Synthesis and characterization of thin film nanocomposite forward osmosis membrane with hydrophilic nanocomposite support to reduce internal concentration polarization

Experimental investigation and comparison of PBI/MWCNT and PSF/MWCNT membranes for recovering water from RO reject of brackish water by FO

The performances of polybenzimidazole (PBI) and polysulfone (PSF) membranes for recovering water from reverse osmosis (RO) reject of brackish water through forward osmosis (FO) were assessed and compared. Non-functionalised multi-walled carbon nanotubes (MWCNT) were added to the membrane casting solutions, with concentrations ranging from 0 to 3 wt%. The experiment was conducted for eight samples using RO reject of brackish water as the feed solution (FS) and 2 M analytical grade MgCl2 as the draw solution (DS). The hydrophilicity, water permeability, salt rejection rate (Rs), water flux (WF) and porosity of the membranes improved with increasing MWCNT content up to 2 wt%. Also, the structural parameter, salt permeability and reverse solute flux decreased. PBI/MWCNT2 wt% exhibited the best performance among the membranes tested compared with porosity of 70 ± 4 %, structural parameter of 0.36 ± 0.2 μm, and Rs of 93.5 %. In contrast with the pristine PBI membrane, an average water flux enhancement of 15 % and 49 % was observed for the FS and DS sides, respectively, for PBI/MWCNT2 wt%. It is evident from the results that including MWCNT improves the performance of both membranes, with better relative performance for PBI membranes than PSF membranes.

Effect of titanium oxide/reduced graphene (TiO2/rGO) addition onto water flux and reverse salt diffusion thin-film nanocomposite forward osmosis membranes

Thin-film nanocomposite (TFN) forward osmosis (FO) membranes have attracted significant attention due to their potential for solving global water scarcity problems. In this study, we investigate the impact of titanium oxide (TiO2) and titanium oxide/reduced graphene (TiO2/rGO) additions on the performance of TFN-FO membranes, specifically focusing on water flux and reverse salt diffusion. Membranes with varying concentrations of TiO2 and TiO2/rGO were fabricated as interfacial polymerizing M-phenylenediamine (MPD) and benzenetricarbonyl tricholoride (TMC) monomers with TiO2 and its reduced graphene composites (TiO2/rGO). The TMC solution was supplemented with TiO2 and its reduced graphene composites (TiO2/rGO) to enhance FO performance and reverse solute flux. All MPD/TMC polyamide membranes are characterized using various techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurements. The results demonstrate that incorporating TiO2/rGO into the membrane thin layer improves water flux and reduces reverse salt diffusion. In contrast to the TFC membrane (10.24 L m-2h-1 and 6.53 g/m2 h), higher water flux and higher reverse solute flux were detected in the case of TiO2and TiO2/rGO-merged TFC skin membranes (18.81 and 24.52 L m-2h-1 and 2.74 and 2.15 g/m2 h, respectively). The effects of TiO2 and TiO2/rGO stacking on the skin membrane and the performance of TiO2 and TiO2/rGO skin membranes have been thoroughly studied. Additionally, being investigated is the impact of draw solution concentration.

Fabrication of PES Modified by TiO2/Na2Ti3O7 Nanocomposite Mixed-Matrix Woven Membrane for Enhanced Performance of Forward Osmosis: Influence of Membrane Orientation and Feed Solutions

Water treatment is regarded as one of the essential elements of sustainability. To lower the cost of treatment, the wastewater volume is reduced via the osmotic process. Here, mixed-matrix woven forward osmosis (MMWFO) PES membranes modified by a TiO₂/Na₂Ti₃O₇ (TNT) nanocomposite were fabricated for treating water from different sources. Various techniques were used to characterize the TNT nanocomposite. The crystal structure of TNT is a mix of monoclinic Na₂Ti₃O₇ and anorthic TiO₂ with a preferred orientation of (2-11). The SEM image shows that the surface morphology of the TNT nanocomposite is a forked nano-fur with varying sizes regularly distributed throughout the sample. The impact of TNT wt.% on membrane surface morphologies, functional groups, hydrophilicity, and performance was investigated. Additionally, using distilled water (DW) as the feed solution (FS), the effects of various NaCl concentrations, draw solutions, and membrane orientations on the performance of the mixed-matrix membranes were tested. Different water samples obtained from various sources were treated as the FS using the optimized PES/TNT (0.01 wt.%) MMWFO membrane. Using textile effluent as the FS, the impact of various NaCl DS concentrations on the permeated water volume was investigated. The results show that the MMWFO membrane generated with the TNT nanocomposite at a 0.01 wt.% ratio performed better in FO mode. After 30 min of use with 1 M NaCl and various sources of water as the FS, the optimized MMWFO membrane provided a steady water flow and exhibited antifouling behavior. DW performed better than other water types whenever it was used owing to its greater flow (136 LMH) and volume reduction (52%). Tap water (TW), textile industrial wastewater (TIWW), gray water (GW), and municipal wastewater (MW) showed volume reductions of 41%, 34%, 33%, and 31.9%, respectively. Additionally, when utilizing NaCl as the DS and TIWW as the FS, 1 M NaCl resulted in more permeated water than 0.25 M and 0.5 M, yet a higher volume reduction of 41% was obtained.

Integration of Porous Nanomaterial-Infused Membrane in UF/FO Membrane Hybrid for Simulated Osmosis Membrane Bioreactor (OsMBR) Process

This study explored the use of a combination of hydrothermal and sol-gel methods to produce porous titanium dioxide (PTi) powder with a high specific surface area of 112.84 m²/g. The PTi powder was utilized as a filler in the fabrication of ultrafiltration nanocomposite membranes using polysulfone (PSf) as the polymer. The synthesized nanoparticles and membranes were analyzed using various techniques, including BET, TEM, XRD, AFM, FESEM, FTIR, and contact angle measurements. The membrane's performance and antifouling properties were also assessed using bovine serum albumin (BSA) as a simulated wastewater feed solution. Furthermore, the ultrafiltration membranes were tested in the forward osmosis (FO) system using a 0.6-weight-percent solution of poly (sodium 4-styrene sulfonate) as the osmosis solution to evaluate the osmosis membrane bioreactor (OsMBR) process. The results revealed that the incorporation of PTi nanoparticles into the polymer matrix enhanced the hydrophilicity and surface energy of the membrane, resulting in better performance. The optimized membrane containing 1% PTi displayed a water flux of 31.5 L/m²h, compared to the neat membrane water value of 13.7 L/m²h. The membrane also demonstrated excellent antifouling properties, with a flux recovery of 96%. These results highlight the potential of the PTi-infused membrane as a simulated osmosis membrane bioreactor (OsMBR) for wastewater treatment applications.

Internal Concentration Polarization in the Polyamide Active Layer of Thin-Film Composite Membranes

A free-standing polyamide (PA) film is fabricated via in situ release from a thin-film composite (TFC) membrane achieved through the removal of the polysulfone support. The structure parameter S of the PA film is measured to be 24.2 ± 12.6 μm, which is about 87-fold of its film thickness. A significant decline in water flux of the PA film from an ideal forward osmosis membrane is observed. We find that the decline is predominantly influenced by the internal concentration polarization (ICP) of the PA film based on our experimental measurements and theoretical calculations. We propose that the asymmetric hollow structures of the PA layer with dense crusts and cavities may be the underlying cause of the occurrence of the ICP. More importantly, the structure parameter of the PA film can be reduced and its ICP effect can be mitigated by tuning its structures with fewer and shorter cavities. Our results for the first time provide experimental evidence to prove that the PA layer of the TFC membrane has the ICP effect, which could potentially provide fundamental insights into the influence of structural properties of PA on the membrane separation performance.

Enhancing Physiochemical Substrate Properties of Thin-Film Composite Membranes for Water and Wastewater Treatment via Engineered Osmosis Process

The commercial thin-film composite (TFC) nanofiltration (NF) membrane is unsuitable for engineered osmosis processes because of its thick non-woven fabric and semi-hydrophilic substrate that could lead to severe internal concentration polarization (ICP). Hence, we fabricated a new type of NF-like TFC membrane using a hydrophilic coated polyacrylonitrile/polyphenylsulfone (PAN/PPSU) substrate in the absence of non-woven fabric, aiming to improve membrane performance for water and wastewater treatment via the engineered osmosis process. Our results showed that the substrate made of a PAN/PPSU weight ratio of 1:5 could produce the TFC membrane with the highest water flux and divalent salt rejection compared to the membranes made of different PAN/PPSU substrates owing to the relatively good compatibility between PAN and PPSU at this ratio. The water flux of the TFC membrane was further improved without compromising salt rejection upon the introduction of a hydrophilic polydopamine (PDA) coating layer containing 0.5 g/L of graphene oxide (PDA/GO0.5) onto the bottom surface of the substrate. When tested using aerobically treated palm oil mill effluent (AT-POME) as a feed solution and 4 M MgCl2 as a draw solution, the best performing TFC membrane with the hydrophilic coating layer achieved a 67% and 41% higher forward osmosis (FO) and pressure retarded osmosis (PRO) water flux, respectively, compared to the TFC membrane without the coating layer. More importantly, the coated TFC membrane attained a very high color rejection (>97%) during AT-POME treatment, while its water flux and reverse solute flux were even better compared to the commercial NF90 and NF270 membranes. The promising outcomes were attributed to the excellent properties of the PAN/PPSU substrate that was coated with a hydrophilic PDA/GO coating and the elimination of the thick non-woven fabric during TFC membrane fabrication.

Forward Osmosis Membrane: Review of Fabrication, Modification, Challenges and Potential

Forward osmosis (FO) is a low-energy treatment process driven by osmosis to induce the separation of water from dissolved solutes/foulants through the membrane in hydraulic pressure absence while retaining all of these materials on the other side. All these advantages make it an alternative process to reduce the disadvantages of traditional desalination processes. However, several critical fundamentals still require more attention for understanding them, most notably the synthesis of novel membranes that offer a support layer with high flux and an active layer with high water permeability and solute rejection from both solutions at the same time, and a novel draw solution which provides low solute flux, high water flux, and easy regeneration. This work reviews the fundamentals controlling the FO process performance such as the role of the active layer and substrate and advances in the modification of FO membranes utilizing nanomaterials. Then, other aspects that affect the performance of FO are further summarized, including types of draw solutions and the role of operating conditions. Finally, challenges associated with the FO process, such as concentration polarization (CP), membrane fouling, and reverse solute diffusion (RSD) were analyzed by defining their causes and how to mitigate them. Moreover, factors affecting the energy consumption of the FO system were discussed and compared with reverse osmosis (RO). This review will provide in-depth details about FO technology, the issues it faces, and potential solutions to those issues to help the scientific researcher facilitate a full understanding of FO technology.

Design Strategies for Forward Osmosis Membrane Substrates with Low Structural Parameters-A Review

This article reviews the many innovative strategies that have been developed to specifically design the support layers of forward osmosis (FO) membranes. Forward osmosis (FO) is one of the most viable separation technologies to treat hypersaline wastewater, but its successful deployment requires the development of new membrane materials beyond existing desalination membranes. Specifically, designing the FO membrane support layers requires new engineering techniques to minimize the internal concentration polarization (ICP) effects encountered in cases of FO. In this paper, we have reviewed several such techniques developed by different research groups and summarized the membrane transport properties corresponding to each approach. An important transport parameter that helps to compare the various approaches is the so-called structural parameter (S-value); a low S-value typically corresponds to low ICP. Strategies such as electrospinning, solvent casting, and hollow fiber spinning, have been developed by prior researchers-all of them aimed at lowering this S-value. We also reviewed the quantitative methods described in the literature, to evaluate the separation properties of FO membranes. Lastly, we have highlighted some key research gaps, and provided suggestions for potential strategies that researchers could adopt to enable easy comparison of FO membranes.

Surface modification of thin film composite forward osmosis membrane using graphene nanosheets for water desalination

In this study, the main motivation of this work is desalination of water for irrigation arid area such as Sidri- Baba basins- south Sinai, Egypt. Also, the novelty of this work is modification of TFC surface membrane by mix of HA, DA and GO to get high performance of FO technique. Interfacial polymerization was employed to modify a thin-film composite (TFC) membrane for forward osmosis (FO) applications; moreover, graphene oxide (GO) nanosheets (GONs), a dopamine solution (DA), and naturally accessible humic acid (HA) were modified on a polyethersulfone (PES) substrate. The effects of the different quantities of GO, HA, and DA on the membrane surfaces, as well as their various cross-sectional morphologies and FO-desalination capabilities, were investigated. The integrated TFC membrane containing appropriate GO, HA, and DA blends outperformed the control membrane, obtaining high water flux, and high salt rejection. Furthermore,.

Boosting the Performance of Nanofiltration Membranes in Removing Organic Micropollutants: Trade-Off Effect, Strategy Evaluation, and Prospective Development

In view of the high risks brought about by organic micropollutants (OMPs), nanofiltration (NF) processes have been playing a vital role in advanced water and wastewater treatment, owing to the high membrane performance in rejection of OMPs, permeation of water, and passage of mineral salts. Though numerous studies have been devoted to evaluating and technically enhancing membrane performance in removing various OMPs, the trade-off effect between water permeance and water/OMP selectivity for state-of-the-art membranes remains far from being understood. Knowledge of this effect is significant for comparing and guiding membrane development works toward cost-efficient OMP removal. In this work, we comprehensively assessed the performance of 88 NF membranes, commercialized or newly developed, based on their water permeance and OMP rejection data published in the literature. The effectiveness and underlying mechanisms of various modification methods in tailoring properties and in turn performance of the mainstream polyamide (PA) thin-film composite (TFC) membranes were quantitatively analyzed. The trade-off effect was demonstrated by the abundant data from both experimental measurements and machine learning-based prediction. On this basis, the advancement of novel membranes was benchmarked by the performance upper-bound revealed by commercial membranes and lab-made PA membranes. We also assessed the potentials of current NF membranes in selectively separating OMPs from inorganic salts and identified the future research perspectives to achieve further enhancement in OMP removal and salt/OMP selectivity of NF membranes.

Construction of PPSU-MoS2/PA-MIL-101(Cr) Membrane with Highly Enhanced Permeance and Stability for Organic Solvent Nanofiltration

Membranes with excellent separation performance and stability are needed for organic solvent nanofiltration in industrial separation and purification processes. Here we reported a newly PPSU-MoS₂/PA-MIL-101(Cr) composite membrane with high permeance, good selectivity and stability. The MIL-101(Cr) was introduced in the polyamide (PA) layer via the PIP/TMC interfacial polymerization process on a microporous PPSU-MoS₂ substrate. At a small doping amount of 0.005 wt% MIL-101(Cr), the PPSU-MoS₂/PA-MIL-101(Cr) composite membrane exhibited a high methanol permeance of 12.03 L m⁻² h⁻¹ bar⁻¹, twice higher than that of the pristine membrane without sacrificing selectivity. Furthermore, embedding MIL-101(Cr) notably enhanced the stability of the composite membrane, with permeance only decreasing by 8% after a long time operation of 80 h (pristine membrane decreased by 25%). This work demonstrated a composite membrane modified by MIL-101(Cr) with superior separation performance, which provides potential application of MOF materials for high-performance membranes in organic solvent nanofiltration and a theoretical foundation for future research in studying MOF’s influence on membrane properties.

Preparation, characterization, and performance of PES/GO woven mixed matrix nanocomposite forward osmosis membrane for water desalination

Mixed matrix woven forward osmosis (MMWFO) membranes made of polyethersulfone (PES)/graphene oxide nanosheets (GO NSs) were made by inserting varying wt% ratios of GO NSs (zero to 0.1 wt%) into the PES matrix. A coated woven fabric material was used to cast the membrane polymer solution. The physical characteristics and chemical structures of the produced PES/GO MMWFO membranes were studied, including contact angle, hydrophilicity, porosity, tortuosity, function groups, chemical and crystallographic structures, nanomorphologies, and surface roughness. The performance of the prepared PES/GO FO membranes for water desalination was evaluated in terms of pure water flux (J_w), reverse salt flux (J_s), and salt rejection (SR). The hydrophilicity and porosity of the FO membrane improved with the addition of GO NSs, as did water permeability due to the development of multiple skin-layer structures with greater GO NS loading. These GO NSs establish shortcut pathways for water molecules to move through, reducing support layer tortuosity by three times, lowering support layer structural features, and minimizing internal concentration polarization (ICP). The PES/0.01 wt% GO MMWFO membrane with a total casting thickness of 215 μm and 1 M NaCl concentration had the best performance, with the highest J_w (114.7 LMH), lowest J_s (0.03 GMH), and lowest specific reverse solute flux (J_s/J_w = 0.00026 g L⁻¹), as well as a more favorable structural parameter (S = 149 μm). The performance of our optimized membrane is significantly better than that of the control woven commercial cellulose triacetate (CTA) FO membrane under optimal FO conditions. As the NaCl concentration increased from 0.6 to 2 M, J_w increased from 105 to 127 LMH which is much higher than the J_w of the commercial one (7.2 to 15 LMH). Our FO membranes have an SR of 99.2%@0.65 M NaCl, which is significantly greater than that of the CTA membrane.

Optimized FO membrane showed water flux 8.5 times that of commercial CTA membrane, salt rejection of 99.2%, and the lowest reported specific reverse solute flux (0.00026 g L⁻¹).

Effect of Nanopatterning on Concentration Polarization during Nanofiltration

Membranes used for desalination still face challenges during operation. One of these challenges is the buildup of salt ions at the membrane surface. This is known as concentration polarization, and it has a negative effect on membrane water permeance and salt rejection. In an attempt to decrease concentration polarization, a line-and-groove nanopattern was applied to a nanofiltration (NF) membrane. Aqueous sodium sulfate (Na2SO4) solutions were used to test the rejection and permeance of both pristine and patterned membranes. It was found that the nanopatterns did not reduce but increased the concentration polarization at the membrane surface. Based on these studies, different pattern shapes and sizes should be investigated to gain a fundamental understanding of the influence of pattern size and shape on concentration polarization.

Preparation of a thin-film nanocomposite forward osmosis membrane for the removal of organic micro-pollutants from aqueous solutions

In this study, a thin-film nanocomposite forward osmosis (TFN FO) membrane was synthesized. The properties and structures of membranes were evaluated for the removal of three organic micro-pollutants from synthetic and real industrial wastewater samples. Laboratory scale fabrication thin-film nanocomposite forward osmosis (FO) membranes composed of a support layer and an active layer. The former was constructed by adding different weight ratios of polyethylene glycol 400 (PEG-400) (0-8 wt.%), polysulfone (PSf), and 1-methyl, 2-pyrrolidone via the phase inversion process, while the latter was synthesized by the incorporation of different weight ratios of graphene oxide (GO) (0-0.012 wt.%), M-phenylenediamine, and 1, 3, 5-benzene trichloride into polyamide layer through the interfacial polymerization reaction. In comparison with thin-film composite (TFC) membranes, the TFN membranes revealed higher hydrophilicity, porosity, water permeability, water flux and salt rejection and lower internal concentration polarization (ICP), reverse salt flux and specific reverse salt flux. The TFN membrane containing 0.008% GO in the active layer and 4% PEG 400 in the support layer exhibited maximum water flux (34.3 LMH) and rejection rate of benzene, phenol and toluene (97%, 84%, and 91%, respectively). The results revealed that the TFN-FO membranes possess a promising potential to improve the water flux and wastewater treatment.

Hybrid forward osmosis/membrane distillation integrated with anaerobic fluidized bed bioreactor for advanced wastewater treatment

Forward osmosis (FO)-membrane distillation (MD) process was integrated with anaerobic fluidized bed bioreactor (AFBR) to advance wastewater treatment. Low removal efficiency of nutrients such as ammonia nitrogen was improved significantly by combining FO-MD process with AFBR. The MD membrane was applied to concentrate the draw solution (DS) which can be diluted by FO filtration. By using 1 M of NaCl as DS, about 80% of ammonia nitrogen was further removed by the FO membrane while the phosphorous was removed almost completely (99%). However, the accumulation of ammonia nitrogen in DS and the reverse salt flux through the FO membrane was unavoidable. Nevertheless, combining MD membrane produced excellent removal efficiency yielding only 4 and 5.6 mg/L of ammonia nitrogen and chemical oxygen demand (COD) in MD permeate, respectively at 15 ℃ of transmembrane temperature. Alternatively, there is the possibility that the FO-MD process can be superior to concentrate resources such as nitrogen and phosphorous present in AFBR. The reverse salt flux from DS into AFBR bulk suspension did not show adverse effects on the performances of bioreactor with respect to COD removal efficiency, conductivity and methane production during operational period. Deposit of the fouling layer on FO membrane was also observed, but the fouling on MD membrane was not severe probably because crystallization rate could be retarded by diluting the DS during FO filtration.

Recent development of pressure retarded osmosis membranes for water and energy sustainability: A critical review

With the goal of zero-liquid discharge and green energy harvest, extraction of abundant green energy from saline water via pressure retarded osmosis (PRO) technology is a promising but challenging issue for water treatment technologies to achieve water and energy sustainability. Development of high performance PRO membranes has received increased concerns yet still under controversy in practical applications. In this review, a comprehensive and up-to-date discussion of some key historical developments is first introduced covering the major advances of PRO engineering applications and novel membranes especially made in recent years. Then the critical performance indicators of PRO membranes including water flux and power density are briefly discussed. Subsequently, sufficient discussion on four performance limiting factors in PRO membrane and process is presented including concentration polarization, reverse solute diffusion, membrane fouling and mechanical stability. To fully address these issues, an updated insight is provided into recent major progresses on advanced fabrication and modification techniques of novel PRO membranes featuring enhanced performance with different configurations and materials, which are also reviewed in detail based on the viewpoint of design rationales. Afterwards, antifouling strategies and engineering applications are critically introduced. Finally, conclusions and future perspective of PRO membrane for practical operation are briefly discussed.

Constructing dense and hydrophilic forward osmosis membrane by cross-linking reaction of graphene quantum dots with monomers for enhanced selectivity and stability

This paper reports a novel thin-film nanocomposite (TFN) membrane with a dense, flat, and hydrophilic polyamide (PA) layer. The atypical PA structure was obtained by the cross-linking reaction of graphene oxide quantum dots containing amino groups (NH₂-GOQDs) with triacyl chloride and polyamide oligomers. And the resulting TFN membrane showed a flat (small-scale ridge structure) and smooth surface. Meanwhile, the introduction of oxygen-containing and amino functional groups increased surface hydrophilicity. The reaction of amino groups on the NH₂-GOQDs with acid chloride groups and the carboxyl groups (in the linear part of the polyamide) enhanced the degree of cross-linking of the PA layer, forming a compact surface. Owning to the dense surface structure, excellent hydrophilicity, and small water transmission distance, the optimized TFN membrane exhibited an enhanced water flux of 26.57 L⋅m^-2⋅h^-1 with a low reverse salt flux of 6.0 g⋅m^-2⋅h^-1. Furthermore, nano-indentation/scratch results showed the interface adhesion between substrate and PA layer was improved due to the physical anchoring of NH₂-GOQDs in the substrate. And in the long-term FO test, the TFN membrane showed stable selectivity. This work proves that the targeted structural design of the PA layer at the nanoscale will have a positive impact on desalination field.

A Critical Review on Thin-Film Nanocomposite Membranes with Interlayered Structure: Mechanisms, Recent Developments, and Environmental Applications

The separation properties of polyamide reverse osmosis and nanofiltration membranes, widely applied for desalination and water reuse, are constrained by the permeability-selectivity upper bound. Although thin-film nanocomposite (TFN) membranes incorporating nanomaterials exhibit enhanced water permeance, their rejection is only moderately improved or even impaired due to agglomeration of nanomaterials and formation of defects. A novel type of TFN membranes featuring an interlayer of nanomaterials (TFNi) has emerged in recent years. These novel TFNi membranes show extraordinary improvement in water flux (e.g., up to an order of magnitude enhancement) along with better selectivity. Such enhancements can be achieved by a wide selection of nanomaterials, ranging from nanoparticles, one-/two-dimensional materials, to interfacial coatings. The use of nanostructured interlayers not only improves the formation of polyamide rejection layers but also provides an optimized water transport path, which enables TFNi membranes to potentially overcome the longstanding trade-off between membrane permeability and selectivity. Furthermore, TFNi membranes can potentially enhance the removal of heavy metals and micropollutants, which is critical for many environmental applications. This review critically examines the recent developments of TFNi membranes and discusses the underlying mechanisms and design criteria. Their potential environmental applications are also highlighted.

ON/OFF Switchable Nanocomposite Membranes for Separations

Although water, air, and other resources are abundant on earth, they have been subjected to strict environmental regulations. This is because of their limitation of availability for human consumption. In the separation industry, the membrane system was introduced to increase the amount of resources available to mankind. Experts used an easy-to-use polymeric material to design several membranes with porous structures for wastewater treatment, gas separation, and chemical removal; consequently, they succeeded in obtaining positive results. However, past polymeric membranes exhibited a chronic drawback such that it was difficult to simultaneously augment the permeate flux and improve its selectivity toward certain substances. Because of the trade-off relationship that existed between permeability and selectivity, the membrane efficiency was not very good; consequently, the cost-effectiveness was significantly hindered because there was no other alternative than to replace the membrane in order to maintain its initial characteristics steadily. This review begins with the introduction of a polymer nanocomposite (PNC) membrane that has been designed to solve the chronic problem of polymeric membranes; subsequently, the stimuli-responsive PNC membrane is elucidated, which has established itself as a popular topic among researchers in the separation industry for several decades. Furthermore, we have listed the different types and examples of stimuli-responsive PNC membranes, which can be switched by external stimuli, while discussing the future direction of the membrane separation industry.

Forward Osmosis: A Critical Review

The use of forward osmosis (FO) for water purification purposes has gained extensive attention in recent years. In this review, we first discuss the advantages, challenges and various applications of FO, as well as the challenges in selecting the proper draw solution for FO, after which we focus on transport limitations in FO processes. Despite recent advances in membrane development for FO, there is still room for improvement of its selective layer and support. For many applications spiral wound membrane will not suffice. Furthermore, a defect-free selective layer is a prerequisite for FO membranes to ensure low solute passage, while a support with low internal concentration polarization is necessary for a high water flux. Due to challenges affiliated to interfacial polymerization (IP) on non-planar geometries, we discuss alternative approaches to IP to form the selective layer. We also explain that, when provided with a defect-free selective layer with good rejection, the membrane support has a dominant influence on the performance of an FO membrane, which can be estimated by the structural parameter (S). We emphasize the necessity of finding a new method to determine S, but also that predominantly the thickness of the support is the major parameter that needs to be optimized.

Investigation of water and salt flux performances of polyamide coated tubular electrospun nanofiber membrane under pressure

In this study, a novel osmotic membrane was developed by polyamide (PA) coating on the tubular electrospun nanofiber (TuEN) support membrane. Water and reverse salt flux properties of the obtained membrane were investigated by applying pressure in addition to the osmotic forces. Surface characterization of the membrane was carried out by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) analyses and flux performance tests were performed in both cross flow and submerged membrane setups. Applying pressure from the feed to the concentrate side had significant effects on the water and salt fluxes. Higher pressure differences between the feed and concentrate sides resulted in unexpected high water fluxes up to 500 Lm^-2h^-1 (LMH). Besides, the pressure helps to transfer the salt content of feed water into the concentrate side, differently from the osmotic process preventing the salinity build-up at the feed side. PA coated TuEN membrane operated under pressure will exhibit a favorable solution in water/wastewater treatment applications, especially for membrane bioreactors (MBR) in terms of preventing salt accumulation in the bioreactor, decreasing the membrane fouling, increasing the volume of product water, and enabling the concentrate management.

Graphene Oxide Incorporated Forward Osmosis Membranes With Enhanced Desalination Performance and Chlorine Resistance

In this work, grapheme oxide (GO) nano-sheets were synthesized and dispersed in the aqueous phase for the interfacial polymerization (IP) process to develop a new type of thin-film composite (TFC) membranes for forward osmosis (FO) applications. The effects of the GO concentrations on the membrane surfaces and cross-sectional morphologies and FO desalination performances of the as-prepared TFC membranes were investigated systematically. Compared with the control membrane, the optimal GO-incorporated TFC membrane displayed higher water flux, less specific reverse solute flux (SRSF) and lower structure parameter. Moreover, the optimized membrane showed 75.0 times higher chlorine resistance than the control membrane. In general, these new type of membranes could be an effective strategy to fabricate high-performance FO membranes with good desalination performance and chlorine resistance.