A broadband high-performance uniform spherical silver microparticle and a preparation method thereof

Abstract

The present application relates to the technical field of colloidal metal particles, and particularly relates to a wideband high-performance uniform spherical silver microparticle and a preparation method thereof. The present application uses an aqueous solution containing citric acid, sodium citrate and ascorbic acid as an active agent solution, adds the aqueous solution into a water-soluble silver salt precursor solution, and obtains a black colloidal solution through reaction. A mercaptan solution is added or not added, and a black precipitate product is obtained through centrifugal separation. The product is cleaned with a solvent through ultrasonic and dried, so that the wideband high-performance uniform spherical silver microparticle is prepared. The surface of the prepared silver microparticle is composed of a large number of nano-sized particle synapses and gaps, and has important application value in surface enhanced infrared absorption (SEIRA), surface enhanced Raman scattering (SERS), mid-infrared photoacoustic imaging, long-wave radiation and photo-thermal conversion. The present application overcomes the technical defects that the prior art cannot prepare multi-hot-spot uniform silver microparticles, and the preparation method has high yield, simple process and important industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of colloidal metal particles, and more particularly to a broadband, high-performance, uniform spherical silver microparticle and its preparation method. Background Technology

[0002] Subwavelength-scale silver particles, due to their unique and prominent localized surface plasmon resonance effect, offer numerous pathways to enhance light-matter interactions, thus giving rise to many unique applications, including surface-enhanced Raman scattering spectroscopy (SERS), surface-enhanced infrared absorption spectroscopy (SEIRAS), enhanced chemical and biological sensing, and biomedical detection. Among these, surface-enhanced infrared spectroscopy, due to its high specificity, sensitivity, and non-destructive testing characteristics, is widely used in the analysis of biological processes and the elucidation of catalytic mechanisms. This technique utilizes the matching of the near-field frequencies of plasmon resonance in silver particles with the frequencies of molecular vibrations, thereby generating a strong coupling effect to enhance the signal intensity of molecular vibrational frequencies in the spectrum. However, because the commonly used molecular vibrational frequencies cover a wide range (2.5 μm–25 μm), the plasmon resonance bands of current silver particles cannot cover the entire region. This frequency detuning directly leads to weak or no enhancement. Furthermore, due to the high optical loss of micrometer-scale silver particles, the enhancement effect is not entirely satisfactory.

[0003] Generally, the nanoscale gaps between noble metal particles and the near-field enhancement effect of plasmon resonances at the particle tips are particularly prominent, and are referred to as "hot spots" in the field. Further coupling between multiple hot spots can significantly broaden the plasmon bandwidth of the material. Theoretically, multi-hot spot silver microparticles are ideal materials for solving these problems. Currently, top-down methods, represented by photolithography, are the main approach to obtaining micron-scale noble metal particles. However, preparing products with numerous small gaps and synapses using this technology is difficult, and the time and economic costs are immeasurable. Wet chemical synthesis is a classic bottom-up synthesis strategy, widely used in the preparation of noble metal colloidal nanoparticles. However, due to energy control issues in chemical growth, the preparation of uniform multi-hot spot micron-sized metal particles remains difficult. Therefore, designing a method to prepare uniform silver micron-sized particles with multiple hot spots will have significant technical implications. Summary of the Invention

[0004] One objective of this invention is to overcome the bottlenecks in existing silver microparticle preparation techniques by providing a simple method for synthesizing broadband, high-performance, uniform spherical silver microparticles. The resulting silver microparticles are spherical microparticles with a surface composed of numerous nanoscale particle synapses and gaps. Due to the coupling effect between surface particles, the extinction spectrum of these silver microparticles not only covers the entire mid-infrared region but also possesses a significant electromagnetic field enhancement effect, resulting in a considerable enhancement of surface-enhanced infrared absorption spectral signals. Furthermore, the preparation method for this silver microparticle material is not only high-yield and simple, but also easy to operate and requires minimal equipment.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a method for preparing broadband, high-performance, uniform spherical silver micron-sized particles, specifically comprising the following steps:

[0006] S1. Add citric acid, sodium citrate and ascorbic acid to water at a concentration of 0.005-0.5 mol / L, and incubate at 2-50℃ to obtain the surfactant solution.

[0007] S2. Add a water-soluble silver salt precursor solution to the surfactant solution. The volume ratio of the surfactant solution to the water-soluble silver salt precursor solution is 1.7:(0.15-0.6). The concentration of the water-soluble silver salt precursor is 0.005-1 mol / L. The mixture is then used as the reaction precursor solution.

[0008] S3. Place the precursor solution at 2-50℃ for 0.5-12 hours to obtain a black colloidal solution;

[0009] S4. The black colloidal solution is directly centrifuged or the solution is added to a thiol solution and allowed to stand before centrifugation. The colorless solution in the centrifuge tube is removed, and the resulting black precipitate is ultrasonically cleaned and dried with a solvent to obtain wide-band high-performance uniform spherical silver micron particles.

[0010] Further improvements to the preparation method of broadband high-performance uniform spherical silver microparticles:

[0011] Preferably, the activator solution in step S1 also contains mandelic acid at a concentration of 0.005-0.5 mol / L.

[0012] Preferably, the mandelic acid is one or more of S-mandelic acid, R-mandelic acid, and S / R-mandelic acid.

[0013] Preferably, the static incubation time in step S1 is 1-30 days.

[0014] Preferably, the water-soluble silver salt precursor solution in step S2 is a silver nitrate solution or a silver acetate solution.

[0015] Preferably, the concentration of the thiol solution in step S4 is 0.0000005-0.05 mol / L, the volume ratio of the black colloidal solution to the thiol solution is 1:(1-10), and it is left to stand for 2-24 hours.

[0016] Preferably, the thiol is one or more of 4-mercaptopyridine, 4-mercaptobenzoic acid, 4-mercaptoaniline and 4-mercaptobenzonitrile.

[0017] Preferably, in step S4, a high-speed centrifuge is used to centrifuge at a speed of 3000-10000 rpm for 5-100 minutes to separate and remove the colorless solution in the centrifuge tube.

[0018] Preferably, the solvent in step S4 is deionized water, distilled water, or anhydrous ethanol.

[0019] The second objective of this invention is to provide a method for preparing broadband, high-performance, uniform spherical silver microparticles as described in any one of the above-mentioned methods, resulting in broadband, high-performance, uniform spherical silver microparticles.

[0020] The advantages of this invention compared to the prior art are as follows:

[0021] 1) This invention provides a one-step synthesis method for obtaining broadband, high-performance, uniform spherical silver microparticles. A capping agent (citric acid, sodium citrate) and a reducing agent (ascorbic acid) are added to water. Based on the principle of hydrogen bond self-assembly, through prolonged static incubation, multiple active agent molecules assemble into a network structure, yielding an active agent solution. A water-soluble silver salt precursor solution is then added to the active agent solution. Utilizing its induced constraint effect combined with a chemical reduction kinetics control strategy, uniform multi-hotspot silver microparticles are obtained. The black precipitate product is then ultrasonically cleaned with a solvent to obtain broadband, high-performance, uniform spherical silver microparticles. Alternatively, mandelic acid can be added as a capping agent to the active agent solution to adjust the microstructure of the spherical silver microparticles.

[0022] To obtain silver microparticles with larger hot spots, the black colloidal solution is directly centrifuged. To obtain silver microparticles with smaller hot spots, a thiol solution is added to the black colloidal solution. This is because thiol can etch silver particles, thereby optimizing the size of surface synaptic silver particles. At the same time, due to the protection of the surface by thiol, the broadband high-performance uniform spherical silver microparticles after drying can be stored for a long time at room temperature and under ambient atmosphere.

[0023] The preparation process of this invention is simple and easy to repeat. The preparation process only requires general-purpose equipment and does not require special equipment. The process is simple and easy to operate. The raw materials used are abundant, pollution-free and inexpensive, making it particularly suitable for the large-scale, low-cost preparation of monodisperse spherical silver micron particles. It is not only suitable for large-scale industrial production, but also easy to apply commercially.

[0024] 2) The product prepared by this invention is a polycrystalline spherical silver microparticle with a wrinkled surface. The wrinkles are composed of nano-silver synapses, resulting in uniform particle size, good dispersibility, and effectively controllable particle size within the range of 1 to 2 micrometers. It exhibits excellent dispersibility and stability in solutions such as water or ethanol, and does not deform or agglomerate under refrigeration conditions for extended periods. The spherical silver microparticles provided by this invention possess strong broadband extinction characteristics across the entire mid-infrared band, making them applicable to surface-enhanced infrared absorption spectroscopy across the entire frequency range. Furthermore, they exhibit strong optical responses in the ultraviolet, visible, and near-infrared regions, making them suitable for multiple enhanced spectral scenarios. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. 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.

[0026] Figure 1 The images are SEM images of the silver microspheres prepared in Example 1, taken using a Sirion 200 field emission scanning electron microscope (SEM); wherein, Figure 1 a is a low-magnification SEM image with a scale bar of 1 micrometer; Figure 1 b is a high-magnification SEM image with a scale bar of 200 nanometers.

[0027] Figure 2 The image shows a low-magnification SEM image of several silver micron-sized spherical particles obtained in Example 1, and a statistical distribution of the diameter of 100 particles in the image. The scale bar in the image is 10 micrometers.

[0028] Figure 3 These are transmission electron microscope (TEM) images of silver micron-sized spherical particles prepared in Example 1, taken using a JEOL-2100F transmission electron microscope; where 3a is a low-magnification TEM image with a scale bar of 1 micrometer. Figure 3 b is a high-angle dark-field scanning transmission electron image with a scale bar of 500 nanometers.

[0029] Figure 4 Image a is a series of transmission electron microscopy (TEM) images of the silver micron-sized spherical particles prepared in Example 1, with a scale bar of 100 nm; image b is a selected area electron diffraction (SED) image, with a scale bar of 5 / 1 nm; image c is a high-resolution transmission electron microscopy (TEM) image, with a scale bar of 2 nm.

[0030] Figure 5The images show the extinction curve and optical photograph of the silver micron-particle solution prepared in Example 1, as detected by ultraviolet-visible absorption spectroscopy.

[0031] Figure 6 The infrared absorption spectrum of the silver microparticles prepared in Example 1 was detected using Fourier transform infrared spectroscopy.

[0032] Figure 7 These are scanning electron microscope images of the silver microparticles obtained in Example 2, wherein... Figure 7 a is a low-magnification photo. Figure 7 b is a high-magnification electron microscope image of a single silver particle.

[0033] Figure 8 These are transmission electron microscope (TEM) images of the silver microparticles obtained in Example 2, wherein... Figure 8 a is a photograph of a single silver particle. Figure 8 b is its scanning transmission electron microscope image.

[0034] Figure 9 The infrared absorption spectrum of the silver microparticles prepared in Example 2 was detected using Fourier transform infrared spectroscopy.

[0035] Figure 10 This is a scanning electron microscope image of the silver microparticles obtained in Example 3.

[0036] Figure 11 This is a scanning electron microscope image of the silver microparticles obtained in Example 4. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] Example 1

[0039] This embodiment provides a method for preparing broadband, high-performance, uniform spherical silver micron-sized particles, specifically including the following steps:

[0040] S1. Citric acid, sodium citrate, D-mandelic acid and ascorbic acid were added to water at a concentration of 0.1 mol / L. The mixture was then incubated at 2°C for 7 days to obtain the surfactant solution.

[0041] S2. Add 300 μL of 0.1 mol / L silver nitrate solution to 1.7 mL of surfactant solution, with a volume ratio of 1.7:0.3, and mix to obtain the reaction precursor solution;

[0042] S3. The precursor solution was placed at 2°C and reacted for 1 hour to obtain a black colloidal solution.

[0043] S4. After centrifuging the black colloidal solution at 4000 rpm for 5 minutes, remove the supernatant. The resulting black precipitate is ultrasonically washed with deionized water and dried to obtain broadband, high-performance, uniform spherical silver micron particles.

[0044] Figure 1 The images are SEM images of the silver microspheres prepared in Example 1, taken using a Sirion 200 field emission scanning electron microscope (SEM); wherein, Figure 1 a is a low-magnification SEM image with a scale bar of 1 micrometer; Figure 1 b is a high-magnification SEM image with a scale bar of 200 nanometers. Figure 1 a and Figure 1 As can be seen from b, the monodisperse silver micron particles prepared in Example 1 are spherical nanoparticles with uniform size and high yield. The particle surface is composed of multiple nanoscale synapses and gaps, and the particle diameter is about 1 micrometer.

[0045] Figure 2 The image shows a low-magnification SEM image of several silver micron-sized spherical particles obtained in Example 1, along with a statistical distribution of the diameter of 100 particles in the image. The scale bar in the image is 10 micrometers. Statistical analysis reveals that the average diameter of the silver micron-sized particles is 0.97 ± 0.08 micrometers, further confirming the high uniformity of the spherical silver micron-sized particles.

[0046] Figure 3 These are transmission electron microscope (TEM) images of silver micron-sized spherical particles prepared in Example 1, taken using a JEOL-2100F transmission electron microscope; where 3a is a low-magnification TEM image with a scale bar of 1 micrometer. Figure 3 b is a high-angle dark-field scanning transmission electron image, with a scale bar of 500 nanometers. Figure 3 a and Figure 3 As can be seen from b, the product has a spherical morphology with a smooth surface, very uniform size, and excellent monodispersity.

[0047] Figure 4 Image a shows multiple transmission electron microscope (TEM) images of the silver micron-sized spherical particles obtained in Example 1, with a scale bar of 100 nm; image b is a selected area electron diffraction (SEED) image, with a scale bar of 5 / 1 nm; image c is a high-resolution TEM image, with a scale bar of 2 nm. Figure 4 As can be seen from a, the diameter of the particle is about 600 nanometers. The ring-like diffraction lattice proves that the silver particle has a polycrystalline structure. The high-resolution TEM image shows that the width of the lattice fringes on the surface of the silver particle is 0.237 nanometers, which is consistent with the standard data of the (111) crystal plane of silver.

[0048] Figure 5 The figures show the extinction curves and optical photographs of the silver micron-particle solution prepared in Example 1, as detected by a UV-Vis absorption spectrometer. The figures show that the silver micron-particles exhibit a high extinction coefficient in the 200-900 nm spectral range, hence their black color, consistent with the optical photograph in the illustration.

[0049] Figure 6 The infrared absorption spectrum of the silver microparticles prepared in Example 1 was detected using Fourier transform infrared spectroscopy. The figure shows that the infrared absorption of the silver microparticles exhibits a broadband characteristic, with peak widths spanning 650-3500 wavenumbers. A distinct Fano resonance peak is observed around 1250 wavenumbers. This is attributed to the near-field coupling between the CO stretching vibration frequency of citric acid molecules on the surface of the silver particles and the plasmon resonance effect of the silver particles. This phenomenon demonstrates that the mid-infrared broadband optical response of the silver microparticles is generated by the plasmon resonance effect.

[0050] Example 2

[0051] This embodiment provides a method for preparing broadband, high-performance, uniform spherical silver micron-sized particles, specifically including the following steps:

[0052] S1. Add citric acid, sodium citrate, D-mandelic acid and ascorbic acid to water at a concentration of 0.1 mol / L, and incubate at 2-8℃ for 7 days to obtain the surfactant solution.

[0053] S2. Add 300 μL of 0.1 mol / L silver nitrate solution to 1.7 mL of surfactant solution, with a volume ratio of 1.7:0.3, and mix to obtain the reaction precursor solution;

[0054] S3. The precursor solution was placed at 50°C and reacted for 1 hour to obtain 2 mL of black colloidal solution.

[0055] S4. Add 4 mL of 0.0001 mol / L 4-mercaptobenzonitrile solution to the black colloidal solution and continue incubation for 4 hours. Then, centrifuge at 4000 rpm for 5 minutes, remove the supernatant, and ultrasonically wash and dry the resulting black precipitate with deionized water to obtain broadband high-performance uniform spherical silver microparticles.

[0056] Figure 7 These are scanning electron microscope images of the silver microparticles obtained in Example 2, wherein... Figure 7 a is a low-magnification photo. Figure 7 b is a high-magnification electron microscope image of a single silver grain. Figure 7 It can be seen that the prepared silver micron particles are uniform in size, well dispersed, and the synaptic morphology of the particle surface is consistent with... Figure 1In comparison, its size is significantly reduced, its shape becomes spiky, and the hot spot size is smaller.

[0057] Figure 8 These are transmission electron microscope (TEM) images of the silver microparticles obtained in Example 2. Figure 8 a is a photograph of a single silver particle. Figure 8 b is its scanning transmission electron microscope (TEM) image. (From...) Figure 8 As can be seen from a, its sharp, columnar morphology further proves the variation in surface synaptic morphology and size; from Figure 8 As can be seen in b, the columnar structure extends into the interior of the silver particle.

[0058] Figure 9 The infrared absorption spectrum of the silver microparticles prepared in Example 2 was detected using Fourier transform infrared spectroscopy. Figure 9 It can be seen that a large number of Fano resonance peaks appeared in the spectrum of silver particles, proving that their plasmon near field and the molecules adsorbed on their surface produced strong coupling resonance.

[0059] Example 3

[0060] This embodiment provides a method for preparing broadband, high-performance, uniform spherical silver micron-sized particles, specifically including the following steps:

[0061] S1. Citric acid, sodium citrate and ascorbic acid were added to water at concentrations of 0.15 mol / L, 0.05 mol / L and 0.1 mol / L, respectively. The mixture was then incubated at 8°C for 7 days to obtain the surfactant solution.

[0062] S2. Add 300 μL of 0.1 mol / L silver nitrate solution to 1.7 mL of surfactant solution, with a volume ratio of 1.7:0.3, and mix to obtain the reaction precursor solution;

[0063] S3. The precursor solution was placed at 20°C and reacted for 1 hour to obtain a black colloidal solution.

[0064] S4. After centrifuging the black colloidal solution at 4000 rpm for 5 minutes, remove the supernatant. The resulting black precipitate is ultrasonically cleaned and dried with anhydrous ethanol to obtain broadband, high-performance, uniform spherical silver microparticles.

[0065] Figure 10 The image shows a scanning electron microscope (SEM) image of the silver microparticles obtained in Example 3. As can be seen from the image, compared to the particles in Examples 1 and 2, the particle diameter is significantly larger, with an average particle size of approximately 2 micrometers. This demonstrates that the particle size of the silver microparticles can be adjusted by regulating the composition and content of the surfactant solution.

[0066] Example 4

[0067] This embodiment provides a method for preparing broadband high-performance uniform spherical silver microparticles. The specific steps are the same as in Example 1, except that D-mandelic acid is not added in step S1 to obtain broadband high-performance uniform spherical silver microparticles.

[0068] Figure 11 The image shows a scanning electron microscope (SEM) image of the silver microparticles prepared in Example 4. As can be seen from the image, compared to the particles in Example 1, the particle size did not change significantly, but the size of the surface synaptic particles was significantly reduced, and the gaps between the synapses increased. This indicates that the surface morphology of the silver microparticles can be adjusted by adding D-mandelic acid.

[0069] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for preparing broadband, high-performance, uniformly spherical silver micron-sized particles, characterized in that, Specifically, the steps include the following: S1. Add citric acid, sodium citrate and ascorbic acid to water at a concentration of 0.005-0.5 mol / L, and incubate at 2-50 ℃ to obtain the surfactant solution. S2. Add a water-soluble silver salt precursor solution to the surfactant solution. The volume ratio of the surfactant solution to the water-soluble silver salt precursor solution is 1.7:(0.15-0.6). The concentration of the water-soluble silver salt precursor is 0.005-1 mol / L. The mixture is then used as the reaction precursor solution. S3. Place the precursor solution at 2-50 °C and react for 0.5-12 hours to obtain a black colloidal solution; S4. The black colloidal solution is directly centrifuged or the solution is added to a thiol solution and allowed to stand before centrifugation. The colorless solution in the centrifuge tube is removed, and the resulting black precipitate is ultrasonically cleaned and dried with a solvent to obtain broadband high-performance uniform spherical silver microparticles. The spherical silver microparticles have a polycrystalline structure and the surface is composed of nano-sized particle synapses and gaps.

2. The method for preparing broadband high-performance uniform spherical silver micron particles according to claim 1, characterized in that, The surfactant solution in step S1 also contains mandelic acid at a concentration of 0.005-0.5 mol / L.

3. The method for preparing broadband high-performance uniform spherical silver micron particles according to claim 2, characterized in that, The mandelic acid is one or more of S-mandelic acid and R-mandelic acid.

4. The method for preparing broadband high-performance uniform spherical silver micron particles according to claim 1, characterized in that, The static incubation time mentioned in step S1 is 1-30 days.

5. The method for preparing broadband high-performance uniform spherical silver micron particles according to claim 1, characterized in that, The water-soluble silver salt precursor solution mentioned in step S2 is a silver nitrate solution or a silver acetate solution.

6. The method for preparing broadband high-performance uniform spherical silver micron particles according to claim 1, characterized in that, The concentration of the thiol solution in step S4 is 0.0000005-0.05 mol / L, the volume ratio of the black colloidal solution to the thiol solution is 1:(1-10), and it is left to stand for 2-24 hours.

7. The method for preparing broadband high-performance uniform spherical silver micron particles according to claim 6, characterized in that, The thiol is one or more of 4-mercaptopyridine, 4-mercaptobenzoic acid, 4-mercaptoaniline, and 4-mercaptobenzonitrile.

8. The method for preparing broadband high-performance uniform spherical silver micron particles according to claim 1 or 6, characterized in that, In step S4, centrifuge at 3000-10000 rpm for 5-100 minutes using a high-speed centrifuge to separate and remove the colorless solution from the centrifuge tube.

9. The method for preparing broadband high-performance uniform spherical silver micron particles according to claim 1, characterized in that, The solvent mentioned in step S4 is deionized water, distilled water, or anhydrous ethanol.

10. Broadband high-performance uniform spherical silver microparticles prepared by the method of any one of claims 1-9.

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