Preparation method of ammonia modified straw biochar and application in adsorption of tnt red water

Abstract

The application discloses a preparation method of ammonia-modified straw biochar and adsorption application of the ammonia-modified straw biochar in TNT red water and belongs to the technical field of environmental remediation. The preparation method comprises the following steps: in step 1, after being washed, dried and crushed, straw is obtained in the form of straw powder, and the straw powder is calcined to obtain calcined powder LS; in step 2, the calcined powder LS obtained in step 1 is soaked in an ammonium ion-containing solution, KOH is added, and solid water bath stirring is carried out, and after filtration and drying, an intermediate biochar is obtained; and in step 3, the intermediate biochar obtained in step 2 is calcined to obtain biochar powder BC, and after being washed, dried and sieved, a biochar sample N-KN is obtained. Through ammonia water pretreatment and KOH activation, the application prepares microporous biochar with high specific surface area and rich nitrogen doping, and provides a low-cost and high-adsorption-efficiency solution for TNT red water treatment.

Description

Technical Field

[0001] This application belongs to the field of environmental remediation technology, specifically relating to a method for preparing ammonia-modified straw biochar and its adsorption application in TNT red water. Background Technology

[0002] TNT red wastewater is a highly toxic wastewater generated during the production of explosives. It contains more than 30 nitro aromatic pollutants, among which 2,4-dinitrotoluenesulfonates (DNTs) and 2,4,6-trinitrotoluene (TNT) are highly carcinogenic. TNT red wastewater is extremely toxic, and the release of these compounds into the environment poses a risk of contaminating soil and groundwater. Furthermore, its complex composition makes it difficult to treat, necessitating appropriate treatment technologies to reduce its harm to the environment and human health.

[0003] Current TNT red water treatment methods typically employ physicochemical and biological approaches. Traditional physicochemical remediation technologies often suffer from low efficiency, high cost, and secondary pollution, while biological methods require long start-up times and significant investment costs. Biochar is an emerging adsorbent material with excellent adsorption efficiency and low cost. As an environmentally friendly adsorbent material, biochar has advantages such as wide availability and low cost. However, ordinary biochar has limited adsorption capacity for nitro aromatic compounds, making it difficult to meet practical needs.

[0004] Existing adsorption materials suffer from high cost and low efficiency. While biochar has adsorption potential, unmodified biochar has a low specific surface area and insufficient functional groups, making it difficult to meet practical needs. KOH activation can increase the specific surface area, but traditional methods have limited effect on modifying lotus stalks. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing high specific surface area, nitrogen-doped lotus straw biochar (N-KN) by promoting KOH activation efficiency through ammonia pretreatment, and controlling reaction conditions to achieve adsorption and removal of nitro compounds, the main substances in TNT red water.

[0006] The objective of this invention can be achieved in the following ways.

[0007] The first aspect of this invention discloses a method for preparing ammonia-modified straw biochar, comprising the following steps: Step 1: After washing, the straw is dried and crushed to obtain straw powder. The straw powder is then calcined to obtain calcined powder LS. Step 2: Immerse the calcined powder LS obtained in Step 1 in a solution containing ammonium ions, add KOH and a solid containing ammonium ions in a water bath and stir, filter and dry to obtain intermediate biochar; Step 3: Calcine the intermediate biochar obtained in Step 2 to obtain biochar powder BC. Wash the biochar powder BC, dry it, and sieve it to obtain biochar sample N-KN.

[0008] Preferably, in step 1, the straw powder is calcined at 800°C under a N2 atmosphere at a rate of 5°C / min.

[0009] Preferably, step 2 includes: Step 2.1: The calcined powder LS is pretreated by immersing it in a solution containing ammonium ions to obtain a pretreated solution; Step 2.2: Add KOH and ammonium ion-containing solids in a set mass ratio to the pretreatment solution, filter, and dry in an oven to obtain intermediate biochar.

[0010] Preferably, in step 2.2, the mass ratio is set to 1:1.

[0011] Preferably, step 3 includes: Step 3.1: The intermediate biochar was calcined at 800℃ in a N2 atmosphere at a heating rate of 5℃ / min to obtain biochar powder BC. Step 3.2: After washing the biochar powder BC with an acidic solution and sonicating, filter the obtained biochar powder, wash, dry, grind and sieve to obtain biochar sample N-KN.

[0012] Preferably, in step 3.2, the concentration of the acidic solution is not higher than 1 mol / L.

[0013] Preferably, in step 3.2, the biochar powder obtained after filtration is washed by washing the filtered solid with ultrapure water, centrifuging multiple times, removing the supernatant, until the pH is neutral.

[0014] A second aspect of the present invention discloses an ammonia-modified straw biochar prepared by the above-described preparation method.

[0015] Preferably, ammonia-modified straw biochar is weighed and added to the DNTs solution, stirred and adsorbed, for adsorption treatment of the DNTs solution.

[0016] Preferably, ammonia-modified straw biochar is weighed and added to TNT red water, stirred and adsorbed, for the adsorption of nitro aromatic compounds in TNT red water.

[0017] Compared with the prior art, the beneficial effects of the present invention include at least the following: Existing technologies commonly employ methods such as KOH modification, nitrogen doping, and alkali metal carbonate modification to prepare biochar, aiming to increase the specific surface area and the number of functional groups. This invention utilizes ammonia pretreatment to increase the number of surface functional groups, thereby promoting higher surface activity in activated carbon. Ammoniation of lignocellulose causes cell wall expansion, resulting in a looser structure. The carboxyl groups on the lignocellulose recombine, significantly increasing the crude protein content of the ammonified biochar precursor. Simultaneously, ammoniation increases available attachment sites for activators and promotes impregnation and activation. Therefore, ammonia pretreatment of ammonified biochar combined with other modification methods enhances the adsorption capacity of the resulting activated carbon, increases the nitrogen doping content, and increases the number of surface functional groups, a significant difference from other biochar materials.

[0018] The biomass used in this invention is waste lotus straw. Pretreatment with ammonia water increases the number of activatable sites on the biomass surface, improving the modification effect. This invention prepares high-performance lotus straw biochar (N-KN) through a synergistic modification strategy of ammoniation and KOH / nitrogen doping. N-KN biochar possesses a large specific surface area and pore size. In the adsorption of TNT red water, N-KN biochar exhibits excellent adsorption performance; its adsorption capacity, stability, and regeneration performance are significantly superior to other biochar materials. This provides an efficient and economical solution for TNT red water treatment and has broad industrial application prospects. Attached Figure Description

[0019] Figure 1 These are SEM images of all the prepared biochars, where af represents LS, N-LS, NLS, KLS, KNLS and N-KN, respectively. Figure 2 This is an N2 adsorption-desorption isotherm diagram of the prepared biochar, where the horizontal axis represents relative pressure (P / P0) and the vertical axis represents nitrogen adsorption capacity under standard conditions (cm³). 3 / g; Figure 3 The graph shows the kinetics of DNT removal by the prepared biochar. The horizontal axis represents the adsorption time in minutes, and the vertical axis represents the adsorption capacity of the target substance per unit mass of biochar in mg / g. Figure 4 This is a kinetic diagram of the adsorption and removal of nitro aromatic compounds from TNT red water by the prepared biochar. The horizontal axis represents the adsorption time in minutes, and the vertical axis represents the adsorption capacity of the target substance per unit mass of biochar in mg / g. Figure 5 The graph shows the adsorption capacity of biochar samples for DNTs under different pH conditions. The horizontal axis represents pH and the vertical axis represents adsorption capacity. The unit is mg / g. Figure 6This is a schematic diagram showing the effect of biochar sample on the adsorbent concentration in TNT red water. The horizontal axis represents the amount of adsorbent added in g / L, and the vertical axis represents the adsorption capacity in mg / g. Figure 7 This is a schematic diagram of the adsorption capacity of N-KN biochar after 5 cycles. The horizontal axis represents the number of cycles, and the vertical axis represents the adsorption capacity. The unit is mg / g. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0021] Example 1 of the present invention provides a method for preparing ammonia-modified straw biochar for adsorbing nitro aromatic compounds in TNT red water. The preparation method includes the following steps: Step 1: After washing, the straw is dried and crushed to obtain straw powder. The straw powder is then calcined to obtain calcined powder LS. In a preferred but non-limiting embodiment of the present invention, step 1 specifically includes: Take an appropriate amount of lotus stalks, wash them with ultrapure water, dry them in an oven at 105°C, crush them with a pulverizer and pass them through a 200-mesh sieve to obtain stalk powder. Place the stalk powder in a tube furnace and calcine it at 800°C for 2 hours under a N2 atmosphere at a rate of 5°C / min. The calcined powder obtained is named LS.

[0022] Step 2: Soak the calcined powder LS obtained in Step 1 in a solution containing ammonium ions, add KOH and solid containing ammonium ions in a water bath and stir, filter and dry to obtain intermediate biochar; The ratio of straw powder to ammonium ion solution is preferably 1:1, the ammonium ion solution is preferably ammonia water, and the ammonium ion solid is preferably urea. In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes: Take 10 g of calcined LS powder and place it in a beaker. Add ammonia solution (10 mL / g) to soak it. Stir in a water bath at 60℃ for 12 hours. Then add an equal mass of KOH (6 g) and urea (6 g) and continue stirring for 12 hours. Filter the well-stirred mixture and dry it in an oven at 60℃ for 12 hours to obtain intermediate biochar.

[0023] It is worth noting that the order in which ammonia solution, KOH, and urea are added can have a significant impact on biochar modification. The purpose of adding ammonia solution first is to ammonify lignocellulose. Ammoniation of lignocellulose in straw leads to cell wall expansion and loosening of the structure, which increases the available attachment sites for activators and promotes impregnation and activation, thereby improving the modification effect of KOH. Urea is added to perform nitrogen doping and increase the N doping content.

[0024] Step 3: Calcine the intermediate biochar obtained in Step 2 to obtain biochar powder BC. Wash the biochar powder BC, dry it, and sieve it to obtain biochar sample N-KN.

[0025] In a preferred but non-limiting embodiment of the present invention, step 3 specifically includes: Step 3.1: Place the intermediate biochar in a quartz boat, put it in a tube furnace, and calcine it at 800℃ for 2 hours under N2 atmosphere with a heating rate of 5℃ / min. After calcination, biochar powder BC is obtained. Step 3.2: The biochar powder obtained after calcination is washed with 1 mol / L hydrochloric acid solution and then sonicated. After filtration, the biochar powder is washed with ultrapure water, dried in an oven at 120℃, and ground through a 200-mesh sieve to obtain a biochar sample, named N-KN.

[0026] More preferably, the calcined biochar powder needs to be ground into powder using a mortar and pestle, then placed in a 1 mol / L hydrochloric acid solution, and then washed with ultrapure water until the pH is neutral. The specific procedure for washing the sample with ultrapure water is as follows: wash the filtered solid with ultrapure water, centrifuge multiple times, and remove the supernatant; The hydrochloric acid solution can be replaced with other acidic solutions, but excessively high concentrations will damage the biochar structure; the concentration should not exceed 1 mol / L.

[0027] Comparative Example 1 Step 1: After washing, the straw is dried and crushed to obtain straw powder. The straw powder is placed directly in a tube furnace and calcined at 800°C for 2 hours under N2 atmosphere at a rate of 5°C / min. The calcined powder is named LS. Step 2: The calcined powder LS obtained in Step 1 is modified with KOH and then calcined. The resulting biochar powder is named KLS.

[0028] In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes: Take 10g of calcined powder and place it in an aqueous solution (10 mL / g). Add 6g of KOH, stir in a water bath at 60℃ for 12 hours, dry, place in an oven and calcine at 800℃ for 2 hours under N2 atmosphere at a rate of 5°C / min. The calcined powder is named KLS. Comparative Example 2 Step 1: After washing, the straw is dried and crushed to obtain straw powder. The straw powder is placed directly in a tube furnace and calcined at 800°C for 2 hours under N2 atmosphere at a rate of 5°C / min. The calcined powder is named LS. Step 2: The calcined powder obtained in Step 1 is nitrogen modified and named NLS after calcination.

[0029] In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes: Take 10g of calcined powder and place it in an aqueous solution (10 mL / g). Add 6g of urea, stir in a water bath at 60℃ for 12 hours, dry, and place in an oven to calcine at 800℃ for 2 hours under N2 atmosphere at a rate of 5°C / min. The calcined powder is named NLS. Comparative Example 3 Step 1: After washing, the straw is dried and crushed to obtain straw powder. The straw powder is placed directly in a tube furnace and calcined at 800°C for 2 hours under N2 atmosphere at a rate of 5°C / min. The calcined powder is named LS. Step 2: The calcined powder obtained in Step 1 is modified with ammonia water and then calcined. The resulting biochar powder is named N-LS.

[0030] In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes: Take 10g of calcined powder and place it in an ammonia solution (10 mL / g). Stir in a water bath at 60℃ for 12 hours and then dry it. Place it in an oven and calcine it at 800℃ for 2 hours under N2 atmosphere at a rate of 5°C / min. The calcined powder is named N-LS. Comparative Example 4 Step 1: After washing, the straw is dried and crushed to obtain straw powder. The straw powder is placed directly in a tube furnace and calcined at 800°C for 2 hours under N2 atmosphere at a rate of 5°C / min. The calcined powder is named LS. Step 2: The calcined powder obtained in Step 1 is modified with KOH and urea and then calcined. The resulting biochar powder is named KNLS.

[0031] In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes: Take 10g of calcined powder and place it in an aqueous solution (10 mL / g). Add 6g of KOH and 6g of urea. Stir in a water bath at 60℃ for 12 hours and then dry. Place it in an oven and calcine at 800℃ for 2 hours under N2 atmosphere with a heating rate of 5°C / min. The calcined powder is named KNLS.

[0032] The inventors observed the surface morphology of the obtained biochar using field emission scanning electron microscopy (SEM, Gemini 300, ZEISS, Germany) in Examples 1-4 and Comparative Examples 1-4, respectively. Figure 1 The pore structure of the N-KN biochar material obtained in Example 1 can be seen in the diagram. After modification with ammonia-KOH, the N-KN biochar forms a disordered and irregular pore structure, which verifies the pore-forming mechanism of KOH activation through gas release. High-temperature KOH pyrolysis is beneficial for increasing the specific surface area of ​​the carbon material, while potassium ions embedding into the carbon framework cause lattice expansion, thereby generating pores. With the increase of calcination temperature, the specific surface area of ​​N-KN biochar also increases compared to other modification methods.

[0033] The LS prepared by direct pyrolysis has a specific surface area of ​​169.530 m² / g and an average pore size of 7.034 nm. However, during the KOH activation process, K... + The embedding of hydroxyl lignin can clog the pores of biochar, leading to a decrease in specific surface area. NLS biochar has the smallest specific surface area (only 27.140 m² / g) and an average pore size of 21.902 nm. In contrast, KNLS biochar prepared by KOH activation and nitrogen doping has a significantly increased specific surface area (268.160 m² / g) and transforms into a microporous structure. Notably, although ammonia treatment does not directly increase the specific surface area, N-KN biochar prepared by ammonia pretreatment followed by KOH activation achieves the largest specific surface area (336.810 m² / g), and its pore structure also changes from mesoporous to microporous. This confirms that the hydroxyl lignin converted by ammonia treatment can indeed promote the impregnation utilization of activator and nitrogen source, resulting in N-KN having a larger specific surface area and total pore volume than KNLS. + The effects of intercalation and nitrogen doping are more pronounced.

[0034] The inventors tested the adsorption isotherms of the biochar described in Examples 1-4 and Comparative Examples 1-4 at 298 K, respectively. Figure 2 The N2 adsorption-desorption isotherms of the synthesized N-KN and KNLS biochar materials show typical Type I isotherms. This shape indicates that the materials have abundant microporous structures, i.e., pores with a diameter of less than 2 nm. These microporous materials have a large specific surface area and unique pore structure, confirming that nitrogen doping after KOH activation effectively changed the carbon lattice structure. LS, N-LS, NLS, and KLS all exhibit typical Type IV isotherms, which are typical adsorption isotherms for mesoporous materials (pore diameter between 2 nm and 50 nm).

[0035] Example 2 of the present invention provides an application of modified biochar in the adsorption of DNTs in TNT-containing red water, comprising the following steps: 1. Weigh 100 mg of each of the biochar from Comparative Examples 1-4 and place them in a 200 ml beaker. Add 100 mL of 200 mg / L DNTs solution and stir at 400 rpm for 240 min at 25 °C and pH=7 to adsorb the biochar.

[0036] 2. Weigh 100 mg of N-KN biochar and place it in a 200 ml beaker. Add 100 mL of 200 mg / L DNTs solution and stir at 400 rpm for 240 min at 25-45℃ and pH = 3-11.

[0037] The method for preparing the DNTs solution is as follows: accurately weigh 200 mg of DNTs solid into a 1 L volumetric flask, dilute to the mark with ultrapure water, and sonicate for 30 min to obtain a 200 mg / L DNTs solution.

[0038] like Figure 3 The diagram shows the kinetics of DNT adsorption by the prepared biochar material. N-KN biochar exhibits a rapid adsorption rate within the first 10 minutes, reaching 90% of its maximum adsorption capacity. Under conditions of 25℃, pH=7, adsorption time of 2 h, and a biochar dosage of 1 g / L, the adsorption capacity of N-KN biochar for DNTs decreased from 195.509 mg / L to 71.657 mg / L, with an adsorption capacity of 123.852 mg / g. This adsorption result is significantly higher than that of other modified biochar samples.

[0039] Example 3 of the present invention provides an application of modified biochar in the adsorption of nitro aromatic compounds in TNT red water, comprising the following steps: 1. Weigh 100 mg of each of the biochars in Comparative Examples 1-4 and place them in a 200 ml beaker. Add 100 mL of TNT red water (COD 500 mg / L) and stir at 400 rpm for 240 min at 25℃ and pH=7.

[0040] 2. Weigh 100 mg of N-KN biochar and place it in a 200 ml beaker. Add 100 mL of TNT red water (COD 500 mg / L) and stir at 400 rpm for 240 min at 25-45℃ and pH = 3-11.

[0041] The method for preparing the TNT red aqueous solution is as follows: dilute the TNT red water obtained from the factory to 500 mg / L by an appropriate factor according to the initial COD, detect the COD by titration, and sonicate for 30 min to obtain a 500 mg / L TNT red aqueous solution.

[0042] like Figure 4The diagram shows the adsorption of nitro aromatic compounds in TNT red water by the prepared biochar material. Under the conditions of 25℃, pH=7, adsorption time of 2h, and biochar dosage of 1g / L, the COD adsorption of TNT red water by N-KN biochar decreased from 504.509 mg / L to 377.811 mg / L, with an adsorption capacity of 126.698 mg / g. Compared with other modified biochars, it achieved a superior adsorption capacity.

[0043] The inventors conducted experiments on KLS, KNLS, and N-KN under different pH conditions and different dosages, and the results are as follows: Figure 5-6 As shown. Figure 5 This diagram illustrates the adsorption of DNTs solutions by KLS, KNLS, and N-KN biochar materials under different pH conditions. The experimental results show that N-KN biochar has excellent adsorption performance in the pH range of 3-11, while the adsorption performance of KLS and KNLS biochar decreases in strong acid and strong alkaline environments.

[0044] Figure 6 This diagram illustrates the adsorption of nitro aromatic compounds in TNT-treated red water by KLS, KNLS, and N-KN biochar materials under different dosage conditions. With increasing dosages of KLS, KNLS, and N-KN biochar, the COD removal rate of the TNT-treated red water continuously increases, but the adsorption capacity per unit area shows the opposite trend; at high dosages, excessive overlap of active sites leads to a decrease in adsorption efficiency. When the N-KN dosage reaches 5 g / L, the COD removal rate approaches 50%, and near-complete removal can be achieved with further increases in dosage.

[0045] In summary, N-KN biochar, with its stable adsorption performance, demonstrates superior application potential compared to KLS and KNLS in the treatment of TNT-treated red water.

[0046] Because the recyclability of biochar greatly limits its practical application, the inventors conducted five consecutive regeneration cycle experiments to evaluate the regeneration efficiency of the obtained biochar. Figure 7 This is a schematic diagram of N-KN biochar material adsorbing nitro aromatic compounds in TNT red water for 5 cycles. After each TNT red water adsorption experiment, N-KN was collected by filtration through a 0.22 μm membrane, transferred to anhydrous ethanol (50 mL / g) and sonicated for 1 hour for desorption, then filtered again and dried in an oven for 12 hours.

[0047] like Figure 7As shown, the adsorption performance of N-KN remained stable in the first three cycles of adsorption experiments, with adsorption capacities ranging from 126.698 to 112.470 mg / g. In the fourth cycle, the adsorption capacity still reached 101.232 mg / g, and in the fifth cycle, it decreased to 81.553 mg / g, but still maintained a high adsorption capacity. This demonstrates that N-KN biochar has excellent regeneration performance and can be reused, providing an efficient and economical solution for TNT-treated red water.

[0048] Compared with the prior art, the beneficial effects of the present invention include at least the following: Existing technologies commonly employ methods such as KOH modification, nitrogen doping, and alkali metal carbonate modification to prepare biochar, aiming to increase the specific surface area and the number of functional groups. This invention utilizes ammonia pretreatment to increase the number of surface functional groups, thereby promoting higher surface activity in activated carbon. Ammoniation of lignocellulose causes cell wall expansion, resulting in a looser structure. The carboxyl groups on the lignocellulose recombine, significantly increasing the crude protein content of the ammonified biochar precursor. Simultaneously, ammoniation increases available attachment sites for activators and promotes impregnation and activation. Therefore, ammonia pretreatment of ammonified biochar combined with other modification methods enhances the adsorption capacity of the resulting activated carbon, increases the nitrogen doping content, and increases the number of surface functional groups, a significant difference from other biochar materials.

[0049] The biomass used in this invention is waste lotus straw. Pretreatment with ammonia water increases the number of activatable sites on the biomass surface, improving the modification effect. This invention prepares high-performance lotus straw biochar (N-KN) through a synergistic modification strategy of ammoniation and KOH / nitrogen doping. N-KN biochar possesses a large specific surface area and pore size. In the adsorption of TNT red water, N-KN biochar exhibits excellent adsorption performance; its adsorption capacity, stability, and regeneration performance are significantly superior to other biochar materials. This provides an efficient and economical solution for TNT red water treatment and has broad industrial application prospects. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for preparing ammonia-modified straw biochar, characterized in that: Includes the following steps: Step 1: After washing, the straw is dried and crushed to obtain straw powder. The straw powder is then calcined to obtain calcined powder LS. Step 2: Immerse the calcined powder LS obtained in Step 1 in a solution containing ammonium ions, add KOH and a solid containing ammonium ions in a water bath and stir, filter and dry to obtain intermediate biochar; Step 3: Calcine the intermediate biochar obtained in Step 2 to obtain biochar powder BC. Wash the biochar powder BC, dry it, and sieve it to obtain biochar sample N-KN.

2. The method for preparing ammonia-modified straw biochar according to claim 1, characterized in that: In step 1, the straw powder is calcined at 800°C under a N2 atmosphere at a rate of 5°C / min.

3. The method for preparing ammonia-modified straw biochar according to claim 1, characterized in that: Step 2 includes: Step 2.1: The calcined powder LS is pretreated by immersing it in a solution containing ammonium ions to obtain a pretreated solution; Step 2.2: Add KOH and ammonium ion-containing solids in a set mass ratio to the pretreatment solution, filter, and dry in an oven to obtain intermediate biochar.

4. The method for preparing ammonia-modified straw biochar according to claim 1, characterized in that: In step 2.2, the mass ratio is set to 1:

1.

5. The method for preparing ammonia-modified straw biochar according to claim 1, characterized in that: Step 3 includes: Step 3.1: The intermediate biochar was calcined at 800℃ in a N2 atmosphere at a heating rate of 5℃ / min to obtain biochar powder BC. Step 3.2: After washing the biochar powder BC with an acidic solution and sonicating, filter the obtained biochar powder, wash, dry, grind and sieve to obtain biochar sample N-KN.

6. The method for preparing ammonia-modified straw biochar according to claim 5, characterized in that: In step 3.2, the concentration of the acidic solution is not higher than 1 mol / L.

7. The method for preparing ammonia-modified straw biochar according to claim 5, characterized in that: In step 3.2, the biochar powder obtained after filtration is washed by washing the filtered solid with ultrapure water, centrifuging multiple times, removing the supernatant, until the pH is neutral.

8. Ammonia-modified straw biochar prepared by any one of claims 1-7.

9. The application of ammonia-modified straw biochar according to claim 8 in the adsorption of DNTs in TNT-treated red water, characterized in that, Ammonia-modified straw biochar was weighed and added to a DNTs solution, and the mixture was stirred for adsorption. This was used for the adsorption treatment of the DNTs solution.

10. The adsorption application of ammonia-modified straw biochar in TNT red water according to claim 8, characterized in that, Ammonia-modified straw biochar was weighed and added to TNT red water, and the mixture was stirred for adsorption. This was used for the adsorption of nitro aromatic compounds in TNT red water.

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