Reverse Salt Flux Research Articles

Computational Fluid Dynamics Modeling of Pressure-Retarded Osmosis: Towards a Virtual Lab for Osmotic-Driven Process Simulations.

Pressure-Retarded Osmosis (PRO) is an osmotically driven membrane-based process that has recently garnered significant attention from researchers due to its potential for clean energy harvesting from salinity gradients. The complex interactions between mixed-mode channel flows and osmotic fluxes in real PRO membrane modules necessitate high-fidelity modeling approaches. In this work, an efficient CFD framework is developed for the 3D simulation of osmotically driven membrane processes. This approach is based on a two-way coupling between a CFD solver, which captures external concentration polarization (ECP) effects, and an analytical representation of internal concentration polarization (ICP). Consequently, the osmotic water flux and reverse salt flux (RSF) can be accurately determined, accounting for all CP effects without any limitations on the geometrical complexity of the membrane chamber or its flow mode/regime. The proposed model is validated against experimental data, showing good agreement across various PRO case studies. Additionally, the model's flexibility to simulate other types of osmotically driven processes such as forward osmosis (FO) is examined. Thus, the contributions of ECP and ICP effects in local osmotic pressure drop along the membrane chamber are comprehensively compared for FO and PRO modes. Finally, the capability of the CFD model to simulate a lab-scale PRO module is demonstrated across a range of Reynolds numbers from low-speed laminar up to turbulent flow regimes.

Forward osmosis membrane with lightweight functionalised multiwall carbon nanotube nanofillers

ABSTRACT Thin-film nanocomposite (TFN) membranes with a polyamide (PA) active layer modified with carbon nanotubes (CNTs) hold promise for water desalination and wastewater reuse via forward osmosis (FO). We hypothesise that modifying the PA active layer with hydroxyl-functionalised multi-wall carbon nanotubes (f-MWCNTs) will enhance the water flux of the FO membrane while maximising salt rejection. TFN membranes were modified using in situ interfacial polymerisation, with varying f-MWCNT mass content to minimise agglomeration. These modified FO membranes are designated as CTFN-x, where x represents the mass content of f-MWCNTs, ranging from 0.001%, CTFN-1 to 0.008%, CTFN-8 (w/v). The surface properties of CTFN-x were characterised using electron microscopy, atomic force microscopy, and molecular spectroscopy. IR spectroscopic data confirm the successful adherence of f-MWCNTs as a bridging agent between the 1,3-phenylenediamine (MPD) and trimesoyl chloride (TMC) polymers, preserving FO membrane integrity. The CTFN-4 FO membrane shows the highest water flux (29 LMH) and the lowest reverse salt flux (2.90 gHM), attributed to preferential water flow channels in the f-MWCNTs. The integration of f-MWCNTs into the active layer improved water flux, reduced reverse salt flux, and enhanced the antifouling properties of FO membranes.

Fertilizer-driven FO and MD integrated process for shale gas produced water treatment: Draw solution evaluation and PAC enhancement

It is a great challenge for effective treatment of shale gas produced water (SGPW), a typical industrial wastewater with complex composition. Single forward osmosis (FO) or membrane distillation (MD) process has been widely used for desalination of SGPW, with membrane fouling not well addressed. Fertilizer draw solution (DS) with high osmotic pressure is less likely to cause FO fouling and can be used for irrigation. An integrated process using fertilizer-driven FO (FDFO) and MD process was proposed for the first time for SGPW treatment, and characteristics of fertilizer DS and powdered activated carbon (PAC) enhancement were assessed. The DS using KCl and (NH4)2SO4 had high MD fluxes (36.8–38.8 L/(m2·h)) and low permeate conductivity (below 50 μS/cm), increasing the contact angle of the MD membrane by 113 % than that without FO, while the DS using MgCl2 and NH4H2PO4 produced a lower reverse salt flux (0.9–3.2 g/(m2·h)). When diluted DS was treated using PAC, the MD permeate conductivity was further reduced to 35 μS/cm without ammonia, and the membrane hydrophobicity was maintained to 71–83 % of the original. The mechanism of the FDFO-MD integrated process for mitigating MD fouling and improving permeate quality was analyzed, providing guidance for efficient SGPW treatment.

Polyvinyl alcohol-modified β-cyclodextrin incorporated forward osmosis membranes with good chlorine resistance

The applications of β-cyclodextrin (β-CD) in chlorine-resistant membranes have always faced the challenge of agglomeration at high concentrations. In this study, polyvinyl alcohol (PVA) modified β-CD was used as a monomer to prepare forward osmosis (FO) membranes with high chlorine resistance. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), automated contact angle meter (CAM), electrodynamic analyzer (EA), X-ray photoelectron spectroscopy (XPS), and true color confocal microscopy (CSM) have been used to characterize the physicochemical properties of the FO membrane. The agglomerated β-CD affected the formation of the selective layer, resulting in reduced water fluxes ranging from 12.4 L m−2 h−1 to 1.75 L m−2 h−1. The modified TFC-PVA-β-CD FO membrane had a complete, defect-free selective layer, and water flux of 16.75 L m−2 h−1 at 1 M NaCl as a draw solution. FTIR spectra showed that the absorption peak intensity of the carbonyl (CO) group generated from β-CD and 1,3,5-Benzene tricarbonyl trichloride (TMC) increased after PVA modification. After 6 hours of chlorination, the reverse salt flux of the thin film composite (TFC) FO membranes abided by the following order: TFC (80.35 g m−2 h−1) > TFC-β-CD (60.95 g m−2 h−1) > TFC-PVA-β-CD (12.45 g m−2 h−1). The results indicated that the PVA effectively promotes uniform dispersion of β-CD. More chlorine-resistant ester bonds (-COO-) were formed in the TFC-PVA-β-CD FO membrane, so it possessed good chlorine resistance. This study provides a green, simple, and environmentally economical method for the preparation of chlorine-resistant FO membranes.

ABPBI-based hollow fiber membranes for forward osmosis (FO) possessing low reverse salt flux

The poly(2,5-Benzimidazole), known for its excellent thermochemical stability, was evaluated as a membrane material for forward osmosis. The dope in methane sulfonic acid was used to make hollow fiber membranes. The availability of bound MSA in HFMs was compared with its neutral form. Aqueous solutions of two common salts reported for FO (NaCl and MgCl2) were used as a draw solution at varying concentrations. The performance was determined in terms of water flux and reverse salt flux. The long-term performance of the membrane was assessed. The heat pretreatment of membranes was beneficial in offering low reverse salt flux, a crucial parameter in FO. The heat treatment at 350 °C exhibited excellent performance of low-RSF, irrespective of the draw solute used. The presence of MSA in the membrane matrix was found to be beneficial. Present HFMs exhibited reverse salt flux as low as 0.003 mol m−2 h−1 using 2 mol L−1 MgCl2 as a draw solution. The water flux of present membranes was lower than that of reported FO-membranes, which is attributable to the larger thickness of the present membranes. The findings will be used to make ABPBI-based membranes in thin form to elevate the fluxes and their practical applicability.

Bilayer cellulosic FO membrane developed by polydopamine and nanochitosan through layer by layer coating process

A highly efficient bilayer cellulose acetate forward osmosis (FO) membrane was developed using polydopamine (PDA) and chitosan nanoparticles (CsNP) through layer by layer coating process and characterized using DLS, FESEM, AFM, EDX, and static contact angle. The use of CsNP and PDA led to an improvement in chemical properties, surface hydrophilicity, and structural parameter. The experimental tests for both RO and FO experiments were carried out to calculate structural parameter (it decreased from 0.59 mm for neat CA to 0.37 mm for CA-PDA/CsNP2) of membranes. Also, the salt rejection and water permeability of membranes were tested in RO mode using 40 mM NaCl, while the water flux and reverse salt flux of membranes were analyzed in FO test. The CA-PDA/CsNP2 membrane with 0.6 wt.% of CsNP in the coating solution not only showed a high water permeation flux about 21.23 LMH for 2 mM NaCl but also decreased its reverse salt flux from 7.08 to 4.52 gMH. According to the fouling test results, the normalized water flux of the neat membrane declined from 1 to about 0.65 while it was higher than 0.85 for CA-PDA/CsNP2 which represents an improvement in the antifouling property. This improvement was mainly due to an increase in the hydrophilicity of the coated membrane and the electrostatic repulsion among the foulant and surface of CA-PDA/CsNP2. The results showed that the fabricated CA-PDA/CsNP2 membrane shows a high potential application in the FO process and is more competitive than other existing FO membranes.

Zr-BTB nanosheets assist in optimizing the structure of forward osmosis membranes to enhance the lithium concentration performance

Recently, low-energy forward osmosis (FO) technology has been employed in the lithium concentration stage during the extraction of lithium from brine sources. The interlayer FO membrane is renowned for its exceptional structural characteristics; however, challenges remain in selecting suitable interlayer materials and exploring their control mechanisms on amine monomers. As interlayer materials, traditional 3D nanomaterials are prone to detachment, while traditional 2D materials without micropores can increase the transmission resistance of water molecules. This study introduces a novel FO membrane utilizing Zr-BTB nanosheets with 5.4 Å micropores as the interlayer material. Based on detection and simulation calculations, it was found that the increase in steric hindrance and interaction forces jointly slowed the diffusion of amine monomers in the presence of the Zr-BTB interlayer. This results in a thinner separation layer, facilitating water transport. The interlayer also plays crucial roles in preventing defective pore formation in the separation layer and assisting in intercepting salt ions. The Zr-BTB interlayer membrane exhibited a water flux of 29.14 L m−2 h−1 and a reverse salt flux of 0.16 g m−2 h−1, which are superior to those of many FO membranes reported in the field. The prepared membrane also has excellent performance in lithium concentration applications, and its separation mechanism was explored by MD simulations.

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.

Effects of substrate (track-etched filter) properties on the performance of forward osmosis membranes

Highly permeable membranes can improve the validity of water treatment using forward osmosis (FO) membranes. This study aims to identify the effects of substrate (track-etched (TE) filter) properties on the permeability of FO membranes. The polyamide active layer properties of three types of TE filters with similarly-sized pore diameters (0.2 μm) were observed to be equivalent regardless of the substrate porosity (13.7%–15.8 %) and substrate thickness (10–25 μm). Under the same fabrication protocol using 1.5 wt% m-phenylenediamine (MPD) solution with 0.25 wt% sodium dodecyl sulfate (SDS) addition, the increased porosity of the TE filter increased water flux. This suggested that further reduction in thickness and increase in porosity can enhance the water flux. The addition of SDS to an MPD solution was crucial in maximizing the water flux of TE filter-based FO membranes, and the other approaches (no surfactant addition or the addition of Tween80 or hexadecyltrimethylammonium bromide) produced lower water flux. The optimized fabrication protocol presented the highest water flux of 43 L/m2h and reverse salt flux of 10 g/m2h with the draw (1.0 M NaCl) and feed (pure water) solutions. This study determined the best approach for forming a highly permeable PA active layer on TE filters.

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.

Defect-Healed Carbon Nanomembranes for Enhanced Salt Separation: Scalable Synthesis and Performance.

Carbon nanomembranes (CNMs), with a high density of subnanometer channels, enable superior salt separation performance compared to conventional membranes. However, defects that occur during the synthesis and transfer processes impede their technical realization on a macroscopic scale. Here, we introduce a practical and scalable interfacial polymerization method to effectively heal defects while preserving the subnanometer pores within CNMs. The defect-healed freestanding CNMs show an exceptional performance in forward osmosis (FO), achieving a water flux of 105 L m-2 h-1 and a specific reverse salt flux of 0.1 g L-1 when measured with 1 M NaCl as draw solution. This water flux is 10 times higher than that of commercially available FO membranes, and the reverse salt flux is 70% lower. Through successful implementation of the defect-healing method and support optimization, we demonstrate the synthesis of fully functional, centimeter-scale CNM-based composite membranes showing high water permeance and a high salt rejection. Our defect-healing method presents a promising pathway to overcome limitations in CNM synthesis, advancing their potential for practical salt separation applications.

A feasibility study of hybrid forward osmosis-solar evaporation process using melamine sponge loaded with polypyrrole (PPy@MS) solar evaporator for desalination of brackish water

The application of the osmotic pressure-driven forward osmosis (FO) process is limited due to the high costs for regeneration and replacement of draw solution. A hybrid FO-solar evaporation (SE) hybrid process was systematically investigated to produce fresh water from desalination of brackish water. The melamine sponge loaded with polypyrrole (PPy@MS) composite material was synthesized by loading light-absorbing polypyrrole (PPy) into a network of melamine sponge (MS) substrates. As a solar evaporator, PPy@MS material showed high light absorption, water evaporation, and anti-pollution abilities in the FO-SE process. Feasibility for operating the hybrid desalination process was studied in terms of solar evaporation rate, salinity tolerance, hydrophilicity, and mechanical strength of PPy@MS, and desalination performance, including water flux, ion removal, reverse salt flux, and membrane fouling. Characterization results indicated that PPy@MS performed a high interfacial molecular transformation, solar energy accessing ability, salt-tolerance, and mechanical stability in a long-term FO-SE operation, achieving an evaporation rate up to 2.80 kg·m−2·h−1 (1 sun, 1 h) and ion removal rate of 99.9 %. A maximum evaporation flux of 17.4 L·m−2·h−1 was monitored in the FO-SE process using 2 M NaCl as the draw solution (FO film area: 5 cm2). Solar-driven evaporation via PPy@MS was able to assist the continuous operation of the FO-SE process with high water flux. This work proposes a novel sustainable hybrid FO-SE technology for FO desalination of brackish water and other saline water bodies.

Membrane performance of pressure-retarded osmosis using simulated hydroxide-based CO2-captured draw solutions

This study proposes a novel hybrid process that integrates direct air capture (DAC) and pressure-retarded osmosis (PRO) to address high water and energy demands of the DAC process and achieve simultaneous decarbonization and energy production. To explore the PRO performance in this hybrid process, membrane fouling behaviors were investigated by employing forward osmosis membranes in the PRO mode with various Na- and K-based draw solutions that simulated hydroxide-based CO2-captured solutions. Especially calcium (Ca2+) and alginate were dosed into the draw solutions as representatives of scaling precursor and organic foulants during long-term DAC-PRO operation respectively. The results revealed that (1) the presence of calcium in the NaHCO3 and KHCO3 draw solutions formed CaCO3 precipitates, whose amounts, morphologies, and particle size were associated with the dosed Ca2+ concentration and alkali solution type. (2) Higher calcium amounts in the NaHCO3 and KHCO3 draw solutions promoted more deposition of rhombohedral CaCO3 crystals on the membrane, leading to a lower water flux (Jw) and higher reverse salt flux (Js) due to increased hydraulic resistance and cake-layer-enhanced concentration polarization. (3) Dosing calcium (40 mM) into a mixture of HCO3- and CO32- draw solution resulted in accumulation of irregular-shape CaCO3 crystals on the membrane and an increase of Jw, possibly relating to the increased membrane hydrophilicity due to decreased solubility of the solute at a higher pH level. (4) The addition of alginate into calcium-dosed (40 mM) draw solutions did not influence Jw and Js but increased deposited foulants. This suggests that deposited alginate may loosely attach to CaCO3 crystals, instead of creating a dense fouling layer by bridging with Ca2+.

Microplastics fouling mitigation in forward osmosis membranes by the molecular assembly of sulfobetaine zwitterion

Forward osmosis (FO) membranes have potential for the efficient water and wastewater treatment applications. However, their development has faced significant challenges due to their fouling propensity. In this study, FO membranes modified with sulfobetaine zwitterions (i.e., [2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide) were fabricated and used for the first time to address microplastic (MP) fouling issue. Water flux, reverse salt flux (RSF), fouling, and flux recovery were evaluated for the membranes loaded with different quantities of the zwitterions ranging from 0.25 % to 2 %. The developed membranes were tested over 49 h with feed solutions containing polyethylene MPs and bovine serum albumin (BSA) to evaluate their fouling resistance. The synergistic effects of the two foulants indicated that the MPs were the primary cause of fouling. The presence of BSA effectively reduced the blocking effect of MPs and therefore lowers overall fouling. Additionally, improved water flux, structural parameter (S), and RSF were reported for the modified membranes. The zwitterion's unique structure with hydrophilic groups (CO and OSO) resulted in high flux recovery rates of over 90 % for all modified membranes within only 30 min of physical cleaning upon fouling tests. The results demonstrate the high potential of the modification method for targeting the removal of MPs in TFC-based membranes.

Systematic investigation of MAX phase (Ti3AlC2) modified polyethersulfone membrane performance for forward osmosis applications in desalination

The current work presented an in-depth investigation of the design and fabrication of thin film membranes for desalination applications by forward osmosis (FO). This includes manipulating the substrate membrane structure aiming to optimize the final thin film composite membrane characteristics. In this context, the MAX phase (Ti3AlC2) as a 2D material has been harnessed to impart novel desirable traits on the prepared membrane. MAX phase has been impregnated in two disparate concentrations and three different scenarios including the substrate membrane and the polyamide layer in both the aqueous and organic phases during the interfacial polymerization. Membranes were comprehensively characterized by a series of experimental tools and methodologies including Atomic Force Microscopy, Scanning Electron Microscopy, Contact Angle, Fourier-transform infrared spectroscopy, pore size and porosity. Results disclosed that substrate membrane structure has a pivotal impact on final TFC/TFN membrane performance. Besides, the MAX phase (Ti3AlC2) could significantly enhance the morphological characteristics of the membrane and ultimately the performance in terms of water flux and reverse salt flux based on the content and the way impregnated. The permeation properties of the composite membranes were significantly superior to the pure PES membrane and the mean pore size also increased with the addition amount of MAX phase (Ti3AlC2) increased.

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.

Preparation of chitosan/citral forward osmosis membrane via Schiff base reaction with enhanced anti-bacterial properties

In this study, hydrogels generated by the Schiff base reaction between citral and chitosan (CS) were used for the first time to improve the anti-bacterial property of forward osmosis (FO) membranes. The composite membranes were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Water contact angle (WCA), Zeta potential and confocal laser scanning microscopic (CLSM). In the FO filtration experiment, the membrane performance of TFC-1 with 1 M sodium chloride solution as the draw solution and deionized water as the feed solution was the best, with the water flux of 25.54 ± 0.7 L m−2 h−1 and the reverse salt flux of 4.7 ± 0.4 g m−2 h−1. Although the hydrogel coating produced a certain hydraulic resistance, the flux of the modified membrane was only reduced by about 8%, compared with the unmodified membrane. However, the anti-bacterial property (Pseudomonas aeruginosa) and anti-fouling properties (bovine serum protein and lysozyme protein) of the modified membranes were improved, showing good antibacterial properties (99%) and flux recovery rate (over 90%). The modified method has the advantages of easy access to raw materials, simple operation and no risk of secondary pollution, which can effectively reduce the cost of chemical cleaning and extend the service life of the membrane. The modification of membrane by chitosan-based hydrogel is a promising option in the field of membrane anti-bacteria.

Forward osmosis TFN membrane prepared by adjusting a PDA/GO-Fe3+-TA interlayer on porous CTA substrates

Cellulose triacetate (CTA) is commonly used as the material for forward osmosis (FO) membranes due to its good chlorine resistance, fouling resistance and wide availability. In this work, the implications of various solvents on the appearance and desalination capacity of CTA FO membranes were systematically investigated. CTA membranes with large pore size and high porosity were constructed by using spray-modified non-solvent induced phase separation (s-NIPS). The water flux of CTA membranes fabricated by s-NIPS using DMSO as the solvent was up to 34.4 L m−2h−1, which was 5.6 times higher than HTI commercial membranes, and the reverse salt flux was only 10.9 g m−2h−1. A poly-dopamine (PDA) /graphene oxide (GO) -Fe3+-tannic acid (TA) interlayer was introduced to adjust the cross-linking degree of the polyamide (PA). And thin-film nanocomposite (TFN) membranes (PA-PDA/GO-Fe3+-TA-CTA) were fabricated successfully. The water flux was 35.8 L m−2h−1 and the reverse salt flux decreased to 5.84 g m−2h−1. These experimental results propose an emerging approach to design and develop high performance FO membranes in a rational way.