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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.

High-entropy carbide (HEC) is a promising alternative to precious metal catalysts for the hydrogen evolution reaction (HER). However, the preparation of nanoscale HECs is a great challenge although many methods have been developed to prepare bulk HEC materials. Herein, an electrical discharge induced bulk-to-nanoparticle transformation method is reported, by which well dispersed sub-10 nm high entropy (MoWVNbTa)C nanoparticles with high-density surface defects can be directly obtained by centrifugation of the waste liquid produced during wire-cut electrical discharge machining of bulk HEC. The resultant HEC nanoparticles exhibit excellent catalytic activity and durability for HER, which is attributed to the combination of unique microstructure generated during the extremely nonequilibrium thermodynamic process and enhanced electronic effects induced by high configurational entropy. This facile and cost-effective bulk-to-nanoparticle transformation method can be extended to other conductive materials and shed light on the development of high-performance catalysts.

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