Síntese e caracterização de complexos de Ferro(III) e Cobre(II) como catalisadores para degradação de corantes poluentes

Abstract

This work addresses the of the dyes methyl orange (MO), methylene blue (MB), crystal violet (CV), Congo red (CR), and Rhodamine B (RhB), using mononuclear Fe(III) and Cu(II) complexes containing NNN ligands, as catalysts by Fenton and photo-Fenton systems. The studied ligands wereN,N-bis-(2-pyridylmethyl)amine (BMPA) and three BMPA derivatives: N-methylpropanoate-N,N-bis-(2-pyridylmethyl)amine (MPBMPA), N-propanoate-N,N-bis-(2-pyridylmethyl)amine (PBMPA), N-propanamide-N,N-bis-(2-pyridylmethyl)amine (PABMPA). The complex [Fe(MPBMPA)Cl3] was the most active for the Fenton system. Kinetic experiments indicated a double first-order reaction occurring in two parallel steps, where the intermediate Fe(III)-OOH is the catalytic species in the first step (k1), followed by the degradation of the dye by the hydroxyl radical in the second step (k2). The percentage of degradation was well correlated with k2, with the degradation of the dye by the hydroxyl radical being the most important step. By the photocatalytic method, the reactions were carried out under a 250 W UV lamp, where 100% degradation was achieved in 90 min for all complexes using hydrogen peroxide as oxidant. Kinetic experiments were also performed to investigate the photodegradation of the dyes under a 24 W UV lamp. The reactions followed a zero-order model in relation to the dye, showing that the concentration and the molecular structure did not play a significant role in rate of the photocatalysis. The reaction order in relation to hydrogen peroxide ranged from 0 to 0.8, from low to high concentration of oxidant. The light intensity and the intrinsic catalytic activity of the complexes are the most important characteristics for the dye photodegradation pathway.