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 × 106 L m-2h−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.