TFC RO Membrane Research Articles

Improving the chlorine resistance property of polyamide TFC RO membrane by polyethylene glycol diacrylate (PEGDA) coating

This study investigated a new application of polyethylene glycol diacrylate (PEGDA) as a chlorine resistance layer in desalination membrane processes. Suitable chlorine resistance and high salt rejection were achieved through PEGDA coating onto thin film composite reverse osmosis (TFC-RO) membranes. The lab-made RO membranes were modified using in-situ polymerization by an aqueous solution of the PEGDA in various concentrations. The performance of the coated polyamide-RO membranes was investigated by a cross-flow permeation setup before and after exposure to 300, 600 and 1200 ppm hypochlorite sodium (NaOCl) for 1 h to test permeability and chlorine stability. The influence of the PEGDA layer on surface characteristics of TFC-RO membranes was also investigated by ATR-FTIR, SEM, X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The results of performance tests and elemental analyses such as XPS indicated that the coating of PEGDA layer could act as a passive and sacrificial layer against the chlorine attack. The investigation of one of the modified membranes including 30% PEGDA proved that in the same comparison after chlorination, the modified membranes (2.42%) kept less chlorine in their surface structure than the bare ones (4.04%). The permeate flux decrease of the PEGDA coated membranes after chlorination was less than the uncoated membrane. With increasing the polymer percentage of the layer, the chlorine resistance ability and salt rejection could be increased. However, the permeability was reduced. The results of the performance tests and analyses showed a chlorine-resistant membrane could be developed, as well as the maximum salt rejection increase and the minimum water flux recline after modification.

Incorporating organic nanospheres into the polyamide layer to prepare thin film composite membrane with enhanced biocidal activity and chlorine resistance

To enhance the antibacterial property and chlorine resistance, organic nanospheres, polypyrrole (PPy), were innovatively incorporated into the polyamide (PA) layer for fabricating thin film nanocomposite (TFN) membranes. Owing to the improved hydrophilicity and compatibility between the PPy nanospheres and the PA layer, the obtained TFN membranes exhibited significant water flux enhancement without sacrificing salt rejection. Under the optimal PPy dosage (0.006 wt%), TFN membranes showed a high water flux of 42.19 L/(m2 h), which was 118.0% higher than that of the pristine membrane. Remarkably, the chlorine resistance of TFN membranes was strengthened after the incorporation of PPy nanospheres, as evidenced by the less decreased salt rejection, as compared with the TFC and commercial RO membrane. In addition, the positively charged PPy nanospheres immobilized in the PA layer endow the TFN membranes with improved biocidal activity, which was much higher than that of the pristine membrane. This study shows that incorporating organic nanospheres into the PA layer is an effective strategy to develop new TFN membranes with enhanced performance for advanced water purification.

Polyamide–surfactant interaction: Exploration of new avenues for reverse osmosis separation applications

AbstractThin‐film composite (TFC) RO membrane has got widespread acceptability for desalination and water reuse applications. A novel approach toward modification of surface of TFC RO membrane using surfactant (anionic, cationic, and nonionic) has been presented. Anionic surfactant, sodium dodecyl sulfate, increased the water flux of TFC RO membrane up to 142% when TFC RO membrane was exposed to sodium hypochlorite solution of 2,000 mg/L for 2 hr followed by sodium dodecyl sulfate for 1 hr at pH 11. However, surface modification by cationic surfactant, that is, cetrimonium bromide resulted in decreased water flux. Boron rejection decreased to 87.31% when cetrimonium bromide of 500 mg/L was exposed after 2,000 mg/L sodium hypochlorite at pH 11 because of positive charge on the membrane surface. Nonionic surfactant Triton X‐100 exposure lower than critical micelle concentration, that is, 100 mg/L for 1 hr after sodium hypochlorite exposure of 2,000 mg/L for 2 hr, resulted in increased water flux of about 22%, however, on increasing surfactant concentration more than critical micelle concentration, that is, 4% with the same sodium hypochlorite pre‐exposure, resulted in 47.5% decline in water flux. Thus, surfactant can bind the top barrier layer of polyamide membrane to alter its performance.

A novel reverse osmosis membrane modified by polyvinyl alcohol with maleic anhydride crosslinking

In the era of increasing energy crisis, it is inevitable to decrease process energy consumption to increase process viability and curtail green-house gas emission. The Reverse Osmosis plant requires significant energy to transfer water overcoming the osmotic pressure. This paper focuses on increasing the water flux for Thin Film Composite Reverse Osmosis (TFC RO) membrane without compromising salt rejection performance leading to the environmentally friendly and economically attractive process. The virgin TFC RO membrane was exposed to solution of sodium hypochlorite of concentration 2000 mg l−1 for 1 h to activate the surface of the membrane, followed by the treatment with the mixture of polyvinyl alcohol and maleic anhydride with varying concentrations for 1 h and curing in the oven at 80 °C temperature for 10 min. Out of all the treated membranes, the membrane treated with 2000 mg l−1 polyvinyl alcohol and 1000 mg l−1 maleic anhydride demonstrated the highest salt rejection of 96.83 % with 2% increase as compared to the virgin TFC RO membrane. The water flux of the membrane was around 44% higher than the virgin TFC RO membrane. The membrane samples were characterized by atomic force micrographs, ATR-FTIR, Nuclear magnetic resonance and Dynamic mechanical analysis.

Antibiofouling thin-film composite membranes (TFC) by in situ formation of Cu-(m-phenylenediamine) oligomer complex

In situ formation of a Cu-(m-phenylenediamine) (Cu-mPD) oligomer complex from copper chloride during the interfacial polymerization process was successfully employed to produce modified thin-film composite reverse osmosis membranes (TFC-RO) with antibiofouling properties. Membranes were characterized by field emission scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy, and contact angle measurements. Antibiofouling properties were studied using a colony-forming unit test with Escherichia coli. Moreover, an antiadhesion test was developed using fluorescence microscopy. Membrane performance using a cross-flow cell was evaluated, and copper concentration in permeate water was measured. FTIR, XPS and XRD results confirmed the formation of a Cu-mPD oligomer complex and its incorporation into the polyamide layer. A mechanism for formation of the oligomer within the membrane was proposed based on the interaction between the oxygen of the carbonyl group of the polyamide layer and copper ion of the Cu-mPD oligomer complex. The modified membrane showed a slight decrease in hydrophilicity and higher surface roughness. However, excellent antibacterial and antiadhesion effects were observed, attributed to copper toxicity as a result of Cu2+ ions release from the membrane surface. Release of copper ions in the permeate water was determined, and the maximum value observed was considered negligible according to the World Health Organization. The desalination performance of modified membrane showed an important salt rejection with stable water flux. In conclusion, a novel chemical method for the incorporation of Cu-mPD oligomer complex into the polyamide layer of TFC-RO membranes to improve their antibiofouling properties and desalination performance was achieved.

Sharkskin-mimetic desalination membranes with ultralow biofouling

The sharkskin-mimetic, patterned TFC RO membranes exhibited superior biofouling resistance compared to conventional and simple patterned membranes.

A novel reverse osmosis membrane by ferrous sulfate assisted controlled oxidation of polyamide layer

With growing desalination capacity, it is very important to evaluate the performance of thin film composite reverse osmosis (TFC RO) membrane in terms of energy consumption for desalination. There is a trade-off between salt rejection and water-flux of TFC RO membrane. This article presents a novel approach of analyzing the effect of mixture of an oxidizing agent sodium hypochlorite and a reducing agent ferrous sulfate on virgin TFC RO membrane. Experiments were carried out by varying the concentrations of both sodium hypochlorite and ferrous sulfate. The negative charge was induced on the membrane due to the treatment of combination of sodium hypochlorite and ferrous sulfate, thereby resulting in higher rejection of negative ions due to repulsive force. Membrane treated with 1000 mg l−1 sodium hypochlorite and 2000 mg l−1 ferrous sulfate showed the best salt rejection i.e. 96.23%. The characterization was carried out to understand the charge on the membrane surface by Zeta potential, morphology of membrane surface by scanning electron microscope (SEM), surface roughness features by atomic force microscope (AFM) and chemical structural changes by nuclear magnetic resonance (NMR) analysis.

Depositing sericin on partially degraded polyamide reverse osmosis membrane for restored salt rejection and simultaneously enhanced resistance to both fouling and chlorine

This work reports the repairing of partially degraded polyamide TFC RO membrane for restored salt rejection and simultaneously enhanced resistance to both chlorine and fouling through adopting an in-situ, simple and upscalable approach of cross-flow filtration of sericin aqueous solution followed by flushing with de-ionized water. The attachment of sericin molecule on membrane surface was confirmed by XPS analysis and was found to be effective in recovering membrane reverse osmosis performance. The membrane with a degraded salt rejection higher than 94.0% exhibited a restored salt rejection the same as or a little higher than that of the new membrane (before chlorination). The deposition of sericin was also found to make membrane surface smoother and more hydrophilic and negatively charged under neutral condition, and thus endow the restored membrane with enhanced fouling resistance to bovine serum albumin compared with the new membrane. Furthermore, the chlorine exposure experiments demonstrated that the restored membrane with the coating of sericin exhibited better resistance to chlorine compared to the new membrane. The simplicity and good reproducibility of the restoration treatment procedure and the satisfactory performance stability of the restored membrane reveal that the in-situ restoration approach of present work is attractive for practical applications.

Probing the thickness and roughness of the functional layer in thin film composite membranes

The thickness and roughness of the functional layer in thin film composite membranes (TFCMs) are important determinants of the membrane performance, whether in reverse osmosis, gas separation or energy applications. This paper describes and compares different techniques for the measurement of these quantities. A new method based on atomic force microscopy (AFM) is developed and compared with techniques based on scanning electron microscopy (FEG-SEM) and profilometry. AFM and profilometry methods allowed a simultaneous determination of thickness and roughness and could be extended for studying the effect of parameters such as support membrane roughness. The methods have been tested on polyamide TFC RO membranes. The membranes were prepared by an interfacial polycondensation technique on polysulfone support, by reaction between m-phenylene diamine and trimesoyl chloride in the organic phase. Based on our earlier work which showed the important role of shear on membrane morphology in such syntheses, preparations both with and without shear were employed. The measurement of thickness using AFM was carried out on specially made membranes in which, by the use of a mask, only a part of the PSF was coated with the PA layer. By scanning a region that contains both the covered and the uncovered parts, thickness values could be obtained. In the second technique, the SEM cross sectional images of TFCMs allowed the determination of the distribution of thickness over the area seleted. In the third, a surface profilometer was used to determine the thickness of de-laminated PA films. The thickness distributions and average thicknesses measured from all three methods matched closely. Overall, these techniques are of great potential in TFC and similar membrane characterization.

Incorporation of CuO nanoparticles into thin-film composite reverse osmosis membranes (TFC-RO) for antibiofouling properties

The effect of the incorporation during the interfacial polymerization process of copper-oxide (CuO) nanoparticles in thin-film composite (TFC) reverse osmosis (RO) membrane on their antibiofouling and desalinization performance have been studied. Membranes were characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), zeta potential and contact angle measurements. Bactericidal tests were performed using Escherichia coli and anti-adhesion properties were confirmed by fluorescence microscopy. Membrane performance using a cross flow cell was evaluated. XRD and SEM–EDX analyses confirmed the incorporation of these nanoparticles into the membrane. Similar contact angle, higher surface roughness and less negatively charged surface on modified membrane compared to that of the pristine membrane were observed. However, an excellent anti-adhesion and bactericidal effect were observed, mainly attributed to the copper toxicity. The desalination performance of the modified membrane showed an important salt rejection with stable water flux. In conclusion, the incorporation of CuO nanoparticles into TFC-RO membranes during the interfacial polymerization process is a potential alternative method to improve the antibiofouling capacities without impairing the performance of the membrane.

A novel high‐flux thin film composite reverse osmosis membrane modified by polysaccharide supramolecular assembly

ABSTRACTThin film composite reverse osmosis (TFC RO) membrane is widely used in desalination and water reuse applications. With increasing capacity of Reverse Osmosis desalination all over the world, the increasing green‐house gas emission for the required power is a cause of concern. TFC RO membrane is composed of the top polyamide layer over which, the linear polysaccharide such as chitosan can bind after activating the surface with oxidizing agent. The present paper analyzes the novel protocol of controlled oxidation of TFC RO membrane by exposing the same to potassium per sulfate with varying concentration of chitosan followed by sodium hypochlorite and sodium hypochlorite followed by potassium per sulfate with varying concentration of chitosan. The optimum performance was obtained when TFC RO membrane was exposed to 1% potassium persulfate with 1000 mg/L chitosan solution followed by 1000 mg/L sodium hypochlorite. Reversing order of the treatment resulted in the decline in permeance of the membrane. The reason of improvement in permeance is super‐hydrophilic surface formed by oxidation of chitosan over polyamide surface. Thus, this article demonstrates the novel protocol of significantly improving the flux of TFC RO membrane and thereby reducing the energy consumption. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45026.

Using PDMS coated TFC-RO membranes for CO2/N2 gas separation: Experimental study, modeling and optimization

Thin film composite (TFC) reverse osmosis (RO) membranes are semipermeable membranes that are utilized in water purification or water desalination systems. Discarding these membranes after end-of-life leads to environmental problems. Reusing old TFC-RO membranes is one way to solve this problem. For this reason, in this study, used TFC-RO membranes were coated with polydimethylsiloxane (PDMS) for CO2/N2 gas separation application. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was utilized to confirm the crosslinking of coated PDMS. The morphology of PDMS/TFC-RO membranes was characterized using scanning electron microscopy (SEM). The parameters that can affect performance of prepared membranes (N2 permeance and CO2/N2 selectivity) are concentration of PDMS solution, coating time, solvent evaporation time and curing temperature and time. Given that the used membranes don't have uniform surfaces, the first step of this study was to investigate the effect of the above mentioned factors on virgin membranes using fractional factorial design (FFD) of experiments. The results obtained showed that PDMS concentration is the most significant factor that has a negative effect on N2 permeance and positive effect on CO2/N2 selectivity. The reported CO2/N2 selectivity of PDMS membranes was 11–12, but this selectivity for prepared PDMS/TFC-RO membranes was in the range of 6.7–22.5. After determining optimum conditions, the gas separation performance of PDMS coated used TFC-RO membrane under these conditions was finally determined. The results showed that the used membranes had a better performance than virgin membranes.

New RO TFC Membranes by Interfacial Polymerization in n-Dodecane with Various co-Solvents.

The objective of this research is to prepare and characterize a new and highly efficient polyamide TFC RO membrane by interfacial polymerization in dodecane solvent mixed with co-solvents. Three co-solvents were tested namely; acetone, ethyl acetate, and diethyl ether of concentration of 0.5, 1, 2, 3, and 5 wt %. The modified membranes were characterized by SEM, EDX, AFM and contact angle techniques. The results showed that addition of co-solvent results in a decrease in the roughness, pore size and thickness of the produced membranes. However, as the concentration of the co-solvent increases the pore size of the membranes gets larger. Among the three co-solvents tested, acetone was found to result in membranes with the largest pore size and contact angle followed by diethyl ether then ethyl acetate. Measured contact angle increases as the concentration of the co-solvent increases reaching a constant value except for ethyl acetate where it was found to drop. Investigating flux and salt rejection by the formulated membranes showed that higher flux was attained when acetone was used as a co-solvent followed by diethyl ether then ethyl acetate. However, the highest salt rejection was achieved with diethyl ether.

Enhancing the flux of brackish water TFC RO membrane by improving support surface porosity via a secondary pore-forming method

A secondary pore-forming method for improving support surface porosity to enhance the flux of TFC RO membrane was proposed. With this method, well-dispersed SiO2 nanospheres were used for preparing polysulfone (PSf)/SiO2 nanocomposite supports via immersion precipitation, and then the supports were treated by a hot NaOH solution. The PSf/SiO2 nanocomposite supports prepared by this method can experience two pore formation processes, which include the leaching out of the SiO2 nanospheres during immersion precipitation (the first pore formation process) and the removal of those SiO2 nanospheres embedded in the support surface by alkali treatment after the solidification of support (the second pore formation process). These two pore formation processes were studied. The results showed that (1) these two pore formation processes occurred during the preparation of PSf/SiO2 nanocomposite support, (2) the secondary pore-forming method was better than the immersion precipitation method for improving support surface porosity and (3) the support surface porosity was improved at most 291% by the secondary pore-forming method. TFC RO membranes were fabricated on pure supports, nanocomposite supports experiencing the first pore formation process only and nanocomposite supports experiencing two pore formation processes via interfacial polymerization, respectively. The brackish water desalination performance of the TFC RO membranes was evaluated using 2000ppm NaCl solutions under the condition of 1.55MPa transmembrane pressure. The influence of support surface porosity on the flux and rejection of TFC RO membrane was firstly analyzed by experimental approach. The results showed that improving the support surface porosity was beneficial for the improvement of the flux and rejection of TFC RO membrane. The flux and rejection of the TFC RO membranes fabricated on PSf/SiO2 nanocomposite supports experiencing two pore formation processes were improved compared to those fabricated on the other two supports. At an optimal condition, the flux was improved obviously with the rejection increasing simultaneously compared to the TFC RO membranes fabricated on the pure supports: a 55.4% increase in flux from 35.4 to 55.0L/(m2*h) with an increase in rejection from 98.74% to 99.10%.

Reverse osmosis membranes prepared by interfacial polymerization in n-heptane containing different co-solvents

The objective of this work was to develop a suitable and highly efficient reverse osmosis membrane incorporating a co-solvent system. A polyamide thin-film composite membrane has been prepared by interfacial polymerization in n-heptane using diethyl ether and ethyl acetate as co-solvents at various concentrations. Heptane has a molecule of larger C–C chain than that of traditionally used hexane. Heptane was selected in order to study its effect on the morphology of the prepared membrane as well as on salt rejection ability and flux volume. Heptane appeared to produce an improved morphology, salt rejection ability, and flux volume, compared to hexane. To the best of our knowledge, this is the first attempt to prepare and characterize TFC RO membrane in n-heptane mixed with co-solvent. The membranes were characterized using microscopy, spectroscopy, and contact angle measurement techniques. From surface spectroscopic analyses, the addition of co-solvents led to a decrease in the roughness properties of the membranes. The synthesized polyamide membranes consist of large and ordinal ridge-and-valley formations. The salt rejection and water permeate flux were well controlled by the categories and amounts of co-solvents that were added. Thermal gravimetric analysis results indicated that all of the membranes exhibited high thermal stability with degradation temperatures of about 481 ± 2°C. The high stability of the membranes was attributed to the sulfonic groups on the polymer chains. The contact angle also increased with an increasing co-solvent concentration. The performance characteristics of the membranes were evaluated by measuring the flux and rejection of isopropyl alcohol, NaCl, and MgCl2 solutions. The rate of flux was proportional to the co-solvent concentration (i.e. flux increases with an increasing concentration), whereas the salt rejection properties were constantly high. Membranes formed with diethyl ether showed the highest salt rejection. Based on these data, membranes prepared using diethyl ether or ethyl acetate as a co-solvent in a non-polar heptane medium performed efficiently and exhibited high salt rejection characteristics with large flux values. These membranes represent promising candidates for freshwater desalination and removal of organic impurities.

Preparation of monodispersed spherical mesoporous nanosilica–polyamide thin film composite reverse osmosis membranes via interfacial polymerization

Monodispersed spherical mesoporous nanosilicas were synthesized by the hydrothermal method using tetraethoxysilane as silica source, cetyltrimethylammonium bromide as template, ethanol as co-solvent, and sodium hydroxide as alkali source. The synthesized silica has an average particle diameter of 164nm with a relative standard deviation of 4.87%, specific surface area of 1141m2·g−1, pore size of 2.47nm, pore volume of 0.77cm3·g−1, and a pore structure radiating from the heart to the outer surface of the sphere. The spherical mesoporous nanosilica–polyamide thin film composite reverse osmosis (TFC RO) membranes were obtained by interfacial polymerization. The silica nanoparticles are visible in the TFC RO membranes based on the surface and cross-sectional SEM images. Correspondingly, energy dispersive X-ray spectroscopy analysis confirms that the silica has been successfully doped into the TFC RO membranes. The hydrophilicity of the TFC RO membranes is improved and water flux is increased from 19L·h−1·m−2 (without nanosilica) to 53L·h−1·m−2 (with 0.1% (w/v) mesoporous nanosilica loading), whereas all solute rejection rates are greater than 96%.

Rejuvenation of discarded RO membrane for new applications

Abstract The sensitivity of thin film composite RO membrane (TFCs) with chlorine has been widely reported. In the present paper, attempt has been made to modify the chemical structure of thin film composite RO membrane by exposing the membrane to free chlorine in order to evaluate potential of utilizing the discarded membrane after its useful life. The different variants of thin film composite RO membrane in terms of flux and rejection could be prepared by altering the exposure time and concentration of sodium hypochlorite solution. Tailoring the membrane for solute rejection offers advantages over the conventional process for instance: (1) It avoids re-mineralization and directly produces the water of required quality; (2) It enhances flux of membrane and thereby improves the productivity of the membrane; (3) Improved recovery leads to lower capacity pre-treatment and thereby improves the operational efficiency; (4) Number of membrane required for the given capacity will be less and the associated unit cost, e.g. pumping cost will also decrease. Successful attempt has been made to enhance permeability seven times that of the terminally fouled membrane by sequential hypochlorite treatment in controlled fashion, i.e. fouled seawater RO membrane with flow 3.36 l/min and solute rejection of 97.21% has been converted to the membrane with flow 24 l/min and solute rejection 82.37%.Moreover, the thin film composite RO membrane has been degraded totally till its solute rejection efficiency falls to approximately zero in order to convert it to microfiltration/ultra-filtration membrane, i.e. the membrane with pure water permeability 257 gfd @50 psig pressure has been made by exposing 3286 mg/l free chlorine for 96 h to TFC RO membrane. The characterization of this membrane was performed by measuring molecular weight cut off of the membrane and pure water permeability of the membrane to evaluate its performance as an ultra-filtration membrane. These membranes were also tested for micro-organism removal and found that their performance resembles the new ultra-filtration membrane. The hypochlorite treated membranes were also evaluated for their permeability after bio-film formation with different micro-organisms where it manifested higher permeability as compared to untreated membrane.

Flux enhancement in TFC RO membranes

AbstractThe effects of varying processing conditions during fabrication of TFC RO membranes were systematically investigated. It was found that the membrane flux is greatly dependent on the processing steps that follow the synthesis of the thin film coating, such as washing, treatment with glycerol, and drying of the membrane. Glycerol is not simply a passive flux ‐ p reserving agent, preventing loss of porosity during oven drying. In combination with a second oven drying step, glycerol actively enhances flux. Membrane flux can be similarly enhanced by treatment with solutions of organic salts, followed by oven drying. The effect of these treatments is quite large, increasing the flux by 30–70%, with no loss of salt rejection. Flux‐enhancing additives were also used in the aqueous polyamine solution used to prepare the thin film coating.