Thin-film Composite Forward Osmosis Research Articles

A high performance of thin film composite based on dextran substrate for effective removal of heavy metal ions

A high performance thin film composite forward osmosis (FO) membrane with dextran as additive in support layer has been developed for effective heavy metal ions removal for the first time. The proposed FO process consists of a thin film composite (TFC) FO membrane made from interfacial polymerization on a high porous and hydrophillic polysulfone embedded dextran support to minimize the internal concentration polarization effect. The created substrates were characterized in terms of surface chemistry and morphology prior to performance evaluation. The support layer incorporating with dextran exhibited lower contact angle and high porosity as an ideal support layer for FO process. Moreover, the ridge-and-valley structure of TFC membranes made with support layers containing larger openings, long finger-like voids and macrovoids was more noticeable for the active layers, according to high-resolution scanning electron microscopy. The removal of metals were demonstrated, water fluxes were around 13 L/m2.h and rejection were above 95 %. The performance of developed membrane was then showed greater water flux and rejection in comparison to the commercial TFC.

Incorporation of zeolitic imidazolate framework-8 (ZIF-8) in the polyamide and polysulfone layers of forward osmosis membranes for enhancing aquaculture wastewater recovery and PPCPs removal

Wastewater recovery is essential to alleviate water resource shortages, and this can be achieved through a high-energy-efficient forward osmosis (FO) process combined with an emerging material, zeolitic imidazolate framework-8 (ZIF-8). Here, we create thin-film composite FO membranes (TF-CFOMs) by incorporating ZIF-8 into the active polyamide (PA) and/or support polysulfone (PSf) layers to address the challenges of low water flux and loss of draw solutes during operation. Experimental factors included the dosage of ZIF-8 nanoparticles in PA preparation solutions and the dosages of 2-methylimidazole (2-Hmim) and zinc nitrate hexahydrate (ZNH) in n-methyl-2-pyrrolidone (NMP) to fabricate the PSf casting solutions with in-situ formed ZIF-8 nanoparticles. Successful ZIF-8 incorporation on the TF-CFOM surface was confirmed, and the ZIF-8 TF-CFOMs exhibited increased surface hydrophilicity and separation performance. Only modifying the PA layer by adding 0.025 wt% ZIF-8 nanoparticles in trimesoyl chloride (TMC) resulted in the membrane (PA0.025T-PSf0) with water flux 2.3 times higher than the pristine TF-CFOM (4.9 LMH). The pristine and modified TF-CFOMs were further applied for aquaculture wastewater (AWW) recovery and removal of pharmaceuticals and personal care products (PPCPs). Results of water recovery demonstrated that the recovery rate reached 89.1% in 3.5 days when using the dual-layer modified TF-CFOM. Results of PPCP removal indicated that both pristine and modified TF-CFOMs can achieve high PPCP rejection efficiency (>90%), with the modified TF-CFOM (PA0.025T-PSf2.0) performing the best. Overall, the PA0.025T-PSf2.0 TF-CFOM achieved high and stable separation efficiency in long-duration AWW recovery, making it well-suited for practical field applications.

Forward osmosis membrane substrates with low structure parameter: Modification with PSf‐g‐PMMA graft copolymer

AbstractIn this work, using the combination of atom transfer radical polymerization and click chemistry, the graft copolymer polysulfone‐graft‐poly (methyl methacrylate) (PSf‐g‐PMMA) was synthesized as a modifying agent. The copolymer was embedded in the PSf substrate using a nonsolvent phase inversion method. Then, the modified substrate was used to make thin film composite forward osmosis (TFC‐FO) membranes using the interfacial polymerization method. Also, the effect of PSf‐g‐PMMA copolymer content on the surface properties of the membrane, as well as the filtration performance, was investigated. The increase in hydrophilicity, porosity, and average pore diameter indicated the favorable effect of PSf‐g‐PMMA copolymer on the characteristics of modified substrates. In addition, the improvement in the membrane morphology (an increase in the length and number of finger‐like pores) provided a substrate with low tortuosity and structure parameters. Therefore, the pure water permeability increased from 79.9 LMH/bar for the control membrane to 372.1 LMH/bar for the membrane containing 20 wt.% of PSf‐g‐PMMA copolymer. Investigating the FO separation properties of TFC‐FO membranes showed an increase in water flux and selectivity due to an improvement in the morphology of the modified substrate with low structural parameters. The new TFC‐FO membranes have been optimized, and water flux has significantly improved. Compared with the control membrane, which did not have copolymer blending, the new membranes have a triply enhanced water flux of 17.1 LMH. In addition, the selectivity of these optimized membranes has improved when 1 M NaCl is used as the draw, and DI water is used as the feed in the FO mode.

Viability of Total Ammoniacal Nitrogen Recovery Using a Polymeric Thin-Film Composite Forward Osmosis Membrane: Determination of Ammonia Permeability Coefficient.

Total ammoniacal nitrogen (TAN) occurs in various wastewaters and its recovery is vital for environmental reasons. Forward osmosis (FO), an energy-efficient technology, extracts water from a feed solution (FS) and into a draw solution (DS). Asymmetric FO membranes consist of an active layer and a support layer, leading to internal concentration polarization (ICP). In this study, we assessed TAN recovery using a polymeric thin-film composite FO membrane by determining the permeability coefficients of NH4+ and NH3. Calculations employed the solution-diffusion model, Nernst-Planck equation, and film theory, applying the acid-base equilibrium for bulk concentration corrections. Initially, model parameters were estimated using sodium salt solutions as the DS and deionized water as the FS. The NH4+ permeability coefficient was 0.45 µm/s for NH4Cl and 0.013 µm/s for (NH4)2SO4 at pH < 7. Meanwhile, the NH3 permeability coefficient was 6.18 µm/s at pH > 9 for both ammonium salts. Polymeric FO membranes can simultaneously recover ammonia and water, achieving 15% and 35% recovery at pH 11.5, respectively.

Design and preparation of woven fabric-reinforced substrate: A new pathway for robust thin film composite membrane

The thin film composite (TFC) membrane possesses the highest commercial application potential among all types of forward osmosis (FO) membranes. The support layer of the membrane plays a crucial role in both bearing mechanical loads and facilitating the active layer formation. Herein, we addressed the issues of low permeability and poor mechanical strength of the conventional TFC FO membrane by selecting suitable fabrics and optimizing membrane design and preparation. Polyester (PS) woven fabric, with its high strength, low thickness, and high porosity, served as an excellent material for reinforcing the strength of the FO membrane. We employed a novel double-blade casting method to address the defect issue associated with the conventional single-blade casting method. The influencing factors and quality control strategies of the fabric-reinforced substrate were systematically investigated. Furthermore, membrane characterization techniques, including scanning electron microscopy (SEM), liquid-liquid displacement porometer, and cross-flow FO system, were used to reveal the influences of different substrates, including polysulfone (PSU), polyacrylonitrile (PAN), and polyetherimide (PEI), on the structure and performance of the fabric-reinforced TFC-FO membrane. Compared to commercial FO membranes, the TFC/PSU membrane exhibited superior FO performance, with a water flux of 24.1 LMH, and outstanding mechanical strength that was more than 10-times higher than that of free-standing membranes. This study demonstrates a new pathway for engineering robust TFC-FO membranes with low structural parameters as well as excellent scalability of the membrane fabrication method.

Optimized preparation route for polyamide top-coated forward osmosis membrane for enhanced water flux using industrial wastewater as feed.

The forward osmosis (FO) process has recently gained significant interest in treating wastewater, brackish/seawater and concentrating feedstocks for various operations, including desalination. The study investigates the effect of different synthesis conditions of the polyamide-based thin-film composite (TFC) FO membranes on the membranes' final performance. Taguchi statistical analyses were used to fabricate and optimize the polyamide TFC FO membrane. The process parameters as factors were the amount of polyethersulfone (PES), polyethylene glycol 400 (PEG-400), polyvinyl pyrrolidone (PVP), m-phenylenediamine (MPD), and trimesoyl chloride (TMC), and TMC reaction-time (RT). The Taguchi method was adopted to investigate the optimal conditions and the significance of individual factors using an L16 (45) orthogonal array. Another Taguchi analysis (Taguchi 2) was adopted to investigate the influence of other important parameters like optimal conditions for MPD, TMC, and TMC reaction-time factors using an L9 (33) orthogonal array. Confirmation tests validated a maximum water flux of 46.4 ± 2.32 L/m2·h with a specific combination of control factors for membrane synthesis: PES/PEG/PVP/MPD/TMC/TMC RT-16/7/0.5/1/0.05/30. These tests demonstrated a high-water flux of 7.05 ± 0.35 L/m2·h when exposed to industrial wastewater (secondary effluent) as the feed solution (FS) and fertilizer as the draw solution (DS) in the FO process. The R2 values were more than 90%. The experimental validation confirmed the models' predictive ability with different FSs, including industrial wastewater.

Synthesis of sandwich structure forward osmosis membrane with calcium-carboxyl modified polyamide and tannic acid-Fe3+ interlayer and its application in coconut water concentration

In this study, a sandwich structure thin-film composite forward osmosis (TFC-FO) membrane based on calcium-carboxyl interfacial polymerization was synthesized using tannic acid-Fe (TA-Fe) as the interlayer. Additionally, the concentration effect of Ca2+ surface modification, TA-Fe intermediate layers, and their combination on coconut water concentration, membrane efficiency, anti-fouling ability, and quality of the concentrate was investigated. Compared to the TFC-Ca or TFC-TA-Fe membrane, the TFC-TA-Fe-Ca membrane significantly enhanced the concentration effect and reverse salt flux (p < 0.05) and exerted the lowest attenuation of permeability. Furthermore, the total soluble solids content increased from 5.13 °Brix to 13.17 °Brix after 8 h. The TFC-TA-Fe-Ca membrane showed a 61.20 % increase in its efficiency compared to the TFC membrane. The total reducing sugar, acids, and polyphenol contents increased by 1.72, 1.34, and 1.22 times, respectively. Overall, the sandwich structure FO membrane exhibited significant feasibility and potential for industrial application in fruit juice concentrate production.

Controlling amine monomers via UiO-66-NH2 defect sites to enhance forward osmosis membrane performance for lithium recovery

The excessive thickness of the separation layer and the presence of cracks cause low water flux and poor lithium recovery in conventional forward osmosis (FO) membranes. According to the influence of the diffusion behavior of amine monomers in interfacial polymerization, the use of an interlayer optimizes the separation layer structure of traditional thin-film composite FO membrane. However, it is difficult to accurately control the separation layer structure by simply adjusting the amount of the interlayer material loaded. Herein, FO membranes with defect-containing metal–organic framework (MOF) interlayers were constructed. By adjusting the concentrations of competitive ligands, the MOFs showed different degrees of linker loss, which exposed the metal ions in the MOFs to different extents. The defective sites of the constructed MOFs increased the interaction between the interlayer and m-phenylenediamine (MPD), and density functional theory (DFT) simulations also revealed an increase in the binding energy of the two materials. Therefore, MPD attachment and diffusion were controlled by changing the proportion of defects in the MOFs, thereby finely regulating the separation layer structure. Additionally, tannic acid (TA) was predeposited to improve the stability of the interlayer. The prepared membrane exhibited water fluxes of 33.84 and 65.81 LMH and reverse salt fluxes of 0.58 and 2.38 gMH in the active layer facing feed solution (AL-FS) and active layer facing draw solution (AL-DS) modes, respectively. Excellent lithium ion recovery and fouling resistance was also demonstrated in battery wastewater treatment.

High-performance thin film composite forward osmosis membrane for efficient rejection of antimony and phenol from wastewater: Characterization, performance, and MD-DFT simulation

The effective removal of heavy metals and phenolic pollutants from aqueous solutions has received widespread attention in the field of wastewater treatment. In this work, a novel PAN/CNTs/UiO-66-NH2 modified forward osmosis (FO) membrane was prepared for efficient removal of antimony (Sb) and phenol from wastewater. The membrane was synthesized using a facile and cost-effective method. The PAN/CNTs substrate membrane was prepared using electrospinning technology, and UiO-66-NH2 MOF particles were loaded onto the surface of the active layer during the interfacial polymerization (IP) process. The presence of CNTs in the spinning solution regulated the pore structure and properties of nanofibers. Characterization of the membrane confirmed its unique structure and enhanced properties. When the CNTs addition was 0.01 g, and UiO-66-NH2 addition was 0.05 wt%, the FO membrane exhibited the optimal operational performance. In the AL-FS mode, the water flux, reverse salt flux (RSF), and Js/Jw ratio were 14.68 LMH, 0.17 gMH, and 0.01 g/L, respectively. As a comparison, the water flux, RSF, and Js/Jw ratio were 21.19 LMH, 0.65 gMH, and 0.032 g/L in the AL-DS mode, respectively. Simultaneously, efficient removal of antimony and phenol was achieved in both modes, with antimony removal efficiencies of 99.26 % and 97.98 %, and phenol removal efficiencies of 96.61 % and 93.18 %, respectively. The modified membrane exhibited excellent performance in rejecting Sb and phenol. Molecular dynamics simulations and density functional theory calculations provide theoretical support for the excellent performance of membranes. The membrane demonstrated a high water flux, making it promising for practical applications. Additionally, it exhibited remarkably low reverse salt flux, highlighting its suitability for desalination processes. The exceptional removal efficiency of Sb and phenol, coupled with the membrane's impressive hydraulic performance, makes it a promising candidate for the treatment of industrial effluents containing these challenging contaminants. The results presented in this study underscore the potential of PAN/CNTs/UiO-66-NH2 FO membranes as an advanced solution for addressing water pollution challenges.

Resilient forward osmosis membranes against microplastics fouling enhanced by MWCNTs/UiO-66-NH2 hybrid nanoparticles

The escalating presence of microplastics (MPs) in wastewater necessitates the investigation of effective tertiary treatment process. Forward osmosis (FO) emerges as an effective non-pressurized membrane process, however, for the effective implementation of FO systems, the development of fouling-resistance FO membranes with high-performance is essential. This study focuses on the integration of MWCNT/UiO-66-NH2 as metal-organic frameworks (MOFs) and multi-wall carbon nanotubes (MWCNT) nanocomposites in thin film composite (TFC) FO membranes, harnessing the synergistic power of hybrid nanoparticles in FO membranes. The results showed that the addition of MWCNT/UiO-66-NH2 in the aqueous phase during polyamide formation changed the polyamide surface structure, and enhanced membranes’ hydrophilicity by 44%. The water flux of the modified FO membrane incorporated with 0.1 wt% MWCNTs/UiO-66-NH2 increased by 67% and the reverse salt flux decreased by 22% as in comparison with the control membrane. Moreover, the modified membrane showed improved antifouling behavior against both organic foulant and MPs. The MWCNT/UiO-66-NH2 membrane experienced 35% flux decline while the control membrane experienced 65% flux decline. This proves that the integration of MWCNT/UiO-66-NH2 nanoparticles into TFC FO membranes is a viable approach in creating advanced FO membranes with high antifouling propensity with potential to be expanded further to other membrane applications.

Ultra-fast green hydrogen production from municipal wastewater by an integrated forward osmosis-alkaline water electrolysis system

Recent advancements in membrane-assisted seawater electrolysis powered by renewable energy offer a sustainable path to green hydrogen production. However, its large-scale implementation faces challenges due to slow power-to-hydrogen (P2H) conversion rates. Here we report a modular forward osmosis-water splitting (FOWS) system that integrates a thin-film composite FO membrane for water extraction with alkaline water electrolysis (AWE), denoted as FOWSAWE. This system generates high-purity hydrogen directly from wastewater at a rate of 448 Nm3 day−1 m−2 of membrane area, over 14 times faster than the state-of-the-art practice, with specific energy consumption as low as 3.96 kWh Nm−3. The rapid hydrogen production rate results from the utilisation of 1 M potassium hydroxide as a draw solution to extract water from wastewater, and as the electrolyte of AWE to split water and produce hydrogen. The current system enables this through the use of a potassium hydroxide-tolerant and hydrophilic FO membrane. The established water-hydrogen balance model can be applied to design modular FO and AWE units to meet demands at various scales, from households to cities, and from different water sources. The FOWSAWE system is a sustainable and an economical approach for producing hydrogen at a record-high rate directly from wastewater, marking a significant leap in P2H practice.

Influence of Polyethersulfone substrate properties on the performance of thin film composite forward osmosis membrane: Effect of additive concentration, polymer concentration and casting thickness

This research seeks to optimize the impact of substrate parameters such as polyvinylpyrrolidone (PVP) additive concentration (3–11 wt%), polyethersulfone (PES) concentration (11–17 wt%), and casting thickness (100–250 µm) on the overall performances of (PES) thin film composite (TFC) FO membrane. Non-solvent induced phase separation (NIPS) method was used to fabricate the substrate membrane, which was then followed by the interfacial polymerization of m-phenylene diamine (MPD) in aqueous solution and trimesoyl chloride (TMC) in hexane-organic solvent to form the active polyamide (PA) layer. Analyses of contact angle, porosity, pore size, functional group, morphology, and surface roughness were performed on membrane substrates and TFC membrane. Membrane performance parameters such as water flux (Jw), reverse salt diffusion (RSD), and specific reverse flux (SRF) were evaluated for the fabricated TFC membranes using the FO filtration system (pure water as feed solution and NaCl as draw solution). In addition, the water permeability coefficient (A), the solute permeability coefficient (B), and the structural parameter (S) were computed mathematically. Optimized membranes were chosen using the specific reverse flux (SRF) as the principal performance indicator. The optimal membranes for each parameter were then evaluated for their antifouling and rejection properties using humic acid (HA) solution. Among the optimized membranes, 15%PES/5%PVP/100 µm membrane exhibited the best performance with high rejection and antifouling properties towards HA.

Support-free interfacial polymerized polyamide membrane on a macroporous substrate to reduce internal concentration polarization and increase water flux in forward osmosis

Macroporous substrates have great potential in the development of high performance thin film composite forward osmosis (TFC FO) membranes. This paper reports on the preparation of TFC FO membrane via support-free interfacial polymerization (SFIP) technology on a macroporous substrate. SFIP technology can effectively break the bottleneck of conventional interfacial polymerization (IP) technology, which makes it difficult to form a complete polyamide (PA) film on the macroporous substrate. Briefly, the complete PA film is formed at the free water-organic phase interface and then attached to the macroporous substrate by vacuum filtration. The monomer concentration and filtration pressure were adjusted to form the optimal SFIP-PA film. Meanwhile, we chose a macroporous polyvinylidene fluoride (PVDF) microfiltration substrate and screened the pore size to reduce the structural parameters and then the internal concentration polarization, which caused the improvement of water flux. The performance of SFIP-PVDF membranes was investigated and discussed. Under the AL-FS mode with DI water and 1.0 M NaCl solution as the feed solution and draw solution, respectively, the SFIP-PVDF membrane, which used a macroporous PVDF substrate with a pore size of 0.45 μm exhibited a water flux (20 L/m2·h) and a reverse salt flux (2.5 g/m2·h). Besides, the membrane showed good stability in the 72 h test. The specific salt flux (Js/Jw) of SFIP-PVDF membranes was much lower than that of IP-PVDF membranes prepared via IP technology, which were incomplete and defective, suggesting that SFIP technology was superior to IP technology. This work effectively exploits the potential of macroporous substrates for the development of high performance TFC FO membranes and provides an insight into the high performance FO membrane design.

Arginine-Functionalized Thin Film Composite Forward Osmosis Membrane Integrating Antifouling and Antibacterial Effects.

Membrane fouling is an inevitable obstacle of polyamide composite forward osmosis (FO) membranes in oily wastewater treatment. In this study, zwitterionic arginine (Arg) is grafted onto nascent self-made FO polyamide poly(ether sulfone) (PA-PES) membrane, imparting superior hydrophilic, antifouling, and antibacterial properties to the membrane. Detailed characterizations revealed that the Arg-modified (Arg-PES) membrane presented obviously surface positively charged and unique morphology. Results showed that our strategy endowed the optimized membrane, the water flux increased by 113.2% compared to the pristine membrane, respectively, meanwhile keeping high NaCl rejection > 93.9% (with DI water as feed solution and 0.5 M NaCl as draw solution, FO mode). The dynamic fouling tests indicated that the Arg-PES membranes exhibited much improved antifouling performance towards oily wastewater treatment. The flux recovery ratios of the membrane were as high as 92.0% for cationic emulsified oil (cetyl pyridinium chloride, CPC), 87.0% for neutral emulsified oil (Tween-80), and 86.0% for anionic emulsified oil (sodium dodecyl sulfate, SDS) after washing, respectively. Meanwhile, the Arg-PES membranes assembled with guanidine cationic groups exhibited an enhanced antibacterial property against E. coli, which exhibited a high antibacterial efficiency of approximately 96%. Consequently, the newly arginine functionalized FO membrane possesses impressive antifouling performance, while simultaneously resisting bacterial invasion, thus rendering it an ideal alternative for oily wastewater treatment in the FO process.

Electric field forward osmosis (EFFO) fouling mitigation in algae harvesting

Efficient microalgae harvesting is crucial for sustainable biofuel production. Forward osmosis (FO) membranes offer a cost-effective solution for algae separation but are prone to membrane fouling. To address this, a bench-scale FO membrane unit was created, utilizing an aquaporin thin film composite FO membrane. The unit was combined with an electric field in both continuous and pulsing modes, employing stainless steel (SS) meshes to mitigate fouling during Chlorella vulgaris dewatering. Generally, applying higher electric potentials in continuous mode demonstrated improved water flux and flux recovery. The electric field forward osmosis (EFFO) configuration achieved significantly higher fluxes at applied potentials of −0.1, −0.4, and −1.0 V compared to the control. An electric potential as high as −10 V effectively removed fouling by inducing H2 gas formation on the SS cathode. Additionally, the application of high electric potential led to increased settling velocity, possibly due to electrocoagulation and the release of metals. Conversely, carbon fiber electrodes had no impact on algal cell morphology. Both higher salinity levels and increased potential enhanced lipid contents in algal biomass. Overall, EFFO technology in algae harvesting offers improved efficiency by reducing membrane fouling and increasing water flux, enabling cost-effective and sustainable biofuel production from microalgae.

A novel antifouling polyamide thin-film composite forward osmosis membrane fabricated by poly(m-phenylene isophthalamide) for seawater desalination

Forward osmosis (FO) technology has attracted the interest of many researchers due to its excellent properties such as low energy consumption, fouling resistance, and easy cleaning. However, the lack of high-performance membrane materials makes it far from being practical on a large scale application. In this study, the poly(m-phenylene isophthalamide) (PMIA) was used as the substrate to be embedded in a high-porosity polyester mesh to form a support layer, and a forward osmosis composite membrane was prepared through an interfacial polymerization process. The effects of preparation conditions such as mesh size, scraping membrane thickness, and casting solution concentration on performance were studied. In the FO operation mode, with DI water as the feed solution and 1 mol/L NaCl as the draw solution, the water flux is 8.62 L•m−2•h−1, the reverse salt flux is 0.118 mol•m−2•h−1, and the rejection for NaCl exceeds 99%. Moreover, the membrane behaved excellent mechanical properties, with a tensile strength of 95 MPa. Compared with the two commercial FO membranes, the self-made PMIA TFC-FO showed excellent hydrophilicity and fouling resistance. This research demonstrated that PMIA is a proper candidate for fabricating of the TFC-FO membranes to achieve high water flux and selectivity in seawater desalination.

Modification of polyacrylonitrile TFC-FO membrane by biowaste-derived hydrophilic N-doped carbon quantum dots for enhanced water desalination performance

Effective membranes are critical for enhancing the productivity of the forward osmosis (FO) desalination process. In this work, a straightforward approach is presented for constructing a hydrophilic and high-flux thin film composite FO (TFC-FO) membrane onto a polyacrylonitrile (PAN) sublayer. To this purpose, biowaste-derived nitrogen-doped carbon quantum dots (BWD-NCQDs) were incorporated into the polymeric structure of the TFC selective layer, which improved surface hydrophilicity and caused the creation of more water channels, resulting in better intrinsic transport properties. In both FO and pressure retarded osmosis (PRO) membrane orientations, TFC-FO membranes containing 0.01–0.1 wt% of BWD-NCQDs showed better water permeation and NaCl rejection than the pristine TFC membrane. In the presence of 0.05 wt% of BWD-NCQDs, water flux increased by 54.7 % and reached 24.6 Lm−2 h−1, and reverse solute flux decreased by 43.3 % to 3.81 g−2 h−1 compared to the pristine membrane. The optimum membrane also showed better fouling and water desalination behavior. Therefore, modification of the membranes by hydrophilic BWD-NCQDs represents superior performance in the FO processes. This study demonstrates the potential of using hydrophilic NCQDs derived from biowaste materials to incorporate into TFC membranes and improve their FO proficiency in water desalination.

High performance forward osmosis membrane with ultrathin hydrophobic nanofibrous interlayer

The novel thin film composite (TFC) forward osmosis (FO) membrane with electrospinning nanofibers as support layer can alleviate internal concentration polarization (ICP). While the macropores of the nanofiber support layer cause defects in the polyamide (PA) layer. Therefore, hydrophobic polyvinylidene fluoride (PVDF) fine nanofibers were used as an interlayer to modulate the process of interfacial polymerization (IP) in this study. The results showed that the introduction of the interlayer improved the hydrophobicity of the support layer for achieving uniform, thin and defect-free selective polyamide (PA) layer. The water flux of TFC-PVDF was 58.26 LMH in the FO mode of 2 M NaCl, which was two times higher than that of the unmodified FO membrane. Lower reverse salt flux (4.91 gMH) and structural parameter (179.43 μm) alleviated the ICP. In addition, TFC-PVDF membrane showed good anti-fouling performance for SA (flux recovery ratio of 93.97%) due to high hydrophilicity, low zeta potential and low roughness. This study provides an easy and promising method to prepare defect-free PA selective layer on the macropores nanofiber support layer. The novel FO membrane shows high desalination performance and anti-fouling properties.

Fabrication of high-performance forward osmosis membrane based on asymmetric integrated nanofiber porous support induced by a new controlled photothermal induction method

The high surface roughness and large pore size of electrospun nanofibers (ESNF) make it impossible to form good polyamide (PA) layers through interfacial polymerization. Therefore, ESNF cannot be directly used as the supporting layer of nanofiber-supported thin film composite forward osmosis (NTFC-FO) membrane. However, its advantages of high porosity and large pore size are required for forward osmosis (FO) process. In this work, for the first time, an asymmetric integrated ESNF is constructed by introducing photothermal materials PANI into the supporting layer and using in situ photothermal annealing to controllably reduce the surface roughness and pore size of the support membrane, which not only meets the requirements of interface polymerization to form a good PA layer, but also maintains the high porosity, large pore size and structural stability of the ESNF. With this strategy, the FO membrane with highly selective PA layer and low membrane structural parameter (S) were obtained. The results shows that NTFC-FO membrane shows high water flux of 40.2 L·m−2·h−1 and low reverse salt flux of 4.9 g·m−2·h−1, and specific salt flux of Js/Jw is only 0.12 with deionized water and 1.0 M NaCl solution as the feed solution and draw solution, respectively, and the FO membrane also exhibit excellent rejection to dye wastewater. It can be considered that the asymmetric integrated ESNF supporting layer constructed by the photothermal annealing strategy provides a simple and feasible method for the preparation of high-performance NTFC-FO membranes.

Highly permeable chlorine-resistant forward osmosis membrane by grafting novel sulfonamide monomers

This paper presents a polyamide (PA) thin film composite (TFC) forward osmosis membranes with high chlorine resistance and permeability which were fabricated via interfacial polymerisation employing novel monomers with distinct stable sulfonamide structures. Three different membranes were produced, commonly having a substrate layer made through the phase inversion approach and a PA layer with piperazine (PIP) and tricarbonyl chloride (TMC) while differing in the additive chemical used to build the upper layers (sulfathiazole (ST), 4-aminobenzenesulfonamide (ABSA), and 2-aminosulfamide hydrochloride (AESA)). The cross-linked structures and surfaces of the developed membranes were rigorously assessed, and the infrared spectra revealed that the membranes' surfaces had been successfully grafted with the sulfonamide groups. The flow rates of fabricated membranes with ST, ABSA, and AESA additions increased by 148.2 %, 110.3 %, and 64.7 %, respectively, whereas their reverse salt fluxes decreased by 30.1 %, 26.9 %, and 35.7 %, respectively. 200 ppm NaClO was used to conduct a chlorine stability test under varied pH circumstances (5.0, 7.0, and 9.0), and the findings indicated that the membranes have excellent durability. As the sulfonamide comprises the NH functional groups, the sulfonamide-based membranes were not eroded by chloride ions; hence, the sulfonamide molecules effectively guarded the PA molecular structure from chloride ion damage, thereby increasing PA's tolerance to chloride ions.