Simply realizing durable dual Janus superwettable membranes integrating underwater low-oil-adhesive with super-water-repellent surfaces for controlled oil-water permeation

Janus wetting/non-wetting membranes are emerging asymmetric materials with opposing wettable interfacial properties. Because of the difference between the sides at an interface, they have been used in various practical applications such as unidirectional liquid transportation. However, newly developed Janus superwettable membranes are still highly desired and challenging, considering their conventional time-consuming preparation, oil-fouling contamination, and susceptible surface to mechanical damage. Herein, we propose a rapid and green fabrication method for durable dual Janus superhydrophilic (underwater superoleophobic)/superhydrophobic (superoleophilic) membranes, which integrate an underwater low-oil-adhesive with super-water-repellent surfaces for controlled oil-water permeation. The robust superhydrophilic and underwater superoleophobic surface can be rapidly created using a one-step chemical etching method. Then, underwater low-oil-adhesion is obtained for anti-oil-fouling. Moreover, a mechanically durable superhydrophobic coating with a super-water-repellent characteristic can be directly capped onto an etched stainless steel mesh (ESSM) through a rapid mechanical transferring process. Therefore, four kinds of wettable behaviors from one common interface can be readily realized for controlled oil-water permeation with an anti-oil-fouling property and high durability. The multifunctional membranes can combine superwettability-based oil-water separation and oil collection by a Janus membrane-based oil diode in the future. This will inspire the development of additional facial Janus superwettable membrane systems with extended applications.