This work reports the characterization of composites prepared by the association between zinc phthalocyanine (ZnPc) and titanium dioxide. These composites are better photocatalysts for wastewater decontamination mediated by solar radiation than pureTiO2, performance that remains even when reused. The UV-Vis diffuse reflectance absorption spectra show for these composites two intense absorption bands. The first covers the ultraviolet and part of the visible spectrum region until 460 nm (2.7 eV), whereas the second, nonstructured, goes from 475 nm until the near infrared with an absorption peak at 683 nm attributed to the Q band of ZnPc. The production of additionale−/h+pairs by these aggregates when photoexcited, their capability to act as charge carrier, the thickness and regularity of their distribution on theTiO2surface seem to be important parameters for the performance observed for these composites.

The sol-gel technique followed by conventional (TiO 2 -1) and hydrothermal (TiO 2 -2) thermal treatment was employed to prepare TiO 2 -based photocatalysts with distinct particle sizes and crystalline structures. The as prepared metal oxides were evaluated as photocatalysts for gaseous HCHO degradation, methanol, and dye oxidation reactions. Additionally, metallic platinum was deposited on the TiO 2 surfaces and H 2 evolution measurements were performed. The photocatalytic activities were rationalized in terms of morphologic parameters along with the electron/hole dynamics obtained from transient absorption spectroscopy (TAS).TiO 2 -2 exhibits smaller particle size, poorer crystallinity, and higher surface area than TiO 2 -1. Moreover the hydrothermal treatment leads to formation of the metastable brookite phase, while TiO 2 -1 exhibits only the anatase phase. TAS measurements show that the electron/hole recombination of TiO 2 -2 is faster than that of the later. Despite of that, TiO 2 -2 exhibits higher photonic efficiencies for photocatalytic oxidation reactions, which is attributed to its larger surface area that compensates the decrease of the surface charge carrier concentration. For H 2 evolution, it was found that the surface area has only a minor effect and the photocatalyst performance is controlled by the efficiency of the electron transfer to the platinum islands. This process is facilitated by the higher crystallinity of TiO 2 -1, which exhibits higher photonic efficiency for H 2 evolution than that observed for TiO 2 -2. The results found here provide new insights into the correlations between thermal treatment conditions and photocatalytic activity and will be useful for the design of high performance photocatalysts.

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In this work, the interaction between fisetin (3,3',4',7-tetrahydroxyflavone) (Fis) and cyclodextrins (CDs) (alpha and beta) was studied through UV-vis absorption, steady-state fluorescence, induced circular dichroism, and (1)H NMR experiments with dependence on temperature and pH. Some experimental data were compared with quantum-mechanics studies based on the SAM1 (AMPAC) semiempirical model, as well as with the B3LYP and MPW1PW91 functional models from density functional theory using the 6-311G and 3-21G basis sets. The spectroscopic measurements show that Fis does not form stable complexes with alpha-CD. On the other hand, at pH 4.0 and 6.5, the complex Fis-beta-CD is formed in a Fis:beta-CD 1:1 stoichiometry and an equilibrium constant (K) of 900 +/- 100 M(-1). In basic medium (pH 11.5), K decreases to 240 +/- 90 M(-1) because Fis deprotonation leads to its better solubilization in water. Molecular modeling points out that Fis is not totally inserted into the inner cavity of beta-CD. The formation of the inclusion complex renders an environment that enhances intramolecular excited state proton transfer. The inclusion complex is formed preferentially via entry of the Fis phenyl group into beta-CD.