Lemon peel-based multicolor luminescent carbon quantum dots and preparation, application and luminescent device thereof

Abstract

This invention belongs to the field of fluorescent materials, specifically lemon peel-based multicolor luminescent carbon quantum dots, their preparation, application, and luminescent devices. The preparation method of lemon peel-based multicolor luminescent carbon quantum dots is as follows: lemon peel and formula 1 () are dispersed in a solvent at a weight ratio of 1:0.1~2, followed by a first-stage reaction at 70~100°C, and then solid-liquid separation to obtain a first-stage reaction solution; the first-stage reaction solution is then subjected to a second-stage solvothermal reaction at 160~220°C. By adjusting the weight ratio of lemon peel and formula 1 and the temperature of the second-stage solvothermal reaction, lemon peel-based multicolor luminescent carbon quantum dots are obtained. This invention can efficiently convert waste lemon peel into multicolor carbon quantum dots with tunable fluorescence color and high quantum yield.

Description

Technical Field

[0001] This invention relates to the field of luminescent materials, specifically to the field of multicolor luminescent carbon quantum dot technology. Background Technology

[0002] Carbon quantum dots (CQDs) are zero-dimensional carbon-based fluorescent nanomaterials typically smaller than 10 nanometers in size. They possess excellent optical properties, good biocompatibility, low toxicity, and ease of functionalization, demonstrating enormous application potential in fields such as bioimaging, optoelectronic devices, chemical sensing, and catalysis. However, traditional synthesis methods using chemical reagents as carbon sources often face challenges such as high cost and potential environmental risks. Utilizing abundant biomass waste as carbon precursors is an important direction for achieving green, sustainable, and low-cost preparation of carbon quantum dots.

[0003] Lemon peel, a type of kitchen waste produced in large quantities, is rich in cellulose, hemicellulose, pectin, citric acid, and various natural oxygen- and nitrogen-containing organic compounds, providing a rich source of carbon skeletons and heteroatoms for the formation of carbon quantum dots. Existing technologies have explored the preparation of carbon quantum dots using lemon peel. For example, Chinese patent document CN116515480A discloses a green synthesis method for lemon peel-based red fluorescent carbon quantum dots. The steps are as follows: washing and drying lemon peel, adding glutathione (reduced form), dispersing it in formamide and sonicating it, transferring the solution to a hydrothermal reactor lined with polytetrafluoroethylene for reaction; after the reactor cools to room temperature, purifying the reaction solution by centrifugation, filtration, and dialysis to obtain a red fluorescent carbon quantum dot solution that emits red light under 395 nm ultraviolet light excitation.

[0004] In summary, although there are reports of using lemon peel to prepare carbon quantum dots with single luminescence characteristics such as red light, the composition of lemon peel is complex, and current technology cannot yet produce high-quality multicolor luminescent carbon quantum dots based on lemon peel in the same raw material system by simply adjusting parameters such as raw material ratio and temperature. Summary of the Invention

[0005] To address the problems existing in the prior art, the primary objective of this invention is to provide a method for preparing lemon peel-based multicolor luminescent carbon quantum dots, aiming to prepare multicolor luminescent carbon quantum dots based on waste lemon peel and the system of Formula 1.

[0006] The second objective of this invention is to provide lemon peel-based multicolor luminescent carbon quantum dots prepared by the aforementioned method and their application as luminescent materials.

[0007] A third objective of this invention is to provide a light-emitting device comprising the aforementioned lemon peel-based multicolor luminescent carbon quantum dots.

[0008] Lemon peel is rich in cellulose, hemicellulose, pectin, citric acid, and various natural oxygen- and nitrogen-containing organic compounds. Its complex composition makes it difficult to efficiently control and produce multicolor luminescent materials. To address this problem, this invention, through in-depth research, provides the following solution:

[0009] A method for preparing lemon peel-based multicolor luminescent carbon quantum dots involves dispersing lemon peel and Formula 1 in a solvent at a weight ratio of 1:0.1~2, followed by a first-stage reaction (atmospheric pressure reaction) at 70~100°C, and then separating the solid and liquid phases to obtain a first-stage reaction solution. The first-stage reaction solution is then subjected to a second-stage solvothermal reaction (pressurized reaction) at a temperature of 160~220°C. By adjusting the weight ratio of lemon peel and Formula 1 and the temperature of the second-stage solvothermal reaction, lemon peel-based multicolor luminescent carbon quantum dots can be obtained.

[0010] Formula 1.

[0011] This invention innovatively employs Formula 1 as a modifier and participates it in the first and second stages of the reaction of lemon peel. Furthermore, by jointly controlling the ratio of lemon peel to the components of Formula 1 and the temperature, multicolor luminescent carbon quantum dots with excellent luminescence properties can be precisely prepared. This method can efficiently convert waste lemon peel into multicolor carbon quantum dots with tunable fluorescence color and high quantum yield.

[0012] In this invention, the weight ratio of lemon peel to Formula 1 is 1:0.1~0.3 (preferably 1:0.15~0.25); the temperature of the second-stage solvothermal reaction is controlled at 160~180℃ (preferably 165~175℃) to obtain blue light emitting carbon quantum dots.

[0013] And / or, the weight ratio of lemon peel to Formula 1 is 1:0.8~1.4 (preferably 1:1.1~1.3); the temperature of the second-stage solvothermal reaction is controlled at 185~200℃ (preferably 190~195℃) to obtain yellow light-emitting carbon quantum dots.

[0014] And / or, the weight ratio of lemon peel to Formula 1 is 1:1.5~2 (preferably 1:1.55~1.65); the reaction temperature is controlled at 200~220℃ (preferably 205~215℃) to obtain red carbon quantum dots.

[0015] In this invention, the solvent is at least one of water and organic solvents; the organic solvents include at least one of C1-C4 alcohols, acetone, formamide, and N,N-dimethylformamide (DMF).

[0016] Water was used as the solvent for preparing blue-emitting carbon quantum dots and yellow-emitting carbon quantum dots; an organic solvent was used for preparing red-emitting carbon quantum dots.

[0017] Preferably, the solid-liquid ratio of lemon peel to solvent in the first stage of the reaction is 10~50mL / g; more preferably, it is 20~30mL / g.

[0018] The temperature of the first stage reaction is 85~95 °C;

[0019] Preferably, the reaction time for the first stage is 0.5 to 2 hours, and more preferably 1 to 2 hours.

[0020] In this invention, the solid-liquid separation after the first stage of reaction can be a conventional solid-liquid separation method such as filtration or centrifugation.

[0021] The second stage of solvothermal activity takes place in a closed container;

[0022] Preferably, the second solvothermal stage lasts for 4–12 hours. For example, the second solvothermal stage for preparing blue-emitting carbon quantum dots lasts for 5–7 hours. The second solvothermal stage for preparing yellow-emitting carbon quantum dots lasts for 7–9 hours. The second solvothermal stage for preparing red-emitting carbon quantum dots lasts for 9–11 hours.

[0023] The present invention also provides a lemon peel-based multicolor luminescent carbon quantum dot prepared by the aforementioned method.

[0024] The present invention also provides an application of the lemon peel-based multicolor luminescent carbon quantum dots prepared by the above preparation method, using them as luminescent materials to prepare luminescent devices;

[0025] Preferably, it is used as a luminescent material to prepare luminescent LEDs.

[0026] The present invention also provides a light-emitting device comprising lemon peel-based multicolor light-emitting carbon quantum dots prepared by the aforementioned method;

[0027] Preferably, the light-emitting device is a light-emitting LED.

[0028] Beneficial effects

[0029] This invention innovatively employs Formula 1 as a modifier and participates it in the first stage of the atmospheric pressure reaction of lemon peel and the subsequent second stage of the solvothermal reaction. Furthermore, by jointly controlling the ratio of lemon peel to the components of Formula 1 and the temperature, multicolor luminescent carbon quantum dots with excellent luminescence properties can be precisely prepared. This invention enables the efficient resource utilization of lemon peel waste, and based on the combined control of Formula 1, the ratio, and the first stage temperature, carbon quantum dot materials with different luminescence properties can be easily and artificially controlled. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the overall process of the method described in this invention, showing the complete process from waste lemon peels to multicolor carbon quantum dots, and then to LED devices.

[0031] Figure 2 Transmission electron microscopy (TEM) images of the blue (B-CQDs), yellow (Y-CQDs), and red (R-CQDs) carbon quantum dots prepared in Examples 1, 2, and 3, showing their morphological features with a size of less than 10 nm.

[0032] Figure 3 The normalized fluorescence emission spectra of the carbon quantum dots prepared in Examples 1, 2, and 3 (excitation wavelengths of 360 nm, 450 nm, and 500 nm, respectively) demonstrate their tunable multicolor luminescence properties.

[0033] Figure 4 The image shows the emission spectrum of the warm white LED device prepared in Example 4 on a spectrophotometer, with the spectral coverage ratio shown.

[0034] Figure 5 These are the CIE3912K chromaticity map coordinates of the warm white LED prepared in Example 4 (shown as the vicinity of the center of the white area). Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. The following embodiments are for illustrative purposes only and should not be considered as limitations on the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0036] The technical solution of this application will be described in detail below with reference to specific embodiments.

[0037] The preparation steps of the material described in this invention are as follows:

[0038] S1. Raw material pretreatment: a. Collect fresh or dried waste lemon peels and wash them repeatedly with deionized water to remove surface dirt and some water-soluble sugars. b. Dry the washed lemon peels in an oven at 60-80°C until constant weight. c. Crush the dried lemon peels using a grinder, sieve (e.g., 60-200 mesh sieve) to obtain uniform lemon peel powder, and seal and store for later use.

[0039] S2. Preparation of the reaction precursor solution:

[0040] Lemon peel and Formula 1 were dispersed in a solvent and sealed in a pressure-resistant reactor for the first stage of reaction.

[0041] The mass ratio of lemon peel powder to Formula 1 is one of the key parameters for controlling the emission color, with a preferred range of 1:0.1 to 1:2. For example, a ratio close to 1:0.2 favors blue light emission, a ratio close to 1:1.2 favors yellow light emission, and a ratio close to 1:1.6 favors red light emission. d. Solvent: Deionized water is preferred due to its environmental friendliness. Polar organic solvents such as formamide and N,N-dimethylformamide (DMF) can also be used to adjust the polarity and carbonization degree of the reaction system. e. Preparation: Accurately weighed lemon peel powder and Formula 1 are added to a certain volume (total volume 20~50mL, solid-liquid ratio can be adjusted as needed) of solvent. Magnetic stirring and water bath treatment (temperature 70~100℃, time 0.5~1 hour) are used to ensure thorough mixing and dispersion. After heating, the supernatant is collected by centrifugation or filtration.

[0042] S3. Solvent Thermothermal (Hydrothermal): a. Transfer the supernatant to a stainless steel high-pressure reactor with a polytetrafluoroethylene liner, maintaining a filling density of 60-80%. b. Seal the reactor and place it in a programmable temperature-controlled oven, heating it to the target reaction temperature at a controlled rate (3-5°C / min). c. Reaction Temperature and Time: Reaction temperature and time are another set of key control parameters. The preferred reaction temperature range is 160-220 °C, and the preferred reaction time is 4-12 hours.

[0043] Part Two: A method for fabricating high-performance LED devices based on multicolor carbon quantum dots. The carbon quantum dots of different colors prepared by the above method are used as fluorescence conversion materials (to replace or partially replace traditional rare earth phosphors) and applied to LED packaging.

[0044] Preparation of fluorescent composite materials: a. Matrix selection: Select optically transparent polymers with good stability and high compatibility as the matrix, such as epoxy resin (e.g., A / B glue), silicone resin, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), etc. b. Dispersion and mixing: Mix one or more colors (blue B-CQDs, yellow Y-CQDs, red R-CQDs) of carbon quantum dots in aqueous dispersion or solid powder with a pre-prepared polymer solution or prepolymer. To improve dispersibility, a small amount of surfactant can be added or ultrasonic treatment can be performed. c. Ratio: The mass fraction of carbon quantum dots in the composite material needs to be optimized, usually between 0.1% and 5%. Too low a ratio will result in weak fluorescence, while too high a ratio may cause concentration quenching or affect the mechanical properties of the material.

[0045] LED Chips and Packaging: a. Chip Selection: Select the LED chip based on the target emission color. For white LEDs, near-ultraviolet (n-UV) chips with an emission wavelength of 365~395nm or blue chips with an emission wavelength of 450~470nm are typically chosen. b. Packaging Process: For near-ultraviolet chips: A fluorescent composite material mixed with blue, yellow, and red (or other proportions) multi-color carbon quantum dots can be uniformly covered on the chip surface and surrounding area through dispensing, potting, or coating. The composite material absorbs near-ultraviolet light and excites visible light of different colors, mixing to form white light. For blue chips: A carbon quantum dot composite material that mainly absorbs blue light and emits yellow / red light (or yellow-green + red light) is typically coated on the chip. The blue light emitted by the chip itself and the yellow / red light emitted by the excited carbon quantum dots complement each other and mix to form white light. c. Curing: Depending on the properties of the selected polymer matrix, curing is carried out by heating (e.g., 80~100°C, 0.5~1.5 hours) or ultraviolet light irradiation to form a stable phosphor conversion layer and complete the primary packaging of the LED device.

[0046] Performance Control: a. Color Coordinate and Color Temperature Control: By changing the types and relative proportions of different colored carbon quantum dots in the fluorescent composite material, the color coordinates (x, y) and correlated color temperature (CCT) of the final emitted light can be precisely adjusted. For example, increasing the proportion of red carbon quantum dots makes white light "warmer" (lower color temperature), and vice versa. b. Color Rendering Index Optimization: By rationally combining carbon quantum dots of various colors (especially red components), the emitted light spectrum of the LED can be broadened, making it more continuous and closer to the solar spectrum, thereby significantly improving the color rendering index (Ra, CRI) of the device to 80~93, meeting the requirements of high-quality lighting.

[0047] In this invention, the weight of the lemon peel refers to its dry weight.

[0048] Example 1

[0049] This embodiment provides a method for preparing blue fluorescent carbon quantum dots (B-CQDs) and blue LEDs, comprising the following steps:

[0050] Step S1: Preparation of carbon quantum dots:

[0051] Step S1-1: First stage reaction:

[0052] Take 1.0 g of pretreated lemon peel powder and 0.2 g of Formula 1, and place them in a 50 mL beaker. Add 30 mL of deionized water, stir magnetically for 30 minutes, and then sonicate (300 W) for 30 minutes to form a uniform brown suspension. Place the mixed suspension in a water bath and heat at 90 °C for 1 hour. After the reaction is complete, centrifuge and collect the supernatant.

[0053] Step S1-2: Second stage reaction:

[0054] The supernatant from step S1-1 was transferred to a 50 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE), with a filling density of approximately 70%. The reactor was placed in an oven and heated to 170°C (heating rate ~5°C / min), and maintained at this temperature for 6 hours. After the reaction, the mixture was allowed to cool naturally. The resulting dark brown liquid was centrifuged at 10,000 rpm for 15 minutes, and the supernatant was collected. The supernatant was dialyzed against deionized water using a dialysis bag with a molecular weight cutoff of 1000 Da for 48 hours, with the water changed every 8 hours. The clear, pale blue solution after dialyzing was freeze-dried to obtain a pale blue solid powder, designated B-CQDs. Under 365 nm UV light irradiation, the B-CQDs aqueous solution emitted bright blue fluorescence. The fluorescence spectrum showed that its maximum emission wavelength was at ~460 nm (excitation wavelength 360 nm). Transmission electron microscopy showed that its particle size distribution was uniform, with an average size of approximately 2.8 nm. XPS analysis confirmed the presence of C, N, O, and S elements, indicating successful doping.

[0055] Step S2: Blue LED fabrication: 10 mg of B-CQDs solid powder was dispersed in 1 mL of a 10 wt% polyvinylpyrrolidone (PVP) aqueous solution and ultrasonically dispersed to form a uniform dispersion. Using a spin-coating method, the dispersion was drop-coated onto the surface of a commercial UV LED chip with an emission wavelength of 395 nm. The chip was dried in an 80°C oven for 2 hours to form a uniform fluorescent film. The chip was soldered onto an LED substrate using conventional processes, followed by wire bonding and encapsulation with transparent silicone for protection. Upon power-up testing, the device emitted bright blue light.

[0056] Example 2

[0057] Compared with Example 1, the main difference lies in changing the ratio of lemon slices to Formula 1 in step S1-1 and the temperature of the hydrothermal treatment. Specifically,

[0058] Step S1: Preparation of carbon quantum dots: Take 1.0 g of lemon peel powder and 1.2 g of Formula 1, add 30 mL of deionized water, and ultrasonically disperse evenly. Then, place the mixture in a water bath and heat at 90°C for 1 hour. After the reaction is complete, centrifuge and collect the supernatant. Place the supernatant in a 50 mL reaction vessel and react at 190°C for 8 hours. Subsequent purification steps are the same as in Example 1, yielding a yellow solid powder, denoted as Y-CQDs. The aqueous solution of Y-CQDs emits bright yellow fluorescence under a 365 nm UV lamp. The maximum fluorescence emission wavelength is located at ~570 nm (excitation wavelength 450 nm). The average particle size is approximately 4.2 nm.

[0059] Step S2: Yellow LED Preparation: 15 mg of Y-CQDs powder and 1.0 g of transparent epoxy resin (components A and B pre-mixed according to the instructions) were thoroughly ground, stirred, and mixed evenly, and then degassed under vacuum. The mixed fluorescent epoxy resin was then dispensed onto a commercially available blue LED chip with an emission wavelength of 450 nm. The chip was cured at 80°C for 2 hours. After encapsulation and testing, the device emitted pure yellow light when excited by the 450 nm blue LED chip.

[0060] Example 3

[0061] This embodiment provides a method for preparing red fluorescent carbon quantum dots (R-CQDs) and red LEDs, comprising the following steps:

[0062] Step S1: Preparation of carbon quantum dots: Take 1.0 g of lemon peel powder and 1.6 g of Formula 1, add 25 mL of formamide solvent, ultrasonically disperse, and then heat in a water bath at 90°C for 1 hour. After the reaction is complete, centrifuge and collect the supernatant. Place the supernatant in a 50 mL reaction vessel and react at 210°C for 10 hours. After the reaction solution cools, precipitate once with ethanol to remove some macromolecular impurities, centrifuge, redisperse in water, and then dialysis for purification (method as in Example 1). After freeze-drying, a reddish-brown solid powder is obtained, denoted as R-CQDs. The aqueous solution of R-CQDs emits deep red fluorescence under a 395 nm UV lamp. The maximum fluorescence emission wavelength is at ~630 nm (excitation wavelength 500 nm). The average particle size is approximately 5.5 nm.

[0063] Step S2: Red LED fabrication: 20 mg of R-CQDs powder was uniformly dispersed in 1.0 g of high-transmittance silicone rubber (A / B adhesive), and vacuum degassed. The mixed fluorescent silicone rubber was then encapsulated in a bowl containing a commercially available UV LED chip with an emission wavelength of 395 nm. The mixture was cured at 120°C for 1 hour. After encapsulation, the device emitted bright red light.

[0064] Example 4

[0065] This embodiment provides a method for preparing a high color rendering index warm white LED, comprising the following steps:

[0066] Phosphor preparation: 5 mg of B-CQDs prepared in Example 1, 20 mg of Y-CQDs prepared in Example 2, and 10 mg of R-CQDs prepared in Example 3 were weighed and added to 350 mg of starch (CQDs:polymer = 10% wt%). The mixture was stirred at room temperature for 8 h. The mixture was then dried in an oven at 80°C to obtain a CQDs / starch fluorescent composite material. The composite material was ground into powder in an agate mortar. 100 mg of silica gel resin (A glue): 400 mg of B glue (A glue:B glue = 1:4 wt / wt) and 60 mg of phosphor were weighed and mixed. The mixture was rapidly stirred until homogeneous and then degassed under vacuum to prepare a fluorescent silica gel composite material.

[0067] LED Packaging: A commercially available high-power ultraviolet LED chip with an emission wavelength of 395nm was selected. The prepared fluorescent silicone composite material was encapsulated into the bowl of the SMD bracket containing the ultraviolet LED chip, ensuring that the chip was completely covered. The mixture was then heated at 150°C for 0.5 hours to allow the silicone to fully cure.

[0068] Performance Testing: The packaged LED device was tested using a spectrophotometer system. Test Results: The device emits bright white light. Its color coordinates are (0.38, 0.36), located in the white light region. The correlated color temperature (CCT) is 4000K, belonging to neutral white light. The color rendering index (Ra) reaches 90. At a drive current of 350mA, the luminous efficacy is 85lm / W. After 1000 hours of continuous operation, the luminous flux maintenance rate is above 95%, demonstrating good stability.

[0069] Comparative Example 1

[0070] Compared with Examples 1-3, the only difference is that Formula 1 is not added:

[0071] The experimental group and the results are as follows:

[0072] Group A:

[0073] Compared with Example 1, the only difference is that Formula 1 was not added. All other operations and parameters are the same as in Example 1. The resulting carbon quantum dot aqueous solution only emits weak blue fluorescence under ultraviolet light, and the quantum yield is 1.0%. However, the quantum yield of Example 1 is 28.3%.

[0074] Group B:

[0075] Compared with Example 2, the only difference is that Formula 1 was not added. All other operations and parameters are the same as in Example 2. The resulting carbon quantum dot aqueous solution only emits weak blue fluorescence under ultraviolet light, and the quantum yield is 1.8%. However, the quantum yield of Example 2 is 21.5%.

[0076] Group C:

[0077] Compared with Example 3, the only difference is that Formula 1 was not added. The other operations and parameters are the same as in Example 3. The carbon quantum dot aqueous solution obtained in Example 3 only emits weak blue fluorescence under ultraviolet light and has a quantum yield of 2.0%. However, the quantum yield of Example 3 is 18.4%.

[0078] It is evident that without the addition of Formula 1, it is difficult to obtain carbon quantum dots with the expected high fluorescence quantum yield, and it is also impossible to prepare materials with different luminescent properties by controlling the ratio.

[0079] Comparative Example 2

[0080] Compared with Examples 1-3, the only difference is that an equal weight of urea is used to replace Form 1.

[0081] The experimental group and the results are as follows:

[0082] Group A:

[0083] Compared with Example 1, the only difference is that an equal weight of urea was used to replace Formula 1. Other operations and parameters were the same as in Example 1. The resulting carbon quantum dot aqueous solution emitted only blue fluorescence under ultraviolet light, and the quantum yield was 7.5%. However, the quantum yield of Example 1 was 28.3%.

[0084] Group B:

[0085] Compared with Example 2, the only difference is that an equal weight of urea was used to replace Formula 1. Other operations and parameters were the same as in Example 2. The resulting carbon quantum dot aqueous solution emitted only blue fluorescence under ultraviolet light, and the quantum yield was 8.0%. However, the quantum yield of Example 2 was 21.5%.

[0086] Group C:

[0087] Compared with Example 3, the only difference is that an equal weight of urea was used to replace Formula 1. Other operations and parameters were the same as in Example 3. The carbon quantum dot aqueous solution obtained in Example 3 only emitted blue-green fluorescence under ultraviolet light, and the quantum yield was 8.5%. However, the quantum yield of Example 3 was 18.4%.

[0088] It is evident that by replacing Form 1 with an equal weight of urea, it is difficult to obtain carbon quantum dots with the expected high fluorescence quantum yield, and it is also impossible to obtain materials with different luminescence properties by controlling the ratio.

[0089] Comparative Example 3

[0090] Compared with Examples 1-3, the only difference is that glycine of equal weight is used to replace Formula 1.

[0091] The experimental group and the results are as follows:

[0092] Group A:

[0093] Compared with Example 1, the only difference is that glycine of equal weight was used to replace Formula 1. Other operations and parameters are the same as in Example 1. The resulting carbon quantum dot aqueous solution emits only blue fluorescence under ultraviolet light, and the quantum yield is 8.5%. However, the quantum yield of Example 1 is 28.3%.

[0094] Group B:

[0095] Compared with Example 2, the only difference is that glycine of equal weight was used to replace Formula 1. Other operations and parameters are the same as in Example 2. The resulting carbon quantum dot aqueous solution emits only blue fluorescence under ultraviolet light, and the quantum yield is 9.0%. However, the quantum yield of Example 2 is 21.5%.

[0096] Group C:

[0097] Compared with Example 3, the only difference is that glycine of equal weight was used to replace Formula 1. Other operations and parameters are the same as in Example 3. The carbon quantum dot aqueous solution obtained in Example 3 only emits blue-green fluorescence under ultraviolet light, and the quantum yield is 9.8%. However, the quantum yield of Example 3 is 18.4%.

[0098] It is evident that by replacing Formula 1 with an equal weight of glycine, it is difficult to obtain the desired fluorescent carbon quantum dots, and it is impossible to prepare materials with different luminescent properties by controlling the ratio.

[0099] Comparative Example 4

[0100] Compared with Examples 1-3, the only difference is that banana peel of equal weight is used instead of lemon peel.

[0101] The experimental group and the results are as follows:

[0102] Group A:

[0103] Compared with Example 1, the only difference is that banana peels of equal weight were used instead of lemon peels. All other operations and parameters were the same as in Example 1. The resulting carbon quantum dot aqueous solution emitted only weak blue fluorescence under ultraviolet light, and the quantum yield was 1.5%. However, the quantum yield of Example 1 was 28.3%.

[0104] Group B:

[0105] Compared with Example 2, the only difference is that glycine of equal weight was used to replace Formula 1. Other operations and parameters are the same as in Example 2. The resulting carbon quantum dot aqueous solution only emits weak blue fluorescence under ultraviolet light, and the quantum yield is 1.9%. However, the quantum yield of Example 2 is 21.5%.

[0106] Group C:

[0107] Compared with Example 3, the only difference is that glycine of equal weight was used to replace Formula 1. Other operations and parameters are the same as in Example 3. The carbon quantum dot aqueous solution obtained in Example 3 only emits blue fluorescence under ultraviolet light, and the quantum yield is 5.0%. However, the quantum yield of Example 3 is 18.4%.

[0108] It is evident that replacing lemon peel with an equal weight of banana peel makes it difficult to obtain the desired fluorescent carbon quantum dots, and it is also impossible to obtain materials with different luminescent properties by controlling the ratio.

[0109] Comparative Example 5

[0110] Compared with Examples 1-3, the only difference is that the high-temperature and high-pressure heating of the sealed reaction vessel in step S1-2 was not performed.

[0111] The experimental group and the results are as follows:

[0112] Group A:

[0113] Compared with Example 1, the only difference is that the high temperature and high pressure heating of the sealed reaction vessel in step S1-2 was not performed. Other operations and parameters were the same as in Example 1. The resulting carbon quantum dot aqueous solution emitted only extremely weak blue fluorescence under ultraviolet light, and the quantum yield was 0.2%. However, the quantum yield of Example 1 was 28.3%.

[0114] Group B:

[0115] Compared with Example 2, the only difference is that the high temperature and high pressure heating of the sealed reaction vessel in step S1-2 was not performed. Other operations and parameters were the same as in Example 2. The resulting carbon quantum dot aqueous solution emitted only weak blue fluorescence under ultraviolet light, and the quantum yield was 0.3%. However, the quantum yield of Example 2 was 21.5%.

[0116] Group C:

[0117] Compared with Example 3, the only difference is that the high temperature and high pressure heating of the sealed reaction vessel in step S1-2 was not performed. Other operations and parameters were the same as in Example 3. The resulting carbon quantum dot aqueous solution emitted only weak blue fluorescence under ultraviolet light, and the quantum yield was 0.5%. However, the quantum yield of Example 3 was 18.4%.

[0118] It is evident that without the high-temperature and high-pressure heating in the sealed reactor in step S1-2, it is difficult to obtain the expected fluorescent carbon quantum dots, and it is also impossible to obtain materials with different luminescent properties by controlling the proportions.

[0119] Comparative Example 6

[0120] Compared with Examples 1-3, the only difference is that the first stage is omitted, and the mixed solution is directly heated at high temperature and high pressure in the closed reaction vessel in step S1-2.

[0121] The experimental group and the results are as follows:

[0122] Group A:

[0123] Compared with Example 1, the only difference is that the first stage of step S1-1 was not performed. All other operations and parameters are the same as in Example 1. The resulting carbon quantum dot aqueous solution only emits blue fluorescence under ultraviolet light, and the quantum yield is 8.5%. However, the quantum yield of Example 1 is 28.3%.

[0124] Group B:

[0125] Compared with Example 2, the only difference is that the first stage of step S1-1 was not performed. All other operations and parameters are the same as in Example 2. The resulting carbon quantum dot aqueous solution only emits blue fluorescence under ultraviolet light, and the quantum yield is 15.0%. However, the quantum yield of Example 2 is 21.5%.

[0126] Group C:

[0127] Compared with Example 3, the only difference is that the first stage of step S1-1 was not performed. The other operations and parameters are the same as in Example 3. The resulting carbon quantum dot aqueous solution only emits blue-green fluorescence under ultraviolet light, and the quantum yield is 9.8%. However, the quantum yield of Example 3 is 18.4%.

[0128] It is evident that without the first stage of processing S1-1, it is difficult to obtain the desired fluorescent carbon quantum dots, and it is impossible to prepare materials with different luminescent properties by controlling the proportions.

[0129] Comparative Example 7

[0130] Compared to Examples 1-3, the only difference is that Formula 1 is not added in step S1-1, but rather in step S1-2. The experimental groups and results are as follows:

[0131] Group A:

[0132] Compared with Example 1, the only difference is that Formula 1 is not added in step S1-1, but added in step S1-2. Other operations and parameters are the same as in Example 1. The resulting carbon quantum dot aqueous solution emits only blue fluorescence under ultraviolet light, and the quantum yield is 8.5%. However, the quantum yield of Example 1 is 28.3%.

[0133] Group B:

[0134] Compared with Example 2, the only difference is that Formula 1 is not added in step S1-1, but added in step S1-2. Other operations and parameters are the same as in Example 2. The resulting carbon quantum dot aqueous solution emits only blue fluorescence under ultraviolet light, and the quantum yield is 10.0%. However, the quantum yield of Example 2 is 21.5%.

[0135] Group C:

[0136] Compared with Example 3, the only difference is that Formula 1 is not added in step S1-1, but added in step S1-2. Other operations and parameters are the same as in Example 3. The resulting carbon quantum dot aqueous solution emits only blue-green fluorescence under ultraviolet light, and the quantum yield is 9.0%. However, the quantum yield of Example 3 is 18.4%.

[0137] It is evident that formula 1 is not added in step S1-1, but rather in step S1-2, making it difficult to obtain the desired fluorescent carbon quantum dots and impossible to prepare materials with different luminescent properties by controlling the proportion.

[0138] Comparative Example 8

[0139] Compared with Examples 1-3, the only difference is that in step S1-1, lemon slices were replaced with an equal weight of citric acid. The experimental groups and results are as follows:

[0140] Group A:

[0141] Compared with Example 1, the only difference is that lemon slices were replaced with an equal weight of citric acid. All other operations and parameters were the same as in Example 1. The resulting carbon quantum dot aqueous solution emitted only blue fluorescence under ultraviolet light, and the quantum yield was 20.0%. However, the quantum yield of Example 1 was 28.3%.

[0142] Group B:

[0143] Compared with Example 2, the only difference is that lemon slices were replaced with an equal weight of citric acid. All other operations and parameters were the same as in Example 2. The resulting carbon quantum dot aqueous solution emitted only blue-green fluorescence under ultraviolet light, and the quantum yield was 15.0%. However, the quantum yield of Example 2 was 21.5%.

[0144] Group C:

[0145] Compared with Example 3, the only difference is that lemon slices were replaced with an equal weight of citric acid. All other operations and parameters were the same as in Example 3. The resulting carbon quantum dot aqueous solution emitted only yellow-green fluorescence under ultraviolet light, and the quantum yield was 10.0%. However, the quantum yield of Example 3 was 18.4%.

[0146] It is evident that replacing lemon slices with an equal weight of citric acid makes it difficult to obtain the desired fluorescent carbon quantum dots, and it is also impossible to control the ratio to produce materials with different luminescent properties.

[0147] Experimental Results Analysis: By comparing Examples 1-4 with Comparative Examples 1-8, it is fully demonstrated that the combination of lemon slices and Formula 1, along with the two-stage reaction approach described above, can unexpectedly achieve synergy. Through the combined control of the proportions, carbon quantum dots with different fluorescence can be obtained in the same system.

[0148] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing lemon peel-based multicolor luminescent carbon quantum dots, characterized in that, Lemon peel and Formula 1 were dispersed in a solvent at a weight ratio of 1:0.1~2, and then a first-stage reaction was carried out at a temperature of 70~100°C. After solid-liquid separation, a first-stage reaction solution was obtained. The first-stage reaction solution was then subjected to a second-stage solvothermal reaction at a temperature of 160~220°C. By adjusting the weight ratio of lemon peel and Formula 1 and the temperature of the second-stage solvothermal reaction, lemon peel-based multicolor luminescent carbon quantum dots were prepared. Formula 1.

2. The method for preparing lemon peel-based multicolor luminescent carbon quantum dots as described in claim 1, characterized in that, The weight ratio of lemon peel to Formula 1 is 1:0.1~0.3; the temperature of the second-stage solvothermal reaction is controlled at 160~180℃ to obtain blue light emitting carbon quantum dots; And / or, the weight ratio of lemon peel to Formula 1 is 1:0.8~1.4; the temperature of the second-stage solvothermal reaction is controlled at 185~200℃ to obtain yellow light-emitting carbon quantum dots; And / or, the weight ratio of lemon peel to Formula 1 is 1:1.5~2; the reaction temperature is controlled at 200~220℃ to obtain red carbon quantum dots.

3. The method for preparing lemon peel-based multicolor luminescent carbon quantum dots as described in claim 1, characterized in that, The solvent is at least one of water and organic solvents; the organic solvents include at least one of C1-C4 alcohols, acetone, formamide, and N,N-dimethylformamide (DMF).

4. The method for preparing lemon peel-based multicolor luminescent carbon quantum dots as described in claim 3, characterized in that, Water was used as the solvent for preparing blue-emitting carbon quantum dots and yellow-emitting carbon quantum dots; an organic solvent was used for preparing red-emitting carbon quantum dots. Preferably, the solid-liquid ratio of lemon slices to solvent in the first reaction process is 10~50mL / g; more preferably, it is 20~30mL / g.

5. The method for preparing lemon peel-based multicolor luminescent carbon quantum dots as described in claim 1, characterized in that, The temperature of the first stage reaction is 85~95 °C; Preferably, the reaction time for the first stage is 0.5 to 2 hours.

6. The method for preparing lemon peel-based multicolor luminescent carbon quantum dots as described in claim 4, characterized in that, The second stage of solvothermal activity takes place in a closed container; Preferably, the second stage of solvothermal activity lasts for 4 to 12 hours.

7. A lemon peel-based multicolor luminescent carbon quantum dot prepared by the method according to any one of claims 1 to 6.

8. The application of the lemon peel-based multicolor luminescent carbon quantum dots prepared by the method according to any one of claims 1 to 6, characterized in that, It can be used as a luminescent material to prepare luminescent devices.

9. The application as described in claim 8, characterized in that, It can be used as a luminescent material to prepare luminescent LEDs.

10. A light-emitting device, characterized in that, It includes lemon peel-based multicolor luminescent carbon quantum dots prepared by the preparation method according to any one of claims 1 to 6; Preferably, the light-emitting device is a light-emitting LED.

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