Unsophisticated one-step synthesis super hydrophilic self-cleaning coating based on ZnO nanosheets

In this paper, zinc oxide nanosheets are coated on a porcelain substrate with reversible wettability using a one-step wet-chemical synthesis and spray-coating method. The wettability of 100-nm-thick ZnO coating surface is switched by ultraviolet illumination. Before UV illumination, the water contact angle of this surface is measured at about 70o. Results show that under UV irradiation, ZnO coating becomes super-hydrophilic (WCA < 9 degrees). Conversely, the water contact angle becomes about 70 degrees after preserving the coating in a dark place. In more detail on ZnO structures, the water absorption on the defective model of ZnO nanosheet is analyzed based on first principle ab initio density functional theory. Simulation results depict water molecule has no tendency to stick to nanosheet with zinc vacancy. While the ZnO nanosheet with oxygen vacancy absorbs the water molecule. Consequently, ZnO coating shows self-cleaning abilities on hydrophilic and super-hydrophilic surfaces. Also, ZnO nanosheet structures with controlled wettability can be applied in different applications such as biosensors and microfluidic devices.