Erbium-doped zinc selenide composite material, preparation method and application thereof

Abstract

The application discloses an erbium-doped zinc selenide composite material and a preparation method and application thereof. The preparation method comprises the following steps: dissolving zinc nitrate hexahydrate and erbium nitrate hexahydrate with a molar ratio of 0.02-0.08 in deionized water; adding sodium selenite and sodium hydroxide; then adding a reducing agent, hydrazine hydrate; after hydrothermal reaction for h, washing and drying to obtain the erbium-doped zinc selenide composite material. The material is a cubic phase ZnSe structure, and the erbium is uniformly doped in the crystal lattice in a near-spherical particle shape. The application introduces rich 4f electron defect states in the ZnSe band gap by erbium doping, significantly promotes charge transfer (chemical enhancement), and improves the free carrier concentration to excite the localized surface plasmon resonance (electromagnetic enhancement), so that the synergistic effect of the two enhancement mechanisms is realized. The detection limit of the SERS substrate for methylene blue is as low as 3.24*10 ‑8 mol / L, and the enhancement factor is as high as 1.73*10 4 , which provides a new way for environmental pollutant monitoring.

Description

Technical Field

[0001] This invention relates to the field of surface-enhanced Raman scattering spectroscopy, and particularly to an erbium-doped zinc selenide composite nanomaterial based on semiconductor materials, its preparation method, and its application as a highly sensitive SERS substrate in trace molecular detection and environmental microplastic detection. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) is a highly sensitive and selective analytical technique widely used in chemical analysis, biomedicine, environmental monitoring, and food safety. SERS enhancement mechanisms are mainly divided into electromagnetic enhancement (EM) and chemical enhancement (CM). Currently, while noble metal SERS substrates possess high enhancement factors, they suffer from limitations such as high cost, poor stability, and complex preparation. In contrast, semiconductor SERS substrates are gaining attention due to their material diversity, good chemical stability, and low cost. However, the SERS enhancement factors of most semiconductor substrates remain relatively low, and the electromagnetic contribution in the enhancement mechanism is usually weak, limiting their practical applications.

[0003] Zinc selenide (ZnSe) is a wide bandgap semiconductor material with excellent optical properties and chemical stability, possessing the potential to serve as a SERS substrate. However, the SERS enhancement effect of pure ZnSe is limited, mainly relying on chemical enhancement mechanisms. Recent studies have shown that SERS performance can be effectively improved by doping to regulate the electronic structure and defect states of semiconductors. Erbium (Er), as a lanthanide rare earth element, can introduce abundant defect states in the ZnSe bandgap region through its 4f electron orbital, promoting charge transfer enhancement. Simultaneously, erbium doping can also increase the free carrier concentration of the material, enhance the local surface plasmon resonance effect, and achieve a synergistic effect of electromagnetic and chemical enhancement. Based on this, this invention proposes an erbium-doped zinc selenide composite material, which significantly improves its SERS performance by optimizing the doping concentration and preparation process, making it suitable for high-sensitivity and high-stability detection of trace molecules and microplastics. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides an erbium-doped zinc selenide composite material with high enhancement factor, good stability, low cost, and simple preparation, as well as its preparation method and application, to solve the problems of limited enhancement effect and low detection sensitivity of existing semiconductor SERS substrates.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] On the one hand, this invention proposes a method for preparing erbium-doped zinc selenide composite materials, comprising the following steps:

[0007] S1: Weigh out a certain molar ratio of zinc-containing compound and erbium-containing compound, dissolve them in deionized water, wherein the molar ratio of Er / (Er+Zn) is x:1, and the value of x ranges from 0.02 to 0.08;

[0008] S2: Add sodium selenite and sodium hydroxide to the solution obtained in step S1 and stir until homogeneous;

[0009] S3: Add the reducing agent hydrazine hydrate to the mixture obtained in step S2 and continue stirring;

[0010] S4: Transfer the mixture obtained in step S3 to a polytetrafluoroethylene high-temperature reactor for hydrothermal reaction;

[0011] S5: After the reaction is complete, allow the mixture to cool naturally to room temperature, centrifuge to collect the precipitate, and wash it several times with deionized water and ethanol in sequence.

[0012] S6: The precipitate is vacuum dried to obtain erbium-doped zinc selenide composite material.

[0013] Furthermore, in step S1, the zinc-containing compound is zinc nitrate hexahydrate, and the erbium-containing compound is erbium nitrate hexahydrate.

[0014] Furthermore, in step S1, the molar ratio of Er / (Er+Zn) is 0.05 to 0.06, i.e., the erbium doping amount is 5 to 6%, preferably 6%. At this preferred doping concentration, the composite material exhibits optimal SERS reinforcement performance.

[0015] Furthermore, in step S2, the molar ratio of sodium selenite to sodium hydroxide is 1:16-20.

[0016] Furthermore, in step S4, the temperature of the hydrothermal reaction is 180-220 °C, and the time is 10-14 h.

[0017] Furthermore, in step S6, the vacuum drying specifically involves vacuum drying at 60-80 ℃ for 6-8 h.

[0018] On the other hand, the present invention also proposes an erbium-doped zinc selenide composite material, which is prepared by the preparation method described above. In the composite material, erbium is uniformly doped into the zinc selenide lattice in the form of substitution doping to form a cubic phase crystal structure without forming an independent impurity phase. The molar ratio of erbium to zinc, Er / (Er+Zn), is 0.02-0.08. The composite material is in the form of nearly spherical particles with a particle size of 1-2 μm, a rough surface, and a polycrystalline structure.

[0019] Thirdly, the present invention also proposes a surface-enhanced Raman scattering substrate, wherein the active material is the erbium-doped zinc selenide composite material as described above.

[0020] Fourthly, the present invention also proposes the application of the erbium-doped zinc selenide composite material as described above or the surface-enhanced Raman scattering substrate as described above in the preparation of devices for detecting trace analytes, including organic dye molecules or environmental microplastic contaminants.

[0021] Furthermore, the organic dye molecule is methylene blue or rhodamine-based dye; the environmental microplastic pollutants include at least one of polyethylene, polyethylene terephthalate, and polytetrafluoroethylene.

[0022] The composite material, as an active substrate for SERS, is suitable for high-sensitivity detection of model organic molecules (such as methylene blue, rhodamine dyes, etc.) and environmental microplastics (such as polyethylene, polyethylene terephthalate, polytetrafluoroethylene, etc.). The material has a very low detection limit and a high enhancement factor for methylene blue, and exhibits good repeatability and stability.

[0023] This invention introduces 4f electron orbitals and lattice defects through erbium doping, achieving a synergistic effect of electromagnetic and chemical enhancement, which significantly improves the performance of SERS substrates. At the same time, the composite material preparation process is simple and low-cost, suitable for large-scale production, and the substrate has good stability and high repeatability, making it suitable for long-term detection of actual samples. It also exhibits high sensitivity in microplastic detection, providing a new approach for the practical application of rapid monitoring of environmental pollutants. Attached Figure Description

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0025] Figure 1 The figures show the relevant test spectra of the prepared erbium-doped zinc selenide composite material. Part A is the XRD spectrum, part B is the Raman spectrum, part C is the XPS spectrum, part D is the Zn 2p high-resolution XPS spectrum, part E is the Se 3d high-resolution XPS spectrum, and part F is the Er 4d high-resolution XPS spectrum.

[0026] Figure 2 These are morphological and microstructure characterization images of ZnSe and 6% Er–ZnSe. Part A of the image is the SEM image of ZnSe, Part B is the SEM image of 6% Er–ZnSe, Part C is the TEM image of 6% Er–ZnSe, Part D is the corresponding SAED pattern, Part E is the HRTEM image of 6% Er–ZnSe, and Part FI is the EDS surface distribution map of Zn, Se and Er elements in 6% Er–ZnSe.

[0027] Figure 3This section presents the SERS selectivity, enhancement effect on MB, detection limit, and stability test results of erbium-doped ZnSe for different probe molecules. Part A shows the SERS selectivity of ZnSe for different probe molecules; Part B shows the normalized Raman spectra of MB on Er–ZnSe; Part C shows the enhancement comparison of MB characteristic peak intensities; Part D shows the detection limit of MB for 6% Er–ZnSe; Part E shows the stability; and Part F shows the repeatability.

[0028] Figure 4 These are the SERS spectra and detection limit curves of three microplastics—polyethylene terephthalate (PE), polyethylene terephthalate (PET), and polytetrafluoroethylene (PTFE)—on composite materials. Part A represents the SERS spectrum of PE, Part B represents the detection limit of PE, Part C represents the SERS spectrum of PET, and Part D represents the detection limit of PET. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] The core of this invention lies in precisely controlling the doping concentration of rare-earth erbium in zinc selenide to optimize the microstructure and electronic properties of the material, thereby obtaining a SERS substrate with both high electromagnetic enhancement and high chemical enhancement activity. The following examples will illustrate in detail the material preparation, characterization, performance testing, and mechanism.

[0031] Example 1: Preparation of Erbium-Doped Zinc Selenide Composite Material

[0032] Weigh out Zn(NO3)2·6H2O and Er(NO3)3·6H2O to make an Er / (Er+Zn) molar ratio of 0.02, and dissolve them in 30 mL of deionized water. Add 1 mmol Na2SeO3 and 20 mmol NaOH, stir for 30 min, and then add 10 mL of 85% hydrazine hydrate. Transfer the mixture to a 50 mL polytetrafluoroethylene reactor and react at 200 °C for 12 h. After cooling, collect the precipitate by centrifugation, wash three times each with deionized water and ethanol, and dry under vacuum at 80 °C for 6 h to obtain a 2% Er-ZnSe composite material.

[0033] Examples 2-4: Preparation of Erbium-Doped Zinc Selenide Composite Materials

[0034] By changing the Er / (Er+Zn) molar ratio to 0.04, 0.06, and 0.08, while keeping other parameters the same as in Example 1, 4% Er-ZnSe composite materials, 6% Er-ZnSe composite materials, and 8% Er-ZnSe composite materials were obtained.

[0035] In contrast, a sample with a doping ratio of 0%, i.e., pure ZnSe, was prepared using the same method.

[0036] Structural characterization of composite materials:

[0037] Figure 1 The figures show the relevant test spectra of the prepared erbium-doped zinc selenide composite material. Part A is the XRD spectrum, part B is the Raman spectrum, part C is the XPS spectrum, part D is the Zn 2p high-resolution XPS spectrum, part E is the Se 3d high-resolution XPS spectrum, and part F is the Er 4d high-resolution XPS spectrum.

[0038] XRD analysis showed that all diffraction peaks of the sample perfectly matched the standard card for cubic zincblende ZnSe, and no diffraction peaks were observed for erbium, erbium oxide, or other impurities. This indicates that erbium was successfully incorporated into the ZnSe lattice without disrupting its main crystal structure; the sample exhibits a cubic ZnSe structure without any impurities.

[0039] 235 cm⁻¹ in Raman spectra -1 The peak at that point represents the longitudinal optical phonon mode of ZnSe, which undergoes a redshift with increasing doping concentration.

[0040] XPS analysis of the 6% Er-ZnSe sample revealed Zn 2p 3 / 2 and Zn 2p 1 / 2 The binding energies of both Zn and Se show slight shifts compared to pure ZnSe, confirming the presence of Zn, Se, and Er elements; the peaks at 175.28 eV and 177.36 eV correspond to Er 4d 5 / 2 The energy levels, while the peaks at 172.51 eV and 179.43 eV, are attributed to Er 4d. 3 / 2 The energy level proves that Er has been successfully doped into the ZnSe lattice.

[0041] Figure 2 These are morphological and microstructural characterization images of ZnSe and 6% Er–ZnSe. Part A of the image is the SEM image of ZnSe, Part B is the SEM image of 6% Er–ZnSe, Part C is the TEM image of 6% Er–ZnSe, Part D is the corresponding SAED pattern, Part E is the HRTEM image of 6% Er–ZnSe, and Part FI is the EDS surface distribution map of Zn, Se, and Er elements in 6% Er–ZnSe.

[0042] SERS performance test

[0043] Using methylene blue as a probe molecule, the SERS enhancement effect of ZnSe with different erbium doping concentrations was tested. Figure 3 This section presents the SERS selectivity, enhancement effect on MB, detection limit, and stability test results of erbium-doped ZnSe for different probe molecules. Part A shows the SERS selectivity of ZnSe for different probe molecules; Part B shows the normalized Raman spectrum of MB on Er–ZnSe; Part C shows the enhancement comparison of MB characteristic peak intensities; Part D shows the detection limit of MB for 6% Er–ZnSe; Part E shows the stability; and Part F shows the repeatability.

[0044] The results showed that, through Figure 3 The comparison of the intensity of this characteristic peak in section B further confirms that the SERS enhancement effect is optimal with 6% Er doping, concluding that 6% Er-ZnSe provides the best enhancement effect, with a detection limit of 3.24 × 10⁻⁶ for MB. -8 mol / L, the enhancement factor is approximately 1.73 × 10⁻⁶. 4 .Depend on Figure 3 As shown in sections E and F, the SERS of the substrate to MB did not change significantly over a period of time, and the SERS signals obtained from multiple measurements were basically consistent, proving that the substrate has good stability and repeatability.

[0045] Electrochemical and Mechanistic Analysis

[0046] Electrochemical impedance spectroscopy and Mott-Schottky analysis showed that 6% Er-ZnSe exhibited the highest carrier concentration and the lowest charge transfer impedance. DFT simulations revealed that Er doping reduced the band gap of ZnSe, and the Se 4p orbitals hybridized with Er 4f orbitals, promoting the charge transfer process.

[0047] Microplastic detection applications

[0048] The composite materials were used for SERS detection of polyethylene (PS), polyethylene terephthalate (PET), and polytetrafluoroethylene (PTFE). Since most microplastics (MPs) are hydrophobic and cannot be uniformly distributed in water, a simple pretreatment of these three types of MPs (PE, PET, and PTFE) was performed using an organic solvent. CH2Cl2 was selected as the organic solvent after evaluation.

[0049] MPs sample pretreatment: Weigh 20 mg, 15 mg, 10 mg, and 5 mg of PS powder, respectively. Disperse them in 10 mL of CH2Cl2 and sonicate for 1 h to ensure complete dissolution. Other low concentrations were obtained by continuous dilution. Repeat the above experimental steps for PET and PTFE.

[0050] MPs sample SERS detection: Take 150 μL of plastic of different concentrations into a glass bottle, add 10 mg of 6% Er-ZnSe sample, vortex for 5 min, take 150 μL of solution and drop it onto the Si wafer, and measure after it is completely dry. The spectral data are collected by a portable Raman spectrometer with an integration time of 5000 ms.

[0051] Figure 4 These are the SERS spectra and detection limit curves of three microplastics—polyethylene terephthalate (PE), polyethylene terephthalate (PET), and polytetrafluoroethylene (PTFE)—on composite materials. Part A represents the SERS spectrum of PE, Part B represents the detection limit of PE, Part C represents the SERS spectrum of PET, and Part D represents the detection limit of PET.

[0052] The results showed that the composite material had high sensitivity to all three microplastics, with a detection limit of 5.33 μg / mL for PET, and the SERS intensity and concentration showed a good linear relationship over a wide range.

[0053] In summary, the erbium-doped zinc selenide composite material prepared by this invention, and optimized as a SERS active substrate, achieves the following beneficial effects:

[0054] (1) Synergistic Enhancement Mechanism, Significantly Improved Performance: This invention creatively achieves effective synergy between electromagnetic and chemical enhancement in the wide-bandgap semiconductor ZnSe by introducing a specific proportion of rare-earth erbium. On the one hand, erbium doping provides a large number of free charge carriers, inducing significant local surface plasmon resonance and contributing to the electromagnetic enhancement component; on the other hand, the 4f energy level of erbium hybridizes with the ZnSe band structure, forming abundant defect states, which greatly promotes the interfacial charge transfer between the analyte and the substrate, strengthening the chemical enhancement. The synergistic effect of these two factors enables the composite material to achieve an enhancement factor of approximately 1.73 × 10⁻⁶ for methylene blue. 4 This breaks through the performance limits of most semiconductor substrates.

[0055] (2) Stable structure and good repeatability: Erbium ions enter the crystal lattice in a substitutional form, resulting in a stable material structure that is not prone to elemental segregation or phase transition. As a SERS substrate, it exhibits high signal repeatability (relative standard deviation <5%) and good long-term stability, overcoming the disadvantages of noble metal substrates such as easy agglomeration and contamination.

[0056] (3) The preparation process is simple and the cost is low: the one-step hydrothermal method is used for synthesis. The process is simple, the conditions are mild, no complex templates or post-processing are required, the repeatability is good, the raw material cost is low, and it is very suitable for large-scale production, which is conducive to promoting the practical application of semiconductor SERS technology.

[0057] (4) Broad application prospects: The material of this invention not only has ultra-high sensitivity to model molecules (the detection limit for methylene blue is 3.24 × 10⁻⁶), but also has a wide range of potential applications. -8 More importantly, it can be directly used to detect emerging pollutants such as environmental microplastics, providing a powerful new detection tool for rapid on-site screening of environmental pollutants.

Claims

1. The application of an erbium-doped zinc selenide composite material in a surface-enhanced Raman scattering substrate, characterized in that, Its active material is an erbium-doped zinc selenide composite material. In the erbium-doped zinc selenide composite material, erbium is uniformly distributed in the zinc selenide lattice in the form of substitution doping to form a cubic phase crystal structure, and the molar ratio of erbium to zinc Er / (Er+Zn) is 0.02-0.

08. The composite material is spherical particles with a particle size of 1-2 μm, a rough surface, and a polycrystalline structure. The preparation method of the erbium-doped zinc selenide composite material includes the following steps: S1: Weigh out a certain molar ratio of zinc-containing compound and erbium-containing compound, dissolve them in deionized water, wherein the molar ratio of Er / (Er+Zn) is x:1, and the value of x ranges from 0.02 to 0.08; S2: Add sodium selenite and sodium hydroxide to the solution obtained in step S1 and stir until homogeneous; S3: Add the reducing agent hydrazine hydrate to the mixture obtained in step S2 and continue stirring; S4: Transfer the mixture obtained in step S3 to a polytetrafluoroethylene high-temperature reactor for hydrothermal reaction; S5: After the reaction is complete, allow the mixture to cool naturally to room temperature, centrifuge to collect the precipitate, and wash it several times with deionized water and ethanol in sequence. S6: The precipitate is vacuum dried to obtain erbium-doped zinc selenide composite material.

2. The application of the erbium-doped zinc selenide composite material according to claim 1 in a surface-enhanced Raman scattering substrate, characterized in that, In step S1, the zinc-containing compound is zinc nitrate hexahydrate, and the erbium-containing compound is erbium nitrate hexahydrate.

3. The application of the erbium-doped zinc selenide composite material according to claim 1 in a surface-enhanced Raman scattering substrate, characterized in that, In step S1, the molar ratio of Er / (Er+Zn) is 0.05 to 0.06, that is, the erbium doping amount is 5 to 6%.

4. The application of the erbium-doped zinc selenide composite material according to claim 1 in a surface-enhanced Raman scattering substrate, characterized in that, In step S2, the molar ratio of sodium selenite to sodium hydroxide is 1:16-20.

5. The application of the erbium-doped zinc selenide composite material according to claim 1 in a surface-enhanced Raman scattering substrate, characterized in that, In step S4, the hydrothermal reaction is carried out at a temperature of 180-220 °C for 10-14 h.

6. The application of the erbium-doped zinc selenide composite material according to claim 1 in a surface-enhanced Raman scattering substrate, characterized in that, In step S6, the vacuum drying specifically involves vacuum drying at 60-80 ℃ for 6-8 h.

7. The application of the surface-enhanced Raman scattering substrate as described in any one of claims 1-6 in the fabrication of devices for detecting trace analytes, characterized in that, The analytes include organic dye molecules or environmental microplastic contaminants.

8. The application according to claim 7, characterized in that, The organic dye molecule is methylene blue or rhodamine-based dye; the environmental microplastic pollutants include at least one of polyethylene, polyethylene terephthalate, and polytetrafluoroethylene.

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