CN118321542A - A size-controllable, highly dispersed ultra-small nanocluster and its preparation method and application - Google Patents

Abstract

The present invention belongs to the field of nanomaterials and heterogeneous catalysis, and is particularly related to a kind of ultra-small nano clusters with controlled size and high dispersion, and its preparation method and application. The preparation method includes: using cyclohexane and ethanol as solvent, adding excessive surface modifier and oxide carrier ultrasonic dispersion, then removing the solvent by rotary evaporator, adsorbing at high temperature for a period of time, using appropriate amount of cyclohexane to control the content of surface modifier by washing, and mixing with metal precursor salt after drying, ball milling and calcining are performed to obtain. The preparation method adopts the mode of liquid phase pretreatment + solid phase combination, so that the obtained ultra-small nano clusters with controlled size and high dispersion have the advantages of controlled size and high dispersion, and solve the problems of uneven size of loaded metal oxides, low dispersion and easy agglomeration in the synthesis process such as existing liquid phase precipitation method, thermal decomposition method and sol-gel method, solution impregnation method.

Description

A size-controllable, highly dispersed ultra-small nanocluster and its preparation method and application

Technical Field

The invention belongs to the field of nano materials and heterogeneous catalysis, and specifically relates to a size-controllable and highly dispersed ultra-small nano cluster and a preparation method and application thereof.

Background technique

Metal nanoclusters with a nanosize of less than 100 nm have unique electronic, magnetic, optical and chemical properties, while clusters smaller than 3 nm have quantum size effects and high specific surface areas, which are of great significance in the field of heterogeneous catalysis.

The current methods for synthesizing nanoclusters are mainly based on chemical methods and methods for re-exposing the surface of nanoclusters, but both have serious problems. For example, the coating agents generally used in wet chemical methods will seriously block the outer surface of the catalyst; heat treatment and oxidation treatment of re-exposing the surface of nanoclusters usually cause irreversible changes in the size and morphology of nanoclusters. There are also some more sophisticated methods for synthesizing nanoclusters, but they are only suitable for the synthesis of laboratory-level products and cannot be prepared on a large scale.

Therefore, based on this, the technical solution of the present invention is proposed.

Summary of the invention

In order to solve the problems existing in the prior art, the present invention proposes the concept of a solid-state "anchoring" strategy to synthesize ultra-small nanoclusters with controllable size and high dispersion. Specifically, the interaction between the surface modifier and the oxide support is strengthened through Lewis acid-based interactions. The anchored surface modifier molecules act as complexing agents in the subsequent synthesis process to further capture and disperse the acetylacetone metal salt complex during the solid-state ball milling process. In addition to providing shear force to disperse the metal precursor salt, the mechanical ball milling process also strengthens the interaction between the metal cations and the oxide support. Therefore, even after calcination in air at 500°C, Ni can still be highly dispersed, and even under high-temperature calcination conditions at 750°C, it can still maintain an ultra-small size of 6.5nm.

The solution of the present invention is to provide a method for preparing size-controllable and highly dispersed ultra-small nanoclusters, the preparation method comprising the following steps:

(1) adding a surface modifier and an oxide into a solvent and performing ultrasonic dispersion to obtain a dispersion;

(2) performing rotary evaporation on the dispersion to remove the solvent, and allowing the surface modifier and the oxide to be completely adsorbed under heating conditions to obtain a rotary evaporator;

(3) washing the rotary evaporation product, centrifuging and drying the product in sequence to obtain a pre-treated oxide;

(4) The pretreated oxide is mixed with a metal precursor salt, and then ball-milled and calcined in sequence to obtain ultra-small nanoclusters with controllable size and high dispersion.

Preferably, in step (1), the surface modifier is one of oleylamine, oleic acid, sodium oleate, glycerol, polyethylene glycol, octadecyl mercaptan, octadecene, and hexadecyltrimethylammonium bromide;

And/or, the oxide is one of aluminum oxide, titanium dioxide, cerium dioxide, silicon dioxide, zirconium oxide, magnesium oxide, iron oxide, and zinc oxide;

And/or, the solvent is cyclohexane and ethanol.

Preferably, the volume ratio of cyclohexane to ethanol is 0.3-0.5:1;

And/or, the molar ratio of oleylamine to aluminum oxide is 0.5-0.9:1.

Preferably, in step (2), the surface modifier and the oxide are completely adsorbed at 70-100°C.

Preferably, in step (3), cyclohexane is used to wash the rotary evaporation product.

Preferably, in step (4), the metal precursor salt is one or a combination of acetylacetonate or acetate;

and/or, the molar ratio of the metal precursor salt to the oxide is 0.005 to 0.1:1;

And/or, the ball milling time is 0.25 to 1 h;

And/or, the calcination temperature is 350-800° C., and the calcination time is 1-4 hours.

Preferably, the acetylacetonate includes platinum acetylacetonate, copper acetylacetonate, nickel acetylacetonate, palladium acetylacetonate, rubidium acetylacetonate, rhodium acetylacetonate, cerium acetylacetonate and lanthanum acetylacetonate;

And/or, the ball mill used in the ball milling process is a planetary ball mill, a high-energy ball mill, a three-dimensional high-speed vibration ball mill (MSK-SFM-3) or manual grinding.

Based on the same technical concept, another solution of the present invention is to provide a size-controllable and highly dispersed ultra-small nanoclusters obtained by the above preparation method.

Based on the same technical concept, another solution of the present invention is to provide an application of size-controllable and highly dispersed ultra-small nanoclusters in the preparation of heterogeneous thermal catalysts, electrocatalysts, photocatalysts and adsorbents.

The beneficial effects of the present invention are:

(1) The present invention adopts a liquid phase + solid phase combined preparation method to prepare ultra-small nano clusters with controllable size and high dispersion. The present invention uses long-chain organic matter as a carrier surface modifier. Under the interaction of Lewis acid (Al-OH and _NH2 -R), the surface modifier is anchored with the oxide carrier. Under the action of solid phase ball milling, the metal precursor salt is dissolved into the lattice of the oxide carrier to achieve uniform mixing of the oxide carrier and the metal precursor salt. Then, the surface modifier present in the calcination process plays a role, increasing the dispersibility of the nano clusters and limiting their excessive growth, thus obtaining ultra-small nano clusters with controllable size and high dispersion. The preparation method solves the problems of uneven size, large particles, and low dispersion of nano clusters with controllable size and high dispersion in the existing liquid phase precipitation method, impregnation method, thermal decomposition method, and sol-gel method. The prepared nano clusters also have a certain hydrophobicity and have unexpected uses in some reactions where water is produced. In addition, the preparation method is simple, has high preparation efficiency, low energy consumption, and the possibility of industrial scale-up synthesis, and is suitable for industrial large-scale production.

(2) The size-controllable and highly dispersed ultrasmall nanoclusters prepared by the present invention have the advantages of uniform size, controllable size, high dispersion, hydrophobicity, particles as small as 1 nm, controllable morphology and environmental friendliness; they can be applied to the fields of multiphase thermal catalysts, electrocatalysts, photocatalysts and adsorbents.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG. 1 is a transmission electron microscope photo and a mapping photo of 1%-Ni-Al ₂ O ₃ -OAm-500 prepared in Example 1. FIG.

FIG. 2 is a test diagram of the hydrophobic angle at each stage in the preparation process of 1%-Ni-Al ₂ O ₃ -OAm-500 prepared in Example 1. FIG.

FIG. 3 is a transmission electron microscope photo and a mapping photo of 5%-Ni-Al ₂ O ₃ -OAm-750 prepared in Example 1. FIG.

FIG. 4 is a transmission electron microscope photo and a mapping photo of 1%-Pt-Al ₂ O ₃ -OAm-500 prepared in Example 2. FIG.

FIG. 5 is a transmission electron microscope photo and a mapping photo of 1%-Cu-SiO ₂ -OAm-500 prepared in Example 3.

Detailed ways

To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

Example 1

This embodiment provides a method for preparing size-controllable and highly dispersed ultra-small nanoclusters, the preparation method comprising the following steps:

2g of _Al2O3 (19.62mmol) and 5mL (15.48mmol) of oleylamine were added to a flask containing 20mL of cyclohexane and 50mL of ethanol, and ultrasonically dispersed _for 30min. The solvents cyclohexane and ethanol were removed by rotary evaporator, and the flask was sealed and placed in a 100℃ oven to allow the alumina to fully absorb the oleylamine for 12h. 50mL of cyclohexane was used to wash and remove the excess oleylamine, and the flask was centrifuged and dried. 21.8mg of nickel acetylacetonate and pretreated alumina were placed in a 50mL stainless steel ball mill jar, which contained 4 stainless steel large balls with a diameter of 20mm and 12 stainless steel small balls with a diameter of 10mm. The ball mill jar was sealed and transferred to a three-dimensional high-speed vibration ball mill (MSK-SFM-3), and the ball milling was run for 0.5h.

Subsequently, the sample was calcined at 500°C for 2 h with a heating rate of 5°C/min. The prepared sample was named "1%-Ni-Al ₂ O ₃ -OAm-500" according to the content, adsorbent and calcination temperature.

The prepared “1%-Ni—Al ₂ O ₃ -OAm-500” was reduced at 500° C. (5° C./min) for 2 h in a 5% H ₂ /Ar atmosphere, and then tested by transmission electron microscopy and EDS (Energy Dispersive Spectrometer), as shown in FIG1 .

As shown in Figure 1, after calcination at 500°C for 2 hours using the OAm anchoring method, there are no nickel particles on the Al ₂ O ₃ substrate after hydrogen reduction. High-angle annular dark field scanning transmission electron microscopy (HADDF) imaging was then performed at the same location. However, no obvious nickel particles were observed. EDS found that Ni was very evenly dispersed on Al ₂ O ₃ and no agglomeration occurred.

From the hydrophobic angle experiment in Figure 2, it was found that the application of OAm changed the catalyst from hydrophilic to hydrophobic, which provides application prospects for the application of catalysts in water resistance.

Subsequently, a high-temperature anti-agglomeration test was conducted on Ni-Al ₂ O ₃ -OAm. In order to observe the particle changes more clearly, a 5% Ni loading was used. As shown in Figure 3, it was calcined at 750°C (5°C/min) for 2h, and then reduced at 500°C (5°C/min) for 2h in a 5% H ₂ /Ar atmosphere. It was named "5%-Ni-Al ₂ O ₃ -OAm-750". According to statistics, the Ni particles were only 6.8nm. EDS also proved that Ni was well dispersed and no obvious agglomeration occurred. This shows that the catalyst prepared by this method has better high-temperature agglomeration resistance and can be used in some applications where high temperature causes particle agglomeration and reaction deactivation.

Example 2

This embodiment provides a method for preparing size-controllable and highly dispersed ultra-small nanoclusters, the preparation method comprising the following steps:

2g of _Al2O3 (19.62mmol) and 5mL (15.48mmol) of oleylamine were added to a flask containing 20mL of cyclohexane and 50mL of ethanol, and ultrasonically dispersed _for 30min. The solvents cyclohexane and ethanol were removed by rotary evaporator, and the flask was sealed and placed in a 100℃ oven to allow the alumina to fully absorb the oleylamine for 12h. 50mL of cyclohexane was used to wash and remove excess oleylamine, and the flask was centrifuged and dried. 10.8mg of acetylacetonate platinum and pretreated alumina were placed in a 50mL stainless steel ball mill jar, which contained 4 stainless steel large balls with a diameter of 20mm and 12 stainless steel small balls with a diameter of 10mm. The ball mill jar was sealed and transferred to a three-dimensional high-speed vibration ball mill (MSK-SFM-3), and the ball milling was run for 0.5h.

Subsequently, the sample was calcined at 500°C for 2 h with a heating rate of 5°C/min. The prepared sample was named "1%-Pt-Al ₂ O ₃ -OAm-500" according to the content, adsorbent and calcination temperature.

The TEM and EDS of "1%-Pt-Al ₂ O ₃ -OAm-500" are shown in FIG4 . As can be seen from FIG4 , the Pt particles are surprisingly only 1.41 nm. EDS confirms the uniform dispersion of Pt on Al ₂ O ₃ .

Example 3

This embodiment provides a method for preparing size-controllable and highly dispersed ultra-small nanoclusters, the preparation method comprising the following steps:

2g of _Al2O3 (19.62mmol) and 5mL (15.48mmol) of oleylamine were added to a flask containing 20mL of cyclohexane and 50mL of ethanol, and ultrasonically dispersed _for 30min. The solvents cyclohexane and ethanol were removed by rotary evaporator, and the flask was sealed and placed in a 100℃ oven to allow the alumina to fully absorb the oleylamine for 12h. 50mL of cyclohexane was used to wash and remove excess oleylamine, and the flask was centrifuged and dried. 20.6mg of copper acetylacetonate and pretreated alumina were placed in a 50mL stainless steel ball mill jar, which contained 4 stainless steel large balls with a diameter of 20mm and 12 stainless steel small balls with a diameter of 10mm. The ball mill jar was sealed and transferred to a three-dimensional high-speed vibration ball mill (MSK-SFM-3), and the ball milling was run for 0.5h.

Subsequently, the sample was calcined at 500°C for 2 h with a heating rate of 5°C/min. The prepared sample was named "1%-Cu-SiO ₂ -OAm-500" according to the content, adsorbent and calcination temperature.

Figure 5 is the TEM and EDS images of 1%-Cu-SiO ₂ -OAm-500. According to the large amount of statistical data shown in Figure 5, the average particle size of 1%-Cu-SiO ₂ -OAm-500 is 2.3nm. This is because the interaction between SiO ₂ and OAm is limited, and only a small number of OAm molecules are adsorbed, resulting in the size of CuNCs being less uniform than that of Ni and PtNCs. However, no metal aggregation phenomenon was observed, which was confirmed by the Cu element energy spectrum shown in Figure 5.

The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (9)

1. The preparation method of the size-controllable high-dispersion ultra-small nanoclusters is characterized by comprising the following steps of:

(1) Adding a surface modifier and an oxide into a solvent for ultrasonic dispersion to obtain a dispersion liquid;

(2) Spin-evaporating the dispersion liquid to remove the solvent, and completely adsorbing the surface modifier and the oxide under the heating condition to obtain a spin-evaporated product;

(3) Washing the rotary steaming material, and sequentially centrifuging and drying to obtain a pretreatment oxide;

(4) And mixing the pretreated oxide with metal precursor salt, and then sequentially ball-milling and calcining to obtain the size-controllable high-dispersion ultra-small nanocluster.

2. The method for preparing the size-controllable high-dispersion ultra-small nanoclusters according to claim 1, wherein in the step (1), the surface modifier is one of oleylamine, oleic acid, sodium oleate, glycerin, polyethylene glycol, stearyl mercaptan, octadecene, and cetyltrimethylammonium bromide;

And/or the oxide is one of alumina, titanium dioxide, cerium dioxide, silicon dioxide, zirconium oxide, magnesium oxide, ferric oxide and zinc oxide;

And/or the solvent is cyclohexane and ethanol.

3. The method for preparing the size-controllable high-dispersion ultra-small nanoclusters according to claim 2, wherein the volume ratio of cyclohexane to ethanol is 0.3 to 0.5:1;

and/or the mol ratio of the oleylamine to the alumina is 0.5-0.9:1.

4. The method for preparing ultra-small nanoclusters of controllable size and high dispersion according to claim 1, wherein the surface modifier and the oxide are fully adsorbed at 70 to 100 ℃ in the step (2).

5. The method for preparing the size-controllable high-dispersion ultra-small nanoclusters according to claim 1, wherein in the step (3), cyclohexane is used for washing the spin-steamed material.

6. The method for preparing size-controllable highly-dispersed ultra-small nanoclusters according to claim 1, wherein in the step (4), the metal precursor salt is one or a combination of two of acetylacetonate and acetate;

and/or the molar ratio of the metal precursor salt to the oxide is 0.005-0.1:1;

And/or the ball milling time is 0.25-1 h;

and/or the calcining temperature is 350-800 ℃ and the calcining time is 1-4 h.

7. The method for preparing the size-controllable high-dispersion ultra-small nanoclusters according to claim 6, wherein the acetylacetonate includes platinum acetylacetonate, copper acetylacetonate, nickel acetylacetonate, palladium acetylacetonate, rubidium acetylacetonate, rhodium acetylacetonate, cerium acetylacetonate and lanthanum acetylacetonate;

and/or the ball mill adopted in the ball milling process is a planetary ball mill, a high-energy ball mill, a three-dimensional high-speed vibration ball mill or manual grinding.

8. The ultra-small nanocluster of controllable size and high dispersion obtained by the preparation method of any one of claims 1 to 7.

9. Use of size-controllable highly dispersed ultra-small nanoclusters according to claim 8 for the preparation of heterogeneous thermal, electrocatalyst, photocatalyst and adsorbent.