Dual-phase chitosan incorporation in alginate/Fe(III) hydrogel beads: Multi-scale spectroscopic evidence for gradient-confined phosphate precipitation and implications for adsorbent design.

Dual-phase chitosan incorporation in alginate/Fe(III) hydrogel beads enables gradient-confined phosphate precipitation, achieving a capacity of 109 mg P g−1 and effective phosphate removal.

• Why it matters: Controlling phosphate levels is critical to prevent eutrophication in aquatic environments, yet understanding how hydrogel microstructure influences ion immobilization remains limited, hindering the design of effective adsorbents.
• What they did: The study employed a dual-phase chitosan strategy combined with multi-scale spectroscopic techniques, including SEM-EDS, XPS, XRD, TEM/SAED, and synchrotron XANES/EXAFS, to investigate phosphate sequestration mechanisms in hydrogel beads.
• The result: Findings reveal a gradient-confined precipitation pathway with nanocluster formation from surface to core, and demonstrate that the design maintains high capacity, recyclability, and low phosphate levels in wastewater, guiding future adsorbent development.