A boron-nitrogen co-doped fluorescent carbon quantum dot, a preparation method thereof and use thereof for preparing a chromium / copper ion sensor

Abstract

This invention relates to boron-nitrogen co-doped fluorescent carbon quantum dots, their preparation method, and their application in the fabrication of chromium / copper ion sensors. It belongs to the field of carbon quantum dot technology and includes the following steps: mixing o-phenylenediamine hydrochloride and boric acid to obtain a mixed solution; adding water to the mixed solution and ultrasonically dissolving it to obtain a mixed solution; treating the mixed solution at high temperature to obtain a boron-nitrogen co-doped carbon material solution; filtering the carbon material solution through a 0.22 μm microporous membrane to obtain a boron-nitrogen co-doped carbon quantum dot aqueous solution, and then dialyzing it using a dialysis bag for 36-48 h; freeze-drying the carbon quantum dot aqueous solution to obtain boron-nitrogen co-doped fluorescent carbon quantum dots. This invention achieves pH-controlled chromium / copper ion sensors using a single quantum dot material and a one-step synthesis process. 6+ / Cu 2+ The dual-channel high-sensitivity detection overcomes the technical barriers of limited probe selectivity, complex processes, and limited functionality in existing probes.

Description

A boron-nitrogen co-doped fluorescent carbon quantum dot, its preparation method, and its application in fabricating a chromium / copper ion sensor. Technical Field

[0001] This invention relates to the field of carbon quantum dot technology, and in particular to a boron-nitrogen co-doped fluorescent carbon quantum dot, its preparation method, and its application in the preparation of chromium / copper ion sensors. Background Technology

[0002] Heavy metal ion pollution has become a global challenge threatening ecological security and human health. Among them, hexavalent chromium (Cr) is particularly problematic. 6+ Copper ions (Cu) are widely present in industrial wastewater as a potent carcinogen. 2+ Although micronutrients are essential for human health, excessive accumulation in the environment (such as in mining wastewater and agricultural non-point source pollution) can accumulate through the food chain, causing irreversible multi-system damage such as neurotoxicity and liver and kidney injury. The environmental exposure risks of these micronutrients urgently necessitate the development of rapid, portable, and highly selective on-site detection technologies to overcome the limitations of traditional monitoring methods.

[0003] Traditional detection techniques such as atomic absorption spectrometry, atomic emission spectrometry, and inductively coupled plasma mass spectrometry, while possessing high accuracy, rely on expensive, large-scale instruments and specialized laboratory environments. Their detection cycles can take hours to days, and they lack portability, making them unsuitable for emergency monitoring of sudden pollution events or dispersed field scenarios. In recent years, some fluorescence sensing methods have overcome the dependence on large instruments to some extent through the specific interaction between probes and ions (fluorescence quenching / enhancement). However, existing fluorescent probes still face key technological bottlenecks, such as single-ion targeting: most probes only target Cr. 6+ or Cu 2+ For single-target detection, it is impossible to achieve simultaneous / switching detection of multiple ions through simple parameter adjustments (such as excitation wavelength and pH), making it extremely impractical in complex pollution scenarios; it is suitable for Cr under acidic / non-alkaline conditions. 6+ / Cu 2+ The lack of fluorescence sensing methods: the actual sample pretreatment process for heavy metal detection usually requires strong acid digestion, and then a large amount of alkali needs to be added to adjust the test system to a suitable pH value, which limits the field application.

[0004] To address the aforementioned issues, there is an urgent need for a fluorescent probe with tunable pH response and no complex modification requirements, and for constructing a rapid fluorescence detection method that integrates pretreatment techniques to simultaneously address Cr. 6+ With Cu 2+ The need for highly selective and rapid detection. Summary of the Invention

[0005] The purpose of this invention is to provide a boron-nitrogen co-doped fluorescent carbon quantum dot, its preparation method, and its application in the fabrication of a chromium / copper ion sensor, enabling pH-controlled chromium ion sensing using a single quantum dot material and a one-step synthesis process. 6+ / Cu 2+ The dual-channel high-sensitivity detection overcomes the technical barriers of limited probe selectivity, complex processes, and single functions, providing a revolutionary solution for heavy metal pollution monitoring.

[0006] On the one hand, the present invention provides a method for preparing boron-nitrogen co-doped fluorescent carbon quantum dots, which adopts the following technical solution:

[0007] A method for preparing boron-nitrogen co-doped fluorescent carbon quantum dots, characterized by comprising the following preparation steps:

[0008] S1. Mix o-phenylenediamine hydrochloride and boric acid to obtain a mixed solution. Add water to the mixed solution and dissolve it by sonication to obtain a mixed solution.

[0009] S2. The mixed solution obtained in step S1 is subjected to high temperature treatment to obtain a boron-nitrogen co-doped carbon material solution.

[0010] S3. The carbon material solution obtained in step S2 is filtered through a 0.22 μm microporous membrane to obtain a boron-nitrogen co-doped carbon quantum dot aqueous solution, and then dialyzed with a dialysis bag for 36-48 h.

[0011] S4. The aqueous solution of carbon quantum dots treated in step S3 is freeze-dried to obtain boron-nitrogen co-doped fluorescent carbon quantum dots.

[0012] Preferably, the molar ratio of o-phenylenediamine hydrochloride to boric acid in step S1 is (0.5-1.2):1.

[0013] Preferably, the mass ratio of the mixture to water in step S1 is (0.006-0.02):1.

[0014] Preferably, the high-temperature treatment process in step S2 involves heat-treating the mixed solution at 140-200°C for 4-9 hours.

[0015] On the other hand, the present invention also provides a boron-nitrogen co-doped fluorescent carbon quantum dot, which adopts the following technical solution:

[0016] A boron-nitrogen co-doped fluorescent carbon quantum dot was prepared using the method described above.

[0017] Preferably, the average particle size of the boron-nitrogen co-doped fluorescent carbon quantum dots is 2.5-5.0 nm;

[0018] The boron-nitrogen co-doped fluorescent carbon quantum dots contain 3-15 wt% boron atoms and 5-15 wt% nitrogen atoms.

[0019] On the other hand, the present invention also provides the above-mentioned boron-nitrogen co-doped fluorescent carbon quantum dots for the preparation of chromium / copper ion sensors, using the following technical method:

[0020] A method for fabricating a chromium / copper ion sensor using boron-nitrogen co-doped fluorescent carbon quantum dots as described above.

[0021] Preferably, the chromium / copper ion sensor includes the following preparation steps:

[0022] S1. Disperse boron-nitrogen co-doped fluorescent carbon quantum dots in water to prepare a boron-nitrogen co-doped fluorescent carbon quantum dot dispersion with a concentration of 0.5-5.0 mg / mL;

[0023] S2. Add the boron-nitrogen co-doped fluorescent carbon quantum dot dispersion obtained in step S1 to a PBS buffer solution with a pH of 2-5 to obtain 0.8-1.0 mL of carbon quantum dot solution. Prepare multiple groups of carbon quantum dot solutions, and add Cr to each group of carbon quantum dot solutions. 6+ In an ion-rich aqueous solution, culturing at 25-35 °C for 10-40 min yields Cr with a chromium ion concentration of 0.1 μM-50 μM. 6+ Ionic solutions;

[0024] Determination of chromium ion concentrations in the range of 0.1 μM to 50 μM. 6+ The fluorescence intensity values ​​of the ionic solution at a wavelength of ~625 nm were used to establish a standard curve of concentration-fluorescence intensity values ​​based on the chromium ion concentration and fluorescence intensity values.

[0025] S3. Prepare the unknown Cr according to the method in step S2. 6+ For solutions with a certain ion concentration, the fluorescence intensity value of the solution is measured;

[0026] Substituting the fluorescence intensity value into the concentration-fluorescence intensity standard curve obtained in step S2, the concentration of chromium ions in the solution is calculated, thereby realizing a chromium ion sensor based on boron-nitrogen co-doped fluorescent carbon quantum dots; or

[0027] S2. The boron-nitrogen co-doped fluorescent carbon quantum dot dispersion obtained in step S1 is added to a PBS buffer solution with a pH of 6-9 to obtain 0.8-1.0 mL of carbon quantum dot solution. Multiple groups of carbon quantum dot solutions are prepared, and Cu is added to each group of carbon quantum dot solutions. 2+ In an aqueous solution containing copper ions, incubation at 25-35 °C for 10-40 min yields Cu with copper ion concentrations ranging from 0.1 μM to 80 μM. 2 +Ionic solutions;

[0028] Determination of Cu ion concentrations in the range of 0.1 μM to 80 μM. 2+ The fluorescence intensity values ​​of the ionic solution at a wavelength of ~575 nm were used to establish a standard curve of concentration-fluorescence intensity values ​​based on the copper ion concentration and fluorescence intensity values.

[0029] S3. Prepare a solution with an unknown copper ion concentration according to the method in step S2, and measure the fluorescence intensity value of the solution.

[0030] Substituting the fluorescence intensity value into the concentration-fluorescence intensity standard curve obtained in step S2, the concentration of copper ions in the solution is calculated, thereby realizing a copper ion sensor based on boron-nitrogen co-doped fluorescent carbon quantum dots.

[0031] In summary, the present invention has the following beneficial technical effects:

[0032] 1. The boron-nitrogen co-doped fluorescent carbon quantum dots of this invention have a simple preparation process, requiring only one synthesis step, without the need for further treatment with surface passivating agents, and have good dispersibility and stability, enabling the visual detection of heavy metal ions.

[0033] 2. The boron-nitrogen co-doped fluorescent carbon quantum dots prepared in this invention exhibit responsiveness to chromium ions (Cr) under both acidic and non-acidic conditions. 6+ ), copper ions (Cu) 2+ Excellent selectivity; Cr is added to boron-nitrogen co-doped fluorescent carbon quantum dots in aqueous solution. 6+ Cu 2+ Subsequently, the fluorescence of boron-nitrogen co-doped fluorescent carbon quantum dots exhibited significant quenching. Therefore, by controlling different pH conditions, boron-nitrogen co-doped fluorescent carbon quantum dots can be used in Cr... 6+ Cu 2+ In the detection, Cr was used to prepare 6+ Cu 2+ Fluorescent sensor. Attached Figure Description

[0034] Figure 1 shows the effect of boron-nitrogen co-doped fluorescent carbon quantum dots prepared in this invention on Cr under different conditions. 6+ Cu 2+ Schematic diagram of ion detection;

[0035] Figure 2 is a comparison of the fluorescence intensity of boron-nitrogen co-doped fluorescent carbon quantum dots prepared by different molar ratios of o-phenylenediamine hydrochloride and boric acid in this invention.

[0036] Figure 3A shows the TEM image and particle size distribution histogram of boron-nitrogen co-doped fluorescent carbon quantum dots.

[0037] Figure 3B shows the XPS image of boron-nitrogen co-doped fluorescent carbon quantum dots.

[0038] Figure 4 shows the fluorescence spectra of boron-nitrogen co-doped fluorescent carbon quantum dots at different excitation wavelengths;

[0039] Figure 5A shows the fluorescence spectra of boron-nitrogen co-doped fluorescent carbon quantum dot solutions at emission wavelengths of ~575 nm under different pH conditions.

[0040] Figure 5B shows the fluorescence spectra of boron-nitrogen co-doped fluorescent carbon quantum dot solutions at emission wavelengths of ~625 nm under different pH conditions.

[0041] In Figure 6A, the solution of boron-nitrogen co-doped fluorescent carbon quantum dots at a wavelength of ~625 nm is obtained by adding different Cr... 6+ Fluorescence spectrum of concentration;

[0042] In Figure 6, B represents different Cr values ​​under natural white light. 6+ Colorimetric images of boron-nitrogen co-doped fluorescent carbon quantum dot solutions at various concentrations;

[0043] In Figure 6, C represents Cr. 6+ At concentrations of 1-15 μM, the fluorescence intensity ratio F / F0 of the fluorescent probe solution varies with Cr. 6+ A dotted graph showing concentration changes (F0, F represents the concentration of added Cr). 6+ Fluorescence intensity of the solutions before and after treatment);

[0044] In Figure 6, D represents Cr. 6+ At concentrations of 15-50 μM, the fluorescence intensity ratio F / F0 of the fluorescent probe solution varies with Cr. 6+ A dotted graph showing concentration changes (F0, F represents the concentration of added Cr). 6+ Fluorescence intensity of the solutions before and after treatment);

[0045] Figure 7 shows the fluorescence quenching effect of different metal ions on boron-nitrogen co-doped fluorescent carbon quantum dot solutions under acidic conditions;

[0046] In Figure 8A, the solution of boron-nitrogen co-doped fluorescent carbon quantum dots at a wavelength of ~575 nm is treated with different Cu... 2+ Fluorescence spectrum of concentration;

[0047] In Figure 8, B represents Cu. 2+ At concentrations of 1-10 μM, the fluorescence intensity ratio F / F0 of the fluorescent probe solution varies with Cu 2+ A dotted graph of concentration changes (F0, F represents the addition of Cu) 2+ Fluorescence intensity of the solutions before and after treatment);

[0048] In Figure 8, C represents Cu. 2+At concentrations of 10-80 μM, the fluorescence intensity ratio F / F0 of the fluorescent probe solution varies with Cu 2+ A dotted graph of concentration changes (F0, F represents the addition of Cu) 2+ Fluorescence intensity of the solutions before and after treatment);

[0049] Figure 9 shows the fluorescence quenching of boron-nitrogen co-doped fluorescent carbon quantum dot solutions by different metal ions under non-acidic conditions. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0051] Example

[0052] Example 1

[0053] A method for preparing boron-nitrogen co-doped fluorescent carbon quantum dots includes the following steps:

[0054] 1) Mix 72.4-173.8 mg of o-phenylenediamine hydrochloride and 50 mg of boric acid, add 6.12-37.3 g of water, and sonicate for 5 min to dissolve and obtain a mixed solution;

[0055] 2) The mixed solution obtained in step 1) is heat-treated at 140-200 °C for 4-9 h to obtain a boron-nitrogen co-doped carbon material solution;

[0056] 3) The carbon material solution obtained in step 2) is filtered through a 0.22 μm microporous membrane to remove insoluble impurities, resulting in a boron-nitrogen co-doped carbon quantum dot aqueous solution. Then, it is dialyzed through a dialysis bag for 36-48 h to remove unreacted reactants.

[0057] 4) The aqueous solution of carbon quantum dots treated in step 3) is freeze-dried to remove the aqueous solution and obtain boron-nitrogen co-doped fluorescent carbon quantum dots.

[0058] Referring to Figure 1, a schematic diagram of the detection of Cr and Cu ions by boron-nitrogen co-doped fluorescent carbon quantum dots under acidic and non-acidic conditions is shown. The addition of metal ions will cause the fluorescence of the carbon dot material to be quenched.

[0059] Comparative test cases

[0060] A method for preparing boron-nitrogen co-doped fluorescent carbon quantum dots is provided. The method is as described in Example 1. The molar ratios of o-phenylenediamine hydrochloride and boric acid are (1:0), (1:1), (1:1.5), and (1.5:1), respectively. The fluorescence intensity at ~625 nm is then measured.

[0061] Referring to Figure 2, the highest fluorescence emission intensity is observed when the molar ratio of o-phenylenediamine hydrochloride to boric acid is 1:1 within the range of (0.5-1.2):1.

[0062] Application examples

[0063] Application Example 1

[0064] Boron-nitrogen co-doped fluorescent carbon quantum dots are used to fabricate chromium ion sensors, including the following steps:

[0065] 1) Disperse boron-nitrogen co-doped fluorescent carbon quantum dots in water to prepare a boron-nitrogen co-doped fluorescent carbon quantum dot dispersion with a concentration of 0.5-5.0 mg / mL;

[0066] 2) Add the boron-nitrogen co-doped fluorescent carbon quantum dot dispersion obtained in step 1) to 0.8-1.0 mL of PBS buffer solution with a pH of 2-5, and then add the corresponding volume of 0.1 mM Cr. 6+ In an ion-rich aqueous solution, culturing at 25-35℃ for 10-40 min yields Cr with a chromium ion concentration of 0.1 μM-50 μM. 6+ Ionic solutions;

[0067] Determination of Cr 6+ The fluorescence intensity values ​​of the solution at a wavelength of ~625 nm were obtained. A standard curve of concentration-fluorescence intensity was established based on the chromium ion concentration and fluorescence intensity values.

[0068] 3) Prepare the unknown Cr according to the method in step 2). 6+ For solutions with a certain ion concentration, the fluorescence intensity value of the solution is measured;

[0069] Substitute the fluorescence intensity value into the concentration-fluorescence intensity standard curve obtained in step 2) to calculate the concentration of chromium ions in the solution, thereby realizing a chromium ion sensor based on boron-nitrogen co-doped fluorescent carbon quantum dots.

[0070] Application Example 2

[0071] Boron-nitrogen co-doped fluorescent carbon quantum dots are used to fabricate copper ion sensors, including the following steps:

[0072] 1) Disperse boron-nitrogen co-doped fluorescent carbon quantum dots in water to prepare a boron-nitrogen co-doped fluorescent carbon quantum dot dispersion with a concentration of 0.5-5.0 mg / mL;

[0073] 2) Add the boron-nitrogen co-doped fluorescent carbon quantum dot dispersion obtained in step 1) to 0.8-1.0 mL of PBS buffer solution with pH 6-9, and then add the corresponding volume of 0.1 mM copper ion aqueous solution. Incubate at 25-35℃ for 10-40 min to obtain a copper ion solution with a copper ion concentration of 0.1 μM-80 μM.

[0074] The fluorescence intensity of the solution with copper ion concentration was measured at a wavelength of ~575 nm. Based on the copper ion concentration and fluorescence intensity, a standard curve of concentration-fluorescence intensity was established.

[0075] 3) Prepare a solution with an unknown copper ion concentration according to the method in step 2), and measure the fluorescence intensity value of the solution;

[0076] Substituting the fluorescence intensity value into the concentration-fluorescence intensity standard curve obtained in step S2, the concentration of copper ions in the solution is calculated, thereby realizing a copper ion sensor based on boron-nitrogen co-doped fluorescent carbon quantum dots.

[0077] Test case

[0078] Experimental Example 1

[0079] Characterization of boron-nitrogen co-doped fluorescent carbon quantum dots

[0080] Referring to Figure 3, Figure 3A is a TEM image and a histogram of particle size distribution of the boron-nitrogen co-doped fluorescent carbon quantum dots prepared in the embodiment of the present invention; Figure 3B is an XPS image of the boron-nitrogen co-doped fluorescent carbon quantum dots prepared in the embodiment of the present invention; the average particle size of the boron-nitrogen co-doped fluorescent carbon quantum dots is 2.5-5.0 nm, and the boron-nitrogen co-doped fluorescent carbon quantum dots mainly include C, B, N and O elements, of which the content of boron atoms is 3-15 wt% and the content of nitrogen atoms is 5-15 wt%.

[0081] Referring to Figure 4, the emission wavelength and intensity of boron-nitrogen co-doped fluorescent carbon quantum dots differ under illumination with different excitation wavelengths. As shown in the figure, boron-nitrogen co-doped fluorescent carbon quantum dots have two characteristic emission wavelengths, located at ~575 nm and ~625 nm. As the excitation wavelength gradually increases, the intensity of the emission wavelength at ~575 nm gradually decreases and disappears, while the intensity of the emission wavelength at ~625 nm gradually increases and becomes dominant.

[0082] Experimental Example 2

[0083] Effect of pH on the optical properties of boron-nitrogen co-doped fluorescent carbon quantum dots

[0084] Referring to Figure 5, Figure A shows the fluorescence spectra of boron-nitrogen co-doped fluorescent carbon quantum dot solutions at an emission wavelength of ~575 nm under different pH conditions. The fluorescence intensity at ~575 nm gradually increases with increasing pH. Figure B shows the fluorescence spectra of boron-nitrogen co-doped fluorescent carbon quantum dot solutions at an emission wavelength of ~625 nm under different pH conditions. The fluorescence intensity at ~625 nm gradually decreases with increasing pH. That is, under acidic conditions, boron-nitrogen co-doped fluorescent carbon quantum dots exhibit better fluorescence intensity at ~625 nm, while under alkaline conditions, they exhibit better fluorescence intensity at ~575 nm.

[0085] Experimental Example 3

[0086] Boron-nitrogen doped carbon quantum dots for Cr 6+ Response of ions

[0087] Referring to Figure 6, A in Figure 6 represents the addition of different Cr values ​​to the boron-nitrogen co-doped fluorescent carbon quantum dot solution at a wavelength of ~625 nm. 6+ Fluorescence spectra of Cr concentrations; construction of Cr under acidic conditions 6+ An ion fluorescence probe was used. 1.0 mL of boron-nitrogen co-doped fluorescent carbon quantum dots (0.1 mg / mL, pH = 3) was added to the reaction system, followed by the addition of a corresponding volume of 0.1 mM chromium ion aqueous solution. Chromium ion solutions with concentrations of 1 μM, 2 μM, 3 μM, 5 μM, 10 μM, 15 μM, 25 μM, ..., 50 μM were obtained, and the fluorescence intensity at an emission wavelength of ~625 nm was measured. With the increase of Cr... 6+ As the concentration gradually increases, the fluorescence intensity of the fluorescent system gradually decreases; the addition of chromium ions quenches the carbon quantum dot fluorescent probe. Figure 6B shows the fluorescence intensity under natural white light with different chromium concentrations. 6+ The colorimetric images of boron-nitrogen co-doped fluorescent carbon quantum dot solutions at different concentrations were shown. Under natural white light, the probe solution colors differed significantly with varying chromium ion concentrations, demonstrating the promising potential of this probe system for visual detection of chromium ions. Further analysis of the system's fluorescence intensity and chromium ion concentrations revealed further color variations. 6+ Concentration analysis revealed that, within a certain range, fluorescence intensity and Cr... 6+ The concentrations showed a good linear relationship. In Figure 6, C represents Cr. 6+ With a concentration range of 1-15 μM, the fluorescence intensity ratio F / F0 of the fluorescent probe solution varies with Cr. 6+ A dotted graph showing the concentration changes (F0, F represents the concentration of Cr added). 6+ The fluorescence intensity of the solutions before and after treatment was measured in the range of 1-15 μM. The linear regression equation was y = -0.0544x + 0.88986, R0. 2 =0.993; D in Figure 6 is Cr 6+With a concentration range of 15-50 μM, the fluorescence intensity ratio F / F0 of the fluorescent probe solution varies with Cr. 6+ A dotted graph showing concentration changes (F0, F represents the concentration of added Cr). 6+ The fluorescence intensity of the solutions before and after treatment was measured in the range of 15-50 μM. The linear regression equation was y = -0.0032x + 0.2527, R0. 2 =0.991. The detection limit of this system was calculated to be 0.069 μM, which is far below the maximum detection limit of Cr in fresh vegetables specified by the Chinese national standard (9.61 μM, 0.5 mg / kg, GB2762-2022 "National Food Safety Standard Limits of Contaminants in Food").

[0088] Referring to Figure 7, the fluorescence sensing system of boron-nitrogen co-doped fluorescent carbon quantum dots under acidic conditions was investigated for Cr. 6+ Selectivity for other interfering ions, including Mg 2+ Cd 2+ Cu 2+ Zn 2+ Fe 3+ Cr 3+ Ca 2+ Ba 2+ Pb 2+ and Hg 2+ Plasma. Only Cr 6+ The presence of Cr significantly reduces fluorescence intensity, while the addition of other ions has little effect on the fluorescence intensity. Therefore, under acidic conditions, the boron-nitrogen co-doped fluorescent carbon quantum dot system in Cr 6+ The test demonstrates advantages and application potential in terms of selectivity.

[0089] Test Example 4

[0090] Boron-nitrogen doped carbon quantum dots for Cu 2+ Response of ions

[0091] Referring to Figure 8, A in Figure 8 represents the addition of different Cu to boron-nitrogen co-doped fluorescent carbon quantum dot solutions at a wavelength of ~575 nm. 2+ Fluorescence spectra of Cu concentrations were obtained by constructing Cu using carbon quantum dots under non-acidic conditions. 2+ An ion fluorescence probe was used. 1.0 mL of boron-nitrogen co-doped fluorescent carbon quantum dot dispersion (0.1 mg / mL, pH=8) was taken, and then a corresponding volume of 0.1 mM copper ion aqueous solution was added to the reaction system to obtain copper ion solutions with concentrations of 1 μM, 2 μM, 3 μM, 5 μM, 10 μM, 15 μM, ... 80 μM. The fluorescence intensity at the emission wavelength ~575 nm was measured. With the increase of Cu... 2+As the concentration gradually increases, the fluorescence intensity of the fluorescent system gradually decreases. This is determined by analyzing the fluorescence intensity values ​​of the system and the Cu content. 2+ Concentration analysis revealed that, within a certain range, the fluorescence intensity value and Cu... 2+ The concentrations showed a good linear relationship. In Figure 8, B represents Cu. 2+ At concentrations of 1-10 μM, the fluorescence intensity ratio F / F0 of the fluorescent probe solution varies with Cu 2+ A dotted graph of concentration changes (F0, F represents the addition of Cu) 2+ The fluorescence intensity of the solutions before and after treatment, within the range of 1-10 μM, showed a linear regression equation of y = -0.05183x + 0.9982, R0. 2 =0.993; C in Figure 8 is Cu 2+ At concentrations of 10-80 μM, the fluorescence intensity ratio F / F0 of the fluorescent probe solution varies with Cu 2+ A dotted graph of concentration changes (F0, F represents the addition of Cu) 2+ The fluorescence intensity of the solutions before and after treatment, within the range of 10-80 μM, showed a linear regression equation of y = -0.00208x + 0.5339, R0. 2 =0.992. The detection limit of this system is 0.074 μM, which is far below the maximum detection limit of Cu in drinking water specified by the Chinese national standard (15.74 μM, 1 mg / kg (GB 5749-2022)).

[0092] Experimental Example 5

[0093] Cu based on boron-nitrogen co-doped fluorescent carbon quantum dots 2+ Selectivity and anti-interference study of fluorescence sensing systems

[0094] Referring to Figure 9, the fluorescence sensing system of boron-nitrogen co-doped fluorescent carbon quantum dots under weakly alkaline conditions was investigated for Cu. 2+ Selectivity for other interfering ions, including Mg 2+ Cd 2+ Cr 6+ Zn 2+ Fe 3+ Cr 3+ Ca 2+ Ba 2+ Pb 2+ and Hg 2+ Plasma. Only Cu 2+ The presence of [a specific ion] leads to a significant decrease in fluorescence intensity, while the addition of other ions has little effect on the fluorescence intensity value. Therefore, under weakly alkaline conditions, the boron-nitrogen co-doped fluorescent carbon quantum dot system in Cu [a specific environment] exhibits [significantly lower fluorescence intensity]. 2+ The test demonstrates advantages and application potential in terms of selectivity.

[0095] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing boron-nitrogen co-doped fluorescent carbon quantum dots, characterized in that, The preparation process includes the following steps: S1, mixing o-phenylenediamine hydrochloride and boric acid in a molar ratio of (0.5-1.2):1 to obtain a mixed solution, adding water to the mixed solution, and dissolving by ultrasonication to obtain a mixed solution; the mass ratio of the mixed solution to water is (0.006-0.02):1; S2, treating the mixed solution obtained in step S1 at high temperature to obtain a boron-nitrogen co-doped carbon material solution; S3, filtering the carbon material solution obtained in step S2 through a 0.22μm microporous membrane to obtain a boron-nitrogen co-doped carbon quantum dot aqueous solution, and then dialyzing it through a dialysis bag for 36-48 hours; S4, freeze-drying the carbon quantum dot aqueous solution treated in step S3 to obtain boron-nitrogen co-doped fluorescent carbon quantum dots; when the boron-nitrogen co-doped fluorescent carbon quantum dots are used to prepare chromium ion sensors or copper ion sensors, by adjusting the pH value of the detection system, chromium ion sensors can be detected at a wavelength of ~625nm under acidic conditions with a pH of 2-5. 6+ Cu was detected at a wavelength of ~575 nm under non-acidic conditions with a pH of 6-9. 2+ .

2. The method for preparing boron-nitrogen co-doped fluorescent carbon quantum dots according to claim 1, characterized in that, The high-temperature treatment process in step S2 involves heat-treating the mixed solution at 140-200℃ for 4-9 hours.

3. A boron-nitrogen co-doped fluorescent carbon quantum dot prepared by the preparation method according to any one of claims 1-2.

4. The boron-nitrogen co-doped fluorescent carbon quantum dot according to claim 3, characterized in that, The boron-nitrogen co-doped fluorescent carbon quantum dots have an average particle size of 2.5-5.0 nm; the boron content in the boron-nitrogen co-doped fluorescent carbon quantum dots is 3-15 wt%, and the nitrogen content is 5-15 wt%; the boron-nitrogen co-doped fluorescent carbon quantum dots exhibit pH-controlled dual-channel fluorescence response characteristics, and under acidic conditions with a pH of 2-5, they respond to Cr at a wavelength of ~625 nm. 6+ It exhibits a specific fluorescence response, showing a fluorescence intensity of ~575 nm for Cu under non-acidic conditions at pH 6-9. 2+ It exhibits a specific fluorescence response.

5. A boron-nitrogen co-doped fluorescent carbon quantum dot prepared by the method according to any one of claims 1-2, used for preparing a chromium ion sensor or a copper ion sensor, characterized in that, The chromium ion sensor or copper ion sensor comprises the following preparation steps: S1, dispersing boron-nitrogen co-doped fluorescent carbon quantum dots in water to obtain a boron-nitrogen co-doped fluorescent carbon quantum dot dispersion with a concentration of 0.5-5.0 mg / mL; S2, adding the boron-nitrogen co-doped fluorescent carbon quantum dot dispersion obtained in step S1 to a PBS buffer solution with a pH of 2-5 to obtain 0.8-1.0 mL of carbon quantum dot solution, preparing multiple groups of carbon quantum dot solutions, and adding Cr to each group of carbon quantum dot solutions. 6+ In an ion-rich aqueous solution, culturing at 25-35℃ for 10-40 min yields Cr with a chromium ion concentration of 0.1 μM-50 μM. 6+ Ionic solutions; Measure the fluorescence intensity of fluorescent probe solutions with chromium ion concentrations of 0.1 μM-50 μM at a wavelength of ~625 nm, and establish a standard curve of concentration-fluorescence intensity based on chromium ion concentration and fluorescence intensity; S3, Prepare unknown Cr... 6+ For solutions with a certain ion concentration, the fluorescence intensity value of the solution is measured; Substitute the fluorescence intensity value into the concentration-fluorescence intensity standard curve obtained in step S2 to calculate the concentration of chromium ions in the solution, thereby realizing a chromium ion sensor based on boron-nitrogen co-doped fluorescent carbon quantum dots; or S2, add the boron-nitrogen co-doped fluorescent carbon quantum dot dispersion obtained in step S1 to a PBS buffer solution with a pH of 6-9 to obtain 0.8-1.0 mL of carbon quantum dot solution, prepare multiple groups of carbon quantum dot solutions, and add Cu to each group of carbon quantum dot solutions. 2+ In an aqueous solution containing copper ions, incubation at 25-35℃ for 10-40 min yields Cu with copper ion concentrations ranging from 0.1 μM to 80 μM. 2+ Ionic solutions; Measure the fluorescence intensity of fluorescent probe solutions with copper ion concentrations of 0.1 μM to 80 μM at a wavelength of ~575 nm, and establish a standard curve of concentration-fluorescence intensity based on copper ion concentration and fluorescence intensity; S3, Prepare a solution with an unknown copper ion concentration according to the method in step S2, and measure the fluorescence intensity of the solution. Substituting the fluorescence intensity value into the concentration-fluorescence intensity standard curve obtained in step S2, the concentration of copper ions in the solution is calculated, thereby realizing a copper ion sensor based on boron-nitrogen co-doped fluorescent carbon quantum dots.

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