Cu NCs@ZIF-8 nanocomposites with AIE properties and Hg 2+ Applications of detection

Abstract

This invention discloses Cu NCs@ZIF-8 nanocomposite materials with AIE properties and Hg 2+ The detection application involves encapsulating Cu NCs in ZIF-8 using a one-pot method. This results in a copper nanocluster metal-organic framework composite (Cu NCs@ZIF-8) with aggregation-induced emission properties, used to detect trace amounts of Hg in environmental water samples via fluorescence mode. 2+ The fluorescence enhancement mechanism of the Cu NCs@ZIF-8 probe is Hg 2+ Induced AIE mechanism, with Hg 2+ The increase in [amount] enhances the fluorescence of the probe. CuNCs@ZIF-8, used as a probe, achieves specific and sensitive detection of Hg based on the aggregation-induced emission enhancement mechanism. 2+ The goal.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nanomaterial synthesis and detection, and specifically relates to a blue fluorescent emission copper nanocluster metal organic framework composite (Cu NCs@ZIF-8) with aggregation-induced emission characteristics, which is used for detecting Hg 2+ in a real environment. BACKGROUND

[0002] In recent years, heavy metal pollution has attracted widespread attention due to its serious threat to human health and the environment. Among them, mercury ion (Hg 2+ ) is one of the most toxic metal pollutants, which can enter the human body through food or drinking water and accumulate in the body, and may cause a series of diseases, including central nervous system dysfunction, chronic poisoning and Minamata disease [Y. Wang, Li. Zhang, X.Y. Han, L.W. Zhang, X.Y. Wang, L.X. Chen, Fluorescent probe for mercury ion imaging analysis: Strategies and applications, Chem. Eng. J. 2021, 406, 127166.]. In view of the public hazard problem caused by heavy metal ions in the environment, it is urgent to develop a sensitive and effective analysis method for detecting trace concentration of Hg 2+ in real samples.

[0003] So far, a variety of methods have been developed for detecting trace amounts of Hg 2+methods, such as atomic absorption spectrometry, surface-enhanced Raman scattering spectroscopy, inductively coupled plasma mass spectrometry and electrochemical methods, etc. [K. Mielcarek, P. Nowakowski, A. Puścion-Jakubik, K. J. Gromkowska-Kępka, J. Soroczyńska, R. Markiewicz-Żukowska, S. K. Naliwajko, M. Grabia, J. Bielecka, A. Żmudzińska, J. Moskwa, E. Karpińska, K. Socha, Arsenic, cadmium, lead and mercury content and health risk assessment of consuming freshwater fish with elements of chemometric analysis, Food Chem. 2022, 379, 132167; P. Zheng, M. Li, R. Jurevic, S. K. Cushing, Y. X. Liu, N. Q. Wu. A gold nanohole array based surface-enhanced Raman scattering biosensor for detection of silver() and mercury( ) in human saliva, Nanoscale. 2015, 7(25), 11005-11012.]. Although these conventional analytical techniques have shown excellent sensitivity and selectivity in detection, they have limitations such as high cost, long time consumption, tedious sample pretreatment process, expensive equipment, professional operation, etc., which make them lose their attractiveness in field applications. In contrast, fluorescence analysis methods have attracted more and more attention from researchers due to their advantages of sensitivity, simplicity, efficiency, visualization, repeatability and rapid real-time monitoring.

[0004] At present, a variety of methods for determining Hg 2+fluorescent sensors. The construction of these sensing systems mainly relies on fluorescent nanomaterials, including metal nanoclusters (MNCs), carbon dots (CDs), luminescent metal-organic frameworks (M-MOFs), etc. Among them, metal nanocluster fluorescent sensors are the preferred nanomaterials for monitoring heavy metal pollution due to their outstanding characteristics such as ultra-small size, excellent optical properties, good biocompatibility, low toxicity, and easy preparation [J. M. Xu, H. M. Zhou, Y. X. Zhang. Y. Zhao, H. Yuan, X. X. He, Y. Wu, S. J. Zhang, Copper nanoclusters-based fluorescent sensor array to identify metal ions and dissolved organic matter, J. Hazard. Mater. 2022, 428, 128158.]. Compared with noble metals gold (Au) and silver (Ag), Cu is inexpensive and its high electrical conductivity can be widely used in industry. Copper is an essential trace element in biological systems. Therefore, copper nanoclusters (CuNCs) are more biocompatible and environmentally friendly than AuNCs and AgNCs. However, CuNCs have poor stability and tend to aggregate during use, which makes their practical application extremely challenging. By electrostatic, covalent or other effects, CuNCs are combined with other nanomaterials such as silica (SiO2), graphene (GO), metal-organic frameworks (MOFs) and nanogels, and CuNCs are wrapped in the above materials to form a core-shell structure, which can effectively protect the Cu element or Cu ) in CuNCs from being oxidized to Cu ), so that its fluorescence is not affected, so that the obtained CuNCs composite material generally has strong fluorescence, improves stability, long fluorescence lifetime and good biocompatibility. Based on this, people are committed to the development and research of CuNCs composite material. Aggregation-induced emission (AIEgens) exhibits excellent optical stability and strong photoluminescence characteristics, so that the fluorescence sensor based on aggregation-induced emission (AIE) is helpful for rapid, trace and in-situ detection. AIE is different from general fluorescence phenomenon, which can be explained as the decrease of non-radiative transition energy caused by molecular aggregation, thereby causing fluorescence enhancement. AIE phenomenon has attracted great interest in academia and industry, and its special fluorescence characteristics have been applied to many fields, including analytical detection, biological imaging, optoelectronic devices, etc. [R. Hu, N.L.C. Leung, B.Z. Tang, AIEmacromolecules: syntheses, structures and functionalities. Chem. Soc. Rev. 2014, 43(13), 4494-4562.]. To our knowledge, there is no literature report on CuNCs composite material with aggregation-induced emission (AIE) characteristics for detecting Hg 2+ . Therefore, it is extremely innovative to design a fluorescence probe with AIE characteristics to detect Hg 2+ by aggregation state. The present research designs a metal-organic framework-wrapped fluorescent copper nanocluster (Cu NCs@ZIF-8) blue fluorescence probe with AIE characteristics, realizes stable fluorescence properties, and is used for detecting Hg 2+ in real environment. SUMMARY

[0005] The purpose of the present application is to provide a Cu NCs@ZIF-8 nanocomposite material with AIE characteristics and application of Hg2+ detection.

[0006] Another purpose of the present application is to develop a fluorescence probe for detecting Hg 2+ in real environment.

[0007] 1Cu NCs@ZIF-8 with blue fluorescence emission with aggregation-induced emission characteristics, prepared by the following method:

[0008] 1) Preparation of Cu NCs: 2-8 mL of 15-30 mM Cu(NO3)2·5H2O was added to 100 mL of ethanol, and after stirring to boiling at 60-100 °C, 2-10 mL of 0.6% folic acid solution and 1-5 mL of 0.1 M ascorbic acid solution were rapidly added; the pH was adjusted to 11-12; after continuing to heat to boiling for 10 min, it was cooled to room temperature; the supernatant was taken by centrifugation and stored in a 4 °C refrigerator;

[0009] 2) Preparation of Cu NCs@ZIF-8: 0.3-0.7 mmol of zinc nitrate hexahydrate and 0.3-0.7 mmol of dimethylimidazole were respectively dispersed in 21 mL of methanol to prepare a zinc nitrate hexahydrate methanol solution and a dimethylimidazole methanol solution, and 4-8 mL of Cu NCs, the zinc nitrate hexahydrate methanol solution and the dimethylimidazole methanol solution were added in turn, and stirred at room temperature for 1-5 h to obtain Cu NCs@ZIF-8.

[0010] Step 1) The Cu(NO3)2·5H2O is 4 mL, and the concentration is 30 mM; the folic acid is 4 mL, and the ascorbic acid is 2 mL.

[0011] Step 2) The Zn(NO3)2·6H2O is 6 mL; the zinc nitrate hexahydrate is 0.1563 g; the dimethylimidazole is 0.0431 g; and the stirring time is 2 h.

[0012] The Cu NCs@ZIF-8 nanocomposite with AIE characteristics is used for detecting Hg 2+ in aspects;

[0013] A method for detecting Hg 2+ using a Cu NCs@ZIF-8 fluorescent probe, which comprises:

[0014] 1) Drawing of a standard curve: the Cu NCs@ZIF-8 solution is mixed with an equal volume of ultrapure water, and the relative fluorescence intensity value I0 of the blank group is determined; the Cu NCs@ZIF-8 solution is mixed with an equal volume of Hg 2+ solution of different known concentrations, and the fluorescence spectrum is recorded and the corresponding relative fluorescence intensity value I is calculated to establish a standard curve of the relative fluorescence intensity value I / I0 versus the Hg 2+ concentration;

[0015] 2) Fluorescent detection of Hg 2+ : the Cu NCs@ZIF-8 solution is mixed with the Hg 2+ solution of the to-be-detected concentration, and the fluorescence intensity value I is determined and the relative fluorescence intensity value I / I0 is calculated, and the concentration of Hg 2+ in the to-be-detected solution is obtained according to the above standard curve.

[0016] The Cu NCs@ZIF-8 solution and Hg 2+ The reaction time is 10-15 min.

[0017] The reaction is carried out at room temperature.

[0018] The fluorescence detection conditions are: excitation wavelength 254-300 nm, and the emission intensity of Cu NCs@ZIF-8 at 340-400 nm is recorded. 2+ Quantitative analysis is carried out. Detailed description of the invention:

[0020] The application provides a ZIF-8 wrapped copper nanocluster Cu NCs@ZIF-8 with a core-shell structure having an aggregation-induced emission characteristic, which can detect Hg 2+ in a real environment. It is obtained by coating Cu NCs in ZIF-8 through a one-pot method. Trace amounts of Hg 2+ in an environmental water sample are detected by fluorescence mode. The fluorescence enhancement mechanism of the Cu NCs@ZIF-8 probe is an AIE mechanism induced by Hg 2+ , and the fluorescence of the probe is enhanced with the increase of Hg 2+ .

[0021] The synthesis method adopted in the application refers to the research of Zhang [Q. Zhang, Z. Zhang, S.H. Xu, L.G. Da, D. Lin, C.L. Jiang, Enzyme-free and rapid visual quantitative detection for pesticide residues utilizing portable smartphone integrated paper sensor. J. Hazard. Mater. 2022, 436, 129320.] and Gao [Q. Gao, S.Y. Xu, C. Guo, Y.G. Chen, L.Y. Wang, Embedding nanocluster in MOF via crystalline ion-triggered growth strategy for improved emission and selective sensing. ACS Appl. Mater. Interfaces. 2018, 10(18), 16059-16065.], and a slightly modified AIE characteristic Hg 2+Blue fluorescent copper cluster complex (Cu NCs@ZIF-8) with specific sensing performance

[0022] The present application has the following advantages:

[0023] 1. The present application synthesizes Cu NCs@ZIF-8 with blue fluorescent emission, which has the characteristics of aggregation-induced emission (AIE).

[0024] 2. The Cu NCs@ZIF-8 fluorescent probe designed in the present application can realize quantitative detection of Hg 2+ .

[0025] 3. The fluorescent probe constructed in the present application can be used for the method for detecting Hg 2+ in an aqueous solution, which has excellent selectivity and high sensitivity, wherein the detection limit of Hg 2+ is 30 nM, which meets the maximum allowable content (30 nM) of Hg 2+ in drinking water specified by the World Health Organization (WHO), indicating that the fluorescent probe can be used for detecting Hg 2+ in drinking water level. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 (a-b) SEM images of Cu NCs@ZIF-8; (c) EDX image of Cu NCs@ZIF-8; (d-f) TEM images of Cu NCs@ZIF-8;

[0027] Figure 2 XRD images of ZIF-8, Cu NCs, Cu NCs@ZIF-8;

[0028] Figure 3 (a) UV-Vis absorption spectrum, fluorescence excitation and emission spectrum of Cu NCs@ZIF-8, the inserted picture: pictures of Cu NCs@ZIF-8 under natural light (left) and ultraviolet lamp irradiation (right); (b) Fluorescence emission spectrum of Cu NCs@ZIF-8 under different excitation wavelengths; (c) Three-dimensional excitation-emission map of Cu NCs@ZIF-8;

[0029] Figure 4 (a) Fluorescence spectrum of Cu NCs@ZIF-8 reacting with different metal ions (100 µM), and fluorescence intensity of Cu NCs@ZIF-8 changing with time after adding Hg 2+ ; (b) Selectivity image of Cu NCs@ZIF-8 detecting Hg 2+ under ultraviolet lamp;

[0030] Figure 5 (a) Fluorescence intensity of Cu NCs@ZIF-8 under different concentrations of Hg2+ Figure 2. (a) Fluorescence spectra of Cu NCs@ZIF-8 in the presence of different concentrations of Hg2+ (0~600 µM). (b) I / I0 vs. Hg2+ concentration (0.1~8 µM) plot. (c) Images of Cu NCs@ZIF-8 after adding different concentrations of Hg2+ (0~600 µM) under 365 nm UV light. 2+ 2+ DETAILED DESCRIPTION

[0031] Example 1 Preparation of Cu NCs@ZIF-8

[0032] 1) Preparation of Cu NCs: Freshly prepared 4 mL of Cu(NO3)2·5H2O (30 mM) and 100 mL of ethanol were added to a 250 mL round bottom flask. After stirring in a water bath at 80 °C until boiling, 4 mL of folic acid (FA) solution (0.6%) and 2 mL of ascorbic acid (AA) solution (0.1 M) were quickly added. The pH was adjusted to 11-12 using sodium hydroxide (NaOH). After continuing to heat to boiling for 10 min, it was cooled to room temperature. Centrifugation was performed at a speed of 6000 r / min for 10 min, and the supernatant was stored in a 4 °C refrigerator

[0033] 2) Preparation of Cu NCs@ZIF-8: 0.1563 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 0.0431 g of 2-MI were respectively dispersed in 21 mL of methanol, and 6 mL of Cu NCs, Zn(NO3)2·6H2O solution and 2-MI solution were sequentially added to a 50 mL round bottom flask, which was stirred at room temperature for 2 h, and the obtained mixture was stored at room temperature for use.

[0034] Example 2 Characterization of Cu NCs@ZIF-8

[0035] (1) Scanning electron microscopy (SEM) and transmission electron microscopy (TEM)

[0036] In order to clarify the morphology of Cu NCs@ZIF-8, SEM and TEM characterization were performed. According to the SEM images in a and b, the synthesized Cu NCs@ZIF-8 presented a flower-like shape with an average size of 500 nm. At the same time, the TEM images also clearly showed the flower-like Cu NCs@ZIF-8, which was consistent with the SEM images. In addition, the EDS spectrum (c) proved the existence of Cu, Zn, C, O and other elements in Cu NCs@ZIF-8, which confirmed the successful synthesis of Cu NCs@ZIF-8. Figure 1 Figure 1 b, the synthesized Cu NCs@ZIF-8 presented a flower-like shape with an average size of 500 nm. At the same time, the TEM images also clearly showed the flower-like Cu NCs@ZIF-8, which was consistent with the SEM images. In addition, the EDS spectrum (c) proved the existence of Cu, Zn, C, O and other elements in Cu NCs@ZIF-8, which confirmed the successful synthesis of Cu NCs@ZIF-8. Figure 1

[0037] ​​​​(2) X-ray diffraction analysis (XRD)

[0038] Figure 2 The XRD image of Cu NCs@ZIF-8 shows characteristic peaks at 7.18°, 12.79°, and 17.22°, which correspond to the (011), (112), and (222) crystal planes of ZIF-8, respectively, proving the successful synthesis of ZIF-8 and its high crystallinity.

[0039] (3) Ultraviolet-visible absorption spectrum

[0040] like Figure 3 As shown in Figure a, the UV-Vis absorption spectrum of Cu NCs@ZIF-8 exhibits a significant absorption peak around 280 nm, which may be related to the π-π α-γ of the FA of Cu NCs. * This is related to the transition. Furthermore, no obvious surface plasmon resonance peak was observed at 520 nm, indicating that there are no large particles in Cu NCs@ZIF-8.

[0041] (4) Fluorescence spectrum

[0042] At the optimal excitation wavelength of 295 nm, Cu NCs@ZIF-8 exhibits an emission peak at 349 nm. Figure 3 a), which is Figure 3 The results from the three-dimensional fluorescence excitation-emission plot in c match. The Cu NCs@ZIF-8 solution is colorless under natural light and exhibits blue fluorescence under a 365 nm UV light source. Figure 3 (an illustration). Figure 3 b shows that as the excitation wavelength increases from 280 nm to 310 nm, the emission peak position of Cu NCs@ZIF-8 at 349 nm remains basically unchanged, indicating that Cu NCs@ZIF-8 does not have excitation dependence.

[0043] Example 3: Detection of Hg using Cu NCs@ZIF-8 as a fluorescent probe 2+

[0044] Using Cu NCs@ZIF-8 as a fluorescent probe, it can be used for Hg 2+ The detection was performed when a certain concentration of Hg was added to the Cu NCs@ZIF-8 probe solution. 2+ A significant enhancement of fluorescence occurs at this time. Therefore, Cu NCs@ZIF-8 can achieve fluorescence differentiation from other metal ions, specifically Hg. 2+ Specific detection. The relative fluorescence intensity (I / I0) of the Cu NCs@ZIF-8 fluorescent probe and Hg 2+ There is a good linear relationship between the concentrations, and the linear relationship equation is used to perform quantitative analysis on samples with unknown concentrations.

[0045] (1) Detection of Hg by fluorescence method 2+ Selective evaluation

[0046] The selectivity of the probe is a prerequisite for studying its sensing applications; therefore, this invention examines the selectivity of Cu NCs@ZIF-8 for Hg. 2+ Detection selectivity. Cu NCs@ZIF-8 probe with 100 µM Hg 2+ Cd 2+ Co 2+ Fe 2+ Mg 2+ Ni 2+ Cr 3+ Ba 2+ Mn 2 + Zn 2+ Pb 2+ Ca 2+ and Ag + The fluorescence spectrum was measured after equal volumes of solutions were mixed. For example... Figure 4 As shown in a, when Hg 2+ In its presence, the fluorescence spectrum showed a significant change. The addition of 100 μM Hg... 2+ Subsequently, the absorption peak of Cu NCs@ZIF-8 at 349 nm was significantly enhanced. This phenomenon is a typical characteristic of aggregation-induced emission enhancement, confirming the AIE properties of Cu NCs@ZIF-8. Furthermore, the UV-Vis image shows (…). Figure 4 b), Hg 2+ The blue fluorescence of Cu NCs@ZIF-8 was significantly enhanced, while the fluorescence color of other ion samples was almost identical to that of the blank sample, which is consistent with the fluorescence spectroscopy results. This result indicates that Cu NCs@ZIF-8 significantly enhances the fluorescence of Hg. 2+ It exhibits high selectivity and specificity compared to other competing metal ions.

[0047] (2) Detection of Hg by fluorescence method 2+ Sensitivity assessment

[0048] Hg based on Cu NCs@ZIF-8 fluorescent probe 2+ Its excellent "single-response on-type" fluorescence response to Hg 2+ Quantitative detection was performed to further investigate the effect of Cu NCs@ZIF-8 on Hg. 2+ Detection sensitivity ( Figure 5 ). Different concentrations of Hg 2 +The (0-600 μM) solution was mixed with Cu NCs@ZIF-8 in an equal volume ratio, and the fluorescence response was monitored by fluorescence spectroscopy after reaction for 10-15 min. Figure 5 As can be seen, with the increase of the concentration of Hg 2+ , the emission at 349 nm gradually increased, which was consistent with the change of the fluorescence intensity under the ultraviolet lamp (Fig. Figure 5 c), the fluorescence intensity ratio I / I0 of Cu NCs@ZIF-8 had a good linear relationship with the concentration of Hg 2+ in the range of 0.1-8 μM (Fig. Figure 5 b), and the detection limit was calculated to be 30 nM.

[0049] (3) Recovery rate analysis of Hg 2+ in actual water samples

[0050] The Cu NCs@ZIF-8 prepared in Example 1 was used for the standard addition recovery experiment to determine Hg 2+ in Changbai Mountain and Yalu River. The solid impurities in the water were removed by a filter membrane before sample determination. The standard addition method was used to simulate the actual detection, and different concentrations of Hg 2+ standard solution (0.6, 12, 5 μM) were added to the two water samples, and then the Cu NCs@ZIF-8 solution was added, and the standard addition recovery rate was measured to be 101.84-107.04%, and the RSD was less than 5%. The specific results of the sample addition recovery rate test (n=3) are shown in Table 1.

[0051] Table 1 Determination of the content of Hg 2+ in water samples

[0052] Sample Added (µM) Found (µM) Recovery (%) n=3 RSD (%) n=3 Chang Bai River 0.6 0.61 102.17 1.45 2 2.05 102.47 0.78 5 5.09 101.84 0.35 Yalu River 0.6 0.64 107.04 2.5 2 2.08 104.15 1.8 5 5.24 104.95 1.1

[0053] In summary, the Cu NCs@ZIF-8 probe with the aggregation-induced emission characteristic is designed, which can be used as an open probe to realize the fluorescence quantitative detection of Hg 2+ ions and identify Hg 2+ in the aqueous solution.

Claims

1. A Cu NCs@ZIF-8 nanocomposite with AIE characteristics, prepared by the following method: 1) Preparation of Cu NCs: 2-8 mL of 15-30 mM Cu(NO3)2·5H2O was added to 100 mL of ethanol, and after stirring to boiling at 60-100℃, 2-10 mL of 0.6% folic acid solution and 1-5 mL of 0.1 M ascorbic acid solution were quickly added; the pH was adjusted to 11-12; after continuing to heat to boiling for 10 min, it was cooled to room temperature; the supernatant was taken by centrifugation and stored in a 4℃ refrigerator; 2) Preparation of Cu NCs@ZIF-8: 0.3-0.7 mmol of zinc nitrate hexahydrate and 0.3-0.7 mmol of dimethylimidazole were respectively dispersed in 21 mL of methanol to prepare zinc nitrate hexahydrate methanol solution and dimethylimidazole methanol solution, 4-8 mL of Cu NCs, zinc nitrate hexahydrate methanol solution and dimethylimidazole methanol solution were added in turn, and stirred at room temperature for 1-5 h to obtain Cu NCs@ZIF-8. 2.The Cu NCs@ZIF-8 nanocomposite with AIE characteristics according to claim 1, characterized in that: In step 1), the Cu(NO3)2·5H2O is 4 mL with a concentration of 30 mM; the folic acid is 4 mL and the ascorbic acid is 2 mL. 3.The Cu NCs@ZIF-8 nanocomposite with AIE characteristics according to claim 1, characterized in that: In step 2), the zinc nitrate hexahydrate is 0.1563 g; the dimethylimidazole is 0.0431 g; and the stirring time is 2 h.

4. The Cu NCs@ZIF-8 nanocomposites with AIE characteristics of claim 1 are applied in the detection of Hg 2+ aspects.

5. Cu NCs@ZIF-8 fluorescent probe for detecting Hg 2+ a method comprising: 1) Standard curve drawing: take Cu NCs@ZIF-8 solution and mix with equal volume of ultrapure water, determine the relative fluorescence intensity value I0 of the blank group, take Cu NCs@ZIF-8 solution and mix with equal volume of different known concentration of Hg 2+ Solutions, record the fluorescence spectrum and calculate the corresponding relative fluorescence intensity value I, establish the standard curve of relative fluorescence intensity value I / I0 and Hg 2+ Concentration corresponding; 2) Fluorescence detection of Hg 2+ : The Cu NCs@ZIF-8 nanocomposites with AIE characteristics of claim 1 and the concentration of Hg to be detected are mixed 2+ After mixing, the fluorescence intensity value I of the solution is measured and the relative fluorescence intensity value I / I0 is calculated, and the concentration of Hg in the solution to be detected is obtained according to the above standard curve. 2+ ​ 6. The Cu NCs@ZIF-8 fluorescent probe for detecting Hg 2+ The method is characterized by comprising the following steps: The CuNCs@ZIF-8 solution and Hg 2+ The reaction time is 10-15 min; the reactions are all carried out at room temperature.

7. The Cu NCs@ZIF-8 fluorescent probe for detecting Hg 2+ characterized in that The fluorescence detection conditions were as follows: excitation wavelength 254-300 nm, and recording the emission intensity of Cu NCs@ZIF-8 at 340-400 nm against Hg 2+ for quantitative analysis.

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