Green paper-based SERS (Surface Enhanced Raman Scattering) substrate modified by tannic acid, preparation method and application

Abstract

The invention relates to a tannic acid modified green paper-based SERS substrate, a preparation method and application, and belongs to the technical field of detection of methylene blue in a water body, the preparation method of the tannic acid modified green paper-based SERS substrate comprises the following steps: step 1, immersing filter paper into a tannic acid solution, and then naturally drying to obtain tannic acid modified filter paper; 2, a mixed solution of silver nitrate and tetrachloroauric acid is dropwise added to the tannic acid modified filter paper, then surface liquid is removed, the tannic acid modified green paper-based SERS substrate is obtained, gold / silver nanoparticles firmly grow on a tannic acid modified layer of cellulose fibers, and the tannic acid modified green paper-based SERS substrate is obtained. The problem that a green paper-based SERS substrate obtained under the current mild green condition is insufficient in MB [mu] g / L-level trace detection capacity is solved, and trace detection of methylene blue in a water body can be rapidly carried out with high sensitivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of methylene blue detection in water bodies, and specifically relates to a tannic acid modified green paper-based SERS substrate, a preparation method and application. BACKGROUND

[0002] The cationic dye methylene blue (abbreviation: MB, full name: Methylene Blue) in the industrial production discharge process can cause water ecological toxicity problems and can produce biological accumulation along the food chain. Based on the above situation, accurate detection of MB in water has important value for maintaining the safety and stability of the water ecosystem and protecting public health. Therefore, developing MB detection technology with high sensitivity has become a core topic in the field of water environment analysis. Surface-enhanced Raman scattering (SERS) technology can carry out ultra-sensitive detection of methylene blue (MB) molecules by means of the local surface plasmon resonance effect induced by noble metal nanostructures. The sensitivity of the technology is extremely high, and it can detect to the trace level, and even realize single molecule level detection. At the same time, it also has excellent fingerprint identification characteristics, and can accurately carry out specific analysis even in the complex matrix environment of water. Among many SERS substrates, the paper-based SERS substrate has very low cost, good flexibility and is easy to process and manufacture. Moreover, the three-dimensional porous fiber structure of paper provides a large specific surface area for the loading of noble metal nanoparticles, thereby significantly improving the detection sensitivity, so it has been widely used in the field of rapid on-site detection.

[0003] The application number 2025116547030, the name of which is "a stable paper-based SERS substrate and its preparation method and application", provides a stable paper-based SERS substrate, solves the problems of poor detection reproducibility, fiber swelling or nanoparticle shedding, and can be used for rapid, accurate and trace detection of methylene blue in water. However, KH-560, tetrabutylammonium nitrate, dichloromethane and cyclohexane are needed, KH-560 is corrosive, corrosive to eyes, skin and mucous membrane tissue; tetrabutylammonium nitrate has acute toxicity (mouse intravenous LD50 is 10 mg / kg); dichloromethane has significant toxicity, long-term contact may cause central nervous system damage (such as dizziness, headache, nausea), lung damage (such as pulmonary edema), increased risk of spontaneous abortion, and acute / chronic toxicity (such as blurred vision, memory loss), and is listed as a 2A carcinogen, long-term exposure may increase the risk of cancer; cyclohexane belongs to low-toxicity chemicals, but has effects on the nervous system, respiratory system and digestive system, and high-concentration cyclohexane inhalation can cause aspiration pneumonia, pulmonary edema, and symptoms such as excitement, balance disorder, anesthesia and coma, so the green chemical paper-based SERS substrate based on the paper-based SERS substrate is of great concern. Green chemical paper-based SERS substrate refers to using paper (usually cellulose material) as a flexible carrier, and using environmentally friendly, low-toxicity and low-energy-consumption methods to construct a SERS active surface for high-sensitivity detection of trace substances. This kind of substrate combines the advantages of low cost, renewability, bendable cutting and three-dimensional porous structure of paper, and is highly consistent with the goal of green analytical chemistry.

[0004] Early green synthesis focuses on reducing or avoiding the use of toxic chemical reagents. For example, the aldehyde components contained in office paper itself are ingeniously used as reducing agents to realize in-situ reduction of silver nitrate on paper fibers, directly generating nano-silver particles (Ag NPs) without any additional reducing agent. This not only simplifies the process, but also fundamentally embodies the green design idea of utilizing the characteristics of materials themselves. In addition, the coffee ring effect, which is traditionally considered a disadvantage, is transformed into a preparation advantage, and by using gravity and the coffee ring effect to drive nanoparticle self-assembly on a paper tip with a temperature gradient, rapid and uniform construction of SERS hot spots is realized. However, under mild green conditions (room temperature / low temperature, aqueous solvent), the crystallinity of nanoparticles is low, the hot spot density is insufficient, the enhancement factor is 1-2 orders of magnitude lower than traditional silicon-based or glass-based substrates, and the trace detection ability for MB μg / L level is insufficient. SUMMARY

[0005] In view of the problems in the prior art, the present application provides a tannic acid modified green paper-based SERS substrate, a preparation method and application, to solve the problem of insufficient trace detection ability for MB μg / L level of the green paper-based SERS substrate obtained under mild green conditions. The present application can perform high-sensitivity and rapid trace detection of methylene blue in water.

[0006] The application is realized by the technical scheme: A preparation method of a tannic acid modified green paper-based SERS substrate, which specifically comprises the following steps: Step 1, immerse filter paper in a tannic acid solution, and then naturally dry to obtain a tannic acid modified filter paper; Step 2, drop a mixed solution of silver nitrate and tetrachloroauric acid on the tannic acid modified filter paper, and then remove the surface liquid to obtain a tannic acid modified green paper-based SERS substrate.

[0007] Preferably, the concentration of the tannic acid solution in step 1 is 4-6 mM, and the solvent of the tannic acid solution is composed of ethanol and deionized water, and the volume ratio of ethanol and deionized water is 1:1.

[0008] Preferably, the filter paper is immersed in the tannic acid solution for 4-6 min in step 1, and then naturally dried.

[0009] Preferably, the concentration of silver nitrate and tetrachloroauric acid in the mixed solution in step 2 is 5-10 mM.

[0010] Preferably, 20-30 μL of the mixed solution of silver nitrate and tetrachloroauric acid is dropped on the tannic acid modified filter paper in step 2, reacted for 4-6 min, and then the surface liquid is removed.

[0011] Preferably, step 3 is further included, which repeats step 2 for 2-4 times to obtain the tannic acid modified green paper-based SERS substrate.

[0012] A tannic acid modified green paper-based SERS substrate obtained by the preparation method of any one of the above-mentioned tannic acid modified green paper-based SERS substrate, wherein the tannic acid is combined with the fiber surface of the filter paper through hydrogen bonds to form a tannic acid modified layer, and gold nanoparticles and silver nanoparticles are attached to the tannic acid modified layer.

[0013] Application of a tannic acid modified green paper-based SERS substrate in trace detection of methylene blue in water.

[0014] Compared with the prior art, the application has the following beneficial technical effects: This invention discloses a method for preparing a tannic acid-modified green paper-based SERS substrate. The filter paper is modified simply by impregnating it with the green solvent tannic acid. This is because tannic acid provides hydroxyl / phenolic groups that can bond to the surface of cellulose fibers via hydrogen bonds. Subsequently, a mixed solution of HAuCl4 / AgNO3 is added dropwise to the tannic acid-modified filter paper using a simple dropwise addition method. Tannic acid is a polyphenolic compound rich in catechol / pyrogallol structural units. When it is modified onto the surface of cellulose filter paper via hydrogen bonding, its exposed phenolic hydroxyl functional groups become chemically active sites. When a solution containing HAuCl4 and AgNO3 comes into contact with the modified filter paper, Au... 3+ (with AuCl4) - (Formal existence) and Ag + The ions are captured by the phenolic hydroxyl groups on the tannic acid molecule through coordination bonds, binding tightly around the hydroxyl groups. Then, the tannic acid molecule, acting as a reducing agent, directly transfers electrons to the Au molecules coordinated with it. 3+ and Ag + Ions. These two metal ions are reduced to zero-valent metal atoms. Because the reaction is confined to the local region where the tannic acid molecules are located, the newly generated metal atoms do not have the opportunity to diffuse freely, but instead aggregate, nucleate, and grow into gold / silver nanoparticles near that site. These nanoparticles thus grow firmly on the tannic acid-modified layer of cellulose fibers. This invention is simple to operate, environmentally friendly, and highly sensitive, making it suitable for rapidly determining whether methylene blue levels in water exceed the standard. Attached Figure Description

[0015] Figure 1a The paper-based SERS substrates synthesized in Examples 1-5 of this invention are at 10 -5 Raman spectrum of M methylene blue mother liquor.

[0016] Figure 1b for Figure 1a The corresponding characteristic peak (449 cm) -1 Response change histogram.

[0017] Figure 2a The paper-based SERS substrates synthesized in Examples 3 and 6-9 of this invention were subjected to 10... -5 Raman spectrum of M-methylene blue mother liquor.

[0018] Figure 2b for Figure 2a The corresponding characteristic peak (449 cm) -1 Response change histogram.

[0019] Figure 3 The images are scanning electron microscope (SEM) images of the SERS paper substrates synthesized in Examples 3 and 6-9 of this invention at 5 μm.

[0020] Figure 4 This is a graph showing the linear relationship between the logarithmic Raman peak intensity and the logarithmic methylene blue concentration described in this invention. Detailed Implementation

[0021] The principles and advantages of this invention will be further explained and described in detail below with reference to specific embodiments, so that those skilled in the art can better understand this invention. The following description is merely exemplary and does not limit its content.

[0022] instrument FA1004 electronic balance (Shimadzu Philippines Manufacturing Co., Ltd.), laboratory deionized water system (Shanghai Hetai Instrument Co., Ltd.), laser confocal micro Raman imaging spectrometer (PERS-RH1700, Xiamen Pushi Nanotechnology Co., Ltd.), SU8100 high-resolution scanning electron microscope (Bruker GmbH, Germany).

[0023] reagents Analytical grade silver nitrate (AgNO3, 99.8%), tannic acid (98%), and methylene blue (98%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Tetrachloroauric acid (HAuCl4, >97.0%) was purchased from Shanghai Haohong Biomedical Technology Co., Ltd. Qualitative filter paper was from Hangzhou Special Paper Co., Ltd. All reagents were ready for use without further purification.

[0024] This invention discloses a method for preparing a tannic acid-modified green paper-based SERS substrate, specifically comprising the following steps: 1) Preparation of tannic acid composite filter paper; Qualitative filter paper (6 mm in diameter) was immersed in a 1:1 mixture of 4-6 mM tannic acid in ethanol / water. v / v After 4-6 minutes, remove the paper and allow it to air dry to obtain tannic acid-modified filter paper, i.e., tannic acid composite filter paper. 2) Preparation of HAuCl4 / AgNO3 reaction precursor solution; Dissolve appropriate amounts of HAuCl4 and AgNO3 in 20-30 μL of deionized water to make the concentrations of HAuCl4 and AgNO3 5-10 mM, respectively, to obtain the HAuCl4 / AgNO3 reaction precursor solution. 3) Preparation of paper-based SERS substrates using the drip-feed method; Add 20-30 μL of HAuCl4 / AgNO3 reaction precursor solution to tannic acid composite filter paper. After reacting for 4-6 min, use toilet paper to absorb the excess liquid. Then, repeat the process of adding the same volume of HAuCl4 / AgNO3 reaction precursor solution and absorbing the excess liquid 2-4 times to obtain a green paper-based SERS substrate modified with tannic acid.

[0025] In the green paper-based SERS substrate, tannic acid is combined with the fiber surface of the filter paper through hydrogen bond to form a tannic acid modification layer, and gold nanoparticles and silver nanoparticles are attached to the tannic acid modification layer.

[0026] Example 1 The application discloses a preparation method of a tannic acid modified green paper-based SERS substrate. 1) Preparation of tannic acid composite filter paper; Dip qualitative filter paper (with a diameter of 6 mm) into a 5 mM tannic acid ethanol / water mixture (1:1, v / v Take out after 5 min, and naturally dry to obtain tannic acid modified filter paper, namely tannic acid composite filter paper. 2) Preparation of HAuCl4 reaction precursor solution; Dissolve a proper amount of HAuCl4 into 25 μL of deionized water to make the concentration of HAuCl4 be 5 mM, and obtain the HAuCl4 reaction precursor solution. 3) Preparation of paper-based SERS substrate based on the dripping method; Drip 25 μL of the HAuCl4 reaction precursor solution on the tannic acid composite filter paper, use daily toilet paper to absorb the excess liquid after 5 min of reaction, and then continue to drip 25 μL of the HAuCl4 reaction precursor solution and absorb the excess liquid for three times to obtain the tannic acid modified green paper-based SERS substrate.

[0027] Example 2 The application discloses a preparation method of a tannic acid modified green paper-based SERS substrate. 1) Preparation of tannic acid composite filter paper; Dip qualitative filter paper (with a diameter of 6 mm) into a 5 mM tannic acid ethanol / water mixture (1:1, v / v Take out after 5 min, and naturally dry to obtain tannic acid modified filter paper, namely tannic acid composite filter paper. 2) Preparation of HAuCl4 / AgNO3 reaction precursor solution; Dissolve a proper amount of HAuCl4 and AgNO3 into 25 μL of deionized water to make the concentration of HAuCl4 and AgNO3 both be 5 mM, and obtain the HAuCl4 / AgNO3 reaction precursor solution. 3) Preparation of paper-based SERS substrate based on the dripping method; The tannic acid modified green paper-based SERS substrate is prepared by adding 25 μL of the HAuCl4 / AgNO3 reaction precursor solution on the tannic acid composite filter paper, and then repeating the adding of 25 μL of the HAuCl4 / AgNO3 reaction precursor solution and the absorption of the excess liquid for three times after 5 minutes of reaction.

[0028] Example 3 The preparation method of the tannic acid modified green paper-based SERS substrate comprises the following steps: 1) Preparation of tannic acid composite filter paper; The qualitative filter paper (with a diameter of 6 mm) is immersed in a 5 mM tannic acid ethanol / water mixture (1:1, v / v ) for 5 minutes, and then taken out and naturally dried to obtain the tannic acid modified filter paper, i.e., the tannic acid composite filter paper. 2) Preparation of HAuCl4 / AgNO3 reaction precursor solution; A proper amount of HAuCl4 and AgNO3 is dissolved in 25 μL of deionized water to obtain the HAuCl4 / AgNO3 reaction precursor solution, and the concentrations of HAuCl4 and AgNO3 are 10 mM and 5 mM, respectively. 3) Preparation of paper-based SERS substrate based on the dripping method; The tannic acid modified green paper-based SERS substrate is prepared by adding 25 μL of the HAuCl4 / AgNO3 reaction precursor solution on the tannic acid composite filter paper, and then repeating the adding of 25 μL of the HAuCl4 / AgNO3 reaction precursor solution and the absorption of the excess liquid for three times after 5 minutes of reaction.

[0029] Example 4 The preparation method of the tannic acid modified green paper-based SERS substrate comprises the following steps: 1) Preparation of tannic acid composite filter paper; The qualitative filter paper (with a diameter of 6 mm) is immersed in a 5 mM tannic acid ethanol / water mixture (1:1, v / v ) for 5 minutes, and then taken out and naturally dried to obtain the tannic acid modified filter paper, i.e., the tannic acid composite filter paper. 2) Preparation of HAuCl4 / AgNO3 reaction precursor solution; A proper amount of HAuCl4 and AgNO3 is dissolved in 25 μL of deionized water to obtain the HAuCl4 / AgNO3 reaction precursor solution, and the concentrations of HAuCl4 and AgNO3 are 5 mM and 10 mM, respectively. 3) Preparation of paper-based SERS substrate based on the dripping method; The tannic acid-modified green paper-based SERS substrate can be obtained by adding 25 μL of the AgNO3 reaction precursor solution on the tannic acid composite filter paper, absorbing the excess liquid with the daily toilet paper after 5 min of reaction, and then repeating the adding of 25 μL of the AgNO3 reaction precursor solution and the absorbing of the excess liquid for three times.

[0030] Example 5 The preparation method of the tannic acid-modified green paper-based SERS substrate provided by the application specifically comprises the following steps: 1) Preparation of tannic acid composite filter paper; The qualitative filter paper (with a diameter of 6 mm) is immersed in a 5 mM tannic acid ethanol / water mixed solution (1:1, v / v ) for 5 min, and then taken out and naturally dried to obtain the tannic acid-modified filter paper, i.e., the tannic acid composite filter paper; 2) Preparation of AgNO3 reaction precursor solution; An appropriate amount of AgNO3 is dissolved in 25 μL of deionized water to obtain an AgNO3 reaction precursor solution with a concentration of 5 mM; 3) Preparation of paper-based SERS substrate based on the dripping method; The tannic acid-modified green paper-based SERS substrate can be obtained by adding 25 μL of the AgNO3 reaction precursor solution on the tannic acid composite filter paper, absorbing the excess liquid with the daily toilet paper after 5 min of reaction, and then repeating the adding of 25 μL of the AgNO3 reaction precursor solution and the absorbing of the excess liquid for three times.

[0031] Example 6 The preparation method of the tannic acid-modified green paper-based SERS substrate provided by the application specifically comprises the following steps: 1) Preparation of tannic acid composite filter paper; The qualitative filter paper (with a diameter of 6 mm) is immersed in a 5 mM tannic acid ethanol / water mixed solution (1:1, v / v ) for 5 min, and then taken out and naturally dried to obtain the tannic acid-modified filter paper, i.e., the tannic acid composite filter paper; 2) Preparation of HAuCl4 / AgNO3 reaction precursor solution; An appropriate amount of HAuCl4 and AgNO3 is dissolved in 25 μL of deionized water to obtain a HAuCl4 / AgNO3 reaction precursor solution with a concentration of 10 mM and 5 mM, respectively; 3) Preparation of paper-based SERS substrate based on the dripping method; The tannic acid-modified green paper-based SERS substrate is prepared by dropping 25 μL of the HAuCl4 / AgNO3 reaction precursor solution on the tannic acid composite filter paper and then absorbing the excess liquid with a daily sanitary paper after 5 min of reaction.

[0032] Example 7 The application also provides a preparation method of the tannic acid-modified green paper-based SERS substrate. 1) Preparation of tannic acid composite filter paper The qualitative filter paper (with a diameter of 6 mm) is immersed in a 5 mM tannic acid ethanol / water mixture (1:1, v / v ) for 5 min, and then taken out and naturally dried to obtain the tannic acid-modified filter paper, i.e., the tannic acid composite filter paper. 2) Preparation of HAuCl4 / AgNO3 reaction precursor solution An appropriate amount of HAuCl4 and AgNO3 is dissolved in 25 μL of deionized water to obtain the HAuCl4 / AgNO3 reaction precursor solution, with the concentrations of HAuCl4 and AgNO3 being 10 mM and 5 mM, respectively. 3) Preparation of paper-based SERS substrate based on the dripping method The tannic acid-modified green paper-based SERS substrate is prepared by dropping 25 μL of the HAuCl4 / AgNO3 reaction precursor solution on the tannic acid composite filter paper and then absorbing the excess liquid with a daily sanitary paper after 5 min of reaction.

[0033] Example 8 The application also provides a preparation method of the tannic acid-modified green paper-based SERS substrate. 1) Preparation of tannic acid composite filter paper The qualitative filter paper (with a diameter of 6 mm) is immersed in a 5 mM tannic acid ethanol / water mixture (1:1, v / v ) for 5 min, and then taken out and naturally dried to obtain the tannic acid-modified filter paper, i.e., the tannic acid composite filter paper. 2) Preparation of HAuCl4 / AgNO3 reaction precursor solution An appropriate amount of HAuCl4 and AgNO3 is dissolved in 25 μL of deionized water to obtain the HAuCl4 / AgNO3 reaction precursor solution, with the concentrations of HAuCl4 and AgNO3 being 10 mM and 5 mM, respectively. 3) Preparation of paper-based SERS substrate based on the dripping method The tannic acid-modified green paper-based SERS substrate was prepared by adding 25 μL of the HAuCl4 / AgNO3 reaction precursor solution dropwise on the tannic acid composite filter paper, and then repeating the addition of 25 μL of the HAuCl4 / AgNO3 reaction precursor solution and the absorption of the excess liquid for 2 times after 5 min of reaction.

[0034] Example 9 The application discloses a preparation method of a tannic acid-modified green paper-based SERS substrate. 1) Preparation of tannic acid composite filter paper The qualitative filter paper (with a diameter of 6 mm) was immersed in a 5 mM tannic acid ethanol / water mixture (1:1, V / V) for 5 min, and then taken out and naturally dried to obtain the tannic acid-modified filter paper, namely the tannic acid composite filter paper. v v 2) Preparation of HAuCl4 / AgNO3 reaction precursor solution A proper amount of HAuCl4 and AgNO3 was dissolved in 25 μL of deionized water to obtain the HAuCl4 / AgNO3 reaction precursor solution, with the concentration of HAuCl4 and AgNO3 being 10 mM and 5 mM respectively. 3) Preparation of paper-based SERS substrate based on the drop injection method The tannic acid-modified green paper-based SERS substrate was prepared by adding 25 μL of the HAuCl4 / AgNO3 reaction precursor solution dropwise on the tannic acid composite filter paper, and then repeating the addition of 25 μL of the HAuCl4 / AgNO3 reaction precursor solution and the absorption of the excess liquid for 2 times after 5 min of reaction.

[0035] 1, 2, 3, 4 and 5 in the table represent the number of times of dropwise addition, and correspond to the results of Examples 6, 7, 3, 8 and 9 respectively. It can be seen that with the increase of the number of times of dropwise addition, the number of Au / Ag nanoparticles generated on the paper gradually increases, and especially when the number of times of dropwise addition reaches 4, the spacing between the nanoparticles is significantly reduced, thus a large number of hot spots are generated, so that the Raman response of methylene blue is significantly enhanced. However, further increase of the HAuCl4 / AgNO3 reaction precursor solution (Example 9) causes the nanoparticles to become larger and the mutual stacking phenomenon to become serious, so that the Raman response of methylene blue is reduced. Figure 3 The application discloses a tannic acid-modified green paper-based SERS substrate, which is used for trace detection of methylene blue in water.

[0036] Step 1, determination of Raman parameters The parameters in the laser confocal microscopic Raman imaging spectrometer are as follows: ​​Excitation wavelength: 785 nm, laser power 10 mW, 50x objective, integration time: 5 s, wave number scan range 200-1800 cm -1 .

[0037] Figure 1a and Figure 1b The results show that the Raman response is low when using HAuCl4 or AgNO3 as the reaction precursor solution alone. When the HAuCl4 and AgNO3 are pre-mixed and then added to the tannic acid treated filter paper, a more obvious Raman enhancement is obtained. The Raman characteristic peak (449 cm -1 ) response of the HAuCl4 / AgNO3 (10 mM / 5 mM) reaction precursor solution of Example 3 is the highest.

[0038] Figure 2a and Figure 2b The results show that the intensity of the methylene blue Raman characteristic peak (449 cm -1 ) significantly increases with the increase of the number of drops. When the number of drops exceeds 4, the characteristic peak intensity does not change significantly (Example 9).

[0039] Step 2, immersion and spectral intensity detection After immersing the above prepared paper-based SERS substrate in 1 mL of the target solution for 30 min, it is taken out and analyzed within 5 s. The spectral data obtained after baseline correction are read for the intensity of the methylene blue target characteristic peak (449 cm -1 ).

[0040] Step 3, linear relationship between logarithmic Raman peak intensity and logarithmic methylene blue concentration: A 10 -4 M methylene blue stock solution is prepared in deionized water (0.0032 g of methylene blue reagent is weighed and dissolved in 10 mL of deionized water), and then sequentially diluted with deionized water to 10 -5 , 10 -6 , 10 -7 , 10 -8 , 10 -9 and 10 -10 M. Taking the logarithmic concentration of methylene blue as the abscissa and the logarithmic SERS response intensity (449 cm -1 ) of methylene blue as the ordinate, it is found that it is linear between the concentration range of 10 -7 ~10 -10 M, the equation y=0.37x+5.60, R 2 =0.9990, as Figure 4The limit of detection (LOD) was calculated as 3.3δ / S, where δ is the standard deviation of the blank samples (n = 6) and S is the slope value from the linear curve equation, LOD = 5.28 x 10 -11 M (0.017 μg / L).

[0041] Step 4 Actual sample analysis Randomly take Bahe River, artificial lake in Shaanxi University of Science and Technology and Weihe River water samples around Xi'an City, Shaanxi Province (n = 30, 30 samples), respectively, immerse for 30 min, then take out, analyze the logarithmic SERS response intensity of each sample solution within 5 s, bring into the equation y = 0.37x + 5.60, after the above analysis, the results show that methylene blue is detected, but the content is lower than 50 μg / L, which is lower than the limit standard of methylene blue in water body in the "Environmental Protection Law of the People's Republic of China".

Claims

1. A method for preparing a tannic acid-modified green paper-based SERS substrate, characterized in that, Includes the following steps: Step 1: Immerse the filter paper in a tannic acid solution and then let it dry naturally to obtain tannic acid-modified filter paper; Step 2: Add a mixed solution of silver nitrate and tetrachloroauric acid to the tannic acid-modified filter paper, then remove the surface liquid to obtain a green paper-based SERS substrate modified with tannic acid.

2. The method for preparing the tannic acid-modified green paper-based SERS substrate according to claim 1, characterized in that, The concentration of the tannic acid solution in step 1 is 4-6 mM.

3. The method for preparing the tannic acid-modified green paper-based SERS substrate according to claim 1, characterized in that, The solvent for the tannic acid solution in step 1 is composed of ethanol and deionized water, with a volume ratio of ethanol to deionized water of 1:

1.

4. The method for preparing the tannic acid-modified green paper-based SERS substrate according to claim 1, characterized in that, Step 1: Immerse the filter paper in a tannic acid solution for 4-6 minutes, then let it air dry.

5. The method for preparing the tannic acid-modified green paper-based SERS substrate according to claim 1, characterized in that, In the mixed solution of silver nitrate and tetrachloroauric acid described in step 2, the concentrations of both silver nitrate and tetrachloroauric acid are 5-10 mM.

6. The method for preparing the tannic acid-modified green paper-based SERS substrate according to claim 5, characterized in that, Step 2: Add 20-30 μL of a mixed solution of silver nitrate and tetrachloroauric acid to the tannic acid-modified filter paper, react for 4-6 min, and then remove the surface liquid.

7. The method for preparing the tannic acid-modified green paper-based SERS substrate according to claim 6, characterized in that, It also includes step 3, which involves repeating step 2 2 to 4 times to obtain a green paper-based SERS substrate modified with tannic acid.

8. A tannic acid-modified green paper-based SERS substrate obtained by the preparation method of the tannic acid-modified green paper-based SERS substrate according to any one of claims 1 to 7.

9. The tannic acid-modified green paper-based SERS substrate according to claim 8, characterized in that, The tannic acid binds to the fiber surface of the filter paper through hydrogen bonds to form a tannic acid modification layer, on which gold nanoparticles and silver nanoparticles are attached.

10. The application of the tannic acid-modified green paper-based SERS substrate as described in claim 8 or 9 in the trace detection of methylene blue in water.

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