Synthesis and characterization of lanthanide-alginate-Ag nanocomposites with enhanced catalytic dye degradation,...

In this study, hydrogel beads were fabricated by ionic gelation of sodium alginate (Na-Alg) blended with Catharanthus roseus extract, which were subsequently cross-linked with various lanthanide salts (lanthanum(III) nitrate, yttrium(III) nitrate, praseodymium(III) nitrate, thulium(III) nitrate, dysprosium(III) nitrate, erbium(III) nitrate, and ytterbium(III) nitrate) followed by in situ generation of silver nanoparticles (AgNPs) to yield Ln-Ag nanocomposites (Ln-AgNCs) beads. This approach leverages the robust coordination between lanthanide ions and alginate together with the surface reactivity of AgNPs to enable synergistic performance. The nanocomposites were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), zeta potential analysis, and X-ray photoelectron spectroscopy (XPS), confirming effective coordination and the formation of stable, well-dispersed nanostructures. The Ln-AgNCs beads were evaluated for NaBH₄-assisted reduction of organic pollutants including methyl orange (MO), methylene blue (MB), acridine orange (AO), and 4-nitrophenol (4-NP). Yttrium‑silver (Y-AgNCs) and praseodymium‑silver (Pr-AgNCs) exhibited superior performance characterized by rapid decolorization, high apparent rate constants, and excellent recyclability over multiple cycles. Dy-Alg beads showed highly efficient catalytic activity in hydrogen generation via NaBH₄ hydrolysis, where hydrogen generation rates were strongly dependent on catalyst loading, NaBH₄ concentration, temperature, and solvent. Furthermore, the Ln-AgNCs beads demonstrated pronounced antimicrobial activity against Gram-positive, Gram-negative bacterial, and fungal strains through colony-forming unit (CFU) reduction assays, attributed to synergistic interactions among AgNPs, lanthanide ions, Catharanthus roseus extract components, and the porous Na-Alg network.