Tuning the morphology of ZnO nanostructures with the ultrasonic spray pyrolysis process

Nanostructured zinc oxide (ZnO) particles were synthesized by the one step Ultrasonic Spray Pyrolysis (USP) process from nitrate salt solution (Zn(NO₃ )₂·6H₂ O). Various influential parameters, from Zn(NO₃ )₂·6H₂ O concentrations (0.01875–0.0375 M) in the initial solution, carrier gas (N₂ ) flow rates (0.5–0.75 L/min) to reaction temperature (400–800^◦ C), were tested to investigate their role on the final ZnO particles’ morphology. For this purpose, Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM) and (Selected Area Electron Diffraction) SAED techniques were used to gain insight into how the ZnO morphology is dependent on the USP process. It was revealed that, by certain parameter selection, different ZnO morphology could be achieved, from spherical to sphere-like structures assembled by interwoven nanoplate and nanoplate ZnO particles. Further, a more detailed crystallographic investigation was performed by XRD and Williamson-Hall (W-H) analysis on the ZnO with unique and non-typical planar morphology that was not reported before by USP synthesis. Moreover, for the first time, a flexible USP formation model was proposed, ending up in various ZnO morphologies rather than only ideal spheres, which is highly promising to target a wide application area.