Preparation method of hexagonal palladium sheet nano material

Abstract

The invention discloses a preparation method of a hexagonal palladium sheet nano material, and relates to the technical field of nano material manufacturing. The method comprises the following steps that PdCl2, trisodium citrate and absolute ethyl alcohol are ultrasonically mixed to be uniform, and a palladium precursor solution is formed; adding NaBH4 into the ice ultrapure water, and adjusting the pH value to be alkaline; slowly dropwise adding a NaBH4 solution into the palladium precursor solution at room temperature, and stirring to enable the mixed solution to fully react; and centrifugally separating, washing and drying the reaction liquid to obtain the hexagonal palladium nanosheet with uniform size. The method is simple, the experiment condition is mild, the cost is low, the controllability is good, and the prepared hexagonal palladium nanosheet is uniform in size and good in dispersity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterial manufacturing, and particularly relates to a preparation method of hexagonal palladium sheet nanomaterial. BACKGROUND

[0002] As an important platinum group noble metal, palladium (Pd) has unique physical and chemical properties in nanomaterials, and exhibits superior performance in the fields of catalysis, sensing, photothermal therapy, hydrogen storage and optoelectronic devices, thus attracting extensive attention. The physical and chemical properties of nanomaterials are strongly dependent on their size, morphology and crystal face structure. Therefore, accurate control of the morphology of palladium nanomaterials is crucial for obtaining excellent performance.

[0003] Among numerous palladium nanostructures, two-dimensional sheet structure, especially hexagonal palladium nanosheet, has high specific surface area and a large number of exposed {110} or {100} high surface energy crystal faces, so that the hexagonal two-dimensional palladium nanosheet exhibits more excellent catalytic activity and selectivity than traditional nanoparticles. Meanwhile, a large number of exposed palladium atoms become potential catalytically active sites, greatly improving the utilization efficiency of noble palladium atoms and helping to reduce the cost of catalysts.

[0004] At present, the existing methods for preparing hexagonal palladium nanosheets mainly include carbon monoxide gas reduction method, polymer polymerization template method, halide ion regulation method and the like. However, these methods all have obvious limitations. For example, although the carbon monoxide method can obtain nanosheets with uniform morphology, the CO gas used is highly toxic and can be strongly adsorbed on the palladium surface to form a poisoning layer, which seriously damages the catalytic activity and brings safety risks; the polymer template method and the halide ion regulation method have the problem that the morphology control agent is difficult to completely remove, and the residual organic matter or halogen ions will cover the active sites, affecting the intrinsic performance of the material. The underpotential deposition method introduces foreign metal impurities, which is not conducive to obtaining palladium nanosheets with high purity. Therefore, it has become an urgent technical requirement in the field to develop a new method for preparing hexagonal palladium nanosheets which is green and safe, simple to operate, mild in conditions and good in repeatability.

[0005] In view of the problems and deficiencies of the prior art, the application provides a preparation method of hexagonal palladium sheet nanomaterial, which uses a room temperature liquid phase reduction method to prepare palladium nanosheets. The method is simple, mild in experimental conditions, low in cost and good in controllability, and the prepared hexagonal palladium nanosheets are uniform in size and good in dispersity. SUMMARY

[0006] The application aims to provide a preparation method of hexagonal palladium sheet nanomaterial to solve the problems of the hexagonal palladium nanosheets prepared by the prior art, such as safety risks, insufficient morphology or low material yield.

[0007] To achieve the above object, the present application adopts the following technical solutions: The present application provides a preparation method of hexagonal palladium sheet nanomaterial, comprising the following steps: S1, adding PdCl2, trisodium citrate and anhydrous ethanol into ultrapure water, ultrasonic mixing to form a palladium precursor solution; the metal Pd precursor PbCl2 in the palladium precursor solution is dissolved in the solvent anhydrous ethanol, and the trisodium citrate is used as a protective agent; S2, adding NaBH4 into ice ultrapure water and adjusting the pH value to be alkaline; the ice ultrapure water can keep low temperature and slow down the decomposition of NaBH4; S3, slowly adding a 0.01-0.1 mol / L concentration NaBH4 solution into the palladium precursor solution at a speed of 5-10 min / mL under room temperature and stirring to make the mixed solution fully react, wherein the molar concentration ratio between the palladium precursor solution and the NaBH4 solution is 1:1-1.5; the NaBH4 solution reduces the palladium precursor solution; S4, centrifugal separation, washing and drying the reaction liquid to obtain hexagonal palladium nanosheets with uniform size.

[0008] Preferably, the molar ratio of PbCl2, trisodium citrate and anhydrous ethanol in S1 is 1:(0.1-0.25):(0.25-0.5).

[0009] Preferably, the concentration of PbCl2 in the palladium precursor solution in S1 is 0.01-0.1 mol / L. Preferably, the ultrasonic mixing time in S1 is 2-5 minutes. Preferably, the pH value in S2 is 11-13.

[0010] Preferably, the molar concentration ratio between the palladium precursor solution and the NaBH4 solution in S3 is 1:1.

[0011] Preferably, the NaBH4 solution is added by using a sample pump at a speed of 5-10 min / mL in S3.

[0012] Preferably, the stirring in S3 is in a mechanical stirring mode, and the mechanical stirring speed is 200-800 rpm.

[0013] Preferably, the reaction time for full reaction in S3 is 60-90 minutes.

[0014] Preferably, the drying temperature in S4 is 45°C.

[0015] Preferably, the hexagonal palladium nanosheet has a side length of 0.5-3 μm, a diameter of 1-5 μm and a thickness of 35-65 nm.

[0016] Compared with the prior art, the present application has the following advantages: (1) The method of the present application can efficiently prepare hexagonal palladium nanosheets with high uniformity of morphology and good dispersibility under mild conditions by a simple room-temperature liquid-phase reduction method. The product has high yield and good process repeatability. Compared with the prior art, the present method does not require complex equipment or high-temperature and high-pressure environment, and has simple process flow, mild conditions, strong controllability, significantly reduced energy consumption and production cost, and lays a solid foundation for large-scale industrial production. The obtained hexagonal palladium nanosheets have broad application prospects in many fields such as catalysis, sensing, energy conversion and storage due to their unique two-dimensional structure and regular morphology.

[0017] (2) In the room-temperature liquid-phase reduction method of the present application, PdCl2 is used as the metal Pd precursor, trisodium citrate dihydrate is used as the protective agent, and anhydrous ethanol is used as the solvent to form a palladium precursor solution, and sodium borohydride (NaBH4) is used as the reducing agent. The molar concentration ratio between the PdCl2 solution and the NaBH4 solution is 1:1-1.5. After NaBH4 is added dropwise into the PdCl2 solution, Pd² + atoms are rapidly reduced to Pd 0 atoms to form fine crystal nuclei. Citrate ions are selectively adsorbed on the {111} crystal face (the lowest energy face) of Pd, inhibiting the growth of the face in the vertical direction and promoting the lateral expansion. Since Pd is an fcc metal, the {111} face has six-fold symmetry, and the isotropic growth naturally forms a hexagonal sheet structure. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 FIG. 1 is a scanning electron microscope image of the regular hexagonal palladium nanosheets prepared in Example 1 of the present application; Figure 2 FIG. 2 is a scanning electron microscope image of the regular hexagonal palladium nanosheets prepared in Example 2 of the present application; Figure 3 FIG. 3 is a scanning electron microscope image of the regular hexagonal palladium nanosheets prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0020] Example 1: The preparation method of hexagonal palladium nanosheets comprises the following steps: Step (1): adding PbCl2, trisodium citrate and anhydrous ethanol into ultrapure water with a molar ratio of 1:0.1:0.25, and mixing uniformly under ultrasonic treatment (stirring speed of 250 rpm and ultrasonic treatment frequency of 40 KHz) for 2 minutes to form a palladium precursor solution; Step (2): adding NaBH4 into ice ultrapure water to adjust the pH value of the solution to 11; Step (3): at room temperature, slowly adding the NaBH4 solution into the palladium precursor solution, wherein the molar concentration ratio between the palladium precursor solution and the NaBH4 solution is 1:1; and fully reacting under mechanical stirring at a speed of 200 rpm for 90 minutes; Step (4): centrifuging, washing and drying the reaction solution to obtain the hexagonal palladium nanosheets with uniform size.

[0021] The scanning electron microscope picture of the hexagonal palladium nanosheets prepared in this example is shown in Figure 1 .

[0022] Example 2: The preparation method of the hexagonal palladium nanosheets comprises the following steps: Step (1): adding PbCl2, trisodium citrate and anhydrous ethanol into ultrapure water with a molar ratio of 1:0.15:0.35, and mixing uniformly under ultrasonic treatment (stirring speed of 250 rpm and ultrasonic treatment frequency of 40 KHz) for 3.5 minutes to form a palladium precursor solution; Step (2): adding NaBH4 into ice ultrapure water to adjust the pH value of the solution to 12; Step (3): at room temperature, slowly adding the NaBH4 solution into the palladium precursor solution, wherein the molar concentration ratio between the palladium precursor solution and the NaBH4 solution is 1:1.2; and fully reacting under mechanical stirring at a speed of 500 rpm for 70 minutes; Step (4): centrifuging, washing and drying the reaction solution to obtain the hexagonal palladium nanosheets with uniform size.

[0023] The scanning electron microscope picture of the hexagonal palladium nanosheets prepared in this example is shown in Figure 2 .

[0024] Example 3: The preparation method of the hexagonal palladium nanosheets comprises the following steps: Step (1): adding PbCl2, trisodium citrate and anhydrous ethanol into ultrapure water with a molar ratio of 1:0.25:0.5, and mixing uniformly under ultrasonic treatment (stirring speed of 250 rpm and ultrasonic treatment frequency of 40 KHz) for 5 minutes to form a palladium precursor solution; Step (2): adding NaBH4 into ice ultrapure water to adjust the pH value of the solution to 13; Step (3): slowly add NaBH4 solution into the palladium precursor solution at room temperature, wherein the molar concentration ratio between the palladium precursor solution and the NaBH4 solution is 1:1.5; mechanically stir at a speed of 800 revolutions per minute for 60 minutes; Step (4): centrifugal separation, washing and drying of the reaction solution to obtain the hexagonal palladium nanosheet with uniform size.

[0025] The scanning electron microscope picture of the hexagonal palladium nanosheet prepared in the embodiment is shown in Figure 3 .

[0026] In summary, the present application adds PdCl2, trisodium citrate and anhydrous ethanol into ultrapure water, ultrasonically mixes them to form a palladium precursor solution with a certain concentration; adds NaBH4 into ice ultrapure water and adjusts the pH value to be alkaline; adds NaBH4 solution into the palladium precursor solution at room temperature, and stirs for a certain time. + After adding NaBH4 into the PdCl2 solution, Pd 0 atoms are rapidly reduced to form fine crystal nuclei. Citrate selectively adsorbs on the {111} crystal face (the lowest energy face) of Pd, inhibits the growth of the face in the vertical direction, and promotes the lateral expansion. Since Pd belongs to fcc metal, the {111} face has six-fold symmetry, and the isotropic growth naturally forms a hexagonal sheet structure. Then the reaction solution is centrifugally separated, washed and dried to obtain the hexagonal palladium nanosheet with uniform size.

[0027] The hexagonal palladium nanosheet prepared in the embodiments 1-3 has a side length of about 1.5 μm, a diameter of about 3 μm and a thickness of about 50 nm. It can be seen that the hexagonal palladium nanosheet has uniform size and good dispersibility. The hexagonal palladium nanosheet has an ultra-thin thickness (50 nm) and lateral extension, so that most of the palladium atoms are exposed on the surface to become active sites. As a catalyst, the abundant surface atoms (especially the low-coordination atoms located at the edges and corners) usually have higher catalytic activity, the atom utilization rate is extremely high, and the amount of noble metal palladium can be greatly reduced to improve the economy. At the same time, the hexagonal palladium nanosheet prepared by the present application has uniform morphology, good dispersibility, high yield, simple preparation method and good controllability, and can be prepared on a large scale.

[0028] The above description is only used to help understand the method of the present application and its core essence, but the protection scope of the present application is not limited thereto. For those skilled in the art, according to the technical solution and the inventive concept of the present application, equivalent replacement or change within the technical scope disclosed by the present application should be covered within the protection scope of the present application. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for preparing hexagonal palladium sheet nanomaterials, characterized in that, The method comprises the following steps: S1, uniformly mixing PdCl2, trisodium citrate and anhydrous ethanol by ultrasonic to form a palladium precursor solution; S2, adding NaBH4 to ice ultrapure water and adjusting the pH value to be alkaline; S3, slowly adding a 0.01-0.1 mol / L concentration NaBH4 solution to the palladium precursor solution at a speed of 5-10 min / mL at room temperature and stirring to make the mixed solution fully react; wherein the molar concentration ratio between the palladium precursor solution and the NaBH4 solution is 1:1-1.5; S4, centrifugally separating, washing and drying the reaction solution to obtain hexagonal palladium nanosheets with uniform size.

2. The method for preparing hexagonal palladium sheet nanomaterials according to claim 1, characterized in that, In the S1, the molar ratio of the three of PbCl2, trisodium citrate and anhydrous ethanol is 1:(0.1-0.25):(0.25-0.5).

3. The method for preparing hexagonal palladium sheet nanomaterials according to claim 1, characterized in that, In the S1, the concentration of PbCl2 in the palladium precursor solution is 0.01-0.1 mol / L.

4. The method for preparing hexagonal palladium sheet nanomaterials according to claim 1, characterized in that, In the S1, the ultrasonic mixing time is 2-5 minutes.

5. The method for preparing hexagonal palladium sheet nanomaterials according to claim 1, characterized in that, In the S2, the pH value is 11-13.

6. The method for preparing hexagonal palladium sheet nanomaterials according to claim 1, characterized in that, In the S3, the stirring is in a mechanical stirring mode, and the mechanical stirring speed is 200-800 rpm.

7. The method for preparing hexagonal palladium sheet nanomaterials according to claim 1, characterized in that, In the S3, the reaction time for fully reacting is 60-90 minutes.

8. The method for preparing hexagonal palladium sheet nanomaterials according to claim 1, characterized in that, In the S4, the drying temperature is 45°C.

9. The method for preparing hexagonal palladium sheet nanomaterials according to any one of claims 1-8, characterized in that, The hexagonal palladium nanosheets have a side length of 0.5-3 μm, a diameter of 1-5 μm and a thickness of 35-65 nm.

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