Effective decolorization of polyazo direct dye Sirius Red F3B using persulfate activated with Fe0 aggregate

Abstract

Fe0 aggregate was used to activate persulfate (PS) in an oxidizing PS/Fe0 system for decolorization of the polyazo dye Sirius Red F3B (SRF3B, Direct red 80). Decolorization was affected by pH, temperature, and persulfate and Fe0 dosages. Low PS dosages hindered decolorization; a two-stage oxidation process (a slow heterogeneous reaction on the Fe0 surface and a fast homogeneous reaction in solution) was observed. SRF3B depletion during the slow and fast stages followed zero-order rate law and modified pseudo-first-order kinetics, respectively. A 95% decolorization efficiency was achieved within 10min of treating 25mg/L SRF3B (American Dye Manufactures Institute color 8276) with PS/Fe0; the four azo links of SRF3B were completely broken down. Through the analysis of gas chromatography–mass spectrometry, intermediates were identified and degradation pathways of SRF3B during PS/Fe0 oxidative process were proposed. Activation energy of the PS/Fe0 system was 0.636kJ/mol, confirming decolorization as a fast reaction. Fe0 aggregate was reusable. Thus, the PS/Fe0 system is fast and effective for SRF3B decolorization.