Bi2O2(OH)NO3/AgI heterojunction with enhanced UV and visible-light responsive photocatalytic activity and mechanism investigation

Highlights: • Bi₂O₂(OH)NO₃/AgI heterojunction is obtained by in-situ crystallization method. • It shows a higher degradation activity than Bi₂O₂(OH)NO₃ and AgI under UV light. • It shows a higher catalytic activity than Bi₂O₂(OH)NO₃ and AgI under visible light. • Enhanced charge separation is responsible for the enhanced degradation activity. - Abstract: Fabricating heterojunction between a wide-band-gap semiconductor and a narrow-band-gap semiconductor has become an important strategy to simultaneously improve the photoabsorption and charge separation. In this work, a new heterojunction photocatalyst Bi₂O₂(OH)NO₃/AgI was prepared through a facile in-situ crystallization method under ambient atmosphere. The crystal morphology, surface structure and element distribution were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) mapping and X-ray photoelectron spectroscopy (XPS). Compared with the pristine Bi₂O₂(OH)NO₃ and AgI, Bi₂O₂(OH)NO₃/AgI shows much enhanced degradation performance for eliminating MO regardless of UV or visible light. Photocurrent, electrochemical impedance spectra (EIS) and photoluminescence (PL) demonstrated that the enhanced photocatalytic activity is ascribed to the greatly promoted charge separation and transfer resulted from the matchable band energy levels of Bi₂O₂(OH)NO₃ and AgI, favoring the formation of heterojunction. In addition, according to the active species trapping experiment, the main active species are superoxide radicals (O₂⁻) and holes (h⁺) during the degradation process.