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Mesoporous nanocrystalline titanium dioxide heterojunction materials and methods of making the same 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 tita

Mesoporous nanocrystalline titanium dioxide heterojunction materials and methods of making the same 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.

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1. 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 sur

1. 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. 2. The method of claim 1, wherein the water-soluble polyoxometallate cluster of the second metal comprises an octahedral arrangement of metal and oxygen atoms. 3. The method of claim 2, wherein the water-soluble polyoxometallate cluster of the second metal comprises octahedral units of structure MO6where M is chosen from the group consisting of V, W, Nb, Mo, Al and combinations thereof. 4. The method of claim 2, 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. 5. The method of claim 4, 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. 6. The method of claim 4, wherein the second metal is Nb and the pH of the solution is from 10 to 13. 7. The method of claim 2, wherein the octahedral arrangement further comprises edge-sharing octahedra of metal and oxygen atoms. 8. The method of claim 1, wherein the water-soluble polyoxometallate cluster is anionic. 9. The method of claim 8, wherein the water-soluble polyoxometallate cluster is chosen from the group consisting of Mo8O264-,V10O286-,Nb6O198-,W12O396-,and mixtures thereof. 10. The method of claim 1, wherein the water-soluble titanium chelate comprises a chelate of titanium with an alpha-hydroxy acid. 11. The method of claim 10, wherein the alpha-hydroxy acid is lactic acid. 12. The method of claim 11, wherein the water soluble titanium chelate is (NH4)2Ti(OH)2(C3H4O2)2. 13. The method of claim 10, wherein the cationic surfactant comprises a tetraalkyl ammonium surfactant. 14. The method of claim 10, wherein the cationic surfactant comprises a tetraalkyl ammonium surfactant with at least one carbon chain of 8 to 24 carbons. 15. The method of claim 10, wherein the cationic surfactant comprises cetyltrimethylammonium chloride. 16. The method of claim 10 further comprising removing a micelle template formed by the surfactant. 17. The method of claim 16, wherein the micelle template is removed by calcining the precipitate. 18. The method of claim 16, wherein the micelle template is removed by solvent extraction of the precipitate. 19. 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.