Effective Removal of Anionic Re(VII) by Surface-Modified Ti₂CT_<i>x</i> MXene Nanocomposites: Implications for Tc(VII) Sequestration

Abstract

Environmental contamination by ⁹⁹Tc(VII) from radioactive wastewater streams is of particular concern due to the long half-life of ⁹⁹Tc and high mobility of pertechnetate. Herein, we report a novel MXene-polyelectrolyte nanocomposite with three-dimensional networks for enhanced removal of perrhenate, which is pertechnetate simulant. The introduction of poly(diallyldimethylammonium chloride) (PDDA) regulates the surface charge and improves the stability of Ti₂CT _x nanosheet, resulting in Re(VII) removal capacity of up to 363 mg g^-1, and fast sorption kinetics. The Ti₂CT _x/PDDA nanocomposite furthermore exhibits good selectivity for ReO₄^- when competing anions (such as Cl^- and SO₄^2-) coexist at a concentration of 1800 times. The immobilization mechanism was confirmed as a sorption-reduction process by batch sorption experiments and X-ray photoelectron spectroscopy. The pH-dependent reducing activity of Ti₂CT _x/PDDA nanocomposite toward Re(VII) was clarified by X-ray absorption spectroscopy. As the pH increases, the local environment gradually changes from octahedral-coordinated Re(IV) to tetrahedral-coordinated Re(VII). The overall results suggest that Ti₂CT _x/PDDA nanocomposite may be a promising candidate for efficient elimination of Tc contamination. The reported surface modification strategy might result in applications of MXene-based materials in environmental remediation of other oxidized anion pollutants.