A nitrogen, silicon, and sulfur co-doped graphene quantum dot and its preparation method and application

Abstract

The present invention provides nitrogen-, silicon-, and sulfur-codoped graphene quantum dots (GQDs) prepared by hydrothermal synthesis from waste carbon powder and reduced glutathione, wherein the mass ratio of waste carbon powder to reduced glutathione is 2:(4.5-5.5). The prepared GQDs exhibit high quantum yield, excellent stability, good water solubility, and good fluorescence properties. A N,Si,S-GQDs / OPD ratiometric fluorescent probe for autocatalytic rapid visual detection of Ag(I) and Fe(III) has been established. OPD is rapidly oxidized by Ag(I) / Fe(Ⅲ) to generate 2,3-diaminophenazine (oxOPD). Due to the inner filter effect between oxOPD and N,Si,S-GQDs, the fluorescence of N,Si,S-GQDs is significantly quenched. With the increase of Ag(I) / Fe(Ⅲ) concentration, the fluorescence of N,Si,S-GQDs at 440nm gradually weakens, while the fluorescence of oxOPD at 560nm gradually increases. Under ultraviolet light, the color of the solution gradually changes from blue to orange-yellow, enabling semi-quantitative visual detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluorescent nanomaterials, and in particular relates to nitrogen, silicon and sulfur co-doped graphene quantum dots, and a preparation method and application thereof. Background Art

[0002] In the past few decades, researchers have proposed a variety of methods and technologies for detecting heavy metal ions, including inductively coupled plasma mass spectrometry, electrochemical methods, high performance liquid chromatography, atomic absorption spectroscopy, fluorescence and colorimetric analysis. Chinese patent CN114894757A discloses a method for detecting various heavy metal ions using lead-doped PEG-passivated graphene quantum dot fluorescent probes. Although this method can detect Fe 3+ 、Cu 2+ 、Ag + 、Co 2+ 、Ni 2+ 、Mn 2+ and Pb 2+ etc., but Fe 3+ The LOD value of Ag was 8.56 μmol / L (ie 0.476 μg / mL). + The LOD value is 10.29 μmol / L (i.e. 1.111 μg / mL), which cannot meet the requirements of drinking water testing; in addition, its preparation method is too complicated and cannot achieve visual detection, making it inconvenient to operate.

[0003] Therefore, it is necessary to propose an alternative solution that has a low detection limit, can meet the needs of drinking water testing, and can achieve visual detection and convenient operation. Summary of the Invention

[0004] In light of this, the present invention provides a simple, pollution-free, and cost-effective synthesis strategy. Using resin from waste carbon powder as a carbon source, silicon dioxide from carbon powder additives as a silicon source, and reduced glutathione (GSH) as a nitrogen and sulfur source, nitrogen-, silicon-, and sulfur-co-doped graphene quantum dots were successfully synthesized via a one-pot hydrothermal method. To achieve this objective, the present invention employs the following technical solutions:

[0005] A nitrogen, silicon and sulfur co-doped graphene quantum dot is prepared from waste carbon powder and reduced glutathione by a hydrothermal synthesis method; wherein the mass ratio of the waste carbon powder to the reduced glutathione is 2:(4.5-5.5).

[0006] In some specific embodiments, preferably, the mass ratio of waste carbon powder to reduced glutathione is 2:5.

[0007] The preparation method of the graphene quantum dots described above comprises the following steps: waste carbon powder, reduced glutathione and secondary deionized water are placed in a reactor, dissolved, reacted at 180-200° C. for 3.5-4.5 hours, cooled after the reaction is completed, and filtered to obtain a yellow liquid, which is the graphene quantum dots.

[0008] Furthermore, the material-liquid ratio of the mixture of waste carbon powder and reduced glutathione to the secondary deionized water is (6.5-7.5):100.

[0009] In some specific embodiments, preferably, the material-liquid ratio of the mixture of waste carbon powder and reduced glutathione to the secondary deionized water is 7:100.

[0010] Furthermore, the filtration is performed using a water-based filter head with a pore size of 0.2 to 0.3 μm.

[0011] Furthermore, the dissolution is performed by ultrasound, the ultrasound power is 90 to 110 W, and the ultrasound time is 4 to 6 minutes.

[0012] A ratiometric fluorescent probe is prepared by mixing the above-mentioned graphene quantum dots, o-phenylenediamine and BR buffer.

[0013] Furthermore, the concentration of o-phenylenediamine in the ratiometric fluorescent probe is 200-1000 μM, and the pH of the BR buffer in the ratiometric fluorescent probe is 7-12.

[0014] In some specific embodiments, preferably, the concentration of o-phenylenediamine in the ratiometric fluorescent probe is 600 μM, and the pH of the BR buffer in the ratiometric fluorescent probe is 8.

[0015] The preparation method of the ratio fluorescent probe comprises the following steps: mixing graphene quantum dots, o-phenylenediamine, and BR buffer, shaking at room temperature, and reacting in the dark for 0.8 to 1.2 minutes. The ratio fluorescent probe is obtained after the reaction is completed.

[0016] Application of the above ratiometric fluorescent probe in the detection of Ag(I) and Fe(III) in water.

[0017] When the above ratio fluorescence probe is used to detect Ag(I) in water, triethanolamine is added as a masking agent to effectively eliminate the interference of Fe(III);

[0018] When detecting Fe(III) in water, NaCl is added as a masking agent to effectively eliminate the interference of Ag(I).

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention utilizes the resin in waste carbon powder as a carbon source, the silicon dioxide in the carbon powder additive as a silicon source, and reduced glutathione (GSH) as a nitrogen source and a sulfur source to successfully synthesize nitrogen, silicon, and sulfur co-doped graphene quantum dots (N,Si,S-GQDs) through a one-pot hydrothermal method; and establishes a new method for the rapid visualization detection of Ag(I) and Fe(III) by autocatalytic fluorescence probe using N,Si,S-GQDs / OPD ratio; the entire preparation scheme is simple, pollution-free, and cost-effective.

[0021] (2) The fluorescence quantum yield of the N, Si, S-GQDs prepared by the present invention is 14.13%; the fluorescence intensity of the N, Si, S-GQDs remains basically unchanged within four months, and has good stability.

[0022] (3) The detection limits (LODs) of the N,Si,S-GQDs / OPD ratiometric fluorescent probe prepared by the present invention for Ag(Ⅰ) and Fe(Ⅲ) are 0.016 μg / mL and 0.010 μg / mL, respectively; and it can specifically detect Ag(Ⅰ) and Fe(Ⅲ) without being affected by the presence of a variety of other interfering heavy metals; visual detection can be achieved through color change differences under 365 nm ultraviolet light, and the operation is convenient and simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Transmission electron microscopy (a); X-ray diffraction (b); Zeta potential (c); Fourier transform infrared (d) spectrum of the material prepared in Example 1 of the present invention.

[0024] Figure 2 This is the XPS characterization diagram of the material prepared in Example 1 of the present invention.

[0025] Figure 3 These are the fluorescence spectrum and UV-visible absorption spectrum of the material prepared in Example 1 of the present invention.

[0026] Figure 4 This is a fluorescence spectrum of the material prepared in Example 1 of the present invention and quinine sulfate.

[0027] Figure 5 Graph showing the effects of pH (a), sodium chloride concentration (b) and storage time (c) on the fluorescence intensity of the material prepared in Example 1.

[0028] Figure 6 Schematic diagram of the process of preparing N,Si,S-GQDs by one-pot hydrothermal method and its fluorescence quenching mechanism for detecting Ag(Ⅰ) and Fe(Ⅲ).

[0029] Figure 7Effect of pH value on the fluorescence intensity of N,Si,S-GQDs (a); Ag(Ⅰ)+OPD+N,Si,S-GQDs; Ag(Ⅰ)+OPD (b); fluorescence images of N,Si,S-GQDs before and after adding oxOPD (c).

[0030] Figure 8 The OPD concentration optimization results for N,Si,S-GQDs / OPD detection of Ag(Ⅰ) are shown.

[0031] Figure 9 Time optimization results for detecting Ag(Ⅰ) using N,Si,S-GQDs / OPD.

[0032] Figure 10 Figures 2 and 3 show the selectivity of the N, Si, S-GQDs / OPD ratio fluorescence probe for metal ions (a) and the masking experimental results of Fe(Ⅲ) (b); Ag(Ⅰ) (c).

[0033] Figure 11 The results show the effects of different concentrations of Ag(Ⅰ) (a) and Fe(Ⅲ) (b) on the N, Si, S-GQDs / OPD ratio fluorescence probe.

[0034] Figure 12 UV-visible absorption spectra of N,Si,S-GQDs, oxOPD, and N,Si,S-GQDs+oxOPD (a); transmission electron microscopy image of silver nanoparticles synthesized during the reaction of Ag(Ⅰ) and OPD (b); UV-visible absorption spectra of phen, phen+OPD, and phen+OPD+Fe(Ⅲ) (c); fluorescence excitation and emission spectra of N,Si,S-GQDs and UV-visible absorption and fluorescence spectra of oxOPD (d); fluorescence lifetime curves of N,Si,S-GQDs before and after addition of oxOPD under 370 nm excitation (e)

[0035] Figure 13 Visual detection of Ag(Ⅰ) in tap water (a) and Fe(Ⅲ) in lake water (b) using N,Si,S-GQDs / OPD ratiometric fluorescent probe. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to specific embodiments so that those skilled in the art can understand the present invention more clearly.

[0037] Example 1

[0038] This embodiment provides a method for preparing nitrogen, silicon, and sulfur co-doped graphene quantum dots (N,Si,S-GQDs), comprising the following steps: weighing 0.1 g of waste carbon powder (purchased from Youcai Technology Co., Ltd.) and 0.25 g of glutathione (GSH) into a 23 mL high-pressure reactor, then adding 5 mL of secondary deionized water, ultrasonically dissolving for 5 minutes, placing in a forced air drying oven, reacting at 200°C for 4 hours, cooling, filtering with a 0.22 μm aqueous filter head, retaining a yellow liquid, and obtaining N,Si,S-GQDs (concentration of 11 mg / mL), which were stored at 4°C for later use.

[0039] Furthermore, in order to understand the quality and performance of the N, Si, S-GQDs prepared above, the following experiments were conducted.

[0040] Characterization of prepared N,Si,S-GQDs materials.

[0041] The material was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Zeta potential, Fourier transform infrared spectroscopy (FT-IR), and X-ray electron spectroscopy (XPS). Figure 1 、 Figure 2 .

[0042] Figure 1 (a) is a transmission electron micrograph of a synthetic material obtained by reacting waste carbon powder with GSH. The material displays nearly spherical particles uniformly distributed in the solution, with an average particle size of approximately 6.72 nm and a uniform dispersion. The lattice spacing is 0.2115 nm, consistent with the (0110) plane of graphene, indicating that the material possesses graphitic properties.

[0043] Figure 1 (b) is the XRD characterization diagram of the material, showing a strong diffraction peak at 2θ = 26.43°, close to the (0,0,2) plane of graphite, which is consistent with the highly disordered graphene-like structure and other previously reported work on this type of nanomaterials, proving that the material is a graphite-like quantum dot.

[0044] Figure 1 (c) is the Zeta potential result diagram of the synthesized material. The results show that the Zeta potential of N, Si, S-GQDs is -9.14 mV, indicating that the surface of the material is rich in electrons and has a negative charge.

[0045] Figure 1 (d) is the FT-IR infrared spectrum characterization of the synthesized material. The results show that the material has a -1 The broad absorption band at 3219 cm corresponds to the stretching vibration of OH; -1The peak at 2927 cm corresponds to the stretching vibration of NH; -1 The peak at 2500 cm corresponds to the CH stretching vibration in the aromatic ring; -1 The characteristic peak of -SH near the ion source is not obvious, which may be because the thiol group has been decomposed under high temperature and high pressure conditions; 1641cm -1 The peak at 1396 cm corresponds to the stretching vibration of C=O and C=C in the conjugated structure, proving that the material still maintains the structure of graphene. -1 The peak at 1108cm corresponds to the absorption peak of CN, which is the absorption peak of aromatic ring skeleton vibration (there is no aromatic ring skeleton vibration in carbon dots and graphene oxide quantum dots); -1 The peak at 1010cm corresponds to the CC / CH stretching vibration absorption peak (incomplete carbonization of waste carbon powder). GOQDs have no CH bond absorption, indicating that the waste carbon powder has been completely carbonized; -1 The peak at 1003 cm corresponds to the stretching vibration absorption peak of COC, confirming the carbonyl group on the surface, which makes it have good water solubility; -1 The peak at 826 cm corresponds to the stretching vibration absorption peak of O-Si; -1 The peak at 695 cm corresponds to the asymmetric stretching vibration absorption peak of CS; -1 The peak at corresponds to the stretching vibration absorption peak of the secondary amine.

[0046] Figure 2 The XPS characterization diagram of the material is shown in Figure 2(a). 2(a) shows that the material has five peaks at 284.86eV, 531.33eV, 399.89eV, 102.45eV, and 163.34eV, which are attributed to graphite C1s, O 1s, N 1s, Si 2p, and S2p, respectively. The contents of these peaks are 56.95%, 28.27%, 12.48%, 0.93%, and 1.37%. C 1s spectrum ( Figure 2 The five peaks in (b) correspond to CO / C=O (287.95 eV), CN / CS (286.0 eV), CC / C=C (284.75 eV), C-Si (284.3 eV), Organic-C (Graphene) (283.6 eV); O 1s ( Figure 2 The three peaks in (c) correspond to C=O (530.8eV), C-OH / COC (531.4eV), O-Si (532.5eV); N 1s ( Figure 2 The two peaks of (d) correspond to NC (Graphene) (399.7eV), NH (401.2eV); Si 2p ( Figure 2The three peaks of (e) correspond to Si-O (101.6eV), Organic-Si (101.9eV), and Si-C (102.4eV); S2p ( Figure 2 The two peaks in (f) correspond to CSC (163.3 eV, S2p3 / 2) and (164.45 eV, S2p1 / 2), respectively. Consistent with the corresponding FT-IR results, these results further indicate that the graphite-like carbon material is graphene quantum dots containing nitrogen, silicon, and sulfur heteroatoms (N,Si,S-GQDs).

[0047] Optical properties of prepared N,Si,S-GQDs materials.

[0048] Figure 3 The fluorescence spectrum and UV-visible absorption spectrum of the material are shown in Figure 1. The solution is light yellow under fluorescent light and blue under UV light (see the inset). The optimal excitation wavelength λ is shown in the figure. ex The optimal emission wavelength is 370nm. em Generally, the UV-visible absorption spectrum of GQDs has two representative peaks. The UV absorption spectrum (blue line) shows two absorption peaks. There is a sharp absorption peak at 298nm corresponding to the aromatic ring sp 2 The π-π* transition of C=C in the structure; there is a broad absorption peak at 310nm-330nm corresponding to the n-π* transition of C=O or CN, indicating the presence of C=O and C=C groups in N,Si,S-GQDs. Compared with other references, these absorption bands shown in the UV-visible spectrum are slightly offset (10-15nm), which may be due to the doping of heteroatoms, resulting in changes in the electronic transition pathway. In addition, the two luminescence mechanisms of GQDs are widely known: intrinsic emission from the graphene core and extrinsic emission from the surface state. Intrinsic emission is a quantum confinement effect, edge effect, and sp 2 The photoluminescence corresponding to the recombination of electrons and holes in the carbon domains and the extrinsic emission corresponding to the photoluminescence of surface defects are the reasons for which N, Si, S-GQDs have fluorescent properties.

[0049] In addition, in order to verify the yield effect of surface functional groups, quinine sulfate was selected as a reference solution. The UV absorption of N, Si, S-GQDs and quinine sulfate was measured. The absorbance of the corresponding quinine sulfate solution was 0.031, and the absorbance of the N, Si, S-GQDs solution was 0.021. The fluorescence quantum yield of N, Si, S-GQDs was calculated by the integrated fluorescence intensity of the two, as shown in Figure 2. Figure 4 , in λ ex= Under 370nm excitation, the integrated fluorescence intensity of quinine sulfate is 583185, while the integrated fluorescence intensity of N,Si,S-GQDs is 103367. The formula is as follows:

[0050]

[0051] The fluorescence quantum yield of the synthesized N,Si,S-GQDs was calculated to be 14.13% by the formula. R is the fluorescence quantum yield of the reference solution quinine sulfate, which is 0.54, and ψ is the fluorescence quantum yield of the analyte N,Si,S-GQDs; A R , A are the absorbances of quinine sulfate and the analyte N, Si, S-GQDs, respectively; I R , I are the integrated fluorescence intensities of quinine sulfate and the analyte N, Si, S-GQDs, respectively. R and η refer to the refractive indices of quinine sulfate and the analyte N, Si, S-GQDs, respectively, and are all 1.33 here.

[0052] Stability of prepared N,Si,S-GQDs materials.

[0053] As a fluorescent nanomaterial for detection applications, N,Si,S-GQDs have an important significance for studying their fluorescence stability. Due to the protonation and deprotonation ability of the carboxyl group, the acidity of quantum dots may affect their stability. The effect of pH = 2.0-12.0 on the fluorescence intensity of N,Si,S-GQDs was investigated. The results are as follows: Figure 5 As shown in (a), the fluorescence intensity remains basically unchanged when pH = 2.0-12.0. We selected pH 6.0 BR buffer solution for subsequent experiments. In addition, the effect of ion concentration on the fluorescence intensity of N, Si, S-GQDs was also studied. We studied the changes in the fluorescence intensity of N, Si, S-GQDs under 0-50 mg / mL NaCl conditions, as shown in Figure 5 As shown in (b), with the increase of NaCl concentration, the fluorescence intensity of N,Si,S-GQDs did not change significantly, indicating that N,Si,S-GQDs are relatively stable under high ionic strength, making N,Si,S-GQDs able to play the role of fluorescent probe in high ionic concentration solution. By measuring the fluorescence intensity of N,Si,S-GQDs solution at 4℃ every 30 days, it can be seen that Figure 5 The data in (c) show that the fluorescence intensity of N,Si,S-GQDs remains basically unchanged within four months, which means that N,Si,S-GQDs have good stability.

[0054] Example 2

[0055] This example provides a method for preparing a ratiometric fluorescent probe (N,Si,S-GQDs / OPD), comprising the following steps: adding 240 μL of 10 mM o-phenylenediamine (OPD), 35 μL of 11 mg / mL N,Si,S-GQDs, and 625 μL of 40 mM BR buffer (pH = 8) to a 5 mL EP tube, shaking the mixture at room temperature, and allowing it to react in the dark for 1 minute to obtain a N,Si,S-GQDs / OPD ratiometric fluorescent probe.

[0056] Furthermore, in order to understand the detection effect of the N,Si,S-GQDs / OPD prepared above on Ag(Ⅰ) and Fe(Ⅲ) in water and optimize the detection conditions, the following experiments were carried out.

[0057] Sample preparation: Take lake water and tap water samples, filter them with 0.22 μm filter membranes respectively, and collect the filtrate for later use.

[0058] Detection steps for Ag(Ⅰ): 35μL N,Si,S-GQDs (11mg / mL), 240μL OPD (10mM), 32μL 5μg / mL Fe(Ⅲ), 20μL 100μg / mL triethanolamine (TEOA) and 625μL 40mM BR buffer (pH=8) were added to a 5mL EP tube in sequence, and then 200μL lake water and tap water were added to the ratio fluorescence probe solution respectively. Finally, the total volume was adjusted to 4mL with secondary deionized water. After a reaction time of 1min, the fluorescence spectra of all environmental water samples were detected under 370nm excitation using a fluorescence spectrophotometer, and the F560 / F440 value was calculated. The content of Ag(Ⅰ) in the sample solution was calculated based on the obtained standard working straight line.

[0059] Fe(Ⅲ) detection steps: 35μL N,Si,S-GQDs (11mg / mL), 240μL OPD (10mM), 32μL Ag(Ⅰ) (5μg / mL), 200μL NaCl (10mM) and 625μL 40mM B-R buffer (pH=8) were added to a 5mL EP tube in sequence, and then 200μL lake water and tap water were added to the ratio fluorescence probe solution respectively. Finally, the total volume was fixed to 4mL with secondary deionized water. After a reaction time of 1min, the fluorescence spectra of all environmental water samples were detected under 370nm excitation using a fluorescence spectrophotometer to calculate F 560 / F 440 The Fe(Ⅲ) content in the sample solution was calculated based on the obtained standard working straight line.

[0060] Figure 6The preparation process of N,Si,S-GQDs by a one-pot hydrothermal method and their fluorescence quenching mechanism for the detection of Ag(I) and Fe(III) are described. First, using resin from waste toner as a carbon source, silica from toner additives as a silicon source, and reduced glutathione (GSH) as nitrogen and sulfur sources, N,Si,S-GQDs were synthesized with a quantum yield of 14.13% via a one-pot hydrothermal method at 200°C for 4 hours.

[0061] OPD is rapidly oxidized by Ag(I) / Fe(Ⅲ) to generate 2,3-diaminophenazine (oxOPD), which emits orange-yellow fluorescence at 560nm. Due to the inner filter effect between oxOPD and N,Si,S-GQDs, the fluorescence of N,Si,S-GQDs is significantly quenched. As the concentration of Ag(I) / Fe(Ⅲ) increases, the fluorescence of N,Si,S-GQDs at 440nm gradually weakens, while the fluorescence of oxOPD at 560nm gradually increases. The two rise and fall, forming a ratio. Under ultraviolet light, the color of the solution gradually changes from blue to orange-yellow, which can achieve semi-quantitative visual detection. The reaction mechanism is: Ag(I) can be reduced to Ag 0 , Ag 0 Silver nanoparticles (AgNPs) are formed, acting as strong catalysts to catalyze the reaction between OPD and Ag(I). Similarly, Fe(III) is reduced by OPD to form Fe(II), which then catalyzes the reaction between OPD and Fe(III). Based on these principles and phenomena, a new method for rapid visual detection of Ag(I) and Fe(III) using a ratiometric N,Si,S-GQDs / OPD fluorescence probe with autocatalysis was established.

[0062] Optimization of conditions for detecting Ag(Ⅰ) and Fe(Ⅲ) using N,Si,S-GQDs / OPD ratiometric fluorescence probe.

[0063] 1. Optimization of pH

[0064] Taking Ag(Ⅰ) as an example, the effects of 40mM B-R buffer system on the corresponding systems of N,Si,S-GQDs, Ag(Ⅰ)+OPD+N,Si,S-GQDs, and Ag(Ⅰ)+OPD at different pH values ​​(2, 4, 6, 7, 8, 10, 12) were studied. Figure 7 As shown in (a), the fluorescence intensity of N, Si, S-GQDs at 440 nm hardly changes; Figure 7(b) is the effect of pH on the fluorescence intensity of Ag(Ⅰ)+OPD+N,Si,S-GQDs at 440nm (blue line) and 560nm (red line) and the fluorescence intensity of Ag(Ⅰ)+OPD at 560nm (green line). The results show that the fluorescence intensity of Ag(Ⅰ)+OPD+N,Si,S-GQDs at 440nm changes little, while the fluorescence intensity at 560nm increases with increasing pH value at pH 2-8. This may be because the amino group of OPD is protonated in a strong acidic medium, which inhibits the oxidation reaction of Ag(Ⅰ) and OPD. It decreases with increasing pH value at pH 8-12. At the same time, the fluorescence intensity of Ag(Ⅰ)+OPD at 560nm also increases with increasing pH value at pH 2-8, and decreases with increasing pH value at pH 8-12. Observing the fluorescence intensity at 560nm (red and green lines), only at pH 8, ΔF 560 There is the smallest difference, and its fluorescence graph is as follows Figure 7 As shown in (c), considering the above results, we selected pH 8 as the optimal condition.

[0065] 2.OPD concentration optimization

[0066] OPD is rapidly oxidized by Ag(I) / Fe(III) to generate 2,3-diaminophenazine (oxOPD), which emits orange-yellow fluorescence at 560nm. The total amount of oxOPD is directly related to the sensitive detection of Ag(I) and Fe(III), and the OPD concentration affects the total amount of oxOPD. Figure 8 The results show that with the increase of OPD concentration, the fluorescence intensity ratio (F 560 / F 440 ) increased significantly, and then gradually leveled off after the concentration reached 600 μM, so we selected 600 μM as the optimal condition.

[0067] 3. Optimize response time

[0068] In order to explore the analytical speed of the probe for Ag(Ⅰ) detection, the reaction time of the N,Si,S-GQDs / OPD sensing platform for detecting Ag(Ⅰ) was tested under optimal conditions, and the results are shown in the figure. Figure 9 The fluorescence intensity ratio (F 560 / F 440 ) changes over time, indicating that the probe responds quickly to Ag(I), meaning that the oxidation reaction between Ag(I) and OPD can be completed quickly within 1 minute. Therefore, considering all factors, 1 minute was selected as the optimal condition.

[0069] Selective detection of Ag(Ⅰ) and Fe(Ⅲ) by N,Si,S-GQDs / OPD ratiometric fluorescence probe.

[0070] When detecting Ag(Ⅰ) under the optimal conditions, the effects of Ba(Ⅱ), Cd(Ⅱ), Mg(Ⅱ), K(Ⅰ), Al(Ⅲ), Na(Ⅰ), Ca(Ⅱ), Cr(Ⅲ), Zn(Ⅱ), Mn(Ⅱ), Fe(Ⅱ), Co(Ⅱ), Mn(Ⅶ), Cr(Ⅵ), Cu(Ⅱ), Fe(Ⅲ), and Ag(Ⅰ) on the N,Si,S-GQDs / OPD probe were studied respectively, and the results are shown in Figure 5. Figure 10 (a) It is obvious that in addition to Ag(Ⅰ), Fe(Ⅲ) can also affect the fluorescence intensity ratio (F 560 / F 440 ), indicating that this sensor exhibits good selectivity for Ag(I) and Fe(III). In order to achieve accurate analysis of Ag(I) and Fe(III), measures must be taken to eliminate their mutual interference during the detection process. When detecting Ag(I), the interference of Fe(III) was effectively eliminated by introducing triethanolamine (TEOA) as a masking agent, such as Figure 10 (b) As shown; when detecting Fe(III), NaCl is used to mask the interference of Ag(I), as shown Figure 10 (c) This strategy can eliminate the interference of one metal ion when detecting the other, thereby achieving accurate detection of a single metal ion. Therefore, N,Si,S-GQDs / OPD was demonstrated to be an effective fluorescence sensor for the detection of Ag(I) and Fe(III).

[0071] Analytical performance of N,Si,S-GQDs / OPD ratiometric fluorescence probe for detecting Ag(Ⅰ) and Fe(Ⅲ).

[0072] In order to evaluate the sensitivity of the probe, we further explored the analytical performance of the N,Si,S-GQDs / OPD ratio fluorescence probe in detecting different concentrations of Ag(Ⅰ) and Fe(Ⅲ) under optimal conditions. By adding different concentrations of Ag(Ⅰ) and Fe(Ⅲ), the fluorescence intensity changes were shown in the following table: Figure 11 As shown in Figure 2, with the increase of Ag(Ⅰ) and Fe(Ⅲ) concentrations, F 440 The fluorescence intensity of F 560 The fluorescence intensity of the 560 / F 440) showed a good linear relationship with the concentrations of Ag(Ⅰ) and Fe(Ⅲ). At this time, the solution also changed from its original blue to orange-yellow under 365nm UV light. This shows that N,Si,S-GQDs / OPD can be used as a ratiometric fluorescent probe for the visual detection of Ag(Ⅰ) and Fe(Ⅲ). Table 1 lists the analytical performance data of this experiment. The linear ranges of Ag(Ⅰ) and Fe(Ⅲ) were 0.1-40μg / mL and 0.05-25μg / mL, respectively, and the limits of detection (LOD) were 0.016μg / mL and 0.010μg / mL, respectively.

[0073] Table 1 Analysis performance data

[0074]

[0075]

[0076] Table 2 Comparison of detection limits between existing technologies and this application

[0077]

[0078] NPCl-CQDs: carbon quantum dots co-doped with nitrogen, phosphorus and chlorine

[0079] BPQDs:black phosphorus quantum dots

[0080] Pd / Pt NFs:Pd / Pt nanoflowers

[0081] Table 2 compares the analytical performance of different analytical methods for the detection of Ag(Ⅰ) and Fe(Ⅲ) in this experiment. As can be seen from the table, the methods based on different probes detected Ag(Ⅰ) and Fe(Ⅲ). When detecting Ag(Ⅰ), the detection limit of this experimental method is lower than that of some of the literature (Ratiometric fluorescent sensors for sequential on-off-on determination of riboflavin, Ag +and l-cysteine based on NPCl-doped carbon quantum dots. Paper test strip for silver ions detection in drinking water samples based on combined fluorometric and colorimetric methods.),与Qi(Carrageenan-derived sulfur, nitrogen co-doped carbon dots for sequential detection of Ag + and Lime Sulfur with “on-off-on” pattern.)的研究相近,比其中一部分文献高(Dual-channel fluorescent / colorimetric-based OPD-Pd / Pt NFs sensor for high-sensitivity detection of silver ions. A ratiometric fluorescent nanoprobe based on CdSe quantum dots for the detection of Ag + in environmental samples and living cells.)。检测Fe(Ⅲ)时,本实验方法的检出限比Chen等人(Carbon dots-embedded zinc-based metal-organic framework as an efficient fluorescent sensor for the detection of ferric and phosphate ions. Fe 3+ -sensitive carbon dots for detection of Fe 3+ in aqueous solution and intracellular imaging of Fe 3 +inside fungal cells.) and slightly lower than that of Yang et al. (Diethylenetriamine-β-CD-modified carbon quantum dots for selective fluorescence sensing of Hg 2+ and Fe 3 + and cellular imaging.The fabrication of fluorescent sensor for Fe 3+ The work by Wang et al. (CuS@CDs nanozymes with photothermal-enhanced peroxidase-like activities for colorimetric / fluorescent detection of glutathione and ferric ions in the coexisting system) is superior to that by Wang et al. (CuS@CDs nanozymes with photothermal-enhanced peroxidase-like activities for colorimetric / fluorescent detection of glutathione and ferric ions in the coexisting system). These observations demonstrate that this experimental method is more economical, simpler, and faster. Furthermore, compared with single-signal fluorescence analysis methods, this ratiometric fluorescence sensing method exhibits a self-calibration capability, eliminating the influence of many analyte-independent factors, reducing quantification errors, and improving the signal-to-noise ratio, resulting in more accurate and reliable analysis results.

[0082] Investigation of the mechanism of detection of Ag(Ⅰ) and Fe(Ⅲ) by N,Si,S-GQDs / OPD ratiometric fluorescence probe.

[0083] The fluorescence of the N,Si,S-GQDs / OPD ratio fluorescence probe decreased significantly at 440nm, and a new peak appeared at 560nm. To explore the detection mechanism, this study selected Ag(Ⅰ) as a representative and examined the UV absorption spectrum. The corresponding UV-visible absorption spectrum is shown in Figure 2. Figure 12 As shown in (a), oxOPD exhibits a significant absorption peak at 416 nm. This result indicates that a redox reaction occurs between Ag(I) and OPD due to its oxidative ability.

[0084] In order to determine the reason why OPD has good selectivity for Ag(Ⅰ), we used transmission electron microscopy to characterize the reaction products of OPD and Ag(Ⅰ). Figure 12As shown in (b), AgNPs with a diameter of approximately 20 nm formed on the film. These strong catalysts catalyzed the reaction between OPD and Ag(I). Therefore, the redox reaction mechanism of OPD and Ag(I) was well verified.

[0085] In order to verify that Fe(Ⅲ) generates Fe(Ⅱ) through electron-accepting reaction and then catalyzes the reaction between OPD and Fe(Ⅲ), 1,10-phenanthroline (phen) was introduced as a ligand of Fe(Ⅱ) to verify the existence of Fe(Ⅱ) and its ability to catalyze the reaction between OPD and Fe(Ⅲ). Figure 12 As shown in (c), there is an absorption peak at 510 nm, which is due to [Fe(phen)3] 2+ Based on the above results, the redox reaction mechanism of OPD and Fe(Ⅲ) has been well verified.

[0086] In order to further explore the interaction mechanism between N,Si,S-GQDs and oxOPD, the fluorescence excitation and emission spectra of N,Si,S-GQDs and the UV-visible absorption and fluorescence spectra of oxOPD were studied. Figure 12 As can be seen in (d), the maximum excitation and emission wavelengths of N,Si,S-GQDs are 370 nm and 440 nm, respectively, while the maximum absorption and emission wavelengths of oxOPD are 416 nm and 560 nm, respectively. The absorption spectrum of oxOPD partially overlaps with the excitation and emission spectra of N,Si,S-GQDs, suggesting the presence of an inner filter effect (IFE) or fluorescence resonance energy transfer (FRET).

[0087] Fluorescence lifetime is considered to be one of the effective methods to distinguish IFE and FRET. Figure 12 (e) shows the fluorescence decay curves of N,Si,S-GQDs in the absence (τ0) and presence (τ) of oxOPD. The fluorescence lifetimes of N,Si,S-GQDs and N,Si,S-GQDs+oxOPD are 6.20 ns and 5.91 ns, respectively. The results show that the fluorescence lifetime of N,Si,S-GQDs does not decay significantly after interaction with oxOPD, indicating that the fluorescence quenching mechanism of oxOPD on N,Si,S-GQDs is mainly attributed to IFE, rather than FRET.

[0088] Example 3

[0089] In this example, the N, Si, S-GQDs / OPD ratio fluorescent probe prepared as described above was used to detect Ag(I) and Fe(III) in actual samples.

[0090] 1. N,Si,S-GQDs / OPD ratio fluorescence probe for detection of Ag(Ⅰ) and Fe(Ⅲ) in actual samples.

[0091] To explore the feasibility and practical application of the N,Si,S-GQDs / OPD ratiometric fluorescent probe for the detection of Ag(I) and Fe(III), we analyzed Ag(I) and Fe(III) in lake and tap water under optimal conditions to verify the practical feasibility of this method. Table 3 shows the Ag(I) content and spiked recoveries in lake and tap water. Spiked recoveries ranged from 99.7% to 114.5%, with relative standard deviations (RSDs) less than 5% (n=5). Concentrations of Fe(III) in lake and tap water were also measured at 0.13 and 0.08 μg / mL, respectively, with recoveries ranging from 95.5% to 102.2%, and relative standard deviations (RSDs) less than 5% (n=5). This demonstrates the promising potential of this ratiometric fluorescent probe for the detection of Ag(I) and Fe(III) in lake and tap water samples.

[0092] Table 3 Detection results of Ag(Ⅰ) and Fe(Ⅲ) in actual samples

[0093]

[0094]

[0095] 2. On-site visualization detection of Ag(Ⅰ) and Fe(Ⅲ) using N,Si,S-GQDs / OPD ratiometric fluorescent probe.

[0096] Under the optimal experimental conditions, the color changes of the sensing system were tested when Ag(Ⅰ) and Fe(Ⅲ) with different concentrations were irradiated under 365nm ultraviolet light. Figure 13 As the Ag(I) content increases from 0 to 35 μg / mL (a) and the Fe(III) content increases from 0 to 48 μg / mL (b), the sensor color gradually changes from blue to orange-yellow fluorescence, enabling the semi-quantitative visual detection of Ag(I) and Fe(III). The top row of images shows the N,Si,S-GQDs / OPD fluorescence sensing system in contact with a series of Ag(I) and Fe(III) standard solutions, while the bottom row shows the same system in contact with spiked tap water and lake water. By using the color change differences, a new semi-quantitative fluorescence sensing method for the detection of Ag(I) in tap water and Fe(III) in lake water has been successfully established. This method offers advantages such as ease of operation, rapidity, low cost, and visualization, making it highly promising for widespread application.

[0097] Based on N,Si,S-GQDs and OPD, this application establishes a new method for the rapid visualization of Ag(Ⅰ) and Fe(Ⅲ) by autocatalytic fluorescence probe of N,Si,S-GQDs / OPD ratio. Through the autocatalytic action of Ag(Ⅰ) and Fe(Ⅲ), OPD is rapidly oxidized to generate oxOPD. Under ultraviolet light, the color of the sensing system solution changes from blue to orange-yellow, thus achieving

[0098] Visualized semi-quantitative detection is now available. This method has the advantages of simplicity, accuracy, rapid response, good selectivity, high sensitivity, and strong anti-interference ability. It is suitable for analyzing and detecting the content of Ag(Ⅰ) and Fe(Ⅲ) in complex matrix samples and has excellent application prospects.

[0099] The raw materials not specifically described in the present invention are all existing materials that can be directly purchased from the market.

[0100] The above is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A nitrogen, silicon, and sulfur co-doped graphene quantum dot, characterized in that: The invention is prepared from waste carbon powder and reduced glutathione by a hydrothermal synthesis method; wherein the mass ratio of the waste carbon powder to the reduced glutathione is 2:(4.5-5.5).

2. A method for preparing graphene quantum dots according to claim 1, characterized in that: The following steps are involved: Waste carbon powder, reduced glutathione and secondary deionized water are placed in a reactor, dissolved, and reacted at 180° C. to 200° C. for 3.5 to 4.5 hours. After the reaction is completed, the mixture is cooled and filtered to obtain a yellow liquid, which is the graphene quantum dots.

3. The preparation method according to claim 2, characterized in that The material-liquid ratio of the mixture of waste carbon powder and reduced glutathione to the secondary deionized water is (6.5-7.5):

100.

4. The preparation method according to claim 2, characterized in that The filtration is performed using a water-based filter head with a pore size of 0.2 to 0.3 μm.

5. The preparation method according to claim 2, characterized in that The dissolution is carried out by ultrasound, with an ultrasound power of 90 to 110 W and an ultrasound time of 4 to 6 minutes.

6. A ratiometric fluorescent probe, characterized in that The method is prepared by mixing the graphene quantum dots according to claim 1, o-phenylenediamine and BR buffer.

7. The ratiometric fluorescent probe according to claim 6, characterized in that The concentration of o-phenylenediamine in the ratio fluorescent probe is 200-1000 μM, and the pH of the BR buffer in the ratio fluorescent probe is 7-12.

8. A method for preparing the ratiometric fluorescent probe according to claim 6 or 7, characterized in that: The following steps are involved: Graphene quantum dots, o-phenylenediamine, and BR buffer were mixed, shaken at room temperature, and reacted in the dark for 0.8 to 1.2 minutes. The ratiometric fluorescent probe was obtained after the reaction was completed.

9. Use of the ratiometric fluorescent probe according to claim 6 or 7 in detecting Ag(I) and Fe(III) in water.

10. The use according to claim 9, characterized in that When detecting Ag(I) in water, triethanolamine is added as a masking agent to effectively eliminate the interference of Fe(III); When detecting Fe(III) in water, NaCl is added as a masking agent to effectively eliminate the interference of Ag(I).

Images