Degradation of organic dyes by water soluble iron(III) mononuclear complexes from bis-(2-pyridylmethyl)amine NNN-derivative ligands

Abstract

This work describes the degradation of the dyes methyl orange (MO), methylene blue (MB), crystal violet (CV), Congo red (CR) and Rhodamine B (RhB), catalyzed by four water soluble mononuclear iron(III) complexes, in presence of hydrogen peroxide. The NNN ligands are bis-(2-pyridylmethyl)amine (BMPA) and three -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). More than 85% of degradation was achieved after 180 min for all dyes. The complex [Fe(MPBMPA)Cl3] was the most active. Kinetic experiments indicated a two-step reaction, where the intermediate Fe(III)-OOH is the catalytic species in the first step (k1), followed by the hydroxyl radical degradation in the second step (k2). The degradation percentage was well correlated with k2, being the degradation of the dye by the hydroxyl radical the most important step.