Bacterial cellulose-mof composite aerogel and preparation method and application thereof

Abstract

The application belongs to the field of aerogels, and particularly relates to a bacterial cellulose (BC) and MOF composite aerogel and a preparation method and application thereof. The preparation method comprises two steps of (I) preparing a modified bacterial cellulose aerogel and (II) preparing a BC / MOF composite aerogel. The application prepares a hydrophobic modified BC aerogel by a freeze-drying method, and then ZIF-8 is in-situ grown on the aerogel to obtain a BC / MOF composite aerogel. The BC / MOF composite aerogel has excellent ultraviolet shielding property, thermal stability, antibacterial and bacteriostatic property and environmental protection and degradability, and has excellent application potential in the field of buffer packaging, for example, has great advantages in prolonging the freshness of fruits such as grapes.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of aerogels, and particularly relates to a bacterial cellulose-MOF composite aerogel and a preparation method and application thereof. BACKGROUND

[0002] Developing new packaging materials with stability, buffering and antibacterial properties is crucial for extending the shelf life of food. Cellulose aerogel is made of nanocellulose as raw material, and forms a three-dimensional network structure by mutual entanglement. It stands out in the field of food packaging due to its good mechanical properties, buffering performance and green degradable characteristics. In order to effectively inhibit the growth of harmful microorganisms, extend the shelf life of food and improve food safety, the food packaging industry often uses high-efficiency antibacterial materials to achieve the purpose of preservation. Metal-organic framework (MOF) is a new type of organic-inorganic hybrid porous solid material, which has gradually attracted attention due to its high porosity, good thermal stability and excellent antibacterial performance. Zeolitic imidazolate framework (ZIF-8) is a metal-organic framework formed by coordination of zinc ions (Zn 2+ ) and 2-methylimidazole (2-MiM). It is one of the most widely studied MOF materials, and has good biocompatibility, thermal stability and chemical stability as well as antibacterial performance. The main antibacterial mechanism of ZIF-8 is that metal ions and some organic ligands can adhere to the surface of bacteria when they come into contact, destroy the structural integrity, hinder their metabolism and reproduction, and eventually lead to their death. This makes ZIF-8 have potential in food packaging materials, which can be used to extend the shelf life of food and protect the quality and nutritional ingredients of food. However, the application of MOF aerogel composite materials in food packaging efficiency or preservation is still in the preliminary research stage, but has shown great potential. Therefore, this study proposes to add MOF materials to modified cellulose aerogel, which can make the buffering packaging more stable, while retaining its excellent buffering capacity, improving the antibacterial performance and preservation safety function, and has important application significance to meet the needs of the food industry for packaging materials.

[0003] Therefore, the technical scheme of the present application is proposed based on the above. SUMMARY

[0004] In order to solve the problems existing in the prior art, the present application provides a preparation method of bacterial cellulose-MOF composite aerogel, which comprises the following steps:

[0005] (I) preparing a hydrophobically modified bacterial cellulose aerogel:

[0006] (1) mixing bacterial cellulose with deionized water to obtain a bacterial cellulose suspension;

[0007] (2) hydrolyzing methyltrimethoxysilane added into an acidic aqueous solution to obtain a silica sol;

[0008] (3) mixing the bacterial cellulose suspension with the silica sol, stirring, and then placing the mixture into a mold, and then placing the mold into liquid nitrogen to grow ice crystals to obtain a frozen sample;

[0009] (4) further freeze-drying the frozen sample to obtain a hydrophobically modified bacterial cellulose aerogel (modified BC aerogel);

[0010] (II) preparing a bacterial cellulose-MOF composite aerogel:

[0011] (5) dissolving zinc nitrate hexahydrate and 2-methylimidazole in deionized water respectively to obtain a zinc nitrate solution and a 2-methylimidazole solution respectively;

[0012] (6) immersing the hydrophobically modified bacterial cellulose aerogel into the 2-methylimidazole solution for soaking, and then adding the zinc nitrate solution for stirring to obtain a pre-prepared composite aerogel;

[0013] (7) cleaning and freeze-drying the pre-prepared composite aerogel to obtain the bacterial cellulose-MOF composite aerogel (BC / MOF composite aerogel).

[0014] Preferably, in step (1), the concentration of the bacterial cellulose suspension is 0.7 wt%.

[0015] Preferably, in step (2), the acidic aqueous solution is an acetic acid aqueous solution or a hydrochloric acid aqueous solution;

[0016] Preferably, the hydrolysis time is 30 min.

[0017] Preferably, in step (3), the stirring is performed by magnetic stirring at room temperature for 2 h.

[0018] Preferably, in step (4), the freeze-drying is performed at -92℃ and 0.74 Pa for 72 h.

[0019] Preferably, in step (6), the soaking time is 2 h.

[0020] Preferably, the stirring temperature is 25℃, and the stirring time is 0.5-6 h.

[0021] Preferably, in step (7), the freeze-drying time is 36 h.

[0022] Based on the same technical concept, another aspect of the present application provides a bacterial cellulose-MOF composite aerogel obtained by the above preparation method.

[0023] Based on the same technical concept, another aspect of the present application provides a use of bacterial cellulose-MOF composite aerogel in the preparation of fresh-keeping packaging products.

[0024] The present application has the following beneficial effects:

[0025] The present application prepared BC / MOF composite aerogel by in-situ growth method, SEM showed that the pore arrangement of the modified aerogel was ordered, the pore size was smaller, and ZIF-8 could be seen loaded on the surface of the aerogel. FTIR and XRD proved that the silane group of MTMS was introduced, and ZIF-8 was in-situ grown on the BC / MOF aerogel.

[0026] In addition, after loading ZIF-8, the water contact angle of the composite aerogel decreased, but as the content of loaded ZIF-8 increased, the hydrophobicity of the BC / MOF composite aerogel gradually increased, and the UV shielding property gradually increased; the thermal stability of the BC / MOF composite aerogel increased. The antibacterial effect of the BC / MOF composite aerogel gradually increased as the loading time of ZIF-8 increased, especially the inhibition effect of the BC / MOF composite aerogel on Botrytis cinerea was the best. Except for the BC / MOF-6 composite aerogel, the degradation rate of all aerogels was higher than 80% after being buried in soil for 90 days.

[0027] The BC / MOF composite aerogel described in the present application has excellent application potential in the field of fresh-keeping packaging products, for example, it has great advantages in prolonging the freshness of fruits such as grapes. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0029] Figure 1 is a micro-morphology diagram of the aerogel sample.

[0030] Figure 2 is an infrared spectrum diagram of the aerogel sample.

[0031] Figure 3 is an X-ray diffraction diagram of the aerogel sample.

[0032] Figure 4 is a TG curve diagram of the aerogel sample.

[0033] Figure 5 is a DTG curve diagram of the aerogel sample.

[0034] Figure 6 is a contact angle data graph of the aerogel sample.

[0035] Figure 7 is a UV transmittance data graph of the aerogel sample.

[0036] Figure 8 is a bacteriostatic effect graph of the aerogel sample.

[0037] Figure 9 is a degradation effect graph of the aerogel sample. DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0039] In the embodiments, the main chemical reagents, experimental instruments and equipment used are shown in Tables 1 and 2.

[0040] Table 1 Experimental chemical reagents

[0041]

[0042]

[0043] Table 2 Experimental instruments and equipment

[0044] Name Model Manufacturer Analytical balance ME204E Mettler Toledo International Corporation Air blast drying oven GZX-9140 Shanghai Bo Xun Industrial Co., Ltd. Freeze dryer LGJ-50FD Henan Brothers Equipment Co., Ltd. Scanning electron microscope JSM-5600LV Japan Electron Optics Co., Ltd. X-ray diffractometer DX-2700 Hao Yuan Instrument Co., Ltd. Fourier infrared spectrometer IS50 Nicolet Corporation of America Tensile testing machine SMT-5000 Yangzhou Saisi Testing Equipment Co., Ltd. Thermogravimetric analyzer STA409C / PC Netzsch Corporation of Germany Water contact angle tester NBSIOSA60 Ningbo New Boundary Scientific Instruments Co., Ltd. Ultraviolet spectrophotometer UV752N Shanghai Huerpu International Trade Co., Ltd.

[0045] Embodiment 1

[0046] The present embodiment provides a preparation method of bacterial cellulose-MOF composite aerogel, which comprises the following steps:

[0047] (1) The bacterial cellulose (BC) dispersion solution in deionized water is diluted to prepare a BC suspension with a concentration of 0.7wt% and a mass of 20g;

[0048] (2) 280μL of methyltrimethoxysilane (MTMS) is added to an aqueous solution containing 5×10 -3 mol / L acetic acid, and hydrolyzed for 30min to obtain completely hydrolyzed MTMS silica sol;

[0049] (3) The 20 g BC suspension was magnetically stirred with the MTMS silica sol at room temperature for 2 h, and then poured into the mold; then the bottom of the copper plate was immersed in liquid nitrogen, and the mold was placed on the surface of the copper plate to form a temperature gradient from bottom to top, so that the ice crystals grew from bottom to top along the temperature gradient, and a frozen sample was obtained;

[0050] (4) The frozen sample was freeze-dried at -92°C and 0.74 Pa for 72 h to obtain a modified bacterial cellulose aerogel;

[0051] (5) 6 g of zinc nitrate hexahydrate and 13.2 g of 2-methylimidazole were completely dissolved in 280 mL of deionized water, respectively, to obtain a zinc nitrate solution and a 2-methylimidazole solution, respectively;

[0052] (6) The modified bacterial cellulose aerogel was immersed in the 2-methylimidazole solution for 2 h, and then the zinc nitrate solution was added and stirred at 25°C for 0.5 h to obtain a pre-prepared composite aerogel;

[0053] (7) The pre-prepared composite aerogel was washed with deionized water three times to remove residual surface impurities, and finally placed in a freeze dryer for 36 h to obtain a bacterial cellulose-MOF composite aerogel.

[0054] Note: The product obtained in this example is named BC / MOF-0.5, wherein "0.5" represents the stirring time of 0.5 h in step (6) (the similar naming method is used below).

[0055] Example 2

[0056] This example provides a method for preparing a bacterial cellulose-MOF composite aerogel, which is different from example 1 in that the stirring time in step (6) is 1 h, and the rest of the operations are the same.

[0057] The product obtained in this example is named BC / MOF-1.

[0058] Example 3

[0059] This example provides a method for preparing a bacterial cellulose-MOF composite aerogel, which is different from example 1 in that the stirring time in step (6) is 3 h, and the rest of the operations are the same.

[0060] The product obtained in this example is named BC / MOF-3.

[0061] Example 4

[0062] This example provides a method for preparing a bacterial cellulose-MOF composite aerogel, which is different from example 1 in that the stirring time in step (6) is 6 h, and the rest of the operations are the same.

[0063] The product obtained in this example is named BC / MOF-6.

[0064] Test Example: Structural characterization and performance analysis of BC / MOF composite aerogel

[0065] (1) Scanning Electron Microscope

[0066] The aerogel sample is placed in liquid nitrogen and brittle fractured, and then cut into a 2mm x 2mm cross section. Next, gold spraying treatment is performed, and it is placed on the electron microscope test table. The sample is observed using a scanning electron microscope, and the image magnification is set between 5000 and 10000 times.

[0067] (2) Fourier Transform Infrared Spectroscopy

[0068] Before testing, the aerogel sample is first placed in an oven for complete drying to completely remove moisture. Then it is cut into pieces and mixed with granular potassium bromide. The mixture is stirred to uniformity using a grinding rod, and is crushed and refined until it is in powder form. The powder is evenly spread on a tablet press to prepare a uniform wafer, and it is dried to remove residual moisture. After completing the preparation, the sample is tested using an infrared spectrometer.

[0069] (3) X-ray Diffraction

[0070] The instrument is started, the aerogel sample is evenly coated on a glass sheet, and it is placed in the X-ray diffractometer. Set the 2θ range to 5-60°, and the scanning rate to 5° / min, to analyze the chemical structure of the aerogel.

[0071] (4) Thermal Stability

[0072] After the aerogel sample is dried under vacuum to remove moisture, thermal gravimetric analysis is performed. The test conditions are that the temperature is raised from room temperature to 600°C at a rate of 10°C / min under a nitrogen atmosphere.

[0073] (5) Hydrophobic Performance

[0074] Ensure that the surface of the aerogel sample is smooth, free of impurities or dirt, to ensure the accuracy of the measurement. The prepared aerogel sample is fixed on the measurement table, ensuring that it is in a horizontal state and the surface is completely exposed. The instrument is then zeroed, 3μL of water droplets are added to the surface of the aerogel using a microsyringe, and finally the image of the water droplets in contact with the surface of the aerogel is captured using a camera.

[0075] (6) Ultraviolet Transmittance

[0076] The aerogel sample was prepared and prepared into appropriate shape and size to fit into the UV spectrophotometer for measurement. The prepared aerogel sample was loaded into the sample chamber of the UV spectrophotometer. Ensure that the surface of the sample is smooth to ensure that the light can pass through the sample uniformly. Before measuring the sample, baseline calibration was performed. Select to measure in the range of 200-800 nm. By known absorbance value, the transmittance of the aerogel sample was calculated.

[0077] (vii) Biodegradability

[0078] In order to preliminarily understand the degradation time of the aerogel, biodegradability research was carried out. The aerogel sample was cut into a shape of 5x7 cm, and then buried in the soil with a depth of 10-15 cm, and water was sprayed regularly to keep the soil moist. Every 6 days, the aerogel was taken out and photographed to record its morphological changes.

[0079] (viii) Antibacterial performance

[0080] The antibacterial activity of the aerogel was evaluated by adopting the disc diffusion method. First, the concentration of Staphylococcus aureus, Escherichia coli, Listeria monocytogenes and Salmonella-enterica was adjusted to 10 6 ~10 7 CFU / mL. Subsequently, 100 μL of the bacterial solution was dropped on the solid culture medium and uniformly spread. Subsequently, the 10 mm diameter circular aerogel was washed with sterile water and placed on the culture medium for constant temperature culture for 48 h. Finally, the antibacterial effect of the composite aerogel was evaluated by measuring the diameter of the antibacterial ring.

[0081] The aerogel was cut into a square of 10x10 mm and placed in the solid culture medium, and then the Botrytis cinerea mycelium was uniformly covered on the whole plate in a clean bench. Subsequently, the mycelial block equidistant from the center point was removed using a punch sampler with a diameter of 5 mm, and placed on the aerogel. The culture dish was incubated in a 25°C incubator, and on the 7th day, the diameter of the Botrytis cinerea plaque was measured.

[0082] (ix) Data statistics and analysis

[0083] All experiments were determined at least in triplicate, and the results were expressed as mean ± standard deviation. Data were processed by Microsoft Excel 2016, and plotted by origin 8.5. All data were analyzed by ANOVA in IBM SPSS Statistics 25, where different lowercase letters indicated significant differences between different treatment groups, i.e. p < 0.05 was considered statistically significant difference.

[0084] Results and discussion

[0085] (I) Microstructure of BC / MOF composite aerogels

[0086] SEM was used to observe the microstructure and surface morphology of aerogels, including information on pore distribution, morphology, connectivity, etc. This is of great significance for optimizing the preparation process of aerogels and evaluating their performance applications. For example, the sample obtained in the preparation process of Example 4, the scanning electron microscope image of the aerogel sample is shown in Figure 1 It can be seen that the microstructure of the BC aerogel ( Figure 1 on the far left, unmodified pure BC aerogel) presents a fibrous network structure, and these fibrous substances are arranged in a staggered manner to form a porous structure with a larger pore size. From the cross-sectional view of the BC aerogel, it can be seen that the fibers are squeezed together because the strength of the aerogel at this time is extremely low and easy to collapse; the microstructure of the modified BC aerogel ( Figure 1 in the middle) has changed significantly compared with the pure BC aerogel, and the overall structure is axially oriented. From the cross-sectional view, it can be seen that the pore size is smaller, the three-dimensional network structure is more uniform, and a honeycomb structure appears, proving that the silane groups of MTMS have been successfully introduced, and the mechanical properties have been enhanced; from the BC / MOF-6 ( Figure 1 on the far right), it can be observed that its surface is flatter than that of the modified BC aerogel, proving that ZIF-8 is grown in situ on the aerogel and uniformly distributed. The aerogel still maintains a three-dimensional network structure, and the basic structure has not changed.

[0087] (II) Fourier transform infrared spectrum of BC / MOF composite aerogels

[0088] Figure 2 The infrared spectrum of the BC aerogel is shown. The peak at 3335 cm -1 is related to the -OH group, while the characteristic peaks at 1601 cm -1 and 1351 cm -1 represent the bending vibration of O-H and C-H, respectively. The peak at 2900 cm -1 is the stretching vibration of C-H, and the peak at 1032 cm -1The peak at 799 cm-1 is related to the side group vibration of the glycosidic ring, and there are also some weak shoulder peaks around it. By comparing the infrared spectrum of the modified BC aerogel with the spectrum of the unmodified BC aerogel, it is found that a new diffraction peak appears at 799 cm -1 This phenomenon is due to the asymmetric stretching vibration of Si-O-Si, indicating that MTMS has reacted with BC and successfully formed polysiloxane. Compared with the infrared spectrum of the modified BC aerogel, the spectrum of the BC / MOF composite aerogel has a new characteristic peak at 1461 cm -1 This is due to the planar stretching of the imidazole ring, further confirming the successful loading of ZIF-8 on the aerogel.

[0089] (III) X-ray diffraction of BC / MOF composite aerogel

[0090] For porous materials such as aerogels, XRD can help determine whether the crystal structure exists and the influence of the crystal structure on the material properties, and can be used to determine the presence and relative content of various components in the aerogel. Figure 3 is the X-ray diffraction pattern of the aerogel, from which it can be seen that the XRD spectra of the four groups of BC / MOF composite aerogels are almost the same, and as the loading time of ZIF-8 increases, the BC substrate is covered by ZIF-8, so the peak intensity of the cellulose I type characteristic peak (110, 2θ = 14.5°) decreases. When the loading time of ZIF-8 gradually increases, the most important characteristic crystallization diffraction peak of ZIF-8 appears, and the diffraction peak intensity increases, and its crystal face is (011, 2θ = 7.1°), (022, 2θ = 14.5°), (222, 2θ = 17.9°), indicating that ZIF-8 is successfully loaded into the BC-MTMS aerogel.

[0091] (Four) Thermal stability of BC / MOF composite aerogel

[0092] TGA can evaluate the mass change of the aerogel during heating, thereby determining its thermal stability, which is crucial for determining the application range and stability of the aerogel at high temperatures. In order to test the thermal properties of the aerogel before and after loading ZIF-8, the thermal gravimetric analysis was carried out from Figure 4-5As can be seen from the figure, the thermal decomposition behavior of the five aerogels can be roughly divided into four stages; the first stage is 50℃-200℃, the mass loss of the aerogel in this stage is within 10%, the reason for this loss is that the aerogel loses free water and bound water. The second stage is 200℃-350℃, the aerogel has the largest mass loss (40%-60%) in this stage, the reason is that the side chain groups in the aerogel are degraded. The third stage is 350℃-600℃, the mass loss of BC aerogel is about 5%, the degradation in this stage is due to the breakage of carbon chain, and the mass loss of ZIF-8 loaded aerogel is about 15%, which is because the collapse of ZIF-8 framework causes decomposition. As can be seen from the figure, the thermal gravimetric curves of the five aerogels before and after modification are similar, and after loading ZIF-8, the maximum mass loss temperature is increased, which proves that loading ZIF-8 can increase the thermal stability of the aerogel.

[0093] (V) Hydrophobic property of BC / MOF composite aerogels

[0094] The hydrophobicity of packaging materials can effectively block the penetration of water, oxygen and other gases, thereby prolonging the shelf life of food. Water and oxygen are one of the main factors leading to food spoilage and oxidation, so blocking their penetration is crucial to maintaining the freshness and quality of food. From Figure 6 As can be seen from the figure, the water contact angle of pure BC aerogel is 0°, and it can be completely wetted by water droplets in 3s. This is because BC has a large number of hydroxyl groups, so it shows strong hydrophilicity when unmodified. After hydrophobic modification, the water contact angle of BC aerogel is 127.2°, and the water droplets cannot wet the aerogel. This is because after silane modification, the hydrophilic groups of the aerogel are reduced and the hydrophobic groups are increased, showing obvious hydrophobic performance. This result shows that MTMS is successfully grafted on the surface of the aerogel. After loading ZIF-8 on the surface of the aerogel, the water contact angle shows a downward trend, this phenomenon is because the roughness of the aerogel surface is increased, and the rough surface has better wettability to water, so it will cause the water contact angle to decrease. With the increase of in-situ growth time of ZIF-8, the content of loaded ZIF-8 gradually increases, making the pore structure of the aerogel surface more ordered or dense, which hinders the diffusion of water molecules on the surface, and thus increases the water contact angle.

[0095] (VI) UV transmittance of BC / MOF composite aerogels

[0096] The role of ultraviolet shielding on aerogel packaging is mainly to protect the contents from ultraviolet damage, extend their shelf life, maintain the appearance of the contents, avoid discoloration, deterioration and degradation, and improve product quality and value, especially for ultraviolet-sensitive items such as pharmaceuticals, cosmetics and food. Packaging materials with good ultraviolet shielding properties can maintain the nutritional substances and natural pigments in food, keeping the original taste. The ultraviolet transmittance of the composite aerogel samples is shown in Figure 7 As shown in Table 1, the BC aerogel exhibits a high transmittance of 36.7% to ultraviolet radiation in the range of 200 nm to 420 nm, i.e., it has a relatively low ultraviolet shielding property. When loaded with ZIF-8, all four aerogels can block more than 70% of ultraviolet light, and the ultraviolet transmittance of the aerogel decreases with increasing loading time, with BC / MOF-6 being the lowest at 23.8%. This is because the crystal structure of ZIF-8 is relatively stable, with high thermal and chemical stability. This stability makes ZIF-8 less likely to be structurally damaged or dissolved under ultraviolet radiation, thereby maintaining its ultraviolet shielding performance. At the same time, ZIF-8 has certain optical properties and can absorb or scatter ultraviolet light when exposed to it, thereby reducing the penetration of ultraviolet light, demonstrating that ZIF-8 has a good effect on blocking ultraviolet light.

[0097] (VII) Antibacterial properties of BC / MOF composite aerogels

[0098] The role of antibacterial performance analysis on aerogel packaging is to improve the hygiene and safety of the packaging. By evaluating the antibacterial properties of aerogel packaging, the reproduction of bacteria in the packaging can be effectively inhibited, reducing the risk of microbial contamination of food and pharmaceutical products that are susceptible to contamination, extending their shelf life, ensuring product quality and safety, and meeting market demand for high-quality and high-safety standards. The antibacterial activity of ZIF-8-loaded composite aerogels and pure BC aerogels was evaluated by the corresponding methods, and the inhibition of the four composite aerogels and pure BC aerogels on Salmonella, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli and Botrytis cinerea is shown in Table 2. Figure 8The observation results show that pure BC aerogel does not exhibit inhibitory effect on the five tested bacteria, while the ZIF-8-loaded composite aerogel exhibits significant antibacterial effect. With the increase of ZIF-8 loading time, the diameter of the inhibition zone gradually expands, indicating that the antibacterial effect gradually increases. This is because zinc ions can penetrate the cell membrane gap, interact with sulfhydryl and dimercapto in enzymes, or adhere to the negatively charged bacterial cell wall, leading to cell rupture during the metabolic process, and ultimately leading to cell death. The composite aerogel has the best inhibitory effect on Botrytis cinerea, and the reason is that ZIF-8 generally has high hydrophobicity, which will adversely affect the growth environment of Botrytis cinerea, and its hydrophobicity may reduce the adhesion and growth of Botrytis cinerea on its surface; another reason is that the metal ions released by ZIF-8 may cause the pH value of the surrounding environment to change, and the sensitivity of Botrytis cinerea to the environmental pH may be affected. It can effectively target pathogenic bacteria that cause grape spoilage and can be used as an antibacterial packaging material in the grape preservation process.

[0099] (Eight) Biodegradability of BC / MOF composite aerogel

[0100] Biodegradability testing evaluates the rate and extent of decomposition of aerogel packaging in living organisms or specific environmental conditions. This helps to determine the environmental friendliness and sustainability of the packaging, reduce plastic pollution, promote the use of biodegradable materials, and meet the Sustainable Development Goals. The soil burial degradation method was used to evaluate the biodegradability of composite aerogels in natural environments. It can be seen from Figure 9 that after 18 days of soil burial, pure BC aerogel showed a high degradation rate. This is because BC is derived from cellulose synthesized during bacterial fermentation, which is a natural biopolymer material, and is closer to natural materials in structure and composition, making it easier to be recognized and degraded by soil microorganisms; microorganisms can secrete corresponding enzymes to decompose cellulose molecules, thereby promoting the degradation of BC aerogel. In contrast, ZIF-8-loaded aerogels have tighter binding between cellulose chains, stronger hydrophobicity, and stronger antibacterial properties, making it more difficult for microorganisms to adhere to the surface of the aerogel. After 90 days of soil burial, the degradation rate of all aerogels exceeded 80%, except for BC / MOF-6. This may be because the BC / MOF-6 has a higher content of ZIF-8 loaded, and its strong antibacterial properties make it less affected by microorganisms, thus slowing down its degradation rate.

[0101] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing bacterial cellulose-MOF composite aerogel, characterized in that, The preparation method comprises the following steps: (I) preparing a hydrophobically modified bacterial cellulose aerogel: (1) diluting bacterial cellulose after mixing with deionized water to obtain a bacterial cellulose suspension; the concentration of the bacterial cellulose suspension is 0.7 wt%; (2) adding methyltrimethoxysilane to an acidic aqueous solution for hydrolysis to obtain a silica sol; the acidic aqueous solution is an acetic acid aqueous solution or a hydrochloric acid aqueous solution; the hydrolysis time is 30 min; (3) mixing the bacterial cellulose suspension and the silica sol after stirring, and then placing them in a mold; then placing the mold in liquid nitrogen to grow ice crystals, forming a temperature gradient from bottom to top, promoting the growth of ice crystals from bottom to top along the temperature gradient direction to obtain a frozen sample; the stirring mode is magnetic stirring at room temperature for 2 h; (4) further freeze-drying the frozen sample to obtain a hydrophobically modified bacterial cellulose aerogel; the freeze-drying conditions are: freeze-drying at -92℃ and 0.74 Pa for 72 h; (II) preparing a bacterial cellulose-MOF composite aerogel: (5) dissolving zinc nitrate hexahydrate and 2-methylimidazole in deionized water respectively to obtain a zinc nitrate solution and a 2-methylimidazole solution respectively; (6) immersing the hydrophobically modified bacterial cellulose aerogel in the 2-methylimidazole solution for soaking, and then adding the zinc nitrate solution for stirring to obtain a pre-prepared composite aerogel; the soaking time is 2 h; the stirring temperature is 25℃, and the stirring time is 0.5-6 h; (7) washing and freeze-drying the pre-prepared composite aerogel to obtain the bacterial cellulose-MOF composite aerogel; the freeze-drying time is 36 h.

2. The bacterial cellulose-MOF composite aerogel obtained by the preparation method of claim 1.

3. The use of the bacterial cellulose-MOF composite aerogel of claim 2 in the preparation of fresh-keeping packaging products.

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