Hierarchical Superwetting ZOMO-PAA@CuC<sub>2</sub>O<sub>4</sub> Nanorod-Coated Copper Mesh for Robust and Efficient Oily Wastewater Treatment.

Abstract

Efficient oil-water separation remains a major challenge in oily wastewater treatment, highlighting the need for advanced materials that combine superwettability, structural durability, and long-term recyclability. Here, we develop a hierarchical ZOMO-PAA@CuC₂O₄ NR@CM membrane via sequential chemical oxidation, oxalic acid etching, and spray-coating of ε-Keggin-type Na-ZnM ZOMO nanoparticles within a polyacrylic acid (PAA) matrix. The resulting architecture couples CuC₂O₄ nanorods with hydrophilic ZOMO-PAA coatings to achieve superhydrophilicity and underwater superoleophobicity. Structural characterization confirmed uniform nanoparticle dispersion, high crystallinity, and robust framework integrity. The membrane exhibits ultrafast water spreading (0°), underwater oil contact angles above 150°, and sliding angles as low as 4°, enabling broad-spectrum oil repellence, antifouling, and self-cleaning. The as-prepared membrane efficiently separates both surfactant-free and surfactant-stabilized emulsions, including aliphatic and aromatic oils stabilized by cationic, anionic, and non-ionic surfactants, with high water fluxes (1695-2675 L·m^-2·h^-1 and ~900 L·m^-2·h^-1, respectively) and separation efficiencies above 99.1%. The membrane further demonstrates chemical stability under acidic, alkaline, and saline conditions, alongside consistent oil-water separation behavior across multiple cycles. These findings establish ZOMO-PAA@CuC₂O₄ NR@CM as a robust and scalable platform for advanced oily wastewater treatment.