Ultrasonic suspension preparation method and application of silver-platinum core-shell alloy

Abstract

This invention relates to the field of nanoparticle preparation technology, specifically to a method and application for the ultrasonic suspension preparation of silver-platinum core-shell alloys. The ultrasonic suspension preparation method for silver-platinum core-shell nanoalloys provided by this invention includes the following steps: under the action of a non-contact ultrasonic field, a silver salt-containing precursor dispersion and a reducing agent solution are mixed in suspension to carry out a first reduction reaction, obtaining a silver nanoparticle colloidal solution; the silver nanoparticle colloidal solution, an alkaline ascorbic acid solution, and a platinum salt solution are mixed in suspension to carry out a second reduction reaction, obtaining the silver-platinum core-shell nanoalloy. The ultrasonic suspension preparation method provided by this invention avoids the heterogeneous nucleation problem caused by the wall surface and the metal contamination and structural damage caused by the inserted ultrasonic probe, resulting in a silver-platinum core-shell nanoalloy with a uniform structure, clear interface, and better catalytic effect.

Description

Technical Field

[0001] This invention relates to the field of nanoparticle preparation technology, specifically to a method for preparing and applying a silver-platinum core-shell alloy using ultrasonic suspension. Background Technology

[0002] Noble metal nanomaterials, due to their unique physicochemical properties, have shown broad application prospects in catalysis, sensing, biomedicine, and optoelectronics. Platinum, as a scarce precious metal, faces limitations in large-scale application due to its high cost and limited reserves. To reduce platinum usage and improve its catalytic performance, platinum is often combined with lower-cost precious metals, optimizing its catalytic performance through electronic and geometric effects. Among numerous bimetallic systems, silver-platinum nanoalloys, which combine silver and platinum to form a core-shell structure, have attracted significant attention due to their unique synergistic effects.

[0003] Currently, the main methods for preparing core-shell structured silver-platinum nanomaterials include co-reduction, seed growth, and thermal decomposition. These methods are typically carried out in reaction vessels (such as beakers, test tubes, and reaction kettles), which inevitably leads to heterogeneous nucleation problems caused by the vessel walls. Furthermore, related technologies disclose the use of conventional immersion ultrasonic probes to directly contact the reaction solution, which may introduce metal contamination, and the intense thermal effect could also damage the delicate core-shell structure. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing silver-platinum core-shell alloys via ultrasonic suspension and its application. The suspension preparation method provided by this invention avoids the heterogeneous nucleation problem caused by container walls and the metal contamination and structural damage caused by inserted ultrasonic probes, resulting in a uniform silver-platinum core-shell nanoalloy structure with clear interfaces and better catalytic effects.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing silver-platinum core-shell nanoalloys by ultrasonic levitation includes the following steps: Under the action of a non-contact ultrasonic field, the silver salt precursor dispersion and the reducing agent solution are mixed in a suspended state to carry out the first reduction reaction, and a silver nanoparticle colloidal solution is obtained. The silver nanoparticle colloidal solution, alkaline ascorbic acid solution, and platinum salt solution are mixed in a suspended state to carry out a second reduction reaction, thereby obtaining a silver-platinum core-shell nanoalloy.

[0006] Preferably, the ultrasonic power of the non-contact ultrasonic field is 200~600W, the frequency is 19~22kHz, and the distance between the transmitting end and the reflecting end is 20~30mm; the sound wave propagation medium of the non-contact ultrasonic field is air, and the suspended position is a sound pressure node.

[0007] Preferably, the silver salt-containing precursor dispersion comprises a silver salt and a dispersant, wherein the silver salt comprises silver nitrate and the dispersant comprises sodium citrate; the concentration of the silver salt in the silver salt-containing precursor dispersion is 0.1~1 mmol / L, and the molar ratio of silver element to dispersant in the silver salt is 1:1~3.

[0008] Preferably, the reducing agent in the reducing agent solution includes sodium borohydride, and the concentration of the reducing agent in the reducing agent solution is 80~120 mmol / L; the volume ratio of the silver salt-containing precursor dispersion to the reducing agent solution is 10~20:1.

[0009] Preferably, the temperature of the first reduction reaction is 20~40℃ and the time is 60~180s.

[0010] Preferably, the alkaline ascorbic acid solution comprises an alkali and ascorbic acid, wherein the alkali comprises sodium hydroxide; the concentration of ascorbic acid in the alkaline ascorbic acid solution is 80~120 mmol / L, and the molar ratio of alkali to ascorbic acid in the alkaline ascorbic acid solution is 100~150:80~120.

[0011] Preferably, the platinum salt in the platinum salt solution includes chloroplatinic acid, and the concentration of the platinum salt in the platinum salt solution is 5~20 mmol / L; the volume ratio of the alkaline ascorbic acid solution to the platinum salt solution is 1:1~9; and the volume ratio of the silver nanoparticle colloidal solution to the alkaline ascorbic acid solution is 20~21:2.

[0012] Preferably, the temperature of the second reduction reaction is 20~40℃ and the time is 60~180s.

[0013] The present invention provides a silver-platinum core-shell nano-alloy prepared by the suspension preparation method described above, comprising silver particles and a platinum layer coating the surface of the silver particles; the silver-platinum core-shell nano-alloy is granular, and the particle size of the silver-platinum core-shell nano-alloy particles is 11.7~13.3 nm; the molar ratio of silver to platinum in the silver-platinum core-shell nano-alloy is 1:9~10.

[0014] This invention provides the application of the silver-platinum core-shell nanoalloy described above in electrocatalysis.

[0015] This invention provides an ultrasonic levitation method for preparing silver-platinum core-shell nanoalloys. It utilizes the nonlinear effect of a high-intensity acoustic field to generate acoustic radiation pressure, overcoming gravity and suspending the reaction droplets in the air. This completely avoids heterogeneous nucleation caused by container walls in conventional synthesis and also avoids metal contamination that may be introduced by probe-type ultrasound, thus producing high-purity nanoparticles. The ultrasonic standing wave field not only provides levitation force, but its generated acoustic flow effect also promotes mass transfer within the droplets, making the nucleation process more synchronous. According to the Lamer model, an increase in the nucleation rate and the number of nuclei is beneficial for forming smaller nanoparticles. Combined with a stepwise reduction method, uniform silver cores are first synthesized, and then a platinum shell is reduced on their surface, ultimately obtaining spherical core-shell particles with small average particle size, concentrated particle size distribution, and regular morphology. This invention reduces platinum in an alkaline ascorbic acid environment, effectively suppressing the etching of the silver core by the galvanic cell displacement reaction in traditional methods, ensuring a uniform and dense platinum shell coating.

[0016] The method for preparing silver-platinum core-shell nanoalloys according to this invention is simple, reproducible, and produces uniformly distributed products. The ultrasonic energy released by an inserted ultrasonic probe generates very strong instantaneous shear forces, which can damage the surface of the formed nanoalloy, and even cause particle breakage and excessive oxidation. This invention avoids the use of an inserted ultrasonic probe, employing a non-contact ultrasonic field to induce a gentle and continuous high-frequency acoustic current and internal circulation within the suspended droplet, forming a microscale ultrasonic stirring effect. This achieves uniform mixing of reactants in a very short time, accomplishing micro-stirring that traditional magnetic stirring cannot achieve. It eliminates micro-concentration gradients, accelerates mass transfer between reactants, and simultaneously suppresses nanoparticle aggregation and core-shell segregation caused by differences in reduction rates. This ensures that the silver-platinum core-shell nanoalloys are uniformly distributed within the droplet. It eliminates the need for surfactants and capping agents to inhibit nanoparticle aggregation, greatly simplifying the experimental procedure and reducing synthesis costs.

[0017] This invention eliminates the interference of heterogeneous nucleation and achieves controllable nucleation mode. In the commonly used nanoparticle synthesis process under container contact conditions, the surface of the reaction vessel wall preferentially triggers heterogeneous nucleation with lower potential barriers, resulting in a concentration of nucleation sites on the vessel wall surface, larger product size, and poor morphological uniformity. The containerless ultrasonic suspension preparation method used in this invention makes the nucleation barrier of the reaction system more uniform, resulting in a more homogeneous product distribution and significantly improving the monodispersity of silver-platinum core-shell nanoalloys.

[0018] The silver-platinum core-shell nanoalloy prepared in this invention has the advantage of precise and controllable core-shell structure. In existing high-temperature synthesis techniques, the temperature required to prepare silver-platinum core-shell nanoalloys using sodium citrate and ethylene glycol reduction processes is 80-120℃. Excessively high temperatures exacerbate the diffusion of Ag and Pt atoms, easily leading to cross-interface mixing and defects such as alloyed shells, hollow cores, and shell fractures, resulting in a blurred core-shell interface. However, this invention synthesizes silver-platinum core-shell nanoalloys at room temperature, significantly reducing the atomic diffusion rate and solving the problem of blurred core-shell interfaces in existing high-temperature synthesis techniques.

[0019] The silver-platinum core-shell nanoalloys prepared in this invention exhibit excellent consistency in size and morphological distribution. The ultrasonic energy released by an extended ultrasonic probe is highly localized, resulting in extremely high cavitation intensity near the probe and rapid attenuation of the acoustic field intensity in the solution at a distance, forming a significant acoustic field intensity gradient that affects the uniformity of the entire reaction system. However, in the ultrasonic levitation process of this invention, the cavitation effect within the suspended droplets originates from the standing wave acoustic field, ensuring uniform cavitation intensity across the entire droplet and achieving synchronous nucleation. The cavitation effect significantly reduces the activation energy required for the reaction, triggering explosive nucleation in the system within a very short time, completely separating the nucleation and growth stages, thereby producing silver-platinum core-shell nanoalloys with excellent morphological distribution consistency.

[0020] The electrocatalytic performance of the silver-platinum core-shell nanoalloy prepared by this invention is significantly improved. Compared to a commercial Pt / C catalyst, the product obtained in Example 1 exhibits a Tafel slope value reduced by 52.92 mV·dec. -1 The performance was improved by 76.70%, with a significantly faster charge transfer rate; the double-layer capacitance was increased by 640%, and the electrochemical active surface area was greatly increased. Compared to Comparative Example 1, the product obtained in Example 1 showed a Tafel slope value reduced by 6.56 mV·dec. -1 The performance was improved by 28.98%, with a significantly faster charge transfer rate; the double-layer capacitance increased by 722.22%, and the electrochemically active surface area increased substantially. The electronic synergistic effect between the silver core and the platinum shell significantly enhanced the catalytic activity of the material, making its rate constant in the catalytic reduction of p-nitrophenol significantly higher than that of similar materials synthesized in traditional liquid phase. Attached Figure Description

[0021] Figure 1 Transmission electron microscopy (TEM) images of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1; Figure 2 This is a comparison of the particle size distribution curves of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1. Figure 3 The image shows a comparison of the linear sweep voltammetry (LSV) curves of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1. Figure 4 The overpotentials of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1 under different current densities; Figure 5 This is a comparison of the Tafel slopes of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1. Figure 6 The double-layer capacitance (C) of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1 dl Comparison chart. Detailed Implementation

[0022] This invention provides a method for preparing silver-platinum core-shell nanoalloys by ultrasonic levitation, comprising the following steps: Under the action of a non-contact ultrasonic field, the silver salt precursor dispersion and the reducing agent solution are mixed in a suspended state to carry out the first reduction reaction, and a silver nanoparticle colloidal solution is obtained. The silver nanoparticle colloidal solution, alkaline ascorbic acid solution, and platinum salt solution are mixed in a suspended state to carry out a second reduction reaction, thereby obtaining a silver-platinum core-shell nanoalloy.

[0023] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0024] This invention involves mixing a silver salt-containing precursor dispersion with a reducing agent solution in suspension under the action of a non-contact ultrasonic field to carry out a first reduction reaction, thereby obtaining a silver nanoparticle colloidal solution. In one embodiment of this invention, the silver salt-containing precursor dispersion comprises a silver salt and a dispersant. The silver salt includes silver nitrate, and the dispersant includes sodium citrate, specifically anhydrous sodium citrate. The concentration of the silver salt in the precursor dispersion is 0.1~1 mmol / L, specifically 0.5 mmol / L; the concentration of the dispersion in the precursor dispersion is 0.5~2 mmol / L, specifically 1.5 mmol / L; and the molar ratio of silver to dispersant in the silver salt is 1:1~3, specifically 1:3.

[0025] In one embodiment of the present invention, the silver salt precursor dispersion is preferably obtained by adding a dispersant to a silver salt solution and then ultrasonicating it; the ultrasonication is performed in an ultrasonic cleaner, the power of the ultrasonication is 400~700W, and the time is 1~10min, specifically 5min.

[0026] After obtaining the silver salt precursor dispersion, this invention utilizes an ultrasonic device to form a non-contact ultrasonic field, providing ultrasonic waves to generate acoustic radiation pressure. This causes the droplets of the silver salt precursor dispersion to overcome gravity and stably suspend at the acoustic pressure node, thereby achieving a containerless reaction environment and obtaining a suspended silver salt precursor dispersion. As one embodiment of this invention, the power of the non-contact ultrasonic field can be 200~600W, specifically 450W; the frequency of the ultrasonic waves can be 19~22kHz, specifically 21.7kHz.

[0027] In one embodiment of the present invention, the ultrasonic device can be a single-axis acoustic levitation device, the core components of which include an ultrasonic transmitting end and a reflecting end. The transmitting end can have a planar structure, with a cross-sectional radius of 10-20 mm, specifically 15 mm; the reflecting end can have a concave spherical structure, with a cross-sectional radius of 15-25 mm, specifically 20 mm, and a radius of curvature of 40-50 mm, specifically 42.5 mm. The distance between the transmitting end and the reflecting end can be 20-30 mm, specifically 27 mm. In one embodiment of the present invention, the transmitting end and the reflecting end are coaxially arranged to ensure the axial symmetry and stability of the sound field distribution. When a concave spherical reflecting end is used, the distance between the transmitting end and the reflecting end is defined as the vertical distance from the lowest point of the concave surface to the bottom surface of the transmitting end. In this invention, the ultrasonic device is a self-developed containerless synthesis device made of metal materials, specifically using the containerless levitation device in patent CN120285915A.

[0028] In one embodiment of the present invention, the ambient temperature of the ultrasonic levitation can be 20~40℃, specifically 25℃; the sound wave propagation medium of the ultrasonic field provided by the ultrasonic device is air.

[0029] In one embodiment of the present invention, the position of the ultrasonic potential well is first determined using a small amount of liquid droplets. Then, the silver salt-containing precursor dispersion is placed in the ultrasonic potential well using a pipette to achieve stable suspension of the silver salt-containing precursor dispersion. Specifically, determining the position of the ultrasonic potential well using a small amount of liquid droplets involves: drawing 50 μL of deionized water using a pipette, gently pushing the pipette piston button to attach a small droplet to the pipette tip, and then slowly moving the pipette between the emitting and reflecting ends until the small droplet detaches from the pipette tip and is stably suspended at the sound pressure node.

[0030] The silver salt-containing precursor dispersion is kept in suspension, and a reducing agent solution is added to the silver salt-containing precursor dispersion to carry out a first reduction reaction, thereby obtaining a silver nanoparticle colloidal solution. In one embodiment of the invention, the reducing agent in the reducing agent solution includes sodium borohydride, and the concentration of the reducing agent in the reducing agent solution is 80~120 mmol / L, specifically 100 mmol / L; the volume ratio of the silver salt-containing precursor dispersion to the reducing solution is 10~20:1.

[0031] In one embodiment of the present invention, while adding a reducing agent solution, the distance between the emitting end and the reflecting end is adjusted to ensure that the suspended droplets remain stable. The distance between the emitting end and the reflecting end is 25~27cm.

[0032] In one embodiment of the present invention, the temperature of the first reduction reaction is 20~40℃, specifically 25℃, and the time is 60~180s, specifically 120s. In the silver salt-containing precursor dispersion, the silver salt and the reducing agent undergo a reduction reaction, and after the silver salt is reduced, silver elemental particles are obtained, ultimately yielding a silver nanoparticle colloidal solution.

[0033] After obtaining the silver nanoparticle colloidal solution, the present invention mixes the silver nanoparticle colloidal solution, the alkaline ascorbic acid solution, and the platinum salt solution in a suspension state to carry out a second reduction reaction, thereby obtaining a silver-platinum core-shell nanoalloy. As one embodiment of the present invention, the alkaline ascorbic acid solution includes an alkali and ascorbic acid, wherein the alkali includes sodium hydroxide; the concentration of the alkali in the alkaline ascorbic acid solution is 100-150 mmol / L, specifically 125 mmol / L; the concentration of the ascorbic acid in the alkaline ascorbic acid solution is 80-120 mmol / L, specifically 100 mmol / L; the molar ratio of the alkali to the ascorbic acid in the alkaline ascorbic acid solution is 100-150:80-120, specifically 125:100.

[0034] In one embodiment of the present invention, the platinum salt in the platinum salt solution includes chloroplatinic acid, and the concentration of the platinum salt in the platinum salt solution is 5~20 mmol / L, specifically 10 mmol / L; the volume ratio of the alkaline ascorbic acid solution to the platinum salt solution is 1:1~9, specifically 1:6 or 1:9; the volume ratio of the silver nanoparticle colloidal solution to the alkaline ascorbic acid solution is 20~21:2.

[0035] As one embodiment of the present invention, mixing the silver nanoparticle colloidal solution, alkaline ascorbic acid solution, and platinum salt solution in a suspended state preferably includes: adding alkaline ascorbic acid solution to the silver nanoparticle colloidal solution to maintain stable suspension, and then adding platinum salt solution in batches; the present invention ensures that the suspended droplets remain stable by adjusting the distance between the emitting end and the reflecting end while adding alkaline ascorbic acid solution, and the distance between the emitting end and the reflecting end is 25~27cm; the platinum salt solution is added in batches 6~9 times, and the time interval between each addition is 20s.

[0036] In one embodiment of the present invention, the temperature of the second reduction reaction is 20~40℃, specifically 25℃, and the time is 60~180s, specifically 120s. The present invention uses ascorbic acid solution as a reducing agent, which has a relatively weak reducing ability. Sodium hydroxide is added to the ascorbic acid solution to adjust its pH to alkaline, thereby improving the reducing ability and reducing the subsequently added chloroplatinic acid hexahydrate. The reduced Pt atoms preferentially nucleate and aggregate on the surface of Ag nanoparticles, thus synthesizing a silver-platinum core-shell nanoalloy.

[0037] In one embodiment of the present invention, the second reduction reaction further includes: centrifuging the silver-platinum core-shell nano-alloy sol obtained from the second reduction reaction, and sequentially ultrasonically washing and drying the precipitate obtained by centrifugation; the centrifugation speed is 12000 rad / min, the time is 5 min, and after centrifugation, the supernatant is completely aspirated with a pipette to collect the precipitate; the ultrasonic washing solvent is anhydrous ethanol, the time is 2 min, and the ultrasonic washing is performed in an ultrasonic cleaner; after ultrasonic washing, the centrifugation operation is repeated to obtain silver-platinum core-shell nano-alloy particle precipitate, and the silver-platinum core-shell nano-alloy particle precipitate is dried, and the drying is performed in an oven. The present invention does not have any special limitations on the drying process.

[0038] The present invention provides a silver-platinum core-shell nano-alloy prepared by the suspension preparation method described above, comprising silver particles and a platinum layer coating the surface of the silver particles; the silver-platinum core-shell nano-alloy is granular, and the particle size of the silver-platinum core-shell nano-alloy is 11.7~13.3 nm; the molar ratio of silver to platinum in the silver-platinum core-shell nano-alloy is 1:9~10.

[0039] This invention provides the application of the silver-platinum core-shell nanoalloy described above in electrocatalysis.

[0040] In one embodiment of the present invention, the electrocatalysis employs a three-electrode system, including a working electrode, a counter electrode, and a reference electrode; the working electrode can be a glassy carbon electrode, the counter electrode can be a platinum sheet electrode, and the reference electrode can be an Ag / AgCl electrode; the electrolyte is a sulfuric acid solution, and the concentration of the sulfuric acid solution is preferably 0.5 mol / L.

[0041] In one embodiment of the present invention, it is preferable to disperse the silver-platinum core-shell nano-alloy in water to obtain a silver-platinum core-shell nano-alloy suspension, which is then drop-coated onto the surface of the working electrode, and cyclic voltammetry is performed in the aforementioned sulfuric acid solution.

[0042] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments thereof. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0043] Example 1 Measure 25 μL of a 0.2 mol / L silver nitrate aqueous solution using a pipette and transfer it to a 10 mL volumetric flask. Dilute to 10 mL with deionized water and place in a 10 mL centrifuge tube. Sonicate for 5 min to obtain 10 mL of a 0.5 mmol / L silver nitrate aqueous solution. Add 3.87 mg of anhydrous sodium citrate and sonicate for 5 min to obtain 10 mL of a silver salt precursor dispersion. The concentration of silver nitrate in the silver salt precursor dispersion is 0.5 mmol / L, and the concentration of anhydrous sodium citrate is 1.5 mmol / L.

[0044] Weigh 18.9 mg of sodium borohydride and dissolve it in 5 mL of deionized water at 10 °C. Disperse the solution by sonication for 5 min to obtain 5 mL of sodium borohydride solution with a concentration of 100 mmol / L.

[0045] Weigh out 88 mg of ascorbic acid and 25 mg of sodium hydroxide, mix them and put them into a 5 mL volumetric flask. Dilute to 5 mL with deionized water and transfer to a 5 mL centrifuge tube. Sonicate for 5 min to obtain 5 mL of alkaline ascorbic acid solution. The concentration of ascorbic acid in the alkaline ascorbic acid solution is 100 mmol / L and the concentration of sodium hydroxide is 125 mmol / L.

[0046] Weigh 25.9 mg of chloroplatinic acid hexahydrate and dissolve it in 5 mL of deionized water. Disperse the solution by sonication for 5 min to obtain 5 mL of chloroplatinic acid solution with a concentration of 10 mmol / L.

[0047] Under 25℃ conditions, a single-axis acoustic levitation device with a power of 450W and a frequency of 21.7kHz was used. The cross-sectional radius of the planar emitting end was 15mm, the cross-sectional radius of the concave reflecting end was 20mm, and the radius of curvature was 42.5mm. The vertical distance between the bottom surface of the planar emitting end and the lowest point of the concave reflecting end was 27mm. 50μL of deionized water was drawn up with a pipette, and the pipette piston button was gently pushed to attach a small droplet to the tip. The pipette was then moved between the emitting end and the reflecting end until the droplet detached from the tip, and the sound pressure node between the emitting end and the reflecting end was found. 50μL of the silver salt-containing precursor dispersion was drawn up with a pipette and placed at the sound pressure node to stabilize it.

[0048] Using a pipette, 2.5 μL of the sodium borohydride solution was injected into the suspended silver salt precursor dispersion. At the same time, the distance between the emitting end and the reflecting end was adjusted between 25 and 27 cm to ensure that the suspended droplet remained stable. The reduction reaction was carried out at the sound pressure node for 2 min to obtain a suspended silver nanoparticle colloidal solution.

[0049] Using a pipette, 2.5 μL of the alkaline ascorbic acid solution was injected into the suspended silver nanoparticle colloidal solution. Simultaneously, the distance between the emitting and reflecting ends was adjusted between 25 and 27 cm to ensure the suspension droplet remained stable for 30 seconds. Then, using a pipette, 22.5 μL of the chloroplatinic acid solution was injected into the suspension droplet in nine portions, with each portion being 2.5 μL and a 20-second interval between injections, for a total injection time of 3 minutes. After the chloroplatinic acid solution was completely added, a reduction reaction was carried out for 3 minutes to obtain a silver-platinum core-shell nano-alloy sol.

[0050] Take 2 mL of silver-platinum core-shell nano-alloy sol and place it in a centrifuge. Centrifuge at 12000 rad / min for 5 min. Use a pipette to remove all the supernatant to obtain a precipitate. Add 2 mL of anhydrous ethanol to the precipitate and ultrasonically disperse it in an ultrasonic cleaner for 2 min. Repeat the above centrifugation operation to obtain silver-platinum core-shell nano-alloy particles. Dry the silver-platinum core-shell nano-alloy in an oven to obtain silver-platinum core-shell nano-alloy.

[0051] Example 2 The procedure is essentially the same as in Example 1, except that 15 μL of the chloroplatinic acid solution was injected into the suspension droplet in six separate injections using a pipette.

[0052] Comparative Example 1 The same silver salt precursor dispersion, sodium borohydride solution, alkaline ascorbic acid solution, and chloroplatinic acid solution as in Example 1 were used.

[0053] Add 5 mL of the silver salt-containing precursor dispersion to a 20 mL beaker. Pipette 250 μL of the sodium borohydride solution into the beaker and let stand for 5 min. Pipette 250 μL of the alkaline ascorbic acid solution into the beaker and let stand for 1 min. Add 2.25 mL of the chloroplatinic acid solution into the beaker in 9 portions, each time using a pipette to add 250 μL of the chloroplatinic acid solution and letting stand for 1 min, to obtain the silver-platinum core-shell nano-alloy sol.

[0054] The subsequent methods are the same as in Example 1.

[0055] Comparative Example 2 The method is basically the same as Comparative Example 1, except that 1.5 mL of the chloroplatinic acid solution was added to the beaker in 6 portions.

[0056] Test Example 1 50 μL of the silver-platinum core-shell nanoalloy sol prepared in Example 1 and Comparative Example 1 were respectively pipetted and dropped onto a 300-mesh carbon film copper grid. After drying, they were observed by transmission electron microscopy. The TEM images are shown below. Figure 1 As shown. Figure 1 These are transmission electron microscope (TEM) images of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1. Figure 1 (a) is a TEM image of the silver-platinum core-shell nanoalloy prepared in Example 1. Figure 1 (b) is a TEM image of the silver-platinum core-shell nanoalloy prepared in Comparative Example 1. According to... Figure 1 It can be seen that the average particle size of the silver-platinum core-shell nanoalloy in Example 1 is 12.3 ± 0.6 nm; the average particle size of the silver-platinum core-shell nanoalloy in Comparative Example 1 is 14.6 ± 0.3 nm. The particle size distribution image obtained after Gaussian fitting based on the histogram of the frequency distribution is shown below. Figure 2 As shown. Figure 2 This is a comparison of the particle size distribution curves of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1. According to... Figure 2 It can be seen that the average particle size of the silver-platinum core-shell nanoalloy prepared by ultrasonic suspension in Example 1 is smaller than that in Comparative Example 1.

[0057] Test Example 2 Electrocatalytic testing was performed using a three-electrode system. The working electrode was a glassy carbon electrode, the counter electrode was a platinum sheet electrode, and the reference electrode was an Ag / AgCl electrode. The electrolyte solution was 50 mL of 0.5 mol / L sulfuric acid. 10 μL of a silver-platinum core-shell nanoalloy suspension (containing 0.1 mg of silver-platinum core-shell nanoalloy) was drop-coated onto the surface of the working electrode. Cyclic voltammetry was performed in the sulfuric acid solution until the scan curve stabilized. Then, LSV testing was conducted at a scan rate of 50 mV / s to obtain the LSV curve. Figure 3 As shown.

[0058] Figure 3 This is a comparison of the linear sweep voltammetry (LSV) curves of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1. Figure 3 LSV data were used to obtain overpotentials at different current densities, such as Figure 4 As shown. Figure 4 The overpotentials of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1 under different current densities are shown. Figure 3 and Figure 4 It can be seen that the catalytic activity and stability of the silver-platinum core-shell nanoalloy prepared in Example 1 are better than those of Comparative Example 1.

[0059] Further calculations using LSV data yielded the Tafel slopes of the silver-platinum core-shell nanoalloys in Example 1 and Comparative Example 1, such as... Figure 5 As shown. Figure 5 This is a comparison of the Tafel slopes of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1. According to... Figure 5 It can be seen that the Tafel slope of the silver-platinum core-shell nanoalloy prepared in Example 1 is b1 = 16.08 mV·dec -1 The Tafel slope of the silver-platinum core-shell nanoalloy prepared in Comparative Example 1 is b2 = 22.64 mV·dec. -1 .

[0060] The double-layer capacitance (C0) of the silver-platinum core-shell nanoalloys in Example 1 and Comparative Example 1 obtained by electrocatalytic testing dl )like Figure 6 As shown. Figure 6 The double-layer capacitance (C) of the silver-platinum core-shell nanoalloys prepared in Example 1 and Comparative Example 1 dl (Comparison chart.) Figure 6 It can be seen that the double-layer capacitance of the silver-platinum core-shell nanoalloy prepared in Example 1 is k1 = 7.4 mF·cm. -2 The double-layer capacitance of the silver-platinum core-shell nanoalloy prepared in Comparative Example 1 is k2 = 0.9 mF·cm. -2 .

[0061] The silver-platinum core-shell nanoalloys and commercial Pt / C catalysts prepared in Examples 1-2 and Comparative Examples 1-2 were subjected to particle size and electrocatalytic tests using the methods of Test Example 1 and Test Example 2. The obtained particle sizes and electrocatalytic parameters are shown in Table 1.

[0062] Table 1. Particle size and electrocatalytic parameters of silver-platinum core-shell nanoalloys and commercial Pt / C catalysts prepared in Examples 1-2 and Comparative Examples 1-2.

[0063] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing silver-platinum core-shell nanoalloys by ultrasonic levitation, comprising the following steps: Under the action of a non-contact ultrasonic field, the silver salt precursor dispersion and the reducing agent solution are mixed in a suspended state to carry out the first reduction reaction, and a silver nanoparticle colloidal solution is obtained. The silver nanoparticle colloidal solution, alkaline ascorbic acid solution, and platinum salt solution are mixed in a suspended state to carry out a second reduction reaction, thereby obtaining a silver-platinum core-shell nanoalloy.

2. The ultrasonic levitation preparation method according to claim 1, wherein, The ultrasonic power of the non-contact ultrasonic field is 200~600W, the frequency is 19~22kHz, and the distance between the transmitting end and the reflecting end is 20~30mm; the sound wave propagation medium of the non-contact ultrasonic field is air, and the suspended position is a sound pressure node.

3. The ultrasonic levitation preparation method according to claim 1, wherein, The silver salt-containing precursor dispersion includes a silver salt and a dispersant, wherein the silver salt includes silver nitrate and the dispersant includes sodium citrate; the concentration of the silver salt in the silver salt-containing precursor dispersion is 0.1~1 mmol / L, and the molar ratio of silver element to dispersant in the silver salt is 1:1~3.

4. The ultrasonic levitation preparation method according to claim 3, wherein, The reducing agent in the reducing agent solution includes sodium borohydride, and the concentration of the reducing agent in the reducing agent solution is 80~120 mmol / L; the volume ratio of the silver salt-containing precursor dispersion to the reducing agent solution is 10~20:

1.

5. The ultrasonic levitation preparation method according to claim 1, wherein, The temperature of the first reduction reaction is 20~40℃ and the time is 60~180s.

6. The ultrasonic levitation preparation method according to claim 1, wherein, The alkaline ascorbic acid solution comprises an alkali and ascorbic acid, wherein the alkali comprises sodium hydroxide; the concentration of ascorbic acid in the alkaline ascorbic acid solution is 80~120 mmol / L, and the molar ratio of alkali to ascorbic acid in the alkaline ascorbic acid solution is 100~150:80~120.

7. The ultrasonic levitation preparation method according to claim 6, wherein, The platinum salt in the platinum salt solution includes chloroplatinic acid, and the concentration of the platinum salt in the platinum salt solution is 5~20 mmol / L; the volume ratio of the alkaline ascorbic acid solution to the platinum salt solution is 1:1~9; and the volume ratio of the silver nanoparticle colloidal solution to the alkaline ascorbic acid solution is 20~21:

2.

8. The ultrasonic levitation preparation method according to claim 1, wherein, The temperature of the second reduction reaction is 20~40℃, and the time is 60~180s.

9. The silver-platinum core-shell nanoalloy prepared by the ultrasonic suspension preparation method according to any one of claims 1 to 8 comprises silver particles and a platinum layer coating the surface of the silver particles; the silver-platinum core-shell nanoalloy is granular, and the particle size of the silver-platinum core-shell nanoalloy particles is 11.7 to 13.3 nm; the molar ratio of silver to platinum in the silver-platinum core-shell nanoalloy is 1:9 to 10.

10. The application of the silver-platinum core-shell nanoalloy of claim 9 in electrocatalysis.

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