A carbon-fixing material and its preparation method and application

Abstract

The present invention relates to the field of soil improvement technology, and discloses a carbon-fixing material, a preparation method thereof, and an application thereof. The carbon-fixing material is aluminum-doped iron mineral nanoparticles with a particle size of 2-8 nm and a specific surface area of ​​350-410 m 2 / g, the particles have good dispersion and a good pore structure; aluminum is doped by replacing the position of iron in the structure, which increases the specific surface area and adsorption sites of the material and improves the organic carbon sequestration capacity of the material; the raw materials for the preparation of carbon-fixing materials are easy to obtain, the preparation method is simple, and the reaction conditions are mild. By regulating the hydrolysis rates of trivalent iron and aluminum ions, materials with different aluminum doping amounts can be obtained. The formation of agglomerates is reduced during the synthesis process, the operation is simple, and the efficiency is high; it is used to improve the carbon sequestration capacity of soil, has good organic carbon sequestration performance, can adapt to soil environments with different pH values, and can maintain long-term stability of organic carbon sequestration under various environmental conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, and in particular to a carbon sequestration material and a preparation method and application thereof. Background Art

[0002] As the largest carbon pool in the world's terrestrial ecosystems, the soil organic carbon pool has a carbon content far higher than that of terrestrial vegetation and atmospheric carbon pools. Small changes in the soil organic carbon pool can lead to large fluctuations in the concentration of carbon dioxide in the atmosphere. The ability of the soil to fix carbon largely determines the concentration of carbon dioxide in the atmosphere. Therefore, increasing soil carbon sequestration is an effective measure to reduce soil carbon emissions and help alleviate the global greenhouse effect. In addition, improving the organic carbon sequestration capacity of the soil can also help improve soil fertility and quality and promote crop growth. However, dissolved organic carbon in the soil is highly mobile and easily degraded. Therefore, reducing the mobility of soil organic carbon and transforming it to a more stable state is the key to enhancing soil organic carbon sequestration and stability.

[0003] Aluminum and iron are the third and fourth most abundant elements in the Earth's crust, often occurring as complex minerals. They significantly influence the compositional changes and stability of soil organic carbon (SOC). Numerous studies have demonstrated the importance of ferroalgae minerals in the sequestration of SOC in sediments, permafrost, forest soils, and agricultural soils. SOC sequestration can be categorized into three main mechanisms: physical protection, where soil aggregates and SOC are embedded and occluded; chemical protection, where soil minerals bind SOC through van der Waals forces, high-order cation bridges, and ligand exchange; and biochemical protection, where refractory SOC molecules resist degradation by external microorganisms or free radicals. Active ferroalgae minerals (such as ferrihydrite, allophane, and ferroalgae hydrated oxides), as important components of soil minerals, are the most common minerals in soils. Their high surface activity allows them to bind SOC through cation bridging, surface complexation, and ligand exchange, resulting in the most stable SOC.

[0004] Based on this, a series of materials related to active iron and aluminum minerals have been developed to promote soil carbon sequestration. However, these materials generally have the following disadvantages: (1) Directly adding minerals with high crystallinity to the soil has a weak ability to store organic carbon, and after the reduction reaction in the soil, most of the adsorbed organic carbon will be released, resulting in the re-release of the organic carbon stored in the soil in the short term; (2) It is difficult to find pure iron minerals in the soil, and they generally exist in the form of iron-aluminum composite minerals. Directly adding pure iron minerals to the soil may cause damage to the local soil ecological environment, which is not conducive to crop growth. For example, CN 115746866A discloses a method for promoting soil carbon sequestration using nano-hematite. By adding nano-hematite to the soil, the soil's carbon sequestration capacity is promoted. However, pure nano-hematite has a low specific surface area and weak adsorption of soil organic carbon. After adsorption saturation, it is difficult to continue to function. Furthermore, nano-hematite easily agglomerates after being applied to the soil, further reducing its adsorption capacity. Furthermore, applying a large amount of pure nano-iron minerals to the soil can cause an imbalance in the iron-aluminum ratio in the soil, which is detrimental to crop growth. The synthesis conditions for pure nano-hematite are also relatively complex, resulting in high synthesis costs, making it unsuitable for large-scale promotion and use. Summary of the Invention

[0005] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, one of the objects of the present invention is to provide a carbon-fixing material; a second object of the present invention is to provide a method for preparing such a carbon-fixing material; and a third object of the present invention is to provide applications of such a carbon-fixing material.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A first aspect of the present invention provides a carbon-fixing material, wherein the carbon-fixing material is aluminum-doped iron mineral nanoparticles.

[0008] In some embodiments of the present invention, the doping amount of aluminum is less than 40 mol% of the total amount of aluminum and iron elements in the carbon-fixing material.

[0009] In some specific embodiments of the present invention, the doping amount of aluminum is less than or equal to 30 mol% of the total amount of aluminum and iron elements in the carbon-fixing material.

[0010] In some embodiments of the present invention, the particle size of the carbon-fixing material is 2-8 nm.

[0011] In some specific embodiments of the present invention, the particle size of the carbon-fixing material is 3-6 nm.

[0012] In some embodiments of the present invention, the specific surface area of ​​the carbon-fixing material is 350-410 m 2 / g.

[0013] In some specific embodiments of the present invention, the specific surface area of ​​the carbon-fixing material is 360-400 m 2 / g.

[0014] In some embodiments of the present invention, the zero point charge of the carbon-fixing material is 7-10.

[0015] In some specific embodiments of the present invention, the zero point charge of the carbon-fixing material is 7-9.

[0016] In some embodiments of the present invention, the raw materials for preparing the carbon-fixing material include an aqueous solution of iron salt and an aqueous solution of aluminum salt.

[0017] In some specific embodiments of the present invention, the concentration of the iron salt aqueous solution is 0.4-0.6 mol / L.

[0018] In some specific embodiments of the present invention, the concentration of the aluminum salt aqueous solution is 0.4-0.6 mol / L.

[0019] In the present invention, since the grain sizes of iron atoms and aluminum atoms are similar, aluminum is doped by replacing the position of iron in the structure. Therefore, using trivalent iron and trivalent aluminum as raw materials, by regulating their co-hydrolysis rate, carbon-fixing materials with different aluminum doping amounts can be obtained.

[0020] In some embodiments of the present invention, the iron salt aqueous solution is selected from one of an aqueous solution of ferric nitrate, an aqueous solution of ferric chloride, an aqueous solution of ferric acetate, and an aqueous solution of ferric citrate.

[0021] In some specific embodiments of the present invention, the aqueous solution of iron salt is an aqueous solution of ferric nitrate.

[0022] In some embodiments of the present invention, the aluminum salt aqueous solution is selected from one of aluminum nitrate solution, aluminum chloride solution, and aluminum acetate solution.

[0023] In some specific embodiments of the present invention, the aluminum salt aqueous solution is an aluminum nitrate aqueous solution.

[0024] The second aspect of the present invention provides a method for preparing the carbon sequestration material according to the first aspect of the present invention, comprising the following steps:

[0025] The iron salt aqueous solution and the aluminum salt aqueous solution are mixed to obtain a suspension, the solid-liquid separation is carried out, and the solid phase is collected to obtain the carbon-fixing material.

[0026] In some embodiments of the present invention, the pH of the suspension is 7-8.

[0027] In some specific embodiments of the present invention, the pH of the suspension is 7.3-7.5.

[0028] In some embodiments of the present invention, the pH of the suspension is adjusted by adding alkaline solution.

[0029] In some embodiments of the present invention, the alkali source of the alkali solution comprises an alkali metal hydroxide.

[0030] In some specific embodiments of the present invention, the alkali source of the alkali solution is selected from at least one of potassium hydroxide and sodium hydroxide.

[0031] In some embodiments of the present invention, the concentration of the alkali solution is 0.8-1.2 mol / L.

[0032] In some embodiments of the present invention, the dropping speed of the alkali solution is 0.8-1.2 mL / min.

[0033] In some embodiments of the present invention, the process of mixing the aqueous solution of iron salt and the aqueous solution of aluminum salt is supplemented with stirring.

[0034] In some embodiments of the present invention, the stirring speed is 200-240 r / min, and the stirring time is 25-35 min.

[0035] In some embodiments of the present invention, the process of adjusting the pH of the suspension is supplemented by stirring.

[0036] In some embodiments of the present invention, the stirring speed is 200-240 r / min, and the stirring time is 20-30 h.

[0037] In some embodiments of the present invention, the rotation speed of the centrifugal separation is 5500-6500 r / min.

[0038] In some embodiments of the present invention, after the centrifugal separation, the steps of washing and drying are further included to obtain the carbon-fixing material.

[0039] The third aspect of the present invention provides the use of the carbon sequestration material described in the first aspect of the present invention in soil improvement.

[0040] In some embodiments of the present invention, the soil improvement includes enhancing the soil carbon sequestration capacity.

[0041] In some embodiments of the present invention, the mass ratio of the carbon sequestration material to soil is 1:(20-45).

[0042] In some specific embodiments of the present invention, the mass ratio of the carbon sequestration material to soil is 1:(25-35).

[0043] In some embodiments of the present invention, the pH of the soil is 3-10.

[0044] In some specific embodiments of the present invention, the pH of the soil is 4-9.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1) The carbon-fixing material provided by the present invention is aluminum-doped iron mineral nanoparticles with a particle size of 2-8 nm and a specific surface area of ​​350-410 m 2 / g, the particles have good dispersion and a good pore structure; aluminum is doped by replacing the position of iron in the structure, which increases the specific surface area and adsorption sites of the material and improves the organic carbon sequestration capacity of the material;

[0047] 2) The raw materials for preparing the carbon-fixing material provided by the present invention are readily available, the preparation method is simple, the reaction conditions are mild, and by regulating the hydrolysis rates of trivalent iron and aluminum ions, materials with different aluminum doping amounts can be obtained. The formation of agglomerates is reduced during the synthesis process, the operation is simple, the efficiency is high, and the obtained carbon-fixing material is high in purity and free of other impurity minerals;

[0048] 3) The carbon sequestration material provided by the present invention is used to enhance the carbon sequestration capacity of soil, has good organic carbon sequestration performance, can adapt to soil environments with different pH values, and can maintain long-term stability of organic carbon sequestration under various environmental conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Transmission electron micrographs of the carbon-fixing materials in Examples 1-4;

[0050] Figure 2 is the X-ray diffraction pattern of the carbon-fixing material in Examples 1-4;

[0051] Figure 3 is a relationship diagram between the unit cell parameters of the carbon-fixing material and the aluminum doping amount in Examples 1-4;

[0052] Figure 4 X-ray photoelectron spectra of Fe 2p (a) and Al 2p (b) of carbon-fixing materials in Examples 1-4;

[0053] Figure 5 is a relationship diagram of soluble iron and soluble aluminum in the carbon-fixing material in Examples 2-4;

[0054] Figure 6 is the zero-point charge of the carbon-fixing material in Examples 1-4;

[0055] Figure 7 is the specific surface area of ​​the carbon-fixing material in Examples 1-4;

[0056] Figure 8 is the X-ray photoelectron spectrum of the carbon-fixing material O1s in Examples 1-4;

[0057] Figure 9 is the adsorbed oxygen of the carbon-fixing material in Examples 1-4;

[0058] Figure 10 The test results of the organic carbon sequestration performance of the carbon sequestration material in Experimental Example 1;

[0059] Figure 11 These are the stability test results of the carbon-fixing material in fixing organic carbon in Experimental Example 2. DETAILED DESCRIPTION

[0060] The present invention is further described in detail below by way of specific examples. Unless otherwise specified, the raw materials, reagents, or devices used in the examples are all commercially available or can be obtained by conventional methods. Unless otherwise specified, all experiments or testing methods are conventional methods in the art.

[0061] In the following examples, iron nitrate aqueous solution and aluminum nitrate aqueous solution were used as raw materials to prepare carbon-fixing materials, and sodium hydroxide solution was used to adjust the pH of the solution. The preparation process of each solution was as follows:

[0062] 1) Weigh 30.30 g of solid ferric nitrate nonahydrate into a beaker and add 150 mL of deionized water to fully dissolve it to prepare 150 mL of a 0.5 mol / L ferric ion solution.

[0063] 2) Weigh 28.1 g of aluminum nitrate nonahydrate solid into a beaker and add 150 mL of deionized water to fully dissolve it, preparing 150 mL of a 0.5 mol / L trivalent aluminum ion solution.

[0064] 3) Weigh 4 g of solid sodium hydroxide into a 250 mL beaker and add 100 mL of deionized water to prepare 100 mL of a 1 mol / L sodium hydroxide solution.

[0065] The water used in the examples was all deionized water, and the reagents used, including ferric nitrate nonahydrate, aluminum nitrate nonahydrate, sodium hydroxide, and sodium chloride, were purchased from Sinopharm Reagents and were all analytically pure.

[0066] Example 1

[0067] This embodiment prepares a carbon sequestration material in the following steps:

[0068] S1. Take 14 mL of 0.5 mol / L ferric ion solution and add it to a 100 mL glass beaker. Place it on a magnetic stirrer, add 70 mL of deionized water, and stir the solution at 200 r / min for 30 min to obtain a mixed solution.

[0069] S2. Sodium hydroxide solution was added dropwise to the mixture at a rate of 1 mL / min. As the sodium hydroxide solution was added, the color of the solution gradually turned red and turbid. The addition was continued until the pH of the solution increased to 7.5. Stirring was continued for 24 h, during which the pH of the solution was kept constant at 7.5.

[0070] S3, centrifuging the solution at 6000 r / min, discarding the supernatant after precipitation, and then adding the same volume of deionized water, mixing thoroughly and centrifuging again, repeating this step three times to remove excess ions on the solid surface;

[0071] S4. The wet solid obtained after washing is placed in a freeze dryer for dehydration and drying. The solid is taken out after 24 hours to obtain iron mineral nanoparticles not doped with aluminum, which are recorded as 0AlFh.

[0072] Example 2

[0073] This embodiment prepares a carbon sequestration material in the following steps:

[0074] S1. Take 12.6 mL of 0.5 mol / L trivalent iron ion solution and add it to a 100 mL glass beaker. Place it on a magnetic stirrer, first add 1.4 mL of 0.5 mol / L trivalent aluminum ion solution, then add 70 mL of deionized water, and stir the solution at a speed of 200 r / min for 30 min to obtain a mixed solution;

[0075] S2. Sodium hydroxide solution was added dropwise to the mixture at a rate of 1 mL / min. As the sodium hydroxide solution was added, the color of the solution gradually turned red and turbid. The addition was continued until the pH of the solution increased to 7.5. Stirring was continued for 24 h, during which the pH of the solution was kept constant at 7.5.

[0076] S3, centrifuging the solution at 6000 r / min, discarding the supernatant after precipitation, and then adding the same volume of deionized water, mixing thoroughly and centrifuging again, repeating this step three times to remove excess ions on the solid surface;

[0077] S4. The wet solid obtained after washing is placed in a freeze dryer for dehydration and drying. After 24 hours, it is taken out to obtain aluminum-doped iron mineral nanoparticles. The aluminum doping amount is 10 mol% of the total amount of iron and aluminum in the nanoparticles, which is recorded as 10AlFh.

[0078] Example 3

[0079] This embodiment prepares a carbon sequestration material in the following steps:

[0080] S1. Take 11.2 mL of 0.5 mol / L trivalent iron ion solution and add it to a 100 mL glass beaker. Place it on a magnetic stirrer, first add 2.8 mL of 0.5 mol / L trivalent aluminum ion solution, then add 70 mL of deionized water, and stir the solution at a speed of 200 r / min for 30 min to obtain a mixed solution;

[0081] S2. Sodium hydroxide solution was added dropwise to the mixture at a rate of 1 mL / min. As the sodium hydroxide solution was added, the color of the solution gradually turned red and turbid. The addition was continued until the pH of the solution increased to 7.5. Stirring was continued for 24 h, during which the pH of the solution was kept constant at 7.5.

[0082] S3, centrifuging the solution at 6000 r / min, discarding the supernatant after precipitation, and then adding the same volume of deionized water, mixing thoroughly and centrifuging again, repeating this step three times to remove excess ions on the solid surface;

[0083] S4. The wet solid obtained after washing is placed in a freeze dryer for dehydration and drying. After 24 hours, it is taken out to obtain aluminum-doped iron mineral nanoparticles. The aluminum doping amount is 20 mol% of the total amount of iron and aluminum in the nanoparticles, which is recorded as 20AlFh.

[0084] Example 4

[0085] This embodiment prepares a carbon sequestration material in the following steps:

[0086] S1. Take 9.8 mL of 0.5 mol / L trivalent iron ion solution and add it to a 100 mL glass beaker. Place it on a magnetic stirrer, first add 4.2 mL of 0.5 mol / L trivalent aluminum ion solution, then add 70 mL of deionized water, and stir the solution at a speed of 200 r / min for 30 min to obtain a mixed solution;

[0087] S2. Sodium hydroxide solution was added dropwise to the mixture at a rate of 1 mL / min. As the sodium hydroxide solution was added, the color of the solution gradually turned red and turbid. The addition was continued until the pH of the solution increased to 7.5. Stirring was continued for 24 h, during which the pH of the solution was kept constant at 7.5.

[0088] S3, centrifuging the solution at 6000 r / min, discarding the supernatant after precipitation, and then adding the same volume of deionized water, mixing thoroughly and centrifuging again, repeating this step three times to remove excess ions on the solid surface;

[0089] S4. The wet solid obtained after washing is placed in a freeze dryer for dehydration and drying. After 24 hours, it is taken out to obtain aluminum-doped iron mineral nanoparticles. The aluminum doping amount is 30 mol% of the total amount of iron and aluminum in the nanoparticles, which is recorded as 30AlFh.

[0090] Example 5

[0091] This embodiment prepares a carbon sequestration material in the following steps:

[0092] S1. Add 9.52 mL of 0.5 mol / L ferric ion solution to a 100 mL glass beaker, place the beaker on a magnetic stirrer, add 4.48 mL of 0.5 mol / L ferric aluminum ion solution, then add 70 mL of deionized water, and stir the solution at 200 rpm for 30 min to obtain a mixed solution.

[0093] S2. Sodium hydroxide solution was added dropwise to the mixture at a rate of 1 mL / min. As the sodium hydroxide solution was added, the color of the solution gradually turned red and turbid. The addition was continued until the pH of the solution increased to 7.5. Stirring was continued for 24 h, during which the pH of the solution was kept constant at 7.5.

[0094] S3, centrifuging the solution at 6000 r / min, discarding the supernatant after precipitation, and then adding the same volume of deionized water, mixing thoroughly and centrifuging again, repeating this step three times to remove excess ions on the solid surface;

[0095] S4. The wet solid obtained after washing is placed in a freeze dryer for dehydration and drying. After 24 hours, it is taken out to obtain aluminum-doped iron mineral nanoparticles. The aluminum doping amount is 32 mol% of the total amount of iron and aluminum in the nanoparticles, which is recorded as 32AlFh.

[0096] Example 6

[0097] This embodiment prepares a carbon sequestration material in the following steps:

[0098] S1. Take 9.4 mL of 0.5 mol / L trivalent iron ion solution and add it to a 100 mL glass beaker. Place it on a magnetic stirrer, first add 5.6 mL of 0.5 mol / L trivalent aluminum ion solution, then add 70 mL of deionized water, and stir the solution at a speed of 200 r / min for 30 min to obtain a mixed solution;

[0099] S2. Sodium hydroxide solution was added dropwise to the mixture at a rate of 1 mL / min. As the sodium hydroxide solution was added, the color of the solution gradually turned red and turbid. The addition was continued until the pH of the solution increased to 7.5. Stirring was continued for 24 h, during which the pH of the solution was kept constant at 7.5.

[0100] S3, centrifuging the solution at 6000 r / min, discarding the supernatant after precipitation, and then adding the same volume of deionized water, mixing thoroughly and centrifuging again, repeating this step three times to remove excess ions on the solid surface;

[0101] S4. The wet solid obtained after washing is placed in a freeze dryer for dehydration and drying. After 24 hours, it is taken out to obtain aluminum-doped iron mineral nanoparticles. The aluminum doping amount is 40 mol% of the total amount of iron and aluminum in the nanoparticles, which is recorded as 40AlFh.

[0102] Example 7

[0103] This embodiment prepares a carbon sequestration material in the following steps:

[0104] S1. Take 3.8 mL of 0.5 mol / L trivalent iron ion solution and add it to a 100 mL glass beaker. Place it on a magnetic stirrer, first add 11.2 mL of 0.5 mol / L trivalent aluminum ion solution, then add 70 mL of deionized water, and stir the solution at a speed of 200 r / min for 30 min to obtain a mixed solution;

[0105] S2. Sodium hydroxide solution was added dropwise to the mixture at a rate of 1 mL / min. As the sodium hydroxide solution was added, the color of the solution gradually turned red and turbid. The addition was continued until the pH of the solution increased to 7.5. Stirring was continued for 24 h, during which the pH of the solution was kept constant at 7.5.

[0106] S3, centrifuging the solution at 6000 r / min, discarding the supernatant after precipitation, and then adding the same volume of deionized water, mixing thoroughly and centrifuging again, repeating this step three times to remove excess ions on the solid surface;

[0107] S4. The wet solid obtained after washing is placed in a freeze dryer for dehydration and drying. After 24 hours, it is taken out to obtain aluminum-doped iron mineral nanoparticles. The aluminum doping amount is 80 mol% of the total amount of iron and aluminum in the nanoparticles, recorded as 80AlFh.

[0108] Example 8

[0109] This embodiment prepares a carbon sequestration material in the following steps:

[0110] S1. Take 15 mL of 0.5 mol / L trivalent aluminum ion solution and add it to a 100 mL glass beaker, place it on a magnetic stirrer, add 70 mL of deionized water, and stir the solution at 200 rpm for 30 min to obtain a mixed solution;

[0111] S2. Sodium hydroxide solution was added dropwise to the mixture at a rate of 1 mL / min. As the sodium hydroxide solution was added, the color of the solution gradually turned red and turbid. The addition was continued until the pH of the solution increased to 7.5. Stirring was continued for 24 h, during which the pH of the solution was kept constant at 7.5.

[0112] S3, centrifuging the solution at 6000 rpm, discarding the supernatant after precipitation, and then adding the same volume of deionized water, mixing thoroughly and centrifuging again, repeating this step three times to remove excess ions on the solid surface;

[0113] S4. The wet solid obtained after washing is placed in a freeze dryer for dehydration and drying. The solid is taken out after 24 hours to obtain aluminum mineral nanoparticles, which are recorded as 100AlFh.

[0114] Material characterization

[0115] The carbon-fixing materials prepared in Examples 1-8 were subjected to transmission electron microscopy characterization, X-ray diffraction characterization and refinement, X-ray photoelectron spectroscopy and specific surface area characterization, and mineral acid dissolution experiments. The specific methods are as follows:

[0116] 1) Transmission electron microscopy characterization

[0117] 5 μL of the carbon-fixing material synthesized in Examples 1-8 was respectively dispersed in an acetone solution, and ultrasonicated for 25 minutes to uniformly disperse it. The resulting suspension was used to prepare samples for transmission electron microscopy analysis. In order to prevent changes in the solid phase components during the ultrasonication process, the entire ultrasonication process was carried out in water at 25°C. The suspension obtained after ultrasonication was added dropwise to an ultra-thin C film supported by a 200-mesh copper mesh, which was then dried under infrared light. The morphology of the aluminum-iron mineral nanoparticle carbon-fixing material was analyzed using a transmission electron microscope (JEOL JEM 2100). In order to ensure reliable results, multiple areas of the sample were selected for analysis.

[0118] 2) X-ray diffraction characterization and refinement

[0119] The solid samples obtained after freeze-drying in Examples 1-8 were placed in an agate mill and ground, and the solid powder was collected and placed in a 1.5 mL centrifuge tube. The solid powder was analyzed using an X-ray diffractometer (XRD, Bruker D8 Advance). The instrument was equipped with Cu Kα and the diffraction wavelength λ was 0.15418 nm. During the testing of all samples, the instrument tube voltage was set to 40 kV, the tube flow was set to 40 mA, the step length was set to 0.02 °, the step speed was set to 2 ° / min, and the collection range of all diffraction spectra was set to 10 ° -70 °. The crystal structure of the test sample was refined using TOPAS software, and the unit cell parameters of the initial sample were referenced to pure water iron ore. The X-ray diffraction pattern of the sample was continuously fitted until Rwp <10%, and the standard deviation of the unit cell parameters is approximately 0.001.

[0120] 3) X-ray photoelectron spectroscopy and specific surface area characterization

[0121] The X-ray photoelectron spectra of Fe 2p, Al 2p, and O 1s of the aluminum-iron mineral nanoparticle carbon-settling materials in Examples 1-8 were measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha). Before collecting the X-ray photoelectron spectra, the instrument was energy calibrated using the binding energy of C 1s to obtain accurate data. To quantify the O species in the aluminum-iron mineral nanoparticles, the O 1s X-ray photoelectron spectra were fitted using Peakfit software (v.4.12) to obtain the percentages of surface-adsorbed water, adsorbed oxygen, and lattice oxygen.

[0122] In order to determine the specific surface area of ​​the aluminum-containing iron mineral nanoparticle carbon-fixing materials doped with different aluminum, 30 mg of the solid samples in Examples 1-8 were weighed in glass tubes and placed in a vacuum (10 -3 The sample was degassed at 400 mbar for 72 hours to remove surface-adsorbed moisture, gases, and impurities. The sample was then analyzed using a surface area analyzer (Micromeritics 3000) at 77 K under a nitrogen atmosphere. Adsorption and desorption isotherms (including 25 adsorption points and 24 desorption points) were collected in the 0.01 to 0.995 P / P0 partial pressure range. The adsorption and desorption curves were analyzed using the BET equation to determine the specific surface area of ​​the solid sample.

[0123] 4) Mineral acid dissolution test

[0124] At room temperature (25°C), 100 mg of each carbon-fixing material from Examples 1-8 was weighed into a 250 mL glass conical flask, and 100 mL of 1 mol / L HCl was added to dissolve the mineral. Sampling was performed at different reaction time points, and 5 mL of the suspension sample was taken from the conical flask each time. The resulting suspension was immediately filtered with a 0.22 μm nylon filter membrane, and the filtrate was collected. The concentrations of Fe and Al in the filtrate were measured using an inductively coupled plasma optical emission spectrometer (ICP-OES, Agilent 5800) to determine the dissolution kinetics of the carbon-fixing material.

[0125] Through characterization and analysis such as transmission electron microscopy, it was found that when the aluminum doping amount in the carbon-fixing material is greater than 30% of the total molar amount of iron and aluminum, hydroalophane impurities will appear in the material, and the particle size is large, which is a non-nanoparticle size. In addition, the specific surface area, zero-point charge, and percentage of adsorbed oxygen of the carbon-fixing material all show a downward trend. Therefore, it is best that the aluminum doping amount in the carbon-fixing material is less than or equal to 30% of the total molar amount of iron and aluminum.

[0126] Figure 1 is a transmission electron microscope image of the carbon-fixing material in Examples 1-4, wherein: Figure 1 (a) is a transmission electron microscope image of the carbon-fixing material 0AlFh in Example 1, Figure 1 (b) is a transmission electron microscope image of the carbon-fixing material 10AlFh in Example 2. Figure 1 (c) is a transmission electron microscope image of the carbon-fixing material 20AlFh in Example 3. Figure 1 (d) is a transmission electron microscope image of the carbon-fixing material 30AlFh in Example 4. Figure 1 It can be seen that the carbon-fixing materials in Examples 1-4 have nano-size, with a particle size of about 3-6 nm, good particle dispersion, and a good pore structure.

[0127] Figure 2 is the X-ray diffraction pattern of the carbon-fixing material in Examples 1-4, Figure 2 It can be seen that no other impurity minerals appear in the carbon-fixing materials in Examples 1-4, and the synthesized nanomaterials have high purity.

[0128] Figure 3 is a relationship diagram between the unit cell parameters of the carbon-fixing material and the aluminum doping amount in Examples 1-4, wherein: Figure 3 (a) is the relationship between the unit cell parameter a and the aluminum doping amount. Figure 3 (b) is the relationship between the unit cell parameter c and the aluminum doping amount, Figure 3 It can be seen that with the increase of aluminum doping amount, the unit cell parameters of carbon-fixing materials gradually decrease.

[0129] Figure 4 is the X-ray photoelectron spectrum of Fe 2p (a) and Al 2p (b) of the carbon-fixing materials in Examples 1-4, Figure 4 It can be seen that with the increase of aluminum content in the material synthesis process, the aluminum content in the carbon-fixing material gradually increases and the iron content gradually decreases.

[0130] Figure 5 The relationship between soluble iron and soluble aluminum in the carbon-fixing material of Example 2-4 is shown in FIG. Figure 5 It can be seen that since the grain sizes of iron atoms and aluminum atoms are similar, the aluminum in the carbon-fixing material is doped by replacing the position of iron in the structure. The doping of aluminum in iron mineral nanoparticles helps to increase the specific surface area and adsorption sites of the material, which is beneficial to improving the storage capacity of organic carbon.

[0131] Figure 6 is the zero-point charge of the carbon-fixing material in Examples 1-4, Figure 6 As the aluminum doping level increases, the zero-point charge of the carbon-storing material gradually increases. As the doping level increases from 0 to 30 mol%, the zero-point charge increases from 7.26 to 8.96. Because organic carbon carries a negative charge, the increase in zero-point charge increases the electrostatic attraction between minerals and organic matter, promoting the adsorption of organic matter by minerals.

[0132] Figure 7 is the specific surface area of ​​the carbon-fixing material in Examples 1-4, Figure 7 It can be seen that with the increase of aluminum doping amount, the specific surface area of ​​carbon-fixing materials gradually increases. When the doping amount increases from 0 to 30 mol%, the specific surface area increases from 362m 2 / g increased to 397m 2 / g.

[0133] Figure 8 is the X-ray photoelectron spectrum of the carbon-fixing material O1s in Examples 1-4, Figure 9 is the adsorbed oxygen of the carbon-fixing material in Examples 1-4, Figure 8 and Figure 9 As shown, the amount of adsorbed oxygen in the carbon-storing material increases with increasing aluminum doping levels. As the doping level increases from 0 to 30 mol%, the percentage of adsorption sites increases from 39.7% to 62.5%. This increase in specific surface area and adsorption sites promotes the surface adsorption of aluminum-iron mineral nanoparticles and organic matter, increasing the adsorption capacity.

[0134] Test Example 1

[0135] 1) Extraction of soil dissolved organic carbon:

[0136] Weigh 10 g of paddy soil into a 100 mL polytetrafluoroethylene bottle, then add 50 mL of deionized water, place the polytetrafluoroethylene bottle on an oscillator, set the speed to 220 r / min, and oscillate for 72 hours; after the oscillation, transfer the soil-water mixture to a 50 mL centrifuge tube and centrifuge at a speed of 6000 r / min for 20 minutes; filter the supernatant after centrifugation using a 0.45 μm polyethersulfone filter membrane to remove other impurities, and collect the filtrate in a brown glass bottle, which is the soil dissolved organic carbon solution, and store it in a refrigerator at 4°C.

[0137] 2) Test on the sequestration performance of carbon-fixing materials on soil dissolved organic carbon:

[0138] Take four 100mL serum bottles, numbered 1-4, and add 47mL of 0.01mol / L NaCl and 3mL of 50mg C / L soil dissolved organic carbon solution, respectively, and then add 0.02g of the carbon sequestration material prepared in Examples 1-4. The contents of the bottle were thoroughly mixed to obtain a suspension, and the pH of the suspension was kept stable at 7.0 by adding 0.1mol / L HCl or 0.1mol / L NaOH, respectively. Then all serum bottles were placed in a constant temperature shaker with a speed of 220r / min and fully shaken at 25°C in the dark for 72h to ensure that adsorption equilibrium was reached. Each experimental condition was repeated three times.

[0139] All suspension samples after the reaction were centrifuged at 6000 rpm for 10 minutes. The supernatants from the different treatment groups were then filtered through a 0.45 μm polyethersulfone filter membrane and collected. To prevent precipitation during sample storage and testing, 50 μL of 6.05 mol / L HCl was added to all supernatants. After the supernatants from the different treatment groups were collected, the dissolved organic carbon concentrations in all supernatants were measured using a total organic carbon analyzer (TOC-L, Shimadzu, Japan).

[0140] Figure 10 The test results of the organic carbon sequestration performance of the carbon sequestration material in Experimental Example 1 are as follows: Figure 10 (a) is the organic carbon concentration in the liquid phase after adsorption equilibrium, Figure 10 (b) is the organic carbon concentration in the solid phase after adsorption equilibrium, Figure 10 It can be seen that when the soil organic carbon sequestration performance test was carried out using the carbon-fixing materials in Examples 1-4, as the aluminum doping amount in the material increased from 0 to 30 mol%, the organic carbon content in the liquid phase decreased from 21.16 mg / L to 12.03 mg / L, while the solid phase organic carbon content increased from 192.29 mg C / g to 265.42 mg C / g, indicating that after aluminum doping, more active soil organic carbon was adsorbed by the aluminum-iron mineral nanoparticle carbon-fixing material, and its mobility was significantly reduced, which promoted the effective sequestration of dissolved organic carbon. Moreover, with the increase of aluminum doping (≤30 mol%), the sequestration performance of dissolved organic carbon in the soil gradually improved.

[0141] Test Example 2

[0142] 1) Prepare the reaction solution:

[0143] Take 4 100mL serum bottles, numbered 1-4, and add 47mL of 0.01mol / L NaCl and 3mL of 50mg C / L soil dissolved organic carbon solution in Experimental Example 1 to each bottle. Then, add 0.4g of the carbon-fixing material prepared in Examples 1-4 to bottles 1-4, respectively. Mix the substances in the bottles thoroughly to obtain a suspension, and keep the pH of the suspension stable at 7.0 by adding 0.1mol / L HCl or 0.1mol / LNaOH, respectively. Then, place all the serum bottles in a constant temperature shaker and oscillate at a speed of 220r / min. Oscillate fully for 72h at 25°C in the dark to ensure that adsorption equilibrium is reached. Each experimental condition is repeated three times.

[0144] After adsorption equilibrium, the suspension was filtered through a 0.45 μm polyethersulfone filter membrane. The solid phase retained on the filter membrane was then rinsed five times with deionized water to ensure that excess ions and other impurities were removed. The suspension was then air-dried under natural ventilation, and the solid was collected to obtain a composite precipitate. The resulting composite precipitate after the adsorption reaction was divided into two parts: one for determining the content of fixed organic carbon in the solid phase, and the other for verifying the release of organic carbon fixed by the carbon-fixing material into soil solutions of different pH values.

[0145] 2) Stability test of organic carbon after fixation:

[0146] Three paddy soils with different pH values ​​were selected from Heshan City, Guangdong Province; Daye City, Hubei Province; and Panzhihua City, Sichuan Province. The pH values ​​were 4.3, 6.5, and 8.1, respectively. Extracts from these three soils were used to conduct an organic carbon fixation stability test on carbon-sequestering materials. 25g of each soil was weighed into a conical flask, and 250mL of deionized water was added. The extracts were shaken at 220 rpm for 3 hours, then allowed to stand for 15 minutes. 220mL of the upper layer of the solution in the conical flask was aspirated to obtain the soil extract.

[0147] 50 mL of soil extract was placed in a 100 mL serum bottle. 0.2 g of the dried composite precipitate was added to each treatment group, while the blank group remained untreated. On day 120, the organic carbon content in the solution was measured. The difference between the organic carbon content in the treatment and blank solutions was the amount of organic carbon released from the carbon-sequestering material.

[0148] Figure 11 The stability test results of the carbon-fixing material in fixing organic carbon in Experimental Example 2, where: Figure 11 (a) Figure 11 (b) Figure 11 (c) represents the soil samples from Heshan City, Guangdong Province (pH=4.3), Daye City, Hubei Province (pH=6.5), and Panzhihua City, Sichuan Province (pH=8.1) respectively. Figure 10In experiments with actual soil samples, organic carbon (OC) in the composite precipitates of carbon-storing materials remained stable over time in three different soil solutions. In slightly acidic soil solutions from Heshan City, Guangdong Province, after 120 days of incubation, 97.2%-98.4% of the organic carbon was fixed in the synthetic carbon-storing materials, with only 1.6%-2.8% of the dissolved organic carbon released. In slightly neutral soil solutions from Daye City, Hubei Province, after 120 days of incubation, the organic carbon fixed in the carbon-storing materials accounted for 96.1%-97.8% of the total stored organic carbon, with only 2.2%-3.9% of the dissolved organic carbon released. In slightly alkaline soil solutions from Panzhihua City, Sichuan Province, after 120 days of incubation, the organic carbon fixed in the materials accounted for 95%-97.2% of the total stored organic carbon, with only 2.8%-5% of the dissolved organic carbon released. These long-term continuous incubation results demonstrate that previously fixed active organic carbon can be stably fixed in the long-term by the aluminum-iron mineral nanoparticle carbon-storing materials. In addition, in soils with different pH values, the higher the aluminum doping content in the carbon sequestration material used, the lower the dissolved organic carbon content released after the incubation, indicating that the stored active organic carbon is more stable.

Claims

1. A carbon-fixing material, characterized in that: The carbon-fixing material is aluminum-doped iron mineral nanoparticles; The particle size of the carbon-fixing material is 2-8 nm; the specific surface area of ​​the carbon-fixing material is 350-410 m 2 / g; The carbon-fixing material is prepared by the following method: mixing an aqueous solution of iron salt and an aqueous solution of aluminum salt to obtain a suspension, separating the solid and the liquid, collecting the solid phase, and freeze-drying to obtain the carbon-fixing material.

2. The carbon-fixing material according to claim 1, characterized in that The doping amount of aluminum is less than 40 mol% of the total amount of aluminum and iron elements in the carbon-fixing material.

3. The carbon-fixing material according to claim 1, characterized in that The pH of the suspension is 7-8.

4. Use of the carbon sequestration material according to any one of claims 1 to 3 in soil improvement.

5. The use according to claim 4, characterized in that The soil improvement includes improving the soil's carbon sequestration capacity.

6. The use according to claim 4, characterized in that The mass ratio of the carbon sequestration material to soil is 1:(20-45).

7. The use according to claim 4, characterized in that The pH of the soil is 3-10.

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