Thin Film Nanocomposite Reverse Osmosis Research Articles

Functionalised carbon nanotube thin film nanocomposite membranes: A comparison study on the role of backbone monomers and hydraulic pressure on membrane's performance and fouling

Thin film nanocomposite (TFN) reverse osmosis (RO) and nanofiltration (NF) membranes have attracted considerable attention for industrial applications in recent years. Among recent nanomaterials used in the fabrication of TFN membranes, carbon nanotubes (CNTs) have gained significant interest due to their unique structure (e.g., tubular shape, mechanical strength, porosity, etc.). Here, the effects of multi-walled carbon nanotubes (MWCNTs) with different functional groups as one of the well proven nanchannel structures and their interaction with two typical monomers, MPD and PIP, were thoroughly investigated. All fabricated membranes were analysed using SEM, FTIR, AFM and contact angle analyzer. Pressure variation significantly affected the performance of membranes over 24 hours of testing. The membranes incorporated with polypyrrole (PPy) modified MWCNTs showed promising results with nearly 37 % and 99 % water flux improvement for the TFN-RO and NF membranes, respectively, compared to the bare (unmodified) TFC RO/NF membranes. Specifically, the water flux of the RO OX-MWCNTs-PPy membrane increased from 18.9 to 25.5 L.m−2.h−1, while the NF OX-MWCNTs-PPy membrane's water flux rose from 45.2 to 90.1 L.m−2.h−1. The salt rejection of RO and NF remained relatively high, with over 90 % salt rejection against NaCl and Na2SO4 for RO and NF membranes. The NF OX-MWCNTs-PPy membrane exhibited a 98.2 % rejection rate for Na2SO4, and the RO OX-MWCNTs-PPy membrane showed around a 98.8 % rejection rate for NaCl. The TFN membranes showed less fouling tendency compared to the TFC membranes. In general, the integration of MWCNTs with various functional groups significantly enhanced the water flux and salt rejection properties of these membranes. Specifically, the modified membranes showed considerable improvements in water flux and maintained high salt rejection rates. Additionally, the interaction between MWCNTs and PIP monomers in TFN-NF membranes exhibited a stronger affinity compared to MPD monomers in TFN-RO membranes, indicating a more promising performance for NF applications. The findings suggest that TFN-NF membranes incorporating MWCNTs hold great promise for future industrial use, offering enhanced performance and reduced fouling rates.

Thin-film nanocomposite membranes with polyol-functionalized layered double hydroxides for boron removal via reverse osmosis

Post-treatment of the permeate from seawater desalination using conventional reverse osmosis (RO) membranes to remove electroneutral boron species is always challenging. In this study, the surfaces of layered double hydroxides (LDHs) have been modified with polyols, namely N-methyl-d-glucamine (GLU), using tannic acid (TA) as the binding agent. By optimizing the loading of the modified LDH nanofillers, the resultant thin-film nanocomposite (TFN) membrane shows an improved water permeance of 3.0 LMH bar−1 while maintaining a high salt rejection of 99.4 %. Moreover, this newly developed TFN membrane delivers a comparable boron rejection of 78.6 % when a feed containing 2,000 ppm NaCl and 15 ppm boron at pH 8 is used. The enhanced separation performance arises from the strong and extensive interactions between the polyols and boron species. This study may provide valuable insights to design next-generation TFN RO membranes for desalination and boron removal applications.

Development of an improved deep network model as a general technique for thin film nanocomposite reverse osmosis membrane simulation

Due to the complexity of the inherent trade-off between water permeability and salt rejection in thin film nanocomposite reverse osmosis membranes (TFN-ROMs), conventional methods have not performed satisfactorily in predicting the performance of TFN-ROMs. In this study, to address the limitations of traditional machine learning in predicting the performance of TFN-ROMs, we developed a three-component residual artificial neural network (R-TNN) and learned from membrane properties, nanoparticle properties, and membrane performance to capture the complex trade-off between water permeability and salt rejection of TFN-ROMs. The coefficients of determination of the trained R-TNN model for relative salt passage (RSP) and relative water permeability (RWP) of TFN-ROMs were 0.910 ± 0.028 and 0.739 ± 0.028, respectively, which showed good performance compared to fully-connected neural network and conventional machine learning models even with small sample data. Meanwhile, subsequent ablation experiments conducted verified that the improvement of the R-TNN model is practical and effective. In addition, we conducted data scale experiments, which showed that the R-TNN model has the potential to become a generalized technical framework for the initial informationization era and the future big data era. Subsequently, we employed the partial dependence plot to mechanistically interpret the model. Specifically, we observed a positive correlation between nanoparticle size and both RWP and RSP, while the loading of nanoparticles initially promoted and later inhibited these performances. The validated R-TNN model can better learn the inherent trade-off between salt rejection and water permeability of TFN-ROMs, which implies that this study can provide decision support for the fabrication of membranes with more outstanding performances, which greatly contributes to the promising applications of TFN-ROMs.

Preparation of ‘Extended Range’ thin-film nanocomposite reverse osmosis membrane with excellent permeability and selectivity

Thin-film nanocomposite (TFN) membrane possesses great potential in breaking through the ‘trade-off’ effect, in which nanomaterials are incorporated in the polyamide layer to improve the membrane structure as well as provide extra lower-resistance water channel. However, the aggregation of nanoparticles under high loading concentration always induces decline of salt rejection though higher water flux can be achieved. Inspired by the concept of ‘Extended Range Electric Vehicles’, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes were selected as the extended range materials to make up the defects of TFN membranes that excess palygorskite (Pal) brought in present study. The results showed that 1.3 mg/ml loading concentration of Pal led to dramatic decline of NaCl rejection from 99.3 % to 96.8 % though 63.1 % flux enhancement achieved compared to thin-film composite (TFC) membranes. Incorporation of 0.008 mg/ml DOPC liposomes brought further 55.5 % flux enhancement compared to TFN-Pal1.3 membrane and total 153.6 % increment compared to TFC membranes (1.98 → 5.02 L/m2·h·bar). Most importantly, the NaCl rejection of TFN-Pal1.3-DOPC0.008 membranes reverted to 99.1 % and the flux recovery rate increased to 92 %. This study provides novel method for increasing the loading concentration of nanoparticles in the selective layer combined with better dispersion, and demonstrates the feasibility of the concept of ‘Extended Range’ TFN reverse osmosis (RO) membrane.

Fabrication of polyamide thin film nanocomposite membranes with enhanced desalination performance modified by silica nanoparticles formed in-situ polymerization of tetramethoxysilane

The high separation performance polyamide (PA) thin film nanocomposite (TFN) reverse osmosis (RO) membrane for desalination was fabricated by incorporating the silica nanoparticles formed by in-situ polymerization of TMOS in the polyamide layer. The different contents and mixing methods of TMOS were investigated. The in-situ synthesized silica was uniformly embedded in the PA layer because TMOS could be fully dissolved in the organic phase solution. The agglomeration and uneven dispersion of traditional nanofillers in the polyamide layer were avoided. The best performance TFN membrane was prepared by mixing 0.8 wt% TMOS in organic phase solution and interfacial polymerization for 2 min. For brackish water desalination and high-pressure seawater desalination, the water flux of best performance membrane reached 58.4 L m−2 h−1 and 72.77 L m−2 h−1 respectively, which was 3 times and 2.6 times of that of pure polyamide thin film composite (TFC) membrane, while maintaining a satisfactory salt rejection (NaCl, 98.5%). The anti-fouling and long-term stability performance of prepared TFN membrane were also superior. This work demonstrated the potential of TMOS in-situ synthesis of nanofillers embedded in PA layer to prepare TFN membrane with high separation performance, and provided a new idea for simple preparation of TFN membrane.

Polyamide thin film nanocomposite membranes with in-situ integration of multiple functional nanoparticles for high performance reverse osmosis

Polyamide (PA) thin film nanocomposite (TFN) reverse osmosis (RO) membranes have been vigorously developed, which could be used in saline water desalination, wastewater treatment and chemicals separation and purification. Aiming at further improving the TFN RO membrane comprehensive performances, such as the perm-selectivity, stability and anti-fouling/-microbial properties remains a great challenge. Herein, we proposed a biomimetic nanoparticle redox strategy to in-situ integration of multiple functional nanoparticles, i.e., biomimetic nanoparticles (BNPs) and silver (Ag) nanoparticles into the PA matrix for simultaneously regulating the membrane microstructure and optimizing the surface property. A much hydrophilic selective layer with interior transporting channel structure renders the resultant RO membrane PA-BNP-Ag with an enhanced water permeance of ∼4.2 L m−2·h−1bar−1 without sacrificing NaCl rejection (∼98.1%). The BNPs induce Ag nanoparticles uniformly distributed within the PA matrix, which significantly improves the membrane anti-fouling/-bacterial property. The water flux recovery ratio of PAM-BNP-Ag was improved to be higher than 96% during several cycles filtration of saline solution containing bovine serum albumin foulants. More importantly, the membrane sterilization rate against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) achieves nearly 100%. This work provides a new strategy for the construction of advanced PA TFN membranes with both high perm-selectivity and anti-fouling/-microbial property in RO desalination.

PVA/TS-1 composite embedded thin-film nanocomposite reverse osmosis membrane with enhanced desalination performance and fouling resistance

Thin-film nanocomposite reverse osmosis (TFN-RO) membranes were fabricated in this study. Titanium silicate-1 (TS-1) was used as an additive during interfacial polymerization. Since nanoparticle dispersion in the membrane matrix is a significant challenge in fabricating high-performance membranes, polyvinyl alcohol/titanium silicate-1 (PVA/TS-1) composite with different PVA polymer dosage was prepared and used in TFN-RO membrane to provide better dispersion of the synthesized TS-1. As a result, the pure water flux increased by 39.5%, and the NaCl rejection improved from 95.03% to 99.1% at the optimum content of 0.1 wt.% (PVA) and 0.1 wt.% (TS-1). The antifouling properties of this membrane for bovine albumin serum (BSA) and humic acid (HA) were enhanced. Characterization of the morphologies of the membranes was investigated using AFM and FESEM. The measurement of water contact angle and zeta potential was accomplished to characterize the surface properties of the membranes. ATR-FTIR was used to study the chemical structure of the membranes. Following the introduction of the PVA/TS-1 composite, the TFN membranes became smoother, thinner, more hydrophilic, and negatively charged. Due to hydroxyl groups and less cross-linked structure of the top layer, water flux was higher. A smoother surface and more negative charges on the top layer also improved fouling resistance.

Synergetic effects of COFs interlayer regulation and surface modification on thin-film nanocomposite reverse osmosis membrane with high performance

Reverse osmosis (RO) membrane technology is of great significance to solve the increasingly serious fresh water supply problem. Researchers have found that substrate and polyamide layer properties influence the separation performance of RO membranes greatly. In this work, an interlayer of ultra-thin and hydrophilic two-dimensional Covalent organic frameworks (COFs) nanomaterial was in-situ constructed on commercial polysulfone (PSf) substrate surface via interfacial reaction between 1,4-phenylenediamine-2-sulfonic acid (Pa-SO3H) and 1,3,5-triformylphloroglucinol (Tp), both with ultra-low concentration. This COFs interlayer successfully adjusted the interfacial polymerization (IP) process between m-phenylenediamine (MPD) and trimesoyl chloride (TMC), and thus helped to fabricate a kind of thin-film nanocomposites (TFN) RO membrane with excellent performance. Compared with the baseline thin-film composite (TFC) RO membrane without COFs interlayer, the water permeance of the TFN RO membrane was increased from 17.0 to 26.3 L m−2 h−1 MPa−1, accompanied with a NaCl rejection remaining about 99.3 %. The TFN RO membrane was further modified by ultra-low concentration Tp aqueous solution to reduce the surface defects and improve the separation performance. The formed TFN-Tp RO membrane has a further increased water permeance from 26.3 to 31.1 L m−2 h−1 MPa−1, and an increased NaCl rejection from 99.3 % to 99.5 % as compared with the TFN RO membrane.

Enhanced negative charge of polyamide thin-film nanocomposite reverse osmosis membrane modified with MIL-101(Cr)-Pyz-SO3H

Negatively charged MIL-101(Cr)-Pyz-SO3H nanoparticles (NPs), with several concentrations (0.001–0.02 wt%), were used as a hydrophilic and charge modifier to make a high performance thin-film nanocomposite reverse osmosis membrane (TFC RO) through the interfacial polymerization between 1,3-phenylenediamine (MPD) and trimesoyl chloride (TMC) monomers. Surface analyses revealed smoother surfaces and higher hydrophilicity for the modified membranes. The zeta potential investigation approved rising the negative surface charge of MIL-101(Cr)-Pyz-SO3H NPs embedded RO membranes. The desalination performance displayed that 0.005 wt% MIL/RO indicated the most incredible separation efficiency for NaCl (98.05%). The desalination performance of seawater was also studied. Observations showed that 0.005 wt% MIL/RO means the best separation efficiency for seawater desalination (94.46%). Water flux for the modified membranes improved and reached the maximum value of 41.4 L/m2.h in 0.005 wt% MIL-101(Cr)-Pyz-SO3H TFC RO membrane. The fouling resistance of the membranes was identified by filtration of humic acid (HA)/NaCl solution. The obtained results demonstrated that modified membranes improved fouling resistance, and the highest fouling resistance was recorded for 0.005 wt% MIL-101(Cr)-Pyz-SO3H TFC RO membrane.

2D COFs interlayer manipulated interfacial polymerization for fabricating high performance reverse osmosis membrane

Covalent organic frameworks (COFs) have been widely used to prepare separation membranes due to their high porosity. In this work, a kind of thin-film nanocomposite (TFN) reverse osmosis (RO) membrane was fabricated by forming a polyamide (PA) selective layer on an in-situ constructed two-dimensional COFs intermediate layer. The TFN RO membrane has a much smooth (∼48 nm) and defect-free PA layer due to the regulated interfacial polymerization (IP) process with the assistance of the conterminous COFs interlayer, thereby achieving synchronously improved water permeance of 29.8 L m−2 h−1 MPa−1 and salt rejection of 99.4 %, as well as excellent chemical stability, including acid / alkali, fouling and chlorine resistance. Moreover, the COFs-interlayered TFN RO membrane exhibited promising separation performance after 80 h long-term filtration test. The current work offers fundamental insights into the critical roles of COFs interlayer in tailoring the IP process and the physicochemical properties of the PA layer, providing a novel strategy for enhancing the separation performance of RO membranes towards efficient desalination and sustainable water purification.

The role of CuO/TS-1, ZnO/TS-1, and Fe2O3/TS-1 on the desalination performance and antifouling properties of thin-film nanocomposite reverse osmosis membranes

The thin-film nanocomposite reverse osmosis (TFN-RO) membranes were prepared by the introduction of hydrophilic nanoparticles into the polyamide (PA) layer to improve desalination performance. First, the hydrothermal method was used to synthesize titanium silicate-1 (TS-1) as a base additive for the fabrication of the TFN-RO membrane. Since the particle size has a significant effect on its dispersion in the membrane matrix, changing the nucleation rate of TS-1 precursor solution with a simple method conducted to reduce the size of TS-1. Then metal oxide composites were prepared via the wet impregnation method. FESEM and AFM analyses were performed to investigate the surface alteration of the membranes due to the introduction of nanoparticles. The results showed that the surface of the TFN membranes was smoother than the unmodified one. To assess the changes in membrane properties after incorporating additives, the water contact angle, and zeta potential were measured. Compared to TFC, the 0.02TS1-Fe-TFN membrane had a ∼ 30% increase in pure water flux. Meanwhile, the rejection of NaCl increased from ∼ 95% to ∼ 99%. The probing of antifouling performance using bovine albumin serum (BSA) and humic acid (HA) contaminants also showed that due to reduced roughness, the modified membranes had higher fouling resistance than TFC. Also, the TFN membranes exhibited good long-term and pH stability.

Thin-Film Nanocomposite Reverse Osmosis Membrane with High Flux and Antifouling Performance via Incorporating Maleic Anhydride-Grafted Graphene Oxide

Water flux is one of the most important performance parameters of the reverse osmosis (RO) membrane. The higher water flux means lower energy cost when treating the same volume of feed solution with membrane separation technology. However, the increase of membrane water flux always corresponds to the decrease of solvent rejection, known as the “trade-off” effect. In addition, the surface fouling of membranes is often a serious problem, as frequent cleaning not only increases the operating cost but also shortens the life of the membranes. Recently, various hydrophilic nanomaterials have been used to improve the performance of membranes. To fabricate thin film nanocomposite (TFN) RO membrane with high flux and antifouling performance, maleic anhydride-grafted graphene oxide (MG) was successfully synthesized and incorporated into the polyamide (PA) layer via the interfacial polymerization (IP) method. We performed the IP reaction with m-phenylenediamine (MPD) and trimesoyl chloride (TMC) as reactive monomers on a polysulfone (PSF) substrate, and acid absorbent (TEA) and surfactant (SDS) were added to improve the separation performance of the membrane. The effects of MG incorporation on the membrane morphology and separation performance were investigated. SEM and AFM results show that the surface of the MG membrane is rougher than that of the membrane without MG. In addition, excessive loading of MG will lead to aggregation of MG nanosheets. FT-IR spectra indicate that the interaction between MG and PA layers results in an increase of hydrophilic groups on the surface of the TFN membrane, which is further confirmed by the results of the contact angle. The optimal MG doping concentration in the aqueous solution is 0.004 wt%, the water flux of the resultant TFN membrane is significantly increased to 51 L·m-2·h-1, 150% higher than the blank control membrane, which also performs a higher NaCI rejection (97.5% vs. 96.6%). Furthermore, the MG-incorporated RO membrane exhibits superior antifouling performance compared with the blank control membrane.

Fabrication of polyamide thin-film nanocomposite reverse osmosis membrane with improved permeability and antibacterial performances using silver immobilized hollow polymer nanospheres

Thin-film nanocomposite (TFN) membrane with polyamide (PA) layer containing nanofillers have attracted extensive attention due to their excellent properties. In this study, hollow polymer phenolic resin nanospheres (HPS) and silver nanoparticles immobilized HPS (Ag/HPS) were synthesized with 2,4-dihydroxy benzoic acid and hexamethylene tetramine, and used as nanofillers to prepare TFN-HPS and TFN-Ag/HPS membrane. In this paper, the effects of HPS and Ag/HPS addition (0.002 wt%, 0.004 wt%, 0.006 wt%, 0.008 wt% and 0.010 wt%) on TFN membranes separation performance were investigated. The results showed that the water fluxes of TFN-HPS and TFN-Ag/HPS membranes reaches 64.7 L·m−2·h−1 and 64.0 L·m−2·h−1, respectively, when the addition amount of HPS and Ag/HPS was 0.006 wt%, which is about 80 % higher than that of TFC membranes (36.0 L·m−2·h−1). Furthermore, the TFN-HPS and TFN-Ag/HPS membrane have excellent long-term stability. After seven days of continuous operation, the water flux of TFN-HPS and TFN-Ag/HPS membranes remains at 50.0 L·m−2·h−1 and 45.6 L·m−2·h−1, respectively. In addition, the fouling resistance of TFN-HPS and TFN-Ag/HPS membranes is significantly improved, with flux recovery rates reaching 88.8 % and 91.4 %, respectively. Importantly, the sterilization rate of TFN-Ag/HPS membrane containing antibacterial silver to Escherichia coli is up to 96.7 %.

Modifying cellulose nanocrystal dispersibility to address the permeability/selectivity trade-off of thin-film nanocomposite reverse osmosis membranes

Thin-film nanocomposite reverse osmosis (TFN-RO) membranes with hydrophilic nanoparticles usually face a trade-off between water permeance and salt rejection. In this study, TFN membranes were produced by embedding different loadings of cellulose nanocrystals (CNCs) into the polyamide (PA) active layer by dispersing the CNCs in an organic monomer solution as opposed to the traditional approach where hydrophilic nanoparticles are added to the aqueous monomer solution. To facilitate the addition of the hydrophilic CNCs to the organic monomer solution, the CNCs were acetylated to form ACNCs with different degrees of substitution (DS = 0.7 and 1.7) of the hydroxyl groups. The successful incorporation of the CNCs and ACNCs into TFN-RO membranes was confirmed with ATR-FTIR spectroscopy, surface zeta potential, scanning electron microscopy, atomic force microscopy and water contact angle measurements. The NaCl rejection of ACNC-based TFN membranes remained stable (98–99 %) while water permeance increased by 40 % in comparison to CNC-TFN membranes. Compared to a reference thin-film composite (TFC) membrane, a two-fold water permeance increase was achieved (2.60 vs. 1.27 L/m2.h.bar) with a 0.4 wt% loading of ACNC2 in the TFN membrane. The ACNC-TFN membranes were significantly closer to the so-called upper-bound line than the best CNC-TFN membranes and the reference TFC membrane. This study shows the potential of using hydrophilic green nanoparticles in overcoming the permeance-selectivity trade-off of TFN-RO membranes. Hydrophobic functionalization of hydrophilic nanoparticles was demonstrated to be an effective approach in overcoming the limit of CNC nanoparticle incorporation in CNC-TFN membranes.

Thin-film nanocomposite reverse osmosis membranes incorporated with citrate-modified layered double hydroxides (LDHs) for brackish water desalination and boron removal

By intercalating citrate anions into the inter-layer of layered double hydroxides (LDHs), the inter-layer spacing of the resultant CA-Mg-LDH is enlarged from 7.5 to 11.8 Å. With the aid of this newly developed CA-Mg-LDH, novel thin-film nanocomposite (TFN) membranes have been prepared, systematically investigated, and demonstrated for brackish water reverse osmosis (BWRO) desalination. By manipulating the nanofiller concentration, a water permeance of 3.21 LMH bar−1 and a salt rejection of 98.9% are obtained for the TFN membrane at the optimal loading of 0.15 wt%. It achieves a 68% higher water permeance than the pristine TFC membrane but without notably sacrificing the selectivity, owing to the moderate enlargement of the inter-layer spacing of CA-Mg-LDH. In addition, this novel TFN membrane has a boron rejection of 75% when using a 2000 ppm NaCl solution containing 10 ppm boron as the feed at 20 bar. This work is the first attempt to use CA-Mg-LDH as nanofillers in TFN membranes for demonstration of BWRO and boron removal, offering new insights and strategies for the design of next-generation TFN membranes for water treatment.

Modifying Cellulose Nanocrystal Dispersibility to Address the Permeability/Selectivity Trade-Off of Thin-Film Nanocomposite Reverse Osmosis Membranes

Modifying Cellulose Nanocrystal Dispersibility to Address the Permeability/Selectivity Trade-Off of Thin-Film Nanocomposite Reverse Osmosis Membranes

Modifying Cellulose Nanocrystal Dispersibility to Address the Permeability/Selectivity Trade-Off of Thin-Film Nanocomposite Reverse Osmosis Membranes

Modifying Cellulose Nanocrystal Dispersibility to Address the Permeability/Selectivity Trade-Off of Thin-Film Nanocomposite Reverse Osmosis Membranes

Antifouling and antibacterial β-cyclodextrin decorated graphene oxide/polyamide thin-film nanocomposite reverse osmosis membranes for desalination applications

• β-cyclodextrin-functionalized graphene oxide enhanced membrane properties. • Membrane with improved surface hydrophilicity and pure water permeability obtained. • Superior antibacterial and antifouling properties imparted on membrane. • Potentially a robust reverse osmosis membrane with an improved life-span. Incorporating functional nanomaterials in polyamide-based membranes has opened up new alternative ways to develop reverse osmosis membranes with excellent performance, biological stability, chemical stability and longer life-span. In this study, β-cyclodextrin functionalized graphene oxide nanosheets (β-CD-f-GO) were synthesized and used to fabricate polyamide thin film nanocomposite membranes possessing excellent reverse osmosis performance, antifouling and antibacterial properties. The β-CD functionalized graphene oxide nanosheets were prepared via an amide-mediated coupling reaction between ethylenediamine-grafted β-CD and graphene oxide. The fabricated nanosheets were then embedded in the polyamide thin film composite membranes via interfacial polymerization of m-phenylenediamine in an aqueous solution containing β-CD-f-GO nanosheets with trimesoyl chloride. The influence of the nanosheets on the membrane surface chemistry, permselectivity performance, antibacterial and antifouling properties was investigated. The results revealed that the water permeation flux and antibacterial activity of the β-CD-f-GO incorporated membranes showed an improvement by approximately 38% and 45.9%, respectively, relative to an unmodified polyamide membrane, with an insignificant change in salt rejection. In addition, the nanocomposite membranes exhibited improved antifouling properties with a lower total fouling ratio of 26.2% and a higher flux recovery ratio of 88.3% in comparison to the respective 46.8% and 74.1% obtained with the unmodified polyamide membrane. Additionally, the nanomposite membranes showed long term stability over a period of 144 h of reverse osmosis testing and improved chlorine resistance. With this study, it can be concluded that the β-cyclodextrin-functionalized graphene oxide nanocomposite has a good potential in the fabrication of membranes with improved stability and lifespan for desalination applications.

Fabrication of defect-free thin-film nanocomposite (TFN) membranes for reverse osmosis desalination

The rise of porous nanomaterials has stimulated a new research thrust on novel thin-film nanocomposite (TFN) reverse osmosis (RO) membranes. While encouraging results of greater permeability have been reported, they are usually companied by an inferior membrane selectivity due to the agglomeration of nanomaterials and low compatibility between the nanomaterials and polyamide matrix. Herein, to sustain the membrane selectivity at the molecular level, a type of metal-organic frameworks (MOFs), namely UiO-66-NH2 nanoparticles, have been modified with different amount of tannic acid (TA) before participating in interfacial polymerization. Due to the inherent porous nature and improved hydrophilicity of the modified MOFs, the resultant TFN membranes (referred to as TFN-TU) show a remarkable increase in water permeance compared to both conventional thin-film composite (TFC) and UiO-66-NH2 incorporated membranes (TFN-U). Thanks to the bridging effects of TA, TFN-TU membranes exhibit a higher salt rejection than TFN-U membranes for brackish water desalination. In addition, for seawater desalination, TFN-TU membranes possess a higher water flux as well as a higher salt rejection than the TFC membranes. This work may offer insights and strategies for the development of advanced TFN membranes for desalination with a high water product quality.

Environmentally friendly approach for the fabrication of polyamide thin film nanocomposite membrane with enhanced antifouling and antibacterial properties

In this work, we employed an environmentally friendly approach based on plasma enhanced chemical vapour deposition (PECVD) to modify titania nanotubes (TNTs), aiming to obtain better dispersion of nanofillers in polyamide (PA) layer of thin film nanocomposite (TFN) reverse osmosis membrane. Owing to the hydrophilic nature of TNTs, dispersing it homogenously in organic solvent during interfacial polymerization process is difficult to achieve. Therefore, the TNTs are mildly modified by PECVD technique in order to ameliorate its stability in organic solvent. Our results showed that depositing thin layer of methyl methacrylate (MMA) on the TNTs surface could enhance its dispersion quality in organic solvent and further improve the properties of PA layer by enhancing membrane water flux by 16% without compromising NaCl rejection. More importantly, the developed TFN membrane showed excellent fouling resistance by recording flux recovery rate of 85.77% compared to 57.94% shown by the control membrane. Its antibacterial property was also obviously better than that of control membrane. Overall, the developed TFN membrane demonstrated good performance stability with respect to NaCl rejection and water permeability and the trace amount of nanofillers detected in the water sample (in the level ofμg/L) did not negatively influence the membrane filtration performance.