Fabrication of fluorine-free ZnO/CuO nanocomposite superantiwetting surfaces with reversible wettability tuning

Tunable dual-responsive superantiwetting hierarchical ZnO/CuO nanocomposite surfaces were prepared with mixing different starting molar ratios of copper and zinc nitrates solutions by the chemical bath deposition method. The fluorine-free composite surfaces indicated excellent superhydrophobic properties. The morphology and structure of the samples were analyzed by SEM, XRD, EDS and Raman analyses. Moreover, the abrasion resistance and underwater stability were evaluated. The SEM results exhibited the formation of dual-scale ZnO/CuO nanostructures combined nanorods, flower-like and urchin-like features on the stainless steel meshes. Compared to the ZnO surface with water contact angle (CA) of 149 degrees +/- 1.4 degrees and contact angle hysteresis (CAH) of 2.5 degrees +/- 0.6 degrees, the ZnO/CuO nanocomposite with Zn2+:Cu2+ initial molar ratio of 4:1 displayed higher CA (161.4 degrees +/- 2.1 degrees) and lower CAH (1.5 degrees +/- 0.5 degrees) values. However, the amounts of CAs decreased dramatically after post-annealing treatment at 300 degrees C (similar to 0 degrees) or UV irradiation (27 degrees +/- 2 degrees) while the water droplets were completely pinned on the surface. The surface again became superhydrophobic by further annealing at 150 degrees C for 30 min. Results revealed that the photo-induced hydrophilic properties of the ZnO/CuO nanocomposites were much better than that of the ZnO surface. Additionally, Raman assessments confirmed that the surface defective sites play key roles in the wettability alteration of the fabricated surfaces.