Low‐Temperature Water‐Assisted Oxidation of Sponge‐Like Zn Nanostructures for Environmental and Energy Harvesting Applications

In this work, the oxidation of sponge‐like nanostructured Zn films exploiting their interaction with water in liquid and vapor phases is investigated. By simply exposing the sputtered porous metal layers to a water vapor atmosphere or incubating them in water at different temperatures, the full conversion to ZnO is obtained. Depending on the kind of treatment, the oxidized ZnO layers exhibit different morphologies and physico‐chemical properties. When in combination with low heating of the surface, a better crystallinity and the growth of hexagonal nanocrystals (nanoprisms and nanoflowers) from the nanobranched Zn structure is observed, preserving the sponge‐like morphology of the starting material. Good photocatalytic activities for the degradation of an organic dye are measured under simulated sunlight irradiation. The piezoelectric and semiconducting response of the oxidized ZnO layers is also examined, revealing appealing performance in both cases and envisaging their use as nanogenerators and photoanode material in dye‐sensitized solar cells. The multifunctional properties of the oxidized ZnO film are discussed in terms of the selected water oxidation approach that tune the corresponding morphology and crystallinity. The low‐temperature oxidation approaches here proposed allow the fabrication of flexible semiconductive ZnO films highly desirable in different fields of nanoelectronics. Semiconductive ZnO films with multifunctional properties are obtained with a low temperature oxidation approach that envisages their integration in flexible devices highly desirable in different fields of nanoelectronics. The photocatalytic, photovoltaic, and piezoelectric charge‐generation behaviors can be maximized by selecting a particular water oxidation approach, that tune the ZnO morphology and crystallinity and finally, the resulting multifunctional properties of ZnO films.