Unidirectional solute transfer using a Janus membrane

A membrane as a selective barrier of mass transfer is of great importance for applications in analysis, environment, energy, and biology. Unidirectional solute transfer that would improve membrane process flow is a challenge. Here, macroscopic extreme wettability of membranes controlling microscopic solute transfer is presented. A Janus membrane is prepared by integrating underoil superhydrophobic (UOSH) and underwater superoleophobic (UWSO) surfaces. Without or with electric field, solutes pass through the Janus membrane from the UOSH side to the UWSO side, but are impeded from penetrating in the reverse direction. The UWSO surface has a high affinity toward solutes in water compared to the UOSH surface at their interface. The composite membrane realizes unidirectional solute transfer, which can be considered as a solute transfer diode. This study may promote the understanding of the correlation between macroscopic and microscopic interfacial behaviors and facilitate the design of interfacial materials for controllable solute transfer and separation.