Graphene spheres, and a preparation method and application thereof

Abstract

The application relates to the technical field of graphene material preparation, and discloses a graphene ball and a preparation method and application thereof. The method comprises the following steps: (1) mixing graphene oxide, sodium alginate and water, and then performing ultrasonic treatment and heating to obtain a mixed dispersion liquid; (2) dripping the mixed dispersion liquid into a Ca 2+ containing water solution through an injection pump to soak, and obtaining graphene oxide / sodium alginate hydrogel; and (3) sequentially performing washing, freeze-drying and calcination on the graphene oxide / sodium alginate hydrogel; wherein in the step (2), the flow rate of the injection pump is 10-200 uL / min. The method has the characteristics of simple preparation process, no need to use complex instruments and equipment, and large-batch production.

Description

Technical Field

[0001] This invention relates to the field of graphene material preparation technology, specifically to a graphene sphere, its preparation method, and its application. Background Technology

[0002] In recent years, graphene has gained attention for its excellent electrical conductivity (reaching 10⁸ S / m). -1 Thermal conductivity (thermal conductivity can reach 5300 W / m) -1 K -1 It also boasts superior mechanical properties (Young's modulus reaches 1 TPa) and a large specific surface area (2630 m²). 2 g -1 This has become one of the hot topics in the research of nano-gas-sensitive materials.

[0003] Common graphene materials can be classified according to their dimensionality into one-dimensional nanofibers, two-dimensional nanofilms, and three-dimensional graphene microspheres. The porous structure of three-dimensional graphene microspheres is highly advantageous for improving their adsorption, energy storage, and gas-sensing properties: First, the three-dimensional structure effectively reduces the stacking of graphene sheets, preserving graphene's high specific surface area and increasing the number of active sites for reactions; second, the interconnected pores facilitate molecular diffusion into the material's interior, enhancing its sensitivity; finally, the three-dimensional graphene framework not only provides support sites for the loading of other nanomaterials but also accelerates the flow of electrons within the material, enhancing its conductivity.

[0004] However, current methods for preparing three-dimensional graphene spheres involve electrostatic spraying (CN103121672A), multiphase flow (CN109896519B), and template agents (CN110357078A). These methods require high-voltage equipment, posing significant risks; the equipment is complex and requires customization; or the addition of template agents necessitates additional template removal steps. These complex processes are unsuitable for the preparation of graphene spheres. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of existing technologies, such as the need for complex preparation instruments, complex preparation processes, and the need for template agents, and to provide a graphene sphere, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides a method for preparing graphene spheres, the method comprising the following steps:

[0007] (1) Graphene oxide, sodium alginate and water are mixed, and then ultrasonicated and heated to obtain a mixed dispersion;

[0008] (2) The mixed dispersion was dripped into a solution containing Ca using an injection pump. 2+The graphene oxide / sodium alginate hydrogel was obtained by soaking the sample in an aqueous solution.

[0009] (3) The graphene oxide / sodium alginate hydrogel was washed, freeze-dried and calcined in sequence;

[0010] In step (2), the flow rate of the injection pump is 10-200 uL / min.

[0011] Preferably, in step (1), the weight ratio of graphene oxide, sodium alginate and water is 1-15:0.1-50:1000;

[0012] The preferred ratio is 5-10:0.1-40:1000.

[0013] Preferably, in step (1), the ultrasound duration is 10-120 min.

[0014] Preferably, in step (1), the heating temperature is 70-95℃ and the heating time is 3-6h.

[0015] Preferably, in step (2), the substance containing Ca 2+ Ca in aqueous solution 2+ The concentration is 0.5-10% by weight.

[0016] Preferably, in step (2), the soaking time is 1-24 hours.

[0017] Preferably, in step (3), the washing process includes rinsing the graphene oxide / sodium alginate hydrogel with water and then soaking it in water.

[0018] Preferably, in the method for preparing graphene spheres according to claim 7, the soaking time during the washing process is 12-48 hours.

[0019] Preferably, in step (3), the freeze-drying conditions include: a temperature of 25-50°C and a time of 12-48h.

[0020] Preferably, in step (3), the roasting atmosphere is an inert atmosphere;

[0021] Preferably, the inert atmosphere is selected from nitrogen, argon or helium.

[0022] Preferably, in step (3), the roasting temperature is 200-700℃ and the roasting time is 1-5h.

[0023] A second aspect of the present invention provides graphene spheres prepared by the method described above.

[0024] Preferably, the graphene spheres have a particle size of 0.5-5 mm.

[0025] A third aspect of the present invention provides the application of the graphene spheres described above in the fields of gas sensing, adsorption, or energy storage.

[0026] This invention provides a method for preparing graphene spheres. Using sodium alginate and graphene oxide as raw materials, and employing a micro-injection method, graphene millimeter spheres with uniform size, controllable size and structure, and high specific surface area are prepared. This method features a simple preparation process, requires no complex instruments or equipment, and enables mass production. The prepared graphene millimeter spheres can be used in multiple fields such as gas sensing, adsorption, and energy storage. Attached Figure Description

[0027] Figure 1 These are the optical microscope observation results of the product prepared in Example 1;

[0028] Figure 2-3 The above are the SEM characterization results of the product prepared in Example 1;

[0029] Figure 4 This is a graph showing the BET test results of the product prepared in Example 1. Detailed Implementation

[0030] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0031] The endpoints and any values ​​of the ranges disclosed herein 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] This invention provides a method for preparing graphene spheres, the method comprising the following steps:

[0033] (1) Graphene oxide, sodium alginate and water are mixed, and then ultrasonicated and heated to obtain a mixed dispersion;

[0034] (2) The mixed dispersion was dripped into a solution containing Ca using an injection pump. 2+ The graphene oxide / sodium alginate hydrogel was obtained by soaking the sample in an aqueous solution.

[0035] (3) The graphene oxide / sodium alginate hydrogel was washed, freeze-dried and calcined in sequence;

[0036] In step (2), the flow rate of the injection pump is 10-200 uL / min.

[0037] In a preferred embodiment, in step (2), the flow rate of the injection pump is 10-100 μL / min.

[0038] In a specific implementation, in step (2), the flow rate of the injection pump can be 10 uL / min, 20 uL / min, 30 uL / min, 40 uL / min, 50 uL / min, 60 uL / min, 70 uL / min, 80 uL / min, 100 uL / min, 120 uL / min, 140 uL / min, 160 uL / min, 180 uL / min or 200 uL / min.

[0039] In the method described in this invention, to facilitate the formation of graphene / sodium alginate hydrogels and obtain graphene microspheres with better performance, it is necessary to rationally control the dosage ranges of graphene oxide, sodium alginate, and water. The addition of sodium alginate can increase the viscosity and strength of the dispersion, preventing the dispersion from dripping from the injection pump into the Ca... 2+ In solution, it deforms due to low strength; however, the amount of sodium alginate should not be too high, as excessive sodium alginate will lead to excessive viscosity of the dispersion and block the injection pump.

[0040] In a preferred embodiment, in step (1), the weight ratio of graphene oxide, sodium alginate, and water is 1-15:0.1-50:1000; preferably 5-10:1-40:1000. Specifically, the weight ratio of graphene oxide to water can be 5:1000, 6:1000, 7:1000, 8:1000, 9:1000, or 10:1000; the weight ratio of sodium alginate to water can be 1:1000, 5:1000, 10:1000, 15:1000, 20:1000, 25:1000, 30:1000, 35:1000, or 40:1000.

[0041] In the method described in this invention, in step (1), due to the increase in viscosity of the entire system after the addition of sodium alginate, it is necessary to completely disperse the graphene oxide by ultrasound. The ultrasound time can be adjusted according to the amount of sodium alginate added. Preferably, in step (1), the ultrasound time is 10-120 min. Specifically, the ultrasound time can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min.

[0042] In the method described in this invention, in step (1), the heating process can help dissolve sodium alginate and prevent agglomeration. The heating temperature is preferably 70-95°C. The heating time can be adjusted according to the amount of sodium alginate added. Preferably, the heating time is 3-6 hours.

[0043] In the method described in this invention, step (2) contains Ca. 2+ In an aqueous solution, if Ca 2+ If the concentration of Ca is too low, the resulting gel strength will be too low; if the concentration of Ca is too low, the gel strength will be too low. 2+ If the concentration is too high, too much will remain in the gel, affecting its structure and performance. Therefore, in a preferred embodiment, preferably, in step (2), the Ca-containing... 2+ Ca in aqueous solution 2+ The concentration is 0.5-10% by weight, more preferably 1-5% by weight. Specifically, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, or 10% by weight.

[0044] In the method described in this invention, the substance containing Ca 2+ An aqueous solution can be obtained by mixing water with various water-soluble calcium salts conventionally used in the art. In one specific embodiment, the Ca-containing... 2+ The solution is an aqueous solution of calcium chloride.

[0045] In the method described in this invention, in step (2), the soaking time is calculated from the time the dripping is completed until the soaking ends. Preferably, in step (2), the soaking time is 1-24 hours, more preferably 6-24 hours. Specifically, the soaking time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 2 hours, or 24 hours.

[0046] In the method described in this invention, in order to fully remove calcium ions from the hydrogel, the product can be washed by rinsing and soaking. Therefore, in step (3), the washing process includes: rinsing the graphene oxide / sodium alginate hydrogel with water, and then soaking it in water.

[0047] Preferably, the soaking time during the washing process is 12-48 hours. Specifically, it can be 12 hours, 16 hours, 18 hours, 20 hours, 24 hours, 30 hours, 32 hours, 36 hours, 40 hours, or 48 hours.

[0048] Preferably, the number of rinsing operations during the washing process is 1-5 times.

[0049] In the method described in this invention, the graphene oxide / sodium alginate hydrogel is treated by freeze-drying, which can prevent the collapse of the gel's pore structure and preserve the three-dimensional structure of its microspheres to the greatest extent. Preferably, in step (3), the freeze-drying conditions include a temperature of 25-50°C and a time of 12-48 hours. More preferably, the drying temperature is 25-40°C and the drying time is 12-36 hours.

[0050] In a preferred embodiment, in step (3), the calcination atmosphere is an inert atmosphere. More preferably, the inert atmosphere is selected from nitrogen, argon, or helium.

[0051] In the method described in this invention, in step (3), the calcination process can remove sodium alginate on the one hand, and reduce graphene oxide on the other hand, thereby improving its electrical conductivity and mechanical properties.

[0052] Preferably, in step (3), the roasting temperature is 200-700℃, more preferably 200-500℃; the roasting time is 1-5h, more preferably 1-4h. Specifically, the roasting temperature can be 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 600℃ or 700℃; the roasting time can be 1h, 2h, 3h, 4h or 5h.

[0053] A second aspect of the present invention provides graphene spheres prepared by the method described above.

[0054] Preferably, the graphene spheres have a particle size of 0.5-5 mm.

[0055] A third aspect of the present invention provides the application of the graphene spheres described above in the fields of gas sensing, adsorption, or energy storage.

[0056] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0057] Unless otherwise specified, all reagents used in the following examples and comparative examples are commercially available products.

[0058] Example 1

[0059] (1) Disperse 50mg of graphene oxide into 10ml of deionized water, add 0.1g of sodium alginate, and stir evenly. The weight ratio of graphene oxide, sodium alginate and water is 5:10:1000. Then sonicate for 30min to completely peel off the graphene oxide sheets and disperse them evenly in water. Then heat at 70℃ for 4h to obtain a mixed dispersion.

[0060] (2) Add the well-dispersed graphene oxide / sodium alginate mixture to a micro-injection pump, controlling the pump flow rate at 30 μL / min, so that the graphene oxide / sodium alginate droplets fall evenly into the calcium chloride aqueous solution (Ca). 2+ The solution was immersed in sodium alginate at a concentration of 1% by weight for 12 hours to form a graphene oxide / sodium alginate hydrogel.

[0061] (3) Rinse the graphene oxide / sodium alginate hydrogel three times with deionized water, and then soak it in deionized water for 24 hours; put the soaked product into liquid nitrogen for freezing, and then dry it in a freeze dryer (temperature 30℃, time 24 hours); then put it into a tube furnace and calcine it at 500℃ for 2 hours under an inert atmosphere (nitrogen).

[0062] Example 2

[0063] (1) Disperse 150mg of graphene oxide into 10ml of deionized water, add 0.1g of sodium alginate, and stir evenly. The weight ratio of graphene oxide, sodium alginate and water is 15:10:1000. Then sonicate for 30min to completely peel off the graphene oxide sheets and disperse them evenly in water. Then heat at 70℃ for 4h to obtain a mixed dispersion.

[0064] (2) Add the well-dispersed graphene oxide / sodium alginate mixture to a micro-injection pump, controlling the pump flow rate at 30 μL / min, so that the graphene oxide / sodium alginate droplets fall evenly into the calcium chloride aqueous solution (Ca). 2+ The solution was immersed in sodium alginate at a concentration of 1% by weight for 12 hours to form a graphene oxide / sodium alginate hydrogel.

[0065] (3) Rinse the graphene oxide / sodium alginate hydrogel three times with deionized water, and then soak it in deionized water for 24 hours; put the soaked product into liquid nitrogen for freezing, and then dry it in a freeze dryer (temperature 25℃, time 24 hours); then put it into a tube furnace and calcine it at 500℃ for 2 hours under an inert atmosphere (nitrogen).

[0066] Example 3

[0067] (1) Disperse 50mg of graphene oxide into 10ml of deionized water, add 0.1g of sodium alginate, and stir evenly. The weight ratio of graphene oxide, sodium alginate and water is 5:50:1000. Then sonicate for 30min to completely peel off the graphene oxide sheets and disperse them evenly in water. Then heat at 70℃ for 4h to obtain a mixed dispersion.

[0068] (2) Add the well-dispersed graphene oxide / sodium alginate mixture to a micro-injection pump, controlling the pump flow rate at 30 μL / min, so that the graphene oxide / sodium alginate droplets fall evenly into the calcium chloride aqueous solution (Ca). 2+ The solution was immersed in sodium alginate at a concentration of 1% by weight for 12 hours to form a graphene oxide / sodium alginate hydrogel.

[0069] (3) Rinse the graphene oxide / sodium alginate hydrogel with deionized water 4 times, and then soak it in deionized water for 24 hours; put the soaked product into liquid nitrogen for freezing, and then dry it in a freeze dryer (temperature 25℃, time 24 hours); then put it into a tube furnace and calcine it at 500℃ for 2 hours under inert atmosphere (nitrogen).

[0070] Example 4

[0071] (1) Disperse 50mg of graphene oxide into 10ml of deionized water, add 0.1g of sodium alginate, and stir evenly. The weight ratio of graphene oxide, sodium alginate and water is 5:10:1000. Then sonicate for 120min to completely peel off the graphene oxide sheets and disperse them evenly in water. Then heat at 70℃ for 4h to obtain a mixed dispersion.

[0072] (2) Add the well-dispersed graphene oxide / sodium alginate mixture to a micro-injection pump, controlling the pump flow rate at 30 μL / min, so that the graphene oxide / sodium alginate droplets fall evenly into the calcium chloride aqueous solution (Ca). 2+ The solution was immersed in a solution of 5% by weight for 12 hours to form a graphene oxide / sodium alginate hydrogel.

[0073] (3) Rinse the graphene oxide / sodium alginate hydrogel three times with deionized water, and then soak it in deionized water for 24 hours; put the soaked product into liquid nitrogen for freezing, and then dry it in a freeze dryer (temperature 25℃, time 24 hours); then put it into a tube furnace and calcine it at 500℃ for 2 hours under an inert atmosphere (nitrogen).

[0074] Example 5

[0075] (1) Disperse 50mg of graphene oxide into 10ml of deionized water, add 0.1g of sodium alginate, and stir evenly. The weight ratio of graphene oxide, sodium alginate and water is 5:10:1000. Then sonicate for 30min to completely peel off the graphene oxide sheets and disperse them evenly in water. Then heat at 70℃ for 4h to obtain a mixed dispersion.

[0076] (2) Add the well-dispersed graphene oxide / sodium alginate mixture to a micro-injection pump, controlling the pump flow rate to 100 μL / min, so that the graphene oxide / sodium alginate droplets fall evenly into the calcium chloride aqueous solution (Ca). 2+ The solution was immersed in sodium alginate at a concentration of 1% by weight for 12 hours to form a graphene oxide / sodium alginate hydrogel.

[0077] (3) Rinse the graphene oxide / sodium alginate hydrogel with deionized water and soak it in deionized water for 24 hours; put the soaked product into liquid nitrogen for freezing, and then dry it in a freeze dryer (temperature 30℃, time 24 hours); then put it into a tube furnace and calcine it at 500℃ for 2 hours under an inert atmosphere (argon).

[0078] Example 6

[0079] (1) Disperse 50mg of graphene oxide into 10ml of deionized water, add 0.1g of sodium alginate, and stir evenly. The weight ratio of graphene oxide, sodium alginate and water is 5:10:1000. Then sonicate for 30min to completely peel off the graphene oxide sheets and disperse them evenly in water. Then heat at 70℃ for 4h to obtain a mixed dispersion.

[0080] (2) Add the well-dispersed graphene oxide / sodium alginate mixture to a micro-injection pump, controlling the pump flow rate at 30 μL / min, so that the graphene oxide / sodium alginate droplets fall evenly into the calcium chloride aqueous solution (Ca). 2+ The solution was immersed in sodium alginate at a concentration of 1% by weight for 12 hours to form a graphene oxide / sodium alginate hydrogel.

[0081] (3) Rinse the graphene oxide / sodium alginate hydrogel three times with deionized water, and then soak it in deionized water for 24 hours; put the soaked product into liquid nitrogen for freezing, and then dry it in a freeze dryer (temperature 30℃, time 24 hours); then put it into a tube furnace and calcine it at 200℃ for 2 hours under an inert atmosphere (nitrogen).

[0082] Example 7

[0083] (1) Disperse 60mg of graphene oxide into 10ml of deionized water, add 0.15g of sodium alginate, and stir evenly. The weight ratio of graphene oxide, sodium alginate and water is 6:15:1000. Then sonicate for 50min to completely peel off the graphene oxide sheets and disperse them evenly in water. Then heat at 70℃ for 4h to obtain a mixed dispersion.

[0084] (2) Add the well-dispersed graphene oxide / sodium alginate mixture to a micro-injection pump, controlling the pump flow rate at 30 μL / min, so that the graphene oxide / sodium alginate droplets fall evenly into the calcium chloride aqueous solution (Ca). 2+ The solution was immersed in sodium alginate at a concentration of 1% by weight for 12 hours to form a graphene oxide / sodium alginate hydrogel.

[0085] (3) Rinse the graphene oxide / sodium alginate hydrogel three times with deionized water, and then soak it in deionized water for 24 hours; put the soaked product into liquid nitrogen for freezing, and then dry it in a freeze dryer (temperature 30℃, time 24 hours); then put it into a tube furnace and calcine it at 450℃ for 2.5 hours under inert atmosphere (nitrogen) protection.

[0086] Example 8

[0087] (1) Disperse 70mg of graphene oxide in 10ml of deionized water, add 0.25g of sodium alginate, and stir evenly. The weight ratio of graphene oxide, sodium alginate and water is 6:25:1000. Then sonicate for 70min to completely peel off the graphene oxide sheets and disperse them evenly in water. Then heat at 80℃ for 4h to obtain a mixed dispersion.

[0088] (2) Add the well-dispersed graphene oxide / sodium alginate mixture to a micro-injection pump, controlling the pump flow rate at 40 μL / min, so that the graphene oxide / sodium alginate droplets fall evenly into the calcium chloride aqueous solution (Ca). 2+ The solution was immersed in a solution of 2% by weight for 12 hours to form a graphene oxide / sodium alginate hydrogel.

[0089] (3) Rinse the graphene oxide / sodium alginate hydrogel three times with deionized water, and then soak it in deionized water for 24 hours; put the soaked product into liquid nitrogen for freezing, and then dry it in a freeze dryer (temperature 30℃, time 24 hours); then put it into a tube furnace and calcine it at 400℃ for 3 hours under inert atmosphere (nitrogen).

[0090] Comparative Example 1

[0091] The method described in Example 1 is implemented, except that sodium alginate is not used in step (1).

[0092] Comparative Example 2

[0093] The method described in Example 1 is implemented, except that in step (2), the flow rate of the syringe pump is controlled to be 2 mL / min.

[0094] Comparative Example 3

[0095] The method described in Example 1 is implemented, except that in step (3), no roasting is performed.

[0096] Test Example 1

[0097] The products prepared in Examples 1-8 and Comparative Examples 1-3 were characterized using an optical microscope.

[0098] The results showed that the products prepared in the examples were uniform spheres with a diameter of 0.5-5 mm. Comparative Example 1 had a flat disc-like appearance and could not form uniform spheres; Comparative Example 2 formed a fibrous product; Comparative Example 3 could not remove sodium alginate and obtained mixed spheres of sodium alginate and graphene.

[0099] The characterization results of the products prepared in the examples are as follows: Figure 1 As shown in the figure, the obtained graphene microspheres are uniformly spherical with a diameter of approximately 1.5 mm.

[0100] Test Example 2

[0101] The products prepared in Examples 1-8 and Comparative Examples 1-3 were characterized using SEM.

[0102] The results showed that the product prepared in the examples had a uniform spherical structure with graphene wrinkles and abundant internal channels. The comparative example, on the other hand, had an uneven appearance and lacked abundant internal channels.

[0103] The characterization results of the product prepared in Example 1 are as follows: Figure 2 and 3 As shown, Figure 3 This is a cross-sectional view. The image shows that the graphene microspheres have many wrinkles on their surface, which result from the stacking that occurs during the reduction of graphene oxide. Simultaneously, the graphene microspheres contain abundant pores.

[0104] Test Example 3

[0105] The products prepared in Examples 1-8 and Comparative Examples 1-3 were characterized using BET. The specific surface area results are shown in Table 1.

[0106] The characterization results of the product prepared in Example 1 are as follows: Figure 4 As shown in the figure, graphene microspheres have a very high specific surface area and hierarchical pores ranging from a few nanometers to 25 nanometers.

[0107] Table 1

[0108] Example 1 1252.7 Example 7 1033.1 Example 2 1123.5 Example 8 1048.4 Example 3 1232.8 Comparative Example 1 853.2 Example 4 1196.3 Comparative Example 2 752.9 Example 5 1078.4 Comparative Example 3 384.9 Example 6 1092.5

[0109] From Table 1 and Figure 4 The results show that the graphene spheres prepared by the method described in this invention have a high specific surface area and hierarchical pores.

[0110] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing graphene spheres, characterized in that, The method includes the following steps: (1) Graphene oxide, sodium alginate and water are mixed, and then ultrasonicated and heated to obtain a mixed dispersion; (2) The mixed dispersion is dripped into a solution containing Ca using an injection pump. 2+ The graphene oxide / sodium alginate hydrogel was obtained by soaking the sample in an aqueous solution. (3) The graphene oxide / sodium alginate hydrogel was washed, freeze-dried and calcined in sequence; In step (2), the flow rate of the syringe pump is 10-200 μL / min; In step (1), the weight ratio of graphene oxide, sodium alginate and water is 1-15:0.1-50:1000, the ultrasonic time is 10-120 min, the heating temperature is 70-95℃, and the heating time is 3-6 h. In step (2), the substance containing Ca 2+ Ca in aqueous solution 2+ The concentration is 0.5-10% by weight. In step (3), the freeze-drying conditions include: a temperature of 25-50℃ and a time of 12-48h, a calcination temperature of 200-700℃ and a calcination time of 1-5h.

2. The method for preparing graphene spheres according to claim 1, characterized in that, In step (1), the weight ratio of graphene oxide, sodium alginate and water is 5-10:0.1-40:1000.

3. The method for preparing graphene spheres according to claim 1, characterized in that, In step (2), the soaking time is 1-24 hours.

4. The method for preparing graphene spheres according to claim 1 or 3, characterized in that, In step (3), the washing process includes rinsing the graphene oxide / sodium alginate hydrogel with water and then soaking it in water.

5. The method for preparing graphene spheres according to claim 4, characterized in that, During the washing process, the soaking time is 12-48 hours.

6. The method for preparing graphene spheres according to claim 1, characterized in that, In step (3), the roasting atmosphere is an inert atmosphere.

7. The method for preparing graphene spheres according to claim 6, characterized in that, The inert atmosphere is selected from nitrogen, argon or helium.

8. Graphene spheres prepared by the method according to any one of claims 1-7.

9. The graphene sphere according to claim 8, characterized in that, The graphene spheres have a particle size of 0.5-5 mm.

10. The application of the graphene spheres according to claim 8 or 9 in the fields of gas sensing, adsorption or energy storage.

Images