Abstract Given the potential of acid-activated clays in adsorptive and catalytic processes, several studies focusing on acid matrices have grown over the years, making it possible to study vermiculite, a mineral composed of a type 2:1 unit cell with tetrahedral and octahedral sheets. Therefore, this work aimed to study vermiculite treated with acids for the production of matrices. In this work, the treatment of natural vermiculite-hydrobiotite, with nitric acid in concentrations of 0.25, 0.50, 0.75, and 1 mol.L-1, followed by the dealumination process with sulfuric acid 25% v/v, aiming the production of acid matrices for applications as support for biocatalysts, chemical adsorbents, among others. The produced materials were characterized using different techniques, including X-ray fluorescence spectroscopy, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and isotherm adsorption using the BET method. The results showed that after acid leaching the vermiculite showed a high SiO2 content, high Brønsted and Lewis surface acidity, good adsorption/desorption performance, and significant growth of the specific surface area, qualifying the vermiculite as a promising material for future applications in catalytic and biocatalytic processes. The acid concentration had a considerable influence on the compositional and textural modification of vermiculite-hydrobiotite.

Velas cerâmicas empregadas para a filtração doméstica de água consistem de elementos porosos sinterizados a base de aluminossilicatos com larga distribuição de tamanhos de poros e grãos. Esses filtros têm se mostrado úteis na retenção de micropartículas em suspensão por exclusão de tamanhos, mas apresentam baixa eficiência com respeito à remoção de compostos químicos e de micro-organismos. Para elevar sua capacidade de filtração, principalmente de contaminantes orgânicos, alterações superficiais foram conduzidas fazendo uso de revestimento de SiO2 pela técnica de sol-gel dip-coating. Análises indicam que o filme de SiO2 obtido por calcinação gera uma redução média de 3,5 µm nos tamanhos de poros causando uma ligeira queda de pressão na permeação, contudo, a superfície vítrea melhora a organofilicidade elevando a eficiência de remoção de bactérias, principalmente para vazões em baixo fluxo.

Water household ceramic filter candles are sintered porous elements based on aluminosilicates and characterized by having a large distribution of pores and grain sizes. Such filters are useful in the retention of microparticles in suspension by size exclusion; however they present low efficiency in microorganism and chemical contaminants removals. In order to increase its filtration capability, mainly concerning organic contaminants, surface modifications were conducted by SiO2 sol-gel dip-coating. Analysis revels that after SiO2 film densification an average reduction in 3.5 µm in pore size is measured what generates a slight decay permeation pressure. Nevertheless, the vitreous surface enhances the organofilicity increasing the bacteria removal efficiency, mainly at low permeation flux.

Foi realizado um estudo do comportamento eletroquímico do herbicida ametrina em meio ácido utilizando a técnica de voltametria de onda quadrada (SWV) combinada com eletrodo de gota suspensa de mercúrio (HMDE). O processo de redução da ametrina envolve a protonação prévia da molécula, seguido da transferência irreversível de dois elétrons com controle de velocidade dado pelo transporte de massa. A corrente de pico apresentou dependência linear com a concentração da espécie, o que permitiu se calcular um limite de detecção de 0,1 mg L-1 (0,1 ppb) em amostras preparadas com água pura de laboratório, valor este que possibilita a aplicação desta metodologia eletroanalítica na análise de traços do herbicida em amostras ambientais.

The determination of the herbicide ametryne in acid solution was performed using square wave voltammetry and a static drop mercury electrode. The electroredution reaction proceeds through a completely irreversible mechanism with the diffusion of the electroactive specie being the rate determining step. It was observed a previous protonation of the reagent molecule followed by the transference of two electrons. The linearity of peak current with concentration allows to calculate a detection limit of 0,1 mg L-1 (0,1 ppb). This value is adequate for the analysis of herbicide contamination (e.g., in drinking water).

Magnetic birefringence measurements are performed under a static field on Electric Double Layered Magnetic Fluids based on copper and zinc ferrite nanostructures. The optical birefringence is related to a single-particle effect and well described by a Langevin model which includes a log- normal distribution of particles. By the field-induced birefringence level, these new magnetic fluids are comparable to usual ones, a result which could offer a new way for biological applications.

This work describes the techniques of construction and several applications of ultramicroelectrodes in electrochemistry and electroanalytical chemistry. Disc shaped UME are produced by embedding metal wires on insulating materials such as glass or epoxy resin. In the field of electrochemistry, UME have been applied in studies of the hydrogen evolution reaction and the electrocrystallization of metals. The negligible values of sensibility for ohmic drop and the enhanced mass transport rate by spherical diffusion are the main advantages of UME in these applications. New important conclusions regarding the phenomena under study were drawn from the experimental results. The applications in electroanalytical chemistry involved the determination of contaminants such as heavy metals and nitrites in natural waters and food products. The use of UME requires little sample manipulation and, in general, no need for oxygen removal or the addition of supporting electrolytes.