Abstract
Nanostructured zinc oxide (ZnO) particles were synthesized by the one step Ultrasonic Spray Pyrolysis (USP) process from nitrate salt solution (Zn(NO3)2·6H2O). Various influential parameters, from Zn(NO3)2·6H2O 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.
Highlights
zinc oxide (ZnO) in a nanosized form is an indispensable candidate for electronic, optical, and gas sensors, as well as in catalysis applications, owing to its band gap value of 3.37 eV, large exciton binding energy of 60 meV and high electron mobility [1,2,3,4,5]
The enhancement in the photocatalytic performance was attributed to the combined effects of the hierarchical surface structure and the large surface area, which suppresses the recombination of photo-generated electrons (e−) and holes (h+), and expedites the diffusion of electrons [15]
In our previous study focusing on Ag/ZnO core shell nanostructured materials for photocatalytic applications, under some synthesis conditions, variation from the typical spherical morphology Ultrasonic Spray Pyrolysis (USP) into entangled plates was observed in ZnO particles without any additives [17]
Summary
ZnO in a nanosized form is an indispensable candidate for electronic, optical, and gas sensors, as well as in catalysis applications, owing to its band gap value of 3.37 eV, large exciton binding energy of 60 meV and high electron mobility [1,2,3,4,5]. ZnO microspheres exhibit excellent cycling stability and superior high-rate performance [16] These previous studies revealed that ZnO finds wide application areas, e.g., planar nano ZnO favors catalytic properties owing to its higher surface area, while granular nano ZnO is preferred in optical applications due to better absorption behavior, and battery applications due to structural stability and anti-corrosion capability [13]. In our previous study focusing on Ag/ZnO core shell nanostructured materials for photocatalytic applications, under some synthesis conditions, variation from the typical spherical morphology Ultrasonic Spray Pyrolysis (USP) into entangled plates was observed in ZnO particles without any additives [17] These findings raised the question of whether it is possible to tune ZnO particles morphology by the USP process with simplicity, good process control, high flexibility, and good scale-up potential, without any additives, obtaining high-purity products [17]. There has been no study in the literature utilizing USP to synthesize ZnO nanoparticles with the aim of obtaining different morphologies
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