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 (Vo), zinc vacancy (VZn) and interstitial zinc (Zni). 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.

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► The flower-like ZnO was successfully prepared with or without ultrasonic assistance.
► A special dual-template directing growth mechanism for such ZnO is proposed.
► The novel photocatalytic activity of such ZnO is highly related to oxygen vacancies.
► Ultrasonic suppresses green emission and decreases the catalytic activity of ZnO.