Salt-resistant agarose-polyvinylpyrrolidone composite hydrogel with pitted-surface towards highly efficient water desalination and purification

In recent years, solar energy interfacial evaporation technology has been extensively explored for seawater desalination and wastewater treatment. However, salt accumulation and complex fabrication of evaporator largely constrains the applications of this technology in practice. Here, one type of interpenetrating polymer network hydrogel composing of agarose (AG) and polyvinylpyrrolidone (PVP) using polypyrrole (PPy) as the light absorbent was fabricated via “hot-ice” template method, which was featured with pitted-surface and microchannels structure. The evenly arranged pits on the surface of the hydrogel can absorb the sunlight as much as possible and convert it into heat energy, improving the efficiency of photothermal absorption. The water channels generated by the formation of CaCl2·6H2O crystals can transport water from the bottom to the evaporation interface elevating the transmission rate and accelerating the exchange of gradient salt concentration. As consequences, excellent salt resistance of the hydrogel can be obtained, achieving seawater evaporation rate as high as 3.2 kg m−2 h−1. In addition, the outstanding ion rejection performance, strong acid/alkali purification capability, and good treatment capacity for heavy metal ions and dye wastewater were also demonstrated.