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

Abstract

The present invention relates to the technical field of carbon-based quantum dots, and in particular to red fluorescent carbon-based quantum dots, a preparation method, and a carbon-based quantum dot light-converting composite film. The preparation method comprises: dissolving an organic small molecule compound containing a conjugated system in a solvent, mixing it with a cross-linking agent, and performing a solvent thermal reaction to obtain a carbon-based quantum dot precursor; and performing a pyrolysis reaction on the carbon-based quantum dot precursor to obtain red fluorescent carbon-based quantum dots. The red fluorescent carbon-based quantum dots prepared by the preparation method of the present invention are evenly distributed on a mesh substrate, and the mesh substrate effectively realizes the spatial isolation function of the red fluorescent carbon-based quantum dots, thereby suppressing the energy transfer loss phenomenon caused by the π-π stacking of the red fluorescent carbon-based quantum dots. Not only does it overcome the problem that the luminous color and intensity of traditional carbon-based quantum dots are prone to drift when compounded with a polymer matrix, but it also solves the problems of uneven dispersion of quantum dots and unstable fluorescence performance in the light-converting film.

Description

Technical Field

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

[0002] Light quality is a key factor influencing plant growth and development, yield formation, and fruit quality. Although sunlight reaching the Earth's surface has a wavelength range of 290nm to 3000nm, only a small fraction of this energy is effectively absorbed by plants, primarily in the blue range of 420nm to 500nm and the red range of 580nm to 700nm. Ultraviolet light, ranging from 280nm to 390nm, is not only detrimental to plant growth but can also increase pests and diseases and accelerate the aging of plastic greenhouse materials. Light-conversion film is a type of functional agricultural film that, by adding specific light-conversion agents, converts light that plants cannot effectively utilize into the wavelengths required for photosynthesis, thereby improving light energy utilization. Research has found that light-conversion film not only converts ultraviolet light into blue and red-orange light, which are beneficial for photosynthesis, but also converts yellow-green light, which has no significant effect on plant growth, into red-orange light, thereby improving photosynthesis efficiency and significantly increasing crop yield and quality. For example, the effective use of red light helps promote the accumulation of starch and sugars, increasing fruit coloration and sweetness. A large number of experiments have shown that the use of light-converting film can increase the yield of spinach, carrots and edible soybeans by about 10%, and improve the content of vitamin C and soluble protein. At the same time, it can significantly promote the growth of tomatoes and increase the vitamin C and lycopene content in the fruit.

[0003] Currently, most light-converting agents used in light-converting films are composed of rare earth elements combined with an inorganic matrix or organic ligand. While these inorganic rare earth light-converting agents exhibit excellent luminescence intensity and stability, their poor compatibility with polymers often leads to uneven dispersion, accumulation, or concentration quenching within the film, which in turn reduces luminescence efficiency. Organic rare earth light-converting agents, by contrast, exhibit better compatibility with polyethylene. By adjusting the ligand structure, variable luminescence intensity and efficiency can be achieved, but these agents are relatively expensive. As a novel light-conversion material, carbon-based quantum dots have demonstrated significant value in the field of light conversion, particularly in red light conversion, due to their excellent optical properties, low toxicity, biocompatibility, and environmental friendliness. However, when carbon-based quantum dots are combined with a polymer matrix, their luminescence color and intensity tend to drift, making it difficult to achieve stable, consistent luminescence across a wide wavelength range in multiple films. Summary of the Invention

[0004] In response to the deficiencies in the prior art, the present invention provides red fluorescent carbon-based quantum dots, a preparation method, and a carbon-based quantum dot light-converting composite film. The present invention uses an organic small molecule compound containing a conjugated system and a cross-linking agent as the main raw materials, and successfully prepares red fluorescent carbon-based quantum dots through a two-step method of solvent thermal reaction and pyrolysis carbonization. The present invention introduces nitrogen-containing or oxygen-containing functional groups for functional group modification, and the cross-linking agent forms a mesh base structure during the thermal decomposition process. This structure not only achieves effective spatial isolation and protection, but also effectively suppresses the energy transfer loss caused by π-π stacking, thereby greatly reducing the fluorescence quenching phenomenon and significantly improving the optical stability of red fluorescent carbon-based quantum dots. In addition, by optimizing the carbonization temperature and time, it is ensured that the thermal decomposition temperature of the carbon-based quantum dot precursor is reached, thereby significantly improving the carbonization degree of the carbon-based quantum dots, further enhancing its 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:

[0006] The first object of the present invention is to provide a method for preparing red fluorescent carbon-based quantum dots, comprising the following steps:

[0007] S1. After dissolving an organic small molecule compound containing a conjugated system in a solvent, mixing it with a cross-linking agent, and conducting 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, wherein the covalent bond includes a C-O bond or a C-N bond. At the same time, nitrogen-containing or oxygen-containing functional groups are introduced to perform functional group modification so as 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 cross-linking agent is 0.01~50:100.

[0008] 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 the conjugated system and the cross-linking agent are first decomposed and dehydrated and condensed at high temperature to form a polycyclic aromatic structure, and then further carbonized to obtain red fluorescent carbon-based quantum dots.

[0009] Preferably, the solvothermal reaction conditions are: reaction at 60° C. to 200° C. for 1 h to 50 h, or reaction using a microwave method at 500 W to 1000 W for 10 min to 30 min.

[0010] Preferably, the pyrolysis reaction conditions are: reaction at 100°C to 500°C for 1 hour to 50 hours. The temperature and time of the pyrolysis reaction play a key role in regulating the functional groups, energy level structure, and forming appropriate spatial isolation of the red fluorescent carbon-based quantum dots. This helps to suppress the energy transfer loss caused by π-π stacking, thereby reducing fluorescence quenching and improving optical performance. However, if the pyrolysis temperature is too low, it will lead to incomplete carbonization, resulting in poor fluorescence performance and uneven structure of the red fluorescent carbon-based quantum dots. On the other hand, if the temperature is too high, it will cause excessive carbonization, leading to fluorescence quenching and loss of functional groups.

[0011] Preferably, 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, aniline, 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 2000 g / mol.

[0012] Preferably, the solvent is selected from at least one of water, methanol, ethanol, propanol, butanol, isopropanol, glycerol, n-butanol, isobutanol, isoamyl alcohol, ethyl acetate, petroleum ether, N,N-dimethylformamide, dimethyl sulfoxide, chloroform, dichloromethane, toluene, xylene, pentane, hexane, chlorobenzene, ether, acetone, methyl butyl ketone or ethylene glycol monobutyl ether.

[0013] Preferably, the crosslinking 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, m-chloroperbenzoic acid, metal salts, glutaraldehyde, chitosan, boric acid, polyvinyl alcohol, ethylene glycol, polyethylene glycol, ethylenediamine, aluminum nitrate, aluminum hydroxide, sodium metaaluminate, ethyl orthosilicate, sodium silicate, silane, silicate, metaboric acid, triethylborane or polysaccharide.

[0014] The second object of the present invention is to provide red fluorescent carbon-based quantum dots prepared by the above preparation method, wherein the particle size of the red fluorescent carbon-based quantum dots is 2nm~10nm.

[0015] Preferably, the fluorescence emission peak of the red fluorescent carbon-based quantum dots is 580nm~700nm, and exhibits excitation-independent characteristic emission, and can convert ultraviolet light or yellow-green light into red light emission.

[0016] Preferably, the fluorescent quantum dots are evenly distributed on the mesh substrate, the mesh substrate is a thermal decomposition product of the cross-linking agent, and the red fluorescent carbon-based quantum dots are also dispersed in the thermal decomposition product of the cross-linking agent, and the thermal decomposition product of the cross-linking agent is a coordination oxide or amorphous carbon; the coating principle is: the remaining cross-linking agent of the carbon-based quantum dot precursor is self-assembled by non-covalent force under non-covalent action or coordination, that is, hydrogen bonding, π-π stacking or electrostatic action, and forms a thermal decomposition product during the pyrolysis process, and the thermal decomposition product uniformly disperses or coats the carbon-based quantum dots. The cross-linking agent of the present invention can also be used as a functional group modifier to achieve stable dispersion or coating of the red fluorescent carbon-based quantum dots while realizing functionalization of the red fluorescent carbon-based quantum dots.

[0017] 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.

[0018] Preferably, the thickness of the carbon-based quantum dot light-conversion composite film is 50 μm to 200 μm.

[0019] Preferably, the carbon-based quantum dot light-conversion composite film can convert ultraviolet light or yellow-green light into red light, wherein 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.

[0020] Preferably, the preparation method of the carbon-based quantum dot light-converting composite film is prepared according to the following steps:

[0021] 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-converting composite film.

[0022] Preferably, the film-making process is selected from solution casting, melt casting, molding, hot pressing, multi-layer co-extrusion, biaxial stretching, film blowing, blow molding or coating.

[0023] Preferably, the specific operation steps of the coating method are: uniformly dispersing red fluorescent carbon-based quantum dots in a coating, and coating the coating on a polymer substrate by a coating method to obtain a carbon-based quantum dot light-converting composite film.

[0024] Preferably, the coating is selected from at least one of epoxy resin, acrylic acid, waterborne polyurethane, waterborne acrylic acid, nano-silicon oxide, nano-titanium dioxide, aluminum sol, silica sol, polyvinyl pyrrolidone, polymethyl methacrylate, polystyrene, polydimethylsiloxane, cellulose, polyimide, polyethylene glycol, polyvinyl butyral, polyacrylonitrile or polyvinylidene fluoride.

[0025] 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.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 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, the mixture is mixed with a cross-linking agent, and a solvent thermal reaction is carried out. During the solvent thermal reaction, the organic small molecule compound containing the conjugated system undergoes a dehydration condensation reaction with the solvent or the cross-linking agent to form a covalent bond. At the same time, nitrogen-containing or oxygen-containing functional groups are introduced and functional group modification is carried out to obtain a carbon-based quantum dot precursor; 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.

[0028] The crosslinking agent in the present invention self-assembles under non-covalent or coordination effects and forms a mesh substrate during the thermal decomposition process. The red fluorescent carbon-based quantum dots are evenly distributed on the mesh substrate, which effectively achieves a spatial isolation function, suppresses the energy transfer loss phenomenon caused by π-π stacking, and thus significantly reduces the possibility of fluorescence quenching and significantly improves the overall optical performance. Not only does it overcome the problem that the luminescent color and intensity of traditional carbon-based quantum dots are prone to drift when composited with a polymer substrate, it also solves the problems of uneven dispersion of quantum dots and unstable fluorescence performance in carbon-based quantum dot composite light-conversion films in the prior art.

[0029] 2. The red fluorescent carbon-based quantum dots of the present invention exhibit excellent chemical compatibility with polymer substrates and can be efficiently dispersed in the polymer substrate through various technical means. Furthermore, when prepared into a carbon-based quantum dot light-conversion composite film, aggregation or sedimentation of the red fluorescent carbon-based quantum dots is effectively avoided. This process not only successfully preserves the original red fluorescent properties of the red fluorescent carbon-based quantum dots, but also ensures that the light-conversion composite film possesses excellent optical stability. In particular, the red fluorescent carbon-based quantum dots of the present invention have a particle size of less than 20 nm and, when mixed with the polymer matrix, have no adverse effect on the visible light transmittance of the composite film.

[0030] 3. The preparation method of the present invention is simple and efficient, significantly reducing raw material and equipment costs, thus enabling the large-scale production of red fluorescent carbon-based quantum dots. In particular, the preparation process does not require complex equipment or high energy consumption, making it highly compatible with the requirements of industrial production. During mass production, the red fluorescent carbon-based quantum dots demonstrated excellent reproducibility and product quality stability, ensuring high consistency between production batches.

[0031] Furthermore, the preparation method of the present invention achieves precise control of the emission wavelength of red fluorescent carbon-based quantum dots by finely regulating reaction conditions, including the selection of precursor materials, temperature setting, reaction time, and pH adjustment, thereby meeting the specific requirements of different light conversion films. This preparation method also possesses excellent optical performance adjustment capabilities, enabling precise control of the emission wavelength and quantum yield of the quantum dots.

[0032] 4. The carbon-based quantum dot light-conversion composite film produced by this invention can convert ultraviolet or yellow-green light into red light. Compared to conventional polyolefin films (PO films), this carbon-based quantum dot light-conversion composite film significantly increases the proportion of red light in greenhouses, speeding up vegetable growth by over 30% and shortening fruit coloring time by approximately 20 days.

[0033] 5. The red fluorescent carbon-based quantum dot powder produced by this invention can maintain a broad-wavelength red fluorescent color in a polymer matrix. This is because the crosslinker spontaneously forms an ordered and stable network structure through non-covalent or coordination interactions, namely hydrogen bonding, π-π stacking, and electrostatic interactions. This structure not only significantly improves thermal stability but also ensures the independence of solid-state fluorescence emission from solvents, thereby achieving long-lasting red fluorescent color in the polymer matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 These are the transmission electron microscopy images and particle size distribution diagrams of the red fluorescent carbon-based quantum dots in Example 1 of the present invention, wherein (a) is a transmission electron microscopy image at a magnification of 50 nm, (b) is a transmission electron microscopy image at a magnification of 20 nm, (c) is a transmission electron microscopy image at a magnification of 5 nm, and (d) is a particle size distribution diagram.

[0035] Figure 2 These are the physical characterization results of the red fluorescent carbon-based quantum dots in Example 1 of the present invention, where (a) is an infrared spectrum, (b) is a thermogravimetric analysis diagram, (c) is a Raman spectrum, and (d) is a high-resolution N 1s spectrum of the X-ray photoelectron spectroscopy.

[0036] Figure 3 These are optical performance diagrams of the red fluorescent carbon-based quantum dots in solvent according to Example 2 of the present invention, wherein (a) is a fluorescence diagram at an excitation wavelength of 365 nm, and (b) is a UV-visible absorption diagram in ethyl acetate and chloroform.

[0037] Figure 4 These are optical performance characterization graphs of the red fluorescent carbon-based quantum dots of Example 1 of the present invention, wherein (a) is an optical performance characterization graph under natural light conditions, (b) is an optical performance characterization graph under 365nm ultraviolet light conditions, and (c) is a fluorescence emission graph under different excitation wavelengths.

[0038] Figure 5These are characterization diagrams of the optical properties of the 2# carbon-based quantum dot light-conversion composite film, where (a) is the fluorescence emission peak diagram at excitation wavelengths of 365nm and 550nm, (b) is the UV-visible transmittance diagram, (c) is the fluorescence lifetime diagram in solution, and (d) is the variable temperature fluorescence test diagram.

[0039] Figure 6 These are the optical performance characterization diagrams of 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 fluorescent light conversion film, among which, (a) is a real photo of 1# carbon-based quantum dot light conversion composite film under natural light and 365nm ultraviolet light, (b) is the excitation diagram of 1# carbon-based quantum dot light conversion composite film at emission wavelengths of 365nm, 550nm and 600nm, (c) is the ultraviolet-visible absorption diagram of 1# carbon-based quantum dot light conversion composite film, (d) is the ultraviolet-visible light transmittance diagram of 1# carbon-based quantum dot light conversion composite film, (e) is the emission peak diagram of inorganic rare earth-based composite red fluorescent light conversion film at excitation wavelengths of 365nm and 550nm, and (f) is the integral area diagram of the emission peaks of 1# carbon-based quantum dot light conversion composite film and inorganic rare earth-based composite red fluorescent light conversion film at excitation wavelengths of 365nm and 550nm.

[0040] Figure 7 This is the outdoor irradiance diagram of 1# carbon-based quantum dot light-conversion composite film and the comparison diagram of the targeted light growth rate of the commercial red film in the 600nm~700nm band, among which (a) is the outdoor irradiance diagram of the carbon-based quantum dot light-conversion composite film and the 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, the low-density polyethylene composite film, and the inorganic and organic rare earth-based composite red fluorescent light-conversion film.

[0041] Figure 8 These are characterization diagrams of the aging results of 1# carbon-based quantum dot light-conversion composite film, where (a) is a characterization diagram of the results before and after ultraviolet aging, and (b) is a characterization diagram of the results before and after ultraviolet aging.

[0042] Figure 9 These are photos of tomatoes and eggplants grown in greenhouses covered with 1# carbon-based quantum dot light conversion composite film and ordinary PO film, among which, (a) is a photo of tomatoes grown in greenhouses covered with 1# carbon-based quantum dot light conversion composite film and PO film, (b) is a photo of eggplants grown in greenhouses covered with 1# carbon-based quantum dot light conversion composite film and PO film, (c) is a statistical graph of the time it takes for tomatoes to turn red when covered with 1# carbon-based quantum dot light conversion composite film and PO film, and (d) is a statistical graph of the size of eggplants grown in greenhouses covered with 1# carbon-based quantum dot light conversion composite film and PO film. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solution of the present invention in conjunction with the data in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] 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 scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods. Among them, the commercial red film includes an inorganic rare earth-based composite red fluorescent light-converting film, organic rare earth 1, organic rare earth 2, inorganic rare earth 1 and inorganic rare earth 2, purchased from an agricultural film product industry exhibition; ordinary PO film, polyolefin film, a polymer material polymerized from olefin monomers, with a thickness of 100 μm; low-density polyethylene, that is, pure LDPE model 7042, purchased from the agent of Xi'an Dehuixing Trading Co., Ltd.

[0045] Prior art uses light-conversion films as an effective means of improving plant light energy utilization. By adding a light-conversion agent, they convert undesirable light waves into those required for photosynthesis, significantly improving crop yield and quality. However, traditional light-conversion agents, such as rare earth inorganic light-conversion agents, suffer from poor compatibility with polymers and uneven dispersion, resulting in reduced luminous efficiency. While organic rare earth light-conversion agents offer better compatibility, they are also expensive. While carbon-based quantum dots, a novel light-conversion material, possess excellent optical properties and biocompatibility, they are prone to luminescence color and intensity drift when combined with a polymer matrix, making stable luminescence difficult to achieve.

[0046] In response to the problems existing in the above-mentioned prior art, the present invention provides a method for preparing red fluorescent carbon-based quantum dots, comprising 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 solvent thermal reaction; during the solvent thermal reaction, the organic small molecule compound containing the 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, nitrogen-containing or oxygen-containing functional groups are 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 the conjugated system to the cross-linking agent is 0.01~50:100; 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.

[0047] By introducing a mesh substrate formed from the thermal decomposition products of a crosslinker, the present invention overcomes the energy transfer loss problem of red fluorescent carbon-based quantum dots in the prior art, which is easily caused by π-π stacking. The mesh substrate effectively achieves spatial isolation, reducing the occurrence of π-π stacking, thereby reducing energy transfer loss and fluorescence quenching.

[0048] The present invention introduces a cross-linking agent and forms stably dispersed carbon-based quantum dots through solvent thermal reaction and pyrolysis treatment, thereby overcoming the problems of poor compatibility of traditional light conversion agents with high molecular weight polymers and uneven dispersion leading to reduced luminous efficiency; the present invention solves the problems of high cost of organic rare earth light conversion agents and easy drift of luminous color and intensity of carbon-based quantum dots when compounded with a polymer matrix through the dual strategy of constructing a mesh base and functional group modification, thereby achieving efficient and stable preparation of red fluorescent carbon-based quantum dots.

[0049] 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 with reference to specific embodiments.

[0050] Example 1

[0051] A method for preparing red fluorescent carbon-based quantum dots comprises the following steps:

[0052] S1. Take pyrene as a precursor, dissolve it in ethanol at a mass concentration of 1 mg / mL, then add urea as a crosslinker, and heat the reaction at 80°C in an air atmosphere for 5 hours to obtain a carbon-based quantum dot precursor; wherein the mass ratio of pyrene to urea is 0.1:100.

[0053] S2. The carbon-based quantum dot precursor is placed in an air atmosphere and heated at 160° C. for a pyrolysis reaction for 5 hours to obtain red fluorescent carbon-based quantum dots.

[0054] The red fluorescent carbon-based quantum dots prepared in Example 1 were prepared into a carbon-based quantum dot light-conversion composite film according to the following steps:

[0055] S1. According to the mass ratio of red fluorescent carbon-based quantum dots to linear low-density polyethylene of 0.05:100, the red fluorescent carbon-based quantum dots and linear low-density polyethylene were evenly mixed, added into 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.

[0056] S2. The composite masterbatch is heated and melted at 180° C. through an extruder, extruded through a die head to form a tube, and blown into a film using compressed air. The film is quickly cooled and shaped by a cooling device; the film is rolled into a roll by a winding device to obtain a carbon-based quantum dot light-conversion composite film with a thickness of 100 μm, which is recorded as 1# carbon-based quantum dot light-conversion composite film, i.e., a red fluorescent light-conversion film.

[0057] Example 2

[0058] A method for preparing red fluorescent carbon-based quantum dots comprises the following steps:

[0059] S1. Aniline was taken as a precursor and dissolved in ethanol at a mass concentration of 1 mg / mL. Then, cross-linking agents citric acid and urea were added, and the mixture was heated at 80°C in an air atmosphere for 2 hours to obtain a carbon-based quantum dot precursor; wherein the mass ratio of aniline to the mixture of citric acid and urea was 0.5:100, and the mass ratio of citric acid to urea was 1:10.

[0060] S2. The carbon-based quantum dot precursor is placed in an air atmosphere and heated at 160° C. for a pyrolysis reaction for 5 hours to obtain red fluorescent carbon-based quantum dots.

[0061] The red fluorescent carbon-based quantum dots prepared in Example 2 were prepared into a carbon-based quantum dot light-conversion composite film according to the following steps: The red fluorescent carbon-based quantum dots and the polyurethane aqueous solution were uniformly mixed at a mass ratio of 0.1:100, and then coated onto a linear low-density polyethylene using a coating rod to obtain a carbon-based quantum dot light-conversion composite film with a thickness of 120 μm. The linear low-density polyethylene had a thickness of 80 μm and was designated as carbon-based quantum dot light-conversion composite film #2, i.e., the red fluorescent light-conversion film.

[0062] Example 3

[0063] A method for preparing red fluorescent carbon-based quantum dots comprises the following steps:

[0064] S1. Perylene is used as a precursor and dissolved in a mixture of methanol and water at a mass concentration of 2 mg / mL. A crosslinking agent, aluminum nitrate, is then added and heated to 90°C in an air atmosphere for 5 hours 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.

[0065] S2. The carbon-based quantum dot precursor is placed in an air atmosphere and heated at 300° C. for a pyrolysis reaction for 5 hours to obtain red fluorescent carbon-based quantum dots.

[0066] The red fluorescent carbon-based quantum dots prepared in Example 3 were prepared into a carbon-based quantum dot light-conversion composite film according to the following steps:

[0067] S1. According to the mass ratio of red fluorescent carbon-based quantum dots and ethylene-vinyl acetate copolymer of 0.2:100, the red fluorescent carbon-based quantum dots and ethylene-vinyl acetate copolymer were evenly mixed, and then added into the hopper of a micro twin-screw extruder. The temperature was raised 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 ethylene-vinyl acetate copolymer.

[0068] S2. The composite masterbatch is heated and melted at 180° C. through an extruder, extruded through a die head to form a tube, and inflated into a film using compressed air. The film is quickly cooled and shaped by a cooling device; the film is rolled into a roll using a winding device to obtain a carbon-based quantum dot light-conversion composite film with a thickness of 120 μm, which is recorded as 3# carbon-based quantum dot light-conversion composite film, i.e., a red fluorescent light-conversion film.

[0069] Example 4

[0070] A method for preparing red fluorescent carbon-based quantum dots comprises the following steps:

[0071] S1. Take polycyclic aromatic hydrocarbons as a precursor, dissolve them in ethanol at a mass concentration of 0.5 mg / mL, then add the crosslinking agent urea, mix them at a ratio of 10 mg / mL, and use microwave irradiation with a power of 600 W for 10 minutes to obtain a carbon-based quantum dot precursor; wherein, the mass ratio of polycyclic aromatic hydrocarbons to urea is 1:100.

[0072] S2. The red fluorescent carbon-based quantum dots are placed in an air atmosphere and heated at 180° C. for a pyrolysis reaction for 5 hours to obtain red fluorescent carbon-based quantum dots.

[0073] The red fluorescent carbon-based quantum dots prepared in Example 4 were prepared into a carbon-based quantum dot light-conversion composite film according to the following steps: using the melt casting method, the red fluorescent carbon-based quantum dots and polystyrene were added to the mixing cavity according to a mass ratio of 1:100, the temperature was raised to 160°C, and after heating and melting, the film was cast into a 150 μm carbon-based quantum dot light-conversion composite film, which was recorded as 4# carbon-based quantum dot light-conversion composite film, i.e., a red fluorescent light-conversion film.

[0074] Example 5

[0075] A method for preparing red fluorescent carbon-based quantum dots comprises the following steps:

[0076] S1. Aniline was used as a precursor and dissolved in ethanol at a mass concentration of 1 mg / mL. Polyethylene glycol (PEG) was then added as a crosslinker. The mixture was heated at 80°C in an air atmosphere for 2 hours to obtain a carbon-based quantum dot precursor. The mass ratio of aniline to polyethylene glycol was 0.5:100.

[0077] S2. The carbon-based quantum dot precursor is placed in an air atmosphere and heated at 150° C. for a pyrolysis reaction for 5 hours to obtain red fluorescent carbon-based quantum dots.

[0078] 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: the red fluorescent carbon-based quantum dots and polyacrylonitrile were uniformly mixed at a mass ratio of 1:100 and added to chloroform. After they were completely dissolved, a mixture was obtained. The mixture was sprayed onto linear low-density polyethylene by a spraying method to obtain a carbon-based quantum dot light-conversion composite film, which was recorded as 5# carbon-based quantum dot light-conversion composite film, i.e., a red fluorescent light-conversion film.

[0079] Example 6

[0080] A method for preparing red fluorescent carbon-based quantum dots comprises the following steps:

[0081] S1. Take pyrene as a precursor, dissolve it in ethanol at a mass concentration of 1 mg / mL, then add urea as a crosslinker, and heat the reaction at 60°C in an air atmosphere for 50 hours to obtain a carbon-based quantum dot precursor; wherein the mass ratio of pyrene to urea is 0.01:100.

[0082] S2. The carbon-based quantum dot precursor is placed in an air atmosphere and heated at 100° C. for a pyrolysis reaction for 50 hours to obtain red fluorescent carbon-based quantum dots.

[0083] 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:

[0084] S1. According to the mass ratio of red fluorescent carbon-based quantum dots to linear low-density polyethylene being 50:100, the red fluorescent carbon-based quantum dots and linear low-density polyethylene are evenly mixed, and then added into the hopper of a micro twin-screw extruder. The mixture is 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.

[0085] S2. The composite masterbatch is heated and melted at 180° C. through an extruder, extruded through a die head to form a tube, and inflated into a film using compressed air. The film is quickly cooled and shaped by a cooling device; the film is rolled into a roll by a winding device to obtain a carbon-based quantum dot light-conversion composite film, which is recorded as 6# carbon-based quantum dot light-conversion composite film, i.e., a red fluorescent light-conversion film.

[0086] Example 7

[0087] A method for preparing red fluorescent carbon-based quantum dots comprises the following steps:

[0088] S1. Take pyrene as a precursor, dissolve it in ethanol at a mass concentration of 1 mg / mL, then add urea as a crosslinker, and heat the reaction at 200°C in an air atmosphere for 1 hour to obtain a carbon-based quantum dot precursor; wherein the mass ratio of pyrene to urea is 0.01:100.

[0089] S2. The carbon-based quantum dot precursor is placed in an air atmosphere and heated at 500° C. for a pyrolysis reaction for 1 hour to obtain red fluorescent carbon-based quantum dots.

[0090] 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:

[0091] S1. According to the mass ratio of red fluorescent carbon-based quantum dots to linear low-density polyethylene of 0.005:100, the red fluorescent carbon-based quantum dots and linear low-density polyethylene were evenly mixed, added into 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.

[0092] S2. The composite masterbatch is heated and melted at 180° C. through an extruder, extruded through a die head to form a tube, and inflated into a film using compressed air. The film is quickly cooled and shaped by a cooling device; the film is rolled into a roll by a winding device to obtain a carbon-based quantum dot light-conversion composite film, which is recorded as 7# carbon-based quantum dot light-conversion composite film, i.e., a red fluorescent light-conversion film.

[0093] a. Microstructure of red fluorescent carbon-based quantum dots:

[0094] observe Figure 1 The results show that the red fluorescent carbon-based quantum dots are evenly distributed on a mesh-like base structure. This mesh-like base structure can prevent the red fluorescent carbon-based quantum dots from producing fluorescence aggregation-induced quenching, allowing 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 ranges from 2nm to 7nm, with an average particle size of approximately 4nm. Further high-resolution transmission electron microscopy revealed that the interplanar spacing of these red fluorescent carbon-based quantum dots is 0.21nm, corresponding to the (100) crystal plane of graphite.

[0095] Depend on Figure 2 (a) shows that the red fluorescent carbon-based quantum dots exhibit specific chemical bond stretching vibration peaks, including the peak at 1700 cm -1 C=O, located at 1620cm -1 C=N, located at 1080cm -1 ~1120cm -1 CO, located at 3100cm -1 ~3650cm -1NH and located at 2875cm -1 The CH of red fluorescent carbon-based quantum dots indicates that the surface of red fluorescent carbon-based quantum dots has more functional groups and can be well dispersed in the polymer matrix.

[0096] b. Phase characterization results of red fluorescent carbon-based quantum dots:

[0097] Depend on Figure 2 (b) shows that the weight loss of red fluorescent carbon-based quantum dots is almost zero before 210°C, indicating that they still have good thermal stability when hot-melted with high molecular polymers.

[0098] Depend on Figure 2 (c) shows that the red fluorescent carbon-based quantum dots have obvious disordered D band (sp 3 structure) and crystal G band (sp 2 structure), the peak intensity of the G band is higher, indicating that the graphene phase of the red fluorescent carbon-based quantum dots is sp 2 The structure is good.

[0099] Depend on Figure 2 (d) in the figure shows that the N 1s spectrum can be fitted into pyrrole nitrogen (398.5 eV), NH (401.9 eV) and NO (406.5 eV), so the surface of the red fluorescent carbon-based quantum dots contains more surface functional groups.

[0100] c. Characterization results of optical properties of red fluorescent carbon-based quantum dots in solvent:

[0101] Figure 3 (a) is the fluorescence image of red fluorescent carbon-based quantum dots under an excitation wavelength of 365nm. Its emission peak in ethyl acetate is 615nm, and its emission peak in chloroform is 630nm. Figure 3 (b) is the UV-visible absorption spectrum of red fluorescent carbon-based quantum dots in ethyl acetate and chloroform respectively. The UV-visible absorption peak around 320nm is usually The specific absorption peak at 520nm is caused by the electronic transition of the conjugated C=C on the surface or in the core structure. This indicates that the surface of carbon-based quantum dots contains polar functional groups, which can significantly affect their optical properties, especially the absorption characteristics in the ultraviolet-visible spectral range.

[0102] d. Optical properties characterization results of red fluorescent carbon-based quantum dots:

[0103] observe Figure 4 (a) shows that the red fluorescent carbon-based quantum dots appear purple-red under natural light and bright red fluorescent color under 365nm ultraviolet light, as shown in Figure 4 As shown in (b) in the figure. Figure 4 (c) shows that the fluorescence properties of red fluorescent carbon-based quantum dots were tested at excitation wavelengths of 365nm, 520nm and 550nm, and their emission peaks were all at 620nm, showing obvious excitation-independent emission fluorescence properties.

[0104] e.2# Characterization of optical properties of carbon-based quantum dot light-converting composite film:

[0105] Figure 5 (a) is the fluorescence emission peak of the carbon-based quantum dot light-conversion composite film at excitation wavelengths of 365nm and 550nm. Its emission peak is 620nm, and it has good fluorescence properties for converting ultraviolet and yellow-green light to red light.

[0106] observe Figure 5 (b) shows that the transmittance of 2# carbon-based quantum dot light-converting composite film in the visible light range is 70%~90%, the transmittance in 300nm~400nm is 50%, and the transmittance in 200nm~300nm is less than 10%. Figure 5 (c) shows that the fluorescence lifetime of the carbon-based quantum dot light-converting composite film in Example 2 reached 4.42ns, compared to only 1.15ns in ethyl acetate. This significant difference is mainly attributed to the stable hydrogen bonds formed between the abundant functional groups on the surface of the red fluorescent carbon-based quantum dots and the polymer substrate polyurethane. This interaction prolongs its fluorescence lifetime. Figure 5 (d) shows that within the test temperature range of -30℃~40℃, the 2# carbon-based quantum dot light-conversion composite film exhibits good optical stability.

[0107] f.1# Characterization of optical properties of carbon-based quantum dot light-converting composite film:

[0108] observe Figure 6 (a) in the figure shows that the 1# carbon-based quantum dot light-conversion composite film is light pink under natural light and exhibits obvious red fluorescence under 365nm ultraviolet light. Further exploration of the optical properties of the 1# carbon-based quantum dot light-conversion composite film reveals that Figure 6 (b) shows that under the excitation wavelengths of 365nm and 550nm, its fluorescence emission peak is 600nm, with obvious optical properties of ultraviolet and green light to red light conversion, and its maximum excitation wavelength at the 600nm emission peak is 550nm; Figure 6 (c) in the figure shows that the absorption peak at 280 nm corresponds to the C=C bond. transition, 550nm is the surface state jump; Figure 6(d) in the figure shows that the transmittance of the 1# carbon-based quantum dot light-converting composite film is over 80% between 550nm and 800nm, and the transmittance in the ultraviolet region is about 20%. Figure 6 (e) in the figure is the fluorescence emission peak of the inorganic rare earth-based composite red fluorescent light conversion film under 365nm and 550nm excitation wavelengths. Under 365nm excitation wavelength, the fluorescence emission peak is located at 620nm, showing obvious red fluorescence emission; while under 550nm excitation wavelength, almost no fluorescence emission is generated. Figure 6 (f) shows that the integral area of ​​1# carbon-based quantum dot light-conversion composite film is larger than that of inorganic rare earth-based composite red fluorescent light-conversion film, and the integral area of ​​the fluorescence emission peak of 1# carbon-based quantum dot light-conversion composite film at an excitation wavelength of 550nm is larger than that of the inorganic rare earth-based composite red fluorescent light-conversion film, both of which show better optical properties of converting ultraviolet and yellow-green light into red light.

[0109] g. Outdoor irradiance diagram of 1# carbon-based quantum dot light-converting composite film and comparison of outdoor irradiance of commercial red film in the 600nm~700nm band:

[0110] Depend on Figure 7 (a) shows that compared with pure LDPE, the irradiance of yellow-green light in the 500nm~600nm range of 1# carbon-based quantum dot light conversion composite film is significantly reduced, while the irradiance in the 600nm~700nm band is increased. The formula for calculating the growth rate of targeted light intensity ratio is:

[0111] ;

[0112] Where:

[0113] T—target light intensity ratio growth rate of test sample, %; PFD —Photon flux of the test sample in the red light region of 600nm~700nm or the blue light region of 400nm~500nm, μmol / (m 2 s); PFD —The photon flux of the test sample in the spectral region of 350nm~800nm, μmol / (m 2 s); PFDt(ck) —The photon flux of the control sample in the red light region of 600nm~700nm or the blue light region of 400nm~500nm, μmol / (m 2 s); PFD(ck) —The photon flux of the control sample in the spectral region of 350nm~800nm, μmol / (m 2 ·s).

[0114] In the formula PFD is the photo flux density, in μmol / (m 2·s), tested using a handheld spectrometer.

[0115] Among them, the targeted growth rate of the 600nm~700nm region of the 1# carbon-based quantum dot light-conversion composite film is higher than that of some other commercial films.

[0116] h.1# Characterization of light aging performance of carbon-based quantum dot light conversion composite film:

[0117] Depend on Figure 8 It is concluded that the 1# carbon-based quantum dot light conversion composite film can absorb ultraviolet light with a wavelength below 400nm and release visible light at the same time, thereby helping to reduce the intensity of ultraviolet radiation on the polymer matrix and significantly improving the anti-ultraviolet aging ability of the composite material. Figure 8 (a) shows that the stress and strain of the aged 1# carbon-based quantum dot light-conversion composite film remain almost unchanged compared to the unaged carbon-based quantum dot light-conversion composite film. Figure 8 Figure (b) shows 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%.

[0118] i. Photos of plants growing under a shed covered with 1# carbon-based quantum dot light-converting composite film:

[0119] observe Figure 9 The results showed that tomatoes grown under the 1# carbon-based quantum dot light-conversion composite film had a reddish color, while those grown under the PO film had a turquoise color. This significant difference resulted in a 20-day reduction in the coloring time for tomatoes grown under the 1# carbon-based quantum dot light-conversion composite film. A further comparison of eggplants grown under the same growth cycle revealed that the size of eggplants grown under the 1# carbon-based quantum dot light-conversion composite film increased by over 30% compared to those grown under the PO film.

[0120] 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 steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes preferred embodiments. Although preferred embodiments of the present invention have been described, those skilled in the art will be able to make additional changes and modifications to these embodiments once they understand the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall 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 form a covalent bond, and nitrogen-containing or oxygen-containing functional groups are 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 to 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; The conditions of the solvothermal reaction are: reaction at 60°C~200°C for 1h~50h; The conditions for the pyrolysis reaction are: reaction at 100°C~500°C for 1h~50h; The organic small molecule compound containing a conjugated system is selected from pyrene, aniline or perylene; The cross-linking agent is selected from at least one of urea, citric acid, aluminum nitrate and polyethylene glycol.

2. 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 claim 1, and the particle size of the red fluorescent carbon-based quantum dots is 2nm~10nm.

3. The red fluorescent carbon-based quantum dots according to claim 2, 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.

4. The red fluorescent carbon-based quantum dots according to claim 2, 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.

5. A carbon-based quantum dot light-conversion composite film, characterized in that: The carbon-based quantum dot light-converting composite film is made of the red fluorescent carbon-based quantum dots according to claim 2 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.

6. The carbon-based quantum dot light-conversion composite film according to claim 5, characterized in that: The thickness of the carbon-based quantum dot light-converting composite film is 50 μm~200 μm.

7. The carbon-based quantum dot light-conversion composite film according to claim 5, 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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