Fabrication of polyamine-modified chitosan aerogels for highly efficient uranium(VI) removal

Uranyl ions (UO₂²⁺), as characteristic pollutants in radioactive wastewater, pose a persistent threat to ecosystems and human health due to their high mobility, combined chemical-radiological toxicity, and bioaccumulation potential. However, conventional adsorbents generally suffer from critical limitations, including limited adsorption capacity, poor selectivity, and inadequate recyclability. In this study, a green and efficient polyamine-modified chitosan aerogel (HPCA) was fabricated using natural chitosan as the matrix via hyperbranched polyethyleneimine (PEI) functionalization and glutaraldehyde crosslinking, followed by an ultrasonic dispersion-assisted freeze-drying process. The microstructure, chemical composition, and pore characteristics were systematically characterized by SEM, XPS, FT-IR, and porosimetry analysis. Batch adsorption experiments demonstrated that U(VI) uptake by HPCA followed the pseudo-second-order kinetic and Langmuir isotherm models, indicating a chemisorption-dominated monolayer process. Under optimized conditions (pH 8.0, dosage 0.125 g/L, initial concentration 35 mg/L, contact time 360 min, and temperature 318 K), the maximum adsorption capacity reached 241.06 mg/g. Mechanistic investigations by FT-IR, XPS, and density functional theory calculations (B3LYP-D3BJ/6-31G(d, p)) revealed that adsorption is primarily governed by coordination complexation between surface hydroxyl (-OH) and amino (-NH₂) groups and U(VI). Notably, electrostatic interaction between protonated amine groups and uranyl hydroxo complexes serves as one of the main driving forces, while hydrogen bonding and van der Waals forces synergistically enhance adsorption stability. Furthermore, HPCA exhibited moderate selectivity for U(VI) in the presence of high salinity and various coexisting ions (Na⁺, K⁺, Ca²⁺, etc.) and displayed satisfactory regeneration performance. In summary, the as-prepared HPCA integrates high adsorption capacity, strong selectivity, and favorable stability, offering a green and efficient adsorbent for the advanced treatment of uranium-containing radioactive wastewater and providing theoretical insights into the molecular design of functionalized aerogels.