Elaine Cristina Rodrigues Maia

Aplicação do delineamento simplex-centroide no estudo da cinética da oxidação de biodiesel B100 em mistura com antioxidantes sintéticos

Antioxidants are an alternative to prevent or slow the degradation of the biofuel. In this study, it was evaluated the oxidative stability of B100 biodiesel from soybean oil in the presence of three commercial synthetic antioxidants, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ), pure or blended, from the experimental design of simplex-centroid mixture. The reaction order and rate constant were also calculated for all tests. The treatment containing pure TBHQ proved to be the most effective, proven by design, the optimum mix obtained and the rate constant. Binary and ternary mixtures containing TBHQ also showed appreciable antioxidant effect.

Cinética da oxidação de biodiesel de óleo de soja em mistura com TBHQ: determinação do tempo de estocagem

Synthetic antioxidants are an alternative to prevent or retard the degradation of biofuels made from vegetable oils. In this study, it was evaluated the oxidative stability of B100 soybean oil biodiesel, in the presence of tercbutylhydroquinone (TBHQ). The results showed that the induction period, that precedes the seeding process, was delayed in the presence of the antioxidant. Moreover, the obtained results suggest that the B100 biodiesel containing TBHQ can present a storage time at 25 oC, three times longer than the estimated time for the pure B100.Synthetic antioxidants are an alternative to prevent or retard the degradation of biofuels made from vegetable oils. In this study, it was evaluated the oxidative stability of B100 soybean oil biodiesel, in the presence of tercbutylhydroquinone (TBHQ). The results showed that the induction period, that precedes the seeding process, was delayed in the presence of the antioxidant. Moreover, the obtained results suggest that the B100 biodiesel containing TBHQ can present a storage time at 25 oC, three times longer than the estimated time for the pure B100.

Complementary study on the electrical and structural properties of poly(3-alkylthiophene) and its copolymers synthesized on ITO by electrochemical impedance and Raman spectroscopy

Abstract Targeting the use of organic conjugated polymers in organic solar cells, this study looks at the electrochemical properties of poly(3-alkylthiophene) films: poly(3-methylthiophene), poly(3-hexylthiophene), poly(3-octylthiophene) and its copolymers electrochemically synthesized on a tin-doped indium oxide (ITO) substrate. Electrochemical impedance spectroscopy (EIS) was used to monitor the change in the electrochemical behavior of these films on the ITO and the charge transfer resistance (RCT) values were determined in open circuit potential (OCP) and at different overpotentials. Together with the EIS, the ex situ and in situ Raman spectroscopy was used to characterize the influence of aromatic radical cation and dication species, present in the polymer matrix of homo and copolymers, in the management processes seen in the Nyquist and Bode-phase diagrams for different systems obtained on ITO. The EIS results in OCP showed an decrease in resistance demonstrating increased conductivity with the copolymerization, and through the Bode-phase diagram and the ex situ Raman spectra, these changes were related to the oscillation of the radical cation and dication along the polymer matrix. By studying Nyquist and Bode-phase diagrams in the overpotentials, an increase in RCT values in higher potentials was seen that could be related to the bipolaronic process, which after the deconvolution of the in situ Raman spectra, was possible to relate these results to the stabilization of the dication species in the homo and copolymers matrix when subjected to high potential.

Aperfeiçoamento da produção de partículas de óxido de zinco para aplicação em células solares

O oxido de zinco (ZnO) nanoestruturado contem caracteristicas fisico-quimicas de elevada importância para utilizacao em celulas solares. A padronizacao e regularidade das dimensoes das particulas nanometricas e de dificil obtencao; fatores como natureza do ânion do sal precursor, temperatura de reacao e quantidade de agua podem interferir no tamanho das particulas. Este trabalho tem como objetivo estudar a influencia das variaveis do processo de sintese das nanoparticulas de ZnO, visando a aplicabilidade em celulas solares. Foi aplicado delineamento fatorial incompleto Box-Behnken (33), de acordo com o metodo de coprecipitacao, para as tres variaveis: concentracao de Zn(NO3)2 (mol.L-1), temperatura do meio reacional (°C) e tempo de reacao (h). Para caracterizacao das particulas foram feitas medidas de espalhamento de luz, analise por difracao de raios X, caracterizacao por espectroscopia Raman, microscopia eletronica de varredura (MEV), aplicacao do ZnO em celula solar com polimero (poli-3-hexiltiofeno - P3HT) e medidas de fotocronoamperometria. A otimizacao resultou em uma concentracao de Zn(NO3)2 igual a 0,05 mol.L-1, tempo de reacao de 20 h e temperatura de 80 oC, onde o menor valor para o tamanho de particula de ZnO mostrado pelo modelo foi de 367 nm. As nanoparticulas apresentaram cristalito com dimensoes de 20 nm, cristalinidade de 82,4% e fase hexagonal do tipo wurtzita. As imagens de MEV mostraram tres tipos diferentes de estruturas devido a variacao de concentracao do Zn(NO3)2. A amostra de ZnO370nm + P3HT + FTO apresentou valor de densidade de corrente (j) de 3,86 mA.cm-2.