Filter membrane and method for producing the same

Abstract

Disclosed is a composite membrane comprising a porous polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or nitrocellulose membrane body. The membrane also comprises graphene oxide disposed on the surface of the membrane body. Also disclosed is an array comprising two or more such composite membranes. Methods for preparing the composite membrane are also disclosed. Additionally, disclosed is a method for removing natural organic matter (NOM) from NOM-contaminated water or water suspected of being contaminated with NOM.

Description

Technical Field

[0001] The present disclosure relates to a filtration membrane and a method for manufacturing the filtration membrane. More specifically, the present disclosure relates to a water filtration membrane that can be used to remove natural organic matter (NOM) from water contaminated with NOM. The membrane can find particular use in commercial water treatment facilities, although not exclusively. Although mainly described in this context, it will be understood that the membrane can find a wide range of applications where removal of NOM from water is desirable.

Background Art

[0002] Natural organic matter (NOM) is found in substantially all surface waters, groundwaters, and soil waters. Aquatic NOM typically results from the decomposition of both decaying plant (including algae) and animal matter. NOM is a complex matrix of organic substances present in substantially all water bodies in the environment. Generally, it includes carboxylic acids, carbohydrates, proteins, and humic substances. In the context of municipal water supply, NOM affects the efficiency and effectiveness of the water treatment process and the final water quality reaching the customer's tap. An increase in the amount of NOM has been observed in the world's raw water supplies over the past 10 - 20 years, which has a significant impact on the treatment processes of municipal water supply.

[0003] The presence of NOM causes many problems in drinking water and the drinking water treatment process, including (i) adverse effects on water quality by causing color, taste, and odor problems, (ii) an increase in the dosage of coagulants and disinfectants (thereby resulting in an increase in the amount of sludge and the production of regulated disinfection by-products (DBPs)), and (iii) the promotion of biological growth in the distribution system.

[0004] Current water filtration systems typically use chemical coagulants and activated carbon adsorption to remove NOM. Nevertheless, their use is not always effective, and in some cases, only up to 50% NOM removal can be achieved. The complexity and variability in the abundance of NOM affect the performance of direct filtration facilities, resulting in a decrease in treatment capacity. For example, in a water treatment facility in Australia, after heavy rain, the treatment capacity decreased by approximately 40% (which increased the NOM in the raw water flowing into the facility). The period during which the treatment capacity decreases may not be predictable and may last for several weeks. If the problems associated with NOM cannot be well controlled, additional costs may be incurred in the water treatment process. Clearly, new and alternative devices and methods for removing NOM from NOM-contaminated water are needed.

[0005] It would be advantageous to provide alternative devices for removing NOM from water, particularly devices that can be used to remove a substantial portion of the NOM from NOM-contaminated water, thereby providing water that contains little or no NOM contaminants. It would also be advantageous to provide a device that can be retrofitted to existing water filtration facilities.

Prior Art Documents

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

[0007] Disclosed herein is a composite membrane comprising a porous polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) or nitrocellulose membrane body, and graphene oxide disposed on the surface of the membrane body.

[0008] In some embodiments, at least a portion of the graphene oxide is bonded to the membrane body via a crosslinking agent. In some specific embodiments, at least a portion of the graphene oxide is covalently bonded to the membrane body via a crosslinking agent. In some specific embodiments, the crosslinking agent is selected from 1,5-pentanediol, glutaraldehyde and glycol. In some embodiments, the graphene oxide is in the form of layers. In some embodiments, the layer is a substantially continuous layer coating the surface of the membrane body. In some embodiments, the graphene oxide has a C / O ratio in the range of about 2.1 to about 4.5. In some specific embodiments, the porous membrane body is a porous polyvinylidene fluoride (PVDF) membrane body. In some embodiments, the composite membrane is in the form of a hollow fiber composite membrane. In some specific embodiments, the graphene oxide is disposed on the outer surface of the hollow fiber membrane.

[0009] Also disclosed herein is an array comprising two or more of the composite membranes described herein, and the two or more composite membranes are arranged in parallel within the array.

[0010] Also disclosed herein is a method for preparing a composite membrane, the method comprising (a) providing a porous polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) or nitrocellulose membrane body; and (b) filtering a dispersion containing graphene oxide through the membrane body, such that the continuous phase of the dispersion passes through the surface of the membrane body, thereby depositing graphene oxide on the surface of the membrane body.

[0011] In some embodiments, the continuous phase of the dispersion containing graphene oxide comprises at least 50% v / v ethanol. In some embodiments, the method further comprises, prior to step (b), an additional step (a1), in which the porous membrane body is treated with a solvent to completely or at least partially remove any protective coating that may be present on the membrane body. In some embodiments, the method further comprises, after step (a), or if included after step (a1), and prior to step (b), an additional step (a2), in which the porous membrane body is contacted with a crosslinking agent.

[0012] The present disclosure also provides a composite membrane prepared by the method described herein.

[0013] Also disclosed herein is a method for removing NOM from NOM-contaminated water or water suspected of being contaminated with NOM, the method comprising passing the NOM-contaminated water or water suspected of being contaminated with NOM through a composite membrane described herein, a composite membrane prepared by the method described herein, or an array described herein.

Brief Description of the Drawings

[0014] Specific embodiments of the present disclosure are described below by way of example only with reference to the accompanying drawings.

[0015]

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Mode for Carrying Out the Invention

[0016] Here, as an example only, specific embodiments will be described.

[0017] In a first aspect, the present disclosure provides - a porous polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) or nitrocellulose membrane body, and - graphene oxide disposed on the surface of the membrane body, a composite membrane comprising.

[0018] The composite membrane is typically used for water filtration. Therefore, the porous membrane body must be porous to allow the passage of water through the membrane body. In some embodiments, the porous membrane body is planar or substantially planar. In other embodiments, the porous membrane body is in the form of a hollow fiber (HF), sometimes referred to as a "hollow fiber membrane" (HFM). As will be understood, the form of the porous membrane body can be used to determine the form of the composite membrane. Therefore, in some embodiments, the composite membrane is planar or substantially planar. In other embodiments, the composite membrane is a hollow fiber composite membrane.

[0019] In some specific embodiments, the porous membrane body is a porous polyvinylidene fluoride (PVDF) membrane body (i.e., a porous membrane body formed from PVDF). In other specific embodiments, the porous membrane body is a polytetrafluoroethylene (PTFE) membrane body. In still other specific embodiments, the porous membrane body is a nitrocellulose membrane body. There are many suppliers that manufacture membranes that may be suitable for use as the porous membrane body for supporting graphene oxide disposed on the surface of the membrane body. Advantageously, the composite membrane can be prepared from commercially available and commercially used membranes of standard sizes, so that the composite membrane can be retrofitted to existing water treatment facilities without the need for large-scale redesign and modification of the water treatment facilities.

[0020] In some embodiments, the porous membrane body has a pore size in the range of about 0.002 μm to about 2 μm, such as about 0.005 μm to about 1 μm, about 0.01 μm to about 0.5 μm, about 0.02 μm to about 0.2 μm, or about 0.05 μm to about 0.15 μm. The porous membrane body is typically supplied by a manufacturer having the specified pore size.

[0021] Graphene oxide (GO) may be referred to in the literature as graphite oxide, graphene oxide, or graphite acid. Thus, "graphene oxide" is intended herein to encompass all such nomenclatures. Advantageously, GO allows water to pass through, but NOM cannot pass through GO. Due to this property, GO is suitable for use in separating NOM from water. Further, it has been observed that when GO is disposed on the surface of the membrane body, a stable composite membrane can be provided that can be used to remove NOM from water contaminated with NOM.

[0022] GO is typically obtained by treating graphite with a strong oxidizing agent. The layer structure of graphite is usually retained during the oxidation process, but the interlayer spacing is typically much larger and irregular in GO than in graphite. GO typically contains carbon, oxygen, and hydrogen, and the ratio between these elements varies depending on the oxidation level of GO. In its most oxidized form, GO can have a low C / O ratio of 2.1. In some embodiments, GO has a C / O ratio in the range of about 2.1 to about 5. In some embodiments, the C / O ratio ranges from about 2.2 to about 4.5, such as about 2.2 to about 4, about 2.2 to about 3.5, about 2.2 to about 3.0, or about 2.2 to about 2.5.

[0023] In the composite membranes of the present disclosure, graphene oxide is disposed on the surface of the membrane body. In embodiments where the membrane body is a hollow fiber membrane, graphene oxide can be disposed on the inner surface, the outer surface, or both the inner and outer surfaces of the hollow fiber membrane. In some specific embodiments, graphene oxide is disposed on the outer surface of the hollow fiber membrane. Embodiments where graphene oxide is disposed on the outer surface of the hollow fiber membrane can have certain advantages such as ease of manufacture (e.g., obtaining a more uniform GO deposition on the outer surface), and can be more easily evaluated (e.g., checking for any deficiencies in GO). The outer surface also has a larger surface area than the inner surface, which can be beneficial in terms of increasing the GO surface area per HFM.

[0024] In some embodiments, graphene oxide is in the form of flakes. In other embodiments, graphene oxide is in the form of nanosheets. In some embodiments, graphene oxide is in the form of a layer comprising graphene oxide flakes and / or nanosheets.

[0025] In some embodiments, the graphene oxide disposed on the surface of the membrane body is in the form of a layer. This layer can be described as a coating or a film. In some embodiments, the layer is a continuous layer that coats the surface of the membrane body. This continuous layer extends across the entire surface of the membrane body such that, in use, the permeate (usually water) passing through the composite membrane must pass through both the GO layer and the porous membrane body. In other embodiments, the layer is a discontinuous layer. In such embodiments, there may be gaps, cracks or holes in the graphene oxide layer such that, in use, the permeate (usually water) passing through the composite membrane may pass through both the GO layer and the porous membrane body or may pass through only the porous membrane body. As will be understood, since the GO layer is typically effective in isolating or otherwise removing contaminants (e.g., NOM) that the porous membrane body typically cannot remove, it is preferred that the GO be in the form of a continuous layer rather than a discontinuous layer. Although not a preferred embodiment, a discontinuous layer can still prove useful in removing at least some of the contaminants (such as NOM) from contaminated water in applications that do not require large-scale removal of contaminants. Further, embodiments having a discontinuous GO layer can have a higher flux compared to embodiments having a continuous GO layer.

[0026] In some embodiments, the graphene oxide is in the form of a layer having a thickness in the range of about 0.5 μm to about 20 μm (e.g., about 1 μm to about 12 μm, about 1 μm to about 10 μm, about 1 μm to about 8 μm, about 1 μm to about 5 μm, about 2 μm to about 12 μm, about 2 μm to about 10 μm, about 2 μm to about 8 μm, about 3 μm to about 12 μm or about 3 μm to about 10 μm). In some embodiments, the thickness is substantially uniform and 90% (based on the surface area of the GO) of the GO layer has a thickness within 20% of the average thickness, e.g., 90% of the GO layer has a thickness within 10% of the average thickness, 90% of the GO layer has a thickness within 5% of the average thickness, 95% of the GO layer has a thickness within 10% of the average thickness, 95% of the GO layer has a thickness within 5% of the average thickness, or 98% of the GO layer has a thickness within 5% of the average thickness.

[0027] In some embodiments, the GO layer comprises a plurality of GO laminates. In some embodiments, the laminate has an interlayer spacing of about 4 Å to about 15 Å, such as about 5 Å to about 12 Å, about 5 Å to about 10 Å, about 6 Å to about 12 Å, about 6 Å to about 10 Å, about 7 Å to about 12 Å, about 7 Å to about 10 Å, about 7 Å to about 9 Å, about 7.5 Å to about 9 Å, about 8 Å to about 9 Å, about 8 Å to about 8.5 Å, or about 8.25 Å. The spacing between two layers in the GO laminate structure can be determined using XRD (see, for example, the spectrum shown in FIG. 3(c)).

[0028] In some embodiments, graphene oxide, or at least a portion thereof, is bonded to the membrane body via a crosslinking agent. As used herein, a "crosslinking agent" is a C 2~20 linear or branched alkyl, alkenyl, or alkynyl group, particularly an alkyl group, substituted at one end with a functional group capable of bonding, preferably covalently, to PVDF, PTFE, or nitrocellulose and at the other end with a functional group capable of bonding, preferably covalently, to graphene oxide. In some embodiments, graphene oxide, or at least a portion thereof, is covalently bonded to the membrane body via a crosslinking agent. In some particular embodiments, graphene oxide is in the form of layers, and the graphene oxide layers are bonded to the membrane body via a crosslinking agent.

[0029] In some embodiments, the crosslinking agent is a C 2~6 alkyl group substituted at a first end with a first functional group capable of bonding, preferably covalently, to PVDF, PTFE, or nitrocellulose and at a second end with a second functional group capable of bonding, preferably covalently, to graphene oxide. In some embodiments, the crosslinking agent has a first functional group selected from -OH, -CHO, and -COOH. In some embodiments, the crosslink The agent has a second functional group selected from -OH, -CHO, and -COOH. As will be appreciated, these functional groups preferably covalently bond to either GO or the membrane body, such that the cross-linking species (i.e., the bonded cross-linking agent) that binds GO and the membrane body is technically a derivative of the cross-linking agent. For example, the -OH of a diol can bond to the carbon of the membrane body and / or GO to form an ether or ester functional group.

[0030] In some embodiments, the cross-linking agent is a diol, a dialdehyde, or a dibasic acid, preferably having 2 to 6 adjacent carbon atoms with associated functional groups at the ends or opposite ends. In some embodiments, the cross-linking agent is a diol. In other embodiments, the cross-linking agent is a dialdehyde. In still other embodiments, the cross-linking agent is a dibasic acid.

[0031] In some embodiments, the cross-linking agent is selected from 1,6-hexanediol, 1,5-pentanediol, 1,4-butanediol, 1,3-propanediol, 1,2-propanediol (propylene glycol), 1,2-ethanediol (glycol), glutaraldehyde (1,5-pentanedial), particularly 1,5-pentanediol, glutaraldehyde, and glycol, more specifically pentanediol.

[0032] Since PVDF is generally considered to be quite inert, it is surprising that PVDF membranes can be functionalized in such a way (i.e., by binding to GO and cross-linking with a cross-linking agent). Similar difficulties have previously also hindered the development of functionalized PTFE and nitrocellulose membranes.

[0033] Advantageously, many of the mechanical properties of PVDF, PTFE, and nitrocellulose membranes are desirable and, in some embodiments, may be superior to the mechanical properties of PAI that render them useful in the composite membranes of the present disclosure. Notable mechanical properties of graphene oxide include tensile strength, flexibility, and shear strength. Further, the resistance of pentanediol-crosslinked graphene oxide on PVDF hollow fiber membranes to delamination was evaluated to be higher than that of PEI-crosslinked graphene oxide on PAI hollow fiber membranes.

[0034] In some embodiments, the crosslinking agent (e.g., pentanediol) is substantially completely bonded and thus does not leach out in water after crosslinking with graphene oxide and PVDF. In such embodiments, contamination of the filtered water by the crosslinking agent can be minimized.

[0035] In some embodiments, the composite membranes disclosed herein have, for example, a high water flux of about 5 lm -2 h -1 bar -1 ~ about 100 lm -2 h -1 bar -1 e.g., about 10 - about 100, about 20 - about 100, about 30 - about 100, about 40 - about 100, about 50 - about 100, about 60 - about 100, about 70 - about 100, about 80 - about 100, about 90 - about 100, about 40 - about 90, about 40 - about 80, or about 60 - about 80 lm -2 h -1 bar -1 In some embodiments, the water flux of the composite membrane is within 10% of the water flux of the membrane in the absence of GO (i.e., the water flux is within 10% of the porous membrane body).

[0036] In some embodiments, the composite membranes disclosed herein are selective in removing NOM from water contaminated with NOM. In this context, "selective" means a high removal rate of NOM. In some embodiments, the composite membrane may provide removal of NOM but allow passage of dissolved minerals. In other embodiments, the composite membrane is for NOM and CaCO 3It can provide simultaneous removal of dissolved minerals such as

[0037] In some embodiments, the composite membranes disclosed herein are resistant to biofouling. In some embodiments, the composite membranes disclosed herein at least somewhat resist the growth and / or accumulation of microorganisms, plants, algae, or animals on the composite membranes. In this regard it has been reported that GO has anti-biofouling properties (Non-Patent Document 1). Since NOM is generally negatively charged, the outer surface of graphene oxide may resist or otherwise impede the entry of NOM into GO, which is thought to potentially confer anti-biofouling properties.

[0038] Also disclosed herein is an array comprising two or more composite membranes arranged in parallel (not in series), where the two or more composite membranes are the composite membranes disclosed herein. In such embodiments, the composite membranes are arranged such that the fluid to be filtered, typically water containing NOM, flows simultaneously through the two or more composite membranes. In some particular embodiments, the two or more composite membranes arranged in parallel are two or more composite hollow fiber membranes arranged in parallel.

[0039] In a further aspect, the present disclosure provides a method for preparing a composite membrane. The method comprises (a) providing a porous polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) or nitrocellulose membrane body; and (b) filtering a dispersion containing graphene oxide through the membrane body, such that the continuous phase of the dispersion passes through the surface of the membrane body, thereby depositing graphene oxide on the surface of the membrane body.

[0040] In some embodiments, the continuous phase of the dispersion is urged through the surface of the membrane body by a positive pressure on the dispersion side of the membrane. In other embodiments, the continuous phase of the dispersion is urged through the surface of the membrane body by a negative pressure on the permeate side of the membrane, for example, at or around a vacuum pressure (e.g., 0.83 atm or 85 kPa). A combination of a positive pressure on the dispersion side of the membrane and a negative pressure on the permeate side of the membrane may also be used.

[0041] In some embodiments, the dispersion containing graphene oxide contains about 0.005 mg / ml to about 5 mg / ml of GO, for example, about 0.01 mg / ml to about 1 mg / ml, about 0.05 mg / ml to about 0.5 mg / ml, about 0.1 mg / ml to about 0.3 mg / ml or about 0.1 mg / ml to about 0.2 mg / ml. In this context, "mg / ml" refers to mg of graphene oxide per ml of the total dispersion (including graphene oxide and the continuous phase).

[0042] In some embodiments, the continuous phase of the dispersion containing graphene oxide is aqueous. The term "aqueous" in this context refers to a continuous phase in which water is the sole continuous phase or at least 50 wt% of the total continuous phase in the dispersion. In some embodiments, the continuous phase of the dispersion containing graphene oxide is an alcohol, for example, methanol, ethanol, propanol, butanol or a mixture thereof, particularly ethanol, methanol or a mixture thereof. In some embodiments, the continuous phase of the dispersion contains at least 50% v / v of alcohol (e.g., at least 60% v / v, at least 70% v / v, at least 80% v / v, at least 90% v / v, at least 95% v / v, at least 99% v / v, at least 99.5% v / v or at least 99.9% v / v of alcohol). In some embodiments, the continuous phase of the dispersion containing graphene oxide is an aqueous alcohol phase. In some specific embodiments, the continuous phase of the dispersion containing graphene oxide contains at least 50% v / v of ethanol, at least 90% v / v or at least 95% v / v of ethanol.

[0043] In some embodiments, graphene oxide is prepared from graphite by the Hummers method (Non-Patent Document 2). In some embodiments, the graphene oxide prepared from graphite by the Hummers method is in the form of a graphene oxide dispersion that is used directly. In other embodiments, the graphene oxide prepared from graphite by the Hummers method is diluted in a continuous phase (e.g., water and / or alcohol) to provide a graphene oxide dispersion.

[0044] In some embodiments, the thickness of GO disposed on the surface of the membrane body is controlled by adjusting the concentration of the GO dispersion. In some embodiments, the thickness of GO disposed on the surface of the membrane body is controlled by adjusting the volume of the GO dispersion filtered through the membrane body.

[0045] In some embodiments, the method further includes an additional step (a1) before step (b), in which the porous membrane body is treated with a solvent. In some embodiments, the solvent treatment is to activate the membrane body, for example, by washing the membrane body, wetting the membrane body, and / or opening the pores of the membrane body. In some embodiments, the solvent treatment is to remove any protective coating that may be present in or on the membrane body. In this regard, many PVDF, PTFE, and nitrocellulose membranes are typically supplied with a protective coating in and / or on them to assist in the stability of the membrane after manufacture. For example, PVDF membranes generally come with a poly(methyl methacrylate) (PMMA) coating layer, which can protect the membrane from contaminants (e.g., dust) that may block the pores, or prevent the membrane from being directly exposed to the atmosphere or other agents that may degrade the membrane. In some embodiments, the solvent in step (a1) is acetone, chloroform, alcohol, aqueous alcohol, or a mixture thereof. In some embodiments, the solvent in step (a1) is an alcohol solvent, such as methanol, ethanol, propanol, butanol, or a mixture thereof, particularly ethanol. In some embodiments, the solvent in step (a1) is an aqueous alcohol solvent containing water and alcohol, and the alcohol is at least 1% v / v of the solvent, for example, about 1% v / v to about 99.5% v / v of alcohol, about 2% v / v to about 99% v / v of alcohol, about 5% v / v to about 95% v / v of alcohol, about 10% v / v to about 90% v / v of alcohol, about 20% v / v to about 80% v / v of alcohol, about 30% v / v to about 70% v / v of alcohol, or about 40% v / v to about 60% v / v of alcohol. In some specific embodiments, the solvent in step (a1) is an aqueous alcohol solvent containing about 40 to about 60% v / v of alcohol, particularly ethanol, and about 40 to about 60% v / v of water, more specifically containing about 50% v / v of ethanol in water.In other specific embodiments, the solvent in step (a1) is an aqueous alcohol solvent, containing about 2 to about 10% v / v of alcohol, particularly ethanol, and about 98 to about 90% v / v of water, more specifically containing about 5% v / v of ethanol in water. In some embodiments, the porous membrane body is rinsed in the solvent. In some embodiments, the porous membrane body is immersed in the solvent for some time, for example, at least 2 hours, at least 12 hours, at least 1 day, or at least 2 days, typically up to about 3 days at most.

[0046] In some embodiments, the method further includes step (a2), which is an additional step after step (a) or, if included, after step (a1) and before step (b), in which the porous membrane body is brought into contact with a crosslinking agent. In such embodiments, the crosslinking agent preferably binds to the surface of the porous membrane body by a covalent bond to form a functionalized surface. Next, during step (b), GO can bind to the functionalized surface preferably by a covalent bond via the crosslinking agent. As a result, GO can thereby be bound to the surface of the membrane body preferably by a covalent bond via the crosslinking agent. In other words, GO can be crosslinked to the membrane body preferably by a covalent bond to form a crosslinked composite membrane, preferably a crosslinked composite membrane by covalent bond. The crosslinked composite membrane exhibits many advantages such as improved stability compared to the non-crosslinked composite membrane.

[0047] In step (a2), contact with the crosslinking agent is carried out. This contact may be by any means of bringing the crosslinking agent into contact with the porous membrane body. In some embodiments, the crosslinking agent is in solution, and the solution contacts the porous membrane body. In such embodiments, the solute can be aqueous, alcoholic, or aqueous-alcoholic. The term "aqueous" in this context refers to a solution in which water is the sole solvent or at least 50 wt% of the total solvent in the solution. The alcohol can be methanol, ethanol, propanol, butanol, or mixtures thereof, particularly ethanol. In some embodiments, the contact is carried out by immersing the porous membrane body in the crosslinking agent or the solution containing the crosslinking agent. In some embodiments, the contact is carried out by passing the crosslinking agent or the solution containing the crosslinking agent through the porous membrane body.

[0048] Also disclosed herein are composite membranes prepared by the methods disclosed herein.

[0049] In a further aspect, the present disclosure provides a method for removing NOM from NOM-contaminated water, or water suspected of being contaminated with NOM. This method includes passing NOM-contaminated water, or water suspected of being contaminated with NOM, through the composite membrane described herein. As will be understood, this method can be described as a method for providing water that is free of NOM or has reduced NOM from NOM-contaminated water, or water suspected of being contaminated with NOM, and this method includes passing NOM-contaminated water, or water suspected of being contaminated with NOM, through the composite membrane described herein. In some embodiments, the passage of water through the composite membrane is facilitated by gravity. In some embodiments, the passage of water through the composite membrane is facilitated by a pressure difference. For example, the pressure difference can be provided by a high pressure on the feed side (e.g., >1 - 20 bar) and / or a low pressure on the permeate side (e.g., 0.1 - <1 bar). One of ordinary skill in the art can readily determine the appropriate pressure to use depending on the system.

[0050] In a further aspect, the present disclosure provides a method of functionalizing a PVDF membrane. The method includes contacting the PVDF membrane with a solvent comprising at least 2% v / v ethanol, at least 5% v / v ethanol, at least 20% v / v ethanol, at least 50% v / v ethanol, at least 80% v / v ethanol, at least 90% v / v ethanol, at least 95% v / v ethanol, or at least 98% v / v ethanol. Without being bound by theory, it is believed that upon contact with ethanol, the pores of the PVDF membrane are cleaned, wetted, and / or opened, thus increasing their reactivity and making their functionalization easier.

[0051] In a further aspect, the present disclosure provides a method of depositing graphene oxide on a permeable solid support such as a filtration membrane. The method includes (a) providing a permeable solid support, and (b) filtering a dispersion comprising graphene oxide through the permeable solid support, such that the continuous phase of the dispersion passes through the surface of the permeable solid support, thereby depositing graphene oxide on the surface of the permeable solid support, wherein the continuous phase of the dispersion comprises at least 50% v / v, at least 90% v / v, at least 95% v / v, or at least 99% v / v ethanol.

[0052] Also disclosed herein is a method of removing NOM from NOM-contaminated water or water suspected of being contaminated with NOM, the method including passing the NOM-contaminated water or water suspected of being contaminated with NOM through graphene oxide disposed on the surface of a membrane body, particularly where the membrane body is a porous polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or nitrocellulose membrane body.

Examples

[0053] PVDF, PTFE, and nitrocellulose are not typically suitable for coating It has not been considered. However, in Examples 1 to 7 described below, it has been shown that it is possible to obtain a GO-coated PVDF membrane. PTFE and nitrocellulose are also quite chemically inert and are therefore considered to behave similarly to PVDF.

[0054] Example 1 Example 1 describes the production of a composite membrane in the form of a graphene oxide membrane comprising a polyvinylidene fluoride (PVDF) membrane coated with graphene oxide.

[0055] A graphene oxide (GO) dispersion was prepared by the Hummers method. In the Hummers method, graphite is oxidized to graphene oxide with a mixture of H 2 SO 4 , KMnO 4 , and NaNO 3 at a controlled temperature. Figure 1 is a schematic diagram of the process used to form the GO dispersion (also referred to as the GO suspension). The C / O ratio was determined to be 2.20 by XPS.

[0056] The GO suspension was filtered through the PVDF membrane to deposit GO flakes on the PVDF membrane, forming a GO layer (i.e., a composite membrane in the form of a GO membrane) on the PVDF membrane. In this example, vacuum filtration was used to prepare a GO layer on PVDF having a pore size of 0.22 μm. The thickness of the GO could be adjusted by changing the volume of the GO dispersion filtered through a given area of the PVDF membrane.

[0057] A scanning electron microscope (SEM) was used to examine the surface morphology and structure of the graphene oxide on the PVDF. X-ray diffraction (XRD) was used to evaluate changes in the crystal structure and, in addition, to determine the interlayer spacing between the stacked structures of the GO membrane. Exemplary results are shown in Figure 3.

[0058] Figure 3(a) is an SEM image showing the surface morphology of the GO film with a wrinkled region indicating the folding of the GO film. Figure 3(b) shows the stacked structure within the GO film. The spacing between two layers in the GO stacked structure was determined to be 8.25 Å using XRD (spectrum shown in Figure 3(c)). The sharp peak at a 2θ value of 10.7° indicates that the d-spacing value of the layer is 8.25 Å.

[0059] Samples of filtered water from Sydney Water's Nepean Water Filtration Plant were used in the water filtration experiments. The filtered water was the product of the standard water treatment process at the facility, namely, coagulation with FeCl 3 and cationic poly-DADMAC, followed by filtration through a deep bed filter. The concentration of NOM was determined by dissolved organic carbon (DOC) and high-sensitivity liquid chromatography - organic carbon detection (LC-OCD).

[0060] The experimental setup is schematically shown in Figure 2. As shown in Figure 2, the pressure-controlled filtration method was used to determine the water flux. While storing the permeate in a container maintaining the mass balance, the pressure P applied during filtration was controlled to about 1.0 bar. A GO film with an average effective area of about 3.0 cm 2 was used in the filtration experiment of this example.

[0061] Based on the DOC and LC-OCD results, the NOM concentration on the feed side was 5 mg / ml. In contrast, when measured by absorption spectroscopy, there were no traces of the test species on the permeate side, suggesting that the permeate either does not contain NOM species or is at least below the detection limit of 5 ppb (0.005 mg / ml) of the LC-OCD technique. The results are shown in Figure 4.

[0062] Once it was confirmed that all NOM was effectively removed from water using the GO film, the measured value of the water flux was investigated at a constant pressure of about 1.0 bar from the permeate side (to avoid misunderstanding , the permeate side is shown in Figure 2).

[0063] The amount of water passing through the GO membrane was measured over time. Each experiment was repeated four or more times. The water flux values shown in Figure 4 are the average water flux values of the experiments with deviations. As expected, since the thicker graphene oxide membrane has a longer path for water transport through the membrane, the thicker GO membrane has a lower water flux. The water flux was estimated using the following equation.

[0064] [Number] In the equation, J W is the water flux, Q is the volume of water, A is the effective area of the GO membrane, P is the vacuum pressure, and Δt is the time.

[0065] To confirm the stability of the water flux over time, a GO membrane with a GO layer thickness of <1 mm was used in a filtration test with 5 mg / L DOC on the feed side. The results are summarized in Figure 5 (water flux vs. time), which clearly shows the suitability of the PVDF / GO composite membrane for purified water when a constant flux is achieved over a long period. The flow rate of the peristaltic pump was kept below 50 ml / min.

[0066] Example 2 Example 2 describes the production of a composite membrane in the form of a GO-coated hollow fiber membrane (HFM). HFM is a type of artificial membrane that contains a semipermeable barrier in the form of hollow fibers. HFM is popular in water treatment facilities, desalination facilities, cell culture, medicine, and tissue engineering. There are commercially available cartridges containing a large number of hollow fibers. These can be used for the separation of various liquids and gases.

[0067] Compared with flat sheet membranes, hollow fiber membranes have several advantages, including high energy efficiency for achieving complete mixing within the module, a larger membrane surface area per unit volume of the module, and a self-supporting structure that does not require the use of permeate and feed spacers. The pore size of commercially available HFM typically ranges from 0.1 to 0.2 μm. Excellent mass transfer characteristics lead to many commercial applications such as ultrafiltration (UF) and microfiltration (MF).

[0068] In this experiment, polyvinylidene fluoride (PVDF) HFM was used. PVDF HFM has been reported to be hydrophilic. PVDF HFM was wetted before use in water treatment, which is considered beneficial for the stability of the membrane structure.

[0069] In this experiment, a syringe containing a single HFM was used, and the apparatus is shown in Figure 6. The syringe contains a single HFM with one end adhered to the tip of the syringe with an epoxy adhesive. Next, the syringe was connected to a vacuum flask. The GO dispersion (described in Example 1 above) was placed inside the syringe outside the HFM. Next, the flask was evacuated (at a vacuum pressure of 85 kPa), the fluid was suctioned through the HFM, and a GO coating was deposited on the outer surface of the HFM. Using this method, it was easy to control the degree of coating (i.e., the thickness of GO) by changing the concentration of the GO dispersion.

[0070] Due to the manufacturing process, the surface of commercially available HFM is usually coated with a protective coating that protects the HFM. The protective coating is considered to have an adverse effect on the coating process disclosed herein. Therefore, before use in the above experiment, the protective coating was removed (or at least removed to a sufficient extent) by immersing the PVDF HFM in ethanol for at least one day. (Or at least removed to a sufficient extent). In this regard, it was proven that 30 ml of a 50% v / v aqueous ethanol solution is sufficient for a 1.2×10 -4 m 2 hollow fiber membrane.

[0071] Using a 0.15 mg / ml dispersion of GO in water, GO was deposited onto HFM immersed in an aqueous ethanol solution. Prior to the coating step, the HFM was washed to remove all residual ethanol. The washing step typically included washing with water with any additional steps of rinsing the membrane with additional water (e.g., drawing additional water through the membrane to further rinse the membrane). The coating process typically lasted several hours. During this time, it was important to keep the HFM completely immersed in the GO dispersion without contacting the syringe walls. For a 9 cm long HFM with an outer diameter of 1.5 mm, approximately 25 - 30 ml of GO dispersion was used. If a shorter length (approx. 5 cm) of HFM was used, this could be reduced to approximately 10 - 15 ml. After the coating was completed, since the PVDF HFM needed to be stored in a wet state to maintain the full functionality of the pores, the GO-coated HFM was immersed in DI water for storage. Importantly, the GO coating was stable in DI water. Figure 7 shows an image of the GO-coated PVDF HFM produced by this method. Figure 8 is an SEM image of the GO-coated HFM prepared in Example 2. This image shows that there is a slight gap between the GO layer and the outer surface of the HFM.

[0072] Example 3 In Example 3, using the same process as in Example 2, multiple GO-coated PVDF HFMs were manufactured simultaneously. In Example 3, the apparatus shown in FIGS. 9(a) and 9(b) was used, where multiple HFMs were connected in parallel, enabling the simultaneous production of multiple GO-coated PVDF HFMs. Another apparatus (shown in FIGS. 9(c) and 9(d)) can also be used in this process. In the apparatus shown in FIGS. 9(c) and 9(d), the GO-coated HFM is fixed to the holes in the intermediate plate using an epoxy adhesive (the left part of FIG. 9(d)). This intermediate plate is screwed between the supply chamber (the right part of FIG. 9(d)) and the permeate chamber (the middle part of FIG. 9(d)) as shown in FIG. 9(c), and there are O-rings between each part (the intermediate plate and the supply chamber, the intermediate plate and the permeate chamber). At this stage, the GO-coated HFM is placed inside the supply chamber. The small tube on the supply chamber functions as a water level gauge to completely fill the NOM-contaminated water in the supply chamber. Both the supply chamber and the permeate chamber are connected to a tube fitting unit (the upper part of the permeate chamber and the bottom part of the supply chamber in FIG. 9(c)). Each unit is connected to a pressure gauge and a peristaltic pump. The pressure gauge measures the water pressure on the supply / permeate side, and the peristaltic pump supplies / sucks water from the supply / permeate side. The apparatus shown in FIGS. 9(a) and 9(b) operates in a similar manner.

[0073] Example 4 In Example 4, the GO coating film was prepared in the same manner as described in Examples 1 and 2, and both a flat GO coating film and a GO coating HF film were obtained. In Example 4, instead of using a GO suspension in water, a GO suspension in ethanol was used to coat the PVDF disk membrane and the PVDF HFM. To obtain the GO suspension in ethanol, first a concentrated GO suspension in water was prepared by the Hummers method. Next, the dispersion was diluted with ethanol to obtain GO in an ethanol dispersion having a concentration of 0.15 mg / mL (no effort was made to remove the residual water remaining by the Hummers method). Next, the diluted dispersion was placed in an ultrasonic crusher for 10 hours to obtain a GO ethanol dispersion / suspension (containing a small amount of water). Using the GO suspension in ethanol enabled much faster deposition, and the vacuum filtration rate (during deposition) became approximately 10 times faster. Furthermore, the layer structure of the flat GO film was observed to be more uniform when using the GO ethanol dispersion than the GO aqueous dispersion. Other coating characteristics were also improved by using the GO ethanol dispersion. and could be improved by this.

[0074] Example 5 Example 5 describes the preparation of a crosslinked GO-coated PVDF HF membrane using pentanediol as a crosslinking agent in an apparatus similar to that described in Example 2. Similar results were obtained using the parallel apparatus described in Example 3. The important steps of the preparation are shown in Fig. 10.

[0075] In this example, the PVDF hollow fiber membrane was first immersed in absolute ethanol for at least 12 hours to dissolve and remove the protective coating from the walls of the hollow fiber membrane present in the commercially available PVDF HFM. After removing the ethanol, the PVDF HFM was completely immersed in an aqueous solution of pentanediol (20% v / v) at room temperature without stirring for 48 hours. Next, the HFM was taken out and immersed in a graphene oxide / ethanol dispersion (0.15 mg / ml of GO in ethanol). A negative pressure was applied to the permeate outlet side for 5 minutes. The excess graphene oxide dispersion was removed, and the GO-coated HFM was stored open to air at room temperature to dry the surface and dry the GO coating.

[0076] Example 6 Example 6 describes another generalized preparation method for preparing a crosslinked GO-coated PVDF HF membrane using pentanediol as a crosslinking agent.

[0077] Wetting / Activation of PVDF - Immerse PVDF hollow fibers in an aqueous ethanol solution (5% v / v) for at least 2 hours. After the wetting process, it is necessary to remove the ethanol solution from the container and wash the surface of the hollow fibers several times, preferably with the same concentration as the wetting, by rinsing with the ethanol solution.

[0078] GO Coating - After the wetting procedure and removal of ethanol, it is necessary to introduce pentanediol as a crosslinking agent. 1. Remove the ethanol solution and fill the rig with the crosslinking agent (pentanediol). 2. Rinse the HFM in the pentanediol solution for 24 hours. 3. Remove the pentanediol solution and fill it with a 0.15 mg / ml GO dispersion in ethanol (the concentration can be changed to adjust the thickness of the GO coating layer). 4. Rinse the HFM in the GO dispersion for 30 minutes (the coating time can be changed to adjust the thickness of the GO coating layer).

[0079] Once the drying - coating is completed, drain the graphene oxide dispersion. Leave the hollow fiber membrane coated with graphene oxide open to air at room temperature for surface drying.

[0080] Example 7 Another rig design (100) is shown in FIG. 12. The rig 100 includes a first pump 101, a NOM inlet 102, an HFM 103 (either GO - coated or uncoated), a permeate outlet 104, a second pump 105, a NOM outlet 106, a solvent (e.g., ethanol, graphene oxide dispersion, NOM - contaminated water) 107, and a chamber 108.

[0081] The rig 100 can be used for either (i) the production of the GO membrane or (ii) the filtration of N OM after the production of the GO membrane is completed.

[0082] This rig can be used to produce a GO membrane using a method similar to that described in Example 1 or Example 2. In the production of the GO membrane, the membrane 103 starts as an uncoated PVDF hollow fiber membrane. The pump 101 re - uses the ethanol 107 used for wetting. Once wetting is complete, a negative pressure (e.g., vacuum) is provided by the pump 105 to remove the ethanol from the system. After the wetting process, the chamber 108 is filled with the graphene oxide dispersion for the coating process. The pump 105 can be used to pump the GO dispersion through the HFM 103. Once the coating process is completed, the pump 105 can be used to empty the chamber 108 and dry the membrane 103.

[0083] In the filtration of NOM, the membrane 103 is a GO membrane. Briefly, the pump 101 is used to supply the NOM contaminated water to the chamber 108, and the pump 105 operates on the permeate side to draw water through the membrane 103, thereby producing clean water at the outlet side 104.

[0084] If any prior art publication is referred to in this specification, it should be understood that such reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or any other country.

[0085] In the following claims and the foregoing description, except where the context requires otherwise for the expression language or necessary implication, the word "comprise", or variations such as "comprises" or "comprising", are used in an inclusive sense, that is, used to specify the presence of the stated features, but not to exclude the presence or addition of further features in various embodiments.

Claims

1. A composite membrane comprising a porous polyvinylidene fluoride (PVDF) membrane body and graphene oxide disposed on the surface of the membrane body, wherein: At least a part of the graphene oxide is covalently bonded to the membrane body via a crosslinking agent; The crosslinking agent is 1,5-pentanediol, said composite membrane.

2. The composite membrane according to claim 1, wherein the graphene oxide is in the form of a layer.

3. The composite membrane according to claim 2, wherein the layer is a substantially continuous layer coating the surface of the membrane body.

4. The composite membrane according to any one of claims 1 to 3, wherein the graphene oxide has a C / O ratio in the range of 2.1 to 4.

5.

5. The composite membrane according to any one of claims 1 to 4, wherein the composite membrane is in the form of a hollow fiber composite membrane.

6. The composite membrane according to claim 5, wherein the graphene oxide is disposed on the outer surface of the hollow fiber composite membrane.

7. An array comprising two or more composite membranes according to any one of claims 1 to 6, wherein the two or more composite membranes are arranged in parallel within the array.

8. A method for preparing a composite membrane, said method comprising: (a) providing a porous polyvinylidene fluoride (PVDF) membrane body; (a1) optionally, treating the membrane body with a solvent to completely or at least partially remove any protective coating that may be present on the membrane body; (a2) contacting the membrane body with a crosslinking agent solution; (b) filtering a dispersion containing graphene oxide through the membrane body, such that the continuous phase of the dispersion passes through the surface of the membrane body, thereby depositing graphene oxide on the surface of the membrane body, said method, wherein: The crosslinking agent is 1,5-pentanediol, said method.

9. The method according to claim 8, further comprising removing the crosslinking agent solution after step (a2) and before step (b).

10. The method according to claim 8 or 9, wherein the continuous phase of the dispersion containing graphene oxide contains at least 50% v / v ethanol.

11. A method for removing NOM from NOM-contaminated water or water suspected of being contaminated with NOM, the method comprising passing the NOM-contaminated water or water suspected of being contaminated with NOM through the composite membrane according to any one of claims 1 to 6 or the array according to claim 7.

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