Rational design of robust flower-like sharp-edge acoustic micromixers towards efficient engineering of functional 3D ZnO nanorod array

Acoustofluidic micromixers have attracted considerable attention in recent years due to their unique features in terms of flexible control, contactless operation, and short mixing distance. However, optimizing geometry in acoustic micromixers to achieve robust mixing performance towards practical chemical engineering is still a great challenge. Herein, we first propose flower-like sharp-edge acoustic micromixers for developing functional 3D ZnO nanorod array. Numerical simulation and experimental validation are conducted to investigate the effect of petal numbers, spreading angles, and tip angles on the mixing performance. Generally, more petals need a larger spreading angle to achieve better mixing while a large spreading angle is unfavorable, and the mixing performance decreases with the increase of tip angles. Compared to single sharp-edge devices, flower-like sharp-edge ones always perform better mixing efficiency. The optimized device is utilized to synthesize well-defined 3D ZnO nanorod array inside a glass capillary and the excellent capabilities of photodegradation of dye and enrichment of heavy metal ions are examined. The photodegradation and enrichment efficiencies can be well regulated by adjusting the flow rates, and superior reusability of the engineered ZnO nanorod array is validated. These results not only provide important guidelines for the rational design of lab-on-a-chip devices, but also shed light on controllable synthesis of functional nanomaterials and other chemical engineering fields.