PRO Mode Research Articles

Synthesis of novel thin film composite (TFC) forward osmosis (FO) membranes incorporated with carboxylated carbon nanofibers (CNFs)

In this study, thin film composite (TFC) membranes were modified using carbon nanofibers (CNFs) for forward osmosis (FO) applications. Carboxyl functionalization of CNFs was performed to increase their surface hydrophilicity and dispersion in a polysulfone (PSF) matrix as the membrane substrate. Different concentrations of both carboxyl functionalized CNFs (f-CNFs) (0.1, 0.3, and 0.5 wt%,) and raw CNFs (0.3 wt%) were incorporated in the polymer matrix and hydrophilicity, porosity, surface roughness, tensile strength and morphology of the nanocomposite substrates were characterized. The optimal membrane was achieved based on the best performance (higher water flux and lower reverse solute flux). Thereby, the TFC membrane containing 0.3 wt% of the f-CNFs was selected as the optimal membrane. The FO water flux of this membrane was almost 2 times higher than the neat TFC membrane in both FO (active layer facing FS) and PRO (active layer facing DS) modes of operation. Water flux of 13.08 L m− 2 h− 1 and specific reverse solute flux of 0.24 g L− 1 were achieved when 1 M NaCl was used as the draw solution (DS) and Deionized (DI) water was used as the feed solution (FS) under the FO mode. Furthermore, incorporation of the f-CNFs decreased the structural parameter (S) of the TFC membranes leading to lower internal concentration polarization (ICP). From the results, it was concluded that the f-CNFs is a suitable candidate for TFC-FO membranes modification to achieve high membrane performance.

Tetrabutylammonium 2,4,6-trimethylbenzenesulfonate as an effective and regenerable thermo-responsive ionic liquid drawing agent in forward osmosis for seawater desalination

Efficient drawing agents are essential in forward osmosis (FO) for clean water production. Monomeric thermo-responsive ionic liquid (IL) [N4444]2,4,6-MeBnSO3 was thoroughly investigated as a drawing agent in FO. The IL can be safely employed due to its thermal stability and low cytotoxicity. It has a van't Hoff factor i = 1.21, with sufficient ionic strength to generate osmotic pressure ~ 58.92 bars (2 M). FO operations especially under PRO mode demonstrate that 2 M [N4444]2,4,6-MeBnSO3 can induce competitive water flux Jv ~ 12.3 L m−2 h−1 with remarkably low reverse solute flux Js < 0.006 mol m−2 h−1 and specific reverse solute flux Js/Jv ~ 4.5 × 10−4 mol L−1. Using 0.6 M NaCl as feed demonstrates its consistency in desalinating seawater (Jv ~ 3.72 L m−2 h−1, Js ~ 0.004 mol m−2 h−1, and Js/Jv ~ 0.91 × 10−3 mol L−1). After FO, [N4444]2,4,6-MeBnSO3 can be effectively retrieved (~98%) through thermal precipitation at 60 °C, above its cloud point temperature (57 °C). Meanwhile, >99% of the remaining 2% can be recovered through reverse osmosis or membrane distillation to produce water effluents with non-toxic IL concentrations (≪100 mg L−1). Results indicate that thermo-responsive [N4444]2,4,6-MeBnSO3 is a promising alternative reusable drawing agent in FO process.

High performance nanofiber-supported thin film composite forward osmosis membranes based on continuous thermal-rolling pretreated electrospun PES/PAN blend substrates

One of the major challenges facing the practical application of forward osmosis (FO) membranes is the need for high performance. Thus, the fabrication of highly permselective FO membranes is of great importance. The objective of this study was to improve the wettability/hydrophilicity of electrospun nanofiber (ESNF)-based substrates for the fabrication of nanofiber-supported thin film composite (NTFC) membranes for FO application. This study explored the impact of electrospun polyethersulfone/polyacrylonitrile (PES/PAN) nanofibers as the blend support to produce NTFC membranes. The blending of PES/PAN in the spinning dope was optimized. The blending of hydrophilic PAN (0–10 wt%) in PES affects the fiber diameter, hydrophilicity, water uptake, and roughness of the ESNF membrane substrates. Continuous thermal-rolling pretreatment was performed on the ESNF substrates prior to interfacial polymerization for polyamide active layer deposition. The results indicated that the fabricated NTFC membrane achieved significantly greater water flux (L/m2 h) while retaining a low specific salt flux (g/L) compared to traditional TFC membranes. The NTFC membrane flux increased with an increase in PAN content in the ESNF substrate. According to the FO performance results, the NTFC-10 (PES/PAN blend ratio of 90:10) exhibited optimal performance: a high water flux of 42.1 and 52.2 L/m2 h for the FO and PRO modes, respectively, and low specific salt flux of 0.27 and 0.24 g/L for the FO and PRO modes, respectively, using 1 M NaCl as the draw solution. This demonstrated the higher selectivity and water flux achieved by the developed NTFC membranes compared to the traditional TFC membranes.

Improved performance of thin-film composite membrane supported by aligned nanofibers substrate with slit-shape pores for forward osmosis

Substrate construction is considered as the most effective approach to alleviate the internal concentration polarization (ICP) effect, and therefore achieves the excellent performance of resultant thin-film composite (TFC) membrane in forward osmosis (FO) process. In this work, a well-aligned nanofiber substrate was prepared and employed for constructing the high-performance TFC-FO membrane for the first time. The physicochemical properties of the substrate, the micro-structure of polyamide layer and the separation performance of resultant TFC-FO membranes were systematically investigated. Taking advantages of the larger pore size and the better pore interconnectivity of the well-aligned nanofiber substrate, the resultant TFC-FO membrane achieves the best water fluxes of 50.7 and 62.9 LMH, accompanied with the ultralow reverse salt flux in FO and PRO modes, using deionized water feed solution and 1 M NaCl aqueous draw solution. This work may provide a new orientation in developing high-performance TFC membranes.

Molecularly tunable thin-film nanocomposite membranes with enhanced molecular sieving for organic solvent forward osmosis

Thin-film nanocomposites (TFN) functionalized with tunable molecular-sieving nanomaterials have been employed to tailor membranes, with an enhanced permeability and selectivity. Herein, water-soluble hollow cup-like macrocyclic molecules, sulfothiacalix[4]arene (STCAss) and sulfocalix[4]arene (SCA), are ionically bonded into the polyamide network to engineer the molecular-sieving properties of TFN membranes for organic solvent forward osmosis (OSFO). Introducing both STCAss and SCA into the polyamide network not only increases the free volume, but also reduces the thickness of the TFN layers. Combining with their molecularly tunable size of the lower cavities, both STCAss and SCA enable the TFN membranes to size exclusively reject the draw solutes, but only STCAss-functionalized membrane has an ethanol flux doubling the pristine one under the FO and PRO modes in OSFO processes; leading the functionalized polyamide network with remarkable improvements in OSFO performance. This study may provide insights to molecularly functionalize TFN membranes using multifunctional nano-fillers for sustainable separations.

4-aminophenyl sulfone (APS) as novel monomer in fabricating paper based TFC composite for forward osmosis: Selective layer optimization

The potential of filter paper as a substrate material and 4-aminophenyl sulfone (APS) as a novel monomer for TFC fabrication is explored for the first time. A novel polyamide selective layer was developed using APS and trimesoyl chloride by interfacial polymerization, whereas the control TFC was prepared by replacing APS with m-phenylenediamine. Formation of the interfacial selective layer was verified by ATR-IR spectra and the stability of the selective surface coatings was discussed by investigating the monomer interaction. Surprisingly, after polymerization, interconnected, cross-linked structure of two monomers was observed. Desalination studies were carried out in FO mode and PRO mode using NH4HCO3 as a draw solution. Maximum of 90% and 95% rejection was obtained for NaCl and Na2SO4 salts with a flux of 2.51 and 2.17 LMH respectively. The separation efficiency of the prepared TFC membrane was compared against the likes of a commercial TFC membrane under the same conditions.

On modeling for Kerr black holes: basis learning, QNM frequencies, and spherical-spheroidal mixing coefficients

Models of black hole (BH) properties play an important role in the ongoing direct detection of gravitational waves from BH binaries. One important aspect of model based gravitational wave (GW) detection, and subsequent estimation of source parameters, is the low level modeling of information related to perturbed Kerr black holes. Here, we present new phenomenological methods to model the analytically understood GW spectra (quasi-normal mode frequencies), and harmonic structure of Kerr black holes (mixing coefficients between spherical and spheroidal harmonics). In particular, we present a greedy-multivariate-polynomial (GMVP) regression method and greedy-multivariate-rational (GMVR) regression method for the automated modeling of polynomial and rational functions, respectively. GMVP is used to develop a model for QNM frequencies that explicitly enforces consistency with the extremal Kerr limit. GMVR is used to develop a model for harmonic mixing coefficients for the dominant multipoles with . The models for the mixing coefficients are the first of their kind to consider BH spin to vary between −1 and 1, thus naturally connecting the pro and retrograde modes. We discuss the potential use of these models in current and future GW signal modeling.

Metal Ion-Bridged Forward Osmosis Membranes for Efficient Pharmaceutical Wastewater Reclamation.

Membrane performance in separation relies largely on the membrane properties. In this study, metal ions of Cu2+, Co2+, and Fe3+ are used individually as a bridge to develop forward osmosis (FO) membranes via a clean complexation reaction. A metal ion-bridged hydration layer is formed and endows the membrane with a more hydrophilic and smoother surface, higher fouling resistance, and renewability. These improvements make the newly developed membranes superior to the pristine one with better FO performances. The Fe3+-bridged membrane produces water fluxes increased up to 133% (FO mode) and 101% (PRO mode) compared with the pristine membrane against DI water with 0.5-2.0 M MgCl2 as the draw solution. The Fe3+-bridged membrane can efficiently reclaim pharmaceuticals such as trimethoprim and sulfamethoxazole from their dilute solutions with good water permeability and a high pharmaceutical retention. This membrane also exhibits a stronger renewability with water flux restored to 98% of its original value after 20 h experiments in trimethoprim-containing water treatment. This study provides a facile and clean approach to develop highly efficient FO membranes for wastewater reclamation and pharmaceutical enrichment.

Antifouling electrically conductive membrane for forward osmosis prepared by polyaniline/graphene nanocomposite

Forward Osmosis (FO) has been listed as one of the best strategies to combat growing worldwide water scarcity. Not only FO, but all membrane-based technologies are still suffering from unpleasant fouling propensity, hindering their continuous performance in a long-term application. Using polyaniline (PANI) and graphene, herein, we fabricated a novel electro-conductive membrane (graphene/PANI laminated membrane, GPANILM) through laminating by facile pressure-assisted technique onto polyamide-imide (PAI) support layer. To improve the mechanical stability of the fabricated film via crosslinking of PANI with graphene nanosheetsthe membrane was thermal treated in 140 °C for 3 h (GPANILM-140). Both nanocomposite membranes (GPANILM and GPANILM-140) demonstrated excellent mechanical stability and their performances in terms of water permeation (JW) and reverse salt flux (Js) were verified using a regular FO desalination system. Our results showed that the selectivity ratios (Js/Jw) of GPANILM and GPANILM-140 membranes are 0.79 and 0.69 g/L in FO mode (top active layer of nanocomposite was facing to feed solution (FS)) and 0.67 and 0.58 g/L in PRO mode (PAI support layer was facing to FS), respectively. The anti-fouling behaviors of the electro-conductive membranes were investigated by a FS containing alginate as a model organic foulant. By applying 2 V anodic potential, both flux recovery rate (FRR) and fouling resistance were substantially improved in both membranes.

Conductive thin film nanocomposite forward osmosis membrane (TFN-FO) blended with carbon nanoparticles for membrane fouling control

Membrane fouling in forward osmosis (FO) significantly affects water flux and membrane life, which restricts the further development of FO. In this work, carbon nanoparticles were blended in polyethersulfone (PES) to prepare a conductive thin film nanocomposite (TFN) FO membrane to control the membrane fouling in FO processes. The membrane containing 4 wt% carbon exhibited an optimum performance with water flux of 14.0 and 17.2 LMH for FO (active layer for FS) and PRO (active layer for DS) modes, respectively, using DI water as feed solution and 1 M NaCl as draw solution and electrical conductivity of 170.1 mS/m. Dynamic antifouling experiments showed that, compared with no voltage applied, the water flux decline of surface charged TFN-FO membrane was significantly retarded. For CaSO4, BSA and LYS as model contaminants, the water fluxes were improved by 31%, 13% and 7% under the voltages of +1.7 V, −1.7 V and +1.7 V, respectively. Moreover, the charged membrane is more effective in relieving the initial membrane fouling, and contaminant-contaminant interactions mechanism dominates the formation of further membrane fouling processes. Therefore, for contaminants with different charge conditions, customizing membrane surface charges is a feasible and promising approach for controlling membrane fouling in situ method.

Preparation and Characterization of Thin‐Film Nanocomposite Membrane Incorporated with MoO3 Nanoparticles with High Flux Performance for Forward Osmosis

AbstractIn this research, thin film nanocomposite (TFN) membranes were developed using novel polyethersulfone– molybdenum oxide (PES–MoO3) nanocomposite substrate. The effects of MoO3 nanoparticles on the PES substrate morphologies, surface roughness, hydrophilicity, and water permeability were investigated by measuring the water contact angles, scanning electron microscope (SEM) imaging, FT‐IR spectroscopy, and atomic force microscope (AFM) analysis. The MoO3 nanoparticle modified membranes were used in the forward osmosis (FO) process with both PRO mode (the membrane active layer facing draw solution) and FO (the membrane active layer facing feed solution) mode. The results indicated enhanced water permeability of the modified membranes upon the MoO3 addition, leading to significant enhancement in the water flux and the desalination performance.

Tuning the selectivity of thin film composite forward osmosis membranes: Effect of co-solvent and different interfacial polymerization synthesis routes

The selectivity of thin film composite membranes supported by a sulfonated polyetheretherketone (sPEEK) hydrophilized polyethersulfone (PES) layer was enhanced by introducing a more volatile co-solvent, i.e. tetrahydrofuran (THF), and by using an alternative simplified preparation method (SIM), which combines the coagulation step of the phase inversion process and the impregnation of the amine monomer of the interfacial polymerization process. The addition of THF to the polymer casting solutions produced TFC membranes with higher retention but lower permeance. The lowest structural parameter (~383 µm) was found for the TFC membrane with a 10% sPEEK – 10% THF support and led to water fluxes of 23 LMH in PRO mode and 11 LMH in FO mode using a DI water feed solution and a 0.5 M NaCl draw solution. A minimal membrane bottom surface porosity was necessary to accomplish satisfying water fluxes in FO. The SIM method resulted in TFC membranes with comparable selectivity but significantly higher permeance and smoother polyamide selective layers.

Layered double hydroxides (LDHs) as novel macropore-templates: The importance of porous structures for forward osmosis desalination

To minimize the effect of the internal concentration polarization (ICP) in the substrates of the forward osmosis (FO) membranes, higher overall porosity and interconnected pore network was engineered into the substrates by erosion of the three-dimensional layered double hydroxides (LDHs) with “sand rose” morphology. As expected, the substrates showed high porosity and macropore structure in the pore-wall after erosion of the LDH nanoparticles by HCl washing, which potentially promoted connectivity of the finger-like pores in the substrates. Therefore, the promising water flux for as-obtained FO membrane prepared from the typical interfacial polymerization was observed. The obtained TFN7.5-HCl membranes displayed the highest water flux up to 47.2 L m−2 h−1 at PRO mode (1 M NaCl as draw solution and DI-water as feed solution) and the water permeability coefficient reaching 7.29 L m−2 h−1 bar−1 at RO mode (DI-water as feed solution, ΔP = 5 bar). These values were much higher than that of the commercial FO membranes. Counterintuitively, the obtained TFN7.5-HCl membrane disentangled successfully the dilemma of permeability–selectivity, e.g. improved selectivity between water and NaCl was achieved. Thus, it is believed that the designation strategy provides a simple and promising method to fabricate the enabled high-performance FO membranes.

Application of polysaccharide derivatives as novel draw solutes in forward osmosis for desalination and protein concentration

In this study, a series of anionic polyelectrolytes, sodium carboxymethyl dextrans with different molecular weights (CM-dextran-1000/5000/20,000), are facilely prepared via a one-step reaction and applied as novel draw solutes in forward osmosis (FO) process. Various characterizations (FTIR, NMR, conductivity titration and cytotoxicity test) are performed to investigate the chemical structure, degree of substitution (DS) and toxicity of synthesized CM-dextrans. Effects of the solution concentration and solute molecular weight on physicochemical properties (relative viscosity, conductivity and osmotic pressure) of CM-dextran draw solutions as well as their corresponding FO performances are investigated systematically. In comparison with FO performance of 1 M NaCl draw solution (water flux of 22.1 LMH; reverse solute flux of 9.8 gMH), 40 wt% CM-dextran-1000 draw solution shows a higher water flux (24.9 LMH) and a much lower reverse solute flux (0.97 gMH) in PRO mode. Furthermore, CM-dextran solution with the low reverse solute diffusion, nontoxicity, and the high osmotic pressure, can be potentially used as draw solution for desalination and protein enrichment via FO. The theoretical calculation also confirms that FO process shows lower special energy consumption than UF process in the application of protein concentration.

Decreased cross-linking in interfacial polymerization and heteromorphic support between nanoparticles: Towards high-water and low-solute flux of hybrid forward osmosis membrane

Realizing that one main factor affecting development of forward osmosis (FO) membrane was internal concentration polarization (ICP), graphene oxide (GO) with two-dimensional structure and oxidized carbon nanotubes (OCNTs) with one-dimensional structure were linked by oxygen-containing groups to form water channels in the polyamide layer. OCNTs and GO were used for producing reactions among oxygen-containing groups of nanoparticles and polymer chains, and oxygen-containing groups were fully exposed because GO and OCNTs restrained aggregation. Decrease of cross-linking degree for interfacial polymerization layer was confirmed due to reaction from GO/OCNTs/m-phenylene diamine/1,3,5-benzenetricarbonyl trichloride. Moreover, OCNTs formed an appropriate supporting effect for GO to improve hydrophilic properties, which was confirmed by transmission electron microscopy, scanning electron microscope and contact angle. Resulting membrane PA-GO-OCNTs showed high water flux (114 LMH and 84.6 LMH in the PRO (active layer facing draw solution) and FO (active layer facing feed solution) mode, respectively) and low solute flux (5.17 gMH and 3.4 gMH in the PRO and FO mode, respectively) under this condition that 0.5 M NaCl and deionized water were used as draw solution and feed solution respectively. It was worth mentioning that water flux of FO membrane was far higher than that in reported literatures while its structural parameter S was only 203 μm, which led to decrease of ICP.

Evaluation of forward osmosis as a pretreatment process for multi stage flash seawater desalination

The present study evaluates the feasibility of applying forward osmosis (FO) process for the pretreatment of feed solution to a Multi Stage Flash (MSF) desalination plant. For the first time, real brine reject and real seawater were used as the draw solution and the feed solution, respectively in the FO process. The FO pretreatment is expected to dilute the brine reject and reduce the concentration of divalent ions, which are responsible for scale formation on the surface of heat exchanger in the MSF evaporator unit. The FO experiments were performed at different draw solution temperatures ranging between 25 and 40 °C, different draw and feed solutions flowrates and different membrane orientations. A maximum average membrane flux of 22.3 L/m2·h was reported at a draw solution temperature of 40 °C and 0.8 and 2.0 LPM flow rate of draw and feed solutions, respectively. The experimental results also revealed the process sensitivity to the feed solution temperature. It was found that the average membrane flux in the FO process operating at 0.8 and 2 LPM draw and feed solution flow rates, respectively was 16.9 L/m2·h at 25 °C brine temperature but increased to 22.3 L/m2·h at 40 °C brine temperature. These membrane fluxes resulted in 3% and 8.5% dilution of the draw solution at 25 °C and 40 °C temperatures, respectively. The average membrane flux in the FO mode was equal to that in the PRO mode at low flow rates but it was lower than that in the PRO mode at high flow rates of the feed and draw solutions. The outcomes of the study are very promising with regard to membrane flux and dilution of draw solution.

Surface modification of forward osmosis membrane using polyoxometalate based open frameworks for hydrophilicity and water flux improvement

Forward osmosis (FO) has emerged as a novel membrane-based separation method for application for wastewater treatment, seawater desalination,and sustainable energy. A major challenge in the development of forward osmosis process is the lack of a high-efficiency membrane. In this study, a next-generation membrane for FO process was investigated by integrating nanotechnology with membrane science. Incorporation of polyoxometalate based open frameworks (POM-OFs) within the polyamide (PA) active layer of thin film composite (TFC) membrane has generated a new type of thin film nanocomposite (TFN) membrane with significantly enhanced hydrophilicity and permeability properties. The successful incorporation of the POM-OFs in the membranes active layer was investigated through Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) methods. The water flux of POM-OFs modified membrane (TFNw3, containing 500 ppm of POM-OFs) in FO and PRO modes was 29.9 and 41.7 LMH, the value of which was about two times those of TFC membrane. In conclusion, we report a novel forward osmosis membrane for wastewater treatment.

The application of forward osmosis for simulated surface water treatment by using trisodium citrate as draw solute.

In this study, trisodium citrate was used as draw solute in forward osmosis (FO) due to its biodegradability and easy reuse after FO dilution. The effect of operating conditions on FO performance was investigated. The study focused on the long-term flux performance and membrane fouling when surface water was used as feed solution. A water flux of 9.8 LMH was observed using 0.5M trisodium citrate as draw solution in PRO mode. In the long-term FO process, trisodium citrate showed a slight decrease in total flux loss (13.06%) after 20h of operation. The membrane fouling was significantly reduced after a two-step physical cleaning. A considerable flux recovery (> 95%) of the fouled membrane was finally obtained. Therefore, this study proves the superiority of trisodium citrate as draw solution and paves a new way in applying FO directly for surface water reclamation.

High-flux thin film nanocomposite forward osmosis membrane incorporated with blue lemon polyoxometalate based open-framework

In this study a novel type of polyoxometalate based open-frameworks (POM-OFs) by using blue lemon (BL) as POM and tetrabutylammonium bromide (TBAB) as organic cationic coordinating agent successfully synthesized (BL.TBA-OFs) and incorporated in polyamide active layer via interfacial polymerization (IP) to fabricate hydrophilic and high water permeable thin-film nanocomposite (TFN) membranes. The prepared POM-OFs and TFN membranes were fully characterized using physicochemical techniques and the effect of POM-OFs incorporation on TFN membranes performance was investigated using reverse osmosis (RO) and forward osmosis (FO) experiments with regard to the water permeability, salt rejection, and selectivity. The enhancement in hydrophilicity of TFN membranes was confirmed by contact angle measurements, which attributed to the presence of superhydrophilic BL.POM. Water flux of the TFN-BL.TBA-4 membrane (with 400 ppm BL.TBA-OFs incorporation) increased from 18.1 to 28.6 LMH in FO mode, and 23.1 to 36.3 LMH in PRO mode, in comparison with unmodified TFC membrane. Enhancement in separation performance of the modified TFN membranes was attributed to the incorporation of nanopores BL.POM, which create short water pathways. By using sodium alginate as a foulant model the novel modified membrane showed better anti-fouling propensity than the TFC one. This report opens up a new modification route in the achieving of high efficient TFN membranes for FO process.

Functionalized imidazolium ionic liquids promote seawater desalination through forward osmosis

Carboxylate-functionalized imidazolium ionic liquids (CFIMILs) were synthesized via a one-pot quaternization reaction and serve as draw solutes for the first time for forward osmosis (FO) desalination. It provides a solution to simultaneously overcome the problems plaguing the use of pressure-driven membrane technologies to extract water from saline water – low water recovery efficiency and high reverse solute diffusion. The CFIMILs contain a substituted 5-membered imidazole ring and fully ionize into ionic species in water. These characteristics endow CFIMILs with capability of high water recovery efficiency and minimal reverse diffusion in FO. Sodium salt of 1-acetate-2,3-dimethyl imidazole ionic liquid (IL-1) at 0.8 M produces water fluxes of 63.6 LMH (PRO mode) and 29.5 LMH (FO mode) against the DI water feed, greatly outperforming conventional NaCl draw solute and other synthetic draw solutes. Efficient water recovery is achieved using IL-1 for seawater desalination with a water flux 5 times higher than that of NaCl. Particularly, CFIMILs draw solutes have negligible reverse diffusion in FO and are recycled completely via an MD process with good reproducibility when reused to FO, demonstrating great potentials of CFIMILs as a new class of draw solutes for FO water treatment.