A gas phase induced endogenous gelation composite gel soil conditioner and its preparation method and application

Abstract

This invention belongs to the field of soil conditioner technology, specifically relating to a gas-phase induced endogenous gel composite gel soil conditioner, its preparation method, and its application. The preparation method includes the following steps: (S1) Acid-soluble polyvalent metal salts, porous carbon, and mineral fillers are dispersed in water, dissolved by adding an anionic polymer, and then a water-insoluble cationic polymer is added to form a precursor slurry; (S2) The precursor slurry is injected into an open mold and placed in a sealed container, where a volatile acid source is used to create an acidic atmosphere to induce gelation, resulting in a composite hydrogel; (S3) The composite hydrogel is washed, dried, and pulverized to obtain the composite gel soil conditioner. The gas-phase induced endogenous gelation method of this invention can induce the formation of polyelectrolyte interactions and ionic cross-linking structures, achieving moderate gelation and uniform composite of fillers. This soil conditioner has good salt tolerance and water absorption capacity, water retention and moisture-increasing effects, and Na+ content. + Migration / rinsing promotion and environmental compatibility.

Description

Technical Field

[0001] This invention belongs to the field of soil conditioner technology, specifically relating to a gas-phase induced endogenous gel soil conditioner, its preparation method, and its application. Background Technology

[0002] Saline-alkali soils are one of the major challenges facing global agriculture, and their improvement and management are of great significance for ensuring food security and ecological sustainable development. These soils typically present the following problems: (a) Insufficient available water: low soil water potential, high evaporation, low irrigation water use efficiency, and crops are susceptible to drought stress; (b) Prominent ion stress: Na+... + Isosal ions cause osmotic stress and ion poisoning, and increased exchangeable sodium leads to soil dispersion and structural damage; (c) Structural degradation: poor pore connectivity, decreased soil permeability and aeration; (d) Difficulty in emergence and seedling establishment: low early survival rate, high cost of re-irrigation and soil improvement, seriously affecting agricultural production efficiency.

[0003] To address the above problems, existing technologies have developed various improved materials and processes, but the following technical bottlenecks still exist:

[0004] (1) Poor salt resistance of water-absorbing and water-retaining materials: Traditional water-absorbing and water-retaining materials (such as polyacrylate SAP) have a high water absorption rate in pure water, but their liquid absorption capacity decreases significantly under high salt ionic strength, and the network is prone to collapse. In addition, some synthetic materials have poor biodegradability, and long-term residues in the soil may pose a risk of secondary pollution.

[0005] (2) Modified materials have limited functionality: Although existing chemical modifiers can provide Ca 2+ To replace Na + However, it is usually difficult to simultaneously improve soil water retention capacity; mineral materials with cation exchange capacity can adsorb salt ions, but their water regulation capacity is limited; traditional hydrogel materials, although they have water retention properties, are difficult to actively regulate Na+. + Isosal ions. Therefore, existing materials cannot simultaneously achieve the multiple improvement goals of "water retention and moisture increase - sodium removal - structural improvement".

[0006] (3) Poor controllability of preparation process: When preparing composite gel soil conditioner, directly adding acid (to induce gelation) or directly adding soluble cross-linking salt (such as CaCl2) can easily lead to local rapid gelation / local precipitation / filler agglomeration, resulting in uneven network structure and filler distribution. That is, the operable window from raw material mixing to gelation is extremely short, batch consistency is poor, which is not conducive to large-scale preparation and stable field effects.

[0007] In summary, the field of saline-alkali soil improvement urgently needs a new material and its preparation process that combines multiple functions such as biodegradability, salt absorption resistance, water retention and moisture increase, ion regulation (sodium removal), and structural improvement. At the same time, the preparation process should be stable, controllable, and suitable for large-scale production. Summary of the Invention

[0008] The present invention aims to provide a degradable gel soil conditioner with good salt resistance and liquid absorption properties, as well as water retention, moisture increase and ion regulation functions, and can provide a material basis for soil structure improvement. Its preparation process is stable and controllable and suitable for large-scale production.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing a gas-phase induced endogenous gel soil conditioner includes the following steps:

[0011] (S1) Disperse acid-soluble polyvalent metal salt, porous carbon, and mineral filler in water, then dissolve anionic polymer in it, and then add non-water-soluble cationic polymer to form a precursor slurry; the ratio of the amount of acid-soluble polyvalent metal salt, anionic polymer and non-water-soluble cationic polymer is (5~15): 100: (30~90).

[0012] (S2) Inject the precursor slurry into an open mold, and then place the open mold containing the precursor slurry into a closed container; set a volatile acid source to create an acidic atmosphere in the closed container, so that the precursor slurry gels under the induction of the acidic atmosphere to obtain a composite hydrogel.

[0013] (S3) The composite hydrogel is washed with water, dried and pulverized to obtain a composite gel soil conditioner with gas phase induced endogenous gelation.

[0014] Preferably, in step (S1), the ratio of the acid-soluble polyvalent metal salt, the anionic polymer, and the water-insoluble cationic polymer is (10~15):100:(50~70).

[0015] Further, in step (S1), the ratio of porous carbon, mineral filler, and anionic polymer is (1~10):(1~15):100, preferably (5~8):(5~10):100. The solid content of the precursor slurry is 2~10 wt%.

[0016] Further, in step (S1), the acid-soluble polyvalent metal salt is a metal salt that is insoluble or sparingly soluble under neutral or alkaline conditions, soluble under acidic conditions, and releases polyvalent cations; specifically selected from at least one of calcium sulfate particles, calcium phosphate particles, calcium carbonate particles, magnesium phosphate particles, and magnesium carbonate particles, with a particle size D50 of 5~30 μm.

[0017] Further, in step (S1), the anionic polymer is a polymer containing carboxyl groups and / or sulfonic acid groups; specifically selected from at least one of alginate, pectin, carboxymethyl cellulose, xanthan gum, hyaluronic acid salt, and polyglutamate; preferably, when the anionic polymer is prepared into a 1 wt% aqueous solution at 25°C, its viscosity is 200~800 mPa·s, more preferably 300~700 mPa·s.

[0018] Further, in step (S1), the water-insoluble cationic polymer is a cationic polymer that is insoluble or only swells under neutral or alkaline conditions, but soluble under acidic conditions, specifically selected from chitosan. Preferably, the number-average molecular weight of the water-insoluble cationic polymer is 2 × 10⁻⁶. 3 ~5×10 5 Da, preferably 5×10 4 ~ 3×10 5 Da. Taking chitosan as an example, it does not dissolve in the system in step (S1), but only swells and disperses to form a uniform slurry system. In the acidic atmosphere of the subsequent step (S2), chitosan is protonated and then forms a network with anionic polymers through electrostatic interaction.

[0019] Further, in step (S1), the porous carbon is biomass porous carbon, with a particle size D50 of 1~500 μm, preferably 5~50 μm, and a specific surface area of ​​300~2000 m². 2 / g, preferably 300~1000 m 2 / g. Porous carbon can be made in-house or commercially available. The preparation method is based on existing technology, such as washing and crushing biomass (straw, rice husk, etc.), and then carbonizing it at 450~650℃ for 2~4h under an inert atmosphere to obtain carbonized material; the carbonized material is then physically activated (CO2 or water vapor as activating agent) for 1~3h.

[0020] Further, in step (S1), the mineral filler is a mineral material with cation exchange capacity (CEC), selected from at least one of palygorskite, attapulgite, montmorillonite, bentonite, zeolite, sepiolite, and kaolinite, preferably palygorskite; the median particle size D50 of the mineral filler is 1~500 μm, preferably 5~50 μm.

[0021] Optionally, based on the total amount of precursor slurry, 0.05-0.5 wt% of a thickener and / or 0.05-0.5 wt% of a suspending agent may also be added in step (S1). For example, the thickener may be selected from at least one of guar gum, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose. For example, the suspending agent may be selected from at least one of polyvinyl alcohol, magnesium aluminum silicate, and fumed silica.

[0022] Further, in step (S2), the volatile acid source is selected from at least one of formic acid, acetic acid, propionic acid, butyric acid, hydrochloric acid, and their aqueous solutions; preferably, aqueous solutions of these, such as aqueous solutions of formic acid, acetic acid, or hydrochloric acid; when the volatile acid source is an aqueous solution of formic acid, acetic acid, propionic acid, or butyric acid, the acid concentration is 10-50 wt%, preferably 30-50 wt%; when the volatile acid source is an aqueous solution of hydrochloric acid, the acid concentration is 20-30 wt%; the temperature inside the sealed container is 15-40°C. The volatile acid source makes the gaseous acid concentration inside the sealed container 500-5000 ppmv; preferably, when the volatile acid source is at least one of formic acid, acetic acid, propionic acid, or butyric acid or their aqueous solutions, the gaseous acid concentration inside the sealed container is 2000-5000 ppmv; when the volatile acid source is hydrochloric acid or an aqueous solution of hydrochloric acid, the gaseous acid concentration inside the sealed container is 500-1500 ppmv. Those skilled in the art will understand that different volatile acids have varying acidity, and the required concentration of fumed acid to achieve the same gelation effect varies. Therefore, the concentration of fumed acid can be adjusted within the aforementioned range depending on the type of volatile acid. In practical applications, the concentration of fumed acid in a sealed container can be controlled by adjusting the type, concentration, and amount of the volatile acid source, as well as the volume of the sealed container. Furthermore, the gelation time can be controlled within 6 to 24 hours based on the thickness of the precursor slurry and the selected concentration of fumed acid.

[0023] Furthermore, in step (S2), the thickness of the precursor slurry in the mold is 10~40 mm, preferably 15~30 mm.

[0024] Furthermore, in step (S2), the method for creating the acidic atmosphere is selected from any of the following, with method one being preferred:

[0025] Method 1: Acidic gas is generated by the volatilization of an external volatile acid source, and then the acidic gas is introduced into a closed space;

[0026] Method 2: Place an open container inside a sealed container to hold the volatile acid source, allowing the volatile acid source to evaporate naturally;

[0027] Method 3: Spray a volatile acid source on the inner wall of a sealed container, and control the amount of spray to avoid acid dripping.

[0028] In this invention, the pH of the precursor slurry is generally 6.5~9.5. Under these neutral or weakly alkaline conditions, the water-insoluble cationic polymer is mainly in an insoluble or swollen dispersion state, and the acid-soluble polyvalent metal salt is in an insoluble or sparingly soluble state. This avoids significant polyelectrolyte complexation or ionic crosslinking between these two components and the anionic polymer in stage S1, thereby ensuring that the precursor slurry maintains good workability and uniformity. After entering step (S2), the acidic component generated by the volatile acid source diffuses into the precursor slurry in gas phase form through the gas-liquid interface, gradually lowering the pH of the system. This induces polyelectrolyte interaction between the cationic polymer and the anionic polymer, and promotes the release of polyvalent cations from the acid-soluble polyvalent metal salt, forming an ionic coordination / crosslinking structure with the anionic polymer, ultimately causing the system to transform from a liquid state to a gel state. During this process, porous carbon and mineral fillers are embedded and composited in the gel network. Compared to the sudden drop in local pH, flocculation, or rapid gelation caused by directly adding liquid-phase acid to the precursor slurry, the gas-phase induced endogenous gelation process of this invention is more gradual, which is beneficial for forming composite hydrogels with uniform structure and consistent properties. The flowchart of the preparation method of the composite gel soil conditioner of this invention is shown below. Figure 1 As shown, the dynamic mechanism diagram of gas-phase induced endogenous gelation is as follows: Figure 2 As shown.

[0029] Furthermore, in this invention, acid-soluble polyvalent metal salts and mineral fillers can have a synergistic effect, jointly participating in the cation exchange process in the soil, which helps to improve the sodium removal efficiency. The possible mechanism of action is as follows: the Ca released by the acid-soluble polyvalent metal salts... 2+ / Mg 2+ Na involved in soil colloids + The substitution of Na, and the cation exchange sites of the mineral filler facilitate the substitution of Na. + Further migration and rinsing.

[0030] Further, in step (S3), the water washing is to wash the composite hydrogel until the filtrate is neutral, so as to remove the residual acidic substances in the gel and reduce the adverse effects on soil pH after application; the drying is to dry at 50~80℃ to constant weight; the pulverized particle size is 0.2~5 mm, and the specific size can be determined according to the actual application requirements.

[0031] Secondly, the present invention provides a composite gel soil conditioner for gas-phase induced endogenous gelation, which is prepared by the above-mentioned preparation method.

[0032] Thirdly, the present invention also provides the application of the above-mentioned gas-phase induced endogenous gel soil conditioner in improving saline-alkali soil; preferably, the dosage of the composite gel soil conditioner is 0.2~5wt% of the dry weight of the soil. Its application scenario, application method and dosage range can be further optimized and determined according to soil type, salinity and alkalinity and application purpose.

[0033] The main material of the composite gel soil conditioner of the present invention is a biodegradable material and does not contain covalent crosslinking agents. It can be gradually degraded in the soil and has good environmental compatibility.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The preparation process is relatively mild and controllable with good uniformity: This invention adopts gas phase induced endogenous gelation technology, which allows acidic components to diffuse into the precursor slurry in gas phase form through the gas-liquid interface, thereby achieving a relatively mild and uniform acidification process, thus reducing the local pH drop, local flocculation or local rapid gelation phenomenon caused by direct addition of acid to the liquid phase.

[0036] 2. Two types of physical interaction network structures can be formed simultaneously: The acidification process of this invention can induce the formation of polyelectrolyte interaction structures between cationic polymers and anionic polymers, and induce polyvalent cations to participate in the formation of ionic cross-linking structures; the two together constitute a composite physical network skeleton without covalent cross-linking bonds, which is beneficial to improving the salt resistance and liquid absorption performance of the material and maintaining the integrity of the gel structure.

[0037] 3. Composite distribution of filler and gel network: The relatively mild sol-gel transition process helps porous carbon and mineral fillers to remain dispersed in the system and to combine with the forming gel network, thus providing a structural basis for their adsorption, ion exchange and other functions.

[0038] 4. Environmentally friendly: The composite gel soil conditioner of the present invention can be gradually degraded in the soil, has good environmental compatibility, and can reduce the environmental burden caused by long-term residue.

[0039] 5. The gas-phase induced endogenous gel composite gel soil conditioner of the present invention exhibits good salt tolerance and liquid absorption capacity, and demonstrates the synergistic effect of water retention and moisture increase with ion regulation, and is biodegradable; in the corn pot experiment, it helps to improve seedling establishment and early growth status. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the preparation method of the composite gel soil conditioner of the present invention.

[0041] Figure 2 This is a dynamic mechanism diagram of gas-phase induced endogenous gelation according to the present invention.

[0042] Figure 3 This is a photograph of the composite gel soil conditioner from Example 1.

[0043] Figure 4 This is a FT-IR comparison image of the composite gel soil conditioner (Gel) from Example 1 and its related raw materials, in which... Figure 4 (a) is a comparison of FT-IR spectra of gel, chitosan (CTS), and sodium alginate (SA). Figure 4 (b) is a comparison of FT-IR images of gel with porous carbon (BC) and palygorskite (Pal).

[0044] Figure 5 The images shown are SEM images of the composite gel soil conditioner in Example 1 before and after water absorption. Figure 5 (a) is a SEM image of the composite gel soil conditioner of Example 1 before water absorption. Figure 5 (b) is a low-magnification SEM image of the composite gel soil conditioner of Example 1 after water absorption. Figure 5 (c) is a high-magnification SEM image of the composite gel soil conditioner of Example 1 after water absorption.

[0045] Figure 6 The image shows the growth status of corn planted in saline-alkali soil 14 days after application of the composite gel soil conditioner from Example 1. Figure 6 (a) is a blank example. Figure 6 (b) represents the application rate of soil conditioner at 2 g / kg. Figure 6 (c) represents the application rate of soil conditioner, which is 4 g / kg. Detailed Implementation

[0046] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of protection of the present invention; all equivalent substitutions or modifications made by those skilled in the art without departing from the concept of the present invention should fall within the scope of protection of the present invention.

[0047] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0048] Calcium carbonate granules and magnesium phosphate granules were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with particle sizes D50 of 5 μm and 10 μm, respectively.

[0049] The porous carbon was a self-made biomass porous carbon, prepared from cotton stalks (Gossypium hirsutum) from farmland in a certain region of Xinjiang. The specific self-production method was as follows: the cotton stalks were first repeatedly washed with deionized water to remove surface dust and impurities, dried at 60℃ to constant weight, and then pulverized; subsequently, they were carbonized at 500℃ for 2 h under nitrogen protection, and then activated at 750℃ for 1 h under CO2 atmosphere; the resulting product was washed with deionized water until the filtrate was nearly neutral, dried at 60℃, pulverized, and passed through a 100-mesh sieve to obtain porous carbon. The obtained porous carbon had a particle size D50 of 15 μm and a specific surface area of ​​330 m². 2 / g.

[0050] Palaequa regia was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a particle size D50 of 8 μm.

[0051] Sodium alginate (SA) was purchased from Shanghai Yuanye Biotechnology Co., Ltd., and its 1 wt% aqueous solution had a viscosity of 400 mPa·s at 25℃; carboxymethyl cellulose was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., and its 1 wt% aqueous solution had a viscosity of 650 mPa·s at 25℃.

[0052] Chitosan (CTS) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a degree of deacetylation of 85% and a number-average molecular weight of approximately 1.5 × 10⁻⁶. 5 Da.

[0053] The soil used for the test was taken from the top 0-20 cm layer of saline-alkali cultivated land in Songyuan area. Its pH was 9.6-10.2, the soluble Na⁺ content was 1450 mg / kg, and the exchangeable Na⁺ content was 10.5 cmol(+) / kg.

[0054] Example 1

[0055] (S1) Disperse 0.2937g of calcium carbonate particles, 0.133g of porous carbon, and 0.133g of palygorskite in 200mL of deionized water and stir at 800rpm for 1h to form a uniform suspension; then dissolve 2.67g of sodium alginate (SA) in it, and add 1.33g of chitosan (CTS), and stir at 800rpm for 2h to form a uniform precursor slurry (i.e., the mass ratio of acid-soluble polyvalent metal salt, porous carbon, mineral filler, anionic polymer, and non-water-soluble cationic polymer is 11:5:5:100:50).

[0056] (S2) Take 150 mL of precursor slurry and inject it into a beaker (slurry thickness about 25 mm). Then place the beaker containing the precursor slurry into a sealed container A (volume about 5.0 L) with a connecting tube (with a regulating valve) on the top. Place 4.0 mL of 50 wt% acetic acid aqueous solution into another sealed container B with a connecting tube on the top. The two sealed containers are connected by the connecting tube, so that the acetic acid gas volatilized in sealed container B can be introduced into sealed container A. The temperature in both sealed containers is controlled at 30℃. Use an online infrared gas detector to monitor the gas phase acid concentration in sealed container A in real time. Adjust the opening of the regulating valve to control it at about 2000 ppmv. Maintain this concentration for 12 h to allow the precursor slurry to gel and obtain a composite hydrogel.

[0057] (S3) Take out the composite hydrogel from the sealed container A, wash it with deionized water until the filtrate is neutral, then dry it at 60°C to constant weight, and crush it to a particle size of about 2 mm to obtain a composite gel soil conditioner with gas phase induced endogenous gelation.

[0058] A photograph of the composite gel soil conditioner (Gel) in Example 1 is shown below. Figure 3 As shown.

[0059] Example 2

[0060] The rest is the same as in Example 1, except that the amount of each raw material in step (S1) is different. Specifically, it is: 0.1335g calcium carbonate particles, 0.0267g porous carbon, 0.0267g palygorskite, 160mL deionized water, 2.67g sodium alginate, and 0.80g chitosan. The mass ratio of acid-soluble polyvalent metal salt, porous carbon, mineral filler, anionic polymer, and non-water-soluble cationic polymer is 5:1:1:100:30. The solid content of the precursor slurry is the same as in Example 1.

[0061] Example 3

[0062] The rest is the same as in Example 1, except that the amount of each raw material in step (S1) is different. Specifically, it is: 0.2136g calcium carbonate particles, 0.0801g porous carbon, 0.1335g palygorskite, 194mL deionized water, 2.67g sodium alginate, and 1.33g chitosan. The mass ratio of acid-soluble polyvalent metal salt, porous carbon, mineral filler, anionic polymer, and non-water-soluble cationic polymer is 8:3:5:100:50. The solid content of the precursor slurry is the same as in Example 1.

[0063] Example 4

[0064] The rest is the same as in Example 1, except that the amount of each raw material in step (S1) is different. Specifically, it is: 0.4005g calcium carbonate particles, 0.2136g porous carbon, 0.2670g palygorskite, 203mL deionized water, 2.67g sodium alginate, and 1.87g chitosan. The mass ratio of acid-soluble polyvalent metal salt, porous carbon, mineral filler, anionic polymer, and non-water-soluble cationic polymer is 15:8:10:100:70. The solid content of the precursor slurry is the same as in Example 1.

[0065] Example 5

[0066] The rest is the same as in Example 1, except that the amount of each raw material in step (S1) is different. Specifically, it is: 0.4005g calcium carbonate particles, 0.2670g porous carbon, 0.4005g palygorskite, 230mL deionized water, 2.67g sodium alginate, and 2.40g chitosan. The mass ratio of acid-soluble polyvalent metal salt, porous carbon, mineral filler, anionic polymer, and non-water-soluble cationic polymer is 15:10:15:100:90. The solid content of the precursor slurry is the same as in Example 1.

[0067] Example 6

[0068] The rest is the same as in Example 1, except that in step (S1), magnesium phosphate is used to replace calcium carbonate particles by mass, and carboxymethyl cellulose is used to replace sodium alginate by mass.

[0069] Example 7

[0070] The rest is the same as in Example 1, except that the slurry thickness, volatile acid source, gas phase acid concentration, and gelation time are different in step (S2), specifically:

[0071] (S1) Same as Example 1;

[0072] (S2) Take 60 mL of precursor slurry and inject it into a beaker (slurry thickness about 10 mm). Then place the beaker containing the precursor slurry into a sealed container A (volume about 5.0 L) with a connecting tube (with a regulating valve) on the top. Place 4.0 mL of 30 wt% hydrochloric acid aqueous solution into another sealed container B with a connecting tube on the top. The two sealed containers are connected by the connecting tube, so that the hydrogen chloride gas volatilized in sealed container B can be introduced into sealed container A. The temperature in both sealed containers is controlled at 30℃. Use an online infrared gas detector to monitor the gas phase acid concentration in sealed container A in real time. Adjust the opening of the regulating valve to control it at about 500 ppmv. Maintain this concentration for 6 hours to allow the precursor slurry to gel and obtain a composite hydrogel.

[0073] (S3) Same as Example 1.

[0074] Example 8

[0075] The rest is the same as in Example 1, except that the slurry thickness, volatile acid source, gas phase acid concentration, and gelation time are different in step (S2), specifically:

[0076] (S1) Same as Example 1;

[0077] (S2) Take 210 mL of precursor slurry and inject it into a beaker (slurry thickness about 35 mm). Then place the beaker containing the precursor slurry into a sealed container A (volume about 5.0 L) with a connecting tube (with a regulating valve) on the top. Place 4.0 mL of 50 wt% butyric acid aqueous solution into another sealed container B with a connecting tube on the top. The two sealed containers are connected by the connecting tube, so that the butyric acid gas volatilized in sealed container B can be introduced into sealed container A. The temperature in both sealed containers is controlled at 40℃. Use an online infrared gas detector to monitor the gas phase acid concentration in sealed container A in real time. Adjust the opening of the regulating valve to control it at about 5000 ppmv. Maintain this concentration for 24 h to allow the precursor slurry to gel and obtain a composite hydrogel.

[0078] (S3) Same as Example 1.

[0079] Comparative Example 1

[0080] Compared with Example 1, the difference is that step (S2) involves the direct addition of acid solution, specifically:

[0081] (S1) Same as Example 1;

[0082] (S2) Under stirring, a 50 wt% aqueous acetic acid solution was slowly added dropwise to the precursor slurry. When the addition was about 30 seconds, it was observed that gel clumps formed immediately at the point where the acid solution was added, which made stirring difficult. In the end, a non-homogeneous mixture of gel clumps and ungelled slurry was obtained.

[0083] (S3) Take out the heterogeneous mixture obtained in step (S2), wash it with deionized water until the filtrate is neutral, then dry it at 60°C to constant weight, and pulverize it to a particle size of about 2 mm to obtain the composite gel soil conditioner.

[0084] Comparative Example 2

[0085] The rest is the same as in Example 1, except that porous carbon is not added in step (S1).

[0086] Comparative Example 3

[0087] The rest is the same as in Example 1, except that palygorskite is not added in step (S1).

[0088] Comparative Example 4

[0089] The rest is the same as in Example 1, except that calcium carbonate particles are not added in step (S1).

[0090] Comparative Example 5

[0091] The rest is the same as in Example 1, except that in step (S1), chitosan is not used and the amount of deionized water is 142 mL, so as to keep the solid content of the precursor slurry basically the same as in Example 1.

[0092] Testing and Analysis

[0093] 1. Structural characterization

[0094] The FT-IR comparison chart of the composite gel soil conditioner (Gel) and the raw material in Example 1 is shown below. Figure 4 As shown, where Figure 4 (a) is a comparison of FT-IR spectra of gel, chitosan (CTS), and sodium alginate (SA). Figure 4 (b) is a FT-IR comparison image of gel, porous carbon (BC), and palygorskite (Pal). Figure 4 As can be seen, the infrared spectrum of gel contains the characteristic absorptions of both the polymer and filler components, but the overall spectral shape differs from that of each individual raw material, exhibiting peak shifts or changes in peak shape. This is particularly evident in the range of approximately 3200–3600 cm⁻¹. -1 A broad absorption band, approximately 1000–1700 cm⁻¹ -1 The polymer functional group-related absorption region and approximately 500–1100 cm⁻¹ -1 The vibrational absorption region of the filler skeleton, and the gel, exhibited spectroscopic characteristics different from those of the single raw materials. This result indicates that during gas-phase induced endogenous gelation, intermolecular interactions occurred between CTS and SA, forming a polyelectrolyte composite network; simultaneously, polyvalent cations and SA underwent ionic cross-linking, with BC and Pal being incorporated into the aforementioned network structure. Therefore, the resulting composite gel soil conditioner forms an organic-inorganic composite structure composed of a polymer network and functional fillers, providing a structural basis for its liquid absorption, water retention, and ion regulation properties.

[0095] SEM images of the composite gel soil conditioner in Example 1 before and after water absorption are shown below. Figure 5 As shown, where Figure 5 (a) is a SEM image of the composite gel soil conditioner of Example 1 before water absorption. Figure 5 (b) is a low-magnification SEM image of the composite gel soil conditioner of Example 1 after water absorption. Figure 5 (c) is a high-magnification SEM image of the composite gel soil conditioner from Example 1 after water absorption. Figure 5 It can be seen that the composite gel soil conditioner of Example 1 has a relatively dense overall structure and a relatively continuous surface before water absorption, with no obvious large-scale pores. After water absorption, its microstructure changes significantly. At low magnification, the material exhibits a loose and porous characteristic after expansion, with relatively well-developed pores and channels forming inside. At higher magnification, it can be further seen that the material after water absorption exhibits a network morphology of interwoven layers / folds, with locally formed internal spaces with good connectivity. The above results indicate that the composite gel soil conditioner obtained in Example 1 can undergo significant structural unfolding and spatial reconstruction during water absorption, forming a porous network structure that facilitates water entry, storage, and retention. That is, the material has obvious swelling response characteristics, which provides a morphological basis for its good water retention performance and application effect in saline-alkali soils.

[0096] The microstructure of the composite gel soil conditioner in the other embodiments is basically the same as that in Example 1, and it also exhibits a loose and porous network structure after absorbing water.

[0097] 2. Performance Testing

[0098] We will first conduct a comprehensive performance test, taking Example 1 as an example.

[0099] Salt tolerance and water absorption test: The water absorption rate of the composite gel soil conditioner prepared in Example 1 was tested in a 0.9wt% NaCl aqueous solution at 25℃. Water absorption rate (g / g) = (W2 - W1) / W1, where W1 is the mass of the composite gel soil conditioner after drying to constant weight, and W2 is the mass after water saturation. The specific results are shown in Table 1.

[0100] Water-holding capacity test: The water-holding capacity of the composite gel soil conditioner prepared in Example 1 was tested at 7 days and 14 days. The specific method was as follows: the composite gel soil conditioner dried to constant weight (mass denoted as W1) was applied to soil samples (dry soil mass denoted as W1) at application rates of 2 g / kg and 4 g / kg, respectively. d The mixture was thoroughly mixed, and water was added to adjust the initial moisture content to 30 wt%. A blank sample without soil conditioner was set up as a control group. Then, a weighing evaporation test was conducted at 25±1℃ and 65±5% relative humidity. The total mass of the mixed sample (denoted as Wt) was weighed on the 7th and 14th days, and the soil moisture content and water holding capacity were calculated according to the following formula:

[0101] Soil moisture content (%) = 100% × (Wt - W) d - W1) / Wd

[0102] Water holding capacity (%) = (soil moisture content / 30%) × 100%

[0103] The water holding capacity results are expressed as the mean ± standard deviation of the three parallel repeated experiments. The differences between groups were statistically analyzed using a two-tailed t-test. The specific results are shown in Table 1.

[0104] Sodium removal performance test: The sodium removal performance of the composite gel soil conditioner was evaluated using a column leaching test. The soil conditioner sample from Example 1 was thoroughly mixed with saline-alkali soil at an application rate of 4 g / kg soil and packed into a column. A blank sample without soil conditioner was included as a control group. Under the same column packing conditions and leaching volume, the same leaching solution was added in multiple rounds for leaching. The leaching solution could be deionized water or a 0.1 wt% NaCl aqueous solution, but the type and volume of leaching solution remained consistent within the same control / treatment group. The leaching solutions from each round were collected, and the sodium content was measured. + Leaching volume. Simultaneously, the soluble Na content of the soil within the column was measured after leaching. + Content and exchangeability of Na + Content, and compared with the initial soluble Na content in the soil. + Content and exchangeability of Na + Content comparison, calculation of soil soluble Na + Content reduction rate and exchangeable Na + Content reduction rate. Na after the first and second rounds of rinsing. + Leaching amount, and soluble Na in the soil within the column after four rounds of leaching + Content and exchangeability of Na + The content reduction rate is shown in Table 1.

[0105] Biodegradability test: Degradation rate was tested by soil burial method (burial depth of 5 cm). Degradation rate (%) = (M1-M2) / M1×100%, where M1 is the initial mass and M2 is the residual mass after a certain number of days of burial. The degradation rate after 5 weeks of burial is shown in Table 1.

[0106] Table 1 Performance test results of the composite gel soil conditioner in Example 1*

[0107]

[0108] *Note: Unless otherwise specified, all data are the mean ± standard deviation of three parallel replicate experiments; blank cases are control groups without soil conditioner.

[0109] As shown in Table 1, the water absorption rate of the composite gel soil conditioner prepared in Example 1 was 36.37 ± 0.51 g / g under conditions of 25℃ and 0.9 wt% NaCl, indicating that it still has good liquid absorption capacity under saline conditions. In the water-holding capacity test, the water-holding capacity of the blank example on day 7 and day 14 was 42.00 ± 0.70% and 22.00 ± 0.70%, respectively, while the water-holding capacity of Example 1 at application rates of 2 g / kg and 4 g / kg was higher than that of the blank example. The difference was statistically significant after a two-tailed t-test (p<0.05), indicating that the material has a good water retention and moisture-increasing effect. In the sodium removal test, the sodium content of Example 1 after the first and second rounds of leaching was significantly lower than that of the blank example. + The leaching amounts were 408 ± 8.7 mg / kg soil and 310 ± 7.0 mg / kg soil, respectively, both higher than the control example; after four rounds of leaching, the soluble Na in the soil of the Example 1 treatment group was... + Content and exchangeability of Na + The content reduction rates were 72.1 ± 1.1% and 62.6 ± 1.2%, respectively, which were also higher than those of the blank example. Combined with the FT-IR and SEM results in the above structural characterization, it can be concluded that the composite network structure is beneficial to the material's water retention, moisture increase, and ion regulation properties. Furthermore, the degradation rate of this material after 5 weeks of burial in soil was 89.9 ± 1.2%, indicating that it has good degradability under the experimental conditions.

[0110] To compare the core performance of each embodiment and comparative example, their salt tolerance, water retention, sodium removal, and biodegradability were tested using the same methods described above. Water retention was evaluated using the 14-day water holding capacity, with a soil conditioner application rate of 4 g / kg soil. Specific results are shown in Table 2.

[0111] Table 2 Performance tests of each embodiment and comparative example

[0112]

[0113] As can be seen from Table 2:

[0114] (a) Within the investigated formulation range, as the amounts of acid-soluble polyvalent metal salts, porous carbon, mineral fillers, and insoluble cationic polymers increased from low to moderate levels, the overall 14-day water holding capacity and sodium removal performance of the material improved, while the water absorption rate decreased. When the amounts of each component were further increased to the levels shown in Example 5, the water absorption rate continued to decrease, and the 14-day water holding capacity and sodium removal index were lower than those in Example 4, indicating that higher amounts of the above components are not necessarily better. Excessive amounts of fillers and insoluble cationic polymers may affect network continuity and filler dispersibility. Among them, Examples 1 and 4 showed better overall performance and are preferred embodiments.

[0115] (b) Examples 7 and 8 demonstrate the performance of composite gel soil conditioners obtained under different combinations of slurry thickness, volatile acid source, gas phase acid concentration, temperature, and gelation time. As shown in Table 2, the products obtained in Examples 7 and 8 both maintained good salt absorption, water retention, and sodium removal properties.

[0116] (c) Compared with Example 1, Comparative Example 1 was prepared by directly adding acid solution. Its water absorption rate, 14-day water holding rate, sodium removal index and 5-week soil burial degradation rate were all lower, indicating that the gas phase induced endogenous gelation method is more conducive to obtaining a composite gel soil conditioner with better comprehensive performance.

[0117] (d) Compared with Example 1, Comparative Examples 2-5 showed varying degrees of decline in relevant properties when porous carbon, palygorskite, calcium carbonate or insoluble cationic polymer were missing, indicating that each component plays an important role in the overall performance of the material.

[0118] (e) In addition, the degradation rates of all examples and comparative examples were at a high level after being buried in the soil for 5 weeks, indicating that the system as a whole has good degradability.

[0119] 3. Application effect test in saline-alkali soil

[0120] The composite gel soil conditioner prepared in Example 1 was applied by mixing with soil at dosages of 2 g / kg and 4 g / kg (dry weight of saline-alkali soil), respectively. The mixture was thoroughly mixed with the saline-alkali soil and applied to a depth of 10 cm. Pot experiments were conducted using maize (Zeamays L.) as the test crop. The pot cultivation conditions were: temperature 25±2℃, light / dark cycle of 12h / 12h, and soil moisture content maintained at a relatively constant level using deionized water during cultivation. Plant growth was continuously observed. The growth status 14 days after planting is as follows: Figure 6 As shown, where Figure 6 (a) is a blank example (no soil conditioner was used). Figure 6 (b) represents the application rate of soil conditioner at 2 g / kg. Figure 6 (c) represents the soil conditioner application rate of 4 g / kg. Figure 6 As can be seen, compared with the blank example, the aboveground growth and root development of corn seedlings were improved after applying the compound gel soil conditioner of Example 1, with the 4 g / kg group showing more significant improvement.

[0121] The composite gel soil conditioners prepared in the other examples were thoroughly mixed with saline-alkali soil at an addition rate of 4 g / kg (dry weight of saline-alkali soil). A potted corn experiment was conducted using the same application process as in Example 1, with the same potted plant care conditions. Seedling survival rate and fresh weight were measured 14 days after planting, and the fresh weight increase rate was calculated based on the average fresh weight of seedlings under the same conditions in the blank example. The seedling survival rate was calculated using the following formula:

[0122] Survival rate (%) = (Number of surviving seedlings / Number of seeds sown) × 100%

[0123] The specific results are shown in Table 3.

[0124] Table 3. Application effect test in saline-alkali soil

[0125]

[0126] As shown in Table 3, under the experimental conditions, the seedling survival rate of the blank example was only 36.7%, indicating that the tested saline-alkali soil had a significant inhibitory effect on corn seedling establishment. Compared with the blank example, the seedling survival rate and fresh weight increase rate of each treatment group were significantly improved. Among them, the seedling survival rate of the preferred treatment groups, Example 1 and Example 4, was 100%, and the fresh weight increase rates were 373% and 415%, respectively. Combined with Table 2, it can be seen that the examples with better water retention and sodium removal performance generally showed better seedling establishment in this corn pot experiment.

[0127] In summary, the gas-phase induced endogenous gel composite soil conditioner of this invention exhibits good salt tolerance and water absorption capacity, water retention and moisture enhancement effects, and Na+ content under the tested conditions. + Migration / leaching promotion and environmental compatibility; under the tested saline-alkali soil and corn potted conditions, it helps improve early seedling growth and promotes seedling establishment.

Claims

1. A method for preparing a gas-phase induced endogenous gel soil conditioner, comprising the following steps: (S1) Acid-soluble polyvalent metal salts, porous carbon, and mineral fillers are dispersed in water, and then an anionic polymer is dissolved in them. Then, a non-water-soluble cationic polymer is added to form a precursor slurry; the mass ratio of the acid-soluble polyvalent metal salt, the anionic polymer and the non-water-soluble cationic polymer is (5~15): 100: (30~90). (S2) Inject the precursor slurry into an open mold, and then place the open mold containing the precursor slurry into a closed container; set a volatile acid source to create an acidic atmosphere in the closed container, so that the precursor slurry gels under the induction of the acidic atmosphere to obtain a composite hydrogel. (S3) The composite hydrogel is washed with water, dried and pulverized to obtain a composite gel soil conditioner with gas phase induced endogenous gelation; In step (S1), the acid-soluble polyvalent metal salt is selected from at least one of calcium sulfate particles, calcium phosphate particles, calcium carbonate particles, magnesium phosphate particles, and magnesium carbonate particles; the anionic polymer is selected from at least one of alginate, pectin, carboxymethyl cellulose, xanthan gum, hyaluronic acid salt, and polyglutamate; the water-insoluble cationic polymer is selected from chitosan; and the porous carbon is biomass porous carbon.

2. The preparation method according to claim 1, characterized in that, In step (S1), the mass ratio of the acid-soluble polyvalent metal salt, the anionic polymer and the water-insoluble cationic polymer is (10~15):100:(50~70).

3. The preparation method according to claim 1, characterized in that, In step (S1), the mass ratio of porous carbon, mineral filler and anionic polymer is (1~10):(1~15):100; the solid content of the precursor slurry is 2~10 wt%.

4. The preparation method according to claim 1, characterized in that, In step (S1), the acid-soluble multivalent metal salt has a particle size D50 of 5 to 30 μm; the non-water-soluble cationic polymer has a number average molecular weight of 2 x 10 3 ~5 x 10 5 Da.

5. The preparation method according to claim 1, characterized in that, In step (S1), the porous carbon has a particle size D50 of 1~500 μm and a specific surface area of ​​300~2000 m². 2 / g; The mineral filler is selected from at least one of palygorskite, attapulgite, montmorillonite, bentonite, zeolite, sepiolite, and kaolinite, and the median particle size D50 of the mineral filler is 5~50 μm.

6. The preparation method according to claim 1, characterized in that, In step (S2), the volatile acid source is selected from at least one of formic acid, acetic acid, propionic acid, butyric acid, hydrochloric acid, and their aqueous solutions; the temperature inside the sealed container is 15~40℃; and the volatile acid source makes the gaseous acid concentration inside the sealed container 500~5000 ppmv.

7. The preparation method according to claim 1, characterized in that, In step (S2), when the volatile acid source is at least one of formic acid, acetic acid, propionic acid, butyric acid or their aqueous solution, the gaseous acid concentration in the closed container is 2000~5000 ppmv; when the volatile acid source is hydrochloric acid or hydrochloric acid aqueous solution, the gaseous acid concentration in the closed container is 500~1500 ppmv.

8. The preparation method according to claim 1, characterized in that, In step (S2), the method for creating the acidic atmosphere is selected from any of the following: Method 1: Acidic gas is generated by the volatilization of an external volatile acid source, and then the acidic gas is introduced into a closed space; Method 2: Place an open container inside a sealed container to hold the volatile acid source, allowing the volatile acid source to evaporate naturally; Method 3: Spray a volatile acid source on the inner wall of a sealed container, and control the amount of spray to avoid acid dripping.

9. A composite gel soil conditioner for gas-phase induced endogenous gelation, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The application of the gas-phase induced endogenous gel soil conditioner prepared by the preparation method according to any one of claims 1-8 in the improvement of saline-alkali soil.

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