Synthesis and application of spherical Alginate/CaCl<sub>2</sub> hydrogel beads for water harvesting from air

This study presents the synthesis and characterization of spherical hydrogel materials based on alginate cross-linked with Ca²⁺ cations, with particle diameters ranging from 0.20 to 0.25 cm. The structural properties of the synthesized materials were evaluated using X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive X-ray mapping (EDX-mapping), Fourier-transform infrared spectroscopy (FT-IR), and Brunauer-Emmett-Teller (BET) surface area analysis. The water vapor adsorption capacity of the Alginate/CaCl₂ hydrogel spheres reached 220 – 270 wt% relative to the dry weight, depending on ambient humidity conditions, with equilibrium sorption capacity reaching 80% of the saturation value within 4 hours. Furthermore, the material demonstrated excellent regeneration capability at 140°C, maintaining 80-90% of its original sorption capacity after 3 cycles regeneration cycles. These results indicate the potential of alginate-based hydrogel spheres as efficient and recyclable sorbents for sustainable atmospheric water harvesting applications.