The surface composition of the structures is determined by XPS and the results are exhibited in Fig. 5. As shown in the survey scan in Fig. 5a, the peaks can be ascribed to K, O, Fe, C and Mn. Fig. 5b shows the Mn2p signal. The binding energies of Mn (2p3/2) and Mn (2p1/2) of S2 are 642.1 eV and 653.8 eV, respectively. Compared to 641.8 and 653.4 eV of S1 (Fig. 5b). The peaks shift of S2 should be contributed to the change in the oxidation states of Mn [30]. According to the Mn 2p core level spectrum, the binding energies of Mn 2p3/2 and Mn 2p1/2 here are in agreement with