Catalytic Degradation of Orange II by MnIII(TPPS) in Basic Hydrogen Peroxide Medium: A Detailed Kinetic Analysis

Abstract

The presence of dyes from inter alia textile industry in wastewater, poses a serious threat for the environment. New methods for the removal of persistent dyestuffs from effluent streams still attract much attention. In this report the application of MnIII(TPPS) [where TPPS = 5,10,15,20‐tetrakis(4‐sulfonatophenyl) –21 H,23H‐porphyrin] as suitable catalyst for the oxidative degradation of a model substrate, Orange II (ORII), was studied. The MnIII(TPPS)/H2O2 system was found to degrade ORII with high efficiency under ambient conditions in carbonate buffer solutions. In order to gain further insight into the degradation mechanism, detailed kinetic studies using rapid‐scan spectrophotometry as a function of [H2O2], [MnIII(TPPS)] and pH, were performed. Evidence for the participation of peroxocarbonate ions (HCO4– and CO42–) as efficient oxidants in carbonate buffer was found. The experimental results suggest rapid formation of an intermediate (TPPS)MnV=O complex, followed by the subsequent degradation of ORII. The reaction showed maximum reactivity at pH ≈ 11. Spectroscopic data demonstrated that the catalytic cycle could be repeated several times without any significant loss in catalytic activity.