Nano-silicon fertilizer, preparation method and application thereof

Abstract

The application discloses a kind of nano silicon fertilizer and its preparation method and application, belong to fertilizer technical field.The nano silicon fertilizer of the application includes the following components: cyclodextrin, chitosan, nano silicon, stress resistance factor, betaine, carbon quantum dots.The application adopts two-step method of cyclodextrin embedding+chitosan chelation, combined with carbon quantum dots synergistic modification.Through cyclodextrin embedding, reduce the surface energy of nano silicon, combined with chitosan chelation modification, improve hydrophilicity, supplemented by the steric hindrance effect of carbon quantum dots, compared with single coating, more effectively solve the problem of nano silicon agglomeration.The finished product of the nano silicon fertilizer of the application can be used for field spraying after one-step compounding, can significantly improve the plant height, proline content and antioxidant enzyme activity of wheat under salt stress after spraying, reduce MDA content, simultaneously realize the selenium-rich quality of agricultural products, improve the photosynthesis efficiency of crops, prolong the fertilizer efficiency period.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, specifically to a nano-silicon fertilizer, its preparation method, and its application. Background Technology

[0002] With the long-term effects of global climate change and improper irrigation, soil salinization is becoming increasingly prominent, severely restricting agricultural production. Salt stress leads to water loss, ion imbalance, and accumulation of reactive oxygen species in plant cells, causing membrane lipid peroxidation, inhibited photosynthesis, and metabolic disorders. Silicon fertilizer, as the fourth largest plant nutrient after nitrogen, phosphorus, and potassium, has significant effects in enhancing crop stress resistance, improving agricultural product quality, and managing obstacle soils. Nano-silicon fertilizer has attracted much attention due to its high specific surface area and bioactivity, but its practical application faces technical bottlenecks such as easy aggregation, poor leaf adhesion, and limited stress resistance effects. Furthermore, existing technologies lack systematic dual-functional carrier design, have insufficient research on synergistic mechanisms, and have complex and costly preparation processes. Summary of the Invention

[0003] To address the problems of existing technologies, the present invention aims to provide a nano-silicon fertilizer, its preparation method, and its application, thereby solving the problems of easy aggregation, poor leaf adhesion, and limited stress resistance of existing silicon fertilizers.

[0004] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a nano-silicon fertilizer is provided, comprising the following components in parts by mass: 5-10 parts of cyclodextrin, 3-8 parts of carboxymethyl chitosan or chitosan derivative, 1-5 parts of nano-silicon, 0.5-2 parts of stress resistance factor, 1-3 parts of betaine, and 0.2-0.8 parts of carbon quantum dots; The cyclodextrin is at least one of β-cyclodextrin, hydroxypropyl-β-cyclodextrin, or methyl-β-cyclodextrin; the chitosan derivative is low molecular weight chitosan, hydroxypropylated low molecular weight chitosan, or quaternized chitosan; and the stress-resistant factor is L-proline, a mixture of L-proline and trehalose, or a mixture of L-proline and salicylic acid. Furthermore, the weight-average molecular weight of hydroxypropylated low molecular weight chitosan is 5000~20000 Da; the weight-average molecular weight of hydroxypropylated low molecular weight chitosan is 5000~20000 Da; and the degree of quaternization of quaternized chitosan is ≥60%.

[0005] Furthermore, the carbon quantum dots have a particle size ≤20nm and a specific surface area ≥300m². 2 / g.

[0006] Furthermore, when the stress-resistance factor is a mixture of L-proline and trehalose, the mass ratio of L-proline to trehalose is 0.8:1 to 1.2:1; when the stress-resistance factor is a mixture of L-proline and salicylic acid in wastewater, the mass ratio of L-proline to salicylic acid is 1.5:1 to 2.5:1.

[0007] This invention provides a method for preparing the above-mentioned nano-silicon fertilizer, comprising the following steps: (1) Preparation of sodium silicate powder; (2) Tetraethyl orthosilicate was prepared using the sodium silicate powder obtained in step (1); (3) Preparation of nano-silicon: Mix ethanol and deionized water, then add ammonia water, mix well and then add tetraethyl orthosilicate obtained in step (2), stir until a milky white SiO2 nanoparticle suspension is formed, centrifuge and wash the precipitate with ethanol, and dry to obtain SiO2 nanoparticle powder. (4) Cyclodextrin-encapsulated silicon nanoparticles: Dissolve cyclodextrin, stir at 60~70℃ for 10~20min, then add the SiO2 nanoparticles obtained in step (3), sonicate and cool down to 20~30℃, then add betaine, centrifuge and wash the precipitate with ethanol, and dry to obtain a light yellow powder. (5) Chitosan chelation modification: The pH of the chitosan solution was adjusted to 5.5~6.5, and the light yellow powder obtained in step (4) was added. After stirring for 1.5~2.5h, the mixture was centrifuged and vacuum dried to obtain a light brown solid. (6) Stress resistance factor compounding: Carbon quantum dots are first added to the light brown solid obtained in step (5), ultrasonically dispersed at 300W for 20min, then stress resistance factor is added and stirred until uniform, filtered, and dried to obtain nano silicon fertilizer product.

[0008] Further, the preparation of sodium silicate powder in step (1) includes the following steps: crushing industrial silicon waste residue with a silicon content ≥60% and sieving it, then adding 10~15wt% hydrochloric acid solution, stirring at 75~85℃ for 1.5~2.5h, filtering and collecting the precipitate, adjusting the pH to 6.5~7.5 with sodium hydroxide solution, and drying at 60~80℃ to obtain sodium silicate powder.

[0009] Further, the preparation of tetraethyl orthosilicate in step (2) includes the following steps: adding deionized water to the sodium silicate powder obtained in step (1) to prepare a sodium silicate solution, then adding ethanol and concentrated hydrochloric acid and stirring to mix, adding sulfuric acid dropwise to adjust the pH of the mixed solution to 1.5~2.5, stirring the reaction for 0.8~1.2h, letting it stand, taking the organic phase, washing it until neutral and drying it, then distilling the obtained product under reduced pressure, collecting the fraction, and obtaining tetraethyl orthosilicate.

[0010] Furthermore, in step (3), the volume ratio of ethanol, deionized water and ammonia is 36:9:1~42:12:1.

[0011] This invention provides an application of the above-mentioned nano-silicon fertilizer in improving the salt stress tolerance of plants, the photosynthetic efficiency of crops, or the selenium enrichment and quality improvement of agricultural products.

[0012] This invention provides a method for improving the salt stress tolerance of plants and enhancing the quality of agricultural products, comprising the following steps: preparing the above-mentioned nano-silicon fertilizer into a spray solution with a mass concentration of 0.1% to 0.3%, and spraying it on the surface of plant leaves once every seven days.

[0013] The present invention has the following beneficial effects: (1) This invention pioneers a four-fold synergistic stress-resistance system combining physical barrier, physiological regulation, photosynthetic enhancement, and quality improvement. Among these, nano-silicon forms a physical barrier in the cell wall, reducing Na+... + Proline and betaine synergistically regulate cell osmotic pressure, protect proteins and membrane structures, and maintain cell water balance; carbon quantum dots enhance the activity of plant antioxidant enzymes and scavenge reactive oxygen species. (2) This invention employs a two-step method of cyclodextrin encapsulation and chitosan chelation, combined with the high specific surface area, abundant functional groups, and excellent steric hindrance effect of carbon quantum dots, which can significantly improve the dispersibility and stability of nanomaterials. Synergistic modification more effectively solves the problem of nano-silicon agglomeration than single coating. By reducing the surface energy of nano-silicon through cyclodextrin encapsulation, improving hydrophilicity through chitosan chelation modification, and supplementing with the steric hindrance effect of carbon quantum dots, the nano-silicon in the spray solution has a stable particle size of ≤60nm within 48h without obvious agglomeration, the leaf contact angle is reduced to <40°, the adhesion is increased by more than 55%, the encapsulation rate is increased to more than 84%, and the cumulative release rate in 24h is reduced to less than 52%, significantly reducing nutrient loss. By using ultrasonic pulse mode (5s working / 2s intermittent) combined with ice bath temperature control (0~5℃), the aggregation of nanoparticles is significantly reduced, ensuring the dispersion stability of each component.

[0014] (3) This invention combines carbon quantum dots and basic stress resistance factors to form a multi-dimensional synergistic effect mechanism. Carboxymethyl chitosan modification reduces the contact angle, improves the adhesion of the solution on the leaf surface and the duration of effect. After spraying, the height of wheat under salt stress increased to more than 12.1 cm, the MDA content decreased to below 10.0 μmol / g FW, the proline content increased to more than 20 μg / g FW, the activity of antioxidant enzymes (SOD, POD) increased by 25%~30%, the selenium content of wheat grains increased to more than 0.15 mg / kg, reaching the national standard for selenium-enriched agricultural products, and the yield of crops in saline-alkali land increased by 15%~20%.

[0015] (4) This invention uses industrial silicon waste residue as silicon source raw material to realize the resource utilization of solid waste and reduce production costs; all components are environmentally friendly materials with no secondary pollution, which is suitable for the development of green agriculture; the finished product can be used for foliar spraying in the field in one step, which is simple to operate and suitable for large-scale promotion and application. Detailed Implementation

[0016] The principles and features of the present invention are described below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, specific conditions or manufacturer-recommended conditions should be followed in the embodiments. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0017] Example 1: A method for preparing nano-silicon fertilizer includes the following steps: (1) Preparation of sodium silicate powder: Take 50g of industrial silicon slag, crush it and pass it through a 200-mesh sieve. Add 200mL of 10% hydrochloric acid solution to the sieved silicon slag, stir at 80℃ for 2h, filter and collect the precipitate, adjust the pH of the filtrate to 7.0 with deionized water, and then vacuum dry at 60℃ for 4h to obtain sodium silicate powder. (2) Preparation of tetraethyl orthosilicate (TEOS): Take 20g of sodium silicate powder obtained in step (1), add 100mL of deionized water to prepare sodium silicate solution, add sodium silicate solution, ethanol and concentrated hydrochloric acid in a volume ratio of 1:3:0.5 to a three-necked flask, stir magnetically at 30℃ for 30min, then slowly add excess sulfuric acid to adjust the pH to 2.0, continue stirring for 1h, take the organic phase after standing, wash with saturated sodium bicarbonate solution until neutral, and then dry with anhydrous magnesium sulfate for 3h; perform vacuum distillation on the obtained product, collect the distillate, and obtain tetraethyl orthosilicate (TEOS, purity ≥98%).

[0018] (3) Preparation of nano-SiO2: Mix 20 mL of ethanol with 5 mL of deionized water, then add 0.5 mL of ammonia water, and stir magnetically at 25 °C for 10 min; then slowly add 1 mL of TEOS obtained in step (2), and continue stirring for 2 h to form a milky white SiO2 nanoparticle suspension, then centrifuge at 8000 rpm for 15 min, wash the precipitate with ethanol 3 times, and vacuum dry at 60 °C for 2 h to obtain pure SiO2 nanoparticle powder.

[0019] (4) Cyclodextrin-encapsulated nano-silicon: Dissolve 5g of β-cyclodextrin in 50mL of deionized water, stir at 60℃ for 15min, then add the nano-SiO2 from step (3), sonicate for 30min (300W), cool to 25℃ and add 1g of betaine, centrifuge at 8000rpm for 15min, wash the precipitate with ethanol 3 times, and vacuum dry at 40℃ for 12h to obtain a light yellow powder.

[0020] (5) Chitosan chelation modification: Take 50 ml of 0.5% carboxymethyl chitosan (CMC) solution and adjust the pH to 6.0 with 1 mol / L hydrochloric acid solution. Add the light yellow powder from step (4), stir at 25℃ for 2 h, centrifuge at 10000 rpm for 10 min, and then vacuum dry at 40℃ to obtain a light brown solid.

[0021] (6) Anti-stress factor compounding: Add 0.002g of carbon quantum dots (Maclean Company, particle size ≤20nm, specific surface area ≥300m² / g) to 0.1g of the light brown solid in step (5), disperse by ultrasonication at 300W for 20min, then add 11.5mg of L-proline, add water to 100mL and stir until uniform, filter with a 0.22μm filter membrane, and vacuum dry at 40℃ to obtain the finished product.

[0022] Example 2: A method for preparing nano-silicon fertilizer includes the following steps: (1) Preparation of sodium silicate powder: Take 50g of industrial silicon slag, crush it and pass it through a 200-mesh sieve. Add 200mL of 10% hydrochloric acid solution to the sieved silicon slag, stir at 80℃ for 2h, filter and collect the precipitate, adjust the pH of the filtrate to 7.0 with deionized water, and then vacuum dry at 60℃ for 4h to obtain sodium silicate powder.

[0023] (2) Preparation of TEOS: Take 20g of sodium silicate powder obtained in step (1), add 100mL of deionized water to prepare sodium silicate solution, add sodium silicate solution, ethanol and concentrated hydrochloric acid in a volume ratio of 1:3:0.5 to a three-necked flask, stir magnetically at 30℃ for 30min, then slowly add excess sulfuric acid to adjust the pH to 2.0, continue stirring for 1h, take the organic phase after standing, wash with saturated sodium bicarbonate solution until neutral, and then dry with anhydrous magnesium sulfate for 3h; perform vacuum distillation on the obtained product, collect the distillate, and obtain tetraethyl orthosilicate (TEOS, purity ≥98%).

[0024] (3) Preparation of nano-SiO2: Mix 20 mL of ethanol with 5 mL of deionized water, then add 0.5 mL of ammonia water, and stir magnetically at 25 °C for 10 min; then slowly add 1 mL of TEOS obtained in step (2), and continue stirring for 2 h to form a milky white SiO2 nanoparticle suspension, then centrifuge at 8000 rpm for 15 min, wash the precipitate with ethanol 3 times, and vacuum dry at 60 °C for 2 h to obtain pure SiO2 nanoparticle powder.

[0025] (4) Cyclodextrin-encapsulated nano-silicon: 6g of hydroxypropyl-β-cyclodextrin was dissolved in 60mL of deionized water and stirred at 60℃ for 15min. Then, the nano-SiO2 from step (3) was added, and the mixture was sonicated for 30min (300W). After cooling to 25℃, 1.2g of betaine was added. The mixture was centrifuged at 8000rpm for 15min. The precipitate was washed three times with ethanol and dried under vacuum at 40℃ for 12h to obtain a light yellow powder.

[0026] (5) Chitosan chelation modification: Adjust the pH of 0.6% quaternized chitosan solution (50 mL) to 6.0 with 0.5 mol / L acetic acid solution, add the light yellow powder from step (4), stir at 25℃ for 2 h, centrifuge at 10000 rpm for 10 min, and then vacuum dry at 40℃ to obtain a light brown solid.

[0027] (6) Anti-stress factor compounding: Add 0.005g of carbon quantum dots (Maclean Company, particle size ≤20nm, specific surface area ≥300m² / g) to 0.1g of the light brown solid in step (5), disperse by ultrasonication at 300W for 20min, then add 12mg of L-proline and 12mg of trehalose, add water to 100mL and stir until uniform, filter with a 0.22μm filter membrane, and vacuum dry at 40℃ to obtain the finished product.

[0028] Example 3: A method for preparing nano-silicon fertilizer includes the following steps: (1) Preparation of sodium silicate powder: Take 50g of industrial silicon slag, crush it and pass it through a 200-mesh sieve. Add 200mL of 10% hydrochloric acid solution to the sieved silicon slag, stir at 80℃ for 2h, filter and collect the precipitate, adjust the pH of the filtrate to 7.0 with deionized water, and then vacuum dry at 60℃ for 4h to obtain sodium silicate powder.

[0029] (2) Preparation of TEOS: Take 20g of sodium silicate powder obtained in step (1), add 100mL of deionized water to prepare sodium silicate solution, add sodium silicate solution, ethanol and concentrated hydrochloric acid in a volume ratio of 1:3:0.5 to a three-necked flask, stir magnetically at 30℃ for 30min, then slowly add excess sulfuric acid to adjust the pH to 2.0, continue stirring for 1h, take the organic phase after standing, wash with saturated sodium bicarbonate solution until neutral, and then dry with anhydrous magnesium sulfate for 3h; perform vacuum distillation on the obtained product, collect the distillate, and obtain tetraethyl orthosilicate (TEOS, purity ≥98%).

[0030] (3) Preparation of nano-SiO2: Mix 20 mL of ethanol with 5 mL of deionized water, then add 0.5 mL of ammonia water, and stir magnetically at 25 °C for 10 min; then slowly add 1 mL of TEOS obtained in step (2), and continue stirring for 2 h to form a milky white SiO2 nanoparticle suspension, then centrifuge at 8000 rpm for 15 min, wash the precipitate with ethanol 3 times, and vacuum dry at 60 °C for 2 h to obtain pure SiO2 nanoparticle powder.

[0031] (4) Cyclodextrin-encapsulated nano-silicon: Dissolve 5g of methyl-β-cyclodextrin in 50mL of deionized water, stir at 60℃ for 15min, then add the nano-SiO2 from step (3), sonicate for 30min (300W), cool to 25℃ and add 1g of betaine, centrifuge at 8000rpm for 15min, wash the precipitate with ethanol 3 times, and vacuum dry at 40℃ for 12h to obtain a light yellow powder.

[0032] (5) Chitosan chelation modification: 0.5% low molecular weight chitosan solution (weight average molecular weight 5000~20000 Da) (take 40 mL) was adjusted to pH 6.0 with 0.8 mol / L acetic acid solution, the light yellow powder from step (4) was added, stirred at 25℃ for 2 h, centrifuged at 10000 rpm for 10 min, and then vacuum dried at 40℃ to obtain a light brown solid.

[0033] (6) Anti-stress factor compounding: Add 0.004g of carbon quantum dots (Maclean Company, particle size ≤20nm, specific surface area ≥300m² / g) to 0.1g of the light brown solid in step (5), disperse by ultrasonication at 300W for 20min, then add 10mg of L-proline and 8mg of salicylic acid, add water to 100mL and stir until uniform, filter with a 0.22μm filter membrane, and vacuum dry at 40℃ to obtain the finished product.

[0034] Comparative example: Four different coating methods were set up as comparative examples, and parallel experiments were conducted with the nano-silicon fertilizers prepared in Examples 1-3 of this invention. The experimental results are shown in Table 2. The nano-SiO2 core particle size, solid content, ultrasonic time, and drying conditions of all samples were consistent with those of Example 1. The only variables were the coating material and number of layers, and whether stress resistance factors and other components were added. The four comparative examples are shown below; Comparative Example 1 (Monolayer β-cyclodextrin coating): The only difference from Example 1 is that monolayer β-cyclodextrin coating is performed on the surface of nano-SiO2, without outer layer modification, and without the addition of L-proline, betaine and other components.

[0035] Comparative Example 2 (single-layer chitosan coating): The difference from Example 1 is that a single layer of chitosan coating is performed on the surface of nano-SiO2, without an inner layer of β-cyclodextrin, and no stress resistance factor or other components are added.

[0036] Comparative Example 3 (double-layer β-cyclodextrin coating): The difference from Example 1 is that both consecutive layers are coated with β-cyclodextrin, without carboxymethyl chitosan, and no stress-resistant factors or other components are added.

[0037] Comparative Example 4 (double-layer chitosan coating): The difference from Example 1 is that both consecutive layers are chitosan coating, without β-cyclodextrin, and no stress resistance factors or other components are added.

[0038] Comparative Example 5 (Carbon-free quantum dots): The difference from Example 1 is that no carbon quantum dots were added to the stress resistance factor.

[0039] Experimental example: (1) Particle size stability value / 48h particle size change rate: Prepare a 0.1%–0.3% spray solution and let it stand at 25℃; use a dynamic light scattering (DLS) instrument to measure the particle size at 0h and 48h respectively; calculate the change rate, the formula is as follows: Change rate = (48h particle size) / 48h particle size stability value ... (0h particle size) / 0h particle size × 100%. Judgment criteria: Particle size ≤ 60nm and change rate < 5% are qualified.

[0040] (2) Leaf contact angle: Fix the plant leaf, add 5 μL of deionized water, and measure the angle between the droplet and the leaf surface using an optical contact angle meter. Repeat 5 times and take the average value. Judgment criteria: Angle <40° is excellent.

[0041] (3) Adhesion improvement rate: Adhesion is the ratio of leaf residue to spray amount determined by the elution method. The specific steps are as follows: ① Quantitative spraying: Select wheat leaves with uniform growth and spray them quantitatively with silicon-containing preparations (experimental group) or water (control group) using a micro-spraying device to ensure accurate spraying amount per unit area (e.g., fixed at 10μL / cm²).

[0042] ② Air dry naturally: Place the treated leaves in a well-ventilated place at room temperature and let them air dry naturally until there are no obvious liquid droplets left on the surface (about 30-60 minutes, avoid direct sunlight).

[0043] ③ Deionized water elution: Place the air-dried leaves into a centrifuge tube containing a fixed volume (e.g., 50 mL) of deionized water, shake thoroughly (or sonicate) for 10 minutes to wash away the silicon-containing substances remaining on the leaf surface.

[0044] ④ Measure silicon content: Take the eluent and determine the silicon content in the eluent using the molybdenum blue colorimetric method or ICP-OES, and calculate the residual amount on the leaf surface (i.e. the total amount of silicon attached to the leaf).

[0045] ⑤ Adhesion calculation: Adhesion (%) = Leaf residue ÷ Theoretical total amount of silica to be sprayed × 100% ⑥ Calculation of lift rate: Adhesion improvement rate (%) = (Adhesion of experimental group - Adhesion of control group) ÷ Adhesion of control group × 100% (4) Encapsulation efficiency: The silicon content was determined by the molybdenum blue colorimetric method / ICP. The encapsulation efficiency was calculated as follows: Encapsulation efficiency = (Total silicon content) / Total silicon content (Free silicon content) / Total silicon content × 100%.

[0046] (5) 24h cumulative release rate: A dialysis bag (MWCO 8000–14000) was used, and the buffer solution simulated the leaf surface environment. The solution was shaken at 25℃ and 100rpm for 24h, and then the silica content was measured. The cumulative release rate was calculated as follows: Cumulative release rate = Cumulative release mass / Encapsulated silica mass × 100%.

[0047] (6) Plant height of wheat under salt stress: ① Salt treatment method: Prepare salt solution with NaCl (analytical grade), with a commonly used concentration of 100-200 mmol / L (0.8%-1.0% concentration is commonly used to simulate moderate salt stress during the seedling stage). ② Treatment plan: When wheat seedlings grow to the three-leaf and one-heart stage, irrigate or hydroponically treat them with salt solution to maintain salt stress; at the same time, spray the leaves with a silicon-containing preparation (concentration gradient of 0.1%, 0.2%, 0.3%), once every 7 days, for a total of 21-28 days (i.e., 3-4 sprays).

[0048] ③ Plant height measurement: After the treatment, the length of wheat from the base to the tip of the uppermost leaf was measured with a ruler. Each treatment was repeated 10 times, and the average value was taken.

[0049] (7) MDA content: ① Weigh 0.5g of fresh wheat leaves, add 5mL of 5% trichloroacetic acid (TCA) solution, and grind in an ice bath to form a homogenate.

[0050] ② Centrifuge the homogenate at 4000 r / min for 10 min and collect the supernatant for later use.

[0051] ③ Take 2 mL of supernatant, add 2 mL of 0.6% thiobarbituric acid (TBA) solution (prepared with 10% TCA), mix well, and heat in a boiling water bath for 15 min.

[0052] ④ Immediately place it in an ice bath to cool, then centrifuge again (4000 r / min, 10 min) and collect the supernatant.

[0053] ⑤ The absorbance of the supernatant at wavelengths of 532 nm, 600 nm and 450 nm was measured using an ultraviolet spectrophotometer.

[0054] The calculation formula is as follows: MDA concentration (μmol / L) = 6.45 × (A 532 -A 600 -0.56×A 450 ; MDA content (μmol / g FW) = [MDA concentration × total volume of extract × dilution factor] ÷ fresh weight of sample.

[0055] (8) Proline content: The acidic ninhydrin colorimetric method was used for measurement, as follows: fresh plant leaves were ground and then extracted with 3% sulfosalicylic acid. After centrifugation, the supernatant was taken, acidic ninhydrin was added to the supernatant, and then heated at 100°C. After extraction with toluene, the absorbance at 520 nm was measured and quantified using a standard curve.

[0056] The test results are shown in Table 1-2.

[0057] Table 1. Test results of core performance before and after modification with nano-silicon fertilizer

[0058] Table 2 Comparison of the effects of silicon fertilizers prepared in Examples 1-3 and Comparative Examples 1-4

[0059] As shown in Tables 1-2, monolayer coating (Comparative Examples 1 and 2) relies solely on the steric hindrance of a single material, which is insufficient to completely suppress the van der Waals forces of nanoparticles, resulting in significant particle size increase. While bilayer coatings using the same material (Comparative Examples 3 and 4) exhibit enhanced steric hindrance, their limited material properties prevent effective control of surface charge and hydrophilic / hydrophobic balance, leading to limited stability. The alternating bilayer structure of this invention combines the hydrophobic cavity embedding of β-cyclodextrin with the steric hindrance of the hydrophilic segments of carboxymethyl chitosan, along with the electrostatic interaction between the two, significantly reducing the aggregation tendency.

[0060] β-Cyclodextrin itself has limited hydrophilicity, and neither monolayer nor bilayer structures can significantly reduce the contact angle (Comparative Examples 1 and 3). Although chitosan has some hydrophilicity, the surface free energy of monolayer or bilayer structures is still relatively high (Comparative Examples 2 and 4). The carboxymethyl chitosan of this invention introduces a large number of -COOH and -OH groups, which greatly improves the surface hydrophilicity, while its film-forming properties enhance the adhesion to the waxy layer on the leaf surface.

[0061] Single-layer structures are not tightly encapsulated, leading to early leakage of silicon (Comparative Examples 1 and 2). While double-layer structures using the same material improve encapsulation efficiency, the lack of interfacial interaction due to the identical materials of the inner and outer layers results in a still relatively high release rate (Comparative Examples 3 and 4). The alternating β-cyclodextrin / carboxymethyl chitosan structure of this invention forms dense "microcapsules" through hydrogen bonding and electrostatic interactions, significantly delaying the release of silicon.

[0062] Comparative examples 1-4 relied solely on the physical barrier effect of silicon, which could not effectively regulate crop physiological metabolism and had limited stress resistance. This invention utilizes the synergistic effect of "physical barrier (nano-silicon) + physiological regulation (L-proline, betaine)" to reduce sodium... + It enters cells and enhances osmotic regulation, thereby significantly reducing salt stress damage.

[0063] The performance data of Examples 2 and 3 are based on the optimization of their preparation process (different cyclodextrin / chitosan types), showing better encapsulation rate, lower release rate and better plant growth promotion effect under salt stress than Example 1, which can more comprehensively verify the performance advantages of the silicon fertilizer of the present invention.

[0064] As can be seen from the results of Comparative Example 5 and Examples 1-3, the present invention significantly reduces the particle size of nano-silicon and greatly improves the suspension stability by adding carbon quantum dots, making the system more stable, which proves that carbon quantum dots have a significant synergistic effect of dispersion and stabilization on nano-silicon.

[0065] In summary, the β-cyclodextrin / carboxymethyl chitosan alternating double-layer encapsulation strategy of this invention, combined with stress-resistance factors, significantly outperforms single-layer or double-layer encapsulation schemes of the same material in terms of dispersion stability, leaf surface adhesion, encapsulation and sustained-release performance, and salt stress resistance. This design fully utilizes the functional complementarity of different materials, achieving a synergistic effect of 1+1>2.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A nano-silicon fertilizer, characterized in that, The components include the following parts by weight: 5-10 parts cyclodextrin, 3-8 parts carboxymethyl chitosan or chitosan derivatives, 1-5 parts nano-silicon, 0.5-2 parts stress-resistant factor, 1-3 parts betaine, and 0.2-0.8 parts carbon quantum dots; Wherein, the cyclodextrin is at least one of β-cyclodextrin, hydroxypropyl-β-cyclodextrin, or methyl-β-cyclodextrin; the chitosan derivative is low molecular weight chitosan, hydroxypropylated low molecular weight chitosan, or quaternized chitosan; and the stress-resistant factor is L-proline, a mixture of L-proline and trehalose, or a mixture of L-proline and salicylic acid.

2. The nano-silicon fertilizer according to claim 1, characterized in that, The weight-average molecular weight of the hydroxypropylated low molecular weight chitosan is 5000~20000 Da; the weight-average molecular weight of the hydroxypropylated low molecular weight chitosan is 5000~20000 Da; and the degree of quaternization of the quaternized chitosan is ≥60%.

3. The nano-silicon fertilizer according to claim 1, characterized in that, The carbon quantum dots have a particle size ≤20nm and a specific surface area ≥300m². 2 / g.

4. The nano-silicon fertilizer according to claim 1, characterized in that, When the stress-resistance factor is a mixture of L-proline and trehalose, the mass ratio of L-proline to trehalose is 0.8:1 to 1.2:1; when the stress-resistance factor is a mixture of L-proline and salicylic acid in wastewater, the mass ratio of L-proline to salicylic acid is 1.5:1 to 2.5:

1.

5. The method for preparing nano-silicon fertilizer according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Preparation of sodium silicate powder; (2) Tetraethyl orthosilicate was prepared using the sodium silicate powder obtained in step (1); (3) Preparation of nano-silicon: Mix ethanol and deionized water, then add ammonia water, mix well and then add tetraethyl orthosilicate obtained in step (2), stir until a milky white SiO2 nanoparticle suspension is formed, centrifuge and wash the precipitate with ethanol, and dry to obtain SiO2 nanoparticle powder. (4) Cyclodextrin-encapsulated silicon nanoparticles: Dissolve cyclodextrin, stir at 60~70℃ for 10~20min, then add the SiO2 nanoparticles obtained in step (3), sonicate and cool down to 20~30℃, then add betaine, centrifuge and wash the precipitate with ethanol, and dry to obtain a light yellow powder. (5) Chitosan chelation modification: The pH of the chitosan solution was adjusted to 5.5~6.5, and the light yellow powder obtained in step (4) was added. After stirring for 1.5~2.5h, the mixture was centrifuged and vacuum dried to obtain a light brown solid. (6) Stress resistance factor compounding: Carbon quantum dots are first added to the light brown solid obtained in step (5), ultrasonically dispersed at 300W for 20min, then stress resistance factor is added and stirred until uniform, filtered, and dried to obtain nano silicon fertilizer product.

6. The preparation method according to claim 5, characterized in that, The preparation of sodium silicate powder in step (1) includes the following steps: crushing industrial silicon waste residue with a silicon content ≥60% and sieving it, then adding 10~15wt% hydrochloric acid solution, stirring at 75~85℃ for 1.5~2.5h, filtering and collecting the precipitate, adjusting the pH to 6.5~7.5 with sodium hydroxide solution, and drying at 60~80℃ to obtain sodium silicate powder.

7. The preparation method according to claim 5, characterized in that, The preparation of tetraethyl orthosilicate in step (2) includes the following steps: adding deionized water to the sodium silicate powder obtained in step (1) to prepare a sodium silicate solution, then adding ethanol and concentrated hydrochloric acid and stirring to mix, adding sulfuric acid dropwise to adjust the pH of the mixed solution to 1.5~2.5, stirring the reaction for 0.8~1.2h, letting it stand, taking the organic phase, washing it until neutral and drying it, then distilling the obtained product under reduced pressure, collecting the fraction, and obtaining tetraethyl orthosilicate.

8. The preparation method according to claim 5, characterized in that, The volume ratio of ethanol, deionized water and ammonia in step (3) is 36:9:1 to 42:12:

1.

9. The application of the nano-silicon fertilizer according to any one of claims 1-4 in improving the salt stress tolerance of plants, the photosynthetic efficiency of crops, or the selenium enrichment and quality improvement of agricultural products.

10. A method for improving the salt stress tolerance of plants and enhancing the quality of agricultural products, characterized in that, The process includes the following steps: preparing the nano-silicon fertilizer described in any one of 1 to 4 into a spray solution with a mass concentration of 0.1% to 0.3%, and spraying it onto the surface of plant leaves once every seven days.

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