CN115321520A

CN115321520A - Carbon quantum dot and preparation method and application thereof

Info

Publication number: CN115321520A
Application number: CN202211136733.9A
Authority: CN
Inventors: 孙昊; 焦浈; 李双; 王蓉
Original assignee: Zhengzhou University
Current assignee: Zhengzhou University
Priority date: 2022-09-20
Filing date: 2022-09-20
Publication date: 2022-11-11

Abstract

The invention provides a carbon quantum dot and a preparation method and application thereof, belonging to the technical field of agriculture. The method comprises the following steps: dissolving citric acid in formamide, heating and stirring for reaction for the first time, cooling to room temperature after the reaction is finished, adding polyethylene glycol, heating and stirring for reaction for the second time, centrifuging reaction liquid after the reaction is finished, washing precipitate with an eluent, purifying, freezing to a solid state, and freeze-drying to obtain the carbon quantum dots. The low-toxicity carbon quantum dot material can convert green light in sunlight into red light, has good water solubility, is simply sprayed on the surface of a plant leaf, is simple and convenient to operate, has a good using effect, and can obviously enhance plant photosynthesis, delay leaf senescence, promote plant growth and enhance plant stress resistance.

Description

Carbon quantum dot and preparation method and application thereof

Technical Field

The invention relates to the technical field of agriculture, in particular to a carbon quantum dot and a preparation method and application thereof.

Background

Photosynthesis, the basis for the development of all biological activities on earth, converts solar energy into chemical energy of organic compounds. Energy required for growth, development and morphogenesis of crops is mainly provided by illumination, and the expression of plant-related genes is regulated through the signal action and energy action of illumination, so that various physiological behaviors in the processes of vegetative growth and reproductive growth of plants are completed (Andreeva & Velichkova 1998). In the weak light weather, the growth and development of crops are restricted by influencing photosynthesis of the crops, so that the weak light is one of main agricultural meteorological disasters of facility agricultural production and is a main factor restricting the growth and yield formation of the facility crops. The facility agriculture is necessarily isolated from natural conditions in the process of building facility equipment, the use of covering materials often causes the loss of illumination intensity inside the facility, the effective photosynthesis of crops is seriously influenced, and the problems of low facility production efficiency, poor quality and the like are caused. At present, light environment regulation and control means required by plant growth mainly occur in facilities, and the light supplement of traditional light sources (high-pressure sodium lamps, fluorescent lamps and LED light sources) is still taken as the main part.

In addition, only red light and blue light in sunlight can be captured by chloroplasts, blue-violet light with the wavelength of 430-470nm and red-orange light with the wavelength of 630-680nm are chlorophyll absorption peak regions, and the partial wave bands only account for 26% of solar radiation (Goins et al 1997), so much energy in the solar energy cannot be utilized by plants. Recent studies have shown that nanomaterials exhibit the ability to enhance plant photosynthesis due to their photoluminescent properties. Therefore, the wave band with low absorption in the sunlight is converted into red orange light or blue-violet light required by photosynthesis, the energy in the sunlight is fully utilized, and the method has strong feasibility and huge development space for enhancing the yield of crops.

In the prior art, a method for converting ineffective or low-efficiency light into blue light and red light which can be absorbed by plants mainly utilizes a light conversion agricultural film or an artificial light supplement device, and a patent CN202010962187.9 discloses an adhesive blue fluorescent coating, a preparation method and application thereof, and discloses a preparation method of an adhesive light conversion coating and application thereof in promoting plant growth and enhancing plant stress resistance.

The traditional light sources (high-pressure sodium lamp, fluorescent lamp and LED light source) mainly supplement light, and further application of the illumination regulation and control means in open fields and facilities is restricted by high power consumption, poor spectrum matching, spectrum single-peak emission and high manufacturing cost.

The light conversion film requires a large amount of capital investment in the early stage, is complex in construction operation, can only be used in facility agriculture such as greenhouses and cannot be used in field planting. In addition, the agricultural light conversion film has the problems of difficult degradation, environmental pollution and the like, and is difficult to popularize and use.

Some containing Au, ag and Fe ₃ O ₄ 、TiO ₂ And ZnO and carbon-based nanomaterials (e.g., fullerenes, carbon nanotubes, and graphene particles) emit red-orange or blue-violet light for chlorophyll photosynthesis under excitation of light of a specific wavelength, thereby promoting plant photosynthesis and carbohydrate accumulation (Qiu et al 2015; song et al 2021; xie et al 2021). However, these nanomaterials are, for example, caS: eu ²⁺ @CaZnOS:Mn ²⁺ ，Sr2-xYxSi5-xAlxN8:Eu ²⁺ Most of the Eu-doped rare earth elements contain Eu and other rare earth metal elements, eu cost is high ²⁺ The alkaline earth metal sulfide of (2) is liable to have adverse effects on the environment; also, most of these nanomaterials have limited applications due to the stringent synthesis conditions (high pressure or high temperature) required (Qiu et al.2015).

Patent CN202010962187.9 discloses an adhesive blue fluorescent coating, its preparation method and application, disclosing that the light conversion coating can convert the ultraviolet part of sunlight into blue light, but can not convert the light of other bands in sunlight, especially the green light whose proportion is more than twice of ultraviolet.

Carbon quantum dots are a carbon-based zero-dimensional material. The carbon quantum dots have the advantages of excellent optical properties, good water solubility, low toxicity, environmental friendliness, wide raw material source, low cost, good biocompatibility and the like (Li et al.2020). In recent years, researches show that some carbon quantum dots show strong absorption in an Ultraviolet (UV) light region and emit strong blue light, far-red light or double-emission light which is completely matched with a chloroplast absorption spectrum, and after the carbon quantum dots are confirmed to be safe through cytotoxicity detection, researchers spray the carbon quantum dots on crops such as lettuce, caraway, garlic, rice and the like, and the photosynthesis intensity and biomass accumulation of plants are found to be obviously increased, which shows that the carbon quantum dots can obviously promote the growth of the plants (Li et al.2020). However, the current reports of using carbon quantum dots to enhance plant photosynthesis all convert ultraviolet light into blue light or red light, thereby improving the photosynthesis intensity of plant cells. The spectrum of green color in sunlight accounts for more than twice of the ultraviolet spectrum, most of the green color cannot be absorbed by plant cells, and no technology for enhancing crop photosynthesis by applying green-to-red carbon quantum dots is reported.

Disclosure of Invention

The invention aims to provide a carbon quantum dot and a preparation method and application thereof, and the implementation scheme in the prior art is realized by a light conversion film containing heavy metals, so that the carbon quantum dot is high in cost, not easy to degrade and easy to pollute the environment; the invention discloses a low-toxicity carbon quantum dot material which can convert green light in sunlight into red light, has good water solubility, is simply sprayed on the surface of a plant leaf, is simple and convenient to operate, has a good using effect, and can obviously enhance the photosynthesis of a plant, delay the senescence of the leaf, promote the growth of the plant and enhance the stress resistance of the plant.

The technical scheme of the invention is realized as follows:

the invention provides a preparation method of carbon quantum dots, which comprises the following steps: dissolving citric acid in formamide, heating and stirring for reaction for the first time, cooling to room temperature after the reaction is finished, adding polyethylene glycol, heating and stirring for reaction for the second time, centrifuging reaction liquid after the reaction is finished, washing precipitate with an eluent, purifying, freezing to a solid state, and freeze-drying to obtain the carbon quantum dots.

As a further improvement of the invention, the first heating and stirring reaction temperature is 150-170 ℃, and the time is 6-10h; the second heating and stirring reaction temperature is 50-90 ℃ and the time is 0.5-1.5h.

As a further improvement of the invention, the first heating and stirring reaction temperature is 160 ℃, and the time is 8 hours; the second heating and stirring reaction temperature is 70 ℃, and the time is 1h.

As a further improvement of the invention, the eluent is dimethyl sulfoxide.

As a further improvement of the invention, the purification method adopts silica gel column chromatography for purification.

As a further improvement of the invention, the mass ratio of the citric acid to the formamide to the polyethylene glycol is 1-2:0.5-1:0.2-0.5.

As a further improvement of the invention, the centrifugation is carried out at 5000-7000g for 3-7min at room temperature.

The invention further protects the carbon quantum dot prepared by the preparation method.

The invention further protects the application of the carbon quantum dots in enhancing plant photosynthesis, delaying leaf senescence, promoting plant growth and enhancing plant stress resistance.

As a further improvement of the invention, the carbon quantum dots are dissolved in DMSO, diluted to 10-1000mg/L with water and uniformly sprayed on the leaves of crops under the illumination condition.

The invention has the following beneficial effects:

1. the method is simple and convenient to operate, and the aim of enhancing the photosynthesis of the crops can be fulfilled by directly spraying the fertilizer.

2. The method of the invention does not need special equipment and has low cost.

3. The method has wide application range and can be used in facility agriculture and fields.

4. The carbon quantum dot material capable of converting green light into red light is prepared by using the low-toxicity carbon quantum dot material, and the material is prepared by using citric acid as a raw material, so that the cost is low; has good water solubility, simple use method, no limitation of crop varieties and cultivation environments and remarkable effect.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a TEM image of a carbon quantum dot prepared in example 3;

FIG. 2 is a particle size histogram of carbon quantum dots obtained in example 3;

FIG. 3 is a photograph comparing carbon quantum dots prepared in examples 1-4 in sunlight and UV;

FIG. 4 is a fluorescence spectrum corresponding to the carbon quantum dots obtained in examples 1 to 4;

FIG. 5 is an absorption spectrum corresponding to carbon quantum dots obtained in examples 1 to 4.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Citric acid as carbon source with a mass of 1.92g and formamide as nitrogen source with a density of 0.45 (density of 1.134 g/cm) ³ ) And g, grinding the mixture in an agate mortar for 5 minutes to uniformly mix the mixture, transferring the mixture to a polytetrafluoroethylene high-pressure reaction kettle, and placing the kettle in a 160 ℃ blast box for 10 hours. And after the reaction is finished, naturally cooling to room temperature, taking out the sample, adding dimethyl sulfoxide, and separating by silica gel column chromatography to obtain a part with bright red fluorescence, namely the target sample.

Example 2

Citric acid as carbon source with mass of 1.92g and formamide as nitrogen source with mass of 0.9g (density of 1.134 g/cm) ³ ) And g, grinding the mixture in an agate mortar for 5 minutes to uniformly mix the mixture, transferring the mixture to a polytetrafluoroethylene high-pressure reaction kettle, and placing the kettle in a 160 ℃ blast box for 8 hours. After the reaction is finished, naturally cooling to room temperature, taking out a sample, adding dimethyl sulfoxide (dmso), and separating by silica gel column chromatography to obtain a part with bright red fluorescenceA target sample;

example 3

Selecting citric acid as carbon source with a mass of 1.92g and formamide as nitrogen source with a mass of 1.3g (density of 1.134 g/cm) ³ ) And g, grinding the mixture in an agate mortar for 5 minutes to uniformly mix the mixture, transferring the mixture to a polytetrafluoroethylene high-pressure reaction kettle, and placing the kettle in a 180-DEG C blast box for 10 hours. After the reaction is finished, naturally cooling to room temperature, taking out a sample, adding dimethyl sulfoxide, and separating by silica gel column chromatography to obtain a part with bright red fluorescence, namely a target sample; fig. 1 is a TEM image of the carbon quantum dots produced in this example, and fig. 2 is a statistical view of the particle diameters of the carbon quantum dots produced in this example. The shape of the particles is spherical under the observation of a transmission electron microscope, and the average particle size of the particles with uniform size is less than 4.5nm.

Example 4

Selecting citric acid as a carbon source, taking the mass of the citric acid as 1.92g, taking formamide as a nitrogen source, grinding 1.3g (the density is 1.134g/cm < 3 >) g and 1g of polyethylene glycol (the average molecular weight is between 1000) in an agate mortar for 5 minutes to be uniformly mixed, then transferring the mixture into a polytetrafluoroethylene high-pressure reaction kettle, and placing the kettle in a 200 ℃ blast box for 10 hours. After the reaction is finished, naturally cooling to room temperature, taking out a sample, adding dimethyl sulfoxide, and separating by silica gel column chromatography to obtain a part with bright red fluorescence, namely the target.

FIG. 3 is a photograph comparing the carbon quantum dots prepared in examples 1-4 in sunlight and UV; FIG. 4 is a fluorescence spectrum corresponding to the carbon quantum dots obtained in examples 1 to 4; FIG. 5 is an absorption spectrum corresponding to carbon quantum dots obtained in examples 1 to 4. As can be seen from the figure, the carbon quantum dot has good visible light absorption characteristics, is black under visible light, and has red fluorescence under ultraviolet excitation.

Example 5

10g of the carbon quantum dots prepared in example 1 were dissolved in 50mL of DMSO, diluted with water to 500mg/L, and uniformly sprayed on crop leaves under the illumination condition.

Example 6

After 10g of the carbon quantum dots prepared in example 2 were dissolved in 50mL of DMSO, diluted to 10mg/L with water and sprayed on the leaves of crops uniformly under the illumination condition.

Example 7

After 10g of the carbon quantum dots prepared in example 3 were dissolved in 50mL of DMSO, the resulting solution was diluted to 1000mg/L with water and uniformly sprayed on crop leaves under light conditions.

Example 8

After 10g of the carbon quantum dots prepared in example 4 were dissolved in 50mL of DMSO, the resulting solution was diluted with water to 700mg/L and uniformly sprayed on the leaves of the crops under illumination.

Test example 1

Selecting 30 healthy and 2-year-old forsythia suspense seedlings without diseases and insect pests and with consistent growth vigor (plant height and ground diameter) in a greenhouse nursery garden, respectively planting the seedlings in 30 pots with the depth of 60cm and the diameter of 40cm, and performing water and fertilizer management and control in the test process. And (3) fully irrigating 3 days before lifting the forsythia from the nursery, keeping the integrity of the root system as much as possible during lifting the forsythia, dipping the roots of the seedlings with slurry after lifting the seedlings, using jute bags for plant division, loading the seedlings to a test greenhouse, and immediately planting the seedlings. Before planting, the root systems of all the plants are trimmed, so that the trimmed roots are about 12cm long. After the seedlings were planted, sufficient water was immediately poured, and then normal water management was performed (water was poured 2 times per week). 20 seedlings with relatively consistent height and ground diameter are selected for test planting. The test was divided into 5 groups, a blank group and examples 5-8 groups, which were sprayed on the leaves of the crop during the test according to the methods of examples 4-6, respectively, and the blank group was sprayed with an equal amount of water.

On day 7 of the experiment, at 9 am: 00-10: at 00 hours, the photoresponse of the gas exchange parameters of 2 leaves marked with a Li-6400 photosynthesis assay system was randomly determined, 3 times for each leaf, and the net photosynthetic rate (Pn, μmol. M) was recorded ^-2 ·s ^-1 ) And gas pore conductance (Gs, mol. M) ^-2 ·s ^-1 )。

The results are shown in Table 1.

TABLE 1

Group of	Net photosynthetic Rate (Pn, μmol. M) ^-2 ·s ^-1 )	Porosity (Gs, mol. M) ^-2 ·s ^-1 )
			Blank group	9.2	0.12
Example 5	14.6	0.19
			Example 6	14.5	0.19
Example 7	14.7	0.21
			Example 8	14.8	0.22

As can be seen from the above table, the carbon quantum dot solution sprayed on the plant leaves in the methods of examples 5 to 8 of the present invention can significantly enhance the photosynthesis of plants.

Example 2

Soaking cucumber seeds, sowing the soaked cucumber seeds in a container with a cover and containing 1% agar, culturing for 72 hours in a dark environment at 25 +/-2 ℃, and selecting leaves with uniform and complete sizes for later use. The cucumber leaves are treated according to the method of the embodiment 5-8 of the invention, the blank group is sprayed with equal amount of water and cultured under the light intensity environment of 3000 +/-200 Lx at the temperature of 25 +/-2 ℃, and the fresh weight of every 10 leaves is measured after 72 hours. The results were averaged for 3 replicates per treatment group and are shown in table 2.

Cucumber cotyledon expansion (%) = (fresh weight of 10 cotyledons after treatment-fresh weight of 10 cotyledons before treatment)/fresh weight of 10 cotyledons before treatment × 100%.

TABLE 2

Group of	Expansion of cucumber cotyledon (%)
		Example 5	65.5
Example 6	65.2
		Example 7	65.7
Example 8	65.9
		Blank group	42.5

By adopting the method of the embodiment 5-8 of the invention, the carbon quantum dot solution can obviously promote the growth of plants after being sprayed on the leaves of the plants.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A preparation method of a carbon quantum dot is characterized by comprising the following steps: dissolving citric acid in formamide, heating and stirring for reaction for the first time, cooling to room temperature after the reaction is finished, adding polyethylene glycol, heating and stirring for reaction for the second time, centrifuging reaction liquid after the reaction is finished, washing precipitate with an eluent, purifying, freezing to a solid state, and freeze-drying to obtain the carbon quantum dots.

2. The method for preparing the carbon quantum dots according to claim 1, wherein the first heating and stirring reaction is carried out at a temperature of 150-170 ℃ for 6-10h; the second heating and stirring reaction temperature is 50-90 ℃ and the time is 0.5-1.5h.

3. The method for preparing the carbon quantum dots according to claim 2, wherein the first heating and stirring reaction temperature is 160 ℃ and the time is 8 hours; the second heating and stirring reaction temperature is 70 ℃, and the time is 1h.

4. The method for preparing the carbon quantum dots according to claim 1, wherein the eluent is dimethyl sulfoxide.

5. The method for preparing carbon quantum dots according to claim 1, wherein the purification method is silica gel column chromatography.

6. The method for preparing the carbon quantum dots according to claim 1, wherein the mass ratio of the citric acid to the formamide to the polyethylene glycol is 1-2:0.5-1:0.2-0.5.

7. The method for preparing the carbon quantum dots according to claim 1, wherein the centrifugation is performed at 5000-7000g for 3-7min at room temperature.

8. A carbon quantum dot produced by the production method according to any one of claims 1 to 7.

9. Use of the carbon quantum dot of claim 8 for enhancing plant photosynthesis, delaying leaf senescence, promoting plant growth, enhancing plant stress resistance.

10. The use of claim 9, wherein the carbon quantum dots are dissolved in DMSO, diluted to 10-1000mg/L with water, and uniformly sprayed on the leaves of the crops under the illumination condition.