Abstract.This study presents an experimental approach for fabricating super-hydrophobic coatings based on a dual roughness structure composed of zinc oxide nanorod arrays coated with a sputtered zinc oxide nano-layer. The ZnO nanorod arrays were grown by mean of low-temperature electrochemical deposition technique (75°C) on FTO substrates with pre-sputtered ZnO seed layer of 30 nm thickness. The ZnO nanorods show a (002) orientation along the c-axis, and have a hexagonal structure, with an average length of 710 nm, and average width of 156 nm. On the other hand, the crystallite size of the top-coating sputtered ZnO layer is of 30 nm. The as-deposited ZnO nanorod arrays exhibited a hydrophobic behavior, with a surface water contact angle of 108°, whereas the dual-scale roughness ZnO nanorods coated with sputtered ZnO exhibited a superhydrophobic behavior, with a surface water contact angle of 157° and high water droplet adhesion. The photo-catalytic degradation of methylene blue in the presence of both the single roughness ZnO nanorod arrays, and dual roughness structured ZnO. The ZnO nanorod arrays showed good activity, with a degradation efficiency of 50% and a degradation constant of (k = 0.00225 min -1 ) after 5 hours of UV illumination. On the other hand, the ZnO dual roughness structure prepared by sputtered ZnO on top of the ZnO nanorod arrays showed minimal activity, with a degradation efficiency of 16% and a degradation constant of (k = 0.000586 min -1 ) after 5 hours of UV exposure. The double structured films exhibited high sensitivity to UV light, with a UV-induced switching behavior from super-hydrophobic to super-hydrophilic after only 30 minutes of UV exposure.Key Words: Super-hydrophobic, water contact angle, zinc oxide, nanorod arrays, rose petal effect, photo-catalysis. Highlights Hydrophobic ZnO nanorod arrays with high water-adhesion are achieved. Sputtered ZnO top-coating is used to reach super-hydrophobicity. Switchable wettability for ZnO single and dual roughness films under UV exposure. Strong pinning to the surface, similar to the rose-petal effect. The higher WCA is responsible for the decrease in the photo-catalysis activity.

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