Effects of Thickness and Preheated Temperature on Grains Orientation of 2D-ZnO Nanostructure and their Photocatalytic Activity

Abstract

The effects of pre-heating temperature and thickness of layers on (002) preferred orientation of ZnO thin films and their photocatalytic activity are reported. All films crystallize into a Zincite-type structure. With increasing pre-heating temperature, the evolution from (002) to (101) diffraction peaks indicates change in growth mode of ZnO films. Pre-heating at 100°C is the most favourable for highly oriented ZnO thin films along (002) plane whereas all films deposited with different number of layers are oriented along (101) plane. The crystallite size is found to be in the range 20 - 32 nm. The observed average optical transmittance for these films is higher than 90% in the visible range. The energy band gap decreases with increasing number of layers but increases with increasing pre-heating temperatures. Wettability tests of ZnO thin films surface show a hydrophobic aspect for all films. The film pre-heated at 400°C with 223nm of thickness exhibits the highest degradation of methyl blue dye of 94% with high levels of photostability over five cycles.