Au-coated DMSN / Ag-coated G composite material and preparation method thereof

Abstract

The invention belongs to the field of nano plastic detection, and particularly relates to an Au (at) DMSN / Ag (at) G composite material and a preparation method thereof. The preparation method comprises the following steps: doping gold nanoparticles with adjustable intergranular gaps into the inner surface of a pore channel of dendritic mesoporous silica (DMSN) in a semi-compatible manner; and silver nanoparticles are deposited on the high-conductivity graphene nanosheets in situ. Then, the two components are compounded through electrostatic attraction, and the Au-coated DMSN / Ag-coated G composite material is obtained. The obtained composite material can be used for an SERS (Surface Enhanced Raman Scattering) substrate, and PS NPs of 200-500 nm can be detected in a range size. Compared with the existing nano plastic analysis method, the composite substrate material has the advantages of high sensitivity, interference resistance, good repeatability, strong quantitative analysis capability and the like, and obtains a good recovery rate in a lake water marking experiment.

Description

Technical Field

[0001] The present invention relates to the field of nano-plastic detection, and particularly to an Au@DMSN / Ag@G composite material and a preparation method thereof. Background Art

[0002] The widespread presence of microplastics (1 μm - 5 mm) and nanoplastics (<1000 nm) in the aquatic environment has attracted extensive global attention. Compared with microplastics, it is particularly important to note that the hazards of nanoplastics are more obvious, mainly because of their high specific surface area, which makes them prone to adsorb organic pollutants, heavy metals, pathogenic microorganisms, and plastic additives released during the degradation process. In order to anticipate and prevent the harm caused by nanoplastics to humans, it is necessary to monitor nanoplastics in the aquatic environment.

[0003] Currently, various complex techniques are used for the analysis and detection of micro / nanoplastics, such as pyrolysis-gas chromatography / mass spectrometry (Pyrolysis-GC / MS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM) observation, biosensor methods, and Raman spectroscopy. Although the above methods can quantitatively detect plastics in the environment, they also have disadvantages such as complex procedures, time-consuming, and destructive analysis. Biosensor methods are usually sensitive to pH values, which can make the detection results of samples unreliable under complex environmental conditions. Raman spectroscopy can accurately identify the fingerprint information of the molecular structure on the surface of nanoplastics. Unfortunately, classical Raman spectroscopy is limited by its limited spatial resolution and sample fluorescence interference.

[0004] Surface-enhanced Raman spectroscopy (SERS) is well-known for its high sensitivity. It can amplify the molecular Raman signals within the local electric field range on the metal substrate at the nanoscale, which helps to detect molecules at extremely low concentrations. However, due to the inherently low-scattering interfaces of various nanoplastics, it is generally considered that the signals obtained by SERS for detecting nanoplastics are weak. Therefore, applying SERS to nanoplastics detection is still challenging. Developing new SERS substrates to improve the detection efficiency is usually a laborious and time-consuming process, and it is still challenging to achieve the detection of ultra-low concentrations of nanoplastics in water bodies. Currently, the amplification of SERS signals comes from the enhancement of the local electromagnetic field of noble metal nanoparticles. Many research groups have successfully detected micro / nanoplastics using SERS substrates functionalized with noble metal nanoparticles. For example, Sang-Woo Joo et al. designed a method for preparing Au NSs@Ag@AAO SERS substrates by ultrasonic-induced self-assembly and achieved ultrasensitive detection of submicron PS plastics. Based on the former, Jing Yu et al. designed an AAO / MoS2 / Ag with a structure of MoS2 particles as a Raman internal standard coating, and achieved the detection of NPs (<300 nm) and Hg 2+ . However, common SERS substrates may have uneven hot spot distributions, resulting in a lack of reliability and consistency in SERS spectral signals. Wei Zhang et al. developed a ZnO nanorod array SERS substrate modified with Ag NPs on polydimethylsiloxane, which has the advantages of high sensitivity and signal reproducibility, and achieved trace analysis of microplastics. The research work of these scholars has improved the detection sensitivity of nanoplastics, and the detection limits of PS NPs (polystyrene nanoparticle suspension) are 50 μg / mL and 25 μg / mL respectively. In order to address the detection challenges of ultra-low concentrations of nanoplastics (at 10 -9 -10 -4 g / mL) in the aquatic environment in real scenarios, it is necessary to develop new SERS substrates to improve the detection sensitivity and accuracy of nanoplastics to meet the detection requirements of nanoplastics in the aquatic environment as much as possible. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides an Au@DMSN / Ag@G composite material and its preparation method to be used as an SERS substrate for the detection of nanoplastics.

[0006] The specific technical solution of the present invention is as follows: In the first aspect of the present invention, a preparation method of an Au@DMSN / Ag@G composite material is provided, including the steps of: S1 Prepare Au@DMSN, S11 Synthesize dendritic mesoporous silica DMSN. Mix and stir triethanolamine with deionized water at 70 - 90 °C, then add cetyltrimethylammonium bromide CTAB and sodium salicylate NaSal, continue stirring and reacting, and then dropwise add tetraethyl orthosilicate TEOS into the above solution, stir and react at 75 - 85 °C. After the reaction is completed, centrifuge and wash. Subsequently, wash the obtained precipitate with a mixed solution of HCl and ethanol to remove the residual organic template, and finally dry in vacuum to obtain dendritic mesoporous silica DMSN.

[0007] S12 Amino modification of DMSN. First, disperse the dendritic mesoporous silica DMSN obtained in step S11 in ethanol, then add ammonia water, deionized water and (3-aminopropyl)triethoxysilane under vigorous stirring, continue vigorous stirring, and finally wash the final product with ethanol and dry in vacuum to obtain DMSN-NH2; S13 Synthesis of Au@DMSN. Disperse the synthesized DMSN-NH2 in step S12 into ultrapure water, then add chloroauric acid solution under ice-water bath conditions, stir and react, then continue to add trisodium citrate solution under vigorous stirring conditions, and then quickly add freshly prepared NaBH4 solution, continue to react. After the reaction is completed, centrifuge, wash and dry to obtain Au@DMSN powder; S2 Prepare Ag@G. Disperse graphene nanosheets G in deionized water, then heat up to a constant temperature of 80 - 85 °C; then add AgNO3 solution and keep stirring and reacting, then heat up to a constant temperature of 90 - 95 °C, and immediately add trisodium citrate solution to react, finally obtaining graphene nanosheets with in-situ deposited plasmonic Ag nanoparticles Ag@G; S3 Synthesis of Au@DMSN / Ag@G; Disperse the Au@DMSN and Ag@G obtained in steps S1 and S2 into deionized water, and uniformly composite them to obtain the Au@DMSN / Ag@G composite material.

[0008] In the present invention, gold nanoparticles (Au NPs) with adjustable interparticle gaps are semi-compatibly incorporated into the inner surface of the pores of dendritic mesoporous silica (DMSN); silver nanoparticles (Ag NPs) are in-situ deposited on highly conductive graphene nanosheets (G), and the two are composited through electrostatic attraction to prepare the Au@DMSN / Ag@G composite material, which can be used to fabricate a SERS active substrate for the detection of nanoplastics.

[0009] Preferably, in the step S11, triethanolamine: deionized water: cetyltrimethylammonium bromide: sodium salicylate: tetraethyl orthosilicate = 0.65 - 0.70 g: 20 - 25 mL: 0.35 - 0.40 g: 0.16 - 0.17 g: 3 - 5 mL. In the mixed solution of HCl and ethanol, by volume, HCl: ethanol = 1:9, and the temperature for washing away the residual organic template is 70 - 90 °C; The mass percentage concentration of the HCl is 38%.

[0010] Preferably, in the step S12, DMSN: ethanol: ammonia water: deionized water: (3 - aminopropyl)triethoxysilane = 90 - 100 mg: 80 - 120 mL: 2 - 3 mL: 2 - 3 mL: 0.5 - 2 mL.

[0011] Preferably, in the step S13, the concentration of the chloroauric acid solution is 200 mg / mL, the concentration of the TSC solution is 1 w / v%, the concentration of the NaBH4 solution is 0.1 M, and by volume, chloroauric acid: TSC: NaBH4 = 15 - 20: 90 - 110: 45 - 55.

[0012] Preferably, in the step S13, ethanol is used for washing, and the drying temperature is 30 - 50 °C.

[0013] Preferably, in the step S2, by mass ratio, graphene nanosheet G: AgNO3 = 10:36.

[0014] Preferably, in the step S3, by mass ratio, Au@DMSN: Ag@G = 1 - 4: 4 - 1.

[0015] On the other hand, the present invention also provides the Au@DMSN / Ag@G composite material prepared by the described preparation method.

[0016] The beneficial effects of the present invention are: The Au@DMSN / Ag@G composite material prepared by the present invention can be used to manufacture a SERS active substrate. This composite material overcomes the limitations of traditional two - dimensional substrates through the synergistic effect of gold / silver. Moreover, since two - dimensional materials and three - dimensional materials with high specific surface areas are simultaneously used, the metal nanoparticles incorporated on their surfaces can exhibit excellent flexibility, enabling more contact space between the active substrate and the analyte. This helps to improve the detection intensity and sensitivity when used for SERS detection, achieve quantitative detection at ultra - low concentrations, and qualitative analysis of wide - size PS NPs in various environments. Description of the Drawings

[0017] Figure 1Reaction flow chart of the Au@DMSN / Ag@G composite material of the present invention; Figure 2 Wide-angle XRD diffraction patterns of DMSN, Au@DMSN, G, Ag@G, Au, and Ag; Figure 3 Ultraviolet-visible light absorption spectra, where (a) are the ultraviolet-visible light absorption spectra of DMSN and Au@DMSN, and (b) are the ultraviolet-visible light absorption spectra of G and Ag@G; Figure 4 High-resolution XPS spectra, where (a) are the high-resolution XPS spectra of Au@DMSN, Ag@G, and Au@DMSN / Ag@G; (b) is the high-resolution XPS spectrum of Ag 3d, (c) is the high-resolution XPS spectrum of Au 4f, and (d) is the high-resolution XPS spectrum of N 1s; Figure 5 Transmission electron microscope images, where (a-f) are the transmission electron microscope images of Au@DMSN, and (g-l) are the transmission electron microscope images of Ag@G; Figure 6 Scanning electron microscope images, where (a,b) are the scanning electron microscope images of DMSN, and (c) is the scanning electron microscope image of Au@DMSN / Ag@G; Figure 7 Infrared spectra, N2 adsorption-desorption isotherms, pore size distribution diagrams of DMSN and DMSN-NH2, and Zeta potential distribution diagrams of DMSN, DMSN-NH2, and Au@DMSN, as well as thermogravimetric characterization diagrams of Au@DMSN, Ag@G, and Au@DMSN / Ag@G, where (a) are the infrared spectra of DMSN and DMSN-NH2, (b) are the Zeta potential distribution diagrams of DMSN, DMSN-NH2, and Au@DMSN, (c) are the N2 adsorption-desorption isotherms and pore size distribution diagrams of DMSN and DMSN-NH2; (d) is the thermogravimetric characterization of Au@DMSN, Ag@G, and Au@DMSN / Ag@G; Figure 8 Raman spectra of Au@DMSN / Ag@G and PS and test results of PS NPs with different particle sizes, where (a) are the Raman spectra of Au@DMSN / Ag@G and PS, and (b) are the test results of PS NPs with different particle sizes; Figure 9 Particle size distribution diagram of the test sample PS NPs; Figure 10 Raman spectra of the samples (different usage ratios of precursor materials) of Examples 1-7 and 1000 cm -1The relevant SERS intensity results at [specific location]; among them, (a) is the Raman spectrogram of different example samples of 200 - 500 nm PS NPs (0.05 mg / mL), and (b) is at 1000 cm -1 The relevant SERS intensity results at [specific location]; Figure 11 It is a statistical chart of the detection results of different concentrations of PS NPs with the samples of Example 1 and Comparative Examples 1 - 5 as substrates; Figure 12 It is the SERS spectrogram of 200 - 500 nm PS NPs with different concentrations and the linear relationship between the SERS intensity and concentration of 200 - 500 nm PS NPs at 1000 cm-1. Among them, (a) is the SERS spectrogram of 200 - 500 nm PS NPs with different concentrations, and (b) is the linear relationship between the SERS intensity and concentration of 200 - 500 nm PS NPs at 1000 cm-1; Figure 13 It is for 10 -2 The SERS intensity results of 10 mg / mL PS NPs in the presence of different interfering substances, the SERS spectrogram of the binary components of PS and PMMA, and the SERS spectrogram of PS NPs (10 -2 mg / mL) at 22 different random sites on the Au@DMSN / Ag@G substrate; and the experimental reproducibility analysis results. Among them, (a) is the SERS intensity results of 10 -2 mg / mL PS NPs in the presence of different interfering substances; (b) is the SERS spectrogram of the binary components of PS and PMMA; (c) is the SERS spectrogram of PS NPs (10 -2 mg / mL) at 22 different random sites on the Au@DMSN / Ag@G substrate; (d) is the experimental reproducibility analysis results; Figure 14 It is the positions of different sampling points for the SERS test of actual water samples, the test chart of the blank Zhujiang River matrix of Zhujiang River water, and the test effect diagrams of the spiked water samples at different sampling points. Among them, (a) is the sampling point positions in the Zhujiang River waters, (b) is the sampling point positions in the Dadonghai Tourist Area of Sanya City, and (c) is the sampling point positions in the suburbs of Ningyuan County, Yongzhou City; (d) is the test chart of the blank Zhujiang River matrix, (e) is the test effect diagram of the spiked water sample of the high - salinity seawater in the Dadonghai Tourist Area, and (f - g) are the test effect diagrams of the spiked water samples of well water and polluted water in the suburbs of Ningyuan County; Figure 15UV-Vis absorption spectra and linear correlation relationships of 200 - 500 nm PS NPs at different concentrations. Among them, (a) is the UV-Vis absorption spectra of 200 - 500 nm PS NPs at different concentrations, and (b) is the linear correlation relationship. Detailed implementation manners

[0018] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings and embodiments. The following are the preferred embodiments of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure content of the present invention more thorough and comprehensive.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0020] Unless otherwise specified, the reagents, materials, and equipment used in the embodiments of the present invention are all commercially available sources; unless otherwise specified, the test methods are all conventional test methods in the art.

[0021] Chemicals and materials Triethanolamine (TEA, analytical grade), cetyltrimethylammonium bromide (CTAB, analytical grade), (3-aminopropyl)triethoxysilane (APTES, analytical grade), sodium salicylate (NaSal, analytical grade), tetraethyl orthosilicate (TEOS, analytical grade), chloroauric acid tetrahydrate (HAuCl4, analytical grade), silver nitrate (AgNO3, analytical grade), absolute ethanol (CH3CH2OH, analytical grade), sodium borohydride (NaBH4, analytical grade), ascorbic acid (analytical grade), trisodium citrate (TSC, analytical grade), graphene nanosheets (G, analytical grade), polystyrene nanoparticle suspension (PS NPs, 2.5%), calcium chloride (CaCl2, analytical grade), magnesium chloride (MgCl2, analytical grade), sodium chloride (NaCl, analytical grade), potassium chloride (KCl, analytical grade), glucose (analytical grade), PMMA (polymethyl methacrylate, 2.5%), polyvinylpyrrolidone (PVP, average molecular weight 58000), ethylene glycol (analytical grade).

[0022] Instruments and equipment: The transmission electron microscope (TEM) images were obtained from a FEI Talos F200X transmission electron microscope; the XPS spectral images were obtained from a Shimadzu AXIS SUPRA X-ray photoelectron spectrometer; the field emission scanning electron microscope (SEM) images were obtained from a Zeiss Ultra 55 scanning electron microscope; the Fourier transform infrared spectra were obtained from a Spectrum Two infrared analyzer; the ultraviolet-visible spectrophotometric spectra were obtained from a Shimadzu UV2700 spectrophotometer; the X-ray powder diffraction (XRD) patterns were obtained from an Ultima IV X-ray diffractometer; the thermogravimetric analysis curves were obtained from a Netzsch TG-209F3 thermogravimetric analyzer; the BET specific surface area and pore size analysis diagrams were obtained from a Quantachrome chrome ASiQwin specific surface area analyzer; the zeta potential data were obtained from a Malvern Zeta potential analyzer; the Raman spectroscopy analysis spectra were obtained from a Horiba confocal laser microscope Raman spectrometer.

[0023] Example 1 Preparation of Au@DMSN / Ag@G composite materials Reference Figure 1 , the preparation of the Au@DMSN / Ag@G composite material includes the following steps: S1 Preparation of Au@DMSN S11 Preparation of dendritic mesoporous silica DMSN 0.68 g of TEA was added to a glass flask containing 25 mL of deionized water, placed in an oil bath at 80 °C and stirred for 30 minutes. Then, 0.38 g of CTAB and 0.168 g of NaSal were added, and after continuing to stir for 1 h, 4 mL of TEOS was uniformly added dropwise to the above mixed solution with a micropipette, and stirring was continued at 80 °C for 2 h. After the reaction was completed, the obtained product was collected by centrifugation at 9000 rpm for 10 min, and washed twice with ethanol and deionized water respectively to remove the residual reactants. Subsequently, the obtained precipitate was washed three times (24 h each time) with a mixed solution of HCl and ethanol (HCl:ethanol = 1:9 V / V) at 80 °C to remove the residual organic template, and finally vacuum dried at 50 °C for 12 h to obtain a white solid sample.

[0024] S12 -NH2 modification of DMSN First, 100 mg of DMSN was dispersed in 100 mL of ethanol, and after ultrasonic treatment for 10 minutes, stirring was continued for 15 min. Then, 2.5 mL of ammonia water, 2.5 mL of deionized water and 1 mL of APTES were added to the above solution under vigorous stirring, and vigorous stirring was continued for 12 h. Finally, the final product was washed several times with ethanol and dried overnight in vacuo at 50 °C to obtain DMSN-NH2 powder.

[0025] Preparation of S13 Au@DMSN Disperse the synthesized DMSN-NH2 in S12 into 20 mL of ultrapure water by ultrasonic treatment, then add 20 μL of 200 mg / mL chloroauric acid solution under ice-water bath conditions. After continuing to stir for 1 h, add 100 μL of 1% TSC solution under vigorous stirring conditions, and then quickly add 50 μL of freshly prepared 0.1 M NaBH4 solution and continue the reaction for 1 h. After the reaction is completed, collect the product by centrifugation at 8000 rpm for 5 min, wash it three times with ethanol, and then dry it overnight at 40 °C to obtain Au@DMSN powder.

[0026] Preparation of S2 Ag@G Weigh 10 mg of G (graphene nanosheets) and add it to a 50 mL glass flask containing 10 mL of deionized water. Ultrasonic for 5 min, then heat up to a constant 85 °C; weigh 36 mg of AgNO3, dissolve it in 5 mL of water, then add it to the above precursor solution and keep stirring. After reacting for 15 min, heat up to a constant 90 °C, immediately add 4 mL of 1% trisodium citrate solution, keep the reaction for 40 min. After the reaction is completed, wash it with ethanol and water, disperse it in deionized water, and store it at low temperature for later use.

[0027] S3 Au@DMSN / Ag@G According to the mass ratio of m Au@DMSN to m Ag@G being 2:1, weigh appropriate amounts of Au@DMSN and Ag@G, disperse them in deionized water, and stir magnetically for 30 min. After the materials are uniformly compounded, centrifuge and precipitate, and finally redissolve the prepared Au@DMSN / Ag@G material in deionized water.

[0028] Examples 2 - 7 The difference from Example 1 is that in step S3, according to the mass ratio of m Au@DMSN to m Ag@G being 1:4, 1:3, 1:2, 1:1, 3:1, 4:1 in sequence, weigh appropriate amounts of Au@DMSN and Ag@G for the final synthesis of Au@DMSN / Ag@G, and the rest are the same.

[0029] Comparative Example 1 Refer to step S2 of Example 1 to prepare Ag@G.

[0030] Comparative Example 2 Refer to step S1 of Example 1 to prepare Au@DMSN.

[0031] Comparative Example 3 Referring to Step S11 of Reference Example 1, DMSN was prepared.

[0032] Comparative Example 4 Au NPs were synthesized by the citrate reduction method. Specifically, 24 μL of an aqueous solution of chloroauric acid tetrahydrate at 200 g / L was added to 50 mL of distilled water. The solution was placed in a water bath at 120 °C and heated to boiling with stirring, and then 0.5 mL of a 1% sodium citrate solution was quickly added. After reacting for 30 min, heating was stopped when the solution color turned into a stable wine red, and it was cooled to room temperature for standby.

[0033] Comparative Example 5 Ag NPs were synthesized. Specifically, 0.3 g of polyvinylpyrrolidone (PVP) was dissolved in 17 mL of ethylene glycol at room temperature, and then placed in an oil bath at 160 °C for heating and stirring. Subsequently, 110 mg of AgNO3 was dissolved in 3 mL of ethylene glycol and slowly added dropwise to the PVP solution, and heating was continued for 30 min. After the reaction ended, centrifugation was performed at a frequency of 9000 r / min, and the centrifugation time was set to 10 min. The obtained product, silver nanoparticles (Ag NPs), was washed twice with ethanol and finally redispersed in 20 mL of ethanol.

[0034] Performance Testing and Characterization: I. Material Characterization 1. XRD Analysis XRD is a commonly used characterization method to verify the immobilization and crystallinity of nanoparticles. Therefore, XRD analyses were performed on DMSN, Au@DMSN, G, and Ag@G respectively. The wide-angle XRD diffraction patterns are as Figure 2 shown. The broad peak at 22.9° is attributed to amorphous silica. The five diffraction peaks of Au@DMSN at 2θ = 38.1°, 44.4°, 64.6°, 77.5°, and 81.8° correspond to the (111), (200), (220), (311), and (222) lattice planes of Au (JCPDS card number 04-0784); this indicates that Au nanoparticles have successfully grown on the surface of DMSN. Similarly, for Ag@G, 2θ = 37.8°, 44.0°, 64.2°, 77.2°, and 81.3° correspond to the (111), (200), (220), (311), and (222) lattice planes of Ag (JCPDS card number 87-0597), confirming the successful loading of Ag nanoparticles. The XRD results confirmed the successful complexation of noble metal nanoparticles on the surfaces of mesoporous silica (DMSN) and graphene nanosheets (G).

[0035] 2. Ultraviolet-Visible Absorption Spectroscopy Due to the local surface plasmon resonance effect of noble metals, noble metal particles have obvious ultraviolet-visible absorption peaks, further proving the successful loading of noble metal nanoparticles. The ultraviolet-visible absorption spectra of Au@DMSN and Ag@G were tested, as shown in Figure 3 a and b in it. The absorption peaks of Au NPs and Ag NPs are at 536 nm and 446 nm respectively. Based on Mie light scattering theory, the particle size of Ag NPs was calculated to be 60.3 nm, which is consistent with the results in SEM characterization.

[0036] 3. XPS Analysis XPS was used to confirm the surface composition and chemical state of the SERS substrate. As shown in Figure 4 it, it further proves the successful loading of Au NPs and Ag NPs and the successful synthesis of the binary material composite. Figure 4 a in it shows that characteristic elements C, Si, N, O, and Au exist in the energy spectrum of Au@DMSN, and characteristic elements C and Ag exist in the energy spectrum of Ag@G, proving that Au NPs were successfully loaded onto the surface of DMSN; Ag NPs were successfully in-situ generated on the surface of G. When Au@DMSN and Ag@G are combined, due to the obvious increase in the content of carbon element, the component ratios of other elements are reduced to a certain extent, making the characteristics of other characteristic elements significantly reduced and difficult to observe. Figure 4 b in it shows that the Ag 3d spectrum of Ag@G presents two peaks at 368.85 and 374.85 eV, and the double-peak interval is 6.0 eV. These peaks are the Ag 3d 5 / 2 and Ag 3d 3 / 2 peaks of Ag NPs. Compared with the standard spectral peaks of pure Ag (374.02 eV and 368.02 eV), the increase in binding energy can be speculated as an increase in the binding energy of AgNPs. Graphene with strong electron interaction is beneficial to SERS detection. In addition, the absence of the Ag2O peak in b of Figure 4 indicates that AgNPs have been successfully loaded onto the surface of graphene nanosheets (G). Figure 4 c in it shows that Au@DMSN has two peaks at 84.56 eV and 88.23 eV, and the double-peak interval is 3.67 eV. These peaks are consistent with the Au 4f 7 / 2 and Au 4f 5 / 2 peaks of metallic Au. In order to comprehensively explore the advantages of Au@DMSN in surface-enhanced Raman scattering (SERS) research, the change trend of the binding energy of nitrogen (N) before and after the modification of nano-gold (Au NPs) on DMSN-NH2 was analyzed in detail, as shown in Figure 4As shown in d of [reference], during the modification process, the formation of -NH- and N-Au bonds is consistent with the reference, and the content of -NH2 decreases. This phenomenon strongly confirms that AuNPs have been successfully loaded in-situ onto the pore surface of DMSN. Further research shows that the binding energy of N 1S increases by 0.74 eV, indicating a slight electron transfer between Au NPs and DMSN. In addition, a certain amount of low-density electron cloud is formed at the contact interface, which is extremely beneficial for the preparation of a highly sensitive SERS substrate.

[0037] TEM analysis TEM images ( Figure 5 a-f in [figure] show that DMSN-NH2 has an obvious dendritic structure with a diameter of about 150 nm. The Au NPs of Au@DMSN are loaded on the surface of DMSN in a semi-compatible state, successfully capturing AuNPs. The EDS elemental mapping shows that Si, O, and Au elements are evenly distributed on the matrix Au@DMSN, which further proves the successful loading of Au nanoparticles. g-l in Figure 5 also show that Ag NPs are successfully deposited on the surface of G. The average particle size of Ag NPs is about 60 nm, which is consistent with the particle size obtained from the UV-visible absorption spectrum. It can be seen from the dotted line of the lattice diagram that the lattice fringe distribution spacing of AuNPs and Ag NPs is about 0.23 nm, which is consistent with the lattice constant of the (111) crystal plane of gold and silver in the face-centered cubic lattice structure. In addition, the EDS elemental mapping shows that Au elements are successfully distributed around the mesopores of DMSN, and Ag elements are successfully distributed on the graphene nanosheets, further proving the successful loading of Au nanoparticles and Ag nanoparticles.

[0038] SEM analysis SEM images ( Figure 6 a, b in [figure] show that the synthesized DMSN has obvious central radial channels and wrinkled morphology, indicating that the prepared DMSN has a semi-compatible loading space for metal Au NPs. Figure 6 c, d in [figure] show that Au@DMSN can be successfully dispersed on the surface of Ag@G with a high-density material arrangement, which provides sufficient 3D space for the reinforcement of nanoplastics and provides an ordered filling gap.

[0039] Infrared and adsorption analysis The preparation method of the embodiment of the present invention uses amino groups as the adsorption and anchoring groups of gold nanoparticles to achieve the purpose of semi-compatible loading of Au NPs in the pore channels on the surface of DMSN. Figure 7 a in [figure] shows the FTIR characteristic spectra of DMSN before and after modification with amino groups. It can be found that the weak symmetric stretching vibration of C-H is at 2850-2950 cm -1Indicates that APTES has been successfully modified. The vibration of N-H at 1546 cm -1 further proves the successful grafting of amino groups.

[0040] Figure 7 As shown in b of, the Zeta potential changes of DMSN, DMSN-NH2, and Au@DMSN indicate that the surface of unmodified DMSN is negatively charged and rich in Si-OH, with a potential value of -37.88 ± 0.8 mV. After amino modification, the surface of DMSN is modified by a large number of -NH2 groups, and the potential change is a positive value of 48.0 ± 2.0 mV, which is consistent with the results of our infrared test. When Au NPs are in-situ loaded on the noble metal surface, a small part of the -NH2 sites are occupied, which slightly reduces the potential value of the material to 45.1 mV ± 1.6 mV. These high positive potential values represent the excellent stability of the synthesized nanoparticles, and the significant change in zeta potential indicates the successful modification of amino groups and the successful loading of noble metal nanoparticles. The above results are mutually verified with the XPS test for the successful synthesis of the two precursor materials. The Bamauer-Enunett-Teller (BET) analysis of DMSN shows a type IV isotherm in c of Figure 7, thus forming a mesoporous structure of medium size. In the Barrett-Joyner-Halenda (BJH) system, the distribution of two peaks of DMSN illustrates the hierarchical pore structure of DMSN, with pore diameters between 10 - 33 nm and an average pore diameter of 13.38 nm, proving that the synthesized DMSN is a mesoporous structure of medium size. The successful grafting of amino groups reduces the total specific surface area of DMSN from 454.67 m 2 / g to 227.69 m 2 / g, and the total pore volume from 1.54 cm 3 / g to 0.937 cm 3 / g, indicating that APTES has successfully coated DMSN. This unique pore structure provides sufficient compatible space for loading noble metal nanoparticles.

[0041] 7. Thermogravimetric analysis As Figure 7The d in it is the thermogravimetric characterization of Au@DMSN, Ag@G, and Au@DMSN / Ag@G. It can be seen from the figure that the thermogravimetric curves of Ag@G and Au@DMSN / Ag@G are roughly similar. It can be seen that Au@DMSN has a certain heat resistance stability due to its carrier being a polymer C and Si polymer, resulting in a process of carbonization from the outer surface to the inside. When the temperature rises to 180 °C, G begins to decompose thermally, generating CO and CO2. Analyzing the mass fraction of the residue can lead to the successful compounding of Au@DMSN and Ag@GNS.

[0042] II. Detection of PS NPs 1. Determine characteristic peaks Sample preparation: Mix the Au@DMSN / Ag@G prepared in Example 1 with PS NPs, then add KI solution as an aggregating agent. After thoroughly mixing the above solution, let it stand for 1 h to wait for the sample to form a stable colloidal solution. Finally, use a glass micropipette to drop the mixed solution (20 μL) onto a 5×5 mm silicon wafer and dry it in an oven at 50 °C for 1 hour. Perform SERS detection on the dried sample. The obtained Raman spectrum results have all been baseline corrected.

[0043] Normal Raman and SERS spectra were obtained through a confocal laser microscope Raman spectrometer and a 564 nm (3.5%) laser. During the Raman spectrum acquisition process, a 50x objective lens was selected, and the acquisition wavelength range was 400 - 1700 cm -1 There were 3 accumulations in the 5 s acquisition time.

[0044] Raman scattering tests and characterizations were performed on PS NPs with a particle size distribution range of 200 - 500 nm. As Figure 8 shown in a of it, the two most prominent characteristic peaks are located at 1000 cm -1 and 1030 cm -1 positions, corresponding to the breathing vibration peak of the benzene ring and the in-plane deformation of C-H respectively. There is a low peak at 1607 cm -1 which belongs to the skeletal stretching vibration of the benzene ring. Since the peak intensity at 1000 cm -1 is the strongest characteristic peak, the concentration of PS NPs is reflected by comparing the intensity of this peak in the follow-up.

[0045] In addition, it can be seen that Au@DMSN / Ag@G as the substrate has no signal near 1000 cm -1 and 1030 cm -1 which can exclude its interference with the detection of PS NPs.

[0046] Secondly, from Figure 8As shown in b in [reference], for PS NPs with the same mass concentration, Au@DMSN / Ag@G can also detect PS NPs with particle sizes of 50 - 100 nm and 20 nm at a mass concentration of 10 -3 mg / mL. In summary, it can be seen that the Au@DMSN / Ag@G prepared in the examples of the present invention can all detect PS NPs with particle sizes of 50 - 100 nm and 20 nm.

[0047] In the actual environment, plastics have the characteristic of differential particle size distribution. The research on PS NPs with a wide range of distributions is more innovative and representative. Here, PS NPs samples with a wide particle size range are used as the main research object, and dynamic light scattering (DLS) experiments are carried out on them ( Figure 9 ), which proves that the particle size distribution range of PS NPs is mainly in the range of 200 - 500 nm. In addition, due to its small nanosize, it can enter the hot spot gap of the SERS composite material for attractive deposition between plastics. On the other hand, since the ordinary Raman characterization signals of the 50 - 100 nm and 20 nm PS suspensions are smaller than those of the 200 - 500 nm PS suspension, subsequent experiments choose to detect 200 - 500 nm PS with more SERS signal advantages.

[0048] 2. Comparison of the detection effects of the materials synthesized in Examples 1 - 7 Using 200 - 500 nm PS NPs (0.05 mg / mL) as a performance probe, and respectively using the Au@DMSN / Ag@G synthesized in Examples 1 - 7 as a substrate, SERS tests are carried out.

[0049] The results are as shown in Figure 10 a, b in [reference], the SERS intensity at 1000 cm -1 increases with the increase of m Au@DMSN :m Ag@G , increasing sharply from 529 at a ratio of 1:4 to 1581 at a ratio of 2:1. However, a further increase in the volume ratio results in a decrease in intensity. Therefore, the optimal response is shown at a ratio of 2:1 in Example 1. This may be attributed to the fact that with the increase in the amount of Au@DMSN, the deficiency of Raman hot spots of Ag@G in three - dimensional space is compensated, but subsequently, due to the excessive amount of Au@DMSN, it is speculated that it hinders the contact between PS NPs and the SERS composite substrate.

[0050] 3. Comparison of the detection effects of each sample in Example 1 and Comparative Examples 1 - 5 Using 10 μg / mL and 1 μg / mL of PS NPs as probes respectively, SERS tests are carried out on each sample in Example 2 and Comparative Examples 1 - 5, and the results are asFigure 11 As shown, it can be seen that: Due to their non-plasmonic structures, DMSN and graphene nanosheets (G) cannot enhance the SERS signal and cannot detect PS NPs; As plasmonic materials, Au NPs and Ag NPs can attach to the surface of PS NPs through hydrophobic / electrostatic interactions and generate SERS enhancement. However, limited by the weak signal characteristics of PS NPs themselves, only weak characteristic peaks can be detected at a concentration of 10 μg / mL; Thanks to the dendritic mesoporous structure and high specific surface area of DMSN, Au@DMSN forms a three-dimensional satellite-like structure with abundant plasmonic nanogaps, successfully enhancing the signal in multiple dimensions and detecting 1 μg / mL of PS NPs; Although Ag@G has a stronger signal than Ag NPs due to the high specific surface area two-dimensional plane and excellent conductivity of graphene nanosheets, it still cannot detect 1 μg / mL of PS NPs due to the lack of three-dimensional spatial hot spot distribution.

[0051] This shows that the Au@DMSN / Ag@G composite material prepared in the embodiment of the present invention realizes a unique three-dimensional "hot spot enclosure" effect: PS NPs form high-intensity hot spot contacts with Ag@G at the bottom, and its surface realizes multi-site electromagnetic field coupling through the three-dimensional porous network constructed by Au@DMSN. The monodispersity of Au@DMSN forms a dynamic pore structure with sub-nanometer precision, generating a hierarchical confinement effect, wrapping PS NPs in the physical potential well formed by the noble metal plasmon oscillation field, and its stacked topological configuration effectively inhibits the aggregation of nanoplastics. At the material science level, the monodispersity of Au@DMSN overcomes the signal fluctuations caused by the broad particle size distribution (20 - 500 nm) of PS NPs and provides a clean Raman background; At the interface engineering level, the introduction of Ag@G realizes a "gravity compensation mechanism" - when PS NPs deposit due to gravity, Ag@G at the bottom provides high-density hot spot contacts, while the upper Au@DMSN extends the hot spots in the vertical direction to form a three-dimensional enhancement network. This synergistic effect enables the composite substrate to clearly detect 1 μg / mL of PS NPs.

[0052] 4. Quantitative detection and evaluation of PS NPs in the sample of Example 1 Using the sample of Example 1, different standard concentrations of PS NPs were detected under the following conditions. Specifically: V Au@DMSN / Ag@G : V PS NPs = 4:4, V Au@DMSN / Ag@G Concentration 1.125 mg / mL; KI concentration in the colloidal solution 0.10 mol / L; 4.1 Quantitative analysis PS NPs with different concentrations in a wide range of particle size distributions (200 - 500 nm) were tested. 1000 cm -1 The Raman peaks obtained were used as the characteristic peaks of PS for quantitative analysis. According to the Raman spectral intensity of the characteristic peaks, a relationship curve between the characteristic peak intensity I and the logarithm of the PS concentration (lgC) was plotted, and a quantitative analysis method was established, as shown in Figure 14 a and b in.

[0053] According to Figure 12 a and b in, as the concentration of PS NPs increased, the SERS intensity increased significantly, and its detection limit was 10 −4 mg / mL. Further, according to the Raman spectral intensity of the characteristic peaks, a relationship curve between the characteristic peak intensity I and the logarithm of the PS concentration (lgC) was plotted. The linear concentration range was within 10 −4 -10 −1 mg / mL. At 1000 cm -1 , the SERS intensity had a good linear relationship with the logarithm of the mass concentration. The linear fitting equation was y = 527.20x + 2318.26, and R 2 = 0.996.

[0054] 4.2 Evaluation of Uniformity, Anti-Interference and Selectivity The anti-interference, uniformity, selectivity and reliability of the detection were evaluated using a PS standard solution.

[0055] (1) Anti-Interference: Taking the main salt interference substances in the ocean, such as NaCl, KCl, CaCl2, MgCl2 and glucose, etc., a single series of salt interference environments in the water-salt environment were simulated, and the signals of PS (200 - 500 nm, 10 −2 mg / mL) were collected and detected.

[0056] The results are as shown in Figure 13 a in, indicating that in a single series of salt interference environments (0.8 mg / mL Ca 2+ , 58 mg / mL Na + , 1.1 mg / ml Mg 2+ , 1.6 mg / ml K + , 2 mg / mL glucose), the SERS intensity of PS was less interfered. This indicates that the detection method based on the Au@DMSN / Ag@G SERS substrate of the present invention can still effectively identify and detect PS in the presence of interference substances.

[0057] (2) Selectivity: PS (200 - 500 nm, 10 −2Mix with PMMA (300 nm, 1 mg / mL) and perform SERS detection.

[0058] As Figure 13 b in [reference] depicts the characteristic spectra of PS NPs (1000 cm -1 ) and PMMA NPs (596, 816 cm −1 ) detected respectively when measuring PS and PMMA NPs. When they are mixed together, these Raman characteristic peaks still exist without obvious peak displacement. The results show that the detection method of the present invention can distinguish the content in the mixture of nanoplastics characteristic peaks and can be used to detect different types of nanoplastics in complex environments.

[0059] (3) Stability: Select 0.01 mg / mL 200 - 500 nm PS NPs as the research object, and randomly select 22 positions on the silicon wafer to collect SERS spectra.

[0060] The results are as shown in Figure 13 c in [reference], and there is no significant difference in the SERS spectra at different detection sites. Further analysis of the response intensity of the characteristic peak at 1000 cm -1 finds that their response intensities are between 1116 and 1327. The average intensity is 1220, and the relative standard deviation (RSD) is 5.48%. Under the same test conditions, further repeatability tests are carried out to improve the reliability of the test results. As shown in d in Figure 13, the test is carried out in parallel with five groups of tests, and three points are randomly selected on each final test sample obtained in each group of tests for Raman spectroscopy analysis. Raman spectral data of each point are collected, and the relative standard deviation (RSD) of the characteristic peak intensities at each point is about 3.49 ± 1.21% on average. The results show that the prepared SERS substrate has good stability.

[0061] 4.3 Practicality and accuracy Add PS NPs (200 - 500 nm) with different concentrations to lake water. The lake water is taken from the Pearl River Lake in summer. After the sample is left standing overnight, the supernatant is taken and used directly without further processing.

[0062] (1) Practicality First, take a certain volume of Pearl River water and let it stand overnight, then take the supernatant for use. Measure a certain volume of PS solution and prepare solutions with concentrations of 100 μg / mL, 10 μg / mL, 2 μg / mL, 1 μg / mL, and 0.5 μg / mL. Then add them to Au@DMSN / Ag@G in equal volumes, add 20 μL of 0.1 M KI and shake, and then let it stand and incubate for 1 h. After incubation, take 20 μL and drop it onto a silicon wafer, dry it in an environment at 50 °C for 30 min, and then perform SERS detection.

[0063] The Pearl River water was taken in summer, and its geographical location is shown as a in Figure 14. After the sample was left standing overnight, the supernatant was directly used without further treatment. As shown in d of Figure 14, no SERS signal response was detected in the initial water sample by the above detection method. Therefore, a spike recovery experiment was carried out on PS NPs, and the results are shown in Table 1. The recovery rate of PS NPs was 91.18% to 109.27%, and the RSD (n = 3) range was 3.24% to 11.66%.

[0064] In addition, simple spike addition tests were also carried out on the nearshore seawater in the Dadonghai tourist area of Sanya City, the groundwater in the suburbs of Ningyuan County, Yongzhou City, and the water samples in the nearby polluted ditches. The sampling locations are shown as b and c in Figure 14. Further analysis showed that no characteristic signal of PS NPs was detected at 1000 cm⁻¹. Therefore, PS NPs with a concentration of 0.5 μg / mL were simulated and added to the above actual water samples. The results are shown in e - g of Figure 14, and all the added nanoplastics could be detected by the SERS substrate. The above results illustrate that the SERS substrate prepared in the embodiment of the present invention overcomes the problem of high detection limits of SERS technology for nanoplastics in saline water and polluted environments, and also proves that the prepared SERS substrate has excellent environmental adaptability.

[0065] (2) Accuracy The ultraviolet - visible spectrophotometry was used for comparative evaluation of accuracy.

[0066] First, a linear equation of the absorbance intensity and concentration of PS NPs with particle sizes in the range of 200 - 500 nm was established. Based on this, a spike addition test of lake water was carried out using the ultraviolet - visible spectrophotometry method and compared with the proposed SERS method.

[0067] As Figure 15 shown in a, b. The RSD value of the ultraviolet - visible spectrophotometer is very small, but the fluctuation range of the recovery rate is very large, from 49.83% to 134.95%. Obviously, the ultraviolet - visible spectrophotometry method is not suitable for testing the PS concentration in real water samples.

[0068] Table 1. Results of the spike recovery experiment for actual environmental water samples

[0069] These results confirm the superiority and feasibility of the detection method of the present invention in the detection of real aquatic environments.

[0070] In summary, the present invention rationally designs a two-dimensional planar substrate with excellent electrical conductivity and loaded with plasma Ag NPs; meanwhile, based on the Stober mechanism and the sol-gel strategy, a semi-compatible pore structure DMSN with embedded Au NPs is synthesized, and then the above-mentioned precursor materials are successfully prepared into Au@DMSN / Ag@G composites through electrostatic attraction. Using the obtained composites as a substrate, PS NPs with a size range of 200-500 nm can be detected. Compared with the current nanoplastics analysis methods, this substrate has the advantages of high sensitivity, anti-interference, good repeatability, and strong quantitative analysis ability. Moreover, a good recovery rate was obtained in the lake water labeling experiment.

[0071] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for preparing an Au@DMSN / Ag@G composite material, characterized in that, Including the steps: S1 Prepare Au@DMSN. S11 Synthesize dendritic mesoporous silica DMSN. Mix triethanolamine with deionized water and stir at 70 - 90 °C. Then add cetyltrimethylammonium bromide and sodium salicylate, and continue stirring and reacting. Subsequently, add tetraethyl orthosilicate dropwise to the above solution and stir and react at 75 - 85 °C. After the reaction ends, centrifuge and wash. Then, wash the obtained precipitate with a mixed solution of HCl and ethanol to remove the residual organic template, and finally dry in vacuum to obtain dendritic mesoporous silica DMSN. S12 Amine modification of DMSN. First, disperse the dendritic mesoporous silica DMSN obtained in step S11 in ethanol. Then, add ammonia water, deionized water, and (3-aminopropyl)triethoxysilane under vigorous stirring, and continue vigorous stirring. Finally, wash the final product with ethanol and dry in vacuum to obtain DMSN-NH2. S13 Synthesis of Au@DMSN. Disperse the DMSN-NH2 synthesized in step S12 into ultrapure water. Then, add chloroauric acid solution under an ice-water bath condition and stir and react. After that, continue to add trisodium citrate solution under vigorous stirring conditions, and then quickly add freshly prepared NaBH4 solution and continue reacting. After the reaction ends, centrifuge, wash, and dry to obtain Au@DMSN powder. S2 Prepare Ag@G. Disperse graphene nanosheets G in deionized water, and then heat to a constant temperature of 80 - 85 °C. Then add AgNO3 solution and keep stirring and reacting. Then heat to a constant temperature of 90 - 95 °C, and immediately add trisodium citrate solution to react, finally obtaining graphene nanosheets Ag@G with in-situ deposited plasmonic Ag nanoparticles. S3 Synthesis of Au@DMSN / Ag@G. Disperse the Au@DMSN and Ag@G obtained in steps S1 and S2 into deionized water, and uniformly compound them to obtain the Au@DMSN / Ag@G composite material.

2. The preparation method of the Au@DMSN / Ag@G composite material according to claim 1, characterized in that The pore size range of the DMSN synthesized in step S11 is 10 - 33 nm.

3. The preparation method of the Au@DMSN / Ag@G composite material according to claim 1, wherein In step S11, Triethanolamine:Deionized water:Cetyltrimethylammonium bromide:Sodium salicylate:Tetraethyl orthosilicate = 0.65 - 0.7 g:20 - 25 mL:0.35 - 0.40 g:0.16 - 0.17 g:3 - 5 mL.

4. The preparation method of the Au@DMSN / Ag@G composite material according to claim 1, wherein In step S11, in the mixed solution of HCl and ethanol, by volume ratio, HCl:Ethanol = 1:9; the temperature for washing away the residual organic template is 70 - 90 °C. The mass percentage concentration of the HCl is 38%.

5. The preparation method of the Au@DMSN / Ag@G composite material according to claim 1, characterized in that, In step S12, DMSN:Ethanol:Ammonia water:Deionized water:(3-aminopropyl)triethoxysilane = 90 - 100 mg:80 - 120 mL:2 - 3 mL:2 - 3 mL:0.5 - 2 mL.

6. The preparation method of the Au@DMSN / Ag@G composite material according to claim 1, characterized in that, In the step S13, the concentration of the chloroauric acid solution is 200 mg / mL, the concentration of the trisodium citrate solution is 1 w / v %, the concentration of the NaBH4 solution is 0.1 M, and according to the volume ratio, chloroauric acid: TSC: NaBH4 = 15-25: 90-110: 45-55.

7. The preparation method of the Au@DMSN / Ag@G composite material according to claim 6, characterized in that, In the step S13, ethanol washing is adopted, and the drying temperature is 30-50 °C.

8. The preparation method of the Au@DMSN / Ag@G composite material according to claim 1, characterized in that, In the step S2, according to the mass ratio, graphene nanosheets G: AgNO3 = 10: 35-40.

9. The preparation method of the Au@DMSN / Ag@G composite material according to claim 1, wherein, In the step S3, according to the mass ratio, Au@DMSN: Ag@G = 1-4: 4-1.

10. The Au@DMSN / Ag@G composite material prepared by the preparation method according to any one of claims 1-9.

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