A TiO₂-SAD Janus membrane for unidirectional water transport in both air and oil

In recent years, Janus membranes with asymmetric wettability have shown broad prospects in fields such as directional liquid transport and oil/water separation. However, current Janus membranes generally exhibit efficacy solely in a single medium (air or oil), a factor that substantially restricts their practical utility across multiple media. Herein, we report a stearic acid modified TiO₂ (TiO₂-SAD) Janus membrane with unidirectional permeation capability in both air and oil. By controlling the UV irradiation time (60 min in air, 120 min in oil), the asymmetric wettability of the membrane is regulated, thereby achieving such dual-medium unidirectional permeation. The membrane exhibits excellent cyclic reusability, maintaining favorable unidirectional permeation performance after 20 cycles. Furthermore, it possesses broad adaptability, showing unidirectional permeability toward aqueous solutions with different pH values in both air and oil, while enabling underoil unidirectional permeation for oils with varying viscosities, tensions, and both light and heavy oils. It facilitates versatile utilization in both air and oil, capable of separating immiscible oil/water mixtures (separation efficiency >99 %) and achieving in-situ demulsification of water-in-oil emulsions, as well as multifunctional applications including fog collection in air and underoil water harvesting. This novel TiO₂-SAD Janus membrane demonstrates versatility in both air and oil, offering new perspectives for Janus membrane development.