Visible light driven Ti³⁺ self-doped TiO₂ for adsorption-photocatalysis of aqueous U(VI)

The photocatalytic reduction of U(VI) is recognized as an economical and effective way for U(VI) removal/recovery from solutions. To improve the photocatalytic activity of TiO₂ under visible light, TiO₂ was hydrogenated by NaBH₄ to generate Ti³⁺ self-doped black TiO₂ (BT_n). The self-doped Ti³⁺ alongside oxygen vacancies (Ov) could act as interband level to increase visible light capture and reduce the recombination of photogenerated carriers. The obtained BT_n samples showed high performance for U(VI) elimination under near neutral conditions, and held an outstanding anti-interference for U(VI) over competing metal cations and anions. Methanol and ethanol could act as sacrificial donors, being favorable for the photocatalytic reduction of U(VI), while the presence of EDTA inhibited the photoreduction of U(VI). The BT_n photocatalysts showed relatively high stability and reusability during the photocatalysis and elution processes. The XPS, TEM and XRD results revealed that U(VI) was photo-reduced to form UO₂ on the surface of BT_n. This work may serve as an important reference for improving the photocatalytic reactivity of TiO₂ as well as for the efficient removal/recovery of U(VI) from aqueous solutions.