A borate intercalated magnesium-iron double metal oxide composite material, a preparation method and application thereof

Abstract

The present application belongs to the field of environmental functional materials and soil improvement technology, and relates to a borate intercalated magnesium-iron bimetallic oxide composite material, a preparation method and application thereof. The material takes straw biochar as a carrier, adopts a coprecipitation method to grow borate intercalated magnesium-iron layered double hydroxide in situ on the surface of biochar, and is prepared by calcination. The material has specific adsorption performance on small-molecule organic carbon sources such as glucose and glutamic acid by using boron hydroxyl functional groups, and still maintains high capacity in a high-salt environment. After being applied to salinized soil, the composite material captures active small-molecule organic carbon by chemical adsorption, significantly improves the microbial biomass carbon content; the proliferation of microorganisms promotes the assimilation and conversion of organic carbon, and finally realizes the increase of total soil organic carbon storage. Through the synergistic mechanism of "chemical capture-microbial driving", the present application realizes the efficient and stable accumulation of organic carbon in salinized soil, and provides a new material and a new way for carbon sequestration and improvement.

Description

Technical Field

[0001] This invention relates to a borate-intercalated magnesium-iron bimetallic oxide composite material, its preparation method and application, belonging to the field of environmental functional materials and soil improvement technology, specifically for carbon sequestration and improvement of saline soil. Background Technology

[0002] Soil, as the largest carbon sink in terrestrial ecosystems, relies on the stability and accumulation of organic carbon to maintain soil productivity and ecosystem services. Organic carbon sequestration primarily depends on three mechanisms: physical encapsulation by aggregates, chemical binding with minerals, and microbial transformation and turnover. However, in coastal saline soils, the high sodium environment leads to the disintegration of soil aggregates, weakening their physical protective function; the scarcity of clay particles and iron and aluminum oxides results in a lack of chemical adsorption sites for organic carbon; simultaneously, the high salinity inhibits microbial activity, hindering the biotransformation of organic matter, leading to the rapid mineralization and loss of exogenous organic carbon after it enters the soil, making effective sequestration difficult. Small molecule active organic carbons such as glucose and amino acids, due to their high solubility and ease of mineralization, are the fastest-losing components. Therefore, effectively intercepting and sequestering easily lost small molecule active carbon has become a key aspect of carbon sequestration technology development in saline soils.

[0003] Biochar, due to its large specific surface area, structural stability, and high carbon content, is considered a potential material for enhancing soil organic carbon and has received widespread attention in soil improvement and carbon sequestration. Its abundant pore structure and surface functional groups provide the physical space for organic carbon adsorption, while its high stability allows it to remain in soil for extended periods. However, the application of biochar to coastal saline soils still faces significant limitations: its surface is typically negatively charged, resulting in electrostatic repulsion with similarly negatively charged small-molecule organic carbon, leading to insufficient affinity for target small molecules; furthermore, biochar lacks specific complexation sites, making it difficult to effectively capture and retain easily mineralized active organic components in high-salt environments. Applying biochar alone has limited ability to capture small-molecule active carbon, failing to fundamentally solve the problem of rapid mineralization and loss of exogenous organic carbon in saline soils.

[0004] In recent years, constructing biochar composites through functional group modification has become an important direction for enhancing their ability to capture small-molecule organic carbon. Combining biochar with high specific surface area and functional groups with specific complexing capabilities holds promise for balancing adsorption capacity and affinity selectivity. Studies have shown that layered bimetallic oxides (LDOs) can enhance their affinity for small-molecule organic carbon by introducing functional groups such as borate through intercalation modification. However, existing composite materials still face a dual challenge in the complex environment of saline soils: on the one hand, the ion competition effect brought about by high salinity conditions easily weakens the binding strength between the material and organic carbon; on the other hand, the stability of the material itself and its compatibility with the soil environment also restrict their practical application effects. Therefore, achieving a balance between "efficient capture" and "long-term retention" remains a key challenge in the current research and development of organic carbon enhancement technologies for saline soils.

[0005] The improvement and utilization of marginal soils such as saline soils has become an important way to ensure food security and ecological security. Developing efficient carbon sequestration technologies suitable for saline soils can not only achieve the sequestration of organic carbon, but also promote the ecological restoration of degraded soils and enhance their productivity recovery capabilities.

[0006] Layered bimetallic hydroxides are a class of anionic functional layered materials composed of two or more metallic elements. Layered bimetallic oxides are products of high-temperature calcination of layered bimetallic hydroxides. Besides retaining the original properties of layered bimetallic hydroxides, they also possess advantages such as larger specific surface area, more active sites, and more stable metal composition. Both have the function of removing pollutants (especially heavy metal cations) from water, mainly through interlayer anion exchange or surface adsorption. Furthermore, they exhibit unique characteristics such as a memory effect, exchangeability of interlayer anions, and controllability of the metal layers, attracting increasing attention for their application in environmental remediation. Currently, no research has been reported on the application of layered bimetallic oxides in organic carbon sequestration. Summary of the Invention

[0007] To address the shortcomings of the prior art, the present invention aims to provide a borate-intercalated magnesium-iron bimetallic oxide composite material, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a borate-intercalated magnesium-iron bimetallic oxide composite material (B-LBC), the borate-intercalated magnesium-iron bimetallic oxide composite material comprising biochar and a borate-intercalated magnesium-iron layered bimetallic oxide supported on the surface of the biochar.

[0009] In this invention, adsorption kinetic studies showed that the adsorption process of glucose and glutamate by B-LBC conforms to a pseudo-second-order kinetic model (R² > 0.99), with chemisorption as the dominant process. The first 2 hours are the rapid adsorption phase, and equilibrium is reached after 18 hours. The adsorption capacity of B-LBC for glucose is 18%–52% higher than that of other comparative materials, and the adsorption capacity for glutamate is 6%–72% higher than that of other comparative materials other than LBC, thus balancing adsorption capacity and adsorption rate.

[0010] Isothermal adsorption analysis showed that the adsorption of glucose by B-LBC conformed to the Freundlich model, belonging to heterogeneous multilayer adsorption; the adsorption of glutamate conformed to the Langmuir monolayer mechanism, with the adsorption affinity constant increased by 57.8% compared with the unmodified material, and the maximum adsorption capacity increased by 30.5%~87.1% compared with BC, S-LBC, TS-LBC and Si-LBC. This is attributed to the optimized interlayer structure formed by borate intercalation and its specific complexation with ortho-hydroxyl or amino groups in small organic molecules.

[0011] The borate-intercalated magnesium-iron bimetallic oxide composite material provided by the present invention is prepared by loading borate-intercalated modified magnesium-iron bimetallic oxide onto biochar.

[0012] A second aspect of the present invention provides a method for preparing the borate-intercalated magnesium-iron bimetallic oxide composite material described in the first aspect, comprising the following steps: S1. Biomass raw materials are pyrolyzed under nitrogen protection to obtain biochar; S2. Disperse the biochar obtained in step S1 in water, add magnesium salt, iron salt and boric acid, and carry out a co-precipitation reaction under alkaline conditions to allow the borate-intercalated layered double hydroxide to grow in situ on the surface of the biochar, thereby obtaining the precursor composite material. S3. Calcine the precursor composite material to convert the layered double hydroxide into a layered bimetallic oxide, thus obtaining the product.

[0013] In step S1, the pyrolysis temperature is 400~600℃, preferably 500℃; the heating rate is 5~15℃ / min, preferably 10℃ / min; the pyrolysis time is 1~3 h, preferably 2 h; the biomass raw material is one of corn straw, wheat straw, rice straw and rice husk, which is dried, crushed and sieved before use, and after pyrolysis is acid washed, water washed until neutral and dried.

[0014] In step S2, the molar ratio of magnesium salt to iron salt is 2:1 to 4:1, preferably 3:1.

[0015] The molar ratio of boric acid to total metal ions is 2:1 to 7:1, preferably 5:1, and more preferably nH3BO3:nMg. 2+ nFe 3+=15:2:1.

[0016] In step S2, the coprecipitation reaction was carried out at pH 9.5–10.5 and temperature 50–70°C. After stirring, the mixture was allowed to stand in a water bath at 60–80°C. The salt solution and alkali solution were added to the biochar suspension in a co-current dropping manner. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain the precursor.

[0017] Furthermore, in step S2, the coprecipitation reaction is carried out in a parallel dropwise manner, in which a mixed salt solution containing magnesium salt and iron salt and a mixed alkaline solution containing sodium hydroxide and sodium carbonate are simultaneously added dropwise to the biochar suspension. After the addition is completed, a borate solution is added dropwise.

[0018] In some embodiments, the magnesium salt is magnesium nitrate hexahydrate (Mg(NO3)2·6H2O), the iron salt is ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and the borate is boric acid (H3BO3); the metal salt solution is composed of 100 mL of a mixture of 0.04 M magnesium nitrate hexahydrate and 0.02 M ferric nitrate nonahydrate; the amount of boric acid added is 0.03 mol, and the amount of biochar added is 1 g.

[0019] In step S3, the calcination temperature is 400~600℃, the time is 1~3 h, the heating rate is 5~15℃ / min, the nitrogen atmosphere is used for protection, and the calcined product is sieved.

[0020] A third aspect of the present invention provides the application of the borate-intercalated magnesium-iron bimetallic oxide composite material described in the first aspect or the borate-intercalated magnesium-iron bimetallic oxide composite material prepared by the method described in the second aspect in the adsorption of organic carbon.

[0021] This invention has found that the borate-intercalated magnesium-iron bimetallic oxide composite material has the following effects: (a1) Adsorbs negatively charged small-molecule organic carbon in saline soil; (a2) Retaining active organic carbon in saline soil; (a3) Increase the organic carbon storage in saline soils; (a4) Promotes the conversion of active organic carbon into a stable mineral-bound carbon pool; (a5) Synergistically improve the physical and chemical properties of saline soil and enhance microbial activity.

[0022] Based on this, a fourth aspect of the present invention provides the use of the borate-intercalated magnesium-iron bimetallic oxide composite material described in the first aspect or the borate-intercalated magnesium-iron bimetallic oxide composite material prepared by the method described in the second aspect in any of the following: (1) Adsorb small molecule organic carbon sources in solution or soil, or prepare products that adsorb glucose and glutamic acid in solution or soil; (2) Improve the retention capacity of organic carbon in saline soil, or prepare products that improve the retention capacity of organic carbon in saline soil; the products may be soil conditioners or soil amendments.

[0023] (3) Reduce the mineralization loss of organic carbon in saline soil, or prepare products that reduce the mineralization loss of organic carbon in saline soil; (4) Increase the carbon content of microbial biomass in saline soil, or prepare products that increase the carbon content of microbial biomass in saline soil.

[0024] This invention verifies the application effect of the above-mentioned modified materials in saline environments.

[0025] To verify the targeted fixation capacity and application effect of the composite material in saline environments, a series of experiments were conducted. In a salt solution (0.3 mol / L NaCl), B-LBC showed the highest adsorption capacity for glucose and glutamic acid, increasing by 332.2% and 49.7% respectively compared to unmodified BC. This is mainly attributed to the specific chemisorption formed between boron hydroxyl groups and small organic molecule functional groups, which remained stable under high salinity conditions. Further incubation experiments in saline soil revealed that B-LBC treatment significantly increased the content of MBC (soil microbial biomass carbon) and SOC (soil organic carbon), achieving effective carbon fixation.

[0026] Based on the above experimental results, the high efficiency of the composite material described in this invention in retaining organic carbon in saline soil can be attributed to a synergistic mechanism of "chemical capture-microbial drive": First, B-LBC, with the boron hydroxyl functional group provided by borate, exhibits specific chemical adsorption capacity for small molecule organic carbon sources such as glucose and amino acids in a saline environment, effectively capturing and enriching active organic carbon in the soil; subsequently, the captured and enriched organic carbon provides sufficient carbon and energy sources for soil microorganisms, significantly stimulating the growth and activity of the microbial community, manifested as a significant increase in MBC; the proliferation of the microbial community further enhances the assimilation and transformation efficiency of organic carbon, ultimately promoting a comprehensive increase in SOC storage. This cascade process of "adsorption capture-biotransformation" enables B-LBC to achieve efficient and stable accumulation of organic carbon in saline soil.

[0027] A fifth aspect of the present invention provides a method for carbon sequestration and improvement of saline soil, the method comprising applying the borate-intercalated magnesium-iron bimetallic oxide composite material described in the first aspect or the borate-intercalated magnesium-iron bimetallic oxide composite material prepared by the method described in the second aspect to saline soil.

[0028] This invention provides a borate-intercalated magnesium-iron bimetallic oxide-biochar composite material. Compared with the prior art, the technical solution of this invention has the following beneficial effects: 1) Strong structural stability: The chemical bonds and strong interface formed by the in-situ growth method overcome the defects of easy detachment of physical mixing and significantly improve the structural stability of the material.

[0029] 2) Significantly improved adsorption selectivity: Borate intercalation not only stabilizes the layered structure of LDO, but also creates a microenvironment conducive to the adsorption of small organic molecules by regulating the charge distribution of the layers and surface functional groups, thus significantly enhancing the selective adsorption capacity for target carbon sources such as glucose and glutamic acid.

[0030] 3) Synergistic effect to achieve long-term retention: The LDO obtained by calcination and conversion retains the "memory effect" and can be slowly reconstructed in saline soil to achieve continuous adsorption and controlled release of small organic molecules; at the same time, the porous structure of biochar provides physical protection. The two work together to effectively delay the mineralization and decomposition of organic carbon.

[0031] 4) Dual function of carbon fixation and soil improvement: When this composite material is applied to saline soil, it can significantly increase the carbon content of soil microbial biomass, promote the conversion of active organic carbon to a stable state, and achieve long-term carbon fixation; at the same time, it improves the physical and chemical properties of the soil and has the effect of soil improvement.

[0032] 5) Green and environmentally friendly, easy to promote: Using agricultural waste such as corn stalks as biochar raw materials, the resource utilization of waste is realized; the preparation process is simple, low cost, and environmentally friendly, making it suitable for large-scale production and promotion. Attached Figure Description

[0033] Figure 1 The figures show the adsorption amounts of glucose and glutamic acid in solution by different composite materials in the embodiments and comparative examples of this invention (different letters in the figures indicate significant differences between treatments). P <0.05); where (a) represents the amount of glucose adsorbed by different composite materials; and (b) represents the amount of glutamic acid adsorbed by different composite materials. Figure 2 The adsorption kinetics curves of glucose in solution by different composite materials in the embodiments and comparative examples of the present invention are shown. Figure 3 The adsorption kinetics curves of glutamic acid in solution by different composite materials in the embodiments and comparative examples of the present invention are shown. Figure 4 The figures show the adsorption amounts of different composite materials on glucose and glutamic acid in solution under salinization conditions in the embodiments and comparative examples of this invention (different letters in the figures indicate significant differences between treatments). P <0.05); where (a) represents the amount of glucose adsorbed by different composite materials; and (b) represents the amount of glutamic acid adsorbed by different composite materials. Figure 5The figures show the changes in microbial biomass carbon content and soil organic carbon content in saline soil under different composite material treatments in the embodiments and comparative examples of this invention (different letters in the figures indicate significant differences between treatments). P <0.05); where (a) represents the soil microbial biomass carbon content under different composite material treatments; and (b) represents the soil organic carbon content under different composite material treatments. Detailed Implementation

[0034] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0036] To fairly compare the effects of different anion types on the properties of composite materials, comparative examples 3-5 were set with equal negative charge equivalents. This is because the intercalation amount of interlayer anions in layered bimetallic hydroxides (LDHs) is mainly determined by the positive charge density of the laminations. Under the premise of satisfying charge balance, the number of intercalated moles of different anions is inversely proportional to the number of charges they carry. Therefore, setting equal negative charge equivalents (0.03 mol of negative charge for all) ensures that the loading of different anions on the charge basis is consistent, so that the comparison results truly reflect the influence of anion type on material properties.

[0037] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0038] Example 1: A method for preparing a borate-intercalated magnesium-iron bimetallic oxide composite material A borate-intercalated magnesium-iron bimetallic oxide composite material is prepared by the following method: Corn stalks were dried, crushed, and passed through a 60-mesh sieve. An appropriate amount of stalk powder was placed in a tube furnace under nitrogen atmosphere protection and pyrolyzed at 500℃ for 2 hours at a heating rate of 10℃ / min. After natural cooling, the pyrolyzed biochar was removed. The resulting biochar was washed with 0.1 M hydrochloric acid solution to remove tar and other impurities, then washed with deionized water until neutral, and dried in a 60℃ oven for 12 hours to obtain corn stalk biochar.

[0039] Weigh 1.0 g of the above corn stalk biochar, disperse it in 200 mL of deionized water, and ultrasonically disperse it for 20 min (300 W, 25℃) to obtain a biochar suspension.

[0040] Preparation of mixed salt solution: Weigh 10.26 g magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) and 8.08 g ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and dissolve them in 100 mL of deionized water.

[0041] Preparation of mixed alkaline solution: Weigh 3.84 g sodium hydroxide (NaOH) and 4.24 g sodium carbonate (Na2CO3) and dissolve them in 100 mL of deionized water.

[0042] Under vigorous stirring, the above-mentioned mixed salt solution and mixed alkali solution were slowly added dropwise to the biochar suspension at a rate of approximately 3-4 mL / min (approximately 1 drop per second) in a parallel-flow manner, with the total addition time controlled within 30 min. The pH of the reaction system was maintained at 10 ± 0.2 by controlling the addition rate. After the addition was complete, 1.85 g of boric acid (H3BO3) was dissolved in 50 mL of deionized water and added dropwise to the above system at the same dropping rate as the mixed salt solution. The reaction was continued at 60 °C with magnetic stirring (600 r / min) for 2 h, and then transferred to an 80 °C water bath for static reaction for 24 h.

[0043] After the reaction was completed, the mixture was centrifuged, and the lower precipitate was washed with deionized water until neutral. It was then dried in an oven at 60°C for 12 hours to obtain the precursor composite material.

[0044] The dried precursor composite material was placed in a tube furnace under nitrogen atmosphere protection and heated to 500℃ at a heating rate of 10℃ / min. It was calcined at a constant temperature for 2 h, and after natural cooling, it was taken out and ground through a 60-mesh sieve to obtain borate intercalated magnesium iron bimetallic oxide composite material (B-LBC).

[0045] Example 2: The preparation method is the same as in Example 1, except that the pyrolysis temperatures are 400℃ and 600℃ respectively.

[0046] Example 3: The preparation method is the same as in Example 1, except that the heating rates are 5℃ / min and 15℃ / min, respectively.

[0047] Example 4: The preparation method is the same as in Example 1, except that the pyrolysis time is 1 h and 3 h respectively.

[0048] Example 5: The preparation method is the same as in Example 1, except that the molar ratio of magnesium salt to iron salt is 3:1 and 4:1, respectively.

[0049] Example 6: The preparation method is the same as in Example 1, except that the molar ratio of borate to metal salt is 3:1 and 7:1, respectively.

[0050] Comparative Example 1: Preparation of Corn Stalk Biochar (BC) Corn stalks were dried, crushed, and sieved through a 60-mesh sieve. An appropriate amount of stalk powder was placed in a tube furnace under nitrogen atmosphere protection and pyrolyzed at 500℃ for 2 h at a heating rate of 10℃ / min. After natural cooling, the powder was removed. The resulting biochar was washed with 0.1 M hydrochloric acid solution to remove tar and other impurities, then washed with deionized water until neutral. It was dried in a 60℃ oven for 12 h, ground, and sieved through a 60-mesh sieve to obtain corn stalk biochar (BC).

[0051] Comparative Example 2: Preparation of Magnesium-Iron Bimetallic Oxide-Biochar Composite (LBC) The method of Example 1 was followed, except that in step S2, the operation of "dissolving 1.85 g of boric acid in 50 mL of deionized water" was not performed. All other conditions were the same as in Example 1, and magnesium-iron bimetallic oxide-biochar composite material (LBC) was obtained.

[0052] Comparative Example 3: Preparation of sulfate-intercalated magnesium-iron bimetallic oxide-biochar composite material (S-LBC) Prepared according to the method of Example 1, except that in step S2, "dissolving 1.85 g of boric acid in 50 mL of deionized water and adding" is replaced with "adding an equivalent amount of SO4 with a negative charge (0.03 mol of negative charge)". 2- (2.61 g K2SO4, 0.015mol, SO4 2- "Add 2) into 50 mL of deionized water", and the rest of the conditions were the same as in Example 1, to obtain sulfate intercalated magnesium iron bimetallic oxide-biochar composite material (S-LBC).

[0053] Comparative Example 4: Preparation of thiosulfate-intercalated magnesium iron bimetallic oxide-biochar composite material (TS-LBC) Prepared according to the method of Example 1, except that in step S2, "dissolving 1.85 g of boric acid in 50 mL of deionized water and adding" is replaced with "adding an equivalent amount of negatively charged S2O3 (0.03 mol of negative charge)". 2- (3.72 g Na2S2O3·5H2O, 0.015 mol, S2O3 2- "Add 'charge-2' to 50 mL of deionized water", with all other conditions being the same as in Example 1, to obtain thiosulfate intercalated magnesium iron bimetallic oxide-biochar composite material (TS-LBC).

[0054] Comparative Example 5: Preparation of Silicate Intercalated Magnesium Iron Bimetallic Oxide-Biochar Composite Material (Si-LBC) Prepared according to the method of Example 1, except that in step S2, "dissolving 1.85 g of boric acid in 50 mL of deionized water" is replaced with "dissolving 2.42 g of fast-dissolving sodium silicate (Na2O·3SiO2, modulus 2.00-2.20) of silicate ions (0.03 mol of negative charge) in 50 mL of deionized water" and the rest of the conditions are the same as in Example 1, to obtain silicate intercalated magnesium iron bimetallic oxide-biochar composite material (Si-LBC).

[0055] Example 7: Basic properties of biochar and borate-intercalated magnesium-iron bimetallic oxide composite materials The pore structure characteristics of the materials obtained in Example 1 and Comparative Examples 1-5 were analyzed using the N2 adsorption-desorption method. After degassing at 105 °C for 12 h, N2 adsorption-desorption tests were performed at 77 K liquid nitrogen temperature, and the specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. The samples were treated with nitric acid digestion, and the elemental composition was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The specific surface area and elemental composition results of the six biochar-based materials are shown in Table 1.

[0056] Table 1 Comparison of properties of different biochar composite materials

[0057] Note: Different letters in the same column of the table indicate significant differences between treatments. P <0.05).

[0058] As shown in Table 1, after loading with layered bimetallic oxides, the Mg and Fe contents of all modified composite materials were significantly increased compared with the original biochar (BC). P The content of magnesium-iron layered bimetallic oxides was <0.05%, which is more than 50 times higher than that of BC. Specifically, LBC had a Mg content of 12.75 mg / g and an Fe content of 23.50 mg / g, while the Mg and Fe contents of B-LBC, S-LBC, TS-LBC, and Si-LBC were not significantly different from those of LBC. These results indicate that magnesium-iron layered bimetallic oxides have been successfully loaded onto the surface of biochar.

[0059] After loading, the specific surface area of ​​the composite material increased significantly, further confirming the structural changes of the modified material. Significant differences in the specific surface area of ​​the composite material were observed after different anion intercalation modifications. P<0.05). Among them, B-LBC had the highest specific surface area, significantly higher than LBC and other intercalated materials; while the specific surface areas of S-LBC, TS-LBC and Si-LBC were all significantly lower than LBC. The above differences in specific surface area correspond to the introduction of intercalation elements, and combined with the characteristic elements (B, S, Si) detected in each intercalated material, provide indirect evidence for the successful intercalation of anions.

[0060] The pH values ​​of the composite materials ranged from 8.10 to 8.47, with no significant differences between treatments, indicating that the modification and intercalation processes did not significantly affect the acid-base properties of the materials. In summary, a series of modified biochar composite materials with high specific surface area and characteristic elemental composition were successfully prepared, laying the foundation for subsequent research on the carbon sequestration performance of saline-alkali soils.

[0061] Example 8: Adsorption effect of different modified materials on carbon source in solution 100 mg / L glucose and glutamate solutions were prepared separately. 0.05 g of B-LBC was weighed into 50 mL centrifuge tubes, and 30 mL of glucose or glutamate solution was added. Equal amounts of BC, LBC, S-LBC, TS-LBC, and Si-LBC were used as controls. The mixture was shaken at 25℃ and 180 r / min for 24 h, then filtered. The remaining concentration was measured, and the adsorption capacity was calculated. Results are shown below. Figure 1 .

[0062] Depend on Figure 1 It can be seen that different modified materials exhibit significant differences in their adsorption capacity for the two carbon sources, and demonstrate obvious adsorption selectivity. Regarding glucose adsorption ( Figure 1 In the middle (a), B-LBC showed the highest adsorption capacity, approximately 110% higher than BC; compared to LBC, S-LBC, TS-LBC, and Si-LBC, the adsorption capacities were increased by approximately 32.86%, 40.28%, 13.56%, and 33.52%, respectively. Regarding glutamate adsorption ( Figure 1 In the first category (b), LBC showed the best performance, with an improvement of approximately 167% compared to BC; B-LBC was second, about 13.12% lower than LBC, but significantly higher than S-LBC, TS-LBC, and Si-LBC, with improvements of 9.81%, 24.52%, and 63.36%, respectively. Overall, all modification treatments effectively improved the adsorption capacity of corn straw biochar for both carbon sources. Among them, B-LBC showed the best adsorption effect for glucose, and its adsorption effect for glutamic acid was second only to LBC, demonstrating the most balanced and excellent overall adsorption performance for both carbon sources, showing good application potential.

[0063] Example 9: Effect of different synthesis conditions on the adsorption performance of glucose and glutamate Prepare 100 mg / L solutions of glucose and glutamic acid, respectively. Weigh 0.05 g of the material from Examples 2-6 into 50 mL centrifuge tubes, add 30 mL of glucose or glutamic acid solution, shake at 25 °C and 180 r / min for 24 h, filter, determine the remaining concentration, and calculate the adsorption capacity. The adsorption results of glucose and glutamic acid are shown in Table 2.

[0064] Table 2 Effects of different synthesis conditions on the adsorption capacity of glucose and glutamate

[0065] Note: Different lowercase letters after the data in the same column indicate significant differences between groups. P <0.05; numerical values ​​are expressed as mean ± standard deviation (n=3).

[0066] According to the screening results in Table 2, pyrolysis temperature, heating rate, pyrolysis time, the molar ratio of magnesium salt to iron salt, and the molar ratio of borate to metal salt all significantly affected the adsorption performance of the material. Among these, the material achieved the highest adsorption capacity for glucose and glutamic acid under the following conditions: pyrolysis temperature of 500℃, heating rate of 10℃ / min, pyrolysis time of 2 h, magnesium salt to iron salt molar ratio of 3:1, and borate to metal salt molar ratio of 5:1. Analysis of variance showed that the adsorption performance under these conditions was significantly better than at other levels. P (<0.05), therefore this combination was determined to be the optimal synthesis condition for material preparation.

[0067] Example 10: Kinetic analysis of adsorption of carbon sources in solution by different modified materials 0.05 g of B-LBC was weighed into 50 mL centrifuge tubes, and 30 mL of 100 mg / L glucose solution and 30 mL of 100 mg / L glutamate solution were added. The mixture was shaken at 25℃ and 180 r / min, and samples were taken at 30, 60, 120, 360, 480, 600, 720, 1080, 1200, and 1440 min. The samples were filtered through a 0.22 μm filter membrane. The residual glucose concentration in the filtrate was determined using the salicylic acid method, and the residual glutamate concentration was determined using the ninhydrin method. The adsorption capacity at different time points was then calculated. Equal amounts of BC, LBC, S-LBC, TS-LBC, and Si-LBC were used as controls. The results are shown in the figure. Figure 2 , Figure 3 And Table 3.

[0068] Depend on Figure 2 and Figure 3It can be seen that the adsorption trends of B-LBC for glucose and glutamate in aqueous solution are basically consistent and conform to the exponential equation. The first 2 hours are the rapid adsorption stage, and the adsorption of glucose and glutamate is basically saturated at 18 hours. Thereafter, the adsorption amount remains basically unchanged with the extension of time.

[0069] The adsorption kinetic models of modified biochar for different carbon sources are shown in Table 3.

[0070] Table 3. Fitting of adsorption kinetic parameters for glucose and glutamic acid in solution by different biochar-modified materials.

[0071] Note: Q e To balance the adsorption capacity, k1 is the pseudo-first-order adsorption rate constant, and k2 is the pseudo-second-order adsorption rate constant.

[0072] It is evident that the adsorption kinetics of glucose and glutamic acid by the six modified biochar materials all conform to the pseudo-second-order kinetic model. R 2 All values ​​were above 0.9, indicating that the adsorption process was dominated by chemisorption, and the adsorption rate was closely related to the number of active sites on the material surface. Different modified materials exhibited significant adsorption selectivity for the two carbon sources: B-LBC showed the largest adsorption capacity for glucose, increasing by 41.62%, 34.01%, 51.79%, 17.78%, and 38.62% compared to BC, LBC, S-LBC, TS-LBC, and Si-LBC, respectively. For glutamic acid adsorption, B-LBC also showed excellent adsorption performance, with its adsorption capacity second only to LBC, increasing by 57.06%, 8.47%, 6.21%, and 72.31% compared to BC, S-LBC, TS-LBC, and Si-LBC, respectively. This difference in selectivity is related to the molecular structure of the adsorbate. Glutamic acid, containing amino and carboxyl groups, is more likely to form multiple interactions with the material surface; glucose is mainly adsorbed through hydrogen bonds and is more sensitive to the number of oxygen-containing functional groups on the surface. In terms of adsorption rate, Si-LBC showed the fastest adsorption rate for both carbon sources. Although B-LBC is slightly inferior to Si-LBC, it still maintains a high adsorption rate while achieving the maximum adsorption capacity, indicating that it has better overall performance in terms of both adsorption capacity and adsorption rate. This may be related to the longer diffusion time of adsorbate molecules in the pores due to its complex pore structure.

[0073] Example 11: Adsorption isotherms of carbon sources in solution by different modified materials 0.05 g of B-LBC was weighed into 50 mL centrifuge tubes, and 30 mL of glucose and glutamic acid solutions with concentrations of 100, 200, 300, 400, 500, and 600 mg / L were added to each tube. Equal volumes of BC, LBC, S-LBC, TS-LBC, and Si-LBC were used as controls. After shaking at 25℃ and 180 r / min for 48 h, the mixture was filtered through a 0.22 μm filter membrane. The residual glucose concentration in the filtrate was determined using the salicylic acid method, and the residual glutamic acid concentration was determined using the ninhydrin method. The adsorption capacity of different materials for different initial carbon source concentrations was then calculated, and Langmuir and Freundlich isotherm adsorption models were fitted. The results are shown in Table 4.

[0074] Table 4. Fitting parameters of the isothermal adsorption model for glucose and glutamic acid in solution by different modified biochars.

[0075] Note: Q m This represents the maximum adsorption capacity. K L 、K F 1 / n represents the adsorption constants of the Langmuir isotherm adsorption model and the Freundlich isotherm adsorption model, respectively, and 1 / n is the adsorption intensity exponent.

[0076] Table 4 shows that the adsorption behaviors of the six modified materials for glucose and glutamic acid exhibit significant differences in model applicability. Regarding glucose adsorption, except for BC, the other materials better fit the Freundlich model, indicating that the adsorption process is dominated by multilayer adsorption. Among them, B-LBC has the highest KF value, indicating its largest adsorption capacity for glucose; while the 1 / n value reflects the adsorption strength and nonlinearity, with Si-LBC having the lowest 1 / n, followed by B-LBC, suggesting that the energy distribution of the adsorption sites in these two materials is relatively uniform, and the adsorption process is closer to linear adsorption. In contrast, in glutamic acid adsorption, all materials generally fit the Langmuir model better than the Freundlich model, indicating that this adsorption is more inclined towards a monolayer mechanism. Although the maximum adsorption capacity of B-LBC is slightly lower than that of LBC, its affinity constant KL is 57.8% higher than that of LBC, indicating that it has a stronger binding affinity for glutamic acid. Further comparison revealed that the maximum adsorption capacity of B-LBC was 30.51%, 3.96%, 20.92%, and 87.00% higher than that of BC, S-LBC, TS-LBC, and Si-LBC, respectively, demonstrating a significantly superior overall adsorption capacity compared to other modified materials.

[0077] In summary, boronic acid-containing hydroxyl groups (B-LBCs) exhibit high adsorption capacity and stable, controllable adsorption behavior in both glucose and glutamate adsorption, demonstrating the best overall performance among the six materials. They are a potential preferred material for organic carbon sequestration in saline-alkali soils. The core of their superior performance lies in the unique properties of borate: the intercalated structure retains abundant adsorption sites, while the "hydroxyl enrichment region" formed by boron hydroxyl groups efficiently captures glucose through hydrogen bonding and enhances its affinity for glutamate through specific interactions with amino and carboxyl groups.

[0078] Example 12: Adsorption effect of different modified materials on carbon sources in solution under saline environment To investigate the effect of salinization conditions on the adsorption performance of the material, a saline solution was prepared using sodium chloride. 17.532 g of NaCl was weighed and diluted to 1 L with 100 mg / L glucose and glutamic acid solutions, respectively, to obtain glucose solutions (conductivity 27.15 mS / cm) and glutamic acid solutions (conductivity 26.97 mS / cm) containing 0.3 mol / L NaCl. 0.05 g of B-LBC was weighed into a 50 mL centrifuge tube, and 30 mL of the above saline solution was added. BC, LBC, S-LBC, TS-LBC, and Si-LBC were used as controls. The mixture was shaken at 25℃ and 180 r / min for 6 h, then filtered through a 0.22 μm filter membrane. The remaining concentration was measured, and the adsorption capacity was calculated. The results are shown below. Figure 4 .

[0079] Depend on Figure 4 As shown in a and b, under saline conditions, the adsorption performance of the six materials for glucose and glutamic acid showed significant differences, with B-LBC exhibiting the best performance in both systems. Regarding glucose adsorption, B-LBC had the highest adsorption capacity, increasing by 332.17% compared to BC; it was slightly higher than LBC, but the difference was not significant; and it increased by 49.75%, 42.57%, and 1.69% compared to S-LBC, TS-LBC, and Si-LBC, respectively. BC and TS-LBC were at a moderate level, while S-LBC had a relatively low adsorption capacity. Regarding glutamic acid adsorption, B-LBC still performed best, increasing by 49.68% compared to BC; and it increased by 6.61%, 51.54%, 79.25%, and 127.37% compared to LBC, S-LBC, TS-LBC, and Si-LBC, respectively. LBC was at a moderate level, BC and S-LBC had relatively low adsorption capacities, and TS-LBC and Si-LBC had the lowest adsorption capacities. B-LBC maintains excellent adsorption performance under saline conditions, mainly due to the specific chemisorption brought about by the introduction of borate. On one hand, the boron hydroxyl functional group can form stable diol complexes with the ortho-hydroxyl groups of glucose, and on the other hand, it can coordinate with the amino and carboxyl groups of glutamic acid. This type of chemisorption exhibits high selectivity and binding energy, thus it is not easily affected by large amounts of Na+ in the solution. + and Cl- The electrostatic shielding effect produced interferes with adsorption. On the other hand, the introduction of borate ions creates a rich porous structure inside the material, increasing the specific surface area and allowing target organic molecules to more effectively contact and bind with the active groups on the material surface. This chemoselective adsorption mechanism enables B-LBC to maintain a high adsorption capacity even in high-salt environments.

[0080] Example 13: The effect of B-LBC composite material on organic carbon in saline soil Topsoil (0-20 cm, salt content 0.32%) from saline-alkali farmland in coastal areas was selected, air-dried, and sieved through a 2 mm sieve. Corn straw biochar was added at 1.0% of the soil mass and mixed thoroughly to serve as the base culture medium. 100 g (dry weight) of the base culture medium was weighed and placed in culture bottles. Four treatments were established: CK (no additive), BC (with 1.0% BC), LBC (with 1.0% LBC composite material), and B-LBC (with 1.0% B-LBC), with each treatment replicated three times. After 60 days of culture, MBC was determined by chloroform fumigation, and SOC content was determined by elemental analysis. The results are shown below. Figure 5 .

[0081] Soil organic carbon accumulation is closely related to microbial activity. MBC, as soil microbial biomass carbon, directly reflects the size and activity of the microbial community. Figure 5 As shown in Figures a and b, the addition of different materials significantly affected the soil MBC and SOC contents. Among them, the B-LBC treatment had the most significant effect, with an MBC content of 0.42 g / kg, which was significantly higher than the CK treatment by 133.33%, higher than the BC treatment by 55.56%, and higher than the LBC treatment by 23.53%. At the same time, the SOC content of the B-LBC treatment also reached the highest, at 14.06 g / kg, which was significantly higher than the CK, BC, and LBC treatments by 79.57%, 38.52%, and 12.66%, respectively.

[0082] Based on the analysis of the adsorption characteristics of glucose and glutamic acid by the B-LBC composite material in this study, the mechanism by which it efficiently enhances organic carbon in saline soil may be as follows: B-LBC, with its unique layered structure and surface properties, exhibits a strong adsorption and enrichment effect on small-molecule organic carbon (such as glucose and amino acids produced by microbial metabolism) in the soil. This "carbon capture" ability directly increases the amount of active organic carbon in the soil, preventing its rapid mineralization loss. Furthermore, the enriched organic carbon provides sufficient carbon and energy sources for microorganisms, significantly stimulating their growth and reproduction, resulting in a significant increase in MBC content. The proliferation of the microbial community further enhances its metabolic transformation function of organic carbon, ultimately leading to a comprehensive increase in SOC content. Therefore, B-LBC effectively promotes the accumulation of organic carbon in saline soil through a cascade effect of "adsorption and retention - microbial drive."

[0083] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of them. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A borate-intercalated magnesium-iron bimetallic oxide composite material, characterized in that, The composite material comprises biochar and a magnesium-iron layered bimetallic oxide with borate intercalation on the surface of the biochar.

2. The method for preparing the borate-intercalated magnesium-iron bimetallic oxide composite material according to claim 1, characterized in that, Includes the following steps: S1. Biomass raw materials are pyrolyzed under a nitrogen protective atmosphere to obtain biochar; S2. Disperse the biochar obtained in step S1 in water, add magnesium salt and iron salt, and carry out a co-precipitation reaction under alkaline conditions to allow layered double hydroxides to grow in situ on the surface of the biochar; then add borate to carry out an intercalation reaction to obtain the precursor composite material. S3. The precursor composite material is calcined to convert the layered double hydroxide into a layered bimetallic oxide, thus obtaining the composite material.

3. The preparation method according to claim 2, characterized in that, In step S1, the pyrolysis temperature is 400~600℃, preferably 500℃; the heating rate is 5~15℃ / min, preferably 10℃ / min; and the pyrolysis time is 1~3 h, preferably 2 h.

4. The preparation method according to claim 2, characterized in that, In step S1, the biomass raw material includes at least one of rice straw, rice husk, corn straw and wheat straw, which is dried, crushed and sieved before use; then pyrolyzed, acid-washed, washed with water until neutral and dried.

5. The preparation method according to claim 2, characterized in that, In step S2, the molar ratio of magnesium salt to iron salt is 2:1 to 4:1, preferably 3:1; the molar ratio of boric acid to total metal ions is 2:1 to 7:1, preferably 5:1, and more preferably nH3BO3:nMg. 2+ nFe 3+ =15:2:1; The coprecipitation reaction is carried out by parallel dropwise addition, in which a mixed salt solution containing magnesium salt and iron salt and a mixed alkaline solution containing sodium hydroxide and sodium carbonate are simultaneously added dropwise to the biochar suspension. After the addition is completed, a borate solution is added dropwise.

6. The preparation method according to claim 2, characterized in that, In step S2, the coprecipitation reaction is carried out at pH 9.5~10.5 and at a reaction temperature of 50~70℃. After stirring, the mixture is placed in a water bath at 60~80℃. After the reaction is completed, the mixture is centrifuged, washed, and dried to obtain the precursor.

7. The preparation method according to claim 2, characterized in that, In step S3, the calcination temperature is 400~600℃, the time is 1~3 h, the heating rate is 5~15℃ / min, the nitrogen atmosphere is used for protection, and the calcined product is sieved.

8. The application of the borate-intercalated magnesium-iron bimetallic oxide composite material according to claim 1 or the borate-intercalated magnesium-iron bimetallic oxide composite material prepared by the preparation method according to any one of claims 2 to 7 in the adsorption of organic carbon.

9. The use of the borate-intercalated magnesium-iron bimetallic oxide composite material according to claim 1 or the borate-intercalated magnesium-iron bimetallic oxide composite material prepared by the preparation method according to any one of claims 2 to 7 in any of the following: (1) Adsorb small molecule organic carbon sources in solution or soil, or prepare products that adsorb glucose and glutamic acid in solution or soil; (2) Improve the organic carbon retention capacity in saline soil, or prepare products that improve the organic carbon retention capacity in saline soil; (3) Reduce the mineralization loss of organic carbon in saline soil, or prepare products that reduce the mineralization loss of organic carbon in saline soil; (4) Increase the carbon content of microbial biomass in saline soil, or prepare products that increase the carbon content of microbial biomass in saline soil.

10. A method for carbon sequestration and improvement of saline soil, characterized in that, The method includes applying the borate-intercalated magnesium-iron bimetallic oxide composite material of claim 1 or the borate-intercalated magnesium-iron bimetallic oxide composite material prepared by the preparation method of any one of claims 2 to 7 to saline soil.

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