Ag-MoO2 composite SERS (Surface Enhanced Raman Scattering) substrate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of SERS (Surface Enhanced Raman Scattering) detection, and particularly relates to an Ag-MoO2 composite SERS substrate as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, preparing Ag nanoparticles which are uniformly distributed and have the same size by a sodium citrate reduction method; secondly, a MoO2 material is prepared through a hydrothermal method; and finally, the novel SERS substrate Ag-MoO2 is prepared through a physical stirring method. According to the invention, the novel SERS substrate made of Ag nanoparticles and MoO2 materials is constructed, which is different from the conventional SERS substrate made of independent Ag nanoparticles, and can detect stronger intrinsic Raman signals of probe molecules. As the SERS substrate needs to be compounded with a MoO2 material during preparation, a charge transfer phenomenon can occur at an interface where the SERS substrate is in contact with probe molecules, so that 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] The present invention belongs to the technical field of SERS detection, and particularly relates to an Ag-MoO2 composite SERS substrate, a preparation method thereof, and an application thereof. Background Art

[0002] p-Mercaptobenzoic acid (4-MBA), as an important organosulfur compound, has a wide range of applications in the fields of organic synthesis and materials science. However, its environmental behavior and potential hazards have also attracted extensive attention. Research shows that after entering the environment, p-mercaptobenzoic acid may have a negative impact on water and soil ecosystems. It has high chemical stability and degrades slowly, which may lead to persistent pollution and pose potential toxicity to higher organisms through bioaccumulation. Therefore, the development of efficient and sensitive detection methods is crucial for evaluating its harm to the environment. Accurately detecting p-mercaptobenzoic acid not only helps to 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 threat to the environment and biological health. In addition, through the optimization of detection techniques, the standardized management of p-mercaptobenzoic acid in industrial applications can be further promoted, contributing to the realization of green chemistry and sustainable development goals.

[0003] SERS, as a highly sensitive, highly selective, and non-destructive analytical technique originating from the metal surface, can generate a large scattering cross-section to achieve several orders of magnitude of enhancement and find applications in different fields such as surface science, catalysis, and chemistry. Most importantly, it has made certain breakthroughs in the micro-detection of pollutants. Ag nanostructures generate strong electromagnetic field enhancement through localized surface plasmon resonance (LSPR) (the electromagnetic enhancement factor reaches 10 6 -10 9 ), while the narrow bandgap of MoO2 (~1.9 eV) forms a heterojunction with Ag, promoting the charge transfer (CT) process between the probe molecule and the substrate and contributing to chemical enhancement (10 1 -10 3times); MoO2 as a rigid carrier can inhibit the Ostwald ripening and oxidation of Ag nanoparticles (MoO2's anti-oxidation temperature is greater than 300℃), and its chemically inert surface reduces the nonspecific adsorption of organic pollutants; the dielectric constant of MoO2 can be regulated to red-shift the LSPR peak of Ag nanostructures to the near-infrared (700-1000nm), breaking through the visible light limitation (400-600nm) of traditional Ag-based SERS substrates, and at the same time, the LSPR dynamic tuning (±50nm) can be achieved through the regulation of MoO2 crystal phase (such as the introduction of oxygen vacancies), so it is an ideal material for SERS substrates. The composite of Ag NPs and MoO2 can realize a SERS substrate with both electromagnetic enhancement and chemical enhancement, which can be efficiently applied to the detection of 4-MBA molecules with high sensitivity and stability. There are no related reports on the composite of Ag NPs and MoO2 as a SERS substrate for the detection of 4-MBA molecules. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention designs and synthesizes an Ag-MoO2 composite SERS substrate. Charge transfer can occur at the interface between the SERS substrate and the probe molecule, thereby enhancing the intrinsic Raman signal of the probe molecule, which can be better used for detecting and analyzing chemical substances.

[0005] The technical solution adopted by the present invention is:

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

[0007] 1) dissolving sodium citrate powder in water, adding silver nitrate, and obtaining Ag nanoparticles by chemical reduction method;

[0008] 2) dissolving molybdenum acetylacetonate in a mixed solution of a certain amount of water and anhydrous ethanol, dispersing by ultrasonication and stirring, placing in a high-pressure reactor, performing a hydrothermal reaction, washing and repeatedly centrifuging, and drying to obtain high-purity MoO2;

[0009] 3) Add MoO2 to the Ag nanoparticle solution and stir thoroughly after ultrasonication;

[0010] 4) Drying the composite substrate obtained in step 3) in an oven to obtain a 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 to maintain a rotation speed of 1100 rpm, a temperature of 100-130°C, and stir for 0.8h.

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

[0013] Further, in the above-mentioned Ag-MoO2 composite SERS substrate, in step 2), the hydrothermal reaction is carried out by heating in an oven using a high-pressure reaction kettle, the temperature is 180 °C, and the time is 20 h.

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

[0015] Further, in the above-mentioned Ag-MoO2 composite SERS substrate, in step 4), the drying temperature is 50 - 70 °C, and the drying time is 1.5 - 4 h.

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

[0017] Further, for the above application, the method is as follows: Under the irradiation of a 532 nm laser, the Ag-MoO2 composite SERS substrate is immersed in a 4-MBA solution, enhancing the Raman signal of 4-MBA molecules, which is convenient for detecting 4-MBA molecules in water.

[0018] The present invention utilizes the constructed Ag-MoO2 composite SERS substrate to enhance the Raman spectrum of 4-MBA molecules, which is convenient for detecting 4-MBA molecules in water. The beneficial effects of this method can be attributed to three aspects:

[0019] 1. MoO2 disperses Ag nanoparticles through lattice matching to form high-density electromagnetic hot spots;

[0020] 2. The metallic interface of MoO2 reduces 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, enhancing the enhancement stability. Description of the Drawings

[0022] Figure 1 It is the XRD pattern of MoO2 and the Ag-MoO2 substrate in Example 1.

[0023] Figure 2It is the Raman spectrum of 4-MBA molecules under a 532 nm laser in Example 1 and the SERS spectra of 4-MBA molecules adsorbed on Ag nanoparticles and Ag-MoO2 composite substrates respectively.

[0024] Figure 3 It is the SERS spectrum collected after randomly performing 10 Raman detections on 4-MBA molecules using a 532 nm laser irradiation on an Ag-MoO2 composite substrate in Example 1.

[0025] Figure 4 It is the SERS spectrum of 4-MBA molecules with different concentrations adsorbed on an Ag-MoO2 composite substrate under a 532 nm laser in Example 1. Detailed implementation manners

[0026] For a better understanding of the technical solution of the present invention, specific examples are used 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 2 g of sodium citrate powder in a clean beaker containing 100 mL of deionized water. After standing for a period of time, put the solution into a 100 mL 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 to 130 °C and stir for 0.8 h while maintaining a rotation speed of 1100 rpm. Collect the obtained Ag nanoparticle solution in a volumetric flask.

[0031] 3) Weigh 0.1 g of molybdenum acetylacetonate and put it into a beaker. Add 41 ml of deionized water and 9 ml of absolute ethanol, ultrasonicate for 20 minutes, place it on a magnetic stirrer and stir for 1 h, put it into a high-pressure reaction kettle and heat it in an oven at 180 °C for 20 h. Centrifuge the obtained liquid, wash it three times with deionized water and ethanol and then centrifuge, and then dry it in an oven at 60 °C for 12 h to obtain MoO2 for standby.

[0032] 4) Mix the Ag nanoparticle solution prepared in step 2) with the MoO2 prepared in step 3), ultrasonicate for 20 - 40 min and stir for 1.5 - 3 h respectively, then put it into an oven, the drying temperature is 50 - 70 °C, and the drying time is 1.5 - 4 h to obtain an Ag-MoO2 composite SERS substrate.

[0033] 5) Immerse the prepared Ag-MoO2 composite SERS substrate in a 4-MBA solution for 2 h, and air-dry it naturally at room temperature for standby.

[0034] Perform XRD on the MoO2 and Ag-MoO2 prepared in steps 3) and 4) respectively. The test results are as Figure 1 shown. It can be seen from the figure that the Ag-MoO2 composite SERS substrate was successfully prepared.

[0035] Use the Ag-MoO2 composite SERS substrate prepared in Example 1 to conduct experiments based on the SERS technology with 4-MBA as the probe molecule. The test process is as follows: Use a laser with a wavelength of 532 nm as the excitation light source, and conduct tests on the Ag-MoO2 composite SERS substrate based on the SERS technology with 4-MBA as the probe molecule. As Figure 2 、 Figure 3 、 Figure 4 shown, it can be known that the Ag-MoO2 composite SERS substrate prepared in Example 1 can enhance the Raman signal of 4-MBA molecules, which is convenient for detecting 4-MBA molecules in water. And randomly conduct 10 Raman detections on 4-MBA molecules on the Ag-MoO2 composite substrate, and it is found that the Raman signal peaks are neat and the Raman intensity has no obvious change, indicating that the Ag-MoO2 composite SERS substrate has good uniformity and reproducibility. In addition, the prepared Ag-MoO2 composite SERS substrate can detect 4-MBA molecules with different concentrations, and can still conduct highly sensitive detection on them when the concentration of 4-MBA molecules is extremely low, indicating the excellent enhancement effect of this Ag-MoO2 composite SERS substrate.

Claims

1. An Ag-MoO2 composite SERS substrate, characterized in that, The preparation method comprises the following steps: 1) dissolving sodium citrate powder in water, adding silver nitrate, and obtaining Ag nanoparticles by chemical reduction method; 2) dissolving molybdenum acetylacetonate in a mixed solution of a certain amount of water and anhydrous ethanol, dispersing by ultrasonication and stirring, placing in a high-pressure reactor, performing a hydrothermal reaction, washing and repeatedly centrifuging, and drying to obtain high-purity MoO2; 3) Add MoO2 to the Ag nanoparticle solution and stir thoroughly after ultrasonication; 4) Drying the composite substrate obtained in step 3) to obtain a Ag-MoO2 composite SERS substrate.

2. The Ag-MoO2 composite SERS substrate according to claim 1, characterized in that In step 1), the chemical reduction method is to maintain the rotation speed at 1100 rpm, the temperature at 100-130° C., and stir for 0.8 h.

3. An Ag-MoO2 composite SERS substrate according to claim 1, wherein In step 2), the ultrasonic time is 20 minutes and the stirring time is 1 hour.

4. The Ag-MoO2 composite SERS substrate according to claim 1, wherein, In step 2), the hydrothermal reaction is carried out by heating a high pressure reactor in an oven at a temperature of 180° C. for 10 h.

5. An Ag-MoO2 composite SERS substrate 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 Ag-MoO2 composite SERS substrate according to claim 1, wherein, In step 4), the drying temperature is 50-70° C. and the drying time is 1.5-4 h.

7. Use of the Ag-MoO2 composite SERS substrate according to any one of claims 1 to 6 in detecting 4-MBA molecules in water.

8. The application according to claim 7, characterized in that, The method is as follows: Under 532nm laser irradiation, the Ag-MoO2 composite SERS substrate is immersed in a 4-MBA solution, which enhances the Raman signal of the 4-MBA molecules and facilitates the detection of 4-MBA molecules in water.

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