Polyvinyl alcohol formaldehyde three-dimensional composite sponges with hierarchical pore structure for W/O emulsion separation

• As-prepared sponge exhibits hierarchical pore structure and porosity being higher than 76 %. • The separation efficiency of sponge to W/O emulsion reaches to 99 %, the maximum flux is 2.94×10 6 L m -2 h -1 bar -1 . • The sponge has excellent recycling ability and separation efficiency has been maintained above 99 % every time. • The hierarchical pore structure has been constructed of the sponge plays a crucial role in size sieving. The emulsion separation of oily wastewater is always a challenge topic in both fundamental research and practical application. In this paper, polyvinyl alcohol formaldehyde composite sponges (PVF/PVF) with hierarchical pore structure were established by physical absorption/chemical crosslinking and hydrophobic modification via introducing hydrophobic long alkyl chain. As a result, pore size was adjusted from 74.8 µm of pristine PVF to less than 20 µm of hydrophobic PVF, the water contact angle was 120 o for final as-prepared sponges, i.e. size sieving and surface wettability could meet the need of emulsion separation. As-prepared sponges could separate W/O (water-in-oil) emulsion efficiently only under the action of gravity, with a maximum flux of 2.9 × 10 5 L m -2 h -1 bar -1 and separation efficiency nearly 100 %. More importantly, the as-prepared sponges displayed excellent reusability, which could be recovered by simply washing. These composite sponges, which were obtained by a simple method and low cost, could be easily scaled up in practical production process, providing an outstanding candidate material for efficient W/O emulsion separation.