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

Abstract

The invention relates to a preparation method and application of an Ag-coated BiOI nanosheet array composite SERS (Surface Enhanced Raman Scattering) substrate. The preparation method comprises the following steps: preparing a bismuth oxyiodide (BiOI) nanosheet array through electro-deposition, sputtering silver nanoparticles to the surface of BiOI nanosheets to obtain an Ag-coated BiOI nanosheet composite array, and irradiating the Ag-coated BiOI nanosheet composite array by a xenon lamp to enhance SERS signals. During preparation, firstly, a large-area uniform BiOI nanosheet array is obtained on the surface of pretreated FTO conductive glass through an electro-deposition method, then silver nanoparticles are sputtered on the surfaces of BiOI nanosheets to obtain an Ag-coated BiOI nanosheet array composite substrate, and then the composite SERS substrate is soaked in a detection solution to adsorb detection molecules. Finally, the soaked Ag-coated BiOI nanosheet composite substrate is placed under a xenon lamp to be irradiated for a certain time, and then Raman detection is conducted. The adsorption capacity of the Ag-coated BiOI nanosheet composite substrate on target detection molecules can be remarkably improved through irradiation of a xenon lamp, so that SERS signals are improved, and the detection sensitivity is improved; the Ag-coated BiOI nanosheet composite substrate based on xenon lamp irradiation shows good SERS sensitivity, and can be used as a substrate to realize low-concentration detection of common harmful substances such as rhodamine 6G (R6G), crystal violet (CV) and pesticide residue glyphosate in food.

Description

Technical Field

[0001] The invention belongs to the field of analytical technology, and in particular relates to a preparation method of a Ag@BiOI nanosheet array composite SERS substrate and application thereof. Background Art

[0002] At present, the commonly used food safety detection methods mainly include chromatography / mass spectrometry, high performance liquid chromatography, gas chromatography, spectral analysis, etc. Among them, spectral analysis refers to an analytical method that uses the experimental methods and principles of spectroscopy to determine the chemical composition and structure of a substance. Spectroscopic analysis is a non-destructive detection method with the characteristics of short detection time, high precision, and low cost, and has become one of the main development directions in the field of food safety detection. Among them, surface enhanced Raman scattering (SERS) spectroscopy has been proven to be an important means for trace detection of harmful substances in food due to its many advantages such as high sensitivity, no need for sample pretreatment, rapid response, and fingerprint recognition characteristics. A large number of studies have shown that the key to obtaining high-quality SERS signals and thus realizing food safety detection is to select and prepare high-quality SERS active substrates. High-quality SERS substrates can not only have high SERS activity, but also have good stability and repeatability of SERS signals, thereby improving the potential of SERS substrates in practical applications. Therefore, the preparation of SERS substrates with high activity, good stability, and low cost has important practical significance in the field of food safety detection.

[0003] Both noble metal nanoparticle substrates and semiconductor substrates are traditional SERS substrates, each with its own advantages. The main mechanism by which metal nanoparticle substrates can effectively enhance Raman signals lies in their special nanostructures, such as the localized surface plasmon resonance effect of noble metals such as Au, Ag, and Cu. Semiconductor substrates are mainly chemical enhancements caused by a near-resonance effect of carrier transfer between probe molecules and substrates. In recent decades, researchers have gradually focused on the combination of noble metal nanoparticles and semiconductors. Noble metal / semiconductor composite substrates not only have physical enhancement effects, but also chemical enhancement effects, which makes the composite substrates have high SERS activity, becoming a hot topic in SERS substrate research and is widely used in the field of food safety trace analysis and detection. Yang et al. reported a silver-modified Cu2O nanoframe material as a SERS substrate. The results showed that the composite substrate had good signal uniformity and the enhancement factor could reach 10 5(Crystengcomm, 2014, 16(11): 2298-2304), but the SERS activity of the Cu2O@Ag substrate is relatively low and the sensitivity is not high. Chen et al. used Au@SiO2 substrate combined with markers to establish a SERS-based lateral flow immunoassay, and measured the detection limit of aflatoxin to be 0.24pg / mL and the detection limit of ochratoxin to be 0.37pg / mL, which is far lower than the detection limit stipulated by the EU, indicating that the substrate has high sensitivity (Talanta, 2023, 258: 124401), but the detection method based on markers and lateral flow immunoassay is relatively cumbersome, which limits its large-scale promotion. Zeng et al. prepared an Ag-NPs@ZnO nanotower array substrate, and used the special structure of the tower layer to generate more hotspots between the Ag-NPs modified in the same tower layer and the adjacent tower layer, and the detection limit of R6G was as low as 1×10 -18 M (Applied Surface Science, 2021, 544: 148924). Although the Ag-NPs@ZnO nanotower array has good SERS activity, the ZnO nanotower structure has poor order, resulting in signal differences between different batches of substrates. Chen et al. prepared Ag-NPs@reduced graphene oxide / MoS2 substrate, which has an enhancement factor of about 8.6×10 6 , and has excellent photocatalytic efficiency, which can realize the recyclability of SERS substrates (Sensors and Actuators B: Chemical, 2021, 339: 129856), but the preparation process of Ag-NPs@reduced graphene oxide / MoS2 substrate is relatively complicated, and it is difficult to ensure structural uniformity. Therefore, it is of great significance to develop a mature, stable, fast and simple method for preparing a morphology-controllable and uniform noble metal / semiconductor composite SERS substrate. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a method for preparing a Ag@BiOI nanosheet array composite SERS substrate and its application, so as to achieve the invention purpose of preparing a metal / semiconductor composite SERS substrate that is fast, simple, morphology controllable and uniform.

[0005] To solve the above technical problems, one of the purposes of the present invention is to provide a method for preparing a metal / semiconductor composite SERS substrate, characterized in that the preparation method comprises pretreatment of FTO conductive glass, preparation of BiOI nanosheet arrays by electrodeposition, and sputtering of silver nanoparticles;

[0006] The FTO conductive glass is pretreated by ultrasonically cleaning the FTO conductive glass with acetone, ethanol and deionized water, and then naturally drying it for use;

[0007] The electrodeposition method for preparing the BiOI nanosheet array comprises the following steps:

[0008] Step 1: prepare a mixed solution of potassium iodide and bismuth nitrate pentahydrate, weigh a certain amount of potassium iodide and bismuth nitrate pentahydrate powder, place them in deionized water and stir until they are completely dissolved, and adjust the pH value to 1.5-2;

[0009] Step 2: prepare a p-benzoquinone ethanol solution, add a certain amount of p-benzoquinone into ethanol, and stir until the p-benzoquinone is completely dissolved in the ethanol;

[0010] Step 3: preparing an electrodeposition solution, slowly dripping a p-benzoquinone ethanol solution into a mixed solution of potassium iodide and bismuth nitrate pentahydrate, wherein the mass ratio of the p-benzoquinone ethanol solution to the mixed solution of potassium iodide and bismuth nitrate pentahydrate is 4:1 to 3:1, and stirring for a period of time as an electrodeposition solution for standby use;

[0011] Step 4: Prepare a BiOI nanosheet array, use the FTO conductive glass as a working electrode, perform electrodeposition on the electrodeposition solution described in step 3, and control the electrodeposition time to obtain the BiOI nanosheet array on the surface of the FTO glass;

[0012] The sputtered silver nanoparticles are sputtered on the surface of the BiOI nanosheet array prepared by electrodeposition using an ion sputtering instrument, and the sputtering time is controlled to obtain the Ag@BiOI nanosheet array composite SERS substrate.

[0013] Preferably, in the mixed solution of potassium iodide and bismuth nitrate pentahydrate in step 1, the mass ratio of potassium iodide to bismuth nitrate pentahydrate is 4:1 to 3:1, and the mass fraction is 6% to 10%.

[0014] Preferably, in the p-benzoquinone ethanol solution in step 2, the mass fraction of p-benzoquinone is 3% to 6%.

[0015] Furthermore, the electrodeposition time in step 4 is 0.5 to 8 minutes.

[0016] Furthermore, the sputtering time is 1 to 12 minutes.

[0017] The second object of the present invention is to provide an application of the Ag@BiOI nanosheet array composite SERS substrate prepared by the above preparation method, characterized in that the application comprises the following steps:

[0018] Step 1: soaking the Ag@BiOI nanosheet array composite substrate in a solution containing the molecule to be tested, taking it out after soaking for 3 to 9 hours, rinsing it with deionized water and drying it naturally;

[0019] Step 2: After the Ag@BiOI nanosheet array composite substrate with the molecules to be tested adsorbed on the surface in step 1 is irradiated under a xenon lamp for 5 to 20 minutes, the Ag@BiOI nanosheet array composite substrate is placed under a Raman instrument for detection.

[0020] Furthermore, the solution of the molecule to be tested is rhodamine 6G (R6G), crystal violet (CV), 4-mercaptothiophenol (4-ATP), and a solution of the pesticide residue glyphosate.

[0021] Furthermore, the Raman instrument adopts a laser Raman spectrometer with an excitation wavelength of 532nm, a laser power of 1%, and an excitation time of 1 to 10s.

[0022] Due to the adoption of the above technical solution, the technical effects achieved by the present invention are:

[0023] 1. A method for preparing a composite substrate of Ag@BiOI nanosheet array provided by the present invention is used to achieve the invention purpose of a composite SERS substrate of semiconductor / silver with controllable morphology and uniformity. The method is simple to operate and low in cost. A large-area, uniform BiOI nanosheet array is obtained by electrodeposition, and a large-area, uniformly distributed, and uniformly morphological Ag@BiOI nanosheet array is further quickly obtained by silver ion sputtering. The ordered Ag@BiOI nanosheet array prepared by this method not only combines the high SERS activity of silver nanoparticles, but also the large-area ordered semiconductor BiOI nanosheets can load more silver nanoparticles, further improving the SERS activity and ensuring the good SERS signal uniformity and repeatability of the substrate.

[0024] 2. Soak the Ag@BiOI nanosheet array in a solution containing the molecules to be tested for 3-9 hours and then irradiate it under a xenon lamp. Since the Ag@BiOI nanosheet has excellent visible light absorption performance and produces more electron-hole pairs, the adsorption amount of the Ag@BiOI nanosheet on the molecules to be tested can be increased under the irradiation of the xenon lamp, thereby increasing the Raman signal of the molecules to be tested, and further improving the detection sensitivity of the molecules to be tested.

[0025] 3. The ordered Ag@BiOI nanosheet array composite substrate prepared by this method has potential application prospects in the fields of chemical analysis, pollutant detection, biosensors, etc. based on SERS technology. Using it as a SERS substrate, rapid detection and identification of rhodamine 6G (R6G), crystal violet (CV), and pesticide residue glyphosate are achieved. It has important development significance in realizing rapid detection of common harmful substances in food through the SERS effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1Schematic diagram of the preparation process of Ag@BiOI nanosheet arrays;

[0027] Figure 2 Scanning electron microscope (SEM) images of BiOI nanosheet arrays obtained at different electrodeposition times: (ac) 0.5 min, (df) 1 min, (gi) 2 min, (ji) 4 min, and (mo) 8 min.

[0028] Figure 3 SEM images of Ag@BiOI nanosheet arrays obtained at different Ag sputtering times: (ac) 1 min, (df) 2 min, (gi) 4 min, (jl) 8 min, (mo) 12 min

[0029] Figure 4 Transmission electron microscopy (TEM) images of different products: (a, b) BiOI nanosheets; (c, d) Ag@BiOI nanosheets.

[0030] Figure 5 XRD patterns of FTO conductive glass, BiOI nanosheets, and Ag@BiOI nanosheet arrays

[0031] Figure 6 EDS spectra of BiOI nanosheets and Ag@BiOI nanosheet arrays

[0032] Figure 7 UV-vis spectra of BiOI nanosheets and Ag@BiOI nanosheet arrays obtained under different silver sputtering times

[0033] Figure 8 Comparison pictures of the SERS activity of the composite substrates obtained after BiOI nanosheets were electro-deposited for different times and sputtered with silver for the same time.

[0034] Fig. 9 Comparison images of SERS activity of Ag@BiOI nanosheet composite substrates obtained at different silver sputtering times.

[0035] Fig.10 The effect of different xenon lamp irradiation time on R6G SERS signal

[0036] Fig.11 The effect of different xenon lamp irradiation time on CV SERS signal

[0037] Fig.12 The effect of different xenon lamp irradiation time on 4-ATP SERS signal

[0038] Fig.13 SERS spectra of different concentrations of R6G adsorbed on Ag@BiOI nanosheet substrates

[0039] Fig.14 SERS spectra obtained by adsorbing different concentrations of CV on Ag@BiOI nanosheet substrates

[0040] Fig.15 SERS spectra of glyphosate at different concentrations adsorbed on Ag@BiOI nanosheet substrates

[0041] Fig.16 (a) SERS spectra of R6G obtained at 35 randomly selected points on the Ag@BiOI nanosheet substrate; (b) 35 Raman spectra obtained at 612 cm -1 The intensity of the characteristic peak at DETAILED DESCRIPTION

[0042] The following is a detailed description of the embodiments and the attached Figure 1-16 , further illustrating the present invention.

[0043] Example 1 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0044] S1. Cut the FTO conductive glass into several 2cm×2cm small pieces. Ultrasonic clean the cut FTO conductive glass with acetone, ethanol and deionized water for 10-30 minutes each and dry it naturally. Then weigh 3g potassium iodide (KI) and 1g bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and place them in 50mL of deionized water and stir until completely dissolved, and adjust the pH value to 1.5-2. Then dissolve 0.5g of p-benzoquinone in 20mL of ethanol and stir until completely dissolved, then slowly drip the p-benzoquinone ethanol solution into the above-mentioned mixed solution of potassium iodide and bismuth nitrate pentahydrate, stir for a period of time, and obtain a uniform mixed solution.

[0045] S2. The FTO conductive glass obtained by rinsing with deionized water and drying is used as the working electrode, the foil is used as the counter electrode, and the saturated Ag / AgCl is used as the reference electrode. Electrodeposition is performed in the above mixed solution using an electrochemical workstation, and the deposition voltage is -0.1 V. By controlling the electrodeposition time for 1 minute, the BiOI nanosheet array structure is finally obtained.

[0046] S3. Place the prepared BiOI nanosheets on the sputtering instrument to sputter silver nanoparticles. The sample is placed directly below the silver target at a distance of about 2 cm. The sputtering current is set to 40 mA / cm 2 , control the silver sputtering time to 1 minute.

[0047] S4. Cut 6 small pieces of sample from the prepared sample base and place them in a centrifuge tube, then soak them for 10 -7MR6G solution, placed in a dark place for 6 hours, take out the sample and dry it naturally. Place the dried substrate under a xenon lamp and perform Raman detection after 5 minutes of illumination. The excitation wavelength of the laser Raman spectrometer is 532nm, the power is 1%, and the excitation time is 2 seconds.

[0048] Example 2 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0049] The difference between this embodiment and embodiment 1 is that the electrodeposition time in step S2 is 0.5 minutes.

[0050] Example 3 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0051] The difference between this embodiment and embodiment 1 is that the electrodeposition time in step S2 is 2 minutes.

[0052] Example 4 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0053] The difference between this embodiment and embodiment 1 is that the electrodeposition time in step S2 is 4 minutes.

[0054] Example 5 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0055] The difference between this embodiment and embodiment 1 is that the electrodeposition time in step S2 is 8 minutes.

[0056] Example 6 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0057] The difference between this embodiment and embodiment 1 is that the silver sputtering time in step S3 is 2 minutes.

[0058] Example 7 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0059] The difference between this embodiment and embodiment 1 is that the silver sputtering time in step S3 is 4 minutes.

[0060] Example 8 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0061] The difference between this embodiment and embodiment 1 is that the silver sputtering time in step S3 is 8 minutes.

[0062] Example 9 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0063] The difference between this embodiment and embodiment 1 is that the silver sputtering time in step S3 is 12 minutes.

[0064] Example 10 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0065] The difference between this embodiment and embodiment 1 is that the xenon lamp irradiation time in step S4 is 10 minutes.

[0066] Example 11 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0067] S1. Cut the FTO conductive glass into several 2cm×2cm small pieces. Ultrasonic clean the cut FTO conductive glass with acetone, ethanol and deionized water for 10-30 minutes each and dry it naturally. Then weigh 3g potassium iodide (KI) and 1g bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and place them in 50mL of deionized water and stir until completely dissolved, and adjust the pH value to 1.5-2. Then dissolve 0.5g of p-benzoquinone in 20mL of ethanol and stir until completely dissolved, then slowly drip the p-benzoquinone ethanol solution into the above-mentioned mixed solution of potassium iodide and bismuth nitrate pentahydrate, stir for a period of time, and obtain a uniform mixed solution.

[0068] S2. The FTO conductive glass rinsed and dried with deionized water was used as the working electrode, the foil was used as the counter electrode, and the saturated Ag / AgCl was used as the reference electrode. Electrodeposition was performed in the above mixed solution using an electrochemical workstation, and the deposition voltage was -0.1 V. By controlling the electrodeposition time for 1 minute, a BiOI nanosheet array structure was finally obtained.

[0069] S3. Place the prepared BiOI nanosheets on the sputtering instrument to sputter silver nanoparticles. The sample is placed directly below the silver target at a distance of about 2 cm. The sputtering current is set to 40 mA / cm 2 , control the silver sputtering time to 4 minutes.

[0070] S4. Cut 6 small pieces of sample from the prepared sample base and place them in a centrifuge tube, then soak them for 10 -7 M CV solution, placed in a dark place for 6 hours, take out the sample and dry it naturally. The dried substrate is placed under a xenon lamp and illuminated for 10 minutes before Raman detection. The excitation wavelength of the laser Raman spectrometer is 532nm, the power is 1%, and the excitation time is 2 seconds.

[0071] Example 12 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0072] The difference between this embodiment and embodiment 11 is that the xenon lamp irradiation time in step S4 is 20 minutes.

[0073] Example 13 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0074] S1. Cut the FTO conductive glass into several 2cm×2cm small pieces. Ultrasonic clean the cut FTO conductive glass with acetone, ethanol and deionized water for 10-30 minutes each and dry it naturally. Then weigh 3g potassium iodide (KI) and 1g bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and place them in 50mL of deionized water and stir until completely dissolved, and adjust the pH value to 1.5-2. Then dissolve 0.5g of p-benzoquinone in 20mL of ethanol and stir until completely dissolved, then slowly drip the p-benzoquinone ethanol solution into the above-mentioned mixed solution of potassium iodide and bismuth nitrate pentahydrate, stir for a period of time, and obtain a uniform mixed solution.

[0075] S2. The FTO conductive glass rinsed and dried with deionized water was used as the working electrode, the foil was used as the counter electrode, and the saturated Ag / AgCl was used as the reference electrode. Electrodeposition was performed in the above mixed solution using an electrochemical workstation, and the deposition voltage was -0.1 V. By controlling the electrodeposition time for 1 minute, a BiOI nanosheet array structure was finally obtained.

[0076] S3. Place the prepared BiOI nanosheets on the sputtering instrument to sputter silver nanoparticles. The sample is placed directly below the silver target at a distance of about 2 cm. The sputtering current is set to 40 mA / cm 2 , control the silver sputtering time to 4 minutes.

[0077] S4. Cut 6 small pieces of sample from the prepared sample base and place them in a centrifuge tube, then soak them for 10 -7 M 4-ATP solution, placed in a dark place for 6 hours, take out the sample and dry it naturally. Place the dried substrate under a xenon lamp and perform Raman detection after 5 minutes of illumination. The excitation wavelength of the laser Raman spectrometer is 532nm, the power is 1%, and the excitation time is 2 seconds.

[0078] Example 14 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0079] The difference between this embodiment and embodiment 13 is that the xenon lamp irradiation time in step S4 is 10 minutes.

[0080] Example 15 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0081] The difference between this embodiment and embodiment 13 is that the xenon lamp irradiation time in step S4 is 20 minutes.

[0082] Example 16 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0083] S1. Cut the FTO conductive glass into several 2cm×2cm small pieces. Ultrasonic clean the cut FTO conductive glass with acetone, ethanol and deionized water for 10-30 minutes each and then dry naturally. Then weigh 3g potassium iodide (KI) and 1g bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and place them in 50mL of deionized water and stir until completely dissolved, and adjust the pH value to 1.5-2. Then dissolve 0.5g of p-benzoquinone in 20mL of ethanol and stir until completely dissolved, then slowly drip the p-benzoquinone ethanol solution into the above-mentioned mixed solution of potassium iodide and bismuth nitrate pentahydrate, stir for a period of time, and obtain a uniform mixed solution.

[0084] S2. The FTO conductive glass rinsed and dried with deionized water was used as the working electrode, the foil was used as the counter electrode, and the saturated Ag / AgCl was used as the reference electrode. Electrodeposition was performed in the above mixed solution using an electrochemical workstation, and the deposition voltage was -0.1 V. By controlling the electrodeposition time for 1 minute, a BiOI nanosheet array structure was finally obtained.

[0085] S3. Place the prepared BiOI nanosheets on the sputtering instrument to sputter silver nanoparticles. The sample is placed directly below the silver target at a distance of about 2 cm. The sputtering current is set to 40 mA / cm 2 , control the silver sputtering time to 4 minutes.

[0086] S4. Cut 6 small pieces of sample from the prepared sample base and place them in a centrifuge tube, then soak them for 10 -6 -10 -11 MR6G solution was placed in a dark place for 6 hours, and the sample was taken out and dried naturally. The dried substrate was placed under a xenon lamp and subjected to Raman detection after 10 minutes of illumination. The excitation wavelength of the laser Raman spectrometer was 532 nm, the power was 1%, and the excitation time was 2 seconds.

[0087] Example 17 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0088] S1. Cut the FTO conductive glass into several 2cm×2cm small pieces. Ultrasonic clean the cut FTO conductive glass with acetone, ethanol and deionized water for 10-30 minutes each and then dry naturally. Then weigh 3g potassium iodide (KI) and 1g bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and place them in 50mL of deionized water and stir until completely dissolved, and adjust the pH value to 1.5-2. Then dissolve 0.5g of p-benzoquinone in 20mL of ethanol and stir until completely dissolved, then slowly drip the p-benzoquinone ethanol solution into the above-mentioned mixed solution of potassium iodide and bismuth nitrate pentahydrate, stir for a period of time, and obtain a uniform mixed solution.

[0089] S2. The FTO conductive glass rinsed and dried with deionized water was used as the working electrode, the foil was used as the counter electrode, and the saturated Ag / AgCl was used as the reference electrode. Electrodeposition was performed in the above mixed solution using an electrochemical workstation, and the deposition voltage was -0.1 V. By controlling the electrodeposition time for 1 minute, a BiOI nanosheet array structure was finally obtained.

[0090] S3. Place the prepared BiOI nanosheets on the sputtering instrument to sputter silver nanoparticles. The sample is placed directly below the silver target at a distance of about 2 cm. The sputtering current is set to 40 mA / cm 2 , control the silver sputtering time to 4 minutes.

[0091] S4. Cut 6 small pieces of sample from the prepared sample base and place them in a centrifuge tube, then soak them for 10 -6 -10 -10 MCV solution, placed in a dark place for 6 hours, take out the sample and dry it naturally. Place the dried substrate under a xenon lamp and perform Raman detection after 10 minutes of illumination. The excitation wavelength of the laser Raman spectrometer is 532nm, the power is 1%, and the excitation time is 2 seconds.

[0092] Example 18 Preparation method and application of a Ag@BiOI nanosheet array composite SERS substrate

[0093] S1. Cut the FTO conductive glass into several 2cm×2cm small pieces. Ultrasonic clean the cut FTO conductive glass with acetone, ethanol and deionized water for 10-30 minutes each and then dry naturally. Then weigh 3g potassium iodide (KI) and 1g bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and place them in 50mL of deionized water and stir until completely dissolved, and adjust the pH value to 1.5-2. Then dissolve 0.5g of p-benzoquinone in 20mL of ethanol and stir until completely dissolved, then slowly drip the p-benzoquinone ethanol solution into the above-mentioned mixed solution of potassium iodide and bismuth nitrate pentahydrate, stir for a period of time, and obtain a uniform mixed solution.

[0094] S2. The FTO conductive glass rinsed and dried with deionized water was used as the working electrode, the foil was used as the counter electrode, and the saturated Ag / AgCl was used as the reference electrode. Electrodeposition was performed in the above mixed solution using an electrochemical workstation, and the deposition voltage was -0.1 V. By controlling the electrodeposition time for 1 minute, a BiOI nanosheet array structure was finally obtained.

[0095] S3. Place the prepared BiOI nanosheets on the sputtering instrument to sputter silver nanoparticles. The sample is placed directly below the silver target at a distance of about 2 cm. The sputtering current is set to 40 mA / cm 2 , control the silver sputtering time to 4 minutes.

[0096] S4. Cut 6 small pieces of sample from the prepared sample base and place them in a centrifuge tube, then soak them for 10 -4 -10 -8 M glyphosate solution, placed in a dark place for 6 hours, and then taken out and dried naturally. The dried substrate was placed under a xenon lamp and subjected to Raman detection after 10 minutes of illumination. The excitation wavelength of the laser Raman spectrometer was 532nm, the power was 1%, and the excitation time was 2 seconds.

[0097] The electrodeposition time of the bismuth iodide nanosheets in step S2 in Examples 1-5 is different. Controlling the electrodeposition time will affect the morphology and SERS performance of the bismuth iodide nanosheets. Figure 2 The SEM images of BiOI nanosheet arrays obtained by electroplating for 0.5-8 minutes. Figure 2 ac), it can be seen from the figure that the BiOI nanosheets are relatively sparsely dispersed on the surface of FTO conductive glass, the thickness of the nanosheets is thin, the size of a single nanosheet is about 350nm, and the thickness is about 20nm. When the electrodeposition time is extended to 1 minute ( Figure 2 df), the length of the nanosheet is about 500nm, the thickness is about 25nm, and the spacing between adjacent nanosheets gradually decreases. The shape of the nanosheet is relatively upright and no longer collapses. Further extending the electrodeposition time to 2 minutes ( Figure 2 gi), the number and density of nanosheets gradually increased, the nanosheets were interlaced, and the distance between adjacent nanosheets was further reduced. When the electrodeposition time was extended to 4 minutes ( Figure 2 jl), the number and size of nanosheets increased significantly, and the coverage of nanosheets on the glass surface increased significantly. Further extending the deposition time to 8 minutes ( Figure 2 When the nanosheet coverage is increased by 2.5 mo, the coverage of the nanosheets is further improved, and the high-magnification image shows that the distance between adjacent nanosheets increases ( Figure 2 o).

[0098] In Examples 6-9, the silver sputtering time in step S3 is different, and the other parameters remain unchanged. When BiOI nanosheets prepared by electrodeposition for 1 minute are selected, silver nanoparticles are further sputtered on the surface for different times. Figure 3 The morphology of the Ag@BiOI nanosheet arrays obtained under different silver sputtering times. When the silver sputtering time is short, i.e., 1 minute ( Figure 3 When the silver sputtering time was 2 min (40 s), almost no obvious silver nanoparticles were observed to adhere to the surface of the BiOI nanosheets. Although a small amount of silver nanoparticles could be seen deposited on the top or edge of the nanosheets, the silver nanoparticles were very sparsely distributed due to the short silver sputtering time, so the surface changes of the nanosheets were not very obvious. Figure 3 df), the surface of BiOI nanosheets becomes rough. Figure 3 f) It can be seen that a small amount of Ag-NPs are scattered on the surface of the nanosheets, and the size of the nanosheets and the number of nanoparticles gradually increase. As the Ag sputtering time increases to 4 min ( Figure 3 gi), it can be seen from the figure that the silver nanoparticles are more evenly covered on the surface of the BiOI nanosheets, the thickness of the nanosheets is significantly increased, and the surface of the nanosheets becomes rougher. When the silver sputtering time is extended to 8 minutes, the thickness of the nanosheets wrapped by the silver nanoparticles is further increased, and some silver nanoparticles are accumulated on the staggered edges of the nanosheets. When the silver sputtering time is extended to 12 minutes ( Figure 3 When the Ag-NPs are added at 200 μm, a large number of Ag nanoparticles accumulate on the surface of BiOI nanosheets to form a thick silver film, which significantly increases the thickness of the nanosheets and significantly reduces the spacing between the Ag-NPs between adjacent nanosheets.

[0099] The morphology of the prepared BiOI nanosheets and the BiOI nanosheet composite substrate with sputtered silver nanoparticles was analyzed by TEM ( Figure 4 ). Figure 4 ab show TEM images of BiOI nanosheets. From the high magnification images ( Figure 4 b) It can be observed that the surface of BiOI nanosheets is smooth and free of impurities, showing a typical sheet-like structure with a length of about 1-2 μm and a width of about 200 nm. Figure 4 cd are TEM images of Ag@BiOI nanosheets. In comparison, many clearly visible silver nanoparticles with a size of about 5-10 nm are attached to the surface of BiOI nanosheets.

[0100] Figure 5Figure 2 shows the XRD patterns of FTO conductive glass, BiOI nanosheet arrays, and Ag@BiOI nanosheet arrays. It can be observed that the diffraction peaks at 2θ angles of 27.4°, 34.65°, 38.67°, 52.43°, 62.385°, and 66.404° correspond to the (110), (101), (200), (211), (310), and (301) crystal planes of FTO, respectively. The diffraction peaks at 2θ angles of 25.61°, 31.1°, 33.04°, 46.88°, 56.89°, 75.13°, and 76.61° correspond to the (101), (110), (111), (201), (212), (310), and (107) crystal planes of BiOI. The diffraction peak at 2θ angle of 44.27° corresponds to the (200) crystal plane of Ag, indicating that BiOI nanosheets were generated on the surface of FTO conductive glass by electrodeposition. Figure 6 Figure 2 is the EDS spectrum of BiOI nanosheet array and Ag@BiOI nanosheet array. Figure 6 a It can be seen that the BiOI nanosheet structure is mainly composed of Bi, I, O and a small amount of C. Figure 6 The Ag@BiOI nanosheets in b are mainly composed of Ag, Bi, I, O and a small amount of C, indicating that the Ag@BiOI nanosheet array composite substrate was successfully prepared. The UV-vis test results show that with the extension of silver sputtering time, a plasmon resonance absorption peak appears at 200-310nm and 310-400nm, which is conducive to promoting electromagnetic field enhancement, thereby improving the SERS signal intensity ( Figure 7 ).

[0101] Keeping the silver sputtering time unchanged, the Ag@BiOI nanosheet array composite substrates obtained under different BiOI nanosheet electrodeposition time conditions all have SERS activity, but the SERS activity is different. Figure 8 It can be seen that with the increase of BiOI nanosheet electrodeposition time, the SERS signal shows a trend of increasing first and then decreasing. When the electrodeposition time is short (0.5-1 minute), the SERS activity of the substrate gradually increases. When the electrodeposition time continues to increase, the SERS signal shows a decreasing trend. This is mainly because in a short electrodeposition time, the specific surface area of ​​the nanosheet is small, the size of the nanosheet is small, and the spacing between the sheets is small. The mutual coupling between the silver nanoparticles produces more "hot spots", which increases the activity of the SERS substrate and promotes the significant enhancement of the SERS signal.

[0102] Keeping the BiOI nanosheet structure unchanged, the Ag@BiOI nanosheet array composite substrates obtained under different silver sputtering times also have SERS activity. Fig. 9The adsorption of 10 on the Ag@BiOI nanosheet array composite substrate prepared by silver sputtering for different time (1-12 minutes) -6 Raman spectrum obtained by MR6G. The results show that as the silver sputtering time increases, the SERS signal shows a trend of first increasing and then decreasing. When the silver sputtering time is short (1-2 minutes), the SERS activity is low and the SERS signal is low. When the silver sputtering time is further extended to 4 minutes, the coverage of silver nanoparticles on the nanosheet surface is improved, the SERS activity of the substrate is increased, and the SERS signal is enhanced. As the silver sputtering time increases (8-12 minutes), the SERS activity decreases.

[0103] The different xenon lamp irradiation times in step S4 in Examples 10-14 have a significant impact on the SERS signals of the molecules to be tested, R6G, CV, and 4-ATP. Fig.10 The composite substrate is immersed in 10 -7 After rinsing and drying the substrate in the M R6G solution, the composite SERS substrate was irradiated with a xenon lamp, and the effect of light on the performance of the SERS substrate was studied by the change in the SERS signal intensity. It can be seen from the figure that the peak intensity of the main characteristic peak of R6G increases with the increase of the xenon lamp irradiation time, and the SERS signal intensity shows a trend of gradual increase. When the light irradiation time is 5 minutes, the peak at 612cm -1 The signal intensity at 612cm -1 The signal intensity at the sample is 9.88 times that of the control sample.

[0104] Fig.11 The composite substrate is immersed in 10 -7 After rinsing and drying the substrate in M ​​CV solution, the composite SERS substrate was irradiated with a xenon lamp, and the effect of light on the performance of the SERS substrate was studied by the change in the SERS signal intensity. It can be seen from the figure that the peak intensity of the main characteristic peak of CV increases with the increase of irradiation time, and the SERS signal intensity also shows a trend of gradual increase. When the light irradiation time is 10 minutes, the peak intensity at 1620cm -1 The signal intensity at 1620cm -1 The signal intensity at the sample is 5.03 times that of the control sample.

[0105] Fig.12 The composite substrate is immersed in 10 -7After rinsing and drying the substrate in M ​​4-ATP solution, the composite SERS substrate was irradiated with a xenon lamp, and the effect of light on the performance of the SERS substrate was studied by the change in the SERS signal intensity. It can be seen from the figure that the peak intensity of the main characteristic peak of 4-ATP increases with the irradiation time, and the SERS signal intensity also shows a trend of gradual increase. When the light irradiation time is 5 minutes, the peak at 1440cm -1 The signal intensity at 1440cm -1 The signal intensity at 1440cm is 3.38 times that of the control sample. When the light irradiation time is 20 minutes, -1 The signal intensity at this point is 22.41 times that of the non-irradiated control sample.

[0106] Examples 15-17 are the low-concentration detection results of R6G, CV and pesticide residue glyphosate solution based on the prepared Ag@BiOI nanosheet array composite substrate. Fig.13 For different concentration gradients of R6G (10 -6 -10 -11 M) SERS spectra obtained by adsorption on the optimized substrate. When the concentration of R6G is as low as 10 -11 M, 612cm -1 Although the signal intensity of the main characteristic peak at is weak, the convex characteristic peak can still be seen, indicating that the prepared Ag@BiOI nanosheet array composite substrate has good SERS activity. -10 M, the main characteristic peaks of CV are still clearly observed, and a high-quality SERS signal is displayed ( Fig.14 ). This indicates that the prepared Ag@BiOI nanosheet array composite substrate still has good SERS activity when the concentrations of R6G and CV are very low. Fig.15 This is the low concentration test result of the pesticide residue glyphosate. When the concentration of glyphosate is diluted to 10 -8 M, the main characteristic peaks of glyphosate can still be identified in the Raman spectrum, indicating that the substrate has good sensitivity. The prepared Ag@BiOI nanosheet array composite substrate has potential application prospects in food safety detection fields such as pesticide residues.

[0107] Fig.16 a is a graph showing the random selection of 35 points on the Ag@BiOI nanosheet array composite substrate for testing the effect of concentration of 10 -6 SERS spectrum of M R6G solution; the results show that in the obtained Raman spectrum, the main characteristic peak of R6G at 612cm -1The signal intensity fluctuation at 612 cm-1 is small, indicating that the substrate has good uniformity and SERS signal reproducibility, which is mainly due to the uniform and orderly morphology of the prepared substrate. In addition, the relative standard deviation of the characteristic peak intensity at 612 cm-1 of the 35 Raman spectra was calculated to be 6.83% ( Fig.16 b), further verifying that the Ag@BiOI nanosheet array composite substrate has good SERS signal reproducibility. The Ag@BiOI nanosheet array composite substrate prepared in the embodiment was tested, and all showed good SERS activity and signal uniformity, and achieved the detection and identification of common harmful substances Rhodamine 6G (R6G), crystal violet (CV), 4-ATP and low concentration of glyphosate, proving its potential application value in detecting harmful substances in food.

[0108] Unless otherwise specified, the ratios and percentages described in the present invention are all weight ratios and weight percentages; and the raw materials are all commercially available.

[0109] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a Ag@BiOI nanosheet array composite SERS substrate, characterized in that: The preparation method comprises pretreatment of FTO conductive glass, preparation of BiOI nanosheet array by electrodeposition, and sputtering of silver nanoparticles to obtain a Ag@BiOI nanosheet array composite SERS substrate; The FTO conductive glass is pretreated by ultrasonically cleaning the FTO conductive glass with acetone, ethanol and deionized water, and then naturally drying it for use; The electrodeposition method for preparing the BiOI nanosheet array comprises the following steps: Step 1: prepare a mixed solution of potassium iodide and bismuth nitrate pentahydrate, weigh a certain amount of potassium iodide and bismuth nitrate pentahydrate powder, place them in deionized water and stir until they are completely dissolved, and adjust the pH value to 1.5-2; Step 2: prepare a p-benzoquinone ethanol solution, add a certain amount of p-benzoquinone into ethanol, and stir until the p-benzoquinone is completely dissolved in the ethanol; Step 3: preparing an electrodeposition solution, slowly dripping a p-benzoquinone ethanol solution into a mixed solution of potassium iodide and bismuth nitrate pentahydrate, wherein the mass ratio of the p-benzoquinone ethanol solution to the mixed solution of potassium iodide and bismuth nitrate pentahydrate is 4:1 to 3:1, and stirring for a period of time as an electrodeposition solution for standby use; Step 4: Prepare a BiOI nanosheet array, use the FTO conductive glass as a working electrode, perform electrodeposition on the electrodeposition solution described in step 3, and control the electrodeposition time to obtain the BiOI nanosheet array on the surface of the FTO glass; The sputtered silver nanoparticles are sputtered on the surface of the BiOI nanosheet array prepared by electrodeposition using an ion sputtering instrument, and the sputtering time is controlled to obtain the Ag@BiOI nanosheet array composite SERS substrate.

2. The method for preparing the Ag@BiOI nanosheet array composite SERS substrate according to claim 1, characterized in that: In the mixed solution of potassium iodide and bismuth nitrate pentahydrate in step 1, the mass ratio of potassium iodide to bismuth nitrate pentahydrate is 4:1 to 3:1, and the mass fraction is 6% to 10%.

3. The method for preparing the Ag@BiOI nanosheet array composite SERS substrate according to claim 1, characterized in that: In the 4-benzoquinone ethanol solution in step 2, the mass fraction of 4-benzoquinone is 3% to 6%.

4. The method for preparing the Ag@BiOI nanosheet array composite SERS substrate according to claim 1, characterized in that: The electrodeposition time in step 4 is 0.5 to 8 minutes.

5. The method for preparing the Ag@BiOI nanosheet array composite SERS substrate according to claim 1, characterized in that: The sputtering time is 1 to 12 minutes.

6. The use of the Ag@BiOI nanosheet array composite SERS substrate prepared by the preparation method of claim 1, characterized in that: The application comprises the following steps: Step 1: soaking the Ag@BiOI nanosheet array composite substrate in a solution containing the molecule to be tested, taking it out after soaking for 3 to 9 hours, rinsing it with deionized water and drying it naturally; Step 2: After the Ag@BiOI nanosheet array composite substrate with the molecules to be tested adsorbed on the surface in step 1 is irradiated under a xenon lamp for 5 to 20 minutes, the Ag@BiOI nanosheet array composite substrate is placed under a Raman instrument for detection.

7. The use of the Ag@BiOI nanosheet array composite SERS substrate according to claim 6, characterized in that: The solutions of the molecules to be tested are rhodamine 6G (R6G), crystal violet (CV), 4-mercaptothiophenol (4-ATP), and pesticide residue glyphosate solution.

8. The use of the Ag@BiOI nanosheet array composite SERS substrate according to claim 6, characterized in that: The Raman instrument adopts a laser Raman spectrometer with an excitation wavelength of 532nm, a laser power of 1%, and an excitation time of 1-10s.

Images