Novel dual-network-structured hydrogel microspheres for efficient atmospheric water collection

Atmospheric water harvesting (AWH) technology is widely regarded as a promising technology to solve the problem of fresh water shortage. Hygroscopic salt-hydrogel composites have attracted extensive attention due to their high hygroscopic salt-carrying capacity. However, their complex preparation process, salting-out and low water collection efficiency restrict their development. In this study, we prepared calcium alginate (CA) and [2-(methylpropoxy) ethyl dimethyl-(3-propyl sulfonic acid)ammonium hydroxide (PDMAPS)] double-network-structured hydrogel microspheres using a novel drip-free polymerization method. Then, a CA/PDMAPS/CNT/LiCl composite adsorbent was prepared by adding carbon nanotubes (CNTs) and LiCl. The preparation process was simple and suitable for mass production. Zwitterionic groups in the double-network structure (cationic -N⁺(CH₃)₂ ^- and anionic -SO₃ ^-) could produce electrostatic effects with Li⁺ and Cl^-, thereby binding LiCl and solving the traditional salting-out problem. A binary salt system could also be formed, which greatly enhanced water-collection capacity. At 22 °C with RH = 90%, the maximum water collection of the hydrogel microspheres was 3.586 g g^-1. Compared with single-network-structured hydrogels, the reported system exhibited an enhancement of 434% in its water collection efficiency. Under natural light, it desorbed more than 80% of the adsorbed water in 3-4 h. In summary, the dual-network-structured hydrogel microspheres represent a promising material for atmospheric water collection.