Preparation method of silver nano rectangular flakes and detection method of acetone in transformer oil

Abstract

A method for preparing silver nano rectangular sheets and a method for detecting acetone in transformer oil include synthesizing a silver nano rectangular sheet sol solution; synthesizing a rectangular silver nano sheet; dissolving the rectangular silver nano sheet in an ethanol solution to obtain a colloidal solution of the silver nano rectangular sheet, and spin coating the colloidal solution of the silver nano rectangular sheet on a silicon wafer, and allowing it to evaporate to a solid state to obtain a silicon-based silver nano rectangular sheet; preparing a gradient solution of acetone of different concentrations dissolved in transformer oil; respectively loading the gradient solutions of acetone of different concentrations into quartz cuvettes, immersing the silver nano rectangular sheet surface enhancement material in the solution, and storing it in the dark; collecting a Raman spectrum of the gradient solution, and pre-processing the Raman spectrum; and quantitative detection. The surface enhancement substrate of the silver nano rectangular sheet has a significant enhancement effect in measuring acetone in transformer oil. The present invention can be widely used in the fields of energy, electricity, etc., and is used for detecting trace aging characteristic substances dissolved in transformer oil.

Description

Technical Field

[0001] The invention belongs to the technical field of transformer safety detection, and particularly relates to a method for preparing silver nano rectangular sheets and a method for detecting acetone in transformer oil. Background Art

[0002] In the operation of the power system, large power transformers are hub equipment, and their stable operation is a necessary condition to ensure high-quality power supply. The insulation inside the transformer is mainly composed of composite insulation composed of mineral oil and insulating paperboard. During long-term operation, its insulating materials such as insulating oil and insulating paper decompose under the action of electricity, heat and other factors, producing furans, alcohols, acids, esters and ketones, etc., which reflect the nature of the fault and the insulation performance, and dissolve in the oil. The concentration can be used as a chemical indicator to evaluate the degree of insulation aging. Testing the degree of polymerization of paper insulation in transformer oil, the content of furfural dissolved in oil and characteristic aging products such as CO and CO2 is the main method to judge the aging state of transformer insulation. The content of dissolved gas and furfural in transformer oil can objectively reflect the aging of the internal insulation of the transformer, but it is difficult to accurately judge the degree of insulation aging of the transformer due to the easy diffusion of gas in oil and the easy adsorption of furfural.

[0003] Acetone is a product produced after long-term operation of transformer insulation. Because it is not easily adsorbed and difficult to diffuse, is less affected by oxygen and moisture, and has a relatively stable composition, it has reference value as an indicator for determining transformer insulation aging.

[0004] At present, the main methods for detecting the content of acetone in transformer oil at home and abroad include headspace gas chromatography, high performance liquid chromatography, ultraviolet spectrophotometry and colorimetry. Headspace gas chromatography can meet the requirements of acetone concentration for transformer aging detection, but it has problems such as complicated water bath heating operation, long sample equilibration time, chromatographic column is easily contaminated and long detection time. In addition, the headspace gas chromatography device is expensive, and parts (such as chromatographic column, etc.) need to be replaced regularly, and the maintenance cost is high, which makes the detection cost of headspace gas chromatography high; high performance liquid chromatography has high detection accuracy and good repeatability, but elution is difficult and there are problems such as "extra-column effect"; ultraviolet spectrophotometry has fast detection speed, but it is easily interfered by organic matter in oil and has poor stability; although the colorimetric method is low in cost, the reagent used (p-toluidine) is a strong carcinogen and the experimental error is also large.

[0005] In recent years, with the development of laser and CCD detection technology, Raman spectroscopy has been widely used in the detection and analysis of trace solid and liquid materials. Compared with the current detection technology, Raman spectroscopy has the advantages of fast detection speed, high sensitivity, and simple operation, and can determine the type and concentration of substances. Therefore, laser Raman spectroscopy can be used to detect trace acetone dissolved in transformer oil. However, the intensity of Raman scattering signals is generally only 1×10 of the incident light intensity. -10 In addition, due to the small number of interface molecules, the Raman scattering signal intensity will be very weak. In addition, the components of the operating transformer oil are complex and the content of dissolved acetone in the transformer oil is low. The current Raman spectroscopy detection technology cannot meet the actual engineering requirements for the detection of aging characteristic substances in transformer oil.

[0006] In order to alleviate the problem of weak Raman scattering signals, it is necessary to increase the cross section of Raman scattering to enhance the Raman signal. In 1974, Fleischmann et al. obtained high-quality Raman spectra of pyridine adsorbed on the surface of a rough silver electrode by electrochemical roughening. Van Duyne et al. and Creighton et al.

[27] It was found that when a Raman scattering material is placed on or near a rough noble metal surface, the intensity of the Raman signal is one million times that of traditional Raman. This phenomenon overcomes the disadvantage of poor sensitivity of traditional Raman scattering. This effect is later called surface-enhanced Raman spectroscopy (SERS). How to prepare surface enhancement materials with high enhancement effect is a key issue that people pay attention to. Colloidal suspensions of noble metals such as Au and Ag nanoparticles are often used as active surface enhancement materials, and the SERS enhancement intensity of Ag nanoparticles is greater than that of Au nanoparticles; at the same time, silver nanomaterials with special morphology show excellent surface enhancement performance, because the sharp edges or branches of metal nanostructures can gather charges and generate larger electric fields than spherical nanoparticles. The edges of the common silver nanosphere particle surface enhancement substrate are relatively smooth, and the surface enhancement performance is poor, which cannot better meet the detection requirements of actual trace features. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing silver nano rectangular sheets and a method for detecting acetone in transformer oil. Surface enhanced Raman spectroscopy (SERS) refers to the phenomenon that the Raman signal of the analyte around the metal nanostructure is amplified by several orders of magnitude due to the local electromagnetic field enhancement caused by surface plasmon resonance excitation. This phenomenon overcomes the disadvantage of poor sensitivity of traditional Raman scattering, and can effectively solve the problem of insufficient signal intensity in the detection and analysis of trace acetone dissolved in transformer oil by Raman spectroscopy.

[0008] The present invention adopts the following technical solution.

[0009] A method for preparing silver nano rectangular sheets,

[0010] The following steps are involved:

[0011] Step 1, synthesizing silver nano rectangular flake sol solution: 0.05mol / L AgNO3 solution and 10mmol / L sodium citrate are placed on a magnetic stirrer for stirring, and 2mmol / L PVP and 30% hydrogen peroxide are added in sequence during the stirring process, and stirred for ten minutes; 10mmol / L sodium borohydride solution is added to the mixed solution to obtain a silver seed solution, and the mixture is continuously stirred for 30 minutes under the irradiation of a sodium lamp to obtain a silver nano rectangular flake sol solution; wherein the volume ratio of the AgNO3 solution, sodium citrate, PVP, 30% hydrogen peroxide and sodium borohydride solution is 2500:1000:225:3:50;

[0012] Step 2, preparing rectangular silver nanosheets using the silver nano rectangular sheet sol solution obtained in step 1;

[0013] Step 3, preparing silicon-based silver nano-rectangular flakes: dissolving the rectangular silver nano-flakes in an ethanol solution to obtain a colloidal solution of the silver nano-rectangular flakes, and spin-coating the colloidal solution of the silver nano-rectangular flakes on a silicon wafer, and allowing it to evaporate to a solid state.

[0014] The silver nano rectangular sheet is a rectangle with a length of 1um to 5um and a width of 1um to 10um. It is made of silver and has a deposition thickness of 1mm on the silicon wafer.

[0015] In step 1, the stirring speed is 800 r / min; the power of the sodium lamp is 250 W.

[0016] Step 2 includes the following steps:

[0017] S201, centrifuging the silver nano rectangular flake sol solution obtained in step 1 to obtain a precipitate using a centrifuge, and washing the precipitate with ultrapure water;

[0018] S202, centrifuging the product obtained by washing the precipitate with ultrapure water again using a centrifuge, and washing the precipitate obtained by centrifugation again using ethanol;

[0019] S203, repeat S201 and S202 three times to obtain rectangular silver nanosheets.

[0020] The concentration of the ethanol solution is 95%-99.5%.

[0021] A method for detecting acetone in transformer oil, the method using silver nano rectangular sheets as a surface enhancement material substrate, comprising the following steps:

[0022] (1) preparing a gradient solution of acetone of different concentrations dissolved in transformer oil;

[0023] (2) respectively placing the gradient solutions into quartz cuvettes, immersing the silver nano rectangular sheet surface enhancement material into the solution, and storing it away from light;

[0024] (3) collecting a surface enhanced Raman spectrum of the gradient solution and preprocessing the surface enhanced Raman spectrum;

[0025] (4) Quantitative detection: Calculate the characteristic peak of acetone and the internal standard peak area of ​​transformer oil, and calculate the relative Raman intensity of acetone. The quantitative calibration curve of acetone concentration in transformer oil is obtained by the least squares method. The content of acetone dissolved in transformer oil is calculated by this quantitative calibration curve.

[0026] The surface enhanced Raman spectrum of the gradient solution is collected by using a 560nm wavelength laser, a laser power of 100mW, an integration time of 1s, an integration number of 15, a slit width of 100μm, and a 1800 / 500nm grating, respectively focusing the laser on the transformer oil and on the surface of the silver nano-rectangular sheet surface enhancement substrate to obtain the surface enhanced Raman spectrum of the gradient solution.

[0027] The preprocessing includes: performing preprocessing of removing impurities, adjusting the baseline and smoothing and denoising on the surface enhanced Raman spectrum data of the measured gradient solution; and performing intensity normalization on the Raman spectrum data.

[0028] The characteristic peak of acetone in transformer oil in surface enhanced Raman spectroscopy is 1340 cm -1 .

[0029] Gaussian function was used to calculate the characteristic peak area of ​​acetone and internal standard peak area of ​​transformer oil in gradient concentration solution.

[0030] The beneficial effect of the present invention is that compared with the existing surface enhancement substrate, the prepared rectangular silver nanosheet surface enhancement substrate has a good enhancement effect, and its detection limit for rhodamine 6g is 10 -11 M, and the detection effect is uniform and stable. The preparation method is simple, no complicated operation is required, the production cost is low, and the process does not produce harmful and polluting gases. It is a simple, low-cost, green, environmentally friendly, stable and efficient surface enhancement substrate.

[0031] The beneficial effects of the present invention also include:

[0032] (1) This patent uses rectangular silver nanosheets as a surface enhancement substrate to detect acetone in transformer oil in situ. The characteristic peak of the Raman intensity of acetone is obtained by the internal standard method, and the enhancement effect of the surface enhancement substrate is analyzed over time. The stability of the surface enhancement substrate is determined, and the relationship between the relative area of ​​the characteristic peak of acetone and acetone solutions of different concentrations is measured. A quantitative analysis model of acetone concentration in transformer oil is established based on the least squares method, which can be used for quantitative detection of acetone concentration in transformer oil. This patent uses laser as a detection method, and can achieve in-situ detection of dissolved acetone in transformer oil without complex pretreatment.

[0033] (2) This patent applies surface enhanced Raman spectroscopy technology. The rectangular silver nanosheet surface enhancement substrate has a significant enhancement effect on acetone in transformer oil, which provides technical support for the use of surface enhanced substrates for Raman spectroscopy detection in transformer oil in the future and can be widely used in the fields of energy and electricity. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is an electron microscope image of the rectangular silver nanosheet surface enhancement substrate of the present invention;

[0035] Figure 2 It is a flow chart of a method for preparing a silver nano rectangular sheet of the present invention;

[0036] Figure 3 It is a flow chart of a method for detecting acetone in transformer oil of the present invention;

[0037] Figure 4 This is the spectrum of the Raman spectrum of oil sample No. Ⅰ after preprocessing;

[0038] Figure 5 It is the Raman spectra of transformer oil, acetone, and acetone oil sample dissolved in transformer oil;

[0039] Figure 6 It is the Raman spectra of oil samples Ⅰ-Ⅵ;

[0040] Figure 7 It is the relationship between the acetone concentration in the oil and the ratio of the Raman peak area. DETAILED DESCRIPTION

[0041] The present application is further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present application.

[0042] A method for preparing silver nano rectangular sheets comprises the following steps:

[0043] Step 1, synthesizing silver nano rectangular flake sol solution: 0.05mol / L AgNO3 solution and 10mmol / L sodium citrate are placed on a magnetic stirrer for stirring, and 2mmol / L PVP and 30% hydrogen peroxide are added in sequence during the stirring process, and stirred for ten minutes; 10mmol / L sodium borohydride solution is added to the mixed solution to obtain a silver seed solution, and the mixture is continuously stirred for 30 minutes under the irradiation of a sodium lamp at a stirring speed of 800r / min to obtain a silver nano rectangular flake sol solution, and the power of the sodium lamp is 250W; wherein the volume ratio of the AgNO3 solution, sodium citrate, PVP, 30% hydrogen peroxide and sodium borohydride solution is 2500:1000:225:3:50;

[0044] Step 2, preparing rectangular silver nanosheets using the silver nano rectangular sheet sol solution obtained in step 1;

[0045] Specifically, S201, centrifuging the silver nano rectangular flake sol solution obtained in step 1 to obtain a precipitate using a centrifuge, and washing the precipitate with ultrapure water;

[0046] S202, centrifuging the product obtained by washing the precipitate with ultrapure water again using a centrifuge, and washing the precipitate obtained by centrifugation again using ethanol;

[0047] S203, repeat S201 and S202 three times to obtain rectangular silver nanosheets.

[0048] Step 3, preparing silicon-based silver nano rectangular sheets: dissolving the rectangular silver nano sheets in an ethanol solution to obtain a colloidal solution of the silver nano rectangular sheets, and spin-coating the colloidal solution of the silver nano rectangular sheets on a silicon wafer, and allowing it to evaporate to a solid state. The obtained silver nano rectangular sheet surface enhancement material is as follows under a microscope: Figure 1 shown.

[0049] The silver nano rectangular sheet is a rectangle with a length of 1um to 5um and a width of 1um to 10um. It is made of silver and has a deposition thickness of 1mm on the silicon wafer.

[0050] The concentration of the ethanol solution in step 3 is 95%-99.5%.

[0051] A method for detecting acetone in transformer oil, the method using the silver nano rectangular sheets provided by the above method as a surface enhancement material substrate, comprising the following steps:

[0052] (1) preparing a gradient solution of acetone of different concentrations dissolved in transformer oil;

[0053] (2) respectively placing the gradient solutions into quartz cuvettes, immersing the silver nano rectangular sheet surface enhancement material into the solutions, and storing them away from light;

[0054] (3) collecting a surface enhanced Raman spectrum of the gradient solution and preprocessing the surface enhanced Raman spectrum;

[0055] In the process of collecting the surface enhanced Raman spectrum of the gradient solution, a 560nm wavelength laser, a laser power of 100mW, an integration time of 1s, an integration number of 15, a slit width of 100μm, and an 1800 / 500nm grating were selected to focus the laser on the transformer oil and on the surface of the silver nano-rectangular sheet surface enhancement substrate, respectively, to obtain the surface enhanced Raman spectrum of the gradient solution.

[0056] The preprocessing includes: performing preprocessing of removing impurities, adjusting the baseline and smoothing and denoising on the surface enhanced Raman spectrum data of the measured gradient solution; and performing intensity normalization on the Raman spectrum data.

[0057] (4) Quantitative detection: Calculate the characteristic peak of acetone and the peak area of ​​the internal standard of transformer oil, and calculate the relative Raman intensity of acetone. The quantitative calibration curve of acetone concentration in transformer oil is obtained by the least square method, and the content of acetone dissolved in transformer oil is calculated by this quantitative calibration curve. The characteristic peak of acetone in transformer oil in surface enhanced Raman spectroscopy detection is selected as 1340 cm -1 .

[0058] Gaussian function was used to calculate the characteristic peak area of ​​acetone and internal standard peak area of ​​transformer oil in gradient concentration solution.

[0059] Example 1: Figure 2 The method for preparing a silver nano rectangular sheet includes the following steps: S1, synthesizing a silver nano rectangular sheet sol solution;

[0060] Specifically, S1 includes: using a double reduction method, at room temperature, in the presence of a certain concentration of AgNO3, Na3C6H5O7, PVP and H2O2, and then adding a certain amount of NaBH4 to reduce AgNO3 to obtain a silver nano rectangular flake sol solution: specifically: placing a 0.05 mol / L AgNO3 solution and a 10 mmol / L sodium citrate solution on a magnetic stirrer for stirring, and adding 2 mmol / L PVP and 30% hydrogen peroxide in turn during the stirring process, and stirring for ten minutes; adding a 10 mmol / L sodium borohydride solution to the mixed solution to obtain a light yellow silver seed solution, and continuously stirring for 30 minutes under the irradiation of a sodium lamp, it can be observed that the color of the solution becomes slightly lighter, and a silver nano rectangular flake sol solution is obtained; wherein the volume ratio of the AgNO3 solution, sodium citrate, PVP, 30% hydrogen peroxide and sodium borohydride solution is 2500:1000:225:3:50.

[0061] S2, synthesizing rectangular silver nanosheets using the silver nano rectangular sheet sol solution obtained in step 1;

[0062] S201, centrifuging the reaction product obtained in the first step using a centrifuge, and washing the precipitate with ultrapure water;

[0063] S202, centrifuging the product after the second step of washing again with a centrifuge, and washing the precipitate with ethanol;

[0064] Ethanol and pure water are used to wash away unreacted substances and impurities such as organic matter, including: AgNO3, Na3C6H5O7, PVP and H2O2, NaBH4, leaving only silver.

[0065] S203, repeating steps S201 and S202 three times to obtain rectangular silver nanosheets.

[0066] S3. Preparation of silicon-based silver nano-rectangular sheet substrate

[0067] The rectangular silver nanosheets are dissolved in an ethanol solution, and the colloidal solution of the silver nanosheets is spin-coated on a silicon wafer and allowed to evaporate naturally. In the present invention, PVP refers to polyvinyl pyrrolidone, referred to as PVP.

[0068] The specific embodiment of the present application also provides a method for detecting acetone in transformer oil, such as Figure 3 As shown, the method uses the silver nano rectangular sheet surface enhancement material prepared by the above method as the surface enhancement material substrate, and comprises the following steps:

[0069] (1) preparing a gradient solution of acetone of different concentrations dissolved in transformer oil;

[0070] (2) placing gradient solutions of acetone of different concentrations into quartz cuvettes respectively, immersing the silver nano rectangular sheet surface enhancement material into the solutions, and storing them away from light;

[0071] (3) collecting a Raman spectrum of the gradient solution and preprocessing the Raman spectrum;

[0072] (4) Quantitative detection: Calculate the characteristic peak of acetone and the peak area of ​​the internal standard of transformer oil, and calculate the relative Raman intensity of acetone = the characteristic peak area of ​​acetone / the internal standard peak area of ​​transformer oil. The quantitative calibration curve of acetone concentration in transformer oil is obtained by the least square method: y = 15.33491x + 167.64513. Calculate the content of acetone dissolved in transformer oil, where y represents the relative Raman intensity of acetone and x represents the acetone concentration.

[0073] Example 2: Method for measuring acetone in transformer oil based on silver nano rectangular sheet surface enhanced substrate, such as Figure 4-6, including the following steps:

[0074] Step 1, prepare a gradient solution of different concentrations of acetone dissolved in transformer oil:

[0075] Specifically include:

[0076] C1, dissolve 1 mL of acetone solution in transformer oil, adjust the volume to obtain 500 mL of mixed solution, and stir with a magnetic stirrer to obtain the first concentration of acetone solution of 1024 mg / L, which is marked as oil sample No. Ⅰ.

[0077] C2. Mix 250 mL of oil sample I with 250 mL of transformer oil and stir with a magnetic stirrer to obtain oil sample II with a concentration of 512 mg / L.

[0078] C3. Take 250mL of No. Ⅱ oil sample and mix it with 250mL of transformer oil, and stir it with a magnetic stirrer to obtain No. Ⅲ oil sample with a concentration of 256mg / L;

[0079] C4. Take 250mL of No. III oil sample and mix it with 250mL of transformer oil, and stir it with a magnetic stirrer to obtain No. IV oil sample with a concentration of 128mg / L;

[0080] C5. Take 250 mL of No. IV oil sample and mix it with 250 mL of transformer oil, and stir it with a magnetic stirrer to obtain No. V oil sample with a concentration of 64 mg / L;

[0081] C6. Take 250mL of transformer oil as the No. VI oil sample with a concentration of 0mg / L.

[0082] Step 2: Place gradient solutions of acetone of different concentrations into quartz cuvettes respectively, immerse the silver nano rectangular sheet surface enhancement material into the solution, and store it away from light; specifically, immerse the substrate in each oil sample:

[0083] The oil samples Ⅰ to Ⅵ were placed in quartz cuvettes respectively, and then six prepared nano-scale silver nano-rectangular sheet surface enhancement substrates were immersed in the oil samples Ⅰ to Ⅵ respectively, and stored in the dark;

[0084] Step 3: Collect the Raman spectrum of the gradient solution and pre-process the Raman spectrum; specifically, measure the Raman spectrum of the oil sample.

[0085] After immersion for 12 hours, the quartz cuvette was placed on the stage of the confocal Raman detection platform, and a 560nm wavelength laser, a laser power of 100mW, an integration time of 1s, an integration number of 15, a slit width of 100μm, and a 1800 / 500nm grating were selected. The laser focus was focused on the oil sample and the surface of the silver nano-rectangular sheet surface enhancement substrate, respectively, and the Raman spectrum of the gradient solution was collected.

[0086] Preprocessing of Raman spectra

[0087] The Raman spectrum data of oil samples Ⅰ to VI obtained by measurement were preprocessed by removing impurities, adjusting baselines and smoothing denoising to eliminate interference from cosmic rays, fluorescence background and instrument noise; the Raman spectrum peak of transformer oil at 1340cm-1 was selected as the internal standard for intensity normalization to correct the peak intensity fluctuation caused by power fluctuation, optical path adjustment and focusing difference.

[0088] Select the Raman characteristic peak of acetone in the solution

[0089] Figure 4 The Raman spectra of transformer oil, acetone and transformer oil acetone mixed solution are shown in Figure 2. By comparing the Raman spectra of transformer oil, acetone and acetone dissolved in transformer oil, it is found that the Raman spectra of acetone dissolved in transformer oil are at 2925cm -1 The Raman signal at 2925 cm is significantly enhanced, which is due to the superposition of the Raman signals of acetone molecules. -1 As the Raman characteristic peak of acetone molecule.

[0090] Step 4, quantitative detection: The characteristic peak of acetone and the internal standard peak area of ​​transformer oil are calculated by using Gaussian function. Those skilled in the art can select drawing software according to experimental requirements. In this embodiment, the Gaussian peak in the origin software is used to calculate the characteristic peak of acetone and the internal standard peak area of ​​transformer oil of oil samples No. Ⅰ to Ⅵ, and the relative Raman intensity of acetone is calculated = characteristic peak area of ​​acetone / internal standard peak area of ​​transformer oil. The content of dissolved acetone in the oil is taken as the independent variable, and the ratio of characteristic peak area of ​​acetone / internal standard Raman peak area of ​​transformer oil is taken as the dependent variable. The quantitative calibration curve of acetone concentration in transformer oil is obtained by least square method, y=15.33491x+167.64513, wherein y represents the ratio of Raman peak area, and x represents acetone concentration, such as Figure 7 As shown in the figure, it can be seen that there is a good linear relationship between the two within the measured concentration range (0 mg / L-1024 mg / L), and the fitting degree is R 2 =0.9882.

[0091] The present application verifies that the surface enhancement substrate provided by the present application can obtain a significant enhancement effect by calculating the enhancement factor. Specifically, according to the Raman characteristic peak of acetone selected in Example 2, the 2925cm-1 peak without and with the substrate is calculated. -1 The Raman peak area of ​​acetone at , calculate the enhancement factor:

[0092]

[0093] In the formula,

[0094] I SERS Represents the effective intensity of the characteristic peak in the SERS spectrum of the sample to be tested;

[0095] I NR is the effective intensity of the Raman peak corresponding to the SERS characteristic peak in the ordinary Raman spectrum of the sample to be tested;

[0096] C SERS is the concentration of the sample to be tested for surface enhanced Raman detection;

[0097] C NR is the concentration of the sample to be tested in ordinary Raman detection.

[0098] Raman analysis of acetone dissolved in transformer oil without surface enhancement substrate at 2925 cm -1 The Raman peak of acetone appears near the surface. In this paper, the enhancement factor is calculated, and the effective intensity of the spectrum peak is expressed as the Lorentz fitting area. Under the same test conditions, when no surface enhancement substrate is used, the Raman peak of 1024 mg / L acetone transformer oil solution at 2925 cm -1 The effective intensity at 2925 cm is about 566.24 au, and the SERS spectrum of 64 mg / L acetone transformer oil solution is 2925 cm -1 The effective intensity at is about 43576.44 au. According to the above formula, the enhancement factor of the silver nano-surface enhanced substrate is about 1231.3. It can be seen that the silver nano-rectangular sheet surface enhanced substrate has a significant enhancement effect in measuring acetone in transformer oil, and this surface enhanced substrate can be used in the detection of aging characteristics of transformer oil.

[0099] The beneficial effect of the present invention is that, compared with the prior art, the surface enhancement effect of the prepared rectangular silver nanosheets is good, and the detection limit of the present invention for rhodamine 6g is 10 -11 M, and the detection effect is uniform and stable. The preparation method is simple, no complicated operation is required, the production cost is low, and the process does not produce harmful and polluting gases. It is a simple, low-cost, green, environmentally friendly, stable and efficient surface enhancement substrate.

[0100] The beneficial effects of the present invention also include:

[0101] (1) This patent uses rectangular silver nanosheets as a surface enhancement substrate to detect acetone in transformer oil in situ. The characteristic peak of the Raman intensity of acetone is obtained by the internal standard method, and the enhancement effect of the surface enhancement substrate is analyzed over time. The stability of the surface enhancement substrate is determined, and the relationship between the relative area of ​​the characteristic peak of acetone and acetone solutions of different concentrations is measured. A quantitative analysis model of acetone concentration in transformer oil is established based on the least squares method, which can be used for quantitative detection of acetone concentration in transformer oil. This patent uses laser as a detection method, and can achieve in-situ detection of dissolved acetone in transformer oil without complex pretreatment.

[0102] (2) This patent applies surface enhanced Raman spectroscopy technology. The rectangular silver nanosheet surface enhancement substrate has a significant enhancement effect on acetone in transformer oil, which provides technical support for the use of surface enhanced substrates for Raman spectroscopy detection in transformer oil in the future and can be widely used in the fields of energy and electricity.

[0103] The applicant of the present invention has made a detailed explanation and description of the implementation examples of the present invention in conjunction with the drawings in the specification. However, those skilled in the art should understand that the above implementation examples are only preferred implementation schemes of the present invention, and the detailed description is only to help readers better understand the spirit of the present invention, but not to limit the scope of protection of the present invention. On the contrary, any improvements or modifications based on the inventive spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing silver nano rectangular flakes, characterized in that: The following steps are involved: Step 1, synthesizing a silver nano rectangular flake sol solution: placing a 0.05 mol / L AgNO3 solution and a 10 mmol / L sodium citrate on a magnetic stirrer for stirring, and adding 2 mmol / L PVP and 30% hydrogen peroxide in sequence during the stirring process, and stirring for ten minutes; adding a 10 mmol / L sodium borohydride solution to the mixed solution to obtain a silver seed solution, and continuously stirring for 30 minutes under the irradiation of a sodium lamp to obtain a silver nano rectangular flake sol solution; wherein the volume ratio of the AgNO3 solution, sodium citrate, PVP, 30% hydrogen peroxide and sodium borohydride solution is 2500:1000:225:3:50; The silver nano rectangular sheet is a rectangle with a length of 1um to 5um and a width of 1um to 10um, made of silver, and deposited on the silicon wafer with a thickness of 1mm; the stirring speed is 800r / min; the power of the sodium lamp is 250W; Step 2, preparing rectangular silver nanosheets using the silver nano rectangular sheet sol solution obtained in step 1; S201, centrifuging the silver nano rectangular flake sol solution obtained in step 1 to obtain a precipitate using a centrifuge, and washing the precipitate with ultrapure water; S202, centrifuging the product obtained by washing the precipitate with ultrapure water again using a centrifuge, and washing the precipitate obtained by centrifugation again using ethanol; S203, repeating S201 and S202 three times to obtain rectangular silver nanosheets; Step 3, preparing silicon-based silver nano rectangular flakes: dissolving the rectangular silver nano flakes in an ethanol solution to obtain a colloidal solution of the silver nano rectangular flakes, and spin-coating the colloidal solution of the silver nano rectangular flakes on a silicon wafer, and allowing it to evaporate to a solid state; the concentration of the ethanol solution is 95%-99.5%.

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