Fabrication of walnut-like BiVO₄@Bi₂S₃ heterojunction for efficient visible photocatalytic reduction of Cr(VI)

As a typical visible-light-responsive photocatalyst, the photoreactivity of BiVO₄ is not high enough for practical application due to its limited visible light harvesting ability and quick recombination rate of photo-generated electron-hole pairs. In the present study, surface modification of BiVO₄ with Bi₂S₃, forming walnut-like core-shell structured BiVO₄@Bi₂S₃, was achieved by a simple ion-exchange reaction between Na₂S and BiVO₄. The photoreactivity of the photocatalyst was evaluated by photoreduction of Cr(VI) in solution under visible light irradiation (λ ≥ 420 nm). The effect of weight ratio of Na₂S·9H2O to BiVO₄ on the structure and photocatalytic performance of BiVO₄@Bi₂S₃ hybridized photocatalyst was systematically studied. It was found that a layer of Bi₂S₃ was successfully covered on the surface of walnut-like BiVO₄ microspheres after introduction of Na₂S. The formed Bi₂S₃ shell not only widely extends the visible-light-responsive range, but also sharply retards the recombination of photo-generated electrons and holes of BiVO₄ photocatalyst. With increase in the weight ratio of Na₂S·9H2O to BiVO₄, the photoreactivity of BiVO₄ increases first and then decreases with an optimal wight ratio of 3.0 (S3 sample). The photocatalytic activity of S3 sample (BiVO₄@Bi₂S₃) increases 57.2 times when compared with that of pristine BiVO₄ sample after irradiation for 40 min. The enhanced photocatalytic activity of walnut-like BiVO₄@Bi₂S₃ microsphere was attributed to the synergistic effect of enhanced visible light harvesting ability due to the sensitization of Bi₂S₃ and retarded recombination of carriers because of the formation of heterojunction between two semiconductors of BiVO₄ and Bi₂S₃. Copyright © 2017 Elsevier Inc. All rights reserved.