# US 9,517,945 B2 · Low-temperature route for precision synthesis of metal oxide nanoparticles

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- Number: US 9,517,945 B2
- Document ID: US9517945B2
- Status: Granted
- Kind: B2
- Application number: 14/092,800
- Filed: 2013-11-27
- Published: 2015-09-17
- Granted: 2016-12-13
- Earliest claimed: 2012-11-28
- Assignees: University of Oregon
- Applicants: University of Oregon
- Inventors: Daisuke Ito; James E. Hutchison
- Web page: https://patentgrep.com/patent/US9517945B2

## CPC

- C01G 51/04: Oxides
- C01B 13/14: Methods for preparing oxides or hydroxides in general (particular individual oxides or hydroxides, see the relevant groups of subclasses C01B - C01G or C25B, according to the element combined with the oxygen or hydroxy group)
- C01G 1/02: Oxides
- C01G 9/02: Oxides; Hydroxides
- C01G 15/00: Compounds of gallium, indium or thallium
- C01G 19/00: Compounds of tin
- C01G 45/028: Trimanganese tetraoxide
- C01G 49/06: Ferric oxide [Fe2O3]
- C01P 2002/72: by d-values or two theta-values, e.g. as X-ray diagram
- C01P 2002/84: by UV- or VIS- data
- C01P 2002/85: by XPS, EDX or EDAX data
- C01P 2004/04: obtained by TEM, STEM, STM or AFM
- C01P 2004/51: Particles with a specific particle size distribution
- C01P 2004/52: highly monodisperse size distribution
- C01P 2004/64: Nanometer sized, i.e. from 1-100 nanometer
- C01P 2004/84: one phase coated with the other
- Y10T 428/2991: Coated
- C01G: COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F (metal hydrides {monoborane, diborane or addition complexes thereof} C01B6/00; salts of oxyacids of halogens C01B11/00; peroxides, salts or peroxyacids C01B15/00; thiosulfates, dithionites, polythionates C01B17/64; compounds containing selenium, or tellurium C01B19/00; binary compounds of nitrogen with metals C01B21/06; azides C01B21/08; {compounds containing nitrogen, other non-metals and metal C01B21/082}; metal amides C01B21/092; nitrites C01B21/50; {compounds of noble gases C01B23/0005}; phosphides C01B25/08; salts of oxyacids of phosphorus C01B25/16; carbides C01B32/90; compounds containing silicon C01B33/00; compounds containing boron C01B35/00; compounds having molecular sieve properties but not having base-exchange properties C01B37/00; compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites, C01B39/00; cyanides C01C3/08; salts of cyanamide C01C3/16; thiocyanates C01C3/20)
- C01B: NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; {METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C}
- C01P: INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Methods for making metal oxide nanoparticles, including mixed metal oxides and core-shell metal oxide nanoparticles, are disclosed. A solution comprising a metal carboxylate and a carboxylic acid is combined with a solvent comprising an alcohol heated to a temperature ≦250° C. for an effective period of time to form metal oxide nanoparticles. The metal may be a group IIIA metal, a group IVA metal, a transition metal, or a combination thereof. A metal oxide shell may be deposited onto metal oxide nanoparticles by dispersing the metal oxide nanoparticles in an alcohol, adding a metal carboxylate, and maintaining the reaction at a temperature ≦200° C. for an effective period of time to form core-shell nanoparticles. The nanoparticles may have a relative size dispersity of ≦20%, and may further comprise a plurality of carboxylic acid, carboxylate, and/or alcohol ligands coordinated to the nanoparticles' outer surfaces.

## Claims

### Claim 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 T1 of 100-290° C. prior to injecting the solution into the solvent; and
maintaining the mixture at a temperature T2 for an effective period of time to form crystalline metal oxide nanoparticles, wherein T2 is less than the thermal decomposition temperature of the corresponding metal carboxylate.

### Claim 2 (depends on 1)

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

### Claim 3 (depends on 1)

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

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 1)

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

### Claim 6 (depends on 1)

The method of claim 1 where R′ is RCH2—.

### Claim 7 (depends on 1)

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

### Claim 8 (depends on 1)

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

### Claim 9 (depends on 1)

The method of claim 1 where T1 and/or T2 is 200° C. to 230° C. and/or the effective period of time is ≦30 minutes.

### Claim 10 (depends on 1)

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.

### Claim 11 (depends on 1)

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

### Claim 12 (depends on 1)

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

### Claim 13 (depends on 1)

The method of claim 1 where the metal carboxylate comprising RCOO− and the metal cation M is soluble in R′OH at the temperature T2.

### Claim 14 (depends on 1)

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

### Claim 15 (depends on 1)

The method of claim 1 where T2 is 100-290° C.

### Claim 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 T1 of 100-290° C. prior to combining the solution with the solvent;
maintaining the mixture at a temperature T2 for an effective period of time to form crystalline metal oxide nanoparticles, wherein T2 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 T3 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 T4 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.

### Claim 17 (depends on 16)

The method of claim 16 where R″ is R, and R′″ and R′ are RCH2—.

### Claim 18 (depends on 16)

The method of claim 16, where T4 is less than a nucleation temperature for a metal oxide comprising M′ and oxygen is excluded during deposition of the metal oxide shell.

### Claim 19 (depends on 16)

The method of claim 16 where T3 and/or T4 is 150-200° C.

### Claim 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.

### Claim 21 (depends on 20)

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.