(339b) Developing Hierarchical Silica-Salt Composites Via Wet Impregnation for Atmospheric Water Harvesting from Arid Air

Providing reliable methods for generating potable drinking water for remote locations remains a great, and increasingly growing, humanitarian challenge. Dehumidifiers generate liquid water from humid air, but the high humidity and energy expenditures needed to operate such systems prevent their use in arid regions. Currently, desalination is the leading method of alternative water harvesting in arid regions, but many limitations still exist such as high operating and transportation costs, as well as the requirement to exist near seawater and limiting water access for inland regions. In recent years, adsorption-based water harvesting has become an area of significant interest, in which the abundant water vapor in the atmosphere can be extracted using porous sorbents. Commonly studied sorbents that strongly adsorb water vapor possess microporous structures that limit their water capacity. Hierarchical silicas are water-stable sorbents with an expansive porous structure containing a wide pore size distribution and large macropore volume, that allow for improved water uptake over strictly microporous sorbents and at %RHs above those where pure hygroscopic salts saturate. However, these materials exhibit limited water adsorption at low relative humidity. Here, we present the synthesis, characterization, and water adsorption testing of an optimized hierarchical silica-salt composite in which a hygroscopic salt is incorporated into the sorbent matrix via a wet impregnation method. The composite is capable of adsorbing large quantities of water (> 0.4 g/g) at humidities as low as 5-10% RH. Additional kinetics and cycling tests indicate the silica-salt composite maintains the same performance after multiple cycles.