Fluorescent carbon quantum dots, preparation method and application thereof

Abstract

The present invention discloses a fluorescent carbon quantum dot, a preparation method and an application thereof, and relates to the technical field of quantum dot materials. The raw materials of the fluorescent carbon quantum dots of the present invention include terephthalaldehyde and thiourea. The fluorescent carbon quantum dots of the present invention use terephthalaldehyde and thiourea as raw materials, have aggregation-induced fluorescence enhancement characteristics, and the preparation method is simple, easy to operate, low in cost, green and mild. The fluorescent carbon quantum dots can be quenched by p-nitrophenol as a fluorescent probe. Therefore, they can be used for rapid, sensitive and highly specific identification of p-nitrophenol, overcoming the shortcomings of existing organic pollutant detection methods such as long detection time, complicated steps and high cost.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum dot materials, and in particular to fluorescent carbon quantum dots, a preparation method thereof, and applications thereof. Background Art

[0002] The birth of quantum dots has played an important role in promoting the development of fluorescent probes. Carbon quantum dots are a type of nanomaterial discovered during the development of quantum dots. They have the advantages of high biocompatibility, controllable particle size, easy preparation and high cost-effectiveness. Due to their various physical signal characteristics, carbon quantum dots are widely used in various rapid measurement fields such as colorimetric detection, fluorescence detection, electrochemical detection and surface-enhanced Raman spectroscopy. Unlike traditional detection methods that rely on the combination of high-resolution detection instruments such as liquid or gas chromatographs and mass spectrometers, rapid detection methods dominated by carbon quantum dots have shown outstanding advantages such as high cost performance, short detection time, obvious detection results, simple operation and portable detection equipment. Therefore, in the field of pollutant detection such as pesticide pollution, heavy metal ion pollution, mycotoxin pollution and other pollutant residue detection, carbon quantum dots have supported the development and application of many rapid detection methods.

[0003] At present, most common carbon quantum dots are synthesized in organic solvent systems and prepared by using carbon and nitrogen sources under high temperature and high pressure conditions. However, carbon quantum dots prepared by this method, after further purification of the reaction solvent, will undergo the common phenomenon of aggregation-induced quenching in water, that is, the fluorescence of the probe is weakened in water. The occurrence of this aggregation-induced quenching phenomenon is mostly due to the intervention of the aqueous solvent, which causes the distance between the probe molecules or nanomaterials to be too close, thereby destroying the original conjugated system. Therefore, the further application of carbon quantum dots in some fields, such as water pollutant detection, is hindered by factors such as low fluorescence yield, solvent interference, and aggregation-induced quenching effect.

[0004] Aggregation-induced fluorescence (AIFE) probes are a new type of fluorescent probe with aggregation-induced luminescence (AIE) properties. Their discovery offers a new solution and approach to the problem of low efficiency of fluorescent probes in aqueous microenvironments. However, common AIE probes are mostly molecular luminescent, which are inferior to carbon quantum dots in luminescence efficiency, stability, and signal modulation capabilities, resulting in a narrower range of applications. Summary of the Invention

[0005] The present invention aims to address at least one of the aforementioned technical problems in the prior art. To this end, the present invention provides fluorescent carbon quantum dots with aggregation-induced fluorescence enhancement properties. These fluorescent carbon dots, using terephthalaldehyde and thiourea as precursors, exhibit high-intensity fluorescence emission in a solvent, thereby addressing the limitations of existing carbon quantum dots due to aggregation-induced quenching.

[0006] The second aspect of the present invention is to provide a method for preparing fluorescent carbon quantum dots.

[0007] The third aspect of the present invention is to provide an application of fluorescent carbon quantum dots.

[0008] A fourth aspect of the present invention provides a method for detecting p-nitrophenol.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A first aspect of the present invention provides fluorescent carbon quantum dots, wherein raw materials of the fluorescent carbon quantum dots include terephthalaldehyde and thiourea.

[0011] The fluorescent carbon quantum dots of the present invention use terephthalaldehyde and thiourea as precursors, have aggregation-induced fluorescence enhancement (AIEE) characteristics, and have high-intensity fluorescence emission in solvents, which solves the aggregation-induced quenching problem of existing carbon quantum dots. Compared with existing molecular luminescence aggregation-induced fluorescence enhancement probes, they have significant advantages in luminescence efficiency, stability and signal modulation ability, and have a wider range of applications.

[0012] In some embodiments of the present invention, the particle size distribution of the fluorescent carbon quantum dots is 2 to 6 nm.

[0013] In some embodiments of the present invention, the particle size distribution of the fluorescent carbon quantum dots is 2 to 6 nm.

[0014] In some embodiments of the present invention, the molar ratio of terephthalaldehyde to thiourea is 1:(0.5-8)

[0015] In some embodiments of the present invention, the molar ratio of terephthalaldehyde to thiourea is 1:(1-4).

[0016] In some specific embodiments of the present invention, the molar ratio of terephthalaldehyde to thiourea is 1:(1-2).

[0017] In some embodiments of the present invention, the fluorescent carbon quantum dots emit green fluorescence in an alcohol solution or an acid solution under irradiation with 365 nm ultraviolet light.

[0018] In some embodiments of the present invention, the alcohol solution includes methanol and / or ethanol; the acid solution includes formic acid and / or acetic acid.

[0019] In some embodiments of the present invention, the fluorescent carbon quantum dots emit green fluorescence in an ethanol solution with a volume fraction of ≥70% under irradiation with 365 nm ultraviolet light.

[0020] In some specific embodiments of the present invention, the volume fraction of ethanol is 70-98%.

[0021] In some examples of the present invention, the volume fraction of ethanol is 85-95%.

[0022] In some embodiments of the present invention, the ethanol solution of the fluorescent carbon quantum dots is added to water and emits blue fluorescence under 365 nm ultraviolet light.

[0023] In some specific embodiments of the present invention, the ethanol solution of the fluorescent carbon quantum dots is added into water, and the volume fraction of water is ≥70%.

[0024] In some examples of the present invention, the volume fraction of water is 85-95%.

[0025] In some embodiments of the present invention, the maximum excitation wavelength of the fluorescent carbon quantum dots in water is 360 nm; the maximum emission wavelength is 440 nm.

[0026] In some embodiments of the present invention, the water contains ethanol, and the volume fraction of the water is 85-95%.

[0027] The fluorescent carbon quantum dots of the present invention present blue light in a mixed solution of water and ethanol, have a maximum excitation wavelength of 360 nm, a maximum emission wavelength of 440 nm, and have the optical characteristic of aggregation-induced fluorescence enhancement.

[0028] In some embodiments of the present invention, the maximum excitation wavelength of the fluorescent carbon quantum dots in ethanol is 380 nm; the maximum emission wavelength is 480 nm.

[0029] In some embodiments of the present invention, the ethanol is an aqueous solution of ethanol; the volume fraction of the ethanol is 85-95%.

[0030] The fluorescent carbon quantum dots of the present invention exhibit significant green light in aqueous ethanol solutions, with a maximum excitation wavelength of 380 nm and a maximum emission wavelength of 480 nm. Compared to the maximum emission wavelength in aqueous ethanol solutions, the emission wavelength is blue-shifted by 40 nm, and the fluorescence intensity increases by approximately 400%. This property provides the fluorescent carbon quantum dots with a more sensitive detection advantage when used as fluorescent probes for pollutant detection.

[0031] The fluorescent carbon quantum dots of the present invention are mixed with a solvent (e.g., water and / or ethanol) to obtain a solution in which the higher the water content, the stronger the fluorescence intensity. That is, the fluorescent carbon quantum dots of the present invention can exhibit significant aggregation-induced fluorescence enhancement in a high-proportion water-ethanol mixed solution.

[0032] In order to achieve better fluorescent imaging effects after the fluorescent carbon quantum dots of the present invention are mixed with a solvent, the volume content of water in the solvent is ≥30%, and further, the volume content of water is ≥90%.

[0033] The second aspect of the present invention provides a method for preparing the fluorescent carbon quantum dots according to the first aspect of the present invention, comprising the following steps:

[0034] The fluorescent carbon quantum dots are obtained by subjecting terephthalaldehyde and thiourea to a solvothermal reaction in an acidic solvent.

[0035] The present invention prepares nitrogen-sulfur co-doped fluorescent carbon quantum dots (N,S-CDs) with aggregation-induced fluorescence enhancement by adding terephthalaldehyde and thiourea to an acidic solvent, which provides acidic conditions. The acidic solvent then undergoes a solvothermal reaction under these conditions. The fluorescent carbon quantum dots have adjustable wavelength and intensity in different solvents, such as water or ethanol. The fluorescent carbon quantum dots of the present invention, which exhibit high-intensity fluorescence emission in solvents (e.g., water), can be used to rapidly detect pollutants, particularly organic pollutants.

[0036] The amount of acidic solvent used is sufficient to dissolve terephthalaldehyde and thiourea.

[0037] In some embodiments of the present invention, the temperature of the solvothermal reaction is 150-240°C.

[0038] In some embodiments of the present invention, the temperature of the solvothermal reaction is 160-240°C.

[0039] In some embodiments of the present invention, the temperature of the solvothermal reaction is 160-220°C.

[0040] In some specific embodiments of the present invention, the temperature of the solvothermal reaction is 170-210°C.

[0041] In some examples of the present invention, the temperature of the solvothermal reaction is 175-185°C.

[0042] In some embodiments of the present invention, the solvent thermal reaction time is 4 to 24 hours.

[0043] In some embodiments of the present invention, the solvent thermal reaction time is 8 to 24 hours.

[0044] In some specific embodiments of the present invention, the solvent thermal reaction time is 10 to 24 hours.

[0045] In some examples of the present invention, the solvent thermal reaction time is 10 to 12 hours.

[0046] In some embodiments of the present invention, the acidic solvent comprises formic acid and / or acetic acid.

[0047] In some embodiments of the present invention, the pH of the acidic solvent is 2-3 as measured by a pH meter.

[0048] In some embodiments of the present invention, the purity of the formic acid and acetic acid is 100%; the acidity coefficient of the acetic acid at room temperature is 4.8.

[0049] In some embodiments of the present invention, the solvothermal reaction further includes precipitation and purification steps.

[0050] In some embodiments of the present invention, the precipitation and purification steps include adding water to form a precipitate and using an acidic solvent to dissolve the precipitate.

[0051] In some specific embodiments of the present invention, the precipitation and purification include the following steps: adding water to the product solution of the solvothermal reaction to form a precipitate, dissolving the precipitate with an acidic solvent after solid-liquid separation, continuing to add water for precipitation, and repeating the process twice or more.

[0052] In some embodiments of the present invention, the volume ratio of the acidic solvent for precipitation and purification to water is 1:(2-48).

[0053] The volume ratio here refers to the volume ratio of the acidic solvent to water when water is added to the acidic solvent containing carbon quantum dots to form a precipitate.

[0054] In some specific embodiments of the present invention, the volume ratio of the acidic solvent to water is 1:(20-30).

[0055] In some specific embodiments of the present invention, the acidic solvent includes formic acid and / or acetic acid.

[0056] In some embodiments of the present invention, after the purification, the fluorescent carbon quantum dots are dissolved in an alcohol solution.

[0057] In some specific embodiments of the present invention, the alcohol solution is methanol and / or ethanol.

[0058] It should be noted that the mixed solution obtained after the solvent thermal reaction of the present invention can be used directly for detection, or it can be purified with water, that is, the purification step is optional. Utilizing the characteristics of the fluorescent carbon quantum dots that aggregate in water, acetic acid and water can be used to repeatedly precipitate and redissolve to remove impurities. The dried fluorescent carbon quantum dot powder can be redissolved in an alcohol solution and then stored at room temperature and taken out when needed.

[0059] The third aspect of the present invention provides an application of the fluorescent carbon quantum dots described in the first aspect of the present invention, or the fluorescent carbon quantum dots obtained by the preparation method described in the second aspect of the present invention, in pollutant detection.

[0060] In some embodiments of the present invention, the pollutants include water pollutants.

[0061] In some embodiments of the invention, the contaminant comprises p-nitrophenol.

[0062] In some embodiments of the present invention, the ratio of the volume of the fluorescent carbon quantum dot solution to the volume of the pollutant solution is 1:(7-11).

[0063] In some embodiments of the present invention, the ratio of the volume of the fluorescent carbon quantum dot solution to the volume of the pollutant solution is 1:(8-10).

[0064] For example, when detecting pollutants, 100 μL of fluorescent carbon quantum dot solution and 700-1100 μL of the pollutant solution to be tested are mixed and then tested.

[0065] In some embodiments of the present invention, the standard system for the detection is 1 to 2 mL.

[0066] For example, 100 μL of fluorescent carbon quantum dot solution was used, and after adding the pollutant solution to be detected, water was added to make up to 1-2 mL.

[0067] In some embodiments of the present invention, the excitation wavelength of the detection is 310-380 nm.

[0068] In some embodiments of the present invention, the excitation wavelength of the detection is 350-370 nm.

[0069] In some embodiments of the present invention, the emission wavelength of the detection is 400-500 nm.

[0070] In some embodiments of the present invention, the emission wavelength of the detection is 440-460 nm.

[0071] In some specific embodiments of the present invention, the emission wavelength of the detection is 450-460 nm.

[0072] In some embodiments of the present invention, the linear range of detection of the pollutant is 1 to 50 μmol / L.

[0073] In some embodiments of the present invention, the detection limit of the pollutant is 0.6-0.7 μmol / L.

[0074] In some embodiments of the present invention, the pH of the solution of the pollutant is 8-12.

[0075] The fourth aspect of the present invention provides a method for detecting p-nitrophenol, using the fluorescent carbon quantum dots described in the first aspect of the present invention or the fluorescent carbon quantum dots prepared by the method described in the second aspect of the present invention as fluorescent probes to detect p-nitrophenol.

[0076] The present invention conducts concentration gradient detection on p-nitrophenol with different concentrations and finds that the fluorescent carbon quantum dots of the present invention have specific selectivity and high sensitivity to p-nitrophenol.

[0077] In some embodiments of the present invention, the excitation wavelength used in the detection is 310-380 nm.

[0078] In some embodiments of the present invention, the excitation wavelength used in the detection is 350-370 nm.

[0079] In some embodiments of the present invention, the emission wavelength used in the detection is 400-500 nm.

[0080] In some embodiments of the present invention, the emission wavelength used for the detection is 440-460 nm.

[0081] In some specific embodiments of the present invention, the emission wavelength used for the detection is 450-460 nm.

[0082] In some embodiments of the present invention, a T-ris (tris(hydroxymethyl)aminomethane) buffer solution is used in the detection process; the concentration of the T-ris buffer solution is 0.01 to 1000 mmol / L.

[0083] In some embodiments of the present invention, the concentration of the T-ris buffer is 5 to 100 mmol / L.

[0084] In some specific embodiments of the present invention, the concentration of the T-ris buffer is 8 to 20 mmol / L.

[0085] In some examples of the present invention, the concentration of the T-ris buffer is 8 to 15 mmol / L.

[0086] Compared with the prior art, the present invention has the following beneficial effects:

[0087] (1) The fluorescent carbon quantum dots of the present invention, made from terephthalaldehyde and thiourea, exhibit high fluorescence intensity and aggregation-induced fluorescence enhancement. They can be uniformly dispersed in solvents such as alcohols and acids and emit green fluorescence. When transferred from a high-proportion organic solvent system to a high-proportion aqueous mixed solution, the fluorescent carbon quantum dots of the present invention exhibit aggregation and fluorescence enhancement, with the fluorescence intensity increasing by approximately 400%. During the fluorescence enhancement process, the wavelength also exhibits a blue shift.

[0088] (2) The present invention obtains fluorescent carbon quantum dots with aggregation-induced fluorescence enhancement characteristics by performing a solvothermal reaction of a specific precursor in an acidic solvent. The preparation method of the fluorescent carbon quantum dots is simple, easy to operate, low in cost, green and mild, and is suitable for large-scale production.

[0089] (3) The fluorescent carbon quantum dots of the present invention can be used as fluorescent probes to be quenched by pollutants, especially organic pollutants. Therefore, they can be used in the detection of pollutants to achieve rapid, sensitive and highly specific identification of pollutants, and are particularly suitable for the detection of p-nitrophenol. Using the fluorescent carbon quantum dots of the present invention as fluorescent probes can overcome the shortcomings of existing organic pollutant detection methods, such as being time-consuming, complex, and costly.

[0090] (4) Compared with common probes of aggregation-induced quenching type, the fluorescent carbon quantum dots of the present invention can be used to develop enhanced fluorescent probes or products in aqueous solution, which is beneficial to the development of high-intensity fluorescent probes in aqueous system environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 This is a photo of the luminescence of the solution of the products obtained in Example 1 and Comparative Examples 1-2 under 365nm ultraviolet light.

[0092] Figure 2 1 and 2 are the fluorescence spectra (excitation wavelength 360 nm) of the fluorescent carbon quantum dots of Example 1 and Examples 6 to 8.

[0093] Figure 3 1 and 2 are the fluorescence spectra (excitation wavelength 360 nm) of the fluorescent carbon quantum dots of Examples 1 and 9 to 13.

[0094] Figure 4 : Fluorescence spectra of the fluorescent carbon quantum dots of Examples 1 to 5 (excitation wavelength 360 nm).

[0095] Figure 5 The images and corresponding characteristic signals of the fluorescent carbon quantum dots of Example 1 scanned by a transmission electron microscope (A) and an infrared spectrometer (B); wherein Figure 5 A is a high-resolution transmission electron microscope image. Figure 5 B is the infrared spectrum.

[0096] Figure 6 Graph showing the fluorescence emission spectra of the fluorescent carbon quantum dots of Example 1 in mixed solvents of ethanol and water at different ratios.

[0097] Figure 7 These are the fluorescence excitation and emission spectra of the fluorescent carbon quantum dots of Example 1 obtained by scanning with a fluorescence spectrometer.

[0098] Figure 8 This is a linear relationship diagram of the fluorescent carbon quantum dots in Example 1 used to detect p-nitrophenol.

[0099] Figure 9 This is a diagram showing the selectivity test results of the fluorescent carbon quantum dots in Example 1 when used in interfering substances. DETAILED DESCRIPTION

[0100] The present invention is further described in detail below using specific examples. Unless otherwise specified, the raw materials, reagents, and apparatus used in the examples and comparative examples are available from conventional commercial sources or by conventional methods. Unless otherwise specified, all experimental or testing methods are conventional in the art.

[0101] Terephthalaldehyde, thiourea, and acetic acid used in the following examples of the present invention were purchased from Aladdin Reagent (Shanghai, China); all chemicals were at least analytical grade and did not require further purification before use.

[0102] The experimental water was double distilled water; the pH of acetic acid was measured by a pH meter to be 2-3.

[0103] The following describes it in detail with reference to specific embodiments.

[0104] Example 1

[0105] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:1.

[0106] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0107] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:1) in 10 mL of acetic acid by sonication.

[0108] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 10 h to perform a solvothermal reaction;

[0109] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0110] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0111] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0112] Example 2

[0113] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 2:1.

[0114] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0115] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 2:1) in 10 mL of acetic acid by sonication.

[0116] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 10 h to perform a solvothermal reaction;

[0117] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0118] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0119] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0120] Example 3

[0121] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:2.

[0122] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0123] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:2) in 10 mL of acetic acid by sonication.

[0124] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 10 h to perform a solvothermal reaction;

[0125] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0126] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0127] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0128] Example 4

[0129] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:4.

[0130] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0131] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:4) in 10 mL of acetic acid by sonication.

[0132] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 10 h to perform a solvothermal reaction;

[0133] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0134] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0135] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0136] Example 5

[0137] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:8.

[0138] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0139] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:8) in 10 mL of acetic acid by ultrasonication.

[0140] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 10 h to perform a solvothermal reaction;

[0141] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0142] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0143] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0144] Example 6

[0145] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:1.

[0146] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0147] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:1) in 10 mL of acetic acid by sonication.

[0148] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 150 ° C for 10 h to perform a solvothermal reaction;

[0149] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0150] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0151] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0152] Example 7

[0153] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:1.

[0154] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0155] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:1) in 10 mL of acetic acid by sonication.

[0156] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 210 ° C for 10 h to perform a solvothermal reaction;

[0157] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0158] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0159] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0160] Example 8

[0161] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:1.

[0162] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0163] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:1) in 10 mL of acetic acid by sonication.

[0164] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 240 ° C for 10 h to perform a solvothermal reaction;

[0165] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0166] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0167] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0168] Example 9

[0169] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:1.

[0170] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0171] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:1) in 10 mL of acetic acid by sonication.

[0172] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 4 h to perform a solvothermal reaction;

[0173] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0174] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0175] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0176] Example 10

[0177] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:1.

[0178] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0179] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:1) in 10 mL of acetic acid by sonication.

[0180] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 8 h to perform a solvothermal reaction;

[0181] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0182] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0183] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0184] Example 11

[0185] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:1.

[0186] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0187] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:1) in 10 mL of acetic acid by sonication.

[0188] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 12 h to perform a solvothermal reaction;

[0189] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0190] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0191] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0192] Example 12

[0193] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:1.

[0194] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0195] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:1) in 10 mL of acetic acid by sonication.

[0196] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 24 h for a solvothermal reaction;

[0197] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0198] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0199] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0200] Example 13

[0201] This embodiment provides fluorescent carbon quantum dots, the raw materials of which include terephthalaldehyde and thiourea; the molar ratio of terephthalaldehyde to thiourea is 1:1.

[0202] The preparation method of fluorescent carbon quantum dots in this embodiment includes the following steps:

[0203] S1. Completely dissolve terephthalaldehyde and thiourea (molar ratio 1:1) in 10 mL of acetic acid by sonication.

[0204] S2. The mixture obtained in step S1 was transferred to a polytetrafluoroethylene reactor and heated in an oven at 180 ° C for 10 h to perform a solvothermal reaction;

[0205] S3. After the product solution of step S2 was cooled to room temperature, the resulting solution was centrifuged at 4700 rpm to remove solid impurities; the supernatant was then diluted with 24 volumes of deionized water to precipitate fluorescent carbon quantum dots (N, S-CDs), centrifuged, and the by-products were removed;

[0206] S4. The precipitate obtained in step S3 was redissolved with acetic acid and precipitated with water (the volume ratio of acetic acid to water was 1:24). The precipitation, centrifugation, and redissolution were repeated twice or more. The obtained fluorescent carbon quantum dot precipitate was dried to completely remove the solvent to obtain a fluorescent carbon quantum powder.

[0207] S5. Finally, the fluorescent carbon quantum dot powder was dissolved in 100 mL of ethanol and stored at room temperature for later use.

[0208] Comparative Example 1

[0209] This comparative example provides a method for preparing quantum dots, which is different from Example 1 only in that thiourea is not added.

[0210] Comparative Example 2

[0211] This comparative example provides a method for preparing quantum dots, which differs from Example 1 only in that terephthalaldehyde is not added.

[0212] Comparative Example 3

[0213] This comparative example provides a method for preparing quantum dots, which is different from Example 1 only in that thiourea is replaced by urea.

[0214] Comparative Example 4

[0215] This comparative example provides a method for preparing quantum dots, which is different from Example 1 only in that terephthalaldehyde is replaced by citric acid.

[0216] Comparative Example 5

[0217] This comparative example provides a method for preparing quantum dots, which is different from Example 1 only in that the acetic acid in step S1 is replaced by water.

[0218] Comparative Example 6

[0219] This comparative example provides a method for preparing quantum dots, which is different from Example 1 only in that the acetic acid in step S1 is replaced by an aqueous solution of sodium hydroxide.

[0220] The preparation methods of Comparative Examples 3 to 6 cannot obtain carbon quantum dots with aggregation-induced fluorescence enhancement properties. Among them, the product obtained in Comparative Example 3 shows fluorescence quenching in water or ethanol, and the products obtained in Comparative Examples 4 to 6 have no obvious fluorescence emission in water or ethanol.

[0221] Take 50 μL of the fluorescent carbon quantum dot solution prepared in Example 1 and Comparative Examples 1-2, add 50 μL of ethanol and 900 μL of water to prepare 1 mL of the test solution; then transfer the test solution to a fluorescence cuvette, and then place it in a fluorescence spectrometer, use 360 ​​nm for excitation, and scan the fluorescence signal at 400-550 nm. The results are as follows: Figure 1 shown. Figure 1 The luminescence images of the products obtained in Example 1 and Comparative Examples 1 to 2 under 365nm ultraviolet light are shown in FIG. Figure 1 It can be observed that the use of terephthalaldehyde or thiourea alone in acetic acid cannot produce fluorescent signal products, which confirms that the synthetic raw material precursors of the present invention are terephthalaldehyde and thiourea, which can obtain aggregation-induced fluorescence enhanced fluorescent carbon quantum dots.

[0222] Figure 2 The fluorescence spectra of the fluorescent carbon quantum dots of Examples 1 and 6 to 8 (excitation wavelength 360 nm) are shown in FIG. Figure 3 is the fluorescence spectrum (excitation wavelength 360 nm) of the fluorescent carbon quantum dots of Example 1 and Examples 9 to 13, Figure 4 The fluorescence spectra of the fluorescent carbon quantum dots of Examples 1 to 5 (excitation wavelength 360 nm) were taken. 50 μL of the fluorescent carbon quantum dot solutions (80 μg / mL) obtained in Examples 1 to 13 were added with 50 μL of ethanol and 900 μL of water to prepare 1 mL of the test solution. The test solution was then transferred to a fluorescence cuvette and placed in a fluorescence spectrometer. The fluorescence signal was scanned at 400 to 550 nm using 360 nm excitation. The results are shown in FIG. Figures 2-4 As shown. Figures 2-4 It can be seen that the fluorescence properties of the fluorescent carbon quantum dots obtained at different temperatures, heating times or precursor material ratios have significant differences. The results show that the fluorescent carbon quantum dots obtained under the reaction conditions of 180℃, 10h and a 1:1 precursor ratio have stronger fluorescence emission intensity.

[0223] Figure 5 The images and corresponding characteristic signals of the fluorescent carbon quantum dots of Example 1 scanned by a transmission electron microscope (A) and an infrared spectrometer (B); wherein Figure 5 A is a high-resolution transmission electron microscopy image (scale bar 10 nm). Figure 5 B is the infrared spectrum. Figure 5 As can be seen in Figure A, the fluorescent carbon quantum dots obtained by the present invention are approximately circular in shape, and further magnification reveals a significant lattice spacing. According to statistical analysis, the particle size distribution of the fluorescent carbon quantum dots of Example 1 of the present invention is 2 to 6 nm, mainly concentrated in the range of 3 to 5 nm, with an average particle size of 3.6 nm and a lattice spacing of 0.21 nm. Figure 5 In B, we can observe 726cm -1 、1165cm -1 、1207cm -1 、1570cm -1 , 1600cm -1 and 1705cm -1The signals correspond to CS, CO, C=S, aromatic C=C, C=O and O=CN bonds, which shows that terephthalaldehyde and thiourea have been bonded through chemical bonds.

[0224] Figure 6 The fluorescence emission spectra of the fluorescent carbon quantum dots in Example 1 in different proportions of ethanol and water are shown in Figure 1. The same amount of the fluorescent carbon quantum dot solution in Example 1 was dissolved in different proportions of water and ethanol mixed solutions (the volume ratios of water: ethanol were 10:90, 30:70, 50:50, 70:30, 90:10, respectively). The fluorescence spectra of the fluorescent carbon quantum dots were tested under the excitation of 360-380 nm wavelength light. Figure 6 As shown, the emission wavelength of the fluorescent carbon quantum dots in the ethanol solution was detected to have a blue shift from 483nm to 440nm as the proportion of water increased, and the fluorescence intensity increased significantly. The fluorescence intensity of the fluorescent carbon quantum dots increased with the increase of the water proportion until the water proportion increased to 90%, and the fluorescence intensity increased by about 400%, indicating that the fluorescent carbon quantum dots of the present invention have solvent-induced aggregation-induced fluorescence enhancement.

[0225] Application Example 1

[0226] Application Example 1 implements the detection of p-nitrophenol in pollutants. The final concentration of the T-ris buffer used is 10mmol / L (i.e., the concentration of T-ris in the test solution). The carbon quantum dots with aggregation-induced fluorescence enhancement and the pollutant solution containing p-nitrophenol are simply mixed for detection. 900μL of pollutant solutions containing p-nitrophenol of different concentrations are added to 50μL of ethanol and 50μL of fluorescent carbon quantum dot ethanol solution to prepare 1mL of test solution. The effects of different concentrations of p-nitrophenol-containing test solutions on the fluorescence signal of fluorescent carbon quantum dots are detected respectively. The final concentrations of p-nitrophenol in the test solution are 0μmol / L, 1μmol / L, 5μmol / L, 10μmol / L, 50μmol / L, and 100μmol / L. The results are as follows. Figure 7 and Figure 8 shown.

[0227] Figure 7 These are the fluorescence excitation and emission spectra of the fluorescent carbon quantum dots of Example 1 obtained by scanning with a fluorescence spectrometer. Figure 8 This is a linear relationship diagram of the fluorescent carbon quantum dots in Example 1 used to detect p-nitrophenol. Figure 7In the experiment, the maximum emission signal was selected for application to ensure the highest sensitivity. Under the excitation of 360nm wavelength light, the fluorescence spectrum of the fluorescent carbon quantum dots was tested, and the emission peak fluorescence intensity at 452nm wavelength was detected as I0; the fluorescence signal of the added p-nitrophenol was tested, and the fluorescence intensity at 452nm was recorded as I. After taking the difference, the proportion of the difference in I0 was calculated. The experiment was repeated 3 times, and the average value of the results was taken as the quenching rate. The linear regression equation was fitted using the final concentration of the target substance and the quenching rate of the fluorescent carbon quantum dots. The response of the fluorescent carbon quantum dots to different concentrations of p-nitrophenol was studied by fluorescence emission spectroscopy, and the results are as follows. Figure 8 As shown in the figure, the fluorescence quenching degree of fluorescent carbon quantum dots increases with the concentration of p-nitrophenol, and the relative fluorescence intensity linear detection curve can be expressed as (I0-I) / I0=0.009[concentration]+0.0866, with a correlation coefficient R 2 =0.99, and the linear range of the constructed detection of p-nitrophenol was 1 μmol / L to 50 μmol / L. The detection limit was calculated by the three-fold signal-to-noise method and was 0.62 μmol / L.

[0228] Application Example 2

[0229] This application example implements the detection of p-nitrophenol in pollutants. The final concentration of the T-ris buffer used is 10mmol / L (i.e., the concentration of T-ris in the test solution), and the results show high selectivity. The fluorescent carbon quantum dots of Example 1 are simply mixed with the test solution containing other interfering substances for detection. The interfering substances include methyl parathion, ethyl parathion, malathion, chlorfenapyr, fenvalerate, glyphosate, and diazinon. The same steps as in Application Example 1 are used to replace p-nitrophenol for selectivity testing. The results are repeated 3 times, and the average quenching rate is compared with the quenching rate of p-nitrophenol. Figure 9 This is a graph showing the selectivity test results of the fluorescent carbon quantum dots in Example 1 in the presence of interfering substances. Figure 9 As shown, the fluorescent carbon quantum dots of the present invention have high selectivity for the detection of p-nitrophenol. It can be seen that the fluorescent carbon quantum dots of the present invention can be used to analyze and detect the content of p-nitrophenol in actual pollutants.

[0230] In summary, the present invention provides an aggregation-induced fluorescence enhanced fluorescent carbon quantum dot, as well as a preparation method and application thereof. The fluorescent carbon quantum dot has the effect of aggregation-induced fluorescence enhancement and has great application potential. In water, the fluorescent carbon quantum dots of the present invention exhibit aggregation-induced fluorescence enhancement and wavelength-tunable fluorescence characteristics, and make full use of the characteristics of aggregation-induced fluorescence enhancement to successfully apply the fluorescent carbon quantum dots to the detection of pollutant samples containing p-nitrophenol. The detection method using the fluorescent carbon quantum dots of the present invention has the advantages of good selectivity, high sensitivity, wide detection range, and simple operation, and can be widely used in the monitoring of pollutants in the environment.

[0231] At the same time, the preparation method of the fluorescent carbon quantum dots of the present invention is simple, easy to operate, low in cost, green and mild, and can be used for mass production.

[0232] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A fluorescent carbon quantum dot, characterized in that The raw materials of the fluorescent carbon quantum dots include terephthalaldehyde and thiourea; The fluorescent carbon quantum dots are prepared by a method comprising the following steps: The fluorescent carbon quantum dots are obtained by subjecting terephthalaldehyde and thiourea to a solvothermal reaction in an acidic solvent; the acidic solvent comprises formic acid and / or acetic acid.

2. The fluorescent carbon quantum dots according to claim 1, wherein The molar ratio of terephthalaldehyde to thiourea is 1:(0.5-8).

3. The fluorescent carbon quantum dots according to claim 1 or 2, characterized in that The particle size distribution of the fluorescent carbon quantum dots is 2-6 nm.

4. A method for preparing fluorescent carbon quantum dots according to any one of claims 1 to 3, characterized in that: The steps include: The fluorescent carbon quantum dots are obtained by subjecting terephthalaldehyde and thiourea to a solvothermal reaction in an acidic solvent; the acidic solvent comprises formic acid and / or acetic acid.

5. The preparation method according to claim 4, characterized in that The temperature of the solvent thermal reaction is 160~240℃; And / or, the solvent thermal reaction time is 4 to 24 hours.

6. The preparation method according to claim 4, characterized in that The pH of the acidic solvent is measured by a pH meter to be 2-3.

7. The preparation method according to claim 4, characterized in that The solvent thermal reaction further includes precipitation and purification steps; And / or, the precipitation step includes adding water to form a precipitate, and using an acidic solvent to dissolve the precipitate.

8. Use of the fluorescent carbon quantum dots according to any one of claims 1 to 3, or the fluorescent carbon quantum dots obtained by the preparation method according to any one of claims 4 to 7, in pollutant detection.

9. The use according to claim 8, characterized in that The pollutants include water pollutants; and / or, the contaminant comprises p-nitrophenol; And / or, the ratio of the volume of the fluorescent carbon quantum dot solution to the volume of the pollutant solution is 1:(7~11).

10. A method for detecting p-nitrophenol, characterized in that, The fluorescent carbon quantum dots according to any one of claims 1 to 3 or the fluorescent carbon quantum dots obtained by the preparation method according to any one of claims 4 to 7 are used as fluorescent probes to detect p-nitrophenol.

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