Blue-green algae-based microporous activated carbon for carbon dioxide adsorption as well as preparation and application thereof

Abstract

The invention discloses blue-green algae-based microporous activated carbon for carbon dioxide adsorption as well as preparation and application of the blue-green algae-based microporous activated carbon. The preparation method comprises the following steps: (1) preparation of blue-green algae powder: taking blue-green algae in natural lake water, and performing pretreatment to obtain the blue-green algae powder; (2) preparation of blue-green algae-based activated carbon: putting the blue-green algae powder obtained in the step (1) into a tubular furnace for pyrolysis and carbonization treatment to obtain prefabricated carbon; then mixing an activating agent and the prefabricated carbon in water for dipping and stirring, drying after full dipping, then putting the mixture into a tubular furnace for activating treatment, removing surface impurities from the activated carbon through acid pickling, then washing with water until the activated carbon is neutral, and drying to obtain the blue-green algae-based activated carbon for CO2 capture. The blue-green algae-based activated carbon has the characteristics of high specific surface area, high micropore volume and N self-doping, and has the advantages of high adsorption capacity, high selectivity, repeatability and the like when being used for CO2 adsorption.

Description

Technical Field

[0001] The present invention relates to a cyanobacteria-based microporous activated carbon for carbon dioxide (CO2) adsorption, a preparation method thereof, and an application thereof. Background Art

[0002] The large release of greenhouse gases after the combustion of fossil fuels has led to global warming. Among them, CO2 is considered to be one of the main components [Nano Energy 110 (2023) 108373]. Therefore, reducing CO2 emissions has become an issue of international concern. An effective technology for reducing CO2 emissions is carbon capture, utilization, and storage (CCUS) technology, which shows unique potential in alleviating environmental crises [Applied Energy 278 (2020) 115627]. Solid adsorbents have been widely used in CO2 capture due to their advantages such as low cost and environmental friendliness [ACS Applied Materials & Interfaces 16 (2024), 21799-21806]. So far, various adsorbents for CO2 capture have been continuously prepared. Among all these candidate materials, activated carbon is more attractive due to its cost-effectiveness, easy preparation, large specific surface area, well-developed micropores, high adsorption capacity, and ideal thermal and chemical stabilities [Separation and Purification Technology 302 (2022) 122134].

[0003] Taihu Lake in China is an inland lake. Due to global warming, it provides a good growth environment for cyanobacteria. At the same time, the eutrophication of the water body has led to frequent occurrences of cyanobacterial blooms, seriously threatening the water environment and water safety of Taihu Lake, and also affecting the living environment of surrounding residents [Science of the Total Environment 942 (2024) 173684]. Currently, the treatment of cyanobacteria mainly relies on mechanical salvage. However, if the algal sludge generated after the separation of algae and water is not treated and piled up, it is prone to rot and produce a foul smell. Moreover, cyanobacteria contain algal toxins, and nitrogen and phosphorus pollutants are likely to cause secondary environmental pollution. Therefore, an effective means for the harmless treatment and resource utilization of cyanobacteria is urgently needed [Algal Research 64 (2022) 102670].

[0004] In previous studies, the inventors found that the common chemical activator KOH can be used as an activator for cyanobacteria powder to prepare activated carbon with a high specific surface area. However, KOH has strong corrosiveness and is prone to cause the coalescence of micropores during the activation process, forming a relatively large proportion of mesopores and macropores [Chinese Journal of Chemical Engineering 67(2024)106-116]. Although such activated carbon has good application performance in the adsorption and removal of organic pollutants such as dyes, the adsorption of CO2 mainly depends on the micropores in the activated carbon material, even ultra-micropores smaller than 1 nm. Therefore, its CO2 adsorption capacity is lacking.

[0005] Based on the above problems, according to the structural requirements of CO2 capture for activated carbon materials, the present invention selects a mild, safe, and efficient activator and establishes a supporting activation process. Using cyanobacteria dry powder as the raw material, high specific surface area and N-self-doped cyanobacteria-based microporous activated carbon are prepared for efficient CO2 capture. The high specific surface area and N-self-doped cyanobacteria-based microporous activated carbon prepared by the present invention has the characteristics of high CO2 adsorption capacity, high selectivity, and repeatability. Summary of the Invention

[0006] An object of the present invention is to provide a preparation method of cyanobacteria-based activated carbon with a high specific surface area, a high micropore volume, and N-self-doping for CO2 adsorption, the obtained cyanobacteria-based activated carbon, and the application of the activated carbon in CO2 adsorption. The preparation method has a simple process, and the obtained cyanobacteria-based activated carbon has the characteristics of high CO2 adsorption capacity, high selectivity, and repeatability.

[0007] To achieve the above invention object, the technical solution adopted by the present invention is:

[0008] In the first aspect, the present invention provides a preparation method of cyanobacteria-based activated carbon for CO2 adsorption, comprising the following steps:

[0009] (1) Preparation of cyanobacteria powder: Take cyanobacteria in natural lake water and obtain cyanobacteria powder through pretreatment;

[0010] (2) Preparation of cyanobacteria-based activated carbon: Place the cyanobacteria powder obtained in step (1) in a tubular furnace for pyrolytic carbonization treatment to obtain pre-carbonized material; Subsequently, mix potassium carbonate with the pre-carbonized material and impregnate and stir in water. The mass ratio of potassium carbonate to the pre-carbonized material is 0.5-5:1. After sufficient impregnation, dry it, and then place it in a tubular furnace for activation treatment. The activation conditions are: in a nitrogen atmosphere, the heating rate is 5-30 °C / min, the activation temperature is 500-900 °C, the constant temperature activation time is 0.5-3 h, and cool down to room temperature; Wash the surface impurities of the activated carbon by pickling, then wash it with water until neutral and dry to obtain cyanobacteria-based activated carbon for CO2 adsorption.

[0011] In step (1) of the present invention, the pretreatment includes: obtaining natural lake water containing cyanobacteria, preliminarily removing impurities (such as branches and other sundries) and water, placing the cyanobacteria in a ventilated place to dry in the air, and initially obtaining sheet-shaped cyanobacteria; drying the sheet-shaped cyanobacteria, then crushing and sieving them to obtain cyanobacteria powder.

[0012] In step (2) of the present invention, the pyrolysis carbonization treatment conditions are as follows: under a nitrogen atmosphere, the heating rate is 5 - 30 °C / min, the pyrolysis temperature is 300 - 500 °C, and the isothermal pyrolysis time is 30 - 120 min. Preferably, the pyrolysis carbonization temperature is 400 °C. Preferably, the heating rate during the pyrolysis carbonization treatment in step (2) is 10 - 20 °C / min. Preferably, the isothermal pyrolysis carbonization time in step (2) is 60 - 80 min. Further preferably, the pyrolysis carbonization treatment conditions in step (2) are: the pyrolysis carbonization temperature is 400 °C, the heating rate is 10 - 20 °C / min, and the isothermal pyrolysis carbonization time is 60 - 80 min.

[0013] In step (2) of the present invention, through in-depth research by the inventor, it is found that the specific surface area of cyanobacteria-based biochar without impregnation with the activator potassium carbonate is relatively low, and its ability to adsorb CO2 is poor. However, the cyanobacteria-based activated carbon prepared by the present invention has a good adsorption function for CO2. During the preparation process, the type of activator, the activation method (solid phase or liquid phase), the prefabricated carbon, and the activation conditions have a significant impact on the structure and performance of the cyanobacteria-based activated carbon. During activation, the pore-expanding effect of potassium carbonate is the most significant. When the mass ratio of the activator to the prefabricated carbon increases from 0 to 1, the specific surface area of the obtained cyanobacteria-based activated carbon increases significantly, the pore size distribution becomes wider, and the pore volume is larger. When the alkali-carbon ratio increases to 2, the micropore volume accounts for the highest proportion of the total pore volume; when the alkali-carbon ratio increases to 5, although the pore volume and specific surface area further increase, the excessive activator leads to over-activation, which will corrode and burn through the formed pore structure, damage the micropore structure of the activated carbon, generate more mesopores and macropores, and cause the micropore volume to decrease. Preferably, in step (2), the mixing mass ratio of potassium carbonate to the prefabricated carbon is 1 - 3, and more preferably 2:1.

[0014] On the other hand, when the activation temperature is relatively low, the micropore volume of the obtained activated carbon accounts for the largest proportion of the total pore volume, but its total pore volume is the smallest; further increasing the activation temperature, the total pore volume increases, and the mesopore volume increases significantly. The increased pore volume can be basically attributed to the formation of more mesoporous structures; a higher activation temperature will cause the pore structure to be damaged and reduce the microporous structure of the cyanobacteria-based activated carbon. Therefore, preferably, in step (2), the activation temperature is 650-900 °C, more preferably 650-800 °C. Preferably, in step (2), the activation heating rate is 10-20 °C / min. Preferably, in step (2), the constant-temperature activation time is 120-150 min, more preferably 120 min.

[0015] In a second aspect, the present invention provides a cyanobacteria-based activated carbon for CO2 adsorption prepared by the preparation method according to the first aspect.

[0016] The cyanobacteria-based activated carbon prepared by the present invention, which has excellent specific surface area and pore structure, can be used for effectively adsorbing CO2.

[0017] In a third aspect, the present invention provides the application of the cyanobacteria-based activated carbon according to the first aspect in CO2 adsorption.

[0018] Specifically, the CO2 adsorption is carried out at 0-25 °C under standard atmospheric pressure.

[0019] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0020] (1) The preparation process of the present invention is simple. By using biomass cyanobacteria, cyanobacteria-based activated carbon with ultra-high specific surface area and excellent pore structure is obtained through pyrolysis and chemical activation. Cyanobacteria itself is a prokaryote and contains a large amount of protein, so it contains a relatively high nitrogen element. When used as a precursor of activated carbon, the activated carbon can not only avoid the loss of specific surface area and pore volume during the nitrogen doping process, but also retain the nitrogen element and functional groups in the activated carbon, realizing the in-situ nitrogen doping of the cyanobacteria-based activated carbon, providing more active sites, and improving the activity on the surface of the activated carbon to improve the adsorption performance of the activated carbon.

[0021] (2) The cyanobacteria-based activated carbon prepared by the present invention is applied to the field of CO2 adsorption, showing high adsorption performance and stability, greatly improving the practical applicability of the cyanobacteria-based activated carbon, and realizing the deep resource utilization of cyanobacteria. Specific Embodiments

[0022] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0023] Example 1:

[0024] Preparation of cyanobacteria powder: Obtain natural lake water containing cyanobacteria on the surface of Lake Taihu. First, preliminarily filter impurities such as branches with a filter screen with a larger pore size to obtain a filtrate containing cyanobacteria. Then, filter the water from the filtrate containing cyanobacteria with a filter screen with a small pore size. Next, spread the obtained cyanobacteria evenly on a drying board and place it in a ventilated place to dry and air-dry for 72 hours to initially obtain sheet-like cyanobacteria. Then, put the sheet-like cyanobacteria into an oven at 70 °C and dry for 72 hours, and then crush and sieve it to obtain cyanobacteria powder.

[0025] Example 2:

[0026] Pyrolysis treatment is carried out using a tubular furnace. Weigh a certain mass of the cyanobacteria powder prepared in Example 1 and place it in a quartz boat. Under a nitrogen atmosphere, prepare the cyanobacteria powder into pre-carbonized carbon under the conditions of a carbonization temperature of 400 °C, a heating rate of 20 °C / min, and a constant-temperature carbonization time of 60 minutes.

[0027] Subsequently, impregnate 2 g of the pre-carbonized carbon in 50 mL of an aqueous potassium carbonate solution for 24 hours (the mass ratio of potassium carbonate to pre-carbonized carbon is 2:1). After drying in an oven at 105 °C for 4 hours, place it in a quartz boat. Under a nitrogen atmosphere, activate the pre-carbonized carbon under the conditions of an activation temperature of 800 °C, a heating rate of 20 °C / min, and a constant-temperature time of 120 minutes. Cool down to room temperature, wash the surface impurities with 1 mol / L hydrochloric acid, wash with a large amount of water until neutral, and dry in an oven at 105 °C for 4 hours to obtain a cyanobacteria-based activated carbon with a super-high specific surface area.

[0028] The specific surface area of the cyanobacteria-based activated carbon is calculated by the BET method, and the pore size distribution is obtained by the DFT method. The specific surface area of the cyanobacteria-based activated carbon prepared by this method is 2177.3 m 2 / g, the pore volume is 1.13 cm 3 / g, the average pore size is 2.23 nm, and the micropore volume is 0.64 cm 3 / g.

[0029] Using CO2 as a simulated waste gas, evaluate the adsorption capacity through the adsorption performance of CO2 at 0 °C and 25 °C. The specific operation steps are as follows:

[0030] Carry out CO2 isothermal adsorption experiments on the samples at 0 °C and 25 °C. Before the experiment, take about 0.1 g of the sample in a test tube and degas it under vacuum conditions at 200 °C for 7 hours to remove impurities. The equilibrium interval for each test point is 5 s to obtain the CO2 isothermal adsorption curves at different temperatures. At 1 standard atmosphere, at 0 °C and 25 °C, the CO2 adsorption amounts of the cyanobacteria-based activated carbon are 5.12 mmol / g and 3.08 mmol / g, respectively.

[0031] Comparative Example 1:

[0032] The preparation method of the cyanobacteria powder refers to Example 1.

[0033] Pyrolysis treatment was carried out using a tube furnace. A certain mass of cyanobacteria powder was weighed and placed in a quartz boat. Under a nitrogen atmosphere, the cyanobacteria powder was prefabricated into cyanobacteria prefabricated carbon under the conditions of a carbonization temperature of 400 °C, a heating rate of 20 °C / min, and a constant temperature time of 60 min. Subsequently, 2 g of the prefabricated carbon was placed in a quartz boat, and under a nitrogen atmosphere, the prefabricated carbon was activated under the conditions of an activation temperature of 800 °C, a heating rate of 20 °C / min, and a constant temperature time of 120 min. The obtained activated carbon after cooling was washed with 1 mol / L hydrochloric acid to remove impurities and then washed with water until neutral, and dried in an oven at 105 °C for 4 hours to obtain a cyanobacteria-based activated carbon material.

[0034] Using the same calculation model for specific surface area and pore size and their distribution as in Example 2, the specific surface area of the activated carbon prepared by this method was 147.26 m 2 / g, the pore volume was 0.10 cm 3 / g, the average pore diameter was 2.95 nm, and the micropore volume was 0.04 cm 3 / g. Using the same CO2 adsorption experimental conditions as in Example 2, the CO2 adsorption amounts of the cyanobacteria-based activated carbon prepared by this method were 1.34 mmol / g and 1.01 mmol / g at one atmosphere, 0 °C and 25 °C temperature conditions. Compared with Example 2, this activated carbon was directly activated at high temperature without adding an activator for impregnation activation, so its specific surface area was lower, the pore structure was not well-developed, and its CO2 adsorption capacity was lower.

[0035] Comparative Example 2:

[0036] Referring to Example 1 for the preparation of cyanobacteria powder and referring to Example 2 for the preparation of cyanobacteria prefabricated carbon.

[0037] 2 g of the prefabricated carbon was impregnated in 50 mL of potassium hydroxide aqueous solution for 24 h (the mass ratio of cyanobacteria prefabricated carbon to potassium hydroxide was 1:1), dried in an oven at 105 °C for 4 hours and then placed in a quartz boat. Under a nitrogen atmosphere, activation was carried out under the conditions of a heating rate of 20 °C / min, an activation temperature of 800 °C, and a constant temperature activation time of 120 min. After activation, the black solid powder was taken out, washed with 1 mol / L hydrochloric acid to remove impurities and repeatedly washed with water until neutral, and then dried in an oven at 105 °C for 4 hours to constant weight to obtain a cyanobacteria-based activated carbon prepared by using potassium hydroxide as the activator and the two-step activation method.

[0038] Using the same calculation model for specific surface area and pore size and their distribution as in Example 2, the specific surface area of the activated carbon prepared by this method was 1298.2 m 2 / g, the pore volume was 0.78 cm 3 / g, the average pore diameter was 2.87 nm, and the micropore volume was 0.28 cm3 / g. Using the same CO2 adsorption experimental conditions as in Example 2, the CO2 adsorption amounts of the cyanobacteria-based activated carbon prepared by this method are 2.31 mmol / g and 1.51 mmol / g under the conditions of one atmosphere, 0 °C and 25 °C. Compared with Example 3, choosing different activators will greatly affect the pore structure of the activated carbon. Since the corrosiveness of potassium hydroxide is stronger than that of potassium carbonate, a higher average pore diameter, a smaller specific surface area, pore volume and micropore volume are formed, which is not conducive to the adsorption of CO2, resulting in a decrease in its adsorption capacity.

[0039] Comparative Example 3:

[0040] Referring to Example 1 for the preparation of cyanobacteria powder, and referring to Example 2 for the preparation of cyanobacteria pre-carbon.

[0041] Immerse 2 g of pre-carbon in 50 mL of potassium hydroxide aqueous solution for 24 h (the mass ratio of cyanobacteria pre-carbon to potassium hydroxide is 1:2). After drying in an oven at 105 °C for 4 hours, place it in a quartz boat. Under a nitrogen atmosphere, activate it under the conditions of a heating rate of 20 °C / min, an activation temperature of 800 °C, and a constant-temperature activation time of 120 min. After the activation is completed, take out the black solid powder, wash it with 1 mol / L hydrochloric acid to remove impurities, and wash it repeatedly with water until neutral, and then dry it in an oven at 105 °C for 4 hours until constant weight to obtain cyanobacteria-based activated carbon prepared by using potassium hydroxide as the activator and the two-step activation method.

[0042] Using the same calculation model for specific surface area and pore size and their distribution as in Example 2, the specific surface area of the activated carbon prepared by this method is 2255.8 m 2 / g, the pore volume is 1.06 cm 3 / g, the average pore diameter is 2.41 nm, and the micropore volume is 0.61 cm 3 / g. Using the same carbon dioxide adsorption experimental conditions as in Example 2, the CO2 adsorption amounts of the cyanobacteria-based activated carbon prepared by this method are 4.04 mmol / g and 2.60 mmol / g under the conditions of one atmosphere, 0 °C and 25 °C. After increasing the amount of potassium hydroxide used, the CO2 adsorption capacity has a certain increase. Compared with Example 2, both of them have a very high specific surface area. Because the pore volume and micropore volume are smaller and the average pore diameter is larger, their CO2 adsorption capacity is significantly lower, indicating that the pore volume and micropore volume may be important factors affecting the CO2 adsorption capacity.

[0043] Comparative Example 4:

[0044] Referring to Example 1 for the preparation of cyanobacteria powder, and referring to Example 2 for the preparation of cyanobacteria pre-carbon.

[0045] After pyrolysis treatment using a tubular furnace, 2 g of the prefabricated carbon was impregnated in 50 mL of an aqueous potassium hydroxide solution for 24 h (the mass ratio of the cyanobacteria prefabricated carbon to potassium hydroxide was 1:3). After drying in an oven at 105 °C for 4 h, it was placed in a quartz boat. Under a nitrogen atmosphere, activation was carried out at a heating rate of 20 °C / min, an activation temperature of 800 °C, and a constant-temperature activation time of 120 min. After the activation was completed, the black solid powder was taken out, washed with 1 mol / L hydrochloric acid to remove impurities, and repeatedly washed with water until neutral, and then dried in an oven at 105 °C for 4 h to constant weight, obtaining cyanobacteria-based activated carbon prepared by potassium hydroxide as the activator and the two-step activation method.

[0046] Using the same calculation model for specific surface area and pore size and its distribution as in Example 2, the specific surface area of the activated carbon prepared by this method was 1112.28 m 2 / g, the pore volume was 0.82 cm 3 / g, the average pore diameter was 2.97 nm, and the micropore volume was 0.32 cm 3 / g. Using the same carbon dioxide adsorption experimental conditions as in Example 2, the CO2 adsorption amounts of the cyanobacteria-based activated carbon prepared by this method were 3.19 mmol / g and 2.05 mmol / g at one atmosphere, 0 °C and 25 °C temperature conditions. After increasing the amount of potassium hydroxide used, the specific surface area and pore volume decreased significantly, and the average pore diameter increased, proving that the activation ability of potassium hydroxide was too strong and not conducive to the formation of microporous structures. Compared with Example 4, the too high mass of potassium hydroxide was too corrosive, seriously destroying the formation of the microporous structure of the activated carbon and not conducive to improving the CO2 adsorption capacity.

[0047] Comparative Example 5:

[0048] Refer to Example 1 for the preparation of cyanobacteria powder and Example 2 for the preparation of cyanobacteria prefabricated carbon.

[0049] 2 g of the prefabricated carbon was impregnated in 50 mL of an aqueous potassium hydroxide solution for 24 h (the mass ratio of the cyanobacteria prefabricated carbon to potassium hydroxide was 1:2). After drying in an oven at 105 °C for 4 h, it was placed in a quartz boat. Under a nitrogen atmosphere, activation was carried out at a heating rate of 20 °C / min, an activation temperature of 700 °C, and a constant-temperature activation time of 120 min. After the activation was completed, the black solid powder was taken out, washed with 1 mol / L hydrochloric acid to remove impurities, and repeatedly washed with water until neutral, and then dried in an oven at 105 °C for 4 h to constant weight, obtaining cyanobacteria-based activated carbon prepared by potassium hydroxide as the activator and the two-step activation method.

[0050] Using the same calculation model for specific surface area and pore size and its distribution as in Example 2, the specific surface area of the activated carbon prepared by this method was 1545.5 m 2 / g, the pore volume was 0.61 cm 3 / g, with an average pore diameter of 1.91 nm and a micropore volume of 0.50 cm 3 / g. Using the same carbon dioxide adsorption experimental conditions as in Example 2, the CO2 adsorption amounts of the cyanobacteria-based activated carbon prepared by this method are 3.62 mmol / g and 2.31 mmol / g under one atmosphere, at temperatures of 0 °C and 25 °C. Compared with Example 5, the activation abilities of potassium hydroxide and potassium carbonate at an activation temperature of 700 °C have a relatively similar influence on the pore structure. Although Comparative Example 5 has a higher specific surface area, pore volume, and micropore volume, its average pore diameter is lower, and its carbon dioxide adsorption ability is lower than that of Example 5, indicating that too small an average pore diameter is not conducive to the entry of CO2 into the pores, resulting in a decrease in CO2 adsorption ability.

[0051] Comparative Example 6:

[0052] Refer to Example 1 for the preparation of cyanobacteria powder, and refer to Example 2 for the preparation of cyanobacteria pre-carbon.

[0053] Use a tube furnace for activation treatment. Weigh a certain mass of cyanobacteria pre-carbon and potassium carbonate powder and place them in a quartz boat (the mass ratio of cyanobacteria pre-carbon to potassium carbonate is 1:2). Under a nitrogen atmosphere, activate under the conditions of a heating rate of 20 °C / min, an activation temperature of 800 °C, and a constant-temperature activation time of 120 min. After the activation is completed, take out the black solid powder, wash it with 1 mol / L hydrochloric acid to remove impurities, wash it repeatedly with water until neutral, and then dry it in an oven at 105 °C for 4 hours until constant weight to obtain cyanobacteria-based activated carbon prepared by using potassium carbonate as the activator and the two-step activation method.

[0054] Using the same calculation model for specific surface area and pore size and its distribution as in Example 2, the specific surface area of the activated carbon prepared by this method is 918.3 m 2 / g, the pore volume is 0.32 cm 3 / g, the average pore diameter is 1.98 nm, and the micropore volume is 0.25 cm 3 / g. Using the same carbon dioxide adsorption experimental conditions as in Example 2, the CO2 adsorption amounts of the cyanobacteria-based activated carbon prepared by this method are 3.20 mmol / g and 1.89 mmol / g under one atmosphere, at temperatures of 0 °C and 25 °C. Compared with Example 2, solid-phase activation is not conducive to generating a higher specific surface area and pore volume. This may be because the activator and cyanobacteria pre-carbon are not evenly mixed, and a lot of the activator exists on the surface. After high-temperature activation, it cannot activate the interior of the activated carbon, resulting in a decrease in its CO2 adsorption performance.

[0055] Comparative Example 7:

[0056] Preparation of peanut shell powder: Select the peanut shells remaining on the market, spread them flat on the drying board, place them in a ventilated place to dry and air-dry for 72 h to initially obtain dried peanut shells; then put the peanut shell waste into an oven at 70 °C to dry for 72 h, crush and sieve it to obtain peanut shell powder. The preparation of prefabricated peanut shell carbon refers to Example 2.

[0057] Pyrolysis treatment was carried out using a tubular furnace. Weigh a certain mass of peanut shell powder and place it in a quartz boat. Under a nitrogen atmosphere, with a carbonization temperature of 400 °C, a heating rate of 20 °C / min, and an isothermal time of 60 min, the peanut shell powder was prepared into prefabricated carbon. Subsequently, 2 g of prefabricated carbon was impregnated in 50 mL of potassium carbonate aqueous solution for 24 h (the mass ratio of prefabricated peanut shell carbon to potassium carbonate is 1:2). After drying in an oven at 105 °C for 4 hours, it was placed in a quartz boat. Under a nitrogen atmosphere, activation was carried out under the conditions of a heating rate of 20 °C / min, an activation temperature of 800 °C, and an isothermal activation time of 120 min. After the activation was completed, the black solid powder was taken out, washed with 1 mol / L hydrochloric acid to remove impurities, and repeatedly washed with water until neutral, and then dried in an oven at 105 °C for 4 hours until constant weight to obtain peanut shell-based activated carbon prepared by using potassium carbonate as the activator and the two-step activation method.

[0058] Using the same calculation model for specific surface area and pore size and its distribution as in Example 2, the specific surface area of the activated carbon prepared by this method is 1342.2 m 2 / g, the pore volume is 0.74 cm 3 / g, the average pore diameter is 2.31 nm, and the micropore volume is 0.61 cm 3 / g. Using the same experimental conditions for carbon dioxide adsorption as in Example 2, the CO2 adsorption amounts of the peanut shell-based activated carbon prepared by this method at one atmosphere, 0 °C and 25 °C are 4.25 mmol / g and 2.49 mmol / g, respectively. Compared with Example 2, the specific surface area and pore volume of the prepared peanut shell-based activated carbon are lower than those of the cyanobacteria-based activated carbon, and its CO2 adsorption performance is also weaker, indicating that cyanobacteria have great value as a precursor for CO2 adsorbents.

[0059] Example 3:

[0060] The preparation method of cyanobacteria powder refers to Example 1.

[0061] Pyrolysis treatment was carried out using a tube furnace. A certain mass of the cyanobacteria powder prepared in Example 1 was weighed and placed in a quartz boat. Under a nitrogen atmosphere, the cyanobacteria powder was prepared into pre-carbonized material under the conditions of a carbonization temperature of 400 °C, a heating rate of 20 °C / min, and a constant temperature time of 60 min. Subsequently, 2 g of the pre-carbonized material was impregnated in 50 mL of an aqueous potassium carbonate solution for 24 h (the mass ratio of potassium carbonate to pre-carbonized material was 1:1). After drying in an oven at 105 °C for 4 h, it was placed in a quartz boat. Under a nitrogen atmosphere, the pre-carbonized material was activated under the conditions of an activation temperature of 800 °C, a heating rate of 20 °C / min, and a constant temperature time of 120 min. After cooling to room temperature, the surface impurities were washed with 1 mol / L hydrochloric acid, washed with a large amount of water until neutral, and dried in an oven at 105 °C for 4 h to constant weight to obtain cyanobacteria-based activated carbon with a super-high specific surface area.

[0062] Using the same calculation model for specific surface area and pore size and its distribution as in Example 2, the specific surface area of the activated carbon prepared by this method was 2101.1 m 2 / g, the pore volume was 1.11 cm 3 / g, the average pore diameter was 2.55 nm, and the micropore volume was 0.56 cm 3 / g. Using the same carbon dioxide adsorption experimental conditions as in Example 2, the CO2 adsorption amounts of the cyanobacteria-based activated carbon prepared by this method were 4.10 mmol / g and 2.64 mmol / g at one atmosphere, 0 °C and 25 °C temperature conditions. The specific surface area, pore volume, and micropore volume were significantly improved, and the CO2 adsorption amount increased significantly.

[0063] Example 4:

[0064] The preparation method of the cyanobacteria powder refers to Example 1.

[0065] Pyrolysis treatment was carried out using a tube furnace. A certain mass of the cyanobacteria powder prepared in Example 1 was weighed and placed in a quartz boat. Under a nitrogen atmosphere, the cyanobacteria powder was prepared into pre-carbonized material under the conditions of a carbonization temperature of 400 °C, a heating rate of 20 °C / min, and a constant temperature time of 60 min. Subsequently, 2 g of the pre-carbonized material was impregnated in 50 mL of an aqueous potassium carbonate solution for 24 h (the mass ratio of potassium carbonate to pre-carbonized material was 3:1). After drying in an oven at 105 °C for 4 h, it was placed in a quartz boat. Under a nitrogen atmosphere, the pre-carbonized material was activated under the conditions of an activation temperature of 800 °C, a heating rate of 20 °C / min, and a constant temperature time of 120 min. After cooling to room temperature, the surface impurities were washed with 1 mol / L hydrochloric acid, washed with a large amount of water until neutral, and dried in an oven at 105 °C for 4 h to constant weight to obtain cyanobacteria-based activated carbon with a super-high specific surface area.

[0066] Using the same calculation model for specific surface area, pore size and their distribution as in Example 2, the specific surface area of the activated carbon prepared by this method is 2492.9 m 2 / g, the pore volume is 1.23 cm 3 / g, the average pore size is 2.71 nm, and the micropore volume is 0.58 cm 3 / g. Using the same experimental conditions for CO2 adsorption as in Example 2, the CO2 adsorption capacities of the cyanobacteria-based activated carbon prepared by this method are 4.11 mmol / g and 2.50 mmol / g at one atmosphere and temperatures of 0 °C and 25 °C, respectively. As the dosage ratio of potassium carbonate increases to 3, the specific surface area and pore volume increase significantly, but the micropore volume decreases, and the CO2 adsorption capacity decreases to some extent, indicating that the micropore volume may be an important factor affecting CO2 adsorption.

[0067] Example 5:

[0068] The preparation method of the cyanobacteria powder refers to Example 1.

[0069] Pyrolysis treatment was carried out using a tubular furnace. Weigh a certain mass of the cyanobacteria powder prepared in Example 1 and place it in a quartz boat. Under a nitrogen atmosphere, the cyanobacteria powder was prepared into pre-carbonized carbon under the conditions of a carbonization temperature of 400 °C, a heating rate of 20 °C / min, and a constant temperature time of 60 min; then 2 g of the pre-carbonized carbon was impregnated in 50 mL of an aqueous potassium carbonate solution for 24 h (the mass ratio of potassium carbonate to pre-carbonized carbon is 2:1), dried in an oven at 105 °C for 4 hours and then placed in a quartz boat. Under a nitrogen atmosphere, the pre-carbonized carbon was activated under the conditions of an activation temperature of 700 °C, a heating rate of 20 °C / min, and a constant temperature time of 120 min. After cooling to room temperature, the surface impurities were washed with 1 mol / L hydrochloric acid, washed with a large amount of water until neutral, and dried in an oven at 105 °C for 4 hours until constant weight to obtain a cyanobacteria-based activated carbon with a super high specific surface area.

[0070] Using the same calculation model for specific surface area, pore size and their distribution as in Example 2, the specific surface area of the activated carbon prepared by this method is 1486.2 m 2 / g, the pore volume is 0.63 cm 3 / g, the average pore size is 2.17 nm, and the micropore volume is 0.46 cm 3 / g. Using the same experimental conditions for CO2 adsorption as in Example 2, the CO2 adsorption capacities of the cyanobacteria-based activated carbon prepared by this method are 4.81 mmol / g and 3.04 mmol / g at one atmosphere and temperatures of 0 °C and 25 °C, respectively. When the amount of potassium carbonate is fixed and the activation temperature is relatively low, the activator cannot fully play its activation role. Therefore, the proportion of the micropore volume in the total pore volume is relatively high, the content of mesopore volume is relatively low, and the specific surface area is relatively low, indicating that the content of mesopore volume has an important impact on the specific surface area.

[0071] Example 6:

[0072] The preparation method of the cyanobacteria powder refers to Example 1.

[0073] The pyrolysis treatment was carried out using a tube furnace. A certain mass of the cyanobacteria powder prepared in Example 1 was weighed and placed in a quartz boat. Under a nitrogen atmosphere, the cyanobacteria powder was prepared into pre-carbonized carbon under the conditions of a carbonization temperature of 400 °C, a heating rate of 20 °C / min, and a constant temperature time of 60 min. Subsequently, 2 g of the pre-carbonized carbon was impregnated in 50 mL of an aqueous potassium carbonate solution for 24 h (the mass ratio of potassium carbonate to pre-carbonized carbon was 2:1), dried in an oven at 105 °C for 4 hours, then placed in a quartz boat, and activated under the conditions of an activation temperature of 900 °C, a heating rate of 20 °C / min, and a constant temperature time of 120 min under a nitrogen atmosphere. After cooling to room temperature, the surface impurities were washed with 1 mol / L hydrochloric acid, washed with a large amount of water until neutral, and dried in an oven at 105 °C for 4 hours until constant weight to obtain a cyanobacteria-based activated carbon with a super-high specific surface area.

[0074] Using the same calculation model for specific surface area and pore size and its distribution as in Example 2, the specific surface area of the activated carbon prepared by this method was 2459.1 m 2 / g, the pore volume was 1.15 cm 3 / g, the average pore diameter was 2.51 nm, and the micropore volume was 0.61 cm 3 / g. Using the same CO2 adsorption experimental conditions as in Example 2, the CO2 adsorption amounts of the cyanobacteria-based activated carbon prepared by this method were 4.76 mmol / g and 2.73 mmol / g at one atmosphere, 0 °C and 25 °C temperature conditions. The specific surface area of the activated carbon prepared at a higher activation temperature was still relatively high, the total pore volume increased to a certain extent, but the micropore volume showed a downward trend, indicating that high-temperature activation burned through the carbon layer and the micropore structure was damaged and merged into a mesopore structure.

[0075] The above examples are only for the description of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of cyanobacteria-based activated carbon for CO2 adsorption, characterized in that: The preparation method includes the following steps: (1) Preparation of cyanobacteria powder: Take cyanobacteria from natural lake water and obtain cyanobacteria powder through pretreatment; (2) Preparation of cyanobacteria-based activated carbon: Place the cyanobacteria powder obtained in step (1) in a tubular furnace for pyrolytic carbonization treatment to obtain prefabricated carbon; subsequently, mix potassium carbonate and the prefabricated carbon and impregnate and stir in water. The mass ratio of potassium carbonate to the prefabricated carbon is 0.5-5:

1. After sufficient impregnation, dry it, and then place it in a tubular furnace for activation treatment. The activation conditions are: in a nitrogen atmosphere, the heating rate is 5-30 °C / min, the activation temperature is 500-900 °C, the constant-temperature activation time is 0.5-3 h, and then cool down to room temperature; wash the activated carbon with acid to remove surface impurities, then wash it with water until neutral and dry to obtain cyanobacteria-based activated carbon for CO2 capture.

2. The preparation method according to claim 1, characterized in that: In step (2), the pyrolytic carbonization treatment conditions are: in a nitrogen atmosphere, the heating rate is 5-30 °C / min, the pyrolysis temperature is 300-500 °C, and the constant-temperature pyrolysis time is 30-120 min.

3. The preparation method according to claim 2, characterized in that: The pyrolytic carbonization treatment conditions in step (2) are: the pyrolytic carbonization temperature is 400 °C, the heating rate is 10-20 °C / min, and the constant-temperature pyrolytic carbonization time is 60-80 min.

4. The preparation method according to claim 1, characterized in that: In step (2), the mixing mass ratio of potassium carbonate to the prefabricated carbon is 1-3.

5. The preparation method according to claim 4, characterized in that: In step (2), the mixing mass ratio of potassium carbonate to the prefabricated carbon is 2:

1.

6. The preparation method according to claim 1, characterized in that: In step (2), the activation temperature is 650-900 °C, the activation heating rate is 10-20 °C / min, and the constant-temperature activation time is 120-150 min.

7. The preparation method according to claim 6, characterized in that: In step (2), the activation temperature is 650-800 °C.

8. The preparation method according to claim 6, characterized in that: In step (2), the constant-temperature activation time is 120 min.

9. A cyanobacteria-based activated carbon for CO2 adsorption prepared by the preparation method according to any one of claims 1-8.

10. Use of the cyanobacteria-based activated carbon according to claim 9 in CO2 adsorption.