Method for detecting perchlorate based on silver nanofilm substrate

Abstract

The application discloses a method for detecting perchlorate based on a silver nanofilm substrate. The application uses polydiene dimethyl ammonium chloride and sodium diethylthio carbamate as a protective agent, polyvinyl pyrrolidone as a stabilizer, and sodium borohydride-ethylene glycol as a reducing agent to obtain polydiene dimethyl ammonium chloride or diethylthio amino modified silver nanoparticles with high activity through one-pot synthesis or microwave synthesis, which are used as a surface-enhanced Raman scattering substrate for the detection of perchlorate. The perchlorate detection technology provided by the application has the advantages of simple preparation process, green and environmentally-friendly synthesis process, high sensitivity and the like, and provides a new technical path for the accurate detection of perchlorate in water.

Description

Technical Field

[0001] This invention relates to the field of perchlorate detection technology, and in particular to a method for detecting perchlorate based on a silver nanofilm substrate. Background Technology

[0002] Against the backdrop of increasingly prominent environmental pollution problems, perchlorate pollution has become a new and far-reaching environmental issue. Perchlorates are a class of substances containing perchlorate anions (ClO4-). - Perchlorate compounds, due to their extremely high water solubility and environmental stability, are widely present in various ecosystems. Simultaneously, as a highly efficient oxidant, it is extensively used in the production of aerospace propellants and fireworks. The widespread use of perchlorate has had a particularly severe impact on aquatic ecosystems, as it competitively inhibits the thyroid gland's absorption of iodides, leading to insufficient thyroid hormone synthesis. Thyroid hormones not only play a crucial role in human metabolic regulation but are also essential for the normal growth and development of children. Perchlorate exposure may also induce damage to the nervous, reproductive, and immune systems, and even increase the risk of birth defects in pregnant women. Therefore, developing rapid, highly sensitive, and non-destructive detection technologies to achieve accurate monitoring of trace amounts of perchlorate in water has significant practical implications and application value.

[0003] Currently, methods for perchlorate detection are mainly divided into two categories: traditional detection methods and rapid detection methods. Among them, traditional detection methods are represented by ion chromatography (IC), ion chromatography-tandem mass spectrometry (IC-MS), liquid chromatography-tandem mass spectrometry (LC-MS), and ion-selective electrodes. Although these methods have high sensitivity and accuracy, they have limitations such as cumbersome sample pretreatment steps, high detection costs, and high operational technical requirements, making it difficult to meet the needs of rapid detection and real-time monitoring in practical applications.

[0004] To overcome the shortcomings of traditional methods, rapid detection methods such as ultraviolet-visible absorption spectroscopy, fluorescence spectroscopy, and surface-enhanced Raman scattering (SERS) have been reported for perchlorate detection. However, ultraviolet-visible absorption spectroscopy suffers from weak anti-interference capabilities, high environmental pollution risk, and low detection sensitivity; fluorescence spectroscopy faces drawbacks such as cumbersome and time-consuming probe synthesis processes and poor stability, making it difficult to achieve efficient and practical detection results. In contrast, SERS, as a vibrational spectroscopy technique, can provide molecular-level structural information and has long played an important role in analytical chemistry and biomolecular detection, possessing significant technical advantages.

[0005] The core enhancement effect of SERS technology is highly dependent on the substrate material. Conventional substrates often utilize rough noble metal surfaces such as gold, silver, and copper, which can amplify the Raman scattering signal of target molecules adsorbed on their surfaces by millions to billions of times. Among these, silver has become the most widely used SERS substrate material due to its optimal electromagnetic enhancement effect and the ease of synthesis and tunable size and shape of silver nanoparticles. Although several research teams have used silver nanoparticle substrates for perchlorate detection, existing silver-based SERS substrates still have many prominent drawbacks: some schemes require complex pretreatment steps such as hydrophobication and have long synthesis times; some rely on precision equipment such as electron evaporation coating, which has stringent requirements for process conditions such as vacuum environment and angle control; at the same time, they generally suffer from weak SERS enhancement effect, narrow applicability range of analytes, and susceptibility to detection errors. Most SERS substrates used for perchlorate detection have a detection limit of only 100 μg / L and have not demonstrated anti-interference capabilities in the detection process. Existing SERS substrates for perchlorate detection struggle to simultaneously meet the comprehensive requirements of ease of preparation, material stability, and detection sensitivity. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a method for detecting perchlorate based on a silver nanofilm substrate.

[0007] This invention provides a method for detecting perchlorate, using PDDA-AgNPs or DDTC-AgNPs as a substrate and employing surface-enhanced Raman scattering technology to detect the concentration of perchlorate; wherein PDDA-AgNPs are silver nanoparticles modified with polydienedimethylammonium chloride, and DDTC-AgNPs are silver nanoparticles modified with sodium diethylthiocarbamate.

[0008] Furthermore, the PDDA-AgNPs are oil-water interface self-assembly substrates, and the DDTC-AgNPs are paper-based substrates.

[0009] Furthermore, the preparation of the PDDA-AgNPS includes the following steps:

[0010] S1: Mix AgNO3 with PDDA and stir at room temperature to allow the reaction to proceed; then add NaBH4 solution and continue stirring at room temperature; the concentration of PDDA is 0.0001%~2%; S2: Place the mixture obtained in S1 at 110-120℃ and continue stirring. After the reaction is complete, cool to room temperature and centrifuge to collect the precipitate and discard the supernatant. Redissolve the precipitate with ultrapure water and centrifuge again. Repeat the operation several times. Finally, dissolve the precipitate in ultrapure water to obtain PDDA-AgNPs solution. S3: Mix the obtained PDDA-AgNPS solution with n-hexane and let it stand to obtain the PDDA-AgNPs substrate.

[0011] Furthermore, the preparation of the DDTC-AgNPs includes the following steps: S1: Heat ethylene glycol to 120~180℃, keep the temperature constant, add Na2S and continue stirring; then add PVP and AgNO3 dissolved in ethylene glycol, microwave heating, and quench the reaction in ice water. S2: Centrifuge the solution obtained in S1, discard the upper turbid liquid, and retain a portion of the liquid; add ethanol, sonicate, and centrifuge again, repeating 2-3 times; finally, dissolve in ethanol and sonicate, then perform vacuum filtration, washing with ethanol during filtration, and drying the resulting filter membrane. S3: The filter membrane obtained in S2 is sequentially immersed in NaBH4 solution and DDTC solution to obtain DDTC-AgNPs substrate.

[0012] Furthermore, the filter membrane is immersed in NaBH4 solution for 5-30 min and in DDTC solution for 0.5-3 h.

[0013] Furthermore, the detection limit of the PDDA-AgNPs substrate for perchlorate is 250 μg / L; the detection limit of the DDTC-AgNPs substrate for perchlorate is 10 μg / L.

[0014] Further steps include the following: S1: Prepare perchloric acid standard solutions with concentration gradients; S2: After mixing the PDDA-AgNPs substrate or DDTC-AgNPs paper-based substrate with the perchloric acid standard solution, Raman detection was performed. A standard curve was established with the concentration of perchlorate in the mixture as the x-axis and the corresponding surface-enhanced Raman scattering response intensity as the y-axis. S3: Mix the sample to be tested with a PDDA-AgNPs substrate or a DDTC-AgNPs paper-based substrate, obtain the surface-enhanced Raman scattering response intensity by Raman detection, and substitute it into the standard curve obtained in S2 to obtain the concentration of perchlorate in the sample to be tested.

[0015] Furthermore, the ordinate is: when PDDA-AgNPs are used as the substrate, the perchlorate concentration is between 920 and 940 cm⁻¹. -1 The surface-enhanced Raman scattering response intensity at the characteristic peak; when using DDTC-AgNPs as a substrate, perchlorate at 920–940 cm⁻¹ -1 The intensity of surface-enhanced Raman scattering response at the characteristic peak.

[0016] Furthermore, the Raman detection wavelength is 532~785 nm, and the scanning range is 600~1200 cm⁻¹. -1 The scoring time is 1 second, and the cumulative number of times is 1.

[0017] Furthermore, the reaction time between the substrate and the perchloric acid standard solution or the sample to be tested is 20 s to 30 min.

[0018] In summary, compared with the prior art, the present invention achieves the following technical effects: (1) Simple preparation: It can be prepared by one-pot method and microwave synthesis; (2) Short detection time: The detection can be completed by incubating at room temperature for 20 s to 30 min; (3) Low detection limit: The detection limit of the oil-water interface self-assembled substrate for perchlorate in the system is 250 μg / L; the detection limit of the paper-based substrate for perchlorate is 10 μg / L. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 a is a flowchart of the preparation process of an oil-water interface self-assembled substrate proposed in Example 1 of the present invention, and b is a schematic diagram of the process of using the substrate for SERS detection of perchlorate.

[0021] Figure 2 This is a schematic diagram illustrating the preparation of a paper-based substrate and its application in SERS detection of perchlorate, as proposed in Embodiment 2 of the present invention.

[0022] Figure 3 This is a graph showing the SERS results of different concentrations of standard perchlorate detected using PDDA-AgNPs as a substrate in Example 3 of the present invention; a) is the SERS spectrum of different concentrations of perchlorate adsorbed on the nanofilm substrate; b) 933 cm⁻¹ -1 Linear relationship between SERS signal intensity and perchlorate concentration at a given location.

[0023] Figure 4 This is a graph showing the SERS results of real soil slurry detection using PDDA-AgNPs as a substrate in Example 4 of the present invention; a) is the SERS spectrum of soil slurry containing different concentrations of perchlorate adsorbed on the nanofilm substrate; b) 933 cm⁻¹ -1 Linear relationship between SERS signal intensity and perchlorate concentration at a given location.

[0024] Figure 5This is a graph showing the SERS results of different concentrations of standard perchlorate detected using DDTC-AgNPs as a substrate in Example 5 of the present invention; a) SERS spectra of perchlorate at different concentrations; b) 930 cm⁻¹ -1 Linear relationship between SERS signal intensity and perchlorate concentration at a given location (inset shows linearity at low concentration). Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0026] Example 1: Preparation of PDDA-AgNPs oil-water self-assembled substrate (1) Preparation of PDDA-AgNPs solution S1: Take 12 mL of AgNO3 solution (10 mM) and 6 mL of PDDA aqueous solution, add them to a 20 mL reaction glass bottle, and stir magnetically for 5 min at room temperature.

[0027] S2: Slowly add the mixture from step S1 into an Erlenmeyer flask containing 36 mL of 2 mM NaBH4 solution, and stir magnetically for 5 min at room temperature.

[0028] S3: Place the solution obtained in step S2 in a 110℃ oil bath and react under magnetic stirring for 30 min to decompose excess NaBH4 in the system. After the reaction, allow it to cool naturally to room temperature. Take 9 mL of the cooled mother liquor and centrifuge at 10,000 rpm for 20 min to remove unreacted PDDA and excess NaBH4. Then wash repeatedly with ultrapure water three times, centrifuging and discarding the supernatant after each wash. Finally, collect the precipitate and redisperse it in 1 mL of ultrapure water to obtain the PDDA-AgNPs solution. The synthesis steps are as follows. Figure 1 As shown in a.

[0029] (2) Oil-water interface self-assembly substrate A PDDA-Ag-NPs solution was prepared by mixing 150 μL of PDDA-Ag-NPs solution with 400 μL of n-hexane. The upper layer of n-hexane solution was removed to obtain a silver film on the surface, which constitutes the oil-water interface substrate. A schematic diagram of the process for detecting perchlorate on the obtained oil-water interface substrate is shown below. Figure 1 As shown in b.

[0030] Example 2: Preparation of DDTC-AgNPs paper-based substrate (1) Synthesis of PVP-AgNPs solution S1: Add 12 mL of ethylene glycol to a 20 mL open glass bottle, place it in a microwave reaction apparatus and heat it to 150°C, then maintain the temperature for 30 min.

[0031] S2: Add 240 μL of 3 mM ethylene glycol-dispersed Na2S solution to the isothermal solution obtained in step S1, and stir continuously for 5 min to mix it evenly.

[0032] S3: Add 3 mL of 0.05 g / mL ethylene glycol-dissolved PVP solution and 1 mL of 0.28 M AgNO3 solution to the mixed solution in step S2 in sequence; during the reaction, the power of the microwave synthesis workstation is maintained at 500 W. After reacting at a constant temperature for 20 min, the reaction flask is quickly immersed in an ice-water bath to quench the reaction, and finally a brown solution is obtained.

[0033] After adding AgNO3, trace amounts of Na2S in the system react rapidly with AgNO3 to generate silver sulfide (Ag2S) crystals. These crystals can serve as catalytic sites to promote the reduction reaction of AgNO3. At the same time, the rapid reduction process can effectively inhibit the formation of twin silver seeds, thereby regulating the growth morphology of silver nanocrystals and preventing them from forming linear or rod-shaped structures. In addition, PVP molecules can selectively adsorb onto specific crystal faces on the surface of silver crystals, further inducing the directional formation of silver nanoparticles and improving their dispersion stability.

[0034] S4: Place the precursor solution obtained in step S3 in a centrifuge and centrifuge at 10,000 rpm for 10 min. Discard the upper turbid liquid and retain about 1 mL of the concentrated liquid at the bottom. Add 5 mL of 50% (volume fraction) ethanol solution to the concentrated liquid, disperse it evenly by ultrasonication, and centrifuge again at 10,000 rpm for 10 min to remove unreacted ethylene glycol and other soluble impurities. Discard the supernatant, redissolve the precipitate in 5 mL of 50% ethanol, disperse it by ultrasonication, and store it in a sealed container at 4 ℃ in the dark.

[0035] Take 5 mL of the AgNPs solution dispersed in 50% ethanol and filter it through a 0.22 μm organic phase filter membrane. During the filtration process, wash the surface of the filter membrane three times with 50% ethanol solution. After filtration, place the obtained silver nanoparticle membrane in an oven and dry it at a suitable temperature to obtain the silver nanoparticle membrane sample.

[0036] (2) Preparation of paper-based substrate The filter paper with PVP-AgNPs was first immersed in 0.1 M sodium borohydride, and then immersed in 10 mM DDTC solution for 1 hour to obtain DDTC-AgNPs paper-based substrate. Figure 2 This is a schematic diagram illustrating the preparation of the paper-based substrate and its detection of perchlorate.

[0037] Example 3: Detection of perchlorate standard solution on oil-water interface self-assembled substrate (1) Prepare standard solutions with perchlorate concentrations of 0, 1, 2, 4, 10, 20, 30, and 40 mg / L (the perchlorate concentration in the mixture after mixing with the substrate is 0, 0.25, 0.5, 1, 2.5, 5, 7.5, and 10 mg / L).

[0038] (2) Take 50 μL of the prepared concentration gradient perchlorate standard solution and mix it thoroughly with 150 μL of LPDDA-AgNPs substrate solution. Remove the upper layer of n-hexane solution to obtain a solution with a silver film on the surface. Irradiate the silver film surface with 532 nm excitation light and collect samples from 600 to 1200 cm⁻¹. -1 Raman spectral signals within the wavenumber range.

[0039] like Figure 3 As shown, using PDDA-AgNPs as a SERS substrate, ClO4 can be realized. - Qualitative identification and quantitative analysis of ClO4 in the system. Figure a shows the presence of ClO4 in the system. - Characteristic peak (933 cm) -1 The intensity gradually increases with increasing concentration, the signal intensity is significantly improved, and the spectral distinction between different concentrations is clear. And at 933 cm⁻¹... -1 The SERS response intensity is plotted on the ordinate, and the ClO4 content in the system is... - A standard curve was established with the concentration as the x-axis. Figure b shows the standard curve at 933 cm⁻¹. -1 SERS response intensity and ClO4 - The concentration showed a good linear relationship (R²=0.9771), which can achieve ClO4 - Quantitative detection.

[0040] Example 4: Detection of perchlorate in real soil solution using an oil-water interface self-assembled substrate. Spiked perchlorate solution in soil slurry. Soil samples were pretreated: 1 g / 10 mL was vortexed into a suspension, sonicated for 2 h, and the supernatant was collected (the bottom soil was reconstituted, vortexed into a suspension, allowed to stand for 5 min, and the supernatant was collected; this process was repeated 3 times). The samples were centrifuged at 10000 rpm for 20 min, and the supernatant was collected. The standard perchlorate was diluted with soil extract to form a series of soil slurries containing different concentrations of perchlorate (0, 1, 2, 4, 10, 20, 30, 40 mg / L). 150 μL of PDDA-AgNPs, 50 μL of soil slurry containing perchlorate, and 400 μL of n-hexane were vortexed for 20 s, the n-hexane layer was removed, and the mixture was inverted onto a 1.5 mL centrifuge tube cap. The silver film surface was irradiated with 532 nm excitation light, and samples were collected from 600–1200 cm⁻¹. -1 Raman spectral signals within the wavenumber range.

[0041] like Figure 4 As shown, using PDDA-AgNPs as a SERS substrate, ClO4 in soil solution can be obtained. - Qualitative identification and quantitative analysis. The spectral results in Figure a indicate that ClO4... - Characteristic peak intensity (933 cm⁻¹) -1 The signal response increases gradient with increasing concentration, and the spectral curves corresponding to different concentrations show clear distinction. The signal response is significantly enhanced at 933 cm⁻¹. -1 The SERS response intensity at a certain point is used as the ordinate, and the ClO4 content in the system is... - A standard curve for quantitative analysis was constructed with concentration on the x-axis. The calibration curve in Figure b shows a value of 933 cm⁻¹. -1 The SERS response intensity at the location and ClO4 - The concentration showed a good linear correlation (R²=0.9901), and this method can be used for ClO4 in actual soil solutions. - Precise quantitative detection.

[0042] Example 5: Detection of perchlorate on paper-based substrates (1) Prepare standard solutions with perchlorate concentrations of 0, 0.005, 0.01, 0.05, 0.1, 0.3, 0.5, 0.7, 1, 2, 3, 4, and 5 mg / L.

[0043] (2) Immerse the paper substrate in the above-mentioned perchlorate standard solution for 30 min. No air drying is required. Place the substrate directly under a Raman instrument for Raman detection. Irradiate the silver film surface with 532 nm excitation light and collect samples from 600 to 1200 cm⁻¹. -1 Raman spectral signals within the wavenumber range.

[0044] like Figure 5As shown, using DDTC-AgNPs as the SERS active substrate, it is possible to achieve the activity of ClO4. - Qualitative identification and quantitative analysis. SERS spectral results for a indicate that, with the increase of ClO4... - The increase in concentration is characterized by a Raman peak (930 cm⁻¹). -1 The intensity gradually increases, the signal response is significantly improved, and the spectral curves corresponding to different concentrations have clear distinction. A 930 cm⁻¹ spectral depth was selected. -1 The SERS response intensity is used as the ordinate, and ClO4 is used as the plot. - A quantitative analysis standard curve was constructed with concentration on the x-axis. The calibration curve for b shows a value of 930 cm⁻¹. -1 The SERS response intensity at ClO4 - Both the high and low concentration ranges showed good linear correlation, indicating that using DDTC-AgNPs as the substrate for SERS can achieve effective control of ClO4. - Precise quantitative detection.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting perchlorate, characterized in that, The concentration of perchlorate was detected using surface-enhanced Raman scattering (SERS) with PDDA-AgNPs or DDTC-AgNPs as substrates. PDDA-AgNPs are silver nanoparticles modified with polydienedimethylammonium chloride, and DDTC-AgNPs are silver nanoparticles modified with sodium diethylthiocarbamate.

2. The method for detecting perchlorate according to claim 1, characterized in that, The PDDA-AgNPs are oil-water interface self-assembly substrates, and the DDTC-AgNPs are paper-based substrates.

3. The method for detecting perchlorate according to claim 1, characterized in that, The preparation of the PDDA-AgNPS includes the following steps: S1: Mix AgNO3 with PDDA and stir at room temperature to carry out the reaction; then add NaBH4 solution and continue stirring at room temperature. S2: Place the mixture obtained in S1 at 100-120 °C and continue stirring. After the reaction is complete, cool to room temperature and centrifuge. Discard the supernatant and collect the precipitate. Redissolve the precipitate with ultrapure water and centrifuge again. Repeat the operation several times. Finally, dissolve the precipitate in ultrapure water to obtain PDDA-AgNPs solution. S3: Mix the obtained PDDA-AgNP solution with n-hexane and let it stand to obtain the PDDA-AgNPs substrate.

4. The method for detecting perchlorate according to claim 1, characterized in that, The preparation of the DDTC-AgNPs includes the following steps: S1: Heat ethylene glycol to 120~180 ℃, keep the temperature constant, add Na2S and continue stirring; then add PVP and AgNO3 dissolved in ethylene glycol, microwave heating, and quench the reaction in ice water. S2: Centrifuge the solution obtained in S1, discard the supernatant, and retain a portion of the liquid; add ethanol, sonicate, and centrifuge again, repeating 2-3 times; finally, dissolve in ethanol, sonicate, and then filter, washing with ethanol during filtration, and drying the resulting filter membrane. S3: The filter membrane obtained in S2 is sequentially immersed in NaBH4 solution and DDTC solution to obtain DDTC-AgNPs substrate.

5. The method for detecting perchlorate according to claim 4, characterized in that, The filter membrane is immersed in NaBH4 solution for 5-30 min and in DDTC solution for 0.5-3 h.

6. The method for detecting perchlorate according to claim 1, characterized in that, The detection limit of the PDDA-AgNPs substrate for perchlorate is 250 μg / L; the detection limit of the DDTC-AgNPs substrate for perchlorate is 10 μg / L.

7. The method for detecting perchlorate according to claim 1, characterized in that, Includes the following steps: S1: Prepare perchloric acid standard solutions with concentration gradients; S2: After mixing the PDDA-AgNPs substrate or DDTC-AgNPs substrate with the perchloric acid standard solution, Raman detection was performed. A standard curve was established with the concentration of perchlorate in the mixture as the x-axis and the corresponding surface-enhanced Raman scattering response intensity as the y-axis. S3: Mix the sample to be tested with a PDDA-AgNPs substrate or a DDTC-AgNPs substrate, obtain the surface-enhanced Raman scattering response intensity by Raman detection, and substitute it into the standard curve obtained in S2 to obtain the concentration of perchlorate in the sample to be tested.

8. The method for detecting perchlorate according to claim 7, characterized in that, The ordinate is: perchlorate concentration in the range of 920–940 cm⁻¹ when PDDA-AgNPs are used as the substrate. -1 The surface-enhanced Raman scattering response intensity at the characteristic peak; when using DDTC-AgNPs as a substrate, perchlorate at 920–940 cm⁻¹ -1 The intensity of surface-enhanced Raman scattering response at the characteristic peak.

9. The method for detecting perchlorate according to claim 7, characterized in that, The Raman detection wavelength is 532~785 nm, and the scanning range is 600~1200 cm⁻¹. -1 .

10. The method for detecting perchlorate according to claim 7, characterized in that, The reaction time between the substrate and the perchloric acid standard solution or the sample to be tested is 20 s to 30 min.

Images