Self-modification of titanium dioxide materials by Ti3+ and/or oxygen vacancies: new insights into defect chemistry of metal oxides

The defect chemistry of metal oxides is a very important research aspect of inorganic solid-state materials. This is because (i) a certain amount of defects or imperfections are always present in metal oxide materials; (ii) the presence of defects affects, and even sometimes determines, the physical and chemical properties of the materials; and (iii) more importantly, defects do not necessarily have adverse effects on the properties of materials, and judicious "defect engineering" can bring about improved properties desired in material systems, and even some new useful functionalities that are not available to the "perfect" material. In this review, we specially highlight the recent research efforts toward understanding the defect chemistry of titanium dioxide (also known as titania, TiO2), a widely-studied multifunctional metal oxide. In the discussion, particular attention is paid to the synthesis of Ti3+/oxygen vacancy self-modified TiO2 materials and the favorable effects of these defects on the materials' properties and applications. This review, focusing on a representative metal oxide (i. e., TiO2), is anticipated to provide some new insights into the general defect chemistry of metal oxides, and to give impetus to the development of the " defect engineering" of metal oxide materials.