Preparation method and application of solar interface evaporation melanin bulk hydrogel

Abstract

The invention discloses an application of an artificial melanin monomer and a method for preparing solar interface evaporation melanin bulk hydrogel by taking the artificial melanin monomer as a main raw material, and the preparation method comprises the following steps: mixing the melanin monomer and oxidized polysaccharide according to a mass ratio of 1: (1.5-8); and mixing the solution containing the melanin monomer with the solution containing the oxidized polysaccharide, and reacting at 50-70 DEG C for 12-36 hours to obtain the solar interface evaporation melanin bulk hydrogel. The hydrogel is synthesized in one step under the alkaline heating condition through copolymerization of the melanin monomer and the oxidized polysaccharide, the hydrogel has excellent photo-thermal performance, and light energy in the full wavelength range of an ultraviolet-visible light-infrared region can be fully utilized to be converted into heat energy.

Description

Technical Field

[0001] The present invention belongs to the field of solar interface evaporation materials, and particularly relates to a preparation method and application of a solar interface evaporation melanin bulk hydrogel. Background Art

[0002] The shortage of fresh water resources has become a global crisis. Approximately 4 billion people are threatened by water shortages, and a quarter of urban water security systems are under severe pressure. How to develop utilization technologies for unconventional water resources such as seawater and wastewater has become a key path to alleviate the water resource bottleneck. Solar water evaporation technology (SWG) is a type of interface evaporation based on continuous solar drive. Its efficient evaporation mechanism and sustainable characteristics show broad prospects in the fields of seawater desalination and sewage purification. Among them, the evaporation system based on hydrogels has become the focus of research due to its excellent water transport ability and water retention characteristics. Research shows that regulating the hydrogen bond interaction between the hydrogel polymer chain and water molecules can reduce the evaporation enthalpy value and achieve an evaporation rate of up to 3.6 kg m-2 h-1 (ZHOU X, ZHAO F, GUO Y, et al. Architecting highly hydratable polymer networks to tunethe water state for solar water purification[J]. 2019, 5(6): eaaw5484).

[0003] However, current mainstream hydrogel materials, such as polyvinyl alcohol and polyacrylamide, lack the ability of photothermal conversion themselves and need to rely on the doping and modification of exogenous photothermal agents. Currently, the commonly used types of exogenous photothermal agents mainly include carbon-based materials, metal compounds, and polymer polymers, such as carbon nanotubes, graphene, CuFeSe 2 、Ti 2 O 3 、polypyrrole, and polydopamine, etc. In the process of implementing the present invention, the inventors found that although the introduction of photothermal agents improved the photothermal performance, it also caused two key technical defects: First, as described in the following research, most photothermal agents are hydrophobic, which will damage the water transport channels in the hydrogel network and inhibit the formation of intermediate water (IW), resulting in a significant attenuation of the evaporation enthalpy optimization effect (ZHAO Q, WEN H, WU J, etal. Galactomannan / graphene oxide / Fe 3 O 4Hydrogel evaporator for solar water evaporation for synergistic photothermal power generation[J]. Desalination, 2024, 570: 117064.; SU J, XIE Y, ZHANG P, et al. Janus MXene-based photothermal membrane for efficient and durable water evaporation[J]. Desalination, 2023, 566: 116905.; YU Z, GU R, ZHANG Y, et al. High-flux flowing interfacial water evaporation under multiple heating sources enabled by a biohybrid hydrogel[J]. Nano Energy, 2022, 98: 107287); Second, the physical separation of the photothermal agent from the polymer chains results in heat being mainly dissipated in the free water phase rather than the intermediate water adjacent to the polymer chains, leading to a significant reduction in the thermal energy utilization efficiency and restricting the improvement of evaporation performance.

[0004] The above problems make it difficult for traditional composite hydrogels to simultaneously achieve efficient water activation, directional heat conduction, and optimized water transport networks. There is an urgent need to develop an integrated construction strategy. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a preparation method and application of a melanin bulk hydrogel for solar interfacial evaporation. The preparation method uses melanin monomers and oxidized polysaccharides as raw materials and synthesizes the hydrogel in one step by copolymerization under alkaline heating conditions. The hydrogel has excellent photothermal properties and can fully convert light energy in the entire wavelength range of ultraviolet-visible-infrared regions into heat energy.

[0006] The present invention has the following advantages compared with the prior art:

[0007] 1. The present invention provides a preparation method of a melanin bulk hydrogel for solar interfacial evaporation. From a chemical perspective, a reasonable analysis and design of the molecular structure are carried out, and the prepared hydrogel has excellent photothermal properties and can fully convert light energy in the entire wavelength range of ultraviolet-visible-infrared regions into heat energy.

[0008] 2. Preferably, the method uses fungal melanin monomer and oxidized dextran as raw materials, and synthesizes a hydrogel in one step by copolymerization of fungal melanin monomer and oxidized dextran in an alkaline heating environment. The hydrogel has excellent photothermal properties and can fully convert light energy in the entire wavelength range of ultraviolet-visible-infrared regions into heat energy, with the highest outdoor evaporation efficiency reaching 5.39 kg m -2 h -1 , which is conducive to popularization and application.

[0009] 3. The present invention provides a method for applying artificial melanin monomer, including using it as a functional molecule, and preparing a solar interface evaporation melanin bulk hydrogel by phenolic reaction and cross-linking with a polysaccharide network by utilizing the self-polymerizable structural characteristics of the melanin monomer itself.

[0010] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0011] Figure 1 It is a scanning electron microscope image of the solar interface evaporation melanin bulk hydrogel of Example 1.

[0012] Figure 2 It is a Fourier transform infrared spectrum of the solar interface evaporation melanin bulk hydrogel of Example 1.

[0013] Figure 3 It is a schematic diagram of the test results of the photothermal properties of the solar interface evaporation melanin bulk hydrogels of Examples 1 to 4.

[0014] Figure 4 It is a schematic diagram of the test results of the spectral absorption ability of the solar interface evaporation melanin bulk hydrogels of Examples 1 to 4 in the ultraviolet-visible-infrared regions.

[0015] Figure 5 It is a schematic diagram of the test results of the evaporation performance of the solar interface evaporation melanin bulk hydrogel of Example 1.

[0016] Figure 6 It is a morphological photo of the solar interface evaporation melanin bulk hydrogel of Example 1.

[0017] Figure 7 It is the test result of the evaporation performance of Gel 5.

[0018] Figure 8 It is the test result of the evaporation performance of Gel 6.

[0019] Figure 9 It is a morphological photo of Gel 7.

[0020] Figure 10 It is a morphological photo of Gel 8.

[0021] Figure 11 Photograph of the appearance of the hydrogel of Comparative Example 1.

[0022] Figure 12 Morphology photograph of the hydrogel of Comparative Example 2. Detailed implementation manners

[0023] Next, the technical solutions will be described clearly and completely in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0024] In the following description, the term "and / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, B exists alone, and both A and B exist simultaneously. Wherein A and B may be singular or plural.

[0025] In the following description, terms such as "including", "comprising", "having", and "containing" are all open-ended terms, that is, they are intended to include but not be limited to.

[0026] Those skilled in the art should understand that in the following description of the embodiments of the present application, the sequence numbers do not mean the order of execution. Some or all of the steps may be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0027] Those skilled in the art should understand that the numerical ranges in the embodiments of the present application should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Intermediate values between any stated value or range of values and each smaller range between any other stated value or intermediate value within the stated range are also included in the present application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present application belongs. Although the present application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present application. 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.

[0029] Technical principle adopted by the present invention: Using melanin monomer and oxidized polysaccharide as the main raw materials, a photothermal agent is in-situ grown based on the crosslinking of hydrogel, and through the phenolic reaction of melanin precursors and crosslinking with the polysaccharide network, the photothermal agent and the gel matrix are deeply integrated at the molecular level.

[0030] Some embodiments provide a method for preparing a solar interfacial evaporation melanin bulk hydrogel, including:

[0031] According to the mass ratio of melanin monomer to oxidized polysaccharide being 1:(1.5 - 8), after mixing the solution containing melanin monomer with the solution containing oxidized polysaccharide, reacting at 50 - 70°C for 12 - 36 h to obtain a solar interfacial evaporation melanin bulk hydrogel; in some preferred embodiments, the mass ratio of melanin monomer to oxidized polysaccharide is 1:(3 - 8), and further preferably, the mass ratio is 1:(3 - 4), the reaction temperature is 65°C, and the reaction time is 24 - 36 h.

[0032] Through a one-step direct reaction, the melanin precursor undergoes a phenolic reaction and crosslinking with the polysaccharide network, enabling the in-situ growth of the photothermal agent in the hydrogel network, structurally solving the problems of poor interfacial compatibility and hydrophilic-hydrophobic contradiction caused by the introduction of exogenous photothermal agents, and specifically solving the problem of low thermal management efficiency of traditional interfacial hydrogels.

[0033] In addition, by limiting the molar ratio of raw materials and reaction conditions, the preparation of a solar interfacial evaporation melanin bulk hydrogel with high photothermal performance is achieved. When the mass ratio of raw materials is higher than 1:8 or lower than 1:1.5, it is difficult to form a gel. When the reaction temperature is higher than 70°C or lower than 50°C, or the reaction time is too short or too long, it will lead to too strong gel crosslinking and serious shrinkage of the product, resulting in the inability to absorb water.

[0034] In some embodiments, the melanin monomer includes 1,8-dihydroxynaphthalene or 5,6-dihydroxyindole; in some preferred embodiments, the melanin monomer is 1,8-dihydroxynaphthalene.

[0035] The melanin monomer is a fungal melanin monomer, specifically 1,8-dihydroxynaphthalene.

[0036] In some embodiments, the oxidized polysaccharide includes one or more of oxidized dextran, oxidized chitosan, and oxidized konjac glucomannan; in some preferred embodiments, the oxidized polysaccharide is oxidized dextran.

[0037] In some embodiments, the solvent in the solution containing melanin monomer includes one or more of N,N-dimethylformamide, acetonitrile, and dimethyl sulfoxide; in some preferred embodiments, the solvent in the solution containing melanin monomer is N,N-dimethylformamide.

[0038] In some embodiments, the solution containing oxidized polysaccharide is a solution obtained by dissolving oxidized polysaccharide and an alkaline preparation in a good solvent; the alkaline preparation includes sodium hydroxide or sodium carbonate, and preferably, the alkaline preparation is sodium carbonate; the good solvent is deionized water.

[0039] On the other hand, a method for applying artificial melanin monomers is provided, which includes using artificial melanin monomers as functional molecules and in-situ assembling them into a polysaccharide network through self-polymerization and copolymerization with polysaccharides to obtain a solar interfacial evaporation melanin bulk hydrogel. In some specific embodiments, the artificial melanin monomer is a fungal melanin monomer, and preferably, the fungal melanin monomer is 1,8-dihydroxynaphthalene.

[0040] On yet another aspect, an application of the above-mentioned solar interfacial evaporation melanin bulk hydrogel in a solar interfacial evaporator is provided.

[0041] A series of experiments were conducted before the application of this invention. Now, some test results are listed to further describe the invention in detail, and it will be described in detail below in conjunction with the embodiments.

[0042] In the following embodiments, the sources of each reagent are not limited. For example, 1,8-DHN was purchased from Shanghai Yuanye Bio-Technology Co., Ltd., and other reagents were all purchased from Shanghai Macklin Biochemical Co., Ltd.; among them, the dextran is a dextran with a number-average molecular weight of 40,000 connected by β-1,3-glycosidic bonds.

[0043] In the following embodiments, the order of preparing the oxidized polysaccharide and the melanin monomer solution is not limited, and the order of preparing the melanin monomer solution and the solution containing oxidized polysaccharide is not limited; those skilled in the art changing the above order do not exceed the protection scope of this invention.

[0044] Example 1

[0045] This example provides a method for preparing a solar interfacial evaporation melanin bulk hydrogel, including:

[0046] Step 1: Dissolve 10 g of polysaccharide in 500 mL of deionized water, add 0.46 mol of sodium periodate, stir in the dark for 1 day, then dialyze with a 1.2 w dialysis bag to remove small molecules, and freeze-dry to obtain oxidized polysaccharide; the polysaccharide is dextran;

[0047] Step 2: Dissolve 80 mg of 1,8-dihydroxynaphthalene (1,8-DHN) in 1 mL of N,N-dimethylformamide (DMF) to obtain a melanin monomer solution;

[0048] Step 3: Mix 300 mg of the oxidized polysaccharide obtained in Step 1 and 10 mg of Na 2 CO 3Dissolve it in 1.5 mL of deionized water and stir at room temperature to obtain a solution containing oxidized polysaccharide;

[0049] Step 4: Under stirring conditions, add the melanin monomer solution described in Step 2 to the solution containing oxidized polysaccharide described in Step 3. After stirring until evenly mixed, seal it and place it in an oven at 65 °C for static reaction for one day to obtain a gel;

[0050] Step 5: Remove impurities from the gel to obtain a solar interfacial evaporation melanin bulk hydrogel, labeled as Gel 3; the impurity removal is carried out by immersing the gel in water, aiming to remove small molecules and unreacted raw materials.

[0051] Example 2

[0052] This example provides a preparation method of a solar interfacial evaporation melanin bulk hydrogel, which is the same as Example 1, except that in Step 3, the mass of oxidized polysaccharide is 640 mg and the volume of deionized water is 2.4 mL, labeled as Gel 1.

[0053] Example 3

[0054] This example provides a preparation method of a solar interfacial evaporation melanin bulk hydrogel, which is the same as Example 1, except that in Step 3, the mass of oxidized polysaccharide is 480 mg and the volume of deionized water is 1.8 mL, labeled as Gel 2.

[0055] Example 4

[0056] This example provides a preparation method of a solar interfacial evaporation melanin bulk hydrogel, which is the same as Example 1, except that in Step 3, the mass of oxidized polysaccharide is 240 mg and the volume of deionized water is 0.8 mL, labeled as Gel 4.

[0057] Performance evaluation:

[0058] Figure 1 is the scanning electron microscope image of the solar interfacial evaporation melanin bulk hydrogel of Example 1. The sample preparation process includes: freezing the solar interfacial evaporation melanin bulk hydrogel with liquid nitrogen and then freeze-drying it to obtain an aerogel, and performing gold spraying treatment on the aerogel to obtain a sample. According to Figure 1 It can be seen that the solar interfacial evaporation melanin bulk hydrogel of the present invention produces a cross-linked gel network and presents a gel-like morphology.

[0059] Figure 2 is the Fourier transform infrared spectrum of the solar interfacial evaporation melanin bulk hydrogel of Example 1. According to Figure 2 It can be seen that the peak position at 1730 cm -1 is attributed to the C=O bond, indicating that the oxidized polysaccharide is successfully synthesized in the present invention. At 1615 cm-1 The peak position at is attributed to the stretching vibration of C═C, 3280 cm -1 and 3496 cm -1 The characteristic peaks at are attributed to O—H. Both are characteristic peaks of 1,8-DHN. Based on Figure 2 It can be seen that the solar interfacial evaporation melanin bulk hydrogel of the present invention shows characteristic peaks attributed to 1,8-DHN and oxidized polysaccharides, indicating that the method of the present invention successfully realizes the in-situ growth of the photothermal agent in the hydrogel network.

[0060] Figure 3 It is a schematic diagram of the test results of the photothermal performance of the solar interfacial evaporation melanin bulk hydrogels of Examples 1 to 4. The test method includes: immersing the above hydrogel in water, irradiating it with a xenon lamp to simulate sunlight, and using an infrared camera to record the surface temperature rise of the hydrogel. The results are as Figure 3 shown; where the light intensity is 1 Wm -2 mm -1 ; Based on Figure 3 It can be seen that as the irradiation time prolongs, the surface temperature of the hydrogel shows a trend of first increasing and then stabilizing. As the photothermal reagent 1,8-DHN increases (from gel 4 to gel 1, the addition amount of 1,8-DHN gradually increases), the increase amplitude of the surface temperature of the hydrogel is fast, and the finally stable temperature value is larger, and the photothermal ability is further enhanced.

[0061] Figure 4 It is a schematic diagram of the test results of the spectral absorption ability of the solar interfacial evaporation melanin bulk hydrogels of Examples 1 to 4 in the ultraviolet-visible-infrared region. The test method includes: placing 0.5 cm 3 of the above hydrogel in a UV / Vis / NIR diffuse reflectance tester for detection. Based on Figure 4 It can be seen that the solar interfacial evaporation melanin bulk hydrogel of the present invention has good light absorption in the full solar irradiation wavelength range of 200-2500 nm, and the absorption rate is above 95%, indicating that the solar interfacial evaporation melanin bulk hydrogel of the present invention can make full use of sunlight and convert light energy into heat energy.

[0062] Figure 5Schematic diagram of the evaporation performance test results of the melanin-based hydrogel for solar interfacial evaporation in Example 1. The test method includes: taking a glass dish, adding clear water, putting the hydrogel into it, covering the water surface between the hydrogel and the glass dish with a PC non-perforated foam, so that only the upper surface of the hydrogel is left for evaporation, obtaining an evaporation performance test device, placing this device on a precision electronic balance, using a xenon lamp to simulate sunlight and vertically irradiating the surface of the hydrogel, and monitoring the mass change caused by water evaporation in real time, calculating the evaporation rate of the hydrogel. The evaporation rate calculation formula is: △v = m / At, where m is the mass change of water during the experiment, with the unit of kg, A is the vertical projection area of the light-irradiated surface of the solar interfacial evaporator, with the unit of m 2 , and t is the evaporation time, with the unit of h.

[0063] Based on Figure 5 It can be seen that the evaporation rate of the hydrogel is basically in a relatively consistent variation law with the sunlight intensity, that is, as the outdoor temperature and sunlight intensity first increase and then decrease, the evaporation rate of the hydrogel shows a relatively consistent parabolic variation trend, and reaches the highest evaporation rate of 5.39 kg m -2 h -1 , indicating that the melanin-based hydrogel for solar interfacial evaporation of the present invention can make full use of external sunlight and has practical application value.

[0064] Figure 6 Morphology diagram of the melanin-based hydrogel for solar interfacial evaporation in Example 1. It can be seen that the melanin-based hydrogel for solar interfacial evaporation of the present invention has a uniform color and moderate strength.

[0065] Example 5

[0066] This example provides a preparation method of a melanin-based hydrogel for solar interfacial evaporation, including:

[0067] Step 1: Dissolve 10 g of polysaccharide in 500 mL of deionized water, add 0.46 mol of sodium periodate, stir in the dark for 1 day, then dialyze with a 1.2 w dialysis bag to remove small molecules, and freeze-dry to obtain oxidized polysaccharide; the polysaccharide is dextran;

[0068] Step 2: Dissolve 80 mg of 1,8-dihydroxynaphthalene (1,8-DHN) in 1 mL of N,N-dimethylformamide (DMF) to obtain a melanin monomer solution;

[0069] Step 3: Dissolve 150 mg of the oxidized polysaccharide obtained in Step 1 and 10 mg of Na 2 CO 3 in 1.5 mL of deionized water, and stir at room temperature to obtain a solution containing oxidized polysaccharide;

[0070] Step 4. Under stirring conditions, add the melanin monomer solution described in Step 2 into the solution containing oxidized polysaccharide described in Step 3. After stirring until evenly mixed, seal it and place it in an oven at 65°C for static reaction for one day to obtain a gel.

[0071] Step 5. Remove impurities from the gel to obtain a solar interface evaporation melanin bulk hydrogel, labeled as Gel 5. The impurity removal is carried out by immersing the gel in water, aiming to remove small molecules and unreacted raw materials.

[0072] Example 6

[0073] This example provides a preparation method of a solar interface evaporation melanin bulk hydrogel, including:

[0074] Step 1. Dissolve 10 g of polysaccharide in 500 mL of deionized water, add 0.46 mol of sodium periodate, stir in the dark for 1 day, then dialyze with a 1.2 w dialysis bag to remove small molecules, and freeze-dry to obtain oxidized polysaccharide; the polysaccharide is dextran.

[0075] Step 2. Dissolve 80 mg of 1,8-dihydroxynaphthalene (1,8-DHN) in 1 mL of N,N-dimethylformamide (DMF) to obtain a melanin monomer solution.

[0076] Step 3. Dissolve 300 mg of the oxidized polysaccharide described in Step 1 and 10 mg of Na 2 CO 3 in 1.5 mL of deionized water, and stir at room temperature to obtain a solution containing oxidized polysaccharide.

[0077] Step 4. Under stirring conditions, add the melanin monomer solution described in Step 2 into the solution containing oxidized polysaccharide described in Step 3. After stirring until evenly mixed, seal it and place it in an oven at 50°C for static reaction for one day to obtain a gel.

[0078] Step 5. Remove impurities from the gel to obtain a solar interface evaporation melanin bulk hydrogel, labeled as Gel 6. The impurity removal is carried out by immersing the gel in water, aiming to remove small molecules and unreacted raw materials.

[0079] The morphologies of Gel 5 and Gel 6 are basically the same as the hydrogel strength in Example 1. The evaporation performance test results of Gel 5 and Gel 6 are as Figure 7 and Figure 8 shown. It can be seen that the evaporation efficiency of Gel 5 is 3.21 kg m -2 h -1 , which is 0.75 times the efficiency of Example 1. The evaporation efficiency of Gel 6 is 2.69 kg m -2 h -1 , which is 0.63 times the efficiency of Example 1.

[0080] Example 7

[0081] This example provides a method for preparing a solar interfacial evaporation melanin bulk hydrogel, including:

[0082] Step 1: Dissolve 10 g of polysaccharide in 500 mL of deionized water, add 0.46 mol of sodium periodate, stir in the dark for 1 day, then dialyze with a 1.2 w dialysis bag to remove small molecules, and lyophilize to obtain oxidized polysaccharide; the polysaccharide is konjac glucomannan;

[0083] Step 2: Dissolve 80 mg of 1,8-dihydroxynaphthalene (1,8-DHN) in 1 mL of N,N-dimethylformamide (DMF) to obtain a melanin monomer solution;

[0084] Step 3: Dissolve 300 mg of the oxidized polysaccharide obtained in Step 1 and 10 mg of Na 2 CO 3 in 1.5 mL of deionized water, and stir at room temperature to obtain a solution containing oxidized polysaccharide;

[0085] Step 4: Under stirring conditions, add the melanin monomer solution obtained in Step 2 to the solution containing oxidized polysaccharide obtained in Step 3. After stirring until evenly mixed, seal and place it in an oven at 65 °C and let it stand for one day to obtain a gel;

[0086] Step 5: Remove impurities from the gel to obtain a solar interfacial evaporation melanin bulk hydrogel, labeled as Gel 7; impurity removal is carried out by immersing the gel in water to remove small molecules and unreacted raw materials.

[0087] Example 8

[0088] This example provides a method for preparing a solar interfacial evaporation melanin bulk hydrogel, including:

[0089] Step 1: Dissolve 10 g of polysaccharide in 500 mL of deionized water, add 0.46 mol of sodium periodate, stir in the dark for 1 day, then dialyze with a 1.2 w dialysis bag to remove small molecules, and lyophilize to obtain oxidized polysaccharide; the polysaccharide is chitosan;

[0090] Step 2: Dissolve 80 mg of 1,8-dihydroxynaphthalene (1,8-DHN) in 1 mL of N,N-dimethylformamide (DMF) to obtain a melanin monomer solution;

[0091] Step 3: Dissolve 300 mg of the oxidized polysaccharide obtained in Step 1 and 10 mg of Na 2 CO 3 in 1.5 mL of deionized water, and stir at room temperature to obtain a solution containing oxidized polysaccharide;

[0092] Step 4: Under stirring conditions, add the melanin monomer solution described in Step 2 to the solution containing oxidized polysaccharide described in Step 3. After stirring until evenly mixed, seal it and place it in an oven at 65 °C for static reaction for one day to obtain a gel.

[0093] Step 5: Remove impurities from the gel to obtain a solar interface evaporation melanin-based hydrogel, labeled as Gel 8. The impurity removal is carried out by immersing the gel in water to remove small molecules and unreacted raw materials.

[0094] The morphology diagrams of Gel 7 and Gel 8 in Example 7 and Example 8 are as Figure 9 and Figure 10 shown. It can be seen that using deacetylated chitosan or konjac glucomannan as the polysaccharide raw material, hydrogels can be prepared by the method of the present invention. Compared with Gel 1 prepared using dextran as the polysaccharide raw material, the strength of Gel 7 and Gel 8 has changed, and the photothermal performance test shows that the evaporation efficiency of Gel 7 and Gel 8 has decreased significantly.

[0095] Comparative Example 1

[0096] This comparative example examines the influence of reaction time on the performance of the solar interface evaporation melanin-based hydrogel. The preparation method is the same as that of Example 1, except that the reaction time is 40 h, labeled as Comparative Gel 1.

[0097] Comparative Example 2

[0098] This comparative example examines the influence of reaction time on the performance of the solar interface evaporation melanin-based hydrogel. The preparation method is the same as that of Example 1, except that the reaction time is 10 h.

[0099] The hydrogel morphologies of Comparative Examples 1-2 are as Figure 11 and 12 shown. It can be seen that when the reaction time is extended to 40 h, the overall elasticity of the hydrogel decreases, showing more solid characteristics. When the reaction time is shortened to 10 h, the hydrogel structure is soft, tending to flow, the strength is significantly reduced, and it is easy to break.

[0100] Comparative Example 3

[0101] This comparative example examines the influence of the alkaline preparation in the solution containing oxidized polysaccharide on the product solar interface evaporation melanin-based hydrogel. The preparation method is the same as that of Example 1, except that in Step 3, sodium hydroxide is used to replace sodium carbonate.

[0102] A stable hydrogel was not obtained in this comparative example. The possible reason is that the alkalinity of sodium hydroxide is too strong and the reaction is too violent.

Claims

1. A method for using an artificial melanin monomer, characterized in that: The method comprises taking artificial melanin monomer as functional molecule and cross-linking with polysaccharide network to prepare solar interfacial evaporated melanin bulk hydrogel.

2. The method for using artificial melanin monomer according to claim 1, characterized in that: The artificial melanin monomer is 1,8-dihydroxynaphthalene.

3. A method for preparing a melanin bulk hydrogel by solar interfacial evaporation, characterized in that: include: According to the mass ratio of melanin monomer to oxidized polysaccharide being 1:(1.5-8), a solution containing melanin monomer is mixed with a solution containing oxidized polysaccharide, and the mixture is reacted at 50-70° C. for 12-36 hours to obtain a solar interfacial evaporated melanin bulk hydrogel.

4. The method for preparing the solar interfacial evaporated melanin bulk hydrogel according to claim 3, characterized in that: The mass ratio of melanin monomer to oxidized polysaccharide is 1:(3-8).

5. The method for preparing the solar interfacial evaporated melanin bulk hydrogel according to claim 4, characterized in that: The mass ratio of melanin monomer to oxidized polysaccharide is 1:(3-4).

6. The method for preparing the solar interfacial evaporated melanin bulk hydrogel according to claim 3, characterized in that: The reaction time is 24 to 36 hours.

7. The method for preparing the solar interfacial evaporated melanin bulk hydrogel according to claim 3, characterized in that: The melanin monomer includes 1,8-dihydroxynaphthalene or 5,6-dihydroxyindole, and / or the oxidized polysaccharide includes one or more of oxidized dextran, oxidized deacetylated chitosan and oxidized konjac glucomannan.

8. The method for preparing the solar interfacial evaporated melanin bulk hydrogel according to claim 7, characterized in that: The melanin monomer is 1,8-dihydroxynaphthalene, and / or the oxidized polysaccharide is oxidized dextran.

9. The method for preparing the solar interfacial evaporated melanin bulk hydrogel according to claim 3, characterized in that: In the solution containing melanin monomers, the solvent includes one or more of N,N-dimethylformamide, acetonitrile and dimethyl sulfoxide, and / or the solution containing oxidized polysaccharide is a solution obtained by dissolving oxidized polysaccharide and alkaline preparation in a good solvent.

10. Use of the solar interfacial evaporated melanin bulk hydrogel prepared by the method for preparing the solar interfacial evaporated melanin bulk hydrogel as claimed in claim 3.

Images