Modified metal oxides with narrow band gaps have attracted great interest in photothermal applications because of their wide optical absorption range. To tune wide band gap metal oxides into visible and near-infrared responsive materials, we deploy a unique interfacial reaction-induced defect engineering approach, which enables us to effectively modify the electronic structure of metal oxides by introducing oxygen vacancy defects. This approach reduced the band gap of zirconia from 5.47 to 1.38 eV, accompanied by a color change to black. More importantly, it is not limited by the size of the metal oxides, and bulk black zirconia was successfully obtained for the first time. It has been demonstrated that the prepared black zirconia can be applied as an effective photothermal therapy agent in vitro. Additionally, the interfacial reaction-induced defect engineering approach has been successfully extended to enhance the optical absorption of other metal oxides.
Keywords: band gap modulation; black zirconia; defect engineering; defective metal oxides; interfacial reaction; photothermal therapy.