Preparation method of wrinkled graphene microspheres and wrinkled graphene microspheres

Abstract

The present invention provides a method for preparing wrinkled graphene microspheres and the wrinkled graphene microspheres. The method for preparing the wrinkled graphene microspheres comprises the following steps: (1) preparing an aqueous solution of graphene oxide with a concentration ≤ 0.3 mg / mL; (2) adding ammonia water to the aqueous solution of graphene oxide, stirring, and adjusting the pH value of the aqueous solution of graphene oxide to 3.5 - 8.5; (3) freezing the aqueous solution of graphene oxide obtained in step (2) with liquid nitrogen and then performing freeze-drying to obtain the wrinkled graphene microspheres. The method of the present invention has simple steps, strong operability and repeatability, is conducive to industrial production, can effectively solve the problem of the reduction of specific surface area caused by the stacking of graphene sheets, and at the same time, the prepared wrinkled microspheres also have good redispersibility, providing a new technical means for the transportation and storage of graphene oxide.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials, and particularly relates to a preparation method of wrinkled graphene microspheres and the wrinkled graphene microspheres. Background Art

[0002] Graphene, known as a "star" material, is a carbon material with a two-dimensional layered structure, having excellent electrical, thermal and mechanical properties, and has wide applications in many fields such as energy storage, biological diagnosis and treatment, and flexible electronic devices. Graphene oxide (GO) is a graphene precursor obtained by exfoliating and chemically oxidizing graphite powder. It can not only produce graphene in large quantities through chemical reduction, but also the abundant oxygen-containing functional groups on its surface are conducive to chemical modification, so it has a wider range of applications. Theoretically, GO has a high specific surface area of 2630 m 2 / g, but the interlayer interactions such as π-π interactions and van der Waals forces make GO prone to sheet re-stacking, resulting in a decrease in specific surface area, which limits its functions and applications.

[0003] Morphology regulation of GO to transform two-dimensional GO into three-dimensional wrinkled microspheres can effectively solve the problem of agglomeration and stacking of GO and maintain the high specific surface area of GO. At the same time, the three-dimensional wrinkled graphene microspheres have additional advantages: (1) The wrinkled structure effectively inhibits the problem of graphene sheet stacking, making graphene have excellent solvent redispersion performance, which is beneficial to subsequent application research; (2) Different from graphene aqueous solution, the high tapped density of the wrinkled graphene microsphere powder saves storage space, is easy to store and transport, and saves production costs; (3) As an electrode material or additive for lithium-ion batteries, compared with two-dimensional graphene, three-dimensional wrinkled graphene can provide volume redundancy during the lithium intercalation process, prevent electrode cracking caused by volume expansion, and significantly improve the cycle life of lithium-ion batteries; (4) The introduction of wrinkles can regulate the physical and chemical properties of graphene itself. For example, the tip effect caused by wrinkles will generate a strong local electric field, and wrinkles can bring about a strain effect and affect the electronic structure of graphene. Therefore, developing an effective strategy to synthesize and prepare three-dimensional wrinkled graphene microspheres has important scientific and technical value.

[0004] At present, the common methods for constructing wrinkled graphene microspheres mainly include: 1) Spray drying method that causes wrinkles by capillary shrinkage force generated by solvent evaporation; 2) Template method that induces the deformation of graphene by the morphology of nanospheres (polystyrene, SiO2, etc.) and then removes them. However, these methods generally have problems such as high equipment dependence, complex experimental steps, inability to achieve mass production, low recovery rate, and difficult redispersion, which are not conducive to the large-scale preparation and popularization of wrinkled graphene microspheres. Therefore, it is particularly important to develop a technical method with simple preparation method, strong operability and repeatability, and conducive to large-scale production of wrinkled graphene microspheres. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a method for preparing wrinkled graphene balls and the wrinkled graphene balls. The method has simple steps, strong operability and repeatability, is conducive to industrial production, can effectively solve the problem of reduced specific surface area caused by the stacking of graphene sheets, and at the same time, the prepared wrinkled balls also have good redispersibility, providing a new technical means for the transportation and storage of graphene oxide.

[0006] To solve the above technical problem, the technical solution proposed by the present invention is as follows:

[0007] A method for preparing wrinkled graphene balls, comprising the following steps:

[0008] (1) Prepare an aqueous solution of graphene oxide with a concentration ≤ 0.3 mg / mL;

[0009] (2) Add ammonia water to the aqueous solution of graphene oxide and stir to make the pH value of the aqueous solution of graphene oxide 3.5 - 8.5;

[0010] (3) Freeze the aqueous solution of graphene oxide obtained in step (2) with liquid nitrogen and then perform freeze-drying to obtain wrinkled graphene balls.

[0011] In the above preparation method, after ammonia water treatment, the content of hydrophilic functional groups such as hydroxyl and amino groups of graphene oxide can be increased. Therefore, the freeze-dried wrinkled graphene balls can still be well redispersed in the aqueous solution, solving the problem that the wrinkled balls prepared by the spray drying method are difficult to redisperse.

[0012] At the same time, the concentration of graphene oxide plays an important role in the formation of the balls. A high concentration will lead to a decrease in the interlayer distance, which is not conducive to the formation of wrinkles. When the concentration of the aqueous solution of graphene oxide is increased to 2 mg / mL, wrinkled graphene balls with uniform particle size cannot be formed. And the pH of the solution also has an important influence on the particle size and formation of the balls. Wrinkled graphene balls cannot be formed under strong acid and strong base conditions. Only when the solution pH is between 3.5 and 8.5, can wrinkled graphene balls with different particle sizes be formed, and the size of the wrinkled graphene balls can be regulated by changing the solution pH.

[0013] In addition, the freeze-drying rate also has an important influence on the formation of wrinkled graphene balls. Rapid cooling with liquid nitrogen can maintain the state of uniform dispersion of graphene oxide sheets in the solution to the greatest extent. Slow freezing of the aqueous solution of graphene oxide will reduce the interlayer distance, which is not conducive to the formation of wrinkles. Therefore, wrinkled graphene balls with uniform particle size cannot be formed from the GO aqueous solution slowly frozen in a -40°C refrigerator.

[0014] Preferably, in step (1), the concentration of the graphene oxide aqueous solution is 0.1 - 0.3 mg / mL. Within this concentration range, wrinkled graphene spheres with uniform particle sizes can be formed. At high concentrations of graphene oxide, wrinkles cannot be formed due to the too small interlayer distance, while too low a concentration will reduce the yield and is not conducive to industrial production.

[0015] Preferably, in step (1), the graphene oxide aqueous solution is the graphene oxide aqueous solution obtained after ultrasonic treatment, and the power of the ultrasonic treatment is 400 - 500 W, and the time is 20 - 30 min. Ultrasonic treatment with high power and appropriate time is conducive to reducing the size of graphene oxide sheets, reducing the resistance of interlayer interaction, and improving the sphericity of the product.

[0016] Preferably, step (1) specifically includes the following steps: subjecting the original graphene oxide aqueous solution with a concentration greater than 4 mg / mL to ultrasonic treatment using a cell disruptor to obtain the ultrasonic-treated graphene oxide aqueous solution; diluting the concentration of the ultrasonic-treated graphene oxide aqueous solution to ≤ 0.3 mg / mL.

[0017] Preferably, step (2) specifically includes the following steps: adding ammonia water to the graphene oxide aqueous solution to adjust the pH value of the solution to 6 - 7, stirring, and then adding or not adding a pH regulator to make the pH value of the obtained graphene oxide aqueous solution between 3.5 and 8.5. If an excessive amount of ammonia water is added, on the one hand, it will increase the repulsive force between the sheets, which is not conducive to the formation of spheres of the product; on the other hand, it will cause a reduction reaction of graphene oxide, reducing the oxygen-containing functional groups of graphene oxide and weakening the hydrogen bond interaction, which is not conducive to the formation of wrinkles. If the amount of ammonia water added is small, the electrostatic repulsion between the sheets is weak, and the sheets tend to stack in a sheet-to-sheet manner and cannot form spheres.

[0018] Preferably, the pH regulator is an HCl solution and / or an NaOH solution.

[0019] Preferably, in step (2), the stirring time is 15 - 30 min. If the above stirring time is too long, it is not conducive to the formation of wrinkles of the graphene spheres.

[0020] Preferably, the specific steps of freezing the graphene oxide aqueous solution obtained in step (2) using liquid nitrogen are as follows: dispensing the graphene oxide aqueous solution obtained in step (2) into glass bottles of 15 - 30 mL, and then placing them in liquid nitrogen for freezing, and the freezing time is 2 - 5 min. Both dispensing and freezing the graphene oxide aqueous solution with liquid nitrogen are helpful for quickly freezing the graphene oxide aqueous solution, thereby maintaining the interlayer distance and being conducive to the formation of wrinkled graphene spheres.

[0021] Preferably, the freeze-drying time is 36 to 48 h, and the temperature is -40 to -70 °C.

[0022] As a general inventive concept, the present invention provides a wrinkled graphene ball prepared by the above preparation method.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) By using the method of the present invention, uniformly sized wrinkled graphene balls can be prepared, and the sphericity of graphene approaches 100%.

[0025] (2) The GO treated with ammonia water in the present invention can generate more hydroxyl and amino groups. Compared with two-dimensional graphene and wrinkled graphene balls prepared by other methods, the prepared wrinkled graphene balls can be easily redispersed in an aqueous solution without the need for technical means such as high-power and long-time ultrasound, providing good conditions for further modification and treatment of GO.

[0026] (3) By adjusting the pH, the present invention can prepare wrinkled graphene balls of different sizes, which is convenient for basic experimental research such as mechanism exploration.

[0027] (4) The method steps of the present invention are simple and the technical difficulty is low. The entire operation process only requires a cell crusher and a freeze dryer, with low equipment dependence, strong repeatability and operability, and a yield close to 100%. It is very suitable for large-scale industrial production. For example, by using an industrial-grade freeze dryer, the production of gram-scale wrinkled graphene balls can be easily achieved. The template method for preparing wrinkled graphene balls includes operations such as chemical modification of GO, mixing of nano microspheres, removal of the template, and centrifugation, which are time-consuming and laborious, greatly limiting the large-scale application of this method.

[0028] (5) Commercially available GO generally adopts a low-concentration aqueous dispersion form. The present invention can significantly reduce the volume of GO by converting the aqueous solution of graphene oxide into the form of graphene oxide powder. The tapped density of the wrinkled balls prepared in the present invention is 35 mg / cm 3 , which can not only save transportation and storage costs, but also effectively improve its shelf life. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1SEM image of the wrinkled graphene microspheres in Example 1;

[0031] Figure 2 TEM image of the wrinkled graphene microspheres in Example 1;

[0032] Figure 3 Appearance image of 540 mg of the wrinkled graphene microsphere powder in Example 1;

[0033] Figure 4 SEM image of the wrinkled graphene microspheres in Example 2;

[0034] Figure 5 SEM image of the wrinkled graphene microspheres in Example 3;

[0035] Figure 6 SEM image of the product obtained in Comparative Example 1;

[0036] Figure 7 SEM image of the product obtained in Comparative Example 2;

[0037] Figure 8 SEM image of the product obtained in Comparative Example 3;

[0038] Figure 9 SEM image of the product obtained in Comparative Example 4.

[0039] Figure 10 Comparison diagram of SEM images and optical photographs of the redispersed aqueous solution of the wrinkled graphene oxide microspheres in Example 1 and the redispersed aqueous solution of flaky graphene oxide in Comparative Example 5. Detailed implementation manner

[0040] For the convenience of understanding the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0041] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0042] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0043] Example 1:

[0044] A preparation method of wrinkled graphene microspheres, comprising the following steps:

[0045] (1) The graphene oxide aqueous solution prepared by the improved Hummers method with a concentration of 4.66 mg / mL was ultrasonically treated using a cell disruptor. The ultrasonic power was 450 W and the time was 30 min to obtain the ultrasonically treated graphene oxide aqueous solution.

[0046] (2) The ultrasonically treated graphene oxide aqueous solution was diluted to obtain a graphene oxide aqueous solution with a concentration of 0.2 mg / mL.

[0047] (3) Ammonia water was added to the graphene oxide aqueous solution obtained in step (2) to adjust the pH value of the solution to 6.5, and it was stirred for 30 min.

[0048] (4) The graphene oxide aqueous solution obtained in step (3) was aliquoted into 15-mL glass bottles and then placed in liquid nitrogen for freezing for 2 min to obtain the graphene oxide freezing solution.

[0049] (5) The above graphene oxide freezing solution was placed in a freeze dryer at -60 °C and freeze-dried for 36 h to obtain wrinkled graphene balls.

[0050] The SEM image of the wrinkled graphene balls prepared in this example is as shown in Figure 1 and the TEM image is as shown in Figure 2 which shows that the wrinkled graphene balls with a particle size of about 280 nm were successfully prepared in this example, and the wrinkled graphene balls are uniform in size. Among them Figure 3 is the appearance image of 540 mg of the wrinkled graphene ball powder prepared in this example. It can be seen from Figure 3 that the wrinkled graphene balls prepared in this example present a uniform particle morphology, and the tapped density is 35 mg / cm 3 . Compared with the graphene oxide aqueous solution, the wrinkled graphene oxide powder occupies significantly less space, which can not only save transportation and storage costs, but also effectively improve its shelf life. Since operations such as filtration and centrifugation are not involved, the wrinkled graphene balls prepared by this method have the production advantage of a yield close to 100%.

[0051] Example 2:

[0052] A method for preparing wrinkled graphene balls, different from Example 1, step (3) includes the following steps: Ammonia water was added to the graphene oxide aqueous solution obtained in step (2) to adjust the pH value of the solution to 6.5, and it was stirred for 20 min, then HCl solution was added to adjust the pH to 3.5, and it was stirred for 10 min. Other processes and parameters are the same as those in Example 1.

[0053] The SEM image of the wrinkled graphene balls in this example is as shown in Figure 4 as shown, Figure 4It shows that the wrinkled graphene balls with a particle size of about 410 nm are successfully prepared in this example.

[0054] Example 3:

[0055] A method for preparing wrinkled graphene balls, different from Example 1, step (3) includes the following steps: adding ammonia water to the graphene oxide aqueous solution obtained in step (2) to adjust the pH value of the solution to 6.5, stirring for 20 min, and then adding NaOH solution to adjust the pH to 8.5, stirring for 10 min. Other processes and parameters are the same as those in Example 1.

[0056] The SEM image of the wrinkled graphene balls in this example is as Figure 5 shown, Figure 5 It shows that the wrinkled graphene balls with a particle size of about 320 nm are successfully prepared in this example.

[0057] Comparative Example 1:

[0058] Different from Example 1, step (3) includes the following steps: adding ammonia water to the graphene oxide aqueous solution obtained in step (2) to adjust the pH value of the solution to 6.5, stirring for 20 min, and then adding HCl solution to adjust the pH to 2.5, stirring for 10 min. Other processes and parameters are the same as those in Example 1.

[0059] The SEM image of the product obtained in this comparative example is as Figure 6 shown, Figure 6 It shows that the method in this comparative example cannot form wrinkled graphene balls.

[0060] Comparative Example 2:

[0061] Different from Example 1, step (3) includes the following steps: adding ammonia water to the graphene oxide aqueous solution obtained in step (2) to adjust the pH value of the solution to 6.5, stirring for 20 min. Then adding NaOH solution to adjust the pH to 9.5, stirring for 10 min. Other processes and parameters are the same as those in Example 1.

[0062] The SEM image of the product obtained in this comparative example is as Figure 7 shown, Figure 7 It shows that the method in this comparative example cannot form wrinkled graphene balls.

[0063] Comparative Example 3:

[0064] Different from Example 1, step (2) includes the following steps: diluting the graphene oxide aqueous solution after ultrasonic treatment above to obtain a graphene oxide aqueous solution with a concentration of 2 mg / mL. Other processes and parameters are the same as those in Example 1.

[0065] The SEM image of the product obtained in this comparative example is as Figure 8 shown, Figure 8 indicating that the method in this comparative example cannot form uniform wrinkled graphene microspheres.

[0066] Comparative Example 4:

[0067] Different from Example 1, step (4) includes the following steps: slowly freezing the graphene oxide aqueous solution obtained in step (3) in a -40°C refrigerator. Other processes and parameters are the same as those in Example 1.

[0068] The SEM image of the product obtained in this comparative example is as Figure 9 shown, Figure 9 indicating that this comparative example cannot form uniform wrinkled graphene microspheres.

[0069] Comparative Example 5:

[0070] A method for preparing lamellar graphene includes the following steps:

[0071] (1) Ultrasonically treat the graphene oxide aqueous solution prepared by the improved Hummers method with a concentration of 4.66 mg / mL using a cell disruptor, with an ultrasonic power of 450 W and a time of 30 min to obtain the ultrasonically treated graphene oxide aqueous solution.

[0072] (2) Dilute the above ultrasonically treated graphene oxide aqueous solution to obtain a graphene oxide aqueous solution with a concentration of 0.2 mg / mL.

[0073] (3) Aliquot the graphene oxide aqueous solution obtained in step (2) into 15 mL glass bottles, and then place them in liquid nitrogen for freezing for 2 min to obtain the graphene oxide frozen solution.

[0074] (4) Place the above graphene oxide frozen solution in a freeze dryer at -60°C and freeze-dry for 36 h to obtain lamellar graphene.

[0075] Dissolve the wrinkled graphene microspheres prepared in Example 1 in water with a concentration of 0.2 mg / mL. After ultrasonic treatment for 10 min, take 20 μL of the re-dispersed aqueous solution and spin-coat it onto a silicon wafer. For comparison, dissolve the freeze-dried lamellar graphene in Comparative Example 5 in water with a concentration of 0.2 mg / mL, and take 20 μL of the re-dispersed aqueous solution and spin-coat it onto a silicon wafer.

[0076] The SEM image of the re-dispersed aqueous solution of the wrinkled graphene microspheres in Example 1 is as Figure 10 (left) shown, and the SEM image of the re-dispersed aqueous solution of the lamellar graphene in Comparative Example 5 is as Figure 10 (right) shown, where the upper left corner of the attached figure is the optical image of the corresponding re-dispersed aqueous solution, Figure 10(Left) It shows that the wrinkled graphene balls in Example 1 can dissolve in water and unfold into sheets again without stacking, while Figure 10 (Right) It shows that the sheet graphene in Comparative Example 5 cannot completely dissolve in water and the sheets are severely stacked.

[0077] The above, in conjunction with the accompanying drawings, is the preferred embodiment of the present invention, but the present invention is not limited to the described embodiments. It should be noted that for those skilled in the art, without departing from the principle described in the present invention, any changes, improvements, and modifications to these embodiments should be regarded as the protection scope of the present invention.

Claims

1. A method for preparing wrinkled graphene microspheres, characterized in that, It includes the following steps: (1) Prepare an aqueous solution of graphene oxide with a concentration ≤ 0.3 mg / mL; (2) Add ammonia water to the aqueous solution of graphene oxide, adjust the pH value of the solution to 6 - 7, stir, and then add or not add a pH regulator to make the pH value of the obtained aqueous solution of graphene oxide between 3.5 and 8.5; (3) Dispense the aqueous solution of graphene oxide obtained in step (2) into glass bottles of 15 - 30 mL, then place it in liquid nitrogen for freezing, and the freezing time is 2 - 5 min; then perform lyophilization to obtain wrinkled graphene spheres.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the aqueous solution of graphene oxide is 0.1 - 0.3 mg / mL.

3. The preparation method according to claim 1, characterized in that, In step (1), the aqueous solution of graphene oxide is the aqueous solution of graphene oxide obtained after ultrasonic treatment, and the power of the ultrasonic treatment is 400 - 500 W and the time is 20 - 30 min.

4. The preparation method according to claim 3, wherein Step (1) specifically includes the following steps: Ultrasonically treat an aqueous solution of graphene oxide with a concentration greater than 4 mg / mL using a cell disrupter to obtain an ultrasonically treated aqueous solution of graphene oxide; Dilute the concentration of the ultrasonically treated aqueous solution of graphene oxide to ≤ 0.3 mg / mL.

5. The preparation method according to claim 1, characterized in that, The pH regulator is an HCl solution and / or an NaOH solution.

6. The preparation method according to claim 1, characterized in that, In step (2), the stirring time is 15 - 30 min.

7. The preparation method according to claim 1, characterized in that, The lyophilization time is 36 - 48 h and the temperature is -40 - -70 °C.

8. A wrinkled graphene sphere prepared by the preparation method according to any one of claims 1 - 7.

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