Salt-confined hierarchical porous carbons for efficient solar-driven atmospheric water harvesting

Abstract

Atmospheric water harvesting (AWH) based on sorption-desorption cycles offers a viable route for decentralized freshwater production, yet its efficiency is often limited by the trade-off between water uptake, vapor transport, and energy-efficient regeneration. Herein, a series of chitosan-derived, salt-confined hierarchical porous carbons (PCa-X) are prepared via freeze-drying, CaCl₂ impregnation, and carbonization, enabling coordinated regulation of pore architecture, surface polarity, and photothermal behavior. Moderate CaCl₂ loading induces an interconnected hierarchical pore network with uniformly confined hygroscopic sites, whereas excessive salt incorporation leads to partial pore densification and restricted vapor accessibility. The optimized PCa-20 exhibits rapid water-vapor uptake across a wide humidity range, achieving 0.35, 0.75, and 1.2 g g⁻¹ at 30%, 60%, and 90% relative humidity, respectively. Owing to its defect-rich carbon framework, PCa-20 shows efficient solar-driven heating, reaching surface temperatures of ∼85 °C under 2.0 kW m⁻² irradiation and enabling fast, reversible water release. Outdoor tests demonstrate autonomous day-night operation with an average daily water collection of ∼1.24 g g⁻¹ and negligible Ca²⁺ leaching. This work provides a scalable strategy for practical AWH through salt-confined photothermal porous carbons.