A method for preparing dimethyldichlorosilane-modified biochar and its application in the remediation of organic pollution.

Abstract

This invention discloses a method for preparing dimethyldichlorosilane-modified biochar and its application in the remediation of organic pollution, belonging to the field of environmental pollution remediation technology. It addresses the shortcomings of conventional biochar, such as strong hydrophilicity, weak selectivity for adsorbing hydrophobic organic pollutants, poor stability, easy desorption of pollutants in soil remediation, and insufficient long-term passivation ability. This invention uses agricultural and forestry waste biomass as raw material to prepare porous biochar, employing dimethyldichlorosilane as a hydrophobic modifier. Hydrophobic functional groups are bonded to the material surface through a liquid-phase covalent grafting process, optimizing the pore structure and surface properties. The modified material exhibits a significant increase in specific surface area and pore volume, enabling efficient removal of organic pollutants from water bodies and passivation of organic pollutants in soil, reducing their migration capacity and bioavailability. This invention utilizes widely available and inexpensive raw materials, employs a mild process, produces no secondary pollution, and is easy to industrialize, making it suitable for the remediation of organic pollution in water and soil, with broad application value.

Description

Technical Field

[0001] This invention relates to the field of environmental pollution remediation technology, specifically to a method for preparing dimethyldichlorosilane-modified biochar and its application in the remediation of organic pollution. Background Technology

[0002] Hydrophobic organic pollution of water and soil is a key challenge in the current ecological and environmental governance field. Human activities such as industrial wastewater discharge, agricultural pesticide application, and solid waste leachate lead to the continuous accumulation of hydrophobic organic pollutants such as polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, polychlorinated biphenyls (PCBs), and phenols in aquatic environments and soils. These pollutants exhibit high chemical stability, long natural degradation cycles, and significant ecotoxicity. They not only disrupt the ecological balance of aquatic bodies and deteriorate water quality but also remain in the soil for extended periods, accumulating through plant roots and entering the food chain, ultimately threatening human health.

[0003] Biochar, a porous carbonaceous functional material prepared by oxygen-limited pyrolysis of biomass, possesses advantages such as large specific surface area, rich pore structure, wide availability of raw materials, good environmental compatibility, and low preparation cost, making it a primary environmental functional material for the remediation of organic pollution in water and soil. However, unmodified raw biochar has a large number of polar hydrophilic functional groups such as hydroxyl and carboxyl groups on its surface, resulting in high surface polarity and poor adsorption selectivity and low effective adsorption capacity for hydrophobic organic pollutants. Furthermore, raw biochar and organic pollutants are mainly bound by physical van der Waals forces, resulting in weak interfacial bonding. Under complex environmental conditions such as water salinity disturbance, alternating soil moisture levels, and acid-base fluctuations, adsorbed pollutants are prone to desorption and secondary migration. In soil remediation scenarios, conventional biochar cannot effectively reduce the bioavailability of organic pollutants, struggles to block plant accumulation pathways for pollutants, and suffers from insufficient remediation sustainability and stability, significantly limiting the large-scale application of biochar in soil remediation and safe soil utilization.

[0004] Currently, biochar modification technologies include acid-base modification, metal-based loading modification, and biological modification. Acid-base modification can only etch the pore structure and control the specific surface area, but it cannot improve the hydrophilic properties of the biochar surface, resulting in limited remediation gains for hydrophobic organic pollutants. Metal-based loading modification can slightly improve adsorption performance, but it easily introduces metal impurities, causing secondary pollution of water and soil. Furthermore, the modification process is complex, the material stability is poor, and the production cost is high. Biologically modified strains have weak adaptability and low survival rates, making them unsuitable for industrial application. A search revealed that no publicly available technology utilizes dimethyldichlorosilane covalently grafted onto modified biochar to simultaneously achieve efficient removal of organic pollutants from water and long-term passivation of organic pollutants in soil, indicating a significant technological gap. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies: ordinary biochar exhibits weak selectivity for adsorbing hydrophobic organic pollutants and poor interfacial bonding stability; existing modification technologies generally suffer from limited remediation functions, susceptibility to secondary pollution, significant loss of pore structure, and inability to effectively passivate soil organic pollutants. This invention provides a method for preparing dimethyldichlorosilane-modified biochar and its application in organic pollution remediation, achieving green remediation of hydrophobic organic pollutants in water and soil, while reducing the risk of plant absorption and accumulation of organic pollutants, thus ensuring the safety of water and soil environments.

[0006] To achieve the above objectives, the technical solution adopted in this invention is as follows: a method for preparing dimethyldichlorosilane-modified biochar, comprising the following steps: S1. Select agricultural and forestry waste biomass, remove dead branches, mud and sand impurities, wash with clean water, dry in an oven, crush and pass through a 40-100 mesh standard sieve to obtain biomass powder with uniform particle size, and seal for later use. S2. The biomass powder is spread evenly in the ceramic boat of the tubular furnace, and inert gas is continuously introduced to purge the air in the furnace and maintain an inert gas atmosphere. The temperature is raised to 400-700℃ at a uniform heating rate of 5-10℃ / min, and pyrolyzed at a constant temperature for 1-3 hours. After pyrolysis, the furnace is allowed to cool naturally to room temperature. The char body is then removed, ground, and passed through a 60-120 mesh sieve to obtain the original biochar with a well-developed pore structure. S3. Disperse the raw biochar evenly in an anhydrous organic solvent and stir continuously for 20-40 min to form a stable and uniform biochar suspension; under constant temperature stirring conditions, slowly and uniformly add dimethyldichlorosilane modifier to the suspension, keep warm and continue the reaction for 2-6 h to complete the surface covalent grafting modification, and keep the reaction temperature constant at 30-60℃. S4. After the reaction is complete, solid-liquid separation is achieved by vacuum filtration. The solid product is washed alternately with anhydrous organic solvent and deionized water to thoroughly remove unreacted modifiers, byproducts and impurities remaining on the surface until the washing filtrate is neutral. The purified solid is placed in a constant temperature oven at 60-80℃ and dried for 12-24 hours to remove residual solvent and water, finally obtaining dimethyldichlorosilane modified biochar with stable structure and excellent hydrophobic properties.

[0007] Preferably, the agricultural and forestry waste biomass includes any one or more combinations of rice straw, wheat straw, corn straw, cotton straw, sawdust, and peanut shells.

[0008] Preferably, the inert gas is nitrogen or argon, and the gas flow rate is controlled at 50-150 mL / min.

[0009] Preferably, the anhydrous organic solvent is at least one of anhydrous ethanol, anhydrous methanol, and acetone; the mass ratio of dimethyldichlorosilane to the original biochar is 1:100 to 10:100.

[0010] Preferably, the pyrolysis process adopts a segmented heating method: first, the temperature is increased to 250-300℃ at 5-7℃ / min and held for 30min, and then the temperature is increased to the target temperature at 8-10℃ / min to promote the full development of the microporous structure.

[0011] A dimethyldichlorosilane-modified biochar prepared by the above method has a surface water contact angle greater than 130°, a specific surface area more than 3 times higher than that of the original biochar, and pores mainly consisting of micropores and mesopores.

[0012] The dimethyldichlorosilane-modified biochar is used for the adsorption and removal of organic pollutants in polluted water bodies and the passivation and remediation of organic pollutants in polluted soil.

[0013] Preferably, in the application of the dimethyldichlorosilane-modified biochar in the adsorption and removal of organic pollutants in polluted water, the organic pollutants are one or more of polycyclic aromatic hydrocarbons, organochlorine pesticides, polychlorinated biphenyls, or hydrophobic phenolic organic pollutants.

[0014] Preferably, in the application of the dimethyldichlorosilane modified biochar in the passivation and remediation of organic pollutants in contaminated soil, the modified biochar is applied to the contaminated soil at a rate of 0.5% to 5% of the soil mass, and after tilling and mixing, it is passivated and cured for 15 to 60 days under a moisture content of 60% to 80%.

[0015] Preferably, in the application of the dimethyldichlorosilane-modified biochar in the passivation and remediation of organic pollutants in contaminated soil, the modified biochar is applied in combination with humic acid or biosurfactants during the passivation and remediation process to synergistically enhance the stability of soil aggregates and further reduce the bioavailability of organic pollutants.

[0016] Compared with the prior art, the advantages of the present invention are as follows: 1. High Adsorption Selectivity and Remediation Stability: This invention employs small-molecule covalent grafting modification, ensuring a strong bond between the modified groups and the biochar matrix, preventing detachment. Through a triple synergistic remediation mechanism, it significantly enhances the adsorption capacity of hydrophobic organic pollutants, increasing it by more than 5 times compared to original biochar. Simultaneously, the material exhibits excellent resistance to environmental disturbances, tolerating water salinity fluctuations, alternating soil moisture levels, and acid-base fluctuations, effectively solving the technical problems of poor adsorption stability and easy desorption and recurrence of pollutants in traditional biochar.

[0017] 2. Ecological safety and no secondary pollution: This invention uses agricultural and forestry solid waste as raw materials to realize the resource recycling of waste, which is green and low-carbon; the overall preparation process is mild, does not require high pressure and high temperature equipment, does not add heavy metals and toxic additives, has few by-products and high controllability; the finished product has stable chemical properties and good biocompatibility, and will not damage the original ecological structure when applied to water and soil pollution remediation, with extremely high safety.

[0018] 3. The process is highly versatile and easy to industrialize: The preparation process of this invention is simple, the process parameters are precise and controllable, and the preparation can be completed with general equipment. The production cost is low, which can meet the needs of small-batch trial production in the laboratory and is also suitable for continuous mass production in the industrial sector. It has good industrialization potential and market promotion value. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation method of dimethyldichlorosilane modified biochar according to the present invention; Figure 2 SEM images of the three materials prepared in Examples 1, 2 and Comparative Example 1 of this invention. Detailed Implementation

[0020] In the description of this invention, it should be noted that the terms "front", "up", "down", "left", "right", "vertical", "horizontal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0022] Example 1 A method for preparing dimethyldichlorosilane-modified biochar, comprising the following steps: Rice straw was selected, washed with clean water to remove surface mud and impurities, and dried in a 70℃ oven for 18 hours. After pulverizing, it was passed through a 60-mesh sieve to obtain uniform rice straw powder. The rice straw powder was placed in a tube furnace, and nitrogen was introduced as a protective gas at a flow rate of 100 mL / min. The temperature was increased to 550℃ at a rate of 8℃ / min, and pyrolyzed at this temperature for 2 hours. After natural cooling to room temperature, it was ground and passed through an 80-mesh sieve to obtain raw rice straw biochar. 10g of raw biochar was taken and anhydrous ethanol was added at a solid-liquid ratio of 1g:50mL, and stirred for 30 minutes to form a uniform suspension. Dimethyldichlorosilane was slowly added dropwise at a mass ratio of 1:20 to biochar, and the reaction was carried out at a constant temperature of 45℃ with continuous stirring for 4 hours. After the reaction was completed, the solid product was separated by filtration. It was washed three times with anhydrous ethanol and then with deionized water until the pH of the filtrate was neutral. The solid product was then dried in an oven at 70°C for 18 hours to obtain dimethyldichlorosilane modified biochar (named OSi-BC-1).

[0023] Example 2 A method for preparing dimethyldichlorosilane-modified biochar, comprising the following steps: Corn stalks were selected, washed clean with water, dried at 65℃ for 20 hours, and pulverized through a 40-mesh sieve to obtain corn stalk powder. The corn stalk powder was placed in a tube furnace under argon protection, with a gas flow rate of 80 mL / min, and the temperature was increased to 450℃ at a rate of 5℃ / min. The mixture was then pyrolyzed at this constant temperature for 3 hours. After cooling and grinding, the powder was passed through a 60-mesh sieve to obtain raw corn stalk biochar. 10 g of the raw biochar was taken and acetone was added at a solid-liquid ratio of 1 g:20 mL, and the mixture was stirred for 20 minutes to form a suspension. Dimethyl dichlorosilane was slowly added dropwise at a biochar to dimethyl dichlorosilane mass ratio of 40:1, and the mixture was stirred at 30℃ for 6 hours. After filtration, the mixture was washed alternately and dried at 60℃ for 24 hours to obtain modified biochar (named OSi-BC-2).

[0024] Example 3 An application of dimethyldichlorosilane-modified biochar is disclosed, wherein the dimethyldichlorosilane-modified biochar is prepared using the method described in Example 1. Organic wastewater was taken from a coking plant workshop in Wuhan City, containing phenanthrene and pyrene concentrations of 18.21 mg / L and 13.64 mg / L, respectively. 1 g / L of dimethyldichlorosilane-modified biochar was mixed with the organic wastewater in a glass beaker, stirred at room temperature for 4 hours, and then a sample was taken to determine the concentrations of phenanthrene and pyrene in the water.

[0025] Example 4 An application of dimethyldichlorosilane-modified biochar was disclosed, wherein the dimethyldichlorosilane-modified biochar was prepared using the method described in Example 1. Organically contaminated soil was taken from a decommissioned resin factory in Wuhan City, with a phenanthrene concentration of 182.62 mg / kg. Modified biochar was added at 1% of the soil mass, the soil was tilled and mixed thoroughly, the soil moisture content was maintained at 60%, and the soil was passivated and cured for 30 days. The bioavailable concentration of phenanthrene in the soil was then measured.

[0026] Example 5 An application of dimethyldichlorosilane-modified biochar, wherein the dimethyldichlorosilane-modified biochar is prepared by the method of Example 2, and other application steps are the same as those in Example 3.

[0027] Example 6 An application of dimethyldichlorosilane-modified biochar, wherein the dimethyldichlorosilane-modified biochar is prepared by the method of Example 2, and other application steps are the same as those in Example 4.

[0028] Comparative Example 1 Using the same rice straw raw material and pyrolysis process as in Example 1, but without modification with dimethyldichlorosilane, primitive biochar (named BC) was prepared.

[0029] Comparative Example 2 An application of raw biochar, wherein the raw biochar is prepared by the method of Comparative Example 1, and other application steps are the same as in Example 3.

[0030] Comparative Example 3 An application of raw biochar, wherein the raw biochar is prepared by the method of Comparative Example 1, and other application steps are the same as in Example 4.

[0031] Figure 2 SEM images of the three materials were prepared for Example 1, Example 2 and Comparative Example 1. Figure 2 The image at point a shows the original biochar, which exhibits a relatively dense blocky structure with few pores. Figure 2 middle b and Figure 2 The image at point c shows dimethyldichlorosilane-modified biochar, exhibiting a loose, porous honeycomb structure with more abundant and interconnected pores. This indicates that dimethyldichlorosilane-modified biochar has a larger specific surface area than the original biochar, which is beneficial for the adsorption of organic pollutants.

[0032] Table 1 shows the pore structure characteristics of the three materials prepared in Examples 1, 2, and Comparative Example 1. The specific surface area and pore volume of the modified biochar prepared in Examples 1 and 2 are significantly higher than those of the original biochar prepared in Comparative Example 1, indicating that the dimethyldichlorosilane modified biochar material has a higher adsorption capacity than the original biochar.

[0033] Table 1. Comparison of Pore Structure Characteristics

[0034] Table 2 compares the removal efficiencies of organic pollutants in wastewater from Examples 3, 5, and Comparative Example 2. The removal rates of phenanthrene and pyrene in the wastewater from Examples 3 and 5 were significantly higher than those from Comparative Example 2, indicating that the dimethyldichlorosilane-modified biochar material exhibits significantly better removal performance of phenanthrene and pyrene from wastewater than the original biochar.

[0035] Table 2. Removal efficiency of organic pollutants in wastewater

[0036] Table 3 compares the passivation efficiency of organic pollutants in contaminated soil in Examples 4, 6, and Comparative Example 3. The passivation rate of phenanthrene in the soil of Examples 4 and 6 is significantly higher than that of Comparative Example 3, indicating that the passivation performance of dimethyldichlorosilane-modified biochar material for phenanthrene in contaminated soil is significantly higher than that of the original biochar.

[0037] Table 3. Passivation efficiency of organic pollutants in soil

[0038] As can be seen from the above examples and comparative examples, the biochar modified with dimethyldichlorosilane in this invention has a significantly improved adsorption capacity, which can efficiently purify organic pollutants in water and passivate organic pollutants in soil, with excellent remediation effect.

[0039] The core technical principle of this invention is as follows: Agricultural and forestry biomass is pyrolyzed under limited oxygen gradient to obtain primary biochar with a multi-level structure of micropores and mesopores, whose surface is distributed with a large number of active hydroxyl sites. Dimethyldichlorosilane has high reactivity and can undergo a dehydrochlorination covalent grafting reaction with the hydroxyl groups on the biochar surface, stably bonding nonpolar dimethylsilane groups to the biochar matrix surface. This effectively passivates the hydrophilic active sites on the surface, reduces the surface polarity of the biochar, and endows the material with excellent hydrophobic and oleophilic properties. Simultaneously, compared to macromolecular modifying agents, small-molecule dimethyldichlorosilane does not clog the internal pores of the biochar, completely preserving the excellent multi-level porous structure of the biochar. After modification, the material constructs a triple synergistic remediation mechanism of porous physical adsorption, hydrophobic interface enrichment, and functional group covalent locking: relying on the multi-level porous structure to achieve physical interception of pollutants; relying on the hydrophobic interface to selectively capture hydrophobic organic pollutants; and relying on the covalently bonded functional groups to stably lock organic pollutants. Dimethyldichlorosilane-modified biochar can efficiently adsorb organic pollutants in water, significantly reduce the mobility and bioavailability of organic pollutants in soil, block the absorption and accumulation pathways of organic pollutants by plants, and improve the safe utilization of soil.

[0040] 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 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 claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for preparing dimethyldichlorosilane-modified biochar, characterized in that: Includes the following steps: S1. Select agricultural and forestry waste biomass, remove dead branches, mud and sand impurities, wash with clean water, dry in an oven, crush and pass through a 40-100 mesh standard sieve to obtain biomass powder with uniform particle size, and seal for later use. S2. The biomass powder is spread evenly in the ceramic boat of the tubular furnace, and inert gas is continuously introduced to purge the air in the furnace and maintain an inert gas atmosphere. The temperature is raised to 400-700℃ at a uniform heating rate of 5-10℃ / min, and pyrolyzed at a constant temperature for 1-3 hours. After pyrolysis, the furnace is allowed to cool naturally to room temperature. The char body is then removed, ground, and passed through a 60-120 mesh sieve to obtain the original biochar with a well-developed pore structure. S3. Disperse the raw biochar evenly in an anhydrous organic solvent and stir continuously for 20-40 min to form a stable and uniform biochar suspension; under constant temperature stirring conditions, slowly and uniformly add dimethyldichlorosilane modifier to the suspension, keep warm and continue the reaction for 2-6 h to complete the surface covalent grafting modification, and keep the reaction temperature constant at 30-60℃. S4. After the reaction is complete, solid-liquid separation is achieved by vacuum filtration. The solid product is washed alternately with anhydrous organic solvent and deionized water to thoroughly remove unreacted modifiers, byproducts and impurities remaining on the surface until the washing filtrate is neutral. The purified solid is placed in a constant temperature oven at 60-80℃ and dried for 12-24 hours to remove residual solvent and water, finally obtaining dimethyldichlorosilane modified biochar with stable structure and excellent hydrophobic properties.

2. The method for preparing dimethyldichlorosilane-modified biochar according to claim 1, characterized in that: The agricultural and forestry waste biomass includes any one or more combinations of rice straw, wheat straw, corn straw, cotton straw, sawdust, and peanut shells.

3. The method for preparing dimethyldichlorosilane-modified biochar according to claim 1, characterized in that: The inert gas is nitrogen or argon, and the gas flow rate is controlled at 50–150 mL / min.

4. The method for preparing dimethyldichlorosilane-modified biochar according to claim 1, characterized in that: The anhydrous organic solvent is at least one of anhydrous ethanol, anhydrous methanol, and acetone; the mass ratio of dimethyldichlorosilane to the original biochar is 1:100 to 10:

100.

5. The method for preparing dimethyldichlorosilane-modified biochar according to claim 1, characterized in that: The pyrolysis process adopts a segmented heating method: first, the temperature is increased to 250-300℃ at 5-7℃ / min and held for 30min, and then the temperature is increased to the target temperature at 8-10℃ / min to promote the full development of the microporous structure.

6. A dimethyldichlorosilane-modified biochar prepared by the preparation method according to any one of claims 1 to 5, characterized in that: Its surface water contact angle is greater than 130°, its specific surface area is more than 3 times that of the original biochar, and its pores are mainly micropores and mesopores.

7. An application of the dimethyldichlorosilane-modified biochar according to claim 6, characterized in that: The dimethyldichlorosilane-modified biochar is used for the adsorption and removal of organic pollutants in polluted water bodies and the passivation and remediation of organic pollutants in polluted soil.

8. The application of the dimethyldichlorosilane-modified biochar according to claim 7 in the adsorption and removal of organic pollutants in polluted water, characterized in that: The organic pollutant is one or more of polycyclic aromatic hydrocarbons, organochlorine pesticides, polychlorinated biphenyls, or hydrophobic phenolic organic pollutants.

9. The application of the dimethyldichlorosilane-modified biochar according to claim 7 in the passivation and remediation of organic pollutants in contaminated soil, characterized in that: The modified biochar was applied to the contaminated soil at a rate of 0.5% to 5% of the soil mass, and after being tilled and mixed evenly, it was passivated and cured for 15 to 60 days at a moisture content of 60% to 80%.

10. The application of dimethyldichlorosilane-modified biochar according to claim 9 in the passivation and remediation of organic pollutants in contaminated soil, characterized in that: In the passivation remediation process, the modified biochar is applied in combination with humic acid or biosurfactants to synergistically enhance the stability of soil aggregates and further reduce the bioavailability of organic pollutants.

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