Effects of reducing agents on the degradation of 2,4,6-tribromophenol in a heterogeneous Fenton-like system with an iron-loaded natural zeolite

Abstract

The effects of reducing agents on the degradation of 2,4,6-tribromophennol (TrBP) were investigated in a heterogeneous Fenton-like system using an iron-loaded natural zeolite (Fe-Z). The catalytic activity for TrBP oxidation in the presence of the Fe-Z and H2O2 was not appreciable. The addition of a reducing agent, such as ascorbic acid (ASC) or hydroxylamine (NH2OH), resulted in an enhancement in the degradation and debromination of TrBP. TrBP was completely degraded and debrominated at pH 3 and 5 in the presence of NH2OH, while the degradation was significantly suppressed at pH 7 and 9. Although the rates of TrBP degradation were relatively constant at pH 3, 5, 7 and 9 in the presence of ASC, the percent degradation reached a plateau at 70%. These results show that ASC functions as a strong HO scavenger, as opposed to NH2OH, at pH 3 and 5. Thus, adding NH2OH is preferable for the degradation of TrBP via a Fenton-like system using Fe-Z as the catalyst. It is noteworthy that the complete mineralization of TrBP was achieved at pH 5, when NH2OH and H2O2 were sequentially added to the reaction mixture. Analysis of the surface of Fe-Z by X-ray photoelectron spectrometry indicated that the Fe(III) on the surface of the catalyst was reduced to Fe(II) after treatment with ASC. Thus, the role of RAs can be of assistance in Fe(III)/Fe(II) redox cycles on the Fe-Z surface and enhance the generation of HO via the decomposition of H2O2.