The 710.8 eV demonstrates the presence of Fe 3+ (32), 711.8 eV suggests hydrated ferric oxide , and 715.2 eV demonstrates the presence of Fe 2+ . The 719.9 eV attributed to Fe 0 , and 723 eV indicates, Fe2p 1/2 . The evidence of the Fe-N bond was found in 725.9 eV, which corresponds to the Fe-Nx sites, providing further evidence of Fe-N sites in the OA nanozyme .