A double fluorescence peak carbon quantum dot and its preparation method and heavy metal lead ion detection method

Abstract

The invention belongs to the field of heavy metal lead ion detection, and discloses a double fluorescence peak carbon quantum dot. By molecular fluorescence spectrophotometer detection, when the excitation wavelength is 365nm, the fluorescence emission maximum wavelength of the double fluorescence peak carbon quantum dot is respectively located at 410nm and 545nm. The preparation method of the double fluorescence peak carbon quantum dot is to dissolve 2,3-diaminobenzoic acid in anhydrous ethanol, and obtain it after ultrasonic treatment, heating reaction, centrifugal filtration, and rotary evaporation. The carbon quantum dot has excellent fluorescence performance and has a double fluorescence peak, which can be selectively quenched by lead ions, so it can be sensitive, rapid, and specific to lead ions. The carbon quantum dot is used for the detection method of heavy metal lead ions, and the process is simple, rapid, sensitive, and highly anti-interference.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal lead ion detection, and in particular relates to a double-fluorescence peak carbon quantum dot and a preparation method thereof, and a heavy metal lead ion detection method. Background Art

[0002] At present, lead is widely used in pigments, batteries, anti-corrosion coatings, etc. Because it is not easily biodegradable, lead ions are harmful to air, water and human body, and are one of the most common toxic heavy metal lead ions. When the lead ion concentration in the blood is higher than 5 µM, it can cause anemia, reproductive dysfunction, nervous system dysfunction, etc. Therefore, it is necessary to develop a method for rapid and sensitive determination of trace lead ions.

[0003] At present, the main methods for determining lead ions are atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry, etc. However, these methods usually require expensive instruments, highly professional operations, and complex and time-consuming sample processing.

[0004] In recent years, fluorescent material carbon quantum dots (Carbon dots, CDs) have shown good application prospects in the detection of heavy metal lead ions with their excellent optical properties and stability. In the past, these applications using carbon quantum dots as detection signals were all carbon quantum dots that emitted a single fluorescence peak, which were easily interfered by environmental factors, resulting in large measurement errors. In order to further enhance the anti-interference and sensitivity of carbon quantum dots in the detection of heavy metal lead ions, it is urgent to develop a synthesis method of carbon quantum dots with dual fluorescence peaks as a ratiometric fluorescent probe for rapid, sensitive and stable detection of heavy metal lead ions. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a dual fluorescence peak carbon quantum dot and a preparation method thereof, which is simple and fast. Another object of the present invention is to provide a method for detecting heavy metal lead ions based on carbon quantum dots, which has a simple detection method, high specificity and high sensitivity.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0007] A double-fluorescence peak carbon quantum dot, when detected by a molecular fluorescence spectrophotometer, when the excitation wavelength is 365 nm, the maximum wavelengths of fluorescence emission of the double-fluorescence peak carbon quantum dot are respectively located at 410 nm and 545 nm.

[0008] The above-mentioned double-fluorescence peak carbon quantum dots have ultraviolet-visible absorption peaks at 270 nm and 385 nm; the double-fluorescence peak carbon quantum dots are prepared by heating 2,3-diaminobenzoic acid to undergo a dehydration condensation reaction.

[0009] Based on a general inventive concept, the present invention also provides a method for preparing dual-fluorescence peak carbon quantum dots, comprising the following steps:

[0010] (1) dissolving 2,3-diaminobenzoic acid in anhydrous ethanol and performing ultrasonic treatment to obtain an ultrasonic solution;

[0011] (2) heating the ultrasonic solution obtained in step (1) to cause a dehydration condensation reaction, and then cooling to room temperature;

[0012] (3) The solution obtained by cooling step (2) is centrifuged to obtain the supernatant, filtered through an organic micromembrane, and then the solvent is replaced by water from anhydrous ethanol by rotary evaporation, and carbon quantum dots are obtained by freeze drying.

[0013] In the above-mentioned method for preparing dual-fluorescence peak carbon quantum dots, preferably, in step (1), the mass ratio of the 2,3-diaminobenzoic acid to anhydrous ethanol is (10-50):1, and the time of the ultrasonic treatment is 5-20 min.

[0014] Preferably, in step (2), the heating to cause the dehydration condensation reaction is carried out in a high-pressure reactor, heated to 140-200° C., and the heating time is 3-7 h.

[0015] Preferably, in step (3), the centrifugation time is 5 to 20 min, the centrifugation speed is 5000 to 8000 rpm / min, and the pore size of the organic micromembrane is 0.22 μm.

[0016] Preferably, in step (3), the rotary evaporation replaces the solvent from anhydrous ethanol with 1 to 10 times the volume of water.

[0017] Based on a general inventive concept, the present invention also provides a method for detecting heavy metal lead ions, comprising the following steps: after configuring the double fluorescence peak carbon quantum dots into a double fluorescence peak carbon quantum dot aqueous solution, mixing it with an acidic buffer solution and a heavy metal lead ion solution sample to be tested, standing it at room temperature for a period of time, and using a molecular fluorescence spectrophotometer to respectively measure the fluorescence intensity ratio at 410nm and 545nm when the excitation wavelength is 365nm, and calculating the concentration of the heavy metal lead ion to be tested using a standard curve of the relationship between the fluorescence intensity ratio and the heavy metal lead ion concentration.

[0018] In the above-mentioned method for detecting heavy metal lead ions, preferably, the concentration of the double-fluorescence peak carbon quantum dot aqueous solution is 0.03-0.1 mg / mL, and the volume ratio of the double-fluorescence peak carbon quantum dot aqueous solution, the acidic buffer solution and the heavy metal lead ion solution sample to be tested is (1.0-5.0): (0.5-1.5): (0.5-1.0).

[0019] Preferably, the acidic buffer solution is potassium hydrogen phthalate buffer or potassium hydrogen tartrate buffer, the pH of the acidic buffer solution is 3.0 to 6.0, and the standing time is 5 to 20 minutes.

[0020] Preferably, the standard curve is established by the following method: the double fluorescence peak carbon quantum dot aqueous solution, the acidic buffer solution and the lead ion solutions of different concentrations are mixed, and the mixture is allowed to stand at room temperature for a period of time, and the fluorescence intensity at 410 nm and 545 nm is measured by a molecular fluorescence spectrophotometer at an excitation wavelength of 365 nm, and the fluorescence intensity ratio Y of the lead ion solutions of different concentrations at 410 nm and 545 nm is obtained, and the standard curve is obtained according to the linear relationship between the ratio Y and the lead ion concentration.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention uses 2,3-diaminobenzoic acid as a synthesis precursor to synthesize a carbon quantum dot with a double fluorescence peak. The ratio of the double fluorescence intensity of the carbon quantum dot at 410 nm and 545 nm is not affected by pH, and the fluorescence property is relatively stable and excellent, laying a foundation for later applications.

[0023] 2. The dual fluorescence of the dual fluorescence peak carbon quantum dots of the present invention can be selectively quenched by lead ions, and thus can be used as a ratiometric fluorescent probe to quickly and specifically detect lead ions; since the detection of lead ions does not require complex sample processing, this method is more convenient and resistant to interference in the application of lead ion detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a schematic diagram of the principle of detecting heavy metal lead ions based on carbon quantum dots of the present invention;

[0026] Figure 2is the ultraviolet-visible absorption spectrum and fluorescence emission spectrum of the carbon quantum dots of Example 1;

[0027] Figure 3 is a graph of the fluorescence emission properties of the carbon quantum dots of Example 1 depending on the excitation wavelength;

[0028] Figure 4 is a graph of fluorescence emission properties of carbon quantum dots in Example 1 that depends on pH value;

[0029] Figure 5 is a fluorescence spectrum diagram of lead ion detection based on carbon quantum dots in Example 2;

[0030] Figure 6 is a linear fitting diagram of lead ion detection based on carbon quantum dots in Example 2;

[0031] Figure 7 is a specific fluorescence spectrum of lead ions detected based on carbon quantum dots in Example 2, Figure A;

[0032] Figure 8 is a bar graph B of lead ion detection based on carbon quantum dots in Example 2;

[0033] Fig. 9 is a transmission electron microscope image of the carbon quantum dots before and after the addition of lead ions in Example 2;

[0034] Fig.10 This is the infrared spectrum of the carbon quantum dots before and after the addition of lead ions in Example 2. DETAILED DESCRIPTION

[0035] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0038] Embodiment 1:

[0039] A method for synthesizing carbon quantum dots comprises the following steps:

[0040] (1) Weigh 20 mg of 2,3-diaminobenzoic acid, dissolve it in 1 mL of anhydrous ethanol, and sonicate for 10 min;

[0041] (2) Transfer the above solution into a high pressure reactor, heat at 180°C for 5 hours, and then cool to room temperature;

[0042] (3) The reaction solution was centrifuged for 10 min and the supernatant was collected. The centrifuge speed was 6000 rpm / min, and the supernatant was filtered through an organic micromembrane with a pore size of 0.22 μm. The solvent was replaced from 1 mL of ethanol to 5 mL of water by a rotary evaporation step. The carbon quantum dot powder was obtained by freeze drying technology, and the aqueous solution was prepared with a concentration of 0.05 mg / mL and stored in a refrigerator at 4°C for use.

[0043] Figure 1 The schematic diagram is a principle diagram of the detection of heavy metal lead ions based on carbon quantum dots. There are adjacent carboxyl and amino groups on the benzene ring of 2,3-diaminobenzoic acid. Under certain temperature conditions, they can undergo dehydration condensation reactions in the same molecule, or they can undergo dehydration condensation reactions by carboxyl and amino groups of different molecules. Therefore, there may be two different forms of dehydration condensation reactions, which may lay the foundation for the synthesis of double-fluorescence peak carbon quantum dots. The present invention has shown through research that the double-fluorescence peak carbon quantum dots synthesized with 2,3-diaminobenzoic acid as a precursor, after reacting with lead ions, their fluorescence at 410nm and 545nm both decrease. With I 410 / 545 In response to the signal, highly sensitive detection of lead ions can be achieved.

[0044] Figure 2 The UV-visible absorption spectrum and fluorescence emission spectrum of carbon quantum dots are shown in Figure 2. The UV-visible absorption peaks are located at 270 nm and 385 nm, which are attributed to the π-π* transition of the C=C bond and the n-π* transition of the C=O bond, respectively. When the excitation wavelength is 365 nm, the maximum wavelengths of fluorescence emission are located at 410 nm and 545 nm, respectively.

[0045] Figure 3 The fluorescence emission properties of carbon quantum dots are dependent on the excitation wavelength. As the excitation wavelength increases from 325 nm to 425 nm, the fluorescence peak of the carbon quantum dots moves, which may be due to the size distribution and surface state of the carbon quantum dots. When the excitation wavelength is 365 nm, the dual fluorescence wavelengths are optimal.

[0046] Figure 4 This is the fluorescence emission diagram of carbon quantum dots that depends on pH value. The ratio of the dual fluorescence intensity of the carbon quantum dots at 410 nm and 545 nm is not affected by pH, indicating that the fluorescence properties are relatively stable, laying the foundation for later applications.

[0047] Embodiment 2:

[0048] A method for detecting heavy metal lead ions based on carbon quantum dots comprises the following steps:

[0049] (1) Accurately prepare a lead ion standard solution with a concentration of 0-10 μM;

[0050] (2) Pipette 220 μL of the aqueous solution of double-fluorescence peak carbon quantum dots obtained in Example 1, 100 μL of potassium hydrogen phthalate buffer (pH 4.0), and 80 μL of lead ion standard solutions of different concentrations, mix them, and let them stand at room temperature for 10 min; with the help of a molecular fluorescence spectrophotometer, when the excitation wavelength is 365 nm, measure the fluorescence intensity of the carbon quantum dots at 410 nm and 545 nm respectively;

[0051] (3) By recording the fluorescence intensity ratio of carbon quantum dots at 410nm and 545nm I 410 / 545 , Explore I 410 / 545 The linear relationship between the concentration of lead ion standard solution: Y=0.07455X+1.00388, R 2 =0.998, where Y is the ratio of the fluorescence intensity of the two fluorescence peaks I 410 / 545 , X is the concentration of lead ions, R 2 is the linear fitting constant;

[0052] (4) The linear range of detection is 96.53 nM-7.72 μM. Substituting the fluorescence intensity change rate of the sample to be tested into the formula, the lead ion concentration in the sample to be tested can be obtained.

[0053] Figure 5-6 This is the sensitivity test result of lead ion detection based on carbon quantum dots. When the lead ion concentration gradually increases, the intensity of the two fluorescence peaks gradually weakens ( Figure 5 ). By recording the ratio of the two fluorescence peak intensities I 410 / 545 , Explore I 410 / 545 The linear relationship between the concentration of lead ion standard solution: Y=0.07455X+1.00388, R 2 =0.998, in this formula Y is I 410 / 545 , X is the concentration of lead ions, R 2 is the linear fitting constant ( Figure 6 The linear range of this method was 96.53 nM-7.72 μM, and the detection limit was 23.90 nM.

[0054] In order to further demonstrate the specificity and accuracy of the carbon quantum dots of the present invention for detecting heavy metal lead ions, the present invention also provides the following experiment:

[0055] 1. Specificity test of the method for detecting heavy metal lead ions based on carbon quantum dots

[0056] (1) Prepare 7.72 μM of other ions (Ag + 、Al 3+ 、As3+ , Ca 2+ 、Cd 2+ 、Co 2+ Cr 3+ Cr 6+ , Cu 2+ , Fe 3+ Mg 2 + 、Ni 2+ 、Zn 2+ , Hg 2+ ) standard solution to investigate the detection specificity;

[0057] (2) Take 220 μL of the aqueous solution of the double-fluorescence peak carbon quantum dots prepared in Example 1, 100 μL of potassium hydrogen phthalate buffer solution (pH 4.0), and 80 μL of the above 14 ion standard solutions, mix them, and let them stand at room temperature for 10 minutes. Then measure the fluorescence intensity of the carbon quantum dots at 410 nm and 545 nm, respectively.

[0058] The results are as follows Figure 7 As shown in Figure 1, when 7.72 μM of different types of heavy metal lead ions were mixed with carbon quantum dots, only lead ions could induce a decrease in the intensity of the two fluorescence peaks of carbon quantum dots. The fluorescence intensity ratio of carbon quantum dots at 410 nm and 545 nm after adding metal ions was recorded. 410 / 545 It was found that the I 410 / 545 The value is significantly higher than that of adding other ions, indicating that the fluorescent probe carbon quantum dots have high specificity for lead ion determination and can be used to more accurately determine the content of heavy metal lead ions. Figure 8 shown.

[0059] Fig. 9 These are transmission electron micrographs of carbon quantum dots before and after the addition of lead ions. After the addition of 7.72 μM lead ion standard solution, the average diameter of the carbon quantum dots increased from 2.25 nm (A) to 2.71 nm (B), indicating that the carbon quantum dots aggregated due to the action of lead ions.

[0060] Fig.10 The infrared spectra of carbon quantum dots before and after the addition of lead ions. After adding 7.72 μM lead ion standard solution, the -OH (1201.2 cm -1 )、CN(1588.0 cm -1 ), C=N / C=O (1626.9 / 1694.9 cm -1 ) vibration is enhanced, indicating that lead ions may strongly adsorb and react with the hydroxyl and carboxyl groups on the surface of carbon quantum dots, affecting the fluorescence properties of carbon quantum dots, thus leading to their higher specificity.

[0061] 2. Accuracy test of the method for detecting heavy metal lead ions based on carbon quantum dots

[0062] The recovery test of mercury ions in drinking water, tap water and river water was carried out. The specific steps are as follows:

[0063] (1) Drinking water, laboratory tap water and Liuyang River water were filtered through a 0.22 μm filter membrane, and different concentrations of mercury ion standard solutions were added to prepare solutions with concentrations of 1.00 μM, 3.86 μM and 7.72 μM;

[0064] (2) Take 220 μL of the carbon quantum dot solution prepared in Example 1, 100 μL of potassium hydrogen phthalate buffer solution (pH 4.0), and 80 μL of the above-mentioned spiked sample, and detect the spiked recovery rate of lead ions by fluorescence spectroscopy.

[0065] The results are shown in Table 1. The results show that the spiked recovery rate of lead ions in drinking water, tap water and river water detected by fluorescence spectroscopy is 98.4%-105.1%, indicating that this method has high accuracy in detecting lead ions in actual samples.

[0066] Table 1: Spike recovery results in actual samples

[0067]

Claims

1. A method for detecting heavy metal lead ions, characterized in that: The method comprises the following steps: preparing a double-fluorescence peak carbon quantum dot aqueous solution from double-fluorescence peak carbon quantum dots, mixing the solution with an acidic buffer solution and a heavy metal lead ion solution sample to be tested, standing the solution for a period of time at room temperature, and using a molecular fluorescence spectrophotometer to respectively measure the fluorescence intensity ratio at 410 nm and at 545 nm when the excitation wavelength is 365 nm, and calculating the concentration of the heavy metal lead ion to be tested using a standard curve of the relationship between the fluorescence intensity ratio and the heavy metal lead ion concentration; The method for preparing the dual-fluorescence peak carbon quantum dots comprises the following steps: (1) dissolving 2,3-diaminobenzoic acid in anhydrous ethanol and performing ultrasonic treatment to obtain an ultrasonic solution; (2) heating the ultrasonic solution obtained in step (1) to cause a dehydration condensation reaction, and then cooling to room temperature; (3) centrifuging the solution obtained in step (2) to obtain the supernatant, filtering it through an organic micromembrane, replacing the solvent from anhydrous ethanol to water by rotary evaporation, and freeze-drying to obtain carbon quantum dots; In step (1), the mass ratio of the 2,3-diaminobenzoic acid to anhydrous ethanol is (10-50):1; In step (2), the heating to cause the dehydration condensation reaction is carried out in a high-pressure reactor, heated to 140-200° C., and the heating time is 3-7 h.

2. The method for detecting heavy metal lead ions according to claim 1, characterized in that: The concentration of the double-fluorescence peak carbon quantum dot aqueous solution is 0.03-0.1 mg / mL, and the volume ratio of the double-fluorescence peak carbon quantum dot aqueous solution, the acidic buffer solution and the heavy metal lead ion solution sample to be tested is (1.0-5.0): (0.5-1.5): (0.5-1.0).

3. The method for detecting heavy metal lead ions according to claim 1, characterized in that: The acidic buffer solution is potassium hydrogen phthalate buffer or potassium hydrogen tartrate buffer, the pH of the acidic buffer solution is 3.0-6.0, and the standing time is 5-20 minutes.

4. The method for detecting heavy metal lead ions according to any one of claims 1 to 3, characterized in that: The standard curve is established by the following method: the double fluorescence peak carbon quantum dot aqueous solution, the acidic buffer solution and the lead ion solutions of different concentrations are mixed, and the mixture is allowed to stand for a period of time at room temperature, and the fluorescence intensity at 410 nm and 545 nm are respectively measured at an excitation wavelength of 365 nm by means of a molecular fluorescence spectrophotometer, and the standard curve is obtained according to the linear relationship between the fluorescence intensity ratio of the lead ion solutions of different concentrations at 410 nm and 545 nm and the lead ion concentration.

5. The method for detecting heavy metal lead ions according to claim 1, characterized in that: In step (1), the ultrasonic treatment time is 5 to 20 minutes.

6. The method for detecting heavy metal lead ions according to claim 1, characterized in that: In step (3), the centrifugation time is 5 to 20 min, the centrifugation speed is 5000 to 8000 rpm / min, and the pore size of the organic micromembrane is 0.22 μm.

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