performed by Powder X-ray diffraction (Bruker AXS, German). The SEM
images were obtained by an S-4800 II Field emission scanning electron
microscope (Hitachi, Japan). The TEM images were obtained by a Tecnai
12 transmission electron microscope (Philips, Netherlands). The Raman
spectra were recorded by an InVia Raman spectrometer (Renishaw, Britain).
The UV–vis spectra were recorded on a Cary 5000 spectrophotometer
(Varian). HRTEM images were obtained by a Tecnai G2 F30 S-TWIN field
emission transmission electron microscope (FEI). The AFM images were
obtained on a nanoscope (Digital Instruments). The wear scar micrographs
were recorded by an LSM 700 3D Laser Scanning Microscope (CARL ZEISS,
German).