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Atmospheric water harvesting (AWH) is critical for providing drinkable water in arid areas. While hygroscopic salt has been identified as a potential AWH material due to its high-water uptake at low humidity, it is prone to leak when exposed to high humidity and has slow kinetics due to void space loss after cycling, which limits its practical application. Composite salt inside porous material (CSPM) has been proposed as a solution to these challenges, but its practical performance and kinetics after impregnation are poorly understood. In this study, commercial silica impregnated with different amounts of LiCl was used to investigate the adsorption rates using gravimetric adsorption kinetic experiments and fitted with both the Pore Diffusion (PD) model and the Linear Driving Force model (LDF). Calibration curves of salt loading vs. mass transfer coefficient and salt loading vs. water uptake were generated, and an isothermal LDF fixed bed model was used to determine the optimal salt loading and the influence of gas flow velocity on the water production rate. Results showed that the optimal salt loading for maximum water production rate was achieved by balancing the water isotherm shape and kinetics, as a higher salt loading resulted in high water uptake in low humidity but caused slower kinetics due to the pore-blocking effect.

This study provides valuable insights into the use of hygroscopic salt for AWH and highlights the importance of considering both water isotherm shape and kinetics when designing AWH materials. The findings could inform the development of more effective AWH materials for sustainable water supply in arid areas.