MXene-Derived 3D Defect-Rich TiO2@Reduced Graphene Oxide Aerogel with Ultrafast Carrier Separation for Photo-Assisted Uranium Extraction: A Combined Batch, X-ray Absorption Spectroscopy, and Density Functional Theory Calculations

Encapsulation of nano-semiconductor materials in three-dimensional (3D) adsorbents to build a typical semiconductor-adsorbent heterostructure is a forward-looking strategy for photo-assisted uranium extraction. Here, we develop 3D MXene-derived TiO₂(M)@reduced graphene oxide (RGO) aerogel for photo-assisted uranium extraction. Theoretical simulations demonstrate that oxygen vacancies on TiO₂(M) tailor the energy level structure and enhance the electron accumulation at gap states of TiO₂(M), thereby further realizing the spatial separation efficiency of electron-hole pairs by the Schottky junction. By virtue of the in situ X-ray photoelectron spectroscopy spectrum, we identify that photogenerated electrons generated over TiO₂(M) were transferred to graphene oxide aerogel by the Schottky junction. Accordingly, TiO₂ (M)@RGO aerogel presents a considerable removal efficiency for U(VI) with a removal ratio of 95.7%. Relying on the X-ray absorption spectroscopy technique, we distinguish the evolution of 2H₂O-2O_ax-U-5O_eq into H₂O-2O_ax-U-3O_eq from dark to light conditions, further confirming the reduction of high-valent uranium. This strategy may open a paradigm for developing novel heterojunctions as photocatalysts for selective U(VI) extraction.