CN111908443A - Preparation method of self-doped porous carbon - Google Patents

Abstract

The invention discloses a preparation method of self-doped porous carbon, which comprises the following steps: putting the pretreated kelp powder into a crucible for carbonization to obtain carbide; mixing and grinding carbide and potassium hydroxide powder according to the proportion of 1: 2-1: 4, and then placing the mixture in a crucible for activation treatment to obtain porous carbon; soaking the porous carbon by adopting HCL solution, and adding deionized water for dilution; then carrying out suction filtration, and adding a diluent for multiple times to wash the mixture to be neutral; and finally, adding deionized water for centrifugal separation and drying to obtain the self-doped graded porous carbon material. The method is simple to operate, economical and environment-friendly, and the obtained self-doped graded porous carbon material has high specific surface area and excellent conductivity and has wide application prospect when being used as an electrode material of a super capacitor.

Description

A kind of preparation method of self-doping porous carbon

technical field

The invention belongs to the technical field of preparation methods of adsorbent materials, and relates to a preparation method of self-doped porous carbon.

Background technique

Porous carbon can maintain chemical inertness in acid and alkali, developed pore structure, high specific surface area, strong surface activity and convenient functional modification due to its good thermodynamic stability and high chemical stability. It has a wide range of applications in many fields such as the environment. The synthesis methods of porous carbon materials include gel method, template method, activation method, etc. Although the gel method can easily control the process and obtain porous carbons with different pore sizes, the preparation cycle is long and the process is complicated, so it cannot be used on a large scale. The template method can be produced on a large scale and has a stable process. The prepared porous carbon has a uniform pore size and an orderly structure, but the template needs to be removed, the process is complicated, and the prepared porous carbon has a single pore size, so its application is limited. The activation method has a wide range of raw material sources and a simple preparation process, which is suitable for large-scale industrial production. However, the prepared porous carbon is mainly micropores and has a wide distribution of pore sizes, which limits its application in the background of catalysis, adsorption and lithium batteries. . Porous materials can be divided into micropores (diameter less than 2nm), mesopores (diameter greater than 2nm but less than 50nm) and macropores (diameter greater than 50nm) according to the pore size. Because the pores of microporous carbon materials are too small, molecules with slightly larger diameters cannot enter the pores to react, and the macromolecules in the reaction products in the pores cannot escape in time, so they cannot be used in adsorption, catalysis and other industries. The pore size is moderate, and it has high thermal and chemical stability, and is widely used in separation, extraction, catalysis and adsorption, but the solution has insufficient fluidity; macroporous carbon materials can provide an effective channel for the circulation of the solution, but its The mechanical stability is poor and the specific surface area is too low, which is limited in the field of electrochemical applications.

A large number of studies have shown that the surface functional groups of porous carbon have a significant impact on its electrochemical performance. Porous carbon can easily be modified by introducing other heteroelements due to its strong surface activity, thereby forming functional functional groups. The introduction of heteroatoms such as N, P, S, F, and B can improve the wettability and catalytic activity of porous carbon, and can also generate additional pseudocapacitance and improve its capacitance. aroused interest. There are two main sources of heteroatoms, one is the heteroatom doped by adding a heteroatom-containing material to react during the preparation process, and the other is the heteroatom carried by the raw material precursor itself. The raw materials for preparing porous carbon mainly include petroleum, asphalt, coal, waste polymer materials, biomass materials, etc. Biomass is rich in resources, low in cost, rich in various heteroelements and belongs to renewable resources. Using biomass materials as precursors to prepare self-doped porous carbon is not only simple and cost-effective, but also can alleviate the shortage of fossil fuels and the environment. pollution problem. In addition, natural plants have developed hierarchical porous structures due to their respiration and metabolism to ensure life activities such as gas exchange and nutrient circulation, which is conducive to the formation of hierarchical porous carbon materials. At present, the biomass commonly used to prepare porous carbon includes straw, agricultural waste residue, wood, fruit peel and husk. However, there are few reports on the use of marine organisms as porous carbon raw materials. As we all know, the ocean has huge algae plant resources, but the processing utilization rate of seaweed products is low and the overcapacity is serious.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a preparation method of self-doped porous carbon, which solves the problem of low processing utilization rate of seaweed products in the prior art.

The technical scheme adopted in the present invention is, a preparation method of self-doping porous carbon, comprising the following steps:

Step 1, placing the pretreated kelp powder in a crucible for carbonization to obtain carbide;

Step 2, mixing and grinding the carbide and potassium hydroxide powder in a ratio of 1:2 to 1:4, and then placing the mixture in a crucible for activation treatment to obtain porous carbon;

Step 3. After soaking the porous carbon with HCL solution, add deionized water to dilute; then perform suction filtration, and add diluent for several times to clean until neutral; finally add deionized water for centrifugal separation and drying to obtain self-doped carbon. Hierarchical porous carbon materials.

The feature of the present invention also lies in:

The pretreatment process of step 1 is as follows: drying the kelp powder in an oven with a temperature of 80-100° C. for 30-60 minutes.

The carbonization process in step 1 is as follows: place the crucible in a tube furnace, and under the protection of 100-300ml/min nitrogen gas flow, heat up to 600-1000°C at a speed of 5-10°C/min, keep the temperature for 90-120min and then naturally. Cool to room temperature.

The activation process of step 2 is as follows: put the crucible into a tube furnace with a cover, under the protection of 100-300ml/min nitrogen gas flow, heat up to 600-800°C at a speed of 5-10°C/min, and keep the temperature for 60-120min. Cool naturally to room temperature.

The concentration of the HCL solution in step 3 is 0.5-1 mol/L.

The diluent is a mixture of deionized water and ethanol.

The parameters of the centrifugal separation process are: the rotation speed is 5000-1000 rpm, and the time is 10-15 min.

The beneficial effects of the present invention are:

The preparation method of the self-doped porous carbon of the present invention selects kelp as the carbon precursor, because the kelp has low price, wide sources, high yield and fast reproduction, and the kelp itself contains nitrogen, phosphorus and sulfur heteroatoms. After carbonization activation treatment The hierarchical porous carbon material containing nitrogen, phosphorus and sulfur can be directly obtained without adding other reagents to dope heteroatoms; the method is simple to operate, economical and environmentally friendly, and the obtained self-doped hierarchical porous carbon material has high specific surface area and excellent electrical conductivity. As an electrode material for supercapacitors, it has broad application prospects; it can not only improve the utilization rate of kelp products, endow them with higher added value, but also effectively alleviate the problem of energy shortage.

Description of drawings

1 is a scanning electron microscope image of the self-doping graded porous carbon material obtained in Example 1 in a method for preparing self-doping porous carbon of the present invention;

2 is a scanning electron microscope image of the self-doping graded porous carbon material obtained in Example 2 in a method for preparing self-doping porous carbon of the present invention;

3 is a scanning electron microscope image of the self-doping hierarchical porous carbon material obtained in Example 3 in a method for preparing self-doping porous carbon of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

A preparation method of self-doped porous carbon, as shown in Figure 1, includes the following steps:

Step 1. First, place the kelp powder in an oven with a temperature of 80 to 100°C for 30 to 60 minutes, then place the kelp powder in a crucible, put the crucible in a lid and place it in a tube furnace for carbonization, 100 to 300ml/ Under the protection of nitrogen gas flow, the temperature is raised to 600 to 1000 °C at a rate of 5 to 10 °C/min, and the temperature is kept for 90 to 120 minutes, and then naturally cooled to room temperature to obtain carbides; the cost of choosing nitrogen as the protective gas is compared to other protective gases such as argon. Lower; the carbonization temperature is 600-1000°C, because the carbonized product needs to be activated later. If the carbonization temperature in step 1 is too low, the carbonized product will form fewer pores and a small pore size, which is not conducive to the sufficient activator and carbon material. If the carbonization temperature is too high, the degree of graphitization of the carbonized product is high, which is not conducive to the reaction between the activator and the carbon material, so it is difficult to create a new pore structure; in addition, the temperature is too high Cause the carbide structure to be broken and collapsed, and if the activator reacts with it further, the corrosion will further damage the original pore structure;

Step 2. The carbide and potassium hydroxide powder are mixed and ground in a ratio of 1:2 to 1:4, then the mixture is placed in a crucible, covered and placed in a tube furnace for activation treatment at 100 to 300 ml/min. Under the protection of nitrogen gas flow, the temperature is raised to 600-800°C at a rate of 5-10°C/min, and the temperature is kept for 60-120min and then cooled to room temperature naturally to obtain porous carbon;

Step 3. Soak the porous carbon with a concentration of 0.5-1mol/L HCL solution, stir magnetically for 2-5 hours, add deionized water to dilute; then perform suction filtration, and add diluent for several times to clean until neutral; then add deionized water The centrifugal separation speed is 5000-10000 rpm, and the time is 10-15 min. Finally, the centrifuged product is dried in an oven for 12 hours at a temperature of 80-100° C. to obtain a self-doped hierarchical porous carbon material. Hydrochloric acid solution, deionized water, and ethanol are used to wash away impurities in the porous carbon material.

The kelp of the present invention is used as a carbon source after drying, and also serves as a source of nitrogen, phosphorus, and sulfur heteroatoms to obtain self-doped carbides through carbonization; KOH is used as an activator, and its reaction activity with the carbonized product is relatively large, and the generated pores are relatively large. KOH activation method is the most effective method to prepare porous carbon with high specific surface area. Different ratios of potassium hydroxide activator have different activation effects. The optimal mass ratio of carbon material to KOH during activation is 1:2 to 1:4. Therefore, in the present invention, potassium hydroxide powder is used as the activator, the mass ratio of the carbon material to KOH is 1:2-1:4, and the self-doped hierarchical porous carbon is obtained after activation.

Through the above method, the preparation method of self-doped porous carbon of the present invention selects kelp as the precursor of carbon, because kelp has low price, wide source, high yield, fast reproduction, and kelp itself contains nitrogen, phosphorus and sulfur heteroatoms, After the carbonization activation treatment, the hierarchical porous carbon material containing nitrogen, phosphorus and sulfur can be directly obtained without adding other reagents to dope heteroatoms; the method is simple to operate, economical and environmentally friendly, and the obtained self-doped hierarchical porous carbon material has high specific surface area, excellent The conductivity of kelp has broad application prospects as an electrode material for supercapacitors; it can not only improve the utilization rate of kelp products, endow it with higher added value, but also effectively alleviate the problem of energy shortage.

Example 1

Step 1. First, 4g of kelp powder was placed in an oven with a temperature of 80 ° C to dry for 60min, then the kelp powder was placed in a crucible, and the crucible was covered and placed in a tube furnace for carbonization treatment, under the protection of 100ml/min nitrogen gas flow , heated to 600°C at a rate of 5°C/min, kept for 120min and then naturally cooled to room temperature to obtain carbide;

Step 2. The carbide and potassium hydroxide powder are mixed and ground at a ratio of 1:4, then the mixture is placed in a crucible, covered and placed in a tube furnace for activation treatment, under the protection of 200ml/min nitrogen gas flow, with The temperature was raised to 800°C at a rate of 5°C/min, and the temperature was kept for 120 min, and then cooled to room temperature naturally to obtain porous carbon;

Step 3. Soak the porous carbon with a concentration of 1mol/L HCL solution, stir magnetically for 5 hours, and then add deionized water for dilution; then perform suction filtration, and add diluent for several times to clean to neutrality; then add deionized water for centrifugal separation. The temperature was 6000 rpm and the time was 15 min. Finally, the centrifuged product was dried in an oven for 12 h at a temperature of 80° C. to obtain a self-doped hierarchical porous carbon material. The SEM image of the self-doped hierarchical porous carbon material in this example is shown in Fig. 1. It can be seen from Fig. 1 that the hierarchical porous carbon obtained in this example has an irregular block-like loose structure and has a very developed pore structure. The pore size ranges from several to several hundreds of nanometers, and most of them are micropores and smaller mesoporous structures.

Example 2

Step 1. First put 6g of kelp powder in an oven with a temperature of 90 ° C to dry for 45min, then place the kelp powder in a crucible, put the crucible in a cover and place it in a tube furnace for carbonization, under the protection of 200ml/min nitrogen gas flow , heated to 800°C at a rate of 6°C/min, kept for 120min and then naturally cooled to room temperature to obtain carbide;

Step 2. The carbide and potassium hydroxide powder are mixed and ground in a ratio of 1:3, then the mixture is placed in a crucible, covered and placed in a tube furnace for activation treatment, under the protection of 200ml/min nitrogen gas flow, with The temperature was raised to 700°C at a rate of 6°C/min, and then cooled to room temperature naturally after being kept for 90 minutes to obtain porous carbon;

Step 3. Soak the porous carbon with a concentration of 0.8mol/L HCL solution, stir magnetically for 4 hours, and then add deionized water for dilution; then perform suction filtration, and add diluent for several times to clean to neutrality; then add deionized water for centrifugal separation The rotating speed was 7000 rpm and the time was 10 min. Finally, the centrifuged product was dried in an oven for 12 h at a temperature of 90° C. to obtain a self-doped hierarchical porous carbon material.

The SEM image of the self-doped hierarchical porous carbon material in this example is shown in FIG. 2 , it can be seen from the figure that the hierarchical porous carbon obtained in this example still has an irregular block honeycomb structure with rich pore structure. Compared with the product obtained in Example 1, the average pore size of the hierarchical porous carbon obtained in this example is increased.

Example 3

Step 1. First put 8g of kelp powder in an oven with a temperature of 100°C for 30 minutes, then place the kelp powder in a crucible, put the crucible in a cover and place it in a tube furnace for carbonization, under the protection of 300ml/min nitrogen gas flow , heat up to 1000°C at a rate of 8°C/min, and cool to room temperature naturally after holding for 90min to obtain carbide;

Step 2. Mix and grind the carbide and potassium hydroxide powder according to the ratio of 1:2, then put the mixture in a crucible, put it into a tube furnace with a cover for activation treatment, and under the protection of 200ml/min nitrogen gas flow, with The temperature was raised to 600°C at a rate of 8°C/min, and the temperature was kept for 120 min, and then cooled to room temperature naturally to obtain porous carbon;

Step 3. Soak the porous carbon with a concentration of 0.5mol/L HCL solution, stir magnetically for 2 hours, and then add deionized water for dilution; then perform suction filtration, and add diluent for several times to clean to neutrality; then add deionized water for centrifugal separation The rotating speed was 7000 rpm and the time was 10 min. Finally, the centrifuged product was dried in an oven for 12 h at a temperature of 90° C. to obtain a self-doped hierarchical porous carbon material.

The SEM image of the self-doped hierarchical porous carbon material in this example is shown in Figure 3. It can be seen from the figure that the hierarchical porous carbon obtained in this example has a honeycomb structure with well-developed pores but a large number of macropores, and the inner wall of the pores becomes thinner. , adjacent pores are interconnected, and even some channels are broken.

Claims (7)

1. a preparation method of self-doping porous carbon, is characterized in that, comprises the following steps: Step 1, placing the pretreated kelp powder in a crucible for carbonization to obtain carbide; Step 2, mixing and grinding the carbide and potassium hydroxide powder in a ratio of 1:2 to 1:4, and then placing the mixture in a crucible for activation treatment to obtain porous carbon; Step 3. After soaking the porous carbon with HCL solution, add deionized water to dilute; then perform suction filtration, and add diluent for several times to clean to neutrality; finally add deionized water for centrifugation and drying to obtain self-mixing Hybrid hierarchical porous carbon materials. 2 . The preparation method of self-doping porous carbon according to claim 1 , wherein the pretreatment process described in step 1 is: placing the kelp powder in an oven with a temperature of 80-100° C. for 30 minutes. 3 . ~60min. 3 . The method for preparing self-doping porous carbon according to claim 1 , wherein the carbonization process in step 1 is: placing the crucible in a tube furnace, at 100-300ml/ml Under the protection of nitrogen gas flow, the temperature was raised to 600-1000 °C at a rate of 5-10 °C/min, and the temperature was kept for 90-120 min, and then cooled to room temperature naturally. 4 . The preparation method of self-doping porous carbon according to claim 1 , wherein the activation process described in step 2 is: putting the crucible into a tube furnace with a cover on it, and putting the crucible into a tube furnace with a lid of 100-300 ml. 5 . Under the protection of nitrogen gas flow/min, the temperature is raised to 600-800°C at a rate of 5-10°C/min, and the temperature is kept for 60-120min and then cooled to room temperature naturally. 5 . The method for preparing self-doped porous carbon according to claim 1 , wherein the concentration of the HCL solution in step 3 is 0.5-1 mol/L. 6 . 6 . The method for preparing self-doping porous carbon according to claim 1 , wherein the diluent is a mixture of deionized water and ethanol. 7 . 7 . The method for preparing self-doped porous carbon according to claim 1 , wherein the parameters of the centrifugal separation process are: the rotation speed is 5000-1000 rpm, and the time is 10-15 min. 8 .

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