Intelligent controlled-release core-shell alginate soil conditioner and preparation method thereof

Abstract

The present invention relates to the technical field of soil conditioners, specifically disclosing an intelligent controlled-release core-shell alginate soil conditioner and its preparation method. This conditioner has a core-shell-layer structure, comprising a core layer, an intermediate shell layer, and an outer layer, with the three layers accounting for 30%, 40%, and 30% of the total weight, respectively. The core layer primarily comprises modified alginate and nutrients; the intermediate shell layer primarily comprises chitosan and a microbial preparation; and the outer layer primarily comprises modified biochar and magnetic nanoparticles. The preparation method includes four steps: core layer preparation, intermediate shell coating, outer layer coating, and post-molding treatment. Utilizing coaxial electrospraying and layer-by-layer self-assembly technology, the core-shell-layer structure and a triple-responsive mechanism for pH, temperature, and microorganisms achieve multiple functions: precise nutrient delivery, efficient heavy metal fixation, and soil microenvironmental regulation. This agent significantly improves sandy and saline-alkali soils, increasing organic matter by up to 40%.

Description

Technical Field

[0001] The present invention relates to an intelligent controlled-release core-shell alginate soil conditioner and a preparation method thereof, in particular to a multifunctional composite soil conditioner with a core-shell-layer three-layer structure, belonging to the technical field of agricultural soil improvers, environmental remediation materials and controlled-release fertilizers. Background Art

[0002] With global population growth and increasing environmental pollution, agricultural production faces severe challenges. Soil problems, such as nutrient deficiencies, heavy metal contamination, and salinization, have become significant constraints on sustainable agricultural development. Traditional soil conditioners and fertilizers often suffer from low efficiency, rapid soil loss, and significant environmental damage.

[0003] Heavy metal contamination of soil is a major global environmental issue. Research indicates that heavy metal contamination affects 20 million hectares of cultivated land in my country, with cadmium and lead exceeding permitted levels at 7% and 1.5%, respectively, making them among the most severely polluted toxic elements in the environment. Heavy metal pollution not only reduces soil quality and crop yields but also poses a serious threat to human health.

[0004] To address these issues, controlled-release fertilizers and multifunctional soil conditioners have emerged. Traditional controlled-release fertilizers primarily achieve slow nutrient release through polymer coating and ion exchange, but these methods suffer from high costs, low nutrient utilization efficiency, and environmentally unfriendly degradation products. Bio-based controlled-release materials, as an environmentally friendly alternative, are gaining increasing attention.

[0005] Chitosan, a natural polysaccharide, exhibits excellent biodegradability, biocompatibility, and antimicrobial activity. Its molecular chains contain numerous active groups, such as amino and hydroxyl groups, which can chelate and adsorb heavy metal ions. Alginate, a natural anionic polysaccharide extracted from seaweed, exhibits excellent gelling properties and biocompatibility. Both materials have been widely used in drug delivery, tissue engineering, and other fields.

[0006] Japanese patent JPH0713233B2, entitled "Soil Conditioner," describes a soil conditioner containing chitosan, primarily used to improve soil physical and chemical properties. However, its simple gel structure lacks the synergistic functions of nutrient controlled release and heavy metal adsorption. Chinese patent CN104311253A, entitled "Chitosan Controlled-Release Fertilizer Microspheres and Their Preparation Method," discloses controlled-release fertilizer microspheres composed of chitosan and sodium alginate. However, its preparation method is complex, the product has poor stability, and it cannot achieve multiple environmentally responsive release.

[0007] In recent years, core-shell materials have garnered widespread attention due to their unique properties. Core-shell structures can integrate diverse functions into a single material, achieving synergistic effects. However, existing core-shell soil conditioners are often prepared using complex emulsification methods, which are not only complex and costly, but also result in uneven particle size distribution, poor stability, and difficulty in achieving precise controlled release.

[0008] As a novel particle preparation method, electrospraying offers advantages such as ease of operation, controllable particle size, and high product uniformity, and has been applied in the field of drug delivery. Coaxial electrospraying allows for the one-step preparation of microcapsules with complex structures, providing new insights into the preparation of multifunctional soil conditioners.

[0009] According to researchers, chitosan and alginate can form a complex through electrostatic interactions, enhancing the material's mechanical properties and stability. Furthermore, chitosan / alginate composites exhibit excellent controlled-release properties in drug delivery systems, but this property has yet to be fully utilized in the field of soil conditioners.

[0010] In summary, existing soil conditioners have the following deficiencies:

[0011] 1. Single function, it is difficult to achieve the synergistic effect of nutrient controlled release and heavy metal adsorption at the same time;

[0012] 2. Poor environmental responsiveness, unable to achieve intelligent controlled release according to changes in soil environment;

[0013] 3. The preparation process is complicated, and the product uniformity and stability are poor;

[0014] 4. Material degradation products may cause secondary pollution to the environment.

[0015] Therefore, the development of a multifunctional soil conditioner with controllable structure, synergistic functions and environmental friendliness is of great significance for improving agricultural production efficiency, repairing contaminated soil and promoting sustainable agricultural development. Summary of the Invention

[0016] The present invention aims to provide an intelligent controlled-release core-shell alginate soil conditioner and its preparation method to address the problems existing in the prior art. This conditioner utilizes a core-shell-shell three-layer structure to achieve synergistic nutrient release and heavy metal adsorption. Through multiple environmental response mechanisms, nutrient release is synchronized with the crop growth cycle, significantly improving nutrient utilization efficiency and soil improvement.

[0017] The object of the present invention is to provide an intelligent controlled-release core-shell alginate soil conditioner, which has a core-shell-layer three-layer structure and includes the following components in percentage by weight:

[0018] A. The core layer accounts for 30% of the total weight, including:

[0019] a) Modified alginate 50-60%;

[0020] b) Humic acid 10-15%;

[0021] c) Nitrogen, phosphorus and potassium complex nutrients 20-25%;

[0022] d) Trace elements 3-5%;

[0023] e) auxiliary materials 5-10%;

[0024] B. The middle shell accounts for 40% of the total weight and includes:

[0025] a) 40-50% of chitosan with a degree of deacetylation greater than or equal to 90%;

[0026] b) Gelatin 10-15%;

[0027] c) Nano zeolite or montmorillonite 15-20%;

[0028] d) Microbial preparations 5-10%;

[0029] e) poly(lactic acid-co-glycolic acid) 5-10%;

[0030] f) Auxiliary materials 5-10%;

[0031] C. The outer layer accounts for 30% of the total weight and includes:

[0032] a) Modified biochar 40-50%;

[0033] b) Bentonite 20-30%;

[0034] c) Magnetic nanoparticles Particles 5-10%;

[0035] d) Cross-linking agent 5-10%;

[0036] e) Auxiliary materials 10-15%.

[0037] Preferably, the modified alginate has an M / G ratio of 1.2-1.5, a viscosity of a 1% aqueous solution greater than or equal to 300 mPa·s, and an organic matter content of 35-45%.

[0038] Preferably, the microbial preparation comprises at least one of Azospirillum brasiliensis, Bacillus subtilis and white rot fungi, wherein the number of viable bacteria of Azospirillum brasiliensis is greater than or equal to , the number of viable Bacillus subtilis is greater than or equal to , the number of viable white rot fungi is greater than or equal to .

[0039] Preferably, the specific surface area of ​​the modified biochar is greater than or equal to , carbon content is greater than or equal to 75%, porosity is greater than or equal to 60%, and pore size distribution is 10nm-100μm.

[0040] Preferably, the conditioning agent is spherical particles with a particle size of 2-4 mm, a uniformity greater than or equal to 95%, a breakage rate less than or equal to 2%, a moisture content less than or equal to 15%, and a pH value of 6.5-7.5; the nutrient release period of the conditioning agent is 120 days, wherein the first stage, 0-15 days, releases 25-30% of the total amount; the second stage, 16-60 days, releases 40-50% of the total amount; and the third stage, 61-120 days, releases 20-30% of the total amount; the adsorption capacity of the conditioning agent for heavy metals is: Greater than or equal to 150 mg / g, Greater than or equal to 80 mg / g, Greater than or equal to 120 mg / g.

[0041] The method for preparing the intelligent controlled-release core-shell alginate soil conditioner comprises the following steps:

[0042] (1) Preparation of core layer: The modified alginate was prepared into a 2-3% aqueous solution, humic acid and nutrients were added, and the solution was homogenized at a speed of 10,000 rpm for 5 min and ultrasonicated at a power of 200 W for 5 min. Then, the solution was sprayed through a coaxial electrospray device at a voltage of 20-25 kV, an inner needle flow rate of 0.5-1.0 mL / h, an outer needle flow rate of 2-4 mL / h, and a collection distance of 15 cm. 2% The cross-linking solution was stirred at pH 7.0 under magnetic stirring at a speed of 200 rpm for 30 min, filtered, washed, pre-frozen at -40°C for 4 h, and freeze-dried at a main drying temperature of -20°C for 24 h and a pressure of 10 Pa to obtain core layer particles.

[0043] (2) Intermediate shell coating: chitosan was prepared into a 2% solution, and gelatin was prepared into a 5% solution in 1% acetic acid at a temperature of 40°C. The two were mixed at a mass ratio of 3:1, and nano-zeolite or montmorillonite suspension was added. The mixture was homogenized at a speed of 8000 rpm for 5 min, and the pH was adjusted to 5.5. The core layer particles were added and stirred at a temperature of 30°C. 0.5% TPP solution was added dropwise for ionic crosslinking, and then 0.25% glutaraldehyde was used for chemical crosslinking at a temperature of 25°C for 2 h. After washing and centrifugation, the composite particles coated with the intermediate shell were obtained by freeze-drying.

[0044] (3) Outer coating: Using layer-by-layer self-assembly technology, the composite particles obtained in step (2) were immersed in modified biochar or bentonite composite suspension, concentration 1-2%, pH 4.5, time 10min, polyelectrolyte solution, PAA, concentration 1%, pH 7.0, time 10min, and magnetic nanoparticles. Suspension, concentration 0.5%, pH 5.5, time 10min, after washing, repeat 3-5 times, finally chemical fixation with 0.5% glutaraldehyde, time 30min, washing and drying;

[0045] (4) Molding and post-processing: The granules obtained in step (3) were pre-frozen at -40 °C for 4 h, and then subjected to composite drying and vacuum freeze drying: main drying temperature -20 °C for 24 h; post-drying temperature 10 °C for 6 h; microwave-assisted final drying: power 100 W, time 2 min, intermittent, after cooling, fluidized bed coating granulation was adopted, inlet temperature 45 ± 2 °C, 5% PVA binder solution was sprayed in, the spraying rate was 5-8 mL / min, and after drying, surface functionalization treatment was carried out, anti-caking agent and degradable film forming agent were added, and the finished product was obtained by screening and packaging.

[0046] As a preferred method for preparing the improved alginate in step (1) is: washing the waste seaweed → crushing to less than or equal to 2mm → 1% Soaking, temperature 80℃, time 2h→ultrasonic treatment, frequency 40kHz, time 30min→cellulase treatment, temperature 50℃, pH 5.5, time 4h→filtration→precipitation→purification→drying→crushing.

[0047] Preferably, the method for preparing chitosan in step (2) is: shrimp and crab shells → cleaning → crushing to less than or equal to 1 mm → deproteinization, 1M NaOH, temperature 90°C, time 1 hour → washing → demineralization, 1M HCl, room temperature, time 2 hours → washing → decolorization → deacetylation, 50% NaOH, temperature 90°C, time 4 hours × 2 times → washing → drying → crushing, and the deacetylation degree of the obtained chitosan is greater than or equal to 90%.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The beneficial effects of the present invention are as follows:

[0050] 1. Through the core-shell-layer three-layer structure design, it achieves multiple functions of precise nutrient supply, efficient fixation of heavy metals and soil microenvironment regulation;

[0051] 2. The triple response mechanism of pH / temperature / microorganisms is used to synchronize nutrient release with the crop growth cycle, significantly improving nutrient utilization efficiency;

[0052] 3. The high-value utilization of discarded seaweed and crustacean shells reduces the cost of raw materials and meets the requirements of green and sustainable development;

[0053] 4. The use of coaxial electrospray and layer-by-layer self-assembly technology simplifies the preparation process and improves product uniformity and stability;

[0054] 5. The product shows excellent improvement effects in sandy wasteland and saline-alkali land, with an organic matter improvement rate of 40% and an inhibition rate of secondary salinization in saline-alkali land of 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a nutrient release curve of the intelligent controlled-release core-shell alginate soil conditioner of the present invention.

[0056] Figure 2 This is a graph showing the test results of the heavy metal adsorption performance of the intelligent controlled-release core-shell alginate soil conditioner of the present invention.

[0057] Figure 3 This is a comparative experimental result diagram of the intelligent controlled-release core-shell alginate soil conditioner of the present invention for improving sandy soil.

[0058] Figure 4 This is a comparative experimental result diagram of the intelligent controlled-release core-shell alginate soil conditioner of the present invention for improving saline-alkali soil.

[0059] Figure 5 Figure 5 is a morphology of the intelligent controlled-release core-shell alginate soil conditioner prepared in Example 1, where 5A is a macroscopic appearance image and 5B is a cross-sectional SEM image of the product. Figure 5 C is a high-magnification SEM image of the outer surface of the product. DETAILED DESCRIPTION

[0060] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] Example 1: Preparation of intelligent controlled-release core-shell alginate soil conditioner

[0062] Core layer preparation:

[0063] (1) Preparation of modified alginate: Take 100g of discarded kelp, wash and chop it, and add 1% 500 mL of the solution was placed in an 80°C water bath for 2 h, ultrasonically treated (40 kHz, 30 min), treated with cellulase (50°C, pH 5.5, 4 h), filtered, precipitated with ethanol, washed, and dried to obtain the modified alginate powder.

[0064] (2) Preparation of core layer particles: Take 2.5g (50%) of modified alginate, 0.5g (10%) of humic acid, nitrogen, phosphorus and potassium compound fertilizer (N: : =15:15:15) 1.0 g (20%), trace element complex (Fe, Mn, Zn, Cu, B, Mo) 0.15 g (3%), auxiliary materials 0.35 g (7%), auxiliary materials including ascorbic acid (antioxidant) 0.08 g (1.6%), sodium polyacrylate (dispersant) 0.12 g (2.4%), citric acid (pH regulator) 0.06 g (1.2%), polyethylene glycol 6000 (solubilizer) 0.05 g (1.0%), trehalose (protective agent) 0.04 g (0.8%), dissolved in 100 mL of deionized water to make a mixed solution with a concentration of 2.5%.

[0065] (3) After homogenization (10000 rpm, 5 min) and ultrasonic treatment (200 W, 5 min), the mixed solution was sprayed into 2% of The cross-linking solution (pH 7.0) was stirred magnetically (200 rpm, 30 min).

[0066] (4) Filter, wash, pre-freeze (-40°C, 4 h) and then freeze-dry (main drying -20°C, 24 h; pressure 10 Pa) to obtain core layer particles.

[0067] Intermediate shell coating:

[0068] (1) Preparation of chitosan solution: 2.0 g of chitosan (40%) with a degree of deacetylation of 90% was dissolved in 100 mL of 1% acetic acid solution and stirred overnight to obtain a 2% chitosan solution.

[0069] (2) Preparation of gelatin solution: Dissolve 0.75 g of gelatin (15%) in 15 mL of warm water (40°C) to obtain a 5% gelatin solution.

[0070] (3) Take 0.75g (15%) of nano-zeolite / montmorillonite, microbial preparation (Azospirillum brasiliensis and Bacillus subtilis, weight ratio 1:1, viable cell count ≥ 5× CFU / g) 0.25 g (5%), PLGA 0.25 g (5%), auxiliary materials 0.5 g (10%), auxiliary materials including potassium dihydrogen phosphate (buffer) 0.15 g (3%), glycerol (plasticizer) 0.12 g (2.4%), potassium sorbate (preservative) 0.08 g (1.6%), povidone K30 (stabilizer) 0.09 g (1.8%), betaine (compatibilizer) 0.06 g (1.2%), were added to the mixture of the above chitosan solution and gelatin solution (mass ratio 3:1).

[0071] (4) After homogenization (8000 rpm, 5 min), the pH was adjusted to 5.5, and the core layer particles prepared in step 1 were added and stirred at 30°C for 30 min.

[0072] (5) 0.5% TPP solution was added dropwise for ionic crosslinking (20 min), and then 0.25% glutaraldehyde was used for chemical crosslinking (25°C, 2 h).

[0073] (6) Washing, centrifugation (3400 rpm, 5 min), and freeze-drying to obtain composite particles coated with the intermediate shell layer.

[0074] Outer coating:

[0075] (1) Preparation of modified biochar: Take straw biochar and ball mill it to obtain powder with particle size ≤100μm. Activation (100℃, 2h), washing and drying were performed to obtain modified biochar.

[0076] (2) Magnetic nanoparticles Particle preparation: Chemical coprecipitation method was used. and As raw materials (molar ratio 2:1), Stir at 60℃ under protection and add NH3 to pH 10-11, stirred at 80℃ for 1h, washed and dried to obtain nanoparticles with a particle size of 15-30nm. particle.

[0077] (3) Modified biochar 1.5g (50%), bentonite 0.6g (20%), nano 0.15 g (5%) of particles, 0.15 g (5%) of cross-linking agent, and 0.6 g (20%) of auxiliary materials were dispersed in water to obtain a 1.5% suspension, and the pH was adjusted to 4.5. The auxiliary materials included 0.14 g (4.7%) of polyvinyl pyrrolidone (dispersant), 0.09 g (3%) of sodium lauryl sulfate (surfactant), 0.12 g (4%) of polyoxyethylene sorbitan monooleate (Tween 80, wetting agent), 0.08 g (2.7%) of sodium carboxymethyl cellulose (thickener), 0.06 g (2%) of sodium glycyrrhizate (suspending agent), 0.07 g (2.3%) of polyvinyl alcohol (film-forming agent), and 0.04 g (1.3%) of magnesium aluminum silicate (anti-caking agent).

[0078] (4) Prepare polyelectrolyte solution: 1% PAA solution, pH adjusted to 7.0.

[0079] (5) Preparation of magnetic nanoparticles Suspension: Nano The particles were dispersed in water to obtain a 0.5% suspension, and the pH was adjusted to 5.5.

[0080] (6) Using the layer-by-layer self-assembly technique, the composite particles obtained in step 2 were sequentially immersed in the above suspension for 10 min each time, followed by washing. After three repetitions, the composite particles were chemically fixed with 0.5% glutaraldehyde for 30 min, washed, and dried.

[0081] Molding and post-processing:

[0082] (1) The particles obtained in step 3 were pre-frozen (-40°C, 4 h) and then subjected to composite drying (vacuum freeze drying: main drying at -20°C, 24 h; post-drying at 10°C, 6 h; microwave-assisted final drying: 100 W, 2 min, intermittent).

[0083] (2) After cooling, the granules were coated using a fluidized bed (inlet temperature 45°C, 5% PVA binder solution was sprayed in at a rate of 5 mL / min).

[0084] (3) After drying, the surface was functionalized by spraying an anti-caking agent (1% talc, 0.5% silica) and a biodegradable film-forming agent (1% polyvinyl alcohol, 0.5% glycerol).

[0085] (4) Screening and packaging to obtain the finished product.

[0086] The final product is spherical particles with a particle size of 2-3 mm, a breakage rate ≤ 2%, a moisture content ≤ 10%, and a pH value of 7.0±0.5.

[0087] Example 2: Preparation of intelligent controlled-release core-shell alginate soil conditioners with different ratios

[0088] According to the method of Example 1, intelligent controlled-release core-shell alginate soil conditioners with different ratios were prepared. The formulation compositions are shown in Table 1:

[0089] Table 1 Composition of intelligent controlled-release core-shell alginate soil conditioner with different ratios

[0090] Components Example 2-1 Example 2-2 Example 2-3 Core layer (30% of total weight) Modified alginate 60% 55% 50% Humic acid 10% 12.50% 15% Nitrogen, phosphorus and potassium complex nutrients 20% 22.50% 25% trace elements 5% 4% 3% Supplementary Materials 5% 6% 7% Middle shell (40% of total weight) Chitosan 50% 45% 40% gelatin 10% 12.50% 15% Nano zeolite / montmorillonite 20% 17.50% 15% Microbial agents 5% 7.50% 10% PLGA 10% 7.50% 5% Supplementary Materials 5% 10% 15% Outer layer (30% of total weight) Modified biochar 50% 45% 40% Bentonite 20% 25% 30% <![CDATA[Magnetic nano-Fe3O4]]> 10% 7.50% 5% crosslinking agent 5% 7.50% 10% Supplementary Materials 15% 15% 15%

[0091] The preparation method is the same as that of Example 1, but the ratio and corresponding amount of each component are adjusted.

[0092] Example 3: Preparation of intelligent controlled-release core-shell alginate soil conditioner under different process parameters

[0093] According to the formula of Example 1, intelligent controlled-release core-shell alginate soil conditioner was prepared under different process parameters. The process parameters are shown in Table 2:

[0094] Table 2 Preparation conditions of intelligent controlled-release core-shell alginate soil conditioner under different process parameters

[0095] Process parameters Example 3-1 Example 3-2 Example 3-3 Core layer preparation Alginate concentration 2% 2.50% 3% EFI voltage 20kV 22.5kV 25kV Inner needle flow rate 0.5 mL / h 0.75 mL / h 1.0 mL / h External needle flow rate 2 mL / h 3 mL / h 4 mL / h <![CDATA[Calcium chloride concentration]]> 2% 2% 2% Intermediate shell coating Chitosan concentration 2% 2% 2% Gelatin concentration 5% 5% 5% TPP concentration 0.50% 0.50% 0.50% Glutaraldehyde concentration 0.25% 0.25% 0.25% Cross-linking time 1h 2h 3h Outer coating Suspension concentration 1% 1.50% 2% Soaking time 5min 10min 15min Number of repetitions 3 4 5 Drying conditions Pre-freezing temperature -40℃ -40℃ -40℃ Main drying temperature -20℃ -20℃ -20℃ Main drying time 24h 24h 24h Microwave power 100W 100W 100W

[0096] The preparation method is the same as that in Example 1, but the process parameters of each step are adjusted.

[0097] Example 4: Intelligent controlled-release core-shell soil conditioner prepared by different modified alginate preparation methods

[0098] According to the formula and process parameters of Example 1, different methods were used to prepare modified alginate, which was then used to prepare the intelligent controlled-release core-shell soil conditioner:

[0099] Example 4-1:

[0100] Improved alginate was prepared by acid extraction method: 100 g of discarded kelp was washed and chopped, and then 500 mL of 0.1 M HCl solution was added, stirred at room temperature for 2 h, filtered, and the residue was washed with 0.1 M The solution was extracted (80°C, 3h), filtered, precipitated with ethanol, washed, and dried to obtain the modified alginate powder.

[0101] Example 4-2:

[0102] The improved alginate was prepared by enzyme-ultrasound synergistic method: 100 g of discarded kelp was washed and chopped, and then added into 500 mL of pH 7.0 phosphate buffer, cellulase (0.5%) and alginate (0.2%). The mixture was enzymatically hydrolyzed at 45 ° C for 6 h, and intermittent ultrasonic treatment (40 kHz, 10 min per hour) was performed. The mixture was filtered, precipitated with ethanol, washed, and dried to obtain the improved alginate powder.

[0103] Example 4-3:

[0104] Improved alginate was prepared by microwave-assisted extraction: 100 g of discarded kelp was washed and chopped, and then 1% 500 mL of the solution was microwave-treated (500 W, 5 min), filtered, and the residue was microwave-treated again (500 W, 5 min), filtered, and the filtrates were combined, precipitated with ethanol, washed, and dried to obtain the modified alginate powder.

[0105] The properties of the improved alginate prepared in each example are shown in Table 3:

[0106] Table 3 Characteristics of modified alginate prepared by different methods

[0107] Characteristic parameters Example 4-1 Example 4-2 Example 4-3 Extraction rate 18% 22% 20% M / G ratio 1.2 1.3 1.5 Molecular weight (kDa) 80-100 60-80 70-90 Viscosity (1% solution, mPa·s) 350 300 320 purity 85% 90% 88%

[0108] The subsequent preparation steps are the same as those in Example 1.

[0109] Example 5: Intelligent controlled-release core-shell alginate soil conditioner with different microbial preparation combinations

[0110] According to the formulation and process parameters of Example 1, different combinations of microbial preparations were added to the intermediate shell layer:

[0111] Example 5-1:

[0112] The microbial preparation combination is a mixture of Azospirillum brasiliensis and Bacillus subtilis, and the number of viable bacteria is , the mixing ratio is 1:1.

[0113] Example 5-2:

[0114] The microbial preparation combination is a mixture of Bacillus subtilis, white rot fungi and phosphate-solubilizing bacteria, and the number of viable bacteria is , the mixing ratio is 1:1:1.

[0115] Example 5-3:

[0116] The microbial preparation combination is a mixture of photosynthetic bacteria, nitrogen-fixing spirilli and actinomycetes, and the number of viable bacteria is , the mixing ratio is 1:1:1.

[0117] The subsequent preparation steps are the same as those in Example 1.

[0118] Example 6: Intelligent controlled-release core-shell alginate soil conditioner with different outer layer component ratios

[0119] According to the core layer and intermediate shell layer formula and process of Example 1, the outer layer component ratio was adjusted to prepare intelligent controlled-release core-shell alginate soil conditioners with different outer layer component ratios:

[0120] Example 6-1:

[0121] Outer layer composition: modified biochar 40%, bentonite 30%, magnetic nano Particles 10%, cross-linking agent 5%, auxiliary materials 15%.

[0122] Example 6-2:

[0123] Outer layer composition: modified biochar 45%, bentonite 25%, magnetic nano Particles 7.5%, cross-linking agent 7.5%, auxiliary materials 15%.

[0124] Example 6-3:

[0125] Outer layer composition: modified biochar 50%, bentonite 20%, magnetic nano Particles 5%, cross-linking agent 10%, auxiliary materials 15%.

[0126] The subsequent preparation steps are the same as those in Example 1.

[0127] Comparative Example 1: Simple mixed soil conditioner without core-shell structure

[0128] The modified alginate 15%, chitosan 20%, humic acid 5%, nitrogen, phosphorus and potassium complex nutrients 10%, trace elements 1.5%, biochar 15%, bentonite 10%, microbial preparation 3%, magnetic nanoparticles 2% of particles and 18.5% of auxiliary materials were directly mixed, and a comparative product was obtained through granulation, drying and sieving.

[0129] The total feed amount is the same as that in Example 1, but instead of adopting a core-shell structure, all components are directly mixed.

[0130] Comparative Example 2: Soil conditioner with only core-shell structure and no outer layer

[0131] According to the method of Example 1, a soil conditioner having only a core layer and an intermediate shell layer was prepared without adding an outer layer.

[0132] The core layer (accounting for 40% of the total weight) is composed of: 55% modified alginate, 12.5% ​​humic acid, 22.5% nitrogen, phosphorus and potassium complex nutrients, 4% trace elements, and 6% auxiliary materials.

[0133] The middle shell (accounting for 60% of the total weight) is composed of: chitosan 45%, gelatin 12.5%, nano zeolite / montmorillonite 17.5%, microbial preparation 7.5%, PLGA 7.5%, and auxiliary materials 10%.

[0134] Comparative Example 3: Core-shell soil conditioner prepared by ordinary water bath emulsification method

[0135] According to the formulation of Example 1, a core-shell soil conditioner was prepared by using the traditional water bath emulsification method instead of the coaxial electrospraying technology:

[0136] The modified alginate solution was mixed with nitrogen, phosphorus and potassium complex nutrients and trace elements, and added dropwise to the mixture containing 2% The alginate gel beads were transferred to a chitosan solution and soaked for 2 hours to form a chitosan coating. The subsequent steps were the same as in Example 1.

[0137] 6. Performance Testing and Application Effects

[0138] 6.1 Product Characterization

[0139] Please refer to Figure 5 , morphological and structural characterization:

[0140] The product prepared in Example 1 was spherical in shape, smooth in surface, and uniform in particle size of 2-3 mm; the interfaces between the core layer, the intermediate shell layer, and the outer layer were clear, and the structure was complete. The product prepared in Comparative Example 3 had an irregular shape, uneven particle size distribution, and a fuzzy interface.

[0141] Figure 5 Figure A shows the macroscopic morphological characteristics of the product of Example 1. It can be observed that the product presents highly regular spherical particles with a smooth surface and uniform gloss, and the diameter is mainly distributed in the range of 2-3 mm. The size difference between the particles is small, the shape regularity is high, the appearance consistency is good, and there is no obvious deformation or damage. The surface of the particles has a subtle texture structure, which is due to the characteristic surface morphology formed during the outer coating process. The 10mm ruler shows the actual size of the particles, which is convenient for intuitive judgment of the size of the product. This uniform spherical structure is conducive to the uniform distribution and stable release of the product in the soil.

[0142] Figure 5 B is a cross-sectional SEM image of the product, which clearly shows the core-shell-layer structure of the product. From the outside to the inside, we can observe the following:

[0143] Outer layer: dense structure, obvious roughness on the surface, and evenly distributed black granular substances can be seen, which are magnetic nanoparticles. Particles (particle size 15-30nm). The interface between the outer layer and the middle shell is clear and tightly combined without gaps.

[0144] The middle shell exhibits a typical cross-linked reticular structure, with a clearly visible three-dimensional network formed by chitosan and gelatin. The pores within this network are uniform in size, approximately 1-2 μm in diameter. This structure facilitates selective permeation and environmental responsiveness.

[0145] Core layer: Approximately 80 μm in diameter, it exhibits a porous, sponge-like structure with pore sizes ranging from 5-10 μm and good pore connectivity. This structure is a cross-linked network formed by modified alginate and humic acid, which facilitates nutrient storage and slow release.

[0146] The interfaces between the three layers are clearly discernible, with a natural structural transition and no apparent fracture or detachment, demonstrating the precision of the fabrication process and the good compatibility between the materials. The 50μm scale indicates a moderate magnification, enabling clear distinction of the microscopic features of the three-layer structure.

[0147] Figure 5 C shows a high-magnification SEM image of the product's outer surface. It can be observed that the surface has a distinct micro-nanoscale rough structure, showing a characteristic "hill-valley" morphology. Black nanoparticles (magnetic nanoparticles) with a diameter of about 3-4μm are evenly distributed on the surface. The particles are spaced approximately 5-10 μm apart, with a moderate distribution density and no apparent agglomeration. Tiny wrinkles and grooves are also observed on the surface, creating a multi-level surface roughness. This multi-level roughness significantly increases the specific surface area (≥500 m² / g), providing abundant active sites for heavy metal ion adsorption. The 10 μm scale indicates the microscopic scale of observation, allowing for clear visualization of surface microstructural features.

[0148] In the product obtained in Example 1, particles in the 2-3 mm particle size range account for the highest proportion, reaching about 70%, which is the main particle size distribution range of the product. The 3-4 mm particle size range is second, accounting for about 20%. The 1-2 mm particle size range is next, accounting for about 5%. The larger particle sizes of 4-5 mm and 5-6 mm account for a very small proportion, approximately 3% and 2%, respectively. This concentrated particle size distribution (70% in the 2-3 mm range) and high uniformity (≥95%) indicate that the preparation process of the present invention has a high degree of controllability and repeatability, and can stably produce products that meet the requirements. The moderate particle size is conducive to the uniform distribution and stable release of the product in the soil, and also facilitates agricultural mechanization and improves application efficiency.

[0149] Physical and chemical properties characterization:

[0150] The product prepared in Example 1 has a pH value of 7.0±0.5, a moisture content of 8.5%, a mechanical strength of >20N, and a bulk density of 0.85 , specific surface area 550 , porosity 65%. The product has good water resistance, and after being soaked in water for 24 hours, the structure remains intact without obvious swelling.

[0151] Nutrient content determination:

[0152] Total nutrient content of the product prepared in Example 1 ( ) is 15.5%, the organic matter content is 42.5%, and the total trace elements are 2.2%, including Fe0.8%, Zn0.4%, Mn0.4%, Cu0.2%, B0.3%, and Mo0.1%.

[0153] 6.2 Nutrient release performance test

[0154] The nutrient release of different samples was determined using the extraction method. 1g of sample was placed in 100mL of deionized water, and the N, P, and K contents in the solution were measured under different conditions. Nutrient release curves were then plotted.

[0155] pH-responsive release testing:

[0156] The nutrient release was measured under pH 5.5, 6.5 and 7.5 conditions. The results showed that under pH 5.5, the nutrient release rate of the sample in Example 1 was significantly higher than that under pH 7.5, with a release rate difference coefficient of 2.5, showing obvious pH responsiveness; while the pH responsiveness of the samples in Comparative Example 1 and Comparative Example 3 was weak, with a release rate difference coefficient of only 1.2-1.4.

[0157] Temperature responsive release test:

[0158] The nutrient release was measured at 10°C, 20°C and 30°C. The results showed that at 30°C, the nutrient release rate of the sample in Example 1 was significantly higher than that at 10°C, with a release rate difference coefficient of 1.8, showing obvious temperature responsiveness. However, the temperature responsiveness of the samples in Comparative Examples 1 and 3 was weak, with a release rate difference coefficient of only 1.1-1.3.

[0159] Microbial responsive release testing:

[0160] The nutrient release was measured with and without the addition of soil microorganisms. The results showed that when microorganisms were added, the nutrient release rate of the sample in Example 1 was significantly accelerated, with a release rate difference coefficient of 2.2, showing obvious microbial responsiveness; while the microbial responsiveness of the samples in Comparative Examples 1 and 3 was weak, with a release rate difference coefficient of only 1.2-1.3.

[0161] Nutrient persistence test:

[0162] Figure 1The nutrient release curve of the intelligent controlled-release core-shell alginate soil conditioner of the present invention is shown. A 120-day long-term release experiment shows that the sample in Example 1 exhibits excellent nutrient persistence, with a three-stage release curve: 28% of the total nutrient release in the first stage (0-15 days), 45% in the second stage (16-60 days), and 27% in the third stage (61-120 days). In contrast, the samples in Comparative Examples 1 and 3 release only 60-70% of the total nutrient release in the first 15 days, showing no significant nutrient persistence. The samples in Comparative Examples 1 and 3 lack this precisely controlled release pattern, releasing the majority of their nutrients within the first 15 days.

[0163] 6.3 Heavy metal adsorption performance test

[0164] The adsorption performance of different samples on heavy metals was determined by batch adsorption method. 0.5 g of sample was placed in a mixture containing different concentrations of heavy metals ( ) solution, shake at 25℃ for 24h, measure the residual heavy metal content in the solution, and calculate the adsorption capacity.

[0165] Figure 2 The results of the test on the adsorption performance of different heavy metals of the present invention are shown. 、 、 The maximum adsorption capacities of the samples were 180 mg / g, 95 mg / g, and 130 mg / g, respectively, which were significantly higher than those of the samples in Comparative Example 1 and Comparative Example 3 (85 mg / g, 40 mg / g, and 65 mg / g for Comparative Example 1 and 120 mg / g, 60 mg / g, and 90 mg / g for Comparative Example 3). The adsorption isotherm of the sample in Example 1 conforms to the Langmuir model, indicating that it is a monolayer adsorption; the kinetics conforms to the pseudo-second-order kinetic model, indicating that a chemical adsorption process exists. 、 、 The maximum adsorption capacity is significantly higher than that of the comparative example product, which proves the advantage of the present invention in the remediation of heavy metal pollution.

[0166] Adsorption mechanism studies have shown that the adsorption mechanism of the sample in Example 1 for heavy metals includes ion exchange, complex chelation and electrostatic adsorption, among which the carboxyl group of the modified alginate, the amino group of chitosan, and the magnetic nanoparticles The magnetic capture works together to achieve efficient adsorption and stable fixation.

[0167] 6.4 Soil improvement effect test

[0168] Sandy soil improvement experiment:

[0169] Different samples were added to sandy soil at a dosage of 5g / kg, and soil physical and chemical properties were measured after 60 days of incubation. The results showed that after treatment with the sample in Example 1, the soil organic matter content increased by 40%, water retention increased by 35%, fertilizer retention capacity increased by 42%, and soil aggregate structure stability increased by 38%. The improvement effects of the samples in Comparative Examples 1 and 3 were 22-25% and 30-32%, respectively.

[0170] Salt-alkali land improvement experiment:

[0171] Different samples were added to saline-alkali soil at a dosage of 7g / kg, and soil physical and chemical properties were measured after 90 days of incubation. The results showed that after treatment with the sample in Example 1, the soil secondary salinization inhibition rate reached 80%, the pH decreased by 0.8 units, the soil electrical conductivity decreased by 45%, and the soil aeration increased by 36%. The improvement effects of the samples in Comparative Examples 1 and 3 were 45-48% and 60-65%, respectively.

[0172] Heavy metal contaminated soil remediation experiment:

[0173] Different samples were added to soil contaminated with Pb, Cd, and Cu at a dose of 10g / kg. After 120 days of incubation, the available heavy metal content in the soil was measured. The results showed that treatment with the sample from Example 1 reduced the available Pb, Cd, and Cu content in the soil by 85%, 78%, and 82%, respectively. The samples from Comparative Examples 1 and 3 achieved fixation efficiencies of 40-45% and 60-65%, respectively.

[0174] Figure 3 and Figure 4 The effects of the present invention on improving sandy soil and saline-alkali soil were demonstrated. In terms of sandy soil improvement, the sample in Example 1 showed significant advantages in three key indicators: organic matter increment, water retention, and aggregate structure. In terms of saline-alkali soil improvement, the sample in Example 1 achieved a salinization inhibition rate of up to 80%, significantly outperforming the comparative example product.

[0175] 6.5 Crop Growth Effect Test

[0176] Wheat, corn and rice were planted in the improved soil to investigate the effects of different samples on crop growth. The results showed that:

[0177] Wheat growth experiment:

[0178] After the sample of Example 1 was treated, the wheat yield increased by 28%, the thousand-grain weight increased by 15%, and the protein content increased by 12%; while the yield-increasing effects of the samples of Comparative Example 1 and Comparative Example 3 after treatment were 15-17% and 20-22%, respectively.

[0179] Corn growth experiment:

[0180] After the sample of Example 1 was treated, the corn yield increased by 32%, the ear length increased by 18%, and the 100-grain weight increased by 14%; while the yield-increasing effects of the samples of Comparative Examples 1 and 3 after treatment were 18-20% and 23-25%, respectively.

[0181] Rice growth experiment:

[0182] After the sample of Example 1 was treated, the rice yield increased by 25%, the fruit setting rate increased by 16%, and the 1000-grain weight increased by 12%; while the yield-increasing effects of the samples of Comparative Examples 1 and 3 after treatment were 14-16% and 18-20%, respectively.

[0183] The preparation and testing of the above examples and comparative examples demonstrate that the intelligent controlled-release core-shell alginate soil conditioner of the present invention has the following advantages:

[0184] 1. The core-shell-layer three-layer structure design realizes the multiple functions of precise nutrient supply, efficient fixation of heavy metals and soil microenvironment regulation;

[0185] 2. It has a triple response mechanism of pH / temperature / microorganisms, which synchronizes nutrient release with the crop growth cycle and improves nutrient utilization efficiency by more than 30%;

[0186] 3. It has high adsorption and fixation ability for heavy metals, and the adsorption capacity is more than 100% higher than that of traditional materials;

[0187] 4. It has a significant improvement effect on sandy soil and saline-alkali land, with the organic matter improvement rate reaching 40% and the secondary salinization inhibition rate of saline-alkali land reaching 80%;

[0188] 5. It has a significant promoting effect on the growth of crops, with an increase in yield of 25-32%.

[0189] The present invention provides a new technical solution for solving the problems of soil impoverishment, heavy metal pollution and salinization in my country, and has broad application prospects.

[0190] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims of the present invention.

Claims

1. Intelligent controlled-release core-shell alginate soil conditioner, characterized in that: The conditioning agent has a core-shell-layer three-layer structure and includes the following components in percentage by weight: A. The core layer accounts for 30% of the total weight, including: a) Modified alginate 50-60%; b) Humic acid 10-15%; c) Nitrogen, phosphorus and potassium complex nutrients 20-25%; d) Trace elements 3-5%; e) auxiliary materials 5-10%; B. The middle shell accounts for 40% of the total weight and includes: a) 40-50% of chitosan with a degree of deacetylation greater than or equal to 90%; b) Gelatin 10-15%; c) Nano zeolite or montmorillonite 15-20%; d) Microbial preparations 5-10%; e) poly(lactic acid-co-glycolic acid) 5-10%; f) Auxiliary materials 5-10%; C. The outer layer accounts for 30% of the total weight and includes: a) Modified biochar 40-50%; b) Bentonite 20-30%; c) Magnetic nanoparticles Particles 5-10%; d) Cross-linking agent 5-10%; e) auxiliary materials 10-15%; The method for intelligent controlled release of core-shell alginate soil conditioner comprises the following steps: (1) Preparation of core layer: The modified alginate was prepared into a 2-3% aqueous solution, humic acid and nutrients were added, and the solution was homogenized at a speed of 10,000 rpm for 5 min and ultrasonicated at a power of 200 W for 5 min. Then, the solution was sprayed through a coaxial electrospray device at a voltage of 20-25 kV, an inner needle flow rate of 0.5-1.0 mL / h, an outer needle flow rate of 2-4 mL / h, and a collection distance of 15 cm. 2% The cross-linking solution was stirred at pH 7.0 under magnetic stirring at a speed of 200 rpm for 30 min, filtered, washed, pre-frozen at -40°C for 4 h, and freeze-dried at a main drying temperature of -20°C for 24 h and a pressure of 10 Pa to obtain core layer particles. (2) Intermediate shell coating: chitosan was prepared into a 2% solution, and gelatin was prepared into a 5% solution in 1% acetic acid at a temperature of 40°C. The two were mixed at a mass ratio of 3:1, and nano-zeolite or montmorillonite suspension was added. The mixture was homogenized at a speed of 8000 rpm for 5 min, and the pH was adjusted to 5.

5. The core layer particles were added and stirred at a temperature of 30°C. 0.5% TPP solution was added dropwise for ionic crosslinking, and then 0.25% glutaraldehyde was used for chemical crosslinking at a temperature of 25°C for 2 h. After washing and centrifugation, the composite particles coated with the intermediate shell were obtained by freeze-drying. (3) Outer coating: Using layer-by-layer self-assembly technology, the composite particles obtained in step (2) were immersed in modified biochar or bentonite composite suspension, concentration 1-2%, pH 4.5, time 10min, polyelectrolyte solution, PAA, concentration 1%, pH 7.0, time 10min, and magnetic nanoparticles. Suspension, concentration 0.5%, pH 5.5, time 10min, after washing, repeat 3-5 times, finally chemical fixation with 0.5% glutaraldehyde, time 30min, washing and drying; (4) Molding and post-processing: The granules obtained in step (3) were pre-frozen at -40 °C for 4 h, and then subjected to composite drying and vacuum freeze drying: main drying temperature -20 °C for 24 h; post-drying temperature 10 °C for 6 h; microwave-assisted final drying: power 100 W, time 2 min, intermittent, after cooling, fluidized bed coating granulation was adopted, inlet temperature 45 ± 2 °C, 5% PVA binder solution was sprayed in, the spraying rate was 5-8 mL / min, and after drying, surface functionalization treatment was carried out, anti-caking agent and degradable film forming agent were added, and the finished product was obtained by screening and packaging.

2. The intelligent controlled-release core-shell alginate soil conditioner according to claim 1, characterized in that: The modified alginate has an M / G ratio of 1.2-1.5, a viscosity of a 1% aqueous solution greater than or equal to 300 mPa·s, and an organic matter content of 35-45%.

3. The intelligent controlled-release core-shell alginate soil conditioner according to claim 1, characterized in that: The microbial preparation comprises at least one of Azospirillum brasiliensis, Bacillus subtilis and white rot fungi, wherein the number of viable bacteria of Azospirillum brasiliensis is greater than or equal to CFU / g, the number of viable Bacillus subtilis is greater than or equal to CFU / g, the number of viable white rot fungi is greater than or equal to CFU / g.

4. The intelligent controlled-release core-shell alginate soil conditioner according to claim 1, characterized in that: The specific surface area of ​​the modified biochar is greater than or equal to 500 , carbon content is greater than or equal to 75%, porosity is greater than or equal to 60%, and pore size distribution is 10nm-100μm.

5. The intelligent controlled-release core-shell alginate soil conditioner according to claim 1, characterized in that: The conditioning agent is spherical particles with a particle size of 2-4 mm, a uniformity greater than or equal to 95%, a breakage rate less than or equal to 2%, a moisture content less than or equal to 15%, and a pH value of 6.5-7.

5. The nutrient release cycle of the conditioning agent is 120 days, wherein the first stage, 0-15 days, releases 25-30% of the total amount; the second stage, 16-60 days, releases 40-50% of the total amount; and the third stage, 61-120 days, releases 20-30% of the total amount. The adsorption capacity of the conditioning agent for heavy metals is: Greater than or equal to 150 mg / g, Greater than or equal to 80 mg / g, Greater than or equal to 120 mg / g.

6. The intelligent controlled-release core-shell alginate soil conditioner according to claim 1, characterized in that: The method for preparing the modified alginate in step (1) is: washing the discarded seaweed → crushing to less than or equal to 2 mm → 1% Soaking, temperature 80℃, time 2h→ultrasonic treatment, frequency 40kHz, time 30min→cellulase treatment, temperature 50℃, pH 5.5, time 4h→filtration→precipitation→purification→drying→crushing.

7. The intelligent controlled-release core-shell alginate soil conditioner according to claim 1, characterized in that: The method for preparing chitosan in step (2) is: shrimp and crab shells → cleaning → crushing to less than or equal to 1 mm → deproteinization, 1M NaOH, temperature 90°C, time 1 hour → washing → demineralization, 1M HCl, room temperature, time 2 hours → washing → decolorization → deacetylation, 50% NaOH, temperature 90°C, time 4 hours × 2 times → washing → drying → crushing, the deacetylation degree of the obtained chitosan is greater than or equal to 90%.

8. The intelligent controlled-release core-shell alginate soil conditioner according to claim 1, characterized in that: The method for preparing modified biochar in step (3) is as follows: straw raw material → crushing to less than or equal to 5 mm → low-temperature pyrolysis, temperature 400-600 ° C, nitrogen protection, time 1-2 hours → cooling → ball milling, planetary ball mill, speed 300 rpm, time 4 hours → screening to less than or equal to 100 μm → functional modification, Activation, temperature 100℃, time 2h→washing→drying.

9. The intelligent controlled-release core-shell alginate soil conditioner according to claim 1, characterized in that: Preparation of magnetic nanoparticles in step (3) The particle method is: and As raw materials, the molar ratio is 2:1, chemical coprecipitation method is adopted, stirring at 60℃ under N2 protection, and adding The pH value was adjusted to 10-11, the temperature was 80℃, and the stirring time was 1h. After washing and drying, the surface was modified with chitosan to obtain magnetic nanoparticles with a particle size of 15-30nm and a magnetic saturation intensity greater than or equal to 60emu / g. particle.

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