ZnO nanoparticle-enhanced Zn/Ni superhydrophobic stainless steel mesh: Microstructural control for high-efficiency oil-water separation

The treatment of oily wastewater requires efficient separation materials. Superhydrophobic materials are promising due to their affinity for oil and repulsion of water, as well as their environmental friendliness. However, the key to their performance is the successful construction of stable micro/nanostructures on the material surface. In this study, a ZnO nanoparticle-enhanced Zn/Ni alloy hierarchical micro-nano composite coating (PZZNM) was successfully fabricated on 304 stainless steel mesh substrates through an electrodeposition-chemical modification synergistic process. Employing Cassie-Baxter theory for surface energy optimization, the developed PZZNM coating demonstrated exceptional superhydrophobic-superoleophilic characteristics: a water contact angle of 164° and an oil contact angle approaching 0°. These characteristics contribute to highly efficient oil-water separation. In chloroform/water separation tests, the PZZNM coating achieved a separation efficiency of 97.3 % and a flux of 6413 L·m−2·h−1. Systematic characterization revealed dual enhancement mechanisms enabled by ZnO nanoparticles: (1) Increased surface roughness (Sa value elevated from 19.251 to 22.955 nm) significantly enhanced superhydrophobicity; (2) Intrinsic chemical inertness substantially improved corrosion and oxidation resistance. Notably, the coating maintained stable superhydrophobicity (water contact angle >158.5°) and oil-water separation efficiency (>93.5 %) under extreme conditions, including strong acids, alkalis, and mechanical abrasion. Therefore, it can be foreseen that the continuous gravity-driven separation system developed based on this innovative material provides a robust solution for complex industrial oil-water separation challenges.