A unique black TiO2 created from CO-induced oxidation of defect-rich TiO2

Abstract Black TiO2 is an emerging semiconductor with a narrowed band gap for visible light absorption. Very recently, CO, as a reductant, was explored as a substitute of H2 to prepare black TiO2. In this work, we surprisedly found that CO could act as an oxidant to remediate the oxygen vacancies in defect-rich TiO2, accompanied with the introduction of carbon species into it, leading to the formation of a unique black TiO2 material. The light absorption of this material was significantly enhanced with an evidently narrowed band gap down to 2.79 eV. Furthermore, a mid-gap state, which was ∼1.49 eV above the valence band, emerged owing to the carbon species. These findings highlight a successful exploration in both black TiO2 synthesis and the application of CO as an oxidant.