Preparation of selenium-doped nano-selenium fertilizer and application of selenium-doped nano-selenium fertilizer in improvement of fruit quality

Abstract

The invention discloses preparation of a selenium-doped nano-selenium fertilizer and application of the selenium-doped nano-selenium fertilizer in improvement of fruit quality. The preparation method comprises the following steps: dissolving selenomethionine and citric acid in water, carrying out hydrothermal reaction, naturally cooling to room temperature, dialyzing the obtained yellow solution, and drying the dialyzed solution to obtain brown powder, namely the selenium-doped nano material. And mixing the selenium-doped nano-material, a surfactant and water, and adjusting the pH value to 5.8-6.0 to obtain the selenium-doped nano-selenium fertilizer. The selenium-doped nano material with the particle size range of 1-6 nm and good dispersity is prepared through a hydrothermal reaction of selenomethionine and citric acid; the crop selenium is doped with the active ingredients of the nano-selenium fertilizer, so that the nutritional requirements of plants on the selenium element can be met by trace application, and the oxidation resistance, the product and the quality of fruits are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nano fertilizers, and in particular to the preparation of a selenium-doped nano selenium fertilizer and its application in improving fruit quality. Background Art

[0002] Selenium significantly enhances antioxidant capacity in plants. During normal physiological metabolism in higher plants, as well as in response to environmental stresses such as drought, high temperatures, ultraviolet radiation, and heavy metal pollution, large numbers of free radicals are generated within their cells. These highly reactive free radicals attack biofilms, proteins, nucleic acids, and other biomacromolecules within cells, causing structural damage and physiological dysfunction, ultimately impacting normal plant growth and development. Fortunately, plants possess a robust antioxidant defense system, in which antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) play a key role. SOD dismutates superoxide anion radicals into oxygen and hydrogen peroxide, thereby mitigating their direct toxic effects on cells. CAT, on the other hand, decomposes hydrogen peroxide into water and oxygen, further eliminating this potentially harmful substance and maintaining a balanced redox state within cells.

[0003] Selenium, as a beneficial element, can interact with these antioxidant enzymes in plants, enhancing their activity. For example, an adequate supply of selenium can significantly increase the activity of SOD in plant cells, accelerating the dismutation reaction of superoxide anion free radicals and reducing their accumulation within cells. Selenium can also promote the activity of CAT, more effectively scavenging hydrogen peroxide, thereby reducing the oxidative damage caused by free radicals to cells.

[0004] Selenium fertilizers currently on the market are categorized by application method, including foliar sprays, water-based fertilizers, and organic fertilizers. These fertilizers are primarily made from sodium selenate or sodium selenite, complexed with amino acids, humic acid, and EDTA, creating formulations that are more easily absorbed by plants. They can be applied alone or mixed with organic or microbial fertilizers. Currently, traditional selenium fertilizers struggle to match their release with demand, resulting in low utilization rates, insignificant increases in fruit selenium content, and environmental pollution. With the rapid development of nanotechnology, the synthesis of specialized selenium rice fertilizers has become a research hotspot. Patents such as CN116041114A disclose a method for preparing and using a biological nanoselenium fertilizer, and CN112961004A discloses a slow-release nanoselenium fertilizer, its preparation method, and its production equipment. These all utilize elemental nanoselenium as the fertilizer. However, the conversion efficiency of elemental nanoselenium fertilizers is affected by the metabolic capacity of the soil and plants. Excessive amounts of selenium can cause acute toxicity, while too little selenium can fail to enhance antioxidant activity. While using a carrier to load elemental selenium nanoparticles can control their release, the preparation process is complex and costly. Selenium-doped nanoselenium fertilizers, on the other hand, have a controlled selenium form, allowing for direct release in a highly active form such as SeO₃²⁻, resulting in a more efficient and rapid release. Furthermore, the amount of selenium released can be controlled. Therefore, there is a need for selenium-doped nanoselenium fertilizers that can enhance plant selenium absorption, promote crop development, and ultimately increase yields. Summary of the Invention

[0005] In response to the above-mentioned prior art, the present invention aims to provide a method for preparing a selenium-doped nano-selenium fertilizer and its application in improving fruit quality. This invention utilizes a hydrothermal reaction between selenomethionine and citric acid to produce a selenium-doped nanomaterial with a particle size range of 1-6 nm and good dispersibility. This selenium-doped nanomaterial, the active ingredient in the nano-selenium fertilizer, can be applied in trace amounts to meet the plant's nutritional needs for selenium, thereby improving the antioxidant capacity, yield, and quality of fruit.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect of the present invention, a selenium-doped nanomaterial is provided, wherein the preparation method is as follows: Selenomethionine and citric acid are dissolved in water, subjected to a hydrothermal reaction, and naturally cooled to room temperature. The resulting yellow solution is dialyzed, and the dialyzed solution is dried to obtain a brown powder, which is a selenium-doped nanomaterial; the particle size of the selenium-doped nanomaterial is 1-6 nm.

[0007] Preferably, the mass ratio of selenomethionine to citric acid is 1:0.5; and the concentration of selenomethionine is 100 g / L.

[0008] Preferably, the temperature of the hydrothermal reaction is 180° C. and the time is 6 h.

[0009] Preferably, the dialysis is performed using a 500D dialysis bag for 24 hours, and the dialysis water is replaced every 6 to 8 hours.

[0010] Preferably, the drying is vacuum freeze drying, and the vacuum freeze drying temperature is -45°C.

[0011] The second aspect of the present invention provides the use of selenium-doped nanomaterials in the preparation of selenium-doped nano-selenium fertilizers.

[0012] In a third aspect of the present invention, a selenium-doped nano-selenium fertilizer is provided, which is prepared by the following method: mixing a selenium-doped nano-material, a surfactant and water and adjusting the pH to acidic.

[0013] Preferably, the pH is adjusted to 5.8-6.0; and the surfactant is Tween-80.

[0014] Preferably, the concentration of the selenium-doped nanomaterial is 50 mg / L; the mass concentration of the surfactant is 0.5% to 0.05%.

[0015] A fourth aspect of the present invention provides the use of selenium-doped nano-selenium fertilizer in improving the antioxidant capacity of fruit, wherein the fruit is apple.

[0016] Improving antioxidant capacity includes: increasing the activity of catalase, superoxide dismutase, and selenium content in the fruit and reducing the content of hydrogen peroxide and superoxide anion in the fruit.

[0017] Beneficial effects of the present invention: (1) The green selenium fertilizer of the present invention is designed to improve the efficiency of selenium absorption by plants, thereby increasing the selenium content of fruits and enhancing the commercial value and economic benefits of the fruits. The selenium fertilizer is prepared using nanotechnology and has the following advantages: on the one hand, its nanostructure can significantly enhance the adsorption capacity of plants for fertilizers, effectively reducing the loss and fixation of fertilizers in the soil, thereby significantly improving the utilization rate of fertilizers; on the other hand, the selenium fertilizer can stimulate the growth of crops, promote their growth and development, and thus increase crop yields.

[0018] (2) The present invention prepares a selenium-doped nanomaterial with uniform particle size distribution, the particle size range of which is 1-6 nm, showing good dispersibility. This nano property significantly improves the absorption efficiency of selenium in plants. When used as a nano-selenium fertilizer, it can meet the nutritional needs of plants for selenium with a trace amount of application. The fruits of fruit trees treated in this way show a significant selenium enrichment effect, and the fertilizer has environmentally friendly characteristics. In terms of application method, the present invention can be applied by foliar spraying, which is simple and easy to operate.

[0019] (3) The synthesis method of the present invention is simple, has good water solubility, high biocompatibility, low toxicity, and good selenium supplementation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The fluorescence spectrum of the selenium-doped nanomaterial prepared in step (1) of Example 1; Figure 2 This is a transmission electron microscope (TEM) image of the selenium-doped nanomaterial prepared in step (1) of Example 1; Figure 3 This is a statistical diagram of the particle size data of the selenium-doped nanomaterial prepared in step (1) of Example 1. Figure 4 This is the infrared spectrum of the selenium-doped nanomaterial prepared in step (1) of Example 1; Figure 5 This is the XRD pattern of the selenium-doped nanomaterial prepared in step (1) of Example 1; Figure 6 This is a comparison of hydrogen peroxide (H2O2) content in apple fruit after different concentrations of nano-selenium fertilizer were sprayed on apple trees; Figure 7 Different concentrations of nano-selenium fertilizer were sprayed on apple trees to treat the superoxide anion (O2 - ) Content comparison chart; Figure 8 This is a comparison of catalase (CAT) activity in apple fruit after different concentrations of nano-selenium fertilizer were sprayed on apple trees. Figure 9 This is a comparison of superoxide dismutase (SOD) activity in apple fruit after different concentrations of nano-selenium fertilizer were sprayed on apple trees. Figure 10 This is a comparison chart of selenium content in apple fruits after different concentrations of nano-selenium fertilizer were sprayed on apple trees; Figure 11 Figure 2 shows the apple fruit phenotypes obtained for each treatment group; Figure 12 Comparison of hydrogen peroxide (H2O2) content in apple fruit obtained from each treatment group; Figure 13 The superoxide anion (O2 - ) Content comparison chart; Figure 14 Comparison of selenium content in apple fruit obtained from each treatment group. DETAILED DESCRIPTION

[0021] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0022] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below with reference to specific embodiments.

[0023] As mentioned in the background, the conversion efficiency of elemental nano-selenium fertilizers is affected by the metabolic capacity of soil and plants. Excessive amounts of selenium can also cause acute toxicity, while too little selenium can't enhance antioxidant activity. While using a carrier to load nano-elemental selenium can control its release, the preparation process is complex and expensive.

[0024] Based on this, the present invention provides a method for preparing a selenium-doped nano-selenium fertilizer and its application in improving fruit quality. Using citric acid as a carbon source and selenomethionine as a selenium source, the present invention uses a hydrothermal method to synthesize a selenium-doped nanomaterial with a particle size range of 1-6 nm and good dispersibility in a single step. This selenium-doped nano-selenium fertilizer, when applied in trace amounts, can satisfy the plant's nutritional needs for selenium, improving the antioxidant capacity, yield, and quality of the fruit.

[0025] In agricultural applications, selenomethionine is an ideal exogenous selenium source because its toxicity is far lower than sodium selenite and sodium selenate, its residual content in soil is low, and its environmental friendliness makes it an ideal exogenous selenium source. Selenocitrate releases carbon during pyrolysis at high temperatures, making it widely used in the synthesis of materials such as nitrogen-doped carbon quantum dots and fluorescent carbon nanodots. Furthermore, citric acid's molecular structure is rich in acidic functional groups, which facilitates its use as a carbon source. When the soil pH is between 5.8 and 6.0, selenium exists primarily in the form of selenite and selenate, making it more readily absorbed by plants. Furthermore, most nutrients are highly available, promoting plant growth. Selenium has relatively low toxicity within an appropriate pH range. However, when the pH is too high or too low, selenium's toxicity may increase, resulting in plant toxicity. Adjusting the pH to 5.8–6.0 can reduce selenium toxicity and mitigate potential plant damage.

[0026] The test materials used in the examples of the present invention are all conventional test materials in the art and can be purchased through commercial channels.

[0027] Example 1: Preparation of selenium-doped nano-selenium fertilizer (1) Preparation of selenium-doped nanomaterials: Dissolve 100 g of selenomethionine and 50 g of citric acid in 1000 mL of ultrapure water and heat and stir until the solution is clear; after natural cooling, pour it into a polytetrafluoroethylene reactor and react at 180°C for 6 h; the reaction produces a yellow solution, which is poured into a 500D dialysis bag and dialyzed for 24 h. The dialyzed water is replaced every 6-8 h to obtain a selenium-doped nanomaterial solution; the purified selenium-doped nanomaterial is divided into 100 mL beakers, pre-frozen with liquid nitrogen, and then freeze-dried in a vacuum freeze dryer at -45°C until the selenium-doped nanomaterial is completely crystallized. The resulting brown powder is the selenium-doped nanomaterial.

[0028] (2) Preparation of nano-selenium fertilizer: The selenium-doped nanomaterial solid was dissolved in water to prepare a 50 mg / L solution, and 0.05% by volume of Tween-80 was added to the solution and stirred evenly. The pH was adjusted to 5.8-6.0 with a NaOH solution to obtain a nano-selenium fertilizer.

[0029] Comparative Example 1 The difference from Example 1 is that in step (1), selenomethionine is replaced with an equal amount of sodium selenite, thereby obtaining nano-selenium fertilizer.

[0030] Comparative Example 2 The difference from Example 1 is that in step (2), 100 g of selenomethionine and 50 g of citric acid are used instead of selenium-doped nanomaterials. Finally, selenium fertilizer is obtained.

[0031] Comparative Example 3 The difference from Example 1 is that in step (2), the pH is adjusted to 7.0-7.5 with a NaOH solution. Finally, nano-selenium fertilizer is obtained.

[0032] Example 2: Characterization The fluorescence spectrum of the selenium-doped nanomaterial prepared in step (1) of Example 1 is as follows: Figure 1 As shown in the figure, when the selenium-doped nanomaterial is prepared into an aqueous solution, it emits obvious fluorescence under ultraviolet light (360 nm) excitation, and has a maximum emission peak at 433 nm, showing excellent optical properties, indicating that the selenium-doped nanomaterial has been successfully prepared. Transmission electron microscopy (TEM) images of selenium-doped nanomaterials are shown in the figure. Figure 2 As shown in the particle size data statistics diagram, Figure 3 As shown in the figure, the particle size of selenium ion doped nanomaterials ranges from 1 to 6 nm, showing good dispersion. Figure 4 As shown in Figure 2, the infrared absorption characteristic peaks of selenium ion-doped nanomaterials include 3500 cm -1OH / NH bond at 3000 cm -1 The peak at 1750 cm corresponds to the vibration of CH. -1 , 1250 cm -1 and 600 cm -1 The absorption band is due to the vibration of C=O, C=O, and CH. The XRD pattern of selenium ion doped nanomaterials is as follows: Figure 5 As shown in the figure, the analysis of its characteristics shows that in the XRD pattern of nano-selenium, 2 θ = 11.8° and 2 θ = 28.2°, two characteristic diffraction peaks, confirming that the sample contains nano-selenium with good crystallinity.

[0033] Test Example 1 The selenium-doped nanomaterial prepared in step (1) of Example 1 was used to prepare nano-selenium fertilizers at concentrations of 30, 50, and 150 mg / mL, respectively, according to the method of step (2) of Example 1. These fertilizers were then applied to apple trees by foliar spraying. Six-year-old 'Fuji' apple trees were selected from the Modern Agricultural Science and Technology Demonstration Garden in Nanma Town, Yiyuan County, Zibo City, Shandong Province. The trees were of similar vigor and location, and five trees were selected as a treatment group. The treatments were named as follows: Control group 1 (CK): sprayed with clean water (containing 0.05% Tween-80); Treatment group 1 (T1): spraying 30 mg / L nano-selenium fertilizer (containing 0.05% Tween-80); Treatment group 2 (T2): spraying 50 mg / L nano-selenium fertilizer (containing 0.05% Tween-80); Treatment group 3 (T3): spraying 150 mg / L nano-selenium fertilizer (containing 0.05% Tween-80).

[0034] All the above treatments were carried out once a month starting from the beginning of June when the fruit was young, under the premise of ensuring the same spraying concentration and spraying dosage, and spraying was carried out on June 2, July 3, August 4 and September 2, 2023, until the fruit was picked and harvested. - ) content, catalase (CAT) activity, superoxide dismutase (SOD) activity and selenium content were tested, and the results are shown in Figures 5 to 9 .

[0035] H2O2、O2 - , CAT, and SOD were detected using corresponding kits, which were purchased from Jiangsu Keming Biotechnology Co., Ltd.; The detection method of selenium content is: Take apple fruit, dry it at 80°C to constant weight (about 2 days), grind it into a powder, weigh 0.3g, place it in a 50ml Erlenmeyer flask, add 5ml of concentrated sulfuric acid overnight (in a fume hood), and cover with a bent-neck funnel (4cm diameter). Boil it at 340°C. When a small amount of bubbles appear in the liquid and white mist appears in the Erlenmeyer flask, add a small amount of 30% H₂O₂, and then slowly add it dropwise until the solution becomes clear.

[0036] After digestion, add a small amount of ddH2O to the liquid, shake well, and filter into a 50ml centrifuge tube using two layers of filter paper after cooling. Rinse the conical flask and filter paper once with ddH2O, and finally adjust the volume to 50ml. Use ICP-OES to determine the selenium concentration.

[0037] Selenium content = selenium concentration × volume / mass (1), Unit: mg / g, sampling form is dry weight / DW; the volume in formula (1) is 50 mL, and the mass is the weight of the weighed apple fruit.

[0038] The selenium-doped nanomaterials prepared in the embodiment of the present invention were sprayed on apple trees to treat the hydrogen peroxide (H2O2) and superoxide anions (O2 - ) content, such as Figure 5 and Figure 6 As shown, H2O2 and O2 in apple fruits after being treated with three different concentrations of selenium-doped nanomaterials - Compared with the clean water treatment, the H2O2 and O2 contents of 30 mg / mL and 50 mg / mL selenium-doped nanomaterials - The contents of selenium-doped nanomaterials were significantly reduced. The 150 mg / mL selenium-doped nanomaterials were toxic due to the high concentration, which caused the content to increase. Selenium-doped nanomaterials were sprayed on apple trees. The catalase (CAT) activity and superoxide dismutase (SOD) activity of the treated apple fruits were significantly reduced. Figure 7 and Figure 8 As shown in the figure, the CAT activity and SOD activity in apple fruit after treatment with three different concentrations of selenium-doped nanomaterials were significantly increased at 30 mg / mL and 50 mg / mL of selenium-doped nanomaterials. The 150 mg / mL of selenium-doped nanomaterials were toxic due to the high concentration, resulting in a decrease in enzyme activity. Selenium-doped nanomaterials were sprayed on apple trees, and the selenium content of the treated apple fruit was as follows: Figure 9 As shown in the figure, the selenium content in apples treated with three different concentrations of selenium-doped nanomaterials increased significantly compared to the water treatment. The selenium content in apples treated with 50 mg / mL of selenium-doped nanomaterials was the highest. Therefore, the 50 mg / mL selenium-doped nanomaterial treatment was more effective.

[0039] Test Example 2 The experiment was divided into 5 groups: the blank control group (CK) was sprayed with clean water (containing 0.05% Tween-80), and the remaining groups were sprayed with nano-selenium fertilizers (T4, T5, T6) prepared in Example 1 (T2) and Comparative Examples 1 to 3 (the concentration of selenium compounds or selenium-containing nanomaterials was 50 mg / L). The specific test method was the same as that of Test Example 1. After spraying on June 2, July 3, August 4, and September 2, 2024, the selenium content and oxidation-related indicators of apple fruits were tested and compared. The results are shown in Table 1. Figures 11-14 .

[0040] The nanomaterial prepared in Example 1 was sprayed on apple trees. The phenotype of the apple fruits after treatment was as follows: Figure 11 At the same time, the hydrogen peroxide (H2O2) and superoxide anion (O2 - ) content, such as Figure 12 and Figure 13 As shown in the figure, compared with Example 1, the nano selenium fertilizer prepared in Comparative Example 1 using sodium selenite as raw material has a high toxicity. Therefore, compared with the selenium fertilizer used in Example 1, the hydrogen peroxide (H2O2) and superoxide anion (O2 - ) content increased. Compared with Example 1, in Comparative Example 2, selenomethionine and citric acid were not prepared into nano-selenium materials but used directly, and their effects were weakened. The hydrogen peroxide (H2O2) and superoxide anion (O2 - Compared with Example 1, the pH of Comparative Example 3 is within the range of 7.0-7.5, and the toxicity will increase, so the hydrogen peroxide (H2O2) and superoxide anion (O2 - ) content increases. The nanomaterial prepared by the embodiment of the present invention is sprayed on apple trees. The selenium content of the treated apple fruits is as follows: Figure 14 As shown, compared with Example 1, there is no difference in the selenium content accumulated in apple fruit using the nano-selenium fertilizer prepared with sodium selenite as raw material. Compared with Example 1, selenomethionine and citric acid are not prepared into nano-selenium materials, and the selenium content accumulated in apple fruit is significantly reduced. Compared with Example 1, the pH is in the range of 7.0-7.5, which affects the absorption of selenium-doped nanomaterials by apples, resulting in a significant decrease in the selenium content accumulated in apple fruit. Test Example 2 verified the effects of the five groups of treatments on crop toxicity, and the results showed that the selenium fertilizer prepared in Example 1 was the most effective.

[0041] The foregoing description is merely a preferred embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A selenium-doped nanomaterial, characterized in that: The preparation method is: Selenomethionine and citric acid are dissolved in water, subjected to a hydrothermal reaction, and naturally cooled to room temperature. The resulting yellow solution is dialyzed, and the dialyzed solution is dried to obtain a brown powder, which is a selenium-doped nanomaterial; the particle size of the selenium-doped nanomaterial is 1-6 nm.

2. The selenium-doped nanomaterial according to claim 1, characterized in that The mass ratio of the selenomethionine to citric acid is 1:0.5; the concentration of the selenomethionine is 25 g / L.

3. The selenium-doped nanomaterial according to claim 1, characterized in that The temperature of the hydrothermal reaction is 180° C. and the time is 6 hours.

4. The selenium-doped nanomaterial according to claim 1, characterized in that The dialysis was performed using a 500D dialysis bag for 24 h, and the dialysis water was replaced every 6 to 8 h.

5. The selenium-doped nanomaterial according to claim 1, characterized in that The drying is vacuum freeze drying, and the vacuum freeze drying temperature is -45°C.

6. Use of the selenium-doped nanomaterial according to any one of claims 1 to 5 in the preparation of selenium-doped nano-selenium fertilizer.

7. A selenium-doped nano-selenium fertilizer, characterized in that: The selenium-doped nanomaterial is prepared by the following method: mixing the selenium-doped nanomaterial according to any one of claims 1 to 5, a surfactant and water, and adjusting the pH to acidic.

8. The selenium-doped nano-selenium fertilizer according to claim 7, characterized in that The pH is adjusted to 5.8-6.0; the surfactant is Tween-80.

9. The selenium-doped nano-selenium fertilizer according to claim 7, characterized in that The concentration of the selenium-doped nanomaterial is 50 mg / L; the mass concentration of the surfactant is 0.5% to 0.05%.

10. Use of the selenium-doped nano-selenium fertilizer according to any one of claims 7 to 9 in improving the antioxidant capacity of fruits, characterized in that: The fruit is apple.

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