Li−Ca bimetallic hydrogel for efficient water harvesting in arid areas

The use of advanced adsorbents to collect atmospheric water for freshwater production has become a promising approach to alleviate water scarcity. However, the water harvesting capacity of most adsorbents is limited when the relative humidity (RH) is below 30 %. In this study, a porous bimetallic hygroscopic polymer hydrogel (Bime-HPH) film was prepared by freeze-drying method using sodium carboxymethyl cellulose (CMC), a low-cost renewable biomass, as a polymer matrix in combination with hygroscopic salts (CaCl2 and LiCl). It was found that the strong hydration energy of Li+ helps to trap water molecules in arid air and transport them to Ca2+ and hydrophilic groups on the CMC, and this synergistic effect contributed to the high capacity of Bime-HPH of 1.64 g g−1 at 30 % RH. Moreover, the porous structure facilitated water release from the hydrogel at nearly 40 °C and demonstrated rapid an adsorption-desorption kinetics. In a natural conditions, 16.0 g of Bime-HPH collected a total of 20.0 g of atmospheric water during the night and achieved a water production rate of 1.0 g g−1 h−1 under sunlight irradiation. The special features of the hydrogel will lead to a high demand for its use in many arid regions and communities facing the crisis of water shortage. •A hydrogel capturing atmospheric water molecules from arid climates was prepared.•The hydrogel exhibited water harvesting capacity of 1.64 g g−1 h−1 at 30 % RH.•The hydrogel device provided 1.0 g g−1 h−1 drinking water in natural environment.•The synergistic effect facilitates capturing and transporting water molecules.