Nanostructures, Systems, and Methods for Photocatalysis

• US 20120267234A1
• Filed: 04/20/2012
• Published: 10/25/2012
• Est. Priority Date: 04/22/2011
• Status: Active Grant

• Current Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Original Assignee: Sun Catalytix Corporation (Martin Marietta Corporation)
• Inventors: Reece, Steven Y., Jarvi, Thomas D.
• Granted Patent: US 9,205,420 B2
• Time in Patent Office: Days
• US Class Current: 204/157.5
• CPC Class Codes: B01J 19/127 Sunlight; Visible light
• CPC Class Codes: B01J 19/2475 Membrane reactors
• CPC Class Codes: B01J 23/745 Iron
• CPC Class Codes: B01J 35/23 in a colloidal state
• CPC Class Codes: B01J 35/39 Photocatalytic properties
• CPC Class Codes: B01J 35/58 Fabrics or filaments
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01B 13/0207 Water
• CPC Class Codes: C01B 3/042 Decomposition of water
• CPC Class Codes: C25B 1/55 Photoelectrolysis
• CPC Class Codes: Y02E 60/36 Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
• CPC Class Codes: Y02P 20/133 Renewable energy sources, e.g. sunlight

Abstract

The present invention generally relates to nanostructures and compositions comprising nanostructures, methods of making and using the nanostructures, and related systems. In some embodiments, a nanostructure comprises a first region and a second region, wherein a first photocatalytic reaction (e.g., an oxidation reaction) can be carried out at the first region and a second photocatalytic reaction (e.g., a reduction reaction) can be carried out at the second region. In some cases, the first photocatalytic reaction is the formation of oxygen gas from water and the second photocatalytic reaction is the formation of hydrogen gas from water. In some embodiments, a nanostructure comprises at least one semiconductor material, and, in some cases, at least one catalytic material and/or at least one photosensitizing agent.

Claims

1. A nanostructure, comprising:

a first region comprising a first material that catalyzes the formation of O₂ from water; and

a second region comprising a second material that catalyzes a reduction reaction,

the first and second regions comprising semiconductors.

2. The nanostructure of claim 1, wherein the reduction reaction is the formation of H₂ from water.

3. The nanostructure of claim 1, wherein the reduction reaction comprises the reduction of CO₂.

4. The nanostructure of claim 1, wherein the reduction reaction comprises the reduction of N₂.

5. The nanostructure of claim 1, wherein the nanostructure further comprises at least one photosensitizing agent.

6. The nanostructure of claim 1, wherein the nanostructure comprises at least one surface-presenting catalytic material.

7. The nanostructure of claim 1, wherein the first region comprises a first type of semiconductor material and the second region comprises a second type of semiconductor material.

8. The nanostructure of claim 1, wherein the first region comprises an n-type semiconductor material and the second region comprises a p-type semiconductor material.

9. The nanostructure of claim 8, wherein a p/n-junction is present between the first region and the second region.

10. The nanostructure of claim 1, wherein a heterojunction is present between the first region and the second region.

11. The nanostructure of claim 7, wherein the first type of semiconductor material and the second type of semiconductor material comprise the same or different metal oxides and/or metal hydroxides.

12. The nanostructure of claim 7, wherein the first type of semiconductor material and the second type of semiconductor material comprise doped iron oxide.

13. The nanostructure of claim 1, wherein the first region comprises a first type of surface-presenting catalytic material and/or the second region comprises a second type of surface-presenting catalytic material.

14. The nanostructure of claim 13, further comprising a bulk material, wherein at least one of the first type of surface-presenting catalytic material or the second type of surface-presenting catalytic material is different than the bulk material.

15. The nanostructure of claim 14, wherein the bulk material comprises a semiconductor material.

16. The nanostructure of claim 15, wherein the bulk material comprises a first type of semiconductor material and a second type of semiconductor material.

17. The nanostructure of claim 14, wherein the first type of surface-presenting catalytic material is associated with the bulk comprising the first type of semiconductor material and the second type of catalytic material is associated with the bulk comprising the second type of semiconductor material.

18. The nanostructure of claim 16, wherein the first bulk type of semiconductor material comprises an n-type semiconductor material and the second bulk type of semiconductor material comprises a p-type semiconductor material.

19. The nanostructure of claim 13, wherein the first surface-presenting catalytic material comprises a metal ionic species in an oxidation state greater than zero and one or more anionic species.

20. The nanostructure of claim 13, wherein the second surface-presenting catalytic material comprises the metal ionic species in an oxidation state of zero.

21. The nanostructure of claim 13, wherein the first surface-presenting catalytic material comprises a metal oxide.

22. The nanostructure of claim 13, wherein the second surface-presenting catalytic material comprises a metal.

23. The nanostructure of claim 22, wherein the first and the second surface-presenting catalytic materials comprise cobalt, nickel, or both .

24. The nanostructure of claim 13, wherein the first catalytic surface-presenting material further comprises one or more anionic species.

25. The nanostructure of claim 24, wherein the anionic species comprise phosphorus, boron, or both.

26. The nanostructure of claim 25, wherein the anionic species is selected from the group comprising forms of phosphate, forms of sulphate, forms of carbonate, forms of arsenate, forms of phosphite, forms of silicate, or forms of borate.

27. The nanostructure of claim 1, wherein the nanostructure comprises a nanowire, a nanorod, a nanotube, a nanoparticle, or any combination thereof.

32. The nanostructure of claim 1, wherein a surface-presenting second catalytic material is associated with the second region.

33. The nanostructure of claim 32, wherein the first surface-presenting catalytic material and the surface-presenting second catalytic material comprises cobalt and/or nickel.

39. A method, comprising:

exposing, to electromagnetic radiation, a plurality of nanostructures, at least one of which is a nanostructure according to claim 1; and

catalyzing the formation of O₂ from water.

40. A method, comprising:

exposing, to electromagnetic radiation, a plurality of nanostructures, at least one of which is a nanostructure according to claim 1; and

effecting a reduction reaction involving at least some of the nanostructures.

28. A nanostructure, comprising:

an iron oxide and comprising a first, n-type region and a second, p-type region.

29. The nanostructure of claim 28, wherein the n-type region comprises a first material that catalyzes the formation of O₂ from water.

30. The nanostructure of claim 28, wherein the p-type region comprises a second material that catalyzes a reduction reaction.

31. The nanostructure of claim 28, wherein a first surface-presenting catalytic material is associated with the first region.

34. The nanostructure of claim 31, wherein the first catalytic material further comprises anionic species comprising phosphorus and/or boron.

35. The nanostructure of claim 28, wherein the nanostructure comprises a nanorod, a nanowire, a nanotube, or a nanoparticle.

36. A photocatalytic device comprising a plurality of nanostructures according to claim 28.

37. The photocatalytic device of claim 36, wherein the plurality of nanostructures is provided in a solution.

43. The nanostructure of claim 28, wherein a p/n-junction is present between the first, n-type region and a second, p-type region.

38. A method of forming a system, comprising:

providing a semiconductor substrate;

exposing the semiconductor substrate to a solution comprising at least one metal ionic species and an anionic species; and

exposing the semiconductor substrate to electromagnetic radiation so as to form a first surface-presenting catalytic material comprising a reduced metal species in a first region and a second surface presenting catalytic material comprising an oxidized metal species in a second region.

41. A composition comprising a catalytic material that catalyzes the production of H₂ from water in the presence of O₂;

the catalytic material being capable of catalyzing the production of H₂ at a current density at least 1000 times greater than the current density for the reduction of O₂ at the catalytic material, at overpotentials less negative than −

400 mV for the production of H₂ from water.

42. A device for solar energy conversion, the device comprising the composition described in claim 41.