Ambient ultrasonic-assisted synthesis, stepwise growth mechanisms, and photocatalytic activity of flower-like nanostructured ZnO and Ag/ZnO

Flower-like nanostructured ZnO and Ag/ZnO catalysts were synthesized at ambient condition by a facile one-pot ultrasonic irradiation process. The ZnO morphology could be modified by both ultrasonic frequency and Ag amount. The acoustic cavitation effect dependent on ultrasonic frequency directly affects ZnO morphology. Doping of Ag not only promotes the transformation of zinc hydroxide to oxide, facilitating the formation of flower-like ZnO, but also enhances the photocatalytic degradation of Rhodamine B due to the promoted electron-hole segregation. The optimized ratio of Ag/Zn is 5 % (atomic ratio); more Ag can cover the surface of ZnO, decreasing the UV-vis light availability and mass transfer efficiency during reaction. The catalysts prepared at different ultrasonic frequencies show different UV-vis light absorbances and different UV-vis light availabilities. Among the catalysts of Ag/ZnO with 5 % Ag (ZA5-x), ZA5-100 prepared using 100 kHz ultrasonic frequency possesses the highest UV-vis light absorbance and best photocatalytic activity. Potential mechanisms for flower-like ZnO growth and Rhodamine B photodegradation are proposed.