Preparation method and application of red light carbon dot material

Abstract

The invention discloses a preparation method and application of a red light carbon dot material, and belongs to the technical field of composite material preparation and pH and heavy metal ion detection. The invention aims to solve the problems that the existing red light carbon quantum dot material cannot eliminate cross interference among metal ions and cannot realize selective detection of heavy metal ions under a strong acid condition. The method comprises the following steps: 1, sequentially adding 2, 3-diaminophenazine, sulfanilic acid and boric acid into ethanol, and then carrying out ultrasonic treatment and constant-temperature reaction; and 2, filtering, washing, dialyzing and freeze-drying. The method is applied to visual detection of pH and heavy metal ions. The invention is used for preparation and application of the red light carbon dot material.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material preparation and pH and heavy metal ion detection. Background Art

[0002] Heavy metal ion pollution is a serious environmental problem, posing a huge threat to human health and the ecological environment. Heavy metal ions are highly toxic and carcinogenic. After absorption by the human body, symptoms such as physical retardation, mental discomfort, nausea, vomiting, and diarrhea may occur. Long-term exposure to heavy metal polluted environments may also lead to acute and chronic diseases such as kidney and liver dysfunction, congenital abnormalities, and various cancers. Specific heavy metals such as mercury, cadmium, and chromium can also cause specific damage to the nervous system, hematopoietic system, and respiratory system. When heavy metal ions enter the water body, they will destroy the ecological balance of aquatic organisms and affect the survival and reproduction of aquatic organisms. Through the transmission of the food chain, heavy metal ions will also be enriched in organisms, thereby posing a threat to human health. Heavy metal pollution can also destroy the fertility of the soil and affect the growth and yield of crops.

[0003] For heavy metal ion pollution, the commonly used treatment methods currently include chemical precipitation, redox treatment, solvent extraction separation, adsorption, membrane separation, ion exchange, etc. These methods remove heavy metal ions from the environment or convert them into harmless substances through different mechanisms. Traditional heavy metal ion detection mainly relies on large-scale precision instruments, mainly spectroscopy and inductively coupled plasma mass spectrometry. The advantage is that the analysis results are highly accurate. The disadvantage is that the instruments are expensive, time-consuming and labor-intensive, and cannot achieve real-time in-situ detection of heavy metal ions. Visual detection of heavy metal ions is an intuitive and rapid detection method, which has received widespread attention in the fields of analytical chemistry and environmental monitoring in recent years.

[0004] Fluorescent carbon quantum dots (CDs) are new carbon nanomaterials with good water solubility and biocompatibility. Compared with traditional heavy metal ion detection methods, carbon quantum dot materials produce less waste during preparation and use, and have less impact on the environment. Therefore, they have significant application advantages in the visualization of heavy metal ion detection. These advantages make carbon quantum dot materials have broad application prospects in environmental monitoring, food safety, and biomedicine. At present, red light carbon quantum dots have been used to detect Hg in ethanol aqueous solution. 2+ , Cu 2+ and Fe 3+ Visual detection [Wang J, Fu J, Chen M, Zhang J, Mater. Today Chem., 2024, 41: 102331], but unfortunately, all three heavy metal ions quench the fluorescence of the carbon dot solution, so it is impossible to eliminate the cross-interference between them, which will limit the application of carbon dot materials.

[0005] At present, although a large number of carbon quantum dot materials have been used in the visual detection of heavy metal ions, there are still huge challenges in the selective detection of heavy metal ions under extreme environments (such as strong acid conditions) using red light carbon quantum dot materials. Summary of the invention

[0006] The present invention aims to solve the problems that the existing red light carbon quantum dot materials cannot eliminate the cross interference between metal ions and cannot achieve selective detection of heavy metal ions under strong acid conditions, and further provide a preparation method of red light carbon dot materials and applications thereof.

[0007] A method for preparing a red light carbon dot material is carried out according to the following steps:

[0008] 1. Add 2,3-diaminophenazine, p-aminobenzenesulfonic acid and boric acid to ethanol in sequence, then perform ultrasonic treatment, and then react at a constant temperature of 180°C to 200°C for 8h to 10h, and finally cool naturally to room temperature to obtain a reaction system;

[0009] 2. The system after the reaction is filtered and washed in sequence to obtain a solid crude product, the solid crude product is dissolved in methanol, and then dialyzed and freeze-dried in sequence to obtain a red light carbon dot material.

[0010] The invention discloses an application of a red light carbon dot material, which is used in the visual detection of pH and heavy metal ions.

[0011] Figure 1 The figure is a schematic diagram of the preparation of the red light carbon dot material and the visual detection of heavy metal ions in the present invention; as can be seen from the figure, the present invention uses 2,3-diaminophenazine as the carbon source and nitrogen source, and p-aminobenzenesulfonic acid as the sulfur source, and the solvent thermal method is used to prepare carbon quantum dots (R-CDs) under the catalysis of boric acid; R-CDs show red light emission in ethanol-HEPES buffer. In the range of pH <7, when the pH decreases, the red light of the solution increases, and when the pH increases, the red light of the solution decreases or even completely quenches. At different pH values, the presence of heavy metal ions (Cr 3+ , Cu 2+ , Fe 3+ ), the red light of R-CDs is quenched or enhanced due to coordination complexation, thus achieving visual detection of heavy metal ions.

[0012] The beneficial effects of the present invention are:

[0013] The surface composition of the carbon dots is confirmed by infrared spectroscopy and X-ray photoelectron spectroscopy, and the transmission electron microscope scanning result shows that the average particle size is about 1.53nm, which is a typical biocompatible carbon nanomaterial.

[0014] R-CDs exhibited good and stable photophysical properties in ethanol-HEPES buffer. The fluorescence quenching / enhancement of R-CDs solution was achieved due to the coordination and complexation of heavy metal ions with the functional groups on the surface of carbon dots, thus realizing the Fe 3+ , Cu 2+ and Cr 3+ Visual detection of three heavy metal ions. This work provides a theoretical basis for the preparation of red light-emitting carbon dots and a feasible solution for early warning of heavy metal ion pollution.

[0015] R-CDs showed red light emission in ethanol-HEPES buffer. When the pH varied in the range of 1.51 to 7.11, the higher the pH, the weaker the red fluorescence of R-CDs in ethanol-HEPES buffer, while the lower the pH, the stronger the red fluorescence of R-CDs in ethanol-HEPES buffer. 3+ , Cu 2+ , Fe 3+ ), the fluorescence of R-CDs in ethanol-HEPES buffer changes due to coordination complexation, thereby achieving visual detection of heavy metal ions.

[0016] It can be seen that the present invention solves the problem that the existing red light carbon quantum dot materials cannot eliminate the cross-interference between metal ions and cannot achieve the selective detection of heavy metal ions under strong acid conditions.

[0017] Instruction Manual

[0018] Figure 1 The schematic diagram is a preparation diagram of the red light carbon dot material and the visual detection diagram of heavy metal ions of the present invention;

[0019] Figure 2 FT-IR and XPS images of R-CDs prepared in Example 1, (a) is FT-IR, (b) is XPS total spectrum, (c) is C1s fine spectrum, (d) is N1s fine spectrum, (e) is O1s fine spectrum, and (f) is S2p ​​fine spectrum;

[0020] Figure 3 TEM (a), HR-TEM (b), Raman spectrum (c) and XRD pattern (d) of the R-CDs prepared in Example 1;

[0021] Figure 4 This is a photograph of the R-CDs prepared in Example 1 in an ethanol-HEPES buffer solution with a pH value of 3.30 to 6.25 under 365 nm ultraviolet light radiation;

[0022] Figure 5UV-visible absorption spectrum-fluorescence spectrum (a), excitation wavelength response diagram (b) and fluorescence solvent effect diagram (c) of R-CDs solution;

[0023] Figure 6 The absolute fluorescence lifetime and quantum yield of the R-CDs prepared in Example 1 in ethanol-HEPES buffer at pH=3;

[0024] Figure 7 The fluorescence spectra of R-CDs prepared in Example 1 in ethanol-HEPES buffers of different pH values ​​(a), the linear relationship between pH and fluorescence intensity (b), and the change in fluorescence intensity of the buffer solution at pH values ​​of 3 and 6 (c);

[0025] Figure 8 Figure 2 is the fluorescence emission of R-CDs in the presence of different metal ions in ethanol-HEPES buffer at pH = 3 and 554 nm excitation (a), Fe 3+ Fluorescence titration spectrum of (b) and Fe 3+ Titration curve between concentration and solution fluorescence intensity (c); the inset is the calculation of LOD;

[0026] Fig. 9 Figure 2 is the fluorescence emission of R-CDs in the presence of different metal ions in ethanol-HEPES buffer at pH = 6 and 554 nm excitation (a), Fe 3+ Fluorescence titration spectrum of (b) and Fe 3+ Titration curve between concentration and solution fluorescence intensity (c); the inset is the calculation of LOD;

[0027] Fig.10 The presence of Cu in the ethanol-HEPES buffer of R-CDs at pH = 6 and 554 nm excitation 2+ Fluorescence titration spectrum (a) and calculation of minimum detection limit (b); the inset is the calculation of LOD;

[0028] Fig.11 The presence of Cr in the ethanol-HEPES buffer of R-CDs at pH = 6 and 554 nm excitation 3+ Fluorescence titration spectrum (a) and calculation of minimum detection limit (b); the inset is the calculation of LOD;

[0029] Fig.12 is the UV-visible absorption spectra of R-CDs in the presence of different heavy metal ions in ethanol-HEPES buffer at pH = 3 / 6;

[0030] Fig.13 To add Fe to the ethanol-HEPES buffer of R-CDs at pH 3 3+IR spectra before and after;

[0031] Fig.14 To add Fe to the ethanol-HEPES buffer of R-CDs at pH 6 3+ , Cu 2+ Cr 3+ IR spectra before and after;

[0032] Fig.15 To add Fe to the ethanol-HEPES buffer of R-CDs at pH 3 / 6 3+ , Cu 2+ Cr 3+ Comparison of C1s fine spectra before and after;

[0033] Fig.16 is the Fe content of R-CDs in ethanol-HEPES buffer at pH 3 / 6 3+ , Cu 2+ Cr 3+ Comparison of the N1s fine spectra before and after;

[0034] Fig.17 is the Fe content of R-CDs in ethanol-HEPES buffer at pH 3 / 6 3+ , Cu 2+ Cr 3+ Comparison of O1s fine spectra before and after;

[0035] Fig.18 is the Fe content of R-CDs in ethanol-HEPES buffer at pH 3 / 6 3+ , Cu 2+ Cr 3+ Comparison of S2p fine spectra before and after. DETAILED DESCRIPTION

[0036] Specific implementation method 1: This implementation method is a method for preparing a red light carbon dot material, which is carried out according to the following steps:

[0037] 1. Add 2,3-diaminophenazine, p-aminobenzenesulfonic acid and boric acid to ethanol in sequence, then perform ultrasonic treatment, and then react at a constant temperature of 180°C to 200°C for 8h to 10h, and finally cool naturally to room temperature to obtain a reaction system;

[0038] 2. The system after the reaction is filtered and washed in sequence to obtain a solid crude product, the solid crude product is dissolved in methanol, and then dialyzed and freeze-dried in sequence to obtain a red light carbon dot material.

[0039] The beneficial effects of this implementation are:

[0040] In this embodiment, the surface composition of the carbon dots is confirmed by infrared spectroscopy and X-ray photoelectron spectroscopy, and the transmission electron microscope scanning result shows that the average particle size is about 1.53 nm, which is a typical biocompatible carbon nanomaterial.

[0041] R-CDs exhibited good and stable photophysical properties in ethanol-HEPES buffer. The fluorescence quenching / enhancement of R-CDs solution was achieved due to the coordination and complexation of heavy metal ions with the functional groups on the surface of carbon dots, thus realizing the Fe 3+ , Cu 2+ and Cr 3+ Visual detection of three heavy metal ions. This work provides a theoretical basis for the preparation of red light-emitting carbon dots and a feasible solution for early warning of heavy metal ion pollution.

[0042] R-CDs showed red light emission in ethanol-HEPES buffer. When the pH varied in the range of 1.51 to 7.11, the higher the pH, the weaker the red fluorescence of R-CDs in ethanol-HEPES buffer, while the lower the pH, the stronger the red fluorescence of R-CDs in ethanol-HEPES buffer. 3+ , Cu 2+ , Fe 3+ ), the fluorescence of R-CDs in ethanol-HEPES buffer changes due to coordination complexation, thereby achieving visual detection of heavy metal ions.

[0043] It can be seen that the present embodiment solves the problem that the existing red light carbon quantum dot materials cannot eliminate the cross-interference between metal ions and cannot achieve the selective detection of heavy metal ions under strong acid conditions.

[0044] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that: the molar ratio of 2,3-diaminophenazine to p-aminobenzenesulfonic acid in step 1 is 1:(2.5-3.5); the molar ratio of 2,3-diaminophenazine to boric acid in step 1 is 1:(1.5-2.5); the volume ratio of the mole of 2,3-diaminophenazine to ethanol in step 1 is 1 mol:(50-56) L. The rest is the same as specific embodiment 1.

[0045] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that the ultrasonic treatment in step 1 is carried out at a power of 40W to 60W for 55min to 65min. The rest is the same as specific implementation method 1 or 2.

[0046] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that: the mass ratio of the solid crude product in step 2 to the volume ratio of methanol is 1 g: (48-52) L; the dialysis in step 2 is specifically performed using a dialysis bag with a molecular weight cutoff of 500 Da to 1000 Da for 24 h to 28 h. Others are the same as specific embodiments 1 to 3.

[0047] Specific embodiment 5: This embodiment is different from specific embodiments 1 to 4 in that: the washing in step 2 is washing with ethanol and water in sequence; the freeze drying in step 2 is freeze drying at a temperature of -80°C to -60°C for 1h to 1.2h. The rest is the same as specific embodiments 1 to 4.

[0048] Specific implementation method 6: This implementation method is an application of a red light carbon dot material, which is used in the visualization detection of pH and heavy metal ions.

[0049] Specific embodiment 7: This embodiment is different from specific embodiment 6 in that: when it is used for pH visualization detection: the red light carbon dot material is dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution is dispersed in an ethanol-HEPES buffer solution with a pH of 1.51 to 7.11 to obtain an ethanol-HEPES buffer solution of R-CDs;

[0050] When the pH value decreases, the fluorescence of the ethanol-HEPES buffer of R-CDs increases, accompanied by the solution fluorescence color deepening red; when the pH increases, the fluorescence of the ethanol-HEPES buffer of R-CDs decreases until it is quenched, accompanied by the solution fluorescence color changing from red to colorless. The rest is the same as the sixth embodiment.

[0051] Specific embodiment eight: This embodiment differs from specific embodiment six or seven in that: the concentration of the red light carbon dot material in the R-CDs solution is 30mg / L to 40mg / L; the concentration of the red light carbon dot material in the R-CDs ethanol-HEPES buffer is 1mg / L to 2mg / L; the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer is 1:(0.8 to 1.2). Others are the same as specific embodiment six or seven.

[0052] Specific embodiment 9: This embodiment is different from any one of specific embodiments 6 to 8 in that when it is used for heavy metal ion detection: the red light carbon dot material is dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution is dispersed in ethanol-HEPES buffers of different pH values ​​to obtain an ethanol-HEPES buffer of R-CDs, and an aqueous solution containing heavy metal ions is added to the ethanol-HEPES buffer of R-CDs; the heavy metal ions are Na +, K + Mg 2+ , Ca 2+ 、Cd 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ , Mn 2+ , Pb 2+ , Ba 2+ , Fe 3+ , Fe 2+ , Cu 2+ , Hg 2+ or Cr 3+ ;

[0053] When the pH of ethanol-HEPES buffer is 3, Fe 3+ The red fluorescence of R-CDs in the ethanol-HEPES buffer solution was quenched, and the solution fluorescence color changed from red to colorless. When the pH of the ethanol-HEPES buffer solution was 6, Cu 2+ The red fluorescence of R-CDs in the ethanol-HEPES buffer was quenched, and the solution fluorescence color changed from red to colorless. When the pH of the ethanol-HEPES buffer was 6, Fe 3+ or Cr 3+ Then the red fluorescence color of the ethanol-HEPES buffer of R-CDs is deepened. The rest is the same as the sixth to eighth embodiments.

[0054] Specific embodiment 10: This embodiment is different from specific embodiments 6 to 9 in that: the concentration of the red light carbon dot material in the R-CDs solution is 30 mg / L to 40 mg / L; the concentration of the red light carbon dot material in the R-CDs ethanol-HEPES buffer is 1 mg / L to 2 mg / L; the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer is 1:(0.8 to 1.2). Others are the same as specific embodiments 6 to 9.

[0055] The following examples are used to verify the beneficial effects of the present invention:

[0056] Embodiment 1:

[0057] A method for preparing a red light carbon dot material is carried out according to the following steps:

[0058] 1. Add 2,3-diaminophenazine, p-aminobenzenesulfonic acid and boric acid to ethanol in sequence, then ultrasonically treat for 1 hour at a power of 50 W, then react at a constant temperature of 180° C. for 10 hours, and finally cool naturally to room temperature to obtain a reaction system;

[0059] The molar ratio of the 2,3-diaminophenazine to p-aminobenzenesulfonic acid is 1:3; the molar ratio of the 2,3-diaminophenazine to boric acid is 1:2; the volume ratio of the molar ratio of the 2,3-diaminophenazine to ethanol is 1 mol:55.3 L;

[0060] 2. Filter the system after the reaction, and then wash it with ethanol and water as washing liquids in turn to obtain a solid crude product, dissolve the solid crude product in methanol, and then dialyze it for 24 hours using a dialysis bag with a molecular weight cutoff of 1000Da, replace the methanol dialysate every 6 hours, and finally freeze-dry it at a temperature of -60°C for 1 hour to obtain a purple solid, i.e., red light carbon dot material, abbreviated as R-CDs;

[0061] The mass ratio of the solid crude product to the volume of methanol is 1g:50L.

[0062] The main reagents: 2,3-diaminophenazine, p-aminobenzenesulfonic acid, boric acid, and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) were purchased from Inokai Reagent Company. Sulfates and hydrochlorides corresponding to different cations were purchased from Chongqing Chuandong Chemical Co., Ltd.; the water used in the experiment was secondary water. All drugs and reagents were not further purified.

[0063] (1) Structural characterization and analysis of R-CDs:

[0064] Figure 2 FT-IR and XPS images of R-CDs prepared in Example 1, (a) is FT-IR, (b) is XPS total spectrum, (c) is C1s fine spectrum, (d) is N1s fine spectrum, (e) is O1s fine spectrum, (f) is S2p ​​fine spectrum; IR and XPS are used to determine the surface composition and chemical state of R-CDs. IR spectrum ( Figure 2 a) 3439cm -1 The absorption is attributed to the stretching vibration of -OH / NH2. The characteristic absorption of C=N and NH appears at 1600, 1521, and 1404 cm -1 The characteristic absorption of CO / O=S=O and -SO3H is located at 1228cm -1 、1093cm -1 . XPS spectrum ( Figure 2 b) shows that the carbon quantum dot material is composed of carbon (61.44%), nitrogen (12.65%), oxygen (13.91%) and sulfur (2.01%) elements. The detailed spectrum further shows that the C1s splitting peak ( Figure 2 c) are 284.80 eV (CC / C=C) and 285.98 eV (CN / CS / CO). The N 1s split peaks are 400.11 and 398.59 eV for pyridine and pyrrole N atomic absorption peaks, respectively. Figure 2 d). The O1s split peaks are located at 531.75 and 533.54 eV ( Figure 2 e). In the fine spectrum of S2p, split peaks of C-SO3-C (168.15 eV) and -SO3H (169.3 eV) can be observed ( Figure 2 f). The results show that there are functional groups such as C=N, CN, CO, -NH2, and -SO3H on the surface of carbon quantum dot materials.

[0065] Figure 3 TEM (a), HR-TEM (b), Raman spectrum (c) and XRD pattern (d) of the R-CDs prepared in Example 1; Figure 3 The TEM image shown in a shows that R-CDs are well-dispersed spherical structures with an average particle size of approximately 1.53±0.32nm. Figure 3 Obvious lattice fringes can be observed in HR-TEM of b, with a spacing of 0.23nm. Raman spectrum ( Figure 3 The ratio of the intensity of the D band to the G band in c) is 1.39, indicating the presence of high disorder defects, which may be caused by tiny graphitized carbon quantum dots embedded in the disordered carbon core, indicating a graphitized structure. Figure 3 The diffraction peak at 26.2° in d) proves that it has a high degree of crystallinity.

[0066] The R-CDs prepared in Example 1 was dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution was dispersed in ethanol-HEPES buffers of different pH values ​​to obtain ethanol-HEPES buffers of R-CDs; the concentration of the red light carbon dot material in the R-CDs solution was 33.33 mg / L; the concentration of the red light carbon dot material in the ethanol-HEPES buffer of R-CDs was 1.67 mg / L; the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer was 1:1; Figure 4 This is a picture of the R-CDs prepared in Example 1 in an ethanol-HEPES buffer with a pH value of 3.30 to 6.25 under 365nm ultraviolet light radiation; as can be seen from the figure, R-CDs show red light emission in the ethanol-HEPES buffer, and in the range of pH <7, when the pH decreases, the red light of the solution increases, and when the pH increases, the red light of the solution weakens or even completely quenches.

[0067] (2) Photophysical properties of R-CDs:

[0068] The R-CDs prepared in Example 1 were dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution was dispersed in ethanol to obtain an ethanol solution of R-CDs; the concentration of the red light carbon dot material in the ethanol solution of R-CDs was 1.67 mg / L; and then the ethanol solution of R-CDs was subjected to UV-visible absorption spectrum-fluorescence spectrum and excitation wavelength responsiveness tests, as shown in FIG. Figure 5 (a) to 5(b).

[0069] The R-CDs prepared in Example 1 was dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution was dispersed in different solvents to obtain an R-CDs solvent solution; the concentration of the red light carbon dot material in the R-CDs solvent solution was 1.67 mg / L; the different solvents were tetrahydrofuran, ethanol, chloroform, acetone, acetonitrile, N,N-dimethylformamide, methanol, dimethyl sulfoxide or water; then the R-CDs solvent solution was subjected to a fluorescence solvent effect test, such as Figure 5 (c).

[0070] Figure 5 The UV-visible absorption spectrum-fluorescence spectrum of R-CDs solution (a), excitation wavelength response diagram (b) and solvent effect diagram of fluorescence (c); In ethanol solution, three obvious absorption peaks can be observed in the UV-visible absorption spectrum of R-CDs, which are located at 290nm and 355nm, respectively, which are attributed to the carbon core center sp 2 The absorption around 554nm originates from the n-π* transition of the CN / C=N or O=S=O bond. Under 554nm excitation, the emission of the R-CDs solution is located at 590nm and 660nm, with no obvious excitation wavelength response, such as Figure 5 a and 5b. The carbon dots have obvious solvent response ( Figure 5 c), which may be due to the dipole–dipole interaction between the solvent and R-CDs.

[0071] The R-CDs prepared in Example 1 was dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution was dispersed in an ethanol-HEPES buffer solution at pH = 3 to obtain an ethanol-HEPES buffer solution of R-CDs; the concentration of the red light carbon dot material in the R-CDs solution was 33.33 mg / L; the concentration of the red light carbon dot material in the ethanol-HEPES buffer solution of R-CDs was 1.67 mg / L; the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer solution was 1:1; then the absolute fluorescence lifetime and quantum yield tests were performed, as shown in FIG. Figure 6 .

[0072] Figure 6This is a graph of the absolute fluorescence lifetime and quantum yield of the R-CDs prepared in Example 1 in ethanol-HEPES buffer at pH = 3; in ethanol-HEPES buffer at pH = 3, the fluorescence lifetime and absolute fluorescence quantum yield of R-CDs were determined to be 2.3 ns and 3.47%, respectively.

[0073] (3) Visual sensing of pH by R-CDs:

[0074] The R-CDs red light carbon dot material prepared in Example 1 was dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution was dispersed in ethanol-HEPES buffer solutions of different pH values ​​(1.51 to 7.11) to obtain an ethanol-HEPES buffer solution of R-CDs; the concentration of the red light carbon dot material in the R-CDs solution was 33.33 mg / L; the concentration of the red light carbon dot material in the ethanol-HEPES buffer solution of R-CDs was 1.67 mg / L; the volume ratio of ethanol to HEPES buffer solution in the ethanol-HEPES buffer solution was 1:1; and then a fluorescence spectrum test of pH was performed, as shown in FIG. Figure 7 ;

[0075] Figure 7 The fluorescence spectra of R-CDs prepared in Example 1 in ethanol-HEPES buffer at different pH values ​​(a), the linear relationship between pH and fluorescence intensity (b), and the change in fluorescence intensity of the buffer solution at pH values ​​of 3 and 6 (c); Figure 7 As shown in a, R-CDs have different fluorescence emission intensities at different pH values ​​(1.51-7.11). As the pH value increases, the fluorescence intensity decreases. Figure 4 As shown in the figure, the red light of the solution becomes lighter under the irradiation of 365nm ultraviolet light. In the pH range of 3.3-6.25, the fluorescence intensity of the solution shows a good linear relationship with the pH value ( Figure 7 b) The linear equation obtained by Boltzmann function fitting is Y=1791.11+27507.44 / (1+e (pH-4.99) / 0.5 ), the linear correlation coefficient is 0.99, the pKa is 4.99, and it has a certain pH reciprocating effect ( Figure 7 c) It can be seen that R-CDs have good visual sensing performance for pH.

[0076] (4) Visual detection of heavy metal ions by R-CDs:

[0077] The R-CDs prepared in Example 1 was dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution was dispersed in an ethanol-HEPES buffer solution with a pH of 3 or 6 to obtain an ethanol-HEPES buffer solution of R-CDs; the concentration of the red light carbon dot material in the R-CDs solution was 33.33 mg / L; the concentration of the red light carbon dot material in the ethanol-HEPES buffer solution of R-CDs was 1.67 mg / L; the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer solution was 1:1; 50 μL of various metal ion solutions were respectively added to 2 mL of the ethanol-HEPES buffer solution of R-CDs, and the concentrations of the various metal ion solutions were all 10 -2 M, and then perform fluorescence spectrum test, and the excitation wavelength is 554nm, the slit width is 5nm during the test, such as Figures 8 to 11 ;

[0078] At pH = 3, if the fluorescence of the R-CDs solution is quenched, accompanied by a change in fluorescence color from red to zero, it means that Fe 3+ ; When other conditions remain unchanged and pH = 6.0, if the fluorescence of R-CDs buffer solution is significantly enhanced, it indicates that Fe 3+ or Cr 3+ , while the fluorescence quenching is Cu 2+ ; In addition, when there is no obvious change in the fluorescence of the R-CDs buffer, other heavy metal ions are added.

[0079] The detection sensitivity of R-CDs to heavy metal ions is expressed by the limit of detection (LOD). LOD is calculated by formula (1).

[0080] LOD = (3 × SD) / S (Formula 1)

[0081] Wherein, SD is the standard deviation, and S is the slope of the linear equation corresponding to the concentration of the analyte to be measured and the luminescence intensity of the detection reagent.

[0082] Figure 8 Figure 2 is the fluorescence emission of R-CDs in the presence of different metal ions in ethanol-HEPES buffer at pH = 3 and 554 nm excitation (a), Fe 3+ Fluorescence titration spectrum of (b) and Fe 3+ Titration curve between concentration and solution fluorescence intensity (c); the inset is the calculation of LOD;

[0083] Fig. 9 Figure 2 is the fluorescence emission of R-CDs in the presence of different metal ions in ethanol-HEPES buffer at pH = 6 and 554 nm excitation (a), Fe 3+ Fluorescence titration spectrum of (b) and Fe 3+Titration curve between concentration and solution fluorescence intensity (c); the inset is the calculation of LOD;

[0084] Fig.10 The presence of Cu in the ethanol-HEPES buffer of R-CDs at pH = 6 and 554 nm excitation 2+ Fluorescence titration spectrum (a) and calculation of minimum detection limit (b); the inset is the calculation of LOD;

[0085] Fig.11 The presence of Cr in the ethanol-HEPES buffer of R-CDs at pH = 6 and 554 nm excitation 3+ Fluorescence titration spectrum (a) and calculation of minimum detection limit (b); the inset is the calculation of LOD;

[0086] First, the spectral response of heavy metal ions to R-CDs at different pH values ​​was investigated. When the pH was 3, heavy metal ions (Na+, K+, Mg+) were added to the R-CDs anhydrous ethanol-HEPES buffer. 2+ , Ca 2+ 、Cd 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ , Mn 2+ , Pb 2 + , Ba 2+ , Fe 3+ , Fe 2+ , Cu 2+ , Hg 2+ Cr 3+ ), found Fe 3+ The red fluorescence of the solution is quenched, and the fluorescence color changes from red to zero ( Figure 8 a), other ions have no effect on the spectrum of R-CDs. 3+ During the titration process, the fluorescence intensity of the R-CDs buffer solution gradually weakened. 3+ When the concentration reached 115 μM, the fluorescence was completely quenched. 3+ When the concentration ranged from 0 to 78.34 μM, there was a linear relationship between the fluorescence quenching efficiency of R-CDs [(F0-F) / F0], and Fe 3+ The minimum detection limit is 0.75 μM. Figure 8 c. When pH is 6, Cu 2+ Causes spectral quenching, the solution fluorescence color fades, Fig. 9 a. When pH is 6, Fe 3+ Cr 3+ The fluorescence of R-CDs is enhanced and the red light color of the solution is deepened. Fig. 9a. It can be seen that R-CDs can realize the visual detection of multiple ions in different environments. Among them, in the concentration range of 0 to 56.87 μM, using Fe 3+ The fluorescence titration spectrum of the product was calculated to have a minimum detection limit of 0.20 μM. Fig. 9 b and c. Similar ( Fig.10 , 11), Cu 2+ Cr 3+ The minimum detection limits were 0.12 and 0.90 μM, respectively (Table 1).

[0087] Table 1 R-CDs to Fe 3+ , Cu 2+ Cr 3+ Visual detection sensitivity

[0088]

[0089] The above experimental data have fully demonstrated that R-CDs have application potential in detecting heavy metal ions.

[0090] (5) Research on the mechanism of R-CDs visual detection of heavy metal ions:

[0091] The R-CDs prepared in Example 1 was dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution was dispersed in an ethanol-HEPES buffer solution with a pH of 3 or 6 to obtain an ethanol-HEPES buffer solution of R-CDs; the concentration of the red light carbon dot material in the R-CDs solution was 33.33 mg / L; the concentration of the red light carbon dot material in the ethanol-HEPES buffer solution of R-CDs was 1.67 mg / L; the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer solution was 1:1; 50 μL of various metal ion solutions were respectively added to 2 mL of the ethanol-HEPES buffer solution of R-CDs, and the concentrations of the various metal ion solutions were all 10 -2 M, and then perform fluorescence spectroscopic titration analysis test, such as Figures 12 to 18 .

[0092] Fig.12 is the UV-visible absorption spectra of R-CDs in the presence of different heavy metal ions in ethanol-HEPES buffer at pH = 3 / 6;

[0093] Fig.13 To add Fe to the ethanol-HEPES buffer of R-CDs at pH 3 3+ IR spectra before and after;

[0094] Fig.14 To add Fe to the ethanol-HEPES buffer of R-CDs at pH 6 3+ , Cu2+ Cr 3+ IR spectra before and after;

[0095] Fig.15 To add Fe to the ethanol-HEPES buffer of R-CDs at pH 3 / 6 3+ , Cu 2+ Cr 3+ Comparison of C1s fine spectra before and after;

[0096] Fig.16 is the Fe content of R-CDs in ethanol-HEPES buffer at pH 3 / 6 3+ , Cu 2+ Cr 3+ Comparison of the N1s fine spectra before and after;

[0097] Fig.17 is the Fe content of R-CDs in ethanol-HEPES buffer at pH 3 / 6 3+ , Cu 2+ Cr 3+ Comparison of O1s fine spectra before and after;

[0098] Fig.18 is the Fe content of R-CDs in ethanol-HEPES buffer at pH 3 / 6 3+ , Cu 2+ Cr 3+ Comparison of the fine spectra of S2p before and after;

[0099] Depend on Figure 2 The results of IR and XPS characterization show that the surface of R-CDs is rich in N, S, O and other atomic groups, which are easy to coordinate and complex with heavy metal ions, resulting in the transfer of electrons from heteroatoms to heavy metal ions, thereby causing changes in the electronic environment of carbon dots, and further affecting the photophysical properties of carbon dot materials. In order to further verify, the coordination effect between the two was first investigated using UV-visible absorption spectroscopy. In the presence of heavy metal ions, the UV absorption peaks of R-CDs all underwent a significant red shift, but no new absorption peaks were generated. Fig.12 .Fe 3+ IR spectrum of the R-CDs surface -C=N (1521cm -1 ) and -SO3H(1093cm -1 ) characteristic absorption peaks disappeared, and 1600cm -1 The vibration absorption of NH at 1585 cm -1 ( Fig.13 ). At pH = 6, there is Fe 3+ / Cr 3+ / Cu 2+After that, the characteristic peaks at -C=N, -SO3H, and NH on the surface of R-CDs also disappeared or moved ( Fig.14 In addition, XPS characterization results show that ( Figure 15-18 ), after adding metal ions at two pH values, the positions of binding energies of C 1s, N 1s, O 1s, and S2p fine spectra shifted and the elemental composition changed compared with those before addition. The above characterizations collectively indicate that there is coordination complexation between R-CDs and heavy metal ions, and that N and S element groups are the key factors for highly sensitive and selective detection.

Claims

1. A method for preparing red light carbon dot material, characterized in that It is carried out in the following steps:

1. Add 2,3-diaminophenazine, p-aminobenzenesulfonic acid and boric acid to ethanol in sequence, then perform ultrasonic treatment, and then react at a constant temperature of 180°C to 200°C for 8h to 10h, and finally cool naturally to room temperature to obtain a reaction system; 2. The system after the reaction is filtered and washed in sequence to obtain a solid crude product, the solid crude product is dissolved in methanol, and then dialyzed and freeze-dried in sequence to obtain a red light carbon dot material.

2. The method for preparing a red light carbon dot material according to claim 1, characterized in that The molar ratio of 2,3-diaminophenazine to p-aminobenzenesulfonic acid in step 1 is 1:(2.5-3.5); the molar ratio of 2,3-diaminophenazine to boric acid in step 1 is 1:(1.5-2.5); the volume ratio of the mole of 2,3-diaminophenazine to ethanol in step 1 is 1 mol:(50-56)L.

3. The method for preparing a red light carbon dot material according to claim 1, characterized in that The ultrasonic treatment described in step 1 is specifically carried out at a power of 40W to 60W for 55min to 65min.

4. The method for preparing a red light carbon dot material according to claim 1, characterized in that The mass ratio of the solid crude product in step 2 to the volume of methanol is 1 g: (48-52) L; the dialysis in step 2 is specifically performed using a dialysis bag with a molecular weight cutoff of 500 Da to 1000 Da for 24 h to 28 h.

5. The method for preparing a red light carbon dot material according to claim 1, characterized in that The washing in step 2 is performed by sequentially using ethanol and water as washing liquids; the freeze drying in step 2 is specifically performed at a temperature of -80°C to -60°C for 1h to 1.2h.

6. The use of a red light carbon dot material prepared as claimed in claim 1, characterized in that It is used for pH and heavy metal ion visualization detection.

7. The use of a red light carbon dot material according to claim 6, characterized in that When it is used for pH visualization detection: the red light carbon dot material is dissolved in methanol to obtain a R-CDs solution, and then the R-CDs solution is dispersed in an ethanol-HEPES buffer solution with a pH of 1.51 to 7.11 to obtain an ethanol-HEPES buffer solution of R-CDs; When the pH value decreases, the fluorescence of R-CDs in ethanol-HEPES buffer increases, accompanied by a deepening of the red color of the solution fluorescence; when the pH value increases, the fluorescence of R-CDs in ethanol-HEPES buffer decreases until it is quenched, accompanied by a change of the solution fluorescence color from red to colorless.

8. The use of a red light carbon dot material according to claim 7, characterized in that The concentration of the red light carbon dot material in the R-CDs solution is 30 mg / L to 40 mg / L; the concentration of the red light carbon dot material in the ethanol-HEPES buffer of the R-CDs is 1 mg / L to 2 mg / L; the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer is 1:(0.8 to 1.2).

9. The use of a red light carbon dot material according to claim 6, characterized in that When it is used for heavy metal ion detection, the red light carbon dot material is dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution is dispersed in an ethanol-HEPES buffer solution of different pH values ​​to obtain an ethanol-HEPES buffer solution of R-CDs, and an aqueous solution containing heavy metal ions is added to the ethanol-HEPES buffer solution of R-CDs; the heavy metal ions are Na + , K + Mg 2+ , Ca 2+ 、Cd 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ , Mn 2 + , Pb 2+ , Ba 2+ , Fe 3+ , Fe 2+ , Cu 2+ , Hg 2+ or Cr 3+ ; When the pH of ethanol-HEPES buffer is 3, Fe 3+ The red fluorescence of R-CDs in the ethanol-HEPES buffer solution was quenched, and the solution fluorescence color changed from red to colorless. When the pH of the ethanol-HEPES buffer solution was 6, Cu 2+ The red fluorescence of R-CDs in the ethanol-HEPES buffer was quenched, and the solution fluorescence color changed from red to colorless. When the pH of the ethanol-HEPES buffer was 6, Fe 3+ or Cr 3+ Then the red fluorescence color of R-CDs in ethanol-HEPES buffer deepened.

10. The use of a red light carbon dot material according to claim 9, characterized in that The concentration of the red light carbon dot material in the R-CDs solution is 30 mg / L to 40 mg / L; the concentration of the red light carbon dot material in the ethanol-HEPES buffer of the R-CDs is 1 mg / L to 2 mg / L; the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer is 1:(0.8 to 1.2).

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