Efficient separation of water-in-oil emulsions using superhydrophobic melamine sponges

Surfactant-stabilized water-in-oil emulsions, characterized by small droplet sizes and high stability, pose significant challenges for separation. Traditional demulsification techniques often require external energy and suffer from poor specificity, making the development of more efficient separation methods imperative. In this work, a three-dimensional material featuring micro/nano-scale hierarchical structures and a hydrophobic coating was fabricated via the facile functionalization of a melamine sponge with dopamine, hydroxy-terminated polydimethylsiloxane, and tetraethyl orthosilicate. The resulting superhydrophobic-superoleophilic material exhibited significant compressibility, with a water contact angle of 153.7° ± 1.1° and an underoil water contact angle of 159.9° ± 1.3°. The material attained a separation efficiency of 99.99% for immiscible oil-water mixtures. Moreover, an emulsion separation device was designed to evaluate the separation efficiency of the material. Even when separating various water-in-oil emulsions with extremely small droplet sizes and an oil-to-water ratio as low as 25:1, the separation efficiency remained consistently above 99.6%. Furthermore, the material demonstrated excellent reusability, maintaining high separation performance over 14 consecutive cycles. It also maintains excellent stability in high-salinity, THF, and weakly acidic and alkaline solutions, retains structural integrity after 24 hours of UV irradiation. Thus, the developed three-dimensional superhydrophobic material provides a straightforward, viable and energy-saving strategy for effective emulsion separation.