A chlorophyll carbon dot-based hydrogel and its preparation method

Abstract

This invention discloses a chlorophyll carbon dot-based hydrogel and its preparation method, belonging to the field of hydrogel materials technology. The chlorophyll carbon dot-based hydrogel of this invention uses chlorophyll carbon dots as nanofillers, prepared by combining them with acrylamide (AM) through a UV-initiated polymerization reaction. Chlorophyll carbon dots not only possess excellent sp... 2 The crystal nucleus can impart excellent interfacial interactions to the material (such as π-π stacking, CH-π, etc.), and the carbonized chlorophyll can retain the functional groups of the carbonized precursor well, possessing good dispersibility and introducing a large number of physical crosslinking reaction sites to the polyacrylamide hydrogel. This endows the hydrogel with ultra-high tensile strength and toughness. The preparation process of this hydrogel is simple and its performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel materials technology, and in particular relates to a chlorophyll carbon dot-based hydrogel and its preparation method. Background Technology

[0002] Hydrogels are sparse network polymer materials composed of polymer chains embedded in an aqueous medium. Due to their unique conductivity, flexibility, and three-dimensional network structure, hydrogels have been widely used and extensively studied in various fields, including wearable electronic devices, soft robots, nano-triboelectric generators, biomedicine, and solid electrolytes. However, the relatively poor mechanical properties of traditional hydrogels greatly limit their potential for real-world applications.

[0003] There are two main reasons for the poor mechanical properties of hydrogels: First, the cross-linking points in the hydrogel network are unevenly distributed, and when subjected to external forces, the hydrogel is prone to breakage due to stress concentration; second, the cross-linking density of polymer chains in the hydrogel is low, and the friction between chains is small, resulting in insufficient mechanical strength of the hydrogel.

[0004] In recent years, researchers have proposed many new strategies to improve the mechanical properties of hydrogels, such as nanocomposite hydrogels, dual-network hydrogels, and ionically crosslinked hydrogels. Hydrogels prepared by these methods have exhibited better mechanical strength. Although some progress has been made in preparing hydrogels with excellent mechanical properties, the tough hydrogels developed so far are still far inferior to water-containing biological tissues and solid engineering plastics in many aspects.

[0005] For example, ligaments and tendons, as bio-hydrogels, have tensile strengths as high as 49 MPa and 65 MPa, respectively, while the tensile strength of most plastics is between ten and tens of megapascals. In contrast, most tough hydrogels have tensile strengths below 1 MPa, with only a few hydrogels reaching the range of 1-10 MPa. Therefore, the design and development of hydrogels with high strength and high toughness is particularly necessary.

[0006] Patent CN119264469A discloses a carbon dot-based high-water-content, strong and tough hydrogel and its preparation method. Using hydroquinone carbon dot solution, sodium alginate, and polyvinyl alcohol as reactants, the method involves high-temperature reaction and freeze-thaw cycles to obtain the carbon dot-based high-water-content, strong and tough hydrogel. The freeze-thaw cycle involves freezing at -20°C for 8 hours, followed by thawing at 20°C for 3 hours, with the freeze-thaw cycle repeated at least once. The hydrogel prepared by this method exhibits a maximum tensile strength of 13.47 MPa and a toughness of 39.61 MJ / m. 3Patent CN119350654A discloses a method for preparing carbon dot-based super-strong hydrogels. Using a carbon source as raw material and water as a solvent, a carbon dot solution is obtained through calcination and cooling. The carbon dot solution and polyvinyl alcohol are then reacted at high temperature and subjected to freeze-thaw cycles to obtain a carbon dot-polyvinyl alcohol hydrogel. The hydrogel prepared by this method achieves a maximum tensile strength of 129.37 MPa and a maximum toughness of 225.2 MJ / m. 3 Existing technologies using polyvinyl alcohol (PVA) as a raw material to prepare hydrogels exhibit good mechanical properties. However, due to its low reactivity, PVA cannot rapidly form a cross-linked network structure through free radical polymerization like monomers such as acrylamide. In the preparation of hydrogels, repeated freeze-thaw cycles are required to promote non-covalent interactions between molecular chains (such as hydrogen bonding and microcrystalline region construction) to build a stable three-dimensional network. Although this method can fully utilize the excellent mechanical properties and biocompatibility of PVA to improve hydrogel performance, its preparation cycle is long, lasting several days to several weeks, and requires a large amount of energy to maintain a low-temperature environment, resulting in low production efficiency and high costs. This limitation severely restricts the widespread application of PVA-based hydrogel materials in large-scale industrial production.

[0007] There is an urgent need in this field for a method to prepare hydrogels that consumes less energy and takes less time. Summary of the Invention

[0008] The purpose of this invention is to provide a chlorophyll carbon dot-based hydrogel and its preparation method to solve the problems existing in the prior art.

[0009] One of the technical solutions provided by this invention:

[0010] A method for preparing a chlorophyll carbon dot-based hydrogel involves using chlorophyll carbon dots and acrylamide as reactants, and initiating a polymerization reaction with ultraviolet light to obtain the chlorophyll carbon dot-based hydrogel.

[0011] Preferably, the preparation method includes the following steps: mixing chlorophyll carbon dot solution, water, photoinitiator, crosslinking agent and acrylamide, and obtaining the chlorophyll carbon dot-based hydrogel through ultraviolet light polymerization reaction.

[0012] More preferably, the mass ratio of the chlorophyll carbon dot solution, water, photoinitiator, crosslinking agent and acrylamide is 5:2.5:0.03:0.003:2.5, and the mass concentration of the chlorophyll carbon dot solution is 0.53wt%.

[0013] In this invention, the introduction of chlorophyll carbon dots with a highly graphitized structure significantly enhances the internal interactions of the hydrogel. These carbon dots interact synergistically with the hydrogel matrix through multiple interactions, including hydrogen bonds, van der Waals forces, and π-π stacking, thereby greatly improving the mechanical properties and interfacial adhesion of the hydrogel. The mechanism is as follows: Under ultraviolet light excitation, the photoinitiator decomposes to generate free radical active species. These free radicals initiate polymerization by attacking the double bonds of acrylamide monomers, forming active monomer free radicals. Subsequently, through a chain growth reaction, the monomer free radicals continuously bind with surrounding acrylamide molecules, gradually forming long polyacrylamide chains. During this process, the crosslinking agent N,N-methylenebisacrylamide establishes covalent crosslinking points by reacting with active sites on the polymer chains, ultimately constructing a stable hydrogel system with a three-dimensional network structure. When coupling reactions occur between free radicals or when they interact with other chain terminators, the polymerization reaction terminates, thereby forming a crosslinked network with a specific topological structure.

[0014] More preferably, the preparation method of chlorophyll carbon dot solution is as follows: using chlorophyll as raw material and water as solvent, chlorophyll carbon dot solution is obtained by firing and cooling.

[0015] More preferably, the ratio of chlorophyll to water is 1g:100mL.

[0016] More preferably, the firing temperature is 180°C and the firing time is 6 hours.

[0017] More preferably, the centrifugation speed is 8000 rpm and the time is 10 min.

[0018] Chlorophyll is a type of green pigment widely found in plants, algae, and some bacteria. It is a core substance for photosynthesis, capturing solar energy and converting it into chemical energy, providing the energy basis for life on Earth. The chlorophyll molecule has a porphyrin ring at its core, with a magnesium ion (Mg²⁺) bonded to the center. 2+ The side chain structure varies depending on the type. Chlorophyll exhibits two types of reactions: the light reaction, where chlorophyll absorbs red light (approximately 660 nm) and blue-violet light (approximately 430 nm) and converts light energy into ATP and NADPH through photosystems I and II; and the dark reaction (Calvin cycle), which utilizes the products of the light reaction to fix carbon dioxide into glucose. Chlorophyll is mainly distributed in the chloroplasts of plant cells, concentrated on the thylakoid membrane. This invention uses chlorophyll as a raw material to prepare hydrogels, which is readily available and extremely low in cost, thus reducing the cost of hydrogel preparation to a certain extent.

[0019] More preferably, the crosslinking agent is N,N-methylenebisacrylamide.

[0020] More preferably, the photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone.

[0021] More preferably, the wavelength of the ultraviolet polymerization reaction is 365 nm and the time is 5 min.

[0022] To improve the mechanical properties of hydrogels, this invention designs a method using chlorophyll carbon dots as nanofillers. Chlorophyll carbon dots possess excellent sp... 2 Crystal nuclei can impart excellent interfacial interactions to materials (e.g., π-π stacking, CH-π, etc.), and carbonization can effectively retain the functional groups of the carbonized precursor, resulting in good dispersibility. Furthermore, the mechanical properties of hydrogels are enhanced through chlorophyll carbon dots and non-covalent bonds of acrylamide, including π-π, CH-π, van der Waals forces, and ionic bonds.

[0023] The second technical solution provided by this invention:

[0024] A chlorophyll carbon dot-based hydrogel prepared by the above preparation method.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] The chlorophyll carbon dot-based hydrogel of this invention uses chlorophyll carbon dots as nanofillers and is prepared by combining them with acrylamide (AM) through a UV-initiated polymerization reaction. Chlorophyll carbon dots not only possess excellent sp... 2 The crystal nucleus imparts excellent interfacial interactions to the material (e.g., π-π stacking, CH-π, etc.). Furthermore, the carbonized chlorophyll retains the functional groups of the carbonized precursor, exhibiting excellent dispersibility and introducing numerous physical cross-linking reaction sites into the polyacrylamide hydrogel. This endows the hydrogel with ultra-high tensile strength and toughness. The hydrogel preparation process is simple, and its performance is superior. Compared with existing technologies, the preparation time of the hydrogel in this invention is significantly reduced, which is beneficial for reducing energy consumption and facilitates further promotion in large-scale industrial production. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The stress-strain curves of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0029] Figure 2The adhesion performance curves of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0030] Figure 3 The stress-strain curves of the hydrogels prepared in Example 1, Comparative Example 5, and Comparative Example 6 are shown.

[0031] Figure 4 The stress-strain curves of the hydrogels prepared in Example 1, Comparative Example 3, and Comparative Example 4 are shown. Detailed Implementation

[0032] Various exemplary embodiments of the present invention will now 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, features, and embodiments of the present invention.

[0033] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0035] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0036] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0037] In this embodiment of the invention, chlorophyll is extracted from spinach, and the specific preparation method is as follows:

[0038] Place 10g of spinach leaf fragments into a mortar, add 1g of quartz sand and 0.1g of calcium carbonate, slowly add 10mL of anhydrous ethanol, and grind thoroughly into a paste. Then transfer the grinding liquid to a centrifuge tube, add ethanol until the leaves are completely submerged, centrifuge at 3000rpm for 5min to accelerate precipitation, filter with filter paper or gauze, collect the dark green filtrate, remove ethanol by vacuum distillation, increase the chlorophyll concentration to 0.5wt.%, and obtain a chlorophyll solution. Place the concentrated chlorophyll solution in a petri dish and dry at room temperature to remove ethanol and water, obtaining solid chlorophyll.

[0039] The room temperature in this invention refers to 25±2℃.

[0040] All raw materials and reagents used in the embodiments of this invention are commercially available products.

[0041] The photoinitiator in this embodiment of the invention is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone.

[0042] Example 1: A method for preparing chlorophyll carbon dot-based hydrogels

[0043] S1. Add 1.5g of chlorophyll to 150mL of deionized water, place it in a reaction vessel and heat to 180℃ for 6h. Let the reaction vessel cool naturally to room temperature. Centrifuge the resulting solution in a centrifuge at 8000rpm for 10min. After removing the precipitate, take 1g of the supernatant and dry it in a constant temperature drying oven to obtain 0.0053g of solid. The concentration of chlorophyll carbon dot solution is calculated to be 0.53%.

[0044] S2. Take the chlorophyll carbon dot solution (5g), deionized water (2.5g), photoinitiator (30mg), and N,N-methylenebisacrylamide (3mg) and acrylamide (2.5g) prepared in S1 and mix them (the mass concentration of carbon dots in the resulting mixture is 0.35%). Stir for 30min, then pour the mixture into a dumbbell-shaped mold and polymerize it under ultraviolet light at 365nm for 5min to obtain chlorophyll carbon dot-polyacrylamide hydrogel, i.e., chlorophyll carbon dot-based hydrogel.

[0045] Comparative Example 1: A method for preparing a chlorophyll-polyacrylamide hydrogel

[0046] In Example 1, the amount of chlorophyll carbon dots added was 5g × 0.53% = 26.5mg. In this comparative example, the chlorophyll carbon dots were replaced with chlorophyll by an equal mass. The mechanical properties of the prepared hydrogel were measured. The specific preparation method is as follows:

[0047] Chlorophyll (26 mg), deionized water (7.5 g), photoinitiator (30 mg), and N,N-methylenebisacrylamide (3 mg) were mixed with acrylamide (2.5 g) and stirred for 30 min. The mixture was then poured into a dumbbell-shaped mold and polymerized under ultraviolet light at 365 nm for 5 min to obtain chlorophyll-polyacrylamide hydrogel.

[0048] Comparative Example 2

[0049] This comparative example provides a polyacrylamide hydrogel, the preparation steps of which are as follows:

[0050] Deionized water (7.5 g), photoinitiator (30 mg), and N,N-methylenebisacrylamide (3 mg) were mixed with acrylamide (2.5 g) and stirred for 30 min. The mixture was then poured into a dumbbell-shaped mold and polymerized under ultraviolet light at 365 nm for 5 min to obtain polyacrylamide hydrogel.

[0051] Comparative Example 3

[0052] S1. Same as Example 1;

[0053] S2. Take the chlorophyll carbon dot solution (5g), deionized water (3.8g), photoinitiator (30mg), and N,N-methylenebisacrylamide (3mg) and acrylamide (2.5g) prepared in S1 and mix them (the mass concentration of carbon dots in the resulting mixture is 0.3%). Stir for 30min, then pour the mixture into a dumbbell-shaped mold and polymerize it under ultraviolet light at 365nm for 5min to obtain chlorophyll carbon dot-polyacrylamide hydrogel, i.e., chlorophyll carbon dot-based hydrogel.

[0054] Comparative Example 4

[0055] S1. Same as Example 1;

[0056] S2. Take the chlorophyll carbon dot solution (5g), deionized water (1.6g), photoinitiator (30mg), and N,N-methylenebisacrylamide (3mg) and acrylamide (2.5g) prepared in S1 and mix them (the mass concentration of carbon dots in the resulting mixture is 0.4%). Stir for 30min, then pour the mixture into a dumbbell-shaped mold and polymerize it under ultraviolet light at 365nm for 5min to obtain chlorophyll carbon dot-polyacrylamide hydrogel, i.e., chlorophyll carbon dot-based hydrogel.

[0057] Comparative Example 5

[0058] S1. Add 1.5g of chlorophyll to 150mL of deionized water, place it in a reaction vessel and heat to 180℃ for 6h. Let the reaction vessel cool naturally to room temperature, and centrifuge the resulting solution in a centrifuge at 8000rpm for 10min to obtain a chlorophyll carbon dot solution with a concentration of 0.53%.

[0059] S2. Take the chlorophyll carbon dot solution (5g), deionized water (5.6g), photoinitiator (30mg), and N,N-methylenebisacrylamide (3mg) and acrylamide (2.5g) prepared in S1 and mix them (the mass concentration of carbon dots in the resulting mixture is 0.25%). Stir for 30min, then pour the mixture into a dumbbell-shaped mold and polymerize it under ultraviolet light at 365nm for 5min to obtain chlorophyll carbon dot-polyacrylamide hydrogel, i.e., chlorophyll carbon dot-based hydrogel.

[0060] Comparative Example 6

[0061] S1. Add 1.5g of chlorophyll to 150mL of deionized water, place it in a reaction vessel and heat to 180℃ for 6h. Let the reaction vessel cool naturally to room temperature, and centrifuge the resulting solution in a centrifuge at 8000rpm for 10min to obtain a chlorophyll carbon dot solution with a concentration of 0.53%.

[0062] S2. Take the chlorophyll carbon dot solution (5g), deionized water (12.6g), photoinitiator (30mg), and N,N-methylenebisacrylamide (3mg) and acrylamide (2.5g) prepared in S1 and mix them (the mass concentration of carbon dots in the resulting mixture is 0.15%). Stir for 30min, then pour the mixture into a dumbbell-shaped mold and polymerize it under ultraviolet light at 365nm for 5min to obtain chlorophyll carbon dot-polyacrylamide hydrogel, i.e., chlorophyll carbon dot-based hydrogel.

[0063] Performance testing

[0064] The mechanical properties and toughness calculations of the hydrogels prepared in Example 1 and Comparative Examples 1-6 were performed as follows, and the results are shown in Table 1.

[0065] The dumbbell-shaped (75mm × 12.5mm × 2m) hydrogels prepared in Example 1 and Comparative Examples 1-6 were subjected to tensile property tests at room temperature. Uniaxial tensile measurements were performed using an electronic universal testing machine (Shenzhen Suntech Power Technology Co., Ltd., China) at an elongation speed of 100mm / min; toughness was calculated based on the area under the stress-strain curve using the following formula:

[0066] ΔU=∫σdε

[0067] In the formula, σ and ε are the stress and strain of the hydrogel, respectively.

[0068] Table 1

[0069] Specimen Tensile strength (kPa) <![CDATA[Toughness (MJ / m 3 )]]> Example 1 431.42 3.47 Comparative Example 1 127.56 0.47 Comparative Example 2 67.52 0.1 Comparative Example 3 295.13 1.12 Comparative Example 4 282.68 1.08 Comparative Example 5 244.77 0.88 Comparative Example 6 202.04 0.79

[0070] As can be seen from the data in Table 1, the hydrogel prepared in Example 1 has the highest tensile strength and toughness, reaching 431.42 kPa and 3.47 MJ / m, respectively. 3 Furthermore, based on the data changes in Comparative Examples 1-2, it can be seen that the chlorophyll carbon dot-based hydrogel prepared in Example 1 exhibits significantly improved performance compared to the hydrogels without carbon dots and without carbonization.

[0071] In Comparative Example 3, due to the low concentration of chlorophyll carbon dots, fewer physical cross-linking points were formed in the hydrogel, resulting in the failure to form a uniform and stable network, which led to a decrease in the performance of the prepared hydrogel. In Comparative Example 4, due to the excessively high concentration of carbon dots (>0.53wt%), a dense network structure may be formed, leading to excessive cross-linking. At the same time, it may cause phase separation or aggregation, affecting the interaction between carbon dots and polyacrylamide molecular chains, resulting in the non-uniformity of the hydrogel and a decrease in the performance of the prepared hydrogel.

[0072] Figure 1 The stress-strain curves of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0073] from Figure 1 As can be seen, compared with hydrogels made without chlorophyll and without carbonized chlorophyll, the mechanical properties of chlorophyll carbon dot-based hydrogels are as high as 431.42 kPa. This is because the introduction of chlorophyll carbon dots into the hydrogel forms multiple physical cross-linking points in the hydrogel, forming a uniform and stable network with polyacrylamide, thereby improving the performance of the hydrogel.

[0074] Figure 2 The adhesion performance curves of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0075] from Figure 2 As can be seen, compared with the adhesion properties of hydrogels made without chlorophyll and without carbonized chlorophyll, the adhesion properties of chlorophyll carbon dot-based hydrogels are as high as 125.8 kPa. This is because the addition of chlorophyll carbon dots can significantly improve its mechanical properties, making it more resistant to external stress, enhancing interfacial interactions, and thus improving adhesion.

[0076] Figure 3 The stress-strain curves of the hydrogels prepared in Example 1, Comparative Example 5, and Comparative Example 6 are shown. Figure 3 As can be seen, the fracture strength and toughness of hydrogels prepared based on different carbon dot concentrations (0.35wt%, 0.25wt%, and 0.15wt%) are 431.42 kPa, 244.77 kPa, 202.04 kPa, and 3.47 MJ / m, respectively. 3 0.88MJ / m 3 0.79MJ / m 3As the chlorophyll carbon dot content decreases, its cross-linking effect in the hydrogel becomes poor, thus affecting mechanical properties and toughness.

[0077] Figure 4 The stress-strain curves of the hydrogels prepared in Example 1, Comparative Example 3, and Comparative Example 4 are shown. Figure 4 As can be seen, the fracture strength and toughness of the hydrogels prepared based on different carbon dot concentrations (0.35wt%, 0.3wt%, and 0.4wt%) are 431.42 kPa, 295.13 kPa, 282.68 kPa, and 3.47 MJ / m, respectively. 3 1.12 MJ / m 3 1.08 MJ / m 3 This is because when the concentration of chlorophyll carbon dots is low, fewer physical cross-linking points are formed in the hydrogel, resulting in a lack of a uniform and stable network. When the concentration of chlorophyll carbon dots is too high, a dense network structure may form, leading to excessive cross-linking. This may also cause phase separation or aggregation, affecting the interaction between the carbon dots and the polyacrylamide molecular chains, resulting in hydrogel inhomogeneity and reduced hydrogel performance.

[0078] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a chlorophyll carbon dot-based hydrogel, characterized in that, Chlorophyll carbon dot solution, water, photoinitiator, crosslinking agent and acrylamide are mixed and subjected to ultraviolet light polymerization reaction to obtain the chlorophyll carbon dot-based hydrogel. The mass ratio of the chlorophyll carbon dot solution, water, photoinitiator, crosslinking agent, and acrylamide is 5:2.5:0.03:0.003:2.5; the mass concentration of the chlorophyll carbon dot solution is 0.53 wt%. The method for preparing the chlorophyll carbon dot solution is as follows: using chlorophyll as raw material and water as solvent, the solution is prepared by calcination, cooling, and centrifugation.

2. The preparation method according to claim 1, characterized in that, When preparing the chlorophyll carbon dot solution, the ratio of chlorophyll to water is 1g:100mL.

3. The preparation method according to claim 1, characterized in that, The firing temperature is 180℃ and the firing time is 6 hours.

4. The preparation method according to claim 1, characterized in that, The crosslinking agent is N,N-methylenebisacrylamide.

5. The preparation method according to claim 1, characterized in that, The ultraviolet light polymerization reaction has a wavelength of 365 nm and a time of 5 min.

6. A chlorophyll carbon dot-based hydrogel prepared by the preparation method according to any one of claims 1-5.

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