Preparation method and application of blue-green algae-based biochar with fenton-like oxidation function

Abstract

The application discloses a preparation method and application of blue-green algae-based biochar with Fenton-like oxidation function. The preparation method comprises the following steps: (1) selecting an iron-containing flocculant, adding the iron-containing flocculant into natural lake water containing blue-green algae, and then performing sufficient stirring, standing, filtration, drying, crushing and sieving to obtain blue-green algae powder; (2) placing the blue-green algae powder in a tubular furnace for pyrolysis treatment to obtain preformed carbon; then, immersing the preformed carbon in an activating agent solution, performing sufficient immersion, drying, placing the preformed carbon in the tubular furnace for activation treatment, and finally performing heat treatment under air atmosphere to obtain blue-green algae-based biochar material with Fenton-like oxidation function. The application provides application of the prepared blue-green algae-based biochar in dye wastewater treatment, and the dye wastewater treatment is performed in the presence of hydrogen peroxide, and the blue-green algae-based biochar has high degradation removal rate and high stability.

Description

Technical Field

[0001] This invention relates to a method for preparing and applying cyanobacterial-based biochar with Fenton-like oxidation function. Background Technology

[0002] Currently, large freshwater lakes in my country, such as Taihu Lake, Chaohu Lake, and Dianchi Lake, are experiencing frequent cyanobacterial blooms, seriously affecting the regional water environment and water security [Environ. Sci. Technol. 2013, 47, 11, 5771-5777]. At present, the main method for treating cyanobacteria is harvesting. However, the cyanobacterial sludge produced after algae-water separation, if piled up without any treatment, is prone to rotting due to its high water content, emitting a foul odor, and releasing algal toxins, nitrogen, phosphorus, and other pollutants, easily causing secondary pollution. Therefore, the harmless treatment and resource utilization of algae are urgently needed [Algal Res. 2022, 64, 102670].

[0003] Pollutants such as dyes in water not only harm the environment but also seriously affect human health. Fenton-like reactions, with their strong oxidizing properties, can efficiently degrade organic pollutants in water [Appl. Catal. B: Environ. 2015, 166-167, 241-250]. However, iron-containing solid catalysts suffer from problems such as iron ion leaching and poor stability. Porous carbon materials, possessing not only high specific surface area but also excellent metal catalyst supports, can effectively solve these problems.

[0004] CN 115196739 A discloses a method for improving the catalytic degradation rate of methylene blue in dye wastewater. The method uses a modified nitrogen-doped cyanobacterial biochar catalyst as the degradation catalyst to enhance the methylene blue degradation rate. The self-doped nitrogen element from the cyanobacterial biochar itself acts as the degradation ligand, and hydrogen peroxide is added to form a metal-ligand-hydrogen peroxide (FeCu-N element-H2O2) system. The modified nitrogen-doped cyanobacterial biochar catalyst uses cyanobacteria from Dianchi Lake in Kunming as raw material, and modifies the cyanobacterial biochar with ferrous sulfate, copper chloride, and polyethylene glycol to obtain nano-Cu-Fe bimetallic functional nitrogen-doped biochar. This system achieves a methylene blue degradation removal rate of over 99%, and is not limited by pH conditions. Although the modified nitrogen-doped cyanobacterial biochar catalyst provided by this patent has a very good degradation effect on methylene blue, the preparation process is complex and not conducive to industrialization.

[0005] CN 113231030 A discloses a magnetic cyanobacterial biochar, its preparation method, and its application. The method involves freeze-drying, grinding, and sieving cyanobacteria to obtain cyanobacterial biomass. Fe₂O₃ is mixed with the cyanobacterial biomass and dried in an oven to obtain an intermediate product. The intermediate product is then placed in a tube furnace and carbonized under an inert atmosphere. After cooling to room temperature, it is ground and sieved to obtain the magnetic cyanobacterial biochar. When this magnetic cyanobacterial biochar is used for methylene blue degradation, the degradation efficiency is only 92.4% after 1 hour. Summary of the Invention

[0006] The first objective of this invention is to provide a method for preparing cyanobacterial-based biochar with Fenton-like oxidation function. This method is simple and efficiently obtains cyanobacterial-based biochar with Fenton-like oxidation function through one-step pyrolysis and activation by using an iron flocculant.

[0007] A second objective of this invention is to provide the application of the prepared cyanobacteria-based biochar in the treatment of dye wastewater.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing cyanobacteria-based biochar with Fenton-like oxidation function, comprising the following steps:

[0010] (1) Preparation of cyanobacterial powder: Select an iron-containing flocculant, add the iron-containing flocculant to the natural lake water containing cyanobacteria, so that the concentration of the iron-containing flocculant is 0.02-1g / L, stir thoroughly, let stand and settle, and then filter to obtain flocculated cyanobacterial mud. The obtained flocculated cyanobacterial mud is dried, crushed and sieved to obtain cyanobacterial powder.

[0011] (2) Preparation of cyanobacteria-based biochar: The cyanobacteria powder obtained in step (1) was placed in a tube furnace for pyrolysis treatment. The pyrolysis treatment conditions were: under a nitrogen atmosphere, the heating rate was 2.5-30℃ / min, the pyrolysis temperature was 300-600℃, and the isothermal pyrolysis time was 5-240min to obtain pre-char. Then, the pre-char was impregnated in an activator solution, wherein the activator was potassium hydroxide, and the mass ratio of the pre-char to the activator was 1:0.5-1:3. After thorough impregnation, the pre-char was dried and then placed in a tube furnace for activation treatment. The activation treatment conditions were: under a nitrogen atmosphere, the heating rate was 2.5-30℃ / min, the activation temperature was 650-900℃, and the isothermal activation time was 5-360min. Finally, the temperature was lowered to 150-250℃ and heat-treated in an air atmosphere for 0.5-4h to obtain cyanobacteria-based biochar material with Fenton oxidation-like function.

[0012] The iron-containing flocculant is selected from at least one of polyferric chloride, potassium ferrate, ferrous sulfate, polyferric sulfate, polyaluminum ferric chloride, and polyphosphoric ferric sulfate.

[0013] Preferably, in step (1), the concentration of the flocculant is 0.05-0.8 g / L, more preferably 0.2-0.8 g / L.

[0014] Preferably, in step (2), the pyrolysis temperature is 300-450°C, more preferably 400°C.

[0015] Preferably, in step (2), the pyrolysis heating rate is 5 to 25 °C / min, more preferably 10 to 25 °C / min.

[0016] Preferably, in step (2), the isothermal pyrolysis time is 60 to 160 min, more preferably 60 to 80 min.

[0017] As a further preferred option, in step (2), the pyrolysis heating rate is 10-25℃ / min, the pyrolysis temperature is 400℃, and the isothermal pyrolysis time is 60-80min.

[0018] Preferably, in step (2), the mass ratio of the pre-made charcoal to the activator is 1:0.75 to 1:2, and more preferably 1:1.2 to 2.

[0019] Preferably, in step (2), the activation temperature is 750-850°C, more preferably 800-850°C, and most preferably 800°C.

[0020] Preferably, in step (2), the activation heating rate is 5 to 25 °C / min, more preferably 10 to 25 °C / min.

[0021] Preferably, in step (2), the isothermal activation time is 60–180 min, more preferably 120–180 min.

[0022] As a further preferred option, in step (2), the activation temperature is 800℃, the activation heating rate is 10~25℃ / min, and the isothermal activation time is 120min.

[0023] Preferably, in step (2), the heat treatment time in an air atmosphere is 1 to 3 hours, more preferably 1.5 to 2.5 hours.

[0024] Through in-depth research, the inventors discovered that cyanobacterial biochar without added iron-based flocculants only has adsorption capabilities and lacks catalytic degradation functionality. However, the cyanobacterial biochar prepared in this invention possesses both catalytic degradation and adsorption functions. During the preparation process, the type of flocculant, the pre-formed char, and the activation conditions significantly affect the structure and properties of the cyanobacterial-based biochar. During activation, KOH exhibits the most significant pore-expanding effect. When the mass ratio of cyanobacterial-based biochar to activator increases from 1:2 to 1:4, the specific surface area of ​​the resulting biochar decreases significantly, the pore size distribution becomes wider, and the proportion of large pores increases. Excessive alkaline activator leads to over-activation, burning through the already formed micropore walls, severely damaging the microporous structure of the biochar, and generating more mesopores and macropores, resulting in a decrease in specific surface area. Excessively high activation temperatures also significantly damage the pore structure, reducing the specific surface area of ​​the cyanobacterial-based biochar. In this invention, the cyanobacterial-based biochar prepared using polyferric chloride as the iron-based flocculant exhibits the optimal catalytic activity.

[0025] The cyanobacteria-based biochar prepared by this invention has a Fenton-like oxidation function and can be used to effectively degrade dye pollutants in water.

[0026] Secondly, the present invention provides the application of the cyanobacteria-based biochar in the treatment of dye wastewater, wherein the dye wastewater treatment is carried out in the presence of hydrogen peroxide.

[0027] In a specific embodiment of the present invention, the dye is methylene blue.

[0028] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0029] (1) The preparation process of this invention is simple. By using an iron-containing flocculant, cyanobacterial biochar with Fenton oxidation function is obtained efficiently through one-step pyrolysis and activation. The iron-containing flocculant has multiple functions: 1) It acts as a flocculant to achieve deep dehydration of cyanobacteria; 2) It acts as a precursor of iron-based Fenton-like catalysts, forming Fenton-like catalysts during pyrolysis and achieving in-situ doping with nitrogen elements of cyanobacteria during pyrolysis, thereby improving the catalytic efficiency and stability of the Fenton-like system; 3) The preparation process reduces the operation steps of soaking in iron salt solution and secondary heat treatment, thereby increasing the specific surface area of ​​cyanobacterial biochar with Fenton oxidation function.

[0030] (2) The cyanobacteria-based biochar prepared by this invention is applied to the field of dye wastewater treatment, showing high degradation and removal rate and high stability, which greatly improves the practical application performance of biochar and realizes the deep resource utilization of cyanobacteria. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0032] Examples 1-2:

[0033] Polyferric chloride was selected as the cyanobacterial flocculant. The flocculant was prepared into flocculant solutions of 0.8 g / L (Example 1) and 0.5 g / L (Example 2) using Taihu Lake water containing cyanobacteria. After thorough stirring, the solutions were allowed to settle and then filtered to obtain flocculent cyanobacterial mud. The mud was then air-dried, pulverized into powder using a pulverizer, and passed through a 30-mesh sieve to obtain cyanobacterial powder.

[0034] Example 3

[0035] The pyrolysis was performed using a tubular 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 pre-carbonized at a carbonization temperature of 400℃, a heating rate of 20℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of potassium hydroxide solution for 24h (the mass ratio of pre-carbonized material to potassium hydroxide was 1:2). After drying, the material was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 800℃, a heating rate of 20℃ / min, and a holding time of 120min. The temperature was then lowered to 200℃ and held in air for 2h. After cooling, a cyanobacteria-based biochar material with Fenton oxidation-like function and loaded with Fe2O3 was obtained.

[0036] The specific surface area of ​​the cyanobacteria-based biochar was calculated using the BET method, and the pore size distribution was obtained using the NLDFT method. The specific surface area of ​​the cyanobacteria-based biochar prepared by this method was 1576 m². 2 / g, pore volume is 1.019cm³ 3 / g, with an average pore size of 2.586nm.

[0037] Methylene blue aqueous solution was used to simulate dye wastewater, and the catalytic activity was evaluated by assessing its degradation performance. The concentration of the methylene blue solution was determined using a UV-Vis spectrophotometer. The specific operating steps are as follows:

[0038] (1) Plot the standard curve of methylene blue solution;

[0039] (2) Parameters for dye degradation experiment: 200 mL of 50 mg / L methylene blue solution was prepared in a 250 mL Erlenmeyer flask; the concentration of cyanobacterial biochar material was 100 mg / L; and the concentration of hydrogen peroxide solution was 1 g / L. The dye adsorption and degradation experiment was carried out at 30 °C under light-shielding conditions.

[0040] (3) Absorbance measurement: The absorbance was measured by spectrophotometry. The supernatant was placed in a cuvette with a 1 cm optical path, and deionized water was used as a blank reference. The absorbance at a wavelength of 664 nm was measured, and the absorbance of the methylene blue solution was measured every 5 minutes.

[0041] After the degradation experiment, the Fe2O3-loaded cyanobacterial-based biochar was separated by centrifugation and washed with methanol solution. The degradation experiment was repeated 5 times to evaluate the stability of the catalytic performance. After 20 min of catalytic reaction, the removal rate of methylene blue reached 99.8%, and after repeating the experiment 5 times, the removal rate of methylene blue still reached 99.0%, indicating that the cyanobacterial-based biochar material has excellent catalytic performance. Comparative Example 1:

[0042] The preparation method of cyanobacteria powder is the same as in Example 1, except that polyaluminum chloride is used as the cyanobacteria flocculant and the flocculant is prepared into a flocculant solution of 0.8 g / L.

[0043] The pyrolysis process was performed using a tubular furnace. A certain mass of cyanobacteria powder was weighed and placed in a quartz boat. Under a nitrogen atmosphere, the cyanobacteria powder was pre-carbonized at a carbonization temperature of 400℃, a heating rate of 20℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of potassium hydroxide solution for 24h (the mass ratio of pre-carbonized material to potassium hydroxide was 1:2). After drying, the material was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 800℃, a heating rate of 20℃ / min, and a holding time of 120min. After cooling, the cyanobacteria-based biochar material was obtained.

[0044] Using the same calculation model for specific surface area, pore size, and their distribution as in Example 3, the biochar prepared by this method has a specific surface area of ​​1035 m². 2 / g, pore volume is 0.822cm³ 3 / g, with an average pore size of 2.436nm. Under the same experimental conditions for dye degradation and adsorption as in Example 3, the cyanobacteria-based biochar prepared by this method showed no catalytic degradation performance, only adsorption function, with a removal rate of 50.5% for methylene blue, and it took 160 minutes to reach dye adsorption equilibrium.

[0045] Comparative Example 2:

[0046] The preparation method of cyanobacterial powder is the same as in Example 1, except that polydimethyldiallylammonium chloride is used as the cyanobacterial flocculant and the flocculant is prepared into a flocculant solution of 0.2 g / L.

[0047] The pyrolysis process was performed using a tubular furnace. A certain mass of cyanobacteria powder was weighed and placed in a quartz boat. Under a nitrogen atmosphere, the cyanobacteria powder was pre-carbonized at a carbonization temperature of 400℃, a heating rate of 20℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of potassium hydroxide solution for 24h (the mass ratio of pre-carbonized material to potassium hydroxide was 1:2). After drying, the pre-carbonized material was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 800℃, a heating rate of 20℃ / min, and a holding time of 120min to obtain cyanobacteria-based biochar material.

[0048] Using the same calculation model for specific surface area, pore size, and their distribution as in Example 3, the biochar prepared by this method has a specific surface area of ​​1845 m². 2 / g, pore volume is 1.082cm³ 3 / g, with an average pore size of 2.149nm. Using the same experimental conditions for dye degradation and adsorption as in Example 3, the cyanobacteria-based biochar prepared by this method showed no catalytic degradation performance, only adsorption function, with a removal rate of 65.5% for methylene blue, and reached dye adsorption equilibrium in 120 minutes.

[0049] Comparative Example 3:

[0050] The preparation method of cyanobacterial powder is the same as in Example 1, except that polydimethyldiallylammonium chloride is used as the cyanobacterial flocculant and the flocculant is prepared into a flocculant solution of 0.2 g / L.

[0051] The pyrolysis was performed using a tubular furnace. A certain mass of cyanobacteria powder was weighed and placed in a quartz boat. Under a nitrogen atmosphere, the cyanobacteria powder was pre-carbonized at a carbonization temperature of 400℃, a heating rate of 20℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of potassium hydroxide solution for 24h (the mass ratio of pre-carbonized material to potassium hydroxide was 1:2). After drying, the material was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 800℃, a heating rate of 20℃ / min, and a holding time of 120min to obtain cyanobacteria-based biochar material.

[0052] Using the same calculation model for specific surface area, pore size, and their distribution as in Example 3, the biochar prepared by this method has a specific surface area of ​​1845 m². 2 / g, pore volume is 1.082cm³ 3 / g, with an average pore size of 2.149nm.

[0053] Weigh 0.5 g of the above-mentioned cyanobacteria-based biochar and impregnate it in 50 mL of 2 g / L ferric chloride solution. Stir at 300 rpm for 2 h. Dry the resulting solid at 70 °C to constant weight, and then calcine it in a muffle furnace at 200 °C for 2 h. This process yields cyanobacteria-based biochar material with Fenton oxidation-like function that is loaded with Fe2O3 through a multi-step method.

[0054] Using the same calculation model as in Example 3 for specific surface area, pore size, and their distribution, the specific surface area of ​​the cyanobacteria-based biochar with Fenton-like oxidation function loaded with Fe2O3 via a multi-step method was determined to be 845 m². 2 / g, pore volume is 0.519cm³ 3 / g, with an average pore size of 2.258nm. Using the same degradation and adsorption dye experimental conditions as in Example 3, after 60 min of catalytic reaction, the removal rate of methylene blue was 97.9%, and after repeating the degradation experiment 5 times, the removal rate of methylene blue was 93.6%.

[0055] Comparative Example 4:

[0056] The pyrolysis was performed using a tubular 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 pre-carbonized at a carbonization temperature of 400℃, a heating rate of 20℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of potassium hydroxide solution for 24h (the mass ratio of pre-carbonized material to potassium hydroxide was 1:4). After drying, the pre-carbonized material was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 800℃, a heating rate of 20℃ / min, and a holding time of 120min. The temperature was then lowered to 200℃ and held in air for 2h. After cooling, a cyanobacteria-based biochar material with Fenton-like oxidation function and loaded with Fe2O3 was obtained.

[0057] Using the same calculation model for specific surface area, pore size, and their distribution as in Example 3, the biochar prepared by this method has a specific surface area of ​​830 m². 2 / g, pore volume is 0.682cm³ 3 / g, with an average pore size of 2.986nm. Using the same degradation and adsorption dye experimental conditions as in Example 3, after 60 min of catalytic reaction, the removal rate of methylene blue was 87.0%, and after repeating the experiment 5 times, the removal rate of methylene blue was 85.7%.

[0058] Comparative Example 5:

[0059] The pyrolysis was performed using a tubular 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 pre-carbonized at a carbonization temperature of 400℃, a heating rate of 20℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of potassium hydroxide solution for 24h (the mass ratio of pre-carbonized material to potassium hydroxide was 1:2). After drying, the pre-carbonized material was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 950℃, a heating rate of 20℃ / min, and a holding time of 120min. The temperature was then lowered to 200℃ and held in air for 2h. After cooling, a cyanobacteria-based biochar material with Fenton-like oxidation function and loaded with Fe2O3 was obtained.

[0060] Using the same calculation model for specific surface area, pore size, and their distribution as in Example 3, the biochar prepared by this method has a specific surface area of ​​679 m². 2 / g, pore volume is 0.667cm³ 3 / g, with an average pore size of 3.098nm. Using the same degradation and adsorption dye experimental conditions as in Example 3, after 60 min of catalytic reaction, the removal rate of methylene blue was 82.6%, and after repeating the experiment 5 times, the removal rate of methylene blue was 81.3%.

[0061] Example 2:

[0062] The pyrolysis was performed using a tubular furnace. A certain mass of the cyanobacteria powder prepared in Example 2 was weighed and placed in a quartz boat. Under a nitrogen atmosphere, the cyanobacteria powder was pre-carbonized at a carbonization temperature of 300℃, a heating rate of 20℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of potassium hydroxide solution for 24h (the mass ratio of pre-carbonized material to potassium hydroxide was 1:1.2). After drying, it was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 800℃, a heating rate of 20℃ / min, and a holding time of 120min. The temperature was then lowered to 200℃ and held in air for 2h. After cooling, a cyanobacteria-based biochar material with Fenton-like oxidation function and loaded with Fe2O3 was obtained.

[0063] Using the same calculation model for specific surface area, pore size, and their distribution as in Example 3, the biochar prepared by this method has a specific surface area of ​​1039 m². 2 / g, pore volume is 0.779cm³ 3 / g, with an average pore size of 2.376nm. Using the same degradation and adsorption dye experimental conditions as in Example 3, after catalytic reaction for 35 min, the removal rate of methylene blue was 95.9%, and after repeating the degradation experiment 5 times, the removal rate of methylene blue was 94.2%.

[0064] Example 3:

[0065] The preparation method of cyanobacteria powder is the same as in Example 1, except that polyferric sulfate is used as the cyanobacteria flocculant.

[0066] The pyrolysis was performed using a tubular furnace. A certain mass of cyanobacterial powder was weighed and placed in a quartz boat. Under a nitrogen atmosphere, the cyanobacterial powder was pre-carbonized at a carbonization temperature of 400℃, a heating rate of 10℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of potassium hydroxide solution for 24h (the mass ratio of pre-carbonized material to potassium hydroxide was 1:2). After drying, it was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 800℃, a heating rate of 10℃ / min, and a holding time of 120min. The temperature was then lowered to 180℃ and held in air for 2.5h. After cooling, a cyanobacterial-based biochar material with Fenton oxidation-like function and loaded with Fe2O3 was obtained.

[0067] Using the same calculation model for specific surface area, pore size, and their distribution as in Example 3, the biochar prepared by this method has a specific surface area of ​​1365 m². 2 / g, pore volume is 0.807cm³ 3 / g, with an average pore size of 2.366nm. Using the same degradation and adsorption dye experimental conditions as in Example 3, after catalytic reaction for 25 min, the removal rate of methylene blue reached 99.3%, and after repeating the experiment 5 times, the removal rate of methylene blue was 98.7%.

[0068] Example 4:

[0069] The pyrolysis was performed using a tubular 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 pre-carbonized at a carbonization temperature of 400℃, a heating rate of 20℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of potassium hydroxide solution for 24h (the mass ratio of pre-carbonized material to potassium hydroxide was 1:2). After drying, the material was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 750℃, a heating rate of 20℃ / min, and a holding time of 180min. The temperature was then lowered to 200℃ and held in air for 2h. After cooling, a cyanobacteria-based biochar material with Fenton-like oxidation function and loaded with Fe2O3 was obtained.

[0070] Using the same calculation model for specific surface area, pore size, and their distribution as in Example 3, the biochar prepared by this method has a specific surface area of ​​1298 m². 2 / g, pore volume is 0.776cm³ 3 / g, with an average pore size of 2.064nm. Using the same degradation and adsorption dye experimental conditions as in Example 3, after catalytic reaction for 35 min, the removal rate of methylene blue was 94.3%, and after repeating the experiment 5 times, the removal rate of dye was 93.8%.

[0071] Example 5:

[0072] The pyrolysis was performed using a tubular 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 pre-carbonized at a carbonization temperature of 400℃, a heating rate of 20℃ / min, and a holding time of 60min. Subsequently, 3g of the pre-carbonized material was immersed in 50mL of zinc chloride solution for 24h (the mass ratio of pre-carbonized material to zinc chloride was 1:2). After drying, the material was placed in a quartz boat and activated under a nitrogen atmosphere at an activation temperature of 850℃, a heating rate of 20℃ / min, and a holding time of 120min. The temperature was then lowered to 220℃ and held in air for 1.5h. After cooling, a cyanobacteria-based biochar material with Fenton oxidation-like function and loaded with Fe2O3 was obtained.

[0073] Using the same calculation model for specific surface area, pore size, and their distribution as in Example 3, the biochar prepared by this method has a specific surface area of ​​1049 m². 2 / g, pore volume is 0.752cm³ 3 / g, with an average pore size of 2.436nm. Using the same degradation and adsorption dye experimental conditions as in Example 3, after catalytic reaction for 35 min, the removal rate of methylene blue was 96.3%, and after repeating the experiment 5 times, the removal rate of methylene blue was 96.1%.

[0074] The above embodiments of the present invention are illustrative and not limiting. Any changes within the meaning and scope of the claims should be considered to be included within the scope of the claims.

Claims

1. A method for preparing cyanobacteria-based biochar with Fenton-like oxidation function, characterized in that: The preparation method includes the following steps: (1) Preparation of cyanobacterial powder: Select an iron-containing flocculant, add the iron-containing flocculant to the natural lake water containing cyanobacteria, so that the concentration of the iron-containing flocculant is 0.02-1g / L, stir thoroughly, let stand and settle, and then filter to obtain flocculated cyanobacterial mud. The obtained flocculated cyanobacterial mud is dried, crushed and sieved to obtain cyanobacterial powder. (2) Preparation of cyanobacteria-based biochar: The cyanobacteria powder obtained in step (1) was placed in a tube furnace for pyrolysis treatment. The pyrolysis treatment conditions were: under a nitrogen atmosphere, the heating rate was 2.5-30℃ / min, the pyrolysis temperature was 300-600℃, and the isothermal pyrolysis time was 5-240min to obtain pre-char. Then, the pre-char was impregnated in an activator solution, wherein the activator was potassium hydroxide, and the mass ratio of the pre-char to the activator was 1:0.5-1:

3. After thorough impregnation, the pre-char was dried and then placed in a tube furnace for activation treatment. The activation treatment conditions were: under a nitrogen atmosphere, the heating rate was 2.5-30℃ / min, the activation temperature was 650-900℃, and the isothermal activation time was 5-360min. Finally, the temperature was lowered to 150-250℃ and heat-treated in an air atmosphere for 0.5-4h to obtain cyanobacteria-based biochar material with Fenton oxidation-like function. The iron-containing flocculant is selected from at least one of polyferric chloride, potassium ferrate, ferrous sulfate, polyferric sulfate, polyaluminum ferric chloride, and polyphosphoric ferric sulfate.

2. The preparation method according to claim 1, characterized in that: In step (1), the concentration of the iron-containing flocculant is 0.05 to 0.8 g / L.

3. The preparation method according to claim 2, characterized in that: In step (1), the concentration of the iron-containing flocculant is 0.2 to 0.8 g / L.

4. The preparation method according to claim 1, characterized in that: In step (2), the pyrolysis temperature is 300-450℃, the pyrolysis heating rate is 5-25℃ / min, and the isothermal pyrolysis time is 60-160min.

5. The preparation method according to claim 1, characterized in that: In step (2), the pyrolysis heating rate is 10-25℃ / min, the pyrolysis temperature is 400℃, and the isothermal pyrolysis time is 60-80min.

6. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of the pre-made charcoal to the activator is 1:0.75 to 1:

2.

7. The preparation method according to claim 6, characterized in that: In step (2), the mass ratio of the pre-made charcoal to the activator is 1:1.2 to 2.

8. The preparation method according to claim 1, characterized in that: In step (2), the activation temperature is 750–850℃; the activation heating rate is 5–25℃ / min. The isothermal activation time is 60–180 min.

9. The preparation method according to claim 8, characterized in that: In step (2), the activation temperature is 800-850℃; the activation heating rate is 10-25℃ / min.

10. The preparation method according to claim 9, characterized in that: In step (2), the activation temperature is 800℃.

11. The preparation method according to claim 1, characterized in that: In step (2), the activation temperature is 800℃, the activation heating rate is 10~25℃ / min, and the isothermal activation time is 120min.

12. The preparation method according to claim 1, characterized in that: In step (2), the heat treatment time in air atmosphere is 1 to 3 hours.

13. The preparation method according to claim 12, characterized in that: In step (2), the heat treatment time in air atmosphere is 1.5 to 2.5 hours.

14. The application of the cyanobacteria-based biochar prepared by any one of claims 1-13 in the treatment of dye wastewater, wherein the dye wastewater treatment is carried out in the presence of hydrogen peroxide; and the dye is methylene blue.