Preparation and photo-electrochemical characterization of the vanadium fluorophosphate Na3V2O2(PO4)(2)F. application to the photo degradation of methyl violet

Abstract

Na3V2O2(PO4)(2)F was synthesized by a facile hydrothermal route at 250 degrees C. The synthesized product (abbreviated NVPOF), characterized by X-ray diffraction (XRD) powder crystallizes in a tetragonal symmetry (space group: I4/mmm) with lattice parameters: a = 6.3956 angstrom, c = 10.6591 angstrom. The FTIR spectroscopy shows the characteristic peaks of (PO4)(3-) and V-O bonds. The morphology studied by scanning electron microscopy (SEM) shows that the image displays crystals with rectangular shape; the energy dispersive X-ray spectrometry (EDX) confirms the elements existing in the compound with a composition close to the chemical formulation. The bandgap energy (E-g = 1.63 eV) of NVPOF is consistent with its green pale color. We also reported for the first time the photo-electrochemical characterization. The Mott-Schottky characteristic, plotted in Na2SO4 solution, displays p-type behavior with holes as majority carriers, a flat band potential (E-fb = 1.31 V-SCE). The Electrochemical Impedance Spectroscopy (EIS) shows one semicircle in the frequency range (10 MHz-100 kHz), attributed to the charge transfer with a high impedance. As an application, the photoactivity of synthesized NVPOF was studied by degrading the methyl violet, a hazardous dye, under visible light irradiation. NVPOF is a potential photocatalyst for the photodegradation through the (OH)-O-center dot and O-2(center dot-) radicals. An abatement of 82% was obtained within 240 min and the kinetic follows a pseudo-first model with a half photocatalytic life of 98 min.