Optical fiber SERS (Surface Enhanced Raman Scattering) sensing method for in-situ monitoring and degradation of thiram in water body

Abstract

The invention discloses a method for synchronously monitoring and degrading thiram in a water body based on an Au-TiO-plated optical fiber surface enhanced Raman scattering (SERS) sensor, and belongs to the technical field of application of an optical fiber sensing technology to photocatalysis. The invention provides an optical fiber SERS (Surface Enhanced Raman Scattering) sensing technical method integrating trace detection and photocatalytic degradation functions aiming at the problems of long detection period, incapability of in-situ monitoring, lack of synchronous degradation capability and the like in the existing pesticide residue detection method. The Au-TiO composite catalytic layer is constructed on the end face of the optical fiber, high-sensitivity Raman enhanced detection of thiram bimolecules is achieved, and target pollutants are synchronously degraded under ultraviolet irradiation by utilizing the photocatalytic performance of TiO. The device solves the problem that in-situ monitoring and rapid treatment of pesticide residues are difficult to realize in the prior art, has the advantages of being compact in structure, suitable for field application and the like, realizes integration of detection and treatment, and is suitable for rapid response and treatment of pesticide pollution in typical water environments such as agricultural drainage and drinking water sources.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber sensing technology applied to monitoring photocatalytic reaction, and relates to a Raman spectrum monitoring method for monitoring a photocatalytic thiram degradation process in real time, which is composed of an optical fiber SERS sensor. BACKGROUND

[0002] Thiram is a widely used high-efficiency low-toxicity fungicide and widely exists in agricultural planting environments. However, thiram has strong water solubility and a long residual time, which causes potential threats to the ecological system and human health.

[0003] Research on the degradation process of pollutants in the environment is crucial for environmental protection. In-depth understanding of the degradation mechanism of pollutants not only helps to optimize the treatment scheme, improve the treatment effect, and improve the quality of air, water and soil, but also maintains the ecological balance and reduces the negative impact on the ecological system. The current widely used pesticide analysis methods mainly include gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. These two methods have large equipment volume, high price, and high requirements for personnel and sample pretreatment during operation, which makes it difficult to meet the demand of on-site instant detection.

[0004] Surface-enhanced Raman scattering (SERS) technology is widely used for trace pollutant detection due to its high sensitivity, label-free and fast response. The combination of SERS technology and photocatalytic degradation function can realize the integration of detection and degradation of pollutants. Optical fibers have the advantages of flexibility, insertability and small volume, which are suitable for building portable and in-situ analysis systems. Traditional Raman detection methods need to move the measured liquid to the SERS substrate, and the combination of optical fiber and SERS technology can simplify the operation and be convenient and fast. The combination of optical fiber, SERS and photocatalysis has important significance for the application of optical fiber SERS sensing probe in the field of photocatalysis to study the properties and performance of catalysts, reaction kinetics and degradation process on the surface of catalysts. SUMMARY

[0005] The application aims to provide an end-face optical fiber SERS sensor for monitoring the interaction of pollutants and dyes in the photocatalytic degradation process and a monitoring method thereof. The application aims to solve the problems that the degradation process of pesticide molecules based on photocatalytic research cannot be monitored in real time, it is difficult to adapt to the needs of in-depth micro research, and it is difficult to explain the reaction mechanism.

[0006] The application is achieved by the following technical means:

[0007] The application relates to an application system for in-situ Raman spectrum of a pesticide pollutant thiram in a water body in a photocatalytic process by using an end-face optical fiber SERS sensor for real-time monitoring, which comprises a 758 nm laser, a portable Raman spectrometer, a Raman probe, an ultraviolet lamp and an optical fiber SERS sensor. The 785 nm laser, the portable Raman spectrometer and the Raman probe are connected, the Raman probe is modified into an FC interface and connected with the optical fiber SERS sensor, and the optical fiber SERS sensor is inserted into a sample cell.

[0008] The catalyst is selected from Au-TiO2.

[0009] In the technical solution, spherical gold nanoparticles synthesized by a traditional sodium citrate reduction method are combined with TiO2. Specifically, 0.239 g of titanium dioxide powder is added into 100 ml of pure water, the water is ultrasonically treated for 30 min, about 1 ml of chloroauric acid is added into the titanium dioxide dispersion liquid, the temperature and rotating speed of a magnetic stirrer are adjusted to uniformly disperse the solution, about 1.0 ml of 1 % sodium citrate is added when the solution is in a boiling and stirring state and reacts for a period of time, and when the solution color changes, it is indicated that Au-TiO2 has been synthesized in the solution. The Au-TiO2 solution is washed and centrifuged with ethanol for three times, heated in a drying oven for 12 h, and then dried in a muffle furnace.

[0010] Further, the catalyst is modified on the end face of the optical fiber by a chemical self-assembly method to realize preparation of the end-face optical fiber SERS sensor.

[0011] In the technical solution, the optical fiber SERS sensor probe comprises the following manufacturing steps.

[0012] In step S1, a multimode optical fiber is cut to a required length, the coating layer and the cladding layer at one end are removed by using an optical fiber hot stripping clamp, and then the optical fiber is cleaned by using a plasma cleaning machine. The end face of the cleaned optical fiber is subjected to hydroxylation treatment, is immersed in an aiptasia solution for reaction for 30 min, is immersed in a 10 % APTES solution for 1 h, is cleaned with ethanol, and is dried at 80 DEG C for 30 min to realize surface silanization treatment.

[0013] In step S2, the silanized end face of the optical fiber is placed in a catalyst dispersant solution prepared in advance for incubation for 30 min, and preparation of the optical fiber SERS sensor is completed.

[0014] In the step S1, the aiptasia solution is prepared by mixing concentrated sulfuric acid and 30 % hydrogen peroxide at a volume ratio of 3:1.

[0015] In the step S2, the catalyst is first aminated, 0.0048 g of Au-TiO2 is weighed, ultrasonic dispersed in 10% ethanol, and 0.5 ml of APTES is added dropwise, and dispersed by using an adjustable vortex mixer, and left overnight. The supernatant is taken out, washed with ethanol, and then centrifuged. The centrifuged Au-TiO2 is dissolved in 10 ml of ethanol, i.e. 0.4 mg / ml of dispersant.

[0016] In the technical solution, different concentrations of thiram solution are configured. The sample solution is connected with the optical fiber SERS sensing probe, and the sample solution is irradiated by an ultraviolet lamp. In the degradation process of thiram, the changes are observed in real time by monitoring the in-situ Raman spectrum.

[0017] The optical fiber SERS sensing probe detects the thiram solution sample, comprising the following steps:

[0018] In step S1, the thiram sample solution is mixed with the gold nanoparticle sol in a centrifuge tube.

[0019] In step S2, the sensing area of the optical fiber SERS sensing probe is immersed in the solution obtained in S1 for surface-enhanced Raman spectrum detection.

[0020] In the step S1, the concentration of the thiram solution ranges from 1 μg / ml to 500 μg / ml.

[0021] Advantages of the present application:

[0022] Firstly, the preparation process of the catalyst modified on the end face of the optical fiber by the chemical self-assembly method is simple and efficient. The method utilizes the principle of molecular layer self-assembly to make the catalyst spontaneously deposit on the end face of the optical fiber, forming an ordered and dense Au-TiO2 particle layer. This not only realizes uniform coverage of the end face, but also provides superior chemical bonding and surface enhancement effect. In addition, the method does not require complex equipment and conditions, reduces the preparation cost, and makes the preparation of the optical fiber end face SERS sensor more economical and feasible.

[0023] Secondly, compared with the traditional gas chromatography and ultraviolet-visible absorption spectrum method, the present application solves the demand for in-situ and real-time monitoring of the degradation process by the traditional gas chromatography and ultraviolet-visible absorption spectrum method, develops a characterization technology for in-situ monitoring of the interface dynamic evolution process of pollutants based on Raman spectrum technology, which provides a molecular level theoretical basis for real-time monitoring of degraded water pollutants and understanding of the degradation mechanism.

[0024] Thirdly, optical fiber has the advantages of small size and strong corrosion resistance. By combining optical fiber sensing technology with SERS spectral monitoring, a SERS-based optical fiber sensor is prepared to realize real-time in-situ monitoring of pesticide pollutant degradation. The optical fiber SERS sensor has high sensitivity and selectivity, which can provide more accurate and comprehensive monitoring data and further reveal the internal reaction mechanism of the degradation process. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The application system structure diagram for in-situ monitoring of dye pollutants based on the end-face optical fiber SERS sensor.

[0026] Figure 2 The structure diagram of the end-face optical fiber SERS sensor.

[0027] Figure 3 The Raman spectrum measurement diagram of different concentrations of thiram.

[0028] Figure 4 The function relationship between the Raman intensity at 1379 cm -1 and the concentration of thiram.

[0029] Figure 5 The in-situ Raman spectrum measurement diagram of thiram at different times under ultraviolet light irradiation.

[0030] In the figure, 1 is a 785 nm laser, 2 is a portable Raman spectrometer, 3 is a spectrum acquisition system, 4 is a Y-type optical fiber, 5 is a Raman probe, 6 is an FC interface coupler, 7 is an optical fiber SERS sensing probe, 8 is a sample cell, 9 is an ultraviolet lamp, 10 is an optical fiber coating layer, 11 is an optical fiber cladding layer, 12 is a laser emission beam, 13 is a laser reflection beam, 14 is an optical fiber end-face sensing area, and 15 is Au-TiO2. DETAILED DESCRIPTION

[0031] Unless otherwise specified, the experimental methods used in the following specific examples are conventional methods. The materials, reagents, methods and instruments used are general materials, reagents, methods and instruments in the field, which can be obtained through commercial channels, unless otherwise specified.

[0032] Example 1:

[0033] Synthesis of Au-TiO2 catalyst: Since the preparation process contains gold nanoparticles, the nanoparticles belong to colloidal solution, and the surface impurities of experimental instruments can cause the aggregation of nanoparticles. Before synthesis, all the glass instruments used must be immersed in aqua regia for 2 h, washed thoroughly with deionized water and dried to ensure that there is no impurity on the surface of the experimental instrument. In a 250 ml round-bottom flask, mix 0.239 g titanium dioxide powder and 100 ml deionized water, ultrasonic for 30 min, and add 1 ml chloroauric acid, stir and heat to boiling, add 1.0 ml 1 % sodium citrate solution, continue to stir for 15 min, and change the color of the solution, indicating that Au-TiO2 has been synthesized in the solution. After the Au-TiO2 solution is washed with ethanol and centrifuged three times, it is heated in a drying oven at 80 °C for 12 h, and then placed in a muffle furnace at 400 °C for 4 h.

[0034] Example 2:

[0035] Preparation of end-face optical fiber: A multimode silica optical fiber with a core diameter of about 200 μm, a cladding diameter of about 220 μm, and a numerical aperture of 0.22 is selected as the base material of the sensing probe. The optical fiber is cut to a length of about 15 cm to facilitate subsequent operation and system integration. The outer coating and part of the cladding of the optical fiber are removed by using a special hot stripping pliers for optical fiber, and a bare core region of about 1 cm in length is exposed. Then, the end is cut and polished using an optical fiber cutting knife, obtaining a smooth fiber cross section, which provides a good foundation for subsequent functional modification.

[0036] Example 3:

[0037] Amino treatment of the catalyst: Weigh Au-TiO2 0.0048 g, add 10% ethanol and ultrasonic dispersion, and add 0.5 ml APTES dropwise, use adjustable vortex mixer to stir and disperse, and stand overnight. The supernatant is removed, washed with ethanol and then centrifuged. The centrifuged Au-TiO2 is dissolved in 10 ml ethanol, i.e. 0.4 mg / ml dispersant.

[0038] Example 4:

[0039] Preparation of end-face optical fiber SERS sensor: cleaning with plasma cleaning machine. Hydroxylation treatment is performed on the end face of the optical fiber, which is immersed in an arowana solution prepared by mixing concentrated sulfuric acid and hydrogen peroxide at a volume ratio of 3:1, and reacted at 65 °C for 30 min to introduce hydroxyl functional groups. After hydroxylation treatment, the optical fiber end face is immersed in a 10% 3-aminopropyltriethoxysilane (APTES) ethanol solution for 1 h to construct a functionalized organic silane molecular interface layer. After sufficient cleaning with ethanol, it is dried at 80 °C for 30 min to complete the surface silanization modification. The treated optical fiber end face is immersed in a uniform dispersion liquid containing Au-TiO2 composite catalytic material for 30 min, so that the catalytic nanomaterials self-assemble on the end face of the optical fiber to form a composite film layer with SERS activity and photocatalytic function, thereby obtaining the final optical fiber SERS sensing probe. The structure of the optical fiber SERS sensing probe 7 is shown in Figure 2 .

[0040] Example 5:

[0041] Preparation of different concentrations of thiram solution: Figure 1 The structure of the optical fiber SERS sensing system of the present application is schematically shown. The optical fiber SERS sensing system detects thiram samples, which comprises the following steps:

[0042] Step S1: Mix deionized water and methanol at a volume ratio of 7:3 uniformly as a basic detection solution. Accurately weigh different amounts of thiram particles as needed, and disperse them into the prepared mixed solution to prepare samples of different concentrations. Before detection, take 100 μL of centrifuged gold nanoparticle solution and mix it with the above-mentioned spiked sample as the final solution to be tested. The spiked concentration of thiram in the sample is set to 1 μg / mL to 500 μg / mL.

[0043] Step S2: Immerse the sensing area 14 of the optical fiber SERS sensing probe in the solution obtained in S1 for surface-enhanced Raman spectrum detection.

[0044] The working principle of the Raman spectrum application system for monitoring the in-situ Raman spectrum of thiram is as follows: Figure 1 and Figure 2, the optical fiber SERS sensing probe 7 is connected to one end of the Raman probe 5 through the improved FC interface coupler 6, the other end of the Raman probe 5 is connected to the Y-shaped optical fiber 4, two branches of the Y-shaped optical fiber 4 are respectively connected to the 785 nm laser 1 and the portable Raman spectrometer 2; the optical fiber SERS sensing probe 7 is inserted into the sample cell 8; the sample cell 8 is irradiated by the ultraviolet lamp 9; the light beam 12 emitted by the 785 nm laser 1 enters the optical fiber SERS sensing probe 5, and total reflection occurs, part of the photons interact with the molinate molecules in the sample cell 8, so that the frequency of the scattered light changes, and then the scattered signal is collected and transmitted to the spectrum collection system 3 through the optical fiber reflection path 13, so that the structure and chemical composition of the molecules in the sample and other information are obtained.

[0045] The surface-enhanced Raman spectrum detection result is shown in the following table: Figure 3 The Raman characteristic peaks of the molinate molecules are shown at 925, 1143 and 1379 cm -1 , and the characteristic peak at 1379 cm -1 is the strongest. With the change of the concentration of the molinate in the sample, the intensity of the characteristic peaks in the Raman spectrum also shows a clear response trend. When the concentration of the molinate in the sample decreases, the intensity of each characteristic peak also decreases, and the detection limit of the optical fiber SERS sensing probe 7 for the molinate in the sample can reach 1 μg / ml.

[0046] Constructing a linear determination model: the functional relationship curve between the Raman intensity at 1379 cm -1 and the concentration of the molinate is shown in the following table: Figure 4 In the concentration range of 1 μg / ml-500 μg / ml, the Raman intensity I at 1379 cm -1 of the molinate sample has a good linear relationship with the sample concentration C, the linear fitting degree R 2 is 0.9891, which indicates that the optical fiber SERS sensing probe 7 has a certain quantitative detection capability for the molinate in a sample with an unknown concentration.

[0047] Example 6:

[0048] The working principle of the Raman spectrum application system for in-situ Raman spectrum of thiram under different time irradiation of ultraviolet lamp is as follows: the optical fiber SERS sensing probe 7 is inserted into the sample pool 8 to be detected, so that the end face of the optical fiber is in sufficient contact with the water solution containing thiram; the pretreatment is carried out in the dark environment for a certain time to promote the thiram molecules to be deposited on the Au-TiO2 composite active sites on the surface of the optical fiber sensing area 14 through physical adsorption; after the adsorption process is completed, the ultraviolet lamp 9 is turned on to irradiate the sample, so that the photocatalytic activity of the TiO2 component is excited, and thus the degradation reaction of the thiram molecules is triggered; during the irradiation, the Raman signal change of the target molecules is collected in real time through the optical fiber SERS probe, so that the dynamic monitoring and reaction process analysis of the degradation process of thiram are realized. Under the irradiation of the ultraviolet light 9, the Au-TiO2 composite catalyst generates electron-hole pairs (e - / h + ) by exciting TiO2, and the gold nanoparticles can capture electrons to inhibit the recombination and enhance the photocatalytic activity. During the catalytic degradation process, the C-H and C-N bonds in the thiram molecules are the main reaction sites, which are attacked by the photo-generated holes and active oxygen species (·OH, ·O2 - ), and then broken, so that the molecular skeleton is disintegrated. The catalytic degradation process is monitored by the change of the Raman spectrum characteristic peaks.

[0049] Figure 5 Fig. 1 is a schematic diagram of the Raman spectrum application system for in-situ Raman spectrum of thiram under different time irradiation of ultraviolet lamp. Fig. 2 is the in-situ Raman spectrum measurement diagram of thiram under different time irradiation of ultraviolet lamp. With the increase of the irradiation time of the ultraviolet lamp, the Raman characteristic peaks of the thiram molecules, such as 1143 cm -1 and 1379 cm -1 , gradually decrease, which indicates that the key chemical bonds are broken, the molecular structure is destroyed, and the degradation effect is significant.

Claims

1. A surface enhanced Raman scattering (SERS) method for in-situ monitoring and degradation of thiram in water bodies, characterized in that, The method integrates a functionalized optical fiber probe with SERS activity and a photocatalytic degradation unit, the functionalized optical fiber probe is composed of a multimode quartz optical fiber, the end face of which is modified with a composite layer of metal nanostructures and photocatalytic material, for simultaneously realizing high-sensitivity Raman signal acquisition and photocatalytic degradation reaction of furmidine; the optical fiber SERS probe is inserted into the water body to directly detect the target pollutant in situ and realize real-time catalytic degradation.

2. The fiber-optic SERS method for monitoring and degrading of thiram in situ according to claim 1, characterized by, The surface of the optical fiber sensing area (14) of the optical fiber SERS sensing probe (7) is modified with a catalyst Au-TiO2 (15) by a chemical method. The preparation method is as follows: a multimode quartz optical fiber jumper with an FC interface is selected and cut to a predetermined length, a wire stripper is used to remove the protective coating layer at one end of the optical fiber to expose the bare fiber, an optical fiber cutter is used to obtain a flat optical fiber end face, the optical fiber end is cleaned and dried to remove surface impurities and moisture; the optical fiber end face is subjected to hydroxylation treatment, and is immersed in an aiptasia solution at 65 DEG C for 30 min; then the optical fiber end face is immersed in a 10% 3-aminopropyl triethoxysilane (APTES) ethanol solution for 1 h, and is thoroughly cleaned with ethanol and dried at 80 DEG C for 30 min to complete the surface silanization modification; the treated optical fiber end face is immersed in a uniform dispersion liquid containing Au-TiO2 composite catalyst material for 30 min, thereby obtaining the final optical fiber SERS sensing probe.

3. A method for the application of a fiber-optic SERS sensing system for in situ monitoring and degradation of thiram in water bodies, characterized by, The application method system comprises a 785 nm laser (1), a spectrum acquisition system (3), a portable Raman spectrometer (2), a Y-shaped optical fiber (4), a Raman probe (5), an FC interface coupler (6), an optical fiber SERS sensing probe (7), a sample cell (8) and an ultraviolet lamp (9). The FC interface coupler is used to connect the Raman probe (5) with the optical fiber SERS sensing probe (7) with an FC interface; the Y-shaped optical fiber (4) is used to connect the 785 nm laser (1), the portable Raman spectrometer (2) and the Raman probe (5); the optical fiber SERS sensing probe (7) is inserted into the sample cell (8); and the ultraviolet lamp (9) irradiates the sample cell (8).

4. The application method of the optical fiber SERS sensing system for monitoring and degrading of thiram in situ according to claim 3, characterized in that, The optical fiber SERS sensing probe (7) detects the furmidine sample, and the steps are as follows: deionized water and methanol are mixed in a volume ratio of 7:3 to prepare a basic detection solution. Different amounts of furmidine particles are accurately weighed as needed and dispersed in the prepared mixed solution to prepare samples with different concentrations. Before detection, 100 μL of centrifuged gold nanoparticle solution is mixed with the above-mentioned standard sample as the final detection solution. The sensing area (14) of the optical fiber SERS sensing probe is immersed in the prepared solution for surface-enhanced Raman spectrum detection.

5. The application method of the optical fiber SERS sensing system for monitoring and degrading of thiram in situ according to claim 4, characterized in that, The standard concentration of furmidine in the sample is set to 1 μg / mL to 500 μg / mL.

6. The application method of the optical fiber SERS sensing system for monitoring and degrading of thiram in situ according to claim 4, characterized in that, The optical fiber SERS sensing probe (7) is inserted into a sample pool (8) to be measured, so that the optical fiber end face fully contacts a water solution containing thiram; a pretreatment is performed in the absence of light, and a dark environment is maintained for a certain time to promote thiram molecules to be deposited on Au-TiO2 composite active sites on the surface of the optical fiber sensing area (14) through physical adsorption; after the adsorption process is completed, an ultraviolet lamp (9) is turned on to irradiate the sample, the photocatalytic activity of the TiO2 component is excited, and thus a degradation reaction of thiram molecules is triggered; during the irradiation, the Raman signal change of the target molecules is collected in real time through the optical fiber SERS probe, and dynamic monitoring and reaction process analysis of the thiram degradation process are realized.

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