All chemical reagents were of analytic purity and were used as purchased from Beijing Chemical Co. Ltd without further purification. Powder X-ray diffraction (XRD) was carried out in a diffractometer using CuKa radiations on D8 advance X-ray diffractometer (Germany, BRUKER Co. Ltd). Transmission electron microscope (Type 2010, Japan, JEOL Co. Ltd) was used to characterize the morphology and structure of the particles under an accelerated voltage of 200 kV. Differential thermal analysis and thermogravimetry (STA449C, Germany,