A three-dimensional snse2 surface-enhanced raman scattering substrate and a preparation method thereof

Abstract

The application relates to the field of surface-enhanced Raman scattering, and specifically provides a three-dimensional SnSe2 surface-enhanced Raman scattering substrate and a preparation method thereof. The three-dimensional SnSe2 surface-enhanced Raman scattering substrate comprises a filter layer, a plurality of filter holes are arranged on the filter layer, a SnSe2 nanostructure layer is fixedly arranged on the upper side of the filter layer, the SnSe2 nanostructure layer is composed of SnSe2 nanostructures, the SnSe2 nanostructure is SnSe2 nanoflower, the SnSe2 nanoflower covers the filter layer, and the SnSe2 nanoflower blocks the filter holes on the filter layer. No vertical gap exists in the SnSe2 nanoflower structure, which makes the local effect of the SnSe2 nanoflower on a light field better, so that the Raman signal enhancement factor is improved. The preparation method of the three-dimensional SnSe2 surface-enhanced Raman scattering substrate comprises the following steps: S1, preparing SnSe2 nanoflower; S2, preparing an aqueous solution of the SnSe2 nanoflower; and S3, performing suction filtration to obtain the SnSe2 surface-enhanced Raman scattering substrate. The preparation method does not use a molecular beam epitaxy method, and the cost is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of surface-enhanced Raman scattering, in particular, to a three-dimensional SnSe2 surface-enhanced Raman scattering substrate and a preparation method thereof. BACKGROUND

[0002] The photon and the scattering center of Rayleigh scattering are elastic collision, and no energy transfer occurs between them, that is, the frequency of incident light and scattered light is the same. Unlike Rayleigh scattering, the photon and the scattering center of Raman scattering are inelastic collision, and there is energy transfer between the photon and the scattering center, that is, the frequency of scattered light is different from that of incident light. The frequency of scattered light becomes larger and the wavelength becomes shorter, which is called anti-Stokes scattering; the frequency of scattered light becomes smaller and the wavelength becomes longer, which is called Stokes scattering. According to the size of the frequency change, the characteristic peak position of the molecule can be obtained. According to the peak intensity, the corresponding content can be obtained. However, the scattering cross section of Raman scattering is small, only 10 -30 cm 2 , and it is easily affected by the environment, which makes the Raman signal very weak and difficult to be detected.

[0003] The rough noble metal surface can enhance the Raman signal and realize surface-enhanced Raman scattering. The Raman scattering signal of pyridine molecules is increased by 6 orders of magnitude by using the rough silver surface for surface-enhanced Raman scattering. This is because the noble metal material can produce localized surface plasmon resonance phenomenon under the irradiation of light source, and under the action of strong electric field, the Raman signal of the noble metal surface molecule such as gold and silver is enhanced, and a higher Raman signal enhancement factor is obtained. However, the cost of noble metal substrate is high, and the biocompatibility is poor; this limits the wide application of noble metal as surface-enhanced Raman scattering substrate.

[0004] The micro-nano structure composed of zinc oxide and titanium dioxide has a low cost, but has a poor light localization effect and cannot produce a high Raman signal enhancement factor. The document published in the journal "Journal of Materials Chemistry C" titled "Tunable 3D light trapping architectures based on self-assembled SnSe2 nanoplate arrays for ultrasensitive SERS detection" discloses a scheme for preparing SnSe2 nanometer-thick flakes on a glass substrate using molecular beam epitaxy technology. The SnSe2 nanometer-thick flakes stand on the glass substrate, and the light field is localized between the SnSe2 nanometer-thick flakes, so that the SnSe2 nanometer-thick flakes produce a high Raman signal enhancement factor, that is, can enhance the Raman signal of the molecules thereon. Both the above document and the invention patent application with the title "A surface-enhanced Raman scattering substrate and a preparation method" with the publication number "CN113296176A" use molecular beam epitaxy technology to prepare SnSe2 flakes, and the prepared SnSe2 flakes have a good light field localization effect. However, the experimental conditions required by the molecular beam epitaxy technology are very harsh, which increases the cost of the SnSe2 surface-enhanced Raman scattering substrate. At the same time, the plane where the SnSe2 flakes in the existing substrate is perpendicular to the underlying glass sheet, and the localization effect of the vertically incident light field is poor. However, the incident light needs to be strictly perpendicular to the substrate during Raman testing, and for the substrate in the area directly below the incident laser, most of the light field is vertically incident and then vertically exits, without being localized in the SnSe2 flakes. Therefore, the existing SnSe2 flake substrate with a straight shape has a poor localization effect on the vertically incident light field, and thus cannot effectively enhance the Raman effect in the area directly below the incident light.

[0005] In summary, the surface-enhanced Raman scattering substrate with a straight SnSe2 flake structure in the prior art has a poor localization effect on the vertically incident light field, resulting in a poor Raman enhancement effect, and has a high preparation cost. SUMMARY

[0006] The present application aims to solve the problems of the surface-enhanced Raman scattering substrate with a straight SnSe2 flake structure in the prior art, which has a poor localization effect on the vertically incident light field, resulting in a poor Raman enhancement effect, and has a high preparation cost.

[0007] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0008] The application provides a three-dimensional SnSe2 surface-enhanced Raman scattering substrate, which comprises a filter layer, a plurality of filter holes on the filter layer, and a SnSe2 nanostructure layer fixedly arranged on the upper side of the filter layer, wherein the SnSe2 nanostructure layer is composed of SnSe2 nanostructures, the SnSe2 nanostructure is SnSe2 nanoflower, the SnSe2 nanoflower covers the filter layer, and the SnSe2 nanoflower blocks the filter holes on the filter layer.

[0009] Further, the SnSe2 nanoflower is composed of a plurality of "petals" that are staggered and rotated relative to each other, the plane where each "petal" is located is neither perpendicular nor parallel to the plane of the filter layer, and the "petals" are overlapped with each other, and there is no vertical gap in the SnSe2 nanoflower.

[0010] Further, the interval of the SnSe2 nanoflower is less than 50 nm, and the size of the SnSe2 nanoflower is 4.0-8.0 μm.

[0011] Further, the SnSe2 nanoflower is prepared by a solvothermal method, and the preparation steps are as follows:

[0012] S11, preparing a solution; SnCl4·5H2O, NaSeO3 and sodium dodecyl benzene sulfonate with a mass ratio of 10:11:15 are weighed and dissolved in ethylene glycol, and stirring is continued for more than 6 hours until SnCl4·5H2O, NaSeO3 and sodium dodecyl benzene sulfonate are completely dissolved;

[0013] S12, performing a solvothermal reaction in a reaction kettle; the solution obtained in step S1 is transferred to the reaction kettle, and the reaction is performed at 200-250 DEG C for 18-20 h;

[0014] S13, collecting the product and performing a drying treatment; the reaction product is collected by centrifugation, then washed with anhydrous ethanol and deionized water, and finally dried to obtain a gray powder product, which is the SnSe2 nanoflower.

[0015] Further, all the filter holes on the filter layer are blocked by the SnSe2 nanoflower.

[0016] Further, the filter layer is one of a metal mesh, a carbon mesh and a filter paper, and the pore size of the filter hole is 3.0-5.0 μm.

[0017] The application further provides a preparation method of the three-dimensional SnSe2 surface-enhanced Raman scattering substrate, which comprises the following steps:

[0018] S1, preparing the SnSe2 nanoflower;

[0019] S2, preparing an aqueous solution of the SnSe2 nanoflower;

[0020] S3 is filtered to obtain a SnSe2 surface-enhanced Raman scattering substrate.

[0021] Further, step S1 includes the following steps:

[0022] S11, prepare the solution; weigh SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate in a mass ratio of 10:11:15, dissolve them in ethylene glycol, and stir continuously for more than 6 hours until SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate are completely dissolved.

[0023] S12, a solvothermal reaction is carried out in a reactor; the solution obtained in step S1 is transferred to the reactor and reacted at 200-250℃ for 18-20h;

[0024] S13, collect the product and dry it; collect the reaction product by centrifugation, then wash it with anhydrous ethanol and deionized water, and finally dry it to obtain a gray powder product, which is SnSe2 nanoflower.

[0025] Furthermore, step S2 includes: weighing 0.05-0.08g of the gray powder obtained in step S13, dissolving it in 200mL of aqueous solution, and stirring thoroughly to obtain an aqueous solution of SnSe2 nanoflowers.

[0026] Furthermore, step S3 includes: pouring the aqueous solution of SnSe2 nanoflowers obtained in step S2 into a filter flask, performing vacuum filtration, stacking and depositing SnSe2 nanoflowers on filter paper, and the volume of the vacuum-filtered SnSe2 nanoflower aqueous solution is 100-150 mL.

[0027] Compared with existing technologies, the advantages of this invention are as follows: The surface-enhanced Raman scattering substrate proposed in this invention consists of filter paper and a SnSe2 nanoflower structure layer. The plane containing the "petals" of the SnSe2 nanoflowers is not perpendicular to the plane containing the filter paper, but rather forms an angle with it. Furthermore, the SnSe2 nanoflowers are composed of multiple "petals," each with a different rotation direction and angle relative to the filter paper plane. Thus, when light perpendicular to the filter paper plane irradiates the SnSe2 nanoflowers, there are no vertical channels between the "petals" penetrating the filter paper; the vertical light field directly irradiates the SnSe2 nanoflowers. After reflection, the light enters the interior of the SnSe2 nanoflowers and is difficult to escape. This localizes the light field within the SnSe2 nanoflowers, allowing for sufficient interaction with the analyte molecules and improving the Raman signal enhancement factor.

[0028] Meanwhile, the size of the nanoflowers in the SnSe2 nanoflower structure layer is larger than the pore size of the filter paper. Thus, some SnSe2 nanoflowers are located on the filter paper, while others are located at the pores, not on the same plane. Since some are below the pores, the height of the SnSe2 nanoflowers at the pores is less than that of the SnSe2 nanoflowers on the filter paper plane. This results in coupling between the SnSe2 nanoflowers at different heights in the direction perpendicular to the filter paper plane, making it less likely for the light field to escape, further enhancing the localization effect of the light field and improving the Raman signal enhancement factor. Furthermore, the preparation method of this invention does not use molecular beam epitaxy, resulting in lower costs. Attached Figure Description

[0029] Figure 1 The above are the SEM characterization results of SnSe2 nanoflowers in the prior art;

[0030] Figure 2 A schematic diagram of a three-dimensional SnSe2 surface-enhanced Raman scattering substrate provided by the present invention;

[0031] Figure 3 This invention provides a schematic diagram of carrier migration between SnSe2 and the molecules to be detected during operation of a three-dimensional SnSe2 surface-enhanced Raman scattering substrate.

[0032] Figure 4 A schematic diagram of a method for preparing a three-dimensional SnSe2 surface-enhanced Raman scattering substrate provided by the present invention.

[0033] Icons: 1-Filter layer; 2-SnSe2 nanoflower structure layer. Detailed Implementation

[0034] To make the implementation process of this invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings.

[0035] This invention provides a three-dimensional SnSe2 surface-enhanced Raman scattering substrate, comprising a filter layer 1 and a SnSe2 nanoflower structure layer 2. The SnSe2 nanoflower structure layer 2 is fixedly disposed on the upper surface of the filter layer 1. The filter layer 1 can be filter paper with distributed filter pores. The SnSe2 nanoflower structure layer 2 consists of multiple SnSe2 nanoflowers distributed on the filter paper, with each filter pore on the filter paper having a SnSe2 nanoflower. The SnSe2 nanoflowers are composed of multiple "petals" that are staggered and rotated relative to each other. The plane of each "petal" is neither perpendicular nor parallel to the plane of the filter paper, and they overlap each other, so that there are no vertically penetrating gaps between the SnSe2 nanoflowers. The structure of the SnSe2 nanoflowers can be as follows: Figure 1The structure shown is the one characterized by SEM from a master's thesis at Lanzhou University entitled "Preparation of Nano-SnSe2-Based Materials and Study on their NH3 Gas Sensing Performance." This thesis utilizes a solvothermal method combined with a calcination process to prepare SnSe2 nanostructures for NH3 gas detection. The distance between adjacent SnSe2 nanoflowers is less than 50 nm, allowing for strong coupling between them and creating strong lateral coupling to the light field, preventing the light from perpendicularly illuminating the filter paper. The SnSe2 nanoflowers in this invention can also be multiple SnSe2 nanoflower "petals" stacked in layers. A metal mesh or carbon mesh can also be used as the filter layer 1, with a pore size of 3.0-5.0 μm. The filter paper material can be cotton fiber, with a pore size of 3.0-5.0 μm. This invention provides a schematic diagram of a three-dimensional SnSe2 surface-enhanced Raman scattering substrate, as shown below. Figure 2 As shown.

[0036] When incident light shines perpendicularly (towards the normal direction to the plane of the filter paper), even directly below the incident light source, the light does not strike the filter paper directly, but rather the surface of the SnSe2 nanoflowers. Specifically, the light first strikes the upper surface of the "petals" of the surface SnSe2 nanoflowers. Because multiple "petals" are staggered, the initial irradiation point is at different heights at different locations, and the plane orientation of the "petals" varies and they are curved, forming a loose porous structure. The light striking the "petals" of the surface SnSe2 nanoflowers is easily reflected and enters the interior of the SnSe2 nanoflowers. This enhances the localization effect of the SnSe2 nanoflowers on the light field, making it difficult for the light field to escape. Thus, the light field fully interacts with the molecules to be detected inside the SnSe2 nanoflowers. Furthermore, the SnSe2 nanoflowers increase the surface area of ​​the substrate, allowing for the attachment of more target molecules. This further enhances the interaction between the SnSe2 nanoflowers, the light field, and the target molecules. Under the influence of the light field, a greater number of charge carriers migrate between the SnSe2 nanoflowers and the target molecules, thus improving the Raman signal enhancement factor and resulting in better Raman enhancement. A schematic diagram of the electron migration process is shown below. Figure 3As shown, the band gaps of the target molecules are mostly greater than 1 eV. A Type-III heterojunction is formed between the SnSe2 nanoflowers and the target molecules. Electrons migrate from the lowest unoccupied molecular orbitals of the target molecules to the conduction band of SnSe2. Due to the short relaxation time, the migrated electrons and the electrons excited to the conduction band by the photons return to the valence band of SnSe2 together. Finally, they move from the valence band of SnSe2 to the highest occupied molecular orbitals of the target molecules with lower energy. During this process, the carrier migration between the SnSe2 nanoflowers and the target molecules enhances the Raman scattering intensity between the photons and the target molecules, resulting in a better Raman signal enhancement effect.

[0037] The diameter of the pores on the filter paper is smaller than the size of the SnSe2 nanoflowers. This allows some of the SnSe2 nanoflowers at or near the pores to become trapped within them without falling out; in other words, the pores effectively hold the SnSe2 nanoflowers in place. This results in the SnSe2 nanoflowers on the filter paper being at different heights, with those on the filter paper plane being higher than those in the pore area. Under light irradiation, the higher and lower SnSe2 nanoflowers exhibit strong vertical coupling at the boundary between these two regions, with a higher coupling strength along the normal direction of the filter paper plane. This localizes the perpendicularly incident light field between the higher and lower SnSe2 nanoflowers, enhancing the localization effect of the light field and strengthening the interaction between the light field and the molecule being detected, thus improving Raman enhancement.

[0038] On the other hand, the SnSe2 nanoflowers block the filter pores, preventing the molecules to be detected from falling out. This allows more molecules to interact with the local light field, generating a stronger Raman signal. Simultaneously, the height difference of the SnSe2 nanoflowers allows more molecules to remain on the surface of the lower SnSe2 nanoflowers, forming a thin film. The light field reflects multiple times between this film and the surface of the lower SnSe2 nanoflowers. Since the film formed by the molecules is not planar but curved and adheres to the surface of the SnSe2 nanoflowers, and the surface area of ​​the SnSe2 nanoflowers is the sum of the surface areas of each "lobe," the SnSe2 nanoflowers have a larger surface area, resulting in varying gaps between them and the film. The reflection of the light field between them is diffuse reflection, which reflects in all directions. This allows the light field to interact with nearby molecules, increasing the number of molecules interacting with the light field. Consequently, there is more carrier transfer between the SnSe2 nanoflowers and the molecules, resulting in a larger Raman signal enhancement factor and a better Raman signal enhancement effect.

[0039] SnSe2 nanoflowers can be prepared by any method, including chemical vapor deposition, mechanical exfoliation, and solvothermal methods. Preferably, the SnSe2 nanoflowers in this invention are prepared using a solvothermal method, specifically according to the following steps:

[0040] S11, preparing a solution;

[0041] SnSe2 nanoflowers were prepared by a solvothermal reaction using analytically pure SnCl4·5H2O as the tin source, analytically pure NaSeO3 as the selenium source, analytically pure sodium dodecylbenzenesulfonate as the surfactant, and ethylene glycol as the solvent. Specifically, SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate were weighed in a mass ratio of 10:11:15 and dissolved in 200-250 ml of ethylene glycol, wherein the mass of sodium dodecylbenzenesulfonate was 0.25-0.35 g. This method ensures a suitable ratio of tin to selenium source and an appropriate surfactant ratio, enabling the preparation of separated SnSe2 nanoflowers with a size of 4.0 μm-8.0 μm and a petal thickness ranging from tens to hundreds of nanometers. When the surfactant ratio is too high, the formed SnSe2 nanoflowers will aggregate and are difficult to separate during centrifugation. Due to their small specific surface area, the aggregated SnSe2 nanoflowers cannot be irradiated by the light field, resulting in poor Raman enhancement. Conversely, if the surfactant ratio is too low, the prepared SnSe2 will appear as rods or tubes. The resulting solution was thoroughly stirred using a magnetic stirrer for at least 6 hours until SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate were completely dissolved, and the solution became transparent.

[0042] S12 undergoes a solvothermal reaction in the reactor;

[0043] Pour the solution obtained in step S1 into a reaction vessel and react at 200-250℃ for 18-20 hours. When the reaction temperature is high, the reaction time can be appropriately reduced. This temperature and reaction time can prepare SnSe2 nanoflowers. With a shorter reaction time, selenium rods or selenium rods with particles on their surface are obtained. SnSe2 is generated only after the reaction has proceeded for more than 10 hours; before that, it is almost entirely Se. The formation of SnSe2 nanoflowers requires 18-20 hours. The initial heating phase of the reaction lasts 20-30 minutes. After the reaction is complete, allow it to cool naturally to room temperature.

[0044] S13, collect the product and dry it.

[0045] The reaction product, SnSe2 nanoflowers, was collected by centrifugation. It was washed with anhydrous ethanol and deionized water to remove solvent and other impurities as much as possible. Finally, it was dried to obtain gray powdered SnSe2 nanoflowers. The drying temperature could be 60℃, and the treatment time could be greater than 2 hours.

[0046] In use, the molecules to be detected are placed on the side of the SnSe2 nanoflowers away from the filter paper. This invention is applicable to the detection of gaseous or liquid samples. When the sample is a solid powder, the powder needs to be prepared into a solution. The solvent should not react with the sample molecules and should have a certain solubility; it can be water or other organic solvents. For gaseous samples, the substrate of this invention needs to be placed in the atmosphere of the gas to be detected. For liquid samples, the liquid sample needs to be spin-coated or directly drop-coated onto the surface of the SnSe2 nanoflowers. After natural drying, the molecules to be detected adhere to the surface of the SnSe2 nanoflowers, and the internal SnSe2 nanoflower "petals" will also have molecules to be detected attached. The band gap of SnSe2 is 1.0 eV. In order for electrons inside SnSe2 to transition from the valence band to the conduction band, the photon energy emitted by the light source needs to be greater than 1.0 eV, that is, the wavelength of the incident light needs to be less than 1240 nm, while avoiding the characteristic absorption peaks of the molecules to be detected. Under illumination, photons cause electrons in SnSe2 and the target molecule to change from the ground state to the excited state. The electrons in the excited state are not stable, and electron transfer occurs between SnSe2 and the target molecule, thereby enhancing the Raman scattering of photons and the target molecule, increasing the intensity of Raman scattering, and thus enhancing the Raman signal.

[0047] This invention provides a method for preparing the above-mentioned surface-enhanced Raman scattering substrate, the preparation process as follows: Figure 4 As shown, the specific steps are as follows:

[0048] S1, Preparation of SnSe2 nanoflowers;

[0049] This invention employs a solvothermal reaction to obtain SnSe2 nanoflowers, followed by drying and calcination to obtain gray powdered SnSe2 nanoflowers. The specific steps are as follows:

[0050] S11, preparing a solution;

[0051] SnSe2 nanoflowers were prepared by a solvothermal reaction using analytically pure SnCl4·5H2O as the tin source, analytically pure NaSeO3 as the selenium source, analytically pure sodium dodecylbenzenesulfonate as the surfactant, and ethylene glycol as the solvent. Specifically, SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate were weighed in a mass ratio of 10:11:15 and dissolved in 200-250 ml of ethylene glycol, wherein the mass of sodium dodecylbenzenesulfonate was 0.25-0.35 g. This method ensures a suitable ratio of tin to selenium source and an appropriate surfactant ratio, enabling the preparation of separated SnSe2 nanoflowers with a size of 4 μm-8 μm and petal thicknesses ranging from tens to hundreds of nanometers. When the surfactant ratio is too high, the formed SnSe2 nanoflowers will aggregate and are difficult to separate during centrifugation. Due to their small specific surface area, the aggregated SnSe2 nanoflowers cannot be irradiated by the light field, resulting in poor Raman enhancement. Conversely, if the surfactant ratio is too low, the prepared SnSe2 will appear as rods or tubes. The resulting solution was thoroughly stirred using a magnetic stirrer for at least 6 hours until SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate were completely dissolved, and the solution became transparent.

[0052] S12 undergoes a solvothermal reaction in the reactor;

[0053] Pour the solution obtained in step S1 into a reaction vessel and react at 200-250℃ for 18-20 hours. When the reaction temperature is high, the reaction time can be appropriately reduced. This temperature and reaction time can prepare SnSe2 nanoflowers. With a shorter reaction time, selenium rods or selenium rods with particles on their surface are obtained. SnSe2 is generated only after the reaction has proceeded for more than 10 hours; before that, it is almost entirely Se. The formation of SnSe2 nanoflowers requires 18-20 hours. The initial heating phase of the reaction lasts 20-30 minutes. After the reaction is complete, allow it to cool naturally to room temperature.

[0054] S13, collect the product and dry it.

[0055] The reaction product was collected by centrifugation, and the product was identified as SnSe2 nanoflowers. The nanoflowers were washed with anhydrous ethanol and deionized water to remove solvent and other impurities as much as possible. Finally, they were dried to obtain a gray powdery SnSe2 nanoflower.

[0056] S2, preparing an aqueous solution of SnSe2 nanoflowers;

[0057] Weigh 0.05-0.08 g of the powdered SnSe2 nanoflowers obtained in step S13 and dissolve them in 200 mL of aqueous solution. This results in a solution with a suitable concentration, allowing for precise control of the thickness of the SnSe2 nanoflower structure layer 2 via vacuum filtration. If the concentration is too high, the nanoflowers will easily clump together after a short filtration time; if the concentration is too low, they will tend to aggregate locally and not spread evenly on the filter layer 1. After addition, the solution needs to be thoroughly stirred using a magnetic stirrer for at least 2 hours. The resulting aqueous solution of SnSe2 nanoflowers is then obtained.

[0058] S3 is filtered to obtain a SnSe2 surface-enhanced Raman scattering substrate.

[0059] The solution obtained in step S2 is poured into a filter flask, and filter paper is placed between the filter flask and the storage bottle. During vacuum filtration, the aqueous solution of SnSe2 nanoflowers flows from the filter flask into the storage bottle, passing through the filter paper. The pore size of the filter paper is smaller than the size of the SnSe2 nanoflowers, and during filtration, the SnSe2 nanoflowers are deposited on the filter paper. Finally, the filter paper with deposited SnSe2 nanoflowers is removed, and after natural drying, it becomes the three-dimensional SnSe2 surface-enhanced Raman scattering substrate disclosed in this invention. During natural drying, the SnSe2 nanoflower structure layer 2 and the filter layer 1 gradually become fixed together, and there are intermolecular interactions between them. Specifically, the filtered solution is the solution obtained in step S2, and the vacuum filtration volume is 100-150 mL. This allows a layer of tightly arranged SnSe2 nanoflowers to be deposited on the filter paper, without stacking or large spacing between the SnSe2 nanoflowers; at the same time, it ensures that each filter pore is covered by SnSe2 nanoflowers. The filter paper used is 3.0-5.0μm pore size. Alternatively, metal mesh or carbon mesh can be used as filter layer 1, with the pore size still being 3.0-5.0μm. When in use, filter layer 1, after being naturally dried, can be cut to the appropriate size and shape according to actual needs, making it convenient to use.

[0060] The method of this invention does not use molecular beam epitaxy to prepare SnSe2 nanoflowers, and the preparation process is simple and low-cost.

[0061] Preferably, the surface of filter layer 1 has recesses, which are circular in shape and flared outwards, narrower at the inside and wider at the outside. The depth of the recesses is 5-30 μm, and the depth is related to the elasticity coefficient of the filter paper. A lower elasticity coefficient results in a shallower recess, and a higher elasticity coefficient results in a deeper recess, with the maximum extent possible without damaging the filter paper or affecting the filtration function. The size of the recess opening is 20-100 μm, allowing for a larger number of SnSe2 nanoflowers to be accommodated on the bottom and sides of the recess. This results in SnSe2 nanoflowers distributed at different heights, with varying heights within the recesses, on the filter paper surface, and at the filter pores. The higher height of the SnSe2 nanoflowers at different heights enhances the vertical coupling strength between them, thus improving the localization effect on the light field. In other words, carrier transfer occurs between the surface "petals" of some SnSe2 nanoflowers and the middle or bottom "petals" of others, improving photon utilization and enhancing the localization effect of the light field. Simultaneously, adjacent SnSe2 nanoflowers exhibit a certain tilt angle, tending to converge. This results in closer proximity at the tips of the SnSe2 nanoflowers, leading to stronger coupling at the edges. Each SnSe2 nanoflower strongly couples with the tips of surrounding SnSe2 nanoflowers, forming multiple strongly coupled hot spots at the tips. This localizes the light field, resulting in a stronger local light field. Consequently, carrier migration between the nanoflowers and the target molecules is faster, leading to a narrower full width at half maximum (FWHM) of the Raman signal. At the same concentration, the peak intensity is greater, further enhancing the Raman signal. Furthermore, the depressions allow for the aggregation of more target molecules, increasing the number of target molecules and thus strengthening the Raman signal. During preparation, embossing can be performed using an embossing device or sandpaper. Specifically, 160-600 grit sandpaper is required. The grit of the sandpaper is related to the size of the particles on the sandpaper, so that a depression of 20-100μm can be prepared.

[0062] More preferably, unlike the above scheme, a layer of SnSe2 nanosheets is first deposited on filter layer 1, and SnSe2 nanoflowers are fixedly placed on the side of the SnSe2 nanosheets away from filter layer 1. The thickness of the SnSe2 nanosheets is tens of nanometers. This forms a structure with SnSe2 nanosheets at the bottom and SnSe2 nanoflowers on top. The SnSe2 nanoflowers have a stronger coupling strength in the vertical direction. The coupling in the lower SnSe2 nanosheets is almost in-plane, and the upper SnSe2 nanoflowers are coupled with the lower SnSe2 nanosheets, resulting in both planar and vertical coupling. This provides a better localization effect on both the vertical and horizontal components of the light field, making the interaction between the light field and the detectable molecules stronger and enhancing the Raman signal. Simultaneously, the SnSe2 nanosheets prevent the detectable molecules from entering the filter paper. Detectable molecules that enter the filter paper do not contribute to the Raman signal and are not easily detected. The curved SnSe2 nanoflowers are coupled to the approximately planar SnSe2 nanosheets at their lower edges. The light field is not easily emitted from the wedge-shaped gap between the curved and planar surfaces, and is localized within this gap. A large number of target molecules are adsorbed on the sidewalls of the wedge-shaped gap, i.e., on the surfaces of the SnSe2 nanoflowers and SnSe2 nanosheets. Excess target solution remains at the bottom. Therefore, the closer to the bottom, the greater the number of target molecules. The target molecules interact with the localized light field, further enhancing the Raman signal. In preparation, a layer of SnSe2 nanosheets is first deposited on filter paper using a vacuum filtration technique to obtain filter paper with deposited SnSe2 nanosheets; then, a layer of SnSe2 nanoflower structures is deposited on top of this.

[0063] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-dimensional SnSe2 surface-enhanced Raman scattering substrate, the substrate comprising a filter layer having a plurality of filter pores, characterized in that, A SnSe2 nanostructure layer is fixedly disposed on the upper side of the filter layer. The SnSe2 nanostructure layer is composed of SnSe2 nanostructures, which are SnSe2 nanoflowers. The SnSe2 nanoflowers cover the filter layer and block the filter pores on the filter layer.

2. The three-dimensional SnSe2 surface-enhanced Raman scattering substrate according to claim 1, characterized in that, The SnSe2 nanoflower is composed of multiple "petals" that are staggered and rotated. The plane of each "petal" is neither perpendicular nor parallel to the plane of the filter layer, and they overlap with each other. There are no vertically penetrating gaps in the middle of the SnSe2 nanoflower.

3. The three-dimensional SnSe2 surface-enhanced Raman scattering substrate according to claim 2, characterized in that, The spacing between the SnSe2 nanoflowers is less than 50 nm, and the size of the SnSe2 nanoflowers is 4.0 μm-8.0 μm.

4. The three-dimensional SnSe2 surface-enhanced Raman scattering substrate according to claim 3, characterized in that, The SnSe2 nanoflowers were prepared by a solvothermal method, and the preparation steps are as follows: S11, prepare the solution; weigh SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate in a mass ratio of 10:11:15, dissolve them in ethylene glycol, and stir continuously for more than 6 hours until SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate are completely dissolved. S12, a solvothermal reaction is carried out in a reactor; the solution obtained in step S1 is transferred to the reactor and reacted at 200-250℃ for 18-20h; S13, collect the product and dry it; collect the reaction product by centrifugation, then wash it with anhydrous ethanol and deionized water, and finally dry it to obtain a gray powder product, which is the SnSe2 nanoflower.

5. The three-dimensional SnSe2 surface-enhanced Raman scattering substrate according to any one of claims 1-4, characterized in that, All the pores on the filter layer are blocked by the SnSe2 nanoflowers.

6. The three-dimensional SnSe2 surface-enhanced Raman scattering substrate according to any one of claims 1-4, characterized in that, The filter layer is one of a metal screen, a carbon screen, or a filter paper, and the pore size of the filter is 3.0-5.0 μm.

7. A method for preparing a three-dimensional SnSe2 surface-enhanced Raman scattering substrate, characterized in that, The method includes the following steps: S1, Preparation of SnSe2 nanoflowers; S2, prepare an aqueous solution of the SnSe2 nanoflowers; S3 is filtered to obtain a SnSe2 surface-enhanced Raman scattering substrate.

8. The method for preparing a three-dimensional SnSe2 surface-enhanced Raman scattering substrate according to claim 7, characterized in that, Step S1 includes the following steps: S11, prepare the solution; weigh SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate in a mass ratio of 10:11:15, dissolve them in ethylene glycol, and stir continuously for more than 6 hours until SnCl4·5H2O, NaSeO3, and sodium dodecylbenzenesulfonate are completely dissolved. S12, a solvothermal reaction is carried out in a reactor; the solution obtained in step S1 is transferred to the reactor and reacted at 200-250℃ for 18-20h; S13, collect the product and dry it; collect the reaction product by centrifugation, then wash it with anhydrous ethanol and deionized water, and finally dry it to obtain a gray powder product, which is the SnSe2 nanoflower.

9. The method for preparing a three-dimensional SnSe2 surface-enhanced Raman scattering substrate according to claim 8, characterized in that, Step S2 includes: weighing 0.05-0.08g of the gray powder obtained in step S13, dissolving it in 200mL of aqueous solution, and stirring thoroughly to obtain an aqueous solution of the SnSe2 nanoflower.

10. The method for preparing a three-dimensional SnSe2 surface-enhanced Raman scattering substrate according to claim 9, characterized in that, Step S3 includes: pouring the aqueous solution of the SnSe2 nanoflowers obtained in step S2 into a filter flask, performing vacuum filtration, and stacking and depositing the SnSe2 nanoflowers on filter paper. The volume of the filtered SnSe2 nanoflower aqueous solution is 100-150 mL.

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