All-natural, eco-friendly composite foam for highly efficient atmospheric water harvesting

Water is vital for life, yet about 10 % of the world population lacks access to it. The atmosphere is a ubiquitous and abundant water reservoir, equivalent to 10 % of the freshwater in all lakes on earth. Existing absorbent materials for atmospheric water extraction, such as silica gels, zeolites, and metal-organic frameworks, suffer from either low water capture capacity or expensive and hazardous fabrication processes. Here we demonstrate an all-natural, eco-friendly composite foam with high performance in atmospheric water harvesting in both non-arid and arid environments, solely powered by natural sunlight without any other energy input. The composite foam is made of natural and earth-abundant cellulose and graphite via an aqueous process (no organic solvent used), followed by carbonization and LiCl doping. The foam can absorb water over 670 % of its weight from an atmosphere at 90 % relative humidity (RH) and quickly release 95 % of absorbed water under sunlight irradiation in 1 h. Remarkable daily water production of 1.24 g g−1 day−1 in an arid environment (30 % RH) and 2.83 g g−1 day−1 in a non-arid environment (30 %−60 % RH) has been achieved, outperforming existing absorbent materials. The all-natural composite foam is also eco-friendly and non-toxic, promising a feasible and efficient green solution to atmospheric water harvesting.