Investigative synthesis and optimization of Ca²⁺/Al³⁺ dual cross-linked alginate hydrogel beads for water vapor adsorption
DOI:
https://doi.org/10.54939/1859-1043.j.mst.110.2026.109-116Keywords:
Alginate; Multivalent cross-linking; Hydrogel; Water harvesting.Abstract
Spherical alginate hydrogel beads simultaneously cross-linked by calcium and aluminium ions were fabricated via extrusion-gelation to investigate their potential for atmospheric water harvesting. Alginate concentration (1–5 wt%) and calcium/aluminium molar ratios (1:1, 1:3, 3:1) were systematically optimized. Scanning electron microscopy demonstrated that 2% alginate with a 1:1 cation ratio yielded the most uniform and porous surface morphology, while elevated aluminium content promoted undesirable surface crystallization. The highest specific surface area was confirmed (15.349 m²/g) for the 1:1 formulation with broad mesopore distribution. Fourier-transform infrared spectroscopy validated calcium-oxygen and aluminium-oxygen cross-links alongside characteristic alginate functional groups, and energy-dispersive X-ray mapping confirmed homogeneous elemental distribution via the egg-box mechanism. Thermogravimetric analysis revealed dehydration at 173.8 °C, alginate pyrolysis total 49.65% mass loss to 700 °C, and approximately 50% thermally stable residue. Water vapor adsorption reached 4.22 g/g at 90% relative humidity and 3.84 g/g at 70%, with over 80% uptake achieved within 15–20 hours. Thermal regeneration retained 92-97% capacity over three cycles, establishing these hydrogels as promising low-cost sorbents for atmospheric water harvesting.
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