One-step rapid synthesis of ultrafine γ-Ga2O3 nanocrystals by microwave hydrothermal method in ammonium hydroxide medium

Ultrafine nanocrystals of gamma-gallium oxide (gamma-Ga2O3) were rapidly synthesized via microwave hydrothermal method at 140 degrees C, in which Ga(NO3)(3) was used as the gallium source and urea was the precipitant. The samples were characterized by X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UVVis), transmission electron microscopy (TEM), nitrogen physisorption and photoluminescence spectroscopy (PL). The crystallite size of ultrafine spinel gamma-Ga2O3 was in the range from 4 to 5 nm and the optical bandgap was 4.61 eV. To improve the crystallinity, the ultrafine gamma-Ga2O3 nanocrystals were calcined at 300-700 degrees C further. The ultrafine gamma-Ga2O3 calcined at 500 degrees C (calcined-gamma-Ga2O3) still remained the metastable gamma-phase with relatively high crystallinity and the crystallite size around 5-7 nm. Photocatalytic performances of the synthesized samples were also evaluated by the degradation of rhodamine B (RhB). Results revealed that the ultrafine gamma-Ga2O3 and the calcined-gamma-Ga2O3 samples exhibited high photocatalytic efficiencies of 68.2 and 90.7%, respectively.