Biochar for adsorbing hydrophobic organic contaminants and methods of making and using the same

Abstract

The present application belongs to the technical field of carbon adsorption, and provides a biochar for adsorbing hydrophobic organic pollutants, and a preparation method and application thereof. The preparation method comprises the following steps: preparing biomass raw materials, drying, crushing and sieving to obtain biomass powder; impregnating the biomass powder with a composite chlorinated salt to obtain a modified precursor; pyrolyzing the modified precursor in an inert gas environment to obtain a pyrolysis product; replacing the inert gas with carbon dioxide, increasing the pyrolysis temperature, and activating to obtain an activated product; and reacting the activated product with a hydrophobization modifier to obtain the biochar for adsorbing hydrophobic organic pollutants. The biochar can efficiently treat hydrophobic organic pollutants in wastewater, especially disperse violet and N,N-diethyl-3-acetamidobenzene, and the biochar has good environmental protection and economy.

Description

Technical Field

[0001] This invention relates to the field of carbon adsorption technology, and in particular to a biochar for adsorbing hydrophobic organic pollutants, its preparation method, and its application. Background Technology

[0002] Organic dyes are widely used in industries such as textiles, printing and dyeing, pharmaceuticals, and fine chemicals. However, their production and use generate large amounts of highly chromatic and toxic industrial wastewater. Among these, the synthetic disperse violet dye and its key intermediate, N,N-diethyl-3-acetaminoaniline, exhibit high biotoxicity and resistance to biodegradation due to their complex chemical structure, containing stable functional groups such as benzene rings, azo groups, and amino groups, large molecular diameter, and strong hydrophobicity. Therefore, developing efficient technologies for removing these recalcitrant macromolecular hydrophobic organic dyes and their intermediates from wastewater is an urgent and practical necessity for protecting the water environment, ensuring ecological security, and safeguarding public health.

[0003] Currently, conventional treatment methods for wastewater containing organic dyes mainly include physical, chemical, and biological methods. Physical methods, such as adsorption and membrane separation, are simple to operate, but generally suffer from problems such as high diffusion and mass transfer resistance due to the microporous structure of large-molecule dyes, limited adsorption capacity, difficult adsorbent regeneration, membrane fouling, and high operating costs. Chemical methods, such as advanced oxidation and coagulation-sedimentation, can effectively degrade some dye molecules, but have limitations such as high reagent consumption, potential secondary pollution, and poor treatment effect on high concentrations or specific structure dyes. Biological methods rely on the degradation of microorganisms, but the treatment cycle is long, and for highly biotoxic dye molecules (such as disperse violet and N,N-diethyl-3-acetaminoaniline), microbial activity is easily inhibited, resulting in unstable treatment effects. In particular, existing activation methods for preparing biochar mostly use one-step pyrolysis or single activator activation, resulting in materials with a simple pore structure that makes it difficult to simultaneously achieve high specific surface area and suitable mesoporous channels for large-molecule diffusion, thus limiting its efficient adsorption of large-molecule dyes. Therefore, existing technologies often fall short in terms of cost, efficiency, or environmental friendliness when treating such high-concentration, highly toxic, and recalcitrant macromolecular organic dye wastewater.

[0004] Therefore, developing a novel adsorbent material and its preparation technology that can achieve efficient and rapid adsorption of hydrophobic organic dyes while also being economical and environmentally friendly has become a technical problem that needs to be solved. Summary of the Invention

[0005] To address the aforementioned problems, this invention aims to provide a biochar for adsorbing hydrophobic organic pollutants, its preparation method, and its application. Through a specially designed preparation method, a biochar for adsorbing hydrophobic organic pollutants is obtained, thereby solving the problem of efficient adsorption of hydrophobic organic dyes, while also possessing good economic efficiency and environmental friendliness.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing biochar for adsorbing hydrophobic organic pollutants includes the following steps:

[0008] S1: Prepare biomass raw materials, dry them, and pulverize and sieve them to obtain biomass powder;

[0009] S2: Biomass powder is impregnated with a composite chloride salt to obtain a modified precursor, wherein the composite chloride salt is zinc chloride and potassium chloride;

[0010] S3: The modified precursor is pyrolyzed in an inert gas environment to obtain the pyrolysis product;

[0011] S4: Replace the inert gas with carbon dioxide, increase the pyrolysis temperature, and activate the product to obtain the activated product;

[0012] S5: The activated product is reacted with a hydrophobic modifier to obtain biochar for adsorbing hydrophobic organic pollutants.

[0013] Furthermore, the biomass raw material is peanut shells.

[0014] Furthermore, in step S2, the molar ratio of zinc chloride to potassium chloride is 6:1.

[0015] Further, step S2 includes:

[0016] S201: Mix biomass powder with compound chloride salt and add ultrapure water;

[0017] S202: Completely immerse and let stand for a predetermined time;

[0018] S203: Filter and dry to obtain modified precursor powder.

[0019] Further, step S3 includes:

[0020] S301: Preheat the modified precursor at 400 °C in a nitrogen atmosphere;

[0021] S302: Increase the temperature to 600 ℃ at a rate of 5 ℃ / min and hold for 60 minutes;

[0022] S303: Pyrolysis products are obtained.

[0023] Further, step S4 includes:

[0024] S401: Replace the inert gas with carbon dioxide;

[0025] S402: Increase the temperature to 750 ℃ ​​at a rate of 5 ℃ / min and hold for 60 minutes;

[0026] S403: Activated product is obtained.

[0027] Furthermore, in step S5, the hydrophobic modifier is hexadecyltrimethoxysilane, and the amount used is 3% of the mass of the activated product.

[0028] The present invention also provides biochar prepared by the preparation method described above.

[0029] The present invention also provides the application of biochar, as described above, in the adsorption treatment of hydrophobic organic pollutants in wastewater.

[0030] Furthermore, the hydrophobic organic pollutant is one or more of Disperse Violet and N,N-diethyl-3-acetaminoaniline.

[0031] In summary, the present invention has at least the following technical effects:

[0032] This invention achieves precise control over the mesoporous structure and hydrophobic modification of biochar through a specially designed preparation method, resulting in advantages such as high mesoporous volume ratio, large specific surface area, and strong surface hydrophobicity. It exhibits high adsorption capacity for hydrophobic organic pollutants, especially macromolecular hydrophobic dyes Disperse Violet and N,N-diethyl-3-acetaminoaniline, providing a new material for the efficient treatment of recalcitrant dyeing and printing wastewater. Attached Figure Description

[0033] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0034] Figure 1 This is a flowchart of the method for preparing biochar for adsorbing hydrophobic organic pollutants according to the present invention;

[0035] Figure 2 This is a molecular configuration diagram of Disperse Violet and N,N-diethyl-3-acetaminoaniline of the present invention;

[0036] Figure 3 The figure shows the experimental results comparing the removal rates of synthetic disperse purple and N,N-diethyl-3-acetaminoaniline by BC1 and BC according to the present invention.

[0037] Figure 4The figure shows the experimental results comparing the removal rates of synthetic disperse purple and N,N-diethyl-3-acetaminoaniline by BC2 and BC according to the present invention.

[0038] Figure 5 The figure shows the experimental results comparing the removal rates of synthetic disperse purple and N,N-diethyl-3-acetaminoaniline by BC3 and BC according to the present invention.

[0039] Figure 6 The figure shows the experimental results comparing the removal rates of synthetic disperse purple and N,N-diethyl-3-acetaminoaniline by BC4 and BC according to the present invention.

[0040] Figure 7 The images shown are scanning electron microscope (SEM) images of biochar used for comparison in this invention; wherein, (a) is the original unmodified biochar; (b) is biochar modified only by ZnCl2 (corresponding to Example 1); (c) is biochar modified by ZnCl2 / KCl composite metal salt (corresponding to Example 3); and (d) is the biochar (BC) prepared in this invention for adsorbing hydrophobic organic pollutants.

[0041] Figure 8 The figure shows the experimental results of the effect of solution pH on the removal rate of BC and N,N-diethyl-3-acetaminoaniline in the synthesis of the present invention.

[0042] Figure 9 The figure shows the experimental results of the effect of solution temperature on the removal rate of BC for the synthesized disperse purple and N,N-diethyl-3-acetaminoaniline in this invention.

[0043] Figure 10 The figure shows the experimental results of the effect of adsorption time on the removal rate of N,N-diethyl-3-acetaminoaniline by BC according to the present invention.

[0044] Figure 11 The figure shows the experimental results of the effect of adsorption time on the removal rate of BC by the synthesized disperse violet according to the present invention. Detailed Implementation

[0045] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0046] Example 1

[0047] Reference Figure 1 This embodiment provides a method for preparing biochar for adsorbing hydrophobic organic pollutants, comprising the following steps:

[0048] S1: Prepare biomass raw materials, dry them, and pulverize and sieve them to obtain biomass powder;

[0049] Specifically, peanut shells, agricultural and forestry waste, are selected, washed, dried, crushed, and sieved; the drying temperature is 90 ℃, and a 200-mesh screen is used for sieving; biomass powder is obtained.

[0050] S2: Biomass powder is impregnated with a composite chloride salt to obtain a modified precursor, wherein the composite chloride salt is zinc chloride and potassium chloride;

[0051] Specifically, 10 g of the above-mentioned biomass powder, along with 3 mol / L zinc chloride (ZnCl2) and 0.5 mol / L potassium chloride (KCl) (mixed in a molar ratio of 6:1) were weighed out as a composite chloride salt. The biomass powder and the composite chloride salt were placed in a 500 mL beaker, and ultrapure water was added until completely impregnated. After mixing thoroughly, the mixture was allowed to stand for 24 h. Subsequently, the mixture was separated by vacuum filtration, and the filter cake was dried to constant weight to obtain a powdered modified precursor.

[0052] S3: The modified precursor is pyrolyzed in an inert gas environment to obtain the pyrolysis product;

[0053] Specifically, the modified precursor was placed in a tube furnace and heated to 400 °C at a rate of 10 °C / min and held for 30 minutes under a nitrogen protective atmosphere. Then, the temperature was increased to 600 °C at a rate of 5 °C / min and held for 60 minutes to obtain the pyrolysis product.

[0054] S4: Replace the inert gas with carbon dioxide, increase the pyrolysis temperature, maintain for a predetermined time, and obtain the activated product;

[0055] Specifically, after the above pyrolysis is completed, without cooling, nitrogen is replaced with carbon dioxide, and the pyrolysis product is heated to 750 °C at a rate of 5 °C / min and activated for 60 minutes to obtain the activated product.

[0056] S5: The activated product is reacted with a hydrophobic modifier to obtain biochar for adsorbing hydrophobic organic pollutants.

[0057] Specifically, the hydrophobic modifier is hexadecyltrimethoxysilane, and its dosage is 3% of the biochar mass.

[0058] The biochar for adsorbing hydrophobic organic pollutants of this invention can be prepared using the above preparation method. The composite zinc chloride and potassium chloride provide a stable and abundant initial pore template for subsequent etching, while CO2 further etches the templated carbon framework at a higher temperature, achieving precise control over the mesoporous structure. After hydrophobication treatment, the prepared biochar simultaneously possesses the advantages of high mesoporous pore volume ratio, large specific surface area, and strong surface hydrophobicity. It exhibits particularly high adsorption capacity for the hydrophobic organic dyes Disperse Violet and N,N-diethyl-3-acetaminoaniline.

[0059] Example 2

[0060] In this embodiment, the adsorption effect of the biochar obtained in Example 1 for adsorbing hydrophobic organic pollutants was verified. The pollutants used in the verification experiment were Disperse Violet 93 (CAS No. 52697-38-8) and N,N-diethyl-3-acetaminoaniline (CAS No. 6375-46-8).

[0061] Based on the preparation method provided in Example 1, the following comparative examples are provided:

[0062] Comparative Example 1: ZnCl2 modified biochar (hereinafter referred to as BC1); compared with Example 1, only steps S1 and S2 were performed, and only ZnCl2 was used to impregnate the biomass powder. The amount of ZnCl2 used was 3.5 mol / L (equal replacement of the original KCl), and BC1 was obtained.

[0063] Comparative Example 2: KCl modified biochar (hereinafter referred to as BC2); Compared with Example 1, only steps S1 and S2 were performed, and in step S2, only KCl was used to impregnate the biomass powder, with the amount of KCl being 3.5 mol / L (equal to replacing the original ZnCl2), to obtain BC2.

[0064] Comparative Example 3: ZnCl2+KCl composite salt modified biochar (hereinafter referred to as BC3); compared with Example 1, only steps S1 and S2 were performed to obtain BC3.

[0065] Comparative Example 4: ZnCl2+KCl composite salt modified biochar was activated by conventional cooling and then heating with CO2 (hereinafter referred to as BC4); compared with Example 1, only steps S1, S2 and S3 were performed, and in step S3, the pyrolysis product was cooled first and then reheated for carbon dioxide activation to obtain BC4.

[0066] Comparative Example 5: Unhydrophobically modified biochar (hereinafter referred to as BC5); compared with Example 1, step S5 was not performed, and the remaining steps were the same.

[0067] The biochar obtained in Example 1 for adsorbing hydrophobic organic pollutants is hereinafter referred to as BC. BC is compared with BC1, BC2, BC3, and BC4 obtained in the comparative examples above.

[0068] The specific experimental conditions are as follows: the solution concentration of N,N-diethyl-3-acetaminoaniline is 400 mg / L, the solution concentration of disperse violet is 60 mg / L, and the molecular configurations of N,N-diethyl-3-acetaminoaniline and disperse violet are as follows. Figure 2As shown in the figure. The adsorbent dosage in the two solution systems was 8 g / L (N,N-diethyl-3-acetaminoaniline system) and 1 g / L (disperse violet system), respectively. The mixture was placed in a constant temperature shaker at 180 rpm and reacted at 50 ℃ for 3 h. After the reaction, the solution was filtered through a 0.45 μm Millipore HA filter membrane, and the absorbance of N,N-diethyl-3-acetaminoaniline (242 nm) and disperse violet (567 nm) in the filtrate was measured by UV-Vis spectrophotometer to calculate the removal rate. The experimental results are as follows. Figures 3 to 6 As shown.

[0069] Reference Figure 3 The removal rates of disperse violet and N,N-diethyl-3-acetaminoaniline by BC were 95.35% and 96.56%, respectively, while the removal rates of disperse violet and N,N-diethyl-3-acetaminoaniline by BC1 were only 43.03% and 40.43%, respectively. This indicates that the adsorption performance of BC for these two organic dyes is far superior to that of BC1.

[0070] Reference Figure 4 The removal rates of disperse violet and N,N-diethyl-3-acetaminoaniline by BC2 were 44.00% and 40.99%, respectively, similar to those of BC1, but lower than those of BC2. This indicates that BC2 has a much better adsorption performance for these two organic dyes than BC2.

[0071] Reference Figure 5 BC3 achieved removal rates of 55.12% for disperse violet and 52.41% for N,N-diethyl-3-acetaminoaniline, which were superior to BC1 and BC2. This is attributed to the synergistic effect of the ZnCl2+KCl composite salt in the formation of the biochar pore structure, thus increasing the adsorption efficiency of the biochar. However, it was still lower than the removal rates of BC for disperse violet and N,N-diethyl-3-acetaminoaniline.

[0072] Reference Figure 6BC4 achieved removal rates of 70.12% for disperse violet and 67.41% for N,N-diethyl-3-acetaminoaniline, showing improved adsorption performance compared to BC1, BC2, and BC3. This improvement is attributed to the pore optimization effect of the CO2 activation step. However, its removal rates for disperse violet and N,N-diethyl-3-acetaminoaniline remained lower than those of BC (95.35% and 96.56%) designed in this invention. This is because, in this invention, the atmosphere was switched from N2 to CO2 without cooling and maintained at a high temperature. The carbon skeleton remained in a "thermoplastic" state, exhibiting a certain degree of flexibility and reactivity. Furthermore, since the temperature did not decrease, the carbon skeleton did not undergo drastic shrinkage or structural rearrangement. The CO2 etching occurred within an "open" framework, optimizing and consolidating the hierarchical porous structure formed in the first stage, resulting in a more developed specific surface area and pore structure of the biochar.

[0073] Referring to Table 1, while keeping other preparation steps consistent, the water contact angle and adsorption performance of unmodified biochar (BC5) and the biochar of this invention (BC) were compared. The results, as shown in Table 1, indicate that hydrophobic modification based on hexadecyltrimethoxysilane increased the water contact angle of the biochar and further improved its adsorption performance for organic dyes. Hydrophobic modification not only improved hydrophobicity but also enhanced the hydrophobic interactions and van der Waals forces with organic pollutants by introducing long-chain alkyl groups, thereby increasing the removal rate of organic dyes by the biochar.

[0074] Table 1. Comparison of parameters and performance between BC5 and BC

[0075]

[0076] Reference Figure 7 Unmodified biochar, Comparative Example 1, Comparative Example 3, and the biochar obtained in Example 1 for adsorbing hydrophobic organic pollutants were characterized by electron microscopy.

[0077] like Figure 7 As shown in 'a', the surface of unmodified biochar (pyrolysis char of biomass raw materials) is relatively flat and smooth, with a relatively dense structure. Only a small number of natural vascular bundle pores can be observed, and there is a lack of well-developed pore structure, which limits its specific surface area and the exposure of adsorption sites.

[0078] like Figure 7 In Figure b, it can be seen that the surface of biochar modified only by ZnCl2 becomes rough, with certain etching marks and scattered particles, indicating that the chemical activator has a certain corrosive and pore-forming effect on the carbon matrix, but the overall pore structure has not been fully opened and there is still some blockage.

[0079] like Figure 7As shown in 'c', after modification with ZnCl2 / KCl composite metal salt, the structure of biochar becomes more porous, exhibiting a distinct layered or sheet-like stacked structure. This indicates that the molten composite salt plays a good template support role during pyrolysis, effectively preventing the shrinkage and collapse of the carbon skeleton and initially constructing a porous framework.

[0080] like Figure 7 As shown in 'd', the biochar (BC) prepared in this invention exhibits a morphology drastically different from the samples described above. A highly developed three-dimensional hierarchical porous structure is clearly observable, presenting a honeycomb-like or sponge-like framework. The biochar surface is covered with numerous clearly visible macropores and mesopores with thin walls and excellent interconnectivity between channels. This structure is attributed to the following: based on the initial framework constructed from composite salts, high-temperature CO2 physical activation without cooling further etches and expands the carbon framework, opening up previously blocked channels. This rich and interconnected macroporous-mesoporous network structure significantly reduces mass transfer resistance, providing a rapid transport channel for larger organic pollutants (such as disperse violet and N,N-diethyl-3-acetaminoaniline) to enter the biochar interior, thereby greatly improving the adsorption rate and saturated adsorption capacity.

[0081] Example 3

[0082] This embodiment uses the biochar prepared in Example 1. The specific surface area and pore size distribution of the sample were determined at 77 K using the nitrogen adsorption-desorption isotherm method. The specific surface area was calculated using the BET model, and the mesopore size distribution was calculated using the BJH model.

[0083] Ultimately, the biochar (BET) involved in this invention has a specific surface area of ​​104.24 m² / g and a mesopore volume of 0.221 cm³. 3 / g, micropore volume is 0.075 cm³ 3 / g, with an average pore size of 4.358 nm.

[0084] The above data show that the biochar of this invention has the highest BET specific surface area and total pore volume, and its average pore size is in the mesoporous range (2~50 nm), while retaining a considerable micropore volume. This indicates that the biochar of this invention successfully constructs a hierarchical porous structure, that is, micropores and mesopores coexist synergistically. This structure is beneficial for the rapid diffusion and efficient adsorption of organic dye macromolecules.

[0085] Example 4

[0086] This embodiment measures the effect of different solution pH values ​​on the adsorption effect of the biochar (BC) prepared in Example 1.

[0087] A solution of N,N-diethyl-3-acetaminoaniline was prepared with a concentration of 250 mg / L and a BC dosage of 0.4 g / 50 mL. A solution of disperse violet was prepared with a concentration of 60 mg / L and a BC dosage of 0.03 g / 50 mL. The pH of the solutions was adjusted to a range of 1–6. Other conditions included a temperature of 50 ℃, a shaking rate of 180 r / min, and a contact time of 3 h. After adsorption, the concentrations of disperse violet and N,N-diethyl-3-acetaminoaniline in the solutions were measured using a UV-Vis spectrophotometer.

[0088] Reference Figure 8 The removal rate of disperse violet by BC is almost unaffected by pH. The removal rate of N,N-diethyl-3-acetaminoaniline by BC is relatively stable at pH 2-6.

[0089] Example 5

[0090] This embodiment measures the effect of different solution temperatures on the adsorption effect of the biochar (BC) prepared in Example 1.

[0091] A solution of N,N-diethyl-3-acetaminoaniline was prepared with a concentration of 250 mg / L and a BC dosage of 0.4 g / 50 mL. A disperse violet solution was prepared with a concentration of 60 mg / L and a BC dosage of 0.05 g / 50 mL. The temperature range was set from 10 to 60 °C, and other conditions included a shaking rate of 180 r / min and a contact time of 1 h. After adsorption, the concentrations of disperse violet and N,N-diethyl-3-acetaminoaniline in the solution were determined using a UV-Vis spectrophotometer.

[0092] Reference Figure 9 The removal rates of disperse purple and N,N-diethyl-3-acetaminoaniline by BC were relatively stable with respect to temperature changes and did not exhibit temperature dependence.

[0093] Example 6

[0094] This embodiment measures the effect of adsorption time on the adsorption effect of biochar (BC) prepared in Example 1.

[0095] A solution of N,N-diethyl-3-acetaminoaniline was prepared at a concentration of 400 mg / L, with a BC dosage of 0.4 g / 50 mL, and the temperature was 50 ℃. The adsorption process of N,N-diethyl-3-acetaminoaniline by BC was tracked over a period of 10–180 min. The concentrations of disperse violet and N,N-diethyl-3-acetaminoaniline in the solution were determined using a UV-Vis spectrophotometer.

[0096] Reference Figure 10The removal rate of N,N-diethyl-3-acetaminoaniline by BC exhibits a two-stage characteristic of rapid adsorption and slow equilibrium over time, reaching adsorption equilibrium at around 180 min.

[0097] The solution of disperse violet was prepared at a concentration of 60 mg / L, with a BC dose of 0.1 g / 50 mL, and the temperature was 50 ℃. The adsorption process of disperse violet by BC over 10–180 min was monitored. The concentrations of disperse violet and N,N-diethyl-3-acetaminophen in the solution were determined using a UV-Vis spectrophotometer.

[0098] Reference Figure 11 The removal rate of disperse purple by BC also exhibited a two-stage characteristic of rapid adsorption and slow equilibrium over time, reaching adsorption equilibrium at around 50 min.

[0099] Example 7

[0100] This embodiment provides the application of the biochar obtained in Example 1 in the adsorption treatment of hydrophobic organic pollutants in wastewater. Further, the hydrophobic organic pollutant is one or more of Disperse Violet and N,N-diethyl-3-acetaminoaniline.

[0101] The foregoing has shown and described 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 embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing biochar for adsorbing hydrophobic organic pollutants, characterized in that, Includes the following steps: S1: Prepare biomass raw materials, dry them, pulverize and sieve them to obtain biomass powder; S2: Biomass powder was impregnated with a composite chloride salt to obtain a modified precursor, wherein the composite chloride salt was zinc chloride and potassium chloride in a molar ratio of 6:1; S3: The modified precursor is pyrolyzed in an inert atmosphere to obtain the pyrolysis product; S4: After the pyrolysis in step S3 is completed, without cooling, the inert atmosphere is directly replaced with carbon dioxide to increase the pyrolysis temperature and activate the product. S5: The activated product is reacted with a hydrophobic modifier to obtain biochar for adsorbing hydrophobic organic pollutants, wherein the hydrophobic modifier is hexadecyltrimethoxysilane and the amount used is 3% of the mass of the activated product.

2. The method for preparing biochar for adsorbing hydrophobic organic pollutants according to claim 1, characterized in that, The biomass raw material is peanut shells.

3. The method for preparing biochar for adsorbing hydrophobic organic pollutants according to claim 2, characterized in that, Step S2 includes: S201: Mix biomass powder with compound chloride salt and add ultrapure water; S202: Completely immerse and let stand for a predetermined time; S203: Filter and dry to obtain modified precursor powder.

4. The method for preparing biochar for adsorbing hydrophobic organic pollutants according to claim 3, characterized in that, Step S3 includes: S301: Preheat the modified precursor at 400 °C in a nitrogen atmosphere; S302: Increase the temperature to 600 ℃ at a rate of 5 ℃ / min and hold for 60 minutes; S303: Pyrolysis products are obtained.

5. The method for preparing biochar for adsorbing hydrophobic organic pollutants according to claim 1, characterized in that, Step S4 includes: S401: Replace the inert atmosphere with carbon dioxide; S402: Increase the temperature to 750 ℃ ​​at a rate of 5 ℃ / min and hold for 60 minutes; S403: Activated product is obtained.

6. Biochar prepared by the preparation method according to any one of claims 1 to 5.

7. The application of biochar as described in claim 6 in the adsorption treatment of hydrophobic organic pollutants in wastewater.

8. The application according to claim 7, characterized in that, The hydrophobic organic pollutant is one or more of Disperse Violet and N,N-diethyl-3-acetaminoaniline.

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