A synthetic method for regulating the morphology of Pd nanosheets by ligands

Abstract

The present invention relates to a wet chemical method for synthesizing palladium (Pd) nanosheets. The method, which belongs to the field of nanosynthesis technology, regulates the morphology of the Pd nanosheets by controlling the ligand ratio. This method utilizes the competitive relationship between cysteine ​​and diethylenetriamine ligands to adjust the morphology of the Pd nanosheets, including thickness, surface wrinkling, and roughness. This further expands the control methods in the field of Pd nanosheet synthesis.

Description

Technical Field

[0001] The invention relates to a wet chemical method for synthesizing Pd nanosheets, in which the morphology of the nanosheets is controlled by regulating the ratio of ligands, and belongs to the technical field of nanosynthesis. Background Art

[0002] It is generally known that the ultrathin properties of two-dimensional nanomaterials can give them better catalytic performance and optical activity, because the two-dimensional nanostructures have abundant low-coordination atoms at the periphery and have a high specific surface area and exposed active centers.

[0003] In the synthesis and control of Pd nanosheets, researchers have made great progress in size and morphology: Zheng's research group can control the diameter of the hexagonal sheets to around 4nm, 12nm, and 30nm by simply adjusting the type of solvent, and can further grow hexagonal sheets of around 80nm using 30nm hexagonal sheets as seeds. Huang et al. used hexagonal nanosheets as templates, deposited Pb and other metal atoms on the templates, controlled the deposition of foreign atoms and the subsequent interatomic diffusion to synthesize ultrathin porous metal nanosheets. However, to date, the synthesis methods of Pd nanosheets have been too dependent on the presence of carbon monoxide. Moreover, the means of controlling the morphology of Pd nanosheets are too simple, and the diameter of the sheet can only be changed by simply changing or adjusting the reagent ratio. The surface of the nanosheets can usually only be controlled by atomic migration.

[0004] According to the applicant's understanding, developing more methods for synthesizing and regulating Pd nanosheets can expand the scope of development in the field of nanosynthesis. Summary of the Invention

[0005] The technical problem solved by the present invention is: a synthesis method for regulating the morphology of Pd nanosheets by ligands, which regulates the morphology of Pd nanosheets by regulating the molar ratio of cysteine ​​to diethylenetriamine, and expands the development of the field of Pd nanosheet synthesis.

[0006] To solve the above technical problems, the present invention proposes a technical solution: a method for regulating the morphology of Pd nanosheets through ligand competition. Cysteine ​​ligands of varying concentrations are introduced into the system for synthesizing Pd nanosheets, forming a competitive relationship between cysteine ​​and diethylenetriamine ligands to adjust the thickness, surface wrinkling, and roughness of the Pd nanosheets. Within a certain range, the higher the cysteine ​​concentration, the smaller the lateral size of the resulting nanosheets, the rougher the surface, and the thicker the nanosheets. The method comprises:

[0007] Step (1) prepares a mixture of N,N-dimethylformamide and ethylene glycol, wherein the ethylene glycol accounts for 40% by volume and the N,N-dimethylformamide accounts for 60% by volume.

[0008] Step (2): Add KOH, sodium chloropalladate (Na2PdCl4) and cysteine ​​to the mixed solution in step (1) to keep the KOH concentration at 1.78M, the Na2PdCl4 concentration at 1.6mM and the cysteine ​​concentration at 1.6×10 -3 -1.28×10 -1 mM;

[0009] Step (3): Add diethylenetriamine. In step (3), diethylenetriamine solvent is added so that the equivalent of diethylenetriamine in the solution is 3.1×10 5 -2.5×10 7 times, mix the mixture evenly;

[0010] Step (4): Place the reaction solution in step (3) in an oil bath and heat it at 150°C for 60 minutes to obtain the product, which is then centrifuged and washed 3-5 times.

[0011] Preferably, the concentration of cysteine ​​in step (2) is 1.6×10 -3 , 1.6×10 -2 , 9.6×10 -2 , 1.28×10 -1 mM.

[0012] Preferably, the diethylenetriamine equivalent in step (3) is 2.5×10 6 times.

[0013] Preferably, during the washing process of step (4), the centrifugal speed is 9000 rpm, the centrifugal time is 2 min, and after removing the supernatant, ethanol is added for dispersion washing and centrifugation is continued, and the washing step is repeated 4 times.

[0014] Beneficial effects of the present invention:

[0015] The morphology of Pd nanosheets, including thickness, surface wrinkling, and roughness, can be easily adjusted. Higher cysteine ​​concentrations within a specific range result in smaller lateral dimensions, rougher surfaces, and thicker nanosheets, enriching the controllable methods for Pd nanosheet synthesis. When cysteine ​​is omitted from the synthesis system, and only diethylenetriamine is added, large-scale, ultrathin Pd nanosheets exceeding 2 μm in size are obtained, with wrinkled but smooth surfaces. Adding even a minimal amount of diethylenetriamine can alter the nanosheet morphology; the amount of diethylenetriamine is 2.5×10 of the amount of cysteine. 6 times, a thick nanosheet with a lateral size of about 200 nm can be obtained. By increasing the amount of cysteine, diethylenetriamine is 3.1×10 5 or 4.2 × 10 5When the concentration of cysteine ​​was 1.6 mM, hollow spheres were formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings.

[0017] Figure 1 The cysteine ​​concentration is (a) 1.6×10 -3 (b) 1.6×10 -2 、(c)9.6×10 -2 (d) 1.28×10 -1 Scanning electron microscopy image of Pd nanosheets at mM

[0018] Figure 2 The cysteine ​​concentration is (a) 1.6×10 -1 (b) Scanning electron microscopy image of the product at 1.6 mM

[0019] Figure 3 Scanning electron microscopy image of Pd nanosheets formed without adding cysteine

[0020] Figure 4 This is a scanning electron micrograph of the hollow spheres formed when no diethylenetriamine is added.

[0021] Figure 5 Cysteine ​​concentration 1.6×10 -2 mM, scanning electron micrograph of the product when 0.1 ml of diethylenetriamine was added. The amount of diethylenetriamine is 5×104 times that of cysteine.

[0022] Figure 6 Cysteine ​​concentration (a) 1.6×10 -3 mM(b)1.6×10 -2 mM, scanning electron micrograph of Pd nanosheets when 1 ml of diethylenetriamine was added. Diethylenetriamine was 5×10 4 , 5×10 5 times DETAILED DESCRIPTION

[0023] Example 1

[0024] Prepare a mixture of ethylene glycol and N, N-dimethylformamide, 4 ml of ethylene glycol and 6 ml of N, N-dimethylformamide, add 1 g of KOH, 0.1 ml of 0.16 M Na2PdCl4 solution (prepared in water) and 0.2 ml of 8×10 - 5 M, 8×10 -4 M, 4.8×10 -3M, 6.4×10 -3 M, 8×10 -3 M cysteine ​​solution (ethylene glycol preparation), so that the concentration of KOH in the mixture is 1.78M, the concentration of Na2PdCl4 is 1.6mM, and the concentration of cysteine ​​is 1.6×10 -3 , 1.6×10 -2 , 9.6×10 -2 , 1.28×10 -1 , 1.6×10 -1 mM, then add 5 ml of diethylenetriamine solvent (purity 99%), mix the mixture evenly in a vortex mixer, heat in an oil bath at 150 ° C for 1 hour, use a centrifuge to remove the product, wash with anhydrous ethanol and centrifuge again, repeat the washing four times to obtain a black solid product. The cysteine ​​concentration is 1.6×10 -3 mM (the molar amount of diethylenetriamine is 2.5×10 7 Scanning electron microscope morphology was observed. Figure 1 a, The Pd sheet is ultra-thin and full of wrinkles, with a lateral distribution of up to 2 μm; when the cysteine ​​concentration increases by one order of magnitude, the concentration is 1.6×10 -2 mM (the molar amount of diethylenetriamine is 2.5×10 6 times), such as Figure 1 b, The Pd sheet becomes thicker and changes from a large piece to a combination of small pieces with a size of about 200 nm. At this time, the surface of the Pd sheet is still smooth and the thickness is significantly thickened. On this basis, the concentration of cysteine ​​is slowly increased to 9.6×10 -2 mM (the molar amount of diethylenetriamine is 4.2×10 5 times) when the size of the nanosheets is further reduced, such as Figure 1 c, the size of each nanosheet is about 100 nm, the surface of the nanosheet becomes rough, and the thickness increases further; Figure 1 d is the cysteine ​​concentration of 1.28×10 -1 mM (the molar amount of diethylenetriamine is 3.1×10 5 times) and the morphology of the nanosheets, Figure 1 The morphology is similar to that shown in c; the cysteine ​​concentration reaches 1.6×10 -1 mM (the molar amount of diethylenetriamine is 2.5×10 5 times), the product is basically in the form of particles with a diameter of about 50nm, but there are still small burrs on the surface ( Figure 2 a); When the cysteine ​​concentration reaches 1.6 mM, the products are all particles and cannot form nanosheets ( Figure 2 b)

[0025] Comparative Example 1

[0026] Unlike Example 1, in which different concentrations of cysteine ​​were added, this comparative example did not add cysteine, and the product was an ultrathin wrinkled Pd nanosheet with a lateral size of more than 2 μm. Figure 3 .

[0027] Comparative Example 2

[0028] Different from Example 1, in which diethylenetriamine was added, this comparative example did not add diethylenetriamine. When the cysteine ​​concentration was 1.6 mM, the product was hollow spheres. Figure 4 .

[0029] Example 2

[0030] Different from Example 1, in which 5 ml of diethylenetriamine was added, this example selected 0.1 ml and 1 ml of diethylenetriamine and combined them with different concentrations of cysteine. Figure 5 The cysteine ​​concentration is 1.6×10 -2 mM added 0.1 ml diethylenetriamine. At this time, the amount of diethylenetriamine was too low to form nanosheets, so adjusting the amount of cysteine ​​based on the amount of diethylenetriamine could not control the nanosheets. Figure 6 a and Figure 6 b are 1.6×10 -3 mM and 1.6×10 -2 mM cysteine ​​plus 1 ml diethylenetriamine, Figure 6 b. Higher cysteine ​​concentrations resulted in smaller lateral dimensions and thicker Pd nanosheets. The conclusion is that decreasing diethylenetriamine concentrations tends to reduce the size and thickness of the nanosheets, similar to the trend observed with increasing cysteine. However, the amount of diethylenetriamine should be kept within a range that ensures nanosheet formation. The morphology of the nanosheets can be controlled by adjusting the amount of cysteine ​​within the range required to achieve this.

[0031] The present invention is not limited to the specific technical solutions described in the above embodiments, and all technical solutions formed by equivalent replacement are within the protection scope required by the present invention.

Claims

1. A method for synthesizing Pd nanosheets with controlled morphology, characterized in that :The synthesis steps are as follows Step (1) preparing a mixture of N,N-dimethylformamide and ethylene glycol, wherein the ethylene glycol accounts for 40% by volume and the N,N-dimethylformamide accounts for 60% by volume; Step (2): Add KOH, sodium chloropalladate Na2PdCl4 and cysteine ​​to the mixed solution in step (1) to keep the KOH concentration at 1.78M, the Na2PdCl4 concentration at 1.6mM and the cysteine ​​concentration at 1.6×10 -3 -1.28×10 -1 mM; Step (3) Add diethylenetriamine solvent so that the equivalent of diethylenetriamine in the solution is 3.1×10 5 -2.5×10 7 times, and mix the mixture evenly; step (4): placing the reaction solution in step (3) in an oil bath and heating it at a temperature of 150° C. for 60 min to obtain the product, which is then washed 3-5 times; the morphology of the nanosheets is controlled by adjusting the molar ratio of cysteine ​​to diethylenetriamine.

2. The method for synthesizing Pd nanosheets by controlling their morphology according to claim 1, wherein: In step (2), the concentration of cysteine ​​was 1.6×10 -3 , 1.6×10 -2 , 9.6×10 -2 , 1.28×10 -1 mM.

3. The method for synthesizing Pd nanosheets with controlled morphology according to claim 1, wherein: The equivalent of diethylenetriamine added in step (3) is 2.5×10 6 times.

4. The method for synthesizing Pd nanosheets with controlled morphology according to claim 1, wherein: The product obtained in step (4) was centrifuged at 9000 rpm for 2 min. After removing the supernatant, ethanol was added for dispersion washing and centrifugation was continued. The washing step was repeated 4 times.

5. The method for synthesizing Pd nanosheets with controlled morphology according to claim 1, wherein: The molar amount of diethylenetriamine is 2.5×10 7 times, the nanosheets are ultra-thin and full of wrinkles, with a lateral distribution of 2 μm, and diethylenetriamine is 2.5×10 6 times, a nanosheet with a lateral size of 200 nm can be obtained, and the amount of cysteine ​​is increased. Diethylenetriamine is 3.1×10 5 or 4.2 × 10 5 times, thick nanosheets with a size of 100 nm and a rough surface can be obtained.

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