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-2Oax-U-5Oeq into H2O-2Oax-U-3Oeq 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.