Preparation method and application of environment functional material rich in persistent free radicals

Abstract

This invention discloses a method for preparing and applying environmentally functional materials rich in persistent free radicals. The preparation method includes: mechanically crushing and sieving agricultural waste, washing it with deionized water, and drying it to constant weight; mixing the obtained agricultural waste powder with alkali at a specific mass ratio, adding deionized water, stirring uniformly at room temperature to promote a complete reaction, and then transferring the mixture to a crucible for drying; and pyrolyzing the precursor in a tube furnace under a nitrogen atmosphere to finally obtain biochar material with a high content of persistent free radicals. This invention utilizes a three-step method of "raw material pretreatment - alkali modification - controlled-temperature pyrolysis" to efficiently transform widely available and low-cost agricultural waste into structurally stable and high-performance environmentally functional materials. The process is simple, low-cost, and environmentally friendly, showing good practicality and promising prospects for widespread application.

Description

Technical Field

[0001] This invention relates to the field of waste resource utilization and advanced environmental materials technology, specifically to a method for preparing and applying an environmental functional material rich in persistent free radicals. Background Technology

[0002] With the continuous deepening of industrialization and the escalating intensity of human activities, the environmental pressure caused by unreasonable waste disposal has become increasingly prominent, triggering a series of complex and severe pollution problems. As a major agricultural and industrial country globally, my country discharges large amounts of wastewater containing persistent new pollutants and heavy metals during industrial and agricultural production. These pollutants are characterized by high environmental persistence, strong bioaccumulation potential, and difficulty in complete removal using traditional treatment processes, posing a long-term threat to the stability of aquatic ecosystems and the quality and safety of agricultural products. New pollutants such as drug residues, endocrine disruptors, and perfluorinated compounds have become one of the key bottlenecks restricting the sustainable development of agriculture and the construction of ecological civilization in my country. Therefore, developing efficient, stable, and economically feasible technologies for the removal of new pollutants and heavy metals is of great strategic significance for maintaining water environmental safety, ensuring the quality of agricultural products, and protecting public health.

[0003] Globally, biomass resources are extremely abundant, with an estimated annual production of approximately 100 billion tons. Taking the European Union as an example, about 70% of the biomass produced by its member states comes from crop residues, 16% from forest residues, and 14% from other organic waste, totaling over 445 million tons. This vast resource has stimulated the potential for high-value utilization of biomass in multiple fields. Among these, biochar, a novel carbon material prepared from lignocellulosic biomass through pyrolysis under limited oxygen conditions, has attracted considerable attention in recent years. Besides agricultural soil improvement and energy utilization, biochar shows broad prospects as a highly efficient adsorbent in environmental pollution remediation, particularly in fixing organic pollutants in water and soil. Its surface is rich in various functional groups (such as oxygen-, nitrogen-, and sulfur-containing functional groups) and a special structure called "persistent free radicals," which are considered key active sites in the pollutant removal process. Unlike transient free radicals, persistent free radicals in biochar have higher stability and a longer environmental lifetime, allowing them to continuously exert catalytic and adsorption functions over a longer timescale. These free radicals mainly form during the breaking of chemical bonds in biomass during pyrolysis, or through electron transfer reactions between organic precursors and transition metals. Common precursors include lignin, aromatic structural units, cellulose, and hemicellulose. Biochar-persistent free radicals carrying unpaired electrons can further induce the generation of various reactive oxygen species, such as hydroxyl radicals, superoxide anions, hydroperoxides, and some non-radical oxygen-containing derivatives. Typically, biochar-persistent free radicals can transfer electrons to oxygen molecules, generating superoxide anions, which then form hydrogen peroxide through a series of reactions and ultimately decompose into highly oxidizing hydroxyl radicals. These reactive oxygen species can efficiently attack and degrade various pollutants, thereby achieving their effective transformation and removal.

[0004] Therefore, in response to the severe challenges posed by the combined pollution of new pollutants and heavy metals, designing and preparing environmental functional materials rich in persistent free radicals not only helps to deepen the understanding of the microstructure of carbon materials and the pollutant removal mechanism, but also provides a promising path for developing a new generation of efficient and green water and soil remediation technologies. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing and applying environmentally functional materials rich in persistent free radicals.

[0006] The technical solution of this invention is: a method for preparing environmental functional materials rich in persistent free radicals, comprising the following steps: S1. Agricultural waste pretreatment: Agricultural waste is mechanically crushed and sieved, washed with deionized water and dried to constant weight to obtain agricultural waste powder. S2. Modification of agricultural waste: The agricultural waste powder is mixed with alkali at a mass ratio of 0.5 to 2:1, deionized water is added, the mixture is stirred evenly at room temperature and reacted for 3 to 5 hours, and then the mixture is transferred to a crucible to dry to obtain the precursor. S3. Preparation of environmental functional materials rich in persistent free radicals: Under nitrogen atmosphere protection, the precursor is placed in a tube furnace for pyrolysis to finally obtain the environmental functional materials rich in persistent free radicals.

[0007] Furthermore, the agricultural waste is selected from one or more of wheat straw, corn straw, rice straw, sawdust, soybean straw, and tobacco stalks.

[0008] Note: The above-mentioned agricultural waste can effectively utilize various biomass resources. Given the abundance of global biomass resources, it can not only make resource-based use of waste but also transform it into advanced environmental materials.

[0009] Furthermore, in S1, agricultural waste is mechanically crushed and then screened to select powder that passes through a 60-100 mesh sieve.

[0010] Note: The particle size range (approximately 0.125~0.295 mm) represents the optimal balance between reactivity, process stability, and economy in practical applications. This particle size range increases the specific surface area of ​​the material by 30~50% compared to coarser particles (<60 mesh), significantly improving mass transfer efficiency in processes such as pyrolysis, gasification, adsorption, and bio-fermentation. In biochar preparation, the organic carbon retention rate of 60~100 mesh powder can reach 85.14%, significantly higher than the 51.96% of large particles (>10 mm).

[0011] Furthermore, in S1, deionized water is used for washing 3 to 5 times.

[0012] Explanation: Washing agricultural waste with deionized water at least three times systematically removes soluble impurities, ensuring the stability of the material's chemical composition and providing a pure matrix for subsequent pyrolysis, adsorption, or biochar preparation. Agricultural waste (such as straw, rice husks, and livestock manure) often contains a large amount of soluble inorganic salts like potassium, sodium, calcium, and magnesium, as well as metal ions from soil particles. Deionized water, being electrolyte-free, effectively dissolves and washes away these ions, significantly reducing ash content and improving the calorific value and purity of subsequent pyrolysis products. Washing also removes residual pesticides (such as organophosphates), organic acids, phenolic metabolites, and other trace organic impurities, preventing side reactions or interference with Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) characterization results during high-temperature treatment. Experiments show that the first two washes remove approximately 70-80% of soluble impurities; after the third wash, the residual ion concentration plateaus, and further washing offers limited improvement in removal efficiency. Therefore, "at least three washes" is a standardized threshold that balances purification efficiency and operating costs, ensuring the chemical stability of the material before it reaches constant weight.

[0013] Furthermore, in S2, the base is potassium hydroxide or sodium hydroxide.

[0014] Explanation: Potassium hydroxide (KOH) or sodium hydroxide (NaOH) is mixed with agricultural waste powder at a mass ratio of 0.5:1 to 2:1. This mild chemical pretreatment efficiently constructs a highly active porous carbon structure, laying the structural and chemical foundation for subsequent pyrolysis preparation of high-performance adsorbents, electrode materials, or soil conditioners. Specifically: OH groups dissociate from KOH and NaOH in an aqueous medium. - Ions can penetrate the amorphous regions of cellulose and hemicellulose, initiating swelling and partial depolymerization, while simultaneously dissolving silicate and ash precursors. This process forms the "etch-expansion" mechanism for the subsequent pyrolysis stage (e.g., K2). + Insertion of carbon layers and generation of CO / CO2 gas to create pores provide structural pre-relaxation, enabling the final biochar to achieve a specific surface area of ​​500–2080 m². 2 / g, significantly better than unactivated materials (<150 m 2 / g); At the lower limit of 0.5:1, the cellulose structure is sufficiently activated, increasing the adsorption capacity to 8.5 times that of the unactivated material while maintaining a high yield (>48%). The micropore volume can be further expanded at the upper limit of 2:1, but the yield drops significantly (<30%) after exceeding 2:1, and the post-treatment washing burden increases, reducing economic efficiency.

[0015] Further, in S3, under nitrogen atmosphere protection, the precursor is placed in a tube furnace and heated to 400-700 °C, and kept pyrolyzed for 1-2 hours; the pyrolysis product is acid washed 3-5 times, then rinsed with ultrapure water to remove ash and inorganic ions, centrifuged and dried to constant weight.

[0016] Note: Pyrolysis under an inert atmosphere effectively isolates oxygen, preventing the organic components (cellulose, lignin) in the precursor from undergoing oxidation, combustion, or incomplete decomposition at high temperatures. This ensures selective graphitization of the carbon skeleton and orderly development of the pore structure. This condition inhibits secondary tar decomposition, increases carbon yield (up to 30-40%), and promotes the synergistic formation of micropores (<2nm) and mesopores (2–50nm), laying the foundation for subsequent high specific surface area (>400m²). 2 / g) Biochar lays the structural foundation; Treating pyrolysis products with dilute hydrochloric acid (HCl) or nitric acid (HNO3) can selectively dissolve metal oxides and inorganic salt ash (such as CaO, Mg(OH)2, K2CO3, Fe2O3), with a dissolution efficiency of 85-95%. This process can remove pore blockages, restore the intrinsic pore structure of the material, and significantly increase the specific surface area and pore volume. At the same time, it reduces conductivity interference, making the material more suitable for applications sensitive to ionic impurities, such as electrochemical electrodes and catalyst supports. Using ultrapure water with a resistivity ≥18.2 MΩ·cm instead of ordinary water or deionized water can completely remove residual acid radicals (Cl). - NO3 - ) and trace metal contaminants (such as Na) + Fe 3+ (Concentration <0.1ppb) to avoid ion residues that could lead to deviations in subsequent adsorption experiments or side reactions at the electrode interface.

[0017] Furthermore, the pyrolysis heating rate is 5-10 °C / min, and the drying temperature is 60-80 °C.

[0018] Note: The above-mentioned pyrolysis heating rate and drying temperature can ensure the modification treatment effect of agricultural waste.

[0019] Furthermore, in S2, during the mixing process of agricultural waste powder and alkali, X% of alkali is added to the agricultural waste powder in advance for ball milling and mixing to form a ball milling system; The alkali solution was prepared by mixing (100-X)% alkali with deionized water. The mass concentration of the alkali solution was 8-15%. The alkali solution was then added to the ball milling system at a rate of 20-40 mL / min until all the alkali solution was added to the ball milling system. After ball milling for another 3-5 min, the mixture was transferred to a crucible and dried to obtain the precursor. The alkaline solution also contains 2-4 mg / mL of 3,4-dihydroxyphenylalanine; X∈[20-50], and X is an integer.

[0020] Note: The above process can simultaneously achieve structural activation and functional modification. Through mechanochemical synergy and precise control of reaction kinetics, a multifunctional biochar material with both high porosity and biomimetic adhesion properties can be constructed, as detailed below: Initially, ball milling is used to mix a portion of the alkali (KOH / NaOH) with the powder. Mechanical force is used to disrupt the cellulose crystalline region and the lignin-carbohydrate complex (LCC) structure, forming microcracks and amorphous regions, significantly enhancing the alkali ion (OH-) content. - The diffusion rate of the virus in the solid phase is reduced, and this process achieves "mechanical-chemical synergistic activation," shortening the reaction time by more than 40% compared to traditional stirring pretreatment. Simultaneously, the slow addition of DOPA-containing alkaline solution allows DOPA to remain stable in a mild alkaline environment (pH 9-11). Its catechol structure forms covalent bonds with cellulose aldehyde groups through Schiff base reaction and with lignin quinone units through Michael addition. At the same time, it is anchored to the material surface through cation-π interaction and hydrogen bonding. This avoids the rapid oxidation and polymerization of DOPA in high-concentration alkali to form ineffective precipitates, ensuring that it is uniformly grafted at the molecular level rather than deposited on the surface. Furthermore, by employing a stepwise alkali addition strategy to effectively buffer the pH gradient of the system, excessive local alkali concentrations can be prevented from leading to excessive lignin degradation or DOPA self-polymerization. This can increase the DOPA grafting efficiency to over 78%, and the density of phenolic hydroxyl groups in the product is 35% higher than that of the traditional total alkali method, significantly enhancing the material's resistance to heavy metal ions (such as Cu). 2+ Zn 2+ The chelating ability of the chelating agent increases the adsorption capacity by 3 to 8 times.

[0021] Furthermore, during the addition of alkali solution to the ball milling system, microwave heating of 300~800W is applied to the ball milling mixture until all the alkali solution is added to the ball milling system, at which point the microwave application is stopped. Specifically, after the microwave application is stopped, the water content in the ball milling system is simultaneously reduced to 25-35%, that is, under the premise that the alkali addition time T1 and the microwave heating time T2 are the same, the water content in the ball milling system is reduced to 25-35% by microwave heating.

[0022] Note: Microwave heating of 300-800W is applied during the addition of alkali solution to the ball milling system. Through the synergistic effect of the electromagnetic field and polar substances, instantaneous, uniform, and selective heating of the reaction system is achieved, significantly enhancing the simultaneous efficiency of alkali solution penetration, structural activation, and functional grafting. This constructs a multifunctional biochar precursor with high porosity and high functional group density, utilizing microwave energy to directly couple water molecules and OH groups. -Ions induce violent dipole rotation and ionic oscillation of molecules, generating an "endogenous heat effect," which enables the alkali solution to achieve local heating at the moment of drop addition (not dependent on heat conduction), increasing the penetration rate by 3 to 5 times. At the same time, the amount of water in the system can be reduced during the modification process, reducing the time required for subsequent crucible drying.

[0023] Furthermore, the environmentally functional materials rich in persistent free radicals are used in the removal of recalcitrant organic pollutants and heavy metals.

[0024] The beneficial effects of this invention are: (1) The present invention successfully constructed a highly active microstructure, realizing the efficient removal of pollutants. Through the synergistic effect of "alkali modification-temperature controlled pyrolysis", the specific surface area, porosity and concentration of persistent free radicals of biochar material were significantly improved. This optimized microstructure not only provides more physical adsorption sites, but its high content of persistent free radicals can also continuously activate molecular oxygen and generate strong oxidizing reactive oxygen species. Thus, through the "adsorption-catalysis" synergistic mechanism, the efficient degradation of recalcitrant organic pollutants and the stable fixation of heavy metals in water bodies can be achieved.

[0025] (2) This invention realizes the high-value-added resource utilization of agricultural waste, which has both environmental and economic benefits. It uses agricultural waste such as wheat straw and corn straw, which are widely available and inexpensive, as raw materials to transform them into high-performance environmental remediation materials. This process not only effectively reduces the disposal pressure of agricultural solid waste, but also turns waste into treasure, providing a green and economical solution of "waste treatment" for complex water pollution control, and has good circular economy value.

[0026] (3) The process of this invention is simple, stable, and environmentally friendly, with good prospects for industrial application. The process is clear, the conditions are mild and controllable, and no complex equipment or expensive reagents are required. The entire process (including the subsequent acid washing step) effectively removes ash and inorganic ions, ensuring the stability of the final product structure and environmental compatibility. This efficient, low-cost, and easily scalable technical approach lays a solid foundation for its large-scale application in actual wastewater treatment projects. Attached Figure Description

[0027] Figure 1 These are the morphological characteristics of the persistent free radical-rich biochar prepared in this invention.

[0028] Figure 2 This refers to the persistent free radical strength in the persistent free radical-rich biochar prepared according to this invention.

[0029] Figure 3 This invention demonstrates the effectiveness of the persistent free radical-rich biochar in removing new pollutants and heavy metals. Detailed Implementation

[0030] The present invention will now be described in more detail with reference to specific embodiments, so as to better demonstrate the advantages of the present invention.

[0031] Example 1: A method for preparing an environmentally functional material rich in persistent free radicals, comprising the following steps: S1. Agricultural waste pretreatment: After mechanical crushing and sieving, agricultural waste is selected. Powder passing through a 60-100 mesh sieve is washed four times with deionized water and dried to constant weight to obtain agricultural waste powder. The drying temperature is 75℃, and the agricultural waste is selected from corn stalks; S2. Modification of agricultural waste: The agricultural waste powder and alkali are mixed at a mass ratio of 1:1, deionized water is added, and the mixture is stirred evenly at room temperature for 4 hours to allow the agricultural waste powder and alkali to react fully. Then the mixture is transferred to a crucible and dried to obtain the precursor. The drying temperature is 75 ℃, and the alkali is potassium hydroxide 0; S3. Preparation of environmental functional materials rich in persistent free radicals: Under nitrogen atmosphere protection, the precursor is placed in a tube furnace and heated to 700 °C for pyrolysis for 2 hours. The pyrolysis product is acid washed 4 times, then rinsed with ultrapure water to remove ash and inorganic ions. After centrifugation, it is dried to constant weight to finally obtain the environmental functional material rich in persistent free radicals.

[0032] The drying temperature is 75 ℃, and the pyrolysis heating rate is 8 ℃ / min.

[0033] Example 2: The difference between this example and Example 1 is that agricultural waste is mechanically crushed and sieved, and the powder that passes through a 60-mesh sieve is selected, washed three times with deionized water and dried to constant weight at a drying temperature of 60 ℃ to obtain agricultural waste powder.

[0034] Example 3: The difference between this example and Example 1 is that agricultural waste is mechanically crushed and sieved, and the powder that passes through a 100-mesh sieve is selected, washed five times with deionized water and dried to constant weight at a drying temperature of 80 ℃ to obtain agricultural waste powder.

[0035] Example 4: The difference between this example and Example 1 is that the agricultural waste powder and alkali are mixed at a mass ratio of 0.5:1, deionized water is added, and the mixture is stirred evenly at room temperature for 3 hours to allow the agricultural waste powder and alkali to react fully. Then the mixture is transferred to a crucible for drying at a temperature of 60°C to obtain the precursor.

[0036] Example 5: This example differs from Example 1 in that the agricultural waste powder and alkali are mixed at a mass ratio of 2:1, deionized water is added, and the mixture is stirred evenly at room temperature for 5 hours to allow the agricultural waste powder and alkali to react fully. The mixture is then transferred to a crucible for drying at a temperature of 80 °C to obtain the precursor.

[0037] Example 6: This example differs from Example 1 in that the precursor is placed in a tube furnace and heated to 600 °C for pyrolysis for 1.5 hours at a heating rate of 5 °C / min. The pyrolysis product is acid-washed three times, then rinsed with ultrapure water to remove ash and inorganic ions. After centrifugation, it is dried to constant weight at a drying temperature of 60 °C, finally yielding a biochar material with a high content of persistent free radicals.

[0038] Example 7: This example differs from Example 1 in that the precursor is placed in a tube furnace and heated to 400 °C for pyrolysis for 1 hour. The pyrolysis heating rate is 10 °C / min. The pyrolysis product is acid-washed 5 times, then rinsed with ultrapure water to remove ash and inorganic ions. After centrifugation, it is dried to constant weight at a drying temperature of 80 °C, finally obtaining a biochar material with a high content of persistent free radicals.

[0039] Example 8: This example differs from Example 1 in that, in S2, during the mixing of agricultural waste powder and alkali, X is set to 45, meaning that 45% of the alkali is added to the agricultural waste powder beforehand for ball milling and mixing to form a ball milling system. It should be noted that 45% of the alkali refers to 45% of the total alkali mass used, and the same applies to 65% below; the ball milling speed is 320 r / min, and the ball loading is 25% (occupying the volume of the ball mill container); 65% alkali was mixed with deionized water to obtain an alkaline solution with a mass concentration of 12%. The alkaline solution was then added to the ball milling system at a rate of 35 mL / min until all the alkaline solution was added to the ball milling system. After ball milling for another 4 min, the mixture was transferred to a crucible and dried to obtain the precursor. The alkaline solution also contains 3.6 mg / mL of 3,4-dihydroxyphenylalanine.

[0040] Example 9: The difference between this example and Example 8 is that X is 20, that is, 20% alkali is added to agricultural waste powder in advance for ball milling and mixing to form a ball milling system; and 80% alkali is mixed with deionized water to obtain an alkali solution with a mass concentration of 8%.

[0041] Example 10: The difference between this example and Example 8 is that X is 50, that is, X% of the alkali is added to the agricultural waste powder in advance for ball milling and mixing to form a ball milling system; and 50% of the alkali is mixed with deionized water to obtain an alkali solution with a mass concentration of 15%.

[0042] Example 11: This example differs from Example 8 in that the alkali solution is added to the ball milling system at a rate of 20 mL / min.

[0043] Example 12: This example differs from Example 8 in that the alkali solution is added to the ball milling system at a rate of 40 mL / min.

[0044] Example 13: This example differs from Example 8 in that the alkaline solution also contains 2 mg / mL of 3,4-dihydroxyphenylalanine.

[0045] Example 14: This example differs from Example 8 in that the alkaline solution also contains 4 mg / mL of 3,4-dihydroxyphenylalanine.

[0046] Example 15: The difference between this example and Example 8 is that after ball milling for 3 minutes, the mixture is transferred to a crucible for drying.

[0047] Example 16: The difference between this example and Example 8 is that after ball milling for another 5 minutes, the mixture is transferred to a crucible for drying.

[0048] Example 17: This example differs from Example 8 in that, during the addition of alkali solution to the ball milling system, a microwave heating treatment of 725W is applied to the ball milling mixing system until all the alkali solution is added to the ball milling system, and then the microwave application is stopped; wherein, after the microwave application is stopped, the water content in the ball milling system simultaneously decreases to 29%.

[0049] The water evaporation rate per minute within the full power range of 300~800W is shown in Table 1 below: Table 1. Evaporation rate within the full power range of 300~800W

[0050] It should be noted that this is not the only reference, and there may be a deviation of ±15% due to factors such as ambient temperature in specific regions and container materials. The actual operating conditions shall prevail.

[0051] Example 18: This example differs from Example 17 in that the water content in the ball milling system simultaneously decreased to 25% after the microwave application was stopped.

[0052] Example 19: The difference between this example and Example 17 is that the water content in the ball milling system decreased to 35% simultaneously after the microwave application was stopped.

[0053] Example 20: This example provides the use of biochar materials with high content of persistent free radicals, which can be used in the removal of recalcitrant organic pollutants and heavy metals.

[0054] Experimental Example: Comparative Example 1 was set up. Corn stalks were mechanically crushed and sieved. Particles passing through a 100-mesh sieve were collected, washed three times with deionized water, and dried to constant weight at 80 °C. Under a nitrogen atmosphere, the precursor was placed in a tube furnace and heated to 700 °C at a heating rate of 5 °C / min, and pyrolyzed at this temperature for 2 hours. After the reaction, the product was collected, and successively acid-washed three times and rinsed with ultrapure water to remove ash and inorganic ions. After centrifugation, it was dried to constant weight at 80 °C.

[0055] The specific surface area and pore size test results of the biochar prepared in Comparative Example 1 and Example 1 are shown in Table 2: Table 2. Specific surface area and pore size tests of biochar

[0056] Conclusion: As shown in Table 2 above, the biochar obtained in Example 1 has a larger specific surface area and a more abundant pore size distribution compared to Comparative Example 1. Furthermore, the morphology of Examples 1 and Comparative Example 1 was analyzed, and the morphology analysis results ( Figure 1 The results show that the biochar in Comparative Example 1 exhibits a disordered morphological structure, while the biochar prepared in Example 1 displays a regular honeycomb structure. This ordered, loose, and porous structure creates a large number of free spaces, endowing it with excellent adsorption potential for organic matter and heavy metals.

[0057] The persistent radical strengths of both were characterized by EPR testing, and the results are as follows: Figure 2 As shown. The biochar in Example 1 exhibited a stronger persistent free radical signal, indicating its higher reactivity in degrading organic matter and immobilizing heavy metals.

[0058] Meanwhile, the specific surface area and pore size test results of the biochar prepared in Examples 1, 8, and 17 were further evaluated, as shown in Table 3: Table 3. Specific surface area and pore size tests of biochar

[0059] Conclusion: As can be seen from the results in Table 3 above, the biochar obtained in Examples 8 and 17 has a larger specific surface area and a more abundant pore size distribution compared to Example 1.

[0060] Comparative Example 2 was set up, in which 3,4-dihydroxyphenylalanine was not added, and the rest of the preparation methods were the same as those in Example 8. Comparative Example 3 was set up. In Comparative Example 3, the alkali was used in steps of X%, 1-X%, and directly mixed and ball-milled until all the alkali solution was added to the ball-milling system. After ball-milling for another 4 minutes, the mixture was transferred to a crucible and dried to obtain the precursor. The alkali solution did not contain 3,4-dihydroxyphenylalanine. The specific surface area and pore size test results of the prepared biochar are shown in Table 4: Table 4. Specific surface area and pore size tests of biochar

[0061] Conclusion: As can be seen from the results in Table 4 above, compared with Example 8, the specific surface area and pore size distribution of biochar obtained in Comparative Example 2 and Comparative Example 3 both decreased significantly. It can be seen that the introduction of 3,4-dihydroxyphenylalanine and the stepwise application of X% and 1-X% significantly improved the specific surface area of ​​biochar.

[0062] Furthermore, regarding the application of biochar, we evaluated the removal performance of the biochar prepared in Example 1 and Comparative Example 1 on typical novel pollutants sulfamethoxazole and heavy metals chromium and nickel. Figure 3 As shown in the figure, horizontal axis 1 represents Comparative Example 1, and horizontal axis 2 represents Example 1. The pyrolysis temperature of each interval was measured. The biochar of Example 1 showed the best removal effect, further verifying its efficient removal ability of organic matter and heavy metals.

Claims

1. A method for preparing an environmentally functional material rich in persistent free radicals, characterized in that, Includes the following steps: S1. Agricultural waste pretreatment: Agricultural waste is mechanically crushed and sieved, washed with deionized water and dried to constant weight to obtain agricultural waste powder. S2. Modification of agricultural waste: The agricultural waste powder is mixed with alkali at a mass ratio of 0.5 to 2:1, deionized water is added, the mixture is stirred evenly at room temperature and reacted for 3 to 5 hours, and then the mixture is transferred to a crucible to dry to obtain the precursor. S3. Preparation of environmental functional materials rich in persistent free radicals: Under nitrogen atmosphere protection, the precursor is placed in a tube furnace for pyrolysis to finally obtain the environmental functional materials rich in persistent free radicals.

2. The method for preparing an environmentally functional material rich in persistent free radicals according to claim 1, characterized in that, The agricultural waste is selected from one or more of the following: wheat straw, corn straw, rice straw, sawdust, soybean straw, and tobacco stalks.

3. The method for preparing an environmentally functional material rich in persistent free radicals according to claim 1, characterized in that, In S1, agricultural waste is mechanically crushed and then screened to select powder that passes through a 60-100 mesh sieve.

4. The method for preparing an environmentally functional material rich in persistent free radicals according to claim 1, characterized in that, In S1, agricultural waste is mechanically crushed and screened, and then washed with deionized water 3 to 5 times.

5. The method for preparing an environmentally functional material rich in persistent free radicals according to claim 1, characterized in that, In S2, the base is potassium hydroxide or sodium hydroxide.

6. The method for preparing an environmentally functional material rich in persistent free radicals according to claim 1, characterized in that, In S3, under a nitrogen atmosphere, the precursor is placed in a tube furnace and heated to 400-700 °C, and kept pyrolyzed for 1-2 hours. The pyrolysis product is acid-washed 3-5 times, then rinsed with ultrapure water to remove ash and inorganic ions, centrifuged and dried to constant weight.

7. The method for preparing an environmentally functional material rich in persistent free radicals according to claim 6, characterized in that, The pyrolysis heating rate is 5-10 ℃ / min, and the drying temperature is 60-80 ℃.

8. The method for preparing an environmentally functional material rich in persistent free radicals according to claim 1, characterized in that, In S2, during the mixing process of agricultural waste powder and alkali, X% of the alkali is added to the agricultural waste powder in advance for ball milling and mixing to form a ball milling system; The alkali solution was prepared by mixing (100-X)% alkali with deionized water. The mass concentration of the alkali solution was 8-15%. The alkali solution was then added to the ball milling system at a rate of 20-40 mL / min until all the alkali solution was added to the ball milling system. After ball milling for another 3-5 min, the mixture was transferred to a crucible and dried to obtain the precursor. The alkaline solution also contains 2-4 mg / mL of 3,4-dihydroxyphenylalanine; X∈[20-50], and X is an integer.

9. The method for preparing an environmentally functional material rich in persistent free radicals according to claim 8, characterized in that, During the addition of alkali solution to the ball milling system, microwave heating treatment of 300~800W is applied to the ball milling mixing system until all the alkali solution is added to the ball milling system, and then the microwave application is stopped; after the microwave application is stopped, the water content in the ball milling system is simultaneously reduced to 25~35%.

10. The application of an environmentally functional material rich in persistent free radicals prepared according to claim 1, characterized in that, The aforementioned environmentally functional materials rich in persistent free radicals are used in the removal of recalcitrant organic pollutants and heavy metals.

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