Quaternary Ammonium-Containing Polyelectrolyte Brush Particles for Removal of Perrhenate Anion From Water: Effect of N-Substituents

Radioactive pertechnetate (TcO₄⁻) from the nuclear fuel cycle presents a severe risk to the environment due to its large solubility in water and non-complexing nature. By utilizing the chaotropic properties of TcO₄⁻ and its nonradioactive surrogate perrhenate (ReO₄⁻) and the principle of chaotropic interactions, a series of quaternary ammonium-containing polyelectrolyte brush-grafted silica particles are designed and applied to remove ReO₄⁻ from water. These cationic hairy particles (HPs) are synthesized by surface-initiated atom transfer radical polymerization of 2-(N,N-dimethylamino)ethyl methacrylate and subsequent quaternization with various halogen compounds. Dynamic light scattering (DLS) studies showed that the HPs with sufficiently long N-alkyl and N-benzyl substituents underwent sharp size reduction transitions in water when titrated with a KReO₄ solution, indicating strong chaotropic interactions between the brushes and ReO₄⁻. All the HPs exhibited fast adsorption kinetics; the HPs with longer N-alkyl and N-benzyl substituents showed higher capabilities of removing ReO₄⁻ than those with shorter N-alkyls. Moreover, the brush particles with longer N-substituents displayed a significantly stronger ability in selective adsorption of ReO₄⁻ than the particles with shorter N-substituents in the presence of competing anions, such as F⁻, Cl⁻, NO₃⁻, and SO₄²⁻. This work opens a new avenue to design high-performance adsorbent materials for TcO₄⁻ and ReO₄⁻.