Visible-light photocatalytic degradation of mordant blue 9 by BiVO4 nanopowder

Abstract

The photocatalytic degradation of highly toxic azo dye Mordant Blue 9 (MB 9) was investigated using single-phase monoclinic BiVO4 nanopowder as a photocatalyst under the simulated solar irradiation. The photodegradation process as a function of different pH values of aqueous dye solution (pH = 1 – 13) and irradiation time was investigated, and the complete degradation mechanism was proposed. MB 9 was resistant to direct photolysis and the BiVO4 nanoparticles exhibited higher photocatalytic activity in a basic medium than in neutral and acid media. Photodegradation of the dye molecules occurred primarily due to a reaction with the photo-generated holes and OH– anions forming ∙OH radicals. The alkaline pH range favors the formation of more ∙OH radicals through the oxidation of hydroxide ions existing at the BiVO4 surface, thus the effectiveness of the photocatalytic process significantly increased. BiVO4 photocatalyst was stable and active under simulated solar irradiation over four consecutive cycles, which confirms its good photocatalytic properties.