Composites (LiCl + CH3COONa)/ACF/SiO2 for multicyclic adsorption-based atmospheric water harvesting

Abstract

Sorption-based atmospheric water harvesting (SAWH) offers an accessible method for fresh water harvesting. Rapid adsorption–desorption kinetics and mass production of adsorbents are core to realizing high water productivity. SAWH systems using composite adsorbent composted of activated carbon fiber, silica gel and LiCl can obtain high daily water productivity (3.9 ∼ 7.7 L_water day⁻¹). However, daily water productivity per unit mass of adsorbent (∼0.4 L_water kg_adsorbent^-1 day⁻¹) is inferior since the strong hygroscopicity of LiCl is like a double-edged sword. A combination of binary salts (LiCl + CH₃COONa) might be a way to improve daily water productivity per unit mass of adsorbent for a rapid-cycling water harvester. In this study, composite samples modified with different ratios of binary salts were prepared. Water uptakes of binary samples were inferior to the LiCl modified sample, whereas the adsorption rate and desorption rate increased by 31% and 155% respectively, with proper proportion of binary salts. Water releases of binary samples improved by 34%∼69% in a 180 mins’ adsorption–desorption cycle under different adsorption/desorption time ratios. Potential daily water productivity of the optimal binary sample can be up to 3.5 L_water kg_adsorbent^-1 day⁻¹ (adsorption at 25 °C&70 %RH and desorption at 70 °C &10 %RH) in an eight times cycles per day. Considering a system efficiency of 20 ∼ 30%, SAWH using this binary sample can still achieve pretty good daily water productivity. This method offers a promising route to develop high-performance materials in kilogram scale for multicyclic SAWH.