Method and application of hydrothermal preparation of PET-based carbon dots

Abstract

The present invention provides PET-based carbon dots and a preparation method thereof. The PET (polyethylene terephthalate)-based carbon dots are prepared by a one-step hydrothermal method using a carbon source and a nitrogen source as main raw materials, avoiding the alcohol degradation process of PET. The preparation method is simple. The PET-based carbon dots have the advantages of high fluorescence intensity and fluorescence quantum yield. The PET-based carbon dots have excellent fluorescence stability and strong anti-interference ability in different metal ion solutions and different pH solutions. In addition, they have the advantages of low biotoxicity and good biosafety, and can be used as luminescent markers for in vivo detection and imaging. The light-blocking film obtained using the PET-based carbon dots as raw materials has excellent blocking capabilities against ultraviolet light, blue light, light emitted by mobile phone screens, and natural light. The PET-based carbon dots have excellent performance and good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of fluorescent nanomaterials, and in particular to a method for preparing PET-based carbon dots using a one-step hydrothermal method and its application. Background Art

[0002] Carbon dots, a novel fluorescent nanomaterial composed primarily of carbon atoms, have become a hot topic of research due to their excellent optical properties, biocompatibility, simple preparation methods, and low cost. They possess significant application value across a wide range of fields, with promising applications in biomedicine, anti-counterfeiting, sensing, catalysis, imaging, light-emitting diodes, solar cells, and photovoltaic devices.

[0003] Due to population growth and rising living standards, global fiber consumption has steadily increased over the past few decades, leading to a dramatic increase in textile waste. Simply landfilling or incinerating textile waste not only creates environmental problems but also depletes petroleum resources. Therefore, finding the best way to utilize textile waste is of vital importance.

[0004] Polyethylene terephthalate (PET) is the largest-volume chemical fiber. It generates a large amount of waste each year, putting enormous pressure on the environment. Therefore, its reuse is essential. Approximately 70 million tons of PET are produced annually for packaging and textiles, of which only a small portion (less than 20%) is recycled, resulting in poor environmental performance. Currently, common PET (polyethylene terephthalate) recycling methods are mainly categorized into three types: physical, chemical, and physicochemical. Today, with severe environmental pollution, society is strongly advocating for green recycling. Not only should physical recycling, a more environmentally friendly method, be used more frequently, but new green chemical recycling methods should also be explored to minimize resource waste and protect the environment. Therefore, the efficient recovery and utilization of PET waste has become a hot topic of widespread concern both domestically and internationally.

[0005] Any substance containing carbon atoms can serve as a raw material for carbon dots. PET, with its numerous benzene rings and relatively high carbon content, has the potential to serve as a carbon dot precursor. Therefore, exploring the preparation of carbon dots using PET as a precursor could provide insights into the high-value recycling of PET waste.

[0006] It can be seen that the research on the preparation and application of carbon dots with PET as the precursor can not only provide new ideas for the high value-added utilization of textile waste, but also be helpful in solving the environmental pollution and oil resource depletion problems caused by textile waste. Summary of the Invention

[0007] Based on the above technical background, the inventors have made great progress and found that the PET-based carbon dots prepared by a one-step hydrothermal method using waste PET (polyethylene terephthalate) as the main carbon source and doped with a nitrogen source have the advantages of high fluorescence intensity and fluorescence quantum yield. The PET-based carbon dots also have the advantages of low biotoxicity and good biosafety. In a high-concentration PET-based carbon dot solution, a large number of cells still maintain biological activity. The light-blocking film obtained using the PET-based carbon dots as raw material is resistant to ultraviolet light. 、 Blu-ray 、 The carbon dots have excellent barrier capabilities for both light emitted from mobile phone screens and natural light. In addition, they have good stability in different metal ion solutions and different pH solutions. They can be used in in vivo detection, cell imaging, LEDs, fluorescent anti-counterfeiting, fluorescent inks, and light-blocking films. They have broad application prospects and have opened up new channels for the reuse of waste PET, thus completing the present invention.

[0008] The first aspect of the present invention is to provide a PET-based carbon dot, wherein the fluorescence quantum yield of the PET-based carbon dot is as high as 85% or more;

[0009] When the concentration of PET-based carbon dots solution was 200 μg / mL, more than 70% of cells still maintained biological activity.

[0010] The second aspect of the present invention is to provide a method for preparing the PET-based carbon dots described in the first aspect of the present invention, wherein the preparation method mainly uses a carbon source and a nitrogen source as raw materials through a one-step hydrothermal method.

[0011] The third aspect of the present invention is to provide an application of the PET-based carbon dots according to the first aspect of the present invention or the PET-based carbon dots prepared by the preparation method described in the second aspect of the present invention, which can be used in in vivo detection, cell imaging, LED, fluorescent anti-counterfeiting, fluorescent ink and light-blocking film. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 a and 1b respectively show the transmission electron microscopy image and particle size distribution diagram of the carbon dots prepared in Example 1;

[0013] Figure 2 a and 2b respectively show the transmission electron microscopy image and particle size distribution diagram of the carbon dots prepared in Example 4;

[0014] Figure 3a The UV-visible absorption spectrum of the carbon dots prepared in Example 1 is shown;

[0015] Figure 3b and 3c The fluorescence emission spectra of carbon dots prepared in Example 1 and Example 4 are shown respectively;

[0016] FIG4 shows the XPS spectrum of carbon dots prepared in Example 1;

[0017] Figure 5a and 5b The absolute fluorescence quantum yield spectra of the carbon dots prepared in Example 1 and Example 4 are shown respectively;

[0018] Figure 6 A histogram showing the fluorescence intensity of carbon dots prepared in Example 1 in different metal ion solutions;

[0019] Figure 7 A histogram showing the fluorescence intensity of carbon dots prepared in Example 4 in different metal ion solutions;

[0020] Figure 8 The fluorescence intensity histogram of the carbon dots prepared in Example 1 in solutions with different pH values ​​is shown;

[0021] Figure 9 and Figure 10 The biological toxicity test diagrams of the carbon dots prepared in Example 1 and Example 4 at different concentrations are shown respectively;

[0022] FIG11 shows a fluorescence spectrum of a light-blocking film prepared using carbon dots as raw materials in Example 1;

[0023] FIG12 shows the blocking effect of the light-blocking film made with carbon dots in Example 1 on ultraviolet light and blue light;

[0024] FIG13 shows the blocking effect of the light-blocking film made from carbon dots in Example 1 on mobile phone screen light and natural light;

[0025] Figure 14 14a and 14b respectively show the spectrum and color coordinate diagram of the LED device prepared using the carbon dots in Example 1 as raw materials. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below, and the characteristics and advantages of the present invention will become clearer and more distinct with the following description.

[0027] The first aspect of the present invention is to provide a PET-based carbon dot, which is prepared by a one-step hydrothermal method using a carbon source and a nitrogen source as main raw materials.

[0028] The carbon source is selected from one or more of polyethylene terephthalate (i.e., PET), trimellitic acid, pyromellitic acid, pyromellitic anhydride, pyromellitic ester, trimellitic ester, and trimellitic ester, preferably selected from one or more of polyethylene terephthalate, trimesic acid, pyromellitic acid, pyromellitic anhydride, pyromellitic ester, and trimellitic ester, more preferably one or more of polyethylene terephthalate, trimesic acid, and pyromellitic acid.

[0029] The inventors discovered that carbon dots produced using this carbon source exhibit high fluorescence quantum yields. Furthermore, their fluorescence intensity is resistant to interference from metal ions and changes in solution pH, exhibiting excellent fluorescence stability, low biotoxicity, and excellent biosafety. Furthermore, this method opens up new avenues for the reuse of waste PET and reduces environmental pollution.

[0030] When the carbon source is polyethylene terephthalate and pyromellitic acid, the mass ratio of pyromellitic acid to polyethylene terephthalate is (1-4):1, preferably (1.2-3):1, and more preferably (1.3-2.5):1.

[0031] The nitrogen source is selected from one or more nitrogen-containing compounds, preferably one or more selected from hydrazine hydrate, ammonia water, urea, and ethylenediamine, more preferably one or two selected from ammonia water and urea, for example, ammonia water.

[0032] Heteroatom doping is an effective and versatile technique for further improving the chemical composition and structural properties of carbon dots. Nitrogen atom doping is currently the most widely used and effective method. This is likely because nitrogen atoms, with five valence electrons and a size comparable to carbon atoms, more readily incorporate into the carbon backbone within the carbon core for heteroatom doping. Experimental results have shown that PET-based carbon dots prepared using ammonia as the nitrogen dopant exhibit high fluorescence quantum yields exceeding 85%.

[0033] The mass ratio of the polyethylene terephthalate to the nitrogen source is (0.04-0.1):1, preferably (0.05-0.09):1, and more preferably (0.06-0.08):1.

[0034] The amount of nitrogen source added as a dopant should not be too much, as too much dopant is not conducive to improving the performance of PET-based carbon dots.

[0035] The PET-based carbon dots of the present invention have optimal excitation and emission wavelengths of 400-450 nm and 460-500 nm, respectively. They are non-excitation wavelength-dependent, emit light in the carbon core state, and have a fluorescence quantum yield of over 85%. They emit bright blue-green fluorescence under excitation of a 365 nm ultraviolet lamp.

[0036] The PET-based carbon dots have a quasi-spherical structure, are evenly distributed without agglomeration, have a particle size range of 1.1 to 3.1 nm, and contain amino and carboxyl groups on the surface.

[0037] The PET-based carbon dots have the advantages of low biotoxicity and good biosafety. When the concentration of the PET-based carbon dots is 200 μg / mL, more than 70% of the cells still maintain bioactivity and can be used as luminescent markers for in vivo detection and imaging.

[0038] The light-blocking film obtained using the PET-based carbon dots as raw material has a blocking rate of over 90% for ultraviolet light and blue light, over 80% for light emitted from mobile phone screens, and over 90% for natural light.

[0039] The PET-based carbon dots have a certain resistance to changes in metal ions and solution pH, and have good stability in different metal ion solutions and different pH solutions.

[0040] A second aspect of the present invention provides a method for preparing PET-based carbon dots. This method utilizes a carbon source and a nitrogen source as raw materials via a one-step hydrothermal process. Rather than first degrading PET to produce oligomers and then hydrothermally reacting them with a dopant, the PET and dopant are directly hydrothermally reacted, effectively shortening the preparation process.

[0041] Specifically, the carbon source and the dopant are mixed, subjected to a hydrothermal reaction at high temperature, and then filtered, dialyzed and dried.

[0042] The carbon source is selected from one or more of polyethylene terephthalate (i.e., PET), trimellitic acid, pyromellitic acid, pyromellitic anhydride, pyromellitic ester, trimellitic ester, and trimellitic ester, preferably selected from one or more of polyethylene terephthalate, trimesic acid, pyromellitic acid, pyromellitic anhydride, pyromellitic ester, and trimellitic ester, more preferably one or more of polyethylene terephthalate, trimesic acid, and pyromellitic acid.

[0043] According to a preferred embodiment of the present invention, when the carbon sources are polyethylene terephthalate and pyromellitic acid, the mass ratio of pyromellitic acid to polyethylene terephthalate is (1-4):1, preferably (1.2-3):1, and more preferably (1.3-2.5):1.

[0044] The nitrogen source is selected from one or more nitrogen-containing compounds, preferably one or more selected from hydrazine hydrate, ammonia water, urea, and ethylenediamine, preferably one or two selected from ammonia water and urea, more preferably ammonia water.

[0045] The mass ratio of the polyethylene terephthalate to the nitrogen source is (0.04-0.1):1, preferably (0.05-0.09):1, and more preferably (0.06-0.08):1.

[0046] The invention uses PET and pyromellitic acid as carbon sources and ammonia water as nitrogen source to prepare carbon dots with a fluorescence emission peak at 485 nm, high fluorescence quantum yield and good fluorescence stability.

[0047] The mixing and reaction are preferably carried out in a hydrothermal reactor, and the reaction temperature is 150-300°C, preferably 180-280°C, and more preferably 200-270°C.

[0048] The reaction temperature significantly influences the properties of the resulting PET-based carbon dots. The fluorescence intensity of the PET-based carbon dots increases initially and then decreases with increasing reaction temperature. The PET-based carbon dots obtained within the aforementioned reaction temperature range exhibit high fluorescence intensity. Furthermore, the fluorescence intensity of the PET carbon dots produced at the aforementioned reaction temperature is similar to that produced by reacting with the addition of a catalyst. This is likely because the rate at which PET aminolysis produces terephthalic acid diamide and ethylene glycol at this temperature is sufficient for dehydration and carbonization to form carbon dots.

[0049] The reaction time is 5 to 40 hours, preferably 7 to 30 hours, and more preferably 10 to 20 hours.

[0050] Experiments have found that when the reaction time is within the above range, the prepared PET-based carbon dots have a higher fluorescence intensity.

[0051] Optionally, a catalyst is added during the reaction. The catalyst is preferably selected from one or more of zinc acetate, sodium carbonate, sodium bicarbonate, magnesium acetate, cobalt acetate and lead dioxide, more preferably zinc acetate.

[0052] Experiments have shown that using zinc acetate as a catalyst favors the amino groups in PET, resulting in carbon dots with stronger fluorescence intensity. The hypothesized reaction mechanism is that PET undergoes aminolysis to form terephthalic acid diamide and ethylene glycol, which then undergo dehydration and carbonization with pyromellitic acid to form carbon dots. Further experiments revealed that the carbon dots produced at the above reaction temperature exhibited higher fluorescence intensity than those produced with the addition of a catalyst.

[0053] The mass ratio of the catalyst to the PET is (0.01-0.5):1, preferably (0.05-0.3):1, and more preferably (0.1-0.2):1.

[0054] The filtration is preferably carried out in a syringe filter to remove large particles, and the pore size of the dialysis membrane is 0.05 to 0.5 μm, preferably 0.1 to 0.4 μm, and more preferably 0.2 to 0.3 μm.

[0055] The dialysis is preferably performed in a dialysis bag with a molecular weight cut-off of 0.5 to 2 kD, preferably 1 kD.

[0056] The dialysis time is 1 to 7 days, preferably 2 to 5 days, and more preferably 3 to 4 days.

[0057] During the dialysis process, the water is changed every once in a while, with an interval of 3 to 10 hours, preferably 4 to 9 hours, and more preferably 5 to 7 hours.

[0058] After dialysis, the solid is taken out and freeze-dried, preferably in a freeze dryer. The freeze-drying time is preferably 2 to 10 days, more preferably 3 to 5 days.

[0059] The preparation is carried out by a one-step hydrothermal method, which not only reduces the preparation process but also reduces the preparation cost. At the same time, the prepared PET-based carbon dots have the advantages of high fluorescence intensity and fluorescence quantum yield.

[0060] The third aspect of the present invention is to provide an application of the PET-based carbon dots according to the first aspect of the present invention or the PET-based carbon dots prepared by the preparation method described in the second aspect of the present invention, which can be used in in vivo detection, cell imaging, LED, fluorescent anti-counterfeiting, fluorescent ink and light-blocking film, and can effectively block the blue light of mobile phones and ultraviolet light and blue light in natural light.

[0061] The fourth aspect of the present invention is to provide a carbon dot with high fluorescence quantum yield. The carbon dot with high fluorescence quantum yield is obtained by first degrading PET as a raw material to obtain PET oligomers, and then hydrothermally reacting the PET oligomers with a dopant and pyromellitic acid.

[0062] The dopant is selected from one or more of nitrogen-containing compounds, phosphorus-containing compounds, zinc-containing compounds and cobalt-containing compounds, preferably one or more of nitrogen-containing compounds, and more preferably urea.

[0063] The mass ratio of the dopant to the PET oligomer is (0.1-10):1, preferably (0.2-8):1, and more preferably (0.3-6):1.

[0064] The mass ratio of pyromellitic acid to PET oligomer is (0.05-1):1, preferably (0.1-0.7):1, and more preferably (0.2-0.5):1.

[0065] The optimal excitation wavelength and emission wavelength of the carbon dot are 380-430 nm and 450-500 nm respectively, which is a typical non-excitation wavelength dependent type, and its fluorescence quantum yield is as high as over 95%.

[0066] The PET-based carbon dots can specifically recognize trivalent iron ions, and their fluorescence intensity increases with Fe 3+ The fluorescence quenching △F and Fe 3+ The concentration showed a good linear relationship between 0 and 15 μmol / L, and the detection limit could reach 0.05 μmol / L.

[0067] The carbon dots are spherical, well-dispersed, and free of agglomeration, with a particle size of 1.6 to 4.6 nm, consistent with the lattice spacing of graphene.

[0068] The carbon dots have very low biotoxicity. After being incubated with Hela cells for 24 hours, more than 70% of the cells still maintain bioactivity when the concentration of the PET-based carbon dots solution is 400 μg / mL.

[0069] The fifth aspect of the present invention is to provide a method for preparing the carbon dots with high fluorescence quantum yield described in the fourth aspect of the present invention. The preparation method uses PET as a raw material to first degrade PET oligomers to obtain PET oligomers, and then hydrothermally reacts them with a dopant and pyromellitic acid.

[0070] The degradation is preferably carried out in an alcohol solvent, which is preferably selected from one or more of ethanol, glycerol, ethylene glycol and pentaerythritol, more preferably ethylene glycol. The amount of the alcohol solvent added is not particularly limited.

[0071] A catalyst is also added during the alcoholysis process, and the catalyst is preferably zinc acetate.

[0072] The degradation is carried out in a microwave reactor. The power of the microwave reactor during the degradation process is 400-700W, preferably 450-650W, and more preferably 500-600W.

[0073] The degradation reaction time is 10 to 60 minutes, preferably 15 to 45 minutes, and more preferably 20 to 30 minutes.

[0074] The mass ratio of the dopant to the PET oligomer is (0.1-10):1, preferably (0.2-8):1, and more preferably (0.3-6):1.

[0075] The mass ratio of pyromellitic acid to PET oligomer is (0.05-1):1, preferably (0.1-0.7):1, and more preferably (0.2-0.5):1.

[0076] The hydrothermal reaction temperature is 200 to 300°C, preferably 220 to 280°C, and more preferably 240 to 270°C.

[0077] The hydrothermal reaction time is 10 to 40 hours, preferably 15 to 30 hours, and more preferably 20 to 25 hours.

[0078] After the hydrothermal reaction, the mixture is filtered, dialyzed and dried to obtain carbon dots with high fluorescence quantum yield.

[0079] The carbon dots with high fluorescence quantum yield can be applied to the detection of trivalent iron ions, in vivo detection, cell imaging, LED and fluorescent anti-counterfeiting.

[0080] The beneficial effects of the present invention are:

[0081] (1) The PET-based carbon dots of the present invention have an original point-like structure, are well dispersed, have no agglomeration phenomenon, and have the same lattice spacing as the 100-plane of graphene;

[0082] (2) The PET-based carbon dots have the advantage of high fluorescence quantum yield, with a fluorescence quantum yield of more than 85%, and good stability in different metal ion solutions and different pH solutions. The fluorescence intensity of the carbon dots with high fluorescence quantum yield can be 3+ Selective quenching, the detection limit can reach 0.2μmol / L, and its fluorescence quantum yield is as high as over 95%;

[0083] (3) The fluorescence intensity of the PET-based carbon dots remains stable within a certain pH range and has low cytotoxicity. Even at high concentrations of the carbon dot solution, a large number of cells still maintain biological activity, making it suitable for cell imaging and LED and fluorescence anti-counterfeiting.

[0084] (4) The light-blocking film made from the PET-based carbon dots has a blocking rate of over 90% for ultraviolet and blue light, over 80% for light emitted from mobile phone screens, and over 90% for natural light;

[0085] (5) The present invention adopts a one-step hydrothermal method to prepare PET-based carbon dots, which has the advantages of simple preparation method and low cost;

[0086] (6) The carbon dots prepared using PET as raw material in the present invention have excellent performance and a wide range of applications, which increases the added value of waste PET. It not only opens up a new channel for the reuse of a large amount of waste PET, but also is beneficial to environmental protection.

[0087] Example

[0088] The present invention is further described below through specific examples. These examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0089] Example 1

[0090] 1.5 g PET, 2.0 g trimesic acid and 20 mL ammonia water were added to a 50 mL para-polyphenylene hydrothermal reactor, and then the reactor was placed in an oven at 260°C. After reacting for 12 h, it was taken out after naturally cooling to room temperature.

[0091] The crude PET-CDs product was injected into a 0.22 μm needle filter membrane using a disposable filter to remove large particles. The filtrate was then injected into a dialysis bag (molecular weight cutoff of 1 kD) for dialysis. The water was changed every 6 hours or so. After dialysis for 3 days, a PET-based carbon dot solution with small molecular impurities removed was obtained.

[0092] The PET-based carbon dot solution obtained after dialysis is placed in a clean container and placed in a refrigerator for freezing. After the sample becomes solid, it is taken out and then placed in a vacuum freeze dryer for freeze drying to obtain a brown powder, PET-based carbon dot solid powder.

[0093] The fluorescence intensity of the carbon dots was tested to be 1.1×10 6 au.

[0094] Example 2

[0095] PET-based carbon dots were prepared in a manner similar to Example 1, except that 1.5 g PET, 3.0 g pyromellitic acid, 0.2 g zinc acetate, and 20 mL of ammonia water were added to a 50 mL para-polyphenylene hydrothermal reactor, which was then placed in an oven at 250°C.

[0096] The fluorescence intensity of the carbon dots was tested to be 6.1×10 5 au.

[0097] Example 3

[0098] PET-based carbon dots were prepared in a manner similar to Example 1, except that 1.5 g PET, 2.0 g pyromellitic acid, 0.2 g zinc acetate, and 20 mL of aqueous ammonia were added to a 50 mL para-polyphenylene hydrothermal reactor, which was then placed in an oven at 260°C.

[0099] The fluorescence intensity of the carbon dots was tested to be 1.0×10 6 au.

[0100] Example 4

[0101] Wash and dry 48 g of PET waste fiber and add it to a round-bottom flask. Then add 14 g of ethylene glycol and 0.4 g of zinc acetate dihydrate. React in a 540 W microwave reactor for 20 min. Pour the hot solution into a beaker, cool to room temperature, and grind it into powder using a grinder to obtain PET oligomer for later use.

[0102] 2 g of PET oligomer, 10 g of hydrazine hydrate, and 0.7 g of pyromellitic acid were weighed and added to a 100 mL hydrothermal kettle lined with para-polyphenol, and 30 mL of deionized water was added. The lid was covered and the shell was tightened. The reactor was then placed in a forced air drying oven at 260 ° C for 24 h. After naturally cooling to room temperature, large particles were filtered with a 0.22 μm syringe filter to obtain a PET-based carbon dot aqueous solution.

[0103] The PET-based carbon dot aqueous solution was dialyzed using a 1 kD dialysis bag for 24 h, during which deionized water was replaced every 4 h. After the dialysis, the PET-based carbon powder was obtained by freeze-drying.

[0104] Experimental example

[0105] Experimental Example 1 TEM test

[0106] The PET-based carbon dots prepared in Example 1 and Example 4 were tested by transmission electron microscopy, the model of the transmission electron microscope was PEI Tecnai G2 F30, and the test results were as follows: Figure 1 and Figure 2 shown.

[0107] from Figure 1 As can be seen from Figure a, the PET-based carbon dots prepared in the present invention have a spherical structure, good dispersibility, no agglomeration, and uniform particle size distribution. Figure 1 In b, the particle size of carbon dots ranges from 1.1 to 3.1 nm.

[0108] Figure 2 In a, the PET-based carbon dots prepared in Example 4 also have a spherical structure and are well dispersed without agglomeration. Figure 2 b, its particle size distribution is 1.6~4.6nm, Figure 2 As shown in the illustration of a, the lattice spacing of PET-based carbon dots is 0.21 nm, which is consistent with the lattice spacing of graphene 100 faces.

[0109] Experimental Example 2 UV-Vis Absorption Spectrum, Fluorescence Emission Spectrum and Excitation Spectrum Test

[0110] The UV-visible absorption spectrum of the PET-based carbon dots prepared in Example 1 was tested using a fluorescence spectrometer FS5. The test results are shown in the figure. Figure 3a shown.

[0111] from Figure 3a It can be seen that the two samples were observed under natural light and ultraviolet light respectively. Under natural light, both carbon dot solutions were brown, while under the excitation of 365nm ultraviolet light, they both emitted bright blue-green fluorescence.

[0112] The fluorescence emission spectra of the PET-based carbon dots prepared in Example 1 and Example 4 were tested by fluorescence spectrometer. The emission spectrum (Ex) and excitation spectrum (Em) test results were as follows: Figure 3b and 3c shown.

[0113] Figure 3b The optimal excitation wavelength and the optimal emission wavelength of the PET-based carbon dots prepared in Example 1 are 434 nm and 485 nm, respectively.

[0114] Figure 3c It can be seen from the figure that the optimal excitation wavelength of the fluorescent carbon dots prepared in Example 4 is 408 nm, and the optimal emission wavelength is 485 nm.

[0115] Experimental Example 3: XPS Test

[0116] The PET-based carbon dots prepared in Example 1 were analyzed by X-ray photoelectron spectroscopy. The instrument used was a 250Xi instrument from Thermo Fisher Scientific, USA. The target material was aluminum palladium. The emission voltage and current were 10 kV and 5 mA, respectively. The test results are shown in FIG4 . Figure 4a are the XPS spectra of C1s, N1s and O1s, Figure 4b is the high-resolution spectrum of C1 s, Figure 4c The high-resolution spectrum of N1 s is shown. Figure 4d A high-resolution spectrum of O1 s is shown.

[0117] from Figure 4a In the XPS spectrum, there are three peaks of C1s, N1s and O1s, which are located at 285.08eV, 400.08eV and 532.08eV respectively, indicating that the PET-based carbon dots contain three elements, namely C, N and O. Figure 4b The high-resolution spectrum of C1s can be divided into three peaks, 288.5eV, 284eV and 286.0eV are the characteristic peaks of carbonyl carbon, sp2 carbon and sp3 carbon, respectively. Figure 4c The high-resolution spectrum of N1s can be divided into three peaks, representing CNC, pyrrolic N, and NH, respectively. Figure 4d In the figure, CO and C=O have two peaks at 532.2 eV and 531.2 eV, respectively. In summary, the XPS spectrum indicates that nitrogen atoms have been successfully doped into the carbon dots, primarily in the form of pyrrole N and amino groups. This confirms the presence of amino and carboxyl groups on the PET-based carbon dots.

[0118] Experimental Example 4 Fluorescence Quantum Yield Test

[0119] The absolute fluorescence quantum yields of the PET-based carbon dots prepared in Example 1 and Example 4 were tested using an integrating sphere with a polytetrafluoroethylene inner coating. The test results are shown in FIG5 .

[0120] from Figure 5a It can be seen that the fluorescence quantum yield of the PET-based carbon dots prepared in the present invention is 87.36%. Figure 5b The fluorescence quantum yield is as high as 97.3%.

[0121] Experimental Example 5 Effect of Metal Ions on the Fluorescence Properties of PET-Based Carbon Dots

[0122] Prepare 13 kinds of 2+ ,Bi 3+ , Na + , Ag + , K + , Fe 3+ , Cu 2+ , Cr 3+, Cd 2+ , Ca 2+ , Pb 2+ , Ni 2+ , Hg 2+ ) salt solution, the metal solution concentration is 10mmol / L, the PET-based carbon dot aqueous solution prepared in Example 1 was diluted 200 times, and 20μL was taken out and added to a 4mL four-way light cuvette. After adding 2mL of deionized water and mixing evenly, the fluorescence intensity I of the PET-based carbon dot solution prepared in Example 1 after adding metal ions and the fluorescence intensity I0 of the original carbon dot solution without adding metal ions were tested under the condition of excitation wavelength of 434nm. The test results are shown in Figure 2. Figure 6 shown.

[0123] The PET-based carbon dot aqueous solution prepared in Example 4 was diluted 200 times, and 10 μL was taken out and added to a 4 mL four-way light cuvette. After adding 2 mL of deionized water and mixing evenly, the fluorescence spectrum was measured in a fluorescence spectrometer. Subsequently, 20 μL of metal ion solution was added, mixed evenly, and the fluorescence spectrum was measured again. The test conditions of the fluorescence spectrum were: excitation wavelength 408 nm, slit width 3.6 nm, and scanning range 420-660 nm. The test results are shown in Figure 2. Figure 7 As shown, Figure 7 a shows the quenching degree of PET-based carbon dots in different metal salt solutions, Figure 7 b shows the fluorescence intensity of PET-based carbon dots and Fe 3+ The concentration relationship diagram, Figure 7 c shows the fluorescence intensity of PET-based carbon dots and Fe 3+ The corresponding relationship of concentration, Figure 7 d shows the fluorescence quenching ΔF and Fe 3+ Linear relationship with concentration.

[0124] from Figure 6 It can be seen from the graph that the fluorescence intensity of the PET-based carbon dots prepared in Example 1 did not change due to the addition of metal ions, and the values ​​were all around 1.0, indicating that these metal ions could not quench the fluorescence of the carbon dots. This indicates that the PET-based carbon dots of the present invention have a certain degree of anti-interference ability to metal ions and excellent fluorescence stability.

[0125] Figure 7 In a, the PET-based carbon dots prepared in Example 4 can specifically recognize Fe 3+ , Figure 7 In b, the fluorescence intensity of PET-based carbon dots increases with the Fe 3+ gradually decreases with the increase of concentration, Figure 7 c and Figure 7 In d, fluorescence quenching △F and Fe 3+The concentration showed a good linear relationship between 0 and 15 μmol / L, and the detection limit could reach 0.05 μmol / L.

[0126] Experimental Example 6 Effect of Solution pH on Fluorescence Properties of PET-Based Carbon Dots

[0127] Take 20 μL of the PET-based carbon dots prepared in Example 1 and add it to 40 mL of deionized water to dilute it 200 times. Then use 1 mol / L hydrochloric acid and 1 mol / L sodium hydroxide to adjust the pH value of the solution. PET-based carbon dot aqueous solutions with different pH values ​​are prepared, and their pH values ​​are 1.90, 2.70, 3.20, 4.30, 5.20, 6.20, 7.50, 8.80, 10.00, 11.20, 12.10 and 13.00, respectively. Take a certain volume of the above solution and add it to a four-way quartz cuvette to test the fluorescence emission spectrum. The excitation light wavelength is 434 nm, the excitation light slit is 1.5 nm, and the emission light slit is 2 nm. The test results are as follows Figure 8 shown.

[0128] from Figure 8 It can be seen from the figure that when the pH of the PET-based carbon dot solution is around 5 to 11, the fluorescence intensity of the PET-based carbon dot solution does not change much, indicating that the carbon dots prepared by the present invention have a certain resistance to changes in the solution pH and have good stability in solutions with different pH values.

[0129] Experimental Example 7 Cytotoxicity Experiment and Cell Imaging

[0130] Hela cells were seeded into a 96-well plate and cultured in a 5% CO2, 37°C constant temperature incubator until the cells adhered. Different concentrations of the PET-based carbon dot cell culture solution (0-400 μg / mL) prepared in Example 1 were injected into the 96-well plate and incubated for 24 hours, and the culture medium containing the sample was removed. Each well was washed three times with PBS, and 100 μL of culture medium containing 0.5 mg / mL of MTT was added to each well. The cells were cultured in a 5% CO2, 37°C constant temperature incubator for 4 hours, the supernatant was discarded, and 100 μL of DMSO was added to each well. After shaking gently for 10 minutes, the absorbance at 570 nm was detected. The cytotoxicity experiment was carried out on the PET-based carbon dots prepared in Example 4 in the same way, and the test results were as follows. Figure 9 and Figure 10 shown.

[0131] Figure 9 In the experiment, after the PET-based carbon dots prepared in Example 1 were co-incubated with Hela cells for 24 hours, 70% of the cells still maintained biological activity when the concentration of PET-based carbon dots was 200 μg / mL, indicating that PET-based carbon dots have low biotoxicity and good biosafety, and can be used as luminescent markers for in vivo detection and imaging.

[0132] from Figure 10It can be seen that after the PET-based carbon dots prepared in Example 4 were co-incubated with Hela cells for 24 h, 75% of the cells still maintained biological activity even when the concentration of the PET-based carbon dots solution was 400 μg / mL, indicating that the biotoxicity of PET-based carbon dots is very low and PET-based carbon dots can be used in cell imaging.

[0133] Experimental Example 8 Preparation and Characterization of Light Blocking Film

[0134] 0.06g, 0.12g, 0.18g, 0.24g, and 0.30g of the PET-based carbon dot powder prepared in Example 1 were weighed, added to 10g of a 15% PVA solution, and placed in a covered glass sample bottle to prepare 0%, 4%, 8%, 12%, 16%, and 20% carbon dot solutions, respectively. After tightening the bottle cap, the solution was ultrasonically treated in 80°C hot water for 60 minutes to obtain a uniformly mixed solution, which was then cooled to room temperature for use. Using a PET film (0.1×210×148mm) and an adjustable applicator, the solution was evenly applied on a heating table. Once the solution solidified into a film of uniform thickness, subsequent performance testing was performed.

[0135] Fluorescence spectrometer FS5, UV spectrophotometer, and multi-function spectrophotometer were used to test the fluorescence spectrum, transmittance, and light-blocking ability of the PET-based carbon dot light-blocking film. The fluorescence spectrum of the PET-based carbon dot light-blocking film was tested using a multi-function spectrophotometer. The test results are shown in Figure 11. Figure 11a The fluorescence spectrum of the light blocking film is shown in FIG. Figure 11b A graph showing the transmittance test of light-blocking films with different carbon dot contents.

[0136] Irradiate the light blocking film and observe the blocking effect of LBFs (light blocking film) on ultraviolet light, blue light, mobile phone screen light and natural light. The test results for ultraviolet light and blue light are as follows: Figure 12a and Figure 12b As shown, the test results for mobile phone screen light and natural light are as follows Figure 13a and Figure 13b shown.

[0137] from Figure 11a It can be seen that the optimal excitation and emission wavelengths of the PET-based carbon dot light-blocking film prepared by the present invention are 435nm and 485nm, respectively, which are basically the same as those of the PET-based carbon dot solution and do not change due to changes in the environment. This further indicates that the fluorescence of the PET-based carbon dots is carbon core luminescence. The fluorescence intensity test shows that the excitation wavelength is 435nm, Figure 11b It can be found that with the increase of the content of PET-based carbon dots in the light-blocking film, its fluorescence intensity shows a trend of first increasing and then decreasing, among which the fluorescence intensity of the light-blocking film with a PET-based carbon dot content of 8% is the highest.

[0138] from Figure 12a and 12b As can be seen from the results, pure PVA film has little ability to block LEDs emitting 365nm and 430nm (harmful blue light). However, as the carbon dot content in the light-blocking film increases, its light-blocking ability gradually increases. At a carbon dot content of 20%, the light-blocking rates for 365nm and 430nm reach 97.7% and 95.2%, respectively. This indicates that the light-blocking film made with the carbon dots described in this invention is as effective at blocking UV and blue light as commercially available eyeglasses, demonstrating its potential for application in the field of UV and blue light protection.

[0139] Test the ability of light blocking film to block blue light emitted by mobile phone screens and ultraviolet light and blue light in natural light. Figure 13a and 13b In the experiment, as the content of carbon dots in the light-blocking film increases, its light-blocking ability gradually increases. When the content of carbon dots is 20%, the blocking rates reach 86.1% and 97.5% respectively.

[0140] Experimental Example 9 Preparation and Characterization of LED Devices

[0141] Weigh 0.24 g of the PET-based carbon dot powder prepared in Example 1 into a covered glass vial. Add 3 g of polyvinyl alcohol and 17 g of deionized water to create an 8% PET-based carbon dot aqueous solution. After tightening the cap, place the vial in 80°C hot water for 30 minutes to obtain a uniformly dispersed solution. Cool to room temperature and set aside.

[0142] 20 μL of the above solution was measured with a pipette and added dropwise to a 395 nm LED chip, which was then placed in a forced air drying oven at 50° C. overnight. After the solvent was completely evaporated, an LED device was obtained.

[0143] The prepared green LED device was tested using a multifunctional spectral illuminance meter (model: OHSP350M, equipped with a 0.3M integrating sphere) with a fixed voltage of 3.0V. The spectrum, color coordinates and correlated color temperature of the corresponding device were obtained. The test results are shown in the figure below. Figure 14 shown.

[0144] Figure 14 Figure a shows the spectrum of an LED device assembled from PET carbon dots dispersed in a PVA matrix and a 395nm LED chip. The inset shows a photo of the device (top) and a photograph at 3V. As can be seen from the figure, the emission spectrum of the LED device made from PET-based carbon dots contains two emission peaks at 395nm and 485nm. These are the emission peaks of the UV chip and the emission peak from the carbon dots, respectively, which are green light. Figure 14b is the color coordinate diagram of the prepared green LED chip, with a correlated color temperature of 2018 K. As can be seen from the figure, the LED prepared using PET-based carbon dots emits high-brightness green fluorescence, indicating its potential application value in the LED field.

[0145] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A PET-based carbon dot, characterized in that: The fluorescence quantum yield of the PET-based carbon dots is over 85%; When the concentration of PET-based carbon dot solution was 200 μg / mL, more than 70% of cells still maintained biological activity. The PET-based carbon dots were prepared by a one-step hydrothermal method using carbon and nitrogen sources as raw materials; Polyethylene terephthalate is used as the carbon source, and the carbon source is also selected from one or more of trimellitic acid, trimesic acid, pyromellitic acid, pyromellitic anhydride, pyromellitic acid ester, trimellitic acid ester, and trimellitic acid ester. The nitrogen source is aqueous ammonia.

2. The PET-based carbon dots according to claim 1, wherein The carbon source is also selected from one or more of trimesic acid, pyromellitic acid, pyromellitic anhydride, pyromellitic acid esters, and trimesic acid esters.

3. The PET-based carbon dots according to claim 2, wherein When the carbon sources are polyethylene terephthalate and pyromellitic acid, the mass ratio of pyromellitic acid to polyethylene terephthalate is (1-4):

1.

4. The PET-based carbon dots according to claim 1, wherein The optimal excitation and emission wavelengths of the PET-based carbon dots are 400-450 nm and 460-500 nm, respectively.

5. The PET-based carbon dots according to claim 1, wherein The light-blocking film made from the PET-based carbon dots has a blocking rate of over 90% for ultraviolet light and blue light, over 80% for light emitted from mobile phone screens, and over 90% for natural light.

6. A method for preparing PET-based carbon dots according to any one of claims 1 to 5, characterized in that: The method uses a carbon source and a nitrogen source as raw materials and is prepared by a one-step hydrothermal method.

7. The preparation method according to claim 6, characterized in that The mass ratio of the polyethylene terephthalate to the nitrogen source is (0.04-0.1):

1.

8. The preparation method according to claim 7, characterized in that The mass ratio of the polyethylene terephthalate to the nitrogen source is (0.05-0.09):

1.

9. The preparation method according to claim 8, characterized in that The mass ratio of the polyethylene terephthalate to the nitrogen source is (0.06-0.08):

1.

10. Use of the PET-based carbon dots according to any one of claims 1 to 5 or the PET-based carbon dots prepared by the preparation method according to any one of claims 6 to 9, in LEDs, fluorescent anti-counterfeiting, fluorescent inks, and light-blocking films.

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