Film Nanocomposite Reverse Osmosis Membranes 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.

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.

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.

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.

Doping MIL-101(Cr)@GO in polyamide nanocomposite membranes with improved water flux

Facile reverse osmosis membranes with different doping concentrations of metal organic framework MIL-101(Cr)@graphene oxide (GO) were synthesized for desalination by interfacial polymerization, and the MIL-101(Cr) polyhedral particles were encapsulated with GO nanosheets. Contact angles of thin film nanocomposite membranes decrease with the increased concentration of MIL-101(Cr)@GO, suggesting improved surface hydrophilicity. And desirable doping can enhance both water flux and NaCl rejection. For example, with a doping concentration of 0.01%, water flux of the membranes can be increased from 20.49 L/m2·h to 37.95 L/m2·h by 85.21% along with slightly improved NaCl rejection. Our findings indicate that MIL-101(Cr)@GO composite particles can be developed as an effective additive material to fabricate thin film nanocomposite reverse osmosis membranes for desalination applications.

Precise assembly of a zeolite imidazolate framework on polypropylene support for the fabrication of thin film nanocomposite reverse osmosis membrane

Polypropylene (PP) has been widely used in the fields of lithium battery separators, proton exchange membranes, membrane bioreactors and polyamide (PA) thin film composite (TFC) reverse osmosis (RO) membranes owing to its excellent mechanical strength, chemical durability and low cost. Nevertheless, its inherent strong hydrophobicity and low surface porosity severely limit its in-depth development in the field of polyamide TFC membranes. Herein, we propose a general strategy for the precise assembly of ZIF-8 nanoparticles on PP support for the fabrication of RO membrane. By this method, position induced nanoporous surface (PINS) was introduced via in-situ synthesis of ZIF-8 assisted by diazonium-induced anchoring process (DIAP) on PP support, and it would achieve precise repair of non-porous regions of PP support, thereby increasing its surface porosity and hydrophilicity of PP support. Subsequently, a high-performance ZIF-8 hybrid reverse osmosis (HPP-ZIF-8-RO) membrane was fabricated by conventional interfacial polymerization (IP) on modified commercialized PP support for the first time. The optimal rejection of HPP-ZIF-8-RO for NaCl is ~99%, and the water flux is up to 50 kg m−2 h−1 under the operating pressure of 1.55 MPa. In addition, the HPP-ZIF-8-RO membrane has a superior chemical stability after the solvent resistance test. To prove the university of DIAP and PINS, we have successfully fabricated other types of HPP-MOF-RO (HPP-ZIF-67-RO, HPP-HKUST-1-RO) which also show enhanced desalination performance. Hence, DIAP and PINS could provide a convenient and versatile method for precise repairing the defect area of the hydrophobic porous substrates.

Facile Fabrication of High-Performance Thin Film Nanocomposite Desalination Membranes Imbedded with Alkyl Group-Capped Silica Nanoparticles.

The advantages of thin film nanocomposite reverse osmosis (TFN-RO) membranes have been demonstrated by numerous studies within the last decade. This study proposes a facile and novel method to tune the microscale and nanoscale structures, which has good potential to fabricate high-performance TFN-RO membranes. This method involves the addition of alkyl capped silica nanoparticles (alkyl-silica NPs) into the organic phase during interfacial polymerization (IP). We discovered for the first time that the high concentration alkyl-silica NPs in organic solvent isopar-G can limit the diffusion of MPD molecules at the interface, therefore shaping the intrinsic thickness and microstructures of the PA layer. Moreover, the alkyl group modification greatly reduces the NPs agglomeration and increases the compatibility between the NPs and the PA matrix. We further demonstrate that the doping of alkyl-silica NPs impacts the performance of the TFN-RO membrane by affecting intrinsic thickness, higher surface area, hydrophobic plugging effect, and higher surface charge by a series of characterization. At brackish water desalination conditions (2000 ppm NaCl, 1.55 MPa), the optimal brackish water flux was 55.3 L/m2∙h, and the rejection was maintained at 99.6%, or even exceeded this baseline. At seawater desalination conditions (32,000 ppm NaCl, 5.5 MPa), the optimized seawater flux reached 67.7 L/m2∙h, and the rejection was sustained at 99.4%. Moreover, the boron rejection was elevated by 11%, which benefits from a hydrophobic plugging effect of the alkyl groups.

Fabrication of polyamide thin film nanocomposite reverse osmosis membrane incorporated with a novel graphite‐based carbon material for desalination

AbstractThe properties of polyamide (PA) thin film composite (TFC) membranes are affected by many variables, especially the additives in the process of interfacial polymerization that play an important role in the properties of membranes. In this study, a new type graphite carbon was added into organic phase containing trimesoyl chloride for interfacial polymerization with aqueous phase containing m‐phenylenediamine to prepare modified polyamide thin film nanocomposite (TFN) membranes for reverse osmosis (RO) adhibition. Polysulfone ultrafiltration membranes were used as the carrier of the interfacial polymerization. The concentration of graphite carbon was selected from 0.002 to 0.01 wt%. The polyamide nanocomposite membrane prepared with the concentration of 0.004 wt% graphite carbon showed the best RO desalination performance, which the water flux of this TFN membrane is over 2.3 times as much as pristine TFC membrane, and the salt rejection is over 99%. This article provides a well‐performing polyamide thin film nanocomposite membrane modified by a new‐type carbon nanoparticles consequently.

Development of high-performance mixed matrix reverse osmosis membranes by incorporating aminosilane-modified hydrotalcite.

Thin film nanocomposite (TFN) reverse osmosis (RO) membranes were prepared by dispersing 3-aminopropyltriethoxysilane (APTES) modified hydrotalcite (HT), designated as A-HT, in aqueous solution and incorporating the nanoparticles in polyamide layers during the interfacial polymerization process. Results of Fourier transform infrared spectroscopy and zeta potential characterization showed the successful modification of nanoparticles by APTES. In addition, Fourier transform infrared spectroscopy suggested that amidation would take place between the aminosilane on APTES and trimesoyl chloride in organic solution, providing firm covalent interaction between the nanoparticles and polyamide matrix. Dynamic light scattering and transmission electron microscopy indicated that aminosilane modification improved dispersibility of the nanoparticles in aqueous solution and obtained membranes, which suppressed the aggregation. Both the covalent interaction and aggregation suppression were beneficial to compatibility between nanoparticles and the polyamide matrix. TFN RO membranes incorporated with A-HT demonstrated excellent performance. Compared with the pristine RO membrane, the water flux of A-HT-0.050 prepared with an optimum A-HT concentration of 0.050 wt% was enhanced by 18.6% without sacrificing the salt rejection. Moreover, the selectivity of A-HT-0.050 was superior to that of HT-0.050 prepared with HT of 0.050 wt%, which proved aminosilane modification of hydrotalcite was beneficial to high membrane performance especially to selectivity.

Novel thin-film composite reverse osmosis membrane with superior water flux using parallel magnetic field induced magnetic multi-walled carbon nanotubes

Abstract In this work, magnetic multi-walled carbon nanotubes (MWCNTs) were aligned vertically in thin film nanocomposite (TFN) reverse osmosis (RO) membranes. Magnetic MWCNTs were synthesized by in situ co-precipitation of MWCNTs, Fe2+ and Fe3+. Meanwhile, a parallel magnetic field created by two ferrite magnets was used to align magnetic MWCNTs. To simulate the magnetic field, the computer software COMSOL-Multiphysics® was applied. In order to demonstrate the impact of parallel magnetic field, two groups of TFN RO membranes (Group A and Group B) were prepared. Before the phase inversion process, polymer solutions of Group A were treated in the parallel magnetic field for 2 min, while polymer solutions of Group B were exposed to air for 2 min. As a result, under magnetic field, magnetic MWCNTs were aligned vertically on the polysulfone surface, and provided efficient water transport channels. The optimized membrane with 0.7 wt% magnetic MWCNTs of Group A obtained remarkable water flux of 11.389 L m−2 h−1 while maintaining high NaCl rejection. The results indicated that a simple and efficient method to improve water flux of TFN RO membranes was successfully developed.

Thin-film nanocomposite reverse osmosis membranes with enhanced antibacterial resistance by incorporating p-aminophenol-modified graphene oxide

Innovative approaches to restraint bacterial adhesion and growth on membranes are significantly needed to avoid membrane performance decaying for biofouling. In this work, a series of thin film nanocomposite (TFN) reverse osmosis (RO) membranes has been prepared by incorporating nano-fillers of p-aminophenol-modified graphene oxide (mGO) into the polyamide skin layer via interfacial polymerization. Our investigations demonstrate that the introduction of mGO nano-fillers into the functional skin layers reduces the hydrophilicities with the water contact angles drop from 69.6° to 48.2° and meanwhile decreases the thickness of functional skin layers from 240 nm to 50 nm, relative to pristine polyamide RO membrane without nano-fillers. As a result, the as-prepared TFN RO membrane at optimized conditions shows a water flux of 23.6 L·m−2·h−1 and a NaCl rejection rate of 99.7%, reflecting a remarkable promotion in water flux (by 24.5%) compared with the pristine RO membrane. In addition, the data statistics of the live/dead fluorescent imaging assay demonstrate that TFN RO membrane with mGO exhibits bacterial killing ratios of 96.78% and 95.26% against E. coli and S. aureus at the additive loading of 0.005 wt%, which are much higher than RO membrane with GO (90.64%; 90.43%) and pristine RO membrane (4.95%; 2.48%). This work demonstrates a facile way to TFN RO membranes with good separation performance and desirable antibacterial capacities.

Antibacterial thin film nanocomposite reverse osmosis membrane by doping silver phosphate loaded graphene oxide quantum dots in polyamide layer

The development of thin film nanocomposite (TFN) reverse osmosis (RO) membranes has promoted the membrane technology for desalination. Novel nanocomposites are urgently being explored to develop superior performance TFN RO membranes. Graphene oxide quantum dots (GOQD) is considered to be an ideal nanofiller for improving membrane permeability due to its rich hydrophilic groups, uniform dispersion and small nanosheet shape. As a silver ion (Ag+) compound, silver phosphate (AP) possesses higher bactericidal effect than silver particle in membrane application. Accordingly, we synthesized the multifunctional nanocomposite of AP loaded GOQD by a facile electrostatically driven method. Subsequently, GOQD/AP was embedded into the dense polyamide (PA) layer via interfacial polymerization reaction. The GOQD/AP incorporated TFN membrane possessed a high flux of 39.6 L·m−2·h−1 at 16 bar, which was 1.5-fold higher than that of the pristine TFC membrane. Meanwhile, the salt rejection was maintained at 98.4%. Noteworthy, the TFN-GOQD/AP membrane exhibited strong bactericidal property against E. coli with a sterilization rate of 99.9% and good stability as well as excellent antifouling performance during RO process. This work provides a feasible strategy to prepare high permselective and anti-bacterial TFN RO membranes for desalination and wastewater reclamation.

Thin film nanocomposite reverse osmosis membrane incorporated with UiO-66 nanoparticles for enhanced boron removal

The removal of boron from seawater remains a challenge and now receives increasing attention worldwide. Boron removal rates offered by conventional reverse osmosis membranes through one-pass desalination processes are not sufficient to achieve WHO standard. In this paper, the UiO-66 nanoparticles, a metal-organic framework (MOF), are proposed to incorporate into the polyamide (PA)-based thin film nanocomposite (TFN) reverse osmosis (RO) membrane for boron removal due to their inherent porous structure, narrow pore size, and strong adsorption to boron. At an optimum blending concentration of 0.05% (w/v), The UiO-66 TFN membrane showed a ∼50% increase in water flux and a marginal increase in rejection compared with the benchmark thin film composite (TFC) membrane in the brackish water desalination test. In a simulated seawater desalination test, the UiO-66 blended TFN membrane promotes the boron rejection by ∼11% compared with the benchmark membrane. The simultaneous increase of water flux and boron rejection at low blending concentrations are likely attributed to the highly porous structure which provides additional pathways for water transport and the strong adsorption to boron which indued a further pore narrowing effect to its intrinsic pore size of ∼6.1 Å. Therefore, this work provides a new and facile approach to enhance the boron removal rate of the polyamide-based RO membrane via the incorporation of UiO-66 nanoparticles.

Synthesis and characterization of novel g-C3N4 modified thin film nanocomposite reverse osmosis membranes to enhance desalination performance and fouling resistance

The modified thin film nanocomposite reverse osmosis (TFN-RO) membranes were fabricated by embedding the synthesized graphitic carbon nitride (g-C3N4) nanosheets as a hydrophilic modifier in the polyamide layer. The g-C3N4 nanosheets were synthesized using thermal oxidation of melamine. SEM and AFM analyses were used to probe the surface changes of the unmodified and modified membranes. The results of AFM analysis showed the decrease in surface roughness of the modified membranes compared to the unmodified one. The contact angle measurement of the membranes indicated the increase in hydrophilicity of the g-C3N4 embedded membranes, which caused to improve in pure water flux. The rejection of NaCl increased with embedding the g-C3N4 nanosheets and reached to its maximum value (99.7%) in the membranes containing 0.015 wt% of nanosheets. The investigation of antifouling performance using BSA/NaCl solution showed that modified membranes with 0.015 wt% of the embedded g-C3N4 nanosheets had the better performance compared with the unmodified membranes.

A novel strategy to fabricate thin film nanocomposite reverse osmosis membranes with enhanced desalination performance

A novel strategy to fabricate thin film nanocomposite reverse osmosis membranes with enhanced desalination performance

Thin film nanocomposite reverse osmosis membrane modified by two dimensional laminar MoS2 with improved desalination performance and fouling-resistant characteristics

Two dimensional (2 D) layered materials with special properties provide opportunities to design energy-efficient membranes for water desalination. A negatively charged layered graphene analogue, molybdenum disulfide (MoS2) was synthesized through liquid exfoliation. A novel thin film nanocomposite (TFN) reverse osmosis (RO) membrane was successfully fabricated with prepared laminar MoS2 as fillers in the organic phase through interfacial polymerization of m-phenylenediamine and trimesoyl chloride monomers. The laminar MoS2 nanosheets were observed by transmission electron microscopy (TEM), and the nanosheets were dispersed in the polyamide (PA) matrix as well as on the membrane surface. The properties of the resultant TFN membranes were effectively modified by taking the advantage of two dimensional features, i.e., the negative charge and the hydrophilic sites of layered MoS2. Compared to a classical TFC membrane, the MoS2 incorporated TFN membranes were found to have an increased salt rejection and higher water flux. Moreover, 0.01 wt% MoS2-TFN membrane showed a superior fouling resistance against proteins as foulants. The antifouling behavior of this TFN membrane was observed by field-emission scanning electron microscopy (FE-SEM). Stability tests demonstrated that there was a loss of MoS2 in the initial 2 h filtration, but the process is stable in the long-term.

Cellulaose acetate based thin film nanocomposite reverse osmosis membrane incorporated with TiO2 nanoparticles for improved performance

In this work, cellulose acetate (CA) based thin film nanocomposite reverse osmosis (RO) membranes were fabricated using dissolution casting method by optimizing the CA/polyethylene glycol (CA/PEG-400) ratios for improved RO performance. The selectivity of optimized membrane was further enhanced by incorporating TiO2 (0–25 wt.%) nanoparticles. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyzer (TGA), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were conducted to characterize control and modified membranes for the analysis of functional groups, thermal properties, morphology and structural investigation respectively. CP-2 of CA/PEG-400 (80/20) was selected for further modification with TiO2 nanoparticles. The maximum salt rejection (95.4%) was observed for the membrane having 15% TiO2 nanoparticles. Further escalation of TiO2 concentration resulted in the agglomeration of nanoparticles which subsequently decreased the permeation flux. The test results demonstrated that the modified membranes had higher salt rejection and chlorine resistance, lower degradation profile, successful inhibition of Escherichia coli growth and facilitating permeation flux compared to the control membrane.

Tip and inner walls modification of single-walled carbon nanotubes (3.5 nm diameter) and preparation of polyamide/modified CNT nanocomposite reverse osmosis membrane

ABSTRACTTo enhance the water flux and salt rejection of reverse osmosis membranes, thin film nanocomposite reverse osmosis membranes were prepared by incorporating functionalised single-walled carbon nanotubes (SWNTs). The functionalised SWNTs were obtained by chemical process such as mixed acid oxidation and substitution reaction. The SWNTs were characterised by HRTEM, FTIR, TGA, Raman spectra, UV-Vis and XPS, etc. The surface morphology and structure of membrane were characterised by SEM and contact angle measurement, respectively. The results showed that carboxyl, acyl, amide and amine were successfully grafted on the tip and inner wall of the single-walled carbon nanotubes. The dispersity of the functionalised SWNTs in water was tested, indicating a good hydrophilic property. The polyamide/modified CNT nanocomposite reverse osmosis membrane was prepared. Compared with the bare polyamide membrane, the SWNT-polyamide thin film nanocomposite membranes showed higher property in hydrophilic surface and its water flux, as along with salt rejection, improved dramatically. The experimental results revealed that the modified SWNTs (especially those containing hydrophilic groups such as carboxyl groups and amino groups) well dispersed in the polyamide thin film layer, and hence improved the water permeation, and the salt rejection.

Fabrication of hydrophobic fluorinated silica-polyamide thin film nanocomposite reverse osmosis membranes with dramatically improved salt rejection

Thin film nanocomposite reverse osmosis (TFN RO) membranes incorporated with hydrophilic nanoparticles show a potential problem that the salt rejection can not be improved significantly. In this study, novel TFN RO membranes incorporated with hydrophobic fluorinated silica nanoparticles were fabricated to improve the salt rejection. Fluorinated silica nanoparticles were well dispersed in organic phase during the interfacial polymerization (IP) process. The TFN RO membranes were characterized with attenuated total reflectance infra-red, field emission scanning electron microscopy, atomic force microscopy and water contact angle measurements. The preparation conditions of TFN RO membranes, including IP reaction time, organic solvent removal time, and fluorinated silica loading, were optimized by characterizing desalination performance using 2000ppm NaCl aqueous solution at 1.55MPa and 25°C. The salt rejection increased significantly from 96.0% without fluorinated silica nanoparticles to 98.6% with the optimal 0.12% (w/v) fluorinated silica nanoparticles, while the water flux decreased slightly from 0.99m3/m2/day to 0.93m3/m2/day. This study demonstrated the potential use of hydrophobic nanoparticles in high-performance TFN RO membranes.