AbstractWater purification through photocatalysis is the most important requirement due to the increased health, environmental and energy conservation concerns. Metal oxide nanostructures have played a very prominent role in this direction. ZnO is a promising material in terms of nanostructuring and photocatalysis. This study presents a unique easy-to-follow synthesis for ZnO micro- and nanowires by a flame-based approach. The photocatalytic activity of these grown ZnO nano- and microwires against methylene blue (MB) has been investigated in detail and a possible decomposition pathway is proposed. During repeated photocatalysis, a significant improvement in the decomposition rate was achieved which is mainly attributed to surface modifications of the ZnO wires due to the reaction with MB as confirmed by Raman-spectroscopy and X-ray photoelectron spectroscopy (XPS) investigations. The impact of the MB over involved nanostructures is thus an important aspect for the efficiency of the photocatalysis which is briefly presented here.