Fig. 2
XPS spectra of a CuO/C-350oC, b CuO/C-400 °C, and c CuO/C-450 °C: survey scan, C1 s, O1 s and Cu2p; d Survey scan, O1 s and Cu2p for commercial CuO (40 nm); e The ratio of oxygen-vacancy and Cu-O for CuO/C-350 °C, CuO/C-400 °C, CuO/C-450 °C and commercial CuO. (MEAN ± SD, n = 3, *p < 0.05)