Preparation method and application of panchromatic luminous carbon dots sourced from tobacco waste

Abstract

The invention relates to a preparation method and application of panchromatic luminous carbon dots sourced from tobacco waste. The preparation method comprises the following steps: step 1, drying tobacco waste, and crushing to obtain tobacco waste chippings; step 2, uniformly mixing one of water, absolute ethyl alcohol and acetone with the tobacco waste chippings and H2O2, standing for 5-30 minutes, and performing ultrasonic treatment by utilizing ultrasonic waves; step 3, filtering out tobacco waste debris residues to obtain a carbon dot crude solution containing blue carbon dots, green carbon dots and red carbon dots; 4, further filtering the carbon dot crude solution through a 0.22 mu m filter membrane, and dialyzing in ultrapure water to obtain a carbon dot concentrated solution; and 5, carrying out rotary evaporation on the carbon dot crude solution in a rotary evaporator at the temperature of 30-50 DEG C until the carbon dot crude solution is dried to obtain a carbon dot solid. By utilizing the tobacco waste, the problems of environmental pollution and resource waste caused by improper treatment of the tobacco waste are solved; compared with the existing method, the method 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] With the increase in food demand, a large amount of pesticides and fertilizers are used in agricultural production, making the problems between agricultural production and resources and the environment more acute. About 90% of the dry matter in crops comes from plant photosynthesis, but the current utilization rate of light by plants is only about 5%.

[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 literature "Progress in Research on Regulating 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] A major carbon source for the preparation of carbon dots is organic matter. Different types of organic matter have different preparation methods for carbon dots, including pyrolysis, hydrothermal, microwave heating, etc. The prior art, such as the patent document with publication number CN113148979A, discloses a method and application of preparing carbon dots showing different colors at the same wavelength using tobacco waste. The hydrothermal method is used to prepare carbon dots. The hydrothermal method for synthesizing carbon dots is limited by the volume of the hydrothermal reactor. The amount of carbon dots prepared at one time is limited, which 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 agricultural production utilization, 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 and crushing tobacco waste to obtain tobacco waste debris, wherein the tobacco waste includes at least one of tobacco leaves and tobacco stems;

[0010] Step 2, mixing a solvent selected from water, anhydrous ethanol and acetone, tobacco waste debris and H2O2 uniformly, standing for 5-30 minutes, and then performing ultrasonic treatment using ultrasound;

[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 is further filtered through a 0.22 μm filter membrane and dialyzed in ultrapure water to obtain a carbon dot concentrate;

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

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

[0015] Furthermore, in step 3, it also includes washing and filtering the filtered tobacco waste debris residue with a solvent several times until the washed solution is clear and transparent, and mixing the solution obtained by washing the tobacco waste debris residue 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 cutoff 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 then 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, 0.4 g of H2O2 and 20 ml of anhydrous ethanol are added according to the ratio of 1 g of tobacco waste debris, and the optimal excitation wavelength λ is obtained by rotary evaporation and drying. ex = Green light 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 of H2O2 and 20ml of acetone are added to each 1g of tobacco waste debris, and then the mixture is dried by rotary evaporation to obtain the optimal excitation wavelength λ ex =Emits yellow light at 551nm, optimal excitation wavelength λex = Orange light 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 the 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 the one hand, the present invention provides a method for preparing full-color luminescent carbon dots from tobacco waste, which solves the environmental pollution and resource waste problems caused by improper treatment of tobacco waste by utilizing tobacco waste, and realizes the redevelopment of carbon dot luminescent materials by taking advantage of its low cost and green environmental protection, and applies it to actual agricultural production. Compared with the existing carbon dot preparation method, the preparation method of the present invention is simpler in process, reduces the use of harmful chemicals, is more green and environmentally friendly, and the output is no longer limited by the volume of the hydrothermal reactor, and is 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 to increase the content of soluble sugar and soluble protein, which is beneficial to improving the yield and quality of lettuce. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It 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 It is an excitation-dependent fluorescence spectrum diagram of the blue carbon dots in the present invention.

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

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

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

[0030] Figure 7 Schematic diagram of dry weight comparison of lettuce in embodiments 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] Fig. 9 Schematic diagram of the determination of soluble protein content in lettuce leaves in an embodiment of the present invention.

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

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

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

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

[0037] Fig.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 Fig.10 As shown, the method includes:

[0041] Step 1: Dry the 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 tobacco waste debris and H2O2 with one of water, anhydrous ethanol and acetone, let stand for 5-30 minutes, and then perform ultrasonic treatment using ultrasound; specifically, during the ultrasonic treatment, perform ultrasonic treatment at 300W / m for 5 minutes in a polytetrafluoroethylene container, such as a polytetrafluoroethylene sealed bottle.

[0043] By adding H2O2, the plant cell walls in the tobacco waste debris are destroyed, which is conducive to the precipitation of components in the tobacco waste debris, including but not limited to phytosolanesol, chlorogenic acid, rutin, tobacco leaf protein, malic acid, polysaccharides, etc. The use of H2O2 will not produce toxic and harmful chemicals, and meets the requirements of green environmental protection.

[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 also 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 into the carbon point crude 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 dialyzed in ultrapure water to remove small molecules that do not participate in the reaction to obtain a carbon dot concentrated solution;

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

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

[0049] More specifically, 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 then the mixture is dried by rotary evaporation to obtain the optimal excitation wavelength λ ex = B-CDs solid emitting blue light at 375nm, with the best emission wavelength λ em =455nm.

[0050] When anhydrous ethanol is mixed with tobacco waste debris and H2O2, 0.4 g of H2O2 and 20 ml of anhydrous ethanol are added according to the ratio of 1 g of tobacco waste debris, and the optimal excitation wavelength λ is obtained by rotary evaporation and drying. ex = Green light emission at 492nm and optimal excitation wavelength λ ex= G-CDs solid emitting yellow light at 546nm; the optimal emission wavelength of G-CDs emitting green light is λ 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 of H2O2 and 20ml of acetone are added to each 1g of tobacco waste debris, and then the mixture is dried by rotary evaporation to obtain the optimal excitation wavelength λ ex =Emits yellow light at 551nm, optimal excitation wavelength λ ex = Orange light 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 process, the water used is ultrapure water, the hydrogen peroxide is analytical grade AR with a concentration of 30wt%, the anhydrous ethanol is analytical grade AR with a purity of ≥99.7%, and the acetone is analytical grade AR with a purity of ≥99.5%. When mixing, hydrogen peroxide is added to the tobacco waste debris while stirring, and then water, anhydrous ethanol or acetone is slowly added dropwise during the stirring process.

[0053] Example 2

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

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

[0056] At elevated excitation wavelengths, both blue and red Cdots exhibit excitation-dependent fluorescence emission, e.g. Figure 3 and Figure 4 As shown in Figure 2, 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 the red carbon dots emitting red light prepared by acetone ex =617nm, optimal emission wavelength λ em =640nm.

[0062] An application of full-color luminescent carbon dots derived from tobacco waste in lettuce cultivation, wherein at least one of the blue carbon dots and the red carbon dots prepared by the method of the above-mentioned embodiment 1 or 2 is 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 the 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 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), three of the pots were sprayed with 500 mg / L B-CDs aqueous solution, 500 mg / L R-CDs aqueous solution, and 500 mg / L B-CDs and R-CDs aqueous solution (the concentration of B-CDs and R-CDs was 250 mg / L each) at a dosage of 5 ml / pot, and the other pot was sprayed with ultrapure water at the same time. Foliar spraying was performed once a day for 15-20 days. During the spraying, it should be carried out evenly and slowly to avoid runoff and shaking the lettuce leaves.

[0065] The above test was repeated three times. The effect after spraying was as follows: Figure 5 As shown, Figure 5 The CK group was the control group sprayed with ultrapure water, the B-CDs group was the group sprayed with only the blue carbon dots aqueous solution, the R-CDs group was the group sprayed with only the red carbon dots aqueous solution, and the BR-CDs group was the group sprayed with both the blue and red carbon dots aqueous solutions.

[0066] The biomass of lettuce was measured separately, and the biomass included 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, as carbohydrates, provides substances and energy for plant development, and its content is an important indicator of plant nutritional quality.

[0070] Select the same position of the lettuce in the above group, such as the third leaf from the outside, and measure the soluble sugar content and protein content. Figure 8 and Fig. 9 As shown:

[0071] Compared with the control group, the soluble sugar content of the treated groups increased. The soluble sugar content of the leaves in the B-CDs, R-CDs and BR-CDs groups increased 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 treated groups was increased. The protein content of the leaves in the B-CDs, R-CDs and BR-CDs groups increased by 27.98%, 26.60% and 41.86% respectively compared with the protein content in 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 observe the absorption and transfer of carbon dots in lettuce more intuitively, CLSM (Confocal laser scanning microscopy) test was performed on the slices of lettuce tissue, which fully utilized the biological probe function of carbon dots.

[0075] Specifically, 15 days after the carbon dot solution was sprayed on the lettuce leaves, the root, stem, and leaf tissues of the lettuce were sliced ​​and observed. The lettuce tissue was processed by transverse frozen sectioning. Figure 11-13 shown. Figure 11-13 The bright field and fluorescence images of the root, stem, and leaf of lettuce are shown respectively. It can be seen that the bright field and fluorescence images of the root, stem, and leaf tissues overlap completely, indicating that the two carbon dots (B-CDs and R-CDs) can easily enter the plant body and be smoothly absorbed and transferred. ex =375nm, λ em =455nm, the confocal images of R-CDs were collected at (λ ex =617nm,λ em =640nm) and collected.

[0076] In order to eliminate the interference of strong spontaneous red fluorescence from mesophyll cells in the R-CDs photography, another characteristic emission wavelength of R-CDs (λ ex =551nm,λ em =576nm) to determine the presence of R-CDs, such as Fig.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 Fig.13The images of leaf tissues in the experiment were highly overlapped. The fluorescence image of lettuce showed that the luminescent signals of carbon dots almost covered the roots, stems, and leaves, including the epidermis and the interior. The two carbon dots, B-CDs and R-CDs, were absorbed by the leaves and diffused downward to the roots through the vascular system of the stems, which was the opposite of the upward transfer path of carbon dots from the roots through the vascular system of the stems to the leaf tissues. The CLSM test proved that both B-CDs and R-CDs can exist in large quantities in lettuce tissues and maintain a high degree of stability.

[0077] This embodiment is only a further explanation of the present invention, 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 it is within the scope of the claims of the present invention, it will be protected by the 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 and crushing tobacco waste to obtain tobacco waste debris, wherein the tobacco waste includes at least one of tobacco leaves and tobacco stems; Step 2, mixing a solvent selected from water, anhydrous ethanol and acetone, tobacco waste debris and H2O2 uniformly, leaving the mixture to stand for 5-30 minutes, and performing ultrasonic treatment using ultrasound; Step 3, filtering out tobacco waste debris residue to obtain a crude carbon dot solution containing one of blue carbon dots, green carbon dots and red carbon dots; Step 4, the crude carbon dot solution is further filtered through a 0.22 μm filter membrane and dialyzed in ultrapure water to obtain a carbon dot concentrate; Step 5: The crude carbon dot solution is subjected to rotary evaporation in a rotary evaporator to dryness to obtain carbon dot solids, and the rotary evaporation temperature is 30-50°C.

2. The method for preparing full-color luminescent carbon dots from tobacco waste according to claim 1, characterized in that: In the step 2, the ultrasonic treatment is carried out in a polytetrafluoroethylene container under an ultrasonic wave 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 also 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 during 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 cutoff of 100-500 for 12-48 hours.

5. The method for preparing full-color luminescent carbon dots from tobacco waste according to claim 1, characterized in that: 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 then the mixture is dried by rotary evaporation to obtain the optimal excitation wavelength λ ex = Blue carbon dot solid emitting blue light at 375nm; When anhydrous ethanol is mixed with tobacco waste debris and H2O2, 0.4 g of H2O2 and 20 ml of anhydrous ethanol are added according to the ratio of 1 g of tobacco waste debris, and the optimal excitation wavelength λ is obtained by rotary evaporation and drying. ex = Green light emission at 492nm and optimal excitation wavelength λ ex = Green carbon dot solid emitting yellow light at 546nm; When acetone is mixed with tobacco waste debris and H2O2, 0.4g of H2O2 and 20ml of acetone are added to each 1g of tobacco waste debris, and then the mixture is dried by rotary evaporation to obtain the optimal excitation wavelength λ ex =Emits yellow light at 551nm, optimal excitation wavelength λ ex = Orange light emission at 585nm and optimal excitation wavelength λ ex =Red carbon dot solid that emits red light at 617nm.

6. 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 5, 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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