In Situ Tuning of Defects and Phase Transition in Titanium Dioxide by Lithiothermic Reduction

Defects engineering of oxides plays a vital role in tuning their physicochemical and electronic properties and thereby determining their potential applications. However, the safe and controllable production of effective defects in the oxides is still challenging. Here, we report a facile one-pot solid lithiothermic reduction approach to generate graded oxygen defects in TiO₂ nanoparticles. Various levels of lithium reduction are systematically studied, and meanwhile, a distinct phase transition from anatase TiO₂ to cubic LiTiO₂ is observed with the increasing lithium ratio. The structure and evolution of surface defects and bulk phase transition are investigated in detail. Afterward, we demonstrate their applications in carbon dioxide photoreduction and photothermal imaging. The slightly reduced TiO₂ with effective oxygen defects affords a highly broadened solar spectrum absorption and yields significantly enhanced visible photocatalytic activity in CO₂ conversion, which is further revealed by theoretical calculations. The highly reduced TiO₂ with obvious phase transition shows enhanced solar absorption and achieves high photo-thermal-conversion efficacy, showing huge potential in photo-thermal-related applications. The lithiothermic reduction is a general and effective approach to produce defects and induce phase transition in oxides, which can be used in multiple applications.