Preparation method and application of MXene (at) ZIF-67 (at) AgNPs composite SERS (Surface Enhanced Raman Scattering) substrate

Abstract

The invention relates to the technical field of Raman scattering, in particular to a preparation method and application of an MXene (at) ZIF-67 (at) AgNPs composite type SERS (Surface Enhanced Raman Scattering) substrate, and the preparation method comprises the following steps: step 1, synthesizing a photoelectric double-gain type MXene (at) ZIF-67 heterojunction based on an in-situ solvothermal method, and step 2, loading AgNPs on MXene (at) ZIF-67 (at) AgNPs under the action of an amido bond to assemble the MXene (at) ZIF-67 (at) AgNPs composite type SERS substrate. And step 3, constructing an endocrine disrupter detection platform. According to the prepared MXene (at) ZIF-67 (at) AgNPs composite SERS substrate, an electromagnetic field is synergistically enhanced through a conductive network of MXene and a surface plasma resonance effect of AgNPs, meanwhile, an endocrine disrupter is enriched through a porous structure of ZIF-67, an SERS'hot spot 'is formed, and the Raman signal intensity and the detection sensitivity of the endocrine disrupter are greatly improved. The stability of the composite substrate can be improved by the inhibition effect of ZIF-67 on surface oxidation of the MXene sheet layer. Experiments show that a detection method based on the substrate is simple and easy to implement, and trace endocrine disrupters under a complex background can be effectively detected.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of Raman scattering technology, and particularly relates to a preparation method of a MXene@ZIF-67@AgNPs composite SERS substrate and application thereof. BACKGROUND

[0002] Surface-enhanced Raman spectroscopy (SERS) technology has become an important tool in the field of trace substance detection due to its unique advantages of in-situ, non-destructive and "fingerprint" identification. Endocrine disruptors (EDCs) are a class of exogenous chemicals that can interfere with the normal function of the human or animal endocrine system, even at very low concentration levels, causing significant health risks, including reproductive abnormalities, developmental disorders, nervous system damage, and decreased immunity. Common EDCs such as bisphenol A (BPA), phthalates, and alkylphenols are widely present in plastic products, daily chemicals, pesticides, and industrial emissions, and are continuously exposed to the human body through food, water, and environmental media. However, the content of EDCs in actual samples (such as water, food, and biological fluids) is extremely low (often at trace or ultra-trace levels), and the matrix is complex with many coexisting interferents. Traditional SERS methods generally face problems such as limited sensitivity, weak anti-interference ability, poor substrate reproducibility, and difficulty in simultaneous identification of multiple components. Therefore, developing a SERS substrate with high enhancement performance, excellent stability, and strong specific recognition ability is of great significance for rapid and accurate monitoring of endocrine disruptors in complex actual samples.

[0003] SERS signal enhancement mainly relies on the synergistic effect of electromagnetic field enhancement (such as local surface plasmon resonance of metal nanoparticles, LSPR) and chemical enhancement (such as charge transfer effect). In recent years, two-dimensional transition metal carbides / nitrides (MXene) have shown unique advantages in SERS substrate design due to their ultra-large specific surface area, adjustable electronic structure, high hydrophilicity, and excellent biocompatibility. For example, the surface of typical MXene material Ti3C2T X The surface of typical MXene material Ti3C2T

[0004] Metal-organic framework (MOFs) materials (such as ZIF-67) have adjustable pore size, high porosity, and rich surface functional groups, which can not only be used as "molecular sieves" to separate interfering substances in complex matrix and improve detection specificity, but also can stabilize metal nanoparticles through confinement effect and inhibit their agglomeration. By combining MOFs with MXene, the advantages of both can be combined: MXene provides efficient charge transfer channels and molecular adsorption sites, while MOFs achieve selective enrichment of target molecules and improved substrate stability. In addition, AgNPs are often used as the core enhancement unit of SERS substrates due to their strong light scattering coefficient and LSPR effect. Therefore, the construction of MXene@MOFs@AgNPs multi-level composite structure is expected to achieve "adsorption-enrichment-enhancement" integration through chemical enhancement of MXene, electromagnetic field enhancement of AgNPs, and selective enrichment / stability of MOFs, breaking through the bottleneck of traditional substrates in sensitivity, specificity, and stability.

[0005] However, there are still challenges in the preparation of existing MXene@MOFs@noble metal nanoparticle composite substrates: (1) interface compatibility problem: the coordination between the surface functional groups of MXene and the MOFs precursor is weak, leading to uneven growth of MOFs on the surface of MXene, affecting the stability of the composite structure; (2) poor dispersion of noble metal nanoparticles: noble metal nanoparticles in the MOFs channels are prone to agglomeration, reducing the "hot spot" density; (3) limited practical application: the composite substrate is prone to structural degradation in complex matrix (such as high salt, high humidity environment), leading to a decrease in SERS signal reproducibility. SUMMARY

[0006] The purpose of the present application is to solve the problems existing in the prior art and provide a preparation method of MXene@ZIF-67@AgNPs composite SERS substrate and its application. By in-situ growth of ZIF-67 to regulate the interface interaction between MXene and AgNPs, and by using the confinement effect of ZIF-67, the capture efficiency, signal enhancement effect, and stability of the substrate for endocrine disruptors are synergistically improved, which is of great significance for efficient detection of endocrine disruptors and provides a new idea for trace pollutant detection in food safety and environmental monitoring fields.

[0007] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] A preparation method of MXene@ZIF-67@AgNPs composite SERS substrate, comprising the following steps:

[0009] Step 1, synthesis of accordion-like MXene sheet structure: lithium fluoride is fully dissolved in concentrated hydrochloric acid (12 mol / L) with magnetic stirring, then aluminum titanium carbide powder is gradually and slowly added to the above solution under stirring; the reactants are stirred at 35 degrees for 24 h, after 24 h of reaction, the obtained powder is washed with deionized water to about pH 7, and centrifuged with ethanol for three times, finally the powder is dried in a vacuum oven at 60 ℃ overnight, and finally Ti3C2T x powder is obtained;

[0010] Step 2, preparation of metal organic framework ZIF-67: zinc nitrate hexahydrate is dissolved in 25 mL of methanol, stirred for 30 min to form solution A; then, 2-methylimidazole is dissolved in 25 mL of methanol, stirred to form solution B; solution B is poured into solution A and mixed, after stirring for 1 h, the mixture is aged for 24 h and then centrifuged; the above mixed solution is washed with methanol for 2 times, and dried at 60 ℃ for 12 h to obtain ZIF-67;

[0011] Step 3, preparation of MXene@ZIF-67@AgNPs composite SERS substrate: 0.018 g of silver nitrate is added to 100 mL of deionized water, heated and stirred, and when the solution boils, 1 mL of 1% sodium citrate solution is added, and after the color does not change, the heating is turned off and the reaction is continued for half an hour, then cooled to room temperature and stored at 4 ℃; 100 mL of AgNPs is concentrated to 20 mL (5 times concentration), and divided into two groups, each taking 10 mL, 50 μL of EDTA (2.5 mM) and 50 μL of NHS (2.5 mM) are added to 10 mL of AgNPs, and the mixture is allowed to react for 3 h to obtain activated Ag nanoparticles; ZIF-67 powder is added to the above activated AgNPs solution, stirred at room temperature for a period of time, then MXene is added and stirred to obtain MXene@ZIF-67@AgNPs composite SERS substrate.

[0012] Preferably, in step 1, the mass of lithium fluoride used is 1 g, the volume of concentrated hydrochloric acid is 10 mL, the concentration is 12 mol / L, and the mass of aluminum titanium carbide powder is 1 g.

[0013] Preferably, in step 2, the mass of zinc nitrate hexahydrate is 0.45 g, and the mass of 2-methylimidazole is 0.5 g.

[0014] Preferably, in step 3, the mass of MXene and ZIF-67 used is 0.1 mg and 0.2 mg, respectively.

[0015] Preferably, in step 3, the time for the AgNPs to react with the MXene@ZIF-67 is 8-12 hours.

[0016] The conductive network of the MXene and the surface plasmon resonance effect of the AgNPs enhance the Raman signal, and the high enrichment of the ZIF-67 forms a SERS "hot spot" to improve the detection sensitivity. The MXene@ZIF-67@AgNPs heterojunction with the photoelectric dual gain type is constructed, and the composite material is used for the surface-enhanced Raman composite SERS substrate to detect endocrine disruptor residues.

[0017] The application further provides a use of the MXene@ZIF-67@AgNPs composite SERS substrate prepared by the above preparation method in detection of endocrine disruptors.

[0018] Preferably, 20 μL of different concentrations of endocrine disruptor solutions are added on the SERS substrate in parallel, respectively, and SERS detection is performed after room temperature reaction for 2 hours; the detection conditions are as follows: excitation wavelength 785 nm, integration time 10 s, and integration number 1.

[0019] By adopting the above technical solution, the AgNPs are uniformly distributed on the MXene@ZIF-67 with a large specific surface area due to the strong light scattering coefficient and the LSPR effect, and are often used as a core enhancement unit of a SERS substrate. The MXene@ZIF-67@AgNPs composite SERS substrate prepared by the above method utilizes the chemical enhancement of the MXene, the electromagnetic field enhancement of the AgNPs, and the enrichment capacity of the ZIF-67 to synergistically improve the enrichment performance, signal enhancement, and stability of the SERS substrate to endocrine disruptors, so that high-sensitivity detection of trace endocrine disruptors is realized.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] 1. The MXene, the ZIF-67, and the AgNPs can be compounded by a simple in-situ growth or self-assembly process, the preparation method is simple to operate, the process complexity and the production cost are significantly reduced, and the method is suitable for industrial large-scale preparation.

[0022] 2. In the MXene@ZIF-67 heterojunction constructed by the application, the porous framework structure of the ZIF-67 can effectively wrap the MXene nanosheet, inhibit the surface oxidation and agglomeration of the MXene nanosheet, and improve the long-term stability of the material; meanwhile, the interface interaction between the ZIF-67 and the MXene can optimize the electron transport path, and further improve the conductivity of the composite substrate.

[0023] 3、The MXene@ZIF-67@AgNPs composite substrate prepared by the method has the advantages that AgNPs are uniformly dispersed on the surface of MXene@ZIF-67 and form a large number of “hot spot” structures, strong electromagnetic field enhancement is generated through the LSPR effect, meanwhile, the high conductivity of MXene and the porous adsorption characteristics of ZIF-67 synergistically promote the charge transfer between the endocrine disruptor and the substrate, the chemical enhancement effect is superimposed, the SERS signal intensity is significantly improved, and trace detection of the endocrine disruptor is realized.

[0024] 4、The MXene@MOFs@AgNPs multi-level composite structure constructed by the method has the advantages that the chemical enhancement of MXene, the electromagnetic field enhancement of AgNPs and the high-efficiency selective enrichment effect of MOFs on the endocrine disruptor are combined to realize the integration of “adsorption-enrichment-enhancement”. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Scanning electron microscope images of silver nanoparticles (a), MXene (b), ZIF-67 (c) and MXene@ZIF-67@AgNPs (d) synthesized by the method of the application;

[0026] Figure 2 (a) is the SERS spectrum of 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) measured after the MXene@ZIF-67@AgNPs composite SERS substrate prepared by the method of the application is placed for different time, (b) is the change graph of the peak intensity of DTNB at 1332 cm -1 ;

[0027] Figure 3 (a) is the SERS spectrum of 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) measured after the MXene@ZIF-67@AgNPs composite SERS substrate prepared by the method of the application is placed for different time, (b) is the change graph of the peak intensity of DTNB at 1332 cm -1 ;

[0028] Figure 4 (a) is the SERS spectrum of 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) measured after the MXene@ZIF-67@AgNPs composite SERS substrate prepared by the method of the application is placed for different time, (b) is the change graph of the peak intensity of DTNB at 1332 cm -1 ;

[0029] Figure 5 SERS spectra of different concentrations of endocrine disruptors (ethinyl estradiol, dienestrol, dexamethasone, fluorgestone acetate, estrone and estradiol) detected by the composite SERS substrate of the application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings, so that the technical personnel in the art can better understand the advantages and features of the present application, and the protection scope of the present application can be defined more clearly. The embodiments described in the present application are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the ordinary technical personnel in the art without creative labor belong to the protection scope of the present application.

[0031] Embodiment 1:

[0032] A preparation method of an MXene@ZIF-67@AgNPs composite SERS substrate, comprising the following steps:

[0033] Synthesis of MXene and ZIF-67: MXene was synthesized by etching method, 1 g of lithium fluoride was fully dissolved in 10 mL of concentrated hydrochloric acid (12 mol / L), and stirred at 35 degrees for 30 min, then 1 g of aluminum titanium carbide powder was gradually and slowly added to the above solution under stirring. The reactants were stirred at 35 degrees for 24 h. After 24 h of reaction, the obtained powder was washed with deionized water to about pH 7, and centrifuged with ethanol for three times, finally the powder was dried in a vacuum oven at 60 ℃ overnight, and finally Ti3C2T x powder was obtained. 0.45 g of zinc nitrate hexahydrate was dissolved in 25 mL of methanol and stirred for 30 min to form solution A. Then, 0.5 g of 2-methylimidazole was dissolved in 25 mL of methanol and stirred to form solution B. Solution B was poured into solution A and mixed, and after stirring for 1 h, the mixture was aged for 24 h and then centrifuged. The above mixed solution was washed with methanol for 2 times, and dried at 60 ℃ for 12 h to obtain ZIF-67.

[0034] Preparation of MXene@ZIF-67@AgNPs composite SERS substrate: 0.018 g silver nitrate was added to 100 mL deionized water, heated and stirred until the solution boiled. Then, 1 mL of 1% sodium citrate solution was added. After the color changed, heating was turned off and the reaction continued for another half hour. The solution was then removed, cooled to room temperature, and stored at 4 °C. 100 mL of AgNPs was concentrated to 20 mL (5-fold concentration), and divided into two groups of 10 mL each. 50 μL of EDC (2.5 mM) and 50 μL of NHS (2.5 mM) were added to each 10 mL AgNPs solution, and the mixture was allowed to stand for 3 h to obtain activated Ag nanoparticles. 0.2 mg of ZIF-67 powder was added to the activated AgNPs solution, and the mixture was stirred at room temperature for 8-12 h. Then, 0.1 mg of MXene was added, and stirring continued for another 8-12 h to obtain the MXene@ZIF-67@AgNPs composite SERS substrate.

[0035] Example 2: Characterization of MXene@ZIF-67@AgNPs composite SERS substrate

[0036] First, the morphology of the prepared silver nanoparticles (AgNPs) was characterized. For example... Figure 1 As shown in Figure a, the silver nanoparticles obtained by the sodium citrate thermal reduction method have uniform particle size and regular spherical shape. Figure 1 b shows that MXene prepared by hydrofluoric acid etching exhibits a typical accordion-like multilayer structure. Subsequently, ZIF-67 particles were grown in situ on the MXene surface, and it was observed that a large number of uniformly sized ZIF-67 crystals with a dodecahedral morphology were successfully loaded on the surface and between the MXene layers. Figure 1 c). Finally, AgNPs were loaded onto the surface of MXene@ZIF-67 via an amide bonding reaction to form an MXene@ZIF-67@AgNPs composite substrate. Figure 1 d). In this structure, ZIF-67 is uniformly distributed on the MXene sheets, and its surface is further modified with high-density AgNPs, indicating that the MXene@ZIF-67@AgNPs composite SERS substrate has been successfully constructed, providing a material basis for its application in the highly sensitive detection of endocrine disruptors.

[0037] Example 3: Evaluation of the stability of the composite SERS substrate

[0038] The present application takes 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) as a probe molecule to evaluate the stability of the MXene@ZIF-67@AgNPs composite SERS substrate. The prepared MXene@ZIF-67@AgNPs composite substrate is placed at room temperature for different lengths of time (0, 7, 14, 21, 28, 35, 42, 49, 56, 63 days), and then used to detect the DTNB solution. As shown in Figure 2 , with the extension of the placement time, the SERS signal intensity of DTNB does not decrease significantly, indicating that the composite substrate has excellent long-term stability. This performance can be attributed to the porous structure of ZIF-67, which can tightly wrap the MXene sheet, effectively inhibit the oxidation of the MXene surface functional groups (such as -OH, -O-), avoid the collapse of the MXene layer or the decrease of the conductivity, and significantly improve the stability and structural integrity of the overall composite structure. The MXene@ZIF-67@AgNPs composite SERS substrate still maintains high SERS activity after at least 56 d of long-term placement, providing key performance support for its practical application in endocrine disruptor detection.

[0039] Example 4: Evaluation of the sensitivity of the composite SERS substrate

[0040] The present application uses p-mercaptobenzoic acid (4-MBA) as a probe molecule for testing to evaluate the sensitivity of the prepared composite SERS substrate. As shown in Figure 3 , by detecting different concentrations of 4-MBA solution on the substrate, it is found that the SERS signal is significantly enhanced with the increase of concentration. When the signal-to-noise ratio (S / N) is 3, the detection limit (LOD) of 4-MBA detected by this method is 5.0×10 -10 M, proving that the composite SERS substrate has excellent detection sensitivity.

[0041] Example 5: Evaluation of the repeatability of the composite SERS substrate

[0042] To verify the detection repeatability of the prepared MXene@ZIF-67@AgNPs composite SERS substrate, the present application randomly selects 10 different areas on the surface of the substrate for SERS spectrum testing of DTNB. The experimental data shows that the SERS spectrum peak shape and intensity at each position are highly consistent, indicating that the composite substrate has a highly uniform enhancement effect in spatial distribution, fully proving its excellent detection repeatability in practical application (RSD < 5%). Figure 4

[0043] Example 6: SERS detection of different concentrations of endocrine disruptors

[0044] ​First, prepare endocrine disruptor solutions with different concentrations. Take 20 μL of endocrine disruptor solutions with different concentrations and drop them on the prepared MXene@ZIF-67@AuNPs composite SERS substrate respectively, and then perform SERS detection after reacting for 2 h at room temperature. The laser wavelength is 785 nm, the integration time is 10 s, and the integration number is 1. The results are shown in Figure 5 Different types of endocrine disruptors have different SERS spectral peaks, which is due to the different molecular structural formulas of the endocrine disruptors. According to the characteristics of the SERS fingerprint spectrum and the MXene@ZIF-67@AgNPs sensor prepared in the present application, the simultaneous presence of six types of endocrine disruptors in milk can be detected and distinguished.

[0045] In summary, the present application controls the interface interaction between MXene and AgNPs by in-situ growth of ZIF-67, utilizes the confinement effect of ZIF-67, and synergistically improves the capture efficiency, signal enhancement effect and stability of the substrate for endocrine disruptors, which is of great significance for efficient detection of endocrine disruptors, and provides a new idea for trace pollutant detection in the fields of food safety and environmental monitoring.

[0046] The description and practice disclosed in the present application are easy to think and understand for ordinary skilled persons in the technical field, and several improvements and refinements can be made without departing from the principles of the present application. Therefore, modifications or improvements made without departing from the spirit of the present application should also be considered within the protection scope of the present application.

Claims

1. A method for preparing a MXene@ZIF-67@AgNPs composite SERS substrate, characterized in that, Comprising the following steps: Step 1, synthesis of accordion-like MXene sheet structure: Lithium fluoride was dissolved in concentrated hydrochloric acid with magnetic stirring, then aluminum titanium carbide powder was gradually and slowly added to the above solution under stirring; the reactants were stirred at 35 degrees for 24 h, after 24 h of reaction, the obtained powder was washed with deionized water to about pH 7, and washed with ethanol three times by centrifugation, finally the powder was dried in a vacuum oven at 60 °C overnight, finally Ti3C2T x powder was obtained; Step 2, preparation of metal organic framework ZIF-67: dissolve zinc nitrate hexahydrate in 25 mL of methanol, stir for 30 min to form solution A; then, dissolve 2-methylimidazole in 25 mL of methanol, stir until uniform to form solution B; pour solution B into solution A and mix, stir for 1 h after reaction, centrifuge after aging for 24 h; wash the above mixed solution with methanol twice, dry at 60°C for 12 h to obtain ZIF-67; Step 3, preparation of MXene@ZIF-67@AgNPs composite SERS substrate: 0.018 g of silver nitrate is added to 100 mL of deionized water, heated and stirred, and when the solution boils, 1 mL of 1% sodium citrate solution is added, and after the color does not change, the heating is turned off and the reaction is continued for half an hour, then cooled to room temperature and stored at 4°C; 100 mL of AgNPs is concentrated to 20 mL, divided into two groups, each taking 10 mL, 50 μL of EDTC and 50 μL of NHS are added to 10 mL of AgNPs, and reacted for 3 h to obtain activated Ag nanoparticles; ZIF-67 powder is added to the above activated AgNPs solution, stirred at room temperature for a period of time, then MXene is added and stirred to obtain MXene@ZIF-67@AgNPs composite SERS substrate.

2. The method for preparing an MXene@ZIF-67@AgNPs composite SERS substrate according to claim 1, characterized in that, In step 1, the mass of lithium fluoride used is 1 g, the volume of concentrated hydrochloric acid is 10 mL, the concentration is 12 mol / L, and the mass of aluminum titanium carbide powder is 1 g.

3. The method for preparing an MXene@ZIF-67@AgNPs composite SERS substrate according to claim 1, characterized in that, In step 2, the mass of zinc nitrate hexahydrate is 0.45 g, and the mass of 2-methylimidazole is 0.5 g.

4. The method for preparing an MXene@ZIF-67@AgNPs composite SERS substrate according to claim 1, characterized in that, In step 3, the mass of MXene and ZIF-67 used is 0.1 mg and 0.2 mg, respectively.

5. The method for preparing an MXene@ZIF-67@AgNPs composite SERS substrate according to claim 1, characterized in that, In step 3, the reaction time of AgNPs with MXene@ZIF-67 is 8 h-12 h.

6. The application of a MXene@ZIF-67@AgNPs composite SERS substrate prepared by the preparation method of any one of claims 1-5 in detecting endocrine disruptors.

7. Use according to claim 6, characterized in that, 20 μL of different concentrations of endocrine disruptor solution is added to the SERS substrate in parallel, and SERS detection is performed after reaction at room temperature for 2 h; the detection conditions are: excitation wavelength 785 nm, integration time 10 s, integration number 1. 20 μL of different concentrations of endocrine disruptor solution is added to the SERS substrate in parallel, and SERS detection is performed after reaction at room temperature for 2 h; the detection conditions are: excitation wavelength 785 nm, integration time 10 s, integration number 1.

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