Hybrid salt-enriched micro-sorbents for atmospheric water sorption

Abstract

Water shortage severely impacts drought-stricken regions, with estimates indicating that almost half a billion people are affected yearly. Composites of Salt and Porous Matrix (CSPMs) are promising functional materials for water vapor sorption. Here, CSPMs were synthesized by loading SAPO-34 porous crystals with highly hygroscopic salts, namely LiCl and CaCl2, individually (mono-salt systems) or combined (binary salt systems) to enhance water sorption capacity and cyclability. The LiCl and CaCl2 content in the impregnation solution impacted the sorption behavior and equilibrium capacity of the resulting composites. Physicochemical, morphological, textural, and sorption properties were evaluated showing that the confinement of binary salts yielded the highest water uptake (0.88 gw/gads at 25 °C and 90 % RH), which was four times higher than that of the parent SAPO-34. The shape of the obtained water vapor isotherms revealed that the salts introduced into the porous structure led to significant changes in the sorption mechanism, with SAPO-34 following a Langmuir behavior (type I isotherm) and the composites a type II isotherm with associated multilayer formation due to the presence of the salts. Kinetic studies also revealed that the materials follow a PSO model dominated by water-surface interactions. Embedding different salts into the same hosting pores to support atmospheric water harvesting was therefore found to enhance capacity and cyclability compared to single inorganic porous structures toward more efficient water sorption processes.