Preparation method of lignocellulose-based aerogel hydrogen storage material

Abstract

This invention belongs to the field of hydrogen energy storage technology and provides a method for preparing a lignocellulosic aerogel hydrogen storage material. The method includes: physically ball-milling agricultural and forestry biomass lignocellulosic fibers to below 100 mesh, dissolving them with an ionic liquid, regenerating the fibers to form a gel, immersing the gel in a solution containing modified carbon nanotubes, adding a crosslinking agent to form a gel network structure, and freeze-drying to prepare the lignocellulosic aerogel. The aerogel involved has low production cost, wide availability, and abundant pores and a controllable network structure, enabling effective capture of hydrogen molecules, thus possessing good practical application value.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen energy storage technology, specifically relating to a method for preparing a wood fiber-based aerogel hydrogen storage material. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way an indication that the information constitutes prior art known to those skilled in the art, or to encourage those skilled in the art to combine the information described in the background section.

[0003] Currently, finding alternative energy sources for both stationary and mobile applications has become a decisive factor in addressing sustainability challenges. Hydrogen, as a substitute for fossil fuels, has many advantages because it produces no pollutants, is energy efficient, and is essentially an inexhaustible resource. However, its storage remains a challenge. Existing hydrogen storage methods include metal hybridization, liquid hydrogen storage, high-pressure hydrogen storage, and adsorption. Magnesium has become a promising candidate metal for hydrogen storage due to its high hydrogen storage capacity, abundant resources, low price, and lack of pollution. However, magnesium has not yet been practically applied due to its high hydrogen adsorption / desorption temperatures and poor kinetic performance. Among these storage methods, adsorption offers advantages such as good chemical stability, good reversibility, and low cost. Therefore, adsorbent materials with porous structures and high porosity play an important role in solid-state hydrogen storage.

[0004] Patent application CN202311211574.9 proposes using metal-organic frameworks (MOFs) as nano-confined materials. These materials possess high specific surface area, effectively improving the dehydrogenation performance of ammonia borane and overcoming the problems of high dehydrogenation temperature, low dehydrogenation capacity, and low dehydrogenation purity found in existing solid hydrogen storage materials. However, their preparation cost is high and the process is complex. Patent application CN201911411873.0 proposes using magnesium hydride, porous materials, and metal oxides to create a hydrogen storage material. This improves the hydrogen storage kinetics of magnesium-based hydrogen storage materials and significantly reduces their storage temperature. However, the raw materials are mostly precious metals, which are expensive, increasing production costs and hindering industrial production.

[0005] Aerogels are three-dimensional, highly porous materials formed by cross-linking organic or inorganic substances. Due to their high porosity, high specific surface area, and low density, they have broad application prospects in the field of gas adsorption. Cellulose is the most widely distributed natural biomass resource, possessing advantages such as low cost, non-toxicity, environmental friendliness, and renewability. Cellulose aerogels have high porosity and a large specific surface area. The carbon atoms in cellulose aerogels attract hydrogen molecules, forming van der Waals forces that create physical bonds, making them ideal hydrogen storage materials. However, due to the uneven pore size distribution of cellulose aerogels, the adsorption of small molecule gases remains challenging, resulting in relatively low hydrogen loading efficiency.

[0006] Therefore, developing a novel cellulose aerogel that can efficiently load hydrogen has significant application value in the field of hydrogen storage. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention proposes a method for preparing a lignocellulosic aerogel hydrogen storage material. The aerogel involved has low production cost and wide availability, and combines properties such as tunable pore structure, excellent pore channels, and high surface area, enabling effective capture of hydrogen molecules. This results in excellent hydrogen adsorption and desorption properties for the aerogel.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a lignocellulosic aerogel hydrogen storage material includes the following steps:

[0010] (1) After grinding the wood fibers, dissolve them with an ionic liquid, add water, and the fibers will regenerate to form a wood fiber hydrogel. Wash with water and set aside.

[0011] (2) Carbon nanotubes were dispersed in a mixed aqueous solution containing organic acid and inorganic acid, a catalyst was added, ultrasonic vibration was performed, and then centrifugation and washing were performed to obtain modified carboxylated carbon nanotubes.

[0012] (3) The carboxylated carbon nanotubes obtained in step (2) are ultrasonically dispersed in an aqueous solution containing a dispersant, and then placed into the wood fiber hydrogel prepared in step (1), and a crosslinking agent is added for soaking to form a wood fiber-based hydrogel.

[0013] (4) Freeze-dry the lignocellulosic hydrogel formed in step (3) to prepare lignocellulosic aerogel, which can be used to store hydrogen.

[0014] In the optimized step (1), the lignocellulose includes wood fiber or non-wood lignocellulose; the wood fiber is selected from poplar and eucalyptus, and the non-wood fiber is selected from wheat straw and rice straw. Compared with the existing preparation schemes that use ionic liquids to dissolve single polymers such as cellulose and chitosan, the lignocellulose dissolved by the present invention is a mixture of cellulose, lignin, and hemicellulose, and the resulting gel network has a rougher surface, thereby increasing the specific surface area of ​​the hydrogen storage material. At the same time, it can reduce the time and chemicals required for component separation, and efficiently utilize the components of the lignocellulose.

[0015] In the optimized step (1), the ionic liquid is a commonly used ionic liquid for dissolving cellulose, selected from imidazole ionic liquids, quaternary ammonium ionic liquids, pyridine ionic liquids or choline ionic liquids.

[0016] The optimized mass ratio of wood fiber to ionic liquid in step (1) is 1:100 to 4:100.

[0017] In the optimized step (2), the types of organic and inorganic acids are as follows: the inorganic acid is one or more of hydrochloric acid, sulfuric acid, and nitric acid, mixed together; the organic acid is one or more of citric acid, salicylic acid, oxalic acid, acetic acid, and benzenesulfonic acid, mixed together; and the molar ratio of the organic acid to the inorganic acid is 1:1 to 1:3.

[0018] Furthermore, in step (2), the mass ratio of carbon nanotubes to the mixed aqueous solution of organic and inorganic acids is 1.0% to 3.0%.

[0019] During their research, the inventors unexpectedly discovered that adding a single acid could not enrich the surface of carbon nanotubes with carboxyl groups, resulting in poor dispersibility. However, using a mixture of organic and inorganic acids could oxidize the surface of carbon nanotubes, enriching it with a large number of carboxyl functional groups. Furthermore, within a certain range, adjusting the ratio of inorganic to organic acids could regulate the adsorption sites on the modified carbon nanotube surface, thereby increasing the micropore size and specific surface area of ​​the carbon aerogel. Therefore, adjusting the ratio allowed for the preparation of lignocellulosic aerogels with adjustable pore size and specific surface area, thus enabling the adjustment of hydrogen gas adsorption.

[0020] The optimized catalyst in step (2) is one or more of the following: ferric sulfate, ferric chloride, zinc sulfate, copper sulfate, and zinc chloride, used in synergy. The addition of the catalyst can accelerate the carboxylation reaction of carbon nanotubes, shorten the reaction time, and increase the carboxylation content of carbon nanotubes.

[0021] The optimized step (2) involves using a catalyst at a rate of 0.5% to 2.0% of the mass of the carbon nanotubes.

[0022] The optimized step (2) involves ultrasonic oscillation for 30 to 90 minutes.

[0023] The optimized dispersant in step (3) is one or a mixture of two of sodium dodecylbenzenesulfonate, sodium tripolyphosphate, and polyoxyethylene alkylphenol ether. The amount of dispersant used is 0.1% to 1.0% of the mass of carboxylated carbon nanotubes.

[0024] The dispersant added in this invention mainly increases the dispersibility of carboxylated carbon nanotubes through crosslinking, so that they are uniformly dispersed in the aqueous solution; the crosslinking agent enables cellulose and carboxylated carbon nanotubes to crosslink through chemical bonds and hydrogen bonds to form a lignocellulose-based gel network structure.

[0025] Optimized, the crosslinking agent in step (3) is one or a mixture of two of polyethylene glycol, epichlorohydrin, and dialdehyde starch, and the amount used is 0.5% to 1.5% of the mass of carboxylated carbon nanotubes.

[0026] The optimal soaking time for the wood fiber hydrogel in step (3) is 12h to 36h.

[0027] The optimized freezing temperature of the wood fiber hydrogel in step (4) is -40℃ to -60℃, and the freezing time is 24h to 48h.

[0028] In step (1), the wood fibers of agricultural and forestry biomass are physically ball-milled to below 100 mesh and dissolved with ionic liquid to form a homogeneous solution. Grinding can not only promote dissolution but also make it more uniform, while reducing the amount of ionic liquid used.

[0029] In step 3, carboxylated carbon nanotubes are uniformly dispersed in the aqueous solution through the bridging effect of the dispersant, and uniformly penetrate into the interior of the wood fiber hydrogel through impregnation and diffusion. The addition of the crosslinking agent enables the wood fibers and carboxylated carbon nanotubes to form a wood fiber-based hydrogel through physicochemical crosslinking.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] (1) This invention provides a method for preparing wood fiber-based aerogels by dissolving agricultural and forestry biomass wood fibers in ionic liquids, introducing carboxylated carbon nanotubes, and freeze-drying. The preparation method is simple to operate, the ionic liquids can be recycled, the preparation cost is low, and it is economical and environmentally friendly.

[0032] (2) The raw materials for preparing lignocellulose-based aerogels according to the present invention are widely available and low in cost, including lignocellulose raw materials such as poplar and eucalyptus, and non-lignocellulose raw materials such as wheat straw and rice straw. This achieves high-value utilization of agricultural and forestry resources and greatly reduces production costs. At the same time, the lignocellulose in the mixture is a mixture containing cellulose, lignin, and hemicellulose, which can form a gel network with a rougher surface and a larger specific surface area compared to a single fiber bundle.

[0033] (3) This invention modifies carbon nanotubes to give them more adsorption sites on their surface, and introduces carboxylated carbon nanotubes into wood fiber aerogels to give the carbon aerogels smaller micropores and larger specific surface areas. By adjusting the carbon nanotube modification method and the gel preparation process, wood fiber-based aerogels with adjustable pore size and specific surface area can be prepared, which is beneficial to the adsorption of hydrogen gas.

[0034] (4) This invention utilizes wood fiber-based aerogel porous material with adjustable pore size as hydrogen carrier, and combines carbon nanotubes with porous material. The excellent pores and high surface area of ​​porous material are combined to make the hydrogen storage material have good characteristics in hydrogen adsorption and desorption kinetics.

[0035] (5) The wood fiber-based aerogel obtained by the present invention has excellent mechanical properties, simple production process, safety and environmental protection, and is suitable for industrial production. Attached Figure Description

[0036] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0037] Figure 1 The image is a scanning electron microscope image of the lignocellulosic aerogel provided in Example 1. Detailed Implementation

[0038] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0039] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0040] Example 1

[0041] Poplar wood chips were physically ball-milled to below 100 mesh, and then dissolved in a 1-butyl-3-methylimidazolium ionic liquid to form a homogeneous solution. The mass ratio of wood chips to ionic liquid was 1:100. After adding water, the fibers were regenerated to form a lignocellulose hydrogel, which was then washed with water and set aside for later use.

[0042] Take 1.0 g of carbon nanotubes and disperse them in a mixed aqueous solution containing oxalic acid and sulfuric acid. The amount of oxalic acid added is 30 g, the amount of sulfuric acid is 32 g, and the amount of water added is 37 g. That is, the carbon nanotubes are dispersed in a mixed aqueous solution containing oxalic acid and sulfuric acid in a 1:1 molar ratio. The mass ratio of carbon nanotubes to the mixed acid is 1.0%. Add 0.5% ferric chloride relative to the mass of carbon nanotubes and sonicate at 100 W for 30 min. Then, centrifuge and wash to obtain modified carboxylated carbon nanotubes.

[0043] Carboxylated carbon nanotubes were ultrasonically dispersed in an aqueous solution containing sodium dodecylbenzenesulfonate dispersant at a concentration of 0.1% of the mass of the carboxylated carbon nanotubes. The dispersed nanotubes were then placed in the prepared wood fiber hydrogel and soaked for 24 hours with polyethylene glycol crosslinking agent at a concentration of 0.5% of the mass of the carboxylated carbon nanotubes to form a wood fiber-based hydrogel.

[0044] A wood fiber-based aerogel was prepared by freeze-drying the wood fiber-based hydrogel at -40℃ for 48 h. This aerogel can be used to store hydrogen.

[0045] Scanning electron microscope image of lignocellulosic aerogel as shown below Figure 1 As shown.

[0046] Example 2

[0047] Wheat straw was physically ball-milled to below 100 mesh, and then dissolved in 2-bromo-1-ethylpyridine tetrafluoroborate ionic liquid to form a homogeneous solution. The mass ratio of wood chips to ionic liquid was 2:100. After adding water, the fibers were regenerated to form a lignocellulose hydrogel, which was then washed with water and set aside for later use.

[0048] Take 2.0 g of carbon nanotubes and disperse them in a mixed aqueous solution containing oxalic acid and sulfuric acid, wherein the amount of oxalic acid added is 20 g, the mass of sulfuric acid is 43 g, and the amount of water added is 35 g. That is, the carbon nanotubes are dispersed in a mixed aqueous solution containing oxalic acid and sulfuric acid in a 1:2 molar ratio, and the mass ratio of carbon nanotubes to the mixed acid is 2.0%. Add zinc chloride at a ratio of 1.0% relative to the carbon nanotubes and sonicate at 100 W for 60 min. Then, centrifuge and wash to obtain modified carboxylated carbon nanotubes.

[0049] Carboxylated carbon nanotubes were ultrasonically dispersed in an aqueous solution containing polyoxyethylene alkylphenol ether dispersant at a concentration of 0.5%. The dispersant was then placed into the prepared wood fiber hydrogel and soaked in 1.0% epichlorohydrin crosslinking agent for 24 hours to form a wood fiber-based hydrogel.

[0050] A wood fiber-based aerogel was prepared by freeze-drying the wood fiber-based hydrogel at -50℃ for 36 h. This aerogel can be used to store hydrogen.

[0051] Example 3

[0052] Poplar wood chips were physically ball-milled to below 100 mesh, and then dissolved in a 1-butyl-3-methylimidazolium ionic liquid to form a homogeneous solution. The mass ratio of wood chips to ionic liquid was 4:100. After adding water, the fibers were regenerated to form a lignocellulose hydrogel, which was then washed with water and set aside for later use.

[0053] Take 3.0g of carbon nanotubes and disperse them in a mixed aqueous solution containing oxalic acid and sulfuric acid, wherein the amount of oxalic acid added is 15g, the amount of sulfuric acid is 50g, and the amount of water added is 32g. That is, the carbon nanotubes are dispersed in a mixed aqueous solution containing oxalic acid and sulfuric acid in a 1:3 molar ratio, and the mass ratio of carbon nanotubes to the mixed acid is 3.0%. Add 2.0% ferric chloride relative to the carbon nanotubes and sonicate at 100W for 90min. Then, centrifuge and wash to obtain modified carboxylated carbon nanotubes.

[0054] Carboxylated carbon nanotubes were ultrasonically dispersed in an aqueous solution containing sodium dodecylbenzenesulfonate dispersant at a concentration of 1.0%. The dispersed dispersant was then placed into the prepared lignocellulosic hydrogel, and 1.5% polyethylene glycol crosslinking agent was added and the mixture was soaked for 24 hours to form a lignocellulosic hydrogel.

[0055] A wood fiber-based aerogel was prepared by freeze-drying the wood fiber-based hydrogel at -60℃ for 48 h. This aerogel can be used to store hydrogen.

[0056] Example 4

[0057] Poplar wood chips were physically ball-milled to below 100 mesh, and then dissolved in a 1-butyl-3-methylimidazolium ionic liquid to form a homogeneous solution. The mass ratio of wood chips to ionic liquid was 1:100. After adding water, the fibers were regenerated to form a lignocellulose hydrogel, which was then washed with water and set aside for later use.

[0058] Take 1.0 g of carbon nanotubes and disperse them in a mixed aqueous solution containing oxalic acid and sulfuric acid. The amount of oxalic acid added is 40 g, the amount of sulfuric acid is 22 g, and the amount of water added is 37 g. That is, the carbon nanotubes are dispersed in a mixed aqueous solution containing oxalic acid and sulfuric acid in a 2:1 molar ratio. The mass ratio of carbon nanotubes to the mixed acid is 1.0%. Add 0.5% ferric chloride relative to the carbon nanotubes and sonicate at 100 W for 30 min. Then, centrifuge and wash to obtain modified carboxylated carbon nanotubes.

[0059] Carboxylated carbon nanotubes were ultrasonically dispersed in an aqueous solution containing sodium dodecylbenzenesulfonate dispersant at a concentration of 0.1%. The dispersant was then placed into the prepared lignocellulosic hydrogel and soaked for 24 hours with 0.5% polyethylene glycol crosslinking agent to form a lignocellulosic hydrogel.

[0060] A wood fiber-based aerogel was prepared by freeze-drying the wood fiber-based hydrogel at -40℃ for 48 h. This aerogel can be used to store hydrogen.

[0061] Example 5

[0062] Poplar wood chips were physically ball-milled to below 100 mesh, and then dissolved in a 1-butyl-3-methylimidazolium ionic liquid to form a homogeneous solution. The mass ratio of wood chips to ionic liquid was 1:100. After adding water, the fibers were regenerated to form a lignocellulose hydrogel, which was then washed with water and set aside for later use.

[0063] Take 1.0 g of carbon nanotubes and disperse them in a mixed aqueous solution containing oxalic acid and sulfuric acid. The amount of oxalic acid added is 12 g, the amount of sulfuric acid is 51 g, and the amount of water added is 33 g. That is, the carbon nanotubes are dispersed in a mixed aqueous solution containing oxalic acid and sulfuric acid in a 1:4 molar ratio. The mass ratio of carbon nanotubes to the mixed acid is 1.0%. Add 0.5% ferric chloride relative to the carbon nanotubes and sonicate at 100 W for 30 min. Then, centrifuge and wash to obtain modified carboxylated carbon nanotubes.

[0064] Carboxylated carbon nanotubes were ultrasonically dispersed in an aqueous solution containing sodium dodecylbenzenesulfonate dispersant at a concentration of 0.1%. The dispersant was then placed into the prepared lignocellulosic hydrogel and soaked for 24 hours with 0.5% polyethylene glycol crosslinking agent to form a lignocellulosic hydrogel.

[0065] A wood fiber-based aerogel was prepared by freeze-drying the wood fiber-based hydrogel at -40℃ for 48 h. This aerogel can be used to store hydrogen.

[0066] Comparative Example 1

[0067] Poplar wood chips were physically ball-milled to below 100 mesh, and then dissolved in a 1-butyl-3-methylimidazolium ionic liquid to form a homogeneous solution. The mass ratio of wood chips to ionic liquid was 3:100. After adding water, the fibers were regenerated to form a lignocellulose hydrogel, which was then washed with water and set aside for later use.

[0068] A wood fiber-based aerogel was prepared by freeze-drying the wood fiber-based hydrogel at -60℃ for 48 h. This aerogel can be used to store hydrogen.

[0069] Comparative Example 2

[0070] Poplar wood chips were physically ball-milled to below 100 mesh, and then dissolved in a 1-butyl-3-methylimidazolium ionic liquid to form a homogeneous solution. The mass ratio of wood chips to ionic liquid was 3:100. After adding water, the fibers were regenerated to form a lignocellulose hydrogel, which was then washed with water and set aside for later use.

[0071] Carbon nanotubes were dispersed in a mixed aqueous solution containing oxalic acid and sulfuric acid in a 1:3 molar ratio, with carbon nanotubes accounting for 1.0% of the mass of the mixed acid. Ferric chloride was added at a concentration of 0.5% relative to the carbon nanotubes, and the mixture was ultrasonically vibrated at 100W for 90 min. The mixture was then centrifuged and washed to obtain modified carboxylated carbon nanotubes.

[0072] Carboxylated carbon nanotubes were ultrasonically dispersed in an aqueous solution containing sodium dodecylbenzenesulfonate dispersant at a concentration of 0.2%. The dispersant was then placed into the prepared lignocellulosic hydrogel and soaked in 0.8% polyethylene glycol crosslinking agent for 24 hours to form a lignocellulosic hydrogel.

[0073] Wood fiber-based hydrogels are dried at high temperatures and used to store hydrogen.

[0074] Comparative Example 3

[0075] Fiber-based aerogels were prepared using cellulose as the raw material and the same method as in Example 1.

[0076] Comparative Example 4

[0077] 4.1 Except for “taking 1.0g of carbon nanotubes and dispersing them in a mixed aqueous solution containing oxalic acid and sulfuric acid, wherein the amount of oxalic acid added is 59g and the amount of water added is 30g”, the other conditions are the same as in Example 1 to prepare lignocellulose-based aerogel, wherein the concentration of oxalic acid solution is the sum of the concentrations of the two acids in Example 1.

[0078] 4.2. Except for “taking 1.0g of carbon nanotubes and dispersing them in a mixed aqueous solution containing oxalic acid and sulfuric acid, wherein the amount of sulfuric acid added is 66g and the amount of water added is 33g”, the other conditions are the same as in Example 1 to prepare lignocellulose-based aerogels, wherein the concentration of oxalic acid solution is the sum of the concentrations of the two acids in Example 1.

[0079] Comparative Example 5

[0080] No catalyst was added, and other materials and conditions were the same as in Example 1.

[0081] The maximum hydrogen absorption and time required for the fiber-based aerogels obtained in Examples 1-5 and the comparative examples were tested at -100°C and 3 bar, and the hydrogen release and time required for the materials at room temperature were also tested. The results are shown in Table 1.

[0082] Table 1. Summary of aerogel properties, hydrogen absorption, and hydrogen release test results for Examples 1-5 and Comparative Examples

[0083]

[0084]

[0085] As can be seen from the table, the wood fiber-based aerogels prepared in the examples have a larger specific surface area and a smaller pore size range. The introduction of carboxylated carbon nanotubes can adjust the specific surface area and pore size range of the aerogel. The maximum hydrogen adsorption capacity of the examples at -100℃ and 3 bar is as high as 3.8 wt%, and their maximum hydrogen adsorption capacity and time required are better than those of comparative examples 1-2. This indicates that wood fibers and modified carbon nanotubes have a promoting effect on the hydrogen storage capacity and speed of the material. The reason for this is that the wood fiber aerogel has a tunable porous structure and a large specific surface area, and the introduction of modified carbon nanotubes gives the wood fiber-based aerogel more hydrogen adsorption sites, thereby increasing the amount of hydrogen adsorbed by the wood fiber-based aerogel.

[0086] Furthermore, by comparing Comparative Example 3 with Example 1, it can be seen that under the same processing time and conditions, the specific surface area of ​​the obtained hydrogen storage material is significantly reduced. This is because the aerogel prepared from cellulose has a larger pore size, and the gel network composed of a single cellulose layer is smoother, resulting in a significant reduction in its specific surface area.

[0087] Comparative Example 4 shows that a single organic or inorganic acid cannot produce a hydrogen storage material with a large specific surface area. Comparative Example 5 shows that without the addition of a catalyst, the reaction is incomplete under the same time and conditions.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lignocellulosic aerogel hydrogen storage material, characterized in that, Includes the following steps: (1) After grinding the wood fibers, dissolve them with an ionic liquid, add water, and regenerate the fibers to form a wood fiber hydrogel. Wash with water and set aside. (2) Carbon nanotubes are dispersed in a mixed aqueous solution containing organic acid and inorganic acid, a catalyst is added, ultrasonic vibration is performed, and then centrifugation and washing are performed to obtain modified carboxylated carbon nanotubes; the molar ratio of organic acid to inorganic acid is 1:1 to 1:3; the mass ratio of carbon nanotubes to the mixed aqueous solution of organic acid and inorganic acid is 1.0% to 3.0%; The catalyst is one or more of the following: ferric sulfate, ferric chloride, zinc sulfate, copper sulfate, and zinc chloride, used in combination; the amount of catalyst used is 0.5% to 2.0% of the mass of carbon nanotubes. (3) The carboxylated carbon nanotubes obtained in step (2) are ultrasonically dispersed in an aqueous solution containing a dispersant, and then placed into the lignocellulosic hydrogel prepared in step (1). A crosslinking agent is added for soaking to form a lignocellulosic hydrogel; the amount of the dispersant is 0.1% to 1.0% of the mass of the carboxylated carbon nanotubes. (4) Freeze-dry the lignocellulosic hydrogel formed in step (3) to prepare lignocellulosic aerogel.

2. The method for preparing the lignocellulosic aerogel hydrogen storage material according to claim 1, characterized in that, In step (1), the wood fibers include wood fibers or non-wood fibers; the wood fibers are selected from poplar and eucalyptus, and the non-wood fibers are selected from wheat straw and rice straw.

3. The method for preparing the lignocellulosic aerogel hydrogen storage material according to claim 1, characterized in that, In step (1), the ionic liquid is selected from imidazole ionic liquids, quaternary ammonium ionic liquids, pyridine ionic liquids, and choline ionic liquids.

4. The method for preparing the lignocellulosic aerogel hydrogen storage material according to claim 1, characterized in that, In step (1), the mass ratio of wood fiber to ionic liquid is 1:100 to 4:

100.

5. The method for preparing the lignocellulosic aerogel hydrogen storage material according to claim 1, characterized in that, In step (2), the inorganic acid is one or a mixture of hydrochloric acid, sulfuric acid, and nitric acid; the organic acid is one or a mixture of citric acid, salicylic acid, oxalic acid, acetic acid, and benzenesulfonic acid.

6. The method for preparing the lignocellulosic aerogel hydrogen storage material according to claim 1, characterized in that, The dispersant in step (3) is one or a mixture of two of sodium dodecylbenzenesulfonate, sodium tripolyphosphate, and polyoxyethylene alkylphenol ether.

7. The method for preparing the lignocellulosic aerogel hydrogen storage material according to claim 1, characterized in that, The crosslinking agent in step (3) is one or a mixture of two of polyethylene glycol, epichlorohydrin, and dialdehyde starch, and the amount used is 0.5% to 1.5% of the mass of carboxylated carbon nanotubes.

8. The method for preparing the lignocellulosic aerogel hydrogen storage material according to claim 1, characterized in that, Step (2) The ultrasonic vibration time is 30 min to 90 min; Step (3) The soaking time for the wood fiber hydrogel is 12h~36h.

9. The method for preparing the lignocellulosic aerogel hydrogen storage material according to claim 1, characterized in that, Step (4) The freezing temperature of the wood fiber hydrogel is -40℃ to -60℃, and the freezing time is 24h to 48h.

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