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Transition metal oxide nanoparticles have been synthesized sonochemically from metal acetates. The metal oxide nanoparticles are characterized using X-ray diffraction (XRD), diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM), and BET nitrogen adsorption. The results of DRS are analyzed in detail, and the band gap energies for CuO, ZnO, and Co 3 O 4 are seen to be 2.18, 3.35, and 2.26 (3.40), respectively. Different particle sizes, morphology, and yields are observed when water and 10% water-N,Ndimethylformamide (DMF) are used as solvents, and the possible mechanisms are discussed.

A nanoporous TiO 2 electrode coated with a thin SrTiO 3 layer was synthesized for photoelectrochemical applications. Introduction of this core-shell electrode to a dye sensitized solar cell increased the open circuit photovoltage while reducing the short circuit photocurrent in comparison with a cell containing the standard noncoated TiO 2 electrode. The photovoltage increases is more significant than the photocurrent reduction resulting in a 15% improvement of the overall conversion efficiency of the solar cell. The performance of the TiO 2 -SrTiO 3 core-shell electrode in the dye sensitized solar cell was analyzed by several methods including photocurrent-voltage correlation, spectro-electrochemistry, dark current measurement, IPCE, and photovoltage spectroscopy. The results indicate that the SrTiO 3 layer shifts the conduction band of the TiO 2 in the negative direction rather than forming energy barrier at the TiO 2 /electrolyte interface as found for similar coating by other materials. The shift of the TiO 2 bands is attributed to a surface dipole that is induced by the SrTiO 3 coating.

Methanol is used to measure the yield of *OH radicals produced in the photolysis of H2O2 in aqueous solutions. The UV photolysis of H202 generates *OH radicals, which in the presence of methanol, oxygen, and phosphate buffer form formaldehyde, namely, phi(HCHO) = phi(*OH). The quantum yield of *OH has been redetermined in view of literature inconsistencies resulting in phi(*OH) = 1.11 +/- 0.07 in the excitation range of 205-280 nm. The constancy of phi(*OH) and the ease and sensitivity of the formaldehyde product analysis makes the H2O2/CH3OH system suitable for polychromatic UV actinometry. In addition, the relatively low cost of the main components and the possibility of destroying the methanol before disposal qualify the system for both monochromatic and polychromatic actinometry in a large volume of water. The H2O2/CH3OH system was applied in different commercial UV photoreactors.

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