CN116037014B - Method for preparing metal nanocrystalline aerogel by metal induction through epitaxial growth of metal on surface of metal nanocrystalline - Google Patents

Method for preparing metal nanocrystalline aerogel by metal induction through epitaxial growth of metal on surface of metal nanocrystalline Download PDF

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CN116037014B
CN116037014B CN202310210749.8A CN202310210749A CN116037014B CN 116037014 B CN116037014 B CN 116037014B CN 202310210749 A CN202310210749 A CN 202310210749A CN 116037014 B CN116037014 B CN 116037014B
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ligand
nmf
aerogel
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CN116037014A (en
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蔡彬
王凌伟
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Shandong University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/0091—Preparation of aerogels, e.g. xerogels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B22F1/0545—Dispersions or suspensions of nanosized particles
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids

Abstract

The present invention relates toThe invention discloses a method for preparing metal nanocrystalline aerogel by metal induction through epitaxial growth of metal on the surface of metal nanocrystalline, which comprises the steps of firstly synthesizing TGA ligand-protected nanocrystalline through NMF/H of nanocrystalline stabilized in TGA 2 Adding metal ions into the O solution and adding NaBH 4 Reducing the nano-crystalline colloid, growing a small amount of metal on the surface of the nano-crystalline colloid to enable the nano-crystalline colloid to be in a metastable state, gradually growing into a multi-network structure to obtain hydrogel, and finally obtaining the metal nano-crystalline aerogel by adopting a supercritical drying means; the method not only solves the difficult problem that the nanocrystalline protected by the strong adsorption ligand and some special alloy nanocrystalline are difficult to gel, but also greatly expands the designability of the composition and structure of the aerogel due to the heterogeneous structure between a large number of nanocrystalline and growing metal in the synthesized aerogel structure, and has wide research prospect in the fields of catalysis and the like.

Description

Method for preparing metal nanocrystalline aerogel by metal induction through epitaxial growth of metal on surface of metal nanocrystalline
Technical Field
The invention relates to a method for preparing metal nanocrystalline aerogel by metal epitaxial growth on the surface of metal nanocrystalline through induction, and belongs to the technical field of metal nanocrystalline and aerogel.
Background
Aerogel (Aerogel) is a non-natural solid material with the smallest density of solids around the world. The Science journal lists the preparation of aerogel materials as one of the ten pandemic techniques at the end of the 90 s of the last century. Because the aerogel has a nano porous three-dimensional network structure, the aerogel has the characteristics of extremely high porosity, extremely low density, extremely high specific surface area, extremely high pore volume rate and the like, and the density of the aerogel is 0.003-0.500 g/cm -3 Adjustable in range (density of air is 0.00129 g/cm) -3 ) The aerogel material has wide application prospect in the fields of energy, catalysis, biology, environmental engineering and the like.
Metal Nanocrystals (NCs) have unique optical, electrical, magnetic and chemical properties different from bulk materials, and show great application potential in numerous fields of catalysis, detection, medical treatment and the like. In the field of catalysis, the high surface atomic ratio of the nanocrystalline can greatly improve the atomic utilization rate, the quantum size effect enables the nanocrystalline to show higher intrinsic catalytic activity, and the special properties enable the nanocrystalline catalyst to be widely researched and applied. However, due to the high surface energy of the nanocrystalline catalyst and its weak interaction with the carrier, the nanocrystalline catalyst inevitably agglomerates during the catalytic reaction, resulting in loss of reactive sites. Therefore, how to improve the stability of metal nanocrystals has been a major concern.
The aerogel material with the three-dimensional network structure can effectively solve the problems, and the formed aerogel material effectively prevents agglomeration among the nanocrystals due to the self-supporting structure formed by tight connection among the nanocrystals. In addition, the tight connection between nanocrystals accelerates the charge transfer process, and the formed nanoscale and microscale channels can accelerate the mass transfer process of reactants and products.
The currently reported method for assembling the colloidal metal nanocrystalline into the nanocrystalline aerogel with the three-dimensional network structure mainly comprises the steps of removing the ligand through oxidization, inducing metal ions and the like, however, for special alloy nanocrystalline or colloid nanocrystalline with stable strong adsorption protection ligand, the strong adsorption protection ligand is difficult to remove from the surface of the nanocrystalline in the gelation process, the steric effect of the ligand can obstruct the connection between the nanocrystalline and can not carry out gelation, and some special alloy nanocrystalline (such as high-entropy alloy (HEA)) has the characteristic of low atomic diffusion rate, and the connection between the nanocrystalline can be difficult in the gelation process. Therefore, the above method cannot achieve gelation of some special alloy nanocrystals (such as High Entropy Alloy (HEA)) or colloid nanocrystals with strong adsorption protection ligand stabilization.
Disclosure of Invention
Aiming at the defects of the existing metal aerogel synthesis method, in particular the difficult problem that special alloy nanocrystalline or colloid nanocrystalline with stable strong adsorption protection ligand cannot be gelled is solved.
The invention adopts NaBH 4 The method for growing a small amount of metal on the surface of the ligand-exchanged nanocrystal by the reduced metal ions through epitaxy induces gelation of the colloidal nanocrystal, so that the colloidal nanocrystal is properly instable, and controllable gelation of the nanocrystal is realized. The gel method is also suitable for synthesizing metal nanocrystalline aerogel of other components.
Description of the terminology:
room temperature: the room temperature of the invention has the conventional meaning, and the temperature range is 25+/-5 ℃.
The invention is realized by the following technical scheme:
the method for preparing metal nanocrystalline aerogel by metal induction through epitaxial growth of metal on the surface of metal nanocrystalline comprises the following steps of utilizing NaBH 4 Reducing metal ions in the sol system, taking a small amount of metal epitaxially grown on the surface of the ligand-exchanged nanocrystalline as an induction factor, triggering the nanocrystalline to gel, forming hydrogel, and performing supercritical drying to obtain the metal nano aerogel.
According to the preferred method for preparing the metal nanocrystalline aerogel by metal induction through epitaxial growth on the surface of the metal nanocrystalline, the method comprises the following steps:
(1) Adding the polar solvent solution of the ligand-exchanged nanocrystalline into water, then adding metal ions and NaBH 4 Forming a mixed solution, and maintaining the mixed solution at 50-70 ℃ for 12-20 h to obtain hydrogel, washing with water to remove residues, and then washing with ethanol until the solvent is completely changed from water to ethanol;
(2) And (3) replacing ethanol in the hydrogel in the step (1) with liquid carbon dioxide, and then performing supercritical drying to obtain the metal nanocrystalline aerogel.
According to a preferred embodiment of the present invention, in step (1), the polar solvent is NMF.
According to a preferred embodiment of the invention, in step (1), the volume ratio of polar solvent to water is 1:10 to 1:39.
According to the present invention, preferably, in the step (1), the concentration of the ligand-exchanged nanocrystals in the mixed solution is 2 to 4mM, and most preferably, the concentration of the ligand-exchanged nanocrystals in the mixed solution is 3mM.
According to a preferred embodiment of the present invention, in the step (1), the metal ion is Pt 4+ 、Au 3+ Or Pd (or) 2+ 。
Most preferably, in step (1), the metal ion is Pt 4+ 。
According to a preferred embodiment of the present invention, in step (1), the metal ion Pt 4+ From H 2 PtCl 6 Providing Au 3+ From HAuCl 4 Provision of Pd 2+ From K 2 PdCl 4 Providing.
According to the present invention, preferably, in the step (1), the concentration of the metal ion in the mixed solution is 0.2 to 0.6mM.
Most preferably, in step (1), the concentration of metal ions in the mixture is 0.3mM.
According to the invention, in the step (1), naBH is preferably added to the mixed solution 4 Is 6-12 mM.
Most preferably, in step (1), naBH is present in the mixture 4 Is 8 mM.
According to a preferred embodiment of the present invention, in step (1), the ligand exchanged nanocrystals are prepared by exchanging all long chain insulating organic ligands on the surface of organic long carbon chain ligand stabilized nanocrystals with thioglycolic acid (TGA).
According to the invention, the ligand-exchanged nanocrystals are prepared as follows:
1) Ligand exchange: thioglycollic acid TGA was added to NMF and N (CH) 3 ) 4 Regulating the pH value of the methanol solution of OH to 9-10 to obtain NMF solution of TGA, mixing n-hexane solution of nano-crystal with stable organic long carbon chain ligand with the NMF solution of TGA, and stirring vigorously; the nanocrystalline is completely transferred from the upper n-hexane phase to the lower NMF phase, and ligand exchange is successful;
2) Purifying: washing the NMF phase with n-hexane for 5-8 times, collecting NMF phase, adding four times of ethyl acetate for centrifugal precipitation, re-dispersing the precipitate in NMF, and membrane filtering to obtain ligand-exchanged nanocrystalline NMF solution.
According to a preferred embodiment of the invention, in step 1), the molar ratio of TGA to the total amount of metal contained in the organic long carbon chain ligand stabilized nanocrystals is 4:1.
according to the invention, NMF is preferably combined with N (CH 3 ) 4 The volume ratio of the methanol solution of OH is 10:1, a step of; the volume ratio of NMF to the organic long carbon chain ligand stable nanocrystalline n-hexane solution is 1:1.
according to the invention is excellentOptionally, N (CH 3 ) 4 Methanol solution of OH N (CH) 3 ) 4 The OH mass concentration was 25wt%.
According to the present invention, the membrane filtration is preferably filtration using a filtration membrane having a pore size of 0.2. Mu.m.
According to a preferred embodiment of the invention, in step (2), the liquid carbon dioxide displacement and supercritical drying are carried out according to the state of the art.
The invention has the beneficial effects that:
1. according to the invention, ligand-exchanged nanocrystals are synthesized, metal ions in a ligand-exchanged nanocrystal solution are reduced by a chemical method, a small amount of metal grows on the surface of the nanocrystals, so that the nanocrystal colloid becomes metastable state and grows gradually into a multi-branch network structure, a hydrogel is obtained, and finally, a supercritical drying means is adopted, so that the nanocrystal aerogel is obtained.
2. The invention provides a method for growing metal on the surface of a nanocrystalline to induce gelation of the metal nanocrystalline by reducing metal ions in a colloid system by a chemical method. The method is also suitable for preparing other metal nanocrystalline aerogel, and solves the problem that nanocrystalline with stable strong adsorption protection ligand and some special alloy nanocrystalline (such as HEA nanocrystalline) are difficult to gel.
3. The aerogel material successfully prepared based on a strategy of growing a small amount of metal on the surface of the nanocrystalline and combining a supercritical drying technology has a large amount of heterostructures between the nanocrystalline and the growing metal, and the structure has wide research prospect in the fields of catalysis and the like.
Drawings
Fig. 1 is a transmission electron microscope image of OAm-CoNiPtRuRh HEA NCs in the embodiment.
FIG. 2 is a photograph before and after ligand exchange in example 1, a is before exchange, and b is after exchange.
FIG. 3 is a transmission electron micrograph of TGA-CoNiPtRuRh HEA NCs of example 1.
FIG. 4 is a photograph of the Pt-CoNiPtRuRh HEA hydrogel of example 2.
FIG. 5 is a transmission electron microscope image of Pt-CoNiPtRuRh HEA Aerogel in example 2.
FIG. 6 is a high power transmission electron micrograph of Pt-CoNiPtRuRh HEA Aerogel in example 2.
FIG. 7 is a scanning electron microscope image of Pt-CoNiPtRuRh HEA Aerogel in example 2.
FIG. 8 is an X-ray diffraction pattern of Pt-CoNiPtRuRh HEA Aerogel in example 2 and OAm-CoNiPtRuRh HEA NPs in example, a is an X-ray diffraction pattern, and b is a partial enlarged view of 36-44 grooves in a.
FIG. 9 is a high angle annular dark field scanning transmission electron micrograph of Pt-CoNiPtRuRh HEA Aerogel in example 2 and a face distribution plot of Co, ni, pt, ru, rh; a is a high-angle annular dark field scanning transmission electron microscope image; b. c, d, e, f are elemental surface profiles of Co, ni, pt, ru, rh, respectively.
FIG. 10 is a photograph of Au-CoNiPtRuRh HEA hydrogel in example 3.
FIG. 11 is a transmission electron microscope image of Au-CoNiPtRuRh HEA Aerogel in example 3.
FIG. 12 is a photograph of Pd-CoNiPtRuRh HEA hydrogel in example 4.
FIG. 13 is a transmission electron microscope image of Pd-CoNiPtRuRh HEA Aerogel in example 4.
FIG. 14 is a transmission electron microscope image of Pt-FeCoNiCuPd HEA Aerogel in example 5.
FIG. 15 is a graph of a Pt-FeCoNiCuPd HEA Aerogel high angle annular dark field scanning Transmission Electron Microscope (TEM) of example 5 and a plot of the pattern Fe, co, ni, cu, pd, pt; a is a high-angle annular dark field scanning transmission electron microscope image; b. c, d, e, f, g are elemental surface profiles of Fe, co, ni, cu, pd, pt, respectively.
FIG. 16 is a transmission electron micrograph of the product obtained in comparative example 1.
FIG. 17 is a transmission electron micrograph of the product obtained in comparative example 2.
FIG. 18 is a transmission electron micrograph of the product obtained in comparative example 3.
FIG. 19 is a transmission electron micrograph of the product obtained in comparative example 4.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to be limiting.
The aerogels prepared in the examples employ a system equipped with critical point dryers 13200J0AB (Spi Supplies) and CO 2 The dryer of the pump is carried out as is known in the art.
The n-hexane solution of OAm-CoNiPtRuRh HEA NCs in the example is OAm-CoNiPtRuRh HEA NCs, and is obtained by adding into n-hexane and mixing uniformly;
N(CH 3 ) 4 the methanol solution of OH is N (CH) 3 ) 4 Adding OH into methanol, and mixing uniformly.
The organic long carbon chain ligand stable CoNiPtRuRh HEA nanocrystalline in the embodiment is prepared according to the following method:
(1) Into a 100 mL three-necked flask, 7.0. 7.0 mg cobalt acetylacetonate, 3.8 mg nickel acetylacetonate, 9.8mg platinum acetylacetonate, 5.0 mg ruthenium acetylacetonate, 6.0 mg rhodium acetylacetonate, 33.0 mg molybdenum hexacarbonyl, 60.0mg glucose, and 5 mL oleylamine (OAm) were sequentially added;
(2) Treating the mixture obtained in the step (1) by ultrasonic treatment for 30-60 min until a uniform solution is formed;
(3) Heating the solution of step (2) to 90 o C degassing at the temperature for 20 min, charging nitrogen, and heating to 230 deg.F o C, keeping 2 h at the temperature to obtain CoNiPtRuRh HEA nanocrystalline;
(4) Closing a heating sleeve, cooling the flask to room temperature, adding ethanol into the flask for centrifugation, dissolving the obtained precipitate in normal hexane, adding ethanol for centrifugation, repeating for 2-3 times, and dispersing CoNiPtRuRh HEA nanocrystals in 10 mL normal hexane for later use; the obtained CoNiPtRuRh HEA nanocrystalline with stable organic long carbon chain ligand is named as OAm-CoNiPtRuRh HEA NCs.
The transmission electron microscope image of OAm-CoNiPtRuRh HEA NCs is shown in fig. 1, and the particle size distribution of OAm-CoNiPtRuRh HEA NCs is uniform as can be seen from fig. 1.
Example 1
The synthesis of ligand-exchanged TGA-CoNiPtRuRh HEA nanocrystals was as follows:
1) Ligand exchange: a5 mLOAm-CoNiPtRuRh HEA NCs solution in n-hexane was mixed with 18. Mu. L TGA. 5 mL NMF and N (CH) with a mass concentration of 25% of 0.5. 0.5 mL 3 ) 4 Mixing methanol solution of OH; stirring vigorously; the nanocrystalline is completely transferred from the upper n-hexane phase to the lower NMF phase, and ligand exchange is successful; can be determined by a color change;
2) Purifying: washing the NMF phase obtained in the step 1) with n-hexane for 5 times, collecting the NMF phase, adding four times of ethyl acetate, centrifuging to precipitate nano crystals, redispersing the obtained precipitate in 0.5 mL NMF, and filtering by a filter membrane with the pore diameter of 0.2 μm to obtain a ligand-exchanged TGA-CoNiPtRuRh HEA NCs NMF solution.
Example 1 a photograph of the phase transfer before and after ligand exchange is shown in fig. 2, where the nanocrystals were completely transferred from the upper n-hexane phase to the lower NMF phase.
The transmission electron microscopy image of TGA-CoNiPtRuRh HEA NCs obtained in example 1 is shown in FIG. 3, and as can be seen, the morphology and particle size of TGA-CoNiPtRuRhHEA NCs are substantially consistent with those of examples OAm-CoNiPtRuRh HEA NCs.
Example 2
A small amount of metal grows on the surface of the nanocrystalline to induce gelation to prepare metal nanocrystalline aerogel:
(1) The 0.5 mL ligand-exchanged TGA-CoNiPtRuRh HEA NPs NMF solution prepared in example 1 was added to 18.9 mL water followed by 120. Mu.L of 50 mM H with vigorous stirring into the system 2 PtCl 6 Aqueous solution and 0.5 mL of 3 mg/mL NaBH 4 Stirring the aqueous solution vigorously for 20 min to form a mixed solution, and mixing the mixed solution at 60 o Maintaining the temperature under the condition C for 12-20 h to obtain hydrogel; removing residues; the resulting hydrogel was washed with water 5-10 times to remove the residue, followed by washing with ethanol 10-20 times until the solvent was completely changed from water to ethanol.
The photograph of the obtained Pt-CoNiPtRuRh HEA hydrogel is shown in FIG. 4, which shows that the Pt-CoNiPtRuRh HEA hydrogel can exist stably, indicating NaBH 4 Reduced metal ions induced gelation of ligand exchanged TGA-coniptrrurh HEA nanocrystals to give gels are stable.
(2) Aerogel: CO in autoclave 2 The dispersed ethanol solvent in the Pt-CoNiPtRuRh HEA hydrogel was replaced, and the aerogel was prepared by supercritical drying at 80 bar and 35℃and designated Pt-CoNiPtRuRh HEA Aerogel.
The transmission electron microscopy images of Pt-CoNiPtRuRh HEA Aerogel obtained are shown in FIGS. 5 and 6, and CoNiPtRuRh HEA Aerogel was successfully prepared as can be seen.
The scanning electron microscope image of CoNiPtRuRh HEA Aerogel obtained is shown in FIG. 7, and it is clear that the Pt-CoNiPtRuRh HEA Aerogel has a porous three-dimensional network structure.
As shown in FIG. 8, the X-ray diffraction pattern of CoNiPtRuRh HEA Aerogel was obtained, and it was found that Pt-CoNiPtRuRh HEA Aerogel had a face-centered cubic crystal structure, and that the X-ray diffraction pattern of OAm-CoNiPtRuRh HEA NPs was compared with that of the gel, and that the crystal structure was not changed before and after the gel.
The high angle annular dark field scanning transmission electron micrograph of Pt-CoNiPtRuRh HEA Aerogel and the plane distribution plot of Co, ni, pt, ru, rh are shown in FIG. 9, as can be seen, co, ni, pt, ru, rh is uniformly distributed in the gel structure, indicating successful synthesis of Pt-CoNiPtRuRh HEA Aerogel.
In conclusion, the metal-induced gelation strategy of the epitaxial growth of metal ions on the surface of the nanocrystals induces the gelation of the ligand-exchanged TGA-CoNiPtRuRh HEA NCs, the obtained hydrogel is stable, and finally, the aerogel is obtained by adopting a supercritical drying means.
Example 3
The procedure is as in example 2, except that:
by HAuCl 4 Instead of H 2 PtCl 6 Other parameters, methods, steps were performed as in example 2.
A photograph of the product Au-CoNiPtRuRh HEA hydrogel obtained in the step (1) is shown in FIG. 10.
As can be seen from FIG. 11, the Au-CoNiPtRuRh HEA Aerogel transmission electron microscope obtained in the step (2) is shown in the FIG. 11 3+ Gelation can still be accomplished in the presence of the catalyst.
Example 4
The procedure is as in example 2, except that:
by K 2 PdCl 4 Instead of H 2 PtCl 6 Other parameters, methods, steps were performed as in example 2.
A photograph of the product Pd-CoNiPtRuRh HEA hydrogel obtained in the step (1) is shown in FIG. 12.
Step (2) Pd-CoNiPtRuRh HEA Aerogel Transmission Electron microscopy image is shown in FIG. 13, from which it can be seen that the system is shown in Pd 2+ Gelation can still be accomplished in the presence of the catalyst.
Thus, pt of the present invention 4+ 、Au 3+ Or Pd (or) 2+ Can initiate TGA-CoNiPtRuRh HEA NCs gelation.
Example 5
The procedure is as in example 2, except that:
replacement of TGA-CoNiPtRuRh HEA NCs with TGA-FeCoNiCuPd HEA NCs, addition of ligand exchanged NMF solution of TGA-FeCoNiCuPd HEA NCs to H 2 O to form a mixed solution, 120. Mu.L of 50 mM H was added to the mixed solution 2 PtCl 6 Aqueous solution and 0.5 mL of 3 mg/mL NaBH 4 Aqueous solution, then at 60 o Maintaining 12-20 h under the condition C to obtain hydrogel; other parameters, methods, steps were performed as in example 2.
Wherein the synthesis procedure of TGA-FeCoNiCuPd HEA NCs is as follows:
(1) Into a 100 mL three-necked flask, 8.8 mg iron acetylacetonate, 8.9 mg cobalt acetylacetonate, 6.4mg nickel acetylacetonate, 6.5 mg copper acetylacetonate, 7.6 mg palladium acetylacetonate, 33.0 mg molybdenum hexacarbonyl, and 5 mL oleylamine were sequentially added.
(2) Treating the mixture obtained in the step (1) by ultrasonic treatment for 30-60 min until a uniform solution is formed;
(3) Heating the solution to 90 o C degassing at the temperature for 20 min, charging nitrogen, and heating to 230 deg.F o C, keeping 2 h at the temperature to obtain FeCoNiCuPd HEA nanocrystalline;
(4) Closing a heating sleeve, cooling the flask to room temperature, adding ethanol into the flask for centrifugation, dissolving the obtained precipitate in normal hexane, adding ethanol for centrifugation, repeating for 2-3 times, and dispersing FeCoNiCuPd HEA nanocrystals in 10 mL normal hexane for later use; obtaining FeCoNiCuPd HEA nanocrystalline with stable organic long carbon chain ligand, which is marked as OAm-FeCoNiCuPd HEA NCs;
(4) Ligand exchange: mixing the organic long carbon chain ligand-stabilized CoNiPtRuRh HEA NCs N-hexane solution obtained in step (4) of 5 mL with 27. Mu.L TGA, 5 mL NMF and 0.5 mL N (CH) 3 ) 4 Mixing with an OH 25% methanol solution; stirring vigorously; the nanocrystalline is completely transferred from the upper n-hexane phase to the lower NMF phase, and ligand exchange is successful; after washing the NMF phase 5 times with n-hexane, four volumes of ethyl acetate were added for centrifugation and redispersion in NMF and filtration to give the final TGA-FeCoNiCuPdHEA NCs.
The transmission electron microscopy image of the final product Pt-FeCoNiCuPd HEA Aerogel is shown in FIG. 14, which shows that the aerogel structure was successfully prepared.
The high angle annular dark field scanning transmission electron micrograph and Co, ni, pt, ru, rh of the final product Pt-FeCoNiCuPd HEA Aerogel are shown in FIG. 15, which shows that HEA aerogel structures were successfully prepared.
Therefore, the strategy of epitaxially growing metal-induced nanocrystalline gel on the surface of the metal nanocrystalline is also applicable to the preparation of other metal nanocrystalline aerogels.
Comparative example 1
The procedure is as in example 2, except that:
H 2 PtCl 6 the amount of aqueous solution was 80. Mu.L and the other parameters, methods and procedures were as in example 2.
As shown in FIG. 16, the system cannot complete gelation with too small a amount of metal ions.
Comparative example 2
The procedure is as in example 2, except that:
H 2 PtCl 6 the amount of the aqueous solution was 300. Mu.L and the other parameters, methods and procedures were carried out as in example 2.
As shown in FIG. 17, the obtained product can be gelled by using an excessive amount of metal ions, but the excessive epitaxially grown metal can mask the surface of the high-entropy alloy to form a core/shell structure of CoNiPtRuRh HEA/Pt, so that the high-entropy alloy cannot be exposed.
Comparative example 3
The procedure is as in example 2, except that:
NaBH 4 the amount of aqueous solution was 1.0. 1.0 mL and the other parameters, methods, steps were as in example 2.
The transmission electron microscope of the obtained product is shown in FIG. 18, from which NaBH is known 4 The excessive amount of aqueous solution CoNiPtRuRh HEA NCs caused aggregation, while the reduced Pt formed a separate gel structure, demonstrating that the system used an excessive amount of NaBH 4 Gelation cannot be completed.
Comparative example 4
The procedure is as in example 2, except that:
NaBH 4 the amount of aqueous solution was 0.2. 0.2 mL and the other parameters, methods, steps were as in example 2.
The transmission electron microscopy image of the resulting product is shown in FIG. 19, which shows that the system uses a too small amount of NaBH 4 Gelation cannot be completed.

Claims (6)

1. A method for preparing high-entropy alloy nanocrystalline aerogel by metal-induced epitaxial growth on the surface of high-entropy alloy nanocrystalline comprises the following steps of utilizing NaBH 4 Reducing metal ions in a sol system, taking a small amount of metal epitaxially grown on the surface of a ligand-exchanged high-entropy alloy nanocrystalline as an induction factor, triggering the nanocrystalline to gel, forming hydrogel, and performing supercritical drying to obtain metal nano aerogel;
the preparation method comprises the following steps:
(1) Adding a polar solvent solution of the ligand-exchanged high-entropy alloy nanocrystalline into water, and then adding metal ions and NaBH 4 Forming a mixed solution, and maintaining the mixed solution at 50-70deg.C for 12-20 h to obtainHydrogels, washed with water to remove the residue, followed by ethanol until the solvent is completely changed from water to ethanol; the polar solvent is NMF, and the volume ratio of the polar solvent to water is 1:10-1:39; the concentration of the ligand-exchanged high-entropy alloy nanocrystalline in the mixed solution is 2-4mM; the metal ion is Pt 4+ 、Au 3+ Or Pd (or) 2+ ；
(2) And (3) replacing ethanol in the hydrogel in the step (1) with liquid carbon dioxide, and then performing supercritical drying to obtain the high-entropy alloy nanocrystalline aerogel.
2. The method according to claim 1, wherein in the step (1), the concentration of the metal ions in the mixed solution is 0.2 to 0.6mM, and the concentration of the NaBH in the mixed solution is 0.2 to 0.6mM 4 Is 6-12 mM.
3. The method according to claim 1, wherein in the step (1), the ligand-exchanged high-entropy alloy nanocrystalline is formed by exchanging all long-chain insulating organic ligands on the surface of the organic long-carbon-chain ligand-stabilized high-entropy alloy nanocrystalline with thioglycolic acid.
4. The method of claim 1, wherein the ligand-exchanged high-entropy alloy nanocrystals are prepared by:
1) Ligand exchange: thioglycollic acid was added to NMF and N (CH) 3 ) 4 Regulating the pH value of the methanol solution of OH to 9-10 to obtain NMF solution of thioglycollic acid, mixing the n-hexane solution of the high-entropy alloy nanocrystalline with stable organic long carbon chain ligand with the NMF solution of thioglycollic acid, and stirring vigorously; the nanocrystalline is completely transferred from the upper n-hexane phase to the lower NMF phase, and ligand exchange is successful;
2) Purifying: washing the NMF phase with n-hexane for 5-8 times, collecting NMF phase, adding four times of ethyl acetate for centrifugal precipitation, re-dispersing the precipitate in NMF, and membrane filtering to obtain NMF solution of ligand-exchanged high-entropy alloy nanocrystalline.
5. The method according to claim 4, wherein in step 1), the molar ratio of thioglycollic acid to the total amount of metal contained in the organic long carbon chain ligand-stabilized high entropy alloy nanocrystals is 4:1.
6. the method according to claim 4, wherein in step 1), NMF is combined with N (CH) 3 ) 4 The volume ratio of the methanol solution of OH is 10:1, a step of; the volume ratio of NMF to the normal hexane solution of the high-entropy alloy nanocrystalline with stable organic long carbon chain ligand is 1:1, N (CH) 3 ) 4 Methanol solution of OH N (CH) 3 ) 4 The OH mass concentration was 25wt%.
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