A solvent thermal preparation method for PET-based doped carbon dots and its application

Abstract

The present invention provides a solvent thermal preparation method for PET-based doped carbon dots and its application. The PET-based doped carbon dots are mainly prepared by solvent thermal reaction using waste PET and a dopant as main raw materials. The dopant is selected from one or more of a nitrogen source, a phosphorus source, a sulfur source, a zinc source, an iron source and a copper source. The PET-based doped carbon dots prepared in this way are spherical as a whole and have no agglomeration. They have the advantages of high fluorescence intensity and fluorescence quantum yield. They have a blocking effect on ultraviolet light, blue light, mobile phone screen light and natural light, and can be used in light-blocking films. At the same time, they can detect the water content in organic solvents with a low detection limit. The present invention uses waste PET as raw material, provides a new idea for the reuse of waste PET, is beneficial to environmental protection and reduces costs.

Description

Technical Field

[0001] The present invention relates to the field of fluorescent nanomaterials, and in particular to a solvent-thermal preparation method of PET-based doped carbon dots and applications thereof. Background Art

[0002] Carbon dots (CDs) are a class of spherical carbon-based nanomaterials mainly composed of carbon elements and with a size of less than 20nm. They are composed of a carbon core and surface functional groups (carboxyl, amino and hydroxyl groups, etc.). Not only can the fluorescence color and luminescence intensity of carbon dots be controlled by regulating the size, but they also have good photostability and excellent biocompatibility, making them the preferred alternative to traditional semiconductor quantum dots. Due to their many advantages mentioned above, carbon dots are widely used in many fields such as analytical detection, bioimaging, light-emitting diodes, photocatalysis, biomedicine, photothermal therapy, etc. In addition, there are many types of raw materials for carbon dots. In theory, any substance containing carbon atoms can be used as a raw material for preparing carbon dots.

[0003] my country, a populous nation at the center of the global textile and apparel industry chain, is experiencing rapid growth, placing immense pressure on resources and the environment. According to the National Bureau of Statistics' bulletin and authoritative statistics from China's chemical fiber industry, polyethylene terephthalate (PET) fiber holds the largest market share among synthetic fibers. As PET fiber usage continues to rise, so too does its waste stock. Improper PET recycling leads to significant waste of petroleum resources and harms the environment on which humanity depends.

[0004] The widespread use and consumption of PET (polyethylene terephthalate) (PET) has put enormous pressure on the environment. Because PET decays very slowly, improper disposal can pose a threat to the environment and result in a significant waste of petroleum resources. Simply landfilling or incinerating PET waste not only creates environmental problems but also depletes petroleum resources. Currently, domestic polyester recovery technologies include mechanical, physical, chemical, and physicochemical methods. However, these methods are incapable of fully utilizing PET. A large amount of PET waste is still processed solely through landfilling, and the processing of PET is far behind the generation of PET waste. Therefore, fully utilizing PET waste is of great significance.

[0005] In-depth research on the preparation of carbon dots using PET as a precursor can not only provide a new way to increase the added value of polyester waste, but also contribute to the protection of resources and the natural environment. Summary of the Invention

[0006] Based on the above technical background, the inventors have made determined efforts and found that: using waste PET (polyethylene terephthalate) as raw material, supplemented with one or more of a nitrogen source, a phosphorus source, a sulfur source, a zinc source, an iron source and a copper source for doping, PET-based doped carbon dots are obtained through a solvent thermal reaction. The PET-based doped carbon dots have a spherical structure, are evenly dispersed, and have the advantages of high fluorescence intensity and fluorescence quantum yield. The light-blocking film prepared using the carbon dots as raw material has a blocking effect on ultraviolet light, blue light, mobile phone screen light and natural light, and can be used in light-blocking films. It can also be used as a fluorescent probe to detect the water content in organic solvents and the pH of the solution with a low detection limit. At the same time, it provides a new direction for the reuse of waste PET, thereby completing the present invention.

[0007] The first aspect of the present invention is to provide a PET-based doped carbon dot, wherein the PET-based doped carbon dot mainly uses PET and a dopant as raw materials;

[0008] The optimal excitation wavelength of the PET-based doped carbon dots is 320-450 nm, and the optimal emission wavelength is 450-600 nm.

[0009] The second aspect of the present invention is to provide a method for preparing the PET-based doped carbon dots according to the first aspect of the present invention, the preparation method comprising the following steps:

[0010] Step 1: alcoholyzing PET in the presence of zinc acetate dihydrate to obtain PET oligomers;

[0011] Step 2: reacting the PET oligomer and the dopant in an organic solvent to obtain a crude product of PET-doped carbon dots;

[0012] Step 3: Filter and dialyze the crude product of PET-doped carbon dots to obtain PET-doped carbon dots.

[0013] The third aspect of the present invention is to provide an application of the PET-doped carbon dots according to the first aspect of the present invention or the PET-doped carbon dots prepared by the preparation method described in the second aspect of the present invention, which can be used to detect the water content and solution pH in organic solvents, as well as be applied to light-blocking films, LED devices, fluorescent inks and anti-counterfeiting fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The transmission electron micrograph and particle size distribution diagram of the carbon dots prepared in Example 1 are shown;

[0015] Figure 2a 、 2b 2c and 2d show the infrared spectra of carbon dots prepared in Example 1, Example 5 and Example 9, respectively;

[0016] Figure 3aThe full XPS spectrum of carbon dots prepared in Example 6 is shown;

[0017] Figure 3b is the C1s high-resolution spectrum;

[0018] Figure 3c is the high-resolution spectrum of N1s;

[0019] Figure 3d is the high-resolution spectrum of O1 s;

[0020] Figure 4 The UV-visible absorption spectrum of the carbon dots prepared in Example 1 is shown;

[0021] Figure 5a 、 5b 5c and 5d are fluorescence emission spectra of carbon dots prepared in Example 1, Example 5 and Example 9, respectively;

[0022] Figure 6a and 6b The fluorescence quantum yield spectra of the carbon dots prepared in Example 1 and Example 9 are shown respectively;

[0023] Figure 7 The fluorescence emission spectra of the carbon dots prepared in Example 1 in 1,4-dioxane with different water contents are shown;

[0024] Figure 8a and 8b The transmittance spectra of the light-blocking films prepared using Examples 5 and 9 as raw materials are shown respectively;

[0025] Figure 9 9b, 9d, 9f and 9h respectively show the blocking test graphs of the light-blocking film prepared in Example 5 against ultraviolet light, blue light, mobile phone screen and natural light;

[0026] Figure 10 10a, 10b, 10c and 10d respectively show the blocking test graphs of the light-blocking film prepared in Example 9 against ultraviolet light, blue light, mobile phone screen and natural light;

[0027] Figure 11a and 11b The spectrum diagram and color coordinate diagram of the LED device prepared in Example 1 are shown respectively;

[0028] Figure 12a The fluorescence spectra of Examples 1 to 4 are shown. Figure 12b The fluorescence spectra of Examples 5 to 8 and Comparative Example 1 are shown. Figure 12c The fluorescence spectra of Examples 9 to 11 and Comparative Example 2 are shown. DETAILED DESCRIPTION

[0029] 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.

[0030] The first aspect of the present invention is to provide a PET-doped carbon dot, which mainly uses PET and a dopant as raw materials, and the dopant is selected from one or more of a nitrogen source, a phosphorus source, a sulfur source, a zinc source, an iron source and a copper source.

[0031] PET contains a large amount of carbon elements. Using PET as raw material to prepare carbon dots can not only solve the environmental pollution problem caused by improper recycling of PET waste, but also the carbon dots prepared with PET as raw material have the advantages of high fluorescence quantum yield and good stability. It has broad application prospects and provides new ideas for the reuse of PET waste.

[0032] The dopant is preferably selected from one or more of a nitrogen source, a phosphorus source and a sulfur source, and more preferably selected from one or more of urea, p-phenylenediamine, phosphoric acid, acetic acid and sulfuric acid.

[0033] The selection of dopants plays an important role in the performance and final effect of PET-based doped carbon dots. Experiments have found that the addition of the above dopants is beneficial to improving the fluorescence quantum yield.

[0034] The mass ratio of the dopant to the PET oligomer is (0.1-30):1, preferably (0.2-25):1, and more preferably (0.4-22):1.

[0035] The experiment found that too high or too low an amount of dopant added would affect the performance of PET-doped carbon dots. When the amount of dopant added was within the above range, the performance of PET-doped carbon dots was excellent.

[0036] The raw materials also include an acid anhydride compound. Experiments have shown that the carbon dots produced by adding the acid anhydride compound can be used as a fluorescent probe to detect the water content in an organic solvent. The acid anhydride compound is selected from one or more of pyromellitic anhydride, phthalic anhydride, and maleic anhydride compounds, preferably one or more of pyromellitic anhydride, phthalic anhydride, and 2-hexyl-3-methylmaleic anhydride, and more preferably pyromellitic anhydride.

[0037] The organic solvent is preferably 1,4-dioxane. Within the water content range of 0.00001% to 0.5%, the degree of fluorescence quenching of the carbon dots is linearly related to the water content, with a detection limit of 0.00001%. The degree of fluorescence quenching refers to the difference between the peak fluorescence intensity of the carbon dots in an organic solvent without water and the peak fluorescence intensity of the carbon dots in organic solvents with varying water contents.

[0038] The PET-based doped carbon dots are spherical in structure, evenly dispersed without agglomeration, and form a graphite carbon structure. The fluorescence quantum yield of the PET-based doped carbon dots is as high as over 45%.

[0039] The PET-based doped carbon dots have excellent light absorption and light conversion properties and can be used in light-blocking films. The resulting light-blocking films have uniform thickness, a smooth, flat surface, and are effective at blocking ultraviolet light, blue light, light from mobile phone screens, and natural light. They block over 80% of ultraviolet light, over 70% of blue light, over 70% of light from mobile phone screens, and over 80% of natural light.

[0040] When the dopant is a nitrogen source only, the PET-doped carbon dots are typically non-excitation wavelength-dependent. When the dopant is a mixed dopant, the PET-doped carbon dots are excitation wavelength-dependent, with the optimal excitation wavelength being 320-450 nm and the optimal emission wavelength being 450-600 nm.

[0041] The fluorescence intensity of the PET-doped carbon dots is unresponsive to interference from metal ions, exhibits good photostability, and is highly salt-tolerant. The fluorescence intensity of the carbon dots decreases with increasing pH, and a linear relationship exists between the pH values and the corresponding fluorescence intensity, making them suitable for measuring the pH of solutions.

[0042] The second aspect of the present invention is to provide a method for preparing the PET-based doped carbon dots according to the first aspect of the present invention, the preparation method comprising the following steps:

[0043] Step 1: alcoholyzing PET in the presence of zinc acetate dihydrate to obtain PET oligomers;

[0044] Step 2: reacting the PET oligomer and the dopant in an organic solvent to obtain a crude product of PET-doped carbon dots;

[0045] Step 3: Filter and dialyze the crude product of PET-doped carbon dots to obtain PET-doped carbon dots.

[0046] This step is described and explained in detail below.

[0047] Step 1: In the presence of zinc acetate dihydrate, PET is alcoholyzed to obtain PET oligomers.

[0048] The reaction is preferably carried out in a microwave reactor at a power of 400-600W, preferably 450-550W, more preferably 500-550W.

[0049] The reaction time is 5 to 60 min, preferably 10 to 45 min, and more preferably 15 to 30 min.

[0050] Zinc acetate dihydrate is used as a catalyst in the present invention, and the mass ratio of PET to zinc acetate dihydrate is (100-150):1, preferably (110-140):1, and more preferably (115-125):1. The amount of catalyst added will affect the degradation effect of the polymer.

[0051] The alcohol solvent used for alcoholysis is one or more of ethylene glycol, glycerol, methanol, ethanol and pentaerythritol, preferably ethylene glycol. The amount of the alcohol solvent used is not particularly limited, as long as the polyester can be completely alcoholysed.

[0052] Step 2: PET oligomer and dopant react in an organic solvent to obtain a crude product of PET-doped carbon dots.

[0053] The reaction is preferably carried out in a solvent thermal reactor, and the organic solvent is selected from one or more of ethanol, tetrahydrofuran, acetic acid, acetone and toluene, preferably one or two of ethanol and tetrahydrofuran.

[0054] There is no specific limit on the amount of solvent added, as long as the PET oligomer and dopant are completely distributed therein. The use of organic solvents can effectively inhibit the oxidation process of the product or oxygen contamination in the water, while greatly expanding the range of raw materials available. Furthermore, the low boiling point of organic solvents facilitates achieving higher pressures, and the unique physicochemical properties in the subcritical or supercritical state greatly expand the range of target products that can be prepared. The mass ratio of dopant to PET oligomer is (0.1-30):1, preferably (0.2-25):1, and more preferably (0.4-22):1.

[0055] The dopant is selected from one or more of a nitrogen source, a phosphorus source, a sulfur source, a zinc source, an iron source and a copper source. The dopant is preferably selected from one or more of a nitrogen source, a phosphorus source and a sulfur source, and more preferably selected from one or more of urea, pyromellitic anhydride, p-phenylenediamine, phosphoric acid, acetic acid and sulfuric acid.

[0056] The type of dopant affects the fluorescence intensity of PET-based doped carbon dots. Different dopants will have different effects on the fluorescence intensity of PET-based doped carbon dots. In addition, the dopant will also affect the application performance of PET-based doped carbon dots. For example, the carbon dots obtained by doping with nitrogen and phosphorus elements have good photostability and salt resistance, and can be used to test the pH of the solution. For example, the carbon dots obtained by doping with nitrogen, phosphorus or nitrogen and sulfur elements at the same time can be used in light-blocking films, which have good blocking effects on ultraviolet light, blue light, mobile phone screen light and natural light. At the same time, the dopant will also affect the fluorescence quantum yield of the obtained carbon dots.

[0057] Optionally, an acid anhydride compound is added during the reaction. The carbon dots prepared by adding the acid anhydride compound can detect the water content in the organic solvent. The acid anhydride compound is selected from one or more of pyromellitic anhydride, phthalic anhydride, and maleic anhydride compounds, preferably one or more of pyromellitic anhydride, phthalic anhydride, and 2-hexyl-3-methylmaleic anhydride, and more preferably pyromellitic anhydride. The detection limit of the water content in the organic solvent is low and the detection is more accurate.

[0058] The mass ratio of the acid anhydride compound to the PET oligomer is (0.05-2):1, preferably (0.1-1.5):1, and more preferably (0.2-0.7):1.

[0059] With the increase of the amount of pyromellitic anhydride, the fluorescence intensity shows a trend of first increasing and then decreasing. When the mass ratio of pyromellitic anhydride to PET oligomer is within the above range, the fluorescence intensity of the prepared PET-based doped carbon dots is the strongest.

[0060] The reaction temperature is 180-300°C, preferably 200-280°C, more preferably 220-270°C.

[0061] The inventors discovered that increasing the reaction temperature maintains essentially unchanged the emission peak position. The reaction temperature and the degree of carbonization of the carbon dots show a positive correlation, favoring the formation of larger conjugated structures. Furthermore, increased chemical crosslinking of the groups and physical crosslinking of the rigid carbon structure produce a crosslinking enhancement effect, gradually increasing the fluorescence intensity. The PET-doped carbon dots produced at this reaction temperature exhibit not only excellent fluorescence properties but also low cost, energy conservation, and environmental protection.

[0062] The reaction time is 5 to 45 hours, preferably 10 to 40 hours, and more preferably 15 to 37 hours.

[0063] As the reaction time increases, the degree of carbonization gradually increases, and the fluorescence intensity increases with the increase in the degree of carbonization. However, if the reaction time is too long, the fluorescence intensity will decrease due to excessive carbonization.

[0064] Step 3: Filter and dialyze the crude product of PET-doped carbon dots to obtain PET-doped carbon dots.

[0065] The filtration is preferably performed using a needle filter membrane to remove large particles of impurities, and the pore size of the filter membrane is preferably 0.15 to 0.3 μm, more preferably 0.2 to 0.25 μm.

[0066] It is preferred to use ethanol dispersion before dialysis, and the dialysis bag is preferably boiled in deionized water for 5 to 10 minutes before use. Dialysis is used to remove small molecular impurities.

[0067] The dialysis time is 20 to 90 hours, preferably 30 to 85 hours. Ethanol is replaced during the dialysis process.

[0068] The replacement interval is 1 to 15 hours, preferably 2 to 12 hours. The concentration of the solution in the dialysis bag is high in the early stage, and the exchange rate between the small molecular weight molecules in the dialysis bag and the ethanol molecules in the beaker is fast. It is preferred that the replacement interval be short in the early stage and long in the later stage to ensure the effectiveness of the dialysis process.

[0069] The third aspect of the present invention is to provide an application of the PET-doped carbon dots according to the first aspect of the present invention or the PET-doped carbon dots prepared by the preparation method described in the second aspect of the present invention, which can be used to detect the water content and solution pH value in organic solvents, as well as applied to light-blocking films, LED devices, fluorescent inks and anti-counterfeiting fields.

[0070] The beneficial effects of the present invention are:

[0071] (1) The PET-doped carbon dots of the present invention are spherical in structure, contain hydroxyl groups on the surface, and are evenly distributed without agglomeration.

[0072] (2) The PET-doped carbon dots of the present invention have a high fluorescence quantum yield of more than 45%, and are stable in saline solutions and can be used to detect the pH value of solutions.

[0073] (3) The PET-doped carbon dots of the present invention can be used to detect the water content in organic solutions. When the water content is in the range of 0.00001% to 0.5%, the degree of fluorescence quenching shows a good linear relationship with the water content. Using PET-doped carbon dots as fluorescent probes can achieve fast and efficient detection of the water content in the organic solvent 1,4-dioxane.

[0074] (4) The PET-doped carbon dots of the present invention have excellent light absorption and light conversion properties and can be applied to light-blocking films (LBFs). They can not only block most of the light but also have adjustable light absorption capacity and good biocompatibility.

[0075] (5) The present invention provides a new idea for the reuse of waste PET by first degrading the waste PET and then reacting it with a dopant, which is beneficial to environmental protection and reducing the cost of carbon dot preparation.

[0076] Example

[0077] 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.

[0078] Example 1

[0079] 192 g of PET waste fiber, 56 mL of ethylene glycol, and 1.6 g of zinc acetate dihydrate were added to a 1000 mL round-bottom flask, which was then placed in a microwave reactor. The microwave reactor was adjusted to gear 06, and the raw materials were reacted at a power of 540 W for 20 minutes. The microwave method was used to fully react the raw materials and cause alcoholysis. After natural cooling, a large amount of white solid product was obtained to obtain PET oligomers.

[0080] 0.2 g of PET oligomer, 0.07 g of pyromellitic anhydride, 0.1 g of urea, and 20 mL of tetrahydrofuran were placed in a 50 mL reactor. The reactor was placed in a forced air drying oven at 260°C for 36 hours and allowed to cool naturally to room temperature. The liquid in the reactor was poured out to obtain a crude product of PET-doped carbon dots.

[0081] Use a disposable syringe and a 0.22μm organic needle filter to remove large particle impurities, and freeze-dry the filtrate. After redispersion with ethanol, dialyze using a dialysis bag with a molecular weight cutoff of 1kD to remove small molecular impurities. Before use, boil the dialysis bag in deionized water for 5-10 minutes, then wash it three times with anhydrous ethanol. Clamp one end of the dialysis bag with a dialysis bag clamp, fill it with anhydrous ethanol, and press it with your fingers to check for leaks. Place the gelatin-based carbon dot filtrate obtained above into the dialysis bag, filling it to 1 / 2-2 / 3. This will prevent the anhydrous ethanol buffer from outside the bag from entering the bag excessively during dialysis and causing it to rupture. After the filtrate is filled, clamp the bag with a clamp and place it in a large beaker filled with anhydrous ethanol. Place a magnet in the glass beaker and place the glass beaker on a magnetic stirrer to accelerate the dialysis speed. During the first 8 hours of dialysis, the anhydrous ethanol solution needs to be changed every 2 hours. After changing the anhydrous ethanol solution four times, leave it overnight and change the solution for the last time the next morning. The total dialysis time is 30 hours to remove the remaining small molecule impurities.

[0082] Collect the liquid in the dialysis bag to obtain the purified PET-doped carbon dot solution. Place the solution in a glass container and place it in a refrigerator until the product solidifies. Then, quickly transfer it to a vacuum freeze dryer for freeze-drying to obtain a brown solid powder, which is the PET-doped carbon dot solid powder.

[0083] Example 2

[0084] The preparation of PET-doped carbon dots was carried out in a manner similar to Example 1, except that the amount of pyromellitic anhydride was 0.03 g.

[0085] Example 3

[0086] The preparation of PET-doped carbon dots was carried out in a similar manner to Example 1, except that the amount of pyromellitic anhydride was 0.05 g.

[0087] Example 4

[0088] The preparation of PET-doped carbon dots was carried out in a similar manner to Example 1, except that the amount of pyromellitic anhydride was 0.09 g.

[0089] Example 5

[0090] PET-doped carbon dots were prepared in a manner similar to Example 1, except that 2 g of PET oligomer, 0.5 g of p-phenylenediamine (PP), 1 mL of phosphoric acid (PA), and 40 mL of acetic acid (AA) were added to a reactor, which was placed in a forced air drying oven at 260°C for 24 h and naturally cooled to room temperature.

[0091] Example 6

[0092] PET-doped carbon dots were prepared in a manner similar to Example 1, except that 2 g of PET oligomer, 1 mL of phosphoric acid, and 40 mL of acetic acid were added to a reactor, which was placed in a forced air drying oven at 260°C for 24 h and then naturally cooled to room temperature.

[0093] Example 7

[0094] PET-doped carbon dots were prepared in a manner similar to Example 1, except that 2 g of PET oligomer, 0.5 g of p-phenylenediamine (PP), and 40 mL of acetic acid (AA) were added to a reactor, which was placed in a forced air drying oven at 260°C for 24 h and then naturally cooled to room temperature.

[0095] Example 8

[0096] The preparation of PET-doped carbon dots was carried out in a manner similar to Example 1, except that 2 g of PET oligomer and 40 mL of acetic acid were added to a reactor, which was placed in a forced air drying oven at 260° C. After 24 h, the reactor was taken out and naturally cooled to room temperature.

[0097] Example 9

[0098] PET-doped carbon dots were prepared in a manner similar to Example 1, except that 2 g of PET oligomer, 1 mL of concentrated sulfuric acid, 1 g of p-phenylenediamine, and 40 mL of anhydrous ethanol were placed in a 100 mL reactor, which was then placed in a forced air drying oven at 260°C. After 18 h, the reactor was taken out and naturally cooled to room temperature.

[0099] The absolute ethanol was changed every 12 h, for a total of seven changes, and the dialysis was continued for 84 h.

[0100] Example 10

[0101] PET-doped carbon dots were prepared in a manner similar to Example 1, with the following difference: 2 g of PET oligomer, 1 mL of concentrated sulfuric acid, and 40 mL of anhydrous ethanol were placed in a 100 mL reactor, which was placed in a forced air drying oven at 260°C for 18 h and naturally cooled to room temperature.

[0102] The absolute ethanol was changed every 12 h, for a total of seven changes, and the dialysis was continued for 84 h.

[0103] Example 11

[0104] PET-doped carbon dots were prepared in a manner similar to Example 1, with the following difference: 2 g of PET oligomer, 1 g of p-phenylenediamine, and 40 mL of anhydrous ethanol were placed in a 100 mL reactor, which was placed in a forced air drying oven at 260°C for 18 h and naturally cooled to room temperature.

[0105] The absolute ethanol was changed every 12 h, for a total of seven changes, and the dialysis was continued for 84 h.

[0106] Comparative Example

[0107] Comparative Example 1

[0108] The carbon dots were prepared in a manner similar to Example 1, except that 0.5 g of p-phenylenediamine, 1 mL of phosphoric acid, and 40 mL of acetic acid were added to a reaction kettle, which was placed in a forced air drying oven at 260° C. After 24 h, the reaction kettle was taken out and naturally cooled to room temperature.

[0109] Comparative Example 2

[0110] The carbon dots were prepared in a manner similar to Example 1, except that 1 mL of concentrated sulfuric acid, 1 g of p-phenylenediamine, and 40 mL of anhydrous ethanol were placed in a 100 mL reactor, which was placed in a forced air drying oven at 260°C for 18 h and allowed to cool naturally to room temperature.

[0111] The absolute ethanol was changed every 12 h, for a total of seven changes, and the dialysis was continued for 84 h.

[0112] Experimental example

[0113] Experimental Example 1 Transmission Electron Microscope Test

[0114] The micromorphology and size of the carbon dots prepared in Example 1 were characterized using a transmission electron microscope (FET Tecnai G2 F30, manufactured by FEI, USA). Figure 1 shown.

[0115] from Figure 1 As can be seen in a, the PET-doped carbon dots are spherical in structure, evenly dispersed and without agglomeration. The lattice spacing is 0.21 nm, which is consistent with the in-plane (100) lattice spacing of graphene. Figure 1 The particle size of the PET-based doped carbon dots in b is between 1.6 and 2.9 nm, with an average particle size of 2.3 nm.

[0116] Experimental Example 2 Fourier Transform Infrared Spectroscopy Test

[0117] The structures of the carbon dots prepared in Example 1, Example 5 and Example 9 were characterized by Fourier transform infrared spectroscopy. The instrument model used was Nicolet Nexus 670, and the scanning range was 4000-400 cm -1 , the number of scans is 64. The test results are as follows Figure 2a 、 2b , as shown in 2c.

[0118] Figure 2a In 3300cm -1 The peaks on the left and right are the characteristic absorption peaks of OH / NH, at 2931cm -1 and 2871cm -1 The absorption peak at 1708 cm corresponds to the hydrogen on the benzene ring in the carbon nucleus. -1 The absorption peak at is attributed to the stretching vibration of C=O, indicating that the carbon dots contain polar functional groups such as amino and hydroxyl groups.

[0119] Figure 2b In 3255cm -1 A broad absorption peak is produced at 2963 cm-1. -1 The stretching vibration absorption peak of NH on the pyrrole ring is at 1590 cm -1 The stretching vibration peak of CN is at 1371 cm -1 , the vibration peak of PO is at 1237cm -1 The CH stretching vibration absorption peak on the benzene ring is at 828 cm -1 , it is speculated that there may be functional groups such as amino and hydroxyl groups on the surface of the carbon dots.

[0120] Figure 2c Medium, 3209cm -1 The absorption peak at 3045cm is relatively broad, which is the stretching vibration peak of NH / OH. -1 The stretching vibration absorption peak of the unsaturated CH group is 2960 cm -1 、2923cm -1 、2867cm -1 It has the saturated stretching vibration absorption peak of CH at 1694 cm -1 There is a bending vibration absorption peak of C=C or C=O at 1594cm -1 There is a deformation vibration absorption peak of C=N group at 1242cm -1There is a stretching vibration absorption peak of SOx at 1086cm -1 There is a stretching vibration absorption peak of CO at 817 cm -1 The stretching vibration absorption peak of CSO is 612 cm -1 There is a stretching vibration absorption peak of CSC at the carbon dots. Analysis shows that there are nitrogen and sulfur groups on the surface of the carbon dots, and the surface nitrogen and sulfur elements are successfully doped into the carbon dots.

[0121] Experimental Example 3: XPS Test

[0122] The elements contained in the carbon dots obtained in Example 6 were analyzed using X-ray photoelectron spectroscopy (XPS). The machine model used was 250Xi, the target material was aluminum palladium, and the emission voltage and current were 10kV and 5mA, respectively. The test results are shown in Figure 3. Figure 3a XPS spectra of C1s, N1s and O1s; Figure 3b XPS spectra of sp2 carbon, sp3 carbon and carbonyl carbon; Figure 3c is the high-resolution spectrum of N1 s; Figure 3d This is the high-resolution spectrum of O1s.

[0123] from Figure 3a It can be seen that the peaks at 285.08, 400.08, and 532.08 eV are the XPS spectra of C1s, N1s, and O1s, respectively, indicating that nitrogen is successfully doped into the PET-based doped carbon dots. Figure 3b There are three peaks in total, 284.68eV, 286.08eV and 288.48eV are the characteristic peaks of sp2 carbon (C=C), sp3 carbon (COC) and carbonyl carbon (C=O), respectively. Figure 3c This is the high-resolution spectrum of O1s, and the peak at 531.88eV is C=O. Figure 3d The high-resolution spectrum of N1s shows a single peak at 399.88 eV, representing CN. In summary, the XPS spectrum indicates that nitrogen atoms have been successfully doped into the carbon dots, further confirming the infrared spectroscopy results that indicate the presence of hydroxyl groups on the surface of the PET-doped carbon dots.

[0124] Experimental Example 4

[0125] The carbon dots prepared in Example 1 were tested by ultraviolet-visible absorption spectrum using a fluorescence spectrometer FS5 manufactured by Edinburgh, UK, to characterize their structure. Figure 4 shown.

[0126] The excitation wavelength, emission wavelength, and fluorescence emission spectrum of the carbon dots prepared in Examples 1, 5, and 9 were measured using a fluorescence spectrometer model FS5 manufactured by Edinburgh, UK. The test process was as follows: 20 μL of the crude carbon dot product and 1980 μL of tetrahydrofuran solution were mixed evenly in a four-way quartz cuvette using a pipette, and the fluorescence emission spectrum of the PET-doped carbon dots was measured using a fluorescence spectrometer. The test results are shown in Figure 2. Figure 5a 、 5b and 5c.

[0127] Figure 4 In the figure, there is an absorption peak at 249 nm, indicating that the PET-based doped carbon dots form a graphitic carbon structure.

[0128] Figure 5a The emission spectra of the PET-doped carbon dots prepared in Example 1 under light excitation of different wavelengths are shown in the figure. As can be seen from the figure, it is a typical non-excitation wavelength-dependent type. As the excitation wavelength increases, the fluorescence intensity of the carbon dots increases first and then decreases. When the excitation wavelength is 360 nm, the emission peak is located at around 470 nm, at which time the fluorescence intensity is the highest.

[0129] Figure 5b In the figure, when the excitation wavelength gradually increases from 300nm to 440nm, the position of the emission peak red-shifts from 450nm to 520nm, indicating that the carbon dots are typical excitation wavelength-dependent. Moreover, with the increase of the excitation wavelength, the fluorescence intensity first increases and then decreases. The fluorescence intensity is highest when the excitation wavelength is 340nm, and the emission peak is located at 460nm.

[0130] Figure 5c In the figure, as the excitation wavelength increases from 320nm to 500nm, the position of the maximum emission peak increases from 475nm to 570nm, and a red shift occurs, indicating that the carbon dots are dependent on the excitation wavelength. At the same time, as the excitation wavelength increases, the fluorescence intensity of the carbon dots first increases. When the excitation wavelength is 420nm, the fluorescence intensity is the largest, and the emission peak is located at 540nm, and then continues to decrease.

[0131] Experimental Example 5 Fluorescence Quantum Yield Test

[0132] The absolute fluorescence quantum yield of the carbon dots prepared in Example 1 and Example 9 was tested using an integrating sphere with a polytetrafluoroethylene inner coating. The test results are shown in Table 1. Figure 6a and 6b .

[0133] from Figure 6a It can be seen from the figure that the fluorescence quantum yield of the PET-doped carbon dots prepared in Example 1 when dispersed in tetrahydrofuran is 48.16%. Figure 6bIn the embodiment 9, the fluorescence quantum yield of the PET-doped carbon dots prepared was as high as 49.36%.

[0134] Experimental Example 6 Detection of water content in organic solvents

[0135] In organic chemical reactions, the presence of water can affect yields, inhibit reactions, and even cause serious disasters or explosions. When water is present in oil, it may cause engine performance to degrade. Therefore, the rapid and efficient detection of water content in organic solvents is of great importance and far-reaching significance.

[0136] The crude PET carbon dot product obtained in Example 1 was diluted 10 times and used as a fluorescent probe. 20 μL of the above probe solution and 1980 μL of 1,4-dioxane with different water contents were mixed evenly in a four-way light cuvette and placed in a fluorescence spectrometer to measure the fluorescence emission spectrum (360 nm excitation, 420-620 nm emission spectrum). The fluorescence intensity at the emission peak of 1,4-dioxane without water was recorded as F0, and the fluorescence intensity at the emission peak of 1,4-dioxane with different water contents was recorded as F. t , F0 and F t The difference is recorded as △F, and a linear relationship between △F and water content (V / V,%) is established. Figure 7 shown

[0137] Figure 7 Figure a shows the fluorescence emission spectra of PET-doped carbon dots in 1,4-dioxane with different water contents (under 470 nm excitation). It can be seen from the figure that the fluorescence intensity of PET-doped carbon dots decreases with increasing water content. Figure 7 b is the relationship between water content and fluorescence quenching degree, which shows that the two show a two-stage linear relationship. Figure 7 c, when the water content is between 0.01% and 0.5%, the linear relationship between the two is: △F=129455C+66128, R 2 =0.9966; see Figure 7 d, when the water content is between 0.00001% and 0.005%, the linear relationship between the two is: △F=5697658C+26569, R 2 =0.9963; the detection limit is 0.00001%. This indicates that the PET-doped carbon dots can be used as fluorescent probes to quickly and accurately detect the water content in the organic solvent 1,4-dioxane.

[0138] Experimental Example 7: Light Blocking Capacity Test of Light Blocking Film

[0139] A 15% polyvinyl alcohol solution was prepared. Different masses of the carbon dot powder prepared in Example 5 were then weighed and mixed with 10 g of the PVA solution to prepare solutions with carbon dot contents of 0%, 2%, 4%, 6%, 8%, 10%, 12%, and 14%. The mixture was ultrasonically treated at 80°C for 30 minutes to obtain a uniform mixture. A certain amount of the solution was then aspirated and an adjustable KTQ-II 150 mm applicator was used to prepare light-blocking films with varying carbon dot contents on a 60°C hot plate for subsequent testing.

[0140] The freeze-dried solid carbon dots prepared in Example 9 were mixed uniformly with a 5% polylactic acid solution in chloroform at different ratios (0%, 1%, 2%, 3%, 4%, 5%, 6%, and 7%) by ultrasonic treatment to obtain mixtures containing carbon dots in different ratios. 20 g of SNL was then weighed and placed in a dry watch glass with a diameter of 15 cm. The mixtures were allowed to stand at room temperature for 24 hours to obtain light-blocking films with different ratios.

[0141] The light blocking film was tested by UV spectrophotometry, and the UV spectrophotometer model was EVO600PC. The test results were as follows: Figure 8a and 8b shown.

[0142] The LBFs (light blocking films) prepared using Examples 5 and 9 as raw materials were irradiated to observe the blocking effects of the LBFs on ultraviolet light, blue light, mobile phone screen light, and natural light. The test results are as follows: Figure 9 and Figure 10 shown.

[0143] Figure 8a The transmittance of the light-blocking film decreases with increasing carbon dot content, while its blocking effect on blue and ultraviolet light becomes increasingly better. The wavelength range of harmful blue light is 415-455nm, within which the transmittance of a light-blocking film with a 14% carbon dot content is less than 30%. The wavelength range of harmful ultraviolet light is 315-400nm, within which the transmittance of a light-blocking film with a 14% carbon dot content is around 10%, blocking the vast majority of ultraviolet light.

[0144] Figure 8b In the experiment, the transmittance of the blocking film without adding carbon dots in the UV to blue light region is about 90%. With the increase of carbon dot content, the transmittance of the light blocking film gradually decreases, indicating that the light blocking film has strong absorption in the UV to blue light region and has adjustable light absorption capacity.

[0145] Figure 9 In b, as the carbon dot content in the light-blocking film increases, the transmittance of ultraviolet light with a wavelength of 380nm gradually decreases and the blocking rate gradually increases. When the carbon dot content is 12% and 14%, the blocking rate of ultraviolet light can reach 90%, which is the best effect. Figure 9 In Figure d, as the carbon dot content in the light-blocking film increases, the blue light (430 nm) blocking ability becomes stronger and stronger. The blocking rate can reach 80% when the carbon dot content is 12% and 14%. Figure 9 In figure f, under the irradiation of mobile phone screen light, as the carbon dot content increases, the light blocking effect becomes better. Among them, the light blocking film with a carbon dot content of 12% has the strongest and best blocking effect on mobile phone screen light. Figure 9 As shown in Figure 3, the higher the carbon dot content in the light-blocking film, the better it blocks natural light. A light-blocking film with a carbon dot content of 14% achieves the best blocking effect, blocking the most natural light. This indicates that the carbon dots of the present invention can be used as a light-blocking film to protect the human body from harmful blue and ultraviolet light.

[0146] from Figure 10 As can be seen in a, as the carbon dot content in the light-blocking film increases, the transmittance of ultraviolet light gradually decreases, and the light-blocking effect of the light-blocking film gradually increases. When the proportion of carbon dot content in the film is 6% and 7%, the blocking effect of 365nm ultraviolet light is close to 100%. Figure 10 In figure b, as the proportion of carbon dots in the light-blocking film increases, the transmittance of 430nm LED light gradually decreases, and the light-blocking effect of the light-blocking film gradually increases. When the proportion of carbon dots in the blocking film is 7%, the light-blocking film has the strongest blocking effect on blue light, which is about 90%. Figure 10 In c, as the carbon dot content increases, the transmittance of blue light emitted from the mobile phone screen gradually decreases. When the proportion of carbon dots in the barrier film is 7%, the blue light protection effect is the best, about 80%. Figure 10 As shown in Figure d, as the proportion of carbon dots in the light-blocking film increases, the film's absorption capacity for short-wavelength photons in natural light gradually increases. The light-blocking film with a 7% carbon dot ratio exhibits the best blue light protection, at approximately 90%. This indicates that the light-blocking film produced using carbon dots in the present invention can effectively block blue light emitted by mobile phones, as well as ultraviolet and blue light in natural light.

[0147] Experimental Example 8 Preparation and Testing of LED Devices

[0148] 100 mg of the PET-doped carbon dots prepared in Example 1 was weighed and placed in a covered glass vial. 2.8 mL of tetrahydrofuran was added and ultrasonicated for 5 minutes to evenly disperse the PET-doped carbon dots in the tetrahydrofuran. 1.1 g of polymethyl methacrylate was then added. After tightening the cap, the vial was ultrasonically dispersed in 70°C hot water for 30 minutes to obtain a uniform solution. The solution was then cooled to room temperature and used. Using a pipette, 50 μL of the resulting solution was added dropwise to a 430 nm LED chip. The chip was then placed in a fume hood and allowed to stand overnight. After the tetrahydrofuran completely evaporated, a white LED device was produced.

[0149] The prepared white LED device was tested using a multifunctional spectral illuminance meter (model: OHSP350M, equipped with a 0.3M integrating sphere) to obtain the spectrum, color coordinates, and correlated color temperature of the device. The voltage was fixed at 3.0 V. The test results are shown in Figure 11.

[0150] Figure 11a In the figure, the illustration is a physical picture of the LED device. It can be seen from the figure that the emission spectrum of the LED device contains two emission peaks: one peak is located at 430nm, which is the emission peak of the blue light chip, and the other wider peak is the emission peak of the carbon dots, with a peak position at 622nm, which is yellow light. The two emission peaks combine to form white light. Figure 11b In the figure, the color coordinates of the LED chip are (0.37, 0.31), which are close to the color coordinates of pure white light (0.33, 0.33). The correlated color temperature is 3787K, which is warm white light.

[0151] Experimental Example 9

[0152] The fluorescence emission spectra of the carbon dots prepared in Examples 1 to 11 and Comparative Examples 1 and 2 were measured using a fluorescence spectrometer model FS5 produced by Edinburgh, UK. The test results of Examples 1 to 4 are shown in FIG. Figure 12a As shown, the test results of Examples 5 to 8 and Comparative Example 1 are as follows Figure 12b As shown, the test results of Examples 9 to 11 and Comparative Example 2 are as follows Figure 12c shown.

[0153] from Figure 12a It can be seen that with the increase in the amount of pyromellitic anhydride, the fluorescence intensity of the carbon dots shows a trend of first increasing and then decreasing. When the amount of pyromellitic anhydride is 0.07 g, the fluorescence intensity of the carbon dots is the strongest.

[0154] Figure 12b When the dopants are different, the fluorescence intensity of the carbon dots is different. The fluorescence intensity of the carbon dots prepared by doping phosphorus and nitrogen elements is the highest, that is, the fluorescence intensity of the carbon dots prepared in Example 5 is the highest.

[0155] Figure 12c Among them, the fluorescence intensity of PET-based carbon dots without sulfur and nitrogen doping is the weakest, and the fluorescence intensity of PET-based carbon dots doped with sulfur and nitrogen elements are both improved to a certain extent. When the precursors are only concentrated sulfuric acid and p-phenylenediamine, the fluorescence intensity is stronger because p-phenylenediamine also contains carbon elements. The fluorescence intensity of carbon dots doped with sulfur and nitrogen elements in PET is the strongest.

[0156] 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 doped carbon dot, characterized in that: The PET-based doped carbon dots are mainly prepared using PET and a dopant as raw materials through a preparation method comprising the following steps: Step 1: alcoholyzing PET in the presence of zinc acetate dihydrate to obtain PET oligomers; Step 2: PET oligomers, dopants, and acid anhydride compounds react in tetrahydrofuran to obtain a crude product of PET-doped carbon dots. Wherein, the acid anhydride compound is pyromellitic anhydride, and the dopant is urea; Step 3, filtering and dialyzing the crude product of PET-doped carbon dots to obtain PET-doped carbon dots; The mass ratio of the dopant to the PET oligomer is (0.1-30):1; The optimal excitation wavelength of the PET-based doped carbon dots is 320-450 nm, and the optimal emission wavelength is 450-600 nm.

2. The PET-based doped carbon dots according to claim 1, characterized in that The fluorescence quenching degree of the PET-doped carbon dots in 1,4-dioxane is linearly related to the water content in 1,4-dioxane; The degree of fluorescence quenching refers to the difference between the peak fluorescence intensity of carbon dots in 1,4-dioxane without water and the peak fluorescence intensity of carbon dots in 1,4-dioxane with different water contents.

3. The PET-based doped carbon dots according to claim 1, characterized in that The PET-doped carbon dots are spherical in structure, with a fluorescence quantum yield of over 45%, and a linear relationship between the fluorescence intensity and the pH value of the solution. The light-blocking film obtained using the carbon dots as raw materials has a UV light blocking rate of over 80%, a blue light blocking rate of over 70%, a mobile phone screen light blocking rate of over 70%, and a natural light blocking rate of over 80%.

4. A method for preparing the PET-based doped carbon dots according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1: alcoholyzing PET in the presence of zinc acetate dihydrate to obtain PET oligomers; Step 2: PET oligomers, dopants, and acid anhydride compounds react in tetrahydrofuran to obtain a crude product of PET-doped carbon dots. Wherein, the acid anhydride compound is pyromellitic anhydride, and the dopant is urea; Step 3: Filter and dialyze the crude product of PET-doped carbon dots to obtain PET-doped carbon dots.

5. The preparation method according to claim 4, characterized in that In step 2, The mass ratio of the acid anhydride compound to the PET oligomer is (0.05-2):

1.

6. A use of the PET-based doped carbon dots according to any one of claims 1 to 3, characterized in that: The PET-based doped carbon dots were used to detect the water content in 1,4-dioxane.

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