Janus Fibrous Mats Based Suspended Type Evaporator for Salt Resistant Solar Desalination and Salt Recovery

Solar desalination has been recognized as an emerging strategy for solving the pressing global freshwater crisis. However, salt crystallization at the photothermal interface frequently causes evaporator failure. In addition, arbitrary discharge of concentrated brine produced during desalination results in potential ecological impacts as well as wastage of valuable minerals. In the present work, a suspended-type evaporator (STEs) constructed using Janus fibrous mats is reported. The fibrous structure wicks brine to the evaporation layer and the salt gets confined in the evaporation layer until crystallization for zero liquid discharge due to the suspended design. Enhanced evaporation is observed because STEs have an additional low-resistance vapor escape path directly from the evaporation layer to the atmosphere compared to traditional floating Janus evaporators. Moreover, owing to the drastically different wettability on both sides, the evaporator allows salt crystallization only on the hydrophilic bottom layer, thus eliminating salt accumulation at the hydrophobic photothermal interface. With this unique structural design, the proposed evaporator not only maintains a high evaporation rate of 1.94 kg m^-2 h^-1 , but also demonstrates zero liquid discharged salt resistance and ideal recovery of the mineral in brine.