Macroporous chitosan-cellulose composite foam for sustainable solar-driven atmospheric water harvesting

Solar-driven atmospheric water harvesting (SAWH) presents a sustainable strategy to global freshwater scarcity. In this work, a purely natural hydrophilic composite foam (LiCl@GQC) with macroporous structure is designed for SAWH sorbents to replace petroleum-derived synthetic polymer matrices. The three-dimensional network porous structure is constructed by rigid cellulose as the structural framework and superhydrophilic quaternized chitosan as a pore-size expander, endowing the biomass-based sorbent with robust mechanical properties, superior moisture sorption performance and excellent water storage capacity. The moisture absorption capacity is up to 4.73 g g^-1 at 25 °C under 95 % relative humidity. The uniformly dispersed graphene oxide in the sorbent has light absorption rate of 94 %, enabling efficient solar thermal desorption performance. Driven by simulated sunlight irradiation (200 mW cm^-2), LiCl@GQC achieves an evaporation rate of 4.19 kg m^-2 h^-1, and stable performance and excellent antibacterial properties over 10 absorption-desorption cycles. Moreover, water was successfully collected by natural sunlight using a homemade device based on LiCl@GQC in outdoor testing. The water production rate reaches up to 1.49 kg m^-2 day^-1, sufficient to meet the drinking water demand of one adult. This work provides the potential of biomass materials for eco-friendly, sustainable SAWH sorbents to mitigate the global water crisis.