Preparation method of potassium-nitrogen co-doped cyanobacteria-based activated carbon

Abstract

The invention relates to a preparation method of potassium-nitrogen co-doped cyanobacteria-based activated carbon, and relates to the field of biomass activated carbon. According to the application, the blue-green algae is taken as a substrate, is carbonized firstly, and then is co-doped and activated by adopting melamine and potassium carbonate, the process operation is simple and easy to control, the utilization rate is high, the cost is low, the economic benefit is high, and the method has great significance on recycling of the blue-green algae; besides, according to the technical scheme, under the condition of controlling the mass ratio of the carbon powder to the potassium carbonate and controlling the mass ratio of the carbon powder to the melamine, the quantity of micropores of the prepared activated carbon can be reduced and the quantity of mesopores can be increased by increasing the addition amount of the melamine; the pore size distribution of the prepared activated carbon is changed from micropores to mesopores, so that the purpose of adjusting the pore size is achieved, and the prepared activated carbon is larger in specific surface area and more excellent in adsorption performance.

Description

Technical Field

[0001] The present application relates to the technical field of biomass activated carbon, and in particular to a method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon. Background Art

[0002] Biomass activated carbon is a porous material widely used in water treatment, air purification, catalyst carrier and other fields. Its performance mainly depends on the pore structure, including pore size, pore volume and specific surface area. The pore structure of activated carbon is irregular, and the pore size is classified according to the standards of the International Union of Pure and Applied Chemistry (IUPAC), which is divided into micropores (<2nm), mesopores (2~50nm) and macropores (>50nm).

[0003] Traditional biomass activated carbon preparation methods, such as physical activation and chemical activation, can produce a certain range of pore size distribution, but it is often difficult to control the pore size and distribution, which limits the performance optimization of biomass activated carbon in specific applications.

[0004] In recent years, researchers have tried to achieve fine adjustment of the pore size of biomass activated carbon by improving the activation process, introducing new activators or adopting composite activation methods. For example, by controlling the type and concentration of the activator, the pore size distribution of the activated carbon can be adjusted; by changing the activation temperature and time, the formation and expansion of the pore size can be affected. Although some progress has been made, the pore size adjustment technology of biomass activated carbon still faces challenges, such as how to achieve pore size control, how to improve the efficiency and repeatability of pore size adjustment, etc.

[0005] In the related art, patent CN115259152A discloses a method for preparing corncob-based activated carbon by nitrogen doping + KOH activation in one step and its application, wherein corncob is used as a raw material for preparing activated carbon; however, the method directly mixes corncob, potassium hydroxide and urea to prepare activated carbon, and does not use corncob as an activated carbon precursor for carbonization to prepare activated carbon, and the pore size of the prepared activated carbon is mainly macropores, with very few mesopores. In addition, patent CN108946727A discloses a method for preparing activated carbon using microalgae-alginate complexes; however, the activated carbon prepared by this method is mainly micropores, and the distribution of mesopore size cannot be controlled. Summary of the invention

[0006] The purpose of the present application is to provide a method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above purpose, the technical solution adopted in this application is: In a first aspect, the present application provides a method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon, the method comprising: S1. Pretreatment: Wash and dry the cyanobacteria powder, add 15-20% by mass of water, mix well, and granulate with a flat die granulator, sieve through a 50-120 mesh sieve, and dry to obtain cyanobacteria granules; S2, carbonization: placing the cyanobacteria particles in an atmosphere rotary kiln, and introducing an inert gas into the atmosphere rotary kiln to replace the remaining air in the atmosphere rotary kiln, heating the atmosphere rotary kiln to a carbonization temperature of 400-450°C at a rate of 7-10°C / min, and carbonizing at a constant temperature for 2-2.5 h, waiting for the atmosphere rotary kiln to cool to room temperature while the inert gas is continuously introduced into the atmosphere rotary kiln, and obtaining a carbonized sample; S3, potassium-nitrogen co-doping to prepare an activated sample: the carbonized sample is crushed with a crusher to obtain carbon powder, potassium carbonate and melamine are uniformly mixed with the carbon powder and placed in the atmosphere rotary furnace, an inert gas is introduced into the atmosphere rotary furnace to replace the remaining air in the atmosphere rotary furnace, the atmosphere rotary furnace is heated to an activation temperature of 800-900° C. at a rate of 7-10° C. / min, and the atmosphere rotary furnace is activated at a constant temperature for 2-2.5 h, and the atmosphere rotary furnace is waited to cool to room temperature while the inert gas is continuously introduced into the atmosphere rotary furnace to obtain an activated sample; S4. The activated sample is washed with hydrochloric acid and deionized water until it is neutral and then dried to obtain cyanobacteria-based activated carbon with different doping amounts.

[0008] In a possible implementation, in step S3: The mass ratio of the potassium carbonate to the carbon powder is 1:1.

[0009] In a possible implementation, in step S3: The mass ratio of the melamine to the carbon powder is 1:10 to 4:10.

[0010] In a possible implementation, in step S1: The drying temperature after screening through the sieve is 105° C. and the drying time is 16 hours.

[0011] In a possible implementation, in step S2 and step S3: The inert gas introduced into the atmosphere rotary kiln is N2 at a flow rate of 350 mL / min.

[0012] In a possible implementation, in step S4, washing the activated sample with hydrochloric acid and deionized water until it becomes neutral comprises: First, wash with 1 mol / L hydrochloric acid, and then wash with deionized water until the pH is 7.

[0013] In a possible implementation, in step S4: The activated sample was washed with hydrochloric acid and deionized water until neutral and then dried at 105° C. for 16 hours.

[0014] In a second aspect, the present application provides a potassium-nitrogen co-doped cyanobacteria-based activated carbon, which is prepared by the preparation method of potassium-nitrogen co-doped cyanobacteria-based activated carbon as described above.

[0015] The beneficial effects of the technical solution provided by this application include at least: The present application uses cyanobacteria as a matrix, first carbonizes it, and then uses melamine and potassium carbonate to co-dope and activate it. The process is simple and easy to control, with high utilization rate, low cost, high economic benefit and great significance for realizing the resource utilization of cyanobacteria. In addition, the present technical solution can reduce the number of micropores and increase the number of mesopores of the prepared activated carbon by increasing the amount of melamine added, while controlling the mass ratio of carbon powder to potassium carbonate and the mass ratio of carbon powder to melamine, so that the pore size distribution of the prepared activated carbon is transformed from micropores to mesopores to achieve the purpose of adjusting the pore size, and can achieve a larger specific surface area and better adsorption performance of the prepared activated carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings: Figure 1 A flow chart showing a method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon provided by an exemplary embodiment of the present application is shown; Figure 2 The nitrogen adsorption and desorption curves of cyanobacteria-based activated carbon under different nitrogen doping conditions in the present application are shown; Figure 3 The pore size distribution diagram of cyanobacteria-based activated carbon under different nitrogen doping conditions in the present application is shown; Figure 4 A schematic diagram showing the phenol adsorption value of cyanobacteria-based activated carbon under different nitrogen doping conditions in the present application is shown; Figure 5 A schematic diagram showing the iodine adsorption value of cyanobacteria-based activated carbon under different nitrogen doping conditions in the present application is shown; Figure 6 The results of the fully automatic specific surface area and pore size analyzer (BET) of the cyanobacteria-based activated carbon in each embodiment are shown. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0018] Among them, the same parts are represented by the same figure marks. It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to the directions in the drawings of the present application specification, and the words "bottom surface" and "top surface", "inside" and "outside" refer to the direction towards or away from a specific component, respectively. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present application specification, the meaning of "multiple" is two or more.

[0019] The present application is further described below in conjunction with the accompanying drawings and embodiments.

[0020] Figure 1 A flow chart of a method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon provided by an exemplary embodiment of the present application is shown. The method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon comprises: Step S1, pretreatment: wash and dry the cyanobacteria powder, add 15-20% by mass of water, mix evenly, and granulate with a flat die granulator, sieve through a 120-mesh sieve, and then dry to obtain cyanobacteria particles.

[0021] In the embodiment of the present application, the drying temperature after the above-mentioned 120-mesh sieve screening is 105° C. and the drying time is 16 hours.

[0022] Step S2, carbonization: placing the cyanobacteria particles in an atmosphere rotary kiln, and introducing an inert gas into the atmosphere rotary kiln to replace the remaining air in the atmosphere rotary kiln, heating the atmosphere rotary kiln to a carbonization temperature of 450°C at a rate of 10°C / min, and carbonizing at a constant temperature for 2 hours. While the inert gas is continuously introduced into the atmosphere rotary kiln, the atmosphere rotary kiln is waited to cool to room temperature to obtain a carbonized sample.

[0023] In the embodiment of the present application, the inert gas introduced into the atmosphere rotary furnace is N2 at a flow rate of 350 mL / min.

[0024] Step S3, potassium-nitrogen co-doping to prepare an activated sample: the carbonized sample is crushed with a crusher to obtain carbon powder, potassium carbonate and melamine are evenly mixed with the carbon powder and placed in an atmosphere rotary furnace, an inert gas is introduced into the atmosphere rotary furnace to replace the remaining air in the atmosphere rotary furnace, the atmosphere rotary furnace is heated to an activation temperature of 900°C at a rate of 10°C / min, and is activated at a constant temperature for 2 hours, and the atmosphere rotary furnace is waited to cool to room temperature while the inert gas is continuously introduced into the atmosphere rotary furnace to obtain an activated sample.

[0025] In the embodiment of the present application, the mass ratio of potassium carbonate to carbon powder is 1:1, and the mass ratio of melamine to carbon powder is 1:10 to 4:10.

[0026] In the embodiment of the present application, the inert gas introduced into the atmosphere rotary furnace is N2 at a flow rate of 350 mL / min.

[0027] Step S4, washing the activated sample with hydrochloric acid and deionized water until neutral and then drying to obtain cyanobacteria-based activated carbon with different doping amounts.

[0028] In the embodiment of the present application, the activated sample is washed with hydrochloric acid and deionized water until it becomes neutral, comprising: first washing with hydrochloric acid having a concentration of 1 mol / L, and then washing with deionized water until the pH value is 7.

[0029] In the embodiment of the present application, the activated sample is washed with hydrochloric acid and deionized water until it is neutral and then dried at a drying temperature of 105° C. and a drying time of 16 hours.

[0030] In order to better understand the present application, the present application is further described with four specific embodiments below. It should be noted that the embodiments described in the specific embodiments are only part of the embodiments of the present application and do not limit the scope of protection of the present application.

[0031] Embodiment 1: (1) Pretreatment: Wash and dry the cyanobacteria powder, add 15% by mass of water, mix well, and granulate it in a flat die granulator. After screening through a 50-mesh sieve, place it in an oven at 105°C for 16 hours to obtain cyanobacteria granules. (2) Carbonization: The cyanobacteria particles were placed in an atmosphere rotary kiln and nitrogen was passed through at a rate of 350 mL / min to replace the remaining air in the atmosphere rotary kiln. The atmosphere rotary kiln was then heated to 400 °C at a rate of 7 °C / min and carbonized at a constant temperature for 2.5 h. The temperature of the atmosphere rotary kiln was lowered to room temperature while nitrogen was passed through at a rate of 350 mL / min to obtain a carbonized sample. (3) Preparation of activated samples by co-doping with potassium carbonate + melamine: the obtained carbonized sample was crushed with a crusher to obtain carbon powder, potassium carbonate and melamine were evenly mixed with the carbon powder and spread in an atmosphere rotary furnace, nitrogen was passed at 350 mL / min to replace the remaining air in the atmosphere rotary furnace, and then the atmosphere rotary furnace was heated to 800°C at a rate of 7°C / min and activated at a constant temperature for 2 h. The temperature of the atmosphere rotary furnace was cooled to room temperature while nitrogen was passed at 350 mL / min to obtain an activated sample; wherein the mass ratio of carbon powder to potassium carbonate was 1:1, and the mass ratio of carbon powder to melamine was 1:0.1; (4) The activated sample was first washed with 1 mol / L hydrochloric acid and then washed with deionized water until the pH value was 7. It was placed in an oven at 105 °C for 16 h to obtain cyanobacteria-based activated carbon, which was recorded as CKN-1-0.1.

[0032] Embodiment 2: (1) Pretreatment: Wash and dry the cyanobacteria powder, add 15% (w) water, mix well, and granulate it in a flat die granulator. After screening with a 120-mesh sieve, place it in an oven at 105°C for 16 hours to obtain cyanobacteria granules. (2) Carbonization: The cyanobacteria particles were placed in an atmosphere rotary kiln and nitrogen was passed through at 350 mL / min to replace the remaining air in the atmosphere rotary kiln. The atmosphere rotary kiln was then heated to 450 °C at a rate of 10 °C / min and carbonized at a constant temperature for 2 h. The temperature of the atmosphere rotary kiln was lowered to room temperature while nitrogen was passed through at 350 mL / min to obtain a carbonized sample. (3) Preparation of activated samples by co-doping with potassium carbonate + melamine: the obtained carbonized sample was crushed with a crusher to obtain carbon powder, potassium carbonate and melamine were evenly mixed with the carbon powder and spread in an atmosphere rotary furnace, nitrogen was passed at 350 mL / min to replace the remaining air in the atmosphere rotary furnace, and then the atmosphere rotary furnace was heated to 900°C at a rate of 10°C / min and activated at a constant temperature for 2 h. The temperature of the atmosphere rotary furnace was cooled to room temperature while nitrogen was passed at 350 mL / min to obtain an activated sample; wherein the mass ratio of carbon powder to potassium carbonate was 1:1, and the mass ratio of carbon powder to melamine was 1:0.2; (4) The activated sample was first washed with 1 mol / L hydrochloric acid and then washed with deionized water until the pH value was 7. It was placed in an oven at 105 °C for 16 h to obtain cyanobacteria-based activated carbon, which was recorded as CKN-1-0.2.

[0033] Embodiment three: (1) Pretreatment: Wash and dry the cyanobacteria powder, add 20% (w) water, mix well, and granulate it in a flat die granulator. After screening with a 100-mesh sieve, place it in an oven at 105°C for 16 h to obtain cyanobacteria granules. (2) Carbonization: The cyanobacteria particles were placed in an atmosphere rotary kiln and nitrogen was passed through at 350 mL / min to replace the remaining air in the atmosphere rotary kiln. The atmosphere rotary kiln was then heated to 450 °C at a rate of 9 °C / min and carbonized at a constant temperature for 2 h. The temperature of the atmosphere rotary kiln was lowered to room temperature while nitrogen was passed through at 350 mL / min to obtain a carbonized sample. (3) Preparation of activated samples by co-doping with potassium carbonate + melamine: the obtained carbonized sample was crushed with a crusher to obtain carbon powder, potassium carbonate and melamine were evenly mixed with the carbon powder and spread in an atmosphere rotary furnace, nitrogen was passed at 350 mL / min to replace the remaining air in the atmosphere rotary furnace, and then the atmosphere rotary furnace was heated to 900°C at a rate of 9°C / min and activated at a constant temperature for 2 h. The temperature of the atmosphere rotary furnace was cooled to room temperature while nitrogen was passed at 350 mL / min to obtain an activated sample; wherein the mass ratio of carbon powder to potassium carbonate was 1:1, and the mass ratio of carbon powder to melamine was 1:0.3; (4) The activated sample was first washed with 1 mol / L hydrochloric acid and then washed with deionized water until the pH value was 7. It was placed in an oven at 105 °C for 16 h to obtain cyanobacteria-based activated carbon, which was recorded as CKN-1-0.3.

[0034] Embodiment 4: (1) Pretreatment: Wash and dry the cyanobacteria powder, add 20% (w) water, mix well, and granulate it in a flat die granulator. After screening through an 80-mesh sieve, place it in an oven at 105°C for 16 hours to obtain cyanobacteria granules. (2) Carbonization: The cyanobacteria particles were placed in an atmosphere rotary kiln and nitrogen was passed through at a rate of 350 mL / min to replace the remaining air in the atmosphere rotary kiln. The atmosphere rotary kiln was then heated to 400 °C at a rate of 8 °C / min and carbonized at a constant temperature for 2.5 h. The temperature of the atmosphere rotary kiln was lowered to room temperature while nitrogen was passed through at a rate of 350 mL / min to obtain a carbonized sample. (3) Preparation of activated samples by co-doping with potassium carbonate + melamine: the obtained carbonized sample was crushed with a crusher to obtain carbon powder, potassium carbonate and melamine were evenly mixed with the carbon powder and spread in an atmosphere rotary furnace, nitrogen was passed at 350 mL / min to replace the remaining air in the atmosphere rotary furnace, and then the atmosphere rotary furnace was heated to 800°C at a rate of 8°C / min and activated at a constant temperature for 2.5 h. The temperature of the atmosphere rotary furnace was cooled to room temperature while nitrogen was passed at 350 mL / min to obtain an activated sample; wherein the mass ratio of carbon powder to potassium carbonate was 1:1, and the mass ratio of carbon powder to melamine was 1:0.4; (4) The activated sample was first washed with 1 mol / L hydrochloric acid and then washed with deionized water until the pH value was 7. It was placed in an oven at 105 °C for 16 h to obtain cyanobacteria-based activated carbon, which was recorded as CKN-1-0.4.

[0035] Performance Test: Next, the cyanobacteria-based activated carbon prepared in the above-mentioned Examples 1 to 4 was subjected to relevant tests, CKN-1-0.1 corresponds to Example 1, CKN-1-0.2 corresponds to Example 2, CKN-1-0.3 corresponds to Example 3, and CKN-1-0.4 corresponds to Example 4. Wherein, CKN-XY symbol explanation: CKN represents potassium carbonate and melamine co-doped activated carbon, X represents the added mass ratio of carbon powder and potassium carbonate, and Y represents the added mass ratio of carbon powder and melamine.

[0036] Figure 2 The nitrogen adsorption-desorption curves of cyanobacteria-based activated carbon under different nitrogen doping conditions implemented in the present application are shown. The results show that the nitrogen adsorption-desorption curves are characterized by a combination of type I and type IV isotherms, and contain obvious H4 type hysteresis loops. There are abundant mesopores on the surface, and the size distribution is continuous.

[0037] Figure 3 The pore size distribution diagram of cyanobacteria-based activated carbon under different nitrogen doping conditions implemented in the present application is shown. The results show that the pore distribution of the activated carbon is concentrated in the mesopore size at , and as the amount of melamine continues to increase, the proportion of mesopores also gradually increases. This indicates that with the increase in the proportion of melamine, the pore structure of the cyanobacteria activated carbon gradually changes from micropores to mesopores, which makes the pore size distribution of the activated carbon controllable.

[0038] Figure 4 A schematic diagram of the phenol adsorption value of cyanobacteria-based activated carbon under different nitrogen doping conditions implemented in the present application (used to characterize the number of mesopores in activated carbon) is shown. The results show that the phenol adsorption value of activated carbon increased from 165 mg / g to 191 mg / g. It can be seen that as the amount of melamine continues to increase, the number of mesopores in activated carbon continues to increase.

[0039] Figure 5 A schematic diagram of the iodine adsorption value of cyanobacteria-based activated carbon under different nitrogen doping conditions in the present application (used to characterize the number of micropores in activated carbon) is shown. The results show that the iodine adsorption value of activated carbon decreased from 744 mg / g to 475 mg / g. It can be seen that as the amount of melamine continued to increase, the number of micropores in activated carbon continued to decrease.

[0040] In detail, Figure 6 The fully automatic specific surface area and pore size analyzer (BET) test results of the cyanobacteria-based activated carbon in various embodiments are shown.

[0041] In summary, the present application uses cyanobacteria as a matrix, first carbonizes it, and then uses melamine and potassium carbonate to co-dope and activate it. The process is simple and easy to control, with high utilization rate, low cost, high economic benefit and great significance for realizing the resource utilization of cyanobacteria. In addition, the present technical solution can reduce the number of micropores and increase the number of mesopores of the prepared activated carbon by increasing the amount of melamine added, while controlling the mass ratio of carbon powder to potassium carbonate and the mass ratio of carbon powder to melamine, so that the pore size distribution of the prepared activated carbon is transformed from micropores to mesopores to achieve the purpose of adjusting the pore size, and can achieve a larger specific surface area and better adsorption performance of the prepared activated carbon.

[0042] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon, characterized in that: The method comprises: S1. Pretreatment: Wash and dry the cyanobacteria powder, add 15-20% by mass of water, mix well, and granulate with a flat die granulator, sieve through a 50-120 mesh sieve, and dry to obtain cyanobacteria granules; S2, carbonization: placing the cyanobacteria particles in an atmosphere rotary kiln, and introducing an inert gas into the atmosphere rotary kiln to replace the remaining air in the atmosphere rotary kiln, heating the atmosphere rotary kiln to a carbonization temperature of 400-450°C at a rate of 7-10°C / min, and carbonizing at a constant temperature for 2-2.5 h, waiting for the atmosphere rotary kiln to cool to room temperature while the inert gas is continuously introduced into the atmosphere rotary kiln, and obtaining a carbonized sample; S3, potassium-nitrogen co-doping to prepare an activated sample: the carbonized sample is crushed with a crusher to obtain carbon powder, potassium carbonate and melamine are uniformly mixed with the carbon powder and placed in the atmosphere rotary furnace, an inert gas is introduced into the atmosphere rotary furnace to replace the remaining air in the atmosphere rotary furnace, the atmosphere rotary furnace is heated to an activation temperature of 800-900° C. at a rate of 7-10° C. / min, and the atmosphere rotary furnace is activated at a constant temperature for 2-2.5 h, and the atmosphere rotary furnace is waited to cool to room temperature while the inert gas is continuously introduced into the atmosphere rotary furnace to obtain an activated sample; S4. The activated sample is washed with hydrochloric acid and deionized water until it is neutral and then dried to obtain cyanobacteria-based activated carbon with different doping amounts.

2. The method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon according to claim 1, characterized in that: In step S3: The mass ratio of the potassium carbonate to the carbon powder is 1:

1.

3. The method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon according to claim 1, characterized in that: In step S3: The mass ratio of the melamine to the carbon powder is 1:10 to 4:

10.

4. The method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon according to claim 1, characterized in that: In step S1: The drying temperature of the product after screening through a 120-mesh sieve is 105° C. and the drying time is 16 hours.

5. The method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon according to claim 1, characterized in that: In step S2 and step S3: The inert gas introduced into the atmosphere rotary kiln is N2 at a flow rate of 350 mL / min.

6. The method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon according to claim 1, characterized in that: In step S4, washing the activated sample with hydrochloric acid and deionized water until it becomes neutral comprises: First, wash with 1 mol / L hydrochloric acid, and then wash with deionized water until the pH is 7.

7. The method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon according to claim 1, characterized in that: In step S4: The activated sample is washed with hydrochloric acid and deionized water until it is neutral and then dried at a drying temperature of 105° C. and a drying time of 16 hours.

8. A potassium-nitrogen co-doped cyanobacteria-based activated carbon prepared by the method for preparing potassium-nitrogen co-doped cyanobacteria-based activated carbon according to any one of claims 1 to 7.

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