Dismutation of Titanium Sub-oxide into TiO and TiO₂ with Structural Hierarchy Assisted by Ammonium Halides

Black TiO_2−x attracts enormous attention due to its large solar absorption and improved conductivity. In this work, a novel structure of TiO2−x with conductive TiO layer, performing full-spectrum absorption, was synthesized in one step by the unforeseen dismutation reaction of titanium sub-oxides (Ti_nO_2n−1) in ammonium halide atmosphere. For this new reaction, a possible mechanism of decomposition-etching-disproportionation-rehydrolysis process was proposed. The vital intermediate reactant TiCl₄, which verifies the assumption, has been captured in the form of (NH₄)₂TiCl₆, especially where Ti₂O₃ is the reactant. Furthermore, this work not only can nominate TiO as an alternative for noble metals or carbon materials in the aim to improve the electron conductivity and solar absorption of black TiO_2-x, which are important in electrochemistry and optoelectronics fields, but also can be a new route to synthesize special structures for other multivalent transition metals. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim