SERS Sensor Based on Ti3C2Tx / (001)TiO2 / W18O49 Composite Heterostructure and Its Application

Abstract

This application discloses an enhanced Raman scattering (SERS) sensor based on a Ti3C2T x / (001)TiO2 / W 18 O 49 composite heterostructure and its application, which relates to the technical fields of microplastics and nanoplastics. The preparation is as follows: Dissolve LiF in HCl and stir, add Ti3AlC2, after a water bath reaction, centrifuge, wash and collect the Ti3C2T x MXene precipitate. After drying, disperse it in deionized water, add NaBF4 and HCl, stir and ultrasonically treat and then react, centrifuge, wash and dry to obtain the Ti3C2T x / (001)TiO2 powder. Add the obtained Ti3C2T x / (001)TiO2 powder to isopropanol, add WCl6 and stir, react in a reaction kettle, centrifuge and wash. Filter the Ti3C2T x / (001)TiO2 / W 18 O 49 by suction on a cellulose filter membrane, and make a three-dimensional SERS sensor with a punch after drying. The detection limit of this sensor for polystyrene (PS) particles is 25 μg / mL, showing a strong linear correlation (R 2 = 0.98), capable of analyzing a mixture of MNPs of three components, PS, polyethylene (PE) and polypropylene (PP), and quantitatively detecting PS microplastics in rainwater, soil and industrial wastewater.

Description

Technical Field

[0001] This application relates to the technical field of microplastics and nanoplastics, and particularly relates to a SERS sensor based on a Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 composite heterostructure and its applications. Background Art

[0002] The extensive industrial production and use of plastics have brought convenience and diversity to many aspects of human life. However, this extensive use has also led to a significant increase in plastic pollution. Over time, after the environmental weathering and degradation process of waste plastics, larger plastic fragments will decompose into smaller microplastics (MPs, 1 μm to 5 mm) and nanoplastics (NPs, less than 1000 nm), collectively referred to as micro / nanoplastics (MNPs). These MNPs are easily dispersed in various environmental media such as air, water bodies, and soil. The accumulation of these microparticles in human tissues may have an adverse impact on organ systems and overall health.

[0003] Currently, methods for detecting MNPs include various analytical techniques such as microscopy, thermal analysis, and spectroscopic analysis. Each technique has its own unique advantages and limitations. Microscopy techniques can provide valuable morphological information of MNPs, but their disadvantage is that they do not have the ability for rapid on-site detection and cannot directly distinguish multi-component MNPs. Thermal analysis techniques are usually used in combination with other techniques, mainly including pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) and thermogravimetry-mass spectrometry (TGA-MS). Although these methods are very practical, they generally have the disadvantages of long time consumption, being destructive, and lacking morphological information. Fourier transform infrared spectroscopy (FTIR) can non-destructively characterize the chemical composition of MNPs. However, this method requires pre-treatment of samples, which is not conducive to rapid on-site analysis. Raman spectroscopy, as a reliable method for characterizing the structure and chemical composition of MNPs, only requires a small amount of samples, but its relatively low sensitivity limits its wide application. Therefore, it is necessary to develop an analytical method that is both convenient and fast and has high sensitivity to effectively detect MNPs in the environment.

[0004] Surface enhanced Raman scattering (SERS) is a detection technique known for its high sensitivity. SERS technology has shown wide application potential in multiple disciplines such as environmental monitoring and biosensing due to its ability to provide molecular fingerprints, non-destructive detection, and the ability to analyze multiple components simultaneously. There are two main SERS enhancement mechanisms: electromagnetic field enhancement (EM) and chemical enhancement (CM). The EM effect mainly originates from the localized surface plasmon resonance (LSPR) phenomenon, which is caused by the excitation of noble metal nanoparticles on the rough substrate surface, while the CM effect is the result of chemical interactions between the substrate and the adsorbed molecules on the surface. SERS technology has become a very promising method for detecting MNPs. For example, Zhang et al. successfully achieved the detection of nanoplastics at a concentration of μg / L by utilizing the aggregation effect between silver nanoparticles (Ag NPs) and plastic particles. Similarly, the Li group prepared AgNPs@PMMA films through a liquid-liquid interface self-assembly method, which enabled the simultaneous detection of polystyrene (PS) and polyethylene terephthalate (PET) nanoplastic particles at very low concentrations. Huang and co-workers employed an electrostatic adsorption strategy to achieve detection of 0.08 wt% PS NPs between oppositely charged Au NPs and PS NPs. Despite these remarkable advances, the detection sensitivity of MNPs still largely depends on the electromagnetic field enhancement provided by the substrate composed of noble metals.

[0005] MXene is a new type of two-dimensional transition metal carbon / nitrogen or carbon nitride material. It has attracted widespread attention in the scientific community due to its unique layered structure, excellent hydrophilicity and strong adsorption properties. These properties have promoted the widespread application of MXene in many fields such as environmental remediation, sensing technology, energy storage and catalytic processes. In the field of SERS technology, MXene is gradually becoming a very promising SERS substrate material. For example, the Dang group developed flexible MXene / Au nanocubes (Au NCs) and TiVC-OH-Au sensors to enhance SERS sensitivity by enriching analytes, thereby enabling sensitive detection of biomarkers in human body fluids. In addition, Peng et al. reported Ag / Nb for the detection of MNPs. 2 CT x MXene substrates have achieved a detection limit of PS as low as 10 μg / mL and demonstrated its ability to distinguish between two-component nanoplastic mixtures. However, MXene materials are currently mainly used as carriers of precious metal nanoparticles. In existing literature reports, the integration of MXene with semiconductor materials as SERS substrates, especially for the detection of MNPs, is still a relatively new field. MXene Ti atoms are oxidized to anatase TiO in air and pressurized water environments. 2Nanocrystals. Currently, in the SERS substrate of the MXene-noble metal composite material, the EM enhancement of the noble metal mainly plays a role, while the SERS enhancement effect of MXene is weak, and Ti atoms are oxidized to anatase TiO in air and pressurized water environments. 2 Nanocrystals limit its application as a SERS substrate alone. Summary of the Invention

[0006] The purpose of this application is to provide a SERS sensor based on Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 composite heterostructure, which solves the technical problem in the prior art of lacking a more efficient and accurate detection substrate for nanoplastics and microplastics.

[0007] This application provides a SERS sensor based on Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 composite heterostructure. The preparation method of the SERS sensor based on the Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 composite heterostructure is as follows:

[0008] Step 1: Dissolve LiF in the HCl solution and stir, then add Ti 3 AlC 2 , after the water bath reaction, centrifuge the mixture, wash it with deionized water until the pH value of the supernatant is in the range of 6.8 - 7.2, and collect the lower layer of Ti 3 C 2 T x MXene precipitate, dry it to obtain multi-layer Ti 3 C 2 T x MXene powder;

[0009] Step 2: Disperse the multi-layer Ti 3 C 2 T x MXene powder obtained in Step 1 in a 1M hydrochloric acid solution, and add NaBF 4, as a crystal plane control agent, after stirring for 30 min, ultrasonic treatment is carried out, and the reaction is carried out in a reaction kettle at 160 °C for 12 h. After the reaction, it is cooled. After centrifuging the obtained mixed solution, the precipitate is washed with deionized water and dried to obtain Ti 3 C 2 T x / (001)TiO 2 powder;

[0010] Step 3: Add the Ti 3 C 2 T x / (001)TiO 2 powder into the isopropanol solution, add WCl 6 to the obtained suspension, continue stirring, and continue the reaction in the reaction kettle. After the reaction is completed, centrifuge the precipitate, wash it, and then vacuum filter the Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 by vacuum filtration on a cellulose filter membrane and let it dry naturally. Use a punch to make a three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensor.

[0011] Preferably, in step 1, the water bath reaction time is 24 h, the water bath reaction temperature is 35 °C, the centrifugation condition is centrifugation at a speed of 3500 revolutions per minute for 5 min, and the drying condition is vacuum drying at 60 °C.

[0012] Preferably, in step 2, the centrifugation condition is centrifugation at 4000 rpm for 5 min.

[0013] Preferably, in step 3, the reaction condition in the reaction kettle is reaction at 200 °C for 20 h, and the centrifugation condition is centrifugation at 5000 rpm for 7 min.

[0014] Preferably, in step 3, the specific washing steps are washing twice with absolute ethanol and then washing once with deionized water.

[0015] This application provides a method based on the above-mentioned Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49Application of SERS sensor with composite heterostructure in microplastics and nanoplastics.

[0016] Preferably, based on Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The detection concentration of the SERS sensor with composite heterostructure for PS particles is at least 25 μg / mL, and the lowest detection concentration for rhodamine is 10 -8 M.

[0017] Preferably, based on Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The SERS sensor with composite heterostructure is applied to analyze the micro / nanoplastic mixture of PS, PE and PP components, and to quantitatively detect PS microplastics in rainwater, soil and industrial wastewater.

[0018] Therefore, the present application adopts the above-mentioned SERS sensor with composite heterostructure based on Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The SERS sensor with composite heterostructure has the following beneficial effects: by using sodium tetrafluoroborate as a crystal plane control agent, (001) crystal plane-exposed TiO is directly in-situ grown on the surface of multilayer Ti 3 C 2 T x MXene, and W 2 is epitaxially grown 18 O 49 to form a semiconductor heterojunction. Through vacuum filtration, Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 is filtered on a cellulose filter membrane to prepare a three-dimensional SERS sensor. The three-dimensional SERS sensor exhibits excellent detection sensitivity, and the detection sensitivity for the rhodamine 6G (R6G) probe molecule is as low as 10 -8 M, and the corresponding enhancement factor (EF) is 2.33×10 6In addition, the detection sensitivity of this SERS sensor for PS is as low as 25 μg / mL. Using its fingerprint recognition characteristics, the sensor successfully identified multi-component mixed MNPs of PS, PE, and PP. In the actual application environment, the three-dimensional SERS sensor developed in this study successfully detected trace PS microspheres in rainwater, soil, and industrial wastewater, highlighting its potential in actual environmental monitoring. Description of the Drawings

[0019] Figure 1 For the three-dimensional Ti of this application 3 C 2 T x / (001)TiO 2 / W 18 O 49 Schematic diagram of the preparation process of the SERS sensor and the SERS detection of micro / nano plastics;

[0020] Figure 2 Among them, (a) is the SEM image of Ti 3 AlC 2 MAX phase; (b) is the SEM image of Ti 3 C 2 T x MXene; (c) is the SEM image of Ti 3 C 2 T x / (001)TiO 2 ; (d) is the SEM image of Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 ; (e) is the SEM image of Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 ; (f), (g) are the SEM images of PS microplastic particles on the Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 substrate; (h) is the HRTEM image of Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 ; (i-l) are Ti3 C 2 T x / (001)TiO 2 / W 18 O 49 Element mapping spectrum of

[0021] Figure 3 Among them, (a) is Ti at 120 °C 3 C 2 T x / (001)TiO 2 SEM image; (b) is Ti at 140 °C 3 C 2 T x / (001)TiO 2 SEM image; (c) is Ti at 160 °C 3 C 2 T x / (001)TiO 2 SEM image; (d) is Ti at 180 °C 3 C 2 T x / (001)TiO 2 SEM image; (e) is when the addition amount of WCl 6 is 30 mg, Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SEM image; (f) is when the addition amount of WCl 6 is 40 mg, Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SEM image; (g) is when the addition amount of WCl 6 is 50 mg, Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SEM image; (h) is when the addition amount of WCl 6 is 60 mg, Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SEM images; (i), (j) Ti3 C 2 T x / (001)TiO 2 SERS performance at different reaction temperatures; (k) and (l) are Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 Substrate in different WCl 6 SERS performance under dosage;

[0022] Figure 4 In (a), different synthetic samples Ti 3 C 2 T x MXene、Ti 3 C 2 T x / (001)TiO 2 , W 18 O 49 and Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 UV-visible absorption spectra of 10 detected in different synthetic samples; (b) -5 SERS spectrum of MR6G; (c) is the SERS spectrum of Ti under laser irradiation. 3 C 2 T x MXene, TiO 2 and W 18 O 49 Schematic diagram of the charge transfer process between

[0023] Figure 5 (a) is the SERS spectra of R6G at different concentrations; (b) is the SERS spectra of PS at different concentrations (from 25 μg / mL to 1000 μg / mL); (c) is the SERS spectra of PS at 1002 cm -1 The relationship between the SERS intensity of the characteristic peak and its concentration; (d) is the SERS spectrum of 250 μg / mL PS at 30 different points; (e) is the SERS spectrum of PS at 1002 cm -1 SERS intensity distribution scatter plot of characteristic peaks; (f) is a three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49Durability Test of SERS Sensor;

[0024] Figure 6 Among them, (a) is the SERS spectrum of single-component plastics (PS, PE, and PP); (b) is the SERS spectrum of multi-component plastics (PS and PE; PS and PP; PE and PP; PS, PE, and PP).

[0025] Figure 7 Among them, (a), (b) are the SERS spectra and linear fitting curves of PS microspheres (800 nm) prepared with rainwater, an actual environmental sample; (c), (d) are the SERS spectra and linear fitting curves of PS microspheres (800 nm) prepared with soil; (e), (f) are the SERS spectra and linear fitting curves of PS microspheres (800 nm) prepared with industrial wastewater;

[0026] Figure 8 is the SEM image of W 18 O 49 ;

[0027] Figure 9 is the SEM image of Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 ;

[0028] Figure 10 is the SEM image of Ti 3 C 2 T x MXene, Ti 3 C 2 T x / (001)TiO 2 、W 18 O 49 and Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 ;

[0029] Figure 11 is the calculation result of the SERS enhancement factor (EF). Specific Embodiments

[0030] Example 1

[0031] Materials

[0032] Lithium fluoride (LiF, purity 99.0%), sodium fluoroborate (NaBF4 , with a purity of 99.0%), isopropanol (purity 99.0%), tungsten chloride (WCl 6 , with a purity of 99.0%) were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Hydrochloric acid (HCl, mass fraction 36.0 - 38.0%) was purchased from Sinopharm Chemical Reagent Co., Ltd. Titanium aluminum carbide (Ti 3 AlC 2 , 400 mesh, purity 99.9%) was purchased from Foshan Xinxi Technology Co., Ltd. Polystyrene (PS, diameter 800 nm) plastic dispersion was purchased from Yiyuan Biology Co., Ltd. Polystyrene (PE) and polyethylene (PE) dispersions were purchased from Zhongke Leiming (Beijing) Technology Co., Ltd. All reagents and materials were not further purified.

[0033] Step 1: Accurately weigh 1.0 g of LiF and add it to a polytetrafluoroethylene (PTFE) reaction vessel containing 20 mL of 9 M HCl. Stir the mixture for 10 min to ensure complete dissolution of LiF. Subsequently, gradually add 1.0 g of Ti 3 AlC 2 , then place the reaction vessel in a water bath and continuously stir at 35 °C for 24 h. After the reaction is completed, centrifuge the mixture at 3500 revolutions per minute (rpm) for 5 min, and then wash it with deionized water until the pH value of the supernatant is within the range of 6.8 - 7.2. Collect the lower-layer Ti 3 C 2 T x MXene precipitate, and dry it in vacuo at 60 °C. The obtained multi-layer Ti 3 C 2 T x MXene powder is stored in a refrigerator at low temperature (5 °C) for subsequent experimental use.

[0034] Step 2: Disperse the accurately weighed 100 mg of multi-layer Ti 3 C 2 T x MXene powder in 24 mL of 1 M HCl until completely dissolved. Subsequently, add 0.2635 g of NaBF 4 , as a crystal plane control agent. Then stir the solution for 30 min, then sonicate it for 10 min, and then transfer it to a 50 mL PTFE reaction kettle and react at 160 °C for 12 h. After the reaction is completed, let the reaction kettle cool naturally to room temperature. Then, centrifuge the solution at 4000 rpm for 5 min, and wash the precipitate twice with deionized water to remove residual reactants or impurities. The obtained precipitate is dried in an oven at 60 °C to obtain Ti 3 C 2 T x / (001)TiO2 Powder

[0035] Step 3: Add 40 mg of Ti 3 C 2 T x / (001)TiO 2 powder into 20 mL of isopropanol and stir well to achieve uniform dispersion. Subsequently, add 40 mg of WCl 6 to it and continue stirring for 2 h. Then transfer the solution to a 50 mL PTFE reactor and react at 200 °C for 20 h. After the reaction is completed, let the reactor cool naturally to room temperature. Then centrifuge the product at 5000 rpm for 7 min. Wash the precipitate twice with absolute ethanol and once with deionized water. Subsequently, filter Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 by vacuum filtration on a cellulose filter membrane and let it dry naturally. Then use a commercial hole punch to make a circular three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensor for subsequent SERS detection.

[0036] I. Material Characterization

[0037] Scanning electron microscope (SEM) images were obtained by Gemini SEM 300; TESCAN MIRA3. The ultraviolet-visible absorption spectra of the samples were measured using a Puxi TU-1950 spectrophotometer. X-ray diffraction (XRD) patterns were recorded using a fixed-target X-ray diffractometer (PANalytical X-Pert PRO MPD). High-resolution transmission electron microscope (HRTEM) images and energy-dispersive X-ray spectroscopy (EDS) analysis were performed using Talos F200X G2.

[0038] II. SERS Detection

[0039] SERS spectra were obtained by a confocal Raman microscope (Thermo DXR2) equipped with a 532 nm laser wavelength. During the measurement, the laser power was set to 2 mW and a 50× objective lens was used to obtain the best signal intensity. When analyzing standard solutions and actual samples, 20 μL and 30 μL of the solution to be measured were dropped onto the three-dimensional Ti 3 C 2 Tx / (001)TiO 2 / W 18 O 49 On the SERS sensor, after the sample was dried, SERS detection was carried out. When analyzing the data, all SERS spectra were baseline corrected to reduce the interference of environmental stray light, thereby improving the accuracy and reliability of spectral analysis.

[0040] III. Characterization of Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 Characterization of

[0041] LiF and HCl were used to selectively etch the Al layer in the Ti 3 AlC 2 MAX phase, and then TiO was in-situ grown on the multi-layer Ti 3 C 2 T x MXene. Subsequently, W 2 nanostructures were epitaxially grown on the Ti 3 C 2 T x / (001)TiO 2 composite material by solvothermal method. 18 O 49 nanostructures. Figure 1 Intuitively shows the synthesis route of the Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 composite structure. Figure 2 (a) shows the SEM image of the Ti 3 AlC 2 MAX phase, showing its unique blocky morphology. After etching, Figure 2 (b) The SEM image shows that the Ti 3 C 2 T x MXene is a multi-layer accordion structure. As Figure 2 (c) shows, after hydrothermal treatment, TiO was successfully synthesized in-situ on the surface of Ti 3 C 2 T x MXene. Subsequently, through the solvothermal process on Ti 2 nanosheets. Subsequently, through the solvothermal process on Ti 3 C 2 T x / (001)TiO2 W was prepared on 18 O 49 nanostructures, as shown in Figure 2 (d). Figure 8 Directly synthesized W prepared by the solvothermal method of tungsten hexachloride was shown, 18 O 49 which presented a unique shuttle-like morphology. Figure 2 (e) confirmed that PS microplastic particles were successfully captured on the surface and in the interlayer structure of the Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 composite substrate, providing a basis for subsequent SERS detection. Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The HRTEM image of the composite material ( Figure 2 (f)) and the corresponding elemental mapping spectra ([[]] Figure 2 (i-l)) clearly revealed the TiO 3 C 2 T x MXene surface and TiO 2 nanosheets in the layered structure. In addition, TiO 2 and Ti 3 C 2 T x W 18 O 49 grown on the surface of MXene were also observed. Figure 2 (g) showed that the crystal spacing of 0.187 nm could be attributed to the (001) crystal plane of anatase TiO 2 ; while the crystal spacing of 0.376 nm could be attributed to the (010) crystal plane of W 18 O 49 . The selected area electron diffraction (SAED) image ([[]] Figure 2 (h)) showed that TiO 2 had (001), (110) and (113) crystal planes, and W 18 O 49 had a (010) crystal plane, which was consistent with the HRTEM image. As shown in Figure 9 , through EDS elemental composition analysis, the percentages of carbon (C), titanium (Ti), oxygen (O) and tungsten (W) were 10.92%, 54.41%, 27.42% and 7.26% respectively.

[0042] Figure 10 shows Ti 3 C 2 T x MXene, Ti 3 C 2 T x / (001)TiO 2 、W 18 O 49 and Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 XRD diffraction patterns of the samples. The observed Ti 3 C 2 T x MXene diffraction peaks are consistent with the values reported in previous literature. Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 In the composite material, the diffraction peaks at 2θ = 25.2°, 38.6°, 53.9° and 62.7° correspond to the (101), (112), (105) and (204) crystal planes of anatase TiO 2 (JCPDS No.21-1272). In addition, diffraction peaks corresponding to the characteristic (004) crystal plane (17.80°) and (223) crystal plane (60.62°) of Ti 3 C 2 T x MXene were detected in the composite material sample, indicating that TiO 3 C 2 T x MXene sheets with exposed (001) crystal planes were successfully grown. For pure W 2 O 18 O 49 the obvious diffraction peaks observed at 23.1° and 47.6° are attributed to the (010) and (020) crystal planes of monoclinic W 18 O 49 respectively. In Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 In the composite material, the diffraction peaks at 25.2°, 38.6°, 53.9° and 62.7° are respectively attributed to anatase TiO 2The peaks at 23.1° and 47.6° correspond to the (101), (112), (105), and (204) planes of W 18 O 49 These XRD analysis results confirm that Ti was successfully synthesized by the two-step solvothermal method. 3 C 2 T x / (001)TiO 2 / W 18 O 49 Composite materials.

[0043] Given that the (001) crystal plane exposed TiO 2 The growth of nanosheets depends on the hydrothermal reaction temperature, so the reaction temperature was adjusted appropriately. SEM images obtained under 120℃ hydrothermal conditions ( Figure 3 (a) shows that almost no flake TiO 2 This is because the reaction temperature is too low, resulting in the oxidation reaction not being fully carried out. When the temperature is raised to 140°C, the SEM image ( Figure 3 (b)) is shown in the multilayer Ti 3 C 2 T x TiO was initially formed on MXene 2 Nanosheets. Figure 3 As shown in (cd), with the further increase of temperature, TiO 2 The number of nanosheets increased significantly, completely covering the Ti 3 C 2 T x MXene layer. R6G was used as a probe molecule to investigate the Ti prepared at different hydrothermal temperatures. 3 C 2 T x / (001)TiO 2 The SERS intensity of R6G first increases and then decreases with the increase of temperature, reaching the maximum value at 160℃ ( Figure 3 (ij)). This SERS intensity peak can be attributed to TiO 2 Nanosheets and multilayer Ti 3 C 2 T x The synergistic effect between MXenes enhances the SERS signal. However, when the reaction temperature exceeds 160 °C, Ti 3 C 2 T x Excessive TiO growth on MXene 2 The nanosheets cover the SERS active sites, resulting in a decrease in signal intensity.18 O 49 The loading amount of 6 is also a key factor affecting the SERS performance. In this study, by controlling the amount of WCl 18 O 49 used, the loading amount of W 6 is adjusted. As the amount of WCl 18 O 49 used increases, the loading amount of W 6 also gradually increases. When the amount of WCl 18 O 49 is 60 mg, W 3 C 2 T x / (001)TiO 2 ( Figure 3 (e-h)). As shown in Figure 3 (k-l), when the amount of WCl 6 is 40 mg, the SERS signal intensity of R6G reaches the best.

[0044] Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 Enhancement mechanism of the substrate

[0045] In this study, by comparing the ultraviolet-visible absorption spectra and SERS characteristics of Ti 3 C 2 T x MXene, Ti 3 C 2 T x / (001)TiO 2 、W 18 O 49 and Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 the SERS enhancement mechanism of Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 is studied. Ti 3 C 2 T x MXene, Ti 3 C 2 T x / (001)TiO 2 , W 18 O 49 and Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The UV-visible absorption spectra of Figure 4 (a). Ti was observed 3 C 2 T x / (001)TiO 2 The absorption peak of Ti 3 C 2 T x MXene shows a significant red shift. 18 O 49 In comparison, Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The absorption of the composite material in the visible light range is significantly enhanced. Figure 4 (b) shows Ti 3 C 2 T x MXene、Ti 3 C 2 T x / (001)TiO 2 , W 18 O 49 and Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The detection intensity of the substrate on R6G shows that Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The SERS signal obtained on the substrate is the highest, about W 18 O 49 2.3 times of the substrate, about Ti 3 C 2 T x / (001)TiO 2 6.6 times of the substrate. To this end, we proposed Ti 3 C 2 Tx / (001)TiO 2 / W 18 O 49 Charge transfer enhancement mechanism of the substrate, such as Figure 4 (c) shown. According to the literature, the bandgap of anatase titanium dioxide is 3.18 eV, the conduction band (CB) position is -4.17 eV, and the valence band (VB) position is -7.35 eV; W 18 O 49 has a bandgap of 2.92 eV, a conduction band position of -5.35 eV, and a valence band position of -8.27 eV. The lowest unoccupied molecular orbital (LUMO) energy level of R6G is -3.40 eV, while the highest occupied molecular orbital (HOMO) energy level is -5.70 eV. Therefore, R6G adsorbed on the substrate can well match the energy band structures of TiO 2 and W 18 O 49 , providing a pathway for charge transfer between them, which further demonstrates the enhancement mechanism of SERS. Under the irradiation of a 532 nm laser, the VB of TiO 2 and W 18 O 49 is excited, and the photo-generated holes transfer from the VB of W 18 O 49 to the VB of TiO 2 and further transfer to Ti 3 C 2 T x MXene, promoting the separation of holes and electrons. The electrons in the CB of TiO 2 can migrate to the CB of W 18 O 49 . At the same time, electrons transition from the HOMO energy level of R6G to the CB of W 18 O 49 , while the electrons in the CB of W 18 O 49 are photo-excited and transition to the LUMO energy level of R6G. This effective charge transfer changes the electron cloud density, resulting in chemical enhancement and improving the SERS enhancement effect.

[0046] Three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 Performance analysis of SERS sensors

[0047] The detection sensitivity of the SERS sensor is a key parameter to measure its analytical performance. Using R6G as the probe molecule, the three-dimensional Ti 3C 2 T x / (001)TiO 2 / W 18 O 49 The sensitivity of the SERS sensor. Figure 5 (a) shows the SERS spectra of R6G at different concentrations. The characteristic Raman peaks of R6G are located at 610 cm -1 , 769 cm -1 , 1186 cm -1 , 1360 cm -1 , 1509 cm -1 and 1648 cm -1 respectively. As the concentration of the R6G solution decreases, the intensity of the Raman peaks also weakens accordingly. However, even at a low concentration of 10 -8 M, the R6G peaks are still clearly distinguishable. As Figure 11 shown, the calculated EF value of this sensor is 2.33×10 6 , indicating that it has a high SERS sensitivity. The specific R6G peaks are related to the vibrations of R6G molecules. The R6G peak at 610 cm -1 corresponds to the in-plane bending of C-C, 769 cm -1 corresponds to the out-of-plane bending of C-H, 1186 cm -1 corresponds to the in-plane bending of C-H, 1360 cm -1 , 1509 cm -1 and 1648 cm -1 correspond to the aromatic C-C stretching vibration.

[0048] The calculation formula of EF is as follows:

[0049] EF = (I SERS / I BULK ) × (N BULK / N SERS )

[0050] where I SERS and I BULK represent the intensities of SERS and normal Raman scattering respectively, while N SERS and N BULK represent the numbers of the corresponding R6G molecules effectively excited by the laser beam. According to the above formula, the EF of the Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 substrate is 2.33×10 6 .

[0051] N BULK=(Laser spot area / Diffusion area)×(N A ×Volume BULK ×Concentration BULK );

[0052] N SERS =(Laser spot area / Substrate area)×(N A ×Volume SERS ×Concentration SERS );

[0053] Diffusion area = 0.25 cm 2 ;

[0054] Substrate area = π(d / 2) 2 = 0.5027 cm 2 ;

[0055] Volume BULK = Volume SERS ;

[0056] Concentration BULK = 10 6 ×Concentration SERS ;

[0057] N BULK / N SERS =(0.5027 / 0.25)×10 6 = 2.01×10 6 ;

[0058] I = intensity of the 610 cm -1 peak;

[0059] I BULK = 3447.13 a.u.;

[0060] I SERS , Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 = 3999.03 a.u.;

[0061] EF = (I SERS / I BULK )×(N BULK / NSERS ) = 2.33×10 6 。

[0062] The sensitivity of the three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensor was further evaluated using PS spheres with a diameter of 800 nm. 20 μL of PS solutions with different concentrations were dropped onto the sensor surface, and after natural drying, SERS detection was carried out. As Figure 5 (b) shows, three distinct PS Raman characteristic peaks were observed at 1002 cm -1 , 1034 cm -1 and 1603 cm -1 , corresponding to the C-C ring breathing vibration, the in-plane C-H deformation vibration, and the C-C stretching vibration, respectively. Even when the minimum concentration of the PS standard solution was 25 μg / mL, the sensor could still maintain its detection ability. The improvement in sensitivity can be attributed to the layered structure of the Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 substrate, which allows PS to enter the surface and interlayer structures of Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 and plays a role in enriching PS, thus improving the detection sensitivity. Figure 5 (c) depicts the linear fitting curve of the SERS intensity of PS at 1002 cm -1 . In the concentration range of 25 μg / mL to 1000 μg / mL, the fitting curve of the intensity of PS at 1002 cm -1 versus concentration shows a strong linear relationship. The correlation coefficient (R 2 ) value of the calibration curve is 0.9906, indicating the potential of the sensor for quantitative detection of PS within the tested concentration range. To evaluate the signal uniformity of the sensor, 30 points were randomly selected on the sensor surface to collect the SERS spectra of PS, and the results are as Figure 5 (d) shows. Figure 5 (e) is a scatter plot of the intensity of the 1002 cm -1 characteristic peak. The calculated relative standard deviation (RSD) value is 12.58%, indicating satisfactory signal uniformity across the entire sensor surface.

[0063] The durability of the three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensor was evaluated through a bending test. SERS measurements were performed every 50 bends, and a total of 300 bends were carried out. This process is very important for evaluating the potential of the sensor in practical applications because the sensor may be affected by mechanical stress. The results of the durability test are shown in Figure 5 (f). Despite 300 bends, the intensity of the PS Raman characteristic peak at 1002 cm -1 only decreased by 26.95%, indicating that the sensor has strong durability.

[0064] These results indicate that the three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensor has high sensitivity, signal uniformity, and excellent durability, and is a promising detection and analysis tool for MNPs.

[0065] Multicomponent analysis of the three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensor

[0066] In actual environmental monitoring, there may be various sizes and types of MNPs. Using the unique fingerprint recognition function of SERS, various MNPs analytes can be accurately distinguished simultaneously. First, SERS detection was performed on the microsphere dispersions of PS, PE, and PP, and their characteristic Raman spectra ( Figure 6 (a)) were obtained. On this basis, by detecting complex plastic mixtures, the multicomponent analysis ability of the three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensor was further demonstrated. We performed SERS analysis on binary mixtures composed of PS and PE, PS and PP, PE and PP, and a ternary mixture composed of PS, PE, and PP. The results are shown in Figure 6(as shown in (b)). By analyzing the specific positions of characteristic Raman peaks, different types of plastics in these mixtures can be distinguished. Therefore, three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The SERS sensor can not only accurately identify a single type of plastic but also effectively distinguish the components of complex plastic mixtures, highlighting its practical application potential in the field of environmental monitoring and providing strong technical support for environmental protection and the treatment of MNPs pollution.

[0067] Three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 The SERS sensor is used for the detection of the actual environment

[0068] To verify the ability of the three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensor to detect MNPs in the actual environment, in this study, spiked samples containing PS microspheres were prepared with rainwater, soil, and industrial wastewater, and SERS detection was carried out. This evaluation aimed to confirm whether the sensor was suitable for the detection application of MNPs under actual environmental conditions. The collected rainwater and industrial wastewater samples were untreated, while the soil samples were dispersed and filtered before use. A series of rainwater, soil, and industrial wastewater solutions with different concentrations containing 800 nm PS microspheres were prepared. 30 μL of each dispersion was dropped on the three-dimensional Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensor, and then allowed to dry naturally and subjected to SERS detection. As Figure 7 shown, the Raman spectra of PS microspheres in these actual environments were consistent with their intrinsic Raman spectra, indicating that the sensor could accurately detect MNPs in complex environments. The detection sensitivity of the three-dimensional SERS sensor for all samples was 25 μg / mL, and it showed a good linear relationship in the concentration range of 25 to 1000 μg / mL. The R 2 values for rainwater, soil, and industrial wastewater were 0.9830, 0.9814, and 0.9831, respectively. These results further confirmed the three-dimensional Ti 3C 2 T x / (001)TiO 2 / W 18 O 49 SERS sensors show strong performance and great potential in detecting MNPs in practical environmental applications. The high sensitivity and good linear response of this sensor make it a powerful tool for environmental monitoring and plastic pollution assessment, contributing to better monitoring of the environmental risks of MNPs.

[0069] Therefore, this application provides a SERS sensor based on Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 composite heterostructure and its application. The sensor has excellent sensitivity, uniformity and durability. The layered structure of Ti 3 C 2 T x / (001)TiO 2 / W 18 O 49 and efficient charge transfer contribute to improving the performance of the SERS sensor. The detection sensitivity for rhodamine 6G (R6G) reaches 10 -8 M, and the corresponding enhancement factor (EF) is 2.33×10 6 . This high SERS sensitivity enables it to detect polystyrene (PS) microplastic microspheres as low as 25 μg / mL, with a relative standard deviation (RSD) of 12.58%. The fingerprint recognition characteristics of this SERS sensor enable it to detect a variety of MNPs, including polyethylene (PE) and polypropylene (PP), and to analyze complex MNPs mixtures. In addition, this sensor can also quantitatively detect PS microplastics in complex environmental samples (such as rainwater, soil and industrial wastewater).

[0070] In the description of this specification, the descriptions referring to terms such as "an experimental example", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with that experimental example or example are included in at least one experimental example or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same experimental example or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more experimental examples or examples.

[0071] Finally, it should be noted that the above experimental examples are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred experimental examples, those of ordinary skill in the art should understand that they can still modify the technical solution of the present invention or make equivalent substitutions, and these modifications or equivalent substitutions cannot make the modified technical solution deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A Ti3C2T based x / (001)TiO2 / W 18 O 49 The application of the composite heterostructure SERS sensor in detecting micro-nano plastics is characterized by: Based on Ti3C2T x / (001)TiO2 / W 18 O 49 The preparation method of the composite heterostructure SERS sensor is as follows: Step 1: Dissolve LiF in HCl solution and stir, then add Ti3AlC2, react in a water bath, centrifuge the mixture, wash with deionized water until the pH value of the supernatant is in the range of 6.8-7.2, collect the lower layer Ti3C2T x MXene precipitation and drying to obtain multilayer Ti3C2T x MXene powder; Step 2: The multilayer Ti3C2T x MXene powder was dispersed in 1M hydrochloric acid solution, and NaBF4 was added as a crystal surface control agent. After stirring for 30 min, ultrasonic treatment was performed, and the mixture was reacted in a reactor at 160 ° C for 12 h. After the reaction, the mixture was cooled and centrifuged. The precipitate was washed with deionized water and dried to obtain Ti3C2T x / (001) TiO2 powder, wherein NaBF4 is used as a crystal plane control agent in a multilayer Ti3C2T x TiO2 with (001) crystal plane exposed is directly grown in situ on the MXene surface; Step 3: The Ti3C2T x / (001) TiO2 powder was added to the isopropanol solution, WCl6 was added to the obtained suspension, and the mixture was stirred and reacted in the reactor. After the reaction, the precipitate was centrifuged and washed. Ti3C2T x / (001)TiO2 / W 18 O 49 Filter on a cellulose filter membrane and let it dry naturally. Use a punch to make three-dimensional Ti3C2T x / (001)TiO2 / W 18 O 49 SERS sensor.

2. A Ti3C2T based on claim 1 x / (001)TiO2 / W 18 O 49 The application of the composite heterostructure SERS sensor in detecting micro-nano plastics is characterized by: In step 1, the water bath reaction time is 24 h, the water bath reaction temperature is 35° C., the centrifugation condition is centrifugation at a speed of 3500 revolutions per minute for 5 min, and the drying condition is vacuum drying at 60° C.

3. A Ti3C2T based on claim 1 x / (001)TiO2 / W 18 O 49 The application of the composite heterostructure SERS sensor in detecting micro-nano plastics is characterized by: In step 2, the centrifugation condition is 4000 rpm for 5 min.

4. A Ti3C2T based on claim 3 x / (001)TiO2 / W 18 O 49 The application of the composite heterostructure SERS sensor in detecting micro-nano plastics is characterized by: In step 3, the reaction conditions in the reactor are 200° C. for 20 h and the centrifugation conditions are 5000 rpm for 7 min.

5. A Ti3C2T based on claim 3 x / (001)TiO2 / W 18 O 49 The application of the composite heterostructure SERS sensor in detecting micro-nano plastics is characterized by: In step three, the specific steps of washing are washing twice with anhydrous ethanol and then washing once with deionized water.

6. A Ti3C2T based on claim 1 x / (001)TiO2 / W 18 O 49 The application of the composite heterostructure SERS sensor in detecting micro-nano plastics is characterized by: Based on Ti3C2T x / (001)TiO2 / W 18 O 49 The detection sensitivity of the composite heterostructure SERS sensor to polystyrene particles is 25µg / mL, and the minimum detection concentration of rhodamine is 10 -8 M.

7. A Ti3C2T based method according to claim 1 x / (001)TiO2 / W 18 O 49 The application of the composite heterostructure SERS sensor in detecting micro-nano plastics is characterized by: Based on Ti3C2T x / (001)TiO2 / W 18 O 49 The composite heterostructure SERS sensor is used to differentiate and analyze the components in a micro-nano plastic mixture of polystyrene, polyethylene and polypropylene.

8. A Ti3C2T based method according to claim 6 x / (001)TiO2 / W 18 O 49 The application of the composite heterostructure SERS sensor in detecting micro-nano plastics is characterized by: Based on Ti3C2T x / (001)TiO2 / W 18 O 49 The composite heterostructured SERS sensor is used for the quantitative detection of polystyrene micro-nanoplastics in rainwater, soil or industrial wastewater.

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