A preparation method of carbon quantum dots, carbon quantum dots, a detection method and application of lead ions and / or chromate ions

Abstract

The application provides a preparation method of carbon quantum dots, a carbon quantum dot, a lead ion and / or chromate ion detection method and application, and comprises the following steps: mixing resorcinol and amino methane into a solvent, and then transferring to a reaction kettle for heating reaction to obtain the carbon quantum dots. The carbon quantum dots prepared by the application have the detection capability of Pb 2+ and CrO4 2‑ , so that the joint detection of Pb 2+ and CrO4 2‑ can be realized in a relatively simple step, and the joint detection cost of Pb 2+ and CrO4 2‑ is reduced. Secondly, the carbon quantum dots have two fluorescence emission centers, so that the concentration of Pb 2+ and CrO4 2‑ can be detected by a double-peak ratio method, so that the concentration of Pb 2+ and CrO4 2‑ can be more accurately detected.

Description

Technical Field

[0001] This invention relates to the field of lead ion and chromate ion detection, and in particular to a method for preparing carbon quantum dots, a method for detecting carbon quantum dots, lead ions and / or chromate ions, and their applications. Background Technology

[0002] With rapid urban expansion and widespread industrial activity, heavy metal pollution has become increasingly severe. Industrial and domestic runoff carries heavy metals from the earth's crust into water systems, while acid rain further promotes the migration of these toxic elements into drinking water sources. Among them, lead ions (Pb) are particularly problematic. 2+ ) and chromate ions (CrO4) 2- Because of its wide application in industry and its frequent coexistence in aquatic environments, it has received special attention.

[0003] Lead possesses various functional properties and is commonly used in battery production, petroleum derivative refining, and paint preparation. However, lead ions are highly toxic and can cause numerous health hazards, including cognitive impairment, immunosuppression, and cardiovascular disease. Therefore, it has been classified as a Group 2A carcinogen by the International Agency for Research on Cancer. Meanwhile, chromium compounds, commonly used in electroplating, leather tanning, and textile industries, are similar to lead ions in that chromate ions are also highly carcinogenic. Once inside cells, chromate ions are reduced to trivalent chromium, triggering oxidative stress and ultimately causing mitochondrial dysfunction.

[0004] Therefore, the detection of lead and chromate ion concentrations in water is of great significance. Carbon quantum dots (CQDs) are widely used in water detection due to their advantages such as low cost and low toxicity. However, CQDs also have high detection specificity, and different CQDs can detect different substances. Therefore, in actual detection processes, two or more different CQDs are often required to achieve the joint detection of lead and chromate ions, making the joint detection process cumbersome and costly. Summary of the Invention

[0005] Therefore, it is necessary to address the issues of cumbersome and costly joint detection processes for lead ions and chromate ions by providing a method for preparing carbon quantum dots, a method for detecting carbon quantum dots, lead ions, and / or chromate ions, and their applications.

[0006] The technical solution provided by this invention is as follows:

[0007] A method for preparing carbon quantum dots includes: mixing resorcinol and aminomethane into a solvent, and then transferring the mixture to a reaction vessel for heating and reaction to obtain the carbon quantum dots.

[0008] In some embodiments of this application, the molar ratio of resorcinol to aminomethane is 1:2.

[0009] In some embodiments of this application, the reaction temperature in the reactor is 160°C and the reaction time is 6 hours.

[0010] In some embodiments of this application, the solvent is deionized water.

[0011] A carbon quantum dot is prepared using the aforementioned method for preparing carbon quantum dots.

[0012] The application of the carbon quantum dots in the detection of lead ions and / or chromate ions.

[0013] A method for detecting lead ions and / or chromate ions includes: irradiating a solution of the carbon quantum dots with natural light, 360nm excitation light or 480nm excitation light, and observing the color of the carbon quantum dots.

[0014] A method for detecting lead ions and / or chromate ions, comprising:

[0015] The solution of the carbon quantum dots was irradiated with 360nm excitation light, and the fluorescence intensity f emitted at 425nm was obtained. 425 ;

[0016] The solution of the carbon quantum dots was irradiated with 480 nm excitation light, and the fluorescence intensity f emitted at 525 nm was obtained. 525 ;

[0017] The solution of the carbon quantum dots is mixed with the test solution to form a mixture;

[0018] The mixture was irradiated with 360nm excitation light, and the fluorescence intensity F emitted at 425nm was obtained. 425 ;

[0019] The mixture was irradiated with 480 nm excitation light, and the fluorescence intensity F emitted at 525 nm was obtained. 525 ;

[0020] Based on F 425 / F 525 and f 425 / f 525 Obtain the concentration of lead ions and / or chromate ions in the test solution.

[0021] The application of LDA and HCA in the detection of lead ion and / or chromate ion concentrations, based on the aforementioned carbon quantum dots.

[0022] The application of LDA and HCA in distinguishing lead ions from chromate ions is based on the aforementioned carbon quantum dots.

[0023] The beneficial effects of this invention are as follows:

[0024] The carbon quantum dots prepared by this invention simultaneously possess the ability to react with Pb 2+ and CrO4 2- Its detection capability allows it to achieve Pb detection in a relatively simple procedure. 2+ and CrO4 2- The combined detection of Pb reduces Pb 2+ and CrO4 2- The cost of joint testing.

[0025] Secondly, the carbon quantum dots of this invention have two fluorescence emission centers, thereby enabling the fluorescence emission of Pb using the bimodal ratio method. 2+ and CrO4 2- Concentration detection is performed to more accurately detect Pb. 2+ and CrO4 2- The concentration.

[0026] Moreover, Pb 2+ and CrO4 2- The fluorescence quenching mechanisms for the two emission wavelengths of carbon quantum dots differ, thus affecting Pb. 2+ and CrO4 2- The fluorescence quenching behavior of carbon quantum dots showed significant differences, thus allowing for further advancements in Pb quenching. 2+ and CrO4 2- The distinction between different types of solutions and the concentration detection of the mixture. Attached Figure Description

[0027] Figure 1 This is a transmission electron microscope (TEM) image of carbon quantum dots in an embodiment of the present invention;

[0028] Figure 2 The X-ray diffraction (XRD) pattern of carbon quantum dots in an embodiment of the present invention;

[0029] Figure 3 The Raman spectrum of carbon quantum dots in an embodiment of the present invention;

[0030] Figure 4 The particle size distribution of carbon quantum dots in this embodiment of the invention;

[0031] Figure 5 This is an atomic force microscope (AFM) image of carbon quantum dots in an embodiment of the present invention;

[0032] Figure 6 The Fourier transform infrared (FT-IR) spectra of Tris, m-DB, and carbon quantum dots in the embodiments of the present invention are shown.

[0033] Figure 7 This is the full-spectrum XPS image of carbon quantum dots in an embodiment of the present invention;

[0034] Figure 8 This is a high-resolution XPS spectrum of C 1s for carbon quantum dots in an embodiment of the present invention;

[0035] Figure 9 This is the N 1s high-resolution XPS spectrum of carbon quantum dots in an embodiment of the present invention;

[0036] Figure 10 This is the O 1s high-resolution XPS spectrum of carbon quantum dots in an embodiment of the present invention;

[0037] Figure 11 The following are the ultraviolet-visible (UV-vis) absorption spectra of carbon quantum dots in this embodiment of the invention: the PL spectrum at an excitation wavelength of 360 nm, the PL spectrum at an excitation wavelength of 480 nm, the PLE spectrum at an emission wavelength of 425 nm, and the PLE spectrum at an emission wavelength of 525 nm.

[0038] Figure 12 The PL spectra of carbon quantum dots under different wavelengths (300nm-600nm) of excitation light in the embodiments of the present invention are shown.

[0039] Figure 13 The excitation-emission matrix spectrum of carbon quantum dots in this embodiment of the invention;

[0040] Figure 14 The figures show the changes in 525 nm and 425 nm fluorescence emission intensities of carbon quantum dots in NaCl solutions of different concentrations in this invention.

[0041] Figure 15 The following are the changes in the 525nm and 425nm fluorescence emission intensities of carbon quantum dots after being exposed to ultraviolet light for different periods in the embodiments of the present invention;

[0042] Figure 16 This illustrates the changes in 525nm and 425nm fluorescence emission intensity of carbon quantum dots after storage for different times in this embodiment of the invention.

[0043] Figure 17 Examples of carbon quantum dots and Pb concentrations in this invention 2+ The PL spectrum of the mixture under 360 nm excitation light and the PL spectrum under 480 nm excitation light;

[0044] Figure 18 F in the embodiments of the present invention 425 / F 525 With Pb 2+ Correspondence curve between concentrations;

[0045] Figure 19 F in the embodiments of the present invention 425 / F525 With Pb 2+ Linear fitting curve between concentrations;

[0046] Figure 20 Examples of carbon quantum dots and CrO4 at different concentrations in this invention 2- The PL spectrum of the mixture under 360 nm excitation light and the PL spectrum under 480 nm excitation light;

[0047] Figure 21 F in the embodiments of the present invention 425 / F 525 With CrO4 2- Correspondence curve between concentrations;

[0048] Figure 22 F in the embodiments of the present invention 425 / F 525 With CrO4 2- Linear fitting curve between concentrations;

[0049] Figure 23 The F values ​​of carbon quantum dots at different temperatures in embodiments of the present invention are shown below. 425 / F 525 ;

[0050] Figure 24 In the embodiments of the present invention, carbon quantum dots and Pb 2+ The time elapsed after mixing and F 425 / F 525 The correspondence between them and carbon quantum dots and CrO4 2- The time elapsed after mixing and F 425 / F 525 The correspondence between them;

[0051] Figure 25 The F values ​​of carbon quantum dots under different pH conditions in the embodiments of the present invention are shown. 425 / F 525 ;

[0052] Figure 26 The F values ​​before and after mixing the first solution with the interfering substance, the second solution with the interfering substance, and the third solution with the interfering substance in the embodiments of the present invention are respectively... 425 (F) 425 (Normalization was performed)

[0053] Figure 27 The F values ​​before and after mixing the first solution with the interfering substance, the second solution with the interfering substance, and the third solution with the interfering substance in the embodiments of the present invention are respectively... 525 (F) 525 (Normalization was performed)

[0054] Figure 28 Pb in the embodiments of the present invention 2+ The UV-vis absorption spectrum of carbon quantum dots, the PL spectrum of carbon quantum dots at an excitation wavelength of 360 nm, the PL spectrum of carbon quantum dots at an excitation wavelength of 480 nm, the PLE spectrum of carbon quantum dots at an emission wavelength of 425 nm, and the PLE spectrum of carbon quantum dots at an emission wavelength of 525 nm.

[0055] Figure 29 Pb is shown in an embodiment of the present invention. 2+ The curve showing the relationship between concentration and F0 / F. Figure 29 F0 in the figure indicates that the carbon quantum dot is not bound to Pb 2+ F corresponding to mixing 425 F represents carbon quantum dots and Pb 2+ F after mixing 425 ;

[0056] Figure 30 Pb is shown in an embodiment of the present invention. 2+ The curve showing the relationship between concentration and F0 / F. Figure 30 F0 in the figure indicates that the carbon quantum dot is not bound to Pb 2+ F corresponding to mixing 525 F represents carbon quantum dots and Pb 2+ F after mixing 525 ;

[0057] Figure 31 Pb in the embodiments of the present invention 2+ UV-vis absorption spectra of carbon quantum dots, UV-vis absorption spectra of Pb 2+ Theoretical UV-vis absorption spectrum of the mixture with carbon quantum dots, Pb 2+ The actual UV-vis absorption spectrum of the mixture with carbon quantum dots;

[0058] Figure 32 In the embodiments of the present invention, carbon quantum dots and Pb 2+ FT-IR before and after mixing;

[0059] Figure 33 In the embodiments of the present invention, carbon quantum dots and Pb 2+ High-resolution XPS spectra of O 1s before and after mixing;

[0060] Figure 34 In this embodiment of the invention, carbon quantum dots are used in conjunction with Pb. 2+ Fluorescence lifetime decay curves before and after mixing;

[0061] Figure 35 CrO4 in the embodiments of the present invention 2-UV-vis absorption spectra of carbon quantum dots, UV-vis absorption spectra of CrO4 2- Theoretical UV-vis absorption spectrum of the mixture with carbon quantum dots, CrO4 2- The actual UV-vis absorption spectrum of the mixture with carbon quantum dots;

[0062] Figure 36 CrO4 in the embodiments of the present invention 2- The UV-vis absorption spectrum of carbon quantum dots, the PL spectrum of carbon quantum dots at an excitation wavelength of 360 nm, the PL spectrum of carbon quantum dots at an excitation wavelength of 480 nm, the PLE spectrum of carbon quantum dots at an emission wavelength of 425 nm, and the PLE spectrum of carbon quantum dots at an emission wavelength of 525 nm.

[0063] Figure 37 In this embodiment of the invention, carbon quantum dots react with CrO4 2- Fluorescence lifetime decay curves before and after mixing;

[0064] Figure 38 Examples of carbon quantum dots and Pb concentrations in this invention 2+ or CrO4 2- The mixed (f1-F1) / f1 and (f2-F2) / f2;

[0065] Figure 39 In this embodiment of the invention, LDA is used to react carbon quanta with different concentrations of Pb. 2+ The classification results of the resulting classification array after mixing;

[0066] Figure 40 In this embodiment of the invention, LDA is used to react carbon quanta with different concentrations of CrO4. 2- The classification results of the resulting classification array after mixing;

[0067] Figure 41 In this embodiment of the invention, when the total concentration of the analyte is 20 μM, the effect of LDA on Pb... 2+ and CrO4 2- Classification results of classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100);

[0068] Figure 42 In this embodiment of the invention, when the total concentration of the analyte is 50 μM, the effect of LDA on Pb... 2+ and CrO4 2- Classification results of classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100);

[0069] Figure 43In this embodiment of the invention, when the total concentration of the analyte is 100 μM, the effect of LDA on Pb... 2+ and CrO4 2- The classification results of the classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100);

[0070] Figure 44 In this embodiment of the invention, when the total concentration of the analyte is 20 μM, HCA affects Pb. 2+ and CrO4 2- Classification results of classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100);

[0071] Figure 45 In this embodiment of the invention, when the total concentration of the analyte is 50 μM, HCA affects Pb. 2+ and CrO4 2- Classification results of classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100);

[0072] Figure 46 In this embodiment of the invention, when the total concentration of the analyte is 100 μM, HCA affects Pb. 2+ and CrO4 2- The classification results of the classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100). Detailed Implementation

[0073] 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.

[0074] Example:

[0075] This embodiment provides a carbon quantum dot preparation method comprising the following steps: 1 mmol of resorcinol (M-dihydroxybenzene, m-DB) and 2 mmol of aminomethane (Tris) are mixed in 20 mL of deionized water, then ultrasonically stirred for 10 min, and then transferred to a reaction vessel and reacted at 160 °C for 6 h. After the reaction is completed and cooled to room temperature (25 °C), the resulting solution is filtered using a filter with a pore diameter of 0.22 μm, then dialyzed against a dialysis membrane with a molecular weight cutoff of 1000 Da for 72 h, and finally vacuum dried for 12 h to obtain the carbon quantum dots.

[0076] Figure 1 The transmission electron microscope (TEM) image of the carbon quantum dots is shown, based on Figure 1 It can be seen that the carbon quantum dots are spherical in shape and have good dispersion. Figure 1 The inset in the upper right corner shows a high-resolution transmission electron microscope (HR-TEM) image of the carbon quantum dots, demonstrating that the interplanar spacing of the carbon quantum dots is 0.22 nm, matching sp... 2 The (100) crystal plane. Figure 2 The X-ray diffraction (XRD) pattern of the carbon quantum dots is shown, which has two broad peaks near 25° and 45°, corresponding to the (002) and (100) crystal planes of the carbon material, respectively. Figure 3 The Raman spectrum of the carbon quantum dots is shown, where 1376 cm⁻¹ -1 The characteristic peak at 1569 cm⁻¹ is the D band, corresponding to structural defects. -1 The characteristic peak at that point is the G band, corresponding to sp. 2 The carbon network structure, with an intensity ratio of 0.71 for the D and G bands, confirms that the carbon quantum dots are highly graphitized. Figure 1 The results shown are consistent. Figure 4 The particle size distribution of the carbon quantum dots is shown. The particle size distribution ranges from 2.6 nm to 9.2 nm, and the average particle size is calculated to be 6.0 nm within the observation area. Figure 5 An atomic force microscopy (AFM) image of the carbon quantum dots is shown, which demonstrates that the average thickness of the carbon quantum dots is approximately 0.76 nm, indicating that the carbon quantum dots consist of a 1-2 layer graphene structure.

[0077] Figure 6 The Fourier transform infrared (FT-IR) spectra of Tris, m-DB, and the carbon quantum dots are shown. The three substances are at 3105 cm⁻¹. -1 -3585cm -1Both exhibit broad absorption peaks, corresponding to the stretching vibrations of -NH and -OH. Furthermore, the carbon quantum dots show a broad absorption peak at 2945 cm⁻¹. -1 The absorption peak at 1583 cm⁻¹ corresponds to the stretching vibration of CH₄. -1 The absorption peak at 1339 cm⁻¹ corresponds to the stretching vibration of C=O. -1 1149cm -1 1021cm -1 794cm -1 The four absorption peaks at 1032 cm⁻¹ correspond to C₂C, C=C, CN, and CO, respectively. FT-IR comparison with Tris and m-DB indicates that the -NH, -OH, CH, and CO of the carbon quantum dots originate from Tris and m-DB. However, it is noteworthy that the carbon quantum dots exhibit absorption peaks at 1032 cm⁻¹. -1 and 3300cm -1 The higher absorption peak intensity indicates that the surface of the carbon quantum dots is enriched with more oxygen- and nitrogen-containing groups compared to Tris and m-DB.

[0078] Figure 7 The full-spectrum XPS image of the carbon quantum dots is shown, where the three peaks at 284.0 eV, 395.9 eV, and 529.1 eV correspond to C 1s, N 1s, and O 1s, respectively. Elemental analysis results show that the carbon quantum dots are composed of 61.75% C, 8.67% N, and 29.58% O. Figure 8 The high-resolution XPS spectrum of the carbon quantum dot C 1s is shown, with the three peaks at 283.86 eV, 285.12 eV, and 285.83 eV attributed to C=C / CC, CO / CN, and C=N, respectively. Figure 9 The N 1s high-resolution XPS spectrum of the carbon quantum dot is shown, in which the characteristic peak at 398.55 eV corresponds to pyridine nitrogen, the characteristic peak at 399.47 eV corresponds to pyrrole nitrogen, and the characteristic peak at 400.93 eV corresponds to amino nitrogen. Figure 10 The O 1s high-resolution XPS spectrum of the carbon quantum dot is shown, where the characteristic peak at 531.48 eV corresponds to CO and the characteristic peak at 532.11 eV corresponds to C=O.

[0079] In summary, the surface of the carbon quantum dots in this embodiment is rich in nitrogen and oxygen-related functional groups and has been fully carbonized.

[0080] Figure 11 The ultraviolet-visible (UV-vis) absorption spectrum, PL spectrum at an excitation wavelength of 360 nm, PL spectrum at an excitation wavelength of 480 nm, PLE spectrum at an emission wavelength of 425 nm, and PLE spectrum at an emission wavelength of 525 nm of the carbon quantum dots are shown. Figure 12 The PL spectra of the carbon quantum dots under excitation light at different wavelengths (300nm-600nm) are shown. Figure 13 The excitation-emission matrix spectrum of the carbon quantum dot is shown.

[0081] Specifically, such as Figure 11 As shown, in the UV-vis absorption spectrum of the carbon quantum dots, the absorption peak at 207 nm corresponds to the aromatic sp. 2 The π-π* transitions of hybrid carbon (C=C) show absorption peaks at 275 nm corresponding to n-π* transitions of the C=O functional group and at 493 nm corresponding to n-π* transitions of the C=N functional group. Furthermore, the carbon quantum dots exhibit a broad absorption band in the 448 nm-530 nm range, originating from electronic transitions related to their surface molecular states. Due to the extremely low overlap between the UV-vis absorption and PL spectra of the carbon quantum dots, they achieve highly efficient fluorescence emission with minimal self-absorption loss. Using quinine sulfate and rhodamine 6G as references, the fluorescence quantum yields of the carbon quantum dots in aqueous solution were measured to be 65.9% and 71.6%, respectively, superior to most reported carbon dot-based probes. The solution of the carbon quantum dots appears light yellowish-brown under natural light, emits bright blue fluorescence under 360 nm excitation light, and exhibits strong green fluorescence under 480 nm excitation light.

[0082] Specifically, such as Figure 12 As shown, when the excitation wavelength varies within the range of 300 nm to 410 nm, a blue fluorescence emission peak is observed at 425 nm, accompanied by a shoulder peak at 525 nm; when the excitation wavelength varies within the range of 420 nm to 600 nm, a green emission peak is observed at 525 nm, and the position of this green emission peak shows independence from the excitation wavelength. Further... Figure 13 As shown, more directly, the carbon quantum dot has two fluorescence emission centers, namely (360nm, 425nm) and (480nm, 525nm).

[0083] Figure 14 The changes in the fluorescence emission intensity at 525 nm and 425 nm of the carbon quantum dots in NaCl solutions of different concentrations are shown. Figure 15 The changes in the fluorescence emission intensity at 525 nm and 425 nm of the carbon quantum dots after exposure to ultraviolet light for different periods are shown. Figure 16 The changes in the fluorescence emission intensity at 525 nm and 425 nm of the carbon quantum dots after storage for different times are shown.

[0084] Depend on Figures 14-16It can be seen that the fluorescence emission intensity of the carbon quantum dots hardly decreases even in a 2.0 mol / L NaCl solution, exhibiting excellent stability. Furthermore, the fluorescence emission intensity of the carbon quantum dots also shows almost no decrease after 20 hours of ultraviolet light irradiation or 50 days of storage. This confirms that the carbon quantum dots possess strong resistance to photobleaching and good long-term stability.

[0085] In the PL spectrum of the carbon quantum dots, the fluorescence intensity at 425 nm is F. 425 The fluorescence intensity at 525 nm is F 525 Unless otherwise specified, the following F in this embodiment 425 The corresponding excitation wavelength is 360 nm, F 525 The corresponding excitation wavelength is 480nm.

[0086] Figure 17 The carbon quantum dots with different concentrations of Pb are shown. 2+ The PL spectra of the mixture under 360 nm excitation light and under 480 nm excitation light. With Pb 2+ With increasing concentration, F 425 and F 525 The gradual decrease indicates that the carbon quantum dots can be used for Pb. 2+ Concentration detection.

[0087] Figure 18 F is shown 425 / F 525 With Pb 2+ Correspondence curve between concentrations, Pb 2+ When the concentration is in the range of 0 μM-1000 μM, as Pb... 2+ With increasing concentration, F 425 / F 525 The concentration is continuously decreasing; in other words, the carbon quantum dots can be used to determine Pb based on the bimodal ratio method. 2+ Concentration. In addition, such as... Figure 18 As shown in the middle illustration, with Pb 2+ With increasing concentration, the carbon quantum dot solution (solvent: water, carbon quantum dot concentration: 15 mg / mL) gradually changed from light yellow to pink under natural light. The blue fluorescence emitted by the carbon quantum dot solution under 360 nm excitation light and the green fluorescence emitted under 480 nm excitation light both gradually decreased. This indicates that the color of the carbon quantum dot solution (under natural light, 360 nm excitation light, or 480 nm excitation light) can also be used to assess the Pb content. 2+ Concentration detection.

[0088] Figure 19 F is shown 425 / F 525 With Pb 2+ A linear fitting curve between concentrations, where Pb 2+ When the concentration is in the range of 0 μM-80 μM and F 425 / F 525 They have a good linear fit relationship (Ri). 2 =0.996), the fitted linear equation is Y=-0.000925X+0.37814, where X represents Pb 2+ Concentration, Y represents F 425 / F 525 The detection limit was calculated to be 83 nM according to the formula LOD=3σ / k, where σ is the standard deviation of the blank sample and k is the slope of the calibration curve.

[0089] Figure 20 The carbon quantum dots with different concentrations of CrO4 are shown. 2- The PL spectra of the mixture under 360 nm excitation light and under 480 nm excitation light. With CrO4 2- With increasing concentration, F 425 and F 525 The gradual decrease indicates that the carbon quantum dots can be used in CrO4. 2- Concentration detection. However, it differs from Pb. 2+ The thing is, CrO4 2- For F 425 The impact is quite severe, for F 525 The impact is very minor.

[0090] Figure 21 F is shown 425 / F 525 With CrO4 2- Correlation curve between concentrations, CrO4 2- When the concentration is in the range of 0 μM-1000 μM, with the change in CrO4 2- With increasing concentration, F 425 / F 525 The value is continuously decreasing; in other words, the carbon quantum dots can be determined based on the bimodal ratio method for CrO4. 2- Concentration. In addition, such as... Figure 21 As shown in the middle illustration, with CrO4 2- With increasing concentration, the color of the carbon quantum dot solution changes from light yellow to dark yellow under natural light. The blue fluorescence emitted by the carbon quantum dot solution under 360 nm excitation light and the green fluorescence emitted under 480 nm excitation light gradually decrease. This indicates that the color of the carbon quantum dot solution (under natural light, 360 nm excitation light, or 480 nm excitation light) can also be observed visually to determine the color of CrO4. 2-Concentration detection.

[0091] Figure 22 F is shown 425 / F 525 With CrO4 2- A linear fitting curve between concentrations, where CrO4 2- When the concentration is in the range of 0 μM-40 μM and F 425 / F 525 They have a good linear fit relationship (Ri). 2 =0.981), the fitted linear equation is Y=-0.00281X+0.34987, where X represents CrO4 2- Concentration, Y represents F 425 / F 525 The detection limit was calculated to be 47 nM based on the formula LOD = 3σ / k.

[0092] Based on the above test results, it can be seen that the carbon quantum dots simultaneously possess Pb 2+ and CrO4 2- The detection capability is such that Pb can be detected using only the carbon quantum dots. 2+ and CrO4 2- The joint detection of Pb effectively simplifies the process. 2+ and CrO4 2- The combined detection process reduces Pb 2+ and CrO4 2- The cost of joint testing.

[0093] To determine the carbon quantum dots' pair with Pb 2+ and CrO4 2- To achieve optimal detection conditions, this embodiment further optimizes the detection temperature, reaction time, and pH value.

[0094] Figure 23 The F values ​​of the carbon quantum dots at different temperatures are shown. 425 / F 525 It can be seen that within the range of 0℃-80℃, F 425 / F 525 The changes are very small. Figure 24 The carbon quantum dots and Pb are shown. 2+ The time elapsed after mixing and F 425 / F 525 The correspondence between them and the carbon quantum dots and CrO4 2- The time elapsed after mixing and F 425 / F 525 The correspondence between them shows that the carbon quantum dots and Pb 2+ After mixing for 5 minutes, F 425 / F 525 The carbon quantum dots tend to stabilize with CrO4. 2- After mixing for 4 minutes, F 425 / F 525 It is trending towards stability. Figure 25 The F values ​​of the carbon quantum dots under different pH conditions are shown. 425 / F 525 As can be seen, when the pH is in the range of 3-11, F 425 / F 525 It remains almost constant.

[0095] In summary, the carbon quantum dots described in this embodiment are effective against Pb. 2+ and / or CrO4 2- During the detection, the pH was 7 and the temperature was room temperature. The carbon quantum dots mixed with Pb 2+ and / or CrO4 2- Test F again after five minutes 425 and F 525 .

[0096] The solution containing the carbon quantum dots is the first solution, and the carbon quantum dots and Pb 2+ The mixed solution is the second solution, consisting of carbon quantum dots and CrO4. 2- The mixed solution is the third solution. Figure 26 The F values ​​before and after mixing the first solution with the interfering substance, the second solution with the interfering substance, and the third solution with the interfering substance are shown. 425 (F) 425 (Normalization was performed) Figure 27 The F values ​​before and after mixing the first solution with the interfering substance, the second solution with the interfering substance, and the third solution with the interfering substance are shown. 525 (F) 525 (Normalization was performed). The interfering substance is K. + Ag + Mg 2+ Ca 2+ Zn 2+ Mn 2+ Fe 2+ Co 2+ Cd 2+ Hg 2+ Ba 2+ Fe 3+ Al 3+ F - Cl - ,Br - NO3 - SO4 2- SO3 2-Cysteine ​​(Cys), asparagine (Asn), alanine (Ala), serine (Ser), or proline (Pro).

[0097] based on Figure 26 and Figure 27 It can be seen that only Pb 2+ and CrO4 2- Able to make F 425 and F 525 The significant reduction in Pb production confirms the effectiveness of the carbon quantum dots in inhibiting Pb production. 2+ and CrO4 2- It has extremely high detection specificity.

[0098] Figure 28 Pb is shown 2+ The UV-vis absorption spectrum of the carbon quantum dots, the PL spectrum of the carbon quantum dots at an excitation wavelength of 360 nm, the PL spectrum of the carbon quantum dots at an excitation wavelength of 480 nm, the PLE spectrum of the carbon quantum dots at an emission wavelength of 425 nm, and the PLE spectrum of the carbon quantum dots at an emission wavelength of 525 nm. Based on Figure 28 It can be seen that Pb 2+ The UV-vis absorption spectra of the carbon quantum dots hardly overlap with the PL and PLE spectra, indicating that Pb 2+ The fluorescence quenching mechanism of the carbon quantum dots is neither the internal filtering effect (IFE) nor fluorescence resonance energy transfer (FRET).

[0099] Figure 29 Pb is shown 2+ The curve showing the relationship between concentration and F0 / F. Figure 29 F0 in the figure indicates that the carbon quantum dot is not bonded to Pb. 2+ F corresponding to mixing 425 F represents the carbon quantum dot and Pb 2+ F after mixing 425 ; Figure 30 Pb is shown 2+ The curve showing the relationship between concentration and F0 / F. Figure 30 F0 in the figure indicates that the carbon quantum dot is not bonded to Pb. 2+ F corresponding to mixing 525 F represents the carbon quantum dot and Pb 2+ F after mixing 525 .

[0100] The Stern-Volmer equation was used to fit the two sets of responses. Figure 29 Pb 2+ The concentration showed a good linear relationship with F0 / F in the range of 0 μM to 35 μM, with a corresponding KSV of 0.00447 μM. -1 Kq is 8.06 × 1010 M -1 ・s -1 Kq represents the quenching rate constant, and KSV represents the Stern-Volmer constant; Figure 30 Pb 2+ The concentration exhibits a good linear relationship with F0 / F in the range of 0 μM to 55 μM, with a corresponding KSV of 0.00225 μM. -1 Kq is 1.28 × 10 11 M -1 ・s -1 This confirms that Pb 2+ The fluorescence quenching mechanism of the carbon quantum dots is static quenching (SQE).

[0101] Figure 31 Pb is shown 2+ UV-vis absorption spectrum of the carbon quantum dots, UV-vis absorption spectrum of the carbon quantum dots, Pb 2+ The theoretical UV-vis absorption spectrum of the carbon quantum dot mixture, Pb 2+ And the actual UV-vis absorption spectrum of the carbon quantum dot mixture. By comparing Pb 2+ The theoretical and actual UV-vis absorption spectra of the carbon quantum dot mixture reveal that the carbon quantum dots interact with Pb. 2+ After mixing, its absorbance at 252 nm and 312 nm was significantly enhanced, while the absorption band at 496 nm disappeared, indicating that Pb 2+ It forms a stable non-fluorescent ground-state complex with the oxygen / nitrogen functional groups on the surface of carbon quantum dots, which is a typical static quenching characteristic.

[0102] Figure 32 The carbon quantum dots and Pb are shown. 2+ FT-IR before and after mixing, by mixing Pb 2+ The vibrational peaks related to -OH and -NH2 in the carbon quantum dots showed a significant red shift and increased intensity, indicating that the -OH and -NH2 on the surface of the carbon quantum dots participated in the inhibition of Pb. 2+ Its strong chelating effect. Figure 33 The carbon quantum dots and Pb are shown. 2+ High-resolution XPS spectra of O 1s before and after mixing, by mixing Pb 2+ The carbon quantum dots exhibited a characteristic peak corresponding to Pb-O at 530.87 eV, indicating that Pb is present. 2+ Direct evidence of coordination between the carbon quantum dots and Pb, which promotes Pb 2+ Electron transfer occurs between the carbon quantum dots and the Pb quantum dots, further inducing fluorescence quenching in the carbon quantum dots. The carbon quantum dots act as electron donors, and Pb...2+ As an electron acceptor. Figure 34 The carbon quantum dots with Pb are shown. 2+ Fluorescence lifetime decay curves before and after mixing, Pb 2+ The fluorescence lifetime at emission wavelength of 425 nm decreased from 55.43 ns to 14.51 ns, and the fluorescence lifetime at emission wavelength of 525 nm decreased from 17.62 ns to 14.99 ns, indicating that Pb... 2+ The fluorescence quenching mechanism of the carbon quantum dots also includes photoinduced electron transfer (PET), which further corroborates the above conclusion.

[0103] Figure 35 It shows CrO4 2- UV-vis absorption spectrum of the carbon quantum dots, UV-vis absorption spectrum of CrO4 2- The theoretical UV-vis absorption spectrum of the carbon quantum dot mixture, CrO4 2- The actual UV-vis absorption spectrum of the carbon quantum dot mixture. Among them, CrO4... 2- The theoretical UV-vis absorption spectrum and UV-vis absorption spectrum of the carbon quantum dot mixture almost completely overlap, indicating that CrO4 2- No covalent bonding or complexation occurred between the carbon quantum dots and the quantum dots.

[0104] Figure 36 It shows CrO4 2- The UV-vis absorption spectrum of the carbon quantum dots, the PL spectrum of the carbon quantum dots at an excitation wavelength of 360 nm, the PL spectrum of the carbon quantum dots at an excitation wavelength of 480 nm, the PLE spectrum of the carbon quantum dots at an emission wavelength of 425 nm, and the PLE spectrum of the carbon quantum dots at an emission wavelength of 525 nm. Among these, CrO4... 2- The UV-vis absorption spectrum of CrO4 shows a significant overlap between the absorption band at 372 nm and the excitation peak at 360 nm of the carbon quantum dots, and a slight overlap with the emission peak at 425 nm, indicating that CrO4 2- The blue light quenching mechanisms of the carbon quantum dots include IFE and FRET. In contrast, the excitation peak of the carbon quantum dots at 480 nm only slightly overlaps with CrO4. 2- The absorption peak of the carbon quantum dots at 525 nm is almost identical to that of CrO4. 2- The absorption peaks overlap, resulting in only a weak IFE, which also explains why CrO4... 2- The reason why the quenching effect on green fluorescence is not obvious.

[0105] Figure 37 The carbon quantum dots are shown in relation to CrO4. 2-Fluorescence lifetime decay curves before and after mixing, CrO4 2- This reduced the fluorescence lifetime at emission wavelength of 425 nm from 55.43 ns to 14.81 ns, thus confirming that the FRET mechanism is involved in the blue quenching process; on the other hand, CrO4 2- The fluorescence lifetime at emission wavelength of 525 nm decreased from 17.62 ns to 16.95 ns, which was almost unchanged, indicating that the FRET mechanism was not involved in the green fluorescence quenching process.

[0106] The carbon quantum dots did not react with the analyte (Pb). 2+ and / or CrO4 2- Before mixing, the fluorescence intensity at 425 nm emitted by the carbon quantum dots under 360 nm excitation light is f1, and the fluorescence intensity at 525 nm emitted under 480 nm excitation light is f2; the carbon quantum dots and the analyte (Pb) 2+ and / or CrO4 2- After mixing, the fluorescence intensity emitted at 425nm under 360nm excitation light is F1, and the fluorescence intensity emitted at 525nm under 480nm excitation light is F2. Figure 38 The carbon quantum dots with different concentrations of Pb are shown. 2+ or CrO4 2- The mixed (f1-F1) / f1 and (f2-F2) / f2 exhibit the carbon quantum pairs Pb. 2+ and CrO4 2- The detection behavior of Pb varies greatly, and this variation provides a basis for further development of Pb detection. 2+ and CrO4 2- This laid the foundation for the distinction.

[0107] The carbon quantum dots, when mixed with the analyte, produce (f1-F1) / f1 and (f2-F2) / f2, which can form a classification array. Figure 39 Linear discriminant analysis (LDA) was shown for the carbon quanta and different concentrations of Pb. 2+ The classification results of the resulting classification array after mixing. Figure 39 A total of 35 samples were collected, of which 5 samples contained Pb. 2+ The concentration was 10 μM, and Pb was found in 5 of the samples. 2+ The concentration was 20 μM, and Pb was found in 5 of the samples. 2+ The concentration was 50 μM, and Pb was found in 5 samples. 2+ The concentration was 100 μM, and Pb was found in 5 samples. 2+ The concentration was 200 μM, and Pb was found in 5 samples. 2+ The concentration was 500 μM, and Pb was found in 5 samples. 2+ The concentration is 1000 μM; Figure 40 The effects of LDA on the carbon quanta and different concentrations of CrO4 are shown. 2- The classification results of the resulting classification array after mixing. Figure 40 A total of 35 samples were collected, of which 5 samples contained CrO4. 2- The concentration was 10 μM, and CrO4 was present in 5 of the samples. 2- The concentration was 20 μM, and CrO4 was present in 5 of the samples. 2- The concentration was 50 μM, and CrO4 was present in 5 of the samples. 2- The concentration was 100 μM, and CrO4 was present in 5 of the samples. 2- The concentration was 200 μM, and CrO4 was present in 5 of the samples. 2- The concentration was 500 μM, and CrO4 was present in 5 samples. 2- The concentration was 1000 μM. The solvent in the above sample was water, and the carbon quantum dot concentration was 15 mg / mL.

[0108] based on Figure 39 and Figure 40 It can be seen that when the analyte is only Pb 2+ and CrO4 2- In one of these cases, LDA can be used to determine Pb very accurately. 2+ or CrO4 2- The specific concentration.

[0109] Figure 41 The figure shows the effect of LDA on Pb when the total concentration of the analyte is 20 μM. 2+ and CrO4 2- Classification results of classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100); Figure 42 The results show the effect of LDA on Pb at a total analyte concentration of 50 μM. 2+ and CrO4 2- Classification results of classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100); Figure 43 The figure shows the effect of LDA on Pb when the total concentration of the analyte is 100 μM. 2+ and CrO4 2- The classification results of the classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100).

[0110] in, Figure 41 The total number of corresponding samples is 25, Pb 2+ and CrO4 2- The number of samples corresponding to each molar ratio is five; Figure 42The total number of corresponding samples is 25, Pb 2+ and CrO4 2- The number of samples corresponding to each molar ratio is five; Figure 43 The total number of corresponding samples is 25, Pb 2+ and CrO4 2- The number of samples corresponding to each molar ratio is five. Figure 41 For example, LDA can effectively separate materials with the same Pb content. 2+ and CrO4 2- The samples with the same molar ratio were classified into the same cluster, with no misclassification.

[0111] Figure 44 The hierarchical clustering analysis (HCA) for Pb is shown when the total concentration of the analyte is 20 μM. 2+ and CrO4 2- Classification results of classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100); Figure 45 The figure shows the effect of HCA on Pb at a total analyte concentration of 50 μM. 2+ and CrO4 2- Classification results of classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100); Figure 46 The figure shows the effect of HCA on Pb when the total concentration of the analyte is 100 μM. 2+ and CrO4 2- The classification results of the classification arrays generated under different molar ratios (100:0, 75:25, 50:50, 25:75, 0:100).

[0112] in, Figure 44 The total number of corresponding samples is 25, Pb 2+ and CrO4 2- The number of samples corresponding to each molar ratio is five; Figure 45 The total number of corresponding samples is 25, Pb 2+ and CrO4 2- The number of samples corresponding to each molar ratio is five; Figure 46 The total number of corresponding samples is 25, Pb 2+ and CrO4 2- Each molar ratio corresponds to five samples. HCA can also achieve 100% accurate classification.

[0113] In other words, due to the carbon quantum dots' affinity for Pb 2+ and CrO4 2- Different detection mechanisms and behaviors enable LDA and HCA to detect Pb. 2+ and CrO42- The differentiation and concentration detection of Pb can effectively improve the performance of Pb. 2+ and CrO4 2- Improve the accuracy of joint testing and reduce the steps and costs of joint testing.

[0114] 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.

[0115] 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 carbon quantum dots, characterized in that, include: Resorcinol and aminomethane are mixed in a solvent and then transferred to a reaction vessel for heating to obtain the carbon quantum dots.

2. The method for preparing carbon quantum dots according to claim 1, characterized in that, The molar ratio of resorcinol to aminomethane is 1:

2.

3. The method for preparing carbon quantum dots according to claim 1, characterized in that, The reaction temperature in the reactor is 160℃, and the reaction time is 6 hours.

4. The method for preparing carbon quantum dots according to claim 1, characterized in that, The solvent is deionized water.

5. A carbon quantum dot, characterized in that, The carbon quantum dots were prepared using the method described in any one of claims 1-4.

6. The application of carbon quantum dots as described in claim 5 in the detection of lead ions and / or chromate ions.

7. A method for detecting lead ions and / or chromate ions, characterized in that, include: The carbon quantum dot solution as described in claim 5 was irradiated with natural light, 360nm excitation light, or 480nm excitation light, and the color of the carbon quantum dots was observed.

8. A method for detecting lead ions and / or chromate ions, characterized in that, include: The carbon quantum dot solution as described in claim 5 was irradiated with 360nm excitation light to obtain the fluorescence intensity f emitted at 425nm. 425 ; The carbon quantum dot solution as described in claim 5 was irradiated with 480 nm excitation light to obtain the fluorescence intensity f emitted at 525 nm. 525 ; The solution of the carbon quantum dots is mixed with the test solution to form a mixture; The mixture was irradiated with 360nm excitation light, and the fluorescence intensity F emitted at 425nm was obtained. 425 ; The mixture was irradiated with 480 nm excitation light, and the fluorescence intensity F emitted at 525 nm was obtained. 525 ; Based on F 425 / F 525 and f 425 / f 525 Obtain the concentration of lead ions and / or chromate ions in the test solution.

9. The application of LDA and HCA in the detection of lead ion and / or chromate ion concentrations, characterized in that, Based on the carbon quantum dots as described in claim 5.

10. The application of LDA and HCA in distinguishing lead ions from chromate ions, characterized in that, Based on the carbon quantum dots as described in claim 5.

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