Preparation method and application of full-color luminescent carbon dots from tobacco waste source

Abstract

The application relates to a preparation method and application of full-color luminescent carbon dots from tobacco waste, and comprises the following steps: step 1, drying and crushing tobacco waste to obtain tobacco waste chips; step 2, uniformly mixing one of water, anhydrous ethanol and acetone with the tobacco waste chips and H2O2, and then standing for 5-30 min, and then performing ultrasonic treatment by using ultrasonic waves; step 3, filtering out tobacco waste chip residues to obtain a carbon dot crude solution containing blue carbon dots, green carbon dots and red carbon dots; step 4, further filtering the carbon dot crude solution through a 0.22 mu m filter membrane, and then dialyzing in ultrapure water to obtain a carbon dot concentrated solution; and step 5, rotary evaporating the carbon dot crude solution in a rotary evaporator until dryness to obtain carbon dot solids, and the rotary evaporation temperature is 30-50 DEG C. Through utilization of tobacco waste, the application solves the environmental pollution and resource waste caused by improper treatment of tobacco waste; compared with the existing method, the application is simpler in process, reduces the utilization of harmful chemical substances, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to the field of carbon dot preparation, and in particular to a method for preparing full-color luminescent carbon dots from tobacco waste and applications thereof. Background Art

[0002] Carbon dots (CDs), as a carbon nanomaterial, have the advantages of small particle size, good water solubility, high biocompatibility, non-toxicity, easy preparation, and wide source of raw materials.

[0003] As food demand increases, large quantities of pesticides and fertilizers are used in agricultural production, exacerbating the challenges posed by agricultural production and the environment. Approximately 90% of the dry matter in crops comes from photosynthesis, yet plants currently utilize only about 5% of the light they produce.

[0004] Carbon dots are known to promote the synthesis of plant chlorophyll and enhance plant photosynthesis, and have certain application prospects in the agricultural field. Existing technologies such as the document "Research Progress on the Regulation of Plant Photosynthesis by Fluorescent Carbon Dots, Li Yadong, Xu Xiaokai, et al., Journal of Luminescence, Vol. 42, No. 8, August 2021" disclose the promoting role of carbon dots in plant photosynthesis.

[0005] Organic matter is a major carbon source for carbon dot preparation. Different organic matter types have different preparation methods for carbon dots, including pyrolysis, hydrothermal, and microwave heating. Existing technologies, such as patent document CN113148979A, disclose a method and application for using tobacco waste to prepare carbon dots that display different colors at the same wavelength. The hydrothermal method is used to prepare carbon dots. The hydrothermal method is limited by the volume of the hydrothermal reactor, and the amount of carbon dots prepared at one time is limited. It is not suitable for large-scale industrial production, especially cannot meet the demand for large-scale use in agricultural production. Summary of the Invention

[0006] In order to simplify the carbon dot preparation method and facilitate its utilization in agricultural production, the present invention provides a method for preparing full-color luminescent carbon dots from tobacco waste and its application, which reduces the use of harmful chemical reagents, utilizes tobacco waste, and realizes the effective utilization of resources.

[0007] The technical objectives of the present invention are achieved through the following technical solutions:

[0008] A method for preparing full-color luminescent carbon dots from tobacco waste, the method comprising:

[0009] Step 1: drying tobacco waste and then pulverizing it to obtain tobacco waste debris, wherein the tobacco waste includes at least one of tobacco leaves and tobacco stems;

[0010] Step 2: uniformly mix the tobacco waste debris and H2O2 with one of water, anhydrous ethanol and acetone, let it stand for 5-30 minutes, and then perform ultrasonic treatment;

[0011] Step 3: filtering out the tobacco waste debris residue to obtain a crude carbon dot solution containing one of blue carbon dots, green carbon dots, and red carbon dots;

[0012] Step 4: The crude carbon dot solution was further filtered through a 0.22 μm filter membrane and then dialyzed in ultrapure water to obtain a carbon dot concentrate;

[0013] Step 5: The crude carbon dot solution is evaporated to dryness in a rotary evaporator to obtain carbon dot solids at a rotary evaporation temperature of 30-50°C.

[0014] Furthermore, in step 2, the ultrasonic treatment was carried out in a polytetrafluoroethylene container under an ultrasonic wave of 300 W / m for 5 minutes.

[0015] Furthermore, in step 3, the filtered tobacco waste debris residue is washed and filtered several times with a solvent until the washed solution is clear and transparent, and the solution obtained by washing the tobacco waste debris residue is mixed into the crude carbon dot solution; the solvent used for washing is consistent with the solvent added during mixing in step 2.

[0016] Furthermore, in step 4, during dialysis, the crude carbon dot solution is dialyzed in ultrapure water in a dialysis bag with a molecular weight cut-off of 100-500 for 12-48 hours.

[0017] Furthermore, when water is mixed with tobacco waste debris and H2O2, 0.4 g of H2O2 and 20 ml of water are added to each 1 g of tobacco waste debris, and the mixture is dried by rotary evaporation to obtain the optimal excitation wavelength λ ex = Blue carbon dots (B-CDs) solid emitting blue light at 375 nm;

[0018] When anhydrous ethanol is mixed with tobacco waste debris and H2O2, the mixture is added in a ratio of 0.4g H2O2 and 20ml anhydrous ethanol per 1g tobacco waste debris, and the mixture is dried by rotary evaporation to obtain the optimal excitation wavelength λ ex = Green emission at 492nm and optimal excitation wavelength λ ex = Green carbon dots (G-CDs) solid emitting yellow light at 546 nm;

[0019] When acetone is mixed with tobacco waste debris and H2O2, 0.4g H2O2 and 20ml acetone are added to each 1g tobacco waste debris, and the optimal excitation wavelength λ is obtained by rotary evaporation and drying. ex =Emit yellow light at 551nm, optimal excitation wavelength λex = Orange emission at 585nm and optimal excitation wavelength λ ex = Red carbon dots (R-CDs) solid emitting red light at 617 nm.

[0020] The present invention also provides an application of full-color luminescent carbon dots derived from tobacco waste in lettuce cultivation. At least one of the blue carbon dots and red carbon dots among the carbon dots prepared by the above method is configured into a 500 mg / L aqueous solution and sprayed on lettuce to promote the biomass accumulation of lettuce and increase the content of soluble sugar and soluble protein in lettuce.

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

[0022] On one hand, the present invention provides a method for preparing full-color luminescent carbon dots from tobacco waste. By utilizing tobacco waste, this method addresses the environmental pollution and resource waste caused by improper tobacco waste disposal. Furthermore, it leverages the advantages of low cost and environmental friendliness to further develop carbon dot luminescent materials for practical agricultural production. Compared to existing carbon dot preparation methods, the present method is simpler in terms of process, reduces the use of harmful chemicals, is more environmentally friendly, and its production output is no longer limited by the volume of the hydrothermal reactor, making it suitable for large-scale industrial production.

[0023] On the other hand, the present invention also provides an application of full-color luminescent carbon dots derived from tobacco waste in lettuce cultivation. The carbon dots are applied to the biomass accumulation of lettuce and the increase of soluble sugar and soluble protein content, which is beneficial to improving the yield and quality of lettuce. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is an electron microscope image of the blue carbon dots in the present invention.

[0025] Figure 2 It is an electron microscope image of the red carbon dots in the present invention.

[0026] Figure 3 This is an excitation-dependent fluorescence spectrum of the blue carbon dots in the present invention.

[0027] Figure 4 This is an excitation-dependent fluorescence spectrum of the red carbon dots in the present invention.

[0028] Figure 5 1 is a diagram showing the growth of lettuce after spraying different solutions in an embodiment of the present invention.

[0029] Figure 6 2 is a schematic diagram comparing the fresh weight of lettuce in an embodiment of the present invention.

[0030] Figure 7 2 is a schematic diagram comparing the dry weight of lettuce in an embodiment of the present invention.

[0031] Figure 8 Schematic diagram of the determination of soluble sugar content in lettuce leaves in an embodiment of the present invention.

[0032] Figure 9 Schematic diagram of the determination of soluble protein content in lettuce leaves in an embodiment of the present invention.

[0033] Figure 10 It is a schematic diagram of the preparation process of full-color luminescent carbon dots from tobacco waste of the present invention.

[0034] Figure 11 This is a CLSM test image of the lettuce root tissue in an embodiment of the present invention.

[0035] Figure 12 This is a CLSM test image of the lettuce stem tissue in an embodiment of the present invention.

[0036] Figure 13 This is a CLSM test image of lettuce leaf tissue in an embodiment of the present invention.

[0037] Figure 14 In the embodiment of the present invention, ex =551nm,λ em = CLSM test image of red carbon dots in leaf tissue at a wavelength of 576 nm. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below in conjunction with specific embodiments:

[0039] Example 1

[0040] A method for preparing full-color luminescent carbon dots from tobacco waste, such as Figure 10 As shown, the method includes:

[0041] Step 1: Dry tobacco waste and then pulverize it to obtain tobacco waste debris. The tobacco waste source includes at least one of tobacco leaves and tobacco stems. In one embodiment, the size of the tobacco waste debris is 1-5 mm.

[0042] Step 2: Evenly mix one of water, anhydrous ethanol and acetone with tobacco waste debris and H2O2, let it stand for 5-30 minutes, and then perform ultrasonic treatment using ultrasound; specifically, during the ultrasonic treatment, perform ultrasonic treatment at 300 W / m for 5 minutes in a polytetrafluoroethylene container, such as a polytetrafluoroethylene sealed bottle.

[0043] The addition of H2O2 destroys the plant cell walls in tobacco waste debris, facilitating the extraction of components from the waste, including but not limited to plant solanesol, chlorogenic acid, rutin, tobacco leaf protein, malic acid, and polysaccharides. The use of H2O2 does not produce toxic or harmful chemicals, thus meeting environmental protection requirements.

[0044] Step 3: filtering out the tobacco waste debris residue to obtain a crude carbon dot solution containing one of blue carbon dots (B-CDs), green carbon dots (G-CDs), and red carbon dots (R-CDs);

[0045] In order to make full use of the substances in the tobacco waste, the filtered tobacco waste debris residue is further washed and filtered several times with a corresponding solvent until the washed solution is clear and transparent, and the solution obtained by washing the tobacco waste debris residue is mixed with the crude carbon dot solution. The solution used for washing is consistent with the solution added during mixing in step 2. That is, if water, tobacco waste debris, and H2O2 are mixed in step 2, water is used for washing; if anhydrous ethanol, tobacco waste debris, and H2O2 are mixed in step 2, anhydrous ethanol is used for washing; if acetone, tobacco waste debris, and H2O2 are mixed in step 2, acetone is used for washing.

[0046] Step 4: The crude carbon dot solution is further filtered through a 0.22 μm filter membrane and then dialyzed in ultrapure water to remove small molecules that do not participate in the reaction, thereby obtaining a carbon dot concentrate.

[0047] Specifically, during dialysis, the crude carbon dot solution is dialyzed in ultrapure water in a dialysis bag with a molecular weight cut-off of 100-500 for 12-48 hours.

[0048] Step 5: The crude carbon dot solution is evaporated to dryness in a rotary evaporator to obtain carbon dot solids at a rotary evaporation temperature of 30-50°C.

[0049] More specifically, when water is mixed with tobacco waste debris and H2O2, the mixture is added in a ratio of 0.4g H2O2 and 20ml water per 1g of tobacco waste debris, and then dried by rotary evaporation to obtain the optimal excitation wavelength λ ex = B-CDs solid that emits blue light at 375nm, its optimal emission wavelength λ em =455nm.

[0050] When anhydrous ethanol is mixed with tobacco waste debris and H2O2, the mixture is added in a ratio of 0.4g H2O2 and 20ml anhydrous ethanol per 1g tobacco waste debris, and the mixture is dried by rotary evaporation to obtain the optimal excitation wavelength λ ex = Green emission at 492nm and optimal excitation wavelength λ ex= G-CDs solid emitting yellow light at 546 nm; the optimal emission wavelength λ of G-CDs emitting green light em =555nm, the optimal emission wavelength λ of G-CDs emitting yellow light em =571nm, mainly emits green light.

[0051] When acetone is mixed with tobacco waste debris and H2O2, 0.4g H2O2 and 20ml acetone are added to each 1g tobacco waste debris, and the optimal excitation wavelength λ is obtained by rotary evaporation and drying. ex =Emit yellow light at 551nm, optimal excitation wavelength λ ex = Orange emission at 585nm and optimal excitation wavelength λ ex = R-CDs solid emitting red light at 617nm; the optimal emission wavelength of R-CDs emitting yellow light is λ em =576nm, the optimal emission wavelength λ of R-CDs emitting orange light em = 606nm, the optimal emission wavelength λ of R-CDs emitting red light em =640nm, the longest emission wavelength is red.

[0052] In a specific implementation, ultrapure water is used, hydrogen peroxide is analytical grade AR with a concentration of 30 wt%, anhydrous ethanol is analytical grade AR with a purity of ≥99.7%, and acetone is analytical grade AR with a purity of ≥99.5%. During mixing, hydrogen peroxide is added to the tobacco waste scraps while stirring, and then water, anhydrous ethanol, or acetone is slowly added dropwise while stirring.

[0053] Example 2

[0054] Based on the requirement of matching the plant chlorophyll absorption spectrum (400-500nm and 600-700nm), blue carbon dots and red carbon dots were selected for lettuce cultivation research. The prepared carbon dots were morphologically determined using transmission electron microscopy, and fluorescence spectroscopy was performed on the carbon dots:

[0055] The morphology of blue carbon dots was determined as Figure 1 As shown, the morphology of red carbon dots was determined as Figure 2 As shown, the blue carbon dots are uniformly distributed and quasi-spherical, while the red carbon dots are unevenly distributed and irregular in shape. Counting analysis of 200 randomly selected points in the size measurement graph revealed an average size distribution of 2.23 ± 0.03 nm for the blue carbon dots and 95.60 ± 1.57 nm for the red carbon dots.

[0056] At elevated excitation wavelengths, both blue and red Cdots exhibit excitation-dependent fluorescence emission, e.g. Figure 3 and Figure 4 As shown, the emission wavelengths of blue and red carbon dots have obvious range characteristics, and the emission range of blue carbon dots is limited to the blue light region (λ emmax =455nm), the luminescence range of red carbon dots is limited to a longer yellow-orange-red region (λ emmax =576m, 606nm and 640nm).

[0057] Among them, the optimal excitation wavelength λ ex and the optimal emission wavelength λ em as follows:

[0058] The λ value of blue carbon dots emitting blue light prepared by water solvent ex =375nm, λ em =455nm;

[0059] The optimal excitation wavelength λ of the red carbon dots prepared by acetone that emit yellow light ex =551nm, optimal emission wavelength λ em =576nm;

[0060] The optimal excitation wavelength λ of the red carbon dots prepared by acetone that emit orange light ex =585nm, optimal emission wavelength λ em =606nm;

[0061] The optimal excitation wavelength λ of red carbon dots emitting red light among the red carbon dots prepared by acetone ex =617nm, optimal emission wavelength λ em =640nm.

[0062] A method for using full-color luminescent carbon dots derived from tobacco waste in lettuce cultivation includes spraying at least one of blue carbon dots and red carbon dots prepared according to the method of Example 1 or 2 to promote biomass accumulation and increase the soluble sugar and soluble protein content of lettuce.

[0063] Specifically, in this embodiment, 7-day-old lettuce seedlings with the same growth potential were selected and transplanted into four water basins containing a nutrient solution of normal concentration, with a density of 6 seedlings per basin.

[0064] On the second day after transplanting (three leaves and one heart), spray three pots with a 500 mg / L aqueous solution of B-CDs, a 500 mg / L aqueous solution of R-CDs, and a 500 mg / L aqueous solution of B-CDs and R-CDs (250 mg / L each of B-CDs and R-CDs) at a dosage of 5 ml / pot. Simultaneously spray one pot with ultrapure water. Foliar spraying should be performed daily for 15-20 days. Spraying should be done evenly and slowly to avoid runoff, and avoid shaking the lettuce leaves.

[0065] The above test was repeated three times, and the effect after spraying was as follows: Figure 5 As shown, Figure 5 The CK group is the control group sprayed with ultrapure water, among which group a) is the growth status picture after spraying ultrapure water, and group e) is the growth status picture of two lettuces selected from group a); the B-CDs group is the group sprayed only with blue carbon dot aqueous solution, among which group b) is the growth status picture after spraying blue carbon dot aqueous solution, and group f) is the growth status picture of two lettuces selected from group b); the R-CDs group is the group sprayed only with red carbon dot aqueous solution, among which group c) is the growth status picture after spraying red carbon dot aqueous solution, and group g) is the growth status picture of two lettuces selected from group c); the BR-CDs group is the group sprayed with blue and red carbon dot aqueous solutions, among which group d) is the growth status picture after spraying red carbon dot aqueous solution, and group h) is the growth status picture of two lettuces selected from group d).

[0066] The biomass of lettuce was measured separately, including dry weight and fresh weight:

[0067] Compared with the CK control group, Figure 6 As shown, the fresh weight of the aboveground lettuce in the B-CDs, R-CDs and BR-CDs groups increased by 92.62%, 87.25% and 118.42%, respectively, and the fresh weight of the underground lettuce in the B-CDs, R-CDs and BR-CDs groups increased by 71.43%, 66.67% and 97.62%, respectively.

[0068] Compared with the CK control group, Figure 7 As shown, the dry weight of the aboveground lettuce in the B-CDs, R-CDs and BR-CDs groups increased by 90.98%, 87.60% and 120.41%, respectively, and the dry weight of the underground lettuce in the B-CDs, R-CDs and BR-CDs groups increased by 69.84%, 62.90% and 101.96%, respectively.

[0069] In addition, the soluble sugar and soluble protein contents of the lettuce were measured for the experimental group and the control group. Soluble sugar in plants acts as carbohydrates to provide substances and energy for plant development, and its content is an important indicator of plant nutritional quality.

[0070] The same positions of the above-mentioned group of lettuce were selected, such as the third leaf from the outside to the inside, for determination of soluble sugar content and protein content, as shown in Figure 8 and Figure 9

[0071] Compared with the control group, the soluble sugar content of the treatment group was improved, and the soluble sugar content of the B-CDs, R-CDs and BR-CDs groups was improved by 41.08%, 39.15% and 55.84% respectively compared with the control group.

[0072] Compared with the control group, the soluble protein content of the treatment group was improved, and the protein content of the B-CDs, R-CDs and BR-CDs groups was improved by 27.98%, 26.60% and 41.86% respectively compared with the control group.

[0073] From the above results, it can be seen that the combined application of B-CDs and R-CDs has better effect.

[0074] In order to more intuitively observe the absorption and transfer of carbon dots in lettuce, CLSM (Confocal laser scanning microscopy) test was performed on the section of lettuce tissue, which fully utilized the biological probe function of carbon dots.

[0075] Specifically, after spraying carbon dot solution on the surface of lettuce leaves for 15 days, the tissues of roots, stems and leaves of lettuce were sectioned and observed, and the lettuce tissues were subjected to transverse frozen sectioning treatment, as shown in Figure 11-13 . Figure 11-13 The bright field and luminescence images of the root, stem and leaf of the lettuce are shown, and it can be seen that the bright field and fluorescence images of the root, stem and leaf tissues are completely overlapped, indicating that the two carbon dots (B-CDs and R-CDs) can easily enter the plant body and be smoothly absorbed and transferred. The confocal images of B-CDs were collected at λ ex = 375 nm, λ em = 455 nm, and the confocal images of R-CDs were collected at (λ ex = 617 nm, λ em = 640 nm).

[0076] In order to exclude the interference of strong spontaneous red fluorescence from leaf cells in the shooting of R-CDs, another characteristic emission wavelength (λ ex = 551 nm, λ em = 576 nm) of R-CDs was selected to determine the presence of R-CDs, as shown in Figure 14 ​As shown in the figure, the bright field and fluorescence images of R-CDs in leaf tissues completely overlap, and the results prove that R-CDs exist in the mesophyll cells of lettuce and are closely related to Figure 13 The images of leaf tissue in the experiment closely overlap. Fluorescence images of lettuce show that the carbon dots' luminescence signal virtually covers the roots, stems, and leaves, including the epidermis and interior. Both B-CDs and R-CDs are absorbed by the leaves and diffuse downward through the stem's vascular system to the roots, a path that is the opposite of the upward migration of carbon dots from the roots through the stem's vascular system to the leaf tissue. CLSM testing demonstrates that both B-CDs and R-CDs are present in significant quantities and maintain high stability in lettuce tissue.

[0077] This embodiment is only a further explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for preparing full-color luminescent carbon dots from tobacco waste, characterized in that: The method includes: Step 1: drying tobacco waste and then pulverizing it to obtain tobacco waste debris, wherein the tobacco waste includes at least one of tobacco leaves and tobacco stems; Step 2: uniformly mix the tobacco waste debris and H2O2 with one of water, anhydrous ethanol and acetone, let it stand for 5-30 minutes, and perform ultrasonic treatment; Step 3: filtering out the tobacco waste debris residue to obtain a crude carbon dot solution containing one of blue carbon dots, green carbon dots, and red carbon dots. When water is mixed with tobacco waste debris and H2O2, the optimal excitation wavelength λ is obtained by adding 0.4g H2O2 and 20ml water per 1g tobacco waste debris and drying by rotary evaporation. ex = Blue carbon dot solid emitting blue light at 375nm; When anhydrous ethanol is mixed with tobacco waste debris and H2O2, the mixture is added in a ratio of 0.4g H2O2 and 20ml anhydrous ethanol per 1g tobacco waste debris, and the mixture is dried by rotary evaporation to obtain the optimal excitation wavelength λ ex = Green emission at 492nm and optimal excitation wavelength λ ex = Green carbon dot solid emitting yellow light at 546 nm; When acetone is mixed with tobacco waste debris and H2O2, 0.4g H2O2 and 20ml acetone are added to each 1g tobacco waste debris, and the optimal excitation wavelength λ is obtained by rotary evaporation and drying. ex =Emit yellow light at 551nm, optimal excitation wavelength λ ex = Orange emission at 585nm and optimal excitation wavelength λ ex = Red carbon dot solid emitting red light at 617nm; Step 4: The crude carbon dot solution was further filtered through a 0.22 μm filter membrane and then dialyzed in ultrapure water to obtain a carbon dot concentrate; Step 5: The crude carbon dot solution is evaporated to dryness in a rotary evaporator to obtain carbon dot solids at a rotary evaporation temperature of 30-50°C.

2. The method for preparing full-color luminescent carbon dots from tobacco waste according to claim 1, characterized in that: In step 2, the ultrasonic treatment was performed in a polytetrafluoroethylene container under ultrasonic waves of 300 W / m for 5 minutes.

3. The method for preparing full-color luminescent carbon dots from tobacco waste according to claim 1, characterized in that: In the step 3, the filtered tobacco waste debris residue is further washed and filtered several times until the washed solution is clear and transparent, and the solution obtained by washing the tobacco waste debris residue is mixed into the crude carbon dot solution; the solvent used for washing is consistent with the solvent added during mixing in step 2.

4. The method for preparing full-color luminescent carbon dots from tobacco waste according to claim 1, characterized in that: In step 4, during dialysis, the crude carbon dot solution is dialyzed in ultrapure water in a dialysis bag with a molecular weight cut-off of 100-500 for 12-48 hours.

5. Application of full-color luminescent carbon dots derived from tobacco waste in lettuce cultivation, characterized in that: The carbon dots are at least one of blue carbon dots and red carbon dots prepared by the method of any one of claims 1 to 4, and the carbon dots are configured into a 500 mg / L aqueous solution for spraying to promote the biomass accumulation of lettuce and increase the soluble sugar and soluble protein content in lettuce.

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