Persulfate reactivity enhanced by Fe2O3–MnO and CaO–Fe2O3–MnO composite: Identification of composite and degradation of CCl4 at various levels of pH

The reactivity of persulfate (PS) was investigated when novel synthesized composites were used as activators. First, two types of composites were prepared by the mixing of an FeSO4 solution into a MnO-suspended solution with the addition of either NaOH (i.e. Composite I) or Ca(OH)2 (i.e. Composite II). SEM−EDS indicated that Fe and Mn were detected on Composite I while Fe and Ca were detected on Composite II. XPS analyses indicated that the crystalline form on the surface of Composite I was identified as maghemite (γ-Fe2O3), not jacobsite (MnFe2O4). On the other hand, the surface of Composite II was predominantly covered by lime (CaO) and maghemite. Based on these results, Composite I and Composite II were represented as Fe2O3–MnO and CaO–Fe2O3–MnO, respectively. BET surface area of MnO, Fe2O3–MnO, and CaO–Fe2O3–MnO were 0.4, 56, and 102 m2 g−1, and PZC of them were measured as 7.1, 8.2, and 12.2, respectively. The greater BET surface area and the higher PZC was due to CaO. Investigating the role of the composite as activator, PS/composite systems at various pH levels (i.e. 3, 7, 9 and 12) were applied for degradation of carbon tetrachloride (CT). The PS/Fe2O3–MnO system degraded CT effectively at pH 7 and 9, while PS/CaO–Fe2O3–MnO system showed effective degradation at pH 9 and 12. The optimum pH conditions in each PS/composite system implied that PS activation to produce reductant was possibly related to the surface charge of the composite. A mechanism to produce reductant, superoxide anion, from the PS/composite system was limitedly proposed.