Composites of BiVO 4 and g-C 3 N 4 : Synthesis, Properties and Photocatalytic Decomposition of Azo Dye AO7 and Nitrous Oxide

The composites of BiVO4 and g-C3N4 (BiVO4/g-C3N4) were synthesised by the calcination of a mixture of monoclinic BiVO4 and bulk g-C3N4 at 300 °C for 4 h. Both components were previously prepared by the precipitation of Bi(NO3)3 with NH4VO3 and annealing of melamine. X-ray photoelectron spectroscopy (XPS) identified the presence of C–O and C=O bonds as well as metal nitrides which confirmed the formation of a heterojunction between BiVO4 and g-C3N4. The heterojunction was also indicated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy. The band gap energies were determined at 2.42–2.46 eV of BiVO4 and 2.75–2.82 eV of bulk g-C3N4. The specific surface area was 23–28 m2 g−1 of the composites and 6 m2 g−1 and 35 m2 g−1 of pure BiVO4 and g-C3N4, respectively. The photocatalytic activity of the composites was investigated by the decomposition of Acid Orange 7 (AO7) and nitrous oxide. In case of AO7, the BiVO4/g-C3N4 (1:3) composite was the most active one and the main role in the reaction was played by photoinduced holes forming hydroxyl radicals. At the decomposition of N2O, the most important species were the photoinduced electrons and the BiVO4/g-C3N4 (1:1) composite was the most active photocatalyst.