An Ag-modified AlPO4-supported PbS heterocomposite material, its preparation method, and its application in the trace detection of Rhodamine B.

Abstract

The application belongs to the technical field of SERS detection, and particularly relates to an Ag modified AlPO4 loaded PbS heterojunction composite material, a preparation method thereof and application thereof in trace detection of rhodamine B. Crystalline AlPO4 rigid carriers are prepared by a hydrothermal method with aluminum nitrate and sodium dihydrogen phosphate as raw materials; lead nitrate and thiourea are introduced to carry out secondary hydrothermal treatment, and PbS semiconductor nanoparticles are in-situ grown on the surface of the AlPO4; Ag nanoparticles are modified on the surface of the composite material by reducing silver nitrate to obtain an Ag-AlPO4 / PbS composite SERS substrate. The two-step hydrothermal synthesis condition is mild, raw materials are cheap, and the morphology is easy to control. The Ag-AlPO4 / PbS substrate is used for SERS detection of rhodamine B, and sensitive identification of pollutants at extremely low concentration can be realized, and the application has good application prospect in the field of rapid trace monitoring of organic dyes in water environment.

Description

Technical Field

[0001] This invention belongs to the field of SERS detection technology, specifically relating to an Ag-modified AlPO4-supported PbS heterocomposite material, its preparation method, and its application in the trace detection of Rhodamine B. Background Technology

[0002] Rhodamine B (RB) is a synthetic oxanthracene basic dye with bright colors and strong tinting strength. It was once illegally added to food and aquatic products to enhance their appearance and color, and is also widely used in printing and dyeing, papermaking, and cell fluorescence labeling industries. Rhodamine B and its metabolites have proven carcinogenic, mutagenic, and cytotoxic properties. Long-term exposure or ingestion can damage liver and kidney tissues. Its use in food processing has been banned in my country and many European and American countries. Trace amounts of rhodamine B in printing and dyeing wastewater and aquaculture water are difficult to degrade naturally. Conventional spectrophotometry and high-performance liquid chromatography (HPLC) methods have drawbacks such as high detection limits, cumbersome pretreatment, and poor instrument portability, making rapid on-site trace screening impossible. Therefore, developing highly sensitive and convenient rapid detection materials and methods for rhodamine B has significant practical value for environmental monitoring.

[0003] Surface-enhanced Raman scattering (SERS) technology relies on a dual mechanism of electromagnetic enhancement via metal plasmon resonance and chemical enhancement via charge transfer at the metal-semiconductor interface. It can amplify the Raman signal of target molecules by millions to hundreds of millions of times. With its advantages of fast detection speed, no need for complex derivatization, and single-molecule recognition, it has become one of the core technologies for the detection of trace organic pollutants. Traditional SERS substrates often use single gold or silver precious metal nanoparticles, which suffer from problems such as easy aggregation, poor signal reproducibility, and high cost. Subsequent research has introduced semiconductor carriers to improve dispersion, but the enhancement efficiency of pure semiconductors is insufficient. Existing metal / semiconductor composite substrates generally suffer from low interfacial charge transfer efficiency and poor controllability of heterostructure construction, making it difficult to simultaneously achieve high enhancement activity and long-term structural stability, thus limiting the accurate detection of ultra-low concentrations of Rhodamine B in actual water samples.

[0004] To address the industry pain points of agglomeration and inactivation on single noble metal substrates and weak synergistic enhancement effects on ordinary metal-semiconductor composite substrates, this invention proposes a two-stage hydrothermal method for preparing Ag-AlPO4 / PbS ternary Schottky heterojunction SERS sensing substrates. This invention uses crystalline AlPO4 as a rigid carrier and performs two-step hydrothermal in-situ growth of PbS semiconductors and Ag plasma nanoparticles, precisely constructing a multi-level metal-semiconductor Schottky interface to simultaneously couple electromagnetic and chemical enhancement effects. The AlPO4 framework effectively prevents nanoparticle agglomeration, significantly improving the substrate's signal uniformity and cycling stability. Compared to traditional noble metal and binary composite SERS materials, this invention uses inexpensive and readily available raw materials, and the two-step hydrothermal process is mild and controllable. It exhibits excellent trace detection sensitivity for Rhodamine B in water, providing a novel material solution for rapid on-site monitoring of organic dye pollutants in aquatic environments. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention designs and synthesizes an Ag-modified AlPO4-supported PbS heterocomposite material, its preparation method, and its application in the trace detection of Rhodamine B. When this SERS substrate interacts with the probe molecules, the intrinsic Raman signal of the target molecule is significantly enhanced through an interfacial charge transfer mechanism, thereby achieving efficient detection and analysis of chemical substances.

[0006] The technical solution adopted in this invention is: a method for preparing Ag-modified AlPO4-supported PbS heterocomposite material, comprising the following steps.

[0007] 1) Dissolve Al(NO3)3 and NaH2PO4·H2O in deionized water and stir until dissolved.

[0008] 2) All of the mixture was transferred to a hydrothermal reactor for hydrothermal reaction. After cooling to room temperature, it was centrifuged, washed, and dried to obtain AlPO4 powder.

[0009] 3) Dissolve the AlPO4 powder obtained in step 2) in water, stir until dissolved, then add lead nitrate and thiourea, and continue stirring.

[0010] 4) The mixed solution was placed in a hydrothermal reactor for hydrothermal reaction. After cooling to room temperature, it was centrifuged, washed and dried to obtain the AlPO4 / PbS composite substrate.

[0011] 5) Disperse the AlPO4 / PbS composite substrate obtained in step 4) in deionized water, sonicate, and then continue stirring to dissolve.

[0012] 6) Add silver nitrate while stirring and stir to dissolve, then add sodium borohydride and continue stirring.

[0013] 7) Centrifuge, wash and dry the mixed solution from step 6) to obtain the Ag-modified AlPO4-supported PbS heterojunction SERS substrate, namely the Ag-AlPO4 / PbS composite SERS substrate.

[0014] In the above-mentioned method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material, in step 1), the molar ratio of Al(NO3)3 and NaH2PO4·H2O is 1:1.2-1.4.

[0015] In the above-mentioned method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material, in step 2), the hydrothermal reaction is carried out at a temperature of 150-160℃ for 11-12 hours, the centrifugation rate is 8000 r / min for 5 minutes, the washing is performed twice with water and once with ethanol, and the drying temperature is 50-60℃ for 10-12 hours.

[0016] In the above-mentioned method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material, in step 3), the molar ratio of AlPO4, lead nitrate, and thiourea is 1:1:2.5-3.

[0017] In the above-mentioned method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material, in step 4), the hydrothermal reaction is carried out at a temperature of 180-190℃ for 16-17h, a centrifugation rate of 8000r / min for 5min, a washing process involving two washes with water and one wash with ethanol, and a drying process at a temperature of 50-60℃ for 10-12h.

[0018] In the above-mentioned method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material, in steps 5) and 6), the molar ratio of AlPO4 / PbS composite substrate: silver nitrate: sodium borohydride is 2.5-3:1:2.5-3.5.

[0019] In the above-mentioned method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material, step 7) involves centrifugation at a rate of 8000 r / min for 10 min, drying at a temperature of 50-60℃ for 12-14 h.

[0020] An Ag-modified AlPO4-supported PbS heterocomposite material prepared according to the preparation method described above.

[0021] The above-mentioned Ag-modified AlPO4-supported PbS heterocomposite material was used in the detection of Rhodamine B in water.

[0022] The above-mentioned Ag-modified AlPO4-supported PbS heterocomposite material was used to detect Rhodamine B in water. The detection method is as follows: Under 532nm laser irradiation, the Ag-modified AlPO4-supported PbS heterocomposite material was immersed in a Rhodamine B solution, dropped onto a clean glass slide, and allowed to air dry at room temperature. Raman spectroscopy was then performed to detect Rhodamine B in the water.

[0023] This material constructs a multi-level metal-semiconductor Schottky interface, which synergistically exerts the dual effects of Ag plasma electromagnetic enhancement and heterojunction interface charge transfer chemical enhancement. The AlPO4 support can effectively prevent the aggregation of PbS and Ag nanoparticles, thereby improving the substrate signal uniformity and structural stability.

[0024] This invention utilizes a constructed Ag-AlPO4 / PbS composite SERS substrate to enhance the Raman spectrum of RB molecules, facilitating their detection in water. The beneficial effects of this method can be attributed to four aspects.

[0025] 1. This invention constructs a bilevel metal-semiconductor Schottky heterointerface through a secondary hydrothermal process. On one hand, Ag nanoparticles generate a localized surface plasmon resonance effect, achieving electromagnetic enhancement; on the other hand, narrow-bandgap PbS forms multilevel charge transfer channels with noble metals and aluminum phosphate supports, accelerating photogenerated electron-hole separation and providing highly efficient chemical enhancement. The synergistic effect of these two enhancement mechanisms significantly amplifies the Raman characteristic signal of Rhodamine B molecules, enabling trace identification of extremely low concentrations of RB in water, with detection performance superior to traditional single noble metal or binary composite SERS substrates.

[0026] 2. Using chemically stable crystalline AlPO4 as a support matrix, PbS semiconductors and Ag nanoparticles can be uniformly anchored, effectively inhibiting the aggregation, detachment, and oxidative deactivation of noble metal and sulfide nanomaterials in aqueous solutions. Compared to carrier-free pure nanoparticle substrates, this composite substrate is less prone to structural collapse after immersion in aqueous phase. Multiple parallel tests show minimal Raman signal fluctuations, demonstrating excellent signal uniformity, reproducibility, and recyclability, making it suitable for long-term testing of complex water samples.

[0027] 3. The entire preparation process of this invention adopts a two-step hydrothermal liquid phase synthesis with moderate reaction temperature, no need for high-temperature calcination, and no need for expensive and precision equipment. The aluminum nitrate, lead nitrate, silver nitrate, thiourea, and sodium dihydrogen phosphate used are all conventional commercial chemical raw materials with low procurement costs. The synthesis steps are controllable and the operation threshold is low. It can prepare large batches of uniform composite powders, which solves the defects of complex preparation process and high mass production difficulty of high-end SERS substrates and has the potential for industrial promotion.

[0028] 4. The inert AlPO4 carrier exhibits excellent chemical resistance, making it resistant to acid and alkali corrosion in actual dyeing and aquaculture wastewater containing salt ions and organic impurities. Its ternary heterostructure provides specific adsorption and charge-matching for Rhodamine B molecules, minimizing interference from coexisting impurities in the water sample with the characteristic Raman peaks of Rhodamine B. The detection process requires no complex sample pretreatment, enabling rapid qualitative and semi-quantitative screening of Rhodamine B in aqueous solutions, meeting the need for convenient on-site emergency environmental monitoring. Attached Figure Description

[0029] Figure 1 X-ray diffraction patterns of the AlPO4 / PbS composite SERS substrates prepared in Example 1 and the Ag-AlPO4 / PbS composite SERS substrates prepared in Example 2.

[0030] Figure 2 The SERS spectra obtained by detecting RB solutions of different concentrations on the Ag-AlPO4 / PbS composite SERS substrate prepared in Example 2 are shown.

[0031] Figure 3 After the Ag-AlPO4 / PbS composite SERS substrate prepared in Example 2 was placed at room temperature for one week, RB solutions were obtained from 8 randomly selected points on the substrate (10). -6 M) Raman spectrum.

[0032] Figure 4 Eight test points were randomly selected from the Ag-AlPO4 / PbS composite SERS substrate prepared in Example 2 at the characteristic Raman peak of RB at 1648 cm⁻¹. -1 A bar chart showing the intensity values ​​at a given location. Detailed Implementation

[0033] 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.

[0034] Example 1.

[0035] The preparation method of AlPO4-supported PbS heterocomposite material, namely AlPO4 / PbS composite SERS substrate, is as follows.

[0036] 0.938 g of aluminum nitrate and 0.4655 g of sodium dihydrogen phosphate monohydrate were dissolved in a beaker containing 40 ml of deionized water and stirred for 1 h until completely dissolved. The solution was then transferred to a hydrothermal reactor and hydrothermally reacted at 155 °C for 12 h. After naturally cooling to room temperature, the mixture was centrifuged at 8000 r / min for 5 min, washed twice with water and once with ethanol, and dried at 60 °C for 11 h to obtain AlPO4 powder for later use. 0.2 g of AlPO4 powder was dispersed in 30 ml of deionized water and stirred for 30 min to dissolve. Then, 0.543 g of lead nitrate and 0.35 g of thiourea were added, and the mixture was magnetically stirred for 1 h. The mixture was then transferred to a hydrothermal reactor and hydrothermally reacted at 185 °C for 16 h. After cooling, the mixture was centrifuged at 8000 r / min for 5 min, washed twice with water and once with ethanol, and dried under vacuum at 50 °C for 10 h. The resulting AlPO4 / PbS composite SERS substrate was obtained by grinding.

[0037] Example 2.

[0038] The preparation method of Ag-modified AlPO4-supported PbS heterocomposite material, namely Ag-AlPO4 / PbS composite SERS substrate, is as follows.

[0039] 0.2 g of the AlPO4 / PbS composite SERS substrate prepared in Example 1 was dissolved in 30 ml of deionized water. After sonication for 30 min, the solution was further dissolved by magnetic stirring. After uniform dispersion, 0.0342 g of silver nitrate was added and stirred for 30 min. Then, 0.025 g of sodium borohydride was added and mixed thoroughly. The mixture was transferred to a centrifuge tube. After centrifugation at 8000 r / min for 10 min, the supernatant was discarded, and the substrate was washed twice with water and once with alcohol. The substrate was dried at 60 °C for 12 h and then ground to obtain the final Ag-AlPO4 / PbS composite SERS substrate.

[0040] Figure 1 X-ray diffraction patterns of the AlPO4 / PbS composite SERS substrate prepared in Example 1 and the Ag-AlPO4 / PbS composite SERS substrate prepared in Example 2 are shown. The orange spectral lines represent the unloaded AlPO4 / PbS material; all its diffraction peaks match the standard PDF cards of crystalline AlPO4 and PbS, respectively, demonstrating the successful preparation of the binary composite support via a secondary hydrothermal method, with both phases exhibiting complete crystallization. The blue spectral lines represent the sample loaded with Ag metal; the characteristic diffraction peaks corresponding to the original AlPO4 and PbS are completely preserved, with no significant peak shift, indicating that the silver modification process does not damage the original crystalline framework of the substrate. Simultaneously, the four new diffraction peaks marked with pink pentagrams on the blue curve perfectly match the standard crystal plane of elemental silver, proving that Ag nanoparticles are uniformly loaded on the material surface, and the Ag-AlPO4 / PbS ternary Schottky heterojunction composite substrate described in this invention has been successfully constructed.

[0041] Example 3.

[0042] Application of Ag-modified AlPO4-supported PbS heterocomposite materials in the detection of Rhodamine B in wastewater.

[0043] 20 μl of the Ag-AlPO4 / PbS solution (1 mg / mL) prepared in Example 2 was immersed in 20 μl of solutions of different concentrations (10 -3 -10 - 8 The substrate was placed in an RB solution (M) for 1 hour, then dropped onto a clean glass slide and allowed to air dry at room temperature. The dried composite SERS substrate was then subjected to Raman scattering spectroscopy.

[0044] Figure 2 To detect different concentrations (10) of Ag-AlPO4 / PbS composite SERS substrate prepared in Example 2. -3 -10 -8 SERS spectra obtained from RB solution (M). All spectral lines are in the range of 1200–1650 cm⁻¹. -1 Characteristic Rhodamine B Raman peaks were observed in all ranges, and the peak shapes matched the standard RB molecular fingerprint peaks, proving that the substrate can effectively identify the target pollutant. As the RB concentration decreased progressively, the intensity of the characteristic peaks decreased synchronously and steadily, without peak shift or interference from other peaks, indicating good stability of the detection process. Even at concentrations as low as 10... -8 M, 1648cm -1 The main peak at the point can still be clearly distinguished, confirming that the composite substrate of the present invention has both extremely high SERS enhancement activity and ultra-low detection capability, enabling trace quantitative detection of Rhodamine B in water over a wide concentration range.

[0045] Example 4.

[0046] Stability testing of Ag-AlPO4 / PbS composite SERS substrate.

[0047] Take 20 μl of the Ag-AlPO4 / PbS solution (1 mg / mL) prepared in Example 2 and immerse it in 20 μl of a 10% concentration solution. -6 In the RB solution of M, the time was 1 hour. The sample was dropped onto a clean glass slide and allowed to air dry at room temperature. After being left at room temperature for one week, eight points were randomly selected on the substrate for Raman spectroscopy. The results are as follows: Figure 3 As shown, the Raman shift peaks corresponding to the eight sets of spectral lines completely overlap, all fully exhibiting the characteristic fingerprint peaks of the Rhodamine B molecule, without any extraneous peaks or characteristic peak shifts. The peaks at each point are 1648 cm⁻¹. -1The signal intensity differences of the main peak and its associated characteristic peaks are extremely small, and the overall fluctuation amplitude is low, proving that the active sites on the surface of the ternary composite substrate of this invention are uniformly distributed. Thanks to the anchoring effect of the AlPO4 rigid support on Ag and PbS nanoparticles, the uneven local enhancement effect caused by noble metal agglomeration is effectively avoided. The substrate possesses excellent signal reproducibility and detection stability, ensuring accurate and reliable quantitative detection results of Rhodamine B in water, and meeting the requirements for multiple parallel tests of actual samples.

[0048] Figure 4 The bar chart extracts the values ​​of Rhodamine B at 1648 cm⁻¹ from the eight different test sites mentioned above. -1 The Raman intensity of the main peak directly characterizes the signal reproducibility of the Ag-AlPO4 / PbS substrate. The horizontal axis represents the numbers of the eight parallel test sites, and the vertical axis represents the signal intensity of the corresponding characteristic peak. The relative standard deviation (RSD) calculated for all peak intensities is 5.51%. The overall fluctuation range of the column heights in each group is small, with only slight numerical differences and no extreme data of sudden increases or decreases in intensity, indicating that the SERS active sites on the substrate surface are uniformly distributed. The low RSD value is far superior to that of traditional pure noble metal nanoparticle substrates, confirming that the crystalline AlPO4 support can stably anchor Ag and PbS nanoparticles and effectively inhibit problems such as aggregation of active components and imbalance of local enhancement effects. These results indicate that the composite substrate of this invention has good repeatability and can effectively reduce the error of parallel test data in the quantitative detection of Rhodamine B in actual water samples, ensuring stable and reliable detection results.

Claims

1. A method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material, characterized in that, Includes the following steps: 1) Dissolve Al(NO3)3 and NaH2PO4·H2O in deionized water and stir until dissolved; 2) All of the mixture was transferred to a hydrothermal reactor for hydrothermal reaction. After cooling to room temperature, it was centrifuged, washed, and dried to obtain AlPO4 powder. 3) Dissolve the AlPO4 powder obtained in step 2) in water, stir until dissolved, then add lead nitrate and thiourea, and continue stirring; 4) The mixed solution was placed in a hydrothermal reactor for hydrothermal reaction. After cooling to room temperature, it was centrifuged, washed, and dried to obtain the AlPO4 / PbS composite substrate. 5) Disperse the AlPO4 / PbS composite substrate obtained in step 4) in deionized water, sonicate, and then continue stirring to dissolve; 6) While stirring, add silver nitrate and stir to dissolve, then add sodium borohydride and continue stirring; 7) Centrifuge, wash and dry the mixed solution from step 6) to obtain Ag-modified AlPO4-supported PbS heterojunction composite material, namely Ag-AlPO4 / PbS composite SERS substrate.

2. The method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material according to claim 1, characterized in that, In step 1), the molar ratio of Al(NO3)3 to NaH2PO4·H2O is 1:1.2-1.

4.

3. The method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material according to claim 1, characterized in that, In step 2), the hydrothermal reaction is carried out at a temperature of 150-160℃ for 11-12 hours, with a centrifugation rate of 8000 r / min and a centrifugation time of 5 minutes. The washing process involves two washes with water and one wash with ethanol. The drying process is carried out at a temperature of 50-60℃ for 10-12 hours.

4. The method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material according to claim 1, characterized in that, In step 3), the molar ratio of AlPO4, lead nitrate and thiourea is 1:1:2.5-3.

5. The method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material according to claim 1, characterized in that, In step 4), the hydrothermal reaction is carried out at a temperature of 180-190℃ for 16-17 hours, at a centrifugation rate of 8000 r / min for 5 minutes, and the washing is performed twice with water and once with ethanol. The drying temperature is 50-60℃ and the drying time is 10-12 hours.

6. The method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material according to claim 1, characterized in that, In steps 5) and 6), the molar ratio of AlPO4 / PbS composite substrate: silver nitrate: sodium borohydride is 2.5-3:1:2.5-3.

5.

7. The method for preparing an Ag-modified AlPO4-supported PbS heterocomposite material according to claim 1, characterized in that, In step 7), the centrifugation rate is 8000 r / min, the centrifugation time is 10 min, the drying temperature is 50-60℃, and the time is 12-14 h.

8. An Ag-modified AlPO4-supported PbS heterocomposite material prepared according to the preparation method of any one of claims 1-7.

9. The application of the Ag-modified AlPO4-supported PbS heterocomposite material as described in claim 8 in the detection of Rhodamine B in water.

10. The application of the Ag-modified AlPO4-supported PbS heterocomposite material according to claim 9 in the detection of Rhodamine B in water, characterized in that, The detection method is as follows: Under 532nm laser irradiation, the Ag-modified AlPO4-supported PbS heterocomposite material is immersed in a Rhodamine B solution, dropped onto a clean glass slide and air-dried at room temperature, and then Raman spectroscopy is performed to detect Rhodamine B in the water.

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