Method for separating metal nanoparticles from colloidal metal solution

1. A method for separating metal nanoparticles from colloidal metal solution, comprising:

providing a colloidal metal solution, including a plurality of metal nanoparticles;

mixing a precipitating agent with the colloidal metal solution for maintaining a pH of the colloidal metal solution in a specific value;

keeping the colloidal metal solution stationary with no external forces applied for a static time at an environmental temperature, such that the metal nanoparticles precipitate from the colloidal metal solution, and the colloidal metal solution forms a supernatant and a precipitating liquid;

separating a precipitate from the precipitating liquid by a filtering process; and

liquid sprinkling the precipitate by a first solvent to obtain the metal nanoparticles,

wherein the precipitating agent is a third solvent including a compound, and the compound is dissolved in the third solvent and is selected from the group consisting of methylamine (CH 3 NH 2 ), ethylamine (CH 3 CH 2 NH 2 ), aminoethanol (H 2 N(CH 2 ) 2 OH), ethylenediamine (C 2 H 4 (NH 2 ) 2 ), dimethylamine ((CH 3 ) 2 NH), trimethylamine (N(CH 3 ) 3 ) triethylamine ((C 2 H 5 ) 3 N), propylamine (C 3 H 7 NH 7 ), isopropylamine, (i-C 3 H 7 NH 2 ), 1,3-propylenediamine (NH 2 (CH 2 ) 3 NH 2 ), 1,2-propylenediamine (CH 3 CH(NH 2 CH 2 NH 2 )), tripropylamine ((CH 3 CH 2 CH 2 ) 3 N), triethanolamine ((HOCH 2 CH 2 ) 3 N), butylamine (C 4 H 9 NH 2 ), isobutylamine (C 4 H 9 NH 2 ), tert-butylamine (C 4 H 9 NH 2 ), n-hexylamine (H(CH 2 ) 6 NH 2 ), n-Octylamine (H(CH 2 ) 8 NH 2 ), benzeneamine (C 6 H 5 NH 2 ), benzylamine (C 7 H 9 N), pyridine (C 5 H 5 N), polyacrylamide ([—C 3 H 5 NO—] n ), polyacrylic acid ([—C 3 H 4 O 2 —] n ), sodium polyacrylate ([—CH 2 —CH(COONa)-] n ), and combinations thereof.

2. The method according to claim 1 , wherein the colloidal metal solution is selected from the group consisting of a colloidal nanosilver (nano-Ag) solution, a colloidal nanosilver/copper (nano-Ag/Cu) solution and a colloidal nanocopper (nano-Cu) solution.

3. The method according to claim 1 , wherein the first solvent is selected from the group consisting of water, methanol, ethanol and acetone.

4. The method according to claim 1 , wherein the colloidal metal solution is obtained by a wet chemical reduction process, and the wet chemical reduction processes comprises mixing a reduction agent, a surfactant, a pH adjustor and a metal salt with a second solvent.

5. The method according to claim 4 , wherein the second solvent is selected from the group consisting of water, methanol, ethanol, propanol, butanol, ethylene glycol and acetone.

6. The method according to claim 4 , wherein the reduction agent is selected from the group consisting of formaldehyde (HCHO), sodium hypophosphite (NaH 2 PO 2 .H 2 O), hydrazine (N 2 H 4 .H 2 O), sodium borohydride (NaBH 4 ), glucose (C 6 H 12 O 6 ), ascorbic acid (C 6 H 8 O 6 ) and sodium citrate (C 6 H 5 O 7 Na.2H 2 O).

7. The method according to claim 4 , wherein the surfactant is selected from the group consisting of polyvinylpyrrolidone (PVP), sodium dodecyle sulfate (SDS), polyvinyl alcohol (PVA) and cetyltrimethylammonium bromide (CTAB).

8. The method according to claim 4 , wherein the pH adjustor is selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonia, sulfuric acid and hydrochloric acid.

9. The method according to claim 4 , wherein the metal salt is selected from the group consisting of silver nitrate, silver acetate, copper nitrate, copper sulfate and copper acetate.

10. The method according to claim 1 , wherein the third solvent is selected from the group consisting of water, methanol, ethanol, propanol, butanol, ethylene glycol and acetone.

11. The method according to claim 1 , wherein the weight percent (wt. %) of the precipitating agent in the colloidal metal solution is between 0.01 and 10.

12. The method according to claim 1 , wherein the range of the specific value is between 2 and 6.

13. The method according to claim 1 , wherein the range of the pH is between 5 and 5.5.

14. The method according to claim 1 , wherein the static time is less than or equal to 48 hours.

15. The method according to claim 1 , wherein the range of the environmental temperature is between 15 and 35° C.

16. The method according to claim 1 , after the step of forming the supernatant and the precipitating liquid, further comprising removing the supernatant by a decantation process or a suction process.

17. The method according to claim 1 , wherein the precipitating agent is used for enabling the metal nanoparticles to form a soft metal-nanoparticle agglomeration layer.

18. The method according to claim 1 , wherein the filtering process is to separate the metal nanoparticles by a vacuum filtration or a gravity filtration.

19. The method according to claim 1 , wherein the step of liquid blasting sprinkling the precipitate is enabling the first solvent to blast the precipitate to remove a plurality of remained impurities on the precipitate.

20. The method according to claim 1 , before the step of obtaining the metal nanoparticles, further comprising drying and powdering the precipitate.

21. The method according to claim 20 , wherein the step of drying the precipitate comprises vacuum drying or natural seasoning.