A three-dimensional graphene aerogel and its preparation method

Abstract

The present invention discloses a preparation method of three-dimensional graphene aerogel, which comprises the following steps: S1. Freeze-drying an aqueous solution of graphene oxide with a concentration of 1.5 mg·mL<supgt;‑1< / supgt; to obtain a golden graphene oxide aerogel; S2. Placing the graphene oxide aerogel into a quartz tube of plasma-enhanced chemical vapor deposition and moving it to the central position of a plasma radio frequency instrument, and adjusting the internal pressure of the quartz tube to 60 Pa; S3. Setting the plasma radio frequency power, starting the plasma radio frequency instrument, and efficiently reducing and exfoliating the graphene oxide aerogel within 1 second to form a graphene aerogel.

Description

Technical Field

[0001] The present invention relates to the field of three-dimensional graphene aerogels, and particularly to a three-dimensional graphene aerogel and a preparation method thereof. Background Art

[0002] Graphene aerogel is a macroscopic three-dimensional material formed by cross-linking graphene sheets, which has the characteristics of high specific surface area, strong adsorption, and high conductivity, providing broad application prospects for its use as a CDI electrode material. Currently, the preparation of graphene aerogel (such as in-situ assembly method, template method, chemical cross-linking method, etc.) usually uses graphene oxide as a precursor and is realized by reduction and sheet assembly methods; for the reduction process, it mainly includes hydrothermal chemical reduction (such as using hydrazine as a reducing agent and reacting at 180°C for 10 - 24 hours) and high-temperature treatment (usually treating at about 1000°C or even >2000°C for several hours in an inert atmosphere).

[0003] However, the harsh preparation conditions, the introduction of reducing agents, and the long reaction time not only lead to energy waste, high cost, and low purity, but also damage the sp2 network structure of graphene sheets. More importantly, while the surface electro-negative oxygen-containing functional groups are removed, the electrostatic repulsion between the sheets is broken, and the inherent van der Waals force and π-π force cause the graphene sheets to re-stack, seriously reducing the specific surface area and ion transport performance of the graphene aerogel. Therefore, aiming at high efficiency, non-toxicity, and low cost, developing a new process for preparing high-quality three-dimensional graphene materials is of great significance for CDI and many other fields. Summary of the Invention

[0004] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a three-dimensional graphene aerogel and a preparation method thereof to solve the problems in the background art that the harsh preparation conditions, the introduction of reducing agents, and the long reaction time not only lead to energy waste, high cost, and low purity, but also damage the sp2 network structure of graphene sheets. More importantly, while the surface electro-negative oxygen-containing functional groups are removed, the electrostatic repulsion between the sheets is broken, and the inherent van der Waals force and π-π force cause the graphene sheets to re-stack, seriously reducing the specific surface area and ion transport performance of the graphene aerogel.

[0005] To solve the above technical problems, the present invention provides the following technical solution: A preparation method of a three-dimensional graphene aerogel, comprising the following steps:

[0006] S1. Freeze-dry an aqueous solution of graphene oxide with a concentration of 1.5 mg·mL -1 to obtain a golden graphene oxide aerogel.

[0007] S2. Place the graphene oxide aerogel into the quartz tube of plasma-enhanced chemical vapor deposition, and move it to the central position of the plasma radio frequency instrument. Adjust the internal pressure of the quartz tube to 60 Pa.

[0008] S3. Set the plasma radio frequency power, start the plasma radio frequency instrument, and the graphene oxide aerogel can be efficiently reduced and exfoliated within 1 second to form a graphene aerogel.

[0009] Preferably, the radio frequency of the plasma radio frequency instrument in step S2 is 13.56 MHz.

[0010] Preferably, at the moment of starting the plasma generator in step S3, it can be visually observed that a bright white flash appears in the quartz tube. At the same time, the color of the graphene oxide aerogel changes from golden yellow to black, and the volume expands significantly.

[0011] Preferably, the plasma radio frequency power in step S3 is 20 - 150 W, preferably 150 W.

[0012] Preferably, as the plasma radio frequency power increases from 20 W to 150 W, the interlayer spacing and specific surface area of the obtained graphene aerogel increase from 0.372 nm and 354.1 m 2 ·g -1 to 0.395 nm and 535.9 m 2 ·g -1 .

[0013] Preferably, the graphene aerogel presents a cross-linked three-dimensional network structure. Under the condition of 150 W, the thickness of the graphene sheets is 1.1 nm. Compared with the graphene oxide aerogel, the mass of the graphene aerogel is reduced by 30 - 35%.

[0014] Preferably, the plasma radio frequency power in step S3 is 20 W.

[0015] Preferably, the plasma radio frequency power in step S3 is 50 W.

[0016] Preferably, the plasma radio frequency power in step S3 is 100 W.

[0017] Preferably, it is made by any of the methods described in claims 1 - 9.

[0018] Compared with the prior art, the beneficial effects that the present invention can achieve are as follows: The preparation method of the present invention takes a short time (1 second), does not require the addition of any reducing agent or gas, greatly simplifies the preparation process of traditional graphene aerogels, improves the preparation efficiency, reduces the production cost, and provides feasibility for large-scale preparation of graphene aerogels; In addition, this preparation method also has good exfoliation characteristics during the process of reducing graphene oxide sheets, effectively solving the problem of sheet stacking during the traditional reduction of graphene oxide; With the help of the inherent three-dimensional network structure of the graphene aerogel, self-supporting sheet electrodes with controllable mass and size can be constructed through a simple mechanical pressing method. The graphene aerogel prepared based on this method has good reduction degree (the removal rate of surface oxygen-containing epoxy functional groups is 78 at%), conductivity (24.7 S·m -1 ), ultra-high specific capacitance (165.5 F·g -1 ), and fast ion transport performance (Warburg diffusion coefficient 5.2 Ω·mg·s -1 / 2 ). When used as an electrode material in a capacitive deionization desalination device, it exhibits excellent salt adsorption capacity (24.1 mg·g -1 ), and can maintain more than 80% of the desalination performance after 4 days of continuous salt ion adsorption / desorption cycle stability test. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Optical photographs of the graphene aerogel after being treated with different plasma radio frequencies of the present invention;

[0020] Figure 2 XRD spectra of the graphene aerogel after being treated with different plasma radio frequencies of the present invention;

[0021] Figure 3 Nitrogen adsorption / desorption isotherms of the graphene aerogel after being treated with different plasma radio frequencies of the present invention, and the pore size distribution of the gas is shown in the figure;

[0022] Figure 4 SEM of the graphene oxide aerogel of the present invention;

[0023] Figure 5 (a) SEM, (b) high-magnification SEM, and (c) TEM of the graphene aerogel in Example 1 of the present invention;

[0024] Figure 6 Optical schematic diagram of the self-supporting electrode prepared from the graphene aerogel in Example 1 of the present invention;

[0025] Figure 7 Conductivity schematic diagrams of the graphene aerogel and the graphene oxide aerogel of the present invention;

[0026] Figure 8 These are the cyclic voltammograms of the graphene aerogel in Examples 1 (a), 2 (b), 3 (c), and 4 (d) of the present invention at different scanning rates;

[0027] Figure 9 This is the capacitance comparison chart of the graphene aerogel in Examples 1-4 of the present invention;

[0028] Figure 10 This is a schematic diagram of the composition and test system of the capacitive deionization device of the present invention;

[0029] Figure 11 This is the change curve of the conductivity of the NaCl salt solution during the desalination process of the present invention;

[0030] Figure 12 This is a schematic diagram before and after the preparation of the present invention; Detailed Embodiments

[0031] In order to make the technical means, creative features, achieved purposes, and functions of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments. However, the following embodiments are only the preferred embodiments of the present invention, not all of them. Based on the embodiments in the implementation manners, other embodiments obtained by those skilled in the art without creative efforts all belong to the protection scope of the present invention. The experimental methods in the following embodiments are all conventional methods unless otherwise specified, and the materials, reagents, etc. used in the following embodiments can all be obtained from commercial channels unless otherwise specified.

[0032] Example 1:

[0033] As Figures 1-12 shown, the present invention provides a method for preparing a three-dimensional graphene aerogel, including the following steps:

[0034] S1. The graphene oxide solution with a concentration of 1.5 mg·mL -1 is freeze-dried to obtain a golden graphene oxide aerogel;

[0035] S2. The graphene oxide aerogel is placed into a quartz tube for plasma-enhanced chemical vapor deposition and moved to the central position of the plasma radio frequency instrument, and the internal pressure of the quartz tube is adjusted to 60 Pa;

[0036] S3. Set the plasma radio frequency power, start the plasma radio frequency instrument, and the graphene oxide aerogel can be efficiently reduced and peeled within 1 second to form a graphene aerogel;

[0037] The present invention can be applied to electrochemical desalination as a high-performance electrode material; wherein, the electrode preparation process is: simply mechanically pressing the graphene aerogel can obtain a self-supporting sheet electrode, and the size and mass of the electrode can be adjusted according to specific applications.

[0038] In this embodiment, specifically, the radio frequency of the plasma radio frequency instrument in the S2 step is 13.56 MHz.

[0039] In this embodiment, specifically, at the moment when the plasma generator is started in the S3 step, it can be visually observed that a bright white flash appears in the quartz tube. At the same time, the color of the graphene oxide aerogel changes from golden yellow to black, and the volume expands significantly.

[0040] In this embodiment, specifically, the plasma radio frequency power in the S3 step is 20 - 150 W, preferably 150 W.

[0041] In this embodiment, specifically, as the plasma radio frequency power increases from 20 W to 150 W, the interlayer spacing and specific surface area of the obtained graphene aerogel increase from 0.372 nm, 354.1 m 2 ·g -1 to 0.395 nm, 535.9 m 2 ·g -1 .

[0042] In this embodiment, specifically, the graphene aerogel presents a cross-linked three-dimensional network structure. Under the condition of 150 W, the thickness of the graphene sheet is 1.1 nm. Compared with the graphene oxide aerogel, the mass of the graphene aerogel is reduced by 30 - 35%.

[0043] A three-dimensional graphene aerogel made by any of the methods described in claims 1 - 9.

[0044] In this embodiment, specifically, as Figure 1 shown, there are significant differences in the macroscopic morphology of the graphene aerogel under different radio frequency powers; after the graphene oxide aerogel is treated by plasma, the color changes from golden yellow to black; and as the radio frequency power increases, the volume of the graphene aerogel also increases; the significant color and volume changes can preliminarily judge from a macroscopic perspective that this method has a reduction and exfoliation effect on the graphene oxide aerogel;

[0045] As Figure 2As shown in the figure, the XRD patterns of graphene aerogels prepared with different radio frequencies; after plasma treatment, the diffraction peak of graphene oxide aerogel at 2θ = 8° completely disappeared, proving that the plasma treatment had a good reduction effect on the graphene oxide sheets; moreover, as the radio frequency increased from 20 W to 150 W, the position of the 2θ diffraction peak of the graphene aerogel decreased from 23.9° to 22.5°, and the corresponding graphene sheet spacing increased from 0.372 nm to 0.395 nm, indicating that the plasma treatment had a good exfoliation effect on the graphene sheets, and the exfoliation effect became more significant with the increase of the radio frequency power;

[0046] As Figure 3 shown, the nitrogen adsorption and desorption isotherms of graphene aerogels prepared with different radio frequencies, and the inset is the corresponding pore size distribution; combined Figure 2 with the test results shown in the following table; it can be seen from the data in the table that increasing the sheet spacing of the graphene aerogel can effectively improve its specific surface area;

[0047] Table 1 shows the performance parameters of the graphene aerogel prepared in this invention:

[0048]

[0049] Table 1

[0050] As Figure 5 shown, a is the scanning electron microscope image of graphene oxide aerogel. It can be seen from the figure that the graphene oxide sheets are severely stacked and the sheets are relatively thick; b and c are the scanning electron microscope images of GA-150. The graphene sheets are cross-linked to present a unique three-dimensional network structure, and the graphene sheets are relatively thin; the above can prove that the plasma treatment can effectively exfoliate the graphene sheets without damaging the sheets;

[0051] As Figure 6 shown, by using a simple pressing treatment, GA-150 can be turned into a self-supporting electrode with good mechanical properties;

[0052] As Figure 7 shown, the conductivity of the graphene aerogel prepared in Example 1 is 24.7 S / m;

[0053] As Figure 8 shown, the cyclic voltammograms of the graphene aerogels prepared in Examples 1-4 all showed a rectangular shape, indicating the characteristics of electric double layer capacitance; the specific capacitance can be obtained by calculating the cyclic voltammograms at different scan rates. Obviously, the graphene aerogel prepared in Example 1 has the highest specific capacitance, reaching 165.5 F·g -1 ;

[0054] The specific capacitance values are shown in Table 2 below.

[0055]

[0056] Table 2

[0057] As Figure 10 shown, the composition of the capacitive deionization device and the test system are presented, where the graphene aerogel is assembled into the device as the electrode material to test its desalination performance;

[0058] As Figure 11 shown, under the conditions that the concentration of the NaCl salt solution is 100 mg / L and the applied voltage is 1.2 V, the desalination tests were carried out on the graphene aerogels prepared in Examples 1-4. The corresponding salt adsorption capacity can be calculated from the decrease value of the conductivity of the salt solution. Among them, Example 1 shows the highest salt adsorption capacity, reaching 12.6 mg·g -1 .

[0059] Example 2:

[0060] The difference between Example 2 and Example 1 is only that: the plasma radio frequency power in the S3 step is 20 W.

[0061] Example 3:

[0062] The difference between Example 3 and Example 1 is only that: the plasma radio frequency power in the S3 step is 50 W.

[0063] Example 4:

[0064] The difference between Example 4 and Example 1 is only that: the plasma radio frequency power in the S3 step is 100 W.

[0065] Working principle: After freeze-drying the graphene oxide solution (1.5 mg·mL -1 ) at -50 °C (pressure 10 Pa) for 48 h, a golden-yellow graphene oxide aerogel can be obtained. Then, the graphene oxide aerogel is placed in a porcelain boat and transferred to the center of the plasma generation area of the quartz tube. The graphene oxide aerogel is subjected to plasma treatment at room temperature and under air conditions. The pressure in the plasma chamber is set to 60 Pa by using a mechanical vacuum pump, the plasma radio frequency frequency is set to 13.56 MHz, and the input power is set to 150 W. After applying the plasma, a significant expansion of the volume of the graphene oxide aerogel is observed within 1 second, and a bright white flash appears in the quartz tube. Finally, a black graphene aerogel (GA-150) is obtained.

[0066] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a three-dimensional graphene aerogel, characterized in that: Including the following steps: S1. Freeze-dry the graphene oxide solution with a concentration of 1.5 mg·mL −1 to obtain a golden graphene oxide aerogel; S2. Place the graphene oxide aerogel into the quartz tube of plasma-enhanced chemical vapor deposition, and move it to the central position of the plasma radio frequency instrument. Adjust the internal pressure of the quartz tube to 60 Pa. S3. Set the plasma radio frequency power, start the plasma radio frequency instrument, and the graphene oxide aerogel can be efficiently reduced and exfoliated within 1 second to form a graphene aerogel.

2. The preparation method of a three-dimensional graphene aerogel according to claim 1, characterized in that: The radio frequency of the plasma radio frequency instrument in step S2 is 13.56 MHz.

3. The preparation method of a three-dimensional graphene aerogel according to claim 1, wherein: At the moment when the plasma radio frequency instrument is started in step S3, it can be visually observed that a bright white flash appears in the quartz tube. At the same time, the color of the graphene oxide aerogel changes from golden yellow to black, and the volume expands significantly.

4. The preparation method of a three-dimensional graphene aerogel according to claim 1, characterized in that: The plasma radio frequency power in step S3 is 20 - 150 W.

5. The preparation method of a three-dimensional graphene aerogel according to claim 1, characterized in that: As the plasma radio frequency power increases from 20 W to 150 W, the interlayer spacing and specific surface area of the obtained graphene aerogel increase from 0.372 nm and 354.1 m 2 ·g −1 to 0.395 nm and 535.9 m 2 ·g −1 .

6. The preparation method of a three-dimensional graphene aerogel according to claim 1, characterized in that: The graphene aerogel presents a cross-linked three-dimensional network structure. Under the condition of 150 W, the thickness of the graphene sheet layer is 1.1 nm. Compared with the graphene oxide aerogel, the mass of the graphene aerogel is reduced by 30 - 35%.

7. The preparation method of a three-dimensional graphene aerogel according to claim 1, characterized in that: The plasma radio frequency power in step S3 is 20 W.

8. The preparation method of a three-dimensional graphene aerogel according to claim 1, characterized in that: The plasma radio frequency power in step S3 is 50 W.

9. The preparation method of a three-dimensional graphene aerogel according to claim 1, characterized in that: The plasma radio frequency power in step S3 is 100 W.

10. A three-dimensional graphene aerogel, characterized in that: It is made by the preparation method of the three-dimensional graphene aerogel according to any one of claims 1 - 9.

Images