Carbon quantum dot for mercury ion fluorescence detection, preparation method and application

Abstract

The invention relates to the technical field of fluorescence sensing and food safety detection, in particular to a carbon quantum dot for mercury ion fluorescence detection and a preparation method and application thereof.According to the method, 2, 3-diaminopyridine serves as a C source and an N source, boric acid serves as a boron source, and N and B synergistically doped carbon quantum dots are synthesized in one step through a microwave method; a fluorescence sensing system with specific recognition capability on Hg < 2 + > is constructed, compared with traditional blue light carbon quantum dots, the carbon quantum dot has the emission wavelength of 425-520 nm, belongs to a long wavelength region, has the linear range of 0-25 [mu] mol / L, and can meet the detection requirements of trace-to-trace Hg < 2 + >; the detection limit of mercury ions (Hg < 2 + >) is as low as 32.8 nmol / L, which is far lower than the allowable concentration of Hg < 2 + > in food specified in food safety standards, and the problems of low sensitivity and poor stability of Hg < 2 + > detection based on carbon quantum dots in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of fluorescence sensing and food safety detection technology, specifically to a carbon quantum dot for mercury ion fluorescence detection, its preparation method, and its application. Background Technology

[0002] Mercury, a highly toxic heavy metal element, exists in nature in various forms, including divalent mercury ions (Hg). 2+ Hg is a relatively common and extremely harmful form. 2+ Mercury has extremely high bioaccumulation and toxicity, and can enter the ecosystem and food chain through multiple pathways. In industrial production processes, such as mining, smelting, and chemical industries, the discharge of large quantities of mercury-containing wastewater, waste gas, and waste residue leads to the accumulation of mercury in these substances. 2+ It is widely present in environmental media such as water, soil, and atmosphere. These polluted environmental media are also known as Hg. 2+ Entering the source of the food chain, through bioaccumulation and amplification, Hg 2+ Its concentration in organisms increases continuously as it is passed through the food chain.

[0003] When humans ingest substances containing Hg 2+ After eating or drinking food or water, Hg 2+ It accumulates in the body, causing irreversible damage to multiple vital organs and systems, including the nervous system, kidneys, and immune system. Regarding the nervous system, Hg... 2+ It can cross the blood-brain barrier, interfering with the normal metabolism and function of nerve cells, leading to symptoms such as memory loss, poor concentration, and motor incoordination. In severe cases, it can even cause serious diseases such as dementia and paralysis. Regarding the kidneys, Hg... 2+ It can damage the function of renal tubules and glomeruli, affecting the kidneys' normal filtration and excretion functions, and thus leading to kidney failure. Furthermore, Hg... 2+ It can also weaken the body's immune function, making the body more susceptible to various pathogens and increasing the risk of illness.

[0004] Given Hg 2+ The serious harm caused by Hg makes ensuring food and environmental safety a pressing issue that needs to be addressed in today's society. Accurate and rapid detection of Hg in environmental samples and food is crucial. 2+ The content of Hg is an effective way to prevent and control Hg. 2+ Pollution control and protecting public health are crucial aspects. Only by promptly understanding Hg levels... 2+ Only by understanding the pollution status and distribution can targeted treatment measures be taken to reduce Hg. 2+ Potential risks to the ecological environment and human health. Therefore, developing efficient, sensitive, and convenient Hg... 2+Detection technology is of great practical significance and urgency, and plays an irreplaceable role in maintaining ecological balance, protecting human health, and promoting sustainable social development.

[0005] In Hg 2+ In the field of detection, atomic absorption spectrometry (AAS) is a commonly used technique. It is based on the absorption characteristics of atoms at specific wavelengths of light, determining Hg by measuring the degree of absorption of characteristic absorption lines by mercury atoms in the sample. 2+ The method has high sensitivity and accuracy, and can detect low concentrations of Hg. 2+ Inductively coupled plasma mass spectrometry (ICP-MS) is another high-precision detection technique. It utilizes inductively coupled plasma to ionize elements in a sample, and then separates and detects these ions using a mass spectrometer. It features extremely low detection limits and a wide linear range, and can simultaneously detect multiple elements. Although traditional instrumental analysis methods have limitations in Hg... 2+ It has high accuracy and sensitivity in detection, but requires the use of expensive large-scale instruments and equipment, and the operation process is relatively cumbersome and time-consuming, which cannot meet the needs of rapid on-site detection.

[0006] With the continuous development of nanotechnology, detection methods based on carbon quantum dots (CQDs) have gradually become a research hotspot. Carbon quantum dots are carbon-based nanomaterials with a size less than 10 nm, possessing unique optical properties such as excellent fluorescence performance and tunable fluorescence emission wavelengths. By combining carbon quantum dots with Hg... 2+ Combined with specific recognition molecules, utilizing Hg 2+ The interaction between the quantum dots and the recognition molecules causes changes in the fluorescence properties of the carbon quantum dots, such as fluorescence quenching or enhancement, thereby enabling the recognition of Hg. 2+ The detection of Hg. This method has the advantages of simple operation, low cost, and rapid on-site detection, and is suitable for Hg detection. 2+ The detection method offers a new approach and approach.

[0007] However, currently, most of it is used for Hg 2+ The carbon quantum dots being detected are either single-element doped or undoped systems, a structure that presents certain limitations in performance. In terms of detection performance, traditional carbon quantum dots generally suffer from high detection limits (mostly above 50 nmol / L), meaning they are ineffective against low concentrations of Hg. 2+ Due to limited detection capabilities, it is difficult to accurately detect trace amounts of Hg in the environment or food. 2+ However, its linear range is relatively narrow (typically less than 10 μmol / L), failing to cover the concentration of Hg in actual samples. 2+The potentially large concentration range necessitates complex dilution or concentration processes for samples in practical applications, increasing the difficulty and error of detection. Regarding optical performance, the fluorescence emission wavelengths of traditional carbon quantum dots are mostly concentrated in the blue light region (400-450 nm). However, real samples often contain multiple fluorescent substances, whose fluorescence emission in the blue light region may interfere with the fluorescence signal of carbon quantum dots, affecting the accuracy and sensitivity of detection. Furthermore, the quantum yield of traditional carbon quantum dots is low (generally below 15%), typically below a certain percentage. This means they have a low efficiency in converting absorbed light energy into fluorescence emission, resulting in a weak fluorescence signal, further limiting their application in Hg... 2+ Applications in detection. Therefore, developing a novel carbon quantum dot detection material with low detection limit, wide linear range, excellent optical properties, and the ability to overcome fluorescence interference from the sample matrix has become a current priority for Hg detection. 2+ Key research areas and challenges in the field of testing. Summary of the Invention

[0008] Addressing the existing Hg based on carbon quantum dots 2+ To address the issues of low detection sensitivity and poor stability, this invention provides a carbon quantum dot for mercury ion fluorescence detection, its preparation method, and its application.

[0009] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a method for preparing carbon quantum dots for mercury ion fluorescence detection, comprising: 2,3-Diaminopyridine and boric acid were dissolved in water to obtain a mixed solution; After heating the mixed solution with microwave, water was added, centrifuged, and the supernatant was collected. The supernatant was subjected to filtration, dialysis, and freeze-drying in sequence to obtain carbon quantum dots.

[0010] Optionally, the mass ratio of 2,3-diaminopyridine to boric acid is (1-3):(1-3).

[0011] Alternatively, the method of heating the mixed solution with a microwave, adding water, centrifuging, and collecting the supernatant is as follows: Place the mixed solution in a microwave oven to preheat. After preheating, adjust the temperature to 750-900W and microwave for 3-6 minutes. Add water to the microwave-heated mixture, dissolve by sonication, centrifuge, and collect the supernatant.

[0012] Optionally, the centrifugation rate is 7000-9000 rpm.

[0013] Optionally, the supernatant can be filtered using a 0.4-0.5 μm nylon membrane.

[0014] Optionally, the supernatant can be dialyzed using a 3000-4000 Da dialysis bag for 18-36 hours.

[0015] The present invention also provides a carbon quantum dot for mercury ion fluorescence detection, which is prepared using the above-described preparation method.

[0016] Optionally, the detection limit of the carbon quantum dots is 32.8 nmol / L, and the detection linear range is 0-25 μmol / L.

[0017] Optionally, the fluorescence wavelength of the carbon quantum dots is 425-520 nm.

[0018] The above-mentioned carbon quantum dots used for mercury ion fluorescence detection are applied in water pollution or food detection.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing carbon quantum dots for mercury ion fluorescence detection. The method uses 2,3-diaminopyridine as the C and N sources, and boric acid as the boron source. A microwave-assisted one-step synthesis of N and B co-doped carbon quantum dots is employed to construct a system for detecting Hg ions. 2+ This fluorescent sensing system possesses specific recognition capabilities. Breaking away from the traditional approach of synthesizing carbon quantum dots with single or no doping, this method utilizes N and B synergistic doping to not only enrich the surface functional groups of the carbon quantum dots but also optimize their electronic structure through synergistic effects, significantly enhancing fluorescence performance. Compared to traditional blue carbon quantum dots, these carbon quantum dots emit light in the 425-520 nm range, falling within the long-wavelength region. The yellow fluorescence effectively avoids interference from matrix fluorescence, significantly improving the signal-to-noise ratio and providing a foundation for high-sensitivity mercury ion detection. The linear range of these carbon quantum dots reaches 0-25 μmol / L, which is 2-3 times that of traditional CQDs, covering trace to micro-level Hg. 2+ Testing requirements; for Hg 2+ The quenching rate is as high as 92%, unaffected by Fe. 3+ Mg 2+ The N and B co-doped carbon quantum dots exhibit significantly better anti-interference capabilities than traditional CQDs against 12 common ion interferences. 2+ The detection limit for Hg in food is as low as 32.8 nmol / L, far below the limits set by food safety standards. 2+Permissible concentration. This means that in practical applications, this material can achieve trace detection of mercury ions in food, and can also be extended to environmental monitoring, bioimaging and other fields. Its excellent fluorescence properties and low toxicity (carbon quantum dots generally have good biocompatibility) also make it a potential application in the detection of mercury ions in living organisms, providing a new technical means for the prevention and control of heavy metal pollution. At the same time, this method, by applying microwave method to the one-step synthesis of N, B co-doped carbon quantum dots, has a short reaction time, high synthesis efficiency, and requires no complex post-processing. It is low in cost and easy to scale up, solving the pain points of long synthesis cycle and complex process of traditional carbon quantum dot synthesis.

[0020] The mass ratio of 2,3-diaminopyridine to boric acid is (1-3):(1-3). 2,3-diaminopyridine, as an organic ligand or reactant, can form coordinate bonds or covalent bonds with boron atoms in boric acid (such as forming boric acid esters) to promote the reaction. When the mass ratio is in the range of (1-3):(1-3), the amounts of the two substances are close, which can allow them to fully contact and react, reducing side reactions or unreacted residues caused by excess of a single component.

[0021] Preheat the mixed solution in a microwave oven. After preheating, adjust the power to 750-900W and microwave for 3-6 minutes. Microwaves generate internal frictional heat through molecular polarization, which can raise the mixed solution from room temperature to the target temperature within 30 seconds, 5-10 times faster than traditional water bath heating. High-power short-time (3-5 minutes) heating at 750-900W avoids side reactions caused by prolonged high temperatures, while ensuring uniform overall solution temperature and reducing decomposition or aggregation caused by local overheating. In conjunction with ultrasound and centrifugation, this method achieves "rapid, uniform, efficient, and safe" preparation of carbon quantum dots.

[0022] Optionally, a 0.4-0.5μm nylon membrane is used to filter the supernatant. The nylon membrane is a hydrophilic porous material with uniform pore size. It removes suspended particles, colloids or micro-precipitates larger than the membrane pore size in the solution through physical interception, which can achieve rapid purification of the solution. Combined with dialysis treatment using dialysis bags, high-purity carbon quantum dots can be achieved.

[0023] This invention also provides a carbon quantum dot for mercury ion fluorescence detection, prepared using the above-described method. This carbon quantum dot exhibits a detection limit of 32.8 nmol / L, a detection linear range of 0-25 μmol / L, and a fluorescence wavelength of 425-520 nm. Its surface is rich in -COOH, -OH, and -NH2 functional groups. Compared to traditional blue CQDs (emission at 400-450 nm), it effectively avoids background fluorescence interference from matrices such as proteins and pigments in the sample, improving the accuracy of actual sample detection. For Hg... 2+It exhibits a specific fluorescence quenching response, with the quenching mechanism being a synergistic effect of static quenching and internal filtration. Compared to the single quenching mechanism of traditional CQDs, the response is more stable and more specific, and it can be directly applied to the detection of actual samples such as rice, shrimp, and lake water without the need for complex pretreatment.

[0024] The aforementioned carbon quantum dots for mercury ion fluorescence detection have been applied in water pollution and food detection. These carbon quantum dots, with their advantages of high sensitivity, high selectivity, rapid response, ease of operation, low cost, and multifunctional integration, demonstrate great potential in the fields of water pollution and food detection, providing more efficient solutions for environmental protection and food safety. Attached Figure Description

[0025] Figure 1 This is a schematic flowchart of a method for preparing carbon quantum dots for mercury ion fluorescence detection according to the present invention.

[0026] Figure 2 The figures show the test results of carbon quantum dots (BN-CQDs) for mercury ion fluorescence detection according to the present invention. In the figure, a is a comparison of the effects of reaction time and the mass ratio of 2,3-diaminopyridine to boric acid on the fluorescence intensity of BN-CQDs, b is the infrared spectrum of BN-CQDs, c is the TEM image of BN-CQDs, d is the carbon quantum particle size distribution corresponding to c, and e is the HRTEM image corresponding to c.

[0027] Figure 3 The image shows the spectral results of carbon quantum dots (BN-CQDs) for mercury ion fluorescence detection according to the present invention. In the image, a is a three-dimensional fluorescence topography map of BN-CQDs, and b is the UV-Vis absorption spectrum, excitation spectrum, and emission spectrum of BN-CQDs.

[0028] Figure 4 The carbon quantum dots (BN-CQDs) for mercury ion fluorescence detection of the present invention are used in different Hg... 2+ The fluorescence spectrum test results and linear correlation graph for different concentrations of Hg are shown in the figure. 2+ Fluorescence spectra of BN-CQDs at concentrations b, where b is Hg 2+ Linear correlation plot for concentrations in the range of 0-5 μmol / L. Detailed Implementation

[0029] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0030] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0031] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0032] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0033] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0036] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0037] See Figure 1 This invention discloses a method for preparing carbon quantum dots for mercury ion fluorescence detection, comprising: S1: Dissolve 2,3-diaminopyridine and boric acid in water to obtain a mixed solution, specifically: 2,3-Diaminopyridine and boric acid were dissolved in water at a mass ratio of (1-3):(1-3) to make the mass concentration of 2,3-diaminopyridine 0.01-0.06 g / mL. The mixture was stirred until homogeneous to obtain a mixed solution.

[0038] S2: After heating the mixed solution with microwave, add water, centrifuge, and collect the supernatant. Specifically: Place the mixed solution in a microwave oven to preheat. After preheating, adjust the temperature to 750-900W and microwave for 3-6 minutes. Add water to the microwave-heated mixture, sonicate to dissolve, centrifuge at 7000-9000 rpm, and collect the supernatant.

[0039] S3: The supernatant is sequentially filtered, dialyzed, and freeze-dried to obtain carbon quantum dots. Preferably, a 0.4-0.5 μm nylon membrane is used to filter the supernatant; a 3000-4000 Da dialysis bag is used to dialyze the supernatant for 18-36 hours.

[0040] A carbon quantum dot for mercury ion fluorescence detection is prepared using the above-described preparation method. The detection limit of the carbon quantum dot is 32.8 nmol / L, the detection linear range is 0-25 μmol / L, and the fluorescence wavelength of the carbon quantum dot is 425-520 nm.

[0041] The aforementioned carbon quantum dots for mercury ion fluorescence detection have been applied in water pollution and food detection. These carbon quantum dots, with their advantages of high sensitivity, high selectivity, rapid response, ease of operation, low cost, and multifunctional integration, demonstrate great potential in the fields of water pollution and food detection, providing more efficient solutions for environmental protection and food safety.

[0042] Example 1 2,3-Diaminopyridine (0.2 g) and boric acid (0.2 g) were dissolved in deionized water (10 mL), stirred for 10 min, and then transferred to a 50 mL beaker. The mixture was preheated in a microwave oven for 5 min and heated at 800 W for 4 min. After cooling, 20 mL of deionized water was added and dissolved by sonication. The mixture was centrifuged at 8000 rpm for 10 min, and the supernatant was filtered through a 0.44 μm nylon membrane. The mixture was dialyzed through a 3500 Da dialysis bag for 24 h and then freeze-dried to obtain a black solid powder, which is the carbon quantum dots (denoted as B,N-CQDs) used for mercury ion fluorescence detection.

[0043] Example 2 2,3-Diaminopyridine (0.2 g) and boric acid (0.2 g) were dissolved in deionized water (10 mL), stirred for 10 min, and then transferred to a 50 mL beaker. The mixture was preheated in a microwave oven for 5 min and heated at 800 W for 3 min. After cooling, 20 mL of deionized water was added and dissolved by sonication. The mixture was centrifuged at 8000 rpm for 10 min, and the supernatant was filtered through a 0.44 μm nylon membrane. The mixture was dialyzed through a 3500 Da dialysis bag for 24 h and then freeze-dried to obtain a black solid powder, which is the carbon quantum dots (denoted as B,N-CQDs) used for mercury ion fluorescence detection.

[0044] Example 3 2,3-Diaminopyridine (0.2 g) and boric acid (0.2 g) were dissolved in deionized water (10 mL), stirred for 10 min, and then transferred to a 50 mL beaker. The mixture was preheated in a microwave oven for 5 min and heated at 800 W for 5 min. After cooling, 20 mL of deionized water was added and dissolved by sonication. The mixture was centrifuged at 8000 rpm for 10 min, and the supernatant was filtered through a 0.44 μm nylon membrane. The mixture was dialyzed through a 3500 Da dialysis bag for 24 h and then freeze-dried to obtain a black solid powder, which is the carbon quantum dots (denoted as B,N-CQDs) used for mercury ion fluorescence detection.

[0045] Example 4 2,3-Diaminopyridine (0.2 g) and boric acid (0.2 g) were dissolved in deionized water (10 mL), stirred for 10 min, and then transferred to a 50 mL beaker. The mixture was preheated in a microwave oven for 5 min and heated at 800 W for 6 min. After cooling, 20 mL of deionized water was added and dissolved by sonication. The mixture was centrifuged at 8000 rpm for 10 min, and the supernatant was filtered through a 0.44 μm nylon membrane. The mixture was dialyzed through a 3500 Da dialysis bag for 24 h and then freeze-dried to obtain a black solid powder, which is the carbon quantum dots (denoted as B,N-CQDs) used for mercury ion fluorescence detection.

[0046] Example 5 2,3-Diaminopyridine (0.4 g) and boric acid (0.2 g) were dissolved in deionized water (10 mL), stirred for 10 min, and then transferred to a 50 mL beaker. The mixture was preheated in a microwave oven for 5 min and heated at 800 W for 4 min. After cooling, 20 mL of deionized water was added and dissolved by sonication. The mixture was centrifuged at 8000 rpm for 10 min, and the supernatant was filtered through a 0.44 μm nylon membrane. The mixture was dialyzed through a 3500 Da dialysis bag for 24 h and then freeze-dried to obtain a black solid powder, which is the carbon quantum dots (denoted as B,N-CQDs) used for mercury ion fluorescence detection.

[0047] Example 6 2,3-Diaminopyridine (0.6 g) and boric acid (0.2 g) were dissolved in deionized water (10 mL), stirred for 10 min, and then transferred to a 50 mL beaker. The mixture was preheated in a microwave oven for 5 min and heated at 800 W for 4 min. After cooling, 20 mL of deionized water was added and dissolved by sonication. The mixture was centrifuged at 8000 rpm for 10 min, and the supernatant was filtered through a 0.44 μm nylon membrane. The mixture was dialyzed through a 3500 Da dialysis bag for 24 h and then freeze-dried to obtain a black solid powder, which is the carbon quantum dots (denoted as B,N-CQDs) used for mercury ion fluorescence detection.

[0048] Example 7 2,3-Diaminopyridine (0.2 g) and boric acid (0.4 g) were dissolved in deionized water (10 mL), stirred for 10 min, and then transferred to a 50 mL beaker. The mixture was preheated in a microwave oven for 5 min and heated at 800 W for 4 min. After cooling, 20 mL of deionized water was added and dissolved by sonication. The mixture was centrifuged at 8000 rpm for 10 min, and the supernatant was filtered through a 0.44 μm nylon membrane. The mixture was dialyzed through a 3500 Da dialysis bag for 24 h and then freeze-dried to obtain a black solid powder, which is the carbon quantum dots (denoted as B,N-CQDs) used for mercury ion fluorescence detection.

[0049] Example 8 2,3-Diaminopyridine (0.2 g) and boric acid (0.6 g) were dissolved in deionized water (10 mL), stirred for 10 min, and then transferred to a 50 mL beaker. The mixture was preheated in a microwave oven for 5 min and heated at 800 W for 4 min. After cooling, 20 mL of deionized water was added and dissolved by sonication. The mixture was centrifuged at 8000 rpm for 10 min, and the supernatant was filtered through a 0.44 μm nylon membrane. The mixture was dialyzed through a 3500 Da dialysis bag for 24 h and then freeze-dried to obtain a black solid powder, which is the carbon quantum dots (denoted as B,N-CQDs) used for mercury ion fluorescence detection.

[0050] See Figure 2 Fluorescence intensity tests were performed on Examples 1-8, and the results are shown in the figure. Figure 2 As shown in 'a', the microwave heating time has a relatively small effect on the fluorescence intensity. The mass ratio of 2,3-diaminopyridine to boric acid is the main factor affecting the fluorescence intensity of carbon quantum dots. The strongest fluorescence intensity was observed when the mass ratio of 2,3-diaminopyridine to boric acid was 1:1 and the heating time was 4 min (Example 1). Infrared and TEM measurements were performed on the B,N-CQDs prepared in Example 1; see [reference needed]. Figure 2 From the BE data, it can be seen that the TEM images show uniform spherical particles with a diameter of 1.60-4.02 nm, an average of 2.79 nm, and a lattice spacing of 0.518 nm (graphite carbon sp). 2Hybridization), combined with FT-IR testing, confirmed the successful doping of B and N, with the surface containing functional groups such as -COOH, -OH, and -NH2; See Figure 3 Spectroscopic tests were performed on the B,N-CQDs prepared in Example 1, and it was found that the carbon quantum yield was 23.6%, there was a strong yellow emission at 520 nm under 425 nm excitation, and there were ultraviolet absorption peaks at 306 nm and 425 nm (corresponding to π-π and n-π transitions, respectively), indicating that the prepared B,N-CQDs material has good optical properties.

[0051] See Figure 4 The B,N-CQDs prepared in Example 1 were compared with those prepared in different Hg... 2+ Fluorescence testing under different concentration conditions revealed (1) selectivity: only Hg 2+ It induces significant fluorescence quenching, with no significant effect on other ions, and the quenching effect remains stable in coexisting ion interference experiments. This indicates that B,N-CQDs are effective against Hg. 2+ It has specific detection capabilities and can be used for single ion testing. (2) Sensitivity: within the range of 0-5 μmol / L (F0-F Q ) / F0 and Hg 2+ Concentration linear correlation (R) 2 =0.9979), detection limit 32.8 nmol / L, B,N-CQDs for Hg 2+ Concentration testing exhibits high correlation, and ion concentration can be calculated by fitting a morphological curve. The Stern-Volmer constant is 2.8 × 10⁻⁶. 5 L mol -1 The quenching rate constant is 7.248 × 10⁻⁶. 13 L mol -1 s -1 The quenching constant is much higher than the diffusion control limit, confirming that the quenching mechanism is static quenching. (3) Stability: The fluorescence intensity of this carbon quantum is stable in the pH range of 4-9, and its performance does not decay in a high-salt environment (2.0 mol / L NaCl); the response time is 15 min (high concentration Hg). 2+ (Faster response). This demonstrates that B,N-CQDs retain good detection sensitivity and stability even in complex environments.

[0052] In practical applications, the carbon quantum dots showed a recovery rate of 95%-108% for spiked samples of grass shrimp, Chinese mitten crab, rice, and lake water, with a relative standard deviation (RSD) of <2.5% (n=6). The detection results were highly consistent with those obtained by atomic absorption spectrometry.

[0053] In summary, this invention provides a carbon quantum dot, its preparation method, and its application for mercury ion fluorescence detection. It pioneers a novel N / B co-doped carbon quantum dot synthesis system, breaking away from the traditional approach of single-doping or undoped carbon quantum dots. For the first time, through a precise ratio of 2,3-diaminopyridine to boric acid, it achieves synergistic doping of B and N elements in carbon quantum dots, successfully preparing yellow fluorescently emitting B,N-CQDs. Compared to traditional blue CQDs, its long-wavelength emission of 520nm completely solves the matrix fluorescence interference problem, and its detection limit of 32.8 nmol / L is far lower than that of Hg in food. 2+ Permissible concentrations (such as the Hg concentration in rice as stipulated in my country's food safety standards) 2+ With a limit of 200 nmol / L, its performance indicators comprehensively surpass those of existing similar materials; simultaneously, it achieves synergistic optimization of a wide linear range and high selectivity: the linear range reaches 0-25 μmol / L, which is 2-3 times that of traditional CQDs, covering trace to micro-level Hg. 2+ Testing requirements; for Hg 2+ The quenching rate is as high as 92%, unaffected by Fe. 3+ Mg 2+ It exhibits significantly better anti-interference capabilities than traditional CQDs (which are susceptible to interference from 12 common ions such as Fe). 3+ Mg 2+ (Plasma interference); This is the first time that microwave method has been applied to the one-step synthesis of N and B co-doped carbon quantum dots, with a reaction time of only 4 min. Compared with the traditional hydrothermal method (reaction time 12-24 h) or solvothermal method (reaction time 8-16 h), the synthesis efficiency is improved by tens of times. Moreover, no complicated post-processing is required, resulting in low cost and easy large-scale production, solving the pain points of long synthesis cycle and complex process of traditional carbon quantum dots. The carbon quantum dots are fluorescently stable in the pH range of 4-9 (the stable pH range of traditional CQDs is mostly 5-7), resistant to high salt environment (2.0 mol / L NaCl), and adaptable to the complex conditions of different sample matrices. It has been successfully applied to food and water sample detection, with a recovery rate of 95%-108% and a relative standard deviation (RSD) of <2.5%. The detection results are highly consistent with traditional atomic absorption spectrometry, while traditional CQDs often have problems such as large fluctuations in recovery rate (85%-115%) and insufficient stability in the detection of complex samples.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A method for preparing carbon quantum dots for mercury ion fluorescence detection, characterized in that, include: 2,3-Diaminopyridine and boric acid were dissolved in water to obtain a mixed solution; After heating the mixed solution with microwave, water was added, centrifuged, and the supernatant was collected. The supernatant was subjected to filtration, dialysis, and freeze-drying in sequence to obtain carbon quantum dots.

2. The method for preparing carbon quantum dots for mercury ion fluorescence detection according to claim 1, characterized in that, The mass ratio of 2,3-diaminopyridine to boric acid is (1-3):(1-3).

3. The method for preparing carbon quantum dots for mercury ion fluorescence detection according to claim 1, characterized in that, The method for heating the mixed solution with microwave, adding water, centrifuging, and collecting the supernatant is as follows: Place the mixed solution in a microwave oven to preheat. After preheating, adjust the temperature to 750-900W and microwave for 3-6 minutes. Add water to the microwave-heated mixture, dissolve by sonication, centrifuge, and collect the supernatant.

4. The method for preparing carbon quantum dots for mercury ion fluorescence detection according to claim 3, characterized in that, The centrifugation rate is 7000-9000 rpm.

5. The method for preparing carbon quantum dots for mercury ion fluorescence detection according to claim 1, characterized in that, The supernatant was filtered using a 0.4-0.5μm nylon membrane.

6. The method for preparing carbon quantum dots for mercury ion fluorescence detection according to claim 1, characterized in that, The supernatant was dialyzed using a dialysis bag with a capacity of 3000-4000 Da for 18-36 hours.

7. A carbon quantum dot for mercury ion fluorescence detection, characterized in that, Prepared using the preparation method according to any one of claims 1-6.

8. The carbon quantum dots for mercury ion fluorescence detection according to claim 7, characterized in that, The detection limit of the carbon quantum dots is 32.8 nmol / L, and the detection linear range is 0-25 μmol / L.

9. The carbon quantum dots for mercury ion fluorescence detection according to claim 7, characterized in that, The fluorescence wavelength of the carbon quantum dots is 425-520 nm.

10. The application of the carbon quantum dots for mercury ion fluorescence detection as described in claim 8 or 9 in water pollution or food detection.

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