Low-temperature route for precision synthesis of metal oxide nanoparticles

1. A method for making nanoparticles comprising a metal oxide, the method comprising:

providing a solution comprising RCOOH and a corresponding metal carboxylate comprising RCOO − and a metal cation M, wherein M is a group IIIA metal, a group IVA metal, a transition metal, or a combination thereof, and R is saturated or unsaturated C1-C21 aliphatic;

injecting the solution at a rate of up to 0.5 mL/min into a solvent comprising R′OH to produce a mixture, wherein R′ is saturated or unsaturated C2-C22 aliphatic, and wherein the solvent is preheated to a temperature T 1 of 100-290° C. prior to injecting the solution into the solvent; and

maintaining the mixture at a temperature T 2 for an effective period of time to form crystalline metal oxide nanoparticles, wherein T 2 is less than the thermal decomposition temperature of the corresponding metal carboxylate.

2. The method of claim 1 where [R′OH]>[RCOOH]>[M] when the solution is injected into the solvent.

3. The method of claim 1 where [R′OH] is at least 10× greater than [M] when the solution is injected into the solvent.

4. The method of claim 1 where providing the solution comprising RCOOH and the metal carboxylate further comprises:

providing a C1-C5 metal carboxylate comprising M;

combining the C1-C5 metal carboxylate with a molar excess of RCOOH; and

heating to convert at least a portion of the C1-C5 metal carboxylate to the metal carboxylate, thereby forming the solution comprising RCOOH and the metal carboxylate.

5. The method of claim 1 where M is Mn, Fe, Co, Zn, Sn, In, or a combination thereof.

6. The method of claim 1 where R′ is RCH 2 —.

7. The method of claim 1 where RCOOH is oleic acid and R′OH is oleyl alcohol.

8. The method of claim 1 where the solution is injected into the solvent at a rate of 0.1-0.5 mL/minute.

9. The method of claim 1 where T 1 and/or T 2 is 200° C. to 230° C. and/or the effective period of time is ≦30 minutes.

10. The method of claim 1 , further comprising flowing a gas across a surface of the mixture, thereby evaporating and removing water produced as the crystalline metal oxide nanoparticles are formed.

11. The method of claim 1 where R and R′ are linear aliphatic and differ in length by five or fewer carbon atoms.

12. The method of claim 1 where R′OH is a liquid at temperatures less than 200° C.

13. The method of claim 1 where the metal carboxylate comprising RCOO − and the metal cation M is soluble in R′OH at the temperature T 2 .

14. The method of claim 1 where the crystalline metal oxide nanoparticles have a relative size dispersity of ≦20%.

15. The method of claim 1 where T 2 is 100-290° C.

16. A method for making core-shell nanoparticles, the method comprising:

providing a solution comprising RCOOH and a corresponding metal carboxylate comprising RCOO − and a metal cation M, wherein M is a group IIIA metal, a group IVA metal, a transition metal, or a combination thereof, and R is saturated or unsaturated C1-C21 aliphatic;

combining the solution with a solvent comprising R′OH to produce a mixture, wherein R′ is saturated or unsaturated C2-C22 aliphatic, and wherein the solvent is preheated to a temperature T 1 of 100-290° C. prior to combining the solution with the solvent;

maintaining the mixture at a temperature T 2 for an effective period of time to form crystalline metal oxide nanoparticles, wherein T 2 is less than the thermal decomposition temperature of the corresponding metal carboxylate; and

depositing a metal oxide shell onto the crystalline metal oxide nanoparticles by

combining the crystalline metal oxide nanoparticles with R′″OH to produce a mixture, where R′″ is saturated or unsaturated C2-C22 aliphatic,

heating the mixture to a temperature T 3 of ≦200° C.,

providing a solution comprising R″COOH and a corresponding metal carboxylate comprising R″COO − and a metal cation M′, where M′ is a group IIIA metal, a group IVA metal, a transition metal, or a combination thereof, M′ and M are different metals, and R″ is saturated or unsaturated C1-C21 aliphatic;

combining the solution with the mixture, and

maintaining the combined solution and mixture at a temperature T 4 of ≦200° C. for an effective period of time to form core-shell nanoparticles comprising a crystalline metal oxide core including M and a metal oxide shell including M′ deposited onto the metal oxide core.

17. The method of claim 16 where R″ is R, and R′″ and R′ are RCH 2 —.

18. The method of claim 16 , where T 4 is less than a nucleation temperature for a metal oxide comprising M′ and oxygen is excluded during deposition of the metal oxide shell.

19. The method of claim 16 where T 3 and/or T 4 is 150-200° C.

20. A method for making nanoparticles, comprising:

providing a C1-C5 metal carboxylate comprising a metal cation M, wherein M is a group IIIA metal, a group IVA metal, a transition metal, or a combination thereof;

combining the C1-C5 metal carboxylate with a molar excess of RCOOH, wherein R is saturated or unsaturated C5-C21 aliphatic;

heating to convert at least a portion of the C1-C5 metal carboxylate to a metal carboxylate comprising RCOO − and M, thereby forming a solution comprising RCOOH and the metal carboxylate comprising RCOO − and M;

preheating a solvent comprising R′OH to a temperature ranging from 100° C.-290° C. to form a preheated solvent, wherein R′ is saturated or unsaturated C6-C22 aliphatic;

injecting the solution at a rate of up to 0.5 mL/min into the preheated solvent to produce a mixture, wherein [R′OH]>[RCOOH]>[M];

maintaining the mixture at a temperature ranging from 100° C.-290° C. under flowing nitrogen or air for an effective period of time to form crystalline nanoparticles comprising a metal oxide;

precipitating the crystalline nanoparticles; and

isolating the crystalline nanoparticles.

21. The method of claim 20 where the C1-C5 metal carboxylate is a metal acetate, RCOOH is oleic acid, and R′OH is oleyl alcohol.