Polysaccharide-based high-permeability carbon dot hydrogel and preparation method thereof

Abstract

The invention discloses polysaccharide-based high-breathability carbon dot hydrogel and a preparation method thereof, and belongs to the field of hydrogel. Specific carbon dots (chitosan carbon dots) are introduced, the chitosan carbon dots are used as nano-filler and are connected to a polyvinyl alcohol hydrogel network through hydrogen bonds, effective cross-linking polymerization is promoted, meanwhile, a sand core filtering device is adopted, vacuum filtration is conducted for 24 h under the condition of 0.1 MPa, and therefore the pore structure of the hydrogel is constructed, the mechanical property of the hydrogel is enhanced, and the mechanical property of the hydrogel is improved. And moreover, the preparation process is simple, and the performance is excellent.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogels, and particularly relates to a polysaccharide-based highly breathable carbon dot hydrogel and a preparation method thereof. Background Art

[0002] As a new type of flexible electronic material, conductive hydrogels have broad application prospects in the field of wearable electronic devices due to their adjustable mechanical flexibility. Polysaccharides, proteins, polyethylene glycol, polyvinyl alcohol, etc. are widely used to construct hydrogels due to their multifunctionality and biocompatibility. Among them, polysaccharides have many advantages such as low cost, non-toxicity, and biodegradability. In addition, polysaccharides have rich functional groups and high gel strength. There are a large number of hydroxyl groups on the molecular chain of polyvinyl alcohol, and PVA hydrogels can be easily obtained by methods such as cyclic freezing and thawing. However, traditional physically cross-linked hydrogels have insufficient mechanical properties and cannot withstand human body movements and support daily activities, resulting in problems such as narrow detection range and poor durability in hydrogel-based sensors prepared therefrom. In addition, most current hydrogel sensors have poor environmental stability, are prone to water loss at high temperatures or even normal temperatures, and will be frozen at low temperatures, seriously affecting their practical applications. Therefore, the preparation of hydrogel sensors with excellent mechanical properties and environmental stability is of great significance for the development of the flexible electronics field. Summary of the Invention

[0003] In view of this, to solve the above technical problems, the present invention provides a polysaccharide-based highly breathable carbon dot hydrogel and a preparation method thereof.

[0004] It should be noted that carbon dots are composed of ultra-fine, dispersed, approximately spherical carbon nanoparticles, and usually have a diameter of less than 10 nm. In recent years, CDs have attracted extensive attention due to their high specific surface area, low cost, good water solubility, easy surface modification, low biological toxicity, etc. Traditional hydrogels have poor mechanical strength. In addition to strategies for strengthening hydrogels such as constructing double networks, topological structures, and supramolecular polymerization, the incorporation of nano-inorganic particles can also significantly improve the mechanical properties of hydrogels. As zero-dimensional carbon nanomaterials, the incorporation of CDs can significantly improve the mechanical strength of materials and play a role in enhancing toughness. Embedding CDs as nano-fillers into hydrogels, CDs can form physical or chemical cross-linking nodes with polymer chains through various interactions, increase the cross-linking density inside the hydrogel, and form a denser hydrogel network structure, thereby enhancing the mechanical properties of the hydrogel.

[0005] The present invention utilizes chitosan to burn carbon dots to prepare a polysaccharide-based highly breathable carbon dot hydrogel. The introduction of carbon dots endows the hydrogel with sensing performance. At the same time, an innovative method of vacuum filtration self-assembly is adopted in the process of constructing the carbon dot hydrogel, which can effectively construct a uniform three-dimensional pore structure. This structure effectively improves the air permeability of the hydrogel. When it adheres to the skin surface, this breathable hydrogel can not only effectively avoid phenomena such as skin discomfort and sweat accumulation caused by long-term wearing, but also further reduce the risk of skin allergies or inflammation, and is particularly suitable for the medical and personal care fields. At the same time, the introduction of CDs also reduces the freezing point and anti-swelling property of the hydrogel, broadening the application range of the hydrogel electronic skin.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A preparation method of a polysaccharide-based highly breathable carbon dot hydrogel, using a chitosan carbon dot solution and polyvinyl alcohol (PVA) as reactants, through high-temperature reaction, vacuum filtration and freeze-thaw cycle, to obtain the polysaccharide-based highly breathable carbon dot hydrogel.

[0009] Preferably, the preparation method of the polysaccharide-based highly breathable carbon dot hydrogel further includes: using a sand core vacuum filtration device with a microporous water-based filter membrane with a pore size of 0.22 μm to perform vacuum filtration on the carbon dot-polyvinyl alcohol hydrogel prepared by high-temperature reaction; performing vacuum filtration at 0.1 MPa for 24 h to construct the pore structure of the hydrogel.

[0010] Preferably, the preparation method of the chitosan carbon dot solution is: using chitosan as the raw material, water as the solvent, assisted by ethanol for dissolution, through hydrothermal reaction and cooling, to obtain the chitosan carbon dot solution.

[0011] Further, in the above preparation method of the chitosan carbon dot solution, the temperature of the hydrothermal reaction is 160 °C and the time is 2 h; the concentration of the chitosan carbon dot solution is (0.5-4) wt%, preferably 1 wt%.

[0012] Preferably, the mass ratio of the chitosan carbon dot solution to polyvinyl alcohol is (16-19):(1-4), preferably 18:2.

[0013] Preferably, the temperature of the high-temperature reaction is 95 °C and the time is 3 h.

[0014] Preferably, the freeze-thaw cycle is to freeze at -20 °C for 8 h, then thaw at 20 °C for 3 h, and repeat the freezing-thawing at least once.

[0015] In order to improve the mechanical properties of the hydrogel, the present invention designs specific carbon dots (chitosan carbon dots) to act as nano-fillers, which are connected to the polyvinyl alcohol network through hydrogen bonds. Since the specific carbon dots have attractive SP 2 crystal nuclei, which can endow the material with good interfacial interactions (such as π-π stacking, CH-π, etc.). Moreover, after carbonization, the functional groups of the carbonization precursor can be well retained, and it has good dispersibility. In addition, the non-covalent bonds between the specific carbon dots and polyvinyl alcohol, including π-π, CH-π, van der Waals forces and ionic bonds, are used to enhance the mechanical properties of the hydrogel.

[0016] The second technical solution of the present invention:

[0017] The present invention also provides a polysaccharide-based highly breathable carbon dot hydrogel prepared according to the above preparation method, which has good conductivity and breathability.

[0018] It should be noted that the fracture strength of the polysaccharide-based highly breathable carbon dot hydrogel prepared and disclosed in the present invention can reach 6.12 MPa, and the toughness can reach 23.39 MJ m -3 , the conductivity can reach 1.44 S m -1 , and the perspiration permeability can reach 120 g m -2 d -1 .

[0019] In short, the present invention prepares a hydrogel with high strength, high toughness, good conductivity and breathability.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1) The polysaccharide-based highly breathable carbon dot hydrogel prepared and disclosed in the present invention uses chitosan carbon dots as nano-fillers to form a cross-linked network with polyvinyl alcohol. Utilizing the intermolecular interactions between polyvinyl alcohol hydrogels, and at the same time using a sand core filtration device, vacuum filtration is carried out for 24 h under the condition of 0.1 MPa, thereby constructing the pore structure of the hydrogel and constructing a hydrogel with excellent mechanical properties, good conductivity and breathability.

[0022] 2) The specific carbon dots (chitosan carbon dots) used in the present invention not only have attractive sp 2 crystal nuclei, which can endow the material with good interfacial interactions (such as π-π stacking, CH-π, etc.), but also, the carbonized chitosan can well retain the functional groups of the carbonization precursor, has good dispersibility, and introduces a large number of physical cross-linking reaction sites into the polyvinyl alcohol hydrogel, which endows the hydrogel with excellent fracture strength and toughness.

[0023] 3) The hydrogel preparation process disclosed in the present invention is simple and has excellent performance. Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0025] Figure 1 Stress-strain curves of the hydrogels prepared in Examples 1 to 4;

[0026] Figure 2 Stress-strain curves of the hydrogels prepared in Examples 1, 5, and 6;

[0027] Figure 3 Stress-strain curves of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2

[0028] Figure 4 FT-IR diagrams of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0029] Figure 5 Nyquist diagrams of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0030] Figure 6 Scanning electron microscope diagrams of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0031] Figure 7 Sweat dissipation diagrams of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed implementation manners

[0032] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0033] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention, and the upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0034] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0035] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of this invention are obvious to those skilled in the art. The specification and examples of this invention are merely exemplary.

[0036] Regarding the use of "comprising", "including", "having", "containing", etc. in this text, they are all open-ended terms, meaning including but not limited to.

[0037] Unless otherwise specified, the room temperature in this invention is calculated as 25 ± 2 °C.

[0038] All raw materials and reagents used in the examples of this invention are commercially available products.

[0039] Example 1

[0040] Preparation steps of polysaccharide-based highly breathable carbon dot hydrogel with a chitosan carbon dot solution concentration of 1 wt% and a polyvinyl alcohol (PVA) concentration of 10 wt%:

[0041] S1. Add 1 g of chitosan to 100 mL of deionized water, add 2 mL of glacial acetic acid, place it in a pressure-resistant reaction flask, heat it to 160 °C and react for 2 h, and let the reaction vessel cool naturally to room temperature to obtain a 1 wt% chitosan carbon dot solution;

[0042] S2. Mix the above chitosan carbon dot solution (18 g) with polyvinyl alcohol (2 g), react at 95 °C for 3 h, after the mixed solution cools to room temperature, perform vacuum filtration at 0.1 MPa for 24 h, and then perform freeze-thaw cycling treatment on the obtained reaction product (the freeze-thaw cycle is freezing at -20 °C for 8 h and then thawing at 20 °C for 3 h, for a total of 3 freeze-thaw cycles) to obtain the chitosan carbon dot / polyvinyl alcohol hydrogel, which is the polysaccharide-based highly breathable carbon dot hydrogel.

[0043] Example 2

[0044] Preparation steps of polysaccharide-based highly breathable carbon dot hydrogel with a carbon dot concentration of 0.5 wt% and a polyvinyl alcohol (PVA) concentration of 10 wt%:

[0045] S1. Add 0.5 g of chitosan to 100 mL of deionized water, add 1 mL of glacial acetic acid, place it in a pressure-resistant reaction flask, heat it to 160 °C and react for 2 h. Let the reaction vessel cool naturally to room temperature to obtain a chitosan carbon dot solution with a concentration of 0.5 wt%.

[0046] S2. Mix the above chitosan carbon dot solution (18 g) with polyvinyl alcohol (2 g), react at 95 °C for 3 h. After the mixed solution cools to room temperature, perform vacuum filtration under the condition of 0.1 MPa for 24 h. Then, perform freeze-thaw cycling on the obtained reaction product (the freeze-thaw cycle is to freeze at -20 °C for 8 h and then thaw at 20 °C for 3 h, for a total of 3 freeze-thaw cycles) to obtain a chitosan carbon dot / polyvinyl alcohol hydrogel.

[0047] Example 3

[0048] Preparation steps of a polysaccharide-based highly breathable carbon dot hydrogel with a carbon dot concentration of 2 wt% and a polyvinyl alcohol (PVA) concentration of 10 wt%:

[0049] S1. Add 1 g of chitosan to 100 mL of deionized water, add 2 mL of glacial acetic acid, place it in a pressure-resistant reaction flask, heat it to 160 °C and react for 2 h. Let the reaction vessel cool naturally to room temperature to obtain a chitosan carbon dot solution with a concentration of 1 wt%.

[0050] S2. Rotavaporize the above chitosan carbon dot solution (36 g) to 18 g, then mix it with polyvinyl alcohol (2 g), react at 95 °C for 3 h. After the mixed solution cools to room temperature, perform vacuum filtration under the condition of 0.1 MPa for 24 h. Then, perform freeze-thaw cycling on the obtained reaction product (the freeze-thaw cycle is to freeze at -20 °C for 8 h and then thaw at 20 °C for 3 h, for a total of 3 freeze-thaw cycles) to obtain a chitosan carbon dot / polyvinyl alcohol hydrogel.

[0051] Example 4

[0052] Preparation steps of a polysaccharide-based highly breathable carbon dot hydrogel with a carbon dot concentration of 4 wt% and a polyvinyl alcohol (PVA) concentration of 10 wt%:

[0053] S1. Add 1 g of chitosan to 100 mL of deionized water, add 2 mL of glacial acetic acid, place it in a pressure-resistant reaction flask, heat it to 160 °C and react for 2 h. Let the reaction vessel cool naturally to room temperature to obtain a chitosan carbon dot solution with a concentration of 1 wt%.

[0054] S2. The above chitosan carbon dot solution (72 g) was rotary evaporated to 18 g, then mixed with polyvinyl alcohol (2 g), and reacted at 95 °C for 3 h. After the mixed solution was cooled to room temperature, it was vacuum filtered at 0.1 MPa for 24 h. Then, the obtained reaction product was subjected to freeze-thaw cycling (the freeze-thaw cycle was freezing at -20 °C for 8 h and then thawing at 20 °C for 3 h, with a total of 3 freeze-thaw cycles), and the obtained chitosan carbon dot / polyvinyl alcohol hydrogel was obtained.

[0055] Example 5

[0056] Preparation steps of polysaccharide-based highly breathable carbon dot hydrogel with a carbon dot concentration of 1 wt% and a polyvinyl alcohol (PVA) concentration of 5 wt%:

[0057] S1. Add 1 g of chitosan to 100 mL of deionized water, add 2 mL of glacial acetic acid, place it in a pressure-resistant reaction flask, heat it to 160 °C and react for 2 h. The reaction vessel was naturally cooled to room temperature to obtain a chitosan carbon dot solution with a concentration of 1 wt%.

[0058] S2. The above chitosan carbon dot solution (19 g) was mixed with polyvinyl alcohol (1 g), reacted at 95 °C for 3 h. After the mixed solution was cooled to room temperature, it was vacuum filtered at 0.1 MPa for 24 h. Then, the obtained reaction product was subjected to freeze-thaw cycling (the freeze-thaw cycle was freezing at -20 °C for 8 h and then thawing at 20 °C for 3 h, with a total of 3 freeze-thaw cycles), and the obtained chitosan carbon dot / polyvinyl alcohol hydrogel was obtained.

[0059] Example 6

[0060] Preparation steps of polysaccharide-based highly breathable carbon dot hydrogel with a carbon dot concentration of 1 wt% and a polyvinyl alcohol (PVA) concentration of 15 wt%:

[0061] S1. Add 1 g of chitosan to 100 mL of deionized water, add 2 mL of glacial acetic acid, place it in a pressure-resistant reaction flask, heat it to 160 °C and react for 2 h. The reaction vessel was naturally cooled to room temperature to obtain a chitosan carbon dot solution with a concentration of 1 wt%.

[0062] S2. The above chitosan carbon dot solution (17 g) was mixed with polyvinyl alcohol (3 g), reacted at 95 °C for 3 h. After the mixed solution was cooled to room temperature, it was vacuum filtered at 0.1 MPa for 24 h. Then, the obtained reaction product was subjected to freeze-thaw cycling (the freeze-thaw cycle was freezing at -20 °C for 8 h and then thawing at 20 °C for 3 h, with a total of 3 freeze-thaw cycles), and the obtained chitosan carbon dot / polyvinyl alcohol hydrogel was obtained.

[0063] Comparative Example 1

[0064] Preparation steps of chitosan-based highly breathable hydrogel with a concentration of 1 wt% and a polyvinyl alcohol (PVA) concentration of 10 wt%:

[0065] S1. Add 1 g of chitosan to 100 mL of deionized water, add 2 mL of glacial acetic acid, and stir at room temperature to obtain a chitosan aqueous solution;

[0066] S2. Mix the above chitosan aqueous solution (18 g) with polyvinyl alcohol (2 g), react at 95 °C for 3 h, after the mixed solution cools to room temperature, perform vacuum filtration under the condition of 0.1 MPa for 24 h, and then perform freeze-thaw cycle treatment on the obtained reaction product (the freeze-thaw cycle is freezing at -20 °C for 8 h, and then thawing at 20 °C for 3 h, a total of 3 freeze-thaw cycles), and the obtained chitosan / polyvinyl alcohol hydrogel is the chitosan / polyvinyl alcohol hydrogel.

[0067] Comparative Example 2

[0068] The preparation steps of the hydrogel with a polyvinyl alcohol (PVA) concentration of 10 wt% are as follows:

[0069] Mix polyvinyl alcohol (2 g) with deionized water (18 g), react at 95 °C for 3 h, after the reaction product cools to room temperature, perform freeze-thaw cycle treatment (the freeze-thaw cycle is freezing at -20 °C for 8 h, and then thawing at 20 °C for 3 h, a total of 3 freeze-thaw cycles), and obtain the polyvinyl alcohol hydrogel, denoted as PVA.

[0070] Perform mechanical property tests and toughness calculations on the hydrogels prepared in Examples 1-6 and Comparative Examples 1-2, and the method is as follows:

[0071] Cut the hydrogels prepared in Examples 1-6 and Comparative Examples 1-2 into samples with a size of 15 mm × 5 mm × 1.5 mm and perform tensile property tests at room temperature. Uniaxial tensile measurement is carried out using an electronic universal testing machine (Shenzhen Sun Technology Co., Ltd., China), and the extension speed is 40 mm / min.

[0072] Toughness is calculated according to the area under the stress-strain curve through the following formula:

[0073] ΔU = ∫σdε

[0074] In the formula, σ and ε are the stress (MPa) and strain (%) of the hydrogel, respectively.

[0075] Perform conductivity tests and calculations on the hydrogels prepared in Examples 1-6 and Comparative Examples 1-2, and the method is as follows:

[0076] The electrochemical properties of the hydrogel were evaluated by an electrochemical workstation (model). The hydrogel sample was cut into strip samples with dimensions of 7 (length) × 8 (width) × 2 mm (thickness). Electrochemical impedance spectroscopy (EIS) was used with a voltage of 0.1 V and a frequency range of 105 - 0.1 Hz. The conductivity was calculated using the following formula:

[0077]

[0078] where L represents the distance (cm) between adjacent electrodes, R represents the resistance (Ω) of the hydrogel, and S represents the contact area (cm 2 ) of the hydrogel with the electrode.

[0079] The tensile strength, elongation at break, and toughness of the hydrogels prepared in Examples 1 - 6 and Comparative Examples 1 - 2 are shown in Table 1.

[0080] Table 1

[0081] Specimen Tensile strength (MPa) Elongation at break (%) <![CDATA[Toughness (MJ / m 3 )]]> Example 1 6.12 672 23.39 Example 2 1.03 292 1.57 Example 3 1.99 290 3.58 Example 4 2.04 227 2.91 Example 5 0.68 50 0.21 Example 6 0.65 135 0.69 Comparative Example 1 2.8 440 6.68 Comparative Example 2 0.22 6.68 0.078

[0082] As can be seen from the data in Table 1, the hydrogel prepared in Example 1 has the highest breaking strength and toughness, reaching 6.12 MPa and 23.39 MJ / m 3 . And from the data changes in Examples 2 - 6 and Comparative Examples 1 - 2, it can be seen that the mechanical properties of the chitosan carbon dots / polyvinyl alcohol hydrogel are affected to a certain extent at different carbon dot concentrations and different polyvinyl alcohol concentrations. This indicates that the hydrogel prepared in the present invention using chitosan carbon dots as nano-fillers for polyvinyl alcohol hydrogels at a carbon dot concentration of 1 wt% and a polyvinyl alcohol concentration of 10 wt% has good mechanical properties.

[0083] Figure 1 The stress-strain curves of the hydrogels prepared in Examples 1 - 4 are shown. It can be seen that as the carbon dot content increases from 0.5 wt% to 1 wt%, 2 wt%, and 4 wt%, the mechanical properties of the prepared hydrogels show a trend of first increasing and then decreasing. Among them, the hydrogel with a carbon dot content of 1 wt% prepared in Example 1 has better tensile strength, elongation at break, and toughness. With the increase of the carbon dot content, the mechanical properties of the hydrogel are improved. This is because an appropriate concentration of carbon dots can not only act as a filler, effectively restricting the movement of polymer chains and increasing the crosslinking density, thereby enhancing the mechanical strength of the hydrogel; in addition, carbon dots can also act as stress concentration points to improve the toughness of the hydrogel. However, when the concentration of carbon dots is too high, it will cause local entanglement of polymer chains, form a dense network structure, lead to over-crosslinking, and also increase the defects in the polymer network, reducing the uniformity of the hydrogel network structure, thus resulting in a decrease in mechanical properties.

[0084] Figure 2The stress-strain curves of the hydrogels prepared in Example 1, Example 5 and Example 6 are shown. It can be seen that with the increase of the content of polyvinyl alcohol, the mechanical strength of the hydrogel is significantly improved. This is because a higher concentration of polyvinyl alcohol means that more polymer chains participate in the cross-linking process, thus forming a denser and stronger network structure. However, when the concentration of polyvinyl alcohol is too high, the crystallinity in the hydrogel is too high and the cross-linking degree is too tight, reducing the ability of the material to absorb impact, which will weaken the ability of the hydrogel to cope with deformation and reduce its mechanical properties.

[0085] Figure 3 The stress-strain curves of the hydrogels prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown. It can be seen that with the introduction of chitosan and chitosan carbon dots, the tensile strength, elongation at break and toughness of the hydrogel all increase significantly. The hydrogel prepared in Example 1 has higher mechanical strength and tensile strain, with a stress of 6.12 MPa and an elongation at break of 672%. Compared with the hydrogel of Comparative Example 2, the hydrogel prepared in Example 1 has higher mechanical properties. This is because the introduction of carbon dots enhances the cross-linking degree of the hydrogel, while the polyvinyl alcohol hydrogel has a higher water content, which, although endowing it with good flexibility and water absorption, also leads to a decrease in the mechanical strength of the material. The presence of water weakens the mechanical strength of the PVA chains, resulting in the hydrogel being prone to deformation and fracture under tension or pressure.

[0086] Figure 4 The FT-IR spectra of the hydrogels prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown. It can be seen that the characteristic absorption band at 3340 cm -1 is related to the O-H stretching vibration, while the characteristic absorption band at 1639 cm -1 is related to the hydrogen bond vibration. In addition, the peaks of the three sample hydrogels, namely the polyvinyl alcohol hydrogel of Comparative Example 2, the chitosan / polyvinyl alcohol hydrogel of Comparative Example 1 and the chitosan carbon dot / polyvinyl alcohol hydrogel of Example 1, in the infrared spectra show a tendency to shift to higher wavenumbers. This indicates an increase in the cross-linking degree in the hydrogel. A higher cross-linking degree may lead to a decrease in the distance between polymer chains, thus affecting the vibration modes of specific functional groups, and further causing the positions of some absorption peaks to shift, that is, the cross-linked structure becomes more compact, resulting in an increase in the vibration frequency and the peak shifting to higher wavenumbers.

[0087] Figure 5Nyquist plots of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2. The chitosan carbon dot / polyvinyl alcohol hydrogel has a relatively high conductivity. The Nyquist plot indicates the stable electrical properties of the hydrogel. The conductivity of 1.44 S / m is different from that of the chitosan / polyvinyl alcohol (not carbonized, Comparative Example 2) hydrogel at 0.33 S / m and the polyvinyl alcohol (Comparative Example 3) hydrogel at 0.08 S / m. This is because the surface of the chitosan carbon dots retains abundant -OH functional groups, which have a relatively high electron mobility and good electron transport performance. Therefore, when the chitosan carbon dots are dispersed in the polyvinyl alcohol hydrogel network, a conductive pathway can be formed, increasing the electron migration rate. In addition, the size of the carbon dots is usually at the nanoscale, and they also exhibit quantum size effects, which can adjust their band structure and electronic properties, thus further optimizing the conductive performance. The carbon dots can form a three-dimensional conductive network in the hydrogel, and this network structure helps to improve the charge transport efficiency and enhance the overall conductivity of the hydrogel. At the same time, the pore structure created by suction filtration also provides a channel for the directional movement of electrons, further improving the conductive performance of the hydrogel prepared in Example 1. Polyvinyl alcohol is a non-conductive polymer that does not contain freely moving charge carriers. The carbon and oxygen atoms mainly exist in the form of covalent bonds, and the molecular structure is stable, which is not conducive to charge transfer, resulting in a low conductivity. The three-dimensional network structure of the polyvinyl alcohol hydrogel is composed of cross-linked polyvinyl alcohol molecular chains, and this structure restricts the migration of charge carriers, thereby reducing the conductivity.

[0088] Figure 6 Scanning electron microscope images of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2. The first row shows the scanning electron microscope images of the surface morphologies of the three hydrogel samples, and the second row shows the scanning electron microscope images of the cross-sectional morphologies of the three hydrogel samples obtained by brittle fracture with liquid nitrogen. From the three prepared hydrogel samples, it can be seen that vacuum suction filtration using a sand core filtration device can effectively construct the pore structure of the hydrogel, and these micropores ensure the breathability of the hydrogel when used on the skin, and can effectively improve the comfort and skin compatibility of the wearable sensor.

[0089] Figure 7 Sweat dissipation diagrams of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2. It can be seen that the breathabilities of the hydrogel samples prepared in Example 1 and Comparative Example 1 are similar. This is because the size of the chitosan carbon dots obtained by high-temperature firing is relatively small, and the degree of carbonization is relatively low, and a large amount of chitosan coexists in the carbon dots. The hydrogels prepared in Example 1 and Comparative Example 1 use the innovative method of suction filtration to construct the pore structure, and these micropores ensure the free water vapor exchange between the human skin and the external environment, thus ensuring the breathability of the hydrogel.

[0090] The above are only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a polysaccharide-based highly air-permeable carbon dot hydrogel, characterized in that: The chitosan carbon dot solution and polyvinyl alcohol are used as reactants, and the polysaccharide-based highly air-permeable carbon dot hydrogel is obtained through high-temperature reaction and freeze-thaw cycles.

2. The method for preparing the polysaccharide-based highly air-permeable carbon dot hydrogel according to claim 1, characterized in that: The preparation method of the chitosan carbon dot solution is: Chitosan is used as a raw material, water is used as a solvent, acetic acid is used as an auxiliary dissolution, and the chitosan carbon dot solution is obtained through hydrothermal reaction and cooling.

3. The method for preparing the polysaccharide-based highly air-permeable carbon dot hydrogel according to claim 2, characterized in that: The temperature of the hydrothermal reaction is 160° C. and the time is 2 hours.

4. The method for preparing the polysaccharide-based highly air-permeable carbon dot hydrogel according to claim 2, characterized in that: The concentration of the chitosan carbon dot solution is (0.5-4) wt%.

5. The method for preparing the polysaccharide-based highly air-permeable carbon dot hydrogel according to claim 1, characterized in that: The mass ratio of the chitosan carbon dot solution to polyvinyl alcohol is (16-19): (1-4).

6. The method for preparing the polysaccharide-based highly air-permeable carbon dot hydrogel according to claim 1 or 5, characterized in that: The temperature of the high temperature reaction is 95° C. and the time is 3 hours.

7. The method for preparing the polysaccharide-based highly air-permeable carbon dot hydrogel according to claim 1, characterized in that: Also includes: The carbon dot-polyvinyl alcohol hydrogel prepared by high temperature reaction was vacuum filtered using a sand core filtration device and a microporous water filter membrane; Vacuum filtration was performed at 0.1 MPa for 24 h.

8. The method for preparing the polysaccharide-based highly air-permeable carbon dot hydrogel according to claim 1, characterized in that: The freeze-thaw cycle operation is as follows: Freeze at -20°C for 8 h, then thaw at 20°C for 3 h, and repeat freeze-thaw at least once.

9. A polysaccharide-based highly air-permeable carbon dot hydrogel prepared by the method according to any one of claims 1 to 8.

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