Zeolite-based SERS (Surface Enhanced Raman Scattering) composite substrate material and preparation method and application thereof

Abstract

The invention relates to a zeolite-based SERS (Surface Enhanced Raman Scattering) composite substrate material as well as a preparation method and application thereof, the SERS composite substrate material is of a double-layer structure, the lower layer is zeolite with a porous structure, and the upper layer is of a metal nanostructure; the specific surface area of the zeolite is 400 m < 2 > / g to 1100 m < 2 > / g; according to the metal nanostructure, the thickness of the nanolayer ranges from 50 nm to 300 nm, and nanometal comprises any one of metal gold, silver or gold-silver alloy. The SERS composite substrate material not only can be used for detecting the VOCs of the asphalt in a gas phase system, but also has the lower detection limit of 8ppm on typical pollutants such as methylbenzene and acetone in the VOCs of the asphalt and the lower detection limit of 6ppm on 2-methylpentane on the basis of the SERS technology, and has higher detection sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of gas phase molecule detection, and more specifically to a zeolite-based SERS composite substrate material and a preparation method and application thereof. Background Art

[0002] Asphalt material is an organic gelling material composed of complex organic hydrocarbons and their derivatives. It is now widely used in waterproofing projects, road construction and other fields. However, due to the high molecular polymer properties of asphalt materials themselves, they will release volatile organic compounds (VOCs) under the influence of environmental factors such as temperature and light, becoming an important precursor of fine particulate matter (PM2.5) and ozone (O3), posing a huge threat to the human body and the atmospheric environment. There are hundreds of types of compounds in asphalt VOCs. For example, the VOCs target calibration compounds selected in patent CN 114019074A mainly include aliphatic hydrocarbons, aromatic hydrocarbons, oxygen-containing hydrocarbons and halogenated hydrocarbons. Typical pollutant components include toluene, acetone, 2-methylpentane, etc. However, the content of asphalt VOCs is usually low. Studies have shown that the VOCs concentration range of asphalt pavement is 46.69~2179μg / m 3 , among which aromatic hydrocarbons are the main pollutants, accounting for more than 70% of the total concentration.

[0003] The existing commonly used detection and analysis method for asphalt VOCs is gas chromatography-mass spectrometry analysis. Although it has the advantages of strong separation ability, high sensitivity, and rich structural information, it needs to be transported to a professional laboratory for detection and analysis due to factors such as complex and expensive instruments and equipment, long analysis time, cumbersome procedures, high costs, and susceptibility to human operation. It is difficult to achieve real-time and rapid detection on-site, and it will also increase the secondary pollution of the samples to be tested due to the transportation process. This greatly limits its application in the actual detection and analysis of VOCs pollutant emissions from asphalt in road projects.

[0004] Surface-Enhanced Raman Scattering (SERS) is a "fingerprint recognition" technology that uses substrate materials such as metal nanostructures to enhance Raman signals and provide information about the material structure of the analyte by giving the vibration spectrum of the analyte. However, this detection technology requires that the analyte is adsorbed on the metal surface through chemical or physical effects and is located within a specific electromagnetic field enhancement range. The choice of its substrate material will also have a significant impact on the detection effect and application scenarios of the SERS technology.

[0005] At present, the research based on SERS technology at home and abroad is mainly aimed at the detection of organic pollutants in liquid samples. Among them, commonly used metal nanostructures such as gold nanoparticles and silver nanoparticles are mainly used to detect and analyze molecules with thiol and amino groups in water systems. However, weakly adsorbed molecules such as benzene, toluene and polycyclic aromatic hydrocarbons are difficult to adsorb on the metal surface; and composite substrate materials such as the double-layer structure substrate material in patent CN104749161B (the lower layer is a gold film with a gold nanoparticle structure, and the upper layer is a polydimethylsiloxane film), based on the adsorption properties of polydimethylsiloxane (PDMS), PDMS is covered on the surface of the gold film to make an Au-PDMS composite substrate, and the physical adsorption effect of the PDMS film is used to fix and enrich the weakly adsorbed molecules, thereby realizing the detection of substances such as toluene, benzene and nitrobenzene in the water system.

[0006] However, compared with the water system, the concentration of gas molecules is lower, and the time it takes for them to reach adsorption equilibrium on the solid surface is short, making them difficult to capture, resulting in slow research progress in the field of gas-phase molecular detection using SERS technology. Although the substrate material MOF@Au / Ag can be used for gas-phase SERS detection research, the MOF material is an organic framework structure, and its own Raman peak easily overlaps with the characteristic peak of the asphalt VOCs component, causing interference and affecting the test effect and accuracy. In addition, the MOF preparation process is complex and costly, which is not conducive to practical promotion and application. In fact, there have been no reports on the detection of asphalt VOCs based on the surface enhanced Raman scattering effect. Therefore, studying a SERS substrate material suitable for asphalt VOCs detection can promote the application of SERS technology in asphalt VOCs detection, which is conducive to the in-situ rapid detection of VOCs in the on-site environment of asphalt pavement. Summary of the invention

[0007] In view of the above defects or improvement needs of the prior art, the present invention provides a zeolite-based SERS composite substrate material and its preparation method and application, the purpose of which is to find a SERS composite substrate material that can be used to detect asphalt VOCs in a gas phase system, which has a double-layer structure, wherein the lower layer has a specific surface area of ​​400m 2 / g-1100m 2 / g of zeolite, the upper layer is a metal nanolayer structure with a thickness of 50nm-300nm, and the SERS composite substrate material has a detection limit of 8ppm for typical pollutants such as toluene and acetone in asphalt VOCs, and a detection limit of 6ppm for 2-methylpentane, thereby solving the technical problem that the existing metal nanostructured substrate materials cannot be used to detect asphalt VOCs in the gas phase system.

[0008] To achieve the above object, according to one aspect of the present invention, a SERS composite substrate material prepared based on zeolite is provided, wherein the composite substrate material is a double-layer structure, wherein the lower layer is a porous zeolite, and the upper layer is a metal nanostructure;

[0009] The zeolite has a specific surface area of ​​400 m 2 / g-1100m 2 / g;

[0010] The metal nanostructure has a nanolayer thickness of 50nm-300nm, wherein the nanometal includes any one of metal gold, silver or a gold-silver alloy.

[0011] Preferably, the zeolite in the SERS composite substrate material is an acid-pretreated zeolite with a specific surface area of ​​700 m 2 / g-1100m 2 / g, pore size is 0.5nm-2nm;

[0012] The size of the nano metal is 30nm-100nm, and the shape is any one of sphere, rod and flower.

[0013] Preferably, in the metal nanostructure of the SERS composite substrate material, the nanometal is nanosilver, and the thickness of the nanolayer is 150nm-200nm.

[0014] According to another aspect of the present invention, a method for preparing the SERS composite substrate material according to the present invention is also provided, which comprises the following steps:

[0015] With a specific surface area of ​​400m 2 / g-1100m 2 / g of zeolite as a substrate, coating a metal nanosol with a size of 30nm-100nm on the surface of the zeolite, and obtaining the SERS composite substrate material after drying and curing, wherein the thickness of the metal nanolayer on the substrate material is 50nm-300nm;

[0016] The metal nanosol includes silver nanosol, and the concentration of the metal nanosol is 0.1M-0.5M.

[0017] Preferably, in the preparation method, the zeolite is a zeolite that has been pretreated by acidification, and the specific pretreatment is as follows:

[0018] The zeolite is added to the acid solution according to a preset ratio, reacted at 20°C-100°C for 6h-24h, the suspension after the reaction is filtered, washed with deionized water until neutral and dried to obtain the pretreated zeolite;

[0019] The acid solution has a concentration of 0.1M-5M and includes one or more combinations of hydrochloric acid, phosphoric acid, sulfuric acid, formic acid, acetic acid, and citric acid.

[0020] Preferably, in the preparation method, the specific surface area of ​​the zeolite after the acidification pretreatment is 700 m 2 / g-1100m 2 / g, zeolite grain size is 1μm-3μm, and pore size is 0.5nm-2nm.

[0021] According to another aspect of the present invention, there is also provided an application of the SERS composite substrate material as described in the present invention, which is applied to surface enhanced Raman spectroscopy detection of organic matter in a gas phase system; the organic matter includes one or more typical pollutants such as toluene, acetone, and 2-methylpentane in asphalt VOCs; and is preferably applied to surface enhanced Raman spectroscopy detection of asphalt VOCs.

[0022] Preferably, the application is used for performing surface enhanced Raman spectroscopy detection on a gas phase system with a toluene concentration of more than 8 ppm.

[0023] Preferably, the application is used for performing surface enhanced Raman spectroscopy detection on a gas phase system with an acetone concentration of more than 8 ppm, and / or for performing surface enhanced Raman spectroscopy detection on a gas phase system with a 2-methylpentane concentration of more than 6 ppm.

[0024] Preferably, the application is used for rapid in-situ detection of VOCs in asphalt.

[0025] In general, compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects due to the SERS composite substrate material provided by the present invention:

[0026] The SERS composite substrate material provided by the present invention has a double-layer structure, the lower layer of which is 400m 2 / g-1100m 2 / g zeolite, the upper layer is a metal nanolayer structure with a thickness of 50nm-300nm. The experiment found that the specific surface area is 400m 2 / g-1100m 2 / g zeolite has a good adsorption and fixation effect on asphalt VOCs. The metal nanostructure with a thickness of 50nm-300nm distributed on its surface can not only enhance the Raman effect, but also increase the roughness of the zeolite surface, which is conducive to further enhancing the adsorption and fixation of asphalt VOCs by zeolite. Experiments have shown that this SERS composite substrate material can be used to detect asphalt VOCs, especially toluene, 2-methylpentane and acetone, the typical substances in asphalt VOCs. The detection limit of gas phase toluene and acetone can reach 8ppm, and the detection limit of gas phase 2-methylpentane can reach 6ppm, which can realize the in-situ rapid detection of asphalt VOCs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 XRD pattern of Ag-zeolite composite SERS substrate material;

[0028] Figure 2 Schematic diagram of asphalt VOCs detection based on SERS technology;

[0029] Figure 3 Raman spectra of asphalt VOCs from base materials prepared by different zeolite treatments;

[0030] Figure 4 Nanosilver SERS substrate and its Raman spectrum of asphalt VOCs;

[0031] Figure 5 Comparison of the effects of ZIF-8@-Ag substrate materials on Raman detection of VOCs in asphalt;

[0032] Figure 6 The influence of different metal nanostructures on the detection of VOCs in asphalt;

[0033] Figure 7 Raman spectra of toluene gas at different concentrations;

[0034] Figure 8 Raman spectra of detection limits of acetone and 2-methylpentane. DETAILED DESCRIPTION

[0035] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0036] Gas-phase surface-enhanced Raman scattering (SERS) detection is a technology used to enhance Raman scattering signals. It uses specific substrate materials to enhance Raman signals, thereby enabling the detection of molecules at lower concentrations. Among them, the commonly used substrate materials in the detection of pollutants in water systems are gold nanoparticles and silver nanoparticles. However, compared with the water system, the concentration of gas molecules is lower, and the time it takes to reach adsorption equilibrium on the solid surface is shorter, making it difficult to capture, making the SERS technology difficult to apply to the detection of asphalt VOCs in the gas phase system.

[0037] The present invention has found a SERS composite substrate material that can be used to effectively detect asphalt VOCs in the gas phase system, and its detection limit for typical pollutants such as toluene and acetone in asphalt VOCs can reach 8ppm, and its detection limit for typical pollutants such as 2-methylpentane in asphalt VOCs can reach 6ppm. The SERS composite substrate material has a double-layer structure, in which the lower layer has a specific surface area of ​​400m 2 / g-1100m 2 / g of zeolite, the upper layer is a metal nanostructure with a thickness of 50nm-300nm, and the metal nanostructure includes any one of nano-gold, nano-silver or nano-gold-silver alloy.

[0038] Based on this, the present invention provides a SERS composite substrate material prepared based on zeolite, which has a double-layer structure, wherein the lower layer is a porous zeolite, and the upper layer is a metal nanolayer structure, wherein the metal nanolayer is uniformly dispersed on the surface of the zeolite; the zeolite has a specific surface area of ​​400m 2 / g-1100m 2 / g; the metal nanostructure has a nanolayer thickness of 50nm-300nm, wherein the nanometal includes any one of metal gold, silver or a gold-silver alloy.

[0039] The SERS composite substrate material has a specific surface area of ​​400 m 2 / g-1100m 2 / g of zeolite can significantly improve the enrichment and fixation of gas VOCs by the base material. In addition, zeolite has good crystallinity and presents a smooth surface. After drop-coating of nano-metal, the nano-metal adheres to the zeolite surface, such as the zeolite surface roughness in the Ag-zeolite substrate, which is conducive to further enhancing the adsorption and fixation of asphalt VOCs by zeolite.

[0040] The metal nanostructure is composed of many crisscrossed nanosheets, and the surface electromagnetic fields of adjacent nanosheets are coupled to each other, resulting in strong local electromagnetic field enhancement, which makes it show strong SERS performance. For example, nano-gold or nano-silver or their alloys can play a Raman enhancement effect.

[0041] In some embodiments, the size of the nanometal is preferably 30nm-100nm, and the specific surface area of ​​the zeolite is 700m 2 / g-1100m 2 / g, the grain size is 1μm-3μm, and the pore size is 0.5nm-2nm.

[0042] In some embodiments, the metal nanostructure has a nanolayer thickness of 150nm-200nm, and the nanometal is nanosilver, wherein the size of the nanosilver is 30nm-100nm, and the shape is any one of sphere, rod, and flower. For example, the size of the nanosilver is 70-80nm, and the shape is preferably flower-shaped.

[0043] Furthermore, the zeolite is a zeolite that has been acidified and pretreated, and the specific pretreatment is as follows:

[0044] The zeolite is added to the acid solution in a preset ratio, reacted at 20°C-100°C for 6h-24h, the suspension after the reaction is filtered, washed with deionized water until neutral and dried to obtain the pretreated zeolite; preferably, the reaction is carried out at a constant temperature of 50-100°C for 6-24h.

[0045] The main function of acid treatment is to remove impurities in zeolite and make the pore structure more complete. Acid treatment of zeolite can further increase its specific surface area, which is beneficial to improving the adsorption effect of composite base materials on asphalt VOC.

[0046] The acid solution has a concentration of 0.1M-5M and includes one or more combinations of hydrochloric acid, phosphoric acid, sulfuric acid, formic acid, acetic acid, and citric acid.

[0047] The preset mass volume ratio of zeolite to acid solution is 1g:10mL-25mL, and the acidification treatment is performed until the specific surface area of ​​the zeolite no longer increases.

[0048] In addition, the present invention also provides a method for preparing the SERS composite substrate material according to the present invention, which comprises the following steps:

[0049] With a specific surface area of ​​400m 2 / g-1100m 2 / g of zeolite is used as a substrate, and a metal nanosol with a size of 30nm-100nm is coated on the surface of the zeolite, so that the thickness of the metal nanolayer on the surface of the zeolite is 50-300nm after drying and curing, thereby obtaining the SERS composite substrate material; preferably, the thickness of the metal nanolayer is 150-200nm.

[0050] The metal nanosol includes gold nanosol, silver nanosol, or gold-silver alloy nanosol.

[0051] Preferably, the zeolite is an acid pretreated zeolite having a specific surface area of ​​700 m 2 / g-1100m 2 / g, the zeolite grain size is 1μm-3μm and the pore size is 0.5nm-2nm.

[0052] In some embodiments, a nano metal sol with a concentration of 0.1M-0.5M is used, and its coating amount is (10μL-50μL) / 15g zeolite; if a drop coating method is used, a nano Ag sol with a concentration of 0.1M is added dropwise once or multiple times, and its total coating amount is 30μL, and the obtained SERS composite substrate material has an Ag nanolayer thickness of 150-200nm.

[0053] The present invention also provides an application of the SERS composite substrate material as described in the present invention, which is applied to surface enhanced Raman spectroscopy detection of organic matter in a gas phase system; the organic matter includes one or more typical gas pollutants such as toluene, acetone, and 2-methylpentane; and is more preferably applied to surface enhanced Raman spectroscopy in-situ detection of asphalt VOCs, and the asphalt VOCs include toluene, acetone, and 2-methylpentane.

[0054] In some embodiments, the application is used to perform surface enhanced Raman spectroscopy detection on a gas phase system with a toluene concentration of more than 8 ppm.

[0055] In some embodiments, the application is used to perform surface enhanced Raman spectroscopy detection on a gas phase system with an acetone concentration above 8 ppm.

[0056] In some embodiments, the application is used to perform surface enhanced Raman spectroscopy detection on a gas phase system with a 2-methylpentane concentration of more than 6 ppm.

[0057] In some embodiments, the application is used for in-situ rapid detection of VOCs in asphalt; for example, based on the SERS composite substrate material provided by the present invention, it is possible to detect VOCs in asphalt at a concentration of 112 mg / m 3 Surface enhanced Raman spectroscopy was performed on the gas phase system.

[0058] The following are examples

[0059] Example 1 Effect of base materials prepared by different zeolite treatments on asphalt VOCs detection results

[0060] (1) Zeolite pretreatment: 15 g of zeolite (zeolite size 1 μm-3 μm, specific surface area 325 m 2 / g) was added into 150mL of a hydrochloric acid solution with a concentration of 1mol / L, and the temperatures were set to 25°C, 50°C, 75°C and 100°C, respectively. After soaking for 24h, the supernatant was removed, the mixture was fully washed with deionized water until neutral, placed in an oven, and vacuum dried at 60°C to obtain the zeolite after acidification. In this embodiment, the hydrochloric acid solution can also be replaced by one or more combinations of phosphoric acid, sulfuric acid, formic acid, acetic acid, and citric acid, with a concentration of 0.1M-5M.

[0061] Taking the untreated zeolite as a control, the pore size of the zeolite after acidification treatment is 0.5nm-2nm, and the specific surface area and porosity of the zeolite after pretreatment under different conditions in Example 1 are compared. The test results are shown in the following table:

[0062] Table 1 Specific surface area and pore volume of zeolite under different acid treatment conditions

[0063]

[0064] (2) Preparation of silver nanosol: At room temperature, weigh 0.1 g of silver nitrate and 0.15 g of trisodium citrate, add 50 mL of deionized water, stir until completely dissolved, and prepare solution A; then weigh 0.5 ascorbic acid, add them to 50 mL of a mixture of water and ethylene glycol (volume ratio 1:1), stir until completely dissolved, and prepare solution B; then, under the stirring of a magnetic stirrer, quickly add solution B to solution A, react for 1 hour, wash with deionized water and anhydrous ethanol several times by centrifugation, and disperse in deionized water to obtain Ag nanosol.

[0065] (3) Preparation of Ag-zeolite composite substrate material: Untreated and treated zeolites are laid flat on a clean substrate as a VOCs gas adsorption layer. Using a drop coating method, 0.1M Ag nanosol (prepared in step (2) above) is dripped onto the zeolite adsorption layer in an amount of 30 μL. The addition can be done once or multiple times to form a uniform layer of nanosilver structure on the zeolite surface after drying. The nanosilver structure formed on the zeolite surface has a nanolayer thickness of 180 nm, and the nanosilver is a flower-like structure with an average diameter of 80 nm.

[0066] These composite substrate materials were placed in a 60°C oven for drying to prepare five different series of SERS substrate materials - Ag-zeolite composite substrate materials. The XRD patterns of the Ag-zeolite composite SERS substrate materials are shown in Figure 2. Figure 1 shown.

[0067] Depend on Figure 1 It can be seen that the characteristic diffraction peaks of zeolite and Ag can be detected, and the peaks are sharp and have good crystallinity, indicating that the Ag-zeolite composite SERS substrate has been successfully prepared.

[0068] In this embodiment, the method of adding the Ag nano-sol is not limited, and any other existing method that can make the metal nano-structure meet the requirements of the present invention can be used.

[0069] (4) Detection of asphalt VOCs based on SERS technology: Figure 2 As shown, the five kinds of SERS substrates obtained above are horizontally placed in a quartz closed box with a volume of 1L (with an openable glass cover on the top, and a sealing ring installed between the cover and the box body to facilitate the replacement of SERS substrate materials), one end of the closed box is connected to the asphalt VOCs generator, and the other end is connected to the gas sampling pump; the air inlet is connected to the on-site environment through a metal gas conduit and a connecting pipe, and the air outlet is connected to the gas sampling pump to generate negative pressure to collect asphalt VOCs in real time in the closed box.

[0070] Weigh 200g of matrix asphalt, put it into an asphalt VOCs generator with a volume of 1L, heat it to 165℃ and keep it warm; turn on the gas sampling pump with a sampling rate of 5mL / min-200mL / min and a sampling time of 10min-2h. For example, in this embodiment, the sampling rate is 5mL / min and the sampling time is 2h; close the gas control valves at the air inlet and outlet to allow the asphalt VOCs gas molecules to fully react with the SERS substrate material in a closed box. The incubation time is 30min.

[0071] The ATR3110-633nm Raman spectrometer was used to detect and analyze the above SERS substrate material, where the Raman laser wavelength represents different excitation energies, and the smaller the wavelength, the stronger the energy. The laser wavelength can be selected as one of 532nm, 633nm, 785nm and 1064nm, and the signal collection time is 2-10min, where 532nm and 633nm are commonly used excitation wavelengths. For some organic compounds that produce fluorescence, it is generally necessary to select a laser with a longer wavelength and lower energy. In this embodiment, the excitation wavelength is 633nm, and the signal collection time is 8min, and the corresponding Raman spectra of each group are obtained, as shown in FIG. Figure 3 shown.

[0072] The obtained spectra were compared with the standard Raman spectra of toluene, 2-methylpentane and acetone, typical substances in asphalt VOCs. It was found that the characteristic substances in asphalt VOCs were almost undetectable on the untreated zeolite substrate. After acidification, due to the increase in the specific surface area of ​​zeolite, the adsorption effect on asphalt VOCs was enhanced, and the spectral peaks corresponding to the characteristic peaks of toluene, 2-methylpentane and acetone began to appear (789cm -1 The symmetric stretching vibration peak of acetone CC is 815 cm -1 The CC stretching vibration peak of 2-methylpentane CH3-CH3 is 1003 cm -1The peak of the breathing vibration of the monocyclic aromatic ring of toluene is 1026 cm -1 is the C-CH stretching vibration peak of toluene).

[0073] As the specific area of ​​zeolite in the SERS composite substrate material increases, the detection effect becomes more obvious and is not affected by the Ag-zeolite substrate material. This shows that the above-mentioned SERS composite substrate material can be used to effectively detect asphalt VOCs based on the SERS technology.

[0074] Comparative Example 1 Detection effect of silver nano-based materials on asphalt VOCs

[0075] (1) Preparation of silver nanosol: At room temperature, weigh 0.1 g of silver nitrate and 0.15 g of trisodium citrate, add 50 mL of deionized water, stir until completely dissolved, and prepare solution A; then weigh 0.5 ascorbic acid, add them to 50 mL of a mixture of water and ethylene glycol (volume ratio 1:1), stir until completely dissolved, and prepare solution B; then, under the stirring of a magnetic stirrer, quickly add solution B to solution A, react for 1 hour, wash with deionized water and anhydrous ethanol several times by centrifugation, and disperse in deionized water to obtain Ag nanosol.

[0076] (2) The Ag nanosol prepared in the above step (1) was prepared into a solution with a concentration of 0.1 M, 30 μL of which was directly dropped onto a clean quartz substrate, and then placed in a 60° C. oven for drying to obtain an Ag nano-based material.

[0077] (3) Detection of VOCs in asphalt based on SERS technology: The Ag nano-based substrate material obtained in step (2) was used for detection. Except for the different substrate materials, other operations were the same as in Example 1. The Raman spectrum obtained was as follows: Figure 4 shown.

[0078] Depend on Figure 4 It can be seen that the Raman signals of the corresponding components of asphalt VOCs were not detected. The possible reason is that asphalt VOCs are gas molecules, which have poor interactions with the surface of nanometal materials and cannot be stabilized on the nanosilver SERS substrate. Therefore, the Raman signals of the corresponding components in asphalt VOCs cannot be detected.

[0079] Comparative Example 2: Using MOF-Ag as the base material to detect asphalt VOCs using SERS technology

[0080] (1) Preparation of MOF-Ag substrate material: with a specific surface area of ​​1200 m 2 / g ZIF-8 was used as a substrate; it was spread flat on a clean substrate as a VOCs gas adsorption layer. Ag nanosol with a concentration of 0.1M was added to the surface of the MOF material by drop coating method, and the amount used was the same as in Example 1. The substrate material was then placed in a 60°C oven for drying to obtain a ZIF-8-Ag substrate material.

[0081] (2) Detection of VOCs in asphalt based on SERS technology: The ZIF-8-Ag substrate material obtained in step (2) was used for detection. Except for the different substrate materials used, other operations were the same as in Example 1. The effects of zeolite, ZIF-8, and ZIF-8-Ag on Raman detection of VOCs in asphalt were compared and analyzed. The results are as follows: Figure 5 shown.

[0082] Taking toluene, a characteristic pollutant in asphalt VOCs, as an example, the characteristic peak of toluene is 1026 cm -1 The C-CH stretching vibration peak is the basis for determining the detection of toluene in asphalt VOCs. Figure 5 It can be seen that ZIF-8 has Raman characteristic peaks at similar wavenumbers, which has a certain impact on the determination of the test results. This is mainly because ZIF-8 is a metal-organic framework material (Metal-Organic Frameworks, MOFs) composed of metal ions and organic ligands. The organic structural characteristics lead to a large number of Raman vibration characteristic peaks, especially the organic ring framework structure is similar to the aromatic ring structure of benzene series, which causes some characteristic peaks of the two to overlap, causing interference to the detection of benzene series. Zeolite is an inorganic substance, and its Raman characteristic peaks are quite different from those of organic substances, so it has little interference with the detection of asphalt VOCs.

[0083] Example 2 Effect of different thickness of metal nanostructures on asphalt VOCs detection effect

[0084] Aromatic hydrocarbons are the main components of asphalt VOCs. Due to their irritation and harmfulness to the human body, they are the key targets for prevention and control of asphalt VOCs. This example uses toluene standard liquid as the detection object to study the effects of different silver nanostructures on the detection effect of asphalt VOCs, as follows:

[0085] The pretreated zeolite obtained at 50° C. in Example 1 was used as a substrate to prepare an Ag-zeolite composite substrate material, which was specifically prepared according to the following method:

[0086] (1) Zeolite pretreatment: According to Example 1, 15 g of zeolite was added to 150 mL of 1 mol / L hydrochloric acid solution at 50° C. After soaking for 24 h, the supernatant was removed, and the mixture was thoroughly washed with deionized water until neutral. The mixture was placed in an oven and vacuum dried at 60° C. to obtain the pretreated zeolite.

[0087] (2) Preparation of Ag nanosol: At room temperature, weigh 0.1 g of silver nitrate and 0.15 g of trisodium citrate, add 50 mL of deionized water, stir until completely dissolved, and prepare solution A; then weigh 0.5 ascorbic acid, add them to 50 mL of a mixture of water and ethylene glycol (volume ratio 1:1), stir until completely dissolved, and prepare solution B; then, under the stirring of a magnetic stirrer, quickly add solution B to solution A, react for 1 hour, wash with deionized water and anhydrous ethanol several times by centrifugation, and disperse in deionized water to obtain Ag nanosol.

[0088] (3) Preparation of Ag-zeolite composite substrate material: The treated zeolite was spread on a clean substrate as a VOCs gas adsorption layer. Using the drop coating method, 0.1M Ag nanosol was added to the zeolite adsorption layer in amounts of 10μL, 20μL, 30μL, 40μL and 50μL, respectively. The addition could be done once or multiple times to prepare surface functional layers with different Ag contents. These composite substrate materials were placed in a 60°C oven for drying to prepare five Ag-zeolite SERS composite substrate materials with different nanometal thicknesses.

[0089] (4) Detection of gaseous toluene based on SERS technology: The five SERS substrate materials obtained in step (3) were placed horizontally in a sealed box, 20 μL of toluene standard sample was added to the sealed box, and the box was sealed and allowed to stand at room temperature for 8 h to volatilize; the SERS substrate material adsorbed with toluene gas was detected and analyzed using an ATR3110-633nm Raman spectrometer, wherein the excitation wavelength was 633 nm and the signal acquisition time was 8 min, and the corresponding Raman spectra of each group were obtained as shown in FIG. Figure 6 .

[0090] The obtained spectrum is compared with the spectrum of the toluene standard sample. Figure 6 It can be seen that the characteristic peak of toluene was detected in the Raman spectra of each group of toluene standard gas: 785cm -1 、1003cm -1 and 1026cm -1 , the other peaks are the spectral peaks of zeolite in the SERS substrate material. Zeolite is an inorganic substance, and its Raman characteristic peaks are quite different from those of organic matter, so the interference is relatively small. Therefore, it has no effect on the detection results of other organic matter in asphalt VOCs.

[0091] The characteristic peak of toluene can be detected by adding 10 μL of 0.1M Ag nanosol (the thickness of the SERS substrate nanosilver layer is 50 nm): 785 cm -1 、1003cm -1 and 1026cm -1As the amount of Ag nanosol added increases, the SERS signal intensity shows a trend of increasing first and then decreasing. The reason may be that when 10 μL of Ag nanosol is added, the Ag content distributed on the zeolite surface is low, the nano-Ag is sparsely distributed, and the spacing between particles is large, resulting in a low SERS signal intensity. As the amount of Ag nanosol increases, the number of nano-Ag gradually increases, the number of "hot spots" on the zeolite surface increases, the distribution density of nano-Ag increases, and the spacing between particles decreases, showing a uniform and moderate distribution, which can significantly enhance the electromagnetic effect and further improve the SERS signal intensity. When the amount of nano-Ag sol increases to 40-50 μL, the nano-Ag particles begin to aggregate (the thickness of the metal nanolayer is 200-300 nm), forming larger clusters, thereby reducing the number of effective hot spots. This aggregation effect weakens the electromagnetic enhancement effect, resulting in a decrease in the SERS signal intensity. It can be seen that the SERS signal intensity is not linearly positively correlated with the total amount of nano-Ag. The thickness of the metal nanolayer in the SERS composite substrate material is in the range of 50nm-300nm, which can detect toluene gas, a typical pollutant in asphalt VOCs. The preferred metal nanolayer thickness is 150nm-200nm, which has a better detection effect.

[0092] Example 3 Sensitivity of Ag-zeolite substrate material to the detection of asphalt VOCs and their characteristic pollutants

[0093] Since the composition of asphalt VOCs is very complex, the present invention takes the characteristic pollutants toluene, 2-methylpentane and acetone in asphalt VOCs as research objects to explore the sensitivity of Ag-zeolite base material to the detection of asphalt VOCs and its characteristic pollutants.

[0094] 3.1 Sensitivity of Ag-zeolite-based materials for the detection of toluene, a characteristic pollutant in asphalt VOCs

[0095] (1) Prepare Ag-zeolite substrate material according to steps (1) to (3) in Example 2, wherein the recommended amount of nano-Ag sol with a concentration of 0.1 M is 30 μL.

[0096] (2) The above-mentioned SERS substrate material is placed horizontally in a sealed box, and 1 μL, 10 μL, 20 μL, 200 μL and 1000 μL of toluene standard samples are added to the sealed box respectively. After sealing, the box is left to stand at room temperature for 8 h. After the toluene standard samples are completely volatilized, the volume of toluene is multiplied by the density of toluene, and then divided by the volume of the sealed container, and the toluene gas concentration corresponding to the toluene standard samples is converted to 1 ppm-900 ppm; ATR3110-633nm Raman spectrometer is used to detect and analyze the SERS substrates adsorbing toluene gas of different concentrations, wherein the excitation wavelength is 633 nm and the signal acquisition time is 8 min, and the corresponding Raman spectra are obtained, as shown in FIG. Figure 7 shown.

[0097] Depend on Figure 7 It can be seen that when the volume of the toluene standard sample is 1 μL, that is, the toluene gas concentration is 1 ppm, the Raman characteristic peak of toluene does not appear due to the low gas content. When the volume of the toluene standard sample increases to 10 μL, that is, the toluene gas concentration increases to 8 ppm, the Raman characteristic peak of 785 cm -1 、1003cm -1 and 1026cm -1 The Raman characteristic peak of toluene begins to appear at 1000 ppm. Although the peak is weak, toluene can be detected. Therefore, the detection limit of toluene gas is 8 ppm. As the concentration of toluene increases, the more obvious the toluene characteristic peak is, the better the detection effect is.

[0098] 3.2 Effect of Ag-zeolite-based materials on characteristic pollutants 2-methylpentane and Figure 8 Sensitivity of Raman spectroscopy detection of acetone and 2-methylpentane detection limits

[0099] The Ag-zeolite substrate material is the same as that in 3.1 above. 10 μL of 2-methylpentane standard or acetone standard is added to the sealed box, and then the box is sealed and left to stand at room temperature for 8 h. After the standard is completely volatilized, the absorption is performed; the SERS substrate adsorbed with 2-methylpentane or acetone gas is detected and analyzed using an ATR3110-633nm Raman spectrometer, where the excitation wavelength is 633nm and the signal acquisition time is 8min. The results are as follows Figure 8 shown.

[0100] Depend on Figure 8 It can be seen that the SERS composite substrate material provided by the present invention can detect 2-methylpentane with a gas phase concentration of 6 ppm and acetone with a gas phase concentration of 8 ppm. It can be seen that the detection lower limit of the method for 2-methylpentane gas can be as low as 6 ppm, and the detection lower limit of the method for acetone gas can be as low as 8 ppm.

[0101] 3.3 In-situ detection of VOCs in asphalt based on Ag-zeolite substrate

[0102] The Ag-zeolite substrate material is the same as that in 3.1 above. According to step (4) in Example 1, 200g of matrix asphalt is weighed and placed in an asphalt VOCs generator with a volume of 1L, heated to 165°C and kept warm; the gas sampling pump is turned on to collect asphalt VOCs gas samples, the sampling rate is 5mL / min, and the sampling time is 2h. The ATR3110-633nm Raman spectrometer is used to detect and analyze the SERS substrate adsorbed with asphalt VOCs gas, wherein the excitation wavelength is 633nm and the signal acquisition time is 8min. It can effectively detect a variety of typical pollutants in asphalt VOCs such as toluene, 2-methylpentane and acetone.

[0103] The same collection conditions as above, GC-MS test was performed to determine the actual concentration of asphalt VOCs. The concentration of asphalt VOCs was 112 mg / m 3 It can be seen that the Ag-zeolite composite SERS substrate material provided by the present invention can realize in-situ rapid detection of asphalt VOCs.

[0104] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A SERS composite substrate material prepared based on zeolite, characterized in that: The SERS composite substrate material is a double-layer structure, wherein the lower layer is a porous zeolite and the upper layer is a metal nanostructure; The zeolite has a specific surface area of ​​400 m 2 / g-1100m 2 / g; The metal nanostructure has a nanolayer thickness of 50nm-300nm, wherein the nanometal includes any one of metal gold, silver or a gold-silver alloy.

2. The SERS composite substrate material according to claim 1, characterized in that: The zeolite is an acid pretreated zeolite with a specific surface area of ​​700 m 2 / g-1100m 2 / g, pore size is 0.5nm-2nm; The size of the nano metal is 30nm-100nm, and the shape is any one of sphere, rod and flower.

3. The SERS composite substrate material according to claim 2, characterized in that: The nano metal of the metal nano structure is nano silver, and the thickness of the nano layer is 150nm-200nm.

4. A method for preparing a SERS composite substrate material according to any one of claims 1 to 3, characterized in that: The following steps are involved: With a specific surface area of ​​400m 2 / g-1100m 2 / g of zeolite as a substrate, coating a metal nanosol with a size of 30nm-100nm on the surface of the zeolite, and obtaining the SERS composite substrate material after drying and curing, wherein the thickness of the metal nanolayer on the substrate material is 50nm-300nm; The metal nanosol includes silver nanosol, and the concentration of the metal nanosol is 0.1M-0.5M.

5. The preparation method according to claim 4, characterized in that: The zeolite is a zeolite that has been acidified and pretreated, and the specific pretreatment is as follows: The zeolite is added to the acid solution according to a preset ratio, reacted at 20°C-100°C for 6h-24h, the suspension after the reaction is filtered, washed with deionized water until neutral and dried to obtain the pretreated zeolite; The acid solution has a concentration of 0.1M-5M and includes one or more combinations of hydrochloric acid, phosphoric acid, sulfuric acid, formic acid, acetic acid, and citric acid.

6. The preparation method according to claim 5, characterized in that: The specific surface area of ​​the acidified pretreated zeolite is 700 m 2 / g-1100m 2 / g, zeolite grain size is 1μm-3μm, and pore size is 0.5nm-2nm.

7. An application of the SERS composite substrate material according to any one of claims 1 to 3, characterized in that: It is applied to the detection of organic matter in the gas phase system by surface enhanced Raman spectroscopy; the organic matter includes one or more typical gaseous pollutants such as toluene, acetone and 2-methylpentane in asphalt VOCs.

8. The use according to claim 7, characterized in that Used for surface enhanced Raman spectroscopy detection of gas phase systems with toluene concentration above 8 ppm.

9. The use according to claim 7, characterized in that Used for surface enhanced Raman spectroscopy detection of a gas phase system with an acetone concentration of more than 8 ppm, and / or used for surface enhanced Raman spectroscopy detection of a gas phase system with a 2-methylpentane concentration of more than 6 ppm.

10. The use according to claim 7, characterized in that Used for rapid in-situ detection of asphalt VOCs.

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