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Photocatalytic TiO(2) powders impart ultraviolet light-induced self-cleaning and antibacterial functions when coated on outdoor building materials. For indoor applications, however, TiO(2) must be modified for visible-light and dark sensitivity. Here we report that the grafting of nanometer-sized Cu(x)O clusters onto TiO(2) generates an excellent risk-reduction material in indoor environments. X-ray absorption near-edge structure using synchrotron radiation and high-resolution transmission electron microscopic analyses revealed that Cu(x)O clusters were composed of Cu(I) and Cu(II) valence states. The Cu(II) species in the Cu(x)O clusters endow TiO(2) with efficient visible-light photooxidation of volatile organic compounds, whereas the Cu(I) species impart antimicrobial properties under dark conditions. By controlling the balance between Cu(I) and Cu(II) in Cu(x)O, efficient decomposition and antipathogenic activity were achieved in the hybrid Cu(x)O/TiO(2) nanocomposites.

The DFT method calculation was carried out to evaluate standard redox potential (SRP) for metal-to-metal cation and metal-to-metal complex systems. With the Born-Haber cycle, standard redox potential was composed of the cohesive energy, ionization energy, and solvation energy. The ligand exchange energy was added in case of metal complex. The solvent effects were incorporated by the self-consistent reaction field theory at the level of the polarized continuum model (PCM). At the highest level of calculations, the geometry optimization and harmonic frequency analysis were evaluated under the PCM. Utilizing experimental values of the cohesive energy of metals, the standard deviations between the calculated and experimental SRP values were 0.20-0.27 V depending on the calculation levels and basis sets used. For three Ag complexes with CN(-), S2O3(2-), and NH3 ligands, the discrepancy was within 0.3 V.

Aurivillius structure Bi(2)MoO(6) (BG: 2.70 eV) that is a low-temperature phase showed an intense absorption band in the visible light region and photocatalytic activity for O(2) evolution from an aqueous silver nitrate solution under visible light irradiation, among various bismuth molybdates (Bi(2)MoO(6), Bi(2)Mo(2)O(9), and Bi(2)Mo(3)O(12)) synthesized by solid-state and reflux reactions. Bi(2)Mo(3)O(12) (BG: 2.88 eV) also showed photocatalytic activity for O(2) evolution under full-arc irradiation of a Xe lamp (lambda > 300 nm). The photocatalytic activity of the Aurivillius structure Bi(2)MoO(6) prepared by the reflux method was dependent on the annealing temperature after the preparation. The crystallinity was the important factor for the activity. Calculation by the density functional method indicated that the conduction band of Aurivillius structure Bi(2)MoO(6) was made up of Mo 4d orbitals. It turned out that the visible-light absorption of this photocatalyst was due to the transition from the valence band consisting of O 2p orbitals to the conduction band. The corner-sharing structure of the MoO(6) octahedra contributed to the visible light response and the photocatalytic performance because excitation energy and/or photogenerated electron and hole pairs began to migrate easily in the Aurivillius structure.