[en] In this study was evaluated the adsorption capacity of trivalent chromium by using commercial activated carbon as adsorbent and elephant grass (Pennisetum purpureum) as bioadsorbent, which was prior treated by steam explosion technique and surfactant impregnated. The samples were characterized by SEM, XRD, XRF and FT-IR analysis. The effect of initial concentration of metal, pH, adsorbent dosage, contact time and temperature were further investigated in batch experiments. Isotherm, kinetic and thermodynamic studies were carried out in optimal process condition. The adsorption capacity reached a maximum of 28.36 mg g^-1 for modified SEEG sample. Thermodynamic parameters reveal that Cr3⁺ adsorption is a non-spontaneous and exothermic chemical process. The Langmuir isotherm model showed a well fit unless to the in nature Elephant Grass, which fitted well to Freundlich model. Furthermore, experimental data adjusted better to PSO kinetic model. So that, it was found that the modification techniques employed significantly enhanced the adsorption capacity of Cr³⁺. (author)

[en] Recent researches involving the mixture of semiconductor oxides with different bandgap energies have shown to be an important alternative to obtain catalysts with better photocatalytic properties. In this study, mixed oxides of α-Fe₂O₃/Nb₂O₅ were prepared from a Pechini sol-gel route, with two different mass ratios of α-Fe₂O₃ and Nb₂O₅ and varying calcination temperatures. The influence of these parameters was investigated on the materials structural, morphological, optical and photocatalytic properties. Crystalline nanoparticles were obtained with significant differences in their properties and in the degradation efficiency of the methylene blue dye under UV–vis radiation. Calcination temperatures between 500 and 800 °C led to the formation of different crystalline phases, including: α-Fe₂O₃, Nb₂O₅, FeNbO₄ and FeNb₂O₆; as well as the formation of materials with multigap behavior. High temperatures caused the increase of the particle size and the agglomerative state of the material. The catalysts produced have potential application for the treatment of effluents under solar radiation, in the presence or not of H₂O₂. (paper)