Reversible switch of wettability of ZnO@stearic acid nanoarray through alternative irradiation and heat-treatment

The superhydrophobic ZnO@stearic acid (ZnO@STA) nanoarrays have been prepared and synchronously introduced plentiful oxygen vacancies by using hydrothermal method on the Zn substrate. After UV-Visible light irradiation, the superhydrophobic ZnO@STA surface is transformed into the superhydrophilic surface, which is mainly attributed to the excitation of electron-hole pairs and reaction with the adsorbed O-2 and H2O from air to form hydroxyl radicals on the ZnO@STA surface, and not photodegradation of STA. Also, the introduced defect energy levels of oxygen vacancies make more electron-hole pairs excited by visible light. Continuing to further heat the ZnO@STA surface, the photoinduced hydroxyl radicals are desorbed from the ZnO@STA surface, making the photoinduced superhydrophilic surface revert to the original superhydrophobic surface. And the reverse wetting transition can be accelerated through the increase of heating temperature. Moreover, the ZnO@STA nanorod array surface also exhibits excellent cycle stability of reversible switch between super hydrophobicity and superhydrophilicity.

Automated summary

Superhydrophobic ZnO@stearic acid nanoarrays prepared by hydrothermal method exhibit a transition to superhydrophilic surface under UV-Visible light irradiation, attributed to the excitation of electron-hole pairs and reaction with adsorbed O-2 and H2O from air. The introduced defect energy levels of oxygen vacancies promote the excitation of more electron-hole pairs by visible light. Heating the surface further desorbs the photoinduced hydroxyl radicals, reverting the superhydrophilic surface back to superhydrophobic, with accelerated transition by increasing temperature. Additionally, the ZnO@STA nanorod array shows excellent cycle stability in reversible switch between superhydrophobicity and superhydrophilicity.