Red fluorescent carbon-based quantum dot, preparation method and carbon-based quantum dot light conversion composite film

Abstract

The invention relates to the technical field of carbon-based quantum dots, in particular to red fluorescent carbon-based quantum dots, a preparation method and a carbon-based quantum dot light conversion composite film. The preparation method comprises the following steps: dissolving an organic small molecule compound containing a conjugated system in a solvent, mixing with a cross-linking agent, and carrying out solvothermal reaction to obtain a carbon-based quantum dot precursor; and performing pyrolytic reaction on the carbon-based quantum dot precursor to obtain the red fluorescent carbon-based quantum dot. The red fluorescent carbon-based quantum dots prepared by adopting the preparation method are uniformly distributed on the net-shaped substrate, the net-shaped substrate effectively realizes a function of isolating the red fluorescent carbon-based quantum dots in space, and an energy transfer loss phenomenon caused by pi-pi accumulation of the red fluorescent carbon-based quantum dots is inhibited. The problem that the light emitting color and intensity are easy to drift when the traditional carbon-based quantum dots are compounded with a polymer matrix is solved, and the problems that the quantum dots in the light conversion film are not uniformly dispersed and the fluorescence performance is not stable are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon-based quantum dots, and particularly to red fluorescent carbon-based quantum dots, a preparation method, and a carbon-based quantum dot light conversion composite film. Background Art

[0002] Light quality is a core factor affecting plant growth, development, yield formation, and fruit quality. Although the wavelength range of sunlight reaching the earth's surface is 290 nm to 3000 nm, only a small part of the light energy can be effectively absorbed by plants, mainly concentrated in the blue light range of 420 nm to 500 nm and the red light range of 580 nm to 700 nm. The ultraviolet light in the range of 280 nm to 390 nm is not only unfavorable for plant growth but also can lead to an increase in pests and diseases and accelerate the aging of plastic greenhouse materials. A light conversion film is a type of functional agricultural film that converts the light that plants cannot effectively utilize into the wavelength band required for photosynthesis by adding specific light conversion agents to improve the light energy utilization rate. Research has found that the light conversion film can not only convert ultraviolet light into blue light and red-orange light beneficial to photosynthesis but also convert yellow-green light that has no obvious effect on plant growth into red-orange light, thereby improving the photosynthesis efficiency and significantly increasing crop yield and quality. For example, the effective utilization of red light helps to promote the accumulation of starch and sugars, improve the fruit coloring rate and sweetness. A large number of experiments have shown that the use of light conversion films can increase the yield of spinach, carrots, and vegetable soybeans by about 10%, improve the content of vitamin C and soluble proteins, and at the same time significantly promote the growth of tomatoes, increasing the content of vitamin C and lycopene in the fruits.

[0003] Currently, the light conversion agents used for light conversion films are mostly composed of rare earth elements combined with inorganic matrices or organic ligands. Although rare earth inorganic light conversion agents have excellent luminescence intensity and stability, due to their poor compatibility with polymer polymers, they often lead to uneven dispersion, aggregation, or concentration quenching in the film, thereby reducing the luminescence efficiency. Relatively speaking, organic rare earth light conversion agents have better compatibility with polyethylene, and different luminescence intensities and efficiencies can be achieved by adjusting the ligand structure, but the cost is relatively high. As a new type of light conversion material, carbon-based quantum dots have shown important value in the field of light conversion with their excellent optical properties, low toxicity, biocompatibility, and environmental friendliness, especially showing significant advantages in red light conversion. However, when carbon-based quantum dots are compounded with polymer matrices, the luminescence color and intensity of carbon-based quantum dots are prone to drift, and it is difficult to achieve stable luminescence with consistent colors in a wide wavelength range in multiple films. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides red fluorescent carbon-based quantum dots, a preparation method thereof, and a light-converting composite film of carbon-based quantum dots. The present invention uses an organic small molecule compound containing a conjugated system and a crosslinking agent as the main raw materials, and successfully prepares red fluorescent carbon-based quantum dots through a two-step method of solvothermal reaction and pyrolytic carbonization. The present invention conducts functional group modification by introducing nitrogen- or oxygen-containing functional groups. During the thermal decomposition process of the crosslinking agent, a network substrate structure is formed. This structure not only realizes effective spatial isolation and protection but also effectively inhibits the energy transfer loss caused by π-π stacking, thereby greatly reducing the fluorescence quenching phenomenon and significantly improving the optical stability of the red fluorescent carbon-based quantum dots. In addition, by optimizing the carbonization temperature and time to ensure that the thermal decomposition temperature of the carbon-based quantum dot precursor is reached, the carbonization degree of the carbon-based quantum dots is significantly improved, further enhancing their structural stability and effectively reducing the spectral drift phenomenon.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The first object of the present invention is to provide a preparation method of red fluorescent carbon-based quantum dots, comprising the following steps: S1. After dissolving the organic small molecule compound containing a conjugated system in a solvent, it is mixed with a crosslinking agent, and a solvothermal reaction is carried out. During the solvothermal reaction, the organic small molecule compound containing a conjugated system forms covalent bonds through dehydration condensation reaction with the solvent or the crosslinking agent. The covalent bonds include C–O bonds or C–N bonds, and at the same time, nitrogen- or oxygen-containing functional groups are introduced for functional group modification to facilitate the regulation of the surface chemical properties of the target product, red fluorescent carbon-based quantum dots, to obtain a carbon-based quantum dot precursor; wherein, the mass ratio of the organic small molecule compound containing a conjugated system to the crosslinking agent is 0.01~50:100.

[0006] S2. The carbon-based quantum dot precursor is subjected to a pyrolysis reaction. During the pyrolysis reaction, the carbon-based quantum dot precursor is carbonized. During the carbonization process, the organic small molecule compound containing a conjugated system and the crosslinking agent first decompose and dehydrate and condense at high temperature to form a polycyclic aromatic structure, and then are further carbonized to obtain red fluorescent carbon-based quantum dots.

[0007] Preferably, the conditions of the solvothermal reaction are: reacting at 60°C~200°C for 1h~50h, or using the microwave method to react at 500W~1000W for 10min~30min.

[0008] Preferably, the conditions for the pyrolysis reaction are: reacting at 100 °C to 500 °C for 1 h to 50 h. Among them, the temperature and time of thermal decomposition play a key role in regulating the functional groups, energy level structure of the red fluorescent carbon-based quantum dots, and forming appropriate spatial isolation, which helps to inhibit the energy transfer loss caused by π-π stacking, thereby reducing fluorescence quenching and improving the optical performance. If the thermal decomposition temperature is too low, incomplete carbonization will occur, resulting in poor fluorescence performance and uneven structure of the red fluorescent carbon-based quantum dots; if the temperature is too high, excessive carbonization will occur, leading to fluorescence quenching and loss of functional groups.

[0009] Preferably, the organic small molecule compound containing a conjugated system is selected from at least one of pyridine dyes, cyanobenzene compounds, anthracene dyes, coumarins, perylene tetracarboxylic diimide derivatives, tetraphenylethylene derivatives, quinine sulfate, rhodamine dyes, sulfonated rhodamine derivatives, Cyanine dyes, anthracene, perylene, pyrene, naphthalene, chitosan, glucose, polysaccharides, aniline, phenol, benzoic acid, benzenesulfonic acid, thiophene, carbazole or polycyclic aromatic hydrocarbons, and the molecular weight of the organic small molecule compound containing a conjugated system is less than 2000 g / mol.

[0010] Preferably, the solvent is selected from at least one of water, methanol, ethanol, propanol, butanol, isopropanol, glycerol, n-butanol, isobutanol, isopentanol, ethyl acetate, petroleum ether, N,N-dimethylformamide, dimethyl sulfoxide, chloroform, dichloromethane, toluene, xylene, pentane, hexane, chlorobenzene, ether, acetone, methyl butanone or ethylene glycol monobutyl ether.

[0011] Preferably, the cross-linking agent is selected from at least one of citric acid, urea, sodium hydroxide, sulfuric acid, nitric acid, hydrogen peroxide, sodium peroxide, ammonium persulfate, sodium sulfate, meta-chloroperoxybenzoic acid, metal salts, glutaraldehyde, chitosan, boric acid, polyvinyl alcohol, ethylene glycol, polyethylene glycol, ethylenediamine, aluminum nitrate, aluminum hydroxide, sodium meta-aluminate, tetraethyl orthosilicate, sodium silicate, silane, silicate ester, metaboric acid, triethyl borane or polysaccharides.

[0012] The second object of the present invention is to provide the red fluorescent carbon-based quantum dots prepared by the above preparation method, and the particle size of the red fluorescent carbon-based quantum dots is 2 nm to 10 nm.

[0013] Preferably, the fluorescence emission peak of the red fluorescent carbon-based quantum dots is 580 nm to 700 nm, and shows excitation-independent characteristic emission, and can convert ultraviolet light or yellow-green light into red light emission.

[0014] Preferably, the fluorescent quantum dots are uniformly distributed on the network substrate. The network substrate is the thermal decomposition product of the crosslinking agent, and the red fluorescent carbon-based quantum dots are also dispersed in the thermal decomposition product of the crosslinking agent. The thermal decomposition product of the crosslinking agent is a coordinated oxide or amorphous carbon. The coating principle is as follows: The remaining crosslinking agent of the carbon-based quantum dot precursor self-assembles by non-covalent forces under non-covalent interaction or coordination, that is, self-assembles by hydrogen bonding, π-π stacking or electrostatic interaction, and forms a thermal decomposition product during the pyrolysis process. The thermal decomposition product uniformly disperses or coats the carbon-based quantum dots. The crosslinking agent of the present invention can also be used as a functional group modifier to functionalize the red fluorescent carbon-based quantum dots while achieving stable dispersion or coating of the red fluorescent carbon-based quantum dots.

[0015] The third object of the present invention is a carbon-based quantum dot light conversion composite film, which is made of the above-mentioned red fluorescent carbon-based quantum dots and a polymer substrate; wherein, the mass ratio of the red fluorescent carbon-based quantum dots to the polymer substrate is 0.005~50:100.

[0016] Preferably, the thickness of the carbon-based quantum dot light conversion composite film is 50μm~200μm.

[0017] Preferably, the carbon-based quantum dot light conversion composite film can convert ultraviolet light or yellow-green light into red light. Among them, the carbon-based quantum dot light conversion composite film has absorption responses to ultraviolet light with wavelengths of 200nm~400nm and yellow-green light with wavelengths of 510nm~580nm, and emits red-orange light with wavelengths of 580nm~700nm.

[0018] Preferably, the preparation method of the carbon-based quantum dot light conversion composite film is obtained according to the following steps: The red fluorescent carbon-based quantum dots and the polymer substrate are processed by a film-making process to obtain a carbon-based quantum dot light conversion composite film.

[0019] Preferably, the film-making process is selected from solution casting, melt casting, molding, hot pressing, multilayer coextrusion, biaxial stretching, blown film, blow molding or coating method.

[0020] Preferably, the specific operation steps of the coating method are as follows: The red fluorescent carbon-based quantum dots are uniformly dispersed in the coating material, and the coating material is coated on the polymer substrate by a coating method to obtain a carbon-based quantum dot light conversion composite film.

[0021] Preferably, the coating material is selected from at least one of epoxy resin, acrylic acid, waterborne polyurethane, waterborne acrylic acid, nano-silica, nano-titanium dioxide, aluminum sol, silica sol, polyvinylpyrrolidone, polymethyl methacrylate, polystyrene, polydimethylsiloxane, cellulose, polyimide, polyethylene glycol, polyvinyl butyral, polyacrylonitrile or polyvinylidene fluoride.

[0022] Preferably, the polymer substrate is selected from at least one of polymethyl methacrylate, polystyrene, polyethylene, metallocene polyethylene, ethylene-vinyl acetate copolymer, polypropylene, polyethylene terephthalate, polyvinyl chloride or polyvinyl fluoride.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides a method for preparing red fluorescent carbon-based quantum dots. After dissolving an organic small molecule compound containing a conjugated system in a solvent, it is mixed with a cross-linking agent and subjected to a solvothermal reaction. During the solvothermal reaction, the organic small molecule compound containing a conjugated system undergoes a dehydration condensation reaction with the solvent or the cross-linking agent to form a covalent bond, and at the same time, a nitrogen-containing or oxygen-containing functional group is introduced for functional group modification to obtain a carbon-based quantum dot precursor; the carbon-based quantum dot precursor is subjected to a pyrolysis reaction, and during the pyrolysis reaction, the carbon-based quantum dot precursor is carbonized to obtain red fluorescent carbon-based quantum dots.

[0024] In the present invention, the cross-linking agent undergoes self-assembly under non-covalent interaction or coordination interaction and forms a network substrate during the pyrolysis process. The red fluorescent carbon-based quantum dots are uniformly distributed on the network substrate. The network substrate effectively realizes the spatial isolation function, inhibits the energy transfer loss phenomenon caused by π-π stacking, thereby significantly reducing the possibility of fluorescence quenching and significantly improving the overall optical performance. It not only overcomes the problem that the luminescence color and intensity of traditional carbon-based quantum dots are prone to drift when compounded with a polymer substrate, but also solves the problems of uneven dispersion of quantum dots and unstable fluorescence performance in the carbon-based quantum dot composite light conversion film in the prior art.

[0025] 2. The red fluorescent carbon-based quantum dots of the present invention exhibit excellent chemical compatibility with the polymer substrate, can be efficiently dispersed in the polymer substrate by various technical means, and effectively avoid the aggregation or sedimentation phenomenon of the red fluorescent carbon-based quantum dots when prepared into a carbon-based quantum dot light conversion composite film. During this process, not only the original red fluorescence characteristics of the red fluorescent carbon-based quantum dots are successfully retained, but also the light conversion composite film has excellent optical stability. In particular, the particle size of the red fluorescent carbon-based quantum dots in the present invention is less than 20 nm, and when it is mixed with the polymer matrix, it has no adverse effect on the visible light transmittance of the composite film.

[0026] 3. The preparation method of the present invention is simple and efficient, significantly reducing the costs of raw materials and equipment, thus making the large-scale production of red fluorescent carbon-based quantum dots possible. In particular, this preparation process does not require complex equipment or high-energy-consuming conditions, and highly meets the requirements of industrial production. During the batch production process, the red fluorescent carbon-based quantum dots exhibit excellent repeatability and product quality stability, ensuring a high degree of consistency between production batches.

[0027] In addition, the preparation method of the present invention realizes the precise control of the emission wavelength of red fluorescent carbon-based quantum dots by finely regulating the reaction conditions, including the selection of precursor materials, temperature setting, reaction time, and adjustment of acidity and alkalinity, thereby meeting the specific requirements of different light conversion films. This preparation method also has excellent optical property regulation ability and can accurately control the emission wavelength and quantum yield of quantum dots.

[0028] 4. The light conversion composite film of carbon-based quantum dots prepared by the present invention can convert ultraviolet light or yellow-green light into red light. Compared with ordinary polyolefin films, that is, ordinary PO films, the proportion of red light in the greenhouse of the light conversion composite film of carbon-based quantum dots of the present invention is significantly enhanced, the growth rate of vegetables is increased by more than 30%, and the fruit coloring time is shortened by about 20 days.

[0029] 5. The red fluorescent carbon-based quantum dot powder prepared by the present invention can maintain a wide-wavelength red fluorescent color in the polymer substrate. This is because the cross-linking agent spontaneously forms an ordered and stable network structure through non-covalent interactions or coordination interactions, that is, hydrogen bonds, π-π stacking, and electrostatic interactions. This structure not only significantly improves the thermal stability but also ensures the independence of solid fluorescence emission from solvents, thereby realizing the persistent maintenance of red fluorescent color in the polymer substrate. Description of the Drawings

[0030] Figure 1 It is the transmission electron microscope image and particle size distribution diagram of the red fluorescent carbon-based quantum dots in Example 1 of the present invention. Among them, (a) is the transmission electron microscope image with a magnification of 50 nm, (b) is the transmission electron microscope image with a magnification of 20 nm, (c) is the transmission electron microscope image with a magnification of 5 nm, and (d) is the particle size distribution diagram.

[0031] Figure 2 It is the phase result characterization diagram of the red fluorescent carbon-based quantum dots in Example 1 of the present invention. Among them, (a) is the infrared spectrum diagram, (b) is the thermogravimetric analysis diagram, (c) is the Raman diagram, and (d) is the high-resolution N 1s diagram of X-ray photoelectron spectroscopy.

[0032] Figure 3 It is the optical property diagram of the red fluorescent carbon-based quantum dots in Example 2 of the present invention in solvents. Among them, (a) is the fluorescence diagram under an excitation wavelength of 365 nm, and (b) is the ultraviolet-visible absorption diagram in ethyl acetate and chloroform.

[0033] Figure 4 It is the optical property characterization diagram of the red fluorescent carbon-based quantum dots in Example 1 of the present invention. Among them, (a) is the optical property characterization diagram under natural light conditions, (b) is the optical property characterization diagram under a 365 nm ultraviolet lamp condition, and (c) is the fluorescence emission diagram under different excitation wavelengths.

[0034] Figure 5Optical property characterization diagrams of the 2# carbon-based quantum dot light conversion composite film. Among them, (a) is the fluorescence emission peak diagram under excitation wavelengths of 365 nm and 550 nm, (b) is the ultraviolet-visible transmittance diagram, (c) is the fluorescence lifetime diagram in solution, and (d) is the variable-temperature fluorescence test diagram.

[0035] Figure 6 Optical property characterization diagrams of the 1# carbon-based quantum dot light conversion composite film, 2# carbon-based quantum dot light conversion composite film, and inorganic rare-earth-based composite red fluorescence light conversion film. Among them, (a) is the physical photo diagram of the 1# carbon-based quantum dot light conversion composite film under natural light and 365 nm ultraviolet light, (b) is the excitation diagram of the 1# carbon-based quantum dot light conversion composite film at emission wavelengths of 365 nm, 550 nm, and 600 nm, (c) is the ultraviolet-visible absorption diagram of the 1# carbon-based quantum dot light conversion composite film, (d) is the transmittance diagram of ultraviolet-visible light of the 1# carbon-based quantum dot light conversion composite film, (e) is the emission peak diagram of the inorganic rare-earth-based composite red fluorescence light conversion film under excitation wavelengths of 365 nm and 550 nm, and (f) is the integral area diagram of the emission peaks of the 1# carbon-based quantum dot light conversion composite film and the inorganic rare-earth-based composite red fluorescence light conversion film under excitation wavelengths of 365 nm and 550 nm.

[0036] Figure 7 Outdoor irradiance diagram of the 1# carbon-based quantum dot light conversion composite film and comparison diagram of the targeted light growth rate in the 600 nm - 700 nm band of the commercial red film. Among them, (a) is the outdoor irradiance diagram of the carbon-based quantum dot light conversion composite film and low-density polyethylene composite film, and (b) is the targeted light intensity ratio growth rate diagram of the carbon-based quantum dot light conversion composite film and low-density polyethylene composite film, as well as the inorganic and organic rare-earth-based composite red fluorescence light conversion film.

[0037] Figure 8 Aging result characterization diagram of the 1# carbon-based quantum dot light conversion composite film. Among them, (a) is the result characterization diagram before and after ultraviolet aging, and (b) is the result characterization diagram before and after ultraviolet aging.

[0038] Figure 9 Photos of tomatoes and eggplants planted in greenhouses covered with the 1# carbon-based quantum dot light conversion composite film and ordinary PO film. Among them, (a) is the photo of tomatoes planted in a greenhouse covered with the 1# carbon-based quantum dot light conversion composite film and PO film, (b) is the photo of eggplants planted in a greenhouse covered with the 1# carbon-based quantum dot light conversion composite film and PO film, (c) is the statistical chart of the time for tomatoes planted in a greenhouse covered with the 1# carbon-based quantum dot light conversion composite film and PO film to turn red, and (d) is the statistical chart of the size of eggplants planted in a greenhouse covered with the 1# carbon-based quantum dot light conversion composite film and PO film. Detailed implementation methods

[0039] The technical solution of the present invention will be clearly and completely described below in combination with the data in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0040] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be obtained through market purchase or prepared by existing methods. Among them, the commercial red film includes inorganic rare earth-based composite red fluorescent light conversion film, organic rare earth 1, organic rare earth 2, inorganic rare earth 1 and inorganic rare earth 2, purchased from the agricultural film product industry exhibition; ordinary PO film, polyolefin film, a polymer material formed by polymerization of olefin monomers, with a thickness of 100 μm; low-density polyethylene, that is, the pure LDPE model is 7042, purchased from the agent of Xi'an Dehui Xing Trading Co., Ltd.

[0041] In the prior art, as an effective means to improve the light energy utilization rate of plants, the light conversion film converts unfavorable light waves into light waves required for photosynthesis by adding a light conversion agent, significantly improving the yield and quality of crops. However, traditional light conversion agents such as rare earth inorganic light conversion agents have problems of poor compatibility with polymer polymers and uneven dispersion, resulting in reduced luminous efficiency; while organic rare earth light conversion agents have better compatibility but high costs. Although the novel light conversion material carbon-based quantum dots have excellent optical properties and biocompatibility, they are prone to luminescence color and intensity drift when compounded with a polymer matrix, making it difficult to achieve stable luminescence.

[0042] In view of the problems existing in the above-mentioned prior art, the present invention provides a preparation method of red fluorescent carbon-based quantum dots, which includes the following steps: dissolving an organic small molecule compound containing a conjugated system in a solvent, mixing it with a cross-linking agent, and performing a solvothermal reaction. During the solvothermal reaction, the organic small molecule compound containing a conjugated system undergoes a dehydration condensation reaction with the solvent or the cross-linking agent to form a covalent bond, and at the same time, a nitrogen-containing or oxygen-containing functional group is introduced for functional group modification to obtain a carbon-based quantum dot precursor; wherein, the mass ratio of the organic small molecule compound containing a conjugated system to the cross-linking agent is 0.01~50:100; performing a pyrolysis reaction on the carbon-based quantum dot precursor, and during the pyrolysis reaction, the carbon-based quantum dot precursor is carbonized to obtain red fluorescent carbon-based quantum dots.

[0043] The present invention overcomes the problem in the prior art that red fluorescent carbon-based quantum dots are prone to energy transfer loss due to π-π stacking by introducing a network substrate formed by the thermal decomposition products of a cross-linking agent. Among them, the network substrate effectively realizes spatial isolation, reduces the occurrence of π-π stacking, thereby reducing energy transfer loss and reducing the fluorescence quenching phenomenon.

[0044] The present invention forms stably dispersed carbon-based quantum dots by introducing a cross-linking agent and performing solvothermal reaction and pyrolysis treatment, overcoming the problem that the compatibility between traditional light conversion agents and polymer polymers is poor and uneven dispersion leads to a decrease in luminescence efficiency; the present invention solves the problems of high cost of organic rare earth light conversion agents and easy drift of the luminescence color and intensity of carbon-based quantum dots when compounded with polymer matrices by constructing a dual strategy of a network substrate and functional group modification, realizing the efficient and stable preparation of red fluorescent carbon-based quantum dots.

[0045] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0046] Example 1 A preparation method of red fluorescent carbon-based quantum dots includes the following steps: S1. Take pyrene as a precursor, dissolve it in ethanol at a mass concentration of 1 mg / mL, then add a cross-linking agent urea, and heat and react at 80 °C for 5 h in an air atmosphere to obtain a carbon-based quantum dot precursor; wherein, the mass ratio of pyrene to urea is 0.1:100.

[0047] S2. Place the carbon-based quantum dot precursor in an air atmosphere and heat and pyrolyze at 160 °C for 5 h to obtain red fluorescent carbon-based quantum dots.

[0048] The red fluorescent carbon-based quantum dots prepared in Example 1 are prepared into a carbon-based quantum dot light conversion composite film according to the following steps: S1. According to the mass ratio of red fluorescent carbon-based quantum dots to linear low-density polyethylene of 0.05:100, mix the red fluorescent carbon-based quantum dots and linear low-density polyethylene evenly, then add them to the hopper of a micro twin-screw extruder, heat up to 180 °C, and extrude at a screw speed of 50 rad / min to obtain a composite masterbatch of red fluorescent carbon-based quantum dots and linear low-density polyethylene.

[0049] S2. After heating and melting the composite masterbatch by an extruder at 180 °C, extrude it through a die head to form a tubular shape, and blow it into a film with compressed air, and quickly cool and shape it through a cooling device; wind up the film into a roll through a winding device to obtain a carbon-based quantum dot light conversion composite film with a thickness of 100 μm, denoted as 1# carbon-based quantum dot light conversion composite film, that is, a red fluorescent light conversion film.

[0050] Example 2 A preparation method of red fluorescent carbon-based quantum dots, comprising the following steps: S1. Take aniline as a precursor, dissolve it in ethanol at a mass concentration of 1 mg / mL, then add cross-linking agents citric acid and urea, and heat and react in an air atmosphere at 80 °C for 2 h to obtain a carbon-based quantum dot precursor; wherein, the mass ratio of aniline to the mixture of citric acid and urea is 0.5:100, and the mass ratio of citric acid to urea is 1:10.

[0051] S2. Place the carbon-based quantum dot precursor in an air atmosphere and heat and pyrolyze at 160 °C for 5 h to obtain red fluorescent carbon-based quantum dots.

[0052] The red fluorescent carbon-based quantum dots prepared in Example 2 are prepared into a carbon-based quantum dot light conversion composite film according to the following steps: According to the mass ratio of red fluorescent carbon-based quantum dots to an aqueous polyurethane solution of 0.1:100, mix the red fluorescent carbon-based quantum dots and the aqueous polyurethane solution evenly, and then coat them on linear low-density polyethylene with a coating rod to obtain a carbon-based quantum dot light conversion composite film with a thickness of 120 μm. Among them, the thickness of the linear low-density polyethylene is 80 μm, denoted as the 2# carbon-based quantum dot light conversion composite film, that is, the red fluorescent light conversion film.

[0053] Example 3 A preparation method of red fluorescent carbon-based quantum dots, comprising the following steps: S1. Take perylene as a precursor, dissolve it in a mixed solution of methanol and water at a mass concentration of 2 mg / mL, then add cross-linking agent aluminum nitrate, and heat and react in an air atmosphere at 90 °C for 5 h to obtain a carbon-based quantum dot precursor; wherein, the volume ratio of methanol to water is 1:1, and the mass ratio of perylene to aluminum nitrate is 0.05:100.

[0054] S2. Place the carbon-based quantum dot precursor in an air atmosphere and heat and pyrolyze at 300 °C for 5 h to obtain red fluorescent carbon-based quantum dots.

[0055] The red fluorescent carbon-based quantum dots prepared in Example 3 are prepared into a carbon-based quantum dot light conversion composite film according to the following steps: S1. According to the mass ratio of red fluorescent carbon-based quantum dots to ethylene-vinyl acetate copolymer of 0.2:100, mix the red fluorescent carbon-based quantum dots and ethylene-vinyl acetate copolymer evenly, then add them to the hopper of a micro twin-screw extruder, raise the temperature to 180 °C, and extrude at a screw speed of 50 rad / min to obtain a composite masterbatch of red fluorescent carbon-based quantum dots and ethylene-vinyl acetate copolymer.

[0056] S2. After heating and melting the composite masterbatch at 180°C by an extruder, it is extruded through a die head to form a tubular shape, and then blown into a film by compressed air, and quickly cooled and shaped by a cooling device; the film is wound into a roll by a winding device to obtain a carbon-based quantum dot light conversion composite film with a thickness of 120 μm, denoted as the 3# carbon-based quantum dot light conversion composite film, that is, a red fluorescent light conversion film.

[0057] Example 4 A preparation method of red fluorescent carbon-based quantum dots, comprising the following steps: S1. Take polycyclic aromatic hydrocarbons as precursors, dissolve them in ethanol at a mass concentration of 0.5 mg / mL, then add the cross-linking agent urea, mix them in a ratio of 10 mg / mL, and irradiate with microwaves at a power of 600 W for 10 min to obtain a carbon-based quantum dot precursor; wherein, the mass ratio of polycyclic aromatic hydrocarbons to urea is 1:100.

[0058] S2. Place the red fluorescent carbon-based quantum dots in an air atmosphere and heat them at 180°C for a pyrolysis reaction for 5 h to obtain red fluorescent carbon-based quantum dots.

[0059] The red fluorescent carbon-based quantum dots prepared in Example 4 are prepared into a carbon-based quantum dot light conversion composite film according to the following steps: Using the melt casting method, according to the mass ratio of red fluorescent carbon-based quantum dots to polystyrene of 1:100, add the red fluorescent carbon-based quantum dots and polystyrene to the mixing cavity, raise the temperature to 160°C, heat and melt them, and then cast them into a 150-μm carbon-based quantum dot light conversion composite film, denoted as the 4# carbon-based quantum dot light conversion composite film, that is, a red fluorescent light conversion film.

[0060] Example 5 A preparation method of red fluorescent carbon-based quantum dots, comprising the following steps: S1. Take aniline as a precursor, dissolve it in ethanol at a mass concentration of 1 mg / mL, then add the cross-linking agent polyethylene glycol, and heat and react in an air atmosphere at 80°C for 2 h to obtain a carbon-based quantum dot precursor; wherein, the mass ratio of aniline to polyethylene glycol is 0.5:100.

[0061] S2. Place the carbon-based quantum dot precursor in an air atmosphere and heat it at 150°C for a pyrolysis reaction for 5 h to obtain red fluorescent carbon-based quantum dots.

[0062] The red fluorescent carbon-based quantum dots prepared in Example 5 were prepared into a carbon-based quantum dot light conversion composite film according to the following steps: According to the mass ratio of the red fluorescent carbon-based quantum dots to polyacrylonitrile of 1:100, the red fluorescent carbon-based quantum dots and polyacrylonitrile were uniformly mixed and added to chloroform. After it was completely dissolved, a mixture was obtained. Using the spraying method, the mixture was sprayed onto linear low-density polyethylene to obtain a carbon-based quantum dot light conversion composite film, denoted as the 5# carbon-based quantum dot light conversion composite film, that is, the red fluorescent light conversion film.

[0063] Example 6 A preparation method of red fluorescent carbon-based quantum dots includes the following steps: S1. Take pyrene as a precursor, dissolve it in ethanol at a mass concentration of 1 mg / mL, and then add a cross-linking agent urea. Heat and react at 60 °C for 50 h in an air atmosphere to obtain a carbon-based quantum dot precursor; wherein, the mass ratio of pyrene to urea is 0.01:100.

[0064] S2. Place the carbon-based quantum dot precursor in an air atmosphere and heat and pyrolyze at 100 °C for 50 h to obtain red fluorescent carbon-based quantum dots.

[0065] The red fluorescent carbon-based quantum dots prepared in Example 6 were prepared into a carbon-based quantum dot light conversion composite film according to the following steps: S1. According to the mass ratio of the red fluorescent carbon-based quantum dots to linear low-density polyethylene of 50:100, mix the red fluorescent carbon-based quantum dots and linear low-density polyethylene evenly, add them to the hopper of a micro twin-screw extruder, heat up to 180 °C, and extrude at a screw speed of 50 rad / min to obtain a composite masterbatch of red fluorescent carbon-based quantum dots and linear low-density polyethylene.

[0066] S2. After heating and melting the composite masterbatch by an extruder at 180 °C, extrude it through a die to form a tubular shape, and use compressed air to blow it into a film, and quickly cool and shape it through a cooling device; wind up the film into a roll through a winding device to obtain a carbon-based quantum dot light conversion composite film, denoted as the 6# carbon-based quantum dot light conversion composite film, that is, the red fluorescent light conversion film.

[0067] Example 7 A preparation method of red fluorescent carbon-based quantum dots includes the following steps: S1. Take pyrene as a precursor, dissolve it in ethanol at a mass concentration of 1 mg / mL, and then add a cross-linking agent urea. Heat and react at 200 °C for 1 h in an air atmosphere to obtain a carbon-based quantum dot precursor; wherein, the mass ratio of pyrene to urea is 0.01:100.

[0068] S2. Place the carbon-based quantum dot precursor in an air atmosphere and heat and pyrolyze at 500 °C for 1 h to obtain red fluorescent carbon-based quantum dots.

[0069] The red fluorescent carbon-based quantum dots prepared in Example 7 were prepared into a carbon-based quantum dot light conversion composite film according to the following steps: S1. According to the mass ratio of red fluorescent carbon-based quantum dots to linear low-density polyethylene of 0.005:100, after mixing the red fluorescent carbon-based quantum dots and linear low-density polyethylene evenly, they were added to the hopper of a micro twin-screw extruder, heated to 180 °C, and extruded at a screw speed of 50 rad / min to obtain a composite masterbatch of red fluorescent carbon-based quantum dots and linear low-density polyethylene.

[0070] S2. After the composite masterbatch was heated and melted at 180 °C by an extruder, it was extruded through a die to form a tubular shape, and blown into a film by compressed air, and quickly cooled and shaped by a cooling device; the film was wound into a roll by a winding device to obtain a carbon-based quantum dot light conversion composite film, denoted as 7# carbon-based quantum dot light conversion composite film, that is, a red fluorescent light conversion film.

[0071] a. Microstructure of red fluorescent carbon-based quantum dots: Observation Figure 1 It was found that the red fluorescent carbon-based quantum dots were evenly distributed on the reticular substrate structure. This reticular substrate structure could avoid the fluorescence aggregation-induced quenching phenomenon of the red fluorescent carbon-based quantum dots, enabling the red fluorescent carbon-based quantum dots to maintain good optical properties and good stability. The particle size of these red fluorescent carbon-based quantum dots was in the range of 2 nm to 7 nm, and their average particle size was about 4 nm. Further, through high-resolution transmission electron microscopy, it was found that the crystal plane spacing of these red fluorescent carbon-based quantum dots was 0.21 nm, corresponding to the (100) crystal plane of graphite.

[0072] From Figure 2 in (a), it was found that the red fluorescent carbon-based quantum dots exhibited stretching vibration peaks of specific chemical bonds, including C=O at 1700 cm -1 −1, C=N at 1620 cm -1 −1, C−O at 1080 cm -1 −1 to 1120 cm -1 −1, N−H at 3100 cm -1 −1 to 3650 cm -1 −1, and C−H at 2875 cm -1 −1, indicating that the surface of the red fluorescent carbon-based quantum dots had many functional groups and could be well dispersed in the polymer substrate.

[0073] b. Results of phase characterization of red fluorescent carbon-based quantum dots: From Figure 2It can be seen from (b) in [reference] that the weight loss of the red fluorescent carbon-based quantum dots is almost zero before 210 °C, indicating that they still have good thermal stability during the thermal melting with polymer.

[0074] It can be seen from Figure 2 (c) in [reference] that the red fluorescent carbon-based quantum dots have obvious disordered D bands (sp 3 structure) and crystalline G bands (sp 2 structure). The peak intensity of the G band is relatively high, indicating that the graphite phase sp 2 structure of the red fluorescent carbon-based quantum dots is good.

[0075] It can be seen from Figure 2 (d) in [reference] that the N 1s spectrum can be fitted into pyrrolic nitrogen (398.5 eV), N-H (401.9 eV) and N-O (406.5 eV). Therefore, the surface of the red fluorescent carbon-based quantum dots contains more surface functional groups.

[0076] c. Characterization results of the optical properties of the red fluorescent carbon-based quantum dots in solvents: Figure 3 (a) in [reference] is the fluorescence image of the red fluorescent carbon-based quantum dots under the excitation wavelength of 365 nm. Its emission peak in ethyl acetate is 615 nm, and its emission peak in chloroform is 630 nm. Figure 3 (b) in [reference] is the UV-visible absorption spectra of the red fluorescent carbon-based quantum dots in ethyl acetate and chloroform respectively. The UV-visible absorption peak around 320 nm is usually related to electronic transitions, related to the electronic transitions of conjugated C=C in the surface or core structure. The specific absorption peak at 520 nm is caused by the transitions of surface functional groups. It shows that the surface of the carbon-based quantum dots contains polar functional groups, and these functional groups can significantly affect their optical properties, especially the absorption characteristics in the UV-visible spectral range.

[0077] d. Characterization results of the optical properties of the red fluorescent carbon-based quantum dots: It can be seen from observing Figure 4 (a) in [reference] that the red fluorescent carbon-based quantum dots are purplish red under natural light and show a bright red fluorescence color under the 365 nm UV lamp, as shown in Figure 4 (b) in [reference]. It can be seen from observing Figure 4 (c) in [reference] that when testing the fluorescence properties of the red fluorescent carbon-based quantum dots with excitation wavelengths of 365 nm, 520 nm and 550 nm, their emission peaks are all 620 nm, showing obvious excitation-independent emission fluorescence properties.

[0078] e. Characterization of the optical properties of the 2# carbon-based quantum dot light conversion composite film: Figure 5In (a), the fluorescence emission peak of the carbon-based quantum dot light conversion composite film at the excitation wavelengths of 365 nm and 550 nm is at 620 nm, showing good fluorescence properties of ultraviolet and yellow-green light to red light conversion.

[0079] Observation Figure 5 From (b) in it, it can be obtained that the transmittance of the 2# carbon-based quantum dot light conversion composite film in the visible light range is 70% - 90%, the transmittance at 300 nm - 400 nm is 50%, and the transmittance at 200 nm - 300 nm is less than 10%. Observation Figure 5 From (c) in it, it can be obtained that the fluorescence lifetime of the carbon-based quantum dot light conversion composite film in Example 2 reaches 4.42 ns. In contrast, its lifetime in ethyl acetate is only 1.15 ns. This significant difference is mainly attributed to the formation of stable hydrogen bonds between the abundant functional groups on the surface of the red fluorescent carbon-based quantum dots and the polymer substrate polyurethane, and this interaction prolongs its fluorescence lifetime. Observation Figure 5 From (d) in it, it can be obtained that in the test temperature range of -30°C to 40°C, the 2# carbon-based quantum dot light conversion composite film shows good optical stability.

[0080] f. Optical property characterization of the 1# carbon-based quantum dot light conversion composite film: Observation Figure 6 From (a) in it, it can be obtained that the 1# carbon-based quantum dot light conversion composite film is light pink under natural light and shows obvious red fluorescence under 365 nm ultraviolet light; further exploring the optical properties of the 1# carbon-based quantum dot light conversion composite film, from Figure 6 From (b) in it, it can be obtained that at the excitation wavelengths of 365 nm and 550 nm, its fluorescence emission peaks are both at 600 nm, showing obvious optical properties of ultraviolet and green light to red light conversion, and the maximum excitation wavelength of its emission peak at 600 nm is 550 nm; from Figure 6 From (c) in it, it can be obtained that the absorption peak at 280 nm corresponds to the transition of C = C bond, and 550 nm is the transition of surface state; from Figure 6 From (d) in it, it can be obtained that between 550 nm and 800 nm, the transmittance of the 1# carbon-based quantum dot light conversion composite film reaches more than 80%, and the transmittance in the ultraviolet region is about 20%; from Figure 6 In (e), it is the fluorescence emission peak of the inorganic rare earth-based composite red fluorescent light conversion film at the excitation wavelengths of 365 nm and 550 nm. At the excitation wavelength of 365 nm, the fluorescence emission peak is at 620 nm, showing obvious red fluorescence emission; while at the excitation wavelength of 550 nm, almost no fluorescence emission occurs. From Figure 6It can be obtained from (f) in [reference] that the integral area of the 1# carbon-based quantum dot light conversion composite film is larger than that of the inorganic rare-earth-based composite red fluorescent light conversion film. The integral area of the fluorescence emission peak of the 1# carbon-based quantum dot light conversion composite film at the excitation wavelength of 550 nm is larger than that of the inorganic rare-earth-based composite red fluorescent light conversion film, all of which show good optical properties of converting ultraviolet and yellow-green light into red light.

[0081] g. Comparison of the outdoor irradiance map of the 1# carbon-based quantum dot light conversion composite film and the outdoor irradiance in the 600 nm - 700 nm band of the commercial red film: It can be obtained from (a) in [reference] that Figure 7 compared with pure LDPE, the irradiance of yellow-green light in the 500 nm - 600 nm interval of the 1# carbon-based quantum dot light conversion composite film decreases significantly, while the irradiance in the 600 nm - 700 nm band increases. The calculation formula for the growth rate of the targeted light intensity ratio: ; In the formula: T - Growth rate of the targeted light intensity ratio of the test sample, %; PFDt — Photon flux in the red light region of 600 nm - 700 nm or the blue light region of 400 nm - 500 nm of the test sample, μmol / (m 2 ·s); PFD — Photon flux in the spectral region of 350 nm - 800 nm of the test sample, μmol / (m 2 ·s); PFDt(ck) — Photon flux in the red light region of 600 nm - 700 nm or the blue light region of 400 nm - 500 nm of the control sample, μmol / (m 2 ·s); PFD(ck) — Photon flux in the spectral region of 350 nm - 800 nm of the control sample, μmol / (m 2 ·s).

[0082] In the formula, PFD is the photo flux density, with the unit of μmol / (m 2 ·s), and it is measured using a handheld spectrometer.

[0083] Among them, the targeted growth rate of the 1# carbon-based quantum dot light conversion composite film in the 600 nm - 700 nm region is relatively high compared to some other commercial films.

[0084] h. Characterization of the photoaging performance of the 1# carbon-based quantum dot light conversion composite film: It can be obtained from [reference] Figure 8It is concluded that the 1# carbon-based quantum dot light conversion composite film can absorb ultraviolet light with a wavelength lower than 400 nm and simultaneously release visible light, thereby helping to reduce the intensity of ultraviolet radiation received by the polymer matrix and significantly improving the ultraviolet aging resistance of the composite material. Among them, from Figure 8 in (a), it can be seen that compared with the unaged carbon-based quantum dot light conversion composite film, the stress-strain of the aged 1# carbon-based quantum dot light conversion composite film remains almost unchanged. From Figure 8 in figure (b), it can be seen that compared with the unaged 1# carbon-based quantum dot light conversion composite film, the peak position of the aged carbon-based quantum dot light conversion composite film remains basically unchanged, and the fluorescence intensity decreases by about 18%.

[0085] i. Growth photos of plants planted in a shed covered with the 1# carbon-based quantum dot light conversion composite film: Observation Figure 9 It is concluded that the tomatoes planted in the shed covered with the 1# carbon-based quantum dot light conversion composite film are redder in color. In contrast, the tomatoes planted using the PO film are greenish. This significant difference results in a 20-day shortening of the coloring time of the tomatoes using the 1# carbon-based quantum dot light conversion composite film. Further comparing eggplants in the same growth period, it is found that the size of the eggplants planted in the shed covered with the 1# carbon-based quantum dot light conversion composite film is increased by more than about 30% compared to those planted under the PO film condition.

[0086] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the adopted step methods are the same as those in the embodiments, in order to prevent repetition, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

Claims

1. A method for preparing red fluorescent carbon-based quantum dots, characterized in that: The steps include: The organic small molecule compound containing a conjugated system is dissolved in a solvent, mixed with a cross-linking agent, and subjected to a solvothermal reaction. During the solvothermal reaction, the organic small molecule compound containing a conjugated system undergoes a dehydration condensation reaction with the solvent or the cross-linking agent to generate a covalent bond, and a nitrogen-containing or oxygen-containing functional group is introduced to perform functional group modification to obtain a carbon-based quantum dot precursor; wherein the mass ratio of the organic small molecule compound containing a conjugated system to the cross-linking agent is 0.01-50:100; The carbon-based quantum dot precursor is subjected to a pyrolysis reaction. During the pyrolysis reaction, the carbon-based quantum dot precursor is carbonized to obtain red fluorescent carbon-based quantum dots.

2. The method for preparing red fluorescent carbon-based quantum dots according to claim 1, characterized in that: The conditions of the solvent thermal reaction are: reaction at 60℃~200℃ for 1h~50h.

3. The method for preparing red fluorescent carbon-based quantum dots according to claim 1, characterized in that: The conditions of the pyrolysis reaction are: reaction at 100°C~500°C for 1h~50h.

4. The method for preparing red fluorescent carbon-based quantum dots according to claim 1, characterized in that: The organic small molecule compound containing a conjugated system is selected from at least one of pyridine dyes, cyanobenzene compounds, anthracene dyes, coumarins, perylenetetracarboxylic acid imide derivatives, tetraphenylethylene derivatives, quinine sulfate, rhodamine dyes, sulfonated rhodamine derivatives, cyanine dyes, anthracene, perylene, pyrene, naphthalene, chitosan, glucose, polysaccharides, anilines, phenol, benzoic acid, benzenesulfonic acid, thiophene, carbazoles or polycyclic aromatic hydrocarbons, and the molecular weight of the organic small molecule compound containing a conjugated system is less than 2000g / mol.

5. A red fluorescent carbon-based quantum dot, characterized in that: The red fluorescent carbon-based quantum dots are prepared by the preparation method according to any one of claims 1 to 4, and the particle size of the red fluorescent carbon-based quantum dots is 2nm to 10nm.

6. The red fluorescent carbon-based quantum dots according to claim 5, characterized in that: The fluorescence emission peak of red fluorescent carbon-based quantum dots is 580nm~700nm, and exhibits excitation-independent characteristic emission, which can convert ultraviolet light or yellow-green light into red light emission.

7. The red fluorescent carbon-based quantum dots according to claim 5, characterized in that: The red fluorescent carbon-based quantum dots are evenly distributed on an orderly arranged mesh substrate, the mesh substrate is a thermal decomposition product of a cross-linking agent, and the red fluorescent carbon-based quantum dots are also dispersed in the thermal decomposition product of the cross-linking agent.

8. A carbon-based quantum dot light-converting composite film, characterized in that: The carbon-based quantum dot light-converting composite film is made of the red fluorescent carbon-based quantum dots described in claim 5 and a polymer substrate, and the red fluorescent carbon-based quantum dots are loaded on the polymer substrate; Among them, the mass ratio of red fluorescent carbon-based quantum dots to polymer substrate is 0.005~50:

100.

9. The carbon-based quantum dot light-converting composite film according to claim 8, characterized in that: The thickness of the carbon-based quantum dot light-converting composite film is 50 μm~200 μm.

10. The carbon-based quantum dot light-converting composite film according to claim 8, characterized in that: The carbon-based quantum dot light-conversion composite film can convert ultraviolet light or yellow-green light into red light. The carbon-based quantum dot light-conversion composite film has an absorption response to ultraviolet light with a wavelength of 200nm~400nm and yellow-green light with a wavelength of 510nm~580nm, and emits red-orange light with a wavelength of 580nm~700nm.

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