A method for preparing melanin-modified cellulose composite aerogel

Abstract

This invention discloses a method for preparing melanin-modified cellulose composite aerogel. This method involves pretreatment, modification, and compounding solutions, controlling the experimental monomers and reaction conditions to obtain the melanin-modified cellulose aerogel. The prepared melanin-modified cellulose aerogel exhibits excellent photothermal properties, and the preparation method and process are simple and easy to implement. The preparation method of the melanin-modified cellulose composite aerogel of this invention includes the following steps: 1) preparation of polydopamine-modified cellulose; 2) preparation of melanin-modified cellulose material; 3) preparation of melanin-modified cellulose aerogel material: the melanin-modified cellulose material obtained in step 2) is added dropwise to a crosslinking agent and continuously stirred to carry out a chemical crosslinking reaction. The resulting mixed solution is poured into a PE mold, placed in an oven to crosslink, and finally freeze-dried under vacuum to obtain the melanin-modified cellulose composite aerogel.

Description

Technical Field

[0001] This invention relates to a method for preparing a composite aerogel, and more specifically to a method for preparing a melanin-modified cellulose composite aerogel, belonging to the field of modified cellulose aerogel preparation. Background Technology

[0002] Industrialization has led to a continuous increase in energy consumption, further exacerbating the global freshwater shortage and putting pressure on sustainable development. Seawater desalination is therefore considered an effective way to alleviate the water crisis, with solar interfacial evaporation attracting attention due to its high photothermal efficiency, low energy consumption, and environmental friendliness. However, to achieve practical application, it is still necessary to construct an evaporation system that maintains high efficiency and long-term stability under varying operating conditions, which is also a key direction for current technological development. Synthetic polymers such as polystyrene (PS), polyurethane (PU), and polyvinylidene fluoride (PVDF) have been widely used as supporting substrates for solar evaporators due to their low price, low density, and low thermal conductivity. However, these synthetic polymers are not environmentally friendly and are not biodegradable. The disposal of these polymer materials poses a significant threat to the environment. Furthermore, the microplastics generated from the decomposition and degradation of polymer substrates can have serious negative impacts on ecosystems. Cellulose is the most abundant biomass on Earth, with its linear chains rich in active groups such as hydroxyl groups. It retains its original chemical stability and is easy to functionalize, thus achieving a variety of properties. The three-dimensional flexible fiber network formed by cellulose has good toughness and compressive strength, making cellulose-based aerogels a key research focus for green porous materials.

[0003] To enhance the photothermal properties of cellulose aerogels, Singamaneni et al. (Advanced Materials 33.28(2021): 2000922.) first constructed a BNC-based solar evaporator: gold nanorods (AuNRs) were densely and uniformly fixed onto cellulose nanofibers using plasma aerogel via van der Waals forces and electrostatic interactions, achieving higher AuNR loading and stronger photothermal performance than "plasma paper." Under the same laser conditions, its evaporation rate was approximately 2.3 times that of the latter; the evaporation efficiency reached 76.3% under 51 kW·m⁻² and 808 nm irradiation. After depositing oxidized CNTs onto cellulose aerogels, the carboxyl groups on the CNTs could form hydrogen bonds with the abundant hydroxyl groups of cellulose, enabling them to adhere firmly. Leveraging the ultra-high porosity of aerogels and the strong light absorption of CNTs, this composite material achieves a light absorption rate of 97.5% in the 300-1200 nm range, with a thermal conductivity of only about 0.06 W·m⁻¹·K⁻¹, effectively suppressing heat loss to water. Under 1 kW·m⁻² and 10 kW·m⁻² light irradiation, its evaporation efficiency is 76.3% and 81.4%, respectively; both dry and wet compression tests show good mechanical properties, and the evaporation performance remains intact after 50 consecutive cycles. Prior art, disclosed in CN112898627A, discloses a composite photothermal gel obtained by in-situ coating a polydopamine / tea polyphenol film onto cellulose aerogel, which achieves a thermal conductivity of approximately 1.12 kg·m⁻¹ under sunlight irradiation. -1 ·h -1 The water evaporation rate is approximately 82%, and the energy efficiency is approximately 82%.

[0004] In the aforementioned existing technologies, immersion and physical interlocking methods for modifying cellulose aerogels suffer from limited adhesion of photothermal materials, uneven distribution, and material waste. Meanwhile, traditional carbon materials and metal nanomaterials also face drawbacks such as high energy consumption, complex preparation processes, and high costs. To further enhance the application value of cellulose aerogels, it is necessary to develop a method for preparing melanin-modified cellulose composite aerogels. This method utilizes melanin to functionalize the cellulose surface, and then chemically cross-links the melanin-modified cellulose to construct a stable three-dimensional aerogel framework, thereby solving the problems existing in the current technologies. Summary of the Invention

[0005] This invention addresses the problems of low adhesion, insufficient photothermal performance, and poor stability of existing cellulose aerogel materials. It provides a method for preparing melanin-modified cellulose composite aerogels. This method involves pretreatment, modification, and solution preparation, controlling the experimental monomers and reaction conditions to obtain melanin-modified cellulose aerogels. The prepared melanin-modified cellulose aerogels exhibit excellent photothermal properties, and the preparation method and process are simple and easy to implement.

[0006] This invention is achieved through the following technical solution: The preparation method of the melanin-modified cellulose composite aerogel of the present invention includes the following steps: 1) Preparation of polydopamine (PDA) modified cellulose Cellulose was dispersed in deionized water to obtain cellulose dispersion A; dopamine hydrochloride (DA) was dissolved in a coating solution whose pH value was adjusted by an alkaline solution to obtain dispersion B; dispersion A was poured into dispersion B and stirred rapidly. After the reaction was complete, dark-colored polydopamine PDA modified cellulose was obtained. 2) Preparation of melanin-modified cellulose materials The melanin precursor monomer was dispersed in the above-mentioned dark-colored polydopamine PDA modified cellulose solution and subjected to ultrasonic treatment. Then, an alkaline solution was added to the above solution to adjust the pH value. The solution was then stirred at room temperature. After the reaction was completed, the solution was centrifuged, the supernatant was removed, and the solution was dried in an oven to obtain the melanin-modified cellulose material. 3) Preparation of melanin-modified cellulose aerogel materials The melanin-modified cellulose material obtained in step 2) was homogenized in deionized water, and a crosslinking agent was added dropwise and stirred continuously to carry out a chemical crosslinking reaction. The resulting mixed solution was poured into a PE mold and placed in an oven to crosslink. After the crosslinked hydrogel was cooled to room temperature, it was placed on a copper plate with liquid nitrogen at the bottom and pre-frozen in a directional manner. Finally, it was freeze-dried under vacuum to obtain the melanin-modified cellulose composite aerogel.

[0007] The preparation method of the melanin-modified cellulose composite aerogel of the present invention is further described in step 1) as follows: the cellulose is one of carboxymethyl cellulose, bacterial cellulose, or cellulose nanofibers; the concentration of the cellulose dispersion A is 0.5-3 wt%; the alkaline solution is one of sodium hydroxide aqueous solution, ammonia, or Tris buffer solution; and the pH value is 8-8.8.

[0008] The preparation method of the melanin-modified cellulose composite aerogel of the present invention can be further described in step 1) as follows: the coating liquid is either a water / alcohol mixed solvent or a pure water solvent; wherein, when using a mixed solvent, the volume ratio of ethanol to deionized water is 1:2~5, and the reaction temperature is room temperature; when using a pure water solvent, the reaction is carried out at 50~60 °C.

[0009] The preparation method of the melanin-modified cellulose composite aerogel of the present invention can be further described in step 1) as follows: the mass ratio of cellulose to dopamine hydrochloride is 1:0.15~1, and the reaction time is 3~5 h.

[0010] The preparation method of the melanin-modified cellulose composite aerogel of the present invention can be further described in step 2) as follows: the melanin precursor monomer is one of 5-hydroxyindole, 5,6-dihydroxyindole, 5,6-dihydroxyindole-2-carboxylic acid, or tryptamine; the mass ratio of the melanin precursor monomer to dopamine hydrochloride is 0.05~0.2:1; the alkaline solution is one of sodium hydroxide aqueous solution, ammonia water, or Tris buffer solution; the pH value of the solution is adjusted to 8~9; and the stirring time is 10~20 h.

[0011] The preparation method of the melanin-modified cellulose composite aerogel described above in this invention can be further described as follows: the centrifugation speed is 8000~10000 rpm, and the aerogel is washed several times with deionized water until the supernatant is clear.

[0012] The preparation method of the melanin-modified cellulose composite aerogel described above in this invention can be further described by having the concentration of the aqueous solution of the melanin-modified cellulose material in step 3) be 1.5~3 wt%.

[0013] The preparation method of the melanin-modified cellulose composite aerogel of the present invention can be further described in step 3) as follows: the crosslinking agent is one of γ-glycidoxypropyltrimethoxysilane, epichlorohydrin, or glutaraldehyde; the volume ratio of the melanin-modified cellulose material aqueous solution to the crosslinking agent is 1:0.005~0.02. A further further embodiment is that when the crosslinking agent is γ-glycidoxypropyltrimethoxysilane, the pH of the chemical crosslinking reaction is 4.0~5.5, the stirring time for the crosslinking reaction is 30~60 min, and the crosslinking temperature is 40~60 ℃; when the crosslinking agent is epichlorohydrin, the pH of the chemical crosslinking reaction is 11~12, the stirring time for the crosslinking reaction is 5~10 min, and the crosslinking temperature is 60~80 ℃; when the crosslinking agent is glutaraldehyde, the pH of the chemical crosslinking reaction is 4~5, and the stirring time for the crosslinking reaction is 5~10 min.

[0014] Compared with the prior art, the present invention has the following advantages: Structural optimization: Melanoid molecules themselves contain polyphenolic hydroxyl groups, indole / pyrrole structures, and a small amount of amine groups, exhibiting strong polarity and multi-coordination activity. They can form tight interfaces with –OH groups on cellulose chains through hydrogen bonds, electrostatic interactions, and even covalent mechanisms, thereby effectively improving the fixation degree of melanoidins on the cellulose surface and preventing the photothermal layer from detaching during long-term water transport and evaporation. The introduction of melanoidins can also significantly improve the dispersion uniformity of photothermal components within the aerogel, reducing material waste caused by adsorption saturation or surface pore blockage, and providing a continuous, multi-scale transport channel for subsequent water rise and vapor escape.

[0015] Enhanced photothermal conversion performance: The abundant conjugated structure and chromophores in melanin molecules have a broad spectrum of light absorption capabilities, enabling effective light capture in the visible and even near-infrared range. This allows the modified cellulose aerogel to achieve a considerable photothermal response with little or no external metal nanomaterials / carbon materials.

[0016] Environmental friendliness and simplified preparation process: This invention employs a three-step preparation process under mild conditions. By controlling the preparation of experimental monomers and reaction conditions, the generation of by-products during the reaction process is effectively reduced. The absence of or minimal use of external photothermal materials lowers system costs and energy consumption, ensuring the environmental friendliness of the modification process. Furthermore, the entire preparation process is simple and easy to implement, facilitating large-scale production. Attached Figure Description

[0017] Figure 1 The image shows Fourier transform infrared (FTIR) images of the melanin-modified cellulose composite aerogels prepared in Examples 1-4.

[0018] Figure 2 The graphs show the adsorption-desorption curves of the melanin-modified cellulose composite aerogels prepared in Examples 1-4.

[0019] Figure 3 This is a pore size distribution diagram of the melanin-modified cellulose composite aerogels prepared in Examples 1-4. Detailed Implementation Example

[0021] (1) Dissolve 0.5 g of cellulose nanofibers in 100 mL of deionized water to form a 0.5 wt% cellulose dispersion. Mix 90 mL of deionized water and 18 mL of ethanol solution to prepare a coating solution B with an alcohol-to-water ratio of 1:5, and adjust the pH of the coating solution to 8 with sodium hydroxide aqueous solution. Dissolve 0.075 g of DA in the coating solution B, and pour the dispersion A into the dispersion B and stir rapidly. The polymerization reaction is carried out for 3 h to obtain dark-colored PDA-modified cellulose.

[0022] 2) Dissolve 0.00375 g of 5-hydroxyindole in the above-mentioned dark-colored PDA-modified cellulose solution and sonicate it to ensure uniform dispersion. Then, add sodium hydroxide solution to the above solution, adjust the pH to 8, and stir at room temperature for 10 h. Centrifuge the solution at 8000 rpm until the supernatant is clear. After removing the supernatant, place the precipitate in a 70℃ oven to dry, thus preparing the melanin-like modified fiber material.

[0023] 3) Weigh 0.3 g of the melanin-modified fiber material prepared above and dissolve it in 20 mL of deionized water. After dispersing evenly, add sodium hydroxide aqueous solution to adjust the pH of the solution to 11, then add 0.1 mL of epichlorohydrin and stir vigorously for 5 min. After the crosslinking agent is evenly dispersed, pour the solution into a PE mold and place it in a 60 ℃ oven for crosslinking. After crosslinking, cool the gel to room temperature, place it on a copper plate with liquid nitrogen at the bottom, and perform directional pre-freezing. Finally, prepare the melanin-modified cellulose composite aerogel by vacuum freeze-drying. The infrared spectrum of the obtained sample is as follows: Figure 1 (a) shows characteristic peaks of melanin-like pigments and cellulose, and the adsorption-desorption curves and pore size distribution curves are as follows. Figure 2 As shown in (a) and 3(a), this sample is a mesoporous hierarchical porous material. Tests revealed that this type of melanin-modified cellulose composite aerogel material has a photothermal conversion efficiency of 92.8% and an evaporation rate of 2.54 kg / m³. 2 ·h.

[0024] Example 2 1) Dissolve 3 g of cellulose nanofibers in 100 mL of deionized water to form a 3 wt% cellulose dispersion. Mix 90 mL of deionized water and 45 mL of ethanol solution to prepare coating solution B with an alcohol-to-water ratio of 1:2, and adjust the pH of the coating solution to 8.8 with ammonia solution. Dissolve 3 g of dopamine hydrochloride in coating solution B, and pour dispersion A into dispersion B and stir rapidly. Polymerize for 5 h to obtain dark-colored PDA-modified cellulose.

[0025] 2) Dissolve 0.6 g of 5-hydroxyindole in the above-mentioned dark-colored PDA-modified cellulose solution and sonicate it to ensure uniform dispersion. Then, add sodium hydroxide aqueous solution to the above solution, adjust the pH value to 9, and stir at room temperature for 20 h. Centrifuge the solution at 10000 rpm until the supernatant is clear. After removing the supernatant, place the precipitate in a 70 ℃ oven to dry, thus preparing the melanin-like modified fiber material.

[0026] 3) Weigh 0.6 g of the melanin-modified fiber material prepared above and dissolve it in 20 mL of deionized water. After dispersing evenly, add sodium hydroxide aqueous solution to adjust the pH of the solution to 12, then add 0.4 mL of epichlorohydrin and stir vigorously for 10 min. After the crosslinking agent is evenly dispersed, pour the solution into a PE mold and place it in an oven at 80 ℃ for crosslinking. After crosslinking, cool the gel to room temperature, place it on a copper plate with liquid nitrogen at the bottom, and perform directional pre-freezing. Finally, prepare the melanin-modified cellulose composite aerogel by vacuum freeze-drying. The infrared spectrum of the obtained sample is as follows: Figure 1 (b) shows characteristic peaks of melanin-like pigments and cellulose, and the adsorption-desorption curves and pore size distribution curves are as follows. Figure 2Images (b) and 3(b) show that the sample is a mesoporous, hierarchical porous material. Tests revealed that this type of melanin-modified cellulose composite aerogel material has a photothermal conversion efficiency of 93.1% and an evaporation rate of 2.61 kg / m³. 2 ·h.

[0027] Example 3 1) Dissolve 2.5 g of cellulose nanofibers in 100 mL of deionized water to form a 2.5 wt% cellulose dispersion. Mix 90 mL of deionized water and 20 mL of ethanol solution to prepare a coating solution B with an alcohol-to-water ratio of 1:4.5, and adjust the pH of the coating solution to 8.5 with sodium hydroxide aqueous solution. Dissolve 0.45 g of dopamine hydrochloride in coating solution B, and pour dispersion A into dispersion B and stir rapidly. Perform polymerization reaction for 4 h to obtain dark-colored PDA-modified cellulose.

[0028] 2) Dissolve 0.05 g of 5-hydroxyindole in the above-mentioned dark-colored PDA-modified cellulose solution and disperse it evenly by ultrasonic treatment. Then, add ammonia solution to the above solution, adjust the pH value to 8.5, and stir at room temperature for 15 h. Centrifuge the solution at 10000 rpm until the supernatant is clear. After removing the supernatant, place the precipitate in a 70 ℃ oven to dry, and prepare the melanin-like modified fiber material.

[0029] 3) Weigh 0.475 g of the melanin-modified fiber material prepared above and dissolve it in 20 ml of deionized water. After dispersing evenly, add sodium hydroxide aqueous solution to adjust the pH of the solution to 11, then add 0.2 mL of epichlorohydrin and stir vigorously for 5 min. After the crosslinking agent is evenly dispersed, pour the solution into a PE mold and place it in a 70 ℃ oven for crosslinking. After crosslinking, cool the gel to room temperature, place it on a copper plate with liquid nitrogen at the bottom, and perform directional pre-freezing. Finally, prepare the melanin-modified cellulose composite aerogel by vacuum freeze-drying. The infrared spectrum of the obtained sample is as follows: Figure 1 (c) shows characteristic peaks of melanin-like pigments and cellulose, and the adsorption-desorption curves and pore size distribution curves are as follows. Figure 2 Images (c) and 3(c) show that the sample is a mesoporous, hierarchical porous material. Tests revealed that this type of melanin-modified cellulose composite aerogel material has a photothermal conversion efficiency of 94.5% and an evaporation rate of 2.72 kg / m³. 2 ·h.

[0030] Example 4 1) Dissolve 2.5 g of carboxymethyl cellulose in 100 mL of deionized water to form a 2.5 wt% cellulose dispersion. Mix 90 mL of deionized water and 20 mL of ethanol solution to prepare coating solution B with an alcohol-to-water ratio of 1:4.5, and adjust the pH of the coating solution to 8.5 with ammonia solution. Dissolve 0.45 g of dopamine hydrochloride in coating solution B, and pour dispersion A into dispersion B and stir rapidly. Perform polymerization reaction for 4 h to obtain dark-colored PDA-modified cellulose.

[0031] 2) Dissolve 0.05 g of 5,6-dihydroxyindole in the above-mentioned dark-colored PDA-modified cellulose solution and sonicate it to ensure uniform dispersion. Then, add ammonia solution to the above solution to adjust the pH to 8.5, and stir at room temperature for 15 h. Centrifuge the solution at 10,000 rpm until the supernatant is clear. After removing the supernatant, place the precipitate in a 70 ℃ oven to dry, thus preparing the melanin-like modified fiber material.

[0032] 3) Weigh 0.475 g of the melanin-modified fiber material prepared above and dissolve it in 20 mL of deionized water. After dispersing evenly, add hydrochloric acid aqueous solution to adjust the pH of the solution to 5.5, then add 0.2 mL of γ-glycidoxypropyltrimethoxysilane solution. Stir vigorously for 30 min to ensure the crosslinking agent is evenly dispersed. Pour the solution into a PE mold and place it in a 50 ℃ oven for crosslinking. After crosslinking, cool the gel to room temperature, place it on a copper plate with liquid nitrogen at the bottom, and perform directional pre-freezing. Finally, prepare the melanin-modified cellulose composite aerogel by vacuum freeze-drying. The infrared spectrum of the obtained sample is as follows: Figure 1 (d) shows characteristic peaks of melanin-like pigments and cellulose. The adsorption-desorption curves and pore size distribution curves are as follows: Figure 2 Figures (d) and (d) show that the sample is a mesoporous, hierarchical porous material. Tests revealed that this type of melanin-modified cellulose composite aerogel material has a photothermal conversion efficiency of 91.7% and an evaporation rate of 2.23 kg / m³. 2 ·h.

[0033] Example 5 1) Dissolve 2.5 g of bacterial cellulose in 100 mL of deionized water to form a 2.5 wt% cellulose dispersion. Mix 90 mL of deionized water and 20 mL of ethanol solution to prepare coating solution B with an alcohol-to-water ratio of 1:4.5, and adjust the pH of the coating solution to 8.5 with ammonia solution. Dissolve 0.45 g of dopamine hydrochloride in coating solution B, and pour dispersion A into dispersion B and stir rapidly. Polymerize for 4 h to obtain dark-colored PDA-modified cellulose.

[0034] 2) Dissolve 0.05 g of 5,6-dihydroxyindole-2-carboxylic acid in the above-mentioned dark-colored PDA-modified cellulose solution and sonicate it to ensure uniform dispersion. Then, add ammonia solution to the above solution to adjust the pH to 8.5, and stir at room temperature for 15 h. Centrifuge the solution at 10,000 rpm until the supernatant is clear. After removing the supernatant, place the precipitate in a 70 ℃ oven to dry, thus preparing the melanin-modified fiber material.

[0035] 3) Weigh 0.475 g of the melanin-modified fiber material prepared above and dissolve it in 20 mL of deionized water. After dispersing evenly, add hydrochloric acid aqueous solution to adjust the pH of the solution to 4, then add 0.2 mL of glutaraldehyde and stir vigorously for 5 min. After the crosslinking agent is evenly dispersed, pour the solution into a PE mold. After crosslinking, cool the gel to room temperature, place it on a copper plate with liquid nitrogen at the bottom, and perform directional pre-freezing. Finally, prepare the melanin-modified cellulose composite aerogel by vacuum freeze-drying. The photothermal conversion efficiency of this melanin-modified cellulose composite aerogel material is 93.6%, and the evaporation rate is 2.49 kg / m³. 2 ·h.

[0036] Example 6 1) Dissolve 1 g of bacterial cellulose in 100 mL of deionized water to form a 1 wt% cellulose dispersion. Prepare a coating solution B of 100 mL of deionized water and adjust the pH of the coating solution to 8.5 with Tris buffer. Dissolve 0.6 g of dopamine hydrochloride in coating solution B, and pour dispersion A into dispersion B and stir rapidly. Perform polymerization reaction for 4 h to obtain dark-colored PDA-modified cellulose.

[0037] 2) Dissolve 0.12 g of 5,6-dihydroxyindole-2-carboxylic acid in the above-mentioned dark-colored PDA-modified cellulose solution and sonicate it to ensure uniform dispersion. Then, add ammonia solution to the above solution to adjust the pH to 8.5, and stir at room temperature for 15 h. Centrifuge the solution at 10,000 rpm until the supernatant is clear. After removing the supernatant, place the precipitate in a 70 ℃ oven to dry, thus preparing the melanin-like modified fiber material.

[0038] 3) Weigh 0.4 g of the melanin-modified fiber material prepared above and dissolve it in 20 mL of deionized water. After dispersing evenly, add hydrochloric acid aqueous solution to adjust the pH of the solution to 4, then add 0.2 mL of glutaraldehyde and stir vigorously. After the crosslinking agent is evenly dispersed, pour the solution into a PE mold. After crosslinking, cool the gel to room temperature, place it on a copper plate with liquid nitrogen at the bottom, and perform directional pre-freezing. Finally, prepare the melanin-modified cellulose composite aerogel by vacuum freeze-drying. The photothermal conversion efficiency of this melanin-modified cellulose composite aerogel material is 91.5%, and the evaporation rate is 2.33 kg / m³. 2 ·h.

Claims

1. A method for preparing a melanin-like modified cellulose composite aerogel, characterized in that, Includes the following steps: 1) Preparation of polydopamine-modified cellulose Cellulose was dispersed in deionized water to obtain cellulose dispersion A; Dopamine hydrochloride was dissolved in a coating solution whose pH was adjusted with an alkaline solution to obtain dispersion B. Dispersion A was poured into dispersion B and stirred rapidly. After the reaction was complete, dark-colored polydopamine-modified cellulose was obtained. 2) Preparation of melanin-modified cellulose materials The melanin precursor monomer was dispersed in the above-mentioned dark polydopamine modified cellulose solution and subjected to ultrasonic treatment. Then, an alkaline solution was added to the above solution to adjust the pH value. The solution was then stirred at room temperature. After the reaction was completed, the solution was centrifuged, the supernatant was removed, and the solution was dried in an oven to obtain the melanin-modified cellulose material. 3) Preparation of melanin-modified cellulose aerogel materials The melanin-modified cellulose material obtained in step 2) was homogenized in deionized water, and a crosslinking agent was added dropwise and stirred continuously to carry out a chemical crosslinking reaction. The resulting mixed solution was poured into a PE mold and placed in an oven to crosslink. After the crosslinked hydrogel was cooled to room temperature, it was placed on a copper plate with liquid nitrogen at the bottom and pre-frozen in a directional manner. Finally, it was freeze-dried under vacuum to obtain the melanin-modified cellulose composite aerogel.

2. The method for preparing melanin-modified cellulose composite aerogel according to claim 1, characterized in that, The cellulose mentioned in step 1) is one of carboxymethyl cellulose, bacterial cellulose, or cellulose nanofibers, and the concentration of the cellulose dispersion A is 0.5~3 wt%; the alkaline solution is one of sodium hydroxide aqueous solution, ammonia, or Tris buffer solution, and the pH value is 8~8.

8.

3. The method for preparing melanin-modified cellulose composite aerogel according to claim 1, characterized in that, The coating solution mentioned in step 1) is either a water / alcohol mixed solvent or a pure water solvent; wherein, when using a mixed solvent, the volume ratio of ethanol to deionized water is 1:2~5, and the reaction temperature is room temperature; when using a pure water solvent, the reaction is carried out at 50~60 ℃.

4. The method for preparing melanin-modified cellulose composite aerogel according to claim 1, characterized in that, The mass ratio of cellulose to dopamine hydrochloride in step 1) is 1:0.15~1, and the sufficient reaction time is 3~5 h.

5. The method for preparing melanin-modified cellulose composite aerogel according to claim 1, characterized in that, The melanin precursor monomer mentioned in step 2) is one of 5-hydroxyindole, 5,6-dihydroxyindole, 5,6-dihydroxyindole-2-carboxylic acid, or tryptamine; the mass ratio of the melanin precursor monomer to dopamine hydrochloride is 0.05~0.2:1; the alkaline solution is one of sodium hydroxide aqueous solution, ammonia water, or Tris buffer solution; the pH value of the solution is adjusted to 8~9; and the stirring time is 10~20 h.

6. The method for preparing melanin-modified cellulose composite aerogel according to claim 1, characterized in that, The centrifugation speed in step 2) is 8000~10000 rpm, and the supernatant is washed several times with deionized water until it is clear.

7. The method for preparing melanin-modified cellulose composite aerogel according to claim 1, characterized in that, The concentration of the aqueous solution of the melanin-modified cellulose material mentioned in step 3) is 1.5~3 wt%.

8. The method for preparing melanin-modified cellulose composite aerogel according to claim 1, characterized in that, The crosslinking agent mentioned in step 3) is one of γ-glycidoxypropyltrimethoxysilane, epichlorohydrin, or glutaraldehyde; the volume ratio of the melanin-modified cellulose material aqueous solution to the crosslinking agent is 1:0.005~0.

02.

9. The method for preparing melanin-modified cellulose composite aerogel according to claim 8, characterized in that, When the crosslinking agent is γ-glycidoxypropyltrimethoxysilane, the pH of the chemical crosslinking reaction is 4.0-5.5, the stirring time for the crosslinking reaction is 30-60 min, and the crosslinking temperature is 40-60 °C. When the crosslinking agent is epichlorohydrin, the pH of the chemical crosslinking reaction is 11-12, the stirring time for the crosslinking reaction is 5-10 min, and the crosslinking temperature is 60-80 °C. When the crosslinking agent is glutaraldehyde, the pH of the chemical crosslinking reaction is 4-5, and the stirring time for the crosslinking reaction is 5-10 min.

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