Highly dispersible aqueous covalent organic framework soil amendment and its application in saline-alkali soil treatment

Abstract

The application provides a high-dispersibility water-based covalent organic framework soil modifier and application thereof in saline-alkali soil treatment. 2 The porous covalent organic framework material is synthesized from p-phthalaldehyde and sulfonated modified tri(4-aminophenyl)amine monomers; and a surfactant and / or a stabilizer are further added. The porous covalent organic framework material is synthesized from p-phthalaldehyde and sulfonated modified tri(4-aminophenyl)amine monomers, in-situ condensation is performed, and sulfonic acid groups are uniformly introduced, so that the hydrophilicity is improved, good adsorption capacity can be maintained in subsequent drip irrigation, and the nanoscale water dispersion liquid is prepared through subsequent high-pressure homogenization process.

Description

Technical Field

[0001] This invention relates to the fields of soil improvement and agricultural irrigation technology, and particularly to a highly efficient soil conditioner for saline-alkali land and its application method. Specifically, this invention provides a highly dispersible, water-based covalent organic framework soil conditioner and its application in the treatment of saline-alkali land. Background Technology

[0002] Globally, saline-alkali land poses a serious threat to agricultural production and the ecological environment. High concentrations of soluble salts and alkaline substances can damage soil structure, reduce aeration, permeability, and water retention, and have a toxic effect on plant roots, thereby inhibiting their growth. Sodium ions (Na+) are particularly problematic. + The accumulation of saline-alkali soil in the soil exacerbates soil compaction, hinders crop absorption of water and nutrients, and ultimately leads to reduced crop yields or even crop failure. Therefore, the efficient improvement of saline-alkali land is crucial for ensuring food security and improving the ecological environment.

[0003] Traditional methods for improving saline-alkali land include physical methods (such as deep tillage and salt leaching), chemical methods (such as applying gypsum and lime), and biological methods (such as planting salt-tolerant plants or using microorganisms for remediation). However, these methods often have limitations such as high water consumption, long improvement cycles, susceptibility to secondary pollution, or difficulty in maintaining long-term effectiveness, making it difficult to meet the demands of modern agriculture for high efficiency, water conservation, environmental protection, and sustainability.

[0004] Furthermore, studies have shown that covalent organic frameworks (COFs), due to their designable framework, porosity, high specific surface area, and good chemical stability, can selectively adsorb alkaline components such as sodium ions, reducing soil salinity. They also possess tunable pore size and excellent porosity, facilitating the continuous improvement of saline-alkali land. However, traditional COF materials generally suffer from strong hydrophobicity and poor water solubility (or water dispersibility), making them difficult to integrate with modern agricultural water-saving irrigation systems (such as drip irrigation). Forcibly adding unmodified COF powder into drip irrigation lines often leads to material agglomeration, clogging, or a significant decrease in adsorption efficiency. While some literature reports introducing hydrophilic groups to enhance the aqueous dispersibility of COF materials, this often sacrifices some of the porous framework stability or adsorption capacity of the COF, making it difficult to maintain good dispersion and anti-clogging performance in large-scale drip irrigation applications over the long term.

[0005] To overcome the problems of COF materials' easy aggregation and clogging in aqueous environments, some technical solutions have proposed introducing hydrophilic groups such as hydroxyl, carboxyl, and sulfonic acid groups onto the COF framework to enhance its affinity in water; or using mechanical force to reduce particle size, increase surface area, and improve dispersion stability through high-pressure homogenization or ultrasonic dispersion. However, surface hydrophilic modification alone may weaken the stability of the internal COF framework or reduce porosity, and simple high-pressure homogenization can easily lead to partial pore collapse or framework damage, resulting in a decrease in adsorption capacity. Summary of the Invention

[0006] This invention creatively synthesizes a porous covalent organic framework material (COF) from terephthalaldehyde and a sulfonated tris(4-aminophenyl)amine monomer. In-situ condensation uniformly introduces -SOH groups, which not only improves hydrophilicity but also maintains good adsorption capacity in subsequent drip irrigation. The COF is then prepared into a nanoscale aqueous dispersion through a high-pressure homogenization process. Furthermore, the uniform introduction of sulfonated modification groups effectively enhances the hydrophilicity and ion exchange sites of the COF, enabling high-pressure homogenization to significantly reduce particle size while maximally preserving the pore structure and adsorption capacity of the framework during nano-sizing.

[0007] This invention first provides a highly dispersible, water-based, covalently organic framework soil conditioner, which is formed by the following components:

[0008] Porous covalent organic framework materials with a particle size of 50-500 nm, preferably 100-400 nm, more preferably 100-300 nm, and a specific surface area greater than 20 m². 2 / g, preferably greater than 300m 2 / g, more preferably greater than 500m 2 / g, and the porous covalent organic framework material is synthesized from terephthalaldehyde and sulfonated tris(4-aminophenyl)amine monomer;

[0009] Surfactants and / or stabilizers.

[0010] Preferably, the covalent organic framework material is prepared by reacting terephthalaldehyde with sulfonated tris(4-aminophenyl)amine (TAPA), wherein the degree of sulfonation of the tris(4-aminophenyl)amine (TAPA) is controlled at 2-3 sulfonic acid groups per molecule, more preferably 2-2.5. A moderate degree of sulfonation enhances the hydrophilicity of the COF material and its ion exchange adsorption capacity for positively charged salt and alkali ions, while also avoiding excessive occupancy of the COF channels, ensuring the material's high specific surface area and structural stability. This feature is also a technical characteristic that synergizes with the high-pressure homogenization step in the preparation process.

[0011] Preferably, the surfactant is a Tween series (e.g., Tween 80, Tween 40, Tween 60, etc.), sodium dodecyl sulfate (SDS), or a combination thereof; the stabilizer includes sodium polyacrylate, xanthan gum, disodium EDTA, a hydrophilic polymer, or a combination thereof; the hydrophilic polymer includes polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), sodium carboxymethyl cellulose (CMC-Na), or a combination thereof. The amount of surfactant and stabilizer used is 0.5-5 wt%, preferably 1-2 wt%, of the mass of the covalent organic framework material, respectively. Adding a Tween series surfactant reduces surface tension and improves the wettability and dispersibility of COF-1 particles in water; adding sodium polyacrylate and disodium EDTA as stabilizers prevents COF-1 particle aggregation through electrostatic repulsion, thus improving the stability of the dispersion; adding polyvinylpyrrolidone (PVP) as a hydrophilic polymer also improves the stability of the dispersion. Preferably, the amount of surfactant used is...

[0012] Preferably, the mass fraction of the covalent organic framework material synthesized from the sulfonated tri(4-aminophenyl)amine (TAPA) monomer is 0.1-50 wt%, preferably 1-30 wt%, of the total mass of the modifier; and preferably, the preparation of the modifier includes the step of mixing the porous covalent organic framework material with a surfactant and / or a stabilizer, and then subjecting it to high-pressure homogenization to form an aqueous dispersion.

[0013] The present invention also provides a method for preparing the aforementioned nanoporous covalent organic framework soil conditioner capable of forming an aqueous dispersion, comprising the following steps:

[0014] 1) Porous covalent organic framework materials were prepared by reacting terephthalaldehyde with sulfonated tris(4-aminophenyl)amine (TAPA);

[0015] 2) The covalent organic framework material obtained in step 1) is mixed with a surfactant and / or stabilizer in an aqueous dispersion system;

[0016] 3) Perform high-pressure homogenization to nanoscale the covalent organic framework material and form a stable aqueous dispersion, or optionally dry the aqueous dispersion into powder.

[0017] In the aqueous dispersion, the average particle size is less than 500 nm, preferably less than 300 nm, and the PDI is less than 0.3.

[0018] Preferably, the preparation of porous covalent organic framework materials includes the following steps:

[0019] A) Preparation of sulfonated modified tris(4-aminophenyl)amine;

[0020] B) The sulfonated tri(4-aminophenyl)amine was dissolved in a mixed solvent of an inert solvent and water to prepare a solution of the sulfonated tri(4-aminophenyl)amine.

[0021] C) Add terephthalaldehyde to a solution of sulfonated tris(4-aminophenyl)amine to obtain a mixed reaction solution, and adjust the pH value to 3-6.5, preferably 3-4, and more preferably, adjust the pH value by adding acetic acid;

[0022] D) The aforementioned mixed reaction solution was added to a hydrothermal reactor to carry out a hydrothermal reaction to obtain the crude product of the porous covalent organic framework material.

[0023] E) The crude product is post-processed to obtain a powdered porous covalent organic framework material.

[0024] Preferably, step A) of preparing sulfonated tri(4-aminophenyl)amine includes dissolving tri(4-aminophenyl)amine in concentrated sulfuric acid and reacting it in a constant temperature water bath at 55-65°C for 3-5 hours. This ensures that the degree of sulfonation of the tri(4-aminophenyl)amine (TAPA) is controlled at 2-3 sulfonic acid groups per molecule, preferably 2-2.5 sulfonic acid groups. This facilitates a balance between the number of hydrophilic sites and the retention of pores after high-pressure homogenization, thereby achieving better saline-alkali land improvement.

[0025] Preferably, in the hydrothermal reaction of step D), the temperature is 80-90℃ and the reaction time is 60-80 hours.

[0026] Preferably, the high-pressure homogenization pressure is 1200-1500 bar, and the process is repeated 3-10 times under this pressure to obtain a particle size distribution between 50-700 nm and a specific surface area greater than 20 m². 2 / g of water-dispersible COF material.

[0027] Preferably, the post-processing step F) includes sequentially performing three anhydrous tetrahydrofuran washes, three washes with a mixed solvent of tetrahydrofuran and water, and three water washes. Thus, the anhydrous tetrahydrofuran wash removes unreacted terephthalaldehyde, byproducts, and residual DMSO solvent; the mixed solvent wash gradually replaces the solvent within the COF channels with water; and finally, water washing thoroughly removes THF and salt impurities.

[0028] Furthermore, this invention also provides a method for treating saline-alkali land, wherein the aforementioned highly dispersible aqueous covalent organic framework soil conditioner is formulated into an aqueous solution and applied to the saline-alkali soil through a drip irrigation system to adsorb and slowly release saline-alkali components, reduce soil salinity and alkalinity, and improve the crop growth environment. The concentration of COF material in the aqueous dispersion is 0.1-5 g / L.

[0029] The present invention also provides the application of the aforementioned highly dispersible waterborne covalent organic framework soil conditioner or the soil conditioner prepared by the aforementioned method in the treatment of saline-alkali land.

[0030] In practical application, the COF amendment of this invention is typically applied to drip irrigation before sowing or in the early stages of crop growth. The application frequency and single application amount should be flexibly adjusted based on soil salinity, crop type, and growth stage. Applying small amounts multiple times can ensure uniform distribution and sustained effectiveness. The COF amendment can also be mixed with water-soluble fertilizers for fertigation, but compatibility testing is necessary beforehand to avoid chemical reactions or precipitation. To maintain the efficiency of the drip irrigation system, pipes and drippers need to be cleaned regularly to prevent particle accumulation. To address situations where water sources have excessively high impurities or metal ion content in some areas, a very small amount of EDTA-Na2 (e.g., 0.1 g / 100 mL) can be selectively added as a chelating agent to further reduce the impact of impurities and improve the dispersibility and stability of the amendment. The additional sodium ion content introduced is negligible.

[0031] To enhance the soil permeability of the soil conditioner and ensure sufficient contact with saline-alkali components, moderate soil tillage or harrowing can be performed before drip irrigation. After drip irrigation, the irrigation volume should be carefully controlled to allow the COF nanoparticles to exert a more efficient adsorption and slow-release effect in the root zone. Combining this with other common agronomic practices, such as increasing the application of organic fertilizer and planting salt-tolerant crops, can further improve the conditioner's effectiveness. After a certain application period, the conditioner's effectiveness should be dynamically evaluated by monitoring soil pH, salinity, and sodium ion content, and crop growth (such as plant height, leaf area, and yield) should be observed.

[0032] At the material preparation level, this invention disperses the synthesized sulfonated COF material into an aqueous system after preliminary drying or washing using a high-pressure homogenization process. The strong shear force, impact force, and cavitation effect generated by high-pressure homogenization effectively break down the micro-agglomerates of the COF material, reducing its particle size to 50-700 nm (preferably 100-500 nm) while maintaining a specific surface area greater than 20 m². 2 / g is more conducive to maintaining the integrity of the porous framework structure of COF materials, ensuring that they maintain efficient ion adsorption performance during drip irrigation. At the formulation optimization level, this invention employs a carefully formulated additive system to further improve the long-term dispersion stability of sulfonated COF nanoparticles in aqueous media and reduce the potential risk of pore collapse. Surfactants (e.g., Tween series, sodium dodecyl sulfate) form an adsorption layer on the surface of COF nanoparticles, reducing surface energy and effectively preventing particle aggregation; stabilizers (e.g., sodium polyacrylate, xanthan gum, or optional chelating agent EDTA-Na2) further prevent particle agglomeration through electrostatic or steric hindrance effects and can chelate metal ion impurities in aqueous solutions, improving the stability of the dispersion; hydrophilic polymers (e.g., polyethylene glycol PEG, polyvinylpyrrolidone PVP, sodium carboxymethyl cellulose CMC-Na) enhance the affinity between COF nanoparticles and water molecules through hydrogen bonding or electrostatic interactions with hydrophilic groups such as sulfonic acid groups on the surface of the sulfonated COF framework, forming a stable aqueous dispersion system.

[0033] Beneficial effects

[0034] The covalent organic framework (COF) material prepared in this invention, due to its inherently high specific surface area and porous skeleton, can efficiently adsorb sodium ions, chloride ions, and other saline-alkali components in the soil, significantly reducing salinity. Preferably, sulfonation modification and high-pressure homogenization effectively balance the hydrophilicity and porosity of the material: on the one hand, the sulfonic acid group (-SO)H enhances the selective adsorption capacity for target ions and reduces the loss of other minerals; on the other hand, the nanoscale particle morphology has better dispersibility and migration ability in the drip irrigation system, enabling it to more fully contact and exert its effect with soil saline-alkali ions.

[0035] The soil conditioner of this invention can be uniformly dispersed in drip irrigation systems, effectively preventing pipe and dripper blockage. Simultaneously, the sulfonated COF material exhibits higher selective adsorption capacity and adsorption capacity for sodium ions and other saline ions, effectively reducing soil salinity, improving the efficiency of saline-alkali land improvement, and creating a more suitable soil environment for crop growth.

[0036] In a preferred embodiment, the present invention further incorporates refined synergistic design and optimization in terms of monomer sulfonation degree, high-pressure homogenization process parameters (e.g., homogenization pressure of 1200-1500 bar), and additive formulation. This further enhances the effectiveness of COF materials in reducing soil pH and salinity. Attached Figure Description

[0037] Figure 1 Infrared spectra of the raw materials, intermediate products and product COF-1 used in Example 1.

[0038] Figure 2XRD characterization diagrams of COF-1 synthesized in Example 1 and COF-2 synthesized in Example 2.

[0039] Figure 3 Scanning electron microscope (SEM) images of COF-1 synthesized in Example 1 and COF-2 synthesized in Example 2. Detailed Implementation

[0040] Method for testing sodium ion adsorption capacity: Static equilibrium adsorption method.

[0041] Example 1

[0042] (1) Sulfonation modification of TAPA

[0043] 1 g of TAPA was dissolved in 10 mL of concentrated sulfuric acid and placed in a constant temperature water bath at 60 °C with continuous stirring for 4 hours. After the reaction was complete, the reaction solution was slowly poured into a beaker containing a large amount of ice water and stirred vigorously to promote the complete precipitation of sulfonated TAPA product. The precipitated solid was collected by vacuum filtration using a Buchner funnel, and the filter cake was repeatedly washed with deionized water until the pH of the washing solution was neutral to completely remove residual sulfuric acid. Finally, the washed solid was placed in a vacuum drying oven and dried at 60 °C to constant weight to obtain sulfonated TAPA. The degree of sulfonation of the obtained sulfonated TAPA was determined by elemental analysis, and the average number of sulfonic acid groups per molecule of TAPA was 2.3.

[0044] (2) Synthesis of COF materials

[0045] a) Solution preparation

[0046] Weigh 1.377g of sulfonated TAPA and slowly add it to a mixed solvent consisting of 40mL of dimethyl sulfoxide (DMSO) and 10mL of deionized water. Stir continuously with a magnetic stirrer until the sulfonated TAPA is completely dissolved or uniformly dispersed in the solution to form a sulfonated TAPA solution.

[0047] b) Adding ingredients and adjusting pH

[0048] Weigh 1.074 g of terephthalaldehyde and slowly add it to the above sulfonated TAPA solution while continuously stirring to obtain a mixed reaction solution. Subsequently, adjust the pH of the reaction system to 3.5 using a 12 mol / L acetic acid solution.

[0049] c) Condensation reaction

[0050] Transfer the prepared reaction mixture to a 100mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene (PTFE), and tighten the seal. Place the reactor in an oven, set the temperature to 80℃, and continue the reaction for 72 hours.

[0051] d) Post-processing

[0052] After the reaction was complete, the reactor was removed from the oven and allowed to cool naturally to room temperature. The reactor was then opened, and the mixture was separated into solid and liquid phases using a vacuum filtration device, collecting the solid product (filter cake). To thoroughly remove any remaining unreacted monomers, oligomers, and solvent, the filter cake was transferred to a beaker, and 100 mL of anhydrous tetrahydrofuran (THF) was added. The mixture was stirred thoroughly on a magnetic stirrer for 30 minutes, followed by filtration. This step was repeated three times to remove unreacted terephthalaldehyde, byproducts, and residual DMSO solvent. Next, the mixture was washed sequentially with mixed solvents of THF / water at volume ratios of 3:1, 1:1, and 1:3, using 100 mL of the mixed solvent each time and stirring for 30 minutes before filtration, to gradually replace the solvent in the COF channels with water. Finally, the mixture was washed three times with 100 mL of deionized water to thoroughly remove THF and salt impurities. The washed filter cake was transferred to a vacuum drying oven and dried at 60°C for 12 hours to obtain sulfonated modified COF material powder (i.e., COF-1 powder).

[0053] Tests showed that the average particle size of COF-1 powder was approximately 230 nm, and its specific surface area was 550 m². 2 / g.

[0054] also, Figure 1 The infrared spectra of the raw materials and products used in Example 1 are shown, from top to bottom: terephthalaldehyde, sulfonated tris(4-aminophenyl)amine (TAPA), and the final condensed COF-1. The main absorption peaks of each spectrum are analyzed below:

[0055] 1. Spectrum of terephthalaldehyde

[0056] At a wavenumber of approximately 1676 cm⁻¹ -1 Nearby, a distinct aldehyde (C=O) characteristic absorption peak is visible, which is due to the carbon-oxygen double bond in the terephthalaldehyde molecule. Additionally, at approximately 830 cm⁻¹... -1 The characteristic absorption peak corresponding to the aromatic ring indicates its aromatic skeleton structure.

[0057] 2. Spectrum of sulfonated TAPA

[0058] Compared to unsulfonated TAPA, sulfonated TAPA exhibits better performance at wavenumbers of 3300–3400 cm⁻¹. -1 The N–H stretching vibration peak is still visible in the region, but its morphology has changed, its intensity has weakened, and the peak shape has broadened. This may be due to the sulfonation reaction consuming some of the amino group, and the introduction of the sulfonic acid group altering the vibrational environment of the NH bond. More importantly, at 1034 cm⁻¹... -1 and 1180cm -1 Symmetric and asymmetric stretching vibration peaks of the S=O bond were observed nearby, as well as at 683 cm⁻¹. -1Stretching vibration peaks of SO bonds were observed nearby, which are characteristic absorption peaks of sulfonic acid groups (-SO3H). Meanwhile, the aromatic ring skeleton showed peaks at 1500–1600 cm⁻¹. -1 Typical vibrational peaks can still be detected in the region, indicating that TAPA has successfully introduced sulfonic acid groups and maintained the basic characteristics of the aromatic ring skeleton.

[0059] 3. Final synthesized COF spectrum

[0060] Compared to terephthalaldehyde and sulfonated TAPA, the COF sample at 1622 cm⁻¹ -1 The presence of a characteristic absorption peak for the C=N bond nearby indicates that a Schiff base condensation reaction occurred between the two, successfully forming an imine bond. Meanwhile, sulfonated TAPA showed an absorption peak at 3300-3400 cm⁻¹. -1 The NH absorption peak intensity at 1034 cm⁻¹ decreased significantly, and its position shifted, indicating that some amino groups participated in the condensation reaction, forming C=N bonds. -1 and 1180cm -1 The characteristic absorption peak of the S=O bond can still be observed nearby, as well as at 683 cm⁻¹. -1 Stretching vibration peaks of SO bonds were observed nearby, but the peak shape and intensity varied, which may be due to the influence of the COF framework formation on the vibrational environment of the sulfonic acid groups. Peaks were observed at 1300–1400 cm⁻¹. -1 New vibrational peaks were also observed in the region, further confirming the formation of the COF framework and the synergistic effect between the sulfonated groups and the backbone.

[0061] (3) Preparation of soil conditioner (aqueous dispersion)

[0062] To prepare a stable aqueous dispersion of COF-1 powder, it is necessary to perform nano-processing using high-pressure homogenization technology and to improve its dispersion stability by adding additives.

[0063] a) Redisperse 1g of the COF-1 powder prepared and dried in step (2) in 100mL of deionized water, and use ultrasonic treatment for 10-20 minutes to assist dispersion to obtain an aqueous dispersion of COF-1.

[0064] b) Add 1% Tween 80 (by mass of COF-1), 2% sodium polyacrylate (by mass of COF-1), and 2% polyvinylpyrrolidone (PVP) (by mass of COF-1) to the aqueous dispersion of COF-1 obtained in step a), mix, and obtain a COF-1 suspension.

[0065] c) The COF-1 suspension was subjected to a high-pressure homogenizer and circulated 5 times at 1200 bar to obtain a stable COF-1 aqueous dispersion, which is also the aqueous dispersion of highly dispersible aqueous covalent organic framework soil conditioner I. During homogenization, the temperature of the suspension was controlled at 25-30℃.

[0066] The particle size distribution of the aqueous dispersion of soil conditioner I was determined using a laser particle size analyzer. The average particle size was 150 nm, and the PDI was 0.2, indicating that the COF-1 particles were dispersed in the aqueous dispersion at the nanoscale. The aqueous dispersion of soil conditioner I was allowed to stand for 24 hours, and its stability was observed; no obvious sedimentation or stratification was observed. This demonstrates that the soil conditioner I obtained in Example 1 has good stability and is not prone to clogging drip irrigation equipment.

[0067] Alternatively, the aqueous dispersion of soil conditioner I can be dried into powder using freeze-drying. The redispersibility of the dried powder was tested by redispersing it in water and then ultrasonically treating it for 10-20 minutes to aid dispersion. The particle size was measured using a laser particle size analyzer. The results showed an average particle size of 180 nm and a PDI of 0.25, indicating good dispersibility. This demonstrates that even when prepared as powder, soil conditioner I of this invention remains stable and will not clog drip irrigation equipment when reconstituted into an aqueous dispersion. This may be because, specifically for the porous framework material synthesized from terephthalaldehyde and sulfonated tris(4-aminophenyl)amine monomers, surfactants and stabilizers synergistically improve the agglomeration properties of the nanoparticles.

[0068] Example 2

[0069] (1) Sulfonation modification of TAPA

[0070] 1 g of TAPA was dissolved in 10 mL of concentrated sulfuric acid and placed in a constant temperature water bath at 60 °C with continuous stirring for 4 hours. After the reaction was complete, the reaction solution was slowly poured into a beaker containing a large amount of ice water and stirred vigorously to promote the complete precipitation of sulfonated TAPA product. The precipitated solid was collected by vacuum filtration using a Buchner funnel, and the filter cake was repeatedly washed with deionized water until the pH of the washing solution was neutral to completely remove residual sulfuric acid. Finally, the washed solid was placed in a vacuum drying oven and dried at 60 °C to constant weight to obtain sulfonated TAPA. The degree of sulfonation of the obtained sulfonated TAPA was determined by elemental analysis, and the average number of sulfonic acid groups per molecule of TAPA was 2.3.

[0071] (2) Synthesis of COF materials

[0072] e) Solution preparation

[0073] Weigh 1.377g of sulfonated TAPA and slowly add it to a mixed solvent consisting of 40mL of dimethyl sulfoxide (DMSO) and 10mL of deionized water. Stir continuously with a magnetic stirrer until the sulfonated TAPA is completely dissolved or uniformly dispersed in the solution to form a sulfonated TAPA solution.

[0074] f) Adding ingredients and adjusting pH

[0075] Weigh 1.074 g of terephthalaldehyde and slowly add it to the above sulfonated TAPA solution while stirring continuously to obtain a mixed reaction solution. Subsequently, adjust the pH of the reaction system to 6.0 using a 12 mol / L acetic acid solution.

[0076] g) Condensation reaction

[0077] Transfer the prepared reaction mixture to a 100mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene (PTFE), and tighten the seal. Place the reactor in an oven, set the temperature to 80℃, and continue the reaction for 72 hours.

[0078] h) Post-processing

[0079] After the reaction was complete, the reactor was removed from the oven and allowed to cool naturally to room temperature. The reactor was then opened, and the mixture was separated into solid and liquid phases using a vacuum filtration device, collecting the solid product (filter cake). To thoroughly remove any remaining unreacted monomers, oligomers, and solvent, the filter cake was transferred to a beaker, and 100 mL of anhydrous tetrahydrofuran (THF) was added. The mixture was stirred thoroughly on a magnetic stirrer for 30 minutes, followed by filtration. This step was repeated three times to remove unreacted terephthalaldehyde, byproducts, and residual DMSO solvent. Next, the mixture was washed sequentially with mixed solvents of THF / water at volume ratios of 3:1, 1:1, and 1:3, using 100 mL of the mixed solvent each time and stirring for 30 minutes before filtration, to gradually replace the solvent in the COF channels with water. Finally, the mixture was washed three times with 100 mL of deionized water to thoroughly remove THF and salt impurities. The washed filter cake was transferred to a vacuum drying oven and dried at 60°C for 12 hours to obtain sulfonated modified COF material powder (i.e., COF-2 powder).

[0080] Tests showed that the average particle size of the COF-2 powder was approximately 400 nm, and its specific surface area was 450 m². 2 / g.

[0081] (3) Preparation of soil conditioner (aqueous dispersion)

[0082] a) Redisperse 1g of the COF-2 powder prepared and dried in step (2) in 100mL of deionized water. The dispersion can be aided by ultrasonic treatment for 10-20 minutes to obtain an aqueous dispersion of COF-2.

[0083] b) Add 1% Tween 80 (by mass of COF-2), 2% sodium polyacrylate (by mass of COF-2), and 2% polyvinylpyrrolidone (PVP) (by mass of COF-2) to the aqueous dispersion of COF-2, mix, and obtain a COF-2 suspension.

[0084] c) The mixed COF-2 suspension was subjected to a high-pressure homogenizer and circulated 5 times at 1200 bar to obtain a stable COF-2 aqueous dispersion, namely, an aqueous dispersion of highly dispersible aqueous covalent organic framework soil conditioner II. During homogenization, the temperature of the suspension was controlled at 25-30℃.

[0085] The particle size distribution of the aqueous dispersion of soil conditioner II was determined using a laser particle size analyzer. The average particle size of COF-2 was 250 nm, and the PDI was 0.22. The aqueous dispersion of soil conditioner II was allowed to stand for 24 hours to observe its stability; no obvious sedimentation or stratification was observed. This indicates that the soil conditioner II obtained in Example 2 has good stability and is not prone to clogging drip irrigation equipment.

[0086] Alternatively, the aqueous dispersion of soil conditioner II can be dried into powder using freeze-drying. The redispersibility of the dried COF-2 powder was tested by redispersing it in water and then ultrasonically treating it for 10-20 minutes to aid dispersion. The particle size was measured using a laser particle size analyzer. The results showed an average particle size of 280 nm and a PDI of 0.28, indicating good dispersibility. This demonstrates that even when prepared as powder, soil conditioner II of this invention remains stable and will not clog drip irrigation equipment when reconstituted into an aqueous dispersion as needed.

[0087] The difference between Example 1 and Example 2 lies in the pH value during the COF synthesis process. As mentioned above, COF powder with the particle size and surface area requirements of this invention can be obtained at pH values ​​of 3.5 and 6.0, but with slight differences. For further analysis and comparison, the inventors further analyzed the XRD patterns and electron micrographs, as detailed below.

[0088] Figure 2 The XRD (X-ray diffraction) patterns of two COF materials prepared according to Example 1 (COF-1) and Example 2 (COF-2) of the present invention are shown. According to the embodiments of the present invention, the catalyst dosage during the synthesis of COF-1 was relatively high (0.7 mL 12 mol / L acetic acid), while the catalyst dosage during the synthesis of COF-2 was relatively low (0.1 mL 12 mol / L acetic acid), and the two exhibited certain differences in crystal structure and crystallinity.

[0089] As shown in the figure, COF-1 exhibits a strong and clear diffraction peak near 2θ≈21°, indicating a higher degree of order and relatively good crystallinity in its framework. In contrast, the same peak position of COF-2 is slightly shifted or the peak intensity is weakened, suggesting that insufficient catalyst dosage may lead to incomplete framework nucleation or slower growth, resulting in a decrease in local order and slightly lower crystallinity. Therefore, the amount of catalyst has a significant impact on the crystal structure characteristics of COF materials.

[0090] Figure 3 The COF-1 prepared according to Example 1 is shown. Figure 3 (A), (B)) and COF-2 prepared according to Example 2 ( Figure 3 Scanning electron microscope (SEM) images (C) and (D). Both COF materials exhibit a dense spherical or quasi-spherical particle structure with a particle size of approximately 200-600 nm. However, COF-1 particles are generally smaller and more uniform (approximately 200-300 nm), while COF-2 particles are slightly larger (approximately 400-500 nm) and have a relatively wider particle dispersion, which corresponds to the differences in framework nucleation rate and crystallinity revealed by XRD tests.

[0091] As seen in the SEM images, COF-1 exhibits a relatively concentrated distribution of microparticles with a dense surface, suggesting that its pore structure can be further preserved during subsequent nano-sizing (e.g., high-pressure homogenization). In contrast, COF-2, due to less catalyst, a slower condensation rate, and a longer particle development time, results in larger particle sizes and a slightly wider size dispersion. Even so, COF-2 still maintains a basic spherical framework and can be refined into a more stable nano-dispersion through subsequent shear dispersion methods (e.g., high-pressure homogenization).

[0092] Example 3

[0093] Other conditions are the same as in Example 1, except that in the sulfonation modification step of TAPA:

[0094] 1 g of TAPA was dissolved in 10 mL of concentrated sulfuric acid and placed in a constant temperature water bath. The mixture was stirred continuously at 70 °C for 4 hours. The degree of sulfonation of the obtained sulfonated TAPA was determined by elemental analysis. On average, each molecule of TAPA contained 3 sulfonic acid groups.

[0095] The sulfonated COF material powder obtained in this embodiment is defined as COF-3 powder. The resulting soil conditioner is defined as soil conditioner III.

[0096] Tests showed that the average particle size of COF-3 powder was approximately 220 nm, and its specific surface area was 470 m². 2 / g. Compared with Example 1, although the average particle size was reduced, the specific surface area was reduced more significantly. This may be because the porosity decreased after the degree of sulfonation was increased.

[0097] Example 4

[0098] Other conditions are the same as in Example 1, except that steps b) and c) of preparing the soil conditioner are different.

[0099] b) Add 1% by mass of Tween 80 and 2% by mass of polyvinylpyrrolidone (PVP) to the aqueous dispersion of COF-1 obtained in step a), mix, and obtain COF-5 suspension.

[0100] c) The COF-5 suspension was circulated 5 times under a high-pressure homogenizer at 1200 bar to obtain a stable COF-5 aqueous dispersion, which is also the aqueous dispersion of the highly dispersible aqueous covalent organic framework soil conditioner IV. During homogenization, the temperature of the suspension was controlled at 25-30℃.

[0101] The particle size distribution of the aqueous dispersion of soil conditioner IV was determined using a laser particle size analyzer. The average particle size was 155 nm, and the PDI was 0.2, indicating that the COF-1 particles were dispersed in the aqueous dispersion at the nanoscale. The aqueous dispersion of soil conditioner IV was allowed to stand for 24 hours, and its stability was observed; no significant sedimentation or stratification was observed. This demonstrates that the soil conditioner IV obtained in Example 4, when directly prepared as an aqueous dispersion, exhibits good stability and is less likely to clog drip irrigation equipment.

[0102] In addition, the aqueous dispersion of soil conditioner IV was dried into powder using a freeze-drying method. The redispersibility of the dried soil conditioner IV powder was tested by redispersing it in water and then ultrasonically treating it for 10-20 minutes to aid dispersion. The particle size was measured using a laser particle size analyzer. The results showed that the average particle size was 280 nm, the PDI was 0.28, and the dispersibility remained good. This indicates that even when prepared as powder, soil conditioner IV of the present invention can be reconstituted into an aqueous dispersion when needed, maintaining good stability and not clogging drip irrigation equipment. However, the particle size was significantly larger than in Example 1, and the dispersibility index also increased.

[0103] Comparative Example 1

[0104] The other conditions are the same as in Example 1, except that the sulfonation modification step of TAPA is different:

[0105] 1 g of TAPA was dissolved in 10 mL of concentrated sulfuric acid and placed in a constant temperature water bath. The mixture was stirred continuously at 70 °C for 4 hours. The degree of sulfonation of the obtained sulfonated TAPA was determined by elemental analysis, and the average number of sulfonic acid groups per TAPA molecule was 1.5.

[0106] The sulfonated COF material powder obtained in this embodiment is defined as COF-5 powder. The resulting soil conditioner is defined as soil conditioner V.

[0107] Tests showed that the average particle size of COF-5 powder was approximately 350 nm, and its specific surface area was 360 m². 2 / g. Compared with Example 1, the average particle size increased and the specific surface area decreased significantly.

[0108] Preparation of soil conditioner (aqueous dispersion)

[0109] To prepare a stable aqueous dispersion of COF-5 powder, it is necessary to perform nano-processing using high-pressure homogenization technology and to improve its dispersion stability by adding additives.

[0110] a) Redisperse 1g of the COF-5 powder prepared and dried in step (2) in 100mL of deionized water, and use ultrasonic treatment for 10-20 minutes to assist dispersion to obtain an aqueous dispersion of COF-5.

[0111] b) Add 1% Tween 80 (by mass of COF-5), 2% sodium polyacrylate (by mass of COF-5), and 2% polyvinylpyrrolidone (PVP) (by mass of COF-5) to the aqueous dispersion of COF-5 obtained in step a), mix, and obtain a COF-5 suspension.

[0112] c) The COF-5 suspension was processed five times using a high-pressure homogenizer at 1200 bar to obtain an aqueous dispersion of COF-5, which is also the aqueous dispersion of aqueous covalent organic framework soil conditioner V. During homogenization, the temperature of the suspension was controlled at 25-30℃.

[0113] The particle size distribution of the aqueous dispersion of soil conditioner V was determined using a laser particle size analyzer. The average particle size was 200 nm, and the PDI was 0.5, indicating that the COF-5 particles were dispersed in the aqueous dispersion at the nanoscale. The aqueous dispersion of soil conditioner V was allowed to stand for 24 hours, and its stability was observed; no obvious sedimentation or stratification was observed. This indicates that the soil conditioner V obtained in Example 1 has good stability and is not prone to clogging drip irrigation equipment, but its dispersibility is poor.

[0114] Alternatively, the aqueous dispersion of soil conditioner V can be dried into powder using freeze-drying. The redispersibility of the dried powder was tested by redispersing it in water and then ultrasonically treating it for 10-20 minutes to aid dispersion. The particle size was measured using a laser particle size analyzer, showing an average particle size of 280 nm and a PDI of 0.55. When needed, it can be reconstituted into an aqueous dispersion. However, some clogging of the drip irrigation equipment occurred in the later stages of the drip irrigation process, possibly due to partial agglomeration of nanoparticles, resulting in some large particles causing blockage.

[0115] Application Example 1

[0116] Saline-alkali soil with an initial pH of 8.2 and a salt content of approximately 1.5% was selected. Wheat was used as the experimental crop, and an experimental group with soil conditioner applied and a control group with deionized water applied only were set up.

[0117] The soil conditioner used in the experimental group was an aqueous dispersion of soil conditioner I prepared in Example 1, with a COF-1 concentration of 2 g / L. It was applied using a laboratory-simulated drip irrigation system, once a week, with 200 mL of conditioner solution applied to each wheat seedling each time. The wheat seedlings in the control group were irrigated using the same drip irrigation method, but with the same amount of deionized water.

[0118] Before the formal application of the soil conditioner, a rigorous compatibility test was conducted on the drip irrigation system. The system used a 120-mesh disc filter and was equipped with pressure-compensated drippers. Test results showed that the aqueous dispersion of soil conditioner I exhibited good flowability in the system, and no dripper or filter clogging was observed throughout the entire irrigation process. The drip flow rate remained consistently at 8 L / h.

[0119] After one month of continuous application of the soil conditioner, soil samples were taken from the experimental field for analysis. The results showed that the pH value of the soil in the experimental group significantly decreased to 7.6, and the soil salinity also decreased from the initial 1.5% to 0.9%. Simultaneously, the growth of wheat seedlings was monitored. The results showed that, compared with the control group, the average plant height of wheat seedlings treated with the soil conditioner of Example 1 increased by approximately 25%, and the chlorophyll content of leaves also increased by approximately 15%. These data strongly demonstrate that the conditioner I prepared in this invention can significantly alleviate salt-alkali stress, effectively reduce soil salinity, and significantly promote the healthy growth of crops in saline-alkali environments.

[0120] Application Example 2

[0121] Saline-alkali soil with an initial pH of 8.2 and a salt content of approximately 1.5% was selected. Wheat was used as the experimental crop, and an experimental group with soil conditioner applied and a control group with deionized water applied only were set up.

[0122] The soil conditioner used in the experimental group was an aqueous dispersion of soil conditioner II prepared in Example 2, with a COF-1 concentration of 2 g / L. It was applied using a laboratory-simulated drip irrigation system, once a week, with 200 mL of conditioner solution applied to each wheat seedling each time. The wheat seedlings in the control group were irrigated using the same drip method, but with the same amount of deionized water.

[0123] Before the formal application of the soil conditioner, rigorous compatibility testing was conducted on the drip irrigation system. The system used a 120-mesh disc filter and was equipped with pressure-compensated drippers. Test results showed that the aqueous dispersion of soil conditioner II exhibited good flowability in the system, and no dripper or filter clogging was observed throughout the entire irrigation process. The drip flow rate remained consistently at 8 L / h.

[0124] One month after continuous application of the soil conditioner, soil samples were taken from the experimental field for analysis. The results showed that the pH value of the soil in the experimental group significantly decreased to 7.8, and the soil salinity also decreased from the initial 1.5% to 1.0%. Simultaneously, the growth of wheat seedlings was monitored. The results showed that, compared with the control group, the average plant height of wheat seedlings treated with the soil conditioner from Example 2 increased by approximately 20%, and the chlorophyll content in the leaves also increased by approximately 13%. These data strongly demonstrate that the sulfonated COF conditioner prepared in this invention can significantly alleviate salt-alkali stress, effectively reduce soil salinity, and significantly promote the healthy growth of crops in saline-alkali environments.

[0125] Comparative Application Example 1

[0126] Saline-alkali soil with an initial pH of 8.2 and a salt content of approximately 1.5% was selected. Wheat was used as the experimental crop, and an experimental group was set up with COF amendment and a control group with deionized water only.

[0127] The COF amendment used in the experimental group was an aqueous dispersion of soil amendment V prepared in Comparative Example 1, with a COF-5 concentration of 2 g / L. It was applied using a laboratory-simulated drip irrigation system, once a week, with 200 mL of the amendment solution applied to each wheat seedling each time. The wheat seedlings in the control group were irrigated using the same drip method, but with the same amount of deionized water.

[0128] Before the formal application of the soil conditioner, rigorous compatibility testing was conducted on the drip irrigation system. The system used a 120-mesh disc filter and was equipped with pressure-compensated drippers. Test results showed that the aqueous dispersion of soil conditioner V exhibited good flowability in the system; however, after two hours of drip irrigation, the drip rate slowed down, and slight clogging began to occur, requiring manual intervention to continue irrigation.

[0129] One month after continuous application of the soil amendment, soil samples were taken from the experimental field for analysis. The results showed that the pH value of the soil in the experimental group significantly decreased to 7.7, and the soil salinity decreased from the initial 1.5% to 1.3%. The slight decrease in salinity indicated insufficient ion exchange capacity. Simultaneously, the growth of wheat seedlings was monitored. The results showed that, compared with the control group, the average plant height of wheat seedlings treated with Comparative Example 1 increased by approximately 12%, and the leaf chlorophyll content increased by approximately 8%.

[0130] Example 5: Recycling Example (Indoor Soil Column Simulation)

[0131] To further investigate the recyclability potential of the soil conditioner of this invention, a soil column simulation device was constructed in the laboratory. The device has a water collection tank at the bottom to collect excess leachate after drip irrigation, thereby obtaining a "post-use conditioner solution" containing some COF nanoparticles. After crop irrigation, the leachate in the water collection tank is collected and regenerated, with the specific steps as follows:

[0132] 1. Recycling operation

[0133] The solution containing soil conditioner I was collected in a container for later use. Some COF particles in this solution had not yet firmly bonded to the soil or had been washed away by water flow, and therefore had recycling value.

[0134] 2. Flocculation and sedimentation

[0135] Add 0.1 g / L of polyacrylamide flocculant (polyacrylamide was chosen because of its high flocculation ability and good applicability to COF materials) to the "post-use modifier solution". After vigorous stirring and thorough mixing, let stand for about 2 hours to allow the dispersed nanoparticles to gradually form flocs and settle. Carefully pour out and discard the supernatant, retaining the precipitate.

[0136] 3. Pickling and washing

[0137] The precipitate was first rinsed repeatedly with sufficient deionized water to remove easily soluble chlorides; then washed three times (100 mL each time) with 0.1 mol / L dilute hydrochloric acid solution to remove the precipitate. + Replace the Na adsorbed on the surface of COF particles + Isocations. After acid washing, perform a thorough water wash to remove residual Cl. - Ions and other soluble salts are washed away until the pH of the washing solution is near neutral. This stepwise washing effectively removes Na+ ions and other soluble salts. + Desorb and remove excess chloride ions. Then rinse the precipitate repeatedly with sufficient deionized water until the pH of the washing solution is close to neutral to ensure that acidic residues are completely removed.

[0138] 4. Drying and redispersing

[0139] Finally, the washed flocs were dried under vacuum at 80°C for 12 hours to obtain regenerated soil conditioner powder. The regenerated soil conditioner powder was redispersed in deionized water, and an appropriate amount of surfactant Tween 80 was added as needed, at a dosage of 0.1% of the COF mass, and it was continued to be used as a conditioner.

[0140] Test results show that the sodium ion adsorption capacity of the regenerated COF material is approximately 1.1 mmol / g, with a performance retention rate of over 90%, indicating that the recovered amendment can still maintain good adsorption characteristics. Therefore, the COF amendment prepared in this invention has significant advantages in soil environment recyclability and reusability, providing a practical and feasible technical approach for saving resource costs and achieving sustainable saline-alkali land management.

Claims

1. A high dispersibility aqueous covalent organic framework soil amendment characterized in that, comprising: a porous covalent organic framework material having a particle size of 50-500 nm, a specific surface area of greater than 20 m 2 / g, and the porous covalent organic framework material is synthesized from terephthaldehyde and a sulfonated modified tris(4-aminophenyl)amine monomer, the degree of sulfonation of the tris(4-aminophenyl)amine being controlled at 2-3 sulfonic acid groups per molecule; surfactants are Tween series, sodium dodecyl sulfate or a combination thereof; the stabilizers include sodium polyacrylate, xanthan gum, hydrophilic polymer, disodium EDTA or a combination thereof.

2. The improver according to claim 1, characterized in that: The hydrophilic polymer includes polyethylene glycol, polyvinylpyrrolidone, sodium carboxymethyl cellulose or a combination thereof. The amount of the hydrophilic polymer is 0.5-5 wt% of the mass of the covalent organic framework material.

3. The improver according to claim 1 or 2, characterized in that, The mass fraction of the covalent organic framework material synthesized from the sulfonated modified tris(4-aminophenyl)amine monomer is 0.1-50 wt%.

4. The improver according to claim 1 or 2, characterized by The mass fraction of the covalent organic framework material synthesized from the sulfonated modified tris(4-aminophenyl)amine monomer is 1-30 wt%.

5. The improver according to claim 1 or 2, characterized in that, The preparation of the modifier includes the step of mixing the porous covalent organic framework material with surfactants and / or stabilizers, and then performing high-pressure homogenization to form an aqueous dispersion.

6. A method of preparing the improver according to any one of claims 1 to 5, characterized in that, The method includes the following steps: 1) preparing a porous covalent organic framework material from the reaction of terephthaldehyde and sulfonated modified tris(4-aminophenyl)amine; 2) mixing the covalent organic framework material obtained in step 1) with surfactants and / or stabilizers in an aqueous dispersion system; 3) performing high-pressure homogenization to nanoize the covalent organic framework material and form a stable aqueous dispersion, or optionally drying the aqueous dispersion into a powder.

7. The method of claim 6, wherein, The preparation of the porous covalent organic framework material includes the following steps: A) preparing sulfonated modified tris(4-aminophenyl)amine; B) dissolving the sulfonated modified tris(4-aminophenyl)amine in a mixed solvent of an inert solvent and water to obtain a solution of the sulfonated modified tris(4-aminophenyl)amine; C) adding terephthaldehyde to the solution of the sulfonated modified tris(4-aminophenyl)amine to obtain a mixed reaction liquid, and adjusting the pH value to 3-6.5; D) adding the foregoing mixed reaction liquid into a hydrothermal reaction kettle to perform hydrothermal reaction, and obtaining a crude product of the porous covalent organic framework material; F) performing post-treatment on the crude product to obtain a powder of the porous covalent organic framework material.

8. The method of claim 6, wherein, The step A) of preparing the sulfonated modified tris(4-aminophenyl)amine includes dissolving tris(4-aminophenyl)amine in concentrated sulfuric acid, and placing in a constant-temperature water bath for reaction at 55-65℃ for 3-5 hours.

9. The method of claim 6, wherein, The high pressure homogenization pressure is 1200-1500 bar, at which pressure the treatment is carried out in cycles 3-10 times to obtain an aqueous dispersion of COF material with a particle size distribution between 50-700 nm and a specific surface area greater than 20 m 2 / g.

10. The use of the high-dispersibility aqueous covalent organic framework soil modifier of any one of claims 1-5 or the soil modifier prepared by the method of any one of claims 6-9 in the treatment of saline-alkali land.

11. A method for treating saline-alkali soil, characterized in that, The high-dispersibility aqueous covalent organic framework soil modifier of any one of claims 1-5 is applied to the soil of the saline-alkali land through a drip irrigation system to adsorb and release saline-alkali components, reduce the salinity of the soil and improve the growth environment of crops.

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