Scanning electron microscopy (SEM, Hitachi S-4800) was used to examine the morphologies of the synthesized catalysts. Elemental composition and mapping of samples were analysed with energy-dispersive X-ray spectroscopy (EDS, Oxford Instruments). X-ray diffraction (XRD) characterization was performed in a Rigaku Miniflex 600 benchtop sixth-generation X-ray diffractometer. The X-ray photoelectron spectroscopy (XPS) spectra were recorded using ESCA+ (Omicron nanotechnology, Oxford Instrument, Germany) equipped with monochromatic aluminum source (Al K radiation h =1486.6 eV), operated at 15 kV and 20 mA. The C 1s binding energy 284.6 eV is taken as a reference. The Raman measurements were obtained at room temperature by BRUKER RFS 27 with a 627 nm laser as source.