Biomimetic Aerogel Composite for Atmospheric Water Harvesting

Adsorption-based atmospheric water harvesting (AWH) with solar-driven photothermal desorption has become an effective means of solving freshwater scarcity in arid regions due to its low energy consumption and high efficiency. Moisture adsorption and desorption capacities are the most critical properties in AWH, and it is a challenge to improve the rate of moisture adsorption and desorption of composite adsorbents. Therefore, this paper reports a SA/carboxymethyl chitosan (CCS)/C/CaCl₂-U composite aerogel adsorbents with simultaneously green, low-cost, degradable, and fast hygroscopicity and desorption kinetics. The composite adsorbent used water-soluble biomass materials sodium alginate (SA) and carboxymethyl chitosan (CCS) as the backbone of the aerogel, constructed a vertically aligned unidirectional pore structure by directional freezing, and introduced nanocarbon powder and moisture-absorbent salt calcium chloride (CaCl₂) to improve the solar photothermal performance and water absorption, respectively. The results showed that the composite adsorbent had good water uptake capacity at 30-90% relative humidity (RH), the time to reach the water uptake of 1 g g^-1 at 90% RH was only 2.5 h, and the final water uptake rate was up to 1.9 g g^-1 within 12 h. Meanwhile, the composite sorbent can be heated and desorbed basically within 1 h at 80 °C and its evaporation efficiency is 1.3 times higher than that of the aerogel sorbent prepared by the conventional method when irradiated with 1000 W m^-2 light intensity for 2 h. Therefore, the SA/CCS/C/CaCl₂-U composite aerogel adsorbent of this study has a potential that can be applied in AWH due to its environmental friendliness, low cost, and faster hygroscopic desorption kinetics.