Gradient nuclear track membrane based on heavy ion irradiation and application of gradient nuclear track membrane in cherry preservation

Abstract

The invention discloses a gradient nuclear track membrane based on heavy ion irradiation and application of the gradient nuclear track membrane in cherry preservation, and belongs to the technical field of nuclear track membrane preparation. The method is used for solving the problems that in the prior art, PET films do not have pore diameters with moderate quantity and particle sizes, so that the PET films for storing cherries are too high in compactness and low in air permeability, and excessive anaerobic respiration exists during cherry storage. In addition, the technical problem that the PET film is poor in biological antibacterial activity is solved. The invention provides a gradient nuclear track membrane based on heavy ion irradiation for cherry preservation. The gradient nuclear track membrane based on heavy ion irradiation is composed of a nuclear track membrane substrate, and a first coating layer and a second coating layer which are sequentially coated on the surface of the nuclear track membrane substrate, the nuclear track membrane substrate is obtained by sequentially carrying out heavy ion irradiation, ultraviolet sensitization and alkaline etching liquid etching on a PET (Polyethylene Terephthalate) film; the first coating solution is obtained by dissolving copper zinc pyrithione and dopamine in ethanol, and the second coating solution is obtained by dissolving silver nitrate in ethanol.

Description

Technical Field

[0001] This invention relates to the field of nuclear pore membrane preparation technology, specifically to a gradient nuclear pore membrane based on heavy ion irradiation and its application in cherry preservation. Background Technology

[0002] Cherries are a type of fruit that is not resistant to storage and transportation. Prolonged storage will cause the fruit to rot and spoil, and it is also susceptible to mold and bacterial diseases. To extend the market supply period of cherries, various storage and preservation technologies have been adopted both domestically and internationally. Among these, using a protective film to preserve cherries can effectively inhibit the growth of fungi already attached to the fruit surface, preventing the fruit from rotting and spoiling due to fungal infection. At the same time, the protective film can also resist secondary infection of the fruit by external airborne and scattered pathogens.

[0003] Polyethylene terephthalate (PET film), as a highly crystalline polymer, has a smooth and glossy surface, high mechanical strength, good dimensional stability, and is less affected by environmental changes; PET film has advantages as a protective film for storing cherries. Patent application CN110982233A discloses a high-barrier RGO-SiO2 / PET protective film and its preparation method. The above-mentioned prior art utilizes the synergistic effect of graphene, carboxyl groups, amino groups, hydroxyl groups on the surface of silicon dioxide, and ethylene glycol to improve the barrier properties of PET, which can effectively block oxygen from entering and inhibit the respiration of food. However, the high density and low permeability of PET film are not conducive to regulating the concentration of O2 and CO2 inside and outside the preservation film. If the PET film can be prepared as a core-porous membrane, a uniformly distributed pore size can be formed on the film surface, which is conducive to creating an environmental atmosphere for storing cherries.

[0004] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a gradient nuclear pore membrane based on heavy ion irradiation and its application in cherry preservation, in order to solve the problem that the existing PET film does not have a sufficient number and appropriate particle size of pores, resulting in the PET film for storing cherries being too dense and having low air permeability, which leads to excessive anaerobic respiration during cherry storage; in addition, PET film itself has the technical problem of poor antibacterial properties.

[0006] The objective of this invention can be achieved through the following technical solutions: A gradient nuclear pore membrane based on heavy ion irradiation, comprising a first coating layer and a second coating layer sequentially coated on a nuclear pore membrane substrate and its surface; The nuclear pore membrane substrate is obtained by sequentially subjecting a PET film to heavy ion irradiation, ultraviolet sensitization, and alkaline etching solution etching. The first coating is obtained by immersing a nuclear pore membrane substrate in a first coating solution, which is obtained by dissolving pyridine copper zinc and dopamine in ethanol; the second coating is obtained by immersing a substrate coated with the first coating in a second coating solution, which is obtained by dissolving silver nitrate in ethanol.

[0007] Furthermore, the preparation method of the alkaline etching solution includes the following steps: A1, N,N-dimethylheptaneamine and 3-bromo-propyltrimethylammonium bromide were added to anhydrous ethanol, dissolved, and mixed to obtain the reaction system. The reaction system was refluxed at 95-100℃ for 24-48 h. After the reaction was completed, the ethanol was removed by distillation to obtain the product. The product was washed three times with ethyl acetate / ethanol (mass ratio of ethyl acetate to ethanol was 1:2-3) to obtain a double-terminated quaternary ammonium salt solid. Using anhydrous ethanol as an organic solvent, the nitrogen containing a lone pair of electrons in N,N-dimethylheptaneamine reacts with 3-bromo-propyltrimethylammonium bromide to form a double-terminated quaternary ammonium salt solid, as shown in the following reaction formula:

[0008] A2. Phenol is added to a 65-75%wt sulfuric acid solution to obtain a mixture; the mixture is reacted at 90-100℃ for 3-4 hours to obtain a product; NaOH solution is added dropwise to the product to adjust the pH value to 8-9, and then 25-35%wt formaldehyde aqueous solution is added, and the reaction is continued at 90-100℃ for 4-5 hours to obtain an intermediate; Phenol undergoes sulfonation with concentrated sulfuric acid, followed by addition reaction with formaldehyde to prepare an intermediate, the reaction formula of which is as follows:

[0009] A3. The double-terminated quaternary ammonium salt solid and the intermediate are added to ethanol and stirred at 65-70℃ until the double-terminated quaternary ammonium salt solid and the intermediate are completely dissolved. Then the temperature is raised to 75-85℃ for reaction, and the ethanol is removed by vacuum distillation and vacuum drying to obtain the composite surfactant solid. The composite surfactant solid is mixed with NaOH solution to obtain alkaline etching solution.

[0010] Using ethanol as a solvent, a substitution reaction occurs between the double-terminated quaternary ammonium salt solid and the intermediate to prepare a composite surfactant. The reaction formula is as follows:

[0011] Further, in step A1, the ratio of N,N-dimethylheptaneamine, 3-bromo-propyltrimethylammonium bromide, and anhydrous ethanol is 7-15g:13-26g:50mL, and the mass ratio of ethyl acetate to ethanol is 1:2-3; in step A2, the ratio of phenol, sulfuric acid solution, and formaldehyde aqueous solution is 4.5-9g:20-30mL:15-25mL; and the concentration of the added NaOH solution is 0.1mol / L.

[0012] Further, in step A3, the ratio of the amount of the double-capped quaternary ammonium salt solid, the intermediate, and ethanol is 10-20g:30-40mL:200mL; the concentration of the NaOH solution is 1-2mol / L; and the ratio of the amount of the composite surfactant solid to the NaOH solution is 3-10g:20-30mL.

[0013] As another aspect of the present invention, a method for preparing a gradient nuclear pore membrane based on heavy ion irradiation includes the following steps: B1. The PET film is cut into circular pieces with a thickness of 8-15μm to obtain the cut PET film; the cut PET film is irradiated with heavy ions to obtain the heavy ion irradiated PET film; then the heavy ion irradiated PET film is sensitized with ultraviolet lamp to obtain the ultraviolet sensitized PET film. This experiment uses PET polymer film as the raw material for preparing core-pore membranes. High-energy heavy ion irradiation of the PET polymer film is performed using a heavy ion accelerator. By controlling the flux of fast heavy ion irradiation, core-pore membranes with specific pore density and pore size are prepared. To accelerate the etching rate of the polymer film, this invention uses a sensitizing lamp to sensitize the heavy ion-irradiated PET film, obtaining an ultraviolet-sensitized PET film.

[0014] B2. The UV-sensitized PET film is immersed in an alkaline etching solution for etching to obtain the etched core pore membrane; the etched core pore membrane is washed with deionized water and dried to remove moisture, thus obtaining the core pore membrane substrate. B3. The nuclear pore membrane substrate is fixed on a filter cup, and the first coating solution is poured into the filter cup. After standing for 5-10 minutes, the first coating solution is poured out to obtain the nuclear pore membrane substrate after one soaking. Then, the second coating solution is poured into the filter cup, and after standing for 5-10 minutes, the second coating solution is poured out to obtain the nuclear pore membrane substrate after two soakings. The nuclear pore membrane substrate after two soakings is dried to obtain a gradient nuclear pore membrane based on heavy ion irradiation.

[0015] Furthermore, in step B1, heavy ion irradiation is performed using an energy of 19-20 MeV. 129 Vertical Xe ion beam irradiation, with a flux of 3-5 × 10⁻⁵ 9 icons / cm -2 The main peak wavelength of the ultraviolet light is 365nm, and the power is 30-35mW / cm².2 The sensitization time is 10-12 hours.

[0016] Furthermore, in step B2, the etching temperature is 70-85℃, the etching time is 6-8h, and the solid-liquid mass ratio of the UV-sensitized PET film and the alkaline etching solution is 1:5-10.

[0017] Further, in step B3, the preparation steps of the first coating solution are as follows: pyridine copper zinc is added to ethanol, then dopamine is added and mixed to obtain the first coating solution; the preparation steps of the second coating solution are as follows: silver nitrate is added to ethanol and mixed to obtain the second coating solution.

[0018] Furthermore, the ratio of pyridine sulfide copper zinc, ethanol and dopamine is 3-5 mg: 100-200 mL: 3-6 mg; the ratio of silver nitrate and ethanol is 1-3 mg: 100-200 mL.

[0019] As another aspect of the present invention, the application of gradient nuclear pore membranes based on heavy ion irradiation in cherry preservation.

[0020] The present invention has the following beneficial effects: 1. This invention uses PET film as a substrate, and applies specific energy and injection volume to the PET film. 129 Xe ions are vertically irradiated, followed by ultraviolet photosensitization and etching with an alkaline etching solution to obtain nuclear pore membrane substrates with regular morphology, a certain number, and a specific pore size. The nuclear pore membrane possesses both a certain degree of permeability, allowing the cherries inside to exchange gases and moisture with the external environment, preventing anaerobic respiration; and a suitable pore size (5-10 μm), maintaining a certain ratio of oxygen and carbon dioxide concentrations within the sealed space, thus preventing accelerated respiration and excessive weight loss in the fruit.

[0021] 2. To achieve better etching results and obtain special etched pore shapes, auxiliary surfactants can be added to the etching solution. The added surfactants can improve the pore shape within the heavy ion microporous membrane, but due to their short molecular chains, their impact on the pore formation of the microporous membrane after heavy ion irradiation is relatively small. This invention uses 3-bromo-propyltrimethylammonium bromide grafted with N,N-dimethylheptaneamine as a double-terminated quaternary ammonium salt solid, and a condensation polymer of formaldehyde and phenol as an extension matrix, increasing the molecular weight and chain length of the double-terminated quaternary ammonium salt solid. In the alkaline etching solution, the surfactant only adheres to the surface of the UV-sensitized PET film, which helps to form a bottleneck-shaped etched pore shape. Furthermore, the synthesized composite surfactant contains various functional groups and anions / cations, which can be adsorbed and reacted with the carboxyl groups and free radicals contained in the PET film after heavy ion irradiation and UV sensitization, thereby deepening the etching effect and avoiding the drawback of poor etching effect for special pore shapes.

[0022] 3. Using ethanol as a solvent, pyridine-copper zinc and dopamine as solutes, a first coating solution is obtained; using silver nitrate as a solute, a second coating solution is obtained. The etched nuclear pore membrane substrate is sequentially coated with the first and second coating solutions, and then dried to obtain a gradient nuclear pore membrane with both first and second coatings on its surface. Utilizing the carboxyl groups abundant on the surface of the heavy-ion irradiated PET film, dopamine can be rapidly deposited on the nuclear pore membrane substrate to form polydopamine. Because polydopamine can generate strong covalent and non-covalent interactions with the nuclear pore membrane substrate, dopamine has strong adhesion to the nuclear pore membrane, easily forming the first coating; silver nitrate can be deposited in the dopamine-containing first coating to form the second coating. Pyridine-copper zinc has excellent inhibitory effects on molds, bacteria, and yeasts, while silver nitrate has good antibacterial properties against Escherichia coli and Staphylococcus aureus. The heavy-ion irradiated gradient nuclear pore membrane prepared in this invention has good biological characteristics and is not easily invaded by microorganisms. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 This embodiment provides a method for preparing an alkaline etching solution for gradient nuclear pore membranes based on heavy ion irradiation, comprising the following steps: A1. At room temperature, 50 mL of anhydrous ethanol and 7 g of N,N-dimethylheptaneamine were added to a 250 mL three-necked flask, followed by 13 g of 3-bromo-propyltrimethylammonium bromide. The mixture was dissolved and stirred to obtain the reaction system. The three-necked flask was transferred to a water bath and refluxed at 95 °C for 24 h. After the reaction was completed, the ethanol was removed by distillation to obtain the product. The product was washed three times with ethyl acetate / ethanol (mass ratio of ethyl acetate to ethanol was 1:3) to obtain a double-terminated quaternary ammonium salt solid.

[0025] A2. Measure 4.5 g of phenol and add it to a flask. Then add 20 mL of 65% wt sulfuric acid solution to the flask to obtain a mixture. React the mixture at 90 °C for 3 h to obtain the product. Add 0.1 mol / L NaOH solution dropwise to the product until the pH value of the product is adjusted to 8. Then add 15 mL of 25% wt formaldehyde aqueous solution to the flask, seal the flask, and continue to react at 90 °C for 4 h to obtain the intermediate.

[0026] A3. Measure 200 mL of ethanol and add it to a 500 mL three-necked flask, then add... 10g of double-terminated quaternary ammonium salt solid and 30mL of intermediate were mixed thoroughly. The mixture was then transferred to a water bath and stirred at 65°C for 30min. The temperature of the three-necked flask was then increased to 75°C and reacted at this temperature for 7h. Ethanol was removed by vacuum distillation, and the mixture was dried under vacuum at 70°C for 20min to obtain the solid, which is the composite surfactant prepared in this invention.

[0027] A4. Measure 3g of the composite surfactant and add it to 20mL of 1mol / L NaOH solution. Mix well to obtain an alkaline etching solution.

[0028] Example 2 This embodiment provides a method for preparing an alkaline etching solution for gradient nuclear pore membranes based on heavy ion irradiation, comprising the following steps: A1. At room temperature, 50 mL of anhydrous ethanol and 10 g of N,N-dimethylheptaneamine were added to a 250 mL three-necked flask, followed by 20 g of 3-bromo-propyltrimethylammonium bromide. The mixture was dissolved and stirred to obtain the reaction system. The three-necked flask was transferred to a water bath and refluxed at 97 °C for 35 h. After the reaction was completed, the ethanol was removed by distillation to obtain the product. The product was washed three times with ethyl acetate / ethanol (mass ratio of ethyl acetate to ethanol was 1:3) to obtain a double-terminated quaternary ammonium salt solid.

[0029] A2. Measure 7g of phenol and add it to a flask. Then add 26mL of 70%wt sulfuric acid solution to the flask to obtain a mixture. React the mixture at 94℃ for 3.3h to obtain the product. Add 0.1mol / L NaOH solution dropwise to the product until the pH value of the product is adjusted to 8.5. Then add 20mL of 30%wt formaldehyde aqueous solution to the flask, seal the flask, and continue to react at 96℃ for 4.4h to obtain the intermediate.

[0030] A3. Measure 200 mL of ethanol and add it to a 500 mL three-necked flask. Then add 16 g of the double-terminated quaternary ammonium salt solid and 37 mL of the intermediate to the three-necked flask and mix well. Transfer the three-necked flask to a water bath and stir at 68 °C for 50 min. Then raise the temperature of the three-necked flask to 80 °C and react at this temperature for 7.7 h. Remove the ethanol by vacuum distillation and dry under vacuum at 73 °C for 25 min to obtain the solid, which is the composite surfactant prepared in this invention.

[0031] A4. Measure 8g of the composite surfactant and add it to 25mL of 1.5mol / L NaOH solution. Mix well to obtain an alkaline etching solution.

[0032] Example 3 This embodiment provides a method for preparing an alkaline etching solution for gradient nuclear pore membranes based on heavy ion irradiation, comprising the following steps: A1. At room temperature, 50 mL of anhydrous ethanol and 15 g of N,N-dimethylheptaneamine were added to a 250 mL three-necked flask, followed by 26 g of 3-bromo-propyltrimethylammonium bromide. The mixture was dissolved and stirred to obtain the reaction system. The three-necked flask was transferred to a water bath and refluxed at 100 °C for 48 h. After the reaction was completed, the ethanol was removed by distillation to obtain the product. The product was washed three times with ethyl acetate / ethanol (ethyl acetate to ethanol mass ratio of 1:3) to obtain a double-terminated quaternary ammonium salt solid.

[0033] A2. Measure 9g of phenol and add it to a flask. Then add 30mL of 75%wt sulfuric acid solution to the flask to obtain a mixture. React the mixture at 100℃ for 4h to obtain the product. Add 0.1mol / L NaOH solution dropwise to the product until the pH value of the product is adjusted to 9. Then add 25mL of 35%wt formaldehyde aqueous solution to the flask, seal the flask, and continue to react at 100℃ for 5h to obtain the intermediate.

[0034] A3. Measure 200 mL of ethanol and add it to a 500 mL three-necked flask. Then add 20 g of the double-terminated quaternary ammonium salt solid and 40 mL of the intermediate to the three-necked flask and mix well. Transfer the three-necked flask to a water bath and stir at 70 °C for 60 min. Then raise the temperature of the three-necked flask to 85 °C and react at this temperature for 8 h. Distill off the ethanol and dry under vacuum at 80 °C for 30 min to obtain the solid, which is the composite surfactant prepared in this invention.

[0035] A4. Measure 10g of the composite surfactant and add it to 30mL of 2mol / L NaOH solution. Mix well to obtain an alkaline etching solution.

[0036] Example 4 This embodiment provides a method for preparing a gradient nuclear pore membrane based on heavy ion irradiation, including the following steps: B1. The PET film was cut into circular pieces with a diameter of 5 cm and a thickness of 15 μm to obtain the cut PET film. The irradiation experiment was conducted on a heavy ion accelerator using an energy of 19 MeV / u. 129 Xe ion beam vertical irradiation of slit PET films, with a fill power of 3×10 9 icons / cm -2 A heavy-ion irradiated PET film was obtained. The heavy-ion irradiated PET film was then sensitized using an ultraviolet lamp, specifically an ultra-high pressure mercury lamp, with a main peak wavelength of 365 nm and a power of 30 mW / cm². 2 The sensitization time was 10 hours to obtain a UV-sensitized PET film.

[0037] B2. The UV-sensitized PET film was immersed in the alkaline etching solution prepared in Example 1 for etching at a temperature of 70°C for 6 hours. The solid-liquid ratio of the UV-sensitized PET film to the alkaline etching solution was 1:5, resulting in an etched core-pore membrane. The etched core-pore membrane was then washed three times with deionized water and dried at 80°C for 20 minutes to remove moisture, yielding the core-pore membrane substrate.

[0038] B3. Using ethanol as a solvent, add 3 mg of zinc pyridine sulfide copper to 100 mL of ethanol, then add 3 mg of dopamine and mix well to obtain the first coating solution; add 1 mg of silver nitrate to 100 mL of ethanol and mix well to obtain the second coating solution.

[0039] B4. Fix the nuclear pore membrane substrate onto a filter cup, and pour 10 mL of the first coating solution into the filter cup. After standing for 5 min, pour out the first coating solution to form a first coating on the surface of the nuclear pore membrane substrate, obtaining a substrate coated with the first coating. Then pour 10 mL of the second coating solution into the filter cup, and after standing for 5 min, pour out the second coating solution to form a second coating on the surface of the substrate coated with the first coating, obtaining the coated nuclear pore membrane. Place the coated nuclear pore membrane in a drying oven and dry it at 60 °C for 20 min to prepare a gradient nuclear pore membrane based on heavy ion irradiation, with an etched pore diameter of 10 μm.

[0040] Example 5 This embodiment provides a method for preparing a gradient nuclear pore membrane based on heavy ion irradiation, including the following steps: B1. The PET film was cut into circular pieces with a diameter of 5 cm and a thickness of 10 μm to obtain the cut PET film. The irradiation experiment was conducted on a heavy ion accelerator using an energy of 19 MeV / u. 129 Xe ion beam vertical irradiation of slit PET films, with a fill power of 4 × 10⁻⁶. 9 icons / cm -2 A heavy-ion irradiated PET film was obtained. The heavy-ion irradiated PET film was then sensitized using an ultraviolet lamp, specifically an ultra-high pressure mercury lamp, with a main peak wavelength of 365 nm and a power of 32 mW / cm². 2 The sensitization time was 11 hours, and a UV-sensitized PET film was obtained.

[0041] B2. The UV-sensitized PET film was immersed in the alkaline etching solution prepared in Example 2 for etching at a temperature of 75°C for 7 hours. The solid-liquid ratio of the UV-sensitized PET film to the alkaline etching solution was 1:8, resulting in an etched core-pore membrane. The etched core-pore membrane was then washed four times with deionized water and dried at 85°C for 25 minutes to remove moisture, yielding the core-pore membrane substrate.

[0042] B3. Using ethanol as a solvent, add 4 mg of zinc pyridine sulfide copper to 150 mL of ethanol, then add 5 mg of dopamine and mix well to obtain the first coating solution; add 2 mg of silver nitrate to 150 mL of ethanol and mix well to obtain the second coating solution.

[0043] B4. Fix the nuclear pore membrane substrate onto a filter cup, and pour 15 mL of the first coating solution into the filter cup. After standing for 8 min, pour out the first coating solution to form a first coating on the surface of the nuclear pore membrane substrate, obtaining a substrate coated with the first coating. Then pour 15 mL of the second coating solution into the filter cup, and after standing for 7 min, pour out the second coating solution to form a second coating on the surface of the substrate coated with the first coating, obtaining the coated nuclear pore membrane. Place the coated nuclear pore membrane in a drying oven and dry it at 62 °C for 25 min to prepare a gradient nuclear pore membrane based on heavy ion irradiation, with an etched pore diameter of 15 μm.

[0044] Example 6 This embodiment provides a method for preparing a gradient nuclear pore membrane based on heavy ion irradiation, including the following steps: B1. The PET film was cut into circular pieces with a diameter of 5 cm and a thickness of 8 μm to obtain the cut PET film. The irradiation experiment was conducted on a heavy ion accelerator using an energy of 19 MeV / u. 129 Xe ion beam vertical irradiation of slit PET films, with a fill power of 5 × 10⁻⁶. 9 icons / cm -2 A heavy-ion irradiated PET film was obtained. The heavy-ion irradiated PET film was then sensitized using an ultraviolet lamp, specifically an ultra-high pressure mercury lamp, with a main peak wavelength of 365 nm and a power of 35 mW / cm². 2 The sensitization time was 12 hours to obtain a UV-sensitized PET film.

[0045] B2. The UV-sensitized PET film was immersed in the alkaline etching solution prepared in Example 3 for etching at a temperature of 85°C for 8 hours. The solid-liquid ratio of the UV-sensitized PET film to the alkaline etching solution was 1:10, resulting in an etched core-pore membrane. The etched core-pore membrane was then washed five times with deionized water and dried at 90°C for 30 minutes to remove moisture, yielding the core-pore membrane substrate.

[0046] B3. Using ethanol as a solvent, add 5 mg of zinc pyridine sulfide copper to 200 mL of ethanol, then add 6 mg of dopamine and mix well to obtain the first coating solution; add 3 mg of silver nitrate to 200 mL of ethanol and mix well to obtain the second coating solution.

[0047] B4. Fix the nuclear pore membrane substrate onto a filter cup, and pour 20 mL of the first coating solution into the filter cup. After standing for 10 min, pour out the first coating solution to form a first coating on the surface of the nuclear pore membrane substrate, obtaining a substrate coated with the first coating. Then pour 20 mL of the second coating solution into the filter cup, and after standing for 10 min, pour out the second coating solution to form a second coating on the surface of the substrate coated with the first coating, obtaining the coated nuclear pore membrane. Place the coated nuclear pore membrane in a drying oven and dry it at 65 °C for 30 min to prepare a gradient nuclear pore membrane based on heavy ion irradiation, with an etched pore diameter of 20 μm.

[0048] Comparative Example 1 The difference between this comparative example and Example 6 is that, in preparing the alkaline etching solution, an equal mass of double-terminated quaternary ammonium salt solid was used instead of the composite surfactant.

[0049] Comparative Example 2 The difference between this comparative example and Example 6 is that the steps for preparing the composite surfactant are as follows: 200 mL of ethanol is added to a 500 mL three-necked flask, followed by 20 g of double-terminated quaternary ammonium salt solid and 40 mL of intermediate, which are then mixed to obtain a mixture. The mixture is then distilled to remove the ethanol and dried under vacuum to obtain a solid, which is the composite surfactant prepared in this invention.

[0050] Comparative Example 3 The difference between this comparative example and Example 6 is that ethanol was used as the solvent. 5 mg of zinc pyridine sulfide copper was added to 200 mL of ethanol, followed by 6 mg of dopamine and 3 mg of silver nitrate. The mixture was stirred to obtain a coating solution. The nuclear pore membrane substrate was fixed on a filter cup, and 20 mL of the coating solution was poured into the filter cup. After standing for 10 min, the coating solution was poured out, forming a coating on the surface of the nuclear pore membrane substrate, resulting in a coated nuclear pore membrane. The coated nuclear pore membrane was placed in a drying oven and dried at 65 °C for 30 min to prepare a gradient nuclear pore membrane based on heavy ion irradiation.

[0051] Performance testing: 1. The air permeability of the gradient nuclear pore membranes based on heavy ion irradiation prepared in Examples 4-6 and Comparative Examples 1-3 was tested sequentially. The instrument used to test the air permeability included a suction pump with a silencer, which evacuated air through a detachable test head with a circular opening. The test head suitable for the selected test standard was mounted on the instrument. The clamping handle was pressed down to open the test head, and the gradient nuclear pore membranes based on heavy ion irradiation prepared in Examples 4-6 and Comparative Examples 1-3 were clamped onto the test head as test samples. The suction pump started automatically. The clamping handle was pressed down for 1 second, the test sample was released, and the suction pump stopped. The pre-selected test pressure was automatically set and remained constant. After a few seconds, the air permeability of the test sample was displayed according to the pre-selected measurement unit.

[0052] 2. Weigh a certain amount of fresh cherries and record it as Mo; then store the cherries in the gradient nuclear pore membranes prepared in Examples 4-6 and Comparative Examples 1-3; after 30 days, record their weight and label it as M. Then calculate the weight loss rate. The formula for calculating the weight loss rate is as follows: Weight loss rate (%) = Mo - M / Mo 3. Antibacterial tests were conducted on the gradient nuclear pore membranes prepared in Examples 4-6 and Comparative Examples 1-3, respectively, using *Escherichia coli* and *Staphylococcus aureus*. The diameters of the inhibition zones for *E. coli* and *Staphylococcus aureus* after 18 hours of incubation were measured. Specific test results are shown in the table below: Table 1. Test data of sample performance [1]

[0053] Data Analysis: By comparing and analyzing the data in the table above, the gradient nuclear pore membranes based on heavy ion irradiation prepared in Examples 4-6 of this invention all exhibit high density, resulting in low weight loss rates. The large spatial extension of the polymer chains, coupled with the effect of hydrophilic groups, gives them a strong attraction to water molecules, which can alleviate water transpiration in fruits, delay wilting, and reduce weight loss, thereby effectively reducing the quality loss of cherries during storage. However, in Comparative Example 1, an equal mass of double-terminated quaternary ammonium salt solid was used to replace the composite surfactant when preparing the alkaline etching solution; in Comparative Example 2, a mixture of double-terminated quaternary ammonium salt solid and intermediates was used to replace the composite surfactant. Because the surfactant molecules synthesized in Comparative Examples 1 and 2 have shorter molecular chains and smaller molecular weights, they can penetrate deeper and further expand the pore size of the PET film surface. The gradient nuclear pore membranes based on heavy ion irradiation prepared using Comparative Examples 1 and 2 have excessively high air permeability and large weight loss rates. Excessive air permeability accelerates fruit respiration, leading to faster energy consumption, aging, and browning.

[0054] In Comparative Example 3, pyridine copper zinc, dopamine, and silver nitrate were mixed to obtain a coating solution. The coating solution was only coated once on the surface of the nuclear pore membrane substrate. Compared with the gradient nuclear pore membranes formed by two coatings and layer-by-layer self-assembly in Examples 4-6, its antibacterial activity was reduced, as evidenced by the smaller diameter of the inhibition zone for Escherichia coli and Staphylococcus aureus.

[0055] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0056] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A gradient nuclear pore membrane based on heavy ion irradiation, characterized in that, It consists of a first coating layer and a second coating layer sequentially coated onto the nuclear pore membrane substrate and its surface; The nuclear pore membrane substrate is obtained by sequentially subjecting a PET film to heavy ion irradiation, ultraviolet sensitization, and alkaline etching solution etching. The first coating is obtained by immersing a nuclear pore membrane substrate in a first coating solution, which is obtained by dissolving pyridine copper zinc and dopamine in ethanol; the second coating is obtained by immersing a substrate coated with the first coating in a second coating solution, which is obtained by dissolving silver nitrate in ethanol.

2. The gradient nuclear pore membrane based on heavy ion irradiation according to claim 1, characterized in that, The preparation method of the alkaline etching solution includes the following steps: A1, N,N-dimethylheptaneamine and 3-bromo-propyltrimethylammonium bromide were added to anhydrous ethanol, dissolved and mixed to obtain a reaction system; the reaction system was refluxed at 95-100℃ for 24-48 h; after the reaction was completed, the ethanol was removed by distillation to obtain the product; the product was washed three times with ethyl acetate / ethanol to obtain a double-terminated quaternary ammonium salt solid. A2. Phenol is added to a 65-75%wt sulfuric acid solution to obtain a mixture; the mixture is reacted at 90-100℃ for 3-4 hours to obtain a product; NaOH solution is added dropwise to the product to adjust the pH value to 8-9, and then 25-35%wt formaldehyde aqueous solution is added, and the reaction is continued at 90-100℃ for 4-5 hours to obtain an intermediate; A3. The double-terminated quaternary ammonium salt solid and the intermediate are added to ethanol and stirred at 65-70℃ until the double-terminated quaternary ammonium salt solid and the intermediate are completely dissolved. Then the temperature is raised to 75-85℃ for reaction, and the ethanol is removed by vacuum distillation and vacuum drying to obtain the composite surfactant solid. The composite surfactant solid is mixed with NaOH solution to obtain alkaline etching solution.

3. The gradient nuclear pore membrane based on heavy ion irradiation according to claim 2, characterized in that, In step A1, the ratio of N,N-dimethylheptaneamine, 3-bromo-propyltrimethylammonium bromide, and anhydrous ethanol is 7-15g:13-26g:50mL, and the mass ratio of ethyl acetate to ethanol is 1:2-3; in step A2, the ratio of phenol, sulfuric acid solution, and formaldehyde aqueous solution is 4.5-9g:20-30mL:15-25mL; the concentration of the added NaOH solution is 0.1mol / L.

4. The gradient nuclear pore membrane based on heavy ion irradiation according to claim 2, characterized in that, In step A3, the ratio of the amount of the double-capped quaternary ammonium salt solid, the intermediate, and ethanol is 10-20g:30-40mL:200mL; the concentration of the NaOH solution is 1-2mol / L; and the ratio of the amount of the composite surfactant solid to the NaOH solution is 3-10g:20-30mL.

5. A method for preparing a gradient nuclear pore membrane based on heavy ion irradiation as described in any one of claims 1-4, characterized in that, Includes the following steps: B1. The PET film is cut into circular pieces with a thickness of 8-15μm to obtain the cut PET film; the cut PET film is irradiated with heavy ions to obtain the heavy ion irradiated PET film; then the heavy ion irradiated PET film is sensitized with ultraviolet lamp to obtain the ultraviolet sensitized PET film. B2. The UV-sensitized PET film is immersed in an alkaline etching solution for etching to obtain the etched core-pore membrane; The etched nuclear pore membrane was washed with deionized water and dried to remove moisture, thus obtaining the nuclear pore membrane substrate. B3. The nuclear pore membrane substrate is fixed on the filter cup, and the first coating solution is poured into the filter cup. After standing for 5-10 minutes, the first coating solution is poured out to obtain the nuclear pore membrane substrate after one soaking. Pour the second coating solution into the filter cup, let it stand for 5-10 minutes, then pour out the second coating solution to obtain the nuclear pore membrane substrate after the second soaking. After a second immersion, the nuclear pore membrane substrate was dried to obtain a gradient nuclear pore membrane based on heavy ion irradiation.

6. The method for preparing a gradient nuclear pore membrane based on heavy ion irradiation according to claim 5, characterized in that, In step B1, heavy ion irradiation is performed using an energy of 19-20 MeV. 129 Vertical Xe ion beam irradiation, with a flux of 3-5 × 10⁻⁵ 9 icons / cm -2 The main peak wavelength of the ultraviolet light is 365nm, and the power is 30-35mW / cm². 2 The sensitization time is 10-12 hours.

7. The method for preparing a gradient nuclear pore membrane based on heavy ion irradiation according to claim 5, characterized in that, In step B2, the etching temperature is 70-85℃ and the etching time is 6-8h; the solid-liquid mass ratio of the UV-sensitized PET film and the alkaline etching solution is 1:5-10.

8. The method for preparing a gradient nuclear pore membrane based on heavy ion irradiation according to claim 5, characterized in that, In step B3, the preparation steps of the first coating solution are as follows: pyridine copper zinc is added to ethanol, then dopamine is added and mixed to obtain the first coating solution; the preparation steps of the second coating solution are as follows: silver nitrate is added to ethanol and mixed to obtain the second coating solution.

9. The method for preparing a gradient nuclear pore membrane based on heavy ion irradiation according to claim 8, characterized in that, The ratio of pyridine sulfide copper zinc, ethanol and dopamine is 3-5 mg: 100-200 mL: 3-6 mg; the ratio of silver nitrate and ethanol is 1-3 mg: 100-200 mL.

10. A gradient nuclear pore membrane based on heavy ion irradiation as described in any one of claims 1-4 Application in cherry preservation.

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