Preparation method of carbon quantum dot solution and litchi spraying application

Abstract

The invention discloses a preparation method of a carbon quantum dot solution derived from orchard wastes, especially litchi leaves, which mainly comprises a series of operations such as pretreatment of the litchi leaves, hydrothermal synthesis, separation and purification and the like. The average particle size of the prepared carbon quantum dots is 2.5 + / -0.9 nm, the carbon quantum dots have fluorescence characteristics and can emit blue light under ultraviolet excitation, the maximum excitation wavelength of the carbon quantum dots is 342 nm, the maximum emission wavelength of the carbon quantum dots is 421 nm, and the fluorescence quantum yield is 11.9%. Based on the preparation method of the carbon quantum dot solution, the invention further discloses a spraying method of the carbon quantum dot solution. The carbon quantum dot solution is sprayed to the Feizixiao smile in the fruit swelling period, so that the fruit peel coloring uniformity can be remarkably improved, and the fruit quality is improved. By resource utilization of the litchi leaf waste, reduction of the raw material cost is facilitated, and when the litchi leaf waste is applied to agricultural production, the uniformity of the peel color and the fruit quality when the litchi is mature can be effectively improved, and the economic loss caused by uneven coloring is reduced.

Description

Technical Field

[0001] This application relates to the technical field of litchi cultivation, and particularly to a method for preparing a carbon quantum dot solution and its application in spraying litchi. Background Art

[0002] Litchi (Litchi chinensis) is an evergreen fruit tree belonging to the Sapindaceae family and the Litchi genus. Among them, Feizixiao is deeply favored by consumers due to its excellent characteristics such as large fruit size, thick flesh, small pit, and good taste. Feizixiao is easy to flower and is one of the main litchi varieties in China. However, Feizixiao has the problems of fruit color turning lagging behind the commercial harvest period and uneven coloring, manifested as the sunny side of the mature fruit being red while the shady side is green or greenish-yellow. Fruit color is one of the important commercial traits and also a key factor for consumers to choose. Uneven coloring affects the fruit appearance and causes obvious economic losses. Therefore, improving the coloring uniformity of Feizixiao fruits is of great significance for enhancing its economic and social benefits. At present, there have been relevant research reports on regulating litchi fruit color and nutritional quality using chemical reagents or mineral fertilizers, but there is no research on using nanomaterials to regulate fruit tree growth and fruit quality. Carbon quantum dots (CDs) are a kind of fluorescent carbon nanomaterials with a particle size usually less than 10 nm, having excellent optical properties, good water solubility, low toxicity, environmental friendliness, biocompatibility, and advantages such as wide raw material sources and low preparation costs. In recent years, carbon quantum dots have been widely and deeply studied in many fields, especially showing great application potential in the agricultural field. With its unique physical and chemical properties, carbon quantum dots have been applied to key links such as plant growth regulation, crop quality improvement, and pest control, providing new ideas and methods for solving practical problems in agricultural production and strongly promoting the innovation and development of agricultural technology. Summary of the Invention

[0003] Based on the application potential of carbon quantum dots in the agricultural field, the present invention aims to realize the resource utilization of litchi leaf waste. Specifically, by preparing litchi leaves into a carbon quantum dot solution and applying it to the coloring and quality regulation of Feizixiao fruits, not only the resource utilization of waste is realized, but also the problem of uneven fruit color distribution of Feizixiao is effectively solved, and at the same time, the comprehensive quality of the fruit can be significantly improved.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for preparing a carbon quantum dot solution, comprising:

[0006] Collecting litchi leaves and performing pretreatment;

[0007] Drying the litchi leaves and grinding the dried product into powder;

[0008] Take a specified mass of the powder, mix it with water, transfer it to a reaction kettle, and heat it to obtain a crude carbon quantum dot solution;

[0009] After the crude solution is cooled, centrifuge it and filter out the insoluble precipitate to obtain a carbon quantum dot solution.

[0010] Further, the collection and pretreatment of litchi leaves specifically include:

[0011] Collect fresh litchi leaves;

[0012] Clean the debris on the surface of litchi leaves.

[0013] Further, the drying of litchi leaves and the grinding of the dried product into powder specifically include:

[0014] Place the litchi leaves in a drying oven at a drying temperature of 105 °C for 30 minutes to obtain a first dried product;

[0015] Place the first dried product in an environment at 65 °C and dry it for 12 hours to obtain a second dried product;

[0016] Grind the second dried product into powder.

[0017] Further, the taking of a specified mass of the powder, mixing it with water, transferring it to a reaction kettle, and heating it to obtain a crude carbon quantum dot solution specifically includes:

[0018] Weigh a quantitative amount of the powder, add deionized water according to a solid-liquid mass ratio of 1:6 to 1:33, and transfer it to a polytetrafluoroethylene reaction kettle;

[0019] Place the reaction kettle in an electrothermal blast drying oven and react it at 220 °C for 8 hours to prepare a crude carbon quantum dot solution.

[0020] Further, the solid-liquid mass ratio is 1:10 to 1:15.

[0021] Further, the centrifuging of the crude solution after cooling and the filtering out of the insoluble precipitate to obtain a carbon quantum dot solution specifically includes:

[0022] Cool the crude carbon quantum dot solution to room temperature;

[0023] Centrifuge it at a speed of 10,000 revolutions per minute for 10 minutes;

[0024] Filter the supernatant after centrifugation through a 0.22-micron microporous filter membrane to filter out the insoluble precipitate, and obtain a carbon quantum dot solution after filtration.

[0025] Further, the carbon quantum dot solution is stored in an environment at 4 °C.

[0026] A spraying method for carbon quantum dot solution, comprising:

[0027] Using litchi leaves as reaction precursors, and preparing a carbon quantum dot solution by the carbon quantum dot solution preparation method described in any one of the above;

[0028] Storing the prepared carbon quantum dot solution in an environment at 4 degrees Celsius for future use;

[0029] Selecting a carbon quantum dot solution with a specified concentration, and periodically spraying it on the surface of litchi fruits during the fruit swelling period until the spraying is complete.

[0030] Further, the concentration of the carbon quantum dot solution is 3 grams per liter, and the spraying amount is 600 ± 20 milliliters per square meter.

[0031] Further, the spraying period is 7 to 10 days, and a total of three to four sprays are carried out from the fruit swelling period to the fruit maturity. The spraying method is uniform spraying;

[0032] The so-called "spraying is complete" specifically means: spraying until the fruit surface is covered with the spraying liquid and the spraying liquid naturally drips on the fruit surface.

[0033] The beneficial effects of the present invention are as follows:

[0034] By recycling waste such as litchi leaves after fruit picking, the present invention prepares a carbon quantum dot solution and sprays the carbon quantum dot solution on litchi fruits during the swelling period, so as to increase the uniformity of the surface color of litchi fruits, improve the appearance performance of the fruits and improve the fruit quality; reduce the economic losses caused by uneven surface color distribution of litchi fruits; at the same time, the raw material for preparing the carbon quantum dot solution is litchi leaf waste, an agricultural product waste, which reduces the raw material cost. Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is the TEM image of the carbon quantum dots and the partially enlarged view of the carbon quantum dot lattice structure of the carbon quantum dot solution prepared by the carbon quantum dot solution preparation method of the present invention;

[0037] Figure 2 It is the particle size distribution diagram of the carbon quantum dot solution prepared by the carbon quantum dot solution preparation method of the present invention;

[0038] Figure 3It is the fluorescence spectrum and ultraviolet-visible absorption spectrum diagram of the carbon quantum dots in the carbon quantum dot solution prepared by the preparation method of the carbon quantum dot solution of the present invention;

[0039] Figure 4 It is the schematic diagram of the spraying position on the fruit tree in the spraying control experiment of the present invention;

[0040] Figure 5 It is the comparison of the front and back coloring of the fruits in the control group and the experimental group of the present invention;

[0041] Figure 6 It is the comparison diagram of the chlorophyll content in the fruit peels of the control group and the experimental group of the present invention;

[0042] Figure 7 It is the comparison diagram of the phenolic substance content in the fruit peels of the control group and the experimental group of the present invention. Detailed implementation manners

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the following further details the present application in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0044] It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present application.

[0045] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more unless otherwise specifically defined.

[0046] The preparation method of the carbon quantum dot solution disclosed by the present invention includes:

[0047] S1, collecting litchi leaves and performing pretreatment;

[0048] S2, drying the litchi leaves and grinding the dried product into powder;

[0049] S3, taking a specified mass of the powder, mixing it with water and transferring it to a reaction kettle, and heating to obtain a crude carbon quantum dot solution;

[0050] S4. After the crude solution is cooled, centrifuge it and filter out the insoluble precipitate to obtain a carbon quantum dot solution.

[0051] Step S1. The collection and pretreatment of litchi leaves specifically include:

[0052] Collect fresh litchi leaves;

[0053] Clean the sundries on the surface of litchi leaves.

[0054] The collected fresh litchi leaves are cleaned to remove the contamination. The fresh litchi leaves are directly collected when pruning the litchi tree for orchard cleaning, which is simple and easy to implement.

[0055] Step S2. Dry the litchi leaves and grind the dried product into powder, which specifically includes:

[0056] S21. Place the litchi leaves in a drying oven at a drying temperature of 105 °C for 30 minutes to obtain the first dried product;

[0057] S22. Place the first dried product in an environment at 65 °C and continue drying for 12 hours to obtain the second dried product;

[0058] S23. Grind the second dried product into powder.

[0059] The purpose of drying is to destroy the enzyme structure and inactivate it, and remove the moisture in the litchi leaves. After continuous drying for 12 hours, it can ensure that the moisture in the litchi leaves is completely removed for subsequent preparation of the carbon quantum dot solution.

[0060] Step S3. Take a specified mass of the powder, mix it with water and transfer it to a reaction kettle, and heat it to obtain a crude carbon quantum dot solution, which specifically includes:

[0061] S31. Weigh the specified powder, mix it with deionized water, and transfer it to a polytetrafluoroethylene reaction kettle; the solid-liquid mixing ratio is between 1:6 and 1:33;

[0062] S32. Place the reaction kettle in an electrothermal blast drying oven and react at 220 °C for 8 hours to prepare a crude carbon quantum dot solution.

[0063] In this step, the high-molecular organic matter of litchi leaves is transformed into carbon-containing nanoparticles, that is, a carbon quantum dot solution. After the reaction, the liquid mixture collected is the crude carbon quantum dot solution. The crude carbon quantum dot solution contains a carbon quantum dot solution and an insoluble precipitate, and is dark brown.

[0064] In a preferred embodiment of the present invention, the solid-liquid mixing ratio range of the powder to deionized water is 1:10 to 1:15, and the optimal is 1:13.

[0065] The sampling quality, the amount of mixed deionized water, and the volume of the reaction kettle in this step are all required for preparation in a laboratory environment. In industrial production, those skilled in the art can prepare according to the above configuration ratio.

[0066] Step S4, after the crude solution is cooled, centrifuge it and filter out the insoluble precipitate to obtain the carbon quantum dot solution, which specifically includes:

[0067] S41, cool the carbon quantum dot crude solution to room temperature;

[0068] S42, centrifuge at a speed of 10000 r / min for 10 min;

[0069] S43, filter the supernatant after centrifugation through a 0.22 μm microporous filter membrane to remove the insoluble precipitate, and obtain the carbon quantum dot solution after filtration.

[0070] Through cooling, centrifugation and filtration, the insoluble substances in the carbon quantum dot crude solution are removed, and the filtrate is the carbon quantum dot solution. The prepared carbon quantum dot solution is stored in an environment at 4°C for preservation.

[0071] To verify that the carbon quantum dot solution preparation method disclosed in the present invention can successfully prepare the carbon quantum dot solution, the TEM image of the prepared solution is as Figure 1 shown, and from Figure 1 it can be observed that the carbon quantum dot particles in the solution, Figure 1 the upper right corner is a partial enlarged view of the carbon quantum dot particles. The diameter distribution diagram of the obtained carbon quantum dot particles is as Figure 2 shown, and the diameters of the carbon quantum dot particles are mostly distributed in the range of 2.5 ± 0.9 nm. The fluorescence spectrum and ultraviolet-visible absorption spectrum diagrams of the carbon quantum dots are as Figure 3 shown. The carbon quantum dots have fluorescence characteristics and can emit blue light under ultraviolet light excitation. Its maximum excitation wavelength is 342 nm, the maximum emission wavelength is 421 nm, and the fluorescence quantum yield is 11.9%. Based on the above carbon quantum dot solution preparation method, the present invention also discloses a method for spraying the carbon quantum dot solution, which is applied to the planting and cultivation process of litchi to improve the color and fruit quality of litchi fruits, including:

[0072] Use litchi leaves as the reaction precursor and prepare the carbon quantum dot solution according to the above preparation method. Store the obtained carbon quantum dot solution in an environment at 4°C for future use.

[0073] Select a carbon quantum dot solution with a specified concentration and periodically spray it on the surface of litchi fruits during the fruit expansion period until the spraying is complete.

[0074] The fruit swelling stage is a developmental stage of the fruit. During this stage, the litchi fruit swells, the pulp becomes plump, and the color of the epidermis gradually turns red. At this time, a carbon quantum dot solution is sprayed to regulate the synthesis of substances such as fruit sugar-acid and peel pigment.

[0075] In an achievable embodiment of the present invention, the parameters of the carbon quantum dot solution used for spraying are as follows: the concentration of the carbon quantum dot solution is 3 g / L, and the spraying amount is 600 ± 20 mL / m 2 . In a preferred embodiment of the present invention, the spraying amount is 600 mL / m 2 .

[0076] In an achievable embodiment of the present invention, the spraying method is as follows: the spraying period is 7 to 10 days, and a total of 3 to 4 sprays are carried out from the fruit swelling stage to the fruit maturity stage; the specific spraying is as follows: spray until the fruit surface is covered with the spraying liquid, and the spraying liquid naturally drips on the fruit surface. The natural dripping of the spraying liquid on the fruit surface can indicate that the fruit surface is covered with the spraying liquid.

[0077] To verify the beneficial effects of the present invention, the embodiments of the present invention are as follows:

[0078] A comparative experiment was carried out in the same experimental field. The control groups were sprayed with water and a carbon quantum dot solution (3000 mg / L) respectively. In the treatments, the control group and the experimental group were marked as CK (clean water control group) and CDs (carbon quantum dot solution) respectively, and 4 replicates were set for each treatment. The experimental fruit trees were divided into different treatment areas. As Figure 4 shown, spraying experiments were carried out on the north, east, south, and west sides of the fruit trees respectively. The fruits in each direction were used as 1 replicate to reduce the experimental differences caused by different light in different directions. When taking fruit samples, 20 fruits without pests, diseases, and mechanical damage were randomly selected from the upper, middle, and lower parts of different treatment areas of each tree, mixed and put into a sample bag, sealed and placed in a foam box with an ice pack, and then transported to the laboratory in time for processing and determination of its relevant indicators.

[0079] I. Comparison of fruit colors

[0080] As Figure 5 shown, the fruits of Feizixiao collected in the experimental orchard showed uneven coloring when they were ripe. Part of the fruits were randomly selected from each group for display. The fruits of the control group and the experimental group were arranged vertically. On the left side of the fruits in the same row within the group was the sunny side, and on the right side was the shaded side. Taking the fruits of the control group (CK) as a reference, the fruits treated with carbon quantum dots (CDs) had a deeper red color on the sunny side, and the distribution area of green on the shaded side was significantly reduced, and the overall coloring of the fruits was more uniform.

[0081] II. Comparison of chlorophyll content in the fruit peel

[0082] The fruit color of litchi is the result of the combined action of multiple pigments. The degradation of chlorophyll provides the prerequisite for the appearance of red anthocyanins in the fruit. An important reason for the color difference in Concubine Smile litchi is the high chlorophyll content in its pericarp, which inhibits the red appearance of anthocyanins. From Figure 6 It can be seen that spraying carbon quantum dots (CDs) significantly reduced the contents of total chlorophyll, chlorophyll a, and chlorophyll b in litchi pericarp. Compared with the control group (CK), the contents of total chlorophyll, chlorophyll a, and chlorophyll b in the litchi pericarp treated with spraying carbon quantum dots (CDs) decreased by 20.88%, 19.31%, and 27.88% respectively (P<0.05).

[0083] III. Comparison of the Contents of Phenolic Substances in Pericarp

[0084] Litchi pericarp is rich in polyphenolic compounds, and its structural feature is ortho-diphenol groups. These compounds significantly enhance the color development characteristics of anthocyanins through intermolecular co-coloring effects, mainly including colored anthocyanins and co-colored flavanols, flavonols, phenolic acids, etc. The main colored anthocyanins in litchi pericarp are red cyanidin-3-rutinoside and cyanidin-3-glucoside. As Figure 7 shown, after treatment with carbon quantum dots (CDs), the contents of these two anthocyanins increased by 158.8% and 125.5% respectively compared with the control group (CK) (P<0.01), significantly enhancing the red phenotype of the pericarp. At the same time, the treatment with CDs increased the synthesis of flavanols (epicatechin, procyanidin A2, and procyanidin B2) in the pericarp. Among them, the contents of procyanidin A2 and procyanidin B2 increased by 12.5% and 39.5% respectively compared with CK (P<0.05), showing a synergistic effect on the color development of anthocyanins. The important co-pigment flavonols (rutin, quercetin-3-glucoside, and kaempferol-3-glucoside) also showed an accumulation trend. Among them, the contents of rutin and kaempferol-3-glucoside increased by 14.1% and 31.6% respectively compared with CK (P<0.05). In addition, the treatment with CDs also increased the contents of phenolic acids such as ferulic acid and gallic acid in the pericarp, which can inhibit the degradation of anthocyanins and enhance their stability. Among them, ferulic acid increased by 24.7% compared with CK (P<0.05). In summary, the treatment with CDs significantly enhanced the color development effect of anthocyanins by simultaneously regulating the synthesis and accumulation of compounds such as anthocyanins, flavanols, flavonols, and phenolic acids in the pericarp, thus effectively improving the red phenotype of litchi pericarp.

[0085] IV. Contents of Soluble Solids, Soluble Sugars, and Titratable Acids in Pulp

[0086] In the evaluation of litchi fruit quality, total soluble solids (TSS), as the sum of substances such as sugars, organic acids, and amino acids, has a significant positive correlation with fruit quality and plays a positive role in extending the fruit storage period. As shown in Table 1, after treatment with carbon quantum dots (CDs), the TSS content in litchi pulp increased significantly by 2.5% compared with the control group (CK) (P<0.05). Titratable acid (TA), as a core index for evaluating the flavor quality and nutritional value of litchi fruit, the change in its content directly affects the taste characteristics and nutritional properties of the fruit. The experimental results showed that the TA content decreased significantly by 19.8% in the CDs treatment compared with CK (P<0.05). The sugar-acid ratio, as a key parameter reflecting the flavor balance of the fruit, the change in its value is closely related to the consumer taste experience. In this experiment, the sugar-acid ratio of litchi pulp treated with CDs increased significantly by 21.8% compared with CK (P<0.05), which was highly consistent with the sensory preference of consumers for the sweetness of litchi fruit. The above results indicate that exogenous spraying of CDs solution increases the TSS content while decreasing the TA content, significantly improving the sugar-acid ratio, and thus effectively improving the comprehensive quality of litchi fruit.

[0087] Table 1 Contents of total soluble solids, soluble sugars, titratable acids and sugar-acid ratios in the pulp of 'Feizixiao' litchi under different spraying treatments

[0088]

[0089] Note: Different lowercase letters in the figure indicate significant differences among different treatments at the 0.05 level.

[0090] The results of this study indicate that exogenous spraying of carbon quantum dots (CDs) can effectively improve the problem of uneven skin coloration of 'Feizixiao' litchi and significantly enhance fruit quality. Specifically, the CDs treatment significantly improved the skin coloration effect by significantly reducing the chlorophyll content in the skin while upregulating the synthesis and accumulation of key polyphenolic substances. From the perspective of fruit quality indicators, the CDs treatment significantly increased the total soluble solids content in the pulp while decreasing the titratable acid content, significantly increasing the sugar-acid ratio of the fruit, and ultimately achieving a comprehensive improvement in fruit quality. Therefore, it is recommended to spray CDs during the fruit expansion period of 'Feizixiao' litchi to improve skin coloration and enhance fruit quality. The present invention discloses a method for preparing a carbon quantum dot solution using litchi leaves as raw materials. By resourcefully utilizing waste, litchi leaves are transformed into carbon quantum dots, achieving efficient utilization of waste in the litchi planting process, reducing the preparation cost of the carbon quantum dot solution, improving resource utilization rate, and being suitable for popularization and application in actual production. The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing a carbon quantum dot solution, characterized in that: include: Collecting litchi leaves and pre-processing them; Drying the litchi leaves and grinding the dried products into powder; A specified mass of powder is taken, mixed with water, transferred to a reactor, and heated to obtain a crude carbon quantum dot solution; After the crude solution is cooled, it is centrifuged and the insoluble precipitate is filtered out to obtain a carbon quantum dot solution.

2. The method for preparing a carbon quantum dot solution according to claim 1, characterized in that: The collecting and pre-processing of litchi leaves specifically includes: Collect fresh litchi leaves; Clean the debris on the surface of litchi leaves.

3. The method for preparing a carbon quantum dot solution according to claim 1, characterized in that: The step of drying the litchi leaves and grinding the dried product into powder specifically comprises: The litchi leaves were placed in a drying oven at a drying temperature of 105 degrees Celsius for 30 minutes to obtain a first drying product; The first drying product was placed in an environment of 65 degrees Celsius and dried for 12 hours to obtain a second drying product; The second drying product is ground into a powder.

4. The method for preparing a carbon quantum dot solution according to claim 1, characterized in that: The method of taking a specified mass of powder, mixing it with water, transferring it to a reactor, and heating it to obtain a crude carbon quantum dot solution specifically includes: Weigh a certain amount of the powder, add deionized water according to a solid-liquid mass ratio of 1:6 to 1:33, and transfer to a polytetrafluoroethylene reactor; The reactor was placed in an electric heated blast drying oven and reacted at 220 degrees Celsius for 8 hours to prepare a crude carbon quantum dot solution.

5. The method for preparing a carbon quantum dot solution according to claim 4, characterized in that: The solid-liquid mass ratio is 1:10 to 1:

15.

6. The method for preparing a carbon quantum dot solution according to claim 1, characterized in that: The step of cooling the crude solution and centrifuging it, and filtering out the insoluble precipitate to obtain the carbon quantum dot solution specifically comprises: Cooling the crude carbon quantum dot solution to room temperature; Centrifuge at 10,000 rpm for 10 min; The supernatant after centrifugation was filtered through a 0.22-micron microporous filter membrane to remove insoluble precipitates, and a carbon quantum dot solution was obtained after filtration.

7. The method for preparing a carbon quantum dot solution according to claim 1, characterized in that: The carbon quantum dot solution is stored in an environment of 4 degrees Celsius.

8. A method for spraying a carbon quantum dot solution, characterized in that: include: Using litchi leaves as a reaction precursor, a carbon quantum dot solution is prepared according to the method for preparing a carbon quantum dot solution according to any one of claims 1 to 7; The prepared carbon quantum dot solution was stored at 4 degrees Celsius for future use; A carbon quantum dot solution of a specified concentration is selected and periodically sprayed on the surface of litchi fruit during the fruit expansion period, and each spraying is performed until the fruit is completely sprayed.

9. The method for spraying a carbon quantum dot solution according to claim 8, characterized in that: The concentration of the carbon quantum dot solution is 3 grams per liter, and the spraying amount is 600±20 milliliters per square meter.

10. The method for spraying a carbon quantum dot solution according to claim 8, characterized in that: The spraying cycle is 7 to 10 days, and the fruit is sprayed three to four times from the fruit expansion stage to the fruit maturity. The spraying method is uniform spraying. The spraying is specifically as follows: spraying until the surface of the fruit is covered with the spraying liquid, and the spraying liquid drips naturally on the surface of the fruit.

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