Transformation of amorphous Bi₂O₃ to crystal Bi₂O₂CO₃ on Bi nanospheres surface for photocatalytic NO_x oxidation: Intensified hot-electron transfer and reactive oxygen species generation

The inevitable amorphous Bi₂O₃ on the surface of plasmonic Bi nanospheres serving as the recombination center of hot electron-hole pairs, hindered the transfer of photo-generated hot electrons and production of reactive oxygen species (ROS) seriously. In this study, Bi@amorphous Bi₂O₃ was transformed to Bi@crystal Bi₂O₂CO₃ by secondary hydrothermal reaction. Bi@Bi₂O₂CO₃ core–shell photocatalyst exhibited higher visible-light catalytic activity (34.1%) than Bi@Bi₂O₃ did (12.3%) in terms of NO_x removal. Photoelectrochemical, surface photovoltage spectroscopy spectra and Kelvin probe force microscopy measurement results indicate that Bi₂O₂CO₃ shell reduced the transmission resistance of hot electrons excited from Bi core. O₂-TPD, trapping experiments and density functional theory further confirmed that the transferred hot electrons were a help for ROS generation and •O₂⁻ radicals were the major contributor. This study not only addresses the unsettled issue of surface amorphous Bi₂O₃, but also provides a facile method to transform the amorphous shell to crystal phase of core–shell photocatalyst and new insights into the hot electrons separation and the formation of main ROS over the surface crystal transition of plasmonic Bi.