Facet engineering of minerals for effective oil-water separation

Minerals have been growing as an emerging ‘hot’ topic in separating water-in-oil emulsions. Whether the intrinsic structure of minerals could precisely regulate water–mineral interactions for enhancing emulsions separation efficiency is still ambiguous. Here, taking half-hydrated gypsum as a case, this study reveals the crystal facet-dependent potential mechanism of minerals in water-in-oil emulsions separation. We show that the (2   0   4) facet of half-hydrated gypsum is more susceptible to water-induced degradation and hydration reaction. With combined experimental and theoretical studies, the facet-dependent mechanism for oil–water separation are revealed; the (2   0   4) facet that exhibited weak internal hydrogen bond and strong binding energy with water accelerated the dissolution and recrystallization of half-hydrated gypsum, thus enhancing oil–water separation efficiency. Through engineering, half-hydrated gypsum with a higher surface fraction of the (2   0   4) facet achieved much higher separation efficiency (99.9%), surpassing those of minerals in disclosed literature. This investigation not only contributes significantly to the comprehension of interactions at the minerals-water interface but also illuminates novel perspectives and avenues for the utilization of facet engineering in advancing research on mineral surface properties.