A preparation method and application of red light carbon dot material

Abstract

A method for preparing a red light carbon dot material and its application, which belongs to the technical field of composite material preparation and pH and heavy metal ion detection. The present invention aims to solve the problem that existing red light carbon quantum dot materials cannot eliminate cross-interference between metal ions and cannot achieve selective detection of heavy metal ions under strong acid conditions. Method: 1. Add 2,3-diaminophenazine, p-aminobenzenesulfonic acid and boric acid to ethanol in sequence, followed by ultrasonic treatment and constant temperature reaction; 2. Filter, wash, dialyze and freeze-dry. Application: It is used for pH and heavy metal ion visualization detection. The present invention is used for the preparation of red light carbon dot materials and their application.

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 significant threat to both human health and the ecological environment. Heavy metal ions are highly toxic and carcinogenic, and absorption by the human body can cause symptoms such as developmental delays, mental discomfort, nausea, vomiting, and diarrhea. Long-term exposure to heavy metal-contaminated environments can also lead to acute and chronic diseases such as kidney and liver dysfunction, congenital anomalies, and various cancers. Certain heavy metals, such as mercury, cadmium, and chromium, can also cause specific damage to the nervous, hematopoietic, and respiratory systems. When heavy metal ions enter water bodies, they disrupt the ecological balance of aquatic organisms, affecting their survival and reproduction. Through the food chain, heavy metal ions can accumulate in organisms, posing a threat to human health. Heavy metal pollution also damages soil fertility, impacting the growth and yield of crops.

[0003] Currently, commonly used treatment methods for heavy metal ion pollution 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 the high accuracy of the analysis results. 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 that 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, biomedicine and other fields. At present, the detection of Hg in ethanol aqueous solution has been achieved using red light carbon quantum dots. 2+ 、Cu 2+ and Fe 3+ Visual detection of carbon dot solutions has been proposed [Wang J, Fu J, Chen M, Zhang J, Mater. Today Chem., 2024, 41: 102331]. Unfortunately, all three heavy metal ions quench the fluorescence of carbon dot solutions, so cross-interference between them cannot be eliminated, which limits 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 using red light carbon quantum dot materials under extreme environments (such as strong acid conditions). Summary of the Invention

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

[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 ultrasonicate, 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 reaction system is filtered and washed in sequence to obtain a solid crude product, which is dissolved in methanol and then dialyzed and freeze-dried in sequence to obtain a red light-emitting 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 prepares carbon quantum dots (R-CDs) by solvent thermal method under boric acid catalysis; 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, in 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, thereby realizing the visual detection of heavy metal ions.

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

[0013] The surface composition of the carbon dots was confirmed by infrared spectroscopy and X-ray photoelectron spectroscopy, and transmission electron microscopy scanning results showed that the average particle size was about 1.53 nm, 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 fluorescence in ethanol-HEPES buffer. When the pH value varied from 1.51 to 7.11, the higher the pH value, the weaker the red fluorescence of R-CDs in ethanol-HEPES buffer, while the lower the pH value, 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 from this 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 selective detection of heavy metal ions under strong acid conditions.

[0017] Figures in the specification

[0018] Figure 1 Schematic diagram of the preparation of the red light-emitting carbon dot material and the visual detection of heavy metal ions of the present invention;

[0019] Figure 2 FT-IR and XPS spectra 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 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 irradiation;

[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 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);

[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 shows the calculation of LOD;

[0026] Figure 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 shows the calculation of LOD;

[0027] Figure 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 the minimum detection limit (b); the inset shows the calculation of LOD;

[0028] Figure 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 the minimum detection limit (b); the inset shows the calculation of LOD;

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

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

[0031] Figure 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] Figure 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] Figure 16 Fe in ethanol-HEPES buffer of R-CDs at pH 3 / 6 3+ 、Cu 2+ Cr 3+ Comparison of N1s fine spectra before and after;

[0034] Figure 17 Fe in ethanol-HEPES buffer of R-CDs at pH 3 / 6 3+ 、Cu 2+ Cr 3+ Comparison of O1s fine spectra before and after;

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

[0036] Specific embodiment 1: This embodiment 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 ultrasonicate, 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 reaction system is filtered and washed in sequence to obtain a solid crude product, which is dissolved in methanol and then dialyzed and freeze-dried in sequence to obtain a red light-emitting carbon dot material.

[0039] The beneficial effects of this embodiment are:

[0040] In this embodiment, the surface composition of the carbon dots was confirmed by infrared spectroscopy and X-ray photoelectron spectroscopy. Transmission electron microscopy scanning results showed that the average particle size was 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 fluorescence in ethanol-HEPES buffer. When the pH value varied from 1.51 to 7.11, the higher the pH value, the weaker the red fluorescence of R-CDs in ethanol-HEPES buffer, while the lower the pH value, 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 this embodiment solves the problem 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.

[0044] Specific embodiment 2: This embodiment differs 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); and the volume ratio of 2,3-diaminophenazine to ethanol in step 1 is 1 mol:(50-56) L. Other aspects are the same as specific embodiment 1.

[0045] Specific embodiment 3: This embodiment differs from specific embodiment 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. Other aspects are the same as specific embodiment 1 or 2.

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

[0047] Specific embodiment 5: This embodiment differs from Specific embodiments 1 to 4 in that the washing in step 2 is performed sequentially using ethanol and water as washing liquids; and the freeze-drying in step 2 is performed at a temperature of -80°C to -60°C for 1 to 1.2 hours. Other aspects are the same as Specific embodiments 1 to 4.

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

[0049] Specific embodiment 7: This embodiment differs from specific embodiment 6 in that: when 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 R-CDs ethanol-HEPES buffer solution;

[0050] When the pH value decreases, the fluorescence of R-CDs in the ethanol-HEPES buffer solution increases, and the red color of the solution fluorescence deepens; when the pH value increases, the fluorescence of R-CDs in the ethanol-HEPES buffer solution decreases until it is quenched, and the solution fluorescence color changes from red to colorless. Other aspects are the same as those of the sixth embodiment.

[0051] Specific embodiment 8: This embodiment differs from either specific embodiment 6 or 7 in that the concentration of the red-light-emitting carbon dot material in the R-CDs solution is 30 mg / L to 40 mg / L; the concentration of the red-light-emitting carbon dot material in the R-CDs ethanol-HEPES buffer is 1 mg / L to 2 mg / L; and the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer is 1:(0.8-1.2). Other aspects are the same as specific embodiment 6 or 7.

[0052] Specific embodiment 9: This embodiment differs from any one of specific embodiments 6 to 8 in that: when 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 fluorescence color of the solution changed from red to colorless. When the pH of the ethanol-HEPES buffer solution was 6, the addition of Cu 2+ The red fluorescence of R-CDs in the ethanol-HEPES buffer solution was quenched, and the fluorescence color of the solution changed from red to colorless. When the pH of the ethanol-HEPES buffer solution was 6, Fe 3+ or Cr 3+ Then, the red fluorescence color of the ethanol-HEPES buffer of the R-CDs is deepened. Other steps are the same as those in the sixth to eighth embodiments.

[0054] Specific embodiment 10: This embodiment differs from any one of specific embodiments 6 to 9 in that the concentration of the red-light-emitting carbon dot material in the R-CDs solution is 30 mg / L to 40 mg / L; the concentration of the red-light-emitting carbon dot material in the R-CDs ethanol-HEPES buffer is 1 mg / L to 2 mg / L; and the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer is 1:(0.8-1.2). Other aspects 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] Example 1:

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

[0058] 1. 2,3-Diaminophenazine, p-aminobenzenesulfonic acid and boric acid were added to ethanol in sequence, and then ultrasonically treated at a power of 50 W for 1 hour, and then kept at a constant temperature of 180°C for 10 hours, and finally cooled 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 2,3-diaminophenazine to ethanol is 1 mol:55.3 L;

[0060] Second, the reaction system was filtered and then washed with ethanol and water in sequence to obtain a solid crude product. The solid crude product was dissolved in methanol and then dialyzed for 24 hours using a dialysis bag with a molecular weight cutoff of 1000 Da, with the methanol dialyzate replaced every 6 hours. Finally, the product was freeze-dried at -60°C for 1 hour to obtain a purple solid, namely 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 Co., Ltd. The sulfates and hydrochlorides corresponding to different cations were purchased from Chongqing Chuandong Chemical Co., Ltd. All water used in the experiments 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) is 284.80eV (CC / C=C), 285.98eV (CN / CS / CO). The N 1s split peaks are pyridine and pyrrole N atomic absorption peaks at 400.11 and 398.59eV 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, the split peaks of C-SO3-C (168.15eV) and -SO3H (169.3eV) 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 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 intensity ratio 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 high crystallinity.

[0066] 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-HEPES buffer solutions of different pH values ​​to obtain R-CDs ethanol-HEPES buffer solutions; 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 R-CDs ethanol-HEPES buffer solution was 1.67 mg / L; and the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer solution was 1:1; Figure 4 The R-CDs prepared in Example 1 were photographed in an ethanol-HEPES buffer solution with a pH range of 3.30 to 6.25 under 365 nm UV light. The figure shows that the R-CDs exhibit red light emission in the ethanol-HEPES buffer solution. Within the pH range of <7, the red light of the solution increases as the pH decreases, and decreases or is even completely quenched as the pH increases.

[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 R-CDs ethanol solution; the concentration of the red light carbon dot material in the R-CDs ethanol solution was 1.67 mg / L; and then the R-CDs ethanol solution 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 were dissolved in methanol to obtain an R-CDs solution, and then the R-CDs solution was dispersed in different solvents to obtain R-CDs solvent solutions; 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; and the R-CDs solvent solution was then subjected to a fluorescence solvent effect test, as shown in FIG. Figure 5 (c).

[0070] Figure 5 The UV-visible absorption spectrum-fluorescence spectrum (a), excitation wavelength response diagram (b), and fluorescence solvent effect diagram (c) of R-CDs solution; in ethanol solution, the UV-visible absorption spectrum of R-CDs can observe three obvious absorption peaks, located at 290nm and 355nm, respectively, which are attributed to the carbon core center sp 2 The absorption around 554nm is due to 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 were 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 R-CDs ethanol-HEPES buffer solution; 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 R-CDs ethanol-HEPES buffer solution was 1.67 mg / L; the volume ratio of ethanol to HEPES buffer in the ethanol-HEPES buffer solution was 1:1; and 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 R-CDs ethanol-HEPES buffer solutions; 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 R-CDs ethanol-HEPES buffer solution was 1.67 mg / L; the volume ratio of ethanol to HEPES buffer solution in the ethanol-HEPES buffer solution was 1:1; and 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, as shown in Figure 4 As shown in the figure, the red light of the solution becomes lighter under the 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 were 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 and the slit width is 5nm during the test. 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+ ; Other conditions remain unchanged, when pH = 6.0, if the fluorescence of R-CDs buffer solution is significantly enhanced, it indicates that Fe 3+ or Cr 3+ , while fluorescence quenching is caused by Cu 2+ ; In addition, when there is no obvious change in the fluorescence of 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). The LOD is calculated by formula (1).

[0080] LOD = (3 × SD) / S (Equation 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 shows the calculation of LOD;

[0083] Figure 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 shows the calculation of LOD;

[0084] Figure 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 the minimum detection limit (b); the inset shows the calculation of LOD;

[0085] Figure 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 the minimum detection limit (b); the inset shows 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 reaches 115 μM, the fluorescence is 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 the Fe 3+ The minimum detection limit is 0.75 μM. Figure 8 c. When pH is 6, Cu 2+ Causes spectral quenching and the fluorescence color of the solution fades. Figure 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. Figure 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, the Fe 3+ The fluorescence titration spectrum of , the minimum detection limit was calculated to be 0.20μM, Figure 9 b and c. Similar ( Figure 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 were 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 spectrometric titration analysis test, such as Figures 12 to 18 .

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

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

[0094] Figure 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] Figure 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] Figure 16 Fe in ethanol-HEPES buffer of R-CDs at pH 3 / 6 3+ 、Cu 2+ Cr 3+ Comparison of N1s fine spectra before and after;

[0097] Figure 17 Fe in ethanol-HEPES buffer of R-CDs at pH 3 / 6 3+ 、Cu 2+ Cr 3+ Comparison of O1s fine spectra before and after;

[0098] Figure 18 Fe in ethanol-HEPES buffer of R-CDs 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 atomic groups such as N, S, and O, which makes it easy to coordinate and complex with heavy metal ions, resulting in the transfer of electrons from heteroatoms to heavy metal ions. This changes the electronic environment of carbon dots, thereby affecting the photophysical properties of carbon dot materials. In order to further verify this, 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. Figure 12 .Fe 3+ IR spectrum of the presence of R-CDs at pH = 3, the surface -C = N (1521 cm -1 ) and -SO3H(1093cm -1 ) characteristic absorption peaks disappeared, and 1600cm -1 The vibration absorption of NH at 1585 cm -1 ( Figure 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 disappear or shift ( Figure 14 ). In addition, XPS characterization results show that ( Figure 15-18 ). After adding metal ions at two pH values, the C 1s, N 1s, O 1s, and S2p fine spectra all shifted in binding energy and elemental composition compared to the pre-addition conditions. These characterizations collectively demonstrate the existence of coordination complexation between R-CDs and heavy metal ions, with the N and S groups being key factors in their 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 ultrasonicate, 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 reaction system is filtered and washed in sequence to obtain a solid crude product, which is dissolved in methanol and then dialyzed and freeze-dried in sequence to obtain a red light-emitting 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 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 1g:(48-52)L; the dialysis in step 2 is specifically performed using a dialysis bag with a molecular weight cut-off of 500Da-1000Da for 24h-28h.

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 1 hour to 1.2 hours.

6. Application of a red light carbon dot material prepared as claimed in claim 1, characterized in that It is used for visual detection of pH and heavy metal ions.

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 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 R-CDs ethanol-HEPES buffer solution; 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 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 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).

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 R-CDs solution, and then the R-CDs solution is dispersed in ethanol-HEPES buffer of different pH values ​​to obtain R-CDs ethanol-HEPES buffer, and an aqueous solution containing heavy metal ions is added to the R-CDs ethanol-HEPES buffer; 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 fluorescence color of the solution changed from red to colorless. When the pH of the ethanol-HEPES buffer solution was 6, the addition of Cu 2+ The red fluorescence of R-CDs in the ethanol-HEPES buffer solution was quenched, and the fluorescence color of the solution changed from red to colorless. When the pH of the ethanol-HEPES buffer solution 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 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).

Images