Synthesis, structural characterization, and application prospects of SiO2/CaCl2 composite materials for atmospheric water harvesting

Abstract

In this study, SiO₂/CaCl₂ composite materials were synthesized via a sol–gel method for atmospheric water harvesting applications. The effects of the SiO₂/CaCl₂ mass ratio and gel aging time on structural characteristics and adsorption performance were systematically investigated. The optimal synthesis conditions were identified at a SiO₂/CaCl₂ mass ratio of 1:1 with a gel aging time of 48 h. Structural properties of the synthesized composites were characterized using SEM–EDX, X-ray diffraction (XRD), and N₂ adsorption–desorption (BET) analysis. The results revealed a biphasic structure consisting of crystalline CaCl₂ dispersed within an amorphous SiO₂ matrix, with a specific surface area of 19.1 m² g⁻¹ and mesoporous characteristics. At room temperature (25–27 °C), the composite exhibited water adsorption capacities of 0.31 g g⁻¹ at 70% relative humidity (RH) and 0.39 g g⁻¹ at 90% RH, reaching equilibrium after approximately 60 h. Although a decrease in adsorption capacity was observed after thermal regeneration, the material retained considerable water uptake, demonstrating its potential for low-cost, decentralized atmospheric water-harvesting systems.