An Ag-MoO2 composite SERS substrate, its preparation method and application

Abstract

The application belongs to the technical field of SERS detection, and particularly relates to an Ag-MoO2 composite SERS substrate and a preparation method and application thereof. First, Ag nanoparticles with uniform distribution and same size are prepared by a sodium citrate reduction method; second, MoO2 material is prepared by a hydrothermal method; and finally, a new type of SERS substrate Ag-MoO2 is prepared by a physical stirring method. The application constructs a new type of SERS substrate of Ag nanoparticles and MoO2 material, which is different from a conventional SERS substrate of Ag nanoparticles alone, and can detect stronger intrinsic Raman signals of probe molecules. Because the preparation of the SERS substrate needs to be combined with MoO2 material, charge transfer can occur at the interface between the SERS substrate and the probe molecules, so that the intrinsic Raman signals of the probe molecules can be enhanced, and the SERS substrate can be better used for detecting and analyzing chemical substances.

Description

Technical Field

[0001] This invention belongs to the field of SERS detection technology, specifically relating to an Ag-MoO2 composite SERS substrate, its preparation method, and its application. Background Technology

[0002] p-Mercaptobenzoic acid (4-MBA), an important organosulfur compound, has wide applications in organic synthesis and materials science; however, its environmental behavior and potential hazards have also attracted widespread attention. Studies have shown that p-Mercaptobenzoic acid, once introduced into the environment, can negatively impact aquatic and soil ecosystems. Its high chemical stability and slow degradation can lead to persistent pollution and potential toxicity to higher organisms through bioaccumulation. Therefore, developing efficient and sensitive detection methods is crucial for assessing its environmental impact. Accurate detection of p-Mercaptobenzoic acid not only helps monitor its distribution and migration patterns in the environment but also provides a scientific basis for pollution control and ecological risk assessment, thereby reducing its potential threats to the environment and biological health. Furthermore, optimization of detection technologies can further promote the standardized management of p-Mercaptobenzoic acid in industrial applications, contributing to the achievement of green chemistry and sustainable development goals.

[0003] SERS, a highly sensitive, selective, and non-destructive analytical technique derived from metal surfaces, generates a large scattering cross-section, achieving enhancements several orders of magnitude. It has applications in various fields such as surface science, catalysis, and chemistry. Most importantly, it has made significant breakthroughs in the detection of trace pollutants. Ag nanostructures generate strong electromagnetic field enhancements (electromagnetic enhancement factor up to 10) through localized surface plasmon resonance (LSPR). 6 -10 9 The narrow band gap of MoO2 (~1.9 eV) forms a heterointerface with Ag, promoting charge transfer (CT) between the probe molecules and the substrate, contributing to chemical enhancement (10). 1 -10 3MoO2, as a rigid support, can suppress the Ostwald ripening and oxidation of Ag nanoparticles (MoO2's oxidation resistance temperature is >300℃), and its chemically inert surface reduces the non-specific adsorption of organic pollutants. The dielectric constant modulation of MoO2 causes the LSPR peak of Ag nanostructures to redshift to the near-infrared (700-1000 nm), breaking through the visible light limitation (400-600 nm) of traditional Ag-based SERS substrates. Simultaneously, dynamic tuning of the LSPR (±50 nm) can be achieved through MoO2 crystal phase modulation (such as the introduction of oxygen vacancies). Therefore, it is an ideal material for SERS substrates. Combining Ag NPs and MoO2 can create SERS substrates with both electromagnetic and chemical enhancement, which can be efficiently applied to the detection of 4-MBA molecules with high sensitivity and stability. There are currently no reports on the use of Ag NPs and MoO2 composites as SERS substrates for the detection of 4-MBA molecules. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention designs and synthesizes an Ag-MoO2 composite SERS substrate. Charge transfer can occur at the interface between this SERS substrate and probe molecules, thereby enhancing the intrinsic Raman signal of the probe molecules and enabling better detection and analysis of chemical substances.

[0005] The technical solution adopted in this invention is as follows:

[0006] An Ag-MoO2 composite SERS substrate, the preparation method of which includes the following steps:

[0007] 1) Dissolve sodium citrate powder in water, add silver nitrate, and obtain Ag nanoparticles by chemical reduction.

[0008] 2) Dissolve molybdenum acetylacetonate in a mixed solution of a certain amount of water and anhydrous ethanol, disperse by sonication and stirring, place in a high-pressure reactor, carry out hydrothermal reaction, wash and repeatedly centrifuge, dry to obtain high-purity MoO2.

[0009] 3) Add MoO2 to the Ag nanoparticle solution, sonicate, and then stir thoroughly;

[0010] 4) The composite substrate obtained in step 3) is dried in an oven to obtain the Ag-MoO2 composite SERS substrate.

[0011] Furthermore, the above-mentioned Ag-MoO2 composite SERS substrate is characterized in that, in step 1), the chemical reduction method is carried out at a speed of 1100 rpm, a temperature of 100-130°C, and stirring for 0.8 h.

[0012] Furthermore, the above-mentioned Ag-MoO2 composite SERS substrate is characterized in that, in step 2), the amount of commercially available molybdenum acetylacetonate is 0.1g, deionized water is 41ml, anhydrous ethanol is 9ml, the ultrasonic time is 20 minutes, and the stirring time is 1h.

[0013] Furthermore, the above-mentioned Ag-MoO2 composite SERS substrate is characterized in that, in step 2), the hydrothermal reaction is carried out in a high-pressure reactor and heated in an oven at a temperature of 180°C for 20 hours.

[0014] Furthermore, the Ag-MoO2 composite SERS substrate described above is characterized in that, in step 3), the ultrasonic time is 20-40 min and the stirring time is 1.5-3 h.

[0015] Furthermore, the Ag-MoO2 composite SERS substrate described above is characterized in that, in step 4), the drying temperature is 50-70°C and the drying time is 1.5-4 hours.

[0016] Application of the Ag-MoO2 composite SERS substrate described in any of the above-mentioned methods in the detection of 4-MBA molecules in water.

[0017] Furthermore, the above application is carried out as follows: under 532nm laser irradiation, the Ag-MoO2 composite SERS substrate is immersed in 4-MBA solution, which enhances the Raman signal of 4-MBA molecules, making it easier to detect 4-MBA molecules in water.

[0018] This invention utilizes a constructed Ag-MoO2 composite SERS substrate to enhance the Raman spectrum of 4-MBA molecules, facilitating their detection in water. The beneficial effects of this method can be attributed to three aspects:

[0019] 1. MoO2 disperses Ag nanoparticles through lattice matching, forming a high-density electromagnetic hotspot;

[0020] 2. The metallic interface of MoO2 lowers the charge transfer barrier and accelerates the electron transfer rate, contributing to synergistic chemical enhancement;

[0021] 3. Oxygen vacancies on the MoO2 surface induce a local electric field and stabilize the charge transfer path, thereby enhancing stability. Attached Figure Description

[0022] Figure 1 These are XRD patterns of the MoO2 and Ag-MoO2 substrates in Example 1.

[0023] Figure 2These are the Raman spectra of 4-MBA molecules under 532nm laser light in Example 1, and the SERS spectra of 4-MBA molecules adsorbed on Ag nanoparticles and Ag-MoO2 composite substrates, respectively.

[0024] Figure 3 The SERS spectrum is the result of 10 random Raman detections of 4-MBA molecules on an Ag-MoO2 composite substrate irradiated with a 532nm laser in Example 1.

[0025] Figure 4 This is the SERS spectrum of different concentrations of 4-MBA molecules adsorbed on the Ag-MoO2 composite substrate under 532nm laser light in Example 1. Detailed Implementation

[0026] 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.

[0027] Example 1: An Ag-MoO2 composite SERS substrate

[0028] The preparation method is as follows:

[0029] 1) Dissolve 2g of sodium citrate powder in a clean beaker containing 100mL of deionized water. After standing for a period of time, put the solution into a 100mL volumetric flask to obtain a 2% sodium citrate solution.

[0030] 2) Add 2 mL of sodium citrate solution and 0.036 g of silver nitrate to a round-bottom flask containing 200 mL of deionized water, and heat at 130 °C and stir for 0.8 h at a speed of 1100 rpm. The resulting Ag nanoparticle solution is collected in a volumetric flask.

[0031] 3) Weigh 0.1g of molybdenum acetylacetonate and put it into a beaker. Add 41ml of deionized water and 9ml of anhydrous ethanol. Sonicate for 20 minutes, stir with a magnetic stirrer for 1 hour, put it into a high-pressure reactor and heat it in an oven at 180℃ for 20 hours. Centrifuge the resulting liquid, wash it three times with deionized water and ethanol and centrifuge it again. Then dry it in an oven at 60℃ for 12 hours to obtain MoO2 for later use.

[0032] 4) The Ag nanoparticle solution prepared in step 2) and the MoO2 prepared in step 3) are mixed and subjected to ultrasonication for 20-40 min and stirring for 1.5-3 h respectively. Then, they are placed in an oven and dried at a temperature of 50-70℃ for 1.5-4 h to obtain the Ag-MoO2 composite SERS substrate.

[0033] 5) Immerse the prepared Ag-MoO2 composite SERS substrate in 4-MBA solution for 2 hours, and air dry at room temperature for later use.

[0034] XRD was performed on the MoO2 and Ag-MoO2 prepared in steps 3) and 4), respectively. The test results are as follows: Figure 1 As shown in the figure, the successful preparation of the Ag-MoO2 composite SERS substrate can be seen.

[0035] The Ag-MoO2 composite SERS substrate prepared in Example 1 was used for experiments based on SERS technology with 4-MBA as the probe molecule. The testing procedure was as follows: a 532nm wavelength laser was used as the excitation source, and 4-MBA was used as the probe molecule for testing on the Ag-MoO2 composite SERS substrate based on SERS technology. Figure 2 , Figure 3 , Figure 4 As shown, the Ag-MoO2 composite SERS substrate prepared in Example 1 can enhance the Raman signal of 4-MBA molecules, facilitating their detection in water. Furthermore, 10 random Raman tests were performed on the Ag-MoO2 composite substrate to detect 4-MBA molecules, revealing uniform Raman signal peaks and no significant changes in Raman intensity, indicating that the Ag-MoO2 composite SERS substrate possesses good uniformity and reproducibility. In addition, the prepared Ag-MoO2 composite SERS substrate can detect different concentrations of 4-MBA molecules, and maintains high sensitivity even at extremely low concentrations, demonstrating the excellent enhancement effect of this Ag-MoO2 composite SERS substrate.

Claims

1. An application of an Ag-MoO2 composite SERS substrate in the detection of 4-MBA molecules in water, characterized in that, The preparation method of the Ag-MoO2 composite SERS substrate includes the following steps: 1) Dissolve sodium citrate powder in water, add silver nitrate, and obtain Ag nanoparticles by chemical reduction. 2) Dissolve molybdenum acetylacetonate in a mixed solution of a certain amount of water and anhydrous ethanol, disperse by sonication and stirring, place in a high-pressure reactor, carry out hydrothermal reaction, wash and repeatedly centrifuge, dry to obtain high-purity MoO2. 3) Add MoO2 to the Ag nanoparticle solution, sonicate, and then stir thoroughly; 4) Dry the composite substrate obtained in step 3) to obtain the Ag-MoO2 composite SERS substrate.

2. The application according to claim 1, characterized in that, In step 1), the chemical reduction method is carried out at a speed of 1100 rpm, a temperature of 100-130 ℃, and stirring for 0.8 h.

3. The application according to claim 1, characterized in that, In step 2), the ultrasonic time is 20 minutes and the stirring time is 1 hour.

4. The application according to claim 1, characterized in that, In step 2), the hydrothermal reaction is carried out by heating in a high-pressure reactor in an oven at a temperature of 180 °C for 10 h.

5. The application according to claim 1, characterized in that, In step 3), the ultrasonic time is 20-40 min and the stirring time is 1.5-3 h.

6. The application according to claim 1, characterized in that, In step 4), the drying temperature is 50-70 ℃ and the drying time is 1.5-4 h.

7. The application according to claim 1, characterized in that, The method is as follows: Under 532 nm laser irradiation, the Ag-MoO2 composite SERS substrate was immersed in 4-MBA solution, which enhanced the Raman signal of 4-MBA molecules, making it easier to detect 4-MBA molecules in water.

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