Sonosynthesis of nanostructured TiO2 doped with transition metals having variable bandgap

Here is described a sonosynthesis method to produce nanostructured TiO₂ pure and doped (Al, C, Co, Fe and Rh). The synthesized TiO₂ is amorphous and is transformed to anatase, brookite or rutile by heat treatments at temperatures between 100 and 300 °C. Pure TiO₂ can be partially transformed to brookite between 100 and 300 °C. The band gap in all heat treated samples from 100–600 °C is relatively constant, 3.2 eV, except for those doped with Fe. This effect on the band gap is the results of a bi/tri-crystal (anatase:brookite:rutile) framework. Rhodium is the most effective dopant to narrow the band gap, the opposite effect is observed with C. In single phase frameworks the bandgap can be modified ranges from 2.38 to 4.10 eV depending on the dopant. TiO₂ lattices are rigid enough to promote an outwards diffusion of the dopants to the surface of the particles forming nanostructured precipitates. The precipitates develop a network of quantum-dots with sizes between 5 and 10 nm.