Synthesis and optical property of ZnO/SiO₂ nanocomposite cryogels

In this paper, ZnO cryogels with a dopant of SiO₂ with molar ratio of 9:1 to 1:1 were prepared by sol-gel technology and dried by a novel vacuum freeze drying using a co-precursor method. The as-prepared ZnO/SiO ₂ nanocomposites were annealed in air at 250, 500 and 800 °C for 45 min, respectively. The structure and morphology of the nanocomposites were determined by X-ray diffraction (XRD) and field emission scanning electron microscopy. The optical properties were estimated not only by UV-visible spectrometer but also theoretical calculation. The annealed nanocomposites exhibited hexagonal Wurtzite structure ZnO and whose crystallinity became better as an increase of annealing temperature. The amounts of doping SiO₂ affect the optical band gaps and morphology of ZnO/SiO₂ nanocomposites significantly. After annealing, the obtained ZnO nanorods grow up in size from the SEM images with annealing temperature ranging from 250 to 500 °C and flowerlike ZnO was formed with tetragonal pillars at 800 °C.