Development of Metal Oxide High-Pressure Phases for Photocatalytic Properties by Severe Plastic Deformation

Abstract

Photocatalytic activity of most metal oxides is restricted to the ultraviolet (UV) range of solar spectrum due to their large band gap. Since UV accounts for only 5% of the solar spectrum, designing metal oxide semiconductors with capability of absorbing visible light has been widely attempted. The large band gap of metal oxides can be reduced by various methods like doping with metallic or non-metallic ions, however a better photocatalytic activity can not be achieved necessarily by these methods due to fast recombinations of electron and hole. In recent years, authors have paid attention to the high pressure phases of metal oxides, which theoretically possess narrow band gaps, being able to absorb visible light. In this review, high pressure phases of well-known metal oxides like titania (TiO₂), zirconia (ZnO), and yttria (Y₂O₃) have been stabilized by applying a severe plastic deformation method, and photocatalytic properties of them have been evaluated.