Zr-PyDC-Au-Ag / GNS composite SERS (Surface Enhanced Raman Scattering) substrate as well as construction method and application thereof

Abstract

The invention belongs to the field of nano plastic detection, and particularly relates to a Zr-PyDC-Au-Ag / GNS composite SERS (Surface Enhanced Raman Scattering) substrate as well as a construction method and application thereof. According to the construction method, Zr-PyDC serves as a carrier of Au NPs, due to the high-porosity structure of the carrier, precious metal nanoparticles can be evenly distributed in and near pores to prepare Zr-PyDC at Au, then Ag NPs is synthesized and loaded to the surface of Zr-PyDC at Au through an in-situ reduction synthesis method to obtain Zr-PyDC at Au-Ag, meanwhile, graphene nanosheets are added to be compounded with the Zr-PyDC at Au-Ag, a Zr-PyDC at Au-Ag / GNS composite substrate is prepared, and the Zr-PyDC at Au-Ag / GNS composite substrate is prepared. Due to the characteristics of the graphene, the graphene can have a synergistic effect with other SERS substrates, so that the SERS detection performance is further enhanced. The relative deviation (RSD) of test signal results of the prepared substrate is less than 10%, and the requirements of quantitative detection are met.

Description

Technical Field

[0001] The present invention relates to the field of nanoplastics detection, and particularly to a Zr-PyDC@Au-Ag / GNS composite SERS substrate, a construction method thereof, and an application thereof. Background Art

[0002] At present, the detection technologies of nanoplastics mainly include microscopic imaging, mass spectrometry analysis, spectroscopic methods, etc. Among them, the Surface-Enhanced Raman Scattering (SERS) technology is regarded as a powerful tool for nanoplastics analysis due to its single-molecule sensitivity, fingerprint recognition ability, and non-destructive detection characteristics. However, traditional SERS substrates (such as gold / silver nanosols) are easily interfered by environmental ions and organic molecules in practical applications, resulting in poor signal repeatability; while SERS substrates designed based on two-dimensional structures such as anodic aluminum oxide (AAO) are limited by the planarization characteristics and the density of "hot spots" in three-dimensional space is difficult to achieve high-sensitivity detection of low-concentration PS NPs. To address the above problems, Metal-Organic Framework (MOF) materials, due to their high porosity, adjustable pore size, and ultra-large specific surface area, provide an ideal carrier for the loading of noble metal nanoparticles. The three-dimensional hierarchical pore structure of MOF can not only effectively anchor nano-metal particles to form high-density and uniformly distributed SERS active sites, but its rich pores can also enrich PS NPs through the confinement effect, significantly enhancing the contact probability between the target and the "hot spots". In addition, the metal nodes or organic ligands of some MOFs can further synergistically enhance the Raman signal through chemical interactions, thus breaking through the sensitivity bottleneck of traditional substrates. Although MOF-based SERS materials show great potential in environmental analysis, their applications in the field of nanoplastics detection are still rarely reported. Summary of the Invention

[0003] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention constructs a composite substrate loaded with noble metal nanoparticles by Zr-PyDC for the detection of PS NPs, broadening the research boundary of SERS technology in environmental pollutant analysis.

[0004] The specific technical solutions of the present invention are as follows: In the first aspect of the present invention, a construction method of a Zr-PyDC@Au-Ag / GNS composite SERS substrate is provided, including the steps: S1 Synthesis of Zr-PyDC Dissolve zirconium chloride in DMF, then add concentrated hydrochloric acid, seal and let stand for 0.5 - 2 h in the absence of light. Subsequently, add pyridine-2,5-dicarboxylic acid to the above solution and disperse until it is completely dissolved. Then transfer the solution to a reaction kettle and react at 110 - 130 °C for 15 - 25 h. After the reaction, centrifuge to obtain the precipitate, wash it, and dry it to obtain the Zr-PyDC; S2 Synthesis of Zr-PyDC@Au-Ag, In the ethanol solution of Zr-PyDC, add chloroauric acid solution under stirring conditions and stir for more than 5 h, then centrifuge to obtain the precipitate and redissolve it in ethanol. Subsequently, under vigorous stirring conditions, dropwise add NaBH4 solution. After the reaction, centrifuge and wash to obtain Zr-PyDC@Au. Then disperse Zr-PyDC@Au in DMF, then add silver nitrate and dissolve it completely, and react at 110 - 130 °C for 2 - 5 h. After the reaction, centrifuge to obtain the precipitate and wash to obtain Zr-PyDC@Au-Ag; S3 Synthesis of Zr-PyDC@Au-Ag / GNS; Disperse graphene nanosheets GNS and Zr-PyDC@Au-Ag obtained in step S2 in DMF, stir at 60 °C, centrifuge to obtain the precipitate, wash it, and obtain the Zr-PyDC@Au-Ag / GNS composite SERS substrate.

[0005] This scheme uses Zr-PyDC as the carrier of Au NPs. Due to its high pore structure, noble metal nanoparticles can be evenly distributed in and near the pores of Zr-PyDC to obtain Zr-PyDC@Au. Subsequently, Ag NPs are synthesized and loaded onto the surface of Zr-PyDC@Au by in-situ reduction synthesis method to obtain Zr-PyDC@Au-Ag, and the high regularity arrangement of its crystal itself is used to reduce the instability of the signal. Then, the ordered material graphene nanosheets are introduced. At the same time, due to the ultra-high conductivity characteristics of graphene itself, it can be combined with the Zr-PyDC@Au-Ag substrate, and the synergistic effect further enhances the detection performance of the SERS substrate and reduces the possible fluorescence background interference of Zr-PyDC.

[0006] In some embodiments of the present invention, in step S1, zirconium chloride:DMF:concentrated hydrochloric acid:pyridine-2,5-dicarboxylic acid = 115 - 118 mg:3 - 8 mL:3 - 8 mL:82 - 85 mg.

[0007] In some embodiments of the present invention, in step S2, the concentration of the ethanol solution of Zr-PyDC is 3-4 mg / mL, the concentration of the chloroauric acid solution is 180-220 mg / mL, and the concentration of the NaBH4 solution is 0.05-0.2 mol / L. In terms of volume ratio, the ethanol solution of Zr-PyDC: chloroauric acid solution: NaBH4 solution = 3:0.02:0.2; in terms of mass ratio, Zr-PyDC: silver nitrate = 10:0.1~40; preferably, Zr-PyDC: silver nitrate = 10:10.

[0008] In some embodiments of the present invention, in step S3, the mass ratio of graphene nanosheets GNS:Zr-PyDC@Au-Ag is 1:4.

[0009] The second aspect of the present invention provides a composite SERS substrate prepared by the above construction method.

[0010] The third aspect of the present invention further provides a method for detecting nanoplastics based on the composite SERS substrate obtained by the above construction method, comprising the following steps: A Zr-PyDC@Au-Ag / GNS solution was prepared and then mixed with a polystyrene nanoparticle suspension, and KI was added as an aggregating agent. After the above solutions were fully mixed, they were left to stand until the sample formed a stable colloidal solution for SERS detection.

[0011] In some embodiments of the present invention, the KI concentration in the colloidal solution is 0.01-0.025 mol / L, preferably, the KI concentration is 0.025 mol / L In some embodiments of the present invention, the concentration of the Zr-PyDC@Au-Ag / GNS solution is 0.1-1 mg / mL, preferably, the concentration of the Zr-PyDC@Au-Ag / GNS solution is 0.5 mg / mL.

[0012] In some embodiments of the present invention, the polystyrene nanoparticles have a particle size of 20-500 nm, such as 20 nm, 50-100 nm, 200-500 nm, etc.

[0013] In some embodiments of the present invention, the nanoplastic detection method includes qualitative detection and / or quantitative detection, wherein the quantitative detection is to draw a curve of the relationship between the characteristic peak intensity and the nanoplastic concentration according to the Raman spectrum intensity of the characteristic peak to determine the nanoplastic concentration of the sample to be tested. For example, in some preferred embodiments, for 20 nm PS NPs, the linear fitting equation y = 19.96x + 532.03, R 2= 0.957; In some preferred embodiments, for 50 - 100 nm PSNPs, the linear fitting equation is y = 12.82x + 711.31, R 2 = 0.951; In some preferred embodiments, for 200 - 500 nm PS NPs, the linear fitting equation is y = 15.03x + 702.04, R 2 = 0.987; y is the characteristic peak intensity, and x is the concentration of nanoplastics.

[0014] The beneficial effects of the present invention are as follows: In the present invention, Zr - PyDC is used as the carrier of Au NPs. Due to its high - porosity structure, noble - metal nanoparticles can be uniformly distributed in and near the pores of Zr - PyDC to prepare Zr - PyDC@Au. Subsequently, Ag NPs are synthesized and loaded onto the surface of Zr - PyDC@Au by in - situ reduction synthesis method to obtain Zr - PyDC@Au - Ag. At the same time, graphene nanosheets are added and compounded with it to prepare the Zr - PyDC@Au - Ag / GNS composite substrate, so that Zr - PyDC@Au - Ag is loaded onto the dispersed graphene nanosheets. At the same time, due to the characteristics of graphene itself, it can synergistically act with other SERS substrates to further enhance the SERS detection performance.

[0015] The prepared Zr - PyDC@Au - Ag / GNS substrate can be used to ultrasensitively detect polystyrene nanoparticle suspensions (20 - 500 nm, ppm level) in different aquatic systems, solving the key gap in quantifying trace nanoplastics with heterogeneous sizes / compositions. This method overcomes the limitations of traditional two - dimensional substrates through the synergistic effect of gold / silver, and the relative deviation (RSD) of the specific test signal results is less than 10%, meeting the requirements of quantitative detection. It is worth mentioning that KI is introduced during the detection process, and its induced - enrichment characteristics are used to improve the SERS performance. Finally, in the actual water - sample environment test, PS NPs in the spiked water samples are successfully detected, and the recovery rate is between 82.26% and 109.43%, and the RSD is between 6.45% and 22.49%, enabling quantitative analysis of wide - size nanoplastics with environmental diversity. Brief Description of the Drawings

[0016] Figure 1 is the synthesis schematic diagram of Zr - PyDC@Au - Ag / GNS; Figure 2a is the XRD powder diffraction pattern of Zr - PyDC and UIO - 66; Figure 2bXRD powder diffraction patterns of Zr-PyDC, Zr-PyDC@Au, Zr-PyDC@Au-Ag, Zr-PyDC@Au-Ag / GNS and GNS; Figure 3 TEM images of Zr-PyDC@Au and Zr-PyDC@Au-Ag, where (a) and (b) are TEM images of Zr-PyDC@Au, and (c), (d), (e), (f), (g), (h) are TEM images of Zr-PyDC@Au-Ag; Figure 4 UV-visible absorption spectra of Zr-PyDC, Zr-PyDC@Au and Zr-PyDC@Au-Ag; Figure 5 XPS spectra, where (a) is the full XPS spectrum of Zr-PyDC@Au-Ag, (b) is the high-resolution XPS spectrum of Au 4f, and (c) is the high-resolution XPS spectrum of Ag 3d; Figure 6 N2 adsorption-desorption isotherm and pore size distribution diagram of Zr-PyDC; Figure 7 Thermogravimetric diagrams of Zr-PyDC, Zr-PyDC@Au, Zr-PyDC@Au-Ag and Zr-PyDC@Au-Ag / GNS materials; Figure 8 Raman spectra of Zr-PyDC@Au-Ag / GNS and PS NPs and SERS test results of PS NPs with different particle sizes; where (a) is the Raman spectrum of Zr-PyDC@Au-Ag / GNS and PS, and (b) is the test results of PS NPs with different particle sizes; Figure 9 Comparison diagram of PS NPs detection results of samples with different silver nitrate dosages in Examples 1-5, where (a) is the spectrogram of the influence of silver nitrate dosage on 200-500 nm PS NPs (0.01 mg / mL) at different masses, and (b) is the SERS intensity diagram corresponding to the position at 1000 cm -1 in diagram (a); Figure 10 Statistical chart of the detection results of different concentrations of PS NPs with the samples in Example 1 and Comparative Examples 1-5 as substrates; Figure 11 Results of the KI dosage optimization experiment, where (a) is the SERS spectrogram of 200-500 nm PS NPs (0.01 mg / mL) at different KI molar concentrations, and (b) is the SERS intensity result corresponding to the position at 1000 cm -1 in diagram (a); Figure 12 Comparison of detection results for different SERS substrate concentrations, where (a) shows the SERS spectra of 200 - 500 nm PS NPs (0.01 mg / mL) at different SERS substrate concentrations, and (b) shows the SERS intensity corresponding to the position at 1000 cm -1 in Figure (a). Figure 13 Raman spectra of PS NPs with particle size distributions of 20 nm, 50 - 100 nm, and 200 - 500 nm detected based on the Zr - PyDC@Au - Ag / GNS substrate in different concentration ranges of 1 - 100 μg / ml, as well as the linear variation relationship between their concentrations and characteristic peak intensities. Among them, (a) and (b) are the Raman spectra of 20 - nm PS NPs in different concentration ranges of 1 - 100 μg / ml and the linear variation relationship between their concentrations and characteristic peak intensities, (c) and (d) are the Raman spectra of 50 - 100 - nm PS NPs in different concentration ranges of 1 - 100 μg / ml and the linear variation relationship between their concentrations and characteristic peak intensities, and (e) and (f) are the Raman spectra of 200 - 500 - nm PS NPs in different concentration ranges of 1 - 100 μg / ml and the linear variation relationship between their concentrations and characteristic peak intensities; Figure 14 Demonstration diagram of the contact behavior between PS NPs with different particle sizes and Zr - PyDC@Au - Ag / GNS; Figure 15 Experimental results of the detection method evaluation of this application, where (a) shows the experimental results of uniformity, (b) shows the experimental results of reproducibility, and (c) shows the experimental results of high - salt environment simulation test. Detailed implementation manners

[0017] For the convenience of understanding 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 of the present invention more thorough and comprehensive.

[0018] 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 specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0019] 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.

[0020] Chemicals and Materials Zirconium tetrachloride (ZrCl4, analytical pure), 2,5-dicarboxypyridine (analytical pure), glacial acetic acid (analytical pure), N,N-dimethylformamide (DMF, analytical pure), absolute ethanol (CH3CH2OH, analytical pure), silver nitrate (AgNO3, analytical pure), sodium borohydride (NaBH4, analytical pure), chloroauric acid trihydrate (HAuCl4·3H2O, analytical pure), graphene nanosheets (GNS, analytical pure), polystyrene nanoparticle suspension (PS NPs, 2.5%), calcium chloride (CaCl2, analytical pure), magnesium chloride (MgCl2, analytical pure), sodium chloride (NaCl, analytical pure), potassium chloride (KCl, analytical pure), glucose (analytical pure), polyvinylpyrrolidone (PVP, average molecular weight 58000), ethylene glycol (analytical pure).

[0021] Example 1 Synthesis of Zr-PyDC@Au-Ag / GNS Refer to Figure 1 , the Zr-PyDC@Au-Ag / GNS of the present invention is synthesized by the following steps, specifically as follows: S1 Synthesis of Zr-PyDC Dissolve 116.5 mg of zirconium tetrachloride in 5 mL of DMF, sonicate until it is completely dissolved, then add 5 mL of concentrated hydrochloric acid and cover the lid, let it stand in the dark for 1 h, then add 83.5 mg of pyridine-2,5-dicarboxylic acid to the above solution, sonicate until it is completely dissolved, then transfer the solution to a 20 mL reaction kettle, react at 120 °C for 20 h, after the reaction is completed, centrifuge to obtain the precipitate, wash it twice with DMF and ethanol respectively, and then dry it under vacuum at 50 °C for use.

[0022] S2 Synthesis of Zr-PyDC@Au and Zr-PyDC@Au-Ag Take 10 mg of Zr-PyDC, add it to 3 mL of ethanol, and ultrasonicate for 20 min. Then, under stirring conditions, add 20 μL of a chloroauric acid solution with a concentration of 200 mg / mL, and stir for more than 5 h. Then, centrifuge to obtain the precipitate and redissolve it in 3 mL of ethanol. Subsequently, under vigorously stirring conditions, slowly dropwise add 200 μL of a 0.1 M NaBH4 solution, react for 40 min, centrifuge, and then wash three times with DMF to obtain Zr-PyDC@Au dispersed in DMF for use. Transfer 40 mL of the well-dispersed Zr-PyDC@Au solution to a 100 mL reaction kettle, then add 20 mg of silver nitrate, ultrasonicate to completely dissolve it, and react at 120 °C for 3 h. After the reaction, centrifuge to obtain the precipitate, wash it three times with DMF, and obtain Zr-PyDC@Au-Ag.

[0023] S3 Synthesis of Zr-PyDC@Au-Ag / GNS Take an appropriate amount of graphene nanosheets GNS and disperse them in DMF. Stir with the prepared Zr-PyDC@Au-Ag at a mass ratio of 1:4 at 60 °C for 1 h, centrifuge to obtain the precipitate, wash it three times with ethanol, and wash it twice with deionized water. The obtained Zr-PyDC@Au-Ag / GNS is formulated into an appropriate mass concentration for use.

[0024] Examples 2 - 5 The difference from Example 1 is that in step S2, the addition amount of silver nitrate is different, which are 0 mg, 10 mg, 30 mg, and 40 mg in sequence, and the rest are the same.

[0025] Comparative Example 1 Refer to step S1 of Example 1 to prepare Zr-PyDC.

[0026] Comparative Example 2 Refer to step S2 of Example 1 to prepare Zr-PyDC@Au.

[0027] Comparative Example 3 Refer to step S2 of Example 1 to prepare Zr-PyDC@Au-Ag.

[0028] 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.

[0029] Comparative Example 5 Ag NPs were synthesized as follows: 0.3 g of polyvinylpyrrolidone (PVP) was dissolved in 17 mL of ethylene glycol at room temperature, and then it was placed in an oil bath at 160 °C and heated with 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.

[0030] Performance Testing and Characterization I. Material Characterization 1. XRD Analysis As shown in Figure 2a, it can be seen that Zr-PyDC synthesized in Example 1 has the same framework structure as UIO-66, and the loss of crystallinity is small. The five diffraction peaks of Zr-PyDC@Au at 2θ = 38.3°, 44.5°, 64.7° and 77.7° correspond to the (111), (200), (220) and (311) lattice planes of Au (JCPDS card number 04-0784); 26.14° and 54.28° belong to the attribution peaks of graphene nanosheets. As Figure 2b shown, for Zr-PyDC@Au-Ag, because the content of Ag NPs is much higher than that of Au NPs, it is speculated that the diffraction peaks of Ag cover the characteristic peaks of Zr-PyDC and also cover the diffraction peak positions of Au, resulting in overlap. Therefore, the five diffraction peaks at 2θ = 38.2°, 44.4°, 64.6° and 77.5° belong to the (111), (200), (220) and (311) lattice planes of Ag (JCPDS card number 87-0597), confirming the successful loading of Ag NPs and Au NPs. At the same time, the characteristic peaks of GNS can be seen in Zr-PyDC@Au-Ag / GNS, confirming the successful composite of Zr-PyDC@Au-Ag and GNS.

[0031] 2. TEM Analysis TEM images ( Figure 3 (a) and (b) in it) show the octahedral cubic structure of Zr-PyDC in Zr-PyDC@Au. At the same time, a large number of Au NPs with a size of about 10 nm are observed to cover the surface of Zr-PyDC, forming a relatively dense AuNPs layer. (c) and (d) in Figure 3 show that the average size of Ag NPs on the surface of Zr-PyDC@Au-Ag is about 60 nm, and a large number of them cover the surface of Zr-PyDC@Au. Au NPs and Ag NPs are scattered on the surface of Zr-PyDC to form a bimetallic hybrid SERS substrate with a synergistic enhancement effect. Figure 3 (e)-(h) in it show the elemental distribution of the main elements (Zr, Ag, Au, and C) of Zr-PyDC@Au-Ag, indicating that Au and Ag elements are evenly distributed on the surface of Zr-PyDC, and at the same time proving the successful synthesis of Zr-PyDC@Au-Ag.

[0032] 3. Ultraviolet-visible absorption spectrum Zr-PyDC, Zr-PyDC@Au, and Zr-PyDC@Au-Ag were further tested by ultraviolet-visible spectroscopy. Figure 4 above confirmed the successful loading of noble metal nanoparticles, showing a characteristic absorption peak of Au NPs near 535 nm, proving the successful synthesis of Au NPs. However, later due to the formation of the surface of Ag NPs, the theoretical characteristic peak at 446 nm and the characteristic peak of Au NPs overlapped in spectral absorption and other reasons, resulting in an upward trend in the entire absorption peak, indirectly proving the successful loading of Au NPs and Ag NPs.

[0033] 4. XPS analysis To further prove the successful loading of gold and silver nanoparticles, XPS tests were performed on the Zr-PyDC@Au-Ag powder sample. The charge was corrected according to the binding energy of contaminated carbon at 284.8 eV. As shown in Figure 5(a), it shows the presence of elements such as C, N, O, Ag, and Au. As shown in Figure 5(b) and (c), Au 4f has two peaks at 84.87 eV and 88.57 eV, and the double-peak spacing is 3.70 eV. These peaks are the Au 4f 7 / 2 and Au 4f 5 / 2 peaks of metallic Au; Ag 3d shows double peaks at 368.97 eV and 374.97 eV, and the double-peak spacing is 6.0 eV. These peaks are the Ag 3d 5 / 2 and Ag 3d 3 / 2Peak. The above results prove that Ag NPs and Au NPs have been successfully modified onto the surface of Zr-PyDC.

[0034] 5. Nitrogen adsorption-desorption characterization Figure 6 shows the nitrogen adsorption-desorption isotherm curve and pore size distribution diagram of Zr-PyDC. It can be seen from the figure that the nitrogen adsorption isotherm of Zr-PyDC is a typical type I isotherm, which is the isotherm possessed by typical microporous materials. The peak distribution of Zr-PyDC in the Barrett-Joyner-Halenda (BJH) results indicates that the pore size range of Zr-PyDC is 1-2 nm, and the average pore size is 1.67 nm, proving that the synthesized Zr-PyDC is a microporous structure. The total surface area of the MOF is 1312.9 m 2 / g, and the total pore volume is 0.5487 cm 3 / g. This unique morphology provides sufficient loading space for the loading of noble metal nanoparticles.

[0035] 6. Thermogravimetric analysis The TG curve is shown in Figure 7. The mass loss trends of Zr-PyDC, Zr-PyDC@Au, Zr-PyDC@Au-Ag, and Zr-PyDC@Au-Ag / GNS are roughly the same. The overall process gradually transitions between the steps of solvation, desolvation, and demethylation. Due to the combination of noble metal nano-gold, noble metal nano-silver, and graphene nanosheets, it can be seen that Zr-PyDC has the highest loss rate. The loss rate decreases due to the addition of noble metals. Later, due to the poor heat resistance of graphene nanosheets, the loss rate of Zr-PyDC@Au-Ag / GNS is higher than that of Zr-PyDC@Au-Ag, confirming the successful combination of the materials.

[0036] II. Comparison of PS NPs detection effects 1. PS NP S Characteristic peak determination Sample preparation: Mix the Zr-PyDC@Au-Ag / GNS prepared in Example 1 with PS NPs, then add KI solution as an aggregating agent. After fully 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 spectroscopy results have all been baseline corrected.

[0037] Normal Raman and SERS spectra were obtained using a confocal laser microscope Raman spectrometer (Horiba LabRAM HR Evolution) and a 564 nm (3.5%) laser. During the Raman spectrum acquisition, a 50x objective lens was selected, and the acquisition wavelength range was 400 - 1700 cm -1 There were 3 accumulations in a 5s acquisition time.

[0038] Raman scattering tests were performed to characterize PS NPs with a particle size distribution range of 200 - 500 nm. As Figure 8 shown in a of -1 , the two most prominent characteristic peaks were located at 1000 cm -1 and 1030 cm -1 , corresponding to the breathing vibration peak of the benzene ring and the in-plane deformation of C-H, respectively. There was a low peak at 1607 cm -1 , attributed to the skeletal stretching vibration of the benzene ring. Since the peak intensity at 1000 cm -1 was the strongest characteristic peak, the concentration of PS NPs was reflected by comparing the intensity of this peak subsequently.

[0039] In addition, it can be seen that for all substrates without signals near 1000 cm -1 and 1030 cm -1 , the interference of SERS substrates on the detection of PS NPs can be excluded.

[0040] Secondly, as Figure 8 shown in b of -2 , for PS NPs with the same mass concentration, the SERS composite substrate was also able to detect PS NPs with particle sizes of 50 - 100 nm and 20 nm at a mass concentration of 10 -2 mg / mL. In summary, the SERS substrates prepared in the present invention were all able to detect PS NPs with particle sizes of 50 - 100 nm and 20 nm.

[0041] In the actual environment, plastics have the characteristic of differential particle size distribution. The study of PS NPs with a wide range distribution is more innovative and representative. Therefore, in the experiment, PS NPs samples with a wide particle size range distribution were used as the main research object, and dynamic light scattering (DLS) experiments were carried out on them, proving that the particle size distribution range of PS NPs was mainly in 200 - 500 nm. In addition, due to their small nano size, they can enter the hot spot gaps of the SERS composite material for attractive deposition between plastics. On the other hand, since the ordinary Raman characterization signals of 50 - 100 nm and 20 nm PS are smaller than those of 200 - 500 nm PS, subsequent experiments selected 200 - 500 nm PS with more SERS signal advantages for detection.

[0042] 2. Comparative Detection Effects of Materials Synthesized in Examples 1 - 5 The SERS substrate performance synthesized with various amounts of silver nitrate in Examples 1 - 5 was measured with 200 - 500 nm PS NPs at a concentration of 0.01 mg / mL as the test target. As depicted in Figure 9 showing the increase in the amount of silver nitrate used, the SERS intensity change of PS at 1000 cm -1 is obvious. It may be attributed to the fact that the content of Ag nanoparticles in Zr - PyDC@Au - Ag / GNS is too low to provide sufficient hot spots for PS nanoparticles in three - dimensional space. When the amount of silver nitrate is 10 mg, the overly dense coverage of silver nanoparticles may reduce the coordination between Ag NPs and Au NPs, thus affecting the SERS signal. These results indicate that loading an appropriate amount of Ag NPs onto Zr - PyDC@Au can significantly improve the performance of the SERS composite substrate.

[0043] 3. Comparative Detection Effects of Samples in Example 1 and Comparative Examples 1 - 5 PS NPs at 10 μg / mL and 1 μg / mL were used as probe molecules to perform SERS tests on each sample in Example 1 and Comparative Examples 1 - 5 respectively.

[0044] As shown in Figure 10, Zr-PyDC and graphene nanosheets (G) cannot enhance the SERS signal due to their non-plasmonic structures, so PS NPs cannot be detected; Au NPs and Ag NPs, as plasmonic materials, can be adsorbed on the surface of PS NPs through hydrophobic / electrostatic interactions and produce 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 octahedral structure and high specific surface area characteristics of Zr-PyDC, the Zr-PyDC@Au substrate constructed in the embodiment of the present invention forms a three-dimensional structure with rich plasmonic nanogaps, and PS NPs at 10 μg / mL are successfully detected. After further introducing Ag NPs to form a Zr-PyDC@Au-Ag bimetallic structure, the synergistic enhancement effect of Au and Ag successfully breaks through the detection limit to 1 μg / mL of PS NPs. Considering that Zr-PyDC itself may have fluorescence background interference, GNS with ultra-high conductivity characteristics is introduced, which effectively quenches the fluorescence background and significantly improves the reliability and accuracy of the detection signal of 1 μg / mL PS NPs. This fact indicates that the combination of plasmonic and high-conductivity materials can provide the best experimental conditions for maximizing the performance of SERS substrates, highlighting the synergistic effect between the two.

[0045] Example 6, Optimization of the dosage of KI in the detection method In this example, the Zr-PyDC@Au-Ag / GNS prepared in Example 1 was mixed with PS NPs, and then KI solution was added as an aggregator. After the above solution was fully mixed, it was allowed to stand for 1 h to wait for the sample to form a stable colloidal solution. Finally, the mixed solution (20 μL) was dropped onto a 5×5 mm silicon wafer with a glass micropipette and dried in an oven at 50°C for 1 hour. The dried sample was subjected to SERS detection. The obtained Raman spectral results were all baseline corrected.

[0046] Among them, PS NPs are PS NPs with a concentration of 0.01 mg / mL and a particle size distribution of 200-500 nm. The volume ratio of Zr-PyDC@Au-Ag / GNS to PS NPs is fixed at 1:1. In the colloidal solution, the concentration of KI is increased from 0.01 mol / L to 0.025 mol / L to screen the optimal dosage of the aggregator KI.

[0047] As shown in Figure 11, 1000 cm -1The SERS intensity at [specific position] increased from 736 to 887 as the KI concentration increased from 0.01 mol / L to 0.025 mol / L. This is attributed to the fact that at the ideal KI level, a strongly bonded monolayer will form on the surface of the SERS substrate. However, when the KI concentration exceeds 0.025 mol / L, a further increase in concentration leads to a decrease in the SERS intensity. This is because the excess KI is physically adsorbed outside the strongly bound surface layer, which prevents the approach of the nanoplastics and reduces the corresponding SERS signal. Therefore, the optimal KI concentration is 0.025 mol / L for subsequent SERS analysis.

[0048] Example 7, Optimization of Substrate Concentration in the Detection Method Fix the KI concentration at 0.025 mol / L. Referring to Example 6, 200 - 500 nm PS NPs (0.01 mg / mL) were also used as performance probes, and the Zr-PyDC@Au-Ag / GNS synthesized in Example 1 was used as the SERS substrate. Raman detection was carried out by adjusting the substrate concentration in the colloidal solution to 0.1 mg / mL, 0.25 mg / mL, 0.5 mg / mL, 0.75 mg / mL, and 1 mg / mL respectively.

[0049] As Figure 12 It can be seen that the SERS intensity at 1000 cm -1 increased sharply from 321 at 0.1 mg / mL to 930 at 0.5 mg / mL as the substrate concentration increased. However, a further increase in mass led to a decrease in intensity. Therefore, the optimal response was shown at a ratio of 0.5 mg / mL. This may be attributed to the generation of a small number of hot spot signals at a low substrate volume. Therefore, the SERS intensity was relatively low. However, when the substrate volume was too large, it was possible that some PS NPs were covered by the SERS substrate. This inevitably led to the loss of SERS signals from these specific nanoplastics. Therefore, a SERS substrate concentration of 0.5 mg / mL was selected for subsequent experiments.

[0050] Example 8, Quantitative Detection of PS NPs Detect different concentrations of PS NPs under the optimal conditions determined above to establish a quantitative detection method.

[0051] Select 1000 cm -1The Raman peak at [specific location] is used as the characteristic peak of PS. 25 mg / mL of PS NPs suspension (20 nm, 50 - 100 nm, 200 - 500 nm) is diluted to prepare a series of PS standard solutions with concentrations of 100 μg / mL, 50 μg / mL, 25 μg / mL, 10 μg / mL, and 1 μg / mL for detection to obtain detection data. Based on the peak intensity, the detection standard curve of PS NPs is plotted. The results are as Figure 13 shown. It can be seen that as the concentration of the PS suspension increases, the SERS intensity increases significantly, and its detection limit is 10 -3 mg / mL. Further, according to the Raman spectral intensity of the characteristic peak, a relationship curve between the characteristic peak intensity I and the PS concentration is plotted. The linear concentration range is within 10 -3 -10 -1 mg / mL. At 1000 cm -1 , the SERS intensity has a good linear relationship with the mass concentration (linear fitting equation for 20 nm PS NPs: y = 19.96x + 532.03, R 2 = 0.957, b in Figure 13; linear fitting equation for 50 - 100 nm PS NPs: y = 12.82x + 711.31, R 2 = 0.951; linear fitting equation for 200 - 500 nm PS NPs: y = 15.03x + 702.04, R 2 = 0.987; y = characteristic peak intensity, x = concentration of PS NPs).

[0052] The above results indicate that the Zr-PyDC@Au-Ag / GNS composite substrate prepared in the embodiments of the present invention has the following advantageous features (as shown in Figure 14): First, the unique chemical hierarchical structure constructs an extended Raman hot spot region in three-dimensional space, significantly enhancing the effective range of electromagnetic field enhancement compared to traditional substrates. Second, the excellent monodisperse characteristics of the substrate material form a rich nano-porous network. This multi-level structure not only effectively inhibits the aggregation of nanoplastics but also adapts to PS NPs with different particle sizes (20 - 500 nm) through the size matching effect, ensuring that the nanoplastic particles can be efficiently embedded in the substrate pores. During this process, the PS NPs can simultaneously establish multiple-point contacts with the Zr-PyDC@Au-Ag coordination layer and the GNS surface, forming a uniform "sandwich"-type enhanced interface. Finally, by introducing KI for surface modification, the binding energy between the PS NPs and the substrate is further increased, forming a denser plasmon coupling system. The results show that the composite substrate has successfully achieved highly sensitive detection of PS NPs with three particle size gradients of 20 nm, 50 - 100 nm, and 200 - 500 nm, and the lowest detection limit reaches the order of 1 μg / mL. This interface optimization strategy based on multi-scale structure regulation provides a new technical path for the trace detection of nanoplastics in complex systems.

[0053] In summary, the detection method established using the substrate of the embodiments of the present invention has the advantages of high sensitivity and wide detection limit.

[0054] Example 9 Evaluation of the Uniformity, Reproducibility, and Anti-Interference Performance of the Detection Method The anti-interference performance, uniformity, and reproducibility of the detection were evaluated using a PS standard solution.

[0055] (1) Uniformity and reproducibility: 0.025 mg / mL 200 - 500 nm PS NPs were selected for the study, and SERS spectra were collected at 15 randomly selected positions on the wafer. As shown in Figure 15a, we analyzed the response intensity of the characteristic peak at 1000 cm -1 and found that their response intensities were between 1035 and 1471. The average intensity was 1231, and the relative standard deviation (RSD) was 9.44%. Under the same experimental conditions, a repeatability test was further carried out to improve the reliability of the experimental results. As shown in Figure 15b, the experiment was carried out in parallel with five groups of experiments, and three points were randomly selected on each final test sample obtained in each group for Raman spectroscopy analysis. Raman spectral data of each point were collected, and the average relative standard deviation (RSD) of the characteristic peak intensities of each point was approximately 6.97%. The results show that the prepared SERS substrate has good stability.

[0056] (2) 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 NPs (200 - 500 nm, 10 − 2 mg / mL) were collected and detected.

[0057] The results are as shown in Figure 15 c in 2+ , indicating that in the interference environment of a single series of salts (0.8 mg / mL Ca + , 58 mg / mL Na 2+ , 1.1 mg / mL Mg + , 1.6 mg / mL K

[0058] Example 10 Application of Zr-PyDC@Au-Ag / GNS in the Detection of PS NPs in Actual Water Samples PS NPs (200 - 500 nm) with different concentrations were added to lake water. The lake water was taken from the Pearl River Lake in summer. After the sample was left standing overnight, the supernatant was taken and used directly without further processing. There was no SERS signal response in the initial water sample, so a standard addition recovery experiment was carried out using the Pearl River water as the matrix.

[0059] The test method is as follows: First, take a certain volume of Pearl River water and leave it standing overnight, then take the supernatant for use. Measure a certain volume of PS solution and prepare it into 100 μg / mL, 10 μg / mL, 2 μg / mL, 1 μg / mL, 0.5 μg / mL, and then add an equal volume to Zr-PyDC@Au-Ag / GNS. Then add 20 μL of 0.025M KI and shake it, and then leave it standing and incubating for 1 h. After the incubation is over, take 20 μL and drop it onto a silicon wafer, dry it in an environment of 50°C for 30 min, and then perform SERS detection.

[0060] There was no SERS signal response in the initial water sample, so the recovery rate of PS NPs was detected by standard addition. 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%.

[0061] Table 1. Results of Standard Addition Recovery Experiment for Actual Environmental Water Samples

[0062] These results confirm the feasibility of the detection method of the present invention in the detection of real aquatic environments.

[0063] In summary, the present invention utilizes the characteristics of high porosity, adjustable pore size and ultra-large specific surface area of metal-organic frameworks, successfully loads noble metal nanoparticles onto the surface of Zr-PyDC, and composites them onto graphene nanosheets through electrostatic attraction. Since Zr-PyDC itself is also a product with metal as the node, it can synergistically interact with the plasma to a certain extent, breaking through the sensitivity bottleneck of traditional SERS substrates. Similarly, graphene nanosheets have excellent synergistic enhancement effects on the construction of SERS substrates due to their own ultra-high order and high electron conductivity. The SERS substrate constructed by the present invention realizes the quantitative detection of 100 μg / mL - 1 μg / mL PS NPs in the water environment. The relative deviation (RSD) of the test results of the SERS substrate materials prepared in the same batch and different batches is less than 10%, meeting the requirements of quantitative detection. When actually detecting water bodies, the corresponding quantitative curve can be selected according to the characteristics of the target substance and the environment where it is located to achieve the goal of accurate quantification. Through the construction of a composite substrate with Zr-PyDC loaded with noble metal nanoparticles, the detection results of this study are more reliable, with higher stability, and one order of magnitude more sensitive than previous studies, providing a new strategy for the efficient detection of PS NPs, having great application potential, and at the same time broadening the research boundary of SERS technology in the analysis of environmental pollutants.

[0064] 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 embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered that 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 construction method of a Zr-PyDC@Au-Ag / GNS composite SERS substrate, characterized in that, Including the steps: S1 Synthesis of Zr-PyDC Dissolve zirconium chloride in DMF, then add concentrated hydrochloric acid, seal and stand still for 0.5 - 2 h under lightless condition. Subsequently, add pyridine-2,5-dicarboxylic acid to the above solution and disperse until it is completely dissolved. Then transfer the solution to a reaction kettle and react at 110 - 130 °C for 15 - 25 h. After the reaction, centrifuge to obtain the precipitate, wash and dry to obtain the Zr-PyDC; S2 Synthesis of Zr-PyDC@Au-Ag In the ethanol solution of Zr-PyDC, add chloroauric acid solution under stirring condition and stir for more than 5 h, then centrifuge to obtain the precipitate and redissolve it in ethanol; Subsequently, under the condition of vigorous stirring, dropwise add NaBH4 solution. After the reaction, centrifuge and wash to obtain Zr-PyDC@Au. Then disperse Zr-PyDC@Au in DMF, and then add silver nitrate to make it completely dissolved. React at 110 - 130 °C for 2 - 5 h. After the reaction, centrifuge to obtain the precipitate and wash to obtain Zr-PyDC@Au-Ag; S3 Synthesis of Zr-PyDC@Au-Ag / GNS Disperse graphene nanosheets GNS and Zr-PyDC@Au-Ag obtained in step S2 in DMF, stir at 60 °C, centrifuge to obtain the precipitate, wash to obtain the Zr-PyDC@Au-Ag / GNS composite SERS substrate.

2. The construction method of the Zr-PyDC@Au-Ag / GNS composite SERS substrate according to claim 1, characterized in that, In the step S1, zirconium chloride:DMF:concentrated hydrochloric acid:pyridine-2,5-dicarboxylic acid = 115 - 118 mg:3 - 8 mL:3 - 8 mL:82 - 85 mg.

3. The construction method of the Zr-PyDC@Au-Ag / GNS composite SERS substrate according to claim 1, characterized in that, In the step S2, The concentration of the ethanol solution of Zr-PyDC is 3 - 4 mg / mL, the concentration of the chloroauric acid solution is 180 - 220 mg / mL, the concentration of the NaBH4 solution is 0.05 - 0.2 mol / L. According to the volume ratio, the ethanol solution of Zr-PyDC:chloroauric acid solution:NaBH4 solution = 3:0.02:0.2; According to the mass ratio, Zr-PyDC:silver nitrate = 10:0.1 - 40.

4. The construction method of the Zr-PyDC@Au-Ag / GNS composite SERS substrate according to claim 1, characterized in that, In the step S3, According to the mass ratio, graphene nanosheets GNS:Zr-PyDC@Au-Ag = 1:

4.

5. The composite SERS substrate prepared by the construction method according to any one of claims 1 - 4.

6. A method for detecting nanoplastics based on the composite SERS substrate as described in claim 5, characterized in that, Including the following steps: Prepare a Zr-PyDC@Au-Ag / GNS solution, then mix it with a polystyrene nanoparticle suspension, and add KI as an aggregating agent. After fully mixing the above solution, stand still and wait for the sample to form a stable colloidal solution for SERS detection.

7. The nano-plastic detection method according to claim 6, wherein In the colloidal solution, the concentration of KI is 0.01 - 0.025 mol / L.

8. The nano-plastic detection method according to claim 6, characterized in that, The concentration of the Zr-PyDC@Au-Ag / GNS solution is 0.1 - 1 mg / mL.

9. The nano-plastic detection method according to claim 6, wherein The particle size of the nanoplastics is 20 - 500 nm.

10. The nano-plastic detection method according to any one of claims 6-9, characterized in that, The SERS detection includes qualitative detection and / or quantitative detection. The quantitative detection plots a relationship curve between the characteristic peak intensity and the nanoplastics concentration based on the Raman spectral intensity of the characteristic peak to determine the nanoplastics concentration of the sample to be tested.

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