Solar-Driven Efficient Atmospheric Water Harvesting of Biomass-Based Porous Composite Hydrogel

Adsorption-based atmospheric water harvesting (AWH) technology shows great potential to alleviate the growing global freshwater shortage, especially in areas without grid coverage. The system combining a hygroscopic salt and a hygroscopic hydrogel network is currently the most widely used adsorbent in SAWH; however, these materials still have limitations such as insufficient hygroscopicity, proneness to salt precipitation and leakage, and difficulty in natural degradation. Here, a novel biomass-based photothermal evaporation composite hydrogel (SSC-LiCl) with a three-dimensional network structure was prepared by introducing LiCl and carboxylated carbon nanotubes through the grafting reaction between sodium alginate and sulfonated lignin. Its water uptake capacity is as high as 0.46–4.37 g·g–1 at 15–90% relative humidity (RH), and no salt leakage is observed during the water absorption process. Meanwhile, the hydrogel exhibits excellent water molecule desorption under light conditions, releasing 89% of adsorbed water after 1 h of exposure to simulated solar intensity. The development of this biomass-based hydrogel offers a promising, environmentally friendly, and cost-effective solution for capturing fresh water in arid regions.