Spent bleaching clay from the oil refining industry was subjected to heat regeneration in a box furnace with air. The heat reactivation was conducted without previous extraction of residual oil and with previous extraction of oil using organic solvent. The experimental temperature ranged from 723 at 873 K. A model for the kinetic of thermal reactivation of spent adsorbent has been proposed. The activation energy involved on the desorption phenomenon was determined.

This work investigates the influence of reaction time (ranging from 12 to 96 h) on the characteristics of zinc stannate (Zn2SnO4) nanoparticles obtained by the hydrothermal method at 200°C. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), surface area measurements (BET) and infrared spectroscopy (IR). The results showed that the reaction time influenced the properties of Zn2SnO4 nanoparticles. The product presented a pure crystalline phase with mean particle size about 20 nm and BET surface area ranging from 34 to 43 m².g-1.

The aim of the present work was to verify the influence of the type of metal used in the presence of niobium pentoxide on the photocatalytic degradation of an industrial leather dye. Niobium oxide alone showed low photocatalytic activity, but with the impregnation of small quantities of metal, this material showed highly activity. It was observed that the type of metal significantly influenced the catalytic activity of niobium oxide. The results indicate that metal/Nb2O5 could be employed for the removal of dyes from wastewater. The order of photocatalytic activity of metal-doped Nb2O5 was as follows: (La, Zn, Ti) > (Sr, Sn, Ag) > (Co, V, Ga) > (Ni, Y, Cu). The metals Ce, Mn and Mo showed not efficient catalytic activity in degrading the leather dye

TiO2 powder was prepared by a hydrothermal process at 200°C for 12 h. The material was characterized by X-ray diffraction and N2 adsorption-desorption isotherm. The synthesized sample presented a pure phase anatase, with nanometric particle size. Its activity was tested for adsorption and degradation of the azo leather dye, Direct Black 38. The adsorption isotherm obtained followed the S-type in terms of the classification of Giles. Thermodynamic parameters were calculated, and the results revealed that the adsorption process is endothermic in nature. The material showed highly photocatalytic activity in the degradation of the dye, similar to that of the TiO2 (P25 Degussa) photocatalyst.

An investigation was carried out on the synthesis of titanium dioxide nanopowders via the hydrothermal method, examining the influence of temperature (150ºC and 200ºC) and reaction time (6 to 36 h). The resulting powders were characterized by X-ray diffraction, infrared absorption spectrophotometry, transmission electron micrographs and surface area. The X-ray diffraction revealed that there was formation of a pure crystalline phase, consisting only of anatase for all conditions of synthesis. Both temperature and reaction time proved to have a slight influence on the crystallite size (from 9 to 17 nm) and a significant influence on the surface area (from 86 to 168 m².g-1).