ZnO-Nanowires-Coated Smart Surface Mesh with Reversible Wettability for Efficient On-Demand Oil/Water Separation

Abstract

The rapid industrial growth has led to the large production of oily wastewater. Treatment of oily wastewater is an inevitable challenge to manage the greater demand of clean water for the rapidly growing population and economy. In the present work, we have developed a smart surface mesh with reversible wetting properties via a simple, ecofriendly, and scalable approach for on-demand oil-water separation. ZnO nanowires (NWs) obtained from the chemical vapor deposition method were coated on a stainless steel (SS) mesh. The as-synthesized ZnO-NWs-coated mesh shows superhydrophilic/underwater superoleophobic behavior. This mesh works in "water-removing" mode, where the superhydrophilic as well as underwater superoleophobic nature allows the water to permeate easily through the mesh while preventing oil. The wetting property of ZnO-NWs-coated mesh can be switched easily from superhydrophilic to superhydrophobic state and vice versa by simply annealing it at 300 °C alternatively under hydrogen and oxygen environment. The separation is solely driven by gravity. Thus, the reversible wettability of ZnO NWs provides a smart surface mesh which can be switched between "oil-removing" and "water-removing" modes. It was found that for more than 10 cycles of mesh reutilization in both modes alternatively, the separation efficiency of 99.9% stayed relatively invariant, indicating a prolonged antifouling property and excellent recyclability. This work provides a simple, fast, cost-effective, and on-demand solution for oily wastewater treatment and opens up new perspectives in the field of controllable oil-water separation.

Surface Engineering of Ceramic Nanomaterials for Separation of Oil/Water Mixtures

“…Inspired by the progress in ZnO-based nanomaterials, a unique approach was adopted to develop a mesh for the separation of oil/water mixtures. A mesh was developed by growing ZnO nanowires on stainless steel mesh by CVD, which demonstrated reversible wettability (Raturi et al, 2017 ). The mesh demonstrated superhydrophilic and underwater superoleophobic behavior, allowing it to let the water penetrate through its pores while blocking the oil.…”

“…(D,E) The separation device used for the separation of oil/water mixtures by using ZnO-coated mesh. Adapted from Raturi et al ( 2017 ). With permission from the American Chemical Society, copyright 2017.…”

External‐Field‐Induced Gradient Wetting for Controllable Liquid Transport: From Movement on the Surface to Penetration into the Surface

“…When a ZnO-nanowire-coated mesh was annealed at 300 °C in an atmosphere of oxygen and hydrogen, its surface wettability could be switched between superhydrophilic and superhydrophobic for different types of oil-water separation (i.e., waterremoval and oil-removal modes, respectively). [166] …”

Colloidal Transfer Printing–Mediated Fabrication of Zinc Oxide Nanorods for Self‐Cleaning Applications

“…Recently, Singh and co‐workers have reported the fabrication of superhydrophilic ZnO nanowires by CVD technique, which shows reversible wettability characteristics when annealed in a H 2 /O 2 gas environment . Such ZnO nanowires coated on stainless steel mesh can be reversibly switched between water‐removing or oil‐removing modes by alternate annealing in oxygen and hydrogen environments . Gong et al have demonstrated that the length of ZnO nanowires, fabricated on silicon pyramid surface, has a significant effect on their wetting characteristics.…”