Sustainable β-cyclodextrin modified polyacrylamide hydrogel for highly efficient solar-driven water purification

Solar-driven water purification is considered as an efficient and green method to solve water scarcity. However, creating a hydrogel evaporator with both long-lasting evaporation performance and an efficient reduction in water vaporization enthalpy remains a significant challenge. Herein, a hydrogel with low water vaporization enthalpy was prepared by introducing β-cyclodextrin (β-CD) to polyacrylamide. The three-dimensional network structure was obtained via a simple freeze-drying process, and the addition of β-CD enhanced its hydrophilicity. Due to the hydration of hydroxyl groups on β-CD, the hydrogel facilitated the formation of intermediate water, substantially reducing the water vaporization enthalpy to 1428 J/g. It enabled the hydrogel to achieve a high evaporation rate of 2.65 kg/m2/h under 1 sun irradiation. Furthermore, the hydrogel demonstrated excellent hydration properties and abundant water transport channels for salt rejection in long-term desalination. After 50 cycles of testing in 3.5% brine, the evaporation rate remained high at 2.38 kg/m2/h. This work provides a sustainable way to develop a highly efficient solar evaporator for clean water production.