Efficient Atmospheric Water Harvesting of Superhydrophilic Photothermic Nanocapsule

Abstract

Drought and water scarcity are two of the world's major problems. Solar-powered sorption-based atmospheric water harvesting technology is a promising solution in this category. The main challenge is to design materials with high water harvesting performance while achieving fast water vapor adsorption/desorption rates. Here, a superhydrophilic photothermic hollow nanocapsule (SPHN) is represented that achieves efficient atmospheric water harvesting in outdoor climates. In SPHN, the hollow mesoporous silica (HMS) is grafted with polypyrrole (PPy) and also loaded with lithium chloride (LiCl). The hollow structure is used to store water while preventing leakage. The hydrophilic spherical nanocapsule and the trapped water produce more free and weakly adsorbed water. Significantly lower the heat of desorption compared to pure LiCl solution. Such SPHN significantly improves the adsorption/desorption kinetics, e.g., absorbs 0.78-2.01 g of water per gram of SPHN at 25 °C, relative humidity (RH) 30-80% within 3 h. In particular, SPHN has excellent photothermal properties to achieve rapid water release under natural sunlight conditions, i.e., 80-90% of water is released in 1 h at 0.7-1.0 kW m^-2 solar irradiation, and 50% of water is released even at solar irradiation as low as 0.4 kW m^-2 . The water collection capacity can reach 1.2 g g^-1 per cycle by using the self-made atmospheric water harvesting (AWH) device. This finding provides a way to design novel materials for efficient water harvesting tasks, e.g., water engineering, freshwater generator, etc.

Keywords: atmospheric water harvesting; photothermic materials; superhydrophilic nanocapsules; vapor sorbents.