CN112362633A - Method for rapidly detecting mercury ions or thiophanate-methyl - Google Patents
Method for rapidly detecting mercury ions or thiophanate-methyl Download PDFInfo
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Abstract
The invention discloses a method for rapidly detecting mercury ions or thiophanate-methyl, which comprises the steps of firstly, taking lipoic acid and trisodium citrate as main raw materials, carrying out hydrothermal reaction to synthesize sulfur-doped carbon quantum dots, and then, under the condition of a buffer solution system with a specific pH value, utilizing fluorescence intensity change to realize rapid and accurate detection of metal mercury ions or thiophanate-methyl pesticides in tap water, grapes and dried orange peel; the carbon quantum dots doped with the sulfur element have high fluorescence yield and strong reaction characteristics, and have high selectivity and specificity on mercury ions and thiophanate-methyl; the related preparation method and operation steps have high repeatability, simplicity, rapidness and low cost, can be put into industrial production and have wide application prospect.
Description
Technical Field
The invention belongs to the technical field of nano material preparation and chemical analysis detection, and particularly relates to a method for rapidly detecting mercury ions or thiophanate methyl.
Background
As a common highly toxic heavy metal, mercury has extremely strong biological enrichment and difficult degradation, and causes great harm to the ecological environment in nature. The long-term intake of mercury-contaminated water and food by oral administration, inhalation or contact can cause brain and liver damage, and the destruction of central nervous system can cause brain death, such as water guarantee. Thiophanate-methyl is a common broad-spectrum systemic fungicide, and is widely applied to the prevention and treatment of diseases of fruits, vegetables, flowers and wheat due to low toxicity and strong bactericidal effect. Clinically, thiophanate-methyl is proved to have teratogenicity and carcinogenicity, damages the human reproductive system after long-term eating by mistake, is forbidden by the United states and is strictly controlled in the global scope. The traditional detection methods of mercury ions and thiophanate-methyl mainly comprise atomic fluorescence spectrometry, atomic emission and absorption spectrometry, cold atomic absorption spectrometry, high performance liquid chromatography and the like, and the methods have the defects of high detection limit, expensive instrument, complex operation, time consumption and the like, cannot be accepted by the masses of people, and are difficult to popularize.
Therefore, there is a need to further establish a mercury ion or thiophanate-methyl detection method which has lower detection limit, better stability and faster response and can be put into industrial production.
Disclosure of Invention
The invention mainly aims to provide a rapid detection method for mercury ions or thiophanate-methyl aiming at the defects in the prior art; the sulfur-doped carbon quantum dots can be specifically combined with mercury ions in a buffer solution system under a specific pH condition to quench fluorescence, and then are specifically combined with thiophanate-methyl to recover the fluorescence, so that the aim of detecting the mercury ions or the thiophanate-methyl is fulfilled; the method has the advantages of simple process, environmental protection, low cost, easy popularization, industrial production and suitability for popularization and application.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for rapidly detecting mercury ions or thiophanate-methyl is characterized by comprising the following steps:
1) firstly, lipoic acid and trisodium citrate are used as main raw materials to carry out hydrothermal reaction to prepare sulfur-doped carbon quantum dots;
2) respectively adding the sulfur-doped carbon quantum dot dispersion liquid into a solution system to be detected containing mercury ions with known concentration or into a solution system to be detected sequentially introducing the mercury ions and thiophanate-methyl with known concentration, carrying out standing reaction, respectively detecting the fluorescence intensity change of the solution system to be detected before and after the standing reaction, and respectively constructing a linear relation between the fluorescence intensity change and the concentration of the mercury ions or thiophanate-methyl; so as to realize the rapid detection of the concentration of mercury ions or thiophanate methyl in different solution systems.
In the above scheme, the preparation method of the sulfur-doped carbon quantum dot comprises the following steps: dissolving lipoic acid in a DMF solution to obtain a lipoic acid solution, dissolving trisodium citrate and sodium hydroxide in water to obtain a sodium citrate solution, uniformly mixing the two solutions, adding the two solutions into a reaction kettle, carrying out hydrothermal reaction, and carrying out ice-bath cooling to obtain a yellowish clear solution; then centrifugal separation and microfiltration (0.22 mu m micropore) are carried out to obtain the dispersion liquid of the sulfur-containing doped carbon quantum dot.
In the scheme, the particle size of the sulfur-doped carbon quantum dot is 2.0-3.0 nm; under the irradiation of an ultraviolet lamp of 365nm, strong blue fluorescence is emitted.
In the scheme, the molar ratio of the lipoic acid to the trisodium citrate is 1 (2.5-10).
In the scheme, the concentration of the lipoic acid in the lipoic acid solution is 48.5-194 mmol/L; the concentration of trisodium citrate in the sodium citrate solution is 79.3-317.2 mmol/L, and the concentration of sodium hydroxide is 1.7-16.8 mmol/L.
In the scheme, the hydrothermal reaction temperature is 160-200 ℃ and the time is 5-8 h.
The method for rapidly detecting the mercury ions specifically comprises the following steps:
1) adding PBS buffer solution and water into the sulfur-doped carbon quantum dot dispersion liquid, uniformly mixing, then adding mercury ion solutions with different known concentrations, and detecting the fluorescence intensity F0 of the obtained solution system I by using a fluorescence spectrophotometer; standing for reaction, and detecting the fluorescence intensity F1 of the solution system II obtained after the standing reaction; establishing a linear relation between the fluorescence intensity change F1/F0 before and after standing reaction and the mercury ion concentration C to obtain a standard curve I about the mercury ion concentration;
2) and replacing the mercury ion solutions with different concentrations with real sample solutions with unknown mercury ion concentrations, measuring the fluorescence intensity and the mercury ion concentrations according to the method, and combining the obtained standard curves to obtain corresponding recovery rate results.
In the scheme, the concentration of the sulfur-doped carbon quantum dots in the solution system I is 36-60 mu g/mL; the concentration of mercury ions is 1 mmol/L-0.05 mu mol/L.
In the scheme, the pH value of the solution system I is 7.0-8.0.
In the scheme, the pH value of the PBS buffer solution is 7.0-9.0.
In the scheme, the standing reaction time is 3-10 min.
The method for rapidly detecting thiophanate methyl specifically comprises the following steps:
1) adding a PBS buffer solution and a mercury ion solution into the sulfur-doped carbon quantum dot dispersion liquid, uniformly mixing, then adding thiophanate methyl solutions with different known concentrations, and detecting the fluorescence intensity F3 of the obtained solution system III by using a fluorescence spectrophotometer; standing for reaction, and detecting the fluorescence intensity F4 of the solution system IV obtained after the standing reaction; establishing a linear relation between the fluorescence intensity change F4/F3 before and after the standing reaction and the concentration C of thiophanate-methyl to obtain a standard curve I about the concentration of thiophanate-methyl;
2) and replacing the thiophanate-methyl solution with different concentrations with a real sample solution with unknown thiophanate-methyl concentration, measuring the fluorescence intensity and the mercury ion concentration by the method, and combining the obtained standard curve to obtain a corresponding recovery rate result.
In the scheme, the concentration of the sulfur-doped carbon quantum dots in the solution system III is 36-60 mu g/mL; the concentration of mercury ions is 1 mmol/L-0.05 mu mol/L, and the concentration of thiophanate methyl is 1 mmol/L-0.05 mu mol/L.
In the scheme, the pH value of the solution system III is 7.0-8.0.
In the scheme, the pH value of the PBS buffer solution is 7.0-9.0.
In the scheme, the standing reaction time is 3-10 min.
The principle of the invention is as follows:
the detection mechanism of mercury ions: the invention firstly takes lipoic acid and trisodium citrate as main raw materials to prepare sulfur-doped carbon quantum dots (SCDs), abundant functional groups such as sulfur-containing and oxygen-containing groups on the surfaces of the SCDs enable the surfaces of SCDs particles to have a large number of surface defects as excitation energy traps (excitation energy traps), and the surface defects and mercury ions form an SCDs-Hg complex, so that electrons transfer the mercury ions from the surfaces of the SCDs, and the electron transfer effect (electron transfer effect) can cause the change of fluorescence intensity, thereby constructing the linear relation between the mercury ions and the change of the fluorescence intensity, and being beneficial to further improving the sensitivity and specificity of mercury ion detection.
The detection mechanism of thiophanate methyl is as follows: based on the interaction between the SCDs and mercury ions, the double sulfydryl in the thiophanate-methyl can strip the mercury ions in the SCDs-Hg compound and combine with the mercury ions through a stable Hg-S bond to form a settleable solid, so that the surface defects of the SCDs are recovered, and the change of fluorescence intensity is further caused.
The sulfur-doped carbon quantum dot has high sensitivity, good specificity and simple operation, and the fluorescence intensity of the sulfur-doped carbon quantum dot is gradually quenched or even quenched to the end along with the gradual increase of the concentration of mercury ions in a sample to be detected; under the condition of fixing the concentration of mercury ions, along with the increase of the concentration of thiophanate methyl in a sample to be detected, the fluorescence intensity of the originally quenched sulfur-doped carbon quantum dots is gradually restored to the original level, which cannot be realized by non-doped carbon quantum dots (except that no lipoic acid is added, and other synthesis conditions are the same). The fluorescent sensor based on the sulfur-doped carbon quantum dots is superior to the traditional non-doped carbon quantum dots, has lower detection limit, higher stability and faster response compared with other detection methods, and can be applied to detection in real samples. The invention detects the LOD of mercury ions on the basis of the fluorescent sensor means of sulfur-doped carbon quantum dots to be 33.3nmol/L, and meets the national standard requirement (the LOD is 50 nmol/L); the LOD of the thiophanate methyl is detected to be 7.6nmol/L, which is far lower than the national standard requirement (8.76 mu mol/L) and the European Union standard requirement (1.46 mu mol/L).
Compared with the prior art, the invention has the beneficial effects that:
the sulfur-doped carbon quantum dot has high sensitivity, good specificity and simple operation, and can show lower detection limit, higher stability and faster response when being applied to detection of mercury ions and thiophanate-methyl in a sample solution; the related detection method is simple and rapid, has high repeatability and wide application prospect, and can be put into industrial production.
Drawings
FIG. 1 is a linear spectrum of mercury ion detection using the sulfur-doped carbon quantum dots obtained in example 1; the inset is the corresponding regression equation.
FIG. 2(A) is a transmission electron microscopy characterization of the sulfur-doped carbon quantum dot obtained in example 1, and (B) is an XRD and SAED characterization of the sulfur-doped carbon quantum dot obtained in example 1; (C) and (D) is the three-dimensional fluorescence spectrum of the sulfur-doped carbon quantum dots.
FIG. 3 is a mid-infrared characterization of the sulfur-doped carbon quantum dots obtained in example 1.
Fig. 4 is an XPS profile of the sulfur-doped carbon quantum dot obtained in example 1, wherein a is a total XPS profile, B is a high-resolution XPS profile of carbon (C1S), C is a high-resolution XPS profile of oxygen (O1S), and D is a high-resolution XPS profile of sulfur (S2 p).
FIG. 5 is a linear spectrum of thiophanate-methyl detection using the sulfur-doped carbon quantum dots obtained in example 1; the inset is the corresponding regression equation.
FIG. 6 is a pH optimization chart of the sulfur-doped carbon quantum dot detection mercury ions and thiophanate-methyl obtained in example 1, and FIG. A is a pH optimization chart of the sulfur-doped carbon quantum dot detection mercury ions; and the graph B is a pH condition optimization graph for detecting thiophanate-methyl by using sulfur-doped carbon quantum dots.
Fig. 7 is a graph of optimizing the reaction time conditions of the sulfur-doped carbon quantum dots for detecting mercury ions and thiophanate-methyl obtained in example 1, where a is a graph of optimizing the reaction time conditions of the sulfur-doped carbon quantum dots for detecting mercury ions, and a graph B is a graph of optimizing the reaction time conditions of the sulfur-doped carbon quantum dots for detecting thiophanate-methyl.
FIG. 8 is a diagram of optimization of the mercury ion concentration conditions of thiophanate-methyl detection by sulfur-doped carbon quantum dots obtained in example 1.
Fig. 9 is a graph of results of a selectivity experiment for detecting mercury ions and thiophanate-methyl by using the sulfur-doped carbon quantum dots obtained in example 1, in which a graph a is a selective reaction graph of the sulfur-doped carbon quantum dots on common metal ions, and a graph B is a selective reaction graph of the sulfur-doped carbon quantum dots on common pesticides.
FIG. 10 is a diagram comparing reaction raw materials for detecting mercury ions and thiophanate-methyl at sulfur-doped carbon quantum dots obtained in example 1.
FIG. 11 is a graph showing the fluorescence lifetime of mercury ions and thiophanate-methyl detected by sulfur-doped carbon quantum dots obtained in example 1.
Fig. 12 is an XPS characterization diagram of the sulfur-doped carbon quantum dot obtained in example 2 for detecting mercury ions and thiophanate-methyl, where a is a high-resolution XPS characterization diagram of S2 p before the sulfur-doped carbon quantum dot reacts, B is a high-resolution XPS characterization diagram of S2 p after the sulfur-doped carbon quantum dot reacts with mercury ions, and C is a high-resolution XPS characterization diagram of S2 p after the sulfur-doped carbon quantum dot reacts with mercury ions and then reacts with thiophanate-methyl.
FIG. 13 is a reaction flow chart (A) and a visual contrast chart (B-E) for detecting mercury ions and thiophanate-methyl by using sulfur-doped carbon quantum dots obtained in example 2. Wherein 1, 2, 3, 4 and 5 respectively represent SCDs, SCDs + Hg2+、SCDs+TM、SCDs/Hg2++TM、Hg2++ TM, panels B and C are the visualization under UV lamp and fluorescent lamp after reaction, and panels D and E are the visualization under UV lamp and fluorescent lamp after centrifugation at 6000r/min for 5 min.
Detailed Description
The present invention will be described in further detail with reference to specific examples below so that those skilled in the art can more clearly understand the present invention. The following should not be construed as limiting the scope of the claimed invention.
The chemicals and solvents used in the examples were all analytical grade. The fluorescence spectrum determination conditions are all emission wavelength of 400-650nm, excitation wavelength of 340nm and slit width of 10 nm.
Example 1
A method for rapidly detecting mercury ions by using sulfur-doped carbon quantum dots comprises the following specific steps:
1) accurately weighing 0.2g of thioctic acid, dissolving in 10mL of DMF solution, weighing 1.0g of trisodium citrate and 0.01g of sodium hydroxide, dissolving in 30mL of water, uniformly mixing the two solutions, adding into a reaction kettle, setting the temperature at 180 ℃, reacting for 6 hours, cooling in an ice bath to obtain a yellowish clear solution, centrifuging for 30 minutes at 8000r/min, filtering the supernatant through a 0.22 mu m microporous membrane to obtain a colorless to yellowish clear solution which is a sulfur-doped carbon quantum dot, diluting 100 times with deionized water, and storing in a refrigerator at 4 ℃ for later use;
2) respectively adding 100 mu L of the fluorescent sensor diluent of the sulfur-doped carbon quantum dots prepared in example 1 with the concentration of 480 mu g/mL, 700 mu L of PBS buffer solution with the pH value of 8.0, 100 mu L of deionized water and 100 mu L of mercury ion water solution with different concentrations into a 1.5mL cuvette; the excitation wavelength was set at 340nm, fluorescence spectroscopy was performed at 400-650nm, and the reaction time was 5 minutes, as shown in fig. 1 (the abscissa is the concentration of mercury ions, the ordinate is F1/F0, pH is 8.0, and the reaction time is 5 minutes), the fluorescence intensity of the sulfur-doped carbon quantum dots gradually decreased and even quenched to the end as the concentration of mercury ions increased. Detects 0, 0.05, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 and 5.8 mu mol/L mercury ion aqueous solution and has good linearity, R2＞0.99，LOD＝33.3μmol/L。
Fig. 2(a) is a transmission electron microscopy characterization graph of the sulfur-doped carbon quantum dots in example 1, wherein a ruler in the graph is 20nm, an inset is a particle size distribution graph of the sulfur-doped carbon quantum dots, and the average particle size of the sulfur-doped carbon quantum dots is calculated to be 2.52nm and the particle size range is 2.0-3.0 nm; (B) the XRD and SAED characterization diagrams of the sulfur-doped carbon quantum dots in example 1 show that the sulfur-doped carbon quantum dots are amorphous according to the peak type; (C) and (D) is a three-dimensional fluorescence spectrum of the sulfur-doped carbon quantum dot in example 1, wherein x-axis and y-axis are an excitation wavelength Ex and an emission wavelength Em, and z-axis is fluorescence intensity, it can be found from fig. 2 that when the excitation wavelength Ex is 340nm, Em is 435nm, which is an optimal condition.
Fig. 3 is a mid-infrared characterization diagram of the sulfur-doped carbon quantum dot in example 1, which shows that the sulfur-doped carbon quantum dot is rich in various groups, which is beneficial to its characteristic reaction. Wherein the abscissa is the wave number and the ordinate is the transmittance.
Fig. 4 is an XPS characterization diagram of the sulfur-doped carbon quantum dot in example 1, in which a is an XPS characterization overall diagram, B is a high-resolution XPS characterization diagram of carbon (C1S), C is a high-resolution XPS characterization diagram of oxygen (O1S), and D is a high-resolution XPS characterization diagram of sulfur (S2 p).
The sulfur-doped carbon quantum dots obtained in the embodiment are further applied to detection of mercury ions in tap water, grapes and dried orange peel, wherein the tap water used in a recovery experiment does not need any treatment, fruit and vegetable raw pulp is squeezed and diluted by ultrapure water by 10 times for standby application, 0.1g of dried orange peel is soaked in 20mL of boiling water for cooling for standby application, the prepared tap water, fruit and vegetable diluent and dried orange peel water are used for replacing the ultrapure water to prepare mercury ion solutions with the concentrations of 0, 0.2 and 5.0 mu mol/L, the mercury ions in a real solution system are respectively measured by adopting the methods, the results are shown in Table 1, and the obtained recovery rate is 96.67-105.75%.
TABLE 1 detection effect of sulfur-doped carbon quantum dots on mercury ions in tap water, grapes and dried orange peel
Example 2
A method for rapidly detecting thiophanate-methyl by using sulfur-doped carbon quantum dots comprises the following specific steps:
1) through optimization of mercury ion concentration (2.0, 4.0, 5.5, 8.0 and 10.0 mu mol/L) conditions, the response to thiophanate-methyl with threshold concentration is still determined when the fixed mercury ion concentration is 5.5 mu mol/L, and the response is strongest;
2) to a 1.5mL cuvette, 100 μ L of the diluted solution of the sulfur-doped carbon quantum dot fluorescence sensor prepared in example 1 (480 μ g/mL), 700 μ L of PBS buffer solution with pH 8.0, 100 μ L of 5.5 μmol/L mercury ions and 100 μ L of different concentrations of thiophanate-methyl aqueous solution were added, the excitation wavelength was set to 340nm, and fluorescence spectroscopy was performed at 400-650nm for a reaction time of 5 minutes, as shown in fig. 5 (the abscissa is the concentration of thiophanate-methyl, the ordinate is F2/F1, the concentration of mercury ions is fixed to 5.5 μmol/L, pH 8.0, and the reaction time is 5 minutes), and as the concentration of thiophanate-methyl was increased, the fluorescence intensity of the originally quenched sulfur-doped carbon quantum dot was gradually restored to the original level. Detecting 0, 0.05, 0.1, 0.5, 1.0, 1.5, 1.75, 2.0, 3.0, 3.5, 4.0 and 5.0 mu mol/L thiophanate methyl aqueous solution and having two sections of good linearity of 0.05-2.0 mu mol/L and 2.0-5.0 mu mol/L respectively, R2＞0.99，LOD＝7.6μmol/L。
Fig. 6 is a pH condition optimization diagram of the sulfur-doped carbon quantum dots for detecting mercury ions and thiophanate-methyl obtained in examples 1 and 2, and the pH solvent used is PBS buffer solution with the concentrations of pH 6.5, 7.5, 8.0, 8.5 and 9.0, and the result shows that the system is more favorable for detecting mercury ions and thiophanate-methyl under the condition of the PBS buffer solution with the pH of 8.0. The graph A is an optimization graph of the pH condition of the sulfur-doped carbon quantum dots for detecting mercury ions, F0 is the original fluorescence intensity of the sulfur-doped carbon quantum dots, and F1 is the fluorescence intensity of the sulfur-doped carbon quantum dots after reaction with the mercury ions. And the graph B is an optimization graph of the pH condition of the thiophanate-methyl detected by the sulfur-doped carbon quantum dots, F4 is the fluorescence intensity of the thiophanate-methyl after the sulfur-doped carbon quantum dots are combined with mercury ions and then react with the thiophanate-methyl, and F3 is the fluorescence intensity before the thiophanate-methyl reacts (the reaction time is 3min, the concentration of the mercury ions is 3 mu mol/L, and the concentration of the thiophanate-methyl is 3 mu mol/L).
Fig. 7 is a graph of optimization of reaction time conditions for detecting mercury ions and thiophanate-methyl at sulfur-doped carbon quantum dots obtained in examples 1 and 2, where the reaction times were collected at 0, 1, 3, 5, 7, 9, 11, 13, and 15 minutes, and the results show that the reaction gradually reached a steady state when the reaction time was 5 minutes. Wherein, the graph A is a graph for optimizing the reaction time condition of detecting mercury ions by using the sulfur-doped carbon quantum dots, the graph B is a graph for optimizing the reaction time condition of detecting thiophanate-methyl by using the sulfur-doped carbon quantum dots, and the notes of F0, F1, F3 and F4 are the same as the above. The pH was 8.0, the concentration of mercury ions was 3. mu. mol/L, and the concentration of thiophanate-methyl was 3. mu. mol/L.
Fig. 8 is an optimized graph of mercury ion concentration conditions of sulfur-doped carbon quantum dots obtained in examples 1 and 2, wherein the concentration of thiophanate-methyl is 1.5 μmol/L (defined by eu standard LOD of 1.46 μmol/L), and the concentration of mercury ions at different concentrations is 2.0, 4.0, 5.5, 8.0 and 10.0 μmol/L, and when the concentration of mercury ions is 5.5 μmol/L, the thiophanate-methyl still has strong response to the threshold value. The abscissa is the mercury ion concentration, the ordinate is F2/F1, pH 8.0, and reaction time 5 minutes.
Fig. 9 is a graph of results of a selective experiment for detecting mercury ions and thiophanate-methyl by using the sulfur-doped carbon quantum dots obtained in examples 1 and 2, wherein a graph a is a selective reaction graph of the sulfur-doped carbon quantum dots to common metal ions, and the results show that the sulfur-doped carbon quantum dots have good response only to mercury ions and almost have no response to other metal ions with ten times of concentration, the concentration of mercury ions is 5 μmol/L, the concentrations of other metal ions are 100 μmol/L, the abscissa is different types of metal ions, and the ordinate is fluorescence intensity. The graph B is a selective reaction graph of sulfur-doped carbon quantum dots on common pesticides, and results show that the sulfur-doped carbon quantum dots are almost quenched to the end after reacting with high-concentration mercury ions, after different kinds of pesticides are added, only thiophanate methyl enables the thiophanate methyl to generate fluorescence recovery, the concentration of the mercury ions is 10 mu mol/L, the concentration of the thiophanate methyl is 5 mu mol/L, the concentration of pesticide residues of other kinds is 100 mu mol/L, the abscissa represents different kinds of pesticides, B represents a blank group, and the ordinate represents fluorescence intensity. pH 8.0 and reaction time 5 min.
FIG. 10 is a comparison graph of reaction raw materials for detecting mercury ions and thiophanate-methyl by using sulfur-doped carbon quantum dots obtained in examples 1 and 2, wherein SCDs represent sulfur-doped carbon quantum dots, CDs represent single carbon quantum dots (the same synthesis steps are adopted but no lipoic acid is added), Blank represents the original fluorescence intensities of the two carbon quantum dots, and TM represents thiophanate-methyl, and the results show that only SCDs synthesized by adding lipoic acid as a raw material can restore the fluorescence intensities by reacting with thiophanate-methyl. This indicates that the SCDs are possibly bonded with mercury ions by S-Hg bonds, and strong bonding occurs by adding TM containing sulfydryl, so that the fluorescence of the sulfur-doped carbon quantum dots is recovered. Wherein the concentration of mercury ions is 10 mu mol/L, the concentration of thiophanate-methyl is 10 mu mol/L, the concentration of L-cysteine is 100 mu mol/L, the pH value is 8.0, and the reaction time is 5 minutes. The SCDs and CDs were diluted by 1000 times and 50 times respectively, which indicates that sulfur doping increases the fluorescence yield of carbon quantum dots.
FIG. 11 is a graph showing the fluorescence lifetime of mercuric ions and thiophanate-methyl detected from the sulfur-doped carbon quantum dots obtained in example 2, and the results show that SCDs 7.30ns (t1 7.30ns), SCDs/Hg2+＝6.69ns(t1＝0.92ns，t2＝7.38ns)，SCDs/Hg2+The reaction can be determined to be static fluorescence quenching or recovery since the mean fluorescence lifetime is unchanged at + TM 7.13ns (t 7.13 ns). And only SCDs and Hg2+The 1 changed after combination and decayed from single index to double index, which shows that not only the conduction band to valence band but also the conduction band to surface defect existed after the mercury ion was added, which is due to SCDs and Hg2+After combination, a complex reaction occurs, the surface defects are changed, and the surface passivation is damaged.
FIG. 12 is an XPS characterization graph of the sulfur-doped carbon quantum dots obtained in examples 1 and 2 for detecting mercury ions and thiophanate-methyl, where A is a high-resolution XPS characterization graph of S2 p before the sulfur-doped carbon quantum dots react, B is a high-resolution XPS characterization graph of S2 p after the sulfur-doped carbon quantum dots react with mercury ions, C is a high-resolution XPS characterization graph of S2 p after the sulfur-doped carbon quantum dots react with mercury ions and then react with thiophanate-methyl, and as can be seen from comparison of the graphs, the sulfur-doped carbon quantum dots have no S-Hg bonds but generate obvious S-Hg bonds after reacting with mercury ions, S-Hg in B should belong to SCDs-Hg, and S-Hg in C should belong to TM-Hg.
FIG. 13 is a reaction scheme (A) and a visual contrast diagram (B-E) for detecting mercury ions and thiophanate-methyl by using the sulfur-doped carbon quantum dots obtained in examples 1 and 2. Wherein the score is 1, 2, 3, 4 and 5Respectively represent SCDs, SCDs + Hg2+、SCDs+TM、SCDs/Hg2++TM、Hg2++ TM, panels B and C are the visualization under UV lamp and fluorescent lamp after reaction, and panels D and E are the visualization under UV lamp and fluorescent lamp after centrifugation at 6000r/min for 5 min. As can be seen, there was a clear bright yellow solid deposition at the bottom of tubes 4 and 5 after centrifugation, while tubes 1, 2, and 3 did not, indicating that the strong binding between mercury ions and thiophanate-methyl is the main reason for the recovery of the sulfur-doped carbon spot fluorescence.
The method for treating the tap water, the grapes and the dried orange peel and the method for preparing the solution are the same as those described in the embodiment 2, and the thiophanate-methyl solution with the concentration of 0, 0.4 and 5.0 mu mol/L is prepared by further applying the sulfur-doped carbon quantum dots obtained in the embodiment to the tap water, the grapes and the dried orange peel recovery experiment for detecting mercury ions in the tap water, the fruits and the dried orange peel. The results of measuring mercury ions in the real solution system by the above methods are shown in table 2, and the recovery rate is 96.28-110.23%.
TABLE 2 detection effect of sulfur-doped carbon quantum dots on thiophanate-methyl in tap water, grapes and dried orange peel
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (10)
1. A method for rapidly detecting mercury ions or thiophanate-methyl is characterized by comprising the following steps:
1) firstly, lipoic acid and trisodium citrate are used as main raw materials to carry out hydrothermal reaction to prepare sulfur-doped carbon quantum dots;
2) respectively adding the sulfur-doped carbon quantum dot dispersion liquid into a solution system to be detected containing mercury ions with known concentration or into a solution system to be detected sequentially introducing the mercury ions and thiophanate-methyl with known concentration, carrying out standing reaction, respectively detecting the fluorescence intensity change of the solution system to be detected before and after the standing reaction, and respectively constructing a linear relation between the fluorescence intensity change and the concentration of the mercury ions or thiophanate-methyl; so as to realize the rapid detection of the concentration of mercury ions or thiophanate methyl in different solution systems.
2. The method according to claim 1, wherein the preparation method of the sulfur-doped carbon quantum dot specifically comprises the following steps: dissolving lipoic acid in a DMF solution to obtain a lipoic acid solution, dissolving trisodium citrate and sodium hydroxide in water to obtain a sodium citrate solution, uniformly mixing the two solutions, adding the two solutions into a reaction kettle, carrying out hydrothermal reaction, and carrying out ice-bath cooling to obtain a clear solution; then centrifugal separation and microfiltration are carried out to obtain the dispersion liquid of the sulfur-containing doped carbon quantum dots.
3. The method of claim 2, wherein the sulfur-doped carbon quantum dots have a particle size of 2.0-3.0 nm.
4. The method as claimed in claim 2, wherein the molar ratio of lipoic acid to trisodium citrate is 1 (2.5-10); the concentration of lipoic acid in the lipoic acid solution is 48.5-194 mmol/L; the concentration of trisodium citrate in the sodium citrate solution is 79.3-317.2 mmol/L, and the concentration of sodium hydroxide is 1.7-16.8 mmol/L.
5. The method according to claim 2, wherein the hydrothermal reaction temperature is 160-200 ℃ and the time is 5-8 h.
6. The method according to claim 1, wherein the standing reaction time is 3-10 min.
7. The method according to claim 1, wherein the method for detecting mercury ions comprises the following steps:
1) adding PBS buffer solution and water into the sulfur-doped carbon quantum dot dispersion liquid, uniformly mixing, then adding mercury ion solutions with different known concentrations, and detecting the fluorescence intensity F0 of the obtained solution system I by using a fluorescence spectrophotometer; standing for reaction, and detecting the fluorescence intensity F1 of the solution system II obtained after the standing reaction; establishing a linear relation between the fluorescence intensity change F1/F0 before and after standing reaction and the mercury ion concentration C to obtain a standard curve I about the mercury ion concentration;
2) and (2) replacing the mercury ion solutions with different concentrations in the step 1) with real sample solutions with unknown mercury ion concentrations, measuring the fluorescence intensity according to the method, calculating to obtain the mercury ion concentrations, and combining the obtained standard curves to obtain corresponding recovery rate results.
8. The method according to claim 7, wherein the concentration of the sulfur-doped carbon quantum dots in the solution system I is 36-60 μ g/mL; the concentration of mercury ions is 1 mmol/L-0.05 mu mol/L; the pH value is 7.0-8.0.
9. The method according to claim 1, wherein the detection method of thiophanate methyl specifically comprises the following steps:
1) adding a PBS buffer solution and a mercury ion solution into the sulfur-doped carbon quantum dot dispersion liquid, uniformly mixing, then adding thiophanate methyl solutions with different known concentrations, and detecting the fluorescence intensity F3 of the obtained solution system III by using a fluorescence spectrophotometer; standing for reaction, and detecting the fluorescence intensity F4 of the solution system IV obtained after the standing reaction; establishing a linear relation between the fluorescence intensity change F4/F3 before and after the standing reaction and the concentration C of thiophanate-methyl to obtain a standard curve II about the concentration of thiophanate-methyl;
2) and replacing the thiophanate-methyl solution with different concentrations with a real sample solution with unknown thiophanate-methyl concentration, measuring the fluorescence intensity and the mercury ion concentration by the method, and combining the obtained standard curve to obtain a corresponding recovery rate result.
10. The method according to claim 9, wherein the concentration of the sulfur-doped carbon quantum dots in the solution system III is 36-60 μ g/mL; the concentration of mercury ions is 1 mmol/L-0.05 mu mol/L, and the concentration of thiophanate methyl is 1 mmol/L-0.05 mu mol/L; the pH value is 7.0-8.0.
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