A series of BiOxIy/GO photocatalysts: synthesis, characterization, activity, and mechanism

Abstract

A series of bismuth oxyiodide (BiO_xI_y)-grafted graphene oxide (GO) sheets with different GO contents were synthesized through a simple hydrothermal method. This is the first report where four composites of BiOI/GO, Bi₄O₅I₂/GO, Bi₇O₉I₃/GO, and Bi₅O₇I/GO have been characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. The assembled BiO_xI_y/GO composites exhibited excellent photocatalytic activities in the degradation of crystal violet (CV) under visible light irradiation. The order of rate constants was as follows: Bi₇O₉I₃/GO > Bi₄O₅I₂/GO > Bi₄O₅I₂ > Bi₇O₉I₃ > Bi₅O₇I/GO > BiOI/GO > BiOI > Bi₅O₇I > GO. The photocatalytic activity of the Bi₇O₉I₃/GO (or Bi₄O₅I₂/GO) composite reached a maximum rate constant of 0.351 (or 0.322) h⁻¹, which was 1.8 (or 1.7) times higher than that of Bi₇O₉I₃ (or Bi₄O₅I₂), 6–7 times higher than that of BiOI/GO, and 119–130 times higher than that of BiOI. The quenching effects of different scavengers and electron paramagnetic resonance demonstrated that the superoxide radical (O₂˙⁻) played a major role and holes (h⁺) and hydroxyl radicals (˙OH) played a minor role as active species in the degradation of crystal violet (CV) and salicylic acid (SA). Possible photodegradation mechanisms are proposed and discussed in this research.