Detoxification of diluted azo-dyes at biocompatible pH with the oxone/Co2+ reagent in dark and light processes

Accelerated bleaching and photobleaching of diluted solutions of Methyl Orange and other dyes occur only when Co2+-ions are present in solution mediating oxone (2KHSO5·KHSO4·K2SO4) decomposition. The bleaching of Methyl Orange, Orange II and Methylene Blue dyes in dilute solutions (0.01 mM) proceeds within a few minutes and occurs at biocompatible pH leading to a decrease in the toxicity of the initial solution under simulated daylight radiation. A reduction in the toxicity of 35% was observed at biocompatible pH-values when a solution Orange II (0.01 mM) was irradiated in the presence of oxone (0.06 mM)/Co2+ (0.004 mM). Only traces of Co2+ were necessary to accelerate the decomposition of the dyes in the presence of oxone in the dark and even more under daylight irradiation. The photobleaching proceeds with a photonic efficiency of ∼0.24. The solution parameters were optimized for the photobleaching of azo-dyes by the oxone/Co2+ reagent. H2O2 generation was observed to be possible only as long as Orange II was present in the solution. The decomposition kinetics of H2O2 was followed under solar radiation. The dye decomposition was also investigated as a function of the applied light intensity. No saturation effects were observed when simulated solar light with 90% AM1 was applied. The photobleaching reaction proceeded with acceptable kinetics with light intensities 5–10 times lower than AM1. This makes the photocatalytic treatment suitable under diffuse daylight.

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