Heterogeneous oxidation of the dye Brilliant Green with H2O2 catalyzed by supported manganese porphyrins

• Brilliant Green dye bleaching by heterogeneous catalysis using H2O2.
• Manganese(III) porphyrins supported at magnetic-silica and halloysite clay.
• 2k full factorial design study of the bleaching catalysis.
• Alternative treatment for dye waste from textile industries.

Synthetic metalloporphyrins can oxidize organic substrates efficiently and selectively in the presence of different oxygen donors. In an attempt to propose new catalytic systems to treat industrial effluents, researchers have recently turned their attention to the performance of metalloporphyrin-based catalysts in bleaching reactions of organic dyes used in the textile industry. The present work has investigated the cationic metalloporphyrins [Mn(T4MPyP)]Ac5 (MnP1) and [Mn(Br8T3MPyP)]Cl5 (MnP2) immobilized on two inorganic supports, namely magnetite coated with silica obtained by the hydrolytic sol-gel process (S-Mag) and nanotubes of raw halloysite clay mineral (Hallo), as catalysts in the bleaching reaction of the dye Brilliant Green by hydrogen peroxide (30%). The catalysts elicited up to 22.9 times higher reaction rates as compared with the rates of the control reactions. It was possible to use the immobilized complexes in successive oxidation reactions without significant decrease in the catalytic activity. The catalysts MnP-S-Mag displayed magnetic properties, which allowed their fast separation from the reaction medium with the aid of a simple magnet. A 2k full factorial design (4 factors and k levels) study of catalyst use under different experimental conditions, showed that time and molar ratio affected the dye bleaching reaction.

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