Highly efficient and long-term stable solar-driven water purification through a rechargeable hydrogel evaporator

Hydrogel-based evaporators that incorporate photothermal materials with hydrophilic polymer networks have been intensively studied for the promising solar-driven seawater desalination and sewage treatment. However, how to achieve highly-efficient evaporation with both long-term stability and reversible water uptake has always been a significant challenge. Herein, a durable and rechargeable solar evaporator is demonstrated by integrating water-absorbing polyacrylamide hydrogels with light-harvesting carbon nanotubes through polymerization in freeze-drying process. The hydrogel can store water 6 times its own weight. Even after being stored for 150 days, it can also restore its original shape after recharge by swelling in water. The hydratable functional groups endow the hydrogel with the formation of intermediate water that has a weak hydrogen bond, leading to reduced evaporation enthalpy. Without additional water supply, 2D flat evaporator with the hydrogel shows an evaporation rate of 3.03 kg m−2 h−1 under one sun irradiation. Further benefiting from net energy gain from the environment, a high and stable evaporation rate of 4.85 kg m−2 h−1 under one sun irradiation can be realized using 3D cylindrical hydrogel. This rechargeable hydrogel can be easily recycled via swelling-evaporation, with outstanding evaporation rate that qualifies for long-term use, making it ideal for practical clean water production.