Unravelling the Efficient Photocatalytic Activity of Boron-induced Ti ³⁺ Species in the Surface Layer of TiO ₂

Abstract

Ti ³⁺ species are highly unstable in air owing to their facile oxidation into Ti ⁴⁺ species, and thus they cannot concentrate in the surface layer of TiO ₂ but are mainly present in its bulk. We report generation of abundant and stable Ti ³⁺ species in the surface layer of TiO ₂ by boron doping for efficient utilization of solar irradiation. The resultant photocatalysts (denoted as B-TiO _2−x) exhibit extremely high and stable solar-driven photocatalytic activity toward hydrogen production. The origin of the solar-light activity enhancement in the B-TiO _2−x photocatalysts has been thoroughly investigated by various experimental techniques and density functional theory (DFT) calculations. The unique structure invoked by presence of sufficient interstitial boron atoms can lead to substantial variations in density of states of B-TiO _2−x, which not only significantly narrow the band gap of TiO ₂ to improve its visible-light absorption, but also promote the photogenerated electron mobility to enhance its solar-light photocatalytic activity.