Preparation method of composite carbon quantum dots, composite carbon quantum dots, application in sunset yellow detection and detection method

Abstract

The application relates to a preparation method of composite carbon quantum dots, application of the composite carbon quantum dots in sunset yellow detection and a detection method, which comprises the following steps: dissolving p-phenylenediamine in a first solvent and transferring to a reaction kettle for heating reaction to obtain carbon quantum dots; dissolving the carbon quantum dots and methylene blue in a second solvent and transferring to a reaction kettle for heating reaction to obtain the composite carbon quantum dots. The prepared composite carbon quantum dots can cause fluorescence quenching to sunset yellow, so that the composite carbon quantum dots can be used to detect sunset yellow. Since the preparation process of the composite carbon quantum dots is simple and the raw material cost is low, the low-cost detection of sunset yellow can be realized.

Description

Technical Field

[0001] This invention relates to the field of food safety, and in particular to a method for preparing composite carbon quantum dots, the application of composite carbon quantum dots in the detection of sunset yellow, and a detection method thereof. Background Technology

[0002] As an important food additive, food colorings are widely used in soft drinks, tea beverages, and pastries to enhance product visual appeal and standardize product color. Food colorings are generally divided into two main categories: synthetic colorings and natural colorings. Synthetic colorings are favored due to their advantages such as good stability, low cost, and ease of use. However, many synthetic colorings, especially azo colorings, raise health concerns because they may degrade into aromatic amines, which are toxic, carcinogenic, and genotoxic. Sunset Yellow, a typical azo coloring, is widely used in the food industry, particularly in carbonated beverages, candies, and baked goods, to impart vibrant color and enhance product stability. However, cumulative intake of Sunset Yellow is associated with potential carcinogenic risks and may induce allergic reactions, gut microbiota imbalances, and even ADHD in children. Given these health risks, strict usage limits are set for Sunset Yellow.

[0003] Currently, the main methods for detecting sunset yellow include high-performance liquid chromatography (HPLC), electrochemical analysis, capillary electrophoresis, chemiluminescence immunoassay, and differential pulse voltammetry. However, these techniques often have limitations such as complex pretreatment, expensive equipment, long analysis time, and the need for specialized operators, which restricts the widespread detection and efficiency of sunset yellow. Summary of the Invention

[0004] Based on this, it is necessary to address the problems by providing a method for preparing composite carbon quantum dots, the application of composite carbon quantum dots in the detection of sunset yellow, and a detection method.

[0005] The technical solution provided by this invention is as follows:

[0006] A method for preparing composite carbon quantum dots, comprising:

[0007] p-Phenylenediamine was dissolved in a first solvent and transferred to a reaction vessel for heating to obtain carbon quantum dots;

[0008] The carbon quantum dots and methylene blue are dissolved in a second solvent and transferred to a reaction vessel for heating reaction to obtain the composite carbon quantum dots.

[0009] In some embodiments of this application, the reaction temperature of p-phenylenediamine in the reactor is 200°C and the reaction time is 10 hours.

[0010] In some embodiments of this application, the reaction temperature of the carbon quantum dots and methylene blue in the reactor is 200°C, and the reaction time is 8 hours.

[0011] In some embodiments of this application, the mass ratio of the carbon quantum dots to methylene blue is 1:1.

[0012] In some embodiments of this application, the first solvent and / or the second solvent is DMF.

[0013] A composite carbon quantum dot was prepared using the method described above.

[0014] Application of composite carbon quantum dots in the detection of sunset yellow.

[0015] A method for detecting sunset yellow concentration, comprising:

[0016] The intensity of the 442nm fluorescence emitted by the composite carbon quantum dots was detected by irradiating the solution with 358nm excitation light. 442 and the intensity of fluorescence at 694nm i 694 ;

[0017] Mix the solution of the composite carbon quantum dots with the solution to be tested;

[0018] The composite carbon quantum dots were irradiated again with 358 nm excitation light, and the intensity I of the 442 nm fluorescence emitted by the composite carbon quantum dots was detected. 442 And the intensity of fluorescence at 694nm I 694 ;

[0019] Based on i 442 / i 694 and I 442 / I 694 Determine the concentration of Sunset Yellow in the test solution.

[0020] In some embodiments of this application, the pH of the environment in which the composite carbon quantum dots are located is maintained at 6 before and after the solution of the composite carbon quantum dots is mixed with the solution to be tested.

[0021] In some embodiments of this application, the solution of the composite carbon quantum dots is mixed with the test solution and then the I is obtained after at least 8 minutes. 442 and I 694 .

[0022] The beneficial effects of this invention are as follows:

[0023] Sunset Yellow can quench the fluorescence of the composite carbon quantum dots prepared in this invention, thereby allowing the detection of Sunset Yellow using the composite carbon quantum dots of this invention. Since the preparation process of the composite carbon quantum dots is simple and the raw material cost is low, low-cost detection of Sunset Yellow can be achieved.

[0024] Furthermore, this invention first utilizes p-phenylenediamine to obtain carbon quantum dots, and then uses the carbon quantum dots and methylene blue to obtain composite carbon quantum dots, giving the composite carbon quantum dots two fluorescence emission centers. This allows the composite carbon quantum dots to be used for sunset yellow concentration detection using the bimodal ratio method. Since the bimodal ratio method is simple to operate and has high detection accuracy, the composite carbon quantum dots of this invention can also facilitate large-scale, high-precision detection of sunset yellow. Attached Figure Description

[0025] Figure 1 This is a TEM image of carbon quantum dots in an embodiment of the present invention;

[0026] Figure 2 The image shows a TEM image of the composite carbon quantum dots in an embodiment of the present invention.

[0027] Figure 3 The DLS spectrum of carbon quantum dots in this embodiment of the invention;

[0028] Figure 4 The DLS spectrum of the composite carbon quantum dots in this embodiment of the invention;

[0029] Figure 5 The XRD spectrum of the composite carbon quantum dots in this embodiment of the invention;

[0030] Figure 6 The Raman spectrum of the composite carbon quantum dots in this embodiment of the invention;

[0031] Figure 7 The XPS spectra of carbon quantum dots and composite carbon quantum dots in the embodiments of the present invention are shown.

[0032] Figure 8 This is the high-resolution N 1s energy spectrum of the carbon quantum dots in this embodiment of the invention;

[0033] Figure 9 This is the high-resolution N 1s energy spectrum of the composite carbon quantum dots in the embodiments of the present invention;

[0034] Figure 10 The FT-IR spectra of carbon quantum dots and composite carbon quantum dots in the embodiments of the present invention are shown below;

[0035] Figure 11 The UV-vis absorption spectrum, PL spectrum, and PLE spectrum of carbon quantum dots in the embodiments of the present invention are shown.

[0036] Figure 12 The PL spectra of carbon quantum dots under different wavelengths of excitation light in the embodiments of the present invention are shown.

[0037] Figure 13 This is an EEM contour plot of carbon quantum dots in an embodiment of the present invention;

[0038] Figure 14 The UV-vis absorption spectrum, PL spectrum, and PLE spectrum of the composite carbon quantum dots in the embodiments of the present invention are shown.

[0039] Figure 15 The PL spectra of composite carbon quantum dots under different wavelengths of excitation light in the embodiments of the present invention are shown.

[0040] Figure 16 This is an EEM contour plot of composite carbon quantum dots in an embodiment of the present invention;

[0041] Figure 17 The graph shows the fluorescence intensity stability test results of the composite carbon quantum dots in NaCl solution, under ultraviolet light and natural storage conditions in the embodiments of the present invention.

[0042] Figure 18 The PL spectra of composite carbon quantum dots mixed with different concentrations of Sunset Yellow in the embodiments of the present invention are shown below.

[0043] Figure 19 As described in embodiment I of the present invention 442 / I 694 The relationship curve between SY concentration and SY concentration;

[0044] Figure 20 The I values ​​are the results of mixing composite carbon quantum dots and Sunset Yellow at different temperatures in the embodiments of the present invention. 442 / I 694 Bar chart;

[0045] Figure 21 The I values ​​are the results of mixing composite carbon quantum dots and Sunset Yellow for different durations in the embodiments of the present invention. 442 / I 694 Bar chart;

[0046] Figure 22 The I values ​​of the composite carbon quantum dots mixed with Sunset Yellow in the embodiments of the present invention are shown in different pH environments. 442 / I 694 Bar chart;

[0047] Figure 23 In this embodiment of the invention, composite carbon quantum dots are mixed with different substances. 442 and I 694 Normalized histogram;

[0048] Figure 24 The UV-vis absorption spectra of SY, the UV-vis absorption spectra of composite carbon quantum dots, the theoretical UV-vis absorption spectra of composite carbon quantum dots and SY, and the actual UV-vis absorption spectra of composite carbon quantum dots and SY in the embodiments of the present invention are shown.

[0049] Figure 25The images show the FT-IR spectra of the composite carbon quantum dots and SY before and after mixing in this embodiment of the invention.

[0050] Figure 26 The UV-vis absorption spectrum of SY, the PL spectrum (excitation wavelength 358 nm) of the composite carbon quantum dots, and the PLE spectrum (emission wavelength 442 nm) of the composite carbon quantum dots are shown in the embodiments of the present invention.

[0051] Figure 27 The fluorescence decay curves at 442nm emission wavelength are shown in the embodiments of the present invention before and after mixing composite carbon quantum dots and SY.

[0052] Figure 28 The fluorescence decay curves at 694nm emission wavelength are shown in the embodiments of the present invention before and after mixing composite carbon quantum dots and SY. Detailed Implementation

[0053] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0054] Example 1:

[0055] This embodiment provides a composite carbon quantum dot, the preparation method of which includes the following steps:

[0056] Step 101: Dissolve 1 g of p-phenylenediamine in 20 mL of N,N-dimethylformamide (DMF), then transfer the solution to a reaction vessel and heat to 200 °C for 10 h. After the reaction is complete, cool to room temperature and centrifuge the reaction product (10,000 rpm, 15 min). Then, take the supernatant and filter it using a filter membrane with a pore diameter of 0.22 μm. Dialyze the supernatant in distilled water for 24 h using a dialysis bag with a molecular weight cutoff of 1000 Da to obtain carbon quantum dots.

[0057] Step 102: Dissolve 0.1g of the carbon quantum dots and 0.1g of methylene blue (MB) in DMF and stir, then transfer to a reaction vessel and heat to 200°C for 8 hours. After the reaction is complete, filter the resulting clear liquid using a filter membrane with a pore diameter of 0.22μm, and then freeze-dry the filtrate to obtain the composite carbon quantum dots.

[0058] Figure 1 The image shown is a transmission electron microscope (TEM) image of the carbon quantum dots. Figure 2 A TEM image of the composite carbon quantum dots is shown. Figure 1 As shown, the carbon quantum dots exhibit a uniform spherical morphology with an average diameter of 3.5 nm. Figure 1 The upper right corner shows a high-resolution transmission electron microscope (HR-TEM) image of the carbon quantum dots, revealing clear lattice fringes. The interplanar spacing of the carbon quantum dots is 0.24 nm, matching the (100) plane of graphene, indicating a high degree of graphitization. Figure 2 As shown, when the carbon quantum dots are grafted with MB, the resulting composite carbon quantum dots still have a well-dispersed spherical morphology, but the average particle size of the composite carbon quantum dots increases to 4.56 nm. Figure 3 The dynamic light scattering (DLS) spectrum of the carbon quantum dots is shown, revealing a hydrated particle size of 3.7 nm. Figure 4 The DLS spectrum of the composite carbon quantum dots is shown, revealing a hydrated particle size of 4.77 nm. Based on Figures 1-4 It can be fully demonstrated that in this embodiment, methylene blue has been successfully coupled to the surface of the carbon quantum dots and formed the composite carbon quantum dots, thereby resulting in a significant increase in the nanoparticle size of the composite carbon quantum dots.

[0059] Figure 5 The X-ray diffraction (XRD) spectrum of the composite carbon quantum dots is shown, which shows that the composite carbon quantum dots have a characteristic diffraction peak at 26°, matching the (002) crystal plane of graphitic carbon. Figure 6 The Raman spectrum of the composite carbon quantum dots is shown, with the D band located at 1365 cm⁻¹. -1 The G-band is located at 1600cm. -1 The strength of the D band I D The ratio of the strength of the G-band to I G The ratio of 0.93 confirms that the composite carbon quantum dots possess graphitic carbon and have a highly ordered structure.

[0060] Figure 7 The X-ray photoelectron spectroscopy (XPS) spectra of the carbon quantum dots and the composite carbon quantum dots are shown, based on Figure 7 Calculations show that the carbon quantum dots contain 70.14% carbon, 19.86% nitrogen, and 10% oxygen, while the composite carbon quantum dots contain 68.7% carbon, 15% nitrogen, and 16.3% oxygen. Figure 8 The high-resolution N 1s energy spectrum of the carbon quantum dot is shown, in which the peak at 398.3 eV corresponds to pyrrole nitrogen, the peak at 399.2 eV corresponds to amino nitrogen, and the peak at 400.11 eV corresponds to graphitic nitrogen. Figure 9 The high-resolution N 1s energy spectrum of the composite carbon quantum dots is shown, compared to Figure 8In particular, it adds a characteristic peak corresponding to quaternary nitrogen at 401.2 eV, indicating that a quaternary ammonia bond is formed between the tertiary amino group on the MB and the amino group on the carbon quantum dot. Figure 10 The Fourier transform infrared (FT-IR) spectra of the carbon quantum dots and the composite carbon quantum dots are shown, both at 3202 cm⁻¹. -1 -3332 cm -1 The broad peak at 2863 cm⁻¹ is attributed to the stretching vibrations of OH and NH. -1 The peak at 1719 cm⁻¹ corresponds to CH. -1 The peak at this location corresponds to C=N, 1634 cm⁻¹ -1 The peak at 1577 cm⁻¹ corresponds to C=O. -1 The peak at 1067 cm⁻¹ corresponds to C. -1 The peak at that location corresponds to CN. Furthermore, the composite carbon quantum dots at 3700 cm⁻¹... -1 -3730 cm -1 A new corresponding quaternary ammonium (CN) has been added at this location. + The stretching vibration peaks of the carbon quantum dots were observed. Based on the above characterization, it can be confirmed that MB was successfully grafted onto the surface of the carbon quantum dots via quaternary ammonium compounds, without altering the basic structure of the carbon quantum dots.

[0061] Figure 11 The UV-vis absorption spectrum, PL spectrum, and PLE spectrum of the carbon quantum dots are shown. Figure 12 The PL spectra of the carbon quantum dots under different wavelengths of excitation light are shown. Figure 13 The excitation-emission matrix (EEM) contour plot of the carbon quantum dots is shown. (See figure.) Figure 11 As shown, the UV-vis absorption spectrum of the carbon quantum dots exhibits a distinct absorption band at 225 nm, corresponding to the C=C bonds within the aromatic ring. The transition also exhibits a weak absorption band at 276 nm, corresponding to the C=O / C=N group. Leap. For example... Figure 11 As shown in the middle inset, the aqueous solution of the carbon quantum dots appears pale yellow under sunlight and emits blue fluorescence under 365 nm excitation light. Figure 12 and Figure 13 As shown, the emission wavelength of the carbon quantum dot varies with the excitation wavelength. The carbon quantum dot has only one fluorescence emission center, which corresponds to an excitation wavelength of 358 nm and an emission wavelength of 442 nm.

[0062] Figure 14 The UV-vis absorption spectrum, PL spectrum, and PLE spectrum of the composite carbon quantum dots are shown. Figure 15The PL spectra of the composite carbon quantum dots under different wavelengths of excitation light are shown. Figure 16 The excitation-emission matrix (EEM) contour plot of the composite carbon quantum dots is shown. Figure 14 As shown, its comparison Figure 11 In contrast, the UV-vis absorption spectrum of the composite carbon quantum dots shows a new absorption band at 660 nm, which corresponds to the characteristic absorption of MB, while the original absorption characteristics of the carbon quantum dots do not show significant changes. Figure 14 As shown in the inset, the composite carbon quantum dots appear deep blue in sunlight and emit blue fluorescence under 365nm excitation light. Figure 15 and Figure 16 As shown, unlike the carbon quantum dots, the composite carbon quantum dots have two fluorescence emission centers. The excitation wavelengths corresponding to the two fluorescence emission centers are both 358 nm, and the emission wavelengths corresponding to the two fluorescence emission centers are 442 nm and 694 nm, respectively.

[0063] The intensity of the 442nm fluorescence emitted by the composite carbon quantum dots under 358nm excitation light is I. 442 The intensity of the 694nm fluorescence emitted by the composite carbon quantum dots under 358nm excitation light is I. 694 . Figure 17 The fluorescence intensity stability test results of the composite carbon quantum dots are shown in NaCl solution, under ultraviolet light irradiation, and under natural storage conditions. Figure 17 As shown, the composite carbon quantum dots in a 2.1 mol / L NaCl solution, I 442 and I 694 There was no significant decrease. After 24 hours of ultraviolet light irradiation, the composite carbon quantum dots showed I 442 and I 694 There was no significant decrease; the composite carbon quantum dots showed no significant decrease after 28 days of natural storage. 442 and I 694 There was no significant decrease. This confirms that the composite carbon quantum dots possess strong stability.

[0064] Figure 18 The PL spectra of the composite carbon quantum dots mixed with different concentrations of Sunset Yellow (SY) are shown. Figure 18 As shown, with the increase of SY concentration, I 442 and I 694 All began to decline, but I 442 The rate of decline was significantly faster than that of I. 694 Therefore, based on I 442 / I 694 It can detect SY concentration. Figure 19 I was shown 442 / I 694The relationship curve between SY concentration and concentration, based on Figure 19 It can be observed that as the concentration of SY increases, I 442 / I 694 The concentration gradually decreases, especially when the SY concentration is in the range of 0.059 μM-30 μM, the SY concentration and I... 442 / I 694 There is a good linear relationship between them, and the linear fitting equation is Y = -0.06813X + 3.39043 (R²). 2 =0.994), where Y and X represent I respectively. 442 / I 694 The limit of detection (LOD) for the SY concentration was calculated using the 3σ / k method and found to be 59 nM, where σ is the standard deviation of the blank sample and k is the slope of the calibration curve.

[0065] Figure 20 The diagram shows the I values ​​corresponding to the mixture of the composite carbon quantum dots and Sunset Yellow at different temperatures. 442 / I 694 Bar chart; Figure 21 The diagram shows the I values ​​corresponding to different mixing times of the composite carbon quantum dots and Sunset Yellow. 442 / I 694 Bar chart; Figure 22 The I values ​​of the composite carbon quantum dots mixed with Sunset Yellow under different pH conditions are shown. 442 / I 694 Bar chart. (e.g.) Figure 20 As shown, I 442 / I 694 It remains basically constant within the range of 10℃-70℃, indicating that I 442 / I 694 The composite carbon quantum dots are insensitive to temperature changes and exhibit a wide temperature window for the detection of Sunset Yellow. Figure 21 As shown, I 442 / I 694 The mixture of composite carbon quantum dots and Sunset Yellow tends to stabilize after 8 minutes, therefore I 442 / I 694 For higher accuracy, the composite carbon quantum dots and Sunset Yellow should be mixed for 8 minutes before detection. Figure 22 As shown, as pH increases from 3 to 11, I 442 / I 694 The pH value first increases and then decreases, reaching its maximum at pH=6. Therefore, this embodiment uses I... 442 / I 694 When testing the concentration of SY, the pH of the solution was uniformly set to 6.

[0066] Figure 23 The composite carbon quantum dots are shown after being mixed with different substances.442 and I 694 Normalized bar charts are shown. The aqueous solution of composite carbon quantum dots is the first solution, and the mixed solution of composite carbon quantum dots and Sunset Yellow is the second solution. The two samples corresponding to the bars at Blank are the first and second solutions, respectively. The two samples corresponding to the other bars are the first solution and the mixture of interfering substances, and the second solution and the mixture of interfering substances, respectively. The interfering substances are KCl (99.0%), NaCl (99.9%), Zn(CH3COO)2 (99.0%), MgSO4 (99.9%), AlCl3 (99.0%), CuCl2 (99.0%), FeCl2 (99.0%), FeCl3 (99.0%), CaCl2 (99.9%), CdCl2 (99.0%), MnCl2 (99.0%), NiCl2 (99.9%), BaCl2 (99.0%), and SnCl2 (99.0%). 0%), HgCl2 (99.0%), CrCl3 (99.9%), ZrCl4 (99.0%), KI (99.0%), NaF (99.0%), KBr (99.0%), K2S (99.0%), Na2CO3 (99.0%), Na2SO3 (99.0%), curcumin (Cur, 99.0%), carmine (Car, 99.0%), acid mordant red (AMR, 99.0%), acid red 18 (AR18, 98.0%), Sudan I (Sudan I, 99.0%), Sudan II (Sudan II, 99.0%), Sudan III (Sudan III, 99.0%). Based on Figure 23 It can be observed that only Sunset Yellow can make I 442 / I 694 Significant changes occurred, thus confirming that the composite carbon quantum dots have specificity for detecting Sunset Yellow.

[0067] Figure 24 The UV-vis absorption spectrum of SY, the UV-vis absorption spectrum of the composite carbon quantum dots, the theoretical UV-vis absorption spectrum of the mixture of composite carbon quantum dots and SY, and the actual UV-vis absorption spectrum of the mixture of composite carbon quantum dots and SY are shown. Figure 24 As shown, the theoretical UV-vis absorption spectrum and the actual UV-vis absorption spectrum of the composite carbon quantum dots and SY are highly consistent, and no new absorption bands or peak shifts appear, ruling out the possibility of a new ground-state complex forming between the composite carbon quantum dots and SY. Figure 25 The FT-IR spectra of the composite carbon quantum dots and SY before and after mixing are shown. The FT-IR spectrum of the composite carbon quantum dots and SY after mixing does not show any additional absorption bands compared to the FT-IR spectrum before mixing, further confirming the above conclusion.

[0068] Figure 26 The UV-vis absorption spectrum of SY, the PL spectrum (excitation wavelength 358 nm) of the composite carbon quantum dots, and the PLE spectrum (emission wavelength 442 nm) of the composite carbon quantum dots are shown. The PL and PLE spectra of the composite carbon quantum dots show significant overlap with the UV-vis absorption spectrum of SY, indicating that the fluorescence quenching mechanism of the composite carbon quantum dots by SY may involve a synergistic effect of fluorescence resonance energy transfer and internal filtering.

[0069] Figure 27 The fluorescence decay curves at 442 nm emission wavelength are shown before and after mixing the composite carbon quantum dots and SY. Figure 27 As shown, the average fluorescence lifetime at 442 nm was significantly shortened after the introduction of Sunset Yellow (from 3.03 ns to 2.19 ns), indicating the occurrence of fluorescence resonance energy transfer. Figure 28 The fluorescence decay curves at 694 nm emission wavelength are shown before and after mixing the composite carbon quantum dots and SY. Figure 28 As shown, after the introduction of Sunset Yellow, the average fluorescence lifetime at 694 nm did not change significantly (from 2.59 ns to 2.56 ns), effectively ruling out the possibility of direct fluorescence resonance energy transfer between Sunset Yellow and composite carbon quantum dots. Therefore, the fluorescence decay is attributed to the internal filtering effect.

[0070] In summary, the fluorescence quenching mechanism of sunset yellow-induced composite carbon quantum dots is as follows: the 442 nm blue emission is quenched through the synergistic effect of fluorescence resonance energy transfer and internal filtering effect, while the attenuation of the 694 nm red emission is mainly attributed to the internal filtering effect.

[0071] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing composite carbon quantum dots, characterized in that, include: p-Phenylenediamine was dissolved in a first solvent and transferred to a reaction vessel for heating to obtain carbon quantum dots; The carbon quantum dots and methylene blue are dissolved in a second solvent and transferred to a reaction vessel for heating reaction to obtain the composite carbon quantum dots.

2. The method for preparing composite carbon quantum dots according to claim 1, characterized in that, The reaction temperature of p-phenylenediamine in the reactor was 200℃, and the reaction time was 10h.

3. The method for preparing composite carbon quantum dots according to claim 1, characterized in that, The reaction temperature of the carbon quantum dots and methylene blue in the reactor is 200°C, and the reaction time is 8 hours.

4. The method for preparing composite carbon quantum dots according to claim 1, characterized in that, The mass ratio of the carbon quantum dots to methylene blue is 1:

1.

5. The method for preparing composite carbon quantum dots according to claim 1, characterized in that, The first solvent and / or the second solvent is DMF.

6. A composite carbon quantum dot, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

7. The application of the composite carbon quantum dots as described in claim 6 in the detection of sunset yellow.

8. A method for detecting the concentration of Sunset Yellow, characterized in that, include: The solution of the composite carbon quantum dots as described in claim 6 was irradiated with 358 nm excitation light, and the intensity of the 442 nm fluorescence emitted by the composite carbon quantum dots was detected. 442 and the intensity of fluorescence at 694nm i 694 ; Mix the solution of the composite carbon quantum dots with the solution to be tested; The composite carbon quantum dots were irradiated again with 358 nm excitation light, and the intensity I of the 442 nm fluorescence emitted by the composite carbon quantum dots was detected. 442 And the intensity of fluorescence at 694nm I 694 ; Based on i 442 / i 694 and I 442 / I 694 Determine the concentration of Sunset Yellow in the test solution.

9. The method for detecting sunset yellow concentration according to claim 8, characterized in that, Before and after mixing the solution of the composite carbon quantum dots with the solution to be tested, the pH of the environment in which the composite carbon quantum dots are located is maintained at 6.

10. The method for detecting sunset yellow concentration according to claim 8, characterized in that, After the solution of the composite carbon quantum dots is mixed with the test solution, I is obtained after at least 8 minutes. 442 and I 694 .

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