Preparation method of a carbon material for electro-adsorbing sodium ions

Abstract

The present invention discloses a preparation method of a carbon material for electro-adsorbing sodium ions, which comprises the following steps: using sorghum husk as a raw material, and successively undergoing washing, high-temperature carbonization, nitric acid hydrothermal oxidation, and nitrogen doping to obtain a carbon material for electro-adsorbing sodium ions. For the carbon material of the present invention, through high-temperature carbonization and hydrothermal oxidation successively, more oxygen-containing functional groups and pores will be generated in the sorghum husk carbon material, that is, more adsorption pores. More importantly, after nitrogen element doping, the layer spacing can be effectively enlarged, and the ion shuttle speed can be accelerated. After the sorghum husk of the present invention is hydrothermally modified and then N-doped, the adsorption of Na+ can be greatly improved, and the adsorption amount of Na+ per unit mass of the carbon material can be significantly increased during the electro-adsorption process.

Description

Technical Field

[0001] The present invention belongs to the field of treatment of biomass materials, and particularly relates to a preparation method of a carbon material for electro-adsorbing sodium ions. Background Art

[0002] In the 1960s and 1970s, China launched seawater desalination projects, mainly using electro-dialysis, reverse osmosis, distillation and other means. In addition, electro-adsorption desalination (also known as capacitive deionization technology, CDI) is a technology that can desalinate continuously and is also a technology that has been widely studied. However, the main disadvantages of current seawater treatment technologies are relatively high costs, high energy consumption, and the fact that the adsorbed Na + cannot be desorbed, resulting in waste of resources.

[0003] At the same time, China is also a large agricultural country with rich biomass resources. There are several tons of lignin-based waste every year, which has the advantages of low cost, sustainability and economy. However, these biomasses cannot be properly utilized.

[0004] In view of this, the inventor of this case conducted in-depth research and strived to find a suitable biomass for sodium ion adsorption with low cost and high efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a carbon material for electro-adsorbing sodium ions.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A preparation method of a carbon material for electro-adsorbing sodium ions, comprising the following steps:

[0008] Step S1, washing sorghum husks with deionized water and alcohol until the dust and alcohol-soluble pollutants on the surface of the sorghum husks are removed, then drying them in a blower at 100 °C for 12 hours, putting the dried sorghum husks into a wall breaker for crushing, and screening out the powder with a 40-mesh sieve;

[0009] Step S2, putting the sorghum husk powder obtained in S1 into a quartz boat, heating it to 1000 °C at a heating rate of 5 °C / min in a tube furnace filled with inert gas and keeping it warm for 2 - 3 hours until the sorghum husks are completely carbonized, finally cooling it to room temperature and taking out the completely carbonized sorghum husks, and grinding them into powder to form carbon powder;

[0010] Step S3, adding concentrated nitric acid and the carbon powder obtained in S2 into polytetrafluoroethylene, performing hydrothermal oxidation treatment at a temperature of 180 °C for 6 hours, and the ratio of concentrated nitric acid to carbon powder is 3 ml: 1 g. Washing the carbon material after hydrothermal treatment with deionized water and alcohol until it is neutral, and performing drying treatment;

[0011] Step S4: Mix and grind the carbon powder and urea dried in S3 into a powder. The mass ratio of the carbon powder to the urea is 1:3. Heat it to 1000 °C at a heating rate of 5 °C / min in a tube furnace filled with inert gas and hold for 2 - 3 hours. Press the obtained carbon material into a carbon felt. Use a platinum electrode as a clip to hold the carbon felt under a DC power supply, and electro-adsorb sodium ions in a 2% (mass concentration) NaCl solution. The electro-adsorption amount reaches 0.286 PPT / g. After applying a reverse voltage, free and complete desorption can be achieved. The number of repeated adsorption and desorption cycles is greater than two. After two adsorption and desorption cycles, the electro-adsorption amount of the carbon material for sodium ions remains at 0.143 PPT / g.

[0012] Further, in step S2, the inert gas used in the experiment is nitrogen or argon.

[0013] Further, in step S3, the concentrated nitric acid used in the hydrothermal process is concentrated nitric acid with a mass fraction of 69%.

[0014] Further, in step S3, add 15 ml of concentrated nitric acid and 5 g of carbon powder to polytetrafluoroethylene, and finally make up the volume to 100 ml and place it in a hydrothermal tank to react for 6 hours.

[0015] Further, in step S3, for the carbon powder oxidized by concentrated nitric acid, first neutralize it with a 1 mol / L sodium hydroxide solution, and then wash it with alcohol multiple times and dry it at 80 °C for 12 hours.

[0016] After adopting the above technical solution, the preparation method of a carbon material for electro-adsorbing sodium ions of the present invention has the following beneficial effects:

[0017] (1) The carbon raw material selects the common waste sorghum husk in daily life, which has a unique microstructure and a high carbon content, and can be mass-produced. The main components of sorghum husk are lignin, cellulose, and a small amount of protein. After carbonization, the microstructure has rich channels, which can provide free transmission of Na⁺. At the same time, sorghum husk contains a large amount of C elements. After N element doping, C-N bonds can be formed with C, making the structure more stable, and stably performing during the adsorption and desorption of Na⁺, and can perform multiple adsorption and desorption. After testing, it can go through at least 5 adsorption and desorption cycles. When adsorbing for the first and second times, the adsorption amount reaches 0.286 PPT / g. When adsorbing for the fifth time, the adsorption amount still reaches 0.143 PPT / g, and complete desorption can be achieved; + Free transmission, and at the same time, sorghum husk contains a large amount of C elements. After N element doping, C-N bonds can be formed with C, making the structure more stable, and stably performing during the adsorption and desorption of Na⁺, and can perform multiple adsorption and desorption. After testing, it can go through at least 5 adsorption and desorption cycles. When adsorbing for the first and second times, the adsorption amount reaches 0.286 PPT / g. When adsorbing for the fifth time, the adsorption amount still reaches 0.143 PPT / g, and complete desorption can be achieved; + The adsorption and desorption process of is stable, and multiple adsorption and desorption can be carried out. After testing, it can go through at least 5 adsorption and desorption cycles. When adsorbing for the first and second times, the adsorption amount reaches 0.286 PPT / g. When adsorbing for the fifth time, the adsorption amount still reaches 0.143 PPT / g, and complete desorption can be achieved;

[0018] (2) The sorghum husk of the present invention has unique properties. The sorghum husk is first subjected to high-temperature carbonization treatment to form a porous material, and then hydrothermal oxidation is carried out using concentrated HNO3. On the basis of the porous structure formed by high-temperature carbonization, nitric acid oxidation can generate more adsorption pores in the carbonized porous structure, which can provide more Na + shuttling. Moreover, more oxygen-containing functional groups (-OH, -COOH) will be generated after hydrothermal oxidation, which plays a positive role in the transport and adsorption of Na + , and at the same time enables elements to be more easily doped. Finally, N element doping is carried out. N element doping can effectively expand the layer spacing, accelerate the ion shuttling speed, and play a more positive role in the transport and adsorption of Na + , and can allow more Na + to be adsorbed and desorbed within a unit time, which has a significant synergistic effect on the adsorption and desorption effect of Na + , and provides more active sites and defects, etc. for Na + to shuttle and adsorb, thereby promoting the amount of adsorption and desorption.

[0019] Therefore, during the electrolysis process, the carbon felt made of the carbon material of the present invention can adsorb a large amount of Na + . The optimized electro-adsorption rate and quantity improve the reaction rate and increase the high adsorption capacity per unit mass.

[0020] (3) The carbon material prepared by the present invention has low cost, large output, and simple process, which is conducive to mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the SEM image of the sorghum husk after carbonization (without hydrothermal oxidation) prepared in Comparative Example 1 of the present invention;

[0022] Figure 2 is the SEM image of the sorghum husk after first performing hydrothermal oxidation treatment and then high-temperature carbonization treatment in Comparative Example 3;

[0023] Figure 3 is the SEM image of the sorghum husk after first performing carbonization treatment and then hydrothermal oxidation treatment in Comparative Example 2.

[0024] Figure 4 is the element proportion diagram of the carbon material prepared in Example 1 after first performing high-temperature carbonization and then modifying and doping with N by concentrated nitric acid oxidation;

[0025] Figure 5 is the SEM of starch carbonized at 1000 °C with starch as the raw material.

[0026] Figure 6 is the quantity diagram of the adsorption and desorption of Na + by the carbon felt prepared with untreated sorghum husk as the raw material;

[0027] Figure 7 The carbon felt for adsorbing and desorbing Na is made from sorghum husk as raw material, which is first subjected to high-temperature carbonization and then hydrothermal oxidation modification. + quantity diagram;

[0028] Figure 8 The carbon felt for adsorbing and desorbing Na is made from sorghum husk as raw material, which is first subjected to hydrothermal oxidation and then high-temperature carbonization. + quantity diagram;

[0029] Figure 9 The carbon felt for adsorbing and desorbing Na is made from sorghum husk as raw material, which is first subjected to high-temperature carbonization, then hydrothermal oxidation, and finally N doping. + quantity diagram;

[0030] Figure 10 The carbon felt for adsorbing and desorbing Na is made from starch as raw material. + quantity diagram; Detailed implementation manners

[0031] In order to further explain the technical solution of the present invention, the present invention will be elaborated in detail through specific embodiments below.

[0032] Embodiment 1

[0033] A preparation method of a carbon material for electro-adsorbing sodium ions according to the present invention includes the following steps:

[0034] Step S1, wash sorghum husk with deionized water and alcohol for multiple times to remove dust and alcohol-soluble pollutants on the surface, and then place it in a blower for drying at 100 °C for 12 hours. Put the dried biomass in a wall breaker for pulverization, and sieve out the powder with a 40-mesh sieve.

[0035] Step S2, place the sorghum husk powder obtained in S1 in a quartz boat, and perform carbonization treatment in a tubular furnace filled with inert gas at a heating rate of 5 °C / min to 1000 °C and keep it warm for 2 - 3 hours. The carbon powder made at high temperature will not only reduce impurities but also increase the pores of the carbon material. Finally, cool it to room temperature and take it out for grinding into powder.

[0036] Specifically, in step S2, the inert gas used during the carbonization treatment is nitrogen or argon. The heat preservation duration can be 2 hours or 3 hours, or other values within this range.

[0037] Step S3, add concentrated nitric acid and the carbon powder obtained in S2 into polytetrafluoroethylene, and perform hydrothermal oxidation treatment at a temperature of 180 °C for 6 hours. The addition ratio of concentrated nitric acid and carbon powder is 3 ml: 1 g. Finally, wash the carbon material after hydrothermal treatment with deionized water and alcohol until it is neutral, and perform overnight drying treatment.

[0038] In step S3, the concentrated nitric acid used in the hydrothermal process is concentrated nitric acid with a mass fraction of 69%.

[0039] In step S3, 15 ml of concentrated nitric acid and 5 g of carbon powder are added to polytetrafluoroethylene, and finally the volume is fixed to 100 ml and placed in a hydrothermal reactor for reaction for 6 hours.

[0040] In step S3, after the carbon powder is oxidized with concentrated nitric acid, it is first neutralized with 1 mol / L sodium hydroxide solution, then washed with alcohol multiple times, and dried at 80 °C for 12 hours. By passing through high-temperature carbonization and hydrothermal oxidation in sequence, more oxygen-containing functional groups and adsorption pores will be generated in the sorghum husk carbon material. If hydrothermal oxidation is carried out first and then high-temperature carbonization, the structure of the carbon powder will not change significantly, and the adsorption effect is much worse than that of carbonization first and then oxidation.

[0041] In step S4, the carbon powder obtained after drying in S3 and urea are mixed and ground into powder. The mass ratio of carbon powder to urea is 1:3. It is heated to 1000 °C at a heating rate of 5 °C / min in a tube furnace filled with inert gas and kept warm for 2 - 3 hours. Specifically, calcination is carried out under inert gas nitrogen or argon at the same heating rate and temperature. Finally, a carbon material for electro-adsorbing sodium ions is obtained. The elemental composition diagram of the carbon material is as Figure 4 shown. Combining with the electron image of the carbon material, it can be seen that N elements are doped into the surface and defect positions.

[0042] After the sorghum husk of the present invention is hydrothermally modified and then N-doped, the adsorption of Na + can be greatly improved, and the adsorption amount of sodium ions per unit mass of the carbon material can be significantly increased during the electro-adsorption process. + Adsorption amount.

[0043] Furthermore, the carbon material obtained in step S4 is made into a carbon felt for electro-adsorbing sodium ions, and sodium ions are repeatedly adsorbed and desorbed, and the number of repeated adsorption and desorption times is greater than two.

[0044] Furthermore, under the conditions of low voltage and low current, a higher adsorption amount of sodium ions can be achieved for electro-adsorption. The low voltage is usually about 1 V, and the low current is 1 - 2 mA. In this embodiment, the voltage is 0.8 V and the current is 2 mA.

[0045] Sodium ion adsorption and desorption experiment: Using a platinum electrode as a clip for holding the carbon felt under a DC power supply (voltage 0.8 V, current 2 mA), electro-adsorbing Na + in a 2% NaCl solution, and free desorption can be achieved after applying a reverse voltage. The experimental results are as Figure 9 shown. After modification, it can efficiently adsorb Na +, and it can be desorbed by applying a reverse voltage, achieving 100% adsorption and desorption. The number of adsorption and desorption cycles can reach at least five times. In the first and second times, the adsorption amount is as high as 0.286 PPT / g, significantly higher than the adsorption amounts of the corresponding cycles in other comparative examples. When the fifth adsorption of the present invention is carried out, the adsorption amount still reaches 0.143 PPT / g, and it can be completely desorbed. This is an effect that the comparative examples do not have at all. It can be seen that the adsorption and desorption performance of the carbon material of the present invention is greatly improved after the treatment solution of the present invention.

[0046] The preparation method of a carbon material for electro-adsorbing sodium ions of the present invention has the following beneficial effects: (1) The carbon raw material is the common waste sorghum husk in daily life, which has a unique microstructure and a high carbon content, and can be mass-produced. The main components of sorghum husk are lignin, cellulose, and a small amount of protein. After carbonization, the microstructure has rich channels, which can provide free transmission of Na + . At the same time, in addition to a large amount of C elements in sorghum husk, after N element doping, C-N bonds can be formed with C, making the structure more stable, and stably carrying out the adsorption and desorption of Na + , and can perform multiple adsorption and desorption cycles. However, some common biomass has a low carbon content and cannot meet the requirements for Na adsorption. Some biomass cannot continue the experiment after two adsorption and desorption cycles of Na. Other biomass is not suitable for Na shuttle due to its microstructure, and the adsorption and desorption cannot achieve the expected effect; (2) The sorghum husk of the present invention has unique properties. The sorghum husk is first subjected to high-temperature carbonization treatment to form a porous material, and then hydrothermal oxidation is carried out using concentrated HNO3. On the basis of the porous structure formed by high-temperature carbonization, more adsorption pores can be generated in the carbonized porous structure through nitric acid oxidation, which can provide more Na shuttle. And, more oxygen-containing functional groups (-OH, -COOH) will be generated after hydrothermal oxidation, which plays a positive role in the transportation and adsorption of Na, and at the same time can make elements easier to dope. Finally, N element doping is carried out. N element doping can effectively expand the layer spacing, accelerate the ion shuttle speed, play a more positive role in the transportation and adsorption of Na, enable more Na to be adsorbed and desorbed per unit time, has a significant synergistic effect on the adsorption and desorption effect of Na, and provides more active sites and defects, etc. for Na shuttle adsorption, thus promoting the amount of adsorption and desorption. Therefore, in the process of electrolysis, the carbon felt made of the carbon material of the present invention can adsorb a large amount of Na + + + + + + + + + + ​​​​​​​​​。The optimized rate and quantity of electro-adsorption improve the reaction rate and enhance the high adsorption capacity per unit mass. (3) The carbon material prepared by the present invention has low cost, large output and simple process, which is conducive to mass production.

[0047] Comparative Example 1

[0048] The main difference between Comparative Example 1 and Example 1 is that the hydrothermal oxidation treatment and nitrogen doping treatment are omitted.

[0049] A preparation method of a carbon material for electro-adsorbing sodium ions includes the following steps:

[0050] Step S1: Wash the sorghum husks with deionized water and alcohol for multiple times to remove the dust and alcohol-soluble pollutants on the surface, and then dry them in a blower at 100 °C for 12 hours. Put the dried biomass into a wall breaker for pulverization, and sieve out the powder with a 40-mesh sieve.

[0051] Step S2: Put the sorghum husk powder obtained in S1 into a quartz boat, and perform carbonization treatment in a tubular furnace filled with inert gas at a heating rate of 5 °C / min to 1000 °C and keep it warm for 2 - 3 hours. The carbon powder prepared at high temperature will not only reduce impurities but also increase the pores of the carbon material. Finally, cool it to room temperature and take it out for grinding into powder.

[0052] In step S2, the inert gas used in the carbonization experiment must be nitrogen or argon, and the heat preservation duration can be 2 hours or 3 hours, or other values within this range.

[0053] The SEM image of the sorghum husk after carbonization in step S2 is as Figure 1 shown. It can be seen that the structure of the sorghum husk is a porous structure. It can be seen that the sorghum husk has a high specific surface area and well-developed pore channels, which can promote electron transfer kinetics during the adsorption process. It is very suitable for adsorbing sodium ions by the electro-adsorption method.

[0054] Step S3: Grind the carbon powder obtained in S2 into powder with a ball mill, and finally compress it into a carbon felt.

[0055] Sodium ion adsorption and desorption experiment: Using a platinum electrode as a clip to hold the carbon felt under a DC power supply (voltage is 0.8V, current is 2mA), electro-adsorb Na in a 2% NaCl solution + , and free desorption can be achieved after applying a reverse voltage. The experimental results are as Figure 6 shown. The amount of desorbed and adsorbed by the unmodified carbon material is very small, and it cannot be commercialized. The number of adsorption and desorption cycles is small. The adsorption amount in the third time is only 0.08 PPT / g, and in the fourth time, the adsorption and desorption function is completely lost.

[0056] Comparative Example 2

[0057] The main difference between Comparative Example 2 and Example 1 is that the nitrogen doping treatment is omitted.

[0058] A preparation method of a carbon material for electro-adsorbing sodium ions includes the following steps:

[0059] Step S1: Wash the sorghum husks with deionized water and alcohol multiple times to remove the dust and alcohol-soluble pollutants on the surface, and then dry them in a blower at 100 °C for 12 hours. Put the dried biomass into a wall breaker for crushing, and sieve out the powder with a 40-mesh sieve.

[0060] Step S2: Put the sorghum husk powder obtained in S1 into a quartz boat, and perform carbonization treatment in a tube furnace filled with inert gas at a heating rate of 5 °C / min to 1000 °C and keep it warm for 2 - 3 hours. The carbon powder produced at high temperature will not only reduce impurities but also increase the pores of the carbon material. Finally, cool it to room temperature and take it out for grinding into powder.

[0061] In step S2, the inert gas used during the carbonization experiment must be nitrogen or argon. And the holding time can be 2 hours or 3 hours, or other values within this range.

[0062] Step S3: Put concentrated nitric acid and the carbon powder obtained in S2 into polytetrafluoroethylene and perform hydrothermal oxidation treatment at a temperature of 180 °C for 6 hours. The addition ratio of concentrated nitric acid to carbon powder is 3 ml: 1 g. Finally, wash and dry the oxidized powder overnight.

[0063] In step S3, the concentrated nitric acid used during the hydrothermal process is concentrated nitric acid with a mass fraction of 69%.

[0064] In step S3, add 15 ml of concentrated nitric acid and 5 g of carbon powder into polytetrafluoroethylene, and finally make up the volume to 100 ml and place it in a hydrothermal tank for reaction for 6 hours.

[0065] In step S3, for the carbon powder oxidized by concentrated nitric acid, first neutralize it with 1 mol / L sodium hydroxide solution, and then wash it with alcohol multiple times and dry it at 80 °C for 12 hours.

[0066] The SEM of the carbonized sorghum husk obtained in step S3 is as Figure 3 shown. Comparing Figure 3 with Figure 2 , it can be seen that many mesopores and macropores will be generated in the carbon material after carbonization and then hydrothermal treatment, providing more channels for the shuttle of Na + .

[0067] Step S4: Grind the carbon powder obtained in S3 into powder using a ball mill, and finally make it into a carbon felt.

[0068] Sodium ion adsorption and desorption experiment: Using a platinum electrode as a clamp for holding the carbon felt under a DC power supply (voltage: 0.8 V, current: 2 mA), Na⁺ is electro-adsorbed in a 2% NaCl solution, and free desorption can be achieved after applying a reverse voltage. The experimental results are as Figure 7 shown. The number of adsorption and desorption cycles is small. The adsorption amount in the third cycle is only 0.1 PPT / g, and by the fourth cycle, the adsorption and desorption function is completely lost.

[0069] Comparative Example 3

[0070] The difference between Comparative Example 3 and Example 1 is that hydrothermal oxidation treatment is carried out first, followed by high-temperature carbonization treatment.

[0071] A preparation method of a carbon material for electro-adsorbing sodium ions, comprising the following steps:

[0072] Step S1: Wash the sorghum husks with deionized water and alcohol multiple times to remove surface dust and alcohol-soluble pollutants, and then dry them in a blower at 100 °C for 12 hours. Put the dried biomass in a blender for crushing, and sieve out the powder with a 40-mesh sieve.

[0073] Step S2: Put the sorghum husk powder obtained in S1 in polytetrafluoroethylene and perform hydrothermal treatment at 180 °C for 6 h. After cooling to room temperature, neutralize it with 1 mol / L sodium hydroxide solution, then wash it with alcohol multiple times, and dry it at 80 °C for 12 hours.

[0074] In step S2, the inert gas used during the carbonization experiment must be nitrogen or argon, and the heat preservation duration can be 2 hours or 3 hours, or other values within this range.

[0075] Step S3: Put the sorghum husk powder obtained in S2 in a quartz boat, and perform carbonization treatment in a tubular furnace filled with inert gas at a heating rate of 5 °C / min to 1000 °C and keep it at this temperature for 2 - 3 hours. The carbon powder produced at high temperature will not only reduce impurities but also increase the pores of the carbon material. The SEM image of the sorghum husk after carbonization in step S3 is as Figure 2 shown, with no obvious change compared to direct pyrolysis. Finally, cool it to room temperature, take it out, and grind it into powder.

[0076] In step S3, the raw material used must be sorghum husk, which is first washed with concentrated nitric acid for hydrothermal oxidation until neutral, and then carbonized, washed, and dried.

[0077] Step S4: Grind the carbon powder obtained in S3 into powder using a ball mill, and finally make it into a carbon felt.

[0078] Sodium ion adsorption and desorption experiment: Using a platinum electrode as a clamp for holding the carbon felt under a DC power supply (voltage: 0.8 V, current: 2 mA), electro-adsorb Na in a 2% NaCl solution. + , and free desorption can be achieved after applying a reverse voltage. The experimental results are as Figure 8 shown. The number of adsorption and desorption cycles is small. The adsorption amount in the third cycle is only 0.1 PPT / g, and by the fourth cycle, the adsorption and desorption function is completely lost.

[0079] Comparative Example 4

[0080] The difference between Comparative Example 4 and Example 1 lies in: different raw materials are used.

[0081] A preparation method of a carbon material includes the following steps:

[0082] Step S1, place starch in a quartz boat, and perform carbonization treatment in a tube furnace filled with inert gas at a heating rate of 5 °C / min up to 1000 °C and hold for 2 - 3 hours. The carbon powder produced at high temperature will have fewer impurities, and finally cool to room temperature and take out and grind into powder.

[0083] In step S1, during the carbonization experiment, the inert gas used must be nitrogen or argon, and the holding time can be 2 hours or 3 hours, or other values within this range.

[0084] The SEM of the starch that has undergone 1000 °C high-temperature carbonization with starch as the raw material obtained in step S1 is as Figure 5 shown. The carbonized material has no pore channels and is not suitable for Na + shuttle.

[0085] Step S2, grind the carbon powder obtained in S1 into powder using a ball mill, and finally make it into a carbon felt.

[0086] In step S2, compress the ground powder into a carbon felt.

[0087] Sodium ion adsorption and desorption experiment: Using a platinum electrode as a clamp for holding the carbon felt under a DC power supply (voltage: 0.8 V, current: 2 mA), electro-adsorb Na+ in a 2% NaCl solution, and free desorption can be achieved after applying a reverse voltage. The experimental results are as Figure 10 shown. The number of adsorption and desorption cycles is only two, and the adsorption amount is also small, only 0.0267 PPT / g, and the adsorption and desorption function is completely lost in the third cycle.

[0088] It should be noted that the experimental conditions of the sodium ion adsorption and desorption experiments in Example 1 and Comparative Examples 1 - 4 of the present invention are the same.

[0089] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made by those of ordinary skill in the relevant technical field shall be regarded as not departing from the patent scope of the present invention.

Claims

1. Application of a carbon material for electroadsorbing sodium ions in electroadsorbing sodium ions, characterized in that, The preparation method of the carbon material comprises the following steps: Step S1: Wash the sorghum husks with deionized water and alcohol until the dust and alcohol-soluble pollutants on the surface of the sorghum husks are removed. Then, place them in a blower and dry at 100 °C for 12 hours. Put the dried sorghum husks into a wall breaker for crushing, and sieve out the powder with a 40-mesh sieve; Step S2: Place the sorghum husk powder obtained in S1 in a quartz boat, and raise the temperature to 1000 °C at a heating rate of 5 °C / min in a tube furnace filled with an inert atmosphere and keep it for 2 - 3 hours until the sorghum husks are completely carbonized. Finally, cool to room temperature and take out the completely carbonized sorghum husks, and grind them into powder to form carbon powder; Step S3: Add 15 ml of concentrated nitric acid and 5 g of the carbon powder obtained in S2 into polytetrafluoroethylene, and finally make up the volume to 100 ml. Carry out hydrothermal oxidation treatment at a temperature of 180 °C for 6 hours. The ratio of concentrated nitric acid to carbon powder is 3 ml: 1 g. Wash the carbon material after hydrothermal treatment with deionized water and alcohol until it is neutral, and then carry out drying treatment; The concentrated nitric acid used is concentrated nitric acid with a mass fraction of 69%; Step S4: Mix and grind the carbon powder dried in S3 with urea. The mass ratio of carbon powder to urea is 1:

3. Raise the temperature to 1000 °C at a heating rate of 5 °C / min in a tube furnace filled with an inert atmosphere and keep it for 2 - 3 hours, and press the obtained carbon material into a carbon felt; Under a DC power supply, use a platinum electrode as a clip to hold the carbon felt, and electro-adsorb sodium ions in a 2% (mass concentration) NaCl solution. The electro-adsorption amount reaches 0.286 PPT / g. After applying a reverse voltage, free and complete desorption can be achieved, and the number of repeated adsorption and desorption is greater than two. After two adsorption and desorption cycles, the electro-adsorption amount of the carbon material for sodium ions is maintained at 0.143 PPT / g.

2. Application of a carbon material for electro-adsorbing sodium ions in electro-adsorbing sodium ions, characterized in that: In Step S2, the experimental inert atmosphere is nitrogen or argon.

3. The application of a carbon material for electro-adsorbing sodium ions in electro-adsorbing sodium ions as described in Claim 1. In Step S3, after oxidizing the carbon powder with concentrated nitric acid, first neutralize it with a 1 mol / L sodium hydroxide solution, and then wash it with alcohol multiple times and dry it at 80 °C for 12 hours.

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