1. A preparation method of a nitrogen-sulfur doped fluorescent carbon nanosheet is characterized by comprising the following steps:

1) mixing trisodium citrate with 6-mercaptopurine, sequentially adding N, N-dimethylformamide and water, and carrying out ultrasonic treatment on the mixture for 5min to obtain a colorless transparent solution;

2) transferring the colorless transparent solution obtained in the step 1) to a high-pressure reaction kettle, and heating and reacting for 0.5-5 hours at the temperature of 150-;

3) centrifuging the yellow solution obtained in the step 2), and dialyzing to obtain the pure nitrogen-sulfur doped fluorescent carbon nanosheet.

2. The method for preparing nitrogen-sulfur-doped fluorescent carbon nanosheets according to claim 1, wherein the trisodium citrate and 6-mercaptopurine in step 1) are taken in parts by mass: 0-10 parts of trisodium citrate and 1.22-14.6 parts of 6-mercaptopurine; preferably, trisodium citrate 2.5 parts, 6-mercaptopurine 13.6 parts.

3. The method for preparing nitrogen-sulfur doped fluorescent carbon nanosheets according to claim 1, wherein the mass to volume ratio of 6-mercaptopurine to N, N-dimethylformamide in step 1) is (0.0813-0.9733): 1, mg/mL.

4. The method for preparing nitrogen-sulfur doped fluorescent carbon nanosheets of claim 1, wherein the autoclave reaction conditions of step 2) are heating at 200 ℃ for 4 hours.

5. The method for preparing nitrogen-sulfur-doped fluorescent carbon nanosheets according to claim 1, wherein the centrifugation in step 3) is performed at 12000r/min for 15 min.

6. The method for preparing nitrogen-sulfur doped fluorescent carbon nanosheets of claim 1, wherein the dialysis of step 3) is a 500Da dialysis bag dialysis for 2 h.

7. Application of nitrogen-sulfur doped fluorescent carbon nanosheets as defined in any one of claims 1-6 to Cr₂O₇ ^2-And (6) detecting.

8. Nitrogen-sulfur-doped fluorescent carbon nanosheet of claim 7 applied to Cr₂O₇ ^2-The detection is carried out, and the detection method is characterized by comprising the following steps:

adding the fluorescent carbon nano-sheets into water, and then adding Cr with different concentrations₂O₇ ^2-The solution was mixed well and incubated at room temperature for 3min, and the solution with an excitation wavelength of 380nm was measured.

9. Nitrogen-sulfur-doped fluorescent carbon nanosheet of claim 7 applied to Cr₂O₇ ^2-Detecting, wherein the fluorescent carbon nano-sheet, water and Cr with different concentrations are adopted₂O₇ ^2-The volume ratio of the solution is 20: 179: 1.

10. nitrogen-sulfur-doped fluorescent carbon nanosheet of claim 7 applied to Cr₂O₇ ^2-Detecting, wherein the nitrogen-sulfur doped fluorescent carbon nano-sheet is Cr₂O₇ ^2-The detection limit of (2) was 0.2. mu. mol/L.

Background

Dichromate ion (Cr)₂O₇ ^2-) In the industries of electroplating, metallurgy, pigment production, leather tanning, wood preservation and the likeHexavalent chromium (cr (vi)) is one of heavy metal pollutants having serious harm to the environment, it has carcinogenicity, its strong oxidizing property can damage DNA and interfere DNA repair, at the same time it can also destroy the skeleton of liver cells, even cause death of liver cells, the probability of respiratory cancer is greatly increased due to long-term exposure to high concentration of cr (vi), and it can enter human body through water, air and food, etc. to cause harm to health. Therefore, Cr (VI) has serious potential threat to human health, and the establishment of efficient and accurate Cr detection is urgently needed₂O₇ ^2-The method of (1).

In recent years, fluorescent carbon nanosheets, as a new nano material, have attracted extensive attention of researchers due to the advantages of good water solubility, low toxicity, good photostability, biocompatibility and the like, and are used in the fields of biosensing, cell imaging, catalysis and the like. The preparation methods reported at present for the fluorescent carbon nanosheets are many, such as laser stripping graphene, an electrochemical oxidation method, an arc discharge method, a chemical oxidation method and the like, most of the methods are complicated in synthesis process, expensive in raw materials, uneconomical and environment-friendly, and the large-scale production of the fluorescent carbon nanosheets is limited to a great extent.

Disclosure of Invention

The invention provides a preparation method of nitrogen-sulfur doped fluorescent carbon nanosheets and Cr thereof₂O₇ ^2-The detection application has the advantages of good selectivity and sensitive detection, and the invention is realized by the following technical scheme:

a preparation method of a nitrogen-sulfur doped fluorescent carbon nanosheet comprises the following steps:

1) mixing trisodium citrate with 6-mercaptopurine, sequentially adding N, N-dimethylformamide and water, and carrying out ultrasonic treatment on the mixture for 5min to obtain a colorless transparent solution;

2) transferring the colorless transparent solution obtained in the step 1) to a high-pressure reaction kettle, and heating and reacting for 0.5-5 hours at the temperature of 150-;

3) centrifuging the yellow solution obtained in the step 2), and dialyzing to obtain the pure nitrogen-sulfur doped fluorescent carbon nanosheet.

Further, the trisodium citrate and 6-mercaptopurine in the step 1) are taken according to the mass parts: 0-10 parts of trisodium citrate and 1.22-14.6 parts of 6-mercaptopurine; preferably, trisodium citrate 2.5 parts, 6-mercaptopurine 13.6 parts.

Further, the mass-to-volume ratio of the 6-mercaptopurine to the N, N-dimethylformamide in the step 1) is (0.0813-0.9733): 1, mg/mL.

Further, the high-pressure reaction kettle in the step 2) is heated for 4 hours at the temperature of 200 ℃.

Further, the centrifugal rotating speed in the step 3) is 12000r/min, and the centrifugal time is 15 min.

Further, the dialysis of the step 3) is dialysis for 2 hours by a 500Da dialysis bag.

Application of nitrogen-sulfur doped fluorescent carbon nanosheet to Cr₂O₇ ^2-The detection is carried out, and the detection method comprises the following steps:

adding the fluorescent carbon nano-sheets into water, and then adding Cr with different concentrations₂O₇ ^2-The solution was mixed well and incubated at room temperature for 3min, and the solution with an excitation wavelength of 380nm was measured.

Further, the fluorescent carbon nanosheets, water and Cr in different concentrations₂O₇ ^2-The volume ratio of the solution is 20: 179: 1.

further, the nitrogen-sulfur doped fluorescent carbon nano-sheet pair Cr₂O₇ ^2-The detection limit of (2) was 0.2. mu. mol/L.

Compared with the prior art, the invention has the beneficial effects that:

according to the invention, the nitrogen-sulfur doped fluorescent nanosheet is prepared by using trisodium citrate and 6-mercaptopurine as precursors and N, N-dimethylformamide and water as solvents through a one-step solvothermal method, and the preparation method is simple, low in cost and easy for large-scale synthesis. The prepared fluorescent carbon nanosheet has the advantages of high fluorescence property, good light stability, adjustable spectrum, easy surface functionalization and the like. Prepared fluorescent carbon nanosheet and Cr₂O₇ ^2-Oxidation-reduction can occur to make carbonThe fluorescence of the nano-sheet is statically quenched, and Cr is rapidly and selectively and sensitively detected based on the static quenching₂O₇ ^2-。

Drawings

Fig. 1 is a three-dimensional fluorescence spectrum of a fluorescent carbon nanoplate.

Fig. 2 is an X-ray photoelectron spectrum (XPS) of fluorescent carbon nanoplatelets.

FIG. 3 shows fluorescent carbon nanosheets with different concentrations of Cr₂O₇ ^2-Fluorescence emission spectrum of (a).

Detailed Description

In order to make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described more clearly and completely with reference to the following embodiments. The examples do not show the specific conditions, and the reagents or apparatuses used are not shown in the manufacturers, and all of them are conventional products commercially available.

Example 1

The preparation method of the nitrogen-sulfur doped fluorescent carbon nanosheet comprises the following steps:

(1) the dosage, heating temperature and time of trisodium citrate and 6-mercaptopurine are optimized. The result shows that the fluorescence intensity of the carbon nanosheet is gradually increased and then gradually balanced with the increase of the dosage of the trisodium citrate, and the optimal dosage is 2.5 parts by mass; with the increase of the dosage of the 6-mercaptopurine, the fluorescence intensity of the carbon nanosheets is gradually enhanced and then gradually balanced, and the optimal dosage is 13.6 parts by mass; the fluorescence is gradually enhanced along with the increase of the reaction temperature, and the optimal temperature is 200 ℃; as the reaction time increases, the fluorescence gradually increases and then gradually equilibrates, with an optimal time of 4 h.

(2) Preparing nitrogen-sulfur doped fluorescent carbon nanosheets under optimal conditions: accurately weighing 2.5mg of trisodium citrate and 13.6mg of 6-mercaptopurine in a beaker, sequentially adding 15mL of N, N-dimethylformamide and 5mL of water, carrying out ultrasonic treatment on the mixture for 5min to obtain a colorless transparent solution, transferring the colorless transparent solution into a high-pressure reaction kettle, heating for 4h at 200 ℃ to obtain a yellow solution, centrifuging for 15min (rotating speed of 12000r/min), and dialyzing for 2h (dialysis bag 500Da) to obtain the nitrogen-sulfur doped fluorescent carbon nanosheet.

Fig. 1 is a three-dimensional fluorescence spectrum of a nitrogen-sulfur doped fluorescent carbon nanosheet, wherein the optimal excitation wavelength is 380nm, and the emission wavelength is 520nm, which shows that the obtained carbon nanosheet emits green fluorescence. Fig. 2 is an XPS diagram of the fluorescent carbon nanosheet, and it can be seen from the diagram that the prepared carbon nanosheet contains nitrogen, sulfur, oxygen and carbon elements.

Example 2

(1) 200 μ L of fluorescent carbon nanoplatelets were added to 1790 μ L of water, followed by 10 μ L of Cr at different concentrations₂O₇ ^2-Mixing uniformly, incubating for 3min at room temperature, and measuring the solution with excitation wavelength of 380 nm; with Cr₂O₇ ^2-The fluorescence of the carbon nano-sheet is gradually weakened as the concentration is increased, and Cr₂O₇ ^2-Concentration and F/F₀(F and F)₀Respectively is the presence or absence of Cr₂O₇ ^2-The fluorescence of the carbon nano sheet) is in good linearity within the range of 0.5-25 mu mol/L, the detection limit is 0.2 mu mol/L, and the method can be used for Cr₂O₇ ^2-Sensitive detection of (3). FIG. 3 shows fluorescent carbon nanosheets with different concentrations of Cr₂O₇ ^2-Fluorescence emission spectrum of (a).

(2) Fluorescent carbon nano-pair Cr₂O₇ ^2-Optionally, other anions (F)^-、Cl^-、Br^-、I^-、NO₃ ^-、CO₃ ^2-、HCO₃ ^-、SO₃ ^2-、S^2-、SO₄ ^2-、ClO₃ ^-、BrO₃ ^-、IO₃ ^-、H₂PO₄ ^-、HPO₄ ^2-、PO₄ ^3-、NO₂ ^-And CH₃COO^-Etc.) are all in pairs of Cr₂O₇ ^2-The detection of (2) does not cause interference, and proves that the fluorescent carbon nano-particles are used for Cr₂O₇ ^2-Has good selectivity in detection.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solutions of the present application and not to limit them; although the present application has been described in detail with reference to preferred embodiments, those of ordinary skill in the art will understand that: modifications to the embodiments of the present application or equivalent replacements of some technical features may still be made, which should all be covered by the scope of the technical solution claimed in the present application.