Photoluminescence and photocatalysis of the flower-like nano-ZnO photocatalysts prepared by a facile hydrothermal method with or without ultrasonic assistance

The flower-like ZnO materials were hydrothermally synthesized with or without ultrasonic assistance. When low dosage of citric acid is used, ultrasonic treatment can enhance the distribution and complexation of Zn ions: the formed complicated citrates can serve as soft template directing the formation of seaweed-like ZnO/Zn(OH)(2) precursor: this precursor with citrates attaching on it serves as hard template for the formation of regular flower-like ZnO in the hydrothermal condition. The photoluminescence spectra have identified several kinds of defects in as-synthesized ZnO materials, such as oxygen vacancy (V-o), zinc vacancy (V-Zn) and interstitial zinc (Zn-i). The activity evaluation and kinetic calculation show that the samples with higher relative content of oxygen vacancy possess larger reaction rate constant and higher catalytic activity for Rhodamine B photodegradation. The employment of ultrasonic treatment during preparation decreases the relative content of oxygen vacancy, thus suppressing green emission and reducing the photocatalytic activity of such flower-like ZnO. (C) 2011 Elsevier B.V. All rights reserved.