On-demand oil/water separation enabled by magnetic super-oleophobic/super-hydrophilic surfaces with solvent-responsive wettability transition

Abstract Materials with common super-wettability are always restricted either by the pores fouling by oil (super-hydrophobicity/super-oleophilicity), or by the formation of hydration layer in advance (super-hydrophilicity/underwater super-oleophobicity) during oil water separation. To resolve this problem, super-oleophobic/super-hydrophilic surfaces were fabricated by introducing magnetic nanoparticles, short-chain fluorine groups and hydrophilic-induced units into the 2D or 3D substrates. Wettability formation mechanism was systematically investigated by combining theoretical calculation with characterization of surface micro-morphology and chemical composition. Surfaces with the uncommon super-wettability exhibited excellent anti-oil fouling ability, and can be directly used for oil water separation in way of “water removing”. Moreover, a solvent-responsive wettability transition strategy was proposed, which can reversibly convert the super-oleophobic/super-hydrophilic surfaces into super-oleophilic/underoil super-hydrophobic surfaces within 10 s. Then, free light or heavy oil/water separation and demulsification of oil-in-water emulsions and water-in-oil emulsions were achieved through the switchable surface wettability toward water and oil. Furthermore, the super-wettability of as-prepared samples are almost unchanged even after the test of immersion in pH = 1 acid and pH = 14 alkali solution for 48 h and 100 cycles of successive cyclic compression. Hence, these unique advantages of the super-oleophobic/super-hydrophilic surfaces are promising for multitasking and highly efficient oil water separation and demulsification.