Sorption of Eu(III) on MXene-derived titanate structures: The effect of nano-confined space

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Developing versatile materials that rapidly and efficiently adsorb radionuclides is an urgent objective for environmental remediation in response to radioactive contamination. Herein, we report the preparation of hierarchical titanate nanostructures (HTNs) by a in situ chemical conversion strategy using a two-dimensional MXene crystal precursor. These HTNs are very stable and can efficiently remove Eu(III) with large sorption capacities, owing to well-maintained layered structures and abundantly exchangeable guest cations. The replacement of sodium or potassium ions with Eu(III) in HTN interlayers has been confirmed by X-ray diffraction (XRD), photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS). The extended X-ray sorption fine structure (EXAFS) results, in combination with density functional theory (DFT) calculations, further indicate that the sequestration of Eu(III) is realized by forming inner-sphere surface complexes in nano-confined space, evidenced by the decrease of Eu-O distances (R) and coordination numbers (N). The finding of the inner-sphere complexation induced by Ti−O/Ti−OH coordination and confinement effect provides new insights into the interaction mechanism between radionuclides and titanates. Given their extraordinary sorption capacity and facile synthesis under mild conditions, these HTNs are promising candidates for the efficient removal of trivalent lanthanides and actinides from aqueous solutions during the cleanup of radioactive pollution in the environment.