Polyamide Layer Research Articles

Intercalation of small molecules in the selective layer of polyamide nanofiltration membranes facilitates the separation of Mg2+/Li+

In addressing lithium supply shortages driven by increased energy demand, nanofiltration membrane technology is crucial for recovering lithium from salt lake brines. Overcoming the challenge of achieving high selectivity for Li+ and water permeability in polymer nanofiltration membranes, this study proposes a simple approach using Aminomalononitrile (AMN) intercalation to modify polyamide layers. Density functional theory simulations predict AMN's superior selectivity and enhanced hydrophilicity. Stable intercalation of AMN between polyethyleneimine (PEI) molecules is demonstrated, synergistically enhancing water permeability and Li+ selectivity. The resulting PEI/AMN-TMC membrane exhibits exceptional Li+ selectivity and improved water permeability (13.1 L·m−2·h−1·bar−1), 2.9 times higher than traditional PEI-TMC membranes. Stable performance for over seven days, along with anti-scaling and anti-bacterial properties, underscores its practicality. This investigation sheds light on membrane structure regulation through small-molecule intercalation, offering insights into precise adjustments for enhanced water permeability and ion selectivity.

Removal of multiple pesticides from water by different types of membranes

Pesticides are used in agriculture to protect crops from pathogens, insects, fungi and weeds, but the release of pesticides into surface/groundwater by agriculture runoff and rain has raised serious concerns not only for the environment but also for human health. This study aimed to investigate the impact of surface properties on the performance of seven distinct membrane types utilized in nanofiltration (NF), reverse osmosis (RO) and forward osmosis (FO) processes in eliminating multiple pesticides from spiked water. Out of the membranes tested, two are self-fabricated RO membranes while the rest are commercially available membranes. Our results revealed that the self-fabricated RO membranes performed better than other commercial membranes (e.g., SW30XLE, NF270, Duracid and FO) in rejecting the targeted pesticides by achieving at least 99% rejections regardless of the size of pesticides and their log Kow value. Despite the marginally lower water flux exhibited by the self-fabricated membrane compared to the commercial BW30 membrane, its exceptional ability to reject both mono- and divalent salts renders it more apt for treating water sources containing not only pesticides but also various dissolved ions. The enhanced performance of the self-fabricated RO membrane is mainly attributed to the presence of a hydrophilic interlayer (between the polyamide layer and substrate) and the incorporation of hydrophilic nanosheets in tuning its surface characteristics. The findings of the work provide insight into the importance of membrane surface modification for the application of not only the desalination process but also for the removal of contaminants of emerging concern.

A sub-10 nm polyamide nanofiltration membrane from polyvinylpyrrolidone-mediated interfacial polymerization

In conventional interfacial polymerization (IP) for thin-film composite nanofiltration membranes, the separation layer is typically thick (∼100 nm), which limits its water permeance. In this study, we successfully synthesized an ultrathin polyamide layer (∼8.6 nm) from polyvinylpyrrolidone (PVP)-mediated IP. With the surfactant concentration over its critical micelle concentration, PVP not only formed a monolayer at the water-heptane interface, but also stayed in the aqueous solution. The CO groups of PVP formed the N–H⋯O hydrogen bond interactions with N–H bonds of piperazine (PIP) monomers in the aqueous phase to slow down the diffusion of PIP monomers. Besides, PVP with amphiphilic groups minimized the interfacial tension at the water-heptane interface to regulate IP processes. By adjusting the concentration of PVP, we obtained a sub-10 nm polyamide nanofiltration membrane. Moreover, hydrophilic PVP macromolecules improved the membrane surface hydrophilicity. Due to the ultrathin thickness and improved hydrophilicity, the optimized polyamide membrane demonstrated a threefold increase in permeance compared to that of the pristine polyamide membrane without PVP addition, and maintained 98.4% rejection for 1000 ppm Na2SO4 solution. This study provides a new insight into fabricating sub-10 nm polyamide membranes for nanofiltration processes.

Enhancing proton conduction by regulating proton carrier position in polyamide layer of forward osmosis membrane in osmotic microbial fuel cell

Osmotic microbial fuel cell (OsMFC) encounters the problem of slow transport of proton, which results in a pH imbalance between the anode and cathode, and then a decreased cell performance. Forward osmosis (FO) membrane plays a critical role in proton transport in OsMFC, but the proton transmembrane migration is greatly hindered by the absence of particular proton transfer unit in FO membrane. In this study, high proton conductive carrier sulfo (−SO3H) was imported in the polyamide (PA) layer of FO membrane. The results demonstrated that the position of sulfo on benzene ring in PA polymer chain had a significant effect on proton migration and further the OsMFC property. As sulfo is in the ortho and para of the amino group on benzene ring, the optimal FO-1 membrane was acquired. It indicated that the OsMFC loaded with FO-1 membrane completed 88.31 % increase of water extraction, 50.72 % promotion of maximum power density and 6.02 % enhancement of chemical oxygen demand (COD) removal compared to those of the OsMFC with commercial FO membrane. The molecular dynamics simulation elucidated that the hydrogen bond and electrostatic interaction between atoms both played crucial roles in the proton-transfer process. This method of introducing proton carrier at molecular level aiming to alleviate the rising catholyte pH is economical and convenient for the potential scale-up applications of the OsMFC.

Antibacterial polyamide nanofiltration membranes with intermediate layers of quaternized cellulose nanocrystal for Mg2+/Li+ separation

Positively charged and non-toxic intermediate layers are highly desirable for the construction of nanofiltration membranes in the field of Mg2+/Li+ separation. Herein, we have prepared dual-electric layer nanofiltration membranes via introducing positively charged quaternized cellulose nanocrystals (Q-CNC) beyond the negatively charged polyamide skin layers. On the one hand, the strong interactions between Q-CNC and piperazine (PIP) could regulate the thickness, roughness, and residual groups of the polyamide (PA) layers, resulting in improved water flux. On the other hand, the Q-CNC has lots of positive charges which are beneficial for enhancing the rejections of negatively charged polyamide skin layers towards divalent cations since the Donnan and electrostatic effects are long-range forces. Moreover, this effect could be amplified by reducing the thickness of skin layers or decreasing the contents of residual carboxyl groups via adjusting the monomer concentrations. The obtained nanofiltration membranes possess high water flux of 51 L/m2/h/bar, and rejection for MgCl2 of 86 %. The separation factor of Mg2+/Li+ is 29 when the Mg2+/Li+ mass ratio in the feed solution is 20:1. Moreover, the nanofiltration membrane with Q-CNC intermediate layers (QNFM) has good antibacterial properties, showing great potential in the fields of lithium extraction from salt lakes.

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.

Hierarchical electroactive ion permselective membrane with electrochemical switched ion pump effect for continuous lithium-ion recovery

Highly selective extraction of lithium ions (Li+) from salt-lake brines is crucial to mitigate lithium supply shortages. In this work, a novel electrochemically switched lithium ion permselective membrane (ESLPM) was rationally designed through an ingenious tactic with an electroactive layer of lithium manganate (LiMn2O4) as the active radical and a dense and positively charged polyamide (PA) on each side of polyethersulfone (PES) substrate for the rapid and selective separation of Li+ from salt-lake brines with high Mg/Li ratios. Here, the reversible uptake/release and enhancement electro-sorption selectivity of Li+ are controlled by changing the electrochemical potential of the membrane with an ion-pump effect coupling with the electric field to achieve the continuous recovery of Li+. As a result, the flux of Li+ in the optimum hierarchical ESLPM-240 of the electrochemically switched ion permselective (ESIP) membrane separation system reached 0.032 mol m−2 h−1 for the separation of Li+ from the salt lake brine with a high Mg/Li ratio (Mg2+/Li+ = 20), which is 25% higher than in electrodialysis (ED) system. Meanwhile, by constructing a hierarchical structure, the separation factor of Li+/Mg2+ was increased to 7.8 under the ESIP system, which is about 3.5 times higher that of PA layer, and about 2.2 times higher than that of the electroactive layer. In addition, theoretical calculation confirmed that electroactive LiMn2O4 and positively charged PA layers are more favorable for Li+ transport when compared to Mg2+. Besides, the ESLPM-240 exhibited excellent long-term stability, indicating that the proposed strategy is promising for large-scale industrial applications in the Li+ extraction from salt lakes.

Tannic acid etched ZIF-8 incorporated thin-film nanocomposite nanofiltration membrane with enhanced performance

Incorporating functionalized nanomaterials in the selective layer of conventional polyamide nanofiltration (NF) membrane is a promising strategy for overcoming the trade-off between permeability and selectivity. Highly hydrodispersible TA/ZIF-8 composite nanomaterials were prepared by etching ZIF-8 with tannic acid, and the thin-film nanocomposite (TFN) NF membranes were prepared by introducing TA/ZIF-8 into the interfacial polymerization aqueous phase solution. The nanomaterials and NF membranes' structure, chemical composition, and hydrophilicity were comprehensively characterized. The influence and mechanism of introducing TA/ZIF-8 into the polyamide layer on the separation performance of the TFN membranes were discussed by separating typical mono- and divalent salts. The optimal TFN membrane had a water flux of 26.59 LMH-bar−1 (increased by 86.6% than that of the TFC-blank membrane) with 94.95% rejection of Na2SO4 while having good antifouling performance and stability. Furthermore, the inverse size exclusion phenomenon of chlorine-contained salts was explored through relevant control experiments. This work is valuable for expanding the application of 3D nanomaterials in membrane separation technology and preparing high-performance TFN nanofiltration membranes.

Optimizing ionic conductivity and ion selectivity in zinc-polyiodide flow batteries with composite polyamide-porous separators

Owing to their superior theoretical energy capacity, zinc-polyiodide flow batteries (ZIFBs) are well-known energy storage devices. The practicality of ZIFBs depends on the development of cost-effective separators that can demonstrate both excellent ionic conductivity and selective ion permeability. Herein, an economical polymer blend comprising poly (ether sulfone) (PES) and sulfonated poly (ether ether ketone) (sPEEK) is fabricated via a phase inversion technique. Due to the formation of a sponge-like structure, the porous substrate indicates high ionic conductivity. Furthermore, the selected porous substrate is coated with a thin-film polyamide, synthesized from m-phenylenediamine (MPD) and 1,3,5-benzene tricarbonyl trichloride (TMC) via interfacial polymerization (IP). This polyamide layer can efficiently mitigate the undesired migration of triiodide ions, while maintaining high ionic conductivity. This innovative approach yields a composite separator having a deftly tunable structure. Using such a separator, ZIFBs can operate stably with high coulombic efficiency (CE) of 91 % over 100 cycles at a current density of 10 mAh cm−2. Overall, this study explores the trade-off between ionic conductivity and ion permeability. It is seen that by adjusting their morphology, the physical characteristics of the composite separators can be improved, ensuring stable and efficient operation of ZIFBs.

Carbon dots regulating microstructure of polyamide layer of forward osmosis membrane for anti-biofouling and unexpected dual-enhancement in water flux and salt rejection

The introduction of hydrophilic nanomaterials into the polyamide (PA) layer of forward osmosis (FO) membranes usually leads to the enhancement in water flux but a reduction in salt rejection. The decrease in salt rejection, however, inevitably influences the osmotic efficiency and operation cost. In this work, m-phenylenediamine (MPD), one of the chemicals of interfacial polymerization, was utilized as a precursor to synthesize carbon dots (MPD-C-dots) with a good photosensitization functionality. The MPD-C-dots were introduced into the PA layer of FO membranes through co-interfacial polymerization (denoted as Single-C-dots-M), and further grafted onto the PA layer by the conjugation of the residual acyl chloride of trimesoyl chloride with the amine of MPD-C-dots (denoted as Double-C-dots-M). The as-prepared Double-C-dots-M exhibited more outstanding FO performances than the pristine membrane (Control-M) and Single-C-dots-M. Most unexpectedly, the dual-enhancement in water flux and salt rejection of Double-C-dots-M was found. The further studies reveal that Double-C-dots-M had smaller and more uniform pore size, but larger porosity than the other two. In addition, the biofouling-resistance tests demonstrate that MPD-C-dots-M had an excellent anti-biofouling performance by generating singlet oxygen (1O2) under light irradiation. The proposed Double-C-dots-M provided a typical protocol for improving the performances of FO membrane, especially for the synchronous enhancement in water flux and salt rejection.

Enhancing water recovery through integrated graphene oxide-modified forward osmosis and membrane distillation for real textile wastewater treatment

The textile industry is a highly water-intensive sector, emphasizing the increasing importance of reclaiming clean water from textile wastewater and advancing water recovery towards zero liquid discharge. This study proposes and assesses an integrated forward osmosis and membrane distillation (FO-MD) process for treating real textile wastewater, aiming for enhanced water recovery and ensure robustness towards zero liquid discharge. Firstly, a newly developed graphene oxide (GO)-enhanced FO membrane (GFO) was fabricated by adding GO into the polyamide layer during the interfacial polymerization process. Furthermore, the real textile wastewater treatment performance of the FO-MD process based on the GFO membrane was compared to that of a commercial FO membrane (CFO). The results indicated the GFO-based FO-MD process outperformed due to enhanced antifouling properties and stable water flux. Remarkably, the GFO membrane-based FO-MD system achieved over 80% water recovery and nearly 100% rejections for COD, Na+, K+, Cl-, and S2- during continuous 24-hour filtration. The findings highlighted FO-MD as a viable solution, surpassing the individual FO and MD processes by overcoming the limitations of FO draw solution dilution and MD membrane wetting challenges. Moreover, a preliminary techno-economic study for a 200 m3 day−1 textile wastewater estimated water production costs of $6.48 m−3 and $5.73 m−3 for CFO-MD and GFO-MD systems. The analysis highlighted maintaining the water flux above 10 L m−2 h−1 is crucial for economic viability. This work demonstrates the potential of the FO-MD system as a sustainable solution to address the textile wastewater treatment challenges, providing insights for FO-MD system design and optimization.

Improving performance prediction of metal-organic framework membranes for reverse osmosis via genetic algorithm optimized artificial neural networks

The pollution of water resources and the rapid development of society are leading to the decrease of available fresh water resources in the world, which intensifies the research on seawater desalination. Metal-organic frameworks (MOFs), as promising membrane materials with diversified sizes, highly porous structures, and tunable chemical functionalities, have been extensively studied for desalination in recent years. In this paper, genetic algorithm (GA) optimized back propagation (BP) artificial neural network was first constructed, which made the prediction model of MOF membranes performances more accurate. Before the GA optimization, the structure of BP model was tuned through cross-validation and hyperparameter adjustment to achieve a better prediction performance and robustness. Then the GA was introduced attaining an enhanced R2 of 0.98 and 0.99 compared to the BP model of 0.90 and 0.97 for water permeability and salt rejection, respectively, which was also superior to the random forest, support vector machine, and multiple linear regression models. In addition, the grey relational analysis was used to screen the feature variables in order to clarify the most influential factors that affect the membrane performances. It is found that the MOF size and the thickness of polyamide layer were the key influential factors. This work will provide insights for the design of high-performance MOF based membranes and further render implications for other membrane developments.

Systematic experiments and multiscale simulation calculations reveal chemical stability differences in dry/wet nanofiltration membranes

This study investigated the chemical stability differences between dry and wet nanofiltration membranes when immersed in strong acid and base environments. Systematic experimental studies were conducted on both types of nanofiltration (NF) membranes, supplemented by Molecular Dynamics (MD) simulations and Density Functional Theory (DFT) calculations. The results indicate that wet NF membranes, soaked in deionized water for a week, exhibit higher chemical stability compared to dry membranes treated only with air. Traditional air heating causes membrane pore contraction and excessive crosslinking. However, after a week of immersion in water, the polyamide (PA) layer gradually becomes a loose and well-extendable PA layer. MD simulations revealed that H+ and OH− ions possess lower diffusion coefficients and extended residence times in dry NF membranes, making them more prone to damage. Additionally, DFT calculations disclosed that the Gibbs free energy (ΔG) for amide bond hydrolysis in wet NF membranes, in the presence of water molecules, is elevated, significantly delaying their hydrolysis rate under extreme conditions. This study highlights the pivotal role of membrane wetness in the chemical durability of NF membranes and offers a novel perspective for improving membrane lifespan and efficiency.

Dissecting the impacts of nanobubbles and heat generated in polymerization on polyamide nanofiltration membranes

In the preparation of nanofiltration (NF) membranes, the introduction of acid acceptors into the aqueous phase generates heat through their interaction with the byproduct HCl from interfacial polymerization (IP), potentially leading to the formation of bubbles. This work aims to dissect the combined influences of heat and nanobubbles on NF membrane structure and performance. Three representative alkalis (i.e., NaHCO3, NaOH, and Ca(OH)2) were employed as acid acceptors into the aqueous phase, resulting in an increase of the consumption of PIP in the IP reaction from 10.75% to 23.65%, 19.35%, and 12.90%, respectively. The use of NaOH and Ca(OH)2 released more heat led to a thicker polyamide layer which reduced flux. While the use of NaHCO3 simultaneously released heat and bubbles, which promoted the development of a rougher surface polyamide layer, resulting in an increased flux from 20.3 to 28.3 L/m2 h bar, while maintaining a salt rejection rate of 97.7%. The attendance of acid acceptors also enhanced the degree of crosslinking and resulted in a decrease in negative charge of the prepared membrane. This study advances the understanding of the impact of heat and bubbles release induced by the addition of acid acceptors on NF membrane structure and performance.

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.

Machine learning – Driven surface grafting of thin-film composite reverse osmosis (TFC-RO) membrane

Modifying reverse-osmosis (RO) membrane performance is challenging and time-consuming due to the complex interplay of various factors that influence the membrane's performance. To address this challenge, we have explored the potential of using machine-learning (ML) to graft the polyamide (PA) surface of an RO membrane to increase water permeability and overcome the limitations of the permeability/selectivity tradeoff. We identified moieties with positive and negative contributions toward water permeability by applying Shapley-Additive-exPlanations (SHAP) analysis to our model as an explainable artificial intelligence (XAI) method. We attempted to improve the subunits of the PA's structure with positive Shapley values and graft the polyamide RO membrane layer of a commercial membrane, Dupont XLE, resulting in a substantial increase in water permeability. The membranes were characterized using FTIR, EDS, and SEM analysis, and their performance was evaluated for water permeance and NaCl rejection using a dead-end stirred cell. The modified membrane exhibited a significant improvement in the commercial membrane's water flux, increasing from 2.45 LMH to 4.9 LMH. Our results demonstrate the potential of using ML to replace traditional trial-and-error methods for modifying PA-RO membrane polyamide layers and advancing the development of higher efficient and sustainable RO membranes for water treatment and purification applications.

In-situ interfacial polymerization of polyamide TFN membranes by adding a diamino-silane coupling agent: Toward enhanced desalination performance

The primary challenge faced by thin film nanocomposite (TFN) membrane in nanofiltration (NF) process is to effectively resolve the trade-off effect between permeability and selectivity. Herein, a polyamide (PA) TFN membrane with enhanced NF performance was prepared through in-situ interfacial polymerization (in-situ IP) method, using piperazine (PIP) and 3-diamino-methyl-cyclohexyl triethoxysilane (DTES) as co-amine monomers to undergo a reaction with 1,3,5-benzenetricarbonyl trichloride (TMC). This study investigated the effects of DTES on the surface chemical composition, morphologies, hydrophilicity, separation efficiency, and anti-fouling properties of the novel DTES/PIP/TMC TFN membranes. It was found that SiO2 nanoparticles were generated in-situ from the reacted DTES through hydrolysis and self-condensation, resulting in their uniform distribution within the formed PA selective layer with high compatibility and without aggregation. The optimal PA TFN membrane was achieved by adjusting the ration of Si-OH group in formed SiO2 nanoparticles through varying the concentration of DTES concentration. Meanwhile, the induction of SiO2 into the PA layer resulted in an enlargement in membrane pore size and improved surface hydrophilicity. When the concentration of added DTES was 0.333 wt%, the optimal PA TFN membrane (TFN-4) exhibited the highest quantity of formed Si-OH groups, resulting in the excellent performance, including a markedly enhanced water permeability flux of 76.8 L·m−2·h−1 (2-fold larger than that of the pure TFC membrane), a great Na2SO4 rejection of 97.5 %, and a superior Cl−/SO42− permeation selectivity of 46.0. Moreover, the TFN-4 membrane exhibited exceptional stability and superior antifouling properties attributed to its unparalleled hydrophilicity. This work provided a strategy for preparing uniform and high-performance TFN membranes.

Preparation of highly efficient nanofiltration membranes resistant to organic solvents by adjusting zinc oxide nanoparticle-loaded attapulgite

Zinc oxide nanoparticle-loaded attapulgite was successfully added to the polyamide layer for the preparation of high-efficiency organic solvent nanofiltration membranes. The addition of zinc oxide nanoparticle-loaded attapulgite to the aqueous monomer regulates the diffusion rate of interfacial polymerization, generating a thin and loosely packed polyamide layer. In addition, the abundant hydrophilicity of the nanoparticles lays the foundation for increased polar solvent permeation. The organic solvent nanofiltration membrane with the best performance exhibited an optimum methanol permeability of 13.19 L m−2h−1 bar−1, which was 1.54 times higher than that of the unadded membrane. Meanwhile, the optimum membrane consistently rejected more than 99.40 % of Evans blue dye, and the rejection rates of different dyes were consistent with the size-sieving effect. Furthermore, the permeation capacities of the membranes were evaluated using organic solvents with different polarities, viscosities, and molecular diameters, and the permeability of acetonitrile reached 16.98 L m−2h−1 bar−1. In addition, the optimum membranes retained excellent rejection capacity after soaking in the strongly polar solvent N, N-dimethylformamide (DMF) for 10 days at room temperature.

Application of a functionalized thin-film composite nanofiltration membrane in water desalination

To prepare a thin-film nanocomposite (TFN) nanofiltration (NF) membrane, characterized with high desalination rate and antifouling performance, carboxylated multi-walled magnetic 1,2,3,4-butanetetracarboxylic acid carbon nanotubes (hereafter, the C-MWCNT-MBTCA) with a choice of hydrophilic groups were initially synthesized in this study, and then incorporated into the polyamide (PA) layer via interfacial polymerization (IP). After that, the surface morphology and hydrophilicity of the fabricated NF membrane was examined by the field emission scanning electron microscopy (FESEM) and water contact angle measurements, respectively. To assess the membrane application, the solutions (2000 mg/L) of sodium sulfate (Na2SO4), magnesium sulfate (MgSO4), calcium chloride (CaCl2), and sodium chloride (NaCl) were consistently tested. On account of the ample carboxylic acid (R-COOH) groups in the modified TFN membrane, the study outcomes revealed that the given membrane could enhance the flux along with the desalination rate upon the addition of the C-MWCNT-MBTCA (0.04 wt%). Likewise, the pure water flux significantly grew from 58.8 to 110.5 Lm-2h−1 after the utilization of the C-MWCNT-MBTCA (0.04 wt%), and the Na2SO4 removal rate promoted from 87 to 98 %. Ultimately, it was established that the C-MWCNT-MBTCA could be used as an economical modifying agent to boost the performance of NF membranes for water desalination purposes.

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.