Heterogeneous growth mechanism of ZnO nanostructures and the effects of their morphology on optical and photocatalytic properties

Zinc oxide (ZnO) nanoflowers have huge potential for various applications. However, the growth mechanism of ZnO nanoflowers is still under debate despite various growth mechanisms having been proposed. The aim of this study is to investigate the growth mechanism of different morphologies in a single sample; hopefully, this might help to understand the exact growth mechanism of ZnO nanoflowers. Herein, two models are proposed: (I) the growth mechanism of different morphologies (shapes) in a single sample; and (II) the growth mechanism of different sized ZnO flowers in a single sample. The present work also investigates the mechanism for how morphology assists in tuning the properties of nanomaterials, which is still unclear to date. New insight into the relationship between morphology and native defects has been introduced in this work. XPS, photoluminescence, and FT-IR analyses reveal the presence of oxygen vacancy defects in the structures of the materials prepared, with respect to their morphology. These defects act as self-dopants. Therefore, a change in their concentration results in tuning the band gap and thereby the photocatalytic activity.Parts of this work were supported by UGC JRF grant No F.19-1/2013(SA-I), dated 27 October 2015, Guangdong Hong Kong joint innovation project (Grant 2016A050503012), and the National Natural Science Foundation of China (Grant 51406075). Thanks are also given for the helpful comments from Professor R. Somashaker, Department of Physics, University of Mysore, Mysuru, India.Scopu