An alkali metal-biochar composite material, its preparation method and application

Abstract

This invention discloses an alkali metal-biochar composite material, its preparation method, and its application, comprising the following steps: mixing and dispersing inorganic nanomaterials and a silane coupling agent in an aqueous solution to form a uniform suspension; adding pretreated biochar (after acid or alkali washing) to the suspension obtained in step S1 and mixing to uniformly load the inorganic nanomaterials onto the surface of the biochar; filtering the mixed material and then performing low-temperature carbonization; immersing the low-temperature carbonized material in a modified magnesium-sodium solution to uniformly load alkali metal ions onto the material; and performing high-temperature carbonization of the loaded material under an inert atmosphere. The composite material of this invention exhibits high adsorption capacity and rapid adsorption rate for heavy metal ions and organic pollutants in water, while avoiding the use of organic solvents, reducing costs, and being environmentally friendly. The process is simple and easy to scale up for production.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials technology, and in particular relates to an alkali metal-biochar composite material, its preparation method and application. Background Technology

[0002] Biochar is a carbon-rich material obtained by pyrolysis of biomass under anaerobic conditions. It possesses advantages such as large specific surface area, well-developed pore structure, and abundant surface functional groups, and is widely used in adsorption and catalysis. However, ordinary biochar has limited adsorption capacity and selectivity, especially when treating complex pollutants. To improve biochar performance, it is often modified by loading metals or metal oxides, but traditional loading methods suffer from problems such as uneven loading, easy metal loss, and damage to the pore structure.

[0003] Current technologies for modifying biochar often focus on single metal loading or physical mixing, failing to systematically construct a synergistic adsorption system with multi-component, hierarchical porous structures. Specifically, while inorganic nanomaterials (such as iron oxide and alumina) can enhance the capture capacity of heavy metals through specific adsorption, their tendency to aggregate leads to a reduction in active sites, and their weak binding force with the biochar matrix makes them prone to detachment and loss in complex environments. The introduction of alkali metals and alkaline earth metals (such as sodium and magnesium) is usually considered to provide an alkaline environment or simple ion exchange sites, but the complex chemical reactions they undergo with biochar and inorganic nanomaterials at high temperatures, as well as their directional regulation of the material's pore structure, have not yet been thoroughly studied and effectively utilized.

[0004] The core role of coupling agents in the modification process is to achieve a strong bridge between the inorganic and organic phases. However, the existing technology has not paid enough attention to their chemical evolution in the subsequent heat treatment process and their impact on the structure and properties of the final composite material.

[0005] Therefore, developing a preparation method capable of achieving uniform dispersion of inorganic nanomaterials, stable loading of alkali metals, and constructing a stable synergistic structure through precise heat treatment is crucial for obtaining high-performance adsorbent materials. This invention proposes a novel solution based on the aforementioned technical bottlenecks. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide an alkali metal-biochar composite material, its preparation method and application, which achieves uniform loading and high loading concentration, and has a porous structure and strong adsorption performance.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is: a method for preparing an alkali metal-biochar composite material, comprising the following steps:

[0008] S1. Inorganic nanomaterials are mixed and dispersed with a silane coupling agent in an aqueous solution to form a uniform suspension; the inorganic nanomaterials are one or a mixture of two of nano-iron oxide, nano-alumina, and nano-titanium dioxide;

[0009] S2. Add the pretreated biochar (after acid or alkali washing) to the suspension obtained in S1 and mix to uniformly load the inorganic nanomaterials onto the surface of the biochar.

[0010] S3. After filtering the material mixed with S2, perform low-temperature carbonization treatment at a temperature of 150-240℃;

[0011] S4. Immerse the material after low-temperature carbonization in S3 into a modified magnesium-sodium solution to uniformly load alkali metal ions onto the material; the modified magnesium-sodium solution is a mixed aqueous solution of magnesium salt and sodium salt, wherein the molar ratio of magnesium ions to sodium ions is 1:1 to 1:3.

[0012] S5. The material loaded in S4 is subjected to high-temperature carbonization at 600-800°C under an inert atmosphere to obtain the alkali metal-biochar composite material.

[0013] As a further improvement, the mass ratio of the inorganic nanomaterial to biochar in S1 is (8-18):100.

[0014] As a further improvement, the amount of silane coupling agent added in S1 is 1-5% of the mass of the inorganic nanomaterial.

[0015] As a further improvement, the pretreatment in S2 is to perform acid washing or alkali washing, followed by washing until neutral and drying; the acid washing is performed by stirring with a 1-2 mol / L hydrochloric acid solution at 60-80°C, and the alkali washing is performed by stirring with a 1-2 mol / L sodium hydroxide solution at 60-80°C.

[0016] As a further improvement, the mixing described in S2 is carried out at a temperature of 50-70°C.

[0017] As a further improvement, the concentration of the modified magnesium sodium solution in S4 is 0.5-1.5 mol / L.

[0018] As a further improvement, in S1 the material is dispersed by stirring for 30-60 minutes, in S2 the mixing is done by stirring for 1-2 hours, and in S4 the material after low-temperature carbonization in S3 is immersed in modified magnesium-sodium solution for 2-4 hours.

[0019] As a further improvement, the low-temperature carbonization time in S3 is 1-2 hours, and the high-temperature carbonization time in S5 is 1-3 hours.

[0020] The present invention provides an alkali metal-biochar composite material, which is prepared by the preparation method described above.

[0021] The present invention provides an application of the alkali metal-biochar composite material, which is used for the adsorption of heavy metal ions or organic pollutants in water.

[0022] This invention solves the problems of uneven loading, poor pore structure, and low adsorption performance in existing technologies. The material possesses a porous structure and strong adsorption properties, making it suitable for environmental remediation applications such as the adsorption of toxic and harmful gases in complex environments.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) High loading concentration and uniformity: By using coupling agent and mixing in an aqueous environment, the loading concentration and uniformity of inorganic nanomaterials and alkali metals on biochar were improved, achieving uniform loading and high loading concentration of inorganic nanomaterials and alkali metals.

[0025] (2) Excellent porous structure: By combining low-temperature carbonization and high-temperature carbonization, pore collapse is avoided and a hierarchical porous structure is formed. Furthermore, by adding inorganic nanomaterials and modifying with magnesium and sodium, the porous structure of biochar is maintained and optimized, thereby enhancing its adsorption performance.

[0026] (3) Strong adsorption performance: By adding inorganic nanomaterials, modifying with magnesium and sodium and combining with the improvement of carbonization process, the adsorption performance is improved. The composite material has high adsorption capacity and fast adsorption rate for heavy metal ions and organic pollutants in water.

[0027] (4) Environmentally friendly: The entire process is carried out in an aqueous solution, avoiding the use of organic solvents, reducing costs and being green and environmentally friendly.

[0028] (5) The process of this invention is simple and easy to scale up. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 These are the pseudo-first-order and pseudo-second-order kinetic fitting curves of the alkali metal-biochar composite adsorption in the examples and comparative examples;

[0031] Figure 2 This is a SEM image of the biochar material prepared without coupling agent in Comparative Example 3.

[0032] Figure 3 This is a SEM image of the biochar material prepared by adding a coupling agent in Example 2. Detailed Implementation

[0033] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0034] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] In some specific embodiments, the preparation method of the alkali metal-biochar composite material of the present invention includes the following steps:

[0037] (1) Pretreatment of biochar: The raw biochar is pretreated to remove impurities and enhance surface activity. Pretreatment methods include acid washing or alkali washing, followed by washing with deionized water until neutral, and drying for later use.

[0038] In some embodiments, the acid washing is performed by stirring a 1-2 mol / L hydrochloric acid solution at 60-80°C for 2-4 hours; the alkaline washing is performed by stirring a 1-2 mol / L sodium hydroxide solution at 60-80°C for 2-4 hours.

[0039] In some embodiments, the biochar may be rice husk biochar, sawdust biochar, etc.

[0040] (2) Dispersion of inorganic nanomaterials: Inorganic nanomaterials are mixed and dispersed with coupling agents in an aqueous solution to form a uniform suspension.

[0041] In some embodiments, the inorganic nanomaterial is one or a mixture of two of nano-iron oxide, nano-alumina, and nano-titanium dioxide. Preferably, the particle size of the inorganic nanomaterial is 50-1000 nm. The mass ratio of the inorganic nanomaterial to biochar is (8-18):100. The inorganic nanomaterial can be generated through a nanogel reaction.

[0042] The inorganic materials such as nano-iron oxide and alumina introduced in this invention play a dual role as "nano-adsorption centers" and "structural frameworks" in the composite material. Adsorption: The abundant hydroxyl (-OH) functional groups on their surfaces can interact with Pb in water through surface complexation reactions. 2+ Cd 2+ Cu 2+ Heavy metal ions form stable inner-layer complexes, achieving efficient and specific adsorption. Structural role: These nanoparticles, dispersed in the pores of biochar, effectively prevent excessive graphitization and shrinkage of the carbon skeleton at high temperatures. Together with the amorphous carbon formed by the decomposition of the coupling agent, they act as "spacer pillars," supporting and stabilizing the high specific surface area and hierarchical porous structure of the composite material.

[0043] In some embodiments, the coupling agent is a silane coupling agent, such as KH-550 or KH-560. The amount of coupling agent added is 1-5% of the mass of the inorganic nanomaterial. It is added in 3-9 portions, followed by stirring and dispersing for 30-60 minutes to form a uniform suspension. The preferred stirring speed is 10,000-20,000 rpm / min.

[0044] Silane coupling agents hydrolyze in an aqueous environment to generate silanols (-SiOH). These silanols can condense with hydroxyl groups on the surface of inorganic nanomaterials to form strong -Si-OM- (M is a metal) covalent bonds, and can also bind with oxygen-containing functional groups on the surface of biochar. A solid "molecular bridge" is constructed between the two, enabling in-situ, uniform, and firm fixation of inorganic nanomaterials on the surface of biochar.

[0045] In the low-temperature carbonization stage at 200℃, the main role of the silane coupling agent is to further condense and crosslink, forming a stable siloxane network (-Si-O-Si-), which anchors the nanoparticles more firmly to the carbon skeleton. This temperature is lower than the thermal decomposition initiation temperature of most silane coupling agents (typically >300℃), so its structure is stable and provides a pre-modified, hydrophilic, and uniform interface for subsequent impregnation and loading of alkali metal solutions. This is a key prerequisite for achieving "uniform alkali metal loading".

[0046] (3) Mixing of biochar and inorganic nanomaterials: The pretreated biochar obtained in step (1) is added to the suspension obtained in step (2) and mixed to uniformly load the inorganic nanomaterials onto the surface of the biochar.

[0047] In some embodiments, the mixing process is carried out at a temperature of 50-70°C for 1-2 hours.

[0048] (4) Low-temperature carbonization: After filtering the material mixed in step (3), it is subjected to low-temperature carbonization at 150-240℃ to stabilize the composite structure and initially form pores.

[0049] In some embodiments, the low-temperature carbonization time is 1-2 hours, and the carbonization atmosphere is a nitrogen atmosphere with a nitrogen purity of 99.999%.

[0050] (5) Preparation of modified magnesium sodium solution: Dissolve magnesium salt and sodium salt in water to prepare modified magnesium sodium solution.

[0051] In some embodiments, magnesium salts such as magnesium chloride and sodium salts such as sodium chloride are used. The modified magnesium-sodium solution contains Mg. 2+ with Na + The molar ratio is 1:1 to 1:3, and the concentration of the modified magnesium-sodium solution is 0.5-1.5 mol / L (total molar concentration of magnesium ions and sodium ions).

[0052] Sodium ions (Na) + As a pore-forming agent, it volatilizes or reacts with carbon during high-temperature carbonization, creating a large number of micropores and mesopores, significantly increasing the specific surface area of ​​the material.

[0053] Magnesium ions (Mg 2+ Under a high-temperature, inert atmosphere, it can be reduced to metallic magnesium or form magnesium oxide (MgO) nanoparticles. MgO itself can serve as an adsorption site. At the same time, magnesium compounds can catalyze the graphitization process of carbon materials at high temperatures, forming locally ordered conductive carbon structures, which are beneficial for adsorbing heavy metal ions through electrostatic interactions.

[0054] Synergistic effect: Mg 2+ with Na + When coexisting in the specific proportions of the present invention, a eutectic can be formed at high temperature, promoting the molten salt template effect, further optimizing the pore structure, and making the surface of the final composite material rich in alkaline oxygen-containing functional groups, thereby enhancing the buffering and adsorption capacity for acidic heavy metal wastewater.

[0055] (6) Loading: Immerse the material after low-temperature carbonization in step (4) into modified magnesium sodium solution to uniformly load alkali metal ions onto the material.

[0056] In some embodiments, the material after low-temperature carbonization is immersed in modified magnesium-sodium solution, and the immersion is accompanied by stirring for 2-4 hours.

[0057] (7) High-temperature carbonization: The material loaded in step (6) is carbonized at a temperature of 600-800℃ under an inert atmosphere to form a porous structure and strong adsorption properties, thus obtaining a high-concentration loaded alkali metal-biochar composite material.

[0058] In some embodiments, the high-temperature carbonization time is 1-3 hours, and the inert atmosphere is a nitrogen or argon atmosphere.

[0059] In an inert atmosphere at 600-800℃, the crystal structure of inorganic nanomaterials may become more complete and their stability enhanced.

[0060] The modified magnesium-sodium solution underwent decomposition or transformation of magnesium and sodium salts during high-temperature carbonization; Na + Mg plays a pore-forming role. 2+ It may be partially reduced by carbothermal processes to Mg vapor (which is then re-oxidized to MgO during subsequent cooling) or exist directly as MgO. This process is intertwined with the carbonization and graphitization of biochar, jointly determining the final chemical and physical structure of the biochar composite material.

[0061] The alkali metal-biochar composite material prepared by the above method has a porous structure and a high specific surface area (≥500 m²). 2 It features a well-developed pore structure (pore size distribution of 1-50 nm) and strong adsorption performance (adsorption capacity for heavy metal ions ≥200 mg / g).

[0062] Example 1

[0063] The preparation method of the alkali metal-biochar composite material in this embodiment includes the following steps:

[0064] 1. Take 100g of rice husk biochar, stir it with 1 mol / L hydrochloric acid solution at 70℃ for 3 hours, wash and dry it for later use.

[0065] 2. Take 10g of nano iron oxide, add 0.3g of silane coupling agent KH-550, and disperse in 200mL of deionized water for 40 minutes to form a suspension.

[0066] 3. Add the pretreated biochar to the suspension and stir at 60°C for 1.5 hours.

[0067] 4. After filtering the mixed material, carbonize it at 200°C for 1.5 hours under a nitrogen atmosphere.

[0068] 5. Prepare modified magnesium-sodium solution: Dissolve magnesium chloride and sodium chloride in a molar ratio of 1:1 to prepare a 1 mol / L solution.

[0069] 6. Immerse the carbonized material in the modified magnesium sodium solution for 3 hours, stirring and loading.

[0070] 7. Carbonize at 700℃ for 2 hours under a nitrogen atmosphere to obtain the composite material.

[0071] The specific surface area of ​​this material is 550 m². 2 / g, for lead ions (Pb) 2+ The adsorption capacity of ) is 220 mg / g.

[0072] Example 2

[0073] The preparation method of the alkali metal-biochar composite material in this embodiment includes the following steps:

[0074] 1. Take 100g of sawdust biochar, stir it with 2 mol / L sodium hydroxide solution at 80℃ for 2 hours, wash and dry it for later use.

[0075] 2. Take 15g of nano-alumina, add 0.5g of silane coupling agent KH-550, and disperse in 300mL of deionized water for 60 minutes to form a suspension.

[0076] 3. Add the pretreated biochar to the suspension and stir at 70°C for 2 hours.

[0077] 4. After filtering the mixed material, carbonize it at 200°C for 2 hours under a nitrogen atmosphere.

[0078] 5. Prepare modified magnesium-sodium solution: Dissolve magnesium chloride and sodium chloride in a molar ratio of 1:2 to prepare a 0.5 mol / L solution.

[0079] 6. Immerse the carbonized material in the modified magnesium sodium solution for 4 hours, stirring and loading.

[0080] 7. Carbonize at 800℃ for 1 hour under an argon atmosphere to obtain the composite material.

[0081] The specific surface area of ​​this material is 600 m². 2 / g, for lead ions (Pb) 2+ The adsorption capacity of ) is 250 mg / g.

[0082] Comparative Example 1: No inorganic nanomaterials added

[0083] 1. Take 100g of rice husk biochar, stir it with 1 mol / L hydrochloric acid solution at 70℃ for 3 hours, wash and dry it for later use.

[0084] 2. Take 0.3g of silane coupling agent KH-550 and disperse it in 200mL of deionized water for 40 minutes to form a suspension.

[0085] 3. Add the pretreated biochar to the suspension and stir at 60°C for 1.5 hours.

[0086] 4. Carbonize the mixed material in a nitrogen atmosphere at 200°C for 1.5 hours.

[0087] 5. Prepare modified magnesium-sodium solution: Dissolve magnesium chloride and sodium chloride in a molar ratio of 1:1 to prepare a 1 mol / L solution.

[0088] 6. Immerse the carbonized material in the modified magnesium sodium solution for 3 hours, stirring and loading.

[0089] 7. Carbonize at 700℃ for 2 hours under a nitrogen atmosphere to obtain the composite material.

[0090] The specific surface area of ​​this material is 380 m². 2 / g, for lead ions (Pb) 2+ The adsorption capacity of ) is 110 mg / g.

[0091] Comparative Example 2: Lack of Magnesium-Sodium Modification

[0092] 1. Take 100g of rice husk biochar, stir it with 1 mol / L hydrochloric acid solution at 70℃ for 3 hours, wash and dry it for later use.

[0093] 2. Take 10g of nano iron oxide, add 0.3g of silane coupling agent KH-550, and disperse in 200mL of deionized water for 40 minutes to form a suspension.

[0094] 3. Add the pretreated biochar to the suspension and stir at 60°C for 1.5 hours.

[0095] 4. Carbonize the mixed material in a nitrogen atmosphere at 200°C for 1.5 hours.

[0096] 5. Carbonize at 700℃ for 2 hours under a nitrogen atmosphere to obtain the composite material.

[0097] The specific surface area of ​​this material is 480 m². 2 / g, for lead ions (Pb) 2+ The adsorption capacity of ) is 135 mg / g.

[0098] Comparative Example 3: Without coupling agent

[0099] 1. Take 100g of rice husk biochar, stir it with 1 mol / L hydrochloric acid solution at 70℃ for 3 hours, wash and dry it for later use.

[0100] 2. Take 10g of nano iron oxide and disperse it in 200mL of deionized water for 40 minutes to form a suspension.

[0101] 3. Add the pretreated biochar to the suspension and stir at 60°C for 1.5 hours.

[0102] 4. Carbonize the mixed material in a nitrogen atmosphere at 200°C for 1.5 hours.

[0103] 5. Prepare modified magnesium-sodium solution: Dissolve magnesium chloride and sodium chloride in a molar ratio of 1:1 to prepare a 1 mol / L solution.

[0104] 6. Immerse the carbonized material in the modified magnesium sodium solution for 3 hours, stirring and loading.

[0105] 7. Carbonize at 700℃ for 2 hours under a nitrogen atmosphere to obtain the composite material.

[0106] The specific surface area of ​​this material is 420 m². 2 / g, for lead ions (Pb) 2+ The adsorption capacity of ) is 95 mg / g.

[0107] Comparative Example 4: One-step high-temperature carbonization

[0108] 1. Take 100g of rice husk biochar, stir it with 1 mol / L hydrochloric acid solution at 70℃ for 3 hours, wash and dry it for later use.

[0109] 2. Take 10g of nano iron oxide, add 0.3g of silane coupling agent KH-550, and disperse in 200mL of deionized water for 40 minutes to form a suspension.

[0110] 3. Add the pretreated biochar to the suspension, stir at 60°C for 1.5 hours, filter and dry to obtain biochar-nano mixture A.

[0111] 4. Prepare modified magnesium-sodium solution: Dissolve magnesium chloride and sodium chloride in a molar ratio of 1:1 to prepare a 1 mol / L solution.

[0112] 5. Immerse biochar-nano mixture A in modified magnesium sodium solution for 3 hours and stir to load.

[0113] 6. Carbonize at 700℃ for 2 hours under a nitrogen atmosphere to obtain the composite material.

[0114] The specific surface area of ​​this material is 350 m². 2 / g, for lead ions (Pb) 2+ The adsorption capacity of ) is 80 mg / g.

[0115] Comparative Example 5:

[0116] 1. Take 100g of rice husk biochar, stir it with 1 mol / L hydrochloric acid solution at 70℃ for 3 hours, wash and dry it for later use.

[0117] 2. Take 10g of nano iron oxide, add 0.3g of silane coupling agent KH-550, and disperse in 200mL of deionized water for 40 minutes to form a suspension.

[0118] 3. Add the pretreated biochar to the suspension and stir at 60°C for 1.5 hours.

[0119] 4. After filtering the mixed material, carbonize it in a nitrogen atmosphere at 200°C for 1.5 hours.

[0120] 5. Prepare modified magnesium-sodium solution: Dissolve magnesium chloride and sodium chloride in a molar ratio of 1:5 to prepare a 1 mol / L solution.

[0121] 6. Immerse the carbonized material in the modified magnesium sodium solution for 3 hours, stirring and loading.

[0122] 7. Carbonize at 700℃ for 2 hours under a nitrogen atmosphere to obtain the composite material.

[0123] Adsorption performance testing procedure: A 20 mg / L Pb(NO3)2 solution was prepared as simulated wastewater. 0.1 g of the material prepared in each example and comparative example was weighed into an Erlenmeyer flask, and 100 mL of the simulated wastewater was added. The flask was shaken at 150 rpm in a constant-temperature shaker at 25°C. 3 mL of the reaction solution was taken at different adsorption times (10, 20, 40, 60, 90, 120, 180, 240 min) and filtered through a 0.45 μm filter membrane. The Pb concentration in the filtrate was determined using atomic absorption spectrometry. 2+ The residual concentration was determined, the solution mass concentration was calculated, and the maximum adsorption capacity was obtained. Kinetic model simulations were then performed using the obtained data, with pseudo-first-order and pseudo-second-order kinetic models used to fit the experimental data. The results were used to determine the dominant adsorption type.

[0124] Adsorption capacity calculation: based on the formula Calculate the equilibrium adsorption capacity.

[0125] Equilibrium adsorption capacity q e mg / g;

[0126] The initial solution concentration C0, mg / L, is [value missing].

[0127] At adsorption equilibrium, the solution concentration C e mg / L;

[0128] Solution volume V, L;

[0129] Mass of adsorbent material m, g.

[0130] The pseudo-first-order and pseudo-second-order kinetic fitting curves of the alkali metal-biochar composite adsorption in the examples and comparative examples are shown below. Figure 1 Based on the fitted data, Examples 1 and 2 showed the best adsorption performance, while Comparative Examples 1, 2, 3, and 4 showed relatively poor adsorption performance. Example 2 (Pb) was the best. 2+ Equilibrium adsorption capacity q e The Pb concentration reached 250 mg / g, obtained from pseudo-second-order kinetic simulation. 2+ The equilibrium adsorption capacity is 242 mg / g.

[0131] The performance data of the alkali metal-biochar composite materials in the above embodiments and comparative examples are shown in Table 1:

[0132]

[0133] Figure 2 This is a SEM image of the biochar material prepared without coupling agent in Comparative Example 3. Figure 3 The image shows the SEM image of the biochar material prepared by adding a coupling agent in Example 2. Without the coupling agent, the prepared carbon material has obvious nanoparticle aggregation on the surface, as shown in the red boxes 1 and 2 in the figure. After adding the coupling agent, the dispersibility of the nanoparticles is enhanced, and nanoparticles are distributed on the surface and in the pores of the biochar material, as shown in the red boxes 3, 4 and 5 in the figure.

[0134] As can be seen from the results of the examples and comparative examples:

[0135] The importance of inorganic nanomaterials (Comparative Example 1): The absence of nanomaterials leads to a significant decrease in specific surface area and adsorption capacity, demonstrating the indispensability of nano-iron oxide as an "adsorption center" and "structural framework".

[0136] The key role of alkali metals (Comparative Example 2): Without magnesium and sodium modification, the pore structure and adsorption performance of the material are significantly deteriorated, confirming their synergistic function as "pore-forming agent" and "structure regulator".

[0137] The bridging effect of coupling agents (Comparative Example 3): Without coupling agents, SEM showed severe agglomeration of nanoparticles, with a significant reduction in specific surface area and adsorption capacity, directly demonstrating that coupling agents are crucial for achieving uniform loading and maintaining excellent structure.

[0138] Advantages of the two-step carbonization process (Comparative Example 4): One-step high-temperature carbonization leads to the collapse of the material structure and the worst performance, highlighting the rationality and innovation of the two-step carbonization process of this invention, which first stabilizes the structure at low temperature and then activates and creates pores at high temperature.

[0139] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing an alkali / alkaline earth metal-biochar composite material, characterized by, Includes the following steps: S1. Inorganic nanomaterials and silane coupling agents are mixed and dispersed in an aqueous solution to form a uniform suspension; the inorganic nanomaterials are one or a mixture of two of nano-iron oxide, nano-alumina, and nano-titanium dioxide; the mass ratio of the inorganic nanomaterials to biochar is (8-18):100; the amount of silane coupling agent added is 1-5% of the mass of the inorganic nanomaterials; S2. The pretreated biochar, after acid washing or alkali washing, is added to the suspension obtained in S1 and mixed to uniformly load the inorganic nanomaterials onto the surface of the biochar; the mixing is carried out at a temperature of 50-70°C. S3. After filtering the material mixed with S2, perform low-temperature carbonization treatment at a temperature of 150-240℃; S4. Immerse the material after low-temperature carbonization in S3 into a modified magnesium-sodium solution to uniformly load magnesium ions and sodium ions onto the material; the modified magnesium-sodium solution is a mixed aqueous solution of magnesium salt and sodium salt, wherein the molar ratio of magnesium ions to sodium ions is 1:1 to 1:

3. S5. The material loaded in S4 is subjected to high-temperature carbonization at 600-800℃ under an inert atmosphere to obtain the alkali metal / alkaline earth metal-biochar composite material.

2. The method for producing an alkali / alkaline earth metal-biochar composite material according to claim 1, characterized by, The pretreatment described in S2 involves acid washing or alkali washing, followed by washing until neutral and drying. The acid washing is performed by stirring with a 1-2 mol / L hydrochloric acid solution at 60-80°C, and the alkali washing is performed by stirring with a 1-2 mol / L sodium hydroxide solution at 60-80°C.

3. The method for preparing the alkali metal / alkaline earth metal-biochar composite material according to claim 1, characterized in that, The concentration of the modified magnesium sodium solution in S4 is 0.5-1.5 mol / L.

4. The method for preparing the alkali metal / alkaline earth metal-biochar composite material according to claim 1, characterized in that, In S1, the material is dispersed by stirring for 30-60 minutes; in S2, the mixing is carried out by stirring for 1-2 hours; and in S4, the material after low-temperature carbonization in S3 is immersed in modified magnesium-sodium solution for 2-4 hours.

5. The method for preparing the alkali metal / alkaline earth metal-biochar composite material according to claim 1, characterized in that, The low-temperature carbonization time described in S3 is 1-2 hours, and the high-temperature carbonization time described in S5 is 1-3 hours.

6. An alkali metal / alkaline earth metal-biochar composite material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

7. An application of the alkali metal / alkaline earth metal-biochar composite material according to claim 6, characterized in that, The application is for the adsorption of heavy metal ions or organic pollutants in water.

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