A Janus evaporator based on Donnan effect for efficient solar thermal desalination

Abstract

Interfacial solar steam generation (ISSG) is a solution to alleviate the energy crisis by obtaining clean water at low cost. In order to maintain high evaporation rates in high salinity brines, it is necessary to develop a new ISSG device with controlled heat loss and good salt resistance. In this paper, polyvinyl alcohol (PVA) was used as the backbone to construct ion-selective hydrogel, and hydrogel network with multiple hydrophilic groups was formed using Fe3O4 as a broadband light absorber. Specifically, the evaporator is suspended on the water surface with evaporation rate of 3.04 kg·m−2·h−1 under one sun irradiation. The bilayer hydrogels can permeate Cl− and Na+ selectively. The improved salt resistance is due to the exclusion mechanism of the Donnan effect, with the formed potential difference of 157.4 mV at a brine concentration of 3.5 wt%. Even if it is suspended on the water surface in a high concentration of brine, there will be no salt crystals generated. The developed Janus ion-selective hydrogel-based evaporator shows great prospect for desalination and other advanced solar thermal applications.