An Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite material, its preparation method, and its application in trace detection of organic pollutants.

Abstract

The application relates to the field of SERS detection, and relates to an Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material, a preparation method thereof and application thereof in trace detection of organic pollutants. Bismuth nitrate is dissolved with dilute nitric acid and stirred until clear, tungsten nitrate and thiourea are added and stirred, a sodium molybdate solution is slowly dropped, a Bi2Mo2O9@WS2 heterojunction is synthesized by using a one-step hydrothermal method, Ag is compounded on the surface of the Bi2Mo2O9@WS2 heterojunction by a chemical reduction method, and the Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material is obtained after drying. Different from mainstream Bi2MoO6 bismuth molybdate phases, the application adopts Bi2Mo2O9 and WS2 to form a Z-type heterojunction. The material forms a multiple interface coupling structure, has plasmonic enhancement effect and a double-charge separation mechanism, and has the characteristics of effectively widening a spectral response interval, increasing reactive sites, improving structural stability and reactivity, etc.

Description

Technical Field

[0001] This invention belongs to the field of SERS detection, specifically relating to an Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material, its preparation method, and its application in the detection of trace organic pollutants. Background Technology

[0002] Surface-enhanced Raman scattering (SERS), as a highly sensitive and specific detection technique, has broad application prospects in trace detection fields such as environmental pollutants, biomolecules, and food safety. Traditional SERS substrates are mostly based on noble metal nanomaterials, which, although possessing excellent plasma enhancement effects, suffer from drawbacks such as high cost, insufficient stability, and limited active sites. While some metal oxide / sulfide substrates are structurally stable, they exhibit problems such as narrow spectral response range, low charge separation efficiency, and limited enhancement effects, making it difficult to meet the needs of ultra-trace detection of organic pollutants.

[0003] Bismuth molybdate-based materials have attracted much attention in photocatalysis and sensing due to their unique crystal and electronic structures. Mainstream research often utilizes the Bi₂MoO₆ phase, but its interface modulation and charge transport performance are limited. WS₂, as a typical two-dimensional layered chalcogenide, possesses characteristics such as large specific surface area, high carrier mobility, and excellent optical properties, and can be used to construct heterojunctions with metal oxides to optimize photoelectric performance. However, single heterojunctions still suffer from weak plasmon resonance and insufficient detection sensitivity. Modifying with noble metal Ag to introduce surface plasmon resonance, combined with the dual charge separation mechanism of Z-type heterojunctions, can significantly improve the SERS enhancement effect and detection stability.

[0004] Currently, there are no reports on the technology of constructing Z-type heterojunctions with Bi2Mo2O9 and WS2 and preparing composite SERS substrates by Ag modification. This invention addresses the gap in existing technology by providing a composite substrate with a simple preparation process and excellent performance, as well as its application in the detection of trace organic pollutants, thus solving the technical problems of low sensitivity, poor stability and narrow spectral response of existing SERS substrates. Summary of the Invention

[0005] To address the technical problems of insufficient sensitivity, poor stability, low charge separation efficiency, and narrow spectral response range in existing SERS substrates, this invention provides a method for preparing Ag-modified Bi2Mo2O9 / WS2 heterojunction composite materials. The method involves synthesizing Bi2Mo2O9 / WS2 Z-type heterojunctions via a one-step hydrothermal method, followed by loading Ag nanoparticles using a chemical reduction method to form a multi-interface coupling structure that combines plasma enhancement effect and dual charge separation mechanism, thereby significantly improving SERS detection performance.

[0006] This invention also provides the application of the above-mentioned composite material in the trace detection of organic pollutants, especially suitable for ultra-trace, high-sensitivity SERS detection of organic pollutants such as methylene blue.

[0007] The present invention adopts the following technical solution: a method for preparing Bi2Mo2O9 / WS2 heterojunction composite material modified with Ag, comprising the following steps.

[0008] 1) Using bismuth nitrate pentahydrate, dilute nitric acid, sodium tungstate dihydrate, thiourea, and sodium molybdate as raw materials, Bi2Mo2O9 / WS2 heterojunctions were prepared by a one-step hydrothermal method. The products were washed, dried, and set aside for later use.

[0009] 2) Ag nanoparticles were modified on the prepared Bi2Mo2O9 / WS2 heterojunction using a chemical reduction method. The product was cooled, centrifuged, washed, and dried to obtain the Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material.

[0010] In the above-mentioned method for preparing Bi2Mo2O9 / WS2 heterojunction composite material modified with Ag, step 1) involves a one-step hydrothermal method for preparing the Bi2Mo2O9 / WS2 heterojunction, in which bismuth nitrate pentahydrate is dissolved in dilute nitric acid, sodium tungstate dihydrate and thiourea are added to the solution, and then sodium molybdate solution is slowly added dropwise to the treated solution for a one-step hydrothermal process. The reaction temperature of the one-step hydrothermal method is 180-200℃, and the time is 12-16h.

[0011] In the above-mentioned method for preparing Bi2Mo2O9 / WS2 heterojunction composite material modified with Ag, in step 1), the molar ratio of bismuth nitrate pentahydrate, sodium tungstate dihydrate, thiourea, and sodium molybdate is 18:1-2:2-3:9-10.

[0012] In the above-mentioned method for preparing Bi2Mo2O9 / WS2 heterojunction composite material modified with Ag, step 2) involves modifying Ag nanoparticles on the prepared Bi2Mo2O9 / WS2 heterojunction using a chemical reduction method as follows: the prepared Bi2Mo2O9 / WS2 heterojunction is mixed into a 1% sodium citrate solution, silver nitrate is added, and the mixture is refluxed at 100-120℃ for 0.5-1h.

[0013] The above-mentioned method for preparing Bi2Mo2O9 / WS2 heterojunction composite material modified with Ag has a mass ratio of Bi2Mo2O9 / WS2:AgNO3=1:50.

[0014] An Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material prepared by the method described above.

[0015] The above-mentioned Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material is used in the detection of trace organic matter.

[0016] In the above application, the organic pollutant is methylene blue.

[0017] In the above application, a Bi2Mo2O9 / WS2 heterojunction composite material modified with Ag was added to a solution of methylene blue, and surface-enhanced Raman scattering detection was performed using a 532 nm wavelength laser as the excitation source.

[0018] The present invention has the following beneficial effects.

[0019] (1) Unlike the mainstream Bi2Mo2O9 bismuth molybdate phase, this invention uses Bi2Mo2O9 and WS2 to construct a Z-type heterojunction to achieve efficient electron-hole separation and improve photoelectric activity.

[0020] (2) The Ag nanoparticle modification introduces the surface plasmon resonance effect, which, combined with the dual charge separation mechanism of the Z-type heterojunction, forms a multi-interface coupling structure, significantly broadening the spectral response range and increasing the active sites.

[0021] (3) This composite substrate has high SERS enhancement factor, excellent stability and strong anti-interference ability, and can realize ultra-trace detection of organic pollutants.

[0022] (3) The composite material is prepared by a one-step hydrothermal method combined with a chemical reduction method. The preparation process is simple, the conditions are mild, and the repeatability is good, making it suitable for large-scale preparation. Attached Figure Description

[0023] Figure 1 These are the Raman spectra of MB molecules under a 532nm laser in Example 2, and the SERS spectra of MB adsorbed on an Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrate.

[0024] Figure 2 This is the XRD pattern of the Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material in Example 1.

[0025] Figure 3 This is the SERS spectrum collected in Example 3 after randomly performing 8 Raman detections on MB molecules on an Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrate using a 532nm laser.

[0026] Figure 4 The SERS spectra are obtained by Raman detection of MB molecules in Example 3 when different laser intensities were applied to the Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrate.

[0027] Figure 5 This is the SERS spectrum of different concentrations of MB molecules adsorbed on an Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrate under a 532nm laser in Example 3.

[0028] Figure 6 The MB concentration in Example 3 and 1623 cm -1 Logarithmic relationship between characteristic peak SERS intensities. Detailed Implementation

[0029] To better understand the technical solution of the present invention, specific embodiments are provided for further detailed description, but the solution is not limited thereto.

[0030] Example 1.

[0031] The preparation scheme of Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrate is as follows.

[0032] 1) Dissolve 1.746 g of bismuth nitrate pentahydrate in 30 ml of 0.5 mol / L dilute nitric acid and stir until the solution is clear. Add 0.06596 g of sodium tungstate dihydrate and 0.1066 g of thiourea to the above solution and stir until completely dissolved. Dissolve 0.4355 g of sodium molybdate dihydrate in 20 ml of deionized water and stir until completely dissolved. Slowly add the sodium molybdate solution dropwise to the mixed solution, stir for 30 min, hydrothermally treat at 180 °C for 12 h, cool to room temperature, centrifuge, wash, and dry the product.

[0033] 2) Take 100 mg of the prepared Bi2Mo2O9 / WS2 heterojunction and add it to 100 ml of deionized water. Add 1 ml of 1% sodium citrate solution and 3.15 mg of silver nitrate, and reflux at 100 °C for 30 min. Centrifuge, wash, and dry the product after the reaction to obtain Ag-modified Bi2Mo2O9 / WS2 heterojunction material. Take 10 mg of Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material and dissolve it in 0.5 ml of deionized water. Sonicate for 10 min, and slowly drop the suspension after sonication onto a glass slide. Dry at 60 °C to obtain Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrate.

[0034] The prepared Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material was subjected to XRD testing, and the test results are as follows: Figure 2As shown, the characteristic diffraction peaks appearing at 2θ = 38.2°, 44.4°, 64.6°, and 77.5° correspond to the characteristic peaks of Ag, while the characteristic diffraction peaks appearing at 2θ = 27.9°, 32.0°, 46.2°, and 55.0° correspond to the characteristic peaks of Bi₂Mo₂O₉, and the characteristic diffraction peaks appearing at 2θ = 14.3°, 28.9°, and 33.5° correspond to the characteristic diffraction peaks of WS₂. The obtained XRD patterns are sufficient to demonstrate the successful synthesis of the Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite substrate.

[0035] Example 2.

[0036] SERS enhancement effect of Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrate.

[0037] The Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite substrate prepared in Example 1 was used for experiments based on SERS technology with MB as the probe molecule. The testing procedure was as follows: a 532 nm wavelength laser was used as the excitation source, and 2 ml of a 10⁻⁶ m² / mL laser solution was used based on SERS technology. -3 MB (mol / L) was used as a probe molecule to test the Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite substrate prepared in Example 1. SERS measurements were performed on both cases: MB alone and a mixture of Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite substrates. The results are as follows: Figure 1 The Raman signal intensity of the Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrate with MB molecules as probes is much higher than that of MB molecules alone, which indicates that the Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrate prepared in this invention has excellent SERS signal enhancement performance.

[0038] Example 3.

[0039] Other excellent properties of Ag-modified Bi2Mo2O9 / WS2 heterojunction composite substrates.

[0040] The Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite substrate prepared in Example 1 was used as the excitation source on the composite substrate with a 532 nm wavelength laser. Based on SERS technology, 2 ml of a 10⁻⁶ concentration laser was used. -3 mol / L MB was used as a probe molecule to test on a 10 mg Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite substrate. Eight sites were randomly selected for testing. The results are as follows: Figure 3 As shown, the Raman signal peaks were uniform and showed no significant changes in the five tests, indicating that the substrate has good stability and uniformity.

[0041] SERS spectra of MB obtained by Raman spectroscopy on Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite substrates irradiated with lasers of different intensities (0.25mW, 0.5mW, and 0.025mW) are shown below. Figure 4 As shown, the results indicate that the composite substrate exhibits good detection sensitivity and excellent enhancement effect.

[0042] Different concentrations of MB molecules were used as probe molecules to detect the effects on Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite substrates. The results are as follows: Figure 5 As shown, although the signal peak intensity decreases with decreasing MB probe molecule concentration, Raman signals can still be detected at extremely low concentrations, indicating that this substrate can detect different concentrations of MB molecules (10). -3 -10 -7 (mol / L), and it still exhibits good performance at extremely low concentrations. The relationship between the SERS signal peak intensities under different concentrations of the MB probe was analyzed, and the results are as follows: Figure 6 As shown, the R obtained after fitting 2 =0.98133, this result further illustrates the relationship between MB concentration and 1623 cm⁻¹. -1 The logarithmic relationship between the characteristic peak SERS intensities confirms the excellent performance of this composite material in SERS-based analytical applications.

Claims

1. A method for preparing an Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite material, characterized in that: Includes the following steps: 1) Bismuth nitrate pentahydrate was dissolved in dilute nitric acid. Sodium tungstate dihydrate and thiourea were added to the solution. Then, sodium molybdate dihydrate solution was slowly added dropwise to the treated solution to prepare Bi2Mo2O9 / WS2 heterojunction by a one-step hydrothermal method. The reaction temperature of the one-step hydrothermal method was 180-200℃ and the time was 12-16h. The product was washed, dried and set aside. The molar ratio of bismuth nitrate pentahydrate, sodium tungstate dihydrate, thiourea and sodium molybdate dihydrate was 18:1:7:

9. 2) According to the mass ratio of Bi2Mo2O9 / WS2 heterojunction: silver nitrate = 100: 3.15, the prepared Bi2Mo2O9 / WS2 heterojunction was mixed into 1% sodium citrate solution, silver nitrate was added, and the mixture was refluxed at 100-120℃ for 0.5-1h. The product was cooled, centrifuged, washed, and dried to obtain Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material.

2. An Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material prepared by the preparation method as described in claim 1.

3. The application of the Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material as described in claim 2 in the trace detection of organic pollutants.

4. The application of the Ag-modified Bi2Mo2O9 / WS2 heterojunction composite material as described in claim 3 in the trace detection of organic pollutants, characterized in that: The organic pollutant mentioned is methylene blue.

5. The application of the Ag-modified Bi₂Mo₂O₉ / WS₂ heterojunction composite material as described in claim 4 in the trace detection of organic pollutants, characterized in that: A Bi2Mo2O9 / WS2 heterojunction composite material modified with Ag was added to a solution of methylene blue, and surface-enhanced Raman scattering was performed using a 532 nm wavelength laser as the excitation source.

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