Nanostructured copper hydroxide-based interfaces for liquid/liquid and liquid/gas separations

• An under-liquid super-repellent surface was fabricated by a facile method. • Exhibits dual superlyophobic under immiscible liquid including oil/oil system. • All separation efficiencies were above 99% and remained stable after 40 cycles. • Separation of gas from bulk water and oil was also achieved. Development of an under-liquid super-repellent (ULSR) surface that can act as a versatile platform for separating both liquid/liquid and liquid/gas mixtures is highly desirable, yet still hard to realize. Herein, to address this challenge, a Cu(OH) 2 nanowire textured surface on copper mesh was developed through a simple immersion process. The resulting Cu(OH) 2 nanowire surface displayed underwater superoleophobicity, underoil superhydrophobicity, and unusual dual superoleophobicity under immiscible oil-oil system. Exploiting its superlyophobicity under-liquid, the Cu(OH) 2 nanowire covered copper mesh was applied to separate oil/water mixtures, emulsions, and oil/oil mixtures effectively, even though the surface tension between two liquids was just 2.4 mN/m. The separation efficiency is higher than 99% for all mixtures, and the oil/water separation efficiency can maintain above 98% even after 40 cycles. Furthermore, owing to its superaerophobicity underwater and underoil, the obtained copper mesh was also able to separate gas from bulk water and oil efficiently. This work is hoped to provide a key addition to the fields of ULSR surfaces as well as membrane-based separation techniques.