A double-shell Ag-ZnAl2O4-MOF composite material, its preparation method, and its application in trace detection of organic pollutants.

Abstract

The application belongs to the field of SERS detection, and particularly relates to a double-shell Ag-ZnAl2O4-MOF composite material, a preparation method thereof and application thereof in trace detection of organic pollutants. ZnAl2O4 nanoparticles are first synthesized by a hydrothermal method, and then the prepared ZnAl2O4 nanoparticles are placed into a prepared MOF growth solution to form a ZnAl2O4-MOF composite structure, and on this basis, Ag nanoparticles are further compounded to form a double-shell Ag-ZnAl2O4-MOF composite material. The Ag-ZnAl2O4-MOF composite substrate has the characteristics of synergistic effect of physical enhancement and electromagnetic enhancement, and due to the large specific surface area, porosity and multi-metal site characteristics of the intermediate layer MOF, more hot spots can be formed. Due to the charge transfer effect caused by the compounding with ZnAl2O4, electromagnetic enhancement effect is generated, and these characteristics can effectively enhance the SERS signal intensity.

Description

Technical Field

[0001] This invention belongs to the field of SERS detection, specifically relating to a double-shell Ag-ZnAl2O4-MOF composite material, its preparation method, and its application in the detection of trace organic pollutants. Background Technology

[0002] Surface-enhanced Raman scattering (SERS), with its unique molecular fingerprinting characteristics, ultra-high detection sensitivity, and rapid response, has become an important spectroscopic technique for screening and quantitative analysis of trace organic pollutants in aquatic environments. Utilizing the synergistic effect of localized plasmon resonance in noble metals and charge transfer in semiconductors, SERS can achieve efficient and accurate detection of trace pollutants, overcoming the shortcomings of traditional detection methods such as complex operation, long processing time, and high detection limits. The enhancement mechanism of SERS detection technology can be divided into physical enhancement (EM) and chemical enhancement (CM). Physical enhancement, also known as electromagnetic enhancement, is mainly related to the localized surface plasmon resonance (LSPR) effect generated by noble metals such as Ag and Au on the substrate surface, forming high-density electromagnetic field "hot spots," which is the dominant factor in signal enhancement. Chemical enhancement is related to charge transfer.

[0003] Methylene blue (MB) is a typical cationic organic dye in the printing and dyeing industry. It is highly water-soluble, structurally stable, and difficult to biodegrade. Large-scale discharge can cause water color pollution, disrupt the aquatic ecological balance, and pose potential biotoxicity with long-term exposure. It is a highly representative organic micropollutant in the aquatic environment. Therefore, developing a high-performance SERS substrate to achieve sensitive detection of MB is of significant practical importance.

[0004] MOFs (Metal-Organic Frameworks) are porous crystalline metal-organic framework materials with advantages such as large specific surface area, tunable pore size, and strong adsorption capacity. They can effectively enrich target organic pollutants while also providing isolation and protection and optimizing interfacial electron transport. ZnAl2O4 is a spinel-type metal oxide with a stable structure and strong chemical corrosion resistance. It can serve as a stable core to provide skeletal support and participate in charge transfer. The combination of these two materials can synergistically compensate for the deficiencies of individual materials, laying the structural foundation for constructing a highly stable and sensitive SERS composite substrate. The double-shell Ag-ZnAl2O4-MOF composite material combines the stable zinc-aluminum spinel framework, the porous enrichment effect of MOFs, and the enhancement advantages of silver plasma. It can effectively improve SERS signal intensity, detection stability, and anti-interference ability, providing a new approach for the rapid monitoring and collaborative treatment of MB-type organic dye pollutants in water. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention designs and synthesizes a double-shell Ag-ZnAl2O4-MOF composite substrate. This substrate achieves synergistic effects of physical and chemical enhancement, significantly improving the sensitivity of SERS detection and enabling better monitoring and analysis of chemical substances.

[0006] This invention provides a method for preparing a double-shell Ag-ZnAl2O4-MOF composite material, comprising the following steps.

[0007] 1) ZnAl2O4 nanoparticles were prepared by hydrothermal method. The product was washed, dried and calcined.

[0008] 2) ZIF-8 was grown in situ using calcined ZnAl2O4 nanoparticles as the core. The sample after the reaction was completed was cooled, centrifuged, washed, and dried to obtain ZnAl2O4-MOF.

[0009] 3) Cover the ZnAl2O4-MOF with Ag nanoparticles, wash the product and dry it.

[0010] In the preparation method of the above-mentioned double-shell Ag-ZnAl2O4-MOF composite material, in step 1), the hydrothermal method for preparing ZnAl2O4 nanoparticles is as follows: zinc nitrate hexahydrate and aluminum nitrate nonahydrate are dissolved in water and mixed in a molar ratio of 1:2:6, urea is added, and a hydrothermal reaction is carried out at a temperature of 120-140℃ for 6-8 hours. After cooling, the mixture is centrifuged, washed, and dried. The calcination temperature is 500-550℃ for 3-4 hours.

[0011] In the above-mentioned method for preparing a double-shell Ag-ZnAl2O4-MOF composite material, step 2) involves the in-situ growth of ZIF-8 using calcined ZnAl2O4 nanoparticles as the core. The specific method is as follows: ZnAl2O4 nanoparticles are mixed into the MOF growth solution and sonicated, then refluxed at 60-80℃ for 4-6 hours.

[0012] In the above-mentioned method for preparing a double-shell Ag-ZnAl2O4-MOF composite material, in step 2), the MOF growth solution is a methanol solution of 2-methylimidazole and zinc nitrate hexahydrate, and the molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is 8:1.

[0013] In the preparation method of the above-mentioned double-shell Ag-ZnAl2O4-MOF composite material, step 3) involves coating Ag nanoparticles onto ZnAl2O4-MOF as follows: the prepared ZnAl2O4-MOF composite material is dissolved in water, sonicated until uniformly suspended, sodium citrate is added, stirred, AgNO3 is added, stirred in the dark, sodium borohydride solution is slowly added dropwise under an ice bath, and stirred until the solution turns gray.

[0014] The above-mentioned method for preparing a double-shell Ag-ZnAl2O4-MOF composite material has a mass ratio of ZnAl2O4-MOF: sodium citrate: AgNO3 = 5:10:9.

[0015] A double-shell Ag-ZnAl2O4-MOF composite material prepared according to the above preparation method.

[0016] Application of the above-mentioned double-shell Ag-ZnAl2O4-MOF composite material in trace detection of organic pollutants.

[0017] In the above application, the organic pollutant is methylene blue.

[0018] In the above application, a double-shell Ag-ZnAl2O4-MOF composite material was added to a methylene blue solution, and surface-enhanced Raman scattering detection was performed using a 532nm wavelength laser as the excitation source.

[0019] The present invention has the following beneficial effects.

[0020] (1) The three-layer core-shell structure constructed in this invention can be precisely controlled in terms of size, shell thickness and Ag loading by hydrothermal method.

[0021] (2) The intermediate MOF shell has chemical inertness and thermal stability, which can isolate air / moisture / sulfur compounds, inhibit Ag oxidation and sulfidation, and solve the problem of easy deactivation of pure Ag substrate. The porous structure of MOF can efficiently adsorb trace molecules, concentrate target molecules to Ag "hot spot" region, and significantly improve the detection signal intensity.

[0022] (3) The ZnAl2O4 core can provide rigid support, and the MOF shell spatially isolates Ag nanoparticles, effectively inhibiting aggregation and improving the reproducibility and service life of the substrate.

[0023] (4) The double-shell Ag-ZnAl2O4-MOF composite substrate prepared by the present invention can achieve the synergistic effect of electromagnetic enhancement and chemical enhancement. The local surface plasmon resonance (LSPR) of the outer Ag nanoparticles generates a high-density "hot spot", and the ZnAl2O4 semiconductor core and the MOF interface can form a charge transfer channel. Attached Figure Description

[0024] Figure 1 These are the Raman spectra of MB molecules under a 532nm laser in Example 2, and the SERS spectra of MB adsorbed on a double-shell Ag-ZnAl2O4-MOF composite substrate.

[0025] Figure 2 This is the XRD pattern of the double-shell Ag-ZnAl2O4-MOF composite substrate in Example 1.

[0026] Figure 3 This is the SERS spectrum collected in Example 3 after randomly performing five Raman detections on MB molecules on a double-shell Ag-ZnAl2O4-MOF composite substrate using a 532nm laser.

[0027] Figure 4 This is the SERS spectrum of different concentrations of MB molecules adsorbed on the double-shell Ag-ZnAl2O4-MOF composite substrate under 532nm laser light in Example 3.

[0028] Figure 5 The RB concentration in Example 3 and 1620 cm -1 Logarithmic relationship between characteristic peak SERS intensities. Detailed Implementation

[0029] To better understand the technical solution of the present invention, specific embodiments are provided for further detailed description, but the solution is not limited thereto.

[0030] Example 1

[0031] The preparation scheme of the double-shell Ag-ZnAl2O4-MOF composite substrate is as follows.

[0032] 1) Dissolve 0.12g Zn(NO3)6H2O and 0.3g Al(NO3)3·9H2O in 40ml of water and stir to mix. Then add 0.16g urea and stir. Transfer the reaction solution to a reaction vessel and hydrothermally heat at 120℃ for 6h. After cooling to room temperature, centrifuge, wash and dry the product and calcine at 500℃ for 3h to obtain ZnAl2O4 nanoparticles.

[0033] 2) To prepare the MOF growth medium, dissolve 0.328 g of 2-methylimidazole and 0.149 g of zinc nitrate hexahydrate in 20 mL of methanol at a molar ratio of 8:1. Slowly add the zinc nitrate solution to the 2-methylimidazole ligand solution and stir magnetically for 5 min.

[0034] 3) Take 100 mg of the ZnAl2O4 nanoparticles prepared in step 1) and add them to the MOF growth solution prepared in step 2), and sonicate for 10 min. Transfer to a round-bottom flask, reflux in an oil bath at 80℃ for 4 h, cool to room temperature, centrifuge, wash 3 times with methanol, and dry to obtain ZnAl2O4-MOF for later use.

[0035] 4) Dissolve 10 mg of ZnAl2O4-MOF composite material in 100 ml of water, sonicate until uniformly suspended, add 20 mg of sodium citrate, stir for 15 min, add 18 mg of AgNO3, and stir in the dark for 1 h. Slowly add 5 ml of 0.1 mol / L sodium borohydride solution in an ice bath, stir until the solution turns gray, centrifuge, wash and dry, and set aside for later use.

[0036] The prepared double-shell Ag-ZnAl2O4-MOF composite substrate was subjected to XRD testing, and the test results are as follows: Figure 2As shown, the characteristic diffraction peaks at 2θ = 38.2°, 44.4°, 64.6°, and 77.5° correspond to the characteristic peaks of Ag, while the characteristic peak unique to ZnAl2O4 at 2θ = 36.8° indicates that ZnAl2O4 was also successfully synthesized. The characteristic peaks at 2θ = 10.4°, 12.7°, and 18.0° also prove the successful synthesis of ZIF-8. The broad peak at 2θ ≈ 20°–25° is due to the residue of 2-methylimidazole, and the amorphous peak at 2θ ≈ 15°–30° is due to the poor crystallinity of the product. The obtained XRD pattern is sufficient to demonstrate the successful synthesis of the Ag-ZnAl2O4-MOF composite substrate.

[0037] Example 2

[0038] SERS enhancement effect of double-shell Ag-ZnAl2O4-MOF composite substrate.

[0039] The double-shell Ag-ZnAl2O4-MOF composite substrate prepared in Example 1 was used for experiments based on SERS technology with MB as the probe molecule. The testing procedure was as follows: a 532 nm wavelength laser was used as the excitation source, and 2 ml of a 10% concentration was used based on SERS technology. -3 A mol / L MB solution was used as a probe molecule to test on a 10 mg double-shell Ag-ZnAl2O4-MOF composite substrate. SERS measurements were performed on both cases: MB alone and a mixture of MB and the double-shell Ag-ZnAl2O4-MOF composite substrate. The results are as follows: Figure 1 The Raman signal intensity of the double-shell Ag-ZnAl2O4-MOF composite substrate with MB molecules as probes is much higher than that of MB molecules alone, which indicates that the double-shell Ag-ZnAl2O4-MOF composite substrate prepared in this invention has excellent SERS signal enhancement performance.

[0040] Example 3

[0041] Other excellent properties of the double-shell Ag-ZnAl2O4-MOF composite substrate.

[0042] The double-shell Ag-ZnAl2O4-MOF composite substrate prepared in Example 1 was used, and MB molecules were randomly subjected to five Raman tests on the composite substrate. The results are as follows. Figure 3 As shown, the Raman signal peaks in the five tests were uniform and showed no significant changes, indicating that the substrate has good stability and homogeneity. Different concentrations of MB molecules were used as probe molecules to detect the double-shell Ag-ZnAl2O4-MOF composite substrate, and the results are as follows. Figure 4 As shown, although the signal peak intensity decreases with decreasing MB probe molecule concentration, Raman signals can still be detected at extremely low concentrations, indicating that this substrate can detect different concentrations of MB molecules (1×10⁻⁶).-3 mol / L, 1×10 -4 mol / L, 1×10 -5 mol / L, 1×10 -6 mol / L, 10 -7 (mol / L), and it still exhibits good performance at extremely low concentrations. The relationship between the SERS signal peak intensities under different concentrations of the MB probe was analyzed, and the results are as follows: Figure 5 As shown, the fitted function is y = (63496.2) + (8161.4) × x, R0 2 =0.9557, this result further illustrates the relationship between RB concentration and 1620 cm⁻¹. -1 The logarithmic relationship between the characteristic peak SERS intensities confirms the excellent performance of this composite material in SERS-based analytical applications.

Claims

1. A method for preparing a double-shell Ag-ZnAl2O4-MOF composite material, characterized in that: Includes the following steps: 1) Zinc nitrate hexahydrate and aluminum nitrate nonahydrate were dissolved in water and mixed in a molar ratio of 1:2:

6. Urea was added, and a hydrothermal reaction was carried out at a temperature of 120-140℃ for 6-8 hours. After cooling, the mixture was centrifuged, washed, dried, and calcined to obtain ZnAl2O4 nanoparticles. The calcination temperature was 500-550℃ and the time was 3-4 hours. 2) After mixing ZnAl2O4 nanoparticles into the MOF growth solution and sonicating, the mixture is refluxed at 60-80℃ for 4-6 hours. After the reaction is completed, the sample is cooled, centrifuged, washed, and dried to obtain ZnAl2O4-MOF. The MOF growth solution is a methanol solution of 2-methylimidazole and zinc nitrate hexahydrate, with a molar ratio of 8:

1. 3) Dissolve the prepared ZnAl2O4-MOF composite material in water, sonicate until uniformly suspended, add sodium citrate, stir, add AgNO3, stir in the dark, slowly add sodium borohydride solution dropwise under ice bath, stir until the solution turns gray, wash the product and dry.

2. The method for preparing a double-shell Ag-ZnAl2O4-MOF composite material as described in claim 1, characterized in that: By mass ratio, ZnAl2O4-MOF: sodium citrate: AgNO3 = 5:10:

9.

3. A double-shell Ag-ZnAl2O4-MOF composite material prepared by the preparation method according to any one of claims 1-2.

4. The application of the double-shell Ag-ZnAl2O4-MOF composite material as described in claim 3 in the trace detection of organic pollutants.

5. The application as described in claim 4, characterized in that: The organic pollutant mentioned is methylene blue.

6. The application as described in claim 5, characterized in that: A double-shell Ag-ZnAl2O4-MOF composite material was added to a solution of methylene blue, and surface-enhanced Raman scattering was performed using a 532 nm wavelength laser as the excitation source.

Images