TFC Reverse Osmosis Research Articles

Complexation of tannic acid/silver nanoparticles on polyamide thin film composite reverse osmosis membrane for enhanced chlorine resistance and anti-biofouling properties

Reverse osmosis (RO) is a well-established and reliable desalination method that has been widely implemented on a commercial scale to resolve water scarcity issues. Constant efforts have been made to develop thin film composite membranes that can strike a balance between selectivity and permeability, while maintaining high durability towards fouling and chlorine attack. In this work, the surface of thin film composite RO membrane was modified by complexing tannic acid (TA) and silver nanoparticles (Ag NPs). TA was used for enhancing the chlorine resistance while Ag NPs act as a biocide to mitigate biofouling. Upon the formation of PA layer through interfacial polymerization, TA was chemically grafted, proceeded by in-situ reduction of Ag NPs. Transmission electron microscopy (TEM) image revealed that Ag NPs were deposited on top of the TA-PA interlayer and reduced as discrete spherical Ag NPs with diameter <15 nm. The greatest flux of 20.57 L/m2·h was produced by TFC-TA/Ag1, representing a 60 % improvement as compared to neat TFC membrane. The NaCl rejection of TFC-TA membrane was 97.83 %, which was slightly increased compared to neat TFC membrane with rejection of 95.14 %. Improved chlorine resistance and improved antibacterial properties against Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli) were witnessed for the TFC-TA/Ag1 membranes. This study demonstrates a facile chemical grafting and deposition to introduce multiple functionalities for improving the physical and separation properties of TFC RO membrane.

Hydrophilic Surface Modification of TFC Reverse Osmosis Membrane Using Blends of Sodium Carboxymethyl Cellulose and Chitosan

ABSTRACT The present work showed a scalable protocol for anchoring hydrophilic layer over the polyamide using biodegradable polysaccharide solutions of carboxymethyl cellulose sodium (CMC) and chitosan. CMC and chitosan were blended in different concentration ratios with and without an oxidative environment. The membrane treated with CMC: Chitosan blend demonstrated upto 153.97% and 240.47% increment in water permeance without and with oxidative environment respectively as compared to the virgin thin film composite reverse osmosis membrane. The modified membranes had shown considerable decline in contact angle from 48.37° to 35.66°, changes in surface roughness, morphology and chemical structural changes of the top surface.

Facile fabrication of hydroxyl-rich polyamide TFC RO membranes for enhanced boron removal performance

The insufficient boron removal performance is a conspicuous infirmity of reverse osmosis (RO) membranes for seawater desalination. Herein, RO membranes with high boron removal performance were prepared by adding 2-hydroxyethyl acrylate (HEA) and acrylamide (AA) into the m-phenylenediamine (MPD) solution and employing ultraviolet (UV) irradiation during the interfacial polymerization (IP) process. During the UV-imported IP process, the radical polymerization between HEA and AA was triggered to produce hydroxyl-containing HEA-co-AA copolymers, while polyamide polymers were simultaneously generated. Attributed to the interspersion of hydroxyl-containing copolymers in the polyamide chain segments, the superior dense and tight structure of the hybrid separation layer was achieved. Crucially, the high electron density hydroxyl groups enriched in the hybrid separation layer could specifically interact with the electron-deficient boric acid via electrostatic interaction and hydrogen bond. Therefore, in the modified membrane, the diffusion of boric acid was inhibited. Consequently, for the modified membrane, the boric acid retention rate was dramatically increased from 84.42% to 92.80%. Additionally, NaCl retention rate and water flux were also promoted. The UV-imported IP process was neither process-intensive nor time-consuming, exhibiting high compatibility with the continuous membrane production. It was expected that this work would guide the innovation of high boron removal RO membranes and other types of IP-made membranes.

High Performance Polyamide Tfc Reverse Osmosis Membrane Fabricated on Co-Deposition Hydrophilic Modified Polyethylene Substrate

High Performance Polyamide Tfc Reverse Osmosis Membrane Fabricated on Co-Deposition Hydrophilic Modified Polyethylene Substrate

Assessment of fouling mechanisms on reverse osmosis (RO) membrane during permeation of 17α-ethinylestradiol (EE2) solutions

ABSTRACT Fouling mechanisms are mainly caused by the deposition of organic compounds that reduce the removal efficiency on reverse osmosis (RO) membranes. It can be described by mathematical models. The aim of this study was to evaluate the membrane fouling and rejection mechanisms when aqueous solutions containing 17α-ethinylestradiol (EE2) in different concentrations are permeated at 5 and 10 bar in a bench-scale dead-end RO system. Adsorption tests were performed and the fouling mechanism was assessed by Hermia’s model for solutions of EE2 at concentrations typically found in the environment (µg L−1). Fourier transform infrared spectroscopy (FTIR) has indicated the presence of EE2 on the fouled membrane surface. Membrane rejection of EE2 ranged from 90% to 98% and the main rejection mechanism was size exclusion at all experimental conditions. However, for the higher concentration of EE2 permeated at 5 and 10 bar, adsorption of 7 and 32 mg m−2, respectively, also took place. The rejection was influenced by fouling and concentration polarisation. Fouled membranes present higher rejection of hydrophobic neutral compounds and the concentration polarisation reduces rejection. Hermia’s model demonstrated that the permeation values fitted better the standard blocking filtration and cake filtration equations for describing fouling mechanism. This study showed that fouling also occurs in the TFC RO membrane after permeation of EE2, which corroborates with studies using other pollutants.

Rapid and eco-friendly technique for surface modification of TFC RO membrane for improved filtration performance

In this work, an environmentally friendly plasma enhanced chemical vapor deposition (PECVD) technique was employed to rapidly alter the surface properties of commercial thin film composite extra-low energy (XLE) reverse osmosis (RO) membrane to improve its fouling resistance and desalination performance. Hereafter, two different hydrophilic precursors, i.e., aniline monomer and oxygen (O2) gas were respectively introduced to the membrane’s polyamide surface at different plasma treatment duration (15 s and 60 s). At 15-s plasma treatment, our results revealed that the O2-modified membrane outperformed the polyaniline (PANI)-modified membrane and unmodified membrane, attributed to the polar functional groups presented on the polyamide surface. Compared to plasma polymerization of aniline, O2 plasma etching can lower polyamide densification degree which potentially reduce membrane resistance. Evidently, the O2-modified membrane exhibited higher pure water permeability (6.64 L/m2.h.bar) compared to the PANI-modified membrane (5.57 L/m2.h.bar). The enhanced surface hydrophilicity of O2-modified membrane could be noticed when its water contact angle was reduced from 88.39⁰ (unmodified) to 79.46⁰ in just 15-s plasma treatment. Furthermore, this O2-modified membrane achieved an outstanding NaCl and Na2SO4 rejection with an increment of 4.2% and 2.6%, respectively compared to the unmodified membrane. However, prolonged gas plasma treatment (60 s) should be avoided as it can damage polyamide selective layer. With respect to fouling resistance, the best O2-modified membrane demonstrated higher flux recovery rate (96%) than that of unmodified membrane (76.5%) after being used to filter 1000-ppm sodium alginate solution. These results highlighted the versatility of O2 plasma treatment to improve RO membrane performance.

Exploring of Polyethylene Membrane as a Porous Support for High-Performance Polyamide TFC Reverse Osmosis Membranes

Exploring of Polyethylene Membrane as a Porous Support for High-Performance Polyamide TFC Reverse Osmosis Membranes

Real-time monitoring of calcium sulfate scale removal from RO desalination membranes using Raman spectroscopy

Chemical characterization of scaling and removal processes was performed in real time via Raman spectroscopy in a bench-scale reverse osmosis (RO) system. A custom RO cross-flow cell was integrated with a Raman microscope objective, allowing for analysis of localized membrane scaling and scale removal. Permeate flux was also measured to provide a real-time metric for comparison. A commercial flat sheet, thin-film composite reverse osmosis (TFC RO) membrane was scaled using a calcium sulfate (CaSO4·H2O) feed solution. Upon CaSO4 scale detection, the feed was switched to DI water, which served as a cleaning agent to remove the CaSO4 scale from the membrane. In addition to the real-time local (Raman) and global (permeate flux) measurements, membrane samples were characterized post-mortem using Raman spectroscopy, gravimetric analysis and scanning electron microscopy to provide important scaling and scale removal metrics. Results from real-time measurements indicated that changes in Raman intensity were a more sensitive indicator of local scale removal than changes in permeate flux, a standard cleaning performance metric; these findings were corroborated by the post-mortem analyses. Overall, the membrane cleaning experiments showed that Raman spectroscopy provided crucial real-time chemical composition and spatial distribution information, which can inform more effective antiscaling and cleaning strategies.

GO/PVA-integrated TFN RO membrane: Exploring the effect of orientation switching between PA and GO/PVA and evaluating the GO loading impact

In this work, a new membrane fabrication strategy is proposed to overcome the challenges of conventional nanofillers deposition and to develop novel thin film nanocomposite (TFN) membrane with enhanced performance for reverse osmosis (RO) application. Using polyvinyl alcohol (PVA) as adhesive for the hydrophilic graphene oxide (GO), TFN membranes with two different GO/PVA orientations (atop polyamide (PA) or between PA and substrate) at varying GO loading (0–0.02 wt/v%) were fabricated and characterized to evaluate their effects on membrane physicochemical properties and performances. Evidently, the membrane pure water flux (PWF) is significantly enhanced upon the incorporation of GO/PVA layer regardless of the orientations. Compared to the membrane without GO incorporation, the PWF of the membrane with GO/PVA atop PA layer and GO/PVA sandwiched between PA and substrate at optimum GO loading (0.015 wt/v%) was improved by 50.94% and 91.93%, respectively, mainly attributed to the improved surface hydrophilicity and altered structural properties. Besides exhibiting comparable separation efficiency (~98% NaCl rejection), the membrane with GO/PVA atop PA layer also showed better antifouling property (100% flux recovery, 5-h filtration using 1000 mg/L organic solutions) than the self-synthesized TFC and commercial RO membranes with negligible nanofillers leaching.

Enhancing the permeability of reverse osmosis membrane by embedding the star‐like rigid supports in the substrate

AbstractThin film composite (TFC) reverse osmosis (RO) membranes with high permeability have been prepared by interfacial polymerization based on tailoring the polysulfone (PSf) substrate structure by in situ embedded poly(p‐phenylene terephthamide) (PPTA) star‐like rigid supports. The star‐like rigid supports were observed by the polarizing optical microscopy (POM) and transmission electron microscope (TEM). The surface properties of the substrates were investigated by FTIR, the water contact angle (WCA), FESEM and AFM. The WCA was decreased from 88.5° to 72.3° with the PPTA increasing from 0% to 8%, and the surface roughness increased from 24.2, 25.1, 33.5 and 58.6 nm, respectively. Furthermore, numerous interconnect micro‐structures were constructed in the substrate when the PPTA content was up to 8%. The pure water flux of 8% PPTA/92%PSf substrate was up to 377.0 L m−2 h−1 and the flux decline rate was lowest (64%) after compacted at 5.5 MPa for 30 min. Otherwise, increasing the PPTA contents in the substrate enhanced the roughness, encouraged nanosheet formation and improved the permeability of TFC RO membranes. The pure water flux of the TFC RO membranes increased from 36.32 to 58.42 L m−2 h−1, where the NaCl rejection was about 99.5% at 5.5 MPa.

Fabrication of high performance polyamide reverse osmosis membrane from monomer 4-morpholino-m-phenylenediamine and tailoring with zwitterions

It is well known that the water flux and antifouling performance of polyamide (PA) membrane are strongly associated with their surface characters, especially for surface hydrophilicity, roughness, and charge. In this study, a zwitterionic surface TFC reverse osmosis (RO) membrane was fabricated by small molecule 3-bromopropionic (3-BPA) modification on the pristine membrane that fabricated through interfacial polymerization (IP) technique using a new aqueous monomer 4-morpholinobenzene-1,3-diamine (MpMPD) and trimesoyl chloride (TMC). The as-fabricated RO membranes were well analyzed by various techniques, that the zwitterionic MpMPD-PA membrane surface exhibited greatly enhanced hydrophilicity with water contact angle of 28.1° and surface roughness as low as 26.0 nm. The water permeability of membrane MpMPD-PA reached 1.65 L m−2 h−1 bar−1, which exhibited ~24% increase compared to our lab-made MPD membrane, meanwhile kept a high NaCl rejection of 97.8%. In addition, the dynamic fouling experiments illustrated that the zwitterionic surface RO membrane possess excellent fouling resistance to protein BSA, polysaccharides SA, and surfactant SDS. Therefore, this work provide a simple and convenient way to fabricate novel zwitterionic surface RO membrane with high performance from the molecular level design.

High flux reverse osmosis membranes fabricated with hyperbranched polymers via novel twice-crosslinked interfacial polymerization method

In this study, two kinds of carboxyl-terminated hyperbranched polyesters (HBPs) with special three-dimensional structure were proposed to act as the substrates to synthesize two new kinds of acyl chloride-terminated hyperbranched polyesters (HBPACs) that were used as the key functional materials to participate in the interfacial polymerization reaction to fabricate the novel thin film composite membranes (TFC) with high water flux and monovalent salt rejection. First, the two HBPACs were synthesized from two HBPs with different molecule weights (Mn ≈ 3289 g/mol and 1964 g/mol) through acylation reaction with thionyl chloride. Then, the resultant HBPACs were used to modify the conventional reverse osmosis (RO) membrane by a new twice-crosslinked interfacial polymerization method. That is, the m-phenylenediamine (MPD) coated on the polysulfone supporting was successively reacted with HBPAC and trimesoyl chloride (TMC) which were solved in different organic solutions, respectively. The resultant HBPAC-based TFC membranes presented smoother surface and showed few change in surface hydrophilicity. Especially, one of the HBPAC-based membrane fabricated with the mixture of two HPBACs (a mass ratio of 1:1), showed a ~50% increase in water flux without sacrificing the salt rejection and exhibited excellent long-term stability compared with the conventional TFC RO membrane. Obviously, the HBPAC-based composite PA layer showed a certain cross-linking network, which not only maintained the salt retention rate but also enhanced the compatibility of HBPAC in PA main body, and as a result promoted the membrane stability. Furthermore, the residual carboxyl groups of HBPAC can act as hydrophilic sites between polyamide chains, which contribute to the rapid diffusion of water molecules through the PA layer of the membrane. Thus, this work provides a new approach to enhance the flux and stability of the membrane via the incorporation of new acyl chloride-terminated hyperbranched polymer.

TFC reverse osmosis polyamide membranes—Effect of increasing sulfonic group concentration on water flux and salt rejection performance

ABSTRACTThin film composite (TFC) membranes for reverse osmosis were prepared with a polyamide top layer with an increasing concentration of sulfonic groups obtained with mixtures of m‐phenylenediamine (MPD), and the sulfonated diamine, 4‐diaminobenzensulfonic acid (DABS) crosslinked with trimesoyl chloride via interfacial polymerization. The presence of sulfonic groups in the top layer diminishes the roughness of the surface of the membrane as observed by scanning electron microscopy and atomic force microscopy. It was also found that the best curing temperature for stabilization of the top polyamide layer in the TFC membrane was 90 °C. Increased hydrophilicity with an increasing concentration of DABS in the top layer of the membrane was confirmed by contact angle measurements. The results show that concentrations above 5 wt % DABS were detrimental for the membrane flux and salt rejection, R(%). The incorporation of sulfonic groups up to 5 wt % DABS improves the flux and R(%) as compared to a TFC membrane without ionic groups. Constant salt rejection was observed in the TFC membrane with 5 wt % DABS which at least maintain a nearly constant water flux after three cycles and improve R(%) after repeated testing of the same membrane in a RO high pressure cell. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46500.

A novel ultra‐low energy reverse osmosis membrane modified by chitosan with glutaraldehyde crosslinking

ABSTRACTThe energy consumption of reverse osmosis (RO) has declined significantly since inception and to further decrease the energy consumption is a challenging task. The present article demonstrates the novel method to increase the membrane productivity and reduce energy consumption of desalination. Thin film composite RO (TFC RO) membrane was subjected to 2000 mg/L sodium hypochlorite for 1 h followed by varying concentrations of chitosan and glutaraldehyde for 1 h each to make a hydrophilic supra‐molecular assembly of linear polysaccharide over the polyamide layer. RO membrane exposed to 1000 mg/L chitosan and glutaraldehyde each reported 180% increase in water‐flux with about 2.7% increase in divalent ion rejection as compared to virgin TFC RO membrane. The superior performance of the membrane was explained by increased hydrophilicity as shown by decline in contact angle from 46.37° to 29.87°, increase in surface area ratio from atomic force microscope image analysis, and modification in chemical structure of polyamide from attenuated total reflectance Fourier transform infrared spectroscopy. It was further investigated that curing of glutaraldehyde treated membrane resulted in decreased water‐flux because of increase in crosslink density. Thus, an ultra‐low energy RO process can be developed based on polyamide–chitosan–glutaraldehyde membrane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45971.

A novel semi-aromatic polyamide TFC reverse osmosis membrane fabricated from a dendritic molecule of trimesoylamidoamine through a two-step amine-immersion mode

In this work, a novel semi-aromatic polyamide RO membrane was fabricated from a new dendritic molecule of trimesoylamidoamine (TMAAM) combined 1,3-diamino-2-propanol (DAP) to react with trimesoyl chloride (TMC) via a new two-step amine immersion method.

Ultra-low energy reverse osmosis with thermal energy recovery from photovoltaic panel cooling and TFC RO membrane modification

The electrical efficiency of solar photovoltaic (PV) panel decreases with increase in its temperature, and therefore transfer of heat from the panel is very important. The capitalization of the transferred heat for useful purpose is of prime importance since the conventional solar PV panel has the conversion efficiency of only 5–17%, and therefore the larger part of incident solar radiation remain unutilized. The present paper addresses the temperature control of solar PV panel by direct contact heat exchange with flowing feed water to reverse osmosis (RO) from top of the panel, thus recovering energy together with improving the performance of PV panel. The RO at higher temperature resulted in the improvement in the flow performance of the membrane. Further, the modification in membrane morphology by controlled sodium hypochlorite treatment improved the flow performance by increasing hydrophilicity of the membrane as evident by decline in contact angle from 48.05° to 26.22°. Thus, a two-pronged technique of controlling the PV panel temperature by heat transfer and tuning the membrane morphology toward more hydrophilicity helped in significant improvement in RO permeate flow and better electrical performance of PV panel. As a result, the overall energy consumption of RO has been reduced by about 40%. This novel approach opens up the avenues for significantly reducing the overall energy consumption for brackish water RO systems.

Fabrication and characterization of a novel poly(amide-urethane@imide) TFC reverse osmosis membrane with chlorine-tolerant property

A novel poly(amide-urethane@imide) reverse osmosis (RO) composite membrane with chlorine-tolerant property was prepared on a polysulfone supporting film through two-step interfacial polymerization. The crosslinking agent – 5-choroformyloxyisophaloyl chloride (CFIC) was first reacted with 4-methyl-phenylenediamine (MMPD) via interfacial polymerization to get the nascent poly(amide-urethane) base membrane (CFIC–MMPD) without curing treatment. Then the resultant base membrane contacted again with the second aqueous solution containing functional secondary amine – N,N′-dimethyl-m-phenylenediamine (DMMPD) to obtain the poly(amide-urethane@imide) TFC RO membrane (MMPD–CFIC@CFIC–DMMPD). X-ray photoelectronic spectroscopy (XPS) was combined with attenuated total reflectance infrared (ATR-IR) to verify that the ultrathin polyimide film (CFIC–DMMPD) has been successfully grafted on the surface of the MMPD–CFIC base membrane. The images of scanning electronic microscopy (SEM) and atomic force microscope (AFM) showed that the poly(amide-urethane@imide) membrane has much smoother, more hydrophilic surface than the poly(amide/imide-urethane) membrane (MMPD/DMMPD–CFIC) prepared by conventional one-step interfacial polymerization of CFIC and composite MMPD/DMMPD. However, the permeation experiment revealed that the poly(amide-urethane@imide) membrane has a slight loss in both salt rejection and water flux than the poly(amide/imide-urethane) membrane and conventional commercialized polyamide membrane (MPD–TMC), but exhibits better chlorine-tolerant property due to the introduction of ultrathin polyimide film (CFIC–DMMPD) on the outmost surface of the TFC RO membrane, and the combination of IR and XPS analyses shows a good agreement with the chlorine exposure results of membranes.

Assessing the major factors affecting the performances of forward osmosis and its implications on the desalination process

This study evaluates the influence of some of the major factors affecting the performances of forward osmosis (FO) desalination and assessed their potential implications on the overall process. The major factors assessed include membrane properties, draw solution (DS) properties, feed solution (FS) properties and the operating conditions. The influence of the membrane properties was evaluated using three types of membranes and in doing so we have also introduced one newly synthesized proprietary thin film composite FO (TFC-FO) membrane. The performances of TFC-FO membrane in terms of water flux and reverse solute flux were significantly higher than the commercial cellulose triacetate FO membrane and TFC reverse osmosis membrane in FO process. Although adequate osmotic pressure of DS is desirable for FO process, the influence of DS osmotic pressure was less significant at higher DS osmotic pressure and therefore selecting an optimum initial osmotic pressure is essential for FO process to minimize pumping energy. A critical DS concentration has been hypothesized to minimize the implications of DS concentrations on the capital and operational cost of the FO desalination plant. Total dissolved solids (TDS) of the FS play a significant role in the performance of FO process however the influence of feed TDS was less significant for feed higher than 20,000mg/L indicating that FO has a promising potential for use with high TDS feed water. Although, water flux decreased, the reverse solute flux (RSF) and specific RSF also decreased slightly at higher feed TDS. For operating parameters, the influence of crossflow velocity and the crossflow direction was also investigated.

Modification to the polyamide TFC RO membranes for improvement of chlorine-resistance

Most current high-performance composite membranes comprise aliphatic or aromatic amines condensed with acyl chlorides or other reactive groups that usually contain substituted amide linkages. Aromatic rings bonded to the N–H group of amide linkages are sensitive to attack by chlorine radicals because of their high electron density. Consequently, the N–H group is converted to an N–Cl group by N-halogenation. This causes the failure of the polyamide reverse osmosis (RO) membrane resulting in decreased salt rejection and increased water flux after exposure to chlorine. In this study, the performance of a silane-coated RO membrane was investigated and its surface analyzed using field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The stability of the coated membranes in the presence of chorine was also studied in order to ascertain the effect of incorporating different silane compounds with alkyl, aryl and vinyl substituents. In the uncoated membrane, degradation of the polyamide network of the RO membrane by free chlorine in the feed solution resulted in decreased salt rejection and increased water flux after 15,000 ppm h. However, the silane-coated membrane maintained a salt rejection of above 99.0% even after 25,000 ppm h.

Effect of silane coupling agents on the performance of RO membranes

This study investigates the effect of silane coupling agents on the performance of reverse osmosis (RO) membranes on the basis of sol–gel coating method. The surfaces of the RO membranes were chemically modified with four different alkoxysilanes in order to reduce their hydrophilicity. The objective of this study is to superpose hydrophobic polysiloxane layer on the surface of a polyamide TFC RO membrane and to increase the extent of salt rejection by the modified membranes. A commercial composite RO membrane (SWC1) was treated with silane coupling agents in ethanol at three different concentrations: 1.0, 1.5, and 2.0% (w/v). The silane coupling agents contain one alkyl or phenyl and three alkoxy groups (e.g., methyltriethoxysilane, octyltriethoxysilane, octadecyltrimethoxysilane and phenyltriethoxysilane). In addition, the effect of alkyl or phenyl group hydrophobicity on the permeability and salt rejection of the modified membrane was examined. The surfaces of the modified membranes were characterized by SEM, AFM, contact angle analyzer, and XPS in order to confirm successful sol–gel methods. The modified membranes showed significantly enhanced salt rejection without a decrease in flux. From the surface analysis results, we can observe the changes in the surface roughness, elemental composition, electron energy, and hydrophilicity.