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

A series of bismuth oxyiodide (BiOxIy)-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 BiOxIy/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 (O-2(center dot-)) played a major role and holes (h(+)) and hydroxyl radicals ((OH)-O-center dot) 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.