Preparation method of perfluorinated and polyfluoroalkyl organic pollutant sensitive SERS (Surface Enhanced Raman Scattering) substrate

Abstract

The invention provides a preparation method of a perfluorinated and polyfluoroalkyl organic pollutant sensitive SERS (Surface Enhanced Raman Scattering) substrate. The method comprises the following steps: respectively carrying out ultrasonic treatment on tetrafluoroterephthalic acid and zirconium nitrate pentahydrate in a water / acetic acid mixed solution, and heating and refluxing in a distillation flask to obtain UiO-66-F4; then, chloroauric acid and sodium citrate are subjected to a reduction reaction to obtain a gold nanoparticle solution, and polyvinylpyrrolidone (PVP) is used for modifying the gold nanoparticle solution; the preparation method comprises the following steps: preparing a UiO-66-F4 aqueous solution, dropwise adding a PVP-modified gold nanoparticle solution into the UiO-66-F4 aqueous solution, fully stirring, dropwise coating the UiO-66-F4 aqueous solution on a silicon wafer, and naturally airing to finally obtain the UiO-66-F4-coated Au SERS substrate. The gold nanoparticles of the substrate are uniformly distributed, the substrate has a relatively strong SERS (Surface Enhanced Raman Scattering) effect, meanwhile, the MOF (Metal Organic Framework) crystallization effect of the substrate is relatively good, the sensitivity is high, the substrate has relatively strong enrichment capacity on perfluoro and polyfluoroalkyl organic pollutants, and the substrate can be used for rapid low-cost detection of perfluoro and polyfluoroalkyl organic pollutants in water.

Description

Technical Field

[0001] The invention relates to a method for preparing a SERS substrate sensitive to perfluoro and polyfluoroalkyl organic pollutants, and belongs to the technical field of SERS. Background Art

[0002] Perfluorinated and polyfluoroalkyl (PFAS) organic pollutants are an emerging class of organic pollutants with strong heat and acid resistance, and are therefore widely used in textiles, firefighting foams, floor oils and other fields. Studies have shown that the presence of PFAS in nature can induce oxidative stress and apoptosis in earthworms, leading to developmental and reproductive toxicity, and can also have negative effects on multiple organs and systems in the human body, including the liver, spleen and nervous system. For the detection of PFAS, the most commonly used method is liquid chromatography / tandem mass spectrometry (LC-MS), which usually uses solid phase extraction (SPE) to concentrate the sample, and then uses liquid chromatography / tandem mass spectrometry to quantitatively analyze the sample. This method has high accuracy in detecting PFAS, but the analysis method is extremely expensive, complicated to operate and takes several hours. For example, the patent number is 202510356574.0, and the patent name is "A pretreatment method for determining perfluorinated and polyfluorinated alkyl compounds in edible oils". It specifically proposes a pretreatment method for perfluorinated and polyfluorinated alkyl compounds, and performs subsequent concentration determination by LC-MS. The detection process includes extraction, enrichment, liquid elution separation, ionization and mass spectrometry analysis, etc. It also requires expensive isotope standards, the steps are complicated, and the detection process takes a very long time.

[0003] Surface-enhanced Raman scattering (SERS) technology, as a highly sensitive detection method, has been widely used in material detection in recent years. SERS technology utilizes the local electric field enhancement effect generated by metal nanoparticles under laser irradiation to significantly enhance the intensity of the Raman scattering signal generated by the interaction with molecular vibrations. This method offers advantages such as extremely high sensitivity, rapid detection, and the provision of molecular structural information. Existing Raman detection of PFAS, such as the paper "Ag Nanoparticle / Au@Ag Nanorod Sandwich Structures for SERS-Based Detection of Perfluoroalkyl Substances" published in ACS Applied Nano Materials, describes the use of Au@Ag structures to detect per- and polyfluoroalkyl substances. However, this method, like most existing Raman detection methods for PFAS, utilizes a single noble metal or core-shell nanoparticle for SERS detection of PFAS. These substrates are prone to aggregation, resulting in uneven hotspot distribution, poor reproducibility, and poor stability. Furthermore, the complex environment of natural water samples and the low concentrations of PFAS make it difficult for common noble metal nanomaterial SERS substrates to achieve ideal detection results in actual detection.

[0004] Metal-organic frameworks (MOFs) are crystalline materials composed of metal ions or metal clusters and organic ligands. They possess large surface areas, controllable pore structures, and tunable chemical properties. MOF-noble metal structures have been used in SERS detection, often exhibiting high sensitivity and stability. However, a MOF-noble metal substrate sensitive to PFAS is still lacking. Summary of the Invention

[0005] To address the deficiencies of the aforementioned prior art, the present invention provides a method for preparing a SERS substrate sensitive to perfluoroalkyl and polyfluoroalkyl organic pollutants. The substrate's gold nanoparticles are uniformly coated on UiO-66-F4, providing a uniform and stable "hotspot" and exhibiting a strong SERS effect. Due to the substrate's high specific surface area, electrostatic forces, fluorine-fluorine interactions, and hydrophobic interactions, the substrate exhibits a strong enrichment capacity for perfluoroalkyl and polyfluoroalkyl organic pollutants. The UiO-66-F4@Au SERS substrate, which combines gold nanoparticles with MOF materials, exhibits excellent enrichment capacity and high sensitivity for perfluoroalkyl and polyfluoroalkyl organic pollutants.

[0006] To achieve the above object, the technical solution of the present invention includes the following steps:

[0007] Step 1: Preparation of mixed solvent: Deionized water and 97% acetic acid were mixed in a beaker to form 50 ml of mixed solvent, wherein the volume ratio of deionized water to acetic acid was 8:5;

[0008] Step 2: Preparation of activated UiO-66-F4 powder: First, 13 ml of the mixed solvent prepared in step 1 was mixed with the tetrafluoroterephthalic acid ligand and ultrasonicated for 15 minutes. Then, another 13 ml of the mixed solvent prepared in step 1 was mixed with zirconium nitrate pentahydrate and ultrasonicated for 15 minutes. The two ultrasonicated solutions were mixed in a distillation flask and then heated to reflux. The two ultrasonicated solutions were mixed in a distillation flask and then heated to reflux. The heating reflux time was 12 hours and the heating reflux temperature was 108°C. The obtained white turbid liquid was then centrifuged and washed three times at 10,000 rpm. The centrifugal washing solution was a mixed solution of methanol and dichloromethane in a volume ratio of 1:1. Finally, the solution was dried in a vacuum drying oven at 70°C for 24 hours to obtain the activated UiO-66-F4 powder.

[0009] Step 3: Preparation of gold nanoparticle solution: Mix 99 ml of deionized water and 1 ml of 1% chloroauric acid aqueous solution in a flask and heat at 105°C. Immediately after boiling, add 1.5 ml of 1% sodium citrate aqueous solution. After the solution turns wine red, continue heating for 15 minutes and then cool to room temperature.

[0010] Step 4: Polyvinylpyrrolidone (PVP) modification of gold nanoparticles: Add 10 ml of 25 mg / ml PVP aqueous solution to the gold nanoparticle solution prepared in step 3, place on a magnetic stirrer at 600 rpm for 2 h, then centrifuge and wash three times with deionized water at 10,000 rpm, and finally dilute to 10 ml to obtain a PVP-modified gold nanoparticle solution;

[0011] Step 5: 5 mg of activated UiO-66-F4 powder from step 2 was suspended in 5 ml of deionized water and sonicated for 5 min to fully dissolve it to obtain a UiO-66-F4 solution; 1 ml of the UiO-66-F4 solution was placed on a magnetic stirrer at 600 rpm and stirred. During the stirring process, 4 ml of the PVP-modified gold nanoparticle solution prepared in step 4 was added dropwise to 1 ml of the solution. The UiO-66-F4 solution was added at a rate of 0.14 ml / min, and magnetic stirring was continued for 2 h after the addition was completed to obtain a UiO-66-F4@Au SERS substrate solution; the UiO-66-F4@Au solution was then mixed with anhydrous ethanol, and the volume ratio of the UiO-66-F4@Au solution to anhydrous ethanol was 4:1. After thorough mixing, 8 microliters of the mixed solution was drop-coated on a 5 mm*5 mm silicon wafer, and naturally dried at 25°C to obtain a UiO-66-F4@Au SERS substrate;

[0012] Compared with the prior art, the present invention has the following advantages and technical effects:

[0013] 1. The MOF material UiO-66-F4 has a strong enrichment ability for perfluorinated and polyfluorinated alkyl organic pollutants due to its high specific surface area, electrostatic forces, fluorine-fluorine interactions, and hydrophobic interactions. The Au nanoparticles loaded on the substrate have a strong SERS effect due to their surface plasmon resonance (LSPR) that can greatly enhance the local electromagnetic field. The UiO-66-F4@Au SERS substrate prepared by combining Au nanoparticles with UiO-66-F4 has excellent enrichment ability and high sensitivity for perfluorinated and polyfluorinated alkyl organic pollutants.

[0014] 2. By fully ultrasonicating the tetrafluoroterephthalic acid ligand and zirconium nitrate pentahydrate in a mixture of water and acetic acid, respectively, and finally mixing the two for subsequent steps, the crystallization effect of UiO-66-F4 can be significantly improved, and UiO-66-F4 particles with uniform size distribution can be obtained, which is conducive to the uniform distribution of subsequent Au nanoparticles on them.

[0015] 3. By strictly controlling the synthesis conditions, heating reflux time for 12 hours, heating reflux temperature at 108°C, centrifugal washing solution with a mixed solution of methanol and dichloromethane in a volume ratio of 1:1, and the droplet speed of the gold nanoparticle solution at 0.14 ml / min, a UiO-66-F4@Au SERS substrate with uniform size, uniform hotspot distribution and good stability was obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 SEM image of the prepared UiO-66-F4@Au composite SERS substrate;

[0017] Figure 2 This is the SEM image of the prepared UiO-66-F4 material;

[0018] Figure 3 This is a locally enlarged SEM image of the prepared UiO-66-F4@Au composite SERS substrate;

[0019] Figure 4 10 measured using UiO-66-F4@Au substrate -5 Raman spectrum of mol / L potassium perfluorobutanesulfonate aqueous solution;

[0020] Figure 5 10 measured using UiO-66-F4@Au substrate -5 Raman spectrum of mol / L perfluorooctanoic acid aqueous solution;

[0021] Figure 6 The Raman spectra of the UiO-66-F4@Au substrate tested at different concentrations of the standard potassium perfluorobutanesulfonate;

[0022] Figure 7 1168cm -1 The standard curve of potassium perfluorobutanesulfonate established by the intensity of the characteristic peak at ;

[0023] Figure 8 This is the Raman spectrum of the UiO-66-F4@Au substrate tested in actual lake water at different concentrations of potassium perfluorobutanesulfonate. DETAILED DESCRIPTION

[0024] like Figure 1 The figure shows the prepared UiO-66-F4@Au composite SERS substrate, and the preparation method includes the following steps:

[0025] Step 1: Preparation of mixed solvent: Deionized water and 97% acetic acid were mixed in a beaker to form 50 ml of mixed solvent, wherein the volume ratio of deionized water to acetic acid was 8:5;

[0026] Step 2: Preparation of activated UiO-66-F4 powder: First, take 13 ml of the mixed solvent prepared in step 1, mix it with tetrafluoroterephthalic acid ligand and ultrasonicate for 15 minutes, then take another 13 ml of the mixed solvent prepared in step 1, mix it with zirconium nitrate pentahydrate and ultrasonicate for 15 minutes, mix the two ultrasonicated solutions in a distillation flask, and then heat and reflux. The two ultrasonicated solutions are mixed in a distillation flask, and then heated and refluxed. The heating and reflux time is 12 hours, and the heating and reflux temperature is 108°C. The obtained white turbid liquid is then centrifuged and washed three times at 10,000 rpm. The centrifugal washing solution is a mixed solution of methanol and dichloromethane in a volume ratio of 1:1. Finally, it is dried in a vacuum drying oven at 70°C for 24 hours to obtain the activated UiO-66-F4 powder. Figure 2 This is the SEM image of the prepared UiO-66-F4 material. It can be clearly observed from the figure that the morphology of UiO-66-F4 is spherical, with nano-scale flaky rough defects on the surface. This is because the presence of F on the benzene ring of the ligand inhibits the isotropic growth of the crystal.

[0027] Step 3: Preparation of gold nanoparticle solution: Mix 99 ml of deionized water and 1 ml of 1% chloroauric acid aqueous solution in a flask and heat at 105°C. Immediately after boiling, add 1.5 ml of 1% sodium citrate aqueous solution. After the solution turns wine red, continue heating for 15 minutes and then cool to room temperature.

[0028] Step 4: Polyvinylpyrrolidone (PVP) modification of gold nanoparticles: Add 10 ml of 25 mg / ml PVP aqueous solution to the gold nanoparticle solution prepared in step 3, place on a magnetic stirrer at 600 rpm for 2 h, then centrifuge and wash three times with deionized water at 10,000 rpm, and finally dilute to 10 ml to obtain a PVP-modified gold nanoparticle solution;

[0029] Step 5: 5 mg of activated UiO-66-F4 powder from step 2 was suspended in 5 ml of deionized water and sonicated for 5 min to fully dissolve it to obtain a UiO-66-F4 solution; 1 ml of the UiO-66-F4 solution was placed on a magnetic stirrer at 600 rpm and stirred. During the stirring process, 4 ml of the PVP-modified gold nanoparticle solution prepared in step 4 was added dropwise to 1 ml of the solution. The UiO-66-F4 solution was added at a rate of 0.14 ml / min, and magnetic stirring was continued for 2 h after the addition was completed to obtain a UiO-66-F4@Au SERS substrate solution; the UiO-66-F4@Au solution was then mixed with anhydrous ethanol, and the volume ratio of the UiO-66-F4@Au solution to anhydrous ethanol was 4:1. After thorough mixing, 8 microliters of the mixed solution was drop-coated on a 5 mm*5 mm silicon wafer, and naturally dried at 25°C to obtain a UiO-66-F4@Au SERS substrate; Figure 3 This is a locally enlarged SEM image of the prepared UiO-66-F4@Au composite SERS substrate. From the image, it can be clearly observed that gold nanoparticles are evenly distributed on the surface of UiO-66-F4.

[0030] Example:

[0031] The present invention will be described in detail below with reference to specific embodiments:

[0032] Example 1: Preparation of UiO-66-F4@Au substrate and detection of potassium perfluorobutanesulfonate in aqueous solution

[0033] Potassium perfluorobutanesulfonate (PPFBS) is a type of perfluoroalkyl organic pollutant. The steps for preparing the UiO-66-F4@Au substrate and detecting potassium perfluorobutanesulfonate in aqueous solution are as follows:

[0034] Step 1: Preparation of mixed solvent: Deionized water and 97% acetic acid were mixed in a beaker to form 50 ml of mixed solvent, wherein the volume ratio of deionized water to acetic acid was 8:5;

[0035] Step 2: Preparation of activated UiO-66-F4 powder: First, 13 ml of the mixed solvent prepared in step 1 was mixed with the tetrafluoroterephthalic acid ligand and ultrasonicated for 15 minutes. Then, another 13 ml of the mixed solvent prepared in step 1 was mixed with zirconium nitrate pentahydrate and ultrasonicated for 15 minutes. The two ultrasonicated solutions were mixed in a distillation flask and then heated to reflux. The two ultrasonicated solutions were mixed in a distillation flask and then heated to reflux. The heating reflux time was 12 hours and the heating reflux temperature was 108°C. The obtained white turbid liquid was then centrifuged and washed three times at 10,000 rpm. The centrifugal washing solution was a mixed solution of methanol and dichloromethane in a volume ratio of 1:1. Finally, the solution was dried in a vacuum drying oven at 70°C for 24 hours to obtain the activated UiO-66-F4 powder.

[0036] Step 3: Preparation of gold nanoparticle solution: Mix 99 ml of deionized water and 1 ml of 1% chloroauric acid aqueous solution in a flask and heat at 105°C. Immediately after boiling, add 1.5 ml of 1% sodium citrate aqueous solution. After the solution turns wine red, continue heating for 15 minutes and then cool to room temperature.

[0037] Step 4: Polyvinylpyrrolidone (PVP) modification of gold nanoparticles: Add 10 ml of 25 mg / ml PVP aqueous solution to the gold nanoparticle solution prepared in step 3, place on a magnetic stirrer at 600 rpm for 2 h, then centrifuge and wash three times with deionized water at 10,000 rpm, and finally dilute to 10 ml to obtain a PVP-modified gold nanoparticle solution;

[0038] Step 5: 5 mg of activated UiO-66-F4 powder from step 2 was suspended in 5 ml of deionized water and sonicated for 5 min to fully dissolve it to obtain a UiO-66-F4 solution; 1 ml of the UiO-66-F4 solution was placed on a magnetic stirrer at 600 rpm and stirred. During the stirring process, 4 ml of the PVP-modified gold nanoparticle solution prepared in step 4 was added dropwise to 1 ml of the solution. The UiO-66-F4 solution was added at a rate of 0.14 ml / min, and magnetic stirring was continued for 2 h after the addition was completed to obtain a UiO-66-F4@Au SERS substrate solution; the UiO-66-F4@Au solution was then mixed with anhydrous ethanol, and the volume ratio of the UiO-66-F4@Au solution to anhydrous ethanol was 4:1. After thorough mixing, 8 microliters of the mixed solution was drop-coated on a 5 mm*5 mm silicon wafer, and naturally dried at 25°C to obtain a UiO-66-F4@Au SERS substrate;

[0039] Step 6: Take potassium perfluorobutanesulfonate powder and mix it into 10 -5The solution with a concentration of 1 mol / L was titrated on the SERS substrate of UiO-66-F4@Au obtained in step 5, and then dried naturally at 25°C for Raman detection. The test conditions were as follows: confocal Raman spectrometer, laser wavelength of 633 nm, laser power of 1%, integration time of 5 seconds, integration times of 3 times, and the results were as follows: Figure 4 Raman spectrum shown.

[0040] Figure 4 10 measured using UiO-66-F4@Au substrate -5 mol / L Raman spectrum of potassium perfluorobutanesulfonate aqueous solution shows that the concentration is 10 -5 mol / L potassium perfluorobutanesulfonate solution at the characteristic peak 1168cm -1 There is still a strong Raman signal at (this characteristic peak comes from the asymmetric stretching vibration of the S=O bond). The graphical results show that the prepared UiO-66-F4@AuSERS substrate has high sensitivity to potassium perfluorobutanesulfonate.

[0041] Example 2: Preparation of UiO-66-F4@Au substrate and detection of perfluorooctanoic acid in aqueous solution

[0042] Perfluorooctanoic acid (PFOA) is a type of perfluoroalkyl organic pollutant. The steps for preparing the UiO-66-F4@Au substrate and detecting potassium perfluorobutanesulfonate in aqueous solution are as follows:

[0043] Step 1: Preparation of mixed solvent: Deionized water and 97% acetic acid were mixed in a beaker to form 50 ml of mixed solvent, wherein the volume ratio of deionized water to acetic acid was 8:5;

[0044] Step 2: Preparation of activated UiO-66-F4 powder: First, 13 ml of the mixed solvent prepared in step 1 was mixed with the tetrafluoroterephthalic acid ligand and ultrasonicated for 15 minutes. Then, another 13 ml of the mixed solvent prepared in step 1 was mixed with zirconium nitrate pentahydrate and ultrasonicated for 15 minutes. The two ultrasonicated solutions were mixed in a distillation flask and then heated to reflux. The two ultrasonicated solutions were mixed in a distillation flask and then heated to reflux. The heating reflux time was 12 hours and the heating reflux temperature was 108°C. The obtained white turbid liquid was then centrifuged and washed three times at 10,000 rpm. The centrifugal washing solution was a mixed solution of methanol and dichloromethane in a volume ratio of 1:1. Finally, the solution was dried in a vacuum drying oven at 70°C for 24 hours to obtain the activated UiO-66-F4 powder.

[0045] Step 3: Preparation of gold nanoparticle solution: Mix 99 ml of deionized water and 1 ml of 1% chloroauric acid aqueous solution in a flask and heat at 105°C. Immediately after boiling, add 1.5 ml of 1% sodium citrate aqueous solution. After the solution turns wine red, continue heating for 15 minutes and then cool to room temperature.

[0046] Step 4: Polyvinylpyrrolidone (PVP) modification of gold nanoparticles: Add 10 ml of 25 mg / ml PVP aqueous solution to the gold nanoparticle solution prepared in step 3, place on a magnetic stirrer at 600 rpm for 2 h, then centrifuge and wash three times with deionized water at 10,000 rpm, and finally dilute to 10 ml to obtain a PVP-modified gold nanoparticle solution;

[0047] Step 5: 5 mg of activated UiO-66-F4 powder from step 2 was suspended in 5 ml of deionized water and sonicated for 5 min to fully dissolve it to obtain a UiO-66-F4 solution; 1 ml of the UiO-66-F4 solution was placed on a magnetic stirrer at 600 rpm and stirred. During the stirring process, 4 ml of the PVP-modified gold nanoparticle solution prepared in step 4 was added dropwise to 1 ml of the solution. The UiO-66-F4 solution was added at a rate of 0.14 ml / min, and magnetic stirring was continued for 2 h after the addition was completed to obtain a UiO-66-F4@Au SERS substrate solution; the UiO-66-F4@Au solution was then mixed with anhydrous ethanol, and the volume ratio of the UiO-66-F4@Au solution to anhydrous ethanol was 4:1. After thorough mixing, 8 microliters of the mixed solution was drop-coated on a 5 mm*5 mm silicon wafer, and naturally dried at 25°C to obtain a UiO-66-F4@Au SERS substrate;

[0048] Step 6: Take perfluorooctanoic acid powder and mix it into 10 -5 The solution with a concentration of 1 mol / L was titrated on the SERS substrate of UiO-66-F4@Au obtained in step 5, and then dried naturally at 25°C for Raman detection. The test conditions were as follows: confocal Raman spectrometer, laser wavelength of 633 nm, laser power of 1%, integration time of 5 seconds, integration times of 3 times, and the results were as follows: Figure 5 Raman spectrum shown.

[0049] Figure 5 10 measured using UiO-66-F4@Au substrate -5 The Raman spectrum of the PFOA aqueous solution with a concentration of 10 -5 mol / L perfluorooctanoic acid solution, at the characteristic peak 735cm -1There is still a strong Raman signal at the position (this characteristic peak comes from the symmetrical stretching of the C-F bond). The results in the figure show that the prepared UiO-66-F4@Au SERS substrate has high sensitivity to perfluorooctanoic acid.

[0050] Example 3: Preparation of UiO-66-F4@Au substrate and application in the detection of potassium perfluorobutanesulfonate in actual water

[0051] Step 1: Preparation of mixed solvent: Deionized water and 97% acetic acid were mixed in a beaker to form 50 ml of mixed solvent, wherein the volume ratio of deionized water to acetic acid was 8:5;

[0052] Step 2: Preparation of activated UiO-66-F4 powder: First, 13 ml of the mixed solvent prepared in step 1 was mixed with the tetrafluoroterephthalic acid ligand and ultrasonicated for 15 minutes. Then, another 13 ml of the mixed solvent prepared in step 1 was mixed with zirconium nitrate pentahydrate and ultrasonicated for 15 minutes. The two ultrasonicated solutions were mixed in a distillation flask and then heated to reflux. The two ultrasonicated solutions were mixed in a distillation flask and then heated to reflux. The heating reflux time was 12 hours and the heating reflux temperature was 108°C. The obtained white turbid liquid was then centrifuged and washed three times at 10,000 rpm. The centrifugal washing solution was a mixed solution of methanol and dichloromethane in a volume ratio of 1:1. Finally, the solution was dried in a vacuum drying oven at 70°C for 24 hours to obtain the activated UiO-66-F4 powder.

[0053] Step 3: Preparation of gold nanoparticle solution: Mix 99 ml of deionized water and 1 ml of 1% chloroauric acid aqueous solution in a flask and heat at 105°C. Immediately after boiling, add 1.5 ml of 1% sodium citrate aqueous solution. After the solution turns wine red, continue heating for 15 minutes and then cool to room temperature.

[0054] Step 4: Polyvinylpyrrolidone (PVP) modification of gold nanoparticles: Add 10 ml of 25 mg / ml PVP aqueous solution to the gold nanoparticle solution prepared in step 3, place on a magnetic stirrer at 600 rpm for 2 h, then centrifuge and wash three times with deionized water at 10,000 rpm, and finally dilute to 10 ml to obtain a PVP-modified gold nanoparticle solution;

[0055] Step 5: 5 mg of activated UiO-66-F4 powder from step 2 was suspended in 5 ml of deionized water and sonicated for 5 min to fully dissolve it to obtain a UiO-66-F4 solution; 1 ml of the UiO-66-F4 solution was placed on a magnetic stirrer at 600 rpm and stirred. During the stirring process, 4 ml of the PVP-modified gold nanoparticle solution prepared in step 4 was added dropwise to 1 ml of the solution. The UiO-66-F4 solution was added at a rate of 0.14 ml / min, and magnetic stirring was continued for 2 h after the addition was completed to obtain a UiO-66-F4@Au SERS substrate solution; the UiO-66-F4@Au solution was then mixed with anhydrous ethanol, and the volume ratio of the UiO-66-F4@Au solution to anhydrous ethanol was 4:1. After thorough mixing, 8 microliters of the mixed solution was drop-coated on a 5 mm*5 mm silicon wafer, and naturally dried at 25°C to obtain a UiO-66-F4@Au SERS substrate;

[0056] Step 6: Prepare the standard curve sample: Take potassium perfluorobutanesulfonate powder and mix it into 10 -3 ~10 -7 mol / L of 5 different concentrations of solution, the solvent is deionized water, titrated on the UiO-66-F4@Au SERS substrate obtained in step 5, and dried naturally at 25℃;

[0057] Step 7: Establish a standard curve: Perform Raman analysis on the dried samples in step 6. The test conditions are: confocal Raman spectrometer, using a laser wavelength of 633 nm, a laser power of 1%, an integration time of 5 seconds, and three integration times. Each concentration is measured five times at different points, and the characteristic peak at 1168 cm is taken. -1 The average value of the intensity at the concentration is taken as the corresponding intensity value, and the following can be obtained: Figure 6 The Raman spectrum shown in the figure clearly shows that even when the concentration of potassium perfluorobutanesulfonate is 10 - 7 mol / L, the characteristic peak is located at 1168cm -1 There is still a strong Raman signal at the surface, and the detection limit of potassium perfluorobutanesulfonate in deionized water can reach 10 -7 M level is conducive to the establishment of a standard curve. Then use the concentration as the horizontal axis (i.e., the Log value of the concentration) and the corresponding concentration Raman signal intensity as the vertical axis to establish a standard curve. Figure 7 The standard curve shown in the figure has the following fitting formula: y = 88.97x + 818.80, R 2 is 0.95;

[0058] Step 8: Test in actual water sample: Take lake water as solvent and filter it with 0.22 micron membrane to remove large suspended solids and impurities. Take potassium perfluorobutanesulfonate powder and mix it into 10-3 ~10 -7 mol / L, a total of five concentrations of lake water solution were titrated on the UiO-66-F4@Au SERS substrate obtained in step 5, and naturally dried at 25°C. The dried samples were subjected to Raman detection. The test conditions were: confocal Raman spectrometer, using a laser wavelength of 633 nm, a laser power of 1%, an integration time of 5 seconds, and three integration times. Each concentration was measured five times at different points, and the characteristic peak at 1168 cm was taken. -1 The average value of the intensity at the concentration is taken as the corresponding intensity value, such as Figure 8 The Raman spectra of the prepared SERS substrate tested in different concentrations of potassium perfluorobutanesulfonate in actual lake water clearly show that even when the concentration of potassium perfluorobutanesulfonate is 10 -7 mol / L, the characteristic peak is located at 1168cm -1 There is still a strong Raman signal at the surface, and the detection limit of potassium perfluorobutanesulfonate in lake water can reach 10 -7 M level. Substitute the signal intensity into the standard curve obtained in step 7 to calculate the concentration of potassium perfluorobutanesulfonate in the water sample to be tested. -1 The Raman signal intensity, Log value of calculated concentration and recovery rate are shown in Table 1.

[0059] Table 1 1168cm corresponding to different actual concentrations -1 Raman signal intensity, calculated concentration Log value and recovery rate

[0060] Log value of actual concentration Raman signal intensity Calculate the Log value of the concentration Recovery (%) ± RSD (%) -3 580.710 -2.676 112.108±8.189 -4 431.523 -4.353 108.820±7.637 -5 394.340 -4.771 95.416±15.219 -6 282.352 -6.030 100.492±9.146 -7 215.630 -6.779 96.849±16.149

[0061] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a SERS substrate sensitive to perfluoroalkyl and polyfluoroalkyl organic pollutants, comprising the following steps: Step 1: Preparation of mixed solvent: Mix deionized water and 97% acetic acid in a beaker to form 50 ml of mixed solvent; Step 2: Preparation of activated UiO-66-F4 powder: 0.595 g of tetrafluoroterephthalic acid ligand, 1.12 g of zirconium nitrate pentahydrate, and the mixed solvent prepared in step 1 were placed in a distillation flask and heated under reflux to obtain a white turbid liquid. The obtained white turbid liquid was centrifuged and washed three times at 10,000 rpm, and finally dried in a vacuum drying oven at 70°C for 24 h to obtain activated UiO-66-F4 powder; Step 3: Preparation of gold nanoparticle solution: Mix 99 ml of deionized water and 1 ml of 1% chloroauric acid aqueous solution in a flask and heat at 105°C. Immediately after boiling, add 1.5 ml of 1% sodium citrate aqueous solution. After the solution turns wine red, continue heating for 15 minutes and then cool to room temperature. Step 4: Polyvinylpyrrolidone (PVP) modification of gold nanoparticles: Add 10 ml of 25 mg / ml PVP aqueous solution to the gold nanoparticle solution prepared in step 3, place on a magnetic stirrer at 600 rpm for 2 h, then centrifuge and wash three times with deionized water at 10,000 rpm, and finally dilute to 10 ml to obtain a PVP-modified gold nanoparticle solution; Step 5: 5 mg of the activated UiO-66-F4 powder prepared in step 2 was suspended in 5 ml of deionized water and sonicated for 5 min to fully dissolve it to obtain a UiO-66-F4 solution; 1 ml of the UiO-66-F4 solution was placed on a magnetic stirrer and magnetically stirred at 600 rpm. During the stirring process, 4 ml of the PVP-modified gold nanoparticle solution prepared in step 4 was added dropwise to the 1 ml of the UiO-66-F4 solution. After the addition was completed, the magnetic stirring was continued for 2 h to obtain a UiO-66-F4@Au SERS substrate solution; the UiO-66-F4@Au solution was then mixed with anhydrous ethanol, and after thorough mixing, 8 μl was drop-coated on a 5 mm*5 mm silicon wafer. After drying, the UiO-66-F4@Au SERS substrate was obtained; The method is characterized in that, in the step 1, the volume ratio of deionized water to acetic acid is 8:5; in the step 2, 13 ml of the mixed solvent prepared in the step 1 is first mixed with the tetrafluoroterephthalic acid ligand and ultrasonicated for 15 minutes, and then another 13 ml of the mixed solvent prepared in the step 1 is mixed with zirconium nitrate pentahydrate and ultrasonicated for 15 minutes, the two ultrasonicated solutions are mixed in a distillation flask, and then heated to reflux; the heating and reflux time in the distillation flask is 12 hours, the heating and reflux temperature is 108° C., and the solution obtained by centrifugation and washing is a mixed solution of methanol and dichloromethane in a volume ratio of 1:1; and the dropping speed of the PVP-modified gold nanoparticle solution in the step 4 is 0.14 ml / min.

2. A method for preparing a SERS substrate sensitive to perfluoroalkyl and polyfluoroalkyl organic pollutants according to claim 1, characterized in that: In the step 5, the volume ratio of the UiO-66-F4@Au solution to anhydrous ethanol is 4:1, and the drying method is natural drying at 25°C.

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