Oxygen-Vacancy-Rich TiO₂ Nanosheets with High Stability for Efficient Photocatalytic Cr(VI) Reduction

Defect engineering of anatase TiO₂ nanosheets by hydrogen reduction is a compelling strategy to boost visible light photocatalytic Cr(VI) reduction, a process of vital importance for detoxifying highly toxic and carcinogenic Cr(VI) pollutants. However, the necessary high-temperature hydrogen treatment invariably induces morphological collapse, negating the structural merits of the two-dimensional nanosheets. Herein, we propose an ethylenediamine reflux protection strategy combined with hydrogen reduction to fabricate defect-rich TiO₂ nanosheets (EN-TiO_2-x-NS) that preserve the original morphology. The resulting EN-TiO_2-x-NS retained the square nanosheet structure and (001) facets, while Ti³⁺ and oxygen vacancies were successfully introduced. The bandgap narrowed from 2.95 to 2.55 eV, leading to enhanced visible light absorption and charge separation efficiency. For photocatalytic Cr(VI) reduction under visible light, EN-TiO_2-x-NS achieved a removal rate of 97.3% within 20 min, with a rate constant 1.93 times higher than that of pristine TiO₂ nanosheets and 3.17 times higher than that of the directly hydrogenated sample. The catalyst also exhibited excellent cycling stability. This work demonstrates a synergistic strategy combining morphology preservation and defect engineering, providing a new approach for designing high-performance TiO₂-based photocatalysts.