Characterization and photocatalytic properties of N-doped BiVO4 synthesized via a sol–gel method

Abstract

A N-doped BiVO4 photocatalyst with high visible light activity was synthesized by the complexing sol–gel method using citric acid as a chelate and hexamethylene tetramine (C6H12N4) as a nitrogen source. The as-prepared N-doped BiVO4 samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (BET) and UV–Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity was evaluated by photocatalytic degradation of methyl orange (MO) solution under visible light. This technique revealed that pure BiVO4 and all the N-doped samples were in a monoclinic phase; no peaks of any other phases or impurities were detected. Nitrogen atoms were doped into the BiVO4 lattice and filled the atomic sites of oxygen to form O–Bi–N–V–O bonds, which contributed to the appearance of the more active species V4+ and oxygen vacancies. The doped nitrogen resulted in a red shift in the absorption edge. However, the N-doping only slightly changed the morphologies and BET special surface areas of the samples. The photocatalytic activity of BiVO4 significantly depended on the N-doping content and the calcination temperature. The maximum activity was observed for the catalyst obtained via calcination at 500°C, for which the molar ratio of N to Bi was 0.20. Excess N-doping decreased the light absorption.