A fluorescent material for rapid detection of cesium ions in water

Abstract

The application discloses a fluorescent material for rapidly detecting cesium ions in water, and a preparation method thereof is as follows: first, synthesizing carbon quantum dots (NCD) with positive charges on the surface through a hydrothermal method, and then preparing a 0.1-100 mg.mL ‑1 0.02-100 mg.mL ‑1 aqueous solution of a heteropoly acid. The surface of the formed composite material presents negative charges and the original strong fluorescence effect is inhibited to be weak fluorescence. When the water contains cesium ions capable of forming an association with the heteropoly acid anions, the heteropoly acid anions are "stolen" by the cesium ions, and then the strong fluorescence performance of the material is recovered, indicating that the water is polluted by containing the cesium ions. The fluorescent material is high in sensitivity, low in detection limit, rapid in detection and simple in operation, and is especially suitable for monitoring of cesium ion pollution in seawater.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of rapid detection and analysis of ions, and particularly relates to a fluorescent material for rapidly detecting cesium ions in water. BACKGROUND

[0002] Nuclear contaminated water contains a large amount of radioactive pollutants, including 134 Cs, 137 Cs, 131 I, and 90 Sr, among which 137 Cs has a half-life of 30.2 years and can bind to the myocardium after entering the human body, causing disorder of the main function of the myocardium and leading to death. In order to timely respond to possible pollution risks, it is very important to rapidly and accurately measure the concentration of cesium ions in water.

[0003] The current seawater pollution monitoring methods mainly include the following three kinds: 1. Using laboratory instruments such as atomic emission spectrometers, atomic absorption spectrometers, and inductively coupled plasma emission spectrometers to detect specific metal ions, which is accurate and sensitive but time-consuming, and is not conducive to real-time sampling observation; 2. Detecting the radioactivity of water, which has a high detection limit and is not conducive to risk prevention and control; 3. Detecting the concentration of metal ions in marine organisms, which is also time-consuming and is not conducive to risk prevention and control.

[0004] Carbon quantum dots refer to monodisperse carbon materials with a size of less than 10 nm and fluorescence properties, which have good biocompatibility, high chemical and optical stability, and are easy to functionalize, and are widely used as fluorescent probes to detect inorganic metal ions such as Cu 2+ , Hg + and Fe 3+ , as well as antibiotic molecules, pigment molecules, pesticide molecules and melamine. Polyoxometalates (POMs) are a class of metal-oxygen cluster compounds composed of transition metals, which are heteropoly acids condensed from different oxygen-containing acids. However, so far, there has been no report on the use of nitrogen-doped carbon quantum dots in situ complexed with heteropoly acid anions for detecting trace cesium ions. SUMMARY

[0005] The present application is to solve the above technical problems existing in the prior art, and provides a fluorescent material for rapidly detecting cesium ions in water.

[0006] The technical solution of the present application is: a fluorescent material for rapidly detecting the concentration of cesium ions in water, which is a fluorescent material of in-situ complexing of a positively charged nitrogen-doped carbon quantum dot with a heteropolyacid anion. The positively charged nitrogen-doped carbon quantum dot is a nitrogen-doped carbon quantum dot containing positive ions such as aliphatic amine salt, pyridine carbonium ion and pyrrole carbon, and the heteropolyacid can be H4SiW 12 O 40 (SiW 12 ), H4PW 12 O 40 (PW 12 ), H4SiMo 12 O 40 (SiMo 12 ), and H4PMo 12 O 40 (PMo 12 ).

[0007] Preferably, the water solution contains the nitrogen-doped carbon quantum dot and the heteropolyacid, the concentration of the nitrogen-doped carbon quantum dot in the water solution is 0.1-100 mg.mL -1 , and the concentration of the heteropolyacid is 0.02-100 mg.mL -1 .

[0008] Preferably, the nitrogen-doped carbon quantum dot is prepared by the following method: citric acid and polyethyleneimine are dissolved in water, the ratio of the citric acid, polyethyleneimine and water is (0.1-0.9) g:(0.1-0.9) g:15 mL; after stirring uniformly, it is transferred into a reaction kettle, heated at 140-180 ℃ for 3-7 h to obtain a dark brown solution; the obtained solution is centrifuged in a centrifuge at 10000 rpm for 10 min, filtered by a 0.22 μm filter membrane and dialyzed in a dialysis bag for 24 h, and then freeze-dried to obtain a brown solid powder, which is the nitrogen-doped carbon quantum dot.

[0009] The present application uses carbon quantum dots with positive charges on the surface and strong fluorescence effect under sunlight, and in-situ complexing of heteropolyacid anions on the carbon quantum dots, so that the composite material has negative charges on the surface and the original strong fluorescence effect is inhibited to have weak fluorescence. When the water contains cesium ions capable of forming an association with the heteropolyacid anions, the heteropolyacid anions are "stolen" by the cesium ions, and then the strong fluorescence performance of the material is restored, indicating that the water is contaminated by cesium ions. The fluorescent material of the present application has high sensitivity, low detection limit, rapidness and simple operation for detecting cesium ions, and is especially suitable for monitoring the cesium ion pollution in seawater. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The infrared spectrum of the NCD solution prepared in Examples 1 and 2 of the present application.

[0011] Figure 2 Fluorescence spectrum of the present application comparative example 1 and example 1.

[0012] Figure 3 Fluorescence spectrum of the present application example 1 aqueous solution after adding different concentrations of cesium ions.

[0013] Figure 4 Fluorescence spectrum of the present application example 2 aqueous solution after adding different concentrations of cesium ions.

[0014] Figure 5 Experimental effect diagram of the present application example. DETAILED DESCRIPTION

[0015] Example 1:

[0016] Step 1. Preparation of nitrogen-doped carbon quantum dots: citric acid and polyethyleneimine (PEI) were dissolved in water, the amount ratio of the citric acid, polyethyleneimine (PEI) and water was 0.225g:0.225g:15mL; after stirring uniformly, it was transferred into a reaction kettle, heated at 140℃ for 7h, a dark brown solution was obtained; the obtained solution was centrifuged in a centrifuge at a speed of 10000rpm for 10min, filtered with a 0.22μm filter membrane and dialyzed in a dialysis bag for 24h, freeze-dried to obtain a brown solid powder, namely nitrogen-doped carbon quantum dots (NCD);

[0017] Step 2. Take the NCD prepared in step 1 and PW 12 Prepare an aqueous solution, the concentration of NCD is 0.1mg.mL-1, the concentration of PW 12 is 0.14mg.mL -1 .

[0018] Example 2:

[0019] Prepare an aqueous solution of NCD and SiW 12 according to the method of example 1, the final concentration of NCD is 0.1mg.mL-1, the final concentration of SiW 12 is 0.14mg.mL -1 .

[0020] The aqueous solution of example 1 and 2 can be added to seawater to form a solution for application in seawater cesium ion detection.

[0021] Experiment and results:

[0022] Comparative example: preparation of NCD-control aqueous solution

[0023] Prepare an aqueous solution of NCD with a concentration of 0.1mg L -1 according to the method of example 1 and 2 of the present application.

[0024] The specific method for detecting the fluorescence of cesium ions in water using the fluorescent material prepared according to the embodiments of the present invention is as follows: Take 0.5 mL of the aqueous solution containing NCD-POM prepared according to the present invention and add it to a 2 mL polyethylene sample tube; take 0.5 mL of the seawater solution to be tested and add it to the sample tube; observe the fluorescence intensity of the sample tube containing the sample to be tested under sunlight irradiation, and estimate the cesium ion concentration in the sample by comparing the fluorescence intensity.

[0025] 1. The infrared spectrum of Comparative Example 1 is as follows: Figure 1 As shown. By Figure 1 It can be seen that at 3438cm -1 The absorption peak at 2920 cm⁻¹ is attributed to the -OH stretching vibration. -1 and 2854cm -1 The absorption peak at 1709 cm⁻¹ is due to alkyl antisymmetric and symmetric stretching vibrations. -1 The absorption peak at 1649 cm⁻¹ is attributed to the stretching vibration of C=O. -1 The absorption peak at 1561 cm⁻¹ is attributed to the carbonyl stretching vibration of the amide bond. -1 The absorption peak is attributed to the C=C stretching vibration of the aromatic skeleton, mainly due to the dehydration and carbonization of citric acid to form sp. 2 Delocalized structure, 1409cm -1 The absorption peak at 1164 cm⁻¹ is attributed to the in-plane bending vibration of CN. -1 The absorption peak is attributed to the stretching vibration of COC.

[0026] 2. The fluorescence spectra of the NCD prepared in the comparative example of this invention and that of Example 1 are shown below. Figure 2 As shown, Figure 2 The black line represents the fluorescence spectrum of the comparative example, and the red line represents the fluorescence spectrum of Example 1. Figure 2 It can be seen that the fluorescence performance of NCD is at a maximum excitation wavelength of 360 nm and a corresponding emission wavelength of 455 nm; after in-situ complexation and anionization of heteropolyacid, the original strong fluorescence effect is suppressed and weak fluorescence is observed.

[0027] 3. Fluorescence spectra of aqueous solutions containing different concentrations of cesium ions as shown in Example 1 of this invention. Figure 3 As shown. By Figure 3 It can be seen that the fluorescence intensity at a wavelength of 360 nm in Example 1 increases with the concentration of cesium ions, and at 0.001 μmol / L... -1 ___ 0.01 μmol L -1 The range is linear, and the linear equation is Y = 16.0064x + 0.98609.

[0028] 4. The fluorescence spectra of aqueous solutions containing different concentrations of cesium ions in Example 2 of this invention are shown below.Figure 4 As shown. By Figure 4 It can be seen that in Example 2, the fluorescence intensity at a wavelength of 360 nm increases with the concentration of cesium ions, and at 0.001 μmol / L... -1 ___ 0.01 μmol L -1 The range is linear, and the linear equation is Y = 188.75391x + 1.05063

[0029] 5. A photograph of the detection effect of Embodiment 1 of the present invention is shown below. Figure 5 As shown, Figure 5 The left side of the image shows Comparative Example 1, the middle side shows Example 1, and the right side shows Example 1 with the addition of CsCl. Figure 5 It is evident that NCD exhibits strong fluorescence, and the addition of POM (PW) further enhances this effect. 12 The fluorescence weakened, but the fluorescence was restored upon the addition of cesium ions.

Claims

1. A fluorescent material for rapidly detecting the concentration of cesium ions in a water body, characterized in that The surface positively charged nitrogen-doped carbon quantum dot in-situ composite heteropolyacid anion fluorescent material is prepared according to the following method: Step 1. Preparation of nitrogen-doped carbon quantum dots: citric acid and polyethyleneimine are dissolved in water, and the amount ratio of the citric acid, polyethyleneimine and water is 0.225 g:0.225 g:15 mL; after stirring uniformly, it is transferred into a reaction kettle, and heated at 140 DEG C for 7 h to obtain a dark brown solution; the obtained solution is centrifuged in a centrifuge at a speed of 10000 rpm for 10 min, filtered by a 0.22 mu m filter membrane and dialyzed in a dialysis bag for 24 h, and freeze-dried to obtain a brown solid powder, namely nitrogen-doped carbon quantum dots; Step 2. Take the nitrogen-doped carbon quantum dots prepared in Step 1 and PW 12 Aqueous solution was prepared, the concentration of the nitrogen-doped carbon quantum dots was 0.1 mg.mL -1 , PW 12 The concentration was 0.14 mg.mL -1 .

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