A Bimetallic Organic Framework Material, Its Preparation Method and Application

Abstract

The present invention discloses a bimetallic organic framework material, its preparation method and application. The crystal structure of the framework material is octahedron, which is formed by the coordination of the organic ligand fumaric acid and the metal ion ligand. The metal ion ligand is zirconium ion and copper ion. Among them, the doping amount of copper ion, calculated by molar ratio, accounts for 20% - 40% of the metal ligand content. The bimetallic organic framework material of the present invention has a water vapor adsorption rate 10 - 20% higher than that without doping Cu<supgt;2+< / supgt> at each humidity gradient, and at the same time has strong thermal stability and recycling performance. After the material undergoes four cycles of high-temperature activation and water vapor absorption, it still maintains a high water absorption efficiency of 0.27 g·g<supgt;‑1< / supgt>, and only decreases by 0.5% compared with the first time. The above framework material is applied in the preparation of a water-absorbing fresh-keeping packaging film, which can regulate the humidity of the microenvironment of fruit and vegetable packaging and inhibit the growth of microorganisms, thereby increasing the shelf life of fruits and vegetables after harvest.

Description

Technical Field

[0001] The present invention relates to an organic framework material, in particular to a bimetallic organic framework material, and also relates to the preparation method and application of the above framework material. Background Art

[0002] Fresh fruits and vegetables have become an indispensable part of people's daily life because they are rich in nutrients such as vitamins, dietary fiber, and minerals. However, after being picked, fruits and vegetables still undergo dynamic physiological processes of respiration and transpiration, which will produce a large amount of liquid water, increasing the relative humidity (RH) of the packaging microenvironment. Currently, plastic films are commonly used for fruit and vegetable packaging, but it is easy to cause water vapor condensation, increasing the humidity inside the packaging. A high-humidity microenvironment is more likely to breed microorganisms, thereby accelerating the spoilage of fruits and vegetables, causing food waste and economic losses. To address the humidity problem in fruit and vegetable packaging, desiccants are mostly used to adsorb water vapor in the packaging microenvironment. A desiccant is a material with high porosity and large pore size, showing a large water vapor absorption capacity. However, this porous material usually can only carry out the adsorption function at high relative humidity, that is, when the humidity is close to saturation, and it has poor thermal stability. Most are disposable products, which are easy to cause waste of resources and increase the cost of fruit preservation.

[0003] Metal-organic frameworks (MOFs), also known as porous coordination polymers (PCPs), are a class of porous crystalline materials with two-dimensional or three-dimensional structures composed of inorganic nodes (metal ions / clusters) and organic ligands through self-assembly. Compared with other MOF materials, MOF-801 prepared based on the interaction between zirconium clusters and fumaric acid ligands in the framework can bind a large amount of water with -COOH on its surface, and its internal porous structure is also conducive to the adsorption of water molecules. However, the water vapor absorption rate of MOF-801 is insufficient in a low-humidity microenvironment, which limits its application as a fresh fruit packaging film. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a bimetallic organic framework material with good water vapor absorption rate in a low-humidity microenvironment, the second object is to provide the preparation method of the above framework material, and the third object is to provide the application of the above framework material.

[0005] Technical Solution: The bimetallic organic framework material described in the present invention has an octahedral crystal structure, which is formed by the coordination of organic ligand fumaric acid and metal ion ligand. The metal ion ligand is zirconium ion and copper ion; in the metal ion ligand, calculated by molar ratio, the added molar amount of copper ion is 20-40% of the total molar amount of the metal ion ligand.

[0006] Preferably, in the bimetallic organic framework material, the molar ratio of the organic ligand fumaric acid to the metal ion ligand is 1:1.

[0007] The preparation method of the above bimetallic organic framework material includes the following steps:

[0008] (1) Dissolve fumaric acid, zirconium oxychloride octahydrate and copper nitrate trihydrate in the formic acid solution of N,N-dimethylformamide, and ultrasonically dissolve to obtain a mixed solution;

[0009] (2) Heat and pressurize the mixed solution for reaction, and after the reaction is completed, cool to room temperature to obtain a solid material;

[0010] (3) Centrifuge, wash and vacuum dry the solid material to obtain the bimetallic organic framework material.

[0011] Preferably, in step (1), the molar ratio of fumaric acid, zirconium oxychloride octahydrate and copper nitrate trihydrate is 1:0.5-1:0.1-0.5; in the formic acid solution of N,N-dimethylformamide, the volume ratio of N,N-dimethylformamide to formic acid is 15-20:5-7.

[0012] Preferably, in step (2), for the heat and pressure reaction, the reaction temperature is 125°C - 135°C, the reaction time is 6 - 7 h, and the pressure is -0.1 MPa.

[0013] Preferably, in step (3), for the centrifugation, the rotation speed is 9500 rpm / min, the centrifugation time is 10 min, and the centrifugation temperature is 10°C - 20°C; for the vacuum drying, the temperature is 45°C - 60°C, the time is 8 - 10 h, and the drying pressure is -0.09 - -0.1 MPa.

[0014] The application of the above bimetallic organic framework material in the preparation of a water-absorbing and fresh-keeping packaging film.

[0015] Preferably, for the water-absorbing and fresh-keeping packaging film, mix the bimetallic organic framework material, a plasticizer, a film-forming agent and sodium carboxymethylcellulose, pour it into a mold, and dry it to obtain.

[0016] Preferably, the mass ratio of the bimetallic organic framework material, the plasticizer glycerol, the film-forming agent gelatin and sodium carboxymethylcellulose is 0.1 - 0.2:0.5 - 1:2:2.

[0017] Preferably, the plasticizer is glycerol and the film-forming agent is gelatin.

[0018] Preferably, the specific preparation method of the water-absorbing and fresh-keeping packaging film is as follows:

[0019] (1) Prepare a gelatin static solution. Dissolve the bimetallic organic framework material in the gelatin static solution and perform ultrasonic treatment to obtain a mixed solution A. Dissolve sodium carboxymethylcellulose in water and perform water bath stirring to obtain a mixed solution B. Mix the mixed solution A and the mixed solution B, add glycerol, and heat and stir to obtain a film-forming solution.

[0020] (2) Pour the film-forming solution into a mold, then let it stand at room temperature, and place it in an oven to dry to obtain a water-absorbing fresh-keeping packaging film.

[0021] Principle of the invention: The bimetallic organic framework material Cu@MOF-801 of the present invention improves the water vapor adsorption efficiency in a low-humidity microenvironment by doping the transition metal Cu into the metal-organic framework material MOF-801. The transition metal (Cu) changes the crystal structure of MOF-801, resulting in a change in its internal voids, increasing the adsorption of water vapor. In addition, the bimetallic active sites are also more conducive to water vapor adsorption. The copper ions doped into MOF-801 can transfer the valence electrons beneficial to water molecule adsorption to the metal cluster, increasing the water absorption rate of MOF-801 under low-humidity conditions. The electronegativities of copper and zirconium are 1.9 and 1.33 respectively. The higher the electronegativity value, the stronger the ability of the metal to attract bonding electrons. Therefore, the Cu-OH bond combines with the Zr-OH bond, which can show more polarity, thus reflecting a higher water absorption rate.

[0022] Therefore, the packaging film prepared with Cu@MOF-801 as the water absorbent is expected to reduce the relative humidity in the microenvironment of fruit and vegetable packaging, inhibit the growth of foodborne microorganisms such as molds, achieve the effect of delaying the spoilage of fruits and vegetables, and at the same time has development potential in water-absorbing products such as desiccants and 3D foams.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) The bimetallic organic framework material of the present invention has a water vapor adsorption rate 10-20% higher than that without doping Cu at each humidity gradient, and at the same time has strong thermal stability and recycling performance. After the material undergoes four cycles of high-temperature activation and water vapor absorption, it still maintains an efficient water absorption efficiency of about 0.27 g·g, with only a 0.5% decrease compared with the first time; (2) The packaging material prepared from the bimetallic organic framework material can regulate the humidity of the microenvironment of fruit and vegetable packaging and inhibit the growth of microorganisms, thereby increasing the post-harvest shelf life of fruits and vegetables. 2+ is 10-20% higher, and at the same time has strong thermal stability and recycling performance. After the material undergoes four cycles of high-temperature activation and water vapor absorption, it still maintains an efficient water absorption efficiency of about 0.27 g·g -1 ; (2) The packaging material prepared from the bimetallic organic framework material can regulate the humidity of the microenvironment of fruit and vegetable packaging and inhibit the growth of microorganisms, thereby increasing the post-harvest shelf life of fruits and vegetables. Description of the drawings

[0024] Figure 1 is a morphological change diagram of strawberries stored under different humidity conditions;

[0025] Figure 2 is a total surface colony count diagram of strawberries under different humidity conditions;

[0026] Figure 3 are the microscopic morphology diagrams of Cu@MOF-801 and MOF-801 with different ratios;

[0027] Figure 4 are the water vapor adsorption diagrams of Cu@MOF-801 and other metal-doped MOF-801 with different ratios;

[0028] Figure 5 are the water vapor adsorption cycle diagrams of Cu@MOF-801 and MOF-801 with different ratios;

[0029] Figure 6 is the transparency diagram of the CuMGCF package;

[0030] Figure 7 is the strawberry fresh-keeping effect diagram of the CuMGCF package. Specific embodiments

[0031] The technical solutions of the present invention will be further described below in conjunction with the drawings and embodiments.

[0032] Example 1

[0033] Cu 1 / 4 @MOF-801 material preparation:

[0034] (1) Weigh 5 mmol of fumaric acid, 3.75 mmol of zirconium oxychloride octahydrate and 1.25 mmol of copper nitrate trihydrate and dissolve them in a mixed solution of 20 mL of DMF and 7 mL of methanol. Among them, the doping amount of copper ions, calculated by molar ratio, accounts for 25% of the metal ligand content.

[0035] (2) Transfer the above mixed solution to a high-pressure reaction kettle, place it in an oven (130 °C, 6 h), and cool it at room temperature after the reaction is completed. Then wash it four times by centrifugation with DMF and methanol.

[0036] (3) Put the washed precipitate into a vacuum drying oven and dry it (50 °C, 8 h). Turn on the vacuum pump to pump vacuum until the pressure reaches -0.1 MPa, and thus obtain the bimetallic organic framework material Cu 1 / 4 @MOF-801 of the present invention.

[0037] Example 2

[0038] Cu 1 / 5 @MOF-801 material preparation:

[0039] Compared with Example 1, the preparation method of the framework material in Example 2 changes the added molar amount of copper ions to 20% of the total molar amount of metal ion ligands:

[0040] (1) Weigh 5 mmol of fumaric acid, 4 mmol of zirconium oxychloride octahydrate, and 1 mmol of copper nitrate trihydrate, and dissolve them in a mixed solution of 20 mL of DMF and 7 mL of methanol.

[0041] (2) Transfer the above mixed solution to a high-pressure reaction kettle, place it in an oven (130 °C, 6 h), cool it to room temperature after the reaction is completed. Then, centrifuge and wash it four times with DMF and methanol.

[0042] (3) Place the washed precipitate in a vacuum drying oven for drying (50 °C, 8 h), turn on the vacuum pump to evacuate and dry until the pressure reaches -0.1 MPa, and thus obtain the bimetallic organic framework material Cu 1 / 5 @MOF-801 of the present invention.

[0043] Example 3

[0044] Cu 1 / 3 Preparation of Cu

[0045] Compared with Example 1, the preparation method of the framework material in Example 3 changes the molar amount of copper ions added to 33.3% of the total molar amount of metal ion ligands:

[0046] (1) Weigh 5 mmol of fumaric acid, 3.3 mmol of zirconium oxychloride octahydrate, and 1.7 mmol of copper nitrate trihydrate, and dissolve them in a mixed solution of 20 mL of DMF and 7 mL of methanol.

[0047] (2) Transfer the above mixed solution to a high-pressure reaction kettle, place it in an oven (130 °C, 6 h), cool it to room temperature after the reaction is completed. Then, centrifuge and wash it four times with DMF and methanol.

[0048] (3) Place the washed precipitate in a vacuum drying oven for drying (50 °C, 8 h), turn on the vacuum pump to evacuate and dry until the pressure reaches -0.1 MPa, and thus obtain the bimetallic organic framework material Cu 1 / 3 @MOF-801 of the present invention.

[0049] As Figure 3 shown, the microscopic morphology diagrams of different ratios of Cu@MOF-801-1 and MOF-801 are presented. It can be seen from the SEM images that MOF-801 shows an irregular morphology. However, with the incorporation of the transition metal Cu 2+ , the morphology of the bimetallic MOF gradually presents a regular octahedral crystal structure, and the particle size distribution is relatively uniform. The change in the crystal form of the material will affect its pore distribution, which may be the factor for improving its water absorption efficiency.

[0050] Comparative Example 1

[0051] Compared with Example 1, the preparation method of the framework material in Comparative Example 1 does not contain metal Cu2+ Doping

[0052] (1) Weigh 5 mmol of fumaric acid and 5 mmol of zirconium oxychloride octahydrate, and dissolve them in a mixed solution of 20 mL of DMF and 7 mL of methanol.

[0053] (2) Transfer the above mixed solution to a high-pressure reaction kettle, place it in an oven (130 °C, 6 h), cool it to room temperature after the reaction is completed. Then wash it four times by centrifugation with DMF and methanol.

[0054] (3) Place the washed precipitate in a vacuum drying oven and dry it (50 °C, 8 h). Turn on the vacuum pump to pump vacuum until the pressure reaches -0.1 MPa, and the bimetallic organic framework material MOF-801 of the present invention is obtained.

[0055] Comparative Example 2

[0056] Compared with Example 1, the preparation method of the framework material in Comparative Example 2 changes the added molar amount of copper ions to 50% of the total molar amount of metal ion ligands.

[0057] (1) Weigh 5 mmol of fumaric acid, 2.5 mmol of zirconium oxychloride octahydrate and 2.5 mmol of copper nitrate trihydrate, and dissolve them in a mixed solution of 20 mL of DMF and 7 mL of methanol.

[0058] (2) Transfer the above mixed solution to a high-pressure reaction kettle, place it in an oven (130 °C, 6 h), cool it to room temperature after the reaction is completed. Then wash it four times by centrifugation with DMF and methanol.

[0059] (3) Place the washed precipitate in a vacuum drying oven and dry it (50 °C, 8 h). Turn on the vacuum pump to pump vacuum until the pressure reaches -0.1 MPa, and the bimetallic organic framework material Cu 1 / 2 @MOF-801 is obtained.

[0060] Comparative Example 3

[0061] Compared with Example 1, the preparation method of the framework material in Comparative Example 3 changes the doping of copper ions to the doping of cobalt ions.

[0062] (1) Weigh 5 mmol of fumaric acid, 3.75 mmol of zirconium oxychloride octahydrate and 1.25 mmol of cobalt nitrate hexahydrate, and dissolve them in a mixed solution of 20 mL of DMF and 7 mL of methanol.

[0063] (2) Transfer the above mixed solution to a high-pressure reaction kettle, place it in an oven (130 °C, 6 h), cool it to room temperature after the reaction is completed. Then wash it four times by centrifugation with DMF and methanol.

[0064] (3) Place the precipitate after washing in a vacuum drying oven for drying (50 °C, 8 h). Turn on the vacuum pump to pump vacuum for drying until the pressure reaches -0.1 MPa, and the bimetallic organic framework material Co 1 / 4 @MOF-801 of the present invention is obtained.

[0065] Comparative Example 4

[0066] Compared with Example 1, in the preparation method of the framework material in Comparative Example 4, the doping of copper ions was changed to the doping of nickel ions.

[0067] (1) Weigh 5 mmol of fumaric acid, 3.75 mmol of zirconium oxychloride octahydrate and 1.25 mmol of copper nitrate trihydrate and dissolve them in a mixed solution of 20 mL of DMF and 7 mL of methanol.

[0068] (2) Transfer the above mixed solution to a high-pressure reaction kettle, place it in an oven (130 °C, 6 h), and cool it to room temperature after the reaction is completed. Then, centrifuge and wash it four times with DMF and methanol.

[0069] (3) Place the precipitate after washing in a vacuum drying oven for drying (50 °C, 8 h). Turn on the vacuum pump to pump vacuum for drying until the pressure reaches -0.1 MPa, and the bimetallic organic framework material Ni 1 / 4 @MOF-801 of the present invention is obtained.

[0070] Preparation of GCF composite film:

[0071] (1) Weigh 2 g of gelatin Gel and dissolve it in 30 mL of distilled water (2%, w / v). Let it stand at room temperature for 30 min to fully absorb water. Then, stir it in a water bath at 60 °C for 30 min to obtain a uniform suspension. At the same time, dissolve 2 g of CMC-Na (2%, w / v) in 70 mL of distilled water, and further stir it in a water bath at 60 °C for 1 h. Mix the two prepared solutions, and add 0.5 mL of glycerol as a plasticizer to the mixed solution, and heat and stir it at 60 °C for 1 h.

[0072] (2) Pour 100 mL of the film-forming solution into an acrylic mold (20×20 cm 2 ), and then let it stand at room temperature for 20 min. Place it in an oven for drying (temperature 37 °C, time 12 h), and name the prepared package GCF composite film.

[0073] Preparation of CuMGCF water-absorbing fresh-keeping packaging film:

[0074] (1) Weigh 2 g of gelatin Gel and dissolve it in 30 mL of distilled water (2%, w / v). Let it stand at room temperature for 30 min to fully absorb water. Take 0.1 g of the Cu@MOF-801 prepared in Example 1 and dissolve it in 30 mL of the Gel standing solution, and then ultrasonically treat it for 5 min. At the same time, dissolve 2 g of CMC-Na (2%, w / v) in 70 mL of distilled water, and further stir it in a water bath at 60 °C for 1 h. Mix the two prepared solutions, and add 0.5 mL of glycerol as a plasticizer to the mixed solution, and heat and stir it at 60 °C for 1 h.

[0075] (2) Pour 100 mL of the film-forming solution into an acrylic mold (20×20 cm 2 ), and then let it stand at room temperature for 20 min. Place it in an oven to dry (temperature 37 °C, time 12 h) to obtain the CuMGCF water-absorbing fresh-keeping packaging film.

[0076] In order to study the fresh-keeping effect of the packaging film of Cu@MOF-801 on fruits and vegetables, in addition, a gelatin / carboxymethyl cellulose sodium packaging (Gel / CMC-Na film, abbreviated as GCF) without adding materials was set as a positive control packaging, and a common commercial plastic packaging (PE film, abbreviated as PEF) was set as a negative control packaging.

[0077] Regarding the water absorption performance research of different ratios of Cu@MOF-801 and other metal-doped MOF-801 in the above examples and comparative examples:

[0078] (1) Vacuum activate the samples in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4 at 120 °C for 3 h, and then place them in a vacuum desiccator to cool to room temperature.

[0079] (2) Weigh the weight of the aluminum box weighing dish and record it as M1. Weigh 0.1 g of the activated sample and place it in the weighing aluminum box, and record its total weight as M2, and place it in a constant temperature and humidity chamber (temperature 25 °C, relative humidity 50%). Take out the aluminum box and weigh it at intervals. When the aluminum box weighs constantly, it means that the water vapor adsorption of the material has reached saturation, and record the weight as M3.

[0080] The formula for the water absorption per gram of the material:

[0081]

[0082] where the unit of Y is g·g -1 .

[0083] Such as Figure 4As shown, it is the water vapor adsorption diagram of Cu@MOF-801 with different ratios and other metal-doped MOF-801. The water absorption per gram of Cu@MOF-801 with different doping amounts is higher than that of MOF-801 when the relative humidity is 50%. Among them, Cu 1 / 4 @MOF-801 has a water absorption of 0.38 g·g -1 , which is 28.4% higher than that of the original MOF. Compared with Ni and Co-doped MOF-801, its water absorption per gram decreases significantly, and the lowest water absorption is only 0.11 g·g -1 . It shows that the water absorption of MOF-801 doped with transition metal Cu is improved, and it has good water vapor adsorption, and is expected to be used to develop packaging films for regulating the storage humidity of fruits and vegetables.

[0084] Study on the water vapor adsorption cycle of Cu@MOF-801

[0085] (1) Vacuum activate the samples in Examples 1 and 2 and Comparative Examples 1 and 2 at 120 °C to remove the adsorbed water vapor in the materials. The specific operation is as follows: put the materials in an oven at 120 °C and dry for 3 h, then transfer them to a vacuum desiccator and cool them under vacuum.

[0086] (2) Weigh the weight of the aluminum box weighing dish and record it as M1; weigh 0.1 g of the activated sample and place it in the weighing aluminum box, and record its total weight as My. Put the weighed sample into a constant temperature and humidity chamber (relative humidity 50%, 18 °C). After the aluminum box reaches a constant weight, take it out and weigh it and record it as Mn. Then repeat the process of step 1 to activate the sample, and put it into the constant temperature and humidity chamber again, repeating four cycles. The formula for the water absorption per gram of the material:

[0087]

[0088] where the unit of Y is g·g -1 .

[0089] As Figure 5 shown, it is the water vapor adsorption cycle diagram of Cu@MOF-801 with different doping amounts. After five cycles of high-temperature activation and water vapor absorption of Cu@MOF-801, it still has good water absorption performance. Among them, Cu 1 / 4 @MOF-801 maintains a high water absorption efficiency of 0.32 g·g -1 , and only decreases by 3.2% compared with the first time. For the original MOF-801 after cycling, its performance decreases by 16.6%. It shows that the thermal stability and cyclic use performance of the Cu-doped material are enhanced, and it has excellent economic cyclic use value.

[0090] Study on the morphological changes of strawberries and the total number of surface colonies under different humidity conditions: Simulating the influence of different humidities on the packaging microenvironment of fruits and vegetables and the fresh-keeping effect of the prepared CuMGCF packaging on post-harvest fruits and vegetables, strawberries were selected as the experimental objects.

[0091] (1) Pretreatment of strawberries: Fresh strawberries were purchased from the market and transported to the laboratory at low temperature within 1 h. Samples with consistent size, appearance, maturity, no mechanical damage, and no pests and diseases were quickly selected. 25 strawberries were taken from the selected samples and placed in a constant temperature and humidity chamber (temperature 25 °C) with relative humidities of 45% and 90% respectively. Three strawberries were randomly taken on the 0th, 1st, 3rd, 5th, and 7th days and photographed for record. As Figure 1 shown are the morphological changes of strawberries stored under different humidity conditions.

[0092] (2) 25 g of the pulp 0.5 cm under the skin of strawberries stored under 45% and 90% relative humidity conditions were randomly taken, and the sampling times were 0, 2, and 4 days. 225 mL of sterile water was added to the 25 g pulp sample for homogenization and dilution. 1 mL of the 1:10 sample homogenate was pipetted with a 1 mL sterile pipette and injected into a centrifuge tube containing 9 mL of sterile water. The above experimental operations were repeated twice, resulting in a dilution factor of 1000 times.

[0093] (3) 100 μL of the homogenates with different dilution gradients was added to the PDA medium for dilution coating. The coated medium was placed in a biochemical incubator at 22 ± 1 °C and incubated upside down for three days to observe the number of colonies; as Figure 2 shown are the total numbers of surface colonies of strawberries under different humidity conditions.

[0094] As Figure 1 and Figure 2 shown, the strawberries stored under high humidity began to rot and mold appeared on the surface on the 3rd day, while there was no obvious mold on the surface of the strawberries stored under low humidity on the 7th day. Therefore, developing a packaging film that can regulate the humidity in the microenvironment has market application potential in the field of fruit and vegetable anti-corrosion and fresh-keeping.

[0095] Sample selection was carried out according to the operation in step (1) of Example 1. The PEF, GCF, and CuMGCF packaging bags sterilized by ultraviolet light were used for packaging. 3 strawberries were packaged in each bag. After sealing, they were stored in a constant temperature and humidity chamber, and samples were taken regularly for determination of quality indicators. Specifically, the storage environment of strawberries was: temperature 15 ± 1 °C, relative humidity 50 ± 5%, and storage for 7 days. Except on the 1st day, samples were taken every 2 days for photographing and recording.

[0096] As Figure 7As shown, strawberries in the PEF packaging control group started to deteriorate on the second day, and strawberry juice had overflowed by the third day; strawberries in the GCF packaging control group were inedible and the fruit peels began to rot at 3 days, and colonies began to appear on the strawberry surface when stored until the seventh day. However, only a small part of the fruit peels of strawberries packaged with CuMGCF began to rot until the seventh day. From the above packaging experiment results, it can be seen that CuMGCF can regulate the humidity of the packaging microenvironment, inhibit the growth of microorganisms, and thus increase the post-harvest shelf life of strawberries.

[0097] Study on the transparency of the CuMGCF water-absorbing fresh-keeping packaging film:

[0098] During the sale process of fruits and vegetables, the transparency of the packaging film will directly affect consumers' intuitive impression and acceptance of the product. Therefore, it was compared with the packaging of PEF and GCF films. From Figure 6 and Figure 7 it can be seen that when the three films were covered on the surface of the picture to observe the clarity of the picture, compared with the GCF and PEF packaging films, the packaging film after adding the material still had good transparency.

Claims

1. Application of a bimetallic organic framework material in preparing a water-absorbing and fresh-keeping packaging film, characterized in that, The crystal structure of the framework material is an octahedron, which is formed by the coordination of the organic ligand fumaric acid and the metal ion ligand. The metal ion ligand is zirconium ion and copper ion. Among them, the doping amount of copper ion, calculated by molar ratio, accounts for 20% - 40% of the metal ligand content.

2. The application according to claim 1, wherein The water-absorbing and fresh-keeping packaging film is obtained by mixing the bimetallic organic framework material, plasticizer, film-forming agent and sodium carboxymethylcellulose, pouring them into a mold and drying.

3. The application according to claim 1, wherein The mass ratio of the bimetallic organic framework material, plasticizer, film-forming agent and sodium carboxymethylcellulose is 0.1 - 0.2:0.5 - 1:2:

2.

4. The application according to claim 1, characterized in that The preparation method of the bimetallic organic framework material includes the following steps: (1) Dissolve fumaric acid, zirconium oxychloride octahydrate and copper nitrate trihydrate in the formic acid solution of N,N-dimethylformamide, and ultrasonically dissolve to obtain a mixed solution; (2) Heat and pressurize the mixed liquid for reaction, and cool to room temperature after the reaction is completed to obtain a solid material; (3) Centrifuge and wash the solid material, and vacuum dry to obtain the bimetallic organic framework material.

5. The application according to claim 4, characterized in that, In step (1), the molar ratio of fumaric acid, zirconium oxychloride octahydrate and copper nitrate trihydrate is 1:0.5 - 1:0.1 - 0.

5.

6. The application according to claim 4, wherein In step (1), in the formic acid solution of N,N-dimethylformamide, the volume ratio of N,N-dimethylformamide to formic acid is 15 - 20:5 - 7.

7. The application according to claim 4, wherein In step (2), for the heat and pressure reaction, the reaction temperature is 125°C - 135°C, and the reaction time is 6 - 7 h.

8. The application according to claim 4, characterized in that In step (3), for the centrifugation, the rotation speed is 9500 rpm / min, the centrifugation time is 10 min, and the centrifugation temperature is 10°C - 20°C.

9. The application according to claim 4, wherein In step (3), for the vacuum drying, the temperature is 45°C - 60°C, the time is 8 - 10 h, and the drying pressure is -0.09 - -0.1 MPa.

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