Effects of the Substrate on Interfacial Polymerization: Tuning the Hydrophobicity via Polyelectrolyte Deposition.
ABSTRACT: Interfacial polymerization (IP) has been the key method for the fabrication of the thin film composite (TFC) membranes that are extensively employed in reverse osmosis (RO) and forward osmosis (FO). However, the role of the substrate surface hydrophilicity in the formation of the IP-film remains a controversial issue to be further addressed. This study characterized the IP films formed on a series of polyacrylonitrile (PAN) substrates whose hydrophilicities (from ~38 to ~93 degrees) were varied via different approaches, including the alkaline treatment and the deposition of various polycations. It was revealed that delamination could occur when the IP film was formed on a relatively hydrophilic surface; the integrity of the TFC membranes was substantially improved, owing to the modification of the polyelectrolyte deposition. On the other hand, the characterization indicated that the TFC membrane could have an enhanced efficiency (with a factor of ~2) when the substrate was relatively hydrophilic. It was established that the polyelectrolyte deposition could be exploited to effectively tune the substrate surface hydrophobicity, thereby providing more degrees of freedom for the optimization of the TFC membranes fabrication.
Project description:In this study, modification of polysulfone (PSf)/sulfonated polysulfone (SPSf) blended porous ultrafiltration (UF) support membranes was proposed to improve the reverse osmosis (RO) performance of aromatic polyamide thin film composite (TFC) membranes. The synergistic effects of solvent, polymer concentration, and SPSf doping content in the casting solution were investigated systematically on the properties of both porous supports and RO membranes. SEM and AFM were combined to characterize the physical properties of the membranes, including surface pore natures (porosity, mean pore radius), surface morphology, and section structure. A contact angle meter was used to analyze the membrane surface hydrophilicity. Permeate experiments were carried out to evaluate the separation performances of the membranes. The results showed that the PSf/SPSf blended porous support modified with 6 wt % SPSf in the presence of DMF and 14 wt % PSf had higher porosity, bigger pore diameter, and a rougher and more hydrophilic surface, which was more beneficial for fabrication of a polyamide TFC membrane with favorable reverse osmosis performance. This modified PSf/SPSf support endowed the RO membrane with a more hydrophilic surface, higher water flux (about 1.2 times), as well as a slight increase in salt rejection than the nascent PSf support. In a word, this work provides a new facile method to improve the separation performance of polyamide TFC RO membranes via the modification of conventional PSf porous support with SPSf.
Project description:Enhancing the water flux while maintaining the high salt rejection of existing reverse osmosis membranes remains a considerable challenge. Herein, we report the use of a porous carbon nitride (C3N4) nanoparticle to potentially improve both the water flux and salt rejection of the state-of-the-art polyamide (PA) thin film composite (TFC) membranes. The organic-organic covalent bonds endowed C3N4 with great compatibility with the PA layer, which positively influenced the customization of interfacial polymerization (IP). Benefitting from the positive effects of C3N4, a more hydrophilic, more crumpled thin film nanocomposite (TFN) membrane with a larger surface area, and an increased cross-linking degree of PA layer was achieved. Moreover, the uniform porous structure of the C3N4 embedded in the "ridge" sections of the PA layer potentially provided additional water channels. All these factors combined provided unprecedented performance for seawater desalination among all the PA-TFC membranes reported thus far. The water permeance of the optimized TFN membrane is 2.1-folds higher than that of the pristine PA-TFC membrane, while the NaCl rejection increased to 99.5% from 98.0%. Our method provided a promising way to improve the performance of the state-of-art PA-TFC membranes in seawater desalination.
Project description:Internal concentration polarization (ICP) is a major issue in forward osmosis (FO) as it can significantly reduce the water flux in FO operations. It is known that a hydrophilic substrate and a smaller membrane structure parameter (S) are effective against ICP. This paper reports the development of a thin film composite (TFC) FO membrane with a hydrophilic mineral (CaCO3)-coated polyethersulfone (PES)-based substrate. The CaCO3 coating was applied continuously and uniformly on the membrane pore surfaces throughout the TFC substrate. Due to the intrinsic hydrophilicity of the CaCO3 coating, the substrate hydrophilicity was significantly increased and the membrane S parameter was reduced to as low as the current best of cellulose-based membranes but without the mechanical fragility of the latter. As a result, the ICP of the TFC-FO membrane could be significantly reduced to yield a remarkable increase in water flux without the loss of membrane selectivity.
Project description:A practical method is reported to enhance water permeability of thin film composite (TFC) polyamide (PA) membranes by decreasing the thickness of the selective PA layer. The composite membranes were prepared by interfacial polymerization (IP) reaction between meta-phenylene diamine (MPD)-aqueous and trimesoyl chloride (TMC)-organic solvents at the surface of polyethersulfone (PES) microporous support. Several PA TFC membranes were prepared at different temperatures of the organic solution ranging from -20?°C to 50?°C. The physico-chemical and morphological properties of the synthesized membranes were carefully characterized using serval analytical techniques. The results confirmed that the TFC membranes, synthesized at sub-zero temperatures of organic solution, had thinner and smoother PA layer with a greater degree of cross-linking and wettability compared to the PA films prepared at 50?°C. We demonstrated that reducing the temperature of organic solution effectively decreased the thickness of the PA active layer and thus enhanced water permeation through the membranes. The most water permeable membrane was prepared at -20?°C and exhibited nine times higher water flux compared to the membrane synthesized at room temperature. The method proposed in this report can be effectively applied for energy- and cost-efficient development of high performance nanofiltration and reverse osmosis membranes.
Project description:The data presented in this paper are produced as part of the original research article entitled "Thin-film composite membrane on a compacted woven backing fabric for pressure assisted osmosis" (Sahebi et al., 2017). This article describes how to fabricate a defect free membrane for forward osmosis (FO) and pressure assisted osmosis (PAO) on the woven mesh backing fabric support. Casting polymer on backing fabric support may limit the interfacial polyemirization due to wrinkled membrane surface. This paper presents data obtained from two different backing fabrics used as support for fabrication of thin film composite FO membrane. Backing fabric support were woven polyester mesh with different opening size. The data include the characterization of the intrinsic properties of the membrane samples, SEM and their performance under FO process. The structural parameters (S value) of the substrate were computed from thickness and porosity of the substrates. Thin film composite (TFC) membrane achieved a water flux of 8.1?L?m2 h-1 in FO process and 37?L?m2 h-1 using 0.5?M NaCl as draw solution (DS) and deionised (DI) water as the feed solution (FS) when applied hydraulic pressure was 10?bar.
Project description:A practical fabrication technique is presented to tackle the trade-off between the water flux and salt rejection of thin film composite (TFC) reverse osmosis (RO) membranes through controlled creation of a thinner active selective polyamide (PA) layer. The new thin film nano-composite (TFNC) RO membranes were synthesized with multifunctional poly tannic acid-functionalized graphene oxide nanosheets (pTA-f-GO) embedded in its PA thin active layer, which is produced through interfacial polymerization. The incorporation of pTA-f-GOL into the fabricated TFNC membranes resulted in a thinner PA layer with lower roughness and higher hydrophilicity compared to pristine membrane. These properties enhanced both the membrane water flux (improved by 40%) and salt rejection (increased by 8%) of the TFNC membrane. Furthermore, the incorporation of biocidal pTA-f-GO nanosheets into the PA active layer contributed to improving the antibacterial properties by 80%, compared to pristine membrane. The fabrication of the pTA-f-GO nanosheets embedded in the PA layer presented in this study is a very practical, scalable and generic process that can potentially be applied in different types of separation membranes resulting in less energy consumption, increased cost-efficiency and improved performance.
Project description:With the blooming of oil and gas industries, oily saline wastewater treatment becomes a viable option to resolve the oily water disposal issue and to provide a source of water for beneficial use. Reverse osmosis (RO) has been touted as a promising technology for oily saline wastewater treatment. However, one great challenge of RO membrane is fouling phenomena, which is caused by the presence of hydrocarbon contents in the oily saline wastewater. This study focuses on the fabrication of antifouling RO membrane for accomplishing simultaneous separation of salt and oil. Thin film nanocomposite (TFN) RO membrane was formed by the layer by layer (LbL) assembly of positively charged TNS (pTNS) and negatively charged TNS (nTNS) on the surface of thin film composite (TFC) membrane. The unique features, rendered by hydrophilic TNS bilayer assembled on TFC membrane in the formation of a hydration layer to enhance the fouling resistance by high concentration oily saline water while maintaining the salt rejection, were discussed in this study. The characterization findings revealed that the surface properties of membrane were improved in terms of surface hydrophilicity, surface roughness, and polyamide(PA) cross-linking. The TFC RO membrane coated with 2-bilayer of TNS achieved >99% and >98% for oil and salt rejection, respectively. During the long-term study, the 2TNS-PA TFN membrane outperformed the pristine TFC membrane by exhibiting high permeability and much lower fouling propensity for low to high concentration of oily saline water concentration (1000 ppm, 5000 ppm and 10,000 ppm) over a 960 min operation. Meanwhile, the average permeability of uncoated TFC membrane could only be recovered by 95.7%, 89.1% and 82.9% for 1000 ppm, 5000 ppm and 10,000 ppm of the oily saline feedwater, respectively. The 2TNS-PA TFN membrane achieved almost 100% flux recovery for three cycles by hydraulic washing.
Project description:This study reported a series of thin film composite (TFC) membranes with single-walled nanotubes (SWCNTs) interlayers for the forward osmosis (FO) application. Pure SWCNTs with ultrahigh length-to-diameter ratio and without any functional group were applied to form an interconnect network interlayer via strong ?-? interactions. Compared to the TFC membrane without SWCNTs interlayer, our TFC membrane with optimal SWCNTs interlayer exhibited more than three times the water permeability (A) of 3.3 L m-2h-1bar-1 in RO mode with 500 mg L-1 NaCl as feed solution and nearly three-fold higher FO water flux of 62.8 L m-2 h-1 in FO mode with the deionized water as feed solution and 1 M NaCl as draw solution. Meanwhile, the TFC membrane with SWCNTs interlayer exhibited significantly reduced membrane structure parameters (S) to immensely mitigate the effect of internal concentration polarization (ICP) in support layer with micro-sized pores in favor of higher water flux. It showed that the pure SWCNTs interlayer could be an effective strategy to apply in FO membranes.
Project description:Forward osmosis (FO) is a concentration process based on the natural phenomena of osmosis. It is considered a breakthrough technology that can be potentially used for concentrating solutions and suspensions. The diluted nature of brine restricts the treatment technologies that can be applied. Then, brine concentration by FO could represent a new emerging technology enabling the application of a wider range of treatment alternatives. The performance of concentrated brine depending upon FO membranes was studied at normal temperature and pressure in this research. Cellulose triacetates on radio-frequency-weldable non-woven support (CTA-NW) and a thin-film composite with embedded polyester screen support (TFC-ES) were compared; and their orientations were considered. The brine was from Chaerhan Salt Lake after extracting potassium as the feed solution, NaCl solution or MgCl2 solution as the draw solution. The results indicated that CTA-NW exhibited better concentration performance than TFC-ES, while the water fluxes of the two membranes were exactly the opposite. In the case of CTA-NW in active layer facing feed solution orientation with MgCl2 as the draw solution, the concentration factor of Li+ was nearly 3.0. Quantitative structure-activity relationship of FO membranes and concentration characteristics was correlated, based on results of SEM, FTIR and contact angles studies. The concentration performance could be mainly attributed to the porosity and the thickness of FO membranes; while the water flux was dependent on the hydrophily of FO membrane surface.
Project description:In this work, colloidal fouling by silica particles of different sizes on micro-patterned pristine and poly-(N-isopropylacylamide)-coated polyamide (PA) thin-film composite (TFC) membranes was studied. The competing impacts of surface micro-patterning vs. surface chemical modification on enhancing antifouling propensity in unstirred dead-end filtration conditions were systematically explored. Spatially selective deposition of silica microparticles (500 nm), driven by unequal flow distribution, was observed on micro-patterned membranes such that silica particles accumulated preferentially within the surface pattern's valleys, while keeping apexes regions not fouled. This interesting phenomenon may explain the substantially enhanced antifouling propensity of micro-patterned PA TFC membranes. A detailed mechanism for spatially selective deposition of silica microparticles is proposed. Furthermore, micro-imprinted surface patterns were revealed to influence deposition behavior/packing of silica nanoparticles (50 nm) resulting in very limited flux decline that was, almost, recovered under influence of triggering stirring stimulus during a continued silica filtration experiment. The current findings provide more insights into the potency of surface micro-patterning consolidated with hydrogel coating toward new fouling-resistant PA TFC membranes.