A surface-enhanced Raman substrate, its preparation method and application

Abstract

This invention discloses a surface-enhanced Raman spectroscopy (SERS) substrate, its preparation method, and its applications. The substrate includes a template, an electromagnetic enhancement layer on the template, the electromagnetic enhancement layer being composed of discontinuously distributed silver nanoparticles, and a tungsten disulfide layer coating the surface of the silver nanoparticles; wherein the template is a porous anodic alumina template (AAO). This invention achieves dual electromagnetic-chemical composite enhancement with high sensitivity: the silver nanoparticles with optimized size and spacing on the AAO provide a strong electromagnetic field; the WS2 layer not only specifically adsorbs furfural, but the heterojunction interface formed by it and Ag promotes efficient charge transfer, resulting in chemical enhancement. The synergistic effect of these two factors significantly improves the Raman signal enhancement factor of the substrate for furfural.

Description

Technical Field

[0001] This invention relates to the technical field of molecular spectroscopy analysis and detection, specifically to a surface-enhanced Raman substrate, its preparation method, and its application. Background Technology

[0002] Transformer oil is a critical insulating medium in power equipment, and its aging state directly affects the operational safety and lifespan of transformers. Furfural (2-furancarbaldehyde) is one of the main characteristic degradation products of cellulose insulation paper during thermal aging and is stably soluble in transformer oil. Therefore, the concentration of dissolved furfural in the oil is widely recognized as an important chemical indicator for assessing the aging degree of transformer insulation paper and predicting its remaining lifespan. Currently, the standard detection method for furfural mainly relies on high-performance liquid chromatography (HPLC). However, this method has drawbacks such as complex sample pretreatment (requiring extraction), time-consuming and labor-intensive processes, expensive equipment, and the need for professional personnel to operate in a laboratory environment, making it difficult to achieve rapid on-site diagnosis and online monitoring.

[0003] Surface-enhanced Raman scattering (SERS) technology has shown great advantages in the field of trace substance detection due to its extremely high detection sensitivity, unique molecular fingerprint recognition capability, and rapid, non-destructive analytical potential.

[0004] However, current research on SERS for the detection of furfural in transformer oil is still in its early stages, and many studies suffer from poor signal reproducibility and low signal intensity of the SERS substrate. There is an urgent need for a new type of SERS substrate. Summary of the Invention

[0005] One of the objectives of this invention is to provide a surface-enhanced Raman spectroscopy (SERS) substrate to address the problems of poor signal reproducibility and low signal intensity in existing SERS substrates used for detecting furfural in transformer oil.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A surface-enhanced Raman substrate includes a template, an electromagnetic enhancement layer on the template, the electromagnetic enhancement layer being composed of discontinuously distributed silver nanoparticles, and a tungsten disulfide layer coating the surface of the silver nanoparticles; wherein the template is a porous anodic aluminum oxide template.

[0007] Furthermore, the pore diameter of the porous anodic aluminum oxide template is 100-200 nm, the pore depth is 300 nm-400 nm, and the spacing between adjacent pores is 50-200 nm.

[0008] Furthermore, the particle size of the silver nanoparticles is 100-200 nm, and the gap between the silver nanoparticles is 50-200 nm. Tungsten disulfide layers are formed by stacking 1 to 8 layers of tungsten disulfide nanosheets.

[0009] The second objective of this invention is to provide a method for preparing a surface-enhanced Raman substrate for one of the objectives, comprising the following steps: Step 1: After immersing the porous anodic aluminum oxide template in silver ammonia solution, it is transferred to a reaction solution containing reducing agent for reduction reaction. Silver ions grow in situ on the surface of the porous anodic aluminum oxide template, thus obtaining a porous anodic aluminum oxide template loaded with nano-silver particles. Step 2: Place the porous anodic aluminum oxide template loaded with silver nanoparticles in a precursor liquid containing tungsten and sulfur sources. Through hydrothermal reaction, the generated tungsten disulfide coats the surface of the silver nanoparticles to obtain a surface-enhanced Raman substrate.

[0010] Furthermore, the concentration of silver ions in the silver ammonia solution is 0.5-20 mM; The concentration of the reducing agent in the reaction solution is 1-50 mM.

[0011] Furthermore, the reducing agent includes at least one of ascorbic acid, sodium citrate, sodium borohydride, and glucose.

[0012] Furthermore, the concentration of the tungsten source in the precursor solution is 1-50 mM, and the concentration of the sulfur source is 2-10 times that of the tungsten source.

[0013] Furthermore, the tungsten source is any one of sodium tungstate, ammonium paratungstate, and tungsten trioxide; the sulfur source is any one of thiourea, thioacetamide, and L-cysteine.

[0014] Furthermore, the conditions for the reduction reaction are: reacting at 20-60℃ for 15-30 minutes; The hydrothermal reaction conditions are: reaction at 160-220℃ for 6-24 hours.

[0015] The third objective of this invention is to provide a method for detecting furfural dissolved in transformer oil, comprising the following steps: Step S1: The test oil sample containing dissolved furfural is dropped onto the surface of one of the target surface-enhanced Raman substrates. The static state promotes the diffusion of furfural molecules and their adsorption by tungsten disulfide in the surface-enhanced Raman substrate. Step S2: Use a Raman spectrometer to collect surface-enhanced Raman spectroscopy data of the surface-enhanced Raman substrate on which the sample to be tested was dropped, at a wavelength of 1700 cm⁻¹. -1 ±10 cm -1 1600 cm -1 ±10 cm -1 and 1500 cm -1 ±10 cm -1 The peak intensity of the characteristic peak at the location is given. The Raman acquisition conditions are: excitation with a 532 nm laser with a power of 0.5-5 mW.

[0016] The present invention has the following beneficial effects: This invention achieves dual electromagnetic-chemical enhancement. First, it exhibits high sensitivity: the optimized size and spacing of silver nanoparticles on the porous anodic alumina (AAO) template provide a strong electromagnetic field; the tungsten disulfide (WS2) layer not only specifically adsorbs furfural, but the heterojunction interface formed with Ag promotes efficient charge transfer, resulting in chemical enhancement. The synergistic effect of these two factors significantly improves the Raman signal enhancement factor of the substrate for furfural, with a measured detection limit below 0.05 mg / L.

[0017] Secondly, the orderliness of the AAO template ensures that the distribution of silver nanoparticles and WS2 layer is relatively uniform, so that the relative standard deviation (RSD) of SERS signals from different batches and different locations within the same batch can be controlled within 10%, which meets the requirements of quantitative analysis. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process of the surface-enhanced Raman substrate in this invention; Figure 2 This is a schematic diagram of the process for detecting dissolved furfural in transformer oil using a surface-enhanced Raman substrate according to the present invention. Figure 3 Here is an SEM image, where, Figure 3 Figure (a) in the image is the SEM image of the AAO template. Figure 3 Figure (b) in the figure is a SEM image of the Ag / AAO substrate; Figure 4 Raman data of R6G tested on three substrates; Figure 5 Raman spectroscopy data for furfural on three substrates. Detailed Implementation

[0019] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0020] According to the inventors' research, existing SERS technology for detecting furfural in transformer oil suffers from poor signal reproducibility and low signal intensity. An ideal substrate would simultaneously meet the following requirements: possessing a three-dimensional ordered structure to provide high-density, uniform electromagnetic "hot spots"; capable of achieving strong specific adsorption and efficient charge transfer chemical enhancement of target molecules through material design; and requiring a simple, economical, and controllable preparation method. This represents a key direction for overcoming the bottleneck in rapid, highly sensitive on-site detection of furfural in transformer oil.

[0021] Based on this, an embodiment of the first aspect of the present invention provides a surface-enhanced Raman substrate, the substrate comprising a template, an electromagnetic enhancement layer located on the template, the electromagnetic enhancement layer being composed of discontinuously distributed silver nanoparticles, and a tungsten disulfide layer coating the surface of the silver nanoparticles; wherein the template is a porous anodic aluminum oxide template.

[0022] This invention provides a composite surface-enhanced Raman spectroscopy (SERS) substrate integrating a three-dimensional ordered structure, electromagnetic "hot spots," and a specific chemically enhanced interface. First, a porous anodic alumina template (AAO template) has a highly ordered nanopore array structure. As a support for fabricating a surface-enhanced Raman spectroscopy substrate with a three-dimensional nanostructure, it controls the array distribution of the silver nanoparticles constituting the electromagnetic enhancement layer, ensuring the uniformity of the substrate test. This, in turn, ensures that the Raman signals generated at different locations on the substrate are approximately the same, avoiding uneven distribution of strong and weak signals. Preferably, in this embodiment, the silver nanoparticles are located on the pore surface and upper surface of the porous anodic alumina template.

[0023] Secondly, tungsten disulfide (WS2, which serves as a chemical reinforcement layer) coated on the surface of the silver nanoparticles tightly binds with the silver nanoparticles (electromagnetic reinforcement layer) to form an Ag-WS2 heterostructure. The localized surface plasmon resonance effect generated by the electromagnetic reinforcement unit and the charge transfer effect induced by the chemical reinforcement layer (tungsten disulfide) at the interface of the heterostructure work synergistically to amplify the Raman scattering signal of furfural molecules adsorbed on the surface of the tungsten disulfide layer. Preferably, in the embodiments of the present invention, the tungsten disulfide (WS2) layer coats the silver nanoparticles in a continuous or island-like manner, and its crystal structure is a 2H phase. In the present invention, the WS2 layer selectively adsorbs furfural molecules through its surface characteristics and forms an Ag-WS2 heterostructure with the underlying silver nanoparticles. This heterostructure interface establishes an effective charge transfer path from silver to WS2 and then to the adsorbed furfural molecules, providing significant chemical reinforcement and producing a synergistic effect with electromagnetic reinforcement. More preferably, the tungsten disulfide layer is formed by stacking 1-8 layers of tungsten disulfide nanosheets; in the embodiments of the present invention, the tungsten disulfide layer formed by stacking 1-8 layers of tungsten disulfide nanosheets is conducive to charge transfer between furfural molecules and tungsten disulfide, changing the polarity of furfural molecules, thereby enhancing the Raman scattering of furfural molecules.

[0024] In some embodiments, the porous anodic alumina template has pores with a diameter of 100-200 nm, a pore depth of 300 nm-400 nm, and a spacing of 50-200 nm between adjacent pores containing silver nanoparticles. In this embodiment, the porous anodic alumina template (AAO template) used has a highly ordered and recessed array of nanopores. This structure provides a high specific surface area and well-ordered capillary channels, which is beneficial for molecular diffusion and enrichment. Furthermore, due to the presence of pores in the AAO template, laser light can undergo multiple reflections within the pores, further enhancing the signal on the substrate.

[0025] In some embodiments, the particle size of the silver nanoparticles is 100-200 nm, and the gap between the silver nanoparticles is 50-200 nm; the tungsten disulfide layer is formed by stacking 1-8 layers of tungsten disulfide nanosheets. In this embodiment of the invention, an electric field is generated on the surface of the metal particles under the action of Raman laser. Under the action of the electric field, the analyte molecules are more likely to generate Raman scattering signals, and the electric field between two silver nanoparticles is stronger; therefore, in this invention, the silver nanoparticles constitute a high-density plasma resonance "hot spot", which is mainly responsible for generating electromagnetic field enhancement.

[0026] A second aspect of the present invention provides a method for preparing a surface-enhanced Raman substrate as described in the first aspect embodiment, the preparation process being as follows: Figure 1 As shown, it includes the following steps: Step 1: After immersing the porous anodic aluminum oxide template in silver ammonia solution, it is transferred to a reaction solution containing reducing agent for reduction reaction. Silver ions grow in situ on the surface of the porous anodic aluminum oxide template, thus obtaining a porous anodic aluminum oxide template loaded with nano-silver particles. Step 2: Place the porous anodic aluminum oxide template loaded with silver nanoparticles in a precursor liquid containing tungsten and sulfur sources. Through hydrothermal reaction, the generated tungsten disulfide coats the surface of the silver nanoparticles to obtain a surface-enhanced Raman substrate.

[0027] In embodiments of the present invention, silver ions are in situ reduced to silver nanoparticles on the surface and within the pores of an AAO template and deposited to form discontinuously distributed silver nanoparticles, thus forming an electromagnetic reinforcement layer. An anodic aluminum oxide template covered with silver particles is then introduced into a hydrothermal reaction, thereby achieving the growth of a tungsten disulfide layer on the surface of the silver nanoparticles. This constructs a heterojunction combining silver and tungsten disulfide. This heterostructure interface establishes an effective charge transfer pathway from silver to WS2 and then to adsorbed furfural molecules, providing significant chemical reinforcement and producing a synergistic effect with electromagnetic reinforcement.

[0028] Preferably, the porous anodic alumina template (AAO template) in this embodiment of the invention is prepared by the following method: Aluminum sheets with a purity of 99.999% were sequentially annealed and electrochemically polished, followed by a first anodizing, a first etching, a second anodizing, and a second etching process. The annealing conditions were: annealing at 500℃ for 3 hours in an argon atmosphere to eliminate internal stress and increase grain size. The electrochemical polishing conditions were: the annealed aluminum sheets were placed in a 1:4 volume ratio mixture of perchloric acid and anhydrous ethanol and electrochemically polished for 3 minutes at 0℃ and a constant voltage of 15 V to obtain a mirror-smooth surface. The first and second anodizing conditions were: using 0.3 M oxalic acid solution as the electrolyte, anodizing was performed at 5℃ and a DC voltage of 40 V. The first anodizing time was 4 hours, and the second anodizing time was 2 hours. The purpose of the first anodizing was to form a porous alumina layer, and the purpose of the second anodizing was to grow a highly ordered, vertically penetrating array of nanopores. The first etching conditions were as follows: the aluminum sheet after the first anodizing was placed in a mixture of 6 wt% phosphoric acid and 1.8 wt% chromic acid and etched at 60°C for 6 hours. The purpose was to remove the aluminum oxide layer generated during the first anodizing, exposing the aluminum metal surface with an ordered pit array. The second anodizing process began with the ordered pit array exposed by the first etching. The second etching conditions were as follows: the aluminum plate after the second anodizing was immersed in a 5 wt% phosphoric acid solution and subjected to a hole-enlarging treatment at 30°C for 30 minutes. The purpose was to enlarge the pore size and open the bottom of the pores, ultimately obtaining an AAO template with a pore size of approximately 150 nm, a pore depth of approximately 350 nm, and a pore spacing of approximately 180 nm.

[0029] In some embodiments, the concentration of silver ions in the silver ammonia solution is 0.5-20 mM; the concentration of the reducing agent in the reaction solution is 1-50 mM. In embodiments of the present invention, silver ammonia solutions within this concentration range are advantageous for synthesizing silver nanoparticles with a corresponding size of 100-200 nm.

[0030] In some embodiments, the reducing agent includes at least one of ascorbic acid, sodium citrate, sodium borohydride, and glucose.

[0031] In some embodiments, the concentration of the tungsten source in the precursor solution is 1-50 mM, and the concentration of the sulfur source is 2-10 times that of the tungsten source. In the embodiments of the present invention, since hydrothermal reactions are usually carried out at high temperature and high pressure (e.g., 160-220°C), the sulfur source is prone to volatilization or decomposition at high temperature (e.g., thiourea decomposes into H2S and NH3), resulting in a decrease in the effective sulfur concentration. Excess sulfur source can maintain the sulfur atmosphere in the reaction system, ensure that the sulfidation reaction proceeds fully, and avoid the appearance of impurities such as tungsten oxide (WO3) in the product due to insufficient sulfur.

[0032] In some embodiments, the tungsten source is any one of sodium tungstate, ammonium paratungstate, and tungsten trioxide; the sulfur source is any one of thiourea, thioacetamide, and L-cysteine.

[0033] In some embodiments, the reduction reaction conditions are: reaction at 20-60°C for 15-30 min; the hydrothermal reaction conditions are: reaction at 160-220°C for 6-24 h. In this embodiment of the invention, the sulfur source is fully decomposed within this temperature range, the tungsten precursor is effectively reduced and sulfided, and well-crystallized 2H-WS2 is easily obtained, avoiding the influence of reaction temperature outside this range on the crystal structure, phase, morphology, size, and defects of the final product.

[0034] The third objective of this invention is to provide a method for detecting furfural dissolved in transformer oil, the detection method being as follows: Figure 2 As shown, the specific steps include: Step S1: First, take the transformer oil sample to be tested (i.e., the oil sample to be tested containing furfural) and filter or centrifuge it to remove solid impurities and obtain a clear oil sample.

[0035] Then, the clarified oil sample is dropped onto the surface of the surface-enhanced Raman substrate in the first aspect embodiment of the present invention, and the quiescent state promotes the diffusion of furfural molecules and their adsorption by tungsten disulfide in the surface-enhanced Raman substrate; preferably, the quiescent state is: standing at 30°C for 30-60 min.

[0036] Step S2: Place the substrate with furfural molecules adsorbed in step S1 into a Raman spectrometer and perform Raman spectroscopy on the substrate located at 1700 cm⁻¹. -1 ±10 cm -1 1600 cm -1 ±10 cm -1 and 1500 cm -1 ±10 cm -1 The intensity of the characteristic peak signal at the location was collected using a 532 nm laser (power 0.5-5 mW) for excitation.

[0037] In practical applications, to further calculate the concentration of furfural in the oil sample, the embodiments of this invention also include the following steps: First, a series of furfural-transformer oil standard solutions were prepared using furfural standard and unaged 25# transformer oil. Preferably, in this embodiment, the concentrations of the series of furfural-transformer oil standard solutions were 0.05 mg / L, 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L and 10 mg / L, respectively.

[0038] Then, the standard solutions of each concentration mentioned above were dropped onto the surface-enhanced Raman substrate prepared in the first aspect embodiment. After standing, the substrate was subjected to the same conditions as in step S1, and the substrate was positioned at 1700 cm⁻¹. -1 The intensity values ​​of the furfural characteristic peak (C=O stretching vibration) at a certain location were collected, and then plotted with the logarithm of furfural concentration on the x-axis at 1700 cm⁻¹. -1 Plot the standard working curve with the logarithm of the peak intensity as the ordinate.

[0039] Finally, the 1700 cm in step S2 -1 The intensity of the characteristic peak is input into the standard working curve to calculate the concentration of furfural in the oil sample.

[0040] Example The present invention will be further described below through specific embodiments.

[0041] Example 1

[0042] A method for preparing a surface-enhanced Raman spectroscopy substrate includes the following steps: Step 1: Preparation of porous anodic alumina (AAO) template High-purity aluminum foil with a thickness of 0.3 mm and a purity of 99.999% was cut into 2 cm × 2 cm samples. The aluminum sheets were annealed at 500℃ in an argon atmosphere for 3 hours. The annealed aluminum sheets were then placed in a mixture of perchloric acid and anhydrous ethanol with a volume ratio of 1:4 and electrochemically polished at 0℃ and a constant voltage of 15 V for 3 minutes to obtain a mirror-smooth surface.

[0043] Then, the electrochemically polished aluminum sheet was anodized for the first time using 0.3 M oxalic acid solution as electrolyte to form a porous aluminum oxide layer; the conditions for the first anodization were: 5℃, 40 V DC voltage for 4 hours.

[0044] The aluminum sheet after the first anodization is then immersed in a mixture of 6 wt% phosphoric acid and 1.8 wt% chromic acid for the first etching at 60°C for 6 hours to completely remove the aluminum oxide layer generated by the first anodization and expose the aluminum metal surface with an ordered pit array.

[0045] The aluminum sheet after the first etching was subjected to a second anodizing using a 0.3 M oxalic acid solution as the electrolyte. The conditions for the second anodizing were: 5℃, 40 V DC voltage for 2 hours.

[0046] Finally, the aluminum sheet after the second anodization was immersed in a 5 wt% phosphoric acid solution for a second etching. After etching at 30°C for 30 min, an AAO template with a pore size of about 150 nm, a pore depth of about 350 nm, and a pore spacing of about 180 nm was obtained. After repeated rinsing with deionized water and drying with nitrogen, it was used for the next reaction.

[0047] Step 2: Preparation of silver nanoparticle layer (electromagnetic enhancement layer) by chemical reduction method To prepare a 0.01 M silver nitrate solution, specifically, concentrated ammonia is slowly added dropwise to the silver nitrate solution until the initially formed brown precipitate is just completely dissolved, resulting in a clear silver ammonia solution. A 0.1 M ascorbic acid solution is prepared as a reducing agent. This solution is prepared immediately before use. Specifically, ascorbic acid is dissolved in deionized water that has been deoxygenated with nitrogen.

[0048] The AAO template obtained in step one was immersed in the aforementioned silver ammonia solution, ensuring the solution fully wetted the pores, and allowed to stand for 10 minutes. The template was then removed and transferred to an ascorbic acid solution for reduction. During the reaction, silver ions were reduced in situ by ascorbic acid on the surface of the AAO template and the inner walls of the pores, generating silver nanoparticles which were then deposited, resulting in an AAO (Ag / AAO) substrate loaded with silver nanoparticles. The reduction reaction conditions were: standing in a 30°C constant temperature water bath for 15 minutes. After the reaction, the AAO substrate loaded with silver nanoparticles (Ag / AAO substrate) was removed and ultrasonically cleaned alternately with deionized water and ethanol for 30 seconds (to remove loosely attached particles). This process was repeated three times, followed by drying with nitrogen gas for use in the next reaction.

[0049] Step 3: Preparation of tungsten disulfide (WS2) layer by chemical deposition Sodium tungstate (Na2WO4·2H2O) and thiourea (CH4N2S) were dissolved in 35 mL of deionized water and stirred magnetically for 30 min to form a clear precursor solution. The concentration of sodium tungstate in the precursor solution was 10 mM and the concentration of thiourea was 50 mM.

[0050] The Ag / AAO substrate obtained in step two was tilted and placed in a 50 mL high-pressure reactor lined with polytetrafluoroethylene. The precursor solution was then poured into the reactor liner, ensuring that the solution partially wetted the substrate. The reactor was sealed and placed in a forced-air drying oven, where it was reacted at 200°C for 12 hours. After naturally cooling to room temperature, the WS2 / Ag / AAO surface-enhanced Raman substrate was obtained.

[0051] Remove the substrate and rinse it repeatedly with deionized water and ethanol to remove unreacted precursors and byproducts. Then dry it in a vacuum drying oven at 60°C for 2 hours before use for subsequent testing and analysis.

[0052] Example 2

[0053] The preparation method of the surface-enhanced Raman substrate in this embodiment is the same as that in Example 1, except that: In step two, the concentration of silver nitrate solution is 0.5 mM, and the concentration of ascorbic acid in ascorbic acid solution is 1 mM. In step three, the concentration of sodium tungstate in the precursor solution is 1 mM, and the concentration of thiourea is 50 mM. The hydrothermal reaction conditions are: react at 160℃ for 24 hours.

[0054] Example 3

[0055] The preparation method of the surface-enhanced Raman substrate in this embodiment is the same as that in Example 1, except that: In step two, the concentration of silver nitrate solution is 20 mM, and the concentration of ascorbic acid in ascorbic acid solution is 50 mM. The concentration of sodium tungstate in the precursor solution is 50 mM, and the concentration of thiourea is 50 mM. The hydrothermal reaction conditions are: reaction at 220℃ for 6 hours.

[0056] Comparative Example 1 The Raman substrate preparation method in this embodiment is the same as that in Example 1. The difference is that the AAO substrate loaded with silver nanoparticles (Ag / AAO substrate) is prepared in this embodiment, and the chemical deposition method in step three to prepare the tungsten disulfide (WS2) layer is not performed.

[0057] Comparative Example 2 The Raman substrate preparation method in this embodiment is the same as that in Example 1. The difference is that in this embodiment, the WS2 layer is directly grown on a blank AAO template to obtain the WS2 / AAO substrate. The preparation of the nano-silver particle layer by chemical reduction in step two is not performed during the preparation process.

[0058] Test Analysis: I. Morphological Analysis The AAO template and Ag / AAO substrate obtained in Example 1 were subjected to SEM testing and analysis, and the results are as follows: Figure 3 As shown. Figure 3 Here is an SEM image, where, Figure 3 Figure (a) in the image is the SEM image of the AAO template. Figure 3 Figure (b) in the figure is a SEM image of the Ag / AAO substrate.

[0059] from Figure 3 It can be seen that, due to the limitation of the porous anodic aluminum oxide template (AAO template), the reduced silver nanoparticles are uniformly distributed in the pores of the template, thus promoting the array distribution of silver nanoparticles on the AAO template, which is beneficial to the preparation of a substrate with good uniformity.

[0060] II. Performance Analysis 1. With a concentration of 10 -4 Using a Rhodamine 6G (R6G) ethanol solution as a probe molecule, the SERS performance of the WS2 / Ag / AAO substrates obtained in Example 1, the Ag / AAO substrates obtained in Comparative Example 1, and the WS2 / AAO substrates obtained in Comparative Example 2 were tested and analyzed under 532 nm laser excitation. The test results are as follows: Figure 4 As shown, where, Figure 4 Raman data for R6G on three substrates are shown.

[0061] from Figure 4 As can be seen, the enhancement factor of the Ag / WS2 / AAO substrate for the R6G characteristic peak is about two orders of magnitude higher than that of the Ag / AAO substrate alone, and about four orders of magnitude higher than that of the WS2 / AAO substrate. This indicates that the introduction of WS2 does indeed produce a significant synergistic enhancement effect with Ag. Furthermore, R6G at 612 cm⁻¹ was measured at 20 randomly selected points on the substrate. -1 The characteristic peak intensity at the substrate has a relative standard deviation (RSD) of 8.5%, indicating that the substrate has good signal uniformity and reproducibility.

[0062] 2. Prepare a furfural-transformer oil standard solution with a furfural concentration of 10 mg / L using furfural standard (i.e., pure furfural solution) and unaged 25# transformer oil.

[0063] Take 20 μL of the above furfural-transformer oil standard solution and drop it onto the surfaces of the Ag / WS2 / AAO substrate prepared in Example 1, the Ag / AAO substrate obtained in Comparative Example 1, and the WS2 / AAO substrate obtained in Comparative Example 2, respectively. Place them on a 30℃ constant temperature stage and let them stand for 40 min. Then, place the substrates with the standard solution on the sample stage of a confocal Raman spectrometer. Use a 532 nm laser, a laser power of 1 mW, a 50x objective lens, and an integration time of 5 seconds to acquire SERS spectra and record the values ​​at approximately 1700 cm⁻¹ in each spectrum. -1 The intensity values ​​of the furfural characteristic peak (C=O stretching vibration) at the specified location are detailed in the test results. Figure 5 ;in, Figure 5 Raman spectroscopy data for furfural on three substrates.

[0064] from Figure 5 As can be seen from the image, the substrate used in Example 1 is located at approximately 1700 cm. -1 The intensity of the furfural characteristic peak (C=O stretching vibration) at 1700 cm⁻¹ is more than three times that of the Ag / AAO substrate in Comparative Example 1, while the intensity of the WS₂ / AAO substrate at 1700 cm⁻¹ is more than three times that of the substrate in Comparative Example 1. -1There are virtually no characteristic peaks at this location. This indicates that Ag, WS2, and AAO in the Ag / WS2 / AAO substrate of this invention exhibit a synergistic effect, significantly enhancing the Raman signal enhancement factor for furfural.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A surface enhanced Raman substrate, characterized by, The device includes a template, an electromagnetic enhancement layer located on the template, the electromagnetic enhancement layer being composed of discontinuously distributed silver nanoparticles, and a tungsten disulfide layer coating the surface of the silver nanoparticles; wherein the template is a porous anodic aluminum oxide template.

2. The surface-enhanced Raman substrate according to claim 1, characterized in that, The porous anodic aluminum oxide template has a pore diameter of 100-200 nm, a pore depth of 300 nm-400 nm, and a spacing of 50-200 nm between adjacent pores.

3. The surface-enhanced Raman substrate according to claim 2, characterized in that, The size of the silver nanoparticles is 100-200 nm, and the gap between the silver nanoparticles is 50-200 nm. The tungsten disulfide layer is formed by stacking 1-8 layers of tungsten disulfide nanosheets.

4. The method for preparing the surface-enhanced Raman substrate according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step 1: After immersing the porous anodic aluminum oxide template in silver ammonia solution, it is transferred to a reaction solution containing reducing agent for reduction reaction. Silver ions grow in situ on the surface of the porous anodic aluminum oxide template, thus obtaining a porous anodic aluminum oxide template loaded with nano-silver particles. Step 2: Place the porous anodic aluminum oxide template loaded with silver nanoparticles in a precursor liquid containing tungsten and sulfur sources. Through hydrothermal reaction, the generated tungsten disulfide coats the surface of the silver nanoparticles to obtain a surface-enhanced Raman substrate.

5. The preparation method according to claim 4, characterized in that, The concentration of silver ions in the silver ammonia solution is 0.5-20 mM; The concentration of the reducing agent in the reaction solution is 1-50 mM.

6. The preparation method according to claim 5, characterized in that, The reducing agent includes at least one of ascorbic acid, sodium citrate, sodium borohydride, and glucose.

7. The preparation method according to claim 6, characterized in that, The concentration of the tungsten source in the precursor solution is 1-50 mM, and the concentration of the sulfur source is 2-10 times that of the tungsten source.

8. The preparation method according to claim 7, characterized in that, The tungsten source is any one of sodium tungstate, ammonium paratungstate, and tungsten trioxide; the sulfur source is any one of thiourea, thioacetamide, and L-cysteine.

9. The preparation method according to claim 8, characterized in that, The conditions for the reduction reaction are: reacting at 20-60℃ for 15-30 min; The hydrothermal reaction conditions are: reaction at 160-220℃ for 6-24 hours.

10. A method for detecting furfural dissolved in transformer oil, characterized in that, Includes the following steps: Step S1: The test oil sample containing dissolved furfural is dropped onto the surface of the surface-enhanced Raman substrate according to any one of claims 1 to 3, and the sample is left to stand to allow furfural molecules to diffuse and be adsorbed by tungsten disulfide in the surface-enhanced Raman substrate. Step S2: Use a Raman spectrometer to collect the peak intensities of the characteristic peaks at 1700 cm⁻¹±10 cm⁻¹, 1600 cm⁻¹±10 cm⁻¹, and 1500 cm⁻¹±10 cm⁻¹ on the surface-enhanced Raman substrate onto which the sample to be tested is dropped. The Raman acquisition conditions are: excitation with a 532 nm laser with a power of 0.5-5 mW.

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