Trace metal element doped carbon dots as well as preparation method and application thereof

Abstract

The invention provides a preparation method of trace metal element doped carbon dots, which comprises the following steps: mixing biomass, trace metal elements, a strong alkali solution and a strong oxidant in ultrapure water, pouring the obtained mixed solution into a reaction kettle for hydrothermal reaction, and cooling to room temperature after the reaction to obtain a reaction solution; and filtering the reaction solution, adjusting the pH value of the obtained filtrate, and dialyzing to obtain a solution which is the trace metal element doped carbon dot material. The prepared trace metal element doped carbon dot material promotes the salt tolerance and metal stress resistance of plants, the trace metal element doped carbon dots are suitable for seed soaking before plant sowing or irrigation and spraying in the plant seedling stage, the adaptability of the plants in a salinization environment or heavy metal contaminated soil is enhanced, and seed germination and seedling growth are promoted. The trace metal element doped carbon dot material prepared by the method is wide in raw material source, low in cost, easy to store, relatively high in practicability and beneficial to popularization.

Description

Technical Field

[0001] The present invention belongs to the fields of environment, biology and agriculture and the technical field of nanomaterial application, and specifically relates to a preparation method and application of carbon dots doped with trace metal elements. Background Art

[0002] Soil salinization and soil heavy metal pollution have become global hot issues.

[0003] To address the two major challenges of soil salt stress and heavy metal contamination, a variety of soil improvement and remediation methods have been developed, primarily encompassing physical, chemical, and biological techniques. The main approaches for alleviating salt stress include physical, chemical, and biological methods. Physical improvement primarily involves leveling the land and flooding the soil to remove salt. While this method is simple in principle and easy to implement, it often faces challenges in large-scale implementation. Chemical improvement typically involves applying amendments such as gypsum to the soil to adjust its pH and ionic composition, thereby improving salinization. While this method is relatively simple to implement, long-term use can lead to soil compaction, affecting both aeration and water permeability. Biological improvement primarily utilizes salt-tolerant plants to absorb and fix soil salt, reducing soil salt concentration. This method offers advantages such as environmental friendliness and high ecological benefits. However, the limited availability of salt-tolerant plants and their slow growth rates make it difficult to achieve significant improvements in the short term. Furthermore, their adaptability to high-salinity soils is relatively limited. For heavy metal pollution, physical, chemical, biological and microbial remediation methods are commonly used. Physical remediation methods such as the soil-addition method and thermal desorption method are relatively straightforward to operate, but they are costly and cause irreversible damage to the soil ecosystem. Chemical remediation methods use the complexation reaction between chelating agents and heavy metal ions to remove heavy metals through leaching. However, the use of eluents not only changes the physical and chemical structure of the soil, but also has an inhibitory effect on the soil microbial community and may also cause secondary pollution. The biological remediation method uses the metabolic activity of microorganisms to reduce the toxicity of heavy metals or promote their morphological transformation. It is environmentally friendly and has no secondary pollution. However, the growth and metabolism of microorganisms are highly dependent on soil environmental conditions, such as temperature, pH value and moisture content, resulting in unstable remediation effects and difficulty in achieving sustained and efficient remediation goals. In recent years, nanomaterials have shown great potential in solving the problems of soil salt stress and heavy metal pollution, and have become a research hotspot. Nano-zero-valent iron can efficiently adsorb and reduce heavy metal ions, significantly reducing the activity and mobility of heavy metals in the soil; functional carbon nanomaterials (FCNs) can enhance plant photosynthesis in Cd-Pb composite-contaminated soil, and have a positive regulatory effect on plant growth and metal removal; chitosan-selenium engineered nanomaterials (CS-SeNMs) effectively alleviate the damage of salt stress to plants by increasing the activity of plant antioxidant enzymes and reshaping the structure of rhizosphere microbial communities. Although nanomaterials have shown great potential in the field of soil remediation, there are also some problems that need to be solved. On the one hand, the preparation process of nanomaterials is usually more complicated and requires specific technology and equipment, resulting in high production costs, which limits large-scale application. On the other hand, some nanomaterials may have high biological toxicity. After entering the organism, they are easily accumulated in organs and tissues, triggering oxidative stress reactions and causing damage to cells and biomolecules.

[0004] Carbon dots, a novel carbon nanomaterial, offer a novel approach to addressing these challenges. They typically refer to fluorescent carbon nanoparticles ranging in size from 1 to 100 nm. They exhibit low toxicity, excellent biocompatibility, and water solubility, and possess superior stability compared to traditional nanomaterials. Their low toxicity and excellent biocompatibility prevent carbon dots from accumulating in organs and tissues, and from damaging cells and biomolecules. Their excellent water solubility also allows for excellent solubility in water, enabling uniform dispersion in aqueous solutions and facilitating their preparation and application.

[0005] In addition, trace elements play an indispensable role in the growth of plants. Existing studies have shown that, for example, Wu et al. prepared MgFe-LDHs nanomaterials by doping nanomaterials with iron and magnesium, which can improve the absorption of iron by cucumber seedlings. Fu Weigang's team found that microbial agents doped with trace elements can not only provide the necessary nutrients for seed germination, but also effectively promote seed metabolism and increase seedling biomass through appropriate trace element stimulation. Field experiments by Chen Yingying et al. showed that the application of trace elements such as Zn, B, and Fe can increase potato yields, and the height and stem thickness of potato plants are increased to varying degrees. However, current research and applications on trace elements are mostly limited to normal environmental conditions. How to use trace elements to promote plant growth and development under adverse stresses such as soil salinization and heavy metal pollution is still an important topic that needs to be explored in depth. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing carbon dots doped with trace metal elements in response to the above-mentioned deficiencies in the existing technology. The trace metal element-doped carbon dot material proposed in the present invention can not only improve the salt tolerance and metal stress resistance of plants, but also significantly increase the germination rate of plants in a short period of time, and promote the growth of plants in salty environments and heavy metal pollution.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] The invention discloses an application of carbon dots doped with trace metal elements to promote the salt tolerance and metal stress tolerance of plants.

[0009] Preferably, the plants include wheat, rice, corn, cotton, sorghum, sunflower and tea.

[0010] Preferably, the trace metal element-doped carbon dots promote the growth of the plant and the germination of seeds in salinized environments and heavy metal-contaminated soil conditions.

[0011] Preferably, the salinized environment refers to an environment with a salt content of 2000.00-7000.00 mg / kg, and the heavy metal contaminated soil refers to a chlorinated soil containing 2.00-7.00 mg / kg; before sowing the seeds, the trace metal element doped carbon dots are applied to the seeds, and the seeds are soaked in a 2-4 times diluted trace metal element doped carbon dot solution for 2-24 hours, and then sown; or after sowing the seeds, the trace metal element doped carbon dots are applied to the seeds, and during the plant seedling stage, 30.00 mL of the trace metal element doped carbon dots with a concentration of 100.00-300.00 μg / mL are used for watering.

[0012] The present invention also provides a method for preparing carbon dots doped with trace metal elements, the method comprising the following steps:

[0013] S1. Biomass, trace metal elements, a strong alkaline solution, and a strong oxidant are uniformly mixed in ultrapure water by ultrasonic oscillation to obtain a mixed solution;

[0014] S2, pouring the mixed solution obtained in S1 into a reactor to perform a hydrothermal reaction, and cooling to room temperature after the hydrothermal reaction to obtain a reaction solution;

[0015] S3. Filter the reaction solution obtained in S2 to obtain a filtrate; adjust the pH value of the filtrate, and then dialyze it to obtain a solution that is the trace metal element-doped carbon dots.

[0016] Preferably, the biomass in S1 is agricultural waste, processing by-products, livestock manure or industrial organic sludge, the agricultural waste is straw powder, rice husks, durian shells, peanut shells or cottonseed shells, the processing by-products are corn cobs or sugarcane bagasse, and the industrial organic sludge is sewage treatment plant sludge; the trace metal elements are zinc chloride, zinc nitrate, magnesium chloride or ferric chloride; the strong alkaline solution is sodium hydroxide solution or potassium hydroxide solution; the strong oxidant is hydrogen peroxide, potassium permanganate or potassium dichromate; the mass volume ratio of biomass, trace metal elements, strong alkaline solution, strong oxidant and ultrapure water in the mixed solution is (0.1-0.4) g: (0.02-0.03) g: (0.5-1.0) mL: (0.3-1.0) mL: (20.0-30.0) mL, and the time of the ultrasonic oscillation is 5-30 minutes.

[0017] Preferably, the concentration of the sodium hydroxide solution is 0.60-1.50 mol / L, the concentration of the potassium hydroxide solution is 0.10-0.50 mol / L; the mass fraction of the hydrogen peroxide is 20.00-40.00%, and the mass fraction of the potassium permanganate is 1.00-3.00%.

[0018] Preferably, the temperature of the hydrothermal reaction in S2 is 150-200° C., and the time is 3-6 hours.

[0019] Preferably, the pore size of the filter membrane used in the filtration in S3 is 0.45 μm, the pH value of the filtrate is adjusted to 6.50-7.50, the specification of the dialysis bag used in the dialysis is 1000 Da, and the dialysis time is 3 h.

[0020] The present invention also provides trace metal element doped carbon dots, which are prepared by the above-mentioned method for preparing trace metal element doped carbon dots.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The present invention provides a trace metal element doped carbon dot and a preparation method thereof, and an application thereof in promoting plant salt tolerance and metal stress resistance. According to the research results of the present invention, the trace metal element doped carbon dot material promotes plant salt tolerance and metal stress resistance, increases the germination rate of seeds, promotes plant growth, increases the stem length and root length of plants, and has a beneficial impact on the development of agriculture.

[0023] 2. This invention proposes a method for preparing a trace metal element-doped carbon dot material. This trace metal element-doped carbon dot material enhances plant salt tolerance by promoting the expression of antioxidant enzyme genes and increasing enzyme activity in plants. This trace metal element-doped carbon dot material also reduces the bioavailability of heavy metals through chelation and displacement, improving plant metal tolerance. This significantly increases plant germination rates in the short term, promotes stem and root growth, and effectively mitigates the harmful effects of heavy metals on plants.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a high-resolution TEM image of the Zn-CDs obtained in Example 1.

[0026] Figure 2 This is a graph showing the particle size distribution of Zn-CDs obtained in Example 1.

[0027] Figure 3 This is a graph comparing the germination rates of rice seeds under salt stress and non-salt stress conditions in Example 1 for 7 days.

[0028] Figure 4 This is a graph showing the root growth results of rice after 7 days of culture under salt stress and non-salt stress conditions in Example 1.

[0029] Figure 5 This is a graph showing the stem length results of rice after 7 days of cultivation under salt stress and non-salt stress conditions in Example 1.

[0030] Figure 6 This is a statistical graph of the fresh weight of rice after culturing for 7 days under salt stress and non-salt stress conditions in Example 1.

[0031] Figure 7 This is a statistical graph of the dry weight of rice after culturing for 7 days under salt stress and non-salt stress conditions in Example 1.

[0032] Figure 8 This is a diagram showing the germination rate of wheat seeds under metal stress and non-metal stress conditions in Example 2.

[0033] Figure 9 This is a comparison of the germination rates of cotton seeds under salt stress and non-salt stress conditions in Example 3 for 7 days.

[0034] Figure 10 This is a comparison of the germination rates of wheat seeds under salt stress and non-salt stress conditions in Example 4 after 7 days.

[0035] Figure 11 This is a graph showing the germination rate of cotton seeds under metal stress and non-metal stress conditions in Example 5.

[0036] Figure 12 This is a comparison of the germination rates of corn seeds under salt stress and non-salt stress conditions in Example 6 after 7 days. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] Example 1

[0039] The method for preparing carbon dots doped with trace metal elements in this embodiment includes the following steps:

[0040] S1, 0.30 g of durian shell, 0.03 g of zinc chloride, 1.00 mL of 1.00 mol / L sodium hydroxide solution, 1.00 mL of 30.00% hydrogen peroxide, and 25.00 mL of ultrapure water were mixed by ultrasonic oscillation for 20 minutes to obtain a mixed solution;

[0041] S2. Pour the mixed solution obtained in S1 into a 50.00 mL reactor and perform a hydrothermal reaction at 180° C. for 5 h. After the hydrothermal reaction, cool to room temperature (25° C.) to obtain a reaction solution.

[0042] S3. The reaction solution obtained in S2 is filtered through a filter membrane with a pore size of 0.45 μm to obtain a filtrate; the pH value of the filtrate is adjusted to 6.50-7.50, and then dialyzed through a 1000 Da dialysis membrane for 3 h. The dialyzed solution is trace zinc-doped carbon dots (Zn-CDs).

[0043] The trace amount of zinc-doped carbon dots obtained in this example are used to improve the salt tolerance of rice. The high-resolution TEM image of the Zn-CDs obtained in this example is shown in FIG. Figure 1 As shown by Figure 1 It is known that Zn-CDs exhibit a typical quasi-spherical structure. The particle size distribution of Zn-CDs obtained in this embodiment is shown in FIG. Figure 2 As shown by Figure 2 It was found that the particle size distribution of Zn-CDs was uniform, with an average diameter of about 4.73 nm.

[0044] Rice seeds were soaked in water and a 2-fold diluted trace zinc-doped carbon dot solution, respectively. After soaking for 24 hours, they were cultured under salt stress and non-salt stress conditions for seven days. Figure 3-7 As shown in the data, the salt stress was 50.00 mM salt content. Compared with simple salt stress, the application of trace zinc-doped carbon dots increased the germination rate of rice (from 87.00% to 92.00%), increased the stem length (increased by 19.80%) and root length (increased by 17.50%) of rice, and increased the fresh weight and dry weight of rice.

[0045] Example 2

[0046] The method for preparing carbon dots doped with trace metal elements in this embodiment includes the following steps:

[0047] S1, 0.30 g of durian shell, 0.03 g of zinc chloride, 1.00 mL of 1.00 mol / L sodium hydroxide solution, 1.00 mL of 30.00% hydrogen peroxide, and 25.00 mL of ultrapure water were mixed by ultrasonic oscillation for 20 minutes to obtain a mixed solution;

[0048] S2. Pour the mixed solution obtained in S1 into a 50.00 mL reactor and perform a hydrothermal reaction at 180° C. for 5 h. After the hydrothermal reaction, cool to room temperature (25° C.) to obtain a reaction solution.

[0049] S3. The reaction solution obtained in S2 is filtered through a filter membrane with a pore size of 0.45 μm to obtain a filtrate; the pH value of the filtrate is adjusted to 6.50-7.50, and then dialyzed through a 1000 Da dialysis membrane for 3 h to obtain a solution that is trace zinc-doped carbon dots (Zn-CDs).

[0050] The trace zinc-doped carbon dots obtained in this example are used to improve the metal stress resistance of wheat.

[0051] After wheat seeds were cultivated in standard soil for one month, the plants were irrigated with nutrient solution, nutrient solution containing 150.00 μM cadmium chloride, and nutrient solution containing 150.00 μM cadmium chloride + 200.00 μg / mL Zn-CDs solution. 30.00 mL of natural water was used for irrigation on the first, fifth, ninth, thirteenth, and seventeenth days, and 30.00 mL of the above solution was used for irrigation on the third, seventh, eleventh, and fifteenth days. The cultivation lasted for 20 days. Figure 8 As shown, compared with simple cadmium stress, the application of trace zinc-doped carbon dots increased the germination rate of wheat seeds (from 83.00% to 90.00%), increased the stem length (increased by 11.30%) and root length (increased by 9.70%) of wheat, and increased the fresh weight and dry weight of wheat.

[0052] The concentration of the Zn-CDs solution can also be 110 μg / mL, 120 μg / mL, 130 μg / mL, 140 μg / mL, 150 μg / mL, 180 μg / mL, 190 μg / mL, 100 μg / mL, 220 μg / mL, 230 μg / mL, 240 μg / mL, 250 μg / mL, 260 μg / mL, 280 μg / mL, 290 μg / mL, or 300.00 μg / mL. The soil configuration is a 3:1:1 ratio of nutrient soil: vermiculite: limestone or a 3:1 ratio of nutrient soil: vermiculite.

[0053] Example 3

[0054] The method for preparing carbon dots doped with trace metal elements in this embodiment includes the following steps:

[0055] S1, 0.30 g of straw powder, 0.03 g of zinc nitrate, 0.80 mL of 1.00 mol / L sodium hydroxide solution, 1.00 mL of 20.00% hydrogen peroxide, and 25.00 mL of ultrapure water were mixed by ultrasonic oscillation for 20 minutes to obtain a mixed solution;

[0056] S2. Pour the mixed solution obtained in S1 into a 50.00 mL reactor and perform a hydrothermal reaction at 200° C. for 3 h. After the hydrothermal reaction, cool to room temperature (25° C.) to obtain a reaction solution.

[0057] S3. The reaction solution obtained in S2 is filtered through a filter membrane with a pore size of 0.45 μm to obtain a filtrate; the pH value of the filtrate is adjusted to 6.50-7.50, and then dialyzed through a 1000 Da dialysis membrane for 3 h. The dialyzed solution is the metal zinc-doped carbon dots.

[0058] The metallic zinc-doped carbon dots obtained in this example are used to improve the salt tolerance of cotton.

[0059] Cotton seeds were soaked in water and 2.5 times diluted metal zinc doped carbon dot solution, respectively. After soaking for 2 hours, they were cultured under salt stress and non-salt stress conditions for seven days. Under 80.00mM salt content, they were cultured for seven days. Figure 9 As shown, the germination rate of cotton seeds soaked with metal zinc-doped carbon dots increased (from 82.50% to 92.50%), and the stem length (increased by 8.75%) and root length (increased by 9.24%) increased.

[0060] Example 4

[0061] The method for preparing carbon dots doped with trace metal elements in this embodiment includes the following steps:

[0062] S1, 0.10 g of corn cob, 0.02 g of magnesium chloride, 0.50 mL of 1.20 mol / L sodium hydroxide solution, 0.70 mL of 20.00% hydrogen peroxide, and 20.00 mL of ultrapure water were mixed by ultrasonic oscillation for 20 minutes to obtain a mixed solution;

[0063] S2. Pour the mixed solution obtained in S1 into a 50.00 mL reactor, perform a hydrothermal reaction at 190° C. for 4 h, and cool to room temperature (25° C.) to obtain a reaction solution;

[0064] S3. The reaction solution obtained in S2 is filtered through a filter membrane with a pore size of 0.45 μm to obtain a filtrate; the pH value of the filtrate is adjusted to 6.50-7.50, and then dialyzed through a 1000 Da dialysis membrane for 3 h. The dialyzed solution is trace magnesium-doped carbon dots (Mg-CDs).

[0065] The trace magnesium-doped carbon dots obtained in this example are used to improve the salt tolerance of wheat.

[0066] Wheat seeds were soaked in water and 3-fold diluted metal zinc carbon nanomaterials for 24 hours, and then cultured for seven days under salt stress and non-salt stress conditions. Salt stress refers to 100.00 mM salt content. Figure 10 As shown, the germination rate of wheat seeds soaked with the material increased (from 85.00% to 94.00%), and the stem length (increased by 9.15%) and root length (increased by 9.34%) increased.

[0067] The corn cobs in Example S1 of this embodiment can also be replaced by bagasse, fruit shells, wood chips, straw, rice husks or peanut shells; the mass fraction of the hydrogen peroxide can also be 21.00%, 22.00%, 23.00%, 25.00%, 26.00%, 27.00%, 28.00%, 29.00%, 30.00%, 31.00%, 32.00%, 33.00%, 34.00%, 35.00%, 36.00%, 37.00%, 38.00%, 39.00% or 40.00%; the sodium hydroxide solution can also be replaced by a 0.30-1.20 mol / L potassium hydroxide solution.

[0068] Example 5

[0069] The method for preparing carbon dots doped with trace metal elements in this embodiment includes the following steps:

[0070] S1, 0.30 g of bagasse, 0.03 g of magnesium chloride, 0.80 mL of 1.00 mol / L sodium hydroxide solution, 1.00 mL of 1.00% potassium permanganate, and 25.00 mL of ultrapure water were mixed by ultrasonic oscillation for 30 minutes to obtain a mixed solution;

[0071] S2. Pour the mixed solution obtained in S1 into a 50.00 mL reactor, perform a hydrothermal reaction at 150° C. for 6 h, and cool to room temperature (25° C.) to obtain a reaction solution;

[0072] S3. The reaction solution obtained in S2 is filtered through a filter membrane with a pore size of 0.45 μm to obtain a filtrate; the pH value of the filtrate is adjusted to 6.50-7.50, and then dialyzed through a 1000 Da dialysis membrane for 3 h. The dialyzed solution is trace magnesium-doped carbon dots (Mg-CDs).

[0073] The trace magnesium-doped carbon dots obtained in this example are used to improve the metal stress resistance of cotton.

[0074] Cotton seeds were cultivated in standard soil for one month and watered with nutrient solution, nutrient solution containing 150.00 μM cadmium chloride, and nutrient solution containing 150.00 μM cadmium chloride + 100.00 μg / mL Mg-CDs solution. 30.00 mL of natural water was used for watering on the first, fifth, ninth, thirteenth, and seventeenth days, and 30.00 mL of the above solution was used for watering on the third, seventh, eleventh, and fifteenth days. The cultivation lasted for 20 days. With respect to metal stress, as Figure 11 As shown, the cotton seeds soaked with diluted trace magnesium-doped carbon dots solution had an increased germination rate (from 83.00% to 90.00%), and the stem length (increased by 9.14%) and root length (increased by 8.78%) increased.

[0075] The concentration of the Mg-CDs solution can also be 110 μg / mL, 120 μg / mL, 130 μg / mL, 140 μg / mL, 150 μg / mL, 180 μg / mL, 190 μg / mL, 200 μg / mL, 220 μg / mL, 230 μg / mL, 240 μg / mL, 250 μg / mL, 260 μg / mL, 280 μg / mL, 290 μg / mL, or 300.00 μg / mL. The soil configuration is a 3:1:1 ratio of nutrient soil: vermiculite:limestone or a 3:1 ratio of nutrient soil:vermiculite.

[0076] In this embodiment S1, the concentration of the sodium hydroxide solution can also be 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L or 1.50mol / L, and the amount can also be 0.5mL, 0.6mL, 0.7mL, 0.8mL, 0.9mL or 1.0mL; the potassium permanganate in S1 can also be replaced with potassium dichromate; the oscillation time can also be 5 minutes, 6 minutes, 8 minutes, 9 minutes, 10 minutes, 13 minutes, 15 minutes, 17 minutes, 19 minutes, 20 minutes, 25 minutes, 28 minutes, 27 minutes or 29 minutes.

[0077] Example 6

[0078] The method for preparing carbon dots doped with trace metal elements in this embodiment includes the following steps:

[0079] S1, 0.40 g of peanut shells, 0.03 g of ferric chloride, 1.00 mL of 1.00 mol / L sodium hydroxide solution, 0.30 mL of 3.00% potassium permanganate, and 30.00 mL of ultrapure water were mixed by ultrasonic oscillation for 30 minutes to obtain a mixed solution;

[0080] S2. Pour the mixed solution obtained in S1 into a 50.00 mL reactor and perform a hydrothermal reaction at 200° C. for 4 h. After the hydrothermal reaction, cool to room temperature (25° C.) to obtain a reaction solution.

[0081] S3. The reaction solution obtained in S2 is filtered through a filter membrane with a pore size of 0.45 μm to obtain a filtrate; the pH value of the filtrate is adjusted to 6.50-7.50, and then dialyzed through a 1000 Da dialysis membrane for 3 h. The dialyzed solution is trace iron-doped carbon dots (Fe-CDs).

[0082] The trace iron-doped carbon dots obtained in this example are used to improve the salt tolerance of corn.

[0083] Corn seeds were soaked in water and a 4-fold diluted solution of trace iron-doped carbon dots, respectively. After 24 hours of soaking, they were cultured under salt stress and normal conditions for seven days. Salt stress refers to a salt content of 100.00 mM. Figure 12 As shown, the germination rate of corn seeds soaked with the material increased (from 87.00% to 92.00%), and the stem length (increased by 8.31%) and root length (increased by 8.75%) increased.

[0084] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. An application of trace metal element doped carbon dots to promote plant salt tolerance and metal stress tolerance.

2. The use of trace metal element-doped carbon dots to promote plant salt tolerance and metal stress tolerance according to claim 1, characterized in that: The plants include wheat, rice, corn, cotton, sorghum, sunflower and tea.

3. The use of trace metal element-doped carbon dots to promote plant salt tolerance and metal stress tolerance according to claim 2, characterized in that: The trace metal element-doped carbon dots promote the growth of the plants and the germination of their seeds in salinized environments and heavy metal-contaminated soils.

4. The use of trace metal element-doped carbon dots to promote plant salt tolerance and metal stress tolerance according to claim 3, characterized in that: The salinized environment refers to an environment with a salt content of 2000.00-7000.00 mg / kg, and the heavy metal contaminated soil refers to a chlorinated soil containing 2.00-7.00 mg / kg; before sowing seeds, the trace metal element-doped carbon dots are applied to the seeds, and the seeds are soaked in a 2-4 times diluted trace metal element-doped carbon dot solution for 2-24 hours, and then sown; or after sowing the seeds, the trace metal element-doped carbon dots are applied to the seeds, and during the plant seedling stage, 30.00 mL of the trace metal element-doped carbon dots with a concentration of 100.00-300.00 μg / mL are used for watering.

5. A method for preparing carbon dots doped with trace metal elements, characterized in that: The preparation method comprises the following steps: S1. Biomass, trace metal elements, a strong alkaline solution, and a strong oxidant are uniformly mixed in ultrapure water by ultrasonic oscillation to obtain a mixed solution; S2, pouring the mixed solution obtained in S1 into a reactor to perform a hydrothermal reaction, and cooling to room temperature after the hydrothermal reaction to obtain a reaction solution; S3. Filter the reaction solution obtained in S2 to obtain a filtrate; adjust the pH value of the filtrate, and then dialyze to obtain trace metal element-doped carbon dots.

6. The method for preparing carbon dots doped with trace metal elements according to claim 5, characterized in that: The biomass described in S1 is agricultural waste, processing by-products, livestock manure or industrial organic sludge, the agricultural waste is straw powder, rice husks, durian shells, peanut shells or cottonseed shells, the processing by-products are corn cobs or sugarcane bagasse, and the industrial organic sludge is sewage treatment plant sludge; the trace metal elements are zinc chloride, zinc nitrate, magnesium chloride or ferric chloride; the strong alkaline solution is sodium hydroxide solution or potassium hydroxide solution; the strong oxidant is hydrogen peroxide, potassium permanganate or potassium dichromate; the mass volume ratio of biomass, trace metal elements, strong alkaline solution, strong oxidant and ultrapure water in the mixed solution is (0.1-0.4) g: (0.02-0.03) g: (0.5-1.0) mL: (0.3-1.0) mL: (20.0-30.0) mL, and the time of the ultrasonic oscillation is 5-30 minutes.

7. The method for preparing carbon dots doped with trace metal elements according to claim 6, characterized in that: The concentration of the sodium hydroxide solution is 0.60-1.50 mol / L, the concentration of the potassium hydroxide solution is 0.10-0.50 mol / L; the mass fraction of the hydrogen peroxide is 20.00-40.00%, and the mass fraction of the potassium permanganate is 1.00-3.00%.

8. The method for preparing carbon dots doped with trace metal elements according to claim 5, characterized in that: The temperature of the hydrothermal reaction in S2 is 150-200° C. and the time is 3-6 hours.

9. The method for preparing carbon dots doped with trace metal elements according to claim 5, characterized in that: The pore size of the filter membrane used in the filtration in S3 is 0.45 μm, the pH value of the filtrate is adjusted to 6.50-7.50, the specification of the dialysis bag used in the dialysis is 1000 Da, and the dialysis time is 3 h.

10. A trace metal element doped carbon dot, characterized in that: The carbon dots are prepared by the method for preparing carbon dots doped with trace metal elements as described in any one of claims 5 to 9.

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