Preparation method and application of CD-MOFs and AgNPs@CD-MOFs, food preservative film

Abstract

The application relates to the field of food preservation technology, in particular to a preparation method and application of CD-MOFs and AgNPs@CD-MOFs and a food preservation film. The preparation method comprises the following steps: mixing cyclodextrin, potassium hydroxide and water to obtain a mixed solution; the concentration of the cyclodextrin in the mixed solution is 2.5-12.5 mmol / L; the concentration of the potassium hydroxide in the mixed solution is 20-100 mmol / L; the mixed solution is heated in a first anhydrous ethanol environment, second anhydrous ethanol is added into the mixed solution after heating, and the nanoscale cyclodextrin metal organic framework is obtained; the second anhydrous ethanol is added through a peristaltic pump; the rotating speed of the peristaltic pump is 25-100 rpm; and the mixed solution and the first anhydrous ethanol do not directly contact. The preparation method can prepare the non-toxic nanoscale CD-MOFs without using a size adjusting agent, and the nanoscale CD-MOFs can be directly applied to the field of food preservation.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, and in particular to the preparation methods and applications of CD-MOFs and AgNPs@CD-MOFs, and food preservation films. Background Technology

[0002] Currently, the synthesis of nanoscale CD-MOFs (cyclodextrin metal-organic frameworks) mostly requires the use of size modifiers, which can effectively reduce the size of the generated CD-MOFs. Size modifiers can affect the adhesion of ligands to metal particles by interfering with the deprotonation of organic ligands. Simultaneously, size modifiers can also act as surface capping agents to prevent further crystal growth. However, conventional size modifiers in existing technologies mainly include high molecular weight polyethylene glycol and triethylamine. These size modifiers all possess a certain degree of toxicity and cannot be completely eliminated during the preparation process; therefore, they are not suitable for direct application in food preservation. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing CD-MOFs and AgNPs@CD-MOFs, as well as their applications and food preservation films. The preparation method yields non-toxic nanoscale CD-MOFs without the need for size modifiers, which can be directly applied in the field of food preservation.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing nanoscale cyclodextrin metal-organic frameworks (CD-MOFs), comprising the following steps:

[0006] Cyclodextrin, potassium hydroxide, and water are mixed to obtain a mixture; the concentration of cyclodextrin in the mixture is 2.5–12.5 mmol / L; the concentration of potassium hydroxide in the mixture is 20–100 mmol / L.

[0007] The mixture was heated in an environment of first anhydrous ethanol, and then second anhydrous ethanol was added to the mixture to obtain the nanoscale cyclodextrin metal-organic framework; the second anhydrous ethanol was added by a peristaltic pump; the rotation speed of the peristaltic pump was 25-100 rpm;

[0008] The mixture and the first anhydrous ethanol do not come into direct contact.

[0009] Preferably, the molar ratio of the cyclodextrin to potassium hydroxide is 1:8.

[0010] Preferably, the mixing is carried out under stirring conditions;

[0011] The stirring speed is 100-400 rpm, and the time is 30-120 min;

[0012] Preferably, the mixture further includes filtration;

[0013] The filtration uses a 0.45μm organic membrane.

[0014] Preferably, the heating temperature is 50–90°C and the heating time is 24–72 h.

[0015] This invention also provides a method for preparing silver-doped nanoscale cyclodextrin metal-organic frameworks (AgNPs@CD-MOFs), comprising the following steps:

[0016] The silver-doped nanoscale cyclodextrin metal-organic framework was obtained by mixing the nanoscale cyclodextrin metal-organic framework dispersion with silver nitrate solution and culturing it in the dark.

[0017] The nanoscale cyclodextrin metal-organic framework in the nanoscale cyclodextrin metal-organic framework dispersion is the nanoscale cyclodextrin metal-organic framework dispersion prepared by the preparation method described in the above technical solution.

[0018] Preferably, the mass ratio of the nano-sized cyclodextrin metal-organic framework in the nano-sized cyclodextrin metal-organic framework dispersion to the silver nitrate in the silver nitrate solution is (10-50):1.

[0019] Preferably, the culture is carried out under oscillation conditions, with the oscillation frequency being 50–200 rpm and the time being 12–72 h.

[0020] This invention also provides the application of the silver-doped nanoscale cyclodextrin metal-organic framework prepared by the preparation method described above in food preservation films.

[0021] The present invention also provides a food preservation film, the raw materials of which include silver-doped nanoscale cyclodextrin metal-organic framework, polylactic acid and polyethylene glycol;

[0022] The mass ratio of the silver-doped nanoscale cyclodextrin metal-organic framework, polylactic acid, and polyethylene glycol is (0.2–1.6):8:0.8.

[0023] This invention provides a method for preparing nanoscale cyclodextrin metal-organic frameworks, comprising the following steps: mixing cyclodextrin, potassium hydroxide, and water to obtain a mixture; the concentration of cyclodextrin in the mixture is 2.5–12.5 mmol / L; the concentration of potassium hydroxide in the mixture is 20–100 mmol / L; heating the mixture in an environment of first anhydrous ethanol, then adding second anhydrous ethanol to the mixture to obtain the nanoscale cyclodextrin metal-organic framework; the second anhydrous ethanol is added via a peristaltic pump; the rotation speed of the peristaltic pump is 25–100 rpm; the mixture and the first anhydrous ethanol do not directly contact each other. This invention successfully prepared nanoscale CD-MOFs by controlling the concentrations of CD and KOH and the ethanol addition rate. Crystal formation is directly related to the critical supersaturation concentration of the solution. First, controlling the concentrations of CD and KOH... + The initial concentration of CD and K can directly affect the rate of nucleation and crystal growth. Appropriate concentrations of CD and K... + This is conducive to the formation of nanoscale CD-MOFs. High concentrations of CD and K... + It increased the nucleation rate, but shortened the K-cycle. + The diffusion path length is increased, leading to a faster crystal growth rate. Furthermore, low concentrations of CD and K... + This leads to reduced crystal nucleation, CD and K + Aggregation around a few atomic nuclei leads to an increase in crystal size. Both high and low concentrations are unfavorable for the formation of nanoscale CD-MOFs. Secondly, the rate of ethanol addition may affect the initial crystallization and recrystallization processes. Specifically, a faster addition rate (100 rpm) may lead to secondary nucleation and the formation of immature crystals, while a slower addition rate may slow down crystal precipitation, both of which are detrimental to the formation of uniformly sized CD-MOFs.

[0024] This invention also provides a method for preparing silver-doped nanoscale cyclodextrin metal-organic frameworks, comprising the following steps: mixing a nanoscale cyclodextrin metal-organic framework dispersion with a silver nitrate solution, and then culturing in the dark to obtain the silver-doped nanoscale cyclodextrin metal-organic framework; wherein the nanoscale cyclodextrin metal-organic framework in the dispersion is the nanoscale cyclodextrin metal-organic framework dispersion prepared by the method described above. Due to the framework confinement and good dispersibility of nanoscale CD-MOFs, the size of the silver nanoparticles is reduced (reaching 1-2 nm), thereby improving the antibacterial ability of the silver nanoparticles. Furthermore, the silver nanoparticles are confined within the framework, thus hindering contact with cells. Therefore, the silver-doped nanoscale cyclodextrin metal-organic framework prepared by this method exhibits good antibacterial and low-toxicity properties.

[0025] This invention also provides a food preservation film, the raw materials of which include silver-doped nanoscale cyclodextrin metal-organic framework, polylactic acid, and polyethylene glycol; the mass ratio of the silver-doped nanoscale cyclodextrin metal-organic framework, polylactic acid, and polyethylene glycol is (0.2-1.6):8:0.8. Compared with PE, the food preservation film of this invention can improve the storage quality of fresh fruits and vegetables (button mushrooms). Attached Figure Description

[0026] Figure 1 The images shown are scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and energy-dispersive X-ray spectroscopy (EDS) images of the γ-CD-MOFs described in Examples 1 to 11.

[0027] Figure 2 TEM images of the γ-CD-MOFs described in Example 5 and particle size distribution diagrams of the γ-CD-MOFs described in Example 5;

[0028] Figure 3 The images shown are SEM (a), TEM (b), EDS (c), EDS point scan (d), EDS area scan (e), C element distribution (f), O element distribution (g), and Ag element distribution (h) of AgNPs@γ-CD-MOFs described in Example 16.

[0029] Figure 4 The N2 adsorption-desorption curves (a) and pore size distribution curves (b) of the γ-CD-MOFs described in Example 1 and the AgNPs@γ-CD-MOFs described in Example 16 are shown.

[0030] Figure 5 The antibacterial activity (a) and cell viability (b) of AgNPs@γ-CD-MOFs described in Example 16;

[0031] Figure 6 The visible light and ultraviolet transmittance (a), water vapor transmittance (b), and oxygen transmittance (c) of the food preservation films described in Examples 23-26 and Comparative Example 1 are shown.

[0032] Figure 7 The bar graphs show the antibacterial rates of the food preservation films described in Example 25 and Comparative Example 1 against different types of bacteria.

[0033] Figure 8 Image showing the preservation effect of button mushrooms. Detailed Implementation

[0034] This invention provides a method for preparing nanoscale cyclodextrin metal-organic frameworks (CD-MOFs), comprising the following steps:

[0035] Cyclodextrin, potassium hydroxide, and water are mixed to obtain a mixture; the concentration of cyclodextrin in the mixture is 2.5–12.5 mmol / L; the concentration of potassium hydroxide in the mixture is 20–100 mmol / L.

[0036] The mixture was heated in an environment of first anhydrous ethanol, and then second anhydrous ethanol was added to the mixture to obtain the nanoscale cyclodextrin metal-organic framework; the second anhydrous ethanol was added by a peristaltic pump; the rotation speed of the peristaltic pump was 25-100 rpm;

[0037] The mixture and the first anhydrous ethanol do not come into direct contact.

[0038] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0039] In this invention, cyclodextrin, potassium hydroxide, and water are mixed to obtain a mixture; the concentration of cyclodextrin in the mixture is 2.5–12.5 mmol / L; and the concentration of potassium hydroxide in the mixture is 20–100 mmol / L.

[0040] In this invention, the cyclodextrin is preferably γ-cyclodextrin (γ-CD). In an embodiment of this invention, the γ-CD was purchased from Shanghai Yuanye Biotechnology Co., Ltd. (Shanghai, China). In an embodiment of this invention, the potassium hydroxide has a purity of 99.99%. In this invention, the water is preferably ultrapure water.

[0041] In this invention, the mixing is preferably carried out under stirring conditions, the stirring speed is preferably 100-400 rpm, more preferably 300 rpm, and the stirring time is preferably 30-120 min, more preferably 1 h. This invention does not impose any special limitations on the stirring method; any method well-known to those skilled in the art can be used. In an embodiment of this invention, the stirring method is magnetic stirring, the stirring speed can be 300 rpm, and the stirring time can be 1 h.

[0042] After the mixing is completed, the present invention preferably includes filtration, which is preferably performed using a 0.45 μm organic membrane. In the present invention, the purpose of filtration is to remove unnecessary impurities from the solution.

[0043] In this invention, the concentration of cyclodextrin in the mixture is 2.5–12.5 mmol / L, preferably 5–10 mmol / L; the concentration of potassium hydroxide in the mixture is 20–100 mmol / L, preferably 40–80 mmol / L. In embodiments of this invention, the concentration of cyclodextrin in the mixture can be 2.5 mmol / L, 5 mmol / L, or 12.5 mmol / L; the concentration of potassium hydroxide in the mixture can be 20 mmol / L, 40 mmol / L, or 100 mmol / L.

[0044] After obtaining the mixture, the present invention heats the mixture in the environment of the first anhydrous ethanol, and then adds the second anhydrous ethanol to the mixture to obtain the nanoscale cyclodextrin metal-organic framework; the second anhydrous ethanol is added by a peristaltic pump; the rotation speed of the peristaltic pump is 25-100 rpm; the mixture and the first anhydrous ethanol do not come into direct contact.

[0045] In an embodiment of the present invention, the purity of both the first anhydrous ethanol and the second anhydrous ethanol is 99.8%.

[0046] In this invention, the process of heating the mixture in the environment of the first anhydrous ethanol is preferably carried out by placing the mixture in a first container, then placing the first container into a second container containing the first anhydrous ethanol, and then placing it in an oven for heating; the volume of the first container is smaller than that of the second container. In this invention, the second container is preferably in a sealed environment.

[0047] In this invention, the volume ratio of the mixture to the first anhydrous ethanol is preferably (1-3):(2-10), more preferably (1-3):5. In an embodiment of this invention, the volume ratio of the mixture to the first anhydrous ethanol can be 2:5.

[0048] In this invention, the heating temperature is preferably 50–90°C, more preferably 60°C; the heating time is preferably 24–72 hours, more preferably 68 hours. In an embodiment of this invention, the heating temperature can be 60°C, and the heating time can be 68 hours.

[0049] In this invention, the above operations are used to achieve the nucleation and partial growth process of the crystal.

[0050] In this invention, the second anhydrous ethanol is preferably added via a peristaltic pump; the rotational speed of the peristaltic pump is preferably 25–100 rpm, more preferably 40–60 rpm. In embodiments of this invention, the rotational speed of the peristaltic pump can be 25 rpm, 50 rpm, or 100 rpm.

[0051] In this invention, the volume ratio of the mixture and the second anhydrous ethanol is preferably (1-2):(1-2), more preferably 1:(1-2). In an embodiment of this invention, the volume ratio of the mixture and the second anhydrous ethanol can be 5:6.

[0052] In this invention, the purpose of adding the second anhydrous ethanol in the manner described above is to achieve secondary nucleation of the crystal and to terminate crystal growth so that it precipitates.

[0053] After the second anhydrous ethanol is added, the present invention preferably includes centrifugation, washing, and drying performed sequentially. In the present invention, the centrifugation speed is preferably 3000–6000 rpm, more preferably 4000 rpm, and the centrifugation time is preferably 5–20 min, more preferably 10 min. In an embodiment of the present invention, the centrifugation speed can be 4000 rpm, and the time can be 10 min. In the present invention, the washing is preferably performed using anhydrous ethanol, and the number of washings is preferably 0–2 times. In an embodiment of the present invention, the washing time can be 0, 1, or 2 times. In the present invention, the drying method is preferably vacuum drying, and the vacuum drying temperature is preferably 30–60°C, more preferably 40°C, and the time is preferably 4–12 h, more preferably 5–10 h. In an embodiment of the present invention, the vacuum drying temperature can be 40°C, and the time can be 8 h. In the present invention, the number of ethanol washings may directly affect crystal growth through the reversible transition layer at the crystal growth interface; with the increase of the number of ethanol washings, the size of the nanoscale cyclodextrin metal-organic framework becomes more uniform.

[0054] In this invention, the preferred particle size of the nanoscale cyclodextrin metal-organic framework is 200–800 nm.

[0055] This invention also provides a method for preparing silver-doped nanoscale cyclodextrin metal-organic frameworks (AgNPs@CD-MOFs), comprising the following steps:

[0056] The silver-doped nanoscale cyclodextrin metal-organic framework was obtained by mixing the nanoscale cyclodextrin metal-organic framework dispersion with silver nitrate solution and culturing it in the dark.

[0057] The nanoscale cyclodextrin metal-organic framework in the nanoscale cyclodextrin metal-organic framework dispersion is the nanoscale cyclodextrin metal-organic framework dispersion prepared by the preparation method described in the above technical solution.

[0058] In this invention, the solvent for the nanoscale cyclodextrin metal-organic framework dispersion is preferably anhydrous ethanol. In this invention, the concentration of the nanoscale cyclodextrin metal-organic framework in the dispersion is preferably 1–20 mg / mL, more preferably 5 mg / mL. In an embodiment of this invention, the concentration of the nanoscale cyclodextrin metal-organic framework in the dispersion can be 5 mg / mL.

[0059] In this invention, the solvent for the silver nitrate solution is preferably ethanol. The concentration of the silver nitrate solution is preferably 0.5–5 mmol / L, more preferably 1 mmol / L. In embodiments of this invention, the concentration of the silver nitrate solution can be 1 mmol / L.

[0060] In this invention, the preferred mass ratio of the nanoscale cyclodextrin metal-organic framework in the nanoscale cyclodextrin metal-organic framework dispersion to the silver nitrate in the silver nitrate solution is (10-50):1, more preferably (20-40):1. In an embodiment of this invention, the mass ratio of the nanoscale cyclodextrin metal-organic framework in the nanoscale cyclodextrin metal-organic framework dispersion to the silver nitrate in the silver nitrate solution can be 30:1.

[0061] In this invention, the culture is preferably carried out under oscillation conditions, with the oscillation frequency preferably being 50–200 rpm, more preferably 120 rpm; and the time preferably being 12–72 h, more preferably 48 h. In an embodiment of this invention, the culture frequency can be 120 rpm and the time can be 48 h.

[0062] In this invention, the cultivation process involves the in-situ reduction of silver ions to generate nano-silver.

[0063] After the culture is completed, the present invention preferably includes centrifugation, washing, and drying performed sequentially. In this invention, the centrifugation speed is preferably 3000–6000 rpm, more preferably 4000 rpm, and the centrifugation time is preferably 5–20 min, more preferably 10 min. In an embodiment of the present invention, the centrifugation speed can be 4000 rpm, and the time can be 10 min. In this invention, the washing is preferably performed using anhydrous ethanol, and the washing is preferably performed twice. In this invention, the drying method is preferably vacuum drying, the vacuum drying temperature is preferably 30–60°C, more preferably 40°C, and the time is preferably 4–12 h, more preferably 5–10 h. In an embodiment of the present invention, the vacuum drying temperature can be 40°C, and the time can be 8 h.

[0064] In this invention, the silver-doped nanoscale cyclodextrin metal-organic framework preferably comprises a nanoscale cyclodextrin metal-organic framework and silver loaded within the nanoscale cyclodextrin metal-organic framework. In this invention, the silver is preferably silver nanosheets. In this invention, the silver loading is preferably 0.05 wt% to 3.01 wt%. In an embodiment of this invention, the silver loading can be 3.01 wt%.

[0065] This invention also provides the application of the silver-doped nanoscale cyclodextrin metal-organic framework prepared by the preparation method described above in food preservation films.

[0066] The present invention also provides a food preservation film, the raw materials of which include silver-doped nanoscale cyclodextrin metal-organic framework, polylactic acid and polyethylene glycol;

[0067] The mass ratio of the silver-doped nanoscale cyclodextrin metal-organic framework, polylactic acid, and polyethylene glycol is (0.2–1.6):8:0.8.

[0068] In this invention, the polyethylene glycol is preferably PEG-4000.

[0069] In this invention, the method for preparing the food preservation film preferably includes the following steps:

[0070] Polylactic acid and an organic solvent are mixed to obtain a homogeneous solution;

[0071] The homogeneous solution, polyethylene glycol, and silver-doped nanoscale cyclodextrin metal-organic framework are mixed and then formed into a film to obtain the food preservation film.

[0072] This invention involves mixing polylactic acid and an organic solvent to obtain a homogeneous solution.

[0073] In this invention, the organic solvent preferably includes dimethyl carbonate.

[0074] In this invention, the preferred ratio of polylactic acid to organic solvent is (6-12) g: 100 mL, more preferably (6-10) g: 100 mL. In an embodiment of this invention, the ratio of polylactic acid to organic solvent can be 8 g: 100 mL.

[0075] In this invention, the mixing is preferably carried out under stirring conditions. The stirring temperature is preferably 60–100°C, more preferably 70°C; the stirring speed is preferably 300–800 rpm, more preferably 500 rpm; and the stirring time is preferably 2–5 hours, more preferably 3 hours. In an embodiment of this invention, the stirring temperature can be 70°C, the stirring time can be 3 hours, and the stirring speed can be 500 rpm.

[0076] After obtaining a homogeneous solution, the present invention mixes the homogeneous solution, polyethylene glycol and silver-doped nanoscale cyclodextrin metal-organic framework, and then forms a film to obtain the food preservation film.

[0077] In this invention, the mixing is preferably performed by sequentially adding molten polyethylene glycol and silver-doped nanoscale cyclodextrin metal-organic framework to the homogeneous solution. After adding the molten polyethylene glycol, the invention further preferably includes stirring, wherein the stirring temperature is preferably 60–100°C, more preferably 70°C, the stirring speed is preferably 300–800 rpm, more preferably 500 rpm, and the stirring time is preferably 2–5 h, more preferably 3 h. In embodiments of this invention, the stirring temperature can be 70°C, the stirring time can be 3 h, and the stirring speed can be 500 rpm. This invention does not impose any special limitations on the method of adding the molten polyethylene glycol and the silver-doped nanoscale cyclodextrin metal-organic framework; any method well known to those skilled in the art can be used.

[0078] The present invention does not impose any special limitations on the film-forming process; any process well known to those skilled in the art can be used.

[0079] The following detailed description, in conjunction with embodiments, illustrates the preparation methods and applications of CD-MOFs and AgNPs@CD-MOFs provided by this invention, as well as food preservation films. However, these descriptions should not be construed as limiting the scope of protection of this invention.

[0080] Example 1

[0081] γ-cyclodextrin and potassium hydroxide were dissolved in ultrapure water and magnetically stirred for 1 hour (300 rpm). The mixture was then filtered through a 0.45 μm organic membrane to obtain a mixture (γ-cyclodextrin concentration of 2.5 mmol / L and potassium hydroxide concentration of 20 mmol / L).

[0082] 10 mL of the mixture was placed in a small bottle and then placed in a large glass bottle containing 25 mL of anhydrous ethanol. After drying at 60 °C for 68 h, 12 mL of anhydrous ethanol was added to the small glass bottle at a rate of 25 rpm using a peristaltic pump. After centrifugation at 4000 rpm for 10 min, the resulting precipitate was washed twice with anhydrous ethanol and then dried under vacuum at 40 °C for 8 h to obtain γ-CD-MOFs (white crystalline powder).

[0083] Example 2

[0084] Referring to Example 1, the difference is that the peristaltic pump rotates at 50 rpm.

[0085] Example 3

[0086] Referring to Example 1, the difference is that the peristaltic pump rotates at 100 rpm.

[0087] Example 4

[0088] Referring to Example 1, the difference is that the concentration of γ-cyclodextrin in the mixture is 5 mmol / L and the concentration of potassium hydroxide is 40 mmol / L.

[0089] Example 5

[0090] Referring to Example 4, the difference is that the peristaltic pump rotates at 50 rpm.

[0091] Example 6

[0092] Referring to Example 4, the difference is that the peristaltic pump rotates at 100 rpm.

[0093] Example 7

[0094] Referring to Example 1, the difference is that the concentration of γ-cyclodextrin in the mixture is 12.5 mmol / L and the concentration of potassium hydroxide is 100 mmol / L.

[0095] Example 8

[0096] Referring to Example 7, the difference is that the peristaltic pump rotates at 50 rpm.

[0097] Example 9

[0098] Referring to Example 7, the difference is that the peristaltic pump rotates at 100 rpm.

[0099] Example 10

[0100] Referring to Example 5, the difference is that the washing was performed 0 times with anhydrous ethanol.

[0101] Example 11

[0102] Referring to Example 5, the difference is that the washing was performed once using anhydrous ethanol.

[0103] Figure 1The images shown are scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and energy-dispersive X-ray spectroscopy (EDS) images of the γ-CD-MOFs described in Examples 1 to 11. Specifically, (a) is a SEM image of the γ-CD-MOFs described in Example 1 at ×200 magnification, (b) is a SEM image of the γ-CD-MOFs described in Example 2 at ×200 magnification, and (c) is a SEM image of the γ-CD-MOFs described in Example 3 at ×200 magnification. (d) is a SEM image of the γ-CD-MOFs described in Example 1 at a magnification of ×10000; (e) is a SEM image of the γ-CD-MOFs described in Example 2 at a magnification of ×10000; (f) is a SEM image of the γ-CD-MOFs described in Example 3 at a magnification of ×10000; (g) is a SEM image of the γ-CD-MOFs described in Example 4 at a magnification of ×10000; and (h) is a SEM image of the γ-CD-MOFs described in Example 5 at a magnification of ×10000. SEM images at a magnification of 10000: (i) is the SEM image of γ-CD-MOFs described in Example 6 at a magnification of 10000; (j) is the SEM image of γ-CD-MOFs described in Example 7 at a magnification of 10000; (k) is the SEM image of γ-CD-MOFs described in Example 8 at a magnification of 10000; (l) is the SEM image of γ-CD-MOFs described in Example 9 at a magnification of 10000; (m) is the SEM image of γ-CD-MOFs described in Example 10 at a magnification of 10000. SEM images of CD-MOFs at a magnification of ×10000, (n) is the SEM image of γ-CD-MOFs described in Example 11 at a magnification of ×10000, (o) is the TEM image of γ-CD-MOFs described in Example 5, (p) is the C element distribution map of γ-CD-MOFs described in Example 5, (q) is the O element distribution map of γ-CD-MOFs described in Example 5, and (r) is the K element distribution map of γ-CD-MOFs described in Example 5; Figure 1 It can be seen that the γ-CD-MOFs prepared by the preparation method described in this invention have a particle size of nanometers and a typical cubic structure. The optimal preparation conditions are that the concentration of γ-cyclodextrin in the mixture is 5 mmol / L, the concentration of potassium hydroxide is 40 mmol / L, the speed of the peristaltic pump is 50 rpm, and the coefficient of ethanol is 2. The particle size of the γ-CD-MOFs prepared under the above optimal preparation conditions is 200-800 nm (as can be seen from (h)).

[0104] Figure 2The images shown are TEM images of the γ-CD-MOFs described in Example 5 and their particle size distribution diagrams. (a) is a TEM image of AgNPs@γ-CD-MOFs prepared with 6 mM AgNO3 dissolved in water, representing silver nanoparticles; (b) is a TEM image of AgNPs@γ-CD-MOFs prepared with 3 mM AgNO3 dissolved in water, representing silver nanoparticles; and (c) is a TEM image of AgNPs@γ-CD-MOFs prepared with 1 mM AgNO3. TEM images of silver nanoparticles after dissolving AgNPs@γ-CD-MOFs in water: (d) shows the lattice spacing of AgNPs@γ-CD-MOFs prepared with 1 mA gNO3 dissolved in water; (e) shows a high-magnification TEM image of AgNPs@γ-CD-MOFs prepared with 1 mA gNO3 dissolved in water; (f) shows the particle size distribution of AgNPs@γ-CD-MOFs prepared with 1 mA gNO3 dissolved in water. Figure 2 It can be seen that reducing the AgNO3 concentration leads to a decrease in the size of the prepared silver nanoparticles.

[0105] Examples 12-22

[0106] 10 mL of ethanol solution containing 1 mmol / L silver nitrate was added to 10 mL of anhydrous ethanol solution containing γ-CD-MOFs described in Examples 1-11 with a concentration of 5 mg / mL. The mixture was cultured in the dark with shaking (frequency 120 rpm) for 48 h. After centrifugation at 4000 rpm for 10 min, the precipitate was washed twice with anhydrous ethanol and dried under vacuum at 40 °C to obtain AgNPs@γ-CD-MOFs (AgNPs@γ-CD-MOFs prepared from γ-CD-MOFs described in Examples 1-11 correspond to Examples 12-22 respectively).

[0107] Figure 3 The images shown are SEM (a), TEM (b), EDS (c), EDS point scan (d), EDS area scan (e), C element distribution (f), O element distribution (g), and Ag element distribution (h) of AgNPs@γ-CD-MOFs described in Example 16. Figure 3 It can be seen that the AgNPs@CD-MOFs maintain a typical cubic morphology, indicating that the in-situ synthesis of silver nanoparticles does not destroy the basic structure of γ-CD-MOFs. In addition, apart from a small amount of silver nanoparticles aggregated on the surface, the remaining small silver nanoparticles are uniformly distributed in the γ-CD-MOFs framework.

[0108] The specific surface area and pore size distribution of the γ-CD-MOFs described in Example 1 and the AgNPs@γ-CD-MOFs described in Example 16 were determined using an N2 adsorption-desorption method with a Micromeritics ASAP 2460 instrument (USA). Figure 4 The N2 adsorption-desorption curves (a) and pore size distribution curves (b) of the γ-CD-MOFs described in Example 1 and the AgNPs@γ-CD-MOFs described in Example 16 are obtained from... Figure 4 It is evident that the reduced size of γ-CD-MOFs leads to a higher BET specific surface area, which further enhances the loading capacity. Furthermore, due to the effective pore filling by AgNPs, the BET specific surface area of ​​AgNPs@γ-CD-MOF is significantly reduced compared to γ-CD-MOFs.

[0109] The silver content of the AgNPs@γ-CD-MOFs described in Example 16 and the release of silver nanosheets by the AgNPs@γ-CD-MOFs in pure water were determined by inductively coupled plasma mass spectrometry (ICP-MS, Aglient 7850, USA). The loading of silver nanosheets in the AgNPs@γ-CD-MOFs described in Example 16 was 3.008% (3.01 ± 0.06%, which is 3.86 times higher than previously reported). The test results are shown in Table 1.

[0110] Table 1 shows the release of silver nanosheets from AgNPs@γ-CD-MOFs in pure water as described in Example 16.

[0111] time Percentage of silver released in pure water (%) 3D 1.59±0.04 6D 2.12±1.10 10D 2.57±0.10

[0112] As shown in Table 1, the silver nanosheets released 2.57% after 10 days, which is lower than the release rate of existing technologies.

[0113] Example 23

[0114] 8g of polylactic acid (PLA) was added to 100mL of dimethyl carbonate (DMC) and stirred at 70℃ for 3h to obtain a homogeneous solution. Then, 0.8g of molten polyethylene glycol (PEG-4000) was added and stirred at 70℃ for 2h. Finally, 0.2g of AgNPs@CD-MOFs described in Example 16 was added and mixed evenly. The resulting slurry was then deposited on the surface of a glass plate to form a food preservation film (denoted as F2 film).

[0115] Example 24

[0116] 8g of polylactic acid (PLA) was added to 100mL of dimethyl carbonate (DMC) and stirred at 70°C for 3 hours to obtain a homogeneous solution. Then, 0.8g of molten polyethylene glycol (PEG-4000) was added and stirred at 70°C for 2 hours. Finally, 0.4g of AgNPs@CD-MOFs described in Example 16 was added and mixed evenly. The resulting slurry was then deposited on the surface of a glass plate to form a food preservation film (denoted as F4 film).

[0117] Example 25

[0118] 8g of polylactic acid (PLA) was added to 100mL of dimethyl carbonate (DMC) and stirred at 70°C for 3 hours to obtain a homogeneous solution. Then, 0.8g of molten polyethylene glycol (PEG-4000) was added and stirred at 70°C for 2 hours. Finally, 0.8g of AgNPs@CD-MOFs described in Example 16 was added and mixed evenly. The resulting slurry was then deposited on the surface of a glass plate to form a food preservation film (denoted as F8 film).

[0119] Example 26

[0120] 8g of polylactic acid (PLA) was added to 100mL of dimethyl carbonate (DMC) and stirred at 70℃ for 3h to obtain a homogeneous solution. Then, 0.8g of molten polyethylene glycol (PEG-4000) was added and stirred at 70℃ for 2h. Finally, 1.6g of AgNPs@CD-MOFs described in Example 16 was added and mixed evenly. The resulting slurry was then deposited on the surface of a glass plate to form a food preservation film (denoted as F16 film).

[0121] Comparative Example 1

[0122] Referring to Example 23, the difference is that the addition of AgNPs@CD-MOFs is omitted, resulting in a food preservation film (denoted as PLA film).

[0123] Comparative Example 2

[0124] Referring to Comparative Example 1, the difference is that PLA is replaced with PE, resulting in food preservation film (denoted as PE film).

[0125] Test case

[0126] The antibacterial activity of AgNPs@γ-CD-MOFs described in Example 16 was determined: Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, and Pseudomonas aeruginosa were used to evaluate the antibacterial activity of AgNPs@γ-CD-MOFs described in Example 16; the minimum inhibitory concentration (MIC) was tested using the broth microdilution method recommended by the Clinical and Laboratory Standards Institute (CLSI) standard M07; the minimum bactericidal concentration (MBC) was tested by inoculating 100 μL of bacterial suspension with a concentration of AgNPs@γ-CD-MOFs described in Example 16 higher than the MIC into agar medium, and after culturing for 24 h, the concentration of samples with fewer than 50 colonies was taken as the minimum bactericidal concentration;

[0127] The cytotoxicity of the AgNPs@γ-CD-MOFs described in Example 16 was determined using undifferentiated human colon cancer cells (HT-29).

[0128] Cell viability testing method: CCK-8;

[0129] Test results are as follows Figure 5 As shown in Table 2, where Figure 5 The antibacterial activity (a) and cell viability (b) of AgNPs@γ-CD-MOFs described in Example 16 were obtained from... Figure 5 As shown in (a), the AgNPs@γ-CD-MOFs described in Example 16 exhibited antibacterial activity against five bacteria: Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, and Pseudomonas aeruginosa, with significantly enhanced antibacterial activity against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa; Figure 5 As can be seen from (b), when the concentration of AgNPs@γ-CD-MOFs described in Example 16 is below 400 μg / mL, the cell viability is above 70% and there is no cytotoxicity.

[0130] Table 2 shows the antibacterial activity of AgNPs@γ-CD-MOFs described in Example 16. As can be seen from Table 2, AgNPs@γ-CD-MOFs exhibited antibacterial activity against all five selected bacteria. Compared with existing reports, AgNPs@γ-CD-MOFs reduced the MIC and MBC values ​​(based on actual silver content) of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, demonstrating better antibacterial activity.

[0131] Table 2. Antibacterial activity of AgNPs@γ-CD-MOFs described in Example 16

[0132]

[0133]

[0134] The visible and ultraviolet transmittance of the food preservation films described in Examples 23-26 was measured using a UV-Vis spectrophotometer (scanning wavelength 200-800nm, resolution 120nm); the oxygen transmittance of the films was measured using an air permeability tester (BTY-B2P, China Languang) (temperature 23±2℃, humidity 49±1%RH); and the water vapor transmittance of the food preservation films was measured using a fabric moisture permeability meter (YG461E, China).

[0135] Figure 6 The visible light and ultraviolet light transmittance (a), water vapor transmittance (b), and oxygen transmittance (c) of the food preservation films described in Examples 23-26 and Comparative Example 1 are obtained from... Figure 6 It can be seen that the addition of AgNPs@γ-CD-MOFs improves the UV blocking and oxygen blocking capabilities of food preservation films. Except for Example 25, the addition of AgNPs@γ-CD-MOFs does not significantly change the water vapor blocking capability.

[0136] Antibacterial properties of food preservation film: 0.5g of the food preservation film described in Example 25 and Comparative Example 1 were mixed with 15mL of physiological saline and sterilized at 121℃ for 20min. After cooling, 0.5mL of bacterial suspension (106CFU / mL) was added, and the mixture was shaken thoroughly on a TY-70B shaker (Tianjin Tester Instrument Co., Ltd.) for 1 hour (220rpm, 37℃) to ensure full contact between the composite film and bacteria. Finally, 0.1mL of the supernatant was spread on nutrient agar medium and incubated at 37℃ for 24h. The total number of bacterial colonies was tested, and the antibacterial rate was calculated. Antibacterial rate = (N0-N) / N×100%, where N0 is the total number of cell colonies in the blank group (without food preservation film as the blank group), and N is the total number of bacterial colonies in the experimental group. Figure 7 The bar graphs show the antibacterial rates of the food preservation films described in Example 25 and Comparative Example 1 against different types of bacteria. Figure 7 It can be seen that the addition of AgNPs@γ-CD-MOFs significantly improved the antibacterial properties of the film against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Pseudomonas tora.

[0137] Fresh button mushrooms were pre-cooled for 24 hours in a constant temperature and humidity chamber at 4°C and 60% relative humidity. Then, button mushrooms with good appearance and uniform size were selected for subsequent storage and preservation. The mushrooms were randomly divided into six groups of six pieces each. The mushrooms were then placed in disposable plastic boxes (polypropylene, 200×140×65mm) and sealed with the food preservation films described in Examples 23-26 and Comparative Examples 1-2, with the food preservation films described in Comparative Examples 1-2 serving as a control group. Finally, the packaged button mushrooms were stored and preserved in a constant temperature and humidity chamber (4°C, 90% RH). Figure 8 This image shows the preservation effect of button mushrooms. Figure 8 It can be seen that, compared with the food preservation films described in Comparative Examples 1-2, the food preservation films described in Examples 23-26 delayed the problem of post-harvest quality deterioration of Agaricus bisporus, and the food preservation film described in Example 25 had the best preservation effect.

[0138] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing nanoscale cyclodextrin metal-organic frameworks, characterized in that, Includes the following steps: Cyclodextrin, potassium hydroxide, and water are mixed to obtain a mixture; the concentration of cyclodextrin in the mixture is 2.5–12.5 mmol / L; the concentration of potassium hydroxide in the mixture is 20–100 mmol / L. The mixture was heated in an environment of first anhydrous ethanol, and then second anhydrous ethanol was added to the mixture to obtain the nanoscale cyclodextrin metal-organic framework; the second anhydrous ethanol was added by a peristaltic pump; the rotation speed of the peristaltic pump was 25-100 rpm; The mixture and the first anhydrous ethanol do not come into direct contact.

2. The preparation method according to claim 1, characterized in that, The molar ratio of cyclodextrin to potassium hydroxide is 1:

8.

3. The preparation method according to claim 2, characterized in that, The mixing is carried out under stirring conditions; The stirring speed is 100-400 rpm, and the stirring time is 30-120 min.

4. The preparation method according to claim 1, characterized in that, The mixing process also includes filtration; The filtration uses a 0.45μm organic membrane.

5. The preparation method according to claim 1, characterized in that, The heating temperature is 50–90°C, and the heating time is 24–72 hours.

6. A method for preparing a silver-doped nanoscale cyclodextrin metal-organic framework, characterized in that, Includes the following steps: The silver-doped nanoscale cyclodextrin metal-organic framework was obtained by mixing the nanoscale cyclodextrin metal-organic framework dispersion with silver nitrate solution and culturing it in the dark. The nanoscale cyclodextrin metal-organic framework in the nanoscale cyclodextrin metal-organic framework dispersion is the nanoscale cyclodextrin metal-organic framework dispersion prepared by the preparation method according to any one of claims 1 to 5.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the nanoscale cyclodextrin metal-organic framework in the nanoscale cyclodextrin metal-organic framework dispersion to the silver nitrate in the silver nitrate solution is (10-50):

1.

8. The preparation method according to claim 6, characterized in that, The culture was carried out under oscillation conditions, with an oscillation frequency of 50–200 rpm and a duration of 12–72 h.

9. The application of the silver-doped nanoscale cyclodextrin metal-organic framework prepared by the preparation method according to any one of claims 6 to 8 in food preservation films.

10. A food preservation film, characterized in that, The raw materials for preparation include silver-doped nanoscale cyclodextrin metal-organic frameworks, polylactic acid, and polyethylene glycol; The mass ratio of the silver-doped nanoscale cyclodextrin metal-organic framework, polylactic acid, and polyethylene glycol is (0.2–1.6):8:0.8.

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