Alkali modified biochar for efficient adsorption of ammonia-nitrogen and preparation method and application thereof
By preparing alkali-modified biochar, the problem of efficient adsorption and stable slow release of ammonia nitrogen in existing biochar modification methods has been solved. This method achieves efficient ammonia nitrogen adsorption and slow release, reduces nitrogen loss, improves nutrient utilization efficiency, and promotes crop growth. At the same time, the material is environmentally friendly and pollution-free.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG FORESTRY UNIVERSITY
- Filing Date
- 2026-04-24
- Publication Date
- 2026-07-03
AI Technical Summary
Existing biochar modification methods are difficult to achieve efficient adsorption and stable slow release of ammonia nitrogen, and there are also risks of heavy metal pollution and process complexity issues.
Using rice straw as raw material, alkali-modified biochar was prepared by strong alkali impregnation combined with high-temperature activation in a nitrogen atmosphere, which significantly improved its specific surface area and mesoporous structure ratio, introduced oxygen-containing functional groups, and the preparation process was simple and environmentally friendly.
It achieves highly efficient adsorption of ammonia nitrogen, with a maximum adsorption capacity of 22 mg/g. It exhibits excellent slow-release performance, reduces nitrogen leaching loss, improves nutrient utilization efficiency, promotes crop growth, and the material is completely degradable with no heavy metal residue.
Smart Images
Figure CN122321797A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of environmental functional materials technology, specifically relating to an alkali-modified biochar that efficiently adsorbs ammonia nitrogen, its preparation method, and its application. Background Technology
[0002] Ammonia nitrogen is a key pollutant causing eutrophication in water bodies and is also the most easily lost and least utilized core nutrient in agricultural production. Excessive application and rapid release of nitrogen in farmland leads to a series of environmental problems, including leaching loss, surface runoff, groundwater pollution, and greenhouse gas emissions. In water bodies, excessive ammonia nitrogen directly causes a decrease in dissolved oxygen, thus damaging the ecosystem. Statistics show that the utilization rate of nitrogen fertilizer in my country's farmland during the current season is only 30%-35%, with large amounts of nitrogen entering the aquatic environment through runoff, leaching, and volatilization, causing algal blooms in surface water, excessive nitrate levels in groundwater, and increased emissions of greenhouse gases such as N2O. Therefore, how to achieve efficient capture, stable storage, and slow release of ammonia nitrogen that can be absorbed by crops has become a core technical challenge faced by both environmental remediation and green agriculture.
[0003] Biochar is widely used for pollutant adsorption and soil improvement due to its abundant raw material sources, large specific surface area, rich pore structure, and strong chemical stability. However, unmodified biochar has a single surface functional group, low negative charge density, and uneven pore structure, resulting in weak electrostatic adsorption capacity for ammonium ions. The actual ammonia nitrogen adsorption capacity is generally less than 10 mg / g, and it is easily desorbed by water after adsorption, making it difficult to meet the requirements of high load and high selectivity capture, and also unable to achieve long-term stable nutrient release.
[0004] To improve the adsorption performance of biochar for ammonia nitrogen, researchers have explored various modification strategies, among which physical / oxidative modification and metal salt modification are the most frequently reported methods. For example, Chinese patent CN108786730A, filed on June 19, 2018, discloses a method for preparing a corn straw biochar-based composite adsorbent. This method involves a multi-step process including ball milling, montmorillonite composite, and polyvinyl alcohol crosslinking to prepare a composite biochar material for ammonia nitrogen adsorption in acidic wastewater. Another Chinese patent CN106345407A, filed on September 19, 2016, discloses a method for preparing modified biochar to improve ammonia nitrogen removal capacity. This method employs a physical modification approach involving cyclic freeze-thaw cycles, improving ammonia nitrogen adsorption performance solely through physical structural regulation. However, while physical / oxidative modified biochar increases the specific surface area to some extent by introducing functional groups through physical structural regulation or oxidation, it still limits its ability to improve the electrostatic adsorption and ion exchange capacity of ammonia nitrogen.
[0005] Chinese patent CN120924281A, filed on July 30, 2025, discloses a magnesium salt-modified biochar soil conditioner and its preparation method. It employs a metal modification method involving impregnation with magnesium salts such as magnesium chloride and compounding with magnesium oxide to enhance the biochar's adsorption of ammonia nitrogen and its soil fertility retention capacity. However, the aforementioned existing metal modification method has significant drawbacks: on the one hand, metal loading causes the surface potential of the biochar to shift in the positive direction, affecting the positively charged NH4+. + Electrostatic repulsion limits the actual increase in ammonia nitrogen adsorption. Furthermore, metal modification primarily relies on surface precipitation or complexation for nitrogen fixation, leading to rapid desorption and loss of adsorbed nitrogen in the soil solution, thus hindering long-term slow release. In addition, multi-metal composite modification processes are complex, costly, and pose a risk of secondary heavy metal pollution, making large-scale application difficult.
[0006] In summary, existing biochar modification strategies for ammonia nitrogen adsorption need to overcome the following technical shortcomings. First, a balance needs to be struck between high adsorption capacity and physical slow release. Second, most modification methods excessively pursue microporousization, which, while increasing specific surface area, leads to an overemphasis on the amount of NH4 adsorbed within the micropores. + Due to excessive diffusion resistance, desorption is difficult, resulting in a reduced actual effective release rate. Conversely, when macropores dominate, the adsorption capacity is insufficient and the release is too rapid. Furthermore, the structural effect of mesopores has been neglected, and there are few reports in existing literature on the regulatory effect of specific pore size ranges on ammonia nitrogen adsorption and slow-release equilibrium.
[0007] Therefore, in order to address the aforementioned technical deficiencies, it is of great application value to utilize the mesoporous confinement effect to overcome the difficulty in balancing adsorption and release in existing technologies, and to develop a biochar modification method that can efficiently adsorb ammonia nitrogen, achieve stable and sustained release, and has a simple preparation process and is environmentally friendly. Summary of the Invention
[0008] To address the problems existing in the prior art, this invention discloses an alkali-modified biochar for efficient ammonia nitrogen adsorption, its preparation method, and its application. Using rice straw as raw material, alkali-modified biochar is prepared by strong alkali impregnation combined with high-temperature activation in a nitrogen atmosphere, which significantly improves its specific surface area, mesoporous structure ratio, and number of oxygen-containing functional groups. After granulation, it can be used as a slow-release nutrient material for soil nitrogen retention, reducing nitrogen leaching loss, improving nutrient utilization efficiency, and promoting crop growth. It can also be applied to the adsorption and removal of ammonia nitrogen in water bodies.
[0009] The technical solution of the present invention is as follows: The purpose of this invention is to provide a method for preparing alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen, comprising the following steps: S1. Rice straw biomass is obtained by washing, drying, crushing and sieving rice straw as raw material; S2. Place rice straw biomass in a KOH solution with a concentration of 1-3 mol / L, adjust the mixing mass-to-volume ratio of rice straw biomass to KOH solution to 1 g : 20 mL, stir and impregnate, and then filter to obtain solid material; S3. The dried solid material is pyrolyzed and activated in a nitrogen atmosphere at 350-750℃. After cooling, the activated product is ground and washed until neutral to obtain alkali-modified biochar with a pore size of 2-5nm and a mesopore volume of ≥65.5% of the total pore volume.
[0010] Furthermore, in S1, the rice straw is dried at 105°C for 0.5 h, followed by heating at 80°C for 24 h; the crushed rice straw is then passed through a 100-mesh sieve. Furthermore, the concentration of KOH solution in S2 is 2 mol / L. Furthermore, in step S2, the rice straw biomass is stirred and soaked in KOH solution for 3.5-4.5 hours. Furthermore, in step S3, the pyrolysis activation temperature is 550°C, the heating rate during the pyrolysis activation process is 5°C / min, the holding time is 120 min, and then it is naturally cooled to room temperature.
[0011] Furthermore, in step S3, the drying temperature of the solid material is 100-110℃; the activated product is ground through a 100-mesh sieve.
[0012] The second objective of this invention is to provide an alkali-modified biochar that can efficiently adsorb ammonia nitrogen.
[0013] Furthermore, in the alkali-modified biochar, the proportion of mesopores with a pore size of 2-5 nm to the total pore volume is ≥65.5%. Furthermore, the specific surface area of the alkali-modified biochar is 152-153 m². 2 / g.
[0014] The third objective of this invention is to provide an application of alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen in the preparation of ammonia nitrogen adsorption materials.
[0015] The fourth objective of this invention is to provide an application of alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen in the preparation of nitrogen-release materials.
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention is the first to propose using the mesopore ratio as the core of biochar modification. During the preparation process, the concentration of KOH solution, impregnation time, and staged temperature-increasing activation under a nitrogen atmosphere are precisely controlled. This allows the KOH solution etching to preferentially consume disordered carbon components while generating a large number of 2-5 nm mesopores. The proportion of mesopores in this pore size range to the total pore volume is ≥65.5%, inhibiting excessive microporous or macroporous formation. At the same time, the high-temperature activation process introduces oxygen-containing functional groups carboxyl and hydroxyl groups, increasing the surface negative charge density and significantly improving the ammonia nitrogen adsorption performance of the biochar. The maximum adsorption capacity is as high as 22 mg / g, which is far superior to unmodified, metal-modified, acid-modified, and oxidized biochar, achieving high-capacity, high-selectivity, and rapid capture of ammonia nitrogen.
[0017] 2. The alkali-modified biochar designed in this invention has a high specific surface area, a high proportion of mesopores, and abundant oxygen-containing functional groups. Specifically, the mesopores within a certain range provide NH4+. + The mesoporous confinement effect allows for rapid diffusion and sufficient contact, avoiding diffusion obstruction caused by micropores or insufficient adsorption caused by macropores, while also enhancing the adsorption of NH4+. + Under moderate van der Waals forces and hydrogen bonding, it is not easily replaced by water molecules and can be released stably in soil solution. At the same time, the oxygen-containing functional groups on the surface enhance the initial capture capacity through electrostatic attraction. The adsorption process is mainly physical adsorption, which conforms to the first-order kinetic model, ensuring the predictability and controllability of the release behavior. Together, they achieve a synergistic mechanism of high-capacity adsorption and stable slow release.
[0018] 3. The innovative alkali-modified biochar of this invention exhibits multiple advantages in environmental remediation and agricultural production. In terms of ammonia nitrogen removal from water bodies, its adsorption capacity for 100 mg / L ammonia nitrogen solution is significantly superior to unmodified, metal-modified, and oxidized biochar, rapidly reducing ammonia nitrogen concentration in water. Regarding soil nitrogen retention, after granulation and application to the soil, the cumulative release rate of ammonium nitrogen within 30 days is only 18%, significantly reducing leaching losses and improving nutrient utilization efficiency. Crop planting verification shows that applying alkali-modified biochar with ammonia nitrogen adsorption resulted in optimal growth of chili pepper plants during the flowering and fruiting stages, with an average plant height of 34.5 cm, significantly higher than the 29.4 cm in the urea group. The content of vitamin C, free amino acids, and soluble sugars in the fruit was significantly increased, while the malondialdehyde content was reduced, resulting in substantial improvements in both growth and nutritional indicators. In addition, the raw materials are rice straw and agricultural and forestry waste, and the preparation process only involves impregnation activation, washing and drying. The material is completely degradable, with no heavy metal or polymer residues, making it environmentally friendly. It has the dual value of pollution control and resource utilization, and is suitable for scenarios such as facility agriculture, high-standard farmland construction and non-point source pollution control. Attached Figure Description
[0019] Figure 1This is a comparison chart of the adsorption effects of alkali-modified biochar prepared in Example 1 of the present invention and other modified biochars on ammonia nitrogen. Figure 2 The adsorption isotherm and fitting curve of ammonia nitrogen by the alkali-modified biochar prepared in Example 1 of this invention are shown. Figure 3 The adsorption kinetics and fitting curves of ammonia nitrogen on alkali-modified biochar and pure biochar prepared in Example 1 of this invention are shown. Figure 4 The ammonium nitrogen release curves of the alkali-modified biochar, urea, and compound fertilizer prepared in Example 1 of this invention in a static water release test; Figure 5 The cumulative release curves of ammonium nitrogen from the alkali-modified biochar, urea, and compound fertilizer prepared in Example 1 of this invention during a soil column leaching test are shown. Figure 6 A comparative diagram showing the growth of plants during the seedling, flowering, and fruiting stages after applying the alkali-modified biochar granulation material prepared in Example 1 of this invention. Figure 7 A comparative chart showing the nutritional and quality indicators of plants under the conditions of applying the alkali-modified biochar granulation material prepared in Example 1 of this invention, urea, soda ash-modified biochar, unmodified biochar, and blank control. Detailed Implementation
[0020] The present invention will be further described below with reference to preferred embodiments. The endpoints and any values of the ranges disclosed in the present invention are not limited to the precise ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed herein. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions.
[0021] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.
[0022] Example 1 This embodiment provides a method for preparing alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen, including the following steps: S1. Clean the rice straw, heat it in a 105℃ oven for 0.5 h, then dry it at 80℃ for 24 h, crush it and pass it through a 100-mesh sieve to obtain rice straw biomass. S2. Add 10 g of rice straw biomass to 200 mL of 2 mol / L KOH solution, stir and soak at room temperature for 4 h, and filter to obtain solid material; S3. Transfer the solid material to a tube furnace, heat it to 550 ℃ at 5 ℃ / min under a nitrogen atmosphere, hold it at that temperature for 120 min, and then let it cool naturally to room temperature. S4. Grind and activate the product, pass it through a 100-mesh sieve, and then wash it repeatedly with deionized water until the pH is neutral. Dry it at 105 °C to obtain alkali-modified biochar with a specific surface area of 152.3367 m² / g and a pore size of 2-5 nm accounting for ≥65.5% of the total pore volume.
[0023] Example 2 This embodiment provides a method for preparing alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen, including the following steps: S1. Add 10 g of rice straw biomass to 200 mL of 1 mol / L KOH solution, stir and soak at room temperature for 4.5 h, and filter to obtain solid material; S2. Transfer the solid material to a tube furnace, heat it to 350°C at 5°C / min under a nitrogen atmosphere, hold it at the temperature for 120 min, and then let it cool naturally to room temperature. S3. Grind and activate the product, pass it through a 100-mesh sieve, and then wash it repeatedly with deionized water until the pH is neutral. Dry it at 100 ℃ to obtain alkali-modified biochar with a pore size of 2-5 nm and a mesopore volume of ≥65.5% of the total pore volume.
[0024] Example 3 This embodiment provides an alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen, and its preparation method includes the following steps: S1. Add 10 g of rice straw biomass to 200 mL of 3 mol / L KOH solution, stir and soak at room temperature for 3.5 h, and filter to obtain solid material; S2. Transfer the solid material to a tube furnace, heat it to 750°C at 5°C / min under a nitrogen atmosphere, hold it at the temperature for 120 min, and then let it cool naturally to room temperature. S3. Grind and activate the product through a 100-mesh sieve, then wash it repeatedly with deionized water until the pH is neutral, and dry it at 110 ℃ to obtain alkali-modified biochar with mesopores of 2-5 nm in diameter accounting for ≥65.5% of the total pore volume.
[0025] Comparative Example 1 This embodiment provides a method for preparing rice straw biochar, including the following steps: The rice straw was cleaned, heated in an oven at 105 ℃ for 0.5 h, and then dried at 80 ℃ for 24 h. After being crushed, it was passed through a 100-mesh sieve to obtain rice straw biochar.
[0026] Comparative Example 2 Commercial urea Comparative Example 3 Ordinary nitrogen, phosphorus, and potassium compound fertilizer, in which the mass ratio of NPK is 4:2:1.
[0027] Performance testing 1. Ammonia nitrogen adsorption performance test Take 0.1 g of the alkali-modified biochar prepared in Example 1 and place it in 100 mL of ammonium chloride solution with an initial concentration of 100 mg / L. Shake at room temperature until adsorption reaches equilibrium. Take samples at regular intervals to determine the ammonia nitrogen concentration and test the ammonia nitrogen adsorption performance.
[0028] like Figure 1 As shown, the maximum adsorption capacity of alkali-modified biochar for ammonia nitrogen is as high as 22 mg / g, which is far superior to unmodified, metal-modified, acid-modified and oxidized biochar. like Figure 2 As shown, when the ammonium concentration reaches 250 mg / L, the adsorption of ammonium by alkali-modified biochar reaches saturation, and further increases in concentration do not increase the adsorption capacity. like Figure 3 As shown, compared with pure biochar, the adsorption kinetics of alkali-modified biochar fits the first-order kinetic model better, indicating that the entire diffusion process is controlled by physical adsorption.
[0029] 2. Sustained-release performance test Take 0.1 g of the alkali-modified biochar prepared in Example 1 and place it in 100 mL of ammonium chloride solution with an initial concentration of 100 mg / L. Shake at room temperature until adsorption reaches equilibrium to obtain alkali-modified biochar that adsorbs ammonia nitrogen. Then, use it to test the slow-release performance, including static water release experiment and soil column leaching experiment.
[0030] (1) Static water release: Weigh 0.1g of alkali-modified biochar, urea and compound fertilizer that adsorb ammonia nitrogen, add 100 mL of deionized water respectively, and take samples at regular intervals to determine the amount of ammonium nitrogen released; like Figure 4 As shown, during 72 h of static water release, the ammonium nitrogen release rate of alkali-modified biochar that adsorbs ammonia nitrogen was significantly slower than that of urea and compound fertilizer. (2) Soil column leaching: 250 g of vermiculite and peat (1:1.5) were loaded into an acrylic column, and 0.1 g of alkali-modified biochar, urea and compound fertilizer were buried 5 cm below the soil. Leaching was carried out every 2 days, and the leachate was collected and the ammonium nitrogen content was determined.
[0031] like Figure 5 As shown, in the 30-day soil column leaching experiment, the cumulative release rate of ammonium nitrogen from the alkali-modified biochar that adsorbed ammonia nitrogen was only about 18%, while urea and compound fertilizer released large amounts in a short period of time. This indicates that the alkali-modified biochar prepared in this invention has excellent nitrogen slow-release performance, far superior to conventional fertilizers.
[0032] 3. Crop growth promotion and quality improvement effect test 0.1 g of the alkali-modified biochar prepared in Example 1 was placed in 100 mL of ammonium chloride solution with an initial concentration of 100 mg / L. The adsorption was carried out by shaking at room temperature until equilibrium was reached, and alkali-modified biochar adsorbing ammonia nitrogen was obtained. After granulation, it was applied to potted chili peppers. After the chili pepper seedlings were transplanted, they were cultured for 60 days, and the growth and nutritional indicators of the plants were measured to verify its growth-promoting and quality-improving effects.
[0033] The experiment was set up with 5 treatment groups: blank control group (CK), unmodified biochar group (BC), urea group (Urea), alkali-modified biochar group without ammonia nitrogen adsorption (OHBC), and alkali-modified biochar group with ammonia nitrogen adsorption (OHBC-N).
[0034] like Figure 6 As shown, during the flowering and fruiting stages, the peppers in the OHBC-N group showed the best growth, with an average plant height of 34.5 cm, which was significantly higher than that of the Urea group (29.4 cm) and the BC group (25.6 cm). like Figure 7 As shown, the quality of chili peppers was significantly improved, with a substantial increase in the content of vitamin C, free amino acids, soluble sugars, and reducing sugars, while the content of malondialdehyde was significantly reduced, and the stress resistance was enhanced.
[0035] The above results demonstrate that the alkali-modified biochar disclosed in this invention can significantly promote crop growth, improve nutrient utilization, and enhance fruit quality, making it suitable for vegetable cultivation and green agricultural production.
[0036] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.
Claims
1. A method for preparing alkali-modified biochar for efficient adsorption of ammonia nitrogen, characterized in that, Includes the following steps: S1. Rice straw biomass is obtained by washing, drying, crushing and sieving rice straw as raw material; S2. Place rice straw biomass in a KOH solution with a concentration of 1-3 mol / L, adjust the mixing mass-to-volume ratio of rice straw biomass to KOH solution to 1 g : 20 mL, stir and impregnate, and then filter to obtain solid material; S3. The dried solid material is pyrolyzed and activated in a nitrogen atmosphere at 350-750℃. After cooling, the activated product is ground and washed until neutral to obtain alkali-modified biochar with a pore size of 2-5nm and a mesopore volume of ≥65.5% of the total pore volume.
2. The method for preparing alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen as described in claim 1, characterized in that, The drying conditions for the rice straw in S1 are: heating at 105°C for 0.5 h, followed by heating at 80°C for 24 h; the crushed rice straw is then passed through a 100-mesh sieve.
3. The method for preparing alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen as described in claim 1, characterized in that, The concentration of KOH solution in S2 is 2 mol / L.
4. The method for preparing alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen as described in claim 1, characterized in that, The soaking time of rice straw biomass with KOH solution in S2 is 3.5-4.5 h.
5. The method for preparing alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen as described in claim 1, characterized in that, The pyrolysis activation temperature in S3 is 550℃, the heating rate during the pyrolysis activation process is 5℃ / min, the holding time is 120 min, and then it is naturally cooled to room temperature.
6. The method for preparing alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen as described in claim 1, characterized in that, In step S3, the drying temperature of the solid material is 100-110℃; The activated product was ground through a 100-mesh sieve.
7. An alkali-modified biochar with high efficiency in adsorbing ammonia nitrogen prepared by the preparation method according to any one of claims 1 to 7, characterized in that, In the alkali-modified biochar, mesopores with a pore size of 2-5 nm account for ≥65.5% of the total pore volume.
8. The alkali-modified biochar for highly efficient adsorption of ammonia nitrogen as described in claim 7, characterized in that, The specific surface area of the alkali-modified biochar is 152-153 m² / g.
9. The application of alkali-modified biochar with high ammonia nitrogen adsorption efficiency as described in claim 8 in the preparation of nitrogen slow-release materials.
10. The application of alkali-modified biochar with high ammonia nitrogen adsorption efficiency as described in claim 8 in the preparation of ammonia nitrogen adsorption materials.