Photocatalytic activity of aluminum oxide by oxygen vacancy generation using high-pressure torsion straining

Alumina is an insulator oxide with a large abundance in the earth's crust, but it shows no photocatalytic activity due to its large bandgap (9 eV). Based on first-principles calculations, the Al₂O₃ bandgap can be reduced below 3 eV, if large oxygen vacancies are generated. Here, Al₂O₃ with large oxygen vacancy concentrations and ~2.5 eV optical bandgap is produced by severe plastic deformation via the high-pressure torsion (HPT) method. The material exhibits photocatalytic dye degradation with a reasonable rate compared with TiO₂ photocatalysis. This finding introduces a simple but effective approach to produce new nature-friendly photocatalysts even from insulator oxides.