4° compared to 119° for the unmodified membrane. In addition, PCL-SiO2/CA membrane has a smaller average pore size of 0.23 ± 0.16 μm and an exceptional liquid entry pressure of water (LEPw), which is 3.8 times higher than that of PCL/CA membrane. Moreover, PCL-SiO2/CA membrane achieved a durable permeate flux of 15.6 kg/m2.h, while PCL/CA membrane showed unstable permeate flux decreasing approximately from 25 to 12 kg/m2.h over the DCMD test time. Furthermore, the modified PCL-SiO2/CA membrane achieved a high salt rejection value of 99.97% compared to a low value of 86.2% for the PCL/CA membrane after 24 h continuous DCMD operation. In conclusion, the proposed modified PCL-SiO2/CA dual-layer biopolymeric-based membrane has considerable potential to be used as an environmentally friendly membrane for the MD process.

Engineering PVDF omniphobic membranes with flower-like micro-nano structures for robust membrane distillation

Conventional PVDF membranes are easily wetted and contaminated in membrane distillation (MD) process, especially when used in separating high-salinity water and oil-contained saline water. To address these issues, an omniphobic membrane was fabricated in this work. ZnO micro-flowers with a rough structure were successfully deposited onto the PVDF membrane with the assistance of polydopamine assistance. After undergoing a fluorination process, the omniphobic membranes were prepared by the synergistic effect of surface microstructure and free energy. The effects of varying Zn(NO3)2 concentrations and deposition times on morphology, pore size and separation efficiency were comprehensively examined. It was demonstrated that at a Zn(NO3)2 concentration of 50 mM and a deposition time of 0.5 h, the resulting PVDF composite membrane exhibited high liquid repellency towards all the test liquids, such as water, ethanol solution, paraffin oil, and etc. Furthermore, the membrane consistently exhibited impressive salt rejection behavior (99.99%) and maintained an average flux (15.54 kg·m−2·h−1) when exposed to high-salinity solution (up to 20 wt%-NaCl). Meanwhile, during treating an oil-contained saline water emulsion with the oil content of 200 ppm, the membrane also displayed high resistance to wetting and fouling during the continuously 24 h tests. The membrane displayed a rejection rate of 99.99 % with an average vapor flux of 18.60 kg·m−2·h−1. In summary, this omniphobic membranes demonstrated a great potential in MD for practical challenging wastewater treatment.

Data‐Driven Strategies for Accelerated Structural Exploration of High‐Performance 2D Carbon‐Based Seawater Desalination Membranes

The insufficiency of freshwater supplies has posed a serious threat to sustainable socioeconomic growth, and seawater desalination is considered to be the most promising solution to alleviate such pressure. Currently, 2D carbon membranes are identified as deserving candidates due to their high permeability and multiple tunable properties. However, they remain challenging to systematically uncover the potential relationships between structures and properties in various 2D carbon materials. For this, a machine learning (ML) model based on feature datasets of 2D carbon materials effecting desalination properties is trained. The results suggest that structures with a maximum pore size of 10–12 atoms and atomic densities between 0.28 and 0.41 are more likely to achieve high properties. Cml‐MOR based on MOR‐type mordenite zeolite for validation is selected. Further, Cml‐MOR is demonstrated to feature remarkable salt ion adsorption. The effective water flux of Cml‐MOR is 113.51 L cm−2 day−1 MPa−1, and the salt rejection at 110 MPa can reach 98.9%. This work is expected to apply this efficient method to investigate the structure and properties of 2D carbon membranes with great structural diversity; this will attract more people to focus on them and explore their important potential for practical applications.

Surface modification of nanofiltration membrane using polyoxometalates for improved separation and antifouling performance.

In this study, polyoxometalates (POMs) as a core-modifying material was used to fabricate the nanofiltration (NF) membrane on the polyvinylidene fluoride (PVDF) microfiltration membrane substrate via a novel interfacial polymerization (IP) method. The formation mechanism of the POMs-modified composite membrane was proposed. The separation and antifouling properties were further investigated. After cross-linking with POMs through the new IP reaction, the modified composite membrane showed improved hydrophilicity, water flux, and salt rejection. In the humic acid fouling experiment, the POMs-modified membrane exhibited the best antifouling performance, with a flux recovery rate of up to 91.3%. Electrochemical impedance spectroscopy was further used to investigate the antifouling performance of the membranes. Nyquist and Bode plots of the POMs-modified membranes showed no significant change before and after fouling compared to the PVDF membrane substrate, indicating reduced fouling attachment on the modified membrane, which was consistent with the fouling index and flux variation observed during the fouling experiment. Our findings provide a simple and valuable route for fabricating POMs-functionalized NF membranes with desirable separation and antifouling performance.

Enhancing separation and long-term performance of reverse osmosis desalination through the incorporation of 15-crown-5 in thin-film composite membranes with Li+ and Na+ augmentation

Thin-film composite (TFC) membranes have been intensively studied for the purpose of improving separation performance. Different additives have been attempted during the interfacial polymerization. In this study, 15-Crown-5 (CE15) was employed as the additive to produce TFC membranes for reverse osmosis. The influences of CE15 on the membrane surface morphology, chemical composition and separation performance were then investigated. By adjusting the CE15 concentration, the optimal membrane demonstrated a significant enhancement in water permeance, which was 117% higher than that of the original TFC membrane while sustaining a comparable salt rejection. Additionally, the effects of introducing Li+ and Na+ in the fabrication of CE15 membranes were explored and found to enhance the performance and long-term stability. Overall, our results indicate the potential for enhancing the separation performance of TFC membranes through the synergistic combination of CE15 with Li+ and Na+, offering a simple way of modifying membranes to achieve a higher efficiency and durability in water purification and other separation processes.

Upcycled PVC support layer from waste PVC pipe for thin film composite nanofiltration membranes

Thin-film-composite (TFC) nanofiltration membranes represent the pinnacle of membrane technology in water treatment and desalination. These membranes typically consist of a polyamide (PA) selective layer and a membrane support layer, often constructed from commercially available materials like polyethersulfone (PES). However, there exists an alternative approach that involves the use of different polymers, preferably upcycled waste polymers, as a viable support layer for TFC membranes. Successfully implementing the upcycling of waste plastics into high-value support membranes can make a significant contribution to addressing the issue of plastic waste pollution. One of the primary challenges associated with utilizing upcycled polymers as support layers is the potential impact on the polyamide selective layer of TFC membranes, subsequently affecting their performance in terms of permeability, rejection, and antifouling properties. In this study, we demonstrate the successful fabrication of TFC membranes with a support layer crafted from upcycled waste PVC pipe. We conducted a comprehensive investigation into the effects of upcycled PVC on the structural and physicochemical properties of the polyamide layer. The ultrafiltration (UF) support membranes were fabricated from waste PVC pipe via the nonsolvent induced phase separation (NIPS) method. Subsequently, a polyamide layer was synthesized atop the Upcycled PVC membrane using interfacial polymerization (IP). The physicochemical properties and performance of the TFC membranes with upcycled PVC support layer were compared with membranes with research-grade (RG) PVC and commercial PES support layers. The results unveiled that the TFC membrane with upcycled PVC support layer exhibited higher water permeability (18.2 LMH/bar), in contrast to RG TFC (15.5 LMH/bar) and PES TFC membranes (13.7 LMH/bar). Furthermore, the salt rejection capabilities of the upcycled PVC TFC membrane were competitive and well within an acceptable range.