CN113500202B

CN113500202B - Preparation method of high-purity hexagonal Cu nanocrystalline

Info

Publication number: CN113500202B
Application number: CN202110794485.6A
Authority: CN
Inventors: 杨文龙; 杨春洋; 刘欣美; 林家齐
Original assignee: Harbin University of Science and Technology
Current assignee: Harbin University of Science and Technology
Priority date: 2021-07-14
Filing date: 2021-07-14
Publication date: 2023-03-31
Anticipated expiration: 2041-07-14
Also published as: CN113500202A

Abstract

The invention discloses a preparation method of high-purity hexagonal Cu nanocrystalline, which mainly comprises the following steps: preparing a copper sulfate solution with a certain concentration; adding a complexing agent into the copper sulfate solution to obtain a mixed solution; dropwise adding a reducing agent into the mixed solution at the speed of 0.5 ml/min by using a separating funnel; stirring and reacting for 6-8 hours at 40-45 ℃. The method utilizes the spontaneous curing of the Cu nanocrystalline at a specific reaction temperature to form a stable hexagonal structure, and does not add any surfactant, thereby ensuring that the obtained hexagonal Cu nanocrystalline has a clean surface. The integrated preparation process can be realized without nitrogen protection, and the operation is simple without implementing higher temperature. The obtained product has high purity and does not contain impurities such as oxides and the like.

Description

Preparation method of high-purity hexagonal Cu nanocrystalline

Technical Field

The invention relates to the technical field of metal nano material preparation, in particular to a preparation method of high-purity hexagonal Cu nanocrystals.

Background

The simple substance Cu has the characteristics of low cost, good conductivity, excellent catalytic performance and the like. In recent years, the simple substance Cu with a nano structure receives wide attention of people, gradually replaces precious metal nanocrystalline, and is widely applied to the electronic industry and the catalysis field. Therefore, how to realize large-scale preparation of high-purity Cu elementary substance nanocrystals becomes an important technical problem for research.

Among the preparation methods of the Cu nanocrystalline, the liquid phase reduction method is the most effective and feasible preparation technology at present due to simple operation and easy realization of equipment. However, few reports of preparing high-purity flaky Cu nanocrystals by liquid phase reduction are reported.

There are two main reasons for this. On one hand, the Cu nanocrystalline is easy to be oxidized, and the flaky Cu nanocrystalline prepared by the conventional method often contains impurity components such as oxide and the like. In addition, the two-dimensional nanosheet structure has a relatively high surface area, which undoubtedly further increases the probability of oxidation of Cu atoms. On the other hand, the two-dimensional sheet structure is caused by higher surface energy and poor thermal stability and mechanical stability. Compared with noble metal materials such as Au, ag and the like, the simple substance Cu nano structure has higher stacking fault energy. Under the condition of not assisting by a template, the Cu nanometer core is difficult to spontaneously grow into a sheet structure, particularly a hexagonal nanometer sheet structure.

At present, the method for preparing the two-dimensional structure Cu nanocrystalline by using the liquid phase reduction method can be summarized as follows:

two-dimensional Cu nanoplates [ Luc, w., fu, x., shi, j., lv, j.j., jouny, m., ko, b.h., & Kang, y. (2019), two-dimensional linker nanosheets for electrochemical reduction of carbon monoxide to acetate, nature Catalysis,2 (5), 423-430 ] were synthesized by wesley Luc et al using cetyltrimethylammonium bromide and hexamethylenetetramine by reducing copper nitrate at 80 degrees celsius with ascorbic acid. However, the product obtained by the method is a triangular Cu nanosheet, the preparation of the hexagonal Cu nanosheet cannot be realized, and hexadecyl trimethyl bromide used in the synthesis is adsorbed on the surface of a Cu nanocrystalline and is difficult to remove. Seriously affecting the further application properties of the metal Cu.

2. The subject group provides a method (ZL 201810454068.5) for preparing a flaky Cu nanocrystalline at room temperature in 2018, and the method takes deionized water as a solvent, copper sulfate as a precursor, sodium citrate as a complexing agent, ascorbic acid as a reducing agent, anhydrous sodium carbonate to improve the reducibility of a reaction solution, potassium bromide as an additive, and the flaky Cu nanocrystalline is obtained by controlling the growth of the Cu nanocrystalline through directional adsorption. However, the product obtained by the method is a set of triangular Cu nanocrystals and hexagonal Cu nanocrystals, and due to the fact that the sizes of the triangular Cu nanocrystals and the hexagonal Cu nanocrystals are close, the hexagonal Cu nanocrystals with high purity are further separated by an effective means.

3. The Kunming noble metal research institute utilizes copper bromide as a precursor, sodium hypophosphite as a reducing agent and polyvinylpyrrolidone as a surfactant to prepare hexagonal Cu nanosheets with side lengths of about 400nm [ Li, Y., fan, Z., yang, H., yuan, X., chao, Y., li, Y., & Wang, C. (2020). Although the method realizes the preparation of the hexagonal Cu nanosheet, the problems that the surfactant is difficult to remove, the product contains the triangular Cu nanosheet and the like still exist.

Disclosure of Invention

The invention overcomes the defects existing in the background technology and provides a preparation method for obtaining high-purity hexagonal Cu nanocrystals. The method can be realized under the protection of no nitrogen, higher reaction temperature is not required to be implemented, and an organic surfactant is not required to be added in the synthesis, so that the hexagonal Cu nanocrystal has a clean surface, and the application of the hexagonal Cu nanocrystal is prevented from being damaged.

The specific operation comprises the following steps:

1) Deionized water is used as a solvent, copper sulfate is used as a solute, and the mixture is stirred uniformly to obtain a mixed solution 1;

2) Adding citrate into the mixed solution 1, and stirring uniformly to obtain a mixed solution 2;

3) Dropwise adding a reducing agent into the mixed solution 2 at the speed of 0.5 ml/min by using a separating funnel to obtain a mixed solution 3;

4) The mixed solution 3 is placed at 40-45 ℃ and stirred for reaction for 6-8 hours;

5) And (3) washing the obtained product with deionized water and ethanol once respectively, and preferably drying the product in a forced air drying oven at 50-60 ℃ for about 10 hours to obtain solid powder, namely the high-purity hexagonal Cu nanosheet.

Correspondingly, the invention also discloses a high-purity hexagonal Cu nanocrystal obtained by the preparation method of the high-purity hexagonal Cu nanocrystal.

The implementation of the invention has the following beneficial effects:

1. simple operation, low reaction temperature and easy industrialized production. The whole preparation environment can be carried out in a low-temperature environment, gas protection is not needed, and production risks such as high-temperature reaction, gas leakage and the like are avoided.

2. And no surfactant is used in the preparation process, so that the property of the material is ensured. Compared with the traditional surfactant-assisted method, the method controls the growth rate of the Cu nanocrystalline by controlling the dropping rate of the reducing agent in the reaction, and forms a stable hexagonal structure by utilizing the spontaneous curing of the Cu nanocrystalline at a specific reaction temperature. The used citrate has water solubility and can be removed by a simple cleaning method, and the method effectively ensures the self property of the hexagonal Cu nanocrystal and is beneficial to wide application of the hexagonal Cu nanocrystal.

Drawings

FIG. 1 is an X-ray diffraction pattern of a sample obtained in example 1.

FIG. 2 is a SEM image of a sample obtained in example 1.

FIG. 3 is a SEM image of the sample obtained in example 2.

FIG. 4 is a SEM image of the sample obtained in example 3.

FIG. 5 is an X-ray diffraction pattern of a sample obtained in comparative example 1.

FIG. 6 is a field emission scanning electron micrograph of the sample obtained in comparative example 1.

FIG. 7 is an X-ray diffraction pattern of the sample obtained in comparative example 2.

FIG. 8 is a SEM image of a sample obtained in comparative example 2.

FIG. 9 is a SEM image of the sample obtained in comparative example 3.

FIG. 10 is a SEM image of the sample obtained in comparative example 4.

Detailed Description

The method takes deionized water as a solvent, copper sulfate as a precursor, preferably sodium citrate as a complexing agent and a pH regulator, preferably hydrazine hydrate as a reducing agent to carry out liquid phase reduction. The reaction rate was controlled by adjusting the dropping rate of the separatory funnel. In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings, and all reagents used are commercially available without further purification unless otherwise specified.

The first embodiment is as follows: preparation of high-purity hexagonal Cu nanocrystals 1

1) Preparing 50 ml of solution with the concentration of 0.04 g/ml by using deionized water as a solvent and copper sulfate as a solute, and stirring the solution uniformly to obtain mixed solution 1;

2) Adding 3.0 g of sodium citrate into the mixed solution 1, and stirring uniformly to obtain a mixed solution 2;

3) Dropwise adding 10 ml of hydrazine hydrate solution with the concentration of 1.7 mol/L into the mixed solution 2 at the speed of 0.5 ml/min by using a separating funnel, stirring the mixture evenly to obtain mixed solution 3,

4) Placing the mixed solution 3 at 40 ℃ and stirring for reacting for 8 hours;

5) And centrifuging the obtained product, washing the product once by using deionized water and ethanol respectively, centrifuging the product again, and drying the product for 10 hours in a blast drying oven at the temperature of 60 ℃. The obtained solid powder is the high-purity hexagonal Cu nanocrystalline.

In order to determine the purity of the product, we first performed X-ray diffraction on the sample, and it can be seen from FIG. 1 that the diffraction peak position of the obtained product corresponds to the standard diffraction card JCPDS89-2838 of Cu, so that the obtained product is Cu nanocrystal with high purity. To determine the morphology of the resulting product, we performed a field emission scanning electron microscope test on the product. As shown in FIG. 2, the elemental Cu obtained in example 1 has a hexagonal plate-like structure with a side length of about 3 μm. Different from the work introduced in the background art, the triangular Cu nanocrystalline does not appear in the sample obtained by the method, and the sample is high-purity hexagonal Cu nanocrystalline.

The second embodiment: preparation of high-purity hexagonal Cu nanocrystal 2

2) Adding 3.5 g of sodium citrate into the mixed solution 1, and stirring uniformly to obtain a mixed solution 2;

3) Dropwise adding 12 ml of hydrazine hydrate solution with the concentration of 1.5 mol/L into the mixed solution 2 at the speed of 0.5 ml/min by using a separating funnel, and stirring the mixture uniformly to obtain a mixed solution 3;

4) Placing the mixed solution 3 in an environment of 45 ℃ and stirring for reaction for 6 hours;

5) And (3) after centrifuging, respectively washing the obtained product once by using deionized water and ethanol, centrifuging again, and drying in a blowing drying oven at the temperature of 50 ℃ for 10 hours. The obtained solid powder is the high-purity hexagonal Cu nanocrystalline.

As shown in fig. 3, the Cu nanocrystals obtained in example 2 were hexagonal nanosheet structures.

Example three: preparation of high-purity hexagonal Cu nanocrystals 3

2) Adding 3.1 g of sodium citrate into the mixed solution 1, and stirring uniformly to obtain a mixed solution 2;

3) Dropwise adding 10 ml of hydrazine hydrate with the concentration of 1.7 mol/L into the mixed solution 2 at the speed of 0.5 ml/min by using a separating funnel, stirring the mixture evenly to obtain mixed solution 3,

4) Placing the mixed solution 3 in an environment of 43 ℃ and stirring for reaction for 7 hours;

5) And centrifuging the obtained product, washing the product once by using deionized water and ethanol respectively, centrifuging the product again, and drying the product for 12 hours in a blast drying oven at the temperature of 60 ℃. The obtained powder is the hexagonal Cu nanocrystalline with high purity.

To determine the morphology of the resulting product, we performed field emission scanning electron microscopy testing on the product. As shown in fig. 4, the Cu nanocrystals obtained in example 3 still have hexagonal nanostructures.

Comparative example one: influence of the dropping Rate of the reducing agent on the morphology of the Cu nanocrystals 1

The key point of the technology of the invention is to adjust the further growth and curing of the Cu nanocrystalline by controlling the reaction rate. To demonstrate this, we proceed with comparative example one, with the following specific procedure:

3) Dropwise adding 10 ml of hydrazine hydrate with the concentration of 1.7 mol/L into the mixed solution 2 at the speed of 2 ml/min by using a separating funnel, stirring the mixture evenly to obtain mixed solution 3,

4) Placing the mixed solution 3 at 40 ℃ and stirring for reaction for 8 hours;

5) And centrifuging the obtained product, respectively washing the product once by using deionized water and ethanol, centrifuging the product again, and drying the product in a blast drying oven at the temperature of 60 ℃ for about 10 hours to obtain solid powder, namely the target product.

And respectively carrying out X-ray diffraction and field emission scanning electron microscope tests on the obtained product. As can be seen from fig. 5, the product had a large number of CuO particles in addition to Cu nanoparticles. This is because the hydrazine hydrate is highly reducing and rapid addition results in an increased reaction rate. The elementary substance Cu is rapidly nucleated and can not be further cured into hexagonal Cu nano crystals. The small Cu nano-crystal has larger specific surface area, and can easily form oxide in the atmosphere without protective gas. This point can also be obtained from the sem image of fig. 6. As shown in fig. 6, due to the excessive reaction rate, the resulting product does not grow into the shape of hexagonal Cu nanoplates, which are agglomerated nanoparticles.

Comparative example two: influence of reducing agent dropping rate on Cu nanocrystalline morphology 2

2) Adding 3 g of sodium citrate into the mixed solution 1, and stirring uniformly to obtain a mixed solution 2;

3) Dropwise adding 10 ml of hydrazine hydrate with the concentration of 1.7 mol/l into the mixed solution 2 by a separating funnel at the speed of 1 ml/min, stirring the mixture evenly to obtain mixed solution 3,

5) And centrifuging the obtained product, respectively washing the product once by using deionized water and ethanol, centrifuging the product again, and drying the product for 10 hours in a blast drying oven at the temperature of 60 ℃ to obtain solid powder, namely the target product.

And respectively carrying out X-ray diffraction and field emission scanning electron microscope tests on the obtained product. As can be seen from fig. 7, the oxide content in the product is greatly reduced, but CuO is still present. As can be seen from fig. 8, the resulting product does not grow into the shape of hexagonal Cu nanoplates, and the dimensional uniformity is poor. The reason for this phenomenon is the same as in comparative example one. Therefore, in the preparation process, the correct reaction rate is an important condition for ensuring that the product is the high-purity hexagonal Cu nanocrystalline.

Comparative example three: effect of reaction time on the product

In the solvent, the small particles are continuously shrunk, the relative large particles are continuously increased, and the integral average radius of the solute is also continuously increased; after a sufficient period of time, all of the solute will eventually become a large particle to achieve the effect of minimizing surface area. This phenomenon is known as Oswald ripening. Is widely applied to the design and preparation of nano structures.

In the invention, no surfactant is adopted, and the growth of the Cu nanocrystalline is spontaneously cured at a specific reaction temperature to form a stable hexagonal structure. Control of the reaction time is critical to the formation of hexagonal Cu nanocrystals. The shortening of the reaction time may result in the ripening of the Cu nanocrystals not proceeding, or partially proceeding. The desired two-dimensional sheet structure cannot be obtained. To verify the above idea, we implemented the following comparative examples:

2) Adding 3.0 g of complexing agent sodium citrate into the mixed solution 1, and stirring uniformly to obtain a mixed solution 2;

4) Placing the mixed solution 3 at 40 ℃ and stirring for reaction for 2 hours;

The obtained sample was subjected to a field emission scanning electron microscope test, and the result is shown in fig. 9. It can be seen from fig. 9 that the resulting sample particle size distribution was uniform and fused into a larger sheet structure after reducing the reaction time, but uniform hexagonal Cu nanocrystals were not yet grown due to insufficient reaction time. In the synthesis process, enough time is needed for reactants to complete the curing process and form the hexagonal Cu nanosheet with regular appearance. This result may prove that sufficient ripening time is an important condition to ensure the formation of hexagonal Cu nanocrystals.

Comparative example four: influence of reaction temperature on product morphology

Besides the reaction rate and time, the proper reaction temperature is an important factor for ensuring the spontaneous aging of the Cu nanocrystalline in the process of preparing the hexagonal Cu nanocrystalline. It is worth mentioning that the environment (20-25 ℃) at normal room temperature is insufficient to ensure that the Cu nanocrystalline is cured into a two-dimensional structure. To demonstrate the above, we carried out comparative example four, operating specifically as follows:

4) Placing the mixed solution 3 at room temperature (20-25 ℃) and stirring for reaction for 8 hours;

5) And centrifuging the obtained product, washing the product once by using deionized water and ethanol respectively, centrifuging the product again, and drying the product for 10 hours in a blast drying oven at the temperature of 60 ℃. Obtaining solid powder as the target product.

The obtained sample was subjected to a field emission scanning electron microscope test, and the result is shown in fig. 10. As can be seen from fig. 10, the obtained sample has uniform particle size distribution and good dispersity, but still cannot be cured into a stable hexagonal sheet structure due to too low reaction temperature. Therefore, the reaction environment of 40-45 ℃ is an important parameter in the preparation process of the hexagonal Cu nanocrystalline.

Claims

1. A preparation method of high-purity hexagonal Cu nanocrystals is characterized by comprising the following steps:

(1) Deionized water is used as a solvent, copper sulfate is used as a solute, and the mixture is stirred uniformly to obtain a mixed solution 1;

(2) Adding citrate into the mixed solution 1, and stirring uniformly to obtain a mixed solution 2;

(3) Dropwise adding a reducing agent into the mixed solution 2 by using a separating funnel at the speed of 0.5 ml/min, and stirring uniformly to obtain a mixed solution 3;

(4) Placing the mixed solution 3 in an environment of 40-45 ℃, and stirring for reaction for 6-8 hours;

(5) After centrifuging, washing the obtained product with deionized water and ethanol once respectively, centrifuging again, and drying in a forced air drying oven at 50-60 ℃ to obtain powder, namely high-purity hexagonal Cu nanocrystalline;

the concentration of the copper sulfate added in the step (1) is 0.04 g/ml; the citrate in the step (2) is sodium citrate, and the concentration ratio of the citrate to the mixed solution 1 is 0.06-0.07 g/ml;

the reducing agent in the step (3) is hydrazine hydrate solution, and the molar concentration of the reducing agent is 1.5-1.7 mol/L; the volume ratio of the reducing agent to the mixed liquid 2 is 1.