Abstract Copper oxide (CuO) is a heterogeneous catalyst applied with success in several systems like vegetable oils transesterifications. The Ce-dopoing CuO is a promisor material with a potential improve catalysis performances. In this work, CuO and Ce-doping CuO were synthesized by the microwave hydrothermal method in only 5 min at low temperature (100 oC) without templates or other petroleum dependent organic substances, using only copper and cerium nitrates and sodium hydroxide as a precursors. Both materials were applied as photocatalysts for the degradation of remazol golden yellow dye (RNL). X-ray diffraction analysis showed that CuO and Ce-doped CuO has monoclic copper oxide structure without secondary phases. SEM analysis showed the Ce-doping full modify the CuO powder morphology. The dye RNL degradation rate of Ce-doping CuO was bigger than pure CuO and the expensive CeO2.

CuO structures were synthesized by microwave hydrothermal treatment using two different mineralizing agents (NaOH and NH4OH) and were evaluated as photocatalysts. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area analysis. The XRD patterns indicated the formation of the monoclinic phase in both samples with 13.78 and 14.23 nm crystallite size. SEM analysis showed different agglomerates morphologies based on the mineralization agent employed. The CuO nanostructure synthesized with NH4OH presented agglomerated like-plates which results in a spherical shape, whereas the material synthesized with NaOH presented an agglomerate of larger plates. Both samples showed photocatalytic activity against RNL azo dye. The quasi-spherical shape CuO material reached 93 % of the discoloration.

In the last ten years, stannates with perovskite structure have been tested as photocatalysts. In spite of the ability of perovskite materials to accommodate different cations in its structure, evaluation of doped stannates is not a common task in the photocatalysis area. In this work, Fe3+ doped BaSnO3 was synthesized by the modified Pechini method, with calcination between 300 and 800ºC/4 h. The powder precursor was characterized by thermogravimetry after partial elimination of carbon. Characterization after the second calcination step was done by X-ray diffraction, Raman spectroscopy and UV-visible spectroscopy. Materials were tested in the photocatalytic discoloration of the Remazol Golden Yellow azo dye under UVC irradiation. Higher photocatalytic efficiency was observed under acid media. As no meaningful adsorption was observed at this condition we believe that an indirect mechanism prevails. Fe3+ doping decreased the band gap and favored the photocatalytic reaction, which may be assigned to the formation of intermediate levels inside the band gap.

In this work, aqueous suspensions of aluminas with different particle sizes were evaluated. The effect of pH on the electrosteric stabilization using PMAA-NH4 (ammonium polymethacrylate) as deflocculant was studied. The amount of deflocculant was optimized and rheologic properties were determined at four different pH values. Sedimentation was also evaluated. For suspensions with pH 4, an electrostatic mechanism of stabilization was observed, probably due to a flat adsorption of PMMA- on the alumina surface, leading to a small efficiency in relation to steric stabilization. For a suspension with pH 12, the steric mechanism of stabilization prevails. Suspensions with pH 7 and 9 present a higher flocculation degree. In relation to particle size, A-1000 samples present a smaller particle size, leading to a smaller interparticle distance (IPS), making stabilization more difficult.

Oxides with spinel structures have been studied for many decades as they have been used in a variety of applications like pigments and refractories. They have also been used as a model structure to evaluate the relative stability of ions in octahedral and tetrahedral sites. Zinc- antimony spinels (Zn7Sb2O12) were synthesized by the Pechini method and the cation Zn2+ was substituted by Co2+, taking into consideration the stoichiometry of Co xZn7-xSb2O12 (x = 0 - 7). Characterization of the thermal properties of pyrolyzed powders was carried out with a TG/DTA analyzer, and mass losses were determined as a function of the cobalt content in the resin. The powders were calcined at temperatures in the range 600 to 1000 °C and characterized by XRD, BET and IR spectroscopy. Maximum cristalinity was obtained in powders calcined at 1000 °C. Materials with x = 5 - 7 revealed the presence of a secondary phase (Co, Zn)Sb2O6. Infrared analysis facilitated in the determination of the possible sites of Zn2+, Co2+ and Sb2+ ions in the lattice.