Mechanism of persulfate activation with CuO for removing cephalexin and ofloxacin in water

CuO was synthesized by a simple hydrothermal method and investigated as a heterogeneous activator of persulfate for the degradation of cephalexin and ofloxacin. X-ray photo-electron spectroscopy and hydrogen temperature-programmed reduction measurements reveal that CuO contains two types of Cu2+: one has more electron deficiency (named as Cu2+-h) and the other has relatively higher electron density (named as Cu2+-l). Electron paramagnetic resonance and radical scavenging experiments demonstrate that ·SO4− and ·O2− are responsible for the efficient degradation of cephalexin and ofloxacin, respectively. ·SO4− can be produced through the electron transfer from Cu2+-l to PS and the cleavage of peroxy bond, while ·O2− can be produced via the electron transfer from PS to Cu2+-h and the cleavage of S–O bond. Finally, the degradation intermediates were identified by liquid chromatograph–mass spectrometry. This study proposed a novel mechanism for the activation of persulfate with CuO, which is useful for the rational design of persulfate activator for controlling the production of active species.