Preparation method and application of artificial melanin carbon aerogel with electromagnetic shielding property

Abstract

The application discloses a preparation method and application of artificial melanin carbon aerogel with electromagnetic shielding property, and comprises the following steps: (1) preparing a mixed solution of dopamine hydrochloride and 5-hydroxyindole by using a mixture of ethanol and water as a mixed solvent; (2) adding an alkaline solution into the mixed solution, and keeping stirring at room temperature to obtain a yellow-green turbid solution; (3) centrifuging and washing the yellow-green turbid solution to obtain yellow artificial melanin nanofibers; (4) dispersing the artificial melanin nanofibers in deionized water, performing ultrasonic dispersion, and performing vacuum freeze-drying to obtain artificial melanin nanofiber aerogel; and (5) performing heat treatment on the artificial melanin nanofiber aerogel to obtain artificial melanin carbon aerogel. The preparation method is simple, green and environment-friendly, the prepared artificial melanin carbon aerogel has excellent electric conductivity and electromagnetic shielding performance, and has wide application in the field of electromagnetic shielding.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of melanin application, and particularly relates to a preparation method and application of an electromagnetic shielding artificial melanin carbon aerogel. BACKGROUND

[0002] Electromagnetic waves are important foundations in the fields of communication and detection, and electromagnetic wave absorbing materials are the main driving force for the development of electromagnetic fields. Due to the wide use of electromagnetic waves and the cross and overlap of their frequency bands, complex electronic devices, communication systems with high frequency requirements and even biological health are harmed. The working range and absorption performance of electromagnetic wave absorbing materials determine the usable electromagnetic frequency bands and application accuracy. With the expansion of application fields, higher requirements for high performance and lightweight are put forward in the fields of aerospace, intelligent electronic devices, wireless communication, etc. Exploring and designing lighter high-performance electromagnetic interference shielding materials is an important research hotspot.

[0003] Artificial melanin is an energy conversion substance that has attracted much attention. Due to its rich conjugated aromatic structure and force, it can realize various energy conversions in the body and play a protective role. However, its disordered stacking structure and limited material morphology limit its electrical conductivity and specific surface area, making it unable to effectively and fully respond to electromagnetic waves. However, due to its disordered encapsulation structure and limited material morphology, the electrical conductivity and specific surface area of the artificial melanin are limited, and the effective and sufficient response to electromagnetic waves is not reported. It is worth noting that three-dimensional porous conductive materials such as sponges, foams and aerogels with multi-scale interfaces can provide sufficient internal reflection space for electromagnetic waves, and a large number of researches have been carried out in recent years. Nanofibers have become an excellent three-dimensional conductive structure network building unit due to their large aspect ratio, outstanding surface area, entanglement effect and possible ordered structure during the formation process. SUMMARY

[0004] The purpose of the present application is to provide a preparation method and application of an electromagnetic shielding artificial melanin carbon aerogel.

[0005] To achieve the above purpose, the present application provides a preparation method of an electromagnetic shielding artificial melanin carbon aerogel, which comprises:

[0006] (1) preparing a mixed solution of dopamine hydrochloride and 5-hydroxyindole by using a mixture of ethanol and water as a mixed solvent;

[0007] (2) adding an alkaline solution to the mixed solution and keeping stirring at room temperature to obtain a yellow-green turbid solution;

[0008] (3) centrifuging and washing the yellow-green turbid solution to obtain yellow artificial melanin nanofibers;

[0009] (4) dispersing the artificial melanin nanofiber in deionized water, ultrasonic dispersion, vacuum freeze-drying to obtain artificial melanin nanofiber aerogel;

[0010] (5) placing the artificial melanin nanofiber aerogel in a nitrogen atmosphere, heating to 600-900℃ at a heating rate of 2-5℃ / min for 1-3 hours, and then cooling to room temperature at a cooling rate of 2-5℃ / min to obtain artificial melanin carbon aerogel.

[0011] In some embodiments, the volume fraction of ethanol in the mixed solvent is 10-40%, and the volume fraction of water is 60-90%.

[0012] In some embodiments, the concentration of dopamine hydrochloride in the mixed solution is 1-5 mg / mL, and the mass ratio of dopamine hydrochloride to 5-hydroxyindole is (0.05-0.4):1.

[0013] In some embodiments, the alkaline solution is sodium hydroxide solution or ammonia water.

[0014] Further, when the alkaline solution is ammonia water, the volume fraction of the ammonia water used is 29%, and the volume of the ammonia water is 1-5% of the volume of the mixed solution.

[0015] In some embodiments, the heat treatment temperature is preferably 700-900℃, and further preferably 800-900℃.

[0016] Another aspect of the present application also provides the use of the artificial melanin carbon aerogel prepared by the above preparation method as an electromagnetic shielding material.

[0017] Another aspect of the present application also provides the use of the artificial melanin carbon aerogel prepared by the above preparation method as an electronic device packaging material.

[0018] In the present application, 5-hydroxyindole similar in structure to dopamine is used as a structure inducer. The single phenolic hydroxyl group of 5-hydroxyindole does not have the multi-site crosslinking effect of hydrogen bonds as in o-diphenol, which can inhibit the disordered crosslinking of hydrogen bonds and enhance chemical coupling, thereby inducing the generation of 5,6-dihydroxyindole cyclic tetramer during the oxidative rearrangement of dopamine. The 5,6-dihydroxyindole cyclic tetramer self-assembles into artificial melanin nanofiber through stronger π-π stacking effect, and the π-π stacking brings effective π electron transmission to the artificial melanin nanofiber, making it have excellent electrical conductivity.

[0019] The artificial melanin nanofiber is treated by freeze-drying, so that the hydrogen bonds and other interactions on the surface of the artificial melanin nanofiber are crosslinked. Due to the entanglement effect of the fiber, the artificial melanin nanofiber carbon aerogel with a three-dimensional crosslinked network is formed. After heat treatment of the aerogel, the artificial melanin nanofiber carbon aerogel is limited to curling sintering, and a unique skin-core structure can be obtained, which can effectively prolong the electromagnetic wave transmission path and enhance the electromagnetic wave reflection effect, so that excellent electromagnetic shielding performance is achieved.

[0020] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0021] (1) The preparation method of the present application is simple and green, and the nanoscale artificial melanin carbon aerogel can be prepared by one-step method, which is simple and easy to control.

[0022] (2) The precursor molecules dopamine hydrochloride and 5-hydroxyindole used in the present application are common reagents, and have standard production specifications, so that the raw materials are easy to obtain and the preparation process has good repeatability.

[0023] (3) The method of the present application has good adjustability, and the density of the carbon aerogel can be controlled by adjusting the concentration of the artificial melanin fiber dispersion liquid, so that the electromagnetic shielding performance can be controlled as needed.

[0024] (4) The artificial melanin carbon aerogel prepared by the present application has excellent electrical conductivity and electromagnetic shielding performance, and has wide application in the field of electromagnetic shielding. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The scanning electron microscope photograph of the sample of Example 1 of the present application;

[0026] Figure 2 The scanning electron microscope photograph of the sample of Example 2 of the present application;

[0027] Figure 3 The residual carbon rate statistical diagram of the samples of Examples 1-4 and Comparative Example 1 of the present application;

[0028] Figure 4 The Raman spectrum of the samples of Examples 1-4 of the present application;

[0029] Figure 5 The electrical conductivity of the samples of Examples 1-4 of the present application;

[0030] Figure 6 The electromagnetic shielding efficiency of the samples of Examples 1-4 of the present application;

[0031] Figure 7Electromagnetic shielding effectiveness of the sample of Example 5 of the present application. DETAILED DESCRIPTION

[0032] The technical solutions of the present application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0033] In the present application, 5-hydroxyindole similar in structure to dopamine is used as a structure inducer to form a 5.6-dihydroxyindole cyclic tetramer in the process of dopamine oxidative rearrangement, and artificial melanin nanofibers are obtained through self-assembly by virtue of a stronger π-π stacking effect, and artificial melanin nanofiber carbon aerogels are obtained through freeze-drying pyrolysis. The π-π stacking brings effective π electron transmission to the artificial melanin nanofibers, so that the artificial melanin nanofibers have excellent electrical conductivity. Meanwhile, the heat treatment process also brings a unique skin-core structure to the artificial melanin nanofiber carbon aerogels, which can effectively prolong the electromagnetic wave transmission path, so that the artificial melanin nanofiber carbon aerogels have excellent electromagnetic shielding performance.

[0034] The present application provides a preparation method of artificial melanin carbon aerogels with electromagnetic shielding performance, which comprises the following specific steps:

[0035] (1) A mixed solution of dopamine hydrochloride and 5-hydroxyindole is prepared by using a mixture of ethanol and water as a mixed solvent.

[0036] In the present specific embodiment, dopamine hydrochloride and 5-hydroxyindole are added to the mixed solvent, and then ultrasonic dispersion treatment is performed for 2-5 minutes, and then the mixed solution is fully stirred at room temperature for 2-8 minutes, preferably for 5 minutes, to obtain a uniform transparent colorless mixed solution. The volume fraction of ethanol in the mixed solvent can be selected from 10-40%, and preferably is 30%; and the volume fraction of water in the mixed solvent can be selected from 60-90%, and preferably is 70%. The concentration of dopamine hydrochloride in the mixed solution is 1 mg / mL-5 mg / mL, and preferably is 4 mg / mL; and the mass ratio of dopamine hydrochloride to 5-hydroxyindole in the mixed solution is (0.05-0.4):1, and the mass ratio is preferably 0.1:1.

[0037] (2) Sodium hydroxide solution or ammonia water is slowly added to the mixed solution, and the mixed solution is stirred at room temperature to obtain a yellow-green turbid solution.

[0038] In the present specific embodiment, the mixed solution is stirred at room temperature for 20 h to obtain a uniform and stable yellow-green turbid solution. The volume fraction of the added ammonia water is 29%, and the volume of the added ammonia water is 1%-5% of the volume of the mixed solution, and preferably is 2%. The volume fraction of the added sodium hydroxide solution is 29%, and the volume of the added sodium hydroxide solution is 1%-5% of the volume of the mixed solution, and preferably is 2%. 、After adding alkaline substances such as ammonia, the phenolic hydroxyl groups of dopamine hydrochloride and 5-hydroxyindole are more prone to phenolic quinone transformation under alkaline conditions, and a semiquinone free radical is simultaneously formed to initiate the reaction, in the process of which, chemical coupling of two molecular phenolic hydroxyl groups at the ortho position is induced, and 5,6-dihydroxyindole cyclic tetramer is formed by oxidative rearrangement of dopamine, and artificial melanin nanofibers are obtained by self-assembly through a stronger π-π stacking effect.

[0039] (3) The yellow-green turbid solution is centrifuged and washed to obtain yellow artificial melanin nanofibers. In this specific embodiment, the centrifugal speed is 12000 r / min-16000 r / min, the centrifugal time is 5 min-10 min, and the washing is performed by washing three times with deionized water.

[0040] (4) The artificial melanin nanofibers are dispersed in deionized water to obtain a freeze-drying liquid, ultrasonic dispersion is performed, and then vacuum freeze-drying is performed to obtain artificial melanin nanofiber aerogels. In this specific embodiment, the ultrasonic dispersion time is 10 min. In this process, the hydrogen bonds and other interactions on the surface of the artificial melanin nanofibers are crosslinked, and a three-dimensionally crosslinked network aerogel is formed due to the entanglement effect of the fibers. By adjusting the concentration of the freeze-drying liquid, artificial melanin nanofiber carbon aerogels with different densities are also obtained.

[0041] (5) The artificial melanin nanofiber aerogels are placed in a tubular furnace under a nitrogen atmosphere, heated to 600-900°C at a heating rate of 2-5°C / min, and then cooled to room temperature at a cooling rate of 2-5°C / min, to obtain artificial melanin nanofiber carbon aerogels. In this specific embodiment, the heating rate is preferably 5°C / min, the cooling rate is preferably 5°C / min, the heat treatment temperature is preferably 900°C, and the heat treatment time is preferably 2 hours.

[0042] Several examples will be provided below to further illustrate the technical solutions of the present application and their technical effects.

[0043] In the following examples, dopamine hydrochloride (C8H 12 ClNO2), 5-hydroxyindole (C8H7NO) and ammonia solution were purchased from Shanghai Titan Science and Technology Co., Ltd.; sodium hydroxide and ethanol were purchased from Chengdu Kelong Chemical Co., Ltd.; deionized water was obtained by purifying water with a water purification system (model UPH-I-10T).

[0044] Several examples will be provided below to further illustrate the technical solutions of the present application and their technical effects.

[0045] Example 1

[0046] The steps of the preparation method of artificial melanin carbon aerogels in this example 1 are as follows:

[0047] (1) A mixture of ethanol and water was used as the mixed solvent, in which the volume fraction of ethanol was 30%; dopamine hydrochloride and 5-hydroxyindole were added into the mixed solvent, and then ultrasonic dispersion treatment was performed for 2 minutes, followed by stirring at room temperature for 5 minutes to obtain a uniform transparent colorless mixed solution. The concentration of dopamine hydrochloride in the obtained mixed solution was 4 mg / mL, and the mass ratio of dopamine hydrochloride to 5-hydroxyindole was 0.1:1.

[0048] (2) Ammonia water was slowly added into the mixed solution, and stirring was performed at room temperature for 20 h to obtain a uniform stable yellow-green turbid solution. The volume fraction of the added ammonia water was 29%, and the volume of the added ammonia water was 2% of the volume of the mixed solution.

[0049] (3) The yellow-green turbid solution was centrifuged at a speed of 15000 r / min for 5 min, and then washed with deionized water for three times to obtain yellow artificial melanin nanofibers.

[0050] (4) The artificial melanin nanofibers were dispersed in deionized water to obtain a freeze-drying liquid, and ultrasonic dispersion was performed for 10 min, followed by vacuum freeze-drying to obtain artificial melanin nanofiber aerogels.

[0051] (5) The artificial melanin nanofiber aerogels were placed in a tubular furnace under a nitrogen atmosphere, and heated to 600°C at a heating rate of 5°C / min for 2 h, and then cooled to room temperature at a cooling rate of 5°C / min to obtain artificial melanin nanofiber carbon aerogels. Due to the mass loss during the heat treatment process, the density of the obtained artificial melanin nanofiber carbon aerogels was 12.78 mg / cm 3 .

[0052] Examples 2-4 and the comparative example differ from Example 1 only in the heat treatment temperature, and other process parameters are the same. The process parameters of Examples 1-4 and the comparative example are shown in Table 1 and Table 2. Table 1 lists the dopamine hydrochloride concentration, the mass ratio of dopamine hydrochloride to 5-hydroxyindole, the volume ratio of water to ethanol, the amount of ammonia water, and Table 2 lists the heat treatment temperature, the heating rate, the cooling rate, and the heat treatment time of Examples 1-4 and the comparative example.

[0053] Table 1 Part of the process parameters of Examples 1-4 and the comparative example

[0054]

[0055] Table 2 Another part of the process parameters of Examples 1-4 and the comparative example

[0056]

[0057]

[0058] The product was subjected to the following performance tests:

[0059] (1) Morphology characterization of the sample

[0060] The sample was artificial melanin carbon aerogel material. The samples obtained in Examples 1 and 2 were subjected to table scanning electron microscope test for observation of micro morphology. The specific operation method was as follows: the sample was pasted on conductive glue, and after drying and gold spraying treatment, observation was carried out. The difference between the process parameters of Examples 1 and 2 was only the heat treatment temperature, and the heat treatment temperature of Example 1 was 600℃, and the heat treatment temperature of Example 2 was 900℃. The sample morphology of Example 1 was shown in Figure 1 , and the sample morphology of Example 2 was shown in Figure 2 . It can be seen from Figure 1 and Figure 2 that the sample still retains the fiber morphology after heat treatment, and the degree of fiber curling and sintering increases significantly with the increase of heat treatment temperature.

[0061] (2) Residual carbon rate characterization of the sample

[0062] The residual carbon rate of the samples of Examples 1-4 and Comparative Example 1, i.e. the percentage of carbon mass retained after heat treatment, was tested, and the residual carbon rate was shown in Figure 3 It can be seen from Figure 3 that with the increase of heat treatment temperature, the residual carbon rate shows a gradually decreasing trend; when the heat treatment temperature reaches 1000℃, the residual carbon rate decreases significantly. Therefore, the heat treatment temperature of the present application should not be higher than 900℃, and preferably 900℃, which can ensure a higher heat treatment degree and a higher residual carbon rate at the same time.

[0063] (3) Graphite phase structure characterization of the sample

[0064] Raman spectrum was used to characterize the graphite phase structure of the sample. The Raman spectrum of the samples of Examples 1-4 was tested, wherein the peaks centered at 1350cm -1 and 1590cm -1 belonged to typical disordered structure (D band) and graphite structure (G band) of carbon material, as shown in Figure 4 . By comparing the I D / I G of each band, it can be seen that with the increase of heat treatment temperature, the proportion of graphite phase structure of the sample gradually increases, and higher graphite phase structure will bring better conjugated structure and electronic transmission capacity, which is beneficial to the improvement of electromagnetic shielding performance.

[0065] (4) Electrical conductivity of the sample

[0066] The conductivity of the samples was tested using a four-probe conductivity meter. Samples from Examples 1-4 were cut into circular pieces with a thickness of 2 mm and a diameter of 3 cm. Their conductivity was measured using a four-probe conductivity meter; the conductivity values ​​are shown below. Figure 5 As shown, from Figure 5 It can be seen that the electrical conductivity of the sample increases with the increase of heat treatment temperature. The sample of Example 2, which was heat treated at 900℃, has an electrical conductivity as high as 103.47 S / m.

[0067] (5) Electromagnetic shielding performance of the sample

[0068] The electromagnetic shielding performance of the samples in the 8.2 GHz–12.4 GHz range was determined using a vector network analyzer. Samples from Examples 1-4 were cut into circular pieces with a thickness of 2 mm and a diameter of 1.2 cm. Their electromagnetic shielding effectiveness in the 8.2 GHz–12.4 GHz range was then measured using a vector network analyzer. The obtained electromagnetic shielding effectiveness is shown in [Figure showing results]. Figure 6 .from Figure 6 It can be seen that as the heat treatment temperature increases, the electromagnetic shielding effectiveness of the sample shows an upward trend. The electromagnetic shielding effectiveness of the sample in Example 2, which has a heat treatment temperature of 900℃, can reach -52.5dB.

[0069] Example 5

[0070] Take the intermediate product artificial melanin nanofiber obtained in step (3) of Example 1, disperse the artificial melanin nanofiber in deionized water, prepare 5 groups of lyophilized solutions with different concentrations, ultrasonically disperse the lyophilized solutions for 10 min, and then freeze-dry them under vacuum to obtain artificial melanin nanofiber aerogel.

[0071] Artificial melanin nanofibers were dispersed in deionized water and ultrasonically dispersed for 10 min, followed by vacuum freeze-drying to obtain artificial melanin nanofiber aerogels. The artificial melanin nanofiber aerogels were then heat-treated in a tube furnace under a nitrogen atmosphere, heated to 900℃ at a rate of 5℃ / min for 2 hours, and then cooled to room temperature at a rate of 5℃ / min, yielding five groups of artificial melanin nanofiber carbon aerogel samples. The densities of the five groups were 21.38 mg / cm³. 3 12.78 mg / cm 3 6.84 mg / cm 3 3.31 mg / cm 3 2.06 mg / cm 3 .

[0072] The electromagnetic shielding effectiveness of the five groups of samples obtained in this embodiment was tested using the aforementioned method. The obtained electromagnetic shielding effectiveness is shown in the figure. Figure 7 .from Figure 7 It can be seen that the electromagnetic shielding effectiveness of the sample increases with the increase of the concentration of the lyophilized solution.

[0073] It is to be understood that the above description is merely a preferred embodiment of the application and the applied technical principles. Those skilled in the art will understand that the application is not limited to the specific embodiments described herein, and that various obvious changes, modifications and substitutions can be made without departing from the scope of the application. Therefore, although the application has been described in detail through the above embodiments, the application is not limited to the above embodiments, and more other equivalent embodiments can be included without departing from the concept of the application, and all belong to the protection scope of the application.

Claims

1. A method for preparing an artificial melanin carbon aerogel having electromagnetic shielding properties, characterized by, The preparation method of the artificial melanin carbon aerogel with electromagnetic shielding property comprises the following steps: (1) preparing a mixed solution of dopamine hydrochloride and 5-hydroxyindole by using a mixture of ethanol and water as a mixed solvent; the concentration of dopamine hydrochloride in the mixed solution is 1 mg / mL-5 mg / mL, and the mass ratio of dopamine hydrochloride to 5-hydroxyindole is (0.05-0.4):1; (2) adding an alkaline solution to the mixed solution and keeping stirring at room temperature to obtain a yellow-green turbid solution; (3) centrifuging and washing the yellow-green turbid solution to obtain yellow artificial melanin nanofibers; (4) dispersing the artificial melanin nanofibers in deionized water, ultrasonic dispersing, and vacuum freeze-drying to obtain artificial melanin nanofiber aerogels; (5) placing the artificial melanin nanofiber aerogels in a nitrogen atmosphere, heating to 600-900 °C at a heating rate of 2-5 °C / min, and then cooling to room temperature at a cooling rate of 2-5 °C / min to obtain artificial melanin carbon aerogels.

2. The preparation method of the artificial melanin carbon aerogel with electromagnetic shielding property according to claim 1, wherein the volume fraction of ethanol in the mixed solvent is 10-40%, and the volume fraction of water is 60-90%.

3. The preparation method of the artificial melanin carbon aerogel with electromagnetic shielding property according to claim 1, wherein the alkaline solution is a sodium hydroxide solution or ammonia water.

4. The preparation method of the artificial melanin carbon aerogel with electromagnetic shielding property according to claim 1, wherein when the alkaline solution is ammonia water, the volume fraction of the ammonia water used is 29%, and the volume of the ammonia water is 1%-5% of the volume of the mixed solution.

5. The preparation method of the artificial melanin carbon aerogel with electromagnetic shielding property according to claim 1, wherein the heat treatment temperature is 600-900 °C.

6. The preparation method of the artificial melanin carbon aerogel with electromagnetic shielding property according to claim 1, wherein the heating and cooling rates are 2-5 °C / min.

7. The artificial melanin carbon aerogel prepared by the preparation method of any one of claims 1-6 for use as an electromagnetic shielding material.

8. The artificial melanin carbon aerogel prepared by the preparation method of any one of claims 1-6 for use as an electronic component packaging material. ​ ​ ​ ​ ​

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