Antifouling composite membrane and preparation method and application thereof

Abstract

This invention relates to antifouling composite membranes, their preparation methods, and applications. The preparation method of the antifouling composite membrane includes the following steps: preparing a coating solution by mixing water-soluble polyphenols, protein, a water-soluble polymer containing carboxyl groups, a soluble calcium salt, and water; placing the coating solution on the surface of a separation membrane; then placing the separation membrane with the coating solution in a sealed container containing bicarbonate; and performing heat treatment to form a pre-formed antifouling layer, thereby obtaining a pre-formed antifouling composite membrane. The heat treatment temperature is greater than or equal to the thermal decomposition temperature of the bicarbonate. Finally, the pre-formed antifouling composite membrane is cleaned to form an antifouling layer, resulting in the antifouling composite membrane. The antifouling composite membrane prepared by this method exhibits high stability, high rejection rate, high water flux, and high antifouling performance when applied to water treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of separation membranes, in particular to an anti-fouling composite membrane and a preparation method and application thereof. BACKGROUND

[0002] In order to improve the anti-fouling property of separation membranes such as reverse osmosis membranes, an anti-fouling layer is usually constructed on the surface of the separation membrane, and the core function thereof is to reduce the interaction between the pollutants and the membrane surface through surface modification, thereby delaying the accumulation of pollution, prolonging the cleaning cycle and reducing the maintenance cost.

[0003] At present, the preparation methods of the anti-fouling layer mainly include the following ways: first, directly coating a hydrophilic polymer on the membrane surface; second, grafting functional molecules on the membrane surface; third, forming a dense and hydrophilic multi-layer structure on the membrane surface by using layer-by-layer self-assembly method; and fourth, introducing nanomaterials such as graphene oxide for compounding. However, the anti-fouling layer prepared by the above preparation methods has the problems of poor stability and easy falling off during use, and at the same time, the anti-fouling layer itself also increases the mass transfer resistance of the membrane, resulting in a decrease in the water flux of the membrane. SUMMARY

[0004] Therefore, it is necessary to provide an anti-fouling composite membrane and a preparation method and application thereof aiming at the above problems, and the anti-fouling composite membrane prepared by the preparation method has the performances of high stability, high rejection rate, high water flux and high anti-fouling when applied to water treatment.

[0005] A preparation method of an anti-fouling composite membrane, comprising the following steps:

[0006] Preparation of a coating solution by mixing a water-soluble polyphenol, a protein, a water-soluble polymer containing a carboxylate, a soluble calcium salt and water;

[0007] Placing the coating solution on the surface of a separation membrane, and then placing the separation membrane with the coating solution in a sealed container containing bicarbonate, and performing heat treatment to form a pre-prepared anti-fouling layer, thereby obtaining a pre-prepared anti-fouling composite membrane, wherein the temperature of the heat treatment is greater than or equal to the thermal decomposition temperature of the bicarbonate;

[0008] Cleaning treatment of the pre-prepared anti-fouling composite membrane to form an anti-fouling layer, thereby obtaining an anti-fouling composite membrane.

[0009] In one embodiment, the mass ratio of the water-soluble polyphenol to the protein is 1:1-1:10;

[0010] And / or, the mass ratio of the water-soluble polymer containing a carboxylate to the soluble calcium salt is 1:1-3:1.

[0011] In one embodiment, the mass fraction of the water-soluble polyphenol in the coating solution is 0.1%-1%;

[0012] And / or, the water-soluble polyphenols are selected from at least one of tannic acid, gallic acid, and tea polyphenols.

[0013] In one embodiment, the mass fraction of protein in the application solution is 0.1%-1%;

[0014] And / or, the protein is selected from at least one of whey protein, sericin, or ovalbumin.

[0015] In one embodiment, the mass fraction of the water-soluble polymer containing carboxylate groups in the coating solution is 0.1%-3%;

[0016] And / or, the water-soluble polymer containing carboxyl groups is selected from sodium polyacrylate and / or polyacrylic acid.

[0017] In one embodiment, the mass fraction of soluble calcium salt in the application solution is 0.1%-1%;

[0018] And / or, the soluble calcium salt is selected from calcium chloride.

[0019] In one embodiment, the bicarbonate is selected from at least one of ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate;

[0020] And / or, the bicarbonate is placed in the sealed container in solid form.

[0021] In one embodiment, the prefabricated antifouling composite membrane is ultrasonically cleaned, wherein the ultrasonic cleaning temperature is 50℃-80℃, the frequency is 40kHz-80kHz, and the time is 5min-10min.

[0022] And / or, the separation membrane is selected from any one of reverse osmosis membrane, nanofiltration membrane, or ultrafiltration membrane.

[0023] An antifouling composite membrane prepared using the aforementioned method.

[0024] Application of the aforementioned antifouling composite membrane in a water treatment device.

[0025] In the preparation method of the antifouling composite membrane of the present invention, when the coating liquid is placed on the surface of the separation membrane, the water-soluble polyphenols in the coating liquid combine with proteins to form a three-dimensional network structure, constituting the framework of the antifouling prefabricated layer; while the water-soluble polymer containing carboxyl groups combines with the three-dimensional network structure through hydrogen bonds and electrostatic interactions to enhance the strength of the three-dimensional network structure and introduce hydrophilic groups into it; calcium ions combine with the carboxyl groups of the polymer through electrostatic interactions and are uniformly dispersed in the three-dimensional network structure. This three-dimensional network structure contains a large number of hydrophilic groups, which can significantly enhance the hydrophilicity of the antifouling layer surface, thereby improving the antifouling properties and water flux of the composite membrane. When the separation membrane loaded with the coating solution is placed in a closed container containing bicarbonate and subjected to heat treatment at a specific temperature, the bicarbonate decomposes to produce carbon dioxide gas. The carbon dioxide gas diffuses into the three-dimensional network structure and dissolves into carbonate ions. Subsequently, under the synergistic regulation of carboxylate ions and proteins, it undergoes an in-situ mineralization reaction with calcium ions in the three-dimensional network structure to generate sheet-like nano-calcium carbonate crystals. These sheet-like nano-calcium carbonate crystals are interspersed in the three-dimensional network structure, forming a prefabricated antifouling layer with a nacreous layered structure. Finally, through a cleaning process, the sheet-like nano-calcium carbonate crystals in the prefabricated antifouling layer are removed, and sheet-like nanochannels are formed in situ to obtain the antifouling layer. These sheet-like nanochannels significantly reduce the mass transfer resistance of the composite membrane, thereby significantly improving the water flux of the antifouling composite membrane. Meanwhile, due to the strong adhesiveness of water-soluble polyphenols, the antifouling layer can be firmly bonded to the surface of the separation membrane, thereby significantly improving the stability of the antifouling composite membrane.

[0026] Therefore, when the antifouling composite membrane of the present invention is applied to water treatment, it can combine high stability, high rejection rate, high water flux and high antifouling performance. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is an electron microscope image of the antifouling composite membrane prepared in Example 1 of the present invention;

[0029] Figure 2 This is an electron microscope image of the antifouling composite membrane prepared in Comparative Example 1 of the present invention;

[0030] Figure 3 This is an electron microscope image of the antifouling composite membrane prepared in Comparative Example 8 of the present invention. Detailed Implementation

[0031] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0032] 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 invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional range of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0033] The method for preparing the antifouling composite membrane provided by the present invention includes the following steps:

[0034] A coating solution is prepared by combining water-soluble polyphenols, proteins, water-soluble polymers containing carboxyl groups, soluble calcium salts, and water.

[0035] The coating liquid is placed on the surface of the separation membrane, and then the separation membrane with the coating liquid is placed in a sealed container containing bicarbonate. After heat treatment, a pre-fabricated antifouling layer is formed, and a pre-fabricated antifouling composite membrane is obtained. The heat treatment temperature is greater than or equal to the thermal decomposition temperature of bicarbonate.

[0036] The prefabricated antifouling composite membrane is cleaned to form an antifouling layer, thus obtaining the antifouling composite membrane.

[0037] In this invention, when the coating solution is placed on the surface of the separation membrane, the water-soluble polyphenols in the coating solution combine with proteins through hydrogen bonds and hydrophobic interactions to form a three-dimensional network structure, constituting the prefabricated antifouling layer framework. Meanwhile, the water-soluble polymers containing carboxyl groups combine with the three-dimensional network structure through hydrogen bonds and electrostatic forces, further enhancing the strength of the three-dimensional network structure and introducing carboxyl groups and hydrophilic groups into it. Simultaneously, calcium ions combine with the carboxyl groups of the water-soluble polymers through electrostatic forces, uniformly dispersing within the three-dimensional network structure. This three-dimensional network structure contains a large number of hydrophilic groups such as phenolic hydroxyl, amino, and carboxyl groups, which can significantly improve the hydrophilicity of the antifouling layer surface, thereby enhancing the antifouling properties and water flux of the composite membrane.

[0038] When the separation membrane with the coating solution is placed in a sealed container containing bicarbonate and heat-treated at a specific temperature, the bicarbonate decomposes to produce carbon dioxide gas. Driven by the concentration gradient, the carbon dioxide gas slowly diffuses into the three-dimensional network structure, rapidly dissolves in the micro-aqueous environment of the three-dimensional network structure, and transforms into carbonate ions. Subsequently, under the synergistic regulation of carboxylate ions and proteins, the carbonate ions undergo an in-situ mineralization reaction with calcium ions in the three-dimensional network structure to generate nano-calcium carbonate crystals. Due to the confinement effect of the three-dimensional network structure and the selective adsorption of protein crystal faces, these nano-calcium carbonate crystals exhibit a plate-like morphology and are arranged along the network orientation, interpenetrating with the three-dimensional network structure to jointly form a prefabricated antifouling layer with a nacre-like layered structure.

[0039] Finally, during the cleaning process, the sheet-like nano-calcium carbonate crystals in the pre-fabricated antifouling layer are removed, forming sheet-like nanochannels in situ. This results in an antifouling layer with sheet-like nanochannels, which significantly reduce the mass transfer resistance of the composite membrane, thereby greatly increasing the water flux of the antifouling composite membrane. Simultaneously, due to the strong adhesiveness of water-soluble polyphenols, the antifouling layer can firmly bind to the separation membrane surface, significantly improving the stability of the antifouling composite membrane.

[0040] Therefore, when the antifouling composite membrane of the present invention is applied to water treatment, it can combine high stability, high rejection rate, high water flux and high antifouling performance.

[0041] It should be noted that in this invention, during the cleaning process, the sheet-like nano-calcium carbonate crystals in the prefabricated antifouling layer can be completely or partially removed. When partially removed, the retained calcium carbonate crystals, together with the three-dimensional network structure, constitute a nacre-like framework. At the same time, the removed portion forms nanochannels, which can effectively reduce the mass transfer resistance of the composite membrane, increase the water flux of the composite membrane, and ensure the structural stability of the antifouling layer.

[0042] In this invention, the mass ratio of the water-soluble polyphenol to the protein is 1:1 to 1:10. By adjusting the mass ratio of the water-soluble polyphenol to the protein, the density of the three-dimensional network structure formed by the two through hydrogen bonds and hydrophobic interactions can be controlled, thereby improving the structural strength of the three-dimensional network structure and enhancing the mechanical properties of the antifouling layer.

[0043] Optionally, the mass fraction of water-soluble polyphenols in the coating solution is 0.1%-1%; the mass fraction of protein in the coating solution is 0.1%-1%. With this setting, by controlling the mass fraction of water-soluble polyphenols and protein in the coating solution, the mass ratio of the two can be controlled within a suitable range, thereby regulating the density of the three-dimensional network structure formed by the two and enhancing the mechanical properties of the anti-fouling layer.

[0044] Optionally, the water-soluble polyphenol is selected from at least one of tannic acid, gallic acid, and tea polyphenols.

[0045] Optionally, the protein is selected from at least one of whey protein, sericin, or ovalbumin.

[0046] In the present invention, the mass ratio of the water-soluble polymer containing carboxylate groups to the soluble calcium salt is 1:1 - 3:1; with such a setting, by regulating the mass ratio of the water-soluble polymer containing carboxylate groups to the soluble calcium salt, calcium ions can be fully combined with the carboxylate groups of the water-soluble polymer through electrostatic interaction, and uniformly anchored as the water-soluble polymer is uniformly distributed in the three-dimensional network structure, thereby effectively avoiding the aggregation of free calcium ions, improving the dispersion of calcium ions in the three-dimensional network structure, and then in-situ generating uniformly distributed flaky calcium carbonate crystals during the heat treatment of bicarbonate. After washing and removal, uniform flaky nanochannels are formed, reducing the mass transfer resistance of the anti-fouling composite membrane and further improving the water flux of the anti-fouling composite membrane.

[0047] Optionally, the mass fraction of the water-soluble polymer containing carboxylate groups in the coating solution is 0.1% - 3%; the mass fraction of the soluble calcium salt in the coating solution is 0.1% - 1%; with such a setting, by controlling the mass fractions of the water-soluble polymer containing carboxylate groups and the soluble calcium salt in the coating solution, the mass ratio of the water-soluble polymer containing carboxylate groups to the soluble calcium salt can be effectively controlled within a suitable range, so that calcium ions are uniformly dispersed in the three-dimensional network structure, and then an anti-fouling layer with uniform flaky nanochannels can be obtained during subsequent bicarbonate heat treatment and cleaning treatment, further improving the water flux of the anti-fouling composite membrane.

[0048] Optionally, the water-soluble polymer containing carboxylate groups is selected from sodium polyacrylate and / or polyacrylic acid.

[0049] Optionally, the soluble calcium salt is preferably calcium chloride.

[0050] It should be noted that in the present invention, the specific method of placing the separation membrane with the coating solution in a closed container containing bicarbonate is not particularly limited. For example, the separation membrane with the coating solution can be in direct contact with the bicarbonate, or can be arranged at an interval from the bicarbonate without contact, as long as the two are placed in the closed container together.

[0051] Meanwhile, in the present invention, the existence form of the bicarbonate is not particularly limited. For example, the bicarbonate can exist in the form of a solution or in the form of a solid, and is preferably in the form of a solid, that is, the bicarbonate is placed in the closed container in a solid form; with such a setting, the operation can be simplified and additional solvents can be avoided.

[0052] It should be noted that in this invention, the temperature of the heat treatment can be adjusted according to the specific type of bicarbonate, as long as the bicarbonate can be slowly decomposed.

[0053] Optionally, the bicarbonate is selected from at least one of ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate, preferably ammonium bicarbonate.

[0054] Furthermore, the heat treatment temperature is 40℃-120℃, and the heat treatment time is 1h-3h. This setup, by controlling the heat treatment temperature and time, allows for the complete decomposition of bicarbonate and the stable release of carbon dioxide gas at a suitable rate. This, in turn, better controls the nucleation and growth of calcium carbonate crystals, enabling them to preferentially grow along specific crystal planes to form plate-like nano-calcium carbonate crystals. These crystals, after subsequent cleaning, form plate-like nanochannels. Simultaneously, this approach can reduce energy consumption to some extent.

[0055] It should be noted that the present invention does not particularly limit the specific method of placing the coating liquid on the surface of the separation membrane. Specifically, in one embodiment, the coating liquid can be placed on the surface of the separation membrane by means of coating, spraying, impregnation, soaking, etc.

[0056] In this invention, the specific method for cleaning the prefabricated antifouling composite membrane is not particularly limited, as long as the flaky calcium carbonate crystals can be effectively removed. Specifically, in one embodiment, the prefabricated antifouling composite membrane is ultrasonically cleaned. This arrangement utilizes the high-frequency mechanical oscillation and cavitation effect generated by ultrasonic treatment to produce localized high-temperature and high-pressure microjets, effectively disrupting the interfacial bonding force between the flaky calcium carbonate crystals and the three-dimensional network structure, thereby removing the flaky calcium carbonate crystals from the three-dimensional network structure.

[0057] Furthermore, the ultrasonic cleaning temperature is 50℃-80℃, the frequency is 40kHz-80kHz, and the time is 5min-10min. By controlling the temperature, time, and frequency of ultrasonic cleaning, it is possible to ensure that the flaky calcium carbonate crystals are completely removed while avoiding damage to the film layer caused by excessive cleaning.

[0058] In one embodiment, the prefabricated antifouling composite membrane is placed in a cleaning solution for ultrasonic cleaning, wherein the cleaning solution is preferably water; it can be understood that the temperature of the cleaning solution is the same as the temperature of the ultrasonic cleaning.

[0059] In this invention, the specific type of separation membrane is not particularly limited. Specifically, in one embodiment, the separation membrane is selected from any one of reverse osmosis membrane, nanofiltration membrane, or ultrafiltration membrane, preferably a reverse osmosis membrane or a nanofiltration membrane.

[0060] It should be noted that the separation membrane in this invention can be obtained commercially or prepared using conventional methods. Specifically, in one embodiment, when the separation membrane is selected from reverse osmosis membranes or nanofiltration membranes, it can be prepared using conventional interfacial polymerization.

[0061] In one embodiment, when the separation membrane is selected from an ultrafiltration membrane, the ultrafiltration membrane is preferably at least one of a polysulfone ultrafiltration membrane, a polyvinylidene fluoride ultrafiltration membrane, and a polyethersulfone ultrafiltration membrane, and is more preferably a polysulfone ultrafiltration membrane.

[0062] Furthermore, this invention also provides an antifouling composite membrane prepared using the aforementioned method. When applied to water treatment, this antifouling composite membrane exhibits high stability, high rejection rate, high water flux, and high antifouling performance.

[0063] Furthermore, the present invention also provides an application of the aforementioned antifouling composite membrane in a water treatment device.

[0064] In one embodiment, the water treatment device can be a water purifier. When the antifouling composite membrane is applied in the water purifier, during the water purification process, the raw water to be purified enters from the separation layer of the antifouling composite membrane, and the raw water passes through the antifouling composite membrane under pressure to form pure water.

[0065] In one embodiment, the water treatment device may also be a seawater desalination device.

[0066] The following specific embodiments will further illustrate the antifouling composite membrane, its preparation method, and its application. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0067] Example 1

[0068] A coating solution was prepared by uniformly mixing tannic acid, whey protein, sodium polyacrylate, calcium chloride, and water. The mass fractions of tannic acid, whey protein, sodium polyacrylate, and calcium chloride in the coating solution were 0.6%, 0.6%, 1.5%, and 0.6%, respectively. An aqueous solution was prepared by uniformly mixing m-phenylenediamine and water. The mass fraction of m-phenylenediamine in the aqueous solution was 1%. An oil solution was prepared by uniformly mixing trimesoyl chloride and isoparaffin solvent (Isopar-L). The mass fraction of trimesoyl chloride in the oil solution was 0.2%.

[0069] The above aqueous solution was applied to the surface of the polysulfone support membrane. After standing for 60 seconds, the excess aqueous solution was poured off, and the membrane surface was dried with cold air. Then, the above oil solution was applied to the same surface of the polysulfone support membrane. After standing for 30 seconds, the excess oil solution was poured off, and after draining, the membrane was placed in a 90°C oven for 2 minutes to form a polyamide layer, thus obtaining the separation membrane.

[0070] The above coating solution was applied to the polyamide layer surface of the separation membrane. After standing for 1 minute, excess coating solution was discarded. Then, the separation membrane with the coating solution was placed in a 5L sealed container containing 200g of ammonium bicarbonate solid. The container was then heated to 50°C and maintained for 2 hours to form a pre-formed antifouling layer, resulting in a pre-formed antifouling composite membrane. Finally, the pre-formed antifouling composite membrane was immersed in water for ultrasonic cleaning to form an antifouling layer. After removal, the membrane was obtained as shown in the image. Figure 1 The antifouling composite membrane shown is subjected to ultrasonic cleaning at a temperature of 50°C, a frequency of 80kHz, and a time of 10min.

[0071] Example 2

[0072] Gallic acid, ovalbumin, polyacrylic acid, calcium chloride, and water were mixed evenly to prepare a coating solution, wherein the mass fraction of gallic acid was 1%, the mass fraction of ovalbumin was 1%, the mass fraction of polyacrylic acid was 3%, and the mass fraction of calcium chloride was 1%. m-phenylenediamine and water were mixed evenly to prepare an aqueous phase solution, wherein the mass fraction of m-phenylenediamine in the aqueous phase solution was 1%. Tristyrene chloride and isoparaffin solvent (Isopar-L) were mixed evenly to prepare an oil phase solution, wherein the mass fraction of tristyrene chloride in the oil phase solution was 0.2%.

[0073] The above aqueous solution was applied to the surface of the polysulfone support membrane. After standing for 60 seconds, the excess aqueous solution was poured off, and the membrane surface was dried with cold air. Then, the above oil solution was applied to the same surface of the polysulfone support membrane. After standing for 30 seconds, the excess oil solution was poured off, and after draining, the membrane was placed in a 90°C oven for 2 minutes to form a polyamide layer, thus obtaining the separation membrane.

[0074] The above coating solution was applied to the surface of the polyamide layer of the separation membrane. After standing for 1 minute, the excess coating solution was poured off. Then, the separation membrane with the coating solution was placed in a 5L sealed container containing 250g of sodium bicarbonate solid. The container was then heated to 50°C and kept at that temperature for 2 hours to form a pre-formed antifouling layer, thus obtaining a pre-formed antifouling composite membrane. Finally, the pre-formed antifouling composite membrane was placed in water for ultrasonic cleaning to form an antifouling layer. The membrane was then removed to obtain the antifouling composite membrane. The ultrasonic cleaning temperature was 70°C, the frequency was 60kHz, and the time was 7 minutes.

[0075] Example 3

[0076] A coating solution was prepared by uniformly mixing tea polyphenols, sericin, sodium polyacrylate, calcium chloride, and water. The mass fractions of tea polyphenols, sericin, sodium polyacrylate, and calcium chloride in the coating solution were 0.2%, 0.3%, 0.3%, and 0.1%, respectively. A aqueous solution was prepared by uniformly mixing m-phenylenediamine and water. The mass fraction of m-phenylenediamine in the aqueous solution was 1%. An oil solution was prepared by uniformly mixing trimesoyl chloride and isoparaffin solvent (Isopar-L). The mass fraction of trimesoyl chloride in the oil solution was 0.2%.

[0077] The above aqueous solution was applied to the surface of the polysulfone support membrane. After standing for 60 seconds, the excess aqueous solution was poured off, and the membrane surface was dried with cold air. Then, the above oil solution was applied to the same surface of the polysulfone support membrane. After standing for 30 seconds, the excess oil solution was poured off, and after draining, the membrane was placed in a 90°C oven for 2 minutes to form a polyamide layer, thus obtaining the separation membrane.

[0078] The above coating solution was applied to the surface of the polyamide layer of the separation membrane. After standing for 1 minute, the excess coating solution was poured off. Then, the separation membrane with the coating solution was placed in a 5L sealed container containing 300g of potassium bicarbonate solid. The container was then heated to 110℃ and kept for 2 hours to form a pre-fabricated antifouling layer, thus obtaining a pre-fabricated antifouling composite membrane. Finally, the pre-fabricated antifouling composite membrane was placed in water for ultrasonic cleaning to form an antifouling layer. The membrane was then removed to obtain the antifouling composite membrane. The ultrasonic cleaning temperature was 80℃, the frequency was 50kHz, and the time was 5 minutes.

[0079] Example 4

[0080] Example 4 differs from Example 1 only in that the mass fraction of tannic acid in the coating solution is 0.05% and the mass fraction of whey protein is 1%; all other conditions are the same, resulting in an antifouling composite film.

[0081] Example 5

[0082] Example 5 differs from Example 1 only in that the mass fraction of tannic acid in the coating solution is 0.6% and the mass fraction of whey protein is 0.3%; all other conditions are the same, resulting in an antifouling composite film.

[0083] Example 6

[0084] Example 6 differs from Example 1 only in that the mass fraction of sodium polyacrylate in the coating solution is 0.8% and the mass fraction of calcium chloride is 1%; all other conditions are the same, resulting in an antifouling composite film.

[0085] Example 7

[0086] Compared with Example 1, Example 7 differs only in that the mass fraction of sodium polyacrylate in the coating solution is 3% and the mass fraction of calcium chloride is 0.5%; all other conditions are the same, resulting in an antifouling composite film.

[0087] Example 8

[0088] Example 8 differs from Example 1 only in that the ultrasonic cleaning temperature is 30°C, the frequency is 30kHz, and the time is 5min; all other conditions are the same, resulting in an anti-fouling composite membrane.

[0089] Example 9

[0090] Compared with Example 1, Example 9 differs only in that a pre-fabricated antifouling layer is formed after heating to 90°C and maintaining it for 1 hour; all other conditions are the same, resulting in an antifouling composite film.

[0091] Example 10

[0092] Example 10 differs from Example 1 only in that the prefabricated antifouling composite membrane is placed in water for cleaning to form an antifouling layer. The cleaning temperature is 50°C and the cleaning time is 15 minutes. All other conditions are the same, resulting in an antifouling composite membrane.

[0093] Example 11

[0094] Example 11 differs from Example 1 only in that the separation membrane with the coating liquid is placed in a 5L sealed container containing sodium bicarbonate solution, then heated to 50°C and kept for 2 hours to form a pre-fabricated antifouling layer; all other conditions are the same, resulting in an antifouling composite membrane.

[0095] Comparative Example 1

[0096] Comparative Example 1 differs from Example 1 only in that it does not include the step of immersing the pre-fabricated antifouling composite membrane in water for ultrasonic cleaning to form an antifouling layer; all other conditions are the same, resulting in the following... Figure 2 The anti-fouling composite membrane shown.

[0097] Comparative Example 2

[0098] Compared with Example 1, Comparative Example 2 differs only in that tannic acid is not added in the step of preparing the coating solution; all other conditions are the same, and an anti-fouling composite film is obtained.

[0099] Comparative Example 3

[0100] Compared with Example 1, Comparative Example 3 differs only in that whey protein is not added in the step of preparing the coating solution; all other conditions are the same, resulting in an anti-fouling composite membrane.

[0101] Comparative Example 4

[0102] Compared with Example 1, Comparative Example 4 differs only in that sodium polyacrylate is not added in the step of preparing the coating solution; all other conditions are the same, and an antifouling composite film is obtained.

[0103] Comparative Example 5

[0104] Compared with Example 1, Comparative Example 5 differs only in that polyvinyl alcohol is used instead of sodium polyacrylate in the step of preparing the coating solution; all other conditions are the same, and an antifouling composite film is obtained.

[0105] Comparative Example 6

[0106] Compared with Example 1, Comparative Example 6 differs only in that calcium chloride is not added in the step of preparing the coating solution; all other conditions are the same, and an antifouling composite film is obtained.

[0107] Comparative Example 7

[0108] Comparative Example 7 differs from Example 1 only in that it does not include the step of placing the separation membrane with the coating liquid in a 5L sealed container containing 200g of ammonium bicarbonate. Instead, the separation membrane with the coating liquid is directly subjected to heat treatment to form a pre-fabricated antifouling layer. The heat treatment temperature is 50°C and the time is 2h. All other conditions are the same, resulting in an antifouling composite membrane.

[0109] Comparative Example 8

[0110] Comparative Example 8 differs from Example 1 only in that carbon dioxide gas is used instead of ammonium bicarbonate. Specifically, the separation membrane with the coating solution is placed in a 5L sealed container, and carbon dioxide gas is introduced into the sealed solution. The mixture is then heated to 50°C and maintained for 2 hours to form a pre-formed antifouling layer. All other conditions remain the same, resulting in the following: Figure 3 The anti-fouling composite membrane shown.

[0111] Comparative Example 9

[0112] Compared with Example 1, Comparative Example 9 differs only in that it is heated to 25°C, i.e., room temperature, and kept there for 1 hour to form a pre-fabricated antifouling layer; all other conditions are the same, resulting in an antifouling composite film.

[0113] The antifouling composite membranes prepared in Examples 1 to 11 and Comparative Examples 1 to 9 were subjected to performance tests. The test results are shown in Table 1. The conditions for testing the membrane water flux and rejection rate were as follows: test pressure was 1.55 MPa, concentrate flow rate was 1.0 GPM, ambient temperature was 25℃, concentrate pH was 6.5-7.5, and concentrate was a 2000 ppm sodium chloride aqueous solution.

[0114] Table 1

[0115]

[0116] Meanwhile, the antifouling performance of the antifouling composite membranes prepared in Examples 1 to 11 and Comparative Examples 1 to 9 was tested. The test conditions were as follows: test pressure of 1.55 MPa, concentrate flow rate of 1.0 GPM, ambient temperature of 25ºC, and concentrate pH of 6.5-7.5. The antifouling performance was tested with concentrate containing 2000 ppm sodium chloride, 100 ppm sodium humate, and 100 ppm bovine serum albumin as feed water. After 100 hours of continuous operation, the membrane was cleaned, and then the performance was tested with concentrate containing 2000 ppm sodium chloride as feed water. The test results are shown in Table 2.

[0117] Table 2

[0118]

[0119] It should be noted that in Tables 1 and 2, the membrane water flux (F) is calculated by the volume of water passing through the antifouling composite membrane within a certain time period, and the formula is: F=V / (A×T), where V is the volume of water passing through the antifouling composite membrane per unit time, A is the effective membrane area, and T is time.

[0120] The rejection rate (R) is calculated using the concentrations of the feed liquid and the permeate liquid. The formula is: R = (1 - C1 / C0) × 100%, where C1 is the concentration of the permeate liquid and C0 is the concentration of the feed liquid.

[0121] The formula for calculating the water flux recovery rate is: (Water flux of the antifouling composite membrane after fouling / Water flux of the initial antifouling composite membrane) × 100%.

[0122] from Figure 1 As can be seen from the data, the antifouling layer of the antifouling composite membrane prepared in Example 1 has a sheet-like nanochannel structure, which can effectively improve the water flux of the antifouling composite membrane. Figure 2 As can be seen, because no cleaning treatment was performed in Comparative Example 1, the sheet-like nano-calcium carbonate crystals could not be removed, resulting in the inability to form sheet-like nanochannels. Consequently, the formed antifouling layer had a pearl-like structure, which in turn affected the water flux of the antifouling composite membrane. From Figure 3 As can be seen, the antifouling layer of the antifouling composite membrane in Comparative Example 8 is irregular and not sheet-like, and it is relatively thick. This is because carbon dioxide gas was directly introduced into Comparative Example 8, causing the carbon dioxide gas to diffuse rapidly into the three-dimensional network structure and dissolve to form carbonate ions. These carbonate ions react rapidly with calcium ions, making it difficult to induce the morphology of nano-calcium carbonate crystals to be sheet-like, which in turn affects the water flux of the antifouling composite membrane.

[0123] 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.

[0124] 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.

Claims

1. A method for preparing an antifouling composite membrane, characterized in that, Includes the following steps: A coating solution is prepared by combining water-soluble polyphenols, proteins, water-soluble polymers containing carboxyl groups, soluble calcium salts, and water. The coating liquid is placed on the surface of the separation membrane, and then the separation membrane with the coating liquid is placed in a sealed container containing bicarbonate. After heat treatment, a pre-fabricated antifouling layer is formed, and a pre-fabricated antifouling composite membrane is obtained. The heat treatment temperature is greater than or equal to the thermal decomposition temperature of bicarbonate. The prefabricated antifouling composite membrane is cleaned to form an antifouling layer, thus obtaining the antifouling composite membrane.

2. The method for preparing the antifouling composite membrane according to claim 1, characterized in that, The mass ratio of the water-soluble polyphenol to the protein is 1:1 to 1:10; And / or, the mass ratio of the water-soluble polymer containing carboxylate to the soluble calcium salt is 1:1 to 3:

1.

3. The method for preparing the antifouling composite membrane according to claim 1, characterized in that, The mass fraction of water-soluble polyphenols in the application solution is 0.1%-1%; And / or, the water-soluble polyphenols are selected from at least one of tannic acid, gallic acid, and tea polyphenols.

4. The method for preparing the antifouling composite membrane according to claim 1, characterized in that, The mass fraction of protein in the application solution is 0.1%-1%; And / or, the protein is selected from at least one of whey protein, sericin, or ovalbumin.

5. The method for preparing the antifouling composite membrane according to claim 1, characterized in that, The mass fraction of the water-soluble polymer containing carboxyl groups in the coating solution is 0.1%-3%. And / or, the water-soluble polymer containing carboxyl groups is selected from sodium polyacrylate and / or polyacrylic acid.

6. The method for preparing the antifouling composite membrane according to claim 1, characterized in that, The mass fraction of soluble calcium salt in the application solution is 0.1%-1%; And / or, the soluble calcium salt is selected from calcium chloride.

7. The method for preparing the antifouling composite membrane according to claim 1, characterized in that, The bicarbonate is selected from at least one of ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate. And / or, the bicarbonate is placed in the sealed container in solid form.

8. The method for preparing the antifouling composite membrane according to any one of claims 1 to 7, characterized in that, The prefabricated antifouling composite membrane is subjected to ultrasonic cleaning, wherein the ultrasonic cleaning temperature is 50℃-80℃, the frequency is 40kHz-80kHz, and the time is 5min-10min. And / or, the separation membrane is selected from any one of reverse osmosis membrane, nanofiltration membrane, or ultrafiltration membrane.

9. An antifouling composite membrane prepared by the method for preparing an antifouling composite membrane as described in any one of claims 1 to 8.

10. The application of the antifouling composite membrane as described in claim 9 in a water treatment device.

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