A SiO2 / C composite material with a multi-level three-dimensional network structure and its preparation method and application

Abstract

A SiO2 / C composite material with a multi-level three-dimensional network structure, and its preparation method and application. The present invention belongs to the technical field of carbon-based composite materials. The purpose of the present invention is to solve the technical problems of existing carbon-based porous materials that are prone to collapse under external forces and have poor uniformity. The method of the present invention comprises: dissolving CTAB in SiO2 sol, then adding a spinning aid, and producing a SiO2 fiber felt containing CTAB by electrospinning; mixing an ethanol solution of citric acid, ferric nitrate, and cobalt nitrate with an ethanol solution of urea to form a small molecule precursor solution; soaking the fiber felt in the small molecule precursor solution, then heating it for a cross-linking reaction, and then carbonizing it to obtain a composite material. The present invention uses SiO2 fibers as a support and introduces CTAB to regulate the carbon structure produced by the small molecule cross-linking reaction. This achieves controllable growth of carbon materials, which can be used as wave-absorbing materials to meet the requirements of wave-absorbing materials for multiple reflection and scattering of electromagnetic waves.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon-based composite materials, and in particular relates to a SiO2 / C composite material with a multi-level three-dimensional network structure, a preparation method thereof, and an application thereof. Background Art

[0002] Carbon-based porous materials are considered to be ideal electromagnetic wave absorbers due to their rich porosity, three-dimensional interconnected structure, excellent conductivity and good chemical stability. The rich porosity enables porous carbon materials to store a large amount of air, which can reduce the density of the absorber. However, traditional carbon-based porous materials are brittle and easily collapse when subjected to external stress, which limits their application. In addition, the structure control process of carbon-based porous materials is complex and their uniformity is difficult to ensure. Therefore, it is particularly important to suppress deformation and cracking under external force, prevent material collapse and ensure its uniformity. Summary of the Invention

[0003] The purpose of the present invention is to solve the technical problems that existing carbon-based porous materials are prone to collapse under external forces and have poor uniformity, and to provide a SiO2 / C composite material with a multi-level three-dimensional network structure and its preparation method and application.

[0004] One of the objects of the present invention is to provide a method for preparing a SiO2 / C composite material having a multi-level three-dimensional network structure, the method being carried out according to the following steps:

[0005] S1: Cetyltrimethylammonium bromide (CTAB) is dissolved in SiO2 sol to form a precursor solution, and then a spinning aid is added and stirred to obtain an electrospinning solution. Then, SiO2 fiber mat containing CTAB is prepared by electrospinning;

[0006] S2: dissolving citric acid, ferric nitrate, and cobalt nitrate in an ethanol solution to form a mixed solution, and then stirring the mixed solution with an ethanol aqueous solution of urea at room temperature to form a small molecule precursor solution;

[0007] S3: The SiO2 fiber felt containing CTAB is immersed in a small molecule precursor solution, and then heated for cross-linking reaction. After the reaction is completed, carbonization treatment is performed to obtain a SiO2 / C composite material.

[0008] It is further defined that the preparation of the SiO2 sol in S1 is as follows: tetraethoxysilane, ethanol, water and hydrochloric acid are mixed, heated, condensed and refluxed to react to obtain a transparent solution, and then continuously stirred under heating conditions until the residual volume is 50-70% of the original solution volume to obtain SiO2 sol.

[0009] It is further defined that the molar ratio of tetraethoxysilane, ethanol, water and hydrochloric acid is 1: (2-4): (0.5-1.5): (6×10-4 -8×10 -4 ).

[0010] It is further defined that the condensation reflux reaction temperature is 70-80°C and the time is 5-7h.

[0011] Further defined, stirring is continued at 80-90°C.

[0012] It is further defined that the CTAB concentration in the precursor solution in S1 is 25-50 mg / mL.

[0013] It is further defined that the spinning aid in S1 is polyethylene oxide, and the added amount is 0.1-0.3% of the mass of the precursor solution.

[0014] It is further defined that the electrospinning parameters in S1 are: feed rate of 0.5-1.5 mL / h, acceleration voltage of 15-25 kV, and distance between the injection needle tip and the collector of 10-20 cm.

[0015] It is further defined that the molar ratio of citric acid, ferric nitrate and cobalt nitrate in S2 is (4-6):(1.5-2.5):1.

[0016] It is further defined that the concentration of citric acid in the mixed solution in S2 is 0.5-1.5 mol / L.

[0017] It is further defined that the volume ratio of ethanol to water in the mixed solution in S2 is (2-3):1.

[0018] It is further defined that the urea concentration in the ethanol aqueous solution of urea in S2 is 6-8 mol / L.

[0019] It is further defined that the volume ratio of ethanol to water in the ethanol-water solution of urea in S2 is (2-3):1.

[0020] It is further defined that the molar ratio of urea to citric acid in S2 is (6-7):1.

[0021] It is further defined that the cross-linking reaction temperature in S3 is 170-190° C. and the time is 10-20 h.

[0022] It is further defined that the carbonization temperature in S3 is 800-1200°C, the time is 0.5-1.5h, and the heating rate is 4-6°C / min.

[0023] The second object of the present invention is to provide a SiO2 / C composite material prepared by the above method, in which the SiO2 fiber felt serves as a support body and the three-dimensional network structure porous carbon formed by interconnected carbon nanotubes is filled in the support body.

[0024] It is further defined that the diameter of carbon nanotubes is 1-5nm, the diameter of the three-dimensional network structure porous carbon mesh is 10-50nm, the diameter of SiO2 fibers in the SiO2 fiber felt is 300-800nm, and the porosity is 80-99%.

[0025] It is further defined that the volume proportion of carbon material in SiO2 / C composite material is 80-95%.

[0026] The third object of the present invention is to provide an application of the SiO2 / C composite material prepared by the above method in electromagnetic wave absorption.

[0027] Compared with the prior art, the present invention has the following significant effects:

[0028] The present invention uses SiO2 fibers as a support and introduces CTAB to regulate the carbon structure produced by the small molecule cross-linking reaction. In order to ensure the dispersibility of CTAB in the system, CTAB is introduced into the SiO2 fibers using electrospinning technology. The SiO2 fibers slowly release CTAB in the small molecule cross-linking reaction system, and a cross-linked porous carbon material is prepared on the one-dimensional SiO2 nanofibers to ensure the dispersibility of CTAB in the system. The abundant Si-OH groups on the surface of the SiO2 fibers ensure that the CTAB portion is widely bound to the entire SiO2 fiber. The presence of CTAB guides the carbon nanomaterial to grow along the SiO2 fibers as a support, and finally forms a SiO2 / C composite material. The method of the present invention realizes the controllable growth of carbon materials, thereby forming a new composite material with structural integrity and carbon network structure, which is used as an absorbing material to meet the absorbing material's requirements for multiple reflections and scattering of electromagnetic waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Macroscopic digital photos and morphological SEM images of the materials obtained in Example 1 and Comparative Examples 1-2; (a) and (d) correspond to Comparative Example 1; (b) and (e) correspond to Comparative Example 2; (c) and (f) correspond to Example 1;

[0030] Figure 2 The macromorphology and local magnification of the SiO2 / C composite material prepared in Example 1; (a) - Macromorphology; (b) - A magnified view of a local position in Figure (a); (c) - Stress response mechanism of the SiO2 / C composite material;

[0031] Figure 3 SEM images of the SiO2 / C composite material prepared in Example 1 at different magnifications; (a) -5k magnification (b) -10k magnification;

[0032] Figure 4TEM image of the SiO2 / C composite material prepared in Example 1; (b) is an enlarged view of a local position in (a);

[0033] Figure 5 Characterization diagram of the wave absorption performance of the SiO2 / C composite material prepared in Example 1; (a) - reflection loss curve; (b) - reflection loss three-dimensional diagram. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained commercially by those skilled in the art unless otherwise specified.

[0036] As used in the following examples, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0037] When amount, concentration or other value or parameter are represented with the range of scope, preferred range or a series of upper preferred value and lower preferred value limit, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, and no matter whether this scope is disclosed separately.For example, when disclosing scope "1 to 5", described scope should be interpreted as including scope "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within the scope.In this application specification and claims, range limitation can be combined and / or interchanged, and if these ranges are not otherwise stated, include all subranges contained therein.

[0038] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirement (i.e. the number of times they appear). Therefore, "a" or "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms, unless the quantity clearly refers to only the singular form.

[0039] The term "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it necessarily refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0040] The endpoints of the ranges and any values ​​disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0041] Example 1: The preparation method of the SiO2 / C composite material having a multi-level three-dimensional network structure in this example is carried out by the following steps:

[0042] (1) Preparation of SiO2 sol

[0043] Tetraethoxysilane, ethanol, water and hydrochloric acid were mixed in a ratio of 1:3:1:7×10 -4 The mixture was uniformly mixed in a molar ratio of 1:1, and then refluxed at 75°C for 6 hours to obtain a transparent solution. The transparent solution was continuously stirred at 85°C until the residual volume was 60% of the original solution, thereby preparing a uniform SiO2 sol.

[0044] (2) Preparation of SiO2 electrospinning precursor containing CTAB

[0045] CTAB was added to the SiO2 sol, completely dissolved, and stirred at room temperature for 3 hours to prepare a precursor solution with a CTAB content of 50 mg / mL. Subsequently, 0.2 wt% polyethylene oxide was added to the precursor solution as a spinning aid and stirred at room temperature for 1 hour to obtain the electrospinning solution.

[0046] (3) Electrospinning process

[0047] The electrospinning solution was placed in a 10 mL syringe. A 6 mm inner diameter syringe needle was connected to the positive terminal of a high-voltage power supply. Electrospinning was performed using a metal plate connected to the negative terminal of the high-voltage power supply as the receiving end. The electrospinning parameters were: a feed rate of 1 mL / h, an accelerating voltage of 20 kV, and a distance of 15 cm between the syringe needle tip and the collector. The resulting CTAB-containing SiO2 fiber mat had a diameter of 800 nm and a thickness of 20 mm.

[0048] (4) Preparation of small molecule cross-linking reaction precursors

[0049] Mix 3.5 mL of deionized water with 7.5 mL of ethanol, add 12 mmol of citric acid, 5 mmol of ferric nitrate, and 2.5 mmol of cobalt nitrate, and completely dissolve at room temperature. Stir thoroughly for 1 hour to form Solution A. Similarly, completely dissolve 80 mmol of urea in a mixture of 3.5 mL of deionized water and 7.5 mL of ethanol to form Solution B. Mix Solutions A and B and stir continuously at room temperature for 3 hours. This forms a small molecule precursor solution with uniform composition distribution.

[0050] (5) Small molecule cross-linking reaction process

[0051] The SiO2 fiber felt containing CTAB was soaked in the small molecule precursor solution, then placed in a sealed container and kept in an oven at 180°C in an air atmosphere for 15 hours. During this stage, the citric acid and urea metal complexes simultaneously underwent solvent evaporation and cross-linking reactions.

[0052] (6) Carbonization stage

[0053] The resulting small molecule cross-linked product was placed in a tube furnace and heated at 1000°C for 1 hour in a nitrogen atmosphere at a heating rate of 5°C / min to remove the carbon structure and residual organic matter from the SiO2, resulting in a SiO2 / C composite with a hierarchical three-dimensional network structure. The carbon material accounted for 85% of the volume of the SiO2 / C composite.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that steps (1) to (3) are omitted, and the small molecule precursor solution obtained in step (4) is directly subjected to the cross-linking reaction in step (5) and the carbonization treatment in step (6) to obtain a pure carbon material. The other steps and parameters are the same as those in Example 1.

[0056] Comparative Example 2

[0057] The difference between this comparative example and Example 1 is that CTAB in step (2) is omitted to obtain a SiO2 / C composite material. The other steps and parameters are the same as those in Example 1.

[0058] The morphology of the materials obtained in Example 1 and Comparative Examples 1-2 was characterized, and the results were as follows: Figure 1 As shown in Figure 1(a), it can be seen that in the absence of SiO2 nanofiber carriers, the product of small molecule cross-linking is mainly composed of flake carbon materials. Due to the aggregation of reactants in the small molecule cross-linking stage, the resulting product does not appear in the form of an integral structure. Figure 1 As shown in the SEM image in (d), the microscopic morphology shows that in the absence of CTAB, the carbon material forms a dense layered structure and cannot produce a porous structure.

[0059] from Figure 1 (b) It can be seen that due to the support of SiO2 nanofibers in the material, it forms a unified structure. However, the lack of CTAB in the system causes the carbon material to aggregate into a dense block structure. Figure 1 This observation is further confirmed by the SEM image in (e), which shows densely packed carbon materials aggregated near the SiO2 nanofibers.

[0060] from Figure 1 As can be seen in (c), the macromorphology of the sample supported by CTAB-SiO2 fibers after the crosslinking stage shows that the carbon structure fills the gaps between the supports without excessive aggregation, as the SiO2 fibers act as supports. Therefore, the obtained product presents a monolithic structure. Figure 1 This is further confirmed by the SEM image in (f). In the SEM image, the carbon material can be observed growing around the SiO2 fibers, forming a porous structure due to the free CTAB in the solution. In summary, the electrospun SiO2 nanofibers serve as a support for the overall structure of the composite material, forming a single, structurally complete component rather than a powdered structure. Furthermore, the structure of the carbon material can be manipulated by CTAB to meet the absorber's requirements for multiple reflections and scattering of electromagnetic waves.

[0061] The macroscopic morphology and local magnification of the SiO2 / C composite material with a multi-level three-dimensional network structure obtained in Example 1 of the present invention are shown in FIG. Figure 2 As shown in the figure, the sample exhibits a layered structure, with the SiO2 fiber mat serving as a support and the porous carbon material filling the structure. This layered structure exhibits an excellent response mechanism to external pressure. Rebound is a phenomenon caused by elastic recovery after unloading. When external pressure is applied to the layered structure, the structure undergoes elastic deformation in response to the external pressure. During this process, energy is stored in the structure as potential energy through the twisting and stretching of bonds. As the external pressure decreases or disappears, the energy stored in the structure begins to be released. The layered structure rebounds, releasing the stored energy, causing the structure to gradually return to its original shape. The entire process is dynamic and continues until equilibrium is reached. This energy storage and release mechanism gives the layered structure its elasticity, allowing it to quickly return to its original state and release stored energy when subjected to pressure.

[0062] The SEM images of the SiO2 / C composite material with a multi-level three-dimensional network structure obtained in Example 1 of the present invention at different magnifications are as follows: Figure 3 As shown, TEM Figure 4As shown in the transmission electron microscope image, it can be observed that the diameter of the silica fiber is about 800nm, and the porous carbon on its surface exists in the form of a tubular structure interconnected into a three-dimensional network with a diameter of about 3-5nm, which means that the SiO2 / C composite material with SiO2 fibers as the support has a multi-level structure, and its carbon material structure is a three-dimensional network structure built by carbon nanotubes.

[0063] Application Examples

[0064] The SiO2 / C composite material with a multi-level three-dimensional network structure obtained in Example 1 was uniformly mixed with molten paraffin wax at a mass ratio of 20:80 and pressed into a ring-shaped wave absorbing test sample. The ring body had an inner diameter of 3 mm, an outer diameter of 7 mm, and a thickness of 2 mm ± 5%.

[0065] Conduct electromagnetic wave absorption test, the results are as follows Figure 5 As shown in the figure, the maximum reflection loss remains minimal at around 14 GHz. At this frequency, the reflection loss for a thickness of 7.5 mm reaches a minimum of -37.8 dB. The introduction of CTAB promotes the formation of a three-dimensional conductive network, resulting in continuous and rapid transport of charge carriers within the material. This process generates and dissipates Joule heat, leading to enhanced conductivity losses.

[0066] The foregoing are merely preferred embodiments of the present invention. These embodiments are all different implementations based on the overall concept of the present invention. The scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a SiO2 / C composite material having a multi-level three-dimensional network structure, characterized in that: The method: S1: CTAB is dissolved in SiO2 sol to form a precursor solution, and then a spinning aid is added and stirred to obtain an electrospinning solution, and then a SiO2 fiber mat containing CTAB is prepared by electrospinning; S2: dissolving citric acid, ferric nitrate, and cobalt nitrate in an ethanol solution to form a mixed solution, and then stirring the mixed solution with an ethanol aqueous solution of urea at room temperature to form a small molecule precursor solution; S3: The SiO2 fiber felt containing CTAB is immersed in a small molecule precursor solution, and then heated for cross-linking reaction. After the reaction is completed, carbonization treatment is performed to obtain a SiO2 / C composite material.

2. The method according to claim 1, characterized in that Preparation of SiO2 sol in S1: Tetraethoxysilane, ethanol, water and hydrochloric acid are mixed, heated, condensed and refluxed to react to obtain a transparent solution, which is then continuously stirred under heating conditions until the residual volume is 50-70% of the original solution volume to obtain SiO2 sol.

3. The method according to claim 2, characterized in that The condensation reflux reaction temperature is 70-80°C, the time is 5-7h, and stirring is continuous at 80-90°C.

4. The method according to claim 1, wherein The CTAB concentration in the precursor solution in S1 was 25-50 mg / mL, and the electrospinning parameters were: feed rate 0.5-1.5 mL / h, acceleration voltage 15-25 kV, and the distance between the injection needle tip and the collector was 10-20 cm.

5. The method according to claim 1, wherein The molar ratio of citric acid, ferric nitrate and cobalt nitrate in S2 is (4-6): (1.5-2.5): 1, and the concentration of citric acid in the mixed solution is 0.5-1.5 mol / L.

6. The method according to claim 1, characterized in that The urea concentration in the ethanol aqueous solution of urea in S2 is 6-8 mol / L, and the molar ratio of urea to citric acid is (6-7):

1.

7. The method according to claim 1, characterized in that The cross-linking reaction temperature in S3 is 170-190°C, the time is 10-20h, the carbonization temperature is 800-1200°C, the time is 0.5-1.5h, and the heating rate is 4-6°C / min.

8. The SiO2 / C composite material obtained by the method according to any one of claims 1 to 7, characterized in that: In the composite material, SiO2 fiber felt serves as a support, and porous carbon with a three-dimensional network structure formed by interconnected carbon nanotubes is filled in the support.

9. The composite material according to claim 8, characterized in that The diameter of carbon nanotubes is 1-5nm, the diameter of the three-dimensional network structure porous carbon mesh is 10-50nm, the diameter of SiO2 fibers in SiO2 fiber felt is 300-800nm, the porosity is 80-99%, and the volume proportion of carbon materials in SiO2 / C composite materials is 80-95%.

10. Use of the SiO2 / C composite material according to claim 9 in electromagnetic wave absorption.

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