Adsorption behavior of Rare-Earth ions on electrospun fibers functionalized with branched polyethyleneimine

Abstract

The development of easily recoverable adsorbents containing abundant and accessible binding sites is essential for the efficient recovery of rare-earth ions from aqueous media. In this study, a branched polyethyleneimine-polyacrylonitrile (bPEI-PAN) fibrous adsorbent was fabricated by incorporating bPEI into PAN through blend electrospinning. Its adsorption performance toward Sc(III), Ce(III), and Y(III) was systematically evaluated through equilibrium, kinetic, thermodynamic, competitive-ion, and regeneration experiments. At 298 K and optimal pH values of 4.00 for Sc(III) and 6.00 for Ce(III) and Y(III), the equilibrium adsorption data were best described by the Langmuir model, yielding fitted maximum adsorption capacities of 56.96, 145.80, and 48.72 mg/g for Sc(III), Ce(III), and Y(III), respectively. The initial concentration ranges used for the isotherm experiments were 10–125 mg/L for Sc(III) and Y(III) and 10–150 mg/L for Ce(III). The adsorption kinetics were well described by the pseudo-second-order model, whereas intraparticle diffusion analysis indicated that the overall adsorption process involved multiple mass-transfer stages. Thermodynamic analysis revealed that the adsorption of the three rare-earth ions was spontaneous and exothermic under the investigated conditions. Ca(II) exerted only a minor effect on rare-earth adsorption, whereas Fe(III) and Al(III) markedly inhibited adsorption, primarily because of competition for nitrogen-containing binding sites. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that the amine groups served as the principal binding sites and that coordination interactions played a dominant role in the adsorption of Sc(III), Ce(III), and Y(III). After five adsorption–desorption cycles, the fibers retained approximately 70 % of their initial adsorption capacities, indicating acceptable regeneration performance. These results demonstrate that the bPEI-PAN fibrous adsorbent is a promising and readily recoverable material for the recovery of Sc(III), Ce(III), and Y(III) from aqueous solutions.