A method for loading ultrasmall-sized noble metal nanoparticles on hollow carbon spheres through a boron cluster / cyclodextrin supramolecule

Abstract

The present invention provides a method for loading ultrasmall-sized noble metal nanoparticles on hollow carbon spheres through a boron cluster / cyclodextrin supramolecule. Using nitrogen-doped hollow carbon spheres as carriers and boron cluster / cyclodextrin supramolecules as confining agents and reducing agents, ultrasmall-sized noble metal nanoparticles are successfully loaded in the shell layer of the nitrogen-doped hollow carbon spheres. The noble metal nanoparticles are uniformly dispersed in the shell layer of the nitrogen-doped hollow carbon spheres, with sizes all less than 10 nanometers, no obvious aggregation phenomenon and high exposure degree, which can improve the utilization rate of the noble metal. Compared with the prior art, the present invention combines two key roles, namely nitrogen-doped hollow carbon spheres and reducing boron cluster / cyclodextrin supramolecules, when preparing noble metal nanomaterials, improves the dispersion degree of the noble metal nanoparticles and reduces the particle size of the noble metal nanoparticles, and can obtain ultrasmall-sized supported noble metal nanoparticles. The method of the invention is simple to operate, reliable in technology, advanced in results and easy to scale up production.

Description

Technical Field

[0001] The present invention relates to the development of a preparation method of nano-precious metal materials, belonging to the field of metal material preparation. Specifically, it is a method for loading ultrasmall-sized nano-precious metals on hollow carbon spheres through boron cluster / cyclodextrin supramolecules. Background Art

[0002] Metal materials are widely used in fields such as chemical production, new material development, and energy (Chem. J. Chinese Universities, 2022, 43, 20220043). Due to advantages such as high catalytic activity and stable catalytic performance, noble metal nano-materials have become the main catalysts in industrial production. Limited by the scarcity of noble metal reserves, the high cost of noble metal catalysts restricts their large-scale use (J. Mater. Chem. A, 2023, 11, 5830). Improving the utilization rate of noble metal catalysts is the key to reducing production. When metal materials in particulate form are used as catalysts, it is difficult to fully expose the internal metal. Continuously minimizing the size of metal sites is beneficial to fully expose metal sites during the reaction process and improve the utilization rate of metal sites (J. Mater. Chem. A, 2021, 9, 16427). Currently, in order to improve the utilization rate of metal sites in metal materials during catalytic reactions, various methods have been developed to reduce the metal particle size, including methods such as introducing additional carriers, mechanical ball milling, chemical vapor deposition, and framework material confinement. At present, even though numerous methods for manufacturing nano-metals have been developed, the development of new technologies for nano-material manufacturing has not stopped. Developing low-cost, highly dispersed, and small-sized metal materials, especially noble metal nano-materials, remains the focus of attention. In the present invention, boron cluster / cyclodextrin supramolecules are deposited on nitrogen-doped hollow carbon spheres with a large specific surface area, and the reduction ability of boron clusters is used to successfully construct supported ultrasmall nano-precious metals, such as supported nano-palladium, supported nano-gold, supported nano-ruthenium, etc., on the interface of hollow carbon spheres. The developed method is simple and effective and suitable for scale-up production. Summary of the Invention

[0003] The technical problem solved by the present invention is to provide a method for preparing ultrasmall-sized nano-precious metal materials. The size of the supported nano-precious metals prepared by the method provided in this application is less than 10 nanometers, including ultrasmall-sized nano-palladium, ultrasmall-sized nano-gold, and ultrasmall-sized nano-ruthenium.

[0004] The specific technical solution adopted by the present invention is as follows

[0005] A method for loading ultrasmall-sized nano-precious metals on nitrogen-doped hollow carbon spheres through boron cluster / cyclodextrin supramolecules, comprising the following steps:

[0006] A. Boron cluster / cyclodextrin supramolecule supported on nitrogen-doped hollow carbon spheres. A certain amount of cyclodextrin and aqueous solution of borane clusters were mixed, stirred at a certain temperature for a period of time, and then nitrogen-doped hollow carbon spheres dispersed in water were added (the nitrogen-doped hollow carbon spheres were prepared by the method we invented, and the invention publication number is CN116713021A). The suspension was continuously stirred for 12 hours, and after removing the aqueous solution by vacuum distillation, the boron cluster / cyclodextrin supramolecule was supported on the nitrogen-doped hollow carbon spheres;

[0007] B. Nano-precious metals were supported on the nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule. The precious metal salt solution was placed in a beaker in advance, and the beaker was placed in an ultrasonic cleaner. While ultrasonicating, the hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule were added. After stirring at room temperature for a period of time, the solid was separated, and the filter cake was washed 3 times with water or ethanol, and then the filter cake was placed in a drying oven to dry, obtaining hollow carbon spheres loaded with ultra-small supported nano-precious metals.

[0008] In step A, the cyclodextrin can be β-cyclodextrin and γ-cyclodextrin.

[0009] In step A, the boron cluster can be closo-dodecahydrododecaborate cluster, closo-decahydrodecaborate cluster and closo-hexahydrohexaborate cluster.

[0010] In step A, the molar amount of the cyclodextrin can be 5 - 20 mmol.

[0011] In step A, the molar amount of the boron cluster can be 2 - 8 mmol.

[0012] In step A, the temperature range is 0 - 100 °C.

[0013] In step A, the time range of the "stirring for a period of time" is 2 - 48 hours.

[0014] In step A, the mass range of the nitrogen-doped hollow carbon spheres can be 0.1 - 10 g.

[0015] A specific implementation of step A is as follows: Weigh 5 mmol (5.675 g) of β-cyclodextrin and dissolve it in 200 mL of water to form solution A. Weigh 2 mmol of boron cluster (0.814 g) and dissolve it in 100 mL of water to form solution B. Mix solution A and solution B, stir magnetically in a 50 °C water bath for 2 hours, then add 0.2 g of nitrogen-doped hollow carbon spheres dispersed in 50 mL of water. After the suspension is continuously stirred for 12 hours, remove the water by vacuum distillation to obtain nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule.

[0016] In step B, the precious metal salt can be Na 2 PdCl 4 、H 3AuCl 4 、RuCl 3 , which may or may not contain crystal water.

[0017] In step B, the concentration of the noble metal salt may be 0.1 - 5 g per 100 mL of water.

[0018] In step B, the volume of the noble metal salt may be 10 - 60 mL.

[0019] In step B, the room temperature range may be 20 - 35 °C.

[0020] In step B, the stirring time may be 1 - 12 hours.

[0021] In step B, the separation method may be atmospheric pressure filtration and vacuum filtration.

[0022] In step B, the drying oven temperature may be 60 - 100 °C.

[0023] In step B, the drying time may be 6 - 12 °C.

[0024] A specific implementation of step B is as follows: Dissolve 1 g of Na 2 PdCl 4 in 100 mL of water to form a Na 2 PdCl 4 solution. Measure 14.7 mL of the Na 2 PdCl 4 solution and disperse it in 200 mL of water. Then add the solid obtained in step A, and magnetically stir the suspension at 1000 rpm for 6 hours. Then, separate the solid by vacuum filtration, and wash the filter cake twice with water and ethanol respectively. Finally, dry the filter cake in an 80 °C drying oven for 3 hours to obtain the nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecules.

[0025] The present invention provides a method for loading ultrasmall-sized noble metal nanoparticles on hollow carbon spheres through boron cluster cyclodextrin supramolecules. The nitrogen-doped hollow carbon spheres, as the carrier of the boron cluster / cyclodextrin supramolecules, can provide a large specific surface area for the loading and utilization of metals. Introducing boron clusters as one of the components of the supramolecule can achieve the conversion of noble metal ions at the sites of boron clusters into ultrasmall-sized loaded noble metal nanoparticles. When constructing the boron cluster / cyclodextrin supramolecule, during the reduction of the noble metal salt, the supramolecular framework can prevent serious aggregation of metal ions. Taking Na 2 PdCl 4 as an example, the size of the metal loaded in the nitrogen-doped hollow carbon spheres by the present invention is less than 10 nanometers, and the dispersion degree is extremely high.

[0026] In the present invention, a nitrogen-doped hollow carbon sphere with a high specific surface area is used as a hard template. The supramolecule assembled by boron clusters and cyclodextrin is desolvated onto the nitrogen-doped hollow carbon sphere. After being transferred to a solution containing a noble metal salt, highly dispersed and small-sized supported noble metal nanoparticles are loaded on the surface of the nitrogen-doped hollow carbon sphere. Among them, using the nitrogen-doped hollow carbon sphere as a carrier can, on the one hand, facilitate the attachment of the boron cluster cyclodextrin, and on the other hand, ensure the uniform dispersion of the noble metal nanoparticles. Using the boron cluster with reducing ability as the supramolecular host-guest, after assembling with cyclodextrin, the reducing agent can be evenly dispersed in the supramolecular structure. When reducing the noble metal salt, the non-accumulated boron clusters can achieve the ability to reductively disperse the noble metal salt discretely, which is conducive to constructing highly dispersed and small-sized supported noble metal nanomaterials. In the present invention, a nitrogen-doped hollow carbon sphere with a large specific surface area is used as a carrier, and a boron cluster cyclodextrin is used as a functional supramolecule to prepare ultra-small-sized supported nanometals. The method of the invention is simple to operate, technically reliable, and the results are advanced.

[0027] Compared with the prior art, the present invention first constructs a reducible supramolecule on the carrier with a large specific surface area of the nitrogen-doped hollow carbon sphere, and realizes the preparation of highly dispersed ultra-small-sized supported noble metal nanoparticles by virtue of the reductive property of the nitrogen-doped hollow carbon sphere and the reducibility of the boron cluster cyclodextrin supramolecule. For example, the size of the palladium metal in the formed nano-palladium material is in the range of 2-5 nm, which is much smaller than the size of the nano-palladium metal reported in most of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Scanning electron microscope image of the prepared hollow carbon sphere loaded with nano-palladium;

[0029] Figure 2 Transmission electron microscope image of the prepared hollow carbon sphere loaded with nano-palladium;

[0030] Figure 3 X-ray photoelectron spectrum of the prepared hollow carbon sphere loaded with nano-palladium;

[0031] Figure 4 X-ray powder diffraction spectrum of the prepared hollow carbon sphere loaded with nano-palladium. DETAILED DESCRIPTION OF THE INVENTION

[0032] The following presents the specific operations of the present invention in conjunction with the examples.

[0033]

Example 1

[0034] A method for loading ultra-small-sized noble metal nanoparticles on a hollow carbon sphere through a boron cluster cyclodextrin supramolecule, comprising the following steps:

[0035] A. Boron cluster / cyclodextrin supramolecule supported on nitrogen-doped hollow carbon spheres: Weigh 5 mmol (5.675 g) of β-cyclodextrin and dissolve it in 200 mL of water to form solution A. Weigh 2 mmol of boron cluster (0.814 g) and dissolve it in 100 mL of water to form solution B. Mix solution A and solution B, and magnetically stir the mixture in a 50 °C water bath for 2 hours. Then add 0.2 g of nitrogen-doped hollow carbon spheres dispersed in 50 mL of water. After continuously stirring the suspension for 12 hours, remove the water by reduced pressure distillation to obtain nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule;

[0036] B. Loading of ultra-small nano-palladium on nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule: Dissolve 1 g of Na 2 PdCl 4 in 100 mL of water to form a Na 2 PdCl 4 solution. Measure 14.7 mL of the Na 2 PdCl 4 solution and disperse it in 200 mL of water. Then add the solid obtained in step A, and magnetically stir the suspension at 1000 rpm for 6 hours. Then separate the solid by vacuum filtration, and wash the filter cake twice with water and ethanol respectively. Finally, dry the filter cake in an 80 °C drying oven for 3 hours to obtain nitrogen-doped hollow carbon spheres loaded with ultra-small sized nano-palladium.

[0037] Characterization results of the product obtained in Example 1.

[0038] Figure 1 Shows a scanning electron microscope image of nitrogen-doped hollow carbon spheres loaded with ultra-small nano-palladium. It can be seen that after loading the noble metal nano-palladium, the material still maintains the shape of hollow carbon spheres. Figure 2 Is a transmission electron microscope image of nitrogen-doped hollow carbon spheres loaded with ultra-small nano-palladium. The result of transmission electron microscope imaging is similar to that of scanning electron microscope imaging. The overall material is in a hollow state, and there are a large number of uniformly dispersed black small spheres in the transmission electron microscope imaging, with a size of about 2 - 5 nm, which are ultra-fine nano-palladium particles. Figure 3 Is the X-ray photoelectron spectroscopy signal (signal of Pd element) of nitrogen-doped hollow carbon spheres loaded with ultra-small nano-palladium. It can be seen that the nano-palladium metal prepared by the present invention is mainly in the zero-valent state. Figure 4 X-ray powder diffraction signal of nitrogen-doped hollow carbon spheres loaded with ultra-small nano-palladium. It can be seen that the signal of palladium is very weak, indicating that the particle size of palladium in the nitrogen-doped hollow carbon spheres is very small.

[0039]

Example 2

[0040] A method for loading ultra-small sized nano-noble metals on hollow carbon spheres through boron cluster cyclodextrin supramolecule, comprising the following steps:

[0041] A. Boron cluster / cyclodextrin supramolecule supported on nitrogen-doped hollow carbon spheres: Weigh 5 mmol (5.675 g) of β-cyclodextrin and dissolve it in 400 mL of water to form solution A. Weigh 5 mmol (2.035 g) of boron cluster and dissolve it in 200 mL of water to form solution B. Mix solution A and solution B, and stir magnetically in a water bath at 50 °C for 2 hours. Then add 0.2 g of nitrogen-doped hollow carbon spheres dispersed in 50 mL of water. After the suspension is stirred for another 12 hours, remove the water by reduced pressure distillation to obtain nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule;

[0042] B. Loading of nano-palladium on nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule: Dissolve 1 g of Na 2 PdCl 4 in 100 mL of water to form a Na 2 PdCl 4 solution. Measure 29.4 mL of the Na 2 PdCl 4 solution and disperse it in 200 mL of water. Then add the solid obtained in step A, and stir the suspension magnetically at 1000 rpm for 6 hours. Then separate the solid by reduced pressure filtration, and wash the filter cake twice with water and ethanol respectively. Finally, dry the filter cake in an oven at 80 °C for 3 hours to obtain nitrogen-doped hollow carbon spheres loaded with ultra-small size nano-palladium.

[0043]

Example 3

[0044] A method for loading ultra-small size nano-precious metals on hollow carbon spheres through boron cluster cyclodextrin supramolecule, comprising the following steps:

[0045] A. Boron cluster / cyclodextrin supramolecule supported on nitrogen-doped hollow carbon spheres: Weigh 10 mmol (11.350 g) of β-cyclodextrin and dissolve it in 400 mL of water to form solution A. Weigh 2 mmol (0.814 g) of boron cluster and dissolve it in 200 mL of water to form solution B. Mix solution A and solution B, and stir magnetically in a water bath at 50 °C for 2 hours. Then add 0.2 g of nitrogen-doped hollow carbon spheres dispersed in 50 mL of water. After the suspension is stirred for another 12 hours, remove the water by reduced pressure distillation to obtain nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule;

[0046] B. Loading of nano-gold on nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule: Dissolve 1 g of HAuCl 4 in 100 mL of water to form a HAuCl 4 solution. Measure 6.8 mL of the HAuCl 4The solution was dispersed in 200 mL of water, and then the solid obtained in step A was added. The suspension was magnetically stirred at 1000 rpm for 6 hours, and then the solid was separated by vacuum filtration. The filter cake was washed twice with water and ethanol respectively. Finally, the filter cake was dried in an oven at 80 °C for 3 hours to obtain nitrogen-doped hollow carbon spheres loaded with ultrasmall-sized gold nanoparticles.

[0047]

Example 4

[0048] A method for loading ultrasmall-sized noble metal nanoparticles on hollow carbon spheres through a boron cluster cyclodextrin supramolecule, comprising the following steps:

[0049] A. Loading of boron cluster / cyclodextrin supramolecule on nitrogen-doped hollow carbon spheres: Weigh 10 mmol (11.350 g) of β-cyclodextrin and dissolve it in 400 mL of water to form solution A. Weigh 2 mmol of boron cluster (0.814 g) and dissolve it in 200 mL of water to form solution B. Mix solution A and solution B, and magnetically stir the mixture in a water bath at 50 °C for 2 hours. Then add 0.2 g of nitrogen-doped hollow carbon spheres dispersed in 50 mL of water. After continuously stirring the suspension for 12 hours, remove the water by vacuum distillation to obtain nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule;

[0050] B. Loading of nano ruthenium on nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecule: Dissolve 1 g of RuCl 3 in 500 mL of water to form a RuCl 3 solution. Measure 20.7 mL of the RuCl 3 solution and disperse it in 200 mL of water. Then add the solid obtained in step A. The suspension was magnetically stirred at 1000 rpm for 6 hours, and then the solid was separated by vacuum filtration. The filter cake was washed twice with water and ethanol respectively. Finally, the filter cake was dried in an oven at 80 °C for 3 hours to obtain nitrogen-doped hollow carbon spheres loaded with ultrasmall-sized ruthenium nanoparticles.

[0051] The material results obtained in Examples 2 - 4 are the same as those in Example 1, all showing similar results. The ultrasmall noble metal obtained in Example 3 is nano gold, and the ultrasmall noble metal obtained in Example 4 is nano ruthenium. The above are only the preferred embodiments of the present invention. All equivalent changes made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for loading ultra-small size nano-precious metals on hollow carbon spheres through boron cluster / cyclodextrin supramolecules, comprising the following steps: (A) dissolving a boron cluster and cyclodextrin in a preset molar ratio in water, respectively, mixing and adding the mixture to nitrogen-doped hollow carbon spheres dispersed by ultrasonication with water, stirring the mixture under a preset temperature for a period of time, and removing the water by reduced pressure distillation to obtain nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecules; the molar ratio of the boron cluster to the cyclodextrin is 2-8:5-20; the feeding ratio of the boron cluster to the nitrogen-doped hollow carbon sphere is 0.1-10 g of nitrogen-doped hollow carbon spheres for every 2-8 mmol of the boron cluster; (B) Adding nitrogen-doped hollow carbon spheres loaded with boron cluster / cyclodextrin supramolecules to an aqueous solution containing a noble metal salt, while promoting dispersion with ultrasound, stirring at room temperature for a period of time, filtering and separating the solid, washing the filter cake with water and ethanol several times, and drying the filter cake to obtain a hollow carbon sphere material loaded with ultrasmall nano-noble metals; the concentration of the aqueous solution of the noble metal salt is 0.1-5 g of noble metal salt per 100 mL of water.

2. The method according to claim 1, characterized in that The boron cluster is a closed dodecahydrogen dodecaborane cluster, a closed decahydrogen decaborane cluster, or a closed hexahydrogen hexaborane cluster.

3. The method according to claim 1, characterized in that The cyclodextrin is β-cyclodextrin or γ-cyclodextrin.

4. The method according to claim 1, characterized in that: The temperature ranges from 0-100°C.

5. The method according to claim 1, characterized in that The noble metal salt is Na2PdCl4 or HAuCl4 or RuCl3.

6. The method according to claim 1, characterized in that Every 2-8 mmol of boron cluster corresponds to 10-60 mL of noble metal salt solution.

7. The nitrogen-doped hollow carbon sphere material loaded with ultra-small nano-palladium prepared by the method according to any one of claims 1 to 6, characterized in that: The nano palladium is uniformly dispersed in the nitrogen-doped hollow carbon sphere shell layer, and the size is less than 10 nanometers.

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