Dynamics of light-induced excited state quenching of ferrioxalate complexes by peroxides. Fast kinetics events and interaction with toxic pollutants

Abstract

The behaviour of the trioxaloferrate (Fe(ox) 3 3−) complex on laser illumination and its quenching in the presence of H 2O 2 were investigated by laser photolysis. At neutral Ph, a short (approximately 30 μs) and a longer (approximately 1 ms) lifetime were observed for transient Fe(ox) 3 3−. The lifetime decreases as the pH becomes more acidic. In light-induced processes, the intensity of the light used is one of the determining reaction parameters and this effects is reported in detail. The excited states of the Fe oxalate complexes induced by laser photolysis are quenched by H 2O 2. The decay observed can be fitted in a simplified way by bi-exponential function. The transient species Fe(ox) 3 3−∗ observed on laser photolysis does not undergo excited state annihilation, but ground state collisional quenching. The fast formation of a hydroxylated phenol adduct is shown by kinetic laser spectroscopy. A detailed account of the kinetics and spectral characteristics of the transients is presented for these reactions. This allows a scheme to be suggested for the intervention of these radicals in agreement with the experimental observations. The results obtained implicate the OH radical in the degradation of pollutants involving Fe complexes in the presence of H 2O 2.