Ultrathin metal-mesh Janus membranes with nanostructure-enhanced hydrophobicity for high-efficiency fog harvesting

Abstract

Fog harvesting has been reckoned to be one of the most facile and economical approaches to alleviating the ever-increasing global water scarcity . Janus membranes, especially metallic ones, outperform other fog collectors in terms of fog harvesting efficiencies , and they are the selection for sustainable water production as passive devices. However, there is a lack of metallic Janus membranes with ultrasmall feature sizes due to the limitation of the laser ablation fabrication method , which restrains parameter optimization for highly efficient fog collectors. In this work, photolithography , electroplating , and nanoimprint lithography processes are employed to enable ultrasmall membrane thickness and nanopatterning on the membrane surface . A 4-μm-thick ultrathin hierarchical metal-mesh Janus membrane with a pitch of 60 μm is fabricated, which achieves a record-high water collection rate of 233 mg cm −2 ·min −1 with nanostructure-enhanced hydrophobicity . The morphology of the membrane is characterized by scanning electron microscopy, while the fog collection process is observed under a high-speed camera and a microscope. Experimental measurement and finite-element numerical modeling unveil that a smaller membrane thickness and a more hydrophobic water-collecting surface contribute to higher water collection rates by accelerating water transport and reducing water re-evaporation. • Photolithography and electroplating replace laser ablation for metallic JM fabrication. • Metallic JMs with unprecedented thickness down to 4 μm are fabricated. • Nanopatterning on JMs changes surface wettability and boosts WCR. • A record-high WCR of 233 mg cm −2 ·min −1 is achieved.