Composite aerogel with humidity-controlled release function and preparation method and application thereof

Abstract

This invention belongs to the field of food preservation technology, specifically relating to a composite aerogel with humidity-controlled release function, its preparation method, and its application. The composite aerogel provided by this invention uses polyvinyl alcohol, carboxymethyl chitosan, cellulose nanofibers, and copper ion solution as a matrix to synthesize a physicochemically double-crosslinked hydrogel. A metal-organic framework HKUST-1 is grown in situ inside the hydrogel, and the composite aerogel is obtained by freeze-drying. Subsequently, hydrophobic volatile essential oils such as carvacrol, cinnamaldehyde, and menthone are loaded onto it. This invention provides a composite aerogel with high safety, structural stability, and significant antibacterial effect. It accelerates the release rate of volatile essential oils with increasing humidity, achieving timely antibacterial preservation, a pleasant aroma, reduced spoilage rate during strawberry storage, and delayed quality deterioration. It possesses excellent antibacterial properties, safety, and promising application prospects.

Description

Technical Field

[0001] This invention belongs to the field of food preservation and active packaging technology, specifically relating to composite aerogels with humidity-controlled release function, their preparation methods, and applications. Background Technology

[0002] Strawberries are highly valued for their vibrant color, sweet and sour taste, and rich content of vitamins, minerals, and antioxidants. However, as a typical berry, strawberries have extremely thin skin, delicate tissue, and high water content, making them highly susceptible to contamination and rotting by microorganisms such as gray mold during post-harvest storage and transportation.

[0003] Currently, traditional physical preservation methods (such as low-temperature refrigeration) and chemical preservation methods (such as preservative spraying) have certain effects, but they also have drawbacks such as high energy consumption or pesticide residues. In recent years, natural active substances have received widespread attention due to their safety, non-toxicity, and broad-spectrum antibacterial properties. Studies have shown that volatile essential oil preservatives still have problems in practical applications, such as high volatility, poor stability, susceptibility to light and temperature, and poor water solubility. This makes it difficult to control their release behavior and their effective period short, thus limiting their further application in the field of food preservation (BORGES JC, DE ALMEIDA CAMPOS LA, KRETZSCHMAR EAM, et al. Incorporation of essential oils in polymeric films for biomedical applications[J]. International Journal of Biological Macromolecules, 2024, 269: 132108.).

[0004] To overcome the short-lived nature of essential oils, metal-organic frameworks (MOFs) have become ideal carriers for essential oils due to their ultra-high specific surface area, tunable pore structure, and excellent loading capacity. In particular, MOF materials such as HKUST-1, which exhibit water instability, experience partial collapse or displacement of their structure under the influence of water molecules. This invention utilizes this characteristic, transforming the humidity sensitivity of HKUST-1 into a "response switch" for active molecules: under high humidity, it triggers the precise release of volatile essential oils from the pores, thereby achieving an intelligent humidity-responsive release mechanism.

[0005] Furthermore, to improve the adaptability of active carriers in actual packaging, aerogels, as solid porous materials with high porosity, low density, and a three-dimensional cross-linked network structure, show excellent application prospects. This invention constructs a composite MOF aerogel composed of polyvinyl alcohol (PVA), carboxymethyl chitosan (CMCS), and TEMPO oxidized cellulose nanoparticles (TOCNF). This composite MOF aerogel, by loading volatile essential oils, achieves humidity-responsive release, enabling the sustained release and precise on-demand release of volatile essential oils. This inhibits microbial growth during strawberry preservation and storage, reduces spoilage, and maintains the sensory quality of strawberries, demonstrating significant practical importance in the field of preservation. Summary of the Invention

[0006] To address the shortcomings of existing technologies, such as uncontrollable release rate and short duration of effect of essential oil preservatives, the primary objective of this invention is to provide a humidity-responsive, long-lasting, and replaceable composite aerogel that can serve as a carrier for one or more essential oils. During strawberry storage, it can detect changes in humidity within the packaging environment to achieve precise release of antibacterial agents as needed.

[0007] In view of the problems in the prior art, the first problem to be solved by the present invention is to provide a composite aerogel that can release moisture in response to humidity, provide sustained release, and absorb moisture.

[0008] The second problem to be solved by the present invention is to provide a method for preparing the above-mentioned composite aerogel.

[0009] The third problem to be solved by the present invention is to provide an application of the above-mentioned composite aerogel in the strawberry preservation scenario.

[0010] To solve the above problems, the present invention adopts the following technical solution: This invention provides a composite aerogel with humidity-controlled release function, comprising a polysaccharide-based hydrogel, a metal-organic framework HKUST-1, and volatile essential oils; wherein: (1) The polysaccharide-based hydrogel is a double-network hydrogel synthesized by polyvinyl alcohol, carboxymethyl chitosan, cellulose nanofibers and copper ion solution in the form of physicochemical double cross-linking; (2) The metal-organic framework HKUST-1 is uniformly fixed in the composite aerogel in an anchoring manner; (3) Volatile essential oils, including carvacrol (CAR), cinnamaldehyde and thymol, are loaded as guest molecules by composite aerogel and metal-organic framework HKUST-1.

[0011] Furthermore, as humidity increases, the release rate of volatile essential oils loaded on a composite aerogel with humidity-controlled release function accelerates, enabling timely release and long-lasting antibacterial effect.

[0012] Volatile essential oil preservatives generally suffer from drawbacks such as uncontrollable release rates, short duration of effect, and limited functionality. The composite aerogel with humidity-controlled release function provided by this invention possesses a three-dimensional porous structure and abundant polar functional groups, enabling it to support single or compound volatile essential oils, including carvacrol, cinnamaldehyde, and thymol. This material is suitable for adsorbing active molecules with small molecular weights, containing polar functional groups, and possessing certain hydrophobic carbon chains or aromatic ring structures, thus endowing the carrier with strong versatility and replaceability of guest molecules.

[0013] During strawberry storage, the fruit's respiration releases moisture, leading to increased humidity in the packaging environment. This causes the aerogel network to swell, and the pores of HKUST-1 are triggered by water molecules, resulting in the slow and continuous release of the volatile essential oils it carries. This reduces the contamination and reproduction of microorganisms on the strawberry surface, provides a certain antioxidant effect, and significantly extends its edible period.

[0014] This invention also provides a method for preparing the above-mentioned composite aerogel with humidity-controlled release function, comprising the following steps: S01, Preparation of carboxymethyl chitosan / polyvinyl alcohol / cellulose nanofiber hydrogel Polyvinyl alcohol (PVA) was added to deionized water and heated and stirred in a water bath. After cooling to room temperature, TEMPO-oxidized nanocellulose (TOCNF) aqueous dispersion was added and magnetically stirred. Subsequently, carboxymethyl chitosan (CMCS) powder was slowly added; a second water bath heating was performed, and stirring was continued at 30-60°C for 0.5-2 hours to obtain a homogeneous PVA / CMCS / TOCNF pregel solution; the obtained pregel solution was injected into a mold and subjected to freeze-thaw cycles to obtain a PVA / CMCS / TOCNF hydrogel, denoted as PCT. S02, In-situ synthesis of HKUST-1 inside the hydrogel The PCT hydrogel obtained in the above steps was cut into small pieces and soaked in a copper acetate monohydrate solution; it was then washed with deionized water until no copper ions remained in the washing solution, yielding PVA / CMCS / TOCNF / Cu. 2+ Hydrogel, denoted as PCT-Cu 2+ ; The PCT-Cu after the above washing process 2+ The hydrogel was immersed in a pyromellitic acid solution; the hydrogel was removed, washed thoroughly, and then freeze-dried to obtain PVA / CMCS / TOCNF / HKUST-1 aerogel, denoted as PCTH; S03, volatile essential oils loaded in composite MOFs aerogel The PCTH aerogel obtained in the above steps is immersed in an essential oil ethanol solution, protected from light, and dried overnight at room temperature in a vacuum drying oven to obtain PVA / CMCS / TOCNF / HKUST-1@essential oil aerogel, denoted as PCTH@essential oil aerogel, which is a composite aerogel with humidity-controlled release function.

[0015] Furthermore, in step S01, the final concentration of polyvinyl alcohol (PVA) is 1-4 g / mL; the final concentration of carboxymethyl chitosan (CMCS) is 2-5 g / mL.

[0016] Furthermore, in step S01, the concentration of the TEMPO-oxidized nanocellulose TOCNF aqueous dispersion is 0.5-4.0 g / mL, and the final concentration of TOCNF is 0.4-0.8 g / mL.

[0017] Furthermore, in step S01, the first water bath temperature is 80-100℃ and the time is 2-4 hours; the second water bath temperature is 30-60℃ and the time is 0.5-2 hours; the number of freeze-thaw cycles is 3-5.

[0018] Furthermore, in step S02, the concentration of the copper acetate monohydrate solution is 0.1-0.5 mol / L, and the soaking time in the copper acetate monohydrate solution is 8-12 hours.

[0019] Furthermore, in step S02, the concentration of the trimellitic acid solution is 0.1-0.5 mol / L, the pH value of the trimellitic acid solution is 2.5-3.5, and the soaking time in the trimellitic acid solution is 2-8 hours.

[0020] Furthermore, in step S03, the volume fraction of the essential oil ethanol solution is 5-40%, and the soaking time in the dark is 10-30 hours.

[0021] This invention also provides the application of the above-mentioned composite aerogel with humidity control and release function in the field of strawberry preservation.

[0022] Furthermore, the specific application method includes the following steps: S01. Cut the prepared composite aerogel with humidity control release function into the required shape, weigh it according to the preset dosage, and encapsulate it in a non-woven bag with good air permeability.

[0023] S02. Fix the sealed non-woven bag or place it on top of the strawberry preservation box so that the released volatile essential oils can penetrate downwards from the top of the packaging and evaporate to the surface of the strawberries under the drive of gravity and concentration gradient, forming a uniform active protective atmosphere.

[0024] S03. Seal the food storage container with the lid and store it in a refrigerator at 4°C or at room temperature.

[0025] The principle of the technical solution adopted in this invention is as follows: This invention introduces carboxymethyl chitosan and cellulose nanofibers into an aerogel. Carboxymethyl chitosan has a large number of carboxyl groups, which can react with copper ions (Cu). 2+ Chelation, forming chemical cross-links, and simultaneously achieving the control of Cu in HKUST-1 2+ The effective immobilization of these molecules significantly inhibits their migration and release in the application environment. Cellulose nanofibers possess a high specific surface area and network-building ability, enabling the construction of multi-scale porous structures within the aerogel matrix to form a uniform microporous network, effectively enhancing the physical adsorption efficiency for hydrophobic small molecules such as carvacrol, cinnamaldehyde, and thymol.

[0026] Furthermore, to improve the mechanical strength of the aerogel structure and prevent internal structural damage caused by swelling after absorbing water, this invention introduces polyvinyl alcohol (PVA). PVA is a water-soluble polymer containing a large number of hydroxyl groups. The molecules form a network through hydrogen bonds. Repeated freeze-thaw cycles cause crystalline micro-regions to aggregate between PVA chains, forming stable physical cross-links through hydrogen bonds, thus forming a three-dimensional gel network.

[0027] This invention combines polyvinyl alcohol, carboxymethyl chitosan, cellulose nanofibers, and copper ions (Cu). 2+ The combination of these components forms a physicochemical dual-network cross-linked hydrogel, allowing for the in-situ growth of humidity-sensitive HKUST-1 within the hydrogel. The introduction of HKUST-1 has dual significance: firstly, HKUST-1 possesses high specific surface area, high porosity, and excellent loading capacity, effectively increasing the loading of hydrophobic active ingredients such as carvacrol, cinnamaldehyde, and thymol; secondly, HKUST-1 suffers from poor water stability, easy aggregation and growth, and high brittleness, limiting its widespread application in practical applications. However, we can fully utilize its poor water stability by transforming its humidity sensitivity into a release "response switch," thereby achieving humidity-responsive release of the hydrophobic active ingredients. To address its easy aggregation and high brittleness, this study introduces HKUST-1 into the gel carrier, pre-immobilizing copper ions (Cu... 2+ The location of the copper ions (Cu) is optimized to ensure uniform dispersion and in-situ growth within the gel system, thereby preventing the loss of copper ions (Cu) from HKUST-1 due to humidity degradation. 2+ This allows the substances to be released externally, thereby reducing the potential safety risks they may pose to the food system.

[0028] The beneficial effects of this invention are as follows: 1. The greatest improvement of this invention lies in expanding upon the traditional method of encapsulating preservatives and antibacterial agents in a slow-release carrier. Considering the changes strawberries undergo during storage, strawberries, due to their high respiration rate, easily create a high-humidity environment in a sealed storage container, accelerating microbial growth and reproduction. Based on this characteristic, a composite aerogel with humidity-controlled release function was constructed. This achieves a humidity-responsive controlled release function, where the release rate increases with higher ambient humidity, enabling timely release and long-lasting antibacterial preservation.

[0029] 2. To prevent the Cu from forming due to structural collapse in the humidity-sensitive metal-organic framework HKUST-1 under high humidity conditions. 2+ The release is controlled, and this invention anchors HKUST-1 in a fixed-site manner within a polysaccharide-based hydrogel. The principle is that during the preparation of the polysaccharide-based hydrogel, copper ions participate in the chemical cross-linking of the hydrogel and are fixed within it. This allows for the in-situ synthesis of HKUST-1, fixing the growth location of HKUST-1 and ensuring that residual copper ions meet standards, thereby achieving antibacterial and preservative effects during food storage and logistics.

[0030] 3. The composite aerogel with humidity-controlled release function provided by this invention can be used as a replacement for the moisture-absorbing liner in strawberry packaging. In strawberry preservation scenarios, it can not only release antibacterial agents such as carvacrol, cinnamaldehyde, and thymol through the gas phase to inhibit mold growth and oxidation on the strawberry surface, but also absorb condensation caused by temperature differences and excess moisture on the strawberry surface, achieving moisture absorption, slow release, and broad-spectrum antibacterial effects to maintain fruit quality. This solution has good operability and adaptability, is suitable for practical application scenarios such as supermarkets, and has high market conversion potential and application prospects. Attached Figure Description

[0031] Figure 1 The flowchart illustrates the preparation process of the PCTH@CAR composite aerogel provided by this invention.

[0032] Figure 2 PC, PCT, and PCT-Cu prepared in Comparative Examples 1-4 2+ Scanning electron microscope (SEM) image of PCTH composite aerogel (10 μm scale).

[0033] Figure 3 The images are scanning electron microscope (SEM) images (10 μm scale) of the PCTH composite aerogels prepared in Examples 1-3 (A is Example 1, B is Example 2, and C is Example 3).

[0034] Figure 4 The humidity response release diagram is shown for the PCTH@CAR prepared in Example 1.

[0035] Figure 5The images show the antibacterial effects of PCTH and PCTH@CAR prepared in Comparative Example 4 and Example 1 against Escherichia coli and Staphylococcus aureus.

[0036] Figure 6 The image shows the antibacterial effect of PCTH and PCTH@CAR prepared in Comparative Example 4 and Example 1 against Botrytis cinerea.

[0037] Figure 7 The images show the preservation effects of PCT, PCTH, and PCTH@CAR prepared in Comparative Examples 2, 4, and 1 on strawberries. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0039] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0040] This embodiment uses carvacrol as a representative essential oil for loading and performance verification, to illustrate the technical effects of the composite aerogel of the present invention in the slow release, antibacterial and practical preservation applications of volatile essential oils, but the scope of protection of the present invention is not limited to carvacrol.

[0041] Example 1 A method for preparing a carvacrol-loaded composite aerogel (denoted as PCTH@CAR) includes the following steps: S01, Preparation of carboxymethyl chitosan / polyvinyl alcohol / cellulose nanofiber hydrogel The final total volume of the reaction system was predetermined (100 mL). Polyvinyl alcohol (PVA) was added to an appropriate amount of deionized water at a final concentration of 2 g / mL. The mixture was heated and stirred in a 95 °C water bath for 2 hours. After cooling to room temperature, a TEMPO oxidized nanocellulose (TOCNF) aqueous dispersion (1.2 g / mL) was added to bring the final concentration in the reaction system to 0.6 g / mL, and the mixture was magnetically stirred. Subsequently, carboxymethyl chitosan (CMCS) powder was slowly added to bring the final concentration in the reaction system to 4 g / mL. A second water bath heating was performed, and stirring was continued at 45 °C for 1 hour to obtain a homogeneous PVA / CMCS / TOCNF pregel solution. The obtained pregel solution was injected into a mold, and the mixture was subjected to three freeze-thaw cycles to obtain a PVA / CMCS / TOCNF hydrogel, denoted as PCT. S02, In-situ synthesis of HKUST-1 inside the hydrogel The PCT hydrogel obtained in the above steps was cut into small pieces of 1cm × 1cm × 0.5cm and soaked in 0.1 mol / L copper acetate monohydrate solution for 12 hours. It was then washed with deionized water at least 5 times until no copper ions remained in the washing solution, yielding PVA / CMCS / TOCNF / Cu. 2+ Hydrogel, denoted as PCT-Cu 2+ .

[0042] The PCT-Cu after the above washing process 2+ The hydrogel was immersed in a prepared 0.2 mol / L pyromellitic acid solution (pre-adjusted to pH 3.1) for 3 hours. The hydrogel was then removed, thoroughly washed, and subsequently freeze-dried for 48 hours to obtain PVA / CMCS / TOCNF / HKUST-1 aerogel, denoted as PCTH.

[0043] S03, composite MOFs aerogel loaded with carvacrol The PCTH aerogel obtained in the above steps was immersed in a 20% (v / v) carvacrol ethanol solution at 4 ℃ in the dark for 24 hours, and then dried overnight at room temperature in a vacuum drying oven to obtain PVA / CMCS / TOCNF / HKUST-1@CAR aerogel, denoted as PCTH@CAR aerogel.

[0044] Example 2 A method for preparing a carvacrol-loaded composite aerogel (denoted as PCTH@CAR) includes the following steps: S01, Preparation of carboxymethyl chitosan / polyvinyl alcohol / cellulose nanofiber hydrogel The total volume of the final reaction system was predetermined to be 100 mL. Polyvinyl alcohol (PVA) was added to an appropriate amount of deionized water at a final concentration of 4 g / mL. The mixture was heated and stirred in an 80°C water bath for 4 hours. After cooling to room temperature, a TEMPO oxidized nanocellulose (TOCNF) aqueous dispersion (4.0 g / mL concentration) was added to achieve a final concentration of 0.8 g / mL in the reaction system, and the mixture was magnetically stirred. Subsequently, carboxymethyl chitosan (CMCS) powder was slowly added to achieve a final concentration of 5 g / mL in the reaction system. A second water bath heating was performed, and stirring was continued at 60°C for 0.5 hours to obtain a homogeneous PVA / CMCS / TOCNF pregel solution. The obtained pregel solution was injected into a mold, and the mixture was subjected to 5 freeze-thaw cycles to obtain a PVA / CMCS / TOCNF hydrogel, denoted as PCT. S02, In-situ synthesis of HKUST-1 inside the hydrogel The PCT hydrogel obtained in the above steps was cut into small pieces of 1cm × 1cm × 0.5cm and soaked in a 0.5 mol / L copper acetate monohydrate solution for 8 hours. It was then washed with deionized water at least 5 times until no copper ions remained in the washing solution, yielding PVA / CMCS / TOCNF / Cu. 2+ Hydrogel, denoted as PCT-Cu 2+ .

[0045] The PCT-Cu after the above washing process 2+ The hydrogel was immersed in a prepared 0.5 mol / L pyromellitic acid solution (pre-adjusted to pH 2.5) for 2 hours. The hydrogel was then removed, thoroughly washed, and subsequently freeze-dried for 48 hours to obtain PVA / CMCS / TOCNF / HKUST-1 aerogel, denoted as PCTH.

[0046] S03, composite MOFs aerogel loaded with carvacrol The PCTH aerogel obtained in the above steps was immersed in a 40% (v / v) carvacrol ethanol solution at 4 ℃ in the dark for 10 hours, and then dried overnight at room temperature in a vacuum drying oven to obtain PVA / CMCS / TOCNF / HKUST-1@CAR aerogel, denoted as PCTH@CAR aerogel.

[0047] Example 3 A method for preparing a carvacrol-loaded composite aerogel (denoted as PCTH@CAR) includes the following steps: S01, Preparation of carboxymethyl chitosan / polyvinyl alcohol / cellulose nanofiber hydrogel The total volume of the final reaction system was predetermined to be 100 mL. Polyvinyl alcohol (PVA) was added to an appropriate amount of deionized water at a final concentration of 1 g / mL. The mixture was heated and stirred in a water bath at 100°C for 2 hours. After cooling to room temperature, a TEMPO oxidized nanocellulose (TOCNF) aqueous dispersion (with a concentration of 0.5 g / mL) was added to achieve a final concentration of 0.4 g / mL in the reaction system, and the mixture was magnetically stirred. Subsequently, carboxymethyl chitosan (CMCS) powder was slowly added to achieve a final concentration of 2 g / mL in the reaction system. A second water bath heating was performed, and stirring was continued at 30°C for 2 hours to obtain a homogeneous PVA / CMCS / TOCNF pregel solution. The obtained pregel solution was injected into a mold, and the mixture was subjected to three freeze-thaw cycles to obtain a PVA / CMCS / TOCNF hydrogel, denoted as PCT. S02, In-situ synthesis of HKUST-1 inside the hydrogel The PCT hydrogel obtained in the above steps was cut into small pieces of 1cm × 1cm × 0.5cm and soaked in 0.1 mol / L copper acetate monohydrate solution for 12 hours. It was then washed with deionized water at least 5 times until no copper ions remained in the washing solution, yielding PVA / CMCS / TOCNF / Cu. 2+ Hydrogel, denoted as PCT-Cu 2+ .

[0048] The PCT-Cu after the above washing process 2+ The hydrogel was immersed in a prepared 0.1 mol / L pyromellitic acid solution (pre-adjusted to pH 3.5) for 8 hours. The hydrogel was then removed, thoroughly washed, and subsequently freeze-dried for 48 hours to obtain PVA / CMCS / TOCNF / HKUST-1 aerogel, denoted as PCTH.

[0049] S03, composite MOFs aerogel loaded with carvacrol The PCTH aerogel obtained in the above steps was immersed in a 5% (v / v) carvacrol ethanol solution at 4 ℃ in the dark for 30 hours, and then dried overnight at room temperature in a vacuum drying oven to obtain PVA / CMCS / TOCNF / HKUST-1@CAR aerogel, denoted as PCTH@CAR aerogel.

[0050] Comparative Example 1 The final total volume of the reaction system was predetermined to be 100 mL. Polyvinyl alcohol (PVA) was added to an appropriate amount of deionized water at a final concentration of 2 g / mL. The mixture was heated and stirred in a 95 °C water bath for 2 hours. After cooling to room temperature, carboxymethyl chitosan (CMCS) powder was slowly added to achieve a final concentration of 4 g / mL. A second water bath heating was then performed, and the mixture was stirred at 45 °C for 1 hour to obtain a homogeneous PVA / CMCS / TOCNF pregel solution. The obtained pregel solution was injected into a mold, subjected to three freeze-thaw cycles, and freeze-dried for 48 hours to obtain a PVA / CMCS aerogel, denoted as PC.

[0051] Comparative Example 2 The total volume of the final reaction system was predetermined to be 100 mL. Polyvinyl alcohol (PVA) was added to an appropriate amount of deionized water at a final concentration of 2 g / mL. The mixture was heated and stirred in a 95 °C water bath for 2 hours. After cooling to room temperature, a TEMPO oxidized nanocellulose (TOCNF) aqueous dispersion (with a concentration of 1.2 g / mL) was added to achieve a final concentration of 0.6 g / mL in the reaction system, and the mixture was magnetically stirred. Subsequently, carboxymethyl chitosan (CMCS) powder was slowly added to achieve a final concentration of 4 g / mL in the reaction system. A second water bath heating was performed, and stirring was continued at 45 °C for 1 hour to obtain a homogeneous PVA / CMCS / TOCNF pregel solution. The obtained pregel solution was injected into a mold, subjected to three freeze-thaw cycles, and freeze-dried for 48 hours to obtain a PVA / CMCS / TOCNF aerogel, denoted as PCT.

[0052] Comparative Example 3 The total volume of the final reaction system was predetermined to be 100 mL. Polyvinyl alcohol (PVA) was added to an appropriate amount of deionized water at a final concentration of 2 g / mL. The mixture was heated and stirred in a 95 °C water bath for 2 hours. After cooling to room temperature, a TEMPO oxidized nanocellulose (TOCNF) aqueous dispersion (with a concentration of 1.2 g / mL) was added to achieve a final concentration of 0.6 g / mL in the reaction system, and the mixture was magnetically stirred. Subsequently, carboxymethyl chitosan (CMCS) powder was slowly added to achieve a final concentration of 4 g / mL in the reaction system. A second water bath heating was performed, and stirring was continued at 45 °C for 1 hour to obtain a homogeneous PVA / CMCS / TOCNF pregel solution. The obtained pregel solution was injected into a mold, and the mixture was subjected to three freeze-thaw cycles to obtain a PVA / CMCS / TOCNF hydrogel, denoted as PCT.

[0053] The PCT hydrogel obtained in the above steps was cut into small pieces of 1 cm × 1 cm × 0.5 cm and soaked in 0.1 mol / L copper acetate monohydrate solution for 12 hours. It was washed with deionized water more than 5 times until no copper ions remained in the washing solution. The gel was then freeze-dried for 48 hours to obtain PVA / CMCS / TOCNF / Cu. 2+ Aerogel, denoted as PCT-Cu 2+ .

[0054] Comparative Example 4 S01, Preparation of carboxymethyl chitosan / polyvinyl alcohol / cellulose nanofiber hydrogel The final total volume of the reaction system was predetermined (100 mL). Polyvinyl alcohol (PVA) was added to an appropriate amount of deionized water at a final concentration of 2 g / mL. The mixture was heated and stirred in a 95 °C water bath for 2 hours. After cooling to room temperature, a TEMPO oxidized nanocellulose (TOCNF) aqueous dispersion (1.2 g / mL) was added to bring the final concentration in the reaction system to 0.6 g / mL, and the mixture was magnetically stirred. Subsequently, carboxymethyl chitosan (CMCS) powder was slowly added to bring the final concentration in the reaction system to 4 g / mL. A second water bath heating was performed, and stirring was continued at 45 °C for 1 hour to obtain a homogeneous PVA / CMCS / TOCNF pregel solution. The obtained pregel solution was injected into a mold, and the mixture was subjected to three freeze-thaw cycles to obtain a PVA / CMCS / TOCNF hydrogel, denoted as PCT. S02, In-situ synthesis of HKUST-1 inside the hydrogel The PCT hydrogel obtained in the above steps was cut into small pieces of 1 cm × 1 cm × 0.5 cm and soaked in 0.1 mol / L copper acetate monohydrate solution for 12 hours. It was then washed with deionized water at least 5 times until no copper ions remained in the washing solution, yielding PVA / CMCS / TOCNF / Cu. 2+ Hydrogel, denoted as PCT-Cu 2+ .

[0055] The PCT-Cu after the above washing process 2+ The hydrogel was immersed in a prepared 0.2 mol / L pyromellitic acid solution (pre-adjusted to pH 3.1) for 3 hours. The hydrogel was then removed, washed thoroughly, and subsequently freeze-dried for 48 hours to obtain PVA / CMCS / TOCNF / HKUST-1 aerogel, denoted as PCTH.

[0056] Experimental Example 1: PC, PCT, and PCT-Cu prepared in Comparative Examples 1-4 2+ SEM characterization of PCTH and PCTH in Examples 1-3 After vacuum sputtering, PC, PCT, and PCT-Cu were observed using a scanning electron microscope (SEM). 2+ The surface microstructure of PCTH aerogel.

[0057] Figure 2 The PC, PCT, and PCT-Cu prepared in Comparative Examples 1-4 are shown. 2+ Scanning electron microscope (SEM) image of the PCTH composite aerogel. Figure 2As shown, pure PC aerogel exhibits a loose and disordered lamellar structure with uneven pore distribution. After introducing TOCNF, the PCT aerogel, while maintaining its original lamellar framework, shows the appearance of a small number of fine filamentous networks supporting the interlayer. With the introduction of copper ions, PCT-Cu²... + It exhibits numerous dense spiderweb-like structures, densely attached to the original lamellar structure. In PCT-Cu² + After in-situ synthesis of HKUST-1 in the matrix, the PCTH aerogel forms a dense, highly cross-linked, spiderweb-like structure with small pores, which can adsorb a certain amount of carvacrol and achieve a sustained-release effect. In addition, a large number of regular polyhedral crystals are uniformly grown on the surface and inside of the spiderweb-like structure. These crystals have a characteristic octahedral shape, similar to the shape of HKUST-1, indicating that HKUST-1 has been successfully anchored inside the aerogel.

[0058] Figure 3 The following are scanning electron microscope (SEM) images of the PCTH composite aerogels prepared in Examples 1-3. Figure 3 In this context, A represents Example 1, B represents Example 2, and C represents Example 3. Figure 3 As shown, the PCTH aerogel obtained exhibits a dense three-dimensional network structure with octahedral HKUST-1 uniformly distributed inside. Examples 1-3 are basically consistent in surface morphology.

[0059] Experimental Example 2: Investigation of the humidity response performance of the PCTH@CAR prepared in Example 1 To verify the humidity response performance of PCTH loaded with volatile essential oil (carvacrol CAR) in Example 1, the loading and performance of the PCTH@CAR prepared in Example 1 were verified. Different saturated salt solutions were used to simulate environments with different relative humidity to evaluate the controlled release capability of the composite material.

[0060] Three saturated salt solutions—potassium carbonate (K₂CO₃, RH 43%), sodium chloride (NaCl, RH 75%), and potassium sulfate (K₂SO₄, RH 98%)—were used to simulate environments with different relative humidity levels. A low-humidity environment (RH 15%) was constructed using desiccant beads. The three saturated salt solutions and the desiccant beads were placed in sealed desiccators with a diameter of 180 mm. After humidity equilibration, approximately 3 g of PCTH@CAR composite aerogel samples were added to each, and the samples were stored under constant humidity conditions for 12 days. Samples were taken every 24 hours to determine the residual amount of the guest CAR molecule in the composite material, thereby analyzing its humidity-responsive release behavior.

[0061] Accurately measure 15 mg of PCTH@CAR composite aerogel and place it in 30 mL of anhydrous ethanol. Extract by ultrasonication for 30 minutes to fully elute the loaded carvacrol. Dilute the extract to an appropriate factor and measure its absorbance at 275 nm using a UV-Vis spectrophotometer. Calculate the CAR content of the sample based on the pre-established CAR standard curve equation, thereby obtaining the actual loading of guest molecules in the PCTH@CAR composite material. The cumulative release rate is calculated using the following formula.

[0062]

[0063] Figure 4 The humidity response release diagram of the PCTH@CAR prepared in Example 1 is shown. Figure 4 As shown, at a humidity level of 98%, the cumulative release rate of PCTH@CAR over 12 days was 81.99%. At 43% and 75% humidity, the cumulative release rates were 57.40% and 66.53%, respectively. The lowest cumulative release rate (54.32%) was observed at 15% humidity. This indicates that the gas-phase release rate of CAR increases with increasing humidity, and the curve rises more rapidly. This demonstrates that PCTH@CAR exhibits typical humidity-triggered controlled-release characteristics; high humidity conditions significantly enhance the release of active ingredients, which is beneficial for achieving adaptive antibacterial activity in the high respiratory humidity environment of fruits and vegetables.

[0064] Experimental Example 3: Study on the antibacterial properties of composite aerogels (1) Study on the antibacterial effects of PCTH and PCTH@CAR prepared in Example 1 and Comparative Example 4 against Escherichia coli and Staphylococcus aureus. Take 10 5 CFU / mL of Escherichia coli E. coli ) and Staphylococcus aureus ( S.aureus 100 μL of bacterial suspension was evenly spread on LB solid medium. A composite aerogel (1 cm × 1 cm × 0.5 cm) was fixed to the inside of the petri dish lid with sterile tape. The control group (without composite aerogel fixation), PCTH and PCTH@CAR treatment groups were incubated upside down at 37°C for 18 hours, and the growth of the two bacteria was observed and recorded.

[0065] Figure 5 The antibacterial effects of PCTH and PCTH@CAR prepared in Comparative Example 4 and Example 1 against Escherichia coli and Staphylococcus aureus are shown in the diagram. Figure 5As shown, for *Escherichia coli* and *Staphylococcus aureus*, abundant colony growth was observed in both the control and PCTH-treated groups, with uniform colony distribution. In the PCTH@CAR-treated group, a clear and large inhibition zone formed in the center of the culture medium. No colony growth was observed near the PCTH@CAR composite aerogel, while a small number of colonies remained at the edge of the petri dish, indicating that its antibacterial effect exhibits a certain spatial gradient characteristic, belonging to a typical gas-phase release inhibition mode. Furthermore, the diameter of the inhibition zone formed by PCTH@CAR for *Staphylococcus aureus* was significantly larger than that in the *Escherichia coli* group, indicating that the sustained release of CAR has a more significant inhibitory effect on Gram-positive bacteria, reflecting the differences in the sensitivity of different bacterial species to volatile active ingredients.

[0066] (2) Study on the antibacterial effect of PCTH and PCTH@CAR prepared in Example 4 and Comparative Example 4 against Botrytis cinerea.

[0067] Scrape Botrytis cinerea ( B.cinerea ) spores were dispersed in sterile PBS buffer to prepare a spore suspension (10 6 (spores / mL), 10 μL of spore suspension was dropped into the center of PDA solid medium. After air drying, a 1cm×1cm×0.5cm composite aerogel was fixed to the inside of the petri dish lid with sterile tape. The control group (without composite aerogel) and the PCTH and PCTH@CAR treatment groups were incubated upside down at 28℃ for 7 days, and the colony growth of Botrytis cinerea was observed and recorded.

[0068] Figure 6 The antibacterial effects of PCTH and PCTH@CAR prepared in Comparative Example 4 and Example 1 against *Botrytis cinerea* are shown in the diagram. Figure 6 As shown, after 7 days of incubation at 28℃, large areas of mold growth were observed in both the control group and the PCTH-treated group. The mycelium grew vigorously and was dark in color, appearing grayish-black, indicating that PCTH had a limited inhibitory effect on Botrytis cinerea. In contrast, no obvious mycelial growth was observed on the surface of the culture medium in the PCTH@CAR-treated group, demonstrating excellent antifungal activity. Its antibacterial effect mainly comes from the gas-phase antibacterial effect produced by the continuous release of carvacrol.

[0069] Experimental Example 4: Test on the Preservation Effect of Composite Aerogel on Strawberries Figure 1 A schematic diagram of the application of the PCTH@CAR composite aerogel provided by the present invention in strawberry preservation is shown.

[0070] Fresh, undamaged, and pest-free strawberries were selected. Four pieces of PCT, PCTH, and PCTH@CAR prepared in Comparative Example 2, Comparative Example 4, and Example 1, each measuring 1cm×1cm×0.5cm, were taken and packaged in non-woven bags with excellent air permeability. These bags were then fixed to the top of a food storage box. The same number (4 strawberries) of strawberries were placed inside the food storage box. The strawberries were stored for 8 days, and their appearance was recorded every 2 days.

[0071] Figure 7 The preservation effects of PCT, PCTH, and PCTH@CAR prepared in Comparative Examples 2, 4, and 1 on strawberries are shown in the diagrams. CK represents the control group without encapsulation of the composite aerogel. From... Figure 7 It can be seen that the PCTH@CAR composite aerogel significantly extends the shelf life of strawberries and has a significant inhibitory effect on mold. During storage, white mycelia appeared on strawberries in all groups starting from the 4th day, gradually covering the entire strawberry over time. In the example, no mold mycelia appeared in the PCTH@CAR treatment group within 8 days, indicating that it has obvious antibacterial and preservation effects.

[0072] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A composite aerogel with humidity-controlled release function, characterized in that, It includes polysaccharide-based hydrogels, a metal-organic framework HKUST-1, and volatile essential oils; among which: (1) The polysaccharide-based hydrogel is a double-network hydrogel synthesized by polyvinyl alcohol (PVA), carboxymethyl chitosan (CMCS), TEMPO oxidized nanocellulose (TOCNF) and copper ion solution in a physicochemical double cross-linking manner. (2) The metal-organic framework HKUST-1 is uniformly fixed in the composite aerogel in an anchoring manner; (3) Volatile essential oils, including carvacrol (CAR), cinnamaldehyde and thymol, are loaded as guest molecules by composite aerogel and metal-organic framework HKUST-1.

2. The composite aerogel with humidity-controlled release function according to claim 1, characterized in that, As humidity increases, the release rate of volatile essential oils loaded on the composite aerogel accelerates, enabling timely release and long-lasting antibacterial effect.

3. The method for preparing a composite aerogel with humidity-controlled release function as described in claim 1, characterized in that, Includes the following steps: S01, Preparation of carboxymethyl chitosan / polyvinyl alcohol / cellulose nanofiber hydrogel Polyvinyl alcohol (PVA) was added to deionized water and heated and stirred in a water bath. After cooling to room temperature, TEMPO-oxidized nanocellulose (TOCNF) aqueous dispersion was added and magnetically stirred. Subsequently, carboxymethyl chitosan (CMCS) powder was slowly added; a second water bath heating was performed, and stirring was continued at 30-60°C for 0.5-2 hours to obtain a homogeneous PVA / CMCS / TOCNF pregel solution; the obtained pregel solution was injected into a mold and subjected to freeze-thaw cycles to obtain a PVA / CMCS / TOCNF hydrogel, denoted as PCT. S02, In-situ synthesis of HKUST-1 inside the hydrogel The PCT hydrogel obtained in the above steps was cut into small pieces, soaked in copper acetate monohydrate solution, and washed with deionized water until no copper ions remained in the washing solution, yielding PVA / CMCS / TOCNF / Cu. 2+ Hydrogel, denoted as PCT-Cu 2+ ; the washed PCT-Cu 2+ The hydrogel was immersed in a pyromellitic acid solution; the hydrogel was removed, washed thoroughly, and then freeze-dried to obtain PVA / CMCS / TOCNF / HKUST-1 aerogel, denoted as PCTH; S03, volatile essential oils loaded in composite MOFs aerogel The PCTH aerogel obtained in the above steps is immersed in an essential oil ethanol solution, protected from light, and dried overnight at room temperature in a vacuum drying oven to obtain PVA / CMCS / TOCNF / HKUST-1@essential oil aerogel, denoted as PCTH@essential oil aerogel, which is a composite aerogel with humidity-controlled release function.

4. The preparation method according to claim 3, characterized in that, In step S01, the final concentration of polyvinyl alcohol (PVA) is 1-4 g / mL; the final concentration of carboxymethyl chitosan (CMCS) is 2-5 g / mL.

5. The preparation method according to claim 3, characterized in that, In step S01, the concentration of the TEMPO-oxidized nanocellulose TOCNF aqueous dispersion is 0.5-4.0 g / mL, and the final concentration of TOCNF is 0.4-0.8 g / mL.

6. The preparation method according to claim 3, characterized in that, In step S01, the first water bath temperature is 80-100℃ and the time is 2-4 hours; the second water bath temperature is 30-60℃ and the time is 0.5-2 hours; the number of freeze-thaw cycles is 3-5.

7. The preparation method according to claim 3, characterized in that, In step S02, the concentration of the copper acetate monohydrate solution is 0.1-0.5 mol / L, and the soaking time in the copper acetate monohydrate solution is 8-12 hours.

8. The preparation method according to claim 3, characterized in that, In step S02, the concentration of the trimellitic acid solution is 0.1-0.5 mol / L, the pH value of the trimellitic acid solution is 2.5-3.5, and the soaking time in the trimellitic acid solution is 2-8 hours.

9. The preparation method according to claim 3, characterized in that, In step S03, the volume fraction of the essential oil ethanol solution is 5-40%, and the soaking time in the dark is 10-30 hours.

10. The application of the composite aerogel with humidity control and release function as described in claim 1 in the field of strawberry preservation.

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