Sandwich-Structured Nanofiber Membranes with Dual-Directional Water-Transport Ability for High-Efficiency Water Harvesting

Abstract

Previous research on water harvesting driven by directional water transport from ubiquitous atmospheric moisture is mainly based on one-dimensional (1D) filaments with asymmetric hydrophilic/hydrophobic wettability along the filaments, two-dimensional (2D) surfaces with hydrophilic and hydrophobic patterns, and three-dimensional (3D) porous structures with "Janus" wettability from hydrophilic to hydrophobic. However, it remains an ongoing challenge to design and construct porous fibrous membranes with efficient directional water transport capability in the thickness direction and excellent water-collection performance. Herein, a sandwich-structured nanofibrous membrane showing unusual dualdirectional wicking capability has been developed for water harvesting. In comparison to the Janus membrane with a water-collection efficiency of 45.92 g/cm 2 /h, such a dual-directional wicking fibrous membrane has a much higher water-collection capacity (425.96 g/cm 2 /h) and excellent water-storage capacity. The highly efficient water-harvesting capacity originates from the strong force to draw water from the outer hydrophobic layer to the middle superhydrophilic layer and the permeable channels formed by the hydrophobic fibrous structures. The large pores in the outer hydrophobic layer and the small pores in the middle superhydrophilic layer facilitate water harvesting because of the dual-directional water-transport ability. The successful preparation of dual-directional wicking nanofiber membranes would be valuable for the development of advanced water harvesters for diversified applications.