A method for preparing quinine derivative-doped enhanced fluorescent carbon dots

Abstract

This invention relates to a method for preparing fluorescent carbon dots enhanced by quinine derivative doping, belonging to the field of fluorescent materials. The preparation method involves dissolving an organic carbon source, a nitrogen source, and a dopant in a solvent and carrying out a hydrothermal reaction. The dopant is a quinine derivative. Before the hydrothermal reaction, a microwave reaction is performed to pre-condense the organic carbon source and nitrogen source, forming carbon dopants. Simultaneously, the quinine derivative is adsorbed and doped into the carbon dopants. The amount of quinine derivative added is 0.5~2.5 wt% of the amount of organic carbon source. The average particle size of the fluorescent carbon dots enhanced by quinine derivative doping is 2~10 nm, the fluorescence quantum yield is 35~50.23%, the fluorescence lifetime is 7.523~8.314 ns, the maximum ultraviolet absorption wavelength is 330~370 nm, and the maximum fluorescence emission wavelength is 430~522 nm. The preparation method of this invention is simple, the obtained product has good fluorescence performance, and the dopant content is low.

Description

Technical Field

[0001] This invention belongs to the field of fluorescent functional materials technology, and relates to a fluorescent carbon dot based on quinine derivative doping and its preparation method. Background Technology

[0002] Carbon dots (CDs) are a class of novel carbon-based nanomaterials typically smaller than 10 nm. Since their discovery, they have attracted widespread attention in numerous fields due to their unique structure and excellent properties. Structurally, carbon dots are mainly composed of carbon atoms as their core, while their surfaces are modified with abundant functional groups, such as hydroxyl, carboxyl, and amino groups. These surface functional groups not only endow carbon dots with good water solubility, enabling them to be stably dispersed in aqueous solutions, but also provide active sites for further functionalization modifications.

[0003] Currently, carbon dot preparation methods are mainly divided into two strategies: "top-down" and "bottom-up." Top-down methods produce relatively uniform carbon dots, but often suffer from complex preparation processes, high costs, and low yields. Bottom-up strategies utilize small-molecule carbon sources, such as glucose, citric acid, and amino acids, to generate carbon dots through reactions such as condensation and carbonization under certain conditions. Common methods include hydrothermal / solvothermal methods, microwave-assisted methods, and ultrasonic methods. These methods have advantages such as a wide range of raw material sources, lower costs, and ease of large-scale preparation.

[0004] Since carbon dots are mainly composed of carbon atoms, they are affected by the photon absorption effect of carbon materials, resulting in extremely low fluorescence yield and short fluorescence lifetime, which limits their applications.

[0005] Introducing high conjugation structures into the molecular structure of carbon dots can improve their fluorescence quantum yield. Patent application CN118516113A discloses a method for preparing phosphorus-sulfur-doped core-shell carbon quantum dots with high fluorescence quantum yield. This method uses citric acid as the carbon source, urea as the nitrogen source, and 1,3-dimethyl-2-phenyl-2-phosphamidazolidine / cephalothiphene as the phosphorus / sulfur source. These are then mixed with deionized water and subjected to a hydrothermal reaction at 180-200°C to obtain phosphorus / sulfur-doped carbon quantum dots. By doping carbon quantum dots, adjusting their band structure, reducing their band gap, and altering their surface states, the fluorescence quantum yield of carbon quantum dots can be significantly improved. The fluorescence quantum yield of phosphorus / sulfur-doped carbon quantum dots reaches as high as 43.27%. This invention has a simple synthesis method and produces carbon quantum dots with high fluorescence quantum yield; however, the amount of dopant used in this method is large, exceeding 20 wt%.

[0006] In the field of fluorescent carbon dots, excessive dopant addition can lead to dopant aggregation, thereby affecting product performance and applications—a common problem in this field. Therefore, reducing the amount of dopant added while ensuring the fluorescence performance of fluorescent carbon dots is of great significance. Summary of the Invention

[0007] The purpose of this invention is to solve the problems in the prior art and provide a method for preparing fluorescent carbon dots based on quinine derivative doping.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing fluorescent carbon dots based on quinine derivative doping involves dissolving an organic carbon source, a nitrogen source, and a dopant in a solvent and carrying out a hydrothermal reaction. The dopant is a quinine derivative. Before the hydrothermal reaction, a microwave reaction is also carried out to pre-condense the organic carbon source and the nitrogen source to form carbon dot prepolymers, while the quinine derivative is adsorbed and doped into the carbon dot prepolymers.

[0010] The amount of quinine derivatives fed is 0.5 to 2.5 wt% of the amount of organic carbon source fed.

[0011] As a preferred technical solution:

[0012] The preparation method of enhanced fluorescent carbon dots based on quinine derivative doping, as described above, involves purification after hydrothermal reaction. First, a filter membrane with a pore size of 0.22 μm is used to remove large aggregates to obtain filtrate. Then, the filtrate is dialyzed for 1-2 days using a dialysis bag with a molecular cutoff of 1000 Da to completely remove unreacted small molecule impurities to obtain dialysate. Finally, the dialysate is freeze-dried for 2-3 days.

[0013] The above describes a method for preparing fluorescent carbon dots based on quinine derivative doping, wherein the quinine derivative is quinine sulfate or quinine hydrochloride.

[0014] The preparation method of fluorescent carbon dots based on quinine derivative doping as described above, wherein the organic carbon source is one or more of citric acid, humic acid, glucose, starch and cellulose; and the nitrogen source is one or more of urea, thiourea and ethylenediamine.

[0015] The preparation method of enhanced fluorescent carbon dots based on quinine derivative doping, as described above, involves a microwave power of 75-150W, a reaction time of 30-50s, and a reaction system temperature of 22-28℃ at the start of the microwave reaction.

[0016] The preparation method of enhanced fluorescent carbon dots based on quinine derivative doping, as described above, involves a hydrothermal reaction at a temperature of 150-200℃ and a reaction time of 2-6 hours.

[0017] As described above, in the preparation method of fluorescent carbon dots based on quinine derivative doping, the molar ratio of organic carbon source to nitrogen source is 0.5~2. Controlling the ratio within this range can better regulate the nucleation and growth process of carbon dots.

[0018] The present invention also provides a fluorescent carbon dot based on quinine derivative doping, which is prepared by the preparation method of the fluorescent carbon dot based on quinine derivative doping as described above; the fluorescent carbon dot based on quinine derivative doping has an average particle size of 2~10nm, a fluorescence quantum yield of 35~50.23%, a fluorescence lifetime of 7.523~8.314ns, a maximum ultraviolet absorption wavelength of 330~370nm, and a maximum fluorescence emission wavelength of 430~522nm.

[0019] Invention principle:

[0020] Quinine derivatives are a class of organic compounds with unique structures. Their basic structure consists of rigid planar nitrogen-containing heterocyclic aromatic compounds formed by the fusion of a benzene ring and a pyridine ring. This special structure endows quinine derivatives with rich chemical activity, unique physical properties, and excellent functional characteristics. Chemically, due to the conjugation of the benzene and pyridine rings, quinine derivatives exhibit high stability. Furthermore, the nitrogen atom on the pyridine ring not only gives them unique activity in electrophilic and nucleophilic reactions but also, together with the intramolecularly modifiable functional groups, endows them with excellent coordination ability. Physically, quinine derivatives typically possess specific melting and boiling points, good solubility in organic solvents, and characteristic absorption peaks in the UV-Vis spectral region. These optical properties, combined with the excited-state stabilization effect of the rigid conjugated structure, enhance their fluorescence performance. Therefore, theoretically, doping quinine derivatives into carbon dots can yield fluorescent carbon dots with good fluorescence properties. However, quinine derivatives have poor heat resistance and thermal stability. Furthermore, it is difficult to achieve structural stability by directly doping the molecular structure onto carbon dots. The commonly used high-temperature and high-pressure hydrothermal synthesis process inevitably leads to the decomposition of the quinoline material structure, making it difficult to achieve the doping of the molecular structure or effective functional groups.

[0021] This invention utilizes a rapid microwave reaction at room temperature to induce prepolymerization of organic carbon and nitrogen sources at extremely fast and low temperatures, forming carbon dot prepolymers. Simultaneously, quinine derivatives are adsorbed and doped into the carbon dot prepolymers, thus forming a prepolymer structure doped with quinine derivatives. This is then further processed via a high-temperature hydrothermal reaction (in the early stage of the high-temperature hydrothermal reaction, the carbon dot prepolymer continues to condense, and in the middle stage, the polymer undergoes carbonization), thereby producing fluorescent carbon dots enhanced by quinine derivative doping. Furthermore, because the quinine derivatives are encapsulated within the carbon dot prepolymers, decomposition of the quinine derivatives during the hydrothermal reaction is avoided.

[0022] Adding low amounts of quinine derivatives avoids the problem of dopant (quinine derivative) aggregation caused by excessive addition, while maintaining strong performance. The specific reasons are as follows:

[0023] The doping in CN118516113A introduces a conjugated structure into the original small conjugated domain of the carbon dot. This conjugated structure is an independent conjugated structure inherent to the dopant, essentially "repairing / expanding the small conjugated domain of the carbon dot itself." The conjugated system is dispersed and unstable. In contrast, the addition of a quinine derivative in this invention allows the quinine derivative to adsorb into the carbon dot prepolymer during the microwave reaction stage. During the hydrothermal reaction stage, the carbon dot prepolymer continues to condense to obtain a polymer, which is then carbonized to form a carbon skeleton. Simultaneously, during the formation of the carbon skeleton, the conjugated structure inherent to the quinine derivative undergoes π–π stacking with the carbon skeleton precursor. After the carbon skeleton is formed, the heterocyclic nitrogen and sulfonic acid groups in the quinine derivative react with the carbon skeleton to form CN and CS covalent bonds, thereby obtaining the carbon dot skeleton. This results in a novel, continuous, large conjugated structure with a larger and more stable electron delocalization range, significantly improving fluorescence performance. Therefore, this invention can achieve excellent fluorescence performance even with a small amount of dopant added.

[0024] The conjugated structure of quinine derivatives exhibits strong characteristic absorption in the 330-370 nm range, thus the resulting products also possess excellent ultraviolet absorption capabilities.

[0025] Beneficial effects:

[0026] (1) The preparation method of the present invention can dope quinine derivatives into carbon dots, avoiding the thermal decomposition of quinine derivatives by hydrothermal reaction, thereby obtaining fluorescent carbon dots based on quinine derivative doping.

[0027] (2) The quinine derivatives added to the fluorescent carbon dots based on quinine derivative doping of the present invention are small in amount but have excellent fluorescence performance. Attached Figure Description

[0028] Figure 1 The infrared spectrum of fluorescent carbon dots based on quinine derivative doping obtained in Example 3;

[0029] Figure 2 The TEM image of fluorescent carbon dots based on quinine derivative doping obtained in Example 3;

[0030] Figure 3 XPS pattern of fluorescent carbon dots based on quinine derivative doping obtained in Example 3;

[0031] Figure 4 The UV absorption spectra of the fluorescent carbon dots prepared in Example 3 based on quinine derivative doping and enhanced fluorescence and those prepared in Comparative Example 1 are shown in comparison.

[0032] Figure 5 The images show a comparison of the fluorescence intensity of the fluorescent carbon dots prepared in Example 3 based on quinine derivative doping and the fluorescent carbon dots prepared in Comparative Example 1. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0034] The test methods for the performance indicators in each embodiment and comparative example are as follows:

[0035] Average particle size: The samples were measured using a Nano-ZS90 Malvern potential analyzer. Each sample was tested three times consecutively, and the average Z-mean particle size of the three tests was taken as the final average particle size. The refractive index was set to 1.75 and the absorbance to 0.001 before the test.

[0036] Fluorescence quantum yield: Refer to GB / T 39725-2020 "Method for testing fluorescence quantum yield of fluorescent nanoparticles in nanotechnology".

[0037] Fluorescence lifetime: Refer to GB / T 41064-2021 "Nanophotonics Fluorescence Lifetime Imaging Terminology and Definitions".

[0038] Maximum UV absorption wavelength: Add the sample to water to prepare a carbon dot solution with a concentration of 0.01 mg / mL. Then, use a UV-1900 UV-Vis spectrophotometer to test 3 mL of the carbon dot solution. Set the scanning range to 800~200 nm. The wavelength corresponding to the highest peak is the maximum UV absorption wavelength.

[0039] Maximum fluorescence emission wavelength: The sample was added to water to prepare a carbon dot solution with a concentration of 0.01 mg / mL, and then the carbon dot solution was tested using an F-4700 fluorescence spectrometer; the scanning speed was 1200 nm / min, the grating was 5, the scanning range was set to 350~650 nm, and the excitation wavelength was set to the same as the maximum absorption wavelength of ultraviolet light.

[0040] Example 1

[0041] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0042] (1) Preparation of raw materials;

[0043] Organic carbon source: citric acid;

[0044] Nitrogen source: a mixture of urea and thiourea in a mass ratio of 2:1;

[0045] Dopant: Quinine sulfate;

[0046] Solvent: Deionized water;

[0047] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 150W, the reaction time is 30s, and the temperature of the reaction system at the beginning of the microwave reaction is 25℃; the reaction temperature of the hydrothermal reaction is 150℃, and the reaction time is 6h; the molar ratio of organic carbon source to nitrogen source is 1; the amount of quinine derivative is 0.5wt% of the amount of organic carbon source; the mass ratio of organic carbon source to solvent is 1:12.5;

[0048] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 2 days with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 3 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0049] The obtained fluorescent carbon dots based on quinine derivative doping had an average particle size of 2 nm, a fluorescence quantum yield of 36.41%, a fluorescence lifetime of 7.891 ns, a maximum ultraviolet absorption wavelength of 340 nm, and a maximum fluorescence emission wavelength of 430 nm.

[0050] Example 2

[0051] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0052] (1) Preparation of raw materials;

[0053] Organic carbon source: citric acid;

[0054] Nitrogen source: urea;

[0055] Dopant: Quinine sulfate;

[0056] Solvent: Deionized water;

[0057] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 75W, the reaction time is 50s, and the temperature of the reaction system at the beginning of the microwave reaction is 25℃; the reaction temperature of the hydrothermal reaction is 160℃, and the reaction time is 4h; the molar ratio of organic carbon source to nitrogen source is 1; the amount of quinine derivative is 0.75wt% of the amount of organic carbon source; the mass ratio of organic carbon source to solvent is 1:12.5;

[0058] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 1 day with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 2 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0059] The average particle size of the fluorescent carbon dots based on quinine derivative doping was 8 nm, the fluorescence quantum yield was 46.41%, the fluorescence lifetime was 8.201 ns, the maximum ultraviolet absorption wavelength was 340 nm, and the maximum fluorescence emission wavelength was 433 nm.

[0060] Example 3

[0061] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0062] (1) Preparation of raw materials;

[0063] Organic carbon source: citric acid;

[0064] Nitrogen source: urea;

[0065] Dopant: Quinine sulfate;

[0066] Solvent: Deionized water;

[0067] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 120W, the reaction time is 45s, and the temperature of the reaction system at the beginning of the microwave reaction is 25℃; the reaction temperature of the hydrothermal reaction is 160℃, and the reaction time is 4h; the molar ratio of organic carbon source to nitrogen source is 1; the amount of quinine derivative added is 1wt% of the amount of organic carbon source added; the mass ratio of organic carbon source to solvent is 1:12.5;

[0068] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 1 day with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 2 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0069] The obtained quinine derivative-doped enhanced fluorescent carbon dots had an average particle size of 5 nm, a fluorescence quantum yield of 50.23%, and a fluorescence lifetime of 8.314 ns; Figures 4-5 As shown, the maximum ultraviolet absorption wavelength is 340 nm, and the maximum fluorescence emission wavelength is 437 nm. Figure 1 The image shown is the infrared spectrum of the quinine derivative-doped enhanced fluorescent carbon dots prepared in Example 3. It can be seen that at 3020 cm⁻¹... -1The presence of a distinctly sharp peak nearby indicates the presence of CH at the edge of the aromatic ring; 767 cm⁻¹ -1 991cm -1 The nearby peaks are correlated with the vibrations of aromatic ring substitution and sulfur-containing functional groups (such as CS, S=O), confirming the successful doping of quinine sulfate into the carbon dot structure. Figure 2 The image shown is a TEM image of the quinine derivative-doped enhanced fluorescent carbon dots prepared in Example 3. It can be seen that the quinine derivative-doped enhanced fluorescent carbon dots prepared in Example 3 are spherical and uniformly distributed as independent individuals, without obvious aggregates, confirming their good dispersion performance. Figure 3 As shown, the XPS spectrum of fluorescent carbon dots based on quinine derivative doping obtained in Example 3 is shown. The fitting peaks in the 161~174 eV range correspond to different sulfur chemical states, further proving the successful doping of quinine derivative (i.e., quinine sulfate in Example 3).

[0070] Comparative Example 1

[0071] A method for preparing fluorescent carbon dots is basically the same as in Example 3, except that no dopant is added in step (2).

[0072] The obtained fluorescent carbon dots had an average particle size of 3 nm, a fluorescence quantum yield of 9.52%, and a fluorescence lifetime of 3.007 ns; Figures 4-5 As shown, the maximum ultraviolet absorption wavelength is 345 nm, and the maximum fluorescence emission wavelength is 430 nm.

[0073] Compared with Example 3, the fluorescence quantum yield and fluorescence lifetime of Comparative Example 1 are lower than those of Example 3. This is because Comparative Example 1 only relies on the basic carbon skeleton formed by the condensation of carbon and nitrogen sources, and the range of conjugated systems is limited. However, after adding quinine derivatives in this invention, the quinine derivatives are adsorbed in the carbon dot prepolymer during the microwave reaction stage. During the hydrothermal reaction stage, the carbon dot prepolymers continue to condense to obtain polymers, which are then carbonized to form carbon skeletons. At the same time, during the formation of carbon skeletons, the conjugated structure of the quinine derivatives undergoes π–π stacking with the carbon skeleton precursor. After the carbon skeleton is formed, the active functional groups such as heterocyclic nitrogen and sulfonic acid groups in the quinine derivatives react with the carbon skeleton to form CN and CS covalent bonds, thereby obtaining the carbon dot skeleton, which forms a brand-new, continuous large conjugated structure with a larger and more stable electron delocalization range and significant fluorescence performance.

[0074] Comparative Example 2

[0075] A method for preparing fluorescent carbon dots is basically the same as in Example 3, except that step (2) only involves a microwave reaction and not a hydrothermal reaction, and the microwave power of the microwave reaction is 150W and the reaction time is 4h.

[0076] This method cannot prepare fluorescent carbon dots because the lack of hydrothermal reaction results in insufficient energy for the carbon dot prepolymers formed during microwave reaction to continue condensation, and there is also insufficient energy for the carbon dot prepolymers to carbonize.

[0077] Comparative Example 3

[0078] A method for preparing fluorescent carbon dots is basically the same as in Example 3, except that step (2) only involves a hydrothermal reaction and not a microwave reaction.

[0079] The obtained fluorescent carbon dots had an average particle size of 10 nm, a fluorescence quantum yield of 10.6%, a fluorescence lifetime of 3.237 ns, a maximum ultraviolet absorption wavelength of 342 nm, and a maximum fluorescence emission wavelength of 435 nm.

[0080] Compared with Example 3, the fluorescence quantum yield and fluorescence lifetime of Comparative Example 3 were lower than those of Example 3. This is because the microwave reaction was not carried out, and the quinine derivative could not be encapsulated by the carbon dot prepolymer. It underwent thermal decomposition during the subsequent high-temperature hydrothermal process, resulting in the failure of the core mechanisms of "construction of continuous large conjugated system" and "fluorescence enhancement".

[0081] Comparative Example 4

[0082] A method for preparing fluorescent carbon dots is basically the same as in Example 3, except that the hydrothermal reaction in step (2) is replaced by a second microwave reaction. The microwave power of the second microwave reaction is 800W and the reaction time is 300s.

[0083] The prepared fluorescent carbon dots agglomerated to form aggregates with an average particle size of 200 nm, a fluorescence quantum yield of 11.3%, a fluorescence lifetime of 3.414 ns, a maximum ultraviolet absorption wavelength of 330 nm, and a maximum fluorescence emission wavelength of 445 nm.

[0084] Compared to Example 3, the fluorescent carbon dots in Comparative Example 4 agglomerated to form aggregates with a particle size much larger than that in Example 3. This is because the core function of the hydrothermal reaction in Example 3 is to allow the prepolymer to slowly condense and carbonize through continuous energy input at 150~200℃, and the rigid conjugated structure of the quinine derivative can provide steric hindrance through π–π stacking, thus hindering particle aggregation. In contrast, the high power (intense and disordered energy output) of the second microwave reaction can cause the carbon dot prepolymer to condense and carbonize, but the quinine derivative cannot form a stable bond with the carbon dot prepolymer under high-power microwave impact, thus failing to play a dispersive and regulatory role, and ultimately forming large-sized aggregates.

[0085] Compared with Example 3, the fluorescence quantum yield and fluorescence lifetime of the fluorescent carbon dots in Comparative Example 4 were lower than those in Example 3. This is because the aggregates of the fluorescent carbon dots prepared in Comparative Example 4 had large particle sizes, resulting in low fluorescence performance. Furthermore, during the preparation process, the quinine derivative could not form a stable bond with the carbon dot prepolymer under high-power microwave shock, which prevented the quinine derivative from π–π stacking with the carbon skeleton precursor. Consequently, the active functional groups such as heterocyclic nitrogen and sulfonic acid groups in the quinine derivative had difficulty reacting with the carbon skeleton, i.e., they could not form a new, continuous, large conjugated structure.

[0086] Comparative Example 5

[0087] A method for preparing fluorescent carbon dots is basically the same as in Example 3, except that the dopant in step (1) is methylene blue (manufactured by Ruiwei Biotechnology Co., Ltd.).

[0088] The obtained fluorescent carbon dots had an average particle size of 10 nm, a fluorescence quantum yield of 3.2%, a fluorescence lifetime of 0.78 ns, a maximum ultraviolet absorption wavelength of 340 nm, and a maximum fluorescence emission wavelength of 437 nm.

[0089] Compared to Example 3, the fluorescence quantum yield and fluorescence lifetime of the fluorescent carbon dots in Comparative Example 5 were lower than those in Example 3. This is because although methylene blue is a conjugated system, after its addition, it is only physically adsorbed onto the carbon dot surface through intermolecular forces and does not participate in the construction of the carbon dot framework. Therefore, it cannot form a continuous conjugated system, the electron delocalization range is limited, and energy is easily dissipated through intramolecular vibrations. However, after adding the quinine derivative in this invention, the quinine derivative is adsorbed into the carbon dot prepolymer during the microwave reaction stage. During the hydrothermal reaction stage, the carbon dot prepolymer continues to condense to obtain a polymer, which is then carbonized to form a carbon framework. At the same time, during the formation of the carbon framework, the conjugated structure of the quinine derivative and the carbon framework precursor undergo π–π stacking. After the carbon framework is formed, the active functional groups such as heterocyclic nitrogen and sulfonic acid groups in the quinine derivative react with the carbon framework to form CN and CS covalent bonds, thereby obtaining the carbon dot framework, which forms a brand-new, continuous, large conjugated structure with a larger and more stable electron delocalization range and significant fluorescence performance.

[0090] Example 4

[0091] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0092] (1) Preparation of raw materials;

[0093] Organic carbon source: citric acid;

[0094] Nitrogen source: urea;

[0095] Dopant: Quinine sulfate;

[0096] Solvent: Deionized water;

[0097] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 120W, the reaction time is 50s, and the temperature of the reaction system at the beginning of the microwave reaction is 25℃; the reaction temperature of the hydrothermal reaction is 170℃, and the reaction time is 4h; the molar ratio of organic carbon source to nitrogen source is 1; the amount of quinine derivative is 1.25wt% of the amount of organic carbon source; the mass ratio of organic carbon source to solvent is 1:12.5;

[0098] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 1 day with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 2 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0099] The obtained fluorescent carbon dots based on quinine derivative doping have an average particle size of 8 nm, a fluorescence quantum yield of 47.36%, a fluorescence lifetime of 8.221 ns, a maximum ultraviolet absorption wavelength of 340 nm, and a maximum fluorescence emission wavelength of 445 nm.

[0100] Example 5

[0101] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0102] (1) Preparation of raw materials;

[0103] Organic carbon source: a mixture of citric acid and humic acid in a 1:1 mass ratio;

[0104] Nitrogen source: urea;

[0105] Dopant: Quinine sulfate;

[0106] Solvent: Deionized water;

[0107] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 120W, the reaction time is 50s, and the temperature of the reaction system at the beginning of the microwave reaction is 25℃; the reaction temperature of the hydrothermal reaction is 180℃, and the reaction time is 3h; the molar ratio of organic carbon source to nitrogen source is 1; the amount of quinine derivative is 1.5wt% of the amount of organic carbon source; the mass ratio of organic carbon source to solvent is 1:12.5;

[0108] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 2 days with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 3 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0109] The average particle size of the fluorescent carbon dots based on quinine derivative doping was 9 nm, the fluorescence quantum yield was 42.89%, the fluorescence lifetime was 8.115 ns, the maximum ultraviolet absorption wavelength was 350 nm, and the maximum fluorescence emission wavelength was 447 nm.

[0110] Example 6

[0111] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0112] (1) Preparation of raw materials;

[0113] Organic carbon source: humic acid;

[0114] Nitrogen source: urea;

[0115] Dopant: Quinine sulfate;

[0116] Solvent: Deionized water;

[0117] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 150W, the reaction time is 30s, and the temperature of the reaction system at the beginning of the microwave reaction is 22℃; the reaction temperature of the hydrothermal reaction is 160℃, and the reaction time is 4h; the molar ratio of organic carbon source to nitrogen source is 0.5; the amount of quinine derivative added is 1wt% of the amount of organic carbon source added; the mass ratio of organic carbon source to solvent is 1:12.5;

[0118] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 2 days with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 3 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0119] The average particle size of the fluorescent carbon dots based on quinine derivative doping was 8 nm, the fluorescence quantum yield was 46.39%, the fluorescence lifetime was 8.197 ns, the maximum ultraviolet absorption wavelength was 370 nm, and the maximum fluorescence emission wavelength was 510 nm.

[0120] Example 7

[0121] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0122] (1) Preparation of raw materials;

[0123] Organic carbon source: glucose;

[0124] Nitrogen source: ethylenediamine;

[0125] Dopant: Quinine sulfate;

[0126] Solvent: Deionized water;

[0127] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 120W, the reaction time is 30s, and the temperature of the reaction system at the beginning of the microwave reaction is 28℃; the reaction temperature of the hydrothermal reaction is 180℃, and the reaction time is 4h; the molar ratio of organic carbon source to nitrogen source is 2; the amount of quinine derivative is 1wt% of the amount of organic carbon source; the mass ratio of organic carbon source to solvent is 1:12.5;

[0128] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 1 day with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 3 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0129] The average particle size of the fluorescent carbon dots based on quinine derivative doping was 7 nm, the fluorescence quantum yield was 44.06%, the fluorescence lifetime was 8.178 ns, the maximum ultraviolet absorption wavelength was 360 nm, and the maximum fluorescence emission wavelength was 522 nm.

[0130] Example 8

[0131] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0132] (1) Preparation of raw materials;

[0133] Organic carbon source: starch, degree of polymerization 500;

[0134] Nitrogen source: urea;

[0135] Dopant: Quinine hydrochloride;

[0136] Solvent: Deionized water;

[0137] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 75W, the reaction time is 30s, and the temperature of the reaction system at the beginning of the microwave reaction is 25℃; the reaction temperature of the hydrothermal reaction is 170℃, and the reaction time is 4h; the molar ratio of organic carbon source to nitrogen source is 1; the amount of quinine derivative is 1wt% of the amount of organic carbon source; the mass ratio of organic carbon source to solvent is 1:12.5;

[0138] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 1 day with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 3 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0139] The average particle size of the fluorescent carbon dots based on quinine derivative doping was 8 nm, the fluorescence quantum yield was 47.83%, the fluorescence lifetime was 8.287 ns, the maximum ultraviolet absorption wavelength was 360 nm, and the maximum fluorescence emission wavelength was 450 nm.

[0140] Example 9

[0141] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0142] (1) Preparation of raw materials;

[0143] Organic carbon source: cellulose, degree of polymerization 1000;

[0144] Nitrogen source: ethylenediamine;

[0145] Dopant: Quinine sulfate;

[0146] Solvent: Deionized water;

[0147] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 150W, the reaction time is 50s, and the temperature of the reaction system at the beginning of the microwave reaction is 25℃; the reaction temperature of the hydrothermal reaction is 160℃, and the reaction time is 4h; the molar ratio of organic carbon source to nitrogen source is 1; the amount of quinine derivative added is 1wt% of the amount of organic carbon source added; the mass ratio of organic carbon source to solvent is 1:12.5;

[0148] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 1 day with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 3 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0149] The average particle size of the fluorescent carbon dots based on quinine derivative doping was 6 nm, the fluorescence quantum yield was 48.75%, the fluorescence lifetime was 8.301 ns, the maximum ultraviolet absorption wavelength was 350 nm, and the maximum fluorescence emission wavelength was 445 nm.

[0150] Example 10

[0151] A method for preparing fluorescent carbon dots based on quinine derivative doping is described below:

[0152] (1) Preparation of raw materials;

[0153] Organic carbon source: citric acid;

[0154] Nitrogen source: urea;

[0155] Dopant: Quinine sulfate;

[0156] Solvent: Deionized water;

[0157] (2) Dissolve the organic carbon source, nitrogen source and dopant in a solvent and carry out microwave reaction and hydrothermal reaction in sequence; wherein, the microwave power of the microwave reaction is 120W, the reaction time is 45s, and the temperature of the reaction system at the beginning of the microwave reaction is 25℃; the reaction temperature of the hydrothermal reaction is 200℃, and the reaction time is 2h; the molar ratio of organic carbon source to nitrogen source is 1; the amount of quinine derivative is 2.5wt% of the amount of organic carbon source; the mass ratio of organic carbon source to solvent is 1:12.5;

[0158] (3) Purification treatment: First, the product of step (2) was filtered with a filter membrane with a pore size of 0.22 μm to obtain filtrate. Then, the filtrate was dialyzed for 2 days with a dialysis bag with a molecular cutoff of 1000 Da to obtain dialysate. Finally, the dialysate was freeze-dried for 3 days to obtain quinine derivative-doped enhanced fluorescent carbon dots.

[0159] The obtained fluorescent carbon dots based on quinine derivative doping have an average particle size of 10 nm, a fluorescence quantum yield of 35%, a fluorescence lifetime of 7.523 ns, a maximum ultraviolet absorption wavelength of 330 nm, and a maximum fluorescence emission wavelength of 450 nm.

Claims

1. A method for preparing fluorescent carbon dots based on quinine derivative doping, comprising dissolving an organic carbon source, a nitrogen source, and a dopant in a solvent and carrying out a hydrothermal reaction, characterized in that, The dopant is a quinine derivative; a microwave reaction is also carried out before the hydrothermal reaction, so that the organic carbon source and nitrogen source undergo pre-condensation to form carbon dot prepolymers, and the quinine derivative is adsorbed and doped in the carbon dot prepolymers. The amount of quinine derivatives fed into the feed is 0.5~2.5 wt% of the amount of organic carbon source fed into the feed; Quinine derivatives are quinine sulfate or quinine hydrochloride; The organic carbon source is one or more of citric acid, humic acid, glucose, starch, and cellulose; the nitrogen source is one or more of urea, thiourea, and ethylenediamine. The microwave power of the microwave reaction is 75~150W, and the reaction time is 30~50s; The hydrothermal reaction temperature is 150~200℃, and the reaction time is 2~6h.

2. The method for preparing fluorescent carbon dots based on quinine derivative doping according to claim 1, characterized in that, After the hydrothermal reaction, purification is carried out. First, the filtrate is obtained by filtration through a filter membrane. Then, the filtrate is dialyzed through a dialysis bag to obtain dialysate. Finally, the dialysate is freeze-dried.

3. The method for preparing fluorescent carbon dots based on quinine derivative doping according to claim 1, characterized in that, The molar ratio of organic carbon source to nitrogen source is 0.5~2.

4. A method for enhancing fluorescent carbon dots based on quinine derivative doping, characterized in that, The fluorescent carbon dots were prepared using the method described in claim 1, which is based on quinine derivative doping to enhance fluorescence. The average particle size of the fluorescent carbon dots based on quinine derivative doping to enhance fluorescence is 2-10 nm, the fluorescence quantum yield is 35-50.23%, the fluorescence lifetime is 7.523-8.314 ns, the maximum ultraviolet absorption wavelength is 330-370 nm, and the maximum fluorescence emission wavelength is 430-522 nm.

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