Ultrasonic cavitation-modulated nanocrystal facets growth of zinc-based oxide

In this study, in situ detection of the transient cavitation intensity during the sonochemical synthesis of Zinc-based Oxide (ZBO) is realized. At a fixed ethanol/water ratio of 25%, the transient cavitation intensity initially increases to a certain level during the nucleation stage of ZBO since the growth units of ZBO serve as supplementary induction sites for transient cavitation bubbles. Once the process surpasses the critical supersaturation point of ZBO growth units, a decrease of transient cavitation intensity is observed because the formation of massive ZBO nanocrystals may cause ultrasonic scattering attention. As a result, high-aspect-ratio ZBO nanorods are formed due to the preferential growth along the [0 0 1] direction. In addition, by increasing the ethanol/water ratio, a similar but decreasing trend in the time-dependent transient cavitation intensity during the ZBO synthesis process is obtained. This results in fewer ethanol molecules detaching from the ZBO (0 0 1) crystal surface, due to reduced cavitation bubble explosions, thereby inhibiting ZBO growth along the [0 0 1] direction. At an ethanol/water ratio of 75%, a morphological transition from slender nanorods to ultra-thin Zn₅(NO₃)₂(OH)₈·2H₂O nanoflakes is facilitated. These ultra-thin nanoflakes demonstrate promising photocatalytic performance. This work provides a rational sonochemical approach for synthesizing facet-controlled growth of nanocrystals.