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A density functional theory (DFT) method (periodic DMol3) with full geometry optimization was used to study the adsorption of nitrogen-containing heterocycles such as pyrazole, imidazole, 1,2,4-triazole, pyridine, pyrimidine, pyrazine, and 4-t-butylpyridine (TBP) on TiO2 anatase (101), (100), and (001) surfaces. All structures displayed a negative shift in the TiO2 Fermi level upon adsorption of N-containing heterocycles. Additionally, the heterocycles were examined as an additive in an I-/I3- redox electrolyte solution of dye-sensitized TiO2 solar cell. The DFT results indicated that the negative shift of TiO2 Fermi level was due to the adsorbate dipole moment component normal to the TiO2 surface plane, and corresponded to the enhanced open-circuit photovoltage (Voc) and the reduced short-circuit photocurrent density (Jsc) in a dye-sensitized solar cell.

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Cs-modification effects of WO3 on photocatalytic O2 evolution and Fe (III) ion reduction over WO3 under visible light irradiation were investigated. WO3 having cation-exchange ability at the surface was successfully prepared by hydrothermal and impregnation methods using cesium aqueous solutions. The photocatalytic activity of Cs-modified WO3 was partially improved by the ion-exchange of Cs+ for H+ and Fe2+, and more than 10 times higher than that of WO3 without any treatment. The optimized WO3 showed 48 times higher quantum efficiency (19% at 420 nm) than that reported previously under visible light, and showed a high solar-to-chemical energy conversion efficiency (ηsun = 0.3%). This ηsun value is comparable to the solar-to-product energy conversion efficiencies of natural plant photosynthesis for biomass energy.

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