Pervaporation membranes, methods of making and using the same

Abstract

The application relates to a pervaporation membrane and a preparation method and application thereof, the pervaporation membrane comprising a support layer and a functional layer arranged on the support layer; the functional layer comprises silver nanowires, graphene oxide quantum dots and an ester-based polymer cross-linking material, and the silver nanowires and the graphene oxide quantum dots are dispersed in the ester-based polymer cross-linking material. The pervaporation membrane has good separation selectivity, stable operation and high permeation flux.

Description

Technical Field

[0001] This application relates to the field of water treatment technology, and in particular to pervaporation membranes, their preparation methods, and applications. Background Technology

[0002] Traditional wastewater treatment or seawater desalination typically employs reverse osmosis technology, which utilizes the difference in osmotic pressure across a semi-permeable membrane to desalinate the solution. However, when the salt concentration in the solution is high, the osmotic pressure across the semi-permeable membrane becomes excessively high, potentially exceeding its pressure resistance limit. In such cases, pretreatment of the solution before reverse osmosis is necessary, making the process cumbersome. In contrast, pervaporation membranes (PV membranes) have lower requirements for solution concentration and require no pretreatment; most wastewater or seawater can be directly desalinated.

[0003] Polyvinyl alcohol (PVA) has become the mainstream material for the functional layer of pervaporation membranes due to its low cost, good hydrophilicity, and almost non-toxicity. However, it has disadvantages such as low permeation flux and easy swelling, which directly limit the separation efficiency and long-term operational stability of PV membranes. Summary of the Invention

[0004] Therefore, it is necessary to provide a pervaporation membrane with high permeation flux and good anti-swelling properties to improve its separation efficiency and long-term stability.

[0005] A first aspect of this application provides a pervaporation membrane, the pervaporation membrane comprising a support layer and a functional layer disposed on the support layer; the functional layer comprising silver nanowires, graphene oxide quantum dots and an ester-based polymer crosslinking material, wherein the silver nanowires and the graphene oxide quantum dots are dispersed in the ester-based polymer crosslinking material.

[0006] In some embodiments, the length of the silver nanowire is 10 μm to 20 μm; and / or, the diameter of the silver nanowire is 30 nm to 50 nm.

[0007] In some embodiments, the particle size of the graphene oxide quantum dots is 2nm to 6nm.

[0008] In some embodiments, the pervaporation membrane satisfies at least one of the following characteristics:

[0009] (1) The thickness of the functional layer is 100nm~1000nm;

[0010] (2) The thickness of the support layer is 100μm~300μm;

[0011] (3) The material of the support layer includes at least one of polypropylene, polytetrafluoroethylene and polyvinylidene fluoride.

[0012] A second aspect of this application provides a method for preparing a pervaporation membrane, comprising the following steps:

[0013] S1. Dicarboxylic acid, silver nanowires, and graphene oxide quantum dots are added sequentially to a polyvinyl alcohol solution and mixed evenly to obtain a casting solution; the dicarboxylic acid has 4 carbon atoms.

[0014] S2. The casting solution is uniformly coated on the surface of the support layer, dried, and heat-treated to obtain the pervaporation membrane.

[0015] In some embodiments, the preparation method satisfies at least one of the following characteristics:

[0016] (1) The polyvinyl alcohol solution contains 1.5% to 6% polyvinyl alcohol by mass.

[0017] (2) The mass ratio of the dicarboxylic acid to polyvinyl alcohol is (0.1~0.3):1;

[0018] (3) The mass ratio of the silver nanowires to polyvinyl alcohol is (0.005~0.01):1;

[0019] (4) The mass ratio of the graphene oxide quantum dots to polyvinyl alcohol is (0.0004~0.001):1.

[0020] In some embodiments, the preparation method satisfies at least one of the following characteristics:

[0021] (1) The length of the silver nanowire is 10 μm to 20 μm;

[0022] (2) The diameter of the silver nanowires is 30 nm to 50 nm;

[0023] (3) The particle size of the graphene oxide quantum dots is 2nm~6nm;

[0024] (4) The dicarboxylic acid includes at least one of malic acid, sulfosuccinic acid and maleic acid.

[0025] In some embodiments, in step S2, the preparation method satisfies at least one of the following characteristics:

[0026] (1) The temperature of the heat treatment is 90℃~120℃, and the time of the heat treatment is 10min~40min;

[0027] (2) The coating is a vacuum rod coating process, which includes the following steps: pouring the casting liquid onto the surface of the support layer; pouring the casting liquid in 2 to 5 times, with a pouring speed of 2 mm / s. - ¹~5mm·s- ¹;

[0028] (3) The viscosity of the casting solution is 20 mPa·s to 50 mPa·s.

[0029] In some embodiments, the preparation method includes at least one of the following features:

[0030] (1) In step S1, before adding the dicarboxylic acid, the silver nanowires, and the graphene oxide quantum dots, the step of degassing the polyvinyl alcohol solution by letting it stand for 5 to 12 hours is also included.

[0031] (2) Step S2 also includes a step of degassing the casting liquid by letting it stand for 5h~12h.

[0032] The third aspect of this application provides the application of the pervaporation membrane in any of the foregoing embodiments or the pervaporation membrane prepared according to the preparation method in any of the foregoing embodiments in seawater desalination or wastewater treatment.

[0033] The functional layer of the pervaporation membrane in this application includes silver nanowires, graphene oxide quantum dots, and ester-based polymer crosslinking materials. The silver nanowires dispersed within the ester-based polymer crosslinking materials can not only improve the antibacterial properties and operational stability of the pervaporation membrane, but also enhance its anti-swelling properties and mechanical properties. The small-sized graphene oxide quantum dots can construct hydrophilic mass transfer channels, which can enhance the rapid transport of water molecules while reducing the impact on permeation flux, and work synergistically with the silver nanowires to further improve the antibacterial properties. At the same time, thanks to the high crosslinking density of the ester-based polymer crosslinking materials, the synergistic effect with the uniformly dispersed silver nanowires and graphene oxide quantum dots can simultaneously improve the permeation flux, separation selectivity, and long-term operational stability of the pervaporation membrane. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments and examples of this application, and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments or examples will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. Those skilled in the art can obtain other drawings based on these drawings without creative effort. It should also be noted that the drawings are all drawn in a simplified form and are only used to conveniently and clearly assist in illustrating this application. The various dimensions of each component shown in the drawings are arbitrarily shown; they may be precise or not drawn to scale. For example, to make the illustration clearer, the dimensions of some components are appropriately exaggerated in the drawings. Unless otherwise specified, the components in the drawings are not drawn to scale. The drawings of this application do not limit each dimension of each component.

[0035] In the following description, the same reference numerals indicate the same parts.

[0036] Figure 1 This is a schematic diagram of the pervaporation membrane along its own thickness direction in one embodiment of this application;

[0037] Figure 2 This is a schematic diagram of the functional layers in one embodiment of this application;

[0038] Figure 3 In the image, a and b are transmission electron microscope images of graphene oxide quantum dots at different magnifications.

[0039] Figure 4 This is a scanning electron microscope image of the surface of the functional layer in the pervaporation membrane in Example 1;

[0040] Figure 5 A scanning electron microscope image of a cross-section of the pervaporation membrane in Example 1;

[0041] Figure 6 The images show the attenuated total reflectance Fourier transform infrared spectra of the pervaporation membranes in Example 1 and Comparative Example 4. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the accompanying drawings, embodiments, and examples. It should be understood that these embodiments and examples are for illustrative purposes only and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to enable a more thorough and comprehensive understanding of the disclosure of the present application. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. For example, features described or illustrated as part of one embodiment can be combined in a suitable manner in another embodiment to produce new embodiments. Furthermore, numerous details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for descriptive purposes only and is not intended to be limiting of the application.

[0044] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0045] The terms “and / or,” “or / and,” and “and / or” as used herein include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. “Any and all combinations” includes any two related listed items, any more related listed items, or a combination of all related listed items. For example, “A and / or B” includes three parallel options: A, B, and “a combination of A and B.”

[0046] In this application, "at least one" or "at least one of" means one or more; where "more" or "multiple" means, unless otherwise specified, a quantity greater than or equal to 2. For example, "at least one" means one or more than or equal to two.

[0047] In this application, the technical features or solutions described in open-ended language include both closed-ended technical features or solutions consisting of the listed contents and open-ended technical features or solutions that include the listed contents.

[0048] In this application, where the method flow involves multiple steps, unless otherwise explicitly stated herein, there is no strict order restriction on the execution of these steps; they can be executed in any order other than those described. Moreover, any step may include multiple sub-steps or multiple stages, which are not necessarily completed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be performed alternately or simultaneously with other steps or parts of the sub-steps or stages of other steps.

[0049] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0050] The first aspect of this application provides a pervaporation membrane, comprising a support layer and a functional layer disposed on the support layer; the functional layer comprises silver nanowires, graphene oxide quantum dots, and an ester-based polymer crosslinking material, wherein the silver nanowires and graphene oxide quantum dots are dispersed in the ester-based polymer crosslinking material. Compared to silver nanoparticles, silver nanowires (Ag-NWs) have a higher aspect ratio, and when dispersed within the functional layer of the pervaporation membrane, they can construct a three-dimensional mechanical reinforcement network, thereby enhancing the anti-swelling performance and mechanical properties of the functional layer; simultaneously, Ag-NWs can release silver ions to exert an antibacterial effect, which is beneficial to improving the operational stability of the pervaporation membrane and extending its service life; furthermore, graphene oxide quantum dots (GOQDs) can physically disrupt the cell membrane structure of bacteria, synergistically enhancing the antibacterial performance with Ag-NWs; and the presence of GOQDs also facilitates the construction of continuous hydrophilic mass transfer channels, thereby improving the separation selectivity of the pervaporation membrane. The ester-based polymer crosslinking material in this application has a high crosslinking density, which is beneficial for further improving the separation selectivity of the pervaporation membrane and enhancing its anti-swelling performance. Furthermore, compared to introducing single nanofillers such as graphene oxide nanosheets or carbon nanotubes into the functional layer, graphene oxide quantum dots are smaller in size. Their synergistic effect with Ag-NWs can also enhance the bonding force with the ester-based polymer crosslinking material, reducing the probability of aggregation. This achieves a synergistic effect between the crosslinked network and the uniformly dispersed GOQDs and Ag-NWs, improving the separation selectivity of the pervaporation membrane while also exhibiting good operational stability and high permeation flux, breaking through the traditional trade-off between permeation flux and separation selectivity. Therefore, the pervaporation membrane of this application possesses good separation selectivity, operational stability, and high permeation flux.

[0051] In some embodiments, the pervaporation flux of the pervaporation membrane of this application is increased by 182.6% compared with that of a pure PVA pervaporation membrane, and the salt rejection rate can be increased to 99.9%.

[0052] The pervaporation membrane of this application also has good economic benefits:

[0053] (1) Reduce operating costs: On the one hand, the pervaporation membrane of this application has good antibacterial properties, which can delay the formation of biofilm and reduce the frequency of sterilization and cleaning operations, thereby reducing cleaning costs; on the other hand, the pervaporation membrane of this application has good anti-swelling properties and mechanical properties, and high operational stability. During operation, the pervaporation membrane is not prone to cracks or damage, thereby reducing the cost of replacing the pervaporation membrane.

[0054] (2) Improved water production efficiency: The pervaporation membrane of this application has a high permeation flux, which can reduce operating energy consumption and improve the unit time processing efficiency under the same separation and treatment capacity, thereby improving water production efficiency.

[0055] Furthermore, in this application, only a very small amount of silver nanowires and graphene oxide quantum dots need to be added to the functional layer. The two work together to achieve the above-mentioned effects with a small amount of addition, and can also extend the service life of the pervaporation membrane. That is, while improving the separation selectivity, operational stability and permeation flux of the pervaporation membrane, cost can also be taken into account.

[0056] In some of these implementations, such as Figure 1 As shown, the pervaporation membrane 01 includes a support layer 12 and a functional layer 11 disposed on one surface of the support layer 12. In some embodiments, such as Figure 2 As shown, the functional layer 11 includes silver nanowires, graphene oxide quantum dots, and an ester-based polymer crosslinking material obtained by reacting polyvinyl alcohol with dicarboxylic acid (malic acid (MA)). The silver nanowires and graphene oxide quantum dots are dispersed in the ester-based polymer crosslinking material.

[0057] In some embodiments, the length of the silver nanowires is 10 μm to 20 μm. In some embodiments, the diameter of the silver nanowires is 30 nm to 50 nm. For example, the length of the silver nanowires can be, but is not limited to, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. For example, the diameter of the silver nanowires can be, but is not limited to, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, or 50 nm. When the length and diameter of the silver nanowires are within the above ranges, their aspect ratio is suitable, which is beneficial for further enhancing the anti-swelling performance and tensile strength of the functional layer, thereby further improving the operational stability of the pervaporation membrane and extending its service life.

[0058] This application does not impose any particular limitation on the aspect ratio of the silver nanowires, as long as the purpose of this application can be achieved. For example, the aspect ratio of the silver nanowires can be 300 to 800. For example, the aspect ratio of the silver nanowires can be, but is not limited to, 300, 400, 500, 600, 700, or 800.

[0059] In some embodiments, the particle size of graphene oxide quantum dots is 2 nm to 6 nm. For example, the particle size of graphene oxide quantum dots can be, but is not limited to, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.3 nm, 5.6 nm, 5.9 nm, and 6 nm. The particle size of graphene oxide quantum dots within the above range, and their uniform dispersion in the ester-based polymer crosslinking material of this application, is beneficial for further increasing hydrophilic mass transfer channels while reducing the impact on permeation flux, thereby achieving a balance between high separation selectivity and permeation flux.

[0060] In some embodiments, the thickness of the functional layer is 100nm to 1000nm. In some embodiments, the thickness of the functional layer is 100nm to 300nm. For example, the thickness of the functional layer may be, but is not limited to, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, or 1000nm.

[0061] In some embodiments, the thickness of the support layer is 100 μm to 300 μm. In some embodiments, the material of the support layer includes at least one selected from polypropylene (PP), polytetrafluoroethylene (PTFE), polyethersulfone, polyamide, cellulose acetate, and polyvinylidene fluoride (PVDF).

[0062] In some embodiments, the types of support layers include composite support layers, such as PP-supported PTFE support layers.

[0063] In this application, the dimensions of the silver nanowires, including their length and diameter, and the particle size of the graphene oxide quantum dots in the pervaporation membrane, are substantially the same as the dimensions of the corresponding raw materials added during the preparation of the pervaporation membrane. For example, the length and diameter of the silver nanowires can be controlled by adding silver nanowires of appropriate length and diameter during the preparation process. Similarly, the particle size of the graphene oxide quantum dots can be controlled by adding graphene oxide quantum dots of appropriate particle size during the preparation process.

[0064] For the specific testing methods of parameters such as the length of silver nanowires, the diameter of silver nanowires, and the particle size of graphene oxide quantum dots in this application, please refer to the section "Testing of the length of silver nanowires, the diameter of silver nanowires, and the particle size of graphene oxide quantum dots".

[0065] The second aspect of this application provides a method for preparing a pervaporation membrane, comprising the following steps: S1, adding dicarboxylic acid, silver nanowires, and graphene oxide quantum dots sequentially to a polyvinyl alcohol solution, mixing them evenly to obtain a casting solution; the dicarboxylic acid has 4 carbon atoms; S2, uniformly coating the casting solution onto the surface of a support layer, drying, and heat-treating to obtain a pervaporation membrane.

[0066] The pervaporation membrane of this application synergistically applies dicarboxylic acid, silver nanowires, and graphene oxide quantum dots to a PVA-based pervaporation membrane. The small-sized graphene oxide quantum dots can construct hydrophilic mass transfer channels, enhancing the rapid transport of water molecules while reducing the impact on permeation flux. At the same time, thanks to the good cross-linking effect between dicarboxylic acid and PVA, the two undergo a dehydration condensation reaction to form an ester-based polymer cross-linked material. The silver nanowires and graphene oxide quantum dots can be relatively uniformly dispersed inside the ester-based polymer cross-linked material. Through the synergistic effect of the above components, the permeation flux, separation selectivity, and long-term operational stability of the pervaporation membrane can be improved simultaneously.

[0067] Therefore, this application utilizes the synergistic effect of covalent cross-linking of dicarboxylic acids and PVA, hydrogen bonding bridging with GOQDs, and three-dimensional intercalation with Ag-NWs to form a stable cross-linked network, which can effectively inhibit the swelling of PVA in an aqueous environment. GOQDs can also construct nanoscale rapid water transfer channels within the formed cross-linked network, enabling rapid permeation and transport of water molecules. Furthermore, GOQDs and Ag-NWs synergistically enhance antibacterial properties, while also improving hydrophilic selectivity, permeation flux, and operational stability. It should be noted that the aforementioned dicarboxylic acids refer to organic acids containing two carboxyl groups.

[0068] Furthermore, on the one hand, the preparation method of the pervaporation membrane of this application adopts solution blending, coating and heat treatment processes, which can be directly compatible with traditional PVA pervaporation membrane and composite membrane production lines without the need for large-scale new equipment, and the process compatibility is high; on the other hand, only a low amount of nanomaterials (Ag-NWs, GOQDs) is needed to achieve the above effects, and the consumption of nanomaterials per unit membrane area is low, and the overall cost increase is controllable; therefore, the preparation method of this application has the conditions for large-scale promotion.

[0069] The polyvinyl alcohol used in this application can be obtained by purchase. For example, polyvinyl alcohol with a degree of alcoholysis ≥99% and a weight-average molecular weight (Mw) of 146,000 Da to 186,000 Da can be purchased.

[0070] The graphene oxide quantum dots in this application can be obtained by purchasing, for example, by purchasing an aqueous solution of graphene oxide quantum dots with a concentration of 0.05 mg / mL to 2 mg / mL.

[0071] The silver nanowires used in this application are available for purchase.

[0072] In some embodiments, step S1 includes a step of degassing the polyvinyl alcohol solution by letting it stand for 5 to 12 hours before adding the dicarboxylic acid, silver nanowires, and graphene oxide quantum dots; for example, but not limited to 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, and 12 hours.

[0073] This application does not impose any particular limitation on the method for preparing polyvinyl alcohol solution, as long as it achieves the purpose of this application. For example, PVA and water can be stirred continuously at 90℃~95℃ for 1h~5h until the PVA powder is completely dissolved to obtain a polyvinyl alcohol solution.

[0074] In some embodiments, the polyvinyl alcohol solution contains 1.5% to 6% by mass. For example, the polyvinyl alcohol content may be, but is not limited to, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, or 6% by mass.

[0075] In some embodiments, the mass ratio of dicarboxylic acid to polyvinyl alcohol is (0.1~0.3):1. For example, the mass ratio of dicarboxylic acid to polyvinyl alcohol may be, but is not limited to, 0.1:1, 0.15:1, 0.2:1, 0.25:1, or 0.3:1.

[0076] In some embodiments, the dicarboxylic acid includes at least one of malic acid, sulfosuccinic acid, and maleic acid.

[0077] In some embodiments, the mass ratio of silver nanowires to polyvinyl alcohol is (0.005~0.01):1. For example, the mass ratio of silver nanowires to polyvinyl alcohol can be, but is not limited to, 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1, or 0.01:1. By controlling the mass ratio of silver nanowires to polyvinyl alcohol within the above range, it is beneficial to promote the uniform distribution of silver nanowires, reduce agglomeration, and thus reduce defects caused by local phase separation in the pervaporation membrane. This helps to improve the separation selectivity, anti-swelling properties, and antibacterial properties of the pervaporation membrane while also considering cost.

[0078] In some embodiments, the length of the silver nanowires is 10 μm to 20 μm. In some embodiments, the diameter of the silver nanowires is 30 nm to 50 nm. For example, the length of the silver nanowires can be, but is not limited to, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. For example, the diameter of the silver nanowires can be, but is not limited to, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, or 50 nm.

[0079] In some embodiments, the mass ratio of graphene oxide quantum dots to polyvinyl alcohol is (0.0004~0.001):1. For example, the mass ratio of graphene oxide quantum dots to polyvinyl alcohol can be, but is not limited to, 0.0004:1, 0.0005:1, 0.0006:1, 0.0007:1, 0.0008:1, 0.0009:1, or 0.001:1. By controlling the mass ratio of graphene oxide quantum dots to polyvinyl alcohol within the above range, graphene oxide quantum dots can form strong interfacial interactions with PVA, i.e., form hydrogen bonds. Simultaneously, this promotes the uniform distribution of graphene oxide quantum dots, reduces agglomeration, and thus reduces defects caused by local phase separation in the pervaporation membrane. This allows for a better balance between the separation selectivity, permeation flux, and cost of the pervaporation membrane.

[0080] In some embodiments, the particle size of graphene oxide quantum dots is 2nm to 6nm; for example, the particle size of graphene oxide quantum dots can be, but is not limited to, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.3nm, 5.6nm, 5.9nm, and 6nm. By controlling the particle size of graphene oxide quantum dots within the above range, and combining them with the diacid and polyvinyl alcohol of this application, it is beneficial to increase the hydrophilic transport channels while promoting the uniform dispersion of graphene oxide quantum dots, which is beneficial to further balance the separation selectivity and permeation flux of the pervaporation membrane.

[0081] In some embodiments, the coating is a vacuum rod coating process, which includes the following steps: pouring a casting solution onto the surface of the support layer; pouring the casting solution in 2 to 5 stages at a pouring speed of 2 mm / s. - ¹~5mm·s - ¹; For example, the pouring speed can be, but is not limited to, 2 mm·s. - ¹、2.5mm·s - ¹、3mm·s - ¹、3.5mm·s - ¹、4mm·s - ¹、4.5mm·s - ¹、5mm·s - ¹. By controlling the number of casting pours within the above-mentioned range, it is beneficial to compensate for potential microscopic defects in a single coating and to control the thickness, thereby facilitating the preparation of a pervaporation membrane with suitable thickness and good integrity. Controlling the pouring speed within the above-mentioned range helps to reduce the probability of uneven thickness or streak defects in the pervaporation membrane. Therefore, the above settings facilitate the preparation of a pervaporation membrane with suitable thickness, good uniformity, and good integrity.

[0082] In some embodiments, the viscosity of the casting solution is 20 mPa·s to 50 mPa·s. For example, the viscosity of the casting solution can be, but is not limited to, 20 mPa·s, 25 mPa·s, 30 mPa·s, 35 mPa·s, 40 mPa·s, 45 mPa·s, or 50 mPa·s. By adjusting the viscosity of the casting solution within the above range, it is beneficial to further improve the controllability of the pervaporation membrane thickness and further improve the uniformity and integrity of the pervaporation membrane.

[0083] In some embodiments, step S2 further includes a degassing step of allowing the casting solution to stand for 5 to 12 hours. For example, the standing time of the casting solution can be, but is not limited to, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. These steps help remove air bubbles from the casting solution, thereby reducing defects in the functional layer and improving the density of the functional layer, resulting in a uniform and intact pervaporated membrane.

[0084] This application does not impose any particular restrictions on the drying conditions in step S2, as long as the purpose of this application can be achieved. For example, after coating is completed, it can be naturally dried at room temperature (25℃±5℃).

[0085] In some embodiments, in step S2, the heat treatment temperature is 90℃~120℃, and the heat treatment time is 10min~40min; for example, the heat treatment temperature can be, but is not limited to, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, or 120℃. For example, the heat treatment time can be, but is not limited to, 10min, 15min, 20min, 25min, 30min, 35min, or 40min. Through the heat treatment process, the three-dimensional network and interface interaction within the functional layer are fixed, which helps to suppress excessive swelling of PVA in the aqueous environment and improves the mechanical properties and chemical stability of the membrane. By controlling the heat treatment temperature and time within the above range, the full crosslinking of polyvinyl alcohol and dicarboxylic acid can be promoted, and the pervaporation membrane can maintain good mechanical properties and chemical stability, thereby obtaining a pervaporation membrane with good crosslinking density, anti-swelling performance, and mechanical properties.

[0086] The third aspect of this application provides the application of the pervaporation membrane in any of the foregoing embodiments, or the pervaporation membrane prepared according to the preparation method in any of the foregoing embodiments, in seawater desalination or wastewater treatment. Benefiting from the excellent separation selectivity, anti-swelling performance, mechanical properties, and high permeation flux of the pervaporation membrane of this application, it can also reduce the frequency of pervaporation membrane replacement, thereby reducing the amount of solid waste (discarded pervaporation membrane) generated, extending equipment life, and conforming to the concept of a circular economy. Therefore, it has good application prospects in seawater desalination or wastewater treatment, such as desalination of high-salinity wastewater.

[0087] In addition to its potential applications in seawater desalination or wastewater treatment, the pervaporation membrane separation method of this application also has the following application prospects:

[0088] (1) Reduce industrial energy consumption: It can also replace traditional high-energy-consuming distillation and extraction processes in industries such as chemical and pharmaceutical manufacturing, which is conducive to reducing energy consumption in the separation process. The pervaporation membrane separation of this application has a higher permeation flux and a higher yield per unit membrane area, which is conducive to further reducing energy consumption per unit product.

[0089] (2) Resource utilization of chemical waste liquid: For high-salt and high-organic waste liquid in chemical production, useful components are extracted and water resources are purified by pervaporation membrane separation.

[0090] (3) Technological scalability: The "synergistic crosslinking of nanomaterials" modification approach can be transferred to other separation membrane fields such as nanofiltration and reverse osmosis, promoting technological innovation in the upstream and downstream industrial chains such as membrane materials, nanofillers, and membrane modules, and driving the overall technological upgrade of the separation industry.

[0091] (4) Breaking through the limitations of traditional membrane technology industrialization: The pervaporation membrane of this application has good operational stability, antibacterial properties and high permeation flux while having separation selectivity. It solves the key problems of traditional PVA pervaporation membranes such as easy swelling, difficulty in balancing permeation flux and separation selectivity, and weak resistance to biofouling. It improves the high-performance pervaporation membrane technology system and promotes the large-scale application of membrane separation technology in the industrial field.

[0092] The embodiments of this application will be described in detail below with reference to some examples. It should be understood that these embodiments are only for illustrating this application and are not intended to limit the scope of this application. For experimental methods in the following embodiments where conditions are not specified, please refer to the guidelines given in this application first, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0093] In the following examples, the measurement parameters of the raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0094] Test method:

[0095] Measurements of the length and diameter of silver nanowires, and the particle size of graphene oxide quantum dots:

[0096] Silver nanowire raw materials from each embodiment or comparative example were observed and tested using transmission electron microscopy (TEM). Silver nanowires were found in the test samples (EDS testing included Ag element), and their length and diameter were tested. A total of 10 silver nanowires were selected and their length and diameter were tested according to the above method. The maximum and minimum values ​​of the test were removed, and the length range and diameter range of the remaining silver nanowires were recorded, which are the length and diameter of the silver nanowires.

[0097] Then, using transmission electron microscopy, 10 graphene oxide quantum dots (EDS testing includes C element) were selected from the graphene oxide quantum dot raw material, and their circumscribed circle diameters were measured. The maximum and minimum values ​​were removed, and the range of circumscribed circle diameters of the remaining graphene oxide quantum dots was recorded; this range represents the particle size of the graphene oxide quantum dots. For example, as shown... Figure 3 Figures a and b show transmission electron microscope (TEM) images of graphene oxide quantum dots. Ten graphene oxide quantum dots were randomly selected from these images. Figure 3 The above method can be used to test at magnification b.

[0098] Tests on ester-based polymer crosslinked materials:

[0099] The ester-based polymer crosslinked material in the pervaporation membrane was characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), with a wavenumber range of 400 cm⁻¹. - ¹~4000cm - ¹, resolution 4cm - ¹, Scan 32 times with background subtraction pre-emptively; Before testing, thoroughly dry and wash the sample to remove unreacted monomers to avoid interference from moisture and residual impurities. The presence of the ester-based polymer crosslinked material is determined by changes in infrared characteristic peaks: Compared to the pervaporation membrane without ester-based polymer crosslinked material, the crosslinked ester-based polymer crosslinked material exhibits higher peak values ​​at 1700 cm⁻¹. - ¹~1750cm - A new peak for the stretching vibration of the ester carbonyl group appears at position ¹, at 3200 cm⁻¹. - ¹~3400cm - ¹The intensity of the hydroxyl absorption peak decreased significantly, at 1080 cm⁻¹ - ¹~1100cm - ¹The carbon-oxygen bond peak shifts and its intensity increases.

[0100] Salt cutoff test:

[0101] During the pervaporation desalination salt cutoff rate test, the conductivity of the feed brine and the permeate was measured and the corresponding salt concentration was calculated. Specifically, after the system was running stably, the salt concentration of the feed solution and the permeate was measured. The salt cutoff rate was calculated according to the formula R=(Cf-Cp) / Cf×100%, where Cf and Cp are the feed salt concentration and the permeate salt concentration, respectively. The feed salt solution contained 3.5wt% sodium chloride. The average value was taken after three tests and verifications as the final value. Multiple sampling tests were conducted and the average value was taken to ensure the accuracy of the data.

[0102] This application evaluates the separation selectivity of the pervaporation membrane by using the salt cutoff ratio. The higher the salt cutoff ratio, the better the separation selectivity of the pervaporation membrane; conversely, the lower the salt cutoff ratio, the worse the separation selectivity of the pervaporation membrane.

[0103] Permeation flux test:

[0104] Under the conditions of an influent water temperature of 30℃ and a membrane permeation vacuum of 100Pa, after the pervaporation system has reached a stable state, the permeate permeated through the membrane is collected periodically and weighed. The membrane flux is calculated according to the formula J=m / (A×t), where m is the mass of the permeate, A is the effective membrane area, and t is the collection time. The average value of the three calculations is taken as the final flux result.

[0105] Run stability test:

[0106] Under conditions of influent water temperature of 30℃, membrane permeation vacuum of 100Pa, and feed flow rate of 0.5m / s, the pervaporation unit was continuously operated without interruption. Throughout the process, process parameters such as temperature, vacuum, and feed flow rate were kept constant. Membrane flux and salt rejection were measured every 0.5 hours. The pervaporation unit was tested for 200 hours, and the rate of decrease in permeate flux was recorded. When the rate of decrease in permeate flux was greater than or equal to 15%, the stability was recorded as low; when the rate of decrease in permeate flux was greater than or equal to 10% but less than 15%, the stability was recorded as medium; and when the rate of decrease in permeate flux was less than 10%, the stability was recorded as high.

[0107] The rate of decrease in permeation flux = 1 - permeation flux at 200 h / initial permeation flux × 100%.

[0108] This application evaluates the operational stability of the pervaporation membrane by the rate of decrease in permeability. The lower the rate of decrease in permeability, the better the antibacterial performance and the better the operational stability of the pervaporation membrane; conversely, the higher the rate of decrease in permeability, the worse the antibacterial performance and the worse the operational stability of the pervaporation membrane.

[0109] Example 1:

[0110] The method for preparing the pervaporation membrane of this application includes the following steps:

[0111] Preparation of polyvinyl alcohol solution: 3g of PVA powder (PVA degree of alcoholysis ≥99%, average molecular weight (Mw) 146000Da~186000Da, purchased from Sigma-Aldrich, product number: 363065-500G) was added to 97g of deionized water and stirred continuously at 100℃ for 3h until the PVA powder was completely dissolved. After standing for 12h to degas, it was ready for use. The polyvinyl alcohol content in the polyvinyl alcohol solution was 3% by mass.

[0112] S1. Malic acid (a dicarboxylic acid), silver nanowires (purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., item number: XFJ95), and graphene oxide quantum dot solution (an aqueous solution with a concentration of 1 mg / mL of graphene oxide quantum dots, purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., item number: XF042) were sequentially added to a polyvinyl alcohol solution and mixed evenly to obtain a casting solution. The solution was allowed to stand for 12 hours to degas. The viscosity of the casting solution was 30 mPa·s; the length of the silver nanowires was 10 μm to 20 μm and the diameter was 20 nm to 50 nm; the particle size of the graphene oxide quantum dots was 2 nm to 6 nm; the mass ratio of dicarboxylic acid to polyvinyl alcohol was 1:5; the mass ratio of silver nanowires to polyvinyl alcohol was 0.007:1; and the mass ratio of graphene oxide quantum dots to polyvinyl alcohol was 0.0008:1.

[0113] S2. Using a vacuum rod coating process, half the total mass of the casting solution is coated at a speed of 3 mm / s. - ¹ The casting liquid is poured onto the surface of the support layer (PP-supported PTFE membrane with a thickness of 200 μm) at a casting speed. After casting, a uniform functional layer liquid film is formed on the surface of the support layer. Then, the functional layer liquid film is uniformly coated to form a functional layer wet film of uniform thickness. Then, it is naturally dried at room temperature (25℃) for 1 hour. Then, the remaining half mass of the casting liquid is poured, coated, and dried according to the above steps. Then, it is placed in an oven at 90℃ for heat treatment for 20 minutes to obtain a pervaporation membrane.

[0114] The thickness of the functional layer in the prepared pervaporation membrane is 300 nm.

[0115] Examples 2 to 7:

[0116] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0117] Example 8:

[0118] Except for adjusting the relevant preparation parameters according to Table 2, everything else is the same as in Example 1.

[0119] Examples 9 to 11:

[0120] Except for adjusting the relevant preparation parameters according to Table 3, everything else is the same as in Example 1.

[0121] Comparative Examples 1 to 3:

[0122] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0123] Comparative Example 4:

[0124] Except for the preparation of the casting solution as described below, the rest is the same as in Example 1.

[0125] Preparation of polyvinyl alcohol solution: Same as in Example 1.

[0126] The polyvinyl alcohol solution described above was used as the casting solution for subsequent preparation steps.

[0127] Comparative Example 5:

[0128] Except for replacing the silver nanowires with silver nanoparticles (with a particle size of 10 nm to 100 nm), the rest is the same as in Example 1; wherein the mass ratio of silver nanoparticles to polyvinyl alcohol is 0.007:1.

[0129] Comparative Example 6:

[0130] Except for replacing graphene oxide quantum dots with graphene oxide (particle size 0.5μm~5μm), the rest is the same as in Example 1; wherein the mass ratio of graphene oxide to polyvinyl alcohol is 0.0008:1.

[0131] Comparative Example 7:

[0132] Except for the absence of dicarboxylic acids, it is the same as in Example 1.

[0133] The pervaporation membranes in each embodiment or comparative example were applied to wastewater treatment.

[0134] The data for each embodiment and comparative example are shown in Tables 1 to 3.

[0135] Table 1

[0136]

[0137] Note: " / " in Table 1 indicates that no relevant preparation parameters exist; m0 is the mass percentage of polyvinyl alcohol in the polyvinyl alcohol solution; m1 is the mass ratio of dicarboxylic acid to polyvinyl alcohol; m2 is the mass ratio of silver nanowires to polyvinyl alcohol; m3 is the mass ratio of graphene oxide quantum dots to polyvinyl alcohol.

[0138] Table 2

[0139]

[0140] Table 3

[0141]

[0142] As can be seen from Examples 1 to 11 and Comparative Examples 1 to 7, the pervaporation membranes prepared according to the preparation method of this application include silver nanowires, graphene oxide quantum dots, and ester-based polymer crosslinking materials. In wastewater treatment applications, the pervaporation membranes have high salt rejection rates, large permeation flux, and long stable operating time. Comparative Example 1 did not include silver nanowires; Comparative Example 2 did not include graphene oxide quantum dots; Comparative Example 3 did not include either silver nanowires or graphene oxide quantum dots. The resulting pervaporation membrane exhibited acceptable salt rejection and operational stability, but low permeation flux. Comparative Example 4 did not include ester-based polymer crosslinking materials, silver nanowires, or graphene oxide quantum dots. The resulting pervaporation membrane had low salt rejection, permeation flux, and operational stability. Comparative Example 5 replaced silver nanowires with silver nanoparticles; Comparative Example 6 replaced graphene oxide quantum dots with graphene oxide. The resulting pervaporation membrane exhibited acceptable salt rejection and operational stability, but low permeation flux. Comparative Example 7 did not include ester-based polymer crosslinking materials. Although the salt rejection and operational stability were acceptable, the permeation flux was low. This demonstrates that the pervaporation membrane of this application possesses high separation selectivity, permeation flux, and operational stability.

[0143] Specifically, such as Figure 4 As shown, the surface of the functional layer in Example 1 is intact, without obvious cracks or defects. For example... Figure 5 As shown, the pervaporation membrane in Example 1 includes a support layer 12 and a functional layer 11. The functional layer 11 has a uniform thickness and good uniformity and integrity. Figure 6 As shown, compared to the pervaporation membrane in Comparative Example 4, the pervaporation membrane in Example 1 has a lower pervaporation rate at 1750 cm⁻¹. - ¹~1950cm - A new peak of stretching vibration of the ester carbonyl group (C=O) appears at ¹, at 3050 cm⁻¹. - ¹~3550cm - The intensity of the hydroxyl absorption peak ¹ decreased significantly at 1200 cm⁻¹. - ¹~1350cm -The simultaneous presence of a carbon-oxygen bond (COC) peak, a new carbonyl (C=O) stretching vibration peak, and a COC peak in the pervaporation membrane of Example 1 indicates that the membrane includes an ester-based polymer crosslinking material. Specifically, a hydrophilic functional layer composed of PVA, GOQDs, Ag-NWs, and an ester-based polymer crosslinking material is attached to the surface of a PP-supported PTFE hydrophobic support membrane (hydrophobic support layer). During the pervaporation process, water molecules in the feed liquid are preferentially adsorbed onto the hydrophilic selective layer, rapidly pass through the two-dimensional selective water channels constructed by GOQDs, and ultimately pass through the hydrophobic support layer for separation. Meanwhile, salt ions in the feed liquid are synergistically retained by the ester-based polymer crosslinking material and the nanofillers (GOQDs, Ag-NWs), thereby achieving efficient separation. This demonstrates that the pervaporation membrane prepared by the method of this application has uniform thickness, uniformity, and good integrity, and can be widely used in various pervaporation separation scenarios such as organic solvent dehydration, fermentation alcohol separation, chemical solvent-containing wastewater treatment, and pharmaceutical intermediate purification. The applicable scenarios cover multiple industrial fields such as fine chemicals, bio-fermentation, and environmental resource utilization.

[0144] As can be seen from Examples 1 to 7, the mass percentage content of polyvinyl alcohol (PVA), the mass ratio of dicarboxylic acid to PVA, and the mass ratio of silver nanowires to PVA affect the separation selectivity, permeate flux, and operational stability of the pervaporation membrane. When the mass percentage content of PVA, the mass ratio of dicarboxylic acid to PVA, and the mass ratio of silver nanowires to PVA are within the range of this application, the salt rejection rate, permeate flux, and operational stability of the pervaporation membrane are all high. This demonstrates that by controlling the mass percentage content of PVA, the mass ratio of dicarboxylic acid to PVA, and the mass ratio of silver nanowires to PVA within the range of this application, the pervaporation membrane can achieve a balance of high separation selectivity, permeate flux, and operational stability.

[0145] As can be seen from Examples 1 and 8, the type of dicarboxylic acid affects the separation selectivity, permeate flux, and operational stability of the pervaporation membrane. When the type of dicarboxylic acid is within the scope of this application, the salt rejection rate, permeate flux, and operational stability of the pervaporation membrane are all high. This demonstrates that by controlling the type of dicarboxylic acid within the scope of this application, the pervaporation membrane can achieve a balance of high separation selectivity, permeate flux, and operational stability.

[0146] As can be seen from Examples 1 and 9, the number of pours, the pouring speed, and the viscosity of the casting solution affect the pervaporation flux and operational stability of the pervaporation membrane. When the number of pours, the pouring speed, and the viscosity of the casting solution are within the range of this application, and the thickness of the functional layer is also within the range of this application, the pervaporation flux and operational stability of the pervaporation membrane are both high. This demonstrates that by controlling the number of pours, the pouring speed, and the viscosity of the casting solution within the range of this application, the pervaporation membrane can achieve both high pervaporation flux and operational stability. It should be noted that the effects of the number of pours, the pouring speed, and the viscosity of the casting solution on the salt rejection rate of the pervaporation membrane are negligible.

[0147] As can be seen from Examples 1, 10, and 11, the temperature and time of heat treatment affect the pervaporation flux and operational stability of the pervaporation membrane. When the temperature and time of heat treatment are within the range of this application, both the pervaporation flux and operational stability of the pervaporation membrane are high. This demonstrates that by controlling the temperature and time of heat treatment within the range of this application, the pervaporation membrane can achieve both high pervaporation flux and operational stability. It should be noted that the effect of the temperature and time of heat treatment on the salt rejection rate of the pervaporation membrane is negligible.

[0148] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0149] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A pervaporation membrane, characterized in that, The pervaporation membrane includes a support layer and a functional layer disposed on the support layer; the functional layer includes silver nanowires, graphene oxide quantum dots and ester-based polymer crosslinking material, wherein the silver nanowires and the graphene oxide quantum dots are dispersed in the ester-based polymer crosslinking material.

2. The pervaporation membrane according to claim 1, characterized in that, The length of the silver nanowire is 10 μm to 20 μm; and / or the diameter of the silver nanowire is 30 nm to 50 nm.

3. The pervaporation membrane according to claim 1, characterized in that, The particle size of the graphene oxide quantum dots is 2nm~6nm.

4. The pervaporation membrane according to any one of claims 1 to 3, characterized in that, The pervaporation membrane satisfies at least one of the following characteristics: (1) The thickness of the functional layer is 100nm~1000nm; (2) The thickness of the support layer is 100μm~300μm; (3) The material of the support layer includes at least one of polypropylene, polytetrafluoroethylene, polyethersulfone, polyamide, cellulose acetate and polyvinylidene fluoride.

5. A method for preparing a pervaporation membrane, characterized in that, Includes the following steps: S1. Dicarboxylic acid, silver nanowires, and graphene oxide quantum dots are added sequentially to a polyvinyl alcohol solution and mixed evenly to obtain a casting solution; the dicarboxylic acid has 4 carbon atoms. S2. The casting solution is uniformly coated on the surface of the support layer, dried, and heat-treated to obtain the pervaporation membrane.

6. The preparation method according to claim 5, characterized in that, The preparation method satisfies at least one of the following characteristics: (1) The polyvinyl alcohol solution contains 1.5% to 6% polyvinyl alcohol by mass. (2) The mass ratio of the dicarboxylic acid to polyvinyl alcohol is (0.1~0.3):1; (3) The mass ratio of the silver nanowires to polyvinyl alcohol is (0.005~0.01):1; (4) The mass ratio of the graphene oxide quantum dots to polyvinyl alcohol is (0.0004~0.001):

1.

7. The preparation method according to claim 5, characterized in that, The preparation method satisfies at least one of the following characteristics: (1) The length of the silver nanowire is 10 μm to 20 μm; (2) The diameter of the silver nanowires is 30 nm to 50 nm; (3) The particle size of the graphene oxide quantum dots is 2nm~6nm; (4) The dicarboxylic acid includes at least one of malic acid, sulfosuccinic acid and maleic acid.

8. The preparation method according to claim 5, characterized in that, In step S2, the preparation method satisfies at least one of the following characteristics: (1) The temperature of the heat treatment is 90℃~120℃, and the time of the heat treatment is 10min~40min; (2) The coating is a vacuum rod coating process, which includes the following steps: pouring the casting liquid onto the surface of the support layer; pouring the casting liquid in 2 to 5 times, with a pouring speed of 2 mm / s. - ¹~5mm·s - ¹; (3) The viscosity of the casting solution is 20 mPa·s to 50 mPa·s.

9. The preparation method according to any one of claims 5 to 8, characterized in that, The preparation method includes at least one of the following features: (1) In step S1, before adding the dicarboxylic acid, the silver nanowires, and the graphene oxide quantum dots, the step of degassing the polyvinyl alcohol solution by letting it stand for 5 to 12 hours is also included. (2) Step S2 also includes a step of degassing the casting liquid by letting it stand for 5h~12h.

10. The application of the pervaporation membrane according to any one of claims 1 to 4 or the pervaporation membrane prepared according to any one of claims 5 to 9 in seawater desalination or wastewater treatment.

Images