Decomposition efficiency of some azo dyes in the systems consist of persulfate, zero-valent iron powder and UV light in water environment

Abstract

This research focused on surveying the decomposition efficiency of methyl orange, alizarin yellow and mordant black -T in the systems without and with UV light in water: alone zero-valent iron; alone persulfate; both zero-valent iron and persulfate. Results of research show that the decomposition efficiency some azo dyes are the highest in the systems of zero-valent iron/persulfate/azo dyes/UV and zero-valent iron/persulfate/azo dyes with the same reaction conditions. After 30 minutes of reaction, the decomposition efficiency of methyl orange, alizarin yellow and mordant black -T are 95.89 %, 90.99 % and 79.85 % in the zero-valent iron/persulfate/azo dyes/UV system and 73.65 %, 71.42 % and 58.94 % in the zero-valent iron/persulfate/azo dyes system. These results can be explained that persulfate has peroxide bond in molecular structure activated by zero-valent iron and UV light to generate in-situ free sulfate radical SO₄^−• (E⁰=2.6 V) and free hydroxide radical ^•OH (E⁰=2.8 V). These radicals are very active and strong oxidation property. They are agents to oxidize those azo dyes strongly in the water environment.