# US 12,595,179 B2 · Synthesis of uniform diamond nanoparticles

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- Number: US 12,595,179 B2
- Document ID: US12595179B2
- Status: Granted
- Kind: B2
- Application number: 18/057,028
- Filed: 2022-11-18
- Published: 2023-05-25
- Granted: 2026-04-07
- Earliest claimed: 2021-11-19
- Assignees: University of North Texas
- Applicants: University of North Texas
- Inventors: Hao Yan; Tengteng Lyu
- Web page: https://patentgrep.com/patent/US12595179B2

## CPC

- C01B 32/26: Preparation (by using ultra-high pressure B01J3/06; by crystal growth C30B29/04)
- C01B 32/28: After-treatment, e.g. purification, irradiation, separation or recovery
- C01P 2004/64: Nanometer sized, i.e. from 1-100 nanometer
- 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

## Abstract

The synthesis of sub-five-nanometer nanodiamonds with high uniformity and purity. Inspired by the formation of natural diamond, iron carbide nanoparticles embedded in iron oxide matrices as the carbon source were used. High-pressure-high-temperature treatment of the precursor yields nanodiamonds with tunable diameters down to 2.13 nm and 0.22-nm standard deviation. The disclosed synthesis procedures also include a method for forming fluorescent nanodiamonds.

## Claims

### Claim 1

A composition comprising nanodiamond particles wherein:
a) each nanodiamond particle is encapsulated by a transition metal oxide layer comprising iron(II) oxide (FeO) encapsulated by a layer comprising iron(III) oxide (Fe2O3); and
b) each nanodiamond particle has a diameter of about 1 nm to about 5 nm;
wherein the diameters the nanodiamond particles of the composition vary by ±0.3 nm or less.

### Claim 2 (depends on 1)

The composition of claim 1 wherein the diameter of the nanodiamond particles is 3.15 nm±0.23 nm.

### Claim 3 (depends on 1)

The composition of claim 1 wherein the diameter of the nanodiamond particles is 2.49 nm±0.22 nm.

### Claim 4 (depends on 1)

The composition of claim 1 wherein the nanodiamond particles do not comprise graphite.

### Claim 5 (depends on 1)

The composition of claim 1 wherein the nanodiamond particles have no defects in their crystal lattice.

### Claim 6 (depends on 1)

The composition of claim 1 wherein the nanodiamond particles are doped with a heteroatom, wherein optionally the doped nanodiamond particles further comprise carbon vacancies.

### Claim 7 (depends on 6)

The composition of claim 6 wherein the nanodiamond particles comprise a nitrogen-vacancy (NV) color center wherein NV is neutral or negatively charged.

### Claim 8 (depends on 1)

The composition of claim 1 wherein the diameter of the nanodiamond particles is 2.22 nm±0.22 nm.

### Claim 9 (depends on 1)

The composition of claim 1 wherein the diameter of the nanodiamond particles is 2.13 nm±0.22 nm or 1.75 nm±0.18 nm.

### Claim 10 (depends on 1)

A method for forming uniformly sized nanodiamond particles comprising:
a) inverting the polarity of hydrophobic iron carbide nanoparticles to hydrophilic iron carbide nanoparticles;
b) dispersing the hydrophilic nanoparticles in a pH neutral solution of iron(III) nitrate (Fe(NO3)3) to form a mixture;
c) heating the mixture to form a colloidal gel;
d) calcining the colloidal gel in the presence of oxygen to form a composite of iron carbide (Fe2C) nanoparticles that are uniformly distributed in iron(III) oxide (Fe2O3); and
e) applying a high pressure and high temperature (HPHT) to the composite suitable for forming uniformly sized nanodiamond particles according to claim 1.

### Claim 11 (depends on 10)

The method of claim 10 wherein the composite has an Fe2C:Fe2O3 molar ratio of about 1:1 to about 1:6; and/or the Fe2C nanoparticles have a diameter of about 5 nm to about 15 nm and the diameter of each of the particles varies by ±1.5 nm or less.

### Claim 12 (depends on 10)

The method of claim 10 wherein inverting the polarity of the hydrophobic nanoparticles comprises exchanging an alkylamine bound to the surface of the hydrophobic nanoparticles with a citrate ion to form hydrophilic nanoparticles.

### Claim 13 (depends on 10)

The method of claim 10 further comprising i) adding silica colloidal particles to the mixture; ii) removing silica from the composite with an alkaline solution to form a mesoporous composite; and iii) annealing the mesoporous composite in ammonia prior to applying HPHT; wherein the uniformly sized nanodiamond particles comprise fluorescent nitrogen vacancies.

### Claim 14 (depends on 13)

The method of claim 13 further comprising hydrogenating the nanodiamond particles to form neutral nitrogen vacancies.

### Claim 15 (depends on 13)

The method of claim 13 further comprising heating the nanodiamond particles in air to form negatively charged nitrogen vacancies.

### Claim 16 (depends on 10)

The method of claim 10 wherein the high pressure is about 6 GPa or more, or the high temperature is about 1200 K or more.

### Claim 17 (depends on 10)

The method of claim 10 wherein the applied HPHT is performed in a diamond anvil cell (DAC) at a pressure of 8 GPa to about 15 GPa and a temperature of about 1300 K to about 1500 K.

### Claim 18 (depends on 10)

The method of claim 10 further comprising dissolving a layer of iron oxide that encapsulates the nanodiamond particles with an acid.

### Claim 19 (depends on 10)

The method of claim 10 wherein the nanodiamond particles have a diameter of about 1 nm to about 5 nm, and the diameters of the particles vary by +0.3 nm or less.

### Claim 20 (depends on 1)

A method for forming uniformly sized fluorescent nanodiamond particles comprising:
a) inverting the polarity of hydrophobic iron carbide nanoparticles comprising exchanging an alkylamine bound to the surface of the hydrophobic nanoparticles with a citrate ion to form hydrophilic nanoparticles;
b) dispersing the hydrophilic nanoparticles in a pH neutral solution of iron(III) nitrate (Fe(NO3)3) and adding silica colloidal particles to form a mixture;
c) heating the mixture to form a colloidal gel;
d) calcining the colloidal gel in the presence of oxygen to form a composite of iron carbide (Fe2C) nanoparticles that are uniformly distributed in iron(III) oxide (Fe2O3), wherein the composite has an Fe2C:Fe2O3 molar ratio of about 1:1 to about 1:6, and/or the Fe2C nanoparticles have a diameter of about 5 nm to about 15 nm and the diameter of each of the particles varies by +1.5 nm or less;
e) removing silica from the composite with an alkaline solution to form a mesoporous composite;
f) annealing the mesoporous composite in ammonia;
g) applying a high pressure and high temperature (HPHT) to the annealed mesoporous composite suitable to form uniformly sized fluorescent nanodiamond particles according to claim 1, wherein the uniformly sized fluorescent nanodiamond particles comprise fluorescent nitrogen vacancies; and
h) optionally hydrogenating the nanodiamond particles to form neutral nitrogen vacancies and/or optionally heating the nanodiamond particles in the presence of oxygen to form negatively charged nitrogen vacancies.