A lignin-based porous carbon material and a preparation method and application thereof

Abstract

The present application relates to the technical field of carbon material preparation, and particularly discloses a lignin-based porous carbon material, a preparation method thereof and application, wherein the ammonium oleate in the modified silicon dioxide can be used as a surfactant to promote the uniform dispersion of the modified silicon dioxide, prevent the agglomeration of nano-silicon dioxide from causing uneven pores, and meanwhile, the hydrophobic alkyl long chain of the ammonium oleate can be partially converted into conductive graphite microcrystals in the carbonization process, thereby enhancing the electrochemical performance of the carbon material; the boronic acid groups in the modified silicon dioxide form borate ester bonds with the ortho-dihydroxy groups of the lignin, realizing the directional combination of the modified silicon dioxide and the lignin, and further optimizing the pore distribution of the carbon material; in addition, the boronic acid groups can be doped into the carbon skeleton in the high-temperature carbonization process to form boron-doped carbon material, further improving the electrochemical performance of the carbon material.

Description

Technical Field

[0001] This invention relates to the field of carbon material preparation technology, specifically to a lignin-based porous carbon material, its preparation method, and its application. Background Technology

[0002] Lignin, a natural and renewable biomass resource, is widely found in plant cell walls and is the second most abundant organic polymer in nature. Due to its rich aromatic ring structure and abundant oxygen-containing functional groups, lignin can form porous carbon materials during high-temperature carbonization. These materials show great application potential in energy storage, environmental adsorption, and catalysis. Compared with traditional fossil-based carbon materials, lignin-based carbon materials not only have the advantages of wide availability and low cost but also align with the concept of green and sustainable development. Therefore, they have become a research hotspot in the high-value utilization of biomass in recent years.

[0003] For lignin raw materials, template methods are generally used to prepare lignin-based carbon materials, and the template agents used include molecular sieves, polyethers, etc. However, the above methods have many problems: 1) Molecular sieves themselves have a pore structure and can be used as mesoporous and macroporous template agents, but the molecular sieve synthesis process is relatively complex and costly; 2) Polyethers are mesoporous template agents, and the commonly used template agent is Pluronic F127, but the specific capacitance of electrode materials prepared with it as a template agent is difficult to meet commercial needs.

[0004] Chinese patent document CN201911018276.1 discloses a method for preparing lignin-based carbon materials rich in mesopores or a mixture of mesopores and macropores. The method uses lignin as the carbon-forming raw material, calcium chloride with good stability at high temperature as a mesopore template agent, and silica spheres as a macropore template agent. Mesopores are formed by the high-temperature crystallization process of highly dispersed calcium chloride, and macropores are formed by silica spheres. At the same time, water-soluble calcium chloride is recovered by washing and reused. However, the electrochemical performance of the prepared lignin-based carbon materials needs to be further improved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a lignin-based porous carbon material, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a lignin-based porous carbon material, comprising the following steps: S1. Dissolve lignin in an organic solvent to obtain solution A, disperse modified silica in anhydrous ethanol to obtain solution B, dissolve Pluronic F127 in deionized water to obtain solution C, and then stir and mix solutions A, B and C evenly to obtain a mixture. S2. After drying the mixture, grind it and then perform carbonization treatment to obtain a carbon / SiO2 composite material. S3. The carbon / SiO2 composite material is etched in a hydrofluoric acid solution, and then washed and dried to obtain lignin-based porous carbon material.

[0007] In the technical solution disclosed in this invention, the preparation method of the modified silica is as follows: (1) Add ammonium oleate, 4-vinylphenylboronic acid and vinyltriethoxysilane to an organic solvent, stir evenly, then add benzoyl peroxide as an initiator, heat and stir to react, and obtain the modifier; (2) Disperse nano-silica in an aqueous ethanol solution, then add a modifier to it, stir and reflux to react, and thus obtain modified silica.

[0008] Specifically, in step (1), the mass ratio of ammonium oleate, 4-vinylphenylboronic acid, vinyltriethoxysilane and benzoyl peroxide is 5-10:5-10:3-6:0.1-0.2.

[0009] Specifically, in step (1), the temperature for heating and stirring the reaction is 60-80℃, for example, 60℃, 65℃, 70℃, 75℃, or 80℃ can be selected; the time for heating and stirring the reaction is 2-4h, for example, 2h, 2.5h, 3h, 3.5h, or 4h can be selected, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0010] Specifically, in step (2), the mass ratio of nano-silica to modifier is 8-12:2-4. For example, 8:2, 8:3, 8:4, 10:2, 10:3, 10:4, 12:2, 12:3, and 12:4 can be selected, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0011] Specifically, in step (2), the temperature of the stirring and reflux reaction is 40-60℃, for example, 40℃, 45℃, 50℃, 55℃, 60℃ can be selected; the stirring and reflux reaction time is 1-3h, for example, 1h, 1.5h, 2h, 2.5h, 3h can be selected, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0012] In the technical solution disclosed in this invention, in step S1, the mass ratio of lignin, modified silica, and Pluronic F127 is 1:0.4-0.6:0.3-0.5. For example, 1:0.4:0.3, 1:0.4:0.4, 1:0.4:0.5, 1:0.5:0.3, 1:0.5:0.4, 1:0.5:0.5, 1:0.6:0.3, 1:0.6:0.4, and 1:0.6:0.5 can be selected, but are not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] In the technical solution disclosed in this invention, in step S2, the carbonization temperature is 580-620℃, for example, 580℃, 590℃, 600℃, 610℃, or 620℃ can be selected; the carbonization time is 10-30min, for example, 10min, 15min, 20min, 25min, or 30min can be selected, but it is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0014] In the technical solution disclosed in this invention, in step S3, the concentration of hydrofluoric acid solution is controlled at 1±0.05 mol / L, and the reaction vessel is made of polytetrafluoroethylene to ensure that the SiO2 template is completely removed and does not corrode the equipment.

[0015] Secondly, the present invention provides lignin-based porous carbon materials prepared by the above-described preparation method.

[0016] Thirdly, the present invention also provides the application of the above-mentioned lignin-based porous carbon material in the preparation of supercapacitor electrode materials.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a dual template synergistic strategy of modified silica and Pluronic F127, wherein modified silica serves as a hard template to provide rigid support to prevent the carbon skeleton from collapsing, and Pluronic F127 serves as a soft template to induce the formation of mesoporous structures, and the two work together to construct pores.

[0018] (2) In this invention, an addition reaction is first carried out with ammonium oleate, 4-vinylphenylboronic acid and vinyltriethoxysilane to obtain a modifier. Then, the siloxane groups in the modifier react with the hydroxyl groups on the surface of SiO2 to obtain modified silica. Among them, ammonium oleate in modified silica can act as a surfactant to promote uniform dispersion of modified silica and prevent nano-silica agglomeration that leads to uneven pores. At the same time, the hydrophobic alkyl long chain of ammonium oleate can be partially converted into conductive graphite microcrystals during carbonization, thereby enhancing the electrochemical performance of carbon materials. The boric acid groups in modified silica form borate ester bonds with the ortho-dihydroxyl groups of lignin, realizing the directional combination of modified silica and lignin, further optimizing the pore distribution of carbon materials. In addition, the boric acid groups will be doped into the carbon skeleton during high-temperature carbonization to form boron-doped carbon materials, further improving the electrochemical performance of carbon materials.

[0019] (3) This invention uses lignin as raw material to realize the high-value utilization of biomass waste, which has significant economic and social benefits. Attached Figure Description

[0020] Figure 1 This is an electron microscope image of the porous carbon material prepared in Example 1 of the present invention; Figure 2 The image shows an electron microscope image of the porous carbon material prepared in Comparative Example 1. Detailed Implementation

[0021] The present invention will be further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0022] It should be noted that, unless otherwise specified, all chemical reagents involved in this invention were purchased through commercial channels.

[0023] The nano-silica used in the embodiments of the present invention has a particle size of 10-15 nm.

[0024] Example 1 A method for preparing a lignin-based porous carbon material includes the following steps: S1. Dissolve 1g of lignin in 40mL of the organic solvent tetrahydrofuran to obtain solution A; disperse 0.5g of modified silica in 10mL of anhydrous ethanol to obtain solution B; dissolve 0.4g of Pluronic F127 in 10mL of deionized water to obtain solution C; then stir solutions A, B and C at room temperature for 12h to obtain a mixed solution. The preparation method of modified silica is as follows: (1) Add 8g ammonium oleate, 8g 4-vinylphenylboronic acid and 4g vinyltriethoxysilane to 150mL organic solvent DMF, stir evenly, then add 0.15g initiator benzoyl peroxide, heat and stir at 60℃ for 4h, and after the reaction is completed, dialyze and dry to obtain the modifier; (2) Disperse 8g of nano silica in 100mL of ethanol aqueous solution (the volume ratio of ethanol to water is 4:1), then add 2g of modifier, stir and reflux at 40℃ for 3h, and after the reaction is completed, filter, wash, dry and grind to obtain modified silica.

[0025] S2. The mixture was dried in a 60℃ forced-air drying oven for 24 hours, then ground to below 200 mesh using an agate mortar and pestle. In a tube furnace under a nitrogen atmosphere, the temperature was increased from room temperature to 600℃ at a rate of 3℃ / min and held constant for 15 minutes. After natural cooling, the carbon / SiO2 composite material was obtained.

[0026] S3. Place the carbon / SiO2 composite material in 200mL of 1mol / L hydrofluoric acid solution and stir magnetically for 12h. Wash with deionized water until neutral and dry at 105℃ for 12h to obtain lignin-based porous carbon material.

[0027] Example 2 A method for preparing a lignin-based porous carbon material includes the following steps: S1. Dissolve 1g of lignin in 40mL of the organic solvent tetrahydrofuran to obtain solution A; disperse 0.4g of modified silica in 10mL of anhydrous ethanol to obtain solution B; dissolve 0.3g of Pluronic F127 in 10mL of deionized water to obtain solution C; then stir solutions A, B and C at room temperature for 12h to obtain a mixed solution. The preparation method of modified silica is as follows: (1) Add 10g ammonium oleate, 10g 4-vinylphenylboronic acid and 6g vinyltriethoxysilane to 150mL organic solvent DMF, stir evenly, then add 0.2g initiator benzoyl peroxide, heat and stir at 80℃ for 2h, and after the reaction is completed, dialyze and dry to obtain the modifier; (2) Disperse 12g of nano silica in 100mL of ethanol aqueous solution (the volume ratio of ethanol to water is 4:1), then add 4g of modifier, stir and reflux at 40℃ for 3h, and after the reaction is completed, filter, wash, dry and grind to obtain modified silica.

[0028] S2. The mixture was dried in a 60℃ forced-air drying oven for 24 hours, then ground to below 200 mesh using an agate mortar and pestle. In a tube furnace under a nitrogen atmosphere, the temperature was increased from room temperature to 600℃ at a rate of 3℃ / min and held constant for 15 minutes. After natural cooling, the carbon / SiO2 composite material was obtained.

[0029] S3. Place the carbon / SiO2 composite material in 200mL of 1mol / L hydrofluoric acid solution and stir magnetically for 12h. Wash with deionized water until neutral and dry at 105℃ for 12h to obtain lignin-based porous carbon material.

[0030] Example 3 A method for preparing a lignin-based porous carbon material includes the following steps: S1. Dissolve 1g of lignin in 40mL of the organic solvent tetrahydrofuran to obtain solution A; disperse 0.6g of modified silica in 10mL of anhydrous ethanol to obtain solution B; dissolve 0.5g of Pluronic F127 in 10mL of deionized water to obtain solution C; then stir solutions A, B and C at room temperature for 12h to obtain a mixed solution. The preparation method of modified silica is as follows: (1) Add 5g ammonium oleate, 5g 4-vinylphenylboronic acid and 3g vinyltriethoxysilane to 150mL organic solvent DMF, stir evenly, then add 0.1g initiator benzoyl peroxide, heat and stir at 80℃ for 2h, and after the reaction is completed, dialyze and dry to obtain the modifier; (2) Disperse 10g of nano silica in 100mL of ethanol aqueous solution (the volume ratio of ethanol to water is 4:1), then add 3g of modifier, stir and reflux at 40℃ for 3h, and after the reaction is completed, filter, wash, dry and grind to obtain modified silica.

[0031] S2. The mixture was dried in a 60℃ forced-air drying oven for 24 hours, then ground to below 200 mesh using an agate mortar and pestle. In a tube furnace under a nitrogen atmosphere, the temperature was increased from room temperature to 600℃ at a rate of 3℃ / min and held constant for 15 minutes. After natural cooling, the carbon / SiO2 composite material was obtained.

[0032] S3. Place the carbon / SiO2 composite material in 200mL of 1mol / L hydrofluoric acid solution and stir magnetically for 12h. Wash with deionized water until neutral and dry at 105℃ for 12h to obtain lignin-based porous carbon material.

[0033] Example 4 A method for preparing a lignin-based porous carbon material includes the following steps: S1. Dissolve 1g of lignin in 40mL of the organic solvent tetrahydrofuran to obtain solution A; disperse 0.5g of modified silica in 10mL of anhydrous ethanol to obtain solution B; dissolve 0.5g of Pluronic F127 in 10mL of deionized water to obtain solution C; then stir solutions A, B and C at room temperature for 12h to obtain a mixed solution. The preparation method of modified silica is as follows: (1) Add 8g ammonium oleate, 6g 4-vinylphenylboronic acid and 5g vinyltriethoxysilane to 150mL organic solvent DMF, stir evenly, then add 0.1g initiator benzoyl peroxide, heat and stir at 60℃ for 4h, and after the reaction is completed, dialyze and dry to obtain the modifier; (2) Disperse 8g of nano silica in 100mL of ethanol aqueous solution (the volume ratio of ethanol to water is 4:1), then add 4g of modifier, stir and reflux at 60℃ for 1h, and after the reaction is completed, filter, wash, dry and grind to obtain modified silica.

[0034] S2. The mixture was dried in a 60℃ forced-air drying oven for 24 hours, then ground to below 200 mesh using an agate mortar and pestle. In a tube furnace under a nitrogen atmosphere, the temperature was increased from room temperature to 600℃ at a rate of 3℃ / min and held constant for 15 minutes. After natural cooling, the carbon / SiO2 composite material was obtained.

[0035] S3. Place the carbon / SiO2 composite material in 200mL of 1mol / L hydrofluoric acid solution and stir magnetically for 12h. Wash with deionized water until neutral and dry at 105℃ for 12h to obtain lignin-based porous carbon material.

[0036] Comparative Example 1 A method for preparing a lignin-based porous carbon material includes the following steps: S1. Dissolve 1g of lignin in 40mL of the organic solvent tetrahydrofuran to obtain solution A; disperse 0.5g of nano-silica in 10mL of anhydrous ethanol to obtain solution B; dissolve 0.4g of Pluronic F127 in 10mL of deionized water to obtain solution C; then stir solutions A, B and C at room temperature for 12h to obtain a mixed solution. S2. The mixture was dried in a 60℃ forced-air drying oven for 24 hours, then ground to below 200 mesh using an agate mortar and pestle. In a tube furnace under a nitrogen atmosphere, the temperature was increased from room temperature to 600℃ at a rate of 3℃ / min and held constant for 15 minutes. After natural cooling, the carbon / SiO2 composite material was obtained.

[0037] S3. Place the carbon / SiO2 composite material in 200mL of 1mol / L hydrofluoric acid solution and stir magnetically for 12h. Wash with deionized water until neutral and dry at 105℃ for 12h to obtain lignin-based porous carbon material.

[0038] Compared with Example 1, no modification treatment was performed on the nano-silica in Comparative Example 1.

[0039] Comparative Example 2 A method for preparing a lignin-based porous carbon material includes the following steps: S1. Dissolve 1g of lignin in 40mL of the organic solvent tetrahydrofuran to obtain solution A; disperse 0.5g of modified silica in 10mL of anhydrous ethanol to obtain solution B; dissolve 0.4g of Pluronic F127 in 10mL of deionized water to obtain solution C; then stir solutions A, B and C at room temperature for 12h to obtain a mixed solution. The preparation method of modified silica is as follows: (1) Add 8g of 4-vinylphenylboronic acid and 4g of vinyltriethoxysilane to 150mL of organic solvent DMF, stir evenly, then add 0.15g of initiator benzoyl peroxide, heat and stir at 60℃ for 4h, and after the reaction is completed, dialyze and dry to obtain the modifier; (2) Disperse 8g of nano silica in 100mL of ethanol aqueous solution (the volume ratio of ethanol to water is 4:1), then add 2g of modifier, stir and reflux at 40℃ for 3h, and after the reaction is completed, filter, wash, dry and grind to obtain modified silica.

[0040] S2. The mixture was dried in a 60℃ forced-air drying oven for 24 hours, then ground to below 200 mesh using an agate mortar and pestle. In a tube furnace under a nitrogen atmosphere, the temperature was increased from room temperature to 600℃ at a rate of 3℃ / min and held constant for 15 minutes. After natural cooling, the carbon / SiO2 composite material was obtained.

[0041] S3. Place the carbon / SiO2 composite material in 200mL of 1mol / L hydrofluoric acid solution and stir magnetically for 12h. Wash with deionized water until neutral and dry at 105℃ for 12h to obtain lignin-based porous carbon material.

[0042] Compared with Comparative Example 2 and Example 1, no ammonium oleate was added to the modifier.

[0043] Comparative Example 3 A method for preparing a lignin-based porous carbon material includes the following steps: S1. Dissolve 1g of lignin in 40mL of the organic solvent tetrahydrofuran to obtain solution A; disperse 0.5g of modified silica in 10mL of anhydrous ethanol to obtain solution B; dissolve 0.4g of Pluronic F127 in 10mL of deionized water to obtain solution C; then stir solutions A, B and C at room temperature for 12h to obtain a mixed solution. The preparation method of modified silica is as follows: (1) Add 8g of ammonium oleate and 4g of vinyltriethoxysilane to 150mL of organic solvent DMF, stir evenly, then add 0.15g of initiator benzoyl peroxide, heat and stir at 60℃ for 4h, and after the reaction is completed, dialyze and dry to obtain the modifier; (2) Disperse 8g of nano silica in 100mL of ethanol aqueous solution (the volume ratio of ethanol to water is 4:1), then add 2g of modifier, stir and reflux at 40℃ for 3h, and after the reaction is completed, filter, wash, dry and grind to obtain modified silica.

[0044] S2. The mixture was dried in a 60℃ forced-air drying oven for 24 hours, then ground to below 200 mesh using an agate mortar and pestle. In a tube furnace under a nitrogen atmosphere, the temperature was increased from room temperature to 600℃ at a rate of 3℃ / min and held constant for 15 minutes. After natural cooling, the carbon / SiO2 composite material was obtained.

[0045] S3. Place the carbon / SiO2 composite material in 200mL of 1mol / L hydrofluoric acid solution and stir magnetically for 12h. Wash with deionized water until neutral and dry at 105℃ for 12h to obtain lignin-based porous carbon material.

[0046] Compared with Example 1, no 4-vinylphenylboronic acid was added in Comparative Example 3.

[0047] The porous carbon materials prepared in Example 1 and Comparative Examples 1-3 were subjected to performance tests. The specific surface area, average pore size, and pore volume of the porous carbon samples were tested using a TriStarII 3020 fully automated specific surface area and pore volume analyzer. The test results are shown in Table 1.

[0048] Table 1. BET test results for different groups sample <![CDATA[Specific surface area (m 2 g)]]> <![CDATA[Total pore volume (m 3 / g)]]> <![CDATA[Micropore volume (m 3 / g)]]> Mesopority % Average pore size (nm) Example 1 789 1.16 0.22 84 5.2 Comparative Example 1 456 0.68 0.26 57 2.9 Comparative Example 2 758 1.06 0.25 76 4.1 Comparative Example 3 747 1.01 0.25 72 3.8 As can be seen from the data in Table 1, the porous carbon material prepared by the present invention using modified silica and Pluronic F127 dual templates has a specific surface area of ​​789 cm² / g, exhibiting a typical hierarchical pore structure with mesopores concentrated at 5.2 nm and a mesopore rate of 84%. By using modified silica and Pluronic F127 as template agents, the problems of agglomeration and skeleton collapse that easily occur during the direct carbonization of lignin are effectively solved.

[0049] Figure 1 This is an electron microscope image of the porous carbon material prepared in Example 1 of the present invention. Figure 2 The image shows an electron microscope image of the porous carbon material prepared in Comparative Example 1. As can be seen from the image, by modifying the nano-SiO2 particles, the pore distribution of the carbon material can be optimized, resulting in an ordered microstructure and high mechanical strength.

[0050] Electrochemical performance testing Electrochemical measurements were performed on a CHI760 electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd., China). A three-electrode system was used: Hg / HgO electrode and Pt sheet were used as the reference and counter electrodes, respectively, and 6 M KOH solution was used as the electrolyte. The working electrode was prepared by mixing porous carbon material (80 mg) prepared in Example 1 and Comparative Examples 1-3, polyvinylidene fluoride, and acetylene black in a mortar at a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone-2-one (NMP) was added to the mixture, and it was ground into a slurry. An appropriate amount of the slurry was evenly spread on carbon cloth (1 cm × 1 cm) and dried at 80 °C for 12 h. The loading of porous carbon material was 1.5 mg. The test voltage was -1 to 0 V, the test current density was 1 A / g, and the number of long-cycle charge-discharge cycles was 20,000. The test results are shown in Table 2.

[0051] Table 2 Electrochemical performance test results for different groups

[0052] Finally, it should be noted that the above embodiments do not limit the present invention in any way. Those skilled in the art can make modifications and improvements based on the present invention. Therefore, any modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a lignin-based porous carbon material, characterized in that, Includes the following steps: S1. Dissolve lignin in an organic solvent to obtain solution A, disperse modified silica in anhydrous ethanol to obtain solution B, dissolve Pluronic F127 in deionized water to obtain solution C, and then stir and mix solutions A, B and C evenly to obtain a mixture. S2. After drying the mixture, grind it and then perform carbonization treatment to obtain a carbon / SiO2 composite material. S3. The carbon / SiO2 composite material is etched in hydrofluoric acid solution, and then washed and dried to obtain lignin-based porous carbon material. In step S1, the modified silica is prepared as follows: (1) Add ammonium oleate, 4-vinylphenylboronic acid and vinyltriethoxysilane to an organic solvent, stir evenly, then add benzoyl peroxide as an initiator, heat and stir to react, and obtain the modifier; (2) Disperse nano-silica in an aqueous ethanol solution, then add a modifier to it, stir and reflux to react, and thus obtain modified silica.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of ammonium oleate, 4-vinylphenylboronic acid, vinyltriethoxysilane and benzoyl peroxide is 5-10:5-10:3-6:0.1-0.

2.

3. The preparation method according to claim 1, characterized in that, In step (1), the temperature for heating and stirring the reaction is 60-80℃, and the reaction time is 2-4h.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of nano-silica to modifier is 8-12:2-4.

5. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the stirring reflux reaction is 40-60℃, and the stirring reflux reaction time is 1-3h.

6. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of lignin, modified silica and Pluronic F127 is 1:0.4-0.6:0.3-0.

5.

7. The preparation method according to claim 1, characterized in that, In step S2, the carbonization temperature is 580-620℃ and the carbonization time is 10-30 minutes.

8. The lignin-based porous carbon material prepared by the preparation method according to any one of claims 1-7.

9. The application of the lignin-based porous carbon material as described in claim 8 in the preparation of supercapacitor electrode materials.

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