Underoil superhydrophilic desert sand layer for efficient gravity-directed water-in-oil emulsions separation with high flux

Abstract

Efficient and rapid separation of emulsified oil/water mixtures is urgently needed and still remains a worldwide challenge. Even though traditional superhydrophobic/superoleophilic filtration membranes have demonstrated to be effective for separation of water-in-oil emulsions, they still suffer from complicated fabrication procedures and lower flux, resulting from their nanoscale pore size. Herein, green desert sands (50 μm to 1 mm) with under-oil superhydrophilicity were introduced, for the first time, to develop into a layer for efficient gravity-directed separation of various water-in-oil emulsions, which could avoid not only sophisticated filtration membranes fabrication process but also the use of expensive low energy materials of fluorosilane involved in traditional superhydrophobic materials. It is worth mentioning that the sand layer could serve as an adsorbent material with under-oil superhydrophilicity, achieving ultrafast gravity-driven separation of tiny water droplets from various water-in-oil emulsions with flux as high as 2342 L m⁻² h even though the interspacing between the sand particles is greater than the size of emulsified droplets. Moreover, the sand can be abundantly obtained from deserts, which is another advantage that the current filtrate materials do not possess. In summary, this study provides a general avenue to design under-oil superhydrophilic materials for rapid separation of water-in-oil emulsions. Such an approach can provide some new perspectives for fabrication of novel emulsion-separating materials.