Pure monoclinic n-BiVO4 prepared by modified sol–gel method for high efficiency photodegradation of methylene blue under solar light irradiation

Abstract

Monoclinic BiVO₄ was synthesized by a modified sol–gel technique, using bismuth nitrate pentahydrate Bi(NO₃)₃·5H₂O and vanadium pentoxide V₂O₅ as precursors, dissolved in nitric acid and hydrochloric acid. The prepared samples were characterized by Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM–EDX), Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and UV–Vis Diffuse Reflectance Spectroscopy (DRS). The band gap of BiVO₄ was determined to be 2.53 eV. The Mott-Schottky plot identifies BiVO₄ as a n-type semiconductor with a flat band potential of 0.64 V/SCE and an electron donor density (Nd) of 1.46 × 10¹⁶ (site cm⁻³). Electrochemical impedance spectroscopy confirmed efficient photogenerated electron–hole (e⁻/h⁺) pair separation. Under solar irradiation, BiVO₄ exhibited high photocatalytic efficiency with 96% methylene blue (MB) degradation achieved within 120 min. The photodegradation process is well fitted by a first-order kinetic model, and parameters affecting MB degradation, such as pH and initial concentration, were optimized. A photocatalytic mechanism was proposed in accordance with the scavenger test.