Preparation method of bio-based mesoporous carbon material

Abstract

The invention relates to a preparation method of a bio-based mesoporous carbon material, and belongs to the technical field of carbon material preparation. The invention provides a preparation method of a bio-based mesoporous carbon material, and the bio-based mesoporous carbon material is prepared by taking agricultural and forestry wastes as raw materials through three steps of pretreatment, phosphoric acid activation and polyaniline-graphene quantum dot compounding. In the pretreatment stage, the raw materials are crushed, soaked in an ethanol-acetone mixed solution at 40-80 DEG C for 2-6 h and dried, and powder B is obtained; in the phosphoric acid activation stage, a 50-80% phosphoric acid solution is used for dipping for 12-48 hours according to the mass ratio of 1: (2-5), and carbonization is performed under the protection of 400-700 DEG C nitrogen to obtain a solid product In the compounding stage, D is dispersed in a 0.1-1 mol / L aniline hydrochloric acid solution, after polymerization is initiated by ammonium persulfate, 0.01-0.1 g / L graphene quantum dot solution is added for compounding, and after centrifugal drying, the high-performance carbon material with the specific surface area larger than or equal to 1800 m < 2 > / g, the proportion of 2-5 nm holes larger than 35% and the mesoporous rate larger than 75% is prepared, and the high-performance carbon material is suitable for the field of supercapacitors.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon material preparation, and relates to a preparation method of a bio-based mesoporous carbon material. BACKGROUND

[0002] Mesoporous carbon materials have irreplaceable application value in the fields of energy storage, environmental governance, catalytic reaction and the like due to high specific surface area, regular pore structure and excellent material transmission performance.

[0003] However, the preparation of traditional mesoporous carbon materials depends on petroleum-based or coal-based fossil raw materials, and has problems such as non-renewable raw materials, high carbon emission in the preparation process, high cost and the like, which are contrary to the development requirements of green manufacturing and circular economy. At the same time, more than 2 billion tons of agricultural and forestry wastes (such as corn stalks, wheat stalks, coconut shells and the like) are produced globally each year as biomass resources, which are rich in cellulose, hemicellulose and lignin. After reasonable activation and functional modification of the carbon skeleton, the agricultural and forestry wastes can be converted into high-performance carbon materials with rich mesoporous structures, which is a key path to realize high-value utilization of biomass resources. However, the existing preparation technology of bio-based mesoporous carbon materials still has bottlenecks such as difficulty in mesoporous structure regulation, insufficient conductivity and single functionalization, which limits the application of the bio-based mesoporous carbon materials in the fields of electrochemical energy storage and complex pollutant treatment.

[0004] Therefore, it is urgent to develop a bio-based mesoporous carbon material with high mesoporous rate and using agricultural and forestry wastes as raw materials. SUMMARY

[0005] The application aims to provide a preparation method of a bio-based mesoporous carbon material, which has the characteristics of controllable pore structure and strong electricity storage capacity.

[0006] The application can be achieved by the following technical solutions.

[0007] A preparation method of a bio-based mesoporous carbon material, and the specific steps of the preparation method are as follows,

[0008] S1: raw material pretreatment

[0009] Agricultural and forestry wastes are selected as bio-based raw materials, and after being washed with deionized water, the bio-based raw materials are dried and crushed to a particle size of less than 200 mesh to obtain bio-based raw material powder A;

[0010] The bio-based raw material powder A is soaked in an ethanol-acetone mixed solution at 40-80 DEG C, the soaking time is 2-6 hours, after soaking, the bio-based raw material powder A is washed with deionized water until neutral, and then dried at 60-100 DEG C for 8-12 hours to obtain powder B;

[0011] S2: phosphoric acid activation treatment

[0012] Mixing powder B with phosphoric acid solution according to the mass ratio of 1:(2-5), immerse at room temperature for 12-48h, filter after the completion of immersion, dry at 60-80℃ for 12h, grind to obtain powder C;

[0013] Carburize powder C under nitrogen atmosphere, the carburizing temperature is 400-700℃, the heating rate is 2-10℃ / min, and the holding time is 1-4h;

[0014] After the completion of carburization, cool to room temperature, wash with deionized water until neutral, and dry at 60-100℃ to constant weight to obtain solid product D;

[0015] S3: compounding of polyaniline and graphene quantum dots

[0016] Weigh solid product D, disperse in aniline monomer solution with a concentration of 0.1-1mol / L according to the solid-liquid ratio of 1:(50-200)g / mL, and ultrasonic treat for 10-30min;

[0017] Add ammonium persulfate solution with a concentration of 0.1-2mol / L dropwise in an ice water bath at a rate of 1-5mL / min, and stir for 2-8h to obtain solid-liquid mixture F;

[0018] Add graphene quantum dot solution of 0.01-0.1g / L to solid-liquid mixture F, and the volume ratio of the two is 1:(5-20), ultrasonic treat for 10-30min;

[0019] Centrifugal separation, collect the solid product, wash with deionized water until neutral, and dry at 60-100℃ to constant weight to obtain the bio-based mesoporous carbon material.

[0020] Further, the agricultural and forestry waste is one or more of corn stalks, wheat stalks, and coconut shells.

[0021] Further, the volume ratio of the ethanol-ketone mixed solution in S1 is (1-3):1.

[0022] Further, the mass concentration of the phosphoric acid solution in S2 is 50-80%.

[0023] Further, the flow rate of nitrogen in S2 is 100-150mL / min.

[0024] Further, the solvent of the aniline monomer solution in S3 is hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.5-2mol / L.

[0025] Further, the molar ratio of ammonium persulfate to aniline in S3 is (1-2):1.

[0026] Further, the parameter of centrifugal separation in the S3 is that the rotating speed is 4000-8000 rpm, and the time length is 10-20 min.

[0027] Further, the specific surface area of the prepared bio-based mesoporous carbon material is greater than or equal to 1800 m 2 / g, the proportion of 2-5 nm pores is greater than 35%, and the mesoporous rate is greater than 75%.

[0028] The present application uses agricultural and forestry wastes (such as straw, fruit shells, etc.) as a carbon source, which is essentially a resource utilization of waste biomass in agricultural recycling economy. These biomasses are rich in natural polymers such as cellulose, hemicellulose and lignin, and their three-dimensional network structure provides a natural template for subsequent formation of porous carbon. The use of ethanol-acetone mixed solution for soaking in the pretreatment has a double mechanism: on the one hand, the organic solvent selectively dissolves the non-carbon components such as waxes, lipids and part of the pigments in the raw materials through the similar-similar principle, reducing the ash content; on the other hand, the solvent molecules penetrate into the microstructure of the biomass, partially destroy the hydrogen bond network, so that the subsequent activator is more easily contacted with the internal components. The crushing to below 200 mesh significantly increases the specific surface area of the raw material, and promotes the diffusion efficiency of the solvent and the activator. These pretreatment operations improve the purity of the raw material from the source, avoiding the generation of disordered carbon or ash blocking the pore channel during the pyrolysis of impurities at high temperature, and clearing the obstacles for forming high-purity mesoporous structure.

[0029] The phosphoric acid activation treatment realizes the precise control of the pore structure. The key role of phosphoric acid as an activator lies in its unique "pore forming-expanding-stabilizing" triple mechanism. In the impregnation stage, phosphoric acid molecules penetrate into the interior of the biomass and form phosphate ester bonds with the hydroxyl groups in cellulose / hemicellulose, while also promoting the crosslinking reaction of lignin, which enhances the thermal stability of the biomass skeleton. In the early stage of carbonization (<300℃), phosphoric acid catalyzes the dehydration and decarboxylation of biomass, inhibits the generation of tar, and reduces the blockage of micropores; in the medium temperature stage (300-400℃), phosphoric acid decomposes to generate polyphosphoric acid and pyrophosphoric acid, which have strong dehydrating properties and promote the aromatization of biomass and the formation of cross-linked condensed ring structures; in the high temperature stage (400-700℃), the decomposition of phosphates generates gases (such as CO, CO2) to form micropores, while molten phosphoric acid acts as a "space barrier" to prevent the carbon layer from excessive graphitization and stacking. The gradient design of the heating rate of 2-10℃ / min can coordinate the balance between the release of pyrolysis gas and the shrinkage of the skeleton: too fast heating leads to the concentrated release of volatile matter and the destruction of the skeleton, and too slow heating reduces the efficiency. Finally, in the range of 400-700℃, a mesopore-based pore distribution is formed, and the mechanism is that the specific mass ratio (1:2-5) of phosphoric acid to biomass components can form a moderate liquid phase package, and the space occupied by the molten phosphoric acid during carbonization is removed by water washing to form mesoporous cavities. The nitrogen atmosphere completely isolates oxygen, prevents the oxidation and consumption of the carbon skeleton, and ensures the carbonization yield.

[0030] In the present application, the graphene quantum dots are prepared by the following steps:

[0031] The single-layer graphene oxide is dispersed in deionized water to prepare a dispersion liquid with a concentration of 1 mg / mL, and is ultrasonically treated for 40 min; a mixed acid of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1 is added to the dispersion liquid, the mass ratio of the mixed acid to the graphene oxide is 10:1, and the mixture is stirred and reacted at 80℃ for 24 h, so that the graphene sheet is cut into nanometer fragments by strong acid stripping; the pH of the reaction solution is adjusted to 8 by using a sodium hydroxide solution, a polyethylene glycol passivation agent is added, the amount of the polyethylene glycol passivation agent is 10 wt% of the mass of the graphene oxide, the mixture is transferred into a reaction kettle and is hydrothermally reacted at 180℃ for 6 h; after cooling, the ion impurities are removed by dialysis treatment for 24 h, the molecular weight cut-off is 2 kDa, and then the mixture is filtered through a 0.22 μm microporous filter membrane, and finally the mixture is concentrated at 40℃ under reduced pressure to a concentration of 0.01-0.1 g / L, so that a graphene quantum dot solution is obtained.

[0032] The polyaniline / graphene quantum dot composite gives double optimization of the chemical and electronic structures of the material surface. In this step, the conductive polymer modification and quantum dot hybridization are integrated on the mesoporous carbon matrix to form a multi-level synergistic effect. First, the polymerization mechanism of aniline monomers on the mesoporous carbon surface includes physical adsorption and chemical bonding: the abundant mesoporous structure of the solid product D adsorbs aniline monomers through capillary action, and the residual oxygen-containing functional groups (such as carboxyl groups) on the surface of the product can form ionic bonds or hydrogen bonds with the amino groups of aniline, thereby forming polymerization sites. An ice water bath environment (0-5℃) and slow addition of ammonium persulfate also have an important influence on the reaction of aniline: low temperature inhibits the homopolymerization reaction rate of aniline, so that the monomers preferentially nucleate and grow on the carbon surface; controlling the addition rate of the oxidant avoids local over-oxidation, which leads to excessive cross-linking of polyaniline and inactivation. The polyaniline layer generated in this way tightly covers the carbon skeleton, and the quinone structure (-NH-=N+-) and benzene structure (-NH-B-NH-) in the molecular chain of polyaniline form a conjugated system, which significantly improves the overall conductivity of the material. The introduction of graphene quantum dots (GQDs) further produces a quantum size effect: the abundant carboxyl and hydroxyl functional groups on the surface of GQDs form a hydrogen bond network with the polyaniline chain segments, enhancing the interfacial bonding force; more importantly, the quantum confinement effect of GQDs enables them to have a semiconductive energy band structure, which can form an electron transfer channel with the π-conjugated system of polyaniline. When GQDs are dispersed in the composite system, the sp 2 The carbon domain accepts the delocalized electrons of polyaniline as an electron acceptor, reducing the interface charge transfer resistance, while the nitrogen / oxygen groups on the surface of the quantum dots contribute to the pseudo-capacitance. This ternary structure of "carbon skeleton-conductive polymer-quantum dots" constructs a continuous electron transport network at the molecular level. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to facilitate the understanding of those skilled in the art, the present application will be further described below with reference to the accompanying drawings.

[0034] Figure 1 Figure 3 is a scanning electron microscope image of the bio-based carbon material of Example 3. DETAILED DESCRIPTION

[0035] In order to further clarify the technical means adopted by the present application to achieve the predetermined inventive purpose and the effects thereof, the specific embodiments, structures, features and effects thereof according to the present application are described in detail below in conjunction with the drawings and preferred embodiments.

[0036] Example 1

[0037] S1: raw material pretreatment

[0038] Corn stalks were selected as bio-based raw materials, washed with deionized water and dried, and the dried corn stalks were crushed to a particle size of less than 200 mesh to obtain bio-based raw material powder A; powder A was soaked in a 40℃ ethanol-acetone mixed solution (ethanol: acetone = 1:1) for 2 hours, washed with deionized water to neutral after soaking, and dried at 60℃ for 12h to obtain powder B;

[0039] S2: phosphoric acid activation treatment

[0040] Powder B was mixed with a 50% phosphoric acid solution at a mass ratio of 1:2, soaked at room temperature for 12h, filtered after soaking, dried at 60℃ for 12h, and ground to obtain powder C; carbonization treatment was carried out under a nitrogen atmosphere (100mL / min) at a temperature increase of 2℃ / min to 400℃, and the temperature was maintained for 1 hour; after cooling, the product was washed with deionized water to neutral and dried at 60℃ to constant weight to obtain solid product D;

[0041] S3: polyaniline and graphene quantum dot compounding

[0042] 1g of product D was dispersed in a 0.1mol / L aniline monomer solution (0.5mol / L HCl solvent) at a solid-liquid ratio of 1:50g / mL, and ultrasonicated for 10min; 0.1mol / L ammonium persulfate solution was added dropwise at a rate of 1mL / min in an ice water bath (ammonium persulfate: aniline molar ratio 1:1), and stirred for 2h to obtain a solid-liquid mixture F; 0.01g / L graphene quantum dot solution was added to F (F and quantum dot volume ratio 1:5), and ultrasonicated for 10min; centrifugal separation was performed, and the product was washed with water to neutral and dried at 60℃ to constant weight to obtain the final product.

[0043] The specific surface area of the carbon material prepared in this example was 1820m 2 / g, the 2-5nm pore ratio was 36%, and the mesopore ratio was 76%.

[0044] Example 2

[0045] S1: raw material pretreatment

[0046] Wheat straw was selected as a bio-based raw material, washed with deionized water and dried, and the dried raw material was crushed to a particle size of less than 200 mesh to obtain powder A; powder A was soaked in a 60°C ethanol-acetone mixed solution (ethanol: acetone = 2:1) for 4 hours, washed with deionized water to neutral after soaking, and dried at 80°C for 10h to obtain powder B;

[0047] S2: Phosphoric acid activation treatment

[0048] Powder B was mixed with a 65% phosphoric acid solution at a mass ratio of 1:3.5, soaked at room temperature for 30h, filtered after soaking, dried at 70°C for 12h, and ground to obtain powder C; carbonization treatment was carried out under a nitrogen atmosphere (125mL / min) at a temperature increase rate of 6°C / min to 550°C, and the temperature was kept for 2.5 hours; after cooling, deionized water was used to wash to neutral, and the product was dried at 80°C to constant weight to obtain solid product D;

[0049] S3: Polyaniline and graphene quantum dot complex

[0050] 1g of product D was dispersed in a 0.55mol / L aniline monomer solution (1.25mol / L HCl solvent) at a solid-liquid ratio of 1:125g / mL, and ultrasonic treatment was performed for 20min; 1.05mol / L ammonium persulfate solution was added dropwise at a rate of 3mL / min in an ice water bath (ammonium persulfate: aniline molar ratio 1.5:1), and stirring reaction was carried out for 5h to obtain a solid-liquid mixture F; 0.055g / L graphene quantum dot solution was added to F (F and quantum dot volume ratio 1:12.5), and ultrasonic treatment was carried out for 20min; centrifugal separation was carried out, water was used to wash to neutral, and the product was dried at 80°C to constant weight to obtain the final product.

[0051] Example 3

[0052] S1: Raw material pretreatment

[0053] Coconut shell was selected as a bio-based raw material, washed with deionized water and dried, and the dried raw material was crushed to a particle size of less than 200 mesh to obtain powder A; powder A was soaked in an 80°C ethanol-acetone mixed solution (ethanol: acetone = 3:1) for 6 hours, washed with deionized water to neutral after soaking, and dried at 100°C for 8h to obtain powder B;

[0054] S2: Phosphoric acid activation treatment

[0055] Powder B was mixed with an 80% phosphoric acid solution at a mass ratio of 1:5, soaked at room temperature for 48h, filtered after soaking, dried at 80°C for 12h, and ground to obtain powder C; carbonization treatment was carried out under a nitrogen atmosphere (150mL / min) at a temperature increase rate of 10°C / min to 700°C, and the temperature was kept for 4 hours; after cooling, deionized water was used to wash to neutral, and the product was dried at 100°C to constant weight to obtain solid product D;

[0056] S3: composite of polyaniline and graphene quantum dots

[0057] The product D1g was weighed, dispersed in a 1.0 mol / L aniline monomer solution (2.0 mol / L HCl solvent) at a solid-liquid ratio of 1:200 g / mL, and ultrasonicated for 30 min; a 2.0 mol / L ammonium persulfate solution (ammonium persulfate:aniline molar ratio 2:1) was added dropwise at a rate of 5 mL / min in an ice water bath, and stirred for 8 h to obtain a solid-liquid mixture F; 0.1 g / L of a graphene quantum dot solution was added to F (F:quantum dot volume ratio 1:20), and ultrasonicated for 30 min; centrifugal separation was performed, and water was washed until neutral, and dried at 100°C to constant weight to obtain the final product.

[0058] Comparative Example 1

[0059] In this comparative example, no graphene quantum dot solution was added, and the remaining steps were the same as in Example 3.

[0060] Comparative Example 2

[0061] In this comparative example, no aniline was added, and the solid product D was directly dispersed in deionized water at a solid-liquid ratio of 1:200 g / mL, and the remaining steps were the same as in Example 3.

[0062] Comparative Example 3

[0063] In this comparative example, no phosphoric acid impregnation was performed, and the remaining steps were the same as in Example 3.

[0064] Comparative Example 4

[0065] In this comparative example, carbonization was performed in an air atmosphere, and the remaining steps were the same as in Example 3.

[0066] The carbon materials prepared in the examples and comparative examples were tested for specific surface area, 2-5 nm pore ratio, and mesopore ratio by nitrogen adsorption / desorption, and the specific capacitance was tested according to the standard GB / T 34870.1-2017, and the experimental results are as follows,

[0067]

[0068] From the above experimental data, it can be seen that Example 3 has the highest specific surface area and the best mesoporous structure, and through Figure 1 It can also be observed that the carbon material of Example 3 is a mesoporous material with uniform pore size distribution, which makes the carbon material of Example 3 have a larger specific surface area, thereby providing sufficient interface for charge storage; simultaneously, the polyaniline composite introduces a pseudo-capacitance to enhance the charge storage capacity, and the graphene quantum dots improve the electrical conductivity, and the three synergistically make the specific capacitance reach 422 F / g.

[0069] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, as long as the changes or modifications do not deviate from the technical solution of the present application. Any modification, change, equivalent change and modification of the above embodiments made according to the technical essence of the present application still belong to the scope of the technical solution of the present application.

Claims

1. A method for preparing a bio-based mesoporous carbon material, characterized in that, The specific steps of the preparation method are as follows: S1: Raw material pretreatment Agricultural and forestry waste was selected as bio-based raw material. After washing with deionized water and drying, the dried bio-based raw material was pulverized to a particle size of less than 200 mesh to obtain bio-based raw material powder A. Bio-based raw material powder A was soaked in an ethanol-acetone mixed solution at 40–80°C for 2–6 hours. After soaking, it was washed with deionized water until neutral and dried at 60–100°C for 8–12 hours to obtain powder B. S2: Phosphoric acid activation treatment Powder B is mixed with phosphoric acid solution at a mass ratio of 1:(2-5), and impregnated at room temperature for 12-48 hours. After impregnation, the mixture is filtered, dried at 60-80℃ for 12 hours, and then ground to obtain powder C. Powder C is carbonized under a nitrogen atmosphere at a temperature of 400–700°C, a heating rate of 2–10°C / min, and a holding time of 1–4 hours. After carbonization, the product was cooled to room temperature, washed with deionized water until neutral, and dried at 60–100 °C to constant weight to obtain solid product D. S3: Composite of polyaniline and graphene quantum dots Weigh solid product D and disperse it in a 0.1-1 mol / L aniline monomer solution at a solid-liquid ratio of 1:(50-200) g / mL. Sonicate the solution for 10-30 min. In an ice-water bath, a 0.1-2 mol / L ammonium persulfate solution is added dropwise at a rate of 1-5 mL / min, and the mixture is stirred for 2-8 h to obtain a solid-liquid mixture F. Add 0.01–0.1 g / L of graphene quantum dot solution to the solid-liquid mixture F, with a volume ratio of 1:(5–20), and sonicate for 10–30 min. Centrifuge to separate the solid product, wash with deionized water until neutral, and dry at 60-100℃ to constant weight to obtain the bio-based mesoporous carbon material.

2. The method for preparing a bio-based mesoporous carbon material according to claim 1, characterized in that, The agricultural and forestry waste is one or more of the following: corn stalks, wheat stalks, and coconut shells.

3. The method for preparing a bio-based mesoporous carbon material according to claim 1, characterized in that, The volume ratio of the ethanol-acetone mixed solution in S1 is (1-3):

1.

4. The method for preparing a bio-based mesoporous carbon material according to claim 1, characterized in that, The phosphoric acid solution in S2 has a mass concentration of 50-80%.

5. The method for preparing a bio-based mesoporous carbon material according to claim 1, characterized in that, The flow rate of nitrogen in S2 is 100-150 mL / min.

6. The method for preparing a bio-based mesoporous carbon material according to claim 1, characterized in that, The solvent for the aniline monomer solution in S3 is hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.5-2 mol / L.

7. The method for preparing a bio-based mesoporous carbon material according to claim 1, characterized in that, The molar ratio of ammonium persulfate to aniline in S3 is (1-2):

1.

8. The method for preparing a bio-based mesoporous carbon material according to claim 1, characterized in that, The parameters for centrifugation in S3 are: rotation speed 4000-8000 rpm and duration 10-20 min.

9. The bio-based mesoporous carbon material obtained by the preparation method according to any one of claims 1 to 8, characterized in that, The material has a specific surface area ≥1800 m². 2 / g, with pores of 2-5nm accounting for more than 35% and mesopority greater than 75%.

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