A magnetic nanocomposite material, its preparation method and application

Abstract

This invention discloses a magnetic nanocomposite material, its preparation method, and its application, belonging to the field of gas sensing material preparation technology. The preparation method of the magnetic nanocomposite material includes the following steps: Fe3O4@SiO2-Au magnetic particles are sequentially modified with a positively charged polyelectrolyte and then with a negatively charged polyelectrolyte, followed by loading with a triphenylmethane dye to obtain the magnetic nanocomposite material. The magnetic nanocomposite material of this invention exhibits a strong Raman spectral signal. Upon reaction with hydrogen gas, the Raman spectral signal is significantly weakened, thereby enabling SERS detection of hydrogen gas and overcoming the problem of low Raman scattering cross-section of hydrogen gas.

Description

Technical Field

[0001] This invention relates to the field of gas sensing material preparation technology, and in particular to a magnetic nanocomposite material, its preparation method, and its application. Background Technology

[0002] Hydrogen energy is an essential path to developing renewable energy and overcoming the fossil fuel and environmental crises, but its safety remains a critical bottleneck throughout its entire lifecycle. Due to hydrogen's inherent properties—its susceptibility to leakage and diffusion, extremely low ignition energy, and colorless and odorless nature—hydrogen leaks can easily go undetected and lead to explosions. Therefore, the development of hydrogen detection technologies is urgently needed. Currently, commonly used hydrogen detection methods include flame retardation, conductivity detection, gas sensor detection, and infrared detection. These methods can accurately detect high concentrations of hydrogen, but some equipment is expensive, the detection process is lengthy, and complex sample pretreatment is required.

[0003] In 1928, Indian physicist Raman discovered the Raman scattering effect, and Raman spectroscopy, based on this discovery, has wide applications in molecular structure and analytical chemistry. In 1974, Fleischmann et al. first observed the surface-enhanced Raman scattering (SERS) effect on a rough silver electrode. Substrate preparation is crucial for achieving excellent SERS detection. Previous studies have shown that SERS-active substrates can be used for gas detection and analysis; however, small gas molecules, such as hydrogen, have low Raman scattering cross-sections, and there are currently no reports on the detection of hydrogen using SERS. Summary of the Invention

[0004] The purpose of this invention is to provide a magnetic nanocomposite material, its preparation method, and its application, to solve the problems existing in the prior art. The magnetic nanocomposite material of this invention is an Fe3O4 / Au core-shell magnetic material. The triphenylmethane dye modified on its surface can react with hydrogen gas, enhancing the Raman spectral signal of the substrate material (FA magnetic particles), thereby enabling SERS detection of hydrogen gas. This method is of great significance in the field of energy security.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of the present invention: a method for preparing a magnetic nanocomposite material, comprising the following steps:

[0007] Fe3O4@SiO2-Au magnetic particles were sequentially modified with positively charged polyelectrolytes and negatively charged polyelectrolytes, and then loaded with triphenylmethane dyes to obtain the magnetic nanocomposite material.

[0008] Furthermore, the positively charged polyelectrolyte includes polydiallyldimethylammonium chloride (PDDA); the negatively charged polyelectrolyte includes sodium polystyrene sulfonate (PSS); and the triphenylmethane dye includes crystal violet (CV) or malachite green (MG).

[0009] Au is the main reason for the enhancement of SERS signal. The role of positive and negative polyelectrolytes is to modify triphenylmethane fuels on the Au surface.

[0010] Furthermore, the mass ratio of the Fe3O4@SiO2-Au magnetic particles to the positively charged polyelectrolyte is 1:1.

[0011] Furthermore, the mass ratio of the Fe3O4@SiO2-Au magnetic particles modified with positively charged polyelectrolyte to the negatively charged polyelectrolyte is 1:3.

[0012] Furthermore, the mass / molar ratio of Fe3O4@SiO2-Au magnetic particles modified with negatively charged polyelectrolyte to triphenylmethane dye is 0.01 g:(1×10⁻⁶). -5 ~1×10 4 )mol.

[0013] Furthermore, the preparation method of the magnetic nanocomposite material specifically includes: adding Fe3O4@SiO2-Au magnetic particles (FA magnetic particles) to a positively charged polyelectrolyte solution to react and obtain positively charged polyelectrolyte-modified FA magnetic particles; adding the positively charged polyelectrolyte-modified FA magnetic particles to a negatively charged polyelectrolyte solution to react and obtain negatively charged polyelectrolyte-modified FA magnetic particles; adding the negatively charged polyelectrolyte-modified FA magnetic particles to a triphenylmethane dye solution to react (temperature 20-30℃, time 10-30 min) to obtain the magnetic nanocomposite material.

[0014] Furthermore, the concentration of the positively charged polyelectrolyte solution is 2 wt.%; the concentration of the negatively charged polyelectrolyte solution is 3 wt.%; and the concentration of the triphenylmethane dye solution is 1 × 10⁻⁶. -3 ~1×10 -6 mol / L.

[0015] Furthermore, the preparation method of the Fe3O4@SiO2-Au magnetic particles includes the following steps: dispersing Fe3O4 / SiO2 nanomagnetic particles in Au nanoparticle sol after modification with a positively charged polyelectrolyte to obtain Fe3O4@SiO2-Au magnetic particles.

[0016] Furthermore, the preparation method of the Fe3O4 / SiO2 nanoparticles specifically includes: dispersing Fe3O4 particles (spherical Fe3O4 particles with a particle size of 300nm to 500nm) in a mixed solution (a mixed solution of ethanol, ammonia and water with a volume ratio of 20:1:4), continuously adding tetraethyl silicate (TEOS) dropwise under mechanical stirring, reacting for 3 hours, and the precipitate is the Fe3O4 / SiO2 nanoparticles.

[0017] Fe3O4 / SiO2 nanoparticles are a type of material in which SiO2 is coated on the surface of Fe3O4 nanoparticles. Coating the surface of Fe3O4 nanoparticles with SiO2 can prevent the oxidation of Fe3O4 nanoparticles from causing a weakening of magnetism. At the same time, the surface of SiO2 is negatively charged, which can better assemble charged Au nanoparticles (Fe3O4@SiO2 is negatively charged, PDDA is positively charged, and Au is negatively charged).

[0018] Furthermore, the preparation method of the Au nanoparticle sol specifically includes: mixing HAuCl4 and water evenly and heating (100°C), then adding anhydrous sodium citrate, reacting for 20 minutes and stopping heating, continuing to stir and cooling to room temperature to obtain Au nanoparticle sol.

[0019] The second technical solution of the present invention: a magnetic nanocomposite material prepared by the above preparation method.

[0020] The third technical solution of the present invention: an application of the above-mentioned magnetic nanocomposite material in hydrogen detection.

[0021] Furthermore, the method of application specifically includes:

[0022] The magnetic nanocomposite material was dispersed in water, and then hydrogen gas was continuously introduced for 10-20 minutes to carry out the reaction. The magnetic nanocomposite material after reacting with hydrogen gas was collected, and 4-10 μL of the magnetic nanocomposite material after reacting with hydrogen gas was taken to measure the Raman spectrum signal.

[0023] Furthermore, the measured laser wavelength is 785 nm, and the integration time is 2–5 s.

[0024] The enhancement of the SERS signal in hydrogen detection is related to both Au nanoparticles and triphenylmethane dyes: In the SERS effect, molecular signals are typically enhanced on the surface of Au and Ag nanoparticles; triphenylmethane is used because SERS cannot directly enhance the hydrogen signal (hydrogen has a low Raman scattering cross section), while hydrogen reacts with triphenylmethane dyes. Therefore, the principle of hydrogen detection is to use an Au magnetic composite substrate (magnetic nanocomposite material) to detect the SERS signal of the reaction product of triphenylmethane dyes and hydrogen. Thus, hydrogen can be indirectly detected through SERS technology.

[0025] The present invention discloses the following technical effects:

[0026] (1) This invention modifies the surface of FA magnetic particles with polyelectrolytes to enable triphenylmethane dye molecules to undergo electro-layer self-assembly modification (through the principle of mutual attraction between opposite charges, charged substances spontaneously adsorb onto the surface of materials with opposite charges, and layer by layer adsorb to generate the desired nanomaterials, thereby achieving layer-by-layer self-assembly modification; the magnetic nanocomposite material of this invention has a total of 5 electro-assemblies, including negatively charged Fe3O4 / SiO2, positively charged PDDA, negatively charged Au, positively charged PDDA, negatively charged PSS and positively charged dye molecules) on the surface of FA magnetic particles, thus obtaining a magnetic nanocomposite material with highly efficient electromagnetic coupling performance; the magnetic nanocomposite material has an enhanced Raman spectral signal, and when it reacts with hydrogen, the Raman spectral signal is significantly weakened, thereby realizing the SERS detection of hydrogen and overcoming the problem of low Raman scattering cross section of hydrogen.

[0027] (2) FA magnetic particles have good stability and biocompatibility. As an enhancement layer of SERS, they have a low detection limit due to the existence of electron transfer mechanism, which can achieve sensitive detection of hydrogen.

[0028] (3) In this invention, triphenylmethane dyes are modified on a SERS substrate (FA magnetic particles) as Raman markers, enabling them to react with hydrogen. The reaction with hydrogen causes the Raman markers on the substrate to change and fall off, thereby causing a change in the SERS signal of the Raman markers, and finally realizing the indirect detection of hydrogen. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A scanning electron microscope image of the magnetic nanocomposite material (FA@MG) prepared in Example 1 of this invention;

[0031] Figure 2 A scanning electron microscope image of the magnetic nanocomposite material (FA@CV) prepared in Example 2 of this invention;

[0032] Figure 3 Raman spectra of FA magnetic particles and magnetic nanocomposite materials (FA@MG) prepared in Examples 1-3 of this invention;

[0033] Figure 4The Raman spectra of the FA magnetic particles and magnetic nanocomposite materials (FA@CV) prepared in Examples 4-6 of this invention are shown.

[0034] Figure 5 The image shows the Raman spectrum of the magnetic nanocomposite material (FA@MG) prepared in Example 1 of this invention after reacting with hydrogen or nitrogen.

[0035] Figure 6 The image shows the Raman spectrum of the magnetic nanocomposite material (FA@CV) prepared in Example 2 of this invention after reacting with hydrogen or nitrogen.

[0036] Figure 7 The magnetic nanocomposite material (FA@CV, concentration 1×10⁻⁶) prepared in Example 4 of this invention -4 (mol / L) reacts with gases of different hydrogen contents at 419 cm⁻¹ -1 The Raman peak intensity spectrum at that location. Detailed Implementation

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0040] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0041] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0042] The preparation method of Fe3O4 / SiO2 nanoparticles used in the following embodiments of the present invention is as follows: 0.1g of nano Fe3O4 (spherical Fe3O4 particles with a particle size of 300nm to 500nm) is dispersed in nitric acid solution, sonicated for 10min, washed 6 times with deionized water, and then dispersed in a mixed solution (20mL ethanol + 1mL ammonia + 4mL deionized water), sonicated for 10min, poured into a three-necked round-bottom flask, and 0.8mL of tetraethyl orthosilicate (TEOS) is continuously added dropwise under mechanical stirring. After the reaction proceeds for 3h, the precipitate is dried under vacuum at 60℃ for 1h to obtain Fe3O4 / SiO2 nanoparticles.

[0043] Example 1

[0044] A method for preparing magnetic nanocomposite materials:

[0045] (1) 30 mg of Fe3O4 / SiO2 nanomagnetic particles were dispersed in 30 mL of a 2 wt.% polydiallyl dimethyl ammonium chloride (PDDA) solution and reacted under mechanical stirring for 20 min. The precipitate was washed with deionized water to obtain PDDA-modified Fe3O4 / SiO2 magnetic particles.

[0046] (2) Synthesis of Au nanoparticle sol: 8 mL of 2 wt.% HAuCl4 solution was added to 184 mL of water and mixed thoroughly. The mixture was sealed and heated (100 °C) under magnetic stirring. 8 mL of an aqueous solution containing 400 mg of anhydrous sodium citrate was added to the solution. The reaction was allowed to proceed for 20 min, then heating was stopped. Stirring was continued and the mixture was cooled to room temperature to obtain Au nanoparticle sol.

[0047] (3) Preparation of Fe3O4 / SiO2 / Au magnetic particles: 0.03g of PDDA-modified Fe3O4 / SiO2 magnetic particles were dispersed in 200mL of Au sol and placed in a shaker (120r / min). The mixture was reacted at room temperature for 20min. The product was washed with deionized water to obtain Fe3O4 / SiO2 / Au magnetic particles (FA magnetic particles).

[0048] (4) Preparation of FA magnetic particles modified with positively charged polyelectrolyte (PDDA): 0.02 g of FA magnetic particles were dispersed in 10 mL of PDDA solution with a concentration of 2 wt.%, and placed in a shaker (120 r / min) and reacted at 30 °C for 20 min. The product was washed with deionized water to obtain PDDA-modified FA magnetic particles (FSPAP magnetic particles).

[0049] (5) Preparation of FA magnetic particles modified with negatively charged polyelectrolytes: 0.01 g of PDDA-modified FA magnetic particles were dispersed in 10 mL of sodium polystyrene sulfonate (PSS) solution with a concentration of 3 wt.%, and placed in a shaker (speed of 150 r / min) and reacted at 30 °C for 20 min. The product was washed 6 times with deionized water to obtain PSS-modified negatively charged magnetic SERS substrate PSS-Fe3O4 / SiO2 / Au (FSPAPP magnetic particles).

[0050] (6) Disperse 0.01g of FSPAPP magnetic particles in 10mL of a solution with a concentration of 1×10⁻⁶. -4 The mixture was placed in a mol / L malachite green (MG) solution and reacted on a shaker (120 r / min) at 25 °C for 20 min. The product was washed with deionized water to obtain a suspension of magnetic nanocomposite material (a magnetic SERS substrate modified with triphenylmethane dye, FA@MG). Scanning electron microscope images are shown below. Figure 1 .

[0051] from Figure 1 As can be seen, after MG modification, 20 nm Au nanoparticles are still uniformly coated on the 370 nm Fe3O4 / SiO2 surface.

[0052] Example 2

[0053] Same as Example 1, except that the concentration of the malachite green (MG) solution is 1×10⁻⁶. -3 mol / L.

[0054] Example 3

[0055] Same as Example 1, except that the concentration of the malachite green (MG) solution is 1×10⁻⁶. -5 mol / L.

[0056] Example 4

[0057] Same as Example 1, except that the malachite green (MG) solution in step (6) is replaced with a crystal violet (CV) solution (concentration of 1×10⁻⁶). -4 Magnetic nanocomposite material (a magnetic SERS substrate modified with triphenylmethane dye, FA@CV) was prepared by (mol / L), and scanning electron microscope images are shown below. Figure 2 .

[0058] from Figure 2 As can be seen, after CV modification, 20 nm Au nanoparticles are still uniformly coated on the 370 nm Fe3O4 / SiO2 surface.

[0059] Example 5

[0060] Same as Example 4, except that the concentration of the crystal violet (CV) solution is 1×10⁻⁶. -3 mol / L.

[0061] Example 6

[0062] Same as Example 4, except that the concentration of the crystal violet (CV) solution is 1×10⁻⁶. -5 mol / L.

[0063] Example 1

[0064] Raman spectra of FA magnetic particles, magnetic nanocomposites prepared in Examples 1-3 (FA@MG), and magnetic nanocomposites prepared in Examples 4-6 (FA@CV) were determined. The results are shown in the figure. Figures 3-4 .

[0065] The determination method is as follows: 4 μL of the above substance is placed on a silicon wafer, and the signal is acquired using a portable Raman spectrometer with a laser wavelength of 785 nm and an integration time of 3 s.

[0066] from Figure 3 As can be seen, MG was successfully modified on the FA surface, and the intensity of the substrate peak decreased as the dye concentration decreased.

[0067] from Figure 4 As can be seen, CV was successfully modified on the FA surface, and the intensity of the substrate peak decreased as the dye concentration decreased.

[0068] Example 2

[0069] 120 μL of the magnetic nanocomposite material (FA@MG) prepared in Example 1 was dispersed in 6 mL of ultrapure water, followed by the introduction of hydrogen (H2) or nitrogen (N2) gas for 10 min (total gas flow rate: 100 mL, hydrogen concentration: 50 vol.%). The magnetic nanocomposite material was collected using an external magnetic field, and the signal was acquired using a Raman spectrometer (4 μL of the magnetic nanocomposite material reacted with hydrogen or nitrogen was placed on a silicon wafer, and the signal was acquired using a portable Raman spectrometer with a laser wavelength of 785 nm and an integration time of 3 s). The Raman spectrum (SERS spectrum) was obtained. Figure 5 ).

[0070] from Figure 5 As can be seen, the FA@MG substrate after reacting with hydrogen gas has a diameter of 423 cm⁻¹. -1 The characteristic peaks decreased significantly, and the characteristic peaks of the substrate remained unchanged when only nitrogen gas was introduced, indicating that MG molecules can react with hydrogen gas and be released from the FA substrate.

[0071] 120 μL of the magnetic nanocomposite material (FA@CV) prepared in Example 2 was dispersed in 6 mL of ultrapure water, followed by the introduction of hydrogen (H2) or nitrogen (N2) gas for 10 min (total gas flow rate: 100 mL, hydrogen concentration: 50 vol.%). The magnetic nanocomposite material was collected using an external magnetic field, and the signal was acquired using a Raman spectrometer (4 μL of the magnetic nanocomposite material reacted with hydrogen or nitrogen was placed on a silicon wafer, and the signal was acquired using a portable Raman spectrometer with a laser wavelength of 785 nm and an integration time of 3 s). The Raman spectrum (SERS spectrum) was obtained. Figure 6 ).

[0072] from Figure 6 As can be seen, the FA@CV substrate after reacting with hydrogen gas reaches a depth of 423 cm⁻¹. -1 The characteristic peaks decreased significantly, and the characteristic peaks of the substrate remained unchanged when only nitrogen gas was introduced, indicating that CV molecules can react with hydrogen gas and be released from the FA substrate.

[0073] Example 3

[0074] Assay method: FA@CV (prepared in Example 4, with a crystal violet (CV) solution concentration of 1×10⁻⁶) was used. -4 A hydrogen concentration of 0%–50% was detected on a substrate (mol / L) (the hydrogen concentration was adjusted by changing the mixing ratio of nitrogen and hydrogen), compared with a 419 cm⁻¹ substrate. -1 The Raman intensity (FA-CV measurement of H2) was at 419 cm⁻¹ -1 The background intensity value (10423 a.u.) at the location did not decrease, indicating that this method is not sensitive for hydrogen detection. See the results below. Figure 7 .

[0075] from Figure 7 As can be seen, the method used in this invention can detect low concentrations of hydrogen (1%). This concentration meets the minimum requirement for the first-level alarm value of a hydrogen alarm, demonstrating the sensitivity and practicality of the detection method.

[0076] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An application of a magnetic nanocomposite material in hydrogen detection, characterized in that, The preparation method of the magnetic nanocomposite material includes the following steps: Fe3O4@SiO2-Au magnetic particles were sequentially modified with positively charged polyelectrolytes and negatively charged polyelectrolytes, and then loaded with triphenylmethane dyes to obtain the magnetic nanocomposite material. The positively charged polyelectrolyte is polydiallyldimethylammonium chloride; the negatively charged polyelectrolyte is sodium polystyrene sulfonate; and the triphenylmethane dye is crystal violet or malachite green. The mass ratio of the Fe3O4@SiO2-Au magnetic particles to the positively charged polyelectrolyte is 1:

1. The mass ratio of Fe3O4@SiO2-Au magnetic particles modified with positively charged polyelectrolyte to negatively charged polyelectrolyte is 1:3; The preparation method of the Fe3O4@SiO2-Au magnetic particles includes the following steps: Fe3O4 / SiO2 nanomagnetic particles are modified with a positively charged polyelectrolyte and then dispersed in Au nanoparticle sol to react and obtain Fe3O4@SiO2-Au magnetic particles; The specific method of the application includes: dispersing the magnetic nanocomposite material in water, then continuously introducing hydrogen gas for 10 to 20 minutes to react, collecting the magnetic nanocomposite material after reacting with hydrogen gas, taking 4 to 10 μL of the magnetic nanocomposite material after reacting with hydrogen gas, and measuring the Raman spectral signal. The measured laser wavelength was 785 nm, and the integration time was 2–5 s; based on the Raman spectral signal at 423 cm⁻¹... -1 The characteristic peak Raman intensity change was used to detect hydrogen concentration.

2. The application according to claim 1, characterized in that, The mass / molar ratio of Fe3O4@SiO2-Au magnetic particles modified with negatively charged polyelectrolytes to triphenylmethane dyes was 0.01 g: 1 × 10⁻⁶. -5 mol.

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