Functionalized porous filtration media for gravity-driven filtration: Reviewing a new emerging approach for oil and water emulsions separation

Oil and water separation technology has been continuously progressing throughout the years. Recently, gravity-assisted filtration has gained considerable attention, although most of the studies have focused on oil and water synthetic mixtures which can be easily separated under gravity. It is deemed challenging for mechanically and chemically stabilized emulsions to be separated without the addition of an external pressure other than static gravity head. For this to be realized, filtration media should have high porosity to attain high flux but controlled pore size to achieve high selectivity. Moreover, in order to break down the emulsion, the surfaces of the filtration media should be endowed with superwetting properties. In this paper, different porous filtration media (metallic meshes, organic membranes, inorganic membranes, filter paper, and 3D materials) and the corresponding modification techniques and/or functionalization strategies utilized to improve their properties for efficient gravity-driven filtration applications are comprehensively reviewed.