Glucose carbon spheres as well as preparation method and application thereof

Abstract

The invention discloses an efficient preparation method and electrochemical energy storage application of glucose carbon spheres, and belongs to the technical field of carbon material preparation. Aiming at the technical defects of low glucose concentration, long reaction time and poor yield in preparation of glucose carbon spheres by a traditional hydrothermal method, the invention creatively provides a method of adding ZIF-8 into a glucose solution as a catalyst. Under the hydrothermal condition of 180 DEG C, ZIF-8 is triggered by organic acid generated by glucose in situ to decompose and release Zn < 2 + >, and by cooperating with the dispersion effect of sodium polyacrylate, high-glucose-concentration preparation (4M at most) is realized, a product is obtained within the shortest time of 2 hours (at least 4 hours in a traditional method), and the yield of glucose carbon spheres is increased by nearly 10% compared with a contrast; after KOH activation (the mass ratio of KOH to the carbon spheres is preferably 1: 1, the activation temperature is preferably 800 DEG C, and the activation time is preferably 2 hours), the carbon material has high specific surface area (1616.7 m < 2 > / g), reasonable pore size (2.48 nm) and abundant pore volume (1.00 cm < 3 > / g), the specific capacitance reaches 171.5 F / g under 0.5 A / g, and the capacity retention rate reaches 85.14% after 10,000 cycles.

Description

Technical Field

[0001] This invention belongs to the field of carbon material preparation technology, specifically relating to a glucose carbon sphere based on the catalytic effect of metal-organic framework materials and its efficient preparation method, as well as its application in the field of electrochemical energy storage. Background Technology

[0002] Hydrothermal carbonization (HTC) is currently the mainstream technology for preparing glucose carbon spheres. It involves dehydrating and carbonizing a glucose solution in a high-temperature, high-pressure (typically 180-220℃) reactor to form solid carbon spheres. This method allows for control of the carbon sphere size (typically a wide diameter distribution spanning the micro-nano range) by adjusting the glucose concentration, temperature, and time. The products exhibit advantages such as uniform morphology and easy surface functionalization, and have been applied in fields such as supercapacitors, lithium-ion battery anodes, and catalyst supports. However, to ensure product morphology uniformity, existing HTC methods cannot use high glucose concentrations (typically ≤1.0M) and cannot react at 180-220℃ for 4-12 hours, and the carbon sphere yield is usually low. In existing technologies, the promoting effect of metal ions on the growth of glucose carbon spheres has been disclosed (see: Synthetic Metals, 2016, Volume 214, pp. 1-4), but is limited to Na. + Mg 2+ Ca 2+ and Fe 3+ The study did not address the relationship between metal ions and the yield of glucose carbon spheres. Notably, ZIF-8 (a metal-organic framework material formed by the coordination of zinc ions with 2-methylimidazole) can decompose and release Zn in acidic environments. 2+ The organic acids generated in situ during the hydrothermal process of glucose can trigger this reaction. In light of this, this technique reveals that the zinc ions released from the decomposition of ZIF-8 during the hydrothermal process of glucose can also catalyze the growth of glucose carbon spheres, simultaneously achieving breakthroughs in concentration limitations, shortening of reaction time, and increasing yield. Furthermore, no practical solution for the efficient preparation of glucose carbon spheres using this synergistic mechanism has been observed to date. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing an efficient method for preparing glucose carbon spheres and its application, thereby solving the problems mentioned in the background section.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a glucose carbon sphere, which refers to a glucose carbon sphere synthesized under high temperature and high pressure by adding a small amount of ZIF-8 to a glucose solution during the HTC method for preparing glucose carbon spheres; the glucose carbon sphere, after activation with KOH, has a specific surface area of ​​1616.7 m².2 / g, pore size 2.48nm, pore volume 1.00cm³ 3 / g.

[0005] A method for preparing glucose carbon spheres includes the following steps:

[0006] S1: Preparation of ZIF-8: Zinc acetate solution and dimethylimidazole solution were mixed and stirred for a period of time; then the resulting milky white suspension was allowed to stand for a period of time; finally, the resulting white precipitate was washed with deionized water, filtered, and dried to obtain ZIF-8.

[0007] S2: Preparation of glucose carbon spheres: ZIF-8 and sodium polyacrylic acid sodium (PAAS) for auxiliary dispersion were added to a glucose solution and sonicated for a period of time to disperse them evenly; the resulting suspension was added to a reaction vessel, heated to the set temperature, and kept for a period of time before heating was stopped; the black product was washed with deionized water and anhydrous ethanol, filtered, and finally dried to obtain glucose carbon spheres.

[0008] S3: Activation of glucose carbon spheres: Glucose carbon spheres and KOH are mixed by impregnation for a period of time to disperse them evenly; then the mixture obtained above is placed in an oven to dry thoroughly; after grinding the KOH-impregnated glucose carbon spheres evenly, they are placed in a tube furnace and heated to the set temperature, and the heating is stopped after a period of time; the activated glucose carbon spheres are taken out, washed with deionized water and filtered until neutral, and finally dried to obtain KOH-activated glucose carbon spheres.

[0009] As a preferred embodiment of the present invention, the concentrations of zinc acetate and dimethylimidazole solutions in S1 are 0.2M and 1.6M, respectively; the volumes of both zinc acetate and dimethylimidazole solutions are 25mL.

[0010] As a preferred embodiment of the present invention, in step S1, the zinc acetate and dimethylimidazole solution are mixed and stirred for 2 hours, and then allowed to stand for 24 hours.

[0011] As a preferred embodiment of the present invention, in S2, the amount of ZIF-8 is 0.1g, the amount of PAAS is 24mg, the glucose concentration is 0.5-4M, and the amount is 40mL.

[0012] As a preferred embodiment of the present invention, the ultrasonic time in S2 is 2 hours; the reaction temperature is 180°C; and the heat preservation time is 2-12 hours.

[0013] As a preferred embodiment of the present invention, the mass ratio of KOH to glucose carbon spheres in S3 is 0.5:1, 1:1, or 2:1.

[0014] As a preferred embodiment of the present invention, the impregnation and mixing time in S3 is 2 hours, and the oven is set to 80°C after impregnation for 12 hours.

[0015] As a preferred embodiment of the present invention, the nitrogen flow rate in the S3 tubular furnace is 200 mL / min, the set temperature is 700-900℃, the heating rate is 5℃ / min, and the holding time is 2h.

[0016] The beneficial effects are:

[0017] The Zn2+ released by the reaction of ZIF-8 with the acidic substances produced during the hydrothermal decomposition of glucose catalyzes and accelerates the formation of glucose carbon spheres.

[0018] 1. The glucose carbon spheres can be formed in 2 hours, the glucose concentration can be extended to 4M, and the yield can be increased by nearly 10%;

[0019] 2. Electrochemical performance: specific capacitance at 0.5 A / g is 171.5 F / g, and specific capacitance retention is 85.14% after 10,000 cycles. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the glucose carbon spheres in Example 1 of the present invention;

[0021] Figure 2 This is a scanning electron microscope image of the carbon spheres activated with KOH in Example 1 of the present invention;

[0022] Figure 3 This is a constant current charge-discharge diagram of the carbon spheres activated by KOH in Example 1 of the present invention;

[0023] Figure 4 This is a rate performance diagram of the carbon spheres activated with KOH in Example 1 of the present invention;

[0024] Figure 5 The image shows scanning electron microscope images of glucose carbon spheres obtained by the conventional HTC method at different hydrothermal times in Comparative Example 1 of this invention.

[0025] Figure 6 The image shows scanning electron microscope images of glucose carbon spheres prepared under different hydrothermal times in Comparative Example 2 of this invention.

[0026] Figure 7 This is a comparison chart of the yield of glucose carbon spheres in Comparative Example 1 and Comparative Example 2 of the present invention;

[0027] Figure 8 This is a scanning electron microscope image of glucose carbon spheres prepared at different glucose concentrations in Comparative Example 3 of the present invention. Detailed Implementation

[0028] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but the present invention is not limited to the following embodiments.

[0029] A method for preparing glucose carbon spheres includes the following steps:

[0030] S1: Preparation of ZIF-8: Mix 25 mL of 0.2 M zinc acetate solution and 25 mL of 1.6 M dimethylimidazole solution and stir for 2 h; then let the resulting milky white suspension stand for 24 h; wash the resulting white precipitate with deionized water, filter, and finally dry to obtain ZIF-8.

[0031] S2: Preparation of glucose carbon spheres: 0.1 g of ZIF-8 and 24 mg of PAAS were added to 40 mL of glucose solution (concentration: 0.5-4 M) and sonicated for 2 h; the resulting suspension was added to a reaction vessel, heated to 180 °C, and maintained for 2-12 h, after which heating was stopped and the mixture was allowed to cool naturally; the black product was washed with deionized water and anhydrous ethanol, filtered, and finally dried to obtain glucose carbon spheres.

[0032] S3: Activation of glucose carbon spheres: KOH and glucose carbon spheres were mixed in a certain mass ratio, and an appropriate amount of water was added for impregnation. The resulting mixture was then dried in an 80℃ oven for 12 hours. The KOH-impregnated glucose carbon spheres were ground evenly and placed in a tube furnace. Nitrogen flow rate was set to 200 mL / min, and the temperature was increased to 800℃ at a rate of 5℃ / min. Heating was maintained for 2 hours and then stopped. The activated glucose carbon spheres were removed, washed with deionized water, filtered until neutral, and finally dried to obtain the activated product. By adjusting the mass ratio of KOH to glucose carbon spheres (e.g., 0.5:1, 1:1, 2:1), a series of activated products can be obtained.

[0033] Example 1:

[0034] The preparation and activation of glucose carbon spheres with added ZIF-8 and PAAS include the following steps:

[0035] 0.1 g of ZIF-8 and 24 mg of PAAS were added to 40 mL of 3 M glucose solution and sonicated for 2 h to make it homogeneous. The resulting suspension was heated to 180 °C in a reaction vessel and held for 2 h. Then the heating was stopped and the mixture was allowed to cool naturally. The black product was washed with deionized water and anhydrous ethanol, filtered, and finally dried to obtain glucose carbon spheres.

[0036] KOH and glucose carbon spheres were mixed at a mass ratio of 1:1, and an appropriate amount of water was added for impregnation. The resulting mixture was then dried in an 80°C oven for 12 hours. The KOH-impregnated glucose carbon spheres were ground evenly and then placed in a tube furnace. Nitrogen flow rate was set to 200 mL / min, and the temperature was heated to 800°C at 5°C / min. The temperature was maintained for 2 hours and then the heating was stopped. The activated glucose carbon spheres were removed, washed with deionized water, filtered until neutral, and finally dried to obtain the activated product.

[0037] Comparative Example 1:

[0038] Glucose carbon spheres prepared by the traditional HTC method: 0.1 g of ZIF-8 was added to 40 mL of 3 M glucose solution and sonicated for 2 h to make it homogeneous; the resulting suspension was heated to 180 °C in a reaction vessel and maintained for 4, 8 and 12 h, after which heating was stopped and the mixture was allowed to cool naturally; the black product was washed with deionized water and anhydrous ethanol, filtered, and finally dried to obtain products with different hydrothermal times.

[0039] Comparative Example 2:

[0040] Glucose carbon spheres obtained by adding ZIF-8: 0.1 g of ZIF-8 was added to 40 mL of 3M glucose solution and sonicated for 2 h to make it homogeneous; the resulting suspension was heated to 180 °C in a reaction vessel and maintained for 2, 4, 8 and 12 h, after which heating was stopped and the mixture was allowed to cool naturally; the black product was washed with deionized water and anhydrous ethanol, filtered, and finally dried to obtain products with different hydrothermal times.

[0041] Comparative Example 3:

[0042] Glucose carbon spheres were obtained by adding only ZIF-8 at different glucose concentrations: 0.1 g of ZIF-8 was added to 40 mL of glucose solution (1-4 M) and sonicated for 2 h to make it homogeneous; the resulting suspension was heated to 180 °C in a reaction vessel and held for 2 h, then heating was stopped and the mixture was allowed to cool naturally; the black product was washed with deionized water and anhydrous ethanol, filtered, and finally dried to obtain glucose carbon spheres.

[0043] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A glucose carbon sphere, characterized in that, The glucose carbon spheres were formed during a hydrothermal preparation process by adding the metal-organic framework material ZIF-8 to a glucose solution as a catalyst; after activation with KOH, the glucose carbon spheres had a specific surface area of ​​1616.7 m². 2 / g, pore size 2.48nm, pore volume 1.00cm³ 3 / g.

2. A method for preparing glucose carbon spheres as described in claim 1, characterized in that, Includes the following steps: S1: Preparation of ZIF-8: Zinc acetate solution and dimethylimidazole solution were mixed and stirred for a period of time, then allowed to stand, and ZIF-8 was obtained by washing and drying. S2: Preparation of glucose carbon spheres: The ZIF-8 obtained in step S1 and the dispersant are added to the glucose solution and reacted in a hydrothermal reactor at the reaction temperature for a period of time. Finally, the glucose carbon spheres are obtained by washing and drying. S3: Activation of glucose carbon spheres: The glucose carbon spheres obtained in step S2 are mixed evenly with KOH and impregnated. After drying, they are activated under an inert atmosphere for 2 hours. After washing and drying, the activated glucose carbon spheres are obtained.

3. The method according to claim 2, characterized in that, The concentrations of zinc acetate solution and dimethylimidazole solution were 0.2M and 1.6M, respectively, and the total volume of both solutions was 25 mL.

4. The method according to claim 2, characterized in that, In step S2, the dispersant is sodium polyacrylate, and the dosage is 24 mg.

5. The method according to claim 2, characterized in that, In step S2, the glucose concentration is 3M.

6. The method according to claim 2, characterized in that, In step S2, the ZIF-8 has a mass of 0.1g and is dissolved in 40mL of glucose solution.

7. The method according to claim 2, characterized in that, In step S2, the reaction temperature is 180°C.

8. The method according to claim 2, characterized in that, In step S2, the reaction time is 2 hours.

9. The method according to claim 2, characterized in that, In step S3, the mass ratio of KOH to glucose carbon spheres is 1:1, and the activation temperature is 800℃.

10. An application of glucose carbon spheres as described in claim 1, characterized in that: Applications in the field of electrochemical energy storage.

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