Synthesis of KVPO4F and its physical and photo-electrochemical properties: Application to degradation of methyl violet

The potassium vanadium fluorophosphate KVPO4F elaborated by hydrothermal route at 180 degrees C for the first time, crystallizes in an orthorhombic system (SG: Pna2(1)) with unit cell constants: a = 12.820 angstrom, b = 6.396 angstrom and c = 10.612 angstrom. It was characterized by X-ray diffraction, FTIR spectroscopy and SEM/EDX analysis to confirm the purity and morphology of the material. A direct optical transition at 1.88 eV, is determined from the diffuse reflectance data. The n-type conduction is evidenced from the Mott-Schottky characteristic with a flat band potential (E-fb = -0.38 VSCE) and an electron concentration (ND = 2.72 x 10(19) cm(-3)). Furthermore, the elec-trochemical impedance spectroscopy (EIS) shows a semicircle at high frequencies assigned to faradic charge transfer. To our knowledge, there is no dyes photodegradation on KVPO4F. Therefore, the synthesized KVPO4F showed promising photocatalytic with 61 % for degradation of methyl violet (MV) under a light flux of 23 mW cm(2). The discoloration follows a pseudo-first order kinetic with a half-life of 5.5 h. under optimal conditions, the photocatalyst showed high stability after five successive cycles with deactivation effect, not exceeding 7 %.