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

In this work, BiVO 4 composites, containing the tetragonal zircon phase ( tz -BiVO 4 ), and monoclinic scheelite phase ( ms -BiVO 4 ), 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 -BiVO 4 composite forms at pH = 1.0 and pure ms -BiVO 4 is obtained in the pH range 4.0–10.0. The three primary steps in preparing BiVO 4 were monitored by optical microscopy and the role played by the microemulsion on the phase composition of BiVO 4 is explained. Photoluminescence spectroscopy (PL), UV–visible diffuse reflectance spectroscopy (UV-DRS), Brunauer-Emmett-Teller (BET), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the physical and chemical properties of BiVO 4 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 (•OH), superoxide radicals (O 2 •− ) and photogenerated holes ( h + ).