Polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system, its preparation and application

Abstract

The application discloses a polydopamine encapsulated CN@mSiO2-NH2 fertilizer loading system, and preparation and application thereof, and belongs to application development of nanotechnology in the agricultural field. The system has good biocompatibility, and has dual application functions of soil and leaf surface. Experiments prove that the product has good slow-release effect and adhesion, can reduce the risk of rainwater scouring and sliding, and effectively improves the residence time on the hydrophobic interface. Application of the product can promote the growth of the Brassica parachinensis seedling root system in the germination period, and improve seed vigor. Compared with ordinary urea, whether the product is applied to soil or leaf surface, the growth of the Brassica parachinensis can be effectively promoted, and yield can be improved. Compared with conventional urea application, soil application of the product is beneficial to the absorption and utilization of nitrogen by the Brassica parachinensis, is beneficial to the retention of residual nitrogen in the soil, and reduces the loss of nitrogen; leaf surface spraying of the product is beneficial to the improvement of the nitrogen utilization rate of the Brassica parachinensis, and reduces the volatilization loss of nitrogen.

Description

Technical Field

[0001] This invention relates to the application and development of nanotechnology in the agricultural field, and specifically to a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system and its preparation and application. Background Technology

[0002] The rapid growth of agricultural production in my country over the past 30 years has proven that applying chemical fertilizers is the fastest, most effective, and most important measure to increase yields. However, numerous studies have shown that my country's fertilizer application has exceeded the economically optimal level. Furthermore, nutrient loss due to irrational fertilizer application has become one of the main sources of non-point source pollution in Chinese agriculture. Foliar fertilization has a higher utilization rate than root fertilization, but the inherent lotus effect of crop leaves makes them hydrophobic. During spraying, most foliar fertilizers detach from the leaves due to poor adhesion and are washed away by rainwater and irrigation, entering the soil, rivers, and other environmental media, causing serious environmental pollution and wasting human resources. The application of slow-release fertilizers helps improve fertilizer utilization and reduce nutrient loss.

[0003] Nanotechnology, a high-tech field that emerged in the 1980s, is hailed as the third industrial revolution of the 21st century and has been widely applied in agriculture. The unique physicochemical properties of nanomaterials, such as their large specific surface area, good biocompatibility, excellent stability, and adsorption capacity, facilitate the continuous absorption of nutrients by plants and effectively control the release rate of fertilizers, thus achieving long-lasting fertilizer retention. Among common nanomaterials, nano-carbon, due to its good biocompatibility, is currently often used as a plant growth promoter and fertilizer synergist in agricultural production. Mesoporous silica nanoparticles, due to their controllable morphology, mesoporous structure and looseness, high biocompatibility, and ease of functionalization, have made rapid progress in drug carriers and are also widely used in agriculture. Although single-component nanomaterials exhibit excellent performance, current classic nanomaterials can no longer meet multiple needs. Because the core and shell materials are of different chemical compositions, the properties of core-shell composite materials will differ from those of single-component materials, enabling successful composite and complementary effects of different materials. Polydopamine (PDA), as a renewable, natural, non-toxic, and biodegradable biopolymer, is rich in catechols and amino acids, which are the same as those in the sticky foot proteins Mefp-3 and Mefp-5 secreted by mussels in nature. It has super adhesion properties and is widely used in the surface modification of nanocarriers to further expand the performance of nanocomposite materials.

[0004] Therefore, utilizing nanotechnology to prepare novel green, efficient, and multifunctional nanocarriers, and exploring their slow-release mechanism and performance-enhancing effects in fertilizers, provides a scientific basis and practical foundation for screening, promoting, and safely utilizing green and high-quality novel nano-fertilizers. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system.

[0006] Another object of the present invention is to provide a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system prepared by the above-described preparation method. This fertilizer loading system has dual application functions in soil and on leaves (slow-release and leaf adhesion properties).

[0007] Another object of the present invention is to provide the application of the above-described polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system includes the following steps:

[0010] (1) Dissolve glucose in solvent A to obtain glucose solution, then react at a constant temperature. After the reaction is completed, centrifuge to collect the precipitate of the reactants to obtain nano carbon (CN).

[0011] (2) The nano-carbon prepared in step (1) was dispersed in a mixed solution of ethanol and water. After adding CTAB and ammonia, the mixture was stirred by ultrasonic and magnetic forces for a period of time. Then, TEOS (tetraethyl orthosilicate) was introduced under continuous stirring. The mixture was stirred at a certain temperature and the reactant was collected by centrifugation to obtain CN@SiO2. The synthesized CN@SiO2 powder was dispersed in a mixed solution of acid and alcohol and refluxed at a certain temperature. This process was repeated three times. The reactant was collected by centrifugation to obtain CN@mSiO2.

[0012] (3) Disperse the CN@mSiO2 prepared in step (2) uniformly in solvent B. After heating the mixture, add APTES (3-aminopropyltriethoxysilane), reflux at a certain temperature, centrifuge to collect the precipitate, and dry to obtain the amino-functionalized CN@mSiO2, i.e. CN@mSiO2-NH2.

[0013] (4) Disperse the CN@mSiO2-NH2 prepared in step (3) in a urea solution, evacuate the reaction system, mix by rotation to allow urea to enter the nanomaterial, centrifuge to separate and collect the precipitate, and the product obtained is CN@mSiO2-NH2@Urea; disperse CN@mSiO2-NH2@Urea in a weakly alkaline Tris-HCl solution, add dopamine hydrochloride, react under stirring at room temperature, centrifuge to separate and collect the precipitate, and dry the product obtained is CN@mSiO2-NH2@Urea@PDA, which is a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system.

[0014] Preferably, solvent A in step (1) is deionized water;

[0015] Preferably, the concentration of the glucose solution in step (1) is 0.15 to 0.60 mol / L; more preferably, it is 0.3 mol / L.

[0016] Preferably, the conditions for the isothermal reaction in step (1) are: the reaction temperature is 160-190°C and the reaction time is 6-12h; further, the reaction temperature is 160°C and the reaction time is 10h.

[0017] Preferably, the precipitate in step (1) needs to be washed several times before drying; the washing is performed with deionized water and ethanol respectively; the drying is vacuum drying.

[0018] Preferably, the concentration of the nano-carbon in the mixed solution in step (2) is 1 to 1.5 mg / mL; more preferably, it is 1.25 mg / mL.

[0019] Preferably, the volume ratio of ethanol to water in the mixed solution in step (2) is 0.4 to 1; more preferably 0.6.

[0020] Preferably, the mass ratio of nano-carbon to CTAB in step (2) is 1:4 to 1:1; more preferably 1:2.

[0021] Preferably, the concentration of the ammonia water in step (2) is 13.38 mol / L;

[0022] Preferably, the final concentration of ammonia in the mixed solution in step (2) is 0.11–0.21 mol / L; more preferably, it is 0.18 mol / L.

[0023] Preferably, the time for ultrasonic and magnetic stirring in step (2) is 20-40 min; more preferably 30 min;

[0024] Preferably, the mass-to-volume ratio of nano-carbon to TEOS in step (2) is 1 g: (3-4) mL; more preferably, it is 1 g: 3 mL.

[0025] Preferably, the conditions for the stirring reaction in step (2) are: a reaction temperature of 35-55°C and a stirring time of 4-8 hours; more preferably, a reaction temperature of 50°C and a stirring time of 6 hours.

[0026] Preferably, in step (2), the precipitate before obtaining CN@SiO2 needs to be washed several times and then dried; the washing is done by alternating washing with deionized water and anhydrous ethanol; the drying is done by vacuum drying at 60°C overnight.

[0027] Preferably, the acid-alcohol mixture in step (2) is an ethanol solution containing 10% v / v of 37% HCl.

[0028] Preferably, the reflux reaction conditions in step (2) are: reflux temperature of 40-70°C and reflux time of 2-4 hours; more preferably, reflux temperature of 60°C and reflux time of 3 hours.

[0029] Preferably, in step (2), the precipitate before obtaining CN@mSiO2 needs to be washed several times and then dried; the washing is done with anhydrous ethanol; the drying is done under vacuum at 60°C for 12 hours.

[0030] Preferably, solvent B in step (3) is toluene;

[0031] Preferably, the concentration of CN@mSiO2 in step (3) is 3-7 mg / mL; more preferably, it is 5 mg / mL.

[0032] Preferably, the mass-to-volume ratio of CN@mSiO2 to APTES in step (3) is 0.3–1.5 g: 1 mL; more preferably, it is 1 g: 1 mL.

[0033] Preferably, the reflux reaction conditions in step (3) are: reflux temperature of 60-90°C and reflux time of 3-5h; more preferably: reflux temperature of 80°C and reflux time of 4h.

[0034] Preferably, the precipitate in step (3) needs to be washed several times before drying; the washing is done with solvent B; the drying is vacuum drying at 40°C for 12 hours.

[0035] Preferably, the concentration of the urea solution in step (4) is 10–500 mg / mL; more preferably, it is 500 mg / mL.

[0036] Preferably, the mass-to-volume ratio of CN@mSiO2-NH2 to urea solution in step (4) is 1g:75-125mL; more preferably, it is 1g:100mL.

[0037] Preferably, the time for rotational mixing in step (4) is 24 hours.

[0038] Preferably, in step (4), the precipitate collected by centrifugation needs to be washed and then dried; the washing is done with deionized water; the drying is vacuum drying, and the condition is vacuum drying overnight.

[0039] Preferably, the concentration of CN@mSiO2-NH2@Urea in step (4) is 0.8–1.2 mg / mL; more preferably, it is 1 mg / mL.

[0040] Preferably, the concentration of the Tris-HCl solution in step (4) is 10 mM and the pH is adjusted to 8.5.

[0041] Preferably, the mass ratio of CN@mSiO2-NH2@Urea to dopamine hydrochloride in step (4) is 1:2 to 3:2; more preferably 1:1.

[0042] Preferably, the reaction time under stirring in step (4) is 18-24 hours; more preferably, it is 20 hours.

[0043] Preferably, in step (4), the precipitate collected by centrifugation needs to be washed and then dried; the washing is done with deionized water; the drying is done under vacuum overnight.

[0044] A polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system was prepared by the above-described preparation method.

[0045] The polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system described above exhibits good slow-release properties in water and good adhesion properties at hydrophobic interfaces.

[0046] The application of the above-mentioned polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system specifically includes at least one of the following applications:

[0047] (a) Application of polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system in promoting root growth during seed germination;

[0048] (b) Application of polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system in improving plant seed vigor;

[0049] (c) Application of polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system in promoting plant growth and increasing plant yield;

[0050] (d) Application of polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system in improving plant nitrogen utilization.

[0051] Preferably, the plant is an agricultural crop; more specifically, it is Chinese cabbage.

[0052] Preferably, in (c), the promotion of plant growth is manifested in increasing plant height, stem height, stem diameter, leaf length, leaf width, and chlorophyll SPAD value.

[0053] Preferably, in (c) and (d), the polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system is applied by soil application and / or foliar spraying.

[0054] The present invention has the following advantages and effects compared with the prior art:

[0055] This invention employs a specific method to prepare a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system. The resulting product, CN@mSiO2-NH2@Urea@PDA, exhibits excellent biocompatibility and combines soil and foliar application functions. Experiments have demonstrated that this product possesses good slow-release effects and adhesion properties, reducing the risk of rainwater runoff and effectively increasing its residence time at hydrophobic interfaces. Application of this product promotes root growth during the germination period of Chinese cabbage seeds and enhances seed vigor. Compared to ordinary urea, both soil and foliar application of this product effectively promotes the growth of Chinese cabbage and increases yield. Compared to conventional urea application, soil application of this product facilitates nitrogen absorption and utilization by Chinese cabbage, helps retain residual nitrogen in the soil, and reduces nitrogen loss; foliar spraying of this product improves nitrogen utilization efficiency in Chinese cabbage and reduces nitrogen volatilization loss. Attached Figure Description

[0056] Figure 1 This is a TEM image of nano-carbon.

[0057] Figure 2 This is a TEM image of CN@mSiO2.

[0058] Figure 3 This is a TEM image of CN@mSiO2-NH2.

[0059] Figure 4 This is a TEM image of CN@mSiO2-NH2@Urea.

[0060] Figure 5 This is a TEM image of CN@mSiO2-NH2@Urea@PDA.

[0061] Figure 6 These are the nitrogen adsorption-desorption curves of CN@mSiO2 and CN@mSiO2-NH2.

[0062] Figure 7 These are the urea release curves of CN@mSiO2-NH2@Urea and CN@mSiO2-NH2@Urea@PDA in water.

[0063] Figure 8 These are SEM images of CN@mSiO2-NH2@Urea(a) and CN@mSiO2-NH2@Urea@PDA(b) on a hydrophobic silicon wafer after several rinsing processes.

[0064] Figure 9 The images show the results of Chinese cabbage seeds after 5 days of cultivation under different treatments; where (a): CK, (b): Urea, (c): CN@mSiO2-NH2@Urea@PDA.

[0065] Figure 10 These are the germination indicators of Chinese cabbage seeds after 5 days of cultivation under different treatments; where a: germination potential and germination rate, b: germination index, c: root length, d: vigor index; Note: different letters represent significant differences between treatments (p<0.05), and the same letter represents no significant differences between treatments (p>0.05).

[0066] Figure 11 These are actual photos of Chinese cabbage grown under different treatments.

[0067] Figure 12 The graph shows the agronomic traits of Chinese cabbage cultivated under different treatments; where a: plant height and stem height, b: stem diameter, c: number of leaves, d: leaf length and leaf width, e: fresh weight and dry weight, f: SPAD value; Note: different letters represent significant differences between treatments (p<0.05), and the same letter represents no significant differences between treatments (p>0.05). Detailed Implementation

[0068] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0069] Example 1 provides a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system, specifically a core-shell structured nanocomposite sphere with good slow-release and adhesion properties. The preparation method includes the following steps:

[0070] (1) Preparation of nano-carbon materials: Prepare 60 mL of 0.30 mol / L glucose solution, stir magnetically for 20 min, then transfer it to a reaction vessel, tighten the lid with a wrench, and place it in a constant temperature oven at 160℃ for 10 hours. After the reaction is complete, wait for the reaction vessel to cool to room temperature before opening it, collect the product by centrifugation, wash it three times with deionized water and ethanol respectively to remove residual by-products, and obtain nano-carbon by vacuum drying.

[0071] (2) Preparation of CN@mSiO2 nanocomposite material: 0.1 g of nano-carbon was dispersed in 80 mL of a mixed solution of ethanol and water with a volume ratio of 0.6. 0.2 g (0.55 mmol) of CTAB and 1.1 mL of ammonia water (13.38 mol / L) were added. The mixture was stirred by sonication and magnetic stirring for 30 min, respectively. Then, under continuous stirring for 10 s, 0.3 mL (1.35 mmol) of TEOS was introduced dropwise. The reaction mixture was stirred at 50 °C for 6 h. After the reaction was completed, the suspension was centrifuged and washed three times each with deionized water and anhydrous ethanol, and then vacuum dried overnight at 60 °C to obtain CN@SiO2. The synthesized CN@SiO2 powder was dispersed in 60 mL of an ethanol solution containing 6 mL of 37% HCl and refluxed at 60 °C for 3 h. This process was repeated three times. The mixture was centrifuged and washed three times with anhydrous ethanol. The mixture was then vacuum dried at 60 °C for 12 h to obtain CN@mSiO2.

[0072] (3) Preparation of CN@mSiO2-NH2 nanocomposite material: Weigh 0.25g of vacuum-activated CN@mSiO2 and add it to 50mL of toluene. Disperse it evenly by ultrasonication. After the mixture is heated to 80℃, add 0.25mL of APTES dropwise and heat it under reflux at 80℃ for 4h. After the reaction is complete, centrifuge the suspension, wash the precipitate three times with toluene, and dry it under vacuum at 40℃ for 12h. The product obtained is amino-functionalized CN@mSiO2, i.e. CN@mSiO2-NH2.

[0073] (4) Add 0.1 g CN@mSiO2-NH2 to 10 mL of 500 mg / mL urea solution, sonicate for 30 min, then evacuate the reaction system for a period of time, and then place it in a rotary mixer at room temperature for 24 h. After loading is complete, centrifuge the mixed solution at 12000 rpm for 15 min, wash the precipitate with deionized water, and vacuum dry overnight. The obtained product is CN@mSiO2-NH2@Urea. 0.1 g CN@mSiO2-NH2@Urea was uniformly dispersed in 100 mL of Tris-HCl (10 mM) solution with pH = 8.5. 0.1 g dopamine hydrochloride was added, and the mixture was stirred and reacted for 20 h. The precipitate was collected by centrifugation at 12000 rpm. The precipitate was washed with deionized water and vacuum dried overnight. The product obtained was CN@mSiO2-NH2@Urea@PDA, which is a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system with a nitrogen loading rate of 20%.

[0074] In addition, 0.1 g CN@mSiO2-NH2 was uniformly dispersed in 100 mL of Tris-HCl (10 mM) solution with pH = 8.5, and 0.1 g dopamine hydrochloride was added. The mixture was stirred and reacted for 20 h. The precipitate was collected by centrifugation at 12000 rpm. The precipitate was washed with deionized water and vacuum dried overnight. The product obtained was CN@mSiO2-NH2@PDA, which is a polydopamine-encapsulated CN@mSiO2-NH2 system without urea loading.

[0075] Example 2: Characterization of Nanomaterial Properties

[0076] The shape, structure, and appearance of the different samples prepared in steps (1)-(4) of Example 1 were observed using transmission electron microscopy (TEM), and the results are as follows: Figures 1-5 As shown in Table 1, the adsorption-desorption curves, specific surface area, pore size, and pore volume of the samples were determined using a fully automated specific surface area and pore volume analyzer. The specific surface area, pore size, and pore volume are shown in Table 1. The adsorption-desorption curves of the samples in steps (2)-(3) are shown in Table 1. Figure 6 As shown.

[0077] Table 1 shows the specific surface area, pore size, and pore volume of the samples from steps (2) to (4).

[0078]

[0079] Figure 1 The nano-carbon particles are smooth spherical and well dispersed. Figure 2The CN@mSiO2 composite nanoparticles exhibit a core-shell structure, indicating that the nano-carbon is successfully encapsulated by the mSiO2 shell. The outer layer displays a rough, porous structure with a spherical shape and a particle size of approximately 200 nm. CN@mSiO2-NH2 composite nanoparticles ( Figure 3 It exhibits a more regular and smooth surface, and its dispersibility is improved compared to CN@mSiO2-NH2. Figure 4 The contrast between the core-shell voids and the outer shell of CN@mSiO2-NH2@Urea is significantly reduced, indicating that urea was successfully loaded. Because the outer shell is coated with polydopamine, CN@mSiO2-NH2@Urea@PDA ( Figure 5 The shell is significantly thickened and the outer layer becomes rougher.

[0080] Depend on Figure 6 As can be seen, both samples CN@mSiO2 and CN@mSiO2-NH2 exhibit typical type IV adsorption isotherms and H3 hysteresis loops, indicating that the surface samples have a mesoporous structure. Furthermore, compared to CN@mSiO2, the pore size, specific surface area, and pore volume of sample CN@mSiO2-NH2 are significantly reduced (Table 1), which is related to the presence of aminosilane molecules within the pores, indicating that amino groups were successfully grafted into the pores of CN@mSiO2. After loading urea, the specific surface area and pore volume of CN@mSiO2-NH2 decreased sequentially to 84.1 m². 2 / g and 0.26cm 3 / g, after coating PDA, the specific surface area and pore volume were further reduced to 23.8m². 2 / g and 0.14cm 3 / g, proving that the pores and surface of the material have been successfully encapsulated by the PDA.

[0081] Example 3: Study on the release behavior of CN@mSiO2-NH2@Urea@PDA

[0082] CN@mSiO2-NH2@Urea and CN@mSiO2-NH2@Urea@PDA nanocomposites with the same urea content were dispersed in 3 mL of deionized water and shaken at 100 rpm at 25 °C. At regular intervals, 2 mL of the dispersion was taken and immediately replenished with fresh solution. The cumulative release of urea was determined using the dimethylbenzaldehyde (DMAB) colorimetric method.

[0083] Figure 7The figures show the urea release curves of different composite nanoparticles in water: As can be seen from the figure, after 14 days of slow release, the CN@mSiO2-NH2@Urea with unblocked mesopores has a relatively fast release rate, with about 78% of the urea being released within 4 days. However, after grafting PDA to block its mesopores, the release of urea is somewhat limited, and the cumulative release rate of urea within 4 days decreases to 54%, indicating that the slow release performance is significantly improved after PDA encapsulation.

[0084] Example 4: Adhesion performance study of CN@mSiO2-NH2@Urea@PDA

[0085] Aqueous suspensions of CN@mSiO2-NH2@Urea and CN@mSiO2-NH2@Urea@PDA nanocomposites with the same urea concentration were dropped onto cleaned hydrophobic silicon wafers, allowed to air dry, and were washed with deionized water 0, 3, 6, and 9 times. The samples were then dried in a vacuum drying oven at 40°C for 6 hours, and their SEM images were observed.

[0086] Figure 8 These are SEM images of different nanocomposite materials on a hydrophobic silicon wafer after several rinsings: As can be seen from the SEM images, the CN@mSiO2-NH2@Urea and CN@mSiO2-NH2@Urea@PDA particles are relatively densely distributed without being rinsed with distilled water. After rinsing with a large amount of distilled water multiple times, only small particles of CN@mSiO2-NH2@Urea remain sparsely distributed on the hydrophobic silicon wafer. In contrast, a large number of CN@mSiO2-NH2@Urea@PDA particles still remain on the hydrophobic silicon wafer, indicating that the adhesion performance is significantly enhanced after PDA encapsulation.

[0087] Example 5 Seed germination test

[0088] Germination tests reflect the impact of nanoparticles on seed physiological characteristics and are an important biosafety test. Plump and uniformly sized Chinese cabbage seeds (specifically, seeds of the Sijiu variety) were selected, disinfected by soaking in a 0.2% potassium permanganate solution for 15 minutes, rinsed three times with deionized water, and air-dried before passing through an 18-mesh sieve. Two layers of sterile filter paper were stacked in clean, dried petri dishes, and 10 mL of sterile water, 0.3 g / L urea solution, and a CN@mSiO2-NH2@Urea@PDA nanocomposite aqueous suspension with the same urea content were added to each dish. Thirty disinfected Chinese cabbage seeds were then evenly and orderly placed in each petri dish and incubated in the dark at 25°C. Each treatment was repeated three times, and the germination potential, germination rate, root length, germination index, and vigor index were measured.

[0089] Figure 9The image shows the results of Chinese choy sum seeds after 5 days of cultivation under different treatments. The germination potential, germination rate, and germination index of the Chinese choy sum seeds are correlated with root length and vigor index as shown below. Figure 10 As shown in the figure, the addition of urea and CN@mSiO2-NH2@Urea@PDA had no significant effect on the germination potential, germination rate, and germination index of Chinese cabbage seeds (p>0.05). Figure 10 a, b). However, the root length and vigor index of the Chinese cabbage seeds after the addition of urea were significantly lower than those of the control group ( Figure 10 c, d), but after adding CN@mSiO2-NH2@Urea@PDA, the root length and vigor index of Chinese cabbage seeds were significantly higher than those of the control group (c, d). Figure 10 c) and d) indicate that the application of CN@mSiO2-NH2@Urea@PDA can promote root growth during seed germination and enhance seed vigor.

[0090] Example 6

[0091] Sijiu Chinese cabbage was selected as the experimental vegetable to investigate its actual nutrient supply performance. The experimental soil was collected from the top 0-20cm layer of farmland in Shaoguan (113.5°E, 24.7°N), after being cleaned, air-dried, and sieved. The soil pH was 5.95, total nitrogen was 1.027 g / kg, available nitrogen was 90.18 mg / kg, available potassium was 133.6 mg / kg, and available phosphorus was 19.02 mg / kg. The experiment involved pot cultivation, with a layer of 200-mesh gauze placed at the bottom of the plastic pot to prevent soil leakage.

[0092] The application rates of nitrogen, phosphorus, and potassium fertilizers were determined according to the technical regulations for soil testing and formula fertilization for leafy vegetables. Except for the control treatment (no nitrogen applied), the application rates of nitrogen, phosphorus, and potassium fertilizers were the same in all other treatments: N 11.89 kg / mu, P2O5 3.74 kg / mu, and K2O 5.25 kg / mu, respectively. The nitrogen, phosphorus, and potassium fertilizers used were urea, superphosphate, and potassium chloride, respectively. All phosphorus fertilizer was applied as basal fertilizer, and 30% of the nitrogen and potassium fertilizers were applied as basal fertilizer, while 70% were applied as top dressing. This was the conventional fertilization method. The experiment included 7 treatments, all with the same total nitrogen application rate; each treatment had 3 replicates. Details of the treatments are shown in Table 2.

[0093] Table 2 Fertilization Treatments in the Experiment

[0094]

[0095] Note: a: Material (containing N) is CN@mSiO2-NH2@Urea@PDA; b: Material (excluding N) is CN@mSiO2-NH2@PDA; Foliar fertilizer in treatments CK and T1-T3 was replaced with water.

[0096] Topdressing fertilizer was applied on days 5, 12, and 19 after transplanting. Chinese cabbage was grown from seedlings and transplanted, then cultivated in an artificial climate chamber at 22°C and 60% humidity, with LED lighting intensity of 250 μmol / m². 2 Harvested 26 days after transplanting, the agronomic traits, yield, soil nitrogen residue rate, plant nitrogen use efficiency, and nitrogen loss rate of Chinese cabbage were measured.

[0097] like Figure 11 As shown, Chinese cabbage cultivated with CN@mSiO2-NH2@Urea@PDA exhibited better growth. Figure 11 T2, T5). Figure 12 It is evident that nitrogen fertilizer application affected the growth of Chinese cabbage. Compared with the control (CK), all treatments significantly increased the plant height and bolt height of the Chinese cabbage. Figure 12 a) Among them, treatments T2 and T5 were significantly better than other treatments (p<0.05); while the stem diameter of treatments T2, T3, and T5 was significantly improved compared with the control (CK), and treatment T2 showed the best effect ( Figure 12 b), compared to conventional fertilization (T1), the fresh weight of the Chinese cabbage in the T2 treatment was increased by 28.75%; compared to other treatments, the fresh weight of the Chinese cabbage in the T2 treatment was significantly better than that in the control group. Figure 12 e) showed a 69.94% increase compared to conventional fertilization (T1), followed by T5 treatment with a 57.10% increase; all treatments had no significant effect on the number of leaves in the Chinese cabbage. Figure 12 c); Compared with other treatments, the T5 treatment showed the best leaf length, leaf width, and chlorophyll SPAD value compared with the blank control group. Figure 12 (d, f). The above experimental results all demonstrate that, compared to ordinary urea, both soil and foliar application of CN@mSiO2-NH2@Urea@PDA can effectively promote the growth of Chinese cabbage and increase yield.

[0098] Different nitrogen fertilizer treatments resulted in varying nitrogen use efficiency in Chinese cabbage. Table 3 shows that compared to T1, the nitrogen use efficiency of Chinese cabbage was significantly improved after treatments T2 and T5 (p<0.05), with T2 treatment showing the highest nitrogen use efficiency at 21.64%, an increase of 15.07% compared to T1. Statistical results indicate that the soil nitrogen residue rates of foliar nitrogen fertilizer treatments T4, T5, and T6 all decreased to varying degrees compared to T1; compared to T1, the soil nitrogen residue rates of treatments T2 and T3 were significantly increased, with T2 treatment showing the highest soil nitrogen residue rate at 56.15%. Among all treatments, T2 treatment had the lowest nitrogen loss rate at 22.21%, a decrease of 25.42% compared to T1; among the foliar treatments, T5 treatment had the lowest nitrogen loss rate at 37.09%, a decrease of 10.54% compared to T1. The above results indicate that, compared with conventional urea application, the application of CN@mSiO2-NH2@Urea@PDA in the soil is beneficial for the absorption and utilization of nitrogen by Chinese cabbage, helps retain the remaining nitrogen in the soil, and reduces nitrogen loss; foliar spraying of CN@mSiO2-NH2@Urea@PDA is beneficial for improving the nitrogen utilization rate of Chinese cabbage and reducing nitrogen volatilization loss.

[0099] Table 3. Effects of different treatments on nitrogen orientation in soil and Chinese cabbage.

[0100]

[0101] Note: Data are expressed as mean ± standard error (n=3); different letters in the same column represent significant differences (p<0.05).

[0102] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system, characterized in that, Includes the following steps: (1) Dissolve glucose in solvent A to obtain a glucose solution with a concentration of 0.15-0.60 mol / L, and then react at a constant temperature of 160-190℃ for 6-12 h. After the reaction is completed, centrifuge to collect the precipitate of the reactants to obtain nano carbon. (2) The nano-carbon prepared in step (1) is dispersed in a mixed solution of ethanol and water. After adding CTAB and ammonia, it is stirred by ultrasound and magnetic force for a period of time. Then, under continuous stirring, TEOS is introduced and stirred at a certain temperature. The reactant precipitate is collected by centrifugation to obtain CN@SiO2. The synthesized CN@SiO2 powder is dispersed in a mixed solution of acid and alcohol and refluxed at 40-70℃ for 2-4 hours. This process is repeated three times. The reactant precipitate is collected by centrifugation to obtain CN@mSiO2. The concentration of nano-carbon in the mixed solution is 1-1.5 mg / mL. The volume ratio of ethanol to water in the mixed solution is 0.4-1. The final concentration of ammonia in the mixed solution is 0.11-0.21 mol / L. The mass ratio of nano-carbon to CTAB is 1:4-1:

1. The mass-volume ratio of nano-carbon to TEOS is 1 g: (3-4) mL. (3) Disperse the CN@mSiO2 prepared in step (2) uniformly in solvent B. After heating the mixture, add APTES and reflux at 60-90℃ for 3-5 hours. Collect the precipitate by centrifugation and dry it to obtain the amino-functionalized CN@mSiO2, i.e. CN@mSiO2-NH2. (4) Disperse the CN@mSiO2-NH2 prepared in step (3) in a urea solution with a concentration of 10-500 mg / mL, evacuate the reaction system, mix by rotation to allow urea to enter the nanomaterial, centrifuge to separate and collect the precipitate, and the product obtained is CN@mSiO2-NH2@Urea; disperse CN@mSiO2-NH2@Urea in a weakly alkaline Tris-HCl solution, add dopamine hydrochloride, react under stirring at room temperature, centrifuge to separate and collect the precipitate, and dry the product obtained is CN@mSiO2-NH2@Urea@PDA, which is a polydopamine-encapsulated CN@mSiO2-NH2 fertilizer system; wherein, the mass-volume ratio of CN@mSiO2-NH2 to urea solution is 1 g: 75-125 mL; the mass ratio of CN@mSiO2-NH2@Urea to dopamine hydrochloride is 1:2-3:

2.

2. The preparation method according to claim 1, characterized in that: The concentration of the glucose solution mentioned in step (1) is 0.30 mol / L; The concentration of the nano-carbon in the mixed solution mentioned in step (2) is 1.25 mg / mL; The volume ratio of ethanol to water in the mixed solution described in step (2) is 0.6; The mass ratio of nano-carbon to CTAB in step (2) is 1:2; The final concentration of ammonia in the mixed solution mentioned in step (2) is 0.18 mol / L; The mass-to-volume ratio of nano-carbon to TEOS in step (2) is 1 g: 3 mL.

3. The preparation method according to claim 1, characterized in that: The conditions for the isothermal reaction described in step (1) are: reaction temperature of 160℃ and reaction time of 10h; The conditions for the stirring reaction described in step (2) are: reaction temperature of 35-55℃ and stirring time of 4-8h; The conditions for the reflux reaction described in step (2) are: reflux temperature of 60℃ and reflux time of 3h; The conditions for the reflux reaction described in step (3) are: reflux temperature of 80℃ and reflux time of 4h.

4. The preparation method according to claim 1, characterized in that: The concentration of CN@mSiO2 mentioned in step (3) is 3-7 mg / mL; The mass-to-volume ratio of CN@mSiO2 to APTES in step (3) is 0.3–1.5 g: 1 mL; The concentration of the urea solution mentioned in step (4) is 500 mg / mL; The mass-to-volume ratio of CN@mSiO2-NH2 to urea solution in step (4) is 1 g: 100 mL; The concentration of CN@mSiO2-NH2@Urea mentioned in step (4) is 0.8–1.2 mg / mL; The mass ratio of CN@mSiO2-NH2@Urea to dopamine hydrochloride in step (4) is 1:

1.

5. The preparation method according to claim 1, characterized in that: Solvent A mentioned in step (1) is deionized water; The acid-alcohol mixture solution mentioned in step (2) is an ethanol solution containing 10% v / v of 37% HCl; Solvent B mentioned in step (3) is toluene; The concentration of the Tris-HCl solution mentioned in step (4) is 10 mM, and the pH is adjusted to 8.

5.

6. The preparation method according to claim 1, characterized in that: The ultrasonic and magnetic stirring times described in step (2) are 20–40 min respectively; The reaction time under stirring in step (4) is 18 to 24 hours.

7. The preparation method according to claim 1, characterized in that: The precipitate described in step (1) needs to be washed several times before drying; the washing is performed with deionized water and ethanol respectively; the drying is vacuum drying. In step (2), the precipitate before obtaining CN@SiO2 needs to be washed several times and then dried; the washing is done by alternating washing with deionized water and anhydrous ethanol; the drying is done by vacuum drying. In step (2), the precipitate before obtaining CN@mSiO2 needs to be washed several times and then dried; the washing is done with anhydrous ethanol; the drying is done under vacuum. The precipitate described in step (3) needs to be washed several times before drying; the washing is done with solvent B; the drying is done under vacuum. In step (4), the precipitate collected from the mixture by centrifugation needs to be washed and then dried; the washing is done with deionized water; the drying is done under vacuum.

8. A polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system according to claim 8, characterized in that, For at least one of the following applications: (a) Application of polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system in promoting root growth during seed germination; (b) Application of polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system in improving plant seed vigor; (c) Application of polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system in promoting plant growth and increasing plant yield; (d) Application of polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system in improving plant nitrogen utilization.

10. The application according to claim 9, characterized in that: The plants mentioned are agricultural crops; In (c), the promotion of plant growth is manifested in increasing plant height, stem height, stem diameter, leaf length, leaf width, and chlorophyll SPAD value; In (c) and (d), the polydopamine-encapsulated CN@mSiO2-NH2 fertilizer loading system is applied by soil application and / or foliar spraying.

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