Janus porous membranes with asymmetric wettability and self-floating properties for solar desalination

Abstract

The scarcity of freshwater is one of the challenges faced by humanity today. Solar desalination technology is gaining increasing attention due to its environmental friendliness and sustainability. However, the service life of the evaporator is significantly reduced by the problem of salt deposition during the evaporation process. In this work, a porous Janus evaporator with asymmetric wettability was fabricated using an atomization-assisted non-solvent induced phase separation method. The bottom surface of the Janus evaporator was fabricated with polyacrylonitrile and polyvinylpyrrolidone, working as capillary "pumps" to ensure adequate water supply. The upper surface was made of polyvinylidene fluoride which endows the evaporator with self-floating properties and the addition of CNTs improves its solar-to-vapor conversion efficiency. The micro-nano composite continuous porous structure of the Janus evaporator is beneficial to the enhancement of the capillary action, leading to good salt-repellent performance. The solar-to-vapor efficiency of the seawater desalination experiment under 1 kW·m−2 of sunlight was 81.61%, and the water evaporation rate was 1.30 kg·m−2·h−1. In addition, the evaporator exhibited excellent stability under multiple cycles. It also functioned well in the treatment of organic wastewater. This work provides a novel method for preparing solar desalination materials.