Fabrication of a tripolyphosphate-modified chitosan-sodium alginate composite for highly efficient uranium adsorption...

The preparation of composite materials with excellent adsorption capacity for uranium in water remains a topic of great interest. In this work, a novel composite adsorbent, tripolyphosphate-modified chitosan-sodium alginate (PCSSA), was successfully prepared by incorporating sodium alginate into tripolyphosphate-modified chitosan via chemical cross-linking. The resulting material exhibited excellent adsorption capacity for U(VI) in aqueous solutions. Within the chitosan matrix, amino, alkyl, and phosphate groups act synergistically to form amino-alkyl phosphate ligands (NH₂-CH₂-PO₄^3-) with chelating functionality, providing abundant adsorption sites for efficient U(VI) removal. SEM and EDS characterization revealed a rugged, plate-like surface morphology, loaded with functional groups such as phosphate and carboxyl/hydroxyl groups. Systematic adsorption experiments indicated that the U(VI) adsorption behavior of PCSSA follows the Langmuir isotherm and the Elovich kinetic model. Under optimal conditions (pH = 3, 298.15 K, adsorbent dose = 30 mg), the maximum adsorption capacity reached 561.86 mg·g^-1. In real water samples with a low U(VI) concentration (30 mg·L^-1), the removal efficiency was as high as 88%, outperforming many similar bio-based adsorbents. FTIR and XPS analyses suggested that the phosphate groups interact with UO₂²⁺ through multiple mechanisms, including electrostatic attraction, ligand exchange, and complexation. The PCSSA composite is environmentally friendly and straightforward to prepare, showing promising potential for application in water pollution control.