Water-splitting using photocatalytic porphyrin-nanotube composite devices

1. A method for generating hydrogen, the method comprising:

illuminating a porphyrin nanotube composite with light having a wavelength that is absorbed by a porphyrin nanotube of the porphyrin nanotube composite to generate a plurality of free electrons; and

reducing at least one hydrogen ion at a reduction catalyst, the reduction catalyst being affixed to the porphyrin nanotube, the step of reducing using the free electrons generated by illuminating the porphyrin nanotube.

2. The method of claim 1 , wherein the porphyrin nanotube composite comprises a multimolecular subunit comprising a combination of at least one porphyrin possessing a positive charge and at least one porphyrini possessing a negative charge, the multimolecular subunit forming a set of noncovalent bonds to a set of neighboring multimolecular subunits to form the porphyrin nanotube.

3. The method of claim 2 , wherein the at least one porphyrin possessing the positive charge comprises a metalloporphyrin with a coordinated metal ion.

4. The method of claim 3 , wherein the coordinated metal ion is selected from the group consisting of tin, antimony, zinc, and germanium.

5. The method of claim 1 , wherein the reduction catalysts is a tethered enzyme.

6. The method of claim 1 , wherein the reduction catalyst is a metal.

7. The method of claim 6 , wherein the metal is selected from the group consisting of Pt, Pd, Co, Ni, and combinations thereof.

8. The method of claim 1 , wherein the porphyrin nanotube comprises an interior surface and an exterior surface and the reduction catalyst is affixed to the exterior surface.

9. The method of claim 1 , wherein the porphyrin nanotube comprises an interior surface and an exterior surface and the reduction catalyst is affixed to the interior surface.

10. The method of claim 1 , wherein a porphyrin of the porphyrin nanotube is selected from the group consisting of an unreduced porphyrin and a reduced porphyrin.

11. A method for generating hydrogen, the method comprising:

illuminating a porphyrin nanotube composite comprising a porphyrin nanotube with light having a wavelength that is absorbed by the porphyrin nanotube to generate a plurality of free electrons;

reducing at least one hydrogen ion at a reduction catalyst, the reduction catalyst being affixed to the porphyrin nanotube, using the free electrons generated by illuminating the porphyrin nanotube; and

oxidizing at least one water at an oxidation catalyst, the oxidation catalyst being electrically connected to the porphyrin nanotube composite to provide a current path between the oxidation catalyst and the reduction catalyst.

12. The method of claim 11 , wherein the porphyrin nanotube composite comprises the porphyrin nanotube, the porphyrin nanotube having an outer surface and a hollow interior with an inner surface, a metal nanorod within the hollow interior of the porphyrin nanotube, the metal nanorod having a first end and a second end, and a metal protuberance attached to the first end of the metal nanorod.

13. The method of claim 12 , wherein the oxidation catalyst and the porphyrin nanotube composite are connected by a plurality of binding molecules.

14. The method of claim 13 , wherein the binding molecules are selected from the group consisting of molecules which can attach to the oxidation catalyst and provide a functional group for attachment to the porphyrin nanotube composite, the functional group being selected from the group consisting of a thiol group and an amino group.

15. The method of claim 13 , wherein the binding molecules are selected from the group consisting of (3-mercaptopropyl)trimethoxysilane and (3-aminopropyl)trimethoxysilane.

16. The method of claim 12 , wherein the metal nanorod and the metal protuberance comprise a metal selected from the group consisting of Au, Pt, Pd, Fe, Co, Ni, Cu, Pb, and combinations thereof.

17. The method of claim 12 , wherein the reduction catalyst is affixed to the outer surface of the porphyrin nanotube.

18. The method of claim 17 , wherein the reduction catalyst is selected from the group consisting of Pt, Pd, Co, Ni, and combinations thereof.

19. The method of claim 11 , wherein the oxidation catalyst comprises a semiconductor.

20. The method of claim 11 , wherein the oxidation catalyst is selected from the group consisting of WO 3 , BiVO 4 , Fe 2 O 3 , TiO 2 , RuO 2 , IrO 2 , and Na 2 B 4 O 7 .

21. A method for generating hydrogen, the method comprising:

illuminating a porphyrin nanotube composite with light, the porphyrin nanotube composite comprising a porphyrin nanotube and a reduction catalyst affixed to a surface of the porphyrin nanotube, the porphyrin nanotube having an outer surface and a hollow interior with an inner surface and the light having a wavelength that is absorbed by the porphyrin nanotube to generate a plurality of free electrons; and

reducing at least one hydrogen ion at the reduction catalyst using the free electrons generated by illuminating the porphyrin nanotube.

22. The method of claim 21 , wherein the reduction catalyst is a metal selected from the group consisting of Pt, Pd, Co, Ni, and combinations thereof.

23. The method of claim 21 , wherein the porphyrin nanotube composite further comprises a metal deposit on the outer surface of the porphyrin nanotube.

24. The method of claim 23 , wherein the metal deposit comprises a metal selected from the group consisting of Au, Pt, Pd, Ag, Fe, Co, Ni, Cu, Pb, and combinations thereof.

25. The method of claim 23 , wherein the porphyrin nanotube composite is affixed to an oxidation catalyst, the porphyrin nanotube composite being electrically connected to the oxidation catalyst to provide a current path between the oxidation catalyst and the reduction catalyst.

26. The method of claim 21 , wherein the reduction catalyst is located within the hollow interior.

27. The method of claim 21 , wherein the reduction catalyst is affixed to the outer surface.