Carbon nitride quantum dot as well as preparation method and application thereof

Abstract

The invention discloses a carbon nitride quantum dot as well as a preparation method and application thereof, and the preparation method comprises the following steps: taking formamide as a precursor and a solvent, taking ammonia water as a doping reagent, taking H2O2 as a redox agent, and carrying out solvothermal reaction to obtain the carbon nitride quantum dot. Wherein the temperature of the solvothermal reaction is 160 to 180 DEG C. The preparation method disclosed by the invention is low in raw material cost, short in synthesis time and simple and convenient to operate, efficient batch production is realized, and the generated carbon nitride quantum dot has good stability, shows efficient peroxidase-like activity as a metal-free nano-enzyme, shows excellent catalytic ability in vitro, and has good application prospects. The compound has a great prospect in the aspect of tumor treatment.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of materials, in particular to carbon nitride quantum dots and a preparation method and application thereof. BACKGROUND

[0002] At present, common tumor treatment strategies in medical clinics mainly include surgical resection, radiotherapy and drug chemotherapy. Although these treatment methods can achieve certain effects, due to the lack of specificity, they usually cause unnecessary damage to normal cells, resulting in serious side effects. As an artificial simulated enzyme with the characteristics of nanomaterials and the catalytic function of an enzyme, a nanoenzyme has shown revolutionary potential in the field of cancer treatment in recent years. However, the existing nanoenzyme system still has obvious limitations: although metal-based nanoenzymes (such as Fe3O4 and CeO2) have outstanding catalytic efficiency, the biological toxicity of metal ions and the environmental accumulation risk restrict their biomedical applications; non-metallic carbon-based nanoenzymes (such as graphene oxide and carbon quantum dots) have good biocompatibility, but they generally have problems such as low active site density and poor substrate selectivity. Therefore, developing a non-metallic nanoenzyme system with high catalytic activity, environmental friendliness and structural stability has become an important challenge in this field.

[0003] As a kind of metal-free semiconductor material with a layered topology similar to graphene, carbon nitride (C3N4) is characterized by periodic arrangement of triazine ring structural units. As a kind of nitrogen-rich polymer, it has great application potential in the fields of photoelectric catalysis, environmental protection, biosensing and the like due to its unique conjugated π-electron structure, adjustable energy band characteristics and excellent chemical and thermal stability. Due to its unique nitrogen-rich structure and layered characteristics similar to graphene, it exhibits significant peroxidase-like (POD-like) activity. However, the low specific surface area and limited active site exposure of bulk g-C3N4 seriously restrict its catalytic efficiency and biological application scenarios. Quantum dot engineering and heteroatom doping strategies provide a new way to optimize the performance of carbon-based nanoenzymes. Carbon nitride quantum dots (CNQDs) can significantly improve the electron transfer rate and substrate binding capacity through quantum confinement effect and edge active site exposure, and gradient doping of nitrogen elements can further regulate the electronic structure and enhance the reactive oxygen species (ROS) generation kinetics.

[0004] Formamide is an organic compound with the molecular formula CH3NO, which is a colorless transparent liquid with a slight ammonia smell. It is a raw material for the synthesis of medicines, spices, dyes and the like, and can also be used as a solvent for the spinning of synthetic fibers, the processing of plastics, the production of wood protein ink, etc. At present, it has been used in the preparation of carbon quantum dots. However, most of the current synthesis methods and post-processing methods are complex, and the catalytic activity is low. SUMMARY

[0005] The technical problem solved by the present application is how to prepare carbon nitride quantum dots with peroxidase-like activity.

[0006] The present application solves the above technical problems by the following technical means:

[0007] A preparation method of carbon nitride quantum dots, which uses formamide as a precursor and a solvent, ammonia as a doping reagent, and H2O2 as a redox reagent to obtain the carbon nitride quantum dots through a solvothermal reaction; wherein the temperature of the solvothermal reaction is 160-180℃.

[0008] Advantages: In the present application, formamide is used as a precursor and a solvent, ammonia is used as a doping reagent, and H2O2 is used as a redox reagent to obtain carbon nitride quantum dots through a solvothermal reaction, which has good stability, good fluorescence characteristics, near-infrared imaging performance, and high peroxidase-like activity.

[0009] Preferably, the preparation method of carbon nitride quantum dots comprises the following steps: mixing formamide, ammonia, and H2O2 aqueous solution uniformly to obtain a reaction solution; and placing the obtained reaction solution in a hydrothermal reaction device to obtain the carbon nitride quantum dots.

[0010] Preferably, the H2O2 aqueous solution is used as a redox reagent, and the mass concentration of the H2O2 aqueous solution is 30%.

[0011] Preferably, the volume ratio of the formamide to the ammonia is 1-13:1.

[0012] Preferably, the volume ratio of the formamide to the ammonia is 12-13:1.

[0013] Preferably, the mass fraction of the ammonia is 25-28%.

[0014] Preferably, the H2O2 aqueous solution with a mass concentration of 30% is used as a redox reagent, and the volume ratio of the formamide to the H2O2 aqueous solution with a mass concentration of 30% is 6-13:1; the hydrogen peroxide is used in an excessive amount.

[0015] Preferably, the H2O2 aqueous solution with a mass concentration of 30% is used as a redox reagent, and the volume ratio of the formamide to the ammonia with a mass fraction of 25-28% and the H2O2 aqueous solution with a mass concentration of 30% is 13:1:1.

[0016] Preferably, the time of the solvothermal reaction is 15-20h.

[0017] Preferably, the method further comprises dialysis and drying of the product after the solvothermal reaction.

[0018] Preferably, the preparation method of the carbon nitride quantum dots comprises the following steps: uniformly mixing formamide, ammonia water with a mass fraction of 25-28%, and a 30% H2O2 aqueous solution with a volume ratio of 6-13:1:1 to obtain a reaction solution; placing the obtained reaction solution in a hydrothermal reaction kettle, reacting at 160-180 DEG C for 15-20 h, cooling to room temperature after the reaction is completed, sucking the product into a dialysis bag with a molecular weight cut-off of 3000D, placing it in water for dialysis, collecting the aqueous solution after dialysis, and freeze-drying to obtain the carbon nitride quantum dots.

[0019] Preferably, the preparation method of the carbon nitride quantum dots comprises the following steps: uniformly mixing formamide, ammonia water with a mass fraction of 25-28%, and a 30% H2O2 aqueous solution with a volume ratio of 6-13:1:1 to obtain a reaction solution; placing the obtained reaction solution in a hydrothermal reaction kettle, reacting at 160-180 DEG C for 15-20 h, cooling to room temperature after the reaction is completed, sucking the product into a dialysis bag with a molecular weight cut-off of 3000D, placing it in water for dialysis, collecting the aqueous solution after dialysis, and freeze-drying to obtain the carbon nitride quantum dots.

[0020] The application further provides a carbon nitride quantum dot prepared by the preparation method.

[0021] Preferably, the carbon nitride quantum dot has peroxidase-like activity.

[0022] The application further provides application of the carbon nitride quantum dot in preparation of a tumor treatment reagent and / or a near-infrared imaging reagent.

[0023] The application further provides application of the carbon nitride quantum dot as a peroxidase-like catalyst.

[0024] The application has the following advantages:

[0025] (1) The carbon nitride quantum dots generated by the application have good optical performance and optical stability, and can be used for near-infrared imaging.

[0026] (2) The preparation raw materials used by the application have low cost, short synthesis time, and simple operation, and the application realizes efficient batch production and provides feasibility for industrial scale application.

[0027] (3) The carbon nitride quantum dots generated by the application have good stability, and as a metal-free nano-enzyme, exhibit high peroxidase-like activity, show excellent catalytic capacity in vitro, and have great prospects in tumor treatment. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a synthesis step schematic diagram for preparing the carbon nitride quantum dots in Example 1 of the application.

[0029] Figure 2 X-ray diffraction pattern of the carbon nitride quantum dots prepared in Example 1 of the present application;

[0030] Figure 3 Raman spectrum of the carbon nitride quantum dots prepared in Example 1 of the present application;

[0031] Figure 4 Infrared spectrum of the carbon nitride quantum dots prepared in Example 1 of the present application;

[0032] Figure 5 Zeta potential of the carbon nitride quantum dots prepared in Example 1 of the present application;

[0033] Figure 6 Digital photograph of the carbon nitride quantum dots prepared in Example 1 of the present application dispersed in aqueous solution for different days;

[0034] Figure 7 Dispersion photograph of the carbon nitride quantum dots prepared in Example 1 of the present application in simulated different physiological environments;

[0035] Figure 8 X-ray photoelectron spectroscopy full spectrum of the carbon nitride quantum dots prepared in Example 1 of the present application;

[0036] Figure 9 X-ray photoelectron spectroscopy C1s spectrum of the carbon nitride quantum dots prepared in Example 1 of the present application;

[0037] Figure 10 X-ray photoelectron spectroscopy N1s spectrum of the carbon nitride quantum dots prepared in Example 1 of the present application;

[0038] Figure 11 X-ray photoelectron spectroscopy O1s spectrum of the carbon nitride quantum dots prepared in Example 1 of the present application;

[0039] Figure 12 EPR spectrum of the carbon nitride quantum dots prepared in Example 1 of the present application;

[0040] Figure 13 Photoluminescence of the carbon nitride quantum dots prepared in Example 1 of the present application excited in the range of 280-430 nm;

[0041] Figure 14 Fluorescence signals of the cells after phagocytosis of the carbon nitride quantum dots prepared in Example 1 of the present application under different excitation wavelengths (from left to right, 405, 488, 561, 640 nm);

[0042] Figure 15Optical images of the carbon nitride quantum dots prepared in Example 1 of this invention without (left image) / irradiated at a wavelength of 365 nm (right image) to show the dispersion of the quantum dots;

[0043] Figure 16 The electron paramagnetic resonance spectrum of the carbon nitride quantum dots prepared in Example 1 of this invention generating ·OH at pH 5.0;

[0044] Figure 17 Michaelis-Menten fitting analysis of the ·OH generation rate of carbon nitride quantum dots prepared in Example 1 of the present invention as a function of different concentrations of H2O2 as a catalytic substrate;

[0045] Figure 18 The X-ray diffraction pattern of the carbon nitride quantum dots prepared in Example 2 of this invention;

[0046] Figure 19 Optical images of the carbon nitride quantum dots prepared in Example 2 of this invention without (left image) or irradiated at a wavelength of 365 nm (right image);

[0047] Figure 20 The electron paramagnetic resonance spectrum of the carbon nitride quantum dots prepared in Example 2 of this invention generating ·OH under pH 5.0 conditions;

[0048] Figure 21 The X-ray diffraction pattern of the carbon nitride quantum dots prepared in Example 3 of this invention;

[0049] Figure 22 The electron paramagnetic resonance spectrum of the carbon nitride quantum dots prepared in Example 3 of this invention generating ·OH under pH 5.0 conditions;

[0050] Figure 23 The X-ray diffraction pattern of the carbon nitride quantum dots prepared in Example 4 of this invention;

[0051] Figure 24 The electron paramagnetic resonance spectrum of the carbon nitride quantum dots prepared in Example 4 of this invention generating ·OH under pH 5.0 conditions;

[0052] Figure 25 The electron paramagnetic resonance spectrum of the carbon nitride quantum dots prepared in Comparative Example 1 of this invention was used to verify the generation of ·OH under pH 5.0 conditions.

[0053] Figure 26 The X-ray diffraction pattern of the quantum dots prepared in Comparative Example 2 of this invention;

[0054] Figure 27 Optical images of the product prepared in Comparative Example 3 of this invention without (left image) / irradiated at a wavelength of 365 nm (right image);

[0055] Figure 28 The electron paramagnetic resonance spectrum of the quantum dots prepared in Comparative Example 5 of this invention generating ·OH under pH 5.0 conditions. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0058] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0059] The ammonia water used in the following examples and comparative examples has a mass fraction of 25-28%.

[0060] Example 1

[0061] A method for preparing carbon nitride quantum dots includes the following steps: 13 mL of formamide, 1 mL of ammonia, and 1 mL of a 30% (w / w) H₂O₂ aqueous solution are measured and mixed evenly to obtain a reaction solution. The reaction solution is transferred to a 25 mL hydrothermal reactor, placed in a vacuum drying oven, heated to 180°C, and reacted for 20 h. After the reaction, the solution is cooled to room temperature, and the solution is aspirated into a dialysis bag with a molecular weight cutoff of 3000D. The bag is then dialyzed in ultrapure water for 48 h. During dialysis, the solution outside the dialysis bag is collected every 24 h, and fresh ultrapure water is added. The collected aqueous solution is freeze-dried until the water is completely removed, yielding the prepared carbon nitride quantum dots.

[0062] Figure 1 This is a schematic diagram of the synthesis in Example 1 of the present invention. In this invention, formamide is used as the precursor and solvent, ammonia is used as the dopant, and H2O2 is used as the redox agent. Carbon nitride quantum dots were obtained through a solvothermal reaction. The optimal reaction conditions are 25 mL reaction vessel, 180 °C for 20 h.

[0063] Figure 2 The X-ray diffraction pattern of the carbon nitride quantum dots prepared in Example 1 of this invention shows a distinct diffraction peak signal around 27°, which is attributed to the π-π interlayer stacking motif of the (002) crystal plane of graphitic carbon nitride.Figure 3 This is a Raman spectroscopy analysis of the carbon nitride quantum dots prepared in Example 1 of the present invention. The results show that the carbon nitride quantum dots exhibit Raman spectroscopy at 1350 cm⁻¹. -1 and 1540cm -1 The signal exhibits typical graphene structure in the D and G bands, with an intensity ratio of 1.04. Figure 4 The infrared spectrum of the carbon nitride quantum dots prepared in Example 1 of this invention is shown at 3400 cm⁻¹. -1 The broad absorption band at 2900 cm⁻¹ can be attributed to the stretching vibrations of NH₄⁺ and OH⁻. Furthermore, the absorption band at 2900 cm⁻¹... -1 This corresponds to the symmetrical stretching vibration of CH, 1610 cm. -1 and 1410cm -1 The two peaks at the point correspond to the skeletal vibrations of the C=C / C=N bonds and the plane vibrations of the CN group in the aromatic ring, respectively.

[0064] Figure 5 The Zeta potential of the carbon nitride quantum dots prepared in Example 1 of this invention is shown to be 25.61 mV, which clearly shows that the surface of the dots carries a positive charge. Figure 6 The images show digital photographs of the carbon nitride quantum dots prepared in Example 1 of this invention after being dispersed in an aqueous solution for different number of days. After different storage days, the carbon nitride quantum dots still maintained excellent stability in the aqueous solution. Figure 7 The images show the dispersion of carbon nitride quantum dots prepared in Example 1 of this invention under simulated physiological environments, demonstrating good stability under different physiological conditions.

[0065] Figure 8 The X-ray photoelectron spectrum of the carbon nitride quantum dots prepared in Example 1 of this invention shows three characteristic peaks observed at 286.1 eV, 398.2 eV and 532.1 eV, indicating the presence of C1s, N1s and O1s, with atomic percentages of 55.57%, 33.19% and 11.24%, respectively. Figure 9 The X-ray photoelectron spectroscopy C1s spectrum of the carbon nitride quantum dots prepared in Example 1 of this invention can be decomposed into four peaks located at 284.8 eV, 285.6 eV, 286.7 eV and 288.6 eV, respectively. These peaks correspond to CC / C=C, CN / CO, C=N and C=O chemical bonds. Figure 10 The X-ray photoelectron spectroscopy (N1s) spectrum of the carbon nitride quantum dots prepared in Example 1 of this invention shows three peaks at 398.3 eV, 399.5 eV, and 400.3 eV, which are attributed to CN=C, N-(C)3, and C-NH, respectively. Figure 11The X-ray photoelectron spectroscopy (O1s) spectrum of the carbon nitride quantum dots prepared in Example 1 of this invention shows that the characteristic peaks at 530.7 eV, 531.8 eV, and 532.9 eV correspond to the presence of CO, C=O, and -OH bonds.

[0066] Figure 12 The EPR spectrum of the carbon nitride quantum dots prepared in Example 1 of this invention shows a vacancy signal at g = 2.003, which is attributed to unpaired electrons in the heptaazine ring unit, reflecting the presence of nitrogen vacancy defects in the structure.

[0067] Figure 15 The image shows the dispersion of carbon nitride quantum dots prepared in Example 1 of this invention without irradiation (left image) or at a wavelength of 365 nm (right image). The synthesized quantum dot aqueous solution is light yellow and emits blue fluorescence under ultraviolet light. Figure 13 The photoluminescence of the quantum dots prepared in Example 1 of this invention, excited in the 280-430 nm range, exhibits the strongest emission upon laser excitation at a wavelength of 340 nm, with the emission peak located at 480 nm. Furthermore, we observed a redshift in the center of the fluorescence emission peak as the excitation wavelength increases. Figure 14 After quantum dots are engulfed by cells, the cells generate fluorescence signals at different excitation wavelengths (405, 488, 561, and 640 nm from left to right). When 4T1 cells are co-incubated with lasers at wavelengths of 405, 488, 561, and 640 nm, respectively, bright fluorescence signals can be observed inside the cells.

[0068] Figure 16 The electron paramagnetic resonance (EPR) spectrum of the carbon nitride quantum dots prepared in Example 1 of this invention for generating ·OH was obtained by using DMPO as a trapping agent and detecting the generation of ·OH using EPR measurement technology. Specifically, the prepared carbon nitride quantum dots were loaded into an EPR capillary, and DMPO was used as a trapping agent. The characteristic peak of the generation of ·OH from H2O2 catalyzed by carbon nitride quantum dots at pH 5.0 was detected. The clear 1:2:2:1 characteristic signal indicates the generation of ·OH under acidic conditions. Figure 17 Michaelis-Menten fitting analysis of the ·OH generation rate of carbon nitride quantum dots prepared in Example 1 of this invention, using different concentrations of H2O2 as the catalytic substrate, shows the maximum catalytic reaction rate V. max Approximately 7.59 × 10 -8 Ms -1 The substrate affinity constant K m It is 154mM.

[0069] Example 2

[0070] A method for preparing carbon nitride quantum dots includes the following steps: 13 mL of formamide, 1 mL of ammonia, and 1 mL of a 30% (w / w) H₂O₂ aqueous solution are measured and mixed evenly to obtain a reaction solution. The reaction solution is transferred to a 25 mL hydrothermal reactor, placed in a vacuum drying oven, heated to 160°C, and reacted for 20 h. After the reaction, the solution is cooled to room temperature, and the solution is aspirated into a dialysis bag with a molecular weight cutoff of 3000D. The bag is then dialyzed in ultrapure water for 48 h. During dialysis, the solution outside the dialysis bag is collected every 24 h, and fresh ultrapure water is added. The collected aqueous solution is freeze-dried until the water is completely removed to obtain the prepared carbon nitride quantum dots.

[0071] Figure 18 The X-ray diffraction pattern of the carbon nitride quantum dots prepared in Example 2 of this invention shows that there are still obvious diffraction peak signals at around 27°, indicating that it is graphitic carbon nitride. Figure 19 The image shows the carbon nitride quantum dots prepared in Example 2 of this invention without (left image) or with 365nm wavelength (right image). The fluorescence produced under ultraviolet light indicates that they are quantum dots. Figure 20 The electron paramagnetic resonance spectrum of the carbon nitride quantum dots prepared in Example 2 of this invention for the generation of ·OH shows a clear 1:2:2:1 characteristic signal, indicating that the carbon nitride quantum dots prepared in Example 2 can also catalyze the generation of ·OH under acidic conditions. Figures 18-20 It can be demonstrated that the carbon nitride quantum dots prepared in Example 2 are similar to those prepared in Example 1.

[0072] Example 3

[0073] A method for preparing carbon nitride quantum dots includes the following steps: 13 mL of formamide, 1 mL of ammonia, and 1 mL of a 30% (w / w) H₂O₂ aqueous solution are measured and mixed evenly to obtain a reaction solution. The reaction solution is transferred to a 25 mL hydrothermal reactor, placed in a vacuum drying oven, heated to 180°C, and reacted for 15 h. After the reaction, the solution is cooled to room temperature, and the solution is aspirated into a dialysis bag with a molecular weight cutoff of 3000D and dialyzed in ultrapure water for 48 h. During dialysis, the solution outside the dialysis bag is collected every 24 h, and fresh ultrapure water is added. The collected aqueous solution is freeze-dried until the water is completely removed to obtain the prepared carbon nitride quantum dots.

[0074] Figure 21 The X-ray diffraction pattern of the carbon nitride quantum dots prepared in Example 3 of this invention shows that they are carbon nitride quantum dots. Figure 22 The electron paramagnetic resonance spectrum of the carbon nitride quantum dots prepared in Example 3 of this invention for the generation of ·OH shows that the carbon nitride quantum dots prepared in Example 3 can also catalyze the generation of ·OH under acidic conditions.

[0075] Example 4

[0076] A method for preparing carbon nitride quantum dots includes the following steps: 12 mL of formamide, 1 mL of ammonia, and 2 mL of a 30% (w / w) H₂O₂ aqueous solution are measured and mixed evenly to obtain a reaction solution. The reaction solution is transferred to a 25 mL hydrothermal reactor, placed in a vacuum drying oven, heated to 180°C, and reacted for 20 h. After the reaction, the solution is cooled to room temperature, and the solution is aspirated into a dialysis bag with a molecular weight cutoff of 3000D. The bag is then dialyzed in ultrapure water for 48 h. During dialysis, the solution outside the dialysis bag is collected every 24 h, and fresh ultrapure water is added. The collected aqueous solution is freeze-dried until the water is completely removed to obtain the prepared carbon nitride quantum dots.

[0077] Figure 23 The X-ray diffraction pattern of the carbon nitride quantum dots prepared in Example 4 of this invention shows that they are carbon nitride quantum dots. Figure 24 The electron paramagnetic resonance spectrum of the carbon nitride quantum dots prepared in Example 4 of this invention for the generation of ·OH shows that the carbon nitride quantum dots prepared in Example 4 can also catalyze the generation of ·OH under acidic conditions.

[0078] Comparative Example 1

[0079] 13 mL of formamide, 1 mL of ammonia, and 1 mL of 30% (w / w) H₂O₂ aqueous solution were measured and mixed thoroughly to obtain a reaction solution. The reaction solution was transferred to a 25 mL hydrothermal reactor and placed in a vacuum drying oven. The temperature was raised to 140 °C and the reaction was carried out for 15 h. After the reaction was completed, the solution was cooled to room temperature, and the solution was aspirated into a dialysis bag with a molecular weight cutoff of 3000 D. The bag was then dialyzed in ultrapure water for 48 h. During the dialysis process, the solution outside the dialysis bag was collected every 24 h and fresh ultrapure water was added. The collected aqueous solution was freeze-dried until the water was completely removed to obtain quantum dots.

[0080] Figure 25 The electron paramagnetic resonance spectrum of the quantum dots prepared in Comparative Example 1 of this invention shows the generation of ·OH. It can be seen that there is no characteristic signal of ·OH at this time, indicating that the quantum dots prepared in Comparative Example 1 do not have peroxidase-like activity.

[0081] Comparative Example 2

[0082] 13 mL of N,N-dimethylformamide, 1 mL of ammonia, and 1 mL of 30% (w / w) H₂O₂ aqueous solution were measured and mixed thoroughly to obtain a reaction solution. The reaction solution was transferred to a 25 mL hydrothermal reactor and placed in a vacuum drying oven. The temperature was raised to 180 °C and the reaction was carried out for 20 h. After the reaction was completed, the solution was cooled to room temperature, and the solution was aspirated into a dialysis bag with a molecular weight cutoff of 3000 D. The bag was then dialyzed in ultrapure water for 48 h. During the dialysis process, the solution outside the dialysis bag was collected every 24 h and fresh ultrapure water was added. The collected aqueous solution was freeze-dried until the water was completely removed to obtain the prepared quantum dots.

[0083] Figure 26 The X-ray diffraction pattern of the quantum dots prepared in Comparative Example 2 of this invention shows that the characteristic signal of graphitic carbon appears, indicating that the quantum dot phase prepared in Comparative Example 2 is not graphitic carbon nitride.

[0084] Comparative Example 3

[0085] 13 mL of toluene, 1 mL of ammonia, and 1 mL of 30% (w / w) H₂O₂ aqueous solution were measured and mixed thoroughly to obtain a reaction solution. The reaction solution was transferred to a 25 mL hydrothermal reactor and placed in a vacuum drying oven. The temperature was raised to 180 °C and the reaction was carried out for 20 h. After the reaction was completed, the solution was cooled to room temperature, and the solution was aspirated into a dialysis bag with a molecular weight cutoff of 3000 D. The bag was then dialyzed in ultrapure water for 48 h. During the dialysis process, the solution outside the dialysis bag was collected every 24 h and fresh ultrapure water was added. The collected aqueous solution was freeze-dried until the water was completely removed to obtain the prepared product.

[0086] Figure 27 The image shows an optical image of the aqueous solution of the product prepared in Comparative Example 3 of this invention without irradiation (left image) or at a wavelength of 365 nm (right image). No fluorescence was produced at this time, indicating that the prepared product is not a quantum dot.

[0087] Comparative Example 4

[0088] Measure 11 mL of formamide, 1 mL of ammonia and 3 mL of 30% H2O2 aqueous solution and mix them evenly to obtain a reaction solution. Transfer the above reaction solution to a 25 mL hydrothermal reactor. Since the amount of H2O2 aqueous solution is high, it will form an unstable solution and is not suitable for continuing the high-temperature solvothermal reaction.

[0089] Comparative Example 5

[0090] 9 mL of toluene, 5 mL of ammonia, and 1 mL of 30% (w / w) H₂O₂ aqueous solution were measured and mixed thoroughly to obtain a reaction solution. The reaction solution was transferred to a 25 mL hydrothermal reactor and placed in a vacuum drying oven. The temperature was raised to 180 °C and the reaction was carried out for 20 h. After the reaction was completed, the solution was cooled to room temperature, and the solution was aspirated into a dialysis bag with a molecular weight cutoff of 3000 D. The bag was then dialyzed in ultrapure water for 48 h. During the dialysis process, the solution outside the dialysis bag was collected every 24 h and fresh ultrapure water was added. The collected aqueous solution was freeze-dried until the water was completely removed to obtain the prepared product.

[0091] Figure 28 The electron paramagnetic resonance spectrum of the quantum dots prepared in Comparative Example 5 of this invention shows the generation of ·OH. It can be seen that there is no characteristic signal of ·OH at this time, indicating that the quantum dots prepared in Comparative Example 5 do not have peroxidase-like activity.

[0092] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing carbon nitride quantum dots, characterized in that: The carbon nitride quantum dots are obtained by a solvothermal reaction using formamide as a precursor and solvent, ammonia as a dopant, and H2O2 as a redox agent; wherein the temperature of the solvothermal reaction is 160-180℃.

2. The method for preparing carbon nitride quantum dots according to claim 1, characterized in that: Includes the following steps: Formamide, ammonia, and H2O2 aqueous solution are mixed evenly to obtain a reaction solution; the obtained reaction solution is placed in a hydrothermal reaction apparatus to react and obtain the carbon nitride quantum dots.

3. The method for preparing carbon nitride quantum dots according to claim 1 or 2, characterized in that: The volume ratio of formamide to ammonia is 1-13:

1.

4. The method for preparing carbon nitride quantum dots according to claim 1, characterized in that: A 30% H2O2 aqueous solution is used as the redox agent, and the volume ratio of formamide to the 30% H2O2 aqueous solution is 6-13:

1.

5. The method for preparing carbon nitride quantum dots according to claim 1, characterized in that: A 30% H2O2 aqueous solution was used as the redox agent, and a 25-28% ammonia solution was used as the dopant. The volume ratio of the formamide, the 25-28% ammonia solution, and the 30% H2O2 aqueous solution was 13:1:

1.

6. The method for preparing carbon nitride quantum dots according to claim 1, characterized in that: The solvothermal reaction takes 15-20 hours.

7. A carbon nitride quantum dot, characterized in that: It is prepared by the method for preparing carbon nitride quantum dots as described in any one of claims 1-6.

8. The carbon nitride quantum dot according to claim 7, characterized in that: It has peroxidase-like activity.

9. The use of carbon nitride quantum dots as described in claim 7 or 8 in the preparation of tumor therapeutic agents and / or near-infrared imaging agents.

10. The use of carbon nitride quantum dots as described in claim 7 or 8 as a peroxidase-like catalyst.

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