“Two birds with one stone” strategy for oil/water separation based on Ni foams assembled using metal–organic frameworks

Membrane separation is a very promising and economical method for gravitational oil/water separation and the collection of oil spills. Both superhydrophilicity/underwater superhydrophobicity (SHL&UWSOB) and superhydrophobicity/superlipophilicity (SHB&SOL) are suitable materials for the solution. In this work, an ingenious design strategy of “two birds with one stone” to modify Ni foams (NFs) was developed, in which SHL&UWSOB was initially fabricated by the in situ growth of a bimetallic Fe/Ni-MOF on an NF surface by solvothermal synthesis. Further modification based on the resultant SHL&UWSOB-NF led to the construction of a SHB&SOL surface by simple immersion of stearic acid. The micro/nano structure beneficial to underwater superoleophobicity was tailored by optimizing the solvothermal reaction time in the range of 10–24 h. The results showed that SHL&UWSOB-NF was obtained with a high oil contact angle (OCA) of 165.9° under water when the time of the solvothermal reaction was kept at about 18 h. Likewise, the further modified NF exhibited an obvious SHB&SOL property with a water contact angle (WCA) of 156.3° and a water rolling angle (SCA) of 9°. The light oil (n-hexane) floating on the water's surface and heavy oil of carbon tetrachloride (CCl4) at the bottom of the water, as well as the mini-separation of oil/water, demonstrated its facile and versatile application as a separation medium. The strategy may offer new approaches for the fabrication of superwetting/superantiwetting separation materials for oil/water separation and oil collection.