Avaliação e aplicação de oxidantes gerados pela ação sonoquímica em sistemas homogêneos para determinação espectrofotométricas de algumas espécies químicas.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

In this work it was evaluated the generation of oxidizing agents by ultrasonic degradation of water and carbon tetrachloride molecules. The sonication of water promotes the formation of H. and .OH radicals, leading to H2O2 generation. The carbon tetrachloride sonolysis generates Cl. radicals, which can form Cl2 and HClO. The exhaustive exposition leads to the complete degradation of CCl4 with formation of Cl- and CO2.The formation rate of H2O2 with aqueous irradiation by 40 W ultrasonic waves at 40 kHz is low. This production occurs at a rate of 4.2x10-4 ìmol s-1, after 2 minutes of sonication. Cl2 is produced at a rate of 0.014 ìmol s-1, immediately after CCl4 aqueous solution exposition to ultrasonic waves. The sonochemical degradation of CCl4 is followed by sensitive decrease of pH solution due to HCl formation. The generation rate of H+ (0.064 ìmol s-1) was related with the Cl- rate (0.068 ìmol s-1) with difference of ca 6%. However, when the pH remains constant, by increasing the sonication time the organic compound was completely degradated. The sonochemical production of oxidizing agents was employed for I-, Fe2+ and Cr3+ oxidation. I- and Fe2+ were oxidized even by the sonicated CCl4 solution. The I- was converted into I2 and HIO. In order to oxidize Cr3+ the chromium in CCl4 solution was sonicated in presence of HCO3 -. CCl4 degradation in aqueous solution was estimated based on pH variation and Fe2+ oxidation rate. The rates of Fe3+ and Cl radicals production in the presence of Fe2+ ions were 0.024 and 0.107 ìmol s-1, respectively. However, by mixing the Fe2+ solution with aqueous CCl4 after sonication, different rates such as 0.028 and 0.0092 ìmol s-1 were obtained. In this work some mechanisms related to I-, Fe2+ and Cr3+ sonochemical oxidation were proposed.A spectrophotometric procedure for Cr3+ determination based on its oxidation provoked by Cl radicals produced during sonication was proposed by using 1,5- diphenylcarbazide. The linear range from 0.1 to 3 ìg of Cr3+ (R = 0.9993) and detection limit of 5 ìg L-1 were obtained. The proposed procedure for Cr3+ determination based on the sonochemical degradation of CCl4 showed good precision (RSD <2%; N = 10). Co2+ ions presence improved the Cr3+ oxidation.

ASSUNTO(S)

quimica analitica oxidantes degradação sonoquímica

ACESSO AO ARTIGO

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