Structure architecture of micro/nanoscale ZIF-L on a 3D printed membrane for a superhydrophobic and underwater superoleophobic surface

Surfaces with superhydrophobicity and underwater superoleophobicity have attracted tremendous attention in oil/water separation due to their high separation efficiency. The key challenge lies in the construction of a hierarchically micro/nanoscale structural surface. In this study, a hierarchically micro/nanoscale structural surface was synthesized by a simple two-step designing of a unique three-dimensional multiscale ZIF-L on a 3D printed membrane for a superhydrophobic and underwater superoleophobic surface. This approach involves the synthesis of two novel ZIF-Ls. The first ZIF-L synthesized by using an aqueous system with a relatively high concentration of 2-methylimidazole (Hmim) and zinc ions displayed a three-dimensional leaf-crossed structure. The second micro/nanostructural ZIF-L is obtained by a second growth of small flat rod-shape and needle-like ZIF-Ls on the surface of leaf-crossed ZIF-L. Two-step deposition of such multiscale ZIF-Ls on a rough 3D printed PA membrane yields a perfect multiscale micro/nano-structural membrane. This hierarchical surface endows the membrane with superwetting properties. When being coated with PDMS, this membrane exhibits extreme superhydrophobicity with a sliding water contact angle as low as 1.56 degrees and superoleophilicity with an oil contact angle of zero simultaneously. In addition, after being wetted with water, it demonstrates superhydrophilicity and underwater superoleophobicity. When these membranes are applied for oil/water separation, a high oil rejection of over 99% and an oil flux of over 24 000 L (m(-2) h(-1)) are attained. The stepwise ZIF-L design provides a facile and effective strategy to construct multiscale micro/nano-structures.