Enhanced photo-degradation methyl orange by N–F co-doped BiVO4 synthesized by sol–gel method

Using ammonium fluoride (NH4F) as the source of nitrogen (N) and fluorine (F), N–F co-doped bismuth vanadate (BiVO4) visible-light-driven photocatalysts have been synthesized via a sol–gel method. The resulting materials were characterized by a series of techniques: X-ray photoelectron spectroscopy, X-ray diffractometry, scanning electron microscopy, Brunauer–Emmett–Teller (BET) surface analysis, and UV–vis diffuse reflectance spectroscopy. Compared with BiVO4, the N–F co-doped BiVO4 photocatalysts exhibited much higher photocatalytic activity for methyl orange (MO) degradation under visible light irradiation. It was revealed that N and F atoms were doped into the lattice of BiVO4. The doped N atoms existed as O–N or V–O–N bonding, and the F atoms replaced some O atoms to form the O–V–F structure, which can be attributed to the appearance of more active species V4+ and oxygen vacancies. The doped N and F atoms resulted in a red shift in the absorption edge. However, the N and F doping only slightly changed the morphologies and BET special surface areas of the samples. The photocatalytic activity of BiVO4 significantly depended on the N–F doping content and the calcination temperature. The maximum activity was observed for the catalyst obtained with calcination at 500 °C, a molar ratio of NH4F to Bi(NO3)3 was 6%.