Facile and feasible synthesis of ZnO nanorods using microwave irradiation and their morphology dependence on capping agents

In the recent past zinc oxide (ZnO) has gained a lot of attention as a piezoelectric material. Its low cost, relative abundance, and ease of processing have made it a promising candidate to be used in various applications. In addition to it’s functional properties, its chemical stability and biocompatibility make ZnO suitable to be used in different environments. The synthesis of nanowires, nanorods, and other nano-structured morphologies of ZnO is highly important for the development of piezoelectric devices and solar cells. There are numerous methods for ZnO nanorod synthesis. The present research focused on the investigation of simple and low-cost synthesis methods of ZnO nanorods, namely microwave irradiation and usage of capping agents. According to the literature, the device performance improves with decreasing widths and increasing aspect ratios of ZnO nanorods. ZnO nanorods with desired size were obtained by chemical precipitation, using the readily available chemicals, ZnSO4 and NaOH, as precursor solutions; separately following microwave irradiation and the using appropriate capping agents, to control the size of the nanorods. The dependence of the size of the nanorods on the microwave cycle time intervals (15 s, 30 s and 60 s) was investigated, and a relative decrease in the size of the ZnO rods with larger cycle time intervals was observed utilizing scanning microscopic images. A width of ~177 nm and aspect ratio of ~6.7 was observed for the rods microwaved in 60 s cycle time intervals. The effect of starch, polyvinyl alcohol (PVA), and polyethylene glycol (PEG) was investigated as capping agents. Starch and PVA showed axial capping, increasing the width and decreasing the aspect ratio. PEG showed lateral capping, decreasing the width and increasing the aspect ratio, giving a width of ~182 nm and an aspect ratio of ~ 6.5. The XRD analysis of ZnO confirmed that the synthesized particles were in a Wurtzite phase. Hence, ZnO nanorods with the required wurtzite crystalline structure were synthesized in this research.