Nanocrystalline heterojunction materials

• US 20020071970A1
• Filed: 05/16/2001
• Published: 06/13/2002
• Est. Priority Date: 10/01/1999
• Status: Active Grant

• Current Assignee: Battelle Memorial Institute
• Original Assignee: Battelle Memorial Institute
• Inventors: Gao, Yufei, Su, Yali, Heald, Steve M., Elder, Scott H.
• Granted Patent: US 6,592,842 B2
• Time in Patent Office: Days
• US Class Current: 428/702
• CPC Class Codes: B01J 21/063 Titanium; Oxides or hydroxides thereof
• CPC Class Codes: B01J 35/30 characterised by their physical properties
• CPC Class Codes: B01J 35/39 Photocatalytic properties
• CPC Class Codes: B01J 35/40 characterised by dimensions, e.g. grain size in a colloidal state B01J35/23; crystallite size B01J35/77

Abstract

Mesoporous nanocrystalline titanium dioxide heterojunction materials are disclosed. In one disclosed embodiment, materials comprising a core of titanium dioxide and a shell of a molybdenum oxide exhibit a decrease in their photoadsorption energy as the size of the titanium dioxide core decreases.

Claims

1. A heterojunction material, comprising:

a nanocrystalline titanium dioxide phase; and

a second metal oxide phase, wherein the nanocrystalline titanium dioxide phase is chemically bonded to the second metal oxide phase through a heterojunction formed at an interface between the nanocrystalline titanium dioxide phase and the second metal oxide phase.

2. The heterojunction material of claim 1, wherein the nanocrystalline titanium dioxide phase is anatase.

3. The heterojunction material of claim 1, wherein the material exhibits a photoabsorption energy lower than 3.2 eV.

4. The heterojunction material of claim 1, wherein the second metal oxide phase forms a shell around a core comprising the nanocrystalline titanium dioxide phase, the heterojunction formed at the interface between the shell and the core.

5. The heterojunction material of claim 4, wherein the shell comprises from less than a complete monolayer to one or more monolayers of the second metal oxide.

6. The heterojunction material of claim 4, wherein the shell is molybdenum oxide and the core is nanocrystalline anatase.

7. The heterojunction material of claim 6, wherein the molybdenum oxide phase has a structure substantially similar to bulk α

-MoO₃.

8. A method for preparing mesoporous nanocrystalline titanium dioxide heterojunction materials, comprising:

combining in water, a water-soluble titanium chelate, a cationic surfactant, and a water-soluble polyoxometallate cluster of a second metal to form a solution containing micelles of the surfactant, the solution yielding a precipitate spontaneously or after further addition of water, and

aging the precipitate hydrothermally.

9. The method of claim 8, wherein the water-soluble polyoxometallate cluster of the second metal comprises an octahedral arrangement of metal and oxygen atoms.

10. The method of claim 9, wherein the water-soluble polyoxometallate cluster of the second metal comprises octahedral units of structure MO₆ where M is chosen from the group consisting of V, W, Nb, Mo, Al and combinations thereof.

11. The method of claim 9, further comprising establishing the pH of the solution at a level suitable to stabilize the octahedral arrangement of metal and oxygen atoms in the cluster.

12. The method of claim 11, wherein the second metal is selected from the group consisting of Al, Mo, W, V and combinations thereof and the pH of the solution is from 3 to 6.

13. The method of claim 11, wherein the second metal is Nb and the pH of the solution is from 10 to 13.

14. The method of claim 9, wherein the octahedral arrangement further comprises edge-sharing octahedra of metal and oxygen atoms.

15. The method of claim 8 wherein the water-soluble polyoxometallate cluster is anionic.

16. The method of claim 15, wherein the water-soluble polyoxometallate cluster is chosen from the group consisting of Mo₈O₂₆⁴⁻

, V₁₀O₂₈⁶⁻

, Nb₆O₁₉⁸⁻

, W₁₂O₃₉⁶⁻

, and mixtures thereof.

17. A method for preparing mesoporous nanocrystalline titanium dioxide heterojunction materials, comprising:

combining in water, a water-soluble titanium chelate, a cationic surfactant, and an anionic water-soluble polyoxometallate cluster of a second metal to form a solution;

the solution having a pH from 3 to 6 if the second metal is selected from the group consisting of Al, V, W, Mo, and mixtures thereof;

the solution having a pH from 10 to 13 if the second metal is Nb;

the solution yielding a precipitate spontaneously or after further addition of water; and

aging the precipitate hydrothermally.