Preparation method and application of Ag-coated NiFe2O4 composite SERS (Surface Enhanced Raman Scattering) substrate

Abstract

The invention belongs to the technical field of SERS (Surface Enhanced Raman Scattering) detection, and particularly relates to a preparation method and application of an Ag-coated NiFe2O4 composite SERS substrate. The preparation method comprises the following steps: firstly, preparing Ag nanoparticles which are uniformly distributed and have the same size through a sodium citrate reduction method; secondly, a nanometer flower type NiFe2O4 material is prepared through a hydrothermal method and a calcination method; and finally, the novel SERS substrate Ag-coated NiFe2O4 is prepared through a physical stirring method. The novel SERS substrate made of the Ag nano particles and the nano-flower type NiFe2O4 material is constructed, and compared with a conventional SERS substrate made of independent Ag nano particles, the SERS substrate can detect stronger intrinsic Raman signals of probe molecules. As the SERS substrate needs to be compounded with a nano-flower type NiFe2O4 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 invention belongs to the technical field of SERS detection, and in particular relates to a preparation method and application of an Ag@NiFe2O4 composite SERS substrate. Background Art

[0002] Surface enhanced Raman scattering (SERS) technology has shown great development potential in the fields of medical diagnosis, catalytic reaction, biological analysis and environmental detection due to its advantages such as fast response, simple operation, high sensitivity, non-destructive detection and no interference in aqueous solution. The enhancement mechanism of SERS is usually attributed to two main theories: one is physical enhancement, which is usually considered to be the main source of SERS enhancement, also known as electromagnetic enhancement effect, which is related to the plasmon resonance (SPR) of the metal surface. Therefore, metal nanoparticles with regular size, uniform arrangement and proper aggregation state usually show stronger SERS enhancement performance. The other theory is chemical enhancement, which is related to the charge transfer (CT) process, involving valence bond binding or chemical adsorption between the SERS substrate and the target molecule, thereby inducing charge transfer phenomenon. The sensitivity of SERS spectrum mainly depends on efficient and stable SERS substrate. Since the discovery of SERS technology, noble metal nanoparticles, especially gold and silver, have been widely used as SERS substrates due to their good SPR effect, conductivity and easy preparation. However, due to the high price and poor stability of noble metals, metal-semiconductor materials have gradually begun to be used as SERS substrates for analysis and detection of chemical substances.

[0003] R6G molecule is a common organic fluorescent dye, which is widely used in biomedicine, fluorescence microscopy, materials science and chemical research. However, R6G may have certain toxicity at high concentrations, so it is inevitable to detect R6G molecules. NiFe2O4 is a commonly used soft magnetic material with excellent chemical stability, high temperature resistance, low toxicity and easy preparation. This makes it widely used in many fields such as lithium-ion battery anode materials and ceramic materials. In addition, NiFe2O4 also performs well in catalysis and is a commonly used catalyst. It can effectively decompose carbon dioxide into carbon and oxygen. In addition, NiFe2O4 can also catalyze the production of fullerenes and act as a photo-Fenton catalyst to degrade organic pollutants. More noteworthy is that NiFe2O4 can be used as a carrier of TiO2 nanophotocatalysts to enhance the efficiency of photocatalytic reactions. Due to the magnetism of NiFe2O4, the composite material has good recycling characteristics. And NiFe2O4 has excellent conductivity and unique conduction band and valence band, which accelerates the propagation rate of electrons and holes, and can be applied to SERS technology to achieve high-sensitivity detection of probe molecules.

[0004] Based on the excellent properties of Ag nanoparticles and NiFe2O4, if the two are combined to form a unique composite SERS substrate, charge transfer will occur at the interface in contact with R6G molecules, thereby chemically enhancing the R6G molecules and achieving highly sensitive detection of R6G molecules, which will be of great significance to the environmental field. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention designs and synthesizes an Ag@NiFe2O4 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.

[0006] The technical solution adopted by the present invention is:

[0007] An Ag@NiFe2O4 composite SERS substrate, the preparation method of which comprises the following steps:

[0008] 1) dissolving sodium citrate powder in water, adding silver nitrate, and obtaining Ag nanoparticles by chemical reduction method;

[0009] 2) nickel nitrate hexahydrate, iron nitrate nonahydrate, urea and ammonium fluoride are added to water, a precursor is obtained by a hydrothermal method, and nano-flower-shaped NiFe2O4 is obtained after calcination;

[0010] 3) Ag nanoparticles and nanoflower-shaped NiFe2O4 are subjected to ultrasound and then fully stirred;

[0011] 4) Drying the composite substrate obtained in step 3) in an oven to obtain an Ag@NiFe2O4 composite SERS substrate.

[0012] Furthermore, in the above-mentioned method for preparing a Ag@NiFe2O4 composite SERS substrate, in step 1), the amount of sodium citrate powder used is 1 g, the amount of water used is 100 mL, and the amount of silver nitrate used is 0.018 g.

[0013] Furthermore, in the above-mentioned method for preparing a Ag@NiFe2O4 composite SERS substrate, in step 1), the chemical reduction method is to maintain a rotation speed of 1000 rpm, a temperature of 100-120° C., and stir for 0.5-1 h.

[0014] Furthermore, in the above-mentioned method for preparing a Ag@NiFe2O4 composite SERS substrate, in step 2), the amount of nickel nitrate hexahydrate is 1 mmol, the amount of ferric nitrate nonahydrate is 0.67 mmol, the amount of urea is 4 mmol, the amount of ammonium fluoride is 2.67 mmol, and the amount of water is 30 mL.

[0015] Furthermore, in the above-mentioned method for preparing a Ag@NiFe2O4 composite SERS substrate, in step 2), the hydrothermal method is to carry out a hydrothermal reaction in a high-pressure reactor at a temperature of 100-120° C. for 4-8 hours.

[0016] Furthermore, in the above-mentioned method for preparing a Ag@NiFe2O4 composite SERS substrate, in step 2), the calcination temperature is 500°C and the calcination time is 3-4h.

[0017] Furthermore, in the above-mentioned method for preparing a Ag@NiFe2O4 composite SERS substrate, in step 3), the ultrasonic time is 10-30 min, and the stirring time is 2-4 h.

[0018] Furthermore, in the above-mentioned method for preparing a Ag@NiFe2O4 composite SERS substrate, in step 4), the drying temperature is 40-60° C., and the drying time is 2-4 h.

[0019] Application of any of the above-mentioned Ag@NiFe2O4 composite SERS substrates in detecting R6G molecules in water.

[0020] Further, the above application,method is as follows: the Ag@NiFe2O4 composite SERS substrate is immersed in the R6G solution under 785nm laser irradiation, which enhances the Raman signal of the R6G molecule and facilitates the detection of the R6G molecule in water.

[0021] The present invention utilizes the constructed Ag@NiFe2O4 composite SERS substrate to enhance the Raman spectrum of R6G molecules, making it easier to detect R6G molecules in water. The beneficial effects of this method can be attributed to three aspects:

[0022] 1. The construction of Ag@NiFe2O4 composite SERS substrate can increase the specific surface area of ​​the material and provide more "hot spots".

[0023] 2. The introduction of NiFe2O4 accelerates the propagation rate of electrons and holes, thereby enhancing the Raman spectrum of R6G molecules.

[0024] 3. Charge transfer occurred at the contact interface between the Ag@NiFe2O4 composite SERS substrate and the R6G molecules, which chemically enhanced the Raman spectrum of the R6G molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the SEM image of the nanoflower-shaped NiFe2O4 in Example 1 at a scale of 1 μm.

[0026] Figure 2This is the SEM image of the Ag@NiFe2O4 composite substrate in Example 1 at a scale of 1 μm.

[0027] Figure 3 This is the XRD diagram of the nanoflower-shaped NiFe2O4 and Ag@NiFe2O4 composite substrate in Example 1.

[0028] Figure 4 This is the photocurrent diagram of the nanoflower-shaped NiFe2O4 and Ag@NiFe2O4 composite substrate in Example 1.

[0029] Figure 5 This is the impedance diagram of the nanoflower-shaped NiFe2O4 and Ag@NiFe2O4 composite substrate in Example 1.

[0030] Figure 6 This is the XPS graph of the Ag@NiFe2O4 composite substrate in Example 1.

[0031] Figure 7 It is the Raman spectrum of R6G molecules under 785nm laser in Example 1 and the SERS spectrum of R6G molecules adsorbed on Ag nanoparticles and Ag@NiFe2O4 composite substrate respectively.

[0032] Figure 8 This is the SERS spectrum collected after randomly performing 10 Raman detections on the R6G molecule on the Ag@NiFe2O4 composite substrate using 785nm laser irradiation in Example 1.

[0033] Fig. 9 It is the SERS spectrum of R6G molecules adsorbed on the Ag@NiFe2O4 composite substrate under 785nm laser in Example 1 at different laser powers.

[0034] Fig.10 This is the SERS spectrum of R6G molecules with different concentrations adsorbed on the Ag@NiFe2O4 composite substrate under 785nm laser in Example 1. DETAILED DESCRIPTION

[0035] In order to better understand the technical solution of the present invention, a specific embodiment is further described in detail, but the solution is not limited thereto.

[0036] Example 1: Ag@NiFe2O4 composite SERS substrate

[0037] The preparation method is as follows:

[0038] 1) Dissolve 1 g of sodium citrate powder in a clean beaker containing 100 mL of deionized water. After standing for a while, put the solution into a 100 mL volumetric flask to obtain a 1% sodium citrate solution.

[0039] 2) 1 mL of sodium citrate solution and 0.018 g of silver nitrate were added to a round-bottom flask containing 100 mL of deionized water, and heated to 120° C. and stirred for 1 hour at a rotation speed of 1000 rpm to collect the resulting Ag nanoparticle solution in a volumetric flask.

[0040] 3) Add 1mmol nickel nitrate hexahydrate, 0.67mmol iron nitrate nonahydrate, 4mmol urea and 2.67mmol ammonium fluoride to 30mL water, transfer the mixed solution to a high-pressure reactor, keep it at 100°C for 6h, cool it to room temperature, centrifuge and wash it, and dry it for use. In a muffle furnace, calcine it at 500°C for 3h, take it out after cooling, and obtain nanoflower-shaped NiFe2O4 for use.

[0041] 4) The Ag nanoparticles prepared in step 2) and the nanoflower-shaped NiFe2O4 prepared in step 3) are subjected to ultrasound for 10-30 minutes, physically stirred for 2-4 hours, and then placed in an oven and dried at a temperature of 50-60°C for 2-4 hours to obtain an Ag@NiFe2O4 composite SERS substrate.

[0042] 5) The prepared Ag@NiFe2O4 composite SERS substrate was immersed in the R6G solution for 2 h, and naturally air-dried at room temperature for later use.

[0043] The nanoflower-shaped NiFe2O4 prepared in step 3) was subjected to SEM test, and the test results are as follows: Figure 1 As shown in the figure, it can be seen that NiFe2O4 is in flower shape, with a diameter of about 4 μm and uniform distribution, indicating the successful preparation of NiFe2O4. The Ag@NiFe2O4 prepared in step 4) was subjected to SEM test, and the test results are shown in Figure 2 As shown in the figure, it can be seen that the Ag nanoparticles are evenly dispersed on the surface of NiFe2O4, indicating the successful preparation of the Ag@NiFe2O4 composite SERS substrate. The NiFe2O4 and Ag@NiFe2O4 prepared in step 3) and step 4) were tested by XRD, photocurrent and impedance, respectively. The test results are shown in Figure 3 , 4 As shown in Figure 5, it can be seen from the figure that the Ag@NiFe2O4 composite SERS substrate is successfully prepared and has excellent photoelectric properties. The Ag@NiFe2O4 prepared in step 4) is subjected to XPS test, and the test results are as follows Figure 6 As shown, it can be seen from the figure that the sample contains Ag, Ni, Fe and O elements, indicating the successful preparation of the Ag@NiFe2O4 composite SERS substrate.

[0044] The Ag@NiFe2O4 composite SERS substrate prepared in Example 1 was tested using R6G as a probe molecule based on the SERS technology. The test process was as follows: using a 785nm wavelength laser as an excitation light source, and using R6G as a probe molecule on the Ag@NiFe2O4 composite SERS substrate based on the SERS technology. Figure 7 , Figure 8 , Fig. 9 and Fig.10 As shown, it can be seen that the Ag@NiFe2O4 composite SERS substrate prepared in Example 1 can enhance the Raman signal of R6G molecules, which is convenient for detecting R6G molecules in water. And 10 random Raman detections were performed on the R6G molecules on the Ag@NiFe2O4 composite substrate, and it was found that the Raman signal peaks were neat and the Raman intensity did not change significantly, indicating that the Ag@NiFe2O4 composite SERS substrate has good uniformity and reproducibility. In addition, the R6G molecules were detected on the Ag@NiFe2O4 composite substrate at different laser powers, indicating the excellent enhancement effect of this Ag@NiFe2O4 composite SERS substrate. The prepared Ag@NiFe2O4 composite SERS substrate can detect R6G molecules of different concentrations, and can still detect R6G molecules with high sensitivity when the concentration is extremely low.

Claims

1. An Ag@NiFe2O4 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) nickel nitrate hexahydrate, iron nitrate nonahydrate, urea and ammonium fluoride are added to water, a precursor is obtained by a hydrothermal method, and nano-flower-shaped NiFe2O4 is obtained after calcination; 3) Ag nanoparticles and nanoflower-shaped NiFe2O4 are subjected to ultrasound and then fully stirred; 4) Drying the composite substrate obtained in step 3) in an oven to obtain an Ag@NiFe2O4 composite SERS substrate.

2. The Ag@NiFe2O4 composite SERS substrate according to claim 1, characterized in that: In step 1), the amount of sodium citrate powder is 1 g, the amount of water is 100 mL, and the amount of silver nitrate is 0.018 g.

3. The Ag@NiFe2O4 composite SERS substrate according to claim 1, characterized in that: In step 1), the chemical reduction method is to maintain the rotation speed at 1000 rpm, the temperature at 100-120° C., and stir for 0.5-1 h.

4. The Ag@NiFe2O4 composite SERS substrate according to claim 1, characterized in that: In step 2), the amount of nickel nitrate hexahydrate is 1 mmol, the amount of ferric nitrate nonahydrate is 0.67 mmol, the amount of urea is 4 mmol, the amount of ammonium fluoride is 2.67 mmol, and the amount of water is 30 mL.

5. The Ag@NiFe2O4 composite SERS substrate according to claim 1, characterized in that: In step 2), the hydrothermal method is to carry out a hydrothermal reaction in a high-pressure reactor at a temperature of 100-120° C. for 4-8 hours.

6. The Ag@NiFe2O4 composite SERS substrate according to claim 1, characterized in that: In step 2), the calcination temperature is 500° C. and the calcination time is 3-4 hours.

7. The Ag@NiFe2O4 composite SERS substrate according to claim 1, characterized in that: In step 3), the ultrasonic time is 10-30 min, and the stirring time is 2-4 h.

8. The Ag@NiFe2O4 composite SERS substrate according to claim 1, characterized in that: In step 4), the drying temperature is 40-60° C. and the drying time is 2-4 hours.

9. Use of the Ag@NiFe2O4 composite SERS substrate according to any one of claims 1 to 8 in detecting R6G molecules in water.

10. The use according to claim 9, characterized in that: The method is as follows: Under 785nm laser irradiation, the Ag@NiFe2O4 composite SERS substrate is immersed in the R6G solution, which enhances the Raman signal of the R6G molecule and facilitates the detection of the R6G molecule in water.

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