Controllable self-foaming preparation of durable superhydrophobic/superlipophilic polyurethane sponge for efficient oily emulsions separation

Superhydrophobic polyurethane (PU) sponges as ideal absorbent materials have attracted significant interest for oil/water separation while their durability is dramatically limited by the poor mechanochemical stability. In this work, a durable superhydrophobic sponge with special hierarchical micro/nano was fabricated by in-situ anchoring of expanded graphite (EG) and TiO2 particles under polarity-induced phase separation during facile self-foaming process. After maturation for 3 h, the prepared sponge exhibited asymmetric wettability with the water contact angle (WCA) was up to 157.9 ± 1.5° and oil contact angle (OCA) was 0°, which could selectively absorb diverse oils range from 11.48 to 41.60 times of its own weight and oily emulsion separation efficiency was up to 99.80 %. In addition, due to the enhancement of the interface bonding force between the prepared sponge skeleton and EG@TiO2 particles through the crosslinking of foaming resin during the self-foaming process, the absorption capacity of the prepared sponge decreased by only 3.74 % and the stress attenuation was only 14.10 % after 150 absorption cycles, indicating its excellent recyclability and mechanical stability. Notably, when subjected to the harsh environment including acid/alkali conditions, high temperatures, salt solutions and organic solvents, the prepared sponge could remain stable superhydrophobicity with the WCAs all over 154.4° ± 1.5°, demonstrating its excellent chemical stability. Besides, PU/EG@TiO2 sponge demonstrated prominent antifouling and self-cleaning properties. Overall, this work provided an advanced idea for the preparation of superhydrophobic sponge with outstanding mechanochemical stability, which exhibited great potential in the treat of oily emulsified wastewater.