Halloysite/polyaniline Nanocomposites for Enhanced Actinide Sorption

Extracting radionuclides from natural and anthropogenic sources addresses two challenges: remediating contaminated environments and enabling the separation of technologically important isotopes. Understanding how actinides interact and form complexes with polymer-based ligands allows the development of efficient extractants for selective remediation, supporting sustainable environmental protection and resource recovery strategies. Here, we report on the structure and actinide sorption properties of eco-friendly hybrid nanocomposite systems based on the natural mineral halloysite and multifunctional conjugated polymers. Three polyaniline (PANI)-based polymers and their nanocomposites with halloysite nanotubes (HNT) were synthesized and evaluated as sorbents for removing uranium and plutonium from aqueous solutions. The study included two PANI variants synthesized at high (60 °C) and low (1-2 °C) temperatures using different acid-dopants, H₂SO₄ and <i>p</i>-toluenesulfonic acid, and a PANI copolymer incorporating aminoterephthalic acid (PANIATA), which introduces carboxylic functional groups. X-ray photoelectron spectroscopy and electron microscopy revealed the formation of core-shell nanocomposites with HNT as the core and a polymer shell several nanometers thick. The HNT/PANI nanocomposites exhibited a synergistic enhancement in actinide retention capacity, exceeding the additive performance of the individual components. Sorption experiments with artificial groundwater and seawater confirmed the nanocomposites' selectivity for uranium. Analysis of the FTIR spectra of the polymer composites before and after uranium sorption provided detailed insight into uranyl cation-polymer complexation mechanisms responsible for high selectivity and sorption performance.