Preparation method of nitrogen-oxygen co-doped modified charcoal and biomass charcoal

Abstract

The invention discloses a preparation method of nitrogen-oxygen co-doped modified biochar and biomass charcoal, and the method comprises the following steps: adding crushed biomass into a carbonate solution, uniformly mixing, drying, grinding into powder, and pyrolyzing in an inert gas atmosphere to obtain first biochar; washing and drying the first biochar, mixing the first biochar with a zeolite imidazole solution containing a metal salt, drying and grinding the mixture, mixing the mixture with melamine, and pyrolyzing the mixture in an inert gas atmosphere to obtain second biochar; the second biochar is washed and dried after being subjected to acid pickling, and the modified carbon nanotube biochar is obtained. Therefore, melamine pyrolysis gas is catalyzed to grow the carbon nanotubes on the carbon material, so that the charge transfer resistance of the carbon material is reduced, the electrochemical performance of the carbon material is improved, the resistance of modified biochar can be remarkably reduced, the conductivity of the biochar can be improved, and the electrochemical performance of porous carbon is improved.

Description

Technical Field

[0001] The present invention relates to the field of biomass carbon production, and in particular to a preparation method of modified biomass carbon. Background Art

[0002] Biomass energy, as an emerging energy source, has attracted widespread attention. By pyrolysis, biomass energy is converted into a general carbon material. Due to its unique structural advantages, including a large specific surface area, good electron diffusion channels, and easily adjustable controllable active sites, carbon materials have received increasing attention and favor in the fields of supercapacitors, catalysts, and adsorption.

[0003] Currently, existing carbon materials also have the disadvantages of complex preparation and high cost. Especially in the traditional preparation process, the most widely used chemicals are toxic and highly corrosive zinc chloride and potassium hydroxide. In this process, there are not only safety hazards but also great corrosion to equipment, which is not conducive to large-scale production.

[0004] When carbon materials are applied to supercapacitors, they often generate a large resistance, which seriously limits the electron transfer rate. At the same time, as a one-dimensional carbon material, carbon nanotubes have excellent electrical conductivity, high chemical stability, and mechanical stability. However, the direct use of carbon nanotubes as carbon materials has unsatisfactory electrochemical performance, so it is not conducive to the application of this carbon material in the field of capacitors. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides a preparation method of nitrogen and oxygen co-doped modified biochar and biomass carbon.

[0006] According to a preparation method of nitrogen and oxygen co-doped modified biochar as a catalyst in the first aspect of the embodiments of the present invention, the method includes the following steps: Adding the crushed biomass into a carbonate solution, mixing evenly, drying, grinding into powder, and pyrolyzing in an inert gas atmosphere to obtain the first biochar; After washing and drying the first biochar, mixing it with a zeolite imidazole solution containing metal salts, drying and grinding, mixing with melamine, and pyrolyzing in an inert gas atmosphere to obtain the second biochar; Performing acid washing on the second biochar, washing and drying to obtain modified carbon nanotube biochar.

[0007] More specifically, in step one, adding the crushed biomass material into a potassium bicarbonate solution to obtain a first mixture; Wherein, first, wash the biomass with water to clean the dust on the surface of the biomass, then dry it in an oven at a low temperature or in the sun, use a crusher to crush it, and screen out bamboo powder with a mesh size of 80 - 120 meshes as the biomass raw material for standby; Then, 6 g of potassium bicarbonate was weighed and placed in a beaker, and 50 ml of deionized water was added to prepare a mixed solution. Then, the pre-mixed biomass raw material was added to the prepared potassium bicarbonate solution, and it was stirred thoroughly for 12 hours to make the biomass raw material evenly dispersed in the mixed solution, increasing the contact area between the biomass and the alkali metal carbonate to achieve a better activation effect.

[0008] Step 2: The above first mixture was dried and then ground to obtain a powdery second mixture; Specifically, after the biomass and the mixed solution were stirred evenly, they were placed in a blast dryer and dried for 24 hours. After drying, a solid mixture was obtained and ground into a powder.

[0009] Step 3: The above powdery second mixture was pyrolyzed in an inert gas atmosphere to obtain the first biochar; Specifically, the second mixture could be placed in a porcelain boat and transferred to a quartz tube. Before putting it into the tubular furnace, a nitrogen flow rate of 200 ml / min was used to evacuate the air in the pyrolysis tube. The pre-carbonization was carried out in a nitrogen atmosphere. The pyrolysis temperature was 850 °C, the heating rate was 10 °C / min, the nitrogen rate was 50 ml / min, and it was maintained for 1 h after reaching the specified temperature. After the quartz tube was taken out of the pyrolysis furnace, it was cooled to room temperature in the air, and thus the solid product in the quartz tube was obtained. The product was filtered, washed, and dried to obtain biochar 1.

[0010] Step 4: The obtained biochar was dispersed with metals through zeolite and imidazole framework; Specifically, a certain mass of cobalt nitrate hexahydrate was weighed and dispersed in an ethanol solution as solution A. Then, a certain mass of 2-methylimidazole was weighed and dissolved in an ethanol solution as solution B. Solution B was slowly poured into solution A as a mixed solution. It was stirred at room temperature for ten minutes. Then, a certain amount of biochar 1 was added to the mixed solution and stirred at room temperature for 12 h. After stirring, the solvent was evaporated in a rotary evaporator. The evaporation temperature was set at 45 °C, and the rotation speed was set at 80 rad / min. After evaporation, it was placed in an oven for drying. After drying, a black solid mixture was obtained and ground into a powder; Step 5: Preparation of carbon nanotube-modified biochar; Specifically, the powder obtained in Step 4 was physically ground with a certain amount of melamine for 5 min to obtain a mixture. The mixture was placed in a porcelain boat and transferred to a quartz tube. Before putting it into the tubular furnace, a nitrogen flow rate of 200 ml / min was used to evacuate the air in the pyrolysis tube.

[0011] The pre-carbonization is carried out in a nitrogen atmosphere. The pyrolysis temperature is 850 °C, the heating rate is 10 °C / min, the nitrogen rate is 50 ml / min. After reaching the specified temperature, it is maintained for 2 hours. After taking out the quartz tube from the pyrolysis furnace, it is cooled to room temperature in air, thus obtaining the biochar 2 in the quartz tube.

[0012] Then, the biochar 2 is stirred in 5M nitric acid at 50 °C for 12 hours. Finally, it is washed with deionized water and absolute ethanol until the pH of the filtrate is neutral, and dried overnight in an oven at 105 °C to obtain the carbon nanotube-modified biochar.

[0013] In the present invention, potassium bicarbonate is mixed with biomass for pyrolysis. Through the activation of potassium bicarbonate, the biochar has a honeycomb-like rich pore structure. Then, the metal salt is dispersed into the imidazole solution, and the porous biochar is added to this mixed solution. In this process, the metal and imidazole are paired to form a metal-organic framework, solving the problem of uneven dispersion of metal agglomeration. Subsequently, the mixed sample is co-pyrolyzed with melamine. Through the metal-catalyzed pyrolysis gas of melamine, carbon nanotubes are grown on the biochar. At the same time, melamine also plays a role in nitrogen doping.

[0014] A biomass carbon in the second aspect of the embodiment of the present invention is a biomass carbon prepared by using the preparation method of any of the above nitrogen and oxygen co-doped modified biochars.

[0015] Beneficial effects

[0016] The invention uses transition metal to catalyze the pyrolysis gas of melamine to grow carbon nanotubes on the carbon material, thereby reducing the charge transfer resistance of the carbon material and improving the electrochemical performance of the carbon material. In this way, combining carbon nanotubes and porous activated carbon can significantly reduce the resistance of the modified biochar and improve the conductivity of the biochar under the condition of having little influence on the electrochemical performance of the porous carbon, thereby improving the electrochemical performance of the porous carbon. At the same time, after treatment with melamine and nitric acid, the nitrogen-containing functional groups and oxygen-containing functional groups of the carbon material are increased, thereby improving the wettability of the material and further improving the electrochemical performance of the material.

[0017] Since the carbon nanotube biochar sacrifices some pores to grow carbon nanotubes, the specific capacitance of the carbon nanotube-modified biochar will be reduced compared with the biochar material activated by potassium bicarbonate. Therefore, by subjecting the carbon nanotube biochar to secondary treatment with nitric acid, it is possible to dissolve and catalyze the metal simple substance after carbon nanotubes with nitric acid, and at the same time introduce oxygen-containing functional groups, thereby enhancing the pseudocapacitance performance of the material applied to the supercapacitor and further improving the wettability of the carbon material, obtaining a nitrogen and oxygen co-doped carbon nanotube-modified biochar with improved specific capacitance and conductivity.

[0018] The carbon nanotube modified biochar prepared by the present invention combines the advantages of carbon nanotubes and porous carbon, obtaining the modified biochar C-CNTO, and generating a better specific surface area, with a significant reduction in the electrochemical impedance of the material.

[0019] In addition, the raw material of moso bamboo biomass used in the present invention has a wide source and low cost, is suitable for industrial production, fully excavates the potential value of moso bamboo, and achieves the effect of making the best use of everything. Brief Description of the Drawings

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, wherein: Figure 1 is a 5um scanning electron microscope schematic diagram of nitrogen and oxygen co-doped carbon nanotube modified biochar according to an embodiment of the present invention; Figure 2 is a 1um scanning electron microscope schematic diagram of nitrogen and oxygen co-doped carbon nanotube modified biochar according to an embodiment of the present invention; Figure 3 is the specific capacitance and electrochemical Nyquist diagram of the carbon material before and after modification according to an embodiment of the present invention. Detailed Description of the Embodiments

[0021] The embodiments of the present invention will be described in detail below. The embodiments described with reference to the drawings are exemplary.

[0022] Example 1

[0023] In this example, the effects of different biomasses on the performance of carbon nanotube modified biochar were tested, while keeping other factors unchanged, and the carbon nanotube modified biochar material was prepared according to the following preparation method; Step 1: Add the crushed biomass material into a potassium bicarbonate solution to obtain mixture 1; Specifically, first wash corn straw, moso bamboo, and birch with water respectively. After cleaning the dust on the surfaces of corn straw, moso bamboo, and birch, dry them at a low temperature in an oven or in the sun, and then use a pulverizer to crush them. Screen out corn straw, moso bamboo, and birch powders with a mesh size of 80-120 as the biomass raw materials for standby; then weigh 6 g of potassium bicarbonate and place it in a beaker, add 50 ml of deionized water to prepare a mixed solution, and then add the pre-mixed biomass raw materials into the prepared potassium bicarbonate solution, and stir well for 12 hours to make the biomass raw materials evenly dispersed in the mixed solution, increasing the contact area between the biomass and the alkali metal carbonate to achieve a better activation effect.

[0024] Step 2: After drying the above mixture, grind it to obtain a powdery mixture 2. Specifically, after the biomass and the mixed solution are fully stirred and homogenized, place them in a blast dryer and dry for 24 hours. After drying is completed, a solid mixture will be obtained, and it is ground into a powder.

[0025] Step 3: Pyrolyze the above powdery solid in an inert gas atmosphere to obtain biochar 1. Specifically, the second mixture can be placed in a porcelain boat and transferred to a quartz tube. Before placing it in a tubular furnace, use a nitrogen gas flow rate of 200 ml / min to evacuate the air in the pyrolysis tube. Pre-carbonization is carried out in a nitrogen atmosphere. The pyrolysis temperature is set at 850 °C, the heating rate is 10 °C / min, the nitrogen gas rate is 50 ml / min, and it is maintained for 1 hour after reaching the specified temperature. After taking the quartz tube out of the pyrolysis furnace, cool it to room temperature in the air, so as to obtain the solid product in the quartz tube. Filter, wash, and dry this product to obtain biochar 1.

[0026] Step 4: Disperse the obtained biochar through zeolite and imidazole framework for metal.

[0027] Specifically, first weigh a certain mass of cobalt nitrate hexahydrate and disperse it in an ethanol solution as solution A. Then weigh a certain mass of 2-methylimidazole and dissolve it in an ethanol solution as solution B. Slowly pour solution B into solution A as a mixed solution. Stir at room temperature for ten minutes. Then add a certain amount of biochar 1 to the mixed solution and stir at room temperature for 12 h. After stirring is completed, evaporate the solvent in a rotary evaporator. The evaporation temperature is set at 45 °C and the rotation speed is set at 80 rad / min. After evaporation is completed, place it in an oven for drying. After drying is completed, a black solid mixture is obtained and ground to a powdery state; Step 5: Preparation of carbon nanotube-modified biochar; Specifically, physically grind the powder obtained in Step 4 with a certain amount of melamine for 5 min to obtain a mixture. Place the mixture in a porcelain boat and transfer it to a quartz tube. Before placing it in a tubular furnace, use a nitrogen gas flow rate of 200 ml / min to evacuate the air in the pyrolysis tube. Pre-carbonization is carried out in a nitrogen atmosphere. The pyrolysis temperature is 850 °C, the heating rate is 10 °C / min, the nitrogen gas rate is 50 ml / min, and it is maintained for 2 hours after reaching the specified temperature. After taking the quartz tube out of the pyrolysis furnace, cool it to room temperature in the air, so as to obtain biochar 2 in the quartz tube. Then stir biochar 2 in 5M nitric acid at 50 °C for 12 hours. Finally, wash it with deionized water and absolute ethanol until the pH of the filtrate is neutral, and dry it overnight in an oven at 105 °C to obtain carbon nanotube-modified biochar.

[0028] The prepared biochar was collected, made into a symmetric supercapacitor, and its performance was tested on an electrochemical workstation. The specific capacitance of the prepared carbon material at a current density of 1 A / g is shown in Table 1: Table 1. Specific capacitance and specific surface area of carbon nanotube-modified biochar prepared from different biomasses Serial number Biomass Specific capacitance (F / g) <![CDATA[Specific surface area (m 2 / g)]]> 1 Corn straw 204.2 2011.4 2 Moso bamboo 246.2 2347.8 3 Birch 230.1 2206.3 As can be seen from the above table, the modified carbon material prepared from moso bamboo has a larger specific surface area and higher capacitance performance. Therefore, moso bamboo can be preferably used as the biomass precursor.

[0029] Example 2

[0030] In this example, the effects of different activators on the performance of carbon nanotube-modified biochar were tested. Other factors were kept unchanged, and the carbon nanotube-modified biochar material was prepared according to the following preparation method.

[0031] Step 1: Add the crushed biomass material to a potassium bicarbonate solution to obtain mixture 1; Specifically, first wash the moso bamboo with water, clean the dust on the surface of the moso bamboo, then dry it at a low temperature in an oven or in the sun, use a pulverizer to crush it, and screen out moso bamboo powder with a mesh size of 80 - 120 as the biomass raw material for standby; then weigh 6 g of potassium carbonate, potassium bicarbonate, and sodium carbonate respectively and place them in a beaker, add 50 ml of deionized water to prepare a mixed solution, and then add the pre-mixed biomass raw material to the prepared potassium bicarbonate solution, and stir well for 12 hours to make the biomass raw material evenly dispersed in the mixed solution, increasing the contact area between the biomass and the alkali metal carbonate to achieve a better activation effect.

[0032] Step 2: Dry and then grind the above mixture to obtain powdery mixture 2; specifically, when the biomass and the mixed solution are stirred evenly, put them into a blast dryer and dry for 24 hours. After drying, a solid mixture will be obtained, and it is ground into a powdery form.

[0033] Step 3: Pyrolyze the above powdery solid in an inert gas atmosphere to obtain biochar 1; specifically, the second mixture can be placed in a porcelain boat and transferred to a quartz tube. Before putting it into the tubular furnace, use a nitrogen flow rate of 200 ml / min to evacuate the air in the pyrolysis tube. The pre-carbonization is carried out in a nitrogen atmosphere. The pyrolysis temperature is set at 850 °C, the heating rate is 10 °C / min, the nitrogen rate is 50 ml / min, and it is kept for 1 hour after reaching the specified temperature. After taking the quartz tube out of the pyrolysis furnace, it is cooled to room temperature in the air, and thus the solid product in the quartz tube is obtained. The product is filtered, washed, and dried to obtain biochar 1.

[0034] Step 4: Disperse the obtained biochar through zeolite and imidazole framework for metal dispersion.

[0035] Specifically, first weigh a certain mass of cobalt nitrate hexahydrate and disperse it in an ethanol solution as solution A. Then weigh a certain mass of 2-methylimidazole and dissolve it in an ethanol solution as solution B. Slowly pour solution B into solution A as a mixed solution. Stir at room temperature for ten minutes. Then add a certain amount of biochar 1 to the mixed solution and stir at room temperature for 12 h. After stirring, evaporate the solvent in a rotary evaporator. The evaporation temperature is set at 45 °C and the rotation speed is set at 80 rad / min. After evaporation, place it in an oven for drying. After drying is completed, a black solid mixture is obtained and ground into a powder; Step 5: Preparation of carbon nanotube-modified biochar; Specifically, physically grind the powder obtained in step 4 with a certain amount of melamine for 5 min to obtain a mixture. Place the mixture in a porcelain boat and transfer it to a quartz tube. Before placing it in a tubular furnace, use a nitrogen flow rate of 200 ml / min to evacuate the air in the pyrolysis tube. Pre-carbonization is carried out in a nitrogen atmosphere. The pyrolysis temperature is 850 °C, the heating rate is 10 °C / min, the nitrogen rate is 50 ml / min, and it is maintained for 2 hours after reaching the specified temperature. After taking the quartz tube out of the pyrolysis furnace, cool it to room temperature in the air to obtain biochar 2 in the quartz tube. Then stir biochar 2 in 5M nitric acid at 50 °C for 12 hours. Finally, wash it with deionized water and absolute ethanol until the pH of the filtrate is neutral, and place it in an oven at 105 °C overnight to obtain carbon nanotube-modified biochar.

[0036] Collect the prepared biochar, fabricate a symmetric supercapacitor and conduct performance tests on an electrochemical workstation. The specific capacitance of the prepared carbon material at a current density of 1 A / g is shown in Table 2: Table 2. Specific capacitance and specific surface area of carbon nanotube-modified biochar prepared with different activators Serial number Biomass Specific capacitance (F / g) <![CDATA[Specific surface area (m 2 / g)]]> 1 Potassium carbonate 196.3 1969.3 2 Potassium bicarbonate 226.2 2347.8 3 Sodium bicarbonate 197.4 2016.8 It can be seen from the above table that by using different types of activators, the specific surface area and specific capacitance values of the prepared modified carbon materials are different. Especially when the activator is potassium bicarbonate, the specific surface area is the highest and the specific capacitance value is also the highest.

[0037] Example 3

[0038] In this example, the effect of different potassium bicarbonate ratios on the performance of carbon nanotube-modified biochar was tested, keeping other factors unchanged, and carbon nanotube-modified biochar materials were prepared according to the following preparation method.

[0039] Among them, the moso bamboo collected from the forest farm is washed, pulverized, and then 2 g of moso bamboo and different masses of potassium bicarbonate are weighed. And the high-performance electrode material is prepared according to the following preparation method; Step 1: Add the pulverized biomass material into the potassium bicarbonate solution to obtain mixture 1; Specifically, first wash the biomass with water to clean the dust on the surface of the biomass, then dry it at a low temperature in an oven or in the sun, use a pulverizer to pulverize it, and screen out moso bamboo powder with a mesh size of 80-120 as the biomass raw material for standby; then weigh 1 g, 2 g, 4 g, 6 g, 8 g, and 10 g of potassium bicarbonate respectively and place them in a beaker, add 50 ml of deionized water to prepare a mixed solution, and then add the pre-mixed biomass raw material into the prepared potassium bicarbonate solution, and stir well for 12 hours to make the biomass raw material evenly dispersed in the mixed solution, increasing the contact area between the biomass and the alkali metal carbonate to achieve a better activation effect.

[0040] Step 2: After drying the above mixture, grind it to obtain powdery mixture 2; specifically, when the biomass and the mixed solution are stirred evenly, put them into a blast dryer and dry for 24 hours. After drying, a solid mixture will be obtained, and it is ground into a powdery form.

[0041] Step 3: Pyrolyze the above powdery solid in an inert gas atmosphere to obtain biochar 1; specifically, the second mixture can be placed in a porcelain boat and transferred to a quartz tube. Before putting it into the tubular furnace, use a nitrogen flow rate of 200 ml / min to evacuate the air in the pyrolysis tube. Pre-carbonization is carried out in a nitrogen atmosphere, the pyrolysis temperature is 850 °C, the heating rate is 10 °C / min, the nitrogen rate is 50 ml / min, and it is maintained for 1 h after reaching the specified temperature. After taking the quartz tube out of the pyrolysis furnace, it is cooled to room temperature in the air, so as to obtain the solid product in the quartz tube. The product is filtered, washed, and dried to obtain biochar 1.

[0042] Step 4: Disperse the obtained biochar through zeolite and imidazole framework for metal.

[0043] Specifically, first weigh a certain mass of cobalt nitrate hexahydrate and disperse it in an ethanol solution as solution A. Then weigh a certain mass of 2-methylimidazole and dissolve it in an ethanol solution as solution B. Slowly pour solution B into solution A as a mixed solution. Stir at room temperature for ten minutes. Then add a certain amount of biochar 1 to the mixed solution and stir at room temperature for 12 h. After stirring, evaporate the solvent in a rotary evaporator. The evaporation temperature is set at 45 °C and the rotation speed is set at 80 rad / min. After evaporation, put it into an oven for drying. After drying, a black solid mixture is obtained and ground into a powdery form; Step 5: Preparation of carbon nanotube-modified biochar; Specifically, the powder obtained in Step 4 is physically ground with a certain amount of melamine for 5 min to obtain a mixture. The mixture is placed in a porcelain boat and transferred into a quartz tube. Before putting it into the tubular furnace, the air in the pyrolysis tube is evacuated with a nitrogen flow rate of 200 ml / min. The pre-carbonization is carried out in a nitrogen atmosphere. The pyrolysis temperature is 850 °C, the heating rate is 10 °C / min, the nitrogen rate is 50 ml / min, and it is maintained for 2 hours after reaching the specified temperature. After the quartz tube is taken out of the pyrolysis furnace, it is cooled to room temperature in the air, thereby obtaining biochar 2 in the quartz tube. Then, biochar 2 is stirred in 5M nitric acid at 50 °C for 12 hours. Finally, it is washed with deionized water and absolute ethanol until the pH of the filtrate is neutral, and it is dried overnight in an oven at 105 °C to obtain carbon nanotube-modified biochar.

[0044] The prepared biochar is collected, made into a symmetric supercapacitor, and its performance is tested on an electrochemical workstation. The specific capacitance of the prepared carbon material at a current density of 1 A / g is shown in Table 3: Table 3. Specific capacitance and specific surface area of carbon nanotube-modified biochar prepared with different potassium bicarbonates Serial number Biomass: Potassium bicarbonate Specific capacitance (F / g) <![CDATA[Specific surface area (m 2 / g)]]> 1 1：0.5 170.4 1131.9 2 1：1 186.6 1223.1 3 1：2 223.6 1864.8 4 1：3 246.2 2347.8 5 1：4 185.6 1813.4 As can be seen from the above table, different potassium bicarbonate ratios have a great influence on the specific capacitance of the final modified carbon. With the increase of the potassium bicarbonate ratio, the specific capacitance increases significantly and reaches the maximum value at a mass ratio of 1:3. Further increasing the amount of potassium bicarbonate, the specific capacitance drops to 185.6 F / g. This may be due to the pore structure collapse caused by excessive activation caused by too much potassium hydroxide, which in turn hinders the adsorption of ions and ultimately leads to the decrease of the specific capacitance. A similar rule can also be obtained from the specific surface area.

[0045] Example 4

[0046] In this example, the influence of different pyrolysis temperatures on the performance of carbon nanotube-modified biochar is tested. Keeping other factors unchanged, only the pyrolysis temperature is changed, and the carbon nanotube-modified biochar material is prepared according to the following preparation method; Step 1: Add the crushed biomass material into the potassium bicarbonate solution to obtain mixture 1; Specifically, first wash the biomass with water to clean the dust on the surface of the biomass, then dry it at a low temperature in an oven or in the sun, crush it using a crusher, and screen out bamboo powder with a mesh size of 80 - 120 as the biomass raw material for standby; then weigh 6 g of potassium bicarbonate and place it in a beaker, add 50 ml of deionized water to prepare a mixed solution, and then add the pre - mixed biomass raw material to the prepared potassium bicarbonate solution, and stir well for 12 hours to make the biomass raw material evenly dispersed in the mixed solution, increasing the contact area between the biomass and the alkali metal carbonate to achieve a better activation effect.

[0047] Step 2: After drying the above - mentioned mixture, grind it to obtain a powdery mixture 2; specifically, when the biomass and the mixed solution are stirred evenly, put them into a blast dryer and dry for 24 hours. After drying, a solid mixture will be obtained, and it is ground into a powdery form.

[0048] Step 3: Pyrolyze the above - mentioned powdery solid under an inert gas atmosphere to obtain biochar 1; specifically, the second mixture can be placed in a porcelain boat and transferred to a quartz tube. Before putting it into the tubular furnace, use a nitrogen gas flow rate of 200 ml / min to evacuate the air in the pyrolysis tube. The pre - carbonization is carried out under a nitrogen atmosphere. The pyrolysis temperatures are set at 800 °C, 850 °C, and 900 °C respectively, the heating rate is 10 °C / min, the nitrogen gas rate is 50 ml / min, and it is maintained for 1 hour after reaching the specified temperature. After taking the quartz tube out of the pyrolysis furnace, it is cooled to room temperature in the air, and thus the solid product in the quartz tube is obtained. The product is filtered, washed, and dried to obtain biochar 1.

[0049] Step 4: Disperse the obtained biochar through zeolite and imidazole framework for metal dispersion.

[0050] Specifically, first weigh a certain mass of cobalt nitrate hexahydrate and disperse it in an ethanol solution as solution A. Then weigh a certain mass of 2 - methylimidazole and dissolve it in an ethanol solution as solution B. Slowly pour solution B into solution A as a mixed solution. Stir at room temperature for ten minutes. Then add a certain amount of biochar 1 to the mixed solution and stir at room temperature for 12 h. After the stirring is completed, evaporate the solvent in a rotary evaporator. The evaporation temperature is set at 45 °C and the rotation speed is set at 80 rad / min. After evaporation is completed, put it into an oven for drying. After drying is completed, a black solid mixture is obtained, and it is ground into a powdery form; Step 5: Preparation of carbon nanotube - modified biochar; Specifically, the powder obtained in step 4 was physically ground with a certain amount of melamine for 5 minutes to obtain a mixture. The mixture was placed in a porcelain boat and transferred to a quartz tube. Before being placed in a tubular furnace, a nitrogen flow of 200 ml / min was used to evacuate the air in the pyrolysis tube. Pre-carbonization was carried out under a nitrogen atmosphere. The pyrolysis temperature was 850 ° C, the heating rate was 10 ° C / min, and the nitrogen flow rate was 50 ml / min. After reaching the specified temperature, it was maintained for 2 hours. The quartz tube was removed from the pyrolysis furnace and cooled to room temperature in air to obtain biochar 2 in the quartz tube. Biochar 2 was then stirred in 5M nitric acid at 50 ° C for 12 hours. Finally, it was washed with deionized water and anhydrous ethanol until the pH of the filtrate was neutral. It was then dried in a 105 ° C oven overnight to obtain carbon nanotube-modified biochar.

[0051] The prepared biochar was collected and made into a symmetrical supercapacitor and the performance was tested on an electrochemical workstation. The specific capacitance of the prepared carbon material at a current density of 1 A / g is shown in Table 4: Table 4. Specific capacitance and specific surface area of carbon nanotube-modified biochar prepared at different pyrolysis temperatures Serial number Pyrolysis temperature (°C) Specific capacitance (F / g) <![CDATA[Specific surface area (m 2 / g)]]> 1 750 186.4 1769.2 2 800 220.3 2034.4 3 850 246.2 2347.8 4 900 223.1 2130.4 5 950 190.6 1854.5 It can be seen from the above table that different pyrolysis temperatures have a great influence on the specific capacitance of the final modified carbon. As the temperature increases, the specific capacitance increases significantly, reaching a maximum value at 850 °C. Further increasing the temperature, the specific capacitance decreases by 137 F / g. This may be due to the collapse of the pore structure caused by excessive activation due to excessive temperature, which in turn hinders the adsorption and decomposition of ions, ultimately leading to a decrease in specific capacitance.

[0052] Example 5

[0053] In this example, the effects of different pyrolysis times on the properties of carbon nanotube-modified biochar were tested, and other factors were kept constant, and carbon nanotube-modified biochar materials were prepared according to the following preparation method; Step 1: adding the crushed biomass material into a potassium bicarbonate solution to obtain a mixture 1; Specifically, the biomass is first washed with water to clean the dust on the surface of the biomass, then dried in an oven at low temperature or in the sun, crushed with a grinder, and 80-120 mesh bamboo powder is screened out as a biomass raw material for later use; then 6 g of potassium bicarbonate is weighed and placed in a beaker, 50 ml of deionized water is added to prepare a mixed solution, and then the premixed biomass raw material is added to the prepared potassium bicarbonate solution, and the mixture is fully stirred for 12 hours to uniformly disperse the biomass raw material in the mixed solution, thereby increasing the contact area between the biomass and the alkali metal carbonate to achieve a better activation effect.

[0054] Step 2: The above mixture is dried and then ground to obtain a powdery mixture 2. Specifically, after the biomass and the mixed solution are fully stirred and homogenized, they are placed in a blast dryer and dried for 24 hours. After drying is completed, a solid mixture is obtained, which is ground into a powder.

[0055] Step 3: The above powdery solid is pyrolyzed in an inert gas atmosphere to obtain biochar 1. Specifically, the second mixture can be placed in a porcelain boat and transferred to a quartz tube. Before placing it in a tubular furnace, a nitrogen gas flow rate of 200 ml / min is used to evacuate the air in the pyrolysis tube. The pre-carbonization is carried out in a nitrogen atmosphere. The pyrolysis temperature is set at 850 °C, the heating rate is 10 °C / min, the nitrogen gas rate is 50 ml / min, and it is maintained for 1 hour after reaching the specified temperature. After the quartz tube is taken out of the pyrolysis furnace, it is cooled to room temperature in the air, so as to obtain the solid product in the quartz tube. The product is filtered, washed and dried to obtain biochar 1.

[0056] Step 4: The obtained biochar 1 is dispersed with metals through zeolite imidazole framework.

[0057] Specifically, first weigh a certain mass of cobalt nitrate hexahydrate and disperse it in an ethanol solution as solution A. Then weigh a certain mass of 2-methylimidazole and dissolve it in an ethanol solution as solution B. Slowly pour solution B into solution A as a mixed solution. Stir at room temperature for ten minutes. Then add a certain amount of biochar 1 to the mixed solution and stir at room temperature for 12 h. After stirring is completed, the solvent is evaporated in a rotary evaporator. The evaporation temperature is set at 45 °C and the rotation speed is set at 80 rad / min. After evaporation is completed, it is placed in an oven for drying. After drying is completed, a black solid mixture is obtained, which is ground into a powder; Step 5: Preparation of carbon nanotube modified biochar; Specifically, the powder obtained in step 4 is physically ground with a certain amount of melamine for 5 min to obtain a mixture. The mixture is placed in a porcelain boat and transferred to a quartz tube. Before placing it in a tubular furnace, a nitrogen gas flow rate of 200 ml / min is used to evacuate the air in the pyrolysis tube. The pre-carbonization is carried out in a nitrogen atmosphere. The pyrolysis temperatures are 850 °C respectively, the heating rate is 10 °C / min, the nitrogen gas rate is 50 ml / min, and it is maintained for 1 h, 1.5 h, 2 h, 2.5 h and 3 h respectively after reaching the specified temperature. After the quartz tube is taken out of the pyrolysis furnace, it is cooled to room temperature in the air, so as to obtain biochar 2 in the quartz tube.

[0058] Then biochar 2 is stirred in 5M nitric acid at 50 °C for 12 hours. Finally, it is washed with deionized water and absolute ethanol until the pH of the filtrate is neutral, and it is placed in an oven at 105 °C overnight to obtain carbon nanotube modified biochar.

[0059] Collect the prepared biochar, fabricate a symmetric supercapacitor, and conduct performance tests on an electrochemical workstation. The specific capacitance of the prepared carbon material at a current density of 1 A / g is shown in Table 5: Table 5. Specific Capacitance and Specific Surface Area of Carbon Nanotube-Modified Biochar Prepared at Different Residence Times Serial number Residence time (h) Specific capacitance (F / g) <![CDATA[Specific surface area (m 2 / g)]]> 1 1 200.3 2264.3 2 1.5 210.6 2278.3 3 2 246.2 2347.8 4 2.5 223.6 2246.5 5 3 216.3 2204.1 It can be seen from the above table that different residence times have a great influence on the specific capacitance of the final modified carbon. As the residence time increases, the specific capacitance increases significantly and reaches the maximum value at 2 h. This may be because the growth time of carbon nanotubes is insufficient when the residence time is short, resulting in some melamine pyrolysis gas blocking the pores of the material. Further increasing the residence time, the specific capacitance remains basically unchanged, which may be because the growth of carbon nanotubes has ended, so the difference in long time is not significant. Considering the time cost, 2 h is adopted as the final residence time.

[0060] Example 6

[0061] In this example, the effects of testing different metal salts on the performance of carbon nanotube-modified biochar were explored. Keeping other factors unchanged, only the pyrolysis temperature was changed, and carbon nanotube-modified biochar materials were prepared according to the following preparation method; Step 1. Add the crushed biomass material into a potassium bicarbonate solution to obtain mixture 1; Specifically, first wash the moso bamboo with water, clean the dust on the surface of the moso bamboo, then dry it at a low temperature in an oven or in the sun, use a pulverizer to crush it, and screen out moso bamboo powder with a mesh size of 80 - 120 as the biomass raw material for standby; then weigh 6 g of potassium bicarbonate and place it in a beaker, add 50 ml of deionized water to prepare a mixed solution, and then add the pre-mixed biomass raw material into the prepared potassium bicarbonate solution, and stir well for 12 hours to make the biomass raw material evenly dispersed in the mixed solution, increasing the contact area between the biomass and the alkali metal carbonate to achieve a better activation effect.

[0062] Step 2. After drying the above mixture, grind it to obtain powdery mixture 2; specifically, when the biomass and the mixed solution are stirred evenly, put them into a blast dryer and dry for 24 hours. After drying is completed, a solid mixture will be obtained, and it will be ground into a powdery form.

[0063] Step 3: Pyrolyze the above powdery solid under an inert gas atmosphere to obtain Biochar 1; specifically, the second mixture can be placed in a porcelain boat and transferred to a quartz tube. Before putting it into a tubular furnace, use a nitrogen gas flow rate of 200 ml / min to evacuate the air in the pyrolysis tube. The pre-carbonization is carried out under a nitrogen atmosphere. The pyrolysis temperature is set at 850 °C, the heating rate is 10 °C / min, the nitrogen gas rate is 50 ml / min, and it is maintained for 1 hour after reaching the specified temperature. After taking out the quartz tube from the pyrolysis furnace, it is cooled to room temperature in the air, so as to obtain the solid product in the quartz tube. Filter, wash, and dry this product to obtain Biochar 1.

[0064] Step 4: Disperse the obtained biochar through zeolite and imidazole framework for metal dispersion.

[0065] Specifically, first weigh a certain mass of ferric chloride and cobalt nitrate hexahydrate respectively, and disperse them in an ethanol solution as Solution A. Then weigh a certain mass of 2-methylimidazole and dissolve it in an ethanol solution as Solution B. Slowly pour Solution B into Solution A as a mixed solution. Stir at room temperature for ten minutes. Then add a certain amount of Biochar 1 to the mixed solution and stir at room temperature for 12 h. After the stirring is completed, evaporate the solvent in a rotary evaporator. The evaporation temperature is set at 45 °C and the rotation speed is set at 80 rad / min. After evaporation is completed, put it into an oven for drying. After drying is completed, a black solid mixture is obtained and ground into a powder; Step 5: Preparation of carbon nanotube-modified biochar; Specifically, physically grind the powder obtained in Step 4 with a certain amount of melamine for 5 min to obtain a mixture. Place the mixture in a porcelain boat and transfer it to a quartz tube. Before putting it into a tubular furnace, use a nitrogen gas flow rate of 200 ml / min to evacuate the air in the pyrolysis tube. The pre-carbonization is carried out under a nitrogen atmosphere. The pyrolysis temperature is 850 °C, the heating rate is 10 °C / min, the nitrogen gas rate is 50 ml / min, and it is maintained for 2 hours after reaching the specified temperature. After taking out the quartz tube from the pyrolysis furnace, it is cooled to room temperature in the air, so as to obtain Biochar 2 in the quartz tube. Then stir Biochar 2 in 5M nitric acid at 50 °C for 12 hours, and finally, wash it with deionized water and absolute ethanol until the pH of the filtrate is neutral, and dry it overnight in an oven at 105 °C to obtain carbon nanotube-modified biochar.

[0066] Collect the prepared biochar, make it into a symmetric supercapacitor and conduct performance tests on an electrochemical workstation. The specific capacitance of the prepared carbon material at a current density of 1 A / g is shown in Table 6: Table 6. Specific capacitance and specific surface area of carbon nanotube-modified biochar prepared with different metal salts Serial number Metal salt Specific capacitance (F / g) <![CDATA[Specific surface area (m 2 / g)]]> 1 Ferric chloride 220.6 1994.3 2 Cobalt nitrate hexahydrate 246.2 2347.8 3 Zinc nitrate hexahydrate 200.4 2176.5 As can be seen from the above table, when different types of metal salts are used, the specific surface area and specific capacitance values of the prepared modified carbon materials are different. Especially when the metal is cobalt nitrate hexahydrate, the specific surface area is the highest and the specific capacitance value is also the highest.

[0067] At the same time, from Figure 1 and Figure 2 it can be known that the modified carbon produced by cobalt nitrate hexahydrate has a nanotube shape, Figure 3 indicating that after modification with carbon nanotubes, the impedance of the material has decreased.

[0068] Comparative Example 1 In this comparative example, to compare the effects on the performance of different carbon materials, mainly including: commercial carbon nanotubes, the first biochar produced in the first step of the present invention, and the carbon nanotube-modified biochar finally obtained in the present invention; at the same time, these three carbon materials are collected separately and made into symmetric supercapacitors.

[0069] The specific results are shown in Table 7: Table 7. Specific Capacitance and Specific Surface Area of Different Carbon Materials at 1 A / g Serial number Material Specific capacitance (F / g) <![CDATA[Specific surface area (m 2 / g)]]> 1 First biochar 225.2 2236 2 Carbon nanotube 110.6 140 3 Carbon nanotube modified biochar 246.2 2168 As can be seen from the above table, the specific surface area and specific capacitance values of the prepared modified carbon materials are not much different from those of the biochar in the first step, but are significantly better than commercial multi-walled carbon nanotubes, and Figure 3 indicating that after modification with carbon nanotubes, the impedance of the material has decreased.

[0070] Table 8. Elemental Analysis of Carbon Materials before and after Modification Serial number Material C(%) N(%) O(%) H(%) Co(%) 1 First-step biochar 91.8 0.7 6.4 1.1 - 2 Nitrogen and oxygen co-doped carbon nanotube modified biochar 83.4 2.6 12.6 0.7 0.7 As can be seen from the above table, for the biochar modified by nitrogen and oxygen co-doped carbon nanotubes, both its nitrogen element and oxygen element have increased, which improves the wettability of the material and brings pseudocapacitance, further increasing the specific capacitance of the material.

[0071] The carbon nanotube-modified biochar prepared in the present invention combines the advantages of carbon nanotubes and porous carbon, obtaining the modified biochar C-CNTO, which has the largest specific surface area. When applied to supercapacitors, it produces a high specific capacitance of 246.2 F / g. Compared with the capacitance of single activated carbon (225.2 F / g), it has increased by 10%. After modification with carbon nanotubes, the electrochemical impedance of the material has decreased significantly, further improving the conductivity of the material, and thus improving the electrochemical performance of the material.

[0072] The biomass carbon of the embodiment of the present invention includes the modified biomass carbon prepared by the preparation method in the above embodiment. Among them, the modified biomass carbon prepared by the preparation method in the above embodiment has good capacitor performance.

[0073] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example.

[0074] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A preparation method of nitrogen and oxygen co-doped modified biochar, characterized in that, The method includes the following steps: After adding the crushed biomass into a carbonate solution, mixing evenly, drying, grinding it into powder, and pyrolyzing it under an inert gas atmosphere, the first biochar is obtained; After washing and drying the first biochar, mixing it with a zeolitic imidazolate solution containing a metal salt, drying and grinding it, mixing it with melamine, and pyrolyzing it under an inert gas atmosphere, the second biochar is obtained; After pickling the second biochar, washing and drying it, the modified carbon nanotube biochar is obtained.

2. The preparation method of a nitrogen and oxygen co-doped modified biochar according to claim 1, wherein, The carbonate solution adopts any one of potassium carbonate solution, potassium bicarbonate solution, and sodium carbonate solution.

3. The preparation method of a nitrogen and oxygen co-doped modified biochar according to claim 2, characterized in that, The mixing mass ratio range of the biomass and the carbonate is 1:1 to 1:

4.

4. The preparation method of a nitrogen and oxygen co-doped modified biochar according to claim 3, characterized in that, The mixing mass ratio of the biomass and the potassium bicarbonate is 1:

3.

5. The preparation method of a nitrogen and oxygen co-doped modified biochar according to claim 1, wherein, When the crushed biomass is added into the carbonate solution, mixed evenly, dried, ground into powder, and pyrolyzed under an inert gas atmosphere, the temperature range is 800°C to 900°C.

6. The preparation method of a nitrogen and oxygen co-doped modified biochar according to claim 5, characterized in that, When the crushed biomass is added into the carbonate solution, mixed evenly, dried, ground into powder, and pyrolyzed under an inert gas atmosphere, the temperature is 850°C.

7. The preparation method of a nitrogen and oxygen co-doped modified biochar according to claim 1, characterized in that, In the zeolitic imidazolate solution containing a metal salt, the metal salt adopts any one of ferric chloride, cobalt(II) nitrate hexahydrate, and zinc(II) nitrate hexahydrate.

8. The preparation method of a nitrogen and oxygen co-doped modified biochar according to claim 1, characterized in that, After washing and drying the first biochar, mixing it with a zeolitic imidazolate solution containing a metal salt, drying and grinding it, mixing it with melamine, and pyrolyzing it under an inert gas atmosphere, the time range is 1.5H to 2.5H.

9. The preparation method of a nitrogen and oxygen co-doped modified biochar according to claim 1, characterized in that, The biomass is any one or a combination of at least two of corn straw, moso bamboo, and birch.

10. A biomass charcoal, characterized in that, The biomass char is the biomass char prepared by the preparation method of any nitrogen and oxygen co-doped modified biochar as claimed in claims 1 to 9.

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