Research Progress on Hygroscopic Agents for Atmospheric Water Harvesting Systems

Adsorptive atmospheric water harvesting systems (AWHs) represent an innovative approach to collecting freshwater resources from the atmosphere, with a hygroscopic agent at their core. This method has garnered significant attention due to its broad applicability, strong recycling capacity, and sustainability. It is being positioned as a key technology to address global freshwater scarcity. The core agent's hygroscopic properties play a crucial role in determining the performance of the AWHs. This article provides a comprehensive review of the latest advancements in hygroscopic agents, including their adsorption mechanisms and classifications. This study of hygroscopic agents analyzes the performance and characteristics of relevant porous material composite polymer composites and plant composites. It also evaluates the design and preparation of these materials. Aiming at the problems of low moisture adsorption and desorption difficulty of the hygroscopic agent, the factors affecting the water vapor adsorption performance and the method of enhancing the hygroscopic performance of the material are summarized and put forward. For the effect of hygroscopic agents on the volume of water catchment devices, the difference in density before and after hygroscopicity is proposed as part of the evaluation criteria. Moisture absorption per unit volume is added as a performance evaluation criterion to assess the effect of hygroscopic agents on the volume of water collection equipment. The article identifies areas that require further research and development for moisture absorbers, exploring their potential applications in other fields and anticipating the future development direction and opportunities of moisture-absorbing materials. The goal is to promote the early realization of adsorptive atmospheric water harvesting technology for large-scale industrial applications.