Efficient Solar-Driven Atmospheric Water Harvesting in Arid Regions Using Recyclable and Biodegradable Composite Aerogel

Abstract

The solar-driven atmospheric water harvesting (SAWH) system is an innovative solution to combat freshwater scarcity. However, achieving consistent moisture absorption kinetics while maintaining efficient operation under varying temperatures and humidity remains a significant challenge. The SAWH system developed in this study utilizes a composite aerogel, prepared through three steps: (1) formation of three-dimensional (3D) poly(3-hydroxybutyrate) (PHB)/carbon nanotubes (CNTs) gels using the thermally induced phase separation method, (2) solvent exchange to incorporate MgCl2·6H2O into the gels, and (3) freezing and freeze-drying to create the final composite aerogels. In this system, MgCl2·6H2O serves as the hygroscopic component, CNTs function as the photothermal conversion agent, and PHB aerogel forms the porous network. These composite aerogels exhibit excellent cyclic stability, quick regeneration, and rapid water absorption/desorption kinetics. These aerogels also demonstrate outstanding water vapor absorption capacity across a broad range of relative humidity (RH) and temperatures. At equilibrium, the aerogels absorb up to 1.64 g g-1 at 90% RH and 0.88 g g-1 at 40% RH. Notably, water release is driven by sunlight, with a desorption rate of 1.8 g g-1 h-1 under 1 sun irradiation. Additionally, the PHB/CNT/MgCl2 aerogels exhibit reliable recyclability, which extends their lifespan. Importantly, the major component of the aerogels is PHB, it breaks down into non-toxic fragments in the soil, enhancing their sustainability and environmental friendliness. This efficient and scalable water harvesting material provides a promising strategy for addressing freshwater scarcity, especially in arid regions, with significant potential for practical applications.