Gold-reduced graphene oxide intimated BiVO4-ZnO mixed oxide composite with leveraged charge carrier transport under solar radiation

In a desire to enhance the photocatalytic activity of the BiVO4-ZnO mixed oxide, the mixed oxide has been encapsulated with gold decorated reduced graphene oxide (Au-rGO) using tetra-n-butylammonium bromide. The Au-rGO/BiVO4-ZnO hybrid composite was characterized for its physicochemical properties. The microscopic images of the composite from HR-TEM studies showed the aggregated spherical morphology of the particles. The images also revealed the intimation of two-dimensional Au-rGO layer over the BiVO4-ZnO mixed oxide surface. X-ray diffraction studies confirm the formation of the composite with the presence of characteristics diffraction pattern for BiVO4-ZnO and Au-rGO. The nature of diffraction peaks also revealed the size reduction of crystallite particles of the composite after inclusion of BiVO4 in the parent ZnO. The optical properties of the prepared materials were deduced using DRS-UV-visible spectroscopic studies and photoluminescence studies. The Tauc plots for ZnO, BiVO4-ZnO and Au-rGO/BiVO4-ZnO showed their optical band gap to be 3.3, 2.8 and 2.9 eV respectively. The emission intensity in photoluminescence spectra revealed the charge carrier recombination order as ZnO > BiVO4-ZnO > Au-rGO/BiVO4-ZnO. The Au-rGO/BiVO4-ZnO composite was employed as pho-tocatalyst in the degradation methylene blue dye under natural solar radiation. The degradation experiment was also repeated with bare ZnO and BiVO4-ZnO mixed oxide. The results revealed the enhanced photocatalytic activity of the Au-rGO/BiVO4-ZnO composite. The rate constant for the degradation reaction with the three catalyst viz., ZnO, BiVO4-ZnO and Au-rGO/BiVO4-ZnO were found to be 2.61 x 10-2 min-1, 3.04 x 10-2 min- 1 and 3.96 x 10-2 min- 1 respectively.