A preparation method of double-excitation carbon quantum dots, double-excitation carbon quantum dots, and a Cr(VI) concentration detection method

Abstract

This invention provides a method for preparing dual-excited carbon quantum dots, the dual-excited carbon quantum dots and their applications, and a method for detecting Cr(VI) concentration. The method includes: dissolving polyethyleneimine and glucose in deionized water, then transferring the solution to a reaction vessel and heating it to obtain the dual-excited carbon quantum dots. The dual-excited carbon quantum dots provided by this invention have two fluorescence emission centers. When the dual-excited carbon quantum dots are mixed with Cr(VI), the fluorescence intensity corresponding to the two fluorescence emission centers decreases, and the rate of decrease is inconsistent. Therefore, the dual-excited carbon quantum dots can be used to detect the concentration of Cr(VI) using the bimodal ratio method, thereby improving the detection accuracy of Cr(VI).

Description

Technical Field

[0001] This invention relates to the field of Cr(VI) detection, and in particular to a method for preparing dual-excited carbon quantum dots, dual-excited carbon quantum dots and their applications, and a method for detecting Cr(VI) concentration. Background Technology

[0002] With urbanization and industrialization, chromium (Cr), a highly toxic substance, is widely used in electroplating, printing, leather tanning, and other industrial processes. When chromium enters the environment, it poses a serious threat to ecosystems and human health. Among these, chromates (Cr(VI)) are the most harmful due to their high mobility and mutagenic and carcinogenic properties. Unlike the relatively less toxic Cr(III), Cr(VI) can easily penetrate cell membranes via sulfate anion transport channels, generating reactive oxygen species and causing DNA damage. Therefore, the detection of Cr(VI) is of great significance.

[0003] Carbon dots (CDs) have wide applications in food and environmental testing due to their low toxicity, good water dispersibility, excellent biocompatibility, and high resistance to photobleaching. Currently, carbon dots used for Cr(VI) detection often have only one fluorescence emission center, making the detection process susceptible to environmental interference and thus affecting detection sensitivity. Summary of the Invention

[0004] Therefore, it is necessary to address the problem of insufficient sensitivity in Cr(VI) detection by providing a method for preparing dual-excited carbon quantum dots, the dual-excited carbon quantum dots and their applications, and a method for detecting Cr(VI) concentration.

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

[0006] A method for preparing dual-excited carbon quantum dots includes: dissolving polyethyleneimine and glucose in deionized water, and then transferring the solution to a reaction vessel for heating and reaction to obtain the dual-excited carbon quantum dots.

[0007] In some embodiments of this application, the molar ratio of polyethyleneimine to glucose is 0.75:1 to 1.25:1.

[0008] In some embodiments of this application, the reaction temperature is 175℃-185℃ and the reaction time is 9h-11h.

[0009] A dual-excited carbon quantum dot is prepared using the aforementioned method for preparing dual-excited carbon quantum dots.

[0010] An application of the aforementioned dual-excited carbon quantum dots in the detection of Cr(VI).

[0011] A method for detecting Cr(VI) concentration, comprising:

[0012] An aqueous solution of the dual-excited carbon quantum dots was irradiated with 355 nm excitation light, and the emitted fluorescence intensity f at 460 nm was detected. 355 ;

[0013] An aqueous solution of the dual-excited carbon quantum dots was irradiated with 400 nm excitation light, and the emitted fluorescence intensity f at 460 nm was measured. 400 ;

[0014] The aqueous solution of the dual-excited carbon quantum dots is mixed with the test solution to form a detection solution;

[0015] The detection liquid was irradiated with 355nm excitation light, and the emitted fluorescence intensity F at 460nm was measured. 355 ;

[0016] The detection liquid was irradiated with 400nm excitation light, and the emitted fluorescence intensity F at 460nm was measured. 400 ;

[0017] At least based on F 355 / F 400 and f 355 / f 400 Determine the concentration of Cr(VI) in the test solution.

[0018] In some embodiments of this application, the following are included:

[0019] Prepare a first solution, wherein the solute of the first solution is the dual-excited carbon quantum dots, the solvent is water, and the concentration of the dual-excited carbon quantum dots is a;

[0020] When the first solution is irradiated with 355nm excitation light, the emitted fluorescence intensity at 460nm is f. 355 ;

[0021] When the first solution is irradiated with 400 nm excitation light, the emitted fluorescence intensity at 460 nm is f. 400 ;

[0022] Cr(VI) was added to the first solution sequentially. After each addition of Cr(VI), the concentration of Cr(VI) in the first solution and the corresponding f were obtained. 355 / f 400 to obtain f 355 / f 400 The first fitted relationship between Cr(VI) concentration and Cr(VI) concentration;

[0023] Prepare a second solution, wherein the solute of the second solution is the dual-excited carbon quantum dots, the solvent is water, the concentration of the dual-excited carbon quantum dots is b, b > a, and the second solution does not contain Cr(VI).

[0024] The second solution is mixed with the test solution to form the detection solution, and the concentration of the dual-excited carbon quantum dots in the detection solution is a;

[0025] Based on F 355 / F 400 The concentration of Cr(VI) in the detection solution is determined by the first fitting relationship, and then the total amount of Cr(VI) in the detection solution is determined based on the volume of the detection solution and the concentration of Cr(VI) in the detection solution.

[0026] The concentration of Cr(VI) in the test solution is determined based on the total amount of Cr(VI) in the test solution and the volume of the test solution.

[0027] In some embodiments of this application, the concentration of the dual-excited carbon quantum dots in the detection solution is 1.2 mg / mL.

[0028] A Cr(VI) detection system includes an illumination device, an imaging device, and a thin film, wherein the illumination device and the imaging device are positioned toward the thin film, and the thin film contains the dual-excited carbon quantum dots.

[0029] A method for detecting Cr(VI) concentration, based on the aforementioned Cr(VI) detection system, the method comprising:

[0030] The solution to be tested is dropped onto the thin film;

[0031] The lighting device irradiates the film to make the film fluoresce;

[0032] The imaging device acquires the fluorescence emitted by the film and obtains its corresponding total RGB value;

[0033] The concentration of Cr(VI) in the test solution is determined based on the total RGB value.

[0034] The beneficial effects of this invention are as follows:

[0035] The dual-excited carbon quantum dots provided by this invention have two fluorescence emission centers. When the dual-excited carbon quantum dots are mixed with Cr(VI), the fluorescence intensity corresponding to the two fluorescence emission centers will decrease and the rate of decrease will be inconsistent. Therefore, the dual-excited carbon quantum dots can be used to detect the concentration of Cr(VI) using the bimodal ratio method, thereby improving the detection accuracy of Cr(VI). Attached Figure Description

[0036] Figure 1 This is a transmission electron microscope image of dual-excited carbon quantum dots in an embodiment of the present invention;

[0037] Figure 2This is a bar chart showing the particle size distribution of dual-excited carbon quantum dots in an embodiment of the present invention;

[0038] Figure 3 This is an atomic force microscope image of dual-excited carbon quantum dots in an embodiment of the present invention;

[0039] Figure 4 This is an X-ray diffraction pattern of dual-excited carbon quantum dots in an embodiment of the present invention;

[0040] Figure 5 The Raman spectrum of the dual-excited carbon quantum dots in this embodiment of the invention;

[0041] Figure 6 The Fourier transform infrared spectrum of the dual-excited carbon quantum dots in this embodiment of the invention;

[0042] Figure 7 This is a full-scan X-ray photoelectron spectroscopy spectrum of dual-excited carbon quantum dots in an embodiment of the present invention;

[0043] Figure 8 This is the high-resolution C 1s spectrum of the dual-excited carbon quantum dots in an embodiment of the present invention;

[0044] Figure 9 This is the high-resolution N 1s spectrum of the dual-excited carbon quantum dots in an embodiment of the present invention;

[0045] Figure 10 This is the high-resolution O 1s spectrum of the dual-excited carbon quantum dots in an embodiment of the present invention;

[0046] Figure 11 The UV-vis absorption spectrum, PL spectrum, and PLE spectrum of the dual-excited carbon quantum dots in this embodiment of the invention are shown below.

[0047] Figure 12 This is the three-dimensional fluorescence excitation-emission matrix of the dual-excitation carbon quantum dots in this embodiment of the invention;

[0048] Figure 13 This is a bar chart showing the fluorescence intensity of an aqueous solution of dual-excited carbon quantum dots after irradiation with ultraviolet light for different times in an embodiment of the present invention.

[0049] Figure 14 This is a bar chart showing the fluorescence intensity of an aqueous solution of dual-excited carbon quantum dots after being irradiated with natural light for different times in an embodiment of the present invention.

[0050] Figure 15 This is a bar chart showing the fluorescence intensity of dual-excited carbon quantum dots mixed with NaCl solutions of different concentrations in an embodiment of the present invention;

[0051] Figure 16 The PLE spectra of dual-excited carbon quantum dots mixed with different concentrations of Cr(VI) in this embodiment of the invention are shown.

[0052] Figure 17 In this embodiment of the invention, dual-excited carbon quantum dots are mixed with different concentrations of Cr(VI) and then... 355 / F 400 The curve showing the relationship between Cr(VI) concentration and Cr(VI) concentration;

[0053] Figure 18 In this embodiment of the invention, dual-excited carbon quantum dots are mixed with different concentrations of Cr(VI) and then subjected to F. 355 / F 400 A linear fitting curve between Cr(VI) concentration and Cr(VI) concentration;

[0054] Figure 19 The F in this embodiment of the invention is a mixture of dual-excited carbon quantum dots and different substances. 355 / F 400 ;

[0055] Figure 20 The F values ​​corresponding to different concentrations of dual-excited carbon quantum dots and Cr(VI) in the embodiments of the present invention are as follows: 355 / F 400 ;

[0056] Figure 21 The F values ​​at different pH levels after mixing dual-excited carbon quantum dots and Cr(VI) in the embodiments of the present invention are shown. 355 / F 400 ;

[0057] Figure 22 This is a curve showing the change in fluorescence intensity over time after mixing dual-excited carbon quantum dots and Cr(VI) in an embodiment of the present invention.

[0058] Figure 23 The UV-vis absorption spectra of dual-excited carbon quantum dots, UV-vis absorption spectra of Cr(VI), actual UV-vis absorption spectra of the mixture of dual-excited carbon quantum dots and Cr(VI), and theoretical UV-vis absorption spectra of the mixture of dual-excited carbon quantum dots and Cr(VI) are shown in the embodiments of the present invention.

[0059] Figure 24 The UV-vis absorption spectrum of Cr(VI), the PL spectrum of the double-excited carbon quantum dots, and the PLE spectrum of the double-excited carbon quantum dots are shown in the embodiments of the present invention.

[0060] Figure 25 The fluorescence lifetime curves of dual-excited carbon quantum dots and Cr(VI) before and after mixing are shown in the embodiments of the present invention.

[0061] Figure 26 This is a curve showing the relationship between Sum / Sum0 and Cr(VI) concentration in an embodiment of the present invention. Detailed Implementation

[0062] 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.

[0063] Example:

[0064] This embodiment provides a dual-excited carbon quantum dot that can be used to detect Cr(VI), specifically potassium chromate. The preparation method of the dual-excited carbon quantum dot includes the following steps: dissolving 1 mmol of polyethyleneimine (PEI) and 1 mmol of glucose in 50 mL of deionized water, then sonicating for 30 min, transferring the sonicated solution to a reaction vessel and reacting at 180°C for 10 h. After the reaction is complete and cooled to room temperature, filtering the resulting solution using a 0.22 μm pore size filter, and then vacuum drying for 24 h to obtain the dual-excited carbon quantum dots.

[0065] Figure 1 The transmission electron microscope (TEM) image of the dual-excited carbon quantum dots is shown, which clearly shows that the dual-excited carbon quantum dots are well-dispersed dot-shaped nanoparticles without obvious aggregation. Figure 1 The inset in the upper right corner shows a high-resolution TEM (HR-TEM) image of the dual-excited carbon quantum dots, which shows that the lattice spacing of the dual-excited carbon quantum dots is 0.23 nm, matching the (100) crystal plane of graphite carbon. Figure 2 A bar chart showing the particle size distribution of the dual-excited carbon quantum dots is presented. The particle size ranges from 3.5 nm to 7 nm, with an average particle size of 5.5 nm. Figure 3 An atomic force microscopy (AFM) image of the dual-excited carbon quantum dots is shown, with the height of the dual-excited carbon quantum dots ranging from 1.8 nm to 5.1 nm. Figure 4 The X-ray diffraction (XRD) pattern of the dual-excited carbon quantum dots is shown, which exhibits a characteristic peak at 25.9°, corresponding to the (002) plane of the carbonaceous material. Figure 5 The Raman spectrum of the dual-excited carbon quantum dot is shown, with its D peak located at 1364 cm⁻¹. -1 At this location, peak G is at 1600cm. -1 At this point, the intensity ratio of peak D to peak G is I D / I GThe value of 0.38 indicates that the dual-excited carbon quantum dots are highly graphitized.

[0066] Figure 6 The Fourier transform infrared (FT-IR) spectrum of the dual-excited carbon quantum dots is shown, with a wavelength of 3427 cm⁻¹. -1 The broad peak at 2839 cm⁻¹ corresponds to -OH and -NH. -1 and 2969cm -1 The peak between them corresponds to CH, 1142 cm⁻¹ -1 1402cm -1 and 1566cm -1 The peaks at these points correspond to the stretching vibrations of CO, C=N / CN, and C=O, respectively. Figure 7 The full-scan X-ray photoelectron spectroscopy (XPS) spectrum of the dual-excited carbon quantum dots is shown. The three peaks at 284.8 eV, 399.1 eV, and 530.5 eV correspond to C 1s, N 1s, and O 1s, respectively. Calculations show that the atomic percentages of C, N, and O in the dual-excited carbon quantum dots are 56.7%, 17.1%, and 26.2%, respectively. Figure 8 The high-resolution C 1s spectrum of the dual-excited carbon quantum dot is shown, with three peaks at 287.1 eV, 285.3 eV, and 284.3 eV corresponding to C=N / C=O, CC, and C=C, respectively. Figure 9 The high-resolution N 1s spectrum of the dual-excited carbon quantum dot is shown, with three peaks at 398.4 eV, 399.4 eV, and 400.2 eV corresponding to pyridine N, pyrrole N, and amino N, respectively. Figure 10 The high-resolution O 1s spectrum of the dual-excited carbon quantum dot is shown, with two peaks at 530.7 eV and 532.0 eV corresponding to C=O and CO, respectively.

[0067] Figure 11 The UV-vis absorption spectrum, PL spectrum, and PLE spectrum of the dual-excited carbon quantum dots are shown. Figure 12 The three-dimensional fluorescence excitation-emission matrix (EEM) of the dual-excited carbon quantum dots is shown. The UV-vis absorption spectrum of the dual-excited carbon quantum dots exhibits two distinct absorption bands at 200 nm and 330 nm, with the absorption band at 200 nm attributed to aromatic sp. 2 Within the domain (C=C) The transition, with the absorption band at 330 nm, is attributed to the surface states of the doubly excited carbon quantum dots (i.e., the nitrogen and oxygen-containing portions). Leap. Based on Figure 11 and Figure 12It can also be observed that the dual-excited carbon quantum dots have two fluorescence emission centers, corresponding to excitation wavelengths of 355 nm and 400 nm, respectively, and emission wavelengths of 460 nm for both. Furthermore, the emission wavelength of the dual-excited carbon quantum dots does not change with the excitation wavelength, a characteristic that facilitates the repeated detection of Cr(VI) by the dual-excited carbon quantum dots. Figure 11 As shown in the inset, the aqueous solution of the dual-excited carbon quantum dots is brown in sunlight and emits blue fluorescence when excited by 355 nm or 400 nm light.

[0068] Figure 13 The following is a bar chart showing the fluorescence intensity of the aqueous solution of the dual-excited carbon quantum dots after irradiation with ultraviolet light for different times. It can be seen that even after irradiation with ultraviolet light for 18 hours, the fluorescence intensity of the aqueous solution of the dual-excited carbon quantum dots did not decrease significantly. Figure 14 The following is a bar chart showing the fluorescence intensity of the aqueous solution of the dual-excited carbon quantum dots after being irradiated with natural light for different times. It can be seen that the fluorescence intensity of the aqueous solution of the dual-excited carbon quantum dots did not decrease significantly even after 21 days of natural light irradiation. Figure 15 The diagram shows fluorescence intensity histograms of the dual-excited carbon quantum dots mixed with NaCl solutions of different concentrations. It can be observed that even in a 1.6 mol / L NaCl solution, the fluorescence intensity of the dual-excited carbon quantum dots did not decrease significantly. Based on this, it can be concluded that the dual-excited carbon quantum dots possess excellent stability.

[0069] Figure 16 The PLE spectra of the dual-excited carbon quantum dots mixed with different concentrations of Cr(VI) are shown. It can be clearly seen that as the Cr(VI) concentration increases, the excitation peak intensities at both 355 nm and 400 nm continuously decrease, and the rate of decrease in the excitation peak intensity at 355 nm is faster than that at 400 nm. This confirms that, based on the dual-excited carbon quantum dots provided in this embodiment, the bipeak ratio method can be used to detect the Cr(VI) concentration.

[0070] The intensity of the excitation peak at 355 nm in the PLE spectrum of the dual-excited carbon quantum dots is F. 355 The excitation peak intensity at 400 nm is F 400 . Figure 17 The image shows the F after the dual-excited carbon quantum dots are mixed with different concentrations of Cr(VI). 355 / F 400 The curve showing the relationship between Cr(VI) concentration and concentration. Figure 18 The image shows the F after the dual-excited carbon quantum dots are mixed with different concentrations of Cr(VI). 355 / F 400A linear fitting curve between Cr(VI) concentration and Cr(VI) concentration. Based on Figure 17 and Figure 18 As can be seen, F 355 / F 400 The concentration of Cr(VI) decreases continuously with increasing Cr(VI) concentration. Specifically, when the Cr(VI) concentration is in the range of 79 nM-80 μM, F... 355 / F 400 There is a good linear relationship between the concentration of Cr(VI) and the concentration of Cr(VI), and the detection limit (LOD) of the dual-excited carbon quantum dots for the concentration of Cr(VI) is 79 nM.

[0071] Figure 19 The F-type carbon quantum dots, after being mixed with different substances, are shown. 355 / F 400 .based on Figure 19 It can be clearly observed that common metal ions (Na) + K + Ag + Cd 2+ Cu + Gd 2+ Pb 2+ Hg 2+ Ca 2+ Ba 2+ Fe 3+ Cu 2+ Mn 2+ And Al 3 + ), anion (Cl) - SO4 2- NO3 - and SO3 2- Neither ascorbic acid (AA), glucose (Glu), L-alanine (L-ala), L-proline (L-pro), D-alanine (D-ala), L-tryptophan (L-try), L-cysteine ​​(L-cys), and urea (Urea) will cause F. 355 / F 400 Significant changes occurred; only Cr(VI) could cause F. 355 / F 400 The significant reduction in Cr(VI) confirms that the dual-excited carbon quantum dots have extremely high detection specificity for Cr(VI).

[0072] Figure 20 The following diagram shows the F values ​​corresponding to different concentrations of dual-excited carbon quantum dots and Cr(VI) mixture. 355 / F 400 As can be seen, as the concentration of dual-excited carbon quantum dots gradually increases from 0 to 3.0 mg / mL, F 355 / F 400 First decrease then increase, until the concentration reaches 1.2 mg / mL, at which point F... 355 / F 400 The minimum value indicates that Cr(VI) has the most significant quenching effect on the fluorescence generated by the double-excited carbon quantum dots at this point.

[0073] Figure 21 The F values ​​of the mixture of dual-excited carbon quantum dots and Cr(VI) at different pH values ​​are shown. 355 / F 400 As can be seen, pH affects F 355 / F 400 Several films had no impact.

[0074] Figure 22 The fluorescence intensity curves of the mixture of dual-excited carbon quantum dots and Cr(VI) over time are shown. It can be seen that the fluorescence intensity tends to stabilize after 5 min of mixing the dual-excited carbon quantum dots and Cr(VI).

[0075] First, the binding constant K between the dual-excited carbon quantum dots and Cr(VI) was calculated using the Benesi-Hildebrand equation, and the obtained binding constant K was 1.19 × 10⁻⁶. 4 mol -1 This indicates a strong interaction between Cr(VI) and the dual-excited carbon quantum dots. Upon addition of Cr(VI), the Zeta potential of the dual-excited carbon quantum dots changed from a positive charge of 0.23 mV to -2.7 mV, suggesting that the opposite charges of the dual-excited carbon quantum dots and Cr(VI) attract each other, which helps to reduce the spatial distance between them.

[0076] Figure 23 The UV-vis absorption spectra of dual-excited carbon quantum dots, Cr(VI), the actual UV-vis absorption spectrum of the mixture of dual-excited carbon quantum dots and Cr(VI), and the theoretical UV-vis absorption spectrum of the mixture are shown. It can be clearly seen that no new absorption bands are generated between the actual and theoretical UV-vis absorption spectra of the mixture of dual-excited carbon quantum dots and Cr(VI), nor is there any shift in the absorption bands. This indicates that no new ground-state complex is formed between the dual-excited carbon quantum dots and Cr(VI).

[0077] Figure 24 The UV-vis absorption spectrum of Cr(VI), the PL spectrum of double-excited carbon quantum dots, and the PLE spectrum of double-excited carbon quantum dots are shown. Figure 25 Fluorescence lifetime curves before and after mixing dual-excited carbon quantum dots and Cr(VI) are shown. From Figure 24As can be seen, there is a significant overlap between the PLE spectrum of dual-excited carbon quantum dots and the UV-vis absorption spectrum of Cr(VI), indicating that the fluorescence quenching effect of Cr(VI) on dual-excited carbon quantum dots may involve internal filtration (IFE) and fluorescence resonance energy transfer (FRET). According to the literature, fluorescence lifetime can distinguish between these two mechanisms: IFE does not affect lifetime, while FRET shortens lifetime. Further... Figure 25 As shown, under 355 nm excitation illumination, the fluorescence lifetime of the dual-excited carbon quantum dots decreased from 2.68 ns to 2.46 ns; under 400 nm excitation illumination, the fluorescence lifetime decreased from 2.70 ns to 2.53 ns. This confirms that the main mechanism of the fluorescence quenching effect of Cr(VI) on dual-excited carbon quantum dots is FRET.

[0078] To quantitatively assess the contribution of IFE, the Parker equation was used for correction. Under 355 nm excitation light, the observed quenching efficiency Fobsd was 27.8%, which decreased to Ecor=12.6% after correction; under 400 nm excitation light, the corresponding values ​​were 42.6% and 36.2%. These results confirm that the joint interaction between FRET and IFE is the cause of fluorescence reduction.

[0079] To conduct testing on actual samples, this embodiment further provides a method for detecting Cr(VI) concentration, including the following steps:

[0080] Step 101: Prepare a first solution, wherein the solute of the first solution is the dual-excited carbon quantum dots, the solvent is water, and the concentration of the dual-excited carbon quantum dots is a.

[0081] As a preferred embodiment, a = 1.2 mg / mL.

[0082] When the first solution is irradiated with 355nm excitation light, the emitted fluorescence intensity at 460nm is f. 355 When the first solution is irradiated with 400nm excitation light, the emitted fluorescence intensity at 460nm is f. 400 .

[0083] Step 102: Add Cr(VI) to the first solution sequentially. After each addition of Cr(VI), obtain the concentration of Cr(VI) in the first solution and the corresponding f. 355 / f 400 to obtain f 355 / f 400 The first fitted relationship between Cr(VI) concentration and Cr(VI) concentration.

[0084] Step 103: Prepare a second solution, wherein the solute of the second solution is the dual-excited carbon quantum dots, the solvent is water, the concentration of the dual-excited carbon quantum dots is b, b > a, and the second solution does not contain Cr(VI).

[0085] Step 104: Measure an appropriate volume of the test solution, then mix the second solution with the test solution to form a detection solution, and the concentration of the dual-excited carbon quantum dots in the detection solution is exactly a.

[0086] Step 105: Irradiate the detection liquid with 355nm excitation light and detect the emitted fluorescence intensity F at 460nm. 355 The detection liquid was irradiated with 400nm excitation light, and the emitted fluorescence intensity F at 460nm was measured. 400 .

[0087] Step 106: Based on F 355 / F 400 The concentration of Cr(VI) in the detection solution is determined by the first fitting relationship, and then the total amount of Cr(VI) in the detection solution is determined based on the volume of the detection solution and the concentration of Cr(VI) in the detection solution.

[0088] Step 107: The Cr(VI) in the test solution comes entirely from the test solution. Therefore, the concentration of Cr(VI) in the test solution can be determined based on the total amount of Cr(VI) in the test solution and the volume of the test solution.

[0089] This embodiment also provides a Cr(VI) detection system, including an illumination device, an imaging device, and a thin film. The illumination device and the imaging device are positioned facing the thin film. The illumination device and the imaging device can be integrated into a mobile phone, and the thin film contains dual-excited carbon quantum dots.

[0090] The preparation method of the thin film includes the following steps: 0.1 g of polyvinyl alcohol (PVA) and 0.01 g of dual-excited carbon quantum dot powder are added to 30 mL of deionized water, and the resulting mixture is then heated to 80°C and continuously stirred for 30 minutes. The resulting solution is then sonicated for 10 minutes. Subsequently, 5 mL of the above solution is poured into a petri dish and dried for 24 hours.

[0091] When the illumination device illuminates the thin film, the film fluoresces. The imaging device can capture the fluorescence emitted by the film and obtain its corresponding total RGB value. When the test solution is added to the thin film, the concentration of Cr(VI) in the test solution can be determined based on the change in the total RGB value.

[0092] When no Cr(VI) solution was added to the film, the total RGB value was Sum0; when Cr(VI) solution was added to the film, the total RGB value was Sum. For example... Figure 26 As shown, the concentrations of Cr(VI) in Sum / Sum0 and Cr(VI) solutions exhibit a good linear relationship.

[0093] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those skilled in the art, several modifications and improvements can be made 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 dual-excited carbon quantum dots, characterized in that, include: Polyethyleneimine and glucose were dissolved in deionized water and then transferred to a reaction vessel for heating to obtain the dual-excited carbon quantum dots.

2. The method for preparing dual-excited carbon quantum dots according to claim 1, characterized in that, The molar ratio of polyethyleneimine to glucose is 0.75:1 to 1.25:

1.

3. The method for preparing dual-excited carbon quantum dots according to claim 1, characterized in that, The reaction temperature is 175℃-185℃, and the reaction time is 9h-11h.

4. A dual-excited carbon quantum dot, characterized in that, The carbon quantum dots were prepared using the method described in claim 1, 2, or 3.

5. An application of the dual-excited carbon quantum dots as described in claim 4 in the detection of Cr(VI).

6. A method for detecting Cr(VI) concentration, characterized in that, include: An aqueous solution of the dual-excited carbon quantum dots as described in claim 4 was irradiated with 355 nm excitation light, and the emitted fluorescence intensity f at 460 nm was detected. 355 ; An aqueous solution of the dual-excited carbon quantum dots as described in claim 4 was irradiated with 400 nm excitation light, and the emitted fluorescence intensity f at 460 nm was detected. 400 ; The aqueous solution of dual-excited carbon quantum dots as described in claim 4 is mixed with the test solution to form a detection solution; The detection liquid was irradiated with 355nm excitation light, and the emitted fluorescence intensity F at 460nm was measured. 355 ; The detection liquid was irradiated with 400nm excitation light, and the emitted fluorescence intensity F at 460nm was measured. 400 ; At least based on F 355 / F 400 and f 355 / f 400 Determine the concentration of Cr(VI) in the test solution.

7. The method for detecting Cr(VI) concentration according to claim 6, characterized in that, include: Prepare a first solution, wherein the solute of the first solution is the dual-excited carbon quantum dots, the solvent is water, and the concentration of the dual-excited carbon quantum dots is a; When the first solution is irradiated with 355nm excitation light, the emitted fluorescence intensity at 460nm is f. 355 ; When the first solution is irradiated with 400 nm excitation light, the emitted fluorescence intensity at 460 nm is f. 400 ; Cr(VI) was added to the first solution sequentially. After each addition of Cr(VI), the concentration of Cr(VI) in the first solution and the corresponding f were obtained. 355 / f 400 to obtain f 355 / f 400 The first fitted relationship between Cr(VI) concentration and Cr(VI) concentration; Prepare a second solution, wherein the solute of the second solution is the dual-excited carbon quantum dots, the solvent is water, the concentration of the dual-excited carbon quantum dots is b, b > a, and the second solution does not contain Cr(VI). The second solution is mixed with the test solution to form the detection solution, and the concentration of the dual-excited carbon quantum dots in the detection solution is a; Based on F 355 / F 400 The concentration of Cr(VI) in the detection solution is determined by the first fitting relationship, and then the total amount of Cr(VI) in the detection solution is determined based on the volume of the detection solution and the concentration of Cr(VI) in the detection solution. The concentration of Cr(VI) in the test solution is determined based on the total amount of Cr(VI) in the test solution and the volume of the test solution.

8. The method for detecting Cr(VI) concentration according to claim 6, characterized in that, The concentration of the dual-excited carbon quantum dots in the detection solution is 1.2 mg / mL.

9. A Cr(VI) detection system, characterized in that, It includes an illumination device, an imaging device, and a thin film, wherein the illumination device and the imaging device are disposed toward the thin film, and the thin film contains dual-excited carbon quantum dots as described in claim 4.

10. A method for detecting Cr(VI) concentration, characterized in that, Based on the Cr(VI) detection system as described in claim 9, the Cr(VI) concentration detection method includes: The solution to be tested is dropped onto the thin film; The lighting device irradiates the film to make the film fluoresce; The imaging device acquires the fluorescence emitted by the film and obtains its corresponding total RGB value; The concentration of Cr(VI) in the test solution is determined based on the total RGB value.

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