Preparation method and application of chitosan-based aerogel with controlled release of citral triggered by CO2 responsiveness

Abstract

The invention belongs to a preparation method of a fresh-keeping material, and particularly relates to a preparation method of chitosan-based aerogel capable of triggering controlled release of citral in a CO2 responsive manner, which comprises the following steps: synthesizing carboxylated carbon nanotube / chitosan aerogel from chitosan and carboxylated carbon nanotubes, loading citral, and drying to obtain the chitosan-based aerogel capable of triggering controlled release of citral in a CO2 responsive manner. Citral / carboxylated carbon nanotube / chitosan aerogel is obtained, the citral / carboxylated carbon nanotube / chitosan aerogel is loaded with a CO2 responsive polymer, and the CO2 responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel is obtained. The problems that an existing environment response type fresh-keeping material is poor in environment responsiveness and difficult to recycle are solved. The method has the advantages that acid-sensitive Schiff base bonds are triggered to break after a large amount of CO2 is adsorbed, rapid and large-amount release of Cit is achieved, microbial growth is efficiently inhibited, and the storage time of mangoes is prolonged; after the Cit is completely released, the Cit can be loaded again, so that the recycling of the aerogel is realized, and the like.

Description

Technical Field

[0001] This invention pertains to the preparation methods of fruit preservation materials, specifically relating to the preparation method and application of a CO2-responsive citral-controlled release chitosan-based aerogel. Background Technology

[0002] Mangoes, a popular tropical fruit, are renowned for their strong adaptability, high resistance to adverse conditions, early maturity, high yield, ease of management, and long economic lifespan. They are loved by consumers not only for their rich nutrition and unique flavor. However, mangoes are climacteric fruits, meaning they release ethylene during storage. This accelerates respiration, producing large amounts of carbon dioxide and water vapor, which react to form carbonic acid, making the environment inside the packaging acidic. This acidic environment promotes microbial growth, accelerates mango decay, and severely restricts the development of the mango industry.

[0003] Currently, mango preservation mainly relies on chemical methods such as fungicides, preservatives, and pesticides as post-harvest treatment. However, with the increasing demand for green and healthy foods, researching and developing safe, efficient, environmentally friendly, and easy-to-implement post-harvest preservation technologies for mangoes has become a major research direction in the field of mango preservation.

[0004] One type of material used in food preservation is the responsive smart material. Responsive smart materials are materials that can undergo physical or chemical changes in response to external environmental influences, thereby altering their properties (such as charge characteristics, hydrophilicity / hydrophobicity, and pore structure). These materials can be categorized into various response types based on different external stimuli, such as temperature, pH, gas, and light. CO2-responsive smart materials, in particular, have seen extensive research in the field of food preservation.

[0005] For example, existing technology researchers Wen et al. (Haiyu Du, Xinru Liu, Xiaoli Sun, Heng An, Yiyi Li, Zhu Zhu, Yongqiang Wen, CO2 responsive multifunctional label based on chitosan and hyaluronic acid for visualizing and maintaining postharvestfreshness, Food Hydrocolloids, 2024, 157, 110438) disclosed that they prepared a composite membrane that releases the antibacterial agent Eug when stimulated by CO2 by incorporating the antibacterial agent eugenol (Eug) into a 3-carboxyphenylboronic acid grafted chitosan / dopamine / hyaluronic acid (CPDH) matrix containing acid-sensitive borate ester bonds. In the acidic environment caused by CO2 accumulation, the composite membrane causes the borate ester bonds to break, releasing the Eug antibacterial agent. The results showed that the composite membrane had a significant inhibitory effect on Escherichia coli, Staphylococcus aureus, and Botrytis cinerea, and could extend the shelf life of strawberries to 5 days.

[0006] Furthermore, existing technology, as disclosed by Tang et al. (Xianhui Tang, Meiyan Zhu, Ling Zhang, Liang Zhu, Development of cinnamaldehyde / aminated gelatin film as pH-responsive controlled-release packaging for cherry preservation: Effects of CO2 and humidity in the microenvironment, Food Packaging and Shelf Life, 2025, 48, 101457), involves the preparation of a Cin / AGel film containing acid-sensitive Schiff base groups (R–CH=N–) through a chemical reaction between the aldehyde group (R–CHO) in the cinnamaldehyde (Cin) molecule and the amino group (–NH2) in the aminated gelatin (AGel) molecule. The study found that the acidic environment created by CO2 accumulation and high humidity triggers the breaking of the Schiff base bond, thereby releasing Cin, exhibiting excellent pH-responsive controlled-release characteristics. Compared to using only AGel film, cherries packaged with Cin / AGel film have a shelf life extended by 6 days.

[0007] However, essential oils typically contain hydrophobic groups, which increases the hydrophobicity of the composite material, reduces its responsiveness to CO2, and weakens the controlled release effect of the essential oil. Furthermore, the membrane material cannot be reused, resulting in high costs for practical applications. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing and applying a CO2-responsive, citral-controlled release chitosan-based aerogel. This chitosan aerogel can control the release of citral through the CO2 released by the mango during the mango preservation process, achieving precise preservation.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] A method for preparing a CO2-responsive citral-controlled release chitosan-based aerogel involves synthesizing a carboxylated carbon nanotube / chitosan aerogel (CCNT / CA) by combining chitosan and carboxylated carbon nanotubes, and loading citral, which has excellent antibacterial properties, to obtain a citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA). The obtained citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA) is then loaded with a CO2-responsive polymer P(AA-co-DMAEMA) to obtain a CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel (P(AA-co-DMAEMA) / Cit@CCNT / CA, abbreviated as P / Cit@CCNT / CA).

[0011] As a further improvement to the technical solution, the preparation of the carboxylated carbon nanotube / chitosan aerogel is as follows: 0.01-0.03g of carboxylated carbon nanotubes are placed in a beaker, 12-16mL of distilled water is added, and the mixture is sonicated for 30-60min. Then, 0.2-0.4g of chitosan is added, followed by 0.2-0.4mL of glacial acetic acid. The mixture is stirred until the chitosan is completely dissolved, and then dispersed using a high-speed homogenizer at 15000-20000rpm for 4-10min to obtain a mixed solution for later use.

[0012] Take 1.5-2 mL of the mixed solution, dispense it into 5 mL beakers, freeze them in a refrigerator, and then freeze-dry them. Take out the sample, add 2-5% ammonia solution and soak for 1-3 hours, wash with distilled water until neutral, freeze-dry, and obtain carboxylated carbon nanotube / chitosan aerogel.

[0013] As a further improvement to the technical solution, the preparation of the citral / carboxylated carbon nanotube / chitosan aerogel is as follows: Take 50-80 mL of anhydrous ethanol into an Erlenmeyer flask, add 0.5 g-1.5 g of citral, shake well, and then add 0.2 g-0.5 g of carboxylated carbon nanotube / chitosan aerogel. React in a shaking water bath at 50-70°C for 24-36 h. Take out the sample and air dry it at room temperature to obtain the citral / carboxylated carbon nanotube / chitosan aerogel.

[0014] As a further improvement to the technical solution, the mass ratio of citral to carboxylated carbon nanotubes / chitosan aerogel is 0.5-1.5:0.1-0.5.

[0015] As a further improvement to the technical solution, the preparation of the CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel is as follows: 0.05-0.07 g N,N-methylenebisacrylamide, 0.01-0.03 g sodium persulfate and 20-30 mL distilled water are added to a single-necked flask and stirred to dissolve. Then, 0.5 mL-2 mL of dimethylaminoethyl methacrylate and 0.5 mL-1 mL of acrylic acid are added dropwise to the mixed solution. The flask is placed in a water bath at 60℃-90℃ and reacted for 2-5 hours. The polymerization reaction must be carried out under an N2 atmosphere. The resulting copolymer is freeze-dried to obtain the CO2-responsive polymer.

[0016] Take 0.1–0.5 g of CO2-responsive polymer in a beaker, add 100–150 mL of distilled water and 0.1–0.2 mL of glacial acetic acid, stir and dissolve in a water bath at 40–70 °C, add 0.5–2 g of citral / carboxylated carbon nanotube / chitosan aerogel, soak in a shaking water bath for 1–3 h, and then freeze-dry to obtain CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel.

[0017] As a further improvement to the technical solution, the volume ratio of dimethylaminoethyl methacrylate to acrylic acid is 0.5-2:0.5-1.

[0018] As a further improvement to the technical solution, the temperature during the polymerization reaction is 60–90°C, and the reaction time is 0.5–5 h.

[0019] As a further improvement to the technical solution, the CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel exhibits hydrophilicity in air, with a surface contact angle of 0–5° with water.

[0020] Application of a CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel as described above in mango preservation.

[0021] As a further improvement to the technical solution, the CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel can extend the shelf life of fresh mangoes to 13-15 days under conditions of 20-25 °C.

[0022] The chitosan (CS) of this invention is obtained by deacetylation of chitin from shrimp and crab shells, and is a natural polymer with excellent biocompatibility and non-toxicity. Its molecular structure is rich in active groups such as amino (–NH2) and hydroxyl (–OH).

[0023] The chitosan-based aerogel of the present invention has a three-dimensional porous network structure, which not only has excellent adsorption and diffusion capabilities, but also makes it an ideal carrier for active substances such as plant essential oils.

[0024] The carboxylated carbon nanotubes of the present invention are rich in carboxyl (-COOH) functional groups, which can generate strong electrostatic interactions with the amino (-NH2) groups in chitosan molecules, thereby enhancing the structural stability and specific surface area of ​​chitosan aerogels.

[0025] The CO2-responsive polymer of the present invention exhibits excellent responsiveness to CO2.

[0026] The preparation principle of this invention: Addressing the problems of poor environmental responsiveness and difficulty in recycling existing environmentally responsive preservation materials, this study combines the raw material characteristics of chitosan, carboxylated carbon nanotubes, citral, and the CO2-responsive polymer P(AA-co-DMAEMA). Using chitosan and carboxylated carbon nanotubes as the main raw materials, a carboxylated carbon nanotube / chitosan aerogel (CCNT / CA) is synthesized via freeze-drying. Subsequently, cinnamaldehyde, which has excellent antibacterial properties, is loaded using a Schiff base reaction to prepare cinnamaldehyde@carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA). Finally, the CO2-responsive polymer P(AA-co-DMAEMA) is loaded via impregnation to obtain P(AA-co-DMAEMA) / cinnamaldehyde@carboxylated carbon nanotube / chitosan aerogel (P(AA-co-DMAEMA) / Cit@CCNT / CA, abbreviated as P / Cit@CCNT / CA), which is then applied to the storage and preservation of mangoes.

[0027] The achievements of this invention are as follows: (1) Since the CO2-responsive polymer is located on the outermost layer of the aerogel composite system, it can encapsulate Cit and act as a "smart switch" to regulate the release of Cit; (2) In the early stage of preservation, the CO2 concentration in the microenvironment is low, and P / Cit@CCNT / CA slowly releases a small amount of Cit through the aerogel channels to achieve antibacterial preservation; (3) As the storage time increases, CO2 and H2O gradually accumulate in the microenvironment. After the CO2-responsive polymer adsorbs a large amount of CO2, the pH of the aerogel system decreases, triggering the breakage of acid-sensitive Schiff base bonds, realizing the rapid and large-scale release of Cit, effectively inhibiting the growth of microorganisms, thereby extending the storage time of mangoes; (4) Based on the reversibility of Schiff base bonds, P / Cit@CCNT / CA after complete release of Cit can be loaded with Cit again to realize the recycling of aerogel. This invention can have an important impact on the development of environmentally friendly, safe, and efficient smart preservation materials, and helps to extend the shelf life of fruits and reduce post-harvest losses.

[0028] The present invention represents a significant advancement over the prior art:

[0029] 1. The chitosan-based aerogel of the present invention has a CO2-responsive polymer located in the outermost layer of the aerogel composite system, which can encapsulate Cit and act as a "smart switch" to regulate the release of Cit.

[0030] 2. In the early stage of preservation, the CO2 concentration in the microenvironment is low. The P / Cit@CCNT / CA of this invention only slowly releases a small amount of Cit through the aerogel channels to achieve antibacterial preservation.

[0031] 3. As storage time increases, CO2 and H2O gradually accumulate in the microenvironment. After the CO2-responsive polymer adsorbs a large amount of CO2, the pH of the P / Cit@CCNT / CA system of the present invention decreases, triggering the breakage of acid-sensitive Schiff base bonds, thereby achieving rapid and large-scale release of Cit and effectively inhibiting microbial growth. The present invention can extend the storage time of mangoes by up to 15 days, which is at least 6 to 9 days longer than the existing technology.

[0032] 4. After the P / Cit@CCNT / CA of this invention completely releases Cit, it can be reloaded with Cit based on the reversibility of the Schiff base bond, enabling the material to be recycled. This invention can have a significant impact on the development of environmentally friendly, safe, and efficient intelligent preservation materials, helping to extend the shelf life of fruits and reduce post-harvest losses. Attached Figure Description

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0034] Figure 1 SEM images of chitosan aerogel (CA), carboxylated carbon nanotube / chitosan aerogel (CCNT / CA), citral / carboxylated carbon nanotube / chitosan aerogel prepared in Comparative Example 1 (Cit@CCNT / CA), and CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel prepared in Example 1 (P / Cit@CCNT / CA).

[0035] Figure 2 FT-IR images of carboxylated carbon nanotubes (CCNT), chitosan (CS), carboxylated carbon nanotube / chitosan aerogel (CCNT / CA), citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA) prepared in Comparative Example 1, and CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel (P / Cit@CCNT / CA) prepared in Example 1.

[0036] Figure 3 The test graphs show the water contact angles of carboxylated carbon nanotube / chitosan aerogel (CCNT / CA), citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA) prepared in Comparative Example 1, and CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel (P / Cit@CCNT / CA) prepared in Example 1.

[0037] Figure 4 The graph shows the effects of the blank control group, carboxylated carbon nanotube / chitosan aerogel (CCNT / CA), citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA) prepared in Comparative Example 1, and CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel (P / Cit@CCNT / CA) prepared in Example 1 on mango preservation. Detailed Implementation

[0038] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions of the present invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only a part of the embodiments in this application. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0039] Example 1:

[0040] A method for preparing a CO2-responsive, citral-controlled release chitosan-based aerogel includes the following steps:

[0041] (1) Preparation of carboxylated carbon nanotube / chitosan aerogel: 0.01 g of carboxylated carbon nanotubes (CCNT) were placed in a beaker, 12 mL of distilled water was added, and the mixture was sonicated for 30 min. Then, 0.2 g of chitosan and 0.2 mL of glacial acetic acid were added, and the mixture was stirred until the chitosan was completely dissolved. The mixture was then dispersed at 20,000 rpm for 4 min using a high-speed homogenizer. 1.5 mL of the mixed solution was taken, dispensed into 5 mL beakers, and frozen in a refrigerator. The samples were then freeze-dried. The samples were then soaked in a 2% ammonia solution for 1 h, washed with distilled water until neutral, and freeze-dried to obtain carboxylated carbon nanotube / chitosan aerogel (CCNT / CA).

[0042] (2) Preparation of citral / carboxylated carbon nanotube / chitosan aerogel: Take 50 mL of anhydrous ethanol into an Erlenmeyer flask, add 1.5 g of citral, shake well, and then add 0.5 g of carboxylated carbon nanotube / chitosan aerogel. React in a shaking water bath at 50 ℃ for 24 h. Take out the sample and air dry at room temperature to obtain citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA).

[0043] (3) Preparation of CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel: 0.05 g N,N-methylenebisacrylamide, 0.01 g sodium persulfate and 20 mL distilled water were added to a single-necked flask and stirred to dissolve. Then, 2 mL dimethylaminoethyl methacrylate and 1 mL acrylic acid were added dropwise to the mixed solution. The flask was placed in a 70 °C water bath for 3 h. The polymerization reaction was carried out under N2 atmosphere. The obtained copolymer was freeze-dried to obtain the CO2-responsive polymer (poly(acrylic acid-dimethylaminoethyl methacrylate)) (P(AA-co-DMAEMA)). Take 0.125 g of P(AA-co-DMAEMA) in a beaker, add 100 mL of distilled water and 0.1 mL of glacial acetic acid, stir and dissolve in a water bath at 40 °C, add 0.5 g of Cit@CCNT / CA, soak in a shaking water bath for 1 h, and then freeze dry to obtain CO2 responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel P(AA-co-DMAEMA) / Cit@CCNT / CA (P / Cit@CCNT / CA).

[0044] Example 2:

[0045] A method for preparing a CO2-responsive, citral-controlled release chitosan-based aerogel includes the following steps:

[0046] (1) Preparation of carboxylated carbon nanotube / chitosan aerogel: 0.02 g of carboxylated carbon nanotubes (CCNT) were placed in a beaker, 14 mL of distilled water was added, and the mixture was sonicated for 45 min. Then, 0.3 g of chitosan and 0.3 mL of glacial acetic acid were added, and the mixture was stirred until the chitosan was completely dissolved. The mixture was then dispersed at 17000 rpm for 7 min using a high-speed homogenizer. 1.7 mL of the mixed solution was taken, dispensed into 5 mL beakers, and frozen in a refrigerator. The mixture was then freeze-dried. The sample was then soaked in 3% ammonia solution for 2 h, washed with distilled water until neutral, and freeze-dried to obtain carboxylated carbon nanotube / chitosan aerogel (CCNT / CA).

[0047] (2) Preparation of citral / carboxylated carbon nanotube / chitosan aerogel: Take 65 mL of anhydrous ethanol into an Erlenmeyer flask, add 1.0 g of citral, shake well, and then add 0.3 g of carboxylated carbon nanotube / chitosan aerogel. React in a shaking water bath at 60 °C for 30 h. Take out the sample and air dry at room temperature to obtain citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA).

[0048] (3) Preparation of CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel: 0.06 g N,N-methylenebisacrylamide, 0.02 g sodium persulfate and 25 mL distilled water were added to a single-necked flask and stirred to dissolve. Then, 1.3 mL dimethylaminoethyl methacrylate and 0.7 mL acrylic acid were added dropwise to the mixed solution. The flask was placed in a 75°C water bath for 3 h. The polymerization reaction was carried out under N2 atmosphere. The obtained copolymer was freeze-dried to obtain the CO2-responsive polymer (poly(acrylic acid-dimethylaminoethyl methacrylate)) (P(AA-co-DMAEMA)).

[0049] Take 0.3 g of P(AA-co-DMAEMA) in a beaker, add 125 mL of distilled water and 0.1 mL of glacial acetic acid, stir and dissolve in a water bath at 55 °C, add 1.25 g of Cit@CCNT / CA, soak in a shaking water bath for 2 h, and then freeze dry to obtain CO2 responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel P(AA-co-DMAEMA) / Cit@CCNT / CA (P / Cit@CCNT / CA).

[0050] Example 3:

[0051] A method for preparing a CO2-responsive, citral-controlled release chitosan-based aerogel includes the following steps:

[0052] (1) Preparation of carboxylated carbon nanotube / chitosan aerogel: 0.03 g of carboxylated carbon nanotubes (CCNT) were placed in a beaker, 16 mL of distilled water was added, and the mixture was sonicated for 60 min. Then, 0.4 g of chitosan and 0.4 mL of glacial acetic acid were added, and the mixture was stirred until the chitosan was completely dissolved. The mixture was then dispersed at 20,000 rpm for 10 min using a high-speed homogenizer. 1.7 mL of the mixed solution was taken, dispensed into 5 mL beakers, and frozen in a refrigerator. The mixture was then freeze-dried. The sample was removed and soaked in a 3% ammonia solution for 3 h. It was then washed with distilled water until neutral and freeze-dried to obtain carboxylated carbon nanotube / chitosan aerogel (CCNT / CA).

[0053] (2) Preparation of citral / carboxylated carbon nanotube / chitosan aerogel: Take 80 mL of anhydrous ethanol into an Erlenmeyer flask, add 1.5 g of citral, shake well, and then add 0.5 g of carboxylated carbon nanotube / chitosan aerogel. React in a shaking water bath at 70 °C for 36 h. Take out the sample and air dry at room temperature to obtain citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA).

[0054] (3) Preparation of CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel: 0.07 g N,N-methylenebisacrylamide, 0.03 g sodium persulfate and 30 mL distilled water were added to a single-necked flask and stirred to dissolve. Then, 2 mL dimethylaminoethyl methacrylate and 1.0 mL acrylic acid were added dropwise to the mixed solution. The flask was placed in a 90 ℃ water bath for 5 h. The polymerization reaction was carried out under N2 atmosphere. The obtained copolymer was freeze-dried to obtain the CO2-responsive polymer (poly(acrylic acid-dimethylaminoethyl methacrylate)) (P(AA-co-DMAEMA)). Take 0.5g of P(AA-co-DMAEMA) in a beaker, add 150 mL of distilled water and 0.2 mL of glacial acetic acid, stir and dissolve in a water bath at 70℃, add 2g of Cit@CCNT / CA, soak in a shaking water bath for 3h, and then freeze dry to obtain CO2 responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel P(AA-co-DMAEMA) / Cit@CCNT / CA (P / Cit@CCNT / CA).

[0055] Example 4:

[0056] A method for preparing a CO2-responsive, citral-controlled release chitosan-based aerogel includes the following steps:

[0057] (1) Preparation of carboxylated carbon nanotube / chitosan aerogel: 0.01 g of carboxylated carbon nanotubes (CCNT) was placed in a beaker, 15 mL of distilled water was added, and the mixture was sonicated for 50 min. Then, 0.3 g of chitosan and 0.3 mL of glacial acetic acid were added, and the mixture was stirred until the chitosan was completely dissolved. The mixture was then dispersed at 18000 rpm for 8 min using a high-speed homogenizer. 1.8 mL of the mixed solution was taken, dispensed into 5 mL beakers, and frozen in a refrigerator. The samples were then freeze-dried. The samples were then soaked in 4% ammonia solution for 2.5 h, washed with distilled water until neutral, and freeze-dried to obtain carboxylated carbon nanotube / chitosan aerogel (CCNT / CA).

[0058] (2) Preparation of citral / carboxylated carbon nanotube / chitosan aerogel: 70 mL of anhydrous ethanol was placed in an Erlenmeyer flask, 1.2 g of citral was added, and after shaking, 0.4 g of carboxylated carbon nanotube / chitosan aerogel was added. The mixture was reacted in a shaking water bath at 65 °C for 28 h. The sample was then removed and dried at room temperature to obtain citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA).

[0059] (3) Preparation of CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel: 0.05 g N,N-methylenebisacrylamide, 0.02 g sodium persulfate and 28 mL distilled water were added to a single-necked flask and stirred to dissolve. Then, 1.5 mL dimethylaminoethyl methacrylate and 0.9 mL acrylic acid were added dropwise to the mixed solution. The flask was placed in an 80 °C water bath for 4 h. The polymerization reaction was carried out under N2 atmosphere. The obtained copolymer was freeze-dried to obtain the CO2-responsive polymer (poly(acrylic acid-dimethylaminoethyl methacrylate)) (P(AA-co-DMAEMA)). Take 0.5 g of P(AA-co-DMAEMA) in a beaker, add 140 mL of distilled water and 0.2 mL of glacial acetic acid, stir and dissolve in a water bath at 60 °C, add 0.8 g of Cit@CCNT / CA, soak in a shaking water bath for 2 h, and then freeze dry to obtain CO2 responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel P(AA-co-DMAEMA) / Cit@CCNT / CA (P / Cit@CCNT / CA).

[0060] Comparative Example 1:

[0061] (1) Preparation of carboxylated carbon nanotube / chitosan aerogel: 0.01 g of carboxylated carbon nanotubes (CCNTs) were placed in a beaker, 12 mL of distilled water was added, and the mixture was sonicated for 30 min. Then, 0.2 g of chitosan and 0.2 mL of glacial acetic acid were added, and the mixture was stirred until the chitosan was completely dissolved. The mixture was then dispersed at 20,000 rpm for 4 min using a high-speed homogenizer. 1.5 mL of the mixed solution was taken, dispensed into 5 mL beakers, and frozen in a refrigerator. The samples were then freeze-dried. The samples were then soaked in a 2% ammonia solution for 1 h, washed with distilled water until neutral, and freeze-dried to obtain chitosan / carboxylated carbon nanotube aerogel (CCNT / CA).

[0062] (2) Preparation of citral / carboxylated carbon nanotube / chitosan aerogel: Take 50 mL of anhydrous ethanol into an Erlenmeyer flask, add 1.5 g of citral, shake well, and then add 0.5 g of carboxylated carbon nanotube / chitosan aerogel. React in a shaking water bath at 50 ℃ for 24 h. Take out the sample and air dry at room temperature to obtain citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA).

[0063] Material characterization analysis

[0064] (I) SEM Analysis

[0065] The chitosan aerogel (CA), carboxylated carbon nanotube / chitosan aerogel (CCNT / CA), citral / carboxylated carbon nanotube / chitosan aerogel prepared in Comparative Example 1 (Cit@CCNT / CA), and CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel prepared in Example 1 (P / Cit@CCNT / CA) were characterized and analyzed by scanning electron microscopy (SEM).

[0066] Characterization analysis results as follows Figure 1 As shown, all aerogel samples exhibit a three-dimensional porous structure, while CA has a smooth skeletal structure, which is not conducive to essential oil loading. In contrast, in CCNT / CA, CCNT is uniformly dispersed within the chitosan skeletal framework, exhibiting a rough surface characteristic, which is beneficial for essential oil loading. When Cit is loaded onto CCNT / CA to form Cit@CCNT / CA, its structure does not change significantly. However, when the CO2-responsive polymer is loaded onto the Cit@CCNT / CA aerogel skeletal framework via impregnation, the P / Cit@CCNT / CA of this invention exhibits a rougher structure. This demonstrates that the CO2-responsive polymer of this invention forms a coating structure on the surface of the aerogel skeletal framework, thereby facilitating essential oil loading.

[0067] (ii) FT-IR analysis

[0068] Fourier transform infrared spectroscopy (FT-IR) was used to characterize and analyze carboxylated carbon nanotubes (CCNT), chitosan (CS), carboxylated carbon nanotube / chitosan aerogel (CCNT / CA), citral / carboxylated carbon nanotube / chitosan aerogel prepared in Comparative Example 1 (Cit@CCNT / CA), and CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel prepared in Example 1 (P / Cit@CCNT / CA) to determine the functional groups of the materials.

[0069] The results are as follows Figure 2 As shown:

[0070] In the CCNT infrared spectrum, the characteristic peaks at 1715, 1567 and 1176 cm⁻¹ originate from the stretching vibrations of the -COOH functional group.

[0071] The CS spectrum shows that the absorption band at 3404 cm⁻¹ is related to the stretching vibrations of the OH and NH bonds, while the absorption peaks at 1657 and 1595 cm⁻¹ are caused by the stretching vibrations of the C=O bond and the bending vibrations of the CH bond in the NHCOCH₃ group of CS. After combining CS with CCNT to form CCNT / CA, the characteristic peaks of -NH₂ and -OH in CS shift to 3367, 1651, and 1588 cm⁻¹, respectively. This indicates that there are electrostatic and hydrogen bonding interactions between the -NH₂ in the CS molecule and the -COOH in the CCNT.

[0072] The spectrum of Cit@CCNT / CA shows a distinct characteristic peak at 1641 cm⁻¹, which is attributed to the imine bond (N=C). Simultaneously, the -NH₂ characteristic peak of CCNT / CA at 3367 cm⁻¹ shifts to 3446 cm⁻¹, indicating a Schiff base reaction between the aldehyde group (-CHO) in the citral molecule and the -NH₂ group in the chitosan molecule. The molecular structure of the CO₂-responsive polymer P(AA-co-DMAEMA) contains tertiary amine groups -N-(CH₃)₂ and -COOH functional groups. When Cit@CCNT / CA is loaded with P(AA-co-DMAEMA) to form P / Cit@CCNT / CA, its -NH₂ characteristic peak shifts to 3452 cm⁻¹, and the intensity of the characteristic peak of the imine bond (N=C) is significantly weakened. It is evident that polymer P(AA-co-DMAEMA) interacts electrostatically with -NH2 in chitosan molecules via -COOH, thereby covering the Cit@CCNT / CA aerogel backbone, causing the characteristic peak of -NH2 to shift and masking the characteristic peak of imine bond (N=C).

[0073] (III) Water Contact Angle Analysis

[0074] The carboxylated carbon nanotube / chitosan aerogel (CCNT / CA) prepared in this invention, the citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA) prepared in Comparative Example 1, and the CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel (P / Cit@CCNT / CA) prepared in Example 1 were characterized and analyzed. The water contact angle (WCA) of the above aerogel materials in air was measured using a Theta Flex contact angle meter from Bio-Ling Technology Co., Ltd., and contact angle photographs were collected.

[0075] The results are as follows Figure 3 As shown, CCNT / CA has a water contact angle of 1°, indicating it is hydrophilic. After loading Cit essential oil, the water contact angle of the aerogel changes to 103°, indicating that Cit@CCNT / CA becomes hydrophobic. This will hinder the adsorption of H2O and CO2 in the fruit preservation microenvironment, reduce the sensitivity of the Schiff base groups to acidic microenvironment stimulation, and impede the release of Cit essential oil through Schiff base bond cleavage, resulting in a poorer fruit preservation effect.

[0076] The P / Cit@CCNT / CA of this invention has a water contact angle of only 5°, indicating that Cit@CCNT / CA becomes hydrophilic after being loaded with CO2-responsive polymers. This will facilitate the adsorption of H2O and CO2 in the fruit preservation microenvironment, improve the sensitivity of Schiff base groups to the influence of acidic microenvironment, promote the release of Cit essential oil in the composite aerogel, and enhance the fruit preservation effect.

[0077] Application Example 1:

[0078] The CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel prepared in Example 1 of this invention was placed in a breathable non-woven bag. These bags were then placed in a mango preservation box, with a ratio of 15 g: 3000 g of aerogel to mango, and compared with a blank control group. The mangoes were stored at room temperature (25°C) for 15 days, and the spoilage rate of the mangoes was measured. The spoilage rate of the mangoes in the blank group was 78.5%, while the spoilage rate of the mangoes preserved with the CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel of this invention was 3.1%.

[0079] Application Example 2

[0080] The CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel prepared in Example 2 of this invention was placed in a breathable non-woven bag. These bags were then placed in a mango preservation box, with a ratio of 15 g: 3000 g for the aerogel and a control group. The mangoes were stored at room temperature (25°C) for 15 days, and the spoilage rate was measured. The spoilage rate of the mangoes in the control group was 76.1%, while the spoilage rate of the mangoes preserved with the CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel of this invention was 3.5%.

[0081] Application Example 3

[0082] The CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel prepared in Example 3 of this invention was placed in a breathable non-woven bag. These bags were then placed in a mango preservation box, with a ratio of 15 g: 3000 g of aerogel to mango, and compared with a blank control group. The mangoes were stored at room temperature (25°C) for 15 days, and the spoilage rate of the mangoes was measured. The spoilage rate of the mangoes in the blank group was 74.5%, while the spoilage rate of the mangoes preserved with the CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel of this invention was 3.9%.

[0083] Application Example 4

[0084] The CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel prepared in Example 4 of this invention was placed in a breathable non-woven bag. These bags were then placed in a mango preservation box, with a ratio of 15 g: 3000 g for the aerogel and mango, respectively. A blank control group was used as a reference. The mangoes were stored at room temperature (25°C) for 15 days, and the spoilage rate of the mangoes was measured. The spoilage rate of the mangoes in the blank control group was 75.9%, while the spoilage rate of the mangoes preserved with the CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel of this invention was 3.3%.

[0085] like Figure 4The figures show the preservation effects of mangoes under different conditions, specifically the preservation effects obtained by using the blank control group, carboxylated carbon nanotube / chitosan aerogel (CCNT / CA), citral / carboxylated carbon nanotube / chitosan aerogel (Cit@CCNT / CA) prepared in Comparative Example 1, and CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel (P / Cit@CCNT / CA) prepared in Example 1. As can be seen from the figures, when using the CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel to preserve mangoes, only a few small black spots appear on the surface of the mangoes after 15 days of preservation. This invention can effectively extend the preservation time of mangoes to 15 days. In the blank control group, small black spots appeared on day 6; in the CCNT / CA group, black spots appeared at the edges on day 6; and in the Cit@CCNT / CA group, a few small black spots appeared on day 9. In comparison, the present invention can effectively preserve mangoes for at least 6 to 9 days, thereby increasing economic benefits.

[0086] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a CO2-responsive, citral-controlled release chitosan-based aerogel, characterized in that: Chitosan and carboxylated carbon nanotubes were synthesized into carboxylated carbon nanotube / chitosan aerogel, and citral was loaded onto it to obtain citral / carboxylated carbon nanotube / chitosan aerogel. The citral / carboxylated carbon nanotube / chitosan aerogel was then loaded with a CO2-responsive polymer to obtain a CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel.

2. The method for preparing CO2-responsive citral-controlled release chitosan-based aerogel according to claim 1, characterized in that, Preparation of the carboxylated carbon nanotube / chitosan aerogel: Take 0.01-0.03g of carboxylated carbon nanotubes in a beaker, add 12-16mL of distilled water, sonicate for 30-60min, then add 0.2-0.4g of chitosan and 0.2-0.4mL of glacial acetic acid, stir until the chitosan is completely dissolved, and disperse it using a high-speed homogenizer at 15000-20000rpm for 4-10min to obtain a mixed solution for later use; Take 1.5-2 mL of the mixed solution, dispense it into 5 mL beakers, freeze them in a refrigerator, and then freeze-dry them. Take out the sample, add 2-5% ammonia solution and soak for 1-3 hours, wash with distilled water until neutral, freeze-dry, and obtain carboxylated carbon nanotube / chitosan aerogel.

3. The method for preparing CO2-responsive citral-controlled release chitosan-based aerogel according to claim 1, characterized in that, Preparation of the citral / carboxylated carbon nanotube / chitosan aerogel: Take 50-80 mL of anhydrous ethanol into an Erlenmeyer flask, add 0.5 g-1.5 g of citral, shake well, then add 0.2 g-0.5 g of carboxylated carbon nanotube / chitosan aerogel, and react in a shaking water bath at 50-70 °C for 24-36 h. Take out the sample and air dry at room temperature to obtain citral / carboxylated carbon nanotube / chitosan aerogel.

4. The method for preparing CO2-responsive citral-controlled release chitosan-based aerogel according to claim 1, characterized in that: The mass ratio of citral to carboxylated carbon nanotubes / chitosan aerogel is 0.5–1.5:0.1–0.

5.

5. The method for preparing CO2-responsive citral-controlled release chitosan-based aerogel according to claim 1, characterized in that, Preparation of the CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel: 0.05-0.07 g N,N-methylenebisacrylamide, 0.01-0.03 g sodium persulfate and 20-30 mL distilled water were added to a single-necked flask and stirred until dissolved. Then, 0.5 mL-2 mL of dimethylaminoethyl methacrylate and 0.5 mL-1 mL of acrylic acid were added dropwise to the mixed solution. The flask was placed in a water bath at 60℃-90℃ and reacted for 2-5 hours. The polymerization reaction was carried out under an N2 atmosphere. The resulting copolymer was freeze-dried to obtain the CO2-responsive polymer. Take 0.1–0.5 g of CO2-responsive polymer in a beaker, add 100–150 mL of distilled water and 0.1–0.2 mL of glacial acetic acid, stir and dissolve in a water bath at 40–70 °C, add 0.5–2 g of citral / carboxylated carbon nanotube / chitosan aerogel, soak in a shaking water bath for 1–3 h, and then freeze-dry to obtain CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel.

6. The method for preparing CO2-responsive citral-controlled release chitosan-based aerogel according to claim 5, characterized in that: The volume ratio of dimethylaminoethyl methacrylate to acrylic acid is 0.5–2:0.5–1.

7. The method for preparing CO2-responsive citral-controlled release chitosan-based aerogel according to claim 5, characterized in that: The polymerization reaction process is carried out at a temperature of 60–90°C and a reaction time of 0.5–5 h.

8. The method for preparing CO2-responsive citral-controlled release chitosan-based aerogel according to any one of claims 1-7, characterized in that: The CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel exhibits hydrophilicity in air, with a surface contact angle of 0–5° with water.

9. The application of the CO2-responsive polymer / citral / carboxylated carbon nanotube / chitosan aerogel as described in any one of claims 1-8 in mango preservation.

10. The CO2-responsive polymer / citral / carboxylated carbon nanotubes / chitosan aerogel according to claim 9 extends the shelf life of fresh mangoes to 13-15 days under conditions of 20-25°C.

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