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

Abstract

• Amorphous Bi 2 O 3 shell on the surface of Bi nanospheres was transformed to crystal Bi 2 O 2 CO 3 . • Bi 2 O 2 CO 3 shell reduced the transmission resistance of hot electrons excited from Bi core. • The generation of reactive oxygen species were enhanced over Bi@crystal Bi 2 O 2 CO 3. • •O 2 − radicals were the major reactive oxidation species contributing to the oxidation of NO x . • Generation mechanisms of ROS were proposed over Bi@crystal Bi 2 O 2 CO 3 photocatalyst. The inevitable amorphous Bi 2 O 3 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 Bi 2 O 3 was transformed to Bi@crystal Bi 2 O 2 CO 3 by secondary hydrothermal reaction. Bi@Bi 2 O 2 CO 3 core–shell photocatalyst exhibited higher visible-light catalytic activity (34.1%) than Bi@Bi 2 O 3 did (12.3%) in terms of NO x removal. Photoelectrochemical, surface photovoltage spectroscopy spectra and Kelvin probe force microscopy measurement results indicate that Bi 2 O 2 CO 3 shell reduced the transmission resistance of hot electrons excited from Bi core. O 2 -TPD, trapping experiments and density functional theory further confirmed that the transferred hot electrons were a help for ROS generation and •O 2 − radicals were the major contributor. This study not only addresses the unsettled issue of surface amorphous Bi 2 O 3 , 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.