Distorted Ultrasmall TiO 2 Nanoparticles as Efficient Visible Light Photocatalyst

Developing efficient and low-cost visible light photocatalysts remains a fundamental challenge. Titanium dioxide (TiO2), although stable and abundant, suffers from a wide bandgap and limited surface area. In this study, visible light active ultrasmall approximately 2 nm (∼2 nm) TiO2 nanoparticles were synthesized to overcome these limitations. Unlike conventional post-annealing routes that promote particle growth, this visible light-active ultrasmall TiO2 was directly obtained through a continuous flow-hydrothermal process with precise temperature control and sub-second reaction time. The ultrasmall (∼2 nm) TiO2 structure reveals the highly distorted lattice structure. The high lattice distortion, which contains an undercoordinated Ti atom, induces the localized states that modify the band structure of TiO2 and decrease its activation energy to the visible light region. The resulting ∼2 nm TiO2 exhibits nearly threefold higher photocatalytic activity for NOx removal under visible irradiation, opening a new direction for designing ultrasmall oxide nanomaterials for next-generation photocatalysis.