Thin Film Nanocomposite Reverse Osmosis Research Articles

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.

Evaluation of carbon nanotube-polyamide thin-film nanocomposite reverse osmosis membrane: Surface properties, performance characteristics and fouling behavior

Abstract Carbon nanotube (CNT)-polyamide (PA) thin-film nanocomposite (TFN) reverse osmosis (RO) membranes have been highlighted due to their high water permeability. We evaluated the surface properties, membrane performance and fouling behavior of CNT-PA TFN RO membranes. The CNT-PA TFN RO membranes showed ∼30% enhanced water flux, which resulted in a lower energy consumption. The smoother surface of the CNT-PA TFN RO membranes led to less membrane fouling, while its biofouling resistance was insignificant due to less positioned CNTs on the membrane surface. These results provide important insights into the factors optimizing CNT-PA TFN RO membranes as a high performance RO membrane.

Enhanced performance of thin-film nanocomposite RO/NWF membrane by adding ZnO nanospheres in aqueous phase during interfacial polymerization process

A novel thin-film nanocomposite (TFN) reverse osmosis (RO)/non-woven fabric (NWF) membrane was prepared by adding zinc oxide (ZnO) nanospheres (30+-10 nm) during the interfacial polymerization process of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) on self-made polysulfone (PSF) membrane/polyester (PET) non-woven fabric support. The improved performance of TFN RO membrane was verified in terms of water contact angle (WCA), water flux, salt rejection, antifouling properties and chlorine resistance. The results showed that the WCA value of TFN RO surface had a continuous decrease with the increasing of ZnO content in MPD aqueous solution. The water flux of composite TFN RO membranes acquired a remarkable increase with a stable high solute rejection (94.5 %) in 1 g.L-1 NaCl aqueous solution under the optimized addition amount of ZnO (1 wt%). The continuous testing of membrane separation performance after the immersion in sodium hypochlorite solution indicated that the introduction of ZnO nanospheres also dramatically enhanced the antifouling properties and the chlorine resistance of composite RO membranes.

Highly and Stably Water Permeable Thin Film Nanocomposite Membranes Doped with MIL-101 (Cr) Nanoparticles for Reverse Osmosis Application.

A hydrophilic, hydrostable porous metal organic framework (MOF) material-MIL-101 (Cr) was successfully doped into the dense selective polyamide (PA) layer on the polysulfone (PS) ultrafiltration (UF) support to prepare a new thin film nanocomposite (TFN) membrane for water desalination. The TFN-MIL-101 (Cr) membranes were characterized by SEM, AFM, XPS, wettability measurement and reverse osmosis (RO) test. The porous structures of MIL-101 (Cr) can establish direct water channels in the dense selective PA layer for water molecules to transport through quickly, leading to the increasing water permeance of membranes. With good compatibility between MIL-101 (Cr) nanoparticles and the PA layer, the lab made TFN-MIL-101 (Cr) membranes integrated tightly and showed a high NaCl salt rejection. MIL-101 (Cr) nanoparticles increased water permeance to 2.2 L/m2·h·bar at 0.05 w/v % concentration, 44% higher than the undoped PA membranes; meanwhile, the NaCl rejection remained higher than 99%. This study experimentally verified the potential use of MIL-101 (Cr) in advanced TFN RO membranes, which can be used in the diversified water purification field.

Preparation of spherical mesoporous aminopropyl-functionalized MCM-41 and its application in polyamide thin film nanocomposite reverse osmosis membranes

Aminopropyl-functionalized MCM-41 (NH2-MCM-41) was synthesized by the one-pot hydrothermal method using tetraethoxysilane (TEOS) and (3-aminopropyl)triethoxysilane (APTES) as silica sources, cetyltrimethylammonium bromide as template, ethanol as a cosolvent, and sodium hydroxide as the alkali source. The synthesized nanoparticles were noticeably monodisperse with standard deviation of under 10% for the mean particle size. The specific surface area, pore size, pore volume and amino group density of the NH2-MCM-41 varied with the content of APTES in the initial solution. The NH2-MCM-41-polyamide thin film nanocomposite reverse osmosis (TFN RO) membranes were obtained by interfacial polymerization of trimesoyl chloride (TMC) and m-phenylene-diamine (MPD). The hydrophilicity of the TFN RO membranes was improved by the incorporation of NH2-MCM-41 nanoparticles. The water flux of 54 L m−2 h−1 at 1.6 MPa for NH2-MCM-41-polyamide TFN RO membrane was nearly 2.8 times that of the pure polyamide thin film composite (TFC) RO membrane and the solute rejection was 96.5% with a 0.1% w/v NH2-MCM-41 loading.

Clay nanosheets as charged filler materials for high-performance and fouling-resistant thin film nanocomposite membranes

Montmorillonite (MMT), a cationic clay, and layered double hydroxide (LDH), an anionic clay were prepared through “top-down” and “bottom-up” methods, respectively, with lateral dimension on hundred-nanometer scale as well as high aspect ratio. These two types of nanosheets, served as additives in interfacial polymerization process, were utilized to fabricate thin film nanocomposite (TFN) reverse osmosis (RO) membranes containing cationic and anionic clay nanosheets. The properties of TFN membranes were effectively modified with the advantage of unique charged properties and hydrophilic nature of these nanoclay filler materials,. Both MMT and LDH filled TFN membranes showed increased hydrophilicity and improved desalination performance. More importantly, the incorporation of MMT and LDH nanoclays resulted in a more and less negatively charged membrane surface, respectively, and thus exhibited different electrostatic repulsion effects and improved antifouling performances towards protein, cationic surfactant, and natural organic matter foulants. The results indicate that clay nanosheets are effective filler materials to tailor membrane surface properties and fouling resistance. Since the modification by nanoclays can be achieved in the membrane preparation process without altering existing procedures, this approach can be considered as a facile way to produce novel high-performance and fouling-resistant TFN RO membrane for desalination.

Thin film nanocomposite reverse osmosis membrane modified by reduced graphene oxide/TiO2 with improved desalination performance

A novel thin film nanocomposite reverse osmosis (TFN-RO) membrane was prepared by interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) monomers and embedding reduced graphene oxide (rGO)/TiO2 nanocomposite in its polyamide layer. The rGO/TiO2 nanocomposite was added to the MPD solution with aim of improving RO performance, enhancing antifouling property and increasing chlorine resistance. Surface scanning electron microscopy (SEM) images show that all of the membranes have a rough surface with a layer of “ridge-and-valley” structure that is typical morphology of MPD/TMC polyamide membranes. The contact angle analysis showed that hydrophilicity of the membranes was improved by increasing the concentration of rGO/TiO2 due to the presence of various hydrophilic and negatively charged functional groups on the rGO/TiO2 nanocomposite. The superior performance of the rGO/TiO2/RO membrane was observed in the case of 0.02wt% rGO/TiO2 with water flux of 51.3L/m2h and salt rejection of 99.45%. Antifouling ability of the membranes studied by bovine serum albumin (BSA) solution filtration showed that 0.02wt% rGO/TiO2/RO membrane had the best antifouling property. Also, after the chlorination tests, the salt rejection of the bare RO membrane decreased by 30%, while this value was only 3% for 0.02wt% rGO/TiO2/RO membrane which confirmed its great chlorine resistance.

Synthesis and characterization of novel thin film nanocomposite reverse osmosis membranes with improved organic fouling properties for water desalination

Incorporation of HNTs into PA layer improved not only the structural and separation characteristics of composite membrane but also its antifouling properties.

A novel thin film nanocomposite reverse osmosis membrane with superior anti-organic fouling affinity for water desalination

In this work, titanate nanotubes (TNTs) were self-synthesized and amino functionalized to produce titanate nanotubes (NH2-TNTs) for thin film nanocomposite (TFN) reverse osmosis (RO) membrane fabrication. The novel RO membranes were fabricated by embedding NH2-TNTs of different quantities into polyamide (PA) layer. The nanotubular morphology of NH2-TNTs was studied using TEM while FTIR was employed to confirm the reaction of TNTs with [1-(2-amino-ethyl)-3-aminopropyl] trimethoxysilane. The effect of NH2-TNTs on the PA layer of TFN with respect to surface morphology, separation performance and antifouling properties was thoroughly investigated and discussed. The presence of NH2-TNTs in PA layer was verified using XPS while the “leaf-like” outgrowth morphology of PA layer was observed using FESEM. Results showed that the TFN membrane with 0.05% NH2-TNTs embedded was the most promising membrane as it exhibited 93% higher water flux than the control thin film composite (TFC) membrane, without compensating NaCl rejection. In terms of organic fouling tendency, the TFN0.05 membrane also showed higher tolerance compared to the control membrane during RO process. Furthermore, as high as 94% of the water flux of TFN0.05 was able to retrieve by a simple water rinse process, which suggests that organic fouling in TFN0.05 is highly reversible.

Improving second-pass permeate quality using thin film nanocomposite (TFN) membranes

Since the initial development of thin film nanocomposite (TFN) reverse osmosis membranes, a concerted effort has been made to optimize performance in first-pass seawater applications in order to lower energy usage. As the potential for greater energy savings can be harder to achieve in brackish water (BW) and second-pass seawater applications, increased membrane rejection is an attractive goal for many BW plants. A pilot plant was identified in Israel utilizing ground water with total dissolved solids of 2,900 ppm that suited an experiment to demonstrate the potential for TFN membranes to provide better salt rejection at the same projected feed pressures as standard Thin Film Composite (TFC) BW membranes. The pilot was undertaken using TFN membranes (400 square foot elements) in Stage 2 of the Lahat BW desalination facility. Eight (8) elements were loaded in a single pressure vessel. Feed water was taken from the concentrate of the plant’s Stage 1 train and had an average conductivity of 5,864 μS/cm. Average feed temperature was 26.8°C, feed pH was 7.6, and feed pressure was 12.2 bar. The pilot’s recovery was 63%. After collecting two months of operating data on a daily basis, the operation of the pilot and, in particular, the permeate quality proved to be stable. Daily data was normalized to element test conditions: 2,000 ppm NaCl, 225 psi, 25°C, 15% recovery, and pH 8. This normalization showed a stable element flux performance of 10,700 GPD (40.5 m3/d) and 99.75% rejection. The flux data obtained compares well with TFC membranes. However, the element rejection is up to 0.25% higher than average TFC elements, based on published specifications from membrane manufacturers. TFN technology is demonstrating the potential to enhance the performance of TFC elements which are applied to BW projects. This study found that TFN membranes deliver higher rejection than standard TFC elements in BW situations.

Desalination energy minimization using thin film nanocomposite membranes

In this study, thin film nanocomposite (TFN) reverse osmosis (RO) membranes were evaluated at a demonstration-scale facility to determine the specific energy consumption (SEC) during seawater desalination. Conventional (same element type within pressure vessel) and hybrid (high and low rejection elements within pressure vessel) configurations were evaluated and compared to commercially available thin film composite (TFC) RO membranes. The specific flux at 25°C for TFN RO membranes was 1.72lm−2h−1/bar when compared to 1.48lm−2h−1/bar for TFC RO membranes. Utilization of TFN RO membranes resulted in reduced feed pressure requirements when compared to TFC RO membranes, resulting in energy savings up to 10%. In order to achieve the same permeate water quality, the SEC for a 2-pass RO system with TFN RO membrane elements in the first pass was 3.24–3.45kWh/m3. The SEC with TFC RO membrane elements for the same conditions was 3.60kWh/m3. Results presented in this study show a promise for the utilization of TFN RO membranes to reduce energy consumption and minimize operational costs associated with electricity usage.

Role of NaA zeolites in the interfacial polymerization process towards a polyamide nanocomposite reverse osmosis membrane

This paper explores the behaviour and role of NaA nanozeolites during an interfacial polymerization process towards a polyamide thin film nanocomposite (TFN) reverse osmosis membrane by incorporating nanozeolites into two different reactive phases. In the two cases, the different interactions occurring between the zeolites and polyamide were investigated by FT-IR spectra, XPS analysis, and examining the membrane morphology and the desalination performance. The polyamide TFN membrane with an increased degree of cross-linking was obtained with nanozeolites in the organic phase, as the NaA zeolite reacted with the acyl chloride monomer in the organic phase. Additionally, the membrane with nanozeolites added to the organic phase had a superior reverse osmosis performance, since the porous zeolite appeared in the top layer as a water channel.

Preparation of high-flux thin film nanocomposite reverse osmosis membranes by incorporating functionalized multi-walled carbon nanotubes

To enhance the water flux of reverse osmosis membranes, thin film nanocomposite reverse osmosis membranes are prepared by incorporating functionalized multi-walled carbon nanotubes (MWNTs). The functionalized MWNTs are obtained by the treatment of pristine MWNTs with the mixed acid of H2SO4 and HNO3 (3:1 v/v). The MWNTs are analyzed by Fourier transform infrared spectrometry (FTIR). The surface morphology and structure of membrane are characterized by scanning electronic microscopy (SEM), transmission electron microscopy (TEM) and contact angle measurement, respectively. Those results show that modified MWNTs yielded some hydrophilic groups, such as -COOH and -OH, which make acidified MWNTs disperse more evenly in the aqueous solution. The SEM and TEM results demonstrate that the functionalized MWNTs penetrated through the polyamide layer, and might play the role of water channel. Compared with the bare polyamide membrane, the MWNT-polyamide thin film nanocomposite membranes have more hydrophilic surface, and the water flux of MWNT-polyamide membranes improve dramatically. For 2000 ppm NaCl, the water permeability increases from 26 l/m2h without MWNTs to 71 l/m2h at the acidified MWNTs loading of 0.1% (w/v), while NaCl rejection of MWNT-polyamide membranes decreases obviously compared to bare polyamide membrane. However, for 200 ppm purified terephthalic acid (PTA) solution, the pure water flux increases from 19 l/m2h up to 49 l/m2h, while PTA rejection is all higher than 98%. The experimental results reveal that the modified MWNTs well dispersed in the polyamide thin film layer, and hence improve the water permeation.

Tailoring the Structure of Thin Film Nanocomposite Membranes to Achieve Seawater RO Membrane Performance

Herein we report on the formation and characterization of pure polyamide thin film composite (TFC) and zeolite-polyamide thin film nanocomposite (TFN) reverse osmosis (RO) membranes. Four different physical-chemical post-treatment combinations were applied after the interfacial polymerization reaction to change the molecular structure of polyamide and zeolite-polyamide thin films. Both TFC and TFN hand-cast membranes were more permeable, hydrophilic, and rough than a commercial seawater RO membrane. Salt rejection by TFN membranes was consistently below that of hand-cast TFC membranes; however, two TFN membranes exhibited 32 g/L NaCl rejections above 99.4%, which was better than the commercial membrane under the test conditions employed. The nearly defect-free TFN films that produced such high rejections were achieved only with wet curing, regardless of other post-treatments. Polyamide films formed in the presence of zeolite nanoparticles were less cross-linked than similarly cast pure polyamide films. At the very low nanoparticle loadings evaluated, differences between pure polyamide and zeolite-polyamide membrane water and salt permeability correlated weakly with extent of cross-linking of the polyamide film, which suggests that defects and molecular-sieving largely govern transport through zeolite-polyamide thin film nanocomposite membranes.

Influence of Zeolite Crystal Size on Zeolite-Polyamide Thin Film Nanocomposite Membranes

Zeolite-polyamide thin film nanocomposite membranes were coated onto polysulfone ultrafiltration membranes by interfacial polymerization of amine and acid chloride monomers in the presence of Linde type A zeolite nanocrystals. A matrix of three different interfacial polymerization chemistries and three different-sized zeolite crystals produced nanocomposite thin films with widely varying structure, morphology, charge, hydrophilicity, and separation performance (evaluated as reverse osmosis membranes). Pure polyamide film properties were tuned by changing polymerization chemistry, but addition of zeolite nanoparticles produced even greater changes in separation performance, surface chemistry, and film morphology. For fixed polymer chemistry, addition of zeolite nanoparticles formed more permeable, negatively charged, and thicker polyamide films. Smaller zeolites produced greater permeability enhancements, but larger zeolites produced more favorable surface properties; hence, nanoparticle size may be considered an additional "degree of freedom" in designing thin film nanocomposite reverse osmosis membranes. The data presented offer additional support for the hypothesis that zeolite crystals alter polyamide thin film structure when they are present during the interfacial polymerization reaction.

Effect of mobile cation on zeolite-polyamide thin film nanocomposite membranes

Hybrid zeolite-polyamide thin film nanocomposite (TFN) reverse osmosis membranes were synthesized by incorporating Linde type A (LTA)-type zeolite molecular sieve nanocrystals in the interfacial polymerization reaction used to form polyamide thin films. Nanocrystals were prepared with two different mobile cations (Na+ and Ag+) exchanged within the LTA crystal matrix. Incorporation of molecular sieve nanocrystals into polyamide thin films during interfacial polymerization was verified by infrared spectroscopy. Both TFN membranes exhibited higher water permeability, while maintaining similar salt rejection to pure polyamide thin film composite membranes. Nanocomposite thin films containing LTA nanocrystals in the silver form (AgA) produced a greater increase in water permeability than those in the sodium form (NaA). Furthermore, AgA-TFN membranes exhibited more hydrophilic and smooth interfaces, which appeared to inhibit adhesion of bacteria cells onto the membranes. The AgA nanocrystals exhibited significant bactericidal activity; however, when encapsulated within polyamide thin films the antimicrobial activity was significantly reduced.