TECHNICAL FIELD

[0001] The present disclosure relates to a separation membrane, and more particularly relates to a dual-layer membrane and a process of preparation of the dual-layer membrane.

BACKGROUND

[0002] A membrane separation process includes separation of contaminants by passing a contaminated fluid via a separation membrane with a pore size of about 100 nanometers to 10 micrometers. Conventional membranes used for microfiltration and ultrafiltration membrane, often suffer from drawbacks such as pore-blocking due to low porosity, and consequent cake layer formation, scaling, and biofouling. This results in inefficient removal of the particles from the fluid (rejection), a reduction in the net water flux, a high fouling rate, high applied pressure (AP-1-10 bar), and a short lifetime for the membrane.

[0003] Generally, polymeric membranes are outstandingly effective in wastewater treatment, but the hydrophobicity of some polymers is a serious impediment because their hydrophobic surface causes fouling. Further, mechanical strength which is a very important factor for the separation processes could be affected by membrane hydrophobicity. Certain other conventional methods include the addition of cross-linkers or inorganic pore-forming agents such as lithium chloride, and sodium nitrate into the membrane to improve properties of the conventional membranes; however, these membranes are associated with an increased manufacturing cost. Hence, there is a need for an efficient separation membrane that may substantially reduce or eliminate the above limitations.

SUMMARY

[0004] In one aspect of the present disclosure, a dual-layer membrane is disclosed. The dual-layer membrane includes a first layer including at least one of polysulfone (PSU) nanofibers, polyphenylene (PPSU) nanofibers, polyethersulfone (PES) nanofibers, and a combination thereof; and a second layer including a sulfone polymer mixed with at least one pore-forming additive. The second layer is cast on the first layer and is held together by hydrophilic interactions. [0005] In an embodiment, the sulfone polymer is at least one selected from a group including PSU, PES, PPSU, and a combination thereof.

[0006] In an embodiment, the first layer includes the PES nanofibers, and the second layer includes the PES polymer mixed with at least one pore-forming additive.

[0007] In an embodiment, the at least one pore-forming additive is selected from a group including diethylene glycol (DEG); ethylene glycol (EG), dimethylacetamide (DMA), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), polyethylene oxide (PEG), and a combination thereof.

[0008] In an embodiment, the at least one pore-forming additive is PEG.

[0009] In an embodiment, the PES nanofibers have a diameter of 190-200 nanometers

(nm).

[0010] In an embodiment, the dual-layer membrane includes a thickness of 240 micrometers (pm).

[0011] In an embodiment, the dual-layer membrane has a pure water flux capacity of about 140-160 liter per square meter per hour (L.m’ ² .h ^-1 ) at a pressure of about 3 bars.

[0012] In an embodiment, the dual-layer membrane includes a water contact angle of about 55°-65° at a pressure of about 3 bars.

[0013] In an embodiment, the dual-layer membrane has a tensile strength of about 10- 12 megapascals (Mpa) and an elongation at break of about 20-22%.

[0014] In an embodiment, the dual-layer membrane has a pore radius of about 0.055- 0.06 pm, and a porosity of about 75-80%.

[0015] In another aspect of the present disclosure, a method of making the dual-layer membrane is disclosed. The method includes preparing at least one of PSU nanofibers, PPSU nanofibers, PES nanofibers, or a combination thereof to form the first layer. The method further includes blending a sulfone polymer with at least one pore-forming additive, to form a second layer. The method further includes casting the second layer on the first layer via hydrophilic interactions to obtain the dual-layer membrane.

[0016] In some embodiments, the sulfone polymer is at least one selected from a group including PSU, PES, PPSU, or a combination thereof.

[0017] In some embodiments, the first layer includes PES nanofibers, and the second layer includes the PES polymer with the at least one pore-forming additive.

[0018] In some embodiments, the at least one pore-forming additive is selected from a group including DEG; EG, DMA, PEG, PVP, PEO, and a combination thereof. [0019] In an embodiment, the method of preparing the PES nanofibers is disclosed. The method includes dissolving a hydrophobic PES polymer in an organic solvent to obtain a first mixture. In an embodiment, the organic solvent includes N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), or a combination thereof. The method further includes fabricating the first mixture with an electrospinning instrument to obtain electrospun PES nanofibers. The method further includes oxidizing the electrospun PES nanofibers to obtain hydrophilic PES nanofibers. In an embodiment, the electrospun PES nanofibers are oxidized with at least one of persulfate salts (ammonium, potassium, and sodium); aluminum nitrate; barium peroxide, hydrogen peroxide, bleach, permanganate, ozone, dichromate, or combinations thereof. The method further includes compacting the hydrophilic PES nanofibers to ensure a homogenous surface, and to obtain the PES nanofibers of reduced pore size.

[0020] In an embodiment, a method of preparing the second layer is disclosed. The method includes dissolving the PES polymer in an organic solvent. In an embodiment, the organic solvent is NMP. The method further includes blending the PES polymer with the at least one pore-forming additive.

[0021] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0022] A better understanding of embodiments of the present disclosure (including alternatives and/or variations thereof) may be obtained with reference to the detailed description of the embodiments along with the following drawings, in which:

[0023] FIG. 1 is a perspective view of a dual-layer membrane, according to an embodiment of the present disclosure;

[0024] FIG. 2 is a schematic flow diagram of a method of making the dual-layer membrane, according to an embodiment of the present disclosure;

[0025] FIG. 3 is an exemplary flow diagram of preparation and characterization of the dual-layer membrane, according to an embodiment of the present disclosure;

[0026] FIG. 4 is a schematic diagram of preparation of the dual-layer membrane, according to an embodiment of the present disclosure; [0027] FIG. 5 is a scanning electron microscope (SEM) image of the dual-layer membrane, according to an embodiment of the present disclosure;

[0028] FIG. 6 is a graph comparing a pure water flux and a water contact angle with a PEG/PES membrane and the dual-layer membrane, respectively, according to an embodiment of the present disclosure;

[0029] FIG. 7 is a graph comparing a tensile strength and elongation-at-break of the PEG/PES membrane and the dual-layer membrane, respectively, according to an embodiment of the present disclosure;

[0030] FIG. 8 is a perspective view depicting rejection of bovine serum albumin (BSA) with the dual-layer membrane, according to an embodiment of the present disclosure; and [0031] FIG. 9 is a graph depicting filtration stability of the PEG/PES membrane and the dual-layer membrane on the BSA at an operating pressure of 3 bars, respectively, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0032] Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts. Moreover, references to various elements described herein, are made collectively or individually when there may be more than one element of the same type. However, such references are merely exemplary in nature. It may be noted that any reference to elements in the singular may also be construed to relate to the plural and vice- versa without limiting the scope of the disclosure to the exact number or type of such elements unless set forth explicitly in the appended claim.

[0033] The terminologies and/or phrases used herein are for the purpose of describing particular embodiments only and are not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0034] As used herein, “porosity” refers to a void volume fraction of a membrane and is defined as the volume of the pores divided by the total volume of the membrane.

[0035] Embodiments of the present disclosure refer to a dual-layer membrane, otherwise referred to as a ‘membrane’. The dual-layer membrane of the present disclosure includes a first layer and a second layer, each having distinctly different pore structures that are held together by hydrophilic interactions. The first layer of the membrane includes PES nanofibers that impart support and mechanical strength to the membrane and the second layer of the membrane is made up of PEG/PES polymer that provides improved hydrophilicity, and selectivity to the membrane. By combining the two layers of the duallayer membrane, by a simple, cost-effective process, significant gain was achieved in terms of filtration efficiency, and mechanical robustness. The membrane prepared by a method of the present disclosure shows high hydrophilicity, high porosity, and significant mechanical strength, thereby circumventing the drawbacks such as low porosity, a cake layer formation, scaling, and fouling, of the prior art. The membrane finds application in water treatment processes. Although the description herein refers to the use of the membrane for separating protein from water, it may be understood by a person skilled in the art, that aspects of the present disclosure may be directed towards the separation of water and enzymes, hormones, interferon, vaccines, bacteria, and viruses, as well.

[0036] Referring to FIG. 1, a perspective view of a membrane 100 is illustrated. The membrane 100 includes two layers - a first layer 102 and a second layer 104, that are held together by hydrophilic interactions. Since the membrane 100 is made up of two layers, the membrane 100 is otherwise referred to as the dual-layer membrane 100. The first layer 102 includes at least one of polysulfone (PSU) nanofibers, polyphenylene (PPSU) nanofibers, polyethersulfone (PES) nanofibers, and a combination thereof. In the present disclosure, the first layer (102) includes the PES nano fibers. In an embodiment, the first layer 102 may include a plurality of sub-layers, each sub-layer including the PES nanofibers. The PES nanofibers are prepared from a PES polymer that is hydrophobic in nature. However, most membrane applications require a hydrophilic surface on the surface of a membrane, hence hydrophilization of the PES polymer is critical for its use in membrane separation applications, for example, water treatment. The PES nanofibers in the present disclosure are obtained by using electrospinning the first mixture, followed by chemical oxidation, and compacting the hydrophilic PES nanofibers to form the PES nanofibers. In an embodiment, the PES nanofibers have a diameter of 190-200 nm.

[0037] The second layer 104 includes a sulfone polymer mixed with at least one poreforming additive. In an embodiment, the sulfone polymer is at least one selected from a group including PSU, PES, PPSU, and a combination thereof. In an embodiment, the second layer (104) includes the PES polymer mixed with at least one pore-forming additive. In an embodiment, the second layer 104 includes one or more sub-layers, each sub-layer including the blend of PES polymer mixed with one or more pore-forming additives. In an embodiment, each sub-layer of the second layer 104 may have same or different pore sizes with same or different porosity. The purpose of the pore-forming additive is to increase the porosity of the PES polymer. In an embodiment, the pore-forming additive can include at least one but are not limited to, polyethylene oxide polymer (PEO), diethylene glycol (DEG); ethylene glycol (EG), dimethylacetamide (DMA), polyamides, polyacrylic amides, polyurethanes, polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP). In some embodiments, the pore-forming additive may also include diethylene glycol, ethylene glycol, dimethylacetamide. In another embodiment, at least one pore-forming additive is PEG. Although the description herein refers to the use of PEG as the pore-forming additive, other pore-forming additives known in the art may be used as well in preparation of the second layer 104 of the membrane 100. In an embodiment, the concentration of the PEG in the second layer 104 can be adjusted based on the desired degree of porosity.

[0038] Further, the second layer 104 is cast on the first layer 102, and the first layer 102 and the second layer 104 are held together by hydrophilic interactions. In other words, the PEG/PES polymer of the second layer 104, and the PES nanofibers of the first layer 102 are held together by hydrophilic interactions. The PEG/PES polymer imparts increased porosity to the membrane 100 owing to the addition of the pore-forming additive, PEG in the second layer 104, while the PES nanofibers in the first layer 102 impart improved mechanical strength and robustness to the membrane 100. Also, since the first layer 102, and the second layer 104 of the membrane 100 are held together by hydrophilic interactions, the combination of two layers in the membrane 100 yields improved selectivity and mechanical strength in comparison to single-layer membranes used in the art. The dual-layer membrane 100 has a thickness of 240 pm.

[0039] Referring to FIG. 2, a schematic flow diagram of a method 200 of making the dual-layer membrane 100 is illustrated. The order in which the method 200 is described is not intended to be construed as a limitation, and any number of the described method steps can be combined in any order to implement the method 200. Additionally, individual steps may be removed or skipped from the method 200 without departing from the spirit and scope of the present disclosure.

[0040] At step 202, the method 200 includes preparing at least one of PSU nanofibers, PPSU nanofibers, PES nanofibers, or a combination thereof to form the first layer 102. In an embodiment, the nanofibers may be prepared by dissolving a hydrophobic PES polymer in an organic solvent to obtain the first mixture. In some embodiments, the organic solvent includes N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), or a combination thereof. In an embodiment, the organic solvent is NMP. Further, the first mixture is fabricated with an electrospinning instrument 400 to obtain electrospun PES nanofibers. The electrospun PES nanofibers are oxidized to obtain hydrophilic PES nanofibers. In some embodiments, the method 300 further includes oxidizing the electrospun PES nanofibers with one or more of persulfate salts (ammonium, potassium, and sodium), aluminum nitrate; barium peroxide, hydrogen peroxide, bleach, permanganate, ozone, dichromate, or combinations thereof. In an embodiment, the electrospun PES nanofibers are oxidized with ammonium persulfate. Moreover, the hydrophilic PES nanofibers were compacted with a help of a heat press machine.

[0041] At step 204, the method 200 includes blending the sulfone polymer with one or more additives, to form the second layer 104. In some embodiments, the sulfone polymer is at least one selected from a group including PSU, PES, PPSU, or a combination thereof. In some embodiments, the first layer includes PES nanofibers, and the second layer includes the PES polymer with at least one pore-forming additive. In some embodiments, at least one pore-forming additive is selected from the group including DEG; EG, DMA, PEG, PVP, PEG, and a combination thereof. In an embodiment, the pore-forming additive is PEG. In an embodiment, the concentration of the pore-forming additive can be adjusted based on the desired degree of porosity.

[0042] In an example, the additive is a pore-forming additive. In an embodiment, the PES polymer is dissolved in an organic solvent prior to blending the PES polymer with one or more pore-forming additives. In an embodiment, the organic solvent is NMP. In another embodiment, the concentration of the solvent can be adjusted based on the desired degree of porosity.

[0043] At step 206, the method 200 includes casting the second layer 104 on the first layer 102 via hydrophilic interactions to obtain the dual-layer membrane 100. The second layer 104 may be obtained by a phase inversion method. In some embodiments, the first and second layers 102, 104 may be obtained by any method known or used in the art. EXAMPLES

[0044] The following examples describe and demonstrate exemplary embodiments of the dual-layer membrane 100 described herein. The examples are provided solely for the purpose of illustration and are not to be construed as limitations of the present disclosure, as many variations thereof are possible without departing from the spirit and scope of the present disclosure.

Example 1

Materials Required

[0045] PES polymer, NMP or DMF solvents, ammonium persulfate ((NH4)2S20s), and PEG.

Example 2: Fabrication and characterization of the dual-layer membrane 100.

[0046] Referring to FIG. 3, an exemplary flow diagram of preparation of the dual-layer membrane 100 is illustrated. 22-28 gram (g) of the PES polymer was dissolved in DMF- NMP solvent in a ratio of (1:1) to (2:1) and was magnetically stirred at room temperature to obtain the first mixture. Further, the first mixture with fabricated by using the electrospinning instrument 400 to obtain the electrospun PES nanofibers. Subsequently, the electrospun PES nanofibers were oxidized with 1-4 g of ammonium persulfate to obtain the hydrophilic PES nanofibers. The hydrophilic PES nanofibers were compacted via a carver heated press to obtain the PES nanofibers to form the first layer 102. The second layer 104, prepared separately, by dissolving 12-17 g of the PES polymer in 90-100 g NMP solvent, to obtain a solution. The concentration of the PES polymer in the organic solvent was adjusted based on the desired porosity of the second layer 104. Further, 1-4 g pore-forming additive, polyethylene glycol (PEG) was added to the solution to obtain a PES/PEG solution. The PES/PEG polymer forms the second layer 104, was further cast on the first layer 102. The membrane 100 prepared by the method 200 was further characterized by analytical techniques to confirm fabrication of the membrane 100.

Example 3: Process of preparation of the PES nanofibers.

[0047] Referring to FIG. 4, a schematic diagram of preparation of the dual-layer membrane 100 is illustrated. The PES nanofibers were prepared using the electro spinner instrument 400. The electro spinner instrument 400 includes a control unit 402 including a distance controller 404, a voltage controller/power supply 406, a flow rate controller 408, a rotational speed controller 410. The electro spinner instrument 400 further includes an injection pump, a syringe, a needle 412, a collector plate 414. Parameters used in the electro spinner instrument 400 are shown in table 1.

[0048] Table 1. Parameters used by the electro spinner instrument

[0049] The first mixture flows at a rate of 0.5 to 1.5 milliliter per hour. The first mixture (the PES polymer dissolved in the organic solvent) is passed in the form of a droplet to needle 412 via the injection pump. An electric field is created between the tip of the needle 412 and the collector plate 414 by applying 20 to 25 kilovolts (kV) in the electro spinner instrument 400. A Taylor cone is formed once a surface tension of the droplet is overcome by the force of the electric field. Distortion of the droplet leads to an electrically charged jet ejection that moves towards the collector plate 414.

[0050] Finally, the PES nanofibers are obtained by rotating the collector plate 414 at 200-240 rotations per minute (rpm). Further, the PES nanofibers were collected on a glass plate 416. The second layer 104 was cast on the first layer 102 via a phase inversion method. This was done by pouring PEG/PES polymer over the PES nanofibers using a glass rod 418. The glass plate 416 was dipped in container 420 including water. The NMP solvent dissolves in water leaving behind the dual-layer membrane 100.

Results and discussion

[0051] SEM images reveal a uniform coating of the second layer 104 over the first layer 102 can be seen in FIG. 5. The uniform coating of the second layer 104 over the first layer 102 is evident in hydrophilic -hydrophilic interactions. The diameter of the PES nanofibers was about 190-200 nm. The membrane 100 was further evaluated in terms of mechanical properties, permeability co-efficient, and membrane morphology based on BSA rejection.

[0052] The pure water permeability, also known as the pure water flux, is defined as the volume of water that passes through a membrane per unit time, per unit area and per unit of transmembrane pressure. This parameter is indicative of initial performance of the membrane. Poor pure water flux values suggest that the membrane might have been damaged or compacted due to pore blocking, thereby reducing water passage. Referring to FIG. 6, a graphical representation of a pure water flux of a PEG/PES single layer membrane and the dual-layer membrane 100, respectively, at an operating pressure of 3 bars, is illustrated. The pure water flux was measured by the following equation (1). where V is a permeate volume, A is the dual-layer membrane 100 surface area, t is filtration time. From the FIG. 6, it can be observed that the pure water flux for the PES/PEG membrane was about 115-120 L.nT ² .h ^-1 , while the dual-layer membrane 100 demonstrated a pure water flux capacity of about 140-160 L.nT ² .h ^-1 at a pressure of about 3 bars.

[0053] A difference of more than 35 L.nT ² .h ^-1 , i.e., about 24% increase, in the pure water flux was observed with the dual-layer membrane 100 in comparison to the PEG/PES membrane. The difference in the pure water flux could be attributed to the increased porosity and improved hydrophilic property of the dual-layer membrane 100 in comparison to the PEG/PES membrane.

[0054] Further, the water contact angle refers to an angle formed between a surface and a line tangent to an edge of a drop of the water. The water contact angle determines the wetting ability of a membrane. In other words, the water contact angle is indicative of the degree of hydrophilicity of the membrane. A greater water contact angle suggests that the membrane is hydrophobic, while a lesser water contact angle is indicative of hydrophilic property. As can be observed from the FIG. 6, the dual-layer membrane 100 was found to be more hydrophilic with a water contact angle of about 55-65°, compared with the PEG/PES membrane with a water contact angle of about 60-70°. The high pure water flux and reduction in the water contact angle confirm hydrophilization or fabrication of the dual-layer membrane 100.

[0055] Referring to FIG. 7, a graphical representation of tensile strength and elongation- at-break of the PEG/PES membrane and the dual-layer membrane 100, respectively, is illustrated. These mechanical properties, i.e., the tensile strength and the elongation at break are indicative of the strength of a membrane. Tensile strength is the largest force that a membrane can withstand before breaking down. Therefore, higher tensile strength suggests a long shelf life of the membrane. As can be observed in the FIG. 7, tensile strength of 10- 12 Mpa was observed with the dual-layer membrane 100, about 3 MPa with the PEG/PES membrane, and 4 MPa with the PES nanofibers. Large differences in tensile strength of the dual-layer membrane 100 were observed in comparison to the PEG/PES membrane or the PES nanofibers. The tensile strength of the dual-layer membrane is greater than the combination of the tensile strength demonstrated by each individual layer of the membrane 100. The increased tensile strength can be attributed due to the presence of strong hydrophilic interactions between the first layer 102 and the second layer 104 of the duallayer membrane 100, because of which a greater force is required to break the membrane before the membrane is completely damaged.

[0056] Elongation at break is yet another important mechanical parameter that is indicative of the mechanical strength or toughness of the membrane 100. Elongation at break is the percentage increase in length that a membrane will achieve before breaking. As can be observed from the FIG. 7, the percentage elongation was found to be maximum with the membrane 100, in comparison to the PES/PEG membrane or the PES nanofibers, suggesting superior mechanical properties of the membrane 100. The membrane 100 includes an elongation at break of about 20-22%. Further, the porosity, and the pore size for each individual layer of the membrane 100 (i.e., PEG/PES layer and the PES nanofiber layer), is presented in Table 2. The membrane 100 includes a pore radius of about 0.055-0.06 pm, and a porosity of about 75-80%.

[0057] Table 2. Porosity and pore size of membranes.

[0058] The performance of the membrane 100 was evaluated for its ability to reject bovine serum albumin (BSA). Referring to FIG. 8, a perspective view depicting rejection of the BSA with the dual-layer membrane 100 is shown. Although the description herein refers to separation of the BSA from water, aspects of the present disclosure may be directed towards the separation of molecules having a size equivalent to that of the BSA, or any other hydrophobic molecules as well with the membrane 100. BSA is one of the critical potential proteins in pharmaceutical and biotechnology research. Its primary biological function has been associated with its lipid-binding properties and is responsible for diabetes and several auto-immune disorders. Given the physical and chemical properties of the BSA, especially its high molecular weight, the membrane 100 was used to evaluate its performance in the separation of BSA from water. For this purpose, BSA protein is dissolved in water. Since the size of the BSA protein is larger than the pore size of the second layer 104, only water passes through the dual-layer membrane 100 leaving behind the BSA protein. However, the hydrophobic nature of the BSA protein resists it to pass through the dual-layer membrane 100. Furthermore, the hydrophilic nature of the dual-layer membrane 100 allows filtration of the present mixture including the BSA protein and water. In some embodiments, the membrane 100 may also be used for the separation of humic acid and water.

[0059] Flux and rejection of the BSA were determined based on a pressure-driven filtration model were determined with the PEG/PES membrane and the dual-layer membrane 100. The results of this study are presented in FIG. 9. From the FIG. 9 it can be observed that the BSA flux with the dual-layer membrane 100 was found to be higher than the PES/PEG membrane. About 110 liters per meter square per hour (L.m’ ² h ^-1 ) of the BSA was filtered with the dual-layer membrane 100, while only 90 L.m’ ² h ^_1 of the BSA was filtered with the PEG/PES single layer membrane, at an operating pressure of 3 bars. The performance of filtration in these two membrane types was closely related to the morphological structure of a membrane. Compared to the PES/PEG membrane, the duallayer membrane 100 has a higher pore volume or porosity. 89.30% of BSA protein was removed or rejected with the dual-layer membrane 100, at lower applied pressure of 3 bars, and a high BSA flux was achieved at 3 bars.

[0060] Yet another interesting observation was that, as can be observed from the FIG. 9, was the long filtration time with the dual-layer membrane 100, in comparison to the PEG/PES membrane. The filtration performance with the membrane 100 was found to be consistent for up to 3 hours, unlike the PES/PEG membrane. The performance of the PEG/PES membrane was found to gradually decrease with time, and this decrease could be due to pore blocking/fouling. The stability of the dual-layer membrane 100 could be attributed to the increased hydrophilicity of the membrane 100. The hydrophilic nature of the membrane 100 resulted in decreased interaction of BSA with the membrane 100. Since the BSA protein was unlikely to attach to the membrane surface, drawbacks such as fouling, and pore-blocking were minimized, thereby allowing for a greater BSA flux for a longer time with increased stability.

[0061] From a combined reading of FIG. 7 to FIG. 9 and Table 2, it can be observed that best results were observed when the combination of PEG to the PES nanofibers was used as the dual-layer membrane 100. Further, the dual-layer membrane 100 demonstrates better performance than a single-layer membrane.

[0062] To conclude, the dual-layer membrane 100 demonstrates significant improvement in mechanical strength by more than 70%, enhanced the porosity by up to 76.93%, 36% enlargement in pore size, and 24% increase for the pure water flux, young modulus increased by almost 3-fold when compared to the PEG/PES membrane. About 89.30% of BSA protein was removed using the membrane 100 and a high BSA flux was achieved at 3 bars. The results disclosed that the membrane 100 demonstrates better performance than conventionally used membranes, like the PEG/PES membrane or the PES nanofibers.

Industrial applicability

[0063] The dual-layer membrane 100 of the present disclosure possesses high hydrophilicity, thereby preventing or minimizing the contact of hydrophobic proteins or solutes to the surface of the membrane 100, overcoming drawbacks associated with membrane fouling. The PES nanofibers of the first layer 102 impart mechanical stability and support to the dual-layer membrane 100. However, the highly selective and porous nature of the second layer 104 in the dual-layer membrane 100 due to the presence of PEG as a pore-forming additive, causes increased water flux. A significant improvement in mechanical strength by more than 70% was observed with the dual-layer membrane 100 as compared to a single layer membrane or conventionally used membranes. Also, the bonding between the first layer 102 and the second layer 104 by way of hydrophilic interactions obviates the need for use of any cross -linkers. Also, the present disclosure provides a simple fabrication process, which is cost-effective, energy-efficient, and can be easily scaled up for large-scale water treatments.

[0064] While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.