Preparation method of monatomic platinum based on acoustic suspension

Abstract

The invention discloses a preparation method of monatomic platinum based on acoustic suspension, and relates to the technical field of monatomic preparation. The method comprises the following steps: dispersing MoS2 powder in a platinum source solution, adding a stabilizer, and uniformly mixing to obtain a precursor solution; suspending the precursor solution by adopting an acoustic suspension method, and modulating sound field parameters to obtain suspension droplets with oscillating motion; and adding a reducing agent into the suspension drops, and carrying out a reduction reaction to obtain monatomic platinum loaded on the MoS2 substrate. According to the invention, an acoustic suspension technology is adopted, the stable loading of monatomic Pt is realized through ultrasonic effects such as fan harmonic oscillation enhanced acoustic streaming excited by an ultrasonic field, and the preparation method has the advantages of high efficiency, stability and uniform loading.

Description

Technical Field

[0001] The invention relates to the technical field of single atom preparation, and in particular to a method for preparing single atom platinum based on acoustic levitation. Background Art

[0002] Due to its excellent catalytic, optoelectronic and wave absorption properties, single-atom platinum-modified MoS2 has shown application potential in many key fields. Specific application examples include: using single-atom platinum modification to passivate the non-radiative surface capture state of MoS2 quantum dots and significantly improve their fluorescence efficiency "CR Li, YL Lei, H. Li, et al. Suppressing Non-Radiative Relaxation through Single-Atom Metal Modificationfor Enhanced Fluorescence Efficiency in Molybdenum Disulfide Quantum Dots[J].Angew. Chem. Int. Ed., 2022, 61: e202207300."; activating the electrocatalytic activity of the MoS2 surface by loading single-atom platinum, exploring a single-atom platinum catalyst for studying the catalytic mechanism "YT Luo, SQ Zhang, HY Pan, et al. Unsaturated Single Atoms on Monolayer Transition Metal Dichalcogenides for Ultrafast Hydrogen Evolution[J]. ACS Nano, 2020, 14(1): 767-776." By loading single atoms on two-dimensional materials and porous materials, the utilization rate of metal atoms is improved, the electronic structure of the material is changed, and the relevant application performance of the material is significantly improved. However, the current single-atom preparation technology has problems such as complex steps, low efficiency, and unclear preparation principles.

[0003] Conventional single-atom preparation technologies mainly include chemical reduction, co-precipitation, chemical vapor deposition, atomic layer deposition, and current displacement. Among them, the chemical reduction method has a complex preparation process, uneven dispersion of metal atoms, and is prone to clustering; the precipitation process in the co-precipitation method is difficult to control, and it is easy to form multiple phases, affecting the catalytic performance; the atomic layer deposition method has low preparation efficiency and high requirements for equipment and processes; the current displacement method has the difficulty of having few applicable carriers and single-atom metal types. Therefore, developing a new single-atom preparation technology and increasing the loading capacity of single atoms are the key to promoting single atoms towards practical industrial applications.

[0004] In view of this, the present invention provides a technical method for simply and efficiently preparing single-atom platinum based on acoustic levitation technology. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned background technology, the present invention mainly solves the limitations of the prior art, such as complex preparation process and expensive equipment, which hinder the further development of single-atom preparation technology and its application. The present invention provides a method for preparing single-atom platinum based on acoustic levitation. The method uses acoustic levitation technology to reduce chloroplatinic acid with sodium borohydride, loads single-atom platinum on a molybdenum disulfide substrate, and realizes the preparation of single-atom platinum with a high loading rate.

[0006] The first object of the present invention is to provide a method for preparing single-atom platinum based on acoustic levitation, comprising the following steps: Dispersing MoS2 powder in a platinum source solution, adding a stabilizer, and uniformly mixing to obtain a precursor solution; The precursor solution is suspended by an acoustic levitation method to obtain suspended droplets; Add a reducing agent to the suspended droplets to carry out a reduction reaction, thereby obtaining single-atom platinum supported on the MoS2 substrate; When the acoustic suspension method is used for suspension, a modulation signal is introduced to make the suspended droplets generate fan-shaped oscillations; when the suspended droplets generate fan-shaped oscillations, the frequency of the sinusoidal sound wave that excites the static suspension is 20-22 kHz, and the modulation frequency that excites the fan-shaped oscillations is 50-250 Hz; The platinum source solution is a chloroplatinic acid solution; the stabilizer is polyvinyl alcohol; the reducing agent is a sodium borohydride solution; the mass percentage of the MoS2 powder and the chloroplatinic acid solution is 0.5-5%; The MoS2 powder is 2H phase MoS2 powder prepared by a hydrothermal method.

[0007] Preferably, the acoustic suspension method is to use an acoustic suspension device for suspension, in which the cross-sectional radius of the curved reflection end of the acoustic suspension device is 15-23 mm, and the curvature radius is 38-42 mm.

[0008] Preferably, the concentration of the chloroplatinic acid solution is 0.5-2 g / L.

[0009] Preferably, the ratio of the mass of polyvinyl alcohol to the mass of the solvent in the precursor solution is 1:100-120.

[0010] Preferably, the concentration of the sodium borohydride solution is 0.05-0.2 mol / L; and the volume percentage of the precursor solution to the sodium borohydride solution is 8-10:1.

[0011] Preferably, the reduction reaction temperature is room temperature, and the reduction reaction time is 1 to 3 minutes.

[0012] Preferably, the MoS2 powder is prepared by a hydrothermal method by dissolving ammonium molybdate tetrahydrate and thiourea in deionized water, stirring them evenly and then placing them in a hydrothermal reactor, and reacting them at 200-250° C. for 12-24 hours.

[0013] The second object of the present invention is to provide a single-atom platinum.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing single-atom platinum based on acoustic levitation. The present invention adopts acoustic levitation technology, uses MoS2 as a loading substrate, and uses NaBH4 to reduce H2PtCl6·H2O solution to achieve stable loading of single-atom Pt. The preparation method has the advantages of high efficiency, stability and uniform loading. Acoustic levitation technology overcomes the gravity of the sample by means of the acoustic radiation force generated by the nonlinear acoustic effect, while introducing the acoustic flow and cavitation effect into the suspended sample, causing the change of the dynamic behavior of the droplet and introducing the fluctuation of local energy, providing a stable container-free environment and high-energy conditions for the loading of single atoms. Based on the uniaxial standing wave acoustic levitation technology, a low-frequency modulation signal of a specific frequency is added to the output sinusoidal sound wave that excites static suspension, which can modulate non-axisymmetric fan-harmonic oscillations of different oscillation modes. The flow inside the fan-harmonic oscillation droplet is more intense than that of static acoustic levitation, especially between the extension sector and the contraction sector, which is conducive to improving the dispersion of the particle loading substrate and the uniformity of the single-atom platinum loading.

[0015] The present invention reduces the adsorption amount of Pt single atoms and clusters at the solid interface under container-free conditions, excites the fan-resonance oscillation of droplets under acoustic suspension conditions, and introduces stronger nonlinear acoustic effects to cause acoustic flow and cavitation as the main influencing mechanisms. The acoustic flow inside the droplet generates eddy currents, as well as significant macroscopic flows between the stretching sector and the contracting sector, which promote the diffusion of solutes. The stirring of the acoustic flow increases the contact area between the MoS2 powder and the solution, and increases the adhesion opportunity of the mass percentage of single atomic platinum generated by the reaction. The rupture of cavitation bubbles in the droplet generates transient high temperature and high pressure, which helps to prevent the formation of Pt clusters and even leads to the disintegration of Pt clusters. In addition, the hydrogen bubbles generated by the reaction help to change the dynamic behavior of the cavitation bubbles and promote the generation and attachment of Pt single atoms.

[0016] The acoustic levitation technology adopted in the present invention overcomes the gravity of the sample with the help of the acoustic radiation force generated by the nonlinear acoustic effect to achieve suspension, and at the same time introduces the acoustic flow and cavitation effect into the suspended sample, and utilizes the strengthening effect of fan-harmonic oscillation on the internal flow and acoustic effect, thereby causing the change of the fluid dynamic behavior of the sample and introducing more dramatic local energy fluctuations, providing an ultra-pure container-free environment and high-energy conditions for the loading of single atoms, and is a simple and efficient preparation technology for single-atom platinum. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a top view of the third-order fan-harmonic oscillation of the suspended droplet in Example 2.

[0018] Figure 2 This is a scanning electron microscope image of molybdenum disulfide loaded with single-atom platinum in Example 2.

[0019] Figure 3 This is a transmission electron micrograph of molybdenum disulfide loaded with single-atom platinum prepared in the suspended droplets of Example 2.

[0020] Figure 4 This is a comparison chart of the electromagnetic wave absorption rates of the products obtained in Examples 1 to 4 in the wave absorption performance test.

[0021] Figure 5 This is a diagram of the wave absorption performance of the MoS2 substrate and the product obtained in Example 2. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0023] The purpose of the present invention is to provide a method for preparing single-atom platinum based on acoustic levitation, which uses acoustic levitation technology to excite droplet fan-resonance oscillation, introduces a stronger nonlinear acoustic effect, and reduces chloroplatinic acid with sodium borohydride to load single-atom platinum on a molybdenum disulfide substrate, thereby achieving the preparation of single-atom platinum with a high loading rate.

[0024] In order to achieve the above object, the present invention provides a method for preparing single-atom platinum based on acoustic levitation, comprising the following steps: Dispersing MoS2 powder in a platinum source solution, adding a stabilizer, and uniformly mixing to obtain a precursor solution; The precursor solution is suspended by an acoustic levitation method to obtain suspended droplets; A reducing agent is added to the suspended droplets, and a modulation signal of a specific frequency is added at the same time to stimulate fan-shaped harmonic oscillation and carry out a reduction reaction to obtain single atomic platinum supported on a MoS2 substrate.

[0025] According to the present invention, the preparation method introduces a modulation signal on the basis of acoustic levitation, so that the droplets undergo fan-shaped oscillation, further enhancing the acoustic streaming effect inside the droplets. The frequency of the sinusoidal sound wave that excites static levitation is 20~22kHz, and the modulation frequency that excites fan-shaped oscillation is 50~250Hz.

[0026] The acoustic suspension method is to suspend using an acoustic suspension device, wherein the cross-sectional radius of the curved reflection end of the acoustic suspension device is 15-23 mm, and the curvature radius is 38-42 mm. Specifically, the oscillation mode of the excited fan-resonance oscillation is the third order, and the modulation frequency is 105-115 Hz.

[0027] Wherein, the platinum source solution is a chloroplatinic acid solution, the concentration of the chloroplatinic acid solution is 0.5~2g / L, preferably 1g / L; the mass percentage of the MoS2 powder and the chloroplatinic acid solution is 0.5%~5%.

[0028] The stabilizer is polyvinyl alcohol; the ratio of the mass of polyvinyl alcohol to the mass of the solvent in the precursor solution is 1:100-120.

[0029] The reducing agent is a sodium borohydride solution, the concentration of the sodium borohydride solution is 0.05-0.2 mol / L, preferably 0.1 mol / L; the volume percentage of the precursor solution to the sodium borohydride solution is 8-10:1, preferably 9:1.

[0030] The temperature of the reduction reaction is room temperature, and the reduction reaction time is 1 to 3 minutes.

[0031] The MoS2 powder is 2H phase MoS2 powder prepared by a hydrothermal method.

[0032] The MoS2 powder is prepared by a hydrothermal method by dissolving ammonium molybdate tetrahydrate and thiourea in deionized water, stirring them evenly and then placing them in a hydrothermal reactor to react at 200-250° C. for 12-24 hours.

[0033] In one embodiment, a method for preparing single-atom platinum based on acoustic levitation comprises the following steps: Step 1: Disperse MoS2 powder in H2PtCl6·H2O solution, add polyvinyl alcohol (PVA) solution, and mix evenly to obtain a precursor solution; Step 2: Use an acoustic suspension device to output static suspension sound waves to suspend the precursor solution; Step 3: Add NaBH4 reducing agent solution to the suspended precursor solution, input a modulation signal to excite the fan-resonant oscillation of the droplets, and perform a reduction reaction to obtain single-atom platinum supported on the MoS2 substrate.

[0034] It should be noted that when preparing the precursor solution, the raw materials are weighed according to the Pt loading mass ratio relative to MoS2 being 0.5~5%.

[0035] After the reduction reaction is completed, the present invention further includes stopping the input of the modulation signal and collecting the sample after the reaction. At the same time, a large-volume pipette is used to absorb the suspension droplets after the reaction and inject them into a centrifuge tube for storage and standby use.

[0036] The present invention uses an acoustic suspension device to excite sectorial oscillation to suspend and treat a precursor solution, and the sample collected after reduction is a molybdenum disulfide nanoparticle loaded with single-atom platinum. The acoustic suspension device is composed of an acoustic emission end and an acoustic reflection end. The schematic diagram of the device is detailed in the paper "CL Shen, WJ Xie, and B. Wei, Parametrically excited sectorial oscillation of liquid drops floating in ultrasound [J], Physical Review E, 2010, 81 (4): 046305".

[0037] The suspension process provided by the present invention comprises the following steps: (1) Setting the acoustic wave output power as required, outputting 20-22 kHz sinusoidal acoustic waves for statically suspending the precursor solution; (2) using a syringe to draw the precursor solution, preferably, using a high-precision pipette to draw 90 μL of the precursor solution; (3) Appropriately increase the distance between the reflector and the emitter, slowly inject the precursor solution while gradually reducing the distance to make the droplets statically suspended; (4) Use a high-precision pipette to draw 10 μL of sodium borohydride solution and inject it into the stably suspended precursor droplets; (5) Add a modulation signal with an initial frequency of 50 Hz and gradually increase the modulation frequency to excite the third-order non-axisymmetric fan-harmonic oscillation of the suspended droplet.

[0038] In the present invention, the acoustic levitation technology is used to reduce chloroplatinic acid with sodium borohydride, so that single-atom platinum is loaded on a molybdenum disulfide substrate, thereby achieving the preparation of single-atom platinum with a high loading rate.

[0039] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0040] Example 1 2.4717 g of ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 ·H2O) and 2.1314g thiourea (CH4N2S) were dissolved in 70mL of ionized water and stirred with a magnetic stirrer at room temperature for 60min to change the solution from a white transparent state to a blue transparent solution.

[0041] The blue transparent solution was transferred to a hydrothermal reactor lined with para-polyphenylene (PPL) with a volume of 100 mL, and reacted under high pressure at 220°C for 21 hours. After cooling to room temperature, the reactor was opened, and the obtained product was filtered and washed several times with deionized water and anhydrous ethanol to obtain a black solid precipitate, which was placed in a vacuum drying oven and heated to 60°C for 12 hours to obtain a black molybdenum disulfide (MoS2) powder sample; it should be noted that high-pressure reaction refers to the high pressure caused by high-temperature reaction in a closed hydrothermal reactor.

[0042] According to the Pt loading mass ratio of 0.5% relative to MoS2, 0.37671g of MoS2 powder sample was added to 5ml of 1g / L chloroplatinic acid aqueous solution, and then a 1% polyvinyl alcohol (PVA) aqueous solution was added to make the mass ratio of polyvinyl alcohol to Pt be 3:2, and mixed evenly to form a black uniform precursor solution.

[0043] The acoustic wave output power is set as needed, the cross-sectional radius of the reflection end is selected as 20 mm and the radius of curvature is 40 mm, and the wave nodes of the standing wave acoustic field are determined; 90 μL of the precursor solution is statically suspended in the acoustic suspension device using a pipette, and then 10 μL of 0.1 mol / L sodium borohydride (NaBH4) aqueous solution is quickly injected using a micro-syringe without contacting the suspended droplets to reduce chloroplatinic acid to single-atom Pt loaded on the carrier MoS2; a modulation signal is input, and the modulation frequency is adjusted to 110 Hz to excite the third-order fan-harmonic oscillation of the suspended droplets.

[0044] Record the reduction reaction time. t =60s, turn off the modulation signal, use a large-capacity pipette to remove the suspended droplets, and store them in a centrifuge tube for later use; use deionized water and anhydrous ethanol to filter and wash the obtained product several times to obtain a black solid precipitate, and place it in a vacuum drying oven and heat it to 60°C for 12h to obtain a black molybdenum disulfide powder sample loaded with single atomic platinum, named 2H-0.5%.

[0045] Example 2 The same as Example 1, except that the specific experimental parameters are shown in Table 1; a black molybdenum disulfide powder sample loaded with single atomic platinum was obtained, named 2H-1%.

[0046] Example 3 The same as Example 1, except that the specific experimental parameters are shown in Table 1; a black molybdenum disulfide powder sample loaded with single atomic platinum was obtained, named 2H-3%.

[0047] Example 4 The same as Example 1, except that the specific experimental parameters are shown in Table 1; a black molybdenum disulfide powder sample loaded with single atomic platinum was obtained, named 2H-5%.

[0048] The experimental parameters of each embodiment are shown in Table 1.

[0049] Table 1 shows the experimental parameters of Examples 1 to 4.

[0050] The loading mass ratio in Table 1 refers to the mass ratio of Pt to MoS2 loading. The concentrations of the chloroplatinic acid solution and the sodium borohydride solution used in Examples 1 to 4 are the same.

[0051] In order to illustrate the relevant properties of the single atomic platinum loaded on the MoS2 substrate prepared by the method provided by the present invention, it is described in conjunction with the accompanying drawings.

[0052] Figure 1 This is a top-view image of the suspended droplet in Example 2 taken after the modulated signal excites the third-order sectoral harmonic oscillation. The droplet shape is an axisymmetric pie with three typical extension sectors.

[0053] Figure 2 This is a scanning electron microscope image of molybdenum disulfide loaded with single-atom platinum provided in Example 2. Figure 2 The SEM image is shown when the loading amount is 1%. Its microscopic morphology is consistent with that of the MoS2 sample without loading. No obvious difference is found, and the presence of Pt is not directly observed on the surface of the nanosheets, indicating that at this loading amount, Pt may exist in the form of a single atom on the carrier MoS2. Figure 3 This is a transmission electron microscopy image of the molybdenum disulfide loaded with single-atom platinum prepared in the suspended droplet of Example 2. Figure 3 The figure shows the TEM image when the loading amount is 1%. From the figure, it can be clearly observed that there are bright spots evenly dispersed on the surface of the carrier molybdenum disulfide. Since the atomic number of Pt is significantly different from that of Mo and S, the brighter the part in the image, the larger the atomic number here. It is judged that Pt exists on the surface of 2H-MoS2 in the form of single atoms and is relatively evenly distributed; among them, the size of single atomic platinum is about 0.133nm.

[0054] In the present invention, when the loading amount is 1%, single-atom Pt loaded uniformly can be observed on the carrier MoS2; when the loading amount is 3%, the existence form of Pt evolves from single atoms to nanoparticles. Preferably, the loading ratio is 1%, and a single-atom Pt loaded MoS2 material with uniform loading can be prepared.

[0055] Figure 4 This is a comparison chart of the electromagnetic wave absorption rates of the products obtained in Examples 1 to 4 in the wave absorption performance test.

[0056] from Figure 4 It can be seen that the electromagnetic wave absorption rate in the wave absorption performance of the MoS2 substrate loaded with single-atom Pt prepared by acoustic levitation. As can be seen from the figure, the electromagnetic wave absorption rate changes with the single-atom Pt loading in the sample. The loading amount of Pt single atom is 1%, which shows better electromagnetic wave absorption performance than the other embodiments. Its higher electromagnetic wave absorption rate is due to the 1% loading amount showing the best loading efficiency in the preparation of acoustically suspended single-atom platinum.

[0057] Figure 5 The microwave absorption performance diagram of the MoS2 substrate (a) and the product obtained in Example 2 (b).

[0058] from Figure 5 It can be seen that the absorption performance image of the MoS2 substrate (a) and the 1% loading amount of Pt-MoS2 (b) obtained in Example 2. Compared with the absorption performance image of the MoS2 substrate, Figure 5 (b) The effective absorption width of Pt-MoS2 with 1% loading is wider, indicating that the attachment of single atomic Pt on the MoS2 substrate changes the electronic structure of the MoS2 substrate and enhances the microwave absorption performance of the MoS2 substrate.

[0059] In the present invention, a method for preparing single-atom platinum acoustic levitation is developed. Preferably, the oscillation mode of the suspended droplet is adjusted by changing the frequency of the modulation signal.

[0060] In summary, the acoustic levitation technology adopted in the present invention overcomes the gravity of the sample with the help of the acoustic radiation force generated by the nonlinear acoustic effect to achieve suspension, and at the same time introduces the acoustic flow and cavitation effect into the suspended sample, and utilizes the strengthening effect of fan-harmonic oscillation on the internal flow and acoustic effect, thereby causing the change of the fluid dynamic behavior of the sample and introducing more dramatic local energy fluctuations, providing an ultra-pure container-free environment and high-energy conditions for the loading of single atoms, and is a simple and efficient preparation technology for single-atom platinum.

Claims

1. A method for preparing single-atom platinum based on acoustic levitation, characterized in that: The following steps are involved: Dispersing MoS2 powder in a platinum source solution, adding a stabilizer, and uniformly mixing to obtain a precursor solution; The precursor solution is suspended by an acoustic levitation method to obtain suspended droplets; Add a reducing agent to the suspended droplets to carry out a reduction reaction, thereby obtaining single-atom platinum supported on the MoS2 substrate; When the acoustic suspension method is used for suspension, a modulation signal is introduced to make the suspended droplets generate fan-shaped oscillations; when the suspended droplets generate fan-shaped oscillations, the frequency of the sinusoidal sound wave that excites the static suspension is 20-22 kHz, and the modulation frequency that excites the fan-shaped oscillations is 50-250 Hz; The platinum source solution is a chloroplatinic acid solution; the stabilizer is polyvinyl alcohol; the reducing agent is a sodium borohydride solution; the mass percentage of the MoS2 powder and the chloroplatinic acid solution is 0.5-5%; The MoS2 powder is 2H phase MoS2 powder prepared by a hydrothermal method.

2. The method for preparing single-atom platinum based on acoustic levitation according to claim 1, characterized in that: The acoustic suspension method adopts an acoustic suspension device for suspension, wherein the cross-sectional radius of the curved reflection end of the acoustic suspension device is 15-23 mm, and the curvature radius is 38-42 mm.

3. The method for preparing single-atom platinum based on acoustic levitation according to claim 1, characterized in that: The concentration of the chloroplatinic acid solution is 0.5-2 g / L.

4. The method for preparing single-atom platinum based on acoustic levitation according to claim 1, characterized in that: The mass ratio of the polyvinyl alcohol to the solvent in the precursor solution is 1:100-120.

5. The method for preparing single-atom platinum based on acoustic levitation according to claim 1, characterized in that: The concentration of the sodium borohydride solution is 0.05-0.2 mol / L; the volume percentage of the precursor solution to the sodium borohydride solution is 8-10:

1.

6. The method for preparing single-atom platinum based on acoustic levitation according to claim 1, characterized in that: The temperature of the reduction reaction is room temperature, and the reduction reaction time is 1 to 3 minutes.

7. The method for preparing single-atom platinum based on acoustic levitation according to claim 1, characterized in that: The MoS2 powder is prepared by a hydrothermal method by dissolving ammonium molybdate tetrahydrate and thiourea in deionized water, stirring them evenly and then placing them in a hydrothermal reactor to react at 200-250° C. for 12-24 hours.

8. A single atomic platinum obtained by the preparation method according to any one of claims 1 to 7.

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