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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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SynopsisAn investigation of the effect of modifying the network structure on moisture absorption of epoxies was performed. The network was modified by crosslinking the epoxides with various mono/diamine proportions, resulting in decreasing density and increasing free volume. It was discovered, however, that concomitant effects, i.e., the formation of a two-phase structure, and changes in resin polarity and in resin-water affinity predominated. Thus, compositions with higher chain molecular weights between crosslink points yet exhibited lower diffusion coefficients. Also, when drastic swelling conditions (such as a water-boil treatment) were employed, moisture absorption was facilitated by penetration via newly formed microcracks.

Radiative cooling devices should ideally operate with a shield substrate that completely blocks solar radiation but is transparent in the “atmospheric window” (8−13 μm) region. In this paper, we introduce a new type of shield for radiative cooling applications based on the use of polyethylene foils pigmented with nanocrystalline TiO2. Homogeneous shields were prepared by spreading colloidal suspension of TiO2 (rutile ca. 60 nm) between two polyethylene sheets followed by hot pressing. Optical and structural properties of the films were investigated using X-ray diffraction, TEM, and UV/vis/NIR and FTIR spectroscopy. The shields show high IR transmittance and high solar reflectance, which are favorable characteristics for solar radiation shields in radiative cooling devices. The mechanism for obtaining improved optical properties of nanocrystalline foils (in comparison with submicrometer bulk foils) is discussed with respect to both the materials and the shield preparation method. The simplicity and low-cost preparation of nanocrystalline TiO2 films, with their superior optical characteristics, could find widespread use in radiative cooling and other environmental applications.

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