Recent studies on tungsten oxide preparation are mainly motivated by its applications in smart windows, energy harvesting and, recently, in cancer therapy. Peroxotungstic acid (PTA) is an important precursor to obtain tungsten oxide in an environmentally-friendly way, through the colloidal synthesis in aqueous media. Despite giving chemically pure products, PTA originates oxides with various morphologies depending on the experimental conditions, a subject open to discussion. PTA, in the presence of sodium dodecyl sulfate (SDS) as architecture-directing agent, was investigated in ethanol/water medium by small angle X-ray scattering (SAXS), fluorescence, surface tension and conductivity measurements; the morphology of tungsten oxide obtained from the precursor systems was also characterized by scanning electron microscopy (SEM). PTA/SDS/ethanol/water systems show a two-level organization in which small micelles are aggregated as fractal structures. There is an inverse correlation between gyration radius of the fractal structures of the PTA/SDS systems and particle size of the tungsten oxide films. The interaction of PTA with SDS is observed by reducing the Gibbs energy of micellization; also, it is evidenced that the supressive effect of PTA on pyrene emission is overrided in presence of SDS.

Óxidos de tungstênio apresentam diferentes estequiometrias, estruturas cristalinas e morfologias. Estas características são importantes principalmente quando se deseja utilizá-los como fotocatalisadores. Neste trabalho foram obtidos filmes finos de óxido de tungstênio por evaporação térmica sobre substratos de silício (100) recobertos com ouro, aquecidos a 350 e 600 ºC. A estequiometria dos filmes formados, morfologia, estrutura cristalina e resistência à lixiviação foram caracterizadas por espectroscopia de fotoelétrons de raios X, espectroscopia micro-Raman, microscopias eletrônicas de varredura e transmissão, difratometria de raios X, espectrometria de retroespalhamento Rutherford e reação nuclear ressonante O16(α,α')O16. Os filmes apresentam estrutura nanométrica, cuja forma torna-se bem definida com o aumento da temperatura. O sistema apresenta-se na forma de WO3.1 e cristaliza principalmente na fase hexagonal, sendo obtidas também estruturas de óxido de tungstênio hidratadas. Os filmes obtidos através de evaporação térmica apresentam resistência à lixiviação em ambiente aquoso e excelente atividade fotocatalítica, que foi testada na degradação do corante alaranjado de metila.

Tungsten oxides show different stoichiometries, crystal lattices and morphologies. These characteristics are important mainly when they are used as photocatalysts. In this work tungsten oxide thin films were obtained by thermal evaporation on (100) silicon substrates covered with gold and heated at 350 and 600 ºC, with different deposition times. The stoichiometry of the films, morphology, crystal structure and resistance to leaching were characterized through X-ray photoelectron spectroscopy, micro-Raman spectroscopy, scanning and transmission electron microscopy, X-ray diffractometry, Rutherford backscattering spectrometry and O16(α,α')O16 resonant nuclear reaction. Films obtained at higher temperatures show well-defined spherical nanometric structure; they are composed of WO3.1 and the presence of hydrated tungsten oxide was also observed. The major crystal structure observed is the hexagonal. Thin films obtained through thermal evaporation present resistance to leaching in aqueous media and excellent performance as photocatalysts, evaluated through the degradation of the methyl orange dye.

Bandas de rodagem de sucatas de pneus apresentam baixos teores de cargas inorgânicas e grande quantidade de negro de fumo em sua formulação. Neste trabalho, esse material foi tratado com hidróxido de potássio e cloreto de zinco e, em seguida, realizou-se a pirólise a 500 e 700 °C. Foi investigado o desempenho dos produtos na remoção dos corantes azul de metileno e alaranjado de metila em condições ambientais de pH e concentração. Carbonos obtidos com KOH e pirólise a 700 °C apresentam uma melhor capacidade de adsorção. A simulação deste processo permitiu a caracterização dos gases que contribuem para o desenvolvimento da superfície. Os produtos obtidos apresentam estrutura mesoporosa e estreita distribuição no tamanho de partícula. A presença de contaminantes oriundos desses carbonos foi investigada em meio aquoso. A ausência de zinco e enxofre e o excelente desempenho para remoção de corantes fazem esses materiais úteis no tratamento de água.

Treads of scrap tires present low contents of inorganic fillers and a large amount of carbon black. In this work, this material was treated with potassium hydroxide and zinc chloride followed by pyrolysis at 500 and 700 °C. The ability to remove methylene blue and methyl orange were investigated under environmental conditions of pH and concentration. Carbons obtained with KOH at 700 °C present superior adsorption capacity. A simulation of this process permitted the characterization of the gases which contributed to surface development. The obtained products present a mesoporous structure and narrow particle size distribution. The presence of contaminants originated from these carbons was investigated in the aqueous media. The absence of zinc and sulfur releasing and the excellent ability to remove organic dye make these materials useful in the treatment of waste water.

Pb/Ti, Sn and Mg-based nanocomposite materials were prepared by the high-energy mechanical milling of commercial powders. The surface of these ceramic compounds was strongly influenced by the doping, diameter of the milling spheres and time of the mechanical milling (amorphization process). Such milling leads to the formation of nanocrystalline materials. The mechanical processing parameters of these compounds were investigated through Brunauer, Emmett and Teller isotherms, wide angle X-ray diffraction, transmission electron microscopy and CO2 adsorption.

Neste trabalho foi investigada a preparação de carbonos ativados através da pirólise de composições elastoméricas provenientes de resíduos de bandas de rodagem de pneus de automóveis. O material foi processado nas temperaturas de 500, 620 e 700 °C, em atmosfera de N2, utilizando-se o hidróxido de potássio como agente ativador. Os produtos resultantes foram caracterizados pela fisisorção de N2 a 77 K, através de isotermas de Brunauer, Emmet e Teller e por microscopia eletrônica de varredura. Esses carbonos ativados apresentam estruturas típicas de sólidos mesoporosos e a temperatura de pirólise tem grande influência na área específica e distribuição de volume de poros. O carbono ativado obtido a 700 °C apresentou maior área específica e estrutura porosa compacta. Esse material apresenta melhor desempenho frente à adsorção de azul de metileno, removendo até 1,0 x 10-1 g de corante por grama de carbono utilizado, em tempos inferiores a 300 s.

In this work, the preparation of activated carbons through the pyrolysis of elastomers, arising from car threads of tire waste, was investigated. The material was processed at 500, 620 and 700 °C, under N2 atmosphere, by using potassium hydroxide as activating agent. The resulting products were characterized by physisorption of N2 at 77 K, through Brunauer, Emmet and Teller isotherms, and scanning electron microscopy. The carbons obtained display a characteristic structure of mesoporous materials and the pyrolysis temperature has strong influence on the specific area and porous volume distribution. The activated carbon obtained at 700 °C has high specific area and compact structure. It exhibited high performance for adsorption of methylene blue solution, removing 1.1 x 10-1 g of the dye per gram of carbon in less than 300 s.