TFC RO Research Articles

The synergistic actions of copper/l-glutamine co-grafting in improving anti-biofouling and desalination performances of reverse osmosis thin film composite membrane

There have been ongoing efforts to improve membrane surfaces by adding specific functional groups through physical or chemical approaches to minimize fouling propensity. This study introduces a facile grafting and deposition approach to enhance the performance of thin film composite polyamide reverse osmosis (TFC PA RO) membrane. The synergistic effects of l-glutamine and Cu nanoparticles in altering the physico-chemical properties and improving desalination performances were investigated. The l-glutamine improved the hydrophilicity of membrane, while Cu NPs offered significant antibacterial characteristics to improve the functionality of membrane. The findings revealed that TFC-l-glutamine/Cu3 showed optimum performance with water flux of 16.5 L.m−2 h−1 and salt rejection of 96.8 % at an operating pressure of 1.5 MPa. The TFC-l-glutamine/Cu3 membrane exhibited an absence of dense colonies against both S. aureus and E. coli, on account of the antibacterial effectiveness of Cu NPs. The S. aureus- and E. coli-fouled TFC-l-glutamine/Cu3 membrane showed the lowest flux decline of 20 % and 25 % for, respectively. The TFC-l-glutamine/Cu3 membrane exhibited promising antifouling performance, with a flux recovery ratio (FRR) of 95.2 % for bovine serum albumin (BSA) foulants. The TFC-l-glutamine/Cu3 membrane exhibited a low copper leaching of ≤3 %, suggesting its high stability. The modification strategy demonstrated in this study provides a feasible solution to simultaneously address multiple issues of TFC RO membranes, which potentially leading to more efficient desalination.

Pilot scale fabrication of low fouling seawater desalination thin film composite reverse osmosis membrane

We report the pilot scale fabrication of thin film composite seawater reverse osmosis membrane (TFC-SW-RO) with low fouling propensity and improved permeate flux. In situ incorporation of poly(ethylene glycol) (PEG) into the polyamide (PA) network simultaneously improves the permeate flux (effect of hydrophilic channels) and antifouling property of the membrane. The PEG chains exhibit good stability during desalination of SW (NaCl = 33,000 mg L−1, applied pressure = 55.2 bar). The mechanism of PEG stabilization into the PA layer has been elucidated on the basis of hydrogen bond formation between ether linkage of PEG and carboxylic acid group of the PA network as well as steric hindrance posed by the network. The TFC-SW-RO membrane (no PEG) in several 100 m2 batches show pure water permeance of 1.4 L m−2 h−1 bar−1 and 98.5–98.8 % NaCl rejection during SW desalination. On the other hand, TFC-SW-RO-PEG shows pure water permeance of 2.2 L m−2 h−1 bar−1 with marginal drop in NaCl rejection (98.4–98.6 %). The TFC-SW-RO-PEG membrane exhibits improved antifouling (flux recovery ratio = 87 %) property during desalination of SW as compared to that of the pristine membrane (flux recovery ratio = 67 %). This work provides an important strategy for the fabrication of SW TFC RO membrane with improved performance.

Synthesis of graphene oxide-silver (GO-Ag) nanocomposite TFC RO membrane to enhance morphology and separation performances for groundwater desalination, (case study Marsa Alam area- Red Sea)

Synthesis of graphene oxide-silver (GO-Ag) nanocomposite TFC RO membrane to enhance morphology and separation performances for groundwater desalination, (case study Marsa Alam area- Red Sea)

A novel UV-initiated modification process for fabricating high-performance TFC RO membrane

Thin film composite reverse osmosis (TFC RO) membrane technology has seen widespread application in seawater/brackish water desalination and wastewater treatment. However, there are still problems such as unsatisfactory perm-selectivity and anti-fouling properties, and low feasibility of membrane manufacturing process. In view of the above problems, a novel UV-initiated modification process integrating with "Semi-interpenetrating polymer networks construction" and "Photo-Fries rearrangement initiation" is proposed. TFC RO membranes with both high perm-selectivity and anti-fouling properties were prepared by introducing polymerizable molecules (MAM, SA, AM) into the aqueous phase and conducting UV irradiation during interfacial polymerization (IP) process. The results showed that under the brackish water test conditions, the water flux and NaCl rejection of the optimal modified membrane (MAM-UV) were 77.5 L m−2 h−1 and 99.44%, respectively, which are 23.8% and 0.2% higher than those of the unmodified membrane (VIR-RO), respectively. The results of the anti-fouling test showed that MAM-UV exhibited good anti-fouling properties against both bovine serum albumin (BSA) and lysozyme (LYZ). In addition, the novel UV-initiated modification process proposed in this paper has broad prospects for industrial application because of its simple operation and easy scale-up.

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

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

Construction of pseudo-zwitterionic polyamide RO membranes surface by grafting positively charged small molecules

Membrane fouling is the major obstacle to hinder the extensive application of polyamide thin-film composite reverse osmosis (PA TFC RO) membranes in the water purification and reclamation fields. In this study, a series of hydrophilic and charge-tuned antifouling RO membranes were fabricated by grafting three kinds of small molecules of multi-grade amines N,N-dimethylethylenediamine (DMEDA), (2-aminoethyl) guanidine (AEGu) and (2-aminoethyl)triethylenediamine (AEDABCO) via layer-by-layer interfacial polymerization (LbL-IP). Detailed characterizations revealed that the three tailored membranes presented obviously diminished surface negative charge and reduced PA layer thickness, the water permeability increased by 67.4 %, 34.7 % and 75.6 % compared to the pristine membrane, reached 4.05 L m−2 h−1 bar−1, 3.26 L m−2 h−1 bar−1, and 4.28 L m−2 h−1 bar−1, respectively, meanwhile kept high NaCl rejection > 98.5 %. The dynamic fouling tests indicated that the tailored membranes exhibited much improved antifouling performance towards most of the model organic foulants. Meanwhile the membranes assembled with cationic groups exhibited an enhanced antibacterial property against E. coli. These functional small charged molecules and the convenient modification method provide a valuable pattern for designing antifouling PA TFC RO membranes, which is important for sustainable water purification.

High-performance zwitterionic TFC polyamide nanofiltration membrane based on a novel triamine precursor

As known, piperazine (PIP) and m-phenylenediamine (MPD) are popularly employed as aqueous monomer to interfacially polymerize with trimesoyl chloride (TMC) for the fabrication of TFC polyamide NF and RO membrane, respectively. In this work, we designed a novel amine monomer 4-(piperazin-1-yl)benzene-1,3-diamine (PMPD) having the combined PIP and MPD units in one molecule and employing it with TMC to prepare the pristine nanofiltration membrane. Subsequently, zwitterionic antifouling PA surface was constructed by modification with 3-bromopropionic acid (3-BPA). The resulting membrane (PMPD-PA) exhibited a smoother surface with enhanced surface hydrophilicity than the membrane made from MPD, and the thickness of the PA active layer was down to ~35 nm. Meanwhile, its pure water permeability was ~19 L m−2 h−1 bar−1, with Na2SO4 rejection of 98.4%, and NaCl rejection as low as 24.1%, performing as a novel selective NF membrane. Furthermore, fouling tests using model foulants BSA and SA well illustrated the good antifouling properties of membrane PMPD-PA with the mitigated flux decline and enhanced flux recovery upon physical cleaning. Thus, this work further demonstrates the fabrication of high-performance TFC NF membrane from the perspective of molecular design.

Preparation of high performance TFC RO membranes by surface grafting of small-molecule zwitterions

Zwitterions have been attracting great attention for researchers to tailor the separation membranes featuring enhanced water permeability and excellent antifouling property. Here we functionalized polyamide membrane surface with small-molecule zwitterions through sequential interfacial polymerization (SIP) technique to improve the performance of RO membranes. Zwitterionic molecules 3-(4-(2-((4-aminophenyl)amino)ethyl)morpholino-4-ium)propane-1-sulfonate (PPD-MEPS) and amino acid arginine were covalently bonded onto the PA surface via the amine groups of two zwitterions. Consequently, the surface hydrophilicity of both modified membranes were significantly improved with WCA decreased from ~60° to ~28°, and their surface negative charge also decreased to some extent at high pH values. The water permeability increased from 2.45 LMH/bar to 3.81–3.85 LMH/bar, increasing by about 57%, while maintained a NaCl rejection as high as 98.5%. In addition, the zwitterions-modified RO membranes exhibited much improved antibacterial attachment (E.coil) and fouling resistance to model foulants bovine serum albumin (BSA), lysozyme (LYZ) and humic acid (HA). Therefore, the facile zwitterions modified membranes possessing high water permeability and excellent antifouling performance, especially using amino acid Arg may find their potential promising application in water treatment.

Biosynthesis of silver nanoparticles and its effect on TFC RO membrane for groundwater desalination

Biosynthesis of silver nanoparticles and its effect on TFC RO membrane for groundwater desalination

Low‐energy reverse osmosis membrane with high boron rejection by surface modification with a polysaccharide

AbstractThe present paper aims at producing a high‐performance low‐energy reverse osmosis membrane by modifying the polyamide layer with potassium persulphate, chitosan, and methacrylic acid and sodium hypochlorite treatment. A supramolecular assembly of chitosan was made on the polyamide layer with methacrylic acid to increase the permeate flux. The concentrations of chitosan and methacrylic acid were varied to investigate the best combination of treatment to achieve superior performance. The membrane treated with 1000 mg/L chitosan and 4 % methacrylic acid showed permeate water‐flux 3.2 times that of virgin TFC RO membrane with a ∼2 % decline in salt rejection and a boron rejection of 97.45 % at pH 10. This membrane demonstrated energy saving of 68.78 % as compared to virgin thin film composite reverse osmosis membrane. Membranes were tested for hydrophilicity by contact angle analysis, surface charge by zeta potential analysis, morphology evaluation by scanning electron microscope, surface features by atomic force microscope, and chemical structural changes by attenuated total reflectance infrared spectroscopy. Significant enhancement in membrane performance was observed by surface modification to achieve ultra‐low energy reverse osmosis process development.

A NOVEL THIN FILM COMPOSITE REVERSE OSMOSIS MEMBRANE MODIFIED BY IONIC LIQUID

ABSTRACT Thin Film Composite Reverse Osmosis (TFC RO) membranes have undergone significant changes since inception; particularly the top polyamide layer has been tuned for optimal performance. The present paper demonstrates the novel approach to alter the polyamide membrane performance by subjecting it to ionic liquids. Ionic liquids 1-Butyl-3-Methylimidazolium Chloride [BMIM][Cl], 1-Methyl-3-Octylimidazolium Chloride [C8MIM][Cl] and 1-Butyl-3-Methylimidazolium Bromide [BMIM][Br] were used to alter the membrane performance. About a 6.5% increase in MgSO4 rejection and about an 87% increase in water-flux were noted when the membrane was subjected to 3000 mg/L [BMIM][Cl] after 2000 mg/L sodium hypochlorite each for 2 hours. Also, the decline in contact angle from 52.86o to 43.12o by this treatment demonstrated higher hydrophilicity. Atomic force microscope images showed a decline in surface roughness with the treatment. Scanning electron micrographs were taken to understand the changes in morphology of thin film composite reverse osmosis membranes with ionic liquid treatment. Attenuated total reflectance, infrared spectroscopy and nuclear magnetic resonance analysis were done to evaluate the changes in chemical structure and it was found that the treatment resulted in chemical structural modification of thin film composite reverse osmosis membranes with ionic liquid treatment.

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.

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.

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.