Preparation method of layered talcum powder / carbon dot composite film

Abstract

The invention discloses a preparation method of a layered talcum powder / carbon dot composite film. The preparation method comprises the following steps: by taking glycerol, m-phenylenediamine and talcum powder as raw materials, carrying out hydrothermal reaction to prepare a talcum powder / carbon dot material (TCDs), and further reacting with metal salt to obtain metal-doped TCDs (M-TCDs). The preparation method comprises the following steps: dispersing M-TCDs in a PVA solution, and carrying out solution blending and curtain coating drying to obtain the composite film. According to the film, the gas barrier property is improved by utilizing a layered structure of talcum powder, and meanwhile, a continuous antibacterial effect is realized through active oxygen generation of metal-doped carbon dots and a metal ion slow release effect, so that a fruit rot process is effectively delayed. The method has the advantages of simple process, easily available raw materials, environmental protection and good application prospect.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial thin films, and in particular to a method for preparing a layered talc / carbon dot composite thin film. Background Technology

[0002] During post-harvest storage and transportation, fruits retain high respiratory metabolic activity, making them susceptible to moisture loss, softening, microbial contamination, and nutrient degradation, leading to quality deterioration and shortened shelf life. Especially under unstable ambient or cold chain conditions, fruits are highly prone to spoilage due to oxygen imbalance, ethylene accumulation, and microbial contamination. Therefore, developing safe, efficient, and controllably released preservative materials is crucial for extending fruit shelf life and reducing spoilage.

[0003] Currently, common fruit preservation technologies include modified atmosphere packaging, low-temperature refrigeration, chemical preservative treatment, and functional packaging materials. Among these, functional preservation films have become a research hotspot due to their ease of operation, wide applicability, and ability to passively or actively control the microenvironment. Traditional polymer packaging materials such as polyethylene (PE) and polypropylene (PP), while possessing good mechanical properties, suffer from problems such as unadjustable air permeability, insufficient antibacterial properties, and non-biodegradability.

[0004] Layered talc, as a natural layered silicate mineral material, possesses a good layered structure, high thermal stability, and excellent barrier properties. Introducing it into a polymer matrix can effectively reduce oxygen and water vapor permeability, thereby improving the gas barrier properties of packaging materials. However, single talc fillers have poor interfacial compatibility with the organic matrix, easily leading to agglomeration and a decrease in the mechanical properties of the film.

[0005] Carbon dots (CDs), as a novel carbon-based nanomaterial, possess excellent water solubility, biocompatibility, and tunable surface functional group structure, exhibiting superior antibacterial activity, antioxidant properties, and adsorption or responsiveness to small molecule gases such as ethylene. Studies have shown that CDs can achieve broad-spectrum antibacterial effects by generating reactive oxygen species or disrupting microbial cell membrane structures. Furthermore, the abundant surface carboxyl and hydroxyl functional groups on CDs help improve the interfacial bonding between inorganic fillers and polymer matrices.

[0006] However, current research on the synergistic construction of composite preservation films using talc and carbon dots (CDs) remains limited. Existing technologies mostly focus on single inorganic filler reinforcement or single-functional nanomaterial modification, failing to fully utilize the synergistic effect between the barrier advantages of layered materials and the antibacterial and antioxidant functions of CDs. Furthermore, the dispersion uniformity, interfacial interactions, and functional stability of the components in the composite system still require further optimization. Therefore, developing a structurally stable, functionally synergistic, and simple-to-controllable method for preparing layered talc / carbon dot composite films is of significant technical importance and application potential for improving fruit preservation. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a layered talc / carbon dot composite film. The prepared layered talc / carbon dot composite film can effectively delay the fruit spoilage process when used for fruit preservation.

[0008] The technical solution of this invention is a method for preparing a layered talc powder / carbon dot composite film, the specific steps of which are as follows:

[0009] (1) Weigh the triamic acid, m-phenylenediamine and talc in a molar ratio of 1~3:1~3:1~3 and transfer them to a beaker. Add 15mL of ultrapure water and sonicate until completely dissolved.

[0010] (2) Transfer the solution to a polytetrafluoroethylene liner, put it into the outer shell and place it in an oven, set the temperature to 100~200℃, and react at a constant temperature;

[0011] (3) After the reaction is complete, cool to room temperature, take out the solution, filter it with an aqueous filter membrane, evaporate it by rotary evaporation, and vacuum dry it to obtain talc / carbon dot material TCDs;

[0012] (4) Dissolve the talc / carbon dot material and metal salt in 3-8 mL of dimethyl sulfoxide solvent at a mass ratio of 1-3:1-2, stir and mix well, add 30-80 mL of water for precipitation, filter, and vacuum dry to obtain metal-doped TCDs.

[0013] (5) Weigh out PVA with a mass ratio of 1:9 to water and add it to deionized water. Heat and stir at 70~90℃ until completely dissolved to obtain a 10 wt% PVA solution.

[0014] (6) Prepare an aqueous solution of M-TCDs with a concentration of 0.1 mg / mL to 1 mg / mL, add it to the PVA solution and stir until homogeneous to obtain a mixed solution;

[0015] (7) Pour the mixed solution into a polytetrafluoroethylene mold, dry it at 40~60℃, cool it and peel it off to obtain the layered talc / carbon dot composite film M-TCDs@PVA.

[0016] Preferably, the talc powder in step (1) has a mesh size of 1500 to 4000. More preferably, the talc powder has a mesh size of 1500, 3000, or 4000.

[0017] Preferably, the ultrasound time in step (1) is 30 minutes.

[0018] Preferably, the isothermal reaction time in step (2) is 2 to 6 hours.

[0019] Preferably, the water filtration membrane in step (3) is 0.22m.

[0020] Preferably, the vacuum drying time in step (3) is 6 to 10 hours.

[0021] Preferably, the vacuum drying temperature in steps (3) and (4) is 60°C.

[0022] Preferably, the metal salt in step (4) is ferric chloride hexahydrate or copper chloride tetrahydrate.

[0023] Preferably, in step (4), the amount of dimethyl sulfoxide solvent is 5 mL and the amount of water added is 50 mL.

[0024] Preferably, the stirring time in step (4) is 30 to 120 minutes.

[0025] Preferably, the vacuum drying time in step (4) is 6 to 10 hours.

[0026] Preferably, the heating and stirring temperature in step (5) is 90°C.

[0027] Preferably, the heating and stirring time in step (5) is 2 hours.

[0028] Preferably, the concentration of the M-TCDs aqueous solution in step (6) is 0.5 mg / mL.

[0029] Preferably, the stirring time in step (6) is 30 minutes.

[0030] Preferably, the drying conditions in step (7) are 50°C.

[0031] Preferably, the drying time in step (7) is 2 hours.

[0032] Preferably, the layered talc / carbon dot composite film is used for fruit preservation.

[0033] Preferably, the fruits include, but are not limited to, bananas, strawberries, and tangerines.

[0034] The prepared layered talc / carbon dot composite film M-TCDs@PVA has the following characteristics:

[0035] (1) M-TCDs@PVA have good antibacterial and bacteriostatic properties;

[0036] (2) M-TCDs@PVA effectively prolongs the freshness of fruits.

[0037] This invention constructs a composite preservation system with both gas regulation and active antibacterial functions by synergistically introducing layered talc powder and metal-doped carbon dots into a PVA matrix. This system features a triple synergistic effect of "gas barrier—antibacterial—antioxidant." By combining the physical barrier properties of layered talc powder with the chemical activity of metal-doped carbon dots, and co-synthesizing talc powder and carbon dot precursors via a hydrothermal method, the problem of poor interfacial compatibility between inorganic fillers and organic matrices is solved. Furthermore, metal ions (Fe3⁺ / Cu) are introduced. 2+ This enhances the free radical generation ability of carbon dots, thereby achieving multiple preservation mechanisms that are difficult to achieve with a single material.

[0038] Layered talc forms a directionally arranged lamellar structure in the polymer matrix, significantly extending the diffusion path of oxygen and water vapor, thereby regulating the gas composition of the internal microenvironment of the packaging and reducing the respiration intensity of the fruit.

[0039] Metal-doped carbon dots disrupt microbial cell membrane structures, inhibit enzyme activity, and interfere with metabolic processes by generating reactive oxygen species and releasing metal ions, thus achieving a sustained antibacterial effect. Simultaneously, the surface-active functional groups of the carbon dots possess antioxidant capabilities, scavenging free radicals and delaying tissue browning. These three factors work synergistically to achieve a multi-layered preservation mechanism: gas barrier, active antibacterial activity, and antioxidant anti-aging.

[0040] In terms of material composition and functional units, this invention comprises three core components: layered talc powder (physical barrier unit), metal-doped carbon dots (chemically active unit, capable of generating superoxide radicals or hydroxyl radicals), and PVA matrix (film-forming material). By reducing oxygen and water vapor permeability through talc powder, and simultaneously generating reactive oxygen species and slow-release metal ions through metal-doped carbon dots, it actively disrupts microbial cell membranes, inhibits enzyme activity, and adsorbs ethylene, achieving synergistic preservation through "passive barrier + active antibacterial + antioxidant". In terms of preparation process, this invention adopts a multi-step wet chemical method combined with solution casting process. First, talc powder and carbon dopant precursor are co-reacted through hydrothermal synthesis to prepare talc powder / carbon dot composite material TCDs. Then, metal doping is used to obtain M-TCDs. Finally, the mixture is blended with PVA solution and cast into a film, realizing in-situ composite of inorganic materials and carbon dots and metal ion doping modification.

[0041] This invention is a single-layer composite film in which functional components are uniformly dispersed in a PVA matrix, and multiple preservation mechanisms are achieved by relying on the synergistic effect between the components.

[0042] This invention is specifically designed for fruit preservation packaging. By comprehensively regulating fruit respiration, microbial infection, and ethylene accumulation, it delays fruit spoilage.

[0043] The beneficial effects of this invention are as follows: Compared with existing single-barrier or single-antibacterial packaging materials, the composite film of this invention simultaneously improves gas barrier performance and antibacterial durability, effectively reduces the growth rate of spoilage microorganisms, delays fruit moisture loss and quality deterioration, thereby significantly extending shelf life and reducing transportation losses. Furthermore, this composite structure is structurally stable, with uniformly dispersed components, a simple preparation process, and safe and environmentally friendly raw materials, possessing excellent application and promotion value and industrialization prospects. Attached Figure Description

[0044] Figure 1 This is a superoxide radical test result of Fe-TCDs in Example 1.

[0045] Figure 2 This is a graph showing the cell viability test of Fe-TCDs in Example 1.

[0046] Figure 3 This is a comparison chart of the preservation effects of Fe-TCDs@PVA on bananas in Example 1.

[0047] Figure 4 This is a graph showing the hydroxyl radical test results of Cu-TCDs@PVA in Example 2.

[0048] Figure 5 This is a transmission electron microscope image of Fe-CDs in Comparative Example 1.

[0049] Figure 6The image shows the superoxide radical test results of Fe-CDs in Comparative Example 1. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments of this invention will be described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Any modifications or equivalent substitutions made based on the inventive concept are within the scope of protection of this invention.

[0051] A method for preparing a layered talc / carbon dot composite film, comprising the following steps:

[0052] (1) Weigh the triamic acid, m-phenylenediamine and talc in a molar ratio of 1~3:1~3:1~3 and transfer them to a beaker. Add 15mL of ultrapure water and sonicate for 30 min until completely dissolved.

[0053] (2) Transfer the solution to a polytetrafluoroethylene liner, put it into the outer shell and place it in an oven, set the temperature to 100~200℃, and react at a constant temperature for 2~6 h;

[0054] (3) After the reaction is complete, cool to room temperature, take out the solution, filter it with a 0.22m aqueous filter membrane, evaporate to dryness by rotation, and vacuum dry at 60℃ for 6~10 h to obtain talc / carbon dot materials (TCDs).

[0055] (4) Dissolve TCDs and metal salts in 5 mL of dimethyl sulfoxide solvent at a mass ratio of 1~3:1~2, stir for 30~120 min, add 50 mL of water to precipitate, filter, and vacuum dry at 60℃ for 6~10 h to obtain metal-doped TCDs (M-TCDs).

[0056] (5) Weigh 10 g of PVA and add it to 90 mL of deionized water. Heat and stir at 90°C for 2 h until completely dissolved to obtain a 10 wt% PVA solution.

[0057] (6) Prepare an aqueous solution of M-TCDs of a certain concentration, add it to the PVA solution and stir for 30 min to obtain a homogeneous composite solution;

[0058] (7) Pour the obtained mixed solution into a polytetrafluoroethylene mold, dry it at 50°C for 24 h, cool it and peel it off to obtain the layered talc / carbon dot composite film (M-TCDs@PVA).

[0059] Example 1:

[0060] (1) Weigh the triamic acid, m-phenylenediamine and 4000 mesh talc powder in a molar ratio of 1:1:1, transfer them to a beaker, add 15 mL of ultrapure water, and sonicate for 30 min until completely dissolved;

[0061] (2) Transfer the solution to a polytetrafluoroethylene liner, put it into the outer shell and place it in an oven, set the temperature to 180℃ and react at a constant temperature for 4 h;

[0062] (3) After the reaction was completed, the solution was cooled to room temperature, removed, filtered using a 0.22 m aqueous filter membrane, evaporated by rotary evaporation, and vacuum dried at 60℃ for 8 h to obtain talc / carbon dot materials (TCDs).

[0063] (4) Dissolve TCDs and ferric chloride hexahydrate in 5 mL of dimethyl sulfoxide solvent at a mass ratio of 2:1, stir for 60 min, add 50 mL of water to precipitate, filter, and vacuum dry at 60℃ for 8 h to obtain iron-doped TCDs (Fe-TCDs).

[0064] (5) Weigh 10 g of PVA and add it to 90 mL of deionized water. Heat and stir at 90°C for 2 h until completely dissolved to obtain a 10 wt% PVA solution.

[0065] (6) Prepare a Fe-TCDs aqueous solution of a certain concentration, add it to the PVA solution and stir for 30 min to obtain a homogeneous composite solution;

[0066] (7) Pour the obtained mixed solution into a polytetrafluoroethylene mold, dry it at 50°C for 24 h, and peel it off after cooling to obtain a layered talc / carbon dot composite film (Fe-TCDs@PVA).

[0067] (8) Under the same conditions, compare the preservation time of bananas before and after using Fe-TCDs@PVA packaging.

[0068] Figure 1 This is a test image of Fe-TCDs superoxide radicals from Example 1. The Fe-TCDs superoxide radicals were tested using paramagnetic resonance spectroscopy. Electron paramagnetic resonance spectroscopy is used to study substances containing unpaired electrons (such as free radicals, transition metal ions, etc.). In the image, the horizontal axis (X-axis) represents the magnetic field strength in Gauss (G), and the vertical axis (Y-axis) represents the signal intensity in arbitrary units (au). When a signal peak appears, it indicates the presence of superoxide radicals, which have antibacterial and bacteriostatic effects. Figure 1 The results show that, through paramagnetic resonance spectroscopy, it can be seen that the Fe-TCDs of Example 1 can generate highly reactive oxygen species such as superoxide radicals.

[0069] Figure 2This is a graph showing the cell viability test of Fe-TCDs in Example 1. The horizontal axis represents the concentration of Fe-TCDs. This test demonstrates that Fe-TCDs have good biocompatibility and low toxicity, making them very suitable for fruit preservation. Figure 2 This indicates that even at concentrations as high as 100 g / mL, cell viability is maintained at over 90%.

[0070] After using Fe-TCDs@PVA packaging, the shelf life of bananas was extended from 5 days to 10 days, and the banana firmness decreased slowly (see Figure 3). This is attributed to the fact that the layered talc powder reduces the respiration intensity of the fruit, produces reactive oxygen species, and has a slow-release effect of iron ions, which damages the cell membrane structure of microorganisms on the banana peel, inhibits enzyme activity, and interferes with their metabolic processes. At the same time, it adsorbs gases such as ethylene produced.

[0071] Example 2:

[0072] (1) Weigh the triamic acid, m-phenylenediamine and 3000 mesh talc powder in a molar ratio of 2:1:1, transfer them to a beaker, add 15 mL of ultrapure water, and sonicate for 30 min until completely dissolved;

[0073] (2) Transfer the solution to a polytetrafluoroethylene liner, put it into the outer shell and place it in an oven, set the temperature to 160℃ and react at a constant temperature for 6 h;

[0074] (3) After the reaction was completed, the solution was cooled to room temperature, removed, filtered using a 0.22 m aqueous filter membrane, evaporated by rotary evaporation, and vacuum dried at 60°C for 6 h to obtain talc / carbon dot materials (TCDs).

[0075] (4) Dissolve TCDs and copper chloride tetrahydrate in 5 mL of dimethyl sulfoxide solvent at a mass ratio of 1:1, stir for 60 min, add 50 mL of water to precipitate, filter, and vacuum dry at 60℃ for 6 h to obtain copper-doped TCDs (Cu-TCDs).

[0076] (5) Weigh 10 g of PVA and add it to 90 mL of deionized water. Heat and stir at 90°C for 2 h until completely dissolved to obtain a 10 wt% PVA solution.

[0077] (6) Prepare a Cu-TCDs aqueous solution of a certain concentration, add it to the PVA solution and stir for 30 min to obtain a homogeneous composite solution;

[0078] (7) Pour the obtained mixed solution into a polytetrafluoroethylene mold, dry it at 50°C for 24 h, and peel it off after cooling to obtain a layered talc / carbon dot composite film (Cu-TCDs@PVA).

[0079] (8) Under the same conditions, compare the preservation time of strawberries before and after using Cu-TCDs@PVA packaging.

[0080] Figure 4 This is a hydroxyl radical test pattern of Cu-TCDs@PVA in Example 2. Results analysis: Cu-TCDs can generate highly reactive oxygen species such as hydroxyl radicals, i.e., characteristic signal peaks with an intensity ratio of 1:2:2:1. Like superoxide radicals, it has antibacterial and bacteriostatic effects. Both superoxide radicals and hydroxyl radicals are reactive oxygen species and both have good antibacterial and bacteriostatic effects.

[0081] After using Cu-TCDs@PVA packaging as described in Example 2, the shelf life of strawberries was extended from 3 days to 6 days, and the strawberry firmness decreased slowly.

[0082] Example 3:

[0083] (1) Weigh the triamic acid, m-phenylenediamine and 1500 mesh talc powder in a molar ratio of 1:1:2, transfer them to a beaker, add 15 mL of ultrapure water, and sonicate for 30 min until completely dissolved;

[0084] (2) Transfer the solution to a polytetrafluoroethylene liner, put it into the outer shell and place it in an oven, set the temperature to 170℃ and react at a constant temperature for 4 h;

[0085] (3) After the reaction was completed, the solution was cooled to room temperature, removed, filtered with a 0.22 m aqueous filter membrane, evaporated by rotation, and dried under vacuum at 60°C for 7 h to obtain talc / carbon dot material (TCDs-1).

[0086] (4) TCDs-1 and ferric chloride hexahydrate were dissolved in 5 mL of dimethyl sulfoxide solvent at a mass ratio of 1:1, stirred for 60 min, 50 mL of water was added for precipitation, filtered, and dried under vacuum at 60 °C for 7 h to obtain iron-doped TCDs (Fe-TCDs-1).

[0087] (5) Weigh 10 g of PVA and add it to 90 mL of deionized water. Heat and stir at 90°C for 2 h until completely dissolved to obtain a 10 wt% PVA solution.

[0088] (6) Prepare a Fe-TCDs-1 aqueous solution of a certain concentration, add it to the PVA solution and stir for 30 min to obtain a homogeneous composite solution;

[0089] (7) Pour the obtained mixed solution into a polytetrafluoroethylene mold, dry it at 50°C for 24 h, cool it and peel it off to obtain a layered talc / carbon dot composite film (Fe-TCDs@PVA-1).

[0090] (8) Under the same conditions, compare the preservation time of tangerines before and after using Fe-TCDs@PVA-1 to package them.

[0091] Results analysis: After using Fe-TCDs@PVA-1 packaging, the shelf life of Satsuma mandarins was extended from 8 days to 12 days, and the firmness of the Satsuma mandarins decreased slowly.

[0092] The preservation experiment was mainly conducted through comparative experiments. Under the same experimental conditions, the effects of packaging fruits with Fe-TCDs@PVA-1 and without packaging were compared. After a certain period of time, the unpackaged fruits began to show spots, rot, and even mold. However, when packaged with the Fe-TCDs@PVA-1 of this invention, the fruits could be stored for a longer period of time.

[0093] Comparative Example 1:

[0094] (1) Weigh the triamic acid and m-phenylenediamine in a molar ratio of 1:1, transfer them to a beaker, add 15 mL of ultrapure water, and sonicate for 30 min until completely dissolved;

[0095] (2) Transfer the solution to a polytetrafluoroethylene liner, put it into the outer shell and place it in an oven, set the temperature to 180℃ and react at a constant temperature for 4 h;

[0096] (3) After the reaction was completed, the solution was cooled to room temperature, removed, filtered using a 0.22 m aqueous filter membrane, evaporated by rotary evaporation, and dried under vacuum at 60°C for 8 h to obtain carbon dot materials (CDs).

[0097] (4) Dissolve CDs and ferric chloride hexahydrate in 5 mL of dimethyl sulfoxide solvent at a mass ratio of 2:1, stir for 60 min, add 50 mL of water to precipitate, filter, and vacuum dry at 60 °C for 8 h to obtain iron-doped CDs (Fe-CDs).

[0098] (5) Weigh 10 g of PVA and add it to 90 mL of deionized water. Heat and stir at 90°C for 2 h until completely dissolved to obtain a 10 wt% PVA solution.

[0099] (6) Prepare a Fe-CDs aqueous solution of a certain concentration, add it to the PVA solution and stir for 30 min to obtain a homogeneous composite solution;

[0100] (7) Pour the obtained mixed solution into a polytetrafluoroethylene mold, dry it at 50°C for 24 h, and peel it off after cooling to obtain a carbon dot composite film (Fe-CDs@PVA).

[0101] (8) Under the same conditions, compare the preservation time of bananas before and after using Fe-CDs@PVA packaging.

[0102] Figure 5 The image shows a transmission electron microscope (TEM) image of Fe-CDs in Comparative Example 1. TEM results indicate that Fe-CDs are uniformly dispersed in water in a near-spherical state (see...). Figure 5 This indicates that nanoscale materials have been successfully prepared, providing a basis for their uniform dispersion in PVA materials.

[0103] Figure 6 The image shows the superoxide radical test result of Fe-CDs in Comparative Example 1. Because Fe-CDs contain Fe atoms, a Fenton-like reaction can form within the carbon particles, generating reactive oxygen species such as superoxide radicals, thus maintaining the antibacterial and bacteriostatic effects. However... Figure 6 The results of paramagnetic resonance (ESR) spectroscopy showed that Fe-CDs emitted a superoxide radical signal peak, indicating antibacterial and bacteriostatic effects. However, the signal peak intensity gradually decreased. This is because, without the layered structure of talc, Fe-CDs exhibited aggregation, leading to a decline in antibacterial and bacteriostatic properties.

[0104] After using Fe-CDs@PVA packaging as in Comparative Example 1, the shelf life of strawberries can be extended from 3 days to 5 days.

[0105] As can be seen, the composite film of this invention utilizes the layered structure of talc to improve gas barrier performance, while achieving a sustained antibacterial effect through the generation of active oxygen from metal-doped carbon dots and the slow release of metal ions, thereby effectively delaying the fruit spoilage process.

[0106] This invention employs rigorous control over parameter optimization and functional verification during preparation. In the synthesis stage, the molar ratios of tricornioic acid, m-phenylenediamine, and talc powder of different mesh sizes, as well as the temperature and time of the hydrothermal reaction, are precisely controlled to ensure the stable formation of TCDs. In the doping and modification stage, the type of metal salt, the doping ratio, and the solvent treatment process directly affect the antibacterial activity. In the film-forming stage, the concentration of the PVA solution, the composite stirring time, and the drying conditions determine the uniformity and mechanical properties of the film. Finally, through reactive oxygen species testing, cytotoxicity assessment, and verification of the actual preservation effects on fruits such as bananas and strawberries, the effectiveness of this composite film in extending shelf life has been established.

[0107] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical principles disclosed in the present invention, such as using hydrolytic enzymes from other sources with similar specificity, or making equivalent substitutions for the chromatographic packing materials and conditions in the purification step, should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a layered talc / carbon dot composite film, characterized in that, The specific steps of the method are as follows: (1) Weigh the triamic acid, m-phenylenediamine and talc in a molar ratio of 1~3:1~3:1~3 and transfer them to a beaker. Add 15mL of ultrapure water and sonicate until completely dissolved. (2) Transfer the solution to a polytetrafluoroethylene liner, put it into the outer shell and place it in an oven, set the temperature to 100~200 ℃, and react at a constant temperature; (3) After the reaction is complete, cool to room temperature, take out the solution, filter it with an aqueous filter membrane, evaporate it by rotary evaporation, and vacuum dry it to obtain talc / carbon dot material TCDs; (4) Dissolve the talc / carbon dot material and metal salt in 3-8 mL of dimethyl sulfoxide solvent at a mass ratio of 1-3:1-2, stir and mix well, add 30-80 mL of water for precipitation, filter, and vacuum dry to obtain metal-doped TCDs. (5) Weigh out PVA with a mass ratio of 1:9 to water and add it to deionized water. Heat and stir at 70~90℃ until completely dissolved to obtain a 10 wt% PVA solution. (6) Prepare an aqueous solution of M-TCDs with a concentration of 0.1 mg / mL to 1 mg / mL, add it to the PVA solution and stir until homogeneous to obtain a mixed solution; (7) Pour the mixed solution into a polytetrafluoroethylene mold, dry it at 40~60℃, cool it and peel it off to obtain the layered talc / carbon dot composite film M-TCDs@PVA.

2. The method for preparing the layered talc / carbon dot composite film as described in claim 1, characterized in that, The talc powder used in step (1) has a mesh size of 1500, 3000, or 4000.

3. The method for preparing the layered talc / carbon dot composite film as described in claim 1, characterized in that, The metal salts mentioned in step (4) are ferric chloride hexahydrate and copper chloride tetrahydrate.

4. The method for preparing the layered talc / carbon dot composite film as described in claim 1, characterized in that, In step (4), the amount of dimethyl sulfoxide solvent is 5 mL, and the amount of water added is 50 mL.

5. The method for preparing the layered talc / carbon dot composite film as described in claim 1, characterized in that, The heating and stirring temperature in step (5) is 90°C.

6. The method for preparing the layered talc / carbon dot composite film as described in claim 1, characterized in that, In step (6), the concentration of the M-TCDs aqueous solution is 0.5 mg / mL.

7. The method for preparing the layered talc / carbon dot composite film as described in claim 1, characterized in that, The layered talc / carbon dot composite film is used for fruit preservation.

8. The method for preparing the layered talc / carbon dot composite film as described in claim 7, characterized in that, The fruits mentioned include, but are not limited to, bananas, strawberries, and tangerines.

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