Janus wood membranes for autonomous water transport and fog collection

Autonomous and directional transport of liquids is crucial for many applications, ranging from microreactors to water harvesting. Particularly, Janus membranes, with asymmetric wettability on two sides, present enticing opportunities to address this challenge. With the inner driving force arising from the asymmetric wettability, Janus membranes can promote the desired transport without an external energy input. However, the elaborate bottom-up fabrication processes and poor mechanical performance of commonly employed membrane substrates often restrict their utilization, especially for engineering applications. Here, we report a wood-based Janus membrane demonstrating directional, spontaneous, and fast transport of water. Mechanically robust bio-based and renewable Janus wood membranes represent a crucial milestone towards larger-scale application of Janus membranes, for example in bilayer structures with excellent fog-capturing efficiency implemented in future smart building applications.