Carbon nano fertilizer as well as preparation method and application thereof

Abstract

The invention relates to the technical field of biological fertilizers, in particular to a carbon nano-fertilizer and a preparation method and application thereof.The carbon nano-fertilizer is spherical particles with the surface modified with a porous structure, the particle size is 3-8 nm, the surface potential is-10 mV to-25 mV, and the carbon nano-fertilizer comprises, by mass, 1.5%-3% of Ca, 0.8%-1.5% of P and the balance Fe and inevitable impurities. The carbon nano fertilizer realizes synchronous improvement of foliar nutrient absorption efficiency, plant stress resistance and fruit quality, has the comprehensive advantages of strong environmental adaptability, small dosage and low cost, and provides an innovative solution for green and efficient agriculture.

Description

Technical Field

[0002] This invention relates to the field of bio-fertilizer technology, and in particular to a carbon nanotube fertilizer, its preparation method, and its application. Background Technology

[0003] As an important member of the nanomaterial family, carbon dots (CDs) are typically spherical particles with a diameter of less than 10 nm. They possess excellent water solubility, photoluminescence, ease of control, low toxicity, and biocompatibility, making them promising candidates for applications in bioimaging, metal-free RTP materials, LED devices, ion detection, energy storage, anti-counterfeiting, and targeted drug delivery. Numerous studies have demonstrated the immense potential of CDs in promoting plant growth and development, regulating photosynthesis, and enhancing plant stress resistance.

[0004] For example, on December 31, 2024, Professor Rui Yu-kui's team from China Agricultural University published a review article entitled "Effects of nanofertilizers on the mechanism of photosynthetic efficiency in plants: A review" in Phyton, outlining the effects of carbon nanofertilizers on plant photosynthesis. These effects include increased biomass, pigment and gas openness, photosynthetic efficiency, and plant stress resistance. Meanwhile, Chinese invention patent CN115259138B discloses a method for improving crop drought resistance and yield based on carbon nanomaterials. Specifically, carbon nanomaterials are applied as plant fertilizer to the roots or leaves of crops. The technical effects include: significantly reducing the accumulation of ROS in crops under drought conditions, avoiding oxidative damage; improving the crop's utilization efficiency of ultraviolet light, enhancing photosynthesis under drought conditions; increasing root absorption of nutrients and water, promoting normal crop growth during drought, reducing crop yield loss, and ensuring crop quality. The preparation method of the carbon nanomaterials involved in this invention is as follows: 20 mL of ultrapure water, 2.2 g of citric acid, and 670 μL of ethylenediamine were mixed thoroughly and heated at 200 °C for 12 h. After heating, 1 mL of polyacrylic acid was added and heated at 80 °C for 4 h. Subsequently, the product was sonicated for 30 minutes using a CNC sonicator to disperse it in the aqueous solution. The solution was then purified using a dialysis bag for 48 h. Finally, the resulting mixture was freeze-dried to obtain carbon nanomaterials.

[0005] This carbon nanomaterial helps crops (soybeans) improve their efficiency in utilizing ultraviolet light, enhancing photosynthesis under drought conditions; it also increases root absorption of nutrients and water, promoting normal crop growth during drought, reducing yield loss, and ensuring crop quality. However, this... Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a carbon nano-fertilizer, its preparation method, and its application. The carbon nano-fertilizer simultaneously improves foliar nutrient absorption efficiency, plant stress resistance, and fruit quality, while possessing comprehensive advantages such as strong environmental adaptability, low dosage, and low cost, thus providing an innovative solution for green and efficient agriculture.

[0007] To achieve the above-mentioned technical effects, the present invention adopts the following technical solution: In a first aspect, the present invention provides a carbon nanotube fertilizer, wherein the fertilizer is a spherical particle with a surface-modified porous structure, a particle size of 3 to 8 nm, a surface potential of -10 to -25 mV, and contains C, O, N, Ca and P elements, wherein the mass percentage of Ca element is 1.5% to 3% and the mass percentage of P element is 0.8% to 1.5%.

[0008] Secondly, the present invention also provides a method for preparing the aforementioned carbon nanofiber fertilizer, comprising the following steps: S1: Citric acid, ethylenediamine, calcium salt, phosphate salt and ultrapure water are mixed and hydrothermally reacted at 160-220℃ for 10-14 hours to generate calcium-phosphorus co-doped carbon nanonuclei. S2: Add polyacrylic acid, sodium alginate and chitosan to the product of step S1, and heat at 70-90°C for 3-5 hours for modification; S3: Add ammonium bicarbonate and sonicate, then dialysis for purification; S4: Load chlorophyll derivatives and superoxide dismutase (SOD) into the purified solution, and freeze-dry to obtain the final product.

[0009] Preferably, in S1, the calcium salt is calcium nitrate, the phosphate salt is potassium dihydrogen phosphate, and the molar ratio of calcium salt to phosphate salt is 1.5:1 to 2.5:1.

[0010] Preferably, the mass ratio of polyacrylic acid, sodium alginate and chitosan in S2 is (1.2-1.8):(0.15-0.25):(0.08-0.12).

[0011] Preferably, the ultrasonic treatment in S3 has a power of 300-500W and a duration of 30-60 minutes, and the system temperature is maintained at 0-10℃ during ultrasonic treatment.

[0012] Preferably, the chlorophyll derivative in S4 is sodium copper chlorophyll salt, and its loading is 0.5% to 1.5% of the total mass of carbon nanomaterials; the loading of the SOD enzyme is 500 to 1500 activity units per gram of carbon nanomaterials.

[0013] Thirdly, the present invention also provides an application of the aforementioned carbon nano-fertilizer in the cultivation of melon and fruit plants.

[0014] Preferably, the cucurbitaceous plant is cucumber.

[0015] Furthermore, the application is carried out during cucumber cultivation using any of the following methods: (a) Prepare a 0.05% to 0.2% aqueous dispersion of carbon nanomaterials and spray it on the leaves during the flowering period of cucumber, with an interval of 5 to 10 days between sprayings; And / or: (b) Carbon nanomaterials and humic acid are mixed at a mass ratio of 1:2 to 1:4 and applied to the root soil through a drip irrigation system.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) High-efficiency foliar absorption and utilization The calcium-phosphorus co-doped carbon nanoparticles have a particle size of 48.2 ± 5.1 nm (much smaller than the pore size of leaf stomata). Combined with a Zeta potential of -25.3 mV, they efficiently penetrate the leaf surface through a dual pathway of electrostatic adsorption and stomatal penetration, achieving a phosphorus absorption rate of 89.7% (compared to only 53.1% for conventional fertilizers). Simultaneously, the nanoparticles directly enter the cytoplasm via endocytosis, avoiding loss through the apoplast pathway, resulting in an intracellular calcium ion concentration 3.8 times higher than that of conventional fertilizers.

[0017] (2) Calcium-phosphorus synergistic mechanism Ca²⁺ activates the ROP GTPase signaling pathway at the pollen tube tip, and PO₄³⁻ drives ATP synthesis, synergistically increasing pollen tube length by 52.3% and fruit set rate to 82.5% (compared to 65.2% with conventional fertilizers).

[0018] (3) Resistance and quality improvement Calcium and phosphorus co-doping activates the MAPK pathway, upregulates SOD gene expression, and increases SOD activity to 398 U / g (compared to 255 U / g in conventional fertilizers). MDA content is reduced to 2.8 μmol / g (a 43% decrease compared to conventional fertilizers). In terms of nutritional quality, it contains 28.6 mg / 100g of vitamin C, and due to the efficient driving of GDP-galactose phosphorylation enzyme activity by phosphorus, the synthesis rate is increased by 1.8 times.

[0019] (4) Synergistic effect of surface modification system The carbon nano-fertilizer provided by this invention is modified with polyacrylic acid, sodium alginate and chitosan in a reasonable ratio to adjust its zeta potential to -25.3 mV, balancing dispersion stability and leaf surface adhesion. Chitosan fixes SOD enzyme through hydrogen bonds, and the activity retention rate is significantly improved.

[0020] (5) Environmental adaptability and application potential Sodium alginate forms a hydrophobic-hydrophilic alternating film, with a nighttime leaching loss rate of only 12.3% (compared to over 35% for conventional fertilizers), making it suitable for rainy areas. Furthermore, it can be applied directly through foliar application, effectively reducing soil dependence. (6) Technological and economic advantages Calcium-phosphorus nanonuclei are slowly released in mesophyll cells (80% release rate in 72 hours), reducing the spraying frequency from twice a week to once a week as usual.

[0021] (7) Feasibility of large-scale preparation: Hydrothermal reaction and ultrasonic technology enable continuous production, reducing costs by 25% compared to similar nano-fertilizers (raw material utilization rate >95%). Detailed Implementation

[0022] The embodiments of the technical solution of the present invention will be described in detail below. These embodiments are only used to illustrate the technical solution of the present invention more clearly, and are therefore merely examples and should not be used to limit the scope of protection of the present invention.

[0023] The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and are therefore merely examples and should not be used to limit the scope of protection of the present invention. For those skilled in the art, any equivalent modifications and substitutions to the embodiments described below are also within the scope of the present invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are commercially available conventional products.

[0024] To better illustrate the invention, numerous specific details are set forth in the following detailed description. Those skilled in the art will understand that the invention can be practiced without certain specific details. In other embodiments, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, all units used in this specification are International Standard Units (SI), and all numerical values ​​and ranges appearing in this invention should be understood to include unavoidable errors in industrial production.

[0025] Example 1 The purpose of this embodiment is to provide a method for preparing carbon nanotube fertilizer, which includes the following steps: S1: 4.72 g (20 mmol) of calcium nitrate (Ca(NO3)2·4H2O, molecular weight 236.15) and 1.36 g (10 mmol) of potassium dihydrogen phosphate (KH2PO4, molecular weight 136.09) were mixed at a molar ratio of 2.0:1. 5 g of citric acid, 3 mL of ethylenediamine, and 100 mL of ultrapure water were added. The mixture was subjected to a hydrothermal reaction at 180 °C for 12 hours to generate calcium-phosphorus co-doped carbon nanonuclei.

[0026] S2: Add 1.5g of polyacrylic acid, 0.2g of sodium alginate, and 0.1g of chitosan (mass ratio 1.5:0.2:0.1) to the reaction product and heat at 80℃ for 4 hours for modification.

[0027] S3: Add 2g of ammonium bicarbonate and sonicate at 400W for 45 minutes, maintaining the system temperature at 5°C with an ice bath during this period. Then, dialysis for 24 hours to purify.

[0028] S4: Add chlorophyll copper sodium salt at 1.0% of the total mass of carbon nanomaterials, load 1000 SOD enzyme activity units per gram of material, freeze dry to obtain a light green powder product, which is recorded as carbon nano-fertilizer 1.

[0029] Example 2 Based on Example 1, the purpose of this example is to provide a method for preparing carbon nanofiber fertilizer, which includes the following steps: S1: Calcium nitrate and potassium dihydrogen phosphate were mixed at a molar ratio of 2.2:1 and subjected to a hydrothermal reaction at 200°C for 13 hours. The amounts of other raw materials were the same as in Example 1.

[0030] S2: Add 1.8g of polyacrylic acid, 0.25g of sodium alginate, and 0.12g of chitosan (mass ratio 1.8:0.25:0.12), and heat at 90℃ for 3.5 hours.

[0031] S3: Treatment was performed using 500W ultrasonic power for 60 minutes, with the temperature maintained at -2℃ using a dry ice-ethanol bath. The conductivity of the solution after dialysis was ≤10μS / cm.

[0032] S4: Chlorophyll copper sodium salt loading 1.2%, SOD enzyme loading 1500 U / g. Freeze-drying yielded a dark green porous solid, recorded as carbon nano-fertilizer 2.

[0033] Example 3 The purpose of this embodiment is to provide a method for preparing carbon nanotube fertilizer, which includes the following steps: S1: Calcium phosphate salts reacted at a molar ratio of 1.8:1 at 220℃ for 11 hours, significantly improving the crystallinity of the carbon core.

[0034] S2: 1.2g polyacrylic acid, 0.18g sodium alginate, and 0.09g chitosan (mass ratio 1.2:0.18:0.09) were modified at 70℃ for 5 hours.

[0035] S3: 300W ultrasonic treatment for 30 minutes, with saline bath temperature controlled at 8℃. The dialysis bag has a molecular weight cutoff of 8000-14000.

[0036] S4: Chlorophyll loading 0.8%, SOD enzyme 800U / g, freeze-dried product is uniformly yellow-green, recorded as carbon nano-fertilizer 3.

[0037] Comparative Example 1 This comparative example provides a method for preparing carbon nanofiber fertilizer, referring to Example 1. The difference between this preparation method and Example 1 is that: S1: Add 30 mmol of calcium nitrate to 5 g of citric acid, 3 mL of ethylenediamine, and 100 mL of ultrapure water. Perform a hydrothermal reaction at 180 °C for 12 hours to generate calcium-doped carbon nanonuclei.

[0038] The remaining reaction steps are the same as in Example 1, and the resulting carbon nano-fertilizer is recorded as control 1.

[0039] Comparative Example 2 This comparative example provides a method for preparing carbon nanofiber fertilizer, referring to Example 1. The difference between this preparation method and Example 1 is that: S1: Add 30 mmol of potassium dihydrogen phosphate to 5g of citric acid, 3mL of ethylenediamine, and 100mL of ultrapure water. Perform a hydrothermal reaction at 180℃ for 12 hours to generate phosphorus-doped carbon nanonuclei.

[0040] The remaining reaction steps are the same as in Example 1, and the resulting carbon nano-fertilizer is recorded as control 2.

[0041] Comparative Example 3 This comparative example provides a method for preparing carbon nanofiber fertilizer, referring to Example 1. The difference between this preparation method and Example 1 is that: S1: Same as Example 1; S2: Add 1.5g of polyacrylic acid and 0.2g of sodium alginate (mass ratio 1.5:0.2) to the reaction product and heat at 80℃ for 4 hours for modification.

[0042] The remaining steps are the same as in Example 1, and the resulting carbon nano-fertilizer is recorded as control 3.

[0043] Comparative Example 4 This comparative example provides a method for preparing carbon nanofiber fertilizer, referring to Example 1. The difference between this preparation method and Example 1 is that: S1: Same as Example 1; S2: Add 1.5g of polyacrylic acid and 0.1g of chitosan (mass ratio 1.5:0.1) to the reaction product and heat at 80℃ for 4 hours for modification.

[0044] The remaining steps are the same as in Example 1, and the resulting carbon nano-fertilizer is recorded as control 4.

[0045] Test case Based on the foregoing embodiments, this embodiment tests the effects of the prepared carbon nano-fertilizers 1-4 and reference standards 1-4, specifically as follows: The prepared carbon nano-fertilizer 1 and reference standards 1-4 were prepared into a suspension with a mass concentration of 0.1%, and the suspension contained 0.01% silane coupling agent.

[0046] 1.1 Standardization of fertilizer application methods Test materials: All examples and comparative examples used the same cucumber variety, Jinyou 35, grown in a greenhouse (temperature 25-30℃, humidity 60%-80%).

[0047] Experimental design: Each group has 3 replicates, with 30 plants per replicate, arranged in a randomized block design.

[0048] Application guidelines: Foliar spraying is used only, and soil moisture content is maintained by conventional irrigation (70%–180% of field capacity). Foliar spraying is carried out during the cucumber flowering period, twice, with an interval of 5 days between each application; a pressure sprayer (droplet diameter 50–100 μm) is used to spray until both sides of the leaves are evenly moistened (about 50 mL / plant).

[0049] 1.2 Experimental Results The fruit setting rate, vitamin C content, MDA content, SOD activity, photosynthetic rate, and leaf phosphorus absorption rate of each group were measured and statistically analyzed. The experimental results are shown in Table 1.

[0050] Table 1: Comparison of cucumber growth and fruit condition among groups Note: Data are presented as mean ± standard deviation (n=3). Different letters in the same column indicate significant differences between groups (p<0.05, Duncan test).

[0051] Foliar phosphorus absorption rate: the ratio of the increase in phosphorus content in leaves to the total amount of phosphorus sprayed within 24 hours after foliar spraying.

[0052] The percentage increase in pollen tube length was calculated based on the control group (pollen tube length 1.2 ± 0.1 mm) that was not fertilized.

[0053] The particle size of the nanoparticles was determined by dynamic light scattering (DLS), and the conventional fertilizer (Comparative Example 5) consisted of ordinary micron-sized particles.

[0054] Zeta potential was measured by dynamic light scattering (DLS). The data is the mean ± standard deviation of three replicates. A negative value indicates that the particle surface is negatively charged. The larger the absolute value, the higher the dispersion stability.

[0055] 1.3 Analysis of Experimental Results (1) Correlation between surface charge (Zeta potential) and nanoparticle properties Charge and dispersibility: When the absolute value of the Zeta potential is >25 mV (Example 1), the particles remain monodisperse due to electrostatic repulsion (agglomeration rate <5%); while in Comparative Example 5 (-5.2 mV), due to the neutral charge, the particles are severely agglomerated (particle size >1 μm).

[0056] Charge and leaf adhesion: The leaf cuticle carries a weak positive charge at pH 6.0. The -25.3 mV in Example 1 enhances adhesion through electrostatic attraction, resulting in 3.2 times higher adhesion than that in Comparative Example 5.

[0057] Charge-size synergy: The absolute value of charge is negatively correlated with the particle size (R²=0.81), indicating that high negative charge inhibits grain growth (e.g., Comparative Example 3 contains only polyacrylic acid / sodium alginate, with a charge of -34.7 mV and a particle size of 61.3 nm).

[0058] (2) Biological synergistic mechanism of calcium-phosphorus co-doping Pollen tube development: In Example 1, Ca²⁺ directly enters pollen cells through nanoparticles, activating ROP GTPase to regulate vesicle transport; phosphorus provides ATP to drive cell wall relaxant expansin, synergistically promoting pollen tube elongation (52.3% vs. conventional 19.5%). Photosynthesis: Calcium ions enhance the stability of the photosystem II (PSII) D1 protein (chlorophyll fluorescence parameter Fv / Fm increases by 15%), and phosphorus drives the Calvin cycle through ATP synthesis. Co-incorporation of both increases the photosynthetic rate by 44.6% (vs. conventional).

[0059] Antioxidant defense: The Ca-P co-incorporated structure is directly absorbed through the leaf surface, activates the MAPK signaling pathway, and upregulates SOD gene expression (qPCR showed that SOD1 expression increased by 2.1 times).

[0060] (3) Biological synergistic mechanism of calcium-phosphorus co-doping Charge balance: The ternary modification (polyacrylic acid-sodium alginate-chitosan) in Example 1 neutralized the carboxyl group (-) of polyacrylic acid with the amino (+) part of chitosan, adjusting the Zeta potential from -34.7 mV (Comparative Example 3) to -25.3 mV, thus avoiding the decrease in leaf surface contact efficiency caused by excessive repulsion.

[0061] Erosion resistance: Sodium alginate forms a hydrophilic-hydrophobic alternating film on the leaf surface, reducing nighttime dew erosion (loss rate 12.3% vs. 19.6% in Comparative Example 4).

[0062] Enzyme stability: Chitosan immobilizes SOD enzyme through hydrogen bonding and electrostatic interaction. The enzyme activity retention rate of Example 1 reached 92% (comparative Example 3 had an 18% increase in inactivation rate due to the lack of chitosan).

[0063] (4) Limitations of conventional fertilizers Physical barrier: The particle size of conventional fertilizers (1200 nm) is much larger than the stomata (50-100 nm) and cell wall pores (<20 nm) of leaves, resulting in more than 90% of nutrients being retained on the leaf surface.

[0064] Chemical damage: Large particles remain on the leaf surface for a long time, clogging stomata and causing the accumulation of reactive oxygen species (ROS) (MDA content increases by 75%), which inhibits photosynthetic electron transport.

[0065] Bioavailability: The Ca²⁺ and PO₄³⁻ in conventional fertilizers exist in ionic form, which are easily washed away by rainwater or inactivated by binding with leaf secretions.

[0066] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A carbon nanofiber fertilizer, characterized in that: The fertilizer is a spherical particle with a porous structure modified on the surface, with a particle size of 3-8 nm and a surface potential of -10 to -25 mV. It contains C, O, N, Ca and P elements, with Ca accounting for 1.5% to 3% by mass and P accounting for 0.8% to 1.5% by mass.

2. The method for preparing a carbon nanotube fertilizer as described in claim 1, characterized in that, Includes the following steps: S1: Citric acid, ethylenediamine, calcium salt, phosphate salt and ultrapure water are mixed and hydrothermally reacted at 160-220℃ for 10-14 hours to generate calcium-phosphorus co-doped carbon nanonuclei. S2: Add polyacrylic acid, sodium alginate and chitosan to the product of step S1, and heat at 70-90°C for 3-5 hours for modification; S3: Add ammonium bicarbonate and sonicate, then dialysis for purification; S4: Load chlorophyll derivatives and superoxide dismutase (SOD) into the purified solution, and freeze-dry to obtain the final product.

3. The method for preparing a carbon nanotube fertilizer as described in claim 2, characterized in that: In S1, the calcium salt is calcium nitrate, the phosphate salt is potassium dihydrogen phosphate, and the molar ratio of calcium salt to phosphate salt is 1.5:1 to 2.5:

1.

4. The method for preparing a carbon nanofiber fertilizer as described in claim 2, characterized in that: The mass ratio of polyacrylic acid, sodium alginate and chitosan in S2 is (1.2-1.8):(0.15-0.25):(0.08-0.12).

5. The method for preparing a carbon nanotube fertilizer as described in claim 2, characterized in that: The ultrasonic treatment in S3 has a power of 300-500W and a duration of 30-60 minutes, and the system temperature is maintained at 0-10℃ during ultrasonic treatment.

6. The method for preparing a carbon nanotube fertilizer as described in claim 2, characterized in that: The chlorophyll derivative in S4 is sodium copper chlorophyll salt, and its loading is 0.5% to 1.5% of the total mass of carbon nanomaterials; the loading of the SOD enzyme is 500 to 1500 activity units per gram of carbon nanomaterials.

7. The application of the carbon nano-fertilizer as described in claim 1 in the cultivation of melon and fruit plants.

8. The application as described in claim 7, characterized in that: The fruit or vegetable mentioned is cucumber.

9. The application as described in claim 7, characterized in that, Apply during cucumber growing using any of the following methods: (a) Prepare a 0.05% to 0.2% aqueous dispersion of carbon nanomaterials and spray it on the leaves during the flowering period of cucumber, with an interval of 5 to 10 days between sprayings; And / or: (b) mix carbon nanomaterials with humic acid at a mass ratio of 1:2 to 1:4 and apply the mixture to the root soil through a drip irrigation system.

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