Smart NiAl-LHDs-based superwetting Janus membrane based on charge demulsification for efficient separation of multiple emulsions and mixtures via multi-strategy synergy

In recent years, there has been an urgent need to remove low surface tension oil from oily wastewater due to the increasing industrial oily wastewater and the frequent occurrence of oil pollution incidents. Among these, emulsion separation in particular has become a global challenge. In previous studies, double layer hydroxides have been found to have hydroxide-rich surface and good hydrophilicity. Surprisingly, it is positively charged underwater, which is able to exert charge on oil-in-water emulsions containing anionic surfactants and thus demulsify them for efficient separation. Inspired by this, we prepared NiAl-LDHs on stainless steel mesh (SSM) by hydrothermal method, and then prepared Janus membrane by spraying method that can easily achieve on-demand separation of oil-in-water and water-in-oil emulsions, heavy oil/water and light oil/water mixtures. What's more, the prepared membrane maintains excellent performance after 10 cycles of emulsion separation and 25 cycles of oil–water separation. It maintains high hydrophobicity even after 50 impacts of sand and exhibits high repellency to acidic and alkaline droplets, so it can function in various harsh environments. The novel materials prepared in this work that can be used for charge demulsification and the proposed combination of multiple separation strategies have unlimited potential in the future of emulsion separation.