“…The peaks at about 933.8 and 952.3 eV are correspondingly attributed to the binding energy of Cu 2p 3/2 and Cu 2p 1/2 , respectively. The binding energy of Cu 2p 3/2 at 933.8 eV is a major XPS characteristic of CuO, indicating the existence of Cu 2+[44]. The XPS analysis also reveals that the surface atomic content of Cu, Fe and O is 1.04, 23.20, 75.76%, respectively.…”