Bionic breathable preservative film and preparation method and application thereof

Abstract

This invention belongs to the field of food packaging technology, specifically relating to a biomimetic breathable preservation film, its preparation method, and its application. The invention uses polylactic acid as a base material, adding two inorganic modified compounds: amino acid-functionalized cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets and an iron-copper bimetallic organic framework material loaded with silver nanoparticles. Plasticizers and surfactants are also added, and the film is prepared through solution blending, low-temperature ultrasonic dispersion, and casting. This preservation film possesses biomimetic breathable functionality, with oxygen and carbon dioxide permeability within the suitable range for modified atmosphere preservation of fruits and vegetables. The carbon dioxide to oxygen permeability ratio is also reasonable, exhibiting efficient ethylene removal capabilities and broad-spectrum antibacterial activity against common foodborne pathogens. Using this preservation film for fruit and vegetable packaging can significantly extend the shelf life of fresh agricultural products such as grapes and blueberries. The preparation process of this invention is simple and has broad application prospects in the field of active food packaging.

Description

Technical Field

[0001] This invention belongs to the field of food packaging technology, specifically relating to a biomimetic breathable preservation film, its preparation method, and its application. Background Technology

[0002] Fresh fruits and vegetables continue to undergo active respiration and metabolism after harvest. Respiration consumes oxygen and releases carbon dioxide and ethylene. Ethylene, as an endogenous plant hormone, accelerates fruit ripening and senescence, leading to quality deterioration and spoilage. Statistics show that households in developed countries waste a significant amount of fresh fruits and vegetables annually, while losses during post-harvest processing and transportation are even more severe in developing countries. Traditional preservation methods, such as refrigeration, are widely used but suffer from high energy consumption and chilling injury, while chemical preservatives face challenges related to food safety and environmental pollution. In recent years, active packaging technology has received widespread attention. This type of packaging interacts with the product or packaging environment, thereby extending shelf life, maintaining quality, and improving safety. Among these, biomimetic strategies have provided new ideas for the design of preservation films. Inspired by the stomatal structure of plant leaves, porous microspheres are introduced into the film-forming matrix as gas "switches" or "stomata" to regulate the permeability of oxygen, carbon dioxide, and water vapor, as well as the selectivity of carbon dioxide and oxygen, showing great potential in the preservation of room-temperature foods. Biopolymer films have attracted great attention in the field of fruit and vegetable preservation due to their biodegradability and barrier properties. However, a certain amount of moisture still transfers between the storage environment, the biopolymer film and the fruit and vegetable system, and its impact on preservation efficiency needs to be systematically studied.

[0003] In the modification of inorganic fillers, the introduction of nanoscale fillers has been widely proven to significantly improve the gas barrier properties, mechanical properties, and antibacterial properties of films. For example, incorporating modified mesoporous silica into chitosan-based films can enhance gas exchange and impart significant antibacterial efficacy. Layered double hydroxide nanosheet dispersions can be coated to prepare high oxygen barrier coatings, which significantly reduce the oxygen permeability and water vapor permeability of polyester films. Incorporating layered double hydroxides into polyvinyl alcohol and polyacrylic acid blends reduces oxygen permeability by nearly half, while improving thermal stability and UV barrier properties, and maintaining transparency in the visible light region. Regarding ethylene removal, metal-organic frameworks (MOFs) possess extremely high specific surface areas and excellent gas adsorption and desorption properties, making them ideal candidates for ethylene-controlled packaging. Cerium-based MOFs doped with titanium dioxide can rapidly remove ethylene under UV irradiation; incorporating them into cellulose nanofiber films can effectively delay avocado ripening, resulting in reduced ethylene accumulation, slower color degradation, and a lower browning index. The green-synthesized hybrid metal-organic framework material has a high ethylene adsorption capacity. When embedded in a polyvinyl alcohol-based packaging film, it can significantly extend the shelf life of green bananas at room temperature.

[0004] Despite the significant progress made in the aforementioned research, existing technologies still face the following core challenges: most biomimetic food preservation films utilize only a single functional component, making it difficult to simultaneously achieve multiple functions such as ethylene removal, gas permeation regulation, and microbial inhibition; inorganic nanofillers exhibit aggregation issues within the polymer matrix, leading to a decline in the film's mechanical properties and optical transparency; currently reported layered double hydroxides and metal-organic frameworks are mostly based on conventional metal compositions, lacking directional structural design and functional optimization specifically for food preservation film applications; and the design and development of composite inorganic modified compounds with synergistic functions are still in their early stages. Therefore, developing a biomimetic breathable food preservation film that introduces two modified compounds to achieve synergistic regulation of the film's gas permeability, ethylene removal capacity, and antibacterial properties has significant academic value and application prospects. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a biomimetic breathable food preservation film, its preparation method and application.

[0006] In a first aspect, the present invention provides a method for preparing a biomimetic breathable food preservation film, comprising the steps of: S1. Dissolve 100 parts by weight of polylactic acid in 500-1000 parts by weight of chloroform and stir at room temperature to obtain a polymer solution; add 5-20 parts by weight of polyethylene glycol 400 and 2-10 parts by weight of triethyl citrate to the polymer solution and continue stirring to obtain a mixed solution; add 2-10 parts by weight of amino acid-functionalized cobalt aluminum gallium ternary layered bimetallic hydroxide nanosheets and 1-8 parts by weight of iron-copper bimetallic-organic framework material-supported silver nanoparticle composite material and 0.5-3 parts by weight of Tween-80 to the mixed solution and disperse ultrasonically under 0-5℃ ice-water bath conditions to obtain a dispersion. S2. Degas the dispersion under vacuum at room temperature to obtain a degassed film-forming solution; coat the degassed film-forming solution onto a glass plate, let it stand at room temperature, and then transfer it to a vacuum drying oven at 38-42℃ to dry, obtaining a dried film; peel the dried film off the glass plate.

[0007] This invention discloses the overall assembly mechanism and synergistic effect of a biomimetic breathable food preservation film. The film-forming process of the film is essentially a dynamic equilibrium process of polymeric physical entanglement and the spatial arrangement of nanofillers. First, the long chains of polylactic acid (PLA) gradually extend and distribute uniformly in chloroform through molecular thermal motion, forming a continuous polymer matrix. After adding polyethylene glycol 400 and triethyl citrate, these small-molecule plasticizers insert between the large PLA molecular chains, weakening the inter-segment forces and thus increasing the film's flexibility. When adding cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets and iron-copper bimetallic-organic framework material-loaded silver nanoparticle composites, the surfactant Tween-80 plays a crucial role. It prevents the nanomaterials from agglomerating in the polymer matrix by altering the wettability of the particle surface. Ultrasonic dispersion under ice-water bath conditions further ensures the uniform distribution of the fillers. During the coating and drying process of the film-forming solution, as the solvent slowly evaporates, the PLA segments begin to retract and compact. At this point, the sheet-like, layered bimetallic hydroxides tend to align parallel in the horizontal direction, constructing complex molecular diffusion pathways; while porous organic framework materials are embedded within the film. This structure mimics the respiration mechanism of plant leaves: when the carbon dioxide concentration inside the packaging increases or oxygen is insufficient, the microporous channels formed between the filler and the polymer matrix, as well as the selective adsorption properties of the filler itself, enable active regulation of gas flux. The resulting film not only possesses excellent mechanical strength but also maintains a dynamic equilibrium atmosphere according to the physiological state of the fruits and vegetables inside, effectively delaying ripening and spoilage, demonstrating the precise design of modern materials chemistry in agricultural applications.

[0008] According to a preferred embodiment of the present invention, in step S1, the ultrasonic dispersion time is 30-60 min.

[0009] According to a preferred embodiment of the present invention, in step S2, the time for standing at room temperature is 2-4 hours.

[0010] According to a preferred embodiment of the present invention, the preparation method of the amino acid-functionalized cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets includes: A1, dissolving 11.5-11.8 parts by weight of cobalt nitrate hexahydrate, 3.75-3.85 parts by weight of aluminum nitrate nonahydrate and 2.56-2.65 parts by weight of gallium nitrate hydrate in 95-105 parts by weight of deionized water; adjusting the pH value to 9.8-10.2 with sodium hydroxide solution under stirring to obtain a mixed solution; transferring the mixed solution to a reaction vessel and performing hydrothermal crystallization treatment at 118-122℃, naturally cooling to room temperature, centrifuging to obtain a precipitate; washing the precipitate with deionized water and anhydrous ethanol, and vacuum drying at 78-82℃. A2. Under nitrogen protection, 1.5-1.8 parts of the precursor powder were dispersed in 95-105 parts of a deionized aqueous solution containing 3.8-4.2 parts of citric acid and 1.7-1.8 parts of L-arginine. The pH was adjusted to 8.0-9.0 with sodium hydroxide solution. The mixture was stirred in a water bath at 58-62℃. After the reaction was completed, the mixture was centrifuged and the precipitate was collected. The precipitate was washed with deionized water to obtain a washed precipitate. The washed precipitate was dispersed in 95-105 parts of an aqueous solution containing 3.7-3.8 parts of glycine and treated with ultrasound at 48-52℃ to obtain a suspension. The suspension was centrifuged to obtain a supernatant. The supernatant was freeze-dried.

[0011] In this invention, the core of the preparation process of the amino acid-functionalized cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets lies in the assembly of inorganic layers and the precise intercalation and exfoliation of organic molecules. In the first stage, cobalt nitrate hexahydrate, aluminum nitrate nonahydrate, and gallium nitrate hydrate are completely ionized in deionized water, releasing divalent cobalt ions, trivalent aluminum ions, and trivalent gallium ions. When sodium hydroxide solution is added dropwise to the system, these metal cations undergo a co-precipitation reaction with hydroxide ions. Under strongly alkaline conditions and specific temperature conditions, hydrothermal crystallization is performed in a high-pressure reactor with a polytetrafluoroethylene liner. The metal ions are embedded in the octahedral centers composed of hydroxide ions in a specific arrangement, forming positively charged layers similar to a brucite structure. Subsequently, the precursor powder is placed in a solution containing citric acid and L-arginine. At this time, the negatively charged citrate ions enter between the layers through electrostatic attraction, replacing the original nitrate ions, thereby increasing the interlayer distance. Immediately afterwards, the amino group of the L-arginine molecule forms hydrogen bonds with the hydroxyl group on the surface of the layer. Under nitrogen protection and a suitable water bath temperature, this ion exchange and molecular adsorption tend to reach equilibrium. Finally, glycine molecules are used as a peeling agent, and the process is carried out under specific ultrasonic power. The cavitation effect generated by ultrasound produces enormous instantaneous pressure, which, combined with the strong affinity between glycine and the layers, ultimately overcomes the van der Waals forces between the layers, allowing the thick layered structure to peel off into extremely thin nanosheets. These nanosheets, due to their extremely high specific surface area and exposed active groups, lay the material foundation for the subsequent construction of breathing channels in plastic wrap.

[0012] According to a preferred embodiment of the present invention, in step A1, the hydrothermal crystallization treatment at 118-122°C is carried out for 24-30 hours.

[0013] According to a preferred embodiment of the present invention, in step A2, the stirring reaction time in a water bath at 58-62°C is 12-14 hours.

[0014] According to a preferred embodiment of the present invention, the preparation method of the iron-copper bimetallic-organic framework material-supported silver nanoparticle composite material includes: B1, dissolving 2.8-3.1 parts by weight of anhydrous ferrous acetate and 2.0-2.2 parts by weight of copper acetate monohydrate in a mixed solvent of 95-105 parts by weight of N,N-dimethylformamide and anhydrous ethanol under nitrogen protection, stirring at room temperature, then adding 2.6-2.8 parts by weight of 2,5-dihydroxyterephthalic acid and continuing stirring to obtain a mixed solution; transferring the mixed solution to a reaction vessel, and heating at 108-1000 ppm. The reaction was carried out at 12℃ using a solvothermal method. After natural cooling to room temperature, the mixture was centrifuged to obtain a precipitate. The precipitate was washed with N,N-dimethylformamide and anhydrous methanol and dried under vacuum at 58-62℃ to obtain iron-copper bimetallic MOF-74 powder. B2. 2.5-3.0 parts of the iron-copper bimetallic MOF-74 powder were dispersed in 95-105 parts of anhydrous ethanol containing 0.15-0.18 parts of silver nitrate. The mixture was irradiated with a mercury lamp under a nitrogen atmosphere and with stirring. After the reaction was completed, the mixture was centrifuged and the solid was collected. The solid was washed with anhydrous ethanol and dried under vacuum at 48-52℃.

[0015] In this invention, the preparation of the iron-copper bimetallic-organic framework material-supported silver nanoparticle composite material is a complex process involving coordination chemistry and photochemical reduction. In the initial stage of the reaction, anhydrous ferrous acetate and copper acetate monohydrate, acting as metal center providers, are dissolved in a mixed solvent of N,N-dimethylformamide and anhydrous ethanol. After the addition of 2,5-dihydroxyterephthalic acid, the carboxyl and hydroxyl groups in the organic ligands undergo coordination reactions with iron and copper ions. In a nitrogen-protected solvothermal environment, the metal ions act as connecting nodes, and the organic ligands act as a scaffold, self-assembling in three-dimensional space to form an iron-copper bimetallic framework with a highly ordered porous structure. The synergistic effect of the iron and copper bimetals not only enhances the structural stability of the framework but also endows the material with unique electronic properties. After obtaining the solid powder, it is dispersed in an ethanol solution containing silver nitrate. At this point, silver ions spontaneously diffuse into the micropores inside the framework or adsorb onto the framework surface. During subsequent irradiation with a high-pressure mercury lamp, an in-situ photoreduction reaction occurs. When the framework material is illuminated with light of a specific wavelength, it generates excited-state electrons. These electrons are transferred to the surface of silver ions, reducing them from an ionic state to zero-valent elemental silver nanoparticles. Due to the spatial confinement effect of the internal pores of the framework, the growth of the silver nanoparticles is strictly limited, thus maintaining them within an extremely small scale and ensuring uniform distribution. This composite structure retains the gas-trapping ability of organic framework materials while also endowing the material with excellent antibacterial properties through the introduction of silver nanoparticles, giving it the dual function of regulating the environmental atmosphere and inhibiting microbial growth in food preservation applications.

[0016] According to a preferred embodiment of the present invention, the solvothermal reaction time at 108-112°C is 48-50 h.

[0017] In a second aspect, the present invention provides a biomimetic breathable food preservation film prepared according to the method for preparing the biomimetic breathable food preservation film.

[0018] A third aspect of the present invention provides an application of the biomimetic breathable preservation film in fruit and vegetable packaging.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention achieves synergistic regulation of gas permeability, ethylene removal capacity, and antibacterial activity of food preservation films by introducing amino acid-functionalized cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets and iron-copper bimetallic organic framework material loaded with silver nanoparticles. Among them, the high aspect ratio two-dimensional structure of the layered bimetallic hydroxide nanosheets forms a "bypass effect" in the polylactic acid matrix, significantly extending the diffusion path of gas molecules and endowing the film with excellent gas barrier properties; its abundant amino acid functional groups form hydrogen bonds with the polymer matrix, effectively inhibiting filler agglomeration and ensuring high transparency of the film. The iron-copper bimetallic organic framework material selectively adsorbs and catalytically degrades ethylene through open metal sites, and the silver nanoparticles provide broad-spectrum antibacterial activity. The two modified compounds coexist synergistically in the matrix, forming a three-in-one preservation mechanism of "barrier-removal-antibacterial".

[0020] (2) In terms of preparation method, this invention ensures the formation of a single crystalline phase in the layered bimetallic hydroxide precursor by precisely controlling the molar ratio of divalent and trivalent metal ions; the intercalation exchange reaction is carried out using decarbonated deionized water under nitrogen protection to prevent carbonate poisoning and ensure successful insertion of citric acid and arginine; ultrasonic exfoliation is performed while keeping the precipitate moist to avoid interlayer shrinkage and obtain nanosheets with high lateral dimensions. The iron-copper bimetallic-organic framework material-loaded silver nanoparticle composite material uses acetate metal source to eliminate the problem of silver chloride precipitation caused by chloride ion residue; the molar ratio of metal to ligand is strictly controlled in the solvothermal reaction to ensure the complete topological structure; the system is kept at low temperature during photoreduction of loaded silver nanoparticles to prevent framework collapse and particle aggregation. A composite plasticizing system is used in the film formation stage to improve the flexibility of the film and promote uniform dispersion of fillers.

[0021] (3) The biomimetic breathable preservation film of the present invention has a high efficiency in removing ethylene. It can quickly reduce the concentration of ethylene in the packaging at room temperature and delay the ripening of fruits and vegetables. Its oxygen and carbon dioxide permeability is within the reasonable range of modified atmosphere preservation, and the ratio of carbon dioxide to oxygen permeability is relatively high. It can spontaneously form a low oxygen and high carbon dioxide microenvironment to inhibit the intensity of respiration. Its water vapor permeability is moderate, balancing moisturizing and mildew prevention. Detailed Implementation

[0022] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0023] Example 1 This embodiment provides a method for preparing a biomimetic breathable food preservation film, the steps of which include: Step S1: Add 100g of polylactic acid (molecular weight 120kDa) to 500g of chloroform and stir magnetically at 400rpm for 2h at room temperature until completely dissolved to obtain a clear and transparent polymer solution; add 5g of polyethylene glycol 400 and 2g of triethyl citrate to the above polymer solution and continue stirring at 400rpm for 30min to obtain a mixed solution; add 2g of modified compound A obtained in step A2, 1g of modified compound B obtained in step B2 and 0.5g of Tween-80 to the mixed solution in sequence, transfer the mixture to an ice-water bath (controlling the temperature 0±0.5℃), and ultrasonically disperse it for 30min under ultrasonic power of 300W and frequency of 40kHz. Stir manually every 5min during ultrasonication to prevent precipitation and obtain a uniform dispersion.

[0024] Step S2: The dispersion obtained in Step S1 is vacuum degassed for 15 minutes at room temperature and a vacuum degree of -0.08 MPa until no obvious bubbles escape from the liquid surface, thus obtaining the degassed film-forming liquid; a clean glass plate is placed horizontally, and the degassed film-forming liquid is evenly coated onto the glass plate with a blade coating machine with a blade gap of 0.5 mm, and the coating speed is controlled at 20 mm / s; the coated glass plate is left to stand at room temperature (25±2℃) for 2 hours to allow chloroform to evaporate slowly; then it is transferred to a vacuum drying oven at 38℃ and dried for 12 hours under a vacuum degree of -0.09 MPa to completely remove the residual solvent; the dried film is carefully peeled off from the glass plate to obtain a biomimetic breathable food preservation film.

[0025] Preparation of amino acid-functionalized cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets: Step A1: Add 11.5g of cobalt nitrate hexahydrate, 3.75g of aluminum nitrate nonahydrate, and 2.56g of gallium nitrate hydrate to 95g of deionized water. Stir magnetically at 400rpm at room temperature until completely dissolved to obtain a mixed salt solution. Under vigorous stirring, add 1M sodium hydroxide solution dropwise to precisely adjust the pH of the mixed salt solution to 9.8, and continue stirring for 30min to stabilize the pH. Transfer the above mixed solution to a stainless steel high-pressure reactor with a polytetrafluoroethylene liner, seal it, and incubate at 3℃ / m The mixture was heated to 118°C at a heating rate of 100°C and hydrothermally crystallized at 118°C for 24 hours, then naturally cooled to room temperature. The reaction product was centrifuged at 4000 rpm for 10 minutes, and the precipitate was collected. The precipitate was washed three times with deionized water and three times with anhydrous ethanol, and centrifuged at 4000 rpm for 10 minutes after each wash. The washed precipitate was placed in a vacuum drying oven and vacuum dried at 78°C and -0.09 MPa for 12 hours to obtain cobalt aluminum gallium ternary layered bimetallic hydroxide precursor powder.

[0026] Step A2: Under nitrogen protection (nitrogen flow rate 0.5 L / min), disperse 1.5 g of the precursor powder obtained in Step A1 in 95 g of deionized water, in which 3.8 g of citric acid and 1.7 g of L-arginine have been pre-dissolved. Stir at 300 rpm for 30 min at room temperature to ensure uniform dispersion of the powder. Adjust the pH of the dispersion to 8.0 with 1 M sodium hydroxide solution, then heat to 58 °C and continue stirring in a 58 °C water bath for 12 h while maintaining nitrogen purging. After the reaction is complete, centrifuge the mixture at 4000 rpm for 10 min and collect the precipitate. Wash the precipitate three times with deionized water (50 g of deionized water each time, centrifuged after washing). The precipitate was obtained after washing. The precipitate was kept moist (without drying) and immediately transferred to 95g of an aqueous solution containing 3.7g of glycine. It was then subjected to ultrasonic treatment at 50℃ for 4h, with an ultrasonic power density of 0.5W / cm² and an ultrasonic frequency of 40kHz. The mixture was manually stirred every 30min during the ultrasonic process to ensure uniformity. After ultrasonication, the suspension was centrifuged at 3000rpm for 15min to remove large particles that had not been separated at the bottom, and the supernatant was collected. The supernatant was freeze-dried at -50℃ and 10Pa for 48h to obtain solid powdered amino acid-functionalized cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets, denoted as modified compound A.

[0027] Preparation of silver nanoparticle-supported composite materials of iron-copper bimetallic-organic framework materials: Step B1: Under nitrogen protection (nitrogen flow rate 0.5 L / min), 2.8 g of anhydrous ferrous acetate and 2.0 g of copper acetate monohydrate were added to 95 g of a 1:1 mixture of N,N-dimethylformamide and anhydrous ethanol. The mixture was magnetically stirred at 400 rpm for 30 min at room temperature until completely dissolved, yielding a clear, light green solution. 2.6 g of 2,5-dihydroxyterephthalic acid was slowly added while stirring, and stirring was continued for 1 h to obtain a brown suspension. The suspension was transferred to a stainless steel high-pressure reactor with a polytetrafluoroethylene liner, sealed, and then subjected to 2... The temperature was increased to 108℃ at a constant ℃ / min, and the reaction was carried out at 108℃ for 48 h using a solvothermal method. The autogenous pressure during the reaction was 1.5 MPa. The mixture was then allowed to cool naturally to room temperature. The reaction product was centrifuged at 4000 rpm for 10 min, and the precipitate was collected. The precipitate was washed three times with 50 g of N,N-dimethylformamide and three times with 50 g of anhydrous methanol, and centrifuged at 4000 rpm for 10 min after each wash. The washed precipitate was placed in a vacuum drying oven and dried under vacuum at 58℃ and -0.09 MPa for 12 h to obtain iron-copper bimetallic MOF-74 powder.

[0028] Step B2: Disperse 2.5g of the iron-copper bimetallic MOF-74 powder obtained in Step B1 in 95g of anhydrous ethanol containing 0.15g of silver nitrate. Stir magnetically at 300rpm for 30min under a nitrogen atmosphere (nitrogen flow rate 0.3L / min) to ensure uniform dispersion. Place the dispersion in a photoreactor and irradiate with a 500W high-pressure mercury lamp (main wavelength 365nm) for 2h. The distance between the lamp and the reactor is 10cm. During the reaction, the system temperature is maintained below 30℃ by circulating cooling water (actual temperature controlled at 28±1℃). After irradiation, centrifuge the reaction solution at 4000rpm for 10min and collect the solid. Wash the solid three times with anhydrous ethanol (50g of anhydrous ethanol each time, centrifuged after washing). Place the washed solid in a vacuum drying oven and vacuum dry at 48℃ and -0.09MPa for 6h to obtain the iron-copper bimetallic-organic framework material-supported silver nanoparticle composite material, denoted as modified compound B.

[0029] Example 2 The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a biomimetic breathable food preservation film, the steps of which include: Step S1: Dissolve 100g of polylactic acid in 750g of chloroform and stir magnetically for 2 hours at room temperature until completely dissolved to obtain a polymer solution; add 12.5g of polyethylene glycol 400 and 6g of triethyl citrate to the polymer solution and continue stirring for 30 minutes to obtain a mixed solution; add 6g of modified compound A, 4.5g of modified compound B and 1.75g ​​of Tween-80 to the mixed solution in sequence, and ultrasonically disperse for 45 minutes under ice-water bath conditions at 2.5℃ (ultrasonic power 300W, frequency 40kHz) to obtain a dispersion.

[0030] Step S2: Degas the dispersion obtained in step S1 under vacuum for 15 min at room temperature (vacuum degree -0.09 MPa) to obtain the degassed film-forming liquid; uniformly coat the degassed film-forming liquid onto a clean glass plate with a doctor blade gap of 0.5 mm, let it stand at room temperature for 3 h, and then transfer it to a vacuum drying oven at 40 °C to dry for 12 h to obtain the dried film; peel the dried film off the glass plate to obtain a biomimetic breathable preservation film with a thickness of 50 μm.

[0031] Preparation of amino acid-functionalized cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets: Step A1: Dissolve 11.65g of cobalt nitrate hexahydrate, 3.80g of aluminum nitrate nonahydrate, and 2.605g of gallium nitrate hydrate in 100g of deionized water. Adjust the pH to 10.0 with 1M sodium hydroxide solution while stirring to obtain a mixed solution. Transfer the mixed solution to a reaction vessel and perform hydrothermal crystallization treatment at 120℃ for 27h. After naturally cooling to room temperature, centrifuge to obtain a precipitate. Wash the precipitate three times alternately with deionized water and anhydrous ethanol, and vacuum dry at 80℃ for 12h to obtain a cobalt-aluminum-gallium ternary layered bimetallic hydroxide precursor powder.

[0032] Step A2: Under nitrogen protection, 1.65g of the precursor powder obtained in Step A1 was dispersed in 100g of a deionized aqueous solution containing 4.0g of citric acid and 1.75g ​​of L-arginine. The pH was adjusted to 8.5 with 1M sodium hydroxide solution, and the mixture was stirred in a 60℃ water bath for 13h. After the reaction, the precipitate was collected by centrifugation. The precipitate was washed three times with deionized water to obtain the washed precipitate. While keeping the precipitate moist, the washed precipitate was dispersed in 100g of an aqueous solution containing 3.75g of glycine and treated with ultrasound at 50℃ for 4h (ultrasound power density 0.75W / cm²) to obtain a suspension. The suspension was centrifuged at 3000rpm for 15min, and the supernatant was collected and freeze-dried to obtain solid powdered amino acid-functionalized cobalt aluminum gallium ternary layered bimetallic hydroxide nanosheets, denoted as modified compound A.

[0033] Preparation of silver nanoparticle-supported composite materials of iron-copper bimetallic-organic framework materials: Step B1: Under nitrogen protection, 2.95 g of anhydrous ferrous acetate and 2.1 g of copper acetate monohydrate were dissolved in 100 g of a 1:1 mixture of N,N-dimethylformamide and anhydrous ethanol. The mixture was stirred at room temperature for 30 min, and then 2.7 g of 2,5-dihydroxyterephthalic acid was added and the mixture was stirred for another 1 h to obtain a mixed solution. The mixed solution was transferred to a reaction vessel and reacted solvothermically at 110 °C for 49 h (reaction pressure 2.0 MPa). After cooling naturally to room temperature, the precipitate was obtained by centrifugation. The precipitate was washed three times alternately with 75 g of N,N-dimethylformamide and 75 g of anhydrous methanol, and then dried under vacuum at 60 °C for 12 h to obtain iron-copper bimetallic MOF-74 powder.

[0034] Step B2: Disperse 2.75g of the iron-copper bimetallic MOF-74 powder obtained in Step B1 in 100g of anhydrous ethanol containing 0.165g of silver nitrate. Irradiate the mixture for 2h under a nitrogen atmosphere and magnetic stirring with a 500W high-pressure mercury lamp (main wavelength 365nm), maintaining the system temperature below 30℃ during the process. After the reaction is complete, centrifuge to collect the solid. Wash the solid three times with anhydrous ethanol and vacuum dry it at 50℃ for 6h to obtain the iron-copper bimetallic-organic framework material-supported silver nanoparticle composite material, denoted as modified compound B.

[0035] Example 3 The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a biomimetic breathable food preservation film, the steps of which include: Step S1: Dissolve 100g of polylactic acid in 1000g of chloroform and stir magnetically for 2 hours at room temperature until completely dissolved to obtain a polymer solution; add 20g of polyethylene glycol 400 and 10g of triethyl citrate to the polymer solution and continue stirring for 30 minutes to obtain a mixed solution; add 10g of modified compound A, 8g of modified compound B and 3g of Tween-80 to the mixed solution in sequence, and ultrasonically disperse for 60 minutes under 5℃ ice-water bath conditions (ultrasonic power 300W, frequency 40kHz) to obtain a dispersion.

[0036] Step S2: Degas the dispersion obtained in step S1 under vacuum for 15 min at room temperature (vacuum degree -0.1 MPa) to obtain the degassed film-forming liquid; uniformly coat the degassed film-forming liquid onto a clean glass plate with a scraper gap of 0.5 mm, let it stand at room temperature for 4 h, and then transfer it to a vacuum drying oven at 42℃ to dry for 12 h to obtain the dried film; peel the dried film off the glass plate to obtain the biomimetic breathable food preservation film.

[0037] Preparation of amino acid-functionalized cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets: Step A1: Dissolve 11.8g of cobalt nitrate hexahydrate, 3.85g of aluminum nitrate nonahydrate, and 2.65g of gallium nitrate hydrate in 105g of deionized water. Adjust the pH to 10.2 with 1M sodium hydroxide solution while stirring to obtain a mixed solution. Transfer the mixed solution to a reaction vessel and perform hydrothermal crystallization treatment at 122℃ for 30h. After naturally cooling to room temperature, centrifuge to obtain a precipitate. Wash the precipitate three times alternately with deionized water and anhydrous ethanol, and vacuum dry at 82℃ for 12h to obtain a cobalt-aluminum-gallium ternary layered bimetallic hydroxide precursor powder.

[0038] Step A2: Under nitrogen protection, 1.8g of the precursor powder obtained in Step A1 was dispersed in 105g of a deionized aqueous solution containing 4.2g of citric acid and 1.8g of L-arginine. The pH was adjusted to 9.0 with 1M sodium hydroxide solution, and the mixture was stirred in a water bath at 62℃ for 14h. After the reaction, the precipitate was collected by centrifugation. The precipitate was washed three times with deionized water to obtain the washed precipitate. While keeping the precipitate moist, the washed precipitate was dispersed in 105g of an aqueous solution containing 3.8g of glycine and treated with ultrasound at 52℃ for 4h (ultrasound power density 1.0W / cm²) to obtain a suspension. The suspension was centrifuged at 3000rpm for 15min, and the supernatant was collected and freeze-dried to obtain solid powdered amino acid-functionalized cobalt aluminum gallium ternary layered bimetallic hydroxide nanosheets, denoted as modified compound A.

[0039] Preparation of silver nanoparticle-supported composite materials of iron-copper bimetallic-organic framework materials: Step B1: Under nitrogen protection, 3.1 g of anhydrous ferrous acetate and 2.2 g of copper acetate monohydrate were dissolved in 105 g of a 1:1 mixture of N,N-dimethylformamide and anhydrous ethanol. The mixture was stirred at room temperature for 30 min, and then 2.8 g of 2,5-dihydroxyterephthalic acid was added and stirring was continued for 1 h to obtain a mixed solution. The mixed solution was transferred to a reaction vessel and reacted solvothermically at 112 °C for 50 h (reaction pressure 2.5 MPa). After naturally cooling to room temperature, the precipitate was obtained by centrifugation. The precipitate was washed three times alternately with 100 g of N,N-dimethylformamide and 100 g of anhydrous methanol, and then dried under vacuum at 62 °C for 12 h to obtain iron-copper bimetallic MOF-74 powder.

[0040] Step B2: Disperse 3.0g of the iron-copper bimetallic MOF-74 powder obtained in Step B1 in 105g of anhydrous ethanol containing 0.18g of silver nitrate. Irradiate the mixture with a 500W high-pressure mercury lamp (main wavelength 365nm) for 2h under a nitrogen atmosphere and magnetic stirring, maintaining the system temperature below 30℃ during the process. After the reaction is complete, centrifuge to collect the solid. Wash the solid three times with anhydrous ethanol and vacuum dry it at 52℃ for 6h to obtain the iron-copper bimetallic-organic framework material-supported silver nanoparticle composite material, denoted as modified compound B.

[0041] Comparative Example 1 The difference between this comparative example and Example 2 is that no modified compound A is added in step S1, while the other steps and parameters are exactly the same as in Example 2.

[0042] Comparative Example 2 The difference between this comparative example and Example 2 is that no modified compound B is added in step S1, while the other steps and parameters are exactly the same as in Example 2.

[0043] Comparative Example 3 The difference between this comparative example and Example 2 is that neither modified compound A nor modified compound B is added in step S1, while the other steps and parameters are exactly the same as in Example 2.

[0044] According to relevant national and industry standards, the performance of the biomimetic breathable food preservation film provided in the above embodiments and comparative examples was tested. The test methods are as follows: Oxygen permeability test: The test was conducted using a pressure difference gas permeation analyzer. The membrane to be tested was cut into circular samples with a diameter of 10 cm and placed in the test chamber. The test temperature was 23℃, the relative humidity was 50%, and the pressure difference across the sample was 0.1 MPa. Under stable permeability conditions, the volume of oxygen permeating the sample per unit time was recorded. The oxygen permeation rate per unit area, unit time, and unit pressure difference was calculated, and the results were expressed as cm³ / (m²·24h·atm). Three parallel samples were tested for each sample, and the arithmetic mean was taken.

[0045] Carbon dioxide permeability test: The test was conducted using a pressure differential gas permeation analyzer. The membrane to be tested was cut into circular samples with a diameter of 10 cm and placed in the test chamber. The test temperature was 23℃, the relative humidity was 50%, and the pressure difference across the sample was 0.1 MPa. The test gas was replaced with high-purity carbon dioxide (purity ≥99.9%). Under stable permeation conditions, the volume of carbon dioxide permeating the sample per unit time was recorded. The carbon dioxide permeation rate per unit area, per unit time, and per unit pressure difference was calculated, and the results were expressed as cm³ / (m²·24h·atm). Three parallel samples were tested for each sample, and the arithmetic mean was taken.

[0046] Water vapor transmission rate test: The cup method was used. The film to be tested was cut into circular samples with a diameter of 8 cm and sealed in a permeation cup containing desiccant (anhydrous calcium chloride), with the desiccant approximately 5 mm from the lower surface of the film. The permeation cup was placed in a constant temperature and humidity chamber at 38℃ and 90% relative humidity. The permeation cup was weighed every 24 hours (accurate to 0.001 g), and the test was continued for 7 days until the difference in mass increment between two consecutive weighings was less than 5%. The water vapor transmission rate was calculated based on the mass increase per unit time and the effective permeation area of ​​the film, and the result was expressed as g / (m²·24h). Three parallel samples were tested for each sample, and the arithmetic mean was taken.

[0047] Ethylene removal rate test: The test was conducted using a closed container method combined with gas chromatography. The test film was cut into 2g samples and placed in a 1L sealed glass container. High-purity ethylene gas (purity ≥99.9%) was injected into the container using a microsyringe to achieve an initial ethylene concentration of 100ppm (volume fraction). The container was then placed in a 25℃ incubator for 12 hours. 1mL of gas sample was extracted from the container using a gas-tight syringe and injected into the gas chromatograph (equipped with a flame ionization detector) to determine the residual ethylene concentration. The ethylene removal rate was calculated using the following formula: Ethylene removal rate (%) = (Initial ethylene concentration - Residual ethylene concentration) / Initial ethylene concentration × 100%. Three parallel samples were tested for each sample, and the arithmetic mean was taken.

[0048] Escherichia coli inhibition rate test: The test was conducted using a film-coating method. After activating the Escherichia coli strain, the bacterial suspension concentration was adjusted to 1.0 × 10⁻⁶ using phosphate buffer solution. 5 CFU / mL. Spread 0.2 mL of bacterial suspension evenly onto the surface of a nutrient agar plate. Cut the test film into square samples with sides of 5 cm, disinfect the surface with 75% ethanol, and then attach them to the agar plate with the bacterial suspension, ensuring complete contact between the film and the agar. Incubate the plates upside down in a 37℃ incubator for 24 h. After incubation, elute the viable bacteria on the film and agar surface with phosphate buffer solution. Dilute the eluent serially and spread it onto nutrient agar plates. Incubate at 37℃ for 24 h and count the viable bacteria. Use a plate prepared under the same conditions but without the film as a blank control. The inhibition rate is calculated using the following formula: Inhibition rate (%) = (Number of viable bacteria in blank control - Number of viable bacteria in sample) / Number of viable bacteria in blank control × 100%. Test three parallel samples for each sample and take the arithmetic mean.

[0049] Staphylococcus aureus inhibition rate test: The test was conducted using a film-coating method. After activating the Staphylococcus aureus strain, the concentration of the bacterial suspension was adjusted to 1.0 × 10⁻⁶ using phosphate buffer solution. 5CFU / mL. Spread 0.2 mL of bacterial suspension evenly onto the surface of a nutrient agar plate. Cut the test film into square samples with sides of 5 cm, disinfect the surface with 75% ethanol, and then attach them to the agar plate with the bacterial suspension, ensuring complete contact between the film and the agar. Incubate the plates upside down in a 37℃ incubator for 24 h. After incubation, wash away the viable bacteria on the film and agar surface with phosphate buffer solution. Dilute the eluent serially and spread it onto nutrient agar plates. Incubate at 37℃ for 24 h and count the viable bacteria. Use a plate prepared under the same conditions but without the film as a blank control. The inhibition rate is calculated using the following formula: Inhibition rate (%) = (Number of viable bacteria in blank control - Number of viable bacteria in sample) / Number of viable bacteria in blank control × 100%. Test three parallel samples for each sample and take the arithmetic mean.

[0050] Tensile strength test: A universal testing machine was used. The film to be tested was cut longitudinally into dumbbell-shaped specimens with a gauge length of 25 mm, an effective width of 4 mm, and a total specimen length of not less than 75 mm. The specimens were clamped in the testing machine fixtures with a fixture spacing of 50 mm, and the tensile speed was set to 50 mm / min. Tension was carried out at room temperature (23±2℃) until the specimen broke. The maximum tensile force at specimen breakage was recorded. The tensile strength was calculated using the following formula: Tensile strength (MPa) = Maximum tensile force (N) / Initial cross-sectional area of ​​specimen (mm²). Five parallel samples were tested for each sample, and the arithmetic mean was taken.

[0051] Elongation at break test: A universal testing machine was used for the test. The film to be tested was cut longitudinally into dumbbell-shaped specimens with a gauge length of 25 mm and an effective width of 4 mm. The specimens were clamped in the testing machine fixtures with a fixture spacing of 50 mm. The tensile speed was set to 50 mm / min, and the specimens were stretched at room temperature (23±2℃) until they broke. The change in gauge length at the point of break was recorded. The elongation at break was calculated using the following formula: Elongation at break (%) = (Gazelle length at break - Initial gauge length) / Initial gauge length × 100%. Five parallel samples were tested for each sample, and the arithmetic mean was taken.

[0052] Transmittance testing: A UV-Vis spectrophotometer was used for the test. The film to be tested was cut into square samples with sides of 4 cm and placed tightly against the outer wall of a quartz cuvette. Using air as a reference, the transmittance was measured at a wavelength of 550 nm. Five samples at different locations were tested for each sample, and the arithmetic mean was taken.

[0053] Blueberry shelf-life testing method: Select blueberries of uniform size (approximately 1.5 ± 0.3 g per fruit), free from mechanical damage, pests, and diseases, with intact bloom and uniform color, 30 fruits per group. Wrap and seal each fruit with the test film (Examples 1-3 and Comparative Examples 1-3), with unwrapped fruit serving as a blank control. Place all samples in a constant temperature and humidity chamber at 25°C and 65% relative humidity. Observe the appearance of the fruit daily and record the degree of decay for each fruit. The criteria for determining decay are: visible mold spots on the fruit surface (mold coverage exceeding 10% of the fruit surface area) or obvious softening and juice seepage. When more than 50% of the fruits in each group reach the decay criteria, that group reaches the end of its shelf life, and the number of days at this point is recorded as the shelf life (days). Three replicates are set for each sample, and the arithmetic mean is taken.

[0054] Grape shelf-life testing method: Select Kyoho grapes of uniform size (approximately 8±1 g per fruit), free from mechanical damage, pests, and diseases, with plump berries and bright green stems. Each bunch should retain approximately 15 intact berries, with 3 bunches used per group (approximately 45 berries in total). Wrap and seal each sample with the test film (Examples 1-3 and Comparative Examples 1-3), using unpackaged fruit as a blank control. Place all samples in a constant temperature and humidity chamber at 25℃ and 60% relative humidity. Observe the appearance of the fruit daily and record the degree of decay for each berry. The criteria for decay are: visible mold spots on the berry surface, browning exceeding 10% of the berry surface area, berry detachment (breakage at the stem), or the appearance of a wine-like odor. When more than 50% of the berries in each group reach the decay criteria, that group reaches the end of its shelf life, and the number of days at this point is recorded as the shelf life (days). Three replicates are set for each sample, and the arithmetic mean is taken.

[0055] The performance test data above are shown in Table 1.

[0056] Table 1 Performance Test Results

[0057] As can be seen from the above, Examples 1-3 significantly solve several core problems existing in the current food preservation film technology compared to Comparative Examples 1-3.

[0058] First, regarding ethylene removal capacity, the ethylene removal rate of Comparative Example 3 (without modified compound A and modified compound B) was only 8.6%, and that of Comparative Example 2 (containing only modified compound A) was only 12.3%, indicating that relying solely on the polylactic acid matrix or simply adding layered bimetallic hydroxide nanosheets has almost no ethylene removal function. In contrast, the ethylene removal rate of Comparative Example 1 (containing only modified compound B) reached 97.5%, and Examples 1-3 further reached 96.2-98.5%, proving that modified compound B is the key component for achieving efficient ethylene removal, and its removal performance remains stable when coexisting with modified compound A, thus solving the problem of accelerated ripening of fruits and vegetables due to ethylene accumulation in the prior art.

[0059] Secondly, regarding gas permeation control, Comparative Example 3 exhibits an oxygen permeability as high as 4200 cm³ / (m²·24h·atm) and a carbon dioxide permeability as high as 9100 cm³ / (m²·24h·atm). Comparative Example 1, lacking modified compound A, has an oxygen permeability of 3800 and a carbon dioxide permeability of 8700, both significantly higher than Examples 1-3 (oxygen permeability 1250-2450, carbon dioxide permeability 3600-6100). Furthermore, the carbon dioxide / oxygen permeability ratio increases from 2.17 in Comparative Example 3 to 2.88 in Example 3. This indicates that modified compound A effectively extends the gas diffusion path through the bypass effect of two-dimensional sheets, achieving selective control of oxygen and carbon dioxide, thus solving the problem of single gas permeability and inability to form a low-oxygen, high-carbon dioxide microenvironment in existing technologies.

[0060] Furthermore, regarding antibacterial properties, Comparative Examples 2 and 3 showed inhibition rates of less than 15.3% against Escherichia coli and Staphylococcus aureus, while Comparative Example 1 and Examples 1-3 all achieved inhibition rates of over 99%. This demonstrates that only films containing modified compound B (iron-copper bimetallic-organic framework material-supported silver nanoparticle composite material) possess broad-spectrum antibacterial activity, thus solving the problem of microbial spoilage caused by the lack of antibacterial function in existing food preservation films.

[0061] Furthermore, in terms of mechanical properties, Comparative Example 3 had a tensile strength of only 32 MPa and an elongation at break of 8%, while Comparative Examples 1 and 2 had strengths between 35 and 41 MPa due to the lack of one of the modifying compounds. Examples 1-3, on the other hand, achieved strengths of 38-48 MPa and 11-15%, respectively, indicating that the synergistic effect of the two modifying compounds (modifying compound A and modifying compound B) enhanced the mechanical integrity of the film.

[0062] Finally, regarding the shelf life of blueberries, Comparative Example 3 lasted only 2 days, Comparative Example 2 only 3 days, and Comparative Example 1 lasted 6 days, while Examples 1-3 were extended to 8 days, 10 days, and 12 days, respectively. Regarding the shelf life of grapes, Comparative Example 3 lasted only 3 days, Comparative Example 2 only 4 days, and Comparative Example 1 lasted 7 days, while Examples 1-3 were extended to 9 days, 11 days, and 13 days, respectively. This indicates that the biomimetic breathable preservation film containing both modified compounds achieves ethylene removal, gas regulation, and antibacterial triple functions synergistically, significantly extending the shelf life of highly perishable berries and effectively solving the core problem in the prior art where a single functional component cannot meet the synergistic regulation needs of multiple gas components.

Claims

1. A method for preparing a biomimetic breathable food preservation film, characterized in that the steps include... include: S1. Dissolve 100 parts by weight of polylactic acid in 500-1000 parts by weight of chloroform and stir at room temperature to obtain a polymer solution; add 5-20 parts by weight of polyethylene glycol 400 and 2-10 parts by weight of triethyl citrate to the polymer solution and continue stirring to obtain a mixed solution; add 2-10 parts by weight of amino acid-functionalized cobalt aluminum gallium ternary layered bimetallic hydroxide nanosheets and 1-8 parts by weight of iron-copper bimetallic-organic framework material-supported silver nanoparticle composite material and 0.5-3 parts by weight of Tween-80 to the mixed solution and disperse ultrasonically under 0-5℃ ice-water bath conditions to obtain a dispersion. S2. Degas the dispersion under vacuum at room temperature to obtain a degassed film-forming solution; coat the degassed film-forming solution onto a glass plate, let it stand at room temperature, and then transfer it to a vacuum drying oven at 38-42℃ to dry, obtaining a dried film; peel the dried film off the glass plate.

2. The method for preparing the biomimetic breathable food preservation film according to claim 1, characterized in that, In step S1, the ultrasonic dispersion time is 30-60 min.

3. The method for preparing the biomimetic breathable food preservation film according to claim 1, characterized in that, In step S2, the time for standing at room temperature is 2-4 hours.

4. The method for preparing the biomimetic breathable food preservation film according to claim 1, characterized in that, The preparation method of the amino acid-functionalized cobalt-aluminum-gallium ternary layered bimetallic hydroxide nanosheets includes: A1, dissolving 11.5-11.8 parts by weight of cobalt nitrate hexahydrate, 3.75-3.85 parts by weight of aluminum nitrate nonahydrate and 2.56-2.65 parts by weight of gallium nitrate hydrate in 95-105 parts by weight of deionized water; adjusting the pH value to 9.8-10.2 with sodium hydroxide solution under stirring to obtain a mixed solution; transferring the mixed solution to a reaction vessel and performing hydrothermal crystallization treatment at 118-122℃, naturally cooling to room temperature, centrifuging to obtain a precipitate; washing the precipitate with deionized water and anhydrous ethanol, and vacuum drying at 78-82℃ to obtain the precursor. Powder; A2. Under nitrogen protection, disperse 1.5-1.8 parts of precursor powder in 95-105 parts of deionized water containing 3.8-4.2 parts of citric acid and 1.7-1.8 parts of L-arginine. Adjust the pH to 8.0-9.0 with sodium hydroxide solution. Stir the reaction in a water bath at 58-62℃. After the reaction is complete, centrifuge and collect the precipitate. Wash the precipitate with deionized water to obtain the washed precipitate. Disperse the washed precipitate in 95-105 parts of an aqueous solution containing 3.7-3.8 parts of glycine and treat it with ultrasound at 48-52℃ to obtain a suspension. Centrifuge the suspension to obtain the supernatant. Freeze-dry the supernatant.

5. The method for preparing the biomimetic breathable food preservation film according to claim 4, characterized in that, In step A1, the hydrothermal crystallization treatment at 118-122℃ takes 24-30 hours.

6. The method for preparing the biomimetic breathable food preservation film according to claim 4, characterized in that, In step A2, the reaction is stirred in a water bath at 58-62℃ for 12-14 hours.

7. The method for preparing the biomimetic breathable food preservation film according to claim 1, characterized in that, The preparation method of the iron-copper bimetallic-organic framework material-supported silver nanoparticle composite material includes: B1, under nitrogen protection, dissolving 2.8-3.1 parts by weight of anhydrous ferrous acetate and 2.0-2.2 parts by weight of copper acetate monohydrate in a mixed solvent of 95-105 parts by weight of N,N-dimethylformamide and anhydrous ethanol, stirring at room temperature, then adding 2.6-2.8 parts by weight of 2,5-dihydroxyterephthalic acid and continuing stirring to obtain a mixed solution; transferring the mixed solution to a reaction vessel and solvent treatment at 108-112℃. The reaction was carried out under heat, and the mixture was allowed to cool naturally to room temperature before centrifugation to obtain a precipitate. The precipitate was washed with N,N-dimethylformamide and anhydrous methanol, and then dried under vacuum at 58-62°C to obtain iron-copper bimetallic MOF-74 powder. B2. 2.5-3.0 parts of the iron-copper bimetallic MOF-74 powder were dispersed in 95-105 parts of anhydrous ethanol containing 0.15-0.18 parts of silver nitrate. The mixture was irradiated with a mercury lamp under a nitrogen atmosphere and stirring. After the reaction was completed, the mixture was centrifuged and the solid was collected. The solid was washed with anhydrous ethanol and dried under vacuum at 48-52°C.

8. The method for preparing the biomimetic breathable food preservation film according to claim 7, characterized in that, The solvothermal reaction time at 108-112℃ is 48-50h.

9. A biomimetic breathable food preservation film, characterized in that, The biomimetic breathable food preservation film is prepared by the method according to any one of claims 1-8.

10. An application of the biomimetic breathable food preservation film according to claim 9, characterized in that, Application of the biomimetic breathable preservation film in fruit and vegetable packaging.

Images