A composite SERS substrate based on a carbon six-membered ring structure and its preparation method and application

Abstract

The invention discloses a composite SERS substrate based on a carbon six-membered ring structure and a preparation method and application thereof, wherein a PAN solution is firstly spin-coated on a silicon wafer or a silicon nanoarray template, dried, and peeled off to obtain a PAN film or a PAN ordered array film, and then the PAN film or the PAN ordered array film is heated and carbonized to form a carbon six-membered ring structure, and finally gold or silver nanoparticles are modified to obtain a composite SERS substrate based on a carbon six-membered ring structure. The composite SERS substrate prepared by the invention utilizes the p-π and π-π conjugated effects of its carbon six-membered ring structure to realize the adsorption of various organic substances on its surface, achieves the effect of efficient enrichment of organic substances, significantly reduces the detection limit of organic pollutants, and can realize efficient and rapid detection of trace organic pollutants.

Description

Technical Field

[0001] The invention belongs to the technical field of surface enhanced Raman spectroscopy detection, and in particular relates to a composite SERS substrate based on a carbon six-membered ring structure and a preparation method and application thereof. Background Art

[0002] Surface enhanced Raman spectroscopy detection technology has developed rapidly in recent years. It has fast response speed, high sensitivity, and fingerprint effect. It has been widely used in sample analysis, medical testing, environmental protection and other fields. The principle is that when two or more noble metal nanoparticles are very close (less than 10nm), a plasma coupling effect will occur between adjacent nanoparticles, and a strong local electric field can be generated in the gap between them, forming a SERS "hot spot". When the probe molecule enters the SERS "hot spot", the Raman signal of the molecule can be amplified millions of times, achieving highly sensitive detection.

[0003] However, there are still many challenges in detecting organic pollutants using surface enhanced Raman spectroscopy. Most organic molecules are not easy to bind to the SERS substrate, and only a very small amount of molecules can be attached to the substrate surface, which will greatly reduce the SERS signal generated by the substrate. Therefore, it is necessary to develop a SERS substrate that can adsorb organic molecules to solve the above problems. Carbon hexagons can produce p-π and π-π conjugated effects, and have good adsorption effects on organic matter. For example, Chen et al. prepared a SERS substrate by in-situ forming gold nanoparticles on reduced graphene oxide (RGO). RGO, as a porous carbon material, can selectively adsorb and enrich organic molecules, and the well-dispersed gold nanoparticles on RGO enable the SERS substrate to effectively detect adsorbed organic matter (Chen Y, Zhang Y, Fei P, et al, Journal of Biomedical Nanotechnology, 2018, 10 (9): 8169). Shu et al. synthesized sub-nano porous carbon films using 1,4-diacetylbenzene (DAB) and terephthalic acid (TA) as raw materials, added colloidal silver particles to the system, and completed SERS detection of various dyes (Shu Z, Liu Z, Cao H, Chemistry–An Asian Journal, 2020, 15(19): 2992-2995). However, these substrates are not prepared in a standardized manner, have low reproducibility, and cannot be applied on a large scale.

[0004] In summary, the preparation and application of SERS substrates for detecting low-concentration organic pollutants for large-scale application has not yet been achieved. Summary of the invention

[0005] In order to solve the problem that traditional SERS substrates are difficult to adsorb and detect low-concentration organic matter and have poor repeatability, the present invention provides a method for preparing a composite SERS substrate based on a carbon hexagonal ring structure to achieve standardized detection of low-concentration organic pollutants with good repeatability.

[0006] In order to achieve the purpose, the present invention adopts the following technical scheme:

[0007] A method for preparing a composite SERS substrate based on a carbon six-membered ring structure comprises the following steps:

[0008] Step 1: Add PAN powder to DMF and heat in a 60°C water bath until the PAN powder is completely dissolved to obtain a PAN solution with a mass concentration of 8%. Spin-coat the PAN solution on a silicon wafer or a silicon nanoarray template, heat and dry it in a 60°C oven for 2 hours, and remove the film after cooling naturally to room temperature to obtain a PAN film or a PAN ordered array film.

[0009] Step 2, heating and carbonizing the PAN film or the PAN ordered array film to form a carbon hexagonal ring structure to obtain a carbonized film; the heating and carbonization is low-temperature carbonization or high-temperature carbonization;

[0010] The low-temperature carbonization method is as follows: placing the PAN film or the PAN ordered array film in a muffle furnace, heating from room temperature to 270°C at a heating rate of 5°C / min in an air atmosphere, and maintaining the temperature for 2 hours, wherein PAN forms a nitrogen-containing carbon hexacyclic structure under the action of oxygen to obtain a carbonized film, which has a good adsorption effect on nitrogen-containing organic matter;

[0011] The high-temperature carbonization method is as follows: the PAN film is placed in a muffle furnace, and heated from room temperature to 270°C at a heating rate of 5°C / min in an air atmosphere, and kept at a constant temperature for 2 hours. Under the action of oxygen, PAN forms a nitrogen-containing carbon hexagonal ring structure; then the film is heated from room temperature to 900°C at a heating rate of 5°C / min in an argon atmosphere, and kept at a constant temperature for 2 hours, and dehydrogenation and denitrification are achieved at high temperature to obtain a carbonized film, which has a good adsorption effect on organic matter containing benzene rings. The ordered array will be completely destroyed at this temperature, so high-temperature carbonization is only studied on PAN films.

[0012] Step 3, modifying gold or silver nanoparticles on the carbonized film to obtain a composite SERS substrate based on a carbon six-membered ring structure; the method for modifying the gold or silver nanoparticles is a physical sputtering method or an in-situ thermal reduction method.

[0013] The method of modifying gold or silver nanoparticles on the surface of the carbonized film by physical sputtering is: using an ion sputtering instrument, sputtering with high-purity gold or high-purity silver as the target material, respectively, to obtain gold nanoparticles or silver nanoparticles. The sputtering time and conditions affect the size of the nanoparticles, and thus affect the detection sensitivity. The optimal sputtering current is 40mA and the sputtering time is 2 minutes.

[0014] The method of modifying gold or silver nanoparticles on the surface of the carbonized film by in-situ thermal reduction is as follows: after preparing the PAN solution, mix it with the DMF solution of silver nitrate or chloroauric acid, and then spin-coat it on a silicon wafer or a silicon nanoarray template, place it in an oven for heating and drying, and remove the film after naturally cooling to room temperature to obtain a PAN film or a PAN ordered array film. During the carbonization process of the PAN film or the PAN ordered array film, the silver nitrate or chloroauric acid will be in-situ high-temperature decomposed to generate silver nanoparticles or gold nanoparticles. The concentration of the DMF solution of silver nitrate or chloroauric acid affects the size and number of the silver nanoparticles or gold nanoparticles finally formed. Optimally, the concentration of the DMF solution of silver nitrate is 0.6 mol / L, the solubility of the DMF solution of chloroauric acid is 0.4 mol / L, and the mixing ratio of the DMF solution of silver nitrate or chloroauric acid to the 8% PAN solution is 1:1 (volume ratio).

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. The composite SERS substrate prepared by the present invention utilizes the p-π and π-π conjugated effects of its carbon six-membered ring structure to achieve the adsorption of various organic substances on its surface, achieving the effect of efficient enrichment of organic substances, significantly reducing the detection limit of organic pollutants, and realizing efficient and rapid detection of trace organic pollutants. Taking R6G, p-nitroaniline and coumarin as examples, the minimum detection concentrations are 10 -10 mol / L、10 -6 mol / L and 10 -8 mol / L.

[0017] 2. The preparation method of the present invention controls different carbonization temperatures and carbonization environments to cause different cross-linking reactions of PAN during the heating carbonization process, such as dehydration, denitrogenation, dehydrogenation, etc., to produce a nitrogen-containing carbon six-membered ring structure or a pure carbon six-membered ring structure. This structure has a very high similarity with benzene ring-containing organic molecules or polycyclic heterocyclic molecules such as polycyclic aromatic hydrocarbons, thereby achieving efficient adsorption and enrichment of this type of organic molecules.

[0018] 3. The preparation method of the present invention has simple process, environmentally friendly process and low cost, and provides an important method for developing a SERS substrate for detecting low-concentration organic pollutants that can be applied on a large scale.

[0019] 4. The preparation method of the present invention has high repeatability and can achieve standardized preparation, laying an important foundation for its industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a SEM image of the composite SERS substrate obtained in Example 1;

[0021] Figure 2 The SERS spectra of the composite SERS substrate obtained in Example 1 detecting different concentrations of R6G;

[0022] Figure 3 The SERS spectra of the carbonized films obtained at different carbonization temperatures in Example 1;

[0023] Figure 4 is the SEM image of the composite SERS substrate obtained in Example 2;

[0024] Figure 5 The SERS spectra of the composite SERS substrate obtained in Example 2 detecting p-nitroaniline at different concentrations;

[0025] Figure 6 is a SEM image of the composite SERS substrate obtained in Example 3;

[0026] Figure 7 The SERS spectra of coumarin at different concentrations were detected on the composite SERS substrate obtained by high-temperature carbonization of PAN film and sputtering of silver nanoparticles. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. The reference embodiments described below are only for the purpose of explanation but not to limit the present invention in any form.

[0028] Example 1

[0029] The composite SERS substrate based on the carbon six-membered ring structure of this embodiment is prepared according to the following steps:

[0030] Step 1: Add PAN powder to DMF and heat in a 60°C water bath until the PAN powder is completely dissolved to obtain a PAN solution with a mass concentration of 8%. Spin-coat the PAN solution on a silicon wafer, heat and dry it in a 60°C oven for 2 hours, and remove the film after cooling naturally to room temperature to obtain a PAN film.

[0031] Step 2: Place the PAN film in a muffle furnace, and heat it from room temperature to 270°C at a heating rate of 5°C / min in an air atmosphere, and keep the temperature constant for 2 hours. Under the action of oxygen, PAN forms a nitrogen-containing carbon hexacyclic structure to obtain a carbonized film.

[0032] Step 3: Using an ion sputtering apparatus, sputter the carbonized film with high-purity silver as a target material to modify silver nanoparticles on the carbonized film, thereby obtaining a composite SERS substrate based on a carbon six-membered ring structure.

[0033] Figure 1 This is a SEM image of the SERS substrate obtained in this example. It can be seen from the image that the surface of the film after low-temperature carbonization is rough and uneven, but no obvious deformation occurs.

[0034] R6G was dissolved in ethanol to prepare standard solutions of different concentrations, which were then added dropwise to the composite SERS substrate obtained in this example. The samples were detected using a Raman spectrometer with a laser wavelength of 532 nm, a power of 3.5 mW, and an integration time of 5 s. Figure 2 As shown, it can be seen that the lowest detection concentration of R6G is 10 -10 mol / L.

[0035] In order to verify the effect of different carbonization temperatures on the obtained substrate, the carbonization temperatures in step 2 were adjusted to 250°C, 260°C, 270°C, 280°C and 290°C, respectively. Then, the carbonized films obtained at different carbonization temperatures were detected by Raman spectrometer. The results are shown in Fig. Figure 3 As shown, it can be seen that the carbon peak is weakest at 270°C. The higher the carbon peak intensity, the stronger the interference to the detection result, so 270°C is the optimal temperature for low-temperature carbonization.

[0036] Example 2

[0037] The composite SERS substrate based on the carbon six-membered ring structure of this embodiment is prepared according to the following steps:

[0038] Step 1: Add PAN powder to DMF and heat in a 60°C water bath until the PAN powder is completely dissolved to obtain a PAN solution with a mass concentration of 8%. Spin-coat the PAN solution on the silicon nanoarray template, heat and dry it in a 60°C oven for 2 hours, and remove the film after cooling naturally to room temperature to obtain a PAN ordered array film.

[0039] Step 2: Place the PAN ordered array film in a muffle furnace, heat it from room temperature to 270°C at a heating rate of 5°C / min in an air atmosphere, and keep the temperature constant for 2 hours. Under the action of oxygen, PAN forms a nitrogen-containing carbon hexacyclic structure to obtain a carbonized film.

[0040] Step 3: Using an ion sputtering apparatus, sputter the carbonized film with high-purity silver as a target material to modify silver nanoparticles on the carbonized film, thereby obtaining a composite SERS substrate based on a carbon six-membered ring structure.

[0041] Figure 4This is a SEM image of the composite SERS substrate obtained in this example. It can be seen from the image that the substrate has a regular nanorod array structure and the substrate does not undergo obvious deformation after low-temperature carbonization.

[0042] p-Nitroaniline was dissolved in ethanol to prepare standard solutions of different concentrations, which were then added dropwise to the composite SERS substrate obtained in this example. The samples were detected using a Raman spectrometer with a laser wavelength of 532 nm, a power of 3.5 mW, and an integration time of 5 s. Figure 5 As shown, it can be seen that the lowest detection concentration of p-nitroaniline is 10 -6 mol / L.

[0043] Example 3

[0044] The composite SERS substrate based on the carbon six-membered ring structure of this embodiment is prepared according to the following steps:

[0045] Step 1: Add PAN powder to DMF and heat in a 60°C water bath until the PAN powder is completely dissolved to obtain a PAN solution with a mass concentration of 8%. Spin-coat the PAN solution on a silicon wafer, heat and dry it in a 60°C oven for 2 hours, and remove the film after cooling naturally to room temperature to obtain a PAN film.

[0046] Step 2: Place the PAN film in a muffle furnace, and heat it from room temperature to 270°C at a heating rate of 5°C / min in an air atmosphere, and keep it at this temperature for 2 hours. Under the action of oxygen, PAN forms a nitrogen-containing carbon hexacyclic structure. Then, heat the film from room temperature to 900°C in an argon atmosphere at a heating rate of 5°C / min, and keep it at this temperature for 2 hours to achieve dehydrogenation and denitrification at high temperature to obtain a carbonized film.

[0047] Step 3: Using an ion sputtering apparatus, sputter the carbonized film with high-purity silver as a target material to modify silver nanoparticles on the carbonized film, thereby obtaining a composite SERS substrate based on a carbon six-membered ring structure.

[0048] Figure 6 This is the SEM picture of the SERS substrate obtained in this example. At high temperature, the PAN film undergoes dehydrogenation and denitrification reactions, the internal shrinkage is obvious, and there are a large number of cracks on the surface.

[0049] Coumarin was dissolved in ethanol to prepare standard solutions of different concentrations, which were then added dropwise to the composite SERS substrate obtained in this example. The samples were detected using a Raman spectrometer with a laser wavelength of 532 nm, a power of 3.5 mW, and an integration time of 5 s. Figure 2 As shown, it can be seen that the lowest detection concentration of coumarin is 10 -8 mol / L.

[0050] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a composite SERS substrate based on a carbon six-membered ring structure, characterized in that: PAN solution is prepared with PAN powder as raw material and DMF as solvent; the PAN solution is spin-coated on a silicon wafer or a silicon nanoarray template, and the solution is placed in an oven for heating and drying, and the film is removed after natural cooling to room temperature to obtain a PAN film or a PAN ordered array film; The PAN film or the PAN ordered array film is heated and carbonized to form a carbon hexagonal ring structure to obtain a carbonized film; and gold or silver nanoparticles are then modified on the carbonized film to obtain a composite SERS substrate based on the carbon hexagonal ring structure.

2. The method for preparing a composite SERS substrate based on a carbon six-membered ring structure according to claim 1, characterized in that: The PAN solution is prepared by adding PAN powder into DMF, heating in a 60° C. water bath until the PAN powder is completely dissolved, and obtaining a PAN solution with a mass concentration of 8%.

3. The method for preparing a composite SERS substrate based on a carbon six-membered ring structure according to claim 1, characterized in that: The heating carbonization is low temperature carbonization or high temperature carbonization; The low-temperature carbonization method is as follows: placing the PAN film or the PAN ordered array film in a muffle furnace, heating from room temperature to 270° C. at a heating rate of 5° C. / min in an air atmosphere, and maintaining the temperature for 2 hours, wherein PAN forms a nitrogen-containing carbon hexacyclic structure under the action of oxygen to obtain a carbonized film; The high-temperature carbonization method is as follows: the PAN film is placed in a muffle furnace, and in an air atmosphere, heated from room temperature to 270°C at a heating rate of 5°C / min, and kept at a constant temperature for 2 hours, so that PAN forms a nitrogen-containing carbon hexacyclic structure under the action of oxygen; and then the film is heated from room temperature to 900°C in an argon atmosphere at a heating rate of 5°C / min, and kept at a constant temperature for 2 hours, so as to achieve dehydrogenation and denitrification at high temperature and obtain a carbonized film.

4. The method for preparing a composite SERS substrate based on a carbon six-membered ring structure according to claim 1, characterized in that: The method for modifying the gold or silver nanoparticles is a physical sputtering method or an in-situ thermal reduction method.

5. The method for preparing a composite SERS substrate based on a carbon six-membered ring structure according to claim 3, characterized in that: The composite SERS substrate obtained by low-temperature carbonization has a good adsorption effect on nitrogen-containing organic matter, and the composite SERS substrate obtained by high-temperature carbonization has a good adsorption effect on organic matter containing benzene rings.

6. A composite SERS substrate based on a carbon six-membered ring structure obtained by the preparation method according to any one of claims 1 to 5.

7. An application of the composite SERS substrate based on a carbon six-membered ring structure according to claim 6, characterized in that: Used to adsorb organic matter to achieve its SERS detection.

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