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

Abstract

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° 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.