Hierarchical Fusiform ZnO-Constructed Nanoflowers Electrodeposited on Stainless-Steel Mesh with Switchable Wettability for On-Demand Separation of Oil–Water Emulsion and Photocatalytic Degradation for Water-Soluble Pollutants

Hierarchical zinc oxide (ZnO) micronano structures have attracted plenty of research interests, which are extensively applied in emulsion separation and photocatalysis. In this study, fusiform ZnO-constructed nanoflowers were coated on a stainless-steel mesh (SSM) via an easy one-step electrodeposition approach. The ZnO@SSM membrane exhibited excellent superhydrophilicity with a water contact angle (WCA) of approximately 0° and underwater superoleophobicity with an underwater–oil contact angle (UOCA) of 164.3°. Reversible wettability transformation of the ZnO@SSM membrane between superhydrophilicity/underwater superoleophobicity and superhydrophobicity/superoleophilicity was quickly achieved by the alternate treatment on the membrane with stearic acid (SA) ethanol solution and NaOH solution. The designed membrane can synchronously possess considerable oil–water emulsion separation capacity and efficient photocatalytic degradation for a water-soluble pollutant. The separation efficiency (SE) of surfactant-stabilized emulsion was greater than 99.0%, along with fast permission fluxes up to 489.4 L·m–2·h–1 (oil-in-water) and 676.0 L·m–2·h–1 (water-in-oil). The maximum degradation efficiency for methylene blue (MB) solution was up to 99.0% under visible-light irradiation in 90 min. This novel, sustainable, and multifunctional membrane with a hierarchical structure of fusiform ZnO-constructed nanoflowers has a wide application prospect in the treatment of practically emulsified wastewater.