Superwettable Janus membranes with unique interfacial characteristics have versatile applications in oil/water separation, microfluid transportation, and membrane distillation. However, it remains a significant challenge to simply fabricate three-dimensional (3D) metallic foams with Janus superwettability using a facile and environment-friendly method. In this study, a novel method is present to construct a Janus copper foam (CF) by combining superhydrophobicity and superhydrophilicity into CF. Based on gravity, the water in the light oil (LO)/water mixture can be transported from the superhydrophilic (SHL) side to the superhydrophobic (SHB) side, while the heavy oil (HO) in the HO/water/mixture can be transported from the SHB side to the SHL side. Therefore, cylindrical Janus oil/water separation devices with superior separation efficiency and excellent repeatability can achieve on-demand oil/water separation effortlessly. This design and fabrication method offers a novel avenue for the preparation of Janus interface materials for practical applications in liquid transportation, sensor devices, energy materials, and oil spills.

Janus membranes with superwetting play an important role in many fields, such as oil/water separation, unidirectional fluid transportation, microfluidic devices, intelligent ion valve, mass/heat transfer applications, etc. Although there has been some progress in the preparation of the Janus membranes with unidirectional penetration, it still remains a great difficulty for facile fabrication of two dimensional Janus membranes with a large pore structure and stable bubble unidirectional transport in the water. Herein, a signal-layer Janus membrane with superwetting is fabricated via the method of liquid-regulated hydrophobic modification strategy. The resultant Janus mesh achieves underwater unidirectional penetration. Namely, Underwater bubbles can pass unidirectionally from superhydrophobic side to hydrophilic side, but are blocked from passing through in the opposite direction. Thus, this Janus membrane with the unidirectional underwater bubbles penetration “diode” performance. We believe this work can promote the development of multi-dimensional Janus materials for fluid directional transport.