First-principles Calculation On Photocatalytic Performance Of TiO₂

Based on ultrasoft pseduopotentia plane wave method, the photocatalytic performance of Rutile/Anatase TiO₂ mixed crystal was evaluated by first principle calculation. The photo adsorption capacity, the separation efficiency of photo-induced electron-hole pair and the transfer probability of charge carrier were all investigated. The results showed that the separation efficiency of electron-hole pair for mixed TiO₂ was clearly higher than single phase TiO₂ ( Rutile or Anatase), and the red-shifting of adsorption peaks was observed notably, which confirmed that the photocatalytic performance of mixed crystal nano-TiO₂ is superior to the single phase TiO₂.Density functional theory (DFT) in periodic DMol3 program was employed to investigate the sensitization mechanism and electronic structural of tris ( 8- hydroxyquinoline -5- carboxylic acid) iron (â…¢), tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) and tris ( 8- hydroxyquinoline -5- sulfonic acid) iron(â…¢) on TiO₂ anatase (101) surface. These sensitizers possesses a very small HOMO (the highest occupied molecular orbital)- LUMO(the lowest unoccupied molecular orbital) energy gap, and this allows for easy electron excitation from HOMO to the LUMO. As the nanocrystalline TiO₂ adsorbs the sensitizer, the energy of the HOMO level, the LUMO and Fermi level increase, These changes lead to an enhancement of the open-circuit photovoltage (VOC) in dye-sensitized TiO₂ solar cells.In addition, we theoretically determined the sensitization mechanis+m of tris (8- hydroxyquinoline -5- carboxylic acid) iron (â…¢) and tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) dyes that are attached by carboxylic acid anchor groups to TiO₂ anatase (101) surface; But tris ( 8- hydroxyquinoline -5- sulfonic acid) iron(â…¢) dyes are attached by sulfonic acid anchor groups to TiO₂ anatase (101) surface. The Energy gap of tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) dyes is larger than the other two sensitizers, and can match the ELUMO level of TiO₂ very well. tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) adsorption more negatively shifted the Fermi level than the other sensitizers adsorption, which corresponded to the enhancement of the Voc values. Consequently, the molecular adsorption of tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) is energetically more favoured than those of the other adsorbed molecules.