2.3. Characterization
Scanning electron microscope (SEM) images were taken on a Hitachi S-4800
FE-SEM equipped with energy-dispersive X-ray spectroscopy (EDS). Transmission
electron microscope (TEM) images and selected area electron diffraction (SAED)
were taken on FEI Tecnai TEM with an acceleration voltage of 300 kV. To prepare
SEM or TEM samples, small amount of dispersion were vacuum-filtered on polycarbonate
membrane (pore size 0.2 lm) or dropped on copper grids, and dried
in vacuum oven. X-ray diffraction (XRD) patterns were measured on Rigaku
D/MAX-2500V/PC X-ray diffractometer with Cu Ka radiation. X-ray photoelectron
spectroscopy (XPS) was performed on a VG Microtech ESCA 2000 X-ray photoelectron
spectrometer using a monochromatized aluminum Ka anode. UV–visible
spectra were collected by a Varian Cary 5000 UV–visible spectrophotometer.