RESUMO Xerogéis de carbono (CXs) são materiais constituídos por uma estrutura tridimensional formada por esferas nanométricas interligadas e poros interconectados. Diversos trabalhos apresentam os CXs como suporte para utilização em catálise. A principal vantagem destes suportes é que suas propriedades físicas e químicas superficiais podem ser adaptadas às exigências catalíticas. Neste trabalho, compósitos CX/TiO2 foram sintetizados em etapa única, por polimerização/condensação sol-gel de solução formaldeído e resorcinol, com simultânea adição de nanopartículas de TiO2 ou Ti(IV), seguido de secagem e tratamento térmico. Os compósitos foram caracterizados por análise termogravimétrica (TG), difratometria de raios X (DRX), microscopia eletrônica de varredura (MEV), espectroscopia Raman e isotermas de adsorção de nitrogênio (N2) com determinação de área superficial (BET) e volume de poros (Vp). Os resultados mostraram a presença de uma mistura das fases anatase e rutilo do TiO2 nos compostos obtidos. Através das imagens de MEV verificouse grande homogeneidade na distribuição das partículas de TiO2 no suporte de CX. As propriedades fotocatalíticas dos compósitos foram investigadas para fotodegradação de azul de metileno (AM). A cinética de degradação de azul de metileno ajustou-se ao modelo de pseudo primeira ordem. Observou-se um efeito sinérgico entre os sólidos, com um aumento da atividade fotocatalítica nos compósitos de CX/TiO2, em relação ao TiO2.

ABSTRACT Carbon xerogels (CXs) are materials with three-dimensional structure of nano-sized balls and interconnected pores. CX have been widely applied as metal support for use in catalysis. The main advantage of these materials is that their physical and chemical properties can be adapted for each catalytic requirements. In this work, CX/TiO2 compounds have been synthesized in a single step, which consisted in the polymerization sol-gel/condensation of resorcinol and formaldehyde solution, with simultaneous addition of TiO2 nanoparticles or Ti(IV), followed by drying and heat treatment. The composites were characterized by thermogravimetric analysis (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and adsorption isotherms of nitrogen (N2) to determination of surface area (BET) and pore volume (VP). The results showed the presence of a mixture of anatase and rutile phases in the composites. Although SEM images it was verified higher uniformity in the distribution of TiO2 particles in CX support. The photocatalytic properties were investigated for the degradation of methylene blue (AM). The kinetics of the photocatalytic process was determined as the pseudo first-order model. There was a synergistic effect between the solids, with an increase of photocatalytic activity in composite CX/TiO2, compared to TiO2.

RESUMO As estruturas enterradas (tanques, bases de linhas de transmissão e dutos) estão expostas a diferentes tipos de solos e níveis de corrosividade. Neste caso, se torna necessário o estudo de corrosão do aço carbono nestes diferentes tipos de solos. Para estudos em laboratório, utiliza-se a solução NS4 para simular solos sintéticos. No entanto, devido aos diversos tipos de solos, é necessário o desenvolvimento de soluções sintéticas para simular estes solos com diferentes níveis de corrosividade. Assim, o objetivo deste trabalho foi desenvolver soluções sintéticas para uso em laboratório que abranjam uma variedade de tipos de solos com diferentes propriedades físico-químicas. Os ensaios eletroquímicos realizados foram curvas de polarização potenciodinâmicas, impedância eletroquímica e perda de massa. As soluções foram desenvolvidas alterando as concentrações da solução padrão NS4 nas seguintes condições: desaerada, na qual foi adicionado tiossulfato de sódio para simular o ambiente anaeróbico das bactérias redutoras de sulfato; em condições aeradas para simular solos contaminados com sulfeto de hidrogênio; adicionando cloreto de sódio para simular solos em região costeira e adição de cimento para simular solos anticorrosivos. Os resultados mostraram que o aço carbono apresenta maior taxa de corrosão quando exposto a soluções de cloreto de sódio e tiossulfato. A adição de 5% (m/v) de cimento foi o suficiente para simular solos anticorrosivos, nos quais ocorreu o processo de passivação. Para garantir o processo passivo no metal nas soluções sintéticas com a presença de tiossulfato de sódio foi necessária adição 5% (m/v) de cimento. O processo de passivação estável não foi alcançado nas soluções sintéticas com cloreto de sódio ao se adicionar 5%, 10% e 15% (m/v) de cimento.

ABSTRACT The buried structures (tanks, bases of line transmissions, pipelines) are commonly exposed to different kind of soils and corrosivity levels. Due to this condition, it is necessary to study the corrosion on the carbon steel on these different environments. In laboratory, the NS4 solution is used to simulate synthetic soils. However, due to different kind of soils, it is necessary to develop synthetic solutions that evaluate these soils and their corrosivity. Therefore, the objective of this work was to develop synthetic solutions for laboratory use that include a large variety of kinds of soil with different physicochemical properties. The performed electrochemical tests were polarization curves, electrochemical impedance and mass loss. The solutions were obtained by altering the concentration of a standard solution of NS4 in these following conditions: in deaerated condition, in which was added sodium thiosulphate to simulate anaerobic environment of sulphate-reducing bacteria; in aerated conditions to simulate soil with the presence of H2S; adding sodium chlorate to simulate seashore areas and cement to simulate anticorrosive soils. The results demonstrated that carbon steel presents the lowest resistance to corrosion when exposed to sodium chlorate and thiosulphate solutions. Adding 5 wt. % of cement was enough to simulate anticorrosive soils, in which the passivation process occurred. To ensure the passivation process actually takes place on the metal immersed in synthetic solution with sodium thiosulfate was necessary to add 5 wt. % of cement. The stable passivation process was not reached in synthetic solutions with sodium chlorate when adding 5, 10 and 15 wt. % of cement.

The potential use of rice husk as biosorbent to remove Cu2+, Al3+, Ni2+ and Zn2+ ions from aqueous solutions was investigated under both noncompetitive and competitive conditions. The biosorbent was used in the form of particles with size smaller than 0.5 μm and in the concentration of 500 mg L-1 (dry weight). The experiments were performed using batch adsorption technique for concentrations of 10, 30 and 70 mg L-1 of metal ions at pH 4.0 and 5.0. The chemical speciation of metals in the experimental conditions used in this work was predicted by the software Visual MINTEQ 2.6.

The present study describes phenol adsorption on commercial active carbon (CAF) under alkaline conditions in the concentration range of 0.01 to 2.08 mmol L-1. Surface characterization has been performed by means of surface area measurements, IR spectroscopy and Boehm titration. The effect of temperature on the adsorption equilibrium isotherm was investigated at 23, 30, 40, 50 and 60 °C. The results showed that adsorption capacity decreased with increasing temperature. The adsorption kinetics and the role of surface characteristics on the adsorption of phenol also discussed.

Didactic experiments are proposed in order to demonstrate the characteristics of flow injection analysis and to extend the applications of FIA to the determination of physical chemistry parameters in undergraduate labs. All experiments can be performed with the same flow manifold by employing usual FIA devices. Analytical characteristics are presented by means of the determination of iron in river water, employing 1,10-phenantroline as chromogenic reagent. Physical chemistry applications were the determination of reaction stoichiometries by continuous variation and mole-ratio methods and the evaluation of the pH and ionic strength effects on the kinetic of the reduction of hexacianoferrate(III) by ascorbic acid.