Basic properties and photo-generated carrier dynamics of bismuth vanadate composites modified with CQDs, MWCNTs and rGO

Three types of carbon materials with different dimensions were successfully combined with bismuth vanadate (BiVO4) using different methods, resulting in BiVO4/carbon quantum dots (CQDs), BiVO4/hydroxylated multi-walled carbon nanotubes (MWCNTs) and BiVO4/reduced graphene oxide (rGO). First, analysis of the basic morphology and elemental characterization of the materials were performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). Second, the effects of conductivity on the separation and recombination efficiency of the photo-generated carriers were investigated using photoluminescence spectroscopy (PL), transient fluorescence, electron spin resonance (ESR), transient photocurrent density (TPD) and electrochemical impedance spectroscopy (EIS). These results showed the addition of carbon promoted the separation of photo-generated carriers. Transient fluorescence measurements showed the separation and recombination of carriers was an ultrafast kinetic process and the photo-generated carriers exhibited the following three recombination mechanisms during fluorescence decay: bulk recombination, surface migration and defect recombination. In this study, photocatalytic carrier separation was improved by the addition of carbon materials, which resulted in improved photocatalytic degradation. Examination of the kinetic process of carbon-modified BiVO4 composites resulted in a deeper understanding of the composite process of the photo-generated carriers and the development of a better research method for improving photocatalytic degradation effects.