Efficient transformation of DDT with peroxymonosulfate activation by different crystallographic MnO₂

In this study, three different structures of MnO₂ were synthesized and used to activate peroxymonosulfate (PMS) for the degradation of DDT in aqueous solutions. It was found that DDT was efficiently degraded in the MnO₂/PMS system and the degradation rate was dependent on the properties of MnO₂ including crystal structure (followed the order: α-MnO₂ > γ-MnO₂ > β-MnO₂), surface area and Mn(III) content. Sulfate radicals (SO₄^-) was primarily responsible for the degradation of DDT based on the results of electron paramagnetic resonance (EPR) and quenching experiments. The degradation of DDT was suppressed at alkaline pH because the formation of SO₄^- was inhibited. The results of GC-MS indicated that dichlorobenzophenone, 4-chlorobenzoic acid and benzylalcohol were the dominant intermediates for DDT degradation. The possible pathways of DDT degradation were proposed according to the identified products.