Oxygen adsorption induced superhydrophilic-to-superhydrophobic transition on hierarchical nanostructured CuO surface

Hierarchical nanostructured CuO surface was embellished to amplify the wettability. The pristine superhydrophilic CuO surface spontaneously transited to be superhydrophobic after exposed in air at room temperature for about 3 weeks. The wettability change is attributed to the adsorption of oxygen molecules on the topmost layer according to the surface chemical analysis. The adsorbed oxygen molecules could be removed by dipping the sample into l-Ascorbic acid solution for 10 s, leading to the recovery of the pristine superhydrophilicity.

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► Hierarchical nanostructured CuO surface mimic lotus leaf was synthesized.
► The fresh surface is pristine superhydrophilic.
► It can spontaneously transit to be superhydrophobic after exposed in air.
► Oxygen adsorption induced that change according to XPS results.
► The superhydrophilicity returns after washed by l-Ascorbic acid solution.