Heterogeneous degradation of organic pollutants by persulfate activated by CuO-Fe₃O₄: Mechanism, stability, and effects of pH and bicarbonate ions

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.