US20090090214A1

US20090090214A1 - Method for forming nano-scale metal particles

Info

Publication number: US20090090214A1
Application number: US12/244,849
Authority: US
Inventors: Chun-Lin Cheng
Original assignee: Chung Yuan Christian University
Current assignee: Chung Yuan Christian University
Priority date: 2007-10-04
Filing date: 2008-10-03
Publication date: 2009-04-09

Abstract

A method for forming nano-scale metal particles by a novel reducing agent is described. The method can be carried out at room temperature and under an atmospheric environment by relatively simple processes to prepare nano-scale metal particles with a diameter less than 20 nm. This method comprises the following steps. At first, a first blending process is performed to blend a metal salt and a first solvent together to form a first solution. Then, a second blending process is performed to blend a reducing agent and a second solvent together to form a second solution. The reducing agent comprises one compound selected from the group consisting of the following or combination thereof: boron-containing hydride and boron-containing hydrocarbon. Following that, a third blending process is performed to blend the first solution and the second solution together to form a third solution. Finally, the reducing agent is used to reduce the metal salt in the third solution to form the nano-scale metal particles. In addition, if a dispersing agent is added after the nano-scale metal particles are formed, the nano-scale metal particles can have a particle diameter less than 10 nm.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention is generally related to a method for forming nano-scale particles and more particularly to a method for forming nano-scale particles by a novel reducing agent.
2. Description of the Prior Art
A nano-scale metal material means a material containing nano-scale metal particles or having the nano-scale structure in the matrix thereof. As the diameter of metal particles is within the nano scale, the surface area of particles becomes very large and new electrical, magnetic, optical, and chemical characteristics different from the bulk material thereof are appeared due to the particle diameter being less than the light wavelength so that these nano-scale particles can be applied in various fields, such as electrode materials, conducting films, biochemical sensing, drug delivery, optical sensing, catalyzed reaction, and electrical engineering.
Nano-scale metal materials can be categorized into nano-scale metal particles, nano-wires, nano-membranes, nano bulk materials. The later three forms can be derived from the first one, that is, nano-scale particles. Therefore, the preparation and development of nano-scale metal particles are more important than that of the rest forms of nano-scale metal materials. A method for forming nano-scale metal particles to effectively control the particle diameter, the distribution of the particle diameters, particle types, and crystal structures, etc., is the current research target.
Currently, the chemical reduction method is commonly used to prepare nano-scale metal particles. The chemical reduction method uses a reducing agent or an electrochemical system to reduce metal oxide into metal in a free space or confined space.
In the above chemical reduction method, the reducing agent in use can easily react with oxygen or moisture to result in burning or an explosion. Base on safety consideration, it should take place under an inactive environment (without oxygen). By doing so, the production cost will be increased.
In light of the above description, a method under mild reaction conditions, such as at room temperature and under an atmospheric environment, to form nano-scale metal particles with shorter reaction time is an important technical development topic for the industry.

SUMMARY OF THE INVENTION

In light of the above background, in order to fulfill the industrial requirements, the invention provides a method for forming nano-scale metal particles.
The invention discloses a method for forming nano-scale metal particles by a novel reducing agent. The method can be carried out at room temperature and under an atmospheric environment by relatively simple processes to prepare nano-scale metal particles with a diameter less than 20 nm. This method comprises the following steps. At first, a first blending process is performed to blend a metal salt and a first solvent together to form a first solution. Then, a second blending process is performed to blend a reducing agent and a second solvent together to form a second solution. The reducing agent comprises one compound selected from the group consisting of the following or combination thereof: boron-containing hydride and boron-containing hydrocarbon. Following that, a third blending process is performed to blend the first solution and the second solution together to form a third solution. Finally, the reducing agent is used to reduce the metal salt in the third solution to form the nano-scale metal particles. In addition, if a dispersing agent is added after the nano-scale metal particles are formed, the nano-scale metal particles can have a particle diameter less than 10 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are particle size spectra of tin-containing nano-scale metal particles;

FIG. 2 shows TEM images of tin-containing nano-scale metal particles;

FIG. 3A and FIG. 3B show TEM images of copper nano-scale metal particles. Image analysis of 30 nm to 60 nm; and

FIG. 4A and FIG. 4B show TEM images of nano-scale metal particles. Image analysis of 30 nm to 60 nm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a first embodiment of the invention, a method for forming nano-scale metal particles at room temperature is disclosed. At first, a first blending process is performed to blend a metal salt and a first solvent together to form a first solution. Then, a second blending process is performed to blend a reducing agent and a second solvent together to form a second solution. The reducing agent comprises one compound selected from the group consisting of the following or combination thereof: boron-containing hydride and boron-containing hydrocarbon. Finally, a third blending process is performed to blend the first solution and the second solution together to form a third solution. The reducing agent is used to reduce the metal salt in the third solution to form the nano-scale metal particles.
The temperature of the first, second, and third blending processes is less than or equal to 40° C. In addition, the processes are carried out under an atmospheric environment. Preferably, the processes are carried out under an inactive environment.
Moreover, in the first solution, the molar concentration of the metal salt is less than or equal to 10⁻⁴M while in the second solution the molar concentration of the reducing agent is less than or equal to 10⁻⁴M.
Besides, the reducing agent is tetraethylammonium borohydride. The metal salt has a general formula: MX where M is selected from the group consisting of the following: tin, copper, silver, and gold; and X is selected from the group consisting of the following: halogen, sulfate ion, phosphate ion, sulfonate ion, nitrate ion, and carboxylate ion.
In a preferred example of this embodiment, the nano-scale metal particles are dispersed in solution by a dispersing agent after formed where the dispersing agent is selected from the group consisting of the following: water, alcohol, n-hexane, toluene, and tetrahydrofuran. In addition, the first solvent and the second solvent are independently selected from the group consisting of the following or combination thereof: water, alcohol, and a polar solvent. On the other hand, the molar ratio of the reducing agent to the metal salt is 60˜300. The particle diameter of the formed nano-scale metal particles is 5˜70 nm and preferably less than 10 nm.
In another preferred example of this embodiment, no additional additive or dispersing agent is needed after the nano-scale metal particles are formed. Furthermore, the first solvent and the second solvent are independently selected from the group consisting of the following: N,N-dimethyl-acetamide (DMAC), dimethyl-sulfoxide (DMSO), and 1-methyl-2-pyrrolidinone (NMP). On the other hand, the molar ratio of the reducing agent to the metal salt is 5˜25. The particle diameter of the formed nano-scale metal particles is 15˜60 nm and preferably less than 20 nm.
In a second embodiment of the invention, a method for forming tin-containing nano-scale metal particles at room temperature is disclosed. At first, a blending process is performed to blend a tin salt, a reducing agent, and a solvent together to form a mixture solution. The reducing agent is used to reduce the metal salt in the mixture solution to form the tin-containing nano-scale metal particles. The mixture solution selectively comprises other metal salts and the reducing agent comprises one compound selected from the group consisting of the following or combination thereof: boron-containing hydride and boron-containing hydrocarbon.
The blending process is carried out under an atmospheric environment. The temperature of the blending processes is less than or equal to 40° C. In addition, the nano-scale metal particles are dispersed in solution by a dispersing agent after formed where the dispersing agent is selected from the group consisting of the following: water, alcohol, n-hexane, toluene, and tetrahydrofuran.
The reducing agent is tetraethylammonium borohydride. The solvent is selected from the group consisting of the following or combination thereof: water, alcohol, and a polar solvent. The tin salt has a general formula: SnX where X is selected from the group consisting of the following: halogen, sulfate ion, phosphate ion, sulfonate ion, nitrate ion, and carboxylate ion. On the other hand, the other metal salt is selected from the group consisting of the following or combination thereof: silver salt, copper salt, and gold salt. In addition, the molar ratio of the reducing agent to all of the metal salts is 60˜300. The particle diameter of the tin-containing nano-scale metal particles formed in this embodiment is 5˜70 nm and preferably less than 10 nm.
In a third embodiment of the invention, a method for forming copper nano-scale metal particles is disclosed. At first, a first blending process is performed to blend a copper salt and a first solvent together to form a first solution. Then, a second blending process is performed to blend a reducing agent and a second solvent together to form a second solution. The reducing agent comprises one compound selected from the group consisting of the following or combination thereof: boron-containing hydride and boron-containing hydrocarbon. The second solvent is independently selected from the group consisting of the following: N,N-dimethyl-acetamide (DMAC), dimethyl-sulfoxide (DMSO), and 1-methyl-2-pyrrolidinone (NMP). Finally, a third blending process is performed to blend the first solution and the second solution together to form a third solution. The reducing agent is used to reduce the copper salt in the third solution to form dispersed copper nano-scale metal particles.
The first, second, and third blending processes are carried out under a nitrogen environment. The temperature of the first, second, and third blending processes is less than or equal to 40° C. Moreover, in the first solution, the molar concentration of the metal salt is preferably less than or equal to 10⁻⁴M while in the second solution the molar concentration of the reducing agent is preferably less than or equal to 10⁻⁴M. In addition, the molar ratio of the reducing agent to the copper-containing metal salts is 5˜25.
The reducing agent is tetraethylammonium borohydride. The copper salt has a general formula: CuX where X is selected from the group consisting of the following: halogen, sulfate ion, phosphate ion, sulfonate ion, nitrate ion, and carboxylate ion.
On the other hand, the first solvent is independently selected from the group consisting of the following or combination thereof: N,N-dimethyl-acetamide (DMAC), dimethyl-sulfoxide (DMSO), and 1-methyl-2-pyrrolidinone (NMP). In a preferred example of this embodiment, the first solvent is N,N-dimethyl-acetamide (DMAC) while the second solvent is dimethyl-sulfoxide (DMSO).
The particle diameter of the copper nano-scale metal particles formed in this embodiment is 15˜60 nm and preferably less than 20 nm.

EXAMPLE 1

Formation and Properties of Tin-Containing Nano-Scale Metal Particles

is example is to prepare and investigate the tin-containing nano-scale metal particles according to the invention. The chemical equation is shown as the following:
SnCl₂+2N(Et)₄(BH₄)→Sn+2N(Et)₄Cl+B₂H₆+H₂.
e detailed steps are given in the following. At room temperature and under an atmospheric environment, a certain amount of the reducing agent and a certain amount of SnCl₂are weighted and placed in a 50 ml graduate cylinder, separately. A magnet is placed in the graduate cylinder for stirring beforehand. Then, a septum is used to seal the container and the septum is then wrapped with paraffin for air-tight. Nitrogen gas is introduced into the graduate cylinder to expel the moisture in air. 20 ml of solvent is added by a syringe and then the mixture is stirred for 30 minutes to ensure completely dissolving in the solvent. Thus, the reducing agent solution and the SnCl₂solution are prepared. The reducing agent solution and the SnCl₂solution with different quantities are taken and mixed under a nitrogen environment. After being stirred, the mixture solution is tested by instruments.
this example, water, alcohols (such as methanol, ethanol, butanol, ethylene glycol), and polar solvents (such as DMAC and NMP) are used as the solvent. It is found that the samples using DMAC and NMP as the solvent have better results and the particle diameter can be controlled easily as well. Besides, according the test results, the added quantity of the SnCl₂solution has great influence on the particle diameter. If a small quantity of the reducing agent solution is added into a large quantity of the SnCl₂solution, the particle diameter of the obtained particles is relatively large after analyzed and can not be nano-scale. If a small quantity of the SnCl₂solution is added into a large quantity of the reducing agent solution, the particle diameter of the obtained particles is clearly relatively small.
According to the above results, this example uses DMAC as the solvent to form tin-containing nano-scale metal particles. As shown in FIGS. 1A and 1B, when less than 1000 μl of tin chloride is added, the particle diameter of the formed tin nano-scale metal particles is less than 50 nm. When 400 μl and 600 μl of tin chloride are added, the average particle diameters are 16 nm and 34 nm, respectively. Since the data show the average particle diameter, the particle diameter being less than 10 nm can also be seen in the figure. This example also tests the same sample by transmission electron microscopy (TEM). The sample is dripped on copper gauze coated with carbon film. The excess liquid is removed and the sample is dried and ready for investigation. The result is shown in FIG. 2.

EXAMPLE 2

Formation of Copper Nano-Scale Metal Particles

The chemical equation for forming copper nano-scale metal particles according to the invention is shown as the following:
CuCl₂+2N(C₂H₅)₄BH₄→Cu+2N(C₂H₅)₄Cl+B₂H₆+H₂.
The detailed steps are given in the following. At room temperature and under a nitrogen environment, a proper quantity of the reducing agent is weighted. The reducing agent is tetraethylammonium borohydride. The reducing agent dissolves in the solvent to form 20 ml of 0.01M reducing agent solution. Then, at room temperature and under a nitrogen environment, a proper quantity of copper chloride is weighted and dissolves in the solvent to form 20 ml of 0.005M copper chloride solution. These solutions are separately stirred by magnets for over 20 minutes to ensure completely dissolution. Finally, under a nitrogen environment, the reducing agent solution is blended with the copper chloride solution with different ratios. An ultrasonic vibrator is used while the reaction takes place for 15 minutes. Thus, the solution containing copper nano-scale metal particles is obtained.
N,N-dimethyl-acetamide (DMAC) is used as the solvent for the reducing agent and the metal salt, the copper nano-scale metal particles with the particle diameter of 30˜60 nm can be formed. The TEM pictures of the copper nano-scale metal particles are shown in FIGS. 3A and 3B. The magnification ratio in FIG. 3A is 50,000 while the magnification ratio in FIG. 3B is 100,000.
N,N-dimethyl-acetamide (DMAC) is used as the solvent for copper chloride and dimethyl-sulfoxide (DMSO) is used as the solvent for the reducing agent, the copper nano-scale metal particles with the particle diameter of 15˜30 nm can be formed. The TEM pictures of the copper nano-scale metal particles are shown in FIGS. 4A and 4B. The magnification ratio in FIGS. 4A and 4B is 100,000.
Obviously many modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the present invention can be practiced otherwise than as specifically described herein. Although specific embodiments have been illustrated and described herein, it is obvious to those skilled in the art that many modifications of the present invention may be made without departing from what is intended to be limited solely by the appended claims.

Claims

1. A method for forming nano-scale metal particles, comprising:

performing a first blending process to blend a metal salt and a first solvent together to form a first solution;

performing a second blending process to blend a reducing agent and a second solvent together to form a second solution wherein said reducing agent comprises one compound selected from the group consisting of the following or combination thereof: boron-containing hydride and boron-containing hydrocarbon;

performing a third blending process to blend said first solution and said second solution together to form a third solution; and

using said reducing agent to reduce said metal salt in said third solution to form said nano-scale metal particles.

2. The method according to claim 1, wherein the temperature in said first, second, and third blending processes is less than or equal to 40° C.

3. The method according to claim 1, wherein in said first solution the molar concentration of said metal salt is less than or equal to 10⁻⁴M.

4. The method according to claim 1, wherein in said second solution the molar concentration of said reducing agent is less than or equal to 10⁻⁴M.

5. The method according to claim 1, wherein said reducing agent is tetraethylammonium borohydride.

6. The method according to claim 1, wherein said metal salt has a general formula: MX where M is selected from the group consisting of the following: tin, copper, silver, and gold; and X is selected from the group consisting of the following: halogen, sulfate ion, phosphate ion, sulfonate ion, nitrate ion, and carboxylate ion.

7. The method according to claim 1, wherein said first solvent and said second solvent are independently selected from the group consisting of the following or combination thereof: water, alcohol, and a polar solvent.

8. The method according to claim 7, wherein said nano-scale metal particles are dispersed in solution by a dispersing agent after formed where said dispersing agent is selected from the group consisting of the following: water, alcohol, n-hexane, toluene, and tetrahydrofuran.

9. The method according to claim 7, wherein the molar ratio of said reducing agent to said metal salt is between 60 and 300.

10. The method according to claim 7, wherein the particle diameter of said formed nano-scale metal particles is 5˜70 nm.

11. The method according to claim 1, wherein said first solvent and said second solvent are independently selected from the group consisting of the following or combination thereof: N,N-dimethyl-acetamide (DMAC), dimethyl-sulfoxide (DMSO), and 1-methyl-2-pyrrolidinone (NMP).

12. The method according to claim 11, wherein the molar ratio of said reducing agent to said metal salt is between 5 and 25.

13. The method according to claim 11, wherein the particle diameter of said formed nano-scale metal particles is 15˜60 nm.

14. A method for forming tin-containing nano-scale metal particles, comprising:

performing a blending process to blend a tin salt, a reducing agent, and a solvent together to form a mixture solution wherein said mixture solution selectively comprises other metal salts and said reducing agent comprises one compound selected from the group consisting of the following or combination thereof: boron-containing hydride and boron-containing hydrocarbon; and

using said reducing agent to reduce said metal salt in said mixture solution to form said tin-containing nano-scale metal particles.

15. The method according to claim 14, wherein the temperature in said blending processes is less than or equal to 40° C.

16. The method according to claim 14, wherein said blending process is performed under an atmospheric environment.

17. The method according to claim 14, wherein said reducing agent is tetraethylammonium borohydride.

18. The method according to claim 14, wherein said solvent is selected from the group consisting of the following or combination thereof: water, alcohol, a polar solvent.

19. The method according to claim 14, wherein said tin salt has a general formula: SnX where and X is selected from the group consisting of the following: halogen, sulfate ion, phosphate ion, sulfonate ion, nitrate ion, and carboxylate ion.

20. The method according to claim 14, wherein said other metal salt is selected from the group consisting of the following or combination thereof: silver salt, copper salt, and gold salt.

21. The method according to claim 14, wherein said nano-scale metal particles are dispersed in solution by a dispersing agent after formed where said dispersing agent is selected from the group consisting of the following: water, alcohol, n-hexane, toluene, and tetrahydrofuran.

22. The method according to claim 14, wherein the molar ratio of said reducing agent to all of said metal salts is between 60 and 300.

23. The method according to claim 14, wherein the particle diameter of said formed tin-containing nano-scale metal particles is 5˜70 nm.

24. A method for forming copper nano-scale metal particles, comprising:

performing a first blending process to blend a copper salt and a first solvent together to form a first solution;

performing a second blending process to blend a reducing agent and a second solvent together to form a second solution wherein said reducing agent comprises one compound selected from the group consisting of the following or combination thereof: boron-containing hydride and boron-containing hydrocarbon and said second solvent is selected from the group consisting of the following: N,N-dimethyl-acetamide (DMAC), dimethyl-sulfoxide (DMSO), and 1-methyl-2-pyrrolidinone (NMP);

performing a third blending process to blend said first solution and said second solution together to form a third solution and using said reducing agent to reduce said copper salt in said third solution to form dispersed copper nano-scale metal particles.

25. The method according to claim 24, wherein the temperature of said first, second, and third blending processes is less than or equal to 40° C.

26. The method according to claim 24, wherein said first, and second, and third blending processes are performed under a nitrogen environment.

27. The method according to claim 24, wherein in said first solution the molar concentration of said metal salt is less than or equal to 10⁻⁴M.

28. The method according to claim 24, wherein in said second solution the molar concentration of said reducing agent is less than or equal to 10⁻⁴M.

29. The method according to claim 24, wherein said reducing agent is tetraethylammonium borohydride.

30. The method according to claim 24, wherein said first solvent is independently selected from the group consisting of the following or combination thereof: N,N-dimethyl-acetamide (DMAC), dimethyl-sulfoxide (DMSO), and 1-methyl-2-pyrrolidinone (NMP).

31. The method according to claim 24, wherein said first solvent is N,N-dimethyl-acetamide (DMAC) and said second solvent is dimethyl-sulfoxide (DMSO).

32. The method according to claim 24, wherein said copper salt has a general formula: CuX where and X is selected from the group consisting of the following: halogen, sulfate ion, phosphate ion, sulfonate ion, nitrate ion, and carboxylate ion.

33. The method according to claim 24, wherein the molar ratio of said reducing agent to said copper-containing metal salts is between 5 and 25.

34. The method according to claim 14, wherein the particle diameter of said formed copper nano-scale metal particles is 15˜60 nm.