Resumo O objetivo deste trabalho foi avaliar a influência dos parâmetros de síntese de organofilização de uma bentonita sódica através da reação de troca catiônica. Os parâmetros avaliados foram: tempo de agitação, tempo de repouso e concentração do surfactante. A principal diferença desse estudo para a literatura publicada é o estudo dos tempos de agitação e de repouso. As argilas organofílicas obtidas foram caracterizadas por difração de raios X, espectroscopia de infravermelho com transformada de Fourier e teste de inchamento Foster realizado em água e hexano. Os resultados permitiram observar a intercalação do surfactante entre as camadas de bentonita, a baixa influência dos tempos de agitação e repouso e que o aumento do tempo de repouso gera maior eficiência no processo de organofilização. O teste de inchamento Foster evidenciou o caráter organofílico da argila obtida.

Abstract The aim of this study was to evaluate the influences of synthesis parameters on the organophilization of a sodium bentonite clay via interlayer cation exchange by organocations. The parameters analyzed were: stirring time, rest time and surfactant concentration. The novelty of this study, when compared to others reported on the literature data, is the evaluation of different stirring and rest times, which is usually used as 20 min and 24 h, respectively. The organoclays obtained were characterized via X-ray diffraction, Fourier transform infrared spectroscopy and Foster swelling test performed in water and hexane. The results allowed to observe the intercalation of the surfactant between the bentonite layers, the low influence of stirring and resting times on basal interplanar distance, and that the increase of the resting time resulted in higher efficiency on the organophilization process. The Foster swelling test evidenced the organophilic character of the obtained clay.

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

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).

O desenvolvimento de nanocompósitos para recobrimento de superfícies de partículas tem sido alvo de inúmeras pesquisas, devido ao fato de que novas e incomuns propriedades físicas e químicas, ausentes em tamanho macro e microscópico, são observadas nesses novos nanomateriais. Este trabalho apresenta o procedimento de preparação de nanocompósitos à base de nanoargila de haloisita nanorecoberta com TiO2 e Ni, usando o método dos precursores poliméricos. Através dessa síntese foram obtidas partículas de tamanho médio variando entre 7 e 35 nm. Os produtos obtidos foram caracterizados por fisissorção de N2 a 77 K, difração de raios X, microscopia eletrônica de varredura e microscopia eletrônica de transmissão de alta ressolução. Os resultados mostram que a obtenção do nanorecobrimento é uma estratégia altamente promissora para a fabricação de novos compósitos, baseados em TiO2/Ni na superfície da argila, com aplicações tecnológicas.

The development of nanocomposites for surface coating of particles have been the main focus of research in several areas. The new unusual physical and chemical properties absent in the same material in macro and microscopic size are observed in these new nanomaterials. This work presents a procedure for preparation of nanocomposites based on "halloysite nanoclay" particles nanocoated with TiO2 and Ni, using the polymeric precursor method. By means of this synthesis, particle size ranging between 7 and 35 nm were obtained. The products were characterized by size, physisorption of N2 at 77 K, X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. The results show that the preparation of nanocoatings is a highly promising strategy for the fabrication of novel composites based on TiO2/Ni on clay surfaces with technological applications.

Amorphous thin films of Pb1-xLaxTiO3 (with x=0, 13 and 27 mol %) were prepared by the polymeric precursor method and deposited by spin coating on glass substrates. The films were characterized by X-ray diffraction (XDR) and scanning electron microscopy (SEM) and the band gap energy of the amorphous PLT films was calculated from the UV-VIS spectra. The obtained values were compared to that theoretically calculated. The observed decrease of the band gap was attributed to increased density of defects in the amorphous structure. Futhermore photoluminescence (PL) at room temperature was observed for thin (PbLa)TiO3 films.

The CO2 reforming of CH4 was carried out over Ni catalysts supported on γ -Al2O3 and CeO2-promoted γ -Al2O3. The catalysts were characterized by means of surface area measurements, TPR, CO2 and H2 chemisorption, XRD, SEM, and TEM. The CeO2 addition promoted an increase of catalytic activity and stability. The improvement in the resistance to carbon deposition is attributed to the highest CO2 adsorption presented by the CeO2 addition. The catalytic behavior presented by the samples, with a different CH4/CO2 ratio used, points to the CH4 decomposition reaction as the main source of carbon deposition.

Neste trabalho são apresentados os procedimentos de preparação de materiais cerâmicos de SiO2, SnO2 e Al2O3 e, também, suas propriedades catalíticas nas reações de reforma do metano e do metanol. As análises dos resíduos de carbono, após testes catalíticos, sugerem que a modificação estrutural dos catalisadores pode minimizar os efeitos de sua desativação.

This work presents the procedures for preparing SiO2, SnO2 and Al2O3 ceramic materials and also their catalytic properties for the reforming reactions of methane and methanol. The analyses of the carbonaceous residues suggest that the structural modification of the catalyst can minimize the deactivation effect upon them.