Chitosan / oxidized chitosan composite aerogel and preparation method and application thereof

Abstract

The application discloses a kind of chitosan / oxidized chitosan composite aerogel and its preparation method and application, it is dissolved in 1-methyl-3-(propyl-3-sulfonic acid group) imidazole salt ionic liquid at room temperature with chitosan and oxidized chitosan, chitosan and oxidized chitosan occur catalytic crosslinking reaction by microwave irradiation, then under the action of ultrasonic wave, 3-glycidylpropyl trimethoxysilane coupling agent is added and chitosan / oxidized chitosan is carried out ultrasonic chemical reaction and crosslinking self-assembly, again adding small molecule auxiliary agent strengthens crosslinking effect, finally by microwave vacuum freeze drying and then preparation structure stable, adsorption capacity, three-dimensional network chitosan / oxidized chitosan composite aerogel.The method of the application is simple and easy to operate, and the obtained composite aerogel has good mechanical properties, small solubility, low density, high porosity, good adsorption and other advantages, and is widely used in the fields of adsorption and purification of dyes, heavy metals, pesticides and other pollutants in wastewater.

Description

Technical Field

[0001] This invention relates to a composite aerogel material, its preparation method and application, specifically to a method for preparing a chitosan / oxidized chitosan composite aerogel and its application in adsorbing dyes, belonging to the field of composite aerogel functional materials. Background Technology

[0002] The textile industry plays a vital role in the national economy. my country's textile and apparel exports account for a quarter of the global total, and its production capacity accounts for one-third. The textile dyeing and printing industry is a crucial link in the textile industry chain, but domestic dyeing and printing enterprises discharge approximately 3 to 4 million tons of wastewater daily, causing serious environmental pollution. Solving the wastewater pollution problem in textile dyeing and printing is essential for my country to transform from a "major textile country" to a "strong textile country." Aerogel materials, with their high porosity and high adsorption capacity, are widely used to adsorb and purify dyes, heavy metals, and pesticides in wastewater.

[0003] Chitosan, chemically known as (1,4)-2-amino-2-deoxy-β-D-glucose, is an alkaline polysaccharide obtained by deacetylation of chitin. It is the second largest biosynthetic resource on Earth after cellulose and has wide applications in water treatment, biomedical materials, food engineering, and textile printing and dyeing. However, the strong hydrogen bonding between the hydroxyl and amino groups in the chitosan molecule makes it difficult to dissolve in water and common solvents. It can only dissolve in acid solutions, which are volatile, difficult to recover, highly corrosive, pollute the environment, and have certain toxicity to organisms, greatly limiting the application of chitosan [Liu XQ, Zhao Xin-Xin, Liu Y, et al. Review on preparation and adsorption properties of chitosan and chitosan composites[J]. Polymer Bulletin, 2021, 2: 1-33.].

[0004] Chitosan-based aerogels, as a typical biomass aerogel, contain a large number of -OH and -NH2 groups, which have a good chelating effect on dyes. However, chitosan-based aerogels are easily soluble in environments with pH ≤ 5.5, which severely limits their application as an effective biosorbent for removing acidic dyes from wastewater [Wang J, Chen C. Chitosan-based biosorbents: modification and application for biosorption of heavy metals and radionuclides[J]. Bioresource technology, 2014, 160: 129-141]. Furthermore, chitosan-based aerogels will dissolve in acidic solutions, and their mechanical properties will be significantly damaged, making them difficult to recycle. Currently, chemical crosslinking agents such as glutaraldehyde and epichlorohydrin are used to enhance the structural stability of chitosan aerogels, thereby expanding their application range under acidic conditions [Vakili M, Deng S, Li T, et al. Novel crosslinked chitosan for enhanced adsorption of hexavalent chromium in acidic solution[J]. Chemical Engineering Journal, 2018, 347: 782-790]. However, these crosslinking agents have poor compatibility, and aldehyde crosslinking agents have certain toxicity to biological cells, posing potential application risks to chitosan-based aerogels. Therefore, seeking biocompatible and environmentally friendly crosslinking agents to enhance the strength of the chitosan aerogel framework and adapt it to applications under acidic conditions has become an urgent problem to be solved.

[0005] Both periodate and the HNO3 / H3PO4-NaNO2 system are important oxidants in the oxidative modification of chitosan [XuY H,Qiu C,Zang XL,et al.Crosslinking chitosan into H3PO4 / HNO3-NANO2 oxidized cellulose fabrics as antibacterial-finished material[J].CarbohydratePolymers,2014,112:186-194]. Addressing the shortcomings of chitosan molecules, such as a limited number of active groups, poor water solubility, and limited adsorption capacity for pollutants like dyes and metals, this study utilizes periodate and the HNO3 / H3PO4-NaNO2 system to selectively oxidize chitosan at the C2, C3, and C6 positions to form aldehyde and carboxyl groups, respectively, to obtain water-soluble oxidized chitosan. The aldehyde and carboxyl groups in the oxidized chitosan are then used to crosslink the amino groups of the chitosan to enhance the composite aerogel framework structure.

[0006] 3-Glycidylpropyltrimethoxysilane (KH560) coupling agent is a widely used epoxy silane. Its molecular structure contains one epoxy functional group and three degradable methoxy groups, which can form covalent bonds with many natural polymers [Tonda-Turo C, Cipriani E, Gnavi S, et al. Crosslinked gelatin nanofibres: Preparation, characterisation and in vitro studies using glial-like cells[J]. Materials Science and Engineering:C,2013,33(5):2723-2735]. KH560 can be easily hydrolyzed to form hydroxysilane groups, and the self-condensation of silanol groups forms -Si-O-Si- bonds. It has been widely used as a non-toxic crosslinking agent for constructing biocompatible and biodegradable materials [Yang Z, Xi Y, Bai J, et al. Covalent grafting of hyperbranched poly-L-lysine on Ti-based implants achieves dual functions of antibacteria and promoted osteointegration in vivo[J]. Biomaterials, 2021, 269:120534], and has improved the mechanical properties, transparency and thermal stability of crosslinked materials. KH560 coupling agent can crosslink with the amino groups in chitosan / chitosan oxide to enhance the structural strength of the composite aerogel, effectively reduce the dissolution of chitosan / chitosan oxide composite aerogel in acidic environments, maintain the complete three-dimensional network structure of the composite aerogel material, and expand the application range of chitosan composite aerogel [Kong D, He L, Li H, et al. Preparation and characterization of graphene oxide / chitosan composite aerogel with high adsorption performance for Cr(VI) by a new crosslinking route[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2021, 625: 126832].

[0007] Furthermore, the chitosan / oxidized chitosan composite aerogel has good acid resistance, rich pore structure, stable framework structure, and advantages such as low solubility and swelling rate, high adsorption capacity, low density, high porosity, and recyclability. It has broad application prospects in the fields of efficient adsorption of dyes, heavy metals, pesticides in wastewater. Summary of the Invention

[0008] In view of the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a chitosan / oxidized chitosan composite aerogel, its preparation method and application, thereby obtaining a composite aerogel material with good mechanical properties, low solubility, low density, high porosity and large adsorption capacity, which can be widely used in the fields of adsorbing and purifying dyes, heavy metals and pesticides in wastewater.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A chitosan / chitosan oxide composite aerogel is characterized by the following steps: chitosan and chitosan oxide are dissolved at room temperature in a 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid. Microwave radiation is used to catalyze a cross-linking reaction between chitosan and chitosan oxide. Then, under ultrasonic treatment, a 3-glycidylpropyltrimethoxysilane coupling agent is added to induce a sonic chemical reaction and cross-linking self-assembly between the chitosan / chitosan oxide. Small molecule auxiliaries are added to enhance the cross-linking effect. Finally, microwave vacuum freeze-drying is performed to prepare a chitosan / chitosan oxide composite aerogel with a stable structure, high adsorption capacity, and a three-dimensional network. This invention offers a simple, low-cost, and mild reaction condition. The resulting composite aerogel exhibits good acid resistance, a rich pore structure, a stable framework, low solubility and swelling rate, high adsorption capacity, low density, high porosity, and recyclability. It can effectively solve wastewater pollution problems in textile dyeing and printing and has broad application prospects in the efficient adsorption of dyes, heavy metals, and pesticides from wastewater.

[0011] The chitosan / oxidized chitosan composite aerogel has a solubility loss rate of 9.18%–18.71% and a specific surface area of ​​12.57–32.94 m². 2 The average pore size is 50.1–113.6 μm, the porosity is 67.42–90.28%, and the density is 12.18–26.54 mg / cm³. 3 The adsorption capacity for methyl orange is 321.5–410.3 mg / g.

[0012] Preferably, the oxidized chitosan has a C6 carboxyl group content of 42.19–75.36%, a C2 and C3 aldehyde group content of 16.08–34.29%, a degree of deacetylation of 88.17–96.33%, a viscosity-average molecular weight of 12,000–34,000, a water solubility of 17.52–27.46 g / 100 mL, and an isoelectric point pH of 4.9–5.1. Its structural formula is as follows:

[0013]

[0014] The preparation method of the chitosan / oxidized chitosan composite aerogel of the present invention is carried out according to the following steps:

[0015] (1) Chitosan and oxidized chitosan are dissolved in 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid at room temperature to prepare a solution with a total mass concentration of 1-4%. The cross-linking reaction is catalyzed under microwave radiation for 1-2 hours to form chemical bonds such as amide bonds and Schiff bases between chitosan and oxidized chitosan. The mass ratio of chitosan to oxidized chitosan is 2-12:1. The microwave radiation power is 620-800W and the microwave radiation temperature is 40-60℃.

[0016] (2) Under the action of ultrasound at 280-360W, 3-glycidylpropyltrimethoxysilane coupling agent is added to the reaction solution of step (1) for ultrasonic chemical reaction for 30-60 min, and then small molecule auxiliaries are added for crosslinking reaction at 45-60℃ for 1-2 h to obtain composite hydrogel; the mass ratio of chitosan to 3-glycidylpropyltrimethoxysilane coupling agent is 3-8:1, and the mass ratio of chitosan to small molecule auxiliaries is 5-10:1; the small molecule auxiliaries are selected from oxalic acid, tartaric acid, malic acid, glutamic acid, maleic acid or maleic anhydride.

[0017] (3) After the reaction is completed, the composite hydrogel is left to stand for 20 to 30 minutes, then placed in an ultra-low temperature freezer at -80 to -55℃ for 3 to 6 hours, and then microwave vacuum freeze-dried for 36 to 48 hours to obtain chitosan / oxidized chitosan composite aerogel.

[0018] Preferably, in step (1), the pH of the 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid is 5.3 to 6.0.

[0019] Preferably, in step (3), the microwave vacuum freeze-drying temperature is -100 to -84°C, the microwave power is 1200 to 4000W, and the vacuum degree is 5 to 15Pa.

[0020] The chitosan / chitosan-oxidized composite aerogel of this invention can be used to adsorb dyes from wastewater. Furthermore, the chitosan / chitosan-oxidized composite aerogel, after adsorbing dye, can be regenerated and reused by immersing it in hydrochloric acid solution to remove the dye. For example, the chitosan / chitosan-oxidized composite aerogel adsorbing methyl orange, after being immersed in 0.05–0.08 mol / L hydrochloric acid solution to remove the dye, can be reused 5–8 times, and the adsorption capacity for methyl orange is ≥250.7 mg / g.

[0021] Composite aerogel materials with different porosities can be obtained by optimizing the mass ratio of chitosan to oxidized chitosan, the microwave radiation reaction temperature and time, the ultrasonic treatment time, and the amount of 3-glycidylpropyltrimethoxysilane coupling agent and small molecule auxiliaries.

[0022] Compared with existing technologies, the preparation principle and beneficial effects of the chitosan / oxidized chitosan composite aerogel in this invention are reflected in the following aspects:

[0023] 1. The oxidized chitosan used in this invention has good water solubility, a small molecular weight, and contains a large number of active groups such as aldehyde and carboxyl groups. Dissolving the oxidized chitosan and chitosan in a 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid at room temperature avoids the degradation of the chitosan molecular chain by the ionic liquid at high temperatures, helping to maintain the stability of the chitosan molecular structure and its physicochemical properties. Furthermore, microwave radiation can accelerate the catalytic cross-linking reaction of chitosan and oxidized chitosan by the 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid, increasing the skeletal strength of the composite aerogel to a certain extent. Simultaneously, the pH of the 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid is 5.3–6.0, higher than the isoelectric point pH (4.9–5.1) of oxidized chitosan, giving it a negative charge. This enhances the interaction between the negatively charged aldehyde and carboxyl groups of oxidized chitosan and the positively charged amino groups (-NH3) in chitosan. + The nucleophilic reaction enhances the cross-linking degree and backbone stability of both.

[0024] 2. In this invention, a 3-glycidylpropyltrimethoxysilane coupling agent is added to chitosan / chitosan oxide for ultrasonic chemical reaction and cross-linking self-assembly. The ethylene oxide ring on the 3-glycidylpropyltrimethoxysilane coupling agent molecule can undergo addition reactions with the amino groups on the chitosan and chitosan oxide molecular chains, respectively, thereby forming multi-site connections between chitosan and chitosan oxide molecules. At the same time, the trimethoxy group on the 3-glycidylpropyltrimethoxysilane coupling agent is easily hydrolyzed to generate a side silanol group Si-OH, which then undergoes a condensation reaction to form Si-O-Si bonds, further enhancing the cross-linking structure of chitosan and chitosan oxide, significantly improving the skeletal stability of the chitosan / chitosan oxide composite aerogel, and promoting the formation of a continuous three-dimensional network structure. Meanwhile, the silanol groups of each molecule of the silane coupling agent associate with each other to form a network structure film covering the surface of the composite aerogel, making the surface of the composite aerogel inorganic, which greatly improves the mechanical strength and acid resistance of the composite aerogel. Moreover, the chitosan / oxidized chitosan aerogel reinforced by the silane coupling agent has a stable and regular porous structure, which increases the adsorption capacity of the composite aerogel material for dye pollutants and the number of times it can be reused.

[0025] 3. The oxidized chitosan used in this invention has a C6 carboxyl group content of 42.19–75.36%, a C2 and C3 aldehyde group content of 16.08–34.29%, a degree of deacetylation of 88.17–96.33%, a water solubility of 17.52–27.46 g / 100 mL, and an isoelectric point pH of 4.9–5.1. Compared with ordinary chitosan, oxidized chitosan has good water solubility, avoiding the use of acids and organic solvents and environmental pollution. Furthermore, oxidized chitosan introduces a carboxyl group at the C6 position of the molecular chain while retaining the original amino functional group at the C2 position, making it an amphoteric polyelectrolyte. Similar in structure to proteins, it possesses advantages such as biocompatibility, biodegradability, and affinity for the human body. In addition, oxidized chitosan has a low molecular weight (viscosity-average molecular weight of 12,000 to 34,000) and low solution viscosity, which allows it to be uniformly mixed with large-molecule chitosan, promoting the cross-linking of oxidized chitosan and chitosan, increasing the structural strength of chitosan / oxidized chitosan composite aerogel and its adsorption capacity for dyes.

[0026] 4. This invention utilizes a small-molecule additive to catalytically crosslink chitosan / chitosan oxide in a 1-methyl-3-(propyl-3-sulfonic acid)imidazolium salt ionic liquid. This allows the carboxyl groups and anhydrides in the small-molecule additive to crosslink with the amino and hydroxyl groups of chitosan / chitosan oxide, respectively. Furthermore, the cationic amino groups of chitosan / chitosan oxide further electrostatically self-assemble with the carbonyl anions of the small-molecule additive to form a stable composite aerogel with a specific framework structure. This self-assembly method can form ordered aggregates with specific structures and functions without the need for surfactants or emulsifiers, offering advantages such as simple process and controllability. Introducing hydrophilic small molecules into the chitosan / chitosan oxide molecules improves the biocompatibility and stability of the composite aerogel in aqueous solution, enabling the chitosan / chitosan oxide composite aerogel to achieve a stable three-dimensional network structure, low solubility, good mechanical properties, low density, high porosity, large adsorption capacity, and easy recyclability.

[0027] 5. This invention crosslinks a composite aerogel by ultrasonic chemical reaction of a 3-glycidylpropyltrimethoxysilane coupling agent with chitosan / chitosan oxide. In this ultrasonic chemical reaction, the multiple effects of ultrasound, including dispersion, pulverization, and activation, promote both the homogeneous reaction of the substances and the dispersion of macromolecular chitosan. Simultaneously, ultrasound generates cavitation, causing the formation, growth, and collapse of cavitation bubbles in the reaction solution. When these cavitation bubbles collapse, temperatures exceeding 5000K and pressures exceeding 200MPa are generated within a very short time and a very small space, providing an energy source for ultrasonic chemical synthesis and greatly accelerating the reaction. Ultrasound significantly disperses the chitosan macromolecules, uniformly separating the entangled chitosan macromolecular chains through the strong impact and cavitation effect of ultrasound. This allows the silane coupling agent to fully contact the amino groups in the chitosan and chitosan oxide molecules, promoting the ultrasonic chemical crosslinking reaction between the silane coupling agent and chitosan / chitosan oxide, thereby forming a composite aerogel material with a stable three-dimensional network structure.

[0028] 6. This invention pre-freezes the composite hydrogel in an ultra-low temperature freezer, then freeze-dries it using microwave vacuum to obtain a chitosan / chitosan oxide composite aerogel. Pre-freezing rapidly solidifies the water inside the chitosan / chitosan oxide hydrogel, forming a stable three-dimensional framework structure within the chitosan / chitosan oxide matrix. During freeze-drying, the solidified water molecules are removed, which is beneficial to the structural stability of the chitosan / chitosan oxide composite aerogel and effectively prevents collapse caused by rapid water removal. This invention uses microwave vacuum freeze-drying to obtain the chitosan / chitosan oxide composite aerogel, combining microwave drying and vacuum drying technologies to fully utilize their respective advantages. Under a certain vacuum level, the water diffusion rate is accelerated, and the material can be dried at low temperatures, maintaining its original properties. Microwaves can provide a heat source for vacuum drying. Polar water molecules in the material rapidly generate frictional heat by constantly changing their polar orientation with the frequency of electromagnetic waves. This overcomes the slow heat conduction rate inherent in conventional vacuum drying, shortening drying time and improving drying efficiency. Furthermore, microwaves offer advantages such as rapid heating, low cost, uniform heating, mold prevention, and sterilization. Microwave vacuum freeze-drying results in uniform temperature, even distribution of water molecules within the composite aerogel, and a consistent moisture drying rate, preserving the porous network structure of the composite aerogel.

[0029] 7. The composite aerogel material prepared by this invention uses chitosan and oxidized chitosan as raw materials. Chitosan and oxidized chitosan are dissolved in 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid and subjected to a catalytic cross-linking reaction by microwave radiation. Then, under ultrasonic action, 3-glycidylpropyltrimethoxysilane coupling agent is added to undergo a sonic chemical reaction and cross-linking self-assembly with chitosan / oxidized chitosan. Small molecule auxiliaries are added to enhance the cross-linking effect. After microwave vacuum freeze-drying, a chitosan / oxidized chitosan composite aerogel with stable structure, large adsorption capacity, and three-dimensional network is obtained. The reaction process is simple, the preparation conditions are controllable, and no organic solvents or aldehyde cross-linking agents are used. It is green, environmentally friendly, safe, non-toxic, and low in cost, making it suitable for large-scale production. Attached Figure Description

[0030] Figure 1 This is a diagram illustrating the preparation mechanism of the chitosan / oxidized chitosan composite aerogel of the present invention.

[0031] Figure 2These are scanning electron microscope images of the chitosan / chitosan-oxidized composite aerogel in test item 2 of this invention, where a, b, c, and d correspond to the following four samples in sequence: the first sample is the chitosan / chitosan-oxidized composite aerogel sample obtained according to the method of Comparative Example 1, the second sample is the chitosan / chitosan-oxidized composite aerogel obtained according to the method of Example 1, the third sample is the chitosan / chitosan-oxidized composite aerogel obtained according to the method of Example 3, and the fourth sample is the chitosan / chitosan-oxidized composite aerogel obtained according to the method of Example 4. Detailed Implementation

[0032] To provide a better understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited to the following embodiments.

[0033] I. Preparation of Chitosan / Oxidized Chitosan Composite Aerogel

[0034] Example 1

[0035] (1) Chitosan and oxidized chitosan (the mass ratio of chitosan to oxidized chitosan is 10:1; the C6 carboxyl group content of oxidized chitosan is 48.17%, the C2 and C3 aldehyde group content is 19.03%, the degree of deacetylation is 94.24%, the viscosity-average molecular weight is 28,000, the water solubility is 18.61 g / 100 mL, and the isoelectric point pH is 5.1) were dissolved at room temperature in 1-methyl-3-(propyl-3-sulfonic acid) imidazole salt ionic liquid with pH 5.5 to prepare a 2% mass concentration solution. The cross-linking reaction was catalyzed under microwave radiation (microwave radiation power is 650 W, microwave radiation temperature is 40 °C) for 1 h to form amide bonds, Schiff bases and other chemical bonds between chitosan and oxidized chitosan, thus preparing a reaction solution.

[0036] (2) Under the action of 300W ultrasound, 3-glycidylpropyltrimethoxysilane coupling agent (the mass ratio of chitosan to 3-glycidylpropyltrimethoxysilane coupling agent is 8:1) was added to the above reaction solution and the ultrasonic chemical reaction was carried out for 40 min. Then, tartaric acid (the mass ratio of chitosan to small molecule auxiliary agent is 8:1) was added and the crosslinking reaction was carried out at 50℃ for 2 h to obtain composite hydrogel.

[0037] (3) After the reaction, the composite hydrogel was allowed to stand for 30 minutes, then pre-frozen in a -60℃ ultra-low temperature freezer for 4 hours, and then subjected to microwave vacuum freeze-drying (microwave vacuum freeze-drying temperature -100℃, microwave power 2000W, vacuum degree 12Pa) for 40 hours to obtain chitosan / chitosan oxidized composite aerogel. The solubility loss rate of the chitosan / chitosan oxidized composite aerogel prepared in this embodiment was 17.94%, and the specific surface area was 15.60 m². 2The average pore size is 105.2 μm, the porosity is 68.75%, and the density is 24.06 mg / cm³. 3 The adsorption capacity for methyl orange was 330.8 mg / g. After the chitosan / oxidized chitosan composite aerogel adsorbing methyl orange was removed by soaking in 0.06 mol / L hydrochloric acid solution, and reused 8 times, the adsorption capacity for methyl orange was 254.6 mg / g.

[0038] Example 2

[0039] (1) Chitosan and oxidized chitosan (the mass ratio of chitosan to oxidized chitosan is 6:1; the C6 carboxyl group content of oxidized chitosan is 55.38%, the C2 and C3 aldehyde group content is 24.67%, the degree of deacetylation is 92.17%, the viscosity-average molecular weight is 22,000, the water solubility is 23.41 g / 100 mL, and the isoelectric point pH is 5.0) were dissolved at room temperature in 1-methyl-3-(propyl-3-sulfonic acid) imidazole salt ionic liquid with pH 5.6 to prepare a 2% mass concentration solution. The cross-linking reaction was catalyzed under microwave radiation (microwave radiation power is 700 W, microwave radiation temperature is 50 °C) for 2 h to form amide bonds, Schiff bases and other chemical bonds between chitosan and oxidized chitosan, thus preparing a reaction solution.

[0040] (2) Under the action of 300W ultrasound, 3-glycidylpropyltrimethoxysilane coupling agent (the mass ratio of chitosan to 3-glycidylpropyltrimethoxysilane coupling agent is 6:1) was added to the above reaction solution and the ultrasonic chemical reaction was carried out for 50 min. Then, the small molecule auxiliary agent glutamic acid (the mass ratio of chitosan to small molecule auxiliary agent is 6:1) was added and the crosslinking reaction was carried out at 50℃ for 2 h to obtain the composite hydrogel.

[0041] (3) After the reaction, the composite hydrogel was allowed to stand for 30 minutes to age, then pre-frozen in a -70℃ ultra-low temperature freezer for 4 hours, and then subjected to microwave vacuum freeze-drying (microwave vacuum freeze-drying temperature -100℃, microwave power 2500W, vacuum degree 10Pa) for 40 hours to obtain chitosan / chitosan oxidized composite aerogel. The solubility loss rate of the chitosan / chitosan oxidized composite aerogel prepared in this embodiment was 14.25%, and the specific surface area was 21.33 m². 2 The average pore size is 89.1 μm, the porosity is 76.09%, and the density is 19.16 mg / cm³. 3 The adsorption capacity for methyl orange was 367.4 mg / g. After the chitosan / oxidized chitosan composite aerogel adsorbing methyl orange was removed by soaking in 0.06 mol / L hydrochloric acid solution, and reused 8 times, the adsorption capacity for methyl orange was 290.6 mg / g.

[0042] Example 3

[0043] (1) Chitosan and oxidized chitosan (the mass ratio of chitosan to oxidized chitosan is 4:1; the C6 carboxyl group content of oxidized chitosan is 63.45%, the C2 and C3 aldehyde group content is 28.31%, the degree of deacetylation is 90.84%, the viscosity-average molecular weight is 19,000, the water solubility is 25.07 g / 100 mL, and the isoelectric point pH is 5.0) were dissolved at room temperature in 1-methyl-3-(propyl-3-sulfonic acid) imidazole salt ionic liquid with pH 5.6 to prepare a 3% mass concentration solution. The cross-linking reaction was catalyzed under microwave radiation (microwave radiation power is 760 W, microwave radiation temperature is 50 °C) for 2 h to form amide bonds, Schiff bases and other chemical bonds between chitosan and oxidized chitosan, thus preparing a reaction solution.

[0044] (2) Under the action of 320W ultrasound, 3-glycidylpropyltrimethoxysilane coupling agent (the mass ratio of chitosan to 3-glycidylpropyltrimethoxysilane coupling agent is 4:1) was added to the above reaction solution and the ultrasonic chemical reaction was carried out for 50 min. Then, maleic acid (the mass ratio of chitosan to small molecule auxiliary agent is 6:1) was added and the crosslinking reaction was carried out at 55℃ for 2 h to obtain composite hydrogel.

[0045] (3) After the reaction, the composite hydrogel was allowed to stand for 30 minutes, then pre-frozen in an ultra-low temperature freezer at -80℃ for 5 hours, and then subjected to microwave vacuum freeze-drying (microwave vacuum freeze-drying temperature -100℃, microwave power 3000W, vacuum degree 8Pa) for 42 hours to obtain chitosan / chitosan oxidized composite aerogel. The solubility loss rate of the chitosan / chitosan oxidized composite aerogel prepared in this embodiment was 11.74%, and the specific surface area was 27.90 m². 2 The average pore size is 66.3 μm, the porosity is 84.72%, and the density is 17.08 mg / cm³. 3 The adsorption capacity for methyl orange was 389.4 mg / g. After the chitosan / oxidized chitosan composite aerogel adsorbing methyl orange was removed by soaking in 0.08 mol / L hydrochloric acid solution, and reused 8 times, the adsorption capacity for methyl orange was 314.7 mg / g.

[0046] Example 4

[0047] (1) Chitosan and oxidized chitosan (the mass ratio of chitosan to oxidized chitosan is 8:1; the C6 carboxyl group content of oxidized chitosan is 70.22%, the C2 and C3 aldehyde group content is 31.50%, the degree of deacetylation is 90.16%, the viscosity-average molecular weight is 15,000, the water solubility is 27.01 g / 100 mL, and the isoelectric point pH is 4.9) were dissolved at room temperature in 1-methyl-3-(propyl-3-sulfonic acid) imidazole salt ionic liquid with pH 5.8 to prepare a 3% mass concentration solution. The cross-linking reaction was catalyzed under microwave radiation (microwave radiation power is 760 W, microwave radiation temperature is 55 °C) for 2 h to form amide bonds, Schiff bases and other chemical bonds between chitosan and oxidized chitosan, thus preparing a reaction solution.

[0048] (2) Under the action of 340W ultrasound, 3-glycidylpropyltrimethoxysilane coupling agent (the mass ratio of chitosan to 3-glycidylpropyltrimethoxysilane coupling agent is 4:1) was added to the above reaction solution and the ultrasonic chemical reaction was carried out for 50 min. Then, maleic acid (the mass ratio of chitosan to small molecule auxiliary agent is 6:1) was added and the crosslinking reaction was carried out at 60℃ for 2 h to obtain composite hydrogel.

[0049] (3) After the reaction, the composite hydrogel was allowed to stand for 30 minutes, then pre-frozen in an ultra-low temperature freezer at -80℃ for 6 hours, and then subjected to microwave vacuum freeze-drying (microwave vacuum freeze-drying temperature -100℃, microwave power 3600W, vacuum degree 6Pa) for 46 hours to obtain chitosan / chitosan oxidized composite aerogel. The solubility loss rate of the chitosan / chitosan oxidized composite aerogel prepared in this embodiment was 9.35%, and the specific surface area was 31.86 m². 2 The average pore size is 52.4 μm, the porosity is 90.12%, and the density is 13.57 mg / cm³. 3 The adsorption capacity for methyl orange was 406.3 mg / g. After the chitosan / oxidized chitosan composite aerogel adsorbing methyl orange was removed by soaking in 0.08 mol / L hydrochloric acid solution, and reused 8 times, the adsorption capacity for methyl orange was 335.8 mg / g.

[0050] Comparative Example 1

[0051] Preparation of chitosan / oxidized chitosan composite aerogel (without adding 3-glycidylpropyltrimethoxysilane coupling agent and small molecule auxiliaries):

[0052] (1) Chitosan and oxidized chitosan (the mass ratio of chitosan to oxidized chitosan is 8:1; the C6 carboxyl group content of oxidized chitosan is 70.22%, the C2 and C3 aldehyde group content is 31.50%, the degree of deacetylation is 90.16%, the viscosity-average molecular weight is 15,000, the water solubility is 27.01 g / 100 mL, and the isoelectric point pH is 4.9) were dissolved at room temperature in 1-methyl-3-(propyl-3-sulfonic acid) imidazole salt ionic liquid with pH 5.8 to prepare a solution with a mass concentration of 3%. The cross-linking reaction was catalyzed under microwave radiation (microwave radiation power is 760 W, microwave radiation temperature is 55 °C) for 2 h, so that amide bonds, Schiff bases and other chemical bonds are formed between chitosan and oxidized chitosan to obtain a composite hydrogel.

[0053] (2) After the reaction, the composite hydrogel was allowed to stand for 30 minutes, then pre-frozen in an ultra-low temperature freezer at -80℃ for 6 hours, and then subjected to microwave vacuum freeze-drying (microwave vacuum freeze-drying temperature -100℃, microwave power 3600W, vacuum degree 6Pa) for 46 hours to obtain chitosan / chitosan oxidized composite aerogel. The solubility loss rate of the chitosan / chitosan oxidized composite aerogel prepared in this embodiment was 46.75%, and the specific surface area was 9.24 m². 2 The average pore size is 180.3 μm, the porosity is 45.27%, and the density is 25.58 mg / cm³. 3 The adsorption capacity for methyl orange was 212.6 mg / g. After the chitosan / chitosan-oxidized composite aerogel adsorbing methyl orange was soaked in 0.08 mol / L hydrochloric acid solution to remove the dye, the composite aerogel was reused three times. The adsorption capacity for methyl orange was 137.8 mg / g. After adsorbing the dye three times, the chitosan / chitosan-oxidized composite aerogel disintegrated and could not be used again.

[0054] Comparative Example 2

[0055] Preparation of chitosan / oxidized chitosan composite aerogel (without adding small molecule additives):

[0056] (1) Chitosan and oxidized chitosan (the mass ratio of chitosan to oxidized chitosan is 8:1; the C6 carboxyl group content of oxidized chitosan is 70.22%, the C2 and C3 aldehyde group content is 31.50%, the degree of deacetylation is 90.16%, the viscosity-average molecular weight is 15,000, the water solubility is 27.01 g / 100 mL, and the isoelectric point pH is 4.9) were dissolved at room temperature in 1-methyl-3-(propyl-3-sulfonic acid) imidazole salt ionic liquid with pH 5.8 to prepare a 3% mass concentration solution. The cross-linking reaction was catalyzed under microwave radiation (microwave radiation power is 760 W, microwave radiation temperature is 55 °C) for 2 h to form amide bonds, Schiff bases and other chemical bonds between chitosan and oxidized chitosan, thus preparing a reaction solution.

[0057] (2) Under the action of 340W ultrasound, 3-glycidylpropyltrimethoxysilane coupling agent (the mass ratio of chitosan to 3-glycidylpropyltrimethoxysilane coupling agent is 4:1) was added to the above reaction solution and the ultrasonic chemical reaction was carried out for 50 minutes to obtain composite hydrogel.

[0058] (3) After the reaction, the composite hydrogel was allowed to stand for 30 minutes, then pre-frozen in an ultra-low temperature freezer at -80℃ for 6 hours, and then subjected to microwave vacuum freeze-drying (microwave vacuum freeze-drying temperature -100℃, microwave power 3600W, vacuum degree 6Pa) for 46 hours to obtain chitosan / chitosan oxidized composite aerogel. The solubility loss rate of the chitosan / chitosan oxidized composite aerogel prepared in this embodiment was 16.24%, and the specific surface area was 17.06 m². 2 The average pore size is 91.4 μm, the porosity is 74.62%, and the density is 20.73 mg / cm³. 3 The adsorption capacity for methyl orange was 351.5 mg / g. After the chitosan / oxidized chitosan composite aerogel adsorbing methyl orange was removed by soaking in 0.08 mol / L hydrochloric acid solution, and reused 8 times, the adsorption capacity for methyl orange was 272.1 mg / g.

[0059] II. Testing the samples obtained in the above embodiments.

[0060] Test Item 1: Dissolution rate, specific surface area, average pore size, porosity, mechanical properties, and methyl orange adsorption capacity of composite aerogels formed by adding small molecule additives in different mass ratios.

[0061] Following the mass ratio (8:1:2) of chitosan, oxidized chitosan, and 3-glycidylpropyltrimethoxysilane coupling agent in Example 4, chitosan / oxidized chitosan composite aerogels were prepared by changing the mass ratio of the small molecule auxiliary agent maleic acid. The test results of the composite aerogels, including the solubility loss rate, specific surface area, average pore size, porosity, mechanical properties, and methyl orange adsorption capacity, are shown in Table 1.

[0062] Table 1. Test results of the physicochemical properties of the composite aerogel.

[0063]

[0064] The data in Table 1 show that, in this invention, chitosan and chitosan oxide are dissolved at room temperature in a 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid. Microwave radiation is used to catalyze a cross-linking reaction between chitosan and chitosan oxide. Then, under ultrasonic treatment, a 3-glycidylpropyltrimethoxysilane coupling agent is added to induce a sonic chemical reaction and cross-linking self-assembly between the chitosan / chitosan oxide. Small molecule additives are then added to enhance the cross-linking effect. After microwave vacuum freeze-drying, a stable, high-capacity, three-dimensional network aerogel is prepared. This significantly improves the porosity, mechanical strength, and structural stability of the chitosan / chitosan oxide composite aerogel. The cross-linking and electrostatic self-assembly effects of the small molecule additives significantly influence the average pore size, specific surface area, solubility, and dye adsorption effect of the composite aerogel. By optimizing the cross-linking reaction temperature and time, and the type and proportion of small molecule additives, the chitosan / chitosan oxide composite aerogel prepared by this invention exhibits a more ideal porous structure, skeletal stability, and higher reusability.

[0065] Test Item 2: Cross-sectional scanning electron microscopy analysis of chitosan / oxidized chitosan composite aerogel

[0066] The micropore distribution of the chitosan / chitosan oxide composite aerogel cross-section was observed using a scanning electron microscope (100×). Four composite aerogel samples were taken: sample 1 was the chitosan / chitosan oxide composite aerogel obtained according to the method of Comparative Example 1; sample 2 was the chitosan / chitosan oxide composite aerogel obtained according to the method of Example 1; sample 3 was the chitosan / chitosan oxide composite aerogel obtained according to the method of Example 3; and sample 4 was the chitosan / chitosan oxide composite aerogel obtained according to the method of Example 4. The test results are detailed below. Figure 2 (a)~(d).

[0067] Depend on Figure 2 The results show that the composite aerogel without the addition of 3-glycidylpropyltrimethoxysilane coupling agent and small molecule auxiliaries has a certain network structure of chitosan and oxidized chitosan crosslinking. This also confirms that the amino groups of chitosan can form chemical bonds with the carboxyl and aldehyde groups in oxidized chitosan, but most of them are unidirectional flat pore structures with poor uniformity of crosslinking, some pores collapse, and the three-dimensional structure is unstable. In contrast, the network structure of the chitosan / oxidized chitosan composite aerogel with the addition of 3-glycidylpropyltrimethoxysilane coupling agent and small molecule auxiliaries gradually becomes more uniform, and the microporous structure tends to be a 3D interpenetrating crosslinked network. Figure 2 (b)~(d)), when the ratio of chitosan: oxidized chitosan: 3-glycidylpropyltrimethoxysilane coupling agent: maleic acid (small molecule auxiliary agent) is 24:3:6:4, the cross-linked pores in the composite aerogel are uniformly distributed, and the three-dimensional pore structure is regular and complete. Figure 2(d) shows high bonding strength, with most micropores around 50 μm in size. This indicates that the ethylene oxide ring on the 3-glycidylpropyltrimethoxysilane coupling agent molecule has undergone addition reactions with the amino groups on the chitosan and oxidized chitosan molecular chains, forming multi-site connections between chitosan and oxidized chitosan molecules. Simultaneously, the carboxyl groups and anhydrides in the small molecule additives crosslink with the amino and hydroxyl groups of chitosan / oxidized chitosan, respectively, and further electrostatically self-assemble with the cationic amino groups of chitosan / oxidized chitosan and the carbonyl anions of the small molecule additives to form a stable framework composite aerogel. The chitosan / oxidized chitosan composite aerogel with enhanced crosslinking by the small molecule additives contains numerous three-dimensional through-pore structures, which can improve the adsorption capacity of dyes. Furthermore, the chitosan and oxidized chitosan in the composite aerogel contain a large number of polar groups such as amino, aldehyde, and carboxyl groups, which also enhance the adsorption capacity of pollutants. Therefore, the chitosan / oxidized chitosan composite aerogel can efficiently adsorb dye pollutants and can be recycled and reused.

[0068] In summary, this invention involves dissolving chitosan and chitosan oxide in a 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid at room temperature. Microwave radiation is then used to catalyze a cross-linking reaction between chitosan and chitosan oxide. Following ultrasonic treatment, a 3-glycidylpropyltrimethoxysilane coupling agent is added to facilitate a sonic chemical reaction and cross-linking self-assembly of the chitosan / chitosan oxide. Small molecule additives are then added to enhance the cross-linking effect. Finally, microwave vacuum freeze-drying is performed to prepare a stable chitosan / chitosan oxide composite aerogel with a large adsorption capacity and a three-dimensional network. This method is simple, low-cost, uses mild reaction conditions, and is environmentally friendly. The resulting composite aerogel possesses advantages such as good mechanical properties, low solubility, low density, high porosity, and good adsorption capacity. It has wide applications in the adsorption and purification of dyes, heavy metals, and pesticides in wastewater. Furthermore, the ionic liquid exhibits good stability, high catalytic efficiency, and easy recycling.

[0069] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A chitosan / oxidized chitosan composite aerogel, characterized in that: The chitosan / chitosan oxide composite aerogel is prepared by dissolving chitosan and chitosan oxide in a 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid, catalyzing a cross-linking reaction under microwave radiation, then adding a 3-glycidylpropyltrimethoxysilane coupling agent under ultrasonic irradiation to induce a sonic chemical reaction and cross-linking self-assembly with the chitosan / chitosan oxide, followed by the addition of small molecule auxiliaries to enhance the cross-linking effect, and finally obtaining the aerogel by microwave vacuum freeze-drying. The preparation method of the chitosan / chitosan oxide composite aerogel includes the following steps: (1) Chitosan and oxidized chitosan were dissolved in 1-methyl-3-(propyl-3-sulfonic acid)imidazolium salt ionic liquid at room temperature to prepare a solution with a total mass concentration of 1-4%. The solution was subjected to a catalytic cross-linking reaction under microwave radiation for 1-2 hours to form chemical bonds between chitosan and oxidized chitosan. The mass ratio of chitosan to oxidized chitosan was 2-12:

1. The oxidized chitosan had a C6 carboxyl group content of 42.19-75.36%, a C2 and C3 aldehyde group content of 16.08-34.29%, a degree of deacetylation of 88.17-96.33%, a viscosity-average molecular weight of 12,000-34,000, a water solubility of 17.52-27.46 g / 100 mL, and an isoelectric point pH of 4.9-5.

1. Its structural formula is as follows: (2) Under the action of ultrasound, 3-glycidylpropyltrimethoxysilane coupling agent is added to the reaction solution of step (1) and subjected to ultrasonic chemical reaction for 30-60 min. Then, small molecule auxiliaries are added and crosslinking reaction is carried out at 45-60℃ for 1-2 h to obtain composite hydrogel. The mass ratio of chitosan to 3-glycidylpropyltrimethoxysilane coupling agent is 3-8:1, and the mass ratio of chitosan to small molecule auxiliaries is 5-10:

1. The small molecule auxiliaries are selected from oxalic acid, tartaric acid, malic acid, glutamic acid, maleic acid or maleic anhydride. (3) After the reaction is completed, the composite hydrogel is left to stand for 20 to 30 minutes, then placed in an ultra-low temperature freezer at -80 to -55℃ for 3 to 6 hours, and then microwave vacuum freeze-dried for 36 to 48 hours to obtain chitosan / oxidized chitosan composite aerogel.

2. The chitosan / oxidized chitosan composite aerogel according to claim 1, characterized in that: The chitosan / oxidized chitosan composite aerogel has a solubility loss rate of 9.18%–18.71% and a specific surface area of ​​12.57–32.94 m². 2 The average pore size is 50.1–113.6 μm, the porosity is 67.42–90.28%, and the density is 12.18–26.54 mg / cm³. 3 The adsorption capacity for methyl orange is 321.5–410.3 mg / g.

3. The chitosan / oxidized chitosan composite aerogel according to claim 1, characterized in that: In step (1), the pH of the 1-methyl-3-(propyl-3-sulfonyl)imidazolium salt ionic liquid is 5.3 to 6.

0.

4. The chitosan / oxidized chitosan composite aerogel according to claim 1, characterized in that: In step (1), the power of the microwave radiation is 620-800W and the temperature of the microwave radiation is 40-60℃.

5. The chitosan / oxidized chitosan composite aerogel according to claim 1, characterized in that: In step (2), the power of the ultrasonic wave is 280-360W.

6. The chitosan / oxidized chitosan composite aerogel according to claim 1, characterized in that: In step (3), the microwave vacuum freeze-drying temperature is -100 to -84°C, the microwave power is 1200 to 4000W, and the vacuum degree is 5 to 15Pa.

7. An application of the chitosan / oxidized chitosan composite aerogel according to claim 1, characterized in that: Used to adsorb dyes from wastewater.

8. The application according to claim 7, characterized in that: The chitosan / oxidized chitosan composite aerogel that has adsorbed dye can be regenerated and reused after the dye is removed by soaking in hydrochloric acid solution.

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