Graphene-based aerogel with gradient pore structure and preparation method thereof

Abstract

The application discloses a graphene-based aerogel with a gradient pore structure and a preparation method thereof. The graphene-based aerogel has a gradually increased pore diameter from top to bottom. The method uses a graphene oxide water dispersion as raw material, and uses bubbles generated by stirring the graphene oxide and a surfactant aqueous solution as a template. Then, a layer of gelatinizer is uniformly scattered on the foamed graphene oxide aqueous solution. In the diffusion process, the graphene oxide sheet layer is induced to gel, and a three-dimensional network structure is formed. After drying, the graphene oxide-based aerogel with the gradient pore structure is obtained. Subsequently, the graphene-based aerogel with the continuous pore structure is obtained through reduction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new material preparation, and also belongs to the technical field of aerogel preparation, in particular to a graphene-based aerogel with a gradient pore structure and a preparation method thereof. BACKGROUND

[0002] Introducing a porous structure into a material not only reduces the density of the material and increases the specific surface area, but also improves the mechanical properties of the material and endows the material with multifunctionality. Gradient pore structure materials are a unique kind of porous materials, in which the pore size and distribution gradually change, and can be applied in the fields of thermal insulation, high-efficiency catalysis, energy storage and dissipation, environmental remediation, etc. For example, the gradient pores inside a bamboo pole endow it with the performance of efficiently resisting bending, and provide buildings with the performance of light weight, thermal insulation, etc.

[0003] Graphene aerogel is a three-dimensional network structure material formed by physical or chemical cross-linking of graphene sheets. It has the dual properties of aerogel and graphene, such as ultralight, porous, conductive, hydrophobic and oleophilic, and excellent compression and rebound performance. These properties make graphene aerogel have great potential application value in the fields of catalyst carrier, conductive device, environmental remediation, and energy storage and dissipation. In recent years, the research on the pore structure of graphene-based aerogel has gradually developed from the initial chaotic state to a controllable and ordered state. Studies have shown that graphene aerogel with ordered pore morphology exhibits excellent performance in many fields. For example, oriented pores not only improve the compression and rebound performance of graphene aerogel, but also improve the transmission capacity of water therein, which is beneficial to the preparation of high-efficiency photothermal water evaporation devices. Chinese invention patent ZL106517160B first used air bubbles as a template combined with a normal pressure drying method to obtain graphene aerogel with uniform spherical pore morphology, which exhibited isotropic super-elastic performance. However, the pore structure inside the graphene aerogel obtained by the current preparation method is uniform. Although we previously explored a layer-by-layer pouring method to prepare graphene-based aerogel with gradient pore structure, the gradient pore structure inside the graphene gel obtained by the method depends on the thickness of each layer poured, and the same thickness layer still presents a uniform pore structure, and it is impossible to obtain graphene-based aerogel with continuously changing pore size. Therefore, it is of great significance to realize the preparation of graphene aerogel with a gradient pore size structure in terms of both preparation method and application. SUMMARY

[0004] In view of the problems existing in the prior art, the present application provides a graphene-based aerogel with a gradient pore structure and a preparation method thereof. The method is simple to operate and can prepare graphene-based aerogel with continuously changing pore size. The pore size of the graphene-based aerogel prepared can be controlled by adjusting the height of the foamed graphene oxide mixed solution in the mold.

[0005] To achieve the above object, the present application provides the following technical solutions.

[0006] A graphene-based aerogel with a gradient pore structure, the pore size of which gradually increases from top to bottom.

[0007] In addition, the present application also provides a method for preparing the graphene-based aerogel with a gradient pore structure as described above, wherein a surfactant is added to a graphene oxide water dispersion, and after stirring and foaming, the mixture is poured into a mold with a certain height; then a gel agent is uniformly scattered on the top layer of the foamed graphene oxide mixture, and the gel agent diffuses and gels from top to bottom to form a three-dimensional network structure with air bubbles as templates; finally, the gel is dried to obtain the graphene oxide-based aerogel with a gradient pore structure, and the graphene oxide-based aerogel is reduced to obtain the graphene-based aerogel with a gradient pore structure.

[0008] Preferably, the specific steps include:

[0009] 1) preparing a graphene oxide water dispersion;

[0010] 2) stirring and uniformly mixing an aqueous surfactant solution with the graphene oxide water dispersion, and then increasing the stirring speed to obtain a foamed graphene oxide mixture;

[0011] 3) pouring the foamed graphene oxide mixture into a mold with a certain height;

[0012] 4) uniformly scattering a gel agent on the surface of the graphene oxide mixture obtained in step 3) so that the gel agent diffuses into the mixture from top to bottom to form a graphene oxide hydrogel;

[0013] 5) drying the hydrogel obtained in step 4) to obtain a graphene oxide-based aerogel with a gradient pore structure;

[0014] 6) reducing the graphene oxide-based aerogel obtained in step 5) to obtain a graphene-based aerogel with a gradient pore structure.

[0015] Preferably, the concentration of graphene oxide in the graphene oxide water dispersion is 2-16 mg·mL -1 .

[0016] Preferably, the surfactant includes one or more of sodium dodecyl sulfonate, sodium dodecyl sulfate, alkyl polyglucoside, and F127 in any proportion.

[0017] Preferably, the volume of the foamed graphene oxide mixture is 1.1-2.5 times the original volume.

[0018] Preferably, the height of the foamed graphene oxide mixture poured into the mold is 0.5-10 cm.

[0019] Preferably, the gel is water-soluble ionic salt and / or positively charged nanoparticles, and the overall concentration of the gel after diffusion is completed is 5-400 mg / mL.

[0020] Preferably, the drying method is freeze drying, normal pressure drying or supercritical drying.

[0021] Preferably, the size of the graphene oxide sheet is 5-50 μm.

[0022] The stirring method is not limited, and preferably magnetic stirring, and the rate of low-speed stirring is 60-300 r·min -1 , and the rate of high-speed stirring is 500-2500 r·min -1 , preferably 1000 r·min -1 .

[0023] Preferably, the gel drying method further comprises: after freezing the graphene oxide hydrogel, melting, and after replacing with ethanol, directly heating under normal pressure to obtain graphene oxide-based aerogel.

[0024] The beneficial effects of the present application are as follows:

[0025] 1. The graphene aerogel prepared by the method has a continuous increase in pore size in the longitudinal section, and the pore size range can reach 30-1000 μm.

[0026] 2. The method is simple to operate, and the preparation of graphene aerogel using the method is more conducive to the realization of its large-scale preparation and the preparation of large graphene aerogel.

[0027] 3. The graphene aerogel prepared by the method further expands the preparation method of graphene aerogel, and widens its application in the fields of photothermal conversion and photothermal water evaporation. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a real object diagram of the graphene-based aerogel with gradient pore structure prepared in Example 1.

[0029] Figure 2 is a scanning electron microscope image of the graphene-based aerogel prepared in Example 1, which is a horizontal section scanning electron microscope image at different positions from top to bottom.

[0030] Figure 3 is an optical microscope image of the graphene-based aerogel prepared in Example 1, which is a longitudinal section optical microscope image. DETAILED DESCRIPTION

[0031] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application.

[0032] Example 1

[0033] Prepare 8 mg / mL -1 Aqueous dispersion of graphene oxide. Take 50 mL of the above aqueous dispersion of graphene oxide (sheet lateral size 20 μm) into a small beaker, and add 8 mL of 50 mg·mL⁻¹ solution. -1 SDS, at 150 r·min -1 Stir for 3 minutes, then at 1000 rpm. -1 A foamed graphene oxide mixture was obtained by stirring at a certain rate, and its volume doubled after foaming. The foamed mixture was poured into a cylindrical flask, and the height of the foamed solution was 1 cm. 2 g of sodium chloride powder was evenly sprinkled on the surface of the foamed graphene oxide mixture and allowed to diffuse slowly. After 12 h, a graphene oxide hydrogel was obtained. Then, after freeze-drying, a graphene oxide-based aerogel with a gradient pore structure was obtained. After high-temperature reduction, a graphene-based aerogel with a gradient pore structure was obtained. Its pore size ranges from 30 to 500 μm.

[0034] Example 2

[0035] The types of materials and the process flow are the same as in Example 1, except that the height of the graphene oxide poured into the cylindrical bottle is 0.5 cm. The final product is a honeycomb-shaped graphene-based aerogel with well-preserved shape and a pore size range of 30–500 μm.

[0036] Example 3

[0037] The types of materials and the process flow are the same as in Example 1, except that the height of the graphene oxide poured into the cylindrical bottle is 8 cm. The final product is a honeycomb-shaped graphene-based aerogel with well-preserved shape and a pore size range of 30–1000 μm.

[0038] Example 4

[0039] The types of materials and the process flow are the same as in Example 1, except that the height of the graphene oxide poured into the cylindrical bottle is 10 cm. The final product is a honeycomb-shaped graphene-based aerogel with well-preserved shape and a pore size range of 30–1000 μm.

[0040] Example 5

[0041] The kind of material and process flow used are the same as in Example 1, except that the concentration of graphene oxide is 2 mg mL -1 A graphene-based aerogel with good shape retention is obtained, with a pore size range of 30-700 μm.

[0042] Example 6

[0043] The kind of material and process flow used are the same as in Example 1, except that the concentration of graphene oxide is 10 mg mL -1 A graphene-based aerogel with good shape retention is obtained, with a pore size range of 30-600 μm.

[0044] Example 7

[0045] The kind of material and process flow used are the same as in Example 1, except that the concentration of graphene oxide is 16 mg mL -1 A graphene-based aerogel with good shape retention is obtained, with a pore size range of 30-800 μm.

[0046] Example 8

[0047] The process flow used is the same as in Example 1, except that the surfactant used is alkyl polyglucoside, and finally a graphene-based aerogel with good shape retention is obtained, with a pore size range of 30-600 μm.

[0048] Example 8

[0049] The process flow used is the same as in Example 1, except that the surfactant used is F127, and finally a graphene-based aerogel with good shape retention is obtained, with a pore size range of 300-600 μm.

[0050] Example 9

[0051] The process flow used is the same as in Example 1, except that the lateral size of the graphene oxide used is 5 μm, and finally a graphene-based aerogel with good shape retention is obtained, with a pore size range of 60-600 μm.

[0052] Example 10

[0053] The process flow used is the same as in Example 1, except that the lateral size of the graphene oxide used is 50 μm, and finally a graphene-based aerogel with good shape retention is obtained, with a pore size range of 30-500 μm.

[0054] Example 11

[0055] The process flow used is the same as in Example 1, except that the amount of surfactant used is 4 mL, and finally a graphene-based aerogel with good shape retention is obtained, with a pore size range of 30-500 μm.

[0056] Example 12

[0057] The process used was the same as Example 1, except that the amount of surfactant used was 10 mL, and finally a graphene-based aerogel with good shape retention was obtained, with a pore size range of 30-600 μm.

[0058] Example 13

[0059] The process used was the same as Example 1, except that the volume of graphene oxide mixed liquid after foaming was 1.1 times the original volume, and finally a graphene-based aerogel with good shape retention was obtained, with a pore size range of 30-500 μm.

[0060] Example 14

[0061] The process used was the same as Example 1, except that the volume of graphene oxide solution after foaming was 2.2 times the original volume, and finally a graphene-based aerogel with good shape retention was obtained, with a pore size range of 30-1000 μm.

[0062] Example 15

[0063] The process used was the same as Example 1, except that the gel agent used was potassium chloride, and finally a graphene-based aerogel with good shape retention was obtained, with a pore size range of 30-600 μm.

[0064] Example 16

[0065] The process used was the same as Example 1, except that the drying method was selected as atmospheric drying, and finally a graphene-based aerogel with good shape retention was obtained, with a pore size range of 30-1000 μm.

[0066] Comparative Example 1

[0067] The types of materials and process used were the same as Example 1, except that the concentration of graphene oxide was 1 mg·mL -1 , and finally a graphene-based aerogel with severe shape collapse was obtained.

[0068] Comparative Example 2

[0069] The types of materials and process used were the same as Example 1, except that the volume of graphene oxide mixed liquid after foaming was 3 times the original volume, and finally a graphene-based aerogel with severe shape collapse was obtained.

[0070] Comparative Example 3

[0071] The types of materials and process used were the same as Example 1, except that the graphene oxide mixed liquid was directly freeze-dried after foaming, and finally a graphene-based aerogel with a relatively uniform pore size was obtained.

[0072] Comparative Example 4

[0073] The kind of material and process flow used are the same as example 1, except that the amount of surfactant used is 1 mL, and the final graphene-based aerogel has a pore size that exhibits a mixture of spherical and disordered morphologies.

[0074] Comparative Example 5

[0075] The kind of material and process flow used are the same as example 1, except that the lateral sheet size of graphene oxide used is 2 μm, and the final graphene-based aerogel has a shape that collapses severely.

[0076] Comparative Example 6

[0077] The kind of material and process flow used are the same as example 1, except that the lateral sheet size of graphene oxide used is 60 μm, and the graphene oxide cannot be stirred to foam, so the aerogel with a gradient pore structure cannot be prepared.

[0078] Comparative Example 7

[0079] The kind of material and process flow used are the same as example 1, except that the height of graphene oxide poured into the cylindrical bottle is 0.2 cm, and the final graphene-based aerogel has a pore size that is approximately uniform.

[0080] Comparative Example 8

[0081] The kind of material and process flow used are the same as example 1, except that the height of graphene oxide poured into the cylindrical bottle is 20 cm, and the final graphene-based aerogel has a shape that collapses severely.

[0082] From Figure 1 It can be seen that the graphene-based aerogel obtained by example 1 has a good shape; upon careful observation of the surface, the pore size exhibits a certain change, and the pore size gradually increases from top to bottom. Figure 2 Upon magnified observation of the cross-sections at different positions, the graphene-based aerogel obtained can be more clearly seen, and the pore size at the top is smaller, while the pore size near the bottom is larger, and the overall exhibits a certain gradient pore structure. Figure 3 The gradient pore structure is more clearly shown, and the pore size ranges from 30 to 500 μm from top to bottom. This is because the sodium ions after sodium chloride dissolves in water have opposite charges to the carboxyl groups on the graphene oxide sheet, so excessive sodium chloride can cause the graphene oxide sheet to gel; because the bubbles in the foamed graphene oxide mixture will fuse into larger bubbles over time. Therefore, during the diffusion of sodium chloride from the top of the foamed graphene oxide solution, the bubbles near the top are first fixed due to the gelation of graphene oxide, and at this time the bubbles near the bottom gradually fuse and become larger, and are finally wrapped and fixed by the gelatinized graphene oxide sheet. Therefore, the pore size of the overall graphene oxide gel exhibits a continuous increase from top to bottom.

[0083] Furthermore, it should be understood that although the specification is described in terms of embodiments, not every embodiment includes only one independent technical solution, and the specification is described in this way only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A graphene-based aerogel having a gradient pore structure, characterized by, The pore size of the graphene-based aerogel gradually increases from top to bottom. The graphene-based aerogel is prepared by adding a surfactant to a graphene oxide aqueous dispersion, stirring and foaming, and then pouring the foamed graphene oxide mixture into a mold with a certain height; then uniformly scattering a gel agent on the top layer of the foamed graphene oxide mixture, allowing it to diffuse and gel from top to bottom, and finally drying the gel to obtain an oxidized graphene-based aerogel with a gradient pore structure, which is reduced to obtain a graphene-based aerogel with a gradient pore structure. The gel agent is a water-soluble ionic salt and / or positively charged nanoparticles.

2. A method of preparing the graphene-based aerogel having a gradient pore structure according to claim 1, characterized by, The graphene-based aerogel is prepared by adding a surfactant to a graphene oxide aqueous dispersion, stirring and foaming, and then pouring the foamed graphene oxide mixture into a mold with a certain height; then uniformly scattering a gel agent on the top layer of the foamed graphene oxide mixture, allowing it to diffuse and gel from top to bottom, and finally drying the gel to obtain an oxidized graphene-based aerogel with a gradient pore structure, which is reduced to obtain a graphene-based aerogel with a gradient pore structure. The gel agent is a water-soluble ionic salt and / or positively charged nanoparticles.

3. The preparation method according to claim 2, characterized in that, The specific steps include: 1) preparing a graphene oxide aqueous dispersion; 2) stirring and mixing the surfactant aqueous solution and the graphene oxide aqueous dispersion uniformly, and then increasing the stirring speed to obtain a foamed graphene oxide mixture; 3) pouring the foamed graphene oxide mixture into a mold with a certain height; 4) uniformly scattering a gel agent on the surface of the graphene oxide mixture obtained in step 3) to allow it to diffuse into the mixture from top to bottom to form a graphene oxide hydrogel; 5) drying the hydrogel obtained in step 4) to obtain an oxidized graphene-based aerogel with a gradient pore structure; 6) reducing the graphene-based aerogel obtained in step 5) to obtain a graphene-based aerogel with a gradient pore structure.

4. The production method according to claim 2 or 3, characterized by, The concentration of graphene oxide in the graphene oxide aqueous dispersion is 2-16 mg·mL -1 .

5. The production method according to claim 2 or 3, characterized by, The surfactant includes one or more of sodium dodecyl sulfonate, sodium dodecyl sulfate, alkyl polyglucoside, and F127 in any proportion.

6. The production method according to claim 2 or 3, characterized by, The volume of the foamed graphene oxide mixture is 1.1-2.5 times the original volume.

7. The production method according to claim 2 or 3, characterized by, The height of the foamed graphene oxide mixture poured into the mold is 0.5-10 cm.

8. The production method according to claim 2 or 3, characterized by, The overall concentration of the gel agent after diffusion is 5-400 mg / mL.

9. The production method according to claim 2 or 3, characterized by, The drying method is freeze-drying, normal pressure drying, or supercritical drying.

10. The production method according to claim 2 or 3, characterized by, The size of the graphene oxide sheet is 5-50 μm.

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