Magnetic CuO-Fe3O4 composite was fabricated by a simple hydrothermal method and characterized as a heterogeneous catalyst for phenol degradation. The effects of pH and bicarbonate ions on catalytic activity were extensively evaluated in view of the practical applications. The results indicated that an increase of solution pH and the presence of bicarbonate ions were beneficial for the removal of phenol in the CuO-Fe3O4 coupled with persulfate (PS) process. Almost 100% mineralization of 0.1 mM phenol can be achieved in 120 min by using 0.3 g/L CuO-Fe3O4 and 5.0 mM PS at pH 11.0 or in the presence of 3.0 mM bicarbonate. The positive effect of bicarbonate ion is probably due to the suppression of copper leaching as well as the formation of Cu(III). The reuse of catalyst at pH0 11.0 and 5.6 showed that the catalyst remains a high level of stability at alkaline condition (e.g., pH0 11.0). On the basis of the characterization of catalyst, the results of metal leaching and EPR studies, it is suggested that phenol is mainly destroyed by the surface-adsorbed radicals and Cu(III) resulting from the reaction between PS and Cu(II) on the catalyst. Taking into account the widespread presence of bicarbonate ions in waste streams, the CuO-Fe3O4/PS system may provide some new insights for contaminant removal from wastewater.

How to effectively activate oxidants like hydrogen peroxide (H 2 O 2 ), peroxydisulfate (PDS) and peroxymonosulfate (PMS) is the focus of advanced oxidation processes (AOPs). In this study, we have found that PMS can directly decolorize cationic dyes without activation in a wide pH range (2.0-12.0). In addition, the presence of Cl À results in the formation of free available chlorine species and thus improves the degradation efficiency as well as broadening the scope of target pollutants. The first-order rate constant increased by 4.3 times when 2.5 mM Cl À was added as observed by an increase from 0.021 to 0.089 min À1 , which further rose to 1.371 min À1 when Cl À was present at a level of 50 mM.Furthermore, it was found that only PMS has such an amazing effect while H 2 O 2 and PDS do not. Radical quenching experiments and electron paramagnetic resonance (EPR) studies show that the decolorization of cationic dyes by PMS does not rely on the formation of sulfate radicals. A plausible mechanism is that cationic dyes (i.e., RhB + ) first form a complex with the active component of PMS (HSO 5 À ) owing to their electrical interaction. Subsequently, direct electron transfer from cationic dyes to HSO 5 À may occur and probably this is responsible for the bleaching of cationic dyes.

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