Microemulsion synthesis of ms/tz-BiVO4 composites: The effect of pH on crystal structure and photocatalytic performance

In this work, BiVO4 composites, containing the tetragonal zircon phase (tz-BiVO4), and monoclinic scheelite phase (ms-BiVO4), were synthesized using the microemulsion method. The effect of pH on phase composition and photocatalytic activity were investigated. Based on X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), a ms/tz-BiVO4 composite forms at pH = 1.0 and pure msBiVO(4) is obtained in the pH range 4.0-10.0. The three primary steps in preparing BiVO4 were monitored by optical microscopy and the role played by the microemulsion on the phase composition of BiVO4 is explained. Photoluminescence spectroscopy (PL), UV-visible diffuse reflectance spectroscopy (UV-DRS), Brunauer-EmmettTeller (BET), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the physical and chemical properties of BiVO4 composites. The composite formed at pH = 1 exhibited the lowest hole-electron (h(+) -e) recombination rate, resulting in the highest photocatalytic activity towards microcystin-LR (MC-LR), with near 100% removal of MC-LR in 5 h. ESR and trapping experiments indicated that MC-LR degradation was mediated primarily by hydroxyl radicals (center dot OH), superoxide radicals (O-2(center dot-)) and photogenerated holes (h(+)).