Part 2: Reducing the Band-Gap Energy
To reduce the band-gap energy, our group speculates that doping TiO2 with other appropriate metal molecules via vapordeposition will be promising. Doping can either add an energy level filled with electrons in the band gap which can be easily excited into the conduction band (n-type) or add a level of extra holes in the band gap to allow the excitation of valence band electrons, to create mobile holes in the valence band (p-type). Hence, by doping with certain appropriate metal molecules, the band-gap energy of TiO2 will be reduced so that visible light is capable of supplying enough energy to generate e-/h+ pairs.
To Part 3: Preventing Recombination