Method for two-stage preparation of nano-biochar from waste straws and application of nano-biochar

Abstract

The invention discloses a method for two-stage preparation of nano biochar from waste straws and application of the nano biochar. The method comprises the following steps: naturally air-drying the waste straws for 72-96 hours, drying at 60-80 DEG C for 24-48 hours, crushing, sieving with a 60-mesh sieve, and sealing for later use; the method comprises the following steps: carrying out hydrothermal reaction on waste straws at 180-240 DEG C for 1-2 hours to obtain hydrothermal carbon, and carrying out pyrolysis on the hydrothermal carbon at 300-900 DEG C under the protection of inert gas for 1-3 hours to obtain biochar; the preparation method comprises the following steps: putting biochar into a ball milling tank, adding agate balls with a mixed size, then adding deionized water to wet a sample, putting the sample into a planetary ball mill, and carrying out wet grinding to obtain the nano biochar. The prepared nano biochar has a smaller hydrodynamic radius, a larger specific surface area and a rich pore structure, active sites on the surface of the nano biochar are increased, activation of PMS can be promoted, more ROS with high reactivity can be generated, and the nano biochar has higher catalytic degradation potential.

Description

Technical Field

[0001] The invention belongs to the technical field of resource utilization of waste biomass and removal of antibiotics in water, and specifically relates to a method for preparing nano biochar in two stages by utilizing waste straw and its application. Background Art

[0002] With the rapid development of agriculture and forestry, a large amount of organic biomass represented by crop straw has been produced. Due to its strong seasonality, scattered distribution, and difficulty in collection, storage and transportation, these agricultural and forestry wastes are randomly discarded or burned in the open air, which will not only cause pollution and waste of land resources, but also cause serious secondary pollution during burning. Therefore, how to realize the resource utilization and high-value utilization of agricultural and forestry biomass is an environmental problem that needs to be solved urgently, and will become an important factor restricting the development of biomass energy.

[0003] In recent years, the preparation of biochar has become a potential method for biomass resource utilization. Biochar is a solid product obtained by high-temperature heat treatment of these waste biomass under anoxic conditions. It has high carbon content, rich pore structure, large specific surface area, rich surface oxygen-containing functional groups and good adsorption performance. It can activate peroxymonosulfate (PMS) by generating environmental persistent free radicals (EPFRs) to promote the reaction to generate reactive oxygen species (ROS), degrade organic pollutants in water, and alleviate water pollution problems. It has attracted widespread attention from researchers. At the same time, with the rapid development of medical and animal husbandry industries, the use of antibiotics has continued to increase, and their residues have entered the environment in large quantities through various channels, causing damage to the ecosystem and the spread of drug-resistant bacteria, which has a significant impact on the ecological environment. Therefore, the removal of antibiotics in water bodies is also an urgent environmental issue. The preparation of biochar can not only realize the resource utilization of waste biomass, but also can be used to remove antibiotics in water bodies, achieving the purpose of treating waste with waste.

[0004] In order to more effectively remove antibiotics from water, biochar needs to be modified. Currently, there are methods such as acid treatment, alkali treatment, amination, and surfactant modification. Among them, ball milling, as a green and environmentally friendly physical modification method, can effectively improve the adsorption and degradation properties of biochar. The ball-milled nano-biochar has a larger specific surface area, larger pore volume, smaller fluid dynamic radius, and more surface oxygen-containing functional groups than the original biochar, which can greatly improve its removal efficiency of antibiotics. Summary of the invention

[0005] The technical problem solved by the present invention is to provide a method for preparing nano biochar using waste straw, which is based on preparing biochar by hydrothermal and pyrolysis carbonization of waste straw, and preparing nano biochar by wet mechanical ball milling modification. The preparation process of the method is simple and green, safe and efficient, and the product yield is high. In addition, the concentration of antibiotics in water can be reduced while realizing the resource utilization of biomass, which greatly alleviates the problem of antibiotic water pollution.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solution, a method for preparing nano biochar in two stages using waste straw, which comprises the following steps: Step S1: air-dry the waste straw for 72-96 hours, and then dry it at 60-80°C for 24-48 hours, and then crush it through a 60-mesh sieve and seal it for later use; Step S2: subjecting the waste straw obtained in step S1 to a hydrothermal reaction at 180-240° C. for 1-2 h to obtain hydrothermal charcoal, and then pyrolyzing the hydrothermal charcoal at 300-900° C. for 1-3 h under the protection of an inert gas to obtain biochar; Step S3: The biochar obtained in step S2 is placed in a ball mill, and agate balls of mixed sizes are added, and then deionized water is added to wet the sample and placed in a planetary ball mill for wet grinding to obtain nano biochar.

[0007] It is further defined that the waste straw in step S1 is one or more of corn straw, wheat straw or rice straw.

[0008] It is further defined that the specific preparation process of the hydrothermal charcoal in step S2 is: placing the waste straw obtained in step S1 in a polytetrafluoroethylene liner and adding deionized water, the solid-liquid ratio is controlled at 1g:4~8mL, and then placing the polytetrafluoroethylene liner in a closed high-pressure hydrothermal reactor, and then placing the reactor in an oven at 180~240℃ for hydrothermal reaction for 1~2h, after the reaction is completed, let it cool to room temperature, take out the sample, let it stand and settle, pour out the supernatant, and then dry it at 60~80℃ for 4~8h to obtain the hydrothermal charcoal.

[0009] It is further defined that the specific preparation process of the biochar described in step S2 is: placing the hydrothermal charcoal into a covered crucible and placing it in a tubular furnace for pyrolysis, and before pyrolysis, vacuuming and injecting N2 to replace O2 three times. N2 is continuously injected during the pyrolysis process, and the gas flow rate is 25~50mL / min until the reaction is completed. The pyrolysis heating rate is 10~30℃ / min, and the pyrolysis time is 2h. The obtained product is crushed using a mortar to obtain biochar.

[0010] Further defined, the specific preparation process of the nano biochar in step S3 is: placing the biochar obtained in step S2 in an agate ball mill, and then adding agate balls of mixed sizes, the mixed-size agate balls including large agate balls with a diameter of 10 mm, medium agate balls with a diameter of 8 mm, and small agate balls with a diameter of 5 mm, wherein the volume percentages of the large agate balls with a diameter of 10 mm, the medium agate balls with a diameter of 8 mm, and the small agate balls with a diameter of 5 mm are 20%, 50%, and 30%, respectively, the volume ratio of the biochar to the agate balls is 1:1, and the volume ratio of the biochar and the agate balls is 1:1. The total volume is not less than 1 / 3 of the total volume of the ball mill jar and not more than 2 / 3 of the total volume of the ball mill jar. Finally, deionized water is added to moisten the sample and placed in a planetary ball mill for wet grinding. After grinding, the sample in the agate jar is rinsed with deionized water and transferred to a beaker, and then placed in an oven at 70-90°C for drying to obtain nano-biochar. The nano-biochar has a smaller fluid dynamic radius, a larger specific surface area and a rich pore structure. The active sites on its surface are increased, which can promote the activation of PMS, produce more highly reactive ROS, and have a stronger catalytic degradation potential.

[0011] It is further defined that the ball milling speed in the wet grinding process in step S3 is 600-800 rpm, and the ball milling time is 24-72 h.

[0012] The application of the nano-biochar in the removal of antibiotics in water bodies of the present invention comprises the following specific processes: adding the nano-biochar to a water sample containing antibiotics, then adding peroxymonosulfate (PMS), and then placing the sample in a constant temperature oscillator at 20-30° C. to react at a constant temperature for catalytic degradation to remove the antibiotics.

[0013] It is further defined that the antibiotic is sulfadimethoxine (SDM), the dosage of nano-biochar is 1-5 g / L, and the dosage of permonosulfate (PMS) is 1-5 mmol / L.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The present invention uses waste straw as raw material, has a simple preparation method, low raw material cost, is economical and environmentally friendly, and realizes effective resource utilization of waste straw, with good economic and environmental benefits; 2. The present invention adopts a two-step (hydrothermal charcoal + pyrolytic charcoal) biochar preparation method, and the obtained biochar has more abundant surface oxygen-containing functional groups, which increases the hydrophilicity of the biochar and further significantly improves the ability to degrade antibiotics; 3. The nano-biochar obtained after mechanical ball milling of the biochar of the present invention has a smaller fluid dynamic radius, a larger specific surface area and a rich pore structure. The active sites on its surface are increased, which can promote the activation of PMS, produce more highly reactive ROS, and have a stronger catalytic degradation potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the SEM image of biochar prepared from waste straw.

[0016] Figure 2 This is the TEM image of nano-biochar obtained after mechanical ball milling modification.

[0017] Figure 3 This is a diagram showing the degradation effect of hydrothermal + pyrolysis biochar on SDM before and after ball milling at different preparation temperatures. DETAILED DESCRIPTION

[0018] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention. Example

[0019] Step S1: Pretreatment of waste wheat straw The waste wheat straw particles were naturally air-dried for 80 hours, and then placed in an oven to dry at 70°C for 32 hours. They were then crushed with a grinder and passed through a 60-mesh sieve. The obtained wheat straw was put into a sealed bag and stored for later use.

[0020] Step S2: Preparation of biochar using waste wheat straw The wheat straw obtained in step S1 is placed in a polytetrafluoroethylene liner and deionized water is added, and the solid-liquid ratio is controlled at 1g:5mL. The polytetrafluoroethylene liner is then placed in a closed high-pressure hydrothermal reactor, and the reactor is then placed in an oven for hydrothermal reaction at 200°C for 2h. After the reaction is completed, it is allowed to cool to room temperature, the sample is taken out and allowed to settle, and the supernatant is poured out. The hydrothermal charcoal is obtained after drying at 70°C for 6h. The hydrothermal charcoal is placed in a covered crucible and placed in a tubular furnace for pyrolysis. Before pyrolysis, N2 is injected to replace O2 by vacuuming three times. N2 is continuously injected during the pyrolysis process, and the gas flow rate is 30mL / min until the reaction is completed. The pyrolysis temperatures are 300°C, 400°C, 500°C, 600°C, 700°C, 800°C and 900°C, respectively. The heating rate is controlled to be 10°C / min during the pyrolysis process, and the pyrolysis time at the corresponding temperature is 2h. The obtained product is crushed using a mortar to obtain biochar.

[0021] Step S3: ball-milling biochar to prepare nano-biochar The biochar obtained in step S2 was placed in a 100 mL agate ball mill, and then agate balls of mixed sizes (the diameters of large agate balls, medium agate balls, and small agate balls were 10 mm, 8 mm, and 5 mm, respectively) were added, and the volume ratio of the added biochar to the agate balls was 1:1. To obtain the best ball milling effect, the large agate balls, medium agate balls, and small agate balls should account for 20%, 50%, and 30% of the total volume of the agate balls, respectively, and the total volume of the added biochar and agate balls should not be less than 1 / 3 of the total volume of the ball mill, and not more than 2 / 3 of the total volume of the ball mill. Finally, deionized water was added to wet the sample and placed in a planetary ball mill for wet grinding. The process was carried out at ambient temperature. After grinding, the sample in the agate jar was rinsed with deionized water and transferred to a beaker, and then placed in an oven at 80°C to dry to obtain nano biochar.

[0022] Removal of Sulfadimethoxine in Water: First, prepare a 500 mg / L sulfadimethoxine solution in a 1000 mL brown flask as a stock solution. Take 4 mL of sulfadimethoxine solution from the stock solution into a 100 mL conical flask and dilute it to 100 mL with deionized water. At this time, the antibiotic concentration in the reaction system is 20 mg / L. Then add 0.3 g of the nano-biochar prepared in step S3 (the addition amount is 3 g / L), and then quickly add peroxymonosulfate PMS (the addition amount is 5 mmol / L), and then oscillate the mixed solution in a constant temperature oscillator at 25 ° C for 30 minutes. After the reaction is completed, the sample is filtered through a 0.22 μm filter membrane and the antibiotic content in the sample supernatant is measured by ultraviolet spectrophotometry. The sulfadimethoxine removal rate is calculated, and the degradation effect is as follows. Figure 3 shown.

[0023] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing nano biochar using waste straw in two stages, characterized in that The following steps are involved: Step S1: air-dry the waste straw for 72-96 hours, and then dry it at 60-80°C for 24-48 hours, and then crush it through a 60-mesh sieve and seal it for later use; Step S2: subjecting the waste straw obtained in step S1 to a hydrothermal reaction at 180-240° C. for 1-2 h to obtain hydrothermal charcoal, and then pyrolyzing the hydrothermal charcoal at 300-900° C. for 1-3 h under the protection of an inert gas to obtain biochar; Step S3: The biochar obtained in step S2 is placed in a ball mill, and agate balls of mixed sizes are added, and then deionized water is added to wet the sample and placed in a planetary ball mill for wet grinding to obtain nano biochar.

2. The method for preparing nano biochar using waste straw in two stages according to claim 1, characterized in that: The waste straw in step S1 is one or more of corn straw, wheat straw or rice straw.

3. The method for preparing nano biochar using waste straw in two stages according to claim 1, characterized in that The specific preparation process of the hydrothermal charcoal in step S2 is as follows: the waste straw obtained in step S1 is placed in a polytetrafluoroethylene liner and deionized water is added, the solid-liquid ratio is controlled at 1g:4~8mL, and the polytetrafluoroethylene liner is placed in a closed high-pressure hydrothermal reactor, and then the reactor is placed in an oven for hydrothermal reaction at 180~240°C for 1~2h, and after the reaction is completed, it is allowed to cool to room temperature, the sample is taken out and allowed to stand and settle, and then the supernatant is poured out, and then it is dried at 60~80°C for 4~8h to obtain the hydrothermal charcoal.

4. The method for preparing nano biochar using waste straw in two stages according to claim 1, characterized in that The specific preparation process of the biochar described in step S2 is: put the hydrothermal charcoal into a covered crucible and place it in a tubular furnace for pyrolysis. Before pyrolysis, vacuum injection of N2 is repeated three times to replace O2. N2 is continuously injected during the pyrolysis process. The gas flow rate is 25~50mL / min until the reaction is completed. The pyrolysis heating rate is 10~30℃ / min, the pyrolysis time is 2h, and the obtained product is crushed in a mortar to obtain biochar.

5. The method for preparing nano biochar using waste straw in two stages according to claim 1, characterized in that The specific preparation process of the nano biochar in step S3 is as follows: the biochar obtained in step S2 is placed in an agate ball mill, and then agate balls of mixed sizes are added, the agate balls of mixed sizes include agate large balls with a diameter of 10 mm, agate medium balls with a diameter of 8 mm, and agate small balls with a diameter of 5 mm, wherein the volume percentages of the agate large balls with a diameter of 10 mm, the agate medium balls with a diameter of 8 mm, and the agate small balls with a diameter of 5 mm are 20%, 50%, and 30%, respectively, the volume ratio of the biochar to the agate balls is 1:1, and the total volume of the biochar and the agate balls is 1:

1. Not less than 1 / 3 and not more than 2 / 3 of the total volume of the ball mill jar. Finally, deionized water is added to moisten the sample and placed in a planetary ball mill for wet grinding. After grinding, the sample in the agate jar is rinsed with deionized water and transferred to a beaker, and then placed in an oven at 70-90°C to dry to obtain nano-biochar. The nano-biochar has a smaller fluid dynamic radius, a larger specific surface area and a rich pore structure. The active sites on its surface are increased, which can promote the activation of PMS, produce more highly reactive ROS, and have a stronger catalytic degradation potential.

6. The method for preparing nano biochar using waste straw in two stages according to claim 1, characterized in that: The ball milling speed of the wet grinding process in step S3 is 600-800 rpm, and the ball milling time is 24-72 hours.

7. Application of nano biochar prepared by the method according to any one of claims 1 to 6 in removing antibiotics from water, characterized in that The specific process is: add nano-biochar to the water sample containing antibiotics, then add peroxymonosulfate, and then place it in a constant temperature oscillator at 20~30℃ to react catalytically and degrade the antibiotics.

8. The use according to claim 7, characterized in that: The antibiotic is sulfadimethoxine, the dosage of nano-biochar is 1-5 g / L, and the dosage of peroxymonosulfate is 1-5 mmol / L.

Images