Charge Engineering of Natural Gelatin Hydrogels for Sustainable Atmospheric Water Harvesting

ABSTRACT Hygroscopic hydrogels have emerged as promising candidates for sorbent‐based atmospheric water harvesting (AWH) technologies. However, most hydrogels are composed of petroleum‐derived synthetic monomers, raising concerns regarding the sustainability of AWH in water management. Although natural polymers and their derivatives are considered alternative resources, they often require complex processing with multiple chemicals to achieve advanced properties, thereby reducing their cost‐effectiveness and environmental friendliness. In this context, this study presents a simple and direct strategy for synthesizing hygroscopic hydrogels from gelatin. Through pH adjustment, gelatin's protonated amine and deprotonated carboxyl groups are activated, resulting in polyzwitterionic‐like properties and tailorable salting‐in effect. Furthermore, the intermolecular bonding network of gelatin can be further disrupted by specific ions via Hofmeister effects. Consequently, the charge‐engineered gelatin (CEG) sorbent achieves a water uptake of 0.92 g g −1 at 30% relative humidity. In practical applications, when incorporated with a photothermal agent, this sorbent can produce 2.7 L m −2 day −1 of desorption under sunlight. The CEG‐based sorbent provides an accessible, cost‐effective AWH material while maintaining sufficient efficiency to meet daily water requirements.