Preparation of a highly efficient composite adsorbent PAM–CMCNa–GO@CaCl2 hydrogel for solar-driven atmospheric water harvesting

Abstract

Water scarcity is a global issue. Solar-driven adsorption-based atmospheric water harvesting (SWAH) is an effective method to address the problem of freshwater shortage. However, the low water absorption capacity of adsorbents and the inability to utilize natural sunlight for desorption and regeneration hinder efficient atmospheric water harvesting. In this study, a high-performance composite hydrogel adsorbent, PAM–CMCNa–GO@CaCl₂, was prepared by free radical-initiated polymerization and impregnation method. By incorporating graphene oxide (GO) into the polyacrylamide–carboxymethyl cellulose sodium (PAM–CMCNa) copolymer hydrogel matrix, a PAM–CMCNa–GO hydrogel is synthesized, which endows the hydrogel with excellent photothermal conversion performance. This allows the hydrogel to undergo desorption and regeneration driven by natural sunlight. By confining hygroscopic calcium chloride (CaCl₂) within the PAM–CMCNa–GO hydrogel matrix, the high moisture absorption capacity of calcium chloride (CaCl₂) and the swelling ability of the hydrogel are utilized to capture and store water vapor from the air. Furthermore, through the synergistic use of a low-concentration salt solution strategy and hydrogel swelling strategy to prevent salt solution leakage, efficient atmospheric water harvesting is achieved. The prepared composite adsorbent, PAM–CMCNa–GO@CaCl₂, achieves a water vapor capture rate of 0.307–2.596 g g⁻¹ within a wide humidity range (30–90% RH), without salt solution leakage under the environmental conditions of 25 °C and 90% RH. Indoor water harvesting experiments demonstrate that the PAM–CMCNa–GO@CaCl₂ composite adsorbent can collect 122% of its own weight of liquid water through 12 hours of adsorption (25 °C, 90% RH) and 6 hours of desorption (1 kW m⁻²) under sunlight.