Microwave modified biochar as well as preparation method and application thereof

Abstract

The invention relates to the field of biochar, in particular to a preparation method of microwave modified biochar. The corn straw biochar is treated through microwaves, amino grafting modification is combined, the number of amino or hydroxyl organic functional groups on the surface of the corn straw biochar is increased, then chelating of Al < 3 + >, Fe < 3 + > and Ca < 2 + > ions in soil is improved, release of nitrogen, phosphorus and potassium ions is promoted, and therefore the carbon, nitrogen, phosphorus and potassium levels of the soil are increased; as the biochar has good dielectric properties and wave-absorbing properties, Joule heat can be quickly released within an ultra-short time under microwave heating, the temperature of the biochar is remarkably increased, quick oxidation is realized in an air atmosphere, and the number of oxygen-containing functional groups in the biochar is effectively increased; a large number of oxygen-containing functional groups chemically react with chitosan in an organic solvent, so that amino / hydroxyl organic functional groups on the surface of the biochar are improved, nutrient release is promoted, soil fertility is improved, and the biochar is suitable for large-scale planting production.

Description

Technical Field

[0001] This invention relates to the field of biochar, and more particularly to a microwave-modified biochar and its preparation method. Background Technology

[0002] Guizhou's land is mainly mountainous and hilly. Terracing is a common technique for agricultural land consolidation, which has created a large number of field ridges and slopes. However, sloping farmland generally suffers from serious soil erosion, soil infertility, heavy clay formation, and acidification. With rainwater erosion, the fertility of the slopes is greatly reduced. In order to improve the growth of crops, it is necessary to supplement fertilizers on the slopes to improve soil fertility.

[0003] In southern regions, available nitrogen, phosphorus, and potassium in the soil are easily adsorbed by iron and aluminum ions, forming insoluble bound nitrogen, phosphorus, and potassium, resulting in low soil availability and limiting plant growth. Increasing organic carbon content can provide the energy and carbon source needed by microorganisms, accelerate soil microbial turnover, and provide more available nitrogen, phosphorus, and potassium to meet plant growth needs. At the same time, the availability of soil nitrogen, phosphorus, and potassium promotes the mineralization of microbial carbon sources. Therefore, the carbon and nitrogen, phosphorus, and potassium cycling processes are interactive and closely related.

[0004] In agricultural production, chemical fertilizers are applied to provide more nitrogen, phosphorus, and potassium to plants. This method is costly and has a low utilization rate of nitrogen, phosphorus, and potassium fertilizers. Nearly half of the nitrogen, phosphorus, and potassium fertilizers cannot be utilized and are easily introduced into the ecosystem, causing non-point source pollution. Therefore, it is extremely urgent to improve the quality and efficiency of artificial nitrogen, phosphorus, and potassium fertilizers and to increase carbon sequestration.

[0005] Currently, most straw is not utilized, which not only occupies a large amount of land resources, but also seriously pollutes the air quality due to burning. At present, biochar, as a low-cost and effective soil conditioner, has been widely used in soil improvement. However, the use of biochar alone can only improve soil properties and fertilizer retention capacity to a certain extent. For crops with high soil fertility requirements, it is still necessary to supplement a large amount of bio-fertilizer before planting and to apply fertilizer to the crops in a timely manner afterward. The overall planting operation is more complicated and the cost is also higher, making it unsuitable for large-scale planting and production. Summary of the Invention

[0006] In order to overcome the problems that the use of biochar alone can only improve soil properties and fertilizer retention capacity to a certain extent, and that the overall planting operation is complicated and costly, making it unsuitable for large-scale planting and production.

[0007] The first aspect of the present invention is a method for preparing microwave-modified biochar, comprising the following steps: S1. Take corn straw biochar and chitosan and disperse them in acetic acid solvent. Shake the resulting suspension for 2 hours and then disperse it in an organic solvent. S2. The obtained suspension is microwave-treated to obtain microwave-oxidized biochar. After heating and reaction, the biochar is centrifuged, washed, and freeze-dried to prepare the microwave-modified biochar.

[0008] In any embodiment of the first aspect, in step S1, 3g of corn stalk biochar is accurately weighed, 3g of chitosan is dispersed in 180ml of acetic acid (2%, V / V), and 3.6g of sodium hydroxide and 10ml of glutaraldehyde are dispersed in 50ml of deionized water. After mixing, a suspension is obtained and placed at 25℃ for constant temperature shaking for 2h (150 rpm·min-1). After the reaction is completed, chitosan-modified biochar is obtained. In step S2, the chitosan-modified biochar is placed in a microwave-heated reactor under an air atmosphere with a power of 600W and microwave-heated for 5 minutes. After cooling, it is washed three times with deionized water, centrifuged, and finally freeze-dried to obtain the modified biochar.

[0009] In any embodiment of the first aspect, in step S1, 3g of corn stalk biochar is accurately weighed, 3g of chitosan is dispersed in 180ml of acetic acid (2%, V / V), and 3.6g of sodium hydroxide and 10ml of glutaraldehyde are dispersed in 50ml of deionized water. After mixing, a suspension is obtained and placed at 25℃ for constant temperature shaking for 2h (150 rpm·min-1). After the reaction is completed, chitosan-modified biochar is obtained. In step S2, the chitosan-modified biochar is placed in a microwave-heated reactor, heated in air at a power of 400W for 5 minutes, cooled, rinsed three times with deionized water, centrifuged, and finally freeze-dried to obtain the modified biochar.

[0010] A microwave-modified biochar was prepared by the above-described method.

[0011] An application of the above-mentioned microwave-modified biochar in improving soil carbon and phosphorus levels.

[0012] The beneficial effects of this invention are: 1. This invention improves the number of amino / hydroxyl organic functional groups on the surface of corn straw biochar by microwave treatment combined with amino grafting modification, thereby enhancing the chelation of Al3+, Fe3+ and Ca2+ ions in the soil and promoting the release of nitrogen, phosphorus and potassium ions, thus improving the carbon, nitrogen, phosphorus and potassium levels in the soil.

[0013] 2. This invention utilizes microwave heating. Due to the excellent dielectric and microwave absorption properties of biochar, it can rapidly release Joule heat in a very short time under microwave heating, significantly increasing the temperature of the biochar and achieving rapid oxidation in an air atmosphere. This effectively increases the number of oxygen-containing functional groups in the biochar. A large number of oxygen-containing functional groups react chemically with chitosan in organic solvents, increasing the number of amino / hydroxyl organic functional groups on the surface of the biochar. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the total phosphorus content in karst soil according to the present invention; Figure 2 This is a schematic diagram of the total nitrogen content in karst soil according to the present invention; Figure 3 This is a schematic diagram of the total potassium content in karst soil according to the present invention; Figure 4 This is a schematic diagram of the total nitrogen content in non-karst soils according to the present invention; Figure 5 This is a schematic diagram of the total phosphorus content in non-karst soils according to the present invention; Figure 6 This is a schematic diagram of the total potassium content in non-karst soils according to the present invention. Detailed Implementation

[0015] The following describes the embodiments and appendices. Figure 1-6 The present invention will be further described below.

[0016] Example 1 A method for preparing microwave-modified biochar includes the following steps: S1. Accurately weigh 3g of corn stalk biochar, disperse 3g of chitosan in 180ml of acetic acid (2%, V / V), disperse 3.6g of sodium hydroxide and 10ml of glutaraldehyde in 50ml of deionized water, mix to obtain a suspension, place at 25℃ and shake for 2h (150 rpm·min-1), after the reaction is completed, obtain chitosan modified biochar; S2. Place the chitosan-modified biochar in a microwave-heated reactor, adjust the power to 600W under air atmosphere, and microwave-heat it for 5 minutes under air atmosphere. Then cool it, rinse it 3 times with deionized water, centrifuge it, and finally freeze-dry it to obtain the modified biochar.

[0017] Example 2 A method for preparing microwave-modified biochar includes the following steps: S1. Accurately weigh 3g of corn stalk biochar, disperse 3g of chitosan in 180ml of acetic acid (2%, V / V), disperse 3.6g of sodium hydroxide and 10ml of glutaraldehyde in 50ml of deionized water, mix to obtain a suspension, place at 25℃ and shake for 2h (150 rpm·min-1), after the reaction is completed, obtain chitosan modified biochar; S2. Place the chitosan-modified biochar in a microwave-heated reactor, adjust the power to 400W under air atmosphere, and microwave-heat it for 5 minutes under air atmosphere. Then cool it, rinse it 3 times with deionized water, centrifuge it, and finally freeze-dry it to obtain the modified biochar.

[0018] Comparative Example 1 A microwave-modified biochar and its preparation method, comprising the following steps: S1. Accurately weigh 3g of corn stalk biochar, disperse 3g of chitosan in 180ml of acetic acid (2%, V / V), disperse 3.6g of sodium hydroxide and 10ml of glutaraldehyde in 50ml of deionized water, mix them to obtain a suspension, place it at 25℃ and shake for 2h (150 rpm·min-1), after the reaction is completed, chitosan modified biochar is obtained.

[0019] Application Example 1 A method for preparing microwave-modified biochar includes the following steps: S1. Five 20m × 20m quadrats were randomly set up in the soil of the karst region, with each quadrat more than 10m apart. Ten soil samples were collected from the 0-5cm topsoil layer of each quadrat, mixed thoroughly, and then placed in self-sealing bags and brought back to the laboratory. In the laboratory, the collected soil was sieved to remove impurities. Five treatments (w / w) were set up for the cultivation experiment with the modified biochar prepared in Example 1: the dosages were 0t / ha (C0), 2.5t / ha (C1), 5t / ha (C2), 10t / ha (C3), and 20t / ha (C4). Each treatment was replicated four times.

[0020] S2. 100g of fresh soil was thoroughly mixed with modified biochar and placed in a 500mL brown culture bottle. The soil moisture content was 60% of field capacity. All culture bottles were placed in the dark at 25℃ for 90 days. Soil samples were collected at 7, 15, 30, 60 and 90 days of culture to determine the relevant indicators of nitrogen, phosphorus and potassium components.

[0021] Application Example 2 A method for preparing microwave-modified biochar includes the following steps: S1. Five 20m × 20m quadrats were randomly set up in the soil of non-karst areas, with each quadrat more than 10m apart. Ten soil samples were collected from the top 0-5cm layer of each quadrat, mixed thoroughly, and then placed in self-sealing bags and brought back to the laboratory. In the laboratory, the collected soil was sieved to remove impurities. Five treatments (w / w) were set up for the incubation experiment with the modified biochar prepared in Example 2: the dosages were 0t / ha (C0), 2.5t / ha (C1), 5t / ha (C2), 10t / ha (C3), and 20t / ha (C4). Each treatment was replicated four times.

[0022] S2. 100g of fresh soil was thoroughly mixed with modified biochar and placed in a 500mL brown culture bottle. The soil moisture content was 60% of field capacity. All culture bottles were placed in the dark at 25℃ for 90 days. Soil samples were collected at 7, 15, 30, 60 and 90 days of culture to determine the relevant indicators of nitrogen, phosphorus and potassium components.

[0023] Application Example 3 A method for preparing microwave-modified biochar includes the following steps: S1. Five 20m × 20m quadrats were randomly set up in the soil of the karst region, with each quadrat being more than 10m apart. Ten soil samples were collected from the 0-5cm topsoil layer of each quadrat, mixed thoroughly, and then placed in self-sealing bags and brought back to the laboratory. In the laboratory, the collected soil samples were sieved to remove impurities. Five treatments (w / w) were set up for the incubation experiment with the modified biochar prepared in Comparative Example 1: the dosage was 0t / ha (denoted as C0) and 5t / ha (denoted as C1), respectively. Each treatment was replicated in 4 places.

[0024] S2. 100g of fresh soil was thoroughly mixed with modified biochar and placed in a 500mL brown culture bottle. The soil moisture content was 60% of field capacity. All culture bottles were placed in the dark at 25℃ for 90 days. Soil samples were collected at 7, 15, 30, 60 and 90 days of culture to determine the relevant indicators of nitrogen, phosphorus and potassium components.

[0025] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, comparative examples, and application examples. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing microwave-modified biochar, characterized in that: Includes the following steps: S1. Take corn straw biochar and chitosan and disperse them in acetic acid solvent. Shake the resulting suspension for 2 hours and then disperse it in an organic solvent. S2. The obtained suspension is microwave-treated to obtain microwave-oxidized biochar. After heating and reaction, the biochar is centrifuged, washed, and freeze-dried to prepare the microwave-modified biochar.

2. The method for preparing microwave-modified biochar according to claim 1, characterized in that: In step S1, 3g of corn stalk biochar was accurately weighed, 3g of chitosan was dispersed in 180ml of acetic acid (2%, V / V), and 3.6g of sodium hydroxide and 10ml of glutaraldehyde were dispersed in 50ml of deionized water. After mixing, a suspension was obtained and placed at 25℃ for 2h of constant temperature shaking (150 rpm·min-1). After the reaction was completed, chitosan-modified biochar was obtained. In step S2, the chitosan-modified biochar is placed in a microwave-heated reactor under an air atmosphere with a power of 600W and microwave-heated for 5 minutes. After cooling, it is washed three times with deionized water, centrifuged, and finally freeze-dried to obtain the modified biochar.

3. The method for preparing microwave-modified biochar according to claim 1, characterized in that: In step S1, 3g of corn stalk biochar was accurately weighed, 3g of chitosan was dispersed in 180ml of acetic acid (2%, V / V), and 3.6g of sodium hydroxide and 10ml of glutaraldehyde were dispersed in 50ml of deionized water. After mixing, a suspension was obtained and placed at 25℃ for 2h of constant temperature shaking (150 rpm·min-1). After the reaction was completed, chitosan-modified biochar was obtained. In step S2, the chitosan-modified biochar is placed in a microwave-heated reactor, heated in air at a power of 400W for 5 minutes, cooled, rinsed three times with deionized water, centrifuged, and finally freeze-dried to obtain the modified biochar.

4. A microwave-modified biochar, characterized in that, It is obtained by the preparation method according to any one of claims 1-3.

5. The application of the microwave-modified biochar according to claim 5 in improving soil carbon and phosphorus levels.

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