Substrates comprising a photocatalytic TiO2 layer

• US 20050191505A1
• Filed: 01/07/2005
• Published: 09/01/2005
• Est. Priority Date: 07/09/2002
• Status: Active Grant

• Current Assignee: Leibniz-Institut für Neue Materialien gGmbH (INM)
• Original Assignee: Institut für Neue Materialien Gemeinnützige GmbH
• Inventors: Arpac, Ertugrul, Schmidt, Helmut, Akarsu, Murat
• Granted Patent: US 7,449,245 B2
• Time in Patent Office: Days
• US Class Current: 428/469
• CPC Class Codes: B01J 35/39 Photocatalytic properties
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01P 2002/30 Three-dimensional structures
• CPC Class Codes: C01P 2002/54 one element only
• CPC Class Codes: C01P 2004/62 Submicrometer sized, i.e. from 0.1-1 micrometer
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C03C 17/007 containing a dispersed phase, e.g. particles, fibres or flakes, in a continuous phase
• CPC Class Codes: C03C 2217/45 Inorganic continuous phases
• CPC Class Codes: C03C 2217/477 Titanium oxide
• CPC Class Codes: C03C 2217/71 Photocatalytic coatings
• CPC Class Codes: C03C 2218/113 by sol-gel processes
• CPC Class Codes: C09C 1/3684 Treatment with organo-silicon compounds
• CPC Class Codes: C23C 18/1216 Metal oxides C23C18/1212 takes precedence
• CPC Class Codes: C23C 18/1225 Deposition of multilayers of inorganic material
• CPC Class Codes: C23C 18/127 Preformed particles
• CPC Class Codes: Y10T 428/249967 Inorganic matrix in void-containing component
• CPC Class Codes: Y10T 428/249969 Of silicon-containing material [e.g., glass, etc.]
• CPC Class Codes: Y10T 428/24997 Of metal-containing material
• CPC Class Codes: Y10T 428/252 Glass or ceramic [i.e., fired or glazed clay, cement, etc.] [porcelain, quartz, etc.]

Abstract

Substrates comprising a photocatalytic layer containing TiO₂ are produced using TiO₂ particles which may optionally be doped with metallic or non-metallic elements or compounds. The photocatalytic layer exhibits a concentration gradient of the TiO₂ particles. An organically modified inorganic hybrid layer may be provided between the substrate and the photocatalytic layer.

Claims

1. A substrate comprising a photocatalytic layer, wherein the photocatalytic layer comprises photocatalytically active TiO₂ and a matrix material and the TiO₂ exhibits a concentration gradient in the matrix material such that the TiO₂ is enriched at a surface of the photocatalytic layer.

2. The substrate of claim 1, wherein a purely inorganic barrier layer is disposed between the photocatalytically active TiO₂ and the substrate.

3. The substrate of claim 1, wherein the photocatalytic layer comprises at least one of an inorganic matrix material and an organically modified inorganic matrix material.

4. The substrate of claims 1, wherein the TiO₂ comprises doped TiO₂.

5. The substrate of claim 4, wherein the doped TiO₂ comprises at least one of a metal, a semimetal, a nonmetal and compounds thereof.

6. The substrate of claim 5, wherein the doped TiO₂ exhibits photocatalytic activity within a region of visible light at wavelengths of >

380 nm.

7. The substrate of claim 1, wherein the substrate comprises an electrically conductive sublayer which is disposed below the photocatalytic layer.

8. The substrate of claim 1, wherein the substrate comprises a hybrid layer of an organically modified inorganic material, which layer is disposed below the photocatalytic layer.

9. The substrate of claim 8, wherein the substrate exhibits a concentration gradient of at least one of TiO₂ and organic groups.

10. The substrate of claim 1, wherein the photocatalytic layer comprises a microstructured photocatalytic layer.

11. A process for producing the substrate of claim 1, wherein the process comprises:

a) mixing TiO₂ particles with a surface modifier to form surface-modified TiO₂ particles which comprise organic groups,

b) adding at least one of an inorganic matrix-forming material and an organically modified inorganic matrix-forming material to the TiO₂ particles of a)to form a dispersion,

c) applying the dispersion of b) to the substrate,

d) hardening the applied dispersion to form a photocatalytic layer which has surface-modified TiO₂ particles enriched at a surface thereof, and

e) photocatalytically decomposing the organic groups of at least those surface-modified TiO₂ particles which are enriched at the surface of the photocatalytic layer.

12. The process of claim 11, wherein the surface modifier comprises at least one hydrophobic group.

13. The process of claim 12, wherein the at least one hydrophobic group comprises at least one of a fluorine atom, a long-chain aliphatic hydrocarbon group and an aromatic group.

14. The process of claim 11, wherein the surface modifier is selected from hydrolyzable silane compounds, carboxylic acids, carbonyl halides, carboxylic esters, carboxylic anhydrides, oximes, β

-dicarbonyl compounds, alcohols, amines, alkyl halides and derivatives thereof.

15. The process of claim 11, wherein the TiO₂ particles comprise TiO₂ particles that have been prepared by

i) preparing a mixture which comprises at least one hydrolyzable titanium compound having hydrolysable groups, water in a substoichiometric amount based on the hydrolyzable groups of the titanium compound, and an organic solvent,

ii) treating the mixture of i) at a temperature of at least 60°

C. to form a dispersion or a precipitate of TiO₂ particles, and

iii) optionally, removing solvent to form a powder of TiO₂ particles and, optionally, adding another solvent.

16. The process of claim 11, further comprising activation of the photocatalytic layer of d) by irradiation.

17. The process of claim 11, wherein the TiO₂ particles comprise nanoscale TiO₂ particles.

18. The process of claim 17, wherein the nanoscale TiO₂ particles have an average particle size of ≦

200 nm.

19. The process of claim 17, wherein the nanoscale TiO₂ particles have an average particle size of ≦

50 nm.

20. The process of claim 17, wherein the nanoscale TiO₂ particles have an average particle size of ≦

10 nm.

21. The process of claim 11, wherein d) comprises at least one of a heat treatment and an irradiation, and in the case of an irradiation the organically modified inorganic matrix-forming material has functional groups through which crosslinking is possible.

51. A substrate which is one of self-cleaning or capable of being cleaned with the aid of irradiation, wherein the substrate comprises the substrate of claim 1.

54. An article for use in the medical or hygiene sector, wherein the article comprises the substrate of claim 51.

22. A substrate comprising a photocatalytic TiO₂-containing layer, wherein a hybrid layer of an organically modified inorganic material comprising organic constituents is disposed between the substrate and the photocatalytic layer and wherein the organic constituents of the organically modified inorganic material have been decomposed photocatalytically at least at an interface to the photocatalytic TiO₂-containing layer to form a purely inorganic barrier layer.

23. The substrate of claim 22, wherein at least at the interface to the substrate the hybrid layer consists of an organically modified inorganic material.

24. The substrate of claim 22, wherein the photocatalytic TiO₂-containing layer comprises doped TiO₂.

25. The substrate of claim 24, wherein the doped TiO₂ comprises at least one of a metal, a semimetal, a nonmetal and compounds thereof.

26. The substrate of claim 25, wherein the doped TiO₂ exhibits photocatalytic activity within a region of visible light at wavelengths of >

380 nm.

27. The substrate of claim 22, wherein the substrate comprises an electrically conductive sublayer which is disposed below the photocatalytic layer.

28. The substrate of claim 22, wherein the photocatalytic layer comprises a microstructured photocatalytic layer.

29. A process for producing the substrate of claim 22, wherein the process comprises:

a) applying an organically modified inorganic matrix-forming material to the substrate to form a hybrid layer comprising organic constituents,

b) applying a composition comprising surface-modified TiO₂ particles having organic groups to the hybrid layer of a) to form the photocatalytic layer, the surface-modified TiO₂ particles having been prepared by mixing TiO₂ particles with a surface modifier, and

c) photocatalytically decomposing the organic groups of the surface-modified TiO₂ and the organic constituents of the hybrid layer at least in an interface region to the photocatalytic layer to form a purely inorganic barrier layer.

30. The process of claim 29, wherein the surface modifier comprises at least one hydrophobic group.

31. The process of claim 30, wherein the at least one hydrophobic group comprises at least one of a fluorine atom, a long-chain aliphatic hydrocarbon group and an aromatic group.

32. The process of claim 29, wherein the surface modifier is selected from hydrolyzable silane compounds, carboxylic acids, carbonyl, halides, carboxylic esters, carboxylic anhydrides, oximes, β

-dicarbonyl compounds, alcohols, amines, alkyl halides and derivatives thereof.

33. The process of claim 29, further comprising activation of the photocatalytic layer by irradiation.

34. The process of claim 29, wherein the organically modified inorganic matrix-forming material comprises a nanocomposite which comprises nanoscale inorganic particles.

35. The process of claim 34, wherein the nanoscale particles have a particle size of ≦

200 nm.

36. The process of claim 34, wherein the nanoscale particles comprise TiO₂ particles.

37. The process of claim 36, wherein the TiO₂ particles have an average particle size of ≦

200 nm.

38. The process of claim 37, wherein the TiO₂ particles have an average particle size of ≦

50 nm.

39. The process of claim 38, wherein the TiO₂ particles have an average particle size of ≦

10 nm.

40. The process of claim 29, wherein the organically modified inorganic matrix-forming material has been formed from at least one of an organically modified inorganic hydrolyzate and an organically modified inorganic polycondensate of at least one hydrolyzable compound which does not comprise a non-hydrolyzable organic group, and at least one hydrolyzable compound which comprises at least one non-hydrolyzable organic group, not more than 10 mol % of the at least one hydrolyzable compound containing a non-hydrolyzable organic group.

52. A substrate which is one of self-cleaning or capable of being cleaned with the aid of irradiation, wherein the substrate comprises the substrate of claim 22.

55. An article for use in the medical or hygiene sector, wherein the article comprises the substrate of claim 52.

41. A process for preparing a photocatalytically active TiO₂powder, wherein the process comprises

a) preparing a mixture comprising at least one hydrolyzable titanium compound comprising hydrolyzable groups, water in a substoichiometric amount based on the hydrolyzable groups of the titanium compound, and an organic solvent,

b) treating the mixture of a) at a temperature of at least 60°

C. to form a dispersion or a precipitate of TiO₂ particles, and

c) removing solvent to form a powder of TiO₂ particles.

42. The process of claim 41, wherein b) comprises at least one of a hydrothermal treatment and a heating under reflux.

43. The process of claim 41, wherein not more than 0.7 mol of water based on 1 mol of the hydrolyzable groups of the at least one titanium compound is used in a).

44. The process of claim 41, wherein the mixture of a) further comprises a dopant.

45. An agglomerate-free, photocatalytically active TiO₂ having an X-ray-determined volume average particle size of ≦

10 nm, obtainable by the process of claims 41.

46. A process for producing a substrate having a photocatalytic layer, wherein the process comprises

a) preparing a mixture comprising at least one hydrolyzable titanium compound comprising hydrolyzable groups, water in a substoichiometric amount based on the hydrolyzable groups of the titanium compound, and an organic solvent,

b) treating the mixture of a) at a temperature of at least 60°

C. to form a dispersion or a precipitate of TiO₂ particles,

c) optionally, removing solvent to form a powder of TiO₂ particles and adding a different solvent to form a dispersion of TiO₂ particles,

d) applying the dispersion of b) or c) to the substrate and

e) heat-treating the applied dispersion to form a photocatalytic layer.

47. The process of claim 46, wherein b) comprises at least one of a hydrothermal treatment and a heating under reflux.

48. The process of claim 46, wherein not more than 0.7 mol of water based on 1 mol of the hydrolyzable groups of the at least one titanium compound is used in a).

49. The process of claim 46, wherein the mixture of a) further comprises a dopant.

50. A substrate comprising a photocatalytic layer, obtainable by the process of claim 46.

53. A substrate which is one of self-cleaning or capable of being cleaned with the aid of irradiation, wherein the substrate comprises the substrate of claim 50.

56. An article for use in the medical or hygiene sector, wherein the article comprises the substrate of claim 53.