Synthesis of silica xerogels with high surface area using acetic acid as catalyst

The influence of acetic acid on the pore structure and surface area of silica prepared by the sol-gel method was investigated. Experimental conditions of synthesis, such as gelation temperature and solvents, were also studied. N2 adsorption isotherms of the samples were type 1, typical of microporous materials, explaining the high surface area values (BET) observed. The simultaneous addition of acetic and hydrochloric acids as catalysts and of acetone as solvent, together with the use of a gelation temperature of 20 ºC, made it possible to prepare amorphous silica materials with surface area values up to 850 m² g-1. The high surface area value of these samples could be explained by the microporosity and the nanometric size of the particles.Nesse trabalho foi estudada a influência do ácido acético na estrutura de poros e na área superficial de sílicas preparadas pelo método sol-gel. Condições experimentais de síntese, tais como temperatura de policondensação e solventes, também foram estudadas. Isotermas de adsorção de N2 das amostras foram classificadas como do tipo 1, típicas de materiais microporosos, o que explica os altos valores de área superficial obtidos. A adição simultânea dos ácidos acético e clorídrico como catalisadores e de acetona como solvente, bem como o emprego de uma temperatura de policondensação de 20 ºC, possibilitaram a preparação de sílicas amorfas com valores de área superficial de até 850 m² g-1. O alto valor de área superficial dessas amostras pode ser explicado principalmente pela microporosidade e também pelo tamanho nanométrico das partículas.886890Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

A METODOLOGIA DE RESOLUÇÃO DE PROBLEMAS: UMA EXPERIÊNCIA PARA O ESTUDO DAS LIGAÇÕES QUÍMICAS

This article presents an experience of the use of the Problem Solving (PR) methodology with undergraduate students of the Licentiate Course in Chemistry of UFRGS, for the study of Ionic Bonding (LI). Salar de Uyuni salts were used to contextualize the problems employed. The Field Log records of the researchers and the presentations of the undergraduates show that the implemented didactic sequence favored conceptual learning, such as the relation between chemical bond theories and some properties of the materials, procedural learning, such as public argument, as reading and handling of different bibliographical reference sources and attitude learning, such as interpersonal relations among students and teachers during the different problem solving stages. Additionally, the results brought to evidence that, from the Problem Solving experience with the Ionic Bond contents, the future teachers were able to perceive work alternatives for their future classrooms

THE PROBLEM SOLVING METHODOLOGY: AN EXPERIENCE FOR THE STUDY OF CHEMICAL BONDS

<p></p><p>This article presents an experience of the use of the Problem Solving (PR) methodology with undergraduate students of the Licentiate Course in Chemistry of UFRGS, for the study of Ionic Bonding (LI). Salar de Uyuni salts were used to contextualize the problems employed. The Field Log records of the researchers and the presentations of the undergraduates show that the implemented didactic sequence favored conceptual learning, such as the relation between chemical bond theories and some properties of the materials, procedural learning, such as public argument, as reading and handling of different bibliographical reference sources and attitude learning, such as interpersonal relations among students and teachers during the different problem solving stages. Additionally, the results brought to evidence that, from the Problem Solving experience with the Ionic Bond contents, the future teachers were able to perceive work alternatives for their future classrooms.</p><p></p

An electrochemical sensor based on graphite electrode modified with silica containing 1-n-propyl-3-methylimidazolium species for determination of ascorbic acid

In the present study, an electrochemical sensor based on the electrode (SiMImCl/C) consisting of graphite and silica, grafted with 1-n-propyl-3-methylimidazolium chloride was used for ascorbic acid (AA) quantification in pharmaceuticals and food formulations. Cyclic voltammetry and electrochemical impedance spectroscopy were applied for electrochemical characterization of the SiMImCl/C electrode. The cyclic voltammetry study revealed that the oxidation of AA on this electrode is an irreversible process, realized by adsorption and diffusion limited step. The differential pulse voltammetry was applied to develop a procedure for the AA determination. The linear range was found to be 0.3-170 mu mol L-1 and the limit of detection - 0.1 mu mol L-1. The proposed SiMImCl/C electrode has long term stability and does not show electrochemical activity towards the analytes, which commonly coexist with AA. The sensor was successfully used for quantification of AA in food and pharmaceutical formulations141514CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP170348/2017-212/50228-

Tuning Anatase-Rutile Phase Transition Temperature: TiO2/SiO2 Nanoparticles Applied in Dye-Sensitized Solar Cells

TiO2/SiO2 nanoparticles with 3, 5, and 10 molar percent of silica, were synthesized by hydrothermal method and characterized by SEM, TEM, N2 adsorption-desorption isotherms, X-ray diffraction, and Raman and UV-Vis spectroscopy. While pristine TiO2 thermally treated at 500°C presents a surface area of 36 m2 g-1 (±10 m2 g-1), TiO2/SiO2 containing 3, 5, and 10 molar percent of silica present surface areas of 93, 124, and 150 m2 g-1 (±10 m2 g-1), respectively. SiO2 is found to form very small amorphous domains well dispersed in the TiO2 matrix. X-ray diffraction and Raman spectroscopy data show that anatase-to-rutile phase transition temperature is delayed by the presence of SiO2, enabling single-anatase phase photoanodes for DSSCs. According to the I×V measurements, photoanodes with 3% of SiO2 result in improved efficiency, which is mainly related to increased surface area and dye loading. In addition, the results suggest a gain in photocurrent related to the passivation of defects by SiO2