CN114477172A - Preparation method and application of straw-based porous carbon with honeycomb-shaped pore structure - Google Patents

Abstract

The invention discloses a preparation method of boron, nitrogen and phosphorus co-doped straw-based biomass carbon with honeycomb pores, and belongs to the technical field of functional material preparation. The invention solves the problem of high cost of the electrode material of the conventional super capacitor. According to the invention, straws are used as raw materials, boric acid, urea and disodium hydrogen phosphate are respectively used as cheap boron source, nitrogen source and phosphorus source, high-temperature treatment is carried out under the protection of nitrogen atmosphere after potassium hydroxide activation, and then acid pickling and drying are carried out, thus finally obtaining the boron, nitrogen, phosphorus and other multi-element co-doped biomass porous carbon. The invention has low production cost and simple process, and the obtained material can be used as an electrode material of a super capacitor, and has high specific capacitance and excellent cycle performance.

Description

Preparation method and application of straw-based porous carbon with honeycomb pore structure

technical field

The invention relates to a preparation method and application of waste straw biomass porous carbon with honeycomb pores, and belongs to the technical field of functional material preparation.

Background technique

With the continuous development of science and technology and industrial engineering, non-renewable resources such as coal, oil, and natural gas are consumed in large quantities, resulting in an increasing scarcity of fossil energy. In order to continue to meet the development of global industry, researching new energy materials that can replace fossil energy is an urgent problem to be solved in today's era. As a major agricultural country in the world, my country has a large amount of waste straws that are burned or buried every year because they cannot be used, which has caused great harm to the global environment. According to data, the total amount of waste straw in my country in 2021 will exceed 800 million tons and is still increasing year by year. In response to the concept of energy conservation and environmental protection advocated by the state, local governments have actively taken measures to prohibit the large-scale incineration of waste straw, but due to the lack of formed technical means to utilize straw resources. In order not to affect normal agricultural production, it can only be packaged and incinerated for thermal power generation in the end. This method of generating electricity is not only inefficient, but also does not substantially improve the environmental pollution problem. Therefore, converting waste straws into biomass energy materials with high utilization value is an urgent problem to be solved.

As a new generation of energy storage materials, supercapacitors have attracted much attention since their inception. Compared with lithium-ion batteries, they show the advantages of fast charge and discharge rate, short time, high power density, good cycle stability, and long service life. The energy storage performance of supercapacitors mainly depends on the well-developed pore structure inside the electrode material. Therefore, designing electrode materials with excellent pore structure and electrical conductivity plays a key role in the development of high-performance supercapacitors. Carbon-based materials are widely used in supercapacitor electrode materials due to their excellent three-dimensional pore structure and electrical conductivity. Commonly used carbon-based electrode materials include graphene, carbon nanotubes, carbon nanospheres, and activated carbon. However, these electrode materials are often short-lived and expensive, which largely limit the practical application of supercapacitors. To this end, the present invention uses low-cost and environmentally friendly waste straw as the electrode material of the supercapacitor.

In recent years, natural biomass wastes such as crop straws and animal excrement can have better pore structure after being treated by certain activation methods due to their advantages of easy acquisition, simple preparation process, low cost, energy saving and environmental protection. Studies have shown that biomass waste usually has a relatively limited number of pores and a single pore structure generated by separate activation techniques.

SUMMARY OF THE INVENTION

The invention uses waste crop straws as biomass carbon sources, and solves the problems of low utilization rate of crop straws and environmental pollution caused by large-scale incineration of crop straws in my country. , urea and disodium hydrogen phosphate are used as cheap sources of boron, nitrogen and phosphorus, and by introducing boron, nitrogen and phosphorus atoms into the biomass carbon system to improve the surface wettability of biomass carbon materials, it can be further improved. Pore structure and electrical properties of biomass carbon materials. The straw-based biomass porous carbon prepared by the invention has excellent specific surface area and developed hierarchical pore structure, and is an ideal electrode material for supercapacitors. In addition, this method is of great significance for alleviating the environmental pollution caused by straw burning.

In order to achieve the above object, the present invention adopts the following technical solutions:

One aspect of the present invention provides a method for preparing straw-based porous carbon with a honeycomb pore structure, the method comprising the following steps:

Step 1: Wash the straw with deionized water and absolute ethanol in turn to remove surface impurities, then put it into an oven to dry, and then pulverize and sieve the dried straw to obtain straw powder;

Step 2: Mix the straw powder obtained in step 1 with potassium hydroxide, boric acid, urea, disodium hydrogen phosphate and deionized water, and then perform cell crushing treatment for 5-10 minutes, and then continue to stir for 1-2 hours;

Step 3: centrifuge the mixed solution obtained in step 2, remove the supernatant, dry the obtained lower layer precipitate at atmospheric pressure for 24-48 hours, and then carry out high-temperature carbonization in a tube furnace with nitrogen to obtain biomass carbon;

Step 4: The biomass carbon obtained in step 3 is washed with a hydrochloric acid solution, then washed with deionized water until the pH is 7, and dried under normal pressure to obtain a straw-based biomass carbon material.

In the above technical solution, further, the mass ratio of the straw powder, potassium hydroxide, boric acid, urea, disodium hydrogen phosphate and deionized water is: 1:1-4:0.5-2:0.5-2:0.5 -2: 30-50.

In the above technical solution, further, the straw includes corn straw, soybean straw and rice straw.

In the above technical solution, further, the particle size of the straw powder is not greater than 0.125mm.

In the above technical solution, further, the high temperature carbonization temperature is 700-900°C.

In the above technical solution, further, the high temperature carbonization time is 1-2h.

In the above technical scheme, further, the molar concentration of the hydrochloric acid is 1-4 mol/L.

Another aspect of the present invention provides a boron, nitrogen and phosphorus co-doped straw-based porous carbon material prepared by the above preparation method, the carbon material has honeycomb pores; the carbon material has boron, nitrogen and phosphorus co-doped , the boron doping amount is 1-4%, the nitrogen doping amount is 1-4%, and the phosphorus doping amount is 0.2-1%.

Another aspect of the present invention provides an application of boron, nitrogen, and phosphorus co-doped straw-based porous carbon material, which is used as a supercapacitor electrode material.

Compared with the prior art, the present invention has the following beneficial effects:

1. The present invention uses straw as the biomass carbon source. As the crop product with the highest yield in my country, straw has a wide range of sources and low cost, and solves the problem of high cost of current supercapacitor electrode materials.

2, the present invention respectively uses cheap potassium hydroxide as activator and boric acid, urea, disodium hydrogen phosphate as boron source, nitrogen source and phosphorus source respectively, and replaces carbon atoms on carbon skeleton by polyatoms such as boron, nitrogen and phosphorus. To create defects, further optimize the pore structure of biomass porous carbon, and optimize the pore structure on the basis of reducing production costs.

3. The present invention pulverizes the straw, and the particle size of the powder is less than or equal to 0.125mm, which greatly increases the contact area between the biomass raw material and the activator, and can better optimize the uniformity of the pores of the biomass carbon material.

4. The specific surface area of the biomass porous carbon material prepared by the present invention can reach up to 3123.5 m ² /g, and the pore volume can reach 3.33 cm ³ /g, showing an excellent hierarchical pore structure. The capacitance is as high as 395.7F/g, and it has excellent electrochemical performance.

Description of drawings

Fig. 1 is the SEM image of the porous carbon material prepared in Example 1;

Fig. 2 is the SEM image of the porous carbon material prepared in Example 2;

3 is an SEM image of the porous carbon material prepared in Example 3;

4 is an SEM image of the porous carbon material prepared in Comparative Example 1;

5 is a BET diagram of the porous carbon material prepared in Example 2;

Fig. 6 is the XRD pattern of the porous carbon material prepared in Example 2;

FIG. 7 is a cyclic charge-discharge comparison diagram of the porous carbon materials of Examples 1-3 and Comparative Example 1. FIG.

Detailed ways

Embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed to limit the present invention.

Example 1

Step 1: Wash the corn stalks with deionized water and anhydrous ethanol in turn, and then put them into an oven for drying. The dried corn stalks are pulverized and screened by a pulverizer to obtain corn stalk powder with a particle size of less than or equal to 0.125 mm. ;

Step 2: Mix the corn stalk powder obtained in step 1 with potassium hydroxide and deionized water and stir magnetically evenly, then add boric acid, urea, disodium hydrogen phosphate in turn, and continue to stir evenly. Xinzhi JY98-IIIDN) was subjected to cell disruption treatment for 10 min, followed by magnetic stirring for 2 h to obtain a mixed solution, wherein the actual mass ratio used was m(Cornstalk):m(KOH):m(Boric Acid):m(Urea): m(Sodium HydrogenPhosphate): m( _H2O )=3:8.25:1.5:1.5:1.5:40;

Step 3: After centrifuging the mixed solution obtained in Step 2, remove the supernatant to dry at normal pressure for 36 hours, and then carbonize for 2 hours at 800°C in a tube furnace with nitrogen gas;

Step 4: The carbon powder obtained in step 3 is stirred in a hydrochloric acid solution at a constant temperature of 60° C. for 2 hours, wherein the molar concentration of hydrochloric acid used is 2 mol/l, then washed with a large amount of deionized water to pH=7, and dried under normal pressure to obtain corn stalks Biomass-based porous carbon materials.

Figure 1 is an SEM image of the product obtained in this example. It can be seen from the figure that the pores of the biomass porous carbon are relatively uniform and the structure of honeycomb pores can be seen, but the integrity of the pore structure is slightly lacking. Through BET test analysis, its specific surface area is 1972.58m ² /g, and its pore volume is 1.30cm ³ /g. The specific capacitance is calculated to be 292.6F/g through the cycle charge-discharge curve.

Example 2

Step 1: Wash the corn stalks with deionized water and anhydrous ethanol in turn, and then put them into an oven for drying. The dried corn stalks are pulverized and screened by a pulverizer to obtain corn stalk powder with a particle size of less than or equal to 0.125 mm. ;

Step 2: Mix the corn stalk powder obtained in step 1 with potassium hydroxide and deionized water and stir magnetically evenly, then add boric acid, urea, disodium hydrogen phosphate in turn, and continue to stir evenly, then use an ultrasonic cell disruptor (Ningbo). Xinzhi JY98-IIIDN) was subjected to cell disruption treatment for 10 min, followed by magnetic stirring for 2 h to obtain a mixed solution, wherein the actual mass ratio used was m(Cornstalk):m(KOH):m(Boric Acid):m(Urea): m(Sodium HydrogenPhosphate): m(H ₂ O)=3:8.25:3:3:3:40;

Step 3: After centrifuging the mixed solution obtained in Step 2, remove the supernatant to dry at normal pressure for 36 hours, and then carbonize for 2 hours at 800°C in a tube furnace with nitrogen gas;

Step 4: The carbon powder obtained in step 3 is stirred in a hydrochloric acid solution at a constant temperature of 60° C. for 2 hours, wherein the molar concentration of hydrochloric acid used is 2 mol/l, then washed with a large amount of deionized water to pH=7, and dried under normal pressure to obtain corn stalks Biomass-based porous carbon materials.

Fig. 2 is an SEM image of the product obtained in this example. It can be seen from the figure that the pores of the biomass porous carbon are dense and evenly distributed, and the pore size is small and honeycomb-shaped. more pores. By BET test analysis, the specific surface area is 3123.5m ² /g, and the pore volume is 3.33cm ³ /g. The specific capacitance is calculated to be 395.7F/g through the cycle charge-discharge curve.

Example 3

Step 1: Wash the corn stalks with deionized water and anhydrous ethanol in turn, and then put them into an oven for drying. The dried corn stalks are pulverized and screened by a pulverizer to obtain corn stalk powder with a particle size of less than or equal to 0.125 mm. ;

Step 2: Mix the corn stalk powder obtained in step 1 with potassium hydroxide and deionized water and stir magnetically evenly, then add boric acid, urea, disodium hydrogen phosphate in turn, and continue to stir evenly, then use an ultrasonic cell disruptor (Ningbo). Xinzhi JY98-IIIDN) was subjected to cell disruption treatment for 10 minutes, and then continued magnetic stirring for 2 hours to obtain a mixed solution, wherein the actual mass ratio used was m(Cornstalk):m(KOH):m(Boric Acid):m(Urea): m(Sodium HydrogenPhosphate): m( _H2O )=3:8.25:4.5:4.5:4.5:40;

Step 3: After centrifuging the mixed solution obtained in Step 2, remove the supernatant to dry at normal pressure for 36 hours, and then carbonize for 2 hours at 800°C in a tube furnace with nitrogen gas;

Step 4: The carbon powder obtained in step 3 is stirred in a hydrochloric acid solution at a constant temperature of 60° C. for 2 hours, wherein the molar concentration of hydrochloric acid used is 2 mol/l, then washed with a large amount of deionized water to pH=7, and dried under normal pressure to obtain corn stalks Biomass-based porous carbon materials.

FIG. 3 is an SEM image of the product obtained in this example. It can be seen from the figure that the honeycomb pore structure of the biomass porous carbon is relatively developed and the pore structure is complete, but there are a few thick macropore walls. By BET test analysis, its specific surface area is 2604.88m ² /g, and the pore volume is 1.95cm ³ /g. The specific capacitance is calculated to be 337.5F/g through the cycle charge-discharge curve.

Comparative Example 1

To prepare nitrogen and phosphorus doped biomass porous carbon material, refer to Example 1 for the preparation method, and the preparation method includes the following steps:

Step 1: Wash the corn stalks with deionized water and anhydrous ethanol in turn, and then put them into an oven for drying. The dried corn stalks are pulverized and screened by a pulverizer to obtain corn stalk powder with a particle size of less than or equal to 0.125 mm. ;

Step 2: Mix the corn stalk powder obtained in step 1 with potassium hydroxide and deionized water and stir magnetically evenly, then add urea and disodium hydrogen phosphate in turn and continue to stir evenly. The model is Ningbo Xinzhi JY98-IIIDN The ultrasonic cell disruptor was used for cell disruption for 10min, and then continued magnetic stirring for 2h to obtain a mixed solution, wherein the actual mass ratio used was m(Cornstalk):m(KOH):m(Urea):m(Sodium Hydrogen Phosphate): m(H ₂ O)=3:8.25:3:3:40;

Step 3: After centrifuging the mixed solution obtained in Step 2, remove the supernatant to dry at normal pressure for 36 hours, and then carbonize for 2 hours at 800°C in a tube furnace with nitrogen gas;

Step 4: The carbon powder obtained in step 3 is stirred in a hydrochloric acid solution at a constant temperature of 60° C. for 2 hours, wherein the molar concentration of hydrochloric acid used is 2 mol/l, then washed with a large amount of deionized water to pH=7, and dried under normal pressure to obtain corn stalks Biomass-based porous carbon materials.

Figure 4 is the SEM image of the product obtained in Comparative Example 1. It can be seen from the figure that the pores of the biomass porous carbon are dispersed and open, with large mesopores and macropores in the majority, and the number of pores is small and the compactness is lacking. Uniform cellular pore structure. By BET analysis, the specific surface area is 1094.85m ² /g, and the pore volume is 0.32cm ³ /g. The specific capacitance is calculated to be 168.1F/g through the cycle charge-discharge curve.

Claims (9)

1. A preparation method of straw-based porous carbon with a honeycomb-shaped pore structure is characterized by comprising the following steps: the method comprises the following steps:

step 1: cleaning straws with deionized water and absolute ethyl alcohol in sequence to remove surface impurities, then putting the straws into an oven for drying, and then crushing and sieving the dried straws to obtain straw powder;

step 2: uniformly mixing the straw powder obtained in the step 1 with potassium hydroxide, boric acid, urea, disodium hydrogen phosphate and deionized water, then carrying out cell disruption treatment for 5-10min, and then continuing stirring for 1-2 h;

and step 3: centrifuging the mixed solution obtained in the step 2, removing supernatant, drying the obtained lower precipitate at normal pressure for 24-48h, and then performing high-temperature carbonization in a nitrogen-filled tube furnace to obtain biomass carbon;

and 4, step 4: and (4) washing the biomass carbon hydrochloric acid solution obtained in the step (3), then washing with deionized water until the pH value is 7, and drying under normal pressure to obtain the straw-based biomass carbon material.

2. The method of claim 1, wherein: the straw powder, the potassium hydroxide, the boric acid, the urea, the disodium hydrogen phosphate and the deionized water are in the following mass ratio: 1:1-4: 0.5-2: 0.5-2: 0.5-2: 30-50.

3. The production method according to claim 1, characterized in that: the straw comprises corn straw, soybean straw and rice straw.

4. The method of claim 1, wherein: the granularity of the straw powder is not more than 0.125 mm.

5. The method of claim 1, wherein: the high-temperature carbonization temperature is 700-900 ℃.

6. The method of claim 1, wherein: the high-temperature carbonization time is 1-2 h.

7. The method of claim 1, wherein: the molar concentration of the hydrochloric acid is 1-4 mol/L.

8. The boron, nitrogen and phosphorus co-doped straw-based porous carbon material prepared by the preparation method of any one of claims 1 to 7 is characterized in that: the carbon material has honeycomb-shaped pores; the carbon material is codoped with boron, nitrogen and phosphorus, wherein the doping amount of boron is 1-4%, the doping amount of nitrogen is 1-4% and the doping amount of phosphorus is 0.2-1%.

9. The application of the boron, nitrogen and phosphorus co-doped straw-based porous carbon material prepared by the preparation method of any one of claims 1 to 7 is characterized in that: the material is used for the electrode material of the super capacitor.

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