The chemical-mineralogical characterization of rupestrian paintings in red, white, black and yellow colors, which decorate the rocky walls from the archaeological sites of Ema and Furna dos Índios (Inhuma, Piauí, Brazil) was performed. The chemical analyses were performed in situ by the non-invasive analytical technique X-ray fluorescence spectrometry (XRF) as well as in laboratory using a non-destructive approach, without previous sample preparation, and Raman microscopy, and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) techniques. The results, when together, allowed unequivocal identification of the main substances responsible for the color pigments, namely, hematite (red pigment), gypsum (white pigment), amorphous carbon from charcoal (black pigment) and goethite (yellow pigment).

ZnO/TiO2 nanocomposites were prepared by impregnating zinc acetate dihydrate on the surface of titanium dioxide P25, followed by thermal treatment at 350, 600, 750, and 900 °C, in order to investigate the TiO2 phase and titanate formation and the role of the latter in the photocatalytic activity of the nanocomposite. In the nanocomposites, the anatase-to-rutile transition is favored due to the presence of Zn2+, and the conversion is nearly complete at 750 °C. The presence of zinc metatitanate in the sample heated at 600 °C had no significant effect on the nanocomposite photocatalytic activity.

Hidroxo-sais lamelares de composição Cu2(OH)3X (X = NO3-, CH3COO- e ClO4-) foram sintetizados através da coprecipitação (sais básicos de nitrato e acetato) e da troca iônica (sal básico de perclorato). Os sólidos cristalinos foram caracterizados por difratometria de raios X, análise termogravimétrica e espectroscopia vibracional. Bandas fracas em 336 e 345 cm-1 (espectro Raman) dos sais de nitrato e perclorato, respectivamente, foram tentativamente atribuídas ao niCu-O (ânion). Os ions nitrato possuem simetria C2v no composto Cu2(OH)3NO3 e, consequentemente, observa-se o desdobramento dos modos E'. A quebra da degenerescência também é observada nos modos F2 do íon ClO4- livre, ocasionando o desdobramento das bandas em 630 e 1100 cm-1 no espectro do hidroxo-perclorato de cobre(II). A pequena diferença de energia entre os modos niasC-O e nisC-O (delta=143 cm-1) do sal de acetato sugere a presença de ligação de hidrogênio entre o oxigênio não coordenado do grupo carboxilato e um íon hidroxila adjacente. Os íons nitrato, acetato e perclorato estão coordenados ao cobre(II) de modo monodentado.

Copper hydroxy salts with a layer-type structure and general composition Cu2(OH)3X (X = NO3-, CH3COO- and ClO4-) were synthesized by co-precipitation (nitrate and acetate salts) and ion exchange (perchlorate salt) methods. The isolated polycrystalline solids were characterized by X-ray diffractometry, thermogravimetric analysis and vibrational spectroscopy. A weak band at 336 and 345 cm-1 (Raman spectrum) of the nitrate and perchlorate salts, respectively, was tentatively assigned to the nCu-O (anion). In Cu2(OH)3NO3 the nitrate ion has a C2v symmetry and, accordingly, a splitting in the E' modes is observed. The same happens to the hydroxy perchlorate salt with the degeneracy breakdown of the F2 modes (free ClO4-) at 630 and 1100 cm-1 leading to band splitting. For the carboxylate salt, the small difference in the energy of nuasC-O and nusC-O (delta=143 cm-1) suggests that hydrogen bonding with neighbor OH group may be present. Nitrate, carboxylate and perchlorate are monocoordinated to copper(II) in the investigated salts.

Raman dispersion refers to the dependence of the position of Raman bands on the energy of the exciting radiation. In this work, the three main models currently used to explain this phenomenon (Conjugated Length Model, Amplitude Mode Model and Effective Conjugation Coordinate Model) are discussed. Raman dispersion is a consequence of pi electron delocalization, but each model describes in a different way how pi electron delocalization affects the position of Raman bands. Here the features, qualities and problems of the three models are highlighted.