Simple and Large-Scale Preparation of Superhydrophobic Zno Surface Mediated by Acetic Acid

A simple, large-scale preparation of superhydrophobic ZnO surfaces from zinc nitrate and hexamethylenetetramine mediated by acetic acid is described. ZnO crystals formed first in solution and then deposited onto the substrate surface forming a thin film. Different amounts of acetic acid offered different morphological ZnO surfaces. These were characterised by scanning electron microscope, X-ray photoelectron spectroscopy and contact angles. When 1.5–2.5 mL 5% acetic acid was added into a solution containing 20 mL (0.1 mol L^-1) Zn(NO₃)₂·6H₂O and 20 mL 0.1 mol L^-1 hexamethyltetramine at 95 ^oC for 2 h, the bulk ZnO surfaces showed superhydrophobic properties with water contact angles higher than 150°. Furthermore, their reversible switching from a superhydrophobic state to a superhydrophilic state was achieved by alternation of the UV irradiation and dark storage. This process was repeated several times without any obvious deterioration in performance.