Janus Membrane with Bioinspired Heterogeneous Morphology for Efficient Fog Harvesting

Claiming water from the atmosphere or fog harvesting could be a promising route to relieve the scarcity of fresh water. The unidirectional water transportation of a Janus membrane has indicated a potential way of efficient fog collection. In this study, a facile two-step electrospun protocol was established to patch hydrophobic PVDF domains on a hydrophilic PAN nanofibrous texture in a designer manner inspired by the heterogeneous back structure of a desert beetle. The tuned heterogeneous surface morphology and the vertically varied wettabilities of the prepared Janus membrane indicated a more significant fog collection rate (FCR) than the homogeneous PAN or PVDF membrane. Moreover, the optimized Janus membrane (10 min of PVDF spinning on PAN to reach a coverage of 44.3%) indicated a promising FCR at 88.5 mg/(min cm²), which was comparable with the highest reported FCR of a more complicated organic/inorganic Janus system. It is possible that the synergistic effect of the capillary force and the Laplace pressure determined the high FCR of the Janus membrane in this study. In addition, the prepared Janus membrane was used for an efficient oil–water phase separation contributed by the excellent unidirectional water transportation effect. The novel morphology design protocol provided new insights of the Janus membrane fabrication, which obviously evoked the potential of the Janus membrane for practical applications.