A self-floating integrated hydrogel evaporator with efficient salt resistance and thermal localization for efficient solar water desalination

Solar-driven interfacial evaporation technology was considered a promising way to effectively alleviate the global freshwater crisis. However, it is still a major challenge to design evaporators with efficient thermal management, salt resistant and self-floating ability to realize efficient clean water production. Here, we design a double-layer hydrogel evaporator with self-floating system. The evaporator is prepared from expanded polystyrene board, poly (vinyl alcohol), polyvinylpyrrolidone, agar and conductive carbon black. The structural design of the evaporator improves water transport capacity of the evaporation system and effectively reduces heat loss, so that the evaporator has efficient salt resistance and thermal localization. The evaporator demonstrates an outstanding evaporation rate and evaporation efficiency of 2.77 kg m-2h- h- 1 and 94.25 % under 1 kW m- 2 illumination. Additionally, the evaporator exhibits good stability in the 10-cycle solar evaporation experiment. Furthermore, the evaporator exhibits excellent salt resistance in 3.5 wt% NaCl solution during continuous evaporation for 9 h at 1 kW m- 2 illumination. Moreover, the purification rates of the organic wastewater 4-nitro- phenol and methylene blue by the evaporator reached 99.8 % and 100 %, respectively. This evaporator has stable and efficient capability of solar water purification, providing a new way for large-scale solar desalination and water purification.